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The secondary structure of nucleic acid molecules can often be uniquely decomposed into stems and loops. The stem-loop structure (also often referred to as an "hairpin"), in which a base-paired helix ends in a short unpaired loop, is extremely common and is a building block for larger structural motifs such as cloverleaf structures, which are four-helix junctions such as those found in transfer RNA. Internal loops (a short series of unpaired bases in a longer paired helix) and bulges (regions in which one strand of a helix has "extra" inserted bases with no counterparts in the opposite strand) are also frequent.
There are many secondary structure elements of functional importance to biological RNAs; some famous examples are the Rho-independent terminator stem-loops and the tRNA cloverleaf. Active research is on-going to determine the secondary structure of RNA molecules, with approaches including both experimental and computational methods (see also the List of RNA structure prediction software). | 0 | Theoretical and Fundamental Chemistry |
*Quillin, M. L., Arduini, R. M., Olson, J. S., & Phillips Jr, G. N. (1993). High-resolution crystal structures of distal histidine mutants of sperm whale myoglobin. Journal of molecular biology, 234(1), 140–155.
*Springer, B. A., Sligar, S. G., Olson, J. S., & Phillips, G. N. J. (1994). Mechanisms of ligand recognition in myoglobin. Chemical Reviews, 94(3), 699–714.
*Eich, R. F., Li, T., Lemon, D. D., Doherty, D. H., Curry, S. R., Aitken, J. F., ... & Olson, J. S. (1996). Mechanism of NO-induced oxidation of myoglobin and hemoglobin. Biochemistry, 35(22), 6976–6983.
*Yang, F., Moss, L. G., & Phillips Jr, G. N. (1996). The molecular structure of green fluorescent protein. Nature biotechnology, 14(10), 1246–1251.
*Schotte, F., Lim, M., Jackson, T. A., Smirnov, A. V., Soman, J., Olson, J. S., ... & Anfinrud, P. A. (2003). Watching a protein as it functions with 150-ps time-resolved x-ray crystallography. Science, 300(5627), 1944–1947. | 1 | Applied and Interdisciplinary Chemistry |
Position-specific isotopes can be used to trace environmental pollutants through local and global environment. This is specifically useful as heavy isotopes are often used to synthesize chemicals and then will get incorporated into the natural environment through biodegradation. Thus, tracing position-specific isotopes in the environment can help trace the movement of these pollutants and chemical products. | 0 | Theoretical and Fundamental Chemistry |
Pure oxygen activated sludge aeration systems are sealed-tank reactor vessels with surface aerator type impellers mounted within the tanks at the oxygen carbon liquor surface interface. The amount of oxygen entrainment, or DO (Dissolved Oxygen), can be controlled by a weir adjusted level control, and a vent gas oxygen controlled oxygen feed valve. Oxygen is generated on site by cryogenic distillation of air, pressure swing adsorption, or other methods. These systems are used where wastewater plant space is at a premium and high sewage throughput is required as high energy costs are involved in purifying oxygen. | 1 | Applied and Interdisciplinary Chemistry |
To derive SUVA, first, UVC light (UV spectrum subtypes) at 254 nm or 280 nm, is measured in units of absorbance per meter of path length, often the sample must be diluted with ultrapure water because absorbance can be high. As increasing dissolved organic carbon concentration increases absorbance in the UV range, the UV light has to be normalized to the concentration of dissolved organic carbon in mg per L to ascertain differences in the aromatic quality of the water.
Aromatic character is used in the study of dissolved organic matter, from mineral soils, or organic soils, to use as an assay to whether or not dissolved organic carbon in the water is labile, a ready source of energy, or is from a relatively old source of carbon (recalcitrant). However, although a good indicator of aromaticity, caution must be used with determination of reactivity.
Measures of water purity often rely on measuring turbidity, not aromaticity. | 0 | Theoretical and Fundamental Chemistry |
The size and shape of the metal powder has a direct impact on the stability of the precursor as well as the resulting foam. For this purpose, powders that increase packing efficiency are most advantageous. The use of spherical particles may result in less contact of particles which consequently leads to larger secondary pores and a higher probability of pore collapse prior to complete sintering. This factor can be limited through different compaction techniques that decrease the degree of interstitial sites around the titanium particles. However, this method also has limitations; for example, the powders cannot be compacted to such a degree that would promote deformation of the spacer (unless anisotropic pore shape is desired). | 0 | Theoretical and Fundamental Chemistry |
In the US, the FDA can audit the files of local site investigators after they have finished participating in a study, to see if they were correctly following study procedures. This audit may be random, or for cause (because the investigator is suspected of fraudulent data). Avoiding an audit is an incentive for investigators to follow study procedures. A covered clinical study refers to a trial submitted to the FDA as part of a marketing application (for example, as part of an NDA or 510(k)), about which the FDA may require disclosure of financial interest of the clinical investigator in the outcome of the study. For example, the applicant must disclose whether an investigator owns equity in the sponsor, or owns proprietary interest in the product under investigation. The FDA defines a covered study as "...any study of a drug, biological product or device in humans submitted in a marketing application or reclassification petition that the applicant or FDA relies on to establish that the product is effective (including studies that show equivalence to an effective product) or any study in which a single investigator makes a significant contribution to the demonstration of safety."
Alternatively, many American pharmaceutical companies have moved some clinical trials overseas. Benefits of conducting trials abroad include lower costs (in some countries) and the ability to run larger trials in shorter timeframes, whereas a potential disadvantage exists in lower-quality trial management. Different countries have different regulatory requirements and enforcement abilities. An estimated 40% of all clinical trials now take place in Asia, Eastern Europe, and Central and South America. "There is no compulsory registration system for clinical trials in these countries and many do not follow European directives in their operations", says Jacob Sijtsma of the Netherlands-based WEMOS, an advocacy health organisation tracking clinical trials in developing countries.
Beginning in the 1980s, harmonization of clinical trial protocols was shown as feasible across countries of the European Union. At the same time, coordination between Europe, Japan and the United States led to a joint regulatory-industry initiative on international harmonization named after 1990 as the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH)
Currently, most clinical trial programs follow ICH guidelines, aimed at "ensuring that good quality, safe and effective medicines are developed and registered in the most efficient and cost-effective manner. These activities are pursued in the interest of the consumer and public health, to prevent unnecessary duplication of clinical trials in humans and to minimize the use of animal testing without compromising the regulatory obligations of safety and effectiveness." | 1 | Applied and Interdisciplinary Chemistry |
:V09CA01 Technetium (Tc) pentetic acid
:V09CA02 Technetium (Tc) succimer
:V09CA03 Technetium (Tc) mertiatide
:V09CA04 Technetium (Tc) gluceptate
:V09CA05 Technetium (Tc) gluconate
:V09CA06 Technetium (Tc) ethylenedicysteine | 1 | Applied and Interdisciplinary Chemistry |
Stainless steel is a material which is difficult to solder because of its stable, self-healing surface oxide layer and its low thermal conductivity. A solution of zinc chloride in hydrochloric acid is a common flux for stainless steels; it has however to be thoroughly removed afterwards as it would cause pitting corrosion. Another highly effective flux is phosphoric acid; its tendency to polymerize at higher temperatures however limits its applications. | 1 | Applied and Interdisciplinary Chemistry |
The Polycomb-group (PcG) regulatory complexes are known for their influence in the epigenetic regulation of stem cells,
especially in hematopoietic stem cells. The Polycomb Repressive Complex 1 (PRC 1) is directly involved in the process of hematopoiesis, and functions together with, for example, the PcG gene “Bmi1”. Studies in mice indicate that organisms with mutated “Bmi1” demonstrate deficient mitochondrial functioning, and also hindered the ability of hematopoietic cells to self-renew. Likewise, mutations in PRC2 genes were related to hematological conditions such as acute lymphoblastic leukemia (ALL), which is a form of leukemia. Hence, Polycomb-group genes and proteins are involved in the proper maintenance of hematopoiesis in the body. | 1 | Applied and Interdisciplinary Chemistry |
Because the molecule d-biotin has a much higher affinity to Strep-Tactin than Strep-tag, it can effectively compete for the binding site. Therefore, a MHC multimer based on the interaction of Strep-tag with Strep-Tactin is easily disrupted in the presence of relatively low concentrations of d-biotin. Without the Strep-Tactin backbone, the single MHC-Strep-tag fusion proteins spontaneously detach from the TCR of the T cell, because of weak binding affinities (monomeric MHC-epitope complexes cannot provide stable binding, see above). | 1 | Applied and Interdisciplinary Chemistry |
Sequential walking is a technique that can be used to solve various 2D NMR spectra. In a 2D experiment, cross peaks must be correlated to the correct nuclei. Using sequential walking, the correct nuclei can be assigned to their crosspeaks. The assigned crosspeaks can give valuable information such as spatial interactions between nuclei.
In a NOESY of DNA, for example, each nucleotide has a different chemical shift associated with it. In general, As are more downstream, Ts are more upstream, and Cs and Gs are intermediate. Each nucleotide has protons on the deoxyribose sugar, which can be assigned using sequential walking. To do this, the first nucleotide in the sequence must be detected. Knowing the DNA sequence helps, but in general the first nucleotide can be determined using the following rules.
1. 2 and 2" protons of a nucleotide will show up in its column, as well as in the column of the next nucleotide in the sequence. For example, in the sequence CATG, in the column for C, its own 2 and 2" protons will be seen, but none of the other nucleotides. For A, its own 2' and 2" protons will be seen, as well as those from C.
2. Methyl groups on the nucleotide are seen in the column for the nucleotide containing a methyl group, as well as for the nucleotide preceding it. For example, in CATG, the A and T will contain the methyl peak corresponding to the methyl group on T, but G will not.
Once the first nucleotide has been found, you determine which nucleotide is next to it because it should contain the 2' and 2" protons from the previous nucleotide. This is done by "walking" across the spectrum. This process is then repeated sequentially until all nucleotides have been assigned. | 0 | Theoretical and Fundamental Chemistry |
Mutations in the HNF4A gene have been linked to maturity onset diabetes of the young 1 (MODY1).
This seems to be caused by HNF4-a's [http://jme.endocrinology-journals.org/content/43/1/19.full.pdf] role in the synthesis of SHBG, which is known to be severely diminished in patients with insulin-resistance. | 1 | Applied and Interdisciplinary Chemistry |
Calculation of reactivity ratios generally involves carrying out several polymerizations at varying monomer ratios. The copolymer composition can be analysed with methods such as Proton nuclear magnetic resonance, Carbon-13 nuclear magnetic resonance, or Fourier transform infrared spectroscopy. The polymerizations are also carried out at low conversions, so monomer concentrations can be assumed to be constant. With all the other parameters in the copolymer equation known, and can be found. | 0 | Theoretical and Fundamental Chemistry |
Deoxyadenosine monophosphate (dAMP), also known as deoxyadenylic acid or deoxyadenylate in its conjugate acid and conjugate base forms, respectively, is a derivative of the common nucleic acid AMP, or adenosine monophosphate, in which the -OH (hydroxyl) group on the 2 carbon on the nucleotides pentose has been reduced to just a hydrogen atom (hence the "deoxy-" part of the name). Deoxyadenosine monophosphate is abbreviated dAMP. It is a monomer used in DNA. | 1 | Applied and Interdisciplinary Chemistry |
A mandrel is a steel rod or linked ball inserted into the tube while it is being bent to give the tube extra support to reduce wrinkling and breaking the tube during this process. The different types of mandrels are as follows.
