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Electrical resistance heating (ERH) is an intensive environmental remediation method that uses the flow of alternating current electricity to heat soil and groundwater and evaporate contaminants. Electric current is passed through a targeted soil volume between subsurface electrode elements. The resistance to electrical flow that exists in the soil causes the formation of heat; resulting in an increase in temperature until the boiling point of water at depth is reached. After reaching this temperature, further energy input causes a phase change, forming steam and removing volatile contaminants. ERH is typically more cost effective when used for treating contaminant source areas. | 1 | Applied and Interdisciplinary Chemistry |
In building services engineering and HVAC, an air-mixing plenum (or mixing box) is used for mixing air from different ductwork systems. | 1 | Applied and Interdisciplinary Chemistry |
In continuum mechanics, a material is said to be under plane stress if the stress vector is zero across a particular plane. When that situation occurs over an entire element of a structure, as is often the case for thin plates, the stress analysis is considerably simplified, as the stress state can be represented by a tensor of dimension 2 (representable as a 2×2 matrix rather than 3×3). A related notion, plane strain, is often applicable to very thick members.
Plane stress typically occurs in thin flat plates that are acted upon only by load forces that are parallel to them. In certain situations, a gently curved thin plate may also be assumed to have plane stress for the purpose of stress analysis. This is the case, for example, of a thin-walled cylinder filled with a fluid under pressure. In such cases, stress components perpendicular to the plate are negligible compared to those parallel to it.
In other situations, however, the bending stress of a thin plate cannot be neglected. One can still simplify the analysis by using a two-dimensional domain, but the plane stress tensor at each point must be complemented with bending terms. | 1 | Applied and Interdisciplinary Chemistry |
Carbon-13 (C13) nuclear magnetic resonance (most commonly known as carbon-13 NMR spectroscopy or C NMR spectroscopy or sometimes simply referred to as carbon NMR) is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It is analogous to proton NMR ( NMR) and allows the identification of carbon atoms in an organic molecule just as proton NMR identifies hydrogen atoms. C NMR detects only the isotope. The main carbon isotope, does not produce an NMR signal. Although ca. 1 mln. times less sensitive than H NMR spectroscopy, C NMR spectroscopy is widely used for characterizing organic and organometallic compounds, primarily because 1H-decoupled 13C-NMR spectra are more simple, have a greater sensitivity to differences in the chemical structure, and, thus, are better suited for identifying molecules in complex mixtures. At the same time, such spectra lack quantitative information about the atomic ratios of different types of carbon nuclei, because nuclear Overhauser effect used in 1H-decoupled 13C-NMR spectroscopy enhances the signals from carbon atoms with a larger number of hydrogen atoms attached to them more than from carbon atoms with a smaller number of H's, and because full relaxation of 13C nuclei is usually not attained (for the sake of reducing the experiment time), and the nuclei with shorter relaxation times produce more intense signals.
The major isotope of carbon, the C isotope, has a spin quantum number of zero and so is not magnetically active and therefore not detectable by NMR. C, with a spin quantum number of 1/2, is not abundant (1.1%), whereas other popular nuclei are 100% abundant, e.g. H, F, P. | 0 | Theoretical and Fundamental Chemistry |
The (tert-butyl)cyclopentadiene is prepared by alkylation of cyclopentadiene with tert-butyl bromide in the presence of sodium hydride and dibenzo-18-crown-6. The intermediate in this synthesis is di-tert-butylcyclopentadiene. This compound is conveniently prepared by alkylation of cyclobutadiene with tert-butyl bromide under phase-transfer conditions.
Illustrative of the unusual complexes made possible with these bulky ligands is molecular iron nitrido complex (BuCH)FeN. In contrast to (CMe)IrCl, (BuCH)IrCl is monomeric. | 0 | Theoretical and Fundamental Chemistry |
The composition of fluxes is tailored for the required properties - the base metals and their surface preparation (which determine the composition and thickness of surface oxides), the solder (which determines the wetting properties and the soldering temperature), the corrosion resistance and ease of removal, and others.
Fluxes for soft soldering are typically of organic nature, though inorganic fluxes, usually based on halogenides or acids, are also used in non-electronics applications. Fluxes for brazing operate at significantly higher temperatures and are therefore mostly inorganic; the organic compounds tend to be of supplementary nature, e.g. to make the flux sticky at low temperature so it can be easily applied.
The surface of the tin-based solder is coated predominantly with tin oxides; even in alloys the surface layer tends to become relatively enriched by tin. Fluxes for indium and zinc based solders have different compositions than fluxes for ordinary tin-lead and tin-based solders, due to different soldering temperatures and different chemistry of the oxides involved.
Organic fluxes are unsuitable for flame soldering and flame brazing, as they tend to char and impair solder flow.
Some metals are classified as "unsolderable" in air, and have to be either coated with another metal before soldering or special fluxes or protective atmospheres have to be used. Such metals are beryllium, chromium, magnesium, titanium, and some aluminium alloys.
Fluxes for high-temperature soldering differ from the fluxes for use at lower temperatures. At higher temperatures even relatively mild chemicals have sufficient oxide-disrupting activity, but the metal oxidation rates become fairly high; the barrier function of the vehicle therefore becomes more important than the fluxing activity. High molecular weight hydrocarbons are often used for this application; a diluent with a lower molecular weight, boiling off during the preheat phase, is usually used to aid application.
Common fluxes are ammonium chloride or resin acids (contained in rosin) for soldering copper and tin; hydrochloric acid and zinc chloride for soldering galvanized iron (and other zinc surfaces); and borax for brazing, braze-welding ferrous metals, and forge welding. | 1 | Applied and Interdisciplinary Chemistry |
Crudden was appointed a Natural Sciences and Engineering Research Council postdoctoral fellow at University of Illinois at Urbana–Champaign working with Scott E. Denmark in 1995. She moved to University of New Brunswick in 1996 where she started her own research group. In 2002, she was appointed a Queen's National Scholar and moved her research lab to Kingston, Ontario.
Crudden was the first to identify an enantiospecific Suzuki-Miyaura cross-coupling reaction of chiral boranes. In 2014 she designed more stable nitrogen-based self-assembled monolayer treatments for metal surfaces. The N-heterocyclic carbene self-assembled monolayers can be used in a range of applications, including biosensors. Her interests lie in hydroboration, organometallic chemistry, chiral materials and persistent carbenes. In 2010 Crudden became head of a Natural Sciences and Engineering Research Council CREATE award in chiral materials, worth $1.6 million. She became President of the Canadian Society of Chemistry.
In 2015, as Principal Investigator of a group of ten collaborators, Crudden was awarded $8.8 million from the Canada Foundation for Innovation for major infrastructure purchases. She won the Queens University Research Opportunities Fund, which she used to create inexpensive, sensitive biosensors. Her group prepares carbon-based ligands for metal surfaces, which can be used as sensing systems based on surface plasmon resonance. In 2016, she and Dr. Suning Wang held a trilateral Canada-Japan-Germany symposium at Queens looking at Elements Functions for Transformative Catalysis and Materials. Crudden is a joint Professor at the Institute of Transformative Bio-Molecules, based out of Nagoya University in Japan, where she runs a satellite lab. She is one of only four international collaborators at this Institute. She was recognised as having made the most distinguished contribution to the field of catalysis by the Chemical Institute of Canada in 2018, when they awarded her the Catalysis Award. Crudden also often comments on developments in the field of organic chemistry in various media outlets. | 0 | Theoretical and Fundamental Chemistry |
An inverse agonist can have effects similar to those of an antagonist, but causes a distinct set of downstream biological responses. Constitutively active receptors that exhibit intrinsic or basal activity can have inverse agonists, which not only block the effects of binding agonists like a classical antagonist but also inhibit the basal activity of the receptor. Many drugs previously classified as antagonists are now beginning to be reclassified as inverse agonists because of the discovery of constitutive active receptors. Antihistamines, originally classified as antagonists of histamine H receptors have been reclassified as inverse agonists. | 1 | Applied and Interdisciplinary Chemistry |
Similar to the unsteady one-dimensional waves, simple waves in steady two-dimensional system cab be derived. In this case, the solution is given by
where and is an arbitrary function of pressure. The characteristics in the - plane are straight lines. Similarly, the case corresponding to is referred as the centred simple wave; the Prandtl–Meyer expansion fan is a special case of this centred wave. | 1 | Applied and Interdisciplinary Chemistry |
A nanofluid is a fluid containing nanometer-sized particles, called nanoparticles. These fluids are engineered colloidal suspensions of nanoparticles in a base fluid. The nanoparticles used in nanofluids are typically made of metals, oxides, carbides, or carbon nanotubes. Common base fluids include water, ethylene glycol and oil.
Nanofluids have novel properties that make them potentially useful in many applications in heat transfer, including microelectronics, fuel cells, pharmaceutical processes, and hybrid-powered engines, engine cooling/vehicle thermal management, domestic refrigerator, chiller, heat exchanger, in grinding, machining and in boiler flue gas temperature reduction. They exhibit enhanced thermal conductivity and the convective heat transfer coefficient compared to the base fluid. Knowledge of the rheological behaviour of nanofluids is found to be critical in deciding their suitability for convective heat transfer applications.
Nanofluids also have special acoustical properties and in ultrasonic fields display additional shear-wave reconversion of an incident compressional wave; the effect becomes more pronounced as concentration increases.
In analysis such as computational fluid dynamics (CFD), nanofluids can be assumed to be single phase fluids; however, almost all new academic papers use a two-phase assumption. Classical theory of single phase fluids can be applied, where physical properties of nanofluid is taken as a function of properties of both constituents and their concentrations. An alternative approach simulates nanofluids using a two-component model.
The spreading of a nanofluid droplet is enhanced by the solid-like ordering structure of nanoparticles assembled near the contact line by diffusion, which gives rise to a structural disjoining pressure in the vicinity of the contact line. However, such enhancement is not observed for small droplets with diameter of nanometer scale, because the wetting time scale is much smaller than the diffusion time scale. | 0 | Theoretical and Fundamental Chemistry |
Identification of active sites is crucial in the process of drug discovery. The 3-D structure of the enzyme is analysed to identify active site residues and design drugs which can fit into them. Proteolytic enzymes are targets for some drugs, such as protease inhibitors, which include drugs against AIDS and hypertension. These protease inhibitors bind to an enzyme's active site and block interaction with natural substrates. An important factor in drug design is the strength of binding between the active site and an enzyme inhibitor. If the enzyme found in bacteria is significantly different from the human enzyme then an inhibitor can be designed against that particular bacterium without harming the human enzyme. If one kind of enzyme is only present in one kind of organism, its inhibitor can be used to specifically wipe them out.
Active sites can be mapped to aid the design of new drugs such as enzyme inhibitors. This involves the description of the size of an active site and the number and properties of sub-sites, such as details of the binding interaction. Modern database technology called CPASS (Comparison of Protein Active Site Structures) however allows the comparison of active sites in more detail and the finding of structural similarity using software. | 1 | Applied and Interdisciplinary Chemistry |
Unlike other ACE inhibitors that are primarily excreted by the kidneys, fosinopril is eliminated from the body by both renal and hepatic pathways. This characteristic of fosinopril makes the drug a safer choice than other ACE inhibitors for heart failure patients with impaired kidney function resulting from poor perfusion as fosinopril can still be eliminated by the liver, preventing accumulation of the drug in the body.
