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An electrolyte is a medium containing ions that are electrically conductive through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dissolving, the substance separates into cations and anions, which disperse uniformly throughout the solvent. Solid-state electrolytes also exist. In medicine and sometimes in chemistry, the term electrolyte refers to the substance that is dissolved.
Electrically, such a solution is neutral. If an electric potential is applied to such a solution, the cations of the solution are drawn to the electrode that has an abundance of electrons, while the anions are drawn to the electrode that has a deficit of electrons. The movement of anions and cations in opposite directions within the solution amounts to a current. Some gases, such as hydrogen chloride (HCl), under conditions of high temperature or low pressure can also function as electrolytes. Electrolyte solutions can also result from the dissolution of some biological (e.g., DNA, polypeptides) or synthetic polymers (e.g., polystyrene sulfonate), termed "polyelectrolytes", which contain charged functional groups. A substance that dissociates into ions in solution or in the melt acquires the capacity to conduct electricity. Sodium, potassium, chloride, calcium, magnesium, and phosphate in a liquid phase are examples of electrolytes.
In medicine, electrolyte replacement is needed when a person has prolonged vomiting or diarrhea, and as a response to sweating due to strenuous athletic activity. Commercial electrolyte solutions are available, particularly for sick children (such as oral rehydration solution, Suero Oral, or Pedialyte) and athletes (sports drinks). Electrolyte monitoring is important in the treatment of anorexia and bulimia.
In science, electrolytes are one of the main components of electrochemical cells.
In clinical medicine, mentions of electrolytes usually refer metonymically to the ions, and (especially) to their concentrations (in blood, serum, urine, or other fluids). Thus, mentions of electrolyte levels usually refer to the various ion concentrations, not to the fluid volumes. | 7 | Physical Chemistry |
Electroless deposition (ED) or electroless plating is defined as the autocatalytic process through which metals and metal alloys are deposited onto nonconductive surfaces.These nonconductive surfaces include plastics, ceramics, and glass etc., which can then become decorative, anti-corrosive, and conductive depending on their final functions. Electroless deposition is a chemical processes that create metal coatings on various materials by autocatalytic chemical reduction of metal cations in a liquid bath. | 8 | Metallurgy |
Methionine sulfoxide (MetO), the oxidized form of the amino acid methionine (Met), increases with age in body tissues, which is believed by some to contribute to biological ageing. Oxidation of methionine residues in tissue proteins can cause them to misfold or otherwise render them dysfunctional. Uniquely, the methionine sulfoxide reductase (Msr) group of enzymes act with thioredoxin to catalyze the enzymatic reduction and repair of oxidized methionine residues. Moreover, levels of methionine sulfoxide reductase A (MsrA) decline in aging tissues in mice and in association with age-related disease in humans. There is thus a rationale for thinking that by maintaining the structure, increased levels or activity of MsrA might retard the rate of aging.
Indeed, transgenic Drosophila (fruit flies) that overexpress methionine sulfoxide reductase show extended lifespan. However, the effects of MsrA overexpression in mice were ambiguous. MsrA is found in both the cytosol and the energy-producing mitochondria, where most of the bodys endogenous free radicals are produced. Transgenically increasing the levels of MsrA in either the cytosol or the mitochondria had no significant effect on lifespan assessed by most standard statistical tests, and may possibly have led to early deaths in the cytosol-specific mice, although the survival curves appeared to suggest a slight increase in maximum (90%) survivorship, as did analysis using Boschloos Exact test, a binomial test designed to test greater extreme variation.
The oxidation of methionine serves as a switch that deactivates certain protein activities such as E.coli ribosomal protein, L12. Proteins with great amount of methionine residues tend to exist within the lipid bilayer as methionine is one of the most hydrophobic amino acids. Those methionine residues that are exposed to the aqueous exterior thus are vulnerable to oxidation. The oxidized residues tend to be arrayed around the active site and may guard access to this site by reactive oxygen species. Once oxidized, the MetO residues are reduced back to methionine by the enzyme methionine sulfoxide reductase. Thus, an oxidation–reduction cycle occurs in which exposed methionine residues are oxidized (e.g., by HO) to methionine sulfoxide residues, which are subsequently reduced.
Methionine(protein)+ HO→ Methionine Sulfoxide(protein)+ HO
Methionine Sulfoxide(protein)+ NADPH+H→ Methionine(protein)+ NADP+HO | 1 | Biochemistry |
The physical properties of compounds such as melting point and boiling point change when other compounds are added. Together they are called colligative properties. There are several ways to quantify the amount of one compound dissolved in the other compounds collectively called concentration. Examples include molarity, volume fraction, and mole fraction.
