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When the cell is operated at open circuit, I = 0 and the voltage across the output terminals is defined as the open-circuit voltage. Assuming the shunt resistance is high enough to neglect the final term of the characteristic equation, the open-circuit voltage V is:
Similarly, when the cell is operated at short circuit, V = 0 and the current I through the terminals is defined as the short-circuit current. It can be shown that for a high-quality solar cell (low R and I, and high R) the short-circuit current I is:
It is not possible to extract any power from the device when operating at either open circuit or short circuit conditions. | 7 | Physical Chemistry |
SH3BP2 (SH3 domain-binding protein 2) is a protein that comes from a gene located on Chromosome 4. SH3BP2 binds differentially to the SH3 domains of certain proteins of signal transduction pathways. It binds to phosphatidylinositols linking the hemopoietic tyrosine kinase fes to the cytoplasmic membrane in a phosphorylation dependent mechanism. It is also associated with cherubism. | 1 | Biochemistry |
The final part dealt with the construction of oxetane ring D starting with protection of the alcohol group in 38 (Scheme 4). as a TROC alcohol 39 with 2,2,2-trichloroethyl chloroformate and pyridine. The OBOM group was replaced by a bromine group in three steps: deprotection to 40 with hydrochloric acid and sodium iodide, mesylation to 41 with mesyl chloride, DMAP and pyridine and nucleophilic substitution with inversion of configuration with lithium bromide to bromide 42. Because the oxidation of the alkene group to the diol 43 with osmium tetroxide was accompanied by the undesired migration of the benzoate group, this step was taken to completion with imidazole as 44. Two additional countermeasures were required: reprotection of the diol as the carbonate ester 45 with triphosgene and removal of the benzoate group (KCN) to alcohol 46 in preparation of the actual ring closure to the oxetane 47 with N,N-diisopropylethylamine. In the final steps the tertiary alcohol was acylated in 48, the TIPS group removed in 49 and the benzoate group re-introduced in 50.
Tail addition of the Ojima lactam 51 was not disclosed in detail but finally taxol 52 was formed in several steps similar to the other efforts. | 0 | Organic Chemistry |
In cells with progressively increasing expression of IL12 and IL6, SOCSs production and activity suppress cytokine signalling and phosphorylation of JAK-STAT pathways in a negative feedback loop.
Other suppressors of the pathways are: protein inhibitor of activated STAT (PAIS) (regulation of transcriptional activity in the nucleus, observed in STAT4-DNA binding complex), protein tyrosine phosphatase (PTP) (removal of phosphate groups from phosphorylated tyrosine in JAK/STAT pathway proteins), STAT-interacting LIM protein (SLIM) (STAT ubiquitin E3 ligase blocking the phosphorylation of STAT4) or microRNA (miRNA) (degradation of STAT4 mRNA and its post-transcriptional regulation). | 1 | Biochemistry |
Before work hardening, the lattice of the material exhibits a regular, nearly defect-free pattern (almost no dislocations). The defect-free lattice can be created or restored at any time by annealing. As the material is work hardened it becomes increasingly saturated with new dislocations, and more dislocations are prevented from nucleating (a resistance to dislocation-formation develops). This resistance to dislocation-formation manifests itself as a resistance to plastic deformation; hence, the observed strengthening.
In metallic crystals, this is a reversible process and is usually carried out on a microscopic scale by defects called dislocations, which are created by fluctuations in local stress fields within the material culminating in a lattice rearrangement as the dislocations propagate through the lattice. At normal temperatures the dislocations are not annihilated by annealing. Instead, the dislocations accumulate, interact with one another, and serve as pinning points or obstacles that significantly impede their motion. This leads to an increase in the yield strength of the material and a subsequent decrease in ductility.
Such deformation increases the concentration of dislocations which may subsequently form low-angle grain boundaries surrounding sub-grains. Cold working generally results in a higher yield strength as a result of the increased number of dislocations and the Hall–Petch effect of the sub-grains, and a decrease in ductility. The effects of cold working may be reversed by annealing the material at high temperatures where recovery and recrystallization reduce the dislocation density.
A material's work hardenability can be predicted by analyzing a stress–strain curve, or studied in context by performing hardness tests before and after a process. | 8 | Metallurgy |
The emergence of metallurgy in pre-Columbian Mesoamerica occurred relatively late in the region's history, with distinctive works of metal apparent in West Mexico by roughly 800 CE, and perhaps as early as 600 CE. Metallurgical techniques likely diffused northward from regions in Central or South America via maritime trade routes; recipients of these metallurgical technologies apparently exploited a wide range of material, including alloys of copper-silver, copper-arsenic, copper-tin and copper-arsenic-tin.
Metal items crafted throughout Mesoamerica may be broken into three classes: utilitarian objects, objects used for individual ornamentation, and ceremonial/ritual objects. The latter two categories comprise the bulk of distinctly Mesoamerican artifacts, with metals playing a particularly important role in the sacred and symbolic cultural realms. | 8 | Metallurgy |
A trace fossil, also known as an ichnofossil (; from ikhnos "trace, track"), is a fossil record of biological activity by lifeforms but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or mineralization. The study of such trace fossils is ichnology and is the work of ichnologists.
Trace fossils may consist of physical impressions made on or in the substrate by an organism. For example, burrows, borings (bioerosion), urolites (erosion caused by evacuation of liquid wastes), footprints, feeding marks, and root cavities may all be trace fossils.
The term in its broadest sense also includes the remains of other organic material produced by an organism; for example coprolites (fossilized droppings) or chemical markers (sedimentological structures produced by biological means; for example, the formation of stromatolites). However, most sedimentary structures (for example those produced by empty shells rolling along the sea floor) are not produced through the behaviour of an organism and thus are not considered trace fossils.
The study of traces – ichnology – divides into paleoichnology, or the study of trace fossils, and neoichnology, the study of modern traces. Ichnological science offers many challenges, as most traces reflect the behaviour – not the biological affinity – of their makers. Accordingly, researchers classify trace fossils into form genera, based on their appearance and on the implied behaviour, or ethology, of their makers. | 2 | Environmental Chemistry |
Dual-flow, also known as dual, countercurrent chromatography occurs when both phases are flowing in opposite directions inside the column. Instruments are available for dual-flow operation for both Hydrodynamic and hydrostatic CCC. Dual-flow countercurrent chromatography was first described by Yoichiro Ito in 1985 for foam CCC where gas-liquid separations were performed. Liquid–liquid separations soon followed. The countercurrent chromatography instrument must be modified so that both ends of the column have both inlet and outlet capabilities. This mode may accommodate continuous or sequential separations with the sample being introduced in the middle of the column or between two bobbins in a hydrodynamic instrument. A technique called intermittent countercurrent
extraction (ICcE) is a quasi-continuous method where the flow of the phases is alternated "intermittently" between normal and reversed-phase elution so that the stationary phase also alternates. | 3 | Analytical Chemistry |
Proteins, unlike nucleic acids, can have varying charges and complex shapes, therefore they may not migrate into the polyacrylamide gel at similar rates, or all when placing a negative to positive EMF on the sample. Proteins, therefore, are usually denatured in the presence of a detergent such as sodium dodecyl sulfate (SDS) that coats the proteins with a negative charge. Generally, the amount of SDS bound is relative to the size of the protein (usually 1.4g SDS per gram of protein), so that the resulting denatured proteins have an overall negative charge, and all the proteins have a similar charge-to-mass ratio. Since denatured proteins act like long rods instead of having a complex tertiary shape, the rate at which the resulting SDS coated proteins migrate in the gel is relative only to their size and not their charge or shape.
Proteins are usually analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), by native gel electrophoresis, by preparative native gel electrophoresis (QPNC-PAGE), or by 2-D electrophoresis.
Characterization through ligand interaction may be performed by electroblotting or by affinity electrophoresis in agarose or by capillary electrophoresis as for estimation of binding constants and determination of structural features like glycan content through lectin binding. | 1 | Biochemistry |
In the United States, Water Quality Standards are defined by state agencies for various water bodies, guided by the desired uses for the water body (e.g., fish habitat, drinking water supply, recreational use). The Clean Water Act (CWA) requires each governing jurisdiction (states, territories, and covered tribal entities) to submit a set of biennial reports on the quality of water in their area. These reports are known as the 303(d) and 305(b) reports, named for their respective CWA provisions, and are submitted to, and approved by, EPA. These reports are completed by the governing jurisdiction, typically a state environmental agency. EPA recommends that each state submit a single "Integrated Report" comprising its list of impaired waters and the status of all water bodies in the state. The National Water Quality Inventory Report to Congress is a general report on water quality, providing overall information about the number of miles of streams and rivers and their aggregate condition. The CWA requires states to adopt standards for each of the possible designated uses that they assign to their waters. Should evidence suggest or document that a stream, river or lake has failed to meet the water quality criteria for one or more of its designated uses, it is placed on a list of impaired waters. Once a state has placed a water body on this list, it must develop a management plan establishing Total Maximum Daily Loads (TMDLs) for the pollutant(s) impairing the use of the water. These TMDLs establish the reductions needed to fully support the designated uses.
Drinking water standards, which are applicable to public water systems, are issued by EPA under the Safe Drinking Water Act. | 3 | Analytical Chemistry |
Deuterium is produced for industrial, scientific and military purposes, by starting with ordinary water—a small fraction of which is naturally-occurring heavy water—and then separating out the heavy water by the Girdler sulfide process, distillation, or other methods.
In theory, deuterium for heavy water could be created in a nuclear reactor, but separation from ordinary water is the cheapest bulk production process.
The world's leading supplier of deuterium was Atomic Energy of Canada Limited until 1997, when the last heavy water plant was shut down. Canada uses heavy water as a neutron moderator for the operation of the CANDU reactor design.
Another major producer of heavy water is India. All but one of India's atomic energy plants are pressurised heavy water plants, which use natural (i.e., not enriched) uranium. India has eight heavy water plants, of which seven are in operation. Six plants, of which five are in operation, are based on D–H exchange in ammonia gas. The other two plants extract deuterium from natural water in a process that uses hydrogen sulfide gas at high pressure.