* Plug mandrel: a solid rod used on normal bends
* Form mandrel: a solid rod with curved end used on bend when more support is needed
* Ball mandrel without cable: unlinked steel ball bearings inserted into tube, used on critical and precise bends
* Ball mandrel with cable: linked ball bearings inserted into tube, used on critical bend and precise bends
* Sand: sand packed into tube
In production of a product where the bend is not critical a plug mandrel can be used. A form type tapers the end of the mandrel to provide more support in the bend of the tube. When precise bending is needed a ball mandrel (or ball mandrel with steel cable) should be used. The conjoined ball-like disks are inserted into the tubing to allow for bending while maintaining the same diameter throughout. Other styles include using sand, cerrobend, or frozen water. These allow for a somewhat constant diameter while providing an inexpensive alternative to the aforementioned styles.
Performance automotive or motorcycle exhaust pipe is a common application for a mandrel. | 1 | Applied and Interdisciplinary Chemistry |
DLS is used to characterize the size of various particles including proteins, polymers, micelles, Protein cages and virus-like particles, vesicles, carbohydrates, nanoparticles, biological cells, and gels. If the system is not disperse in size, the mean effective diameter of the particles can be determined. This measurement depends on the size of the particle core, the size of surface structures, particle concentration, and the type of ions in the medium.
Since DLS essentially measures fluctuations in scattered light intensity due to diffusing particles, the diffusion coefficient of the particles can be determined. DLS software of commercial instruments typically displays the particle population at different diameters. If the system is monodisperse, there should only be one population, whereas a polydisperse system would show multiple particle populations. If there is more than one size population present in a sample then either the CONTIN analysis should be applied for photon correlation spectroscopy instruments, or the power spectrum method should be applied for Doppler shift instruments.
Stability studies can be done conveniently using DLS. Periodical DLS measurements of a sample can show whether the particles aggregate over time by seeing whether the hydrodynamic radius of the particle increases. If particles aggregate, there will be a larger population of particles with a larger radius. In some DLS machines, stability depending on temperature can be analyzed by controlling the temperature in situ. | 0 | Theoretical and Fundamental Chemistry |
The understanding of CHF phenomenon and an accurate prediction of the CHF condition are important for safe and economic design of many heat transfer units including nuclear reactors, fossil fuel boilers, fusion reactors, electronic chips, etc. Therefore, the phenomenon has been investigated extensively over the world since Nukiyama first characterized it. In 1950 Kutateladze suggested the hydrodynamical theory of the burnout crisis. Much of significant work has been done during the last decades with the development of water-cooled nuclear reactors. Now many aspects of the phenomenon are well understood and several reliable prediction models are available for conditions of common interests.
The use of the term critical heat flux (CHF) is inconsistent among authors. The United States Nuclear Regulatory Commission has suggested using the term “critical boiling transition” (CBT) to indicate the phenomenon associated with a significant reduction in two-phase heat transfer. For a single species, the liquid phase generally has considerably better heat transfer properties than the vapor phase, namely thermal conductivity. So in general CBT is the result of some degree of liquid deficiency to a local position along a heated surface. The two mechanisms that result in reaching CBT are: departure from nucleate boiling (DNB) and liquid film dryout.
Departure from nucleate boiling (DNB) occurs in sub-cooled flows and bubbly flow regimes. DNB happens when many bubbles near the heated surface coalesce and impede the ability of local liquid to reach the surface. The mass of vapor between the heated surface and local liquid may be referred to as a vapor blanket.
Dryout means the disappearance of liquid on the heat transfer surface which results in the CBT. Dryout of liquid film occurs in annular flow. Annular flow is characterized by a vapor core, liquid film on the wall, and liquid droplets entrained within the core. Shear at the liquid-vapor interface drives the flow of the liquid film along the heated surface. In general, the two-phase HTC increases as the liquid-film thickness decreases. The process has been shown to occur over many instances of dryout events, which span a finite duration and are local to a position. The CBT occurs when the fraction of time a local position is subjected to dryout becomes significant. A single dryout event, or even several dryout events, may be followed by periods of sustained contact between the liquid film and the previously dry region [https://mediaspace.wisc.edu/media/Dryout-rewet/1_7sn93wd2] . Many dryout events (hundreds or thousands) occurring in sequence are the mechanism for significant reduction in heat transfer-associated dryout CBT.
Post-CHF is used to denote the general heat transfer deterioration in flow boiling process, and liquid could be in the form of dispersed spray of droplets, continuous liquid core, or transition between the former two cases. Post-dryout can be specifically used to denote the heat transfer deterioration in the condition when liquid is only in the form of dispersed droplets, and denote the other cases by the term Post-DNB. | 0 | Theoretical and Fundamental Chemistry |
Sedimentation equilibrium experiments reports the molar mass of analytes and their chemical equilibrium constants. The rotor speed is adjusted such that a steady-state concentration profile c(r) of the sample in the cell is formed, where sedimentation and diffusion cancel out each other. | 1 | Applied and Interdisciplinary Chemistry |
The study of spinor condensates was initiated in 1998 by experimental groups at JILA
and MIT. These experiments utilised
Na and Rb atoms, respectively.
In contrast to most prior experiments on ultracold gases, these experiments utilised a purely
optical trap, which is spin-insensitive. Shortly thereafter, theoretical work appeared
which described the possible mean-field phases of spin-one spinor condensates. | 0 | Theoretical and Fundamental Chemistry |
An SADP is acquired under parallel electron illumination. In the case of convergent beam, a convergent beam electron diffraction (CBED) is achieved. The beam used in SAD is broad illuminating a wide sample area. In order to analyze only a specific sample area, the selected area aperture in the image plane is used. This is in contrast with nanodiffraction, where the site-selectivity is achieved using a beam condensed to a narrow probe. SAD is important in direct imaging for instance when orienting the sample for high resolution microscopy or setting up dark-field imaging conditions.
High-resolution electron microscope images can be transformed into an artificial diffraction pattern using Fourier transform. Then, they can be processed the same way as real diffractograms allowing to determine crystal orientation, measure interplanar angles and distances even with picometric precision.
SAD is similar to X-ray diffraction, but unique in that areas as small as several hundred nanometers in size can be examined, whereas X-ray diffraction typically samples areas much larger. | 0 | Theoretical and Fundamental Chemistry |
The physical manifestation of leaving group ability is the rate at which a reaction takes place. Good leaving groups give fast reactions. By transition state theory, this implies that reactions involving good leaving groups have low activation barriers leading to relatively stable transition states.
It is helpful to consider the concept of leaving group ability in the case of the first step of an S1/E1 reaction with an anionic leaving group (ionization), while keeping in mind that this concept can be generalized to all reactions that involve leaving groups. Because the leaving group bears a larger negative charge in the transition state (and products) than in the starting material, a good leaving group must be able to stabilize this negative charge, i.e. form stable anions. A good measure of anion stability is the pK of an anions conjugate acid (pK), and leaving group ability indeed generally follows this trend, with a lower pK' correlating well with better leaving group ability.
The correlation between pK and leaving group ability, however, is not perfect. Leaving group ability represents the difference in energy between starting materials and a transition state (ΔG) and differences in leaving group ability are reflected in changes in this quantity (ΔΔG). The pK, however, represents the difference in energy between starting materials and products (ΔG°) with differences in acidity reflected in changes in this quantity (ΔΔG°). The ability to correlate these energy differences is justified by the Hammond postulate and the Bell–Evans–Polanyi principle. Also, the starting materials in these cases are different. In the case of the acid dissociation constant, the "leaving group" is bound to a proton in the starting material, while in the case of leaving group ability, the leaving group is bound to (usually) carbon. It is with these important caveats in mind that one must consider pK to be reflective of leaving group ability. Nevertheless, one can generally examine acid dissociation constants to qualitatively predict or rationalize rate or reactivity trends relating to variation of the leaving group. Consistent with this picture, strong bases such as and tend to make poor leaving groups, due their inability to stabilize a negative charge.
What constitutes a reasonable leaving group is dependent on context. For S2 reactions, typical synthetically useful leaving groups include , , and . Substrates containing phosphate and carboxylate leaving groups are more likely to react by competitive addition-elimination, while sulfonium and ammonium salts generally form ylides or undergo E2 elimination when possible. With reference to the table above, phenoxides () constitute the lower limit for what is feasible as S2 leaving groups: very strong nucleophiles like or have been used to demethylate anisole derivatives through S2 displacement at the methyl group. Hydroxide, alkoxides, amides, hydride, and alkyl anions do not serve as leaving groups in S2 reactions.
On the other hand, when anionic or dianionic tetrahedral intermediates collapse, the high electron density of the neighboring heteroatom facilitates the expulsion of a leaving group. Thus, in the case of ester and amide hydrolysis under basic conditions, alkoxides and amides are commonly proposed as leaving groups. For the same reason, E1cb reactions involving hydroxide as a leaving group are not uncommon (e.g., in the aldol condensation). It is exceedingly rare for groups such as (hydrides), (alkyl anions, R = alkyl or H), or (aryl anions, Ar = aryl) to depart with a pair of electrons because of the high energy of these species. The Chichibabin reaction provides an example of hydride as a leaving group, while the Wolff-Kishner reaction and Haller-Bauer reaction feature unstabilized carbanion leaving groups. | 0 | Theoretical and Fundamental Chemistry |
Paste tailings is a modification to the conventional methods of disposal of tailings (pond storage). Conventional tailings slurries are composed of a low percent of solids and relatively high water content (normally ranging from 20% to 60% solids for most hard rock mining) and when deposited into the tailings pond the solids and liquids separate. In paste tailings the percent of solids in the tailings slurry is increased through the use of paste thickeners to produce a product where the minimal separation of water and solids occurs and the material is deposited into a storage area as a paste (with a consistency somewhat like toothpaste). Paste tailings has the advantage that more water is recycled in the processing plant and therefore the process is more water efficient than conventional tailings and there is a lower potential for seepage. However the cost of the thickening is generally higher than for conventional tailings and the pumping costs for the paste are also normally higher than for conventional tailings as positive displacement pumps are normally required to transport the tailings from the processing plant to the storage area. Paste tailings are used in several locations around the world including Sunrise Dam in Western Australia and Bulyanhulu Gold Mine in Tanzania. | 1 | Applied and Interdisciplinary Chemistry |
Compared to more commonly encountered states of matter, Bose–Einstein condensates are extremely fragile. The slightest interaction with the external environment can be enough to warm them past the condensation threshold, eliminating their interesting properties and forming a normal gas.
