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Over 50 years ago, in a lab in France, Ephrussi, et al. discovered a non-Mendelian inherited factor that is essential to respiration in the yeast, Saccharomyces cerevisiae. S. cerevisiae without this factor, known as the ρ-factor, is described by the development of small colonies when compared to the wild-type yeast. These smaller colonies were dubbed petite colonies. These petite mutants were observed to be spontaneously produced naturally at a rate of 0.1%-1.0% every generation. They also found that treatment of wild-type S. cerevisiae with DNA-intercalating agents would more rapidly produce this mutation.
Schatz identified a region of the yeast's nuclear DNA that was associated with the mitochondria in 1964. Later, it was discovered that mutants without the ρ-factor had no mitochondrial DNA (called ρ isolates), or that they possessed a difference in density or amount of the mitochondrial DNA (called ρ isolates). The use of electron microscopy to view the DNA in the mitochondrial matrix helped to verify the actuality of the mitochondrial genome.
S. cerevisiae has since become a useful model for aging. It has been shown that as yeast ages, it loses functional mitochondrial DNA, which leads to replicative senescence, or the inability to further replicate. It has been suggested that there is a link between mitochondrial DNA loss and replicative life span (RLS), or the number of times a cell can reproduce before it dies, as it has been found that an increase in RLS is established with the same changes in the genome that enhance the propagation of cells that do not contain mitochondrial DNA. Genetic screens for replicative life span associated genes and pathways could be made easier and quicker by selecting genetic suppressors of the petite negative mutants. | 1 | Applied and Interdisciplinary Chemistry |
The first step to deriving the Grashof number is manipulating the volume expansion coefficient, as follows.
The in the equation above, which represents specific volume, is not the same as the in the subsequent sections of this derivation, which will represent a velocity. This partial relation of the volume expansion coefficient, , with respect to fluid density, , given constant pressure, can be rewritten as
where:
* is the bulk fluid density
* is the boundary layer density
* , the temperature difference between boundary layer and bulk fluid.
There are two different ways to find the Grashof number from this point. One involves the energy equation while the other incorporates the buoyant force due to the difference in density between the boundary layer and bulk fluid. | 1 | Applied and Interdisciplinary Chemistry |
Nevado joined the University of Zurich as an Assistant Professor in 2007. Her research has concentrated on catalysis and the development of selective, sustainable approaches to develop new materials. In particular, Nevado is interested in new approaches to construct C–C and C–X bonds based on transition metal catalysts. In 2011 Nevado was awarded a Starting Grant from the European Research Council to develop catalysts based on nature. These gold(I) and gold(III)-catalytic tools look to promote the synthesis of biologically relevant small molecules with high levels of stereocontrol. She was promoted to Professor in 2013. Nevado develops computational tools to study biological processes in an effort to understand cancer metastasis and progression.
She serves on the editorial board of the ACS Central Science and the advisory board of the Reaxys Doctoral Prize. | 0 | Theoretical and Fundamental Chemistry |
All elements aside from argon, neon, and helium form fluorides by direct reaction with fluorine. Chlorine is slightly more selective, but still reacts with most metals and heavier nonmetals. Following the usual trend, bromine is less reactive and iodine least of all. Of the many reactions possible, illustrative is the formation of gold(III) chloride by the chlorination of gold. The chlorination of metals is usually not very important industrially since the chlorides are more easily made from the oxides and hydrogen chloride. Where chlorination of inorganic compounds is practiced on a relatively large scale is for the production of phosphorus trichloride and disulfur dichloride. | 0 | Theoretical and Fundamental Chemistry |
Composite iron/bronze cannons were far less common, but were produced in substantial numbers during the Ming and Qing dynasties. The resulting bronze-iron composite cannons were superior to iron or bronze cannons in many respects. They were lighter, stronger, longer lasting, and able to withstand more intensive explosive pressure. Chinese artisans also experimented with other variants such as cannons featuring wrought iron cores with cast iron exteriors. While inferior to their bronze-iron counterparts, these were considerably cheaper and more durable than standard iron cannons. Both types were met with success and were considered "among the best in the world" during the 17th century. The Chinese composite metal casting technique was effective enough that Portuguese imperial officials sought to employ Chinese gunsmiths for their cannon foundries in Goa, so that they could impart their methods for Portuguese weapons manufacturing. The Gujarats experimented with the same concept in 1545, the English at least by 1580, and Hollanders in 1629. However the effort required to produce these weapons prevented them from mass production. The Europeans essentially treated them as experimental products, resulting in very few surviving pieces today. Of the currently known extant composite metal cannons, there are 2 English, 2 Dutch, 12 Gujarati, and 48 from the Ming-Qing period. | 1 | Applied and Interdisciplinary Chemistry |
Passive transport of ions across a membrane can take place by three main mechanisms: by ferrying, through defects in a disrupted membrane, or through a defined trajectory; these corresponds to ionophore, detergent, and ion channel transporters. While synthetic ion channel research attempts to prepare compounds that show conductance via a defined path, the elucidation of mechanism is difficult and seldom unambiguous. The two main methods of characterization both have their drawbacks, and as a consequence, often function is defined but mechanism presumed. | 0 | Theoretical and Fundamental Chemistry |
The 5' UTR of eukaryotes is more complex than prokaryotes. It contains a Kozak consensus sequence (ACCAUGG). This sequence contains the initiation codon. The initiation codon is the start site of translation into protein. | 1 | Applied and Interdisciplinary Chemistry |
Though polysaccharides are also biopolymers, it is not so common to talk of sequencing a polysaccharide, for several reasons. Although many polysaccharides are linear, many have branches. Many different units (individual monosaccharides) can be used, and bonded in different ways. However, the main theoretical reason is that whereas the other polymers listed here are primarily generated in a template-dependent manner by one processive enzyme, each individual join in a polysaccharide may be formed by a different enzyme. In many cases the assembly is not uniquely specified; depending on which enzyme acts, one of several different units may be incorporated. This can lead to a family of similar molecules being formed. This is particularly true for plant polysaccharides. Methods for the structure determination of oligosaccharides and polysaccharides include NMR spectroscopy and methylation analysis. | 1 | Applied and Interdisciplinary Chemistry |
Keplerates are cages that are similar to edge-transistive {Cu} MOFs with AX stoichiometry. In fact, they can be thought of as metal-organic polyhedra. These cages are quite different than the types previously discussed as they are much larger, and contain many cavities. Complexes with large diameters can be desirable as target guest molecules are becoming more large and complex. These cages have multiple shells, like an onion. Secondary building units such as dinuclear {Cu} acetate species are used as building blocks.
In the cage above, the outer shell is a cuboctohedron; its structure comes from two adjacent benzoate moieties from the m-BTEB ligand. The third benzoate is attached to the inner shell. The {Cu} units in the inner sphere adapt several different orientations. The labile complexes in the inner sphere allow binding of large target guests on the nanometer scale. Building a complex of this size that is still soluble is a challenge. | 0 | Theoretical and Fundamental Chemistry |
The mechanism(s) of photoinhibition are under debate, several mechanisms have been suggested. Reactive oxygen species, especially singlet oxygen, have a role in the acceptor-side, singlet oxygen and low-light mechanisms. In the manganese mechanism and the donor side mechanism, reactive oxygen species do not play a direct role. Photoinhibited PSII produces singlet oxygen, and reactive oxygen species inhibit the repair cycle of PSII by inhibiting protein synthesis in the chloroplast. | 0 | Theoretical and Fundamental Chemistry |
Runoff is analyzed by using mathematical models in combination with various water quality sampling methods. Measurements can be made using continuous automated water quality analysis instruments targeted on pollutants such as specific organic or inorganic chemicals, pH, turbidity etc. or targeted on secondary indicators such as dissolved oxygen. Measurements can also be made in batch form by extracting a single water sample and conducting any number of chemical or physical tests on that sample.
In the 1950s or earlier hydrology transport models appeared to calculate quantities of runoff, primarily for flood forecasting. Beginning in the early 1970s computer models were developed to analyze the transport of runoff carrying water pollutants, which considered dissolution rates of various chemicals, infiltration into soils and ultimate pollutant load delivered to receiving waters.
One of the earliest models addressing chemical dissolution in runoff and resulting transport was developed in the early 1970s under contract to the United States Environmental Protection Agency (EPA). This computer model formed the basis of much of the mitigation study that led to strategies for land use and chemical handling controls.
Increasingly, stormwater practitioners have recognized the need for Monte Carlo models to simulate stormwater processes because of natural variations in multiple variables that affect the quality and quantity of runoff. The benefit of the Monte Carlo analysis is not to decrease uncertainty in the input statistics, but to represent the different combinations of the variables that determine potential risks of water-quality excursions. One example of this type of stormwater model is the stochastic empirical loading and dilution model (SELDM) is a stormwater quality model. SELDM is designed to transform complex scientific data into meaningful information about the risk of adverse effects of runoff on receiving waters, the potential need for mitigation measures, and the potential effectiveness of such management measures for reducing these risks. SELDM provides a method for rapid assessment of information that is otherwise difficult or impossible to obtain because it models the interactions among hydrologic variables (with different probability distributions) that result in a population of values that represent likely long-term outcomes from runoff processes and the potential effects of different mitigation measures. SELDM also provides the means for rapidly doing sensitivity analyses to determine the potential effects of different input assumptions on the risks for water-quality excursions.
Other computer models have been developed (such as the DSSAM Model) that allow surface runoff to be tracked through a river course as reactive water pollutants. In this case the surface runoff may be considered to be a line source of water pollution to the receiving waters. | 1 | Applied and Interdisciplinary Chemistry |
As studies of the consequences of ocean acidification for marine organisms and ecosystems expanded rapidly over the past decade, the methods employed to evaluate the effects of expected future changes in ocean chemistry have become more sophisticated. Initial studies frequently involved measurements of the survival or physiological response of individuals of marine species to large changes in pCO2 or pH, while held in small containers under laboratory conditions. This approach increased the level of understanding of the effects of these environmental changes on individual species but provided little information concerning the response of natural assemblages of interacting species, in which the direct impacts of ocean acidification as well as their cascading indirect consequences (e.g. changes in the intensity of interaction strengths among predators or competitors) may be evident. Pelagic mesocosm experiments that examined the response of natural plankton communities to controlled pH perturbations helped move methods of ocean acidification research toward more comprehensive studies of whole communities and embedded processes under mostly natural conditions. The FOCE approach represents an analogous advance for benthic assemblages, by allowing examination of the direct effects of acidification on particular species, but also potential changes in interactions among species. Moreover, FOCE methods provide precise control of pH, while allowing many other parameters to vary naturally. Like mesocosm studies, FOCE methods exploit the advantages of studying a natural community under mostly natural ranges of environmental variability. | 0 | Theoretical and Fundamental Chemistry |
CFC-113 can be prepared from hexachloroethane and hydrofluoric acid:
This reaction may require catalysts such as antimony, chromium, iron and alumina at high temperatures.
Another synthesis method uses HF on tetrachloroethylene instead. | 1 | Applied and Interdisciplinary Chemistry |
Some physical constraints are usually incorporated in the calculations. For example, all the concentrations of free reactants and species must have positive values and association constants must have positive values.
With spectrophotometric data the calculated molar absorptivity (or emissivity) values should all be positive. Most computer programs do not impose this constraint on the calculations. | 0 | Theoretical and Fundamental Chemistry |
Targeted temperature management is used during open-heart surgery because it decreases the metabolic needs of the brain, heart, and other organs, reducing the risk of damage to them. The patient is given medication to prevent shivering. The body is then cooled to 25–32 °C (79–89 °F). The heart is stopped and an external heart-lung pump maintains circulation to the patient's body. The heart is cooled further and is maintained at a temperature below 15 °C (60 °F) for the duration of the surgery. This very cold temperature helps the heart muscle to tolerate its lack of blood supply during the surgery. | 1 | Applied and Interdisciplinary Chemistry |
In a simple reaction such as the isomerization:
there are two reactions to consider, the forward reaction in which the species A is converted into B and the backward reaction in which B is converted into A. If both reactions are elementary reactions, then the rate of reaction is given by
where is the rate constant for the forward reaction and is the rate constant for the backward reaction and the square brackets, , denote concentration. If only A is present at the beginning, time , with a concentration [A], the sum of the two concentrations, [A] and [B], at time , will be equal to [A].
