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Jeewanu (Sanskrit for "particles of life") are synthetic chemical particles that possess cell-like structure and seem to have some functional properties; that is, they are a model of primitive cells, or protocells. It was first synthesised by Krishna Bahadur (20 January 1926 — 5 August 1994), an Indian chemist and his team in 1963. Using photochemical reaction, they produced coacervates, microscopic cell-like spheres from a mixture of simple organic and inorganic compounds. Bahadur named these particles Jeewanu because they exhibit some of the basic properties of a cell, such as the presence of semipermeable membrane, amino acids, phospholipids and carbohydrates. Further, like living cells, they had several catalytic activities. Jeewanu are cited as models of protocells for the origin of life, and as artificial cells. | 9 | Geochemistry |
A Rotary Vacuum Filter Drum consists of a cylindrical filter membrane that is partly sub-merged in a slurry to be filtered. The inside of the drum is held lower than the ambient pressure. As the drum rotates through the slurry, the liquid is sucked through the membrane, leaving solids to cake on the membrane surface while the drum is submerged. A knife or blade is positioned to scrape the product from the surface.
The technique is well suited to slurries, flocculated suspensions, and liquids with a high solid content, which could clog other forms of filter. It is common to pre-coated with a filter aid, typically of diatomaceous earth (DE) or Perlite. In some implementations, the knife also cuts off a small portion of the filter media to reveal a fresh media surface that will enter the liquid as the drum rotates. Such systems advance the knife automatically as the surface is removed. | 3 | Analytical Chemistry |
Sealants are an alternative to solder where additional strength is not required. In most cases, sealants should not be necessary with a properly designed copper installation. They are at best a relatively short-term solution requiring frequent maintenance. Regardless, sealant-filled joints have been used successfully as a secondary waterproofing measure for standing seam and batten seam roofing applications where low-sloped roofs are less than . Sealants can also be used in joints that are primarily designed to accommodate thermal movement of the copper.
The sealants used should be tested by the manufacturer and designated as compatible for use with copper.
In general, butyl, polysulfide, polyurethane, and other inorganic or rubber-based sealants are reasonably compatible with copper. Acrylic, neoprene, and nitrile-based sealants actively corrode copper. Silicone sealants are somewhat successful with copper but their suitability should be verified before application. | 8 | Metallurgy |
Studies from various international working groups have revealed a significantly increased amount of Tumor M2-PK in EDTA-plasma samples of patients with renal, lung, breast, cervical and gastrointestinal tumors (oesophagus, stomach, pancreas, colon, rectum), as well as melanoma, which correlated with the tumor stage.
The combination of Tumor M2-PK with the appropriate classical tumor marker, such as CEA for bowel cancer, CA 19-9 for pancreatic cancer and CA 72-4 for gastric cancer, significantly increases the sensitivity to detect various cancers.
An important application of the Tumor M2-PK test in EDTA-plasma is for follow-up during tumor therapy, to monitor the success or failure of the chosen treatment, as well as predicting the chances of a “cure” and survival.
If Tumor M2-PK levels decrease during therapy and then remain low after therapy it points towards successful treatment. An increase in the Tumor M2-PK values during or after therapy points towards relapse and/or metastasis.
Increased Tumor M2-PK values can sometimes also occur in severe inflammatory diseases, which must be excluded by differential diagnosis. | 1 | Biochemistry |
By considering the arrangement of atoms relative to each other, their coordination numbers, interatomic distances, types of bonding, etc., it is possible to form a general view of the structures and alternative ways of visualizing them. | 3 | Analytical Chemistry |
Migratory aptitude is the relative ability of a migrating group to migrate in a rearrangement reaction. Migratory aptitudes vary in different reactions, depending on multiple factors.
In the Baeyer-Villiger reaction, the more substituted group, in general, migrates. In the pinacol rearrangement, the order of migratory aptitude has not been determined unambiguously, but some trends have been determined. For example, relative migratory aptitudes for alkyl substituents is Hydride >Phenide>C(CH)> CH > CH.
More bulky groups have more tendency to migrate. | 0 | Organic Chemistry |
Naturally occurring crude bitumen impregnated in sedimentary rock is the prime feed stock for petroleum production from "oil sands", currently under development in Alberta, Canada. Canada has most of the worlds supply of natural bitumen, covering 140,000 square kilometres (an area larger than England), giving it the second-largest proven oil reserves in the world. The Athabasca oil sands are the largest bitumen deposit in Canada and the only one accessible to surface mining, although recent technological breakthroughs have resulted in deeper deposits becoming producible by in situ' methods. Because of oil price increases after 2003, producing bitumen became highly profitable, but as a result of the decline after 2014 it became uneconomic to build new plants again. By 2014, Canadian crude bitumen production averaged about per day and was projected to rise to per day by 2020. The total amount of crude bitumen in Alberta that could be extracted is estimated to be about , which at a rate of would last about 200 years. | 7 | Physical Chemistry |
The paramagnetic ring current resulting from the electron delocalization in antiaromatic compounds can be observed by NMR. This ring current leads to a deshielding (downfield shift) of nuclei inside the ring and a shielding (upfield shift) of nuclei outside the ring. [[Cyclododecahexaene|[12]annulene]] is an antiaromatic hydrocarbon that is large enough to have protons both inside and outside of the ring. The chemical shift for the protons outside its ring is 5.91 ppm and that for the protons inside the ring is 7.86 ppm, compared to the normal range of 4.5-6.5 ppm for nonaromatic alkenes. This effect is of a smaller magnitude than the corresponding shifts in aromatic compounds.
Many aromatic and antiaromatic compounds (benzene and cyclobutadiene) are too small to have protons inside of the ring, where shielding and deshielding effects can be more diagnostically useful in determining if a compound is aromatic, antiaromatic, or nonaromatic. Nucleus Independent Chemical Shift (NICS) analysis is a method of computing the ring shielding (or deshielding) at the center of a ring system to predict aromaticity or antiaromaticity. A negative NICS value is indicative of aromaticity and a positive value is indicative of antiaromaticity. | 7 | Physical Chemistry |
In 1987, an elderly couple was exposed to sulfuryl fluoride in their house already cleared for reentry. While the fumigation company opened windows and doors, and aerated the house with fans, sulfuryl fluoride level was not measured. It was not detected when the air was sampled 12 days after aeration. The couple experienced weakness, nausea and shortness of breath that evening. The man suffered a seizure and died the following day. His wife's condition got worse with pulmonary edema, and she died after a cardiovascular arrest 6 days later.
In 2015, a 10-year-old boy suffered severe brain damage and lost function of his left arm and leg after his home was treated with sulfuryl fluoride and insufficiently aerated, prompting a criminal investigation by the Department of Justice and the Florida Department of Agricultural and Consumer Services. Two pest control workers later pled guilty to charges of misuse of the pesticide resulting in the boy's poisoning, and were each sentenced to one year in prison.
In 2016, a 24-year-old man who allegedly entered an apartment that was being fumigated in Fremont, California to commit a burglary was exposed to sulfuryl fluoride and chloropicrin and died shortly thereafter. According to a police officer, he experienced labored breathing and was sweating before he collapsed just a few steps from the first floor window of the apartment he allegedly burglarized. | 2 | Environmental Chemistry |
One of the most prevalent features of iron chemistry is its redox chemistry. Iron has three oxidation states: metallic iron (Fe), ferrous iron (Fe), and ferric iron (Fe). Ferrous iron is the reduced form of iron, and ferric iron is the oxidized form of iron. In the presence of oxygen, ferrous iron is oxidized to ferric iron, thus ferric iron is the dominant redox state of iron at Earth's surface conditions. However, ferrous iron is the dominant redox state below the surface at depth. Because of this redox chemistry, iron can act as either an electron donor or receptor, making it a metabolically useful species.
Each form of iron has a specific distribution of electrons (i.e., electron configuration), tabulated below: | 9 | Geochemistry |
At low doses, levonorgestrel is used in monophasic and triphasic formulations of combined oral contraceptive pills, with available monophasic doses ranging from 100 to 250 µg, and triphasic doses of 50 µg/75 µg/125 µg. It is combined with the estrogen ethinylestradiol in these formulations.
At very low daily dose of 30 µg, levonorgestrel is used in some progestogen-only pill formulations.
Levonorgestrel is the active ingredient in a number of intrauterine devices including Mirena and Skyla. It is also the active ingredient in the birth control implants Norplant and Jadelle.
One of the more common forms of contraception that contains only levonorgestrel is an IUD. One IUD, the Mirena, is a small hollow cylinder containing levonorgestrel and polydimethylsiloxane and covered with a release rate controlling membrane. | 4 | Stereochemistry |
Strong electrolytes are hypothesized to dissociate completely in solution. The conductivity of a solution of a strong electrolyte at low concentration follows Kohlrausch's Law
where is known as the limiting molar conductivity, is an empirical constant and is the electrolyte concentration. (Limiting here means "at the limit of the infinite dilution".) In effect, the observed conductivity of a strong electrolyte becomes directly proportional to concentration, at sufficiently low concentrations i.e. when
As the concentration is increased however, the conductivity no longer rises in proportion.
Moreover, Kohlrausch also found that the limiting conductivity of an electrolyte;
: and are the limiting molar conductivities of the individual ions.
The following table gives values for the limiting molar conductivities for some selected ions.
