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Kenneth Ross MacKenzie (June 15, 1912 – July 3, 2002) was an American nuclear physicist. Together with Dale R. Corson and Emilio Segrè, he synthesized the element astatine, in 1940. MacKenzie received his PhD under Ernest Lawrence at Lawrence Livermore National Laboratory. Lawrence, MacKenzie, and their colleagues devised the first cyclotron.
MacKenzie was a professor of physics at the University of California, Los Angeles (UCLA), where he and Reg Richardson built UCLAs first cyclotron and later a bevatron. MacKenzie devised MacKenzie buckets which are plasma sources created by lining vacuum chamber walls with permanent magnets of alternating polarity to suppress plasma electron losses, that are widely used to this day. He later traveled around the world, helping to troubleshoot various countrys cyclotron problems. Later in life, he studied plasma physics and dark matter. | 1 | Applied and Interdisciplinary Chemistry |
Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made from seaweed (macroalgae) it can be known as seaweed fuel or seaweed oil.
In December 2022, ExxonMobil, the last large oil company to invest in algae biofuels, ended its research funding.
Algal fuels boast high yields, a high ignition point, and can be cultivated with minimal impact on freshwater resources. | 1 | Applied and Interdisciplinary Chemistry |
Supramolecular chemistry has been used to demonstrate computation functions on a molecular scale. In many cases, photonic or chemical signals have been used in these components, but electrical interfacing of these units has also been shown by supramolecular signal transduction devices. Data storage has been accomplished by the use of molecular switches with photochromic and photoisomerizable units, by electrochromic and redox-switchable units, and even by molecular motion. Synthetic molecular logic gates have been demonstrated on a conceptual level. Even full-scale computations have been achieved by semi-synthetic DNA computers. | 0 | Theoretical and Fundamental Chemistry |
It is surprising to note that In 1980, there was no single chiral stationary phase available in the market for performing chiral chromatography. However, In late 1980s the subject of enantioselective chromatography attracted growing interest, particularly under the drive of the institution of Okamoto in Japan, the teams of Pirkle, and Armstrong in the US, Schurig and König in Germany, Lindner in Austria, and Francotte in Switzerland . The Polysaccharides, amylose and cellulose, form the most abundant chiral polymers on earth. These naturally occurring polysaccharides form basis for an important class of chiral selectors. | 0 | Theoretical and Fundamental Chemistry |
3-Methylcrotonyl-CoA (β-Methylcrotonyl-CoA or MC-CoA) is an intermediate in the metabolism of leucine.
It is found in mitochondria, where it is formed from isovaleryl-coenzyme A by isovaleryl coenzyme A dehydrogenase. It then reacts with CO to yield 3-Methylcrotonyl-CoA carboxylase. | 1 | Applied and Interdisciplinary Chemistry |
* Ligand-gated ion channels such as the nicotinic acetylcholine receptor and GABA receptor are composed of five subunits arranged around a central pore that opens to allow ions to pass through. There are many different subunits available that can come together in a wide variety of combinations to form different subtypes of the ion channel. Sometimes the channel can be made from only one type of subunit, such as the α7 nicotinic receptor, which is made up from five α7 subunits, and so is a [http://en.wiktionary.org/wiki/homomer homomer] rather than a heteromer, but more commonly several different types of subunit will come together to form a heteromeric complex (e.g., the α4β2 nicotinic receptor, which is made up from two α4 subunits and three β2 subunits). Because the different ion channel subtypes are expressed to different extents in different tissues, this allows selective modulation of ion transport and means that a single neurotransmitter can produce varying effects depending on where in the body it is released.
* G protein-coupled receptors are composed of seven membrane-spanning alpha-helical segments that are usually linked together into a single folded chain to form the receptor complex. However, research has demonstrated that a number of GPCRs are also capable of forming heteromers from a combination of two or more individual GPCR subunits under some circumstances, especially where several different GPCRs are densely expressed in the same neuron. Such heteromers may be between receptors from the same family (e.g., adenosine A/A heteromers and dopamine D/D and D/D heteromers) or between entirely unrelated receptors such as CB/A, glutamate mGluR / adenosine A heteromers, cannabinoid CB / dopamine D heteromers, and even CB/A/D heterotrimers where three different receptors have come together to form a heteromer. The ligand binding properties and intracellular trafficking pathways of GPCR heteromers usually show elements from both parent receptors, but may also produce quite unexpected pharmacological effects, making such heteromers an important focus of current research. | 1 | Applied and Interdisciplinary Chemistry |
The principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, animal agriculture, factories, and motor vehicles. These also include power plants, which use electric power generators that account for a quarter of nitrogen oxides and two-thirds of sulfur dioxide within the atmosphere. Industrial acid rain is a substantial problem in China and Russia and areas downwind from them. These areas all burn sulfur-containing coal to generate heat and electricity.
The problem of acid rain has not only increased with population and industrial growth, but has become more widespread. The use of tall smokestacks to reduce local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulation; dispersal from these taller stacks causes pollutants to be carried farther, causing widespread ecological damage. Often deposition occurs a considerable distance downwind of the emissions, with mountainous regions tending to receive the greatest deposition (because of their higher rainfall). An example of this effect is the low pH of rain which falls in Scandinavia. Regarding low pH and pH imbalances in correlation to acid rain, low levels, or those under the pH value of 7, are considered acidic. Acid rain falls at a pH value of roughly 4, making it harmful to consume for humans. When these low pH levels fall in specific regions, they not only affect the environment but also human health. With acidic pH levels in humans comes hair loss, low urinary pH, severe mineral imbalances, constipation, and many cases of chronic disorders like Fibromyalgia and Basal Carcinoma. | 1 | Applied and Interdisciplinary Chemistry |
TFA is the precursor to many other fluorinated compounds such as trifluoroacetic anhydride, trifluoroperacetic acid, and 2,2,2-trifluoroethanol. It is a reagent used in organic synthesis because of a combination of convenient properties: volatility, solubility in organic solvents, and its strength as an acid. TFA is also less oxidizing than sulfuric acid but more readily available in anhydrous form than many other acids. One complication to its use is that TFA forms an azeotrope with water (b. p. 105 °C).
TFA is popularly used as a strong acid to remove protecting groups such as Boc used in organic chemistry and peptide synthesis.
At a low concentration, TFA is used as an ion pairing agent in liquid chromatography (HPLC) of organic compounds, particularly peptides and small proteins. TFA is a versatile solvent for NMR spectroscopy (for materials stable in acid). It is also used as a calibrant in mass spectrometry.
TFA is used to produce trifluoroacetate salts. | 0 | Theoretical and Fundamental Chemistry |
In the beginning the X-ray crystallography did not have a very good resolution so the initial focus was on substrate derived inhibitors instead of structurally based. The Neu5Ac-derived 2-deoxy-α-D-N-acetylneuraminic acid (2-deoxy- α-Neu5Ac) was the first template used and also the first inhibitor tried in vivo in a mouse model of an influenza infection. The unsubstituted template showed minor effect. Another template Neu5Ac2en (DANA) was tried under same conditions and showed good in vivo effect. With new crystal structure images of the enzyme and Neu5Ac complex emerging and Neu5Ac2en confirmed as an in vivo inhibitor, the focus was on making structure based DANA derivatives. With better X-ray crystal structure a number of important residues in the active site were identified, specifically C4 hydroxyl group. Better effect was achieved by substituting the C4 hydroxyl group with a more basic group, for example an amino group. Further analysis showed that a larger group could be accommodated in the active site. 4-amino-4-deoxy-Neu5Ac2en and 4-deoxy-4-guanidino-Neu5Ac2en were synthesized and proved to be competitive inhibitors for viral neuraminidase and significantly inhibited both A and B influenza replication in vitro and in vivo. 4-deoxy-4-guanidino-Neu5Ac2en showed not only to be the better inhibitor but also showed considerable lower affinity for other isoforms of neuraminidase. For these reasons 4-deoxy-4-guanidino-Neu5Ac2en was selected as the main drug candidate under the name Zanamivir. High polar nature and rapid excretion contribute to the drugs low bioavailability and rapid elimination. | 1 | Applied and Interdisciplinary Chemistry |
Greece was an early adopter of the concept of green Infrastructure with the invention of Greek agora. Agoras were meeting spaces that were built for social conversations and allowed Greeks to converse in public. Many were built across Greece, and some incorporated nature as a design aspect, giving nature a space among the public. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry the reactivity–selectivity principle or RSP states that a more reactive chemical compound or reactive intermediate is less selective in chemical reactions. In this context selectivity represents the ratio of reaction rates.
This principle was generally accepted until the 1970s when too many exceptions started to appear. The principle is now considered obsolete.
A classic example of perceived RSP found in older organic chemistry textbooks concerns the free radical halogenation of simple alkanes. Whereas the relatively unreactive bromine reacts with 2-methylbutane predominantly to 2-bromo-2-methylbutane, the reaction with much more reactive chlorine results in a mixture of all four regioisomers.
Another example of RSP can be found in the selectivity of the reaction of certain carbocations with azides and water. The very stable triphenylmethyl carbocation derived from solvolysis of the corresponding triphenylmethyl chloride reacts 100 times faster with the azide anion than with water. When the carbocation is the very reactive tertiary adamantane carbocation (as judged from diminished rate of solvolysis) this difference is only a factor of 10.
Constant or inverse relationships are just as frequent. For example, a group of 3- and 4-substituted pyridines in their reactivity quantified by their pKa show the same selectivity in their reactions with a group of alkylating reagents.
The reason for the early success of RSP was that the experiments involved very reactive intermediates with reactivities close to kinetic diffusion control and as a result the more reactive intermediate appeared to react slower with the faster substrate.
General relationships between reactivity and selectivity in chemical reactions can successfully be explained by Hammond's postulate.
When reactivity-selectivity relationships do exist they signify different reaction modes. In one study the reactivity of two different free radical species (A, sulfur, B carbon) towards addition to simple alkenes such as acrylonitrile, vinyl acetate and acrylamide was examined.
