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1966-1979: University of Vienna<br />
Starting in 1966 Falk was an assistant at the [http://www.univie.ac.at/orgchem/ Institute of Organic Chemistry] at the University of Vienna. In 1975 he was promoted to associate professor of physical organic chemistry at the University of Vienna. In the summer of 1978 Falk was invited to speak at the Gordon Research Conference in Wolfeboro.<br />
1979–present: Johannes Kepler University of Linz<br />
In 1979 Falk received a call to become full professor of organic chemistry at Johannes Kepler University of Linz, where he founded the new
[http://www.orc.uni-linz.ac.at/ Institute of Organic Chemistry]. From 1989 through 1991 he was elected Dean of the Faculty of Engineering and Natural Sciences ([http://www.tn.jku.at/ TNF]) at Johannes Kepler University of Linz. In 2005 Falk was ranked #3 among the "Top 10" scientists in Upper Austria by the newspaper "OÖ Nachrichten". In 2008 he retired as Professor emeritus at the Institute of Organic chemistry of the JKU. | 0 | Organic Chemistry |
Nitrosoarenes typically participate in a monomer–dimer equilibrium. The azobenzene N,N-dioxide (Ar(O)N=N(O)Ar) dimers, which are often pale yellow, are generally favored in the solid state, whereas the deep-green monomers are favored in dilute solution or at higher temperatures. They exist as cis and trans' isomers.
When stored in protic media, primary and secondary nitrosoalkanes isomerize to oximes.
Due to the stability of the nitric oxide free radical, nitroso organyls tend to have very low C–N bond dissociation energies: nitrosoalkanes have BDEs on the order of , while nitrosoarenes have BDEs on the order of . As a consequence, they are generally heat- and light-sensitive. Compounds containing O–(NO) or N–(NO) bonds generally have even lower bond dissociation energies. For instance, N-nitrosodiphenylamine, PhN–N=O, has a N–N bond dissociation energy of only . Organonitroso compounds serve as a ligands giving transition metal nitroso complexes. | 0 | Organic Chemistry |
The system can be adapted for situations where environmental or clinical pathogens require monitoring. For example, APDS could test for mold or fungal spores in buildings or for the airborne spread of contagious materials in hospitals. It also could identify disease outbreaks in livestock transport centers or feedlots. In water, APDS can detect pathogens in wastewater, agricultural irrigation lines, food processors, fish farms, and beaches. | 3 | Analytical Chemistry |
Flow cytometry is most frequently used to detect apoptotic DNA fragmentation. Analysis of DNA content by flow cytometry can identify apoptotic cells with fragmented DNA as the cells with fractional DNA content, often called the sub-G cells. The flow-cytometric assay utilizing the fluorochrome acridine orange shows that DNA fragmentation within individual cells is discontinuous likely reflecting different levels of restriction in accessibility of DNA to DNase, by the supranucleosomal and nucleosomal levels of chromatin structure. The presence of apoptotic "sub-Gcells" can also be detected in cells pre-fixed in ethanol but not after fixation in the crosslinking fixatives such as formaldehyde. The late-S and G apoptotic cells may not be detected with this approach because their fractional DNA content may overlap with that of the non-apoptotic G cells.
Treatment of cells with detergent, prior or concurrently with DNA fluorochrome, also reveals DNA fragmentation by virtue of the presence of the sub-G cells or cell fragments, as defined by Nicoletti et al.
Apoptotic DNA fragmentation can also be detected by the TUNEL assay. The fluorochrome-based TUNEL assay applicable for flow cytometry, correlates the detection of DNA strand breaks with the cellular DNA content and thus with cell cycle-phase position. The avidin-peroxidase labeling TUNEL assay is applicable for light absorption microscopy. Many TUNEL-related kits are commercially available.
Apoptotic DNA fragmentation is also analyzed using agarose gel electrophoresis to demonstrate a "ladder" pattern at ~180-BP intervals. Necrosis, on the other hand, is usually characterized by random DNA fragmentation which forms a "smear" on agarose gels. | 1 | Biochemistry |
The basic LPB tool is a ball, wheel or other similar tip that is supported in a spherical hydrostatic bearing. The tool can be held in any CNC machine or by industrial robots, depending on the application. The machine tool coolant is used to pressurize the bearing with a continuous flow of fluid to support the ball. The ball does not contact the mechanical bearing seat, even under load. The ball is loaded at a normal state to the surface of a component with a hydraulic cylinder that is in the body of the tool. LPB can be performed in conjunction with chip forming machining operations in the same CNC machining tool.
The ball rolls across the surface of a component in a pattern defined in the CNC code, as in any machining operation. The tool path and normal pressure applied are designed to create a distribution of compressive residual stress. The form of the distribution is designed to counter applied stresses and optimize fatigue and stress corrosion performance. Since there is no shear being applied to the ball, it is free to roll in any direction. As the ball rolls over the component, the pressure from the ball causes plastic deformation to occur in the surface of the material under the ball. Since the bulk of the material constrains the deformed area, the deformed zone is left in compression after the ball passes. | 8 | Metallurgy |
APP undergoes extensive post-translational modification including glycosylation, phosphorylation, sialylation, and tyrosine sulfation, as well as many types of proteolytic processing to generate peptide fragments. It is commonly cleaved by proteases in the secretase family; alpha secretase and beta secretase both remove nearly the entire extracellular domain to release membrane-anchored carboxy-terminal fragments that may be associated with apoptosis. Cleavage by gamma secretase within the membrane-spanning domain after beta-secretase cleavage generates the amyloid-beta fragment; gamma secretase is a large multi-subunit complex whose components have not yet been fully characterized, but include presenilin, whose gene has been identified as a major genetic risk factor for Alzheimer's.
The amyloidogenic processing of APP has been linked to its presence in lipid rafts. When APP molecules occupy a lipid raft region of membrane, they are more accessible to and differentially cleaved by beta secretase, whereas APP molecules outside a raft are differentially cleaved by the non-amyloidogenic alpha secretase. Gamma secretase activity has also been associated with lipid rafts. The role of cholesterol in lipid raft maintenance has been cited as a likely explanation for observations that high cholesterol and apolipoprotein E genotype are major risk factors for Alzheimer's disease. | 1 | Biochemistry |
Philippa Marion Wiggins (nee Glasgow) (16 July 1925 – 16 March 2017) was a New Zealand academic, who made significant contributions to the understanding of the structure of water in living cells. | 7 | Physical Chemistry |
In petroleum geology, the maturity of a rock is a measure of its state in terms of hydrocarbon generation. Maturity is established using a combination of geochemical and basin modelling techniques.
Rocks with high total organic carbon, (termed source rocks), will alter under increasing temperature such that the organic molecules slowly mature into hydrocarbons (see diagenesis). Source rocks are therefore broadly categorised as immature (no hydrocarbon generation), sub-mature (limited hydrocarbon generation), mature (extensive hydrocarbon generation) and overmature (most hydrocarbons have been generated).
The maturity of a source rock can also be used as an indicator of its hydrocarbon potential. That is, if a rock is sub-mature, then it has a much higher potential to generate further hydrocarbons than one that is overmature. | 9 | Geochemistry |
In the case of bacteria, transposition mutagenesis is usually accomplished by way of a plasmid from which a transposon is extracted and inserted into the host chromosome. This usually requires a set of enzymes including transposase to be translated. The transposase can be expressed either on a separate plasmid, or on the plasmid containing the gene to be integrated. Alternatively, an injection of transposase mRNA into the host cell can induce translation and expression. Early transposon mutagenesis experiments relied on bacteriophages and conjugative bacterial plasmids for the insertion of sequences. These were very non-specific, and made it difficult to incorporate specific genes. A newer technique called shuttle mutagenesis uses specific cloned genes from the host species to incorporate genetic elements. Another effective approach is to deliver transposons through viral capsids. This facilitates integration into the chromosome and long-term transgene expression. | 1 | Biochemistry |
In chemical thermodynamics, the reaction quotient (Q or just Q) is a dimensionless quantity that provides a measurement of the relative amounts of products and reactants present in a reaction mixture for a reaction with well-defined overall stoichiometry at a particular point in time. Mathematically, it is defined as the ratio of the activities (or molar concentrations) of the product species over those of the reactant species involved in the chemical reaction, taking stoichiometric coefficients of the reaction into account as exponents of the concentrations. In equilibrium, the reaction quotient is constant over time and is equal to the equilibrium constant.
A general chemical reaction in which α moles of a reactant A and β moles of a reactant B react to give ρ moles of a product R and σ moles of a product S can be written as
The reaction is written as an equilibrium even though, in many cases, it may appear that all of the reactants on one side have been converted to the other side. When any initial mixture of A, B, R, and S is made, and the reaction is allowed to proceed (either in the forward or reverse direction), the reaction quotient Q, as a function of time t, is defined as
where {X} denotes the instantaneous activity of a species X at time t.
A compact general definition is
where П denotes the product across all j-indexed variables, a(t) is the activity of species j at time t, and ν is the stoichiometric number (the stoichiometric coefficient multiplied by +1 for products and –1 for starting materials). | 7 | Physical Chemistry |
Initiation in archaea is governed by TATA-binding protein (TBP), Archaeal transcription factor B (TFB), and Archaeal transcription factor E (TFE) that are homologous to eukaryotic TBP, TFIIB, and TFIIE respectively. These factors recognize the promoter core sequence (TATA box, B recognition element) upstream of the coding region and recruits the RNAP to form a closed transcription preinitiation complex (PIC).
The PIC is turned into an open state with the local DNA helix "melting" to load the template strand of DNA. The RNAP undergoes "abortive initiation": it makes and releases many short (2-15nt) segments before generating a transcript of significant length. This continues until it moves past the promoter (promoter escape), loosening TBP's grasp on the DNA, and swapping TFE out for elongation factors Spt4/5. How this escape happens exactly remains to be studied. | 1 | Biochemistry |
Nesslers reagent, named after Julius Neßler (Nessler), is a 0.09 mol/L solution of potassium tetraiodomercurate(II) in 2.5 mol/L potassium hydroxide. This pale solution becomes deeper yellow in the presence of ammonia (). At higher concentrations, a brown precipitate derivative of Millons base () may form. The sensitivity as a spot test is about 0.3 μg Ammonia| in 2 μL.
The brown precipitate is not fully characterized and may vary from to . | 3 | Analytical Chemistry |
The name "gentian violet" (or Gentianaviolett in German) is thought to have been introduced by the German pharmacist Georg Grübler, who in 1880 started a company in Leipzig that specialized in the sale of staining reagents for histology. The gentian violet stain marketed by Grübler probably contained a mixture of methylated pararosaniline dyes. The stain proved popular and in 1884 was used by Hans Christian Gram to stain bacteria. He credited Paul Ehrlich for the aniline-gentian violet mixture. Grüblers gentian violet was probably very similar, if not identical, to Lauths methyl violet, which had been used as a stain by Victor André Cornil in 1875.