Nevertheless, they have proven useful in exploring a wide range of questions in fundamental physics, and the years since the initial discoveries by the JILA and MIT groups have seen an increase in experimental and theoretical activity. Examples include experiments that have demonstrated interference between condensates due to wave–particle duality, the study of superfluidity and quantized vortices, the creation of bright matter wave solitons from Bose condensates confined to one dimension, and the slowing of light pulses to very low speeds using electromagnetically induced transparency. Vortices in Bose–Einstein condensates are also currently the subject of analogue gravity research, studying the possibility of modeling black holes and their related phenomena in such environments in the laboratory. Experimenters have also realized "optical lattices", where the interference pattern from overlapping lasers provides a periodic potential. These have been used to explore the transition between a superfluid and a Mott insulator, and may be useful in studying Bose–Einstein condensation in fewer than three dimensions, for example the Tonks–Girardeau gas. Further, the sensitivity of the pinning transition of strongly interacting bosons confined in a shallow one-dimensional optical lattice originally observed by Haller has been explored via a tweaking of the primary optical lattice by a secondary weaker one. Thus for a resulting weak bichromatic optical lattice, it has been found that the pinning transition is robust against the
introduction of the weaker secondary optical lattice. Studies of vortices in nonuniform Bose–Einstein condensates as well as excitations of these systems by the application of moving repulsive or attractive obstacles, have also been undertaken. Within this context, the conditions for order and chaos in the dynamics of a trapped Bose–Einstein condensate have been explored by the application of moving blue and red-detuned laser beams (hitting frequencies slightly above and below the resonance frequency, respectively) via the time-dependent Gross-Pitaevskii equation.
Bose–Einstein condensates composed of a wide range of isotopes have been produced.
Cooling fermions to extremely low temperatures has created degenerate gases, subject to the Pauli exclusion principle. To exhibit Bose–Einstein condensation, the fermions must "pair up" to form bosonic compound particles (e.g. molecules or Cooper pairs). The first molecular condensates were created in November 2003 by the groups of Rudolf Grimm at the University of Innsbruck, Deborah S. Jin at the University of Colorado at Boulder and Wolfgang Ketterle at MIT. Jin quickly went on to create the first fermionic condensate, working with the same system but outside the molecular regime.
In 1999, Danish physicist Lene Hau led a team from Harvard University which slowed a beam of light to about 17 meters per second using a superfluid. Hau and her associates have since made a group of condensate atoms recoil from a light pulse such that they recorded the light's phase and amplitude, recovered by a second nearby condensate, in what they term "slow-light-mediated atomic matter-wave amplification" using Bose–Einstein condensates.
Another current research interest is the creation of Bose–Einstein condensates in microgravity in order to use its properties for high precision atom interferometry. The first demonstration of a BEC in weightlessness was achieved in 2008 at a drop tower in Bremen, Germany by a consortium of researchers led by Ernst M. Rasel from Leibniz University Hannover. The same team demonstrated in 2017 the first creation of a Bose–Einstein condensate in space and it is also the subject of two upcoming experiments on the International Space Station.
Researchers in the new field of atomtronics use the properties of Bose–Einstein condensates in the emerging quantum technology of matter-wave circuits.
In 1970, BECs were proposed by Emmanuel David Tannenbaum for anti-stealth technology.
In 2020, researchers reported the development of superconducting BEC and that there appears to be a "smooth transition between" BEC and Bardeen–Cooper–Shrieffer regimes. | 0 | Theoretical and Fundamental Chemistry |
John Ulric Nef (Johann Ulrich Nef; June 14, 1862 – August 13, 1915) was a Swiss-born American chemist and the discoverer of the Nef reaction and Nef synthesis. He was a member of the American Academy of Arts and Sciences and the National Academy of Sciences. | 0 | Theoretical and Fundamental Chemistry |
bonds adjacent to the carbonyl in ketones are more acidic pK ≈ 20) than the bonds in alkane (pK ≈ 50). This difference reflects resonance stabilization of the enolate ion that is formed upon deprotonation. The relative acidity of the α-hydrogen is important in the enolization reactions of ketones and other carbonyl compounds. The acidity of the α-hydrogen also allows ketones and other carbonyl compounds to react as nucleophiles at that position, with either stoichiometric and catalytic base. Using very strong bases like lithium diisopropylamide (LDA, pK of conjugate acid ~36) under non-equilibrating conditions (–78 °C, 1.1 equiv LDA in THF, ketone added to base), the less-substituted kinetic enolate is generated selectively, while conditions that allow for equilibration (higher temperature, base added to ketone, using weak or insoluble bases, e.g., sodium ethoxide| in ethanol|, or NaH) provides the more-substituted thermodynamic enolate.
Ketones are also weak bases, undergoing protonation on the carbonyl oxygen in the presence of Brønsted acids. Ketonium ions (i.e., protonated ketones) are strong acids, with pK values estimated to be somewhere between –5 and –7. Although acids encountered in organic chemistry are seldom strong enough to fully protonate ketones, the formation of equilibrium concentrations of protonated ketones is nevertheless an important step in the mechanisms of many common organic reactions, like the formation of an acetal, for example. Acids as weak as pyridinium cation (as found in pyridinium tosylate) with a pK of 5.2 are able to serve as catalysts in this context, despite the highly unfavorable equilibrium constant for protonation (K ). | 0 | Theoretical and Fundamental Chemistry |
Pyruvic acid (IUPAC name: 2-oxopropanoic acid, also called acetoic acid) (CHCOCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CHCOCOO, is an intermediate in several metabolic pathways throughout the cell.
Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates (such as glucose) via gluconeogenesis, or converted to fatty acids through a reaction with acetyl-CoA. It can also be used to construct the amino acid alanine and can be converted into ethanol or lactic acid via fermentation.
Pyruvic acid supplies energy to cells through the citric acid cycle (also known as the Krebs cycle) when oxygen is present (aerobic respiration), and alternatively ferments to produce lactate when oxygen is lacking. | 1 | Applied and Interdisciplinary Chemistry |
If the SAD is taken from one a or a few single crystals, the diffractogram depicts a regular pattern of bright spots. Since the diffraction pattern can be seen as a two-dimensional projection of reciprocal crystal lattice, the pattern can be used to measure lattice constants, specifically the distances and angles between crystallographic planes. The lattice parameters are typically distinctive for various materials and their phases which allows to identify the examined material or at least differentiate between possible candidates.
Even though the SAD-based analyses were not considered quantitative for a long time, computer tools brought accuracy and repeatability allowing to routinely perform accurate measurements of interplanar distances or angles on appropriately calibrated microscopes. Tools such as CrysTBox are capable of automated analysis achieving sub-pixel precision.
If the sample is tilted against the electron beam, diffraction conditions are satisfied for different set of crystallographic planes yielding different constellation of diffraction spots. This allows to determine the crystal orientation, which can be used for instance to set up the orientation needed for particular experiment, to determine misorientation between adjacent grains or crystal twins. Since different sample orientations provide different projections of the reciprocal lattice, they provide an opportunity to reconstruct the three-dimensional information lost in individual projections. A series of diffractograms varying in tilt can be acquired and processed with diffraction tomography analysis in order to reconstruct an unknown crystal structure.
SAD can also be used to analyze crystal defects such as stacking faults. | 0 | Theoretical and Fundamental Chemistry |
Secondary metabolites are often characterized as either qualitative or quantitative. Qualitative metabolites are defined as toxins that interfere with a herbivore's metabolism, often by blocking specific biochemical reactions. Qualitative chemicals are present in plants in relatively low concentrations (often less than 2% dry weight), and are not dosage dependent. They are usually small, water-soluble molecules, and therefore can be rapidly synthesized, transported and stored with relatively little energy cost to the plant. Qualitative allelochemicals are usually effective against non-adapted generalist herbivores.
Quantitative chemicals are those that are present in high concentration in plants (5 – 40% dry weight) and are equally effective against all specialists and generalist herbivores. Most quantitative metabolites are digestibility reducers that make plant cell walls indigestible to animals. The effects of quantitative metabolites are dosage dependent and the higher these chemicals proportion in the herbivores diet, the less nutrition the herbivore can gain from ingesting plant tissues. Because they are typically large molecules, these defenses are energetically expensive to produce and maintain, and often take longer to synthesize and transport.
The geranium, for example, produces the amino acid, quisqualic acid in its petals to defend itself from Japanese beetles. Within 30 minutes of ingestion the chemical paralyzes the herbivore. While the chemical usually wears off within a few hours, during this time the beetle is often consumed by its own predators. | 1 | Applied and Interdisciplinary Chemistry |
* 2023: Arthur C. Cope Scholar Award (American Chemical Society)
* 2018: University of California, Irvine Physical Science Outstanding Contributions to the Undergraduate Education
* 2017: Fellow of the AAAS
* 2013-2016: Humboldt Fellowship
* 2013: Japan Society for the Promotion of Science Fellowship
* 2008: NSF CAREER Award
* 2005-2006: National Institutes of Health Postdoctoral Fellow | 0 | Theoretical and Fundamental Chemistry |
In biology, quorum sensing or quorum signaling (QS) is the ability to detect and respond to cell population density by gene regulation. Quorum sensing is a type of cellular signaling, and more specifically can be considered a type of paracrine signaling. However, it also contains traits of both autocrine signaling: a cell produces both the autoinducer molecule and the receptor for the autoinducer. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at which the resulting phenotypes will be most beneficial, especially for phenotypes that would be ineffective at low cell densities and therefore too energetically costly to express. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. In a similar fashion, some social insects use quorum sensing to determine where to nest. Quorum sensing in pathogenic bacteria activates host immune signaling and prolongs host survival, by limiting the bacterial intake of nutrients, such as tryptophan, which further is converted to serotonin. As such, quorum sensing allows a commensal interaction between host and pathogenic bacteria. Quorum sensing may also be useful for cancer cell communications.
In addition to its function in biological systems, quorum sensing has several useful applications for computing and robotics. In general, quorum sensing can function as a decision-making process in any decentralized system in which the components have: (a) a means of assessing the number of other components they interact with and (b) a standard response once a threshold number of components is detected. | 1 | Applied and Interdisciplinary Chemistry |
Inertial cavitation can also occur in the presence of an acoustic field. Microscopic gas bubbles that are generally present in a liquid will be forced to oscillate due to an applied acoustic field. If the acoustic intensity is sufficiently high, the bubbles will first grow in size and then rapidly collapse. Hence, inertial cavitation can occur even if the rarefaction in the liquid is insufficient for a Rayleigh-like void to occur.
Ultrasonic cavitation inception will occur when the acceleration of the ultrasound source is enough to produce the needed pressure drop. This pressure drop depends on the value of the acceleration and the size of the affected volume by the pressure wave. The dimensionless number that predicts ultrasonic cavitation is the Garcia-Atance number. High power ultrasonic horns produce accelerations high enough to create a cavitating region that can be used for homogenization, dispersion, deagglomeration, erosion, cleaning, milling, emulsification, extraction, disintegration, and sonochemistry. | 1 | Applied and Interdisciplinary Chemistry |
WDTC1 ("Adipose") is a gene associated with obesity.
WDTC1 is a gene that codes for a protein acting as a suppressor in lipid accumulation. WDTC1 protein consists of seven WD40 domains, three transient receptor potential channel protein-protein interaction domains, DDB1 binding elements, and a prenylated C-terminus. Reduced expression or disruption of WDTC1 gene is associated with obesity, increased triglyceride accumulation, and adipogenesis. WDTC1 is a factor in a complex composed of DDB1, CUL4, and ROC1 that restricts transcription in adipogenesis. | 1 | Applied and Interdisciplinary Chemistry |
4-Nitrophenol can be used as a pH indicator. A solution of 4-nitrophenol appears colorless below pH 5.4 and yellow above pH 7.5. This color-changing property makes this compound useful as a pH indicator.