The sulfur radical was found to be more reactive (6*10 vs. 1*10 M.s) and less selective (selectivity ratio 76 vs 1200) than the carbon radical. In this case, the effect can be explained by extending the Bell–Evans–Polanyi principle with a factor accounting for transfer of charge from the reactants to the transition state of the reaction which can be calculated in silico:
with the activation energy and the reaction enthalpy change. With the electrophilic sulfur radical the charge transfer is largest with electron-rich alkenes such as acrylonitrile but the resulting reduction in activation energy (β is negative) is offset by a reduced enthalpy. With the nucleophilic carbon radical on the other hand both enthalpy and polar effects have the same direction thus extending the activation energy range. | 0 | Theoretical and Fundamental Chemistry |
Let us define a non-dimensional scalar variable or progress variable such that at the unburnt mixture and at the burnt gas side. For example, if is the unburnt gas temperature and is the burnt gas temperature, then the non-dimensional temperature can be defined as
The progress variable could be any scalar, i.e., we could have chosen the concentration of a reactant as a progress variable. Since the reaction sheet is infinitely thin, at any point in the flow field, we can find the value of to be either unity or zero. The transition from zero to unity occurs instantaneously at the reaction sheet. Therefore, the probability density function for the progress variable is given by
where and are the probability of finding unburnt and burnt mixture, respectively and is the Dirac delta function. By definition, the normalization condition leads to
It can be seen that the mean progress variable,
is nothing but the probability of finding burnt gas at location and at the time . The density function is completely described by the mean progress variable, as we can write (suppressing the variables )
Assuming constant pressure and constant molecular weight, ideal gas law can be shown to reduce to
where is the heat release parameter. Using the above relation, the mean density can be calculated as follows
The Favre averaging of the progress variable is given by
Combining the two expressions, we find
and hence
The density average is | 1 | Applied and Interdisciplinary Chemistry |
With further increases of temperature and density, fusion processes produce nuclides only up to nickel-56 (which decays later to iron); heavier elements (those beyond Ni) are created mainly by neutron capture. The slow capture of neutrons, the s-process, produces about half of elements beyond iron. The other half are produced by rapid neutron capture, the r-process, which probably occurs in core-collapse supernovae and neutron star mergers. | 0 | Theoretical and Fundamental Chemistry |
Adenylate Kinase 2 (AK2) deficiency in humans causes hematopoietic defects associated with sensorineural deafness. Reticular dysgenesis is an autosomal recessive form of human combined immunodeficiency. It is also characterized by an impaired lymphoid maturation and early differentiation arrest in the myeloid lineage. AK2 deficiency results in absent or a large decrease in the expression of proteins. AK2 is specifically expressed in the stria vascularis of the inner ear which indicates why individuals with an AK2 deficiency will have sensorineural deafness. | 1 | Applied and Interdisciplinary Chemistry |
During the many years that cassette decks were popular, many audio magazines published comparative measurements of the performance characteristics of the wide variety of different tapes that were available in the marketplace. These measurements typically included parameters such as MOL, SOL, frequency response at 0-dB and −20-dB re Dolby Level, signal-to-noise ratio, modulation noise, bias level, and sensitivity. The first figure shows frequency response plots for sample TypeI, TypeII, and TypeIV cassette tapes comparing their MOL, SOL, and 0-dB performance.
The second figure shows the frequency response performance of typical TypeI, TypeII, and TypeIV cassette tapes, obtained for a number of different input signal levels, using a high quality Pioneer CT-93 stereo cassette deck from the 1990s. For each of the three tape formulations, the record/replay characteristics of the cassette deck were aligned with the relevant IEC Reference Tape, and each tested tape was measured with the bias and equalization unchanged from that reference position. The record/replay frequency response was tested at four levels: +6VU, 0VU, −10VU and −20VU (Dolby Level is marked at +3VU for the CT-93). Thus, these plots provide data
on the linearity of the different tape formulations at both high and moderate recording levels. It is interesting to note that the TypeI tape shows +6VU and at 0VU responses that are much flatter than that of the TypeII tape. At +6VU, the TypeII tape displays significant amounts of signal level compression across the entire frequency range, reducing to about 2dB of signal compression between 80Hz and 1kHz.
Some representative measured performance characteristics of a small number of commercially available tape types are presented in the table below. | 0 | Theoretical and Fundamental Chemistry |
Oxidoreductases are enzymes that catalyze the transfer of a hydride ion between a substrate and a cofactor, in many cases, particularly those in metabolic reactions, that cofator is a form of nicotinamide adenine dinucleotide. Nicotinamide adenine dinucleotide phosphate (NADPH) is used in anabolic reactions while nicotinamide adenine dinucleotide (NAD+) is used in catabolic reactions. | 1 | Applied and Interdisciplinary Chemistry |
Hyperspectral remote sensing is used in a wide array of applications. Although originally developed for mining and geology (the ability of hyperspectral imaging to identify various minerals makes it ideal for the mining and oil industries, where it can be used to look for ore and oil), it has now spread into fields as widespread as ecology and surveillance, as well as historical manuscript research, such as the imaging of the Archimedes Palimpsest. This technology is continually becoming more available to the public. Organizations such as NASA and the USGS have catalogues of various minerals and their spectral signatures, and have posted them online to make them readily available for researchers. On a smaller scale, NIR hyperspectral imaging can be used to rapidly monitor the application of pesticides to individual seeds for quality control of the optimum dose and homogeneous coverage. | 0 | Theoretical and Fundamental Chemistry |
In an Iowa prairie restoration project, meadow voles experienced an initial population increase during the initial stage of vegetation succession (old field dominated by foxtail grass (Setaria spp.), red clover (Trifolium pratense), annual ragweed (Ambrosia artemisiifolia), alfalfa (Medicago sativa), and thistles (Cirsium spp.). However, populations reached their peak abundance during the perennial grass stage of succession from old field to tallgrass prairie. Meadow vole habitat devoid of tree cover and grasses dominated the herb layer. with low tolerance for habitat variation (i. e., a species that is intolerant of variations in habitat, is restricted to few habitats, and/or uses habitats less evenly than tolerant species).
In most areas, meadow voles clearly prefer habitat with dense vegetation. In tallgrass prairie at Pipestone National Monument, they were positively associated with dense vegetation and litter. The variables important to meadow vole habitat in Virginia include vegetative cover reaching a height of 8 to 16 inches (20–41 cm) and presence of litter. Meadow voles appeared to be randomly distributed within a grassland habitat in southern Quebec. Grant and Morris were not able to establish any association of meadow vole abundance with particular plant species. They were also unable to distinguish between food and cover as the determining factor in meadow vole association with dense vegetation. In South Dakota, meadow voles prefer grasslands to Rocky Mountain juniper (Juniperus scopulorum) woodlands. In New Mexico, meadow voles were captured in stands of grasses, wild rose (Rosa sp.), prickly pear (Opuntia sp.), and various forbs; meadow voles were also captured in wet areas with tall marsh grasses.
Open habitat with a thick mat of perennial grass favors voles. In west-central Illinois, they were the most common small mammals on Indian grass (Sorghastrum nutans)-dominated and switchgrass (Panicum virgatum)-dominated study plots. They were present in very low numbers on orchard grass (Dactylis glomerata)-dominated plots. The most stable population occurred on unburned big bluestem (Andropogon gerardii)-dominated plots. In Ontario, meadow voles and white-footed mice (Peromyscus leucopus) occur together in ecotones. Meadow voles were the most common small mammals in oak savanna/tallgrass prairie dominated by northern pin oak (Quercus ellipsoidalis) and grasses including bluejoint reedgrass (Calamagrostis canadensis), prairie cordgrass (Sporobolus michauxianus), big bluestem, switchgrass, and Indian grass.
In Michigan, strip clearcuts in a conifer swamp resulted in an increase in the relative abundance of meadow voles. They were most abundant in clearcut strip interiors and least abundant in uncut strip interiors. Slash burning did not appear to affect meadow vole numbers about 1.5 years after treatment. | 1 | Applied and Interdisciplinary Chemistry |
In 2018, researchers from the Moscow Institute of Physics and Technology (MIPT), the Technological Institute for Superhard and Novel Carbon Materials (TISNCM), and the National University of Science and Technology (MISIS) announced a prototype using 2-micron thick layers of Ni foil sandwiched between 200 10-micron diamond converters. It produced a power output of about 1 μW at for power density of 10 μW/cm. At those values, its energy density would be approximately 3.3 Wh/g over its 100-year half-life, about 10 times that of conventional electrochemical batteries. This research was published in April 2018 in the Diamond and Related Materials journal. | 0 | Theoretical and Fundamental Chemistry |
Sphingolipidoses are a group of diseases that are associated with the accumulation of sphingolipids which have not been degraded correctly, normally due to a defect in a glycoside hydrolase enzyme. Sphingolipidoses are typically inherited, and their effects depend on which enzyme is affected, and the degree of impairment. One notable example is Niemann–Pick disease which can cause pain and damage to neural networks. | 0 | Theoretical and Fundamental Chemistry |
This mechanism is found very commonly in everyday life, including central heating, air conditioning, steam turbines, and in many other machines. Forced convection is often encountered by engineers designing or analyzing heat exchangers, pipe flow, and flow over a plate at a different temperature than the stream (the case of a shuttle wing during re-entry, for example). | 0 | Theoretical and Fundamental Chemistry |
In semiconductor physics, this equation is called the drift–diffusion equation. The word "drift" is related to drift current and drift velocity. The equation is normally written:
where
* and are the concentrations (densities) of electrons and holes, respectively,
* is the elementary charge,
* and are the electric currents due to electrons and holes respectively,
* and are the corresponding "particle currents" of electrons and holes respectively,
* represents carrier generation and recombination ( for generation of electron-hole pairs, for recombination.)
* is the electric field vector
* and are electron and hole mobility.
The diffusion coefficient and mobility are related by the Einstein relation as above:
where is the Boltzmann constant and is absolute temperature. The drift current and diffusion current refer separately to the two terms in the expressions for , namely:
This equation can be solved together with Poisson's equation numerically.
An example of results of solving the drift diffusion equation is shown on the right. When light shines on the center of semiconductor, carriers are generated in the middle and diffuse towards two ends. The drift–diffusion equation is solved in this structure and electron density distribution is displayed in the figure. One can see the gradient of carrier from center towards two ends. | 1 | Applied and Interdisciplinary Chemistry |
For hard particles, Pauling's rules are useful in understanding the structure of ionic compounds in the early days, and the later entropy maximization principle shows favor of dense packing in the system. Therefore, finding the densest packing for a given shape is a starting point for predicting the structure of hard nanoparticle superlattices. For spherical particles, the densest packings are face-centered cubic and hexagonal close-packed from the Kepler–Hales theorem.
Different particle shapes / polyhedra create diverse complex packing structures in order to minimize the entropy of the system. By computer simulations, four structure categories are classified for faceted polyhedra nanoparticles according to their long-range order and short-range order, which are liquid crystals, plastic crystals, crystals, and disordered structures. | 0 | Theoretical and Fundamental Chemistry |
An S1 reaction occurs when a molecule separates into a positively charged component and a negatively charged component. This generally occurs in highly polar solvents through a process called solvolysis. The positively charged component then reacts with a nucleophile forming a new compound. S1 reactions are reactions whose rate is dependent only on haloalkane concentration.
In the first stage of this reaction (solvolysis), the C-L bond breaks and both electrons from that bond join LG (the leaving group) to form LG and RC ions. This is represented by the curved arrow pointing away from the C-LG bond and towards LG. The nucleophile Nu, being attracted to the RC, then donates a pair of electrons forming a new C-Nu bond.