The solution to this differential equation is
and is illustrated at the right. As time tends towards infinity, the concentrations [A] and [B] tend towards constant values. Let approach infinity, that is, , in the expression above:
In practice, concentration changes will not be measurable after Since the concentrations do not change thereafter, they are, by definition, equilibrium concentrations. Now, the equilibrium constant for the reaction is defined as
It follows that the equilibrium constant is numerically equal to the quotient of the rate constants.
In general they may be more than one forward reaction and more than one backward reaction. Atkins states that, for a general reaction, the overall equilibrium constant is related to the rate constants of the elementary reactions by | 0 | Theoretical and Fundamental Chemistry |
According to textbook knowledge, it is possible to transform a liquid continuously into a gas, without undergoing a phase transition, by heating and compressing strongly enough to go around the critical point. However, different criteria still allow to distinguish liquid-like and more gas-like states of a supercritical fluid. These criteria result in different boundaries in the pT plane. These lines emanate either from the critical point, or from the liquid–vapor boundary (boiling curve) somewhat below the critical point. They do not correspond to first or second order phase transitions, but to weaker singularities.
The Fisher–Widom line is the boundary between monotonic and oscillating asymptotics of the pair correlation function .
The Widom line is a generalization thereof, apparently so named by H. Eugene Stanley. However, it was first measured experimentally in 1956 by Jones and Walker, and subsequently named the hypercritical line by Bernal in 1964, who suggested a structural interpretation. The Frenkel line is a boundary between "rigid" and "non-rigid" fluids characterized by the onset of transverse sound modes.
One of the above mentioned criteria is based on the velocity autocorrelation function (vacf): below the Frenkel line the vacf demonstrates oscillatory behaviour, while above it the vacf monotonically decays to zero. The second criterion is based on the fact that at moderate temperatures liquids can sustain transverse excitations, which disappear upon heating. One further criterion is based on isochoric heat capacity measurements. The isochoric heat capacity per particle of a monatomic liquid near to the melting line is close to (where is the Boltzmann constant). The contribution to the heat capacity due to the potential part of transverse excitations is . Therefore at the Frenkel line, where transverse excitations vanish, the isochoric heat capacity per particle should be , a direct prediction from the phonon theory of liquid thermodynamics.
Another criterion for the Widom line is a peak in the isobaric heat capacity. In the subcritical region, the phase transition is associated with an effective spike in the heat capacity (i.e., the latent heat). Approaching the critical point, the latent heat falls to zero but this is accompanied by a gradual rise in heat capacity in the pure phases near phase transition. At the critical point, the latent heat is zero but the heat capacity shows a diverging singularity. Beyond the critical point, there is no divergence, but rather a smooth peak in the heat capacity; the highest point of this peak identifies the Widom line.
Anisimov et al. (2004), without referring to Frenkel, Fisher, or Widom, reviewed thermodynamic derivatives (specific heat, expansion coefficient, compressibility) and transport coefficients (viscosity, speed of sound) in supercritical water, and found pronounced extrema as function of pressure up to 100 K above T. | 0 | Theoretical and Fundamental Chemistry |
One of the more common cell-sorting systems makes use of flow cytometry through fluorescence imaging. In this method, a suspension of biologic cells is sorted into two or more containers, based upon specific fluorescent characteristics of each cell during an assisted flow. By using an electrical charge that the cell is "trapped" in, the cells are then sorted based on the fluorescence intensity measurements. The sorting process is undertaken by an electrostatic deflection system that diverts cells into containers based upon their charge.
In the optically actuated sorting process, the cells are flowed through into an optical landscape i.e. 2D or 3D optical lattices. Without any induced electrical charge, the cells would sort based on their intrinsic refractive index properties and can be re-configurability for dynamic sorting. An optical lattice can be created using diffractive optics and optical elements.
On the other hand, K. Ladavac et al. used a spatial light modulator to project an intensity pattern to enable the optical sorting process. K. Xiao and D. G. Grier applied holographic video microscopy to demonstrate that this technique can sort colloidal spheres with part-per-thousand resolution for size and refractive index.
The main mechanism for sorting is the arrangement of the optical lattice points. As the cell flow through the optical lattice, there are forces due to the particles drag force that is competing directly with the optical gradient force (See Physics of optical tweezers) from the optical lattice point. By shifting the arrangement of the optical lattice point, there is a preferred optical path where the optical forces are dominant and biased. With the aid of the flow of the cells, there is a resultant force that is directed along that preferred optical path. Hence, there is a relationship of the flow rate with the optical gradient force. By adjusting the two forces, one will be able to obtain a good optical sorting efficiency.
Competition of the forces in the sorting environment need fine tuning to succeed in high efficient optical sorting. The need is mainly with regards to the balance of the forces; drag force due to fluid flow and optical gradient force due to arrangement of intensity spot.
Scientists at the University of St. Andrews have received considerable funding from the UK Engineering and Physical Sciences Research Council (EPSRC) for an optical sorting machine. This new technology could rival the conventional fluorescence-activated cell sorting. | 1 | Applied and Interdisciplinary Chemistry |
The GLODAPv1.1 climatology contains analysed fields of "present day" (1990s) dissolved inorganic carbon (DIC), alkalinity, carbon-14 (C), CFC-11 and CFC-12. The fields consist of three-dimensional, objectively-analysed global grids at 1° horizontal resolution, interpolated onto 33 standardised vertical intervals from the surface (0 m) to the abyssal seafloor (5500 m). In terms of temporal resolution, the relative scarcity of the source data mean that, unlike the World Ocean Atlas, averaged fields are only produced for the annual time-scale. The GLODAP climatology is missing data in certain oceanic provinces including the Arctic Ocean, the Caribbean Sea, the Mediterranean Sea and Maritime Southeast Asia.
Additionally, analysis has attempted to separate natural from anthropogenic DIC, to produce fields of pre-industrial (18th century) DIC and "present day" anthropogenic . This separation allows estimation of the magnitude of the ocean sink for anthropogenic , and is important for studies of phenomena such as ocean acidification. However, as anthropogenic DIC is chemically and physically identical to natural DIC, this separation is difficult. GLODAP used a mathematical technique known as C* (C-star) to deconvolute anthropogenic from natural DIC (there are a number of alternative methods). This uses information about ocean biogeochemistry and surface disequilibrium together with other ocean tracers including carbon-14, CFC-11 and CFC-12 (which indicate water mass age) to try to separate out natural from that added during the ongoing anthropogenic transient. The technique is not straightforward and has associated errors, although it is gradually being refined to improve it. Its findings are generally supported by independent predictions made by dynamic models.
The GLODAPv2 climatology largely repeats the earlier format, but makes use of the large number of observations of the oceans carbon cycle made over the intervening period (2000–2013). The analysed "present-day" fields in the resulting dataset are normalised to year 2002. Anthropogenic carbon was estimated in GLODAPv2 using a "transit-time distribution" (TTD) method (an approach using a Greens function). In addition to updated fields of DIC (total and anthropogenic) and alkalinity, GLODAPv2 includes fields of seawater pH and calcium carbonate saturation state (Ω; omega). The latter is a non-dimensional number calculated by dividing the local carbonate ion concentration by the ambient saturation concentration for calcium carbonate (for the biomineral polymorphs calcite and aragonite), and relates to an oceanographic property, the carbonate compensation depth. Values of this below 1 indicate undersaturation, and potential dissolution, while values above 1 indicate supersaturation, and relative stability. | 0 | Theoretical and Fundamental Chemistry |
Similar to the development of flow at the entrance of the [http://альтернатив.рф/news/2017-12-29/raschet-konomicheskogo-ffekta-pri-primenenii-stekloplastikovykh- pipe], the flow velocity profile changes before the exit of a pipe. The exit length is much shorter than the entrance length, and is not significant at moderate to high Reynolds numbers.
Hydraulic exit length for laminar flows may be approximated as:
where
* is the exit length,
* is the pipe inner diameter, and
* is the Reynolds number. | 1 | Applied and Interdisciplinary Chemistry |
Proteins formed by the translation of the mRNA (messenger RNA, a coded information from DNA for protein synthesis) play a major role in regulating gene expression. To understand how they regulate gene expression it is necessary to identify DNA sequences that they interact with. Techniques have been developed to identify sites of DNA-protein interactions. These include ChIP-sequencing, CUT&RUN sequencing and Calling Cards. | 1 | Applied and Interdisciplinary Chemistry |
Thioamides are also a class of drugs that are used to control thyrotoxicosis.
Thioamides have been incorporated into peptides as isosteres for the amide bond. Peptide modifications are analogues of the native peptide, which can reveal the structure-activity relationship (SAR). Analogues of peptides can also be used as drugs with an improved oral bioavailability.
Thioamides inhibit the enzyme thyroid peroxidase in the thyroid, reducing the synthesis of triiodothyronine (T) and thyroxine (T), thereby blocking uptake of iodotyrosines from the colloid. They also block iodine release from peripheral hormone. Maximum effects occur only after a month, since hormone depletion is caused by reduced synthesis, which is a slow process. | 0 | Theoretical and Fundamental Chemistry |
Variations in iron isotopic composition have been observed in meteorite samples from other planetary bodies. The Moon has variations in iron isotopes of 0.4‰ per atomic mass unit. Mars has very small isotope fractionation of 0.001 ± 0.006‰ per atomic mass unit. Vesta has iron fractionations of 0.010 ± 0.010‰ per atomic mass unit. The chondritic reservoir exhibits fractionations of 0.069 ± 0.010‰ per atomic mass unit. Isotopic variations observed on planetary bodies can help to constrain and better understand their formation and processes occurring in the early Solar System. | 0 | Theoretical and Fundamental Chemistry |
In 2021, a study proposed that L1 elements may be responsible for potential endogenisation of the SARS-CoV-2 genome in Huh7 mutant cancer cells, which would possibly explain why some patients test PCR positive for SARS-CoV-2 even after clearance of the virus. These results however have been criticized as not reproducible, misleading and infrequent or artefactual. | 1 | Applied and Interdisciplinary Chemistry |
An example of a simple, well-studied sulfinic acid is phenylsulfinic acid. A commercially important sulfinic acid is thiourea dioxide, which is prepared by the oxidation of thiourea with hydrogen peroxide.
:(NH)CS + 2HO → (NH)(NH)CSOH + 2HO
Another commercially important sulfinic acid is hydroxymethyl sulfinic acid, which is usually employed as its sodium salt (HOCHSONa). Called Rongalite, this anion is also commercially useful as a reducing agent. | 0 | Theoretical and Fundamental Chemistry |
At the continental shelf the reflection and transmission of the tidal wave can lead to the generation of internal tides on the pycnocline. The surface (i.e. barotropic) tide generates these internal tides where stratified waters are forced upwards over a sloping bottom topography. The internal tide extracts energy from the surface tide and propagates both in shoreward and seaward direction. The shoreward propagating internal waves shoals when reaching shallower water where the wave energy is dissipated by wave breaking. The shoaling of the internal tide drives mixing across the pycnocline, high levels carbon sequestration and sediment resuspension. Furthermore, through nutrient mixing the shoaling of the internal tide has a fundamental control on the functioning of ecosystems on the continental margin. | 1 | Applied and Interdisciplinary Chemistry |
Highlighting a few of the published works that have employed SRCD in their research studies best illustrates the power of this technique. | 0 | Theoretical and Fundamental Chemistry |
* For a polymer to exhibit the thermally induced shape-memory effect, it must have anchor points for temporary and permanent shape. These can be physical (chain entanglements, crystals) or chemical (chemical crosslinking, curing, vulcanization).
* This effect in polymers depends on entropic forces and not on martensitic transitions like metals.
* The most important physical properties are: elastic modulus, recovery speed, temporary shape stability.
* The transition temperature T can be Tm or Tg or a mixture of both.
* All crystalline polymers (except for PP) can exhibit thermally induced shape-memory effect.
* Inelastic mechanisms that decrease the effect are: moisture degradation (for moisture sensitive polymers e.g. polyurethanes), unraveling of the chains, degradation of the bonds that fix the permanent or temporary shape. | 0 | Theoretical and Fundamental Chemistry |
Kinetic theory provides insight into the macroscopic properties of gases by considering their molecular composition and motion. Starting with the definitions of momentum and kinetic energy, one can use the conservation of momentum and geometric relationships of a cube to relate macroscopic system properties of temperature and pressure to the microscopic property of kinetic energy per molecule. The theory provides averaged values for these two properties.
The kinetic theory of gases can help explain how the system (the collection of gas particles being considered) responds to changes in temperature, with a corresponding change in kinetic energy.
