Terrestrial laser scanning for non-destructive estimates of liana stem biomass
Lianas are important and yet understudied components of tropical forests. Recent studies have shown that lianas are increasing in abundance and biomass in neotropical forests. However, aboveground biomass estimates of lianas are highly uncertain when calculated from allometric relations. This is mainly because of the limited sample size, especially for large lianas, used to construct the allometric models. Furthermore, the allometry of lianas can be weakly constrained mechanically throughout its development from sapling to mature form. In this study, we propose to extract liana stem biomass from terrestrial laser scanning (TLS) data of tropical forests. We show good agreement with a concordance correlation coefficient (CCC) of 0.94 between the TLS-derived volume to reference volume from eleven synthetic lianas. We also compare the TLS-derived biomass for ten real lianas in Nouragues, French Guiana, with the biomass derived from all existing allometric equations for lianas. Our results show relatively low CCC values for all the allometric models with the most commonly used pantropical model overestimating the total biomass by up to 133% compared to the TLS-derived biomass. Our study not only facilitates the testing of allometric equations but also enables non-destructive estimation of liana stem biomass. Since lianas are disturbance-adapted plants, liana abundance is likely to increase with increased forest disturbance. Our method will facilitate the long-term monitoring of liana biomass change in regenerating forests after disturbance, which is critical for developing effective forest management strategies.
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: Inverse Problems, Universiteit Gent, Smithsonian Tropical Research Institute
Contributors: Krishna Moorthy, S. M., Raumonen, P., Van den Bulcke, J., Calders, K., Verbeeck, H.
Peer-reviewed: Yes
Journal: FOREST ECOLOGY AND MANAGEMENT
Original language: English
ASJC Scopus subject areas: Forestry, Nature and Landscape Conservation, Management, Monitoring, Policy and Law
Keywords: Liana biomass, Quantitative structure models, Terrestrial laser scanning, Total forest biomass, Tropical forests
Electronic versions:
10.1016/j.foreco.2019.117751
http://urn.fi/URN:NBN:fi:tuni-201912136856
Source: Scopus
Source ID: 85075200207
Tomographic inversion of gravity gradient field for a synthetic Itokawa model
This article investigates reconstructing the internal mass density of a numerical asteroid model using the gradient of a simulated gravity field as synthetic measurement data. Our goal is to advance the mathematical inversion methodology and find feasibility constraints for the resolution, noise and orbit selection for future space missions. We base our model on the shape of the asteroid Itokawa as well as on the recent observations and simulation studies which suggest that the internal density varies, increasing towards the center, and that the asteroid may have a detailed structure. We introduce randomized multiresolution scan algorithm which might provide a robust way to cancel out bias and artifact effects related to the measurement noise and numerical discretization. In this scheme, the inverse algorithm can reconstruct details of various sizes without fixing the exact resolution a priori, and the randomization minimizes the effect of discretization on the solution. We show that the adopted methodology provides an advantageous way to diminish the surface bias of the inverse solution. The results also suggest that a noise level below 80 Eotvos will be sufficient for the detection of internal voids and high density anomalies, if a sparse set of measurements can be obtained from a close-enough distance to the target.
Organisations: Computing Sciences, Research group: Inverse Problems, Max Planck Institute for Solar System Research, Gedex Systems Inc., Royal Observatory of Belgium
Contributors: Sorsa, L., Takala, M., Bambach, P., Deller, J., Vilenius, E., Agarwal, J., Carroll, K. A., Karatekin, Ö., Pursiainen, S.
Early online date: 3 Sep 2019
Journal: Icarus
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Keywords: Asteroid Itokawa, Geophysical techniques, Interiors
10.1016/j.icarus.2019.113425
Graph entropy based on the number of spanning forests of c-cyclic graphs
Graph entropies have been introduced to quantitatively measure the structural information content of graphs and networks; they have plenty of applications in various fields. Utilizing the number of subgraphs to establish measures for determining the complexity of molecular graphs are also prevalent in the study of mathematical chemistry. In this paper, we develop a new graph entropy measure that is based on the number of spanning forests. We prove explicit expressions for the entropy for trees, unicyclic and bicyclic graphs, and show that the cycle graph Cn attains the maximal value of the entropy for unicyclic graphs with order n and large cycle lengths. Based on generating numerical results, we conjecture extremal unicyclic graphs with respect to the entropy as well as we compare the values of our entropy for c-cyclic graphs, and generate graphs of bicyclic graphs and tricyclic graphs with 6 vertices for performing further research.
Organisations: Computing Sciences, Research group: Predictive Society and Data Analytics (PSDA), Northwestern Polytechnical University, Yulin University, Beijing University of Chemical Technology, University of Applied Sciences Upper Austria, School of Management, Nankai University, Hall in Tyrol, Mathematics Faculty of Information Technology and Communication Sciences
Contributors: Wan, P., Tu, J., Dehmer, M., Zhang, S., Emmert-Streib, F.
Journal: Applied Mathematics and Computation
ASJC Scopus subject areas: Computational Mathematics, Applied Mathematics
Keywords: Graph entropy, Spanning forest, Subgraph
10.1016/j.amc.2019.124616
Formula size games for modal logic and mu-calculus
We propose a new version of formula size game for modal logic. The game characterizes the equivalence of pointed Kripke models up to formulas of given numbers of modal operators and binary connectives. Our game is similar to the well-known Adler–Immerman game. However, due to a crucial difference in the definition of positions of the game, its winning condition is simpler, and the second player does not have a trivial optimal strategy. Thus, unlike the Adler–Immerman game, our game is a genuine two-person game. We illustrate the use of the game by proving a non-elementary succinctness gap between bisimulation invariant first-order logic FO and (basic) modal logic ML⁠. We also present a version of the game for the modal μ-calculus Lμ and show that FO is also non-elementarily more succinct than Lμ⁠.
Organisations: Computing Sciences, University of Tampere
Contributors: Hella, L. T., Vilander, M. S.
Journal: JOURNAL OF LOGIC AND COMPUTATION
Article number: exz025
ISSN (Print): 0955-792X
ASJC Scopus subject areas: Logic, Computational Theory and Mathematics
Keywords: succinctness, formula size game, modal logic, modal mu-calculus, bisimulation invariant first-order logic
Hella, Vilander - Formula size games for modal logic and mu-calculus
10.1093/logcom/exz025
INT=comp."Hella, Lauri"
Accelerated simulation of a neuronal population via mathematical model order reduction
Mathematical modeling of biological neuronal net-
works is important in order to increase understanding of the
brain and develop systems capable of brain-like learning. While
mathematical analysis of these comprehensive, stochastic, and
complex models is intractable, and their numerical simulation
is very resource intensive, mean-field modeling is an effective
tool in enabling the analysis of these models. The mean-field
approach allows the study of populations of biophysically detailed
neurons with some assumptions of the mean behaviour of the
population, but ultimately requires numerical solving of high-
dimensional differential equation systems. Mathematical model
order reduction methods can be employed to accelerate the anal-
ysis of high-dimensional nonlinear models with a purely software-
based approach. Here we compare state-of-the-art methods for
improving the simulation time of a neuronal mean-field model
and show that a nonlinear Fokker-Planck-McKean-Vlasov model
can be accurately approximated in low-dimensional subspaces
with these methods. Using Proper Orthogonal Decomposition
and different variations of the Discrete Empirical Interpolation
Method, we improved the simulation time by over three orders
of magnitude while achieving low approximation error.
Publication status: Accepted/In press
MoE publication type: A4 Article in a conference publication
Organisations: BioMediTech, Computing Sciences, Research group: Computational Neuro Science-CNS
Contributors: Lehtimäki, M., Seppälä, I., Paunonen, L., Linne, M.
Host publication information
Title of host publication: Proceedings of the IEEE International Conference on Artificial Intelligence Circuits and Systems
Publisher: IEEE Xplore
Ei ilm. 9.1.20 M. K.
Applications of Spatially Localized Active-Intensity Vectors for Sound-Field visualization
This article details and evaluates three alternative approaches to sound-field visualization, which all employ the use of spatially-localized active-intensity (SLAI) vectors. SLAI vectors are particularly interesting as they allow direction-of-arrival (DoA) estimates to be extracted in multiple spatially-localized sectors, such that sound sources and/or noise present in one sector has reduced influence on the DoA estimate made in the other sectors. These DoA estimates may then be used to visualize the sound-field by either: i) directly depicting the estimates as icons, with their relative size dictated by the corresponding energy of each sector; ii) generating traditional activity-maps via histogram analysis of the DoA estimates; or iii) by using the DoA estimates to re-assign energy and subsequently sharpen traditional beamformer-based activity-maps. Since SLAI-based DoA estimates are continuous, these approaches are inherently computationally efficient, as they forgo the need for dense scanning grids to attain high-resolution imaging.
Organisations: Computing Sciences, Aalto University, Department of Signal Processing and Acoustics, University of Crete, University of Parma
Contributors: McCormack, L., Delikaris-Manias, S., Politis, A., Pavlidi, D., Farina, A., Pinardi, D., Pulkki, V.
Journal: Journal of the Audio Engineering Society
Issue number: 11
10.17743/jaes.2019.0041
Model order reduction of multiscale models in neuroscience
The current trend in computational neuroscience is to incorporate multiple physical levels of the brain into mathematical models, which often results in large networks of interconnected neural cells. Comprehensive models with accurate system dynamics are necessary in order to increase understanding of different mechanisms in the whole brain, but these models are analytically intractable. Additionally, their numerical simulation is very resource intensive. Useful ways of mitigating the computational burden include using a mean-field approach, as well as mathematical model order reduction (MOR).
Using mean-field approximation, one can account for the random fluctuations of variables by replacing them by their mean averages. The cells are grouped together into populations based on their statistical similarities, in order to represent the dynamics of the system in terms of the averaged out ensemble behaviour. These populations can then be described by a probability density function expressing the distribution of neuronal states at a given time. This approach ensures that the essential system dynamics converge to a stationary attractor consistent with the steady-state dynamics of the original system.Here we use the Fokker-Planck formalism, which results in a nonlinear system of partial differential equations (PDEs).
PDE systems can be difficult to solve analytically, and thus discretisation for numerical analysis is necessary. This discretisation often leads to very high-dimensional numerical models that correspond to equally high computational demand. Discretised PDE systems can be reduced using mathematical model order reduction methods [1]. MOR methods are well established in engineering sciences, such as control theory, as they improve computational efficiency of simulations of large-scale nonlinear mathematical models. In computational neuroscience MOR is underutilised, although the potential benefits in enabling multilevel simulations are obvious [2].
In this study we use mathematical MOR methods to reduce the dimensions of a PDE model derived using the mean-field approach. The system can be reduced with minimal information loss, by deriving a subspace that approximates the entire system and its dynamics with a smaller number of dimensions compared to the original model. Here we use Proper Orthogonal Decomposition with Discrete Empirical Interpolation Method (POD+DEIM), a subspace projection method for reducing the dimensionality of general nonlinear systems [1]. By applying these methods, the simulation time of the model is radically shortened, albeit not without dimension-dependent approximation error. The tolerated amount of inaccuracy depends on the final application of the model.
Due to being well-suited for depicting mesoscopic behaviour, the mean-field approach in combination with the POD+DEIM method allows us to describe the behaviour of any large multiscale brain model with a relatively low computational burden. This can be particularly useful when attempting to model whole-brain connectivity, for which there is an immediate demand in clinical and robotic applications.
1.Chaturantabut, S. and Sorensen, D.C., Nonlinear model reduction via discrete empirical interpolation. SIAM Journal on Scientific Computing. 2010, 32(5),pp.2737-2764.
2. Lehtimäki, M. , Paunonen, L., Pohjolainen, S. and Linne, M.-L., Order reduction for a signaling pathway model of neuronal synaptic plasticity. IFAC Papers OnLine. 2017, 50-1:7687–7692.
MoE publication type: Not Eligible
Organisations: BioMediTech, Computing Sciences
Contributors: Seppälä, I., Lehtimäki, M., Paunonen, L., Linne, M.
Peer-reviewed: Unknown
Event: Paper presented at 28th Annual Computational Neuroscience Meeting (CNS*2019), Barcelona, Spain.
Keywords: Neuroscience, Control theory, model reduction
Best poster award
Hyperbolic Function Theory in the Skew-Field of Quaternions
We are studying hyperbolic function theory in the total skew-field of quaternions. Earlier the theory has been studied for quaternion valued functions depending only on three reduced variables. Our functions are depending on all four coordinates of quaternions. We consider functions, called α-hyperbolic harmonic, that are harmonic with respect to the Riemannian metric dsα2=dx02+dx12+dx22+dx32x3αin the upper half space R+4={(x0,x1,x2,x3)∈R4:x3>0}. If α= 2 , the metric is the hyperbolic metric of the Poincaré upper half-space. Hempfling and Leutwiler started to study this case and noticed that the quaternionic power function xm(m∈Z), is a conjugate gradient of a 2-hyperbolic harmonic function. They researched polynomial solutions. Using fundamental α-hyperbolic harmonic functions, depending only on the hyperbolic distance and x3, we verify a Cauchy type integral formula for conjugate gradient of α-hyperbolic harmonic functions. We also compare these results with the properties of paravector valued α-hypermonogenic in the Clifford algebra Cℓ0,3.
Organisations: Computing Sciences, Department of Mathematics and Statistics, Helsinki University
Contributors: Eriksson, S., Orelma, H.
Publication date: 1 Nov 2019
Journal: Advances in Applied Clifford Algebras
Article number: 97
ASJC Scopus subject areas: Applied Mathematics
Keywords: Clifford algebra, Hyperbolic Laplace operator, Hyperbolic metric, Laplace–Beltrami operator, Monogenic function, Quaternions, α-hyperbolic harmonic, α-hypermonogenic
Eriksson-Orelma2019_Article_HyperbolicFunctionTheoryInTheS
EXT="Eriksson, Sirkka-Liisa"
Non-destructive tree volume estimation through quantitative structure modelling: Comparing UAV laser scanning with terrestrial LIDAR
Above-Ground Biomass (AGB) product calibration and validation require ground reference plots at hectometric scales to match space-borne missions' resolution. Traditional forest inventory methods that use allometric equations for single tree AGB estimation suffer from biases and low accuracy, especially when dealing with large trees. Terrestrial Laser Scanning (TLS) and explicit tree modelling show high potential for direct estimates of tree volume, but at the cost of time demanding fieldwork. This study aimed to assess if novel Unmanned Aerial Vehicle Laser Scanning (UAV-LS) could overcome this limitation, while delivering comparable results. For this purpose, the performance of UAV-LS in comparison with TLS for explicit tree modelling was tested in a Dutch temperate forest. In total, 200 trees with Diameter at Breast Height (DBH) ranging from 6 to 91 cm from 5 stands, including coniferous and deciduous species, have been scanned, segmented and subsequently modelled with TreeQSM. TreeQSM is a method that builds explicit tree models from laser scanner point clouds. Direct comparison with TLS derived models showed that UAV-LS reliably modelled the volume of trunks and branches with diameter ≥30 cm in the mature beech and oak stand with Concordance Correlation Coefficient (CCC) of 0.85 and RMSE of1.12 m3. Including smaller branch volume led to a considerable overestimation and decrease in correspondence to CCC of 0.51 and increase in RMSE to 6.59 m3. Denser stands prevented sensing of trunks and further decreased CCC to 0.36 in the Norway spruce stand. Also small, young trees posed problems by preventing a proper depiction of the trunk circumference and decreased CCC to 0.01. This dependence on stand indicated a strong impact of canopy structure on the UAV-LS volume modelling capacity. Improved flight paths, repeated acquisition flights or alternative modelling strategies could improve UAV-LS modelling performance under these conditions. This study contributes to the use of UAV-LS for fast tree volume and AGB estimation on scales relevant for satellite AGB product calibration and validation.
Organisations: Computing Sciences, Wageningen University and Research Centre, Universiteit Gent
Contributors: Brede, B., Calders, K., Lau, A., Raumonen, P., Bartholomeus, H. M., Herold, M., Kooistra, L.
Journal: Remote Sensing of Environment
ASJC Scopus subject areas: Soil Science, Geology, Computers in Earth Sciences
Keywords: Above-Ground Biomass (AGB), Forest, Laser scanning, Quantitative Structure Model (QSM), UAV
10.1016/j.rse.2019.111355
Fast fourier color constancy and grayness index for ISPA illumination estimation challenge
We briefly introduce two submissions to the Illumination Estimation Challenge, in the Int'l Workshop on Color Vision, affiliated to the 11th Int'l Symposium on Image and Signal Processing and Analysis. The fourier-transform-based submission is ranked 3rd, and the statistical Gray-pixel-based one ranked 6th.
Organisations: Computing Sciences, South China University of Technology
Contributors: Qian, Y., Chen, K., Yu, H.
Title of host publication: ISPA 2019 - 11th International Symposium on Image and Signal Processing and Analysis
Publisher: IEEE
Editors: Loncaric, S., Bregovic, R., Carli, M., Subasic, M.
ISBN (Electronic): 9781728131405
Name: International Symposium on Image and Signal Processing and Analysis, ISPA
Volume: 2019-September
ASJC Scopus subject areas: Computational Theory and Mathematics, Computer Graphics and Computer-Aided Design, Computer Vision and Pattern Recognition, Signal Processing
Keywords: Color constancy, FFCC, Gray pixel, Illumination
10.1109/ISPA.2019.8868451
EXT="Chen, Ke"
Studying the inertias of LCM matrices and revisiting the Bourque-Ligh conjecture
Let S={x1,x2,…,xn} be a finite set of distinct positive integers. Throughout this article we assume that the set S is GCD closed. The LCM matrix [S] of the set S is defined to be the n×n matrix with lcm(xi,xj) as its ij element. The famous Bourque-Ligh conjecture used to state that the LCM matrix of a GCD closed set S is always invertible, but currently it is a well-known fact that any nontrivial LCM matrix is indefinite and under the right circumstances it can be even singular (even if the set S is assumed to be GCD closed). However, not much more is known about the inertia of LCM matrices in general. The ultimate goal of this article is to improve this situation. Assuming that S is a meet closed set we define an entirely new lattice-theoretic concept by saying that an element xi∈S generates a double-chain set in S if the set meetcl(CS(xi))∖CS(xi) can be expressed as a union of two disjoint chains (here the set CS(xi) consists of all the elements of the set S that are covered by xi and meetcl(CS(xi)) is the smallest meet closed subset of S that contains the set CS(xi)). We then proceed by studying the values of the Möbius function on sets in which every element generates a double-chain set and use the properties of the Möbius function to explain why the Bourque-Ligh conjecture holds in so many cases and fails in certain very specific instances. After that we turn our attention to the inertia and see that in some cases it is possible to determine the inertia of an LCM matrix simply by looking at the lattice-theoretic structure of (S,|) alone. Finally, we are going to show how to construct LCM matrices in which the majority of the eigenvalues is either negative or positive.
Publication status: E-pub ahead of print
Organisations: Computing Sciences, Research group: Computer Science and Applied Logics, Tampere University
Contributors: Haukkanen, P., Mattila, M., Mäntysalo, J.
Publication date: 1 Apr 2020
Early online date: 14 Oct 2019
Journal: Journal of Combinatorial Theory. Series A
ASJC Scopus subject areas: Theoretical Computer Science, Discrete Mathematics and Combinatorics, Computational Theory and Mathematics
Keywords: Bourque-Ligh conjecture, GCD matrix, LCM matrix, Smith determinant
10.1016/j.jcta.2019.105161
On Computational Complexity Reduction Methods for Kalman Filter Extensions
The Kalman filter and its extensions are used in a vast number of aerospace and navigation applications for nonlinear state estimation of time series. In the literature, different approaches have been proposed to exploit the structure of the state and measurement models to reduce the computational demand of the algorithms. In this tutorial, we survey existing code optimization methods and present them using unified notation that allows them to be used with various Kalman filter extensions. We develop the optimization methods to cover a wider range of models, show how different structural optimizations can be combined, and present new applications for the existing optimizations. Furthermore, we present an example that shows that the exploitation of the structure of the problem can lead to improved estimation accuracy while reducing the computational load. This tutorial is intended for persons who are familiar with Kalman filtering and want to get insights for reducing the computational demand of different Kalman filter extensions.
Organisations: Computing Sciences, Research group: Automation and Systems Theory
Contributors: Raitoharju, M., Piche, R.
Publication date: 7 Oct 2019
Journal: IEEE Aerospace and Electronic Systems Magazine
Raitoharju_Piche_2019
10.1109/MAES.2019.2927898
Multiplierless filtered-OFDM transmitter for narrow-band IoT devices
In cyclic-prefix orthogonal frequency-division multiplexing (CP-OFDM) based radio access, the coexistence of different technologies without precise time-frequency synchronization is limited due to high out-of-band emissions. Therefore, spectrum enhancement techniques play a key role to relax the synchronization and power control requirements. This allows higher degree of opportunistic spectrum use with minimized interference. In addition, all transmitting devices have to fulfill specific transmitted signal quality requirements, including the maximum out-of-band radiated signal power. With OFDM based radio access, some additional signal processing for improved spectrum containment is commonly needed to achieve these requirements. Filtering and time-domain windowing are two fundamentally different approaches for spectrum enhancement. Filtered OFDM (F-OFDM) provides better spectrum localization than the timewindowing schemes (such as windowed overlap-add, WOLA), with the cost of higher complexity. This paper introduces lowcomplexity solutions for spectrally enhanced narrow-band OFDM transmitters based on the use of a look-up tables (LUTs). The proposed LUT approach, requiring only memory units and a low number of additions, allows to avoid all computationally expensive operations in on-line transmitter processing, as it builds the transmitted signal by summing the stored partial waveforms optimized off-line. In certain cases, completely multiplication and summation free designs are possible. The transmitters of narrowband Internet of things (NB-IoT) devices are natural applications for the proposed LUT approach, as they require additional digital baseband signal processing to reach the emission requirements. It is shown that the proposed LUT schemes can provide signicant savings in real-time computations of NB-IoT devices, while fulfilling the 3GPP requirements.
Organisations: Electrical Engineering, Research group: Wireless Communications and Positioning, Nokia Bell Labs
Contributors: Loulou, A. E., Yli-Kaakinen, J., Levanen, T., Lehtinen, V., Schaich, F., Wild, T., Renfors, M., Valkama, M.
Journal: IEEE Internet of Things Journal
Loulou, A. (2019, JIOT) Multiplierless Implementation of Filtered OFDM for Narrow Band Transmitters in Future Mobile Networks
10.1109/JIOT.2019.2945186
Satisfiability of modal inclusion logic: Lax and strict semantics
We investigate the computational complexity of the satisfiability problem of modal inclusion logic. We distinguish two variants of the problem: one for the strict and another one for the lax semantics. Both problems turn out to be EXPTIME-complete on general structures. Finally,we showhowfor a specific class of structures NEXPTIME-completeness for these problems under strict semantics can be achieved.
Organisations: Computing Sciences, Leibniz-Universität Hannover, Tampere University
Contributors: Hella, L., Kuusisto, A., Meier, A., Vollmer, H.
Journal: ACM TRANSACTIONS ON COMPUTATIONAL LOGIC
Article number: 7
ASJC Scopus subject areas: Theoretical Computer Science, Computer Science(all), Logic, Computational Mathematics
Keywords: Computational complexity, Modal inclusion logic, Satisfiability, Team semantics
DUPL=50949587
The Graph Curvature Calculator and the curvatures of cubic graphs
We classify all cubic graphs with either non-negative Ollivier-Ricci curvature or non-negative Bakry-Émery curvature everywhere. We show in both curvature notions that the non-negatively curved graphs are the prism graphs and the Möbius ladders. We also highlight an online tool for calculating the curvature of graphs under several variants of these curvature notions that we use in the classification. As a consequence of the classification result we show, that non-negatively curved cubic expanders do not exist.
Organisations: Computing Sciences, Aalto University, Newcastle University, United Kingdom, Durham University, University of Science and Technology of China
Contributors: Cushing, D., Kangaslampi, R., Lipiäinen, V., Liu, S., Stagg, G. W.
Early online date: 14 Sep 2019
Journal: Experimental Mathematics
Steering Capacitor Film Development with Methods for Correct and Adequate Dielectric Performance Assessment
The transition of electric power systems towards renewable generation has created an increasing market for power electronics using film capacitors as one of their key components. Size, weight, and cost reduction can be achieved with better capacitors – an objective achievable with advanced dielectric films. The current state-of-the-art biaxially oriented polypropylene (BOPP) films are already operated close to their fundamental limits, causing a growing demand for next-generation technologies. To perform well when used in a capacitor, a film needs to have a wide range of fundamental and applied properties, all of which should be evaluated during film development to ensure there are no unwanted trade-offs. Power capacitors are used in applications with high downtime costs, e.g. HVDC, thus especially the reliability aspects must be given scrutiny. This thesis work was inspired by the lack of knowledge of the long-term performance of next generation dielectrics, e.g. polymer nanocomposites. Equally important was to fill the gaps in published knowledge of measurement methods to evaluate long-term properties, voltage endurance, and surprisingly, also the dielectric permittivity of thin (≈10 μm) low-loss films. In this thesis, a suitable measurement for each three is presented along with examples of their capability and an approach to applying them to steer film development. The large-area multi-breakdown method developed in our research group is extended to measurements at realistic operating temperatures, and industrial BOPP films are shown to exhibit an 11–20 % decrease in the DC breakdown strength between room temperature and 100 ◦C. The results align with literature, which supports the validity of the approach. BOPP films made of base materials varying in terms of molecular weight are measured: these films exhibit similar short-term breakdown performance at room temperature, yet at 100 ◦C differences emerge. The difference did not correlate with the reduction of breakdown performance after DC electro-thermal aging, demonstrating the necessity of long-term tests. Electron beam evaporation in high vacuum (P<10−6 mbar) is established as a repeatable and suitable method to metallize electrodes on ultra low-loss BOPP films, solving earlier issues of abnormally high dielectric losses or unrealistically low real permittivity. Metallization process is identified as the crucial factor: no pre- or post-treatments are required, and valid results are obtainable with various electrode metals. The method was demonstrated by measuring true "literature value" dielectric permittivity of commercial BOPP films: E≈2.25 and tanδ≈10−4. The importance of successful metallization process for measuring the intrinsic losses is demonstrated: samples with sputter deposited electrodes exhibited abnormally high dielectric losses, as also did samples metallized using another e-beam evaporator. The multi-breakdown approach is also extended to times-to-breakdown tests, and accelerated ageing tests are conducted on an industrial BOPP film. High-field degradation and drastically reduced insulation life are observed. Analysis of the Weibull failure rate supports the notion that at current design stresses, BOPP is already operated close to the fundamental material limits, and also that the life in operating conditions cannot be determined by simple inverse power law extrapolation of accelerated rapid ageing data. Again, long-term ageing testing is advocated. Space charge measurements on "classic" BOPP films reveal charge accumulation at high fields, as expected. Interestingly, no space charge accumulation is detected in a novel nanostructured material under similar conditions, demonstrating the potentiality of nanofilled DC insulation. A DC electro-thermal ageing test method is presented to investigate long-term phenomena in realistic operating conditions. Two 1000 h DC electro-thermal ageing tests associate ageing with the formation of electrically weak points. Large-area breakdown behavior, being sensitive to local changes, is established as a recommended ageing indicator. Material characterization does not reveal ageing-induced changes in bulk properties, supporting the literature-backed conclusion that early ageing progresses by localized degradation. A trial with eight pilot-scale materials demonstrate that weak point formation may be inhibited in nanostructured materials, but also that material-specific optimization of film processing is required to reach optimal dielectric performance. Ultimately, the methods developed are fused into one resource-efficient approach to capacitor film development, in which the short-, mid-, and long-term properties are evaluated in three overlapping phases. Reliance on individual performance metrics to steer film development is discouraged: all properties need to be at an appropriate level for a film to perform in application, and there are trade-offs to be managed.
MoE publication type: G5 Doctoral dissertation (article)
Organisations: Research group: High voltage engineering, Electrical Engineering
Contributors: Ritamäki, M.
Publisher: Tampere University
ISBN (Print): 978-952-03-1175-9
ISBN (Electronic): 978-952-03-1176-6
Name: Tampere University Publications
http://urn.fi/URN:ISBN:978-952-03-1176-6
Research output: Book/Report › Doctoral thesis › Collection of Articles
Hypermonogenic Plane Wave Solutions of the Dirac Equation in Superspace
In this paper, we obtain Cauchy–Kovalevskaya theorems for hypermonogenic superfunctions depending only on purely bosonic and fermionic vector variables. In addition, we use these results to construct plane wave examples of such functions.
Organisations: Civil Engineering, Universiteit Gent
Contributors: Adán, A. G., Orelma, H., Sommen, F.
Publication date: 1 Sep 2019
Keywords: Cauchy–Kovalevskaya extension, Clifford analysis, Hypermonogenic functions, Plane waves, Superspace
Similar temperature sensitivity of soil mineral-associated organic carbon regardless of age
Most of the carbon (C) stored in temperate arable soils is present in organic matter (OM) intimately associated with soil minerals and with slow turnover rates. The sensitivity of mineral-associated OM to changes in temperature is crucial for reliable predictions of the response of soil C turnover to global warming and the associated flux of carbon dioxide (CO2) from the soil to the atmosphere. We studied the temperature sensitivity of C in <63 μm fractions rich in mineral-associated organic matter (MOM) and of C in >63 μm fractions rich in particulate organic matter (POM). The fractions were isolated by physical separation of two light-textured arable soils where the C4-plant silage maize had replaced C3-crops 25 years ago. Differences in 13C abundance allowed for calculation of the age of C in the soil-size fractions (old C, C3–C > 25 years; recent C, C4–C < 25 years). We incubated bulk soils (<2 mm) and size fractions sequentially at 6, 18, 26 and 34 °C (ramping up and down the temperature scale) and calculated the temperature sensitivity of old and recent C from 12CO2 and 13CO2 evolution rates. The temperature sensitivity was similar or slightly higher for POM than for MOM. Within the POM fraction, old C3–C was more sensitive to changes in temperature than recent C4–C. For the MOM fraction, the temperature sensitivity was unrelated to the age of C. Quantitative PCR analysis indicated that the proportions of bacteria, archaea and fungi did not change during incubation. Our results suggest that while OM stabilizing mechanisms affect the temperature sensitivity of soil C, temperature sensitivity appears unrelated to the age of mineral-associated OM.
Organisations: Computing Sciences, University of Helsinki, Finnish Environment Institute, Finnish Museum of Natural History, Aarhus Universitet, Natural Resources Institute Finland (Luke), Finnish Meteorological Institute
Contributors: Karhu, K., Hilasvuori, E., Järvenpää, M., Arppe, L., Christensen, B. T., Fritze, H., Kulmala, L., Oinonen, M., Pitkänen, J. M., Vanhala, P., Heinonsalo, J., Liski, J.
Journal: Soil Biology and Biochemistry
ASJC Scopus subject areas: Microbiology, Soil Science
Keywords: C natural abundance, Bayesian statistics, Climate change, Decomposition, Soil organic matter, Temperature sensitivity
10.1016/j.soilbio.2019.107527
Nanosatellite attitude estimation using Kalman-type filters with non-Gaussian noise
In order to control the orientation of a satellite, it is important to estimate the attitude accurately. Time series estimation is especially important in micro and nanosatellites, whose sensors are usually low-cost and have higher noise levels than high end sensors. Also, the algorithms should be able to run on systems with very restricted computer power. In this work, we evaluate five Kalman-type filtering algorithms for attitude estimation with 3-axis magnetometer and sun sensor measurements. The Kalman-type filters are selected so that each of them is designed to mitigate one error source for the unscented Kalman filter that is used as baseline. We investigate the distribution of the magnetometer noises and show that the Student's t-distribution is a better model for them than the Gaussian distribution. We consider filter responses in four operation modes: steady state, recovery from incorrect initial state, short-term sensor noise increment, and long-term increment. We find that a Kalman-type filter designed for Student's t sensor noises has the best combination of accuracy and computational speed for these problems, which leads to a conclusion that one can achieve more improvements in estimation accuracy by using a filter that can work with heavy tailed noise than by using a nonlinearity minimizing filter that assumes Gaussian noise.
