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GEOMETRICPRESENTATION,Computational Geometry and Object Modeling — Geometric
Voxel-Based Haptic Rendering Using Implicit Sphere Trees
Emanuele Ruffaldi1 Dan
Morris2 Federico
Barbagli3 Ken
Salisbury3 Massimo
Bergamasco1 1Scuola Superiore S. Anna 2Microsoft Research 3Stanford University
A BSTRACT
Haptic interaction in six degrees of freedom is critical to
numerous applications, but is still prohibitively complex for
realistic environments. This paper presents an approach to rendering six-degree-of-freedom contact among virtual objects
using a novel data structure referred to as an implicit sphere tree.
This data structure allows an extremely compact representation of volumetric objects and extremely rapid intersection testing among objects, which broadens the scope of virtual environments that can be rendered in six degrees of freedom at interactive rates. We introduce this data structure, along with appropriate techniques for collision detection and haptic rendering, and demonstrate its efficiency in representing and manipulating complex models.
K EYWORDS: haptics, collision detection, volumetric models
I NDEX T ERMS: H.5.2 [Information Interfaces and Presentation]: User Interfaces — Haptic I/O; I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling — Geometric algorithms, languages, and systems
1 I NTRODUCTION
As haptic applications in virtual prototyping, medical simulation, and entertainment demand increasing immersiveness and realism, the perceptual limitations of three-degree-of-freedom (3-DOF) haptic rendering become increasingly problematic. Six-degree-of-freedom (6-DOF) haptic rendering intrinsically provides increased realism for such applications (since real-world interactions typically use at least six degrees of freedom) and leverages the full capacity of haptic devices that can render force and torque simultaneously (e.g. [18],[5]). However, this increased realism comes at a cost: 6-DOF rendering requires significantly more complex collision detection among virtual objects and fundamentally prevents the frequently-used approach of representing a haptic tool as a single point or as a small cluster of points [42].
To cope with this increased computational cost, many approaches to 6-DOF haptic rendering leverage voxel-based models as a fundamental representation, in contrast to the surface-based (and generally polygon-based) models used to represent most objects in computer graphics and 3-DOF haptic rendering. Voxel-based rendering offers inherently more rapid collision tests among primitives. But again, this comes at a cost: in this case, voxel-based models are less accurate in representing object boundaries than surface models. However, this loss in accuracy can be mitigated to a nearly-arbitrary degree by maximizing the resolution of voxel-based models. Therefore, the goal of the present work, and previous work in 6-DOF haptic rendering, is to maximize the resolution of voxel-based objects that can be rendered interactively.
This goal – processing increasingly complex volumetric geometry – also supports the growth in complexity and resolution of application-specific data sources that are supplying increasingly complex models to virtual environments. For example, the resolution of medical imaging devices continues to improve, so voxel-based anatomical models used for haptic surgical simulation continue to increase in complexity. Similarly, as haptic feedback becomes increasingly relevant for virtual prototyping and CAD applications [16], designers will need to represent increasingly complex parts – made up of numerous sub-parts – if they are to make use of haptic simulation tools.
Thus the goal of maximizing the complexity of voxel-based models that can be manipulated interactively improves both the general realism of haptic environments and the suitability of haptic simulation for specific applications.
This paper therefore addresses the problem of 6-DOF manipulation of unconstrained rigid bodies represented as volumetric models. Our primary contributions are threefold:
1)We introduce the implicit sphere tree, a novel data
structure for representing volumetric models, and describe
an optimized approach for building this data structure.
2)We introduce collision-detection and force-rendering
schemes that are suitable for interactive use of the implicit
sphere tree.
3)We present benchmarking results that demonstrate the
computational efficiency of this data structure.
In Section 2, we survey previous work related to 6-DOF haptic rendering, volumetric representations, and dynamic simulation. In Section 3, we describe the implicit sphere tree and our approach to interactive rendering. In Section 4, we present results demonstrating the computational efficiency of our approach. In Section 5, we discuss the relevance of this work and discuss future extensions.
2 R ELATED W ORK
In this section, we survey previous work on volumetric representation of objects (Section 2.1) and six-degree-of-freedom haptic simulation (Section 2.2), and place our own work within the context of the existing literature.
2.1 Volumetric
As we discuss above, volumetric models present an advantage over surface models for rapid intersection testing in complex virtual environments. In addition, volumetric models present an inherent advantage for representing objects when the interior of an object has information associated directly with it, e.g. vector fields or medical image data.
Address correspondence to emanuele.ruffaldi@sssup.it .
2.1.1 Basic voxel representations
The most basic representation for a volume is the classic voxel array, in which each discrete spatial location has a one-bit label indicating the presence or absence of material. A slightly more detailed representation used in [25] includes a "Surface Descriptor" at each voxel, labeling each voxel as "empty", "full", "surface", or "proximity". A "surface voxel" is a full voxel that is near one or more empty voxels, and a "proximity voxel" is an empty voxel that is near a surface voxel. This additional representation, which can be encoded using only two bits per voxel, allows more sophisticated handling of the volume's surface for collision-detection.
Another frequently-used adaptation of the classic voxel array is the distance field, in which each voxel is labeled with the distance between that voxel and the nearest surface point. This allows rapid computation of local gradients, which can be used for optimizing collision detection and computing collision response forces [13].
2.1.2 Voxel
Independent of the data stored with each location in a voxel representation, the storage of voxel data can be classified roughly into approaches based on a uniform grid and approaches based on volume hierarchies.
The uniform grid stores every voxel in the volume of an object using a tri-dimensional matrix or a hash table. Matrices are suitable for small objects and allow for extremely rapid data access, good spatial locality, and extremely rapid point-volume intersection tests. Hash tables or related indirect-access structures allow for a much more compact representation of sparse voxel arrays, but are more complex to address and manipulate, and can result in decreased cache performance relative to dense arrays when nearby voxels are accessed sequentially.
Approaches based on volume hierarchies store volume information at multiple levels of detail for compactness and rapid intersection-testing. These approaches are generally adaptations of the classic octree, itself an adaptation of the classic n-ary tree, in which each node represents a cube in space and each child of a node, if present, represents additional detail within a subspace of that cube [41]. Although voxel-based representations typically suffer from inadequate detail around high-frequency surface features, octrees can be optimized with adaptive sampling [12] to provide additional information in such regions. Another variant of the octree is the generalized spatial tree, in which each cube is partitioned into a larger number of subspaces (typically 64, 256, etc.), which in some applications reduces access time by flattening the hierarchy [25].
The implicit sphere tree presented in this paper builds upon the Surface Descriptor and generalized octree presented in [25] and the octree-based collision detection tree presented in [39].
2.2 6-DOF Haptic Rendering
Previous approaches to six-degree-of-freedom (6-DOF) haptic rendering can be classified into two main categories – direct rendering and virtual coupling – depending on the way they relate the physical position of the haptic device with the virtual position of the haptic interface point.
2.2.1 Direct
Direct rendering approaches (e.g. [14],[22],[20],[30]) to 6-DOF haptic rendering do not de-couple the physical device and virtual probe positions: the virtual haptic interface point is a simple linear transformation of the physical haptic device position. This guarantees that a user's control of a virtual haptic probe is direct, intuitive, and without latency, but allows for a large penetration depth between the probe and objects in the virtual environment, potentially resulting in perceptual inaccuracy, reduced frame rate, and instability.