For example: Imagine you have a sealed container of a fixed-size (a constant volume), containing a fixed-number of gas particles; starting from absolute zero (the theoretical temperature at which atoms or molecules have no thermal energy, i.e. are not moving or vibrating), you begin to add energy to the system by heating the container, so that energy transfers to the particles inside. Once their internal energy is above zero-point energy, meaning their kinetic energy (also known as thermal energy) is non-zero, the gas particles will begin to move around the container. As the box is further heated (as more energy is added), the individual particles increase their average speed as the system's total internal energy increases. The higher average-speed of all the particles leads to a greater rate at which collisions happen (i.e. greater number of collisions per unit of time), between particles and the container, as well as between the particles themselves.
The macroscopic, measurable quantity of pressure, is the direct result of these microscopic particle collisions with the surface, over which, individual molecules exert a small force, each contributing to the total force applied within a specific area. (Read "Pressure" in the above section "Macroscopic view of gases".)
Likewise, the macroscopically measurable quantity of temperature, is a quantification of the overall amount of motion, or kinetic energy that the particles exhibit. (Read "Temperature" in the above section "Macroscopic view of gases".) | 0 | Theoretical and Fundamental Chemistry |
By the turn of the 21st century, several factors gave rise to concerns about a shortage of primary care in the United States . From an aging generation of baby boomers to increasing numbers of physician retirees, it was projected that the United States would be short about 40,000-52,000 physicians by the 2020s. Furthermore, "implementation of the Affordable Care Act identifies millions of newly insured patients needing primary care." This shortage was viewed by many as an opportunity to expand the scope of practice of existing healthcare professionals, such as pharmacists. | 1 | Applied and Interdisciplinary Chemistry |
1961: Eugène Schuëller Prize (ENSCP)
1971: prize of the Organic Chemistry Division of the French Chemical Society
1986: La Caze Prize of the French Academy of sciences and Berthelot Medal of the French Academy of sciences
1988: CNRS silver medal
1993: Corresponding member of the French Academy of sciences.
1994: Achille-Le-Bel Grand Prize of the Chemical Society of France.
2000: Officier of the Ordre National du Mérite
2012: Officier of the Ordre national de la Légion d'Honneur
2018: Commandeur in the Ordre des Palmes Académiques | 0 | Theoretical and Fundamental Chemistry |
Carbon nanofoam is an allotrope of carbon discovered in 1997 by Andrei V. Rode and co-workers at the Australian National University in Canberra. It consists of a cluster-assembly of carbon atoms strung together in a loose three-dimensional web. The fractal-like bond structure consists of sp graphite-like clusters connected by sp bonds. The sp bonds are located mostly on the surface of the structure and make up 15% to 45% of the material, making its framework similar to diamond-like carbon films. The material is remarkably light, with a density of 2-10 x 10 g/cm (0.0012 lb/ft) and is similar to an aerogel. Other remarkable physical properties include the large surface area of 300–400 m/g (similar to zeolites). of nanofoam weighs about .
Each cluster is about 6 nanometers wide and consists of about 4000 carbon atoms linked in graphite-like sheets that are given negative curvature by the inclusion of heptagons among the regular hexagonal pattern. This is the opposite of what happens in the case of buckminsterfullerenes in which carbon sheets are given positive curvature by the inclusion of pentagons.
The large-scale structure of carbon nanofoam is similar to that of an aerogel, but with 1% of the density of previously produced carbon aerogels—or only a few times the density of air at sea level. Unlike carbon aerogels, carbon nanofoam is a poor electrical conductor. The nanofoam contains numerous unpaired electrons, which Rode and colleagues propose is due to carbon atoms with only three bonds that are found at topological and bonding defects. This gives rise to what is perhaps carbon nanofoam's most unusual feature: it is attracted to magnets, and below −183 °C can itself be made magnetic.
Carbon nanofoam is the only form of pure carbon known to be ferromagnetic which is unusual for a carbon allotrope. Ferromagnetism is an intrinsic property observed in the carbon nanofoam and may be accounted for by its complex structure. Impurities in the material are excluded as the source of magnetism as they are not sufficient for the strong magnetization observed. Researchers postulate that embedded carbon atoms with unpaired electrons carry enough of a magnetic moment to lead to strong magnetization. The sheet curvature localizes unpaired electrons by breaking up the π-electron clouds and sterically protects the electrons which normally would be too reactive to persist. The ferromagnetism of the carbon nanofoam is sensitive to time and temperature. Some magnetism is lost within the first few hours of synthesis, however most of it is persistent. Carbon nanofoam may have some application in spintronic devices which exploits electron spin as a further degree of freedom.
Carbon nanofoam may be suitable for hydrogen storage due to its low density and high surface area. Preliminary experimentation has shown that hydrogen can be stored in the nanofoam at room temperature in a reversible process.
Synthesis
Carbon nanofoam clusters can be synthesized through high-repetition-rate laser ablation in inert gases such as argon. Short (fs), low-energy (µJ) pulses delivered at high rates of repetition (10 kHz – 100 MHz) generate carbon vapors for deposition. Ambient gas is heated from room temperature with the atomized carbon which leads to an increase in the partial density of the carbon in the chamber. In optimal conditions, the inert gas does not cool down but maintains its high temperature between cycles of formation. Subsequent cycles in the chamber are carried out at temperatures above the formation threshold temperature initiating sp bonding. The increase in density and temperature promotes favorable conditions for the formation of carbonaceous clusters. The rate of consumption exceeds the rate of evaporation by laser ablation and thus the formation is in a non-equilibrium state. | 0 | Theoretical and Fundamental Chemistry |
The Annual Review of Chemical and Biomolecular Engineering defines its scope as covering significant developments relevant to chemical engineering. It includes disciplines such as applied chemistry and biology, physics, and engineering with a focus on the development of chemical products and processes. As of 2023, Journal Citation Reports lists the journal's impact factor as 8.4, ranking it sixth of 72 journal titles in the category "Chemistry, Applied" and thirteen of 140 titles in "Engineering, Chemical". It is abstracted and indexed in Scopus, Science Citation Index Expanded, CAB Abstracts, EMBASE, and MEDLINE, among others. | 1 | Applied and Interdisciplinary Chemistry |
William Frohring was brought on as part of the team with Gerstenberger and Ruh, and eventually became chief chemist on the project. The group's formula was based on diluted skimmed milk, with lactose and potassium chloride added to reach the human milk level. Among their novel contributions was to use mixtures of fats and oils rather than cream to duplicate human milk fat.
Experimental batches of SMA distributed to local pediatricians were well received. The group began getting orders for more. Frohring stepped forward as the business leader of the group. His idea was to give the patent of the formula to Babies Dispensary and Children's Hospital, and license the manufacture to Telling-Belle Vernon Dairy.
By 1919, Frohring was director of the laboratory at Telling-Belle Vernon Dairy, and had invented several pieces of laboratory and dairy processing equipment. In 1921, he was made a director and placed in charge of Laboratory Products Company, the company's new subsidiary to manufacture SMA, located in Mason, Michigan.
Laboratory Products Company diversified into the development of research into other newly identified biochemicals. Frohring recruited Albert Fredrick Ottomar Germann to study carotene. The company went on to become the world's major supplier of carotene.
As an employee of the dairy, Frohring accumulated patents on a process for the production of soluble casein, an improved process for lactose production, a vitamin C concentrate from orange and tomato juice for addition to SMA, and a formulation called "Frohs Malted Chocolate Milk". The company was renamed the SMA Corporation, and added carotene concentrate, refined from palm oil, to its product line. Frohring set up a company to process the palm oil. He made his younger brother Paul (formerly sales manager for SMA Corporation), president and general manager. In 1939, SMA, its subsidiary, and all rights to the infant formula were purchased by American Home Products Corporation (AHPC). Frohring stayed on as president of the SMA Corporation, now owned by AHPC. He later became a director of AHPC. | 0 | Theoretical and Fundamental Chemistry |
In chemistry and physics, cohesion (), also called cohesive attraction or cohesive force, is the action or property of like molecules sticking together, being mutually attractive. It is an intrinsic property of a substance that is caused by the shape and structure of its molecules, which makes the distribution of surrounding electrons irregular when molecules get close to one another, creating electrical attraction that can maintain a macroscopic structure such as a water drop. Cohesion allows for surface tension, creating a "solid-like" state upon which light-weight or low-density materials can be placed.
Water, for example, is strongly cohesive as each molecule may make four hydrogen bonds to other water molecules in a tetrahedral configuration. This results in a relatively strong Coulomb force between molecules. In simple terms, the polarity (a state in which a molecule is oppositely charged on its poles) of water molecules allows them to be attracted to each other. The polarity is due to the electronegativity of the atom of oxygen: oxygen is more electronegative than the atoms of hydrogen, so the electrons they share through the covalent bonds are more often close to oxygen rather than hydrogen. These are called polar covalent bonds, covalent bonds between atoms that thus become oppositely charged. In the case of a water molecule, the hydrogen atoms carry positive charges while the oxygen atom has a negative charge. This charge polarization within the molecule allows it to align with adjacent molecules through strong intermolecular hydrogen bonding, rendering the bulk liquid cohesive. Van der Waals gases such as methane, however, have weak cohesion due only to van der Waals forces that operate by induced polarity in non-polar molecules.
Cohesion, along with adhesion (attraction between unlike molecules), helps explain phenomena such as meniscus, surface tension and capillary action.
Mercury in a glass flask is a good example of the effects of the ratio between cohesive and adhesive forces. Because of its high cohesion and low adhesion to the glass, mercury does not spread out to cover the bottom of the flask, and if enough is placed in the flask to cover the bottom, it exhibits a strongly convex meniscus, whereas the meniscus of water is concave. Mercury will not wet the glass, unlike water and many other liquids, and if the glass is tipped, it will roll around inside. | 0 | Theoretical and Fundamental Chemistry |
Nuclear fusion is a reaction in which two or more atomic nuclei, usually deuterium and tritium (hydrogen isotopes), combine to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifested as either the release or absorption of energy. This difference in mass arises due to the difference in nuclear binding energy between the atomic nuclei before and after the reaction. Nuclear fusion is the process that powers active or main-sequence stars and other high-magnitude stars, where large amounts of energy are released.
A nuclear fusion process that produces atomic nuclei lighter than iron-56 or nickel-62 will generally release energy. These elements have a relatively small mass and a relatively large binding energy per nucleon. Fusion of nuclei lighter than these releases energy (an exothermic process), while the fusion of heavier nuclei results in energy retained by the product nucleons, and the resulting reaction is endothermic. The opposite is true for the reverse process, called nuclear fission. Nuclear fusion uses lighter elements, such as hydrogen and helium, which are in general more fusible; while the heavier elements, such as uranium, thorium and plutonium, are more fissionable. The extreme astrophysical event of a supernova can produce enough energy to fuse nuclei into elements heavier than iron. | 0 | Theoretical and Fundamental Chemistry |
Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl·nHO, with x ranging from 0 to 4.5, forming hydrates. Zinc chloride, anhydrous and its hydrates are colorless or white crystalline solids, and are highly soluble in water. Five hydrates of zinc chloride are known, as well as four forms of anhydrous zinc chloride. This salt is hygroscopic and even deliquescent. Zinc chloride finds wide application in textile processing, metallurgical fluxes, and chemical synthesis. No mineral with this chemical composition is known aside from the very rare mineral simonkolleite, . | 0 | Theoretical and Fundamental Chemistry |
Hemoproteins have diverse biological functions including the transportation of diatomic gases, chemical catalysis, diatomic gas detection, and electron transfer. The heme iron serves as a source or sink of electrons during electron transfer or redox chemistry. In peroxidase reactions, the porphyrin molecule also serves as an electron source, being able to delocalize radical electrons in the conjugated ring. In the transportation or detection of diatomic gases, the gas binds to the heme iron. During the detection of diatomic gases, the binding of the gas ligand to the heme iron induces conformational changes in the surrounding protein. In general, diatomic gases only bind to the reduced heme, as ferrous Fe(II) while most peroxidases cycle between Fe(III) and Fe(IV) and hemeproteins involved in mitochondrial redox, oxidation-reduction, cycle between Fe(II) and Fe(III).
It has been speculated that the original evolutionary function of hemoproteins was electron transfer in primitive sulfur-based photosynthesis pathways in ancestral cyanobacteria-like organisms before the appearance of molecular oxygen.
