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The International Society of Electrochemistry (ISE) is a global scientific society founded in 1949. The Head Office of ISE is located now in Lausanne, Switzerland. ISE is a Member Organization of IUPAC. The Society has now more than 1900 Individual Members, 15 Corporate Members (Universities and non-profit research organizations from Belgium, Croatia, Finland, Germany, India, Italy, New Zealand, Poland, Spain, Switzerland and Serbia) and 16 Corporate Sustaining Members. ISE has also 8 Divisions and Regional Representatives.
ISE's objectives are:
* to advance electrochemical science and technology
* to disseminate scientific and technological knowledge
* to promote international cooperation in electrochemistry
* to maintain a high professional standard among its members. | 7 | Physical Chemistry |
* Superelastic nitinol finds a variety of applications in civil structures such as bridges and buildings. One such application is Intelligent Reinforced Concrete (IRC), which incorporates NiTi wires embedded within the concrete. These wires can sense cracks and contract to heal macro-sized cracks.
* Another application is active tuning of structural natural frequency using nitinol wires to damp vibrations. | 8 | Metallurgy |
A thermocouple can produce current to drive some processes directly, without the need for extra circuitry and power sources. For example, the power from a thermocouple can activate a valve when a temperature difference arises. The electrical energy generated by a thermocouple is converted from the heat which must be supplied to the hot side to maintain the electric potential. A continuous transfer of heat is necessary because the current flowing through the thermocouple tends to cause the hot side to cool down and the cold side to heat up (the Peltier effect).
Thermocouples can be connected in series to form a thermopile, where all the hot junctions are exposed to a higher temperature and all the cold junctions to a lower temperature. The output is the sum of the voltages across the individual junctions, giving larger voltage and power output. In a radioisotope thermoelectric generator, the radioactive decay of transuranic elements as a heat source has been used to power spacecraft on missions too far from the Sun to use solar power.
Thermopiles heated by kerosene lamps were used to run batteryless radio receivers in isolated areas. There are commercially produced lanterns that use the heat from a candle to run several light-emitting diodes, and thermoelectrically powered fans to improve air circulation and heat distribution in wood stoves. | 8 | Metallurgy |
Experimental error is usually assumed to affect the rate and not the substrate concentration , so is the dependent variable. As a result, both ordinate and abscissa are subject to experimental error, and so the deviations that occur due to error are not parallel with the ordinate axis but towards or away from the origin. As long as the plot is used for illustrating an analysis rather than for estimating the parameters, that matters very little. Regardless of these considerations various authors have compared the suitability of the various plots for displaying and analysing data. | 1 | Biochemistry |
Aqueous normal-phase chromatography (ANP) is a chromatographic technique that involves the mobile phase compositions and polarities between reversed-phase chromatography (RP) and normal-phase chromatography (NP), while the stationary phases are polar. | 3 | Analytical Chemistry |
Those phenomena which involve the change in color of a chemical compound under an external stimulus fall under the generic term of chromisms. They take their individual names from the type of the external influence, which can be either chemical or physical, that is involved. Many of these phenomena are reversible. The following list includes all the classic chromisms plus many others of increasing interest in newer outlets.
There are also chromisms which involve two or more stimuli. Examples include:
*Photoelectrochromism – Photovoltachromism – Bioelectrochromism – Solvatophotochromism – Thermosolvatochromism – Halosolvatochromism – Electromechanochromism.
Color changes are also observed on the interaction of metallic nanoparticles and their attached ligands with another stimulus. Examples include plasmonic solvatochromism, plasmonic ionochromism, plasmonic chronochromism and plasmonic vapochromism. | 5 | Photochemistry |
It often has additives such as citrus fruits, apples, berry juices, or artificial flavorings. Flavored kilju from fruits for example doesn't necessarily have to be sweet as long as all sugar is consumed by the yeast.
Kilju (15-17% ABV) contains 2.4-2.7 times more water than 40% distilled spirit. Since kilju contains approximately 85% water, it can be mixed with concentrates like a drink mixer, fruit syrup, or squash concentrate. | 1 | Biochemistry |
Living organisms typically consist of large quantities of water. Many anisotropic materials of interest are biological in nature and as such require hydration during spectroscopic measurements. While some limited novel techniques to measure properties of materials inside a hydrated sample chamber have been recently reports, the primary design requirement of ATM is that the material is accessible through a window that is transparent to THz light such as quartz. Similarly, samples requiring cryo-cooling or low pressure vacuum environment are readily interrogated in ATM using THz-transparent window materials. | 7 | Physical Chemistry |
LPA is the result of phospholipase A2 action on phosphatidic acid. The SN-1 position can contain either an ester bond or an ether bond, with ether LPA being found at elevated levels in certain cancers. LPA binds the high-affinity G-protein coupled receptors LPA1, LPA2, and LPA3 (also known as EDG2, EDG4, and EDG7, respectively). | 1 | Biochemistry |
Currently, there is no commercialization of these products. More research is still ongoing on these composite materials as to ascertain the properties and how best to utilize these materials. | 9 | Geochemistry |
The competition between orientation produced by surface anchoring and by electric field effects is often exploited in liquid crystal devices. Consider the case in which liquid crystal molecules are aligned parallel to the surface and an electric field is applied perpendicular to the cell. At first, as the electric field increases in magnitude, no change in alignment occurs. However at a threshold magnitude of electric field, deformation occurs. Deformation occurs where the director changes its orientation from one molecule to the next. The occurrence of such a change from an aligned to a deformed state is called a Fréedericksz transition and can also be produced by the application of a magnetic field of sufficient strength.
The Fréedericksz transition is fundamental to the operation of many liquid crystal displays because the director orientation (and thus the properties) can be controlled easily by the application of a field. | 7 | Physical Chemistry |
* Pharmaceutical and cosmetic creams, gels, and ointments, e.g. petroleum jelly, toothpaste, hand sanitizer
* Foods, e.g. pudding, guacamole, salsa, mayonnaise, whipping cream, peanut butter, jelly, jam | 7 | Physical Chemistry |
As a β-lactam antibiotic, piperacillin inhibits penicillin-binding proteins, preventing the spread of bacteria and infections. Responsible for catalyzing the cross-linkage between peptidoglycan strands that protect the bacterial cell from osmotic rupture, penicillin-binding proteins are unique to bacterial organisms, where every known bacteria with a peptidoglycan cell wall consists of homologous sub-families. By sharing a similar stereochemistry with the substrates that bind to penicillin-binding proteins, piperacillin is able to bind to serine residues found at the active site of the enzyme through the formation of a covalent complex, preventing other substrates from binding. Moreover, this leads to the release of autolysins that break down the bacteria's cell wall.
Some β-lactamase enzymes also consist of residue at their active site, enabling them to hydrolyze the β-lactam ring found within these antibiotics. However, this hydrolytic activity is inhibited when piperacillin works in conjunction with tazobactam. Tazobactam binds to these enzymes to form a stable acyl-enzyme complex; similar to one formed during the hydrolysis of the β-lactam ring. Thus, protecting piperacillin from hydrolysis.
The inclusion of a β-lactamase inhibitor does not always increase drug efficacy. Some bacteria may produce certain types of β-lactamase such as AmpC, which are intrinsically resistant to tazobactam. | 4 | Stereochemistry |
Rainfall is naturally acidic due to carbonic acid forming from carbon dioxide in the atmosphere. This compound causes rainfall pH to be around 5.0–5.5. When rainfall has a lower pH than natural levels, it can cause rapid acidification of soil. Sulfur dioxide and nitrogen oxides are precursors of stronger acids that can lead to acid rain production when they react with water in the atmosphere. These gases may be present in the atmosphere due to natural sources such as lightning and volcanic eruptions, or from anthropogenic emissions. Basic cations like calcium are leached from the soil as acidic rainfall flows, which allows aluminum and proton levels to increase.
Nitric and sulfuric acids in acid rain and snow can have different effects on the acidification of forest soils, particularly seasonally in regions where a snow pack may accumulate during the winter. Snow tends to contain more nitric acid than sulfuric acid, and as a result, a pulse of nitric acid-rich snow meltwater may leach through high elevation forest soils during a short time in the spring. This volume of water may comprise as much as 50% of the annual precipitation. The nitric acid flush of meltwater may cause a sharp, short term, decrease in the drainage water pH entering groundwater and surface waters. The decrease in pH can solubilize Al that is toxic to fish, especially newly-hatched fry with immature gill systems through which they pass large volumes of water to obtain O for respiration. As the snow meltwater flush passes, water temperatures rise, and lakes and streams produce more dissolved organic matter; the Al concentration in drainage water decreases and is bound to organic acids, making it less toxic to fish. In rain, the ratio of nitric-to-sulfuric acids decreases to approximately 1:2. The higher sulfuric acid content of rain also may not release as much Al from soils as does nitric acid, in part due to the retention (adsorption) of SO by soils. This process releases OH into soil solution and buffers the pH decrease caused by the added H from both acids. The forest floor organic soil horizons (layers) that are high in organic matter also buffer pH, and decrease the load of H+ that subsequently leaches through underlying mineral horizons. | 9 | Geochemistry |
Biochemical CCMs concentrate carbon dioxide in one temporal or spatial region, through metabolite exchange. C and CAM photosynthesis both use the enzyme Phosphoenolpyruvate carboxylase (PEPC) to add to a 4-Carbon sugar. PEPC is faster than RuBisCO, and more selective for . | 5 | Photochemistry |
A rule-of-thumb is that any molecule that will dissolve in methanol or a less polar solvent is compatible with SFC, including non-volatile polar solutes. CO has polarity similar to n-heptane at its critical point. The solvent's elution strength can be increased just by increasing density or alternatively, using a polar co-solvent. In practice, when the fraction of the co-solvent is high, the mobile phase might not be truly at supercritical fluid state, but this terminology is used regardless, and the chromatograms show better elution and higher efficiency nevertheless. | 3 | Analytical Chemistry |
The Council of Scientific and Industrial Research awarded Ghatak the Shanti Swarup Bhatnagar Prize, one of the highest Indian science awards, in 1974. The Indian Academy of Sciences elected him as a fellow in 1976 and he became a fellow of the Indian National Science Academy in 1980. The Chemical Research Society of India awarded him the Lifetime Achievement Award in 2003. Among the several award orations he delivered were Professor K. Venkataraman Endowment Lecture (1982), Acharya P. C. Ray Memorial Lecture of Indian Chemical Society (1985), Professor N. V. Subba Rao Memorial Lecture (1986), Prof. R. C. Shah Memorial Lecture of Indian Science Congress Association (1986), T. R. Sheshadri Memorial Lecture of Delhi University (1987), Baba Kartar Singh Memorial Lecture of Panjab University (1990) and S. Swaminathan Sixtieth Birthday Commemoration Lecture of Indian National Science Academy (1994). He was also associated with the Royal Society of Chemistry and Chemical Society of London as an associate member. The Indian Association for the Cultivation of Science have instituted an annual oration, Professor U. R. Ghatak Endowment Lecture, in honor of Ghatak. | 4 | Stereochemistry |
The alkali–silica reaction (ASR) is a deleterious chemical reaction between the alkali ( and ), dissolved in concrete pore water as NaOH and KOH, with reactive amorphous (non-crystalline) siliceous aggregates in the presence of moisture. The simplest way to write the reaction in a stylized manner is the following (other representations also exist):
: (young N-S-H gel)
This reaction produces a gel-like substance of sodium silicate ( • n ), also noted • n , or N-S-H (sodium silicate hydrate). This hygroscopic gel swells inside the affected reactive aggregates which expand and crack. In its turn, it causes concrete expansion. If concrete is heavily reinforced, it can first cause some prestressing effect before cracking and damaging the structure. ASR affects the aggregates and is recognizable by cracked aggregates. It does not directly affect the hardened cement paste (HCP). | 8 | Metallurgy |
The most common supercomplexes observed are Complex I/III, Complex I/III/IV, and Complex III/IV. Most of Complex II is found in a free-floating form in both plant and animal mitochondria. Complex V can be found co-migrating as a dimer with other supercomplexes, but scarcely as part of the supercomplex unit.