2.2.2 Virtual
In contrast, approaches to 6-DOF haptic rendering based on virtual coupling [6] use a dynamic simulation to compute the position of the virtual haptic probe based on the position of the physical haptic device. For example, a bi-directional spring is frequently used to simulate this coupling. This solution provides a much more stable response and maintains perceptual accuracy for graphic rendering, but it has the often-undesirable effect of smoothing the haptic feedback forces provided to the user.
There are several more sophisticated dynamic simulation methods used for this coupling; we can classify them loosely as penalty-based, constraint-based, and impulse-based methods. Penalty-based methods (e.g. [7],[14],[24],[25],[29],[32],[39]) identify two discrete simulation states: contact and non-contact. Such approaches respond to the contact state – in which the virtual probe is immersed in another object in the virtual environment – with a force that is proportional to the penetration depth between the object and the stiffness of the materials. These approaches are suitable for haptics because they are computationally efficient, but limit the perceived stiffness of haptic interactions. The approach described in [17] uses the volume of intersection – instead of the penetration depth – for computing penalty forces. In [32], penalty-based approaches were extended to a multi-rate computation scheme to maintain haptic fidelity even during variable-rate collision detection. Penalty-based approaches are also used for non-haptic dynamic simulation (e.g. [21],[24],[37]).
Constraint-based methods (e.g. [3],[35]) represent objects or other environmental phenomena as analytic constraints, and typically integrate forces as necessary to ensure that those constraints are not violated. Work in this area has focused on schemes for smooth and variable-time integration and on real-time translation of analytic constraints into computationally-efficient penalty-based rendering schemes at the level of the haptic controller (e.g. [3],[33],[34],[35],[42]). Again, constraint-based methods for dynamic simulation have been used extensively outside of haptics, particularly in computer graphics (e.g. [1],[2]). Finally, impulse-based methods (e.g. [4],[8]) respond to collisions between a haptic probe and other objects in the virtual environment with an impulsive force intended to both simulate the interaction between rigid objects and eliminate penetration among objects. This problem has been explicitly addressed by the use of braking forces ([36],[25]), by an open-loop or event-based response ([11],[23]), or by a hybrid approach [9] that generates force pulses at the initial contact but uses a penalty-based response for the resting contact.
In this work, an impulse-based method has been used for the resolution of contacts, as presented in Section 3.3.
2.3 Summary of Related Work
Figure 1 presents a subset of the broad hierarchy of techniques used for 6-DOF haptic rendering and volume modeling, particularly focusing on those approaches discussed in this section. This figure is intended to situate our work within this increasingly-complex research space and highlight the highest-level design choices that guide our methods.
3 M ETHODS
This section introduces the implicit sphere tree (Section 3.1), the central data structure in the present work, then describes appropriate collision-detection (Section 3.2) and force computation (Section 3.3) approaches for working with implicit sphere trees.
3.1 The Implicit Sphere Tree
In section 2.1.2, we discuss the octree, a hierarchical series of cubes traditionally used for compactly representing complex objects. While this data structure is efficient, intersection testing among cubes is computationally expensive, relative to spheres, when working with objects at arbitrary rotations. The rotational invariance of the sphere makes it a particularly desirable geometry for bounding-volume hierarchies. Consequently, hierarchical sphere trees [19] have been explored in previous work as an alternative to octrees. However, sphere trees are much more complex to construct and manipulate than octrees, and suffer from much less efficient bounding of voxel arrays than octrees.
The data structure presented here – the implicit sphere tree – combines the intersection-testing advantages of the sphere tree with the spatial efficiency of octrees by building a hierarchy of spheres directly from the nodes of an octree while traversing the tree for collision-detection, with minimal additional storage.
The use of the implicit sphere tree begins with the construction of a traditional octree representation for an object of interest; each
octree node stores – in addition to the traditional list of child-node pointers – the level L of the tree at which this node sits. A leaf node (typically a single voxel) is assigned a level L =0. Each node is assigned a level one greater than the level of its children, so – for example – the root of an octree containing 256 voxels per side has a level L =8. In practice, we need only store the level L of the root node of the octree .
We build a standard octree [27] (enhanced by these node-level labels) and compute – from the known dimensions of the octree – the radius of the bounding sphere around the root of the tree (bounding the entire object). We note that for a cube of side x , this bounding sphere has a radius of x √3/2, and we can thus compute the radius of the sphere that bounds the root of the octree as:
r 0 = s2L-1/√3
…where r 0 is the radius of the bounding sphere at the root of the tree, s is the edge length of an individual voxel, and L is the node level of the root octree node. In the case of the generalized N-tree, this radius is s 2N (L-1)/ √3, where N is 1 for the octree, 2 for the 64-tree and 3 for the 512-tree.
During the collision-detection process, as with traditional octree-based collision-detection, we will be descending the tree from the root to determine regions that merit further intersection testing (Section 3.2 will provide more detail on collision detection). As we descend the tree, choosing to descend to certain nodes in the octree, we compute the bounding spheres of each
Figure 1. Situating our work (orange) among the methods and representations used in the literature for 6DOF haptic rendering (left) and volumetric modeling (right). Work referenced elsewhere in this paper is cited here for context.
6DOF Haptic
Rigid Body Simulation
Force Feedback
Constraint-based
Penalty-based
Direct Rendering
Virtual Coupling
Contact Resolution
Collsion Propagation
Simultaneous Chronological
Volume Modeling
Polygonization
Uniform Octree
Point Sampling
Voxelization
Marching Cubes
Scan Line Binary Surface Type
[Gregory 2000][Colgate 1997][Colgate 1995][McNeely 1999]
[Ruspini 2000]
[Berkelman 1999]
[Guendelman 2003]
[Westermann 1999]
[McNeely 1999]
[Frisken 2000][McNeely 1999]
[Constantinescu 2004][Mirtich 1994][Gregory 2000][Kim 2003]
[Meagher 1982]
[Fuhrmann 2003]
child of a given octree node by simply scaling the radius of the parent node's bounding sphere by ? and offsetting the current node's bounding sphere center by s2L-2 along each axis, where s is the size of a voxel and L is the current octree level (which we know based on how many levels we've descended so far). We thus implicitly compute the bounding sphere for each child node based only on very limited global storage (the number of levels in the octree) and on our real-time information about this node's parent node.
We can further optimize the computation of our implicit sphere tree when the octree (or the generalized n-tree) is not full, by computing a bounding sphere at each node that takes into account the real distribution of the children of the octree node. This optimization has the objective of reducing the volume of each sphere and thus reducing the number of collision tests necessary to eliminate intersection candidates. We can do this without complex computation at each node, leveraging the small set of possible bounding configurations that can exist at each level of an octree. In other words, there are only so many possible configurations of non-empty child nodes within an octree node, and therefore there are only so many possible bounding spheres needed to represent all possible child-node configurations. By pre-computing this very limited set, and using a simple integer representation for each node in our octree, where each bit represents the presence or absence of a child node, we can compute a tight bounding sphere for an octree node by taking this integer representation and directly indexing into a table containing scale/offset information for all possible bounding spheres.