While India is self-sufficient in heavy water for its own use, India also exports reactor-grade heavy water. | 9 | Geochemistry |
The emission directly after the excitation is spectrally very broad, yet still centered in the vicinity of the strongest exciton resonance. As the carrier distribution relaxes and cools, the width of the PL peak decreases and the emission energy shifts to match the ground state of the exciton (such as an electron) for ideal samples without disorder. The PL spectrum approaches its quasi-steady-state shape defined by the distribution of electrons and holes. Increasing the excitation density will change the emission spectra. They are dominated by the excitonic ground state for low densities. Additional peaks from higher subband transitions appear as the carrier density or lattice temperature are increased as these states get more and more populated. Also, the width of the main PL peak increases significantly with rising excitation due to excitation-induced dephasing and the emission peak experiences a small shift in energy due to the Coulomb-renormalization and phase-filling.
In general, both exciton populations and plasma, uncorrelated electrons and holes, can act as sources for photoluminescence as described in the semiconductor-luminescence equations. Both yield very similar spectral features which are difficult to distinguish; their emission dynamics, however, vary significantly. The decay of excitons yields a single-exponential decay function since the probability of their radiative recombination does not depend on the carrier density. The probability of spontaneous emission for uncorrelated electrons and holes, is approximately proportional to the product of electron and hole populations eventually leading to a non-single-exponential decay described by a hyperbolic function. | 7 | Physical Chemistry |
The intermolecular oxidations of olefins with alcohols as nucleophile typically generate ketals, where as the palladium-catalyzed oxidations of olefins with carboxylic acids as nucleophile generates vinylic or allylic carboxylates. In case of diols, their reactions with alkenes typically generate ketals, whereas reactions of olefins bearing electron-withdrawing groups tend to form acetals.
Palladium-catalyzed intermolecular oxidations of dienes with carboxylic acids and alcohols as donors give 1,4-addition products. In the case of cyclohexadiene (Figure 4, A), Backvall found that stereochemical outcome of product was found to depend on concentration of LiCl. This reaction proceeds by first generating the Pd(OAc)(benzoquinone)(allyl) complex, through anti-nucleopalladation of diene with acetate as nucleophile. The absence of LiCl induces an inner sphere reductive elimination to afford the trans-acetate stereochemistry to give the trans-1,4-adduct. The presence of LiCl displaces acetate with chloride due to its higher binding affinity, which forces an outer sphere acetate attack anti to the palladium, and affords the cis-acetate stereochemistry to give the cis-1,4-adduct. Intramolecular oxidative cyclization: 2-(2-cyclohexenyl)phenol cyclizes to corresponding dihydro-benzofuran (Figure 4, B); 1-cyclohexadiene-acetic acid in presence of acetic acid cyclizes to corresponding lactone-acetate 1,4 adduct (Figure 4, C), with cis and trans selectivity controlled by LiCl presence. | 0 | Organic Chemistry |
TEOS-10 includes the Gibbs Seawater (GSW) Oceanographic Toolbox which is available as open source software in MATLAB, Fortran, Python, C, C++, R, Julia and PHP. While TEOS-10 is generally expressed in basic SI-units, the GSW package uses input and output data in commonly used oceanographic units (such as g/kg for Absolute Salinity S and dbar for pressure p).
In addition to the GSW Oceanographic Toolbox, the Seawater-Ice-Air (SIA) Library is available for Fortran and VBA (for the use in Excel), and covers the thermodynamic properties of seawater, ice and (moist) air. In contrast to the GSW Toolbox, the SIA-Library exclusively uses basic SI-units. | 7 | Physical Chemistry |
:* A graft polymer molecule is a branched polymer molecule in which one or more of the side chains are different, structurally or configurationally, from the main chain.
:* A star-shaped polymer molecule is a branched polymer molecule in which a single branch point gives rise to multiple linear chains or arms. If the arms are identical the star polymer molecule is said to be regular. If adjacent arms are composed of different repeating subunits, the star polymer molecule is said to be variegated.
:* A comb polymer molecule consists of a main chain with two or more three-way branch points and linear side chains. If the arms are identical the comb polymer molecule is said to be regular.
:* A brush polymer molecule consists of a main chain with linear, unbranched side chains and where one or more of the branch points has four-way functionality or larger.
:* A polymer network is a network in which all polymer chains are interconnected to form a single macroscopic entity by many crosslinks. See for example thermosets or interpenetrating polymer networks.
:* A dendrimer is a repetitively branched compound. | 7 | Physical Chemistry |
Pressure Injection Cells, sometimes referred to as "bomb-loading devices" are used in proteomic research to enable controlled dispensing of small-volume liquid samples. | 3 | Analytical Chemistry |
The word "alcohol" derives from the Arabic kohl (), a powder used as an eyeliner. The first part of the word () is the Arabic definite article, equivalent to the in English. The second part of the word () has several antecedents in Semitic languages, ultimately deriving from the Akkadian (), meaning stibnite or antimony.
Like its antecedents in Arabic and older languages, the term alcohol was originally used for the very fine powder produced by the sublimation of the natural mineral stibnite to form antimony trisulfide . It was considered to be the essence or "spirit" of this mineral. It was used as an antiseptic, eyeliner, and cosmetic. Later the meaning of alcohol was extended to distilled substances in general, and then narrowed again to ethanol, when "spirits" was a synonym for hard liquor.
Paracelsus and Libavius both used the term alcohol to denote a fine powder, the latter speaking of an alcohol derived from antimony. At the same time Paracelsus uses the word for a volatile liquid; alcool or alcool vini occurs often in his writings.
Bartholomew Traheron, in his 1543 translation of John of Vigo, introduces the word as a term used by "barbarous" authors for "fine powder." Vigo wrote: "the barbarous auctours use alcohol, or (as I fynde it sometymes wryten) alcofoll, for moost fine poudre."
The 1657 Lexicon Chymicum, by William Johnson glosses the word as "antimonium sive stibium." By extension, the word came to refer to any fluid obtained by distillation, including "alcohol of wine," the distilled essence of wine. Libavius in Alchymia (1594) refers to "". Johnson (1657) glosses alcohol vini as "." The word's meaning became restricted to "spirit of wine" (the chemical known today as ethanol) in the 18th century and was extended to the class of substances so-called as "alcohols" in modern chemistry after 1850.
The term ethanol was invented in 1892, blending "ethane" with the "-ol" ending of "alcohol", which was generalized as a libfix.
The term alcohol originally referred to the primary alcohol ethanol (ethyl alcohol), which is used as a drug and is the main alcohol present in alcoholic drinks.
The suffix -ol appears in the International Union of Pure and Applied Chemistry (IUPAC) chemical name of all substances where the hydroxyl group is the functional group with the highest priority. When a higher priority group is present in the compound, the prefix hydroxy- is used in its IUPAC name. The suffix -ol in non-IUPAC names (such as paracetamol or cholesterol) also typically indicates that the substance is an alcohol. However, some compounds that contain hydroxyl functional groups have trivial names that do not include the suffix -ol or the prefix hydroxy-, e.g. the sugars glucose and sucrose. | 0 | Organic Chemistry |
Trace fossils are important paleoecological and paleoenvironmental indicators, because they are preserved in situ, or in the life position of the organism that made them. Because identical fossils can be created by a range of different organisms, trace fossils can only reliably inform us of two things: the consistency of the sediment at the time of its deposition, and the energy level of the depositional environment. Attempts to deduce such traits as whether a deposit is marine or non-marine have been made, but shown to be unreliable. | 2 | Environmental Chemistry |
FSP was used to modify a Mg alloy and insert nano-sized SiO. The test was conducted a total four times with the average grain size varying from 0.5–2μm. This nearly doubled the hardness of the Mg and also increased the super-plasticity. At room temperature, the yield stress of the FSP composites was improved in the 1D and in the 2D specimens signifying a larger resistance of the product metal under high stress conditions without deforming. The tensile strength was shown to increase along with the yield stress. | 8 | Metallurgy |
Genetic variants in the CYP21A2 gene cause a disturbance in the development of the enzyme, leading to congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency. Gene conversion events involving the functional gene and the pseudogene account for many cases of steroid 21-hydroxylase deficiency. CAH is an autosomal recessive disorder. There are multiple forms of CAH, defined as classical and nonclassical forms based on the amount of enzyme function still present in the patient.
The classical forms occur in approximately 1 in to 1 in births globally, and includes both the salt-wasting (excessive excretion of sodium via the urine causing hyponatremia and dehydration) and simple-virilizing forms. Complete loss of enzymatic activity causes the salt-wasting form. Variations in the structure of steroid 21-hydroxylase are related to the clinical severity of congenital adrenal hyperplasia. Cortisol and aldosterone deficits are associated with life-threatening sodium loss, as the steroids play roles in regulating sodium homeostasis. Simple-virilizing CAH patients (~1-2% enzyme function) maintain adequate sodium homeostasis, but exhibit other symptoms shared by the salt-wasting form, including accelerated growth in childhood and ambiguous genitalia in female neonates.
The nonclassical form is the mildest condition, retaining about 20% to 50% of enzyme function. This form is associated with mild and clinically silent cortisol impairment, but an excess of androgens post-puberty. | 1 | Biochemistry |
García Mancheño was successful is acquiring funding from the European Research Council in 2017 to start her research program at the University of Münster. She has been a speaker at several training events to help other early career scientists in Germany to acquire funding for their research programs. In 2018 she was a speaker at the Interactive Information Event: ERC Consolidator Grant at the University of Münster to share advice about applying for that specific grant opportunity. She was invited by the German Fulbright Association and Research Corporation for Science Advancement to speak at workshops that are aimed to prepare university professors in Germany to be successful. She spoke at the Fulbright-Cottrell Junior Faculty Professional Development Workshops in 2018 (Berlin) and in 2019 (Göttingen). | 0 | Organic Chemistry |
The presence of a vapor bubble adds an additional component for analysis given that the vapor bubble could contain a significant proportion of the HO and CO originally in the melt sampled by the melt inclusion. If the vapor bubble is composed primarily of CO, Raman spectroscopy can be used to determine the density of CO present. | 9 | Geochemistry |
Because of the widespread use and importance of iron and steel products, the prevention or slowing of rust is the basis of major economic activities in a number of specialized technologies. A brief overview of methods is presented here; for detailed coverage, see the cross-referenced articles.
Rust is permeable to air and water, therefore the interior metallic iron beneath a rust layer continues to corrode. Rust prevention thus requires coatings that preclude rust formation. | 8 | Metallurgy |
Biogenic silica is the major source of silica for diagenesis. One of the prominent examples is the presence of silica in phytoliths in the leaves of plants, ie. grasses, and Equisetaceae. Some suggested that silica present in phytoliths can serve as a defense mechanism against the herbivores, where the presence of silica in leaves increases the difficulty in digestion, harming the fitness of herbivores. However, evidence on the effects of silica on the wellbeing of animals and plants is still insufficient.