Hemoproteins achieve their remarkable functional diversity by modifying the environment of the heme macrocycle within the protein matrix. For example, the ability of hemoglobin to effectively deliver oxygen to tissues is due to specific amino acid residues located near the heme molecule. Hemoglobin reversibly binds to oxygen in the lungs when the pH is high, and the carbon dioxide concentration is low. When the situation is reversed (low pH and high carbon dioxide concentrations), hemoglobin will release oxygen into the tissues. This phenomenon, which states that hemoglobin's oxygen binding affinity is inversely proportional to both acidity and concentration of carbon dioxide, is known as the Bohr effect. The molecular mechanism behind this effect is the steric organization of the globin chain; a histidine residue, located adjacent to the heme group, becomes positively charged under acidic conditions (which are caused by dissolved CO in working muscles, etc.), releasing oxygen from the heme group. | 1 | Applied and Interdisciplinary Chemistry |
*Natural agents − Different natural products and their extracts, such as onion, pineapple, lemon, and white wine, are known to inhibit or slow the browning of some products. Onion and its extract exhibit potent anti-browning properties by inhibiting the PPO activity. Pineapple juice have shown to possess anti-browning effect on apples and bananas. Lemon juice is used in making doughs to make the pastry products look brighter. This effect is possibly explained by the anti-browning properties of citric and ascorbic acids in the lemon juice.
*Genetic modification − Arctic apples have been genetically modified to silence the expression of PPO, thereby delaying the browning effect, and improving apple eating quality. | 1 | Applied and Interdisciplinary Chemistry |
Let be the effective absorption cross-section be effective emission cross-sections at frequency , and let be the effective temperature of the medium. The McCumber relation is
where
is thermal steady-state ratio of populations; frequency is called "zero-line" frequency;
is the Planck constant and
is the Boltzmann constant. Note that the right-hand side of Equation (1) does not depend on . | 0 | Theoretical and Fundamental Chemistry |
The US Government Standard Bathroom Malodor, said to be one of the worst-smelling substances, is quoted as having this composition: (Note that this substance is a concoction) | 1 | Applied and Interdisciplinary Chemistry |
Alkylation reactions of chiral (S)-1-amino-2-methoxymethylpyrrolidine (SAMP) and (R)-1-amino-2-methoxymethylpyrrolidine (RAMP) hydrazones were developed by Dieter Enders and E.J. Corey. | 0 | Theoretical and Fundamental Chemistry |
Although there are numerous benefits in using the SQT approach, drawbacks in its use have been identified. The major limitations include: lack of statistical criteria development within the framework, large database requirements, difficulties in chemical mixture application, and data interpretation can be laboratory intensive (Chapman 1989). The SQT does not evidently consider the bioavailability of complexed or sediment-associated contaminants (FDEP 1994). Lastly, it is difficult to translate laboratory toxicity results to biological effects seen in the field (Kamlet 1989). | 1 | Applied and Interdisciplinary Chemistry |
Activity coefficients of electrolyte solutions may be calculated theoretically, using the Debye–Hückel equation or extensions such as the Davies equation, Pitzer equations or TCPC model. Specific ion interaction theory (SIT) may also be used.
For non-electrolyte solutions correlative methods such as UNIQUAC, NRTL, MOSCED or UNIFAC may be employed, provided fitted component-specific or model parameters are available. COSMO-RS is a theoretical method which is less dependent on model parameters as required information is obtained from quantum mechanics calculations specific to each molecule (sigma profiles) combined with a statistical thermodynamics treatment of surface segments.
For uncharged species, the activity coefficient γ mostly follows a salting-out model:
This simple model predicts activities of many species (dissolved undissociated gases such as CO, HS, NH, undissociated acids and bases) to high ionic strengths (up to 5 mol/kg). The value of the constant b for CO is 0.11 at 10 °C and 0.20 at 330 °C.
For water as solvent, the activity a can be calculated using:
where ν is the number of ions produced from the dissociation of one molecule of the dissolved salt, b is the molality of the salt dissolved in water, φ is the osmotic coefficient of water, and the constant 55.51 represents the molality of water. In the above equation, the activity of a solvent (here water) is represented as inversely proportional to the number of particles of salt versus that of the solvent. | 0 | Theoretical and Fundamental Chemistry |
The most notable effects of eutrophication are vegetal blooms, sometimes toxic, loss of biodiversity and anoxia, which can lead to the massive death of aquatic organisms.
Due to the hypoxic conditions present in dead zones, marine life within these areas tends to be scarce. Most fish and motile organisms tend to emigrate out of the zone as oxygen concentrations fall, and benthic populations may experience severe losses when oxygen concentrations are below 0.5 mg l O. In severe anoxic conditions, microbial life may experience dramatic shifts in community identity as well, resulting in an increased abundance of anaerobic organisms as aerobic microbes decrease in number and switch energy sources for oxidation such as nitrate, sulfate, or iron reduction. Sulfur reduction is a particular concern as Hydrogen sulfide is toxic and stresses most organisms within the zone further, exacerbating mortality risks.
Low oxygen levels can have severe effects on survivability of organisms inside the area while above lethal anoxic conditions. Studies conducted along the Gulf Coast of North America have shown hypoxic conditions lead to reduction of reproductive rates and growth rates in a variety of organisms including fish and benthic invertebrates. Organisms able to leave the area typically do so when oxygen concentrations decrease to less than 2 mg l. At these oxygen concentrations and below, organisms that survive inside the oxygen deficient environment and are unable to escape the area will often exhibit progressively worsening stress behavior and die. Surviving organisms tolerant of hypoxic conditions often exhibit physiological adaptations appropriate for persisting within hypoxic environments. Examples of such adaptations include increased efficiency of oxygen intake and use, lowering required amount of oxygen intake through reduced growth rates or dormancy, and increasing the usage of anaerobic metabolic pathways.
Community composition in benthic communities is dramatically disrupted by periodic oxygen depletion events, such as those of seasonal dead zones and occurring as a result of Diel cycles. The longterm effects of such hypoxic conditions result in a shift in communities, most commonly manifest as a decrease in species diversity through mass mortality events. Reestablishment of benthic communities depend upon composition of adjacent communities for larval recruitment. This results in a shift towards faster establishing colonizers with shorter and more opportunistic life strategies, potentially disrupting historic benthic compositions. | 0 | Theoretical and Fundamental Chemistry |
As a consequence of the Pauli exclusion principle, nuclei with an excess of protons or neutrons have a higher average energy per nucleon. Nuclei with a sufficient excess of neutrons have a greater energy than the combination of a free neutron and a nucleus with one less neutron, and therefore can decay by neutron emission. Nuclei which can decay by this process are described as lying beyond the neutron drip line.
Two examples of isotopes that emit neutrons are beryllium-13 (decaying to beryllium-12 with a mean life ) and helium-5 (helium-4, ).
In tables of nuclear decay modes, neutron emission is commonly denoted by the abbreviation n. | 0 | Theoretical and Fundamental Chemistry |
The Campo de Cartagena has valuable remains of its ancient past. In the city of Cartagena can be seen numerous monuments, museums and archaeological remains.
An attempt was made during the First Spanish Republic, on July 12 of 1873 to establish a canton in the Cartagena area. The insurgency took the name Cantonal Revolution and in the following days it spread through many other regions. Following the revolt the city of Cartagena endured for several months the attack of the troops sent by Nicolás Salmerón to restore order. | 1 | Applied and Interdisciplinary Chemistry |
Excitotoxicity can occur from substances produced within the body (endogenous excitotoxins). Glutamate is a prime example of an excitotoxin in the brain, and it is also the major excitatory neurotransmitter in the central nervous system of mammals. During normal conditions, glutamate concentration can be increased up to 1mM in the synaptic cleft, which is rapidly decreased in the lapse of milliseconds. When the glutamate concentration around the synaptic cleft cannot be decreased or reaches higher levels, the neuron kills itself by a process called apoptosis.
This pathologic phenomenon can also occur after brain injury and spinal cord injury. Within minutes after spinal cord injury, damaged neural cells within the lesion site spill glutamate into the extracellular space where glutamate can stimulate presynaptic glutamate receptors to enhance the release of additional glutamate. Brain trauma or stroke can cause ischemia, in which blood flow is reduced to inadequate levels. Ischemia is followed by accumulation of glutamate and aspartate in the extracellular fluid, causing cell death, which is aggravated by lack of oxygen and glucose. The biochemical cascade resulting from ischemia and involving excitotoxicity is called the ischemic cascade. Because of the events resulting from ischemia and glutamate receptor activation, a deep chemical coma may be induced in patients with brain injury to reduce the metabolic rate of the brain (its need for oxygen and glucose) and save energy to be used to remove glutamate actively. (The main aim in induced comas is to reduce the intracranial pressure, not brain metabolism).
Increased extracellular glutamate levels leads to the activation of Ca permeable NMDA receptors on myelin sheaths and oligodendrocytes, leaving oligodendrocytes susceptible to Ca influxes and subsequent excitotoxicity. One of the damaging results of excess calcium in the cytosol is initiating apoptosis through cleaved caspase processing. Another damaging result of excess calcium in the cytosol is the opening of the mitochondrial permeability transition pore, a pore in the membranes of mitochondria that opens when the organelles absorb too much calcium. Opening of the pore may cause mitochondria to swell and release reactive oxygen species and other proteins that can lead to apoptosis. The pore can also cause mitochondria to release more calcium. In addition, production of adenosine triphosphate (ATP) may be stopped, and ATP synthase may in fact begin hydrolysing ATP instead of producing it, which is suggested to be involved in depression.
Inadequate ATP production resulting from brain trauma can eliminate electrochemical gradients of certain ions. Glutamate transporters require the maintenance of these ion gradients to remove glutamate from the extracellular space. The loss of ion gradients results in not only the halting of glutamate uptake, but also in the reversal of the transporters. The Na-glutamate transporters on neurons and astrocytes can reverse their glutamate transport and start secreting glutamate at a concentration capable of inducing excitotoxicity. This results in a buildup of glutamate and further damaging activation of glutamate receptors.
On the molecular level, calcium influx is not the only factor responsible for apoptosis induced by excitoxicity. Recently, it has been noted that extrasynaptic NMDA receptor activation, triggered by both glutamate exposure or hypoxic/ischemic conditions, activate a CREB (cAMP response element binding) protein shut-off, which in turn caused loss of mitochondrial membrane potential and apoptosis. On the other hand, activation of synaptic NMDA receptors activated only the CREB pathway, which activates BDNF (brain-derived neurotrophic factor), not activating apoptosis. | 1 | Applied and Interdisciplinary Chemistry |
* It requires extra computation to produce and optimize a set of loops.
* The dimension of the equations to be solved is smaller but they are much less sparse. | 1 | Applied and Interdisciplinary Chemistry |
Dispersants can be used to dissipate oil slicks. They may rapidly disperse large amounts of certain oil types from the sea surface by transferring it into the water column. They will cause the oil slick to break up and form water-soluble micelles that are rapidly diluted. Then effectively spread throughout a larger volume of water than the surface from where the oil was dispersed. They can also delay the formation of persistent oil-in-water emulsions. However, laboratory experiments showed that dispersants increased toxic hydrocarbon levels in fish by a factor of up to 100 and may kill fish eggs.
Dispersant Corexit 9527 was for example used to disperse an oil slick in the Gulf of Mexico in 1979 (Ixtoc) over one thousand square miles of sea. The same dispersant was also used in an attempt to clean up the Exxon Valdez oil spill in 1989, though its use was discontinued as there was not enough wave action to mix the dispersant with the oil in the water. During the Deepwater Horizon oil spill in 2010, unprecedented amounts of the dispersants Corexit 9500 and 9527 were used (approximately 7 million liters). | 0 | Theoretical and Fundamental Chemistry |
Oil extraction is simply the removal of oil from the reservoir (oil pool). There are many methods on extracting the oil from the reservoirs for example; mechanical shaking, water-in-oil emulsion, and specialty chemicals called demulsifiers that separate the oil from water. Oil extraction is costly and often environmentally damaging. Offshore exploration and extraction of oil disturb the surrounding marine environment. | 0 | Theoretical and Fundamental Chemistry |
Biomaterials are used in:
# Joint replacements
# Bone plates
# Intraocular lenses (IOLs) for eye surgery
# Bone cement
# Artificial ligaments and tendons
# Dental implants for tooth fixation
# Blood vessel prostheses
# Heart valves
# Skin repair devices (artificial tissue)
# Cochlear replacements
# Contact lenses
# Breast implants
# Drug delivery mechanisms
# Sustainable materials
# Vascular grafts
# Stents
# Nerve conduits
# Surgical sutures, clips, and staples for wound closure
# Pins and screws for fracture stabilisation
# Surgical mesh
Biomaterials must be compatible with the body, and there are often issues of biocompatibility, which must be resolved before a product can be placed on the market and used in a clinical setting. Because of this, biomaterials are usually subjected to the same requirements as those undergone by new drug therapies. All manufacturing companies are also required to ensure traceability of all of their products, so that if a defective product is discovered, others in the same batch may be traced. | 1 | Applied and Interdisciplinary Chemistry |
Bharat is the author or co-author of over 46 scientific publications. These include:
* Jan Böhning, Mnar Ghrayeb, Conrado Pedebos, Daniel K. Abbas, Syma Khalid, Liraz Chai & Tanmay A. M. Bharat (2022) [https://www.nature.com/articles/s41467-022-34700-z Donor-strand exchange drives assembly of the TasA scaffold in Bacillus subtilis biofilms.] Nature Communications volume 13, article number 7082.