An interpretation of these results was based on the theory of Debye and Hückel, yielding the Debye–Hückel–Onsager theory:
where and are constants that depend only on known quantities such as temperature, the charges on the ions and the dielectric constant and viscosity of the solvent. As the name suggests, this is an extension of the Debye–Hückel theory, due to Onsager. It is very successful for solutions at low concentration. | 7 | Physical Chemistry |
In eukaryotes, oxidative phosphorylation occurs in the mitochondrial cristae. It comprises the electron transport chain that establishes a proton gradient (chemiosmotic potential) across the boundary of the inner membrane by oxidizing the NADH produced from the Krebs cycle. ATP is synthesized by the ATP synthase enzyme when the chemiosmotic gradient is used to drive the phosphorylation of ADP. The electrons are finally transferred to exogenous oxygen and, with the addition of two protons, water is formed. | 1 | Biochemistry |
Firstly, equilibrium constants are determined at a number of different ionic strengths, at a chosen temperature and particular background electrolyte. The interaction coefficients are then determined by fitting to the observed equilibrium constant values. The procedure also provides the value of K at infinite dilution. It is not limited to monobasic acids. and can also be applied to metal complexes. The SIT and Pitzer approaches have been compared recently. The Bromley equation has also been compared to both SIT and Pitzer equations. | 7 | Physical Chemistry |
An example of a prototype for a synthetic chemically driven rotary molecular motor was reported by Kelly and co-workers in 1999. Their system is made up from a three-bladed triptycene rotor and a helicene, and is capable of performing a unidirectional 120° rotation.
This rotation takes place in five steps. The amine group present on the triptycene moiety is converted to an isocyanate group by condensation with phosgene (a). Thermal or spontaneous rotation around the central bond then brings the isocyanate group in proximity of the hydroxyl group located on the helicene moiety (b), thereby allowing these two groups to react with each other (c). This reaction irreversibly traps the system as a strained cyclic urethane that is higher in energy and thus energetically closer to the rotational energy barrier than the original state. Further rotation of the triptycene moiety therefore requires only a relatively small amount of thermal activation in order to overcome this barrier, thereby releasing the strain (d). Finally, cleavage of the urethane group restores the amine and alcohol functionalities of the molecule (e).
The result of this sequence of events is a unidirectional 120° rotation of the triptycene moiety with respect to the helicene moiety. Additional forward or backward rotation of the triptycene rotor is inhibited by the helicene moiety, which serves a function similar to that of the pawl of a ratchet. The unidirectionality of the system is a result from both the asymmetric skew of the helicene moiety as well as the strain of the cyclic urethane which is formed in c. This strain can be only be lowered by the clockwise rotation of the triptycene rotor in d, as both counterclockwise rotation as well as the inverse process of d are energetically unfavorable. In this respect the preference for the rotation direction is determined by both the positions of the functional groups and the shape of the helicene and is thus built into the design of the molecule instead of dictated by external factors.
The motor by Kelly and co-workers is an elegant example of how chemical energy can be used to induce controlled, unidirectional rotational motion, a process which resembles the consumption of ATP in organisms in order to fuel numerous processes. However, it does suffer from a serious drawback: the sequence of events that leads to 120° rotation is not repeatable. Kelly and co-workers have therefore searched for ways to extend the system so that this sequence can be carried out repeatedly. Unfortunately, their attempts to accomplish this objective have not been successful and currently the project has been abandoned. In 2016 David Leigh's group invented the first autonomous chemically-fuelled synthetic molecular motor.
Some other examples of synthetic chemically driven rotary molecular motors that all operate by sequential addition of reagents have been reported, including the use of the stereoselective ring opening of a racemic biaryl lactone by the use of chiral reagents, which results in a directed 90° rotation of one aryl with respect to the other aryl. Branchaud and co-workers have reported that this approach, followed by an additional ring closing step, can be used to accomplish a non-repeatable 180° rotation.
Feringa and co-workers used this approach in their design of a molecule that can repeatably perform 360° rotation. The full rotation of this molecular motor takes place in four stages. In stages A and C rotation of the aryl moiety is restricted, although helix inversion is possible. In stages B and D the aryl can rotate with respect to the naphthalene with steric interactions preventing the aryl from passing the naphthalene. The rotary cycle consists of four chemically induced steps which realize the conversion of one stage into the next. Steps 1 and 3 are asymmetric ring opening reactions which make use of a chiral reagent in order to control the direction of the rotation of the aryl. Steps 2 and 4 consist of the deprotection of the phenol, followed by regioselective ring formation. | 6 | Supramolecular Chemistry |
Its membership in the amphetamine class has made pseudoephedrine a sought-after chemical precursor in the illicit manufacture of methamphetamine and methcathinone. As a result of the increasing regulatory restrictions on the sale and distribution of pseudoephedrine, pharmaceutical firms have reformulated medications to use alternative compounds, particularly phenylephrine, even though its efficacy as an oral decongestant has been demonstrated to be indistinguishable from placebo.
In the United States, federal laws control the sale of pseudoephedrine-containing products. Retailers in the US have created corporate policies restricting the sale of pseudoephedrine-containing products. Their policies restrict sales by limiting purchase quantities and requiring a minimum age and government issued photographic identification. These requirements are similar to and sometimes more stringent than existing law. Internationally, pseudoephedrine is listed as a Table I precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances. | 4 | Stereochemistry |
The process of splat quenching involves rapid quenching or cooling of molten metal. A typical procedure for splat quenching involves pouring the molten metal between two cooled copper rollers that are circulated with water to transfer the heat away from the metal, causing it to almost instantaneously solidify.
A more efficient splat quenching technique is Duwezs and Willens gun technique. Their technique produces higher rates of cooling of the droplet of metal because the sample is propelled at high velocities and hits a quencher plate causing its surface area to increase which immediately solidifies the metal. This allows for a wider range of metals that can be quenched and be given amorphous-like features instead of the general iron alloy.
Another technique involves the consecutive spraying of the molten metal onto a chemical vapor deposition surface. However, the layers do not fuse together as desired and this causes oxides to be contained in the structure and pores to form around the structure. Manufacturing companies take an interest in the resultant products because of their near-net shaping capabilities. | 8 | Metallurgy |
* Ephemeroptera
* Plecoptera
* Mollusca
* Trichoptera
* Escherichia coli (E. coli)
* Coliform bacteria
* Pimephales promelas (fathead minnow)
* Americamysis bahia (Mysid shrimp)
* Sea urchin
* Protists, e.g. Paratrimastix pyriformis
Biological monitoring metrics have been developed in many places, and one widely used family of measurements for freshwater is the presence and abundance of members of the insect orders Ephemeroptera, Plecoptera and Trichoptera (EPT) (of benthic macroinvertebrates whose common names are, respectively, mayfly, stonefly and caddisfly). EPT indexes will naturally vary from region to region, but generally, within a region, the greater the number of taxa from these orders, the better the water quality. Organisations in the United States, such as EPA. offer guidance on developing a monitoring program and identifying members of these and other aquatic insect orders. Many US wastewater dischargers (e.g., factories, power plants, refineries, mines, municipal sewage treatment plants) are required to conduct periodic whole effluent toxicity (WET) tests.
Individuals interested in monitoring water quality who cannot afford or manage lab scale analysis can also use biological indicators to get a general reading of water quality. One example is the IOWATER volunteer water monitoring program of Iowa, which includes an EPT indicator key.
Bivalve molluscs are largely used as bioindicators to monitor the health of aquatic environments in both fresh water and the marine environments. Their population status or structure, physiology, behaviour or the level of contamination with elements or compounds can indicate the state of contamination status of the ecosystem. They are particularly useful since they are sessile so that they are representative of the environment where they are sampled or placed. A typical project is the U.S. Mussel Watch Programme, but today they are used worldwide.
The Southern African Scoring System (SASS) method is a biological water quality monitoring system based on the presence of benthic macroinvertebrates (EPT). The SASS aquatic biomonitoring tool has been refined over the past 30 years and is now on the fifth version (SASS5) which has been specifically modified in accordance with international standards, namely the ISO/IEC 17025 protocol. The SASS5 method is used by the South African Department of Water Affairs as a standard method for River Health Assessment, which feeds the national River Health Programme and the national Rivers Database. | 3 | Analytical Chemistry |
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convention. The net charge of an ion is not zero because its total number of electrons is unequal to its total number of protons.
A cation is a positively charged ion with fewer electrons than protons while an anion is a negatively charged ion with more electrons than protons. Opposite electric charges are pulled towards one another by electrostatic force, so cations and anions attract each other and readily form ionic compounds.
Ions consisting of only a single atom are termed atomic or monatomic ions, while two or more atoms form molecular ions or polyatomic ions. In the case of physical ionization in a fluid (gas or liquid), "ion pairs" are created by spontaneous molecule collisions, where each generated pair consists of a free electron and a positive ion. Ions are also created by chemical interactions, such as the dissolution of a salt in liquids, or by other means, such as passing a direct current through a conducting solution, dissolving an anode via ionization. | 7 | Physical Chemistry |
Basic research on supercritical water oxidation was undertaken in the 1990s at Sandia National Laboratory's Combustion Research Facility (CRF), in Livermore, CA. Originally proposed as a hazardous waste destruction technology in response to the Kyoto protocol, multiple waste streams were studied by Steven F. Rice and Russ Hanush, and hydrothermal (supercritical water) flames were investigated by Richard R. Steeper and Jason D. Aiken. Among the waste streams studied were military dyes and pyrotechnics, methanol, and isopropyl alcohol. Hydrogen peroxide was used as an oxidizing agent, and Eric Croiset was tasked with detailed measurements of the decomposition of hydrogen peroxide at supercritical water conditions.