The properties of ideal solutions can be calculated by the linear combination of the properties of its components. If both solute and solvent exist in equal quantities (such as in a 50% ethanol, 50% water solution), the concepts of "solute" and "solvent" become less relevant, but the substance that is more often used as a solvent is normally designated as the solvent (in this example, water). | 7 | Physical Chemistry |
In November 1945, Smolková-Keulemansová's dream to return to Prague and continue her studies became a reality. She completed grammar school and realized that her biggest struggle in her supplementary exams was chemistry, so she began to study chemistry at Charles University in Prague, leading to her lifelong devotion and love for the subject. She graduated from the Faculty of Natural Sciences at Charles University in 1952. | 3 | Analytical Chemistry |
In higher plants thylakoids are organized into a granum-stroma membrane assembly. A granum (plural grana) is a stack of thylakoid discs. Chloroplasts can have from 10 to 100 grana. Grana are connected by stroma thylakoids, also called intergranal thylakoids or lamellae. Grana thylakoids and stroma thylakoids can be distinguished by their different protein composition. Grana contribute to chloroplasts' large surface area to volume ratio. A recent electron tomography study of the thylakoid membranes has shown that the stroma lamellae are organized in wide sheets perpendicular to the grana stack axis and form multiple right-handed helical surfaces at the granal interface. Left-handed helical surfaces consolidate between the right-handed helices and sheets. This complex network of alternating helical membrane surfaces of different radii and pitch was shown to minimize the surface and bending energies of the membranes. This new model, the most extensive one generated to date, revealed that features from two, seemingly contradictory, older models coexist in the structure. Notably, similar arrangements of helical elements of alternating handedness, often referred to as "parking garage" structures, were proposed to be present in the endoplasmic reticulum and in ultradense nuclear matter. This structural organization may constitute a fundamental geometry for connecting between densely packed layers or sheets. | 5 | Photochemistry |
The ribosomal protein S1 binds to adenine sequences upstream of the RBS. Increasing the concentration of adenine upstream of the RBS will increase the rate of ribosome recruitment. | 1 | Biochemistry |
Two-step thermochemical cycles, often involving metal oxides, can be divided into two categories depending on the nature of the reaction: volatile and non-volatile. Volatile cycles utilize metal species that sublime during the reduction of the metal oxides, and non-volatile cycles can be further categorized into stoichiometric cycles and non-stoichiometric cycles. During the reduction half-cycle of the stochiometric cycle, the metal oxide is reduced and forms a new metal oxide with different oxidation states (FeO → 3FeO + 1/2 O); a non-stochiometric cycle's reduction of the metal oxide will produce vacancies, often oxygen vacancies, but the crystal structure remains stable and only a portion of the metal atoms change their oxidation state (CeO → CeO + δ/2 O). | 7 | Physical Chemistry |
In some archaea, i.e. members of the Methanobacteriales and in the genus Methanopyrus, pseudopeptidoglycan (pseudomurein) has been found. In pseudopeptidoglycan the sugar residues are β-(1,3) linked N-acetylglucosamine and N-acetyltalosaminuronic acid. This makes the cell walls of such archaea insensitive to lysozyme. The biosynthesis of pseudopeptidoglycan has been described. | 1 | Biochemistry |
In the brewing industry flocculation has a different meaning. It is a very important process in fermentation during the production of beer where cells form macroscopic flocs. These flocs cause the yeast to sediment or rise to the top of a fermentation at the end of the fermentation. Subsequently, the yeast can be collected (cropped) from the top (ale fermentation) or the bottom (lager fermentation) of the fermenter in order to be reused for the next fermentation.
Yeast flocculation is primarily determined by the calcium concentration, often in the 50-100ppm range. Calcium salts can be added to cause flocculation, or the process can be reversed by removing calcium by adding phosphate to form insolubable calcium phosphate, adding excess sulfate to form insoluble calcium sulfate, or adding EDTA to chelate the calcium ions. While it appears similar to sedimentation in colloidal dispersions, the mechanisms are different. | 8 | Metallurgy |
ATSDR conducts surveillance by maintaining projects to collect and analyze information on diseases and chemical exposures. Research using that information and data can then be used to prevent future and control injury, disease, and death. | 1 | Biochemistry |
Plastocyanin was the first of the blue copper proteins to be characterised by X-ray crystallography. It features an eight-stranded antiparallel β-barrel containing one copper center.
Structures of the protein from poplar, algae, parsley, spinach, and French bean plants have been characterized crystallographically. In all cases the binding site is generally conserved. Bound to the copper center are four ligands: the imidazole groups of two histidine residues (His37 and His87), the thiolate of Cys84 and the thioether of Met92. The geometry of the copper binding site is described as a ‘distorted trigonal pyramidal’. The Cu-S (cys) contact is much shorter (207 picometers) than Cu-S (met) (282 pm) bond. The elongated Cu-thioether bond appears to destabilise the Cu state thereby enhancing its oxidizing power. The blue colour (597 nm peak absorption) is assigned to a charge transfer transition from S to Cu-y</sub>.
In the reduced form of plastocyanin, His-87 becomes protonated.
