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Unfortunately, the Tsuji–Wilkinson decarbonylation is stoichiometric. The product bis(triphenylphosphine)rhodium carbonyl chloride is not readily converted back to a CO-free reagent. Above 200 °C, carbon monoxide RhCl(CO)(PPh) does decarbonylate, however these high temperatures are often prohibitive. The ideal Tsuji–Wilkinson decarbonylation would be by catalytic near ambient temperatures.
The reaction has been carried out in flow conditions at low temperatures in which a biphasic liquid-gas flow decarbonylation was developed employing N as a gas carrier. However, the temperature required for this reaction is 200 °C.
Significant improvements of the Tsuji–Wilkinson decarbonylation have been made by using cationic rhodium complexes with chelating bisphosphines. | 0 | Organic Chemistry |
Leigh and co-workers recently began to explore a strategy in which template ions could also play an active role in promoting the crucial final covalent bond forming reaction that captures the interlocked structure (i.e., the metal has a dual function, acting as a template for entwining the precursors and catalyzing covalent bond formation between the reactants). | 6 | Supramolecular Chemistry |
The calorimeter constants are used in constant pressure calorimetry to calculate the amount of heat required to achieve a certain raise in the temperature of the calorimeter's contents. | 7 | Physical Chemistry |
Microcystins—or cyanoginosins—are a class of toxins produced by certain freshwater cyanobacteria; primarily Microcystis aeruginosa but also other Microcystis, as well as members of the Planktothrix, Anabaena, Oscillatoria and Nostoc genera.
Microcystin-LR (i.e. X = leucine, Z = arginine) is the most toxic form of over 80 known toxic variants, and is also the most studied by chemists, pharmacologists, biologists, and ecologists. Microcystin-containing blooms are a problem worldwide, including China, Brazil, Australia, South Africa, the United States and much of Europe. Hartebeespoort Dam in South Africa is one of the most contaminated sites in Africa, and possibly in the world. | 2 | Environmental Chemistry |
IR Spectrum Table by Frequency
IR Spectra Table by Compound Class
To use an IR spectrum table, first need to find the frequency or compound in the first column, depending on which type of chart that is being used. Then find the corresponding values for absorption, appearance and other attributes. The value for absorption is usually in cm. | 7 | Physical Chemistry |
Electrochemistry is the study of processes driven through an applied potential at a solid-liquid or liquid-liquid interface. The behavior of an electrode-electrolyte interface is affected by the distribution of ions in the liquid phase next to the interface forming the electrical double layer. Adsorption and desorption events can be studied at atomically flat single crystal surfaces as a function of applied potential, time, and solution conditions using spectroscopy, scanning probe microscopy and surface X-ray scattering. These studies link traditional electrochemical techniques such as cyclic voltammetry to direct observations of interfacial processes. | 7 | Physical Chemistry |
PIK3CA frequently have gain of function mutations in urothelial cancer. Similar to PI3Ka, PI3Kb is expressed in many different cells, and it is mainly involved in the activation of platelets and development of thrombotic diseases. Studies have shown that PI3Kb contribute to tumor proliferation as well. Specifically, it has an important role in tumorigenesis in PTEN-negative cancers. It's reported that interfering with the gene for PI3Kb might be a therapeutic approach for high-risk bladder cancers with mutant PTEN and E-cadherin loss. Specific isoform inhibitors to PI3Kb is a potential treatment for PTEN-deficient cancers. | 1 | Biochemistry |
The Hüttenwerke Kayser smelter at Lünen in Germany installed an ISASMELT plant in 2002 to replace three blast furnaces and one Peirce-Smith converter used for smelting scrap copper. The company was subsequently bought by Norddeutsche Affinerie AG, which in turn became Aurubis.
The process used at the Lünen smelter involves charging the furnace with copper residues and scrap containing between 1 and 80% copper and then melting it in a reducing environment. This produces a "black copper phase" and a low-copper silica slag. Initially the black copper was converted to blister copper in the ISASMELT furnace. However, in 2011 the smelter was expanded as part of the "KRS Plus" project. A top-blown rotary converter is used to convert the black copper and the ISASMELT furnace runs continuously in smelting mode.
The installation of the ISASMELT furnace increased the overall copper recovery in the plant by reducing losses to slag, reduced the number of furnaces in operation, decreased the waste gas volume, and decreased energy consumption by more than 50%. The production capacity exceeds the original design by 40%.
Kandanshi
Atlantic Copper | 8 | Metallurgy |
Like hot black oxide, mid-temperature black oxide converts the surface of the metal to magnetite (FeO). However, mid-temperature black oxide blackens at a temperature of , significantly less than hot black oxide. This is advantageous because it is below the solution's boiling point, meaning there are no caustic fumes produced.
Since mid-temperature black oxide is most comparable to hot black oxide, it also can meet the military specification MIL-DTL-13924, as well as AMS 2485. | 7 | Physical Chemistry |
The number of workers in the United States exposed to beryllium vary but has been estimated to be as high as 800,000 during the 1960s and 1970s. A more recent study from 2004 estimated the number of exposed workers in the United States to be around 134,000.
The rate of workers becoming sensitized to beryllium varies based on genetics and exposure levels. In one study researchers found the prevalence of beryllium sensitization to range from 9–19% depending on the industry. Many workers who are found to be sensitive to beryllium also meet the diagnostic criteria for chronic beryllium disease. In one study of nuclear workers, among those who were sensitized to beryllium, 66% were found to have chronic beryllium disease as well. The rate of progression from beryllium sensitization to chronic beryllium disease has been estimated to be approximately 6–8% per year. Stopping exposure to beryllium in those sensitized has not been definitively shown to stop the progression to chronic beryllium disease.
The overall prevalence of chronic beryllium disease among workers exposed to beryllium has ranged from 1–5% depending on industry and time period of study.
The general population is unlikely to develop acute or chronic beryllium disease because ambient air levels of beryllium are normally very low (). However, a study found 1% of people living within 3/4 of a mile of a beryllium plant in Lorain, Ohio, had berylliosis after exposure to concentrations estimated to be less than 1 milligram per cubic metre of air. In the United States the Beryllium Case Registry contained 900 records, early cases relating to extraction and fluorescent lamp manufacture, later ones coming from the aerospace, ceramics and metallurgical industries. | 1 | Biochemistry |
The growth rates of calthemite stalactite straws, stalagmites and flowstone etc., is very much dependent on the supply rate and continuity of the saturated leachate solution to the location of CaCO deposition. The concentration of atmospheric CO in contact with the leachate, also has a large influence on how quickly the CaCO can precipitate from the leachate. Evaporation of the leachate solution and ambient atmospheric temperature appears to have very minimal influence on the CaCO deposition rate.
Calthemite straw stalactites precipitated (deposited) from hyperalkaline leachate have the potential to grow up to ≈200 times faster than normal cave speleothems precipitated from near neutral pH solution. One calthemite soda straw has been recorded as growing 2 mm per day over several consecutive days, when the leachate drip rate was a constant 11 minutes between drips. When the drip rate is more frequent than one drop per minute, there is no discernible deposition of CaCO at the tip of the stalactite (hence no growth) and the leachate solution falls to the ground where the CaCO is deposited to create a calthemite stalagmite. If the leachate supply to the stalactite straw's tip reduces to a level where the drip rate is greater than approximately 25 to 30 minutes between drops, there is a chance that the straw tip will calcify over and block up. New straw stalactites can often form next to a previously active, but now dry (dormant) straw, because the leachate has simply found an easier path through the micro cracks and voids in the concrete structure.
Despite both being composed of Calcium Carbonate, Calthemite straws are on average just 40% the mass per unit length of speleothem straws of equivalent external diameter. This is due to the different chemistry involved in creating the straws. The calthemite straws have a thin wall thickness and a less-dense calcium carbonate structure compared to speleothem straws.
Calthemite straws can vary in outside diameter as they grow in length. Changes in diameter can take a matter of days or weeks and are due to changes in drip rate over time. A slow dripping calthemite straw tends to be slightly larger in diameter than a fast-dripping straw. | 8 | Metallurgy |
It is possible to create IBIs for use by minimally trained monitoring personnel, however the precision obtainable is lower than that conducted by trained professionals. Safeguards to assure robustness in spite of potential misidentifications or protocol variations require careful testing. Ongoing quality control by established experts is needed to maintain data integrity, and the analysis of IBI results becomes more complex. Use of trained volunteers is being pioneered by government agencies responsible for monitoring large numbers of water bodies with limited resources, such as the Minnesota Pollution Control Agency (MPCA) and local volunteer stream monitoring programs supported by MPCA. EPA has published guidance to assist volunteer programs in formulating IBIs and related findings. While IBIs from such programs are legally admissible in US courts, defending the validity of conclusions based solely on such results is unlikely to be feasible.
Agreement among multiple IBIs from data collected by established professionals can be more conclusive. A case in point is the phenomenon that stream IBI scores indicate significant impairment, or partial ecological collapse where more than 10 to 15 percent of the immediately surrounding watershed is impervious due to urbanization. Identifying reasons for such impairments, and possible exceptions to these trends, are major research challenges for academics studying cumulative watershed effects, and the use of low-impact development techniques to mitigate the impacts of stormwater runoff pollution. | 2 | Environmental Chemistry |
Solid-phase microextraction (SPME), is a solid phase extraction technique that involves the use of a fiber coated with an extracting phase, that can be a liquid (polymer) or a solid (sorbent), which extracts different kinds of analytes (including both volatile and non-volatile) from different kinds of media, that can be in liquid or gas phase. The quantity of analyte extracted by the fibre is proportional to its concentration in the sample as long as equilibrium is reached or, in case of short time pre-equilibrium, with help of convection or agitation. | 3 | Analytical Chemistry |
* Citalopram: steps were taken to separate the more potent enantiomer, escitalopram.
* Thalidomide is a drug whose two enantiomers cause distinctly different effects from one another. The unforeseen teratogenicity of the (R)-(+)-isomer caused it to become an important case study of stereochemistry in medicine. Although it is possible to chemically isolate just the desired (S)-(−)-isomer from the racemic mixture, the two enantiomers rapidly interconvert in vivo; thus rendering their separation to be of little use.
