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Gaussian plume models can be used in several fluid dynamics scenarios to calculate concentration distribution of solutes, such as a smoke stack release or contaminant released in a river. Gaussian distributions are established by Fickian diffusion, and follow a Gaussian (bell-shaped) distribution. For calculating the expected concentration of a one dimensional instantaneous point source we consider a mass released at an instantaneous point in time, in a one dimensional domain along . This will give the following equation:
where is the mass released at time and location , and is the diffusivity . This equation makes the following four assumptions:
# The mass is released instantaneously.
# The mass is released in an infinite domain.
# The mass spreads only through diffusion.
# Diffusion does not vary in space. | 1 | Applied and Interdisciplinary Chemistry |
One of the main sources of information about the Earths composition comes from understanding the relationship between peridotite and basalt melting. Peridotite makes up most of Earths mantle. Basalt, which is highly concentrated in the Earths oceanic crust, is formed when magma reaches the Earths surface and cools down at a very fast rate. When magma cools, different minerals crystallize at different times depending on the cooling temperature of that respective mineral. This ultimately changes the chemical composition of the melt as different minerals begin to crystallize. Fractional crystallization of elements in basaltic liquids has also been studied to observe the composition of lava in the upper mantle. This concept can be applied by scientists to give insight on the evolution of Earth's mantle and how concentrations of lithophile trace elements have varied over the last 3.5 billion years. | 0 | Theoretical and Fundamental Chemistry |
The journal is abstracted and indexed in:
According to the Journal Citation Reports, its 2012 impact factor is 1.922, ranking it 12th out of 31 journals in the category "Medical Laboratory Technology". | 1 | Applied and Interdisciplinary Chemistry |
Aqueous monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), diisopropanolamine (DIPA) and methyldiethanolamine (MDEA) are widely used industrially for removing carbon dioxide (CO) and hydrogen sulfide (HS) from natural gas and refinery process streams. They may also be used to remove CO from combustion gases and flue gases and may have potential for abatement of greenhouse gases. Related processes are known as sweetening. | 0 | Theoretical and Fundamental Chemistry |
A reaction is said to be second order when the overall order is two. The rate of a second-order reaction may be proportional to one concentration squared, or (more commonly) to the product of two concentrations, As an example of the first type, the reaction is second-order in the reactant and zero order in the reactant CO. The observed rate is given by and is independent of the concentration of CO.
For the rate proportional to a single concentration squared, the time dependence of the concentration is given by
The time dependence for a rate proportional to two unequal concentrations is
if the concentrations are equal, they satisfy the previous equation.
The second type includes nucleophilic addition-elimination reactions, such as the alkaline hydrolysis of ethyl acetate:
This reaction is first-order in each reactant and second-order overall:
If the same hydrolysis reaction is catalyzed by imidazole, the rate equation becomes
The rate is first-order in one reactant (ethyl acetate), and also first-order in imidazole, which as a catalyst does not appear in the overall chemical equation.
Another well-known class of second-order reactions are the S2 (bimolecular nucleophilic substitution) reactions, such as the reaction of n-butyl bromide with sodium iodide in acetone:
This same compound can be made to undergo a bimolecular (E2) elimination reaction, another common type of second-order reaction, if the sodium iodide and acetone are replaced with sodium tert-butoxide as the salt and tert-butanol as the solvent: | 0 | Theoretical and Fundamental Chemistry |
K2.3 channels play a major role in human physiology, particularly in smooth muscle relaxation. The expression level of K2.3 channels in the endothelium influences arterial tone by setting arterial smooth muscle membrane potential. The sustained activity of K2.3 channels induces a sustained hyperpolarisation of the endothelial cell membrane potential, which is then carried to nearby smooth muscle through gap junctions. Blocking the K2.3 channel or suppressing K2.3 expression causes a greatly increased tone in resistance arteries, producing an increase in peripheral resistance and blood pressure. | 1 | Applied and Interdisciplinary Chemistry |
The production of butanol by biological means was first performed by Louis Pasteur in 1861. In 1905, Austrian biochemist Franz Schardinger found that acetone could similarly be produced. In 1910 Auguste Fernbach (1860–1939) developed a bacterial fermentation process using potato starch as a feedstock in the production of butanol.
Industrial exploitation of ABE fermentation started in 1916, during World War I, with Chaim Weizmann's isolation of Clostridium acetobutylicum, as described in U.S. patent 1315585.
The Weizmann process was operated by Commercial Solvents Corporation from about 1920 to 1964 with plants in the US (Terre Haute, IN, and Peoria, IL), and Liverpool, England. The Peoria plant was the largest of the three. It used molasses as feedstock and had 96 fermenters with a volume of 96,000 gallons each.
After World War II, ABE fermentation became generally non-profitable, compared to the production of the same three solvents (acetone, butanol, ethanol) from petroleum. During the 1950s and 1960s, ABE fermentation was replaced by petroleum chemical plants. Due to different raw material costs, ABE fermentation was viable in South Africa until the early 1980s, with the last plant closing in 1983. Green Biologics Ltd operated the last attempt to resurrect the process at scale but the plant closed in Minnesota in June 2019.
A new ABE biorefinery has been developed in Scotland by Celtic Renewables Ltd and will begin production in early 2022. The key difference in the process is the use of low value spent materials or residues from other processes removing the variable costs of raw feedstock crops and materials. | 1 | Applied and Interdisciplinary Chemistry |
Zanamivir and Oseltamivir have been tested as hNEU inhibitors. Only Zanamivir shows moderate inhibition activity for hNEU. Isoenzyme selective inhibitors could potentially be very important. At present there are limited studies for the hNEU substrate specificity. DANA is a pan-selective inhibitor for all hNEU isoenzymes, with a difference from 2 to 10 fold inhibition activity, most effective for hNEU3 and hNEU4. Several reports have tested DANA-derivatives as inhibitors for hNEU2 and hNEU3. Most derivatives showed reduced inhibition in vitro. However, N5-azidoacetate-C9-azido derivative of DANA showed improved inhibition for hNEU2 and hNEU3. These studies concluded that the active site in the enzymes could tolerate large modifications at C9 better than at N5. Testing of C9 amido derivatives of DANA showed hNEU1-selective inhibitors. These compounds showed more activity then DANA and only minor activity for hNEU3 with around 25-fold selectivity for hNEU1. These studies show that the glycerol side-chain pocket in the active site can potentially be manipulated in the design of isoenzyme selective inhibitors for hNEU. A combination of C4 and C7 modified DANA derivatives has been reported with moderate selectivity for hNEU2 and hNEU3. Finally C9-triazole derivatives of DANA containing an alkoxy group with a nanomolar activity against hNEU4 isoenzyme have been reported. With a 500-fold selectivity for hNEU4, this is the highest reported selectivity for a hNEU isoenzyme to date. | 1 | Applied and Interdisciplinary Chemistry |
The Mg ion tends to bind only weakly to proteins (K ≤ 10) and this can be exploited by the cell to switch enzymatic activity on and off by changes in the local concentration of Mg. Although the concentration of free cytoplasmic Mg is on the order of 1 mmol/L, the total Mg content of animal cells is 30 mmol/L and in plants the content of leaf endodermal cells has been measured at values as high as 100 mmol/L (Stelzer et al., 1990), much of which buffered in storage compartments. The cytoplasmic concentration of free Mg is buffered by binding to chelators (e.g., ATP), but also, what is more important, it is buffered by storage of Mg in intracellular compartments. The transport of Mg between intracellular compartments may be a major part of regulating enzyme activity. The interaction of Mg with proteins must also be considered for the transport of the ion across biological membranes. | 1 | Applied and Interdisciplinary Chemistry |
The reflection point groups, defined by 1 to 3 mirror planes, can also be given by their Coxeter group and related polyhedra. The [3,3] group can be doubled, written as , mapping the first and last mirrors onto each other, doubling the symmetry to 48, and isomorphic to the [4,3] group. | 0 | Theoretical and Fundamental Chemistry |
Erosion corrosion is a form of corrosion damage usually on a metal surface caused by turbulence of a liquid or solid containing liquid and the metal surface. Aluminum can be particularly susceptible due to the fact that the aluminum oxide layer which affords corrosion protection to the underlying metal is eroded away. | 1 | Applied and Interdisciplinary Chemistry |
Nonribosomal peptides are synthesized by one or more specialized nonribosomal peptide-synthetase (NRPS) enzymes. The NRPS genes for a certain peptide are usually organized in one operon in bacteria and in gene clusters in eukaryotes. However the first fungal NRP to be found was ciclosporin. It is synthesized by a single 1.6MDa NRPS. The enzymes are organized in modules that are responsible for the introduction of one additional amino acid. Each module consists of several domains with defined functions, separated by short spacer regions of about 15 amino acids.
The biosynthesis of nonribosomal peptides shares characteristics with the polyketide and fatty acid biosynthesis. Due to these structural and mechanistic similarities, some nonribosomal peptide synthetases contain polyketide synthase modules for the insertion of acetate or propionate-derived subunits into the peptide chain.
Note that as many as 10% percent of bacterial NRPS are not laid out as large modular proteins, but as separate enzymes. Some NRPS modules deviate from the standard domain structure, and some extra domains have been described. There are also NRPS enzymes that serve as a scaffold for other modifications to the substrate to incorporate unusual amino acids. | 1 | Applied and Interdisciplinary Chemistry |
The James Webb Space Telescope uses radiative cooling to reach its operation temperature of about 50 K. To do this, its large reflective sunshield blocks radiation from the Sun, Earth, and Moon. The telescope structure, kept permanently in shadow by the sunshield, then cools by radiation. | 0 | Theoretical and Fundamental Chemistry |
The structure function, like the fragmentation function, is a probability density function in physics. It is somewhat analogous to the structure factor in solid-state physics, and the form factor (quantum field theory).
The nucleon (proton and neutron) electromagnetic form factors describe the spatial distributions of electric charge and current inside the nucleon and thus are intimately related to its internal structure; these form factors are among the most basic observables of the nucleon. (Nucleons are the building blocks of almost all ordinary matter in the universe. The challenge of understanding the nucleon's structure and dynamics has occupied a central place in nuclear physics.)
The structure functions are important in the study of deep inelastic scattering.
The fundamental understanding of structure functions in terms of QCD is one of the outstanding problems in hadron physics. Why do quarks form colourless hadrons with only two stable configurations, proton and neutron? One important step towards answering this question is to characterize the internal structure of the nucleon. High energy electron scattering provides one of the most powerful tools to investigate this structure. | 0 | Theoretical and Fundamental Chemistry |
Hot water service piping can also be traced, so that a circulating system is not needed to provide hot water at outlets. The combination of trace heating and the correct thermal insulation for the operating ambient temperature maintains a thermal balance where the heat output from the trace heating matches the heat loss from the pipe. Self-limiting or regulating heating tapes have been developed and are very successful in this application.
A similar principle can be applied to process piping carrying fluids which may congeal at low temperatures, for example, tars or molten sulfur. Hit-temperature trace heating elements can prevent blockage of pipes.