Besides, sponges are another biogenic source of naturally occurring silica in animals. They belong to the phylum Porifera in the classification system. Silicious sponges are commonly found with silicified sedimentary layers, for example in the Yanjiahe Formation in South China. Some of them occur as sponge spicules and are associated with microcrystalline quartz or other carbonates after silicification. It could also be the main source of precipitative beds such as cherts beds or cherts in petrified woods.
Diatoms, an important group of microalgae living in marine environments, contribute significantly to the source of diagenetic silica. They have cell walls made of silica, also known as diatom frustules. In some silicified sedimentary rocks, fossils of diatoms are unearthed. This suggests that diatoms frustules were sources of silica for silicification. Some examples are silicified limestones of Miocene Astoria Formation in Washington, silicified ignimbrite in El Tatio Geyser Field in Chile, and Tertiary siliceous sedimentary rocks in western pacific deep sea drills. The presence of biogenic silica in various species creates a large-scale marine silica cycle that circulates silica through the ocean. Silica content is therefore high in active silica upwelling areas in the deep-marine sediments. Besides, carbonate shells that deposited in shallow marine environments enrich silica contents at continental shelf areas. | 9 | Geochemistry |
One approach to prevent PDs consists of physical-chemical optimization of the PCR system, i.e. changing the concentrations of primers, magnesium chloride, nucleotides, ionic strength and temperature of the reaction. This method is somewhat limited by the physical-chemical characteristics that also determine the efficiency of amplification of the target sequence in the PCR. Therefore, reducing PDs formation may also result in reduced PCR efficiency. To overcome this limitation, other methods aim to reduce the formation of PDs only, including primer design, and use of different PCR enzyme systems or reagents. | 1 | Biochemistry |
Mass spectrometry provides information about the structure and composition of the complexes. Spectra for metal polycarbonyls are often easily interpretable, because the dominant fragmentation process is the loss of carbonyl ligands (m/z = 28).
: → + CO
Electron ionization is the most common technique for characterizing the neutral metal carbonyls. Neutral metal carbonyls can be converted to charged species by derivatization, which enables the use of electrospray ionization (ESI), instrumentation for which is often widely available. For example, treatment of a metal carbonyl with alkoxide generates an anionic metallaformate that is amenable to analysis by ESI-MS:
:LM(CO) + RO → [LM−C(=O)OR]
Some metal carbonyls react with azide to give isocyanato complexes with release of nitrogen. By adjusting the cone voltage or temperature, the degree of fragmentation can be controlled. The molar mass of the parent complex can be determined, as well as information about structural rearrangements involving loss of carbonyl ligands under ESI-MS conditions.
Mass spectrometry combined with infrared photodissociation spectroscopy can provide vibrational informations for ionic carbonyl complexes in gas phase. | 0 | Organic Chemistry |
Gene nomenclature is the scientific naming of genes, the units of heredity in living organisms. It is also closely associated with protein nomenclature, as genes and the proteins they code for usually have similar nomenclature. An international committee published recommendations for genetic symbols and nomenclature in 1957. The need to develop formal guidelines for human gene names and symbols was recognized in the 1960s and full guidelines were issued in 1979 (Edinburgh Human Genome Meeting). Several other genus-specific research communities (e.g., Drosophila fruit flies, Mus mice) have adopted nomenclature standards, as well, and have published them on the relevant model organism websites and in scientific journals, including the Trends in Genetics Genetic Nomenclature Guide. Scientists familiar with a particular gene family may work together to revise the nomenclature for the entire set of genes when new information becomes available. For many genes and their corresponding proteins, an assortment of alternate names is in use across the scientific literature and public biological databases, posing a challenge to effective organization and exchange of biological information. Standardization of nomenclature thus tries to achieve the benefits of vocabulary control and bibliographic control, although adherence is voluntary. The advent of the information age has brought gene ontology, which in some ways is a next step of gene nomenclature, because it aims to unify the representation of gene and gene product attributes across all species. | 1 | Biochemistry |
In chemical kinetics, an intrinsic low-dimensional manifold is a technique to simplify the study of reaction mechanisms using dynamical systems, first proposed in 1992.
The ILDM approach fixes a low dimensional surface which describes well the slow dynamics and assumes that after a short time the fast dynamics are less important and the system can be described in the lower-dimensional space. | 7 | Physical Chemistry |
Inoculate MacConkey's (Glucose phosphate broth) with pure culture of test organism. Incubate the broth at 35 °C for 48–72 hours.
After incubation add 5 drops of methyl red directly into the broth, through the sides of the tube. | 3 | Analytical Chemistry |
An important use of MLPA is to determine relative ploidy. For example, probes may be designed to target various regions of chromosome 21 of a human cell. The signal strengths of the probes are compared with those obtained from a reference DNA sample known to have two copies of the chromosome. If an extra copy is present in the test sample, the signals are expected to be 1.5 times the intensities of the respective probes from the reference. If only one copy is present the proportion is expected to be 0.5. If the sample has two copies, the relative probe strengths are expected to be equal. | 1 | Biochemistry |
Spectral purity is a term used in both optics and signal processing. In optics, it refers to the quantification of the monochromaticity of a given light sample. This is a particularly important parameter in areas like laser operation and time measurement. Spectral purity is easier to achieve in devices that generate visible and ultraviolet light, since higher frequency light results in greater spectral purity.
In signal processing, spectral purity is defined as the inherent stability of a signal, or how clean a spectrum is compared to what it should be. | 7 | Physical Chemistry |
Some examples of stannide Zintl ions are listed below. Some of them contain 2-centre 2-electron bonds (2c-2e), others are "electron deficient" and bonding sometimes can be described using polyhedral skeletal electron pair theory (Wades rules) where the number of valence electrons contributed by each tin atom is considered to be 2 (the s electrons do not contribute). There are some examples of silicide and plumbide ions with similar structures, for example tetrahedral , the chain anion (Si), and .
*Sn found for example in MgSn.
*, tetrahedral with 2c-2e bonds e.g. in CsSn.
*, tetrahedral closo-cluster with 10 electrons (2n + 2).
*(Sn) zig-zag chain polymeric anion with 2c-2e bonds found for example in BaSn.
* closo-cluster, 12 electrons (2n + 2), (i.e. trigonal bipyramidal) in (2,2,2-crypt-Na)Sn.
* polymeric two-dimensional anion in NaSn.
* nido-cluster 22 electrons (2n + 4), capped square antiprismatic with as per polyhedral skeletal electron pair theory, in the intermetallic KSn, and a distorted ion in the salt NaSn·7 en.
* a paramagnetic, 21 electrons, closo- cluster anion (D symmetry), 1 more electron than the 20 (2n + 2) predicted by polyhedral skeletal electron pair theory.
* polymeric two-dimensional anion in NaSn | 7 | Physical Chemistry |
The maskant to be used is determined primarily by the chemical used to etch the material, and the material itself. The maskant must adhere to the surface of the material, and it must also be chemically inert enough with regard to the etchant to protect the workpiece. Most modern chemical milling processes use maskants with an adhesion around ; if the adhesion is too strong, the scribing process may be too difficult to perform. If the adhesion is too low, the etching area may be imprecisely defined. Most industrial chemical milling facilities use maskants based upon neoprene elastomers or isobutylene-isoprene copolymers. | 8 | Metallurgy |
A solvent will be more likely to promote ionization of a dissolved acidic molecule in the following circumstances:
# It is a protic solvent, capable of forming hydrogen bonds.
# It has a high donor number, making it a strong Lewis base.
# It has a high dielectric constant (relative permittivity), making it a good solvent for ionic species.
pK values of organic compounds are often obtained using the aprotic solvents dimethyl sulfoxide (DMSO) and acetonitrile (ACN).
DMSO is widely used as an alternative to water because it has a lower dielectric constant than water, and is less polar and so dissolves non-polar, hydrophobic substances more easily. It has a measurable pK range of about 1 to 30. Acetonitrile is less basic than DMSO, and, so, in general, acids are weaker and bases are stronger in this solvent. Some pK values at 25 °C for acetonitrile (ACN) and dimethyl sulfoxide (DMSO). are shown in the following tables. Values for water are included for comparison.
Ionization of acids is less in an acidic solvent than in water. For example, hydrogen chloride is a weak acid when dissolved in acetic acid. This is because acetic acid is a much weaker base than water.
Compare this reaction with what happens when acetic acid is dissolved in the more acidic solvent pure sulfuric acid:
The unlikely geminal diol species is stable in these environments. For aqueous solutions the pH scale is the most convenient acidity function. Other acidity functions have been proposed for non-aqueous media, the most notable being the Hammett acidity function, H, for superacid media and its modified version H for superbasic media.
In aprotic solvents, oligomers, such as the well-known acetic acid dimer, may be formed by hydrogen bonding. An acid may also form hydrogen bonds to its conjugate base. This process, known as homoconjugation, has the effect of enhancing the acidity of acids, lowering their effective pK values, by stabilizing the conjugate base. Homoconjugation enhances the proton-donating power of toluenesulfonic acid in acetonitrile solution by a factor of nearly 800.
In aqueous solutions, homoconjugation does not occur, because water forms stronger hydrogen bonds to the conjugate base than does the acid. | 7 | Physical Chemistry |
Hydrogen–deuterium exchange (also called H–D or H/D exchange) is a chemical reaction in which a covalently bonded hydrogen atom is replaced by a deuterium atom, or vice versa. It can be applied most easily to exchangeable protons and deuterons, where such a transformation occurs in the presence of a suitable deuterium source, without any catalyst. The use of acid, base or metal catalysts, coupled with conditions of increased temperature and pressure, can facilitate the exchange of non-exchangeable hydrogen atoms, so long as the substrate is robust to the conditions and reagents employed. This often results in perdeuteration: hydrogen-deuterium exchange of all non-exchangeable hydrogen atoms in a molecule.
An example of exchangeable protons which are commonly examined in this way are the protons of the amides in the backbone of a protein. The method gives information about the solvent accessibility of various parts of the molecule, and thus the tertiary structure of the protein. The theoretical framework for understanding hydrogen exchange in proteins was first described by Kaj Ulrik Linderstrøm-Lang and he was the first to apply H/D exchange to study proteins. | 7 | Physical Chemistry |
A major source of differentiation is fractionation, an unequal distribution of elements and isotopes. This can be the result of chemical reactions, phase changes, kinetic effects, or radioactivity.