Figure 2 demonstrates this principle in two dimensions for the quadtree (the two-dimensional equivalent of the octree). In the quadtree case, we would use four bits to represent the set of child nodes within each quadtree node. The case where no child nodes are present does not require further computation, since this node will never be a candidate for object intersections, so we have only fifteen possible arrangements of present/absent child nodes. As illustrated in Figure 2, three of these cases yield a bounding circle that is equivalent to the circle bounding the complete square, and each of the other twelve cases yields one of three other possible (smaller) bounding circles. For these twelve reduced-bounding-circle cases, we can store a single, global table that contains the relative offset and scale of these bounding circles, which can be quickly looked up with a single integer-indexing operation.
When we move to the octree we have 255 combinations, among which 85 yield bounding spheres that are smaller than the largest possible bounding sphere. Looking up the appropriate, optimized bounding sphere for an octree node proceeds exactly as in the quadtree case, making use of a single, global lookup table containing a scale and three-dimensional offset (relative to node centers) for each possible bounding sphere.
3.2 Collision Detection for Implicit Sphere Trees Collision detection using the implicit sphere tree is similar to traditional collision detection using octrees; the sphere tree is used to greatly accelerate intersection testing by making all intersection tests rotationally-invariant.
When we wish to determine whether two objects are intersecting, we begin with the root node of each object's octree and, as described in Section 3.1, compute the two global bounding spheres in global coordinates, testing for intersection between those spheres using a simple distance/radius comparison. If the two root spheres intersect, we compute the bounding spheres at the next level of each octree, as described in Section 3.1. We note that computing the next level of bounding spheres is dependent on rotational state, since it involves offsetting each parent node's center along each axis; however, we can take advantage of the fact that within an object, these axes do not change from level to level within the tree, and we can therefore simply compute these primary axes once per iteration of our program's main simulation loop and scale them appropriately each time we descend the tree. Once we have computed these second-level bounding spheres for each root octree node, we test for intersections between the child-node spheres of one octree with the root-node sphere of the other, and vice versa. Again, all computations can be performed without respect to the rotational state of each object using the rotationally-invariant implicit sphere tree.
If intersections are detected, we continue this process, descending the tree as needed until either all possible intersections are eliminated or leaf nodes (voxels) from each tree are found to intersect. As with any bounding volume hierarchy, the descent of the collision tree can be interrupted at a certain level when the number of generated collisions is too large or an application-specific resolution limit is reached. Also, for applications that are interested specifically in intersections between surfaces and are able to assume a limited penetration depth among objects, it is possible to simplify collision detection by using only voxels labelled as "surface" voxels (using the Surface Descriptor approach presented in [25]), and building the octree (and thus the implicit sphere tree) such that it only contains nodes whose children ultimately contain surface voxels.
In order to maximize the parallelism of our approach in environments with multiple processors, a breadth-first recursion is used. This allows each level to be assigned to an independent processor. This approach also allows the descent of the collision tree to be interrupted at a certain level when the number of generated collisions is too large. Otaduy and Lin [31] present a perceptually-derived metric for early termination of a collision search that maximally preserves haptic fidelity.
3.3 Collision Response: Haptic Rendering with
Implicit Sphere Trees
This section describes our collision response algorithm, suitable
for use with the implicit sphere tree presented above, and the
overall structure of our 6-DOF haptic rendering algorithm. We follow the approach of [25] in assuming that the virtual
environment is represented as a voxel model (the "world voxel
model"). A finite set of samples points (the "point shell") is used to represent the surface of a probe object (being controlled by a haptic device); this point shell is treated as a voxel array for purposes of collision detection. As in [25], we assume that the
Figure 2. A two-dimensional quadtree is used to illustrate the finite set of bounding circles that exist for an octree node, and the dependence of those bounding circles on the empty/full state of child nodes. Dotted lines indicate the largest possible bounding circle; solid lines indicate optimized bounding circles. Dark child nodes are empty, light (blue) nodes are full.
world voxel model is static and the probe object is dynamic.
Although the present work uses the voxel representation presented by McNeely et al., [25], our work differs from [25] both in terms of the collision detection scheme and the force computation scheme. In particular, our work has been designed to support multibody dynamics.
3.3.1 Contact Resolution
This work uses the implicit sphere tree described above to detect collisions between points in the point shell (the dynamic object)
and voxels in the (static) world voxel model. Collisions detected in a single simulation time step are treated as having occurred simultaneously, as detecting the precise sequence of contact events would require a prohibitively-complex rewinding of the simulation whenever collisions occur.
When collisions are detected, an impulse is applied to the probe object to eliminate penetration between the probe object and the world voxel model. We adapt the methods of [28] and [15] to compute this impulse, and we describe this adaptation here.
The contact response system receives a list of intersecting voxel pairs; each pair is described by the two voxel centers, the normal
at each voxel, the relative velocity of the intersecting voxels, and the penetration depth between the two voxels. The contact response system selects the colliding voxel pair that has the largest penetration depth, ignoring any contact pairs whose velocities would result in a resolution of the intersection in the next integration step. In other words, we do not apply impulses to resolve contacts that would be resolved in the next time step by inertia alone. When an intersecting voxel pair is selected, the contact response system resolves the contact using an impulse that imposes a separating velocity condition in the next integration step [2].
The impulse computed above will be applied to the object in a subsequent integration step, but other intersecting voxel pairs may still require resolution. Instead of immediately applying the computed impulse to the body and re-computing the set of
intersecting voxel pairs, we continue to use the same set of intersecting voxel pairs but use the computed impulse to update the velocity of the body. This update allows us to discard most of the intersecting voxel pairs that are geometrically close to the one computed in the previous step, since those will now be resolved in the next integration step without an additional impulse, as described above. The system thus proceeds to the next intersecting voxel pair that would not now be separated in the subsequent integration step. This operation is repeated until there are no eligible intersecting voxel pairs, or until a maximum number of iterations is reached. The result of the collision response is the cumulative impulse, which is then applied to the probe object. The resulting impulsive forces are applied to the haptic device through virtual coupling [6]. At the cost of some damping, virtual coupling provides smoother, more stable haptic feedback than direct coupling, and allows force feedback computation to proceed at haptic rates even when collision detection and dynamic simulation are slowed by scene complexity. 4 B ENCHMARKING
The algorithms described above have been implemented in C++ using the CHAI3D [10] open source haptics library. In this section, we present the results a series of benchmark tests applied to this implementation. Tests have been conducted with a Phantom Desktop haptic device on a Intel Core2 Quad running at 2.4GHz with 4GB of memory under Windows XP.
Our first benchmark assesses the impact of voxelization resolution on collision detection performance. For this evaluation, a simulation was repeated several times, identical in each case other than the resolution of the world voxel model. In this simulation, a model is moved along a trajectory toward another object; collision response forces are disabled. Figure 3 presents an analysis of this simulation. We highlight in particular that for a relatively high number of collisions (around 1000) the algorithm requires less than 1ms of computation time, allowing it to run within a typical haptic simulation timestep. We also note that the more complex simulation timesteps occurring toward the end of
Figure 3. The relationship between collision detection performance and the resolution of a volumetric model (collision response disabled). Graphs show the distance between the centers of the two voxel models being tested (upper-left), the number of contacts detected between these objects (upper-right), the computation time required for each simulation time step (lower-left), and the number of intersection tests required at each simulation time step (lower-right).