Because an S1 reaction proceeds with the Substitution of a leaving group with a Nucleophile, the S designation is used. Because the initial solvolysis step in this reaction involves a single molecule dissociating from its leaving group, the initial stage of this process is considered a uni-molecular reaction. The involvement of only 1 species in the initial phase of the reaction enhances the mechanistic designation to S1. An S1 reaction has two steps. | 0 | Theoretical and Fundamental Chemistry |
Geminal dithiols have the formula RR'C(SH). They are derived from aldehydes and ketones by the action of hydrogen sulfide. Their stability contrasts with the rarity of geminal diols. Examples include methanedithiol, ethane-1,1-dithiol, and cyclohexane-1,1-dithiol. Upon heating, gem-dithiols often release hydrogen sulfide, giving the transient thioketone or thial, which typically convert to oligomers. | 0 | Theoretical and Fundamental Chemistry |
Because of the full or partial positive charge on the element directly attached to the ring for each of these groups, they all have a moderate to strong electron-withdrawing inductive effect (known as the -I effect). They also exhibit electron-withdrawing resonance effects, (known as the -M effect):
Thus, these groups make the aromatic ring very electron-poor (δ+) relative to benzene and, therefore, they strongly deactivate the ring (i.e. reactions proceed much slower in rings bearing these groups compared to those reactions in benzene.) | 0 | Theoretical and Fundamental Chemistry |
A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Definitions vary, but nanocrystalline material is commonly defined as a crystallite (grain) size below 100 nm. Grain sizes from 100 to 500 nm are typically considered "ultrafine" grains.
The grain size of a NC sample can be estimated using x-ray diffraction. In materials with very small grain sizes, the diffraction peaks will be broadened. This broadening can be related to a crystallite size using the Scherrer equation (applicable up to ~50 nm), a Williamson-Hall plot, or more sophisticated methods such as the Warren-Averbach method or computer modeling of the diffraction pattern. The crystallite size can be measured directly using transmission electron microscopy. | 1 | Applied and Interdisciplinary Chemistry |
Victoria F. Samanidou is a Greek analytical chemist. She is a professor at Aristotle University of Thessaloniki in Thessaloniki, Greece. | 0 | Theoretical and Fundamental Chemistry |
It is possible to run experiments in flow using more sophisticated techniques, such as solid phase chemistries. Solid phase reagents, catalysts or scavengers can be used in solution and pumped through glass columns, for example, the synthesis of alkaloid natural product oxomaritidine using solid phase chemistries.
There is an increasing interest in polymerization as a continuous flow process. For example, Reversible Addition-Fragmentation chain Transfer or RAFT polymerization.
Continuous flow techniques have also been used for the controlled generation of nanoparticles. The very rapid mixing and excellent temperature control of microreactors are able to give consistent and narrow particle size distribution of nanoparticles. | 1 | Applied and Interdisciplinary Chemistry |
As already described, chiral liquid-crystal molecules usually give rise to chiral mesophases. This means that the molecule must possess some form of asymmetry, usually a stereogenic center. An additional requirement is that the system not be racemic: a mixture of right- and left-handed molecules will cancel the chiral effect. Due to the cooperative nature of liquid crystal ordering, however, a small amount of chiral dopant in an otherwise achiral mesophase is often enough to select out one domain handedness, making the system overall chiral.
Chiral phases usually have a helical twisting of the molecules. If the pitch of this twist is on the order of the wavelength of visible light, then interesting optical interference effects can be observed. The chiral twisting that occurs in chiral LC phases also makes the system respond differently from right- and left-handed circularly polarized light. These materials can thus be used as polarization filters.
It is possible for chiral LC molecules to produce essentially achiral mesophases. For instance, in certain ranges of concentration and molecular weight, DNA will form an achiral line hexatic phase. An interesting recent observation is of the formation of chiral mesophases from achiral LC molecules. Specifically, bent-core molecules (sometimes called banana liquid crystals) have been shown to form liquid crystal phases that are chiral. In any particular sample, various domains will have opposite handedness, but within any given domain, strong chiral ordering will be present. The appearance mechanism of this macroscopic chirality is not yet entirely clear. It appears that the molecules stack in layers and orient themselves in a tilted fashion inside the layers. These liquid crystals phases may be ferroelectric or anti-ferroelectric, both of which are of interest for applications.
Chirality can also be incorporated into a phase by adding a chiral dopant, which may not form LCs itself. Twisted-nematic or super-twisted nematic mixtures often contain a small amount of such dopants. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, isodiazomethane, also known as isocyanamide, aminoisonitrile, or systematically as isocyanoamine, is the parent compound of a class of derivatives of general formula RN–NC. It has the condensed formula HN–N≡C, making it an isomer of diazomethane. It is prepared by protonating an ethereal solution of lithiodiazomethane, LiCHN, with aqueous NaHPO or NHCl. The parent compound is only marginally stable at room temperature and is isolated by removal of solvent at –50 °C. Derivatives are generally prepared by dehydration of the corresponding substituted formylhydrazine with COCl and EtN.
Earlier, the compound was misidentified as the isomeric nitrilimine, HN–N≡CH. However, this structure was disproven by H NMR studies, which show a compound with a single signal at δ 6.40 ppm in (CDCD)O instead of two signals expected for nitrilimine. Moreover, an infrared band at 2140 cm was assigned to the isocyano group. Transition metal complexes of isodiazomethane have been prepared. In bulk form isodiazomethane is a liquid which decomposes when the temperature exceeds 15 °C. If it is heated to 40 °C, the substance explodes. A solution of isodiazomethane in diethyl ether at –30 °C gradually isomerizes to diazomethane upon exposure to sodium hydroxide for 20 min.
Microwave spectroscopy indicates that unlike diazomethane, isodiazomethane is not completely planar, with the amino nitrogen undergoing inversion. An ab initio study indicated that there is some N–N double bond character in HN–N≡C, although less so than in the N–C bond of HN–C≡N. Like other isocyanide derivatives and carbon monoxide, its primary resonance form carries a negative charge and lone pair on carbon, a comparatively rare situation for neutral molecules. A resonance form with zero formal charge on all atoms also has some importance; however, the carbon atom only has a sextet of electrons and is formally a carbene. | 0 | Theoretical and Fundamental Chemistry |
In coordination chemistry, a stability constant (also called formation constant or binding constant) is an equilibrium constant for the formation of a complex in solution. It is a measure of the strength of the interaction between the reagents that come together to form the complex. There are two main kinds of complex: compounds formed by the interaction of a metal ion with a ligand and supramolecular complexes, such as host–guest complexes and complexes of anions. The stability constant(s) provide(s) the information required to calculate the concentration(s) of the complex(es) in solution. There are many areas of application in chemistry, biology and medicine. | 0 | Theoretical and Fundamental Chemistry |
The first case is a thick ring in an external magnetic field (Fig. 3a). The currents in a superconductor only flow in a thin layer at the surface. The thickness of this layer is determined by the so-called London penetration depth. It is of μm size or less. We consider a loop far away from the surface so that v = 0 everywhere so κ = 0. In that case the fluxoid is equal to the magnetic flux (Φ = Φ). If v = 0 Eq. () reduces to
Taking the rotation gives
Using the well-known relations and shows that the magnetic field in the bulk of the superconductor is zero as well. So, for thick rings, the total magnetic flux in the loop is quantized according to | 0 | Theoretical and Fundamental Chemistry |
Patches have been demonstrated to be a promising detection platform for sweat diagnostics. Simple, long-term collection devices which check for drugs of abuse or alcohol are already on the market and operate on the following principle: a user applies the patch which then collects sweat over a period of hours or days, then the patch is analyzed utilizing techniques such as GC-MS which are accurate but have the drawback of lack of continuous measurements and high costs. For example, sweat diagnostic products for illicit drugs and alcohol are manufactured and supplied by PharmChek and AlcoPro, respectively. Recently several efforts have been made to develop low cost polymer based continuous perspiration monitoring devices and are in early stages of commercialization.
More recently, startup companies such as [http://www.Xsensio.com Xsensio] have begun developing products targeted towards the consumer, healthcare and athletics market for sweat diagnostics. Ultimately, it is the hope that these devices will have the ability to detect changes in human physiology within minutes without the need for repeated sample collection and analysis. | 1 | Applied and Interdisciplinary Chemistry |
Current research related to VMAT uses VMAT2 knockout mice to explore the behavioral genetics of this transporter in an animal model. VMAT2 knockouts are known to be lethal as homozygotes, but heterozygote knockouts are not lethal and are used in many studies as a durable animal model.
From knockout and knockdown mice, researchers have discovered that it is good to have over-expression or under-expression of the VMAT genes in some circumstances. Mice are also used in drug studies, particularity studies involving the effect cocaine and methamphetamine have on VMATs. Studies involving animals have prompted scientists to work on developing drugs that inhibit or enhance the function of VMATs. Drugs that inhibit VMATs may have use in addiction but further studies are needed. Enhancing the function of VMATs may also have therapeutic value. | 1 | Applied and Interdisciplinary Chemistry |
Protocell research has created controversy and opposing opinions, including criticism of vague definitions of "artificial life". The creation of a basic unit of life is the most pressing ethical concern, although the most widespread worry about protocells is their potential threat to human health and the environment through uncontrolled replication.
Additionally, postulation into the conditions for protocellular origins of life on Earth remain debated. Scientists in the field emphasize the importance of further hypothesis based experimentation over theoretical conjecture to more concretely constrain the prebiotic plausibility of different protocell morphologies, geologic conditions, and synthetic schemes. | 0 | Theoretical and Fundamental Chemistry |
On subcellular distribution, histamine N-methyltransferase protein in humans is mainly localized to the nucleoplasm (which is an organelle, i.e., a subunit of a cell) and cytosol (which is the intracellular fluid, i.e., a fluid inside cells). In addition, it is localized to the centrosome (another organelle).
In humans, the protein is present in many tissues and is most abundantly expressed in the brain, thyroid gland, bronchus, duodenum, liver, gallbladder, kidney, and skin. | 1 | Applied and Interdisciplinary Chemistry |
Coupled reactions are reactions whose rate or equilibrium constant is not the same for the oxidized and reduced forms of the species that is being investigated. For example, reduction should favour protonation (): the protonation reaction is coupled to the reduction at . The binding of a small molecule (other than the proton) may also be coupled to a redox reaction.
Two cases must be considered depending on whether the coupled reaction is slow or fast (meaning that the time scale of the coupled reaction is larger or smaller than the voltammetric time scale ).
* Fast chemical reactions that are coupled to electron transfer (such as protonation) only affect the apparent values of and , but the peaks remain symmetrical. The dependence of on ligand concentration (e.g. the dependence of on pH plotted in a Pourbaix diagram) can be interpreted to obtain the dissociation constants (e.g. acidity constants) from the oxidized or reduced forms of the redox species.