* Methorphan is another drug whose two enantiomers possess very different binding profiles, with the L enantiomer being a potent opioid analgesic, and the D enantiomer being a commonly used over-the-counter cough suppressant which acts as an NMDA-antagonist but possesses nearly no opioid activity. In the case of morphinan, the eudysmic ratio is preserved after metabolism as the D and L metabolites possess the same pharmacological targets as the corresponding methorphan enantiomers, but are considerably more potent than their parent compounds.
* Amino acids are also an example of eudysmic ratio. Nearly all of the amino acids in the human body are called "L" amino acids; despite being chiral, the body almost exclusively creates and uses amino acids in this one configuration. D amino acids, the enantiomers — or "mirror images" — of the amino acids in the human body cannot be incorporated into proteins. D-aspartate and D-serine are two notable counterexamples, since they do not appear to ever be incorporated into proteins, but instead act individually as signalling molecules. However, mammals can metabolize significant amount of D amino acids by oxidizing them to alpha-ketoacids (most of which are non-chiral) and then transaminases can create L amino acids. There are no reasons to believe that humans are exceptional, they have all required enzymes (DDO, DAO). Some common foods contain near-racemic mixtures of amino acids. | 4 | Stereochemistry |
In the 1990s, Southern Peru Copper Corporation ("SPCC") was seeking to modernise its smelter at Ilo in southern Peru as part of 1997 commitment to the Peruvian government to capture at least 91.7% of the sulfur dioxide generated in its smelting operations by January 2007. It initially selected flash smelting technology to replace its reverberatory furnaces, at a cost of almost US$1 billion; however, one of the first actions following Grupo México's acquisition of ASARCO was to review the proposed Ilo smelter modernisation plans. | 8 | Metallurgy |
Cryoneurolysis is performed with a cryoprobe, which is composed of a hollow cannula that contains a smaller inner lumen. The pressurized coolant (nitrous oxide, carbon dioxide or liquid nitrogen) travels down the lumen and expands at the end of the lumen into the tip of the hollow cannula. No coolant exits the cryoprobe. The expansion of the pressurized liquid causes the surrounding area to cool (known as the Joule–Thomson effect) and the phase change of the liquid to gas also causes the surrounding area to cool. This causes a visible iceball to form and the tissue surrounding the end of the cryoprobe to freeze. The gas form of the coolant then travels up the length of the cryoprobe and is safely expelled. The tissue surrounding the end of the cryoprobe can reach as low as −88.5 °C with nitrous oxide as the coolant, and as low as −195.8 °C with liquid nitrogen. Temperatures below −100 °C are damaging to nerves.
Cryo-S Painless cryoanalgesia device is the next generation of apparatus used by many experts in the field since 1992. The working medium for Cryo-S Painless is carbon dioxide: (−78 °C) or nitrous oxide: (−89 °C), very efficient and easy to use gases. Cryo-S Painless is controlled by a microprocessor and all the parameters are displayed and monitored on a LCD screen. Mode selection probe, cleaning and freezing can be performed automatically using footswitch or touch screen which allows to keep the site of a procedure under sterile conditions. Electronic communication (chip system) between the connected probe and device allows recognition of optimal operating parameters and auto-configures to cryoprobe characteristics. Pressure and gas flow are set automatically, any manual adjustment is not necessary. Cryoprobe temperature, cylinder pressure, gas flow inside of cryoprobe and procedure time are displayed during freezing. Built-in voice communication Built-in neurostimulation (sensory, motor). | 1 | Biochemistry |
The reversible work is the maximal useful work which can be obtained, , and can only be fully utilized in an ideal reversible process. An irreversible process produces some work , which is less than . The lost work is then ; in other words, is the work which was lost or not exploited during the process due to irreversibilities. In terms of lost work, the theorem generally stateswhere is the rate at which work is lost, and is the rate at which entropy is generated. Time derivatives are denoted by dots. The theorem, as stated above, holds only for the entire thermodynamic universe - the system along with its surroundings, together:where the index "tot" denotes the total quantities produced within or by the entire universe.
Note that is a relative quantity, in that it is measured in relation to a specific thermal reservoir. In the above equations, is defined in reference to the environment reservoir, at . When comparing the actual process to an ideal, reversible process between the same endpoints (in order to evaluate , so as to find the value of ), only the heat interaction with the reference reservoir is allowed to vary. The heat interactions between the system and other reservoirs are kept the same. So, if a different reference reservoir is chosen, the theorem would read , where this time is in relation to , and in the corresponding reversible process, only the heat interaction with is different.
By integrating over the lifetime of the process, the theorem can also be expressed in terms of final quantities, rather than rates: . | 7 | Physical Chemistry |
Wood is a natural organic material consisting primarily of cellulose fibers embedded in a matrix of lignin. Regarding mechanical properties, the fibers are strong in tension, and the lignin matrix resists compression. Thus wood has been an important construction material since humans began building shelters and using boats. Wood to be used for construction work is commonly known as lumber or timber. In construction, wood is not only a structural material, but is also used to form the mould for concrete.
Wood-based materials are also extensively used for packaging (e.g. cardboard) and paper, which are both created from the refined pulp. The chemical pulping processes use a combination of high temperature and alkaline (kraft) or acidic (sulfite) chemicals to break the chemical bonds of the lignin before burning it out. | 7 | Physical Chemistry |
Two papers describe MgtE, a fourth Mg uptake protein in bacteria unrelated to MgtA/B or CorA. This gene has been sequenced and the protein, 312 amino acids in size, is predicted to contain either four or five TM spanning domains that are closely arranged in the C-terminal part of the protein (see figure). This region of the protein has been identified in the Pfam database as a conserved protein domain (PF01769) and species containing proteins that have this protein domain are roughly equally distributed throughout the Eubacteria and Archaea, although it is quite rare in comparison with the distribution of CorA. However, the diversity of the proteins containing the domain is significantly larger than that of the CorA domain. The Pfam database lists seven distinct groups of MgtE domain containing proteins, of which six contain an archaic or eubacterial member. The expression of MgtE is frequently controlled by a conserved RNA structure, YkoK leader or M-box.
The figure (right), adapted from Smith et al. (1995) and the PFAM database entry, shows the computer-predicted membrane topology of the MgtE protein in Bacillus firmus OF4. The TM domains are shown in light blue. The CBS domains, named for the protein they were identified in, cystathionine-beta synthase, shown in orange, are identified in the Pfam database as regulatory domains, but the mechanism of action has not yet been described. They are found in several voltage-gated chloride channels. The orientation in the membrane and the positions of the N- and C-termini are indicated. This figure is not drawn to scale. This transporter has recently had its structure solved by x-ray crystallography.
The MgtE gene was first identified by Smith et al. (1995) during a screen for CorA-like proteins in bacteria and complements the Mg-uptake-deficient S. typhimurium strain MM281 (corA mgtA mgtB), restoring wild type growth on standard media. The kinetics of Mg transport for the protein were not determined, as Mg was unavailable. As a substitute, the uptake of Co was measured and was shown to have a km of 82 μM and a Vmax of 354 pmol min 10 cells. Mg was a competitive inhibitor with a Ki of 50 μM—the Ki of Mg inhibition of Co uptake via CorA is 10 μM. A comparison of the available kinetic data for MgtA and CorA is shown in the table. Clearly, MgtE does not transport Co to the same degree as CorA, and the inhibition of transport by Mg is also less efficient, which suggests that the affinity of MgtE for Mg is lower than that of CorA. The strongest inhibitor of Co uptake was Zn, with a Ki of 20 μM. The transport of Zn by this protein may be as important as that of Mg.
The table shows a comparison of the transport kinetics of MgtE and CorA, and key kinetic parameter values for them are listed. As shown, the data has been generated at differing incubation temperatures. km and Ki are not significantly altered by the differing incubation temperature. Conversely, Vmax shows a strong positive correlation with temperature, hence the value of Co Vmax for MgtE is not directly comparable with the values for CorA. | 1 | Biochemistry |
For most purposes, ozone production would be a detrimental side effect of lamp operation. To prevent this, most germicidal lamps are treated to absorb the 185 nm mercury emission line (which is the longest wavelength of mercury light which will ionize oxygen).
In some cases (such as water sanitization), ozone production is precisely the point. This requires specialized lamps which do not have the surface treatment. | 5 | Photochemistry |
The carbonate pump, sometimes called the carbonate counter pump, starts with marine organisms at the ocean's surface producing particulate inorganic carbon (PIC) in the form of calcium carbonate (calcite or aragonite, CaCO). This CaCO is what forms hard body parts like shells. The formation of these shells increases atmospheric CO due to the production of CaCO in the following reaction with simplified stoichiometry:Coccolithophores, a nearly ubiquitous group of phytoplankton that produce shells of calcium carbonate, are the dominant contributors to the carbonate pump. Due to their abundance, coccolithophores have significant implications on carbonate chemistry, in the surface waters they inhabit and in the ocean below: they provide a large mechanism for the downward transport of CaCO. The air-sea CO flux induced by a marine biological community can be determined by the rain ratio - the proportion of carbon from calcium carbonate compared to that from organic carbon in particulate matter sinking to the ocean floor, (PIC/POC). The carbonate pump acts as a negative feedback on CO taken into the ocean by the solubility pump. It occurs with lesser magnitude than the solubility pump. | 9 | Geochemistry |
The thionyl group is SO, a sulfur atom plus an oxygen atom.
It occurs in compounds such as thionyl fluoride, SOF.
Thionyl chloride, SOCl, is a common reagent used in organic synthesis to convert carboxylic acids to acyl chlorides.