Organisations: Computing Sciences, Research group: Automation and Systems Theory, Istanbul Technical University
Contributors: Cilden-Guler, D., Raitoharju, M., Piche, R., Hajiyev, C.
Journal: Aerospace Science and Technology
10.1016/j.ast.2019.05.055
http://urn.fi/URN:NBN:fi:tuni-201911186034. Embargo ends: 30/09/21
On the Structure of Octonion Regular Functions
In this paper, we study octonion regular functions and the structural differences between regular functions in octonion, quaternion, and Clifford analyses.
Organisations: Computing Sciences, Civil Engineering
Contributors: Kauhanen, J., Orelma, H.
Early online date: 2 Aug 2019
Kauhanen-Orelma2019_OnTheStructureOfOctonionRegular
http://urn.fi/URN:NBN:fi:tty-201909092083
On the Succinctness of Atoms of Dependency
Propositional team logic is the propositional analog to first-order team logic. Non-classical atoms of dependence, independence, inclusion, exclusion and anonymity can be expressed in it, but for all atoms except dependence only exponential translations are known. In this paper, we systematically compare their succinctness in the existential fragment, where the splitting disjunction only occurs positively, and in full propositional team logic with unrestricted negation. By introducing a variant of the Ehrenfeucht-Fra\"{i}ssé game called formula size game into team logic, we obtain exponential lower bounds in the existential fragment for all atoms. In the full fragment, we present polynomial upper bounds also for all atoms.
Organisations: Computing Sciences, Leibniz-Universität Hannover
Contributors: Vilander, M., Lück, M.
Pages: 17:1-17:28
Journal: Logical Methods in Computer Science
Keywords: team semantics, succinctness, dependence atom
https://lmcs.episciences.org/5698
Graph Analysis and Applications in Clustering and Content-based Image Retrieval
About 300 years ago, when studying Seven Bridges of Königsberg problem - a famous problem concerning paths on graphs - the great mathematician Leonhard Euler said, "This question is very banal, but seems to me worthy of attention". Since then, graph theory and graph analysis have not only become one of the most important branches of mathematics, but have also found an enormous range of important applications in many other areas. A graph is a mathematical model that abstracts entities and the relationships between them as nodes and edges. Many types of interactions between the entities can be modeled by graphs, for example, social interactions between people, the communications between the entities in computer networks and relations between biological species. Although not appearing to be a graph, many other types of data can be converted into graphs by cer- tain operations, for example, the k-nearest neighborhood graph built from pixels in an image.
Cluster structure is a common phenomenon in many real-world graphs, for example, social networks. Finding the clusters in a large graph is important to understand the underlying relationships between the nodes. Graph clustering is a technique that partitions nodes into clus- ters such that connections among nodes in a cluster are dense and connections between nodes in different clusters are sparse. Various approaches have been proposed to solve graph clustering problems. A common approach is to optimize a predefined clustering metric using different optimization methods. However, most of these optimization problems are NP-hard due to the discrete set-up of the hard-clustering. These optimization problems can be relaxed, and a sub-optimal solu- tion can be found. A different approach is to apply data clustering
algorithms in solving graph clustering problems. With this approach, one must first find appropriate features for each node that represent the local structure of the graph. Limited Random Walk algorithm uses the random walk procedure to explore the graph and extracts ef- ficient features for the nodes. It incorporates the embarrassing parallel paradigm, thus, it can process large graph data efficiently using mod- ern high-performance computing facilities. This thesis gives the details of this algorithm and analyzes the stability issues of the algorithm.
Based on the study of the cluster structures in a graph, we define the authenticity score of an edge as the difference between the actual and the expected number of edges that connect the two groups of the neighboring nodes of the two end nodes. Authenticity score can be used in many important applications, such as graph clustering, outlier detection, and graph data preprocessing. In particular, a data clus- tering algorithm that uses the authenticity scores on mutual k-nearest neighborhood graph achieves more reliable and superior performance comparing to other popular algorithms. This thesis also theoretically proves that this algorithm can asymptotically find the complete re- covery of the ground truth of the graphs that were generated by a stochastic r-block model.
Content-based image retrieval (CBIR) is an important application in computer vision, media information retrieval, and data mining. Given a query image, a CBIR system ranks the images in a large image database by their "similarities" to the query image. However, because of the ambiguities of the definition of the "similarity", it is very diffi- cult for a CBIR system to select the optimal feature set and ranking algorithm to satisfy the purpose of the query. Graph technologies have been used to improve the performance of CBIR systems in var- ious ways. In this thesis, a novel method is proposed to construct a visual-semantic graph—a graph where nodes represent semantic concepts and edges represent visual associations between concepts. The constructed visual-semantic graph not only helps the user to locate the target images quickly but also helps answer the questions related to the query image. Experiments show that the efforts of locating the target image are reduced by 25% with the help of visual-semantic graphs.
Graph analysis will continue to play an important role in future data analysis. In particular, the visual-semantic graph that captures important and interesting visual associations between the concepts is worthyof further attention.
Organisations: Computing Sciences, Research group: Multimedia Research Group - MRG
Contributors: Zhang, H.
Publication date: 9 Aug 2019
Name: Tampere University Dissertations
Metric Stabilization of Invariants for Topological Persistence
Rank or the minimal number of generators is a natural invariant attached to any n-dimensional persistent vector space. However, rank is highly unstable. Building an algorithmic framework for stabilizing the rank in one-dimensional persistence and proving its usefulness in concrete data analysis are the main objectives of this thesis. Studied stabilization process relies on choosing a pseudometric between tame persistent vector spaces. This allows to minimize the rank of a persistent vector space in larger and larger neighbourhoods around it with respect to the chosen pseudometric. The result is the stable rank invariant, a simple non-increasing function from non-negative reals to non-negative reals.
We show how the needed pseudometrics arise from so called persistence contours. Contour is a certain function system which can be generated very efficiently and in implementable way by integrating a so called density function from non-negative reals to strictly positive reals. We prove an algorithmic way of computing the stable rank invariant with respect to a chosen contour. The result of the theoretical development is an embedding theorem showing that persistent vector spaces embed into Lebesgue measurable functions through stable rank.
The success of persistent homology in data analysis has been largely due to the barcode decomposition and its efficient computation. One result of this thesis is that the barcode decomposition can be proved using the monotonicity of the rank with respect to taking a subspace of persistent vector space. This property of the rank only holds in one-dimensional case. We claim that rank is more fundamental for persistence and barcode is but a technical artifact of its properties. Even though barcode is a powerful tool, progress in persistence theory requires invariants generalizing to multi-dimensional persistence and not relying on decomposition theorems.
Recent years have seen active research around mapping barcodes to some representation that enables statistics of results from persistent homology analysis and connects naturally to machine learning algorithms. Our embedding theorem shows that the stable rank provides a connection to machine learning. One of our main results is the full applicability of our pipeline in practical data analysis. We demonstrate how choosing an appropriate contour can enhance results of supervised learning. Contour can also be seen to act as a form of feature selection on the bar decomposition.
MoE publication type: G4 Doctoral dissertation (monograph)
Organisations: Computing Sciences, Research group: Inverse Problems
Contributors: Riihimäki, H.
Research output: Book/Report › Doctoral thesis › Monograph
Reduced Order Controller Design for Robust Output Regulation
We study robust output regulation for parabolic partial differential equations and other infinite-dimensional linear systems with analytic semigroups. As our main results we show that robust output tracking and disturbance rejection for our class of systems can be achieved using a finite-dimensional controller and present algorithms for construction of two different internal model based robust controllers. The controller parameters are chosen based on a Galerkin approximation of the original PDE system and employ balanced truncation to reduce the orders of the controllers. In the second part of the paper we design controllers for robust output tracking and disturbance rejection for a 1D reaction-diffusion equation with boundary disturbances, a 2D diffusion-convection equation, and a 1D beam equation with Kelvin-Voigt damping.
Organisations: Computing Sciences, Research group: Computer Science and Applied Logics
Contributors: Paunonen, L., Phan, D.
Journal: IEEE Transactions on Automatic Control
Keywords: Mathematical model, Method of moments, Closed loop systems, Hilbert space, Reduced order systems, Adaptive control, Robust output regulation, partial differential equation, controller design, Galerkin approximation, model reduction
Author accepted version
10.1109/TAC.2019.2930185
Source: Bibtex
Source ID: 8768063
Projection-based order reduction of a nonlinear biophysical neuronal network model
In this study mathematical model order reduction
is applied to a nonlinear model of a network of biophysically
realistic heterogeneous neurons. The neuron model describes a
pyramidal cell in the hippocampal CA3 area of the brain and
includes a state-triggered jump condition. The network displays
synchronized firing of action potentials (spikes), a fundamental
phenomenon of sensory information processing in the brain.
Simulation of the system is computationally expensive, which
limits network size and hence biological realism. We reduce the
network using advanced variations of Proper Orthogonal De-
composition and Discrete Empirical Interpolation Method. The
reduced models should recreate the original spiking activity. We
show that reduction methods with online adaptivity achieve the
most accurate reduction results. Some of the reduced models
consume less computational resources than the original, at the
cost of changes in population activity of the tested network
model.
Contributors: Lehtimäki, M., Paunonen, L., Linne, M.
Title of host publication: Proceedings of the IEEE Conference on Decision and Control
Presented as a talk. Ei ilm. 9.1.20 M. K.
Hosoya entropy of fullerene graphs
Entropy-based methods are useful tools for investigating various problems in mathematical chemistry, computational physics and pattern recognition. In this paper we introduce a general framework for applying Shannon entropy to fullerene graphs, and used it to investigate their properties. We show that important physical properties of these molecules can be determined by applying Hosoya entropy to their corresponding graphs.
Organisations: Computing Sciences, Research group: Predictive Society and Data Analytics (PSDA)
Contributors: Ghorbani, M., Dehmer, M., Rajabi-Parsa, M., Emmert-Streib, F., Mowshowitz, A.
Publication date: 1 Jul 2019
Keywords: Graph entropy, Graph automorphism, Fullerene graphs
10.1016/j.amc.2019.01.024
Source: RIS
Source ID: urn:DFAB2DC41C0C5DDD065F5B790B659EFA
Approximate Controllability for Navier–Stokes Equations in 3D Rectangles Under Lions Boundary Conditions
The 3D Navier–Stokes system, under Lions boundary conditions, is proven to be approximately controllable provided a suitable saturating set does exist. An explicit saturating set for 3D rectangles is given.
Organisations: Mathematics, Johann Radon Institute for Computational and Applied Mathematics
Contributors: Phan, D., Rodrigues, S. S.
Early online date: 10 Jul 2018
Journal: Journal of Dynamical and Control Systems
ASJC Scopus subject areas: Control and Systems Engineering, Algebra and Number Theory, Numerical Analysis, Control and Optimization
Keywords: Approximate controllability, Navier–Stokes equations, Saturating set
An architectural understanding of natural sway frequencies in trees
The relationship between form and function in trees is the subject of a longstanding debate in forest ecology and provides the basis for theories concerning forest ecosystem structure and metabolism. Trees interact with the wind in a dynamic manner and exhibit natural sway frequencies and damping processes that are important in understanding wind damage. Tree-wind dynamics are related to tree architecture, but this relationship is not well understood. We present a comprehensive view of natural sway frequencies in trees by compiling a dataset of field measurement spanning conifers and broadleaves, tropical and temperate forests. The field data show that a cantilever beam approximation adequately predicts the fundamental frequency of conifers, but not that of broadleaf trees. We also use structurally detailed tree dynamics simulations to test fundamental assumptions underpinning models of natural frequencies in trees. We model the dynamic properties of greater than 1000 trees using a finite-element approach based on accurate three-dimensional model trees derived from terrestrial laser scanning data. We show that (1) residual variation, the variation not explained by the cantilever beam approximation, in fundamental frequencies of broadleaf trees is driven by their architecture; (2) slender trees behave like a simple pendulum, with a single natural frequency dominating their motion, which makes them vulnerable to wind damage and (3) the presence of leaves decreases both the fundamental frequency and the damping ratio. These findings demonstrate the value of new three-dimensional measurements for understanding wind impacts on trees and suggest new directions for improving our understanding of tree dynamics from conifer plantations to natural forests.
Organisations: Computing Sciences, University of Oxford, SCION, University of Connecticut, Delft University of Technology, Wageningen University and Research Centre, University of Massachusetts Amherst, National Parks Board, University of Melbourne, Oregon State University, Universiteit Gent, National Physical Laboratory, University College London, NERC National Centre for Earth Observation (NCEO), 16 Center for International Forestry Research (CIFOR), Swedish University of Agricultural Sciences, INRA
Contributors: Jackson, T., Shenkin, A., Moore, J., Bunce, A., van Emmerik, T., Kane, B., Burcham, D., James, K., Selker, J., Calders, K., Origo, N., Disney, M., Burt, A., Wilkes, P., Raumonen, P., Gonzalez de Tanago Menaca, J., Lau, A., Herold, M., Goodman, R. C., Fourcaud, T., Malhi, Y.
Journal: Journal of the Royal Society. Interface
Issue number: 155
ASJC Scopus subject areas: Biotechnology, Biophysics, Bioengineering, Biomaterials, Biochemistry, Biomedical Engineering
Keywords: finite-element analysis, fundamental frequency, natural frequencies, terrestrial laser scanning, tree architecture, wind damage
10.1098/rsif.2019.0116
Mean-field methods for multiscale models in neuroscience
Multiscale modelling of the brain is necessary in order to understand how
interactions on the molecular and cellular levels can give rise to higher-level
brain functions. As microscale processes tie into mesoscopic populations that
facilitate whole-brain behaviour, being able to describe the full-scale
interconnectivity of the brain is clearly imperative. In order to interpret all
of the different mechanisms, we need comprehensive models with accurate system dynamics. However, incorporating multiple levels into mathematical models often results in large networks of interlinked neural cells that are analytically intractable. Additionally, their numerical simulation is resource intensive. Useful ways of mitigating the computational burden include using a mean-field approach, as well as mathematical model order reduction (MOR).
Using mean-field approximation, random fluctuations of variables can be
accounted for by replacing them by their averages. Cells are grouped together
into populations based on their statistical similarities, in order to represent
the dynamics of the system in terms of the mean ensemble behaviour. These
populations can then be described by a probability density function expressing
the distribution of neuronal states at a given time. We use the Fokker-Planck
formalism, which results in a nonlinear system of partial differential
equations (PDEs).
With mathematical MOR methods the dimensions of a PDE model can be reduced with minimal information loss. The simulation time of the model is radically
shortened, albeit not without dimension-dependent approximation error. The
tolerated amount of inaccuracy depends on the final application of the model.
Due to being well-suited for depicting mesoscopic behaviour, the mean-field
approach in combination with the MOR methods allows us to describe the
behaviour of any large multiscale brain model with a relatively low computational burden. This can be particularly useful when attempting to model whole-brain connectivity, for which there is an immediate demand in clinical and robotic applications.
Event: Paper presented at 3RD Nordic Neuroscience Meeting 2019, Helsinki, Finland.
Robust output regulation of counter-flow heat exchangers
We consider a partial differential equation model widely used for counter-flow heat exchangers and the related robust output regulation problem with boundary control and boundary observation. We show that the control system is an exponentially stable regular linear system, which enables us to use a specific known controller design to robustly regulate the system. The results are illustrated with numerical simulations.
Contributors: Huhtala, K., Paunonen, L.
Publication date: 1 Jun 2019
Title of host publication: 3rd IFAC Workshop on Control of Systems Governed by Partial Differential Equations, CPDE 2019
Publisher: IFAC
Name: IFAC-PapersOnLine
ASJC Scopus subject areas: Control and Systems Engineering
Keywords: Heat exchangers, Linear control systems, Output regulation, Partial differential equations, Robust control
Robust Output Regulation of Counter-Flow Heat Exchangers. Embargo ended: 23/08/19
10.1016/j.ifacol.2019.08.036
jufoid=86671
The internal model principle for boundary control systems with polynomially bounded exogenous signals
We extend the internal model principle for boundary control system to cover robust tracking of sinusoidal reference signals with polynomial coefficients. The internal model principle is presented in the form of both the internal model structure and the G-conditions. A controller structure will be presented and its internal model properties will be analyzed in order to solve the tracking problem in a robust manner. As an example, a robust controller is constructed for the one-dimensional heat equation with Dirichlet boundary control at one endpoint and temperature measurement at the other endpoint of the interval. The performance of the controller is demonstrated by numerical simulations.
Contributors: Humaloja, J., Paunonen, L.
Keywords: Distributed parameter systems, Feedback control, Linear control systems, Output regulation, Regulator theory, Robust control
Additional files:
Tree biomass equations from terrestrial LiDAR: A case study in Guyana
Large uncertainties in tree and forest carbon estimates weaken national efforts to accurately estimate aboveground biomass (AGB) for their national monitoring, measurement, reporting and verification system. Allometric equations to estimate biomass have improved, but remain limited. They rely on destructive sampling; large trees are under-represented in the data used to create them; and they cannot always be applied to different regions. These factors lead to uncertainties and systematic errors in biomass estimations. We developed allometric models to estimate tree AGB in Guyana. These models were based on tree attributes (diameter, height, crown diameter) obtained from terrestrial laser scanning (TLS) point clouds from 72 tropical trees and wood density. We validated our methods and models with data from 26 additional destructively harvested trees. We found that our best TLS-derived allometric models included crown diameter, provided more accurate AGB estimates (R2 = 0.92-0.93) than traditional pantropical models (R2 = 0.85-0.89), and were especially accurate for large trees (diameter > 70 cm). The assessed pantropical models underestimated AGB by 4 to 13%. Nevertheless, one pantropical model (Chave et al. 2005 without height) consistently performed best among the pantropical models tested (R2 = 0.89) and predicted AGB accurately across all size classes-which but for this could not be known without destructive or TLS-derived validation data. Our methods also demonstrate that tree height is difficult to measure in situ, and the inclusion of height in allometric models consistently worsened AGB estimates. We determined that TLS-derived AGB estimates were unbiased. Our approach advances methods to be able to develop, test, and choose allometric models without the need to harvest trees.
Organisations: Computing Sciences, Research group: Inverse Problems, Wageningen University and Research Centre, 16 Center for International Forestry Research (CIFOR), Universiteit Gent, Center for International Forestry Research (CIFOR) Germany, University College London, Guyana Forestry Commission, Swedish University of Agricultural Sciences
Contributors: Lau, A., Calders, K., Bartholomeus, H., Martius, C., Raumonen, P., Herold, M., Vicari, M., Sukhdeo, H., Singh, J., Goodman, R. C.
Journal: Forests
Article number: 527
ASJC Scopus subject areas: Forestry
Keywords: 3D tree modelling, Aboveground biomass estimation, Destructive sampling, Guyana, LiDAR, Local tree allometry, Model evaluation, Quantitative structural model
forests-10-00527-v2
Algorithms and Logic as Programming Primers
To adapt all-immersive digitalization, the Finnish National Curriculum 2014 (FNC-2014) 'digi-jumps' by integrating programming into elementary education. However, applying the change to mathematics teachers' everyday praxis is hindered by a too high-level specification. To elaborate FNC-2014 into more concrete learning targets, we review the computer science syllabi of countries that are well ahead, as well as the education recommendations set by computer science organizations, such as ACM and IEEE. The whole mathematics syllabus should be critically viewed in the light of these recommendations and feedback collected from software professionals and educators. The feedback reveals an imbalance between supply and demand, i.e., what is over-taught versus under-taught, from the point of the requirements of current working life. The surveyed software engineers criticize the unnecessary surplus of calculus and differential equations, i.e., continuous mathematics. In contrast, the emphasis should shift more towards algorithms and data structures, flexibility in handling multiple data representations, and logic: in short – discrete mathematics. The ground for discrete mathematics should be prepared early enough, started already from primary level and continued consistently throughout the secondary till tertiary education. This paper aims to contribute to the further refinement of the mathematics syllabus by proposing such a discrete mathematics subset that especially supports the needs of computer science education, the focus being on algorithms and data structures, and logic in particular.
MoE publication type: A3 Part of a book or another research book
Organisations: Computing Sciences, University of Jyväskylä
Contributors: Niemelä, P., Valmari, A., Ali-Löytty, S.
Publication date: Jun 2019
Title of host publication: Computer Supported Education : 10th International Conference, CSEDU 2018, Revised Selected Papers
ISBN (Print): 9783030211509
Name: Communications in Computer and Information Science
Volume: 1022
Keywords: Computational thinking, algorithms, logic
http://urn.fi/URN:NBN:fi:tty-201908282040. Embargo ends: 20/06/20
EXT="Valmari, Antti"
Gaussian Process Regression for Forest Attribute Estimation From Airborne Laser Scanning Data
While the analysis of airborne laser scanning (ALS) data often provides reliable estimates for certain forest stand attributes-such as total volume or basal area-there is still room for improvement, especially in estimating species-specific attributes. Moreover, while the information on the estimate uncertainty would be useful in various economic and environmental analyses on forests, a computationally feasible framework for uncertainty quantifying in ALS is still missing. In this paper, the species-specific stand attribute estimation and uncertainty quantification (UQ) is approached using Gaussian process regression (GPR), which is a nonlinear and nonparametric machine learning method. Multiple species-specific stand attributes are estimated simultaneously: tree height, stem diameter, stem number, basal area, and stem volume. The cross-validation results show that GPR yields on average an improvement of 4.6&#x0025; in estimate root mean square error over a state-of-the-art k-nearest neighbors (kNNs) implementation, negligible bias and well performing UQ (credible intervals), while being computationally fast. The performance advantage over kNN and the feasibility of credible intervals persists even when smaller training sets are used.
Organisations: Mathematics, University of Eastern Finland
Contributors: Varvia, P., Lähivaara, T., Maltamo, M., Packalen, P., Seppänen, A.
Early online date: 2018
Journal: IEEE Transactions on Geoscience and Remote Sensing
ASJC Scopus subject areas: Electrical and Electronic Engineering, Earth and Planetary Sciences(all)
Keywords: Area-based approach (ABA), forest inventory, Gaussian process (GP), light detection and ranging (LiDAR), machine learning.
10.1109/TGRS.2018.2883495
Complex-domain Joint Broadband Hyperspectral Image Denoising
In this paper, we propose a novel complex domain denoising algorithm for hyperspectral data. The algorithm is based on the Complex Domain Block-Matching 3D (CDBM3D) filter and on similarity of hyperspectral data, which are usually slow varying for close values of wavelengths. Singular Value Decomposition (SVD) of the hyperspectral data is used in order to define an optimal small dimension data subspace. The CDBM3D is applied for 2D images of this subspace. The efficiency of the algorithm is demonstrated in simulation tests and for experimental data obtained by spectrally resolved digital holography of a transparent color object. It is proved that the proposed filtering algorithm retrieves amplitude and phase distributions even from very noisy data.
Organisations: Computing Sciences, Research group: Computational Imaging-CI, Institut für Lasertechnologien in der Medizin und Messtechnik, University of Stuttgart
Contributors: Katkovnik, V., Shevkunov, I., Claus, D., Pedrini, G., Egiazarian, K.
Journal: Sensors and Transducers
https://www.sensorsportal.com/HTML/DIGEST/may_2019/Vol_233/P_3080.pdf
Remarks on Similarities among Ternary Bent Functions
Bent functions have low autocorrelation and it is interesting to consider if there are some relationships that may be found among values a bent function takes, i.e., to find some possible patterns expressing similarity among certain bent functions in terms of the structure of their value-vectors. A possible approach towards exploring that problem proposed in this paper is based on partial Vilenkin-Chrestenson spectra, which are conveniently interpreted as matrix-valued Vilenkin-Chrestenson spectra of matrix-valued equivalents of ternary bent functions.
Organisations: Computing Sciences, Mathematical Institute of SANU, Faculty of Electronic Engineering, Technical University of Dortmund
Contributors: Stankovic, R. S., Stankovic, M., Astola, J. T., Moraga, C.
Title of host publication: 2019 IEEE 49th International Symposium on Multiple-Valued Logic, ISMVL 2019
ASJC Scopus subject areas: Computer Science(all), Mathematics(all)
Keywords: Bent functions, Matrix-valued bent functions, Ternary functions, Vilenkin-Chrestenson spectrum, Vilenkin-Chrestenson transform
10.1109/ISMVL.2019.00022
EXT="Stankovic, Radomir S."
Asymptotics for periodic systems
This paper investigates the asymptotic behaviour of solutions of periodic evolution equations. Starting with a general result concerning the quantified asymptotic behaviour of periodic evolution families we go on to consider a special class of dissipative systems arising naturally in applications. For this class of systems we analyse in detail the spectral properties of the associated monodromy operator, showing in particular that it is a so-called Ritt operator under a natural 'resonance' condition. This allows us to deduce from our general result a precise description of the asymptotic behaviour of the corresponding solutions. In particular, we present conditions for rational rates of convergence to periodic solutions in the case where the convergence fails to be uniformly exponential. We illustrate our general results by applying them to concrete problems including the one-dimensional wave equation with periodic damping.
Organisations: Mathematics, St Giles
Contributors: Paunonen, L., Seifert, D.
Journal: Journal of Differential Equations
ASJC Scopus subject areas: Analysis, Applied Mathematics
Keywords: Damped wave equation, Evolution family, Non-autonomous system, Periodic, Rates of convergence, Ritt operator
On the complexity of restoring corrupted colorings
In the r-Fix problem, we are given a graph G, a (non-proper) vertex-coloring c: V(G) → [r] , and a positive integer k. The goal is to decide whether a proper r-coloring c′ is obtainable from c by recoloring at most k vertices of G. Recently, Junosza-Szaniawski et al. (in: SOFSEM 2015: theory and practice of computer science, Springer, Berlin, 2015) asked whether the problem has a polynomial kernel parameterized by the number of recolorings k. In a full version of the manuscript, the authors together with Garnero and Montealegre, answered the question in the negative: for every r≥ 3 , the problem r-Fix does not admit a polynomial kernel unless [InlineEquation not available: see fulltext.]. Independently of their work, we give an alternative proof of the theorem. Furthermore, we study the complexity of r-Swap, where the only difference from r-Fix is that instead of k recolorings we have a budget of k color swaps. We show that for every r≥ 3 , the problem r-Swap is [InlineEquation not available: see fulltext.]-hard whereas r-Fix is known to be FPT. Moreover, when r is part of the input, we observe both Fix and Swap are [InlineEquation not available: see fulltext.]-hard parameterized by the treewidth of the input graph. We also study promise variants of the problems, where we are guaranteed that a proper r-coloring c′ is indeed obtainable from c by some finite number of swaps. For instance, we prove that for r= 3 , the problems r-Fix-Promise and r-Swap-Promise are [InlineEquation not available: see fulltext.]-hard for planar graphs. As a consequence of our reduction, the problems cannot be solved in 2o(n) time unless the Exponential Time Hypothesis fails.
Organisations: Mathematics, Bell Labs
Contributors: De Biasi, M., Lauri, J.
Journal: Journal of Combinatorial Optimization
ASJC Scopus subject areas: Computer Science Applications, Discrete Mathematics and Combinatorics, Control and Optimization, Computational Theory and Mathematics, Applied Mathematics
Keywords: Combinatorial reconfiguration, Computational complexity, Graph coloring, Local search, Parameterized complexity
The shape of (7) Iris as evidence of an ancient large impact?
Context. Asteroid (7) Iris is an ideal target for disk-resolved imaging owing to its brightness (V ~ 7-8) and large angular size of 0.33′′ during its apparitions. Iris is believed to belong to the category of large unfragmented asteroids that avoided internal differentiation, implying that its current shape and topography may record the first few 100 Myr of the solar system's collisional evolution. Aims. We recovered information about the shape and surface topography of Iris from disk-resolved VLT/SPHERE/ZIMPOL images acquired in the frame of our ESO large program. Methods. We used the All-Data Asteroid Modeling (ADAM) shape reconstruction algorithm to model the 3D shape of Iris, using optical disk-integrated data and disk-resolved images from SPHERE and earlier AO systems as inputs. We analyzed the SPHERE images and our model to infer the asteroid's global shape and the morphology of its main craters. Results. We present the 3D shape, volume-equivalent diameter D eq = 214 ± 5 km, and bulk density ρ = 2.7 ± 0.3 g cm -3 of Iris. Its shape appears to be consistent with that of an oblate spheroid with a large equatorial excavation. We identified eight putative surface features 20-40 km in diameter detected at several epochs, which we interpret as impact craters, and several additional crater candidates. Craters on Iris have depth-To-diameter ratios that are similar to those of analogous 10 km craters on Vesta. Conclusions. The bulk density of Iris is consistent with that of its meteoritic analog based on spectroscopic observations, namely LL ordinary chondrites. Considering the absence of a collisional family related to Iris and the number of large craters on its surface, we suggest that its equatorial depression may be the remnant of an ancient (at least 3 Gyr) impact. Iris's shape further opens the possibility that large planetesimals formed as almost perfect oblate spheroids. Finally, we attribute the difference in crater morphology between Iris and Vesta to their different surface gravities, and the absence of a substantial impact-induced regolith on Iris.
Organisations: Computing Sciences, Charles University in Prague, Massachusetts Institute of Technology, Queen's University, Belfast, Northern Ireland, Laboratoire d'Astrophysique de Marseille, CNRS, ONERA - The French Aerospace Lab, SETI Institute, IMCCE - Institut de Mecanique Celeste et de Calcul des Ephemerides, Adam Mickiewicz University, University of Szczecin, Université de Liège, Open University, Jet Propulsion Laboratory, California Institute of Technology, ESTEC - European Space Research and Technology Centre, TMT Observatory, Pontifical Catholic University of Peru San Miguel, European Southern Observatory (ESO)
Contributors: Hanuš, J., Marsset, M., Vernazza, P., Viikinkoski, M., Drouard, A., Broa, M., Carry, B., Fetick, R., Marchis, F., Jorda, L., Fusco, T., Birlan, M., Santana-Ros, T., Podlewska-Gaca, E., Jehin, E., Ferrais, M., Grice, J., Bartczak, P., Berthier, J., Castillo-Rogez, J., Cipriani, F., Colas, F., Dudziński, G., Dumas, C., Äž Urech, J., Kaasalainen, M., Kryszczynska, A., Lamy, P., Le Coroller, H., Marciniak, A., Michalowski, T., Michel, P., Pajuelo, M., Tanga, P., Vachier, F., Vigan, A., Witasse, O., Yang, B.
Journal: Astronomy and Astrophysics
Article number: A121
Keywords: Methods: numerical, Methods: observational, Minor planets, asteroids: individual: 7 Iris
10.1051/0004-6361/201834541
Robust and Model Predictive Control for Boundary Control Systems
In this thesis, robust and model predictive control are considered for boundary control systems. In terms of robust control, the existing results, especially the internal model principle, are generalized to cover this class of systems. The concept of approximate robust regulation for boundary control systems is presented, as, due to the internal model principle, in practice it is not possible to construct an exact robust regulating controller if the output space of the controlled system is infinite-dimensional. A practical controller design is presented to achieve robust regulation in this approximate sense.
Model predictive control (MPC) is considered for the class of regular linear systems which includes regular boundary control systems. The continuous-time system is approximated by a discrete-time one by using the Cayley-Tustin transform, and MPC is considered for the discrete-time system. Stability and optimality are proved for the proposed discrete-time MPC designs, which extends the corresponding finitedimensional MPC designs to the class of regular linear systems.
Organisations: Computing Sciences
Contributors: Humaloja, J.