* Asymmetry may result from slow chemical reactions that are coupled to (and gate) the electron transfer. From fast scan voltammetry, information can be gained about the rates of the reactions that are coupled to electron transfer. The case of and reversible surface electrochemical reactions followed by irreversible chemical reactions was addressed by Laviron in refs but the data are usually interpreted using the numerical solution of the appropriate differential equations. | 0 | Theoretical and Fundamental Chemistry |
Potentiometric pH meters measure the voltage between two electrodes and display the result converted into the corresponding pH value. They comprise a simple electronic amplifier and a pair of electrodes, or alternatively a combination electrode, and some form of display calibrated in pH units. It usually has a glass electrode and a reference electrode, or a combination electrode. The electrodes, or probes, are inserted into the solution to be tested. pH meters may also be based on the antimony electrode (typically used for rough conditions) or the quinhydrone electrode.
In order to accurately measure the potential difference between the two sides of the glass membrane reference electrode, typically a silver chloride electrode or calomel electrode are required on each side of the membrane. Their purpose is to measure changes in the potential on their respective side. One is built into the glass electrode. The other, which makes contact with the test solution through a porous plug, may be a separate reference electrode or may be built into a combination electrode. The resulting voltage will be the potential difference between the two sides of the glass membrane possibly offset by some difference between the two reference electrodes, that can be compensated for. The article on the glass electrode has a good description and figure.
The design of the electrodes is the key part: These are rod-like structures usually made of glass, with a bulb containing the sensor at the bottom. The glass electrode for measuring the pH has a glass bulb specifically designed to be selective to hydrogen-ion concentration. On immersion in the solution to be tested, hydrogen ions in the test solution exchange for other positively charged ions on the glass bulb, creating an electrochemical potential across the bulb. The electronic amplifier detects the difference in electrical potential between the two electrodes generated in the measurement and converts the potential difference to pH units. The magnitude of the electrochemical potential across the glass bulb is linearly related to the pH according to the Nernst equation.
The reference electrode is insensitive to the pH of the solution, being composed of a metallic conductor, which connects to the display. This conductor is immersed in an electrolyte solution, typically potassium chloride, which comes into contact with the test solution through a porous ceramic membrane. The display consists of a voltmeter, which displays voltage in units of pH.
On immersion of the glass electrode and the reference electrode in the test solution, an electrical circuit is completed, in which there is a potential difference created and detected by the voltmeter. The circuit can be thought of as going from the conductive element of the reference electrode to the surrounding potassium-chloride solution, through the ceramic membrane to the test solution, the hydrogen-ion-selective glass of the glass electrode, to the solution inside the glass electrode, to the silver of the glass electrode, and finally the voltmeter of the display device. The voltage varies from test solution to test solution depending on the potential difference created by the difference in hydrogen-ion concentrations on each side of the glass membrane between the test solution and the solution inside the glass electrode. All other potential differences in the circuit do not vary with pH and are corrected for by means of the calibration.
For simplicity, many pH meters use a combination probe, constructed with the glass electrode and the reference electrode contained within a single probe. A detailed description of combination electrodes is given in the article on glass electrodes.
The pH meter is calibrated with solutions of known pH, typically before each use, to ensure accuracy of measurement. To measure the pH of a solution, the electrodes are used as probes, which are dipped into the test solutions and held there sufficiently long for the hydrogen ions in the test solution to equilibrate with the ions on the surface of the bulb on the glass electrode. This equilibration provides a stable pH measurement. | 0 | Theoretical and Fundamental Chemistry |
The electric dipole moment of the dioxygen molecule, is zero, but the molecule is paramagnetic with two unpaired electrons so that there are magnetic-dipole allowed transitions which can be observed by microwave spectroscopy. The unit electron spin has three spatial orientations with respect to the given molecular rotational angular momentum vector, K, so that each rotational level is split into three states, J = K + 1, K, and K - 1, each J state of this so-called p-type triplet arising from a different orientation of the spin with respect to the rotational motion of the molecule. The energy difference between successive J terms in any of these triplets is about 2 cm (60 GHz), with the single exception of J = 1←0 difference which is about 4 cm. Selection rules for magnetic dipole transitions allow transitions between successive members of the triplet (ΔJ = ±1) so that for each value of the rotational angular momentum quantum number K there are two allowed transitions. The O nucleus has zero nuclear spin angular momentum, so that symmetry considerations demand that K have only odd values. | 0 | Theoretical and Fundamental Chemistry |
A historic example of L1-conferred disease is Haemophilia A, which is caused by insertional mutagenesis. There are nearly 100 examples of known diseases caused by retroelement insertions, including some types of cancer and neurological disorders. Correlation between L1 mobilization and oncogenesis has been reported for epithelial cell cancer (carcinoma). Hypomethylation of LINES is associated with chromosomal instability and altered gene expression and is found in various cancer cell types in various tissues types. Hypomethylation of a specific L1 located in the MET onco gene is associated with bladder cancer tumorogenesis, Shift work sleep disorder is associated with increased cancer risk because light exposure at night reduces melatonin, a hormone that has been shown to reduce L1-induced genome instability. | 1 | Applied and Interdisciplinary Chemistry |
In 2008, Ardisson and his co-workers reported a strategy that applies a crotyltitanation reaction repeatedly to yield homoallylic (Z)-O-ene-carbamate alcohols with excellent selectivity. This crotyltitanation reaction not only efficiently produces the syn-anti methyl-hydroxy-methyl triads of (+)-discodermolide, but also yields products that can be easily converted to terminal (Z)-diene. The C13-C14 (Z)-olefin is installed through a highly selective dyotropic rearrangement. The Ardission synthesis of (+)-discodermolide has an overall yield of 1.6% with a longest linear sequence of 21 steps. | 0 | Theoretical and Fundamental Chemistry |
There are three common types of chemical reaction where normality is used as a measure of reactive species in solution:
*In acid-base chemistry, normality is used to express the concentration of hydronium ions (HO) or hydroxide ions (OH) in a solution. Here, is an integer value. Each solute can produce one or more equivalents of reactive species when dissolved.
*In redox reactions, the equivalence factor describes the number of electrons that an oxidizing or reducing agent can accept or donate. Here, can have a fractional (non-integer) value.
*In precipitation reactions, the equivalence factor measures the number of ions which will precipitate in a given reaction. Here, is an integer value.
Normal concentration of an ionic solution is also related to conductivity (electrolytic) through the use of equivalent conductivity. | 0 | Theoretical and Fundamental Chemistry |
The configuration index has two digits which are the priority numbers of the ligands separated by the largest angle. The lowest priority number of the pair is quoted first. | 0 | Theoretical and Fundamental Chemistry |
Upon working on the Manhattan Project, the German physicist Maria Goeppert Mayer became interested in the properties of nuclear fission products, such as decay energies and half-lives. In 1948, she published a body of experimental evidence for the occurrence of closed nuclear shells for nuclei with 50 or 82 protons or 50, 82, and 126 neutrons.
It had already been known that nuclei with 20 protons or neutrons were stable: that was evidenced by calculations by Hungarian-American physicist Eugene Wigner, one of her colleagues in the Manhattan Project. Two years later, in 1950, a new publication followed in which she attributed the shell closures at the magic numbers to spin-orbit coupling. According to Steven Moszkowski, a student of Goeppert Mayer, the term "magic number" was coined by Wigner: "Wigner too believed in the liquid drop model, but he recognized, from the work of Maria Mayer, the very strong evidence for the closed shells. It seemed a little like magic to him, and that is how the words Magic Numbers were coined."
These magic numbers were the bedrock of the nuclear shell model, which Mayer developed in the following years together with Hans Jensen and culminated in their shared 1963 Nobel Prize in Physics. | 0 | Theoretical and Fundamental Chemistry |
The chloroplast NADH dehydrogenase F (ndhF) gene is found in all vascular plant divisions and is highly conserved. Its DNA fragment resides in the small single-copy region of the chloroplast genome, and is thought to encode a hydrophobic protein containing 664 amino acids and to have a mass of 72.9 kDa. | 0 | Theoretical and Fundamental Chemistry |
A quinone dimethide (or "xylylene") is a compound with the formula CH(=CH). Thus they are related to quinone monomethides (the topic of this article) by replacing the keto group with methylidene. A well studied example is tetracyanoquinodimethane. | 0 | Theoretical and Fundamental Chemistry |
The element is named after ytterbite, a mineral first identified in 1787 by the chemist Carl Axel Arrhenius. He named the mineral after the village of Ytterby, in Sweden, where it had been discovered. When one of the chemicals in ytterbite was later found to be a previously unidentified element, the element was then named yttrium after the mineral. | 1 | Applied and Interdisciplinary Chemistry |
The polyprismanes consist of multiple prismanes stacked base-to-base. The carbons at each intermediate level—the n-gon bases where the prismanes fuse to each other—have no hydrogen atoms attached to them. | 0 | Theoretical and Fundamental Chemistry |
The atomic number or nuclear charge number (symbol Z) of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (n) or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary uncharged atom, the atomic number is also equal to the number of electrons.
For an ordinary atom which contains protons, neutrons and electrons, the sum of the atomic number Z and the neutron number N gives the atoms atomic mass number A. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes) and the mass defect of the nucleon binding is always small compared to the nucleon mass, the atomic mass of any atom, when expressed in daltons (making a quantity called the "relative isotopic mass"), is within 1% of the whole number A'.
Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as isotopes. A little more than three-quarters of naturally occurring elements exist as a mixture of isotopes (see monoisotopic elements), and the average isotopic mass of an isotopic mixture for an element (called the relative atomic mass) in a defined environment on Earth determines the element's standard atomic weight. Historically, it was these atomic weights of elements (in comparison to hydrogen) that were the quantities measurable by chemists in the 19th century.
The conventional symbol Z comes from the German word number, which, before the modern synthesis of ideas from chemistry and physics, merely denoted an elements numerical place in the periodic table, whose order was then approximately, but not completely, consistent with the order of the elements by atomic weights. Only after 1915, with the suggestion and evidence that this Z number was also the nuclear charge and a physical characteristic of atoms, did the word (and its English equivalent atomic number') come into common use in this context.
The rules above do not always apply to exotic atoms which contain short-lived elementary particles other than protons, neutrons and electrons. | 0 | Theoretical and Fundamental Chemistry |
A widespread experimental investigation of DSW material systems and evolution of related practical devices has been largely limited by the stringent anisotropy conditions necessary for successful DSW propagation, particularly the high degree of birefringence of at least one of the constituent materials and the limited number of naturally available materials fulfilling this requirement. However, this is about to change in light of novel artificially engineered metamaterials and revolutionary material synthesis techniques.