Industrial applications for trace heating range from chemical industry, oil refineries, nuclear power plants, food factories. For example, wax is a material which starts to solidify below 70 °C which is usually far above the temperature of the surrounding air. Therefore, the pipeline must be provided with an external source of heat to prevent the pipe and the material inside it from cooling down. Trace heating can also be done with steam, but this requires a source of steam and may be inconvenient to install and operate.
In laboratories, researchers working in the field of materials science use trace heating to heat a sample isotropically. They may use trace heating in conjunction with a variac, so as to control the heat energy delivered. This is an effective means of slowly heating an object to measure thermodynamic properties such as thermal expansion. | 1 | Applied and Interdisciplinary Chemistry |
ECS Meeting Abstracts contain extended abstracts of the technical papers presented at the ECS biannual meetings and ECS-sponsored meetings. This publication offers a first look into current research in the field. ECS Meeting Abstracts are freely available to all visitors to the ECS Digital Library. | 0 | Theoretical and Fundamental Chemistry |
Three major forms of hCG are produced by humans, with each having distinct physiological roles. These include regular hCG, hyperglycosylated hCG, and the free beta-subunit of hCG. Degradation products of hCG have also been detected, including nicked hCG, hCG missing the C-terminal peptide from the beta-subunit, and free alpha-subunit, which has no known biological function. Some hCG is also made by the pituitary gland with a pattern of glycosylation that differs from placental forms of hCG.
Regular hCG is the main form of hCG associated with the majority of pregnancy and in non-invasive molar pregnancies. This is produced in the trophoblast cells of the placental tissue. Hyperglycosylated hCG is the main form of hCG during the implantation phase of pregnancy, with invasive molar pregnancies, and with choriocarcinoma.
Gonadotropin preparations of hCG can be produced for pharmaceutical use from animal or synthetic sources. | 1 | Applied and Interdisciplinary Chemistry |
TNP-ATP should be stored at −20 degrees Celsius, in the dark, and used under minimal lighting conditions. When in solution, TNP-ATP has a shelf-life of about 30 days. | 0 | Theoretical and Fundamental Chemistry |
Hägg studied chemistry at Stockholm University from 1922, was a Ramsay Fellow at the University of London in 1926, studying under Frederick G. Donnan. He obtained his PhD in Stockholm in 1929 under Arne Westgren for the work X-ray studies on the binary systems of iron with nitrogen, phosphorus, arsenic, antimony and bismuth. After that he became a lecturer at the Stockholm University and in 1930 at the University of Jena, Germany. In 1937 he became professor of inorganic and general chemistry at Uppsala University. He retired in 1969.
Hägg's research dealt with nitrides, borides, carbides and hydrides of transition metals and determined their crystal structure with X-ray diffraction. He also developed X-ray cameras and calculating machines for this purpose. His investigations into phases and phase transformations in steel had practical applications. In Sweden he is known for his university chemistry textbooks. | 0 | Theoretical and Fundamental Chemistry |
Due to its inherent microbial nature, nitrification in soils is greatly susceptible to soil conditions. In general, soil nitrification will proceed at optimal rates if the conditions for the microbial communities foster healthy microbial growth and activity. Soil conditions that have an effect on nitrification rates include:
*Substrate availability (presence of NH)
*Aeration (availability of O)
*Soil moisture content (availability of HO)
*pH (near neutral)
*Temperature | 1 | Applied and Interdisciplinary Chemistry |
Analytical International Methods & Standards (AIMS) program focuses on capability gaps in laboratory testing, emerging microbial threats to food safety, and developing standards for using cutting-edge technologies. | 0 | Theoretical and Fundamental Chemistry |
The AMoN measures ambient ammonia gas concentrations over a two-week period via a Radiello®-passive sampler, which is a simple diffusive sampler that offers higher capacity and faster sampling rates than other devices. Therefore, AMoN can provide reliable data to aid in meeting air quality policies and administration needs. AMoN collects data biweekly to determine the spatial variability and seasonality of ammonia concentrations. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, dynamic stereochemistry studies the effect of stereochemistry on the reaction rate of a chemical reaction. Stereochemistry is involved in:
* stereospecific reactions
* stereoselective or asymmetric reactions
* racemisation processes | 0 | Theoretical and Fundamental Chemistry |
Baroclinic instability is a fluid dynamical instability of fundamental importance in the atmosphere and in the oceans. In the atmosphere it is the dominant mechanism shaping the cyclones and anticyclones that dominate weather in mid-latitudes. In the ocean it generates a field of mesoscale eddies (100 km or smaller) that play various roles in oceanic dynamics and the transport of tracers.
Whether a fluid counts as rapidly rotating is determined in this context by the Rossby number, which is a measure of how close the flow is to solid body rotation. More precisely, a flow in solid body rotation has vorticity that is proportional to its angular velocity. The Rossby number is a measure of the departure of the vorticity from that of solid body rotation. The Rossby number must be small for the concept of baroclinic instability to be relevant. When the Rossby number is large, other kinds of instabilities, often referred to as inertial, become more relevant.
The simplest example of a stably stratified flow is an incompressible flow with density decreasing with height.
In a compressible gas such as the atmosphere, the relevant measure is the vertical gradient of the entropy, which must increase with height for the flow to be stably stratified.
The strength of the stratification is measured by asking how large the vertical shear of the horizontal winds has to be in order to destabilize the flow and produce the classic Kelvin–Helmholtz instability. This measure is called the Richardson number. When the Richardson number is large, the stratification is strong enough to prevent this shear instability.
Before the classic work of Jule Charney and Eric Eady on baroclinic instability in the late 1940s, most theories trying to explain the structure of mid-latitude eddies took as their starting points the high Rossby number or small Richardson number instabilities familiar to fluid dynamicists at that time. The most important feature of baroclinic instability is that it exists even in the situation of rapid rotation (small Rossby number) and strong stable stratification (large Richardson's number) typically observed in the atmosphere.
The energy source for baroclinic instability is the potential energy in the environmental flow. As the instability grows, the center of mass of the fluid is lowered.
In growing waves in the atmosphere, cold air moving downwards and equatorwards displaces the warmer air moving polewards and upwards.
Baroclinic instability can be investigated in the laboratory using a rotating, fluid filled annulus. The annulus is heated at the outer wall and cooled at the inner wall, and the resulting fluid flows give rise to baroclinically unstable waves.
The term "baroclinic" refers to the mechanism by which vorticity is generated. Vorticity is the curl of the velocity field. In general, the evolution of vorticity can be broken into contributions from advection (as vortex tubes move with the flow), stretching and twisting (as vortex tubes are pulled or twisted by the flow) and baroclinic vorticity generation, which occurs whenever there is a density gradient along surfaces of constant pressure. Baroclinic flows can be contrasted with barotropic flows in which density and pressure surfaces coincide and there is no baroclinic generation of vorticity.
The study of the evolution of these baroclinic instabilities as they grow and then decay is a crucial part of developing theories for the fundamental characteristics of midlatitude weather. | 1 | Applied and Interdisciplinary Chemistry |
For low nuclearity clusters, bonding is often described as if it is localized. For this purpose, the 18-electron rule is used. Thus, 34 electrons in an organometallic complex predicts a dimetallic complex with a metal-metal bond. For higher nuclearity clusters, more elaborate rules are invoked including Jemmis mno rules and polyhedral skeletal electron pair theory.
Although clusters are often written with discrete M-M bonds, the nature of this bonding is unclear, especially when there are bridging ligands. | 0 | Theoretical and Fundamental Chemistry |
Rothalpy (or trothalpy) , a short name of rotational stagnation enthalpy, is a fluid mechanical property of importance in the study of flow within rotating systems. | 1 | Applied and Interdisciplinary Chemistry |
Wilson was born in Colonia Pacheco, Chihuahua (one of the Mormon colonies in Mexico). He did his undergraduate work at BYU in 1953 and then attended and graduated from Massachusetts Institute of Technology (MIT) with a PhD in physical chemistry in 1957.
While at MIT he began his career by developing one of the first computer-based activity coefficient equations. Known as the Wilson Equation, it is one of the most widely used equations in the field of industrial thermodynamics for the prediction of phase equilibria.
Wilson has been a research scientist measuring and reporting physical properties and phase equilibria data for most of his career. He joined Shell Research and Development in California upon graduating from MIT, he then joined Air Products and later moved to PVT Inc. of Houston, Texas. While there he performed a number of Research Projects for the Gas Processors Association. At this time he also did extensive work with cubic equations of state (EOS), he was one of the first to modify the alpha form of the Redlich-Kwong EOS to better represent pure component vapor pressures.
He next taught at BYU in Provo, Utah, from 1970 to 1978 while there he was a part of the on-campus research group, the Thermochemical Institute founded by Profs. James J. Christensen and Reed M. Izatt. Wilson left BYU to create the company Wilco (now [http://www.wiltecresearch.com/ Wiltec]) Research Company in 1977 which measured data for the Chemical Process Industries (CPI).
The Wilson equation was published by Grant M. Wilson as "Vapor-Liquid Equilibrium. XI. A New Expression for the Excess Free Energy of Mixing" in the Journal of the American Chemical Society 86:127-130, 1964.
Wilson and his wife, Reta Raphiel were married in the Logan Temple on September 18, 1950. Together in 2002, they served as missionaries for the Church of Jesus Christ of Latter-day Saints in Bangalore, India for two years.
Wilson died on September 10, 2012, in Orem, Utah.
Wilson's hobby was hiking in the mountains. His favorite climb was Mt. Timpanogos. | 0 | Theoretical and Fundamental Chemistry |
Brownrigg returned to Britain and took up medicine with an established doctor called Richard Senhouse in Whitehaven. Senhouse died soon after, making Brownrigg the principal doctor in the area for many years to come. His casebook for 1737-1742 survives and was recently transcribed. It contains descriptions of his patients and remedies and some of the earliest English references to puerperal fever.
In 1741, Brownrigg married Mary Spedding. Marys father and uncle ran the collieries for James Lowther, whose family had developed Whitehaven into a major seaport. This increased Williams local influence and also promoted his interest in the health and welfare of the miners.
Later in 1771, with the threat of an epidemic from Europe, Brownrigg who had studied the subject from outbreaks of typhus at Whitehaven, published a paper "Considerations on the means of pestilential contagion, and of Eradicating it in Infected Places." | 1 | Applied and Interdisciplinary Chemistry |
The Goldich dissolution series can be applied to Lithosequences, which are a way characterizing of a soil profile based on its parent material. Lithosequences include soils that have undergone relatively similar weathering conditions, so variations in composition are based on the relative weathering rates of parent minerals. Therefore, the weathering rates of these soils and their compositions are primarily influenced by the relative proportion of minerals in the Goldich dissolution series. | 0 | Theoretical and Fundamental Chemistry |
Frankland took the view that the valence (he used the term "atomicity") of an element was a single value that corresponded to the maximum value observed. The number of unused valencies on atoms of what are now called the p-block elements is generally even, and Frankland suggested that the unused valencies saturated one another. For example, nitrogen has a maximum valence of 5, in forming ammonia two valencies are left unattached; sulfur has a maximum valence of 6, in forming hydrogen sulphide four valencies are left unattached.