Although the name gentian violet continued to be used for the histological stain, the name was not used in the dye and textile industries. The composition of the stain was not defined and different suppliers used different mixtures. In 1922, the Biological Stain Commission appointed a committee chaired by Harold Conn to look into the suitability of the different commercial products. In his book Biological Stains, Conn describes gentian violet as a "poorly defined mixture of violet rosanilins".
The German ophthalmologist Jakob Stilling is credited with discovering the antiseptic properties of gentian violet. He published a monograph in 1890 on the bactericidal effects of a solution that he christened "pyoktanin", which was probably a mixture of aniline dyes similar to gentian violet. He set up a collaboration with E. Merck & Co. to market "Pyoktanin caeruleum" as an antiseptic.
In 1902, Drigalski and Conradi found that although crystal violet inhibited the growth of many bacteria, it has little effect on Bacillus coli (Escherichia coli) and Bacillus typhi (Salmonella typhi), which are both gram-negative bacteria. A much more detailed study of the effects of Grübler's gentian violet on different strains of bacteria was published by John Churchman in 1912. He found that most gram-positive bacteria (tainted) were sensitive to the dye, while most gram-negative bacteria (not tainted) were not, and observed that the dye tended to act as a bacteriostatic agent rather than a bactericide. | 3 | Analytical Chemistry |
The Folin–Wu and the Somogyi–Nelson methods are both based on the same principles. In the first step, glucose (or a reducing sugar) is oxidised using a solution of Cu(II) ion, which is reduced to Cu(I) by the process. In the second step, the Cu(I) ions are then oxidised back to Cu(II) using a colourless hetero-polymolybdate complex, which is, in the process, reduced to give the characteristic blue colour. Finally the absorption of the hetero-poly molybdenum blue is measured using a colorimeter and compared to standards prepared from reacting sugar solutions of known concentration, to determine the amount of reducing-sugar present. <br />
The Folin–Wu method uses a reagent that contains sodium tungstate. The exact nature of the blue complex in this procedure is not known.<br />
The Somogyi-Nelson method uses an arsenomolybdate complex formed by the reaction of ammonium molybdate, (NH) MoO, with sodium arsenate, NaHAsO. | 7 | Physical Chemistry |
The main finding of Haber and Weiss was that hydrogen peroxide (HO) is decomposed by a chain reaction.
The Haber–Weiss reaction chain proceeds by successive steps: (i) initiation, (ii) propagation and (iii) termination.
The chain is initiated by the Fenton reaction:
:Fe + HO → Fe + HO + HO (step 1: initiation)
Then, the reaction chain propagates by means of two successive steps:
:HO + HO → HO + O + H (step 2: propagation)
:O + H + HO → O + HO + HO (step 3: propagation)
Finally, the chain is terminated when the hydroxyl radical is scavenged by a ferrous ion:
:Fe + HO + H → Fe + HO (step 4: termination)
George showed in 1947 that, in water, step 3 cannot compete with the spontaneous disproportionation of superoxide, and proposed an improved mechanism for the disappearance of hydrogen peroxide. See for a summary. The reactions proposed therein are:
:Fe + HO → Fe + HO + HO (initiation)
:Fe + HO → Fe + HO (termination)
:HO + HO → HO + HO (propagation)
:Fe + HO → Fe + HO (termination)
:Fe + HO → Fe + HO + H (termination) | 2 | Environmental Chemistry |
The regulation of transcription by enhancers has been studied since the 1980s. Large or multi-component transcription regulators with a range of mechanistic properties, including locus control regions, clustered open regulatory elements, and transcription initiation platforms, were observed shortly thereafter. More recent research has suggested that these different categories of regulatory elements may represent subtypes of super-enhancer.
In 2013, two labs identified large enhancers near several genes especially important for establishing cell identities. While Richard A. Young and colleagues identified super-enhancers, Francis Collins and colleagues identified stretch enhancers. Both super-enhancers and stretch enhancers are clusters of enhancers that control cell-specific genes and may be largely synonymous.
As currently defined, the term “super-enhancer” was introduced by Young’s lab to describe regions identified in mouse embryonic stem cells (ESCs). These particularly large, potent enhancer regions were found to control the genes that establish the embryonic stem cell identity, including Oct-4, Sox2, Nanog, Klf4, and Esrrb. Perturbation of the super-enhancers associated with these genes showed a range of effects on their target genes’ expression. Super-enhancers have been since identified near cell identity-regulators in a range of mouse and human tissues. | 1 | Biochemistry |
One last area that has been actively studied is the synergy of different materials in promoting superior electroactive performance. Whether through various charge transport material, electrochemical species, or morphologies, exploiting the synergetic relationship between different materials has paved the way for even newer counter electrode materials.
In 2016, Lu et al. mixed nickel cobalt sulfide microparticles with reduced graphene oxide (rGO) nanoflakes to create the counter electrode. Lu et al. discovered not only that the rGO acted as a co-catalyst in accelerating the triiodide reduction, but also that the microparticles and rGO had a synergistic interaction that decreased the charge transfer resistance of the overall system. Although the efficiency of this system was slightly lower than its platinum analog (efficiency of NCS/rGO system: 8.96%; efficiency of Pt system: 9.11%), it provided a platform on which further research can be conducted. | 5 | Photochemistry |
Different biocatalytic approaches have been developed toward the synthesis of glycosides in the past decades, which using "glycosyltransferases" and "glycoside hydrolases" are among the most common catalysis. The former often needs expensive materials and the later often shows low yields, De Winter et al.
investigated use of cellobiose phosphorylase (CP) toward synthesis of alpha-glycosides in ionic liquids. The best condition for use of CP was found to be in the presence of IL AMMOENG 101 and ethyl acetate. | 0 | Organic Chemistry |
Inputs to the marine carbon cycle are numerous, but the primary contributions, on a net basis, come from the atmosphere and rivers. Hydrothermal vents generally supply carbon equal to the amount they consume. | 9 | Geochemistry |
The model permits a maximum of 240 internal and 120 external polygons with a minimum of 3 and a maximum of 6 sides each. The subdivision of the area into polygons, based on nodal points with known coordinates, should be governed by the characteristics of the distribution of the cropping, irrigation, drainage and groundwater characteristics over the study area.
The nodes must be numbered, which can be done at will. With an index one indicates whether the node is internal or external. Nodes can be added and removed at will or changed from internal to external or vice versa. Through another index one indicates whether the internal nodes have an unconfined or semi-confined aquifer. This can also be changed at will.
Nodal network relations are to be given indicating the neighboring polygon numbers of each node. The program then calculates the surface area of each polygon, the distance between the nodes and the length of the sides between them using the Thiessen principle.
The hydraulic conductivity can vary for each side of the polygons.
The depth of the water table, the rainfall and salt concentrations of the deeper layers are assumed to be the same over the whole polygon. Other parameters can very within the polygons according to type of crops and cropping rotation schedule. | 9 | Geochemistry |
This period was one of rapid growth for the Jameson Cells in the existing applications. Seventy-seven Cells were installed in concentrators around the world, mainly in coal and base metal operations. However, during this time, the Cell also moved into the Canadian oil sands industry for the flotation of bitumen. | 8 | Metallurgy |
There have been some reports of algae operating a biochemical CCM: shuttling metabolites within single cells to concentrate in one area. This process is not fully understood. | 5 | Photochemistry |
Even though enamines are more nucleophilic than their enol counterparts, they can still react selectively, rendering them useful for alkylation reactions. The enamine nucleophile can attack haloalkanes to form the alkylated iminium salt intermediate which then hydrolyzes to regenerate a ketone (a starting material in enamine synthesis). This reaction was pioneered by Gilbert Stork, and is sometimes referred to by the name of its inventor (the Stork enamine alkylation). Analogously, this reaction can be used as an effective means of acylation. A variety of alkylating and acylating agents including benzylic, allylic halides can be used in this reaction. | 0 | Organic Chemistry |
As in other areas of chemistry, electron counting is useful for organizing organometallic chemistry. The 18-electron rule is helpful in predicting the stabilities of organometallic complexes, for example metal carbonyls and metal hydrides. The 18e rule has two representative electron counting models, ionic and neutral (also known as covalent) ligand models, respectively. The hapticity of a metal-ligand complex, can influence the electron count. Hapticity (η, lowercase Greek eta), describes the number of contiguous ligands coordinated to a metal. For example, ferrocene, [(η-CH)Fe], has two cyclopentadienyl ligands giving a hapticity of 5, where all five carbon atoms of the CH ligand bond equally and contribute one electron to the iron center. Ligands that bind non-contiguous atoms are denoted the Greek letter kappa, κ. Chelating κ2-acetate is an example. The covalent bond classification method identifies three classes of ligands, X,L, and Z; which are based on the electron donating interactions of the ligand. Many organometallic compounds do not follow the 18e rule. The metal atoms in organometallic compounds are frequently described by their d electron count and oxidation state. These concepts can be used to help predict their reactivity and preferred geometry. Chemical bonding and reactivity in organometallic compounds is often discussed from the perspective of the isolobal principle.
A wide variety of physical techniques are used to determine the structure, composition, and properties of organometallic compounds. X-ray diffraction is a particularly important technique that can locate the positions of atoms within a solid compound, providing a detailed description of its structure. Other techniques like infrared spectroscopy and nuclear magnetic resonance spectroscopy are also frequently used to obtain information on the structure and bonding of organometallic compounds. Ultraviolet-visible spectroscopy is a common technique used to obtain information on the electronic structure of organometallic compounds. It is also used monitor the progress of organometallic reactions, as well as determine their kinetics. The dynamics of organometallic compounds can be studied using dynamic NMR spectroscopy. Other notable techniques include X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and elemental analysis.
Due to their high reactivity towards oxygen and moisture, organometallic compounds often must be handled using air-free techniques. Air-free handling of organometallic compounds typically requires the use of laboratory apparatuses such as a glovebox or Schlenk line. | 0 | Organic Chemistry |
The master regulator concept has been criticized for being a "simplified paradigm" that fails to account for the multifactorial influences on some cell fates. | 1 | Biochemistry |
Biologically synthesized organofluorines are few in number, although some are widely produced. The most common example is fluoroacetate, with an active poison molecule identical to commercial "1080". It is used as a defense against herbivores by at least 40 green plants in Australia, Brazil, and Africa; other biologically synthesized organofluorines include ω-fluoro fatty acids, fluoroacetone, and 2-fluorocitrate. In bacteria, the enzyme adenosyl-fluoride synthase, which makes the carbon–fluorine bond, has been isolated. The discovery was touted as possibly leading to biological routes for organofluorine synthesis.