The yellow color of the 4-nitrophenolate form (or 4-nitrophenoxide) is due to a maximum of absorbance at 405 nm (ε = 18.3 to 18.4 mM cm in strong alkali). In contrast, 4-nitrophenol has a weak absorbance at 405 nm (ε = 0.2 mM cm).
The isosbestic point for 4-nitrophenol/4-nitrophenoxide is at 348 nm, with ε = 5.4 mM cm. | 0 | Theoretical and Fundamental Chemistry |
The daughter of Morris and Etty Mizrahi, she was born in Harare, Zimbabwe and was educated there. Her family is a Sephardi Jewish family from the Greek island of Rhodes. | 1 | Applied and Interdisciplinary Chemistry |
The sievert has its origin in the röntgen equivalent man (rem) which was derived from CGS units. The International Commission on Radiation Units and Measurements (ICRU) promoted a switch to coherent SI units in the 1970s, and announced in 1976 that it planned to formulate a suitable unit for equivalent dose. The ICRP pre-empted the ICRU by introducing the sievert in 1977.
The sievert was adopted by the International Committee for Weights and Measures (CIPM) in 1980, five years after adopting the gray. The CIPM then issued an explanation in 1984, recommending when the sievert should be used as opposed to the gray. That explanation was updated in 2002 to bring it closer to the ICRP's definition of equivalent dose, which had changed in 1990. Specifically, the ICRP had introduced equivalent dose, renamed the quality factor (Q) to radiation weighting factor (W), and dropped another weighting factor "N" in 1990. In 2002, the CIPM similarly dropped the weighting factor "N" from their explanation but otherwise kept other old terminology and symbols. This explanation only appears in the appendix to the SI brochure and is not part of the definition of the sievert. | 0 | Theoretical and Fundamental Chemistry |
The mission of EPA is to protect human health and the environment.
EPA works to ensure that:
* Americans have clean air, land and water;
* National efforts to reduce environmental risks are based on the best available scientific information;
* Federal laws protecting human health and the environment are administered and enforced fairly, effectively and as Congress intended;
* Environmental stewardship is integral to U.S. policies concerning natural resources, human health, economic growth, energy, transportation, agriculture, industry, and international trade, and these factors are similarly considered in establishing environmental policy;
* All parts of society--communities, individuals, businesses, and state, local and tribal governments--have access to accurate information sufficient to effectively participate in managing human health and environmental risks;
* Contaminated lands and toxic sites are cleaned up by potentially responsible parties and revitalized; and
* Chemicals in the marketplace are reviewed for safety. | 0 | Theoretical and Fundamental Chemistry |
This is an actual reading obtained from such as an ambient dose gamma monitor, or a personal dosimeter. Such instruments are calibrated using radiation metrology techniques which will trace them to a national radiation standard, and thereby relate them to an operational quantity. The readings of instruments and dosimeters are used to prevent the uptake of excessive dose and to provide records of dose uptake to satisfy radiation safety legislation; such as in the UK, the Ionising Radiations Regulations 1999. | 0 | Theoretical and Fundamental Chemistry |
Despite the cancellation of funding by the DOE, the FutureGen Alliance continued to move forward with the project, opening an office in Mattoon and planning to buy the land for the plant in August 2008, in partnership with a local group.
During the 2008 U.S. presidential campaigns, Sen. Barack Obama pledged his support to clean coal technologies, with plans to develop five commercial-scale coal plants equipped with CCS technology.
In November 2008, Fred Palmer, senior vice president at Peabody Energy shared his outlook on FutureGen with the American Coalition for Clean Coal Electricity (ACCCE), saying that the FutureGen Alliance would "Make a concerted effort in the Obama administration to reinstate the project and get this built as originally planned."
On June 12, 2009, the DOE announced a restart of design work for the FutureGen project. "Following the completion of the detailed cost estimate and fundraising activities," the press release states, "the Department of Energy and the FutureGen Alliance will make a decision either to move forward or to discontinue the project early in 2010." | 1 | Applied and Interdisciplinary Chemistry |
The museum is also home to a large number of old tractors. Two D8 Caterpillars, a D9, a few large 1930s Caterpillars, some Best crawlers and many other examples of tracked tractors can be seen at the museum. The typical tractors such as Farmall, John Deere, Oliver, and Allis-Chalmers can be seen out at the museum, but there are more than a few rarer examples too. There is a 1924 Buffalo-Springfield road roller, a gigantic 1918 30-60 Aultman-Taylor gas tractor, a 1911 Fairbanks-Morse 15-25 kerosene tractor, a 1915 International Harvester Mogul 8-16, several Rumely Oil-Pulls, and many more. | 1 | Applied and Interdisciplinary Chemistry |
Downregulation refers to the decrease in the number of receptor molecules. This is usually the result of receptor endocytosis. In this process, the bound LCGR-hormone complex binds arrestin and concentrates in clathrin coated pits. Clathrin coated pits recruit dynamin and pinch off from the cell surface, becoming clathrin-coated vesicles. Clathrin-coated vesicles are processed into endosomes, some of which are recycled to the cell surface while others are targeted to lysosomes. Receptors targeted to lysosomes are degraded. Use of long-acting agonists will downregulate the receptor population by promoting their endocytosis. | 1 | Applied and Interdisciplinary Chemistry |
Its activities are focused on both fundamental objectives in analytical sciences and interactions with the socio-economic environment at local, national and international levels. The Institute has partnerships with international research centers (e.g. MIT, the École Polytechnique Fédérale de Lausanne, International Agency for Research on Cancer) and national academic partners (e.g. LabexIMUST, , ...) and industrial partners (BioMérieux, , Sanofi, Solvay, Total) and manufacturers (Agilent, Bruker, Waters ...).
The institute is involved in competitiveness clusters (Axelera, , Techtera, Plastipolis) and regional cluster (). Some scientists are experts in standardization committees at national and European levels. In addition, the Institute of Analytical Sciences plays a «Business incubator» role and hosts start-ups: ANAQUANT, metabolomics technical platform, etc. | 0 | Theoretical and Fundamental Chemistry |
Fucosylation is the process of adding fucose sugar units to a molecule. It is a type of glycosylation.
It is important clinically, and high levels of fucosylation have been reported in cancer. In cancer and inflammation there are significant changes in the expression of fucosylated molecules. Therefore, antibodies and lectins that are able to recognize cancer associated fucosylated oligosaccharides have been used as tumor markers in oncology.
It is performed by fucosyltransferase enzymes.
Fucosylation has been observed in vertebrates, invertebrates, plants, bacteria, and fungi. It has a role in cellular adhesion and immune regulation. Fucosylation inhibition applications are being explored for a range of clinical application including some associated with sickle cell disease, rheumatoid arthritis, tumor inhibition, and chemotherapy improvements. Recent studies on melanoma patient specimens indicated that melanoma fucosylation and fucosylated HLA-DRB1 are associated with anti-programmed cell death protein 1 (PD1) responder status, pointing to the potential use of melanoma fucosylation as a method for immunotherapy patient stratification. Moreover, it has been reported that fucosylation is an important regulator of anti-tumor immunity and -fucose can be used as a potent tool for increasing immunotherapy efficacy in melanoma.
Fucosylation can help with immune response when a foreign pathogen is introduced in the body. Rapid fucosylation can occur in the epithelial lining of the small intestine as a protective mechanism to support the body’s symbiotic gut bacteria. This may regulate the bacterial genes responsible for quorum sensing or virulence, thus resulting in an increased tolerance of the infection. | 0 | Theoretical and Fundamental Chemistry |
Kalpasutra mentions nine Ganas and 11 Ganadharas of Mahavira. Bhadrabahu is mentioned as prime Ganadhara of Mahavira. Bhadrabahu's disciple Godasa is mentioned to have founded Godasa Gana. | 1 | Applied and Interdisciplinary Chemistry |
Christian G. Hartinger (born 1974) is an Austrian-born New Zealand bioinorganic chemist known for his work in metal-based anticancer drugs. In 2022 he was elected a Fellow of the Royal Society Te Apārangi. | 0 | Theoretical and Fundamental Chemistry |
Bryan Research & Engineering, Inc. (BR&E) is a privately owned provider of software and engineering solutions to the oil, gas, refining and chemical industries. Since the company’s inception in 1974, BR&E has combined research and development in process simulation to provide clients with simulation tools. | 1 | Applied and Interdisciplinary Chemistry |
The reducing agents NADH, NADPH, and FADH, as well as metal ions, act as cofactors at various steps in anabolic pathways. NADH, NADPH, and FADH act as electron carriers, while charged metal ions within enzymes stabilize charged functional groups on substrates. | 1 | Applied and Interdisciplinary Chemistry |
Durrant has proposed an alternative definition of hypervalency, based on the analysis of atomic charge maps obtained from atoms in molecules theory. This approach defines a parameter called the valence electron equivalent, γ, as “the formal shared electron count at a given atom, obtained by any combination of valid ionic and covalent resonance forms that reproduces the observed charge distribution”. For any particular atom X, if the value of γ(X) is greater than 8, that atom is hypervalent. Using this alternative definition, many species such as PCl, , and XeF, that are hypervalent by Musher's definition, are reclassified as hypercoordinate but not hypervalent, due to strongly ionic bonding that draws electrons away from the central atom. On the other hand, some compounds that are normally written with ionic bonds in order to conform to the octet rule, such as ozone O, nitrous oxide NNO, and trimethylamine N-oxide , are found to be genuinely hypervalent. Examples of γ calculations for phosphate (γ(P) = 2.6, non-hypervalent) and orthonitrate (γ(N) = 8.5, hypervalent) are shown below. | 0 | Theoretical and Fundamental Chemistry |
In the 1989 Queen's Birthday Honours, Campbell was appointed an Officer of the Order of the British Empire, for services to science. | 0 | Theoretical and Fundamental Chemistry |
Pancreatic lipase is the most important lipolytic enzyme in the gastrointestinal tract and is essential for fat digestion.
Pancreatic lipase is secreted from acinar cells in the pancreas and its secretion, with the pancreatic juice to the small intestine, is stimulated by hormones. These hormones are induced in the stomach by hydrolysed products in gastric digestion.
The pancreatic lipase is secreted to the small intestine where it is most active, at pH 7-7,5.
Pancreatic lipase hydrolyses triglycerides and diglycerides by cleaving acyl chains at the sn-1 and sn-3 position
and releases free fatty acids and 2-monoglycerides.