Supercomplex assembly appears to be dynamic and respiratory enzymes are able to alternate between participating in large respirasomes and existing in a free state. It is not known what triggers changes in complex assembly, but research has revealed that the formation of supercomplexes is heavily dependent upon the lipid composition of the mitochondrial membrane, and in particular requires the presence of cardiolipin, a unique mitochondrial lipid. In yeast mitochondria lacking cardiolipin, the number of enzymes forming respiratory supercomplexes was significantly reduced. According to Wenz et al. (2009), cardiolipin stabilizes the supercomplex formation by neutralizing the charges of lysine residues in the interaction domain of Complex III with Complex IV. In 2012, Bazan et al. was able to reconstitute trimer and tetramer Complex III/IV supercomplexes from purified complexes isolated from Saccharomyces cerevisiae and exogenous cardiolipin liposomes.
Another hypothesis for respirasome formation is that membrane potential may initiate changes in the electrostatic/hydrophobic interactions mediating the assembly/disassembly of supercomplexes. | 1 | Biochemistry |
Levonorgestrel, also known as 17α-ethynyl-18-methyl-19-nortestosterone or as 17α-ethynyl-18-methylestr-4-en-17β-ol-3-one, is a synthetic estrane steroid and a derivative of testosterone. It is the C13β or levorotatory stereoisomer and enantiopure form of norgestrel, the C13α or dextrorotatory isomer being inactive. Levonorgestrel is more specifically a derivative of norethisterone (17α-ethynyl-19-nortestosterone) and is the parent compound of the gonane (18-methylestrane or 13β-ethylgonane) subgroup of the 19-nortestosterone family of progestins. Besides levonorgestrel itself, this group includes desogestrel, dienogest, etonogestrel, gestodene, norelgestromin, norgestimate, and norgestrel. Levonorgestrel acetate and levonorgestrel butanoate are C17β esters of levonorgestrel. Levonorgestrel has a molecular weight of 312.45 g/mol and a partition coefficient (log P) of 3.8. | 4 | Stereochemistry |
Efrapeptins are peptides produced by fungi in the genus Tolypocladium that have antifungal, insecticidal, and mitochondrial ATPase inhibitory activities. They are produced via a biosynthetic pathway similar to, but simpler than, the ciclosporin pathway with nonribosomal peptide synthase (NRPS) and/or polyketide synthase (PKS) being the key elements.
The amino acid sequences of efrapeptins are:
:Efrapeptin F: Ac-Pip-Aib-Pip-Aib-Aib-Leu-bAla-Gly-Aib-Aib-Pip-Aib-Ala-Leu-Iva-Unk
:Efrapeptin G: Ac-Pip-Aib-Pip-Iva-Aib-Leu-bAla-Gly-Aib-Aib-Pip-Aib-Ala-Leu-Iva-Unk
::Aib: 2-methylalanine; Iva: 2-ethylalanine; Unk: does not match to a known amino acid | 0 | Organic Chemistry |
An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a target entity. The measured entity is often called the analyte, the measurand, or the target of the assay. The analyte can be a drug, biochemical substance, chemical element or compound, or cell in an organism or organic sample. An assay usually aims to measure an analyte's intensive property and express it in the relevant measurement unit (e.g. molarity, density, functional activity in enzyme international units, degree of effect in comparison to a standard, etc.).
If the assay involves exogenous reactants (the reagents), then their quantities are kept fixed (or in excess) so that the quantity and quality of the target are the only limiting factors. The difference in the assay outcome is used to deduce the unknown quality or quantity of the target in question. Some assays (e.g., biochemical assays) may be similar to chemical analysis and titration. However, assays typically involve biological material or phenomena that are intrinsically more complex in composition or behavior, or both. Thus, reading of an assay may be noisy and involve greater difficulties in interpretation than an accurate chemical titration. On the other hand, older generation qualitative assays, especially bioassays, may be much more gross and less quantitative (e.g., counting death or dysfunction of an organism or cells in a population, or some descriptive change in some body part of a group of animals).
Assays have become a routine part of modern medical, environmental, pharmaceutical, and forensic technology. Other businesses may also employ them at the industrial, curbside, or field levels. Assays in high commercial demand have been well investigated in research and development sectors of professional industries. They have also undergone generations of development and sophistication. In some cases, they are protected by intellectual property regulations such as patents granted for inventions. Such industrial-scale assays are often performed in well-equipped laboratories and with automated organization of the procedure, from ordering an assay to pre-analytic sample processing (sample collection, necessary manipulations e.g. spinning for separation, aliquoting if necessary, storage, retrieval, pipetting, aspiration, etc.). Analytes are generally tested in high-throughput autoanalyzers, and the results are verified and automatically returned to ordering service providers and end-users. These are made possible through the use of an advanced laboratory informatics system that interfaces with multiple computer terminals with end-users, central servers, the physical autoanalyzer instruments, and other automata. | 1 | Biochemistry |
In summary: Light closes cGMP-gated sodium channels, reducing the influx of both Na and Ca ions. Stopping the influx of Na ions effectively switches off the dark current. Reducing this dark current causes the photoreceptor to hyperpolarise, which reduces glutamate release which thus reduces the inhibition of retinal nerves, leading to excitation of these nerves. This reduced Ca influx during phototransduction enables deactivation and recovery from phototransduction, as discussed below in .
# A photon interacts with a retinal molecule in an opsin complex in a photoreceptor cell. The retinal undergoes isomerisation, changing from the 11-cis-retinal to the all-trans-retinal configuration.
# Opsin therefore undergoes a conformational change to metarhodopsin II.
# Metarhodopsin II activates a G protein known as transducin. This causes transducin to dissociate from its bound GDP, and bind GTP; then the alpha subunit of transducin dissociates from the beta and gamma subunits, with the GTP still bound to the alpha subunit.
# The alpha subunit-GTP complex activates phosphodiesterase, also known as PDE6. It binds to one of two regulatory subunits of PDE (which itself is a tetramer) and stimulates its activity.
# PDE hydrolyzes cGMP, forming GMP. This lowers the intracellular concentration of cGMP and therefore the sodium channels close.
# Closure of the sodium channels causes hyperpolarization of the cell due to the ongoing efflux of potassium ions.
# Hyperpolarization of the cell causes voltage-gated calcium channels to close.
# As the calcium level in the photoreceptor cell drops, the amount of the neurotransmitter glutamate that is released by the cell also drops. This is because calcium is required for the glutamate-containing vesicles to fuse with cell membrane and release their contents (see SNARE proteins).
# A decrease in the amount of glutamate released by the photoreceptors causes depolarization of on-center bipolar cells (rod and cone On bipolar cells) and hyperpolarization of cone off-center bipolar cells. | 1 | Biochemistry |
Receptor uncoupling/phosphorylation is the most rapid form of desensitization that happens within a cell, as its effects are seen within seconds to minutes of agonist application. The ß adrenergic receptor was the first to have its desensitization studied and characterized. The mechanism of desensitization involves the action of a specific GRK, denoted ßARK, and also ß-arrestins. The ß-arrestins show high affinity for receptors that are both phosphorylated and activated, but are still able to bind non-phosphorylated receptors with a lower affinity. Additionally, ß-arrestins are better at inactivating ßARK-phosphorylated receptors rather than protein kinase A-phosphorylated receptors, which suggests that the arrestins preferentially mediate homologous desensitization.
The mechanism of homologous desensitization for the β receptor is as follows:
# Agonist binds and activates the receptor, which changes to an active conformational state.
# Beta adrenergic receptor kinase (βARK), a cytoplasmic kinase is activated and phosphorylates the C-terminus of the β receptor.
