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Gene regulatory networks are generally thought to be made up of a few highly connected nodes (hubs) and many poorly connected nodes nested within a hierarchical regulatory regime. Thus gene regulatory networks approximate a hierarchical scale free network topology. This is consistent with the view that most genes have limited pleiotropy and operate within regulatory modules. This structure is thought to evolve due to the preferential attachment of duplicated genes to more highly connected genes. Recent work has also shown that natural selection tends to favor networks with sparse connectivity.
There are primarily two ways that networks can evolve, both of which can occur simultaneously. The first is that network topology can be changed by the addition or subtraction of nodes (genes) or parts of the network (modules) may be expressed in different contexts. The Drosophila Hippo signaling pathway provides a good example. The Hippo signaling pathway controls both mitotic growth and post-mitotic cellular differentiation. Recently it was found that the network the Hippo signaling pathway operates in differs between these two functions which in turn changes the behavior of the Hippo signaling pathway. This suggests that the Hippo signaling pathway operates as a conserved regulatory module that can be used for multiple functions depending on context. Thus, changing network topology can allow a conserved module to serve multiple functions and alter the final output of the network. The second way networks can evolve is by changing the strength of interactions between nodes, such as how strongly a transcription factor may bind to a cis-regulatory element. Such variation in strength of network edges has been shown to underlie between species variation in vulva cell fate patterning of Caenorhabditis worms. | 1 | Applied and Interdisciplinary Chemistry |
The most common nuclear fission process is "binary fission." It produces two charged asymmetrical fission products with maximally probable charged product at 95±15 and 135±15 u atomic mass. However, in this conventional fission of large nuclei, the binary process happens merely because it is the most energetically probable.
In anywhere from 2 to 4 fissions per 1000 in a nuclear reactor, the alternative ternary fission process produces three positively charged fragments (plus neutrons, which are not charged and not counted in this reckoning). The smallest of the charged products may range from so small a charge and mass as a single proton (Z=1), up to as large a fragment as the nucleus of argon (Z=18).
Although particles as large as argon nuclei may be produced as the smaller (third) charged product in the usual ternary fission, the most common small fragments from ternary fission are helium-4 nuclei, which make up about 90% of the small fragment products. This high incidence is related to the stability (high binding energy) of the alpha particle, which makes more energy available to the reaction. The second-most common particles produced in ternary fission are Tritons (the nuclei of tritium), which make up 7% of the total small fragments, and the third-most are helium-6 nuclei (which decay in about 0.8 seconds to lithium-6). Protons and larger nuclei are in the small fraction (< 2%) which make up the remainder of the small charged products. The two larger charged particles from ternary fission, particularly when alphas are produced, are quite similar in size distribution to those produced in binary fission. | 0 | Theoretical and Fundamental Chemistry |
Mg and Mn are critical cofactors in the integration phase. Inactivating these cofactors (e.g. through chelation) causes functional impairment of IN. This concept gives researchers the opportunity to design and develop highly efficient IN inhibitors (INIs). In fact, all small molecule HIV-1 INIs that are now being researched contain a structural motif that coordinates the two divalent magnesium ions in the enzyme's active site.
Raltegravir and elvitegravir share the same mechanism of action against integrase: to bind to the active site of Mg ions. Competitive inhibitors compete directly with viral DNA for binding to integrase in order to inhibit 3‘-end processing. In doing this the inhibitors completely block the active site from binding to target DNA. This inhibition is called strand transfer inhibition. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes () from alkenes (). This chemical reaction entails the net addition of a formyl group () and a hydrogen atom to a carbon-carbon double bond. This process has undergone continuous growth since its invention: production capacity reached 6.6 tons in 1995. It is important because aldehydes are easily converted into many secondary products. For example, the resultant aldehydes are hydrogenated to alcohols that are converted to detergents. Hydroformylation is also used in speciality chemicals, relevant to the organic synthesis of fragrances and pharmaceuticals. The development of hydroformylation is one of the premier achievements of 20th-century industrial chemistry.
The process entails treatment of an alkene typically with high pressures (between 10 and 100 atmospheres) of carbon monoxide and hydrogen at temperatures between 40 and 200 °C. In one variation, formaldehyde is used in place of synthesis gas. Transition metal catalysts are required. Invariably, the catalyst dissolves in the reaction medium, i.e. hydroformylation is an example of homogeneous catalysis. | 0 | Theoretical and Fundamental Chemistry |
In chemistry and materials science, ultrahydrophobic (or superhydrophobic) surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet on an ultrahydrophobic material exceed 150°. This is also referred to as the lotus effect, after the superhydrophobic leaves of the lotus plant. A droplet striking these kinds of surfaces can fully rebound like an elastic ball. Interactions of bouncing drops can be further reduced using special superhydrophobic surfaces that promote symmetry breaking, pancake bouncing or waterbowl bouncing. | 0 | Theoretical and Fundamental Chemistry |
Sphingosine is synthesized from palmitoyl CoA and serine in a condensation required to yield dihydrosphingosine.
Dehydrosphingosine is then reduced by NADPH to dihydrosphingosine (sphinganine), acylated to dihydroceramide finally oxidized by FAD to ceramide. Sphingosine is then solely formed via degradation of sphingolipid in the lysosome. | 1 | Applied and Interdisciplinary Chemistry |
Waste heat can be forced to heat incoming fluids and objects before being highly heated. For instance outgoing water can give its waste heat to incoming water in a heat exchanger before heating in homes or power plants. | 0 | Theoretical and Fundamental Chemistry |
Photoinhibition follows simple first-order kinetics if measured from a lincomycin-treated leaf, cyanobacterial or algal cells, or isolated thylakoid membranes in which concurrent repair does not disturb the kinetics. Data from the group of W. S. Chow indicate that in leaves of pepper (Capsicum annuum), the first-order pattern is replaced by a pseudo-equilibrium even if the repair reaction is blocked. The deviation has been explained by assuming that photoinhibited PSII centers protect the remaining active ones.
Both visible and ultraviolet light cause photoinhibition, ultraviolet wavelengths being much more damaging. Some researchers consider ultraviolet and visible light induced photoinhibition as a two different reactions, while others stress the similarities between the inhibition reactions occurring under different wavelength ranges. | 0 | Theoretical and Fundamental Chemistry |
An example of back titration, the Volhard method, named after Jacob Volhard, involves the addition of excess silver nitrate to the analyte; the silver chloride is filtered, and the remaining silver nitrate is titrated against ammonium thiocyanate, with ferric ammonium sulfate as an indicator which forms blood-red [[Thiocyanate#Test for iron.28III.29|[Fe(OH)(SCN)]]] at the end point:
: Ag (aq) + SCN (aq) → AgSCN (s) (K = 1.16 × 10)
: Fe(OH)(OH) (aq) + SCN (aq)→ [Fe(OH)(SCN)] + OH | 0 | Theoretical and Fundamental Chemistry |
Janot was a French Government Overseas Fellow in 1981 at Churchill College, University of Cambridge. He was also a visiting professor at Sapienza University of Rome. | 1 | Applied and Interdisciplinary Chemistry |
Prairie provinces (mainly Saskatchewan and Manitoba) contain high quantities of calcium and magnesium, often as dolomite, which are readily soluble in the groundwater that contains high concentrations of trapped carbon dioxide from the last glaciation. In these parts of Canada, the total hardness in ppm of calcium carbonate equivalent frequently exceeds 200 ppm, if groundwater is the only source of potable water. The west coast, by contrast, has unusually soft water, derived mainly from mountain lakes fed by glaciers and snowmelt.
Some typical values are:
* Montreal 116 ppm
* Calgary 165 ppm
* Regina 496 ppm
* Saskatoon 160–180 ppm
* Winnipeg 77 ppm
* Toronto 121 ppm
* Vancouver < 3 ppm
* Charlottetown, PEI 140–150 ppm
* Waterloo Region 400 ppm
* Guelph 460 ppm
* Saint John (West) 160–200 ppm
* Ottawa 30 ppm | 0 | Theoretical and Fundamental Chemistry |
Often there is more to the analytical method than just performing a reaction or submitting the analyte to direct analysis. Many analytical methods developed in the laboratory, especially these involving the use of a delicate scientific instrument, require a sample preparation, or a pretreatment of the samples prior to being analysed. For example, it might be necessary to heat a sample that is to be analyzed for a particular metal with the addition of acid first (digestion process). The sample may also be diluted or concentrated prior to analysis by means of a given instrument. Additional steps in an analysis method add additional opportunities for errors. Since detection limits are defined in terms of errors, this will naturally increase the measured detection limit. This "global" detection limit (including all the steps of the analysis method) is called the method detection limit (MDL). The practical way for determining the MDL is to analyze seven samples of concentration near the expected limit of detection. The standard deviation is then determined. The one-sided Student's t-distribution is determined and multiplied versus the determined standard deviation. For seven samples (with six degrees of freedom) the t value for a 99% confidence level is 3.14. Rather than performing the complete analysis of seven identical samples, if the Instrument Detection Limit is known, the MDL may be estimated by multiplying the Instrument Detection Limit, or Lower Level of Detection, by the dilution prior to analyzing the sample solution with the instrument. This estimation, however, ignores any uncertainty that arises from performing the sample preparation and will therefore probably underestimate the true MDL. | 0 | Theoretical and Fundamental Chemistry |
The Société de Chimie Industrielle (American Section) is an independent learned society inspired by the creation of the Société de Chimie Industrielle in Paris in 1917. The American Section was formed on January 18, 1918, and held its first meeting on April 4, 1918.
The Société de Chimie Industrielle (American Section) hosts speakers, grants scholarships, and gives awards. It has given the International Palladium Medal roughly every second year since 1961, and helps to award the Othmer Gold Medal and the Winthrop-Sears Medal every year. The Société also hosts monthly talks, and presents scholarships to writers, educators, and historians of science. | 1 | Applied and Interdisciplinary Chemistry |
Melzer's is used by exposing fungal tissue or cells to the reagent, typically in a microscope slide preparation, and looking for any of three color reactions:
* Amyloid or Melzer's-positive reaction, in which the material reacts blue to black.
* Pseudoamyloid or dextrinoid reaction, in which the material reacts brown to reddish brown.
* Inamyloid or Melzer's-negative, in which the tissues do not change color, or react faintly yellow-brown.
Among the amyloid reaction, two types can be distinguished:
* Euamyloid reaction, in which the material turns blue without potassium hydroxide (KOH)-pretreatment.
* Hemiamyloid reaction, in which the material turns red in Lugols solution, but shows no reaction in Melzers reagent; when KOH-pretreated it turns blue in both reagents (hemiamyloidity).
Melzer's reactions are typically almost immediate, though in some cases the reaction may take up to 20 minutes to develop.
The function of the chemicals that make up Melzers reagent are several. The chloral hydrate is a clearing agent, bleaching and improving the transparency of various dark-colored microscopic materials. The potassium iodide is used to improve the solubility of the iodine, which is otherwise only semi-soluble in water. Iodine is thought to be the main active staining agent in Melzers; it is thought to react with starch-like polysaccharides in the cell walls of amyloid material, however, its mechanism of action is not entirely understood. It has been observed that hemiamyloid material reacts differently when exposed to Melzers than it does when exposed to other IKI solutions such as Lugols, and that in some cases an amyloid reaction is shown in material that had prior exposure to KOH, but an inamyloid reaction without such pretreatment.
An experiment in which spores from 35 species of basidiomycetes were tested for reactions to both Melzers and Lugols showed that spores in a large percentage of the species tested display very different reactions between the two reagents. These varied from being weakly or non-reactive in Lugols, to giving iodine-positive reactions in Lugols but not in Melzers, to even giving dextrinoid reactions in Lugols while giving amyloid reactions in Melzers.