In mid-1992, Thomas G. McGuinness, PE invented what is now known as the "transpiring-wall SCWO reactor" (TWR) while seconded to Los Alamos National Laboratory on behalf of Summit Research Corporation. McGuinness subsequently received the first US patent for a TWR in early 1995. The TWR was designed to mitigate problems of salt/solids deposition, corrosion and thermal limitations occurring in other SCWO reactor designs (eg. tubular & vat-type reactors) at the time. The upper part of the vertical reactor incorporates a permeable liner through which a clean fluid permeates to help prevent salts and other solids from accumulating at the inner surface of the liner. The liner also insulates the outer pressure containment vessel from high temperatures within the reaction zone. The liner can be manufactured from a variety of materials resistant to corrosion and high reaction temperatures. The bottom end of the TWR incorporates a "quench cooler" for cooling the reaction byproducts while neutralizing any components that might form acids during transition to subcritical temperature. Proof-of-concept and performance advantages of the TWR for a variety of feedstocks was demonstrated by Eckhard Dinjus and Johannes Abeln at Forschungszentrum Karlsruhe (FZK), via direct comparison between a TWR and an adjacent tubular reactor.
Major engineering challenges were associated with the deposition of salts and chemical corrosion in these supercritical water reactors. Anthony Lajeunesse led the team investigating these issues. To address these issues Lajeunesse designed a transpiring wall reactor which introduced a pressure differential through the walls of an inner sleeve filled with pores to continuously rinse the inner walls of the reactor with fresh water. Russ Hanush was charged with the construction and operation of the supercritical fluids reactor (SFR) used for these studies. Among its design intricacies were the Inconel 625 alloy necessary for operation at such extreme temperatures and pressures, and the design of the high-pressure, high-temperature optical cells used for photometric access to the reacting flows which incorporated 24 carat gold pressure seals and sapphire windows. | 7 | Physical Chemistry |
The tetrahydrocannabinol (THC) content of hash oil varies tremendously, since the manufacturers use a varying assortment of marijuana plants and preparation techniques. Dealers sometimes cut hash oils with other oils. The form of the extract varies depending on the extraction process used; it may be liquid, a clear amber solid (called “shatter"), a sticky semisolid substance (called "wax"), or a brittle honeycombed solid (called "honeycomb wax").
Hash oil seized in the 1970s had a THC content ranging from 10% to 30%. The oil available on the U.S. West Coast in 1974 averaged about 15% THC. Samples seized across the United States by the Drug Enforcement Administration over an 18-year period (1980–1997) showed that THC content in hashish and hashish oil averaging 12.9% and 17.4%, respectively, did not show an increase over time. The highest THC concentrations measured were 52.9% in hashish and 47.0% in hash oil. Hash oils in use in the 2010s had THC concentrations as high as 90% and other products achieving higher concentrations. Following an outbreak of vaping-related pulmonary illnesses and deaths in 2019, NBC News conducted tests on different black market THC vape cartridges and found cartridges containing up to 30% Vitamin E acetate, and trace amounts of fungicides and pesticides that may be harmful.
The following compounds were found in naphtha extracts of Bedrocan Dutch medical cannabis:
* Cannabinoids: THC (~ 30%) and THCA (~ 60%).
* Monoterpenes (~ 5%): β-pinene, myrcene, β-phellandrene, cis-ocimene, terpinolene, and terpineol.
* Sesquiterpenes (~ 5%): β-caryophyllene, humulene, δ-guaiene, γ-cadinene, eudesma-3,7(11)-diene, and elemene. | 7 | Physical Chemistry |
Bartlett and Beaudry discovered that IBX is a valuable reagent for the transformation of β-hydroxyketones to β-diketones. IBX provides yields superior to both the Swern and Dess–Martin oxidation protocols. | 0 | Organic Chemistry |
Using experimental data as a starting point, homology transfer is one way to predict interactomes. Here, PPIs from one organism are used to predict interactions among homologous proteins in another organism ("interologs"). However, this approach has certain limitations, primarily because the source data may not be reliable (e.g. contain false positives and false negatives). In addition, proteins and their interactions change during evolution and thus may have been lost or gained. Nevertheless, numerous interactomes have been predicted, e.g. that of Bacillus licheniformis.
Some algorithms use experimental evidence on structural complexes, the atomic details of binding interfaces and produce detailed atomic models of protein–protein complexes as well as other protein–molecule interactions. Other algorithms use only sequence information, thereby creating unbiased complete networks of interaction with many mistakes.
Some methods use machine learning to distinguish how interacting protein pairs differ from non-interacting protein pairs in terms of pairwise features such as cellular colocalization, gene co-expression, how closely located on a DNA are the genes that encode the two proteins, and so on. Random Forest has been found to be most-effective machine learning method for protein interaction prediction. Such methods have been applied for discovering protein interactions on human interactome, specifically the interactome of Membrane proteins and the interactome of Schizophrenia-associated proteins. | 1 | Biochemistry |
Salahuddin died on 29 November 1996 at the age of 59 after a difficult illness. His passing away saddened his family and his students. Eulogies by his former students were read at the Annual meeting of the Aligarh Alumni Association Washington DC;
by others at a session at AMU Aligarh on 3 Jan 2019. At his death he was survived by his wife and two daughters. | 1 | Biochemistry |
The and distances are 117 and 158 pm. By contrast, in methyl thiocyanate, and distances are 116 and 176 pm.
Typical bond angles for in aryl isothiocyanates are near 165°. Again, the thiocyanate isomers are quite different with angle near 100°. In both isomers the angle approaches 180°. | 0 | Organic Chemistry |
In anatomic pathology, ammonical silver nitrate is used in the Fontana–Masson Stain, which is a silver stain technique used to detect melanin, argentaffin and lipofuscin in tissue sections. Melanin and the other chromaffins reduce the silver nitrate to metallic silver. | 3 | Analytical Chemistry |
D. C. Grahame modified the Stern model in 1947. He proposed that some ionic or uncharged species can penetrate the Stern layer, although the closest approach to the electrode is normally occupied by solvent molecules. This could occur if ions lose their solvation shell as they approach the electrode. He called ions in direct contact with the electrode "specifically adsorbed ions". This model proposed the existence of three regions. The inner Helmholtz plane (IHP) passes through the centres of the specifically adsorbed ions. The outer Helmholtz plane (OHP) passes through the centres of solvated ions at the distance of their closest approach to the electrode. Finally the diffuse layer is the region beyond the OHP. | 7 | Physical Chemistry |
Mairanovsky was born to a Jewish family in Batumi in 1899.
Mairanovsky was the head of several secret laboratories in the Bach Institute of Biochemistry in Moscow (1928–1935). As the head of Laboratory No. 1 (1938–1946), he initiated the secret poison program conducted by the NKVD. He used political prisoners for experiments with poisons. His classified PhD thesis defended in 1940 was entitled "Biological activity of the products of interaction of mustard gas with [human] skin tissues".
Mairanovsky participated personally in political assassinations as a member of Pavel Sudoplatov's team in the 1940s, including assassination of Isaiah Oggins.
He was arrested as a part of the doctors' plot in 1951, in connection with the case of Viktor Abakumov, and spent 10 years in prison. After his release, he headed a biochemical laboratory in Makhachkala, Dagestan ASSR. | 1 | Biochemistry |
The ability of AMGs modulating the metabolic capacities of their hosts can influence the abundance and distribution of specific microbial taxa. In turn, this shapes the overall composition of microbial communities, with potential cascading effects on higher trophic levels. | 1 | Biochemistry |
In a controversial 2009 article in the New England Journal of Medicine, "Lost in Transmission — FDA Drug Information That Never Reaches Clinicians", it was reported that the largest of three Lunesta trials found that compared to placebo Lunesta "was superior to placebo" while it only shortened initial time falling asleep by 15 minutes on average. "Clinicians who are interested in the drug’s efficacy cannot find efficacy information in the label: it states only that Lunesta is superior to placebo. The FDA’s medical review provides efficacy data, albeit not until page 306 of the 403-page document. In the longest, largest phase 3 trial, patients in the Lunesta group reported falling asleep an average of 15 minutes faster and sleeping an average of 37 minutes longer than those in the placebo group. However, on average, Lunesta patients still met criteria for insomnia and reported no clinically meaningful improvement in next-day alertness or functioning." | 4 | Stereochemistry |
Disorders in mtFASII lead to the following metabolic diseases:
* ACSF3: Combined malonic and methylmalonic aciduria (CMAMMA)
* MCAT: Medium-chain acyl-CoA dehydrogenase deficiency (MCAD)
* MECR: Mitochondrial enoyl-CoA reductase protein-associated neurodegeneration (MEPAN) | 1 | Biochemistry |
Before 1800 A.D., the iron and steel industry was located where raw material, power supply and running water were easily available. After 1950, the iron and steel industry began to be located on large areas of flat land near sea ports. The history of the modern steel industry began in the late 1850s. Since then, steel has become a staple of the worlds industrial economy. This article is intended only to address the business, economic and social dimensions of the industry, since the bulk production of steel began as a result of Henry Bessemers development of the Bessemer converter, in 1857. Previously, steel was very expensive to produce, and was only used in small, expensive items, such as knives, swords and armor. | 8 | Metallurgy |
A native of California, Fahy holds a Bachelor of Science degree in Biology from the University of California, Irvine and a PhD in pharmacology and cryobiology from the Medical College of Georgia in Augusta.