# This phosphorylation increases the affinity of β-arrestin for the receptor, resulting in uncoupling of the α subunit of the heterotrimeric G-protein from the receptor, producing desensitization. | 1 | Biochemistry |
A Norrish reaction, named after Ronald George Wreyford Norrish, is a photochemical reaction taking place with ketones and aldehydes. Such reactions are subdivided into Norrish type I reactions and Norrish type II reactions. While of limited synthetic utility these reactions are important in the photo-oxidation of polymers such as polyolefins, polyesters, certain polycarbonates and polyketones. | 5 | Photochemistry |
Nitric acid can be used to convert metals to oxidized forms, such as converting copper metal to cupric nitrate. It can also be used in combination with hydrochloric acid as aqua regia to dissolve noble metals such as gold (as chloroauric acid). These salts can be used to purify gold and other metals beyond 99.9% purity by processes of recrystallization and selective precipitation. Its ability to dissolve certain metals selectively or be a solvent for many metal salts makes it useful in gold parting processes. | 3 | Analytical Chemistry |
In the field of cellular biology, single-cell analysis and subcellular analysis is the study of genomics, transcriptomics, proteomics, metabolomics and cell–cell interactions at the single cell level. The concept of single-cell analysis originated in the 1970s. Before the discovery of heterogeneity, single-cell analysis mainly referred to the analysis or manipulation of an individual cell in a bulk population of cells at a particular condition using optical or electronic microscope. To date, due to the heterogeneity seen in both eukaryotic and prokaryotic cell populations, analyzing a single cell makes it possible to discover mechanisms not seen when studying a bulk population of cells. Technologies such as fluorescence-activated cell sorting (FACS) allow the precise isolation of selected single cells from complex samples, while high throughput single cell partitioning technologies, enable the simultaneous molecular analysis of hundreds or thousands of single unsorted cells; this is particularly useful for the analysis of transcriptome variation in genotypically identical cells, allowing the definition of otherwise undetectable cell subtypes. The development of new technologies is increasing our ability to analyze the genome and transcriptome of single cells, as well as to quantify their proteome and metabolome. Mass spectrometry techniques have become important analytical tools for proteomic and metabolomic analysis of single cells. Recent advances have enabled quantifying thousands of protein across hundreds of single cells, and thus make possible new types of analysis. In situ sequencing and fluorescence in situ hybridization (FISH) do not require that cells be isolated and are increasingly being used for analysis of tissues. | 1 | Biochemistry |
Plant defense against herbivory or host-plant resistance (HPR) is a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants can sense being touched, and they can use several strategies to defend against damage caused by herbivores. Many plants produce secondary metabolites, known as allelochemicals, that influence the behavior, growth, or survival of herbivores. These chemical defenses can act as repellents or toxins to herbivores or reduce plant digestibility. Another defensive strategy of plants is changing their attractiveness. To prevent overconsumption by large herbivores, plants alter their appearance by changing their size or quality, reducing the rate at which they are consumed.
Other defensive strategies used by plants include escaping or avoiding herbivores at any time in any placefor example, by growing in a location where plants are not easily found or accessed by herbivores or by changing seasonal growth patterns. Another approach diverts herbivores toward eating non-essential parts or enhances the ability of a plant to recover from the damage caused by herbivory. Some plants encourage the presence of natural enemies of herbivores, which in turn protect the plant. Each type of defense can be either constitutive (always present in the plant) or induced (produced in reaction to damage or stress caused by herbivores).
Historically, insects have been the most significant herbivores, and the evolution of land plants is closely associated with the evolution of insects. While most plant defenses are directed against insects, other defenses have evolved that are aimed at vertebrate herbivores, such as birds and mammals. The study of plant defenses against herbivory is important, not only from an evolutionary viewpoint, but also for the direct impact that these defenses have on agriculture, including human and livestock food sources; as beneficial biological control agents in biological pest control programs; and in the search for plants of medical importance. | 1 | Biochemistry |
Benthic macroinvertebrates are found within the benthic zone of a stream or river. They consist of aquatic insects, crustaceans, worms and mollusks that live in the vegetation and stream beds of rivers. Macroinvertebrate species can be found in nearly every stream and river, except in some of the world's harshest environments. They also can be found in mostly any size of stream or river, prohibiting only those that dry up within a short timeframe. This makes the beneficial for many studies because they can be found in regions where stream beds are too shallow to support larger species such as fish. Benthic indicators are often used to measure the biological components of fresh water streams and rivers. In general, if the biological functioning of a stream is considered to be in good standing, then it is assumed that the chemical and physical components of the stream are also in good condition. Benthic indicators are the most frequently used water quality test within the United States. While benthic indicators should not be used to track the origins of stressors in rivers and streams, they can provide background on the types of sources that are often associated with the observed stressors. | 2 | Environmental Chemistry |
Silicon carbide exists in about 250 crystalline forms. Through inert atmospheric pyrolysis of preceramic polymers, silicon carbide in a glassy amorphous form is also produced. The polymorphism of SiC is characterized by a large family of similar crystalline structures called polytypes. They are variations of the same chemical compound that are identical in two dimensions and differ in the third. Thus, they can be viewed as layers stacked in a certain sequence.
Alpha silicon carbide (α-SiC) is the most commonly encountered polymorph, and is formed at temperatures greater than 1700 °C and has a hexagonal crystal structure (similar to Wurtzite). The beta modification (β-SiC), with a zinc blende crystal structure (similar to diamond), is formed at temperatures below 1700 °C. Until recently, the beta form has had relatively few commercial uses, although there is now increasing interest in its use as a support for heterogeneous catalysts, owing to its higher surface area compared to the alpha form.
Pure SiC is colorless. The brown to black color of the industrial product results from iron impurities. The rainbow-like luster of the crystals is due to the thin-film interference of a passivation layer of silicon dioxide that forms on the surface.
The high sublimation temperature of SiC (approximately 2700 °C) makes it useful for bearings and furnace parts. Silicon carbide does not melt but begins to sublimate near 2700 °C like graphite, having an appreciable vapor pressure near that temp. It is also highly inert chemically, partly due to the formation of a thin passivated layer of SiO2. There is currently much interest in its use as a semiconductor material in electronics, where its high thermal conductivity, high electric field breakdown strength and high maximum current density make it more promising than silicon for high-powered devices. SiC has a very low coefficient of thermal expansion of about 2.3 × 10 K near 300 K (for 4H and 6H SiC) and experiences no phase transitions in the temperature range 5 K to 340 K that would cause discontinuities in the thermal expansion coefficient. | 8 | Metallurgy |
Amides () take the suffix "-amide", or "-carboxamide" if the carbon in the amide group cannot be included in the main chain. The prefix form is "carbamoyl-". e.g., methanamide, ethanamide.
Amides that have additional substituents on the nitrogen are treated similarly to the case of amines: they are ordered alphabetically with the location prefix N: is N,N-dimethylmethanamide, is N,N-dimethylethanamide. | 0 | Organic Chemistry |
Tetrafluoromethane, also known as carbon tetrafluoride or R-14, is the simplest perfluorocarbon (CF). As its IUPAC name indicates, tetrafluoromethane is the perfluorinated counterpart to the hydrocarbon methane. It can also be classified as a haloalkane or halomethane. Tetrafluoromethane is a useful refrigerant but also a potent greenhouse gas. It has a very high bond strength due to the nature of the carbon–fluorine bond. | 2 | Environmental Chemistry |
The Teck Cominco smelter, also known as the Teck Cominco Lead-Zinc Smelter, Cominco Smelter, and Trail smelter located in Trail, British Columbia, Canada, is the largest integrated lead-zinc smelter of its kind in the world. It is situated approximately north of the border between British Columbia, Canada and Washington, in the United States, on the Columbia River. It is owned and operated by Vancouver, British Columbia-based Teck Cominco Metals Ltd—renamed Teck Resources.
Since 1896, there has been a copper and gold smelting operation in the area. The original company, Consolidated Mining and Smelting Company of Canada, was founded in 1906 through a merger of several entities then under the control of the Canadian Pacific Railway (CPR). In July 2001, Cominco and Tech Resources merged and in 2008, Teck Cominco renamed itself as Teck. By 2018, the Teck Cominco smelter complex had been in operation for over a century. It provided 1,400 jobs in 2018, making it the largest employer in the small city of Trail, with a population of 7800. In 2017, the smelter produced more than 230,000 tons of zinc, which is used in rustproofing both iron and steel. Teck reported that they had invested CA$525 million in the late 2010s to "improve efficiency and performance at its Trail Operations" and that they intend to invest an added CA$150 million. The Trail Operations contributed CA$169 million to Teck Resources CA$3.3-billion gross profit in 2017. | 8 | Metallurgy |
Microphthalmia-associated transcription factor also known as class E basic helix-loop-helix protein 32 or bHLHe32 is a protein that in humans is encoded by the MITF gene.
MITF is a basic helix-loop-helix leucine zipper transcription factor involved in lineage-specific pathway regulation of many types of cells including melanocytes, osteoclasts, and mast cells. The term "lineage-specific", since it relates to MITF, means genes or traits that are only found in a certain cell type. Therefore, MITF may be involved in the rewiring of signaling cascades that are specifically required for the survival and physiological function of their normal cell precursors.
MITF, together with transcription factor EB (TFEB), TFE3 and TFEC, belong to a subfamily of related bHLHZip proteins, termed the MiT-TFE family of transcription factors. The factors are able to form stable DNA-binding homo- and heterodimers. The gene that encodes for MITF resides at the mi locus in mice, and its protumorogenic targets include factors involved in cell death, DNA replication, repair, mitosis, microRNA production, membrane trafficking, mitochondrial metabolism, and much more. Mutation of this gene results in deafness, bone loss, small eyes, and poorly pigmented eyes and skin. In human subjects, because it is known that MITF controls the expression of various genes that are essential for normal melanin synthesis in melanocytes, mutations of MITF can lead to diseases such as melanoma, Waardenburg syndrome, and Tietz syndrome. Its function is conserved across vertebrates, including in fishes such as zebrafish and Xiphophorus.
An understanding of MITF is necessary to understand how certain lineage-specific cancers and other diseases progress. In addition, current and future research can lead to potential avenues to target this transcription factor mechanism for cancer prevention. | 1 | Biochemistry |
The compound is in the form of non-hygroscopic orange granulate. It is stable in the air for several days when stored away from light, and is stable up to several months if dried in vacuo over potassium hydroxide, decomposing into a white paste. Its stability can be attributed to its insolubility in both polar and non-polar solvents.
The compound decomposes at 137 °C. It dissolves in concentrated nitric acid without reduction, and is converted to the black silver(II) oxide in aqueous sodium hydroxide solution.
It is a powerful oxidizing agent, and is illustrated by the fact that it oxidizes Mn ions to permanganates. When the pyridine ligands were removed, the transient square planar [Ag(HO)] remains, which spontaneously oxidizes water to oxygen.
