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Charles law (also known as the law of volumes) is an experimental gas law that describes how gases tend to expand when heated. A modern statement of Charles law is:
This relationship of direct proportion can be written as:
So this means:
where:
* is the volume of the gas,
* is the temperature of the gas (measured in kelvins), and
* is a non-zero constant.
This law describes how a gas expands as the temperature increases; conversely, a decrease in temperature will lead to a decrease in volume. For comparing the same substance under two different sets of conditions, the law can be written as:
The equation shows that, as absolute temperature increases, the volume of the gas also increases in proportion. | 0 | Theoretical and Fundamental Chemistry |
The hydrogen evolution reaction in alkaline conditions starts with water adsorption and dissociation in the Volmer step and either hydrogen desorption in the Tafel step or Heyrovsky step. | 0 | Theoretical and Fundamental Chemistry |
Since the late 1970s, the use of CFCs has been heavily regulated because of their destructive effects on the ozone layer. After the development of his electron capture detector, James Lovelock was the first to detect the widespread presence of CFCs in the air, finding a mole fraction of 60 ppt of CFC-11 over Ireland. In a self-funded research expedition ending in 1973, Lovelock went on to measure CFC-11 in both the Arctic and Antarctic, finding the presence of the gas in each of 50 air samples collected, and concluding that CFCs are not hazardous to the environment. The experiment did however provide the first useful data on the presence of CFCs in the atmosphere. The damage caused by CFCs was discovered by Sherry Rowland and Mario Molina who, after hearing a lecture on the subject of Lovelocks work, embarked on research resulting in the first publication suggesting the connection in 1974. It turns out that one of CFCs most attractive features—their low reactivity—is key to their most destructive effects. CFCs lack of reactivity gives them a lifespan that can exceed 100 years, giving them time to diffuse into the upper stratosphere. Once in the stratosphere, the suns ultraviolet radiation is strong enough to cause the homolytic cleavage of the C-Cl bond. In 1976, under the Toxic Substances Control Act, the EPA banned commercial manufacturing and use of CFCs and aerosol propellants. This was later superseded in the 1990 amendments to the Clean Air Act to address stratospheric ozone depletion.
By 1987, in response to a dramatic seasonal depletion of the ozone layer over Antarctica, diplomats in Montreal forged a treaty, the Montreal Protocol, which called for drastic reductions in the production of CFCs. On 2 March 1989, 12 European Community nations agreed to ban the production of all CFCs by the end of the century. In 1990, diplomats met in London and voted to significantly strengthen the Montreal Protocol by calling for a complete elimination of CFCs by 2000. By 2010, CFCs should have been completely eliminated from developing countries as well.
Because the only CFCs available to countries adhering to the treaty is from recycling, their prices have increased considerably. A worldwide end to production should also terminate the smuggling of this material. However, there are current CFC smuggling issues, as recognized by the United Nations Environmental Programme (UNEP) in a 2006 report titled "Illegal Trade in Ozone Depleting Substances". UNEP estimates that between 16,000–38,000 tonnes of CFCs passed through the black market in the mid-1990s. The report estimated between 7,000 and 14,000 tonnes of CFCs are smuggled annually into developing countries. Asian countries are those with the most smuggling; as of 2007, China, India and South Korea were found to account for around 70% of global CFC production, South Korea later to ban CFC production in 2010. Possible reasons for continued CFC smuggling were also examined: the report noted that many of the refrigeration systems that were designed to be operated utilizing the banned CFC products have long lifespans and continue to operate. The cost of replacing the equipment of these items is sometimes cheaper than outfitting them with a more ozone-friendly appliance. Additionally, CFC smuggling is not considered a significant issue, so the perceived penalties for smuggling are low. In 2018 public attention was drawn to the issue, that at an unknown place in east Asia an estimated amount of 13,000 metric tons annually of CFCs have been produced since about 2012 in violation of the protocol. While the eventual phaseout of CFCs is likely, efforts are being taken to stem these current non-compliance problems.
By the time of the Montreal Protocol, it was realised that deliberate and accidental discharges during system tests and maintenance accounted for substantially larger volumes than emergency discharges, and consequently halons were brought into the treaty, albeit with many exceptions. | 1 | Applied and Interdisciplinary Chemistry |
Conventionally, they are displayed as isosurfaces with positive density—electron density where theres nothing in the model, usually corresponding to some constituent of the crystal that hasnt been modelled, for example a ligand or a crystallisation adjutant -- in green, and negative density—parts of the model not backed up by electron density, indicating either that an atom has been disordered by radiation damage or that it is modelled in the wrong place—in red. The typical contouring (display threshold) is set at 3σ. | 0 | Theoretical and Fundamental Chemistry |
Baldwin's rules in organic chemistry are a series of guidelines outlining the relative favorabilities of ring closure reactions in alicyclic compounds. They were first proposed by Jack Baldwin in 1976.
Baldwin's rules discuss the relative rates of ring closures of these various types. These terms are not meant to describe the absolute probability that a reaction will or will not take place, rather they are used in a relative sense. A reaction that is disfavoured (slow) does not have a rate that is able to compete effectively with an alternative reaction that is favoured (fast). However, the disfavoured product may be observed, if no alternate reactions are more favoured.
The rules classify ring closures in three ways:
*the number of atoms in the newly formed ring
*into exo and endo ring closures, depending whether the bond broken during the ring closure is inside (endo) or outside (exo) the ring that is being formed
*into tet, trig and dig geometry of the atom being attacked, depending on whether this electrophilic carbon is tetrahedral (sp hybridised), trigonal (sp hybridised) or diagonal (sp hybridised).
Thus, a ring closure reaction could be classified as, for example, a 5-exo-trig.
Baldwin discovered that orbital overlap requirements for the formation of bonds favour only certain combinations of ring size and the exo/endo/dig/trig/tet parameters. Interactive 3D models of several of these transition states can be seen [http://www.chemtube3d.com/Baldwin'sRule-Classes.html here] (javascript required).
There are sometimes exceptions to Baldwins rules. For example, cations often disobey Baldwins rules, as do reactions in which a third-row atom is included in the ring. An expanded and revised version of the rules is available:
The rules apply when the nucleophile can attack the bond in question in an ideal angle. These angles are 180° (Walden inversion) for exo-tet reactions, 109° (Bürgi–Dunitz angle) for exo-trig reaction and 120° for endo-dig reactions. Angles for nucleophilic attack on alkynes were reviewed and redefined recently. The "acute angle" of attack postulated by Baldwin was replaced with a trajectory similar to the Bürgi–Dunitz angle. | 0 | Theoretical and Fundamental Chemistry |
Chemical Geology is an international peer-reviewed academic journal. The journal is affiliated with the European Association of Geochemistry and it is published by Elsevier., publishing both subscription and open access articles. The journal is a hybrid open-access journal.
Chemical Geology publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry.
The journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry. | 0 | Theoretical and Fundamental Chemistry |
Van't Hoff argued that the temperature of a reaction and the standard equilibrium constant exhibit the relation:
where denotes the apposite standard internal energy change value.
Let and respectively denote the forward and backward reaction rates of the reaction of interest, then
, an equation from which naturally follows.
Substituting the expression for in eq.(), we obtain .
The preceding equation can be broken down into the following two equations:
and
where and are the activation energies associated with the forward and backward reactions respectively, with .
Experimental findings suggest that the constants in eq.() and eq.() can be treated as being equal to zero, so that and
Integrating these equations and taking the exponential yields the results and , where each pre-exponential factor or is mathematically the exponential of the constant of integration for the respective indefinite integral in question. | 0 | Theoretical and Fundamental Chemistry |
Beyond domatia and nutritional rewards, other plant characteristics influence the colonization of plants by natural enemies. These can include the physical size, shape, density, maturity, colour, and texture of a given plant species. Specific plant features such as the hairiness or glossiness of vegetation can have mixed effects on different natural enemies. For example, trichomes decrease hunting efficiency of many natural enemies, as trichomes tend to slow or prevent movement due to the physical obstacles they present or the adhesive secretions they produce. However, sometimes the prey species may be more impeded than the predator. For example, when the whitefly prey of the parasitoid Encarsia formosa is slowed by plant hairs, the parasitoid can detect and parasitize a higher number of juvenile whiteflies.
Many predatory coccinelid beetles have a preference for the type of leaf surface they frequent. Presented with the opportunity to land on glossy or hairy Brassica oleracea foliage, the beetles prefer the glossy foliage as they are better able to cling to these leaves. Studies are evaluating the effect of various plant genotypes on natural enemies. | 1 | Applied and Interdisciplinary Chemistry |
Hydrogen halides such as hydrogen chloride (HCl) adds to alkenes to give alkyl halides in hydrohalogenation. For example, the reaction of HCl with ethylene furnishes chloroethane. The reaction proceeds with a cation intermediate, being different from the above halogen addition. An example is shown below:
#Proton (H) adds (by working as an electrophile) to one of the carbon atoms on the alkene to form cation 1.
#Chloride ion (Cl) combines with the cation 1 to form the adducts 2 and 3.
In this manner, the stereoselectivity of the product, that is, from which side Cl will attack relies on the types of alkenes applied and conditions of the reaction. At least, which of the two carbon atoms will be attacked by H is usually decided by Markovnikov's rule. Thus, H attacks the carbon atom that carries fewer substituents so as the more stabilized carbocation (with the more stabilizing substituents) will form.
This is another example of an Ad2 mechanism. Hydrogen fluoride (HF) and hydrogen iodide (HI) react with alkenes in a similar manner, and Markovnikov-type products will be given. Hydrogen bromide (HBr) also takes this pathway, but sometimes a radical process competes and a mixture of isomers may form. Although introductory textbooks seldom mentions this alternative, the Ad2 mechanism is generally competitive with the Ad3 mechanism (described in more detail for alkynes, below), in which transfer of the proton and nucleophilic addition occur in a concerted manner. The extent to which each pathway contributes depends on the several factors like the nature of the solvent (e.g., polarity), nucleophilicity of the halide ion, stability of the carbocation, and steric effects. As brief examples, the formation of a sterically unencumbered, stabilized carbocation favors the Ad2 pathway, while a more nucleophilic bromide ion favors the Ad3 pathway to a greater extent compared to reactions involving the chloride ion.
In the case of dialkyl-substituted alkynes (e.g., 3-hexyne), the intermediate vinyl cation that would result from this process is highly unstable. In such cases, the simultaneous protonation (by HCl) and attack of the alkyne by the nucleophile (Cl) is believed to take place. This mechanistic pathway is known by the Ingold label Ad3 ("addition, electrophilic, third-order"). Because the simultaneous collision of three chemical species in a reactive orientation is improbable, the termolecular transition state is believed to be reached when the nucleophile attacks a reversibly-formed weak association of the alkyne and HCl. Such a mechanism is consistent with the predominantly anti addition (>15:1 anti:syn for the example shown) of the hydrochlorination product and the termolecular rate law, Rate = k[alkyne][HCl]. In support of the proposed alkyne-HCl association, a T-shaped complex of an alkyne and HCl has been characterized crystallographically.