Figure 4. The relationship between collision detection performance and the resolution of a volumetric model (collision response enabled). Graphs show the distance between the centers of the two voxel models being tested (upper-left), the number of contacts detected between these objects (upper-right), the computation time required for each simulation time step (lower-left), and the number of intersection tests required at each simulation time step (lower-right).
this simulation, which require more computation time, are not representative of typical interactive simulation timesteps, as collision response was disabled for this evaluation. Figure 4 summarizes the results of the same analysis performed with collision response enabled.
It is interesting to understand the effect of the optimizations discussed above, in particular the use of the one-child optimization for skipping intersection tests and the side optimization for adjusting the position. To assess the utility of
these optimizations, we again simulate an approach between two voxel objects, in this case with a fixed size. The results of this analysis are illustrated in Figure 5. We highlight that the one-child optimization provides a significant performance benefit.
The overall performance of the algorithms presented in this paper has been tested by generating random trajectories of collision between two objects. The large 6DOF search space has been randomly sampled using a sphere method [38]. One of the two models is fixed, and in each simulation the other object is moved along the randomly-generated trajectory. Each trajectory is a translation from an initial position randomly generated in spherical coordinates to a final position that has the same angular coordinates of the starting point but a radius that is known to result in contact between the simulated objects. The translating object is moved with constant velocity according to the method of [38]. The result of this evaluation is summarized in Figure 6. 5 C ONCLUSIONS
The use of volumetric models for collision detection allows more complex objects to be simulated interactively, but requires specific collision detection schemes. In this paper, we have introduced the implicit sphere tree , a data structure that allows rapid intersection testing among complex voxel-based objects. Future work will focus on more sophisticated parallelization of the proposed approaches, particularly on implementing the proposed approach in massively-parallel computing environments
such as GPUs. Additional work will apply the sensation-preserving optimizations presented in [31] to the implicit sphere tree.
A CKNOWLEDGMENTS
This work was supported by NIH LM07295, BioX 2DMA178, and by the European Commission within the Enactive Network of Excellence. R EFERENCES
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Systems. In Advances in Robot Kinematics (ARK) 1998. [35] D. Ruspini and O. Khatib. A framework for multi-contact multi-
body dynamic simulation and haptic display. Proc Intl Conf on Intelligent Robots and Systems,2000.
[36]S. Salcudean and T. Vlaar. On the Emulation of Stiff Walls and
Static Friction with a Magnetically Levitated Input/Output Device.
Proc ASME Haptics Symposium, 1997.
[37] D. Terzopoulos, J. Platt, A. Barr, and K. Fleischer. Elastically
Deformable Models. Proc SIGGRAPH 1987.
[38]S. Trenkel, R. Weller, and G. Zachmann. A Benchmarking Suite for
Static Collision Detection Algorithms. In Proc of the Intl Conf in Central Europe on Computer Graphics, Visualization and Computer Visiion (WSCG), January 2007.
[39] C. Tzafestas and P. Coiffet. Real-Time Collision Detection using
Spherical Octrees: Virtual Reality Application. 5th IEEE Intl Workshop on Robot and Human Communication, 1996.
[40]M. Wan and W.A. McNeely. Quasi-static approximation for 6
degrees-of-freedom haptic rendering. Proc IEEE Visualization 2003.
[41]R. Westermann, L. Kobbelt, and T. Ertl. Real-time exploration of
regular volume data by adaptive reconstruction of isosurfaces. The Visual Computer, 15(2):100–111, 1999.
[42] C. B. Zilles and J. K. Salisbury. A constraint-based god-object
method for haptic display. Proc Intl Conf on Intelligent Robots and Systems, 1995.
dgdifferentialgeometry
GeometryandObjectModeling—Geometric
GeometricGroupTheory下载
怎样做presentation
presentation什么意思
个人presentation
presentation的中文
评价presentation
geometric分布

redpajama_set_name: RedPajamaCommonCrawl


Dr. Ciara Smalls Glover is faculty in the Psychology Department and is affiliated with the Partnership for Urban Health Research at Georgia State University. Prior to her current appointment, Dr. Glover held an NIH funded postdoctoral training fellowship at the University of North Carolina at Chapel Hill. In addition, Dr. Glover is a NIMH-Career Opportunities in Research alum and alum of the American Psychological Association's Minority Fellowship Program. She began her career at GSU in 2009.
Dr. Glover's work highlights the importance of diversity in familial contexts in which socialization occurs. Dr. Glover's research includes an investigation of 1) patterns of racial socialization and racial identity as factors that directly promote positive development and reduce the impact of racial discrimination, and 2) the parenting context surrounding these factors as assessed with multiple analytic approaches. She is also interested in culturally distinctive family processes that buffer risk behaviors for African American and Latino American emerging adults. This work contributes to the development of interventions that build on the cultural strengths of youth and their families.
For a complete list of publications please see my Google Scholar profile.


text:
(786) 462-9500 optical@gouldvision.com Request an Appointment
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Frames & Eyeglasses
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What Are Convex Lenses?
Contact lenses are extremely useful optical aids that are made out of a substance that's known as Hydrogel. Hydrogel is firm enough that it will not be easily torn, yet malleable enough to remain on someone's eyeball as they go about their day. Your eye doctor in Miami can tell you more about how the Hydrogel substance allows oxygen to permeate it, thus providing the eyes with proper oxygen. People used to have problems with optical oxygen deprivation in the past from wearing contacts that were made out of actual glass. However, because glass contacts haven't been in use for more than almost 100 years, you will likely have to ask your eye doctor in Miami Beach to further educate you on the history of the convex lens.
Facts About the Convex Lens
Most people wear their contacts and never think twice about their actual prescription and what it means–the vast majority of people simply visit their Miami eye doctor, get a prescription, then wear either their contacts or glasses. However, those who are interested in learning more about their contacts may be pleased to find out these facts about convex contact lenses:
Convex lenses are only prescribed to patients who have been diagnosed with hyperopia, or farsightedness.
The center portion of a convex contact lens is much thicker than the outer portion. This is because the Hydrogel material acts like glass in the fact that it will allow light to penetrate it, but still has the capability of bending the rays.
The thickness of a farsighted person's particular contacts will depend upon measurements and examinations the eye doctors get from their patients.
The purpose of a convex contact lens is to bend the rays of light so they converge and land on the retina perfectly. A farsighted person's eyes normally cause light rays to land behind the retina, in which case a convex lens can correctly manipulate the light so that it ends up directly on the retina, thus solving a person's visual complications.
The Significance of Convex Contact Lenses
After learning this information about convex lenses, you are likely wondering how it will change your perception of contacts or cause you to act differently in the future. However, knowing the intricacies of your contact lenses should not change the way you handle them at all. Your Miami Beach eye doctor can tell you more interesting information about your eyes if you are a naturally farsighted person. Knowing more about your eyes allows you to communicate more effectively with your eye doctor in the future, should the need to modify your current prescription arise.
photo credit: Sky Noir window of the soul via photopin (license)
We offer a discount of 20% off designer eyewear & exam fees when you use this code: GOULD20 (Not to be combined with other discounts or insurance. Can't be used for Maui Jim or contact lens fitting exam).