Fosinopril is de-esterified by the liver or gastrointestinal mucosa and is converted to its active form, fosinoprilat. Fosinoprilat competitively binds to ACE, preventing ACE from binding to and converting angiotensin I to angiotensin II. Inhibiting the production of AII lowers peripheral vascular resistance, decreases afterload, and decreases blood pressure, thus helping to alleviate the negative effects of AII on cardiac performance. | 0 | Theoretical and Fundamental Chemistry |
In the 1950s and 60s, McCrone conducted extensive research on the microscopic characterization of polymorphs, which he defined as materials that are "different in crystal structure but identical in the liquid or vapor states." He investigated the difference in the properties of polymorphs of medications, co-authoring with John Haleblian a review article on "the pharmaceutical application of polymorphism", published in 1969. McCrone's work on polymorphism exerted a strong influence upon the scientific career of Joel Bernstein. | 0 | Theoretical and Fundamental Chemistry |
Alkyl selenocyanates are generally prepared by treatment of potassium selenocyanate with alkyl halides in alcohol or acetone solution. Aryl selenocyanates are generally prepared by treatment of potassium selenocyanate with aryl diazonium salts. | 0 | Theoretical and Fundamental Chemistry |
Ultraviolet illumination can be produced from longer wavelengths using non-linear optical materials. These can be a second harmonic generator. They must have a suitable birefringence in order to phase match the output frequency doubled UV light. One compound commercially used is L-arginine phosphate monohydrate known as LAP. Research is underway for substances that are very non-linear, have a suitable birefringence, are transparent in the spectrum and have a high degree of resistance to damage from lasers. | 0 | Theoretical and Fundamental Chemistry |
Gels are used as stationary phase for GPC. The pore size of a gel must be carefully controlled in order to be able to apply the gel to a given separation. Other desirable properties of the gel forming agent are the absence of ionizing groups and, in a given solvent, low affinity for the substances to be separated. Commercial gels like PLgel & Styragel (cross-linked polystyrene-divinylbenzene), LH-20 (hydroxypropylated Sephadex), Bio-Gel (cross-linked polyacrylamide), HW-20 & HW-40 (hydroxylated methacrylic polymer), and agarose gel are often used based on different separation requirements. | 0 | Theoretical and Fundamental Chemistry |
Diphoterine is a decontamination solution used in first aid for the emergency treatment of chemical spills to the eyes and body. | 0 | Theoretical and Fundamental Chemistry |
Carbon dioxide sequestration in basalt involves the injecting of into deep-sea formations. The first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of and ions forming stable carbonate minerals.
Underwater basalt offers a good alternative to other forms of oceanic carbon storage because it has a number of trapping measures to ensure added protection against leakage. These measures include "geochemical, sediment, gravitational and hydrate formation." Because hydrate is denser than in seawater, the risk of leakage is minimal. Injecting the at depths greater than ensures that the has a greater density than seawater, causing it to sink.
One possible injection site is Juan de Fuca plate. Researchers at the Lamont–Doherty Earth Observatory found that this plate at the western coast of the United States has a possible storage capacity of 208 gigatons. This could cover the entire current U.S. carbon emissions for over 100 years.
This process is undergoing tests as part of the CarbFix project, resulting in 95% of the injected 250 tonnes of CO to solidify into calcite in two years, using 25 tonnes of water per tonne of CO. | 0 | Theoretical and Fundamental Chemistry |
A cumulative equilibrium constant, denoted by is related to the product of stepwise constants, denoted by For a dibasic acid the relationship between stepwise and overall constants is as follows
Note that in the context of metal-ligand complex formation, the equilibrium constants for the formation of metal complexes are usually defined as association constants. In that case, the equilibrium constants for ligand protonation are also defined as association constants. The numbering of association constants is the reverse of the numbering of dissociation constants; in this example | 0 | Theoretical and Fundamental Chemistry |
Ultraviolet radiation is invisible to the human eye, but illuminating certain materials with UV radiation causes the emission of visible light, causing these substances to glow with various colors. This is called fluorescence, and has many practical uses. Black lights are required to observe fluorescence, since other types of ultraviolet lamps emit visible light which drowns out the dim fluorescent glow. | 0 | Theoretical and Fundamental Chemistry |
Numerous schemes have been described as artificial photosynthesis.
*Photocatalytic water splitting, the conversion water into hydrogen and oxygen:
This scheme is the simplest form of artificial photosynthesis conceptually, but has not been demonstrated in any practicable way.
*Light-driven carbon dioxide reduction, the conversion water, carbon dioxide into carbon monoxide or organic compounds and oxygen. In the conceptually simplest manifestation, this process gives CO:
Related processes give formic acid (HCO2H):
Variations might produce formaldehyde or, equivalently, carbohydrates:
These processes replicate natural carbon fixation.
Because of the socio-economic implications, Artificial photosynthesis is very topical, despite the many challenges.
Ideally the only inputs to produce such solar fuels would be water, carbon dioxide, and sunlight. The only by-product would be oxygen.
by using direct processes, | 0 | Theoretical and Fundamental Chemistry |
Itch has been shown to interact with a number of proteins, including:
* CXCR4,
* c-Jun,
* MAP2K4,
* MAP3K1,
* MAP3K7,
* MAPK8,
* N4BP1,
* NOTCH1,
* TP63, and
* TP73. | 1 | Applied and Interdisciplinary Chemistry |
Iron is important for the growth of phytoplankton. In phytoplankton, iron is used for electron transfer reactions in photosynthesis in both photosystem I and photosystem II. Additionally, iron is an important component of the enzyme nitrogenase, which is used to fix nitrogen. In measurements at open ocean stations, phytoplankton are isotopically light, with the fractionation as a result of biological uptake measured between -0.25‰ and -0.13‰. Improvement in the understanding of this fractionation will enable the more precise understanding of phytoplankton photosynthetic processes. | 0 | Theoretical and Fundamental Chemistry |
In pre-modern medicine, diasebesten (from Greek dia "[made] with" + modern Latin sebesten, Arab. sabastān, from Persian sepestān, possibly from Persian sag-pestān سگپستان, literally "dogs teats"), is a soft, purgative electuary, containing sebesten, the plum-like fruit of the tree Cordia myxa', as one of its ingredients.
The other ingredients are prunes, tamarinds, juices of iris, anguria, and mercurialis, penide, simple diaprunum (made of damask prunes), violet seed, the four cold seeds (melon, gourd, purslane, and quince), and diagrydium. It was said to be good in intermittent and continued fevers, appease thirst, promote sleep, and expel morbid humours through urine. | 1 | Applied and Interdisciplinary Chemistry |
Contraindications are hypersensitivity against ACE inhibitors, especially if it has resulted in angioedema; idiopathic or hereditary angioedema; kidney failure; the second and third trimesters in pregnancy; and combination with the drug aliskiren in people with diabetes. | 0 | Theoretical and Fundamental Chemistry |
In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below, which is referred to as the biological pump. Export production is the amount of organic matter produced in the ocean by primary production that is not recycled (remineralised) before it sinks into the aphotic zone. Because of the role of export production in the ocean's biological pump, it is typically measured in units of carbon (e.g. mg C m d). The term was coined by explorer William Beebe as observed from his bathysphere. As the origin of marine snow lies in activities within the productive photic zone, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents. Marine snow can be an important food source for organisms living in the aphotic zone, particularly for organisms that live very deep in the water column. | 0 | Theoretical and Fundamental Chemistry |
Other than standard fluorescence optical tweezers are now being built with multiple color Confocal, Widefield, STED, FRET, TIRF or IRM.
This allows applications such as measuring: protein/DNA localization binding, protein folding, condensation, motor protein force generation, visualization of cytoskeletal filaments and motor dynamics, microtubule dynamics, manipulating liquid droplet (rheology) or fusion. These setups are difficult to build and traditionally are found in non correlated academic setups. In the recent years even home builders (both biophysics and general biologists) are converting to the alternative and are acquiring total correlated solution with easy data acquisition and data analysis. | 1 | Applied and Interdisciplinary Chemistry |
Planar chirality, also known as 2D chirality, is the special case of chirality for two dimensions.
Most fundamentally, planar chirality is a mathematical term, finding use in chemistry, physics and related physical sciences, for example, in astronomy, optics and metamaterials. Recent occurrences in latter two fields are dominated by microwave and terahertz applications as well as micro- and nanostructured planar interfaces for infrared and visible light. | 0 | Theoretical and Fundamental Chemistry |
A tree wrap or tree wrapping is a wrap of garden tree saplings, roses, and other delicate plants to protect them from frost damage (e.g. frost cracks or complete death). In the past it was made of straw (straw wrap) . Now there are commercial tree wrap materials, such as crepe paper or burlap tapes. Tree wrapping is also used to prevent saplings from sunscald and drying of the bark. A disadvantage of tape wrapping is dampness under the wrapping during rainy seasons. | 1 | Applied and Interdisciplinary Chemistry |
Besides the introduction of mutations, Overlap Extension PCR is widely used to assemble complex DNA sequences without the introduction of undesired nucleotides at any position. This is possible since OE-PCR relies on the utilization of complementary overhangs to guide the scarless splicing of custom DNA fragments in a desired order. This is the main advantage of OE-PCR and other long-homology based cloning methos such as Gibson assembly, which overcome the limitations of traditional restriction enzyme digestion and ligation cloning methods.
Assembly of custom DNA sequences with OE-PCR consists on three main steps. First, individual DNA sequences are amplified by PCR from different templates and flanked with the required complementary overhangs. Second, the formerly obtained PCR products are combined together into the overlap extension PCR reaction, where the complementary overhangs bind pair-wise allowing the polymerase to extend the DNA strand. Eventually, outer primers targeting the external overhangs are used and the desired DNA product is amplified in the final PCR reaction. | 1 | Applied and Interdisciplinary Chemistry |
A Piper diagram is a graphic procedure proposed by Arthur M. Piper in 1944 for presenting water chemistry data to help in understanding the sources of the dissolved constituent salts in water. This procedure is based on the premise that cations and anions in water are in such amounts to assure the electroneutrality of the dissolved salts, in other words the algebraic sum of the electric charges of cations and anions is zero.
A Piper diagram is a graphical representation of the chemistry of a water sample or samples.
The cations and anions are shown by separate ternary plots. The apexes of the cation plot are calcium, magnesium and sodium plus potassium cations. The apexes of the anion plot are sulfate, chloride and carbonate plus hydrogen carbonate anions. The two ternary plots are then projected onto a diamond. The diamond is a matrix transformation of a graph of the anions (sulfate + chloride/ total anions) and cations (sodium + potassium/total cations).
The Piper diagram is suitable for comparing the ionic composition of a set of water samples, but does not lend itself to spatial comparisons. For geographical applications, the Stiff diagram and Maucha diagram are more applicable, because they can be used as markers on a map. Colour coding of the background of the Piper diagram allows linking Piper Diagrams and maps
Water samples shown on the Piper diagram can be grouped in hydrochemical facies. The cation and anion triangles can be separated in regions based on the dominant cation(s) or anion(s) and their combination creates regions in the diamond shaped part of the diagram. | 0 | Theoretical and Fundamental Chemistry |
The Wulff construction is a method to determine the equilibrium shape of a droplet or crystal of fixed volume inside a separate phase (usually its saturated solution or vapor). Energy minimization arguments are used to show that certain crystal planes are preferred over others, giving the crystal its shape. | 0 | Theoretical and Fundamental Chemistry |
By raising the water table, after damage has been inflicted due to over-intensive drainage, the soils can be restored.