In contrast, phenylpropyne reacts by the Ad2 ("addition, electrophilic, second-order, ion pair") mechanism to give predominantly the syn product (~10:1 syn:anti). In this case, the intermediate vinyl cation is formed by addition of HCl because it is resonance-stabilized by the phenyl group. Nevertheless, the lifetime of this high energy species is short, and the resulting vinyl cation-chloride anion ion pair immediately collapses, before the chloride ion has a chance to leave the solvent shell, to give the vinyl chloride. The proximity of the anion to the side of the vinyl cation where the proton was added is used to rationalize the observed predominance of syn addition.
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In 1915, James married Marion Templeton. Their only child, Marion James, became a historian of ancient Greece and Rome, and an art collector.
In addition to his work, Charles James became an avid gardener, specializing in delphinium propagation. He also became a beekeeper, and an expert on the social life of bees. | 1 | Applied and Interdisciplinary Chemistry |
Electrochemical energy is one of the many interchangeable forms of potential energy through which energy may be conserved. It appears in electroanalytical chemistry and has industrial applications such as batteries and fuel cells. In biology, electrochemical gradients allow cells to control the direction ions move across membranes. In mitochondria and chloroplasts, proton gradients generate a chemiosmotic potential used to synthesize ATP, and the sodium-potassium gradient helps neural synapses quickly transmit information.
An electrochemical gradient has two components: a differential concentration of electric charge across a membrane and a differential concentration of chemical species across that same membrane. In the former effect, the concentrated charge attracts charges of the opposite sign; in the latter, the concentrated species tends to diffuse across the membrane to an equalize concentrations. The combination of these two phenomena determines the thermodynamically-preferred direction for an ion's movement across the membrane.
The combined effect can be quantified as a gradient in the thermodynamic electrochemical potential: with Sometimes, the term "electrochemical potential" is abused to describe the electric potential generated by an ionic concentration gradient; that is, .
An electrochemical gradient is analogous to the water pressure across a hydroelectric dam. Routes unblocked by the membrane (e.g. membrane transport protein or electrodes) correspond to turbines that convert the water's potential energy to other forms of physical or chemical energy, and the ions that pass through the membrane correspond to water traveling into the lower river. Conversely, energy can be used to pump water up into the lake above the dam, and chemical energy can be used to create electrochemical gradients. | 0 | Theoretical and Fundamental Chemistry |
Reductive elimination has found widespread application in academia and industry, most notable being hydrogenation, the Monsanto acetic acid process, hydroformylation, and cross-coupling reactions. In many of these catalytic cycles, reductive elimination is the product forming step and regenerates the catalyst; however, in the Heck reaction and Wacker process, reductive elimination is involved only in catalyst regeneration, as the products in these reactions are formed via β–hydride elimination. | 0 | Theoretical and Fundamental Chemistry |
During the day, the stomata close to conserve water, and the -storing organic acids are released from the vacuoles of the mesophyll cells. An enzyme in the stroma of chloroplasts releases the , which enters into the Calvin cycle so that photosynthesis may take place. | 0 | Theoretical and Fundamental Chemistry |
In the case of antiques, a range of views are held on the value of patination and its replacement if damaged, known as repatination.
Preserving a piece's look and character is important and removal or reduction may dramatically reduce its value. If patination has flaked off, repatination may be recommended. Appraiser Reyne Haines notes that a repatinated metal piece will be worth more than one with major imperfections in the patina, but less than a piece still with its original finish. | 1 | Applied and Interdisciplinary Chemistry |
In everyday language, and often in materials science, a chemical substance is said to be "stable" if it is not particularly reactive in the environment or during normal use, and retains its useful properties on the timescale of its expected usefulness. In particular, the usefulness is retained in the presence of air, moisture or heat, and under the expected conditions of application. In this meaning, the material is said to be unstable if it can corrode, decompose, polymerize, burn or explode under the conditions of anticipated use or normal environmental conditions. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups (where R = alkyl, aryl, or just hydrogen). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly soluble in organic solvents, but soluble in water and common alcohols.
Many commercially important compounds are phosphonates, including glyphosate (the active molecule of the herbicide Roundup), and ethephon, a widely used plant growth regulator. Bisphosphonates are popular drugs for treatment of osteoporosis.
In biochemistry and medicinal chemistry, phosphonate groups are used as stable bioisosteres for phosphate, such as in the antiviral nucleotide analog, Tenofovir, one of the cornerstones of anti-HIV therapy. And there is an indication that phosphonate derivatives are "promising ligands for nuclear medicine." | 0 | Theoretical and Fundamental Chemistry |
Rivaroxaban chemically belongs to the group of n-aryloxazolidinones. Other drugs of that group are linezolid and tedizolid, both of whom are antibiotics. A synthesis of n-aryloxazolidinones starting with an O-silyl protected ethyl(2,3-dihydroxypropyl)-carbamate was published in 2016. In a one-pot reaction the carbamate cyclisizes to a 2-oxazolidone ring under slightly basic conditions while simultaneously the oxazolidone nitrogen is arylized by copper-catalization. For rivaroxaban in particular, 3-morpholinone substitutes the iodine in p-position of the benzene ring by copper-catalization. Afterwards, the silyl protecting group is removed and the resulting alcohol is replaced by an amino group which is then acylated in the last step.
An industrial preparation of rivaroxaban was registered as a patent by Bayer Healthcare in 2005. It starts from N-(4-aminophenol)-morpholinone which is alkylated by a propylene oxide derivate that also contains a primary amine involved in a phthalimide protection group. Next, a phosgene equivalent is added to form the 2-oxazolidone ring and the phthalimide is removed. The free amine can now be acylated which leads to rivaroxaban.
However, according to the patent the synthesis has “various disadvantages in the reaction management which has particularly unfavourable effects for preparation“. The patent also explains another synthesis starting from a chlorothiophene derivate that would be more suitable for the industrial process but points out that toxic solvents or reagents have to be removed from the final product. Therefore, this way is not an alternative.
Various other synthesis pathways of rivaroxaban have been described. | 1 | Applied and Interdisciplinary Chemistry |
A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases (see also flash point). Flashover normally occurs at or for ordinary combustibles and an incident heat flux at floor level of .
An example of flashover is the ignition of a piece of furniture in a domestic room. The fire involving the initial piece of furniture can produce a layer of hot smoke, which spreads across the ceiling in the room. The hot buoyant smoke layer grows in depth, as it is bounded by the walls of the room. The radiated heat from this layer heats the surfaces of the directly exposed combustible materials in the room, causing them to give off flammable gases, via pyrolysis. When the temperatures of the evolved gases become high enough, these gases will ignite throughout their extent. | 0 | Theoretical and Fundamental Chemistry |
A quinone methide is a type of conjugated organic compound that contain a cyclohexadiene with a carbonyl and an exocyclic methylidene or extended alkene unit. It is analogous to a quinone, but having one of the double bonded oxygens replaced with a carbon. The carbonyl and methylidene are usually oriented either ortho or para to each other. There are some examples of transient synthetic meta quinone methides. | 0 | Theoretical and Fundamental Chemistry |
Modern high-pressure thermal cracking operates at absolute pressures of about 7,000 kPa. An overall process of disproportionation can be observed, where "light", hydrogen-rich products are formed at the expense of heavier molecules which condense and are depleted of hydrogen. The actual reaction is known as homolytic fission and produces alkenes, which are the basis for the economically important production of polymers.
Thermal cracking is currently used to "upgrade" very heavy fractions or to produce light fractions or distillates, burner fuel and/or petroleum coke. Two extremes of the thermal cracking in terms of the product range are represented by the high-temperature process called "steam cracking" or pyrolysis (ca. 750 °C to 900 °C or higher) which produces valuable ethylene and other feedstocks for the petrochemical industry, and the milder-temperature delayed coking (ca. 500 °C) which can produce, under the right conditions, valuable needle coke, a highly crystalline petroleum coke used in the production of electrodes for the steel and aluminium industries.
William Merriam Burton developed one of the earliest thermal cracking processes in 1912 which operated at and an absolute pressure of and was known as the Burton process. Shortly thereafter, in 1921, C.P. Dubbs, an employee of the Universal Oil Products Company, developed a somewhat more advanced thermal cracking process which operated at and was known as the Dubbs process. The Dubbs process was used extensively by many refineries until the early 1940s when catalytic cracking came into use. | 0 | Theoretical and Fundamental Chemistry |
Using etching techniques such as focused ion beam milling, micro- or nano-sized pillars can be formed in magnetic materials. However, repeated bending of crystal pillars can cause defect formation and fatigue damage. This damage comes from the nucleation of cracks on the pillars surface, even in the elastic regime, due to localized plasticity. Crack propagation during successive compression and tension cycles can lead to pillar fracture. This is similar to what can be seen in cantilever magnetometry when operating under strong fields. Because of this, it is desirable to link smaller magnetic particles together with tougher, elastic materials, such as a polymer, rather than use a continuous alloy filament. | 0 | Theoretical and Fundamental Chemistry |
Many organic chemicals are thermodynamically unstable in the presence of oxygen; however, their rate of spontaneous oxidation is slow at room temperature. In the language of physical chemistry, such reactions are kinetically limited. This kinetic stability allows the accumulation of complex environmental structures in the environment. Upon the absorption of light, triplet oxygen converts to singlet oxygen, a highly reactive form of the gas, which effects spin-allowed oxidations. In the atmosphere, the organic compounds are degraded by hydroxyl radicals, which are produced from water and ozone.
Photochemical reactions are initiated by the absorption of a photon, typically in the wavelength range 290–700 nm (at the surface of the Earth). The energy of an absorbed photon is transferred to electrons in the molecule and briefly changes their configuration (i.e., promotes the molecule from a ground state to an excited state). The excited state represents what is essentially a new molecule. Often excited state molecules are not kinetically stable in the presence of O or HO and can spontaneously decompose (oxidize or hydrolyze). Sometimes molecules decompose to produce high energy, unstable fragments that can react with other molecules around them. The two processes are collectively referred to as direct photolysis or indirect photolysis, and both mechanisms contribute to the removal of pollutants.
The United States federal standard for testing plastic for photodegradation is 40 CFR Ch. I (7–1–03 Edition) PART 238. | 0 | Theoretical and Fundamental Chemistry |
Synthetic biopolymers are human-made copies of biopolymers obtained by abiotic chemical routes. Synthetic biopolymer of different chemical nature have been obtained, including polysaccharides, glycoproteins, peptides and proteins, polyhydroxoalkanoates, polyisoprenes. | 1 | Applied and Interdisciplinary Chemistry |
EBSD and digital image correlation (DIC) can be used together to analyse the microstructure and deformation behaviour of materials. DIC is a method that uses digital image processing techniques to measure deformation and strain fields in materials. By combining EBSD and DIC, researchers can obtain both crystallographic and mechanical information about a material simultaneously. This allows for a more comprehensive understanding of the relationship between microstructure and mechanical behaviour, which is particularly useful in fields such as materials science and engineering.