In organic chemistry, the thionyl group is known as a sulfoxide group or sulfinyl group, and has the general structure RS(=O)R'. | 0 | Organic Chemistry |
Grain boundaries can cause failure mechanically by embrittlement through solute segregation (see Hinkley Point A nuclear power station) but they also can detrimentally affect the electronic properties. In metal oxides it has been shown theoretically that at the grain boundaries in AlO and MgO the insulating properties can be significantly diminished. Using density functional theory computer simulations of grain boundaries have shown that the band gap can be reduced by up to 45%. In the case of metals grain boundaries increase the resistivity as the size of the grains relative to the mean free path of other scatters becomes significant. | 8 | Metallurgy |
There are relatively few CRESU apparatuses in existence for the simple reason that the gas throughput and pumping requirements are huge, which makes them expensive to run. Two of the leading centres have been the University of Rennes (France) and the University of Birmingham (UK). A more recent development has been a pulsed version of the CRESU, which requires far less gas and therefore smaller pumps. | 7 | Physical Chemistry |
Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe chemistry. In the Mond process, nickel tetracarbonyl is used to produce pure nickel. In organometallic chemistry, metal carbonyls serve as precursors for the preparation of other organometallic complexes.
Metal carbonyls are toxic by skin contact, inhalation or ingestion, in part because of their ability to carbonylate hemoglobin to give carboxyhemoglobin, which prevents the binding of oxygen. | 0 | Organic Chemistry |
Hydrogenated starch hydrolysates (HSHs), also known as polyglycitol syrup (INS 964), are mixtures of several sugar alcohols (a type of sugar substitute). Hydrogenated starch hydrolysates were developed by the Swedish company Lyckeby Starch in the 1960s. The HSH family of polyols is an approved food ingredient in Canada, Japan, and Australia. HSH sweeteners provide 40 to 90% sweetness relative to table sugar.
Hydrogenated starch hydrolysates are produced by the partial hydrolysis of starch – most often corn starch, but also potato starch or wheat starch. This creates dextrins (glucose and short glucose chains). The hydrolyzed starch (dextrin) then undergoes hydrogenation to convert the dextrins to sugar alcohols.
Hydrogenated starch hydrolysates are similar to sorbitol: if the starch is completely hydrolyzed so that only single glucose molecules remain, then after hydrogenation the result is sorbitol. Because in HSHs the starch is not completely hydrolyzed, a mixture of sorbitol, maltitol, and longer chain hydrogenated saccharides (such as maltotriitol) is produced. When no single polyol is dominant in the mix, the generic name hydrogenated starch hydrolysates is used. However, if 50% or more of the polyols in the mixture are of one type, it can be labeled as "sorbitol syrup", or "maltitol syrup", etc. | 0 | Organic Chemistry |
The enzyme N-myristoyltransferase (NMT) or glycylpeptide N-tetradecanoyltransferase is responsible for the irreversible addition of a myristoyl group to N-terminal or internal glycine residues of proteins. This modification can occur co-translationally or post-translationally. In vertebrates, this modification is carried about by two NMTs, NMT1 and NMT2, both of which are members of the GCN5 acetyltransferase superfamily. | 1 | Biochemistry |
Ceramic microstructures are most often analyzed by reflected visible-light microscopy in brightfield. Darkfield is used in limited circumstances, e.g., to reveal cracks. Polarized transmitted light is used with thin sections, where the contrast between grains comes from birefringence. Very fine microstructures may require the higher magnification and resolution of a scanning electron microscope (SEM) or confocal laser scanning microscope (CLSM). The cathodoluminescence microscope (CLM) is useful for distinguishing phases of refractories. The transmission electron microscope (TEM) and scanning acoustic microscope (SAM) have specialty applications in ceramography.
Ceramography is often done qualitatively, for comparison of the microstructure of a component to a standard for quality control or failure analysis purposes. Three common quantitative analyses of microstructures are grain size, second-phase content and porosity. Microstructures are measured by the principles of stereology, in which three-dimensional objects are evaluated in 2-D by projections or cross-sections. Microstructures exhibiting heterogeneous grain sizes, with certain grains growing very large, occur in diverse ceramic systems and this phenomenon is known as abnormal grain growth or AGG. The occurrence of AGG has consequences, positive or negative, on mechanical and chemical properties of ceramics and its identification is often the goal of ceramographic analysis.
Grain size can be measured by the line-fraction or area-fraction methods of ASTM E112. In the line-fraction methods, a statistical grain size is calculated from the number of grains or grain boundaries intersecting a line of known length or circle of known circumference. In the area-fraction method, the grain size is calculated from the number of grains inside a known area. In each case, the measurement is affected by secondary phases, porosity, preferred orientation, exponential distribution of sizes, and non-equiaxed grains. Image analysis can measure the shape factors of individual grains by ASTM E1382.
Second-phase content and porosity are measured the same way in a microstructure, such as ASTM E562. Procedure E562 is a point-fraction method based on the stereological principle of point fraction = volume fraction, i.e., P = V. Second-phase content in ceramics, such as carbide whiskers in an oxide matrix, is usually expressed as a mass fraction. Volume fractions can be converted to mass fractions if the density of each phase is known. Image analysis can measure porosity, pore-size distribution and volume fractions of secondary phases by ASTM E1245. Porosity measurements do not require etching. Multi-phase microstructures do not require etching if the contrast between phases is adequate, as is usually the case.
Grain size, porosity and second-phase content have all been correlated with ceramic properties such as mechanical strength σ by the Hall–Petch equation. Hardness, toughness, dielectric constant and many other properties are microstructure-dependent. | 8 | Metallurgy |
Gilbert studied for a Bachelor of Science at the University of Florida, from 1940 to 1942. He then moved to the University of Wisconsin–Madison for this PhD, which he obtained in 1945 under the supervision of Samuel M. McElvain. While at Wisconsin he met Carl Djerassi, with whom he would go on to form a lasting friendship. | 0 | Organic Chemistry |
The bacterial, archaeal and plant plastid code (translation table 11) is the DNA code used by bacteria, archaea, prokaryotic viruses and chloroplast proteins. It is essentially the same as the standard code, however there are some variations in alternative start codons. | 1 | Biochemistry |
The main use of Woollins reagent is the selenation of carbonyl compounds. For instance, Woollins reagent will convert a carbonyl into a selenocarbonyl. Additionally, Woollins' reagent has been used to selenonate carboxylic acids, alkenes, alkynes, and nitriles. | 0 | Organic Chemistry |
A monosubstituted cyclohexane is one in which there is one non-hydrogen substituent in the cyclohexane ring. The most energetically favorable conformation for a monosubstituted cyclohexane is the chair conformation with the non-hydrogen substituent in the equatorial position because it prevents high steric strain from 1,3 diaxial interactions. In methylcyclohexane the two chair conformers are not isoenergetic. The methyl group prefers the equatorial orientation. The preference of a substituent towards the equatorial conformation is measured in terms of its A value, which is the Gibbs free energy difference between the two chair conformations. A positive A value indicates preference towards the equatorial position. The magnitude of the A values ranges from nearly zero for very small substituents such as deuterium, to about 5 kcal/mol (21 kJ/mol) for very bulky substituents such as the tert-butyl group. Thus, the magnitude of the A value will also correspond to the preference for the equatorial position. Though an equatorial substituent has no 1,3 diaxial interaction that causes steric strain, it has a Gauche interaction in which an equatorial substituent repels the electron density from a neighboring equatorial substituent. | 4 | Stereochemistry |
A Newman projection is a drawing that helps visualize the 3-dimensional structure of a molecule. This projection most commonly sights down a carbon-carbon bond, making it a very useful way to visualize the stereochemistry of alkanes. A Newman projection visualizes the conformation of a chemical bond from front to back, with the front atom represented by the intersection of three lines (a dot) and the back atom as a circle. The front atom is called proximal, while the back atom is called distal. This type of representation clearly illustrates the specific dihedral angle between the proximal and distal atoms.
This projection is named after American chemist Melvin Spencer Newman, who introduced it in 1952 as a partial replacement for Fischer projections, which are unable to represent conformations and thus conformers properly. This diagram style is an alternative to a sawhorse projection, which views a carbon–carbon bond from an oblique angle, or a wedge-and-dash style, such as a Natta projection. These other styles can indicate the bonding and stereochemistry, but not as much conformational detail.
A Newman projection can also be used to study cyclic molecules, such as the chair conformation of cyclohexane:
Because of the free rotation around single bonds, there are various conformations for a single molecule. Up to six unique conformations may be drawn for any given chemical bond. Each conformation is drawn by rotation of either the proximal or distal atom 60 degrees. Of these six conformations, three will be in a staggered conformation, while the other three will be in an eclipsed conformation. These six conformations can be represented in a relative energy diagram.
A staggered projection appears to have the surrounding species equidistant from each other. This kind of conformation tends to experience both anti and gauche interactions. Anti interactions refer to the molecules (usually of the same type) sitting exactly opposite of each other at 180° on the Newman projection. Gauche interactions refer to molecules (also usually of the same type) being 60° from each other on a Newman projection. Anti interactions experience less steric strain than gauche interactions, but both experience less steric strain than the eclipsed conformation.
An eclipsed projection appears to have the surrounding species almost on top of each other. In reality, these species are in line with each other, but are drawn slightly staggered to help format the projection onto paper. These types of conformations are generally higher in energy due to increased bond strain. However, this strain can be somewhat lower if a hydrogen is eclipsed over a larger species, as opposed to two large species eclipsed over each other. | 4 | Stereochemistry |
Cytochrome c is widely believed to be localised solely in the mitochondrial intermembrane space under normal physiological conditions. The release of cytochrome c from mitochondria to the cytosol, where it activates the caspase family of proteases, is believed to be the primary trigger leading to the onset of apoptosis. Measuring the amount of cytochrome c leaking from mitochondria to cytosol, and out of the cell to culture medium, is a sensitive method to monitor the degree of apoptosis. However, detailed immuno-electronmicroscopic studies with rat tissues sections employing cytochrome c specific antibodies provide compelling evidence that cytochrome c under normal cellular conditions is also present at extramitochondrial locations. In pancreatic acinar cells and the anterior pituitary, strong and specific presence of cytochrome c was detected in zymogen granules and in growth hormone granules, respectively. In the pancreas, cytochrome c was also found in condensing vacuoles and in the acinar lumen. The extramitochondrial localisation of cytochrome c was shown to be specific as it was completely abolished upon adsorption of the primary antibody with purified cytochrome c. Besides cytochrome c, extramitochondrial localisation has also been observed for large numbers of other proteins including those encoded by mitochondrial DNA. This raises the possibility of the existence of yet-unidentified specific mechanisms for protein translocation from mitochondria to other cellular destinations. | 1 | Biochemistry |
In water solution, orthophosphoric acid and its three derived anions coexist according to the dissociation and recombination equilibria below
Values are at 25°C and 0 ionic strength.