* Tanmay A.M. Bharat, Andriko von Kügelgen & Vikram Alva (2021) [https://pubmed.ncbi.nlm.nih.gov/33121898/ Molecular Logic of Prokaryotic Surface Layer Structures.] Trends in Microbiology May;29(5):405-415.
* Charlotte Melia, Jani Bolla, Stefan Lanwermeyer, Daniel Mihaylov, Patrick Hoffmann, Jiandong Huo, Michael Wozny, Louis Elfari, Jan Böhning, Ray Owens, Carol Robinson, George O’Toole & Tanmay A.M. Bharat (2021) [https://www.biorxiv.org/content/10.1101/2021.02.08.430230v1 Architecture of cell-cell junctions in situ reveals a mechanism for bacterial biofilm inhibition.] Proceedings of the National Academy of Sciences of the United States of America 118(31):
* Andriko von Kügelgen, Vikram Alva and Tanmay A.M. Bharat (2021) [https://www.cell.com/cell-reports/fulltext/S2211-1247(21)01538-2 Complete atomic structure of a native archaeal cell surface.] Cell Reports volume 37, issue 8, 110052.
* Abul K. Tarafder, Andriko von Kügelgen, Adam J. Mellul & Tanmay A. M. Bharat (2020) [https://www.pnas.org/doi/full/10.1073/pnas.1917726117 Phage liquid crystalline droplets form occlusive sheaths that encapsulate and protect infectious rod-shaped bacteria.] Proceedings of the National Academy of Sciences of the United States of America volume 117, issue 9, pages 4724-4731.
* Andriko von Kügelgen, Haiping Tang., Gail Hardy, Danguole Kureisaite-Ciziene, Yves Brun, Phillip Stansfeld, Carol Robinson, & Tanmay A.M. Bharat (2020) [https://pubmed.ncbi.nlm.nih.gov/31883796/ In Situ Structure of an Intact Lipopolysaccharide-Bound Bacterial Surface Layer.] Cell 180(2): 348-358
* Tanmay A.M. Bharat, Christopher J. Russo, Jan Löwe, Lori A. Passmore & Sjors H.W. Scheres (2015) [https://www.cell.com/structure/fulltext/S0969-2126(15)00279-8 Advances in Single-Particle Electron Cryomicroscopy Structure Determination applied to Sub-tomogram Averaging] Structure volume 23, issue 9, pages 1743-1753.
* Tanmay A. M. Bharat, James D. Riches, Larissa Kolesnikova, Sonja Welsch, Verena Krähling, Norman Davey, Marie-Laure Parsy, Stephan Becker & John A. G. Briggs (2011) [https://doi.org/10.1371/journal.pbio.1001196 Cryo-Electron Tomography of Marburg Virus Particles and Their Morphogenesis within Infected Cells.] PLOS Biology | 1 | Applied and Interdisciplinary Chemistry |
Robert Edward Corbett (13 June 1923 – 3 February 2018) was a New Zealand organic chemist. He is noted for his contribution to natural product chemistry through the isolation and structural elucidation of compounds from New Zealand native plants. | 0 | Theoretical and Fundamental Chemistry |
DiffractGUI allows for an automated analysis of diffraction patterns and high-resolution images of single crystal or limited number of crystallites. It is able to determine crystal orientation, index individual diffraction spots and measure interplanar angles and distances in picometric precision. The input image may depict:
* selected area diffraction pattern,
* high-resolution image,
* nanodiffraction pattern or
* convergent beam electron diffraction.
The input image is processed in the following steps:
# Preprocessing with accordance to the settings and image nature (resolution and noise reduction, Fourier transform for direct space images etc.).
# Detection of diffraction reflections at various scales (difference of Gaussians typically used for spot detection, Hough transform for CBED disk detection).
# The strongest detections are selected across the scale space.
# A regular lattice is fit to the set of the strongest detections using RANSAC algorithm.
# Lengths and angles of the lattice basis vectors are measured.
# Crystal lattice orientation is determined and diffraction reflections are identified using theoretical parameters of the sample material.
Compared to human evaluation, considers tens or even hundreds of diffraction spots at once and, therefore, can localize the pattern with sub-pixel precision. | 0 | Theoretical and Fundamental Chemistry |
There are a large number of proteins yet to be identified that transport Mg. Even in the best studied eukaryote, yeast, Borrelly has reported a Mg/H exchanger without an associated protein, which is probably localised to the Golgi. At least one other major Mg transporter in yeast is still unaccounted for, the one affecting Mg transport in and out of the yeast vacuole. In higher, multicellular organisms, it seems that many Mg transporting proteins await discovery.
The CorA-domain-containing Mg transporters (CorA, Alr-like and Mrs2-like) have a similar but not identical array of affinities for divalent cations. In fact, this observation can be extended to all of the Mg transporters identified so far. This similarity suggests that the basic properties of Mg strongly influence the possible mechanisms of recognition and transport. However, this observation also suggests that using other metal ions as tracers for Mg uptake will not necessarily produce results comparable to the transporter's ability to transport Mg. Ideally, Mg should be measured directly.
Since Mg is practically unobtainable, much of the old data will need to be reinterpreted with new tools for measuring Mg transport, if different transporters are to be compared directly. The pioneering work of Kolisek and Froschauer using mag-fura 2 has shown that free Mg can be reliably measured in vivo in some systems. By returning to the analysis of CorA with this new tool, we have gained an important baseline for the analysis of new Mg transport systems as they are discovered. However, it is important that the amount of transporter present in the membrane is accurately determined if comparisons of transport capability are to be made. This bacterial system might also be able to provide some utility for the analysis of eukaryotic Mg transport proteins, but differences in biological systems of prokaryotes and eukaryotes will have to be considered in any experiment. | 1 | Applied and Interdisciplinary Chemistry |
The Z-factor is defined in terms of four parameters: the means () and standard deviations () of samples (s) and controls (c). Given these values (, , and , ), the Z-factor is defined as:
For assays of agonist/activation type, the control (c) data (, ) in the equation are substituted with the positive control (p) data (, ) which represent maximal activated signal; for assays of antagonist/inhibition type, the control (c) data (, ) in the equation are substituted with the negative control (n) data (, ) which represent minimal signal.
In practice, the Z-factor is estimated from the sample means and sample standard deviations | 1 | Applied and Interdisciplinary Chemistry |
If the aquifer has recharging boundary conditions a steady-state may be reached (or it may be used as an approximation in many cases), and the diffusion equation (above) simplifies to the Laplace equation.
This equation states that hydraulic head is a harmonic function, and has many analogs in other fields. The Laplace equation can be solved using techniques, using similar assumptions stated above, but with the additional requirements of a steady-state flow field.
A common method for solution of this equations in civil engineering and soil mechanics is to use the graphical technique of drawing flownets; where contour lines of hydraulic head and the stream function make a curvilinear grid, allowing complex geometries to be solved approximately.
Steady-state flow to a pumping well (which never truly occurs, but is sometimes a useful approximation) is commonly called the Thiem solution. | 1 | Applied and Interdisciplinary Chemistry |
Waste from the front end of the nuclear fuel cycle is usually alpha-emitting waste from the extraction of uranium. It often contains radium and its decay products.
Uranium dioxide (UO) concentrate from mining is a thousand or so times as radioactive as the granite used in buildings. It is refined from yellowcake (UO), then converted to uranium hexafluoride gas (UF). As a gas, it undergoes enrichment to increase the U-235 content from 0.7% to about 4.4% (LEU). It is then turned into a hard ceramic oxide (UO) for assembly as reactor fuel elements.
The main by-product of enrichment is depleted uranium (DU), principally the U-238 isotope, with a U-235 content of ~0.3%. It is stored, either as UF or as UO. Some is used in applications where its extremely high density makes it valuable such as anti-tank shells, and on at least one occasion even a sailboat keel. It is also used with plutonium for making mixed oxide fuel (MOX) and to dilute, or downblend, highly enriched uranium from weapons stockpiles which is now being redirected to become reactor fuel. | 0 | Theoretical and Fundamental Chemistry |
Jung sets out the central thesis of the book: that Alchemy draws upon a vast array of symbols, images and patterns drawn from the Collective Unconscious. Jung defends his exploration of the Psyche and Soul against various critics who have accused him of being both religious and anti-religious depending on their point of view. He argues for a deeper understanding of the Western spiritual traditions e.g. Esoteric Christianity and Alchemy alongside an examination of the Eastern ones e.g. Buddhism, Hinduism etc. Jung diagnoses the spiritual laziness of the West in not truly embracing the Christian Myth as an inner journey of transformation. Alchemy, he argues, is a Western Yoga which was designed to facilitate this. The book will begin with a description of a whole cycle of dreams described by an unnamed patient (to protect confidentiality) which will be interpreted in their archetypal and mythological sense by Jung. This is designed to illustrate the existence of Jung's theory of the Collective Unconscious and the psychological goal or Great Work of psychic and spiritual integration or wholeness through the individuation process
that affects the mind state. | 1 | Applied and Interdisciplinary Chemistry |
Gunpowder was used for hydraulic engineering in China by 1541. Gunpowder blasting followed by dredging of the detritus was a technique which Chen Mu employed to improve the Grand Canal at the waterway where it crossed the Yellow River. In Europe, gunpowder was used in the construction of the Canal du Midi in Southern France. It was completed in 1681 and linked the Mediterranean sea with the Atlantic with 240 km of canal and 100 locks. Another noteworthy consumer of black powder was the Erie Canal in New York, which was 585 km long and took eight years to complete, starting in 1817. | 1 | Applied and Interdisciplinary Chemistry |
The name "photo-reflectance" or "photoreflectance" is shortened from the term "photo-modulated reflectance," which describes the use of an intensity modulated light beam to perturb the reflectance of a sample. The technique has also been referred to as "modulated photo-reflectance," "modulated optical reflectance," and "photo-modulated optical reflectance." It has been known at least since 1967. | 0 | Theoretical and Fundamental Chemistry |
Due to the regulatory role during transcription of epigenetic modifications in genes, it is not surprising that changes in epigenetic markers, such as acetylation, can contribute to cancer development. HDACs expression and activity in tumor cells is very different from normal cells. The overexpression and increased activity of HDACs has been shown to be characteristic of tumorigenesis and metastasis, suggesting an important regulatory role of histone deacetylation on the expression of tumor suppressor genes. One of the examples is the regulation role of histone acetylation/deacetylation in P300 and CBP, both of which contribute to oncogenesis.
Approved in 2006 by the U.S. Food and Drug Administration (FDA), Vorinostat represents a new category for anticancer drugs that are in development. Vorinostat targets histone acetylation mechanisms and can effectively inhibit abnormal chromatin remodeling in cancerous cells. Targets of Vorinostat includes HDAC1, HDAC2, HDAC3 and HDAC6.