: Ag + e Ag {E° = +1.980 V} | 0 | Organic Chemistry |
This vast scope of functionality for a single protein makes it the ideal model for research regarding other zinc proteases of unknown structure. Recent biomedical research on collagenase, enkephalinase, and angiotensin-converting enzyme used carboxypeptidase A for inhibitor synthesis and kinetic testing. For example, a drug that treats high blood pressure, Captopril, was designed based on a carboxypeptidase A inhibitor. Carboxypeptidase A and the target enzyme of Captopril, angiotensin-converting enzyme, have very similar structures, as they both contain a zinc ion within the active site. This allowed for a potent carboxypeptidase A inhibitor to be used to inhibit the enzyme and, thus, lower blood pressure through the renin-angiotensin-aldosterone system. | 1 | Biochemistry |
Photosynthetic dinoflagellates contain membrane-bound light-harvesting complexes similar to those found in green plants. They additionally contain water-soluble protein-pigment complexes that exploit carotenoids such as peridinin to extend their photosynthetic capacity. Peridinin absorbs light in the blue-green wavelengths (470 to 550 nm) which are inaccessible to chlorophyll by itself; instead the PCP complex uses the geometry of the relative pigment orientations to effect extremely high-efficiency energy transfer from the peridinin molecules to their neighboring chlorophyll molecule. PCP has served as a common model system for spectroscopy and for theoretical calculations relating to the protein's photophysics.
PCP complexes are thought to occupy the thylakoid lumen. After energy transfer from the peridinin to the chlorophyll pigment, PCP complexes are believed to then transfer energy from the excited chlorophyll to membrane-bound light harvesting complexes. | 5 | Photochemistry |
The GeneXpert Infinity is an automated cartridge-based nucleic acid amplification test (NAAT) which is able to tell whether the subject fluid contains shreds of the SARS-CoV-2 virus, amongst others. It is manufactured by Cepheid Inc. | 1 | Biochemistry |
Non-target screening is useful when needing to investigate the presences of all the organic compounds within a sample. In this case, since no information is known about the compounds contained in the sample, no reference standard can be used for comparison, at least initially, overall making non-target screening one of the most challenging approaches. Rather, a full automated scan with mass filtering, peak detection, and other characteristics is used to make initial compound detection. Then elemental composition of detected compounds is deduced using accurate mass of the ions. Database searches can be performed to get a lock on what the most plausible structures are given the elemental composition. Like suspect screening, the initial work performed in non-target screening is largely qualitative, with more quantitative work to potentially follow. Similar to suspect screening, the downside to a fully non-targeted approach is the data-intensive nature of the processes, requiring multivariate statistical models, and the wide variety of data processing workflows used by researchers further complicates evaluation of method performance of those data analysis processes. | 3 | Analytical Chemistry |
The introduction of the three-centered two-electron delocalized bond invoked in the non-classical picture of the 2-norbornyl cation allowed chemists to explore a whole new realm of chemical bonds. Chemists were eager to apply the characteristics of hypovalent electronic states to new and old systems alike (though several got too carried away). One of the most fundamentally important concepts that emerged from the intense research focused around non-classical ions was the idea that electrons already involved in sigma bonds could be involved with reactivity. Though filled pi orbitals were known to be electron donors, chemists had doubted that sigma orbitals could function in the same capacity. The non-classical description of the 2-norbornyl cation can be seen as the donation of an electron pair from a carbon-carbon sigma bond into an empty p-orbital of carbon 2. Thus this carbocation showed that sigma-bond electron donation is as plausible as pi-bond electron donation.
The intense debate that followed Brown’s challenge to non-classical ion proponents also had a large impact on the field of chemistry. In order to prove or disprove the non-classical nature of the 2-norbornyl cation, chemists on both sides of the debate zealously sought out new techniques for chemical characterization and more innovative interpretations of existing data. One spectroscopic technique that was further developed to investigate the 2-norbornyl cation was nuclear magnetic resonance spectroscopy of compounds in highly acidic media. Comparisons of the 2-norbornyl cation to unstable transition states with delocalized electronic states were often made when trying to elucidate whether the norbornyl system was stable or not. These efforts motivated closer investigations of transition states and vastly increased the scientific community’s understanding of their electronic structure. In short, vigorous competition between scientific groups led to an extensive research and a better understanding of the underlying chemical concepts. | 7 | Physical Chemistry |
When compounds contain more than one functional group, the order of precedence determines which groups are named with prefix or suffix forms. The table below shows common groups in decreasing order of precedence. The highest-precedence group takes the suffix, with all others taking the prefix form. However, double and triple bonds only take suffix form (-en and -yn) and are used with other suffixes.
Prefixed substituents are ordered alphabetically (excluding any modifiers such as di-, tri-, etc.), e.g. chlorofluoromethane, not fluorochloromethane. If there are multiple functional groups of the same type, either prefixed or suffixed, the position numbers are ordered numerically (thus ethane-1,2-diol, not ethane-2,1-diol.) The N position indicator for amines and amides comes before "1", e.g., is N,2-dimethylpropanamine.
The order of remaining functional groups is only needed for substituted benzene and hence is not mentioned here. | 0 | Organic Chemistry |
Translational regulation refers to the control of the levels of protein synthesized from its mRNA. This regulation is vastly important to the cellular response to stressors, growth cues, and differentiation. In comparison to transcriptional regulation, it results in much more immediate cellular adjustment through direct regulation of protein concentration. The corresponding mechanisms are primarily targeted on the control of ribosome recruitment on the initiation codon, but can also involve modulation of peptide elongation, termination of protein synthesis, or ribosome biogenesis. While these general concepts are widely conserved, some of the finer details in this sort of regulation have been proven to differ between prokaryotic and eukaryotic organisms. | 1 | Biochemistry |
The Ripper Method, developed in 1898, is an analytical chemistry technique used to determine the total amount of sulfur dioxide (SO) in a solution. This technique uses iodine standard and a starch indicator to titrate the solution and determine the concentration of free SO. The titration is done again with a new sample of the solution, but the sample is pretreated with sodium hydroxide (NaOH) to release bound SO. The result of these two titrations can then be used to determine the bound, free, and total amount of SO in the solution. Instead of using a starch indicator, an electrode can be used to determine the presence of free iodine. This technique is widely used in wine making. | 3 | Analytical Chemistry |
In occupational safety and health, biomonitoring may be done for reasons of regulatory compliance, workplace health surveillance and research, confirming effectiveness of hazard controls, or as a component of occupational risk assessment. It can also be used to reconstruct exposures following acute or accidental events, and to assess the effectiveness of personal protective equipment. It is useful for dermal exposures, for which sampling methods are often not readily available, and for finding unexpected exposures or routes. There are also biomarkers not just for chemical hazards, but also other types such as noise and stress. Occupational health differs from environmental health in that the former has smaller number of exposed individuals, but with a wider range of exposure levels.
Biomonitoring is complementary to exposure monitoring in that it measures the internal dose of a toxicant within the body rather than its concentration outside the body, with the advantage that it confirms whether not only exposure but uptake has actually occurred. It also takes into account differences in metabolism, physical exertion, and mixtures of toxicants between individuals that affect the internal dose. It can be done in an individual or collective manner.
A major use of occupational toxicology data is for determining what biomarkers (including both the a toxicant and its metabolites) may be used for biomonitoring, and establishing biological exposure indices. These are used during exposure assessment and workplace health surveillance activities to identify overexposure, and to test the validity of occupational exposure limits. These biomarkers are intended to aid in prevention by identifying early adverse affects, unlike diagnostics for clinical medicine that are designed to reveal advanced pathologic states.
In the United States, the Occupational Safety and Health Administration as of 2017 has three regulations that require biomonitoring: after exposure to benzene in an unplanned release, and for employees exposed to cadmium or lead at or above a specified level over a specified amount of time. In the European Union, biological limit values are health-based, while biological guidance values are statistically derived and indicate background exposures in the general population. As of 2020 lead is the only substance that has a binding biological limit value in the EU. Voluntary lists of biological exposure limits or action levels are maintained by the American Conference of Governmental Industrial Hygienists, German Research Foundation, UK Health and Safety Executive, France's ANSES, and the Swiss Accident Insurance Fund. Biomonitoring for research purposes is performed by the U.S. National Institute for Occupational Safety and Health as part of its Adult Blood Lead Epidemiology and Surveillance program, as well as other occupational health studies. | 2 | Environmental Chemistry |
Glide symmetry can be observed in nature among certain fossils of the Ediacara biota; the machaeridians; and certain palaeoscolecid worms. It can also be seen in many extant groups of sea pens.
In Conway's Game of Life, a commonly occurring pattern called the glider is so named because it repeats its configuration of cells, shifted by a glide reflection, after two steps of the automaton. After four steps and two glide reflections, the pattern returns to its original orientation, shifted diagonally by one unit. Continuing in this way, it moves across the array of the game. | 3 | Analytical Chemistry |
The area of hypoxic bottom water that occurs for several weeks each summer in the Gulf of Mexico has been mapped most years from 1985 through 2017. The size varies annually from a record high in 2017 when it encompassed more than 22,730 square kilometers (8,776 square miles) to a record low in 1988 of 39 square kilometers (15 square miles). The 2015 dead zone measured 16,760 square kilometers (6,474 square miles).
Nancy Rabalais of the Louisiana Universities Marine Consortium in Cocodrie, Louisiana predicted the dead zone or hypoxic zone in 2012 will cover an area of 17,353 square kilometers (6,700 square miles) which is larger than Connecticut; however, when the measurements were completed, the area of hypoxic bottom water in 2012 only totaled 7,480 square kilometers. The models using the nitrogen flux from the Mississippi River to predict the "dead zone" areas have been criticized for being systematically high from 2006 to 2014, having predicted record areas in 2007, 2008, 2009, 2011, and 2013 that were never realized.
In late summer 1988 the dead zone disappeared as the great drought caused the flow of Mississippi to fall to its lowest level since 1933. During times of heavy flooding in the Mississippi River Basin, as in 1993, "the "dead zone"
dramatically increased in size, approximately larger than the previous year". | 9 | Geochemistry |
Calcium (Ca) deficiency is a plant disorder that can be caused by insufficient level of biologically available calcium in the growing medium, but is more frequently a product of low transpiration of the whole plant or more commonly the affected tissue. Plants are susceptible to such localized calcium deficiencies in low or non-transpiring tissues because calcium is not transported in the phloem. This may be due to water shortages, which slow the transportation of calcium to the plant, poor uptake of calcium through the stem, or too much nitrogen in the soil. | 1 | Biochemistry |
Dispersive adhesion, also called adsorptive adhesion, is a mechanism for adhesion which attributes attractive forces between two materials to intermolecular interactions between molecules of each material. This mechanism is widely viewed as the most important of the five mechanisms of adhesion due to its presence in every type of adhesive system and its relative strength. | 6 | Supramolecular Chemistry |
The technique was discovered by a team of researchers at Peking University in Beijing, China. The discovery was announced in the journal Nature Biotechnology in July 2019. | 1 | Biochemistry |
In practice, the Wigner–Seitz cell itself is actually rarely used as a description of direct space, where the conventional unit cells are usually used instead. However, the same decomposition is extremely important when applied to reciprocal space. The Wigner–Seitz cell in the reciprocal space is called the Brillouin zone, which contains the information about whether a material will be a conductor, semiconductor or an insulator. | 3 | Analytical Chemistry |
Uncontrolled growth is a necessary step for the development of all cancers. In many cancers (e.g. melanoma), a defect in the MAP/ERK pathway leads to that uncontrolled growth. Many compounds can inhibit steps in the MAP/ERK pathway, and therefore are potential drugs for treating cancer, such as Hodgkin disease.