Fluoride is considered a semi-essential element for humans: not necessary to sustain life, but contributing (within narrow limits of daily intake) to dental health and bone strength. Daily requirements for fluorine in humans vary with age and sex, ranging from 0.01 mg in infants below 6 months to 4 mg in adult males, with an upper tolerable limit of 0.7 mg in infants to 10 mg in adult males and females. Small amounts of fluoride may be beneficial for bone strength, but this is an issue only in the formulation of artificial diets. (See also fluoride deficiency.) | 1 | Biochemistry |
The exhaled human breath contains a few thousand volatile organic compounds and is used in breath biopsy to serve as a VOC biomarker to test for diseases, such as lung cancer. One study has shown that "volatile organic compounds ... are mainly blood borne and therefore enable monitoring of different processes in the body." And it appears that VOC compounds in the body "may be either produced by metabolic processes or inhaled/absorbed from exogenous sources" such as environmental tobacco smoke. Chemical fingerprinting and breath analysis of volatile organic compounds has also been demonstrated with chemical sensor arrays, which utilize pattern recognition for detection of component volatile organics in complex mixtures such as breath gas. | 0 | Organic Chemistry |
We may make a more elaborate calculation by treating the atmosphere as compounded of many thin layers. For each such layer, at height y and thickness dy, the weight of this layer in determining the radiation temperaure seen from outer space is a generalization of the expression arrived at earlier for the troposphere. It is:
where OD(y) is the optical depth of the part of the atmosphere from y upwards.
The total effect of CO on the radiation at wavelengths λ to λ+dλ is therefore:
where B is the expression for radiation according to Planck's law presented above:
and the infinity here can be taken actually as the top of the tropopause.
Thus the effect of a relative change in CO concentration, dN/N = dn/n (where n is the density number near ground), would be (noting that dN/N = d(ln N) = d(ln n):
where we have used integration by part.
Because B does not depend on N, and because , we have:
Now, is constant in the troposphere and zero in the tropopause. We denote the height of the border between them as U. So:
The optical depth is proportional to the integral of the number density over y, as does the pressure. Therefore, OD(y) is proportional to the pressure p(y), which within the troposphere (height 0 to U) falls exponentially with decay constant 1/H (H~5.6 km for CO), thus:
Since + constant, viewed as a function of both y and N, we have:
And therefore differentiating with respect to ln N is the same as differentiating with respect to y, times a factor of .
We arrive at:
Since the temperature only changes by ~25% within the troposphere, one may take a (rough) linear approximation of B with T at the relevant wavelengths, and get:
Due to the linear approximation of B we have:
with T taken at H, so that totally:
giving the same result as in the one-layer model presented above, as well as the logarithmic dependence on N, except that now we see T is taken at 5.6 km (the pressure drop height scale), rather than 6.3 km (the density drop height scale). | 2 | Environmental Chemistry |
The proteins in these excitable domains of neuron when injured may result in cognitive disorders and various neuropathic ailments. | 1 | Biochemistry |
The traditional way to analyze the ascorbic acid content is the process of titration with an oxidizing agent, and several procedures have been developed.
The popular iodometry approach uses iodine in the presence of a starch indicator. Iodine is reduced by ascorbic acid, and, when all the ascorbic acid has reacted, the iodine is then in excess, forming a blue-black complex with the starch indicator. This indicates the end-point of the titration.
As an alternative, ascorbic acid can be treated with iodine in excess, followed by back titration with sodium thiosulfate using starch as an indicator.
This iodometric method has been revised to exploit reaction of ascorbic acid with iodate and iodide in acid solution. Electrolyzing the solution of potassium iodide produces iodine, which reacts with ascorbic acid. The end of process is determined by potentiometric titration in a manner similar to Karl Fischer titration. The amount of ascorbic acid can be calculated by Faraday's law.
Another alternative uses N-bromosuccinimide (NBS) as the oxidizing agent, in the presence of potassium iodide and starch. The NBS first oxidizes the ascorbic acid; when the latter is exhausted, the NBS liberates the iodine from the potassium iodide, which then forms the blue-black complex with starch. | 1 | Biochemistry |
Mesoionic carbenes (MICs) are similar to N-heterocyclic carbenes (NHCs) except that canonical resonance structures with the carbene depicted cannot be drawn without adding additional charges. Mesoionic carbenes are also referred to as abnormal N-heterocyclic carbenes (aNHC) or remote N-heterocyclic carbenes (rNHC). A variety of free carbenes can be isolated and are stable at room temperature. Other free carbenes are not stable and are susceptible to intermolecular decomposition pathways. | 0 | Organic Chemistry |
In most instances, baseline data for biotic conditions within a pre-determined reference site are collected. Reference sites must be characterized by little to no outside disturbance (e.g. anthropogenic disturbances, land use change, invasive species). The biotic conditions of a specific indicator species are measured within both the reference site and the study region over time. Data collected from the study region are compared against similar data collected from the reference site in order to infer the relative environmental health or integrity of the study region.
An important limitation of bioindicators in general is that they have been reported as inaccurate when applied to geographically and environmentally diverse regions. As a result, researchers who use bioindicators need to consistently ensure that each set of indices is relevant within the environmental conditions they plan to monitor. | 2 | Environmental Chemistry |
A black light may also be formed by simply using a UV filter coating such as Wood's glass on the envelope of a common incandescent bulb. This was the method that was used to create the very first black light sources. Although incandescent black light bulbs are a cheaper alternative to fluorescent tubes, they are exceptionally inefficient at producing UV light since most of the light emitted by the filament is visible light which must be blocked. Due to its black body spectrum, an incandescent light radiates less than 0.1% of its energy as UV light. Incandescent UV bulbs, due to the necessary absorption of the visible light, become very hot during use. This heat is, in fact, encouraged in such bulbs, since a hotter filament increases the proportion of UVA in the black-body radiation emitted. This high running-temperature drastically reduces the life of the lamp, however, from a typical 1,000 hours to around 100 hours. | 5 | Photochemistry |
Temperature affects the elasticity of elastomers in an unusual way. When the elastomer is assumed to be in a stretched state, heating causes them to contract. Vice versa, cooling can cause expansion.
This can be observed with an ordinary rubber band. Stretching a rubber band will cause it to release heat (press it against your lips), while releasing it after it has been stretched will lead it to absorb heat, causing its surroundings to become cooler. This phenomenon can be explained with the Gibbs free energy. Rearranging ΔG=ΔH−TΔS, where G is the free energy, H is the enthalpy, and S is the entropy, we get . Since stretching is nonspontaneous, as it requires external work, TΔS must be negative. Since T is always positive (it can never reach absolute zero), the ΔS must be negative, implying that the rubber in its natural state is more entangled (with more microstates) than when it is under tension. Thus, when the tension is removed, the reaction is spontaneous, leading ΔG to be negative. Consequently, the cooling effect must result in a positive ΔH, so ΔS will be positive there.
The result is that an elastomer behaves somewhat like an ideal monatomic gas, inasmuch as (to good approximation) elastic polymers do not store any potential energy in stretched chemical bonds or elastic work done in stretching molecules, when work is done upon them. Instead, all work done on the rubber is "released" (not stored) and appears immediately in the polymer as thermal energy. In the same way, all work that the elastic does on the surroundings results in the disappearance of thermal energy in order to do the work (the elastic band grows cooler, like an expanding gas). This last phenomenon is the critical clue that the ability of an elastomer to do work depends (as with an ideal gas) only on entropy-change considerations, and not on any stored (i.e., potential) energy within the polymer bonds. Instead, the energy to do work comes entirely from thermal energy, and (as in the case of an expanding ideal gas) only the positive entropy change of the polymer allows its internal thermal energy to be converted efficiently (100% in theory) into work. | 7 | Physical Chemistry |
In organic chemistry, Baird's rule estimates whether the lowest triplet state of planar, cyclic structures will have aromatic properties or not. The quantum mechanical basis for its formulation was first worked out by physical chemist N. Colin Baird at the University of Western Ontario in 1972.
The lowest triplet state of an annulene is, according to Bairds rule, aromatic when it has 4n π-electrons and antiaromatic when the π-electron count is 4n + 2, where n is any positive integer. This trend is opposite to that predicted by Hückels rule for the ground state, which is usually the lowest singlet state (S). Bairds rule has thus become known as the photochemical analogue of Hückels rule.
Through various theoretical investigations, this rule has also been found to extend to the lowest lying singlet excited state (S) of small annulenes. | 7 | Physical Chemistry |
The Hunter–Sanders model has been criticized by numerous research groups offering contradictory experimental and computational evidence of pi stacking interactions that are not governed primarily by electrostatic effects.
The clearest experimental evidence against electrostatic substituent effects was reported by Rashkin and Waters. They used meta- and para-substituted N-benzyl-2-(2-fluorophenyl)-pyridinium bromides, which stack in a parallel displaced conformation, as a model system for pi stacking interactions. In their system, a methylene linker prohibits favorable T-shaped interactions. As in previous models, the relative strength of pi stacking interactions was measured by NMR as the rate of rotation about the biaryl bond, as pi stacking interactions are disrupted in the transition state. Para-substituted rings had small rotational barriers which increased with increasingly electron-withdrawing groups, consistent with prior findings. However, meta-substituted rings had much larger barriers of rotation despite having nearly identical electron densities in the aromatic ring. The authors explain this discrepancy as direct interaction of the edge of hydrogen atoms of one ring with the electronegative substituents on the other ring. This claim is supported by chemical shift data of the proton in question.
Much of the detailed analyses of the relative contributions of factors in pi stacking have been borne out by computation. Sherill and Sinnokrot reported a surprising finding using high-level theory that all substituted benzene dimers have more favorable binding interactions than a benzene dimer in the sandwich configuration. Later computational work from the Sherill group revealed that the substituent effects for the sandwich configuration are additive, which points to a strong influence of dispersion forces and direct interactions between substituents. It was noted that interactions between substituted benzenes in the T-shaped configuration were more complex. Finally, Sherill and Sinnokrot argue in their review article that any semblance of a trend based on electron donating or withdrawing substituents can be explained by exchange-repulsion and dispersion terms.
Houk and Wheeler also provide compelling computational evidence for the importance of direct interaction in pi stacking. In their analysis of substituted benzene dimers in a sandwich conformation, they were able to recapitulate their findings using an exceedingly simple model where the substituted benzene, Ph–X, was replaced by H–X. Remarkably, this crude model resulted in the same trend in relative interaction energies, and correlated strongly with the values calculated for Ph–X. This finding suggests that substituent effects in the benzene dimer are due to direct interaction of the substituent with the aromatic ring, and that the pi system of the substituted benzene is not involved. This latter point is expanded upon below.
In summary, it would seem that the relative contributions of electrostatics, dispersion, and direct interactions to the substituent effects seen in pi stacking interactions are highly dependent on geometry and experimental design. The lack of consensus on the matter may simply reflect the complexity of the issue. | 6 | Supramolecular Chemistry |
Zero-valent metals are the main reductants used in ISCR. The most common metal used is iron, in the form of ZVI (zero valent iron), and it is also the metal longest in use. However, some studies show that zero valent zinc (ZVZ) could be up to ten times more effective at eradicating the contaminants than ZVI. Some applications of ZVMs are to clean up Trichloroethylene (TCE) and Hexavalent chromium (Cr(VI)). ZVMs are usually implemented by a permeable reactive barrier. For example, iron that has been embedded in a swellable, organically modified silica creates a permanent soft barrier underground to capture and reduce small, organic compounds as groundwater passes through it. | 2 | Environmental Chemistry |
Radiation pressure is the force that electromagnetic radiation exerts on matter. In 1873 Maxwell published his treatise on electromagnetism in which he predicted radiation pressure. The force was experimentally demonstrated for the first time by Lebedev and reported at a conference in Paris in 1900, and later published in more detail in 1901. Following Lebedev's measurements Nichols and Hull also demonstrated the force of radiation pressure in 1901, with a refined measurement reported in 1903.