The International Union of Pure and Applied Chemistry (IUPAC) has made several attempts to arrive at an unambiguous definition of valence. The current version, adopted in 1994:
:The maximum number of univalent atoms (originally hydrogen or chlorine atoms) that may combine with an atom of the element under consideration, or with a fragment, or for which an atom of this element can be substituted.
Hydrogen and chlorine were originally used as examples of univalent atoms, because of their nature to form only one single bond. Hydrogen has only one valence electron and can form only one bond with an atom that has an incomplete outer shell. Chlorine has seven valence electrons and can form only one bond with an atom that donates a valence electron to complete chlorines outer shell. However, chlorine can also have oxidation states from +1 to +7 and can form more than one bond by donating valence electrons'.
Hydrogen has only one valence electron, but it can form bonds with more than one atom. In the bifluoride ion (), for example, it forms a three-center four-electron bond with two fluoride atoms:
Another example is the three-center two-electron bond in diborane (). | 0 | Theoretical and Fundamental Chemistry |
* Lamprophyres and melilitic rocks
* Kimberlite
* Lamproite
* Orangeite (see Group II kimberlite)
* Feldspathoid-bearing rocks such as leucitites
* K-feldspar enriched leucogranites
* Vaugnerite and Durbachite | 0 | Theoretical and Fundamental Chemistry |
Polar liquids have a tendency to be more viscous than nonpolar liquids. For example, nonpolar hexane is much less viscous than polar water. However, molecule size is a much stronger factor on viscosity than polarity, where compounds with larger molecules are more viscous than compounds with smaller molecules. Thus, water (small polar molecules) is less viscous than hexadecane (large nonpolar molecules). | 0 | Theoretical and Fundamental Chemistry |
The Society for Applied Spectroscopy was selected by Kowalskis family to administer an award in Kowalskis name, the Bruce R. Kowalski Award in Chemometrics - Administered by the Society for Applied Spectroscopy, "to honor the legacy of Professor Kowalski by recognizing outstanding young researchers in the field of chemometrics and by extension, for advanced mathematical and/or statistical methods in chemistry."
The University of Washington has three scholarships set up in Kowalskis honor, the Kowalski Excellence in Graduate Education Fund, Bruce Kowalski Endowed Fund for Graduate Student Support, and the chemistry departments Bruce R. Kowalski Endowed Fund in Chemistry.
In 2015 the American Chemical Society published a symposium series in Kowalskis honor, 40 Years of Chemometrics – From Bruce Kowalski to the Future.'
The Kowalski Prize, worth $1,000, is given annually by the Journal of Chemometrics, alternating between "the best theoretical paper and best applied paper published in the journal in the previous two years." | 0 | Theoretical and Fundamental Chemistry |
Because of their high mechanical, thermal and chemical stability, variable manufacturing of pore sizes with a small pore size distribution and variety of surface modifications, a wide array of applications are possible. The fact that porous glasses can be produced in many different shapes is another advantage for application in industry, medicine, pharmacy research, biotechnology and sensor technology.
Porous glasses are ideal for material separation, because of the small pore size distribution. This is why they are used in gas chromatography, thin layer chromatography and affinity chromatography. An adaptation of stationary phase for a separation problem is possible by a specific modification of the surface of the porous glass.
In biotechnology, porous glasses have benefits for the cleaning of DNA and the immobilization of enzymes or microorganisms. Controlled pore glass (CPG) with pore sizes between 50 and 300 nm is also excellently suited for the synthesis of oligonucleotides. In this application, a linker, a nucleoside or a non-nucleosidic compound, is first attached to the surface of CPG. The chain length of produced oligonucleotides is dependent on the pore size of CPG.
In addition, porous glasses are used for manufacturing implants, especially dental implants, for which porous glass powder is processed with plastics to form a composite. The particle size and the pore size influence the elasticity of the composite so as to fit the optical and mechanical properties to surrounding tissue, for example, the appearance and hardness of dental enamel.
With the ability to form porous glasses as platelets, membrane technology is another important area of application. Hyper filtration of sea – and brackish water and ultra filtration in "downstream process" are but two. Additionally, they are often appropriate as a carrier for catalysts. For example, the olefin – metathesis was realized on the system metal – metal oxide/porous glass.
Porous glasses can be used as membrane reactors as well, again because of their high mechanical, thermal and chemical stability. Membrane reactors can improve conversion of limited balance reactions, while one reaction product is removed by a selective membrane. For example, in the decomposition of hydrogen sulfide on a catalyst in a glass capillary, the conversion by reaction was higher with glass capillary than without. | 0 | Theoretical and Fundamental Chemistry |
Phenolphthalein has been used for over a century as a laxative, but is now being removed from over-the-counter laxatives over concerns of carcinogenicity. Laxative products formerly containing phenolphthalein have often been reformulated with alternative active ingredients: Feen-a-Mint switched to bisacodyl, and Ex-Lax was switched to a senna extract.
Thymolphthalein is a related laxative made from thymol.
Despite concerns regarding its carcinogenicity based on rodent studies, the use of phenolphthalein as a laxative is unlikely to cause ovarian cancer. Some studies suggest a weak association with colon cancer, while others show none at all.
Phenolphthalein is described as a stimulant laxative. In addition, it has been found to inhibit human cellular calcium influx via store-operated calcium entry (SOCE, see ) in vivo. This is effected by its inhibiting thrombin and thapsigargin, two activators of SOCE that increase intracellular free calcium.
Phenolphthalein has been added to the European Chemicals Agency's candidate list for substance of very high concern (SVHC). It is on the IARC group 2B list for substances "possibly carcinogenic to humans".
The discovery of phenolphthalein's laxative effect was due to an attempt by the Hungarian government to label genuine local white wine with the substance in 1900. Phenolphthalein did not change the taste of the wine and would change color when a base is added, making it a good label in principle. However, it was found that ingestion of the substance led to diarrhea. Max Kiss, a Hungarian-born pharmacist residing in New York, heard about the news and launched Ex-Lax in 1906. | 0 | Theoretical and Fundamental Chemistry |
The reaction substrate has also been extended to allenes. In this specific ring expansion the AAA reaction is also accompanied by a Wagner–Meerwein rearrangement: | 0 | Theoretical and Fundamental Chemistry |
If the structure is not known, the average bond valence, S can be calculated from the atomic valence, V, if the coordination number, N, of the atom is known using Eq. 3.
: (Eq. 3)
If the coordination number is not known, a typical coordination number for the atom can be used instead. Some atoms, such as sulfur(VI), are only found with one coordination number with oxygen, in this case 4, but others, such as sodium, are found with a range of coordination numbers, though most lie close to the average, which for sodium is 6.2. In the absence of any better information, the average coordination number observed with oxygen is a convenient approximation, and when this number is used in Eq. 3, the resulting average bond valence is known as the bonding strength of the atom.
Since the bonding strength of an atom is the valence expected for a bond formed by that atom, it follows that the most stable bonds will be formed between atoms with the same bonding strengths. In practice some tolerance is allowed, but bonds are rarely formed if the ratio of the bonding strengths of the two atoms exceeds two, a condition expressed by the inequality shown in Eq. 4. This is known and the valence matching rule.
: (Eq. 4)
Atoms with non-bonding valence electrons, i.e., with lone pairs, have more flexibility in their bonding strength than those without lone pairs depending on whether the lone pairs are stereoactive or not. If the lone pairs are not stereoactive, they are spread uniformly around the valence shell, if they are stereoactive they are concentrated in one portion of the coordination sphere preventing that portion from forming bonds. This results in the atom having a smaller coordination number, hence a higher bonding strength, when the lone pair is stereoactive. Ions with lone pairs have a greater ability to adapt their bonding strength to match that of the counter-ion. The lone pairs become stereoactive when the bonding strength of the counter-ion exceeds twice the bonding strength of the ion when its lone pairs are inactive.
Compounds that do not satisfy Eq. 4 are difficult, if not impossible, to prepare, and chemical reactions tend to favour the compounds that provide the best valence match. For example, the aqueous solubility of a compound depends on whether its ions are better matched to water than they are to each other. | 0 | Theoretical and Fundamental Chemistry |
The shape of a powder diffraction reflection is influenced by the characteristics of the beam, the experimental
arrangement, and the sample size and shape. In the case of monochromatic neutron sources the convolution
of the various effects has been found to result in a reflex almost exactly Gaussian in shape. If this
distribution is assumed then the contribution of a given reflection to the profile at position
is:
where is the full width at half peak height (full-width half-maximum), is the center of the reflex, and is the calculated intensity of the reflex (determined from the structure factor,
the Lorentz factor, and multiplicity of the reflection).
At very low diffraction angles the reflections may acquire an asymmetry due to the vertical divergence of the beam.
Rietveld used a semi-empirical correction factor, to account for this asymmetry:
where is the asymmetry factor and is , , or depending on the difference being positive, zero, or negative respectively.
At a given position more than one diffraction peak may contribute to the profile. The intensity is simply the sum of all reflections contributing at the point . | 0 | Theoretical and Fundamental Chemistry |
Binary subcomplexes in proteins database (BISC) is a protein–protein interaction database about binary subcomplexes. | 1 | Applied and Interdisciplinary Chemistry |
Nowadays, most radical photopolymerization pathways are based on addition reactions of carbon double bonds in acrylates or methacrylates, and these pathways are widely employed in photolithography and stereolithography.
Before the free radical nature of certain polymerizations was determined, certain monomers were observed to polymerize when exposed to light. The first to demonstrate the photoinduced free radical chain reaction of vinyl bromide was Ivan Ostromislensky, a Russian chemist who also studied the polymerization of synthetic rubber. Subsequently, many compounds were found to become dissociated by light and found immediate use as photoinitiators in the polymerization industry.
In the free radical mechanism of radiation curable systems, light absorbed by a photoinitiator generates free-radicals which induce cross-linking reactions of a mixture of functionalized oligomers and monomers to generate the cured film
Photocurable materials that form through the free-radical mechanism undergo chain-growth polymerization, which includes three basic steps: initiation, chain propagation, and chain termination. The three steps are depicted in the scheme below, where R• represents the radical that forms upon interaction with radiation during initiation, and M is a monomer. The active monomer that is formed is then propagated to create growing polymeric chain radicals. In photocurable materials the propagation step involves reactions of the chain radicals with reactive double bonds of the prepolymers or oligomers. The termination reaction usually proceeds through combination, in which two chain radicals are joined, or through disproportionation, which occurs when an atom (typically hydrogen) is transferred from one radical chain to another resulting in two polymeric chains.