On the largest scale, planetary differentiation is a physical and chemical separation of a planet into chemically distinct regions. For example, the terrestrial planets formed iron-rich cores and silicate-rich mantles and crusts. In the Earths mantle, the primary source of chemical differentiation is partial melting, particularly near mid-ocean ridges. This can occur when the solid is heterogeneous or a solid solution, and part of the melt is separated from the solid. The process is known as equilibrium or batch melting if the solid and melt remain in equilibrium until the moment that the melt is removed, and fractional or Rayleigh' melting if it is removed continuously.
Isotopic fractionation can have mass-dependent and mass-independent forms. Molecules with heavier isotopes have lower ground state energies and are therefore more stable. As a result, chemical reactions show a small isotope dependence, with heavier isotopes preferring species or compounds with a higher oxidation state; and in phase changes, heavier isotopes tend to concentrate in the heavier phases. Mass-dependent fractionation is largest in light elements because the difference in masses is a larger fraction of the total mass.
Ratios between isotopes are generally compared to a standard. For example, sulfur has four stable isotopes, of which the two most common are S and S. The ratio of their concentrations, , is reported as
where is the same ratio for a standard. Because the differences are small, the ratio is multiplied by 1000 to make it parts per thousand (referred to as parts per mil). This is represented by the symbol . | 9 | Geochemistry |
Things become slightly more complicated than this because organisms contain two (or more) copies of each gene, known as the two alleles. So, if a sample is taken from a patient and amplified using PCR both copies of the region of DNA (alleles) of interest are amplified. So if we are looking for mutation there are now three possibilities:
# Neither allele contains a mutation
# One or other allele contains a mutation
# Both alleles contain a mutation.
These three scenarios are known as "Wild–type", "Heterozygote" or "Homozygote" respectively. Each gives a melt curve that is slightly different. With a high quality HRM assay it is possible to distinguish between all three of these scenarios.
Homozygous allelic variants may be characterised by a temperature shift on the resulting melt curve produced by HRM analysis. In comparison, heterozygotes are characterised by changes in melt curve shape. This is due to base-pair mismatching generated as a result of destabilised heteroduplex annealing between wild-type and variant strands. These differences can be easily seen on the resulting melt curve and the melt profile differences between the different genotypes can be amplified visually via generating a difference curve | 1 | Biochemistry |
The unlinked galR gene encodes the repressor for this system. A tetrameric GalR repressor binds to 2 operators, one located at +55 and one located at -60 relative to the PG1 start site. Looping of the DNA blocks the access of RNA polymerase to promoters and/or inhibits formation of the open complex. This looping requires the presence of the histone-like protein, HU to facilitate the formation of the structure and allow for proper repression. When GalR binds as a dimer to the -60 site only, the promoter PG2 is activated, not repressed, allowing basal levels of GalE to be produced. In this state, the PG1 promoter is inactivated through interactions with the alpha subunit of RNA polymerase. Activity of this repressor protein is controlled based on the levels of D-galactose in the cell. Increased levels of this sugar inhibit the activity of the repressor by binding allosterically, resulting in a conformational change of the protein, which suppresses its interactions with RNA polymerase and DNA. This induces the activity of the operon, which will increase the rate of galactose metabolism.
The gal operon is also controlled by CRP-cAMP, similarly to the lac operon. CRP-cAMP binds to the -35 region, promoting transcription from PG1 but inhibiting transcription from PG2. This is accomplished due to the location of the activation sequence. When CRP-cAMP binds the activating sequence, it blocks RNA polymerase from establishing an open complex with PG2, but enhances a closed complex with RNA polymerase at PG1. This represses the activity of the PG2 promoter, and increases the activity of the PG1 promoter. When cells are grown in glucose, basal level transcription occurs from PG2. | 1 | Biochemistry |
The basis for the COD test is that nearly all organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic conditions. The amount of oxygen required to oxidize an organic compound to carbon dioxide, ammonia, and water is given by:
This expression does not include the oxygen demand caused by nitrification, the oxidation of ammonia into nitrate:
Dichromate, the oxidizing agent for COD determination, does not oxidize ammonia into nitrate, so nitrification is not included in the standard COD test.
The International Organization for Standardization describes a standard method for measuring chemical oxygen demand in ISO 6060 [http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=12260&ICS1=13&ICS2=60&ICS3=50]. | 9 | Geochemistry |
Orobol can be found in Streptomyces neyagawaensis (an Actinobacterium). Phenolic compounds can be found in the cyanobacterium Arthrospira maxima, used in the dietary supplement, Spirulina. The three cyanobacteria Microcystis aeruginosa, Cylindrospermopsis raciborskii and Oscillatoria sp. are the subject of research into the natural production of butylated hydroxytoluene (BHT), an antioxidant, food additive and industrial chemical.
The proteobacterium Pseudomonas fluorescens produces phloroglucinol, phloroglucinol carboxylic acid and diacetylphloroglucinol. Another example of phenolics produced in proteobacteria is 3,5-dihydroxy-4-isopropyl-trans-stilbene, a bacterial stilbenoid produced in Photorhabdus bacterial symbionts of Heterorhabditis nematodes. | 0 | Organic Chemistry |
The electric eel, Electrophorus, is capable of delivering a powerful electric shock that can stun or kill its prey. Bluntnose knifefishes, Brachyhypopomus, create an electric discharge pattern similar to the low voltage electrolocation discharge of the electric eel. This is thought to be Batesian mimicry of the powerfully protected electric eel. | 1 | Biochemistry |
Fretting decreases fatigue strength of materials operating under cycling stress. This can result in fretting fatigue, whereby fatigue cracks can initiate in the fretting zone. Afterwards, the crack propagates into the material. Lap joints, common on airframe surfaces, are a prime location for fretting corrosion. This is also known as frettage or fretting corrosion. | 8 | Metallurgy |
Glycosyltransferases have been widely used in both the targeted synthesis of specific glycoconjugates as well as the synthesis of differentially glycosylated libraries of drugs, biological probes or natural products in the context of drug discovery and drug development (a process known as glycorandomization). Suitable enzymes can be isolated from natural sources or produced recombinantly. As an alternative, whole cell-based systems using either endogenous glycosyl donors or cell-based systems containing cloned and expressed systems for synthesis of glycosyl donors have been developed. In cell-free approaches, the large-scale application of glycosyltransferases for glycoconjugate synthesis has required access to large quantities of the glycosyl donors. On the flip-side, nucleotide recycling systems that allow the resynthesis of glycosyl donors from the released nucleotide have been developed. The nucleotide recycling approach has a further benefit of reducing the amount of nucleotide formed as a by-product, thereby reducing the amount of inhibition caused to the glycosyltransferase of interest – a commonly observed feature of the nucleotide byproduct. | 0 | Organic Chemistry |
The natural selection power for dephosphorylation is less understood. A recent study has found that IRF9, which is from the interferon-regulatory factors family (IRFs), a critical family for anti-viral immune response, could be influenced by natural selection during Human species evolution. The positive selection has been found on the amino acid site Val129 (NP_006075.3:p.Ser129Val) of human IRF9. The ancestral state (Ser129) is conserved among mammals, while the novel state (Val129) was fixed before the "out-of-Africa" event ~ 500,000 years ago. This young amino acid (Val129) may serve as a dephosphorylation site of IRF9. The dephosphorylation may affect the immune activity of IRF9. | 1 | Biochemistry |
The pyroelectric coefficient may be described as the change in the spontaneous polarization vector with temperature:
where p (CmK) is the vector for the pyroelectric coefficient. | 7 | Physical Chemistry |
Contig can also refer to the overlapping clones that form a physical map of a chromosome when the top-down or hierarchical sequencing strategy is used. In this sequencing method, a low-resolution map is made prior to sequencing in order to provide a framework to guide the later assembly of the sequence reads of the genome. This map identifies the relative positions and overlap of the clones used for sequencing. Sets of overlapping clones that form a contiguous stretch of DNA are called contigs; the minimum number of clones that form a contig that covers the entire chromosome comprise the tiling path that is used for sequencing. Once a tiling path has been selected, its component BACs are sheared into smaller fragments and sequenced. Contigs therefore provide the framework for hierarchical sequencing.
The assembly of a contig map involves several steps. First, DNA is sheared into larger (50–200kb) pieces, which are cloned into BACs or PACs to form a BAC library. Since these clones should cover the entire genome/chromosome, it is theoretically possible to assemble a contig of BACs that covers the entire chromosome. Reality, however, is not always ideal. Gaps often remain, and a scaffold—consisting of contigs and gaps—that covers the map region is often the first result. The gaps between contigs can be closed by various methods outlined below. | 1 | Biochemistry |
The convention for a nucleic acid sequence is to list the nucleotides as they occur from the 5 end to the 3 end of the polymer chain, where 5 and 3 refer to the numbering of carbons around the ribose ring which participate in forming the phosphate diester linkages of the chain. Such a sequence is called the primary structure of the biopolymer. | 1 | Biochemistry |
Dibasic esters are used in paints, coil coatings, paint strippers, coatings, plasticisers, resins, binders, solvents, polyols, soil stabilization, chemical grouting, oilfield drilling fluids, crop protection products, cedar spray, and adhesives. | 0 | Organic Chemistry |
Endoreversible thermodynamics is a subset of irreversible thermodynamics aimed at making more realistic assumptions about heat transfer than are typically made in reversible thermodynamics. It gives an upper bound on the power that can be derived from a real process that is lower than that predicted by Carnot for a Carnot cycle, and accommodates the exergy destruction occurring as heat is transferred irreversibly.
It is also called finite-time thermodynamics, entropy generation minimization, or thermodynamic optimization. | 7 | Physical Chemistry |
In thermochemistry, the Thomsen–Berthelot principle is a hypothesis in the history of chemistry which argued that all chemical changes are accompanied by the production of heat and that processes which occur will be ones in which the most heat is produced. This principle was formulated in slightly different versions by the Danish chemist Julius Thomsen in 1854 and by the French chemist Marcellin Berthelot in 1864. This early postulate in classical thermochemistry became the controversial foundation of a research program that would last three decades.