The following table gives an example.
Drainage and yield of Malaysian oil palm on acid sulfate soils (after Toh Peng Yin and Poon Yew Chin, 1982)<br>
Yield in tons of fresh fruit per ha:
Drainage depth and intensity were increased in 1962. The water table was raised again in 1966 to counter negative effects.
In the "millennium drought" in the Murray-Darling Basin in Australia, exposure of acid sulfate soils occurred. Large scale engineering interventions were undertaken to prevent further acidification, including construction of a bund and pumping of water to prevent exposure and acidification of Lake Albert. Management of acidification in the Lower Lakes was also undertaken using aerial limestone dosing. | 0 | Theoretical and Fundamental Chemistry |
Arthur Cushny (1866–1926) was the first holder of the newly instituted Chair of Pharmacology, from 1905 until 1918.
After graduating in medicine from Aberdeen, Cushny had studied in Berne, Würzburg, and Strasbourg, where he became Assistant to the famed Oswald Schmiedeberg. In 1893, at the age of 27, he was appointed Professor of Pharmacology at the University of Michigan, Ann Arbor. Eight years later Cushny came to the chair at UCL where he soon expanded the department from the single room he had been given. He raised the funds for the building which the remnants of the department still occupies.
His main interests were in the heart and kidney. His work on the involvement of calcium in the action of digitalis was prescient. He was interested in optical isomers. Data from an early clinical trial using hyoscine isomers was used by William Sealy Gossett who, under the pseudonym "Student" published in 1908 the first small-sample test of significance, Students t' test. His use of these data has given rise to much discussion. Later reanalysis of the same data by a randomisation tests gave a similar result.
Cushny published a textbook Textbook of Pharmacology and Therapeutics (eighth edition 1924). He introduced the Cushny myograph, an ingenious arrangement of counterbalanced levers that allowed the faithful recording of the rate and force of contraction of the rapidly beating animal heart. It was still in use in practical classes at UCL, and elsewhere, in the 1960s.
Cushny left UCL in 1918, to become Professor of Materia Medica and Pharmacology at Edinburgh. he was succeeded by A.J. Clark/ | 1 | Applied and Interdisciplinary Chemistry |
Leo Yaffe, (July 6, 1916 – May 14, 1997) was a Canadian nuclear chemistry scientist and a proponent of the peaceful uses of nuclear power.
Born in Devils Lake, North Dakota, his family moved to Winnipeg in 1920. He studied at the University of Manitoba receiving a B.Sc.(Hons) in 1940, a M.Sc. in 1941, and was awarded an honorary D.Sc. in 1982. He received a Ph.D. in 1943 from McGill University.
In 1943, he was recruited by Atomic Energy of Canada Limited to work at the Manhattan Project's Montreal Laboratory, moving to the Chalk River Laboratories, on the banks of the Ottawa River, in Ontario, at the end of the war. He remained with the AECL until 1952.
In 1952, he moved to Montreal, where the J.S. Foster cyclotron had just been built at McGill University. In 1958 he became the Macdonald Professor of Chemistry.
From 1963 to 1965 he was director of research at the International Atomic Energy Agency in Vienna. Returning to McGill he was appointed head of the department of chemistry until 1972. In 1974 he was appointed vice-principal (administration) which he held until he retired in 1981. From 1981 to 1982, he was the president of the Chemical Institute of Canada.
He married Betty Workman and has two children: Carla Krasnick, and Mark Yaffe. Yaffe died in Montreal in 1997. The McGill University Archives holds a collection of his personal papers and photographs. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. These surrounded solute particles then move away from the solid solute and out into the solution. The mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution usually has the state of the solvent when the solvent is the larger fraction of the mixture, as is commonly the case. One important parameter of a solution is the concentration, which is a measure of the amount of solute in a given amount of solution or solvent. The term "aqueous solution" is used when one of the solvents is water. | 0 | Theoretical and Fundamental Chemistry |
While most iron is oxidized as a result of interaction with atmospheric oxygen or oxygenated waters, oxidation by bacteria is an active process in anoxic environments and in oxygenated, low pH (Fe values between 2 and 3‰ were measured. However, a Rayleigh trend with a fractionation factor of α ~ 1.0022 was observed, which is smaller than the fractionation factor in the abiotic control experiments (α ~ 1.0034), which has been inferred to reflect a biological isotope effect. Using iron isotopes, an improvement in the understanding of the metabolic processes controlling iron oxidation and energy production in these organisms can be developed.
Photoautrophic bacteria, which oxidize Fe(II) under anaerobic conditions, have also been studied. The Thiodictyon bacteria precipitate poorly crystalline hydrous ferric oxide when they oxidize iron. The precipitate was enriched in the Fe relative to Fe(II), with a δFe value of +1.5 ± 0.2‰. | 0 | Theoretical and Fundamental Chemistry |
The relationship between combustion and respiration had long been recognized from the essential role which air played in both processes. Lavoisier was almost obliged, therefore, to extend his new theory of combustion to include the area of respiration physiology. His first memoirs on this topic were read to the Academy of Sciences in 1777, but his most significant contribution to this field was made in the winter of 1782–1783 in association with Laplace. The result of this work was published in a memoir, "On Heat." Lavoisier and Laplace designed an ice calorimeter apparatus for measuring the amount of heat given off during combustion or respiration. The outer shell of the calorimeter was packed with snow, which melted to maintain a constant temperature of around an inner shell filled with ice. By measuring the quantity of carbon dioxide and heat produced by confining a live guinea pig in this apparatus, and by comparing the amount of heat produced when sufficient carbon was burned in the ice calorimeter to produce the same amount of carbon dioxide as that which the guinea pig exhaled, they concluded that respiration was, in fact, a slow combustion process. Lavoisier stated, "la respiration est donc une combustion," that is, respiratory gas exchange is a combustion, like that of a candle burning.
This continuous slow combustion, which they supposed took place in the lungs, enabled the living animal to maintain its body temperature above that of its surroundings, thus accounting for the puzzling phenomenon of animal heat. Lavoisier continued these respiration experiments in 1789–1790 in cooperation with Armand Seguin. They designed an ambitious set of experiments to study the whole process of body metabolism and respiration using Seguin as a human guinea pig in the experiments. Their work was only partially completed and published because of the Revolutions disruption, but Lavoisiers pioneering work in this field inspired similar research on physiological processes for generations. | 1 | Applied and Interdisciplinary Chemistry |
Thermogravimetric analysis (TGA) is conducted on an instrument referred to as a thermogravimetric analyzer. A thermogravimetric analyzer continuously measures mass while the temperature of a sample is changed over time. Mass, temperature, and time are considered base measurements in thermogravimetric analysis while many additional measures may be derived from these three base measurements.
A typical thermogravimetric analyzer consists of a precision balance with a sample pan located inside a furnace with a programmable control temperature. The temperature is generally increased at constant rate (or for some applications the temperature is controlled for a constant mass loss) to incur a thermal reaction. The thermal reaction may occur under a variety of atmospheres including: ambient air, vacuum, inert gas, oxidizing/reducing gases, corrosive gases, carburizing gases, vapors of liquids or "self-generated atmosphere"; as well as a variety of pressures including: a high vacuum, high pressure, constant pressure, or a controlled pressure.
The thermogravimetric data collected from a thermal reaction is compiled into a plot of mass or percentage of initial mass on the y axis versus either temperature or time on the x-axis. This plot, which is often smoothed, is referred to as a TGA curve. The first derivative of the TGA curve (the DTG curve) may be plotted to determine inflection points useful for in-depth interpretations as well as differential thermal analysis.
A TGA can be used for materials characterization through analysis of characteristic decomposition patterns. It is an especially useful technique for the study of polymeric materials, including thermoplastics, thermosets, elastomers, composites, plastic films, fibers, coatings, paints, and fuels. | 0 | Theoretical and Fundamental Chemistry |
Major developments: Earliest stage of gunpowder development. Mentions of gunpowder ingredients and their uses in conjunction with each other. | 1 | Applied and Interdisciplinary Chemistry |
Otto Hahn (; 8 March 1879 – 28 July 1968) was a German chemist who was a pioneer in the fields of radioactivity and radiochemistry. He is referred to as the father of nuclear chemistry and father of nuclear fission. Hahn and Lise Meitner discovered radioactive isotopes of radium, thorium, protactinium and uranium. He also discovered the phenomena of atomic recoil and nuclear isomerism, and pioneered rubidium–strontium dating. In 1938, Hahn, Meitner and Fritz Strassmann discovered nuclear fission, for which Hahn alone, was awarded the 1944 Nobel Prize for Chemistry. Nuclear fission was the basis for nuclear reactors and nuclear weapons.
A graduate of the University of Marburg, which awarded him a doctorate in 1901, Hahn studied under Sir William Ramsay at University College London and at McGill University in Montreal under Ernest Rutherford, where he discovered several new radioactive isotopes. He returned to Germany in 1906; Emil Fischer placed a former woodworking shop in the basement of the Chemical Institute at the University of Berlin at his disposal to use as a laboratory. Hahn completed his habilitation in the spring of 1907 and became a Privatdozent. In 1912, he became head of the Radioactivity Department of the newly founded Kaiser Wilhelm Institute for Chemistry. Working with the Austrian physicist Lise Meitner in the building that now bears their names, he made a series of groundbreaking discoveries, culminating with her isolation of the longest-lived isotope of protactinium in 1918.
During World War I he served with a Landwehr regiment on the Western Front, and with the chemical warfare unit headed by Fritz Haber on the Western, Eastern and Italian fronts, earning the Iron Cross (2nd Class) for his part in the First Battle of Ypres. After the war he became the head of the Kaiser Wilhelm Institute for Chemistry, while remaining in charge of his own department. Between 1934 and 1938, he worked with Strassmann and Meitner on the study of isotopes created through the neutron bombardment of uranium and thorium, which led to the discovery of nuclear fission. He was an opponent of national socialism and the persecution of Jews by the Nazi Party that caused the removal of many of his colleagues, including Meitner, who was forced to flee Germany in 1938. During World War II, he worked on the German nuclear weapons program, cataloguing the fission products of uranium. As a consequence, at the end of the war he was arrested by the Allied forces; he was incarcerated in Farm Hall with nine other German scientists, from July 1945 to January 1946.
Hahn served as the last president of the Kaiser Wilhelm Society for the Advancement of Science in 1946 and as the founding president of its successor, the Max Planck Society from 1948 to 1960. In 1959 he co-founded in Berlin the Federation of German Scientists, a non-governmental organization, which has been committed to the ideal of responsible science. As he worked to rebuild German science, he became one of the most influential and respected citizens of the post-war West Germany. | 0 | Theoretical and Fundamental Chemistry |
In May 2010, an application of SNALPs to the Ebola Zaire virus made headlines, as the preparation was able to cure rhesus macaques when administered shortly after their exposure to a lethal dose of the virus, which can be up to 90% lethal to humans in sporadic outbreaks in Africa. The treatment used for rhesus macaques consisted of three siRNAs (staggered duplexes of RNA) targeting three viral genes. The SNALPs (around 81 nm in size here) were formulated by spontaneous vesiculation from a mixture of cholesterol, dipalmitoyl phosphatidylcholine, 3-N-[(ω-methoxy
poly(ethylene glycol)2000)carbamoyl]-1,2-dimyrestyloxypropylamine, and cationic 1,2-dilinoleyloxy-3-N,N-dimethylaminopropane.