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So funny! Here's one: "Mister President, I know you won't be able to listen to my jokes abou the Secret Service, so cover your ears, if that's humanly possible."
And the one about the GSA after-party: "...Don't be late, or you'll miss out on your complimentary white tiger club."
One more: "Mister President, remember when the country rallied around you in hopes of a better tomorrow? That was hilarious....You know, there's a term for guys like President Obama. Probably not two, but one term."
This version has the supposedly unscripted "live-mic" comments, too. Enjoy!
With apologies to Aunt Louise's readers for being late with this post, Madame L is finally getting around to writing about J.D. Salinger's second short novel about Seymour Glass. Seymour is the oldest brother of Buddy (the narrator), Franny, Walt, Waker, Boo Boo, and Zooey. These seven are the children of Les (an Australian Jew) and Bessie (an Irish American) Glass, vaudeville performers.
In "Raise High the Roof Beam, Carpenters," Buddy has gotten leave from the Army to attend Seymour's wedding. The problem with that---one of the problems with that---is that Seymour does not attend the wedding. Eventually Buddy finds out that Seymour just couldn't stand the thought of the fancy wedding, so he waited for his bride to come home from the big church and hundreds of guests, then took her away to be married quietly.
But, as we learn from the short story "A Perfect Day for Bananafish," which appears in J.D. Salinger's "Nine Stories," Seymour's marriage has not been any happier or more successful than his wedding.
In "Seymour An Introduction," we learn more about Seymour but even more about Buddy and the rest of the family. We find out even more about them in the "Nine Stories" and in "Franny and Zooey," all of which Madame L recommends highly.
At the dibache.com website you'll also find links to some other great short stories, articles about the art of fiction, and even a prose rendering of the great "Romeo and Juliet." If you have a chance to read any of those, and if you enjoy them, please let Madame L know.
We kept hearing a booming sound that we thought was a huge frog, but then we saw this bittern and realized it was making the noise, which the Wikipedia entry describes as "a call that resembles a congested pump."
You can hear the call for yourself here.
As we walked back to the car, we met a woman hiking in. She asked us if we were driving a black Honda, and when we said yes (and you know how you worry when someone asks you that!), she said, "There's a male Mallard under your car, right behind the front tire. I tried to move it, but it only moved a little."
We thanked her profusely, and when we got back to the car, we saw the Mallard and saw why it was staying there: it was eating something, apparently some tasty ants or grubs in the gravel.
I carefully shooed it away and across the parking lot toward the refuge, but it came back as we left.
It's just down the road from us, and it's beautiful.
Madame L wants to share with you this passage from "The Penderwicks on Gardam Street" to show you the skill and brilliance of Ms. Birdsall's writing. You know how hard it is to convey in a few words, a few READABLE words, the feelings and behaviors of young teens? Here's how the master does it. In this passage, Rosalind is going to the neighbor's house to pick up a white toy duck for the little boy she's babysitting, when the neighbor's cat, Asimov, streaks out the front door, which worries Rosalind.
"...but a moment later she'd forgotten about Asimov, because all of her attention was being used up on pretending she didn't notice the Geiger brothers drivng up Gardam Street and pulling into their driveway. She pretended so well not to notice that she would have sworn it never happened, but all the pretending fell apart when Tommy ran across the street and stood in front of her. And looked at her, even.
"She looked back at him.
"Then he even talked to her.
"'I want to tell you something. You don't have to listen, but I'm going to tell you anyway.' He had a footbal with him, which he was anxiously tossing from one hand to the other---back and forth, and back and forth, and back and forth, until Rosalind tok it away from him.
"[Finally Rosalind says,] 'I'm glad you broke up with her. I mean, not because I missed you or anything.'"
"'You didn't miss me.' It wasn't a question.
"'No, of course you didn't'...I'm sorry, but I'd better go. I have to get a duck.'"
Madame L's favorite line in this book was "Holy bananas, I hope not," a line spoken by Skye when it's suggested that she might eventually become friends with a person she thoroughly detests.
...which you simply must do.
"The Penderwicks on Gardam Street" is the sequel to "The Penderwicks: A Summer Tale of Four Sisters, Two Rabbits, and a Very Interesting Boy," which won the National Book Award, and the sequel should win another one. (Both, by Jeanne Birdsall, have already become bestsellers.) A third book, "The Penderwicks at Point Mouette," will be coming out next month, and Madame L can't wait to get her hands (and eyes) on it.
In the first book, four charming girls (Rosalind, 12, Skye, 11, Jane, 10, and Batty, 4), and their widowed professor dad, and the family dog (Hound), take a vacation in Massachusetts.
Do you ever wonder about all the books where the mom is missing? Dear Readers, wonder not: As a literary device, it has worked for ages, and it's necessary for stories about children who get into trouble and grow up (because if there were a mom around, none of that fun stuff could happen, now, could it?).
So, set that aside and let yourself enjoy this book, which is a Yearling book, for third- through sixth-graders (age 9 and up), and of course people who used to be third- through sixth-graders; it will remind you of the books you loved when you were a child and will be fun to pass on to your young friends.
The first Penderwicks book is available new from Amazon.com for $6.99 and used for prices starting at one cent (that's ten mills). The Gardam Street sequel is available at Amazon.com for $7.99 new and prices starting from 28 cents used; and the Point Mouette book can be advance-ordered from Amazon.com for $7.99 new.
The first two book are certainly available in your local library, too. Holy bananas, I hope you'll read them because you'll be glad you did!
A Planet? Or Another Plane?
I've had my fair share of weird air-travel experiences, but I'm glad I wasn't on this flight, where a sleepy pilot (just wakened from a long nap) put the plane into a dive because he thought the bright light ahead was another plane heading straight for him.
The Transportation Safety Board of Canada has already posted the full report of the incident.
"Fatigue reduces performance levels and increases the desire to obtain sleep. This effect is magnified during circadian lows, which are encountered by people who normally sleep at night and work during the day (diurnal). For example, North American pilots flying eastward at night across the Atlantic experience circadian lows that magnify performance decrements and increase desire to sleep.
"Night flights from North America to Europe have an inherent risk of fatigue for North American–based pilots. Most of these pilots fly a small number of night–time legs per month and revert to sleeping at night when not working. The circadian system of pilots who fly only a small number of night–time legs will not adapt to working at night and these pilots are likely to display performance decrements during the night–time legs in spite of any countermeasures.
"To counter fatigue, some pilots will try to nap before a night–time leg. While this can be helpful in some cases, it cannot prevent fatigue in all pilots. Moreover, it is not always possible to obtain an adequate amount of good quality sleep during the day and, coupled with a small number of night–time legs, performance decrements will persist."
I saw it on the Rachel Maddow, sub-hosted by Chris Hayes, on Monday (April 16), and found more details in this article at Physics Central Buzz Blog.
Dmitri Krioukov, a physicist at the University of California, San Diego, argued successfully in court that the speeding ticket he received was issued in error. Then he posted a paper online detailing his argument.
He said, "It is widely known that an observer measuring the speed of an object passing by, measures not its actual linear velocity [but] the angular one. For example ... watching a train approaching us from far away at a constant speed, we first perceive the train not moving at all, when it is really far, but when the train comes closer, it appears to us moving faster and faster, and when it actually passes us, its visual speed is maximized."