This principle came to be associated with what was called the thermal theory of affinity, which postulated that the heat evolved in a chemical reaction was the true measure of its affinity. | 7 | Physical Chemistry |
Industrially, tert-butyl hydroperoxide is used to prepare propylene oxide. In the Halcon process, molybdenum-based catalysts are used for this reaction:
:(CH)COOH + CH=CHCH → (CH)COH + CHOCHCH
The byproduct t-butanol can be dehydrated to isobutene and converted to MTBE.
On a much smaller scale, tert-butyl hydroperoxide is used to produce some fine chemicals by the Sharpless epoxidation. | 0 | Organic Chemistry |
To date, few in-depth studies on the in vivo behavior of PAMAM dendrimers have been carried out. This could be in part due to the diverse behavior of PAMAMs depending on surface modification (see below), which make characterization of their in vivo properties largely case-dependent. Nonetheless, the fate and transport of unmodified PAMAM dendrimers is an important case study as any biological applications could involve unmodified PAMAM as a metabolic byproduct. In the only major systematic study of in vivo PAMAM behavior, injections of high levels of bare PAMAMs over extended periods of time in mice showed no evidence of toxicity up through G5 PAMAM, and for G3-G7 PAMAM, low immunogenicity was observed. These systemic-level observations seem to align with the observation that PAMAM dendrimers are not extremely cytotoxic overall; however, more in-depth studies of the pharmacokinetics and biodistribution of PAMAM are required before a move toward in vivo applications can be made. | 6 | Supramolecular Chemistry |
A micellar cubic phase is a lyotropic liquid crystal phase formed when the concentration of micelles dispersed in a solvent (usually water) is sufficiently high that they are forced to pack into a structure having a long-ranged positional (translational) order. For example, spherical micelles a cubic packing of a body-centered cubic lattice. Normal topology micellar cubic phases, denoted by the symbol I, are the first lyotropic liquid crystalline phases that are formed by type I amphiphiles. The amphiphiles' hydrocarbon tails are contained on the inside of the micelle and hence the polar-apolar interface of the aggregates has a positive mean curvature, by definition (it curves away from the polar phase). The first pure surfactant system found to exhibit three different type I (oil-in-water) micellar cubic phases was observed in the dodecaoxyethylene mono-n-dodecyl ether (C12EO12)/water system.
Inverse topology micellar cubic phases (such as the Fd3m phase) are observed for some type II amphiphiles at very high amphiphile concentrations. These aggregates, in which water is the minority phase, have a polar-apolar interface with a negative mean curvature. The structures of the normal topology micellar cubic phases that are formed by some types of amphiphiles (e.g. the oligoethyleneoxide monoalkyl ether series of non-ionic surfactants are the subject of debate. Micellar cubic phases are isotropic phases but are distinguished from micellar solutions by their very high viscosity. When thin film samples of micellar cubic phases are viewed under a polarising microscope they appear dark and featureless. Small air bubbles trapped in these preparations tend to appear highly distorted and occasionally have faceted surfaces. A reversed micellar cubic phase has been observed, although it is much less common. It was observed that a reverse micellar cubic phase with Fd3m (Q227) symmetry formed in a ternary system of an amphiphilic diblock copolymer (EO17BO10, where EO represents ethylene oxide and BO represents butylene oxide), water, and p-xylene. | 7 | Physical Chemistry |
Early examples were often uncovered by the observation of precipitates or color changes from samples that were exposed to sunlights. The first reported case was by Ciamician that sunlight converted santonin to a yellow photoproduct:
An early example of a precipitate was the photodimerization of anthracene, characterized by Yulii Fedorovich Fritzsche and confirmed by Elbs. Similar observations focused on the dimerization of cinnamic acid to truxillic acid. Many photodimers are now recognized, e.g. pyrimidine dimer, thiophosgene, diamantane.
Another example was uncovered by Egbert Havinga in 1956. The curious result was activation on photolysis by a meta nitro group in contrast to the usual activation by ortho and para groups.
Organic photochemistry advanced with the development of the Woodward-Hoffmann rules. Illustrative, these rules help rationalize the photochemically driven electrocyclic ring-closure of hexa-2,4-diene, which proceeds in a disrotatory fashion.
Organic reactions that obey these rules are said to be symmetry allowed. Reactions that take the opposite course are symmetry forbidden and require substantially more energy to take place if they take place at all. | 5 | Photochemistry |
Super-enhancers have been most commonly identified by locating genomic regions that are highly enriched in ChIP-Seq signal. ChIP-Seq experiments targeting master transcription factors and co-factors like Mediator or BRD4 have been used, but the most frequently used is H3K27ac-marked nucleosomes. The program “ROSE” (Rank Ordering of Super-Enhancers) is commonly used to identify super-enhancers from ChIP-Seq data. This program stitches together previously identified enhancer regions and ranks these stitched enhancers by their ChIP-Seq signal. The stitching distance selected to combine multiple individual enhancers into larger domains can vary. Because some markers of enhancer activity also are enriched in promoters, regions within promoters of genes can be disregarded. ROSE separates super-enhancers from typical enhancers by their exceptional enrichment in a mark of enhancer activity. Homer is another tool that can identify super-enhancers. | 1 | Biochemistry |
Hassan Naim received his Ph.D. degree in biochemistry from the University of Bern, Switzerland. Following appointments at the Biochemistry Department, University of Lausanne (membrane transport in T cells) and the University Children’s Hospital Bern (structure and function of brush border membrane proteins) he moved in 1989 to the Biochemistry Department, University of Texas Southwestern Medical Center at Dallas, USA to continue his work on structure-function relationships of brush border proteins. In 1991 he was recruited as a group leader and Faculty member at the University of Düsseldorf, Germany. In 1997 he was appointed as a Professor and Chair of the Department of Biochemistry at the University of Veterinary Medicine in Hannover, Germany. | 1 | Biochemistry |
A Pd–Cu bimetallic system was not discovered until 2006 when Goossen et al. reported a decarboxylative cross-coupling of aryl halides with ortho-substituted aromatic carboxylic acids.
Through subsequent studies it was found that the use of aryl triflates allowed substrate scope for cross-coupling to be extended to some aromatic carboxylates lacking any ortho-substitution (less reactive). This was a result of the fact that any halide anion generated in the reaction inhibited the Cu-catalyzed decarboxylation process.
Further optimization of the system and catalyst conditions has made decarboxylative cross-coupling using bimetallic Pd–Cu systems applicable to organic synthesis, most predominantly in the formation of biaryls.
As well, the variability of this combined catalytic system allows for promotion of a large spectrum of reactions, including aryl ketone formation, c-heteroatom cross-coupling, and many others. | 0 | Organic Chemistry |
In contrast to animals, fungi and non-vascular plants, the cells of flowering plants lack dynein motors. However, they contain a larger number of different kinesins. Many of these plant-specific kinesin groups are specialized for functions during plant cell mitosis. Plant cells differ from animal cells in that they have a cell wall. During mitosis, the new cell wall is built by the formation of a cell plate starting in the center of the cell. This process is facilitated by a phragmoplast, a microtubule array unique to plant cell mitosis. The building of cell plate and ultimately the new cell wall requires kinesin-like motor proteins.
Another motor protein essential for plant cell division is kinesin-like calmodulin-binding protein (KCBP), which is unique to plants and part kinesin and part myosin. | 6 | Supramolecular Chemistry |
Dendrimers have potential applications in sensors. Studied systems include proton or pH sensors using poly(propylene imine), cadmium-sulfide/polypropylenimine tetrahexacontaamine dendrimer composites to detect fluorescence signal quenching, and poly(propylenamine) first and second generation dendrimers for metal cation photodetection amongst others. Research in this field is vast and ongoing due to the potential for multiple detection and binding sites in dendritic structures. | 6 | Supramolecular Chemistry |
The utility of palladium-catalyzed cross-coupling reactions is enhanced by the use of N-heterocyclic carbene ligands. Indeed, Pd-NHC complexes have been proven effective in Suzuki-Miyaura, Negishi, Sonogashira, Kumada-Tamao-Corriu, Hiyama, and Stille cross-coupling. Compared to the corresponding Pd-phosphine catalysts, Pd-NHC catalysts can be faster, exhibit broader substrate scope, all with higher turnover numbers. | 0 | Organic Chemistry |
Spin chemistry is a sub-field of chemistry positioned at the intersection of chemical kinetics, photochemistry, magnetic resonance and free radical chemistry, that deals with magnetic and spin effects in chemical reactions. Spin chemistry concerns phenomena such as chemically induced dynamic nuclear polarization (CIDNP), chemically induced electron polarization (CIDEP), magnetic isotope effects in chemical reactions, and it is hypothesized to be key in the underlying mechanism for avian magnetoreception and consciousness. | 7 | Physical Chemistry |
In information theory, the Kraft–McMillan theorem establishes that any directly decodable coding scheme for coding a message to identify one value out of a set of possibilities can be seen as representing an implicit probability distribution over , where is the length of the code for in bits. Therefore, relative entropy can be interpreted as the expected extra message-length per datum that must be communicated if a code that is optimal for a given (wrong) distribution is used, compared to using a code based on the true distribution : it is the excess entropy.
where is the cross entropy of and , and is the entropy of (which is the same as the cross-entropy of P with itself).
The relative entropy can be thought of geometrically as a statistical distance, a measure of how far the distribution is from the distribution . Geometrically it is a divergence: an asymmetric, generalized form of squared distance. The cross-entropy is itself such a measurement (formally a loss function), but it cannot be thought of as a distance, since is not zero. This can be fixed by subtracting to make agree more closely with our notion of distance, as the excess loss. The resulting function is asymmetric, and while this can be symmetrized (see ), the asymmetric form is more useful. See for more on the geometric interpretation.
Relative entropy relates to "rate function" in the theory of large deviations.
Arthur Hobson proved that relative entropy is the only measure of difference between probability distributions that satisfies some desired properties, which are the canonical extension to those appearing in a commonly used characterization of entropy. Consequently, mutual information is the only measure of mutual dependence that obeys certain related conditions, since it can be defined in terms of Kullback–Leibler divergence. | 7 | Physical Chemistry |
Weatherization is a set of measures and practices aimed at improving the energy efficiency of a building or home, primarily to reduce energy consumption and lower utility bills. The main goal of weatherization is to make a structure more comfortable and cost-effective to live in, especially during extreme weather conditions. It involves making various improvements to a building's insulation, air sealing, and overall energy systems.