In addition to the rhesus macaque application, SNALPs have also been proven to protect cavia porcellua from viremia and death when administered shortly after postexposure to ZEBOV. A polymerase (L) gene-specific siRNAs delivery system was imposed upon four genes associated with the viral genomic RNA in the ribonucleoprotein complex found within EBOV particles (three of which match the application above): NP, VP30, VP35, and the L protein. The SNALPs ranged from 71 – 84 nm in size and were composed of synthetic cholesterol, phospholipid DSPC, PEG lipid PEGC-DMA, and cationic lipid DLinDMA at the molar ratio of 48:20:2:30. The results confirm complete protection against viremia and death in guinea pigs when administered a SNALP-siRNA delivery system after diagnosis of the Ebola virus, thus proving this technology to be an effective treatment. Future studies will focus mainly upon evaluating the effects of siRNA ‘cocktails’ on EBOV genes to increase antiviral effects. | 1 | Applied and Interdisciplinary Chemistry |
Complementing alkylation reactions are the reverse, dealkylations. Prevalent are demethylations, which are prevalent in biology, organic synthesis, and other areas, especially for methyl ethers and methyl amines. | 0 | Theoretical and Fundamental Chemistry |
In the human ventricles, repolarization can be seen on an ECG (electrocardiogram) via the J-wave (Osborn), ST segment, T wave and U wave. Due to the complexity of the heart, specifically how it contains three layers of cells (endocardium, myocardium and epicardium), there are many physiological changes effecting repolarization that will also affect these waves. Apart from changes in the structure of the heart that effect repolarization, there are many pharmaceuticals that have the same effect.
On top of that, repolarization is also altered based on the location and duration of the initial action potential. In action potentials stimulated on the epicardium, it was found that the duration of the action potential needed to be 40–60 msec to give a normal, upright T-wave, whereas a duration of 20–40 msec would give an isoelectric wave and anything under 20 msec would result in a negative T-wave.
Early repolarization is a phenomenon that can be seen in ECG recordings of ventricular cells where there is an elevated ST segment, also known as a J wave. The J wave is prominent when there is a larger outward current in the epicardium compared to the endocardium. It has been historically considered to be a normal variant in cardiac rhythm but recent studies show that it is related to an increased risk of cardiac arrest. Early repolarization occurs mainly in males and is associated with a larger potassium current caused by the hormone testosterone. Additionally, although the risk is unknown, African American individuals seem more likely to have the early repolarization more often. | 0 | Theoretical and Fundamental Chemistry |
All fluids, except superfluids, are viscous, meaning that they exert some resistance to deformation: neighbouring parcels of fluid moving at different velocities exert viscous forces on each other. The velocity gradient is referred to as a strain rate; it has dimensions . Isaac Newton showed that for many familiar fluids such as water and air, the stress due to these viscous forces is linearly related to the strain rate. Such fluids are called Newtonian fluids. The coefficient of proportionality is called the fluid's viscosity; for Newtonian fluids, it is a fluid property that is independent of the strain rate.
Non-Newtonian fluids have a more complicated, non-linear stress-strain behaviour. The sub-discipline of rheology describes the stress-strain behaviours of such fluids, which include emulsions and slurries, some viscoelastic materials such as blood and some polymers, and sticky liquids such as latex, honey and lubricants. | 1 | Applied and Interdisciplinary Chemistry |
Dallol lies in the evaporitic plain of the Danakil Depression at the Afar Triangle, in the prolongation of the Erta Ale basaltic volcanic range. The intrusion of basaltic magma in the marine sedimentary sequence of Danakil resulted in the formation of a salt dome structure, where the hydrothermal system is hosted. The age of the hydrothermal system is unknown and the latest phreatic eruption that resulted in the formation of a diameter crater within the dome, took place in 1926. The wider area of Dallol is known as one of the driest and hottest places on the planet. It is also one of the lowest land points, lying below mean sea level. Other known hydrothermal features nearby Dallol are Gaet'Ale Pond and Black Lakes.
The hydrothermal springs of Dallol discharge anoxic, hyper-acidic (pH < 0), hyper-saline (almost 10 times more saline than seawater), high temperature (hotter than ) brines that contain more than 26 g/L of iron. The main gases emitted from the springs and fumaroles are carbon dioxide, hydrogen sulfide, nitrogen, sulfur dioxide; and traces of hydrogen, argon, and oxygen. Although several other hyper-acidic (pH < 2) volcanic systems exist, mainly found in crater lakes and hydrothermal sites, the pH values of Dallol decrease far below zero. The coexistence of such extreme physicochemical characteristics (pH, salinity, high temperature, lack of oxygen, etc.) render Dallol one of the very few ‘poly-extreme’ sites on Earth. This is why Dallol is a key system for astrobiological studies investigating the limits of life. Parts of the region are nearly sterile, except for a diverse array of "ultrasmall" archaea.
Dallol is highly dynamic; active springs go inactive and new springs emerge in new places in the range of days, and this is also reflected in the colors of the site that change with time, from white to green, lime, yellow, gold, orange, red, purple and ochre. In contrast to other hydrothermal systems known for their colorful pools (e.g. Grand Prismatic Spring), where the colors are generated by biological activity, the color palette of Dallol is produced by the inorganic oxidation of the abundant iron phases. Another fascinating feature of Dallol is the wide array of unusual mineral patterns, such as, salt-pillars, miniature geysers, water-lilies, flower-like crystals, egg-shaped crusts, and pearl-like spheres. The main mineral phases encountered at Dallol are halite, jarosite, hematite, akaganeite and other Fe-oxyhydroxides, gypsum, anhydrite, sylvite and carnallite. | 0 | Theoretical and Fundamental Chemistry |
Lasso peptides are short peptides containing an N-terminal macrolactam macrocycle "ring" through which a linear C-terminal "tail" is threaded. Because of this threaded-loop topology, these peptides resemble lassos, giving rise to their name. They are a member of a larger class of amino-acid-based lasso structures. Additionally, lasso peptides are formally rotaxanes.
The N-terminal "ring" can be from 7 to 9 amino acids long and is formed by an isopeptide bond between the N-terminal amine of the first amino acid of the peptide and the carboxylate side chain of an aspartate or glutamate residue. The C-terminal "tail" ranges from 7 to 15 amino acids in length.
The first amino acid of lasso peptides is almost invariably glycine or cysteine, with mutations at this site not being tolerated by known enzymes. Thus, bioinformatics-based approaches to lasso peptide discovery have thus used this as a constraint. However, some lasso peptides were recently discovered that also contain serine or alanine as their first residue.
The threading of the lasso tail is trapped either by disulfide bonds between ring and tail cysteine residues (class I lasso peptides), by steric effects due to bulky residues on the tail (class II lasso peptides), or both (class III lasso peptides). The compact structure makes lasso peptides frequently resistant to proteases or thermal unfolding. | 1 | Applied and Interdisciplinary Chemistry |
In addition to naturally occurring types of catalytic triads, protein engineering has been used to create enzyme variants with non-native amino acids, or entirely synthetic amino acids. Catalytic triads have also been inserted into otherwise non-catalytic proteins, or protein mimics.
Subtilisin (a serine protease) has had its oxygen nucleophile replaced with each of sulfur, selenium, or tellurium. Cysteine and selenocysteine were inserted by mutagenesis, whereas the non-natural amino acid, tellurocysteine, was inserted using auxotrophic cells fed with synthetic tellurocysteine. These elements are all in the 16th periodic table column (chalcogens), so have similar properties. In each case, changing the nucleophile reduced the enzyme's protease activity, but increased a different activity. A sulfur nucleophile improved the enzymes transferase activity (sometimes called subtiligase). Selenium and tellurium nucleophiles converted the enzyme into an oxidoreductase. When the nucleophile of TEV protease was converted from cysteine to serine, it protease activity was strongly reduced, but was able to be restored by directed evolution.
Non-catalytic proteins have been used as scaffolds, having catalytic triads inserted into them which were then improved by directed evolution. The Ser-His-Asp triad has been inserted into an antibody, as well as a range of other proteins. Similarly, catalytic triad mimics have been created in small organic molecules like diaryl diselenide, and displayed on larger polymers like Merrifield resins, and self-assembling short peptide nanostructures. | 1 | Applied and Interdisciplinary Chemistry |
siRNAs have been chemically modified to enhance their therapeutic properties, Short interfering RNA (siRNA) must be delivered to the site of action in the cells of target tissues in order for RNAi to fulfill its therapeutic promise. A detailed database of all such chemical modifications is manually curated as [http://crdd.osdd.net/servers/sirnamod siRNAmod] in scientific literature. Chemical modification of siRNA can also inadvertently result in loss of single-nucleotide specificity. | 1 | Applied and Interdisciplinary Chemistry |
Ceramic chemistry studies the relationship between the physical and chemical properties of fired ceramic bodies and ceramic glazes. The field is largely concerned with the reactions of silicates. | 0 | Theoretical and Fundamental Chemistry |
Scott Blair was born 23 July 1902, in Weybridge and went to Winchester College. He studied chemistry at Trinity College, Oxford receiving a BA in 1923.
He began work as a colloid chemist, studying flour suspensions which led to a series of papers on baker's dough. In 1926 he joined the Rothamsted Experimental Station, where the focus was on soil science. In 1928 he married Rita, a child psychologist, who survived him.
In December 1929 Scott Blair attended (and chaired) the founding meeting of the Society of Rheology in Washington, D.C. Chemist Eugene C. Bingham led the new society concerned with the problems of flow. Scott Blair held a Rockefeller Fellowship at the time. In 1931 Markus Reiner visited Scott Blair in England beginning a long friendship.
In 1936 he submitted his PhD thesis to the University of London.
In 1940, along with Vernon Harrison, he founded the British Rheologists' Club, later to become the British Society of Rheology.
In 1937 he became Head of the Chemistry Department (and later headed the Physics Department as well) at the National Institute for Research in Dairying, at Shinfield near Reading until his retirement in 1967. He died on 30 September 1987, at Iffley, Oxfordshire. | 0 | Theoretical and Fundamental Chemistry |
Excimer lamps are quasimonochromatic light sources operating over a wide range of wavelengths in the ultraviolet (UV) and vacuum ultraviolet (VUV) spectral regions. Operation of an excimer lamp is based on the formation of excited dimers (excimers), which spontaneously transiting from the excited state to the ground state result in the emission of UV photons. The spectral maximum of excimer lamp radiation is specified by a working excimer molecule:
Excimers are diatomic molecules (dimers) or polyatomic molecules that have stable excited electronic states and an unbound or weakly bound (thermally unstable) ground state. Initially, only homonuclear diatomic molecules with a stable excited state but a repulsive ground state were called excimers (excited dimers). The term "excimer" was later extended to refer any polyatomic molecule with a repulsive or weakly bound ground state. One can also come across the term "exciplex" (from "excited complex"). It is also an excimer molecule but not a homonuclear dimer. For instance, Xe*, Kr*, Ar* are excimer molecules, while XeCl*, KrCl*, XeBr*, ArCl*, XeCl* are referred to exciplex molecules. Dimers of rare gases and rare-gas–halogen dimers are the most spread and studied excimers. Rare-gas–halide trimers, metal excimers, metal–rare-gas excimers, metal–halide excimers, and rare-gas–oxide excimers are also known, but they are rarely used.