DIC can identify regions of strain localisation in a material, while EBSD can provide information about the microstructure in these regions. By combining these techniques, researchers can gain insights into the mechanisms responsible for the observed strain localisation. For example, EBSD can be used to determine the grain orientations and boundary misorientations before and after deformation. In contrast, DIC can be used to measure the strain fields in the material during deformation. Or EBSD can be used to identify the activation of different slip systems during deformation, while DIC can be used to measure the associated strain fields. By correlating these data, researchers can better understand the role of different deformation mechanisms in the material's mechanical behaviour.
Overall, the combination of EBSD and DIC provides a powerful tool for investigating materials' microstructure and deformation behaviour. This approach can be applied to a wide range of materials and deformation conditions and has the potential to yield insights into the fundamental mechanisms underlying mechanical behaviour. | 0 | Theoretical and Fundamental Chemistry |
In Conia-ene reactions proceeding via alkyne activation, a suitable late transition metal (Au, Ag, Pt, Pd) coordinates to the alkyne and increases its electrophilicity; thus, the enol tautomer of the carbonyl can attack more readily. Toste et al. pioneered two of the first examples of alkyne activation in 2004. Using a cationic Au(I) complex, the authors formed a wide variety of cyclized products from linear β-ketoester starting materials. Notably, the reactions are run under mild conditions and give high diastereoselectivity. Moreover, by shortening the alkyne tether from three carbons to two, substituted cyclopentenes can also be accessed. | 0 | Theoretical and Fundamental Chemistry |
Automation and low volume assay formats were leveraged by scientists at the NIH Chemical Genomics Center (NCGC) to develop quantitative HTS (qHTS), a paradigm to pharmacologically profile large chemical libraries through the generation of full concentration-response relationships for each compound. With accompanying curve fitting and cheminformatics software qHTS data yields half maximal effective concentration (EC50), maximal response, Hill coefficient (nH) for the entire library enabling the assessment of nascent structure activity relationships (SAR).
In March 2010, research was published demonstrating an HTS process allowing 1,000 times faster screening (100 million reactions in 10 hours) at 1-millionth the cost (using 10 times the reagent volume) than conventional techniques using drop-based microfluidics. Drops of fluid separated by oil replace microplate wells and allow analysis and hit sorting while reagents are flowing through channels.
In 2010, researchers developed a silicon sheet of lenses that can be placed over microfluidic arrays to allow the fluorescence measurement of 64 different output channels simultaneously with a single camera. This process can analyze 200,000 drops per second.
In 2013, researchers have disclosed an approach with small molecules from plants. In general, it is essential to provide high-quality proof-of-concept validations early in the drug discovery process. Here technologies that enable the identification of potent, selective, and bioavailable chemical probes are of crucial interest, even if the resulting compounds require further optimization for development into a pharmaceutical product. Nuclear receptor RORα, a protein that has been targeted for more than a decade to identify potent and bioavailable agonists, was used as an example of a very challenging drug target. Hits are confirmed at the screening step due to the bell-shaped curve. This method is very similar to the quantitative HTS method (screening and hit confirmation at the same time), except that using this approach greatly decreases the data point number and can screen easily more than 100.000 biological relevant compounds.
Whereby traditional HTS drug discovery uses purified proteins or intact cells, recent development of the technology is associated with the use of intact living organisms, like the nematode Caenorhabditis elegans and zebrafish (Danio rerio).
In 2016-2018 plate manufacturers began producing specialized chemistry to allow for mass production of ultra-low adherent cell repellent surfaces which facilitated the rapid development of HTS amenable assays to address cancer drug discovery in 3D tissues such as organoids and spheroids; a more physiologically relevant format. | 1 | Applied and Interdisciplinary Chemistry |
A Canadian study of pregnant women suggests that those taking any type or amount of NSAIDs (including ibuprofen, diclofenac, and naproxen) were 2.4 times more likely to miscarry than those not taking the medications. However, an Israeli study found no increased risk of miscarriage in the group of mothers using NSAIDs. | 0 | Theoretical and Fundamental Chemistry |
August Wilhelm von Hofmann, Auguste Laurent and Charles Frédéric Gerhardt challenged Frankland and Kolbe by suggesting that the ethyl radical was in fact a dimer called dimethyl. Frankland and Kolbe countered that ethyl hydride was also a possibility and in 1864 Carl Schorlemmer proved that dimethyl and ethyl hydride were in fact one and the same compound.
Radical theory was eventually replaced by a number of theories each advocating specific entities. One adaptation of radical theory was called theory of types (theory of residues), advocated by Charles-Adolphe Wurtz, August Wilhelm von Hofmann and Charles Frédéric Gerhardt. Another was water type as promoted by Alexander William Williamson. Jean-Baptiste Dumas and Auguste Laurent (an early supporter of radical theory) challenged radical theory in 1840 with a Law of Substitution (or Theory of Substitution). This law acknowledged that any hydrogen atom even as part of a radical could be substituted by a halogen.
Eventually Frankland in 1852 and August Kekulé in 1857 introduced valence theory with the tetravalency of carbon as its central theme, making trivalent carbon obsolete for the time being. | 0 | Theoretical and Fundamental Chemistry |
Electrofusion welding employs fittings that are placed around the joint to be welded. Metal coils are implanted into the fittings, and electric current is run through the coils to generate heat and melt part of the pipes, forming a joint upon solidification. There are two possible fittings used in electrofusion welding: couplers and tapping tees (saddles). Coupler fittings contain two separate regions of coils, creating two distinct fusion zones during welding. The inner diameter of the coupler is typically slightly larger than the outer diameter of the pipes. This is to increase the ease of assembly in the field and allows for minor inconsistencies in pipe diameter. Proper insertion of the pipes in the coupler is critical for the creation of a strong joint. Incorrect placement of the coupler can cause the coils to move and lead to the extrusion of molten polymer material from the joint, reducing the joint's strength. Tapping tees, or saddles, are less common but operate under the same principles as a coupler. They require clamping to ensure a proper fit up with the pipes. | 0 | Theoretical and Fundamental Chemistry |
Azoles are a class of five-membered heterocyclic compounds containing a nitrogen atom and at least one other non-carbon atom (i.e. nitrogen, sulfur, or oxygen) as part of the ring. Their names originate from the Hantzsch–Widman nomenclature. The parent compounds are aromatic and have two double bonds; there are successively reduced analogs (azolines and azolidines) with fewer. One, and only one, lone pair of electrons from each heteroatom in the ring is part of the aromatic bonding in an azole. Names of azoles maintain the prefix upon reduction (e.g., pyrazoline, pyrazolidine). The numbering of ring atoms in azoles starts with the heteroatom that is not part of a double bond, and then proceeds towards the other heteroatom.
Imidazole and other five-membered aromatic heterocyclic systems with two nitrogens are extremely common in nature and form the core of many biomolecules, such as histidine. | 0 | Theoretical and Fundamental Chemistry |
Beilstein was founded as German-language standard reference work for organic chemistry was intended to supplement the content of the Chemisches Zentralblatt. In light of the leading role of German chemistry in international science, Beilstein's handbook quickly became renowned as a standard reference throughout the world. The first edition of his "Handbuch der organischen Chemie" appeared in two volumes in 1881 and 1883, referencing 15,000 compounds in about 2,200 pages. The second edition appeared in three volumes from 1885 to 1889 and 4,080 pages, and from 1892 to 1899 came the third edition in 4 volumes and 6,844 pages. In 1896, the continuation of the handbook was placed in the care of the German Chemical Society, which first published the supplementary volumes of the 3rd edition and, from 1918, the fourth edition. Starting with the 5th supplement, following the superseding of German by English as most relevant scientific language, the handbook appeared in English. | 0 | Theoretical and Fundamental Chemistry |
Common side effects include vomiting, diarrhea, headaches, and a rash. Severe side effects requiring hospitalization are rare, but include mental health problems such as depression, hallucinations, anxiety and neurological side effects such as poor balance, seizures, and ringing in the ears. Mefloquine is therefore not recommended in people with a history of psychiatric disorders or epilepsy. | 0 | Theoretical and Fundamental Chemistry |
Like pheromones (communication chemicals used within a species), kairomones can be utilized as an attracticide to lure a pest species to a location containing pesticide. However, they might also be used to lure desired species. Kairomones produced by the hosts of parasitic wasps have been used in an attempt to attract them and keep them around in crops where they reduce herbivory, but this could instead result in fewer attacks on the herbivorous pest if the applied kairomone distracts them from finding real hosts. For example, studies have shown that kairomones are effective in attracting female African sugarcane borers to deposit eggs on dead leaf material.
Recent discoveries have highlighted that predators are attracted to the odour of co-existing predators.
Kairomones have been extensively studied, and some are in successful usage, in Floridas Anastrepha suspensa' eradication zone in support of the citrus, and various other orchard industries there. | 1 | Applied and Interdisciplinary Chemistry |
Developing well-constructed models (accounting for variables such as oil type, salinity and surfactant) are necessary to select the appropriate dispersant in a given situation. Two models exist which integrate the use of dispersants: Mackays model and Johansens model. There are several parameters which must be considered when creating a dispersion model, including oil-slick thickness, advection, resurfacing and wave action. A general problem in modeling dispersants is that they change several of these parameters; surfactants lower the thickness of the film, increase the amount of diffusion into the water column and increase the amount of breakup caused by wave action. This causes the oil slick's behavior to be more dominated by vertical diffusion than horizontal advection.
One equation for the modeling of oil spills is:
where
* h is the oil-slick thickness
* is the velocity of ocean currents in the mixing layer of the water column (where oil and water mix together)
* is the wind-driven shear stress
* f is the oil-water friction coefficient
* E is the relative difference in densities between the oil and water
* R is the rate of spill propagation
Mackay's model predicts an increasing dispersion rate, as the slick becomes thinner in one dimension. The model predicts that thin slicks will disperse faster than thick slicks for several reasons. Thin slicks are less effective at dampening waves and other sources of turbidity. Additionally, droplets formed upon dispersion are expected to be smaller in a thin slick and thus easier to disperse in water.
The model also includes:
* An expression for the diameter of the oil drop
* Temperature dependence of oil movement
* An expression for the resurfacing of oil
* Calibrations based on data from experimental spills
The model is lacking in several areas: it does not account for evaporation, the topography of the ocean floor or the geography of the spill zone.
Johansens model is more complex than Mackays model. It considers particles to be in one of three states: at the surface, entrained in the water column or evaporated. The empirically based model uses probabilistic variables to determine where the dispersant will move and where it will go after it breaks up oil slicks. The drift of each particle is determined by the state of that particle; this means that a particle in the vapor state will travel much further than a particle on the surface (or under the surface) of the ocean. This model improves on Mackay's model in several key areas, including terms for:
* Probability of entrainment – depends on wind
* Probability of resurfacing – depends on density, droplet size, time submerged and wind
* Probability of evaporation – matched with empirical data
Oil dispersants are modeled by Johansen using a different set of entrainment and resurfacing parameters for treated versus untreated oil. This allows areas of the oil slick to be modeled differently, to better understand how oil spreads along the water's surface. | 1 | Applied and Interdisciplinary Chemistry |
As previously mentioned, cis-isomers of cycloalkenes exhibit more stability than trans-isomers; however, on an experimental and computational level, this property is only applicable to cycloalkenes with 10 carbons or less. As the number of carbons increase, the possibility of a trans-isomer occurring also increase. The geometrical considerations as analyzed by computational analysis are as follows.