In 1933, Otto Frisch deflected an atomic beam of sodium atoms with light.
This was the first realization of radiation pressure acting on a resonant absorber. | 7 | Physical Chemistry |
Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space. The macroscopic physical properties of a polymer are related to the interactions between the polymer chains.
* Disordered polymers: In the solid state, atactic polymers, polymers with a high degree of branching and random copolymers form amorphous (i.e. glassy structures). In melt and solution, polymers tend to form a constantly changing "statistical cluster", see freely-jointed-chain model. In the solid state, the respective conformations of the molecules are frozen. Hooking and entanglement of chain molecules lead to a "mechanical bond" between the chains. Intermolecular and intramolecular attractive forces only occur at sites where molecule segments are close enough to each other. The irregular structures of the molecules prevent a narrower arrangement.
* Linear polymers with periodic structure, low branching and stereoregularity (e. g. not atactic) have a semi-crystalline structure in the solid state. In simple polymers (such as polyethylene), the chains are present in the crystal in zigzag conformation. Several zigzag conformations form dense chain packs, called crystallites or lamellae. The lamellae are much thinner than the polymers are long (often about 10 nm). They are formed by more or less regular folding of one or more molecular chains. Amorphous structures exist between the lamellae. Individual molecules can lead to entanglements between the lamellae and can also be involved in the formation of two (or more) lamellae (chains than called tie molecules). Several lamellae form a superstructure, a spherulite, often with a diameter in the range of 0.05 to 1 mm.
:The type and arrangement of (functional) residues of the repeat units effects or determines the crystallinity and strength of the secondary valence bonds. In isotactic polypropylene, the molecules form a helix. Like the zigzag conformation, such helices allow a dense chain packing. Particularly strong intermolecular interactions occur when the residues of the repeating units allow the formation of hydrogen bonds, as in the case of p-aramid. The formation of strong intramolecular associations may produce diverse folded states of single linear chains with distinct circuit topology. Crystallinity and superstructure are always dependent on the conditions of their formation, see also: crystallization of polymers. Compared to amorphous structures, semi-crystalline structures lead to a higher stiffness, density, melting temperature and higher resistance of a polymer.
* Cross-linked polymers: Wide-meshed cross-linked polymers are elastomers and cannot be molten (unlike thermoplastics); heating cross-linked polymers only leads to decomposition. Thermoplastic elastomers, on the other hand, are reversibly "physically crosslinked" and can be molten. Block copolymers in which a hard segment of the polymer has a tendency to crystallize and a soft segment has an amorphous structure are one type of thermoplastic elastomers: the hard segments ensure wide-meshed, physical crosslinking. | 7 | Physical Chemistry |
Equilibrium, in general, is a state in which opposing forces are balanced, and hence a system does not change in time. Radiative equilibrium is the specific case of thermal equilibrium, for the case in which the exchange of heat is done by radiative heat transfer.
There are several types of radiative equilibrium. | 7 | Physical Chemistry |
Microencapsulated pheromones (MECs) are small droplets of pheromone enclosed within polymer capsules. The capsules control the release rate of the pheromone into the surrounding environment. The capsules are small enough to be applied in the same method as used to spray insecticides. The effective field longevity of the microencapsulated pheromone formulations ranges from a few days to slightly more than a week, depending on climatic conditions, capsule size and chemical properties. Microcapsules in the pheromone formulations are usually kept above a prescribed diameter to avoid the risk of inhalation by humans. | 1 | Biochemistry |
Change in physical interactions can be utilized for the solidification process, and the fibrous state is usually achieved outside of the extrusion nozzle. Due to the reversibility of those physical interactions, subsequent crosslinking is traditionally required. | 7 | Physical Chemistry |
The discovery of an animal cell AMPylase, followed by the discovery of its ER localisation and that BiP is a prominent substrate for its activity were important breakthroughs. BiP (also known as Grp78) had long been known to undergo an inactivating post-translational modification, but it nature remain elusive. Widely assumed to be ADP-ribosylation, it turns out to be FICD-mediated AMPylation, as inactivating the FICD gene in cells abolished all measurable post-translational modification of BiP.
BiP is an ER-localised protein chaperone whose activity is tightly regulated at the transcriptional level via a gene-expression program known as the Unfolded Protein Response (UPR). The UPR is a homeostatic process that couples the transcription rate of BiP (and many other proteins) to the burden of unfolded proteins in the ER (so-called ER stress) to help maintain ER proteostasis. AMPylation adds another rapid post-translational layer of control of BiPs activity, as modification of Thr518 of BiPs substrate-binding domain with an AMP locks the chaperone into an inactive conformation. This modification is selectively deployed as ER stress wanes, to inactivate surplus BiP. However, as ER stress rises again, the same enzyme, FICD, catalyses the opposite reaction, BiP de-AMPylation.
An understanding of the structural basis of BiP AMPylation and de-AMPylation is gradually emerging, as are clues to the allostery that might regulate the switch in FICD's activity but important details of this process as it occurs in cells remain to be discovered.
The role of FICD in BiP AMPylation (and de-AMPylation) on Thr518 is well supported by biochemical and structural studies. Evidence has also been presented that in some circumstances FICD may AMPylate a different residue, Thr366 in BiP's nucleotide binding domain. | 1 | Biochemistry |
Basic helix-loop-helix leucine zipper transcription factors are, as their name indicates, transcription factors containing both Basic helix-loop-helix and leucine zipper motifs.
Examples include Microphthalmia-associated transcription factor and Sterol regulatory element binding protein (SREBP). | 1 | Biochemistry |
The Zerewitinoff determination or Zerevitinov determination is a quantitative chemical test for the determination of active hydrogens in a chemical substance. A sample is treated with the Grignard reagent, methylmagnesium iodide, which reacts with any acidic hydrogen atom to form methane. This gas can be determined quantitatively by measuring its volume. For example: | 3 | Analytical Chemistry |
The Cahn–Ingold–Prelog priority rules (often abbreviated as the CIP system) were first published in 1966; allowing enantiomers to be more easily and accurately described.
The same year saw first successful enantiomeric separation by gas chromatography an important development as the technology was in common use at the time.
Metal-catalysed enantioselective synthesis was pioneered by William S. Knowles, Ryōji Noyori and K. Barry Sharpless; for which they would receive the 2001 Nobel Prize in Chemistry. Knowles and Noyori began with the development of asymmetric hydrogenation, which they developed independently in 1968. Knowles replaced the achiral triphenylphosphine ligands in Wilkinson's catalyst with chiral phosphine ligands. This experimental catalyst was employed in an asymmetric hydrogenation with a modest 15% enantiomeric excess. Knowles was also the first to apply enantioselective metal catalysis to industrial-scale synthesis; while working for the Monsanto Company he developed an enantioselective hydrogenation step for the production of L-DOPA, utilising the DIPAMP ligand.
Noyori devised a copper complex using a chiral Schiff base ligand, which he used for the metal–carbenoid cyclopropanation of styrene.
In common with Knowles findings, Noyoris results for the enantiomeric excess for this first-generation ligand were disappointingly low: 6%. However continued research eventually led to the development of the Noyori asymmetric hydrogenation reaction.
Sharpless complemented these reduction reactions by developing a range of asymmetric oxidations (Sharpless epoxidation, Sharpless asymmetric dihydroxylation, Sharpless oxyamination) during the 1970s and 1980s. With the asymmetric oxyamination reaction, using osmium tetroxide, being the earliest.
During the same period, methods were developed to allow the analysis of chiral compounds by NMR; either using chiral derivatizing agents, such as Mosher's acid,
or europium based shift reagents, of which Eu(DPM) was the earliest.
Chiral auxiliaries were introduced by E.J. Corey in 1978 and featured prominently in the work of Dieter Enders. Around the same time enantioselective organocatalysis was developed, with pioneering work including the Hajos–Parrish–Eder–Sauer–Wiechert reaction.
Enzyme-catalyzed enantioselective reactions became more and more common during the 1980s, particularly in industry, with their applications including asymmetric ester hydrolysis with pig-liver esterase. The emerging technology of genetic engineering has allowed the tailoring of enzymes to specific processes, permitting an increased range of selective transformations. For example, in the asymmetric hydrogenation of statin precursors. | 4 | Stereochemistry |
Martha was born in Georgia, Vermont on February 13, 1870. She grew up in Easthampton, Massachusetts where she graduated high school. She earned her B.S. degree from Smith College in 1892. Prior to enrolling in graduate school at Yale University, she taught as a science teacher in New York and Massachusetts. She started graduate school in 1896 and graduated with her Ph.D. in chemistry in 1898. After completing her Ph.D., she continued working for her Ph.D. advisor, Andrew Gooch in the Kent Chemistry Laboratory for one year and then transferred to the Rhode Island Experiment Station where she worked as an assistant chemist in 1900. From 1901-1904, she went back to being a science teacher and taught chemistry and physics at Wilson College. In 1904, she also married Issac King Phelps, who was working as a chemistry instructor at Yale and George Washington University at the time. In 1908, the couple moved to Washington D.C. where Martha went to work for the Bureau of Standards as a chemistry researcher and Issac went to work for the U.S. Department of Agriculture. Martha ceased working as researcher in 1909. Martha was one of the first female scientists to be employed by the Bureau of Standards. After 1909, she began her activist work in women's education clubs until retirement. Martha and Issac lived in Washington D.C until 1923, until they moved to New Haven, Connecticut where Martha eventually died on March 15, 1933. | 3 | Analytical Chemistry |
Hordein is a prolamin glycoprotein, present in barley and some other cereals, together with gliadin and other glycoproteins (such as glutelins) coming under the general name of gluten. Hordeins are found in the endosperm where one of their functions is to act as a storage unit.
In comparison to other proteins, hordeins are less soluble when compared to proteins such as albumin and globulins.
In relation to amino acids, hordeins have a substantial amount of proline and glutamine but lack charged amino acids such as lysine.
Some people are sensitive to hordein due to disorders such as celiac disease or gluten intolerance.
Along with gliadin (the prolamin gluten found in wheat), hordein is present in many foods and also may be found in beer. Hordein is usually the main problem for coeliacs wishing to drink beer.
Coeliacs are able to find specialist breads that are low in hordein, gliadin and other problematic glycoproteins, just as they can find gluten free beer which either uses ingredients that do not contain gluten, or otherwise has the amounts of gliadin or hordein present controlled to stated limits. | 1 | Biochemistry |
Some turbofans have an intermediate pressure (IP) compressor located between the fan and the high pressure (HP) compressor to increase overall pressure ratio. US civil engines tend to mount the IP compressor on the LP shaft, directly behind the fan, whereas Rolls-Royce normally mount the IP compressor on a separate (i.e. IP) shaft, which is driven by an IP turbine. Either way, matching problems can arise.