;Initiation
;Propagation
;Termination
:combination
:disproportionation
Most composites that cure through radical chain growth contain a diverse mixture of oligomers and monomers with functionality that can range from 2-8 and molecular weights from 500 to 3000. In general, monomers with higher functionality result in a tighter crosslinking density of the finished material. Typically these oligomers and monomers alone do not absorb sufficient energy for the commercial light sources used, therefore photoinitiators are included. | 0 | Theoretical and Fundamental Chemistry |
Two compounds are said to be enantiomers if their molecules are mirror images of each other, that cannot be made to coincide only by rotations or translations – like a left hand and a right hand. The two shapes are said to be chiral.
A classical example is bromochlorofluoromethane (). The two enantiomers can be distinguished, for example, by whether the path turns clockwise or counterclockwise as seen from the hydrogen atom. In order to change one conformation to the other, at some point those four atoms would have to lie on the same plane – which would require severely straining or breaking their bonds to the carbon atom. The corresponding energy barrier between the two conformations is so high that there is practically no conversion between them at room temperature, and they can be regarded as different configurations.
The compound chlorofluoromethane , in contrast, is not chiral: the mirror image of its molecule is also obtained by a half-turn about a suitable axis.
Another example of a chiral compound is 2,3-pentadiene a hydrocarbon that contains two overlapping double bonds. The double bonds are such that the three middle carbons are in a straight line, while the first three and last three lie on perpendicular planes. The molecule and its mirror image are not superimposable, even though the molecule has an axis of symmetry. The two enantiomers can be distinguished, for example, by the right-hand rule. This type of isomerism is called axial isomerism.
Enantiomers behave identically in chemical reactions, except when reacted with chiral compounds or in the presence of chiral catalysts, such as most enzymes. For this latter reason, the two enantiomers of most chiral compounds usually have markedly different effects and roles in living organisms. In biochemistry and food science, the two enantiomers of a chiral molecule – such as glucose – are usually identified, and treated as very different substances.
Each enantiomer of a chiral compound typically rotates the plane of polarized light that passes through it. The rotation has the same magnitude but opposite senses for the two isomers, and can be a useful way of distinguishing and measuring their concentration in a solution. For this reason, enantiomers were formerly called "optical isomers". However, this term is ambiguous and is discouraged by the IUPAC.
Stereoisomers that are not enantiomers are called diastereomers. Some diastereomers may contain chiral center, some not.
Some enantiomer pairs (such as those of trans-cyclooctene) can be interconverted by internal motions that change bond lengths and angles only slightly. Other pairs (such as CHFClBr) cannot be interconverted without breaking bonds, and therefore are different configurations. | 0 | Theoretical and Fundamental Chemistry |
In condensed matter physics, a quantum spin liquid is a phase of matter that can be formed by interacting quantum spins in certain magnetic materials. Quantum spin liquids (QSL) are generally characterized by their long-range quantum entanglement, fractionalized excitations, and absence of ordinary magnetic order.
The quantum spin liquid state was first proposed by physicist Phil Anderson in 1973 as the ground state for a system of spins on a triangular lattice that interact antiferromagnetically with their nearest neighbors, i.e. neighboring spins seek to be aligned in opposite directions. Quantum spin liquids generated further interest when in 1987 Anderson proposed a theory that described high-temperature superconductivity in terms of a disordered spin-liquid state. | 0 | Theoretical and Fundamental Chemistry |
Electron-deficient olefins, such as enones and acryl derivatives can be epoxidized using nucleophilic oxygen compounds such as peroxides. The reaction is a two-step mechanism. First the oxygen performs a nucleophilic conjugate addition to give a stabilized carbanion. This carbanion then attacks the same oxygen atom, displacing a leaving group from it, to close the epoxide ring.. | 0 | Theoretical and Fundamental Chemistry |
Microscale thermophoresis (MST) is a technology for the biophysical analysis of interactions between biomolecules. Microscale thermophoresis is based on the detection of a temperature-induced change in fluorescence of a target as a function of the concentration of a non-fluorescent ligand. The observed change in fluorescence is based on two distinct effects. On the one hand it is based on a temperature related intensity change (TRIC) of the fluorescent probe, which can be affected by binding events. On the other hand, it is based on thermophoresis, the directed movement of particles in a microscopic temperature gradient. Any change of the chemical microenvironment of the fluorescent probe, as well as changes in the hydration shell of biomolecules result in a relative change of the fluorescence detected when a temperature gradient is applied and can be used to determine binding affinities. MST allows measurement of interactions directly in solution without the need of immobilization to a surface (immobilization-free technology). | 1 | Applied and Interdisciplinary Chemistry |
If , that is, a power law with , the streamlines (i.e. lines of constant ) are a system of straight lines parallel to the -axis. This is easiest to see by writing in terms of real and imaginary components:
thus giving and . This flow may be interpreted as uniform flow parallel to the -axis. | 1 | Applied and Interdisciplinary Chemistry |
Uranium tetrafluoride is the inorganic compound with the formula UF. It is a green solid with an insignificant vapor pressure and low solubility in water. Uranium in its tetravalent (uranous) state is important in various technological processes. In the uranium refining industry it is known as green salt. | 0 | Theoretical and Fundamental Chemistry |
Other common ylides include sulfonium ylides and sulfoxonium ylides; for instance, the Corey-Chaykovsky reagent used in the preparation of epoxides or in the Stevens rearrangement. | 0 | Theoretical and Fundamental Chemistry |
PA is kept low in the bulk of the membrane in order to transiently burst and signal locally in high concentration. For example TREK-1 channels are activated by local association with PLD and production of PA. The dissociation constant of PA for TREK-1 is approximately 10 micromolar. The relatively weak binding combined with a low concentration of PA in the membrane allows the channel to turn off. The local high concentration for activation suggests at least some restrictions in local lipid diffusion. The bulk low concentration of PA combined with high local bursts is the opposite of PIP2 signaling. PIP2 is kept relatively high in the membrane and then transiently hydrolized near a protein in order to transiently reduce PIP2 signaling. PA signaling mirrors PIP2 signaling in that the bulk concentration of signaling lipid need not change to exert a potent local effect on a target protein.
As described above, PLD hydrolyzes PC to form PA and choline. Because choline is very abundant in the cell, PLD activity does not significantly affect choline levels; and choline is unlikely to play any role in signaling.
The role of PLD activation in numerous signaling contexts, combined with the lack of a role for choline, suggests that PA is important in signaling. However, PA is rapidly converted to DAG, and DAG is also known to be a signaling molecule. This raises the question as to whether PA has any direct role in signaling or whether it simply acts as a precursor for DAG production. If it is found that PA acts only as a DAG precursor, then one can raise the question as to why cells should produce DAG using two enzymes when they contain the PLC that could produce DAG in a single step.
PA produced by PLD or by DAGK can be distinguished by the addition of [γ-P]ATP. This will show whether the phosphate group is newly derived from the kinase activity or whether it originates from the PC.
Although PA and DAG are interconvertible, they do not act in the same pathways. Stimuli that activate PLD do not activate enzymes downstream of DAG, and vice versa. For example, it was shown that addition of PLD to membranes results in the production of [P]-labeled PA and [P]-labeled phosphoinositides. The addition of DAGK inhibitors eliminates the production of [P]-labeled PA but not the PLD-stimulated production of phosphoinositides.
It is possible that, though PA and DAG are interconvertible, separate pools of signaling and non-signaling lipids may be maintained. Studies have suggested that DAG signaling is mediated by polyunsaturated DAG, whereas PLD-derived PA is monounsaturated or saturated. Thus functional saturated/monounsaturated PA can be degraded by hydrolysing it to form non-functional saturated/monounsaturated DAG, whereas functional polyunsaturated DAG can be degraded by converting it into non-functional polyunsaturated PA.
This model suggests that PA and DAG effectors should be able to distinguish lipids with the same headgroups but with differing acyl chains. Although some lipid-binding proteins are able to insert themselves into membranes and could hypothetically recognize the type of acyl chain or the resulting properties of the membrane, many lipid-binding proteins are cytosolic and localize to the membrane by binding only the headgroups of lipids. Perhaps the different acyl chains can affect the angle of the head-group in the membrane. If this is the case, it suggests that a PA-binding domain must not only be able to bind PA specifically but must also be able to identify those head-groups that are at the correct angle. Whatever the mechanism is, such specificity is possible. It is seen in the pig testes DAGK that is specific for polyunsaturated DAG and in two rat hepatocyte LPPs that dephosphorylate different PA species with different activities. Moreover, the stimulation of SK1 activity by PS in vitro was shown to vary greatly depending on whether dioleoyl (C18:1), distearoyl (C18:0), or 1-stearoyl, 2-oleoyl species of PS were used.
Thus it seems that, though PA and DAG are interconvertible, the different species of lipids can have different biological activities; and this may enable the two lipids to maintain separate signaling pathways. | 1 | Applied and Interdisciplinary Chemistry |
There are variations on the standard genetic code, and alternative stop codons have been found in the mitochondrial genomes of vertebrates, Scenedesmus obliquus, and Thraustochytrium. | 1 | Applied and Interdisciplinary Chemistry |
Using , , (assuming body temperature) and the fact that one volt is equal to one joule of energy per coulomb of charge, the equation
can be reduced to
which is the Nernst equation. | 0 | Theoretical and Fundamental Chemistry |
A silylium ion is a silicon cation with only three bonds and a positive charge. The abstraction of the silylium ion is seen from the ruthenium complex shown below.
In the first step of this mechanism one of the acetonitrile groups is replaced by a silicon molecule where the bond between the silicon and the hydrogen is coordinating to the ruthenium. In the second step a ketone is added for the nucleophilic abstraction of the silylium ion and the hydrogen is left on the metal. | 0 | Theoretical and Fundamental Chemistry |
The GUS assay, as well as other reporter gene systems, can be used for other kinds of studies other than the classical promoter activity assay. Reporter systems have been used for the determination of the efficiency of gene delivery systems, the intracellular localization of a gene product, the detection of protein-protein or protein-DNA interactions, the efficiency of translation initiation signals and the success of molecular cloning efforts. | 1 | Applied and Interdisciplinary Chemistry |
Whilst the method of PDC electrolysis has been proven by Ghoroghichian and Bockris in 1952 and 1985 to work extremely well in theory, it is difficult to replicate with consistently positive results in practical experimentation. Hence, the many mechanisms that have been patented are unable to be repeated and used in industry.
According to Shabaan, during the pulse-off period, if the electrolytic cell is not constructed properly, the current polarity can reverse. This can cause the cathode to deteriorate. In electrolysis, the cathode is where the reduction of hydrogen occurs, forming the desired hydrogen gas. Any loss in mass can reduce the speed and effectiveness of the electrolytic reaction, reducing the overall efficiency of the pulse electrolysis method.
Shaaban also states that due to expected internal losses, such as through heat, the current density required will increase, which increases the required voltage. As a result, greater over potentials are needed that further converts to heat. | 0 | Theoretical and Fundamental Chemistry |
The biochemistry of body odor pertains to the chemical compounds in the body responsible for body odor and their kinetics. | 1 | Applied and Interdisciplinary Chemistry |
# Prepare standard concentrations of protein of 1, 5, 7.5 and 10 µg/mL. Prepare a blank of NaCl only. Prepare a series of sample dilutions.