He currently serves on the board of directors of two organizations and as a referee for numerous scientific journals and funding agencies, and holds 35 patents on cryopreservation methods, aging interventions, transplantation, and other topics. | 1 | Biochemistry |
Peroxides are also strong oxidizers and easily react with skin, cotton and wood pulp. For safety reasons, peroxidic compounds are stored in a cool, opaque container, as heating and illumination accelerate their chemical reactions. Small amounts of peroxides, which emerge from storage or reaction vessels are neutralized using reducing agents such as iron(II) sulfate. Safety measures in industrial plants producing large amounts of peroxides include the following:
1) The equipment is located within reinforced concrete structures with foil windows, which would relieve pressure and not shatter in case of explosion.
2) The products are bottled in small containers and are moved to a cold place promptly after the synthesis.
3) The containers are made of non-reactive materials such as stainless steel, some aluminium alloys or dark glass.
For safe handling of concentrated organic peroxides, an important parameter is temperature of the sample, which should be maintained below the self accelerating decomposition temperature of the compound.
The shipping of organic peroxides is restricted. The US Department of Transportation lists organic peroxide shipping restrictions and forbidden materials in 49 CFR 172.101 Hazardous Materials Table based on the concentration and physical state of the material: | 0 | Organic Chemistry |
After fatal accidents, it is common to check the blood alcohol levels of involved persons. However, soon after death, the body begins to putrefy, a biological process which produces ethanol. This can make it difficult to conclusively determine the blood alcohol content in autopsies, particularly in bodies recovered from water. For instance, following the 1975 Moorgate tube crash, the driver's kidneys had a blood alcohol concentration of 80 mg/100 mL, but it could not be established how much of this could be attributed to natural decomposition. Newer research has shown that vitreous (eye) fluid provides an accurate estimate of blood alcohol concentration that is less subject to the effects of decomposition or contamination. | 1 | Biochemistry |
Polarization spectroscopy comprises a set of spectroscopic techniques based on polarization properties of light (not necessarily visible one; UV, X-ray, infrared, or in any other frequency range of the electromagnetic radiation). By analyzing the polarization properties of light, decisions can be made about the media that emitted the light (or the media the light passes/scatters through). Alternatively, a source of polarized light may be used to probe a media; in this case, the changes in the light polarization (compared to the incidental light) allow inferences about the media's properties.
In general, any kind of anisotropy in the media results in some sort of change in polarization. Such an anisotropy can be either inherent to the media (e.g., in the case of a crystal substance), or imposed externally (e.g., in the presence of magnetic field in plasma or by another laser beam). | 7 | Physical Chemistry |
Especially in meteorology they are used to analyze the actual state of the atmosphere derived from the measurements of radiosondes, usually obtained with weather balloons. In such diagrams, temperature and humidity values (represented by the dew point) are displayed with respect to pressure. Thus the diagram gives at a first glance the actual atmospheric stratification and vertical water vapor distribution. Further analysis gives the actual base and top height of convective clouds or possible instabilities in the stratification.
By assuming the energy amount due to solar radiation it is possible to predict the 2 m (6.6 ft) temperature, humidity, and wind during the day, the development of the boundary layer of the atmosphere, the occurrence and development of clouds and the conditions for soaring flight during the day.
The main feature of thermodynamic diagrams is the equivalence between the area in the diagram and energy. When air changes pressure and temperature during a process and prescribes a closed curve within the diagram the area enclosed by this curve is proportional to the energy which has been gained or released by the air. | 7 | Physical Chemistry |
In the glassy state, the movements of the long chain segments are frozen, the movements of these segments depend on an activation temperature that brings the polymer to a smoothing and elastic state, the rotation on the carbon bonds and the movements of the chains no longer have strong impediments to accommodate and acquire the conformation that requires less energy, the chains then "unravel" forming random strings, without order and therefore with higher entropy.
If a polymer sample is stretched for a short time in the elastic range, when the load is removed, the sample will recover its original shape, but if the load remains for a sufficiently long period, the chains rearrange and the original shape is not recovered, the result is an irreversible deformation, also called relaxation process (in this case: creep).
In order for a polymer to exhibit the thermally induced shape-memory effect, it is necessary to fix the chains with anchor points to avoid these relaxation processes that inelastically modify the system. | 7 | Physical Chemistry |
The extrusion of stationary phase from the column at the end of a separation experiment by stopping rotation and pumping solvent or gas through the column was used by CCC practitioners before the term EECCC was suggested. In elution-extrusion mode (EECCC), The mobile phase is extruded after a certain point by switching the phase being pumped into the system whilst maintaining rotation. For example, if the separation has been initiated with the aqueous phase as the mobile phase at a certain point the organic phase is pumped through the column which effectively pushes out both phases that are present in the column at the time of switching. The complete sample is eluted in the order of polarity (either normal or reversed) without loss of resolution by diffusion. It requires only one column volume of solvent phase and leaves the column full of fresh stationary phase for the subsequent separation. | 3 | Analytical Chemistry |
Triethyl orthoacetate is the organic compound with the formula CHC(OCH). It is the ethyl orthoester of acetic acid. It is a colorless oily liquid.
Triethyl orthoacetate is used in organic synthesis for acetylation.
It is also used in the Johnson-Claisen rearrangement. | 0 | Organic Chemistry |
According to the IUPAC definition, mixed potential is the potential of an electrode (against a suitable
reference electrode, often the standard hydrogen electrode) when an appreciable fraction of the anodic or cathodic current arises from two or more different redox couples, but when the total current on the electrode remains at zero. | 7 | Physical Chemistry |
In the special case where one hydrogen is replaced by deuterium (D) and another hydrogen by tritium (T), the methyl substituent becomes chiral. Methods exist to produce optically pure methyl compounds, e.g., chiral acetic acid (deuterotritoacetic acid ). Through the use of chiral methyl groups, the stereochemical course of several biochemical transformations have been analyzed. | 0 | Organic Chemistry |
Urea-containing creams are used as topical dermatological products to promote rehydration of the skin. Urea 40% is indicated for psoriasis, xerosis, onychomycosis, ichthyosis, eczema, keratosis, keratoderma, corns, and calluses. If covered by an occlusive dressing, 40% urea preparations may also be used for nonsurgical debridement of nails. Urea 40% "dissolves the intercellular matrix" of the nail plate. Only diseased or dystrophic nails are removed, as there is no effect on healthy portions of the nail. This drug (as carbamide peroxide) is also used as an earwax removal aid.
Urea has also been studied as a diuretic. It was first used by Dr. W. Friedrich in 1892. In a 2010 study of ICU patients, urea was used to treat euvolemic hyponatremia and was found safe, inexpensive, and simple.
Like saline, urea has been injected into the uterus to induce abortion, although this method is no longer in widespread use.
The blood urea nitrogen (BUN) test is a measure of the amount of nitrogen in the blood that comes from urea. It is used as a marker of renal function, though it is inferior to other markers such as creatinine because blood urea levels are influenced by other factors such as diet, dehydration, and liver function.
Urea has also been studied as an excipient in Drug-coated Balloon (DCB) coating formulation to enhance local drug delivery to stenotic blood vessels. Urea, when used as an excipient in small doses (~3 μg/mm) to coat DCB surface was found to form crystals that increase drug transfer without adverse toxic effects on vascular endothelial cells.
Urea labeled with carbon-14 or carbon-13 is used in the urea breath test, which is used to detect the presence of the bacterium Helicobacter pylori (H. pylori) in the stomach and duodenum of humans, associated with peptic ulcers. The test detects the characteristic enzyme urease, produced by H. pylori, by a reaction that produces ammonia from urea. This increases the pH (reduces the acidity) of the stomach environment around the bacteria. Similar bacteria species to H. pylori can be identified by the same test in animals such as apes, dogs, and cats (including big cats). | 0 | Organic Chemistry |
To quantify the exposure of particular individuals or populations two approaches are used, primarily based on practical considerations: | 2 | Environmental Chemistry |
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis is the cleavage of biomolecules where a water molecule is consumed to effect the separation of a larger molecule into component parts. When a carbohydrate is broken into its component sugar molecules by hydrolysis (e.g., sucrose being broken down into glucose and fructose), this is recognized as saccharification.
Hydrolysis reactions can be the reverse of a condensation reaction in which two molecules join into a larger one and eject a water molecule. Thus hydrolysis adds water to break down, whereas condensation builds up by removing water. | 7 | Physical Chemistry |
Video spectroscopy combines spectroscopic measurements with video technique. This technology has resulted from recent developments in hyperspectral imaging. A video capable imaging spectrometer can work like a camcorder and provide full frame spectral images in real-time that enables advanced (vehicle based) mobility and hand-held imaging spectroscopy. Unlike hyperspectral line scanners, a video spectrometer can spectrally capture randomly and quickly moving objects and processes. The product of a conventional hyperspectral line scanner has typically been called a hyperspectral data cube. A video spectrometer produces a spectral image data series at much higher speeds (1 ms) and frequencies (25 Hz) that is called a hyperspectral video. This technology can initiate novel solutions and challenges in spectral tracking, field spectroscopy, spectral mobile mapping, real-time spectral monitoring and many other applications. | 7 | Physical Chemistry |
tert-Butyllithium is a chemical compound with the formula (CH)CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong base, capable of deprotonating many carbon molecules, including benzene. tert-Butyllithium is available commercially as solutions in hydrocarbons (such as pentane); it is not usually prepared in the laboratory. | 0 | Organic Chemistry |
GGT is elevated by ingestion of large quantities of alcohol (needs reference) However, determination of high levels of total serum GGT activity is not specific to alcohol intoxication, and the measurement of selected serum forms of the enzyme offer more specific information. Isolated elevation or disproportionate elevation compared to other liver enzymes (such as ALT or alanine transaminase) can indicate harmful alcohol use or alcoholic liver disease, and can indicate excess alcohol consumption up to 3 or 4 weeks prior to the test. The mechanism for this elevation is unclear. Alcohol might increase GGT production by inducing hepatic microsomal production, or it might cause the leakage of GGT from hepatocytes. | 1 | Biochemistry |
Modern day antique collectors have since coined the term "Piloncitos" to describe the small "bead-like" pieces of gold which were used as currency in Precolonial Philippines, comparing the cone-shaped pieces to a pilon of sugar. Early historical descriptions of the term include the Spanish "granitas de oro" (small grains of gold), or simply by whatever local language terms were used to mean "gold" in those times, such as "bulawan." | 8 | Metallurgy |
Methyl phenyldiazoacetate is the organic compound with the formula CHC(N)COMe. It is a diazo derivative of methyl phenylacetate. Colloguially referred to as "phenyldiazoacetate", it is generated and used in situ after isolation as a yellow oil.