While the molecular surface of the protein near the copper binding site varies slightly, all plastocyanins have a hydrophobic surface surrounding the exposed histidine of the copper binding site. In plant plastocyanins, acidic residues are located on either side of the highly conserved tyrosine-83. Algal plastocyanins, and those from vascular plants in the family Apiaceae, contain similar acidic residues but are shaped differently from those of plant plastocyanins—they lack residues 57 and 58. In cyanobacteria, the distribution of charged residues on the surface is different from eukaryotic plastocyanins and variations among different bacterial species is large. Many cyanobacterial plastocyanins have 107 amino acids. Although the acidic patches are not conserved in bacteria, the hydrophobic patch is always present. These hydrophobic and acidic patches are believed to be the recognition/binding sites for the other proteins involved in electron transfer. | 5 | Photochemistry |
Silicothermic reactions are thermic chemical reactions using silicon as the reducing agent at high temperature (800-1400°C). The most prominent example is the Pidgeon process for reducing magnesium metal from ores. Other processes include the Bolzano process and the magnetherm process. All three are commercially used for magnesium production.
The silicothermic process for magnesium production was developed commercially in Canada during the Second World War by Lloyd Montgomery Pidgeon. | 8 | Metallurgy |
Vibrational transitions and optical phonon transitions take place in the infrared part of the spectrum, at wavelengths of around 1-30 micrometres. | 7 | Physical Chemistry |
There are two main variants of thermochromic ink, one composed of leuco dyes and one composed of liquid crystals. For both types of ink, the chemicals need to be contained within capsules around 3 to 5 microns long. This protects the dyes and crystals from mixing with other chemicals that might affect the functionality of the ink. | 7 | Physical Chemistry |
Marine biogeochemical cycles are biogeochemical cycles that occur within marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. These biogeochemical cycles are the pathways chemical substances and elements move through within the marine environment. In addition, substances and elements can be imported into or exported from the marine environment. These imports and exports can occur as exchanges with the atmosphere above, the ocean floor below, or as runoff from the land.
There are biogeochemical cycles for the elements calcium, carbon, hydrogen, mercury, nitrogen, oxygen, phosphorus, selenium, and sulfur; molecular cycles for water and silica; macroscopic cycles such as the rock cycle; as well as human-induced cycles for synthetic compounds such as polychlorinated biphenyl (PCB). In some cycles there are reservoirs where a substance can be stored for a long time. The cycling of these elements is interconnected.
Marine organisms, and particularly marine microorganisms are crucial for the functioning of many of these cycles. The forces driving biogeochemical cycles include metabolic processes within organisms, geological processes involving the Earth's mantle, as well as chemical reactions among the substances themselves, which is why these are called biogeochemical cycles. While chemical substances can be broken down and recombined, the chemical elements themselves can be neither created nor destroyed by these forces, so apart from some losses to and gains from outer space, elements are recycled or stored (sequestered) somewhere on or within the planet. | 9 | Geochemistry |
Although IP Standard test methods exist, the more common methods for BN are ASTM standardised, such as the potentiometric titration for fresh oils (Test method BN ASTM D2896). A sample is typically dissolved in a pre-mixed solvent of chlorobenzene and acetic acid and titrated with standardised perchloric acid in glacial acetic acid for fresh oil samples. The end point is detected using a glass electrode which is immersed in an aqueous solution containing the sample, and connected to a voltmeter/potentiometer. This causes an ion exchange in the outer solvated layer at the glass membrane, so a change in potential is generated which can be measured by the electrode. When the end point of the chemical reaction is reached, which is shown by an inflection point on the titration curve using a specified detection system, the amount of titrant required is used to generate a result which is reported in milligrams of potassium hydroxide equivalent per gram of sample (mg of KOH/g). Potentiometric titration for used oils (Test method BN ASTM D4739): a sample is dissolved in a solvent mixture of Toluene/ Propan-2-ol /Chloroform with 0.5% deionised water and then titrated with standardised alcoholic hydrochloric acid. The detection system is equivalent to the fresh oil method. The used oil method uses a less polar solvent and weaker titrant, which will not dissolve the wear metals produced during operation, hence it is more suitable to analyse used oils. | 3 | Analytical Chemistry |
In 2006 a new polymorph of maleic acid was discovered, 124 years after the first crystal form was studied. Maleic acid is manufactured on an industrial scale in the chemical industry. It forms salt found in medicine. The new crystal type is produced when a co-crystal of caffeine and maleic acid (2:1) is dissolved in chloroform and when the solvent is allowed to evaporate slowly. Whereas form I has monoclinic space group P2/c, the new form has space group Pc. Both polymorphs consist of sheets of molecules connected through hydrogen bonding of the carboxylic acid groups: in form I, the sheets alternate with respect of the net dipole moment, while in form II, the sheets are oriented in the same direction. | 3 | Analytical Chemistry |
Snf3 is a plasma membrane protein in yeasts that consists of 12 (2x6) transmembrane domains, like the homologous glucose transporters. Its structure is distinct from the homologous transporters in particular by a long C-terminal tail which is predicted to reside in the cytoplasm.