An excimer molecule can exist in an excited electronic state for a limited time, as a rule from a few to a few tens of nanoseconds. After that, an excimer molecule transits to the ground electronic state, while releasing the energy of internal electronic excitation in the form of a photon. Owing to a specific electronic structure of an excimer molecule, the energy gap between the lowest bound excited electronic state and the ground state amounts from 3.5 to 10 eV, depending on a kind of an excimer molecule and provides light emission in the UV and VUV spectral region. A typical spectral characteristic of excimer lamp radiation consists mainly of one intense narrow emission band. About 70–80% of the whole radiation power of an excimer lamp is concentrated in this emission band. The full width at half maximum of the emission band depends on a kind of an excimer molecule and excitation conditions and ranges within 2 to 15 nm. In fact, excimer lamps are sources of quasimonochromatic light. Therefore, such sources are suitable for spectral-selective irradiation and can even replace lasers in some cases. | 0 | Theoretical and Fundamental Chemistry |
The Pulvermacher chain, or in full as it was sold the Pulvermacher hydro-electric chain, was a type of voltaic battery sold in the second half of the 19th century for medical applications. Its chief market was amongst the numerous quack practitioners who were taking advantage of the popularity of the relatively new treatment of electrotherapy, or "electrification" as it was then known. Its unique selling point was its construction of numerous linked cells, rendering it mechanically flexible. A variant intended to be worn wrapped on parts of the body for long periods was known as Pulvermacher's galvanic chain or electric belt.
The Pulvermacher Company attracted a great deal of antagonism from the medical community due to their use of the names of well-known physicians in their advertising without permission. The nature of their business; in selling to charlatans and promoting quack practices also made them unpopular with the medical community. Despite this, the Pulvermacher chain was widely reported as a useful source of electricity for medical and scientific purposes, even amongst the most vocal critics of the Pulvermacher Company. | 0 | Theoretical and Fundamental Chemistry |
The standard state for liquids and solids is simply the state of the pure substance subjected to a total pressure of (or 1 bar). For most elements, the reference point of ΔH = 0 is defined for the most stable allotrope of the element, such as graphite in the case of carbon, and the β-phase (white tin) in the case of tin. An exception is white phosphorus, the most common allotrope of phosphorus, which is defined as the standard state despite the fact that it is only metastable. This is because the thermodynamically stable black allotrope is difficult to prepare pure. | 0 | Theoretical and Fundamental Chemistry |
Spin column-based nucleic acid purification is a method of purifying DNA, RNA or plasmid from a sample using a spin column filter. The method is based on the principle of selectively binding nucleic acids to a solid matrix in the spin column, while other contaminants, such as proteins and salts, are washed away. The conditions are then changed to elute the purified nucleic acid off the column using a suitable elution buffer. | 1 | Applied and Interdisciplinary Chemistry |
The Gulf of Maine frequently experiences blooms of the dinoflagellate Alexandrium fundyense, an organism that produces saxitoxin, the neurotoxin responsible for paralytic shellfish poisoning. The well-known "Florida red tide" that occurs in the Gulf of Mexico is a HAB caused by Karenia brevis, another dinoflagellate which produces brevetoxin, the neurotoxin responsible for neurotoxic shellfish poisoning. California coastal waters also experience seasonal blooms of Pseudo-nitzschia, a diatom known to produce domoic acid, the neurotoxin responsible for amnesic shellfish poisoning.
The term red tide is most often used in the US to refer to Karenia brevis blooms in the eastern Gulf of Mexico, also called the Florida red tide. K. brevis is one of many different species of the genus Karenia found in the world's oceans.
Major advances have occurred in the study of dinoflagellates and their genomics. Some include identification of the toxin-producing genes (PKS genes), exploration of environmental changes (temperature, light/dark, etc.) have on gene expression, as well as an appreciation of the complexity of the Karenia genome. These blooms have been documented since the 1800s, and occur almost annually along Florida's coasts.
There was increased research activity of harmful algae blooms (HABs) in the 1980s and 1990s. This was primarily driven by media attention from the discovery of new HAB organisms and the potential adverse health effects of their exposure to animals and humans. The Florida red tides have been observed to have spread as far as the eastern coast of Mexico. The density of these organisms during a bloom can exceed tens of millions of cells per litre of seawater, and often discolor the water a deep reddish-brown hue.
Red tide is also sometimes used to describe harmful algal blooms on the northeast coast of the United States, particularly in the Gulf of Maine. This type of bloom is caused by another species of dinoflagellate known as Alexandrium fundyense. These blooms of organisms cause severe disruptions in fisheries of these waters, as the toxins in these organism cause filter-feeding shellfish in affected waters to become poisonous for human consumption due to saxitoxin.
The related Alexandrium monilatum is found in subtropical or tropical shallow seas and estuaries in the western Atlantic Ocean, the Caribbean Sea, the Gulf of Mexico, and the eastern Pacific Ocean. | 0 | Theoretical and Fundamental Chemistry |
The Earth began as an iron aquatic world with low oxygen. The Great Oxygenation Event occurred approximately 2.4 Ga (billion years ago) as cyanobacteria and photosynthetic life induced the presence of dioxygen in the planet's atmosphere. Iron became insoluble (as did other metals) and scarce while other metals became soluble. Sulfur was a very important element during this time. Once oxygen was released into the environment, sulfates made metals more soluble and released those metals into the environment; especially into the water. Incorporation of metals perhaps combatted oxidative stress.
The central chemistry of all these cells has to be reductive in order that the synthesis of the required chemicals, especially biopolymers, is possible. The different anaerobic, autocatalysed, reductive, metabolic pathways seen in the earliest known cells developed in separate energised vesicles, protocells, where they were produced cooperatively with certain bases of the nucleic acids.
Hypotheses proposed for how elements became essential is their relative quantity in the environment as life formed. This has produced research on the origin of life; for instance, Orgel and Crick hypothesized that life was extraterrestrial due to the alleged low abundance of molybdenum on early Earth (it is now suspected that there were larger quantities than previously thought). Another example is life forming around thermal vents based on the availability of zinc and sulfur. In conjunction with this theory is that life evolved as chemoautotrophs. Therefore, life occurred around metals and not in response to their presence. Some evidence for this theory is that inorganic matter has self-contained attributes that life adopted as shown by life's compartmentalization. Other evidence includes the ready binding of metals by artificial proteins without evolutionary history. | 0 | Theoretical and Fundamental Chemistry |
Basic helix-loop-helix leucine zipper transcription factors are, as their name indicates, transcription factors containing both Basic helix-loop-helix and leucine zipper motifs.
Examples include Microphthalmia-associated transcription factor and Sterol regulatory element binding protein (SREBP). | 1 | Applied and Interdisciplinary Chemistry |
Women of royal families painted red spots on the center of their cheeks, right under their eyes. However, it is a mystery why. They said that red cheeks (Face Blush) are a reason of happy queen. Blusher helps to enhance the face shape to bring out the cheek bones to lift the makeup look. | 1 | Applied and Interdisciplinary Chemistry |
In particle physics, the quantum yield (denoted ) of a radiation-induced process is the number of times a specific event occurs per photon absorbed by the system. | 0 | Theoretical and Fundamental Chemistry |
Hamiltonian fluid mechanics is the application of Hamiltonian methods to fluid mechanics. Note that this formalism only applies to nondissipative fluids. | 1 | Applied and Interdisciplinary Chemistry |
A digester is a vessel where chemical or biological reactions are carried out, which may involve the use of heat, enzymes or solvent. They are used in different types of process industries, such as in the production of biogas. Digesters are referred to as reactors in some applications. | 1 | Applied and Interdisciplinary Chemistry |
Metallomesogens are metal complexes that exhibit liquid crystalline behavior. Thus, they adopt ordered structures in the molten phase, e.g. smectic and nematic phases. The dominant interactions responsible for their phase behavior are the nonbonding contacts between organic substituents. Two early classes of such materials are based on substituted ferrocenes and dithiolene complexes; more recent work shows that alkoxystilbazoles have similar utility. | 0 | Theoretical and Fundamental Chemistry |
Recently PPARGC1A has been implicated as a potential therapy for Parkinson's disease conferring protective effects on mitochondrial metabolism.
Moreover, brain-specific isoforms of PGC-1alpha have recently been identified which are likely to play a role in other neurodegenerative disorders such as Huntington's disease and amyotrophic lateral sclerosis.
Massage therapy appears to increase the amount of PGC-1α, which leads to the production of new mitochondria.
PGC-1α and beta has furthermore been implicated in polarization to anti-inflammatory M2 macrophages by interaction with PPAR-γ with upstream activation of STAT6. An independent study confirmed the effect of PGC-1 on polarisation of macrophages towards M2 via STAT6/PPAR gamma and furthermore demonstrated that PGC-1 inhibits proinflammatory cytokine production.
PGC-1α has been recently proposed to be responsible for β-aminoisobutyric acid secretion by exercising muscles. The effect of β-aminoisobutyric acid in white fat includes the activation of thermogenic genes that prompt the browning of white adipose tissue and the consequent increase of background metabolism. Hence, the β-aminoisobutyric acid could act as a messenger molecule of PGC-1α and explain the effects of PGC-1α increase in other tissues such as white fat.
PGC-1α increases BNP expression by coactivating ERRα and / or AP1. Subsequently, BNP induces a chemokine cocktail in muscle fibers and activates macrophages in a local paracrine manner, which can then contribute to enhancing the repair and regeneration potential of trained muscles.
Most studies reporting effects of PGC-1α on physiological functions have used mouse models in which the PGC-1α gene is either knocked out or overexpressed from conception. However, some of the proposed effects of PGC-1α have been questioned by studies using inducible knockout technology to remove the PGC-1α gene only in adult mice. For example, two independent studies have shown that adult expression of PGC-1α is not required for improved mitochondrial function after exercise training. This suggests that some of the reported effects of PGC-1α are likely to occur only in the developmental stage. | 1 | Applied and Interdisciplinary Chemistry |
X-ray diffraction shows that all six carbon-carbon bonds in benzene are of the same length, at 140 picometres (pm). The C–C bond lengths are greater than a double bond (135 pm) but shorter than a single bond (147 pm). This intermediate distance is caused by electron delocalization: the electrons for C=C bonding are distributed equally between each of the six carbon atoms. Benzene has 6 hydrogen atoms, fewer than the corresponding parent alkane, hexane, which has 14. Benzene and cyclohexane have a similar structure, only the ring of delocalized electrons and the loss of one hydrogen per carbon distinguishes it from cyclohexane. The molecule is planar. The molecular orbital description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the valence bond description involves a superposition of resonance structures. It is likely that this stability contributes to the peculiar molecular and chemical properties known as aromaticity. To reflect the delocalized nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms.
Derivatives of benzene occur sufficiently often as a component of organic molecules, so much so that the Unicode Consortium has allocated a symbol in the Miscellaneous Technical block with the code U+232C (⌬) to represent it with three double bonds, and U+23E3 (⏣) for a delocalized version. | 1 | Applied and Interdisciplinary Chemistry |
While only one oxhide ingot fragment has been recovered from Egypt (in the context of a LBA smelting workshop), there is a wide array of painted scenes in Egypt that show oxhide ingots. The earliest scene dates to the 15th century BC and the latest scene to the 12th century BC. The ingots display their typical four protrusions, and red paint (which suggests they are copper) is preserved on them. The captions accompanying the scenes explain that the men who bring the ingots come from the north, specifically Retnu (Syria) and Keftiu (unidentified). They are shown being carried on the shoulders of men, sitting with other goods in storage, or as part of scenes in smelting workshops. In a relief from Karnak, the pharaoh Amenhotep II is seen riding a chariot and spearing an oxhide ingot with five arrows. A laudatory caption emphasizing the pharaoh’s strength accompanies the scene.