The pK values are the pH values where the concentration of each species is equal to that of its conjugate bases. At pH 1 or lower, the phosphoric acid is practically undissociated. Around pH 4.7 (mid-way between the first two pK values) the dihydrogen phosphate ion, , is practically the only species present. Around pH 9.8 (mid-way between the second and third pK values) the monohydrogen phosphate ion, , is the only species present. At pH 13 or higher, the acid is completely dissociated as the phosphate ion, .
This means that salts of the mono- and di-phosphate ions can be selectively crystallised from aqueous solution by setting the pH value to either 4.7 or 9.8.
In effect, , and behave as separate weak acids because the successive pK differ by more than 4.
Phosphate can form many polymeric ions such as pyrophosphate, , and triphosphate, . The various metaphosphate ions (which are usually long linear polymers) have an empirical formula of and are found in many compounds. | 0 | Organic Chemistry |
The results of glycol adsorption, cation exchange capacity, X-ray diffraction, differential thermal analysis, and chemical tests all give data that may be used for quantitative estimations. After the quantities of organic matter, carbonates, free oxides, and nonclay minerals have been determined, the percentages of clay minerals are estimated using the appropriate glycol adsorption, cation exchange capacity, K20, and DTA data. The amount of illite is estimated from the K20 content since this is the only clay mineral containing potassium. | 9 | Geochemistry |
Site-directed spin labeling (SDSL) was pioneered in the laboratory of Dr. W.L. Hubbell. In SDSL, sites for attachment of spin labels are introduced into recombinantly expressed proteins by site-directed mutagenesis. Functional groups contained within the spin label determine their specificity. At neutral pH, protein thiol groups specifically react with the functional groups methanethiosulfonate, maleimide, and iodoacetamide, creating a covalent bond with the amino acid Cys.
Spin labels are a unique molecular reporter, in that they are paramagnetic (contain an unpaired electron). Spin labels were first synthesized in the laboratory of H. M. McConnell in 1965. Since then, a variety of nitroxide spin labels have enjoyed widespread use for the study of macromolecular structure and dynamics because of their stability and simple EPR signal.
The nitroxyl radical (N-O) is usually incorporated into a heterocyclic ring (e.g. pyrrolidine), and the unpaired electron is predominantly localized to the N-O bond. Once incorporated into the protein, a spin label's motions are dictated by its local environment. Because spin labels are exquisitely sensitive to motion, this has profound effects on its EPR spectrum.
The assembly of multi-subunit membrane protein complexes has also been studied using spin labeling. The binding of the PsaC subunit to the PsaA and PsaB subunits of the photosynthetic reaction center, Photosystem I, has been analyzed in great detail using this technique.
Dr. Ralf Langens group showed that SDSL with EPR (University of Southern California, Los Angeles) can be used to understand the structure of amyloid fibrils and the structure of membrane bound Parkinsons disease protein alpha-synuclein. A 2012 study generated a high resolution structure of IAPP fibrils using a combination of SDSL, pulse EPR and computational biology.
<br /> | 7 | Physical Chemistry |
Cyclic compounds may or may not exhibit aromaticity; benzene is an example of an aromatic cyclic compound, while cyclohexane is non-aromatic. In organic chemistry, the term aromaticity is used to describe a cyclic (ring-shaped), planar (flat) molecule that exhibits unusual stability as compared to other geometric or connective arrangements of the same set of atoms. As a result of their stability, it is very difficult to cause aromatic molecules to break apart and to react with other substances. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, but only aromatic rings have especial stability (low reactivity).
Since one of the most commonly encountered aromatic systems of compounds in organic chemistry is based on derivatives of the prototypical aromatic compound benzene (an aromatic hydrocarbon common in petroleum and its distillates), the word “aromatic” is occasionally used to refer informally to benzene derivatives, and this is how it was first defined. Nevertheless, many non-benzene aromatic compounds exist. In living organisms, for example, the most common aromatic rings are the double-ringed bases in RNA and DNA. A functional group or other substituent that is aromatic is called an aryl group.
The earliest use of the term “aromatic” was in an article by August Wilhelm Hofmann in 1855. Hofmann used the term for a class of benzene compounds, many of which do have odors (aromas), unlike pure saturated hydrocarbons. Today, there is no general relationship between aromaticity as a chemical property and the olfactory properties of such compounds (how they smell), although in 1855, before the structure of benzene or organic compounds was understood, chemists like Hofmann were beginning to understand that odiferous molecules from plants, such as terpenes, had chemical properties we recognize today are similar to unsaturated petroleum hydrocarbons like benzene.
In terms of the electronic nature of the molecule, aromaticity describes a conjugated system often made of alternating single and double bonds in a ring. This configuration allows for the electrons in the molecules pi system to be delocalized around the ring, increasing the molecules stability. The molecule cannot be represented by one structure, but rather a resonance hybrid of different structures, such as with the two resonance structures of benzene. These molecules cannot be found in either one of these representations, with the longer single bonds in one location and the shorter double bond in another (See Theory below). Rather, the molecule exhibits bond lengths in between those of single and double bonds. This commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds (cyclohexatriene), was developed by August Kekulé (see History section below). The model for benzene consists of two resonance forms, which corresponds to the double and single bonds superimposing to produce six one-and-a-half bonds. Benzene is a more stable molecule than would be expected without accounting for charge delocalization. | 4 | Stereochemistry |
The Goldich dissolution series is a method of predicting the relative stability or weathering rate of common igneous minerals on the Earth's surface, with minerals that form at higher temperatures and pressures less stable on the surface than minerals that form at lower temperatures and pressures. | 9 | Geochemistry |
(E)-4-Hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP or HMB-PP) is an intermediate of the MEP pathway (non-mevalonate pathway) of isoprenoid biosynthesis. The enzyme HMB-PP synthase (GcpE, IspG) catalyzes the conversion of 2-C-methyl--erythritol 2,4-cyclodiphosphate (MEcPP) into HMB-PP. HMB-PP is then converted further to isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) by HMB-PP reductase (LytB, IspH).
HMB-PP is an essential metabolite in most pathogenic bacteria including Mycobacterium tuberculosis as well as in malaria parasites, but is absent from the human host.
HMB-PP is the physiological activator ("phosphoantigen") for human Vγ9/Vδ2 T cells, the major γδ T cell population in peripheral blood. With a bioactivity of 0.1 nM it is 10,000-10,000,000 times more potent than any other natural compound, such as IPP or alkyl amines. HMB-PP functions in this capacity by binding the B30.2 domain of BTN3A1. | 1 | Biochemistry |
The term ‘acid sulfate soils’ (ASS) was coined by the Working Party on Nomenclature and Methods for the first International Symposium on Acid Sulfate Soils (1972, Wageningen) to mean soils that contain, or have the potential to produce, sulfuric acid in quantities that cause significant and long-lasting changes in key soil properties. This term was gradually adopted by the international scientific community for the sake of international consistency and cooperation. Prior to this, different regions used colloquial terms such as:
* argilla vitriolacea (Latin, ‘clay with sulfuric acid’ – coined by Carl Linnaeus);
* Kattekleigronden or Katte Klei (Dutch, ‘cat clay’);
* Gifterde (German, ‘cursed / poisoned earth’); and
* Maibolt (an Austro-Germanic spirit or creature that, when angered, would curse the soil to spoil crops).
The term ‘acid sulfate soil’ is useful for general discussion, but fails to capture nuances required for technical classification of soils. Additional terms such as ‘potential acid sulfate soil’ (PASS), ‘active acid sulfate soil’ (AASS) and ‘post-active acid sulfate soil’ (PAASS) helped researchers distinguish between the following:
* PASS: non-acidic soils that did not contain substantial quantities of sulfuric acid, but contained the necessary materials to produce it under certain conditions;
* AASS: soils that were acidic due to the presence of sulfuric acid; and
* PAASS: soils that were once active acid sulfate soils, but have since weathered or ‘ripened’ to the point they were similar to ‘normal’ sub-aerial soil in terms of their chemical and physical properties (e.g., pH and drainage).
As a single soil profile may contain PASS, AASS, and PAASS at different depths, the term ‘material’ was added as a modifier (i.e., PASS-material, AASS-material, and PAASS-material) to allow for more nuanced descriptions of complex soils. However, these terms are still somewhat awkward and unsuitable for technical classification. Additionally, acid sulfate soils and the variations thereof imply that acid sulfate soils are an altogether different type or class of soil, rather than a feature soils may exhibit under certain conditions. Consequently, there has been a gradual movement away from these terms in favour of more standardised, operationally-defined definitions. | 9 | Geochemistry |
With diffusion together with a uniform flow with velocity in the lateral direction, the autocorrelation is:
where is the average residence time if there is only a flow (no diffusion). | 7 | Physical Chemistry |
Unlike direct DNA damage, which occurs in areas directly exposed to UV-B light, reactive chemical species can travel through the body and affect other areas—possibly even inner organs. The traveling nature of the indirect DNA damage can be seen in the fact that the malignant melanoma can occur in places that are not directly illuminated by the sun—in contrast to basal-cell carcinoma and squamous cell carcinoma, which appear only on directly illuminated locations on the body. | 5 | Photochemistry |
In 2016, John Zhang and a mixed team of scientists from Mexico and New York used the spindle transfer technique to help a Jordanian woman to give birth to a baby boy. The mother had Leigh disease and already had four miscarriages and two children who had died of the disease. Valery Zukin, director of the Nadiya clinic in Kyiv, Ukraine, reported in June 2018 that doctors there had used the pronuclear transfer method of MRT to help four women give birth (three boys and a girl) and three women to become pregnant (one from Sweden); the team had 14 failed attempts. In January 2019 it was reported that seven babies had been born using MRT. The doctors had first gotten approval from an ethical committee and a review board of the Ukrainian Association of Reproductive Medicine and the Ukrainian Postgraduate Medical Academy, under the auspices of the Ukrainian Ministry of Healthcare; there was no law in the Ukraine against MRT. One of the first children, a boy, was born to a 34-year-old woman in January 2017, and genetic test results were reported as normal. In August and October 2017 the British HFEA authorized MRT for two women who had a genetic mutation in their mitichondria that causes myoclonic epilepsy with ragged red fibers. In January 2019, Embryotools, Barcelona, Spain announced that a 32-year-old Greek woman had become pregnant using the spindle transfer technique. MRT was not legal in Spain so they had performed the trial in Greece where there was no law against MRT. They were helped by the Institute of Life in Athens, Greece and had obtained approval from the Greek National Authority of Assisted Reproduction. The pregnant Greek woman had already had four failed IVF cycles and surgery twice for endometriosis.