# Add 100 µL of each of the above to separate tubes (use microcentrifuge tubes) and add 1.0 mL of Coomassie Blue to each tube.
# Turn on and adjust a spectrophotometer to a wavelength of 595 nm, and blank the spectrophotometer using 1.5 mL cuvettes or use a mobile smartphone camera (RGBradford method).
# Wait 2 minutes and read the absorbance of each standard and sample at 595 nm.
# Plot the absorbance of the standards vs. their concentration. Compute the extinction coefficient and calculate the concentrations of the unknown samples. | 0 | Theoretical and Fundamental Chemistry |
Before detonation, a few grams of tritium–deuterium gas are injected into the hollow "pit" of fissile plutonium or uranium. The early stages of the fission chain reaction supply enough heat and compression to start deuterium–tritium fusion; then both fission and fusion proceed in parallel, the fission assisting the fusion by continuing heating and compression, and the fusion assisting the fission with highly energetic (14.1 MeV) neutrons. As the fission fuel depletes and also explodes outward, it falls below the density needed to stay critical by itself, but the fusion neutrons make the fission process progress faster and continue longer than it would without boosting. Increased yield comes overwhelmingly from the increase in fission. The energy released by the fusion itself is much smaller because the amount of fusion fuel is so much smaller. The effects of boosting include:
* increased yield (for the same amount of fission fuel, compared to detonation without boosting)
* the possibility of variable yield by varying the amount of fusion fuel
* allowing the bomb to require a smaller amount of the very expensive fissile material – and also eliminating the risk of predetonation by nearby nuclear explosions
* not so stringent requirements on the implosion setup, allowing for a smaller and lighter amount of high-explosives to be used
The tritium in a warhead is continually undergoing radioactive decay, hence becoming unavailable for fusion. Furthermore, its decay product, helium-3, absorbs neutrons if exposed to the ones emitted by nuclear fission. This potentially offsets or reverses the intended effect of the tritium, which was to generate many free neutrons, if too much helium-3 has accumulated from the decay of tritium. Therefore, it is necessary to replenish tritium in boosted bombs periodically. The estimated quantity needed is per warhead. To maintain constant levels of tritium, about per warhead per year must be supplied to the bomb.
One mole of deuterium-tritium gas would contain about of tritium and of deuterium. In comparison, the 20 moles of plutonium in a nuclear bomb consists of about of plutonium-239. | 0 | Theoretical and Fundamental Chemistry |
Another example is the combination of non-steroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids. Although NSAIDs and glucocorticoids have different mechanisms of action, the drugs are able to diminish the protective effect of gastric mucosa from gastric acid. As a result, the concomitant use of NSAIDs and glucocorticoids increases the risk of gastric bleeding and worsens peptic ulcer disease. As a result, the combination of NSAIDs and glucocorticoids is not recommended. | 1 | Applied and Interdisciplinary Chemistry |
Werner also described a second achiral hexol (a minor byproduct from the production of Fremy's salt) that he incorrectly identified as a linear tetramer. The second hexol is hexanuclear (contains six cobalt centres in each ion), not tetranuclear. Its point group is C, and its formula is , whereas that of hexol is . | 0 | Theoretical and Fundamental Chemistry |
Measuring contact angles for pendant drops is much more complicated than for sessile drops due to the inherent unstable nature of inverted drops. This complexity is further amplified when one attempts to incline the surface. Experimental apparatus to measure pendant drop contact angles on inclined substrates has been developed recently. This method allows for the deposition of multiple microdrops on the underside of a textured substrate, which can be imaged using a high resolution CCD camera. An automated system allows for tilting the substrate and analysing the images for the calculation of advancing and receding contact angles. | 0 | Theoretical and Fundamental Chemistry |
Concentration of in the blood and tissues is so low that they feel weak and are unable to think properly, a condition called hypoxia. | 0 | Theoretical and Fundamental Chemistry |
In the muon-catalyzed fusion of most interest, a positively charged deuteron (d), a positively charged triton (t), and a muon essentially form a positively charged muonic molecular heavy hydrogen ion (d–μ–t). The muon, with a rest mass 207 times greater than the rest mass of an electron, is able to drag the more massive triton and deuteron 207 times closer together to each other
in the muonic (d–μ–t) molecular ion than can an electron in the corresponding electronic (d–e–t) molecular ion. The average separation between the triton and the deuteron in the electronic molecular ion is about one angstrom (100 pm), so the average separation between the triton and the deuteron in the muonic molecular ion is 207 times smaller than that. Due to the strong nuclear force, whenever the triton and the deuteron in the muonic molecular ion happen to get even closer to each other during their periodic vibrational motions, the probability is very greatly enhanced that the positively charged triton and the positively charged deuteron would undergo quantum tunnelling through the repulsive Coulomb barrier that acts to keep them apart. Indeed, the quantum mechanical tunnelling probability depends roughly exponentially on the average separation between the triton and the deuteron, allowing a single muon to catalyze the d–t nuclear fusion in less than about half a picosecond, once the muonic molecular ion is formed.
The formation time of the muonic molecular ion is one of the "rate-limiting steps" in muon-catalyzed fusion that can easily take up to ten thousand or more picoseconds in a liquid molecular deuterium and tritium mixture (D, DT, T), for example. Each catalyzing muon thus spends most of its ephemeral existence of 2.2 microseconds, as measured in its rest frame, wandering around looking for suitable deuterons and tritons with which to bind.
Another way of looking at muon-catalyzed fusion is to try to visualize the ground state orbit of a muon around either a deuteron or a triton. Suppose the muon happens to have fallen into an orbit around a deuteron initially, which it has about a 50% chance of doing if there are approximately equal numbers of deuterons and tritons present, forming an electrically neutral muonic deuterium atom (d–μ) that acts somewhat like a "fat, heavy neutron" due both to its relatively small size (again, 207 times smaller than an electrically neutral electronic deuterium atom (d–e)) and to the very effective "shielding" by the muon of the positive charge of the proton in the deuteron. Even so, the muon still has a much greater chance of being transferred to any triton that comes near enough to the muonic deuterium than it does of forming a muonic molecular ion. The electrically neutral muonic tritium atom (t–μ) thus formed will act somewhat like an even "fatter, heavier neutron," but it will most likely hang on to its muon, eventually forming a muonic molecular ion, most likely due to the resonant formation of a hyperfine molecular state within an entire deuterium molecule D (d=e=d), with the muonic molecular ion acting as a "fatter, heavier nucleus" of the "fatter, heavier" neutral "muonic/electronic" deuterium molecule ([d–μ–t]=e=d), as predicted by Vesman, an Estonian graduate student, in 1967.
Once the muonic molecular ion state is formed, the shielding by the muon of the positive charges of the proton of the triton and the proton of the deuteron from each other allows the triton and the deuteron to tunnel through the Coulomb barrier in time span of order of a nanosecond The muon survives the d–t muon-catalyzed nuclear fusion reaction and remains available (usually) to catalyze further d–t muon-catalyzed nuclear fusions. Each exothermic d–t nuclear fusion releases about 17.6 MeV of energy in the form of a "very fast" neutron having a kinetic energy of about 14.1 MeV and an alpha particle α (a helium-4 nucleus) with a kinetic energy of about 3.5 MeV. An additional 4.8 MeV can be gleaned by having the fast neutrons moderated in a suitable "blanket" surrounding the reaction chamber, with the blanket containing lithium-6, whose nuclei, known by some as "lithions," readily and exothermically absorb thermal neutrons, the lithium-6 being transmuted thereby into an alpha particle and a triton. | 0 | Theoretical and Fundamental Chemistry |
When there is no equilibrium between phases or chemical compounds, kinetic fractionation can occur. For example, at interfaces between liquid water and air, the forward reaction is enhanced if the humidity of the air is less than 100% or the water vapor is moved by a wind. Kinetic fractionation generally is enhanced compared to equilibrium fractionation and depends on factors such as reaction rate, reaction pathway and bond energy. Since lighter isotopes generally have weaker bonds, they tend to react faster and enrich the reaction products.
Biological fractionation is a form of kinetic fractionation since reactions tend to be in one direction. Biological organisms prefer lighter isotopes because there is a lower energy cost in breaking energy bonds. In addition to the previously mentioned factors, the environment and species of the organism can have a large effect on the fractionation. | 0 | Theoretical and Fundamental Chemistry |
Binary mixture VLE data at a certain overall pressure, such as 1 atm, showing mole fraction vapor and liquid concentrations when boiling at various temperatures can be shown as a two-dimensional graph called a boiling-point diagram. The mole fraction of component 1 in the mixture can be represented by the symbol . The mole fraction of component 2, represented by , is related to in a binary mixture as follows:
In multi-component mixtures in general with n components, this becomes:
The preceding equilibrium equations are typically applied for each phase (liquid or vapor) individually, but the result can be plotted in a single diagram. In a binary boiling-point diagram, temperature () (or sometimes pressure) is graphed vs. . At any given temperature (or pressure) where both phases are present, vapor with a certain mole fraction is in equilibrium with liquid with a certain mole fraction. The two mole fractions often differ. These vapor and liquid mole fractions are represented by two points on the same horizontal isotherm (constant ) line. When an entire range of temperatures vs. vapor and liquid mole fractions is graphed, two (usually curved) lines result. The lower one, representing the mole fraction of the boiling liquid at various temperatures, is called the bubble point curve. The upper one, representing the mole fraction of the vapor at various temperatures, is called the dew point curve.
These two curves necessarily meet where the mixture becomes purely one component, namely where (and , pure component 2) or (and , pure component 1). The temperatures at those two points correspond to the boiling points of each of the two pure components.
For certain pairs of substances, the two curves also coincide at some point strictly between and . When they meet, they meet tangently; the dew-point temperature always lies above the boiling-point temperature for a given composition when they are not equal. The meeting point is called an azeotrope for that particular pair of substances. It is characterized by an azeotrope temperature and an azeotropic composition, often expressed as a mole fraction. There can be maximum-boiling azeotropes, where the azeotrope temperature is at a maximum in the boiling curves, or minimum-boiling azeotropes, where the azeotrope temperature is at a minimum in the boiling curves.