The pancreatic lipase consists of 465 amino acids. Schematic picture of pancreatic lipase is shown in figure 2. Pancreatic and gastric lipases share little homology but have the same hydrophobic region at the active site, which is important for the lipolytic activity. The hydrophobic region has the hexapeptide sequence Val-Gly-His-Ser-Gln-Gly and is at Ser153 in pancreatic lipases but Ser152 in gastric lipases. | 1 | Applied and Interdisciplinary Chemistry |
Neutron emission usually happens from nuclei that are in an excited state, such as the excited O* produced from the beta decay of N. The neutron emission process itself is controlled by the nuclear force and therefore is extremely fast, sometimes referred to as "nearly instantaneous". This process allows unstable atoms to become more stable. The ejection of the neutron may be as a product of the movement of many nucleons, but it is ultimately mediated by the repulsive action of the nuclear force that exists at extremely short-range distances between nucleons. | 0 | Theoretical and Fundamental Chemistry |
The surface of any liquid is an interface between that liquid and some other medium. The top surface of a pond, for example, is an interface between the pond water and the air. Surface tension, then, is not a property of the liquid alone, but a property of the liquid's interface with another medium. If a liquid is in a container, then besides the liquid/air interface at its top surface, there is also an interface between the liquid and the walls of the container. The surface tension between the liquid and air is usually different (greater) than its surface tension with the walls of a container. And where the two surfaces meet, their geometry must be such that all forces balance.
Where the two surfaces meet, they form a contact angle, , which is the angle the tangent to the surface makes with the solid surface. Note that the angle is measured through the liquid, as shown in the diagrams above. The diagram to the right shows two examples. Tension forces are shown for the liquid–air interface, the liquid–solid interface, and the solid–air interface. The example on the left is where the difference between the liquid–solid and solid–air surface tension, , is less than the liquid–air surface tension, , but is nevertheless positive, that is
In the diagram, both the vertical and horizontal forces must cancel exactly at the contact point, known as equilibrium. The horizontal component of is canceled by the adhesive force, .
The more telling balance of forces, though, is in the vertical direction. The vertical component of must exactly cancel the difference of the forces along the solid surface, .
| rowspan="6" style="text-align:center;"|0°
| ethanol
| diethyl ether
| carbon tetrachloride
| glycerol
| acetic acid
| rowspan="2"|water
| paraffin wax
| style="text-align:center;"|107°
| silver
| style="text-align:center;"|90°
| rowspan="3"| methyl iodide
| soda-lime glass
| style="text-align:center;"|29°
| lead glass
| style="text-align:center;"|30°
| fused quartz
| style="text-align:center;"|33°
| mercury
| soda-lime glass
| style="text-align:center;"|140°
Since the forces are in direct proportion to their respective surface tensions, we also have:
where
* is the liquid–solid surface tension,
* is the liquid–air surface tension,
* is the solid–air surface tension,
* is the contact angle, where a concave meniscus has contact angle less than 90° and a convex meniscus has contact angle of greater than 90°.
This means that although the difference between the liquid–solid and solid–air surface tension, , is difficult to measure directly, it can be inferred from the liquid–air surface tension, , and the equilibrium contact angle, , which is a function of the easily measurable advancing and receding contact angles (see main article contact angle).
This same relationship exists in the diagram on the right. But in this case we see that because the contact angle is less than 90°, the liquid–solid/solid–air surface tension difference must be negative: | 0 | Theoretical and Fundamental Chemistry |
For species A:
For species B:
:Here the first (positive) term represents the formation of B by the first step , whose rate depends on the initial reactant A. The second (negative) term represents the consumption of B by the second step , whose rate depends on B as the reactant in that step.
For species C: | 0 | Theoretical and Fundamental Chemistry |
In combustion, flame stretch () is a quantity which measures the amount of stretch of the flame surface due to curvature and due to the outer velocity field strain. The early concept of flame stretch was introduced by Karlovitz in 1953, although the correct definition was introduced two decades later by Forman A. Williams in 1975.
George H. Markstein studied flame stretch by treating the flame surface as a hydrodynamic discontinuity (known as flame front). The flame stretch is also discussed by Bernard Lewis and Guenther von Elbe in their book. All these discussions treated flame stretch as an effect of flow velocity gradients. The stretch can be found even if there is no velocity gradient, but due to the flame curvature. So, the definition required a more general formulation and its precise definition was first introduced by Forman A. Williams in 1975 as the ratio of rate of change of flame surface area to the area itself
When , the flame is stretched, otherwise compressed. Sometimes the flame stretch is defined as non-dimensional quantity
where is the laminar flame thickness and is the laminar propagation speed of unstretched premixed flame. | 1 | Applied and Interdisciplinary Chemistry |
The sodium fusion extract is boiled with concentrated HNO followed by the addition of AgNO solution which yields a white (AgCl) or yellow (AgBr or AgI) precipitate if halogen is present.</blockquote> | 0 | Theoretical and Fundamental Chemistry |
Aerobic metabolism occurs in Bacteria, Archaea and Eucarya. Although most bacterial species are anaerobic, many are facultative or obligate aerobes. The majority of archaeal species live in extreme environments that are often highly anaerobic. There are, however, several cases of aerobic archaea such as Haiobacterium, Thermoplasma, Sulfolobus and Yymbaculum. Most of the known eukaryotes carry out aerobic metabolism within their mitochondria which is an organelle that had a symbiogenesis origin from prokarya . All aerobic organisms contain oxidases of the cytochrome oxidase super family, but some members of the Pseudomonadota (E. coli and Acetobacter) can also use an unrelated cytochrome bd complex as a respiratory terminal oxidase. | 1 | Applied and Interdisciplinary Chemistry |
Earlier mechanistic proposals for the EPOC phenomenon with solid electrolytes mainly emphasized tuning of the local work function of the surface of conductive catalysts by spilled-over species, which are in-situ generated during electrochemical polarization processes. It has been proposed that the spilled-over species can subsequently modulate the chemisorption strength between surface adsorbates (intermediates) and catalyst binding sites, thereby influencing the rate or selectivity of the target reactions significantly. Particularly in the case of oxygen-ion conducting electrolyte systems, for instance, the migrated anionic O species from the solid electrolyte to the metal-gas interface has been suggested as the origin of the corresponding EPOC effects along with the evidence that the migrated charged species on the surface can be identified via in-situ spectroscopic methods. On the other hand, the hypothesis of modification of the local work function to explain the origin of EPOC was recently criticized with a different view that heterogeneous catalysis needs to be explained by more recent concepts such as d-band center theory, rather than the surface work function, which might play a more trivial role in understanding of surface reactions. | 0 | Theoretical and Fundamental Chemistry |
The Swamee–Jain equation is used to solve directly for the Darcy–Weisbach friction factor f for a full-flowing circular pipe. It is an approximation of the implicit Colebrook–White equation. | 1 | Applied and Interdisciplinary Chemistry |
Theodore William Richards (January 31, 1868 – April 2, 1928) was an American physical chemist and the first American scientist to receive the Nobel Prize in Chemistry, earning the award "in recognition of his exact determinations of the atomic weights of a large number of the chemical elements." | 1 | Applied and Interdisciplinary Chemistry |
Launched in the 1940s by the Shirley Institute, the Shirley Togmeter is the standard apparatus for rating thermal resistance of textiles, commonly known as the Tog Test. This apparatus, described in BS 4745:2005, measures a sample of textile, either between two metal plates (for underclothing) or between a metal plate and free air (for outer layers). Each industry has its own specifications and methods for measuring thermal properties. | 0 | Theoretical and Fundamental Chemistry |
"Blue infrastructure" refers to urban infrastructure relating to water. Blue infrastructure is commonly associated with green infrastructure in urban environments and may be referred to as "blue-green infrastructure" when being viewed in combination. Rivers, streams, ponds, and lakes may exist as natural features within cities, or be added to an urban environment as an aspect of its design. Coastal urban developments may also utilize pre-existing features of the coastline specifically employed in their design. Harbours, quays, piers, and other extensions of the urban environment are also often added to capture benefits associated with the marine environment. Blue infrastructure can support unique aquatic biodiversity in urban areas, including aquatic insects, amphibians, and water birds. There may considerable co-benefits to the health and wellbeing of populations with access to blue spaces in the urban context. Accessible blue infrastructure in urban areas is also referred as to blue spaces. | 1 | Applied and Interdisciplinary Chemistry |
To neglect the influences by hydrodynamic instabilities such as Darrieus–Landau instability, Rayleigh–Taylor instability etc., the analysis usually neglects effects due to the thermal expansion of the gas mixture by assuming a constant density model. Such an approximation is referred to as diffusive-thermal approximation or thermo-diffusive approximation which was first introudced by Grigory Barenblatt, Yakov Zeldovich and A. G. Istratov in 1962. With a one-step chemistry model and assuming the perturbations to a steady planar flame in the form , where is the transverse coordinate system perpendicular to flame, is the time, is the perturbation wavevector and is the temporal growth rate of the disturbance, the dispersion relation for one-reactant flames is given implicitly by
where , , is the Lewis number of the fuel and is the Zeldovich number. This relation provides in general three roots for in which the one with maximum would determine the stability character. The stability margins are given by the following equations
describing two curves in the vs. plane. The first curve is associated with condition , whereas on the second curve The first curve separates the region of stable mode from the region corresponding to cellular instability, whereas the second condition indicates the presence of traveling and/or pulsating instability. | 1 | Applied and Interdisciplinary Chemistry |
The reaction steps are reversible reactions and the reaction is driven to completion by removal of water e.g. by azeotropic distillation, molecular sieves or titanium tetrachloride. Primary amines react through an unstable hemiaminal intermediate which then splits off water.
Secondary amines do not lose water easily because they do not have a proton available and instead they often react further to an aminal:
or when an α-carbonyl proton is present to an enamine:
In acidic environment the reaction product is an iminium salt by loss of water.
This reaction type is found in many Heterocycle preparations for example the Povarov reaction and the Friedländer-synthesis to quinolines. | 0 | Theoretical and Fundamental Chemistry |
* From Small Disturbances
: (subsonic)
* From Divergence Theorem
* Let Velocity U be a twice continuously differentiable function in a region of volume V in space. This function is the stream function .
* Let P be a point in the volume V
* Let S be the surface boundary of the volume V.
* Let Q be a point on the surface S, and .
As Q goes from inside V to the surface of V,
* Therefore:
For :, where the surface normal points inwards.
This equation can be broken down into both a source term and a doublet term.
The Source Strength at an arbitrary point Q is:
The Doublet Strength at an arbitrary point Q is:
The simplified potential flow equation is:
With this equation, along with applicable boundary conditions, the potential flow problem may be solved. | 1 | Applied and Interdisciplinary Chemistry |
Iron minerals can active for dechlorination. These minerals use . Particular minerals that can be used include green rust, magnetite, pyrite, and glauconite. The most reactive of the iron minerals are the iron sulfides and oxides. Pyrite, an iron sulfide, is able to dechlorinate carbon tetrachloride in suspension. | 1 | Applied and Interdisciplinary Chemistry |
In the study of the structure of mercury b- , lead- and organotin derivatives of nitrosophenols, Nesmeyanov discovered the phenomenon of metallotropy, that is, a special tautomerism in which a reversible transfer of an organometallic group occurs. Joint studies by A. N. Nesmeyanov and I. F. Lutsenko discovered heteroatomic tautomerism (between carbon and oxygen atoms) in keto-enol systems of tin , o- and germanium compounds. Nesmeyanov, together with Yu. A. and N. A. Ustynyuk, discovered a new type of metallotropy: it was found that in fluorenylchromium tricarbonyl anions, η 6 -complexes are equilibrium and reversibly isomerized into η 5 -complexes. | 0 | Theoretical and Fundamental Chemistry |
Emeléus was born in Poplar, London on 22 June 1903, the son of Karl Henry Emeléus (1869–1948), a pharmacist who was born in Vaasa, Finland. The family moved to the Old Pharmacy in Battle, Sussex shortly after Emeléus was born. His elder brother Karl George Emeléus (1901–1989) went on to become professor of physics at the Queen's University of Belfast.