The most stable trans-isomers of 10 ring or greater cycloalkenes exhibit 4 irregularities from standard geometric norms. The first irregularity is twisted planes of substituents along the C=C. Using C=C as the stable axis, 2 substituents of 1 carbon can be visualized on the same plane, equally applied to the other carbon. These planes are not planar and instead one carbon substituent plane twists along the axis away or toward the other carbon’s plane. This twisting leads to pyramidalization forming a pyramidal alkene which is the second irregularity. A greater angle of twisting, usually results in lower carbon number rings and decreases as the carbon number increases. Pyramidalization is important in highered number rings, because it increases p-orbital overlap for stability, and reduces torsional strain.
Bond length between the C=C and corresponding vinylic carbons also vary. In smaller cycloalkenes, it is expected for the bonds to be greater in length uniformly to account for increased strain, but for example, trans-cycloheptane has varying bond lengths. Also, the vinylic carbons on trans cyclohexanes exhibit longer bond lengths than their respective cis isomer for trans-cycloheptane through trans-cyclononene (7 carbon and 9 carbon cycloalkenes). | 0 | Theoretical and Fundamental Chemistry |
Uranium dioxide is a black semiconducting solid. It can be made by heating uranyl nitrate to form .
This is then converted by heating with hydrogen to form UO. It can be made from enriched uranium hexafluoride by reacting with ammonia to form a solid called ammonium diuranate, . This is then heated (calcined) to form and UO which is then converted by heating with hydrogen or ammonia to form UO.
The UO is mixed with an organic binder and pressed into pellets, these pellets are then fired at a much higher temperature (in H/Ar) to sinter the solid. The aim is to form a dense solid which has few pores.
The thermal conductivity of uranium dioxide is very low compared with that of zirconium metal, and it goes down as the temperature goes up.
Corrosion of uranium dioxide in water is controlled by similar electrochemical processes to the galvanic corrosion of a metal surface.
While exposed to the neutron flux during normal operation in the core environment a small percentage of the in the fuel absorbs excess neutrons and is transmuted into . rapidly decays into which in turn rapidly decays into . The small percentage of has a higher neutron cross section than . As the accumulates the chain reaction shifts from pure at initiation of the fuel use to a ratio of about 70% and 30% at the end of the 18 to 24 month fuel exposure period. | 0 | Theoretical and Fundamental Chemistry |
* 1981: Invention of the SNIF-NMR method by Professor Gerard Martin, Maryvonne Martin and their team at the University of Nantes / CNRS
* 1987: Creation of Eurofins Nantes Laboratories - specializing in wine analysis, and purchase of operating the CNRS patent rights (this patent is now public and the name “SNIF-NMR” is now a registered trademark
The OIV adopts it as an official method
* 1987-1990: Eurofins Laboratories apply the SNIF-NMR method to the analysis of fruit juices and certain natural flavors
* 1990: The SNIF-NMR method is recognized by the European Union as an official method for the analysis of wines
→ Implementation of the SNIF-NMR method for official laboratories in Europe
* 1990-1992: the method is tested on aromatic molecules
* 1996: The SNIF- NMR method is recognized in the United States by the AOAC for fruit juices
→ Implementation of the SNIF-NMR< method for official laboratories in US
* 2001: The SNIF-NMR< method is recognized by the AOAC for vanillin
* 2013: The SNIF-NMR method is recognized by the CEN for acetic acid
→ Implementation of the SNIF-NMR method for official laboratories in Asia | 0 | Theoretical and Fundamental Chemistry |
Emanuel Gil-Av (Zimkin) (7 August 1916 – 24 March 1996) was an Israeli chemist. The main emphasis of his work constituted chiral chromatography for the analytical separation of enantiomers. | 0 | Theoretical and Fundamental Chemistry |
Biochemical oxygen demand (also known as BOD or biological oxygen demand) is an analytical parameter representing the amount of dissolved oxygen (DO) consumed by aerobic bacteria growing on the organic material present in a water sample at a specific temperature over a specific time period. The BOD value is most commonly expressed in milligrams of oxygen consumed per liter of sample during 5 days of incubation at 20 °C and is often used as a surrogate of the degree of organic water pollution.
Biochemical Oxygen Demand (BOD) reduction is used as a gauge of the effectiveness of wastewater treatment plants. BOD of wastewater effluents is used to indicate the short-term impact on the oxygen levels of the receiving water.
BOD analysis is similar in function to chemical oxygen demand (COD) analysis, in that both measure the amount of organic compounds in water. However, COD analysis is less specific, since it measures everything that can be chemically oxidized, rather than just levels of biologically oxidized organic matter. | 0 | Theoretical and Fundamental Chemistry |
Yeast artificial chromosome are used as vectors to clone DNA fragments of more than 1 mega base (1Mb=1000kb) in size. They are useful in cloning larger DNA fragments as required in mapping genomes such as in the Human Genome Project. It contains a telomeric sequence, an autonomously replicating sequence (features required to replicate linear chromosomes in yeast cells). These vectors also contain suitable restriction sites to clone foreign DNA as well as genes to be used as selectable markers. | 1 | Applied and Interdisciplinary Chemistry |
Potential renal acid load (PRAL) is a measure of the acid that the body produces after ingesting a food. This is different from pH, which is the acidity of a food before being consumed. PRAL is a different acidity measure than the food ash measurement.
Some acidic foods actually have a negative PRAL measurement, meaning they reduce acidity in the stomach.
A low PRAL diet (not to be confused with an alkaline diet) can lower acidity in the stomach, which can be helpful for people suffering GERD or Acid Reflux. However, it does not lower the pH of blood and therefore cannot treat osteoporosis or other conditions. | 1 | Applied and Interdisciplinary Chemistry |
The position-specific isotope effect of an enzymatic reaction is expressed as the ratio of rate constants for a monoisotopic substrate and a substrate substituted with one rare isotope. For example, enzyme formate dehydrogenase catalyzes the reaction of formate and NAD+ to carbon dioxide and NADH. The hydrogen of formate is directly transferred to NAD+. This step has an isotope effect, because the rate of protium transfer from formate to NAD+ is nearly three times faster than the rate of the same reaction with a deuterium transfer. This is also an example of a primary isotope effect. A primary isotope effect is one in which the rare isotope is substituted where a bond is broken or formed. Secondary isotope effects occur on other positions in the molecule and are controlled by the molecular geometry of the transition state. These are generally considered to be negligible but do arise in certain cases, especially for hydrogen isotopes.
Unlike abiotic reactions, enzymatic reactions occur through a series of steps, including substrate-enzyme binding, conversion of substrate to product, and dissociation of enzyme-product complex. The observed isotope effect of an enzyme will be controlled by the rate limiting step in this mechanism. If the step that converts substrate to product is rate limiting, the enzyme will express its intrinsic isotope effect, that of the bond forming or breaking reaction. | 0 | Theoretical and Fundamental Chemistry |
The Cromer cycle is primarily used in air conditioning and drying applications. The cold surface portion of the cycle is most often a result of a reversed Carnot or refrigeration cycle. For the Cromer cycle to operate, a desiccant must be exposed to two air streams, one with higher humidity from a cold surface, and one with lower humidity to dry it. This is most easily accomplished by moving the desiccant. Any cycling mechanism can be used, such as pumping a liquid desiccant, however an easy mechanical application is a rotating wheel, loaded with desiccant, through which the different air streams pass. This is shown in Figure 1 where a desiccant wheel has been applied to a standard air conditioning set-up.
The psychrometric process of the air passing through the system with four state points is shown on the psychrometric chart of Figure 2 as 1, 2, 3 and 4. The state points of the air are also depicted in Figure 1. In this application, the air returning from the space, typically around 50% relative humidity (RH), is presented to the desiccant wheel and dries the desiccant. The air picks up moisture and cools in process 1 to 2. The moist air is now presented to the cooling surface (cooling coil of the air conditioner), which cools it below its dew point and dries the air in process 2 to 3. This represents the work done by the cold coil. In the meantime, the dried desiccant from below is rotated to the upper air stream. The saturated air leaving the coil, typically 93–98% RH, is presented to the desiccant at 3, where the air is dried further in process 3 to 4, where it is presented to the space as supply air. The desiccant, now loaded with moisture, rotates to the return air, where the cycle repeats.
Typical cooling and drying by the cold coil without the Cromer cycle is depicted on the psychrometric chart and is also shown in Figure 2. State point 1 is the air that returns from the space to the system (return air). For a typical air conditioning system, this air at state point 1 enters the cooling coil and leaves at about state point 4 after cooling and drying. State point 4 represents the temperature and moisture content of the air that leaves the typical unit, about and 95–98% RH. | 0 | Theoretical and Fundamental Chemistry |
Ligands are ordered alphabetically by name and precede the central atom name. The number of ligands coordinating is indicated by the prefixes di-, tri-, tetra- penta- etc. for simple ligands or bis-, tris-, tetrakis-, etc. for complex ligands. For example:
*[CoCl(NH)]Cl pentaamminechloridocobalt(3+) chloride where ammine (NH)precedes chloride. The central atom come after the ligands. Where there is more than one central atom it is preceded by di- tri-, tetra- etc.
* Os(CO), dodecacarbonyltriosmium
Where there are different central atoms they are sequenced using the electronegativity list.
*[ReCo(CO)] nonacarbonylrheniumcobalt | 0 | Theoretical and Fundamental Chemistry |
Some cases of many genetic diseases are associated with variations in promoters or transcription factors.
Examples include:
* Asthma
* Beta thalassemia
* Rubinstein-Taybi syndrome | 1 | Applied and Interdisciplinary Chemistry |
There are 2 main application techniques of applying foam onto a fire, recognized by the European (EN1568) and international (ISO7203) standards:
Sweep (roll-on) method - Use only on a pool of flammable product on open ground. Direct the foam stream onto the ground in front of the product involved. May need to move the hose line or use multiple lines to cover the material. If multiple lines are used, be aware of other firefighters in the area.
Bankshot (bankdown) method - Firefighter uses an object to deflect the foam stream so it flows down the burning surface. Application should be as gentle as possible. Direct the foam at a vertical object. Allow the foam to spread over the material and form a foam blanket.