Melzers degrades into a cloudy precipitate when combined with alkaline solutions, hence it cannot be used in combination or in direct series with such common mycological reagents such as potassium hydroxide or ammonium hydroxide solutions. When potassium hydroxide is used as a pretreatment, the alkalinity must be first neutralized before adding Melzers. | 0 | Theoretical and Fundamental Chemistry |
Many specialized methods have been developed for forming unsymmetrical disulfides. Reagents that deliver the equivalent of "" react with thiols to give asymmetrical disulfides:
where is the phthalimido group.
Bunte salts, derivatives of the type are also used to generate unsymmetrical disulfides: | 0 | Theoretical and Fundamental Chemistry |
Three-letter abbreviations are used to describe phenotypes in bacteria including E. coli.
Examples include:
* Lac (the ability to use lactose),
* His (the ability to synthesize the amino acid histidine)
* Mot (swimming motility)
* Sm (resistance to the antibiotic streptomycin)
In the case of Lac, wild type cells are Lac and are able to use lactose as a carbon and energy source, while Lac mutant derivatives cannot use lactose. The same three letters are typically used (lower-case, italicized) to label the genes involved in a particular phenotype, where each different gene is additionally distinguished by an extra letter. The lac genes encoding enzymes are lacZ, lacY, and lacA. The fourth lac gene is lacI, encoding the lactose repressor—"I" stands for inducibility.
One may distinguish between structural genes encoding enzymes, and regulatory genes encoding proteins that affect gene expression. Current usage expands the phenotypic nomenclature to apply to proteins: thus, LacZ is the protein product of the lacZ gene, β-galactosidase. Various short sequences that are not genes also affect gene expression, including the lac promoter, lac p, and the lac operator, lac o. Although it is not strictly standard usage, mutations affecting lac o are referred to as lac o, for historical reasons. | 1 | Applied and Interdisciplinary Chemistry |
Linear material constitutive relations in physics can be expressed in the form
where are two vectors representing physical quantities and is a second-order material tensor. In matrix form,
Examples of physical problems that fit the above template are listed in the table below.
Using in the matrix implies that . Using leads to and . Energy restrictions usually require and hence we must have . Therefore, the material properties of a transversely isotropic material are described by the matrix | 0 | Theoretical and Fundamental Chemistry |
Hazards in the arts have been an issue for artists for centuries, even though the toxicity of their tools, methods, and materials was not always adequately realized. Lead and cadmium, among other toxic elements, were often incorporated into the names of artist's oil paints and pigments, for example, "lead white" and "cadmium red".
20th-century printmakers and other artists began to be aware of the toxic substances, toxic techniques, and toxic fumes in glues, painting mediums, pigments, and solvents, many of which in their labelling gave no indication of their toxicity. An example was the use of xylol for cleaning silk screens. Painters began to notice the dangers of breathing painting mediums and thinners such as turpentine. Aware of toxicants in studios and workshops, in 1998 printmaker Keith Howard published Non-Toxic Intaglio Printmaking which detailed twelve innovative Intaglio-type printmaking techniques including photo etching, digital imaging, acrylic-resist hand-etching methods, and introducing a new method of non-toxic lithography. | 1 | Applied and Interdisciplinary Chemistry |
Because the intensity of nuclear magnetic resonance signals and, hence, the sensitivity of the technique depends on the strength of the magnetic field, the technique has also advanced over the decades with the development of more powerful magnets. Advances made in audio-visual technology have also improved the signal-generation and processing capabilities of newer instruments.
As noted above, the sensitivity of nuclear magnetic resonance signals is also dependent on the presence of a magnetically susceptible nuclide and, therefore, either on the natural abundance of such nuclides or on the ability of the experimentalist to artificially enrich the molecules, under study, with such nuclides. The most abundant naturally occurring isotopes of hydrogen and phosphorus (for example) are both magnetically susceptible and readily useful for nuclear magnetic resonance spectroscopy. In contrast, carbon and nitrogen have useful isotopes but which occur only in very low natural abundance.
Other limitations on sensitivity arise from the quantum-mechanical nature of the phenomenon. For quantum states separated by energy equivalent to radio frequencies, thermal energy from the environment causes the populations of the states to be close to equal. Since incoming radiation is equally likely to cause stimulated emission (a transition from the upper to the lower state) as absorption, the NMR effect depends on an excess of nuclei in the lower states. Several factors can reduce sensitivity, including:
* Increasing temperature, which evens out the population of states. Conversely, low temperature NMR can sometimes yield better results than room-temperature NMR, providing the sample remains liquid.
* Saturation of the sample with energy applied at the resonant radiofrequency. This manifests in both CW and pulsed NMR; in the first case (CW) this happens by using too much continuous power that keeps the upper spin levels completely populated; in the second case (pulsed), each pulse (that is at least a 90° pulse) leaves the sample saturated, and four to five times the (longitudinal) relaxation time (5T) must pass before the next pulse or pulse sequence can be applied. For single pulse experiments, shorter RF pulses that tip the magnetization by less than 90° can be used, which loses some intensity of the signal, but allows for shorter recycle delays. The optimum there is called an Ernst angle, after the Nobel laureate. Especially in solid state NMR, or in samples containing very few nuclei with spin (diamond with the natural 1% of carbon-13 is especially troublesome here) the longitudinal relaxation times can be on the range of hours, while for proton-NMR they are more in the range of one second.
* Non-magnetic effects, such as electric-quadrupole coupling of spin-1 and spin- nuclei with their local environment, which broaden and weaken absorption peaks. , an abundant spin-1 nucleus, is difficult to study for this reason. High resolution NMR instead probes molecules using the rarer isotope, which has spin-. | 0 | Theoretical and Fundamental Chemistry |
The moisture sorption properties of food products are recognized as critical factors in determining their storage, stability, processing and application performance. DVS is also used to measure moisture and flavor diffusion properties for packaging and barrier applications. Further, moisture sorption plays critical roles in the storage and performance of agricultural products like pesticides, herbicides, fertilizers, and seeds. | 0 | Theoretical and Fundamental Chemistry |
sEH is widely expressed in mammalian cells as a cytosolic enzyme where it primarily serves the function of converting epoxyeicosatrienoic acids (EETs), epoxyeicosatetraenoic acids (EPAs), and epoxydocosapentaenoic acids (DPAs) to their corresponding diols, thereby limiting or ending their cell signaling actions; in this capacity, sEH appears to play a critical in vivo role in limiting the effects of these epoxides in animal models and possibly humans. However, sEH also metabolizes the epoxides of linoleic acid viz., Vernolic acid (leukotoxins) and Coronaric acids (isoleukotoxins) to their corresponding diols which are highly toxic in animal models and possibly humans (see Vernolic acid#toxicity, Coronaric acid#toxicity, and soluble epoxide hydrolase). sEH also possesses hepoxilin-epoxide hydrolase activity, converting bioactive hepoxilins to their inactive trioxilin products (see below section "Hepoxilin-epoxide hydrolase"). | 1 | Applied and Interdisciplinary Chemistry |
The combinatorial complexity of signaling systems involving multi-state proteins poses two kinds of problems. The first problem is concerned with how such a system can be specified; i.e. how a modeler can specify all complexes, all changes those complexes undergo and all parameters and conditions governing those changes in a robust and efficient way. This problem is called the "specification problem". The second problem concerns computation. It asks questions about whether a combinatorially complex model, once specified, is computationally tractable, given the large number of states and the even larger number of possible transitions between states, whether it can be stored electronically, and whether it can be evaluated in a reasonable amount of computing time. This problem is called the "computation problem". Among the approaches that have been proposed to tackle combinatorial complexity in multi-state modeling, some are mainly concerned with addressing the specification problem, some are focused on finding effective methods of computation. Some tools address both specification and computation. The sections below discuss rule-based approaches to the specification problem and particle-based approaches to solving the computation problem. A wide range of computational tools exist for multi-state modeling. | 1 | Applied and Interdisciplinary Chemistry |
There are three different variations of seipin's amino acid sequence:
* a N → S change in position 88, does not affect protein subcellular location.
* a S → L change in position 90, does not affect the function in lipid storage.
* a A → P change in position 212 that increases localization to nuclear envelope.
All seipin mutations occur within its loop domain. Between some of these, four large deletions can be found which indicate that at least exons 4 and 5 are required for seipin function in humans. In addition, other six mutations have been identified in the loop domain. The majority of these cluster at the single asparagine-linked glycosylation site (NVS) in seipin. The two mutations that cause neuronal seipinopathy, N88S and S90L, are located directly within this site. Apart from suspending the glycosylation process, these mutations engender an aggregation of seipin and, consequently, the initiation of the ER stress response. The seipin protein can also have a modification residue, that can transform the 289’ and 372’ serine into a phosphoserine, an ester of serine and phosphoric acid.
Overexpression of mutated seipin proteins N88S or S90L can also activate autophagy, and substantially altering the sub-cellular distribution of the autophagosome marker GFP-LC3, which leads to a number of large vacuoles appearing in the cytoplasm. The sub-cellular location of GFP-LC3 and mutated seipin proteins highly overlap. Moreover, these seipin proteins can diffuse small lipid droplets to fuse into larger lipid.
Seipin mutations have been associated with congenital generalized lipodystrophy (see below), and mutations in an N-glycosylation motif links seipin to two other disorders, i.e. Silver syndrome and autosomal-dominant distal hereditary motor neuropathy type V. | 1 | Applied and Interdisciplinary Chemistry |
The most significant adverse reactions (≥2%) reported in clinical trials were diarrhea, abdominal pain, bloating, nausea, upper respiratory tract infection, vomiting, and flatulence.
Serious side effects are rare but may include allergic reactions, severe stomach pain, or persistent diarrhea. | 0 | Theoretical and Fundamental Chemistry |
Eukaryotes have a much larger genome and thus have different methods of gene regulation than in prokaryotes. All cells in a eukaryotic organism have the same DNA but are specified through differential gene expression, a phenomenon known as genetic totipotency. However, in order for a cell to express the genes for proper functioning, the genes must be closely regulated to express the correct properties. Genes in eukaryotes are controlled on the transcriptional, post-transcriptional, translational, and post-translational levels. On the transcriptional level, gene expression is regulated by altering transcription rates. Genes that encode proteins include exons which will encode the polypeptides, introns that are removed from mRNA before the translation of proteins, a transcriptional start site in which RNA polymerase binds, and a promoter. | 1 | Applied and Interdisciplinary Chemistry |
NBR2 is a gene best known for its location near the breast cancer associated gene BRCA1. Like BRCA1, NBR2 has been a subject of research, but links to breast cancer are currently inconclusive.