The American Council for an Energy-Efficient Economy estimates that over 7 million homes have been weatherized, giving yearly savings of 2.6 TWh of electricity, of fossil gas and of reduced carbon dioxide emissions. The US Department of Energy estimates weatherization returns $2.69 for each dollar spent on the program, realized in energy and non-energy benefits. Families whose homes are weatherized are expected to save $358 on their first year's utility bills.
Low Income Home Energy Assistance Programs in many states work side by side with WAP to provide both immediate and long-term solutions to energy poverty. | 7 | Physical Chemistry |
It has been shown that host cells regulate L1 retrotransposition activity, for example through epigenetic silencing.
For example, the RNA interference (RNAi) mechanism of small interfering RNAs derived from L1 sequences can cause suppression of L1 retrotransposition.
In plant genomes, epigenetic modification of LINEs can lead to expression changes of nearby genes and even to phenotypic changes: In the oil palm genome, methylation of a Karma-type LINE underlies the somaclonal, mantled variant of this plant, responsible for drastic yield loss.
Human APOBEC3C mediated restriction of LINE-1 elements were reported and it is due to the interaction between A3C with the ORF1p that affects the reverse transcriptase activity. | 1 | Biochemistry |
Transition metal benzyne complexes are organometallic complexes that contain benzyne ligands (CH). Unlike benzyne itself, these complexes are less reactive although they undergo a number of insertion reactions. | 0 | Organic Chemistry |
Vortex tubes have lower efficiency than traditional air conditioning equipment. They are commonly used for inexpensive spot cooling, when compressed air is available. | 7 | Physical Chemistry |
Both the legacy NACE and SSPC organizations were ANSI-accredited standards developers, which AMPP plans to continue. The merged standards program includes 25 standing standards committees that develop technical standards for industries including cathodic protection, coatings, defense, highways and bridges, rail, maritime, oil and gas, power and utilities, research and testing, tanks and pipelines, and water and wastewater. | 8 | Metallurgy |
Gases exhibit by far the greatest space (and, consequently, the weakest intermolecular forces) between their atoms or molecules; since intermolecular interactions are minuscule in comparison to those in liquids and solids, dilute gases very easily form solutions with one another. Air is one such example: it can be more specifically described as a gaseous solution of oxygen and other gases dissolved in nitrogen (its major component). | 7 | Physical Chemistry |
"Biological activity is a dominant force shaping the chemical structure and evolution of the earth surface environment. The presence of an oxygenated atmosphere-hydrosphere surrounding an otherwise highly reducing solid earth is the most striking consequence of the rise of life on earth. Biological evolution and the functioning of ecosystems, in turn, are to a large degree conditioned by geophysical and geological processes. Understanding the interactions between organisms and their abiotic environment, and the resulting coupled evolution of the biosphere and geosphere is a central theme of research in biogeology. Biogeochemists contribute to this understanding by studying the transformations and transport of chemical substrates and products of biological activity in the environment."
"Since the Cambrian explosion, mineralized body parts have been secreted in large quantities by biota. Because calcium carbonate, silica and calcium phosphate are the main mineral phases constituting these hard parts, biomineralization plays an important role in the global biogeochemical cycles of carbon, calcium, silicon and phosphorus" | 9 | Geochemistry |
*Calcium carbonate (limestone or chalk) decomposes into calcium oxide and carbon dioxide when heated. The chemical reaction is as follows:
::CaCO → CaO + CO
:The reaction is used to make quick lime, which is an industrially important product.
:Another example of thermal decomposition is 2Pb(NO) → 2PbO + O + 4NO.
*Some oxides, especially of weakly electropositive metals decompose when heated to high enough temperature. A classical example is the decomposition of mercuric oxide to give oxygen and mercury metal. The reaction was used by Joseph Priestley to prepare samples of gaseous oxygen for the first time.
*When water is heated to well over , a small percentage of it will decompose into OH, monatomic oxygen, monatomic hydrogen, O, and H.
*The compound with the highest known decomposition temperature is carbon monoxide at ≈3870 °C (≈7000 °F). | 7 | Physical Chemistry |
The eukaryotic genome is organized into a compact chromatin structure that allows only regulated access to DNA. The chromatin structure can be globally "open" and more transcriptionally permissive, or globally "condensed" and transcriptionally inactive. The former (euchromatin) is lightly packed and rich in genes under active transcription. The latter (heterochromatin) includes gene-poor regions such as telomeres and centromeres but also regions with normal gene density but transcriptionally silenced. Transcription can be silenced by histone modification (deacetylation and methylation), RNA interference, and/or DNA methylation.
The gene expression patterns that define cell identity are inherited through cell division. This process is called epigenetic regulation. DNA methylation is reliably inherited through the action of maintenance methylases that modify the nascent DNA strand generated by replication. In mammalian cells, DNA methylation is the primary marker of transcriptionally silenced regions. Specialized proteins can recognize the marker and recruit histone deacetylases and methylases to re-establish the silencing. Nucleosome histone modifications could also be inherited during cell division, however, it is not clear whether it can work independently without the direction by DNA methylation. | 1 | Biochemistry |
The first synthetic immobilized enzyme was made in the 1950s, performed by the inclusion of enzyme into polymeric matrices or binding onto carrier substances. Also cross-linking procedure was applied by cross-linking of protein alone or along with the addition of inert materials. Over the last decade various immobilization methods have been developed. Binding the enzyme to previously synthesized carrier materials for example is the mostly preferred method so far. Newly, the procedure of cross-linking of crystals of enzyme is also considered as an exciting substitute. Utilization rate of immobilized enzymes is growing constantly. | 4 | Stereochemistry |
As a result of these criticisms and the renewed awareness of the three-dimensional effects of drug action fueled by the exponential explosion of chiral technology emerged the new area "stereo-pharmacology". A more specific term is "chiral pharmacology", a phrase popularized by John Caldwell. This field has grown itself into a specialized discipline concerned with the three-dimensional aspects of drug action and disposition. This approach essentially views each version of the chiral twins as separate chemical species. To express the pharmacological activities of each of the chiral twins two technical terms have been coined, eutomer and distomer. The member of the chiral twin that has greater physiological activity is referred to as the eutomer and the other one with lesser activity is referred to as distomer. It is generally understood that this reference is necessarily to a single activity being studied. The eutomer for one effect may well be the distomer when another is studied. The eutomer/distomer ratio is called the eudysmic ratio. | 4 | Stereochemistry |
Matrix isolation is an experimental technique used in chemistry and physics. It generally involves a material being trapped within an unreactive matrix. A host matrix is a continuous solid phase in which guest particles (atoms, molecules, ions, etc.) are embedded. The guest is said to be isolated within the host matrix. Initially the term matrix-isolation was used to describe the placing of a chemical species in any unreactive material, often polymers or resins, but more recently has referred specifically to gases in low-temperature solids. A typical matrix isolation experiment involves a guest sample being diluted in the gas phase with the host material, usually a noble gas or nitrogen. This mixture is then deposited on a window that is cooled to below the melting point of the host gas. The sample may then be studied using various spectroscopic procedures. | 7 | Physical Chemistry |
Ketamine is a widely used anaesthetic agent. It is a chiral molecule that is administered as a racemate. Studies show that (S)-(+)-ketamine is the active anaesthetic and the undesired side-effects (hallucination and agitation) reside in the distomer, (R)-(-)-ketamine. | 4 | Stereochemistry |
The nitrogen cycle is an important process in the ocean as well. While the overall cycle is similar, there are different players and modes of transfer for nitrogen in the ocean. Nitrogen enters the water through the precipitation, runoff, or as from the atmosphere. Nitrogen cannot be utilized by phytoplankton as so it must undergo nitrogen fixation which is performed predominately by cyanobacteria. Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 years. Phytoplankton need nitrogen in biologically available forms for the initial synthesis of organic matter. Ammonia and urea are released into the water by excretion from plankton. Nitrogen sources are removed from the euphotic zone by the downward movement of the organic matter. This can occur from sinking of phytoplankton, vertical mixing, or sinking of waste of vertical migrators. The sinking results in ammonia being introduced at lower depths below the euphotic zone. Bacteria are able to convert ammonia to nitrite and nitrate but they are inhibited by light so this must occur below the euphotic zone. Ammonification or Mineralization is performed by bacteria to convert organic nitrogen to ammonia. Nitrification can then occur to convert the ammonium to nitrite and nitrate. Nitrate can be returned to the euphotic zone by vertical mixing and upwelling where it can be taken up by phytoplankton to continue the cycle. can be returned to the atmosphere through denitrification.
Ammonium is thought to be the preferred source of fixed nitrogen for phytoplankton because its assimilation does not involve a redox reaction and therefore requires little energy. Nitrate requires a redox reaction for assimilation but is more abundant so most phytoplankton have adapted to have the enzymes necessary to undertake this reduction (nitrate reductase). There are a few notable and well-known exceptions that include most Prochlorococcus and some Synechococcus that can only take up nitrogen as ammonium.
The nutrients in the ocean are not uniformly distributed. Areas of upwelling provide supplies of nitrogen from below the euphotic zone. Coastal zones provide nitrogen from runoff and upwelling occurs readily along the coast. However, the rate at which nitrogen can be taken up by phytoplankton is decreased in oligotrophic waters year-round and temperate water in the summer resulting in lower primary production. The distribution of the different forms of nitrogen varies throughout the oceans as well.
Nitrate is depleted in near-surface water except in upwelling regions. Coastal upwelling regions usually have high nitrate and chlorophyll levels as a result of the increased production. However, there are regions of high surface nitrate but low chlorophyll that are referred to as HNLC (high nitrogen, low chlorophyll) regions. The best explanation for HNLC regions relates to iron scarcity in the ocean, which may play an important part in ocean dynamics and nutrient cycles. The input of iron varies by region and is delivered to the ocean by dust (from dust storms) and leached out of rocks. Iron is under consideration as the true limiting element to ecosystem productivity in the ocean.