The extreme sensitivity of DSW to anisotropy, and thereby to stress, along with their low-loss (long-range) character render them particularly attractive for enabling high sensitivity tactile and ultrasonic sensing for next-generation high-speed transduction and read-out technologies. Moreover, the unique directionality of DSW can be used for the steering of optical signals. | 0 | Theoretical and Fundamental Chemistry |
A wallpaper is a mathematical object covering a whole Euclidean plane by repeating a motif indefinitely, in manner that certain isometries keep the drawing unchanged. For each wallpaper there corresponds a group of congruent transformations, with function composition as the group operation. Thus, a wallpaper group (or plane symmetry group or plane crystallographic group) is a mathematical classification of a two‑dimensional repetitive pattern, based on the symmetries in the pattern. Such patterns occur frequently in architecture and decorative art, especially in textiles, tessellations, tiles and physical wallpaper. | 0 | Theoretical and Fundamental Chemistry |
Most companies pursuing algae as a source of biofuels pump nutrient-rich water through plastic or borosilicate glass tubes (called "bioreactors" ) that are exposed to sunlight (and so-called photobioreactors or PBR).
Running a PBR is more difficult than using an open pond, and costlier, but may provide a higher level of control and productivity. In addition, a photobioreactor can be integrated into a closed loop cogeneration system much more easily than ponds or other methods. | 1 | Applied and Interdisciplinary Chemistry |
Shiny metal surfaces, have low emissivities both in the visible wavelengths and in the far infrared. Such surfaces can be used to reduce heat transfer in both directions; an example of this is the multi-layer insulation used to insulate spacecraft.
Since any electromagnetic radiation, including thermal radiation, conveys momentum as well as energy, thermal radiation also induces very small forces on the radiating or absorbing objects. Normally these forces are negligible, but they must be taken into account when considering spacecraft navigation. The Pioneer anomaly, where the motion of the craft slightly deviated from that expected from gravity alone, was eventually tracked down to asymmetric thermal radiation from the spacecraft. Similarly, the orbits of asteroids are perturbed since the asteroid absorbs solar radiation on the side facing the Sun, but then re-emits the energy at a different angle as the rotation of the asteroid carries the warm surface out of the Sun's view (the YORP effect). | 0 | Theoretical and Fundamental Chemistry |
* Bacteria: The code is used in Entomoplasmatales and Mycoplasmatales (Bove et al. 1989). The situation in the Acholeplasmatales is unclear. Based on a study of ribosomal protein genes, it had been concluded that UGA does not code for tryptophan in plant-pathogenic mycoplasma-like organisms (MLO) and the Acholeplasmataceae (Lim and Sears, 1992) and there seems to be only a single tRNA-CCA for tryptophan in Acholeplasma laidlawii (Tanaka et al. 1989). In contrast, in a study of codon usage in Phytoplasmas, it was found that 30 out of 78 open reading frames analysed translated better with this code (UGA for tryptophan) than with the bacterial, archaeal and plant plastid code while the remainder showed no differences between the two codes (Melamed et al. 2003). In addition, the coding reassignment of UGA Stop → Trp can be found in an alpha-proteobacterial symbiont of cicadas: Candidatus Hodgkinia cicadicola (McCutcheon et al. 2009). Mycoplasma pneumoniae also uses the codon UGA to code for tryptophan rather than using it as a stop codon.
* Fungi: Emericella nidulans, Neurospora crassa, Podospora anserina, Acremonium (Fox, 1987), Candida parapsilosis (Guelin et al., 1991), Trichophyton rubrum (de Bievre and Dujon, 1992), Dekkera/Brettanomyces, Eeniella (Hoeben et al., 1993), and probably Ascobolus immersus, Aspergillus amstelodami, Claviceps purpureaand Cochliobolus heterostrophus.
* Protists: the red algae of Gigartinales (Boyen et al. 1994), the protozoa Trypanosoma brucei, Leishmania tarentolae, Paramecium tetraurelia, Tetrahymena pyriformis and probably Plasmodium gallinaceum (Aldritt et al., 1989), and the stramenopile Cafileria marina.
* Metazoa: Coelenterata (Ctenophora and Cnidaria).
* Other: this code is also used for the kinetoplast DNA (maxicircles, minicircles). Kinetoplasts are modified mitochondria (or their parts). | 1 | Applied and Interdisciplinary Chemistry |
: M–R + M → M + M–R.
In redox-transmetalation a ligand is transferred from one metal to the other through an intermolecular mechanism. During the reaction one of the metal centers is oxidized and the other is reduced. The electronegativities of the metals and ligands is what causes the reaction to go forward. If M is more electronegative than M, it is thermodynamically favorable for the R group to coordinate to the less electronegative M. | 0 | Theoretical and Fundamental Chemistry |
Two key properties of β-W have been well-established: the high electrical resistivity and the giant spin Hall effect.
Although the exact value depends on the preparation conditions, β-W has an electrical resistivity of at least five to ten times higher than that of α-W (5.3 μΩ.cm), and this high conductivity will remain almost unchanged in a temperature range of 5 to 380 K, making β-W a potential thin film resistor while α-W is a thin film conductor.
Thin films of β-W display a giant spin Hall effect with a spin Hall angle of 0.30 ± 0.02 and a spin-diffusion length of around 3.5 nm. In contrast, α-W exhibits a much smaller spin Hall angle of less than 0.07 and a comparable spin-diffusion length. In the spin Hall effect, the application of a longitudinal electric current through a nonmagnetic material generates a transverse spin current due to the spin–orbit interaction, and the spin Hall angle is defined as the ratio of the transverse spin current density and the longitudinal electric current density. The spin Hall angle of β-W is large enough to generate spin torques capable of flipping or setting the magnetization of adjacent magnetic layers into precession by means of the spin Hall effect. | 0 | Theoretical and Fundamental Chemistry |
The primary translation product of SFRP1 contains an atypical signaling sequence, where a chain of 15 hydrophilic amino acids precede the hydrophobic domain. Looking at 7 tumors without the truncating mutation, the retained SFRP1 allele contained an in-frame three-base insertion after nucleotide 37. This is thought to lead to an extra alanine in the protein after codon 13. However, no significant association was found between the development of colorectal cancer and the presence of the 3-bp insertion. | 1 | Applied and Interdisciplinary Chemistry |
The excavations at Hammeh are part of the Deir 'Alla Regional Project, a joint undertaking of Yarmouk University in Irbid, Jordan, and Leiden University in the Netherlands, in collaboration with the Jordanian Department of Antiquities.
The site's most intriguing feature is the presence of a substantial and very early iron smelting operation, as evidence by large quantities of slag, technical ceramics, furnace remnants etc. This activity dates to 930 BC.
Fieldwork at Tell Hammeh took place in 1996, 1997, and 2000. The first two (rescue) seasons were directed by Dr E.J. van der Steen; the third season was directed by Dr H.A. Veldhuijzen. A fourth season, planned in 2003, had to be abandoned due to the invasion of Iraq. As with the third season, the focus of new excavation would primarily be on the iron smelting evidence. A new excavation was to start in May 2009. | 1 | Applied and Interdisciplinary Chemistry |
EFDA (1999 — 2013) has been followed by EUROfusion, which is a consortium of national fusion research institutes located in the European Union and Switzerland.
The European Union has a strongly coordinated nuclear fusion research programme. At the European level, the so-called [http://europa.eu/legislation_summaries/institutional_affairs/treaties/treaties_euratom_en.htm EURATOM Treaty] is the international legal framework under which member states cooperate in the fields of nuclear fusion research.
The [https://web.archive.org/web/20140914125632/http://www.efda.org/ European Fusion Development Agreement] (EFDA) is an agreement between European fusion research institutions and the European Commission (which represents Euratom) to strengthen their coordination and collaboration, and to participate in collective activities in the field of nuclear fusion research.
In Europe, fusion research takes place in a great number of research institutes and universities. In each member state of the European Fusion Programme at least one research organisation has a "Contract of Association" with the European Commission. All the fusion research organisations and institutions of a country are connected to the program through this (these) contracted organisation(s). After the name of the contract, the groups of fusion research organisations of the member states are called "Associations". | 0 | Theoretical and Fundamental Chemistry |
Ribonucleic acid (RNA) functions in converting genetic information from genes into the amino acid sequences of proteins. The three universal types of RNA include transfer RNA (tRNA), messenger RNA (mRNA), and ribosomal RNA (rRNA). Messenger RNA acts to carry genetic sequence information between DNA and ribosomes, directing protein synthesis and carries instructions from DNA in the nucleus to ribosome . Ribosomal RNA reads the DNA sequence, and catalyzes peptide bond formation. Transfer RNA serves as the carrier molecule for amino acids to be used in protein synthesis, and is responsible for decoding the mRNA. In addition, many other classes of RNA are now known. | 1 | Applied and Interdisciplinary Chemistry |
With the publication of "Expansion of C ecosystems as an indicator of global ecological change in the late Miocene" in 1993, Cerling, helped by Yang Wang and Jay Quade, made relevant studies relatively to carbon isotopes. Thanks to a deep analysis of palaeovegetation from palaeosols and palaeodiet measured in fossil tooth enamel, was demonstrated a global increase in the biomass of plants using C photosynthesis between 7 and 5 million years ago. The decrease of atmospheric concentrations over the history below a threshold that favored the C-photosynthesizing plants was considered as a valid reason for the global expansion of C biomass.
The publication "Global vegetation change through the Miocene/Pliocene boundary" in 1997 confirmed these results, demonstrating even how at lower latitudes the change appeared to occur earlier because of the threshold for C photosynthesis is higher at warmer temperatures. | 0 | Theoretical and Fundamental Chemistry |
In 1983, Philip P. Power synthesized a transition-metal complex containing P=P double bond (trans–{[2}) via a simple one-step procedure. They mixed Na[Fe(CO)] and dichlorobis(trimethylsilyl)methylphosphine and got dark red-brown crystals, which was the first complex that contained an unbridged P-P double bond. Each phosphorus exhibited terminal coordination nature and the P-P distance was essentially unchanged. Later in 1983, A. H. Cowley reported ArP=PArFe(CO) (with Ar=2,4,6-tri-tert-butylphenyl) by treating diphosephene with Fe(CO) or NaFe(CO). In this synthesis procedure, there was only one terminal P-coordination and P-P double bond had Z configuration. Apart from iron, other similar transition metal complexes by reacting diphosphenes with transition metal carbonyls of nickel, tungsten, and chromium were discovered and they all exhibited Z configuration. M. Yoshifuji proved E/Z isomerization can take place under lighting, probably via migration of the metal moiety from one side to the other. | 0 | Theoretical and Fundamental Chemistry |
Ubiquinol oxidases () are enzymes in the bacterial electron transport chain that oxidise ubiquinol into ubiquinone and reduce oxygen to water. These enzymes are one set of the many alternative terminal oxidases in the branched prokaryotic electron transport chain. The overall structure of the E. coli ubiquinol oxidase is similar to that of the mammalian Cytochrome c oxidase, with the addition of a polar ubiquinol-binding site embedded in the membrane. | 1 | Applied and Interdisciplinary Chemistry |
These results in optics have been confirmed in 2011 in hydrodynamics with experiments carried out in a 15-m long water wave tank. In 2013, complementary experiments using a scale model of a chemical tanker ship have discussed the potential devastating effects on the ship. | 1 | Applied and Interdisciplinary Chemistry |
In 1965, Chinese scientists first synthesized crystalline bovine insulin (), which was the first functional crystalline protein being fully synthesized in the world. Research on synthesizing bovine insulin started on 1958. Members in the research group were from the Chemistry Department of Beijing University (), Shanghai Institute of Biochemistry, CAS () and Shanghai Institute of Organic Chemistry, CAS ().