In August 2017, in a letter to two clinics, including Zhang's, the FDA warned that the technique should not be marketed in the U.S. | 1 | Biochemistry |
Ferroin sulfate may be prepared by combining phenanthroline to ferrous sulfate in water.
:3 phen + Fe → [Fe(phen)]
The main reaction is 1-electron oxidation.
[Fe(phen)] → [Fe(phen)] + 1 e
Addition of sulfuric acid to an aqueous solution of [Fe(phen)] causes hydrolysis:
:[Fe(phen)] + 3 HSO + 6 HO → [Fe(OH)] + 3 [phenH]HSO | 3 | Analytical Chemistry |
Higher dietary intakes of magnesium correspond to lower diabetes incidence. For people with diabetes or at high risk of diabetes, magnesium supplementation lowers fasting glucose. | 1 | Biochemistry |
*4.A.1 The PTS Glucose-Glucoside (Glc) Family
*4.A.2 The PTS Fructose-Mannitol (Fru) Family
*4.A.3 The PTS Lactose-N,N'-Diacetylchitobiose-β-glucoside (Lac) Family
*4.A.4 The PTS Glucitol (Gut) Family
*4.A.5 The PTS Galactitol (Gat) Family
*4.A.6 The PTS Mannose-Fructose-Sorbose (Man) Family
*4.A.7 The PTS L-Ascorbate (L-Asc) Family | 1 | Biochemistry |
Organic peroxides are widely used to initiate polymerization of olefins, e.g. the formation of polyethylene. A key step is homolysis:
The tendency to homolyze is also exploited to modify polymers by grafting or visbreaking, or cross-link polymers to create a thermoset. When used for these purposes, the peroxide is highly diluted, so the heat generated by the exothermic decomposition is safely absorbed by the surrounding medium (e.g. polymer compound or emulsion). | 0 | Organic Chemistry |
Hammond's postulate is especially important when looking at the rate-limiting step of a reaction. However, one must be cautious when examining a multistep reaction or one with the possibility of rearrangements during an intermediate stage. In some cases, the final products appear in skewed ratios in favor of a more unstable product (called the kinetic product) rather than the more stable product (the thermodynamic product). In this case one must examine the rate-limiting step and the intermediates. Often, the rate-limiting step is the initial formation of an unstable species such as a carbocation. Then, once the carbocation is formed, subsequent rearrangements can occur. In these kinds of reactions, especially when run at lower temperatures, the reactants simply react before the rearrangements necessary to form a more stable intermediate have time to occur. At higher temperatures when microscopic reversal is easier, the more stable thermodynamic product is favored because these intermediates have time to rearrange. Whether run at high or low temperatures, the mixture of the kinetic and thermodynamic products eventually reach the same ratio, one in favor of the more stable thermodynamic product, when given time to equilibrate due to microreversal. | 7 | Physical Chemistry |
MCD can be used as an optical technique for the detection of electronic structure of both the ground states and excited states. It is also a strong addition to the more commonly used absorption spectroscopy, and there are two reasons that explain this. First, a transition buried under a stronger transition can appear in MCD if the first derivative of the absorption is much larger for the weaker transition or it is of the opposite sign. Second, MCD will be found where no absorption is detected at all if ΔA > (ΔA) but A , where (ΔA) and A are the minimum of ΔA and A that are detectable. Typically, (ΔA) and A are of the magnitudes around 10 and 10 respectively. So, a transition can only be detected in MCD, not in the absorption spectroscopy, if ΔA/A > 10. This happens in paramagnetic systems that are at lower temperature or that have sharp lines in the spectroscopy.
In biology, metalloproteins are the most likely candidates for MCD measurements, as the presence of metals with degenerate energy levels leads to strong MCD signals. In the case of ferric heme proteins, MCD is capable of determining both oxidation and spin state to a remarkably exquisite degree. In regular proteins, MCD is capable of stoichiometrically measuring the tryptophan content of proteins, assuming there are no other competing absorbers in the spectroscopic system.
In addition, the application of MCD spectroscopy greatly improved the level of understanding in the ferrous non-heme systems because of the direct observation of the d–d transitions, which generally can not be obtained in optical absorption spectroscopy owing to the weak extinction coefficients and are often electron paramagnetic resonance silent due to relatively large ground-state sublevel splittings and fast relaxation times. | 7 | Physical Chemistry |
The most common standard in Europe is ISO 9454-1 (also known as DIN EN 29454-1).
This standard specifies each flux by a four-character code: flux type, base, activator, and form. The form is often omitted.
Therefore, 1.1.2 means rosin flux with halides. | 8 | Metallurgy |
Types B, R, and S thermocouples use platinum or a platinum/rhodium alloy for each conductor. These are among the most stable thermocouples, but have lower sensitivity than other types, approximately 10 μV/°C. Type B, R, and S thermocouples are usually used only for high-temperature measurements due to their high cost and low sensitivity. For type R and S thermocouples, HTX platinum wire can be used in place of the pure platinum leg to strengthen the thermocouple and prevent failures from grain growth that can occur in high temperature and harsh conditions. | 8 | Metallurgy |
Samarium iodide is easily prepared in nearly quantitative yields from samarium metal and either diiodomethane or 1,2-diiodoethane. When prepared in this way, its solutions is most often used without purification of the inorganic reagent.
Solid, solvent-free SmI forms by high temperature decomposition of samarium(III) iodide (SmI). | 0 | Organic Chemistry |
k+-transporting ATPase - karyotype - KduI/IolB isomerase family - kilobase - kinase - Klenow fragment - Knock-down - knock-out - knock-out experiment - knockout - Kozak sequence | 1 | Biochemistry |
In 2009, Stephen Bustin led an international group of scientists including Mikael Kubista to put together a set of guidelines on how to perform qPCR and what forms of data should be collected and published in the process. This also allowed editors and reviewers of scientific journals to employ the guidelines when looking over a submitted paper that included qPCR data. Thus, the guidelines were set up as a sort of checklist for each step of the procedure with certain items being marked as essential (E) when submitting data for publication and others marked as just desirable (D).
An additional version of the guidelines was published in September 2010 for use with fluorescence-based quantitative real-time PCR. It also acted as a précis for the broader form of the guidelines. Other researchers have been creating further versions for specific forms of qPCR that may require a supplementary or different set of items to check, including single-cell qPCR and digital PCR (dPCR). Appropriate adherence to the existing MIQE guidelines has also been overviewed in other scientific areas, including photobiomodulation and clinical biomarkers.
It was noted by Bustin in 2014 (and again by him in 2017) that there was some amount of uptake and usage of the MIQE guidelines within the scientific community, but there were still far too many published papers with qPCR experiments that lacked even the most basic of data presentation and proper confirmation of effectiveness for said data. These studies retained major reproducibility issues, where the conclusions of their evidence could not be replicated by other researchers, throwing the initial results into doubt. All of this was despite many papers directly citing Bustin's original MIQE publication, but not following through on the guideline checklist of material in their own experiments. However, some researchers have pointed out at least some success, with a number of papers being rejected by academic journals for publication due to failing to pass MIQE checklists. Other studies have been retracted after the fact once their lack of proper data to pass the MIQE guidelines was noted and publicly pointed out to the journal editors. | 1 | Biochemistry |
In 1929, the conversion of oleic acid to stearic acid in the presence of hydrazine was observed. The short-lived intermediate diimide was not implicated in this reductive process until the 1960s. Since that time, several methods of generating transient amounts of diimide have been developed. In the presence of unpolarized alkenes, alkynes or allenes, diimide is converted into dinitrogen with reduction (net addition of dihydrogen) of the unsaturated functionality. Diimide formation is the rate-limiting step of the process, and a concerted mechanism involving cis-diimide has been proposed. This reduction represents a metal-free alternative to catalytic hydrogenation reductions, and does not lead to the cleavage of sensitive O–O and N–O bonds. | 0 | Organic Chemistry |
Patina ( or ) is a thin layer that variously forms on the surface of copper, brass, bronze, and similar metals and metal alloys (tarnish produced by oxidation or other chemical processes), or certain stones and wooden furniture (sheen produced by age, wear, and polishing), or any similar acquired change of a surface through age and exposure.
Additionally, the term is used to describe the aging of high-quality leather. The patinas on leather goods are unique to the type of leather, frequency of use, and exposure.
Patinas can provide a protective covering to materials that would otherwise be damaged by corrosion or weathering. They may also be aesthetically appealing. | 8 | Metallurgy |
Some organic matter not already in the soil comes from groundwater. When the groundwater saturates the soil or sediment around it, organic matter can freely move between the phases. Groundwater has its own sources of natural organic matter including:
* organic matter deposits, such as kerogen and coal.
* soil and sediment organic matter.