Ammonium and nitrite show a maximum concentration at 50–80 m (lower end of the euphotic zone) with decreasing concentration below that depth. This distribution can be accounted for by the fact that nitrite and ammonium are intermediate species. They are both rapidly produced and consumed through the water column. The amount of ammonium in the ocean is about 3 orders of magnitude less than nitrate. Between ammonium, nitrite, and nitrate, nitrite has the fastest turnover rate. It can be produced during nitrate assimilation, nitrification, and denitrification; however, it is immediately consumed again. | 1 | Biochemistry |
Ortho esters are readily hydrolyzed in mild aqueous acid to form esters:
: RC(OR′) + HO → RCOR′ + 2 R′OH
For example, trimethyl orthoformate CH(OCH) may be hydrolyzed (under acidic conditions) to methyl formate and methanol; and may be further hydrolyzed (under alkaline conditions) to salts of formic acid and methanol. | 0 | Organic Chemistry |
Multi-wavelength anomalous diffraction (sometimes Multi-wavelength anomalous dispersion; abbreviated MAD) is a technique used in X-ray crystallography that facilitates the determination of the three-dimensional structure of biological macromolecules (e.g. DNA, drug receptors) via solution of the phase problem.
MAD was developed by Wayne Hendrickson while working as a postdoctoral researcher under Jerome Karle at the United States Naval Research Laboratory. The mathematics upon which MAD (and progenitor Single-wavelength anomalous diffraction) was based were developed by Jerome Karle, work for which he was awarded the 1985 Nobel Prize in Chemistry (along with Herbert Hauptman).
Compared to the predecessor SAD, MAD has greatly elevated phasing power from using multiple wavelengths close to the edge. However, because it requires a synchrotron beamline, a longer exposure (risking radiation damage), and only allows a limited choice of heavy atoms (those with edges reachable by a synchrotron), MAD has declined in popularity relative to SAD. | 3 | Analytical Chemistry |
The arrangement of atoms and ions within a material is one of the most important structural properties of a biomaterial. The atomic structure of a material can be viewed at different levels, the sub atomic level, atomic or molecular level, as well as the ultra-structure created by the atoms and molecules. Intermolecular forces between the atoms and molecules that compose the material will determine its material and chemical properties.
The sub atomic level observes the electrical structure of an individual atom to define its interactions with other atoms and molecules. The molecular structure observes the arrangement of atoms within the material. Finally the ultra-structure observes the 3-D structure created from the atomic and molecular structures of the material. The solid-state of a material is characterized by the intramolecular bonds between the atoms and molecules that comprise the material. Types of intramolecular bonds include: ionic bonds, covalent bonds, and metallic bonds. These bonds will dictate the physical and chemical properties of the material, as well as determine the type of material (ceramic, metal, or polymer). | 1 | Biochemistry |
In chemistry, alpha elimination refers to particular types of elimination reactions. The definition of alpha elimination differs for organometallic and organic chemistry. | 0 | Organic Chemistry |
Consider the simple three step pathway:
where and are fixed boundary species, the control equations for this pathway can be derived in a similar manner to the simple two step pathway although it is somewhat more tedious.
where D the denominator is given by
Note that every term in the numerator appears in the denominator, this ensures that the flux control coefficient summation theorem is satisfied.
Likewise the concentration control coefficients can also be derived, for
And for
Note that the denominators remain the same as before and behave as a normalizing factor. | 1 | Biochemistry |
While small-scale columns range from inner diameters of 0.5 cm and withstand pressures of up to 130 MPa, industrial large scale columns reach diameters of up to 2 m and operate at considerable lower pressures (below 1 MPa). While it is favorable to view the packed bed of a column large scale columns are manufactured from steel due to its superior resilience.
Chromatography columns can be used as stand-alone devices or in combination with manual or automated chromatography systems. Medium to large columns are almost exclusively operated together with automated systems to decrease the risk of process failure and loss of product. | 3 | Analytical Chemistry |
Three conditions must be present for oil reservoirs to form:
* A source rock rich in hydrocarbon material buried deeply enough for subterranean heat to cook it into oil,
* A porous and permeable reservoir rock where it can accumulate,
* A caprock (seal) or other mechanism to prevent the oil from escaping to the surface. Within these reservoirs, fluids will typically organize themselves like a three-layer cake with a layer of water below the oil layer and a layer of gas above it, although the different layers vary in size between reservoirs. Because most hydrocarbons are less dense than rock or water, they often migrate upward through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as reservoirs) by impermeable rocks above. However, the process is influenced by underground water flows, causing oil to migrate hundreds of kilometres horizontally or even short distances downward before becoming trapped in a reservoir. When hydrocarbons are concentrated in a trap, an oil field forms, from which the liquid can be extracted by drilling and pumping.
The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where hydrocarbons are broken down to oil and natural gas by a set of parallel reactions, and oil eventually breaks down to natural gas by another set of reactions. The latter set is regularly used in petrochemical plants and oil refineries.
Petroleum has mostly been recovered by oil drilling (natural petroleum springs are rare). Drilling is carried out after studies of structural geology (at the reservoir scale), sedimentary basin analysis, and reservoir characterisation (mainly in terms of the porosity and permeability of geologic reservoir structures). Wells are drilled into oil reservoirs to extract the crude oil. "Natural lift" production methods that rely on the natural reservoir pressure to force the oil to the surface are usually sufficient for a while after reservoirs are first tapped. In some reservoirs, such as in the Middle East, the natural pressure is sufficient over a long time. The natural pressure in most reservoirs, however, eventually dissipates. Then the oil must be extracted using "artificial lift" means. Over time, these "primary" methods become less effective and "secondary" production methods may be used. A common secondary method is "waterflood" or injection of water into the reservoir to increase pressure and force the oil to the drilled shaft or "wellbore." Eventually "tertiary" or "enhanced" oil recovery methods may be used to increase the oil's flow characteristics by injecting steam, carbon dioxide and other gases or chemicals into the reservoir. In the United States, primary production methods account for less than 40 percent of the oil produced on a daily basis, secondary methods account for about half, and tertiary recovery the remaining 10 percent. Extracting oil (or "bitumen") from oil/tar sand and oil shale deposits requires mining the sand or shale and heating it in a vessel or retort, or using "in-situ" methods of injecting heated liquids into the deposit and then pumping the liquid back out saturated with oil. | 7 | Physical Chemistry |
There are 4 superfamilies of viruses that cover all RNA-containing viruses with no DNA stage:
* Viruses containing positive-strand RNA or double-strand RNA, except retroviruses and Birnaviridae
** All positive-strand RNA eukaryotic viruses with no DNA stage
** All RNA-containing bacteriophages; there are two families of RNA-containing bacteriophages: Leviviridae (positive ssRNA phages) and Cystoviridae (dsRNA phages)
** dsRNA virus family Reoviridae, Totiviridae, Hypoviridae, Partitiviridae
* Mononegavirales (negative-strand RNA viruses with non-segmented genomes; )
* Negative-strand RNA viruses with segmented genomes (), such as orthomyxoviruses and bunyaviruses
* dsRNA virus family Birnaviridae ()
Flaviviruses produce a polyprotein from the ssRNA genome. The polyprotein is cleaved to a number of products, one of which is NS5, an RNA-dependent RNA polymerase. This RNA-directed RNA polymerase possesses a number of short regions and motifs homologous to other RNA-directed RNA polymerases.
RNA replicase found in positive-strand ssRNA viruses are related to each other, forming three large superfamilies. Birnaviral RNA replicase is unique in that it lacks motif C (GDD) in the palm. Mononegaviral RdRp (PDB 5A22) has been automatically classified as similar to (+)−ssRNA RdRps, specifically one from Pestivirus and one from Leviviridae. Bunyaviral RdRp monomer (PDB 5AMQ) resembles the heterotrimeric complex of Orthomyxoviral (Influenza; PDB 4WSB) RdRp.
Since it is a protein universal to RNA-containing viruses, RdRp is a useful marker for understanding their evolution. The overall structural evolution of viral RdRps has been reviewed. | 1 | Biochemistry |
Selenium is an essential micronutrient for animals, though it is toxic in large doses. In plants, it sometimes occurs in toxic amounts as forage, e.g. locoweed. Selenium is a component of the amino acids selenocysteine and selenomethionine. In humans, selenium is a trace element nutrient that functions as cofactor for glutathione peroxidases and certain forms of thioredoxin reductase. Selenium-containing proteins are produced from inorganic selenium via the intermediacy of selenophosphate (PSeO). | 1 | Biochemistry |
* History of organic chemistry
* IUPAC nomenclature of organic chemistry
* Organic reaction
* Organic compound
* Organic synthesis
** Retrosynthetic analysis | 0 | Organic Chemistry |
The premise behind these skimmers is that a high pressure pump combined with a venturi, can be used to introduce the bubbles into the water stream. The tank water is pumped through the venturi, in which fine bubbles are introduced via pressure differential, then enters the skimmer body. This method was popular due to its compact size and high efficiency for the time but venturi designs are now outdated and surpassed by more efficient needle-wheel designs. | 3 | Analytical Chemistry |
Foldit is an online puzzle video game about protein folding. It is part of an experimental research project developed by the University of Washington, Center for Game Science, in collaboration with the UW Department of Biochemistry. The objective of Foldit is to fold the structures of selected proteins as perfectly as possible, using tools provided in the game. The highest scoring solutions are analyzed by researchers, who determine whether or not there is a native structural configuration (native state) that can be applied to relevant proteins in the real world. Scientists can then use these solutions to target and eradicate diseases and create biological innovations. A 2010 paper in the science journal Nature credited Foldit's 57,000 players with providing useful results that matched or outperformed algorithmically computed solutions. | 1 | Biochemistry |
Most detection mechanisms involved in small molecule sensors comprise some modulation in the fluorescent behavior of the sensing molecule upon binding the target metal. When a metal coordinates to such a sensor, it may either enhance or reduce the original fluorescent emission. The former is known as the Chelation Enhancement Fluorescence effect (CHEF), while the latter is called the Chelation Enhancement Quenching effect (CHEQ). By changing the intensity of emission at different wavelengths, the resulting fluorescent spectrum may attenuate, amplify, or shift upon the binding and dissociation of a metal. This shift in spectra can be monitored using a detector such as a microscope or a photodiode.
Listed below are some examples of mechanisms by which emission is modulated. Their participation in CHEQ or CHEF is dependent on the metal and small molecule sensor in question. | 5 | Photochemistry |
In inorganic chemistry, a homoleptic chemical compound is a metal compound with all ligands identical. The term uses the "homo-" prefix to indicate that something is the same for all. Any metal species which has more than one type of ligand is heteroleptic.