Raindown method - Used when unable to employ the bankshot method or the roll-on method. Loft the foam stream into the air above the material and let it fall gently onto the surface. Effective as long as the foam stream completely covers the material. Might not be effective if wind conditions are unfavorable | 0 | Theoretical and Fundamental Chemistry |
There are five UCP homologs known in mammals. While each of these performs unique functions, certain functions are performed by several of the homologs. The homologs are as follows:
*UCP1, also known as thermogenin or SLC25A7
*UCP2, also known as SLC25A8
*UCP3, also known as SLC25A9
*UCP4, also known as SLC25A27
*UCP5, also known as SLC25A14 | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, a directing group (DG) is a substituent on a molecule or ion that facilitates reactions by interacting with a reagent. The term is usually applied to C–H activation of hydrocarbons, where it is defined as a "coordinating moiety (an internal ligand), which directs a metal catalyst into the proximity of a certain C–H bond." In a well known example, the ketone group () in acetophenone is the DG in the Murai reaction.
The Murai reaction is related to directed ortho metalation, a reaction is typically applied to the lithiation of substituted aromatic rings.
A wide variety of functional groups can serve as directing groups. | 0 | Theoretical and Fundamental Chemistry |
FSM is a critical sanitation service in cities and towns in all countries where households use onsite sanitation systems. Citywide FSM programs may utilize multiple or one treatment facility, use stationary and mobile transfer stations, and engage with micro, small and medium-sized enterprises that may conduct some or all of the services. Programs may be phased in over time to accommodate growing demand. | 1 | Applied and Interdisciplinary Chemistry |
Sodium aluminosilicate refers to compounds which contain sodium, aluminium, silicon and oxygen, and which may also contain water. These include synthetic amorphous sodium aluminosilicate, a few naturally occurring minerals and synthetic zeolites. Synthetic amorphous sodium aluminosilicate is widely used as a food additive, E 554. | 0 | Theoretical and Fundamental Chemistry |
* 2000 – First demonstration proving that bending carbon nanotubes changes their resistance
* 2001 April — First report on a technique for separating semiconducting and metallic nanotubes.
* 2002 January — Multi-walled nanotubes demonstrated to be fastest known oscillators (> 50 GHz).
* 2003 September — NEC announced stable fabrication technology of carbon nanotube transistors.
* 2004 March — Nature published a photo of an individual 4 cm long single-wall nanotube (SWNT).
** May — A prototype high-definition 10-centimetre flat screen made using nanotubes was exhibited.
** August — University of California finds Y-shaped nanotubes to be ready-made transistors.
** August — General Electric announced the development of an ideal carbon nanotube diode that operates at the "theoretical limit" (the best possible performance). A photovoltaic effect was also observed in the nanotube diode device that could lead to breakthroughs in solar cells, making them more efficient and thus more economically viable.
** August — Nanotube sheet synthesised with dimensions 5 × 100 cm.
** March — IBM announces that they have built an electronic circuit around a CNT.
** March — Nanotubes used as a scaffold for damaged nerve regeneration.
** May — Method of placing nanotube accurately is developed by IBM.
** June — Gadget invented by Rice University that can sort nanotubes by size and electrical properties.
** July — Nanotubes were alloyed into the carbon fiber bike that was ridden by Floyd Landis to win the 2006 Tour de France.
** April — Nanotubes incorporated in virus battery.
** A single-walled carbon nanotube was grown by chemical vapor deposition across a 10-micron gap in a silicon chip, then used in cold atom experiments, creating a blackhole like effect on single atoms. | 1 | Applied and Interdisciplinary Chemistry |
Thomas Albrecht-Schönzart received his undergraduate education in chemistry at Southwest Minnesota State University, during which time he also performed research at Texas A&M with J. P. Fackler on gold chemistry and Ron Caple on organometallic chemistry at the University of Minnesota-Duluth via REU-NSF programs. He received his doctorate in inorganic chemistry in 1997 from Northwestern University under James Ibers where he studied the synthesis, structures, and reactivity of transition metal polychalcogenides. Following a postdoctoral position at the University of Illinois in 1998 with J. R. Shapley on metal-fullerene chemistry, he became an assistant professor at Auburn University later that year, transitioning to associate professor in 2002 and full professor in 2007. While at Auburn, he built a large program dedicated to understanding the chemistry and physics of f-block compounds. He opened the first new transuranium laboratory in decades in the U.S. while at Auburn, and continued this theme as the Frank M. Freimann Chair at the University of Notre Dame from 2009 to 2012. He moved to Florida State University in 2012 to become the first Gregory R. Choppin Chair in Chemistry. In 2022 he joined the faculty at the Colorado School of Mines in Golden, Colorado, and was a part of the inaugural group of University Distinguished Professors. | 0 | Theoretical and Fundamental Chemistry |
The radioactive decay of strontium-90 generates a significant amount of heat, 0.95 W/g in the form of pure strontium metal or approximately 0.460 W/g as strontium titanatePu. It is used as a heat source in many Russian/Soviet radioisotope thermoelectric generators, usually in the form of strontium titanate. It was also used in the US "Sentinel" series of RTGs. Startup company Zeno Power is developing RTGs that use strontium-90 from the DOD, and is aiming to ship product by 2026. | 0 | Theoretical and Fundamental Chemistry |
A recent trend is to change the method by which the skimmer is fed dirty water from the aquarium as a means to recirculate water within the skimmer multiple times before it is returned to the sump or the aquarium. Aspirating pump skimmers are the most popular type of skimmer to use recirculating designs although other types of skimmers, such as Beckett skimmers, are also available in recirculating versions. While there is a popular belief among some aquarist that this recirculation increases the dwell or contact time of the generated air bubbles within the skimmer there is no authoritative evidence that this is true. Each time water is recirculated within the skimmer any air bubbles in that water sample are destroyed and new bubbles are generated by the recirculating pump venturi apparatus so the air-water contact time begins again for these newly created bubbles. In non-recirculating skimmer designs, a skimmer has one inlet supplied by a pump that pulls water in from the aquarium and injects it with air into the skimmer and releasing the foam or air/water mix into the reaction chamber. With a recirculating design, the one inlet is usually driven by a separate feed pump, or in some cases may be gravity fed, to receive the dirty water to process, while the pump providing the foam or air/water mix into the reaction chamber is set up separately in a closed loop on the side of the skimmer. The recirculating pump pulls water out of the skimmer and injects air to generate the foam or air/water mix before returning it to the skimmer reaction chamber—thus recirculating it. The feed pump in a recirculating design typically injects a smaller amount of dirty water than co/counter-current designs. The separate feed pump allows easy control of the rate of water exchange through the skimmer and for many aquarists this is one of the important attractions of recirculating skimmer designs. Because the pump configuration of these skimmers is similar to that of aspirating pump skimmers, the power consumption advantages are also similar. | 0 | Theoretical and Fundamental Chemistry |
Ribbon silicon is a type of polycrystalline silicon—it is formed by drawing flat thin films from molten silicon and results in a polycrystalline structure. These cells are cheaper to make than multi-Si, due to a great reduction in silicon waste, as this approach does not require sawing from ingots. However, they are also less efficient. | 0 | Theoretical and Fundamental Chemistry |
Ketones engage in many organic reactions. The most important reactions follow from the susceptibility of the carbonyl carbon toward nucleophilic addition and the tendency for the enolates to add to electrophiles.
Nucleophilic additions include in approximate order of their generality:
* With water (hydration) gives geminal diols, which are usually not formed in appreciable (or observable) amounts
* With an acetylide to give the α-hydroxyalkyne
* With ammonia or a primary amine gives an imine
* With secondary amine gives an enamine
* With Grignard and organolithium reagents to give, after aqueous workup, a tertiary alcohol
* With an alcohols or alkoxides to gives the hemiketal or its conjugate base. With a diol to the ketal. This reaction is employed to protect ketones.
* With sodium amide resulting in C–C bond cleavage with formation of the amide RCONH and the alkane or arene R'H, a reaction called the Haller–Bauer reaction.
* With strong oxidizing agents to give carboxylic acids. Ketones are generally oxidized under vigorous conditions, i.e., strong oxidizing agents and at elevated temperatures. Their oxidation involves carbon–carbon bond cleavage to afford a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.
* Electrophilic addition, reaction with an electrophile gives a resonance stabilized cation
* With phosphonium ylides in the Wittig reaction to give the alkenes
* With thiols to give the thioacetal
* With hydrazine or 1-disubstituted derivatives of hydrazine to give hydrazones.
* With a metal hydride gives a metal alkoxide salt, hydrolysis of which gives the alcohol, an example of ketone reduction
* With halogens to form an α-haloketone, a reaction that proceeds via an enol (see Haloform reaction)
* With heavy water to give an α-deuterated ketone
* Fragmentation in photochemical Norrish reaction
* Reaction of 1,4-aminodiketones to oxazoles by dehydration in the Robinson–Gabriel synthesis
* In the case of aryl–alkyl ketones, with sulfur and an amine give amides in the Willgerodt reaction
* With hydroxylamine to produce oximes
* With reducing agents to form secondary alcohols
* With peroxy acids to form esters in the Baeyer–Villiger oxidation | 0 | Theoretical and Fundamental Chemistry |
This type of phase transformation is known as spinodal decomposition, and can be illustrated on a phase diagram exhibiting a miscibility gap. Thus, phase separation occurs whenever a material transition into the unstable region of the phase diagram. The boundary of the unstable region sometimes referred to as the binodal or coexistence curve, is found by performing a common tangent construction of the free-energy diagram. Inside the binodal is a region called the spinodal, which is found by determining where the curvature of the free-energy curve is negative. The binodal and spinodal meet at the critical point. It is when a material is moved into the spinodal region of the phase diagram that spinodal decomposition can occur.
The [https://www.doitpoms.ac.uk/tlplib/phase-diagrams/freeenergy.php#:~:text=The%20phase%20with%20the%20lowest,the%20liquid%20phase%20is%20stable. free energy curve] is plotted as a function of composition for a temperature below the convolute temperature, T. Equilibrium phase compositions are those corresponding to the free energy minima. Regions of negative curvature (∂f/∂c f/∂c = 0 ) which are called the spinodes. Their locus as a function of temperature defines the spinodal curve. For compositions within the spinodal, a homogeneous solution is unstable against infinitesimal fluctuations in density or composition, and there is no thermodynamic barrier to the growth of a new phase. Thus, the spinodal represents the limit of physical and chemical stability.
To reach the spinodal region of the phase diagram, a transition must take the material through the binodal region or the critical point. Often phase separation will occur via nucleation during this transition, and spinodal decomposition will not be observed. To observe spinodal decomposition, a very fast transition, often called a quench, is required to move from the stable to the spinodal unstable region of the phase diagram.