Closing the gap between Earth-based and interplanetary mission observations: Vesta seen by VLT/SPHERE
Context. Over the past decades, several interplanetary missions have studied small bodies in situ, leading to major advances in our understanding of their geological and geophysical properties. These missions, however, have had a limited number of targets. Among them, the NASA Dawn mission has characterised in detail the topography and albedo variegation across the surface of asteroid (4) Vesta down to a spatial resolution of ~20 m pixel -1 scale. Aims. Here our aim was to determine how much topographic and albedo information can be retrieved from the ground with VLT/SPHERE in the case of Vesta, having a former space mission (Dawn) providing us with the ground truth that can be used as a benchmark. Methods. We observed Vesta with VLT/SPHERE/ZIMPOL as part of our ESO large programme (ID 199.C-0074) at six different epochs, and deconvolved the collected images with a parametric point spread function (PSF). We then compared our images with synthetic views of Vesta generated from the 3D shape model of the Dawn mission, on which we projected Vesta's albedo information. Results. We show that the deconvolution of the VLT/SPHERE images with a parametric PSF allows the retrieval of the main topographic and albedo features present across the surface of Vesta down to a spatial resolution of ~20-30 km. Contour extraction shows an accuracy of ~1 pixel (3.6 mas). The present study provides the very first quantitative estimate of the accuracy of ground-based adaptive-optics imaging observations of asteroid surfaces. Conclusions. In the case of Vesta, the upcoming generation of 30-40 m telescopes (ELT, TMT, GMT) should in principle be able to resolve all of the main features present across its surface, including the troughs and the north-south crater dichotomy, provided that they operate at the diffraction limit.
Organisations: Computing Sciences, Laboratoire d'Astrophysique de Marseille, Massachusetts Institute of Technology, Queen's University, Belfast, Northern Ireland, ONERA - The French Aerospace Lab, CNRS, SETI Institute, Charles University in Prague, IMCCE - Institut de Mecanique Celeste et de Calcul des Ephemerides, Adam Mickiewicz University, Jet Propulsion Laboratory, California Institute of Technology, ESTEC - European Space Research and Technology Centre, TMT Observatory, Université de Liège, Pontifical Catholic University of Peru San Miguel, University of Szczecin, European Southern Observatory (ESO)
Contributors: Fétick, R. J., Jorda, L., Vernazza, P., Marsset, M., Drouard, A., Fusco, T., Carry, B., Marchis, F., Hanuš, J., Viikinkoski, M., Birlan, M., Bartczak, P., Berthier, J., Castillo-Rogez, J., Cipriani, F., Colas, F., Dudziński, G., Dumas, C., Ferrais, M., Jehin, E., Kaasalainen, M., Kryszczynska, A., Lamy, P., Le Coroller, H., Marciniak, A., Michalowski, T., Michel, P., Mugnier, L. M., Neichel, B., Pajuelo, M., Podlewska-Gaca, E., Santana-Ros, T., Tanga, P., Vachier, F., Vigan, A., Witasse, O., Yang, B.
Publication date: 1 Mar 2019
Article number: A6
Keywords: Methods: observational, Minor planets, asteroids: individual: Vesta, Techniques: high angular resolution, Techniques: image processing
Homogeneous internal structure of CM-like asteroid (41) Daphne
Context. CM-like asteroids (Ch and Cgh classes) are a major population within the broader C-complex, encompassing about 10% of the mass of the main asteroid belt. Their internal structure has been predicted to be homogeneous, based on their compositional similarity as inferred from spectroscopy and numerical modeling of their early thermal evolution. Aims. Here we aim to test this hypothesis by deriving the density of the CM-like asteroid (41) Daphne from detailed modeling of its shape and the orbit of its small satellite. Methods. We observed Daphne and its satellite within our imaging survey with the Very Large Telescope extreme adaptive-optics SPHERE/ZIMPOL camera and complemented this data set with earlier Keck/NIRC2 and VLT/NACO observations. We analyzed the dynamics of the satellite with our Genoid meta-heuristic algorithm. Combining our high-angular resolution images with optical lightcurves and stellar occultations, we determine the spin period, orientation, and 3D shape, using our ADAM shape modeling algorithm. Results. The satellite orbits Daphne on an equatorial, quasi-circular, prograde orbit, like the satellites of many other large main-belt asteroids. The shape model of Daphne reveals several large flat areas that could be large impact craters. The mass determined from this orbit combined with the volume computed from the shape model implies a density for Daphne of 1.77 ± 0.26 g cm -3 (3 σ). This densityis consistent with a primordial CM-like homogeneous internal structure with some level of macroporosity (≈ 17%). Conclusions. Based on our analysis of the density of Daphne and 75 other Ch/Cgh-type asteroids gathered from the literature, we conclude that the primordial internal structure of the CM parent bodies was homogeneous.
Organisations: Computing Sciences, CNRS, IMCCE - Institut de Mecanique Celeste et de Calcul des Ephemerides, Queen's University, Belfast, Northern Ireland, Laboratoire d'Astrophysique de Marseille, Open University, Southwest Research Institute, Université Côte d'Azur, University of Arizona, Adam Mickiewicz University, University of Szczecin, Charles University in Prague, Thirty-Meter-Telescope, Leidos Inc., Binary Astronomy, Universite de Geneve, Cadi Ayyad University, Jet Propulsion Laboratory, California Institute of Technology, ESTEC - European Space Research and Technology Centre, Observatoire du Bois de Bardon, Université de Liège, Max Planck Institute for Astronomy, SETI Institute, Pontifical Catholic University of Peru San Miguel, Center for Solar System Studies, European Southern Observatory (ESO), Universidad Diego Portales
Contributors: Carry, B., Vachier, F., Berthier, J., Marsset, M., Vernazza, P., Grice, J., Merline, W. J., Lagadec, E., Fienga, A., Conrad, A., Podlewska-Gaca, E., Santana-Ros, T., Viikinkoski, M., Hanuš, J., Dumas, C., Drummond, J. D., Tamblyn, P. M., Chapman, C. R., Behrend, R., Bernasconi, L., Bartczak, P., Benkhaldoun, Z., Birlan, M., Castillo-Rogez, J., Cipriani, F., Colas, F., Drouard, A., Durech, J., Enke, B. L., Fauvaud, S., Ferrais, M., Fetick, R., Fusco, T., Gillon, M., Jehin, E., Jorda, L., Kaasalainen, M., Keppler, M., Kryszczynska, A., Lamy, P., Marchis, F., Marciniak, A., Michalowski, T., Michel, P., Pajuelo, M., Tanga, P., Vigan, A., Warner, B., Witasse, O., Yang, B., Zurlo, A.
Keywords: asteroids: general, Methods: observational, Minor planets, Minor planets, asteroids: individual: Daphne, Techniques: high angular resolution
Improved EEG source localization with Bayesian uncertainty modelling of unknown skull conductivity
Electroencephalography (EEG) source imaging is an ill-posed inverse problem that requires accurate conductivity modelling of the head tissues, especially the skull. Unfortunately, the conductivity values are difficult to determine in vivo. In this paper, we show that the exact knowledge of the skull conductivity is not always necessary when the Bayesian approximation error (BAE) approach is exploited. In BAE, we first postulate a probability distribution for the skull conductivity that describes our (lack of) knowledge on its value, and model the effects of this uncertainty on EEG recordings with the help of an additive error term in the observation model. Before the Bayesian inference, the likelihood is marginalized over this error term. Thus, in the inversion we estimate only our primary unknown, the source distribution. We quantified the improvements in the source localization when the proposed Bayesian modelling was used in the presence of different skull conductivity errors and levels of measurement noise. Based on the results, BAE was able to improve the source localization accuracy, particularly when the unknown (true) skull conductivity was much lower than the expected standard conductivity value. The source locations that gained the highest improvements were shallow and originally exhibited the largest localization errors. In our case study, the benefits of BAE became negligible when the signal-to-noise ratio dropped to 20 dB.
Organisations: Mathematics, University of Bath, Institute for Biomagnetism and Biosignalanalysis, University of Münster, Aristotle University of Thessaloniki, Centrum Wiskunde & Informatica, University College London, The University of Auckland, University of Eastern Finland
Contributors: Rimpiläinen, V., Koulouri, A., Lucka, F., Kaipio, J. P., Wolters, C. H.
Early online date: 6 Dec 2018
Journal: NeuroImage
ASJC Scopus subject areas: Neurology, Cognitive Neuroscience
Keywords: Bayesian inverse problem, Electroencephalography, Skull conductivity, Source localization, Uncertainty modelling
UNMARKED_rimpilainen_20190213. Embargo ended: 15/12/19
http://urn.fi/URN:NBN:fi:tuni-201910013624. Embargo ended: 15/12/19
EXT="Rimpiläinen, Ville"
Finite element analysis of trees in the wind based on terrestrial laser scanning data
Wind damage is an important driver of forest structure and dynamics, but it is poorly understood in natural broadleaf forests. This paper presents a new approach in the study of wind damage: combining terrestrial laser scanning (TLS) data and finite element analysis. Recent advances in tree reconstruction from TLS data allowed us to accurately represent the 3D geometry of a tree in a mechanical simulation, without the need for arduous manual mapping or simplifying assumptions about tree shape. We used this simulation to predict the mechanical strains produced on the trunks of 21 trees in Wytham Woods, UK, and validated it using strain data measured on these same trees. For a subset of five trees near the anemometer, the model predicted a five-minute time-series of strain with a mean cross-correlation coefficient of 0.71, when forced by the locally measured wind speed data. Additionally, the maximum strain associated with a 5 ms−1 or 15 ms-1 wind speed was well predicted by the model (N = 17, R2 = 0.81 and R2 = 0.79, respectively). We also predicted the critical wind speed at which the trees will break from both the field data and models and find a good overall agreement (N = 17, R2 = 0.40). Finally, the model predicted the correct trend in the fundamental frequencies of the trees (N = 20, R2 = 0.38) although there was a systematic underprediction, possibly due to the simplified treatment of material properties in the model. The current approach relies on local wind data, so must be combined with wind flow modelling to be applicable at the landscape-scale or over complex terrain. This approach is applicable at the plot level and could also be applied to open-grown trees, such as in cities or parks.
Organisations: Mathematics, Research group: Inverse Problems, University of Oxford, Facility for Airborne Atmospheric Measurements, Universiteit Gent, National Physical Laboratory, University College London, NERC National Centre for Earth Observation (NCEO), EFI Planted Forest Facility, Wageningen University and Research Centre, INRA
Contributors: Jackson, T., Shenkin, A., Wellpott, A., Calders, K., Origo, N., Disney, M., Burt, A., Raumonen, P., Gardiner, B., Herold, M., Fourcaud, T., Malhi, Y.
Journal: Agricultural and Forest Meteorology
ASJC Scopus subject areas: Forestry, Global and Planetary Change, Agronomy and Crop Science, Atmospheric Science
Keywords: Critical wind speed, Finite element analysis, Resonant frequency, Terrestrial laser scanning, TLS, Wind damage
10.1016/j.agrformet.2018.11.014
Mathematical model order reduction in computational neuroscience
Multi-scale models in neuroscience typically integrate detailed biophysical
neurobiological phenomena from molecular level up to network and system levels. Such models are very challenging to simulate despite the availability of
massively parallel computing systems. Model Order Reduction (MOR) is an
established method in engineering sciences, such as control theory. MOR is used in improving computational efficiency of simulations of large-scale and complex
nonlinear mathematical models. In this study the dimension of a nonlinear
mathematical model of plasticity in the brain is reduced using mathematical MOR methods.
Traditionally, models are simplified by eliminating variables, such as
molecular entities and ionic currents, from the system. Additionally,
assumptions of the system behavior can be made, for example regarding the
steady state of the chemical reactions. However, the current trend in
neuroscience is incorporating multiple physical scales of the brain in
simulations. Comprehensive models with full system dynamics are needed in order to increase understanding of different mechanisms in one brain area. Thus the elimination approach is not suitable for the consequent analysis of neural
phenomena.
The loss of information typically induced by eliminating variables of the system
can be avoided by mathematical MOR methods that strive to approximate the
entire system with a smaller number of dimensions compared to the original
system. Here, the effectiveness of MOR in approximating the behavior of all
the variables in the original system by simulating a model with a radically
reduced dimension, is demonstrated.
In the present work, mathematical MOR is applied in the context of an experimentally verified signaling pathway model of plasticity [kim2013]. This nonlinear chemical equation based model describes the biochemical calcium signaling steps required for plasticity and learning in the subcortical area of the brain. In addition to nonlinear characteristics, the model includes time-dependent terms which pose an additional challenge both computational efficiency and reduction wise.
The MOR method employed in this study is Proper Orthogonal Decomposition with Discrete Empirical Interpolation Method (POD+DEIM), a subspace projection
method for reducing the dimensionality of nonlinear systems [chaturantabut2010]. By applying these methods, the simulation time of the
model is radically shortened. However, our preliminary studies show
approximation error if the model is simulated for a very long time. The
tolerated amount of approximation error depends on the final application of the
model. Based on these promising results, POD+DEIM is recommended for
dimensionality reduction in computational neuroscience.
In summary, the reduced order model consumes a considerably smaller amount of
computational resources than the original model, while maintaining a low root
mean square error between the variables in the original and reduced models.
This was achieved by simulating the system dynamics in a lower dimensional
subspace without losing any of the variables from the model. The results presented here are novel as mathematical MOR has not been studied in neuroscience without linearisation of the mathematical model and never in the context of the model presented here.
Publication date: 6 Feb 2019
Event: Paper presented at 3rd HBP Student Conference on Interdisciplinary Brain Research, Ghent, Belgium.
Keywords: Computational Neuroscience, Control theory, Mathematics
A realistic, accurate and fast source modeling approach for the EEG forward problem
The aim of this paper is to advance electroencephalography (EEG) source analysis using finite element method (FEM) head volume conductor models that go beyond the standard three compartment (skin, skull, brain) approach and take brain tissue inhomogeneity (gray and white matter and cerebrospinal fluid) into account. The new approach should enable accurate EEG forward modeling in the thin human cortical structures and, more specifically, in the especially thin cortices in children brain research or in pathological applications. The source model should thus be focal enough to be usable in the thin cortices, but should on the other side be more realistic than the current standard mathematical point dipole. Furthermore, it should be numerically accurate and computationally fast. We propose to achieve the best balance between these demands with a current preserving (divergence conforming) dipolar source model. We develop and investigate a varying number of current preserving source basis elements n (n=1,…,n=5). For validation, we conducted numerical experiments within a multi-layered spherical domain, where an analytical solution exists. We show that the accuracy increases along with the number of basis elements, while focality decreases. The results suggest that the best balance between accuracy and focality in thin cortices is achieved with n=4 (or in extreme cases even n=3) basis functions, while in thicker cortices n=5 is recommended to obtain the highest accuracy. We also compare the current preserving approach to two further FEM source modeling techniques, namely partial integration and St. Venant, and show that the best current preserving source model outperforms the competing methods with regard to overall balance. For all tested approaches, FEM transfer matrices enable high computational speed. We implemented the new EEG forward modeling approaches into the open source duneuro library for forward modeling in bioelectromagnetism to enable its broader use by the brain research community. This library is build upon the DUNE framework for parallel finite elements simulations and integrates with high-level toolboxes like FieldTrip. Additionally, an inversion test has been implemented using the realistic head model to demonstrate and compare the differences between the aforementioned source models.
Organisations: Mathematics, Signal Processing, Research group: Inverse Problems, University of Münster, University of Eastern Finland, Laboratory of Signal Processing
Contributors: Miinalainen, T., Rezaei, A., Us, D., Nüßing, A., Engwer, C., Wolters, C. H., Pursiainen, S.
Early online date: 28 Aug 2018
Keywords: Divergence conforming vector fields, DUNE toolbox, Electroencephalography (EEG), Finite element method (FEM), Focal sources
Cuts for 3-D magnetic scalar potentials: Visualizing unintuitive surfaces arising from trivial knots
A wealth of literature exists on computing and visualizing cuts for the magnetic scalar potential of a current carrying conductor via Finite Element Methods (FEM) and harmonic maps to the circle. By a cut we refer to an orientable surface bounded by a given current carrying path (such that the flux through it may be computed) that restricts contour integrals on a curl-zero vector field to those that do not link the current-carrying path, analogous to branch cuts of complex analysis. This work is concerned with a study of a peculiar contour that illustrates topologically unintuitive aspects of cuts obtained from a trivial loop and raises questions about the notion of an optimal cut. Specifically, an unknotted curve that bounds only high genus surfaces in its convex hull is analyzed. The current work considers the geometric realization as a current-carrying wire in order to construct a magnetic scalar potential. Moreover, we consider the problem of choosing an energy functional on the space of maps, suggesting an algorithm for computing cuts via minimizing a conformally invariant functional utilizing Newton iteration.
Organisations: Electrical Engineering, Boston University
Contributors: Stockrahm, A., Lahtinen, V., Kangas, J. J., Kotiuga, P. R.
Journal: Computers and Mathematics with Applications
ASJC Scopus subject areas: Modelling and Simulation, Computational Theory and Mathematics, Computational Mathematics
Keywords: Homology, Magnetic fields, Visualization
10.1016/j.camwa.2019.05.023
Emptiness problems for distributed automata
We investigate the decidability of the emptiness problem for three classes of distributed automata. These devices operate on finite directed graphs, acting as networks of identical finite-state machines that communicate in an infinite sequence of synchronous rounds. The problem is shown to be decidable in LOGSPACE for a class of forgetful automata, where the nodes see the messages received from their neighbors but cannot remember their own state. When restricted to the appropriate families of graphs, these forgetful automata are equivalent to classical finite word automata, but strictly more expressive than finite tree automata. On the other hand, we also show that the emptiness problem is undecidable in general. This already holds for two heavily restricted classes of distributed automata: those that reject immediately if they receive more than one message per round, and those whose state diagram must be acyclic except for self-loops. Additionally, to demonstrate the flexibility of distributed automata in simulating different models of computation, we provide a characterization of constraint satisfaction problems by identifying a class of automata with exactly the same computational power.
Organisations: Computing Sciences, Helsinki University, UPEM
Contributors: Kuusisto, A., Reiter, F.
Journal: Information and Computation
ASJC Scopus subject areas: Theoretical Computer Science, Information Systems, Computer Science Applications, Computational Theory and Mathematics
Keywords: Distributed computing, Emptiness problem, Finite automata
10.1016/j.ic.2019.104503
Flexible Identification Procedure for Thermodynamic Constitutive Models for Magnetostrictive Materials
We present a novel approach for identifying a multiaxial thermodynamic magneto-mechanical constitutive law by direct bi- or trivariate spline interpolation from available magnetization and magnetostriction data. Reference data are first produced with a multiscale model in the case of a magnetic field and uniaxial and shear stresses. The thermodynamic model fits well to the results of the multiscale model, after which the models are compared under complex multiaxial loadings. A surprisingly good agreement between the two models is found, but some differences in the magnetostrictive behaviour are also pointed out. Finally, the model is fitted to measurement results from an electrical steel sheet. The spline-based constitutive law overcomes several drawbacks of analytical approaches used earlier. The presented models and measurement results are openly available.
Organisations: Electrical Engineering, Research area: Power engineering, Research group: Electromechanics, Civil Engineering, Research group: Structural Mechanics, Aalto University, Group of Electrical Engineering - Paris, CNRS, CNRS Centre National de la Recherche Scientifique
Contributors: Rasilo, P., Singh, D., Jeronen, J., Aydin, U., Martin, F., Belahcen, A., Daniel, L., Kouhia, R.
Journal: Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences
10.1098/rspa.2018.0280
Neighbour species richness and local structural variability modulate aboveground allocation patterns and crown morphology of individual trees
Local neighbourhood interactions are considered a main driver for biodiversity–productivity relationships in forests. Yet, the structural responses of individual trees in species mixtures and their relation to crown complementarity remain poorly understood. Using a large-scale forest experiment, we studied the impact of local tree species richness and structural variability on above-ground wood volume allocation patterns and crown morphology. We applied terrestrial laser scanning to capture the three-dimensional structure of trees and their temporal dynamics. We found that crown complementarity and crown plasticity increased with species richness. Trees growing in species-rich neighbourhoods showed enhanced aboveground wood volume both in trunks and branches. Over time, neighbourhood diversity induced shifts in wood volume allocation in favour of branches, in particular for morphologically flexible species. Our results demonstrate that diversity-mediated shifts in allocation pattern and crown morphology are a fundamental mechanism for crown complementarity and may be an important driver of overyielding.
Organisations: Computing Sciences, Leuphana University Lüneburg, Martin-Luther-Universität Halle-Wittenberg, German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Technische Universität Dresden
Contributors: Kunz, M., Fichtner, A., Härdtle, W., Raumonen, P., Bruelheide, H., von Oheimb, G.
Journal: ECOLOGY LETTERS
ASJC Scopus subject areas: Ecology, Evolution, Behavior and Systematics
Keywords: BEF-China, biodiversity, crown complementarity, ecosystem functioning, forests, productivity, terrestrial laser scanning
ele.13400
10.1111/ele.13400
Research output: Contribution to journal › Letter › Scientific › peer-review
Optimal energy decay for the wave-heat system on a rectangular domain
We study the rate of energy decay for solutions of a coupled wave-heat system on a rectangular domain. Using techniques from the theory of C 0 -semigroups, and in particular a well-known result due to Borichev and Tomilov, we prove that the energy of classical solutions decays like t - 2/ 3 as t \rightarrow \infty . This rate is moreover shown to be sharp. Our result implies in particular that a general estimate in the literature, which predicts at least logarithmic decay and is known to be best possible in general, is suboptimal in the special case under consideration here. Our strategy of proof involves direct estimates based on separation of variables and a refined version of the technique developed in our earlier paper for a one-dimensional wave-heat system.
Organisations: Computing Sciences, St Giles
Contributors: Batty, C., Paunonen, L., Seifert, D.
Journal: SIAM JOURNAL ON MATHEMATICAL ANALYSIS
ASJC Scopus subject areas: Analysis, Computational Mathematics, Applied Mathematics
Keywords: C -semigroups, Coupled, Energy, Heat equation, Rates of decay, Rectangular domain, Resolvent estimates, Wave equation
10.1137/18M1195796
Quaternionic Hyperbolic Function Theory
We are studying hyperbolic function theory in the skew-field of quaternions. This theory is connected to k-hyperbolic harmonic functions that are harmonic with respect to the hyperbolic Riemannian metric (Formula Presented) in the upper half space (Formula Presented). In the case k = 2, the metric is the hyperbolic metric of the Poincaré upper half-space. Hempfling and Leutwiler started to study this case and noticed that the quaternionic power function xm(m ε Z), is a conjugate gradient of a 2-hyperbolic harmonic function. They researched polynomial solutions. We find fundamental k-hyperbolic harmonic functions depending only on the hyperbolic distance and x3. Using these functions we are able to verify a Cauchy type integral formula. Earlier these results have been verified for quaternionic functions depending only on reduced variables (x0, x1, x2). Our functions are depending on four variables.
Organisations: Computing Sciences, Department of Mathematics and Statistics, University of Helsinki
Title of host publication: Topics in Clifford Analysis
ISBN (Print): 978-3-030-23853-7
ISBN (Electronic): 978-3-030-23854-4
Name: Trends in Mathematics
ISSN (Electronic): 2297-024X
ASJC Scopus subject areas: Mathematics(all)
Keywords: Clifford algebra, Hyperbolic Laplace operator, Hyperbolic metric, Laplace-Beltrami operator, Monogenic function, Quaternions, α-Hyperbolic harmonic, α-Hypermonogenic
10.1007/978-3-030-23854-4_2
Simulating solar-induced chlorophyll fluorescence in a boreal forest stand reconstructed from terrestrial laser scanning measurements
Solar-induced chlorophyll fluorescence (SIF) has been shown to be a suitable remote sensing proxy of photosynthesis at multiple scales. However, the relationship between fluorescence and photosynthesis observed at the leaf level cannot be directly applied to the interpretation of retrieved SIF due to the impact of canopy structure. We carried out a SIF modelling study for a heterogeneous forest canopy considering the effect of canopy structure in the Discrete Anisotropic Radiative Transfer (DART) model. A 3D forest simulation scene consisting of realistic trees and understory, including multi-scale clumping at branch and canopy level, was constructed from terrestrial laser scanning data using the combined model TreeQSM and FaNNI for woody structure and leaf insertion, respectively. Next, using empirical data and a realistic range of leaf-level biochemical and physiological parameters, we conducted a local sensitivity analysis to demonstrate the potential of the approach for assessing the impact of structural, biochemical and physiological factors on top of canopy (TOC) SIF. The analysis gave insight into the factors that drive the intensity and spectral properties of TOC SIF in heterogeneous boreal forest canopies. DART simulated red TOC fluorescence was found to be less affected by biochemical factors such as chlorophyll and dry matter contents or the senescent factor than far-red fluorescence. In contrast, canopy structural factors such as overstory leaf area index (LAI), leaf angle distribution and fractional cover had a substantial and comparable impact across all SIF wavelengths, with the exception of understory LAI that affected predominantly far-red fluorescence. Finally, variations in the fluorescence quantum efficiency (Fqe) of photosystem II affected all TOC SIF wavelengths. Our results also revealed that not only canopy structural factors but also understory fluorescence should be considered in the interpretation of tower, airborne and satellite SIF datasets, especially when acquired in the (near-) nadir viewing direction and for forests with open canopies. We suggest that the modelling strategy introduced in this study, coupled with the increasing availability of TLS and other 3D data sources, can be applied to resolve the interplay between physiological, biochemical and structural factors affecting SIF across ecosystems and independently of canopy complexity, paving the way for future SIF-based 3D photosynthesis models.
Organisations: Computing Sciences, Chinese Academy of Sciences, University of Chinese Academy of Sciences, University of Helsinki, VTT Technical Research Centre of Finland, University of Toulouse, INP, LAAS-CNRS, University of Tasmania, Natural Resources Institute Finland (Luke)
Contributors: Liu, W., Atherton, J., Mõttus, M., Gastellu-Etchegorry, J. P., Malenovský, Z., Raumonen, P., Åkerblom, M., Mäkipää, R., Porcar-Castell, A.
Keywords: Boreal forest, DART, FaNNI, Far-red SIF, LiDAR, Red SIF, Silver birch, Solar-induced chlorophyll fluorescence, TreeQSM, Understory
Software-defined radio prototype for fast-convolution-based filtered OFDM in 5G NR
In this work, we provide first-in-class measurement results for fast-convolution-based filtered orthogonal frequencydivision multiplexing (FC-F-OFDM) processing implemented on a universal software radio peripheral (USRP) software-defined radio (SDR). The fast-convolution-based processing offers a highly efficient and flexible filtered OFDM scheme allowing to achieve high spectral utilization in different channel bandwidths. Through the SDR implementation and transmitter spectrum emission measurements, we show that FC-F-OFDM allows to increase spectrum utilization compared to the fifth generation new radio (5G NR) Release-15 requirements. Furthermore, considering the out-of-band emission masks and adjacent-channel-leakage-ratio requirements, FC-F-OFDM provides a larger interference margin than well-known windowed overlap-and-add OFDM processing.
Organisations: Electrical Engineering, Nokia Mobile Networks
Contributors: Gokceli, S., Levanen, T., Yli-Kaakinen, J., Turunen, M., Allen, M., Riihonen, T., Palin, A., Renfors, M., Valkama, M.
Title of host publication: 2019 European Conference on Networks and Communications, EuCNC 2019
Software_Defined_Radio_Prototype_for_Fast_Convolution_Based_Filtered_OFDM_in_5G_NR__Final
10.1109/EuCNC.2019.8802008
INT=elen,"Turunen, Matias"
DISCUS – The Deep Interior Scanning CubeSat mission to a rubble pile near-Earth asteroid
We have performed an initial stage conceptual design study for the Deep Interior Scanning CubeSat (DISCUS), a tandem 6U CubeSat carrying a bistatic radar as the main payload. DISCUS will be operated either as an independent mission or accompanying a larger one. It is designed to determine the internal macroporosity of a 260–600 m diameter Near Earth Asteroid (NEA) from a few kilometers distance. The main goal will be to achieve a global penetration with a low-frequency signal as well as to analyze the scattering strength for various different penetration depths and measurement positions. Moreover, the measurements will be inverted through a computed radar tomography (CRT) approach. The scientific data provided by DISCUS would bring more knowledge of the internal configuration of rubble pile asteroids and their collisional evolution in the Solar System. It would also advance the design of future asteroid deflection concepts. We aim at a single-unit (1U) radar design equipped with a half-wavelength dipole antenna. The radar will utilize a stepped-frequency modulation technique the baseline of which was developed for ESA's technology projects GINGER and PIRA. The radar measurements will be used for CRT and shape reconstruction. The CubeSat will also be equipped with an optical camera system and laser altimeter to support navigation and shape reconstruction. We provide the details of the measurement methods to be applied along with the requirements derived from the known characteristics of rubble pile asteroids. Additionally, an initial design study of the platform and targets accessible within 20 lunar distances are presented.
Organisations: Mathematics, Max Planck Institute for Solar System Research, RST Radar Systemtechnik AG, MEW-Aerospace UG
Contributors: Bambach, P., Deller, J., Vilenius, E., Pursiainen, S., Takala, M., Braun, H. M., Lentz, H., Wittig, M.
Journal: Advances in Space Research
Scopus rating (2018): CiteScore 1.97 SJR 0.589 SNIP 1.186
ASJC Scopus subject areas: Aerospace Engineering, Space and Planetary Science
Keywords: Computed radar tomography, Deep-space CubeSat, Near earth asteroid, Radar, Rubble pile asteroid
10.1016/j.asr.2018.06.016
(16) Psyche: A mesosiderite-like asteroid?
Context. Asteroid (16) Psyche is the target of the NASA Psyche mission. It is considered one of the few main-belt bodies that could be an exposed proto-planetary metallic core and that would thus be related to iron meteorites. Such an association is however challenged by both its near- and mid-infrared spectral properties and the reported estimates of its density. Aims. Here, we aim to refine the density of (16) Psyche to set further constraints on its bulk composition and determine its potential meteoritic analog. Methods. We observed (16) Psyche with ESO VLT/SPHERE/ZIMPOL as part of our large program (ID 199.C-0074). We used the high angular resolution of these observations to refine Psyche's three-dimensional (3D) shape model and subsequently its density when combined with the most recent mass estimates. In addition, we searched for potential companions around the asteroid. Results. We derived a bulk density of 3.99 ± 0.26 ± cm-3 for Psyche. While such density is incompatible at the 3-sigma level with any iron meteorites (∼7.8 ± cm-3), it appears fully consistent with that of stony-iron meteorites such as mesosiderites (density ∼4.25 ± cm-3). In addition, we found no satellite in our images and set an upper limit on the diameter of any non-detected satellite of 1460 ± 200 m at 150 km from Psyche (0.2% × RHill, the Hill radius) and 800 ± 200 m at 2000 km (3% × RHill). Conclusions. Considering that the visible and near-infrared spectral properties of mesosiderites are similar to those of Psyche, there is merit to a long-published initial hypothesis that Psyche could be a plausible candidate parent body for mesosiderites.