NBR2 recently was identified as a glucose starvation-induced long non-coding RNA. NBR2 interacts with AMP-activated protein kinase (AMPK), a critical energy sensor in most eukaryotic cells, and promotes AMPK function to mediate energy stress response. Knockdown of NBR2 attenuates energy stress-induced AMPK activation, resulting in unchecked cell cycling, altered apoptosis/autophagy response, and increased tumour development in vivo. It is now appreciated that NBR2, a former junk gene, plays critical roles in tumor suppression. | 1 | Applied and Interdisciplinary Chemistry |
Administered to patients whose pituitary glands generate insufficient quantities to support normal growth and development. Before recombinant HGH became available, HGH for therapeutic use was obtained from pituitary glands of cadavers. This unsafe practice led to some patients developing Creutzfeldt–Jakob disease. Recombinant HGH eliminated this problem, and is now used therapeutically. It has also been misused as a performance-enhancing drug by athletes and others. | 1 | Applied and Interdisciplinary Chemistry |
Magnetofection attempts to unite the advantages of biochemical (cationic lipids or polymers) and physical (electroporation, gene gun) transfection methods. It allows for local delivery with high transfection efficiency, faster incubation time, and biocompatibility. | 1 | Applied and Interdisciplinary Chemistry |
Much of the current interest in oil exploration in the Arctic regions is directed towards the Azolla deposits . The burial of large amounts of organic material provides the source rock for oil, so given the right thermal history, the preserved Azolla blooms might have been converted to oil or gas. In 2008 a research team was set up in the Netherlands devoted to Azolla. | 1 | Applied and Interdisciplinary Chemistry |
A therapy or medical treatment is the attempted remediation of a health problem, usually following a medical diagnosis. Both words, treatment and therapy, are often abbreviated tx, Tx, or T.
As a rule, each therapy has indications and contraindications. There are many different types of therapy. Not all therapies are effective. Many therapies can produce unwanted adverse effects.
Treatment and therapy are often synonymous, especially in the usage of health professionals. However, in the context of mental health, the term therapy may refer specifically to psychotherapy. | 1 | Applied and Interdisciplinary Chemistry |
Thioesters are common intermediates in many biosynthetic reactions, including the formation and degradation of fatty acids and mevalonate, precursor to steroids. Examples include malonyl-CoA, acetoacetyl-CoA, propionyl-CoA, cinnamoyl-CoA, and acyl carrier protein (ACP) thioesters. Acetogenesis proceeds via the formation of acetyl-CoA. The biosynthesis of lignin, which comprises a large fraction of the Earth's land biomass, proceeds via a thioester derivative of caffeic acid. These thioesters arise analogously to those prepared synthetically, the difference being that the dehydration agent is ATP. In addition, thioesters play an important role in the tagging of proteins with ubiquitin, which tags the protein for degradation.
Oxidation of the sulfur atom in thioesters (thiolactones) is postulated in the bioactivation of the antithrombotic prodrugs ticlopidine, clopidogrel, and prasugrel. | 0 | Theoretical and Fundamental Chemistry |
A variety of reasons for a Phase I study to be performed exist, the most common being:
* Purchase of real property by a person or entity not previously on title.
* Contemplation by a new lender to provide a loan on the subject real estate.
* Partnership buyout or principal redistribution of ownership.
* Application to a public agency for change of use or other discretionary land use permit.
* Existing property owner's desire to understand toxic history of the property.
* Compulsion by a regulatory agency who suspects toxic conditions on the site.
* Divestiture of properties. | 1 | Applied and Interdisciplinary Chemistry |
Addition of tricyclohexylphosphine to the carbene complex (PPh)(Cl)Ru=C(CHCOMe) results in olefin extrusion and yields an air stable anionic carbido complex. This species displaces a dimethyl sulfide ligand from PdCl(SMe) to give the μ-carbido bimetallic complex (PCy)ClRu≡C-PdCl(SMe). Spark towards a novel type of bonding was proposed following empirical observations wherein the carbido-palladium interaction could be readily disturbed. Reversible coordination ensues upon exposure of the bimetallic complex to carbon monoxide. Additionally, no coordination occurs if the anionic carbido complex contains bulky ligands such as HIMes. This indicates that the thermodynamic sink towards making the C-M bond is not very favorable, suggesting a weak interaction. Although not intuitive, characterization of this type of bonding can be inferred if C NMR shifts are observed to be far downfield, and C-M bond lengths are similar to those of complexes proven to contain carbon-based σ-donor ligands such as [(EtHIm)PdCl(μ-Cl)] | 0 | Theoretical and Fundamental Chemistry |
By using a rotating mirror, a high-speed camera and correcting for geometric changes, PIV can be performed nearly instantly on a set of planes throughout the flow field. Fluid properties between the planes can then be interpolated. Thus, a quasi-volumetric analysis can be performed on a target volume. Scanning PIV can be performed in conjunction with the other 2-dimensional PIV methods described to approximate a 3-dimensional volumetric analysis. | 1 | Applied and Interdisciplinary Chemistry |
The development of the Isa Process tank house technology had its beginning in the zinc industry. During the mid-1970s, MIM Holdings Limited (“MIM”) was considering building a zinc refinery in Townsville to treat the zinc concentrate produced by its Mount Isa operations. As a result, MIM staff visited the zinc smelters using the best-practice technology and found that modern electrolytic zinc smelters had adopted permanent cathode plate and mechanised stripping technology.
MIM recognised that the performance of traditional copper refineries was constrained by the poor cathode geometry inherent in using copper starter sheets.
MIM then developed a research program aimed at developing similar permanent cathode technology for copper refining. CRL had been operating in Townsville since 1959, using conventional starter-sheet technology and treating blister copper produced in the Mount Isa Mines Limited copper smelter at Mount Isa in Queensland. CRL incorporated the permanent cathode technology in its 1978 refinery modernisation project. The material initially selected was 316L stainless steel, stitch-welded to a 304L stainless-steel hanger bar. The hanger-bar assembly was then electroplated with copper to a thickness of 1.3 millimeters (“mm”) (later increased to 2.5 mm and then 3.0 mm to improve the corrosion resistance of the hanger bar) to approximately 15 mm down onto the blade, which provided sufficient electrical conductivity and gave the assembly some corrosion resistance.
Electrodeposited copper adheres quite firmly to the stainless steel so that it does not detach during refining. The vertical edges of the stainless steel plates are covered with tight-fitting polymer edge strips to prevent copper depositing around the edge of the cathode plate and so make it easier to strip the cathode copper from them. The bottom of the cathode plates were masked with a thin film of wax, again to prevent the copper depositing around the bottom edge. Wax was used rather than an edge strip to avoid having a ledge that would collect falling anode slimes and contaminate the cathode copper.
Wax was also used on the vertical edges to prolong the life of the vertical edge strip.
The original cathode stripping machine was based on that used at the Hikoshima plant of the Mitsui Mining and Smelting Company of Japan. However, considerable development work was necessary to modify the design to handle the copper cathodes, which were heavier than those at Hikoshima, and to process the cathode plates without damaging them. The machines also had to be redesigned to allow for waxing the sides and bottoms of the cathode plates to allow the next copper cathode sheets to be removed easily.
The stripping machines included receiving and discharge conveyors, washing, separation, cathode stacking and discharging, cathode plate separation for refurbishing, and the wax applications for the sides and bottoms of the cathode plates.
The original CRL stripping machine had the capability of stripping 250 cathode plates per hour.
The lower cost of the cathode plates compared to starter sheets means that shorter cathode cycle times are possible. The cycle time can range from 5 to 14 days, but a seven-day cathode cycle is common. This shorter cycle time improves current efficiency as less short circuits occur and there is less nodulation of the cathode surface.
Initially, other refinery operators regarded the developments at CRL with scepticism. Stainless steel had been tried unsuccessfully as mother-plate material for copper starter sheets. They suffered from rapid deterioration of their strippability, resulting in “an almost daily increase in difficulty of stripping”. However, following the success of early installations in Townsville, Timmins, and many other places, the permanent stainless steel cathode technology has had widespread introduction. | 1 | Applied and Interdisciplinary Chemistry |
Semicarbazide is frequently reacted with aldehydes and ketones to produce semicarbazones via a condensation reaction. This is an example of imine formation resulting from the reaction of a primary amine with a carbonyl group. The reaction is useful because semicarbazones, like oximes and 2,4-DNPs, typically have high melting points and crystallize, facilitating purification or identification of reaction products. | 0 | Theoretical and Fundamental Chemistry |
JIC fittings, defined by the SAE J514 and MIL-DTL-18866 standards, are a type of flare fitting machined with a 37-degree flare seating surface. JIC (Joint Industry Council) fittings are widely used in fuel delivery and fluid power applications, especially where high pressure (up to ) is involved. The SAE J514 standard replaces the MS16142 US military specification, although some tooling is still listed under MS16142. JIC fittings are dimensionally identical to AN (Army-Navy) fittings, but are produced to less exacting tolerances and are generally less costly. SAE 45-degree flare fittings are similar in appearance, but are not interchangeable, though dash sizes 2, 3, 4, 5, 8, and 10 share the same thread size. Some couplings may have dual machined seats for both 37-degree and 45-degree flare seats.
Komatsu and JIS (Japanese Industrial Standard) fittings have flare ends similar to JIC fittings. Komatsu and JIS both use a 30-degree flare seating surface. The only difference is Komatsu uses millimeter thread sizes while JIS use a BSP (British Standard Pipe) thread.
JIC fitting systems have three components that make a tubing assembly: fitting, flare nut, and sleeve. As with other flared connection systems, the seal is achieved through metal-to-metal contact between the finished surface of the fitting nose and the inside diameter of the flared tubing. The sleeve is used to evenly distribute the compressive forces of the flare nut to the flared end of the tube. Materials commonly used to fabricate JIC fittings include forged carbon steel, forged stainless steel, forged brass, machined brass, Monel and nickel-copper alloys.
JIC fittings are commonly used in the Fluid Power industry in a diagnostic and test-point setting. A three-way JIC coupling provides a port inline of circuit by which a user can connect a measurement or diagnostic device to take pressure readings and perform circuit and system diagnostics. | 1 | Applied and Interdisciplinary Chemistry |
-A simple example of the Evelyn effect is the sophomore level chemistry lab experiment involving two popular examples that are listed below.
a) Dehydration of 4-methylcyclohexanol
b) Dehydration of 2-Methylcyclohexanol
c) Mechanism for the dehydration of 2-methylcyclohexanol | 0 | Theoretical and Fundamental Chemistry |
The first article relating to continuous flow peptide synthesis was published in 1986, but due to technical limitations, it was not until the early 2010's when more academic groups started using continuous flow for the rapid synthesis of peptides. The advantages of continuous flow over traditional batch methods is the ability to heat reagents with good temperature control, allowing the speed of reaction kinetics while minimising side reactions. cycles times vary from 30 seconds, up to 6 minutes, depending on reaction conditions and excess of reagent.
Thanks to inline analytics, such as UV/Vis spectroscopy and the use of Variable Bed Flow reactor (VBFR) that monitor the resin volume, on-resin aggregation can be identified and coupling efficiency can be evaluated. | 1 | Applied and Interdisciplinary Chemistry |
In the ocean where salinity is important, or in fresh water lakes near freezing, where density is not a linear function of temperature:where , the potential density, depends on both temperature and salinity. An example of Brunt–Väisälä oscillation in a density stratified liquid can be observed in the Magic Cork movie [https://www.youtube.com/watch?v=_DqOyvWwqWI here] . | 1 | Applied and Interdisciplinary Chemistry |
Power plants can use an air-cooled condenser, traditionally in areas with a limited or expensive water supply. Air-cooled condensers serve the same purpose as a cooling tower (heat dissipation) without using water. They consume additional auxiliary power and thus may have a higher carbon footprint compared to a traditional cooling tower. | 1 | Applied and Interdisciplinary Chemistry |
A prescription drug (Cystadane) containing betaine has limited use for oral treatment of genetic homocystinuria to lower levels of homocysteine in circulating blood. | 0 | Theoretical and Fundamental Chemistry |
Dr Robin Brown has been the company's chairman since July 2018; he has a PhD in molecular biology and has worked in venture capital at Advent Healthcare. The company has no shareholders.