Carbon source availability is reflected in histone acetylation in cancer. Glucose and glutamine are the major carbon sources of most mammalian cells, and glucose metabolism is closely related to histone acetylation and deacetylation. Glucose availability affects the intracellular pool of acetyl-CoA, a central metabolic intermediate that is also the acetyl donor in histone acetylation. Glucose is converted to acetyl-CoA by the pyruvate dehydrogenase complex (PDC), which produces acetyl-CoA from glucose-derived pyruvate; and by adenosine triphosphate-citrate lyase (ACLY), which generates acetyl-CoA from glucose-derived citrate. PDC and ACLY activity depend on glucose availability, which thereby influences histone acetylation and consequently modulates gene expression and cell cycle progression. Dysregulation of ACLY and PDC contributes to metabolic reprogramming and promotes the development of multiple cancers. At the same time, glucose metabolism maintains the NAD+/NADH ratio, and NAD+ participates in SIRT-mediated histone deacetylation. SIRT enzyme activity is altered in various malignancies, and inhibiting SIRT6, a histone deacetylase that acts on acetylated H3K9 and H3K56, promotes tumorigenesis. SIRT7, which deacetylates H3K18 and thereby represses transcription of target genes, is activated in cancer to stabilize cells in the transformed state. Nutrients appear to modulate SIRT activity. For example, long-chain fatty acids activate the deacetylase function of SIRT6, and this may affect histone acetylation. | 0 | Theoretical and Fundamental Chemistry |
Cryoprotectants operate by increasing the solute concentration in cells. However, in order to be biologically viable they must easily penetrate and must not be toxic to cells. | 1 | Applied and Interdisciplinary Chemistry |
For two homogeneous layers of fluids, of mean thickness h below the interface and h′ above – under the action of gravity and bounded above and below by horizontal rigid walls – the dispersion relationship ω = Ω(k) for gravity waves is provided by:
where again ρ and ρ′ are the densities below and above the interface, while coth is the hyperbolic cotangent function. For the case ρ′ is zero this reduces to the dispersion relation of surface gravity waves on water of finite depth h.
When the depth of the two fluid layers becomes very large (h→∞, h′→∞), the hyperbolic cotangents in the above formula approaches the value of one. Then: | 1 | Applied and Interdisciplinary Chemistry |
The efficiency of a heat engine relates how much useful work is output for a given amount of heat energy input.
From the laws of thermodynamics, after a completed cycle:
:and therefore
:where
: is the net work extracted from the engine in one cycle. (It is negative, in the IUPAC convention, since work is done by the engine.)
: is the heat energy taken from the high temperature heat source in the surroundings in one cycle. (It is positive since heat energy is added to the engine.)
: is the waste heat given off by the engine to the cold temperature heat sink. (It is negative since heat is lost by the engine to the sink.)
In other words, a heat engine absorbs heat energy from the high temperature heat source, converting part of it to useful work and giving off the rest as waste heat to the cold temperature heat sink.
In general, the efficiency of a given heat transfer process is defined by the ratio of "what is taken out" to "what is put in". (For a refrigerator or heat pump, which can be considered as a heat engine run in reverse, this is the coefficient of performance and it is ≥ 1.) In the case of an engine, one desires to extract work and has to put in heat , for instance from combustion of a fuel, so the engine efficiency is reasonably defined as
The efficiency is less than 100% because of the waste heat unavoidably lost to the cold sink (and corresponding compression work put in) during the required recompression at the cold temperature before the power stroke of the engine can occur again.
The theoretical maximum efficiency of any heat engine depends only on the temperatures it operates between. This efficiency is usually derived using an ideal imaginary heat engine such as the Carnot heat engine, although other engines using different cycles can also attain maximum efficiency. Mathematically, after a full cycle, the overall change of entropy is zero:
Note that is positive because isothermal expansion in the power stroke increases the multiplicity of the working fluid while is negative since recompression decreases the multiplicity. If the engine is ideal and runs reversibly, and , and thus
which gives and thus the Carnot limit for heat-engine efficiency,
where is the absolute temperature of the hot source and that of the cold sink, usually measured in kelvins.
The reasoning behind this being the maximal efficiency goes as follows. It is first assumed that if a more efficient heat engine than a Carnot engine is possible, then it could be driven in reverse as a heat pump. Mathematical analysis can be used to show that this assumed combination would result in a net decrease in entropy. Since, by the second law of thermodynamics, this is statistically improbable to the point of exclusion, the Carnot efficiency is a theoretical upper bound on the reliable efficiency of any thermodynamic cycle.
Empirically, no heat engine has ever been shown to run at a greater efficiency than a Carnot cycle heat engine.
Figure 2 and Figure 3 show variations on Carnot cycle efficiency with temperature. Figure 2 indicates how efficiency changes with an increase in the heat addition temperature for a constant compressor inlet temperature. Figure 3 indicates how the efficiency changes with an increase in the heat rejection temperature for a constant turbine inlet temperature. | 0 | Theoretical and Fundamental Chemistry |
One important class of condensation polymers are polyamides. They arise from the reaction of carboxylic acid and an amine. Examples include nylons and proteins. When prepared from amino-carboxylic acids, e.g. amino acids, the stoichiometry of the polymerization includes co-formation of water:
:n HN-X-COH → [HN-X-C(O)] + (n-1) HO
When prepared from diamines and dicarboxylic acids, e.g. the production of nylon 66, the polymerization produces two molecules of water per repeat unit:
:n HN-X-NH + n HOC-Y-COH → [HN-X-NHC(O)-Y-C(O)] + (2n-1) HO | 0 | Theoretical and Fundamental Chemistry |
Supramolecular complexes are held together by hydrogen bonding, hydrophobic forces, van der Waals forces, π-π interactions, and electrostatic effects, all of which can be described as noncovalent bonding. Applications include molecular recognition, host–guest chemistry and anion sensors.
A typical application in molecular recognition involved the determination of formation constants for complexes formed between a tripodal substituted urea molecule and various saccharides. The study was carried out using a non-aqueous solvent and NMR chemical shift measurements. The object was to examine the selectivity with respect to the saccharides.
An example of the use of supramolecular complexes in the development of chemosensors is provided by the use of transition-metal ensembles to sense for ATP.
Anion complexation can be achieved by encapsulating the anion in a suitable cage. Selectivity can be engineered by designing the shape of the cage. For example, dicarboxylate anions could be encapsulated in the ellipsoidal cavity in a large macrocyclic structure containing two metal ions. | 0 | Theoretical and Fundamental Chemistry |
Demand-controlled ventilation (DCV, also known as Demand Control Ventilation) makes it possible to maintain air quality while conserving energy. ASHRAE has determined that: "It is consistent with the ventilation rate procedure that demand control be permitted for use to reduce the total outdoor air supply during periods of less occupancy." In a DCV system, CO sensors control the amount of ventilation. During peak occupancy, CO levels rise, and the system adjusts to deliver the same amount of outdoor air as would be used by the ventilation-rate procedure. However, when spaces are less occupied, CO levels reduce, and the system reduces ventilation to conserves energy. DCV is a well-established practice, and is required in high occupancy spaces by building energy standards such as ASHRAE 90.1. | 1 | Applied and Interdisciplinary Chemistry |
The manufacture of asbestos products began on the site in 1879, and by 1970 the factory had an annual output of 2,250,000 yards of asbestos cloth and of asbestos yarn. The dangerous nature of asbestos fibres had first been suspected in 1898, when Factory Inspector Lucy Deane reported: "The evil effects of asbestos dust have also instigated a microscopic examination of the mineral dust by HM Medical Inspector [Thomas Legge]. Clearly revealed was the sharp glass-like jagged nature of the particles, and where they are allowed to rise and to remain suspended in the air of the room in any quantity, the effects have been found to be injurious as might have been expected." In 1924 a 33-year-old Turners employee, Nellie Kershaw, became the first officially recognised victim of asbestosis but the firm refused to accept responsibility for her death, saying it would "create a precedent". Her family received no compensation, and she was buried in a paupers grave in Rochdale.
In 1937, Turners director Robert H. Turner wrote: "All asbestos fibre dust is a danger to lungs. If we can produce evidence from this country that the industry is not responsible for any asbestosis claims, we may be able to avoid tiresome regulations and the introduction of dangerous occupational talk." Despite an awareness of the potentially lethal effects of asbestos, the factory site remained heavily contaminated: measurements taken in 1950 and again in 1957 showed levels of asbestos dust in the air outside the factory roof were between 18 and 60 particles per cubic centimetre - far above the companys own safe working level of 2 to 3 particles, while a measurement taken near houses outside the factory premises was 47 particles. In August 1957, Turners revealed that they were dumping 15,000 lb (6.8 tonnes) of asbestos dust recovered from ventilation filters alone each week. The same document reported that the levels of asbestos dust on the factorys roof exceeded those in the actual production areas inside the factory. In the 1950s people living near the factory joked that the area had frost all year round and the local woods were nicknamed "the snow trees" due to the permanent dusting with asbestos particles.
In 1964 a letter to Turners directors from solicitors James Chapman & Co admitted: "We have over the years been able to talk our way out of claims or compromise for comparatively small amounts, but we have always recognised that at some stage solicitors of experience would, with the advance in medical knowledge and the development of the law, recognise there is no real defence to these claims and take us to trial." By the mid-1970s however the number of asbestos-related deaths began to increase steadily and from 1980 onwards the asbestos market began to decline dramatically. In 1982 the company posted losses of £30million, including compensation payouts of £6million. In 1998, with 263,000 claims for industrial injury pending, Turners was bought by Federal-Mogul. In 2001, Federal-Mogul filed for Chapter 11 bankruptcy protection as a result of asbestos-related claims amounting to $351million. In the United Kingdom the business went into administration in October 2001 leaving a pension fund deficit estimated at £400 million. UK victims of the company's asbestos pollution were offered only a fraction of the compensation to which they were entitled. The weaving and asbestos producing areas of the Spodden Valley site were subsequently demolished in 2001. | 1 | Applied and Interdisciplinary Chemistry |
In retrosynthetic analysis, a synthon is a hypothetical unit within a target molecule that represents a potential starting reagent in the retroactive synthesis of that target molecule. The term was coined in 1967 by E. J. Corey. He noted in 1988 that the "word synthon has now come to be used to mean synthetic building block rather than retrosynthetic fragmentation structures".
It was noted in 1998 that the phrase did not feature very prominently in Coreys 1981 book The Logic of Chemical Synthesis', as it was not included in the index. Because synthons are charged, when placed into a synthesis an uncharged form is found commercially instead of forming and using the potentially very unstable charged synthons. | 0 | Theoretical and Fundamental Chemistry |
Most systems are asymmetric under time reversal, but there may be phenomena with symmetry. In classical mechanics, a velocity v reverses under the operation of T, but an acceleration does not. Therefore, one models dissipative phenomena through terms that are odd in v. However, delicate experiments in which known sources of dissipation are removed reveal that the laws of mechanics are time reversal invariant. Dissipation itself is originated in the second law of thermodynamics.
The motion of a charged body in a magnetic field, B involves the velocity through the Lorentz force term v×B, and might seem at first to be asymmetric under T. A closer look assures us that B also changes sign under time reversal. This happens because a magnetic field is produced by an electric current, J, which reverses sign under T. Thus, the motion of classical charged particles in electromagnetic fields is also time reversal invariant. (Despite this, it is still useful to consider the time-reversal non-invariance in a local sense when the external field is held fixed, as when the magneto-optic effect is analyzed. This allows one to analyze the conditions under which optical phenomena that locally break time-reversal, such as Faraday isolators and [http://magnetooptics.phy.bme.hu/research/topics/optical-properties-of-multiferroic-materials/ directional dichroism], can occur.)
In physics one separates the laws of motion, called kinematics, from the laws of force, called dynamics. Following the classical kinematics of Newton's laws of motion, the kinematics of quantum mechanics is built in such a way that it presupposes nothing about the time reversal symmetry of the dynamics. In other words, if the dynamics are invariant, then the kinematics will allow it to remain invariant; if the dynamics is not, then the kinematics will also show this. The structure of the quantum laws of motion are richer, and we examine these next. | 0 | Theoretical and Fundamental Chemistry |
Nanocrystalline metals can be produced by rapid solidification from the liquid using a process such as melt spinning. This often produces an amorphous metal, which can be transformed into an nanocrystalline metal by annealing above the crystallization temperature. | 1 | Applied and Interdisciplinary Chemistry |
A standard method for the preparation of N-acylamino acids is the Schotten-Baumann reaction, in which oleoyl chloride (from oleic acid and, e.g. phosphorus trichloride) is added to an aqueous solution of N-methylglycine at pH 10 (kept constant by the addition of sodium hydroxide solution).
Fatty acid-free N-oleoylsarcosine is obtained as an oil. The method is not suitable for industrial surfactant synthesis because of the relatively expensive production of the carboxylic acid chlorides and the expensive disposal of the phosphonic acid obtained as a byproduct.
N-Oleoylsarcosine can be obtained in the reaction of oleic acid, N-methylglycine and its sodium salt at 170 °C for 8 to 10 hours upon elimination of water.