The long C-terminal tail plays an important role in glucose signaling and is probably the signaling domain itself. A soluble version of the C-terminal tail alone is sufficient to induce glucose transport.
All glucose transporters including Snf3 contain an arginine residue situated in a cytoplasmic loop preceding the fifth transmembrane domain. If this position is mutated, Snf3 adopts a state of constant glucose induction irrespective of whether there are nutrients present or not; this suggests an involvement in the glucose sensing process. | 1 | Biochemistry |
Front-of-house testing provides testing services to clients at events. It provides real-time, as-you-wait results. An example is the testing at BOOM festival in Portugal where drug testers are legally allowed to handle samples. Where testers are not allowed to handle samples, for fear of breaking laws around possession, clients themselves must handle the substance to be tested. Examples of this model are KnowYourStuffNZ in New Zealand. | 3 | Analytical Chemistry |
Biofumigation is a method of pest control in agriculture, a variant of fumigation where the gaseous active substance—fumigant—is produced by decomposition of plant material freshly chopped and buried in the soil for this purpose.
Plants from the Brassicaceae family (e.g., mustards, cauliflower, and broccoli) are primarily used due to their high glucosinolate content; in the process of decomposition, glucosinolates are broken down to volatile isothiocyanates which are toxic to soil organisms such as bacteria, fungi and nematodes, but less toxic and persistent in the environment than synthetic fumigants. Alternatively, grasses such as sorghum can be used, in which case hydrogen cyanide is produced to similar effect.
The method consists of mowing and chopping the plants during flowering to ensure maximum glucosinolate content and speed up decomposition. The ground needs to be irrigated to field capacity, after which the chopped material is incorporated into the top layer and covered with impermeable film to prevent the gas from escaping. After three or four weeks, the film is removed and the ground is ready for planting 24 hours later. Burying biofumigant crops after the growing season to plant cash crops normally next year may in theory lead to buildup of active substance in the soil after a few cycles of crop rotation, but direct short-term suppression of pests is not notable in this case.
The method can be used as a more sustainable and environment-friendly alternative to classic fumigation and other chemical pest control methods. Additionally, it can serve to replenish the nutrient content of the soil and promote growth of beneficial organisms. On the other hand, it requires changes in cultivation practice due to the time needed for the method to take effect, can be costly if biofumigant-producing plants need to be brought from elsewhere (i. e. if they are not used in crop rotation to be chopped and buried on site), and is difficult to standardize due to varying active substance content in different cultivars. | 2 | Environmental Chemistry |
Nitrile groups in organic compounds can undergo a variety of reactions depending on the reactants or conditions. A nitrile group can be hydrolyzed, reduced, or ejected from a molecule as a cyanide ion. | 0 | Organic Chemistry |
*2.B.1 The Valinomycin Carrier Family
*2.B.2 The Monensin Family
*2.B.3 The Nigericin Family
*2.B.4 The Macrotetrolide Antibiotic (MA) Family
*2.B.5 The Macrocyclic Polyether (MP) Family
*2.B.6 The Ionomycin Family
*2.B.7 The Transmembrane α-helical Peptide Phospholipid Translocation (TMP-PLT) Family
*2.B.8 The Bafilomycin A1 (Bafilomycin) Family
*2.B.9 The Cell Penetrating Peptide (CPP) Functional Family
*2.B.10 The Synthetic CPP, Transportan Family
*2.B.11 The Calcimycin or A23187 Carrier-type Ionophore Family
*2.B.12 The Salinomycin Family
*2.B.13 The Tetrapyrrolic Macrocyclic Anion Antiporter (TPMC-AA) Family
*2.B.14 The Lasalocid A or X-537A Ionophore (Lasalocid) Family
*2.B.15 The Tris-thiourea Tripodal-based Chloride Carrier (TTT-CC) Family
*2.B.16 The Halogen-bond-containing Compound Anion Carrier (HCAC) Family
*2.B.17 The Isophthalaminde Derivative H:Cl Co-transporter (IDC) Family
*2.B.18 The Pyridine-2,6-Dicarboxamine Derivative (PDCA) H+:Cl Co-transporter Family
*2.B.19 The Calix(4)pyrrole Derivative (C4P) Family
*2.B.20 The Prodigiosin (Prodigiosin) Chloride/Bicarbonate Exchanger Family
*2.B.21 The ortho-Phenylenediamine-bis-Urea Derivative Anion Transporter (oPDA-U) Family
*2.B.22 The Imidazolium-functionalized Anion Transporter (IAT) Family
*2.B.23 The Homotetrameric Transmembrane Zn/Co:Proton Synthetic Antiporter, Rocker (Rocker) Family
*2.B.24 The Anion Carrier (BBP-AC) Family
*2.B.25 The Peptide-mediated Lipid Flip-Flop (PLFF) Family
*2.B.26 The Conjugate (BIBCC) Family
*2.B.27 The Tris-Urea Anion Transporter Family
*2.B.29 The Anionophoric Marine Alkaloid Tambjamine Family | 1 | Biochemistry |