Some compounds with names that suggest that they are homoleptic are in fact heteroleptic, because they have ligands in them which are not featured in the name. For instance dialkyl magnesium complexes, which are found in the equilibrium which exists in a solution of a Grignard reagent in an ether, have two ether ligands attached to each magnesium centre. Another example is a solution of trimethyl aluminium in an ether solvent (such as THF); similar chemistry should be expected for a triaryl or trialkyl borane.
It is possible for some ligands such as DMSO to bind with two or more different coordination modes. It would still be reasonable to consider a complex which has only one type of ligand but with different coordination modes to be homoleptic. For example, the complex dichlorotetrakis(dimethyl sulfoxide)ruthenium(II) features DMSO coordinating via both sulfur and oxygen atoms (though this is not homoleptic since there are also chloride ligands). | 0 | Organic Chemistry |
The LTFT facility Pearl GTL at Ras Laffan, Qatar, is the second largest FT plant in the world after Sasol's Secunda plant in South Africa. It uses cobalt catalysts at 230 °C, converting natural gas to petroleum liquids at a rate of , with additional production of of oil equivalent in natural gas liquids and ethane.
Another plant in Ras Laffan, called Oryx GTL, has been commissioned in 2007 with a capacity of . The plant utilizes the Sasol slurry phase distillate process, which uses a cobalt catalyst. Oryx GTL is a joint venture between QatarEnergy and Sasol. | 0 | Organic Chemistry |
There is an extension to DLTS known as a high resolution Laplace transform DLTS (LDLTS). Laplace DLTS is an isothermal technique in which the capacitance transients are digitized and averaged at a fixed temperature. Then the defect emission rates are obtained with a use of numerical methods being equivalent to the inverse Laplace transformation. The obtained emission rates are presented as a spectral plot. The main advantage of Laplace DLTS in comparison to conventional DLTS is the substantial increase in energy resolution understood here as an ability to distinguish very similar signals.
Laplace DLTS in combination with uniaxial stress results in a splitting of the defect energy level. Assuming a random distribution of defects in non-equivalent orientations, the number of split lines and their intensity ratios reflect the symmetry class of the given
defect.
Application of LDLTS to MOS capacitors needs device polarization voltages in a range where the Fermi level extrapolated from semiconductor to the semiconductor-oxide interface intersects this interface within the semiconductor bandgap range. The electronic interface states present at this interface can trap carriers similarly to defects described above. If their occupancy with electrons or holes is disturbed by a small voltage pulse then the device capacitance recovers after the pulse to its initial value as the interface states start to emit carriers. This recovery process can be analyzed with the LDLTS method for different device polarization voltages. Such a procedure allows to obtain the energy state distribution of the interface electronic states at the semiconductor-oxide (or dielectric) interfaces. | 7 | Physical Chemistry |
In 1988, The NIST group in Washington led by William Phillips first measured temperatures below the Doppler limit in sodium atoms in an optical molasses, prompting the search for the theoretical underpinnings of sub-Doppler cooling.
The next year, Jean Dalibard and Claude Cohen-Tannoudji identified the cause as the multi-photon process of Sisyphus cooling,
and Steven Chu's group likewise modeled sub-Doppler cooling as fundamentally an optical pumping scheme.
As a result of their efforts, Phillips, Cohen-Tannoudji, and Chu jointly won the 1997 Nobel Prize in Physics. T.W. Hänsch, et al., first outlined the theoretical formulation of gray molasses in 1994,
and a four-beam experimental realization in cesium was achieved by G. Grynberg the next year.
It has since been regularly used to cool all the other alkali (hydrogenic) metals. | 7 | Physical Chemistry |
Ascorbic acid is a furan-based lactone of 2-ketogluconic acid. It contains an adjacent enediol adjacent to the carbonyl. This −C(OH)=C(OH)−C(=O)− structural pattern is characteristic of reductones, and increases the acidity of one of the enol hydroxyl groups. The deprotonated conjugate base is the ascorbate anion, which is stabilized by electron delocalization that results from resonance between two forms:
For this reason, ascorbic acid is much more acidic than would be expected if the compound contained only isolated hydroxyl groups. | 1 | Biochemistry |
Despite being larger and heavier than other bioaerosols, some studies show that pollen can be transported thousands of kilometers. They are a major source of wind-dispersed allergens, coming particularly from seasonal releases from grasses and trees. Tracking distance, transport, resources, and deposition of pollen to terrestrial and marine environments are useful for interpreting pollen records. | 7 | Physical Chemistry |
* [https://dx.doi.org/10.1016/1359-6454(95)00146-7 A one-parmenter approach to determining the critical conditions for the initiation of dynamic recrystallization], onset of DRX
* [https://dx.doi.org/10.1007/s11661-009-0029-5 Flow Curve Analysis of 17–4 PH Stainless Steel under Hot Compression Test], comprehensive study of DRX
* [http://www.tdx.cat/bitstream/handle/10803/6043/09Vggf09de11.pdf?sequence=9 Constitutive relations to model the hot flow of commercial purity copper, chapter 6], doctoral thesis by V.G. García, UPC (2004)
* [https://dx.doi.org/10.1016/j.matdes.2016.09.012 A review of dynamic recrystallization phenomena in metallic materials], Latest review paper on DRX
* [https://www.researchgate.net/publication/316989956_Cellular_Automaton_Simulation_of_Dynamic_Recrystallization_Introduction_into_Self-Organization_and_Emergence A Cellular Automaton Model of Dynamic Recrystallization: Introduction & Source Code], Software simulating DRX by CA: Introduction, [https://www.researchgate.net/publication/317013011_Self-Organization_Video_Sequence_Depicting_Numerical_Experiments_with_Cellular_Automaton_Model_of_Dynamic_Recrystallization_with_source-code_link Video of software run] | 8 | Metallurgy |
Vapor phase osmometry is well suited for the analysis of oligomers and short polymers while higher polymers can be analyzed using other techniques such as membrane osmometry and light scattering. As of 2008, VPO faces competition from matrix-assisted laser desorption ionisation mass spectrometry (MALDI-MS), but VPO still has some advantages when fragmentation of samples for mass spectrometry may be problematic. | 7 | Physical Chemistry |
Various methods for the production of singlet oxygen exist. Irradiation of oxygen gas in the presence of an organic dye as a sensitizer, such as rose bengal, methylene blue, or porphyrins—a photochemical method—results in its production. Large steady state concentrations of singlet oxygen are reported from the reaction of triplet excited state pyruvic acid with dissolved oxygen in water. Singlet oxygen can also be produced in non-photochemical, preparative chemical procedures. One chemical method involves the decomposition of triethylsilyl hydrotrioxide generated in situ from triethylsilane and ozone.
:(CH)SiH + O → (CH)SiOOOH → (CH)SiOH + O(Δ)
Another method uses the aqueous reaction of hydrogen peroxide with sodium hypochlorite:
: HO + NaOCl → O(Δ) + NaCl + HO
A third method liberates singlet oxygen via phosphite ozonides, which are, in turn, generated in situ such as triphenyl phosphite ozonide. Phosphite ozonides will decompose to give singlet oxygen:
:(RO)P + O → (RO)PO
:(RO)PO → (RO)PO + O(Δ)
An advantage of this method is that it is amenable to non-aqueous conditions. | 7 | Physical Chemistry |
Dielectrophoretic digital sorting method utilizes a semiconductor controlled array of electrodes in a microfluidic chip to trap single cells in Dielectrophoretic (DEP) cages. Cell identification is ensured by the combination of fluorescent markers with image observation. Precision delivery is ensured by the semiconductor controlled motion of DEP cages in the flow cell.
Hydrodynamic traps allow for the isolation of an individual cell in a "trap" at a single given time by passive microfluidic transport. The number of isolated cells can be manipulated based on the number of traps in the system.
The Laser Capture Microdissection technique utilizes a laser to dissect and separate individual cells, or sections, from tissue samples of interest. The methods involve the observation of a cell under a microscope, so that a section for analysis can be identified and labeled so that the laser can cut the cell. Then, the cell can be extracted for analysis.
Manual single cell picking is a method where cells in a suspension are viewed under a microscope and individually picked using a micropipette.
Microfluidics allows for the isolation of individual cells for further analyses. The following principles outline the various microfluidic processes for single-cell separation: droplet-in-oil based isolation, pneumatic membrane valving, and hydrodynamic cell traps. Droplet-in-oil based microfluidics uses oil-filled channels to hold separated aqueous droplets. This allows the single cell to be contained and isolated from the inside the oil based channels. Pneumatic membrane valves use the manipulation of air pressure, to isolate individual cells by membrane deflection. The manipulation of the pressure source allows the opening or closing of channels in a microfluidic network. Typically, the system requires an operator and is limited in throughput.
The technique Raman tweezers combines the use Raman spectroscopy and optical tweezers, which use a laser beam to trap and manipulate cells.
The development of hydrodynamic-based microfluidic biochips has been increasing over the years. In this technique, the cells are trapped in a particular region for single cell analysis (SCA). This usually occurs without any application of external force fields such as optical, electrical, magnetic or acoustic. There is a need to explore the insights of SCA in the cell's natural state, and development of these techniques is highly essential for that study. Researchers have highlighted the need to develop biochip devices to suit market and researcher demands. Hydrodynamic microfluidics facilitate the development of passive lab-on-chip applications. | 1 | Biochemistry |
Phosphagens, also known as macroergic compounds, are high energy storage compounds, also known as high-energy phosphate compounds, chiefly found in muscular tissue in animals. They allow a high-energy phosphate pool to be maintained in a concentration range, which, if it all were adenosine triphosphate (ATP), would create problems due to the ATP-consuming reactions in these tissues. As muscle tissues can have sudden demands for much energy, these compounds can maintain a reserve of high-energy phosphates that can be used as needed, to provide the energy that could not be immediately supplied by glycolysis or oxidative phosphorylation. Phosphagens supply immediate but limited energy.
The actual biomolecule used as a phosphagen is dependent on the organism. The majority of animals use arginine as phosphagen; however, the phylum Chordata (i.e., animals with spinal cords) use creatine. Creatine phosphate (CP), or phosphocreatine (PCr), is made from ATP by the enzyme creatine kinase in a reversible reaction:
* Creatine + ATP creatine phosphate + ADP + H (this reaction is Mg-dependent)
However, annelids (segmented worms) use a set of unique phosphagens; for example, earthworms use the compound lombricine.
Phosphagens were discovered by Philip Eggleton and his wife Grace Eggleton. | 1 | Biochemistry |
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