The first drug licensed to act on this pathway is sorafenib — a Raf kinase inhibitor. Other Raf inhibitors include SB590885, PLX4720, XL281, RAF265, encorafenib, dabrafenib, and vemurafenib.
Some MEK inhibitors include cobimetinib, CI-1040, PD0325901, binimetinib (MEK162), selumetinib, and trametinib (GSK1120212)
It has been found that acupoint-moxibustion has a role in relieving alcohol-induced gastric mucosal injury in a mouse model, which may be closely associated with its effects in up-regulating activities of the epidermal growth factor/ERK signal transduction pathway.
RAF-ERK pathway is also involved in the pathophysiology of Noonan syndrome, a polymalformative disease.
Protein microarray analysis can be used to detect subtle changes in protein activity in signaling pathways. The developmental syndromes caused by germline mutations in genes that alter the RAS components of the MAP/ERK signal transduction pathway are called RASopathies. | 1 | Biochemistry |
Williams commenced lecturing at McGill University in 1960, and was selected to be the Chairman of the Department of Mining and Metallurgy in 1966. As Chairman, he was instrumental in expanding the department at a time when only six degree programs in Metallurgical Engineering were being offered in Canadian universities, among which McGill's department was the oldest. During his tenure, seven new faculty members were added to the department, with the new faculty primarily focusing its research on extractive (hydro and pyro), process and physical metallurgy. Ties between the department and Canadian industries were also strengthened during this time. Throughout his career, Williams conducted research on a variety of topics ranging from esoteric studies of grain shape to the practical aspects of abrasion resistant cast irons for mineral comminution. Williams held the position of Chairman until 1980, and retired from teaching in 1992. From 1972 to 1973, he was President of the Metallurgical Society of CIM.
As a specialist in failure analysis, Williams was consulted to investigate numerous engineering failures including such notable events as the 1965 LaSalle Heights disaster, the Mississauga train derailment of 1979, and the crash of Quebecair Flight 255. From 1990 to 2000, he was a consultant metallurgist for Via Rail. Williams also served as an expert witness in about 40 court cases in Canada and the United States, and was twice appointed Judge's Expert by justices James K. Hugessen and Antonio Lamar respectively. | 8 | Metallurgy |
The thermodynamic description of gravity has a history that goes back at least to research on black hole thermodynamics by Bekenstein and Hawking in the mid-1970s. These studies suggest a deep connection between gravity and thermodynamics, which describes the behavior of heat. In 1995, Jacobson demonstrated that the Einstein field equations describing relativistic gravitation can be derived by combining general thermodynamic considerations with the equivalence principle. Subsequently, other physicists, most notably Thanu Padmanabhan, began to explore links between gravity and entropy. | 7 | Physical Chemistry |
If one wants to use a theory based on plane parallel layers, optimally the samples would be describable as layers. But a particulate sample often looks a jumbled maze of particles of various sizes and shapes, showing no structured pattern of any kind, and certainly not literally divided into distinct, identical layers. Even so, it is a tenet of Representative Layer Theory that for spectroscopic purposes, we may treat the complex sample as if it were a series of layers, each one representative of the sample as a whole. | 7 | Physical Chemistry |
Slow strain rate testing (SSRT), also called constant extension rate tensile testing (CERT), is a popular test used by research scientists to study stress corrosion cracking. It involves a slow (compared to conventional tensile tests) dynamic strain applied at a constant extension rate in the environment of interest. These test results are compared to those for similar tests in a, known to be inert, environment. A 50-year history of the SSRT has recently been published by its creator. The test has also been standardized and two ASTM symposia devoted to it. | 8 | Metallurgy |
Brown and Goldstein discovered the LDL receptor and showed cholesterol is loaded into cells through receptor mediated endocytosis. Until recently cholesterol was thought of primarily as a structural component of the membrane. However, more recently, cholesterol uptake was shown to signal an immune response in macrophages. More importantly, the ability to efflux cholesterol through ABC transporters was shown to attenuate (i.e., shut down) the inflammatory response. | 1 | Biochemistry |
Amorphous solids typically exhibit higher localization of heat carriers compared to crystalline, giving rise to low thermal conductivity. Products for thermal protection, such as thermal barrier coatings and insulation, rely on materials with ultralow thermal conductivity. | 7 | Physical Chemistry |
Alexander Nikiforovich Popov ( 1840 – 18 August 1881) was a Russian organic chemist. He taught chemistry at the University of Kazan and at the University of Warsaw. He discovered what is now called Popovs Rule (or Popoffs Rule) which states that in the oxidation of an unsymmetrical ketone, the cleavage of the C−CO bond so that the smaller alkyl group is retained.
Popov was born in Vitebsk where his father was a military officer. He studied at Kazan University and attended the chemistry lectures of A.M. Butlerov. Graduating in 1865 he worked as a chemical lab assistant and in 1868 received a masters degree and became a professor at the University of Warsaw. In 1871 he went to work in Bonn with August Kekulé and E.K. Theodor Zinkce. It was during this period that he established the so-called Popovs Rule on the oxidation of benzene homologues being directed to the carbon atom bonded directly to the ring. He received a doctorate in 1872 for work on ketone oxidation. He identified an ordering of stability of radicals based on his examination of oxidation of asymmetric ketones which has been called Popov's rule. He served in the Russo-Turkish War (1877-1878). He introduced the use of potassium dichromate (KCrO) and sulphuric acid as oxidation reagent in organic analysis. | 0 | Organic Chemistry |
Prof. Dr. Petko Stoyanov Dimitrov () (16 September 1944 – 29 April 2023) was a Bulgarian marine geologist and oceanographer from the Institute of Oceanology - Bulgarian Academy of Sciences in Varna. He has been an early proponent of the Black Sea deluge hypothesis which gained public notoriety at the end of the XXc. | 9 | Geochemistry |
Many co-receptor-related disorders occur due to mutations in the receptor's coding gene. LRP5 (low-density lipoprotein receptor-related protein 5) acts as a co-receptor for the Wnt-family of glycoproteins which regulate bone mass. Malfunctions in this co-receptor lead to lower bone density and strength which contribute to osteoporosis.
Loss of function mutations in LRP5 have been implicated in Osteoporosis-pseudoglioma syndrome, Familial exudative vitreoretinopathy, and a specific missense mutation in the first β-propeller region of LRP5 can lead to abnormally high bone density or osteopetrosis. Mutations in LRP1 have also been found in cases of Familial Alzheimer's disease
Loss of function mutations in the Cryptic co-receptor can lead to random organ positioning due to developmental left-right orientation defects.
Gigantism is believed to be caused, in some cases, by a loss of function of the Glypican 3 co-receptor. | 1 | Biochemistry |
There are many challenges for the successful translation of mRNA into drugs because mRNA is a very large and heavy molecule(10^5 ~ 10^6 Da). Moreover, mRNA is unstable and easily degraded by nucleases, and it also activates the immune systems. Furthermore, mRNA has a high negative charge density and it reduces the permeation of mRNA across cellular membranes. Due to these reasons, without the appropriate delivery system, mRNA is degraded easily and the half-life of mRNA without a delivery system is only around 7 hours. Even though some degrees of challenges could be overcome by chemical modifications, delivery of mRNA remains an obstacle. The methods that have been researched to improve the delivery system of mRNA are using microinjection, RNA patches (mRNA loaded in a dissolving micro-needle), gene gun, protamine condensation, RNA adjuvants, and encapsulating mRNA in nanoparticles with lipids.
Even though In Vitro Translated (IVT) mRNA with delivery agents showed improved resistance against degradation, it needs more studies on how to improve the efficiency of the delivery of naked mRNA in vivo. | 1 | Biochemistry |
This section describes the surface coverage when the adsorbate is in liquid phase and is a binary mixture.
For ideal both phases no lateral interactions, homogeneous surface the composition of a surface phase for a binary liquid system in contact with solid surface is given by a classic Everett isotherm equation (being a simple analogue of Langmuir equation), where the components are interchangeable (i.e. "1" may be exchanged to "2") without change of equation form:
where the normal definition of multi-component system is valid as follows:
By simple rearrangement, we get
This equation describes competition of components "1" and "2". | 7 | Physical Chemistry |
The endocannabinoid transporters (eCBTs) are transport proteins for the endocannabinoids. Most neurotransmitters are water-soluble and require transmembrane proteins to transport them across the cell membrane. The endocannabinoids (anandamide, AEA, and 2-arachidonoylglycerol, 2-AG) on the other hand, are non-charged lipids that readily cross lipid membranes. However, since the endocannabinoids are water immiscible, protein transporters have been described that act as carriers to solubilize and transport the endocannabinoids through the aqueous cytoplasm. These include the heat shock proteins (Hsp70s) and fatty acid-binding proteins for anandamide (FABPs). FABPs such as FABP1, FABP3, FABP5, and FABP7 have been shown to bind endocannabinoids. FABP inhibitors attenuate the breakdown of anandamide by the enzyme fatty acid amide hydrolase (FAAH) in cell culture. One of these inhibitors (SB-FI-26), isolated from a virtual library of a million compounds, belongs to a class of compounds (named the "truxilloids') that act as an anti-nociceptive agent with mild anti-inflammatory activity in mice. These truxillic acids and their derivatives have been known to have anti-inflammatory and anti-nociceptive effects in mice and are active components of a Chinese herbal medicine ((−)-Incarvillateine Incarvillea sinensis) used to treat rheumatism and pain in human. The blockade of anandamide transport may, at least in part, be the mechanism through which these compounds exert their anti-nociceptive effects.