Methyl phenyldiazoacetate and many related derivatives are precursors to donor-acceptor carbenes, which can be used for cyclopropanation or to insert into C-H bonds of organic substrates. These reactions are catalyzed by dirhodium tetraacetate or related chiral complexes. Methyl phenyldiazoacetate is prepared by treating methyl phenylacetate with p-acetamidobenzenesulfonyl azide in the presence of base. | 0 | Organic Chemistry |
Vitamin A deficiency (VAD) has been linked to compromised resistance to infectious diseases. In countries where early childhood VAD is common, vitamin A supplementation public health programs initiated in the 1980s were shown to reduce the incidence of diarrhea and measles, and all-cause mortality. VAD also increases the risk of immune system over-reaction, leading to chronic inflammation in the intestinal system, stronger allergic reactions and autoimmune diseases.
Lymphocytes and monocytes are types of white blood cells of the immune system. Lymphocytes include natural killer cells, which function in innate immunity, T cells for adaptive cellular immunity and B cells for antibody-driven adaptive humoral immunity. Monocytes differentiate into macrophages and dendritic cells. Some lymphocytes migrate to the thymus where they differentiate into several types of T cells, in some instances referred to as "killer" or "helper" T cells and further differentiate after leaving the thymus. Each subtype has functions driven by the types of cytokines secreted and organs to which the cells preferentially migrate, also described as trafficking or homing.
Reviews based on in vitro and animal research describe the role that retinoic acid (RA) has in the immune system. RA triggers receptors in bone marrow, resulting in generation of new white blood cells. RA regulates proliferation and differentiation of white blood cells, the directed movement of T cells to the intestinal system, and to the up- and down-regulation of lymphocyte function. If RA is adequate, T helper cell subtype Th1 is suppressed and subtypes Th2, Th17 and iTreg (for regulatory) are induced. Dendritic cells located in intestinal tissue have enzymes that convert retinal to all-trans-retinoic acid, to be taken up by retinoic acid receptors on lymphocytes. The process triggers gene expression that leads to T cell types Th2, Th17 and iTreg moving to and taking up residence in mesenteric lymph nodes and Peyer's patches, respectively outside and on the inner wall of the small intestine. The net effect is a down-regulation of immune activity, seen as tolerance of food allergens, and tolerance of resident bacteria and other organisms in the microbiome of the large intestine. In a vitamin A deficient state, innate immunity is compromised and pro-inflammatory Th1 cells predominate. | 1 | Biochemistry |
Dated back to 1956, the first protein modified transition metal catalyst was documented. The Palladium(II) salt was absorbed onto silk fibroin fiber, reduced by hydrogen to get the first reported ArM, which can catalyze asymmetric hydrogenation.
First attempt to anchor an abiotic metal center onto a protein was reported by Whitesides using biotin-avidin interaction, making an artificial hydrogenase. The presence of avidin can significantly increase the catalytic capacity of Rhodium(I) cofactor in aqueous phosphate buffer. | 0 | Organic Chemistry |
A mold for casting an oxhide ingot was discovered in the LBA north palace at Ras Ibn Hani in Syria. It is made of fine-grained "ramleh", a shelly limestone. Archaeologists found burnt copper droplets around the mold. In spite of the questionable durability of limestone, Paul Craddock et al. concluded that limestone can be used for casting “large simple shapes” such as oxhide ingots. Evolution of carbon dioxide from the limestone would damage the metal surface that touched the mold. Thus, metal objects requiring surface detail could not be produced successfully.
This is not to say that oxhide ingots were normally cast in limestone molds. Using an experimental clay mold, Bass et al. argue that the ingot's smooth side was in contact with the mold while its rough side was exposed to the atmosphere. The roughness results from the interaction of the atmosphere and the cooling metal. | 8 | Metallurgy |
Metal arene complexes are organometallic compounds of the formula (CR)ML. Common classes are of the type (CR)ML and (CR)M. These compounds are reagents in inorganic and organic synthesis. The principles that describe arene complexes extend to related organic ligands such as many heterocycles (e.g. thiophene) and polycyclic aromatic compounds (e.g. naphthalene). | 0 | Organic Chemistry |
Outside the field of polarography, Harveys book Spectrochemical Procedures was the next earliest reference book to mention standard addition. Harveys approach, which involves the successive addition of standards, closely resembles the most commonly used method of standard addition today.
To apply this method, analysts prepare multiple solutions containing equal amounts of unknown and spike them with varying concentrations of the analyte. The amount of unknown and the total volume are the same across the standards and the only difference between the standards is the amount of analyte spiked. This leads to a linear relationship between the analyte signal and the amount of analyte added, allowing for the determination of the unknown's concentration by extrapolating the zero analyte signal. One disadvantage of this approach is that it requires sufficient amount of the unknown. When working with limiting amount of sample, an analyst might need to make a single addition, but it is generally considered a best practice to make at least two additions whenever possible.
Note that this is not limited to liquid samples. In atomic absorption spectroscopy, for example, standard additions are often used with solid as the sample.
In atomic emission spectroscopy, background signal cannot be resolved by standard addition. Thus, background signal must be subtracted from the unknown and standard intensities prior to extrapolating for the zero signal.
As this approach involves varying amount of standards added, it is often referred in the plural form as standard additions. | 3 | Analytical Chemistry |
Compared to other heteroallenes, carbodiimides are very weak electrophiles and only react with nucleophiles in the presence of catalysts, such as acids. In this way, guanidines can be prepared. As weak bases, carbodiimides bind to Lewis acids to give adducts. | 0 | Organic Chemistry |
Calcium silicide is used for manufacture of special metal alloys, e.g. for removing phosphorus and as a deoxidizer. | 8 | Metallurgy |
The exploration of challenges in understanding the effects of gene alterations on phenotypes, particularly within natural genetic diversity, is highlighted. Emphasis is placed on the potential of systems biology and advancements in genotyping/phenotyping technologies for studying complex traits. Despite progress, persistent difficulties in predicting the influence of gene alterations on phenotypic changes are acknowledged, emphasizing the ongoing need for research in this area.
Some congenital disorders (such as those affecting the muscoskeletal system) may affect physical appearance, and in some cases may also cause physical discomfort. Modifying the genes causing these congenital diseases (on those diagnosed to have mutations of the gene known to cause these diseases) may prevent this.
- Phenotypic Impacts of CRISPR-Cas9 Editing in Mice Targeting the Tyr Gene:
In a comprehensive CRISPR-Cas9 study on gene editing, the Tyr gene in mice was targeted, seeking to instigate genetic alterations. The analysis found no off-target effects across 42 subjects, observing modifications exclusively at the intended Tyr locus. Though specifics were not explicitly discussed, these alterations may potentially influence non-defined aspects, such as coat color, emphasizing the broader potential of gene editing in inducing diverse phenotype changes.
Also changes in the myostatin gene may alter appearance. | 1 | Biochemistry |
One of the largest and most diverse uses of the intercalation process by the early 2020s is in lithium-ion electrochemical energy storage, in the batteries used in many handheld electronic devices, mobility devices, electric vehicles, and utility-scale battery electric storage stations.
By 2023, all commercial Li-ion cells use intercalation compounds as active materials, and most use them in both the cathode and anode within the battery physical structure.
In 2012 three researchers, Goodenough, Yazami and Yoshino, received the 2012 IEEE Medal for Environmental and Safety Technologies for developing the intercalated lithium-ion battery and subsequently Goodenough, Whittingham, and Yoshino were awarded the 2019 Nobel Prize in Chemistry "for the development of lithium-ion batteries". | 6 | Supramolecular Chemistry |
Two groups of well-known mimicking molecules include halogenated furanones, which mimic AHL molecules, and synthetic Al peptides (AIPs), which mimic naturally occurring AIPs. These groups inhibit receptors from binding substrate or decrease the concentration of receptors in the cell. Furanones have also been found to act on AHL-dependant transcriptional activity, whereby the half life of the autoinducer-binding LuxR protein is significantly shortened. | 1 | Biochemistry |
For 1,2- and 1,4-disubstituted cyclohexanes, a cis configuration leads to one axial and one equatorial group. Such species undergo rapid, degenerate chair flipping. For 1,2- and 1,4-disubstituted cyclohexane, a trans configuration, the diaxial conformation is effectively prevented by its high steric strain. For 1,3-disubstituted cyclohexanes, the cis form is diequatorial and the flipped conformation suffers additional steric interaction between the two axial groups. trans-1,3-Disubstituted cyclohexanes are like cis-1,2- and cis-1,4- and can flip between the two equivalent axial/equatorial forms.