In some systems, ordering of the material leads to a compositional instability and this is known as a conditional spinodal, e.g. in the feldspars. | 0 | Theoretical and Fundamental Chemistry |
Besides inhibiting human acetylcholinesterase (although to a lesser degree than the insect enzyme), carbamate insecticides also target human melatonin receptors. The human health effects of carbamates are well documented in the list of known endocrine disruptor compounds. Clinical effects of carbamate exposure can vary from slightly toxic to highly toxic depending on a variety of factors including such as dose and route of exposure with ingestion and inhalation resulting in the most rapid clinical effects. These clinical manifestations of carbamate intoxication are muscarinic signs, nicotinic signs, and in rare cases central nervous system signs. | 0 | Theoretical and Fundamental Chemistry |
Polymer devolatilization, also known as polymer degassing, is the process of removing low-molecular-weight components such as residual monomers, solvents, reaction by-products and water from polymers. | 1 | Applied and Interdisciplinary Chemistry |
Alex G. Streng was an experimental chemist, notable for his work with fluorine compounds. His work on the synthesis and properties of dioxygen difluoride, published in 1963 in the Journal of the American Chemical Society, is notorious for Streng's willingness to push the limits of experimental endeavour with this highly reactive and dangerous material.
He was married to Lucia V. Streng, who was also known for her work with fluorine compounds. The Strengs fled Russia in the 1940s, moving first to Germany, then to Philadelphia in the United States, where both eventually took research posts at Temple University. | 0 | Theoretical and Fundamental Chemistry |
Monatomic cations are named by taking the element name and following it with the charge in brackets e.g
* sodium(1+)
* chromium(3+)
Sometimes an abbreviated form of the element name has to be taken, e.g. germide for germanium as germanide refers to .
Polyatomic cations of the same element are named as the element name preceded by di-, tri-, etc., e.g.:
* dimercury(2+)
Polyatomic cations made up of different elements are named either substitutively or additively, e.g.:
* phosphanium
* tetrafluorostibanium (substitutive) or tetrafluoridoantimony(1+)
* Note that ammonium and oxonium are acceptable names for and respectively. (Hydronium is not an acceptable name for ) | 0 | Theoretical and Fundamental Chemistry |
The nomenclature of organic acid anhydrides is derived from the names of the constituent carboxylic acids. In symmetrical acid anhydrides, only the prefix of the original carboxylic acid is used and the suffix "anhydride" is added. For most unsymmetrical acid anhydrides - also called mixed anhydrides- the prefixes from both acids reacted are listed before the suffix, e.g., benzoic propanoic anhydride. | 0 | Theoretical and Fundamental Chemistry |
Z-HIT is a special case of the Hilbert transform and through restriction by the Kramers–Kronig relations it can be derived for one-Port-systems. The frequency-dependent relationship between impedance and phase angle can be observed in the Bode plot of an impedance spectrum. Equation (1) is obtained as a general solution of the correlation between impedance modulus and phase shift.
Equation (1) indicates that the logarithm of the impedance () at a specific frequency can be calculated up to a constant value of (), if the phase shift is integrated up to the frequency point of interest , while the starting value of the integral can be freely chosen. As an additional contribution to the calculation of , the odd-numbered derivatives of the phase shift at the point have to be added, weighted with the factors .
The factors can be calculated according to equation (2), whereat represents the Riemann ζ-function.
The practically applied Z-HIT approximation is obtained from equation (1) by limitation to the first derivative of the phase shift neglecting higher derivatives (equation (3)), where C represents a constant.
The free choice of the integration boundaries in the ZHIT algorithm is a fundamental difference concerning the Kramers-Kronig relations; in ZHIT the integration boundaries are
and .
The greatest advantage of the ZHIT results from the fact, that both integration boundaries can be chosen within the measured spectrum, and thus does not require extrapolation to frequencies 0 and , as with the Kramers-Kronig relations. | 0 | Theoretical and Fundamental Chemistry |
Dispersants are used as plasticizers or superplasticizers in concrete formulations to lower the use of water while retaining the needed slump (flow) property. A lower water content makes the concrete stronger and more impervious to water penetration.
Similarly, dispersants are used as plasticizers in the gypsum slurry during wallboard manufacture, to reduce the amount of water used. The lower water usage allows lower energy use to dry the wallboard. | 0 | Theoretical and Fundamental Chemistry |
Iron–sulfur proteins are proteins characterized by the presence of iron–sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states. Iron–sulfur clusters are found in a variety of metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase, hydrogenases, coenzyme Q – cytochrome c reductase, succinate – coenzyme Q reductase and nitrogenase. Iron–sulfur clusters are best known for their role in the oxidation-reduction reactions of electron transport in mitochondria and chloroplasts. Both Complex I and Complex II of oxidative phosphorylation have multiple Fe–S clusters. They have many other functions including catalysis as illustrated by aconitase, generation of radicals as illustrated by SAM-dependent enzymes, and as sulfur donors in the biosynthesis of lipoic acid and biotin. Additionally, some Fe–S proteins regulate gene expression. Fe–S proteins are vulnerable to attack by biogenic nitric oxide, forming dinitrosyl iron complexes. In most Fe–S proteins, the terminal ligands on Fe are thiolate, but exceptions exist.
The prevalence of these proteins on the metabolic pathways of most organisms leads to theories that iron–sulfur compounds had a significant role in the origin of life in the iron–sulfur world theory.
In some instances Fe–S clusters are redox-inactive, but are proposed to have structural roles. Examples include endonuclease III and MutY. | 0 | Theoretical and Fundamental Chemistry |
Many drugs are supplied as salts, with a cation and an anion. The way the INN system handles these is explained by the WHO at its "Guidance on INN" webpage. For example, amfetamine and oxacillin are INNs, whereas various salts of these compounds – e.g., amfetamine sulfate and oxacillin sodium – are modified INNs (INNM). | 1 | Applied and Interdisciplinary Chemistry |
Neuromuscular blocking drugs are often classified into two broad classes:
*Pachycurares, which are bulky molecules with nondepolarizing activity
*Leptocurares, which are thin and flexible molecules that tend to have depolarizing activity.
It is also common to classify them based on their chemical structure.
*Acetylcholine, suxamethonium, and decamethonium
Suxamethonium was synthesised by connecting two acetylcholine molecules and has the same number of heavy atoms between methonium heads as decamethonium. Just like acetylcholine, succinylcholine, decamethonium and other polymethylene chains, of the appropriate length and with two methonium, heads have small trimethyl onium heads and flexible links. They all exhibit a depolarizing block.
* Aminosteroids
Pancuronium, vecuronium, rocuronium, rapacuronium, dacuronium, malouètine, dihydrochandonium, dipyrandium, pipecuronium, chandonium (HS-310), HS-342 and other HS- compounds are aminosteroidal agents. They have in common the steroid structural base, which provides a rigid and bulky body. Most of the agents in this category would also be classified as non-depolarizing.
* Tetrahydroisoquinoline derivatives
Compounds based on the tetrahydroisoquinoline moiety such as atracurium, mivacurium, and doxacurium would fall in this category. They have a long and flexible chain between the onium heads, except for the double bond of mivacurium. D-tubocurarine and dimethyltubocurarine are also in this category. Most of the agents in this category would be classified as non-depolarizing.
* Gallamine and other chemical classes
Gallamine is a trisquaternary ether with three ethonium heads attached to a phenyl ring through an ether linkage. Many other different structures have been used for their muscle relaxant effect such as alcuronium (alloferin), anatruxonium, diadonium, fazadinium (AH8165) and tropeinium.
*Novel NMB agents
In recent years much research has been devoted to new types of quaternary ammonium muscle relaxants. These are asymmetrical diester isoquinolinium compounds and bis-benzyltropinium compounds that are bistropinium salts of various diacids. These classes have been developed to create muscle relaxants that are faster and shorter acting. Both the asymmetric structure of diester isoquinolinium compounds and the acyloxylated benzyl groups on the bisbenzyltropiniums destabilizes them and can lead to spontaneous breakdown and therefore possibly a shorter duration of action. | 1 | Applied and Interdisciplinary Chemistry |
Injection formulations of esomeprazole are used for gastroprotection in veterinary medicine. In goats administered the drug by intravenous or subcutaneous injection rapid elimination was noted. In that study the sulfone metabolite was detectable for several hours after injection of the parent drug. | 0 | Theoretical and Fundamental Chemistry |
A spectrochemical series is a list of ligands ordered by ligand "strength", and a list of metal ions based on oxidation number, group and element. For a metal ion, the ligands modify the difference in energy Δ between the d orbitals, called the ligand-field splitting parameter in ligand field theory, or the crystal-field splitting parameter in crystal field theory. The splitting parameter is reflected in the ion's electronic and magnetic properties such as its spin state, and optical properties such as its color and absorption spectrum. | 0 | Theoretical and Fundamental Chemistry |
Countercurrent chromatography (CCC, also counter-current chromatography) is a form of liquid–liquid chromatography that uses a liquid stationary phase that is held in place by inertia of the molecules composing the stationary phase accelerating toward the center of a centrifuge due to centripetal force and is used to separate, identify, and quantify the chemical components of a mixture. In its broadest sense, countercurrent chromatography encompasses a collection of related liquid chromatography techniques that employ two immiscible liquid phases without a solid support. The two liquid phases come in contact with each other as at least one phase is pumped through a column, a hollow tube or a series of chambers connected with channels, which contains both phases. The resulting dynamic mixing and settling action allows the components to be separated by their respective solubilities in the two phases. A wide variety of two-phase solvent systems consisting of at least two immiscible liquids may be employed to provide the proper selectivity for the desired separation.
Some types of countercurrent chromatography, such as dual flow CCC, feature a true countercurrent process where the two immiscible phases flow past each other and exit at opposite ends of the column. More often, however, one liquid acts as the stationary phase and is retained in the column while the mobile phase is pumped through it. The liquid stationary phase is held in place by gravity or inertia of the molecules composing the stationary phase accelerating toward the center of a centrifuge due to centripetal force. An example of a gravity method is called droplet counter current chromatography (DCCC). There are two modes by which the stationary phase is retained by centripetal force: hydrostatic and hydrodynamic. In the hydrostatic method, the column is rotated about a central axis. Hydrostatic instruments are marketed under the name centrifugal partition chromatography (CPC). Hydrodynamic instruments are often marketed as high-speed or high-performance countercurrent chromatography (HSCCC and HPCCC respectively) instruments which rely on the Archimedes' screw force in a helical coil to retain the stationary phase in the column.
The components of a CCC system are similar to most liquid chromatography configurations, such as high-performance liquid chromatography (HPLC). One or more pumps deliver the phases to the column which is the CCC instrument itself. Samples are introduced into the column through a sample loop filled with an automated or manual syringe. The outflow is monitored with various detectors such as ultraviolet–visible spectroscopy or mass spectrometry. The operation of the pumps, CCC instrument, sample injection, and detection may be controlled manually or with a microprocessor. | 0 | Theoretical and Fundamental Chemistry |
The activating groups are mostly resonance donors (+M). Although many of these groups are also inductively withdrawing (–I), which is a deactivating effect, the resonance (or mesomeric) effect is almost always stronger, with the exception of Cl, Br, and I.
In general, the resonance effect of elements in the third period and beyond is relatively weak. This is mainly because of the relatively poor orbital overlap of the substituent's 3p (or higher) orbital with the 2p orbital of the carbon.