Insulin is a protein (peptide) consisting of two chain, A and B. Chain A consists of 21 amino acid residues while chain consists of 30 amino acid residues. The main function of insulin is to regulate the concentrate of sugar in blood. Type 1 diabetes are caused by dysfunction on the synthesis or secretory of insulin while injecting insulin can treat type 1 diabetes.
In 1979, Wang Yinglai, the project's lead scientist, nominated Niu Jingyi, a team member who had made significant contributions, for the Nobel Chemistry Prize, but the nomination was unsuccessful. | 1 | Applied and Interdisciplinary Chemistry |
Polymers, especially conductive ones, have been widely researched to coat electrode surfaces. Conductive polymers are organic materials that have properties similar to metals and semiconductors in their ability conduct electricity and attractive optical properties. These materials have rough surfaces, resulting in large surface area and charge density. Conducting polymer coatings have been shown to improve the performance and stability of neural electrode.
Conductive polymers have been shown to lower the impedance of electrodes (an important property as mentioned above), increase the charge density, and improve the mechanical interface between the soft tissue and hard electrode. The porous (rough) structure of many conductive polymer coatings on the electrode increases the surface area. The high surface area of conductive polymers is directly related to decreased impedance and charge transfer improvement at the tissue-electrode interface. This improved charge transfer allows for better recording and stimulating in neural application. Table 2 below shows some common impedance and charge density values of different electrodes at a frequency of 1 kHz, which is the characteristic of neural biological activity. The porous, high surface area of the conductive polymer coatings allows for target cell adhesion (increased cell and tissue integration), which increase the bio-compatibility and stability of the device.
Conducting polymer coatings as mentioned above can greatly improve the interface between the soft tissue in the body and the hard electrode surface. Polymers are softer, which reduces the inflammation from strain mismatch between tissue and electrode surface. The reduced inflammatory reaction causes a decrease in thickness of the glial encapsulation which causes signal degeneration. The elastic modulus of silicon (a common material that electrodes are made from) is around 100 GPa and the tissue in the brain is about 100 kPa. The electrode modulus (stiffness) is about 100 times greater than that of the tissue in the brain. For the best device integration in the body, it is important to get the stiffness between the two to be as similar as possible. To improve this interface, a conductive polymer coating (smaller modulus than the electrode) can be applied to the electrode surface which causes a gradient of mechanical properties to act as a mediator between the hard and soft surfaces. The added polymer coating reduces the stiffness of the electrode and allows for better integration of the electrode. The figure to the right shows a graph of how the modulus changes when integrating the polymer coating onto the electrode. | 0 | Theoretical and Fundamental Chemistry |
In these methods, the time measurement has been replaced by a measurement of the inverse of time (frequency).
Kundt's tube is an example of an experiment which can be used to measure the speed of sound in a small volume. It has the advantage of being able to measure the speed of sound in any gas. This method uses a powder to make the nodes and antinodes visible to the human eye. This is an example of a compact experimental setup.
A tuning fork can be held near the mouth of a long pipe which is dipping into a barrel of water. In this system it is the case that the pipe can be brought to resonance if the length of the air column in the pipe is equal to where n is an integer. As the antinodal point for the pipe at the open end is slightly outside the mouth of the pipe it is best to find two or more points of resonance and then measure half a wavelength between these.
Here it is the case that v = fλ. | 1 | Applied and Interdisciplinary Chemistry |
Samples with very low concentrations are difficult to measure accurately due to the radioactive atoms unexpectedly depositing on surfaces. Sample loss at trace levels may be due to adhesion to container walls and filter surface sites by ionic or electrostatic adsorption, as well as metal foils and glass slides. Sample loss is an ever present concern, especially at the beginning of the analysis path where sequential steps may compound these losses.
Various solutions are known to circumvent these losses which include adding an inactive carrier or adding a tracer. Research has also shown that pretreatment of glassware and plastic surfaces can reduce radionuclide sorption by saturating the sites. | 0 | Theoretical and Fundamental Chemistry |
In humans, L-2-Hydroxyglutaric aciduria was the first disease linked to a missing metabolite repair enzyme. Mutations in the L2HGDH gene cause accumulation of L-2-hydroxyglutarate, which is a structural analog to glutamate and alpha-ketoglutarate and presumably inhibits other enzymes or transporters. | 1 | Applied and Interdisciplinary Chemistry |
The presence of swirling motion, i.e., is shown not to influence the axial motion given by provided . If is very large, the presence of swirl completely alters the motion on the axial plane. For , the azimuthal solution can be solved in terms of the circulation , where . The solution can be described in terms of the self-similar solution of the second kind, , where is an unknown constant and is an eigenvalue. The function satisfies
subjected to the boundary conditions and as . | 1 | Applied and Interdisciplinary Chemistry |
Adenosine triphosphate (ATP) is a major "energy currency" of the cell. The high energy bonds between the phosphate groups can be broken to power a variety of reactions used in all aspects of cell function.
Substrate-level phosphorylation occurs in the cytoplasm of cells during glycolysis and in mitochondria either during the Krebs cycle or by MTHFD1L ([https://www.uniprot.org/uniprot/Q6UB35 EC 6.3.4.3]), an enzyme interconverting ADP + phosphate + 10-formyltetrahydrofolate to ATP + formate + tetrahydrofolate (reversibly), under both aerobic and anaerobic conditions. In the pay-off phase of glycolysis, a net of 2 ATP are produced by substrate-level phosphorylation. | 1 | Applied and Interdisciplinary Chemistry |
Discodermolide was first isolated in 1990 from the Caribbean marine sponge Discodermia dissoluta by chemist Dr. Sarath Gunasekera and biologist Dr. Ross Longley, scientists at the Harbor Branch Oceanographic Institution. The sponge contained 0.002% of discodermolide (7 mg/434 g of sponge). Since the compound is light-sensitive, the sponge must be harvested at a minimum depth of 33 meters. Discodermolide was initially found to have immunosuppressive and antifungal activities. | 0 | Theoretical and Fundamental Chemistry |
This kind of equilibrium constant measures how a substance distributes or partitions itself between two immiscible solvents. It is called the partition coefficient or distribution coefficient. | 0 | Theoretical and Fundamental Chemistry |
Avoiding the use of pressure to introduce the mobile phase into the column, results in a number of important advantages. Firstly, the pressure driven flow rate across a column depends directly on the square of the particle diameter and inversely on the length of the column. This restricts the length of the column and size of the particle, particle size is seldom less than 3 micrometer and the length of the column is restricted to 25 cm. Electrically driven flow rate is independent of length of column and size. A second advantage of using electroosmosis to pass the mobile phase into the column is the plug-like flow velocity profile of EOF, which reduces the solute dispersion in the column, increasing column efficiency. | 1 | Applied and Interdisciplinary Chemistry |
The chemical and biochemical properties of Mg present the cellular system with a significant challenge when transporting the ion across biological membranes. The dogma of ion transport states that the transporter recognises the ion then progressively removes the water of hydration, removing most or all of the water at a selective pore before releasing the ion on the far side of the membrane. Due to the properties of Mg, large volume change from hydrated to bare ion, high energy of hydration and very low rate of ligand exchange in the inner coordination sphere, these steps are probably more difficult than for most other ions. To date, only the ZntA protein of Paramecium has been shown to be a Mg channel. The mechanisms of Mg transport by the remaining proteins are beginning to be uncovered with the first three-dimensional structure of a Mg transport complex being solved in 2004.
The hydration shell of the Mg ion has a very tightly bound inner shell of six water molecules and a relatively tightly bound second shell containing 12–14 water molecules (Markham et al., 2002). Thus, it is presumed that recognition of the Mg ion requires some mechanism to interact initially with the hydration shell of Mg, followed by a direct recognition/binding of the ion to the protein. Due to the strength of the inner sphere complexation between Mg and any ligand, multiple simultaneous interactions with the transport protein at this level might significantly retard the ion in the transport pore. Hence, it is possible that much of the hydration water is retained during transport, allowing the weaker (but still specific) outer sphere coordination.
In spite of the mechanistic difficulty, Mg must be transported across membranes, and a large number of Mg fluxes across membranes from a variety of systems have been described. However, only a small selection of Mg transporters have been characterised at the molecular level. | 1 | Applied and Interdisciplinary Chemistry |
Bioaerosols include fungi, bacteria, viruses, and pollen. Their concentrations are greatest in the planetary boundary layer (PBL) and decrease with altitude. Survival rate of bioaerosols depends on a number of biotic and abiotic factors which include climatic conditions, ultraviolet (UV) light, temperature and humidity, as well as resources present within dust or clouds.
Bioaerosols found over marine environments primarily consist of bacteria, while those found over terrestrial environments are rich in bacteria, fungi and pollen. The dominance of particular bacteria and their nutrient sources are subject to change according to time and location.
Bioaerosols can range in size from 10 nanometer virus particles to 100 micrometers pollen grains. Pollen grains are the largest bioaerosols and are less likely to remain suspended in the air over a long period of time due to their weight.
Consequently, pollen particle concentration decreases more rapidly with height than smaller bioaerosols such as bacteria, fungi and possibly viruses, which may be able to survive in the upper troposphere. At present, there is little research on the specific altitude tolerance of different bioaerosols. However, scientists believe that atmospheric turbulence impacts where different bioaerosols may be found. | 0 | Theoretical and Fundamental Chemistry |
A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobile genetic elements to proliferate within the host genome, and by eukaryotic cells to extend the telomeres at the ends of their linear chromosomes. Contrary to a widely held belief, the process does not violate the flows of genetic information as described by the classical central dogma, as transfers of information from RNA to DNA are explicitly held possible.