Organisations: Mathematics, Laboratoire d'Astrophysique de Marseille, Charles University in Prague, CNRS, Queen's University, Belfast, Northern Ireland, SETI Institute, IMCCE - Institut de Mecanique Celeste et de Calcul des Ephemerides, Adam Mickiewicz University, Thirty-Meter-Telescope, Jet Propulsion Laboratory, California Institute of Technology, ESTEC - European Space Research and Technology Centre, Université de Liège, Open University, Université de Versailles Saint-Quentin-en-Yvelines, Pontifical Catholic University of Peru San Miguel, University of Szczecin, Center for Solar System Studies, European Southern Observatory (ESO)
Contributors: Viikinkoski, M., Vernazza, P., Hanuš, J., Le Coroller, H., Tazhenova, K., Carry, B., Marsset, M., Drouard, A., Marchis, F., Fetick, R., Fusco, T., Ďurech, J., Birlan, M., Berthier, J., Bartczak, P., Dumas, C., Castillo-Rogez, J., Cipriani, F., Colas, F., Ferrais, M., Grice, J., Jehin, E., Jorda, L., Kaasalainen, M., Kryszczynska, A., Lamy, P., Marciniak, A., Michalowski, T., Michel, P., Pajuelo, M., Podlewska-Gaca, E., Santana-Ros, T., Tanga, P., Vachier, F., Vigan, A., Warner, B., Witasse, O., Yang, B.
Article number: L3
Keywords: Methods: observational, Minor planets, asteroids: general, Minor planets, asteroids: individual: (16) Psyche, Techniques: high angular resolution
Compute mindlessly. Not! map consciously
This paper utilizes concept mapping as a tool for conscious and deliberate knowledge building in mathematics and its extension to algorithms. Currently, alleged defects in mathematics education are obvious: instead of conceptual elaboration, everyday praxis relies on routine computations that are likely to lead into alienated concepts with weak connections to prior knowledge. A concept map visualizes the existing conceptual structure, and whenever new information is brought in, it will be placed in the map by clearly explicating its linkage to the previous concepts. In the Finnish mathematics education, such new knowledge is programming content that is integrated into elementary school mathematics in 2014 Finnish National Curriculum. This content is crystallized as the requirements of computational and algorithmic thinking, the utilization of respective data structures, and adequate amount of hands-on practice to internalize good coding conventions. This study examines secondary (N = 19) and higher education students (N = 10) and their conceptual knowledge of mathematics concentrating on the domain of algorithms in particular. The concept maps drawn by the students are evaluated using the SOLO taxonomy. To conclude, a consensus map of algorithms is represented and linked to the elementary mathematics syllabus.
Organisations: Research area: Software engineering, Computing Sciences, Department of Education, Ideal Learning Oy
Contributors: Niemelä, P., Mikkolainen, V., Vuorinen, J.
Journal: Universal Journal of Educational Research
ASJC Scopus subject areas: Education
Keywords: Concept Mapping, Meta-cognitive Skills, SOLO Taxonomy, Visualizations
UJER33-19511998-1
10.13189/ujer.2018.061133
The impact crater at the origin of the Julia family detected with VLT/SPHERE?
Context. The vast majority of the geophysical and geological constraints (e.g., internal structure, cratering history) for main-belt asteroids have so far been obtained via dedicated interplanetary missions (e.g., ESA Rosetta, NASA Dawn). The high angular resolution of SPHERE/ZIMPOL, the new-generation visible adaptive-optics camera at ESO VLT, implies that these science objectives can now be investigated from the ground for a large fraction of D 100 km main-belt asteroids. The sharp images acquired by this instrument can be used to accurately constrain the shape and thus volume of these bodies (hence density when combined with mass estimates) and to characterize the distribution and topography of D 30 km craters across their surfaces. Aims. Here, via several complementary approaches, we evaluated the recently proposed hypothesis that the S-type asteroid (89) Julia is the parent body of a small compact asteroid family that formed via a cratering collisional event. Methods. We observed (89) Julia with VLT/SPHERE/ZIMPOL throughout its rotation, derived its 3D shape, and performed a reconnaissance and characterization of the largest craters. We also performed numerical simulations to first confirm the existence of the Julia family and to determine its age and the size of the impact crater at its origin. Finally, we utilized the images/3D shape in an attempt to identify the origin location of the small collisional family. Results. On the one hand, our VLT/SPHERE observations reveal the presence of a large crater (D 75 km) in Julias southern hemisphere. On the other hand, our numerical simulations suggest that (89) Julia was impacted 30-120 Myrs ago by a D 8 km asteroid, thereby creating a D 60 km impact crater at the surface of Julia. Given the small size of the impactor, the obliquity of Julia and the particular orientation of the family in the (a,i) space, the imaged impact crater is likely to be the origin of the family. Conclusions. New doors into ground-based asteroid exploration, namely, geophysics and geology, are being opened thanks to the unique capabilities of VLT/SPHERE. Also, the present work may represent the beginning of a new era of asteroid-family studies. In the fields of geophysics, geology, and asteroid family studies, the future will only get brighter with the forthcoming arrival of 30-40 m class telescopes like ELT, TMT, and GMT.
Organisations: Mathematics, Laboratoire d'Astrophysique de Marseille, Charles University in Prague, Queen's University, Belfast, Northern Ireland, CNRS, SETI Institute, IMCCE - Institut de Mecanique Celeste et de Calcul des Ephemerides, Adam Mickiewicz University, University of Szczecin, Université de Liège, Jet Propulsion Laboratory, California Institute of Technology, ESTEC - European Space Research and Technology Centre, TMT Observatory, Pontifical Catholic University of Peru San Miguel, Center for Solar System Studies, European Southern Observatory (ESO), Arizona State University, University of Maryland, Cadi Ayyad University
Contributors: Vernazza, P., Broz, M., Drouard, A., Hanuš, J., Viikinkoski, M., Marsset, M., Jorda, L., Fetick, R., Carry, B., Marchis, F., Birlan, M., Fusco, T., Santana-Ros, T., Podlewska-Gaca, E., Jehin, E., Ferrais, M., Bartczak, P., Dudziński, G., Berthier, J., Castillo-Rogez, J., Cipriani, F., Colas, F., Dumas, C., Urech, J., Kaasalainen, M., Kryszczynska, A., Lamy, P., Le Coroller, H., Marciniak, A., Michalowski, T., Michel, P., Pajuelo, M., Tanga, P., Vachier, F., Vigan, A., Warner, B., Witasse, O., Yang, B., Asphaug, E., Richardson, D. C., Ševeček, P., Gillon, M., Benkhaldoun, Z.
Keywords: Methods: numerical, Methods: observational, Minor planets asteroids: individual: (89) Julia, Techniques: high angular resolution
Quantifying branch architecture of tropical trees using terrestrial LiDAR and 3D modelling
Key message: A method using terrestrial laser scanning and 3D quantitative structure models opens up new possibilities to reconstruct tree architecture from tropical rainforest trees. Abstract: Tree architecture is the three-dimensional arrangement of above ground parts of a tree. Ecologists hypothesize that the topology of tree branches represents optimized adaptations to tree's environment. Thus, an accurate description of tree architecture leads to a better understanding of how form is driven by function. Terrestrial laser scanning (TLS) has demonstrated its potential to characterize woody tree structure. However, most current TLS methods do not describe tree architecture. Here, we examined nine trees from a Guyanese tropical rainforest to evaluate the utility of TLS for measuring tree architecture. First, we scanned the trees and extracted individual tree point clouds. TreeQSM was used to reconstruct woody structure through 3D quantitative structure models (QSMs). From these QSMs, we calculated: (1) length and diameter of branches > 10 cm diameter, (2) branching order and (3) tree volume. To validate our method, we destructively harvested the trees and manually measured all branches over 10 cm (279). TreeQSM found and reconstructed 95% of the branches thicker than 30 cm. Comparing field and QSM data, QSM overestimated branch lengths thicker than 50 cm by 1% and underestimated diameter of branches between 20 and 60 cm by 8%. TreeQSM assigned the correct branching order in 99% of all cases and reconstructed 87% of branch lengths and 97% of tree volume. Although these results are based on nine trees, they validate a method that is an important step forward towards using tree architectural traits based on TLS and open up new possibilities to use QSMs for tree architecture.
Organisations: Mathematics, Research group: Inverse Problems, Wageningen University and Research Centre, Center for International Forestry Research (CIFOR), Sonoma State University, University of Oxford
Contributors: Lau, A., Bentley, L. P., Martius, C., Shenkin, A., Bartholomeus, H., Raumonen, P., Malhi, Y., Jackson, T., Herold, M.
Publication date: Oct 2018
Early online date: 25 May 2018
Journal: Trees - Structure and Function
ASJC Scopus subject areas: Forestry, Physiology, Ecology, Plant Science
Keywords: Destructive harvesting, Quantitative structure models, Terrestrial LiDAR, Tree architecture, Tree metrics
Lau2018_Article_QuantifyingBranchArchitectureO
Improvement of computational efficiency of a biochemical plasticity model
Multi-scale models in neuroscience integrate detailed neurobiological phenomena from molecular level up to network and system levels. such models are very challenging to simulate despite the availability of massively parallel
computing systems. model order reduction (mor) is an established method in
engineering sciences, such as control theory. mor is used in improving
computational efficiency of simulations of complex nonlinear mathematical
models. in this study the dimension of a nonlinear mathematical model of
plasticity in the brain is reduced using mathematical mor methods.
steady state of the chemical reactions. however, comprehensive models with full
system dynamics are needed in order to increase understanding of different
mechanisms in one brain area. thus the elimination approach is not suitable for
the consequent analysis of neural phenomena.
The loss of information induced by eliminating variables of the system can be
avoided by mathematical mor methods that approximate the entire system with a smaller number of dimensions compared to the original system. here,
mathematical MOR is applied in the context of an experimentally verified
signaling pathway model of plasticity (Kim et al., PLoS Comp. Biol., 2013).
This nonlinear chemical equation based model describes the biochemical calcium signaling steps required for plasticity and learning in the subcortical area of the brain. By applying these methods, the simulation time of the model is radically shortened.
Organisations: Faculty of Biomedical Sciences and Engineering, Mathematics
Event: Paper presented at Brain and Mind Symposium 2018, Helsinki, Finland.
Keywords: Neuroscience, Computational Neuroscience, Control theory
On the complexity of rainbow coloring problems
An edge-colored graph G is said to be rainbow connected if between each pair of vertices there exists a path which uses each color at most once. The rainbow connection number , denoted by rc(G), is the minimum number of colors needed to make G rainbow connected. Along with its variants, which consider vertex colorings and/or so-called strong colorings, the rainbow connection number has been studied from both the algorithmic and graph-theoretic points of view.
In this paper we present a range of new results on the computational complexity of computing the four major variants of the rainbow connection number. In particular, we prove that the Strong Rainbow Vertex Coloring problem is View the MathML source-complete even on graphs of diameter 3, and also when the number of colors is restricted to 2. On the other hand, we show that if the number of colors is fixed then all of the considered problems can be solved in linear time on graphs of bounded treewidth. Moreover, we provide a linear-time algorithm which decides whether it is possible to obtain a rainbow coloring by saving a fixed number of colors from a trivial upper bound. Finally, we give a linear-time algorithm for computing the exact rainbow connection numbers for three variants of the problem on graphs of bounded vertex cover number.
Organisations: Department of Mathematics, TU Vienna
Contributors: Eiben, E., Ganian, R., Lauri, J.
Journal: Discrete Applied Mathematics
Scopus rating (2018): CiteScore 1.2 SJR 0.815 SNIP 1.263
10.1016/j.dam.2016.10.021
A study of crown development mechanisms using a shoot-based tree model and segmented terrestrial laser scanning data
Background and Aims Functional-structural plant models (FSPMs) allow simulation of tree crown development as the sum of modular (e.g. shoot-level) responses triggered by the local environmental conditions. The actual process of space filling by the crowns can be studied. Although the FSPM simulations are at organ scale, the data for their validation have usually been at more aggregated levels (whole-crown or whole-tree). Measurements made by terrestrial laser scanning (TLS) that have been segmented into elementary units (internodes) offer a phenotyping tool to validate the FSPM predictions at levels comparable with their detail. We demonstrate the testing of different formulations of crown development of Scots pine trees in the LIGNUM model using segmented TLS data. Methods We made TLS measurements from four sample trees growing in a forest on a relatively poor soil from sapling size to mature stage. The TLS data were segmented into internodes. The segmentation also produced information on whether needles were present in the internode. We applied different formulations of crown development (flushing of buds and length of growth of new internodes) in LIGNUM. We optimized the parameter values of each formulation using genetic algorithms to observe the best fit of LIGNUM simulations to the measured trees. The fitness function in the estimation combined both tree-level characteristics (e.g. tree height and crown length) and measures of crown shape (e.g. spatial distribution of needle area). Key Results Comparison of different formulations against the data indicates that the Extended Borchert-Honda model for shoot elongation works best within LIGNUM. Control of growth by local density in the crown was important for all shoot elongation formulations. Modifying the number of lateral buds as a function of local density in the crown was the best way to accomplish density control. Conclusions It was demonstrated how segmented TLS data can be used in the context of a shoot-based model to select model components.
Organisations: Mathematics, Research group: Inverse Problems, Natural Resources Institute Finland (Luke), University of Helsinki
Contributors: Sievänen, R., Raumonen, P., Perttunen, J., Nikinmaa, E., Kaitaniemi, P.
Journal: Annals of Botany
ASJC Scopus subject areas: Plant Science
Keywords: forest stand, Functional-structural model, Scots pine, terrestrial laser scanning
10.1093/aob/mcy082
Linear Model Predictive Control for Schrödinger Equation
The paper considers the finite-horizon constrained optimal control problem for Schrödinger equation with boundary controls and boundary observations. The plant is mapped from continuous to discrete time using the Cayley-Tustin transform, which preserves input-output-stability of the plant. The proposed transformation is structure and energy preserving and does not induce order reduction associated with the spatial discretization. The controller design setting leads to the finite horizon constrained quadratic regulator problem, which is easily realized and accounts in explicit manner for input and output/state constraints. The model predictive control (MPC) design is realized for Schrödinger equation and the results are illustrated with numerical simulations showing successful stabilization of Schrödinger equation with simultaneous satisfaction of input and output/state constraints.
Organisations: Mathematics, University of Alberta
Contributors: Humaloja, J., Dubljevic, S.
Title of host publication: 2018 Annual American Control Conference, ACC 2018
ASJC Scopus subject areas: Electrical and Electronic Engineering
HumDubACC18
10.23919/ACC.2018.8431686
A Partial Internal Model for Approximate Robust Output Regulation of Boundary Control Systems
Introduced for finite-dimensional systems by Fran- cis and Wonham in the mid 70's, the internal model principle states that a stabilizing controller achieves asymptotic output tracking and disturbance rejection robustly if and only if it contains a p-copy of the exosystem frequencies, where p is the dimension of the output space of the plant. Later, the internal model principle has been extended, e.g., to boundary control systems on multidimensional spatial domains, and in this setting it follows from the principle that every robust output regulator is necessarily infinite-dimensional. However, it was recently established by the authors that robust approximate output tracking can be achieved with a finite-dimensional controller, and in the present paper, we formulate an internal model for this purpose. The efficiency of the method is numerically demonstrated using the heat equation on the unit square in $\mathbb{R}^2$ with boundary control and boundary observation.
MoE publication type: D3 Professional conference proceedings
Organisations: Mathematics, Research group: Computer Science and Applied Logics, Åbo Akademi University
Contributors: Humaloja, J., Paunonen, L., Kurula, M.
Title of host publication: 23rd International Symposium on Mathematical Theory of Networks and Systems
HumPauMTNS18
Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › Professional
Robust controllers for a heat equation using the Galerkin approximation
We consider the robust output tracking problem for an unstable one-dimensional heat equation. As the main contribution we propose a new way of designing infinite-dimensional robust controllers based on Galerkin approximations of infinite-dimensional observer-based controllers. The results are illustrated with a concrete example where the finite-dimensional controllers are constructed using the Finite Element Method. The results are extendable for more general parabolic control systems.
Organisations: Mathematics, Research group: Computer Science and Applied Logics
Contributors: Phan-Duc, D., Paunonen, L.
Title of host publication: Proceedings of the 23rd International Symposium on Mathematical Theory of Networks and Systems
Light, Shape and Space: Direct and Inverse Problems of Individual Objects and Populations
In this thesis, we examine two case studies. The first case studies how the shape of a celestial body influences an effect caused by light, while the second case analyzes how the light, in the form of brightness measurements, can give us information about the shapes of celestial bodies. In the first problem, we discuss an effect where sunlight produces a torque that affects the rotational dynamics of small bodies. The effect was named YORP, after its observers Yarkovsky, O'Keefe, Radzievskii and Paddack. We derive analytical formulas for the YORP torques and a new quantity that expresses the maximum YORP effect caused by the sunlight for a given shape. We called this quantity YORP capacity. In addition, we estimate the upper bound of the YORP capacity, showing how it is theoretically unbounded, but for practical shapes, there is an approximate, finite upper bound. We also study the stability of the YORP effect against noise in the shape model, discovering that the absolute change in YORP capacity remains small with minor shape perturbations, but the relative change becomes large if the YORP capacity was initially small. Analyzing the shape models found in an asteroid database, we discovered that a majority of the shapes is unstable against shape perturbations, while a fraction of the shapes is semistable. The former case may explain why astronomers have obtained completely different results on the YORP effect when using shapes with different resolutions. All of the aforementioned are new results in the field of YORP research.
In the second case, we study an inverse problem where the quality of the data, given as time series, is so weak that it is no longer possible to reconstruct a model for an individual target. Therefore, rather than examining single targets, we focus on a large population of targets, and attempt to obtain information on the population. That is, we attempt to reconstruct a population-wide model. The characteristics of the population are described with a distribution function. This approach is completely new in the field of inverse problems. We discuss the forward model and the inverse problem, showing that even with weak data and a crude model, it is possible to obtain a unique joint distribution that gives us information about our two parameters, shape elongation and spin latitude. The accuracy of the solution is rough, but brings out the information that can be recovered from the data, and the distribution method is tolerant to data and model noise. We introduce some applications of the distribution method, such as a synthetic simulator for estimating the accuracy of the obtained solution, and some ways to measure the differences between the distributions obtained for different populations. In addition, we developed a software package that implements the distribution method and the above-mentioned applications on a user-given asteroid database. The software package can be used for experimenting with different populations, and inspecting different hypotheses or correlations. For example, we confirmed a previous study that the YORP effect has a noticeable effect on the distribution of spin latitudes on a specific asteroid family.
Organisations: Mathematics, Research group: Inverse Problems
Contributors: Nortunen, H.
Publisher: Tampere University of Technology
Name: Tampere University of Technology. Publication
nortunen 1555
Multigrid-Based Inversion for Volumetric Radar Imaging With Asteroid Interior Reconstruction as a Potential Application
This study concentrates on advancing mathematical and computational methodology for radar tomography imaging in which the unknown volumetric velocity distribution of a wave within a bounded domain is to be reconstructed. Our goal is to enable effective simulation and inversion of a large amount of full-wave data within a realistic 2-D or 3-D geometry. For propagating and inverting the wave, we present a rigorous multigrid-based forward approach that utilizes the finite-difference time-domain method and a nested finite element grid structure. We also introduce and validate a multigrid-based inversion algorithm that allows regularization of the unknown distribution through a coarse-to-fine inversion scheme. Using this approach, sparse signals can be effectively inverted, as the coarse fluctuations are reconstructed before the finer ones. Furthermore, the number of nonzero entries in the system matrix can be compressed and, thus, the inversion procedure can be speeded up. As the test scenario, we investigate satellite-based asteroid interior reconstruction. We use both full-wave and projected wave data and estimate the accuracy of the inversion under different error sources: noise and positioning inaccuracies. The results suggest that the present inversion technique allows recovering the interior with a single satellite recording backscattering data. Robust results can be achieved, when the peak-to-peak signal-to-noise ratio is above 10 dB. Furthermore, the robustness for the deep interior part can be enhanced if two satellites can be utilized in the measurements.
Organisations: Mathematics
Contributors: Takala, M., Us, D., Pursiainen, S.
Journal: IEEE Transactions on Computational Imaging
Scopus rating (2018): CiteScore 5.4 SJR 0.837 SNIP 3.18
Keywords: finite difference time-domain analysis, geometry, inverse problems, radar imaging, tomography, unknown volumetric velocity distribution, bounded domain, full-wave data, 3-D geometry, rigorous multigrid-based forward approach, finite-difference time-domain method, nested finite element grid structure, multigrid-based inversion algorithm, coarse-to-fine inversion scheme, asteroid interior reconstruction, inversion technique, single satellite recording backscattering data, peak-to-peak signal-to-noise ratio, deep interior part, volumetric radar imaging, mathematical methodology, computational methodology, radar tomography imaging, Image reconstruction, Solar system, Radar imaging, Permittivity, Tomography, Computational modeling, Multigrid methods, radio tomography, microw-ave tomography, asteroids, biomedical imaging
10.1109/TCI.2018.2811908
Source ID: urn:e8d6524261193d516a9b65740487b26d
Stabilization to trajectories for parabolic equations
Both internal and boundary feedback exponential stabilization to trajectories for semilinear parabolic equations in a given bounded domain are addressed. The values of the controls are linear combinations of a finite number of actuators which are supported in a small region. A condition on the family of actuators is given which guarantees the local stabilizability of the control system. It is shown that a linearization-based Riccati feedback stabilizing controller can be constructed. The results of numerical simulations are presented and discussed.
Journal: Mathematics of Control, Signals, and Systems
ASJC Scopus subject areas: Control and Systems Engineering, Signal Processing, Control and Optimization, Applied Mathematics
Keywords: Feedback stabilization to trajectories, Semilinear parabolic equations
Asymptotic Behaviour of Coupled Systems in Discrete and Continuous Time
This paper investigates the asymptotic behaviour of solutions to certain infinite systems of coupled recurrence relations. In particular, we obtain a characterisation of those initial values which lead to a convergent solution, and for initial values satisfying a slightly stronger condition we obtain an optimal estimate on the rate of convergence. By establishing a connection with a related problem in continuous time, we are able to use this optimal estimate to improve the rate of convergence in the continuous setting obtained by the authors in a previous paper. We illustrate the power of the general approach by using it to study several concrete examples, both in continuous and in discrete time.
Organisations: Department of Mathematics, Research group: MAT Mathematical and semantic modelling, St Giles
Journal: JOURNAL OF DYNAMICS AND DIFFERENTIAL EQUATIONS
ASJC Scopus subject areas: Analysis
Keywords: $C_0$-semigroups, Asymptotic behaviour, Power-boundeness, Rates of convergence, Recurrence relations, Spectral theory, System
Author accepted manuscript
Quantitative Tree Reconstruction from Terrestrial Laser Scanning Data and Applications
Understanding the structure and dynamics of trees and forest is key in studying the environment and understanding current and future climates. Development has been fast in measurement technology for these purposes, as it is currently possible to measure forest terrestrially with photography-based instruments or either static or mobile laser scanning, and airborne using drones, helicopters or aeroplanes, and even from space using satellitemounted instruments. However, as all these measurements are indirect presentations of the key attributes to study, they require powerful analysis methods to accompany them. This thesis focuses on terrestrial laser scanning data and presents a method for reconstructing comprehensive, quantitative structure models of trees from such data. The method is designed to be a tool for understanding tree and forest structure, as well as, dynamics and functionality, without the need for destructive measurements. The reconstructed models provide access to tree attributes previously impossible or laborious to measure, either at a single tree-scale, at forest-plot-scale or even at forest-scale. The thesis will present the reconstruction method and will focus on two of its applications: automatic tree species recognition and augmenting the produced structure models with leaves or needles, enabling more accurate simulations involving light propagation and plant interaction with the atmosphere. Additionally, parts of the thesis describe forms of dissemination used to promote the reconstruction method and its applications, increasing the rate of adoption into operational use. The dissemination approaches include several animations, interactive 3D models and open-source software.
Contributors: Åkerblom, M.
akerblom 1547
The StarT Project Competition from the Perspective of Mathematics and Academic Literacy
This article concerns mathematical project work in the context of Finnish StarT project competition. The focus is on how well pupils achieve the learning objective of their project work: learning mathematics and practicing 21st century skills. Development of the learning objectives is considered from the viewpoint of Finnish national core curriculum and evaluated using the framework of academic literacy. The research material consists of teams' project reports, observation, and questionnaires. Project work in the StarT competition seems to develop the learning objectives of project-based learning: pupils practice 21st century skills while studying mathematical contents.
Contributors: Viro, E., Joutsenlahti, J.
Journal: EDUCATION SCIENCES
Scopus rating (2018): SNIP 5.305
Keywords: project-based learning, academic literacy, Mathematics, Education
education-08-00067
10.3390/educsci8020067
Paraconsistent Many-Valued Logic in GUHA Framework
The primary aim of this paper is to establish a formal connection between a particular many-valued paraconsistent logic and the logic of a KDD method, namely the GUHA data mining method by introducing a new quantifier called Paraconsistent Separation quantifier. This quantifier is implemented to LISp-Miner Software. The secondary aim is to demonstrate a possible usefulness of this quantifier in social and other applied sciences by examples taking from family planning context.
Contributors: Turunen, E.
Journal: Acta Informatica Pragensia, University of Economics, Prague
10.18267/j.aip.116
Uncertainty in multispectral lidar signals caused by incidence angle effects
Multispectral terrestrial laser scanning (TLS) is an emerging technology. Several manufacturers already offer commercial dual or three wavelength airborne laser scanners, while multispectral TLS is still carried out mainly with research instruments. Many of these research efforts have focused on the study of vegetation. The aim of this paper is to study the uncertainty of the measurement of spectral indices of vegetation with multispectral lidar. Using two spectral indices as examples, we find that the uncertainty is due to systematic errors caused by the wavelength dependency of laser incidence angle effects. This finding is empirical, and the error cannot be removed by modelling or instrument modification. The discovery and study of these effects has been enabled by hyperspectral and multispectral TLS, and it has become a subject of active research within the past few years. We summarize the most recent studies on multi-wavelength incidence angle effects and present new results on the effect of specular reflection from the leaf surface, and the surface structure, which have been suggested to play a key role. We also discuss the consequences to the measurement of spectral indices with multispectral TLS, and a possible correction scheme using a synthetic laser footprint.
Organisations: Mathematics, Department of Navigation and Positioning, FGI
Contributors: Kaasalainen, S., Åkerblom, M., Nevalainen, O., Hakala, T., Kaasalainen, M.
Journal: Interface Focus
ASJC Scopus subject areas: Biotechnology, Biophysics, Bioengineering, Biochemistry, Biomaterials, Biomedical Engineering
Keywords: Hyperspectral, Incidence angle, Laser scanning, Vegetation
20170033.full
10.1098/rsfs.2017.0033
Distribution of shape elongations of main belt asteroids derived from Pan-STARRS1 photometry
Context. A considerable amount of photometric data is produced by surveys such as Pan-STARRS, LONEOS, WISE, or Catalina. These data are a rich source of information about the physical properties of asteroids. There are several possible approaches for using these data. Light curve inversion is a typical method that works with individual asteroids. Our approach in focusing on large groups of asteroids, such as dynamical families and taxonomic classes, is statistical; the data are not sufficient for individual models.Aim. Our aim is to study the distributions of shape elongation ba and the spin axis latitude β for various subpopulations of asteroids and to compare our results, based on Pan-STARRS1 survey, with statistics previously carried out using various photometric databases, such as Lowell and WISE.Methods. We used the LEADER algorithm to compare the ba and β distributions for various subpopulations of asteroids. The algorithm creates a cumulative distributive function (CDF) of observed brightness variations, and computes the ba and β distributions with analytical basis functions that yield the observed CDF. A variant of LEADER is used to solve the joint distributions for synthetic populations to test the validity of the method.Results. When comparing distributions of shape elongation for groups of asteroids with different diameters D, we found that there are no differences for D < 25 km. We also constructed distributions for asteroids with different rotation periods and revealed that the fastest rotators with P = 0 - 4 h are more spheroidal than the population with P = 4-8 h.
Organisations: Mathematics, Research group: Inverse Problems, Charles University in Prague, Harvard-Smithsonian Center for Astrophysics, Institute for Astronomy University of Hawaii, Northern Arizona University
Contributors: Cibulková, H., Nortunen, H., Ďurech, J., Kaasalainen, M., Vereš, P., Jedicke, R., Wainscoat, R. J., Mommert, M., Trilling, D. E., Schunová-Lilly, E., Magnier, E. A., Waters, C., Flewelling, H.
Article number: A86
Keywords: asteroids, general, Methods, Minor planets, photometric, statistical, Techniques
Analysis of common rail pressure signal of dual-fuel large industrial engine for identification of injection duration of pilot diesel injectors
In this paper, we address the problem of identification of injection duration of common rail (CR) diesel pilot injectors of dual-fuel engines. In these pilot injectors, the injected volume is small and the repeatability of injections and identification of drifts of injectors are important factors, which need to be taken into account in order to achieve good repeatability (shot-to-shot with every cylinder) and therefore a well-balanced engine and furthermore reduced overall wear. This information can then be used for calibration and diagnostics purposes to guarantee engine longevity facilitated by consistent operating conditions throughout the life of the unit. A diagnostics method based on analysis of CR pressure with experimental results is presented in this paper. Using the developed method, the relative duration of injection events can be identified for multiple injectors. We use the phenomenon of drop in rail pressure due to an injection event as a feature of the injection process. The method is based on filtered CR pressure data during and after the injection event. First, the pressure signal during injection is extracted after control of each injection event. After that, the signal is normalized and filtered. Then a derivative of the filtered signal is calculated. Change in the derivative of the filtered signal larger than a predefined threshold indicates an injection event that can be detected and its relative duration can be identified. We present the experimental results and demonstrate the efficacy of the proposed methods using two different
types of pressure sensors. We are able to properly identify a change of ≥10 μs (2%, 500 μs) in injection time. This shows that the developed method detects drifts in injection duration and the magnitude of drift. This information can be used for adaptive control of injection duration, so that finally the injected fuel volume is the same as the original.
Organisations: Automation and Hydraulic Engineering
Contributors: Krogerus, T., Hyvönen, M., Huhtala, K.
Publication date: Mar 2018
Journal: Fuel
ASJC Scopus subject areas: Mechanical Engineering, Signal Processing, Modelling and Simulation, Applied Mathematics
Keywords: Analysis , Dual-fuel engine , Diesel , Common rail , Injector , Rail pressure
Accepted author manuscript. Embargo ended: 6/12/19
10.1016/j.fuel.2017.11.152
http://urn.fi/URN:NBN:fi:tty-201712222489. Embargo ended: 6/12/19
Approximate Bayesian inference methods for stochastic state space models
This thesis collects together research results obtained during my doctoral studies related to approximate Bayesian inference in stochastic state-space models. The published research spans a variety of topics including 1) application of Gaussian filtering in satellite orbit prediction, 2) outlier robust linear regression using variational Bayes (VB) approximation, 3) filtering and smoothing in continuous-discrete Gaussian models using VB approximation and 4) parameter estimation using twisted particle filters. The main goal of the introductory part of the thesis is to connect the results to the general framework of estimation of state and model parameters and present them in a unified manner.
Bayesian inference for non-linear state space models generally requires use of approximations, since the exact posterior distribution is readily available only for a few special cases. The approximation methods can be roughly classified into to groups: deterministic methods, where the intractable posterior distribution is approximated from a family of more tractable distributions (e.g. Gaussian and VB approximations), and stochastic sampling based methods (e.g. particle filters). Gaussian approximation refers to directly approximating the posterior with a Gaussian distribution, and can be readily applied for models with Gaussian process and measurement noise. Well known examples are the extended Kalman filter and sigma-point based unscented Kalman filter. The VB method is based on minimizing the Kullback-Leibler divergence of the true posterior with respect to the approximate distribution, chosen from a family of more tractable simpler distributions.
The first main contribution of the thesis is the development of a VB approximation for linear regression problems with outlier robust measurement distributions. A broad family of outlier robust distributions can be presented as an infinite mixture of Gaussians, called Gaussian scale mixture models, and include e.g. the t-distribution, the Laplace distribution and the contaminated normal distribution. The VB approximation for the regression problem can be readily extended to the estimation of state space models and is presented in the introductory part.