Due to a stronger resonance effect and inductive effect than the heavier halogens, fluorine is anomalous. The partial rate factor of electrophilic aromatic substitution on fluorobenzene is often larger than one at the para position, making it an activating group. Conversely, it is moderately deactivated at the ortho and meta positions, due to the proximity of these positions to the electronegative fluoro substituent. | 0 | Theoretical and Fundamental Chemistry |
Also known as heated persulfate, the method utilizes the same free radical formation as UV persulfate oxidation except uses heat to magnify the oxidizing power of persulfate. Chemical oxidation of carbon with a strong oxidizer, such as persulfate, is highly efficient, and unlike UV, is not susceptible to lower recoveries caused by turbidity in samples. The analysis of system blanks, necessary in all chemical procedures, is especially necessary with heated persulfate TOC methods because the method is so sensitive that reagents cannot be prepared with carbon contents low enough to not be detected. Persulfate methods are used in the analysis of wastewater, drinking water, and pharmaceutical waters. When used in conjunction with sensitive NDIR detectors heated persulfate TOC instruments readily measure TOC at single digit parts per billion (ppb) up to hundreds of parts per million (ppm) depending on sample volumes. | 0 | Theoretical and Fundamental Chemistry |
Calcium hydroxide is commonly used to prepare lime mortar.
One significant application of calcium hydroxide is as a flocculant, in water and sewage treatment. It forms a fluffy charged solid that aids in the removal of smaller particles from water, resulting in a clearer product. This application is enabled by the low cost and low toxicity of calcium hydroxide. It is also used in fresh-water treatment for raising the pH of the water so that pipes will not corrode where the base water is acidic, because it is self-regulating and does not raise the pH too much.
It is also used in the preparation of ammonia gas (NH), using the following reaction:
: Ca(OH) + 2 NHCl → 2 NH + CaCl + 2 HO
Another large application is in the paper industry, where it is an intermediate in the reaction in the production of sodium hydroxide. This conversion is part of the causticizing step in the Kraft process for making pulp. In the causticizing operation, burned lime is added to green liquor, which is a solution primarily of sodium carbonate and sodium sulfate produced by dissolving smelt, which is the molten form of these chemicals from the recovery furnace.
In orchard crops, calcium hydroxide is used as a fungicide. Applications of lime water prevent the development of cankers caused by the fungal pathogen Neonectria galligena. The trees are sprayed when they are dormant in winter to prevent toxic burns from the highly reactive calcium hydroxide. This use is authorised in the European Union and the United Kingdom under Basic Substance regulations.
Calcium hydroxide is used in dentistry, primarily in the specialty of endodontics. | 0 | Theoretical and Fundamental Chemistry |
The pseudo-Voigt profile (or pseudo-Voigt function) is an approximation of the Voigt profile V(x) using a linear combination of a Gaussian curve G(x) and a Lorentzian curve L(x) instead of their convolution.
The pseudo-Voigt function is often used for calculations of experimental spectral line shapes.
The mathematical definition of the normalized pseudo-Voigt profile is given by
where now, is a function of Lorentz (), Gaussian () and total () Full width at half maximum (FWHM) parameters. The total FWHM () parameter is described by: | 0 | Theoretical and Fundamental Chemistry |
Many organisms have a ribonucleoprotein enzyme called telomerase, which carries out the task of adding repetitive nucleotide sequences to the ends of the DNA. Telomerase "replenishes" the telomere "cap" and requires no ATP In most multicellular eukaryotic organisms, telomerase is active only in germ cells, some types of stem cells such as embryonic stem cells, and certain white blood cells. Telomerase can be reactivated and telomeres reset back to an embryonic state by somatic cell nuclear transfer. The steady shortening of telomeres with each replication in somatic (body) cells may have a role in senescence and in the prevention of cancer. This is because the telomeres act as a sort of time-delay "fuse", eventually running out after a certain number of cell divisions and resulting in the eventual loss of vital genetic information from the cell's chromosome with future divisions. | 1 | Applied and Interdisciplinary Chemistry |
Solvent suppression is any technique in nuclear magnetic resonance spectroscopy (NMR) to decrease undesired signal from a sample's solvent. | 0 | Theoretical and Fundamental Chemistry |
Eduard Farber, also Eduard Färber or Eduard Faerber, (17 April 1892, in Brody, Galicia – 15 July 1969) was an Austrian-American industrial chemist and historian of chemistry. | 1 | Applied and Interdisciplinary Chemistry |
It is sometimes necessary to split tablets into halves or quarters. Tablets are easier to break accurately if scored, but there are devices called pill-splitters which cut unscored and scored tablets. Tablets with special coatings (for example, enteric coatings or controlled-release coatings) should not be broken before use, as this exposes the tablet core to the digestive juices, circumventing the intended delayed-release effect. | 1 | Applied and Interdisciplinary Chemistry |
Reaction of the anhydrous compound with sodium cyclopentadienide gives cobaltocene . This 19-electron species is a good reducing agent, being readily oxidised to the yellow 18-electron cobaltocenium cation . | 0 | Theoretical and Fundamental Chemistry |
Today, MBBR technology is used for municipal sewage treatment, industrial wastewater treatment, and decentralized wastewater treatment. This technology has been used in many different industries, some of them being:
* Automotive industry
* Chemical industry
* Food and beverage
* Metal plating and finishing
The MBBR system is considered a biofilm or biological process, not a chemical or mechanical process. Other conventional biofilm processes for wastewater treatment are called trickling filter, rotating biological contactor (RBC) and biological aerated filter (BAF).
Important applications:
* Denitrification
* Nitrification
* BOD/COD removal
* Anaerobic ammonium oxidation (ANAMMOX) process | 1 | Applied and Interdisciplinary Chemistry |
In 1985, the first public symposium on the Gaia hypothesis, Is The Earth a Living Organism? was held at University of Massachusetts Amherst, August 1–6. The principal sponsor was the National Audubon Society. Speakers included James Lovelock, Lynn Margulis, George Wald, Mary Catherine Bateson, Lewis Thomas, Thomas Berry, David Abram, John Todd, Donald Michael, Christopher Bird, Michael Cohen, and William Fields. Some 500 people attended. | 0 | Theoretical and Fundamental Chemistry |
Cosmids are plasmids that incorporate a segment of bacteriophage λ DNA that has the cohesive end site (cos) which contains elements required for packaging DNA into λ particles. Under apt origin of replication (ori), it can replicate as a plasmid It is normally used to clone large DNA fragments between 28 and 45 Kb. | 1 | Applied and Interdisciplinary Chemistry |
The amino acid is not genetically coded, but it arises by post-translational methylation of cysteine. One pathway involves methyl transfer from alkylated DNA by zinc-cysteinate-containing repair enzymes.
Beyond its biological context, it has been examined as a chelating agent. | 1 | Applied and Interdisciplinary Chemistry |
A threaded pipe has a screw thread at one or both ends for assembly. Steel pipe is often joined with threaded connections; tapered threads are cut into the end of the pipe, and sealant is applied in the form of thread-sealing compound or thread seal tape (also known as PTFE or Teflon tape) and the pipe is screwed into a threaded fitting with a pipe wrench.
Threaded steel pipe is widely used in buildings to convey natural gas or propane fuel and is also a popular choice in fire sprinkler systems due to its resistance to mechanical damage and high heat (including the threaded joints). Threaded steel pipe may still be used in high-security or exposed locations because it is more resistant to vandalism, more difficult to remove, and its scrap value is much lower than copper or brass.
A galvanized coating of metallic zinc was often used to protect steel water pipes from corrosion, but this protective coating eventually would dissolve away, exposing the iron to deterioration. Pipes used to convey fuel gas are often made of "black iron", which has been chemically treated to reduce corrosion, but this treatment does not resist erosion from flowing water. Despite its ruggedness, steel pipe is no longer preferred for conveying drinking water because corrosion can eventually cause leakage (especially at threaded joints), deposits on internal surfaces will eventually restrict flow, and corrosion will shed black or rusty residues into the flowing water.
These disadvantages are less problematic for fire sprinkler installations because standing water in the steel pipes does not flow, except during occasional tests or activation by a fire. Introducing oxygen dissolved in freshwater supplies will cause some corrosion, but this soon stops without any source of additional water-borne oxygen.
In older installations, the threaded brass pipe was similarly used and was considered superior to steel for drinking water because it was more resistant to corrosion and shed much fewer residues into the flowing water.
Assembling threaded pipe is labor-intensive, and requires skill and planning to allow lengths of pipe to be screwed together in sequence. Most threaded-pipe systems require strategically located pipe-union fittings in final assembly. The threaded pipe is heavy and requires adequate attachment to support its weight.
To ensure a comprehensive pressure test, it is crucial to explicitly request a 3.1 certificate in accordance with EN HFF 10204:2004. This certificate attests that the metallic products meet the stipulated order requirements and provides detailed test results. Typically, each fitting is associated with a unique heat number, which corresponds to the information documented in the 3.1 certificate datasheet. | 1 | Applied and Interdisciplinary Chemistry |
In 2014, the International Institute of Ammonia Refrigeration introduced a specialized label design for use when marking pipes associated with refrigeration systems using ammonia, including information such as the physical state, pressure and purpose in the system. | 1 | Applied and Interdisciplinary Chemistry |
The pronunciation of the compound reflects its origin and first isolation from sugar beets (Beta vulgaris subsp. vulgaris), and does not derive from the Greek letter beta (β). It is commonly pronounced beta-INE or BEE-tayn. | 0 | Theoretical and Fundamental Chemistry |
In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the solar system was formed, and were formed in, or after, the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and potentially from other processes. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet accretion until the present; 286 such nuclides are known. | 0 | Theoretical and Fundamental Chemistry |
Green roofs create natural habitat as part of an urban wilderness. Even in high-rise urban settings as tall as 19 stories, it has been found that green roofs can attract beneficial insects, birds, bees and butterflies. A recent list of the bee species recorded from green roofs (worldwide) highlights both the diversity of species, but also the (expected) bias towards small ground-nesting species (Hofmann and Renner, 2017). Rooftop greenery complements wild areas by providing stepping stones for songbirds, migratory birds and other wildlife facing shortages of natural habitat. Bats have also been reported to be more active over green roofs due to the foraging opportunities these roofs provide. Research at the Javits Center green roof in New York, NY, has shown a correlation between higher numbers of certain insects on the roof, particularly moths, with an increased amount of bat foraging activity.
Green roofs also serve as a green wall, filtering pollutants and carbon dioxide out of the air, helping to lower rates of diseases such as asthma. They can also filter pollutants and heavy metals out of rainwater. | 1 | Applied and Interdisciplinary Chemistry |
Physical methods are the conceptually simplest, using some physical means to force the transfected material into the target cell's nucleus. The most widely used physical method is electroporation, where short electrical pulses disrupt the cell membrane, allowing the transfected nucleic acids to enter the cell. Other physical methods use different means to poke holes in the cell membrane: Sonoporation uses high-intensity ultrasound (attributed mainly to the cavitation of gas bubbles interacting with nearby cell membranes), optical transfection uses a highly focused laser to form a ~1 µm diameter hole.