Studies have found the involvement of cholesterol in membrane uptake and transport of anandamide. Cholesterol stimulates both the insertion of anandamide into synthetic lipid monolayers and bilayers, and its transport across bilayer membranes, suggest that besides putative anandamide protein-transporters, cholesterol could be an important component of the anandamide transport machinery, and as cholesterol-dependent modulation of CB1 cannabinoid receptors in nerve cells. The catalytic efficiency (i.e., the ratio between maximal velocity and Michaelis–Menten constant) of the AEA membrane transporter (AMT) is almost doubled compared with control cells, demonstrate that, among the proteins of the “endocannabinoid system,” only CB1 and AMT critically depend on membrane cholesterol content, an observation that may have important implications for the role of CB1 in protecting nerve cells against (endo)cannabinoid-induced apoptosis. This can be a reason, why the use of drugs to lower cholesterol is tied to a higher depression risk, and the correlation between levels and increased death rates from suicide and other violent causes.
Activation of CB1 enhances AMT activity through increased nitric oxide synthase (NOS) activity and subsequent increase of NO production, whereas AMT activity instead is reduced by activation of the CB2 cannabinoid receptor, which inhibits NOS and NO release, also suggesting the distribution of these receptors may drive AEA directional transport through the blood–brain barrier and other endothelial cells.
As reviewed in 2016; "Many of the AMT (EMT) proposals have fallen by the wayside." To date a transmembrane protein transporter has not been identified. | 1 | Biochemistry |
The second type of browning, non-enzymatic browning, is a process that also produces the brown pigmentation in foods but without the activity of enzymes. The two main forms of non-enzymatic browning are caramelization and the Maillard reaction. Both vary in the reaction rate as a function of water activity (in food chemistry, the standard state of water activity is most often defined as the partial vapor pressure of pure water at the same temperature).
Caramelization is a process involving the pyrolysis of sugar. It is used extensively in cooking for the desired nutty flavor and brown color. As the process occurs, volatile chemicals are released, producing the characteristic caramel flavor.
The other non-enzymatic reaction is the Maillard reaction. This reaction is responsible for the production of the flavor when foods are cooked. Examples of foods that undergo Maillard reaction include breads, steaks, and potatoes. It is a chemical reaction that takes place between the amine group of a free amino acid and the carbonyl group of a reducing sugar, usually with the addition of heat. The sugar interacts with the amino acid, producing a variety of odors and flavors. The Maillard reaction is the basis for producing artificial flavors for processed foods in the flavoring industry since the type of amino acid involved determines the resulting flavor.
Melanoidins are brown, high molecular weight heterogeneous polymers that are formed when sugars and amino acids combine through the Maillard reaction at high temperatures and low water activity. Melanoidins are commonly present in foods that have undergone some form of non-enzymatic browning, such as barley malts (Vienna and Munich), bread crust, bakery products and coffee. They are also present in the wastewater of sugar refineries, necessitating treatment in order to avoid contamination around the outflow of these refineries. | 1 | Biochemistry |
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 | Organic Chemistry |
In complex variable the H equation is
then for , a unique solution is given by
where the imaginary part of the function can vanish if is real i.e., . Then we have
The above solution is unique and bounded in the interval for conservative cases. In non-conservative cases, if the equation admits the roots , then there is a further solution given by | 7 | Physical Chemistry |
Instead of the hemiacetal hydroxyl group, a hydrogen atom can be removed to form a substituent, for example the hydrogen from the C3 hydroxyl of a glucose molecule. Then the substituent is called D-glucopyranos-3-O-yl as it appears in the name of the drug Mifamurtide.
Recent detection of the Au in living organism was possible through the use of C-glycosyl pyrene, where its permeability through cell membrane and fluorescence properties were used to detect Au. | 0 | Organic Chemistry |
Labourers working in the smelting industry have reported respiratory illnesses inhibiting their ability to perform the physical tasks demanded by their jobs. | 8 | Metallurgy |
Wet deposition of acids occurs when any form of precipitation (rain, snow, and so on) removes acids from the atmosphere and delivers it to the Earth's surface. This can result from the deposition of acids produced in the raindrops (see aqueous phase chemistry above) or by the precipitation removing the acids either in clouds or below clouds. Wet removal of both gases and aerosols are both of importance for wet deposition.
CAM plants are predominantly found in arid environments, where water availability is limited. | 2 | Environmental Chemistry |
miR-324-5p is a microRNA that functions in cell growth, apoptosis, cancer, epilepsy, neuronal differentiation, psychiatric conditions, cardiac disease pathology, and more. As a microRNA, it regulates gene expression through targeting mRNAs. Additionally, miR-324-5p is both an intracellular miRNA, meaning it is commonly found within the microenvironment of the cell, and one of several circulating miRNAs found throughout the body. Its presence throughout the body both within and external to cells may contribute to miR-324-5p's wide array of functions and role in numerous disease pathologies – especially cancer – in various organ systems. | 1 | Biochemistry |
* Polyhydroxoalkanoates and polyesters obtained by enzyme-assisted esterification using lipases.<nowiki/>
* Heparin, heparan sulfate and other glycosaminoglycans and plant glycans.
*Polysaccharides such as cellulose, amylose, chitin and derivatives
*Natural and non-natural polynucleotides can be successfully obtained by enzyme-assisted synthesis using ligase- or polymerase-based approaches and template-assisted polymerisation.
Human-made biopolymers obtained through approaches that involve genetic engineering or recombinant DNA technology are different from synthetic biopolymers and should be referred to as artificial biopolymer (e.g., artificial protein, artificial polynucleotide, etc.). | 1 | Biochemistry |
Potentiometric titrimetry has been the predominant automated titrimetric technique since the 1970s, so it is worthwhile considering the basic differences between it and thermometric titrimetry.
Potentiometrically-sensed titrations rely on a free energy change in the reaction system. Measurement of a free energy dependent term is necessary.
: ΔG = -RT lnK (1)
Where:
: ΔG = change on free energy
: R = universal gas constant
: T = temperature in kelvins (K) or degrees Rankine (°R)
: K = equilibrium constant at temperature T
: ln is the natural logarithm function
In order for a reaction to be amenable to potentiometric titrimetry, the free energy change must be sufficient for an appropriate sensor to respond with a significant inflection (or "kink") in the titration curve where sensor response is plotted against the amount of titrant delivered.
However, free energy is just one of three related parameters in describing any chemical reaction:
: ΔH = ΔG + TΔS (2)
where:
: ΔH = change in enthalpy
: ΔG = change in free energy
: ΔS = change in entropy
: T = temperature in K
For any reaction where the free energy is not opposed by the entropy change, the enthalpy change will be significantly greater than the free energy. Thus a titration based on a change in temperature (which permits observation of the enthalpy change) will show a greater inflection than will curves obtained from sensors reacting to free energy changes alone. | 3 | Analytical Chemistry |
The mammalian PDEs share a common structural organization and contain three functional domains, which include the conserved catalytic core, a regulatory N-terminus, and the C-terminus. The conserved catalytic core is much more similar within PDE families, with about 80% amino acid identity, than between different families. It is believed that the core contains common structural elements that are important for the hydrolysis of cAMP and cGMP phosphodiester bonds. It is also believed that it contains family-specific determinants for differences in affinity for substrates and sensitivity for inhibitors.
The catalytic domain of PDE3 is characterized by a 44-amino acid insert, but this insert is unique to the PDE3 family, and is a factor when determining a structure for a potent and selective PDE3 inhibitor.
The crystal structure of the catalytic domains of several PDEs, including PDE3B, have shown that they contain three helical subdomains:
# N-terminal cyclin fold region
# Linker region
# C-terminal helical bundle
At the interface of these domains a deep hydrophobic pocket is formed by residues that are highly conserved among all PDEs. This pocket is the active site and is composed of four subsites :
# Metal binding site (M site)
# Core pocket (Q pocket)
# Hydrophobic pocket (H pocket)
# Lid region (L region)
The M site is at the bottom of the hydrophobic binding pocket and contains two divalent metal binding sites. The metal ions that can bind to these sites are either zinc or magnesium. The zinc binding site has two histidine and two aspartic acid residues that are absolutely conserved among those PDEs studied to date.
The N-terminal portions of PDEs are widely divergent and contain determinants that are associated with regulatory properties specific to different gene families. For PDE3, those determinants are the hydrophobic membrane association domains and cAMP-dependent protein kinase phosphorylation sites. | 1 | Biochemistry |
ILs improve the catalytic performance of palladium nanoparticles. Furthermore, ionic liquids can be used as pre-catalysts for chemical transformations. In this regard dialkylimidazoliums such as [EMIM]Ac have been used in the combination with a base to generate N-heterocyclic carbenes (NHCs). These imidazolium based NHCs are known to catalyse a number transformations such as the Benzoin condensation and the OTHO reaction. | 7 | Physical Chemistry |
Available dosage forms include liquids, syrups, drops, elixirs, effervescent tablets and powders for mixing with water, capsules, tablets including extended-release formulations, suppositories, compounding powder, and injections. | 4 | Stereochemistry |
Recently, EDHF has been implicated in gender-related differences in blood pressure control. The generation of animals that lack both endothelial nitric oxide synthase (eNOS) and COX-1 (Cyclooxygenase-1, a protein that acts as an enzyme to speed up the production of certain chemical messengers), has allowed a direct assessment of the involvement of EDHF to endothelium-dependent relaxation in small arteries. In mice lacking both eNOS and COX-1, EDHF-mediated response appeared to compensate the absence of endothelial NO in females but not in males. In female mice, the deletion of eNOS and COX-1 did not affect mean arterial blood pressure, while males become hypertensive
In accordance with this study, EDHF has been suggested to be more important in female arteries to confer endothelium-dependent dilatation, while NO played a predominant role in arteries from males. The latter finding indeed concurs with previous reports in several vascular beds, including mesenteric and tail arteries from rats as well as genital arteries from rabbits. These findings together suggest that under pathological conditions EDHF could compensate for the loss of NO in female rather than in male arteries | 1 | Biochemistry |
Fermentation can be simply defined, in this context, as the conversion of sugar molecules into ethanol and carbon dioxide by yeast.
Fermentation practices have led to the discovery of ample microbial and antimicrobial cultures on fermented foods and products. | 1 | Biochemistry |
In chemistry, photoisomerization is molecular behavior in which structural change between isomers is caused by photoexcitation. Both reversible and irreversible photoisomerization reactions exist. However, the word "photoisomerization" usually indicates a reversible process. Photoisomerizable molecules are already put to practical use, for instance, in pigments for rewritable CDs, DVDs, and 3D optical data storage solutions. In addition, recent interest in photoisomerizable molecules has been aimed at molecular devices, such as molecular switches, molecular motors, and molecular electronics.