"Therefore my argument in the court went as follows: that what he saw would be easily confused by the angle of speed of this hypothetical object that failed to stop at the stop sign. And therefore, what he saw did not properly reflect reality, which was completely different."
Best I've seen yet. Oh, yeah, these people around here with their "Keep Portland Weird" and "Keep Vancouver Normal" bumper stickers think they're so cool and whatever.
so rich people won't have to."
"The day the child realizes that all adults are imperfect, he becomes an adolescent; the day he forgives them, he becomes an adult; the day he forgives himself, he becomes wise."
...and "Seymour: An Introduction," both by J.D. Salinger, are about the best short novellas or long short stories Madame L has ever read.
They go along with "A Perfect Day for Bananafish" and the rest of Salinger's "Nine Stories" and "Franny and Zooey."
You know that list Madame L has on her own blog site, the list of books she wishes she had time to re-read?
Well, every year or two Madame L takes the time to re-read these books, all of them, because they remind her of what really good writing is.
Yes, Salinger was apparently not a fun person to spend time with, not a happy camper, not a great dad, and all that. But Madame L forgives him on account of these books.
...not that I'm complaining about the rain!
Which Came First, The Dinosaur or the Egg?
Grandma: "Which came first, the dinosaur or the egg?"
"R" (with a shrug to indicate how obvious the answer is): "The egg. Some dinosaur had babies, and then they grew up to be different. So then when they laid their eggs, the babies that came out were different. And they came out in an egg. So the egg was first."
"Not any mutation in one individual can be considered as constituting a new species. A speciation event involves the separation of one population from its parent population, so that interbreeding ceases; this is the process whereby domesticated animals are genetically separated from their wild forebears. The whole separated group can then be recognized as a new species..."
Of course that's not the whole answer to the question. In fact, that same Wikipedia article shows that the answer depends on your view of the world, the view in which you frame the question.
"S": "Did you know that we're descended from monkeys?"
"S": "Our great-great-great-great-great-great grandparents were monkeys. It's called evolution."
"S": "Yeah, like a long time ago there was a monkey that married something more like a human and then it had a baby that was more like a human and then that married something that was more like a human and then it had a baby that was more like a human and then it married something that was really close to a human and then the baby was a human."
"F" (skeptically): "I don't know about that."
"S": "It's true! My dad told me."
"F": "Well... monkeys like bananas, and I like bananas..."
"S": "Yeah, and we're good on the monkey bars, and so are monkeys."
"F": "Monkeys aren't good on the monkey bars."
"S": "Yes they are! They're professionals on the monkey bars. They're *for* monkeys."
"F": "Oh yeah, I guess that's true." (Then, cheerfully:) "OK, I guess we do come from monkeys!"
How many people do you think have tried to cross the Empty Quarter (Rub' al Khali)?
Well, this website tells what it's like. I still want to do it, don't you?
"As the sun would set, we would set up tents in the late afternoon sand-storm, some of us wearing swim-goggles to protect our contacts from the stinging grit. Dinner was almost always mixed with flying sand; you could feel it grinding in your teeth: sand-burgers, grit-goulash, sand-pudding. Sleeping at night consisted of first securing the tent against scorpions and camel-spiders, which would leave tracks during the night showing that they were constantly searching for a way in. We then slept on top of our sleeping bags - the temperature normally didn't go below 40 degrees C (100 degrees F) during the night. We had to carefully brush the grit from our eyes before we dared to open them, and burning throats in the extremely dry conditions (down to 2% humidity) forced us to drink from our individually-issued water-jugs at least 5 times every night."
Imagine a book that has as many pages with just pictures as it has pages with words. You, Dear Reader, get to tell the story yourself, and it's fun!
It's a lot like a movie, in fact.Still, Madame L was pleasantly surprised at what a great movie Martin Scorcese made from the book. Yes, of course, he's a great director, but Madame L didn't expect him to be able to make a movie that would appeal to children and adults. He told an interviewer, though, that having a twelve-year-old daughter helped him see the world from a child's point of view.
The black-and-white book is transformed into a beautiful and carefully designed world of colors that match every scene and mood. Madame L didn't even get to see the 3-D version in the theater, just the regular DVD on a small screen at home, and she was blown away by it.
Madame L would love to show here a deleted page from the book so you can Oooh! and Aaah! with her over the intricate drawing, but in order to avoid copyright problems, she instead hopes you'll follow this link to see the picture yourself, Dear Reader.
The author, Brian Selznick, describes the research he did to make this drawing: "On one of my research trips to Paris I spent an entire day visiting old camera shops and photographing cameras from the 1930's and earlier, as well as the facades of the shops themselves. I researched original French camera posters and made sure that the counter and the shelves were accurate to the time period. I did all the drawings in the book at 1/4 scale, so they were very small and I often had to use a magnifying glass to help me see what I was drawing."
He hated to delete the drawing, so, he writes, "I'm glad to see it up on the Amazon website because otherwise no one would have ever seen all those tiny cameras I researched and drew so carefully!"
The book and the movie are about movies and photographs and mechanical men (automata), and about the early history of movies, but also about love and devotion; and about how lives can be transformed by all these. Enjoy!
Thanks to everyone for your comments and questions on my photos from eastern Australia.
Ellen, I'm glad you asked about the spiders because they're so interesting and beautiful in a kind of creepy-deadly way, and I'm always glad to learn more about the natural world.
I found out that the spider I posted some photos of is a golden orb-weaving spider. I don't know which species, but all these spiders (named by the way not for their color but for the golden color of their webs) are part of the Nephila genus (Nephilidae family, Aranaea order, Arachnida class, Arthropoda phylum, Animalia kingdom). Here's another photo taken by someone named Mark David (fourth photo down the page).
The one I photographed would have overlapped the palm of my hand (if I'd wanted to hold it, which, of course, NOT).
"Golden orb weaving spiders prey items include flies, beetles, locusts, wood moths and cicadas. Sometimes their strong webs manage to trap small birds or bats, and the spider will wrap them and feed upon them."
And indeed I found several photos and even some YouTube video of these spiders eating birds. I'm not adding any of those here: too grim for me, and I'm sorry I even glanced at them once.
"Predators of orb weavers include several bird species and wasps of the family Sphecidae. The wasps land on the web, lure the spider to the perimeter by imitating a struggling insect's vibrations, and then carry the spider away to be paralysed and stored as live food for their young."
"Orb weavers are reluctant to bite. Symptoms are usually negligible or mild local pain, numbness and swelling. Occasionally nausea and dizziness can occur after a bite....Seek medical attention if symptoms persist."


I am a little busy at the moment to find time to write much. Instead here are links to recent articles that I found very interesting.
The first is a good clear (long article) on who and what is Syriza, the party that recently emerged as a major force in Greek politics.
The second article is aptly called Ground zero exploring the scenario of a Greek exit from the Euro. That article is not hugely optimistic.
The last article is written by Arianna Huffington for the NY Times: A Greek tragedy. I guess the title says it all.
Interesting articles. I wonder how this troublesome development might affect tourism to Greece already this summer. I know a couple of Crete-afficianados here in Sweden who have decided not to go to the island this year.
I think Greece should go their own Hellenic's way. Stay in the Schengen zone, but outside the eurozone. And of course should increase political, economic and cultural relationships with Russia.