The IP compressor outlet corrected flow must match the entry corrected flow of the HP compressor, which is decreasing as the engine is throttled back. At a certain IP compressor working line slope, the IP compressor outlet corrected flow remains constant. However, by adopting a shallower working line, the extra IP compressor pressure ratio at a given IP compressor entry corrected flow enables the IP compressor outlet corrected flow to decrease and match up with the falling HP compressor entry corrected flow. Unfortunately this can lead to a poor IP compressor surge margin at part flow.
Surge margin can be improved by adding variable stators to the IP compressor and/or adding a blow-off valve between the IP and HP compressors. The former makes the IP compressor surge line shallower, swinging it away from the shallow working line, thus improving IP compressor surge margin.
At a given IP compressor pressure ratio, opening the blow-off valve forces the IP compressor entry corrected flow to increase, to a point where the IP compressor surge margin tends to be better. Effectively, opening the blow-off valve lowers the IP compressor working line. Any flow surplus to that demanded by the HP compressor passes through the blow-off valve into the bypass duct. The blow-off valve is normally only opened at throttled conditions, since it wastes energy. | 7 | Physical Chemistry |
Conductivity measurement is a versatile tool in process control. The measurement is simple and fast, and most advanced sensors require only a little maintenance. The measured conductivity reading can be used to make various assumptions on what is happening in the process. In some cases it is possible to develop a model to calculate the concentration of the liquid.
Concentration of pure liquids can be calculated when the conductivity and temperature is measured. The preset curves for various acids and bases are commercially available. For example, one can measure the concentration of high purity hydrofluoric acid using conductivity-based concentration measurement [Zhejiang Quhua Fluorchemical, China Valmet Concentration 3300]. A benefit of conductivity- and temperature-based concentration measurement is the superior speed of inline measurement compared to an on-line analyzer.
Conductivity-based concentration measurement has limitations. The concentration-conductivity dependence of most acids and bases is not linear. Conductivity-based measurement cannot determine on which side of the peak the measurement is, and therefore the measurement is only possible on a linear section of the curve.
Kraft pulp mills use conductivity-based concentration measurement to control alkali additions to various stages of the cook. Conductivity measurement will not determine the specific amount of alkali components, but it is a good indication on the amount of effective alkali (NaOH + NaS as NaOH or NaO) or active alkali (NaOH + NaS as NaOH or NaO) in the cooking liquor. The composition of the liquor varies between different stages of the cook. Therefore, it is necessary to develop a specific curve for each measurement point or to use commercially available products.
The high pressure and temperature of cooking process, combined with high concentration of alkali components, put a heavy strain on conductivity sensors that are installed in process. The scaling on the electrodes needs to be taken into account, otherwise the conductivity measurement drifts, requiring increased calibration and maintenance. | 7 | Physical Chemistry |
The majority of rivers on the planet and many lakes have received or are receiving inputs from human-kind's activities. In the industrialised world, many rivers have been very seriously polluted, at least during the 19th and the first half of the 20th centuries. Although in general there has been much improvement in the developed world, there is still a great deal of river pollution apparent on the planet. | 2 | Environmental Chemistry |
HNF4 (Hepatocyte Nuclear Factor 4) is a nuclear receptor protein mostly expressed in the liver, gut, kidney, and pancreatic beta cells that is critical for liver development. In humans, there are two paralogs of HNF4, HNF4α and HNF4γ, encoded by two separate genes and respectively. | 1 | Biochemistry |
The hormone research he became involved with in 1940 was initiated by the RAF who then believed German fighter pilots were given cortical hormones He remained a research Fellow at Oxford until 1948 working under Sir Robert Robinson, when he became the Smithson Fellow at the University of Cambridge where he remained until 1952. At Cambridge he worked with Lord Todd.
He returned to Australia in 1952 to take up a Professorship in organic chemistry at the University of Sydney, he was made a fellow of the Australian Academy of Science in 1954. He held his position at the University of Sydney until 1955 when he took a similar position at Manchester University. He was made a Fellow of the Royal Society in 1958.
Birch returned to Australia again in 1967 to establish the Research School of Chemistry at the Australian National University in Canberra, becoming its founding dean. He remained involved with the school until 1980. He served as President of the Royal Australian Chemical Institute from 1977 to 1978, and also chaired the 1977 Independent Inquiry into CSIRO.
He served as President of the Australian Academy of Science from 1982 to 1986. Birch was made a Companion of the Order of Australia (AC) in 1987 for his contributions to science in Australia. He was awarded Honorary Fellowship of the Royal Australian Chemical Institute, in 1994. He was also a founding member of the Australian Science and Technology Council.
Before his death in 1995, the Research School of Chemistry building at ANU was named the "Birch Building" in his honour. | 0 | Organic Chemistry |
The Curtin–Hammett principle is a principle in chemical kinetics proposed by David Yarrow Curtin and Louis Plack Hammett. It states that, for a reaction that has a pair of reactive intermediates or reactants that interconvert rapidly (as is usually the case for conformational isomers), each going irreversibly to a different product, the product ratio will depend both on the difference in energy between the two conformers and the energy barriers from each of the rapidly equilibrating isomers to their respective products. Stated another way, the product distribution reflects the difference in energy between the two rate-limiting transition states. As a result, the product distribution will not necessarily reflect the equilibrium distribution of the two intermediates. The Curtin–Hammett principle has been invoked to explain selectivity in a variety of stereo- and regioselective reactions. The relationship between the (apparent) rate constants and equilibrium constant is known as the Winstein-Holness equation. | 7 | Physical Chemistry |
In Russia, starting from May 18, 2012, modafinil is Schedule II controlled substance. Being classified as a schedule II controlled substance in Russia means that it is seen as a drug with a high potential for abuse and dependence. This classification imposes strict regulations on the production, distribution, and use of modafinil. Possession of a few modafinil pills can lead to three to ten years imprisonment. Modafinil is not approved for medical use in Russia and cannot be bought even in pharmacies. It also cannot be imported from abroad, even if you have a prescription issued outside Russia. There are multiple cases of criminal proceedings initiated against Russian residents who tried to import modafinil by mail from abroad. | 4 | Stereochemistry |
This originates from permanent and induced dipoles aligning to an electric field. Their orientation polarisation is disturbed by thermal noise (which mis-aligns the dipole vectors from the direction of the field), and the time needed for dipoles to relax is determined by the local viscosity. These two facts make dipole relaxation heavily dependent on temperature, pressure, and chemical surrounding. | 7 | Physical Chemistry |
Molecular recognition is the specific binding of a guest molecule to a complementary host molecule to form a host–guest complex. Often, the definition of which species is the "host" and which is the "guest" is arbitrary. The molecules are able to identify each other using non-covalent interactions. Key applications of this field are the construction of molecular sensors and catalysis. | 6 | Supramolecular Chemistry |
Different sigma factors are utilized under different environmental conditions. These specialized sigma factors bind the promoters of genes appropriate to the environmental conditions, increasing the transcription of those genes.
Sigma factors in E. coli:
*σ(RpoD) – σ – the "housekeeping" sigma factor or also called as primary sigma factor (Group 1), transcribes most genes in growing cells. Every cell has a "housekeeping" sigma factor that keeps essential genes and pathways operating. In the case of E. coli and other gram-negative rod-shaped bacteria, the "housekeeping" sigma factor is σ. Genes recognized by σ all contain similar promoter consensus sequences consisting of two parts. Relative to the DNA base corresponding to the start of the RNA transcript, the consensus promoter sequences are characteristically centered at 10 and 35 nucleotides before the start of transcription (−10 and −35).
*σ (FecI) – the ferric citrate sigma factor, regulates the fec gene for iron transport and metabolism
*σ (RpoE) – extreme heat stress response and the extracellular proteins sigma factor
*σ (RpoF/FliA) – the flagellar synthesis and chemotaxis sigma factor
*σ (RpoH) – the heat shock sigma factor, it is turned on when the bacteria are exposed to heat. Due to the higher expression, the factor will bind with a high probability to the polymerase-core-enzyme. Doing so, other heatshock proteins are expressed, which enable the cell to survive higher temperatures. Some of the enzymes that are expressed upon activation of σ are chaperones, proteases and DNA-repair enzymes.
*σ (RpoS) – the starvation/stationary phase sigma factor
*σ (RpoN) – the nitrogen-limitation sigma factor
There are also anti-sigma factors that inhibit the function of sigma factors and anti-anti-sigma factors that restore sigma factor function. | 1 | Biochemistry |
Photoinhibition can be measured from isolated thylakoid membranes or their subfractions, or from intact cyanobacterial cells by measuring the light-saturated rate of oxygen evolution in the presence of an artificial electron acceptor (quinones and dichlorophenol-indophenol have been used).
The degree of photoinhibition in intact leaves can be measured using a fluorimeter to measure the ratio of variable to maximum value of chlorophyll a fluorescence (F/F). This ratio can be used as a proxy of photoinhibition because more energy is emitted as fluorescence from Chlorophyll a when many excited electrons from PSII are not captured by the acceptor and decay back to their ground state.
When measuring F/F, the leaf must be incubated in the dark for at least 10 minutes, preferably longer, before the measurement, in order to let non-photochemical quenching relax. | 5 | Photochemistry |
Thionyl chloride reacts exothermically with water to form sulfur dioxide and hydrochloric acid:
By a similar process it also reacts with alcohols to form alkyl chlorides. If the alcohol is chiral the reaction generally proceeds via an Si mechanism with retention of stereochemistry; however, depending on the exact conditions employed, stereo-inversion can also be achieved. Historically the use of with pyridine was called the Darzens halogenation, but this name is rarely used by modern chemists.
Reactions with an excess of alcohol produce sulfite esters, which can be powerful methylation, alkylation and hydroxyalkylation reagents.
For example, the addition of to amino acids in methanol selectively yields the corresponding methyl esters. | 0 | Organic Chemistry |
Emulsions are used to manufacture polymer dispersions – polymer production in an emulsion phase has a number of process advantages, including prevention of coagulation of product. Products produced by such polymerisations may be used as the emulsions – products including primary components for glues and paints. Synthetic latexes (rubbers) are also produced by this process. | 7 | Physical Chemistry |
Side effects of the tablet form in conjunction with levodopa include, in decreasing order of frequency, nausea, hallucinations, confusion, depression, loss of balance, insomnia, increased involuntary movements, agitation, slow or irregular heart rate, delusions, hypertension, new or increased angina pectoris, and syncope. Most of the side effects are due to a high dopamine signaling, and can be alleviated by reducing the dose of levodopa.
The main side effects of the patch form for depression include application-site reactions, insomnia, diarrhea, and sore throat. The selegiline patch carries a black box warning about a possible increased risk of suicide, especially for young people, as do all antidepressants since 2007. | 4 | Stereochemistry |
Aluminium chloride is manufactured on a large scale by the exothermic reaction of aluminium metal with chlorine or hydrogen chloride at temperatures between .
Aluminium chloride may be formed via a single displacement reaction between copper(II) chloride and aluminium.