Emeléus was educated at St Leonards Collegiate School, Hastings, and Hastings Grammar School followed by the Royal College of Science, Imperial College, London, graduating in 1923. He gained his PhD in 1926 and a DSc three years later. During his post-graduate studies he spent time at the University of Karlsruhe as a student of Alfred Stock and two years at Princeton University with Professor Hugh Stott Taylor. Among his many students and research colleagues, notable are Norman Greenwood, Ken McTaggart and F. Gordon A. Stone. | 0 | Theoretical and Fundamental Chemistry |
The VICARTE – Vidro e Cerâmica para as Artes (Glass and Ceramic for the Arts) is a research unit composed of the Faculty of Sciences and Technology of the Universidade Nova de Lisboa and the Faculty of Fine Arts of the Universidade de Lisboa which works to further the research of glass and ceramics. In partnership with cultural heritage institutions across the country, they offer a Master's program in Glass and Ceramic Art and Science with an interdisciplinary approach to the coursework. | 0 | Theoretical and Fundamental Chemistry |
Like its counterpart, RB-E2F, the DREAM complex is also affected by similar growth stimuli and subsequent cyclin-CDK activity. Increasing cyclin D-CDK4 and cyclin E-CDK2 activity dissociates the DREAM complex from the promoter by phosphorylation of p130. Hyper-phosphorylated p130 is subsequently degraded and E2F4 exported from the nucleus. Once the repressive E2Fs are vacated, activating E2Fs bind to the promoter to up-regulate G1/S genes that promote DNA synthesis and transition of the cell cycle. BMYB is also up-regulated during this time, which then binds to genes that peak at G2/M phase. Binding of BMYB to late cell cycle genes is dependent on its association with the MuvB core to form the BMYB-MuvB complex, which is then able to up-regulate genes in the G2/M phase. | 1 | Applied and Interdisciplinary Chemistry |
Thiolactones can be prepared by dehydration of thiol-containing carboxylic acids. Thiolactones can be hydrolyzed back to the thiol acids under basic conditions. β-Thiolactones can be opened by reaction at the 4-position via S2 nucleophilic reactions. | 0 | Theoretical and Fundamental Chemistry |
The availability of phosphorus in an ecosystem is restricted by the rate of release of this element during weathering. The release of phosphorus from apatite dissolution is a key control on ecosystem productivity. The primary mineral with significant phosphorus content, apatite [Ca(PO)OH] undergoes carbonation.
Little of this released phosphorus is taken up by biota (organic form), whereas a larger proportion reacts with other soil minerals. This leads to precipitation into unavailable forms in the later stage of weathering and soil development. Available phosphorus is found in a biogeochemical cycle in the upper soil profile, while phosphorus found at lower depths is primarily involved in geochemical reactions with secondary minerals. Plant growth depends on the rapid root uptake of phosphorus released from dead organic matter in the biochemical cycle. Phosphorus is limited in supply for plant growth. Phosphates move quickly through plants and animals; however, the processes that move them through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest biogeochemical cycles.
Low-molecular-weight (LMW) organic acids are found in soils. They originate from the activities of various microorganisms in soils or may be exuded from the roots of living plants. Several of those organic acids are capable of forming stable organo-metal complexes with various metal ions found in soil solutions. As a result, these processes may lead to the release of inorganic phosphorus associated with aluminum, iron, and calcium in soil minerals. The production and release of oxalic acid by mycorrhizal fungi explain their importance in maintaining and supplying phosphorus to plants.
The availability of organic phosphorus to support microbial, plant and animal growth depends on the rate of their degradation to generate free phosphate. There are various enzymes such as phosphatases, nucleases and phytase involved for the degradation. Some of the abiotic pathways in the environment studied are hydrolytic reactions and photolytic reactions. Enzymatic hydrolysis of organic phosphorus is an essential step in the biogeochemical phosphorus cycle, including the phosphorus nutrition of plants and microorganisms and the transfer of organic phosphorus from soil to bodies of water. Many organisms rely on the soil derived phosphorus for their phosphorus nutrition. | 0 | Theoretical and Fundamental Chemistry |
PTEN is a tumor suppressor that inhibits the PI3K/AKT pathway. PTEN inhibitors, such as bisperoxovanadium, can enhance the PI3K/AKT pathway to promote cell migration, survival and proliferation. While there are some concerns over possible cell cycle dysregulation and tumorigenesis, temporary and moderate PTEN inhibition may confer neuroprotection against traumatic brain injury and improve CNS recovery by reestablishing lost connections by axonogenesis. Medicinal value of PTEN inhibitors remains to be determined. | 1 | Applied and Interdisciplinary Chemistry |
Modafinil is generally well-tolerated but can have potential risks and side effects. Common adverse effects of modafinil, experienced by less than 10% of users, include headaches, nausea, and reduced appetite. Anxiety, insomnia, dizziness, diarrhea, and rhinitis are also reported in 5% to 10% of users. Psychiatric reactions have occurred in individuals with and without a preexisting psychiatric history.
No significant changes in body weight have been observed in clinical trials, although decreased appetite and weight loss have been noted in children and adolescents. Modafinil can cause a slight increase in aminotransferase enzymes, indicative of liver function, but there is no evidence of serious liver damage when levels are within reference ranges.
Rare but serious adverse effects include severe skin rashes and allergy-related symptoms. Between December 1998 and January 2007, the FDA received reports of six cases of severe cutaneous adverse reactions, including erythema multiforme, Stevens–Johnson syndrome, toxic epidermal necrolysis, and DRESS syndrome. The FDA has issued alerts regarding these risks and also noted reports of angioedema and multi-organ hypersensitivity reactions in postmarketing surveillance. In 2007, the FDA required Cephalon to modify the Provigil leaflet to include warnings about these serious conditions. The long-term safety and effectiveness of modafinil have not been conclusively established.
The FDA does not endorse modafinil for children's medical conditions due to an increased risk of rare but serious dermatological toxicity (Stevens–Johnson syndrome). However, in Europe, modafinil may be prescribed for treating narcolepsy in children. | 0 | Theoretical and Fundamental Chemistry |
Lactic acid fermentation is used in many areas of the world to produce foods that cannot be produced through other methods. The most commercially important genus of lactic acid-fermenting bacteria is Lactobacillus, though other bacteria and even yeast are sometimes used. Two of the most common applications of lactic acid fermentation are in the production of yogurt and sauerkraut. | 1 | Applied and Interdisciplinary Chemistry |
The non-dimensional energy equation for fluid flow in a boundary layer can simplify to the following, when heating from viscous dissipation and heat generation can be neglected:
Where and are the velocities in the x and y directions respectively normalized by the free stream velocity, and are the x and y coordinates non-dimensionalized by a relevant length scale, is the Reynolds number, is the Prandtl number, and is the non-dimensional temperature, which is defined by the local, minimum, and maximum temperatures:
The non-dimensional species transport equation for fluid flow in a boundary layer can be given as the following, assuming no bulk species generation:
Where is the non-dimensional concentration, and is the Schmidt number.
Transport of heat is driven by temperature differences, while transport of species is due to concentration differences. They differ by the relative diffusion of their transport compared to the diffusion of momentum. For heat, the comparison is between viscous diffusivity () and thermal diffusion (), given by the Prandtl number. Meanwhile for mass transfer, the comparison is between viscous diffusivity () and mass Diffusivity (), given by the Schmidt number.
In some cases direct analytic solutions can be found from these equations for the Nusselt and Sherwood numbers. In cases where experimental results are used, one can assume these equations underlie the observed transport.
At an interface, the boundary conditions for both equations are also similar. For heat transfer at an interface, the no-slip condition allows us to equate conduction with convection, thus equating Fouriers law and Newtons law of cooling:
Where q” is the heat flux, is the thermal conductivity, is the heat transfer coefficient, and the subscripts and compare the surface and bulk values respectively.
For mass transfer at an interface, we can equate Ficks Law with Newtons law for convection, yielding:
Where is the mass flux [kg/s ], is the diffusivity of species a in fluid b, and is the mass transfer coefficient. As we can see, and are analogous, and are analogous, while and are analogous. | 1 | Applied and Interdisciplinary Chemistry |
Dendrimers have been prepared via click chemistry, employing Diels-Alder reactions, thiol-ene and thiol-yne reactions and azide-alkyne reactions.
There are ample avenues that can be opened by exploring this chemistry in dendrimer synthesis. | 0 | Theoretical and Fundamental Chemistry |
The set of strategies that comprise biosorption, bioaccumulation and biomineralization are closely related to each other, because one way or another have a direct contact between the cell and radionuclide. These mechanisms are evaluated accurately using advanced analysis technologies such as electron microscopy, X-ray diffraction and XANES, EXAFS and X-ray spectroscopies.
Biosorption and bioaccumulation are two metabolic actions that are based on the ability to concentrate radionuclides over a thousand times the concentration of the environment. They consist of complexation of radioactive waste with phosphates, organic compounds and sulfites so that they become insoluble and less exposed to radiotoxicity. They are particularly useful in biosolids for agricultural purposes and soil amendments, although most properties of these biosolids are unknown.
Biosorption method is based on passive sequestration of positively charged radioisotopes by lipopolysaccharides (LPS) on the cell membrane (negatively charged), either live or dead bacteria. Its efficiency is directly related to the increase in temperature and can last for hours, being a much faster method than direct bioreduction. It occurs through the formation of slimes and capsules, and with a preference for binding to the phosphate and phosphoryl groups (although it also occurs with carboxyl, amine or sulfhydryl groups). Bacillota and other bacteria like Citrobacter freudii have significant biosorption capabilities; Citrobacter does it through electrostatic interaction of uranium with phosphates of their LPS.
Quantitative analyzes determine that, in the case of uranium, biosorption may vary within a range between 45 and 615 milligrams per gram of cell dry weight. However, it is a technique that requires a high amount of biomass to affect bioremediation; it presents problems of saturation and other cations that compete for binding to the bacterial surface.
Bioaccumulation refers to uptake of radionuclides into the cell, where they are retained by complexations with negatively charged intracellular components, precipitation or granules formations. Unlike biosorption, this is an active process: it depends on an energy-dependent transport system. Some metals or radionuclides can be absorbed by bacteria accidentally because of its resemblance to dietary elements for metabolic pathways. Several radioisotopes of strontium, for example, are recognized as analogs of calcium and incorporated within Micrococcus luteus. Uranium, however, has no known function and is believed that its entry into the cell interior may be due to its toxicity (it is able to increase membrane permeability).