Several methods use tools that force the nucleic acid into the cell, namely: microinjection of nucleic acid with a fine needle; biolistic particle delivery, in which nucleic acid is attached to heavy metal particles (usually gold) and propelled into the cells at high speed; and magnetofection, where nucleic acids are attached to magnetic iron oxide particles and driven into the target cells by magnets.
Hydrodynamic delivery is a method used in mice and rats, in which nucleic acids can be delivered to the liver by injecting a relatively large volume in the blood in less than 10 seconds; nearly all of the DNA is expressed in the liver by this procedure. | 1 | Applied and Interdisciplinary Chemistry |
GABA degradation pathways exists in almost all eukaryotic organisms and takes place by the action of similar enzymes. Although, GABA in E.coli is predominantly used as an alternative source of energy through GABA degradation pathways, GABA in higher eukaryotic organisms acts as an inhibitory neurotransmitter and also as regulator of muscle tone. GABA degradation pathways in eukaryotes are responsible for the inactivation of GABA. | 1 | Applied and Interdisciplinary Chemistry |
Concomitant with the displacement of two N-H protons, porphyrins bind metal ions in the N4 "pocket". The metal ion usually has a charge of 2+ or 3+. A schematic equation for these syntheses is shown:
:Hporphyrin + [ML] → M(porphyrinate)L + 4 L + 2 H, where M = metal ion and L = a ligand | 1 | Applied and Interdisciplinary Chemistry |
The problem of defining a radius for the atomic nucleus has some similarity to that of defining a radius for the entire atom; neither has well defined boundaries. However, basic liquid drop models of the nucleus imagine a fairly uniform density of nucleons, theoretically giving a more recognizable surface to a nucleus than an atom, the latter being composed of highly diffuse electron clouds with density gradually reducing away from the centre. For individual protons and neutrons or small nuclei, the concepts of size and boundary can be less clear. A single nucleon needs to be regarded as a "color confined" bag of three valence quarks, binding gluons, and a so-called "sea" of quark-antiquark pairs. Also, the nucleon is surrounded by its Yukawa pion field responsible for the strong nuclear force. It could be difficult to decide whether to include the surrounding Yukawa meson field as part of the proton or nucleon size or to regard it as a separate entity.
Fundamentally important are realizable experimental procedures to measure some aspect of size, whatever that may mean in the quantum realm of atoms and nuclei. Foremost, the nucleus can be modeled as a sphere of positive charge for the interpretation of electron scattering experiments: the electrons "see" a range of cross-sections, for which a mean can be taken. The qualification of "rms" (root mean square) arises because it is the nuclear cross-section, proportional to the square of the radius, which is determining for electron scattering.
This definition of charge radius is often applied to composite hadrons such as a proton, neutron, pion, or kaon, that are made up of more than one quark. In the case of an anti-matter baryon (e.g. an anti-proton), and some particles with zero net electric charge, the composite particle must be modeled as a sphere of negative rather than positive electric charge for the interpretation of electron scattering experiments. In these cases, the square of the charge radius of the particle is defined to be negative, with the same absolute value with units of length squared equal to the positive squared charge radius that it would have had if it was identical in all other respects but each quark in the particle had the opposite electric charge (with the charge radius itself having a value that is an imaginary number with units of length). It is customary when charge radius takes an imaginary numbered value to report the negative valued square of the charge radius, rather than the charge radius itself, for a particle.
The best known particle with a negative squared charge radius is the neutron. The heuristic explanation for why the squared charge radius of a neutron is negative, despite its overall neutral electric charge, is that this is the case because its negatively charged down quarks are, on average, located in the outer part of the neutron, while its positively charged up quark is, on average, located towards the center of the neutron. This asymmetric distribution of charge within the particle gives rise to a small negative squared charge radius for the particle as a whole. But, this is only the simplest of a variety of theoretical models, some of which are more elaborate, that are used to explain this property of a neutron.
For deuterons and higher nuclei, it is conventional to distinguish between the scattering charge radius, r (obtained from scattering data), and the bound-state charge radius, R, which includes the Darwin–Foldy term to account for the behaviour of the anomalous magnetic moment in an electromagnetic field and which is appropriate for treating spectroscopic data. The two radii are related by
where m and m are the masses of the electron and the deuteron respectively while λ is the Compton wavelength of the electron. For the proton, the two radii are the same. | 0 | Theoretical and Fundamental Chemistry |
Flux, or metabolic flux is the rate of turnover of molecules through a metabolic pathway. Flux is regulated by the enzymes involved in a pathway. Within cells, regulation of flux is vital for all metabolic pathways to regulate the pathway's activity under different conditions. Flux is therefore of great interest in metabolic network modelling, where it is analysed via flux balance analysis and metabolic control analysis.
In this manner, flux is the movement of matter through metabolic networks that are connected by metabolites and cofactors, and is therefore a way of describing the activity of the metabolic network as a whole using a single characteristic. | 1 | Applied and Interdisciplinary Chemistry |
The market for membrane bioreactors is segmented based on end-user type, such as municipal and industrial users, and end-user geography, for instance Europe, Middle East and Africa (EMEA), Asia-Pacific (APAC), and the Americas.
In this line, in 2016, some studies and reports showed that the APAC region took the lead in terms of market share, owning 41.90%. On the other hand, the EMEA region's market share is approximately 31.34% and the Americas constitute 26.67% of the market.
APAC has the largest membrane bioreactors market. Developing economies such as India, China, Indonesia, and the Philippines are major contributors to growth in this market region. APAC is considered one of the most disaster-prone regions in the world: in 2013, thousands of people died from water-related disasters in the region, accounting for nine-tenth of the water-related deaths, globally. In addition to this, the public water supply system in the region is not as developed when compared to other countries such as the US, Canada, the countries in Europe, etc.
The membrane bioreactors market in the EMEA region has witnessed stable growth. Countries such as Saudi Arabia, the UAE, Kuwait, Algeria, Turkey, and Spain are major contributors to that growth rate. Scarcity of clean and fresh water is the key driver for the increasing demand for efficient water treatment technologies. In this regard, increased awareness about water treatment and safe drinking water is also driving the growth.
Ultimately, the Americas region has been witnessing major demand from countries including the US, Canada, Antigua, Argentina, Brazil, and Chile. The membrane bioreactor market has grown on account of stringent regulatory enforcement towards the safe discharge of wastewater. The demand for this emerging technology comes mainly from the pharmaceuticals, food & beverages, automotive, and chemicals industries. | 1 | Applied and Interdisciplinary Chemistry |
The idea of photostimulation as a method of controlling biomolecule function was developed in the 1970s. Two researchers, Walther Stoeckenius and Dieter Oesterhelt discovered an ion pump known as bacteriorhodopsin which functions in the presence of light in 1971. In 1978, J.F. Hoffman invented the term “caging”. Unfortunately, this term caused some confusion among scientists due to the fact that the term is often used to describe a molecule which is trapped within another molecule. It could also be confused with the “caged effect” in the recombination of radicals. Therefore, some authors decided to use the term “light-activated” instead of “caging”. Both terms are currently in use. The first “caged molecule” synthesized by Hoffman et al. at Yale was the caged precursor to ATP derivative 1. | 1 | Applied and Interdisciplinary Chemistry |
There are at least 25 enzymes and specific transport proteins in the β-oxidation pathway. Of these, 18 have been associated with human disease as inborn errors of metabolism.
Furthermore, studies indicate that lipid disorders are involved in diverse aspects of tumorigenesis, and fatty acid metabolism makes malignant cells more resistant to a hypoxic environment. Accordingly, cancer cells can display irregular lipid metabolism with regard to both fatty acid synthesis and mitochondrial fatty acid oxidation (FAO) that are involved in diverse aspects of tumorigenesis and cell growth. Several specific β-oxidation disorders have been identified. | 1 | Applied and Interdisciplinary Chemistry |
In the energy range used in CEMS, the incident radiation can interact with the absorber through two kinds of processes: (a) conventional interactions – photoelectric and Compton effects, and (b) nuclear resonant absorption – Mössbauer effect. Due to conventional interactions the beam is attenuated and electrons are emitted from the sample. The nuclear de-excitation following the resonant absorption takes place by emission of either a gamma ray or an internal conversion (IC) electron. In the latter case, the atom is left in an ‘excited’ state with a hole in an inner shell; the energy excess is given away with emission of Auger electrons and/or X-rays. Thus, the electrons emitted from the sample as a consequence of the Mössbauer absorptions are: (a) primary (IC or Auger) electrons originated in the de-excitations of the nuclei excited by the incident beam, and (b) secondary electrons originated by conventional interactions of photons (or resonant absorption of gamma rays) emitted after resonant absorptions. | 0 | Theoretical and Fundamental Chemistry |
Arenediazonium cations reduced by hypophosphorous acid, ethanol, sodium stannite or alkaline sodium thiosulphate gives benzene:
An alternative way suggested by Baeyer & Pfitzinger is to replace the diazo group with H is: first to convert it into hydrazine by treating with then to oxidize it into hydrocarbon by boiling with cupric sulphate solution. | 0 | Theoretical and Fundamental Chemistry |
In the mid-20th century, prior to the development of solid state components such as Zener diodes, voltage regulation in circuits was often accomplished with voltage-regulator tubes, which used glow discharge. | 0 | Theoretical and Fundamental Chemistry |
Homoepitaxial growth of semiconductor thin films are generally done by chemical or physical vapor deposition methods that deliver the precursors to the substrate in gaseous state. For example, silicon is most commonly deposited from silicon tetrachloride (or germanium tetrachloride) and hydrogen at approximately 1200 to 1250 °C:
:SiCl + 2H ↔ Si + 4HCl
where (g) and (s) represent gas and solid phases, respectively. This reaction is reversible, and the growth rate depends strongly upon the proportion of the two source gases. Growth rates above 2 micrometres per minute produce polycrystalline silicon, and negative growth rates (etching) may occur if too much hydrogen chloride byproduct is present. (Hydrogen chloride may be intentionally added to etch the wafer.) An additional etching reaction competes with the deposition reaction:
:SiCl + Si ↔ 2SiCl
Silicon VPE may also use silane, dichlorosilane, and trichlorosilane source gases. For instance, the silane reaction occurs at 650 °C in this way:
:SiH → Si + 2H
VPE is sometimes classified by the chemistry of the source gases, such as hydride VPE (HVPE) and metalorganic VPE (MOVPE or MOCVD).
The reaction chamber where this process takes place may be heated by lamps located outside the chamber. A common technique used in compound semiconductor growth is molecular beam epitaxy (MBE). In this method, a source material is heated to produce an evaporated beam of particles, which travel through a very high vacuum (10 Pa; practically free space) to the substrate and start epitaxial growth. Chemical beam epitaxy, on the other hand, is an ultra-high vacuum process that uses gas phase precursors to generate the molecular beam.
Another widely used technique in microelectronics and nanotechnology is atomic layer epitaxy, in which precursor gases are alternatively pulsed into a chamber, leading to atomic monolayer growth by surface saturation and chemisorption. | 0 | Theoretical and Fundamental Chemistry |
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