In the US in 1993, approximately 21,000 tons were produced, not counting the amounts consumed in the production of aluminium.
Hydrated aluminium trichloride is prepared by dissolving aluminium oxides in hydrochloric acid. Metallic aluminium also readily dissolves in hydrochloric acid ─ releasing hydrogen gas and generating considerable heat. Heating this solid does not produce anhydrous aluminium trichloride, the hexahydrate decomposes to aluminium hydroxide when heated:
Aluminium also forms a lower chloride, aluminium(I) chloride (AlCl), but this is very unstable and only known in the vapour phase. | 0 | Organic Chemistry |
Mauveine is a mixture of four related aromatic compounds differing in number and placement of methyl groups. Its organic synthesis involves dissolving aniline, p-toluidine, and o-toluidine in sulfuric acid and water in a roughly 1:1:2 ratio, then adding potassium dichromate.
Mauveine A () incorporates 2 molecules of aniline, one of p-toluidine, and one of o-toluidine. Mauveine B () incorporates one molecule each of aniline, p-toluidine, and two of o-toluidine. In 1879, Perkin showed mauveine B related to safranines by oxidative/reductive loss of the p-tolyl group. In fact, safranine is a 2,8-dimethyl phenazinium salt, whereas the parasafranine produced by Perkin is presumed to be the 1,8- (or 2,9-) dimethyl isomer.
The molecular structure of mauveine proved difficult to determine, finally being identified in 1994. In 2007, two more were isolated and identified: mauveine B2, an isomer of mauveine B with methyl on different aryl group, and mauveine C, which has one more p-methyl group than mauveine A.
In 2008, additional mauveines and pseudomauveines were discovered, bringing the total number of these compounds up to 12. In 2015 a crystal structure was reported for the first time. | 7 | Physical Chemistry |
*Addition reaction
**Aldol addition
**Electrophilic addition
**Michael addition
**Mukaiyama aldol addition
**Nucleophilic addition
*Cyclization
**Bergman cyclization
**Nazarov cyclization reaction
*Elimination reaction
**Beta elimination
**Cope elimination
**E1cB elimination reaction
**Hofmann elimination
*Organic redox reaction
**Cannizzaro reaction
**Oxidation
***Baeyer-Villiger oxidation
***Corey-Kim oxidation
***Dess-Martin oxidation
***Fleming-Tamao oxidation
***Jones oxidation
***Nucleophilic epoxidation
***Oppenauer oxidation
***Prilezhaev reaction
***Rubottom oxidation
***Schmidt reaction
***Swern oxidation
***Wacker-Tsuji oxidation
**Reduction
***Birch reduction
***Bouveault-Blanc reduction
***CBS reduction
***Clemmensen reduction
***Corey-Bakshi-Shibata reduction
***Corey–Itsuno reduction
***Fukuyama reduction
***Luche reduction
***Meerwein-Ponndorf-Verley reduction
***Rosenmund reduction
***Staudinger reduction
***Wolff-Kishner reduction
*Pericyclic reaction
**Cheletropic reaction
**Cycloaddition
***1,3-Dipolar cycloaddition
****Azide-alkyne Huisgen cycloaddition
***Diels–Alder reaction
***Nitrone-olefin (3+2) cycloaddition
***Staudinger ketene-imine cycloaddition
**Dyotropic reaction
**Electrocyclic reaction
**Group transfer reaction
**Sigmatropic reaction
*Polymerization
**Ring-opening metathesis polymerisation
*Rearrangement reaction
**Baker–Venkataraman rearrangement
**Beckmann rearrangement
**Benzilic acid rearrangement
**Brook rearrangement
**Claisen rearrangement
**Cope rearrangement
**Curtius rearrangement
**Fries rearrangement
**Ireland–Claisen rearrangement
**Newman–Kwart rearrangement
**Overman rearrangement
**Oxy-Cope rearrangement
**Pinacol rearrangement
**1,2-Wittig rearrangement
**2,3-Wittig rearrangement
*Substitution reaction
**Electrophilic aromatic substitution
**Nucleophilic aromatic substitution
**Electrophilic substitution
**Nucleophilic substitution
***S1 reaction
***S2 reaction
**Vicarious nucleophilic substitution | 0 | Organic Chemistry |
A supramolecular host could bind to a guest molecule in such a way that the guests labile group is positioned close to the reactive group of another reactive species. The proximity of the two groups enhances the probability that the reaction could occur and thus the reaction rate is increased. This concept is similar to the principle of preorganization which states that complexation could be improved if the binding motifs are preorganized in a well-defined position so that the host does not require any major conformational change for complexation. In this case, the catalyst is preorganized such that no major conformational changes is required for the reaction to occur. A notable example of catalysts that employ this mechanism is Jean-Marie Lehns crown ether. In addition, catalysts based on functionalized cyclodextrins often employ this mode of catalysis. | 6 | Supramolecular Chemistry |
Silicon carbide can host point defects in the crystal lattice which are known as color centers. These defects can produce single photons on demand and thus serve as a platform for single-photon source. Such a device is a fundamental resource for many emerging applications of quantum information science. If one pumps a color center via an external optical source or electric current, the color center will be brought to the excited state and then relax with the emission of one photon.
One well known point defect in silicon carbide is the divacancy which has a similar electronic structure as the nitrogen-vacancy center in diamond. In 4H-SiC, the divacancy has four different configurations which correspond to four zero-phonon lines (ZPL). These ZPL values are written using the notation V-V and the unit eV: hh(1.095), kk(1.096), kh(1.119), and hk(1.150). | 8 | Metallurgy |
His academic teaching experience spans in both undergraduate level at the University of Massachusetts and postgraduate level at the University of Connecticut and the University of Patras.
His published work as co-author includes three books, six chapters in other authors' books, 92 scientific papers and 146 research presentations. Vasilis Gregoriou is also co-inventor of 15 patents. His research interests include flexible photovoltaic cells based on organic semiconductors, optically active materials based on conjugated oligomers, and nanostructured polymer materials. He has served as President of Society for Applied Spectroscopy (SAS) in 2001 and now he participates as National Representative of Greece in the Committee of the European Research Council (ERC) for the Horizon 2020 program, the Mari Sklodowska-Curie actions and the Future and Emerging Technologies (FET). Vasilis Gregoriou has been the Director of the National Hellenic Research Foundation since 2013.
As a technology entrepreneur, Vasilis Gregoriou is the co-founder and the CEO of Advent Technologies which is based in Cambridge, Massachusetts. Advent Technologies develops advanced technology and devices in the field of energy and defense and it has also developed research collaborations with Northeastern University in Boston, US, Patras University in Greece, and the Institute of Chemical Engineering Sciences (ICE-HT/FORTH). | 7 | Physical Chemistry |
Electron-counting rules are used to predict the preferred electron count for molecules. The octet rule, the 18-electron rule, and Hückels 4n + 2 pi-electron rule are proven to be useful in predicting the molecular stability. Wades rules were formulated to explain the electronic requirement of monopolyhedral borane clusters. The Jemmis mno rules are an extension of Wade's rules, generalized to include condensed polyhedral boranes as well.
The first condensed polyhedral borane, , is formed by sharing four vertices between two icosahedra. According to Wades n + 1 rule for n-vertex closo structures, should have a charge of +2 (n + 1 = 20 + 1 = 21 pairs required; 16 BH units provide 16 pairs; four shared boron atoms provide 6 pairs; thus 22 pairs are available). To account for the existence of as a neutral species, and to understand the electronic requirement of condensed polyhedral clusters, a new variable, m, was introduced and corresponds to the number of polyhedra (sub-clusters). In Wades n + 1 rule, the 1 corresponds to the core bonding molecular orbital (BMO) and the n corresponds to the number of vertices, which in turn is equal to the number of tangential surface BMOs. If m polyhedra condense to form a macropolyhedron, m core BMOs will be formed. Thus the skeletal electron pair (SEP) requirement of closo-condensed polyhedral clusters is m + n.
Single-vertex sharing is a special case where each subcluster needs to satisfy Wades rule separately. Let a and b be the number of vertices in the subclusters including the shared atom. The first cage requires a + 1 and the second cage requires b + 1 SEPs. Therefore, a total of a + b + 2 or a + b + m SEPs are required; but a + b = n + 1, as the shared atom is counted twice. The rule can be modified to m + n + 1, or generally m + n + o, where o corresponds to the number of single-vertex sharing condensations. The rule can be made more general by introducing a variable, p, corresponding to the number of missing vertices, and q', the number of caps. As such, the generalized Jemmis rule can be stated as follows:
:The SEP requirement of condensed polyhedral clusters is m + n + o + p − q, where m is the number of subclusters, n is the number of vertices, o is the number of single-vertex shared condensations, p is the number of missing vertices and q is the number of caps. | 7 | Physical Chemistry |
The insert is created by PCR using Taq polymerase. This polymerase lacks 3 to 5 proofreading activity and, with a high probability, adds a single, 3-adenine overhang to each end of the PCR product. It is best if the PCR primers have guanines at the 5 end as this maximizes probability of Taq DNA polymerase adding the terminal adenosine overhang. Thermostable polymerases containing extensive 3´ to 5´ exonuclease activity should not be used as they do not leave the 3´ adenine-overhangs. | 1 | Biochemistry |
Thermometric titrimetry is particularly suited to the determination of a range of analytes where a precipitate is formed by reaction with the titrant. In some cases, an alternative to traditional potentiometric titration practice can be offered. In other cases, reaction chemistries may be employed for which there is no satisfactory equivalent in potentiometric titrimetry. | 3 | Analytical Chemistry |
The following panels show sea surface concentrations of fields prepared by GLODAPv1.1. The "pre-industrial" is the 18th century, while "present-day" is approximately the 1990s.
The following panels show sea surface concentrations of fields prepared by GLODAPv2. The "pre-industrial" is the 18th century, while "present-day" is normalised to 2002. Note that these properties are shown in mass units (per kilogram of seawater) rather than the volume units (per cubic metre of seawater) used in the GLODAPv1.1 panels. | 9 | Geochemistry |
There is a hypothesis that states that TEs might provide a ready source of DNA that could be co-opted by the cell to help regulate gene expression. Research showed that many diverse modes of TEs co-evolution along with some transcription factors targeting TE-associated genomic elements and chromatin are evolving from TE sequences. Most of the time, these particular modes do not follow the simple model of TEs and regulating host gene expression. | 1 | Biochemistry |
In terms of applications, a popular allyl complex is allyl palladium chloride.