* organic matter infiltrating into the subsurface from rivers, lakes, and marine systems."
Organisms decompose into organic matter, which is then transported and recycled. Not all biomass migrates, some is rather stationary, turning only over the course of millions of years. | 0 | Organic Chemistry |
Deflagration (Lat: de + flagrare, to burn down) is subsonic combustion in which a pre-mixed flame propagates through an explosive or a mixture of fuel and oxidizer. Deflagrations in high and low explosives or fuel–oxidizer mixtures may transition to a detonation depending upon confinement and other factors. Most fires found in daily life are diffusion flames. Deflagrations with flame speeds in the range of 1 m/s differ from detonations which propagate supersonically with detonation velocities in the range of km/s. | 7 | Physical Chemistry |
The photocytes present in Amphipholis squamata have been found to contain a golgi apparatus and rough endoplasmic reticulum. They have also been found to contain up to six different kinds of vesicles within their cytoplasm. | 1 | Biochemistry |
Drospirenone is marketed in combination with an estrogen under a variety of brand names throughout the world. Among others, it is marketed in combination with ethinylestradiol under the brand names Yasmin and Yaz, in combination with estetrol under the brand name Nextstellis, and in combination with estradiol under the brand name Angeliq. | 4 | Stereochemistry |
In the presence of copper(II) chloride, methanesulfonyl chloride will add across alkynes to form β-chloro sulfones. | 0 | Organic Chemistry |
Following multiphoton or tunnel ionization the electron is being accelerated by inverse Bremsstrahlung and can collide with the nearby molecules and generate new electrons through collisions. If the pulse duration is long, the newly ionized electrons can be accelerated and eventually avalanche or cascade ionization follows. Once the density of the electrons reaches a critical value, breakdown occurs and high density plasma is created which has no memory of the laser pulse. So, the criterion for the shortness of a pulse in dense media is as follows: A pulse interacting with a dense matter is considered to be short if during the interaction the threshold for the avalanche ionization is not reached. At the first glance this definition may appear to be too limiting. Fortunately, due to the delicately balanced behavior of the pulses in dense media, the threshold cannot be reached easily. The phenomenon responsible for the balance is the intensity clamping through the onset of filamentation process during the propagation of strong laser pulses in dense media.
A potentially important development to LIBS involves the use of a short laser pulse as a spectroscopic source. In this method, a plasma column is created as a result of focusing ultrafast laser pulses in a gas. The self-luminous plasma is far superior in terms of low level of continuum and also smaller line broadening. This is attributed to the lower density of the plasma in the case of short laser pulses due to the defocusing effects which limits the intensity of the pulse in the interaction region and thus prevents further multiphoton/tunnel ionization of the gas. | 7 | Physical Chemistry |
There are two common mechanisms by which the size of a particular restriction fragment can vary. In the first schematic, a small segment of the genome is being detected by a DNA probe (thicker line). In allele A, the genome is cleaved by a restriction enzyme at three nearby sites (triangles), but only the rightmost fragment will be detected by the probe. In allele a, restriction site 2 has been lost by a mutation, so the probe now detects the larger fused fragment running from sites 1 to 3. The second diagram shows how this fragment size variation would look on a Southern blot, and how each allele (two per individual) might be inherited in members of a family.
In the third schematic, the probe and restriction enzyme are chosen to detect a region of the genome that includes a variable number tandem repeat (VNTR) segment (boxes in schematic diagram). In allele c, there are five repeats in the VNTR, and the probe detects a longer fragment between the two restriction sites. In allele d, there are only two repeats in the VNTR, so the probe detects a shorter fragment between the same two restriction sites. Other genetic processes, such as insertions, deletions, translocations, and inversions, can also lead to polymorphisms. RFLP tests require much larger samples of DNA than do short tandem repeat (STR) tests. | 1 | Biochemistry |
The above techniques can be combined with computational methods to estimate staining levels without staining the cell. These approaches, generally, rely on training a deep-convolutional neural network to perform imaging remapping, converting the bright-field or phase image into a fluorescent image. By decoupling the training corpus from the cells under investigation, these approaches provide an avenue for using stains that are otherwise incompatible with live cell imaging, such as anti-body staining. | 1 | Biochemistry |
The Angeli–Rimini reaction is an organic reaction between an aldehyde and N-hydroxybenzenesulfonamide in presence of base forming a hydroxamic acid.
The other reaction product is a sulfinic acid. The reaction was discovered by the two Italian chemists Angelo Angeli and Enrico Rimini (1874–1917), and was published in 1896. | 3 | Analytical Chemistry |
In oceanography, a prime example of a limiting factor is a limiting nutrient. Nutrient availability in freshwater and marine environments plays a critical role in determining what organisms survive and thrive. Nutrients are the building blocks of all living organisms, as they support biological activity. They are required to make proteins, DNA, membranes, organelles, and exoskeletons. The major elements that constitute >95% of organic matter mass are carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus. Minor elements are iron, manganese, cobalt, zinc and copper. These minor elements are often only present in trace amounts but they are key as co-limiting factors as parts of enzymes, transporters, vitamins and amino acids. Within aquatic environments, nitrogen and phosphorus are leading contenders for most limiting nutrients.
Discovery of the Redfield ratio was a major insight that helped understand the relationship between nutrient availability in seawater and their relative abundance in organisms. Redfield was able to notice elemental consistencies between carbon, nitrogen and phosphorus when looking at larger organisms living in the ocean (C:N:P = 106:16:1). He also observed consistencies in nutrients within the water column; nitrate to phosphate ratio was 16:1. The overarching idea was that the environment fundamentally influences the organisms that grow in it and the growing organisms fundamentally influence the environment. Redfield's opening statement in his 1934 paper explains "It is now well recognized that the growth of plankton in the surface layers of the sea is limited in part by the quantities of phosphate and nitrate available for their use and that the changes in the relative quantities of certain substances in seawater are determined in their relative proportions by biological activity". Deviations from Redfield can be used to infer elemental limitations. Limiting nutrients can be discussed in terms of dissolved nutrients, suspended particles and sinking particles, among others. When discussing dissolved nutrient stoichiometry, large deviations from the original Redfield ratio can determine if an environment is phosphorus limited or nitrogen limited. When discussing suspended particle stoichiometry, higher N:P ratios are noted in oligotrophic waters (environments dominated by cyanobacteria; low latitudes/equator) and lower N:P ratios are noted in nutrient rich ecosystems (environments dominated by diatoms; high latitudes/poles).
Many areas are severely nitrogen limited, but phosphorus limitation has also been observed. In many instances trace metals or co-limitation occur. Co-limitations refer to where two or more nutrients simultaneously limit a process. Pinpointing a single limiting factor can be challenging, as nutrient demand varies between organisms, life cycles, and environmental conditions (e.g. thermal stress can increase demand on nutrients for biological repairs). | 7 | Physical Chemistry |
Hess's law states that enthalpy changes are additive. Thus the value of the standard enthalpy of reaction can be calculated from standard enthalpies of formation of products and reactants as follows:
Here, the first sum is over all products and the second over all reactants, and are the stoichiometric coefficients of products and reactants respectively, and are the standard enthalpies of formation of products and reactants respectively, and the </sup> superscript indicates standard state values. This may be considered as the sum of two (real or fictitious) reactions:
:Reactants → Elements (in their standard states)
and Elements → Products <br> | 7 | Physical Chemistry |
The height h of a liquid column is given by Jurin's law
where is the liquid-air surface tension (force/unit length), θ is the contact angle, ρ is the density of liquid (mass/volume), g is the local acceleration due to gravity (length/square of time), and r is the radius of tube.
As r is in the denominator, the thinner the space in which the liquid can travel, the further up it goes. Likewise, lighter liquid and lower gravity increase the height of the column.
For a water-filled glass tube in air at standard laboratory conditions, at 20°C, , and . Because water spreads on clean glass, the effective equilibrium contact angle is approximately zero. For these values, the height of the water column is
Thus for a radius glass tube in lab conditions given above, the water would rise an unnoticeable . However, for a radius tube, the water would rise , and for a radius tube, the water would rise . | 7 | Physical Chemistry |
Beryllium derivatives and reagents are often prepared by alkylation of beryllium chloride. Examples of known organoberyllium compounds are dineopentylberyllium, beryllocene (CpBe), diallylberyllium (by exchange reaction of diethyl beryllium with triallyl boron), bis(1,3-trimethylsilylallyl)beryllium and Be(mes)2. Ligands can also be aryls and alkynyls. | 0 | Organic Chemistry |
The Gibbs–Thomson effect, in common physics usage, refers to variations in vapor pressure or chemical potential across a curved surface or interface. The existence of a positive interfacial energy will increase the energy required to form small particles with high curvature, and these particles will exhibit an increased vapor pressure. See Ostwald–Freundlich equation.
More specifically, the Gibbs–Thomson effect refers to the observation that small crystals are in equilibrium with their liquid melt at a lower temperature than large crystals. In cases of confined geometry, such as liquids contained within porous media, this leads to a depression in the freezing point / melting point that is inversely proportional to the pore size, as given by the Gibbs–Thomson equation. | 7 | Physical Chemistry |
If the quasi-steady-state hypothesis is assumed in addition to BFEI hypothesis, then the complex concentration can be assumed to be in a stationary (steady) state according to the Briggs–Haldane hypothesis, and the GEBIK equations become
which are written in a form similar to the classical Micaelis-Menten equations for any substrate and product. Here, the equations also show that the various isotopologue and isotopomer substrates appear as competing species. Eqs. () for isotopic compositions, Eq. () for the fractionation factor and Eq. () for the enrichment factor equally applies to the GEBIK equations under the BFEI and QSS hypothesis. | 7 | Physical Chemistry |
Cementite changes from ferromagnetic to paramagnetic upon heating to its Curie temperature of approximately .