Previously, Professor Graham Boulnois was chairman from January 2016; he was head of research from 1992 to 2000 at Zeneca Pharmaceuticals in Cheshire, and Professor of Microbiology from 1984 to 1992 at the University of Leicester. | 1 | Applied and Interdisciplinary Chemistry |
Acid sulfate soils are naturally occurring soils, sediments or organic substrates (e.g. peat) that are formed under waterlogged conditions. These soils contain iron sulfide minerals (predominantly as the mineral pyrite) and/or their oxidation products. In an undisturbed state below the water table, acid sulfate soils are benign. However, if the soils are drained, excavated or otherwise exposed to air, the sulfides react with oxygen to form sulfuric acid.
Release of this sulfuric acid from the soil can in turn release iron, aluminium, and other heavy metals and metalloids (particularly arsenic) within the soil. Once mobilized in this way, the acid and metals can create a variety of adverse impacts: killing vegetation, seeping into and acidifying groundwater and surface water bodies, killing fish and other aquatic organisms, and degrading concrete and steel structures to the point of failure. | 0 | Theoretical and Fundamental Chemistry |
In phytoextraction (also phytoaccumulation, phytosequesteration or phytoabsorption) plants carry radioactive waste from the root system to the vascular tissue and become concentrated in the biomass of shoots. It is a technique that removes radionuclides without destroying the soil structure, with minimal impact on soil fertility and valid for large areas with a low level of radioactivity. Its efficiency is evaluated through bioaccumulation coefficient (BC) or total removal of radionuclides per m, and is proven to attract cesium-137, strontium-90, technetium-99, cerium-144, plutonium-240, americium-241, neptunium-237 and various radioisotopes of thorium and radium. By contrast, it requires large biomass production in short periods of time.
Species like common heather or amaranths are able to concentrate cesium-137, the most abundant radionuclide in the Chernobyl Exclusion Zone. In this region of Ukraine, mustard greens could remove up to 22% of average levels of cesium activity in a single growing season. In the same way, bok choy and mustard greens can concentrate 100 times more uranium than other species. | 1 | Applied and Interdisciplinary Chemistry |
The subgroups discussed so far are not only infinite, they are also continuous (Lie groups). Any subgroup containing at least one non-zero translation must be infinite, but subgroups of the orthogonal group can be finite. For example, the symmetries of a regular pentagon consist of rotations by integer multiples of 72° (360° / 5), along with reflections in the five mirrors which perpendicularly bisect the edges. This is a group, D, with 10 elements. It has a subgroup, C, of half the size, omitting the reflections. These two groups are members of two families, D and C, for any n > 1. Together, these families constitute the rosette groups.
Translations do not fold back on themselves, but we can take integer multiples of any finite translation, or sums of multiples of two such independent translations, as a subgroup. These generate the lattice of a periodic tiling of the plane.
We can also combine these two kinds of discrete groups — the discrete rotations and reflections around a fixed point and the discrete translations — to generate the frieze groups and wallpaper groups. Curiously, only a few of the fixed-point groups are found to be compatible with discrete translations. In fact, lattice compatibility imposes such a severe restriction that, up to isomorphism, we have only 7 distinct frieze groups and 17 distinct wallpaper groups. For example, the pentagon symmetries, D, are incompatible with a discrete lattice of translations. (Each higher dimension also has only a finite number of such crystallographic groups, but the number grows rapidly; for example, 3D has 230 groups and 4D has 4783.) | 0 | Theoretical and Fundamental Chemistry |
In the presence of excess of triphenylphosphine, RuCl(PPh) binds a fourth phosphine to give black RuCl(PPh). The triphenylphosphine ligands in both the tris(phosphine) and tetrakis(phosphine) complexes are readily substituted by other ligands. The tetrakis(phosphine) complex is a precursor to the Grubbs catalysts.
Dichlorotris(triphenylphosphine)ruthenium(II) reacts with hydrogen in the presence of base to give the purple-colored monohydride HRuCl(PPh).
:RuCl(PPh) + H + NEt → HRuCl(PPh) + [HNEt]Cl
Dichlorotris(triphenylphosphine)ruthenium(II) reacts with carbon monoxide to produce the all trans isomer of dichloro(dicarbonyl)bis(triphenylphosphine)ruthenium(II).
:RuCl(PPh) + 2 CO → trans,trans,trans-RuCl(CO)(PPh) + PPh
This kinetic product isomerizes to the cis adduct during recrystallization. trans-RuCl(dppe) forms upon treating RuCl(PPh) with dppe.
:RuCl(PPh) + 2 dppe → RuCl(dppe) + 3 PPh
RuCl(PPh) catalyzes the decomposition of formic acid into carbon dioxide and hydrogen gas in the presence of an amine. Since carbon dioxide can be trapped and hydrogenated on an industrial scale, formic acid represents a potential storage and transportation medium. | 0 | Theoretical and Fundamental Chemistry |
A typical example of a conserved moiety in biochemistry is the Adenosine diphosphate (ADP) subgroup that remains unchanged when it is phosphorylated to create adenosine triphosphate (ATP) and then dephosphorylated back to ADP forming a conserved cycle. Moiety-conserved cycles in nature exhibit unique network control features which can be elucidated using techniques such as metabolic control analysis. Other examples in metabolism include NAD/NADH, NADP/NADPH, CoA/Acetyl-CoA. Conserved cycles also exist in large numbers in protein signaling networks when proteins get phosphorylated and phosphorylated.
Most, if not all, of these cycles, are time-scale-dependent. For example, although a protein in a phosphorylation cycle is conserved during the interconversion, over a longer time scale, there will be low levels of protein synthesis and degradation, which change the level of protein moiety. The same applies to cycles involving ATP, NAD, etc. Thus, although the concept of a moiety-conserved cycle in biochemistry is a useful approximation, over time scales that include significant net synthesis and degradation of the moiety, the approximation is no longer valid. When invoking the conserved-moiety assumption on a particular moiety, we are, in effect, assuming the system is closed to that moiety. | 1 | Applied and Interdisciplinary Chemistry |
Prp24 has a human homolog, SART3. SART3 is a tumor rejection antigen (SART3 stands for "squamous cell carcinoma antigen recognized by T cells, gene 3). The RRMs 1 and 2 in yeast are similar to RRMs in human SART3. The C-terminal domain is also highly conserved from yeast to humans. This protein, like Prp24, interacts with the LSm proteins for the recycling of U6 into the U4/U6 snRNP. It has been proposed that SART3 target U6 to a Cajal body or a nuclear inclusion as the site of assembly of the U4/U6 snRNP. SART3 is located on chromosome 12, and a mutation is likely the cause of disseminated superficial actinic porokeratosis. | 1 | Applied and Interdisciplinary Chemistry |
, GOSAT-GW, the successor of GOSAT-2 and GCOM-W "Shizuku", is under development for launch in JFY2024 on the last flight of the H-IIA launch vehicle. | 1 | Applied and Interdisciplinary Chemistry |
It is possible to build a computer simulation of a linear biochemical pathway. This can be done by building a simple model that describes each intermediate through a differential equation. The differential equations can be written by invoking mass conservation. For example, for the linear pathway:
where and are fixed boundary species, the non-fixed intermediate can be described using the differential equation:
The rate of change of the non-fixed intermediates and can be written in the same way:
To run a simulation the rates, need to be defined. If mass-action kinetics are assumed for the reaction rates, then the differential equation can be written as:
If values are assigned to the rate constants, , and the fixed species and the differential equations can be solved. | 1 | Applied and Interdisciplinary Chemistry |
The criterion for aromaticity has evolved as new developments and insights continue to contribute to our understanding of these remarkably stable organic molecules. The required characteristics of these molecules has thus remained the subject of some controversy. Classically, aromatic compounds were defined as planar molecules that possess a cyclically delocalized system of (4n+2)π electrons, satisfying Huckel's rule. Most importantly, these conjugated ring systems are known to exhibit enormous thermochemical stability relative to predictions based on localized resonance structures. Succinctly, three important features seem to characterize aromatic compounds:
#molecular structure (i.e. coplanarity: all contributing atoms in the same plane)
#molecular energetics (i.e. increased thermodynamic stability)
#spectroscopic and magnetic properties (i.e. magnetic field induced ring current)
A number of exceptions to these conventional rules exist, however. Many molecules, including Möbius 4nπ electron species, pericyclic transition states, molecules in which delocalized electrons circulate in the ring plane or through σ (rather than π) bonds, many transition-metal sandwich molecules, and others have been deemed aromatic though they somehow deviate from the conventional parameters for aromaticity.
Consequently, the criterion for homoaromatic delocalization remains similarly ambiguous and somewhat controversial. The homotropylium cation, (CH), though not the first example of a homoaromatic compound ever discovered, has proven to be the most studied of the compounds classified as homoaromatic, and is therefore often considered the classic example of homoaromaticity. By the mid-1980s, there were more than 40 reported substituted derivatives of the homotropylium cation, reflecting the importance of this ion in formulating our understanding of homoaromatic compounds. | 0 | Theoretical and Fundamental Chemistry |
In 1933 Strassmann resigned from the Society of German Chemists when it became part of a Nazi-controlled public corporation. He was blacklisted by the Nazi regime. As a result, he could not work in the chemical industry nor could he receive his habilitation as required to be an independent researcher in Germany at the time. Lise Meitner encouraged Otto Hahn to find an assistantship for Strassmann at half pay, and he eventually became a special assistant to Meitner and Hahn. Strassmann considered himself fortunate, for "despite my affinity for chemistry, I value my personal freedom so highly that to preserve it I would break stones for a living."
Strassman's wife Maria supported his refusal to join the Nazi Party. During World War II they concealed a Jewish woman, musician Andrea Wolfenstein, in their apartment for months, putting themselves and their three-year-old son at risk. Strassmann continued his research in radiochemistry during World War II, although he did not work on weapons development. He disdained the Nazi regime and is reported to have said, "If my work would lead to Hitler having an atomic bomb I would kill myself." | 0 | Theoretical and Fundamental Chemistry |
As a chiral derivatizing agent, it reacts with an alcohol or amine of unknown stereochemistry to form an ester or amide. The absolute configuration of the ester or amide is then determined by proton and/or F NMR spectroscopy.
Mosher's acid chloride, the acid chloride form, is sometimes used because it has better reactivity. | 0 | Theoretical and Fundamental Chemistry |
When blood glucose levels are too low, the pancreas is signaled to release glucagon, which has essentially the opposite effect of insulin and therefore opposes the reduction of glucose in the blood. Glucagon is delivered directly to the liver, where it connects to the glucagon receptors on the membranes of the liver cells, signals the conversion of the glycogen already stored in the liver cells into glucose. This process is called glycogenolysis.
Conversely, when the blood glucose levels are too high, the pancreas is signaled to release insulin. Insulin is delivered to the liver and other tissues throughout the body (e.g., muscle, adipose). When the insulin is introduced to the liver, it connects to the insulin receptors already present, that is tyrosine kinase receptor. These receptors have two alpha subunits (extracellular) and two beta subunits (intercellular) which are connected through the cell membrane via disulfide bonds. When the insulin binds to these alpha subunits, glucose transport 4 (GLUT4) is released and transferred to the cell membrane to regulate glucose transport in and out of the cell. With the release of GLUT4, the allowance of glucose into cells is increased, and therefore the concentration of blood glucose might decrease. This, in other words, increases the utilization of the glucose already present in the liver. This is shown in the adjacent image. As glucose increases, the production of insulin increases, which thereby increases the utilization of the glucose, which maintains the glucose levels in an efficient manner and creates an oscillatory behavior. | 1 | Applied and Interdisciplinary Chemistry |
Allele-specific oligonucleotide (ASO) is a technique that allows detection of single base mutations without the need for PCR or gel electrophoresis. Short (20–25 nucleotides in length), labeled probes are exposed to the non-fragmented target DNA, hybridization occurs with high specificity due to the short length of the probes and even a single base change will hinder hybridization. The target DNA is then washed and the labeled probes that did not hybridize are removed. The target DNA is then analyzed for the presence of the probe via radioactivity or fluorescence. In this experiment, as in most molecular biology techniques, a control must be used to ensure successful experimentation.