Several of the “Amarna letters” dating to the mid-14th century BC refer to hundreds of copper talents—in addition to goods such as elephant tusks and glass ingots—sent from the kingdom of Alashiya to Egypt. Some scholars identify Cyprus with Alashiya. In particular, the Uluburun cargo is similar to the goods that, according to the letters, Alashiya sent to Egypt. | 1 | Applied and Interdisciplinary Chemistry |
The prismanes are a class of hydrocarbon compounds consisting of prism-like polyhedra of various numbers of sides on the polygonal base. Chemically, it is a series of fused cyclobutane rings (a ladderane, with all-cis/all-syn geometry) that wraps around to join its ends and form a band, with cycloalkane edges. Their chemical formula is (CH), where n is the number of cyclobutane sides (the size of the cycloalkane base), and that number also forms the basis for a system of nomenclature within this class. The first few chemicals in this class are:
Triprismane, tetraprismane, and pentaprismane have been synthesized and studied experimentally, and many higher members of the series have been studied using computer models. The first several members do indeed have the geometry of a regular prism, with flat n-gon bases. As n becomes increasingly large, however, modeling experiments find that highly symmetric geometry is no longer stable, and the molecule distorts into less-symmetric forms. One series of modelling experiments found that starting with [11]prismane, the regular-prism form is not a stable geometry. For example, the structure of [12]prismane would have the cyclobutane chain twisted, with the dodecagonal bases non-planar and non-parallel. | 0 | Theoretical and Fundamental Chemistry |
Nonribosomal peptides (NRP) are a class of peptide secondary metabolites, usually produced by microorganisms like bacteria and fungi. Nonribosomal peptides are also found in higher organisms, such as nudibranchs, but are thought to be made by bacteria inside these organisms. While there exist a wide range of peptides that are not synthesized by ribosomes, the term nonribosomal peptide typically refers to a very specific set of these as discussed in this article.
Nonribosomal peptides are synthesized by nonribosomal peptide synthetases, which, unlike the ribosomes, are independent of messenger RNA. Each nonribosomal peptide synthetase can synthesize only one type of peptide. Nonribosomal peptides often have cyclic and/or branched structures, can contain non-proteinogenic amino acids including -amino acids, carry modifications like N-methyl and N-formyl groups, or are glycosylated, acylated, halogenated, or hydroxylated. Cyclization of amino acids against the peptide "backbone" is often performed, resulting in oxazolines and thiazolines; these can be further oxidized or reduced. On occasion, dehydration is performed on serines, resulting in dehydroalanine. This is just a sampling of the various manipulations and variations that nonribosomal peptides can perform. Nonribosomal peptides are often dimers or trimers of identical sequences chained together or cyclized, or even branched.
Nonribosomal peptides are a very diverse family of natural products with an extremely broad range of biological activities and pharmacological properties. They are often toxins, siderophores, or pigments. Nonribosomal peptide antibiotics, cytostatics, and immunosuppressants are in commercial use. | 1 | Applied and Interdisciplinary Chemistry |
One of the most important advantages of Fourier-transform spectroscopy was shown by P. B. Fellgett, an early advocate of the method. The Fellgett advantage, also known as the multiplex principle, states that when obtaining a spectrum when measurement noise is dominated by detector noise (which is independent of the power of radiation incident on the detector), a multiplex spectrometer such as a Fourier-transform spectrometer will produce a relative improvement in signal-to-noise ratio, compared to an equivalent scanning monochromator, of the order of the square root of m, where m is the number of sample points comprising the spectrum. However, if the detector is shot-noise dominated, the noise will be proportional to the square root of the power, thus for a broad boxcar spectrum (continuous broadband source), the noise is proportional to the square root of m, thus precisely offset the Fellgetts advantage. For line emission sources the situation is even worse and there is a distinct `multiplex disadvantage as the shot noise from a strong emission component will overwhelm the fainter components of the spectrum. Shot noise is the main reason Fourier-transform spectrometry was never popular for ultraviolet (UV) and visible spectra. | 0 | Theoretical and Fundamental Chemistry |
* [http://bibliothek.bbaw.de/kataloge/literaturnachweise/klaproth/literatur.pdf Publication list of Klaproth] | 1 | Applied and Interdisciplinary Chemistry |
Eschenmoser developed synthetic pathways for artificial nucleic acids, specifically modifying the sugar backbone of the polymer. Having developed a number of structural alternatives to the naturally occurring nucleic acids, Eschenmoser and his colleagues were able to contrast the properties of these synthetic nucleic acids with naturally occurring ones to effectively determine the properties of RNA and DNA vital to modern biochemical processes. This work demonstrated that hydrogen-bonding interactions between the base-paring surfaces of the nucleobases alone might not have provided sufficient selection pressure to lead to the eventual rise of ribose in the structure of modern nucleic acids. He determined that pentose sugars, particularly ribose, conform to a geometry that contributes significantly to the helical structure of DNA by optimizing base-pair stacking distances in naturally occurring oligonucleotides. These base-stacking interactions orient and stabilize the base-paring surfaces of the nucleobases (A, G, C, T or U in RNA) and give rise to the canonical Watson-Crick base-paring rules that are well understood today.
Threose nucleic acid is an artificial genetic polymer invented by Eschenmoser. TNA strings composed of repeating threose sugars linked together by phosphodiester bonds. Like DNA and RNA, the molecule TNA can store genetic information in strings of nucleotide sequences. John Chaput, a professor at UC Irvine, has theorized that issues concerning the prebiotic synthesis of ribose sugars and the non-enzymatic replication of RNA may provide circumstantial evidence of an earlier genetic system more readily produced under primitive earth conditions. TNA could have been an early pre-DNA genetic system. | 0 | Theoretical and Fundamental Chemistry |
In a crystal, the constitutive particles are arranged periodically, with translational symmetry forming a lattice. The crystal structure can be described as a Bravais lattice with a group of atoms, called the basis, placed at every lattice point; that is, [crystal structure] = [lattice] [basis]. If the lattice is infinite and completely regular, the system is a perfect crystal. For such a system, only a set of specific values for can give scattering, and the scattering amplitude for all other values is zero. This set of values forms a lattice, called the reciprocal lattice, which is the Fourier transform of the real-space crystal lattice.
In principle the scattering factor can be used to determine the scattering from a perfect crystal; in the simple case when the basis is a single atom at the origin (and again neglecting all thermal motion, so that there is no need for averaging) all the atoms have identical environments. Equation () can be written as
: and .
The structure factor is then simply the squared modulus of the Fourier transform of the lattice, and shows the directions in which scattering can have non-zero intensity. At these values of the wave from every lattice point is in phase. The value of the structure factor is the same for all these reciprocal lattice points, and the intensity varies only due to changes in with . | 0 | Theoretical and Fundamental Chemistry |
Arabinosyl nucleosides are derivatives of the nucleosides. They contain β--arabinofuranose, in contrast to most nucleosides which contain β--ribofuranose. They are used as cytostatics or virostatics. | 0 | Theoretical and Fundamental Chemistry |
In the 2010s, machine learning emerged as a powerful tool for guiding catalyst discovery. More specifically, machine learning models such as multivariate linear regression have been applied to study the linear free energy relationships (LFERs) in catalytic asymmetric organic reactions. These relationships describe the effects that ligand substituents have on reaction outcomes, namely enantioselectivity, and can be extrapolated to predict the performance of ligands outside the known dataset. However, machine learning approaches require well-defined molecular descriptors for the steric and electronic properties of ligands in order to make accurate predictions. Sterimol parameters emerged as a good candidate for quantifying the steric environment induced by ligands.
In Matthew Sigmans seminal work published in 2012, Sterimol parameters were implemented in asymmetric catalysis for the first time in the analysis of an asymmetric Nozaki-Hiyama-Kishi reaction (Figure 2). In initial ligand screening the team found that the steric hindrance of the ester substituent on the oxazoline-proline-based ligand scaffold was pertinent to the overall enantioselectivity of the reaction. When attempting to use the Charton modification of the Tafts parameters for probing the LFERs, they observed breaks in linearity with respect to several "isopropyl-like" substituents with large Charton values (Figure 3, left). However, this break did not exist when the Sterimol B parameter was used instead. All of the substituents studied demonstrated good linear correlation between their Sterimol B value and the reaction enantioselectivity (Figure 3, right).
Sigman attributed the superiority of Sterimol B in this prediction over Charton values to the inherent limitations of the experimentally based Charton values. He noted that the Charton model assumes that the substituent can rapidly rotate around the X-axis. However, in the context of asymmetric catalysis, only one conformation of the substituent provides the transition state with lowest energy, which leads to the formation of the major enantiomer. Therefore, Charton values tend to overestimate the steric effects of substituents that are non-symmetrical around the X-axis, because they can only describe the net conformer of a certain substituent. Sterimol parameters, in contrast, are not derived from experimental results, which are sometimes idiosyncratic as a result of distinct mechanisms. By virtue of their origin, namely quantum chemical calculations, Sterimol parameters can more accurately interpret the steric effects of a substituent in its static form. Sterimol B, in particular, can approximate the steric repulsive effect of the exact conformer with the lowest energy. Table 1 demonstrates the differences of the two parameters. For example, while they have the same Sterimol B values, the Charton value of the isopropyl-like CHPr substituent is significantly larger than that of i-Pr due to overestimation. This explains why better correlation was obtained with Sterimol B.
To date, the Sigman lab has applied Sterimol parameters in the analysis of several catalytic asymmetric reactions. Sterimol parameters are also utilized by chemists worldwide to improve the enantioselectivity for various catalytic reactions, such as conjugative addition, Tsuji-Trost reaction, C–H activation, cyclopropanation, etc. | 0 | Theoretical and Fundamental Chemistry |
Nickel allergy is the most common contact allergy in industrialized countries, affecting around 8% to 19% of adults and 8% to 10% of children. Women are affected 4–10 times as frequently as men. | 1 | Applied and Interdisciplinary Chemistry |
The term typically applies in electrochemistry, when electrical energy in the form of an applied voltage is used to modulate the thermodynamic favorability of a chemical reaction. In a battery, an electrochemical potential arising from the movement of ions balances the reaction energy of the electrodes. The maximum voltage that a battery reaction can produce is sometimes called the standard electrochemical potential of that reaction. | 0 | Theoretical and Fundamental Chemistry |
The so-called carbamate insecticides feature the carbamate ester functional group. Included in this group are aldicarb (Temik), carbofuran (Furadan), carbaryl (Sevin), ethienocarb, fenobucarb, oxamyl, and methomyl. These insecticides kill insects by reversibly inactivating the enzyme acetylcholinesterase (AChE inhibition) (IRAC mode of action 1a). The organophosphate pesticides also inhibit this enzyme, although irreversibly, and cause a more severe form of cholinergic poisoning (the similar IRAC MoA 1b).
Fenoxycarb has a carbamate group but acts as a juvenile hormone mimic, rather than inactivating acetylcholinesterase.
The insect repellent icaridin is a substituted carbamate.
Besides their common use as arthropodocides/insecticides, they are also nematicidal. One such is Oxamyl.