Cis-1,4-Di-tert-butylcyclohexane has an axial tert-butyl group in the chair conformation and conversion to the twist-boat conformation places both groups in more favorable equatorial positions. As a result, the twist-boat conformation is more stable by at as measured by NMR spectroscopy.
Also, for a disubstituted cyclohexane, as well as more highly substituted molecules, the aforementioned A values are additive for each substituent. For example, if calculating the A value of a dimethylcyclohexane, any methyl group in the axial position contributes 1.70 kcal/mol- this number is specific to methyl groups and is different for each possible substituent. Therefore, the overall A value for the molecule is 1.70 kcal/mol per methyl group in the axial position. | 4 | Stereochemistry |
The chemical intuition suggests that the glycan-binding sites may be enriched in polar amino acid residues that form non-covalent interactions, such as hydrogen bonds, with polar carbohydrates. Indeed, a statistical analysis of carbohydrate-binding pockets shows that aspartic acid and asparagine residues are present twice as often as would be predicted by chance. Surprisingly, there is an even stronger preference for aromatic amino acids: tryptophan has a 9-fold increase in prevalence, tyrosine a 3-fold one, and histidine a 2-fold increase. It has been shown that the underlying force is the interaction between the aromatic system and the in carbohydrate as shown in Figure 1. The interaction is identified if the °, the distance (distance from to ) is less than 4.5Å. | 1 | Biochemistry |
* Polyethylene glycol (PEG) hydrogels
* Poly (2-hydroxyethyl methacrylate) (PHEMA) hydrogels
Polyethylene glycol(PEG) polymers are synthetic materials that can be crosslinked to form hydrogels. PEG hydrogels are not toxic to the body, do not elicit an immune response, and have been approved by the US Food and Drug Administration for clinical use. The surfaces of PEG polymers are easily modified with peptide sequences that can attract cells for adhesion and could therefore be used for tissue regeneration.
Poly (2-hydroxyethyl methacrylate) (PHEMA) hydrogels can be combined with rosette nanotubes (RNTs). RNTs can emulate skin structures such as collagen and keratin and self-assemble when injected into the body. This type of hydrogel is being explored for use in skin regeneration and has shown promising results such as fibroblast and keratinocyte proliferation. Both of these cell types are crucial for the production of skin components. | 7 | Physical Chemistry |
The South African company Rand Refinery Limited rebuilt its smelter in 1986, incorporating two 1.5 t TBRCs and a small static reverberatory furnace for cupellation to produce doré bullion containing gold and silver. The original concept was to produce doré bullion directly from the TBRCs, but this proved impossible, as it was found impossible to take the oxidation stage to completion while maintaining temperatures at which the doré would remain molten. Consequently, the reverberatory cupellation furnace was necessary to complete the process.
In January 1993, the management team of Rand Refinery decided to review alternate technologies to replace the TBRC–reverberatory furnace circuit, with the objective of having cupellation undertaken in a single stage. After evaluating the possibility of modifying the existing TBRCs by replacing the existing lance–burner combination with a separate lance and burner, and considering complete replacement of the TBRCs with an Ausmelt top-submerged lance furnace, Rand Refinery decided to replace one of the TBRC with a 4 t BBOC. The remaining TBRC is used to treat litharge slag to recover the lead for sale.
The Rand Refinery BBOC was commissioned in 1994. The operators reported a 28% reduction in the operating costs when the BBOC’s costs were compared with those of the TBRC–reverberatory furnace combination. This included a 45% reduction in bulk oxygen costs and halving the number of operators required to run the plant. The BBOC’s refractory life was 13 weeks, compared to an average refractory life of 2 weeks for the TBRCs. Other maintenance costs also fell. | 8 | Metallurgy |
Flammability of furniture is of concern as cigarettes and candle accidents can trigger domestic fires. In 1975, California began implementing Technical Bulletin 117 (TB 117), which required that materials such as polyurethane foam used to fill furniture be able to withstand a small open flame, equivalent to a candle, for at least 12 seconds. In polyurethane foam, furniture manufacturers typically meet TB 117 with additive halogenated organic flame retardants. No other U.S. states had similar standards, but because California has such a large market, manufacturers meet TB 117 in products that they distribute across the United States. The proliferation of flame retardants, and especially halogenated organic flame retardants, in furniture across the United States is strongly linked to TB 117. When it became apparent that the risk-benefit ratio of this approach was unfavorable and industry had used falsified documentation (i.e. see David Heimbach) for the use of flame retardants, California modified TB 117 to require that fabric covering upholstered furniture meet a smolder test replacing the open flame test. Gov. Jerry Brown signed the modified TB117-2013, which became effective in 2014. | 7 | Physical Chemistry |
Electrical pulses are also used to intracellularly deliver siRNA into cells. The cell membrane is made of phospholipids which makes it susceptible to an electric field. When quick but powerful electrical pulses are initiated the lipid molecules reorient themselves, while undergoing thermal phase transitions because of heating. This results in the making of hydrophilic pores and localized perturbations in the lipid bilayer cell membrane also causing a temporary loss of semipermeability. This allows for the escape of many intracellular contents, such as ions and metabolites as well as the simultaneous uptake of drugs, molecular probes, and nucleic acids. For cells that are difficult to transfect electroporation is advantageous however cell death is more probable under this technique.
This method has been used to deliver siRNA targeting VEGF into the xenografted tumors in nude mice, which resulted in a significant suppression of tumor growth. | 1 | Biochemistry |
Flow injection techniques have proven very useful in marine science for both organic and inorganic analytes in marine animal samples/seafood. Flow Injection methods applied to the determination of amino acids (histidine, L-lysine and tyrosine), DNA/RNA, formaldehyde, histamine, hypoxanthine, polycyclic aromatic hydrocarbons, diarrheic shellfish poisoning, paralytic shellfish poisoning, succinate/glutamate, trimethylamine/ total volatile basic nitrogen, total lipid hydroperoxides, total volatile acids, uric acid, vitamin B12, silver, aluminium, arsenic, boron, calcium, cadmium, cobalt, chromium, copper, iron, gallium, mercury, indium, lithium, manganese, molibdenum, nickel, lead, antimony, selenium, tin, strontium, thallium, vanadium, zinc, nitrate/nitrite, phosphorus/phosphate and silicate. | 3 | Analytical Chemistry |
A possible link between inflammatory processes and depressive disorders has stimulated preliminary research on modafinil for its potential anti-inflammatory effects. | 4 | Stereochemistry |
Eutectic NaK (NaK-77, an alloy of 77% potassium and 23% sodium by mass) can be used as a hydraulic fluid in high-temperature and high-radiation environments, for temperature ranges of . Its bulk modulus at is 2.14 GPa, higher than of a hydraulic oil at room temperature. Its lubricity is poor, so positive-displacement pumps are unsuitable and centrifugal pumps have to be used. Addition of caesium shifts the useful temperature range to . NaK-77 was tested in hydraulic and fluidic systems for the Supersonic Low Altitude Missile. NaK may also be used to transmit forces inside high temperature pressure transducers as an alternative to mercury. | 8 | Metallurgy |
The BioCyc website contains a variety of software tools for searching, visualizing, comparing, and analyzing genome and pathway information. It includes a genome browser, and browsers for metabolic and regulatory networks. The website also includes tools for painting large-scale ("omics") datasets onto metabolic and regulatory networks, and onto the genome. | 1 | Biochemistry |
Surprisal analysis is an information-theoretical analysis technique that integrates and applies principles of thermodynamics and maximal entropy. Surprisal analysis is capable of relating the underlying microscopic properties to the macroscopic bulk properties of a system. It has already been applied to a spectrum of disciplines including engineering, physics, chemistry and biomedical engineering. Recently, it has been extended to characterize the state of living cells, specifically monitoring and characterizing biological processes in real time using transcriptional data. | 7 | Physical Chemistry |
It is used as a chelating agent:
* In Wilson's disease, a rare genetic disorder of copper metabolism, penicillamine treatment relies on its binding to accumulated copper and elimination through urine.
* Penicillamine was the second line treatment for arsenic poisoning, after dimercaprol (BAL). It is no longer recommended.
In cystinuria, a hereditary disorder in which high urine cystine levels lead to the formation of cystine stones, penicillamine binds with cysteine to yield a mixed disulfide which is more soluble than cystine.
Penicillamine has been used to treat scleroderma.
Penicillamine can be used as a disease-modifying antirheumatic drug (DMARD) to treat severe active rheumatoid arthritis in patients who have failed to respond to an adequate trial of conventional therapy, although it is rarely used today due to availability of TNF inhibitors and other agents, such as tocilizumab and tofacitinib. Penicillamine works by reducing numbers of T-lymphocytes, inhibiting macrophage function, decreasing IL-1, decreasing rheumatoid factor, and preventing collagen from cross-linking. | 4 | Stereochemistry |
The emulsion test is a simple method used educational settings to determine the presence of lipids using wet chemistry. The procedure is for the sample to be suspended in ethanol, allowing lipids present to dissolve (lipids are soluble in alcohols). The liquid (alcohol with dissolved fat) is then decanted into water. Since lipids do not dissolve in water while ethanol does, when the ethanol is diluted, it falls out of the solution to give a cloudy white emulsion. This method is not typically used in research or industry.