In molecular biology, procedures and technologies are continually being developed and older technologies abandoned. For example, before the advent of DNA gel electrophoresis (agarose or polyacrylamide), the size of DNA molecules was typically determined by rate sedimentation in sucrose gradients, a slow and labor-intensive technique requiring expensive instrumentation; prior to sucrose gradients, viscometry was used. Aside from their historical interest, it is often worth knowing about older technology, as it is occasionally useful to solve another new problem for which the newer technique is inappropriate. | 1 | Applied and Interdisciplinary Chemistry |
The crystal structure of the nucleosome core particle () - different views showing details of histone folding and organization. Histones , , , and are coloured. | 1 | Applied and Interdisciplinary Chemistry |
Mars is differentiated, which—for a terrestrial planet—implies that it has a central core made up of high density matter (mainly metallic iron and nickel) surrounded by a less dense, silicate mantle and crust. Like Earth, Mars appears to have a molten iron core, or at least a molten outer core. However, there does not appear to be convection in the mantle. Presently Mars shows little geological activity.
The elemental composition of Mars is different from Earths in several significant ways. First, Martian meteorite analysis suggests that the planets mantle is about twice as rich in iron as the Earths mantle. The planets distinctive red color is due to iron oxides on its surface. Second, its core is richer in sulphur. Third, the Martian mantle is richer in potassium and phosphorus than Earths and fourth, the Martian crust contains a higher percentage of volatile elements such as sulphur and chlorine than the Earths crust does. Many of these conclusions are supported by in situ analyses of rocks and soils on the Martian surface.
Much of what we know about the elemental composition of Mars comes from orbiting spacecraft and landers. (See Exploration of Mars for list.) Most of these spacecraft carry spectrometers and other instruments to measure the surface composition of Mars by either remote sensing from orbit or in situ analyses on the surface. We also have many actual samples of Mars in the form of meteorites that have made their way to Earth. Martian meteorites (often called SNCs, for Shergottites, Nakhlites, and Chassignites—the groups of meteorites first shown to have a martian origin) provide data on the chemical composition of Mars crust and interior that would not otherwise be available except through a sample return mission.
Based on these data sources, scientists think that the most abundant chemical elements in the Martian crust are silicon, oxygen, iron, magnesium, aluminium, calcium, and potassium. These elements are major components of the minerals comprising igneous rocks. The elements titanium, chromium, manganese, sulfur, phosphorus, sodium, and chlorine are less abundant but are still important components of many accessory minerals in rocks and of secondary minerals (weathering products) in the dust and soils (the regolith). On September 5, 2017, scientists reported that the Curiosity rover detected boron, an essential ingredient for life on Earth, on the planet Mars. Such a finding, along with previous discoveries that water may have been present on ancient Mars, further supports the possible early habitability of Gale Crater on Mars.
Hydrogen is present as water (HO) ice and in hydrated minerals. Carbon occurs as carbon dioxide (CO) in the atmosphere and sometimes as dry ice at the poles. An unknown amount of carbon is also stored in carbonates. Molecular nitrogen (N) makes up 2.7 percent of the atmosphere. As far as we know, organic compounds are absent except for a trace of methane detected in the atmosphere. On 16 December 2014, NASA reported the Curiosity rover detected a "tenfold spike", likely localized, in the amount of methane in the Martian atmosphere. Sample measurements taken "a dozen times over 20 months" showed increases in late 2013 and early 2014, averaging "7 parts of methane per billion in the atmosphere." Before and after that, readings averaged around one-tenth that level.
On 25 October 2023, scientists, helped by information from the InSight lander, reported that the planet Mars has a radioactive magma ocean under its crust. | 0 | Theoretical and Fundamental Chemistry |
The first refinements of copper alloys by a converter took place in Ducktown, Tennessee where A. Raht worked on a partial refinement of the matte from 1866 to 1875. In 1867, the Russians Jossa and Latelin tried to experimentally verify the studies of Semenikow. In 1870, they stopped their experiments after only having succeeded to increase the copper content from 31% to 72-80%.
In England, John Hollway continued these trials until 1878. Like his predecessors, he observed that if blowing began in a satisfactory manner, it became more and more intermittent as the refinement progressed. The obstacles he encountered were numerous:
* The weight of produced slag was equal to that of copper and its volume was much greater than that in the converter. It was thus necessary to drain the retort regularly.
* The density of the molten metal changed greatly (with copper having a density three times as great as the pyrite from which it is made).
* The duration of the air blowing, which can reach two hours, involved large thermal losses.
* The siliceous refractory material was absorbed by the slag, in which it acted as flux.
All of the encountered difficulties could not be easily resolved: the thermal heat balance of the refinement reaction in air of copper was not as favorable as for iron, and the matte solidified in the tuyeres before being refined. Even when modified, a Bessemer converter was capable at best of removing iron and a portion of sulfur. Hollway failed, but by publishing all of the details of his experiments, he identified the essential problems. | 1 | Applied and Interdisciplinary Chemistry |
Self-assembly of nanoscale structures from functional nanoparticles has provided a powerful path to developing small and powerful electronic components. Nanoscale objects have always been difficult to manipulate because they cannot be characterized by molecular techniques and they are too small to observe optically. But with advances in science and technology, there are now many instruments for observing nanostructures. Imaging methods span electron, optical and scanning probe microscopy, including combined electron-scanning probe and near-field opticalscanning probe instruments. Nanostructure characterization tools include advanced optical spectro-microscopy (linear, non-linear, tipenhanced and pump-probe) and Auger and x-ray photoemission for surface analysis. 2D self-assembly monodisperse particle colloids has a strong potential in dense magnetic storage media. Each colloid particle has the ability to store information as known as binary number 0 and 1 after applying it to a strong magnetic field. In the meantime, it requires a nanoscale sensor or detector in order to selectively choose the colloid particle. The microphase separation of block copolymers shows a great deal of promise as a means of generating regular nanopatterns at surfaces. They may, therefore, find application as a means to novel nanomaterials and nanoelectronics device structures. | 0 | Theoretical and Fundamental Chemistry |
The term intermetallic is used to describe compounds involving two or more metals such as the cyclopentadienyl complex CpNiZn. | 1 | Applied and Interdisciplinary Chemistry |
Selective laser melting (also known as powder bed fusion) is an additive manufacturing procedure used to create intricately detailed forms from a CAD file. A shape is designed and then converted into slices. These slices are sent to a laser writer to print the final product. In brief, a bed of metal powder is prepared, and a slice is formed in the powder bed by a high energy laser sintering the particles together. The powder bed moves downwards, and a new batch of metal powder is rolled over the top. This layer is then sintered with the laser, and the process is repeated until all slices have been processed. Additive manufacturing can leave pores behind. Many products undergo a heat treatment or hot isostatic pressing procedure to densify the product and reduce porosity. | 1 | Applied and Interdisciplinary Chemistry |
Many scenarios in the real world are affected by thermal degradation. One of the things affected is fingerprints. When anyone touches something, there is residue left from the fingers. If fingers are sweaty, or contain more oils, the residue contains many chemicals. De Paoli and her collogues conducted a study testing thermal degradation on certain components found in fingerprints. For heat exposure, the amino acid and urea samples started degradation at and for lactic acid, the decomposition process started around . These components are necessary for further testing, so in the forensics discipline, decomposition of fingerprints is significant. | 0 | Theoretical and Fundamental Chemistry |
The most common of these uses a group contribution method and is termed cLogP. It has been shown that the log P of a compound can be determined by the sum of its non-overlapping molecular fragments (defined as one or more atoms covalently bound to each other within the molecule). Fragmentary log P values have been determined in a statistical method analogous to the atomic methods (least-squares fitting to a training set). In addition, Hammett-type corrections are included to account of electronic and steric effects. This method in general gives better results than atomic-based methods, but cannot be used to predict partition coefficients for molecules containing unusual functional groups for which the method has not yet been parameterized (most likely because of the lack of experimental data for molecules containing such functional groups). | 0 | Theoretical and Fundamental Chemistry |
Pharmacogenomics was first recognized by Pythagoras around 510 BC when he made a connection between the dangers of fava bean ingestion with hemolytic anemia and oxidative stress. In the 1950s, this identification was validated and attributed to deficiency of G6PD and is called favism. Although the first official publication was not until 1961, the unofficial beginnings of this science were around the 1950s. Reports of prolonged paralysis and fatal reactions linked to genetic variants in patients who lacked butyrylcholinesterase (pseudocholinesterase) following succinylcholine injection during anesthesia were first reported in 1956. The term pharmacogenetics was first coined in 1959 by Friedrich Vogel of Heidelberg, Germany (although some papers suggest it was 1957 or 1958). In the late 1960s, twin studies supported the inference of genetic involvement in drug metabolism, with identical twins sharing remarkable similarities in drug response compared to fraternal twins. The term pharmacogenomics first began appearing around the 1990s.
The first FDA approval of a pharmacogenetic test was in 2005 (for alleles in CYP2D6 and CYP2C19) | 1 | Applied and Interdisciplinary Chemistry |
The Kelvin–Helmholtz instability (KHI) is an application of hydrodynamic stability that can be seen in nature. It occurs when there are two fluids flowing at different velocities. The difference in velocity of the fluids causes a shear velocity at the interface of the two layers. The shear velocity of one fluid moving induces a shear stress on the other which, if greater than the restraining surface tension, then results in an instability along the interface between them. This motion causes the appearance of a series of overturning ocean waves, a characteristic of the Kelvin–Helmholtz instability. Indeed, the apparent ocean wave-like nature is an example of vortex formation, which are formed when a fluid is rotating about some axis, and is often associated with this phenomenon.
The Kelvin–Helmholtz instability can be seen in the bands in planetary atmospheres such as Saturn and Jupiter, for example in the giant red spot vortex. In the atmosphere surrounding the giant red spot there is the biggest example of KHI that is known of and is caused by the shear force at the interface of the different layers of Jupiter's atmosphere. There have been many images captured where the ocean-wave like characteristics discussed earlier can be seen clearly, with as many as 4 shear layers visible.
Weather satellites take advantage of this instability to measure wind speeds over large bodies of water. Waves are generated by the wind, which shears the water at the interface between it and the surrounding air. The computers on board the satellites determine the roughness of the ocean by measuring the wave height. This is done by using radar, where a radio signal is transmitted to the surface and the delay from the reflected signal is recorded, known as the "time of flight". From this meteorologists are able to understand the movement of clouds and the expected air turbulence near them. | 1 | Applied and Interdisciplinary Chemistry |
Some common radionuclides that decay solely by electron capture include:
For a full list, see the table of nuclides. | 0 | Theoretical and Fundamental Chemistry |
The Vuilleumier cycle was patented by a Swiss-American engineer named Rudolph Vuilleumier in 1918. The purpose of Vuilleumier's machine was to create a heat pump that would use heat at high temperature as energy input. The Vuilleumier cycle...The Vuilleumier cycle is a thermodynamic cycle with applications in low-temperature cooling. In some respects it resembles a Stirling cycle or engine, although it has two "displacers" with a mechanical linkage connecting them as compared to one in the Stirling cycle. The hot displacer is larger than the cold displacer. The coupling maintains the appropriate phase difference. The displacers do no workthey are not pistons. Thus no work is required in an ideal case to operate the cycle. In reality friction and other losses mean that some work is required.