If one wants to represent a VLE data for a three-component mixture as a boiling point "diagram", a three-dimensional graph can be used. Two of the dimensions would be used to represent the composition mole fractions, and the third dimension would be the temperature. Using two dimensions, the composition can be represented as an equilateral triangle in which each corner represents one of the pure components. The edges of the triangle represent a mixture of the two components at each end of the edge. Any point inside the triangle represents the composition of a mixture of all three components. The mole fraction of each component would correspond to where a point lies along a line starting at that component's corner and perpendicular to the opposite edge. The bubble point and dew point data would become curved surfaces inside a triangular prism, which connect the three boiling points on the vertical temperature "axes". Each face of this triangular prism would represent a two-dimensional boiling-point diagram for the corresponding binary mixture. Due to their three-dimensional complexity, such boiling-point diagrams are rarely seen. Alternatively, the three-dimensional curved surfaces can be represented on a two-dimensional graph by the use of curved isotherm lines at graduated intervals, similar to iso-altitude lines on a map. Two sets of such isotherm lines are needed on such a two-dimensional graph: one set for the bubble point surface and another set for the dew point surface. | 0 | Theoretical and Fundamental Chemistry |
Photocytes are found distributed unevenly near the plate cilia cells. Gastric cells form a barrier that keep the photocytes away from the opening of the radially canal which they are found to exist along. | 1 | Applied and Interdisciplinary Chemistry |
Unruh demonstrated theoretically that the notion of vacuum depends on the path of the observer through spacetime. From the viewpoint of the accelerating observer, the vacuum of the inertial observer will look like a state containing many particles in thermal equilibrium—a warm gas.
The Unruh effect would only appear to an accelerating observer. And although the Unruh effect would initially be perceived as counter-intuitive, it makes sense if the word vacuum is interpreted in the following specific way. In quantum field theory, the concept of "vacuum" is not the same as "empty space": Space is filled with the quantized fields that make up the universe. Vacuum is simply the lowest possible energy state of these fields.
The energy states of any quantized field are defined by the Hamiltonian, based on local conditions, including the time coordinate. According to special relativity, two observers moving relative to each other must use different time coordinates. If those observers are accelerating, there may be no shared coordinate system. Hence, the observers will see different quantum states and thus different vacua.
In some cases, the vacuum of one observer is not even in the space of quantum states of the other. In technical terms, this comes about because the two vacua lead to unitarily inequivalent representations of the quantum field canonical commutation relations. This is because two mutually accelerating observers may not be able to find a globally defined coordinate transformation relating their coordinate choices.
An accelerating observer will perceive an apparent event horizon forming (see Rindler spacetime). The existence of Unruh radiation could be linked to this apparent event horizon, putting it in the same conceptual framework as Hawking radiation. On the other hand, the theory of the Unruh effect explains that the definition of what constitutes a "particle" depends on the state of motion of the observer.
The free field needs to be decomposed into positive and negative frequency components before defining the creation and annihilation operators. This can only be done in spacetimes with a timelike Killing vector field. This decomposition happens to be different in Cartesian and Rindler coordinates (although the two are related by a Bogoliubov transformation). This explains why the "particle numbers", which are defined in terms of the creation and annihilation operators, are different in both coordinates.
The Rindler spacetime has a horizon, and locally any non-extremal black hole horizon is Rindler. So the Rindler spacetime gives the local properties of black holes and cosmological horizons. It is possible to rearrange the metric restricted to these regions to obtain the Rindler metric. The Unruh effect would then be the near-horizon form of Hawking radiation.
The Unruh effect is also expected to be present in de Sitter space.
It is worth stressing that the Unruh effect only says that, according to uniformly-accelerated observers, the vacuum state is a thermal state specified by its temperature, and one should resist reading too much into the thermal state or bath. Different thermal states or baths at the same temperature need not be equal, for they depend on the Hamiltonian describing the system. In particular, the thermal bath seen by accelerated observers in the vacuum state of a quantum field is not the same as a thermal state of the same field at the same temperature according to inertial observers. Furthermore, uniformly accelerated observers, static with respect to each other, can have different proper accelerations (depending on their separation), which is a direct consequence of relativistic red-shift effects. This makes the Unruh temperature spatially inhomogeneous across the uniformly accelerated frame. | 0 | Theoretical and Fundamental Chemistry |
When cumulative constants have been refined it is often useful to derive stepwise constants from them. The general procedure is to write down the defining expressions for all the constants involved and then to equate concentrations. For example, suppose that one wishes to derive the pKa for removing one proton from a tribasic acid, LH, such as citric acid.
The stepwise association constant for formation of LH is given by
Substitute the expressions for the concentrations of LH and into this equation
whence
and since its value is given by
Note the reverse numbering for pK and log β. When calculating the error on the stepwise constant, the fact that the cumulative constants are correlated must accounted for. By error propagation
and | 0 | Theoretical and Fundamental Chemistry |
There are a number of other fermentation pathways that occur in microbes. All these pathways begin by converting pyruvate, but their end products and the key enzymes they require are different.
These pathways include:
*Ethanol fermentation
*Lactic acid fermentation
*Propionic acid fermentation
*Butanol fermentation
*Butanediol fermentation | 1 | Applied and Interdisciplinary Chemistry |
Nanoscale particles are used in biomedical applications as drug carriers or imaging contrast agents in microscopy. Anisotropic nanoparticles are a good candidate in biomolecular detection. Moreover, nanoparticles for nucleic acid delivery offer an unprecedented opportunity to overcome some drawbacks related to the delivery, owing to their tunability with diverse physico-chemical properties, they can readily be functionalized with any type of biomolecules/moieties for selective targeting. | 0 | Theoretical and Fundamental Chemistry |
The Barton decarboxylation is a radical reaction in which a carboxylic acid is converted to a thiohydroxamate ester (commonly referred to as a Barton ester). The product is then heated in the presence of a radical initiator and a suitable hydrogen donor to afford the decarboxylated product. This is an example of a reductive decarboxylation. Using this reaction it is possible to remove carboxylic acid moieties from alkyl groups and replace them with other functional groups. (See Scheme 1) This reaction is named after its developer, the British chemist and Nobel laureate Sir Derek Barton (1918–1998). | 0 | Theoretical and Fundamental Chemistry |
On the base of space measured distribution of magnetic field parameters (e.g. amplitude or direction), the magnetovision images may be generated. Such presentation of magnetic data is very useful for further analyse and data fusion. | 0 | Theoretical and Fundamental Chemistry |
Traditionally, Chinese hamster ovary (CHO) cells are associated with the establishment of stable cell lines for biologics. Recently, however, attempts to engineer CHO cells for transient protein production have garnered recognition. CHO cells were among the earliest established cell lines for in vitro cultivation, and their potential as a host for production and manufacturing of biological products remains popular. CHO cells are preferable for transient expression due to their easy industrial scale-up, versatility for the production of diverse biomolecules, and low risk of infection of human viruses, among other advantages. Three primary expression systems have been established:
# EBNA-1-engineered CHO cell line
# CHO EBNA LT cell line, which is carried apart from the EBNA-1 gene and the mouse polyomavirus large T antigen
# EpiCHO system, which consists of a CHO cell line transfected with the polyomavirus large T antigen gene and a DNA expression vector encoding polyomavirus origin (PyOri) for autonomous replication and EBV EBNA-1 and OriP for plasmid retention. | 1 | Applied and Interdisciplinary Chemistry |
Halohydrins may also be prepared from the reaction of an epoxide with a hydrohalic acid, or a metal halide.
This reaction is produced on an industrial scale for the production of chlorohydrin precursors to two important epoxides, epichlorohydrin and propylene oxide. At one time, 2-chloroethanol was produced on a large scale as a precursor to ethylene oxide, but the latter is now prepared by the direct oxidation of ethylene. | 0 | Theoretical and Fundamental Chemistry |
A widely studied class are photochromic compounds which are able to switch between electronic configurations when irradiated by light of a specific wavelength. Each state has a specific absorption maximum which can then be read out by UV-VIS spectroscopy. Members of this class include azobenzenes, diarylethenes, dithienylethenes, fulgides, stilbenes, spiropyrans and phenoxynaphthacene quinones.
Chiroptical molecular switches are a specific subgroup with photochemical switching taking place between an enantiomeric pairs. In these compounds the readout is by circular dichroism rather than by ordinary spectroscopy. Hindered alkenes such as the one depicted below change their helicity (see: planar chirality) as response to irradiation with right or left-handed circularly polarized light
Chiroptical molecular switches that show directional motion are considered synthetic molecular motors: When attached to the end of a helical poly (isocyanate) polymer, they can switch the helical sense of the polymer. | 0 | Theoretical and Fundamental Chemistry |
Coordination cages are three-dimensional ordered structures in solution that act as hosts in host–guest chemistry. They are self-assembled in solution from organometallic precursors, and often rely solely on noncovalent interactions rather than covalent bonds. Coordinate bonds are useful in such supramolecular self-assembly because of their versatile geometries. However, there is controversy over calling coordinate bonds noncovalent, as they are typically strong bonds and have covalent character. The combination of a coordination cage and a guest is a type of inclusion compound. Coordination complexes can be used as "nano-laboratories" for synthesis, and to isolate interesting intermediates. The inclusion complexes of a guest inside a coordination cage show intriguing chemistry as well; often, the properties of the cage will change depending on the guest. Coordination complexes are molecular moieties, so they are distinct from clathrates and metal-organic frameworks. | 0 | Theoretical and Fundamental Chemistry |
Jin-Quan Yu () is a Chinese-born American chemist. He is the Frank and Bertha Hupp Professor of Chemistry at Scripps Research, where he also holds the Bristol Myers Squibb Endowed Chair in Chemistry. He is a 2016 recipient of the MacArthur Fellowship, and is a member of the American Academy of Arts and Sciences, American Association for the Advancement of Science, and the Royal Society of Chemistry. Yu is a leader in the development of C–H bond activation reactions in organic chemistry, and has reported many C–H activation reactions that could be applicable towards the synthesis of drug molecules and other biologically active compounds. He also co-founded Vividion Therapeutics in 2016 with fellow Scripps chemists Benjamin Cravatt and Phil Baran, and is a member of the scientific advisory board of Chemveda Life Sciences. | 0 | Theoretical and Fundamental Chemistry |
In solid rocket propellants and some translucent smokeless powders, the primary method of heat transfer into the propellant grain from the combustion process is by radiation, and opacifiers such as "lamp black" may be added to the propellant mixture to ensure the heat does not penetrate far below the surface of the grain, which could cause detonation. The opacifiers also prevent sub-surface overheating and localized premature ignition in the grains where imperfections absorbing the thermal radiation are present. Carbon black is commonly used for this purpose; other possible additives are nigrosin, Prussian blue, methylene blue, etc. in amounts ranging commonly between 0.1 and 0.5%. | 0 | Theoretical and Fundamental Chemistry |
A combustion train is an analytical tool for the determination of elemental composition of a chemical compound. With knowledge of elemental composition a chemical formula can be derived. The combustion train allows the determination of carbon and hydrogen in a succession of steps:
* combustion of the sample at high temperatures with Copper(II) oxide as the oxidizing agent,
* collection of the resulting gas in a hygroscopic agent (magnesium perchlorate or calcium chloride) to trap generated water,
* collection of the remainder gas in a strong base (for instance potassium hydroxide) to trap generated carbon dioxide.
Analytical determination of the amounts of water and carbon dioxide produced from a known amount of sample gives the empirical formula. For every hydrogen atom in the compound 1/2 equivalent of water is produced, and for every carbon atom in the compound 1 equivalent of carbon dioxide is produced.