Biomarkers of susceptibility are indicators of the natural characteristics of an organism that make it more susceptible to the effects of an exposure to a chemical. They can help define what sensitivities are more susceptible as well as critical times when exposures can be most detrimental. For example, the exhalation strength of an asthmatic will indicate how susceptible that person would be to the respiratory effects of exposure to brevetoxin, the toxic compound produced during a red tide. | 2 | Environmental Chemistry |
The International Tables for Crystallography is an eight-book series that outlines the standard notations for formatting, describing and testing crystals. The series contains books that covers analysis methods and the mathematical procedures for determining organic structure through x-ray crystallography, electron diffraction, and neutron diffraction. The International tables are focused on procedures, techniques and descriptions and do not list the physical properties of individual crystals themselves. Each book is about 1000 pages and the titles of the books are:
:Vol A - Space Group Symmetry,
:Vol A1 - Symmetry Relations Between Space Groups,
:Vol B - Reciprocal Space,
:Vol C - Mathematical, Physical, and Chemical Tables,
:Vol D - Physical Properties of Crystals,
:Vol E - Subperiodic Groups,
:Vol F - Crystallography of Biological Macromolecules, and
:Vol G - Definition and Exchange of Crystallographic Data. | 3 | Analytical Chemistry |
The azo group in DEAD is a Michael acceptor. In the presence of a copper(II) catalyst, DEAD assists conversion of β-keto esters to the corresponding hydrazine derivatives.
The substitution of boronic acid esters proceeds similarly: | 0 | Organic Chemistry |
Giuliana Tesoro (née Cavaglieri) (June 1, 1921 – September 29, 2002) was an Italian-born American chemist who earned more than 125 patents, with her most notable consisting of improvements in fabric comfort, practicality, and flame resistance. | 0 | Organic Chemistry |
Methanesulfonyl chloride is a precursor to many compounds because it is highly reactive. It is an electrophile, functioning as a source of the "CHSO" synthon. | 0 | Organic Chemistry |
Trace amounts of benzene are found in petroleum and coal. It is a byproduct of the incomplete combustion of many materials. For commercial use, until World War II, much of benzene was obtained as a by-product of coke production (or "coke-oven light oil") for the steel industry. However, in the 1950s, increased demand for benzene, especially from the growing polymers industry, necessitated the production of benzene from petroleum. Today, most benzene comes from the petrochemical industry, with only a small fraction being produced from coal. Benzene has been detected on Mars. | 2 | Environmental Chemistry |
The compounds are generally prepared by salt metathesis reactions of alkali-metal cyclopentadienyl compounds with transition metal chlorides. Sodium cyclopentadienide (NaCp) and lithium cyclopentadienide are commonly used. Trimethylsilylcyclopentadiene cyclopentadienylthallium (CpTl) are alternative sources. For the preparation of some particularly robust complexes, e.g. nickelocene, cyclopentadiene is employed in the presence of a conventional base such as KOH. When only a single Cp ligand is installed, the other ligands typically carbonyl, halogen, alkyl, and hydride.
Most Cp complexes are prepared by substitution of preformed Cp complexes by replacement of halide, CO, and other simple ligands. | 0 | Organic Chemistry |
Finnish lichenologist William Nylander is generally considered to have been the first to demonstrate the use of chemicals to help with lichen identification. In papers published in 1866, he suggested spot tests using KOH and bleaching powder to get characteristic colour reactions—typically yellow, red, or green. In these studies he showed, for example, that the lichens now known as Cetrelia cetrarioides and C. olivetorum could be distinguished as distinct species due to their different colour reactions: C+ red in the latter, contrasted with no reaction in the former. Nylander showed how KOH could be used to distinguish between the lookalikes Xanthoria candelaria and Candelaria concolor because the presence of parietin in the former species results in a strong colour reaction. He also knew that in some cases the lichen chemicals were not evenly distributed throughout the cortex and the medulla due to the differing colour reactions on these areas. In the mid-1930s, Yasuhiko Asahina created the test with para-phenylendiamine, which gives yellow to red reactions with secondary metabolites that have a free aldehyde group. This spot test was later shown to be particularly useful in the taxonomy of the family Cladoniaceae. | 3 | Analytical Chemistry |
Shape-memory alloys are typically made by casting, using vacuum arc melting or induction melting. These are specialist techniques used to keep impurities in the alloy to a minimum and ensure the metals are well mixed. The ingot is then hot rolled into longer sections and then drawn to turn it into wire.