The reactivity of allyl ligands depends on the overall complex, although the influence of the metal center can be roughly summarized as
:(more reactive) Fe ≫ Pd > Mo > W (less reactive)
Such complexes are usually electrophilic (i.e., react with nucleophiles), but nickel allyl complexes are usually nucleophilic (resp. with electrophiles). In the former case, the addition may occur at unusual locations, and can be useful in organic synthesis. | 0 | Organic Chemistry |
Research has shown that applying 5 to 15 volts of electricity for 50 ms to the segmental nerve that innervates the light organ leads to a glow 1.5 seconds after that lasts for five to ten seconds. Stimulation of the segmental nerve has been found to lead to several different nerve impulses, and frequency of nervous impulses has been found to be proportional to the intensity of the stimulus applied. A high frequency of nervous impulse was found to lead to a constant latency. The light organ is inactive in the absence of nerve impulses. Constant nerve signaling was shown to coincide with constant emission of light from the light organ with a higher frequency coinciding with a higher amplitude of light emitted up to 30 impulses per second. Impulses beyond this frequency were not found to be associated with a more intense glow. The fact that the frequency of nerve impulses was able to exceed beyond the maximum intensity of light emission suggests some limitations in the mechanism either arising from the synapse or the cell's light producing process. Additionally, a series of action potentials have been shown to lead to the sporadic, discontinuous emission to light. It was also found that a higher frequency of action potentials lead to a higher likelihood of any emission of light. Nerve impulses are associated with a depolarization of the photocyte which plays a role in its light emitting mechanism, and greater depolarization events were found to be associated with more intense lightning. The nerve innervating the light organ containing photocytes has only two axons, but they branch repeatedly allowing the numerous photocytes to be innervated with each cell being associated with several nerve terminals with each terminal possibly being associated with several synapses.
It was found that the junction between at the end of the neuron innervating the light organ differs from the kind of junction found between two different neurons or between neurons and muscles in the neuromuscular junction. The depolarization of the photocyte following nervous stimulation was found to be one-hundred times slower than the with the other two kinds of junctions and this slow response cannot be attributed to the rate of diffusion because the synapse between the neuron and photocyte is relatively small. It has been found that the neurons that control the light mechanism terminate at the tracheal cells rather than the photocytes themselves. | 1 | Biochemistry |
Flash photolysis is an alternative to pulse radiolysis that uses high-power light pulses (e.g. from an excimer laser) rather than beams of electrons to initiate chemical reactions. Typically ultraviolet light is used which requires less radiation shielding than required for the X-rays emitted in pulse radiolysis. | 5 | Photochemistry |
In July 2016 Florida declared a state of emergency for four counties as a result of blooms. They were said to be "destroying" a number of businesses and affecting local economies, with many needing to shut down entirely. Some beaches were closed, and hotels and restaurants suffered a drop in business. Tourist sporting activities such as fishing and boating were also affected.
In 2019, the biggest Sargassum bloom ever seen created a crisis in the Tourism industry in North America. This event was likely caused by climate change and nutrient pollution from fertilizers. Several Caribbean countries considered declaring a state of emergency due to the impact on tourism as a result of environmental damage and potentially toxic and harmful health effects. | 3 | Analytical Chemistry |
Size of sea salt aerosols ranges widely from ~0.05 to 10 μm in diameter, with most of masses concentrated in super-micron range (coarse mode), and highest number concentration in sub-micron range. Correspondingly, sea salt aerosols have a wide range of atmospheric lifetimes. As the sea salt aerosols are hygroscopic, their particle sizes may vary with humidity by up to a factor of 2. Sea salt aerosols influence the sulfate aerosol formation in different ways due to the different sizes. Very small sea salt aerosols, which are below the critical diameter for droplet activation at low supersaturations, can serve as nuclei for the growth of sulfate particles, while larger sea salt particles serve as a sink for gaseous hydrogen sulfate (HSO) molecules, reducing the amount of sulfate available for the formation of accumulation mode particles. | 9 | Geochemistry |
The signs and symptoms of acute beryllium pneumonitis usually resolve over several weeks to months, but may be fatal in 10 percent of cases, and about 15–20% of cases may progress to chronic beryllium disease.
Acute beryllium poisoning approximately doubles the risk of lung cancer. The mechanism by which beryllium is carcinogenic is unclear, but may be due to ionic beryllium binding to nucleic acids; it is not mutagenic. | 1 | Biochemistry |
IRsweep was founded in 2014 as a spin-off from the Swiss Federal Institute of Technology (ETH Zurich). The company commercialized its first product after having developed its prototypes for academic research projects. The first derived product is the IRcell, a cylindrical multipass cell combining a long optical path in a small detection volume. | 7 | Physical Chemistry |
Influenza neuraminidase is a mushroom-shaped projection on the surface of the influenza virus. It has a head consisting of four co-planar and roughly spherical subunits, and a hydrophobic region that is embedded within the interior of the virus' membrane. It comprises a single polypeptide chain that is oriented in the opposite direction to the hemagglutinin antigen. The composition of the polypeptide is a single chain of six conserved polar amino acids, followed by hydrophilic, variable amino acids. β-Sheets predominate as the secondary level of protein conformation.
The structure of trans-sialidase includes a catalytic β-propeller domain, a N-terminal lectin-like domain and an irregular beta-stranded domain inserted into the catalytic domain.
Recent emergence of oseltamivir and zanamivir resistant human influenza A(H1N1) H274Y has emphasized the need for suitable expression systems to obtain large quantities of highly pure and stable, recombinant neuraminidase through two separate artificial tetramerization domains that facilitate the formation of catalytically active neuraminidase homotetramers from yeast and Staphylothermus marinus, which allow for secretion of FLAG-tagged proteins and further purification. | 0 | Organic Chemistry |
Schlögl received numerous scientific awards for his work, including the Erwin Schrödinger Prize of the Austrian Academy of Sciences in 1985, the prize for natural sciences of the city of Vienna in 1989, and the Wilhelm Exner Medal of the Austrian Economic Association in 1991. | 0 | Organic Chemistry |
For his work, Woodward received many awards, honors and honorary doctorates, including election to the American Academy of Arts and Sciences in 1948, the National Academy of Sciences in 1953, the American Philosophical Society in 1962, and membership in academies around the world. He was also a consultant to many companies such as Polaroid, Pfizer, and Merck. Other awards include:
* John Scott Medal, from the Franklin Institute and City of Philadelphia, 1945
* Leo Hendrik Baekeland Award, from the North Jersey Section of the American Chemical Society, 1955
* Elected a Foreign Member of the Royal Society (ForMemRS) in 1956
* Davy Medal, from the Royal Society in 1959
* Roger Adams Medal, from the American Chemical Society in 1961
* Pius XI Gold Medal, from the Pontifical Academy of Sciences in 1969
* National Medal of Science from the United States in 1964 ("For an imaginative new approach to the synthesis of complex organic molecules and, especially, for his brilliant syntheses of strychnine, reserphine, lysergic acid, and chlorophyll.")
* Nobel Prize in Chemistry in 1965
* Willard Gibbs Award from the Chicago Section of the American Chemical Society in 1967
* Lavoisier Medal from the Société chimique de France in 1968
* The Order of the Rising Sun, Second Class from the Emperor of Japan in 1970
* Hanbury Memorial Medal from The Pharmaceutical Society of Great Britain in 1970
* Pierre Bruylants Medal from the University of Louvain in 1970
* AMA Scientific Achievement Award in 1971
* Cope Award from the American Chemical Society, shared with Roald Hoffmann in 1973
* Copley Medal from the Royal Society, London in 1978 | 4 | Stereochemistry |
The marine carbon cycle is composed of processes that exchange carbon between various pools within the ocean as well as between the atmosphere, Earth interior, and the seafloor. The carbon cycle is a result of many interacting forces across multiple time and space scales that circulates carbon around the planet, ensuring that carbon is available globally. The Oceanic carbon cycle is a central process to the global carbon cycle and contains both inorganic carbon (carbon not associated with a living thing, such as carbon dioxide) and organic carbon (carbon that is, or has been, incorporated into a living thing). Part of the marine carbon cycle transforms carbon between non-living and living matter.
Three main processes (or pumps) that make up the marine carbon cycle bring atmospheric carbon dioxide (CO) into the ocean interior and distribute it through the oceans. These three pumps are: (1) the solubility pump, (2) the carbonate pump, and (3) the biological pump. The total active pool of carbon at the Earth's surface for durations of less than 10,000 years is roughly 40,000 gigatons C (Gt C, a gigaton is one billion tons, or the weight of approximately 6 million blue whales), and about 95% (~38,000 Gt C) is stored in the ocean, mostly as dissolved inorganic carbon. The speciation of dissolved inorganic carbon in the marine carbon cycle is a primary controller of acid-base chemistry in the oceans. | 9 | Geochemistry |
Weak links play a very important role in modern superconductivity. In most cases weak links are oxide barriers between two superconducting thin films, but it can also be a crystal boundary (in the case of high-Tc superconductors). A schematic representation is given in Fig. 4. Now consider the ring which is thick everywhere except for a small section where the ring is closed via a weak link (Fig. 3b). The velocity is zero except near the weak link. In these regions the velocity contribution to the total phase change in the loop is given by (with Eq. ())
The line integral is over the contact from one side to the other in such a way that the end points of the line are well inside the bulk of the superconductor where . So the value of the line integral is well-defined (e.g. independent of the choice of the end points). With Eqs. (), (), and ()
Without proof we state that the supercurrent through the weak link is given by the so-called DC Josephson relation
The voltage over the contact is given by the AC Josephson relation
The names of these relations (DC and AC relations) are misleading since they both hold in DC and AC situations. In the steady state (constant ) Eq. () shows that V=0 while a nonzero current flows through the junction. In the case of a constant applied voltage (voltage bias) Eq. () can be integrated easily and gives
Substitution in Eq. () gives
This is an AC current. The frequency
is called the Josephson frequency. One μV gives a frequency of about 500 MHz. By using Eq. () the flux quantum is determined with the high precision as given in Eq. ().
The energy difference of a Cooper pair, moving from one side of the contact to the other, is . With this expression Eq. () can be written as which is the relation for the energy of a photon with frequency ν.
:The AC Josephson relation (Eq. ()) can be easily understood in terms of Newtons law, (or from one of the London equations). We start with Newton's law
:Substituting the expression for the Lorentz force and using the general expression for the co-moving time derivative gives
:Eq. () gives so
:Take the line integral of this expression. In the end points the velocities are zero so the ∇v term gives no contribution. Using and Eq. (), with and , gives Eq. (). | 7 | Physical Chemistry |
Temporins are a family of peptides isolated originally from the skin secretion of the European red frog, Rana temporaria. Peptides belonging to the temporin family have been isolated also from closely related North American frogs, such as Rana sphenocephala. | 1 | Biochemistry |
The structure of P680 consists of a heterodimer of two distinct chlorophyll molecules,
referred to as P and P. This “special pair” forms an excitonic dimer that functions as a single unit, excited by light energy as if they were a single molecule. | 5 | Photochemistry |
In medical testing applications and industrial samples with high concentrations or interfering material, there is often a dialyzer module in the instrument in which the analyte permeates through a dialysis membrane into a separate flow path going on to further analysis. The purpose of a dialyzer is to separate the analyte from interfering substances such as protein, whose large molecules do not go through the dialysis membrane but go to a separate waste stream. The reagents, sample and reagent volumes, flow rates, and other aspects of the instrument analysis depend on which analyte is being measured. The autoanalyzer is also a very small machine | 3 | Analytical Chemistry |
The reaction of a strong acid with a strong base is essentially a quantitative reaction. For example,
In this reaction both the sodium and chloride ions are spectators as the neutralization reaction,
does not involve them. With weak bases addition of acid is not quantitative because a solution of a weak base is a buffer solution. A solution of a weak acid is also a buffer solution. When a weak acid reacts with a weak base an equilibrium mixture is produced. For example, adenine, written as AH, can react with a hydrogen phosphate ion, .