A natural iron carbide (containing minor amounts of nickel and cobalt) occurs in iron meteorites and is called cohenite after the German mineralogist Emil Cohen, who first described it. | 8 | Metallurgy |
An inverse agonist can have effects similar to those of an antagonist, but causes a distinct set of downstream biological responses. Constitutively active receptors that exhibit intrinsic or basal activity can have inverse agonists, which not only block the effects of binding agonists like a classical antagonist but also inhibit the basal activity of the receptor. Many drugs previously classified as antagonists are now beginning to be reclassified as inverse agonists because of the discovery of constitutive active receptors. Antihistamines, originally classified as antagonists of histamine H receptors have been reclassified as inverse agonists. | 1 | Biochemistry |
The Staudinger reaction is a chemical reaction of an organic azide with a phosphine or phosphite produces an iminophosphorane. The reaction was discovered by and named after Hermann Staudinger. The reaction follows this stoichiometry:
:RP + RN → RP=NR + N | 0 | Organic Chemistry |
Because the urea conversion is incomplete, the urea must be separated from the unconverted reactants, including the ammonium carbamate. Various commercial urea processes are characterized by the conditions under which urea forms and the way that unconverted reactants are further processed. | 7 | Physical Chemistry |
The plausibility that life was imported to Earth from elsewhere was tested by subjecting plant seeds to 1.5 years of exposure to solar UV, solar and galactic cosmic radiation, temperature fluctuations, and space vacuum outside the International Space Station. Of the 2100 exposed wild-type Arabidopsis thaliana and Nicotiana tabacum (tobacco) seeds, 23% produced viable plants after being returned to Earth. Germination was delayed in seeds shielded from solar light, yet full survival was attained, which indicates that longer space travel would be possible for seeds embedded in an opaque matrix. The team conclude that a naked, seed-like entity could have survived exposure to solar UV radiation during a hypothetical transfer from Mars to Earth, and even if seeds do not survive, components (e.g., their DNA) might survive transfer over cosmic distances. | 1 | Biochemistry |
In geometry, a sphere packing is an arrangement of non-overlapping spheres within a containing space. The spheres considered are usually all of identical size, and the space is usually three-dimensional Euclidean space. However, sphere packing problems can be generalised to consider unequal spheres, spaces of other dimensions (where the problem becomes circle packing in two dimensions, or hypersphere packing in higher dimensions) or to non-Euclidean spaces such as hyperbolic space.
A typical sphere packing problem is to find an arrangement in which the spheres fill as much of the space as possible. The proportion of space filled by the spheres is called the packing density of the arrangement. As the local density of a packing in an infinite space can vary depending on the volume over which it is measured, the problem is usually to maximise the average or asymptotic density, measured over a large enough volume.
For equal spheres in three dimensions, the densest packing uses approximately 74% of the volume. A random packing of equal spheres generally has a density around 63.5%. | 3 | Analytical Chemistry |
The line-operated vacuum tube receiver was invented in 1925 by Edward S. Rogers, Sr. The unit operated with 5 Rogers AC vacuum tubes and the Rogers Battery-Eliminator Power Unit (power supply). This unit was later marketed for $120 as "Type 120". He established the Toronto station CFRB (an abbreviation of Canadas First Rogers Batteryless') to promote sales of the product. Batteryless radios were not introduced into the United States until May 1926 and then into Europe in 1927.
Crystal radio receivers are a very simple kind of batteryless radio receiver. They do not need a battery or power source, except for the power that they receive from radio waves using their long outdoor wire antenna. Sharp Electronics first electrical product was a batteryless crystal radio introduced in 1925. It was Japans first -- and sold extremely well.
Thermoelectricity was widely used in the remote parts of the Soviet Union from the 1920s to power radios. The equipment comprised some bi-metal rods (thermocouples), one end of which could be inserted into the fireplace to get hot with the other end left out in the cold.
After the Second World War, kerosene radios were made in Moscow for use in rural areas. These all-wave radios were powered by the kerosene lamp hanging above them. A group of thermocouples was heated internally to by the flame. Fins cooled the outside to about . The temperature differential generated enough current to operate the low-drain receiver.
Foot-operated radio or pedal radio was once used in Australia. Other ways of achieving the same function are clockwork radio, hand crank radio and solar radio, especially for the Royal Flying Doctor Service and School of the Air.
As part of an energy harvesting electronics system, some batteryless radios render electricity to storage by means of storage capacitors. In this batteryless type of radio, the storage capacitors cache the electricity as static on layers of dielectric instead of chemical changes, providing energy like batteries do but batteryless. This can be quite effective. Storage capacitors recharge millions of times, they are relatively cheap, somewhat insensitive to temperature, and they never need replacing -- which is why they are usually soldered on. As part of an energy autarkic or energy harvesting batteryless radio, therefore, storage capacitors are an integral part, storing electricity like battery does for lean energy periods, but in a batteryless way which is more sustainable. About 15 billion batteries are consumed every year worldwide. | 7 | Physical Chemistry |
In organic chemistry, diazirines are a class of organic molecules consisting of a carbon bound to two nitrogen atoms, which are double-bonded to each other, forming a cyclopropene-like ring, 3H-diazirine (). They are isomeric with diazocarbon groups (), and like them can serve as precursors for carbenes by loss of a molecule of dinitrogen. For example, irradiation of diazirines with ultraviolet light leads to carbene insertion into various , , and bonds. Hence, diazirines have grown in popularity as small, photo-reactive, crosslinking reagents. They are often used in photoaffinity labeling studies to observe a variety of interactions, including ligand-receptor, ligand-enzyme, protein-protein, and protein-nucleic acid interactions. | 5 | Photochemistry |
In chemistry, a strong electrolyte is a solute that completely, or almost completely, ionizes or dissociates in a solution. These ions are good conductors of electric current in the solution.
Originally, a "strong electrolyte" was defined as a chemical compound that, when in aqueous solution, is a good conductor of electricity. With a greater understanding of the properties of ions in solution, its definition was replaced by the present one.
A concentrated solution of this strong electrolyte has a lower vapor pressure than that of pure water at the same temperature. Strong acids, strong bases and soluble ionic salts that are not weak acids or weak bases are strong electrolytes. | 3 | Analytical Chemistry |
In chemistry, a disulfide (or disulphide in British English) is a compound containing a functional group or the anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups.
In inorganic chemistry, the anion appears in a few rare minerals, but the functional group has tremendous importance in biochemistry. Disulfide bridges formed between thiol groups in two cysteine residues are an important component of the secondary and tertiary structure of proteins.
Compounds of the form are usually called persulfides instead. | 0 | Organic Chemistry |
In organic chemistry, pentanonide is a functional group which is composed of a cyclic ketal of a diol with 3-pentanone. It is seen in amcinafal (triamcinolone pentanonide). | 0 | Organic Chemistry |
Dimethyl malonate is a diester derivative of malonic acid. It is a common reagent for organic synthesis used, for example, as a precursor for barbituric acid. It is also used in the malonic ester synthesis. It can be synthesized from dimethoxymethane and carbon monoxide.
Dimethyl malonate is used extensively in the fragrance industry as a raw material in the synthesis of jasmonates. For example, methyl dihydrojasmonate is synthesized from cyclopentanone, pentanal and dimethyl malonate. Hedione is used in almost all fine fragrances and is found in Christian Diors Eau Sauvage and "Diorella", Hermes "Voyage dHermes Parfum", Calvin Kleins "CKOne", Chanels "Chanel No. 19", and Mark Jacobs "Blush", among others. As of 2009, Hedione was Firmenich's top selling compound by volume.
Hebei Chengxin is the world's largest producer of dimethyl malonate by volume and uses a chloroacetic acid/sodium cyanide process developed in the 1940s. | 0 | Organic Chemistry |
Kinetic studies show that malate dehydrogenase enzymatic activity is ordered. The cofactor NAD/NADH is bound to the enzyme before the substrate. The Km value for malate, i.e., the concentration at which the enzyme activity is half-maximal, is 2 mM. The Kcat value is 259.2 s. | 1 | Biochemistry |
The term clone is used in horticulture to refer to descendants of a single plant which were produced by vegetative reproduction or apomixis. Many horticultural plant cultivars are clones, having been derived from a single individual, multiplied by some process other than sexual reproduction. As an example, some European cultivars of grapes represent clones that have been propagated for over two millennia. Other examples are potato and banana.
Grafting can be regarded as cloning, since all the shoots and branches coming from the graft are genetically a clone of a single individual, but this particular kind of cloning has not come under ethical scrutiny and is generally treated as an entirely different kind of operation.
Many trees, shrubs, vines, ferns and other herbaceous perennials form clonal colonies naturally. Parts of an individual plant may become detached by fragmentation and grow on to become separate clonal individuals. A common example is in the vegetative reproduction of moss and liverwort gametophyte clones by means of gemmae. Some vascular plants e.g. dandelion and certain viviparous grasses also form seeds asexually, termed apomixis, resulting in clonal populations of genetically identical individuals. | 1 | Biochemistry |
The parent metallacyclopentadiene, or metallole, has the formula LM(CH). Most arise from the coupling of two alkynes at a low valent metal centers such as derivatives of Co(I) and Zr(II). Late metal derivatives (Co, Ni) are intermediates in the metal-catalysed trimerization of alkynes to arenes. Early metal derivatives, i.e. derivatives of Ti and Zr, are used stoichiometrically. For example, the zirconacyclopentadiene CpZrCMe is a useful carrier for CMe. Some of the oldest metallacycles are the ferroles, which are dimetallacyclopentadiene complexes of the formula Fe(CR)(CO). They are derived from coupling of alkynes as well as from the desulfurization of thiophenes.