The way in which the alloys are "trained" depends on the properties wanted. The "training" dictates the shape that the alloy will remember when it is heated. This occurs by heating the alloy so that the dislocations re-order into stable positions, but not so hot that the material recrystallizes. They are heated to between and for 30 minutes, shaped while hot, and then are cooled rapidly by quenching in water or by cooling with air. | 8 | Metallurgy |
A diazaquinone is a chemical compound that has an heterocyclic aromatic core including two consecutive doubly-bonded nitrogen atoms , with the two carbon units adjacent to the nitrogens replaced by carbonyl (ketone) groups . These carbon and nitrogen atoms then comprise a diacyl diimide unit, .
Two canonical examples are 3,6-pyridazinedione (a quinone of pyridine), emerald-green; and 1,4-phthalazinedione (a quinone of phthalazine) a green crystalline solid (both soluble in acetone and stable at -77 °C).
The name was proposed by Thomas J. Kealy in 1962. | 0 | Organic Chemistry |
In the context of scattering light on extended bodies, the scattering cross section, , describes the likelihood of light being scattered by a macroscopic particle. In general, the scattering cross section is different from the geometrical cross section of a particle, as it depends upon the wavelength of light and the permittivity in addition to the shape and size of the particle. The total amount of scattering in a sparse medium is determined by the product of the scattering cross section and the number of particles present. In terms of area, the total cross section () is the sum of the cross sections due to absorption, scattering, and luminescence:
The total cross section is related to the absorbance of the light intensity through the Beer–Lambert law, which says that absorbance is proportional to concentration: , where is the absorbance at a given wavelength , is the concentration as a number density, and is the path length. The extinction or absorbance of the radiation is the logarithm (decadic or, more usually, natural) of the reciprocal of the transmittance : | 7 | Physical Chemistry |
A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cells genetic identity and genome size. Transposition often results in duplication of the same genetic material. In the human genome, L1 and Alu elements are two examples. Barbara McClintocks discovery of them earned her a Nobel Prize in 1983. Its importance in personalized medicine is becoming increasingly relevant, as well as gaining more attention in data analytics given the difficulty of analysis in very high dimensional spaces.
Transposable elements make up a large fraction of the genome and are responsible for much of the mass of DNA in a eukaryotic cell. Although TEs are selfish genetic elements, many are important in genome function and evolution. Transposons are also very useful to researchers as a means to alter DNA inside a living organism.
There are at least two classes of TEs: Class I TEs or retrotransposons generally function via reverse transcription, while Class II TEs or DNA transposons encode the protein transposase, which they require for insertion and excision, and some of these TEs also encode other proteins. | 1 | Biochemistry |
Starting in the 1980s, scientific advances allowed the use of DNA as a material for the identification of an individual. The first patent covering the direct use of DNA variation for forensics ([https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US5593832.pdf US5593832A]) was filed by Jeffrey Glassberg in 1983, based upon work he had done while at Rockefeller University in the United States in 1981.
British geneticist Sir Alec Jeffreys independently developed a process for DNA profiling in 1985 while working in the Department of Genetics at the University of Leicester. Jeffreys discovered that a DNA examiner could establish patterns in unknown DNA. These patterns were a part of inherited traits that could be used to advance the field of relationship analysis. These discoveries lead to the first use of DNA profiling in a criminal case.
The process, developed by Jeffreys in conjunction with Peter Gill and Dave Werrett of the Forensic Science Service (FSS), was first used forensically in the solving of the murder of two teenagers who had been raped and murdered in Narborough, Leicestershire in 1983 and 1986. In the murder inquiry, led by Detective David Baker, the DNA contained within blood samples obtained voluntarily from around 5,000 local men who willingly assisted Leicestershire Constabulary with the investigation, resulted in the exoneration of Richard Buckland, an initial suspect who had confessed to one of the crimes, and the subsequent conviction of Colin Pitchfork on January 2, 1988. Pitchfork, a local bakery employee, had coerced his coworker Ian Kelly to stand in for him when providing a blood sample—Kelly then used a forged passport to impersonate Pitchfork. Another coworker reported the deception to the police. Pitchfork was arrested, and his blood was sent to Jeffreys lab for processing and profile development. Pitchforks profile matched that of DNA left by the murderer which confirmed Pitchfork's presence at both crime scenes; he pleaded guilty to both murders. After some years, a chemical company named Imperial Chemical Industries (ICI) introduced the first ever commercially available kit to the world. Despite being a relatively recent field, it had a significant global influence on both criminal justice system and society.
Although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different that it is possible to distinguish one individual from another, unless they are monozygotic (identical) twins. DNA profiling uses repetitive sequences that are highly variable, called variable number tandem repeats (VNTRs), in particular short tandem repeats (STRs), also known as microsatellites, and minisatellites. VNTR loci are similar between closely related individuals, but are so variable that unrelated individuals are unlikely to have the same VNTRs.
Before VNTRs and STRs, people like Jeffreys used a process called Restriction Fragment Length Polymorphism (RFLP). This process regularly used large portions of DNA to analyze the differences between two DNA samples. RFLP was among the first technologies used in DNA profiling and analysis. However, as technology has evolved, new technologies, like STR, emerged and took the place of older technology like RFLP.