Furthermore, biomineralization —also known as bioprecipitation— is the precipitation of radionuclides through the generation of microbial ligands, resulting in the formation of stable biogenic minerals. These minerals have a very important role in the retention of radioactive contaminants. A very localized and produced enzymatically ligand concentration is involved and provides a nucleation site for the onset of biomineral precipitation. This is particularly relevant in precipitations of phosphatase activity-derivate biominerals, which cleavage molecules such as glycerol phosphate on periplasm. In Citrobacter and Serratia genera, this cleavage liberates inorganic phosphates (HPO) that precipitates with uranyl ion (UO) and cause deposition of polycrystalline minerals around the cell wall. Serratia also form biofilms that promote precipitation of chernikovite (rich in uranium) and additionally, remove up to 85% of cobalt-60 and 97% of cesium-137 by proton substitution of this mineral. In general, biomineralization is a process in which the cells do not have limitations of saturation and can accumulate up to several times its own weight as precipitated radionuclides.
Investigations of terrestrial and marine bacterial isolates belonging to the genera Aeromonas, Bacillus, Myxococcus, Pantoea, Pseudomonas, Rahnella and Vibrio have also demonstrated the removal of uranium radioisotopes as phosphate biominerals in both oxic and anoxic growth conditions. | 1 | Applied and Interdisciplinary Chemistry |
Contributors to the field of fluid dynamics in turn come from a wide array of fields, and in addition to their other titles, each is also a fluid dynamicist. Following is a list of notable fluid dynamicists: | 1 | Applied and Interdisciplinary Chemistry |
Ion-exchange chromatography separates molecules based on their respective charged groups. Ion-exchange chromatography retains analyte molecules on the column based on coulombic (ionic) interactions. The ion exchange chromatography matrix consists of positively and negatively charged ions. Essentially, molecules undergo electrostatic interactions with opposite charges on the stationary phase matrix. The stationary phase consists of an immobile matrix that contains charged ionizable functional groups or ligands. The stationary phase surface displays ionic functional groups (R-X) that interact with analyte ions of opposite charge. To achieve electroneutrality, these immobilized charges couple with exchangeable counterions in the solution. Ionizable molecules that are to be purified, compete with these exchangeable counterions, for binding to the immobilized charges on the stationary phase. These ionizable molecules are retained or eluted based on their charge. Initially, molecules that do not bind or bind weakly to the stationary phase are first to be washed away. Altered conditions are needed for the elution of the molecules that bind to the stationary phase. The concentration of the exchangeable counterions, which competes with the molecules for binding, can be increased, or the pH can be changed to affect the ionic charge of the eluent or the solute. A change in pH affects the charge on the particular molecules and, therefore, alter their binding. When reducing the net charge of the solute's molecules, they start eluting out. This way, such adjustments can be used to release the proteins of interest. Additionally, concentration of counterions can be gradually varied to affect the retention of the ionized molecules, thus separate them. This type of elution is called gradient elution. On the other hand, step elution can be used, in which the concentration of counterions are varied in steps. This type of chromatography is further subdivided into cation exchange chromatography and anion-exchange chromatography. Positively charged molecules bind to cation exchange resins, while negatively charged molecules bind to anion exchange resins. The ionic compound consisting of the cationic species M+ and the anionic species B− can be retained by the stationary phase.
Cation exchange chromatography retains positively charged cations because the stationary phase displays a negatively charged functional group:
Anion exchange chromatography retains anions using positively charged functional group:
Note that the ion strength of either C+ or A− in the mobile phase can be adjusted to shift the equilibrium position, thus retention time.
The ion chromatogram shows a typical chromatogram obtained with an anion exchange column. | 0 | Theoretical and Fundamental Chemistry |
Chromatographic peak resolution is given by
where t is the retention time and w is the peak width at baseline. Here compound 1 elutes before compound 2.
If the peaks have the same width | 0 | Theoretical and Fundamental Chemistry |
Buddhist atomism is a school of atomistic Buddhist philosophy that flourished on the Indian subcontinent during two major periods. During the first phase, which began to develop prior to the 6th century CE, Buddhist atomism had a very qualitative, Aristotelian-style atomic theory. This form of atomism identifies four kinds of atoms, corresponding to the standard elements. Each of these elements has a specific property, such as solidity or motion, and performs a specific function in mixtures, such as providing support or causing growth. Like the Hindus and Jains, the Buddhists were able to integrate a theory of atomism with their logical presuppositions.
According to Noa Ronkin, this kind of atomism was developed in the Sarvastivada and Sautrantika schools for whom material reality can be: The second phase of Buddhist atomism, which flourished in the 7th century CE, was very different from the first. Indian Buddhist philosophers, including Dharmakirti and Dignāga, considered atoms to be point-sized, durationless, and made of energy. In discussing Buddhist atomism, Stcherbatsky writes: | 1 | Applied and Interdisciplinary Chemistry |
CeCoIn ("Cerium-Cobalt-Indium 5") is a heavy-fermion superconductor with a layered crystal structure, with somewhat two-dimensional electronic transport properties. The critical temperature of 2.3 K is the highest among all of the Ce-based heavy-fermion superconductors. | 1 | Applied and Interdisciplinary Chemistry |
Esmirtazapine (ORG-50,081) is a tetracyclic antidepressant drug that was under development by Organon for the treatment of insomnia and vasomotor symptoms (e.g., hot flashes) associated with menopause. Esmirtazapine is the (S)-(+)-enantiomer of mirtazapine and possesses similar overall pharmacology, including inverse agonist actions at H and 5-HT receptors and antagonist actions at α-adrenergic receptors.
Notably, esmirtazapine has a shorter half life of around 10 hours, compared to R-mirtazapine and racemic mixture, which has a half-life of 18–40 hours. Merck has run several studies on low dose (3–4.5 mg) esmirtazapine for the treatment of insomnia. It is attractive for treating insomnia since it is a potent H-inhibitor and a 5-HT antagonist. Unlike low-dose mirtazapine, the half life (10 hours) is short enough that next-day sedation may be manageable, however, for people with CYP2D6 polymorphisms, which constitute a sizable fraction of the population, the half-life is expected to be quite a bit longer. Merck researchers claimed that the incidence of next-day sedation was not a problem in one of their studies, but this claim has been challenged (15% of patients complained of daytime sleepiness vs 3.5% in the placebo group).
In March 2010, Merck terminated its internal clinical development program for esmirtazapine for hot flashes and insomnia, "for strategic reasons". | 0 | Theoretical and Fundamental Chemistry |
Radionuclides are incorporated either into compounds normally used by the body such as glucose (or glucose analogues), water, or ammonia, or into molecules that bind to receptors or other sites of drug action. Such labelled compounds are known as radiotracers. PET technology can be used to trace the biologic pathway of any compound in living humans (and many other species as well), provided it can be radiolabeled with a PET isotope. Thus, the specific processes that can be probed with PET are virtually limitless, and radiotracers for new target molecules and processes are continuing to be synthesized. As of this writing there are already dozens in clinical use and hundreds applied in research. In 2020 by far the most commonly used radiotracer in clinical PET scanning is the carbohydrate derivative FDG. This radiotracer is used in essentially all scans for oncology and most scans in neurology, thus makes up the large majority of radiotracer (>95%) used in PET and PET-CT scanning.
Due to the short half-lives of most positron-emitting radioisotopes, the radiotracers have traditionally been produced using a cyclotron in close proximity to the PET imaging facility. The half-life of fluorine-18 is long enough that radiotracers labeled with fluorine-18 can be manufactured commercially at offsite locations and shipped to imaging centers. Recently rubidium-82 generators have become commercially available. These contain strontium-82, which decays by electron capture to produce positron-emitting rubidium-82.
The use of positron-emitting isotopes of metals in PET scans has been reviewed, including elements not listed above, such as lanthanides. | 1 | Applied and Interdisciplinary Chemistry |
Ionic micelles are typically very affected by the salt concentration. In ionic micelles the monomers are typically fully ionized, but the high electric field strength at the surface of the micelles will cause adsorption of some proportion of the free counter-ions. In this case a chemical equilibrium process can be assumed between the charged micelles and its constituents, the bile salt monomers, and bound counter-ions :
where is the average aggregation number and is the average degree of counter-ion binding to the micelle. In this case, the Gibbs free energy is given by:
where is the Gibbs energy of micellization and is the free counter-ion concentration at CMC. For large , that is in the limit when then the micelles becomes a true macroscopic phase, the Gibbs free energy is usually approximated by: | 0 | Theoretical and Fundamental Chemistry |
The Salvinia effect defines surfaces which are able to permanently keep relatively thick air layers as a result of their hydrophobic chemistry, in combination with a complex architecture in nano- and microscopic dimensions.
This phenomenon was discovered during a systematic research on aquatic plants and animals by Wilhelm Barthlott and his colleagues at the University of Bonn between 2002 and 2007. Five criteria have been defined, they enable the existence of stable air layers under water and as of 2009 define the Salvinia effect: (1) hydrophobic surfaces chemistry in combination with (2) nanoscalic structures generate superhydrophobicity, (3) microscopic hierarchical structures ranging from a few mirco- to several millimeters with (4) undercuts and (5) elastic properties. Elasticity appears to be important for the compression of the air-layer in dynamic hydrostatic conditions. An additional optimizing criterion is the chemical heterogeneity of the hydrophilic tips (Salvinia Paradox). This is a prime example of a hierarchical structuring on several levels.
In plants and animals, air retaining salvinia effect surfaces are always fragmented in small compartments with a length of 0.5 to 8 cm and the borders are sealed against loss of air by particular microstructures. Compartments with sealed edges are also important for technical applications.
The working principle is illustrated in for the Giant Salvinia. The leaves of S. molesta are capable of keeping an air layer on its surfaces for a long time when submerged in water. If a leaf is pulled under water, the leaf surface shows a silvery shine. The distinctive feature of S. molesta lies in the long term stability. While the air layer on most hydrophobic surfaces vanishes shortly after submerging, S. molesta is able to stabilize the air for several days to several weeks. The time span is thereby just limited by the lifetime of the leaf.
The high stability is a consequence of a seemingly paradoxical combination of a superhydrophobic (extremely water repellent) surface with hydrophilic (water attractive) patches on the tips of the structures.
When submerged under water, no water can penetrate the room between the hairs due to the hydrophobic character of the surfaces. However, the water is pinned to the tip of each hair by the four wax free (hydrophilic) end cells. This fixation results in a stabilization of the air layer under water. The principle is shown in the figure.
Two submerged, air retaining surfaces are schematically shown: on the left hand side: a hydrophobic surface. On the right hand side: a hydrophobic surface with hydrophilic tips.
If negative pressure is applied, a bubble is quickly formed on the purely hydrophobic surfaces (left) stretching over several structures. With increasing negative pressure the bubble grows and can detach from the surface. The air bubble rises to the surface and the air layer decreases until it vanishes completely.
In case of the surface with hydrophilic anchor cells (right) the water is pinned to the tips of every structure by the hydrophilic patch on top. These linkages allow the formation of a bubble stretching over several structures; bubble release is suppressed because several links have to be broken first. This results in a higher energy input for the bubble formation. Therefore, an increased negative pressure is needed to form a bubble able to detach from the surface and rise upwards. | 0 | Theoretical and Fundamental Chemistry |
Fat suppression is useful for example to distinguish active inflammation in the intestines from fat deposition such as can be caused by long-standing (but possibly inactive) inflammatory bowel disease, but also obesity, chemotherapy and celiac disease. Without fat suppression techniques, fat and fluid will have similar signal intensities on fast spin-echo sequences.