Retroviral RT has three sequential biochemical activities: RNA-dependent DNA polymerase activity, ribonuclease H (RNase H), and DNA-dependent DNA polymerase activity. Collectively, these activities enable the enzyme to convert single-stranded RNA into double-stranded cDNA. In retroviruses and retrotransposons, this cDNA can then integrate into the host genome, from which new RNA copies can be made via host-cell transcription. The same sequence of reactions is widely used in the laboratory to convert RNA to DNA for use in molecular cloning, RNA sequencing, polymerase chain reaction (PCR), or genome analysis. | 1 | Applied and Interdisciplinary Chemistry |
During World War II, Huizenga supervised teams at the Manhattan Project in Oak Ridge, Tenn., involved in enriching uranium used in the atomic weapon dropped on Hiroshima in August 1945. During his Argonne years, as a result of examining debris from the "Ivy Mike" nuclear test in 1952, Huizenga was part of the team that added two new synthetic chemical elements, einsteinium and fermium, to the periodic table. Huizenga and his colleagues were at first unable to publish papers on their discoveries in the open literature, because of classification concerns relating to the nuclear test, but these concerns were eventually resolved and the team was able to publish in Physical Review and thus claim priority for their discovery. During his Argonne years he was one of the founders of the Gordon Research Conferences on nuclear chemistry, serving as chairman of the nuclear chemistry Gordon Conference in 1958. He received a Guggenheim Fellowship in 1964 and took a sabbatical from Argonne to further his studies as a visiting professor at the University of Paris for the 1964–1965 academic year.
In 1967, he became a professor of chemistry and physics at the University of Rochester where he worked for the remainder of his career, apart from a second Guggenheim Fellowship that allowed him to engage in research during the 1973–1974 school year at the University of California, Berkeley, the Technische Universität München, and the Niels Bohr Institute in Copenhagen. His research interests at Rochester covered topics in nuclear structure of actinides, nuclear fission, and nuclear reactions between heavy ions. He was chairman of the Department of Chemistry from 1983 to 1988, retiring as Tracy H. Harris Professor (later Professor Emeritus) of Chemistry.
During Huizenga's time at Rochester, the university had its own particle accelerator, a tandem Van de Graaff accelerator that produced beams of nuclei accelerated to energies of several MeV per nucleon. This facility, which opened in 1966, afforded him the opportunity to continue his research program in experimental nuclear science. However, the limited beam energies available led him to more powerful accelerators, such as the SuperHILAC at Berkeley and the Los Alamos Meson Physics Facility, LAMPF, at Los Alamos National Laboratory, for his experimental work. His LAMPF proposal to study actinide muonic atoms was one of the earliest experiments to receive beam time at the LAMPF stopped-muon facility.
In 1989, Huizenga co-chaired, with Norman Ramsey, a panel convened by the United States Department of Energy which attempted to debunk claims by two University of Utah chemists that they had achieved nuclear fusion at room temperature. The findings of the Huizenga/Ramsey panel, although highly skeptical of the reality of cold fusion, were cautious:
However, Huizenga later published a book titled "Cold Fusion: The Scientific Fiasco of the Century". | 0 | Theoretical and Fundamental Chemistry |
Lawrence Elgin Glendenin (November 8, 1918November 22, 2008) was an American chemist who co-discovered the element promethium. | 1 | Applied and Interdisciplinary Chemistry |
Information about quantities at the lateral boundaries can be taken into account as surface measurements and upper air soundings. Therefore, a key word and the time when boundary data is given must occur in front of a set of boundary information. | 1 | Applied and Interdisciplinary Chemistry |
Fluorescence cross-correlation spectroscopy (FCCS) is a spectroscopic technique that examines the interactions of fluorescent particles of different colours as they randomly diffuse through a microscopic detection volume over time, under steady conditions. | 0 | Theoretical and Fundamental Chemistry |
Dai is editor of books including:
* Hai-Lung Dai, Robert W. Field (editors) (1995). [https://www.worldcat.org/oclc/31901502 Molecular dynamics and spectroscopy by stimulated emission pumping]. Singapore; New Jersey; London; Hong Kong: World Scientific. .
* Hai-Lung Dai, Wilson Ho (editors) (1995). [https://www.worldcat.org/oclc/32468614 Laser spectroscopy and photochemistry on metal surfaces]. Singapore; New Jersey; London; Hong Kong: World Scientific. . | 0 | Theoretical and Fundamental Chemistry |
RiPPs constitute one of the major superfamilies of natural products, like alkaloids, terpenoids, and nonribosomal peptides, although they tend to be large, with molecular weights commonly in excess of 1000 Da. The advent of next-generation sequencing methods has made genome mining of RiPPs a common strategy. In part due to their increased discovery and hypothesized ease of engineering, the use of RiPPs as drugs is increasing. Although they are ribosomal peptides in origin, RiPPs are typically categorized as small molecules rather than biologics due to their chemical properties, such as moderate molecular weight and relatively high hydrophobicity.
The uses and biological activities of RiPPs are diverse.
RiPPs in commercial use include nisin, a food preservative, thiostrepton, a veterinary topical antibiotic, and nosiheptide and duramycin, which are animal feed additives. Phalloidin functionalized with a fluorophore is used in microscopy as a stain due to its high affinity for actin. Anantin is a RiPP used in cell biology as an atrial natriuretic peptide receptor inhibitor.
In 2012-2013, a derivatized RiPP in clinical trials was LFF571. Phase II clinical trials of LFF571, a derivative of the thiopeptide GE2270-A, for the treatment of Clostridium difficile infections, with comparable safety and efficacy to vancomycin, was terminated early as the results were unfavorable. Also recently in clinical trials was the NVB302 (a derivative of the lantibiotic actagardine) which is used for the treatment of Clostridium difficile infection. Duramycin has completed phase II clinical trials for the treatment of cystic fibrosis.
Other bioactive RiPPs include the antibiotics cyclothiazomycin and bottromycin, the ultra-narrow spectrum antibiotic plantazolicin, and the cytotoxin patellamide A. Streptolysin S, the toxic virulence factor of Streptococcus pyogenes, is also a RiPP. Additionally, human thyroid hormone itself is a RiPP due to its biosynthetic origin as thyroglobulin. | 1 | Applied and Interdisciplinary Chemistry |
The Rayleigh flow model begins with a differential equation that relates the change in Mach number with the change in stagnation temperature, T. The differential equation is shown below.
Solving the differential equation leads to the relation shown below, where T* is the stagnation temperature at the throat location of the duct which is required for thermally choking the flow.
These values are significant in the design of combustion systems. For example, if a turbojet combustion chamber has a maximum temperature of T* = 2000 K, T and M at the entrance to the combustion chamber must be selected so thermal choking does not occur, which will limit the mass flow rate of air into the engine and decrease thrust.
For the Rayleigh flow model, the dimensionless change in entropy relation is shown below.
The above equation can be used to plot the Rayleigh line on a Mach number versus ΔS graph, but the dimensionless enthalpy, H, versus ΔS diagram is more often used. The dimensionless enthalpy equation is shown below with an equation relating the static temperature with its value at the choke location for a calorically perfect gas where the heat capacity at constant pressure, c, remains constant.
The above equation can be manipulated to solve for M as a function of H. However, due to the form of the T/T* equation, a complicated multi-root relation is formed for M = M(T/T*). Instead, M can be chosen as an independent variable where ΔS and H can be matched up in a chart as shown in Figure 1. Figure 1 shows that heating will increase an upstream, subsonic Mach number until M = 1.0 and the flow chokes. Conversely, adding heat to a duct with an upstream, supersonic Mach number will cause the Mach number to decrease until the flow chokes. Cooling produces the opposite result for each of those two cases. The Rayleigh flow model reaches maximum entropy at M = 1.0 For subsonic flow, the maximum value of H occurs at M = 0.845. This indicates that cooling, instead of heating, causes the Mach number to move from 0.845 to 1.0 This is not necessarily correct as the stagnation temperature always increases to move the flow from a subsonic Mach number to M = 1, but from M = 0.845 to M = 1.0 the flow accelerates faster than heat is added to it. Therefore, this is a situation where heat is added but T/T* decreases in that region. | 1 | Applied and Interdisciplinary Chemistry |
Functional Ensemble of Temperament (FET) is a neurochemical model suggesting specific functional roles of main neurotransmitter systems in the regulation of behaviour. | 1 | Applied and Interdisciplinary Chemistry |
Between 1882 and 1886 Schuyler Wheeler invented a fan powered by electricity. It was commercially marketed by the American firm Crocker & Curtis electric motor company. In 1885 a desktop direct drive electric fan was commercially available by Stout, Meadowcraft & Co. in New York.
In 1882, Philip Diehl developed the world's first electric ceiling mounted fan. During this intense period of innovation, fans powered by alcohol, oil, or kerosene were common around the turn of the 20th century.
In 1909, KDK of Japan pioneered the invention of mass-produced electric fans for home use. In the 1920s, industrial advances allowed steel fans to be mass-produced in different shapes, bringing fan prices down and allowing more homeowners to afford them. In the 1930s, the first art deco fan (the "Silver Swan") was designed by Emerson. By the 1940s, Crompton Greaves of India became the world's largest manufacturer of electric ceiling fans mainly for sale in India, Asia, and the Middle East. By the 1950s, table and stand fans were manufactured in bright colors and eye-catching.
Window and central air conditioning in the 1960s caused many companies to discontinue production of fans, but in the mid-1970s, with an increasing awareness of the cost of electricity and the amount of energy used to heat and cool homes, turn-of-the-century styled ceiling fans became popular again as both decorative and energy-efficient.
In 1998 William Fairbank and Walter K. Boyd invented the high-volume low-speed (HVLS) ceiling fan, designed to reduce energy consumption by using long fan blades rotating at low speed to move a relatively large volume of air. | 0 | Theoretical and Fundamental Chemistry |
Public Analysts are scientists in the British Isles whose principal task is to ensure the safety and correct description of food by testing for compliance with legislation. Most Public Analysts are also Agricultural Analysts who carry out similar work on animal feedingstuffs and fertilisers. Nowadays this includes checking that the food labelling is accurate. They also test drinking water, and may carry out chemical and biological tests on other consumer products. While much of the work is done by other scientists and technicians in the laboratory, the Public Analyst has legal responsibility for the accuracy of the work and the validity of any opinion expressed on the results reported. The UK-based Association of Public Analysts includes members with similar roles if different titles in other countries. | 1 | Applied and Interdisciplinary Chemistry |
Letters in Organic Chemistry (usually abbreviated as Lett. Org. Chem.), is a peer-reviewed monthly scientific journal, published since 2004 by Bentham Science Publishers. Letters in Organic Chemistry is indexed in: Chemical Abstracts Service (CAS), EBSCOhost, British Library, PubMed, Web of Science, and Scopus.
Letters in Organic Chemistry publishes letters and articles on all areas related to organic chemistry.
According to the Journal Citation Reports, the impact factor of this journal is 0.867 for the year 2020. The Editor-in-Chief is Alberto Marra (University of Montpellier, France). who took over from Gwilherm Evano (Université libre de Bruxelles, Belgium) who resigned in February 2018 after a strong disagreement with Bentham on the scientific management of this journal. | 0 | Theoretical and Fundamental Chemistry |
Many mechanisms exist reflecting the myriad types of cross-couplings, including those that do not require metal catalysts. Often, however, cross-coupling refers to a metal-catalyzed reaction of a nucleophilic partner with an electrophilic partner.