The admissibility of DNA evidence in courts was disputed in the United States in the 1980s and 1990s, but has since become more universally accepted due to improved techniques. | 1 | Biochemistry |
Group 6 and group 7 transition metal complexes have been found to be the most prominent in regards to dissociation of the CO cis to ligand X. CO is a neutral ligand that donates 2 electrons to the complex, and therefore lacks anionic or cationic properties that would affect the electron count of the complex. For transition metal complexes that have the formula , group 6 metals (M, where the oxidation state of the metal is zero) paired with neutral ligand X, and group 7 metals (M, where the oxidation state of the metal is +1), paired anionic ligands, will create very stable 18 electron complexes. Transition metal complexes have 9 valence orbitals, and 18 electrons will in turn fill these valences shells, creating a very stable complex, which satisfies the 18-electron rule. The cis-labilization of 18 e complexes suggests that dissociation of ligand X in the cis position creates a square pyramidal transition state, which lowers the energy of the complex, enhancing the rate of reaction. The scheme below shows the dissociation pathway of a CO ligand in the cis and trans position to the X, followed by the association of ligand Y. This is an example of a dissociative mechanism, where an 18 e complex loses a CO ligand, making a 16 e intermediate, and a final complex of 18 e results from an incoming ligand inserting in place of the CO. This mechanism resembles the S1 mechanism in organic chemistry, and applies to coordination compounds as well.
Figure 1. Intermediates in the substitution of complexes.
If ligands X and Y are neutral donors to the complex:
M = Group 6 metal (m = 0)
M = Group 7 metal (m = +1) | 0 | Organic Chemistry |
An example of back titration, the Volhard method, named after Jacob Volhard, involves the addition of excess silver nitrate to the analyte; the silver chloride is filtered, and the remaining silver nitrate is titrated against ammonium thiocyanate, with ferric ammonium sulfate as an indicator which forms blood-red [[Thiocyanate#Test for iron.28III.29|[Fe(OH)(SCN)]]] at the end point:
: Ag (aq) + SCN (aq) → AgSCN (s) (K = 1.16 × 10)
: Fe(OH)(OH) (aq) + SCN (aq)→ [Fe(OH)(SCN)] + OH | 3 | Analytical Chemistry |
RIP causes G:C to A:T transition mutations within repeats, however, the mechanism that detects the repeated sequences is unknown. RID is the only known protein essential for RIP. It is a DNA methyltransferease-like protein, that when mutated or knocked out results in loss of RIP. Deletion of the rid homolog in Aspergillus nidulans, dmtA, results in loss of fertility while deletion of the rid homolog in Ascobolus immersens, masc1, results in fertility defects and loss of methylation induced premeiotically (MIP). | 1 | Biochemistry |
Bacterial initiation factor 1 is a bacterial initiation factor.
IF1 associates with the 30S ribosomal subunit in the A site and prevents an aminoacyl-tRNA from entering. It modulates IF2 binding to the ribosome by increasing its affinity. It may also prevent the 50S subunit from binding, stopping the formation of the 70S subunit. It also contains a β-domain fold common for nucleic acid binding proteins.
IF1–IF3 may also perform ribosome recycling. | 1 | Biochemistry |
Carboxylation of the 2,3-enediolate results in the intermediate 3-keto-2-carboxyarabinitol-1,5-bisphosphate and Lys334 is positioned to facilitate the addition of the substrate as it replaces the third -coordinated water molecule and add directly to the enediol. No Michaelis complex is formed in this process. Hydration of this ketone results in an additional hydroxy group on C3, forming a gem-diol intermediate. Carboxylation and hydration have been proposed as either a single concerted step or as two sequential steps. Concerted mechanism is supported by the proximity of the water molecule to C3 of RuBP in multiple crystal structures. Within the spinach structure, other residues are well placed to aid in the hydration step as they are within hydrogen bonding distance of the water molecule. | 5 | Photochemistry |
Let and be the numerical values of the concentrations of a given contaminant, respectively before and after treatment, following a defined process.
It is irrelevant in what units these concentrations are given, provided that both use the same units.
Then an and -log reduction is achieved, where
For the purpose of presentation, the value of is rounded down to a desired precision, usually to a whole number.
;Example:
Let the concentration of some contaminant be 580 ppm before and 0.725 ppm after treatment. Then
Rounded down, is 2, so a 2-log reduction is achieved.
Conversely, an -log reduction means that a reduction by a factor of has been achieved. | 3 | Analytical Chemistry |
The Lippmann–Schwinger equation (named after Bernard Lippmann and Julian Schwinger) is one of the most used equations to describe particle collisions – or, more precisely, scattering – in quantum mechanics. It may be used in scattering of molecules, atoms, neutrons, photons or any other particles and is important mainly in atomic, molecular, and optical physics, nuclear physics and particle physics, but also for seismic scattering problems in geophysics. It relates the scattered wave function with the interaction that produces the scattering (the scattering potential) and therefore allows calculation of the relevant experimental parameters (scattering amplitude and cross sections).