Sales have declined dramatically over recent decades. | 0 | Theoretical and Fundamental Chemistry |
Ions can be created by electrons formed in high-frequency electromagnetic field. The discharge is formed in a tube located between electrodes, or inside a coil. Over 90% proportion of atomic ions is achievable. | 0 | Theoretical and Fundamental Chemistry |
Ethylenediamine pyrocatechol (EDP), also known as ethylenediamine-pyrocatechol-water (EPW), is an anisotropic etchant solution for silicon. A typical formulation consists of ethylenediamine, pyrocatechol, pyrazine and water. It is carcinogenic and very corrosive. It is mainly used in research labs, and is not used in mainstream semiconductor fabrication processes. | 0 | Theoretical and Fundamental Chemistry |
One of the earliest cultures to use cosmetics was ancient Egypt, where both Egyptian men and women used makeup to enhance their appearance. The first cosmetics appeared 5,000 years ago in Egypt. To achieve a pleasant smell and softness of the skin, incense oils were used, and women applied white to protect their faces from the sun. The Egyptians were also the first to use black antimony-based paint as eyeliner. And to create a natural blush, crushed flowers were used.
The use of cosmetics in Ancient Egypt is well documented. Kohl has its roots in north Africa. The use of black kohl eyeliner and eyeshadows in dark colours such as blue, red, and black was common, and was commonly recorded and represented in Egyptian art, as well as being seen in Egyptian hieroglyphs. Ancient Egyptians also extracted cosmetic face paint from fucus-algin, 0.01% iodine, and bromine mannite, however the bromine-based makeup was severely toxic. Lipsticks with shimmering effects were initially made using a pearlescent substance found in fish scales, which are still used extensively today. Despite the hazardous nature of some Egyptian cosmetics, ancient Egyptian makeup was also thought to have antibacterial properties that helped prevent infections. Remedies to treat wrinkles contained ingredients such as gum of frankincense and fresh moringa. For scars and burns, a special ointment was made of red ochre, kohl, and sycamore juice. An alternative treatment was a poultice of carob grounds and honey, or an ointment made of knotgrass and powdered root of wormwood. To improve breath the ancient Egyptians chewed herbs or frankincense which is still in use today. Jars of what could be compared with setting lotion have been found to contain a mixture of beeswax and resin. These doubled as remedies for problems such as baldness and greying hair. They also used these products on their mummies, because they believed that it would make them irresistible in the after life. | 1 | Applied and Interdisciplinary Chemistry |
James determined that thulium, thought to be a mixture of three substances, was really a single element. James was the first researcher to isolate nearly pure thulium. In 1911 he reported his results, having used the method he discovered for bromate fractional crystallization to do the purification. He famously needed 15,000 purification operations to establish that the material was homogeneous. | 1 | Applied and Interdisciplinary Chemistry |
Achinewhu has analyzed more than fifty homegrown foodstuffs, which include seeds, nuts, tubers, spices, and herbs. These indigenous food items where examined and explored for their nutrient compositions and quality of protein content. Details of his findings are being used along with others in the compendium of Nigeria's food composition table.
He evolved the processing and production of coffee from coffee seed grown in Bayelsa State, Nigeria.
He did research on cassava processing, which identified upgrade cassava cultivars with superior quality food values with regards to product output and other physico-chemical properties. He identified new cultivars with high starch yield and therefore high export potentials.
He developed a baby food (weaning) supplement employing the use of a combination of fermented plant food products. This was used to nourish children who were undernourished, in the days of Better Life Programme for Rural Women. | 1 | Applied and Interdisciplinary Chemistry |
B3/B4 tRNA-binding domain - B5 protein domain - BAC - back mutation - bacteria - bacterial artificial chromosome - bacteriophage - bacteriophage lambda - bacteriophage scaffolding proteins - band shift assay - base - base pair - benzoyl-CoA 2,3-dioxygenase - benzyl benzoate/disulfiram - benzyl-2-methyl-hydroxybutyrate dehydrogenase - beta-carotene 3-hydroxylase - beta-cyclopiazonate dehydrogenase - beta-glucan-transporting ATPase - beta2-adaptin C-terminal domain - binding site - biological organisation - biological process - Biomolecular gradient - Biomolecule Stretching Database - biotin - birth defect - blotting - blunt end - bone marrow transplantation - box - BP - BRCA1 - BRCA2 - Brix (database) - BSD domain - BURP domain - | 1 | Applied and Interdisciplinary Chemistry |
Giner-Delgado, Carla, et al. described a variant of MLPA combining it with iPCR. They call these new method iMLPA and its procedure is the same as MLPA but there are necessary two additional steps at the beginning:
# First, a DNA treatment with restriction enzymes that cut on both sides of the region of interest is necessary.
# The fragments obtained from digestion are recircularized and linked
The probe design is quite similar. Each probe will be formed by two parts that have at least: a target sequence, which is a region that contains the sequence complementary to the region of interest, so that the correct hybridization can occur. And a primer sequence at the end, it is a sequence whose design varies and is what will allow the design of primers and subsequent fragment amplification. In addition, one of the parts of the probe usually contains a stuffer between the target sequence and the primer sequence. The use of different stuffers allows the identification of probes with the same primer sequences but different target sequences, that is key for multiple amplification of several different fragments in a single reaction.
The next step continues with the typical MLPA protocol. | 1 | Applied and Interdisciplinary Chemistry |
The mathematics of radioactive decay depend on a key assumption that a nucleus of a radionuclide has no "memory" or way of translating its history into its present behavior. A nucleus does not "age" with the passage of time. Thus, the probability of its breaking down does not increase with time but stays constant, no matter how long the nucleus has existed. This constant probability may differ greatly between one type of nucleus and another, leading to the many different observed decay rates. However, whatever the probability is, it does not change over time. This is in marked contrast to complex objects that do show aging, such as automobiles and humans. These aging systems do have a chance of breakdown per unit of time that increases from the moment they begin their existence.
Aggregate processes, like the radioactive decay of a lump of atoms, for which the single-event probability of realization is very small but in which the number of time-slices is so large that there is nevertheless a reasonable rate of events, are modelled by the Poisson distribution, which is discrete. Radioactive decay and nuclear particle reactions are two examples of such aggregate processes. The mathematics of Poisson processes reduce to the law of exponential decay, which describes the statistical behaviour of a large number of nuclei, rather than one individual nucleus. In the following formalism, the number of nuclei or the nuclei population N, is of course a discrete variable (a natural number)—but for any physical sample N is so large that it can be treated as a continuous variable. Differential calculus is used to model the behaviour of nuclear decay. | 0 | Theoretical and Fundamental Chemistry |
Plasmids may be classified in a number of ways. Plasmids can be broadly classified into conjugative plasmids and non-conjugative plasmids. Conjugative plasmids contain a set of transfer genes which promote sexual conjugation between different cells. In the complex process of conjugation, plasmids may be transferred from one bacterium to another via sex pili encoded by some of the transfer genes (see figure). Non-conjugative plasmids are incapable of initiating conjugation, hence they can be transferred only with the assistance of conjugative plasmids. An intermediate class of plasmids are mobilizable, and carry only a subset of the genes required for transfer. They can parasitize a conjugative plasmid, transferring at high frequency only in its presence.
Plasmids can also be classified into incompatibility groups. A microbe can harbour different types of plasmids, but different plasmids can only exist in a single bacterial cell if they are compatible. If two plasmids are not compatible, one or the other will be rapidly lost from the cell. Different plasmids may therefore be assigned to different incompatibility groups depending on whether they can coexist together. Incompatible plasmids (belonging to the same incompatibility group) normally share the same replication or partition mechanisms and can thus not be kept together in a single cell.
Another way to classify plasmids is by function. There are five main classes:
* Fertility F-plasmids, which contain tra genes. They are capable of conjugation and result in the expression of sex pili.
* Resistance (R) plasmids, which contain genes that provide resistance against antibiotics or antibacterial agents. Historically known as R-factors, before the nature of plasmids was understood.
* Col plasmids, which contain genes that code for bacteriocins, proteins that can kill other bacteria.
* Degradative plasmids, which enable the digestion of unusual substances, e.g. toluene and salicylic acid.
* Virulence plasmids, which turn the bacterium into a pathogen. e.g. Ti plasmid in Agrobacterium tumefaciens
Plasmids can belong to more than one of these functional groups. | 1 | Applied and Interdisciplinary Chemistry |
Sodium molybdate, NaMoO, is useful as a source of molybdenum. This white, crystalline salt is often encountered as the dihydrate, NaMoO·2HO. | 0 | Theoretical and Fundamental Chemistry |
The usage of the term canonical sequence to refer to a promoter is often problematic, and can lead to misunderstandings about promoter sequences. Canonical implies perfect, in some sense.
In the case of a transcription factor binding site, there may be a single sequence that binds the protein most strongly under specified cellular conditions. This might be called canonical.
However, natural selection may favor less energetic binding as a way of regulating transcriptional output. In this case, we may call the most common sequence in a population the wild-type sequence. It may not even be the most advantageous sequence to have under prevailing conditions.
Recent evidence also indicates that several genes (including the proto-oncogene c-myc) have G-quadruplex motifs as potential regulatory signals. | 1 | Applied and Interdisciplinary Chemistry |
In 1968, the artist Robert Smithson made Mono Lake Non-Site (Cinders near Black Point) using pumice collected while visiting Mono on July 27, 1968, with his wife Nancy Holt and Michael Heizer (both prominent visual artists). In 2004, Nancy Holt made a short film entitled Mono Lake using Super 8 footage and photographs of this trip. An audio recording by Smithson and Heizer, two songs by Waylon Jennings, and Michel Legrands Le Jeu, the main theme of Jacques Demys film Bay of Angels (1963), were used for the soundtrack.
The Diver, a photo taken by Aubrey Powell of Hipgnosis for Pink Floyds album Wish You Were Here' (1975), features what appears to be a man diving into a lake, creating no ripples. The photo was taken at Mono Lake, and the tufa towers are a prominent part of the landscape. The effect was actually created when the diver performed a handstand underwater until the ripples dissipated. | 1 | Applied and Interdisciplinary Chemistry |
In atomic physics, a dark state refers to a state of an atom or molecule that cannot absorb (or emit) photons. All atoms and molecules are described by quantum states; different states can have different energies and a system can make a transition from one energy level to another by emitting or absorbing one or more photons. However, not all transitions between arbitrary states are allowed. A state that cannot absorb an incident photon is called a dark state. This can occur in experiments using laser light to induce transitions between energy levels, when atoms can spontaneously decay into a state that is not coupled to any other level by the laser light, preventing the atom from absorbing or emitting light from that state.
A dark state can also be the result of quantum interference in a three-level system, when an atom is in a coherent superposition of two states, both of which are coupled by lasers at the right frequency to a third state. With the system in a particular superposition of the two states, the system can be made dark to both lasers as the probability of absorbing a photon goes to 0. | 0 | Theoretical and Fundamental Chemistry |
Fluoride salts, like all salts, cause corrosion in most metals and alloys. FliNak is different from FLiBe in the sense that is a basic melt—or it has an excess of fluorine ions. As FLiNak melts, all three components are alkali fluorides and therefore disassociate into positive and negative ions. The concentration of molten fluorine ions are able to corrode any metallic structures if it is energetically favorable. This is in contrast to FLiBe, which in a 66-34 mol% mixture will be a chemically neutral mix, as fluorine ions from LiF are donated to BeF to create the tetrafluoroberyllate ion BeF. | 0 | Theoretical and Fundamental Chemistry |
Somatic recombination, as opposed to the genetic recombination that occurs in meiosis, is an alteration of the DNA of a somatic cell that is inherited by its daughter cells. The term is usually reserved for large-scale alterations of DNA such as chromosomal translocations and deletions and not applied to point mutations. Somatic recombination occurs physiologically in the assembly of the B cell receptor and T-cell receptor genes (V(D)J recombination), as well as in the class switching of immunoglobulins. Somatic recombination is also important in the process of carcinogenesis.