In such cases, the mechanism generally involves reductive elimination of R-R from LMR(R) (L = spectator ligand). This intermediate LMR(R) is formed in a two step process from a low valence precursor LM. The oxidative addition of an organic halide (RX) to LM gives LMR(X). Subsequently, the second partner undergoes transmetallation with a source of R. The final step is reductive elimination of the two coupling fragments to regenerate the catalyst and give the organic product. Unsaturated substrates, such as C(sp)−X and C(sp)−X bonds, couple more easily, in part because they add readily to the catalyst. | 0 | Theoretical and Fundamental Chemistry |
The high strength of silicon–halogen bonds can be leveraged toward the synthesis of phosphaalkynes. Heating bis-trimethylsilylated methyldichlorophosphines ((SiMe)CRPCl) under vacuum results in the expulsion of two equivalents of chlorotrimethylsilane and the ultimate formation of a new phosphaalkyne. This synthetic strategy has been applied in the synthesis of 2-phenylphosphaacetylene and 2-trimethylsilylphosphaacetylene. As in the case of synthetic routes reliant upon the elimination of a hydrogen halide, this route is suspected to involve an intermediate phosphaethylene species containing a C=P double bond, though such a species has not yet been observed. | 0 | Theoretical and Fundamental Chemistry |
HRI (encoded in humans by the gene EIF2AK1) also dimerizes in order to autophosphorylate and activate. This activation is dependent on the presence of heme. HRI has two domains that heme may bind to, including one on the N-terminus and one on the kinase insertion domain. The presence of heme causes a disulfide bond to form between the monomers of HRI, resulting in the structure of an inactive dimer. However, when heme is absent, HRI monomers form an active dimer through non-covalent interactions. Therefore, the activation of this kinase is dependent on heme deficiency. HRI activation can also occur due to other stressors such as heat shock, osmotic stress and proteasome inhibition. Activation of HRI in response to these stressors does not depend on heme, but rather relies on the help of two heat shock proteins (HSP90 and HSP70). HRI is mainly found in the precursors of red blood cells, and has been observed to increase during erythropoiesis. | 1 | Applied and Interdisciplinary Chemistry |
The Boyle temperature is formally defined as the temperature for which the second virial coefficient, , becomes zero.
It is at this temperature that the attractive forces and the repulsive forces acting on the gas particles balance out
This is the virial equation of state and describes a real gas.
Since higher order virial coefficients are generally much smaller than the second coefficient, the gas tends to behave as an ideal gas over a wider range of pressures when the temperature reaches the Boyle temperature (or when or are minimized).
In any case, when the pressures are low, the second virial coefficient will be the only relevant one because the remaining concern terms of higher order on the pressure. Also at Boyle temperature the dip in a PV diagram tends to a straight line over a period of pressure. We then have
where is the compressibility factor.
Expanding the van der Waals equation in one finds that . | 0 | Theoretical and Fundamental Chemistry |
Stability is among the essential properties of a CRM (see definitions above), and stability assessment is accordingly required for certified reference materials. Stability under long term storage and also under conditions of transport are both expected to be assessed. "Assessment" is not synonymous with "testing"; some materials - for example, many minerals and metal alloys - may be so stable that experimental tests are not considered necessary. Other reference materials will usually undergo experimental tests of stability at some point prior to the material being distributed for sale.
Where reference materials are certified for more than one property, stability is expected to be demonstrated for every certified property.
There are two important strategies for CRM stability testing; simple real-time studies and accelerated testing. Real-time studies simply keep units of the material at their planned storage temperature for a suitable period of time and observe the material at intervals. Accelerated studies use a range of more stringent conditions, most commonly increased temperature, to test whether the material is likely to be stable over longer time scales. | 0 | Theoretical and Fundamental Chemistry |
Because of resonance stabilization of the conjugate base, an α-hydrogen in an aldehyde is weakly acidic with a pK near 17. Note, however, this is much more acidic than an alkane or ether hydrogen, which has pK near 50 approximately, and is even more acidic than a ketone α-hydrogen which has pK near 20. This acidification of the α-hydrogen in aldehyde is attributed to:
* the electron-withdrawing quality of the formyl center and
* the fact that the conjugate base, an enolate anion, delocalizes its negative charge.
The formyl proton itself does not readily undergo deprotonation. | 0 | Theoretical and Fundamental Chemistry |
Herbicide resistance became a critical problem in Australian agriculture, after many Australian sheep farmers began to exclusively grow wheat in their pastures in the 1970s. Introduced varieties of ryegrass, while good for grazing sheep, compete intensely with wheat. Ryegrasses produce so many seeds that, if left unchecked, they can completely choke a field. Herbicides provided excellent control, while reducing soil disrupting because of less need to plough. Within little more than a decade, ryegrass and other weeds began to develop resistance. In response Australian farmers changed methods. By 1983, patches of ryegrass had become immune to Hoegrass (diclofop-methyl), a family of herbicides that inhibit an enzyme called acetyl coenzyme A carboxylase.
Ryegrass populations were large, and had substantial genetic diversity, because farmers had planted many varieties. Ryegrass is cross-pollinated by wind, so genes shuffle frequently. To control its distribution farmers sprayed inexpensive Hoegrass, creating selection pressure. In addition, farmers sometimes diluted the herbicide in order to save money, which allowed some plants to survive application. When resistance appeared farmers turned to a group of herbicides that block acetolactate synthase. Once again, ryegrass in Australia evolved a kind of "cross-resistance" that allowed it to rapidly break down a variety of herbicides. Four classes of herbicides become ineffective within a few years. In 2013 only two herbicide classes, called Photosystem II and long-chain fatty acid inhibitors, were effective against ryegrass. | 1 | Applied and Interdisciplinary Chemistry |
Iodine-129 decays with a half-life of 15.7 Ma into Xe, resulting in excess Xe in primitive meteorites relative to primordial Xe isotopic compositions. The property of I can be used in radiometric chronology. However, as detailed below, the age of Earth's formation cannot be deduced directly from I-Xe dating. The major problem is the Xe closure time, or the time when the early Earth system stopped gaining substantial new material from space. When the Earth became closed for the I-Xe system, Xe isotope evolution began to obey a simple radioactive decay law as shown below and became predictable.
The principle of radiogenic chronology is, if at time t the quantity of a radioisotope is P while at some previous time this quantity was P, the interval between t and t is given by the law of radioactive decay as
Here is the decay constant of the radioisotope, which is the probability of decay per nucleus per unit time. The decay constant is related to the half life t, by t= ln(2)/ | 0 | Theoretical and Fundamental Chemistry |
TEs are mutagens and due to the contribution to the formation of new cis-regulatory DNA elements that are connected to many transcription factors that are found in living cells; TEs can undergo many evolutionary mutations and alterations. These are often the causes of genetic disease, and gives the potential lethal effects of ectopic expression.
TEs can damage the genome of their host cell in different ways:
* A transposon or a retrotransposon that inserts itself into a functional gene can disable that gene.
* After a DNA transposon leaves a gene, the resulting gap may not be repaired correctly.
* Multiple copies of the same sequence, such as Alu sequences, can hinder precise chromosomal pairing during mitosis and meiosis, resulting in unequal crossovers, one of the main reasons for chromosome duplication.
TEs use a number of different mechanisms to cause genetic instability and disease in their host genomes.
* Expression of disease-causing, damaging proteins that inhibit normal cellular function.
** Many TEs contain promoters which drive transcription of their own transposase. These promoters can cause aberrant expression of linked genes, causing disease or mutant phenotypes. | 1 | Applied and Interdisciplinary Chemistry |
A pulsed Fourier-transform spectrometer does not employ transmittance techniques. In the most general description of pulsed FT spectrometry, a sample is exposed to an energizing event which causes a periodic response. The frequency of the periodic response, as governed by the field conditions in the spectrometer, is indicative of the measured properties of the analyte. | 0 | Theoretical and Fundamental Chemistry |
Collected water is filtered through the strata of soil or engineering growing soil, called substrate. After the soil reaches its saturation limit, excess water pools on the surface of the soil and eventually infiltrates the natural soil below. The bioretention soil mixture should typically contain 60% sand, 20% compost, and 20% topsoil. Soils with higher concentrations of compost have shown improved effects on filtering groundwater and rainwater. Non-permeable soil needs to be removed and replaced periodically to generate maximum performance and efficiency if used in the bioretention system. The sandy soil (bioretention mixture) cannot be combined with a surrounding soil that has a lower sand content because the clay particles will settle in between the sand particles and form a concrete-like substance that is not conducive to infiltration, according to a 1983 study. Compact lawn soil cannot harbor groundwater nearly as well as sandy soils, because the micropores within the soil are not sufficient for retaining substantial runoff levels.
When an area's soils are not permeable enough to allow water to drain and filter at an appropriate rate, the soil should be replaced and an underdrain installed. Sometimes a drywell with a series of gravel layers near the lowest spot in the rain garden will help facilitate percolation and avoid clogging at the sedimentation basin. However, a drywell placed at the lowest spot can become clogged with silt prematurely, turning the garden into an infiltration basin and defeating its purpose as a bioretention system. The more polluted the runoff water, the longer it must be retained in the soil for purification. Capacity for a longer purification period is often achieved by installing several smaller rain garden basins with soil deeper than the seasonal high water table. In some cases lined bioretention cells with subsurface drainage are used to retain smaller amounts of water and filter larger amounts without letting water percolate as quickly. A five-year study by the U.S. Geological Survey indicates that rain gardens in urban clay soils can be effective without the use of underdrains or replacement of native soils with the bioretention mix. Yet it also indicates that pre-installation infiltration rates should be at least .25 in/hour. Type D soils will require an underdrain paired with the sandy soil mix in order to drain properly.
Rain gardens are often located near a buildings roof drainpipe (with or without rainwater tanks). Most rain gardens are designed to be an endpoint of a buildings or urban site's drainage system with a capacity to percolate all incoming water through a series of soil or gravel layers beneath the surface plantings. A French drain may be used to direct a portion of the rainwater to an overflow location for heavier rain events. If the bioretention site has additional runoff directed from downspouts leading from the roof of a building, or if the existing soil has a filtration rate faster than 5 inches per hour, the substrate of the rain garden should include a layer of gravel or sand beneath the topsoil to meet that increased infiltration load. If not originally designed to include a rain garden onsite, downpipes from the roof can be disconnected and diverted to a rain garden for retrofit stormwater management. This reduces the amount of water load on the conventional drainage system, and instead directs water for infiltration and treatment through bioretention features. By reducing peak stormwater discharge, rain gardens extend hydraulic lag time and somewhat mimic the natural water cycle displaced by urban development and allow for groundwater recharge. While rain gardens always allow for restored groundwater recharge, and reduced stormwater volumes, they may not improve pollution unless remediation materials are included in the design of the filtration layers. | 1 | Applied and Interdisciplinary Chemistry |
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