Nowadays, modern instruments are sufficiently automated to be able to do these analyses routinely. Samples required are also extremely small — 0.5 mg of sample can be sufficient to give satisfactory CHN analysis. | 0 | Theoretical and Fundamental Chemistry |
ODS steels creep properties are dependent on the characteristics of the oxide particles in the metal matrix, specifically their ability to prevent dislocation motion as well as the size and distribution of the particles. Hoelzer and coworkers showed that an alloy containing a homogeneous dispersion of 1-5 nm YTiO nanoclusters has superior creep properties to an alloy with a heterogeneous dispersion of 5-20 nm nanoclusters of the same composition.
ODS steels are commonly produced through ball-milling an oxide of interest (e.g. YO, AlO) with pre-alloyed metal powders followed by compression and sintering. It is believed that the oxides enter into solid solution with the metal during ball-milling and subsequently precipitate during the thermal treatment. This process seems simple but many parameters need to be carefully controlled to produce a successful alloy. Leseigneur and coworkers carefully controlled some of these parameters and achieved more consistent and better microstructures. In this two step method the oxide is ball-milled for longer periods to ensure a homogeneous solid solution of the oxide. The powder is annealed at higher temperatures to begin a controlled nucleation of the oxide clusters. Finally the powder is again compressed and sintered to yield the final material. | 1 | Applied and Interdisciplinary Chemistry |
In all three spectroscopic methods, the sample usually needs to be present in solution, which may present problems during forensic examination because it necessarily involves sampling solid from the object to be examined.
In FTIR, three types of samples can be analyzed: solution (KBr), powder, or film. A solid film is the easiest and most straight forward sample type to test. | 0 | Theoretical and Fundamental Chemistry |
At present, single entity electrochemistry is not sensitive enough to quantify the turnover of a single enzyme. | 0 | Theoretical and Fundamental Chemistry |
John Lilley states, "...neutron-induced fission generates extra neutrons which can induce further fissions in the next generation and so on in a chain reaction. The chain reaction is characterized by the neutron multiplication factor k, which is defined as the ratio of the number of neutrons in one generation to the number in the preceding generation. If, in a reactor, k is less than unity, the reactor is subcritical, the number of neutrons decreases and the chain reaction dies out. If k > 1, the reactor is supercritical and the chain reaction diverges. This is the situation in a fission bomb where growth is at an explosive rate. If k is exactly unity, the reactions proceed at a steady rate and the reactor is said to be critical. It is possible to achieve criticality in a reactor using natural uranium as fuel, provided that the neutrons have been efficiently moderated to thermal energies." Moderators include light water, heavy water, and graphite.
According to John C. Lee, "For all nuclear reactors in operation and those under development, the nuclear fuel cycle is based on one of three fissile materials, U, U, and Pu, and the associated isotopic chains. For the current generation of LWRs, the enriched U contains 2.5~4.5 wt% of U, which is fabricated into UO fuel rods and loaded into fuel assemblies."
Lee states, "One important comparison for the three major fissile nuclides, U, U, and Pu, is their breeding potential. A breeder is by definition a reactor that produces more fissile material than it consumes and needs a minimum of two neutrons produced for each neutron absorbed in a fissile nucleus. Thus, in general, the conversion ratio (CR) is defined as the ratio of fissile material produced to that destroyed...when the CR is greater than 1.0, it is called the breeding ratio (BR)...U offers a superior breeding potential for both thermal and fast reactors, while Pu offers a superior breeding potential for fast reactors." | 0 | Theoretical and Fundamental Chemistry |
NFP is used in the development of a to scale, direct-write nanomanufacturing platform. The platform is capable of constructing complex, highly-functional nanoscale devices from a diverse suite of materials (e.g., nanoparticles, catalysts (increase rate of reaction), biomolecules, and chemical solutions). Demonstrated nanopatterning capabilities include:
• Biomolecules (proteins, DNA) for biodetection assays or cell adhesion studies
• Functional nanoparticles for drug delivery studies and nanosystems making (fabrication)
• Catalysts for carbon nanotube growth in nanodevice fabrication
• Thiols for directed self-assembly of nanostructures. | 1 | Applied and Interdisciplinary Chemistry |
For molecules adsorbed on surfaces there have been various conventions proposed based on hypothetical standard states. For adsorption that occurs on specific sites (Langmuir adsorption isotherm) the most common standard state is a relative coverage of , as this choice results in a cancellation of the configurational entropy term and is also consistent with neglecting to include the standard state (which is a common error). The advantage of using is that the configurational term cancels and the entropy extracted from thermodynamic analyses is thus reflective of intra-molecular changes between the bulk phase (such as gas or liquid) and the adsorbed state. There may be benefit to tabulating values based on both the relative coverage based standard state and in an additional column the absolute coverage based standard state. For 2D gas states, the complication of discrete states does not arise and an absolute density base standard state has been proposed, similar for the 3D gas phase. | 0 | Theoretical and Fundamental Chemistry |
Chloroplasts develop from proplastids when seedlings emerge from the ground. Thylakoid formation requires light. In the plant embryo and in the absence of light, proplastids develop into etioplasts that contain semicrystalline membrane structures called prolamellar bodies. When exposed to light, these prolamellar bodies develop into thylakoids. This does not happen in seedlings grown in the dark, which undergo etiolation. An underexposure to light can cause the thylakoids to fail. This causes the chloroplasts to fail resulting to the death of the plant.
Thylakoid formation requires the action of vesicle-inducing protein in plastids 1 (VIPP1). Plants cannot survive without this protein, and reduced VIPP1 levels lead to slower growth and paler plants with reduced ability to photosynthesize. VIPP1 appears to be required for basic thylakoid membrane formation, but not for the assembly of protein complexes of the thylakoid membrane. It is conserved in all organisms containing thylakoids, including cyanobacteria, green algae, such as Chlamydomonas, and higher plants, such as Arabidopsis thaliana. | 0 | Theoretical and Fundamental Chemistry |
The cost of surfactants is partially dependent on the crude oil market. As a stock ingredient for production of surfactants, paints highly dependent on surfactants will be affected by this market. More intricate surfactants with larger, more difficult to synthesize structure are more expensive to produce and have a greater effect on end market price of their applications. As a result, simple, easy to produce and more environmentally friendly surfactants are used more widely. | 0 | Theoretical and Fundamental Chemistry |
Edward Ambrose Martell (February 23, 1918 – July 12, 1995) was an American radiochemist for the US National Center for Atmospheric Research (NCAR) in Boulder, Colorado. He fought fervently throughout his life against the medical establishment and the National Institute of Health for what he perceived to be insufficient research into radiation-induced lung cancer, particularly in regard to cigarette smoking. | 0 | Theoretical and Fundamental Chemistry |
Transmetalation (alt. spelling: transmetallation) is a type of organometallic reaction that involves the transfer of ligands from one metal to another. It has the general form:
:M–R + M–R′ → M–R′ + M–R
where R and R′ can be, but are not limited to, an alkyl, aryl, alkynyl, allyl, halogen, or pseudohalogen group. The reaction is usually an irreversible process due to thermodynamic and kinetic reasons. Thermodynamics will favor the reaction based on the electronegativities of the metals and kinetics will favor the reaction if there are empty orbitals on both metals. There are different types of transmetalation including redox-transmetalation and redox-transmetalation/ligand exchange. During transmetalation the metal-carbon bond is activated, leading to the formation of new metal-carbon bonds. Transmetalation is commonly used in catalysis, synthesis of main group complexes, and synthesis of transition metal complexes. | 0 | Theoretical and Fundamental Chemistry |
* Dylan M. Burns, " μίξεώς τινι τέχνῃ κρείττονι : Alchemical Metaphor in the Paraphrase of Shem (NHC VII,1) ", Aries 15 (2015), p. 79–106.
* Alberto Camplani, " Procedimenti magico-alchemici e discorso filosofico ermetico " in Giuliana Lanata (ed.), Il Tardoantico alle soglie del Duemila, ETS, 2000, p. 73–98.
* Alberto Camplani and Marco Zambon, " Il sacrificio come problema in alcune correnti filosofice di età imperiale ", Annali di storia dellesegesi' 19 (2002), p. 59–99.
* Régine Charron and Louis Painchaud, " God is a Dyer, The Background and Significance of a Puzzling Motif in the Coptic Gospel According to Philip (CG II, 3), Le Muséon 114 (2001), p. 41-50.
* Régine Charron, " The Apocryphon of John (NHC II,1) and the Greco-Egyptian Alchemical Literature ", Vigiliae Christinae 59 (2005), p. 438-456.
* Philippe Derchain, "LAtelier des Orfèvres à Dendara et les origines de lalchimie," Chronique dÉgypte', 65, 219–242.
* Korshi Dosoo, " A History of the Theban Magical Library ", Bulletin of the American Society of Papyrologists 53 (2016), p. 251–274.
* Olivier Dufault, Early Greek Alchemy, Patronage and Innovation in Late Antiquity, California Classical Studies, 2019, [https://escholarship.org/uc/item/2ks0g83x Early Greek Alchemy, Patronage and Innovation in Late Antiquity].
* Sergio Knipe, " Sacrifice and self-transformation in the alchemical writings of Zosimus of Panopolis ", in Christopher Kelly, Richard Flower, Michael Stuart Williams (eds.), Unclassical Traditions. Volume II: Perspectives from East and West in Late Antiquity, Cambridge University Press, 2011, p. 59–69.
* André-Jean Festugière, La Révélation dHermès Trismégiste', Paris, Les Belles Lettres, 2014 , .
* Kyle A. Fraser, " Zosimos of Panopolis and the Book of Enoch: Alchemy as Forbidden Knowledge ", Aries 4.2 (2004), p. 125–147.
* Kyle A. Fraser, " Baptized in Gnosis: The Spiritual Alchemy of Zosimos of Panopolis ", Dionysius 25 (2007), p. 33–54.
* Kyle A. Fraser, " Distilling Natures Secrets: The Sacred Art of Alchemy ", in John Scarborough and Paul Keyser (eds.), Oxford Handbook of Science and Medicine in the Classical World,' Oxford University Press, 2018, p. 721–742. 2018. [https://www.oxfordhandbooks.com/view/10.1093/oxfordhb/9780199734146.001.0001/oxfordhb-9780199734146-e-76].
* Shannon Grimes, Becoming Gold: Zosimos of Panopolis and the Alchemical Arts in Roman Egypt, Auckland, Rubedo Press, 2018,
* Paul T. Keyser, " Greco-Roman Alchemy and Coins of Imitation Silver ", American Journal of Numismatics 7–8 (1995–1996), p. 209–234.
* Paul Keyser, " The Longue Durée of Alchemy ", in John Scarborough and Paul Keyser (eds.), Oxford Handbook of Science and Medicine in the Classical World, Oxford University Press, 2018, p. 409–430.
* Jean Letrouit, "Chronologie des alchimistes grecs," in Didier Kahn and Sylvain Matton, Alchimie: art, histoire et mythes, SEHA-Archè, 1995, 11–93.