Photoisomerization behavior can be roughly categorized into several classes. Two major classes are trans-cis (or E-Z) conversion, and open-closed ring transition. Examples of the former include stilbene and azobenzene. This type of compounds has a double bond, and rotation or inversion around the double bond affords isomerization between the two states. Examples of the latter include fulgide and diarylethene. This type of compounds undergoes bond cleavage and bond creation upon irradiation with particular wavelengths of light. Still another class is the di-π-methane rearrangement. | 7 | Physical Chemistry |
Sublimation is a technique used by chemists to purify compounds. A solid is typically placed in a sublimation apparatus and heated under vacuum. Under this reduced pressure, the solid volatilizes and condenses as a purified compound on a cooled surface (cold finger), leaving a non-volatile residue of impurities behind. Once heating ceases and the vacuum is removed, the purified compound may be collected from the cooling surface.
For even higher purification efficiencies, a temperature gradient is applied, which also allows for the separation of different fractions. Typical setups use an evacuated glass tube that is heated gradually in a controlled manner. The material flow is from the hot end, where the initial material is placed, to the cold end that is connected to a pump stand. By controlling temperatures along the length of the tube, the operator can control the zones of re-condensation, with very volatile compounds being pumped out of the system completely (or caught by a separate cold trap), moderately volatile compounds re-condensing along the tube according to their different volatilities, and non-volatile compounds remaining in the hot end.
Vacuum sublimation of this type is also the method of choice for purification of organic compounds for use in the organic electronics industry, where very high purities (often > 99.99%) are needed to satisfy the standards for consumer electronics and other applications. | 3 | Analytical Chemistry |
The use of P,N ligands in asymmetric hydrogenation can be traced to the C symmetric bisoxazoline ligand. However, these symmetric ligands were soon superseded by monooxazoline ligands whose lack of C symmetry has in no way limits their efficacy in asymmetric catalysis. Such ligands generally consist of an achiral nitrogen-containing heterocycle that is functionalized with a pendant phosphorus-containing arm, although both the exact nature of the heterocycle and the chemical environment phosphorus center has varied widely. No single structure has emerged as consistently effective with a broad range of substrates, although certain privileged structures (like the phosphine-oxazoline or PHOX architecture) have been established. Moreover, within a narrowly defined substrate class the performance of metallic complexes with chiral P,N ligands can closely approach perfect conversion and selectivity in systems otherwise very difficult to target. Certain complexes derived from chelating P-O ligands have shown promising results in the hydrogenation of α,β-unsaturated ketones and esters. | 0 | Organic Chemistry |
* Coupled substitutions are common in the silicate minerals where substitutes for in tetrahedral sites.
For example, when a plagioclase feldspar solid solution series forms, albite (Na Al SiO) can change to anorthite (Ca AlSiO) by having replace . However, this leaves a negative charge that has to be balanced by the (coupled) substitution of for .
* Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold. Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37% gold by weight.
* The possible replacement of by in Corundum.
* and in Haematite
* → Diopside (MgCaSiO) → Jadeite: (NaAlSiO or
* 2 → 2 As in the Spinel groups
* The site being filled to maintain charge does not have to be a substitution. It can also involve filling a site that is normally vacant in order to achieve charge balance. For example, in the amphibole mineral Tremolite - (Ca(MgFe)SiO(OH)), replaces then can go into a site that is normally vacant to maintain charge balance. This new mineral would then be edenite a variety of hornblende.
* Bityite’s structure consists of a coupled substitution it exhibits between the sheets of polyhedra; the coupled substitution of beryllium for aluminium within the tetrahedral sites allows a single lithium substitution for a vacancy without any additional octahedral substitutions. The transfer is completed by creating a tetrahedral sheet composition of SiBeAl. The coupled substitution of lithium for vacancy and the beryllium for the tetrahedral aluminium maintains all the charges balanced; thereby, resulting in the trioctahedral end member for the margarite sub-group of the phyllosilicate group.
* Ferrogedrite is related to anthophyllite amphibole and gedrite through coupled substitution of (Al, Fe) for (Mg, Fe, Mn) and Al for Si. | 3 | Analytical Chemistry |
Insulin stimulates the activity of pyruvate dehydrogenase phosphatase. The phosphatase removes the phosphate from pyruvate dehydrogenase activating it and allowing for conversion of pyruvate to acetyl-CoA. This mechanism leads to the increased rate of catalysis of this enzyme, so increases the levels of acetyl-CoA. Increased levels of acetyl-CoA will increase the flux through not only the fat synthesis pathway but also the citric acid cycle. | 1 | Biochemistry |
The leucine synthesis pathway diverges from the valine pathway beginning with α-ketoisovalerate. α-Isopropylmalate synthase catalyzes this condensation with acetyl CoA to produce α-isopropylmalate. An isomerase converts α-isopropylmalate to β-isopropylmalate. The third step is the NAD-dependent oxidation of β-isopropylmalate catalyzed by a dehydrogenase. The final step is the transamination of the α-ketoisocaproate by the action of a glutamate-leucine transaminase.
Leucine, like valine, regulates the first step of its pathway by inhibiting the action of the α-Isopropylmalate synthase. Because leucine is synthesized by a diversion from the valine synthetic pathway, the feedback inhibition of valine on its pathway also can inhibit the synthesis of leucine. | 1 | Biochemistry |
Wood-tar creosote is a colourless to yellowish greasy liquid with a smoky odor, produces a sooty flame when burned, and has a burned taste. It is non-buoyant in water, with a specific gravity of 1.037 to 1.087, retains fluidity at a very low temperature, and boils at 205-225 °C. In its purest form, it is transparent. Dissolution in water requires up to 200 times the amount of water as the base creosote. This creosote is a combination of natural phenols: primarily guaiacol and creosol (4-methylguaiacol), which typically constitutes 50% of the oil; second in prevalence are cresol and xylenol; the rest being a combination of monophenols and polyphenols.
The simple phenols are not the only active element in wood-tar creosote. In solution, they coagulate albumin, which is a water-soluble protein found in meat, so they serve as a preserving agent, but also cause denaturation. Most of the phenols in the creosote are methoxy derivatives: they contain the methoxy group linked to the benzene nucleus. The high level of methyl derivates created from the action of heat on wood (also apparent in the methyl alcohol produced through distillation) make wood-tar creosote substantially different from coal-tar creosote. Guaiacol is a methyl ether of pyrocatechin, while creosol is a methyl ether of methyl-pyrocatechin, the next homolog of pyrocatechin. Methyl ethers differ from simple phenols in being less hydrophilic, caustic, and poisonous. This allows meat to be successfully preserved without tissue denaturation, and allows creosote to be used as a medical ointment.
Because wood-tar creosote is used for its guaiacol and creosol content, it is generally derived from beechwood rather than other woods, since it distills with a higher proportion of those chemicals to other phenolics. The creosote can be obtained by distilling the wood tar and treating the fraction heavier than water with a sodium hydroxide solution. The alkaline solution is then separated from the insoluble oily layer, boiled in contact with air to reduce impurities, and decomposed by diluted sulfuric acid. This produces a crude creosote, which is purified by re-solution in alkali, re-precipitation with acid, then redistilled with the fraction passing over between 200° and 225° constituting the purified creosote.
When ferric chloride is added to a dilute solution, it will turn green: a characteristic of ortho-oxy derivatives of benzene. It dissolves in sulfuric acid to a red liquid, which slowly changes to purple-violet. Shaken with hydrochloric acid in the absence of air, it becomes red, the color changing in the presence of air to dark brown or black.
In preparation of food by smoking, guaiacol contributes mainly to the smoky taste, while the dimethyl ether of pyrogallol, syringol, is the main chemical responsible for the smoky aroma. | 7 | Physical Chemistry |
The American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME) is a professional association for mining and metallurgy, with over 145,000 members. The association was founded in 1871 by 22 mining engineers in Wilkes-Barre, Pennsylvania, and was one of the first national engineering societies in the country.
The association's charter is to "advance and disseminate, through the programs of the Member Societies, knowledge of engineering and the arts and sciences involved in the production and use of minerals, metals, energy sources and materials for the benefit of humankind."
It is the parent organization of four Member Societies, the Society for Mining, Metallurgy, and Exploration (SME), The Minerals, Metals & Materials Society (TMS), the Association for Iron and Steel Technology (AIST), and the Society of Petroleum Engineers (SPE). The organization is currently based in San Ramon, California. | 8 | Metallurgy |
As long as natural enemies have some potential to be omnivorous, plants can provide food resources to encourage their retention and increase the impact they have on herbivore populations. This potential, however, can hinge on a number of the insect's traits. For example, hemipteran predators can use their sucking mouthparts to make use of leaves, stems, and fruits, but spiders with chelicerae cannot. Still, insects widely considered to be purely carnivorous have been observed to diverge from expected feeding behavior. Some plants simply tolerate a low level of herbivory by natural enemies for the service they provide in ridding the plant of more serious herbivores. Others, however, have structures thought to serve no purpose other than attracting and provisioning natural enemies. These structures derive from a long history of coevolution between the first and third trophic levels. A good example is the extrafloral nectaries that many myrmecophytes and other angiosperms sport on leaves, bracts, stems, and fruits. Nutritionally, extrafloral nectaries are similar to floral nectaries, but they do not lead the visiting insect to come into contact with pollen. Their existence is therefore not the product of a pollinator–plant mutualism, but rather a tritrophic, defensive interaction. | 1 | Biochemistry |
A protein subject to regulation through raft-associated translocation can undergo activation upon substrate presentation. For instance, an enzyme that translocates within the membrane towards its substrate can be activated by localizing to the substrate, irrespective of any conformational changes in the enzyme itself. | 1 | Biochemistry |
Arsenate esters, such as those that would be present in DNA, are generally expected to be orders of magnitude less stable to hydrolysis than corresponding phosphate esters. dAMAs, the structural arsenic analog of the DNA building block dAMP, has a half-life of 40 minutes in water at neutral pH. Estimates of the half-life in water of arsenodiester bonds, which would link the nucleotides together, are as short as 0.06 seconds—compared to 30 million years for the phosphodiester bonds in DNA. The authors speculate that the bacteria may stabilize arsenate esters to a degree by using poly-β-hydroxybutyrate (which has been found to be elevated in "vacuole-like regions" of related species of the genus Halomonas
) or other means to lower the effective concentration of water. Polyhydroxybutyrates are used by many bacteria for energy and carbon storage under conditions when growth is limited by elements other than carbon, and typically appear as large waxy granules closely resembling the "vacuole-like regions" seen in GFAJ-1 cells. The authors present no mechanism by which insoluble polyhydroxybutyrate may lower the effective concentration of water in the cytoplasm sufficiently to stabilize arsenate esters. Although all halophiles must reduce the water activity of their cytoplasm by some means to avoid desiccation, the cytoplasm always remains an aqueous environment. | 1 | Biochemistry |
When purifying by electrolysis, an aqueous sulfate solution at 50 to 70 °C is typically used with a lead anode (corrosion products from which will not contaminate the cobalt oxy-hydroxide (CoOOH) electrolyte solution) and a stainless steel cathode which will allow for the easy removal of the deposited cobalt. Electro refining in a chloride or sulfate medium at −0.3 V will make a cathode coating of 99.98% cobalt. | 8 | Metallurgy |
The idea of a quantized time crystal was theorized in 2012 by Frank Wilczek, a Nobel laureate and professor at MIT. In 2013, Xiang Zhang, a nanoengineer at University of California, Berkeley, and his team proposed creating a time crystal in the form of a constantly rotating ring of charged ions.