Devices operating on this cycle have been able to produce temperatures as low as 15 K using liquid nitrogen to pre-cool. Without precooling 77 K was reached with a heat flow of 1 W.
The cycle was first patented by Vuilleumier in 1918 [https://www.google.com/patents/US1275507 with patent US1275507], and again in Leiden by KW Taconis in 1951. In March 2014, the Vuilleumier Cycle was tested in application with updating conventional HVAC (heating, ventilation, and air-conditioning) systems by utilizing the cycle's proposed thermodynamic process of moving heat energy, and having results of increased output efficiencies coupled with a reduced carbon footprint. This work was completed by ThermoLift (http://www.tm-lift.com/), a company based out of the Advanced Energy Research and Technology Center at Stony Brook University, with collaboration from the US Department of Energy and the New York State Energy Research and Development Authority (NYSERDA). This work culminated in the demonstration of the ThermoLift system at Oak Ridge National Laboratory in August, 2018. The demonstration showed that the ThermoLift technology (TCHP), is able to achieve coefficients of performance (COP) for the cycle that well exceeded the DOE’s target COPs for cold-climate heat pumps (although not at all exceeding Geothermal heat pump efficiencies). Furthermore, due to the nature of the TCHP, there is no significant capacity decrease as the inlet temperature to the cold HX decreases. | 0 | Theoretical and Fundamental Chemistry |
The reactor operates by converting organic analytes after GC separation into methane before detection by FID. The oxidation and reduction reactions occur sequentially, wherein the organic compound is first combusted into molecules of carbon dioxide, which are subsequently reduced to methane molecules. The following reactions demonstrate the combustion/reduction process for formic acid.
HCOH + 0.5O ↔ CO + HO
CO + 4H ↔ CH + 2HO
The reactions are faster compared to the time scales of typical chromatography, resulting in manageable peak broadening and tailing. Elements other than carbon are not ionized in the hydrogen and oxygen flames of the FID and thus do not contribute to the FID signal. | 0 | Theoretical and Fundamental Chemistry |
The metals involved in a bimetallic strip can vary in composition so long as their thermal expansion coefficients differ. The metal of lower thermal expansion coefficient is sometimes called the passive metal, while the other is called the active metal. Copper, steel, brass, iron, and nickel are commonly used metals in bimetallic strips. Metal alloys have been used in bimetallic strips as well, such as invar and constantan. Material selection has a significant impact on the working temperature range of a bimetallic strip, with some having a temperature limit up to 500°C, with others only reaching 150°C before failing. | 1 | Applied and Interdisciplinary Chemistry |
* 2Fe–2S: AOX1; FDX1; FDX2; NDUFS1; SDHB; XDH;
* 4Fe–4S: ABCE1; DPYD; NDUFS8; | 0 | Theoretical and Fundamental Chemistry |
In astrophysics, particularly the study of accretion disks, the epicyclic frequency is the frequency at which a radially displaced fluid parcel will oscillate. It can be referred to as a "Rayleigh discriminant". When considering an astrophysical disc with differential rotation , the epicyclic frequency is given by
: , where R is the radial co-ordinate.
This quantity can be used to examine the boundaries of an accretion disc: when becomes negative, then small perturbations to the (assumed circular) orbit of a fluid parcel will become unstable, and the disc will develop an edge at that point. For example, around a Schwarzschild black hole, the innermost stable circular orbit (ISCO) occurs at three times the event horizon, at .
For a Keplerian disk, . | 1 | Applied and Interdisciplinary Chemistry |
Intermetallic particles often form during solidification of metallic alloys, and can be used as a dispersion strengthening mechanism. | 1 | Applied and Interdisciplinary Chemistry |
Methylation of rRNA upholds structural rigidity by blocking base pair stacking and surrounds the 2’-OH group to block hydrolysis. It occurs at specific parts of eukaryotic rRNA. The template for methylation consists of 10-21 nucleotides. 2-O-methylation of the ribose sugar is one of the most common rRNA modifications. Methylation is primarily introduced by small nucleolar RNAs, referred to as snoRNPs. There are two classes of snoRNPs that target methylation sites, and they are referred to box C/D and box H/ACA. One type of methylation, 2′-O-methylation, contributes to helical stabilization. | 1 | Applied and Interdisciplinary Chemistry |
Transcription begins with the RNA polymerase and one or more general transcription factors binding to a DNA promoter sequence to form an RNA polymerase-promoter closed complex. In the closed complex, the promoter DNA is still fully double-stranded.
RNA polymerase, assisted by one or more general transcription factors, then unwinds approximately 14 base pairs of DNA to form an RNA polymerase-promoter open complex. In the open complex, the promoter DNA is partly unwound and single-stranded. The exposed, single-stranded DNA is referred to as the "transcription bubble".
RNA polymerase, assisted by one or more general transcription factors, then selects a transcription start site in the transcription bubble, binds to an initiating NTP and an extending NTP (or a short RNA primer and an extending NTP) complementary to the transcription start site sequence, and catalyzes bond formation to yield an initial RNA product.
In bacteria, RNA polymerase holoenzyme consists of five subunits: 2 α subunits, 1 β subunit, 1 β' subunit, and 1 ω subunit. In bacteria, there is one general RNA transcription factor known as a sigma factor. RNA polymerase core enzyme binds to the bacterial general transcription (sigma) factor to form RNA polymerase holoenzyme and then binds to a promoter.
(RNA polymerase is called a holoenzyme when sigma subunit is attached to the core enzyme which is consist of 2 α subunits, 1 β subunit, 1 β' subunit only). Unlike eukaryotes, the initiating nucleotide of nascent bacterial mRNA is not capped with a modified guanine nucleotide. The initiating nucleotide of bacterial transcripts bears a 5′ triphosphate (5′-PPP), which can be used for genome-wide mapping of transcription initiation sites.
In archaea and eukaryotes, RNA polymerase contains subunits homologous to each of the five RNA polymerase subunits in bacteria and also contains additional subunits. In archaea and eukaryotes, the functions of the bacterial general transcription factor sigma are performed by multiple general transcription factors that work together. In archaea, there are three general transcription factors: TBP, TFB, and TFE. In eukaryotes, in RNA polymerase II-dependent transcription, there are six general transcription factors: TFIIA, TFIIB (an ortholog of archaeal TFB), TFIID (a multisubunit factor in which the key subunit, TBP, is an ortholog of archaeal TBP), TFIIE (an ortholog of archaeal TFE), TFIIF, and TFIIH. The TFIID is the first component to bind to DNA due to binding of TBP, while TFIIH is the last component to be recruited. In archaea and eukaryotes, the RNA polymerase-promoter closed complex is usually referred to as the "preinitiation complex".
Transcription initiation is regulated by additional proteins, known as activators and repressors, and, in some cases, associated coactivators or corepressors, which modulate formation and function of the transcription initiation complex. | 1 | Applied and Interdisciplinary Chemistry |
The Margules activity model is a simple thermodynamic model for the excess Gibbs free energy of a liquid mixture introduced in 1895 by Max Margules. After Lewis had introduced the concept of the activity coefficient, the model could be used to derive an expression for the activity coefficients of a compound i in a liquid, a measure for the deviation from ideal solubility, also known as Raoult's law.
In chemical engineering the Margules Gibbs free energy model for liquid mixtures is better known as the Margules activity or activity coefficient model. Although the model is old it has the characteristic feature to describe extrema in the activity coefficient, which modern models like NRTL and Wilson cannot. | 0 | Theoretical and Fundamental Chemistry |
Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula CaSi(OH)(CO)(SO)·12HO, also sometimes more simply written as CaSiO·CaCO·CaSO·15HO.
Thaumasite is formed under special conditions in the presence of sulfate ions in concrete containing, or exposed to, a source of carbonate anions such as limestone aggregates, or finely milled limestone filler (). Bicarbonate anions () dissolved in groundwater may also contribute to the reaction. The detrimental reaction proceeds at the expense of calcium silicate hydrates (C-S-H, with dashes denoting here their non-stoichiometry) present in the hardened cement paste (HCP). The thaumasite form of sulfate attack (TSA) is a particular type of very destructive sulfate attack. C-S-H are the "glue" in the hardened cement paste filling the interstices between the concrete aggregates. As the TSA reaction consumes the silicates of the "cement glue", it can lead to a harmful decohesion and a softening of concrete. Expansion and cracking are more rarely observed. Unlike the common sulfate attack, in which the calcium hydroxide (portlandite) and calcium aluminate hydrates react with sulfates to respectively form gypsum and ettringite (an expansive phase), in the case of TSA the C-S-H ensuring the cohesion of HCP and aggregates are destroyed. As a consequence, even concrete containing low- sulfate-resisting Portland cement may be affected.
TSA is sometimes easily recognizable on the field when examining the altered concrete. TSA-affected concrete becomes powdery and can be dug with a scoop, or even scrapped with the fingers. Concrete decohesion is very characteristic of TSA.
TSA was first identified during the years 1990 in England in the United Kingdom in the foundation piles of bridges of the motorway M5 located in the Kimmeridgian marls. These marls are a mixture of clay and limestone sedimented under anoxic conditions and are rich in pyrite (, a disulfide). Once these marls were excavated, pyrite was exposed to atmospheric oxygen or oxygen-rich infiltration water and rapidly oxidized. Pyrite oxidation produces sulfuric acid. In its turn, reacts with portlandite (present in the hardened cement paste, HCP) and calcite ( (present in limestone aggregates or in carbonated HCP). The strong acidification of the medium caused by pyrite oxidation releases bicarbonate ions () or carbon dioxide () along with calcium () and sulfate ions ().
Full pyrite oxidation can be schematized as:
The sulfuric acid released by pyrite oxidation then reacts with portlandite ()) present in the hardened cement paste to give gypsum:
When concrete also contains limestone aggregates or a filler addition, reacts with calcite () and water to also form gypsum while releasing :
Gypsum is relatively soluble in water , so there is plenty of calcium and sulfates ions available for TSA.
Simultaneously, carbonic acid () dissolves calcite to form soluble calcium bicarbonate:
So, when all the chemical ingredients necessary to react with C-S-H from the hardened cement paste in concrete are present together the TSA reaction can occur. When grounds rich in pyrite, such as many clays or marls, are excavated for civil engineering works, the strong acidification produced by pyrite oxidation is the powerful driving force triggering TSA because it frees up and mobilizes all the ions needed to attack C-S-H and to form thaumasite ().
TSA is favored by a low temperature, although it can be encountered at higher temperature in warm areas. The reason is to be found in the retrograde solubility of most of the ingredients needed for the TSA reaction. Indeed, the solubility of dissolved carbon dioxide (), portlandite (), calcite (), and gypsum (·2), increases when the temperature is lowered. This is because the dissolution reactions of these mineral species are exothermic and release heat. A lower temperature facilitates the heat release and therefore favors the exothermic reaction. Only the solubility of silica (from C-S-H) increases with temperature because silica dissolution is an endothermic process which requires heat to proceed. | 1 | Applied and Interdisciplinary Chemistry |
The reciprocal lattice to a BCC lattice is the FCC lattice, with a cube side of .