* Lindsay, Jack. The Origins of Alchemy in Greco-Roman Egypt. Barnes & Noble, 1970.
* Paul Magdalino and Maria Mavroudi (eds.), The Occult Sciences in Byzantium, La Pomme d'or, 2006.
* Matteo Martelli, " Alchemy, Medicine and Religion: Zosimus of Panopolis and the Egyptian Priests ", Religion in the Roman Empire 3.2 (2017), p. 202–220.
* Daniel Stolzenberg, " Unpropitious Tinctures: Alchemy, Astrology & Gnosis According to Zosimos of Panopolis ", Archives internationales dhistoire des sciences' 49 (1999), p. 3–31.
* Cristina Viano, " Byzantine Alchemy, or the Era of Systematization ", in John Scarborough and Paul Keyser (eds.), Oxford Handbook of Science and Medicine in the Classical World, Oxford University Press, 2018, p. 943–964. | 1 | Applied and Interdisciplinary Chemistry |
Tertiary alcohols react with strong acids to generate carbocations. The reaction is related to their dehydration, e.g. isobutylene from tert-butyl alcohol. A special kind of dehydration reaction involves triphenylmethanol and especially its amine-substituted derivatives. When treated with acid, these alcohols lose water to give stable carbocations, which are commercial dyes. | 0 | Theoretical and Fundamental Chemistry |
A wider wire results in smaller current density and, hence, less likelihood of electromigration. Also, the metal grain size has influence; the smaller grains, the more grain boundaries and the higher likelihood of electromigration effects. However, if you reduce wire width to below the average grain size of the wire material, grain boundaries become "crosswise", more or less perpendicular to the length of the wire. The resulting structure resembles the joints in a stalk of bamboo. With such a structure, the resistance to electromigration increases, despite an increase in current density. This apparent contradiction is caused by the perpendicular position of the grain boundaries; the boundary diffusion factor is excluded, and material transport is correspondingly reduced.
However, the maximum wire width possible for a bamboo structure is usually too narrow for signal lines of large-magnitude currents in analog circuits or for power supply lines. In these circumstances, slotted wires are often used, whereby rectangular holes are carved in the wires. Here, the widths of the individual metal structures in between the slots lie within the area of a bamboo structure, while the resulting total width of all the metal structures meets power requirements. | 0 | Theoretical and Fundamental Chemistry |
Kineticists have historically relied on linearization of rate data to extrapolate rate constants, perhaps best demonstrated by the widespread use of the standard Lineweaver–Burk linearization of the Michaelis–Menten equation. Linearization techniques were of particular importance before the advent of computing techniques capable of fitting complex curves, and they remain a staple in kinetics due to their intuitively simple presentation. It is important to note that linearization techniques should NOT be used to extract numerical rate constants as they introduce a large degree of error relative to alternative numerical techniques. Graphical rate laws do, however, maintain that intuitive presentation of linearized data, such that visual inspection of the plot can provide mechanistic insight regarding the reaction at hand. The basis for a graphical rate law rests on the rate (v) vs. substrate concentration ([S]) plots discussed above. For example, in the simple cycle discussed with regard to different-excess experiments a plot of vs. [B] and its twin vs. [A] can provide intuitive insight about the order of each of the reagents. If plots of vs. [B] overlay for multiple experiments with different-excess, the data are consistent with a first-order dependence on [A]. The same could be said for a plot of vs. [A]; overlay is consistent with a first-order dependence on [B]. Non-overlaying results of these graphical rate laws are possible and are indicative of higher order dependence on the substrates probed. Blackmond has proposed presenting the results of different-excess experiments with a series of graphical rate equations (that she presents in a flow-chart adapted here), but it is important to note that her proposed method is only one of many possible methods to display the kinetic relationship. Furthermore, while the presentation of graphical rate laws may at times be considered a visually simplified way to present complex kinetic data, fitting the raw kinetic data for analysis by differential or other rigorous numerical methods is necessary to extract accurate and quantitative rate constants and reaction orders. | 0 | Theoretical and Fundamental Chemistry |
Structures for lossless ion manipulations (SLIM) are a form of ion optics to which various radio frequency and dc electric potentials can be applied and used to enable a broad range of ion manipulations, such as separations based upon ion mobility spectrometry, reactions (unimolecular, ion-molecule, and ion-ion), and storage (i.e. ion trapping). SLIM was developed by Richard D. Smith and coworkers at Pacific Northwest National Laboratory (PNNL) and are generally fabricated from arrays of electrodes on evenly spaced planar surfaces. In 2017, Erin S. Baker, Sandilya Garimella, Yehia Ibrahim, Richard D. Smith and Ian Webb from the Interactive Omics Group of PNNL received the R&D 100 Award for the development of SLIM.
In SLIM, ions move in the space between the two surfaces, in directions controlled using electric fields, and also moved between different of multi-level SLIM, as can be constructed from a stack of printed circuit boards (PCBs). The lossless nature of SLIM is derived from the use of rf electric fields, and particularly the pseudo potential derived from the inhomogeneous electric fields resulting from rf of appropriate frequency applied to multiple adjacent electrodes, and that serves to prevent ions from closely approaching the electrodes and surface where loss would conventionally be expected. SLIM are generally used in conjunction with mass spectrometry for analytical applications. | 0 | Theoretical and Fundamental Chemistry |
In 1931, Paul Kubelka (with Franz Munk) published "An article on the optics of paint", the contents of which has come to be known as the Kubelka-Munk theory. They used absorption and remission (or back-scatter) constants, noting (as translated by Stephen H. Westin) that "an infinitesimal layer of the coating absorbs and scatters a certain constant portion of all the light passing through it". While symbols and terminology are changed here, it seems clear from their language that the terms in their differential equations stand for absorption and backscatter (remission) fractions. They also noted that the reflectance from an infinite number of these infinitesimal layers is "solely a function of the ratio of the absorption and back-scatter (remission) constants , but not in any way on the absolute numerical values of these constants". This turns out to be incorrect for layers of finite thickness, and the equation was modified for spectroscopic purposes (below), but Kubelka-Munk theory has found extensive use in coatings.
However, in revised presentations of their mathematical treatment, including that of Kubelka, Kortüm and Hecht (below), the following symbolism became popular, using coefficients rather than fractions:
* is the Absorption Coefficient ≡ the limiting fraction of absorption of light energy per unit thickness, as thickness becomes very small.
* is the Back-Scattering Coefficient ≡ the limiting fraction of light energy scattered backwards per unit thickness as thickness tends to zero. | 0 | Theoretical and Fundamental Chemistry |
The measurement of regional bone metabolism is critical to understand the pathophysiology of metabolic bone diseases.
* Bone biopsy is considered the gold standard to quantify bone turnover; however, it is invasive, complex and costly to perform and subject to significant measurement errors.
* Measurements of serum or urine biomarkers of bone turnover are simple, cheap, quick, and non-invasive in measuring changes in bone metabolism, but only provide information on the global skeleton.
* The functional imaging technique of dynamic [F]NaF PET scans can quantify regional bone turnover at specific sites of clinical importance such as the lumbar spine and hip and has been validated by comparison with the gold standard of bone biopsy. | 1 | Applied and Interdisciplinary Chemistry |
Beginning in 1670 and progressing over three decades, Isaac Newton developed and championed his corpuscular theory, arguing that the perfectly straight lines of reflection demonstrated lights particle nature, as at that time no wave theory demonstrated travel in straight lines. He explained refraction by positing that particles of light accelerated laterally upon entering a denser medium. Around the same time, Newtons contemporaries Robert Hooke and Christiaan Huygens, and later Augustin-Jean Fresnel, mathematically refined the wave viewpoint, showing that if light traveled at different speeds in different media, refraction could be easily explained as the medium-dependent propagation of light waves. The resulting Huygens–Fresnel principle was extremely successful at reproducing lights behaviour and was consistent with Thomas Youngs discovery of wave interference of light by his double-slit experiment in 1801. The wave view did not immediately displace the ray and particle view, but began to dominate scientific thinking about light in the mid 19th century, since it could explain polarization phenomena that the alternatives could not.
James Clerk Maxwell discovered that he could apply his previously discovered Maxwell's equations, along with a slight modification to describe self-propagating waves of oscillating electric and magnetic fields. It quickly became apparent that visible light, ultraviolet light, and infrared light were all electromagnetic waves of differing frequency. This theory became a critical ingredient in the beginning of quantum mechanics. | 1 | Applied and Interdisciplinary Chemistry |
The enzymology of proteases provides some of the clearest known examples of convergent evolution. The same geometric arrangement of triad residues occurs in over 20 separate enzyme superfamilies. Each of these superfamilies is the result of convergent evolution for the same triad arrangement within a different structural fold. This is because there are limited productive ways to arrange three triad residues, the enzyme backbone and the substrate. These examples reflect the intrinsic chemical and physical constraints on enzymes, leading evolution to repeatedly and independently converge on equivalent solutions. | 1 | Applied and Interdisciplinary Chemistry |
The eluate contains the analyte material that emerges from the chromatograph. It specifically includes both the analytes and coeluting solutes passing through the column, while the eluent is only the carrier. | 0 | Theoretical and Fundamental Chemistry |
Generally, Polymer-Protein hybrids can be synthesized by interfacial self-assembly of protein–polymer conjugates in emulsions. | 1 | Applied and Interdisciplinary Chemistry |
A supramolecular host could bind to a guest molecule in such a way that the guests labile group is positioned close to the reactive group of another reactive species. The proximity of the two groups enhances the probability that the reaction could occur and thus the reaction rate is increased. This concept is similar to the principle of preorganization which states that complexation could be improved if the binding motifs are preorganized in a well-defined position so that the host does not require any major conformational change for complexation. In this case, the catalyst is preorganized such that no major conformational changes is required for the reaction to occur. A notable example of catalysts that employ this mechanism is Jean-Marie Lehns crown ether. In addition, catalysts based on functionalized cyclodextrins often employ this mode of catalysis. | 0 | Theoretical and Fundamental Chemistry |
The term "siphon" is used for a number of structures in human and animal anatomy, either because flowing liquids are involved or because the structure is shaped like a siphon, but in which no actual siphon effect is occurring: see Siphon (disambiguation).
There has been a debate if whether the siphon mechanism plays a role in blood circulation. However, in the closed loop of circulation this was discounted; "In contrast, in closed systems, like the circulation, gravity does not hinder uphill flow nor does it cause downhill flow, because gravity acts equally on the ascending and descending limbs of the circuit", but for "historical reasons", the term is used. One hypothesis (in 1989) was that a siphon existed in the circulation of the giraffe. But further research in 2004 found that, "There is no hydrostatic gradient and since the fall of fluid does not assist the ascending arm, there is no siphon. The giraffe’s high arterial pressure, which is sufficient to raise the blood 2 m from heart to head with sufficient remaining pressure to perfuse the brain, supports this concept." However, a paper written in 2005 urged more research on the hypothesis: | 1 | Applied and Interdisciplinary Chemistry |
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