I never thought I would be talking about branding as a psychologist. I just assumed that branding was for people trying to sell products- like Nike :) . As therapists, we are not necessarily selling products, so why the need to discuss branding?
Cultivating and developing your brand helps clarify your message to future clients.
So how do I go about doing this? I feel like I have been hearing about branding more and more these days. I included a link to Joe Sanok's Practice of the Practice Podcast where he interviews a branding expert. Below are some of the key points Nicole Bonsol makes about discovering your brand. Check it out!
1. Your Message: What do you stand for? What's the heart-felt mission statement that rallies your tribe? Figuring this out is the foundation for creating great written content AND a stunning website.
2. Your Voice: What is it about your personality – your essence – that helps your message connect with the right people? How you consistently deliver your message is just as important as the message itself.
3. Your Visual Brand: Do your website and marketing materials make a visual impact that matches the power of your healing work? Having a website that instantly communicates your warmth and your spirit is a wonderful way to welcome potential clients into your practice.


text:
Q: iPhone app non-app store (safari) purchases I wanted to develop an iphone magazine application which will allow a user to purchase single issues or subscriptions through safari with a user id instead of the app store. What does my website require to be able to handle this?

A: It won't require anything special. Just a way to collect money from users (CreditCard, PayPal, Google Checkout support), a user database, a registration mechanism and you are done.   If I were you, I would reconsidering selling your content through AppStore with IN-APP purchases, because you will have immediate access to all technical stuff I just mentioned and a huge instant potential client you will have to build yourself otherwise.
Hope it helps.

redpajama_set_name: RedPajamaStackExchange


Nur Syahidah Alim is an artist with a bow but also with a brush.
Singapore's top para-archer is an amateur painter and one of the themes she enjoys painting is nature. Among her pieces is a sampan floating on a calm lake, depicting the tranquillity of water, and she brought a similar serenity to her performance at the Asean Para Games yesterday.
The 32-year-old defended her 2015 title successfully, defeating Malaysia's Nor Sa'adah Abdul Wahab 140-132 in the women's individual compound final at the KL Sports City.
Thailand's R. Katemongkon took bronze.
"I'm feeling great," Syahidah said. "It was quite exciting, the crowd was very loud cheering for the Malaysian team.
"When I was at the gold medal match, it was more of doing my best out there and just whack.
"Me versus myself, the conditions and the target."
When I was at the gold medal match, it was more of doing my best out there and just whack. Me versus myself, the conditions and the target.
NUR SYAHIDAH ALIM, on not worrying about her opponents.
The Spex Scholarship recipient - who won Singapore's first individual and team archery gold on home soil at the last Games - was set to become the Republic's first para-athlete to feature at last month's SEA Games and had been competing in able-bodied events since joining the SEA Games training squad earlier this year.
However, Syahidah, who has cerebral palsy, had her proposal - to shoot while seated on a stool with another person collecting her arrows - rejected by the SEA Games organisers.
"It's a disappointing outcome in the SEA Games, but I was really glad that I went through the experience, and it goes to show that the preparation can be applied to the Asean Para Games," she said.
Training was increased from 20 hours a week to 30 after the senior executive at Sport Singapore received the Spex Scholarship in April, which allowed her to train full time.
Syahidah's hard work has paid off for she broke her personal best in a single qualifying round at this edition of the APG. Her score of 345 points was 21 points better than 2015 and it left national coach Rachel Sng delighted.
Sng said: "Her scores during training are much higher. We used to go up and down, now she can hit a certain end score, and then another two or three points more.
"I can comfortably judge her arrow landings and adjust her sights to get her a higher score."
Syahidah faces another challenge today: Defending her mixed team compound crown alongside compatriot Robert Fuchs.
She said: "There's a little bit of pressure to try to defend the title. We've practised and trained very hard for (today's) event, and we'll do our best for (today)."


text:
AO Edited
Lukiškės Prison
A century-old prison in the heart of Vilnius is now a lively bar, dance club, and artist residency.
Lukiškės Prison Alma Pater (CC BY 3.0)
Lukiškės Prison Juliux (Juliux)
Inside the Lukiškės Prison Amelie Haupt (Atlas Obscura User)
Top Places in Vilnius
One Million Cent Pyramid
Stebuklas Miracle Tile
Museum of Occupations and Freedom Fights
Lukiškės Prison prison was built in 1904 and held prisoners for over a century, with the last prisoners transferred in 2019. Afterward, the prison was turned into a cultural hub that is open for guided tours, as well as a dance club, music venue, and residency space for over 250 artists.
In 1904, Vilnius belonged to the Russian Empire, and the Lukiškės Prison was built under Czar Nicholas II. A revision of the criminal code in 1874 had introduced the concept of serving time in prison. Before, prisoners were detained for a transition period and then either released, sent to the gallows, or moved to labor camps. With the reformed criminal code, delinquents could be sentenced anywhere from six months to six years, a change which led to an overcrowding of Vilnius' existing prison complex.
In its place, the new Lukiškės complex was built, holding space for 421 prisoners and a detention center for 278 inmates. The new prison also included an Orthodox Church, a Catholic Chapel, and a Jewish Synagogue. (The latter was destroyed during World War II while Vilnius was occupied by German forces.)
Today, the Lukiškės Prison can be explored with a guided tour. The prison building itself is well preserved and is considered a cultural heritage from the time of the Russian Empire. Daytime tours examine the historic architecture and facilities, outlining the daily activities of former inmates; flashlight-led nighttime tours look to thrill visitors with tales of lingering spirits.
Unlike former inmates, visitors today can celebrate their freedom with a drink at the bar situated in the former Catholic Chapel. On weekends, the bar turns into a dance club featuring a range of musical genres from electronic to swing. The toilets are located in one of the former cell wings, giving the unique opportunity to have a look into the still intact prison cells before relieving oneself. If the party hasn't started yet, visitors can also hear the occasional band practice from artists residing at the prison.
Under the name Lukiskes Prison 2.0, the barbed-wire prison walls now offer a space for creators, reviving the former prison with a new free spirit. Additionally, the Lukiškės Prison is of interest to all fans of Stranger Things as the fourth season was partly shot here.
lithuania europe jails prisons architecture
Amelie Haupt
https://www.govilnius.lt/visit-vilnius/places/lukiskes-prison-en
https://www.govilnius.lt/visit-vilnius/latest-tips/the-curious-case-of-lukiskes-prison
https://www.academia.edu/27953160/Luki%C5%A1k%C4%97s_a_Prison_as_Microcosm_of_Modern_Vilna?pop_sutd=false
https://emerging-europe.com/after-hours/in-vilnius-lithuania-a-notorious-prison-becomes-a-cultural-hub/
Lukiškių skg. 6
Vilnius, 01108
View on Google Maps Book a hotel on Kayak
Female Pedestrian Lights
'Sėkmės pilvas' ('Lucky Belly')
This former KGB building is now a museum memorializing the people who suffered during the Soviet regime.
These traffic lights celebrate the 100 year anniversary of the women's suffrage movement in Lithuania.
Rub it for a bit of good luck.
Frank Zappa Memorial
The Frank Zappa fan club erected this monument to their prog-rock hero to mark a new era of post-Soviet Lithuania.