In neurons of the human brain, somatic recombination occurs in the gene that encodes the amyloid precursor protein APP. Neurons from individuals with sporadic Alzheimer's disease show greater APP gene diversity due to somatic recombination than neurons from healthy individuals. | 1 | Applied and Interdisciplinary Chemistry |
A soap bubble (commonly referred to as simply a bubble) is an extremely thin film of soap or detergent and water enclosing air that forms a hollow sphere with an iridescent surface. Soap bubbles usually last for only a few seconds before bursting, either on their own or on contact with another object. They are often used for children's enjoyment, but they are also used in artistic performances. Assembling many bubbles results in foam.
When light shines onto a bubble it appears to change colour. Unlike those seen in a rainbow, which arise from differential refraction, the colours seen in a soap bubble arise from light wave interference, reflecting off the front and back surfaces of the thin soap film. Depending on the thickness of the film, different colours interfere constructively and destructively. | 1 | Applied and Interdisciplinary Chemistry |
In the solar thermochemical process, water is split into hydrogen and oxygen using direct solar heat, rather than electricity, inside a high temperature solar reactor which receives highly concentrated solar flux from a solar field of heliostats that focus the highly concentrated sunlight into the reactor.
The two most promising routes are the two step cerium oxide cycle and the copper chlorine hybrid cycle. For the cerium oxide cycle the first step is to strip the CeO into CeO at more than 1400 °C. After the thermal reduction step to reduce the metal oxide, hydrogen is then produced through hydrolysis at around 800 °C. The copper chloride cycle requires a lower temperature (~500°C), which makes this process more efficient, but the cycle contains more steps and is also more complex than the cerium oxide cycle.
Because hydrogen manufacture requires continuous performance, the solar thermochemical process includes thermal energy storage. Another thermochemical method uses solar reforming of methane, a process that replicates traditional fossil fuel reforming process but substitutes solar heat.
In a November 2021 publication in Nature, Aldo Steinfeld of Swiss technological university ETH Zurich reported an artificial photosynthesis where carbon dioxide and water vapour absorbed from the air are passed over a cerium oxide catalyst heated by concentrated solar power to produce hydrogen and carbon monoxide, transformed through the Fischer-Tropsch process into complex hydrocarbons forming methanol, a liquid fuel.
Scaling could produce the of aviation fuel used in 2019 with a surface of : 0.5% of the Sahara Desert.
One author, Philipp Furler, leads specialist Synhelion, which in 2022 was building a solar fuel production facility at Jülich, west of Cologne, before another one in Spain.
Swiss airlines, part of the Lufthansa Group, should become its first customer in 2023. | 0 | Theoretical and Fundamental Chemistry |
Improper maintenance can lead to high restoration costs to address inefficient bioswales. An accumulation of large sediments, trash, and improper growth of vegetation can all affect the quality and performance of bioswales. It is beneficial at the planning stages to set apart easements to allow for easier maintenance of biowales, whether it be adequate space to locate machinery or safety to those working. Different types of filters can be used to catch sediments. Grass filter strips or rock inlets can be used to filter sediments and particulates; however, without proper maintenance, runoff could flow away from the bioswales due to blockage. Structural inlets have become more common due to the ease of maintenance, use, and its effectiveness. Avoiding the use of floating mulch and selecting the best fit low-maintenance plants ensure better efficiency in the bioswales. Depending on a community's needs for a bioswale, a four step assessment program can be developed. Visual inspection, capacity testing, synthetic runoff, and monitoring are the four steps that can be used to evaluate performance and maintenance of bioswales.
Routine inspection is required to ensure that the performance and aesthetics of bioswales are not compromised. Time and frequency of inspections vary based on different local governments, but should occur at least once a year. Various aspects of inspection can take place, either visually or mechanically. Visual observation of the vegetation, water, and inlets are all crucial to ensure performance. Some organizations utilize checklists to streamline the visual inspection process.
There are different methods to determine if a bioswale needs maintenance. Bioswales are benchmarked to meet a specific level of infiltration to determine if maintenance is required. A staff gauge is used to measure the infiltration rate. Soil chemistry testing is also required to determine if the soil has a certain off-level of any pollutant. Phosphorus and high levels of salinity in the soil are two common pollutants that should be attended to. Analysis of inflow and outflow pollutant concentration is also another way to determine the performance level of bioswales.
Maintenance can span to three different levels of care. Aesthetic maintenance is required to remove weeds that affect the performance of the other plants and the bioswale itself, clean and remove trash, and maintaining the looks of the vegetation. Partial restoration is needed when the inlet is blocked by sediments or when vegetation needs to be replaced. Full restoration is required when the bioswales no longer filter pollutants adequately and overall performance is severely lacking. | 1 | Applied and Interdisciplinary Chemistry |
Magnesium is required as a co-factor for thermostable DNA polymerase. Taq polymerase is a magnesium-dependent enzyme and determining the optimum concentration to use is critical to the success of the PCR reaction. Some of the components of the reaction mixture such as template concentration, dNTPs and the presence of chelating agents (EDTA) or proteins can reduce the amount of free magnesium present thus reducing the activity of the enzyme. Primers which bind to incorrect template sites are stabilized in the presence of excessive magnesium concentrations and so results in decreased specificity of the reaction. Excessive magnesium concentrations also stabilize double stranded DNA and prevent complete denaturation of the DNA during PCR reducing the product yield. Inadequate thawing of MgCl may result in the formation of concentration gradients within the magnesium chloride solution supplied with the DNA polymerase and also contributes to many failed experiments . | 1 | Applied and Interdisciplinary Chemistry |
The wide variety of methods of calculation of electronegativities, which all give results that correlate well with one another, is one indication of the number of chemical properties that might be affected by electronegativity. The most obvious application of electronegativities is in the discussion of bond polarity, for which the concept was introduced by Pauling. In general, the greater the difference in electronegativity between two atoms the more polar the bond that will be formed between them, with the atom having the higher electronegativity being at the negative end of the dipole. Pauling proposed an equation to relate the "ionic character" of a bond to the difference in electronegativity of the two atoms, although this has fallen somewhat into disuse.
Several correlations have been shown between infrared stretching frequencies of certain bonds and the electronegativities of the atoms involved: however, this is not surprising as such stretching frequencies depend in part on bond strength, which enters into the calculation of Pauling electronegativities. More convincing are the correlations between electronegativity and chemical shifts in NMR spectroscopy or isomer shifts in Mössbauer spectroscopy (see figure). Both these measurements depend on the s-electron density at the nucleus, and so are a good indication that the different measures of electronegativity really are describing "the ability of an atom in a molecule to attract electrons to itself". | 0 | Theoretical and Fundamental Chemistry |
As ionizing radiation moves through matter its energy is deposited through interactions with the electrons of the absorber. The result of an interaction between the radiation and the absorbing species is removal of an electron from an atom or molecular bond to form radicals and excited species. The radical species then proceed to react with each other or with other molecules in their vicinity. It is the reactions of the radical species that are responsible for the changes observed following irradiation of a chemical system.
Charged radiation species (α and β particles) interact through Coulombic forces between the charges of the electrons in the absorbing medium and the charged radiation particle. These interactions occur continuously along the path of the incident particle until the kinetic energy of the particle is sufficiently depleted. Uncharged species (γ photons, x-rays) undergo a single event per photon, totally consuming the energy of the photon and leading to the ejection of an electron from a single atom. Electrons with sufficient energy proceed to interact with the absorbing medium identically to β radiation.
An important factor that distinguishes different radiation types from one another is the linear energy transfer (LET), which is the rate at which the radiation loses energy with distance traveled through the absorber. Low LET species are usually low mass, either photons or electron mass species (β particles, positrons) and interact sparsely along their path through the absorber, leading to isolated regions of reactive radical species. High LET species are usually greater in mass than one electron, for example α particles, and lose energy rapidly resulting in a cluster of ionization events in close proximity to one another. Consequently, the heavy particle travels a relatively short distance from its origin.
Areas containing a high concentration of reactive species following absorption of energy from radiation are referred to as spurs. In a medium irradiated with low LET radiation, the spurs are sparsely distributed across the track and are unable to interact. For high LET radiation, the spurs can overlap, allowing for inter-spur reactions, leading to different yields of products when compared to the same medium irradiated with the same energy of low LET radiation. | 0 | Theoretical and Fundamental Chemistry |
According to the Ronen Fissile rule, for a heavy element with 90 ≤ Z ≤ 100, its isotopes with , with few exceptions, are fissile (where N = number of neutrons and Z = number of protons).
The term fissile is distinct from fissionable. A nuclide capable of undergoing fission (even with a low probability) after capturing a neutron of high or low energy is referred to as fissionable. A fissionable nuclide that can be induced to fission with low-energy thermal neutrons with a high probability is referred to as fissile. Fissionable materials include also those (such as uranium-238) for which fission can be induced only by high-energy neutrons. As a result, fissile materials (such as uranium-235) are a subset of fissionable materials.
Uranium-235 fissions with low-energy thermal neutrons because the binding energy resulting from the absorption of a neutron is greater than the critical energy required for fission; therefore uranium-235 is fissile. By contrast, the binding energy released by uranium-238 absorbing a thermal neutron is less than the critical energy, so the neutron must possess additional energy for fission to be possible. Consequently, uranium-238 is fissionable but not fissile.
An alternative definition defines fissile nuclides as those nuclides that can be made to undergo nuclear fission (i.e., are fissionable) and also produce neutrons from such fission that can sustain a nuclear chain reaction in the correct setting. Under this definition, the only nuclides that are fissionable but not fissile are those nuclides that can be made to undergo nuclear fission but produce insufficient neutrons, in either energy or number, to sustain a nuclear chain reaction. As such, while all fissile isotopes are fissionable, not all fissionable isotopes are fissile. In the arms control context, particularly in proposals for a Fissile Material Cutoff Treaty, the term fissile is often used to describe materials that can be used in the fission primary of a nuclear weapon. These are materials that sustain an explosive fast neutron nuclear fission chain reaction.
Under all definitions above, uranium-238 () is fissionable, but not fissile. Neutrons produced by fission of have lower energies than the original neutron (they behave as in an inelastic scattering), usually below 1 MeV (i.e., a speed of about 14,000 km/s), the fission threshold to cause subsequent fission of , so fission of does not sustain a nuclear chain reaction.
Fast fission of in the secondary stage of a thermonuclear weapon, due to the production of high-energy neutrons from nuclear fusion, contributes greatly to the yield and to fallout of such weapons. Fast fission of tampers has also been evident in pure fission weapons. The fast fission of also makes a significant contribution to the power output of some fast-neutron reactors. | 0 | Theoretical and Fundamental Chemistry |
Radiogenic heating occurs as a result of the release of heat energy from radioactive decay during the production of radiogenic nuclides. Along with heat from the Primordial Heat (resulting from planetary accretion), radiogenic heating occurring in the mantle and crust make up the two main sources of heat in the Earth's interior. Most of the radiogenic heating in the Earth results from the decay of the daughter nuclei in the decay chains of uranium-238 and thorium-232, and potassium-40. | 0 | Theoretical and Fundamental Chemistry |
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