The parent metallacyclobenzenes have the formula LM(CH). They can be viewed as derivatives of benzene wherein a CH center has been replaced by a transition metal complex. | 0 | Organic Chemistry |
* Methylphosphine and dimethylphosphine (garlic-metallic, two of the most potent odorants known)
* Phosphine (zinc phosphide poisoned bait)
* Diacetyl (butter flavor)
* Acetoin (butter flavor)
* Nerolin (orange flowers)
* Tetrahydrothiophene (added to natural gas)
* 2,4,6-Trichloroanisole (cork taint)
* Substituted pyrazines | 0 | Organic Chemistry |
Previous studies have shown that progesterone supports the normal development of neurons in the brain, and that the hormone has a protective effect on damaged brain tissue. It has been observed in animal models that females have reduced susceptibility to traumatic brain injury and this protective effect has been hypothesized to be caused by increased circulating levels of estrogen and progesterone in females. | 0 | Organic Chemistry |
Microtubules formed from pure tubulin undergo subunit uptake and loss at ends by both random exchange diffusion, and by a directional (treadmilling) element. Treadmilling is inefficient, and for microtubules at steady state: the Wegner s-value (the reciprocal of the number of molecular events required for the net uptake of a subunit) is equal to 0.0005-0.001; i.e., it requires >1000 events. Microtubule treadmilling with pure tubulin also occurs with growing microtubules and is enhanced by proteins that bind to ends. Rapid treadmilling occurs in cells.
FtsZ treadmilling
The bacterial tubulin homolog FtsZ is one of the best documented treadmilling polymers. FtsZ assembles into protofilaments that are one subunit thick, which can further associate into small patches of parallel protofilaments. Single filaments and/or patches have been demonstrated to treadmill in vitro and inside bacterial cells. A Monte Carlo model of FtsZ treadmilling has been designed, based on a conformational change of subunits upon polymerization and GTP hydrolysis. | 1 | Biochemistry |
There are actually several physical mechanisms that produce the elastic forces within the network chains as a rubber sample is stretched. Two of these arise from entropy changes and one is associated with the distortion of the molecular bond angles along the chain backbone. These three mechanisms are immediately apparent when a moderately thick rubber sample is stretched manually. Initially, the rubber feels quite stiff, i.e. the force must be increased at a high rate with respect to the strain. At intermediate strains, the required increase in force is much lower to cause the same amount of stretch. Finally, as the sample approaches the breaking point, its stiffness increases markedly. What the observer is noticing are the changes in the modulus of elasticity that are due to the different molecular mechanisms. These regions can be seen in Fig. 1, a typical stress vs. strain measurement for natural rubber. The three mechanisms (labelled Ia, Ib and II) predominantly correspond to the regions shown on the plot. The concept of entropy comes to us from the area mathematical physics called statistical mechanics which is concerned with the study of large thermal systems, e.g. rubber networks at room temperature. Although the detailed behavior of the constituent chains are random and far too complex to study individually, we can obtain very useful information about their average behavior from a statistical mechanics analysis of a large sample. There are no other examples of how entropy changes can produce a force in our everyday experience. One may regard the entropic forces in polymer chains as arising from the thermal collisions that their constituent atoms experience with the surrounding material. It is this constant jostling that produces a resisting (elastic) force in the chains as they are forced to become straight. While stretching a rubber sample is the most common example of elasticity, it also occurs when rubber is compressed. Compression may be thought of as a two dimensional expansion as when a balloon is inflated. The molecular mechanisms that produce the elastic force are the same for all types of strain.
When these elastic force models are combined with the complex morphology of the network, it is not possible to obtain simple analytic formulae to predict the macroscopic stress. It is only via numerical simulations on computers that it is possible to capture the complex interaction between the molecular forces and the network morphology to predict the stress and ultimate failure of a rubber sample as it is strained. | 7 | Physical Chemistry |
The main advantage of locating a space power station in geostationary orbit is that the antenna geometry stays constant, and so keeping the antennas lined up is simpler. Another advantage is that nearly continuous power transmission is immediately available as soon as the first space power station is placed in orbit, LEO requires several satellites before they are producing nearly continuous power.
Power beaming from geostationary orbit by microwaves carries the difficulty that the required optical aperture sizes are very large. For example, the 1978 NASA SPS study required a 1 km diameter transmitting antenna and a 10 km diameter receiving rectenna for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although they have increased atmospheric absorption and even potential beam blockage by rain or water droplets. Because of the thinned array curse, it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.
A collection of LEO (low earth orbit) space power stations has been proposed as a precursor to GEO (geostationary orbit) space-based solar power. | 7 | Physical Chemistry |
Resazurin (7-Hydroxy-3H-phenoxazin-3-one 10-oxide) is a phenoxazine dye that is weakly fluorescent, nontoxic, cell-permeable, and redox‐sensitive. Resazurin has a blue to purple color above pH 6.5 and an orange color below pH 3.8. It is used in microbiological, cellular, and enzymatic assays because it can be irreversibly reduced to the pink-colored and highly fluorescent resorufin (7-Hydroxy-3H-phenoxazin-3-one). At circum-neutral pH, resorufin can be detected by visual observation of its pink color or by fluorimetry, with an excitation maximum at 530-570 nm and an emission maximum at 580-590 nm.
When a solution containing resorufin is submitted to reducing conditions (E of this same solution is increased, dihydroresorufin is oxidized back to resorufin, and this reversible reaction can be used to monitor if the redox potential of a culture medium remains at a sufficiently low level for anaerobic organisms.
Resazurin solution has one of the highest values known of Kreft's dichromaticity index. This means that it has a large change in perceived color hue when the thickness or concentration of observed sample increases or decreases.
Usually, resazurin is available commercially as the sodium salt. | 3 | Analytical Chemistry |
Almost all functional transcripts are derived from known genes. The only exceptions are a small number of transcripts that might play a direct role in regulating gene expression near the prompters of known genes. (See Enhancer RNA.)
Gene occupy most of prokaryotic genomes so most of their genomes are transcribed. Many eukaryotic genomes are very large and known genes may take up only a fraction of the genome. In mammals, for example, known genes only account for 40-50% of the genome. Nevertheless, identified transcripts often map to a much larger fraction of the genome suggesting that the transcriptome contains spurious transcripts that do not come from genes. Some of these transcripipts are known to be non-functional because they map to transcribed pseudogenes or degenerative transposons and viruses. Others map to unidentified regions of the genome that may be junk DNA.
Spurious transcription is very common in eukaryotes, especially those with large genomes that might contain a lot of junk DNA. Some scientists claim that if a transcript has not been assigned to a known gene then the default assumption must be that it is junk RNA until it has been shown to be functional. This would mean that much of the transcriptome in species with large genomes is probably junk RNA. (See Non-coding RNA)
The transcriptome includes the transcripts of protein-coding genes (mRNA plus introns) as well as the transcripts of non-coding genes (functional RNAs plus introns).
*Ribosomal RNA/rRNA: Usually the most abundant RNA in the transcriptome.
*Long non-coding RNA/lncRNA: Non-coding RNA transcripts that are more than 200 nucleotides long. Members of this group comprise the largest fraction of the non-coding transcriptome other than introns. It is not known how many of these transcripts are functional and how many are junk RNA.
*transfer RNA/tRNA
*micro RNA/miRNA: 19-24 nucleotides (nt) long. Micro RNAs up- or downregulate expression levels of mRNAs by the process of RNA interference at the post-transcriptional level.
*small interfering RNA/siRNA: 20-24 nt
*small nucleolar RNA/snoRNA
*Piwi-interacting RNA/piRNA: 24-31 nt. They interact with Piwi proteins of the Argonaute family and have a function in targeting and cleaving transposons.
*enhancer RNA/eRNA: | 1 | Biochemistry |
Sulfur dioxide is a convenient and widely used source of the sulfonyl functional group. Specifically, Sulfur dioxide participates in cycloaddition reactions with dienes.
The industrially useful solvent sulfolane is prepared by addition of sulfur dioxide to buta-1,3-diene followed by hydrogenation of the resulting sulfolene. | 0 | Organic Chemistry |
Salt spray testing is popular because it is relatively inexpensive, quick, well standardized, and reasonably repeatable. Although there may be a weak correlation between the duration in salt spray test and the expected life of a coating in certain coatings such as hot-dip galvanized steel, this test has gained worldwide popularity due to low cost and quick results. Most Salt Spray Chambers today are being used NOT to predict the corrosion resistance of a coating, but to maintain coating processes such as pre-treatment and painting, electroplating, galvanizing, and the like, on a comparative basis. For example, pre-treated + painted components must pass 96 hours Neutral Salt Spray, to be accepted for production. Failure to meet this requirement implies instability in the chemical process of the pre-treatment, or the paint quality, which must be addressed immediately so that the upcoming batches are of the desired quality. The longer the accelerated corrosion test, the longer the process remains out of control, and larger is the loss in the form of non-conforming batches.
The principal application of the salt spray test is, therefore, enabling quick comparisons to be made between actual and expected corrosion resistance. Most commonly, the time taken for oxides to appear on the samples under test is compared to expectations, to determine whether the test is passed or failed. For this reason, the salt spray test is most often deployed in a quality audit role, where, for example, it can be used to check the effectiveness of a production process, such as the surface coating of a metallic part.
The salt spray test has little application in predicting how materials or surface coatings will resist corrosion in the real world, because it does not create, replicate or accelerate real-world corrosive conditions. Cyclic corrosion testing is better suited to this. | 8 | Metallurgy |
The form of the crucible has varied through time, with designs reflecting the process for which they are used, as well as regional variation. The earliest crucible forms derive from the sixth/fifth millennium B.C. in Eastern Europe and Iran. | 3 | Analytical Chemistry |
The excretion of urea is called ureotelism. Land animals, mainly amphibians and mammals, convert ammonia into urea, a process which occurs in the liver and kidney. These animals are called ureotelic. Urea is a less toxic compound than ammonia; two nitrogen atoms are eliminated through it and less water is needed for its excretion. It requires 0.05 L of water to excrete 1 g of nitrogen, approximately only 10% of that required in ammonotelic organisms. | 1 | Biochemistry |
Dislocations in a crystal lattice are line defects that are associated with local stress fields. Dislocations allow shear at lower stress than that needed for a perfect crystal structure. The local stress fields result in interactions between the dislocations which then result in strain hardening or cold working. | 3 | Analytical Chemistry |
In 2018, RT001 was given to a patient with amyotrophic lateral sclerosis (ALS) under a "compassionate use scheme". | 1 | Biochemistry |
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