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Solids are often modeled as linear springs because under the action of a force they contract or elongate, and when the force is lifted, they return to their original lengths, like a spring. This is true as long as the force is in the elastic range, that is, not large enough to cause permanent or plastic deformation. Therefore, the equations given for a linear spring can also be used for elastic solid bars. Alternately, we can determine the work associated with the expansion or contraction of an elastic solid bar by replacing the pressure P by its counterpart in solids, normal stress in the work expansion
where A is the cross sectional area of the bar. | 7 | Physical Chemistry |
In contrast to the library types described above, a variety of artificial methods exist for making libraries of variant genes. Variation throughout the gene can be introduced randomly by either error-prone PCR, DNA shuffling to recombine parts of similar genes together, or transposon-based methods to introduce indels.
Alternatively, mutations can be targeted to specific codons during de novo synthesis or saturation mutagenesis to construct one or more point mutants of a gene in a controlled way. This results in a mixture of double stranded DNA molecules which represent variants of the original gene.
The expressed proteins from these libraries can then be screened for variants which exhibit favorable properties (e.g. stability, binding affinity or enzyme activity). This can be repeated in cycles of creating gene variants and screening the expression products in a directed evolution process. | 1 | Biochemistry |
Oxidative lesions are an umbrella category of lesions caused by reactive oxygen species (ROS), reactive nitrogen species (RNS), other byproducts of cellular metabolism, and exogenous factors such as ionizing or ultraviolet radiation. Byproducts of oxidative respiration are the main source of reactive species which cause a background level of oxidative lesions in the cell. DNA and RNA are both affected by this, and it has been found that RNA oxidative lesions are more abundant in humans compared to DNA. This may be due cytoplasmic RNA having closer proximity to the electron transport chain. Known oxidative lesions characterized in DNA and RNA are many in number, as oxidized products are unstable and may resolve quickly. The hydroxyl radical and singlet oxygen are common reactive oxygen species responsible for these lesions. 8-oxo-guanine (8-oxoG) is the most abundant and well characterized oxidative lesion, found in both RNA and DNA. Accumulation of 8-oxoG may cause dire damage within the mitochondria and is thought to be a key player in the aging process. RNA oxidation has direct consequences in the production of proteins. mRNA affected by oxidative lesions is still recognized by ribosome, but the ribosome will undergo stalling and dysfunction. This results in proteins having either decreased expression or truncation, leading to aggregation and general dysfunction. | 1 | Biochemistry |
Superalloys were originally iron-based and cold wrought prior to the 1940s when investment casting of cobalt base alloys significantly raised operating temperatures. The 1950s development of vacuum melting allowed for fine control of the chemical composition of superalloys and reduction in contamination and in turn led to a revolution in processing techniques such as directional solidification of alloys and single crystal superalloys.
Processing methods vary widely depending on the required properties of each item. | 8 | Metallurgy |
𝜶 and β particles are both used in the treatment of cancers, depending on the size and location of the particular tumor. Alpha particles contain overall higher energy and have a shorter path length, and have greater cytotoxic properties for this reason as compared to β particles. However, due to the shorter path length of these particles, the method of delivery needs to be extremely close to the location of the tumor. Currently, treatments using alpha-emitters exist which consist of alpha emitters attached to carrier molecules. Some examples of alpha-emitting radioligands include actinium-225, Ra-223-chloride, and Lead-212.36
β particles emit lower energy as compared to α-emitters, but they have the advantage of having longer path length. However, due to their lower energy, more β particles are required to cause damage to tumor cells as compared to α-emitters. Some examples of β-emitters include Lu-177, Y-90, and I-131. | 1 | Biochemistry |
In inorganic extended solids, valence tautomerism can manifest itself in the change of oxidation states its spatial distribution upon the change of macroscopic thermodynamic conditions. Such effects have been called charge ordering or valence mixing to describe the behavior in inorganic oxides. | 4 | Stereochemistry |
Platinum-samarium is a binary inorganic compound of platinum and samarium with the chemical formula PtSm. This intermetallic compound forms crystals. | 8 | Metallurgy |
The conjugation of 1,3-butadiene was first evaluated by Kistiakowsky, a conjugative contribution of 3.5 kcal/mol was found based on the energetic comparison of hydrogenation between conjugated species and unconjugated analogues. Rogers who used the method first applied by Kistiakowsky, reported that the conjugation stabilization of 1,3-butadiyne was zero, as the difference of ΔH between first and second hydrogenation was zero. The heats of hydrogenation (ΔH) were obtained by computational G3(MP2) quantum chemistry method.
Another group led by Houk suggested the methods employed by Rogers and Kistiakowsky was inappropriate, because that comparisons of heats of hydrogenation evaluate not only conjugation effects but also other structural and electronic differences. They obtained -70.6 kcal/mol and -70.4 kcal/mol for the first and second hydrogenation respectively by ab initio calculation, which confirmed Rogers’ data. However, they interpreted the data differently by taking into account the hyperconjugation stabilization. To quantify hyperconjugation effect, they designed the following isodesmic reactions in 1-butyne and 1-butene.
Deleting the hyperconjugative interactions gives virtual states that have energies that are 4.9 and 2.4 kcal/mol higher than those of 1-butyne and 1-butene, respectively. Employment of these virtual states results in a 9.6 kcal/mol conjugative stabilization for 1,3-butadiyne and 8.5 kcal/mol for 1,3-butadiene. | 7 | Physical Chemistry |
As established by X-ray crystallography, octachlorodimolybdate(II) anion ([MoCl]) has an eclipsed conformation. This sterically unfavorable geometry is given as evidence for a quadruple bond between the Mo centers.
Experiments such as X-ray and electron diffraction analyses, nuclear magnetic resonance, microwave spectroscopies, and more have allowed researchers to determine which cycloalkane structures are the most stable based on the different possible conformations. Another method that was shown successful is molecular mechanics, a computational method that allows the total strain energies of different conformations to be found and analyzed. It was found that the most stable conformations had lower energies based on values of energy due to bond distances and bond angles.
In many cases, isomers of alkanes with branched chains have lower boiling points than those that are unbranched, which has been shown through experimentation with isomers of CH. This is because of a combination of intermolecular forces and size that results from the branched chains. The more branches that an alkane has, the more extended its shape is; meanwhile, if it is less branched then it will have more intermolecular attractive forces that will need to be broken which is the cause of the increased boiling point for unbranched alkanes. In another case, 2,2,3,3-tetramethylbutane is shaped more like an ellipsoid causing it to be able to form a crystal lattice which raises the melting point of the molecule because it will take more energy to transition from a solid to a liquid state. | 4 | Stereochemistry |
The impact of ultraviolet radiation on human health has implications for the risks and benefits of sun exposure and is also implicated in issues such as fluorescent lamps and health. Getting too much sun exposure can be harmful, but in moderation, sun exposure is beneficial. | 5 | Photochemistry |
The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in an aqueous solution and to be excluded by water. The word hydrophobic literally means "water-fearing", and it describes the segregation of water and nonpolar substances, which maximizes the entropy of water and minimizes the area of contact between water and nonpolar molecules. In terms of thermodynamics, the hydrophobic effect is the free energy change of water surrounding a solute. A positive free energy change of the surrounding solvent indicates hydrophobicity, whereas a negative free energy change implies hydrophilicity.
The hydrophobic effect is responsible for the separation of a mixture of oil and water into its two components. It is also responsible for effects related to biology, including: cell membrane and vesicle formation, protein folding, insertion of membrane proteins into the nonpolar lipid environment and protein-small molecule associations. Hence the hydrophobic effect is essential to life. Substances for which this effect is observed are known as hydrophobes. | 6 | Supramolecular Chemistry |
Adverse events include hypoglycemia, pruritis (itching), nasopharyngitis, headache, and upper respiratory tract infection. It may also cause joint pain that can be severe and disabling. Like other DDP-4 inhibitors, alogliptin is weight-neutral.
A 2014 letter to the editor claimed alogliptin is not associated with increased risk of cardiovascular events. In April 2016, the U.S. Food and Drug Administration (FDA) added a warning about increased risk of heart failure. | 4 | Stereochemistry |
In chemistry, π-effects or π-interactions are a type of non-covalent interaction that involves π systems. Just like in an electrostatic interaction where a region of negative charge interacts with a positive charge, the electron-rich π system can interact with a metal (cationic or neutral), an anion, another molecule and even another π system. Non-covalent interactions involving π systems are pivotal to biological events such as protein-ligand recognition. | 6 | Supramolecular Chemistry |
Biological crosstalk refers to instances in which one or more components of one signal transduction pathway affects another. This can be achieved through a number of ways with the most common form being crosstalk between proteins of signaling cascades. In these signal transduction pathways, there are often shared components that can interact with either pathway. A more complex instance of crosstalk can be observed with transmembrane crosstalk between the extracellular matrix (ECM) and the cytoskeleton. | 1 | Biochemistry |
Barium has a diffuse series running from infrared to ultraviolet with wavelengths at 25515.7, 23255.3, 22313.4; 5818.91, 5800.30, 5777.70; 4493.66, 4489.00; 4087.31, 4084.87; 3898.58, 3894.34; 3789.72, 3788.18; 3721.17, and 3720.85 Å | 7 | Physical Chemistry |
TIVA tags are created initially via solid-phase synthesis with the cell-penetrating peptide conjugated afterwards. The functional components of the tag can be summarized as following:
* Biotin: binds to streptavidin beads for tag isolation.
* Cy3 fluorophore: used to validated cleavage of photocleavable linker. If cleaved, cell will appear green upon exposure to 514 nm light.
* Cy5 fluorophore: used to validate uptake into cells. If uptake is successful, and if Cy5 is not yet cleaved from the TIVA tag, energy from a 514 nm light will be absorbed via FRET from Cy3 to Cy5, where cells that have taken up the TIVA will appear red.