VB approximations can be also used for approximate inference in continuous-discrete Gaussian models, where the dynamics are modeled with stochastic differential equations and measurements are obtained at discrete time instants. The second main contribution is the presentation of a VB approximation for these models and the explanation of how the resulting algorithm connects to the Gaussian filtering and smoothing framework.
The third contribution of the thesis is the development of parameter estimation using particle Markov Chain Monte Carlo (PMCMC) method and twisted particle filters. Twisted particle filters are obtained from standard particle filters by applying a special weighting to the sampling law of the filter. The weighting is chosen to minimize the variance of the marginal likelihood estimate, and the resulting particle filter is more efficient than conventional PMCMC algorithms. The exact optimal weighting is generally not available, but can be approximated using the Gaussian filtering and smoothing framework.
Contributors: Ala-Luhtala, J.
alaluhtala 1528
Minimal Characterization of O-notation in Algorithm Analysis
Previously, we showed that linear dominance is the only definition of O-notation suitable for algorithm analysis [1,2]. Linear dominance was characterized by 8 primitive properties as a down-set of a non-trivial scale-invariant preorder which is preserved under certain modifications to algorithms and is consistent with pointwise partial order. In this paper, we provide a minimal characterization of O-notation, where there are no redundant properties. Such is given by excluding locality from primitive properties.
Contributors: Rutanen, K.
Publication date: Feb 2018
Early online date: 27 Dec 2017
Journal: Theoretical Computer Science
Keywords: O-notation, characterization, minimal
10.1016/j.tcs.2017.12.026
Source ID: urn:31587026E9CB9CBC88F2461C9E8F550F
Robust output tracking and disturbance rejection for a 2D heat equation
MoE publication type: I1 Audiovisual material
Contributors: Paunonen, L.
Media of output: Online
https://www.youtube.com/watch?v=BkUZ0jt2ogY
Research output: Artistic and non-textual form › Digital or Visual Products › Scientific
Analysing and Improving Student's Mathematics Skills using ICT-tools
In this paper the supportive actions taken at Tampere University of Technology (TUT) for the first year students in engineering mathematics are discussed. The measures include Basic Skill's Test (BST), Mathematics Remedial Instruction (MRI), and student profiling based on students' attitudes on learning. Specially, we describe how MRI was implemented in Math-Bridge and carried out at TUT. The effects of MRI for different learner groups using success indicators, log file analysis, and statistical methods are presented and clarified using data visualization.
Organisations: Mathematics, Research group: Computer Science and Applied Logics, School of Ylöjärvi
Contributors: Pohjolainen, S., Nykänen, O., Venho, J., Kangas, J.
Publication date: 8 Jan 2018
Journal: EURASIA JOURNAL OF MATHEMATICS, SCIENCE & TECHNOLOGY EDUCATION
Article number: 14(4)
Scopus rating (2018): CiteScore 1.27
Keywords: Science education, Teacher education, Biology Education, Environmental education
Analysing and Improving
10.29333/ejmste/81869
NP-completeness results for partitioning a graph into total dominating sets
A total domatic k-partition of a graph is a partition of its vertex set into k subsets such that each intersects the open neighborhood of each vertex. The maximum k for which a total domatic k-partition exists is known as the total domatic number of a graph G, denoted by dt(G). We extend considerably the known hardness results by showing it is[Formula presented]-complete to decide whether dt(G)≥3 where G is a bipartite planar graph of bounded maximum degree. Similarly, for every k≥3, it is[Formula presented]-complete to decide whether dt(G)≥k, where G is split or k-regular. In particular, these results complement recent combinatorial results regarding dt(G) on some of these graph classes by showing that the known results are, in a sense, best possible. Finally, for general n-vertex graphs, we show the problem is solvable in 2nnO(1) time, and derive even faster algorithms for special graph classes.
Organisations: Mathematics, University of Helsinki
Contributors: Koivisto, M., Laakkonen, P., Lauri, J.
ASJC Scopus subject areas: Theoretical Computer Science, Computer Science(all)
Keywords: Combinatorics, Computational complexity, Graph theory, Total domatic number
On the spectral and Frobenius norm of a generalized Fibonacci r-circulant matrix
Consider the recursion g0 = a, g1 = b, gn = gn-1 + gn-2, n = 2, 3, . . . . We compute the Frobenius norm of the r-circulant matrix corresponding to g0, . . . , gn-1. We also give three lower bounds (with equality conditions) for the spectral norm of this matrix. For this purpose, we present three ways to estimate the spectral norm from below in general.
Organisations: Mathematics, Lulea University of Technology
Contributors: Merikoski, J. K., Haukkanen, P., Mattila, M., Tossavainen, T.
Journal: Special Matrices
ASJC Scopus subject areas: Algebra and Number Theory, Geometry and Topology
Keywords: Euclidean norm, Frobenius norm, generalized Fibonacci numbers, r-circulant matrix, spectral norm
spma-2018-0003
10.1515/spma-2018-0003
10 kA Joints for HTS Roebel Cables
Future HTS high field magnets using multi-tape HTS cables need 10 kA low resistance connections. The connections are needed between the poles of the magnets and at the terminals in a wide operating temperature range, from 1.9-85 K. The EuCARD WP10 Future Magnets collaboration aims at testing HTS based Roebel cables in an accelerator magnet. Usually, LTS cables are jointed inside a relatively short soldered block. Powering tests at CERN have highlighted excess heating of a joint following classical LTS joint design. The HTS Roebel cables are assembled from REBCO coated conductor tapes in a transposed configuration. Due to this, the tapes surface the cable at an angle with the cable axis. A low-resistance joint requires a sufficiently large interface area for each tape. Within one twist pitch length, each tape is located at the surface of the cable over a relatively small non-constant area. This geometry prevents making a well-controlled joint in a compact length along the cable. This paper presents a compact joint configuration for the Roebel cable overcoming these practical challenges. A new joint called fin-block is designed. The joint resistance is estimated computationally. Finally the test results as a function of current and temperature are presented.
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research
Contributors: Murtomaeki, J. S., Kirby, G., van Nugteren, J., Contat, P. A., Fleiter, J., De Frutos, O. S., Pincot, F. O., DeRijk, G., Rossi, L., Ruuskanen, J., Stenvall, A., Wolf, F.
Early online date: 9 Feb 2018
Journal: IEEE Transactions on Applied Superconductivity
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Cables and current leads, Heating systems, High-temperature superconductors, HTS Magnets, Pressure Measurement, Resistance, Resistance measurement, Soldering, Superconducting cables, Superconducting magnets, Superconducting Magnets, Temperature measurement
10.1109/TASC.2018.2804951
A case study of focal bayesian EEG inversion for whitney element source spaces: Mesh-based vs. cartesian orientations
This paper concentrates on the Bayesian detection of the neuronal current distributions in the electroencephalography (EEG) imaging of the brain activity. In particular, we focus on a hierarchical maximum a posteriori inversion technique applicable when the lead field matrix is constructed via the finite element method. We utilize the linear Whitney (Raviart-Thomas) basis functions as source currents. In the numerical experiments, the accuracy was investigated using two spherical head models. The results obtained suggest that the interpolation of the dipolar source space does not necessarily bring any advantage for FEM based inverse computations. Furthermore, the divergence conforming Whitney-type sources were found to be sufficient for precise and highly focal Bayesian modeling of dipole-like currents.
Contributors: Miinalainen, T., Pursiainen, S.
Title of host publication: EMBEC and NBC 2017 - Joint Conference of the European Medical and Biological Engineering Conference EMBEC 2017 and the Nordic-Baltic Conference on Biomedical Engineering and Medical Physics, NBC 2017
Publisher: Springer Verlag
Name: IFMBE Proceedings
ASJC Scopus subject areas: Biomedical Engineering, Bioengineering
Keywords: Electroencephalography (EEG), Finite element method (FEM), Hierarchical Bayesian inverse model, Whitney elements
10.1007/978-981-10-5122-7_266
Cauchy–Riemann Operators in Octonionic Analysis
In this paper we first recall the definition of the octonion algebra and its algebraic properties. We derive the so called e4-calculus and using it we obtain the list of generalized Cauchy–Riemann systems for octonionic monogenic functions.
Organisations: Mathematics, Research group: Computer Science and Applied Logics, Civil Engineering
Early online date: Jan 2018
Scopus rating (2018): CiteScore 0.9 SJR 0.4 SNIP 0.899
Keywords: Cauchy–Riemann operators, Dirac operators, Monogenic functions, Octonions
CauchyRiemannOperators
Computing minimum rainbow and strong rainbow colorings of block graphs
A path in an edge-colored graph G is rainbow if no two edges of it are colored the same. The graph G is rainbowconnected if there is a rainbow path between every pair of vertices. If there is a rainbow shortest path between every pair of vertices, the graph G is strongly rainbow-connected. The minimum number of colors needed to make G rainbow-connected is known as the rainbow connection number of G, and is denoted by rc(G). Similarly, the minimum number of colors needed to make G strongly rainbow-connected is known as the strong rainbow connection number ofG, and is denoted by src(G). We prove that for every k ≥ 3, deciding whether src(G) ≤ k is NP-complete for split graphs, which form a subclass of chordal graphs. Furthermore, there exists no polynomial-time algorithm for approximating the strong rainbow connection number of an n-vertex split graph with a factor of n1-2-ϵ for any ϵ > 0 unless P = NP. We then turn our attention to block graphs, which also form a subclass of chordal graphs. We determine the strong rainbow connection number of block graphs, and show it can be computed in linear time. Finally, we provide a polynomial-time characterization of bridgeless block graphs with rainbow connection number at most 4.
Organisations: Mathematics, Michigan Technological University, Bell Labs
Contributors: Keranen, M., Lauri, J.
Journal: Discrete Mathematics and Theoretical Computer Science
ASJC Scopus subject areas: Theoretical Computer Science, Computer Science(all), Discrete Mathematics and Combinatorics
Keywords: Block graph, Computational complexity, Rainbow coloring
10.23638/DMTCS-20-1-22
Engineering Mathematics Education in Finland: A Comparative Analysis of EU, Russia, Georgia and Armenia
MoE publication type: D2 Article in professional manuals or guides or professional information systems or text book material
Contributors: Pohjolainen, S., Myllykoski, T.
Title of host publication: Modern Mathematics Education for Engineering Curricula in Europe
Publisher: Birkhäuser
Editors: Pohjolainen, S., Myllykoski, T., Mercat, C., Sosnovsky, S.
https://link.springer.com/book/10.1007%2F978-3-319-71416-5
Fair testing and stubborn sets
Partial order methods alleviate state explosion by considering only a subset of actions in each constructed state. The choice of the subset depends on the properties that the method promises to preserve. Many methods have been developed ranging from deadlock-preserving to CTL(Formula presented.)-preserving and divergence-sensitive branching bisimilarity preserving. The less the method preserves, the smaller state spaces it constructs. Fair testing equivalence unifies deadlocks with livelocks that cannot be exited and ignores the other livelocks. It is the weakest congruence that preserves whether or not the system may enter a livelock that it cannot leave. We prove that a method that was designed for trace equivalence also preserves fair testing equivalence. We demonstrate its effectiveness on a protocol with a connection and data transfer phase. This is the first practical partial order method that deals with a practical fairness assumption.
Organisations: Mathematics, University of Augsburg
Contributors: Valmari, A., Vogler, W.
Journal: International Journal on Software Tools for Technology Transfer
ASJC Scopus subject areas: Software, Information Systems
Keywords: Fair testing equivalence, Fairness, Partial order methods, Progress, Stubborn sets
fairSTTT. Embargo ended: 11/12/18
http://urn.fi/URN:NBN:fi:tty-201811222757. Embargo ended: 11/12/18
Far-Field Inversion for the Deep Interior Scanning CubeSat
This study aims at advancing mathematical and computational techniques for reconstructing the interior structure of a small Solar System body via Computed Radar Tomography (CRT). We introduce a far-field model for full-wave CRT and validate it numerically for an orbiting distance of 5 km using a synthetic 3D target asteroid and sparse limited-angle data. As a potential future application of the proposed method, we consider the Deep Interior Scanning CUbeSat (DISCUS) concept in which the goal is to localize macroporosities inside a rubble pile near-Earth asteroid with two small spacecraft carrying a bistatic radar.
Organisations: Mathematics, Research group: Inverse Problems, Max Planck Institute for Solar System Research, MEW-Aerospace, RST Radar Systemtechnik AG
Contributors: Takala, M., Bambach, P., Deller, J., Vilenius, E., Wittig, M., Lentz, H., Braun, H. M., Kaasalainen, M., Pursiainen, S.
Journal: IEEE Transactions on Aerospace and Electronic Systems
ASJC Scopus subject areas: Aerospace Engineering, Electrical and Electronic Engineering
Keywords: Cathode ray tubes, Computed Radar Tomography, Extraterrestrial measurements, Far-Field Measurements, Frequency measurement, Inverse Imaging, Near-Earth Asteroids, Radar, Small Solar System Bodies, Space vehicles
10.1109/TAES.2018.2874755
Kehittämistutkimus: vuorovaikutteisten Matlab-opetusohjelmien vaikutus minäpystyvyyteen ja oppimistuloksiin yliopistomatematiikassa
Organisations: Mathematics, Research group: Computer Science and Applied Logics, Research group: Positioning
Contributors: Kaarakka, T. E., Ali-Löytty, S., Huhtanen, M.
Journal: FMSERA Journal
Original language: Finnish
https://journal.fi/fmsera/issue/view/5356
Matematiikan oppimisen tukeminen teknillisessä yliopistokoulutuksessa
Organisations: Mathematics, Guangdong Technion-Israel Institute of Technology, Technion
Contributors: Pohjolainen, S., Rasila, A., Kuosa, K.
Title of host publication: Matematiikan opetus ja oppiminen
Place of publication: Porvoo
Publisher: Niilo Mäki Instituutti
Editors: Joutsenlahti, J., Silfverberg, H., Räsänen, P.
ASJC Scopus subject areas: Mathematics(all), Social Sciences(all)
Keywords: mathematics education, mathematics teaching, mathematics learning
Mathematics Education in EU for STEM Disciplines
MoE publication type: B2 Part of a book or another research book
Contributors: Pohjolainen, S.
Title of host publication: Modern Mathematics Education for Engineering Curricula in Europe : A Comparative Analysis of EU, Russia, Georgia and Armenia
Pohjolainen2018_Chapter_Introduction
Modern Mathematics Education for Engineering Curricula in Europe: A Comparative Analysis of EU, Russia, Georgia and Armenia
MoE publication type: C2 Edited books
Organisations: Mathematics, Universite Claude Bernard Lyon 1, France, October 19th, 2009, German Research Center for Artificial Intelligence
Contributors: Pohjolainen, S. (ed.), Myllykoski, T. (ed.), Mercat, C. (ed.), Sosnovsky, S. (ed.)
Research output: Book/Report › Anthology › Scientific › peer-review
On the fine-grained complexity of rainbow coloring
The Rainbow k-Coloring problem asks whether the edges of a given graph can be colored in k colors so that every pair of vertices is connected by a rainbow path, i.e., a path with all edges of different colors. Our main result states that for any k ≥ 2, there is no algorithm for Rainbow k-Coloring running in time 2o(n 3/2), unless the exponential time hypothesis fails. Motivated by this negative result we consider two parameterized variants of the problem. In the Subset Rainbow k-Coloring problem, introduced by Chakraborty et al. [J. Comb. Optim., 21 (2009), pp. 330-347], we are additionally given a set S of pairs of vertices and we ask if there is a coloring in which all the pairs in S are connected by rainbow paths. We show that Subset Rainbow k-Coloring is fixed parameter tractable (FPT) when parameterized by |S|. We also study the Maximum Rainbow k-Coloring problem, where we are additionally given an integer q, and we ask if there is a coloring in which at least q anti-edges are connected by rainbow paths. We show that the problem is FPT when parameterized by q and has a kernel of size O(q) for every k ≥ 2, extending the result of Ananth, Nasre, and Sarpatwar, in FSTTCS, LIPIcs, Schloss Dagstuhl-Leibniz-Zentum für Informatik, Dagstuhl, Germany, 2011, pp. 241-251. We believe that our techniques used for the lower bounds may shed some light on the complexity of the classical Edge Coloring problem, where it is a major open question if a 2O(n)-time algorithm exists.
Organisations: Mathematics, University of Warsaw, Institute of Informatics, Bell Labs
Contributors: Kowalik, L., Lauri, J., La, A. S.
Journal: SIAM Journal on Discrete Mathematics
Keywords: Computational complexity, FPT algorithms, Graph coloring, Lower bounds
Overview of the Results and Recommendations
Organisations: Mathematics, Research group: Computer Science and Applied Logics, Department of Information and Computing Sciences (Utrecht University), Universite Claude Bernard Lyon 1, France, October 19th, 2009
Contributors: Pohjolainen, S., Sosnovsky, S., Mercat, C.
Place of publication: Switzerland
Sosnovsky2018_Chapter_OverviewOfTheResultsAndRecomme
Projektityöskentelyn kehittäminen yläkoulun matematiikan opetuksessa
Perusopetuksen opetussuunnitelman perusteiden 2014 aikana ovat ilmiölähtöinen oppiminen ja projektiluontoinen työskentely lisääntyneet peruskouluissa merkittävästi. Tässä tutkimuksessa tarkastellaan oppilaan ja opettajan näkökulmasta lähinnä yläkoulun matematiikan opetukseen liitetyn projektityöskentelyn kehittämiskohteita sekä niihin mahdollisia kehittämisehdotuksia. Tutkimusaineistoa on kerätty kyselylomakkeilla ja havainnoinnilla LUMA Suomen Projektioppiminen-kehittämishankkeesta, StarT-projektikilpailusta ja Teknologiateollisuuden My TecH –ohjelmasta. Tutkimukseen osallistui 365 oppilasta ja 19 opettajaa. Projektityöskentelyn suurimmat haasteet voidaan luokitella oppilaan ja opettajan toimintaan, itse projektiin tai koulutoiminnan puitteisiin liittyviksi. Jokaiseen osa-alueeseen opettaja voi omalla toiminnallaan vaikuttaa.
Organisations: Mathematics, Tampereen yliopisto
Contributors: Viro, I. E., Joutsenlahti, J.
https://journal.fi/fmsera/article/view/69879
Robust Regulation of Infinite-Dimensional Port-Hamiltonian Systems
We will give general sufficient conditions under which a controller achieves robust regulation for a boundary control and observation system. Utilizing these conditions we construct a minimal order robust controller for an arbitrary order impedance passive linear port-Hamiltonian system. The theoretical results are illustrated with a numerical example where we implement a controller for a one-dimensional Euler-Bernoulli beam with boundary controls and boundary observations.
ASJC Scopus subject areas: Control and Systems Engineering, Computer Science Applications, Electrical and Electronic Engineering
Keywords: Aerospace electronics, Closed loop systems, distributed parameter systems, Generators, Impedance, linear systems, port-Hamiltonian systems, robust control, Robustness, Transfer functions
Wearable RFID perspiration sensor tags for well-being applications – From laboratory to field use
RFID technology has proven to have many possibilities in sensing applications. Smart sensor solutions would be especially helpful in the health and well-being sectors. There is already research on wearable RFID-based sensors, but most are only tested in controlled laboratory environments. The emphasis of this paper is 1) to analyze the performance of two moisture sensor textile tags in realistic field use and through this 2) to discuss their application possibilities. Based on the measurement results, different kinds of textile tags were differently affected by moisture. Especially with embroidered tags the presence of moisture could be detected, including in field conditions. Many applications were also found for the tags. The results indicate potential of RFID-based sensing also in field use, but the actual use environment must be carefully taken into account when implementing the technology.
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Wireless Identification and Sensing Systems Research Group, Mathematics, Research group: Inverse Problems, BioMediTech, Satakunta University of Applied Sciences, Satakunta University of Applied Sciences
Contributors: Mulholland, K., Virkki, J., Raumonen, P., Merilampi, S.
Keywords: Field use, Perspiration sensing, RFID-based sensing, Textile antennas, Welfare technology
EXT="Merilampi, S."
What's inside a rubble pile asteroid? DiSCUS - A tomographic twin radar Cubesat to find out
A large fraction of asteroids with diameter d > 240 m are suspected to be loose piles of rocks and boulders bound together mainly by gravity and only weak cohesion. Still to date the size and distribution of voids and monolithic fragments inside these "rubble-piles" are not known. To perform a full tomographic interior reconstruction a bistatic CubeSat configuration has been investigated by Tampere University of Technology (TUT), Radar Systemtechnik GmbH (RST) and the Max Planck Institute for Solar System Research (MPS). The concept is based on two 6U CubeSats, both carrying an identical 1U sized stepped frequency radar. As stepped frequency radars can be built compact, require less power and generate less data volume compared to other radar applications they are well-suited for small satellite platforms. In 2017 the Concurrent Design Facility of ESA/ESTEC conducted two studies relevant for DISCUS. In the Small Planetary Probes (SPP) study DISCUS served as a reference payload for a piggyback mission to a Near-Earth Asteroid (NEA) or even a Main Belt Asteroid (MBA). The M-ARGO study investigated a stand-alone mission to a NEA, with a DISCUS sized instrument. Based on the spacecraft design of SPP and M-ARGO we could prove the instrument requirements as feasible and evaluate our science case from the orbits and mission duration that have been identified by these studies. Using inversion methods developed for medical tomography the data would allow to reconstruct the large scale interior structure of a small body. Simulations have shown that the measurement principle and the inversion method are robust enough to allow full reconstruction of the interior even if the orbits do not cover the entire surface of the asteroid. The measurement results of the mission will help to gain a better understanding of asteroids and the formation mechanisms of the solar system. In addition, the findings will increase the predictability of asteroid impact consequences on Earth and improve future concepts of asteroid deflection.
Organisations: Computing Sciences, Research group: Inverse Problems, Max Planck Institute for Solar System Research, GomSpace A/S, 3D Profi GmbH, RST Radar Systemtechnik AG, University of Bern, MEW-Aerospace UG, GMV Innovating Solutions S.L, Royal Observatory of Belgium
Contributors: Bambach, P., Deller, J., Martel, J., Vilenius, E., Goldberg, H., Sorsa, L., Pursiainen, S., Takala, M., Wurster, A., Braun, H. M., Lentz, H., Jutzi, M., Wittig, M., Chitu, C. C., Ritter, B., Karatekin, O.
Title of host publication: 69th International Astronautical Congress, IAC 2018
Name: Proceedings of the International Astronautical Congress, IAC
ASJC Scopus subject areas: Aerospace Engineering, Astronomy and Astrophysics, Space and Planetary Science
Yliopistomatematiikan sähköisten tehtävien ja matemaattisen ajattelun kehittäminen
Organisations: Mathematics, Research group: Positioning, Research group: Computer Science and Applied Logics
Contributors: Myllykoski, T. J., Mattila, P., Ali-Löytty, S., Kaarakka, T., Viro, E.
https://journal.fi/fmsera/article/view/69887/38422
Myllykoski_et_al
A Reduced-Order Two-Degree-of-Freedom Composite Nonlinear Feedback Control for a Rotary DC Servo Motor
We study in this paper nonlinear control of a rotary DC servo motor application. To be more specific, we design a reduced-order two-degree-of-freedom (2DOF) composite nonlinear feedback (CNF) controller for a Quanser QUBE-Servo 2 unit with a disc attachment. We compare our results with a carefully tuned proportional-derivative (PD) controller with set point weighting. Our simulation and experimental results show that the closed-loop system using 2DOF CNF controller yields much better set point tracking performance compared with the system using conventional PD-controller in terms of settling time.
Organisations: Automation and Hydraulic Engineering, Research area: Information Systems in Automation, Research area: Dynamic Systems, Research area: Information Systems in Automation
Contributors: Pyrhönen, V., Koivisto, H., Vilkko, M.
Title of host publication: Proceedings of the 56th IEEE Conference on Decision and Control
Place of publication: Melbourne, Australia
ISBN (Electronic): 978-1-5090-2872-6
ASJC Scopus subject areas: Control and Systems Engineering, Electrical and Electronic Engineering, Mechanical Engineering
Keywords: Nonlinear control, Composite nonlinear feedback, motion control, Robust control, High performance control, Servo systems
10.1109/CDC.2017.8263951
Using GUHA Data Mining Method in Analyzing Road Traffic Accidents Occurred in the Years 2004–2008 in Finland
The suitability of the GUHA data mining method in analyzing a big data matrix is studied in this report in general, and, in particular, a data matrix containing more than 80,000 road traffic accidents occurred in Finland in 2004–2008 is examined by LISp-Miner, a software implementation of GUHA. The general principles of GUHA are first outlined, and then, the road accident data is analyzed. As a result, more than 10,000 associations and dependencies, called hypothesis in the GUHA language, were found; some easily understandable of them are presented here. Our conclusion is that the GUHA method is useful, in particular when one wants to explore relatively small size, but still significant dependencies in a given large data matrix.
Journal: Data Science and Engineering
s41019-017-0044-2
Estimation of above-ground biomass of large tropical trees with terrestrial LiDAR
1. Tropical forest biomass is a crucial component of global carbon emission estimations. However, calibration and validation of such estimates require accurate and effective methods to estimate in situ above-ground biomass (AGB). Present methods rely on allometric models that are highly uncertain for large tropical trees. Terrestrial laser scanning (TLS) tree modelling has demonstrated to be more accurate than these models to infer forest AGB. Nevertheless, applying TLS methods on tropical large trees is still challenging. We propose a method to estimate AGB of large tropical trees by three-dimensional (3D) tree modelling of TLS point clouds.
2. Twenty-nine plots were scanned with a TLS in three study sites (Peru, Indonesia and Guyana). We identified the largest tree per plot (mean diameter at breast height of 73.5 cm), extracted its point cloud and calculated its volume by 3D modelling its structure using quantitative structure models (QSM) and converted to AGB using species-specific wood density. We also estimated AGB using pantropical and local allometric models. To assess the accuracy of our and allometric methods, we harvest the trees and took destructive measurements.
3. AGB estimates by the TLS–QSM method showed the best agreement in comparison to destructive harvest measurements (28.37% coefficient of variation of root mean square error [CV-RMSE] and concordance correlation coefficient [CCC] of 0.95), outperforming the pantropical allometric models tested (35.6%–54.95% CV-RMSE and CCC of 0.89–0.73). TLS–QSM showed also the lowest bias (overall underestimation of 3.7%) and stability across tree size range, contrasting with the allometric models that showed a systematic bias (overall underestimation ranging 15.2%–35.7%) increasing linearly with tree size. The TLS–QSM method also provided accurate tree wood volume estimates (CV RMSE of 23.7%) with no systematic bias regardless the tree structural characteristics.
4. Our TLS–QSM method accounts for individual tree biophysical structure more effectively than allometric models, providing more accurate and less biased AGB estimates for large tropical trees, independently of their morphology. This non-destructive method can be further used for testing and calibrating new allometric models, reducing the current under-representation of large trees in and enhancing present and past estimates of forest biomass and carbon emissions from tropical forests.
Organisations: Mathematics, Wageningen Univ, Wageningen University & Research Center, Swedish University of Agricultural Sciences, University College London
Contributors: Gonzalez de Tanago, J., Lau, A., Bartholomeus, H., Herold, M., Avitabile, V., Raumonen, P., Martius, C., Goodman, R., Disney, M., Manuri, S., Burt, A., Calders, K.
Journal: Methods in Ecology and Evolution
Menaca_et_al-2017-Methods_in_Ecology_and_Evolution
10.1111/2041-210X.12904
Adaptive optics and lightcurve data of asteroids: Twenty shape models and information content analysis
We present shape models and volume estimates of twenty asteroids based on relative photometry and adaptive optics images. We discuss error estimation and the effects of myopic deconvolution on shape solutions. For further analysis of the information capacities of data sources, we also present and discuss ambiguity and uniqueness results for the reconstruction of nonconvex shapes from photometry.
Organisations: Mathematics, Charles University in Prague, SETI Institute
Contributors: Viikinkoski, M., Hanuš, J., Kaasalainen, M., Marchis, F., Ďurech, J.
Keywords: Instrumentation: adaptive optics, Methods: analytical, Methods: numerical, Minor planets, asteroids: general, Techniques: photometric
Adaptive Optics and lightcurve
Opiskelijoiden oppimistyökalujen käyttö tietokoneavusteisessa Matematiikkajumppa -tukiopetuksessa
Organisations: Mathematics, Research group: Positioning, Research group: MAT Intelligent Information Systems Laboratory, Research group: Computer Science and Applied Logics
Contributors: Myllykoski, T., Ali-Löytty, S. S., Pohjolainen, S.
Title of host publication: 2017: Proceedings of the annual FMSERA symposium 2016
Name: Proceedings of the FMSERA annual symposium
Publisher: Finnish Mathematics and Science Education Research Association (FMSERA)
Myllykoski_FIMSERA
Projektityöskentely matematiikan opiskelussa yläkoululaisten ja heidän opettajiensa kokemana
Organisations: Mathematics, Research group: Computer Science and Applied Logics, University of Helsinki
Contributors: Viro, E., Joutsenlahti, J., Eriksson, S.
FMSERA
EXT="Eriksson, Sirkka-Liisa"
Sähköisen matematiikan tentin toteuttaminen ja opiskelijoiden kokemukset sähköisestä tentistä
Tässä tutkimuksessa selvitettiin substanssiosaamisen integroinnin vaikutusta ensimmäisen vuoden Insinöörimatematiikka 2-opintojakson opiskelijoiden asenteisiin ja motivaatioon matematiikkaa kohtaan. Tutkimus toteutettiin jakamalla opiskelijat verrokki- ja interventioryhmään, joista toisessa opiskelijat tekivät perinteisiä harjoitustehtäviä koko kurssin kuuden harjoitusviikon ajan ja toisessa opiskelijat tekivät enemmän alasoveltavia tehtäviä harjoitusviikoilla 2-4. Tutkimusta varten muodostettiin kyselylomake, johon opiskelijat vastasivat kolme kertaa kurssin aikana Moodlessa. Tulosten perusteella substanssiosaamisen integroinnilla on vaikutuksia asenteisiin ja motivaation, mutta tulosten vahvistaminen vaatii lisää tutkimuksia. Integroinnilla ei ollut vaikutusta opiskelijoiden tentistä saatuihin pisteisiin.
Organisations: Teaching and Learning Services, Mathematics, Research group: Positioning
Contributors: Koskinen, S., Kela, J., Ali-Löytty, S. S., Joutsenlahti, J.
Koskinen_FMSERA
INT=mat,"Kela, Jesse"
Substanssiosaamisen integroinnin vaikutus asenteisiin ja motivaatioon yliopistomatematiikassa
Organisations: Mathematics, Research group: Computer Science and Applied Logics, Research group: Positioning, Industrial and Information Management, Research group: Knowledge and Learning Research Center
Contributors: Tengvall, M., Kaarakka, T., Ali-Löytty, S. S., Nokelainen, P.
Tengvall_FMSERA
INT=mat,"Tengvall, Mira"
FiB: Squeezing loop invariants by interpolation between forward/backward predicate transformers
Loop invariant generation is a fundamental problem in program analysis and verification. In this work, we propose a new approach to automatically constructing inductive loop invariants. The key idea is to aggressively squeeze an inductive invariant based on Craig interpolants between forward and backward reachability analysis. We have evaluated our approach by a set of loop benchmarks, and experimental results show that our approach is promising.
Contributors: Lin, S., Sun, J., Xiao, H., Liu, Y., Sanán, D., Hansen, H.
Title of host publication: Proceedings of the 32nd IEEE/ACM International Conference on Automated Software Engineering : ASE 2017
Publisher: IEEE Press
Editors: Rosu, G., Di Penta, M., Nguyen, T. N.