More gentle conditions (120 °C) and shorter reaction times (3.5 hours) can be used when methyl oleate is reacted with sodium N-methylglycinate upon the addition of equimolar amounts of sodium methoxide in methanol. After absorption in water, acidification with concentrated sulfuric acid and extraction with butanone, N-Oleoylsarcosine is obtained in 92.5% yield. | 0 | Theoretical and Fundamental Chemistry |
Moroidin, a bicyclic octapeptide, has been isolated from Dendrocnide moroides (also called Laportea moroides) and Celosia argentea. The structure of moroidin was confirmed in 2004 by X-ray crystallography. It contains two unusual crosslinks, one between leucine and tryptophan and the other between tryptophan and histidine. These linkages are also present in an analogous family of compounds, the celogentins. | 0 | Theoretical and Fundamental Chemistry |
Deviations from perfect absorption and perfect black body behavior lead to light losses. For selective emitters, any light emitted at wavelengths not matched to the bandgap energy of the photovoltaic may not be efficiently converted, reducing efficiency. In particular, emissions associated with phonon resonances are difficult to avoid for wavelengths in the deep infrared, which cannot be practically converted. An ideal emitter would emit no light at wavelengths other than at the bandgap energy, and much TPV research is devoted to developing emitters that better approximate this narrow emission spectrum. | 0 | Theoretical and Fundamental Chemistry |
In first order reactions, the rate of reaction will be proportional to the concentration of the reactant. Thus the concentration will decrease exponentially.
as time progresses until it reaches zero, and the half-life will be constant, independent of concentration.
The time for to decrease from to in a first-order reaction is given by the following equation:It can be solved forFor a first-order reaction, the half-life of a reactant is independent of its initial concentration. Therefore, if the concentration of at some arbitrary stage of the reaction is , then it will have fallen to after a further interval of Hence, the half-life of a first order reaction is given as the following:The half-life of a first order reaction is independent of its initial concentration and depends solely on the reaction rate constant, . | 0 | Theoretical and Fundamental Chemistry |
In June 2020, the Cold Atom Laboratory experiment on board the International Space Station successfully created a BEC of rubidium atoms and observed them for over a second in free-fall. Although initially just a proof of function, early results showed that, in the microgravity environment of the ISS, about half of the atoms formed into a magnetically insensitive halo-like cloud around the main body of the BEC. | 0 | Theoretical and Fundamental Chemistry |
SWAT is a continuous time model that operates on a daily time step at basin scale. The objective of such a model is to predict the long-term impacts in large basins of management and also timing of agricultural practices within a year (i.e., crop rotations, planting and harvest dates, irrigation, fertilizer, and pesticide application rates and timing).
It can be used to simulate at the basin scale water and nutrients cycle in landscapes whose dominant land use is agriculture. It can also help in assessing the environmental efficiency of best management practices and alternative management policies. SWAT uses a two-level dissagregation scheme; a preliminary subbasin identification is carried out based on topographic criteria, followed by further discretization using land use and soil type considerations. Areas with the same soil type and land use form a Hydrologic Response Unit (HRU), a basic computational unit assumed to be homogeneous in hydrologic response to land cover change. | 1 | Applied and Interdisciplinary Chemistry |
The disulfide anion is , or S−S. In disulfide, sulfur exists in the reduced state with oxidation number −1. Its electron configuration then resembles that of a chlorine atom. It thus tends to form a covalent bond with another S center to form group, similar to elemental chlorine existing as the diatomic Cl. Oxygen may also behave similarly, e.g. in peroxides such as HO. Examples:
*Hydrogen disulfide (SH), the simplest inorganic disulfide
*Disulfur dichloride (SCl), a distillable liquid.
*Iron disulfide (FeS), or pyrite. | 0 | Theoretical and Fundamental Chemistry |
*[http://www.acadsoft.co.uk/scdbase/scdbase.htm IUPAC SC-Database] A comprehensive database of published data on equilibrium constants of metal complexes and ligands
*[https://www.nist.gov/ts/msd/srd/nist46.cfm NIST Standard Reference Database 46] : Critically selected stability constants of metal complexes
*[https://web.archive.org/web/20081009060809/http://www.chem.wisc.edu/areas/reich/pkatable/ Inorganic and organic acids and bases] pK data in water and DMSO
*[https://web.archive.org/web/20060928231137/http://www.grc.nasa.gov/WWW/CEAWeb/ceaHome.htm NASA Glenn Thermodynamic Database webpage with links to (self-consistent) temperature-dependent specific heat, enthalpy, and entropy for elements and molecules] | 0 | Theoretical and Fundamental Chemistry |
Sauvagine is a neuropeptide from the corticotropin-releasing factor (CRF) family of peptides and is orthologous to the mammalian hormone, urocortin 1, and the teleost fish hormone, urotensin 1. It is 40 amino acids in length, and has the sequence XGPPISIDLSLELLRKMIEIEKQEKEKQQAANNRLLLDTI-NH2, with a pyrrolidone carboxylic acid modification at the N-terminal and amidation of the C-terminal isoleucine residue. It was originally isolated from the skin of the frog Phyllomedusa sauvagii. Given its relation to other CRF-related peptides, it exerts similar physiological effects as corticotropin-releasing hormone.
Sauvagine belongs to the corticotropin-releasing factor (CRF) family that also includes CRF, urocortin l/urotensin l, urocortin II and urocortin III. | 1 | Applied and Interdisciplinary Chemistry |
ChemPRO 100 Chemical Detection System is a handheld chemical detector for field detection and classification of Chemical Warfare Agents. If mail arrives with an unidentified substance, this hand held detector can be used to immediately identify the chemical.
Hardened Mobile Trace Explosive Particle tests for a wide range of explosives and narcotics in seconds. The system will identify explosives in packages or envelopes that are often undetectable by x-ray machines. This handheld detector expands the range of target explosives you can identify in a single sample for faster more comprehensive screening. As noted, this system also detects a wide range of narcotics. The system tests for explosives and narcotics simultaneously in a single sample, for faster, more comprehensive screening. | 0 | Theoretical and Fundamental Chemistry |
Survey magnetometers can be divided into two basic types:
*Scalar magnetometers measure the total strength of the magnetic field to which they are subjected, but not its direction
*Vector magnetometers have the capability to measure the component of the magnetic field in a particular direction, relative to the spatial orientation of the device.
A vector is a mathematical entity with both magnitude and direction. The Earths magnetic field at a given point is a vector. A magnetic compass is designed to give a horizontal bearing direction, whereas a vector magnetometer' measures both the magnitude and direction of the total magnetic field. Three orthogonal sensors are required to measure the components of the magnetic field in all three dimensions.
They are also rated as "absolute" if the strength of the field can be calibrated from their own known internal constants or "relative" if they need to be calibrated by reference to a known field.
A magnetograph is a magnetometer that continuously records data over time. This data is typically represented in magnetograms.
Magnetometers can also be classified as "AC" if they measure fields that vary relatively rapidly in time (>100 Hz), and "DC" if they measure fields that vary only slowly (quasi-static) or are static. AC magnetometers find use in electromagnetic systems (such as magnetotellurics), and DC magnetometers are used for detecting mineralisation and corresponding geological structures. | 0 | Theoretical and Fundamental Chemistry |
There are different ways to derive the summation theorems. One is analytical and rigorous using a combination of linear algebra and calculus. The other is less rigorous, but more operational and intuitive. The latter derivation is shown here.
Consider the two-step pathway:
where and are fixed species so that the system can achieve a steady-state.
Let the pathway be at steady-state and imagine increasing the concentration of enzyme, , catalyzing the first step, , by an amount, . The effect of this is to increase the steady-state levels of S and flux, J. Let us now increase the level of by such that the change in S is restored to the original value it had at steady-state.
The net effect of these two changes is by definition, .
There are two ways to look at this thought experiment, from the perspective of the system and from the perspective of local changes. For the system we can compute the overall change in flux or species concentration by adding the two control coefficient terms, thus:
We can also look at what is happening locally at every reaction step for which there will be two: one for , and another for . Since the thought experiment guarantees that , the local equations are quite simple:
where the terms are the elasticities. However, because the enzyme elasticity is equal to one, these reduce to:
Because the pathway is linear, at steady-state, . We can substitute these expressions into the system equations to give:
Note that at steady state the change in and must be the same, therefore .
Setting , we can rewrite the above equations as:
We then conclude through cancelation of since , that: | 1 | Applied and Interdisciplinary Chemistry |
In optics, Lamberts cosine law says that the radiant intensity or luminous intensity observed from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle θ between the observers line of sight and the surface normal; . The law is also known as the cosine emission law or Lamberts emission law. It is named after Johann Heinrich Lambert, from his Photometria', published in 1760.
A surface which obeys Lamberts law is said to be Lambertian', and exhibits Lambertian reflectance. Such a surface has the same radiance/luminance when viewed from any angle. This means, for example, that to the human eye it has the same apparent brightness. It has the same radiance because, although the emitted power from a given area element is reduced by the cosine of the emission angle, the solid angle, subtended by surface visible to the viewer, is reduced by the very same amount. Because the ratio between power and solid angle is constant, radiance (power per unit solid angle per unit projected source area) stays the same. | 0 | Theoretical and Fundamental Chemistry |
Electrochemistry, a branch of chemistry, went through several changes during its evolution from early principles related to magnets in the early 16th and 17th centuries, to complex theories involving conductivity, electric charge and mathematical methods. The term electrochemistry was used to describe electrical phenomena in the late 19th and 20th centuries. In recent decades, electrochemistry has become an area of current research, including research in batteries and fuel cells, preventing corrosion of metals, the use of electrochemical cells to remove refractory organics and similar contaminants in wastewater electrocoagulation and improving techniques in refining chemicals with electrolysis and electrophoresis. | 0 | Theoretical and Fundamental Chemistry |
Reporter genes can be used to assay for the activity of a particular promoter in a cell or organism. In this case there is no separate "gene of interest"; the reporter gene is simply placed under the control of the target promoter and the reporter gene product's activity is quantitatively measured. The results are normally reported relative to the activity under a "consensus" promoter known to induce strong gene expression. | 1 | Applied and Interdisciplinary Chemistry |
The catalytic properties of eukaryotic complex I are not simple. Two catalytically and structurally distinct forms exist in any given preparation of the enzyme: one is the fully competent, so-called “active” A-form and the other is the catalytically silent, dormant, “inactive”, D-form. After exposure of idle enzyme to elevated, but physiological temperatures (>30 °C) in the absence of substrate, the enzyme converts to the D-form. This form is catalytically incompetent but can be activated by the slow reaction (k~4 min) of NADH oxidation with subsequent ubiquinone reduction. After one or several turnovers the enzyme becomes active and can catalyse physiological NADH:ubiquinone reaction at a much higher rate (k~10 min). In the presence of divalent cations (Mg, Ca), or at alkaline pH the activation takes much longer.
The high activation energy (270 kJ/mol) of the deactivation process indicates the occurrence of major conformational changes in the organisation of the complex I. However, until now, the only conformational difference observed between these two forms is the number of cysteine residues exposed at the surface of the enzyme. Treatment of the D-form of complex I with the sulfhydryl reagents N-Ethylmaleimide or DTNB irreversibly blocks critical cysteine residues, abolishing the ability of the enzyme to respond to activation, thus inactivating it irreversibly. The A-form of complex I is insensitive to sulfhydryl reagents.
It was found that these conformational changes may have a very important physiological significance. The inactive, but not the active form of complex I was susceptible to inhibition by nitrosothiols and peroxynitrite. It is likely that transition from the active to the inactive form of complex I takes place during pathological conditions when the turnover of the enzyme is limited at physiological temperatures, such as during hypoxia, ischemia or when the tissue nitric oxide:oxygen ratio increases (i.e. metabolic hypoxia). | 1 | Applied and Interdisciplinary Chemistry |
Mesoscopic methods operate on length and time scales between the particle and continuum levels. For this reason, they combine elements of particle-based dynamics and continuum hydrodynamics.
An example is the lattice Boltzmann method, which models a fluid as a collection of fictitious particles that exist on a lattice. The particles evolve in time through streaming (straight-line motion) and collisions. Conceptually, it is based on the Boltzmann equation for dilute gases, where the dynamics of a molecule consists of free motion interrupted by discrete binary collisions, but it is also applied to liquids. Despite the analogy with individual molecular trajectories, it is a coarse-grained description that typically operates on length and time scales larger than those of true molecular dynamics (hence the notion of "fictitious" particles).
Other methods that combine elements of continuum and particle-level dynamics include smoothed-particle hydrodynamics, dissipative particle dynamics, and multiparticle collision dynamics. | 0 | Theoretical and Fundamental Chemistry |
In step-growth polymerization, in order to achieve a high degree of polymerization (and hence molecular weight), , a high fractional monomer conversion, p, is required, according to Carothers equation For example, a monomer conversion of p' = 99% would be required to achieve .