It can be proven that only the Bravais lattices which have 90 degrees between (cubic, tetragonal, orthorhombic) have primitive translation vectors for the reciprocal lattice, , parallel to their real-space vectors. | 0 | Theoretical and Fundamental Chemistry |
Most atoms in a nanocluster are surface atoms. Thus, it is expected that the magnetic moment of an atom in a cluster will be larger than that of one in a bulk material. Lower coordination, lower dimensionality, and increasing interatomic distance in metal clusters contribute to enhancement of the magnetic moment in nanoclusters. Metal nanoclusters also show change in magnetic properties. For example, vanadium and rhodium are paramagnetic in bulk but become ferromagnetic in nanoclusters. Also, manganese is antiferromagnetic in bulk but ferromagnetic in nanoclusters. A small nanocluster is a nanomagnet, which can be made nonmagnetic simply by changing its structure. So they can form the basis of a nanomagnetic switch. | 0 | Theoretical and Fundamental Chemistry |
Potassium permanganate (KMnO) is a dark violet colored powder. Its reaction with glycerol (commonly known as glycerin or glycerine) (CH(OH)) is highly exothermic, resulting rapidly in a flame, along with the formation of carbon dioxide and water vapour:
14 KMnO(s) + 4 CH(OH)(l) → 7 KCO(s) + 7 MnO(s) + 5 CO(g) + 16 HO(g).
Crystalline potassium permanganate (KMnO) is placed in an evaporating dish. A depression is made at the center of the permanganate powder and glycerol liquid is added to it. The white smoke-like vapor produced by the reaction is a mixture of carbon dioxide gas and water vapor. Since the reaction is highly exothermic, initial sparking occurs, followed by a lilac- or pink-colored flame. When energy or heat is added to electrons, their energy level increases to an excited state. This state is short-lived, and once the electrons release the energy, they return to their normal energy levels. During this process the energy is visibly observed as light. When the reaction is complete, it leaves behind a grayish solid with green regions. | 1 | Applied and Interdisciplinary Chemistry |
Applying an organic solvent such as toluene onto a balloons surface can pop it, since the solvent can partially dissolve the material making up the balloons surface.
cis-1,4-polyisoprene (solid) + organic solvent → cis-1,4-polyisoprene (partly dissolved)
Baby oil can also be applied to water balloons to pop them. | 1 | Applied and Interdisciplinary Chemistry |
Japan has one assay office, situated at the Saitama branch of Japan Mint in Saitama Prefecture. Japan Mint has assayed and hallmarked from 1929, and the Saitama branch moved from Tokyo in 2016. Japanese hallmarking is optional. Gold, silver and platinum are subject to assay. The articles combined with the golden parts and the platinum parts are hallmarked with special marks. | 0 | Theoretical and Fundamental Chemistry |
The primary concerns to take into consideration when using a CDA in NMR spectroscopy are kinetic resolution, racemization during the derivatization reaction and that the reagent should have 100% optical purity. Kinetic resolution is especially significant when determining optical purity, but it is somewhat negligible when the CDA is being used to assign the absolute configuration of an optically pure substrate. Kinetic resolution can be overcome using excess of the CDA. Racemization can occur to either the CDA or the substrate and in both cases it has the potential to significantly affect the results. | 0 | Theoretical and Fundamental Chemistry |
The natural flows of carbon between the atmosphere, ocean, terrestrial ecosystems, and sediments are fairly balanced; so carbon levels would be roughly stable without human influence. Carbon dioxide is removed from the atmosphere primarily through photosynthesis and enters the terrestrial and oceanic biospheres. Carbon dioxide also dissolves directly from the atmosphere into bodies of water (ocean, lakes, etc.), as well as dissolving in precipitation as raindrops fall through the atmosphere. When dissolved in water, carbon dioxide reacts with water molecules and forms carbonic acid, which contributes to ocean acidity. It can then be absorbed by rocks through weathering. It also can acidify other surfaces it touches or be washed into the ocean. | 1 | Applied and Interdisciplinary Chemistry |
The mole (symbol mol) is a unit of measurement, the base unit in the International System of Units (SI) for amount of substance, a quantity proportional to the number of elementary entities of a substance. One mole contains exactly elementary entities (approximately 602 sextillion or 602 billion times a trillion), which can be atoms, molecules, ions, or other particles. The number of particles in a mole is the Avogadro number (symbol N) and the numerical value of the Avogadro constant (symbol N) expressed in mol. The value was chosen based on the historical definition of the mole as the amount of substance that corresponds to the number of atoms in 12 grams of C, which made the mass of a mole of a compound expressed in grams numerically equal to the average molecular mass of the compound expressed in daltons. With the 2019 redefinition of the SI base units, the numerical equivalence is now only approximate but may be assumed for all practical purposes.
The mole is widely used in chemistry as a convenient way to express amounts of reactants and amounts of products of chemical reactions. For example, the chemical equation can be interpreted to mean that for each 2 mol molecular hydrogen (H) and 1 mol molecular oxygen (O) that react, 2 mol of water (HO) form. The concentration of a solution is commonly expressed by its molar concentration, defined as the amount of dissolved substance per unit volume of solution, for which the unit typically used is mole per litre (mol/L). | 0 | Theoretical and Fundamental Chemistry |
H) tritium (T, hydrogen-3, H) fusion reactions are the most common accelerator based (as opposed to radioactive isotopes) neutron sources. In these systems, neutrons are produced by creating ions of deuterium, tritium, or deuterium and tritium and accelerating these into a hydride target loaded with deuterium, or deuterium and tritium. The DT reaction is used more than the DD reaction because the yield of the DT reaction is 50–100 times higher than that of the DD reaction.
D + T → n + He E = 14.1 MeV
D + D → n + He E = 2.5 MeV
Neutrons produced by DD and DT reactions are emitted somewhat anisotropically from the target, slightly biased in the forward (in the axis of the ion beam) direction. The anisotropy of the neutron emission from DD and DT reactions arises from the fact the reactions are isotropic in the center of momentum coordinate system (COM) but this isotropy is lost in the transformation from the COM coordinate system to the laboratory frame of reference. In both frames of reference, the He nuclei recoil in the opposite direction to the emitted neutron consistent with the law of conservation of momentum.
The gas pressure in the ion source region of the neutron tubes generally ranges between 0.1 and 0.01 mm Hg. The mean free path of electrons must be shorter than the discharge space to achieve ionization (lower limit for pressure) while the pressure must be kept low enough to avoid formation of discharges at the high extraction voltages applied between the electrodes. The pressure in the accelerating region, however, has to be much lower, as the mean free path of electrons must be longer to prevent formation of a discharge between the high voltage electrodes.
The ion accelerator usually consists of several electrodes with cylindrical symmetry, acting as an einzel lens. The ion beam can thus be focused to a small point at the target. The accelerators typically require power supplies of 100–500 kV. They usually have several stages, with voltage between the stages not exceeding 200 kV to prevent field emission.
In comparison with radionuclide neutron sources, neutron tubes can produce much higher neutron fluxes and consistent (monochromatic) neutron energy spectra can be obtained. The neutron production rate can also be controlled. | 0 | Theoretical and Fundamental Chemistry |
The structure of etheniums ground state was in dispute for many years, but it was eventually agreed to be a non-classical structure, with the two carbon atoms and one of the hydrogen atoms forming a three-center two-electron bond. Calculations have shown that higher homologues, like the propyl and n-'butyl cations also have bridged structures. Generally speaking, bridging appears to be a common means by which 1° alkyl carbocations achieve additional stabilization. Consequently, true 1° carbocations (with a classical structure) may be rare or nonexistent. | 0 | Theoretical and Fundamental Chemistry |
A modification of canonical variational transition state theory in which, for energies below the threshold energy, the position of the dividing surface is taken to be that of the microcanonical threshold energy. This forces the contributions to rate constants to be zero if they are below the threshold energy. A compromise dividing surface is then chosen so as to minimize the contributions to the rate constant made by reactants having higher energies. | 0 | Theoretical and Fundamental Chemistry |
The dependence of the diffusion coefficient on temperature for gases can be expressed using Chapman–Enskog theory (predictions accurate on average to about 8%):
where
* D is the diffusion coefficient (cm/s),
* A is approximately (with Boltzmann constant , and Avogadro constant )
* 1 and 2 index the two kinds of molecules present in the gaseous mixture,
* T is the absolute temperature (K),
* M is the molar mass (g/mol),
* p is the pressure (atm),
* is the average collision diameter (the values are tabulated page 545) (Å),
* Ω is a temperature-dependent collision integral (the values tabulated for some intermolecular potentials, can be computed from correlations for others, or must be evaluated numerically.) (dimensionless).
The relation
is obtained when inserting the ideal gas law into the expression obtained directly from Chapman-Enskog theory, which may be written as
where is the molar density (mol / m) of the gas, and
with the universal gas constant. At moderate densities (i.e. densities at which the gas has a non-negligible co-volume, but is still sufficiently dilute to be considered as gas-like rather than liquid-like) this simple relation no longer holds, and one must resort to Revised Enskog Theory. Revised Enskog Theory predicts a diffusion coefficient that decreases somewhat more rapidly with density, and which to a first approximation may be written as
where is the radial distribution function evaluated at the contact diameter of the particles. For molecules behaving like hard, elastic spheres, this value can be computed from the Carnahan-Starling Equation, while for more realistic intermolecular potentials such as the Mie potential or Lennard-Jones potential, its computation is more complex, and may involve invoking a thermodynamic pertubation theory, such as SAFT. | 1 | Applied and Interdisciplinary Chemistry |
The AR belongs to the steroid receptor subfamily of the nuclear receptor superfamily. Its function is regulated by the binding of androgens, which initiates sequential conformation changes of the receptor that affects receptor-protein and receptor-DNA interactions. Endogenous androgens are mainly testosterone and DHT. AR is expressed in cells of a wide range of tissues, throughout the entire body, beyond primary and secondary sexual organs.
The AR gene is more than 90kb long and codes for a protein of 919 amino acids. Only one AR gene has been identified in humans which is located on chromosome X. It comprises four main regions, see figure 1:
# N-terminal domain (NTD) which serves a modulatory function.
# DNA-binding domain (DBD) which recognises and binds to androgen response elements (ARE) in target gene sequence.
# Ligand binding domain (LBD) which is responsible for ligand recognition and binding.
# A small hinge region between the DBD and LBD.
Two functions have been identified in AR that have critical roles in the regulation of target gene transactivation, the N-terminal activation function 1 (AF1) and the C-terminal activation function 2 (AF2). AF1 is ligand-independent and plays the primary role in target gene transactivation. The AF2 is a ligand-dependent and only shows limited function. | 1 | Applied and Interdisciplinary Chemistry |
Alterations in the pathways leading to the addition of the removal of the mA mark result in impaired gene expression and cellular function, which can lead to disease.
Normal mA levels are altered in a number of cancers. Reduced mA levels due to down regulation of METTL3 and/or METTL14 lead to the activation of a number of oncogenes, such as the gene encoding ADAM metallopeptidase domain 19 (ADAM19). Moreover, loss of mA also results in the down regulation of tumor suppressors like cyclin-dependent kinase inhibitor 2A (CDKN2A) and breast cancer 2 (BRCA2). On the other hand, increased mA levels inhibit tumor progression in certain types of cancer. In addition, single nucleotide polymorphisms (SNPs) on the gene encoding FTO have been associated with increased risk of breast and pancreatic cancer. Altered mA levels also contribute to hypoxia-induced enrichment of breast cancer stem cells phenotype. All things considered, "writers" and "erasers" of the mA mark may be good potential drug targets in cancer therapy.
Metabolic disorders are also affected by the mA mark due to the role of FTO. Overexpression of FTO results in increased body and fat mass, whereas loss of FTO leads to a reduction in lean body mass. However, the mechanisms by which changes in FTO expression affect body and fat mass are not understood.