Name: IEEE/ACM International Conference on Automated Software Engineering
10.1109/ASE.2017.8115690
Supporting an estimation of satellite locations
An apparatus computes first locations of a satellite for several points in time based on a first set of parameters values broadcast by the satellite for a first validity period and second locations of the satellite for these points in time based on a second set of parameter values with associated second validity period. The first or second validity period is extended by an equation of motion, which includes forces acting on the satellite. The apparatus computes a value of an error component for points in time by comparing first with second locations and fits parameter values of a model to the values of the error component to obtain a model of a time-evolution of values of the error component. The apparatus provides the model of the time-evolution as a basis for a correction of locations of the satellite that are computed based on the first set of parameter values.
MoE publication type: H1 Granted patent
Organisations: Mathematics, Research group: Positioning, Automation and Hydraulic Engineering, Research group: Positioning, Research area: Dynamic Systems
Contributors: Rautalin, S., Ali-Löytty, S., Piche, R., Ala-Luhtala, J.
IPC: G01S19/40
Patent number: US20170269221
Priority date: 15/03/16
https://www.google.com/patents/US20170269221
Research output: Patent › Scientific
Finite-dimensional regulators for a class of regular hyperbolic PDE systems
In this paper, the output regulation problem is addressed for a class of linear hyperbolic infinite-dimensional systems with spatially varying coefficients modelling a large class of convection-dominated transport reaction systems. In particular, distributed parameter systems with bounded input and unbounded output operators are considered. First, we demonstrate a general conclusion about the exponential stability of the considered system by relating the stability to the solution of an associated differential equation. Based on the assumption that the hyperbolic system satisfies the exponential stability conditions, the main manuscript contribution is the development of two novel finite-dimensional regulators, output and error feedback regulators, such that the controlled output of the plant tracks a reference signal generated by a known signal process (exosystem). In order to guarantee the feasibility of the proposed regulators, the solvability of the corresponding Sylvester equations is discussed and the solvability conditions are provided. Finally, simulations of output regulation of an axial dispersion reactor and a relevant numerical example illustrate the main results and performance of the proposed regulators synthesis.
Organisations: Mathematics, Research group: Computer Science and Applied Logics, Univ Alberta, University of Alberta
Contributors: Xu, X., Pohjolainen, S., Dubljevic, S.
Journal: International Journal of Control
Keywords: Hyperbolic PDE systems, finite-dimensional regulators, output feedback regulator, Sylvester equation
Semantic Labeling of User Location Context Based on Phone Usage Features
In mobile phones, the awareness of the user's context allows services better tailored to the user's needs. We propose a machine learning based method for semantic labeling that utilizes phone usage features to detect the user's home, work, and other visited places. For place detection, we compare seven different classification methods. We organize the phone usage data based on periods of uninterrupted time that the user has been in a certain place. We consider three approaches to represent this data: visits, places, and cumulative samples. Our main contribution is semantic place labeling using a small set of privacy-preserving features and novel data representations suitable for resource constrained mobile devices. The contributions include (1) introduction of novel data representations including accumulation and averaging of the usage, (2) analysis of the effect of the data accumulation time on the accuracy of the place classification, (3) analysis of the confidence on the classification outcome, and (4) identification of the most relevant features obtained through feature selection methods. With a small set of privacy-preserving features and our data representations, we detect the user's home and work with probability of 90% or better, and in 3-class problem the overall classification accuracy was 89% or better.
Organisations: Automation and Hydraulic Engineering, Research group: Positioning, Research area: Dynamic Systems, Mathematics, Research group: MAT Intelligent Information Systems Laboratory, Research group: Positioning, Research group: Positioning, Tampere University of Technology, HD Automotive Positioning Solutions at HERE, GE Healthcare Finland
Contributors: Leppäkoski, H., Rivero-Rodriguez, A., Rautalin, S., Muñoz Martínez, D., Käppi, J., Ali-Löytty, S., Piche, R.
Journal: Mobile Information Systems
SemanticLabeling_3876906
INT=mat,"Rautalin, Sakari"
3D shape of asteroid (6) Hebe from VLT/SPHERE imaging: Implications for the origin of ordinary H chondrites
Context. The high-angular-resolution capability of the new-generation ground-based adaptive-optics camera SPHERE at ESO VLT allows us to assess, for the very first time, the cratering record of medium-sized (D ∼ 100-200 km) asteroids from the ground, opening the prospect of a new era of investigation of the asteroid belt's collisional history. Aims. We investigate here the collisional history of asteroid (6) Hebe and challenge the idea that Hebe may be the parent body of ordinary H chondrites, the most common type of meteorites found on Earth (∼34% of the falls). Methods. We observed Hebe with SPHERE as part of the science verification of the instrument. Combined with earlier adaptive-optics images and optical light curves, we model the spin and three-dimensional (3D) shape of Hebe and check the consistency of the derived model against available stellar occultations and thermal measurements. Results. Our 3D shape model fits the images with sub-pixel residuals and the light curves to 0.02 mag. The rotation period (7.274 47 h), spin (ECJ2000 λ, β of 343°, +47°), and volume-equivalent diameter (193 ± 6 km) are consistent with previous determinations and thermophysical modeling. Hebe's inferred density is 3.48 ± 0.64 g cm-3, in agreement with an intact interior based on its H-chondrite composition. Using the 3D shape model to derive the volume of the largest depression (likely impact crater), it appears that the latter is significantly smaller than the total volume of close-by S-type H-chondrite-like asteroid families. Conclusions. Our results imply that (6) Hebe is not the most likely source of H chondrites. Over the coming years, our team will collect similar high-precision shape measurements with VLT/SPHERE for ∼40 asteroids covering the main compositional classes, thus providing an unprecedented dataset to investigate the origin and collisional evolution of the asteroid belt.
Organisations: Mathematics, Research group: Inverse Problems, Queen's University, Belfast, Northern Ireland, CNRS, IMCCE - Institut de Mecanique Celeste et de Calcul des Ephemerides, TMT Observatory, Charles University in Prague, Laboratoire d'Astrophysique de Marseille, Max-Planck-Institut für Extraterrestrische Physik, Université de Liège, Open University, European Southern Observatory (ESO), ONERA - The French Aerospace Lab, Planetary Science Institute, Universite de Geneve
Contributors: Marsset, M., Carry, B., Dumas, C., Hanuš, J., Viikinkoski, M., Vernazza, P., Müller, T. G., Delbo, M., Jehin, E., Gillon, M., Grice, J., Yang, B., Fusco, T., Berthier, J., Sonnett, S., Kugel, F., Caron, J., Behrend, R.
Keywords: asteroids: individual: (6) Hebe, Meteorites, meteoroids, meteors, Minor planets, Techniques: high angular resolution
3D shape of asteroid (6) Hebe
How management intensity and neighborhood composition affect the structure of beech (Fagus sylvatica L.) trees
Key message: The intensity of silvicultural interventions and the neighborhood composition determine branching patterns, crown shape, and trunk attributes of beech (Fagus sylvaticaL.) trees.Abstract: The intensity of silvicultural interventions and the composition of tree species are important forest management decisions. Both determine tree shape and thus influence the value of a tree, be it in terms of economy (trunk form, branchiness), or in terms of ecology (microhabitats). However, our knowledge on the distinct changes in tree architecture due to silvicultural management intensity or different neighborhood diversities is still limited, especially if the focus is on single tree attributes, e.g., branching patterns or crown shapes. We used terrestrial laser scanner data to calculate 25 structural measures for 55 European beech (Fagus sylvatica L.) trees that grew either in pure stands along a gradient of management intensity or in intra or interspecific neighborhoods in unmanaged stands. We found a lower height of maximal horizontal crown extension, a higher crown surface area, and straighter trunks with increasing management intensity. Moreover, our study revealed that beech trees surrounded by valuable hardwoods showed a lower height of maximal horizontal crown extension, a lower height–diameter ratio, and longer branches with flatter branch angles than beech trees surrounded by conspecific neighbors. Our findings provide evidence of phenotypic plasticity of European beech to diverse environmental conditions. The differences in tree structure indicate an increasing crown competition with decreasing management intensity and stronger competitive pressure for beech surrounded by conspecific neighbors in comparison to alien neighbors.
Organisations: Mathematics, Research group: Inverse Problems, University of Goettingen, Department of Applied Health Research
Contributors: Juchheim, J., Annighöfer, P., Ammer, C., Calders, K., Raumonen, P., Seidel, D.
Journal: TREES-STRUCTURE AND FUNCTION
Keywords: Competition, Crown plasticity, Quantitative structural models, Terrestrial laser scanning, Thinning, Tree architecture
Order reduction for a signaling pathway model of neuronal synaptic plasticity
In this study a nonlinear mathematical model of plasticity in the brain is reduced using the Proper Orthogonal Decomposition and Discrete Empirical Interpolation Method. Such methods are remarkably useful for connecting reduced small scale models via the inputs and outputs to form optimally performing large scale models. Novel results were obtained as mathematical model order reduction has not been applied in neuroscience without linearization of the mathematical model and never to the model presented here. The reduced order model consumes considerably less computational resources than the original while maintaining a low root mean square error between the original and reduced model.
Organisations: BioMediTech, Faculty of Biomedical Sciences and Engineering, Mathematics, Research group: Computational Neuro Science-CNS
Contributors: Lehtimäki, M., Paunonen, L., Pohjolainen, S., Linne, M.
Title of host publication: 20th IFAC World Congress
Keywords: cell signaling, Discrete Empirical Interpolation Method, model reduction, nonlinear models, Proper Orthogonal Decomposition, synaptic plasticity
10.1016/j.ifacol.2017.08.1143
INT=mat,"Lehtimäki, Mikko"
Robust Regulation of MIMO systems: A Reformulation of the Internal Model Principle
The internal model principle is a fundamental result stating a necessary and sufficient condition for a stabilizing controller to be robustly regulating. Its classical formulation is given in terms of coprime factorizations and the largest invariant factor of the signal generator which sets unnecessary restrictions for the theory and its applicability. In this article, the internal model principle is formulated using a general factorization approach and the generators of the fractional ideals generated by the elements of the signal generator. The proposed results are related to the classical ones.
Contributors: Laakkonen, P.
Keywords: Algebraic systems theory, Factorization approach, MIMO, Output regulation, Robust control
Predicting Heat Propagation in Roebel-Cable Based Accelerator Magnet Prototype: One-Dimensional Approach with Coupled Turns
When designing superconductor based magnets, it is of the utmost importance to be prepared for the loss of thermal stability under operation. In this paper, heat propagation during a quench in Roebel-cable based accelerator magnet prototype is predicted using one-dimensional approach. The heat diffusion equation is solved using the finite element method and thermal coupling between the turns is taken into account using thermal network model. However, when reducing the dimensions of the problem, modelling decisions are often unavoidable. Here, we present the challenges of this approach and discuss the appropriateness of these decisions via simulations.
Organisations: Department of Electrical Engineering, Research area: Electromagnetics
Contributors: Ruuskanen, J., Stenvall, A., Lahtinen, V.
Early online date: 21 Nov 2016
Keywords: Delays, Heating, Magnetic domains, Magnetosphere, Mathematical model, Superconducting magnets, Switches, Accelerator magnets, Finite element methods, HTS cables, Quench
Source ID: urn:92c2b5fa9629fd4e2a7b4073195a4e32
The effect of hardware-computed travel time on localization accuracy in the inversion of experimental (acoustic) waveform data
This study aims to advance hardware-level computations for travel-time tomography applications in which the wavelength is close to the diameter of the information that has to be recovered. Such can be the case, for example, in the imaging applications of 1) biomedical physics; 2) astrogeophysics; and 3) civil engineering. Our aim is to shed light on the effect of that preprocessing the digital waveform signal has on the inversion results and to find computational solutions that guarantee robust inversion when there are incomplete and/or noisy measurements. We describe a hardware-level implementation for integrated and thresholded travel-time computation (ITT and TTT). We compare the ITT and TTT approaches in inversion analysis with experimental acoustic travel-time data recorded using a ring geometry for the transmission and measurement points. The results obtained suggest that ITT is essential for maintaining the robustness of the inversion with imperfect signal digitization and sparsity. In order to ensure the relevance of the results, the specifications of the test setup were related to those of applications 1-3.
Organisations: Mathematics, Research group: Inverse Problems, Pervasive Computing, Research area: Computer engineering
Contributors: Takala, M., Hämäläinen, T., Pursiainen, S.
A fractional representation approach to the robust regulation problem for SISO systems
The purpose of this article is to develop a new approach to the robust regulation problem for plants which do not necessarily admit coprime factorizations. The approach is purely algebraic and allows us dealing with a very general class of systems in a unique simple framework. We formulate the famous internal model principle in a form suitable for plants defined by fractional representations which are not necessarily coprime factorizations. By using the internal model principle, we are able to give necessary and sufficient solvability conditions for the robust regulation problem and to parameterize all robustly regulating controllers.
Organisations: Mathematics, Parc Scientifique de la Haute Borne
Contributors: Laakkonen, P., Quadrat, A.
Journal: Systems and Control Letters
ASJC Scopus subject areas: Control and Systems Engineering, Computer Science(all), Mechanical Engineering, Electrical and Electronic Engineering
Keywords: Fractional representation approach, Linear systems, Robust regulation
10.1016/j.sysconle.2017.02.006
Asymptotic behaviour in the robot rendezvous problem
This paper presents a natural extension of the results obtained by Feintuch and Francis in (2012a,b) concerning the so-called robot rendezvous problem. In particular, we revisit a known necessary and sufficient condition for convergence of the solution in terms of Cesàro convergence of the translates Skx0, k≥0, of the sequence x0 of initial positions under the right-shift operator S, thus shedding new light on questions left open in Feintuch and Francis (2012a,b). We then present a new proof showing that a certain stronger ergodic condition on x0 ensures that the corresponding solution converges to its limit at the optimal rate O(t−1/2) as t→∞. After considering a natural two-sided variant of the robot rendezvous problem already studied in Feintuch and Francis (2012a) and in particular proving a new quantified result in this case, we conclude by relating the robot rendezvous problem to a more realistic model of vehicle platoons.
Organisations: Mathematics, Research group: MAT Mathematical and semantic modelling, St Giles
Journal: Automatica
ASJC Scopus subject areas: Control and Systems Engineering, Electrical and Electronic Engineering
Keywords: Autonomous systems, Mobile robots, Rates of convergence, Stability
Author accepted version. Embargo ended: 6/03/19
10.1016/j.automatica.2017.02.015
Volumes and bulk densities of forty asteroids from ADAM shape modeling
Context. Disk-integrated photometric data of asteroids do not contain accurate information on shape details or size scale. Additional data such as disk-resolved images or stellar occultation measurements further constrain asteroid shapes and allow size estimates. Aims. We aim to use all the available disk-resolved images of approximately forty asteroids obtained by the Near-InfraRed Camera (Nirc2) mounted on the W.M. Keck II telescope together with the disk-integrated photometry and stellar occultation measurements to determine their volumes. We can then use the volume, in combination with the known mass, to derive the bulk density. Methods. We downloaded and processed all the asteroid disk-resolved images obtained by the Nirc2 that are available in the Keck Observatory Archive (KOA). We combined optical disk-integrated data and stellar occultation profiles with the disk-resolved images and use the All-Data Asteroid Modeling (ADAM) algorithm for the shape and size modeling. Our approach provides constraints on the expected uncertainty in the volume and size as well. Results. We present shape models and volume for 41 asteroids. For 35 of these asteroids, the knowledge of their mass estimates from the literature allowed us to derive their bulk densities. We see a clear trend of lower bulk densities for primitive objects (C-complex) and higher bulk densities for S-complex asteroids. The range of densities in the X-complex is large, suggesting various compositions. We also identified a few objects with rather peculiar bulk densities, which is likely a hint of their poor mass estimates. Asteroid masses determined from the Gaia astrometric observations should further refine most of the density estimates.
Organisations: Mathematics, Research group: Inverse Problems, Charles University in Prague, SETI Institute, CNRS Centre National de la Recherche Scientifique, RASNZ Occultation Section, Euraster, JOIN-Japan Occultation Infomation Network, International Occultation Timing Association (IOTA), RASNZ Occultation Section
Contributors: Hanuš, J., Viikinkoski, M., Marchis, F., Durech, J., Kaasalainen, M., Delbo, M., Herald, D., Frappa, E., Hayamizu, T., Kerr, S., Preston, S., Timerson, B., Dunham, D., Talbot, J.
Keywords: Methods: Numerical, Methods: Observational, Minor planets, asteroids: General, Techniques: Photometric
Output Regulation of Infinite-Dimensional Time-Delay Systems
We study output tracking and disturbance rejection for linear infinite-dimensional time-delay systems using dynamic error feedback controllers with state delays. The class of systems covers many partial differential equations with state, input, and output delays. As our main result we characterize the solvability of the control problem in terms of the solvability of the associated regulator equations.
Title of host publication: American Control Conference (ACC), 2017
Name: Proceedings of the American Control Conference
ASJC Scopus subject areas: Analysis, Control and Systems Engineering
The logics taught and used at high schools are not the same
Typical treatises on propositional and predicate logic do not tell how to deal with undefined expressions, such as division by zero. However, there seems to be a sound (albeit inexplicit) reasoning system that addresses undefined expressions, because equations and inequations involving them are routinely solved in schools and universities without running into fundamental inconsistencies. In this study we discover this school logic and formalize its semantics. The need to do so arose when developing software that gives students feedback on every reasoning step of their solution, instead of just telling whether the roots that they finally report are the correct roots. The problem of undefined expressions has been addressed in computer science. However, school logic proves different from those approaches. School logic is based on a Kleene-style third "undefined" truth value and the treatment of "⇒" and "⇔" not as propositional operators but as reasoning operators.
Organisations: Pervasive Computing, University of Tampere
Contributors: Valmari, A., Hella, L.
Title of host publication: Proceedings of the Fourth Russian Finnish Symposium on Discrete Mathematics
Place of publication: Turku
Publisher: TURKU CENTRE FOR COMPUTER SCIENCE
Editors: Karhumäki, J., Matiyasevich, Y., Saarela, A.
Name: TUCS Lecture Notes
Keywords: logic
http://www.doria.fi/handle/10024/143322
A Mixed Finite Element Method to Solve the EEG Forward Problem
Finite element methods have been shown to achieve high accuracies in numerically solving the EEG forward problem and they enable the realistic modeling of complex geometries and important conductive features such as anisotropic conductivities. To date, most of the presented approaches rely on the same underlying formulation, the continuous Galerkin (CG)-FEM. In this article, a novel approach to solve the EEG forward problem based on a mixed finite element method (Mixed-FEM) is introduced. To obtain the Mixed-FEM formulation, the electric current is introduced as an additional unknown besides the electric potential. As a consequence of this derivation, the Mixed-FEM is, by construction, current preserving, in contrast to the CG-FEM. Consequently, a higher simulation accuracy can be achieved in certain scenarios, e.g., when the diameter of thin insulating structures, such as the skull, is in the range of the mesh resolution. A theoretical derivation of the Mixed-FEM approach for EEG forward simulations is presented, and the algorithms implemented for solving the resulting equation systems are described. Subsequently, first evaluations in both sphere and realistic head models are presented, and the results are compared to previously introduced CG-FEM approaches. Additional visualizations are shown to illustrate the current preserving property of the Mixed-FEM. Based on these results, it is concluded that the newly presented Mixed-FEM can at least complement and in some scenarios even outperform the established CG-FEM approaches, which motivates a further evaluation of the Mixed-FEM for applications in bioelectromagnetism.
Organisations: Mathematics, Research group: Inverse Problems, University of Utah, Cluster of Excellence EXC, University of Münster
Contributors: Vorwerk, J., Engwer, C., Pursiainen, S., Wolters, C. H.
Journal: IEEE Transactions on Medical Imaging
Article number: 7731161
ASJC Scopus subject areas: Software, Radiological and Ultrasound Technology, Computer Science Applications, Electrical and Electronic Engineering
Keywords: EEG, forward problem, mixed finite element method, realistic head modeling, source analysis
10.1109/TMI.2016.2624634
Comparison of wood volume estimates of young trees from terrestrial laser scan data
Many analyses in ecology and forestry require wood volume estimates of trees. However, non-destructive measurements are not straightforward because trees are differing in their three-dimensional structures and shapes. In this paper we compared three methods (one voxel-based and two cylinder-based methods) for wood volume calculation of trees from point clouds obtained by terrestrial laser scanning. We analysed a total of 24 young trees, composed of four different species ranging between 1.79 m to 7.96 m in height, comparing the derived volume estimates from the point clouds with xylometric reference volumes for each tree. We found that both voxel-and cylinder-based approaches are able to compute wood volumes with an average accuracy above 90% when compared to reference volumes. The best results were achieved with the voxel-based method (r2 = 0.98). Cylinder-model based methods (r2 = 0.90 and 0.92 respectively) did perform slightly less well but offer valuable additional opportunities to analyse structural parameters for each tree. We found that the error of volume estimates from point clouds are strongly species-specific. Therefore, species-specific parameter sets for point-cloud based wood volume estimation methods are required for more robust estimates across a number of tree species.
Organisations: Mathematics, Research group: Inverse Problems, Vodafone Department of Mobile Communications Systems, Leuphana University Lüneburg, INRA Centre de Nancy
Contributors: Kunz, M., Hess, C., Raumonen, P., Bienert, A., Hackenberg, J., Maas, H. G., Härdtle, W., Fichtner, A., Von Oheimb, G.
Journal: iForest - Biogeosciences and Forestry
ASJC Scopus subject areas: Forestry, Ecology, Nature and Landscape Conservation
Keywords: Mixed forests, Quantitative structure models, Voxel-based, Xylometry
10.3832/ifor2151-010
Meeting a deadline: shortest paths on stochastic directed acyclic graphs with information gathering
We consider the problem of an agent traversing a directed graph with the objective of maximizing the probability of reaching a goal node before a given deadline. Only the probability of the travel times of edges is known to the agent. The agent must balance between traversal actions towards the goal, and delays due to actions improving information about graph edge travel times. We describe the relationship of the problem to the more general partially observable Markov decision process. Further, we show that if edge travel times are independent and the underlying directed graph is acyclic, a closed loop solution can be computed. The solution specifies whether to execute a traversal or information-gathering action as a function of the current node, the time remaining until the deadline, and the information about edge travel times. We present results from two case studies, quantifying the usefulness of information-gathering as opposed to applying only traversal actions.
Organisations: Department of Automation Science and Engineering
Contributors: Lauri, M., Ropponen, A., Ritala, R.
Publication date: Apr 2017
Journal: Annals of Mathematics and Artificial Intelligence
ASJC Scopus subject areas: Artificial Intelligence, Applied Mathematics
Keywords: Applied probability, Decision processes, Dynamic programming, Markov processes, Transportation
Automatic tree species recognition with quantitative structure models
We present three robust methods to accurately and automatically recognize tree species from terrestrial laser scanner data. The recognition is based on the use of quantitative structure tree models, which are hierarchical geometric primitive models accurately approximating the branching structure, geometry, and volume of the trees. Fifteen robust tree features are presented and tested with all different combinations for tree species classification. The classification methods presented are k-nearest neighbours, multinomial regression, and support vector machine based approaches. Three mainly single-species forest plots of Silver birch, Scots pine and Norway spruce, and two mixed-species forest plots located in Finland and a total number of trees over 1200 were used for demonstration. The results show that by using single-species forest plots for training and testing, it is possible to find a feature combination between 5 and 15 features, that results in an average classification accuracy above 93% for all the methods. For the preliminary mixed-species forest plot testing, accuracy was lower but the classification approach presented potential to generalize to more diverse cases. Moreover, the results show that the post-processing of terrestrial laser scanning data of multi-hectare forest, from tree extraction and modelling to species classification, can be done automatically.
Organisations: Mathematics, Research group: Inverse Problems, Natural Resources Institute Finland (Luke)
Contributors: Åkerblom, M., Raumonen, P., Mäkipää, R., Kaasalainen, M.
Keywords: Quantitative structure model, Terrestrial laser scanning, Tree reconstruction, Tree species recognition
Author post-print. Embargo ended: 19/01/19
10.1016/j.rse.2016.12.002
Complexity of Rainbow Vertex Connectivity Problems for Restricted Graph Classes
A path in a vertex-colored graph G is vertex rainbow if all of its internal vertices have a distinct color. The graph G is said to be rainbow vertex connected if there is a vertex rainbow path between every pair of its vertices. Similarly, the graph G is strongly rainbow vertex connected if there is a shortest path which is vertex rainbow between every pair of its vertices. We consider the complexity of deciding if a given vertex-colored graph is rainbow or strongly rainbow vertex connected. We call these problems Rainbow Vertex Connectivity and Strong Rainbow Vertex Connectivity, respectively. We prove both problems remain NP-complete on very restricted graph classes including bipartite planar graphs of maximum degree 3, interval graphs, and kk-regular graphs for k≥3k≥3. We settle precisely the complexity of both problems from the viewpoint of two width parameters: pathwidth and tree-depth. More precisely, we show both problems remain NP-complete for bounded pathwidth graphs, while being fixed-parameter tractable parameterized by tree-depth. Moreover, we show both problems are solvable in polynomial time for block graphs, while Strong Rainbow Vertex Connectivity is tractable for cactus graphs and split graphs.
Organisations: Department of Mathematics
Contributors: Lauri, J.
Shape model of asteroid (130) Elektra from optical photometry and disk-resolved images from VLT/SPHERE and Nirc2/Keck
Context. Asteroid (130) Elektra belongs to one of the six known triple asteroids in the main belt, so its mass has been reliably determined.
Aims. We aim to use all available disk-resolved images of (130) Elektra obtained by the SPHERE instrument at VLT and by the Nirc2 of the Keck telescope together with the disk-integrated photometry to determine its shape model and its size. The volume can be then used in combination with the known mass to derive the bulk density of the primary.
Methods. We have applied the All-Data Asteroid Modeling (ADAM) algorithm to the optical disk-integrated data, two disk-resolved images obtained by the SPHERE instrument, and 13 disk-resolved images from the Nirc2 of the Keck telescope. We have also derived the shape model and size of Elektra.
Results. We present the shape model, volume-equivalent diameter (199 ± 7 km) and bulk density (1.60 ± 0.13 g cm-3) of the C-type asteroid Elektra.
Organisations: Mathematics, Research group: MAT Inverse Problems, Charles University in Prague, SETI Institute, European Southern Observatory (ESO)
Contributors: Hanuš, J., Marchis, F., Viikinkoski, M., Yang, B., Kaasalainen, M.
Keywords: Methods: numerical, Methods: observational, Minor planets, asteroids: individual: (130) Elektra
shape model of asteroid (130) Elektra
Forward and Inverse Effects of the Complete Electrode Model in Neonatal EEG
This paper investigates finite element method (FEM) based modeling in the context of neonatal electroencephalography (EEG). In particular, the focus lies on electrode boundary conditions. We compare the complete electrode model (CEM) to the point electrode model (PEM), which is the current standard in EEG. In the CEM, the voltage experienced by an electrode is modeled more realistically as the integral average of the potential distribution over its contact surface, whereas the PEM relies on a point value. Consequently, the CEM takes into account the sub-electrode shunting currents which are absent in the PEM. In this study, we aim to find out how the electrode voltage predicted by these two models differ, if standard size electrodes are attached to a head of a neonate. Additionally, we study voltages and voltage variation on electrode surfaces with two source locations: (A) next to the 5-th electrode and (B) directly under the frontal fontanel. A realistic model of a neonatal head including a skull with fontanels and sutures is used. Based on the results, the forward simulation differences between CEM and PEM are in general small, but significant outliers can occur in the vicinity of the electrodes. The CEM can be considered as an integral part of the outer head model. The outcome of this study helps understanding volume conduction of neonatal EEG as it enlightens the role of advanced skull and electrode modeling in forward and inverse computations.
Contributors: Pursiainen, S., Lew, S., Wolters, C. H.
Journal: Journal of Neurophysiology
Scopus rating (2017): CiteScore 2.51 SJR 1.65 SNIP 0.897
Copyright © 2016, Journal of Neurophysiology.
Source: PubMed
The Congruences Below Fair Testing with Initial Stability
When analysing behaviours of concurrent systems with process-algebraic methods, the notion of congruence plays a central role. It means an equivalence that remains valid if any subsystem is replaced by an equivalent one. It facilitates powerful compositional methods for the verification of systems. Unfortunately, so many congruences have been defined in the literature that it is difficult to know about them all. Furthermore, it may be that the best congruence for the task at hand is not yet known. The present study continues a line of research that tries to help the situation by choosing a region, listing all congruences in it, and proving that there are no others. The present study covers the congruences that are implied by fair testing equivalence with initial stability. The most important finding is that this region contains only few previously unknown congruences, and none of them seems interesting.
Organisations: Mathematics, Research group: MAT Computer Science and Applied Logics
Contributors: Valmari, A.
Title of host publication: 2016 16th International Conference on Application of Concurrency to System Design
ISBN (Print): 978-1-5090-0763-9
ASJC Scopus subject areas: Computer Science(all)
Keywords: congruence; fair testing equivalence; initial stability
10.1109/ACSD.2016.15
Abstractions for transition systems with applications to stubborn sets
Partial order reduction covers a range of techniques based on eliminating unnecessary transitions when generating a state space. On the other hand, abstractions replace sets of states of a system with abstract representatives in order to create a smaller state space. This article explores how stubborn sets and abstraction can be combined. We provide examples to provide intuition and expand on some recent results. We provide a classification of abstractions and give some novel results on what is needed to combine abstraction and partial order reduction in a sound way.
Organisations: Research group: MAT Computer Science and Applied Logics, Mathematics
Contributors: Hansen, H.
Title of host publication: Concurrency, Security, and Puzzles : Essays Dedicated to Andrew William Roscoe on the Occasion of His 60th Birthday
Publisher: Springer International Publishing
Editors: Gibson-Robinson, T., Hopcroft, P., Lazić, R.
Name: Lecture Notes in Computer Science
Volume: 10160
More stubborn set methods for process algebras
Six stubborn set methods for computing reduced labelled transition systems are presented. Two of them preserve the traces, and one is tailored for on-the-fly verification of safety properties. The rest preserve the tree failures, fair testing equivalence, or the divergence traces. Two methods are entirely new, the ideas of three are recent and the adaptation to the process-algebraic setting with non-deterministic actions is new, and one is recent but slightly generalized. Most of the methods address problems in earlier solutions to the so-called ignoring problem. The correctness of each method is proven, and efficient implementation is discussed.
http://www.scopus.com/inward/record.url?scp=85006810860&partnerID=8YFLogxK (Link to publication in Scopus)
Stop it, and be stubborn!
This publication discusses how automatic verification of concurrent systems can be made more efficient by focusing on always may-terminating systems. First, making a system always may-terminating is a method formeeting a modelling need that exists independently of this publication. It is illustrated that without doing so, non-progress errors may be lost. Second, state explosion is often alleviated with stubborn, ample, and persistent set methods. They use expensive cycle or terminal strong component conditions in many cases. It is proven that for many important classes of properties, if the systems are always may-terminating, then these conditions can be left out.
Journal: ACM Transactions on Embedded Computing Systems
ASJC Scopus subject areas: Software, Hardware and Architecture
Keywords: Ignoring problem, Safety/progress/liveness properties, Stubborn set/ample set/persistent set/partial order methods
Advanced boundary electrode modeling for tES and parallel tES/EEG
This paper explores advanced electrode modeling in the context of separate and parallel transcranial electrical stimulation (tES) and electroencephalography (EEG) measurements.We focus on boundary condition based approaches that do not necessitate adding auxiliary elements, e.g. sponges, to the computational domain. In particular, we investigate the complete electrode model (CEM) which incorporates a detailed description of the skin-electrode interface including its contact surface, impedance and normal current distribution. The CEM can be applied for both tES and EEG electrodes which is advantageous when a parallel system is used. In comparison to the CEM, we test two important reduced approaches: the gap model (GAP) and the point electrode model (PEM). We aim to find out the differences of these approaches for a realistic numerical setting based on the stimulation of the auditory cortex. The results obtained suggest, among other things, that GAP and GAP/PEM are sufficiently accurate for the practical application of tES and parallel tES/EEG, respectively. Differences between CEM and GAP were observed mainly in the skin compartment, where only CEM explains the heating effects characteristic to tES.