For chain-growth free radical polymerization, however, Carothers' equation does not apply. Instead long chains are formed from the beginning of the reaction. Long reaction times increase the polymer yield, but have little effect on the average molecular weight. The degree of polymerization is related to the kinetic chain length, which is the average number of monomer molecules polymerized per chain initiated. However it often differs from the kinetic chain length for several reasons:
* chain termination may occur wholly or partly by recombination of two chain radicals, which doubles the degree of polymerization
* chain transfer to monomer starts a new macromolecule for the same kinetic chain (of reaction steps), corresponding to a decrease of the degree of polymerization
* chain transfer to solvent or to another solute (a modifier or regulator also decreases the degree of polymerization | 0 | Theoretical and Fundamental Chemistry |
Zn isotope ratios vary on small scales throughout the terrestrial biosphere. Zn is released into soils during mineral weathering, and isotopes of Zn fractionate upon interaction with mineral and organic components in the soil. In 5 soil profiles collected from Iceland (all derived from the same parent basalt), soil δZn values varied from +0.10 to +0.35‰, and the organic-rich layers were Zn-depleted relative to the mineral-rich layers, likely due to contribution by isotopically light organic matter and Zn loss by leaching.
Isotopic discrimination of Zn varies in different components of higher plants, likely due to the various processes involved in Zn uptake, binding, transport, diffusion, speciation and compartmentalization. For example, Weiss et al. observed heavier δZn values in the roots of several plants (rice, lettuce and tomato) relative to the bulk solution in which the plants were grown, and the shoots of those plants were Zn-depleted relative to both their roots and bulk solution. Furthermore, Zn isotopes partition differently between different Zn-ligand complexes, so the form of Zn incorporated by organisms in the terrestrial biosphere plays a role in driving Zn isotope compositions of the organisms. In particular, based on ab initio calculations, Zn-phosphate complexes are expected to be isotopically heavier than Zn-citrates, Zn-malates and Zn-histidine complexes by 0.6 to 1‰.
The discharge- and [Zn]-weighted average δZn value of rivers throughout the world is +0.33‰. In particular, the average δZn values of the Kalix and Chang Jiang rivers are +0.64 and +0.56‰, respectively. The Amazon, Missouri and Brahmaputra rivers have average δZn values near +0.30‰, and the average δZn value of the Nile river is +0.21‰. | 0 | Theoretical and Fundamental Chemistry |
n-Butyllithium CHLi (abbreviated n-BuLi) is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene (SBS). Also, it is broadly employed as a strong base (superbase) in the synthesis of organic compounds as in the pharmaceutical industry.
Butyllithium is commercially available as solutions (15%, 25%, 1.5 M, 2 M, 2.5 M, 10 M, etc.) in alkanes such as pentane, hexanes, and heptanes. Solutions in diethyl ether and THF can be prepared, but are not stable enough for storage. Annual worldwide production and consumption of butyllithium and other organolithium compounds is estimated at 2000 to 3000 tonnes.
Although butyllithium is colorless, n-butyllithium is usually encountered as a pale yellow solution in alkanes. Such solutions are stable indefinitely if properly stored, but in practice, they degrade upon aging. Fine white precipitate (lithium hydride) is deposited and the color changes to orange. | 0 | Theoretical and Fundamental Chemistry |
Carbonaceous chondrite fission xenon (CCF Xe), are a collection of different isotopes of xenon that were thought to have arisen from the decay of a superheavy element within the island of stability. Early studies proposed that the half life of the theoretical progenitor of CCF Xe to be on the order of 10 years. A later attempt at characterization of the progenitor in 1975 by Edward Anders, a professor of chemistry at the University of Chicago, and colleague John Larimer suggested a heat of vaporization of 54 kJ/mol and a boiling point of 2500K for the element and, based on estimated accretion temperatures, they also proposed elements 111 and 115 (today named roentgenium and moscovium) as the most likely candidates assuming the element condensed in pure form. | 0 | Theoretical and Fundamental Chemistry |
A number of formal [2+2+2] cycloadditions have been realized under Nb catalysis, including alkyne trimerizations and couplings of alkynes with alkenes or nitriles to form cyclohexadienes or pyridines, respectively. Typically a Nb(III) catalyst will form a Nb(V) metallocyclopropene with a terminal alkyne component and then engage in sequential migratory insertions and reductive elimination to furnish the six membered ring and regenerate the Nb(III).
An organoniobium catalyst has also been developed for (Z)-selective semihydrogenation of alkynes. The mechanistic pathway for this reaction is distinct from other transition metal catalyzed hydrogenations, proceeding through the Nb(V) metallocyclopropene which engages with hydrogen either through direct sigma-bond metathesis or outer sphere 1,2-addition. | 0 | Theoretical and Fundamental Chemistry |
Calcium hydroxide is poorly soluble in water, with a retrograde solubility increasing from 0.66 g/L at 100 °C to 1.89 g/L at 0 °C. With a solubility product K of 5.02 at 25 °C, its dissociation in water is large enough that its solutions are basic according to the following dissolution reaction:
: Ca(OH) → Ca + 2 OH
At ambient temperature, calcium hydroxide (portlandite) dissolves in water to produce an alkaline solution with a pH of about 12.5. Calcium hydroxide solutions can cause chemical burns. At high pH values due to a common-ion effect with the hydroxide anion, its solubility drastically decreases. This behavior is relevant to cement pastes. Aqueous solutions of calcium hydroxide are called limewater and are medium-strength bases, which react with acids and can attack some metals such as aluminium (amphoteric hydroxide dissolving at high pH), while protecting other metals, such as iron and steel, from corrosion by passivation of their surface. Limewater turns milky in the presence of carbon dioxide due to the formation of insoluble calcium carbonate, a process called carbonatation:
: Ca(OH) + CO → CaCO + HO
When heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101kPa (normal atmospheric pressure), which decomposes calcium hydroxide into calcium oxide and water:
: Ca(OH) → CaO + HO
Calcium hydroxide reacts with hydrogen chloride to first give calcium hydroxychloride and then calcium chloride. | 0 | Theoretical and Fundamental Chemistry |
ScBSi has a tetragonal crystal structure with space group P422 (No. 92) or P422 and lattice constants of a, b = 1.03081(2) and c = 1.42589(3) nm; it is
isotypic to the α-AlB structure type. There are 28 atomic sites in the unit cell, which are assigned to 3 scandium atoms, 24 boron atoms and one silicon atom. Atomic coordinates, site occupancies and isotropic displacement factors are listed in table VI.
The boron framework of ScBSi is based on one B icosahedron and one B unit. This unit can be observed in β-tetragonal boron and is a modification of the B unit of α-AlB (or B unit in early reports). The B unit is a twinned icosahedron made from B13 to B22 sites with two vacant sites and one B atom (B23) bridging both sides of the unit. The twinned icosahedron is shown in figure 18a. B23 was treated as an isolated atom in the early reports; it is bonded to each twinned icosahedra through B18 and to another icosahedron through B5 site. If the twinned icosahedra were independent without twinning then B23 would be a bridge site linking three icosahedra. However, because of twinning, B23 shifts closer to the twinned icosahedra than another icosahedron; thus B23 is currently treated as a member of the twinned icosahedra. In ScBSi, the two B24 sites which correspond to the vacant sites in the B unit are partially occupied; thus, the unit should be referred to as a B cluster which is occupied by about 20.6 boron atoms. Scandium atoms occupy 3 of 5 Al sites of α-AlB, that is Sc1, Sc2 and Sc3 correspond to Al4, Al1 and Al2 sites of α-AlB, respectively. The Al3 and Al5 sites are empty for ScBSi, and the Si site links two B units. This phase also exists without silicon.
Figure 19a shows the network of boron icosahedra in the boron framework of ScBSi. In this network, 4 icosahedra form a supertetrahedron (figure 18b); its one edge is parallel to the a-axis, and the icosahedra on this edge make up a chain along the a-axis. The opposite edge of the supertetrahedron is parallel to the b-axis and the icosahedra on this edge form a chain along the b-axis. As shown in figure 19, there are wide tunnels surrounded by the icosahedron arrangement along the a- and b-axes. The tunnels are filled by the B units which strongly bond to the surrounding icosahedra; the connection of the B units is helical and it runs along the c-axis as shown in figure 19b. Scandium atoms occupy the voids in the boron network as shown in figure 19c, and the Si atoms bridge the B units. | 0 | Theoretical and Fundamental Chemistry |
Despite early successes such as the determination of the positions of hydrogen atoms in NHCl crystals by W. E. Laschkarew and I. D. Usykin in 1933, boric acid by John M. Cowley in 1953 and orthoboric acid by William Houlder Zachariasen in 1954, electron diffraction for many years was a qualitative technique used to check samples within electron microscopes. John M Cowley explains in a 1968 paper: This has changed, in transmission, reflection and for low energies. Some of the key developments (some of which are also described later) from the early days to 2023 have been:
*Fast numerical methods based upon the Cowley-Moodie multislice algorithm, which only became possible once the fast Fourier transform (FFT) method was developed. With these and other numerical methods Fourier transforms are fast, and it became possible to calculate accurate, dynamical diffraction in seconds to minutes with laptops using widely available multislice programs.
*Developments in the convergent-beam electron diffraction approach. Building on the original work of Walther Kossel and Gottfried Möllenstedt in 1939, it was extended by Peter Goodman and Gunter Lehmpfuhl, then mainly by the groups of John Steeds and Michiyoshi Tanaka who showed how to determine point groups and space groups. It can also be used for higher-level refinements of the electron density; for a brief history see CBED history. In many cases this is the best method to determine symmetry.
*The development of new approaches to reduce dynamical effects such as precession electron diffraction and three-dimensional diffraction methods. Averaging over different directions has, empirically, been found to significantly reduce dynamical diffraction effects, e.g., see PED history for further details. Not only is it easier to identify known structures with this approach, it can also be used to solve unknown structures in some cases – see precession electron diffraction for further information.
*The development of experimental methods exploiting ultra-high vacuum technologies (e.g. the approach described by in 1953) to better control surfaces, making LEED and RHEED more reliable and reproducible techniques. In the early days the surfaces were not well controlled; with these technologies they can both be cleaned and remain clean for hours to days, a key component of surface science.
*Fast and accurate methods to calculate intensities for LEED so it could be used to determine atomic positions, for instance references. These have been extensively exploited to determine the structure of many surfaces, and the arrangement of foreign atoms on surfaces.
*Methods to simulate the intensities in RHEED, so it can be used semi-quantitatively to understand surfaces during growth and thereby to control the resulting materials.
*The development of advanced detectors for transmission electron microscopy such as charge-coupled device and direct electron detectors, which improve the accuracy and reliability of intensity measurements. These have efficiencies and accuracies that can be a thousand or more times that of the photographic film used in the earliest experiments, with the information available in real time rather than requiring photographic processing after the experiment. | 0 | Theoretical and Fundamental Chemistry |
Volatile organic compounds (VOCs) are organic compounds that have a high vapor pressure at room temperature. High vapor pressure correlates with a low boiling point, which relates to the number of the sample's molecules in the surrounding air, a trait known as volatility.
VOCs are responsible for the odor of scents and perfumes as well as pollutants. VOCs play an important role in communication between animals and plants, e.g. attractants for pollinators, protection from predation, and even inter-plant interactions. Some VOCs are dangerous to human health or cause harm to the environment. Anthropogenic VOCs are regulated by law, especially indoors, where concentrations are the highest. Most VOCs are not acutely toxic, but may have long-term chronic health effects. Some VOCs have been used in pharmacy, while others are target of administrative controls because of their recreational use. | 0 | Theoretical and Fundamental Chemistry |
Imaging of biophotons from leaves has been used as a method for assaying R gene responses. These genes and their associated proteins are responsible for pathogen recognition and activation of defense signaling networks leading to the hypersensitive response, which is one of the mechanisms of the resistance of plants to pathogen infection. It involves the generation of reactive oxygen species (ROS), which have crucial roles in signal transduction or as toxic agents leading to cell death.
Biophotons have been also observed in the roots of stressed plants. In healthy cells, the concentration of ROS is minimized by a system of biological antioxidants. However, heat shock and other stresses changes the equilibrium between oxidative stress and antioxidant activity, for example, the rapid rise in temperature induces biophoton emission by ROS. | 1 | Applied and Interdisciplinary Chemistry |
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