The equilibrium constant for this reaction can be derived from the acid dissociation constants of adenine and of the dihydrogen phosphate ion.
The notation [X] signifies "concentration of X". When these two equations are combined by eliminating the hydrogen ion concentration, an expression for the equilibrium constant, is obtained. | 7 | Physical Chemistry |
Liquids with low vapor pressures are preferred for the working fluids to minimize evaporation loss due to flash evaporation.
Liquids have been found that in the range of 300 to 900 K have a vapor pressure so low that the evaporation loss during the normal lifetime of a space system
(possibly as long as 30 years) will be only a small fraction of the total mass of the radiator.
Operating life of the fluid in the LDR environment is affected by thermal stability, oxidative stability, and resistance to radiation.
If a liquid metal is used as the coolant, the pumping of the liquid may use an electromagnetic device. The device induces eddy currents in the metal that generate a Lorentz force with their associated magnetic fields. The effect is the pumping of the liquid metal resulting in a simplified design with no moving parts. This is known as MHD pumping.
For example, a simple mixture of mineral oil and iron filings was found to approximate a suitable ferrofluid for several seconds, before separation of the iron filings and oil was observed in the presence of a magnetic field. At droplet sizes of approximately 200 µm, surface tension will hold the two components at accelerations up to about 1 g.
If an ionic fluid is used as the coolant, the fluid can be used for momentum transfer between spacecraft traveling at different speeds. It may be possible to synthesize the fluid in-situ. For example, BMIM-BF4 ( [CHN]BF) is 42.5% carbon by mass. Lunar regolith typically contains several compounds with carbon and about 5% of asteroids are carbonaceous chondrites which are rich in carbon as well as metals and water.
It may be possible to mine the moon for carbon and combine it with other elements to produce ionic fluid. Another good source of carbon is Mars' largest moon, Phobos, which is a captured asteroid believed to be rich in carbon. | 7 | Physical Chemistry |
The Australian Society for Biochemistry and Molecular Biology (ASBMB) is an academic society founded in 1955. Originally named Australian Biochemical Society, it was renamed to its current title in 1990. Its main activities include hosting scientific conferences, supporting ancillary symposia, workshops and publishing an educational magazine. | 1 | Biochemistry |
Kerr frequency combs (also known as microresonator frequency combs) are optical frequency combs which are generated from a continuous wave pump laser by the Kerr nonlinearity. This coherent conversion of the pump laser to a frequency comb takes place inside an optical resonator which is typically of micrometer to millimeter in size and is therefore termed a microresonator. The coherent generation of the frequency comb from a continuous wave laser with the optical nonlinearity as a gain sets Kerr frequency combs apart from today's most common optical frequency combs. These frequency combs are generated by mode-locked lasers where the dominating gain stems from a conventional laser gain medium, which is pumped incoherently. Because Kerr frequency combs only rely on the nonlinear properties of the medium inside the microresonator and do not require a broadband laser gain medium, broad Kerr frequency combs can in principle be generated around any pump frequency.
While the principle of Kerr frequency combs is applicable to any type of optical resonator, the requirement for Kerr frequency comb generation is a pump laser field intensity above the parametric threshold of the nonlinear process. This requirement is easier to fulfill inside a microresonator because of the possible very low losses inside microresonators (and corresponding high quality factors) and because of the microresonators’ small mode volumes. These two features combined result in a large field enhancement of the pump laser inside the microresonator which allow the generation of broad Kerr frequency combs for reasonable powers of the pump laser.
One important property of Kerr frequency combs, which is a direct consequence of the small dimensions of the microresonators and their resulting large free spectral ranges (FSR), is the large mode spacing of typical Kerr frequency combs. For mode-locked lasers this mode spacing, which defines the distance in between adjacent teeth of the frequency comb, is typically in the range of 10 MHz to 1 GHz. For Kerr frequency combs the typical range is from around 10 GHz to 1 THz.
The coherent generation of an optical frequency comb from a continuous wave pump laser is not a unique property of Kerr frequency combs. Optical frequency combs generated with cascaded optical modulators also possess this property. For certain application this property can be advantageous. For example, to stabilize the offset frequency of the Kerr frequency comb one can directly apply feedback to the pump laser frequency. In principle it is also possible to generate a Kerr frequency comb around a particular continuous wave laser in order to use the bandwidth of the frequency comb to determine the exact frequency of the continuous wave laser.
Since their first demonstration in silica micro-toroid resonators, Kerr frequency combs have been demonstrated in a variety of microresonator platforms which notably also include crystalline microresonators and integrated photonics platforms such as waveguide resonators made from silicon nitride. More recent research has expanded the range of available platforms further which now includes diamond, aluminum nitride,
lithium niobate, and, for mid-infrared pump wavelengths, silicon.
Because both use the nonlinear effects of the propagation medium, the physics of Kerr frequency combs and of supercontinuum generation from pulsed lasers is very similar. In addition to the nonlinearity, the chromatic dispersion of the medium also plays a crucial role for these systems. As a result of the interplay of nonlinearity and dispersion, solitons can form. The most relevant type of solitons for Kerr frequency comb generation are bright dissipative cavity solitons, which are sometimes also called dissipative Kerr solitons (DKS). These bright solitons have helped to significantly advance the field of Kerr frequency combs as they provide a way to generate ultra-short pulses which in turn represent a coherent, broadband optical frequency comb, in a more reliable fashion than what was possible before.
In its simplest form with only the Kerr nonlinearity and second order dispersion the physics of Kerr frequency combs and dissipative solitons can be described well by the Lugiato–Lefever equation.
Other effects such as the Raman effect and higher order dispersion effects require additional terms in the equation. | 7 | Physical Chemistry |
Amylases are used in breadmaking and to break down complex sugars, such as starch (found in flour), into simple sugars. Yeast then feeds on these simple sugars and converts it into the waste products of ethanol and carbon dioxide. This imparts flavour and causes the bread to rise. While amylases are found naturally in yeast cells, it takes time for the yeast to produce enough of these enzymes to break down significant quantities of starch in the bread. This is the reason for long fermented doughs such as sourdough. Modern breadmaking techniques have included amylases (often in the form of malted barley) into bread improver, thereby making the process faster and more practical for commercial use.
α-Amylase is often listed as an ingredient on commercially package-milled flour. Bakers with long exposure to amylase-enriched flour are at risk of developing dermatitis or asthma. | 1 | Biochemistry |
Multiomics currently holds a promise to fill gaps in the understanding of human health and disease, and many researchers are working on ways to generate and analyze disease-related data. The applications range from understanding host-pathogen interactions and infectious diseases, cancer, to understanding better chronic and complex non-communicable diseases and improving personalized medicine. | 1 | Biochemistry |
Free fatty acids cannot penetrate any biological membrane due to their negative charge. Free fatty acids must cross the cell membrane through specific transport proteins, such as the SLC27 family fatty acid transport protein. Once in the cytosol, the following processes bring fatty acids into the mitochondrial matrix so that beta-oxidation can take place.
# Long-chain-fatty-acid—CoA ligase catalyzes the reaction between a fatty acid with ATP to give a fatty acyl adenylate, plus inorganic pyrophosphate, which then reacts with free coenzyme A to give a fatty acyl-CoA ester and AMP.
# If the fatty acyl-CoA has a long chain, then the carnitine shuttle must be utilized (shown in the table below):
#* Acyl-CoA is transferred to the hydroxyl group of carnitine by carnitine palmitoyltransferase I, located on the cytosolic faces of the outer and inner mitochondrial membranes.
#* Acyl-carnitine is shuttled inside by a carnitine-acylcarnitine translocase, as a carnitine is shuttled outside.
#* Acyl-carnitine is converted back to acyl-CoA by carnitine palmitoyltransferase II, located on the interior face of the inner mitochondrial membrane. The liberated carnitine is shuttled back to the cytosol, as an acyl-carnitine is shuttled into the matrix.
# If the fatty acyl-CoA contains a short chain, these short-chain fatty acids can simply diffuse through the inner mitochondrial membrane. | 1 | Biochemistry |
The following is a list of common functional groups. In the formulas, the symbols R and R' usually denote an attached hydrogen, or a hydrocarbon side chain of any length, but may sometimes refer to any group of atoms. | 0 | Organic Chemistry |
Sex pheromones have found applications in pest monitoring and pest control. For monitoring, pheromone traps are used to attract and catch a sample of pest insects to determine whether control measures are needed. For control, much larger quantities of a sex pheromone are released to disrupt the mating of a pest species. This can be either by releasing enough pheromone to prevent males from finding females, effectively drowning out their signals, or by mass trapping, attracting and removing pests directly. For example, research on the control of the spruce bud moth (Zeiraphera canadensis) has focused on the use of the pheromone E-9-tetradecenyl-acetate, a chemical the spruce bud moth releases during mating. | 1 | Biochemistry |
In this method, plant nuclei are isolated by physically grinding tissues and reconstituting the intact nuclei in a unique Nuclear Isolation Buffer (NIB). The plastid DNAs are released from organelles and eliminated with an osmotic buffer by washing and centrifugation. The purified nuclei are then lysed and further cleaned by organic extraction, and the genomic DNA is precipitated with a high concentration of CTAB. The highly pure, high molecular weight gDNA is extracted from the nuclei, dissolved in a high pH buffer, allowing for stable long-term storage. | 1 | Biochemistry |
# During the afterhyperpolarization period after an action potential, the membrane potential is more negative than when the cell is at the resting potential. In the figure to the right, this undershoot occurs at approximately 3 to 4 milliseconds (ms) on the time scale. The afterhyperpolarization is the time when the membrane potential is hyperpolarized relative to the resting potential.
# During the rising phase of an action potential, the membrane potential changes from negative to positive, a depolarization. In the figure, the rising phase is from approximately 1 to 2 ms on the graph. During the rising phase, once the membrane potential becomes positive, the membrane potential continues to depolarize (overshoot) until the peak of the action potential is reached at about +40 millivolts (mV). After the peak of the action potential, a hyperpolarization repolarizes the membrane potential to its resting value, first by making it less positive, until 0 mV is reached, and then by continuing to make it more negative. This repolarization occurs in the figure from approximately 2 to 3 ms on the time scale. | 7 | Physical Chemistry |
Akkermansia is a genus in the phylum Verrucomicrobiota (Bacteria). The genus was first proposed by Derrien et al. (2004), with the type species Akkermansia muciniphila (gen. nov., sp. nov).
Until 2016 the genus contained a single known species, namely A. muciniphila. In 2016, Akkermansia glycaniphila was isolated in the feces of a reticulated python. | 1 | Biochemistry |
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