Techniques to suppress fat on MRI mainly include:
* Identifying fat by the chemical shift of its atoms, causing different time-dependent phase shifts compared to water.
* Frequency-selective saturation of the spectral peak of fat by a "fat sat" pulse before imaging.
* Short tau inversion recovery (STIR), a T1-dependent method
* Spectral presaturation with inversion recovery (SPIR) | 0 | Theoretical and Fundamental Chemistry |
was a Japanese organic chemist and marine biologist, and professor emeritus at Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts and Boston University School of Medicine. He was awarded the Nobel Prize in Chemistry in 2008 for the discovery and development of green fluorescent protein (GFP) with two American scientists: Martin Chalfie of Columbia University and Roger Tsien of the University of California-San Diego. | 0 | Theoretical and Fundamental Chemistry |
A plasmid is a double stranded circular DNA molecule commonly used for molecular cloning. Plasmids are generally 2 to 4 kilobase-pairs (kb) in length and are capable of carrying inserts up to 15kb. Plasmids contain an origin of replication allowing them to replicate inside a bacterium independently of the host chromosome. Plasmids commonly carry a gene for antibiotic resistance that allows for the selection of bacterial cells containing the plasmid. Many plasmids also carry a reporter gene that allows researchers to distinguish clones containing an insert from those that do not. | 1 | Applied and Interdisciplinary Chemistry |
The expression of tides as a bounded Kelvin wave is well observable in enclosed shelf seas around the world (e.g. the English channel, the North Sea or the Yellow sea). Animation 1 shows the behaviour of a simplified case of a Kelvin wave in an enclosed shelf sea for the case with (lower panel) and without friction (upper panel). The shape of an enclosed shelf sea is represented as a simple rectangular domain in the Northern Hemisphere which is open on the left hand side and closed on the right hand side. The tidal wave, a Kelvin wave, enters the domain in the lower left corner and travels to the right with the coast on its right. The sea surface height (SSH, left panels of animation 1), the tidal elevation, is maximum at the coast and decreases towards the centre of the domain. The tidal currents (right panels of animation 1) are in the direction of wave propagation under the crest and in the opposite direction under the through. They are both maximum under the crest and the trough of the waves and decrease towards the centre. This was expected as the equations for and are in phase as they both depend on the same arbitrary function describing the wave motion and exponential decay term.
On the enclosed right hand side, the Kelvin wave is reflected and because it always travels with the coast on its right, it will now travel in the opposite direction. The energy of the incoming Kelvin wave is transferred through Poincare waves along the enclosed side of the domain to the outgoing Kelvin wave. The final pattern of the SSH and the tidal currents is made up of the sum of the two Kelvin waves. These two can amplify each other and this amplification is maximum when the length of the shelf sea is a quarter wavelength of the tidal wave. Next to that, the sum of the two Kelvin waves result in several static minima's in the centre of the domain which hardly experience any tidal motion, these are called Amphidromic points. In the upper panel of figure 2, the absolute time averaged SSH is shown in red shading and the dotted lines show the zero tidal elevation level at roughly hourly intervals, also known as cotidal lines. Where these lines intersect the tidal elevation is zero during a full tidal period and thus this is the location of the Amphidromic points.
In the real world, the reflected Kelvin wave has a lower amplitude due to energy loss as a result of friction and through the transfer via Poincare waves (lower left panel of animation 1). The tidal currents are proportional to the wave amplitude and therefore also decrease on the side of the reflected wave (lower right panel of animation 1). Finally, the static minima's are no longer in the centre of the domain as wave amplitude is no longer symmetric. Therefore, the Amphidromic points shift towards the side of the reflected wave (lower panel figure 2).
The dynamics of a tidal Kelvin wave in enclosed shelf sea is well manifested and studied in the North Sea. | 1 | Applied and Interdisciplinary Chemistry |
PCR works readily with a DNA template of up to two to three thousand base pairs in length. However, above this size, product yields often decrease, as with increasing length stochastic effects such as premature termination by the polymerase begin to affect the efficiency of the PCR. It is possible to amplify larger pieces of up to 50,000 base pairs with a slower heating cycle and special polymerases. These are polymerases fused to a processivity-enhancing DNA-binding protein, enhancing adherence of the polymerase to the DNA.
Other valuable properties of the chimeric polymerases [http://www.fidelitysystems.com/TopoTaq.html TopoTaq] and PfuC2 include enhanced thermostability, specificity and resistance to contaminants and inhibitors. They were engineered using the unique helix-hairpin-helix (HhH) DNA binding domains of topoisomerase V from hyperthermophile Methanopyrus kandleri. Chimeric polymerases overcome many limitations of native enzymes and are used in direct PCR amplification from cell cultures and even food samples, thus by-passing laborious DNA isolation steps. A robust strand-displacement activity of the hybrid TopoTaq polymerase helps solve PCR problems that can be caused by hairpins and G-loaded double helices. Helices with a high G-C content possess a higher melting temperature, often impairing PCR, depending on the conditions. | 1 | Applied and Interdisciplinary Chemistry |
A blank value in analytical chemistry is a measurement of a blank. The reading does not originate from a sample, but the matrix effects, reagents and other residues. These contribute to the sample value in the analytical measurement and therefore have to be subtracted.
The limit of blank is defined by the Clinical And Laboratory Standards Institute as the highest apparent analyte concentration expected to be found when replicates of a sample containing no analyte are tested. | 0 | Theoretical and Fundamental Chemistry |
In the region known as the viscous sublayer, below 5 wall units, the variation of to is approximately 1:1, such that:
:For
where,
This approximation can be used farther than 5 wall units, but by the error is more than 25%. | 1 | Applied and Interdisciplinary Chemistry |
The dehydration theory explains why mucoadhesion can arise rapidly. When two gels capable of rapid gelation in an aqueous environment are brought into contact, movement occurs between the two gels until a state of equilibrium is reached. Gels associated with a strong affinity for water will have high osmotic pressures and large swelling forces. The difference in osmotic pressure when these gels contact mucus gels will draw water into the formulation and quickly dehydrate the mucus gel, forcing intermixing and consolidation until equilibrium results.
This mixture of formulation and mucus can increase contact time with the mucous membrane, leading to the consolidation of the adhesive bond. However, the dehydration theory does not apply to solid formulations or highly hydrated forms. | 1 | Applied and Interdisciplinary Chemistry |
By the historical periods of the Pharaohs in Egypt, the Vedic Kings in India, the Tribes of Israel, and the Maya civilization in North America, among other ancient populations, precious metals began to have value attached to them. In some cases rules for ownership, distribution, and trade were created, enforced, and agreed upon by the respective peoples. By the above periods metalworkers were very skilled at creating objects of adornment, religious artifacts, and trade instruments of precious metals (non-ferrous), as well as weaponry usually of ferrous metals and/or alloys. These skills were well executed. The techniques were practiced by artisans, blacksmiths, atharvavedic practitioners, alchemists, and other categories of metalworkers around the globe. For example, the granulation technique was employed by numerous ancient cultures before the historic record shows people traveled to far regions to share this process. Metalsmiths today still use this and many other ancient techniques.
As time progressed, metal objects became more common, and ever more complex. The need to further acquire and work metals grew in importance. Skills related to extracting metal ores from the earth began to evolve, and metalsmiths became more knowledgeable. Metalsmiths became important members of society. Fates and economies of entire civilizations were greatly affected by the availability of metals and metalsmiths. The metalworker depends on the extraction of precious metals to make jewelry, build more efficient electronics, and for industrial and technological applications from construction to shipping containers to rail, and air transport. Without metals, goods and services would cease to move around the globe on the scale we know today. | 1 | Applied and Interdisciplinary Chemistry |
Photobiology is the scientific study of the beneficial and harmful interactions of non-ionizing radiation in living organisms, conventionally demarcated around 10 eV, the first ionization energy of oxygen. UV ranges roughly from 3 to 30 eV in energy. Hence photobiology entertains some, but not all, of the UV spectrum. | 0 | Theoretical and Fundamental Chemistry |
In 2020, the FDA granted orphan drug designation RT001 for the treatment of patients with progressive supranuclear palsy (PSP). PSP is a disease involving modification and dysfunction of tau protein; RT001's mechanism of action both lowers lipid peroxidation and prevents mitochondrial cell death of neurons which is associated with disease onset and progression. | 1 | Applied and Interdisciplinary Chemistry |
The contact stage is the initial wetting that occurs between the adhesive and membrane. This can occur mechanically by bringing together the two surfaces, or through the bodily systems, like when particles are deposited in the nasal cavity by inhalation. The principles of initial adsorption of small molecule adsorbates can be described by DLVO theory. | 1 | Applied and Interdisciplinary Chemistry |
One can characterise a surface that has undergone certain finishing operations by three main properties of: roughness, waviness, and fractal dimension. Among these, roughness and fractality are of most importance, with roughness often indicated in terms of a rms value, and surface fractality denoted generally by D. The effect of surface structures on thermal conductivity at interfaces is analogous to the concept of electrical contact resistance, also known as ECR, involving contact patch restricted transport of phonons rather than electrons. | 0 | Theoretical and Fundamental Chemistry |
In addition to being manipulated for medical and energy applications, capillary pressure is the cause behind various natural phenomena as well. For example, needle ice, seen in cold soil, occurs via capillary action. The first major contributions to the study of needle ice, or simply, frost heaving were made by Stephen Taber (1929) and Gunnar Beskow (1935), who independently aimed to understand soil freezing. Taber’s initial work was related to understanding how the size of pores within the ground influenced the amount of frost heave. He also discovered that frost heave is favorable for crystal growth and that a gradient of soil moisture tension drives water upward toward the freezing front near the top of the ground. In Beskow’s studies, he defined this soil moisture tension as “capillary pressure” (and soil water as “capillary water”). Beskow determined that the soil type and effective stress on the soil particles influenced frost heave, where effective stress is the sum of pressure from above ground and the capillary pressure.
In 1961, D.H. Everett elaborated on Taber and Beskow’s studies to understand why pore spaces filled with ice continue to experience ice growth. He utilized thermodynamic equilibrium principles, a piston cylinder model for ice growth and the following equation to understand the freezing of water in porous media (directly applicable to the formation of needle ice):
where:
: is the pressure of the solid crystal
: is the pressure in the surrounding liquid
: is the interfacial tension between the solid and the liquid
: is the surface area of the phase boundary
: is the volume of the crystal
: is the mean curvature of the solid/liquid interface
With this equation and model, Everett noted the behavior of water and ice given different pressure conditions at the solid-liquid interface. Everett determined that if the pressure of the ice is equal to the pressure of the liquid underneath the surface, ice growth is unable to continue into the capillary. Thus, with additional heat loss, it is most favorable for water to travel up the capillary and freeze in the top cylinder (as needle ice continues to grow atop itself above the soil surface). As the pressure of the ice increases, a curved interface between the solid and liquid arises and the ice will either melt, or equilibrium will be reestablished so that further heat loss again leads to ice formation. Overall, Everett determined that frost heaving (analogous to the development of needle ice) occurs as a function of the pore size in the soil and the energy at the interface of ice and water. Unfortunately, the downside to Everett's model is that he did not consider soil particle effects on the surface. | 1 | Applied and Interdisciplinary Chemistry |
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