Organisations: Mathematics, Research group: Inverse Problems, University of Münster
Contributors: Pursiainen, S., Agsten, B., Wagner, S., Wolters, C. H.
Journal: IEEE Transactions on Neural Systems and Rehabilitation Engineering
ASJC Scopus subject areas: Neuroscience(all), Biomedical Engineering, Computer Science Applications
Keywords: Boundary conditions, Brain modeling, Complete electrode model (CEM), Computational modeling, Electric potential, Electrodes, Electroencephalography, Electroencephalography (EEG) electrode modeling, Finite element method (FEM)., Skin, Transcranial electrical stimulation (tES)
10.1109/TNSRE.2017.2748930
Asymptotics for infinite systems of differential equations
This paper investigates the asymptotic behavior of solutions to certain infinite systems of ordinary differential equations. In particular, we use results from ergodic theory and the asymptotic theory of C0-semigroups to obtain a characterization, in terms of convergence of certain Cesàro averages, of those initial values which lead to convergent solutions. Moreover, we obtain estimates on the rate of convergence for solutions whose initial values satisfy a stronger ergodic condition. These results rely on a detailed spectral analysis of the operator describing the system, which is made possible by certain structural assumptions on the operator. The resulting class of systems is sufficiently broad to cover a number of important applications including, in particular, both the so-called robot rendezvous problem and an important class of platoon systems arising in control theory. Our method leads to new results in both cases.
Journal: SIAM Journal on Control and Optimization
ASJC Scopus subject areas: Control and Optimization, Applied Mathematics
Keywords: Asymptotic behavior, C0-semigroup, Ergodic theory, Ordinary differential equations, Rates of convergence, Spectrum, System
Bayes Forest: A data-intensive generator of morphological tree clones
Detailed and realistic tree form generators have numerous applications in ecology and forestry. For example, the varying morphology of trees contributes differently to formation of landscapes, natural habitats of species, and eco-physiological characteristics of the biosphere. Here, we present an algorithm for generating morphological tree "clones" based on the detailed reconstruction of the laser scanning data, statistical measure of similarity, and a plant growth model with simple stochastic rules. The algorithm is designed to produce tree forms, i.e., morphological clones, similar (and not identical) in respect to tree-level structure, but varying in fine-scale structural detail. Although we opted for certain choices in our algorithm, individual parts may vary depending on the application, making it a general adaptable pipeline. Namely, we showed that a specific multipurpose procedural stochastic growth model can be algorithmically adjusted to produce the morphological clones replicated from the target experimentally measured tree. For this, we developed a statistical measure of similarity (structural distance) between any given pair of trees, which allows for the comprehensive comparing of the tree morphologies by means of empirical distributions describing the geometrical and topological features of a tree. Finally, we developed a programmable interface to manipulate data required by the algorithm. Our algorithm can be used in a variety of applications for exploration of the morphological potential of the growth models (both theoretical and experimental), arising in all sectors of plant science research.
Organisations: Mathematics, Research group: Inverse Problems, Department of Computer Science, Aalto University
Contributors: Potapov, I., Järvenpää, M., Åkerblom, M., Raumonen, P., Kaasalainen, M.
Journal: GigaScience
Article number: gix079
ASJC Scopus subject areas: Health Informatics, Computer Science Applications
Keywords: Empirical distributions, Large scale data, Morphological clone, Quantitative structure tree model, Stochastic data driven model, Terrestrial laser scanning
gix079
10.1093/gigascience/gix079
EXT="Järvenpää, Marko"
Computational Model for Simulating Multifocal Imaging in Optical Projection Tomography
We present a computational model describing the blurring of particles with respect to focal distance in 3D optical imaging. The model can be used to improve reconstructions in optical projection tomography.
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Computational Biophysics and Imaging Group, Mathematics, Research group: Inverse Problems, International Iberian Nanotechnology Laboratory
Contributors: Koskela, O., Belay, B., Pursiainen, S., Figueiras, E., Hyttinen, J.
Title of host publication: Mathematics in Imaging 2017
Publisher: Optical Society of America
Article number: MTu1C.3
ISBN (Electronic): 978-1-943580-29-3
osa17FINAL. Embargo ended: 29/06/18
10.1364/MATH.2017.MTu1C.3
Context Awareness for Semantic Mobile Computing
In a plethora of smart phones and related mobile applications, users crave innovative and personalized services that adapt to their situation. To achieve that, smart phones need to understand user context and needs for latter providing them with adequate services. This chapter discusses how context can be understood, represented and exploited in smart phones, using techniques from the fields of Semantic Computing, Machine Learning and Graph Theory.
Organisations: Mathematics, Research group: MAT Intelligent Information Systems Laboratory
Contributors: Rivero-Rodriguez, A., Nykänen, O.
Title of host publication: Multi-Technology Positioning
Place of publication: Cham
Editors: Nurmi, J., Lohan, E., Wymeersch, H., Seco-Granados, G., Nykänen, O.
Source ID: urn:2f5582c69455f55e5551e9f220081242
General Integral Formulas for k-hyper-mono-genic Functions
We are studying a function theory of k-hypermonogenic functions connected to k-hyperbolic harmonic functions that are harmonic with respect to the hyperbolic Riemannian metric k2=xn2k1-n(dx02+⋯+dxn2)in the upper half space R+n+1={(x0,…,xn)|xi∈R,xn>0}. The function theory based on this metric is important, since in case k= n- 1 , the metric is the hyperbolic metric of the Poincaré upper half space and Leutwiler noticed that the power function xm(m∈N0), calculated using Clifford algebras, is a conjugate gradient of a hyperbolic harmonic function. We find a fundamental k-hyperbolic harmonic function. Using this function we are able to find kernels and integral formulas for k-hypermonogenic functions. Earlier these results have been verified for hypermonogenic functions (k= n- 1) and for k-hyperbolic harmonic functions in odd dimensional spaces.
Organisations: Department of Mathematics, Research group: MAT Clifford analysis
Source ID: urn:3be942d6de9c9305f7f491e2b5180855
Independent Loops Search in Flow Networks Aiming for Well-Conditioned System of Equations
We approach the problem of choosing linearly independent loops in a pipeflow network as choosing the best-conditioned submatrix of a given larger matrix. We present some existing results of graph theory and submatrix selection problems, based on which we construct three heuristic algorithms for choosing the loops. The heuristics are tested on two pipeflow networks that differ significantly on the distribution of pipes and nodes in the network.
Organisations: Mathematics, Research group: Computer Science and Applied Logics, Research group: Positioning, Research group: MAT Intelligent Information Systems Laboratory, Tekes
Contributors: Humaloja, J., Ali-Löytty, S., Pohjolainen, S., Hämäläinen, T.
Title of host publication: Progress in Industrial Mathematics at ECMI 2016
Editors: Quintela, P., Barral, P., Gómez, D., Pena, F. J., Rodríguez, J., Salgado, P., Vázquez-Mendéz, M. E.
Name: Mathematics in industry
ASJC Scopus subject areas: Applied Mathematics, Modelling and Simulation
Keywords: pipeflow analysis, independent loops
ecmi16. Embargo ended: 4/12/18
https://www.springer.com/gp/book/9783319630816
Integral kernels for k-hypermonogenic functions
We consider the modified Cauchy–Riemann operator (Formula presented.) in the universal Clifford algebra (Formula presented.) with the basis (Formula presented.). The null-solutions of this operator are called k-hypermonogenic functions. We calculate the k-hyperbolic harmonic fundamental solutions, i.e. solutions to (Formula presented.), and use these solutions to find k-hypermonogenic kernels for a Cauchy-type integral formula in the upper half-space.
Contributors: Vuojamo, V., Eriksson, S.
Early online date: 21 Feb 2017
Journal: Complex Variables and Elliptic Equations
ASJC Scopus subject areas: Analysis, Numerical Analysis, Computational Mathematics, Applied Mathematics
Keywords: Cauchy integral formula, Clifford algebra, hyperbolic Laplace–Beltrami, k-hyperbolic harmonic, k-hypermonogenic
Kriging prediction of stand-level forest information using mobile laser scanning data adjusted for nondetection
This study presents an approach for predicting stand-level forest attributes utilizing mobile laser scanning data collected as a nonprobability sample. Firstly, recordings of stem density were made at point locations every 10th metre along a subjectively chosen mobile laser scanning track in a forest stand. Secondly, kriging was applied to predict stem density values for the centre point of all grid cells in a 5 m x 5 m lattice across the stand. Thirdly, due to nondetectability issues, a correction term was computed based on distance sampling theory. Lastly, the mean stem density at stand level was predicted as the mean of the point-level predictions multiplied with the correction factor, and the corresponding variance was estimated. Many factors contribute to the uncertainty of the stand-level prediction; in the variance estimator, we accounted for the uncertainties due to kriging prediction and due to estimating a detectability model from the laser scanning data. The results from our new approach were found to correspond fairly well to estimates obtained using field measurements from an independent set of 54 circular sample plots. The predicted number of stems in the stand based on the proposed methodology was 1366 with a 12.9% relative standard error. The corresponding estimate based on the field plots was 1677 with a 7.5% relative standard error.
Organisations: Mathematics, Research group: Inverse Problems, Norwegian Inst Bioecon Res, Swedish University of Agricultural Sciences, University System Of New Hampshire
Contributors: Saarela, S., Breidenbach, J., Raumonen, P., Grafström, A., Ståhl, G., Ducey, M. J., Astrup, R.
Journal: CANADIAN JOURNAL OF FOREST RESEARCH-REVUE CANADIENNE DE RECHERCHE FORESTIERE
Keywords: covariogram, detectability function, forest management, model-based inference, TREE STEM, ABOVEGROUND BIOMASS, ASSISTED ESTIMATION, SPACEBORNE LIDAR, BOUNDARY OVERLAP, AIRBORNE, INVENTORY, MODELS, SYSTEM, VOLUME
10.1139/cjfr-2017-0019
Source: WOS
Source ID: 000408223000012
Kullback-Leibler Divergence Approach to Partitioned Update Kalman Filter
Kalman filtering is a widely used framework for Bayesian estimation. The partitioned update Kalman filter applies a Kalman filter update in parts so that the most linear parts of measurements are applied first. In this paper, we generalize partitioned update Kalman filter, which requires the use of the second order extended Kalman filter, so that it can be used with any Kalman filter extension such as the unscented Kalman filter. To do so, we use a Kullback-Leibler divergence approach to measure the nonlinearity of the measurement, which is theoretically more sound than the nonlinearity measure used in the original partitioned update Kalman filter. Results show that the use of the proposed partitioned update filter improves the estimation accuracy.
Organisations: Department of Automation Science and Engineering, Research area: Dynamic Systems, Research group: Positioning
Contributors: Raitoharju, M., García-Fernádez, Á., Piche, R.
Journal: Signal Processing
KLPUKF. Embargo ended: 15/07/18
10.1016/j.sigpro.2016.07.007
https://arxiv.org/pdf/1503.02857v2
LEADER: fast estimates of asteroid shape elongation and spin latitude distributions from scarce photometry
Context. Many asteroid databases with lightcurve brightness measurements (e.g. WISE, Pan-STARRS1) contain enormous amounts of data for asteroid shape and spin modelling. While lightcurve inversion is not plausible for individual targets with scarce data, it is possible for large populations with thousands of asteroids, where the distributions of the shape and spin characteristics of the populations are obtainable.
Aims. We aim to introduce a software implementation of a method that computes the joint shape elongation p and spin latitude β distributions for a population, with the brightness observations given in an asteroid database. Other main goals are to include a method for performing validity checks of the algorithm, and a tool for a statistical comparison of populations.
Methods. The LEADER software package read the brightness measurement data for a user-defined subpopulation from a given database. The observations were used to compute estimates of the brightness variations of the population members. A cumulative distribution function (CDF) was constructed of these estimates. A superposition of known analytical basis functions yielded this CDF as a function of the (shape, spin) distribution. The joint distribution can be reconstructed by solving a linear constrained inverse problem. To test the validity of the method, the algorithm can be run with synthetic asteroid models, where the shape and spin characteristics are known, and by using the geometries taken from the examined database.
Results. LEADER is a fast and robust software package for solving shape and spin distributions for large populations. There are major differences in the quality and coverage of measurements depending on the database used, so synthetic simulations are always necessary before a database can be reliably used. We show examples of differences in the results when switching to another database.
Contributors: Nortunen, H., Kaasalainen, M.
Matematiikan Perustaitojen Testi: Testin tehtävien ja vuosien 2010-2016 tulosten analyysi
Tampereen teknillisessä yliopistossa aloittavat uudet opiskelijat ovat vuodesta 2002 lähtien suorittaneet opintojensa aluksi matematiikan perustaitotestin. Perustaitotesti koostuu 16:sta kysymyksestä, joihin vastaamiseen opiskelijoilla on aikaa 45 minuuttia. Opiskelijat käyttävät testissä vain kynää ja paperia, ja syöttävät vastauksensa tietokoneelle. Samanlainen testi on ollut TTY:n lisäksi käytössä myös mm. Aalto-yliopistossa sekä Tampereen yliopistossa. Tässä tutkimuksessa on tavoitteena tutkia Perustaitotestin tehtävien linkittymistä vuonna 2003 laadittuun lukion opetussuunnitelmaan, sekä analysoida tilastollisin menetelmin Perustaitotestin pisteiden kehitystä vuosien 2007-2016 aikana.
Vuoden 2003 opetussuunnitelman mukaan "matematiikan asema aikamme kulttuurissa edellyttää valmiutta ymmärtää, hyödyntää ja tuottaa matemaattisesti esitettyä tietoa". Tämän lisäksi "opetuksen tehtävänä on tutustuttaa opiskelija matemaattisen ajattelun malleihin sekä matematiikan perusideoihin ja rakenteisiin". Perustaitotesti on pyritty laatimaan siten, että se mittaisi mahdollisimman laaja-alaisesti opiskelijoiden kykyä ratkaista yksinkertaisia yhtälöitä ja manipuloida matemaattisia lausekkeita. Tehtäviä on yhteensä 16, ja ne ovat seuraavista aihealueista: luvut, lausekkeet, yhtälöt, epäyhtälöt, logaritmi, eksponentti, trigonometria, derivaatta ja integraali.
TTY kouluttaa pääasiassa diplomi-insinöörejä, ja tämä sanelee pitkälti sen, minkälaisia matemaattisia taitoja yliopisto toivoisi opiskelijoillaan olevan. TTY:llä ei kuitenkaan ole laadittu omaa standardia siitä, mitkä matematiikan osat ovat insinöörille tärkeimpiä. Sen sijaan, Euroopan insinöörikoulutuksen yhteisö (European Society of Engineering Education, SEFI) on määrittänyt insinöörien tärkeimmät matemaattiset kompetenssit dokumentissaan "A Framework for Mathematics Curricula in Engineering Education". Perustaitotestin vaatimia kompetensseja voidaan tarkistella myös kyseisen dokumentin Core 0 -tason (yliopistoon tulevien toivottu pohjataso) kompetenssien kanssa.
Komparatiivisen analyysin lisäksi paperissa esitetään perustaitotestin tehtäväkohtainen analyysi perinteisin tilastollisin menetelmin. Testidataa on kerätty useita vuosia testin pysyessä muuttumattomana. Tästä johtuen testitulosten tilastollisesti merkittävimpiä vaihteluita voidaan yrittää ymmärtää paremmin tarkistelemalla koulutuspoliittisia päätöksiä kuten ylioppilaskirjoitusten sallitut työkalut.
Publication status: In preparation
MoE publication type: D4 Published development or research report or study
Contributors: Myllykoski, T., Ali-Löytty, S. S.
Maximal perpendicularity in certain Abelian groups
We define perpendicularity in an Abelian group G as a binary relation satisfying certain five axioms. Such a relation is maximal if it is not a subrelation of any other perpendicularity in G. A motivation for the study is that the poset (P, ⊆) of all perpendicularities in G is a lattice if G has a unique maximal perpendicularity, and only a meet-semilattice if not. We study the cardinality of the set of maximal perpendicularities and, on the other hand, conditions on the existence of a unique maximal perpendicularity in the following cases: G ≅ ℤn, G is finite, G is finitely generated, and G = ℤ ⊕ ℤ ⊕⋯. A few such conditions are found and a few conjectured. In studying ℝn, we encounter perpendicularity in a vector space.
Contributors: Mattila, M., Merikoski, J. K., Haukkanen, P., Tossavainen, T.
Journal: ACTA UNIVERSITATIS SAPIENTIAE: MATHEMATICA
Keywords: Abelian group, Perpendicularity
10.1515/ausm-2017-0016
Minimal solutions of general fuzzy relation equations on linear carriers. An algebraic characterization
This paper considers a general fuzzy relation equation, which has minimal solutions, if it is solvable. In this case, an algebraic characterization is introduced which provides an interesting method to compute minimal solutions in this general setting. Moreover, a comparison with other frameworks is also given.
Organisations: Research Community on Data-to-Decision (D2D), Mathematics, Research group: Computer Science and Applied Logics
Contributors: Diaz-Moreno, J. C., Medina, J., Turunen, E.
Journal: Fuzzy Sets and Systems
10.1016/j.fss.2016.02.004
Modelling anisotropy in non-oriented electrical steel sheet using vector Jiles-Atherton model
Organisations: Electrical Energy Engineering, Research area: Power engineering, Aalto University, Graz University of Technology, Tallinn University of Technology
Contributors: Upadhaya, B., Martin, F., Rasilo, P., Handgruber, P., Belahcen, A., Arkkio, A.
Journal: COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
epnc_brijesh
10.1108/COMPEL-09-2016-0399
A total domatic k-partition of a graph is a partition of its vertex set into k subsets such that each intersects the open neighborhood of each vertex. The maximum k for which a total domatic k-partition exists is known as the total domatic number of a graph G, denoted by d:t(G). We extend considerably the known hardness results by showing it istextsc {NP} -complete to decide whether d:t(G)ge 3 where G is a bipartite planar graph of bounded maximum degree. Similarly, for every kge 3, it istextsc {NP} -complete to decide whether d:t(G)ge k, where G is a split graph or k-regular. In particular, these results complement recent combinatorial results regarding d:t(G) on some of these graph classes by showing that the known results are, in a sense, best possible. Finally, for general n-vertex graphs, we show the problem is solvable in 2^n n^{O(1)} time, and derive even faster algorithms for special graph classes.
Organisations: Mathematics, Research group: Computer Science and Applied Logics, University of Helsinki, Bell Labs
Title of host publication: Computing and Combinatorics - 23rd International Conference, COCOON 2017, Proceedings
On homomorphisms between products of median algebras
Homomorphisms of products of median algebras are studied with particular attention to the case when the codomain is a tree. In particular, we show that all mappings from a product (Formula presented.) of median algebras to a median algebra (Formula presented.) are essentially unary whenever the codomain (Formula presented.) is a tree. In view of this result, we also characterize trees as median algebras and semilattices by relaxing the defining conditions of conservative median algebras.
Organisations: Mathematics, Université de Lorraine, TEI of Epirus
Contributors: Couceiro, M., Foldes, S., Meletiou, G. C.
Journal: Algebra Universalis
ASJC Scopus subject areas: Algebra and Number Theory
Positive definite arithmetical functions
We are going to define a concept of positive definiteness for arithmetical functions by using GCD matrices. At the same time we are able to define a partial ordering in the set of arithmetical functions.
Contributors: Mattila, M.
Event: Paper presented at Finnish Number Theory Days 2017, Tampere, Finland.
Robust controllers for regular linear systems with infinite-dimensional exosystems
We construct two error feedback controllers for robust output tracking and disturbance rejection of a regular linear system with nonsmooth reference and disturbance signals. We show that for sufficiently smooth signals the output converges to the reference at a rate that depends on the behavior of the transfer function of the plant on the imaginary axis. In addition, we construct a controller that can be designed to achieve robustness with respect to a given class of uncertainties in the system, and we present a novel controller structure for output tracking and disturbance rejection without the robustness requirement. We also generalize the internal model principle for regular linear systems with boundary disturbance and for controllers with unbounded input and output operators. The construction of controllers is illustrated with an example where we consider output tracking of a nonsmooth periodic reference signal for a two-dimensional heat equation with boundary control and observation, and with periodic disturbances on the boundary.
Keywords: Controller Design, Feedback, Regular Linear Systems, Robust Output Regulation, Stability
10.1137/16M107181X
Some Theoretical Remarks of Octonionic Analysis
In this article we first review the classical results of octonions and octonionic analysis. Then we consider some theoretical properties of the theory and compare it to quaternionic analysis and Clifford analysis.
Title of host publication: Proceedings of the 8th International Conference On Mathematical Modeling (ICMM-2017)
Publisher: American Institute of Physics AIP
Editors: Egorov, I. E., Popov, S. V., Vabishchevich, P. N., Antonov, M. Y., Lazarev, N. P., Troeva, M. S., Ivanova, A. O., Grigor'ev, Y. M.
Name: AIP Conference Proceedings
Publisher: American Institute of Physics
Some-function-theoretical-remarks-of-octonionic-analysis. Embargo ended: 14/11/18
Structure-preserving mesh coupling based on the Buffa-Christiansen complex
The state of the art for mesh coupling at nonconforming interfaces is presented and reviewed. Mesh coupling is frequently applied to the modeling and simulation of motion in electromagnetic actuators and machines. The paper exploits Whitney elements to present the main ideas. Both interpolation- and projection-based methods are considered. In addition to accuracy and efficiency, we emphasize the question whether the schemes preserve the structure of the de Rham complex, which underlies Maxwell's equations. As a new contribution, a structure-preserving projection method is presented, in which Lagrange multiplier spaces are chosen from the Buffa-Christiansen complex. Its performance is compared with a straightforward interpolation based on Whitney and de Rham maps, and with Galerkin projection.
Contributors: Niemimäki, O., Kurz, S., Kettunen, L.
Journal: Mathematics of Computation
10.1090/mcom/3121
Stubborn set intuition explained
This study focuses on the differences between stubborn sets and other partial order methods. First a major problem with step graphs is pointed out with an example. Then the deadlock-preserving stubborn set method is compared to the deadlock-preserving ample set and persistent set methods. Next, conditions are discussed whose purpose is to ensure that the reduced state space preserves the ordering of visible transitions, that is, transitions that may change the truth values of the propositions that the formula under verification has been built from. Finally solutions to the ignoring problem are analysed both when the purpose is to preserve only safety properties and when also liveness properties are of interest.
Organisations: Pervasive Computing, Mathematics
Contributors: Valmari, A., Hansen, H.
Title of host publication: Transactions on Petri Nets and Other Models of Concurrency XII
Teollinen internet ja semanttinen mallinnus
Organisations: Mathematics, Research group: MAT Intelligent Information Systems Laboratory, Research group: Computer Science and Applied Logics
Contributors: Nykänen, O.
Title of host publication: Teollinen internet uudistaa palveluliiketoimintaa ja kunnossapitoa
Place of publication: Kerava
Publisher: Kunnossapitoyhdistys ProMaint
Editors: Martinsuo, M., Kärri, T.
ISBN (Print): 978-952-68687-0-7
ISBN (Electronic): 978-952-68687-1-4
The arithmetic Jacobian matrix and determinant
Let α1,…, αm be such real numbers that can be expressed as a finite product of prime powers with rational exponents. Using arithmetic partial derivatives, we define the arithmetic Jacobian matrix Ja of the vector a = (α1,…, αm) analogously to the Jacobian matrix Jf of a vector function f. We introduce the concept of multiplicative independence of {α1,…, αm} and show that Ja plays in it a similar role as Jf does in functional independence. We also present a kind of arithmetic implicit function 1 theorem and show that Ja applies to it somewhat analogouslytheorem and show that Ja applies to it somewhat analogously as Jf applies to the ordinary implicit function theorem.
Contributors: Haukkanen, P., Merikoski, J. K., Mattila, M., Tossavainen, T.
Journal: Journal of Integer Sequences
Article number: 17.9.2
ASJC Scopus subject areas: Discrete Mathematics and Combinatorics
Keywords: Arithmetic derivative, Arithmetic partial derivative, Implicit function theorem, Jacobian determinant, Jacobian matrix, Multiplicative independence
https://cs.uwaterloo.ca/journals/JIS/VOL20/Tossavainen/tossa11.pdf
Two-Sided Hypergenic Functions
In this paper we present an analogous of the class of two-sided axial monogenic functions to the case of axial κ-hypermonogenic functions. In order to do that we will solve a Vekua-type system in terms of Bessel functions.
Organisations: Department of Mathematics, Research group: MAT Clifford analysis, Department of Mathematics, CIDMA, Center for Research and Development in Mathematics and Applications
Contributors: Eriksson, S., Orelma, H., Vieira, N.
Keywords: $${\kappa}$$κ-Hypergenic functions, Clifford algebras, Hypergenic functions, Two-side hypergenic functions
RS-BL-algebras are MV-algebras
We prove that RS-BL-algebras are MV-algebras.
Organisations: Department of Mathematics, Research group: MAT Computer Science and Applied Logics
Journal: Iranian Journal of Fuzzy Systems
http://ijfs.usb.ac.ir/article_2826.html
Distribution of spin-axes longitudes and shape elongations of main-belt asteroids
Organisations: Department of Mathematics, Research group: MAT Inverse Problems
Contributors: Cibulkova, H., Durech, J., Vokrouhlicky, D., Kaasalainen, M., Oszkiewicz, D. A.
A New Cauchy Type Integral Formula for Quaternionic k-hypermonogenic Functions
In complex function theory holomorphic functions are conjugate gradient of real harmonic functions. We may build function theories in higher dimensions based on this idea if we generalize harmonic functions and define the conjugate gradient operator. We study this type of function theory in R3 connected to harmonic functions with respect to the Laplace–Beltrami operator of the Riemannian metric ds2=x−2k2(∑2i=0dx2i). The domain of the definition of our functions is in R3 and the image space is the associative algebra of quaternions H generated by 1, e1, e2 and e12 = e1e2 satisfying the relation e i e j + e j e i = –2δ ij , i, j = 1, 2. The complex field C is identified by the set {x0+x1e1|x0,x1εB}. The conjugate gradient is defined in terms of modified Dirac operator, introduced by Mkf=Df+kx−12Qf¯¯¯¯¯¯¯, where Qf is given by the decomposition f (x) = Pf (x) + Qf (x) e2 with Pf (x) and Qf (x) in C and Qf¯¯¯¯¯¯¯ is the usual complex conjugation.
Leutwiler noticed around 1990 that if the usual Euclidean metric is changed to the hyperbolic metric of the Poincaré upper half-space model (k = 1), then the power function (x0 + x1e1 + x2e2) n , calculated using quaternions, is the conjugate gradient of the a hyperbolic harmonic function. We study functions, called k-hypermonogenic, satisfying M k f = 0. Monogenic functions are 0-hypermonogenic. Moreover, 1-hypermonogenic functions are hypermonogenic defined by H. Leutwiler and the first author.
We prove a new Cauchy type integral formulas for k-hypermonogenic functions where the kernels are calculated using the hyperbolic distance and are k-hypermonogenic functions. This formula gives the known formulas in case of monogenic and hypermonogenic functions. It also produces new Cauchy and Teodorescu type integral operators investigated in the future research.
Organisations: Department of Mathematics, University of Helsinki
Title of host publication: Modern Trends in Hypercomplex Analysis
Editors: Bernstein, S., Kähler, U., Sabadini, I., Sommen, F.
Source ID: Eriksson2016
Electroencephalography (EEG) forward modeling via H(div) finite element sources with focal interpolation
The goal of this study is to develop focal, accurate and robust finite element method (FEM) based approaches which can predict the electric potential on the surface of the computational domain given its structure and internal primary source current distribution. While conducting an EEG evaluation, the placement of source currents to the geometrically complex grey matter compartment is a challenging but necessary task to avoid forward errors attributable to tissue conductivity jumps. Here, this task is approached via a mathematically rigorous formulation, in which the current field is modeled via divergence conforming H(div) basis functions. Both linear and quadratic functions are used while the potential field is discretized via the standard linear Lagrangian (nodal) basis. The resulting model includes dipolar sources which are interpolated into a random set of positions and orientations utilizing two alternative approaches: the position based optimization (PBO) and the mean position/orientation (MPO) method. These results demonstrate that the present dipolar approach can reach or even surpass, at least in some respects, the accuracy of two classical reference methods, the partial integration (PI) and St. Venant (SV) approach which utilize monopolar loads instead of dipolar currents.
Contributors: Pursiainen, S., Vorwerk, J., Wolters, C. H.
Journal: Physics in Medicine and Biology
10.1088/0031-9155/61/24/8502
Chasing the Rainbow Connection: Hardness, Algorithms, and Bounds
We study rainbow connectivity of graphs from the algorithmic and graph-theoretic points of view. The study is divided into three parts. First, we study the complexity of deciding whether a given edge-colored graph is rainbow-connected. That is, we seek to verify whether the graph has a path on which no color repeats between each pair of its vertices. We obtain a comprehensive map of the hardness landscape of the problem. While the problem is NP-complete in general, we identify several structural properties that render the problem tractable. At the same time, we strengthen the known NP-completeness results for the problem. We pinpoint various parameters for which the problem is fixed-parameter tractable, including dichotomy results for popular width parameters, such as treewidth and pathwidth. The study extends to variants of the problem that consider vertex-colored graphs and/or rainbow shortest paths. We also consider upper and lower bounds for exact parameterized algorithms. In particular, we show that when parameterized by the number of colors k, the existence of a rainbow s-t path can be decided in O∗ (2k ) time and polynomial space. For the highly related problem of finding a path on which all the k colors appear, i.e., a colorful path, we explain the modest progress over the last twenty years. Namely, we prove that the existence of an algorithm for finding a colorful path in (2 − ε)k nO(1) time for some ε > 0 disproves the so-called Set Cover Conjecture.
Second, we focus on the problem of finding a rainbow coloring. The minimum number of colors for which a graph G is rainbow-connected is known as its rainbow connection number, denoted by rc(G). Likewise, the minimum number of colors required to establish a rainbow shortest path between each pair of vertices in G is known as its strong rainbow connection number, denoted by src(G). We give new hardness results for computing rc(G) and src(G), including their vertex variants. The hardness results exclude polynomial-time algorithms for restricted graph classes and also fast exact exponential-time algorithms (under reasonable complexity assumptions). For positive results, we show that rainbow coloring is tractable for e.g., graphs of bounded treewidth. In addition, we give positive parameterized results for certain variants and relaxations of the problems in which the goal is to save k colors from a trivial upper bound, or to rainbow connect only a certain number of vertex pairs.
Third, we take a more graph-theoretic view on rainbow coloring. We observe upper bounds on the rainbow connection numbers in terms of other well-known graph parameters. Furthermore, despite the interest, there have been few results on the strong rainbow connection number of a graph. We give improved bounds and determine exactly the rainbow and strong rainbow connection numbers for some subclasses of chordal graphs. Finally, we pose open problems and conjectures arising from our work.
lauri 1428
Projektipankki yläkoulun matematiikkaan
MoE publication type: D1 Article in a trade journal
Contributors: Viro, E.