Lincoln Heights Jail
Once the central jail for Los Angeles, this building housed inmates like Al Capone, those arrested from the Zoot Suit and Watts Riots, and individuals imprisoned for their sexuality.
Rotherham, England
The Chapel of Our Lady
This oddly placed 15th-century church is one of only six bridge chapels left in England.
The Sugar House Prison Window
An odd, ancient window that may have once been part of a brutal prison is embedded in the side of New York's Police Plaza.
Council Bluffs, Iowa
Pottawattamie Squirrel Cage Jail
The world's only three-story rotary jail is now a museum to a bizarre trend in prison design.


text:
"Creating a Measurable Social Media Marketing Strategy for Hokey Pokey: Increasing the Value and ROI of Intangibles & Tangibles"
2012 – Legends in Marketing
Dr. Kumar was selected as one of the exclusive "Legends in Marketing", and his research work is compiled and featured in the "Legends in Marketing" Series (more info)...
View Dr. Kumar's
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American Marketing Association
Marketing Science Institute
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The CLV calculator calculates the lifetime value of a customer.
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Understanding the Role of Artificial Intelligence in Personalized Engagement Marketing
How Legacy Firms Can Embrace the Digital Ecosystem Via Digital Customer Orientation
Unlocking the power of marketing: understanding the links between customer mindset metrics, behavior, and profitability
Understanding the Structural Characteristics of a firm's whole buyer-supplier network and its impact on International Business Performance
Modeling Emerging Market Firms' Competitive Price and Retail Distribution Strategies
Driving the Growth of M-Wallets in Emerging Markets: A Retailer's Perspective
Lifetime Recognitions
Inducted into the inaugural Analytics Hall of Fame, 2019
Inducted as the Fellow of the American Marketing Association, 2017
2017 Texas A & M University TIAS Faculty Fellow
Dr. V. Kumar was presented with the 2017 Eminent Scholar Award by the Hagler Institute for Advanced Study at Texas A & M University.
2016 Routledge – Taylor & Francis/SMA Distinguished Scholar Award
Dr. V. Kumar was recently given the 2016 Routledge – Taylor & Francis/SMA Distinguished Scholar Award at the 54th Annual SMA Conference in Atlanta, GA.
2015 AMS/CUTCO-Vector Marketing
Distinguished Marketing Educator Award
Received from the Academy of Marketing Science (AMS) in recognition of the outstanding career achievement of a marketing educator.
Lee Kong Chian Fellow (2015-16) at Singapore Management University, Singapore
Dr. V. Kumar was presented with the Lee Kong Chian (LKC) Research Fellowship which aims to facilitate new research and publishing about Singapore and Southeast Asian culture, economy and heritage.
2014 iSIG Fellow Award
Received from the School of Management at Fudan University, China, in recognition of his academic achievements and for his support for the iSIG
2013 Chang Jiang Scholar Award
Received from the Ministry of Education of the People's Republic of China and the Li Ka Shing Foundation, in recognition of his outstanding contributions to the field of Marketing.
2013 Regents' Professor
Received from the Board of Regents of the University System of Georgia for exemplary work ethic by a professor with a substantial, significant, and sustained record of scholarly achievement in research, teaching, and service.
Winner, 2012 Paul D. Converse Award
Received from the Department of Business Administration at the University of Illinois for his achievements and contributions to the Customer Lifetime Value (CLV) body of work.
More Lifetime Recognitions
Click the link above to see more Lifetime Recognitions
Waiter, There's a Fly in My Soup
Courtesy of BBC 4
Customer Engagement Marketing
This book provides a synthesis of research perspectives on customer engagement through a collection
Marketing Research, 13th edition
Marketing Research, 13th Edition prepares marketing students to make data d
VK Felicitated for JM Editorship
Engagement Marketing
IIMB Distinguished Faculty(Marketing) Lecture & Interaction Series IIMB, Bangalore, India
Engagement Marketing: What, Why and How
Customer Centricity World Hansa Cequity, Mumbai, India
AMA-Sheth Foundation Consortium University of Leeds, Leeds, England
How CEBCM Functions
Marketing Research Workshop International Institute for Management Development (IMD) Lausanne, Switzerland,
More appearances
Society for Marketing Science
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INFORMS Society


I have read The Madras Mangler by Ms. Narayanan. She had given me quite a bit of chills and thrills in that read. When I got the copy of Pradyumna, a mythology no less, I was a bit surprised. The genre-jumping author has a talent which very few authors can boast of. Adding to her list is an upcoming romance by Harlequin, India. So keeping her versatility in mind, one must confess, we have very few authors who explore multiple genres with such ease.
Is one which many of us have heard as 'grandparent's tale', cuddled in our blankets during the cold wintry nights. I did. My tryst with mythology started with Rick Riordon. Not very authentic, but he got me interested in the mighty ones above us. Pradyumna, or rather Kama, is my personal favourite. Not because of Kama Sutra, but due to the pain he has endured in love, after being the God of Love. Strange how the Greeks, Romans and we Indians have the same sagas for our Gods. Cupid or Kama both come out as star-crossed lovers of their respective realms.
Ms.Narayanan takes us on a journey where Lord Kama is reborn as Pradyumna, and fate plays a role by sending him to fulfill his destiny. Rati too has taken the form of Mayavati as she waits for her lord to reach his age of maturity.
Ms. Narayana has woven many small tales together, although the central character is Pradyumna. Stories of Ghatotkacha, Abhimanyu, Krishna etc. are all in relationship with Pradyumna. Even though the story starts as a love story between Mayavati and Vama, the focus is not romance. It covers many a topics like the rise and fall of the Yadus, death of Abhimanyu, and of course, an untold one—the clash between the two brothers, Samba and Pradyumna. (I'm sure Ms.Narayanan is planning the second part as I write this review).
In a mythology, authors have to maintain the authenticity of the period. In this regard, Ms. Narayanan has not disappointed me. The clothing and the dialogues were in accordance with the era the characters lived in. It shows the great research work done by the author.
No two authors can be compared. But in the genre of mythology there are two sects of writers. One who has more fiction and fewer facts like Amsih Tripathi and Rick Riordon, and the other who has more facts with tiny bits and pieces of fiction woven in the story like Devdutt Pattanaik. Ms. Narayanan belongs to the latter. My only peeve would be, as a lover of mythology, I wanted some of the re-telling part to have been more imaginative. Yes, of course, the presentation is unique to the author, but parts where Gandhari broke down or Abhimanyu met his death, were more of a re-telling than weaving in of imagination that would transport us to the battlefield.
But again, parts where Mayavati faces the Rakshashas, or is presented as a jealous mother, or even the hatred between Rukmini and Jambavati has a lot of emotional drama—enough for one to visualize the scenes. Very well written.
Transitions of Maya to Rati and Vama to Pradyuman and then to Kama are well-written.
Re-telling the episodes in Mahabharata by keeping the characters larger than life. We need that in a mythology, for these are the characters we look up to. Keeping them ordinary will take away our visualizations of these characters.
The blending of reality with myth and that of fiction with facts needed a bit more difference in its ratio. This is something for you to find out as a reader!
There are some parts where the nesting of the stories is complicated. I would have loved to follow Pradyumna in a more linear path.
He got married in the next scene. Men!! I tell you!