* PolyU 18-mer oligonucleotide: used to bind mRNA via complementary base pairing of their polyadenylated tails. Before cleavage of photocleavable linkers, it is caged by complementary base pairing to two polyA 7-mer oligonucleotides.
* PolyA 7-mer oligonucleotides: before the cleavage of photocleavable linkers, 2 polyA 7-mer molecules conjugate to polyU oligonucleotides to cage the TIVA tag, and thus prevent it from binding mRNA molecules. After photocleavable linkers are cleaved, the melting temperature decreases from 59 °C to less than 25 °C, leading to the disassociation of the PolyA 7-mer oligonucleotides from the TIVA tag.
* Photocleavable linker: links and stabilizes Cy5 fluorophore and PolyA 7-mer oligonucleotides to the TIVA tag. It is cleaved upon photoactivation.
* Cell-penetrating peptide CPP: guides the TIVA tag through cell membranes into tissues. It is linked to the TIVA tag by a disulphide bond that is cleaved once exposed to extracellular environment. | 1 | Biochemistry |
Sulfuric acid is used for a variety of other purposes in the chemical industry. For example, it is the usual acid catalyst for the conversion of cyclohexanone oxime to caprolactam, used for making nylon. It is used for making hydrochloric acid from salt via the Mannheim process. Much is used in petroleum refining, for example as a catalyst for the reaction of isobutane with isobutylene to give isooctane, a compound that raises the octane rating of gasoline (petrol). Sulfuric acid is also often used as a dehydrating or oxidizing agent in industrial reactions, such as the dehydration of various sugars to form solid carbon. | 7 | Physical Chemistry |
Hormone producing cells are found in the endocrine glands, such as the thyroid gland, ovaries, and testes. Hormonal signaling involves the following steps:
# Biosynthesis of a particular hormone in a particular tissue.
# Storage and secretion of the hormone.
# Transport of the hormone to the target cell(s).
# Recognition of the hormone by an associated cell membrane or intracellular receptor protein.
# Relay and amplification of the received hormonal signal via a signal transduction process: This then leads to a cellular response. The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a downregulation in hormone production. This is an example of a homeostatic negative feedback loop.
# Breakdown of the hormone.
Exocytosis and other methods of membrane transport are used to secrete hormones when the endocrine glands are signaled. The hierarchical model is an oversimplification of the hormonal signaling process. Cellular recipients of a particular hormonal signal may be one of several cell types that reside within a number of different tissues, as is the case for insulin, which triggers a diverse range of systemic physiological effects. Different tissue types may also respond differently to the same hormonal signal. | 1 | Biochemistry |
Defect sites can interfere with the stability of metal oxide surfaces, so it is important to locate and determine methods to control these sites. Oxides exhibit an abundance of point defect sites. In rocksalt surfaces, oxygen and metal cation vacancies are the most common point defects. The vacancies are produced by electron bombardment and annealing to extremely high temperatures. However, oxygen vacancies are more common and have a greater impact than metal cation vacancies. Oxygen vacancies cause reduction in between surface cations, which significantly affect the electronic energy levels. Steps and kinks are two other defects that impact rocksalt surfaces. These structural defects reduce the coordination environment of the four adjacent surface cations from 5 to 4.
In rutile surfaces, the most common type of defect is oxygen vacancies. There are two types of oxygen vacancies, which result from either the removal of a bridging O ions or the removal of an inplane O ion. Both of these will reduce the coordination of the surface cations. | 7 | Physical Chemistry |
Between 1857 and 1865, Macadam served as honorary secretary to the Exploration Committee of the Royal Society of Victoria, which organised the Burke and Wills expedition.
The expedition was organised by the society with the aim of crossing the continent of Australia from the south to the north coasts, map it, and collect scientific data and specimens. At that time, most of the interior of Australia had not been explored by the European settlers and was unknown to them.
In 1860–61, Robert O'Hara Burke and William John Wills led the expedition of 19 men with that intention, crossing Australia from Melbourne in the south, to the Gulf of Carpentaria in the north, a distance around 2,000 miles.
Three men ultimately travelled over 3,000 miles from Melbourne to the shores of the Gulf of Carpentaria and back to the Depot Camp at Cooper Creek. Seven men died in the attempt, including the leaders Burke and Wills. Of the four men who reached the north coast, only one, John King, survived with the help of the indigenous people to return to Melbourne.
This expedition became the first to cross the Australian continent. It was of great importance to the subsequent development of Australia and could be compared in importance to the Lewis and Clark Expedition overland to the North American Pacific Coast to the development of the United States.
After the heavy death toll of the expedition, initial criticism fell on the Royal Society, but it became clear that their foresight could not have prevented the deaths and this was then widely recognised when it became known that as Secretary of the Exploration Committee of the Burke and Wills expedition, Dr. Macadam had insisted on adequate provisions for their safety. | 3 | Analytical Chemistry |
Frequency domain (FD) sensor is an instrument developed for measuring soil moisture content. The instrument has an oscillating circuit, the sensing part of the sensor is embedded in the soil, and the operating frequency will depend on the value of soil's dielectric constant. | 7 | Physical Chemistry |
Incoherent grain boundaries are those in which there is a significant mismatch in crystallographic orientation between adjacent grains. This results in a discontinuity in the crystal lattice across the boundary, and the formation of a variety of defects such as dislocations, stacking faults, and grain boundary ledges.The presence of these defects creates a barrier to the motion of dislocations and leads to a strengthening effect. This effect is more pronounced in materials with smaller grain sizes, as there are more grain boundaries to impede dislocation motion. In addition to the barrier effect, incoherent grain boundaries can also act as sources and sinks for dislocations. This can lead to localized plastic deformation and affect the overall mechanical response of a material.
When small particles are formed through precipitation from supersaturated solid solutions, their interphase boundaries may not be coherent with the matrix. In such cases, the atomic bonds do not match up across the interface and there is a misfit between the particle and the matrix. This misfit gives rise to a non-coherency strain, which can cause the formation of dislocations at the grain boundary. As a result, the properties of the small particle can be different from those of the matrix. The size at which non-coherent grain boundaries form depends on the lattice misfit and the interfacial energy. | 8 | Metallurgy |
CDw17 antigen is a lactosylceramide, a class of glycosphingolipids found in microdomains on the plasma layers of numerous cells.
The enzyme A4GALT acts upon it, aiding transfer of galactose to lactosylceramide to form globotriaosylceramide. | 1 | Biochemistry |
Solid-phase epitaxy (SPE) is a transition between the amorphous and crystalline phases of a material. It is usually produced by depositing a film of amorphous material on a crystalline substrate, then heating it to crystallize the film. The single-crystal substrate serves as a template for crystal growth. The annealing step used to recrystallize or heal silicon layers amorphized during ion implantation is also considered to be a type of solid phase epitaxy. The impurity segregation and redistribution at the growing crystal-amorphous layer interface during this process is used to incorporate low-solubility dopants in metals and silicon. | 3 | Analytical Chemistry |
The genome of the P1 phage is maintained as a low copy number plasmid in the bacterium. The relatively large size of the plasmid requires it to keep a low copy number lest it become too large a metabolic burden while it is a lysogen. As there is usually only one copy of the plasmid per bacterial genome, the plasmid stands a high chance of not being passed to both daughter cells. The P1 plasmid combats this by several methods:
* The plasmid replication is tightly regulated by a RepA protein dependent mechanism. This is similar to the mechanism used by several other plasmids. It ensure that the plasmid divides in step with the host genome.
* Interlocked plasmids are quickly unlinked by Cre-lox recombination
* The plasmid encodes a plasmid addiction system that kills daughter cells that lose the plasmid. It consists of a stable protein toxin and an antitoxin that reversibly binds to and neutralizes it. Cells that lose the plasmid get killed as the antitoxin gets degraded faster than the toxin. | 1 | Biochemistry |
A blocked isocyanate can be added to materials that would normally react with the isocyanate such as polyols. They do not react at normal ambient room temperature. A formulation containing a blocked isocyanate is a single component material (and thus usually considered more convenient) but reacts like a two-component product but will not react until heated to the temperature required for activation which varies depending on the blocking agent. The shelf lives when stored at ambient temperature have been reported as good. On heating up to the activation temperature, cure can be as short as 20 minutes depending on the blocking agent and other formulation parameters.
Blocked isocyanates are particularly useful in products with a dual cure mechanisms. As an example, Ultraviolet light initiates the polymerization of an acrylate based polymer that contains hydroxy groups on the polymer backbone. The system would also contain an isocyanate blocked with a malonate. This is now a one-component system. When heat is applied, the polymerization is initiated. Higher temperatures then unblock the isocyanate, allowing the cure and crosslinking of the urethane. | 0 | Organic Chemistry |
The photochemical mechanisms that give rise to the ozone layer were discovered by the British physicist Sydney Chapman in 1930. Ozone in the Earth's stratosphere is created by ultraviolet light striking ordinary oxygen molecules containing two oxygen atoms (O), splitting them into individual oxygen atoms (atomic oxygen); the atomic oxygen then combines with unbroken O to create ozone, O. The ozone molecule is unstable (although, in the stratosphere, long-lived) and when ultraviolet light hits ozone it splits into a molecule of O and an individual atom of oxygen, a continuing process called the ozone-oxygen cycle. Chemically, this can be described as:
About 90 percent of the ozone in the atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about , where they range from about 2 to 8 parts per million. If all of the ozone were compressed to the pressure of the air at sea level, it would be only thick. | 5 | Photochemistry |
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