Journal: Dimensio
Identifying weak ties from publicly available social media data in an event
The concept of weak ties was introduced by Granovetter through the seminal paper titled "Strength of weak ties". Since then the role of weak ties in general and their specific role as occupying the structural hole has been explored in many different fields. In this study, we identify actual or potential weak ties using publicly available social media data in the context of an event. Our case study environment is community managers' online discussions in social media in connection to the yearly-organized Community Manager Appreciation Day (CMAD 2016) event in Finland. We were able to identify potential weak ties using the conversation based structural holes, making use of social network analysis methods (like clustering) and content analysis in the context of events. We add to the understanding of and useful data sources for the Strength of weak ties theory originated from Granovetter, and developed further by other researchers. Our approach may be used in future to make more sophisticated conference recommendation systems, and significantly automate the data extraction for making useful contact recommendations from them for conference participants.
Organisations: Department of Information Management and Logistics, Research group: Novi, Department of Mathematics, Research group: MAT Intelligent Information Systems Laboratory, Managing digital industrial transformation (mDIT), Copenhagen Business School
Contributors: Gupta, J. P., Menon, K., Kärkkäinen, H., Huhtamäki, J., Mukkamala, R. R., Hussain, A., Vatrapu, R., Jussila, J., Pirkkalainen, H.
Title of host publication: AcademicMindtrek '16 Proceedings of the 20th International Academic Mindtrek Conference
Publisher: ACM
ASJC Scopus subject areas: Computational Theory and Mathematics, Sociology and Political Science
Keywords: weak ties, social media
http://www.mindtrek.org/2016/
Resurssitehokkaampi ja ilmastoneutraalimpi energiajärjestelmä, mutta miten? Suomalaiset avaintoimijat vastaavat
Organisations: Department of Automation Science and Engineering, Research area: Dynamic Systems, Research area: Measurement Technology and Process Control, Department of Electrical Engineering, Research area: Power engineering, Department of Physics, Research area: Aerosol Physics, University of Tampere, Tampere University of Applied Science
Contributors: Lehtonen, P., Toivanen, P., Aalto, P., Björkqvist, T., Hakkarainen, M., Harsia, P., Holttinen, H., Järventausta, P., Jaakkola, I., Kallioharju, K., Kojo, M., Mylläri, F., Oksa, A. M.
Publisher: EL-TRAN Analyysi
Volume: 5/2016
https://tt.eduuni.fi/sites/EL-TRAN/Julkiset%20tiedostot/Pinja%20Lehtonen%20et%20al.,%20Resurssitehokkaampi%20ja%20ilmastoneutraalimpi%20energiaj%C3%A4rjestelm%C3%A4%20--%20avaintoimijat%20vastaavat,%20miten.pdf
Research output: Book/Report › Commissioned report › Professional
Students' Use of Learning Tools and Tool Types: Solving Self-Study Assignments on an Online Platform
ince 2002, a test titled Mathematics Basic Skills Test (BST) has been organized annually at Tampere University of Technology.In order to pass the Basic Skills Test, a student should be able to complete a set amount out of the 16 assignments within 45 minutes (in fall of 2015, the passing limit was 6 for engineering students, 8 for science and mathematics students). Students who failed the test were directed to the Remedial Instruction (RI). The Remedial Instruction is a set of 71 high school mathematics problems designed to brush up the skills of engineering students.
TUT students have, since 2006, been divided into different learner profile groups. This paper is the summary of studies on the behaviour of these different learner profile groups in the Remedial Instruction regarding their use of time and learning tools when solving their assignments.
Different types of learners indicate that their self-study habits on an online platform are very different. Students that are surface oriented in their studies use a lot of different learning tools, but do not produce good examination results. Skillful students seem to do well even without using a lot of tools. Thus, the current way at TUT, where students work on their remedial mathematics problems on their own could be developed further. Some change is needed, and one suggestion is using testing to ensure that the remedial training has had the desired effect.
Organisations: Department of Mathematics, Research group: MAT Intelligent Information Systems Laboratory, Research group: MAT Positioning
Contributors: Myllykoski, T., Pohjolainen, S., Ali-Löytty, S.
Title of host publication: SEFI 2016 Annual Conference Proceedings : Engineering Education on Top of the World: Industry University Cooperation
Publisher: European Society for Engineering Education SEFI
Keywords: math-bridge, mathematics teaching, e-learning
http://www.sefi.be/conference-2016/papers/Mathematics_and_Engineering_Education/myllykoski-students-use-of-learning-tools-and-tool-types-in-solving-self-study-assignments-93_a.pdf
Developing Learning and Teaching in Engineering Mathematics with and without Technology
University teachers of mathematics have begun to observe that nowadays new students when beginning their studies do not have as good a mathematical proficiency as before. The phenomenon has been noticed in all western countries during recent decades [1, 2]. What shall we do? We think that there are at least two available courses of action for improved learning results in university mathematics: 1) to identify as soon as possible the students who have an insufficient knowledge base in mathematics, and to begin remedial instruction for them, and 2) to develop mathematics learning environments both with and without technology.
The aim of this paper is to describe how Tampere University of Technology (TUT) has developed learning environments in mathematics during the last decade. We focus in the paper on two cases: 1) a multisemiotic approach to mathematical concepts and procedures, and 2) computer aided assessment and learning systems.
The first case consists of developing studies in mathematical exercises in which new kinds of problem-solving have been constructed. In the second case new students have participated in an ICT –based basic skills test at the beginning of their mathematics studies, to enable them to practice mathematical procedures in solving processes [3]. Electronic and web-based tools make it possible for students to learn independently at any time, and for teachers, offer an effective way to evaluate students' proficiency.
Organisations: Mathematics, Research group: MAT Positioning, Research group: Positioning, Research group: MAT Intelligent Information Systems Laboratory
Contributors: Joutsenlahti, J., Ali-Löytty, S., Pohjolainen, S.
http://www.sefi.be/conference-2016/papers/Mathematics_and_Engineering_Education/joutsenlahti-developing-learning-and-teaching-in-engineering-mathematics-with-and-without-technology-153_a.pdf
Application and theory of Petri nets and other models of concurrency: Special issue of selected papers from Petri Nets 2015
MoE publication type: B1 Article in a scientific magazine
Contributors: Devillers, R., Valmari, A., Penczek, W.
Pages: v-vi
Peer-reviewed: No
Journal: Fundamenta Informaticae
ASJC Scopus subject areas: Theoretical Computer Science, Algebra and Number Theory, Information Systems, Computational Theory and Mathematics
10.3233/FI-2016-1373
Interval decomposition lattices are balanced
Intervals in binary or n-ary relations or other discrete structures generalize the concept of an interval in a linearly ordered set. They are defined abstractly as closed sets of a closure system on a set, satisfying certain axioms. Join-irreducible partitions into intervals are characterized in the lattice of all interval decompositions. This result is used to show that the lattice of interval decompositions is balanced, and the case when this lattice is distributive is also characterised.
Organisations: Department of Mathematics, University of Miskolc
Contributors: Foldes, S., Radeleczki, S.
Journal: DEMONSTRATIO MATHEMATICA
Keywords: Balanced lattice, Closure system, Interval decomposition, Join-irreducible element, Semimodular lattice, Strong set
dema-2016-0023.xml
10.1515/dema-2016-0023
MathCheck: a tool for checking math solutions in detail
Contributors: Valmari, A., Kaarakka, T.
Optimal energy decay in a one-dimensional coupled wave–heat system
We study a simple one-dimensional coupled wave–heat system and obtain a sharp estimate for the rate of energy decay of classical solutions. Our approach is based on the asymptotic theory of C0-semigroups and in particular on a result due to Borichev and Tomilov (Math Ann 347:455–478, 2010), which reduces the problem of estimating the rate of energy decay to finding a growth bound for the resolvent of the semigroup generator. This technique not only leads to an optimal result, it is also simpler than the methods used by other authors in similar situations.
Journal: Journal of Evolution Equations
ASJC Scopus subject areas: Mathematics (miscellaneous)
Keywords: C-semigroups, Coupled, Energy, Heat equation, Rates of decay, Resolvent estimates, Wave equation
Safety Property-Driven Stubborn Sets
A new reduced state space construction method is presented where in every constructed state, the set of transitions that are fired is chosen based on the safety property that is being verified. Typical earlier methods only take the property into account in one state of each cycle or in one state of each terminal strong component of the reduced state space. They may fire totally irrelevant transitions in the other states. Where the property is taken into account, typically many or all enabled transitions are fired. This has spoiled attempts to be property-driven in every state. The present study exploits an idea that was published in 2016 with which this can be avoided. Furthermore, most earlier methods classify the transitions to visible and invisible. The new method uses a novel improved concept. An experiment is presented where the new concept provides significant improvement to the reduction results.
Contributors: Hansen, H., Valmari, A.
Title of host publication: Reachability Problems : 10th International Workshop, RP 2016, Aalborg, Denmark, September 19-21, 2016, Proceedings
Editors: Larsen, K., Potapov, I., Srba, J.
Organisations: Department of Mathematics, Research group: MAT Intelligent Information Systems Laboratory, Research group: MAT Mathematical and semantic modelling, Lappeenranta Univ Technol, Lappeenranta University of Technology, Dept Math & Phys, Univ Eastern Finland, University of Eastern Finland, Dept Appl Phys, University of Oulu, Tampere University, University of Vaasa, Huawei Technologies Oy, Tampere Univ Technol, Tampere University of Technology, University of Jyväskylä, University of Eastern Finland
Contributors: Heiliö, M., Lähivaara, T., Laitinen, E., Mantere, T., Merikoski, J., Pohjolainen, S., Raivio, K., Silvennoinen, R., Suutala, A., Tarvainen, T., Tiihonen, T., Tuomela, J., Turunen, E., Vauhkonen, M.
Experienced risks in social media use – longitudinal study among university students
Several recent studies indicate that there is a need for increased use of ICT and social media in the Finnish education [1], [2]. This research was conducted in order to explore the attitude towards social media use among university students. The motivation for seeking answer to the research question: "What risks students experience in social media use?" derived from the need to discover learning barriers in social media based learning environments. In particular, there is a need for novel interaction means in order to co-create and learn informally [3] also beyond the traditional classroom. The assumptions, beliefs and attitudes towards social media are studied from the perspective of perceived risks of the students. The study was conducted among graduate students attending "Communities and Social Media in Knowledge Management" course between the years 2012-2016. A web-based survey was executed annually, with a total of 113 respondents. Based on the results we were able to categorize the perceived risks and derive implications on how to lower learning barriers of students in social media based learning environments.
Organisations: Department of Information Management and Logistics, Research group: Novi, Pori Department, Research group: Business Ecosystems, Networks and Innovations, Managing digital industrial transformation (mDIT)
Contributors: Jussila, J., Aramo-Immonen, H.
Title of host publication: EDULEARN16 Proceedings : 8th annual International Conference on Education and New Learning Technologies, Barcelona (Spain). 4th - 6th of July, 2016.
Publisher: IATED Academy
Editors: Gómez Chova, L., López Martínez, A., Candel Torres, I.
ISBN (Electronic): 978-84-608-8860-4
Name: EDULEARN Proceedings
Keywords: social media, social media risks, e-communication, knowledge management
10.21125/edulearn.2016.1257
https://iated.org/edulearn/
Asymptotic Behaviour of Platoon Systems
In this paper we study the asymptotic behaviour of various platoon-type systems using the general theory developed by the authors in a recent article. The aim is to steer an infinite number of vehicles towards a target configuration in which each vehicle has a prescribed separation from its neighbour and all vehicles are moving at a given velocity. More specifically, we study systems in which state feedback is possible, systems in which observer-based dynamic output feedback is required, and also a situation in which the control objective is modified to allow the target separations to depend on the vehicles' velocities. We show that in the first and third cases the objective can be achieved, but that in the second case the system is unstable in the sense that the associated semigroup is not uniformly bounded. We also present some quantified results concerning the rate of convergence of the platoon to its limit state when the limit exists.
Organisations: Department of Mathematics, Research group: MAT Mathematical and semantic modelling, University of Oxford
Title of host publication: Proceedings of the 22nd International Symposium on Mathematical Theory of Networks and Systems
Publisher: University of Minnesota
ASJC Scopus subject areas: Analysis, Control and Optimization
Keywords: Vehicle platoon, ordinary differential equations, asymptotic behaviour, state feedback, rates of convergence
Paunonen & Seifert - MTNS 2016 preprint
Acoustic Modelling
Let us examine the behaviour of sound in a gas or in a liquid medium. From a physical point of view, the sound we hear is created by the pressure change in the medium surrounding us that is sensed by our ears. The equations describing the behaviour of a liquid or a gas are based on well-known equations of fluid mechanics. Therefore in acoustics, they are often referred to as fluids. In the following sections we present a simple wave equation, which is the simplest of (linear) equations used to model acoustical phenomena. Even though the wave equation is quite a simplified model, it has proven to be extremely useful for describing the behaviour of sound in the most common fluid we face every day, namely air.
Organisations: Department of Mathematics, Research group: MAT Intelligent Information Systems Laboratory, Research group: MAT Mathematical and semantic modelling, Tampere Univ Technol, Tampere University of Technology
Contributors: Pohjolainen, S., Suutala, A.
Title of host publication: Mathematical Modelling
Editor: Pohjolainen, S.
ASJC Scopus subject areas: Applied Mathematics, Modelling and Simulation, Acoustics and Ultrasonics
INT=mat,"Suutala, Antti"
The Structure of Robust Controllers for Distributed Parameter Systems
Using a very general formulation of the Internal Model Principle for infinite-dimensional systems it is shown that a robust controller tracking/rejecting signals generated by an infinite-dimensional exosystem can be decomposed into a servocompensator and a stabilizing controller. The servocompensator contains an internal model of the exosystem generating the reference and disturbance signals and the stabilizing controller stabilizes the infinite-dimensional closed-loop system. As such the decomposition gives a parametrization of robustly regulating controllers in the time domain. Various ways of stabilizing the closed-loop system are presented.
Organisations: Department of Mathematics, Research group: MAT Mathematical and semantic modelling, Research group: MAT Intelligent Information Systems Laboratory
Contributors: Hämäläinen, T., Pohjolainen, S.
Title of host publication: Proceedings of the European Control Conference, June 29 - July 1, 2016, Aalborg Denmark
Place of publication: Aalborg, Denmark
Keywords: Internal Model Principle, Robust Regulation, Infinite-Dimensional Systems
ECC16
10.1109/ECC.2016.7810619
Partitioned Update Kalman Filter
In this paper we present a new Kalman filter extension for state update called Partitioned Update Kalman Filter (PUKF). PUKF updates state using multidimensional measurements in parts. PUKF evaluates the nonlinearity of the measurement function within Gaussian prior by comparing the innovation covariance caused by the second order linearization to the Gaussian measurement noise. A linear transformation is applied to measurements to minimize the nonlinearity of a part of the measurement. The measurement update is applied then using only the part of the measurement that has low nonlinearity and the process is then repeated for the updated state using the remaining part of the transformed measurement until the whole measurement has been used. PUKF does the linearizations numerically and no analytical differentiation is required. Results show that when measurement geometry allows effective partitioning, the proposed algorithm improves estimation accuracy and produces accurate covariance estimates.
Organisations: Department of Automation Science and Engineering, Research area: Dynamic Systems, Department of Mathematics, Research group: MAT Positioning, Research group: Positioning
Contributors: Raitoharju, M., Piché, R., Ala-Luhtala, J., Ali-Löytty, S.
Journal: Journal of Advances in Information Fusion
Keywords: math.OC, math.PR
http://confcats_isif.s3.amazonaws.com/web-files/journals/entries/Partitioned%20Update%20Kalman%20Filter.pdf
ORG=ase,0.75 ORG=mat,0.25
Source: ArXiv
Source ID: http://arxiv.org/abs/1503.02857v1
Two Consistent Many-Valued Logics for Paraconsistent Phenomena
Organisations: Department of Mathematics, Research group: MAT Computer Science and Applied Logics, Research Community on Data-to-Decision (D2D)
Contributors: Turunen, E., Rodrigues, J. T.
Title of host publication: New Directions in Paraconsistent Logic : 5th WCP, Kolkata, India, February 2014
Place of publication: New Delhi Heidelberg New York Dordrecht London
Editors: Beziau, J., Chakraborty, M., Dutta, S.
ISBN (Print): 978-81-322-2717-5
Name: Springer Proceedings in Mathematics & Statistics
10.1007/978-81-322-2719-9
Constructing Minimal Coverability Sets
This publication addresses two bottlenecks in the construction of minimal coverability sets of Petri nets: the detection of situations where the marking of a place can be converted to ω, and the manipulation of the set A of maximal ω-markings that have been found so far. For the former, a technique is presented that consumes very little time in addition to what maintaining A consumes. It is based on Tarjan's algorithm for detecting maximal strongly connected components of a directed graph. For the latter, a data structure is introduced that resembles BDDs and Covering Sharing Trees, but has additional heuristics designed for the present use. Results from a few experiments are shown. They demonstrate significant savings in running time and varying savings in memory consumption compared to an earlier state-of-the-art technique.
Contributors: Piipponen, A., Valmari, A.
Issue number: 3-4
ASJC Scopus subject areas: Information Systems, Computational Theory and Mathematics, Theoretical Computer Science, Algebra and Number Theory
Keywords: antichain data structure, coverability set, Tarjan's algorithm
An edge-colored graph G is said to be rainbow connected if between each pair of vertices there exists a path which uses each color at most once. The rainbow connection number, denoted by rc(G), is the minimum number of colors needed to make G rainbow connected. Along with its variants, which consider vertex colorings and/or so-called strong colorings, the rainbow connection number has been studied from both the algorithmic and graph-theoretic points of view.
In this paper we present a range of new results on the computational complexity of computing the four major variants of the rainbow connection number. In particular, we prove that the Strong Rainbow Vertex Coloring problem is NP-complete even on graphs of diameter 3. We show that when the number of colors is fixed, then all of the considered problems can be solved in linear time on graphs of bounded treewidth. Moreover, we provide a linear-time algorithm which decides whether it is possible to obtain a rainbow coloring by saving a fixed number of colors from a trivial upper bound. Finally, we give a linear-time algorithm for computing the exact rainbow connection numbers for three variants of the problem on graphs of bounded vertex cover number.
Title of host publication: Combinatorial Algorithms : 26th International Workshop, IWOCA 2015, Verona, Italy, October 5-7, 2015, Revised Selected Papers
Editors: Lipták, Z., Smyth, W. F.
http://iwoca2015.di.univr.it/ (IWOCA 2015 website)
Projekteja yläkoulun matematiikkaan
Contributors: Eriksson, S., Salminen, J., Viro, E.
Journal: LUMA-sanomat
http://www.luma.fi/artikkelit/4242/projekteja-ylakoulun-matematiikkaan
On the Underlying Mathematical and Quantum Structure of Quantum Cryptography
Quantum cryptography is a novel approach to provide secure communication, based on the laws of physics. It offers perfect security for the communication between two authorized parties, while assuming very high computational capacity for the eavesdropper, who may be attempting to intrude into this communication. It provides a very high rate of intrusion detection as against the classical systems. Classical cryptography is built on a fundamental assumption that it is difficult to invert some of mathematical functions, in a limited time, with the use of efficient computing resources. While, quantum cryptography is based on formidable laws of nature, making it less prone to attack. With the advent of quantum computing, boundaries between various subjects like quantum physics, computer science and mathematics are getting reduced. In the early seventies, Steven Wiesner made pioneering efforts in the field Quantum Cryptography. In its present form, Quantum Cryptography depends on two essential principles of Quantum Mechanics. One is that no information is available without causing disturbance in the system and other is Principle of No-Cloning. In this paper we present some of fundamental aspects of Quantum Cryptography and the underlying structures that makes it a credible option for providing perfect security of information.
Contributors: Gotkhindikar, A. D.
Journal: International Journal of Engineering and Computer Science
10.18535/ijecs/v5i2.7
Source ID: urn:7250acb0df8a579e30de45499bead3c2
Opetusteknologiaa hyödyntävä oppimisympäristö MATLABin alkeiden opiskeluun
Organisations: Department of Mathematics, Research group: MAT Positioning, Research group: MAT Intelligent Information Systems Laboratory, Research group: MAT Mathematical and semantic modelling
Contributors: Ali-Löytty, S., Parviainen, P., Pohjolainen, S.
http://www.math.utu.fi/materiaali/mathdays16/proceedings.pdf
INT=mat,"Parviainen, Panu"
Shape reconstruction from generalized projections
In this thesis we develop methods for recovering the three-dimensional shape of an object from generalized projections. We particularly focus on the problems encountered when data are presented as discrete image fields. We demonstrate the usefulness of the Fourier transform in transferring the image data and shape model projections to a domain more suitable for gradient based optimization. To substantiate the general applicability of our methods to observational astronomy, we reconstruct shape models for several asteroids observed with adaptive optics, thermal infrared interferometry, or range-Doppler radar. The reconstructions are carried out with the ADAM software package that we have designed for general use.
Contributors: Viikinkoski, M.
viikinkoski_1358
Awarding institution:Tampere University of Technology
viikinkoski_1358 ok 8.1.2016 KK
Studying the various properties of MIN and MAX matrices - elementary vs. more advanced methods
Let T = {z1, z2, . . . , zn} be a finite multiset of real numbers, where z1 ≤ z2 ≤ · · · ≤ zn. The purpose of this article is to study the different properties of MIN and MAX matrices of the set T with min(zi , zj) and max(zi , zj) as their ij entries, respectively.We are going to do this by interpreting these matrices as so-called meet and join matrices and by applying some known results for meet and join matrices. Once the theorems are found with the aid of advanced methods, we also consider whether it would be possible to prove these same results by using elementary matrix methods only. In many cases the answer is positive.
Organisations: Department of Mathematics, University of Tampere, School of Information Sciences
Contributors: Mattila, M., Haukkanen, P.
Scopus rating (2016): SJR 0.221 SNIP 0.468
Keywords: MIN matrix, MAX matrix, meet matrix, join matrix
A Simple Controller with a Reduced Order Internal Model in the Frequency Domain
We use frequency domain methods to study robust output regulation of a stable plant in a situation where the controller is only required to be robust with respect to a predefined class of perturbations. We present a characterization for the solvability of the control problem and design a minimal order controller that achieves robustness with respect to a given class of uncertainties. The construction of the controller is illustrated with an example.
Organisations: Department of Mathematics, Research group: MAT Mathematical and semantic modelling
Contributors: Laakkonen, A., Paunonen, L.
Title of host publication: Proceedings of European Control Conference 2016
Asteroid models from photometry and complementary data sources
I discuss inversion methods for asteroid shape and spin reconstruction with photometry (lightcurves) and complementary data sources such as adaptive optics or other images, occultation timings, interferometry, and range-Doppler radar data. These are essentially different sampling modes (generalized projections) of plane-of-sky images. An important concept in this approach is the optimal weighting of the various data modes. The maximum compatibility estimate, a multimodal generalization of the maximum likelihood estimate, can be used for this purpose. I discuss the fundamental properties of lightcurve inversion by examining the two-dimensional case that, though not usable in our three-dimensional world, is simple to analyze, and it shares essentially the same uniqueness and stability properties as the 3-D case. After this, I review the main aspects of 3-D shape representations, lightcurve inversion, and the inclusion of complementary data.
Contributors: Kaasalainen, M.
Title of host publication: Graduate School In Astronomy : Xvi Special Courses At The National Observatory Of Rio De Janeiro: Xvi Cce
Publisher: AMER INST PHYSICS
Editors: Chavero, C., Cunha, K., Carvano, J., Fernandes, M., Dupke, R.
Keywords: Asteroids, Inverse problems, Photometry, Adaptive optics, Interferometry, LIGHTCURVE INVERSION, OPTIMIZATION METHODS, SHAPE, RECONSTRUCTION, POLYHEDRON
Controller Design for Robust Output Regulation of Regular Linear Systems
We present three dynamic error feedback controllers for robust output regulation of regular linear systems. These controllers are (i) a minimal order robust controller for exponentially stable systems (ii) an observer-based robust controller and (iii) a new internal model based robust controller structure. In addition, we present two controllers that are by construction robust with respect to predefined classes of perturbations. The results are illustrated with an example where we study robust output tracking of a sinusoidal reference signal for a two-dimensional heat equation with boundary control and observation.
Keywords: Linear systems, Robustness, Robust output regulation, controller design, feedback, regular linear systems
Source ID: urn:da65ce94eaad6e902a97ef0e5d16351d
Data-based stochastic modeling of tree growth and structure formation
We introduce a general procedure to match a stochastic functional-structural tree model (here LIGNUM augmented with stochastic rules) with real tree structures depicted by quantitative structure models (QSMs) based on terrestrial laser scanning. The matching is done by iteratively finding the maximum correspondence between the measured tree structure and the stochastic choices of the algorithm. First, we analyze the match to synthetic data (generated by the model itself), where the target values of the parameters to be estimated are known in advance, and show that the algorithm converges properly. We then carry out the procedure on real data obtaining a realistic model. We thus conclude that the proposed stochastic structure model (SSM) approach is a viable solution for formulating realistic plant models based on data and accounting for the stochastic influences.
Early online date: 3 Nov 2015
Journal: Silva Fennica
ASJC Scopus subject areas: Ecological Modelling, Forestry
Keywords: Data fitting, Form diversity, Morphological plasticity, Plant model, Quantitative structure models, Stochastic functional-structural, Terrestrial lidar
10.14214/sf.1413
Further hardness results on rainbow and strong rainbow connectivity
A path in an edge-colored graph is rainbow if no two edges of it are colored the same. The graph is said to be rainbow connected if there is a rainbow path between every pair of vertices. If there is a rainbow shortest path between every pair of vertices, the graph is strong rainbow connected. We consider the complexity of the problem of deciding if a given edge-colored graph is rainbow or strong rainbow connected. These problems are called Rainbow connectivity and Strong rainbow connectivity, respectively. We prove both problems remain NP-complete on interval outerplanar graphs and k-regular graphs for k≥3. Previously, no graph class was known where the complexity of the two problems would differ. We show that for block graphs, which form a subclass of chordal graphs, Rainbow connectivity is NP-complete while Strong rainbow connectivity is in P. We conclude by considering some tractable special cases, and show for instance that both problems are in XP when parameterized by tree-depth.
Scopus rating (2016): CiteScore 1 SJR 0.863 SNIP 1.23
ASJC Scopus subject areas: Applied Mathematics, Discrete Mathematics and Combinatorics
Keywords: Computational complexity, Rainbow connectivity
Fuzzy Logic of Quasi-Truth: An Algebraic Treatment
MoE publication type: C1 Separate scientific books
Contributors: Di Nola, A., Grigolia, R., Turunen, E.
Name: Studies in Fuzziness and Soft Computing
Keywords: MV-algebra
Research output: Book/Report › Book › Scientific › peer-review
Integer Models
The examples on "network design" (p. 15), "river and flood models" (p. 20) and "urban water systems" (p. 21) lead us to consider networks. A useful way to describe a network is to define for each pair of nodes a function whose value is 1 if there is a direct connection between these nodes in the network, and 0 otherwise. More generally, x = 1 can be used to indicate that a certain event occurs and x = 0 that it does not. Indeed, binary (i.e., 0-1-valued) variables appear in many models, and so do also other integer-valued variables. In this chapter we shall take a look at such models.
Contributors: Silvennoinen, R., Merikoski, J.
Source ID: urn:189c06c4e9adf0f563c32e7b3d719e29
Mobile Context-Aware Systems: Technologies, Resources and Applications
Mobile applications often adapt their behavior according to user context, however, they are often limited to consider few sources of contextual information, such as user position or language. This article reviews existing work in context-aware systems (CAS), e.g., how to model context, and discusses further development of CAS and its potential applications by looking at available information, methods and technologies. Social Media seems to be an interesting source of personal information when appropriately exploited. In addition, there are many types of general information, ranging from weather and public transport to information of books and museums. These information sources can be combined in previously unexplored ways, enabling the development of smarter mobile services in different domains. Users are, however, reluctant to provide their personal information to applications; therefore, there is a crave for new regulations and systems that allow applications to use such contextual data without compromising the user privacy.
Organisations: Department of Mathematics, Research group: MAT Intelligent Information Systems Laboratory
Contributors: Rivero-Rodriguez, A., Pileggi, P., Nykänen, O. A.
Journal: International Journal of Interactive Mobile Technologies
Keywords: Context-aware Services , Context Awareness, Context Management, Mobile Computing
Mobile Context-Aware Systems
10.3991/ijim.v10i2.5367
Source ID: urn:416cbddcc24982dbb51c9c6e1123e281
Moodlen työpaja: Vertaisarviointi osana opetusta yliopistomatematiikan ensimmäisellä peruskurssilla
Organisations: Department of Mathematics, Research group: MAT Positioning
Contributors: Mäkelä, A., Ali-Löytty, S., Joutsenlahti, J., Kauhanen, J.
Title of host publication: Matematiikan ja luonnontieteiden opetuksen tutkimusseuran tutkimuspäivät 2015
Publisher: Matematiikan ja luonnontiteiden opetuksen tutkimusseura r.y.
Editors: Silfvenberg, H., Hästö, P.
Keywords: Moodle, työpaja, workshop
http://www.protsv.fi/mlseura/julkaisut/MALU2015_Final.pdf
INT=mat,"Joutsenlahti, Jorma"
On Detecting the Shape of an Unknown Object in an Electric Field
The problem discussed in this paper is detecting the shape of an unknown object in a 2-dimensional static electric field. For simplicity, the problem is defined in a partially rectangular domain, where on a part of the boundary the potential and/or its normal derivative are known. On the other part of the boundary the boundary curve is unknown, and this curve is to be determined. The unknown part of the boundary curve describes the shape of the unknown object.
The problem is defined in the complex plane by an analytic function w=f(z) = u(x,y)+iv(x,y) with the potential u as its real part. Then the inverse function is given as f^{-1}(w) = x(u,v)+iy(u,v), where the functions x and y are harmonic in a rectangle with an unknown boundary condition on one boundary. The alternating-field technique is used to solve the unknown boundary condition.
Contributors: Humaloja, J., Hämäläinen, T., Pohjolainen, S.
Editors: Russo, G., Capasso, V., Nicosia, G., Romano, V.
Publisher: Springer-Verlag
Keywords: free boundary problem, industrial mathematics
http://urn.fi/URN:NBN:fi:tty-201606014205. No embargo end date input
Embargo avoinna, koska ei vielä julkaistu (Due May 3, 2017)
HO / 2.5.2016
On finding rainbow and colorful paths
In the Colorful Path problem we are given a graph G=(V,E) and an arbitrary vertex coloring function c:V→[k]. The goal is to find a colorful path, i.e., a path on k vertices, that visits each color. This problem has been introduced in the classical work of Alon et al. (1995) [1], and the authors proposed a dynamic programming algorithm that runs in time 2knO(1) and uses O(2k) space. Since then the only progress obtained is reducing the space size to a polynomial at the cost of using randomization. In this work we show that a progress in time complexity is unlikely: if Colorful Path can be solved in time (2-ε)knO(1), then Set Cover admits a (2-ε')n(nm)O(1)-time algorithm. The same applies to other versions of the problem: when edges are colored instead of vertices, or we ask for a walk instead of a path, or when the requested path/walk has specified endpoints.We study also a second, very related problem. In Rainbow s t -Connectivity, we are given a k-edge-colored graph and two vertices s and t. The goal is to decide whether there is a rainbow path between s and t, that is, a path on which no color repeats. In its vertex variant (Rainbow Vertex s t -Connectivity) the input graph is k-vertex-colored, and a rainbow path is defined analogously. Uchizawa et al. (2011) [14] show that both variants can be solved in 2knO(1) time and exponential space. We show that the space size can be reduced to a polynomial, while keeping the same running time. In contrast to the polynomial space algorithm for Colorful Path, our algorithm for finding rainbow paths is deterministic.
Organisations: Department of Mathematics, University of Warsaw
Contributors: Kowalik, Ł., Lauri, J.
On k-Hypermonogenic Functions and Their Mean Value Properties
We study a hyperbolic version of holomorphic functions to higher dimensions. In this frame work, a generalization of holomorphic functions are called (Formula presented.)-