In response to Wilczek and Zhang, Patrick Bruno (European Synchrotron Radiation Facility) and Masaki Oshikawa (University of Tokyo) published several articles stating that space–time crystals were impossible.
Subsequent work developed more precise definitions of time-translation symmetry-breaking, which ultimately led to the Watanabe–Oshikawa "no-go" statement that quantum space–time crystals in equilibrium are not possible. Later work restricted the scope of Watanabe and Oshikawa: strictly speaking, they showed that long-range order in both space and time is not possible in equilibrium, but breaking of time-translation symmetry alone is still possible.
Several realizations of time crystals, which avoid the equilibrium no-go arguments, were later proposed. In 2014 at Jagiellonian University in Kraków predicted the behaviour of discrete time crystals in a periodically driven system with "an ultracold atomic cloud bouncing on an oscillating mirror".
In 2016, research groups at Princeton and at Santa Barbara independently suggested that periodically driven quantum spin systems could show similar behaviour. Also in 2016, Norman Yao at Berkeley and colleagues proposed a different way to create discrete time crystals in spin systems. These ideas were successful and independently realized by two experimental teams: a group led by Harvards Mikhail Lukin and a group led by Christopher Monroe at University of Maryland. Both experiments were published in the same issue of Nature' in March 2017.
Later, time crystals in open systems, so called dissipative time crystals, were proposed in several platforms breaking a discrete and a continuous time-translation symmetry. A dissipative time crystal was experimentally realized for the first time in 2021 by the group of Andreas Hemmerich at the Institute of Laser Physics at the University of Hamburg. The researchers used a Bose–Einstein condensate strongly coupled to a dissipative optical cavity and the time crystal was demonstrated to spontaneously break discrete time-translation symmetry by periodically switching between two atomic density patterns. In an earlier experiment in the group of Tilman Esslinger at ETH Zurich, limit cycle dynamics was observed in 2019, but evidence of robustness against perturbations and the spontaneous character of the time-translation symmetry breaking were not addressed.
In 2019, physicists Valerii Kozin and Oleksandr Kyriienko proved that, in theory, a permanent quantum time crystal can exist as an isolated system if the system contains unusual long-range multiparticle interactions. The original "no-go" argument only holds in the presence of typical short-range fields that decay as quickly as for some . Kozin and Kyriienko instead analyzed a spin-1/2 many-body Hamiltonian with long-range multispin interactions, and showed it broke continuous time-translational symmetry. Certain spin correlations in the system oscillate in time, despite the system being closed and in a ground energy state. However, demonstrating such a system in practice might be prohibitively difficult, and concerns about the physicality of the long-range nature of the model have been raised.
In 2022, the Hamburg research team, supervised by Hans Keßler and Andreas Hemmerich, demonstrated, for the first time, a continuous dissipative time crystal exhibiting spontaneous breaking of continuous time-translation symmetry.
In February 2024, a team from Dortmund University in Germany built a time crystal from indium gallium arsenide that lasted for 40 minutes, nearly 10 million times longer than the previous record of around 5 milliseconds. In addition, the lack of any decay suggest the crystal have lasted even longer, stating that it could last
"at least a few hours, perhaps even longer".https://phys.org/news/2024-02-physicists-highly-robust-crystal.html | 3 | Analytical Chemistry |
Enzyme-mediated (biological) chiral inversion of organic compounds is caused by highly chiral endogenous molecules found in receptors, enzymes, and other structures. While enzyme inhibitors suppress enzyme activity, enzyme inducers boost enzyme concentration and activity. The primary determinants of inter-individual variability in drug metabolism in humans are thought to include genetic polymorphism and a variety of other variables, including age, gender, biological conditions, pregnancy, illnesses, stress, nutrition, and drugs. For instance, Reichel et al. reported that a 2-arylpropionyl-coenzyme-A epimerase was molecularly cloned and expressed as a crucial enzyme in the inversion metabolism of ibuprofen. Ibuprofen's chiral inversion by enzymes has been documented in humans. | 4 | Stereochemistry |
tolerance seems to differ between various marine organisms, as well as tolerance at different life cycle stages (e.g. larva and adult). The first stage in the life cycle of marine calcifiers at serious risk from high content is the planktonic larval stage. The larval development of several marine species, primarily sea urchins and bivalves, are highly affected by elevations of seawater p. In laboratory tests, numerous sea urchin embryos were reared under different concentrations until they developed to the larval stage. It was found that once they reached this stage, larval and arm sizes were significantly smaller, as well as abnormal skeleton morphology was noted with increasing p.
Similar findings have been found in treated-mussel larvae, which showed a larval size decrease of about 20% and showed morphological abnormalities such as convex hinges, weaker and thinner shells and protrusion of mantle. The larval body size also impacts the encounter and clearance rates of food particles, and if larval shells are smaller or deformed, these larvae are more prone to starvation. structures also serve vital functions for calcified larvae, such as defense against predation, as well as roles in feeding, buoyancy control and pH regulation.
Another example of a species which may be seriously impacted by ocean acidification is Pteropods, which are shelled pelagic molluscs which play an important role in the food-web of various ecosystems. Since they harbour an aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic emissions. Laboratory tests showed that calcification exhibits a 28% decrease of the pH value of the Arctic ocean expected for the year 2100, compared to the present pH value. This 28% decline of calcification in the lower pH condition is within the range reported for other calcifying organisms such as corals. In contrast with sea urchin and bivalve larvae, corals and marine shrimps are more severely impacted by ocean acidification after settlement, while they developed into the polyp stage. From laboratory tests, the morphology of the -treated polyp endoskeleton of corals was disturbed and malformed compared to the radial pattern of control polyps.
This variability in the impact of ocean acidification on different life cycle stages of different organisms can be partially explained by the fact that most echinoderms and mollusks start shell and skeleton synthesis at their larval stage, while corals start at the settlement stage. Hence, these stages are highly susceptible to the potential effects of ocean acidification. Most calcifiers, such as corals, echinoderms, bivalves and crustaceans, play important roles in coastal ecosystems as keystone species, bioturbators and ecosystem engineers. The food web in the arctic ocean is somewhat truncated, meaning it is short and simple. Any impacts to key species in the food web can cause exponentially devastating effects on the rest of the food chain as a whole, as they will no longer have a reliable food source. If these larger organisms no longer have any source of nutrients, they too will eventually die off, and the entire Arctic ocean ecosystem will be affected. This would have a huge impact on the arctic people who catch arctic fish for a living, as well as the economic repercussions which would follow such a major shortage of food and living income for these families. | 9 | Geochemistry |
In organic chemistry, the acetoxy group (abbr. AcO or OAc; IUPAC name: acetyloxy), is a functional group with the formula and the structure . As the -oxy suffix implies, it differs from the acetyl group () by the presence of an additional oxygen atom. The name acetoxy is the short form of acetyl-oxy. | 0 | Organic Chemistry |
Phase separation is the creation of two distinct phases from a single homogeneous mixture. The most common type of phase separation is between two immiscible liquids, such as oil and water. This type of phase separation is known as liquid-liquid equilibrium. Colloids are formed by phase separation, though not all phase separations forms colloids - for example oil and water can form separated layers under gravity rather than remaining as microscopic droplets in suspension. | 7 | Physical Chemistry |
In organic chemistry, an ortho ester is a functional group containing three alkoxy groups attached to one carbon atom, i.e. with the general formula . Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic acids and it is from these that the name ortho ester is derived. An example is ethyl orthoacetate, , more correctly known as 1,1,1-triethoxyethane. | 0 | Organic Chemistry |
p90 Rsk-1 is located at 1p.
p90 Rsk-2 is located at Xp22.2 and contains 22 exons. Mutations in this gene have been associated with Coffin–Lowry syndrome, a disease characterised by severe psychomotor retardation and other developmental abnormalities.
p90 Rsk-3 is located at 6q27. | 1 | Biochemistry |
The term agostic is reserved to describe two-electron, three-center bonding interactions between carbon, hydrogen, and a metal. Two-electron three-center bonding is clearly implicated in the complexation of H, e.g., in W(CO)(PCy)H, which is closely related to the agostic complex shown in the figure. Silane binds to metal centers often via agostic-like, three-centered Si┄H−M interactions. Because these interactions do not include carbon, however, they are not classified as agostic. | 0 | Organic Chemistry |
Disproportionation of ferrous iron at lower mantle conditions also affect the mantle oxidation state. This reaction is different from the reactions mentioned above as it does not incorporate the participation of free oxygen.
FeO resides in the form of ferropericlase (Fp) and FeO resides in the form of bridgmanite (Bdg). There is no oxygen fugacity change associated with the reaction. However, as the reaction products differ in density significantly, the metallic iron phase could descend downwards to the Earth's core and get separated from the mantle. In this case, the mantle loses metallic iron and becomes more oxidized. | 9 | Geochemistry |
In 1981, the UK banned closed uses of PCBs in new equipment, and nearly all UK PCB synthesis ceased; closed uses in existing equipment containing in excess of 5 litres of PCBs were not stopped until December 2000. | 2 | Environmental Chemistry |
The ascidian mitochondrial code (translation table 13) is a genetic code found in the mitochondria of Ascidia. | 1 | Biochemistry |
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