Current research of the m6a epitranscriptome is continuing to uncover the implications of m6a and its post-physiological effects on ischemic stroke incidents. Microglial-mediated responses and contributing demethylases, including FTO and ALKBH5, appear to be a contributing factor for alterations of the cerebral m6a epitranscriptome. Mood disorders, such as major depressive disorder, have also been identified as disease processes associated with m6a epitranscriptome changes. | 1 | Applied and Interdisciplinary Chemistry |
A putative gene is a segment of DNA that is believed to be a gene. Putative genes can share sequence similarities to already characterized genes and thus can be inferred to share a similar function, yet the exact function of putative genes remains unknown. Newly identified sequences are considered putative gene candidates when homologs of those sequences are found to be associated with the phenotype of interest. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, a sulfonanilide group is a functional group found in certain organosulfur compounds. It possesses the chemical structure , and consists of a sulfonamide group () where one of the two nitrogen substituents (R' or R") is a phenyl group (). It can be viewed as a derivative of aniline (). | 0 | Theoretical and Fundamental Chemistry |
The antitubercular agent Ethambutol contains two constitutionally symmetrical stereogenic centers in its structure and exists in three stereoisomeric forms. An enantiomeric pair (S,S)- and (R,R)-ethambutol, along with the achiral stereoisomer called meso-form, it holds a diastereomeric relationship with the optically active stereoisomers. The activity of the drug resides in the (S,S)-enantiomer which is 500 and 12 fold more potent than the (R,R)-ethambutol and the meso-form. The drug had initially been introduced for clinical use as the racemate and was changed to the (S,S)-enantiomer, as a result of optic neuritis leading to blindness. Toxicity is related to both dose and duration of treatment. All the three stereoisomers were almost equipotent with respect to side effects. Hence the use of S,S)-enantiomer greatly enhanced the risk/benefit ratio. | 0 | Theoretical and Fundamental Chemistry |
Grignard was drafted into the French military as part of obligatory military service in 1892. Within the two years of his first session of service he rose to the rank of corporal. He was demobilized in 1894 and returned to Lyon to pursue his education. He was awarded a medal of the Legion of Honour and made a Chevalier in 1912 after winning the Nobel Prize. When World War I broke out, Grignard was drafted back into the military, keeping his rank of corporal. He was placed on sentry duty, and served there for several months until he was brought to the attention of the General Staff. Grignard had been wearing his Medal of the Legion of Honour, despite being ordered to take it off by a superior. After looking more into Grignard, the General Staff decided that he would be better suited for research than sentry duty, so they assigned him to the explosives division. Grignard's research shifted to antidotes to chemical weapons when production of TNT was no longer sustainable, and eventually Grignard was assigned to research new chemical weapons for the French army. | 0 | Theoretical and Fundamental Chemistry |
Metal–organic biohybrids (MOBs) are a family of materials containing a metal component, such as copper, and a biological component, such as the amino acid dimer cystine. One of the MOB families first described was the copper-high aspect ratio structure called CuHARS. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of CuHARS revealed linear morphology and smooth surface texture. SEM, TEM and light microscopy showed that CuHARS composites had scalable dimensions from nano- to micro-, with diameters as low as 40 nm, lengths exceeding 150 microns, and average aspect ratios of 100. | 0 | Theoretical and Fundamental Chemistry |
In 1959, the geneticist Edward B. Lewis computed that children exposed to fallout from nuclear tests may have received very high doses of radioactivity from iodine-131 in cow milk. His estimates prompted the Joint Committee on Atomic Energy to request that the AEC produce a report on the risks of short-lived isotopes. In 1960, Harold A. Knapp, a mathematician working within the AEC Division of Biology and Medicines Fallout Studies Branch, authored this report, but since it was finished during an international moratorium on atmospheric nuclear tests, it had no notable impact. Then, in 1962, while the USSR and the USA had resumed nuclear tests and the Limited Test Ban Treaty was being prepared in response to huge international pressure, Knapp took on the task of estimating the radioiodine exposure of Americans before 1958, at a time when milk was not monitored. Knapp conclusions were alarming, and blatantly departed from preceding AECs reassurances that the public had never been exposed to harmful levels of radioactivity. He "showed that, from just one 1953 test, infants who had been living in a radiation hotspot around St. George, Utah, might well have received I-131 doses anywhere from 150 to 750 times existing annual permissible doses."
Beginning in fall 1962, the AEC resorted to diverse pretexts to block the publication of Knapps findings. In spring 1963, Gofman, was solicited to participate in a so-called "Ad Hoc Working Group on Radioiodine and the Environment" assembled by AECs Division of Operational Safetys director, Gordon Dunning. Gofman reported that "In essence, the message to [this] Committee […] was « How can we stop this report - a report which will, in effect, make the AEC reports over the past 10 years look untrue? »". In spite of AECs Headquarters objections, the committee recommended publication of Knapps report, which was finally published by the AEC in June 1963, followed by a summary in Nature. | 0 | Theoretical and Fundamental Chemistry |
Newton extensively studied and wrote about the Temple of Solomon, dedicating an entire chapter of The Chronology of Ancient Kingdoms Amended to his observations of the temple. Newton's primary source for information was the description of the structure given within 1 Kings of the Hebrew Bible as well as the Book of Ezekiel, which he translated himself from Hebrew with the help of dictionaries, as his knowledge of that language was limited.
In addition to scripture, Newton also relied upon various ancient and contemporary sources while studying the temple. He believed that many ancient sources were endowed with sacred wisdom and that the proportions of many of their temples were in themselves sacred. This concept, often termed prisca sapientia (sacred wisdom and also the ancient wisdom that was revealed to Adam and Moses directly by God), was a common belief of many scholars during Newton's lifetime.
A more contemporary source for Newtons studies of the temple was Juan Bautista Villalpando, who just a few decades earlier had published an influential manuscript entitled In Ezechielem explanationes et apparatus urbis, ac templi Hierosolymitani (1596–1605), in which Villalpando comments on the visions of the biblical prophet Ezekiel, including within this work his own interpretations and elaborate reconstructions of Solomons Temple. In its time, Villalpando's work on the temple produced a great deal of interest throughout Europe and had a significant impact upon later architects and scholars.
Newton believed that the temple was designed by King Solomon with privileged eyes and divine guidance. To Newton, the geometry of the temple represented more than a mathematical blueprint, it also provided a time-frame chronology of Hebrew history. It was for this reason that he included a chapter devoted to the temple within The Chronology of Ancient Kingdoms Amended, a section which initially may seem unrelated to the historical nature of the book as a whole.
Newton felt that just as the writings of ancient philosophers, scholars, and biblical figures contained within them unknown sacred wisdom, the same was true of their architecture. He believed that these men had hidden their knowledge in a complex code of symbolic and mathematical language that, when deciphered, would reveal an unknown knowledge of how nature works.
In 1675 Newton annotated a copy of Manna – a disquisition of the nature of alchemy, an anonymous treatise which had been given to him by his fellow scholar Ezechiel Foxcroft. In his annotation Newton reflected upon his reasons for examining Solomon's Temple by writing:
During Newtons lifetime, there was great interest in the Temple of Solomon in Europe, due to the success of Villalpandos publications, and augmented by a vogue for detailed engravings and physical models presented in various galleries for public viewing. In 1628, Judah Leon Templo produced a model of the temple and surrounding Jerusalem, which was popular in its day. Around 1692, Gerhard Schott produced a highly detailed model of the temple for use in an opera in Hamburg composed by Christian Heinrich Postel. This immense and model was later sold in 1725 and was exhibited in London as early as 1723, and then later temporarily installed at the London Royal Exchange from 1729 to 1730, where it could be viewed for half-a-crown. Isaac Newtons most comprehensive work on the temple, found within The Chronology of Ancient Kingdoms Amended', was published posthumously in 1728, only adding to the public interest in the temple. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, pentanonide is a functional group which is composed of a cyclic ketal of a diol with 3-pentanone. It is seen in amcinafal (triamcinolone pentanonide). | 0 | Theoretical and Fundamental Chemistry |
A Ramsden emulsion, sometimes named Pickering emulsion, is an emulsion that is stabilized by solid particles (for example colloidal silica) which adsorb onto the interface between the water and oil phases. Typically, the emulsions are either water-in-oil or oil-in-water emulsions, but other more complex systems such as water-in-water, oil-in-oil, water-in-oil-in-water, and oil-in-water-in-oil also do exist. Pickering emulsions were named after S.U. Pickering, who described the phenomenon in 1907, although the effect was first recognized by Walter Ramsden in 1903.
If oil and water are mixed and small oil droplets are formed and dispersed throughout the water (oil-in-water emulsion), eventually the droplets will coalesce to decrease the amount of energy in the system. However, if solid particles are added to the mixture, they will bind to the surface of the interface and prevent the droplets from coalescing, making the emulsion more stable.
Particle properties such as hydrophobicity, shape, and size, as well as the electrolyte concentration of the continuous phase and the volume ratio of the two phases can have an effect on the stability of the emulsion. The particle’s contact angle to the surface of the droplet is a characteristic of the hydrophobicity of the particle. If the contact angle of the particle to the interface is low, the particle will be mostly wetted by the droplet and therefore will not be likely to prevent coalescence of the droplets. Particles that are partially hydrophobic are better stabilizers because they are partially wettable by both liquids and therefore bind better to the surface of the droplets. The optimal contact angle for a stable emulsion is achieved when the particle is equally wetted by the two phases (i.e. 90° contact angle). The stabilization energy is given by
where r is the particle radius, is the interfacial tension, and is the contact angle of the particle with the interface.
When the contact angle is approximately 90°, the energy required to stabilize the system is at its minimum.
Generally, the phase that preferentially wets the particle will be the continuous phase in the emulsion system. The most common type of Pickering emulsions are oil-in-water emulsions due to the hydrophilicity of most organic particles.
One example of a Pickering-stabilized emulsion is homogenized milk. The milk protein (casein) units are adsorbed at the surface of the milk fat globules and act as surfactants. The casein replaces the milkfat globule membrane, which is damaged during homogenization. Other examples of emulsions where Pickering particles may be the stabilizing species are for example detergents, low-fat chocolates, mayonnaises and margarines.
Pickering emulsions have gained increased attention and research interest during the last 20 years when the use of traditional surfactants was questioned due to environmental, health and cost issues. Synthetic nanoparticles as Pickering emulsion stabilizers with well-defined sizes and compositions have been the primarily particles of interest until recently when also natural organic particles have gained increased attention. They are believed to have advantages such as cost-efficiency and degradability, and are issued from renewable resources.
Pickering emulsions find applications for enhanced oil recovery or water remediation. Certain Pickering emulsions remain stable even under gastric conditions and show an extraordinary resistance against gastric lipolysis, facilitating their use for controlled lipid digestion and satiation or oral delivery systems.
Additionally, it has been demonstrated that the stability of the Pickering emulsions can be improved by the use of amphiphilic "Janus particles", namely particles that have one hydrophobic and one hydrophilic side, due to the higher adsorption energy of the particles at the liquid-liquid interface. This is evident when observing emulsion stabilization using polyelectrolytes.
It is also possible to use latex particles for Pickering stabilization and then fuse these particles to form a permeable shell or capsule, called a colloidosome. Moreover, Pickering emulsion droplets are also suitable templates for micro-encapsulation and the formation of closed, non-permeable capsules. This form of encapsulation can also be applied to water-in-water emulsions (dispersions of phase-separated aqueous polymer solutions), and can also be reversible.
Pickering-stabilized microbubbles may have applications as ultrasound contrast agents. | 0 | Theoretical and Fundamental Chemistry |
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