The most fundamental equation to describe any quantum phenomenon, including scattering, is the Schrödinger equation. In physical problems, this differential equation must be solved with the input of an additional set of initial and/or boundary conditions for the specific physical system studied. The Lippmann–Schwinger equation is equivalent to the Schrödinger equation plus the typical boundary conditions for scattering problems. In order to embed the boundary conditions, the Lippmann–Schwinger equation must be written as an integral equation. For scattering problems, the Lippmann–Schwinger equation is often more convenient than the original Schrödinger equation.
The Lippmann–Schwinger equation's general form is (in reality, two equations are shown below, one for the sign and other for the sign):
The potential energy describes the interaction between the two colliding systems. The Hamiltonian describes the situation in which the two systems are infinitely far apart and do not interact. Its eigenfunctions are and its eigenvalues are the energies . Finally, is a mathematical technicality necessary for the calculation of the integrals needed to solve the equation. It is a consequence of causality, ensuring that scattered waves consist only of outgoing waves. This is made rigorous by the limiting absorption principle. | 7 | Physical Chemistry |
Biocatalysis underpins some of the oldest chemical transformations known to humans, for brewing predates recorded history. The oldest records of brewing are about 6000 years old and refer to the Sumerians.
The employment of enzymes and whole cells have been important for many industries for centuries. The most obvious uses have been in the food and drink businesses where the production of wine, beer, cheese etc. is dependent on the effects of the microorganisms.
More than one hundred years ago, biocatalysis was employed to do chemical transformations on non-natural man-made organic compounds, with the last 30 years seeing a substantial increase in the application of biocatalysis to produce fine chemicals, especially for the pharmaceutical industry.
Since biocatalysis deals with enzymes and microorganisms, it is historically classified separately from "homogeneous catalysis" and "heterogeneous catalysis". However, mechanistically speaking, biocatalysis is simply a special case of heterogeneous catalysis. | 0 | Organic Chemistry |
Retrotransposons (also called Class I transposable elements or transposons via RNA intermediates) are a type of genetic component that copy and paste themselves into different genomic locations (transposon) by converting RNA back into DNA through the reverse transcription process using an RNA transposition intermediate.
Through reverse transcription, retrotransposons amplify themselves quickly to become abundant in eukaryotic genomes such as maize (49–78%) and humans (42%). They are only present in eukaryotes but share features with retroviruses such as HIV, for example, discontinuous reverse transcriptase-mediated extrachromosomal recombination.
These retrotransposons are regulated by a family of short non-coding RNAs termed as PIWI [P-element induced wimpy testis]-interacting RNAs (piRNAs). piRNA is a recently discovered class of ncRNAs, which are in the length range of ~24-32 nucleotides. Initially, piRNAs were described as repeat-associated siRNAs (rasiRNAs) because of their origin from the repetitive elements such as transposable sequences of the genome. However, later it was identified that they acted via PIWI-protein. In addition to having a role in the suppression of genomic transposons, various roles of piRNAs have been recently reported like regulation of 3’ UTR of protein-coding genes via RNAi, transgenerational epigenetic inheritance to convey a memory of past transposon activity, and RNA-induced epigenetic silencing.
There are two main types of retrotransposons, long terminal repeats (LTRs) and non-long terminal repeats (non-LTRs). Retrotransposons are classified based on sequence and method of transposition. Most retrotransposons in the maize genome are LTR, whereas in humans they are mostly non-LTR. Retrotransposons (mostly of the LTR type) can be passed onto the next generation of a host species through the germline.
The other type of transposon is the DNA transposon. DNA transposons encode a transposase which, when translated, catalyses the excision of the transposase gene and its flanking region and its insertion into a different genomic location: a jumping DNA element. Hence retrotransposons can be thought of as replicative, whereas DNA transposons are non-replicative. Due to their replicative nature, retrotransposons can increase eukaryotic genome size quickly and survive in eukaryotic genomes permanently. It is thought that staying in eukaryotic genomes for such long periods gave rise to special insertion methods that do not affect eukaryotic gene function drastically. | 1 | Biochemistry |
A key consideration of hydroformylation is the "normal" vs. "iso" selectivity. For example, the hydroformylation of propylene can afford two isomeric products, butyraldehyde or isobutyraldehyde:
These isomers reflect the regiochemistry of the insertion of the alkene into the M–H bond. Since both products are not equally desirable (normal is more stable than iso), much research was dedicated to the quest for catalyst that favored the normal isomer. | 0 | Organic Chemistry |
In the early 20th century, -contaminated gold, from gold seeds that were used in radiotherapy which had held , were melted down and made into a small number of jewelry pieces, such as rings, in the U.S.
Wearing such a contaminated ring could lead to a skin exposure of 10 to 100 millirad/day (0.004 to 0.04 mSv/h). | 2 | Environmental Chemistry |
4-Maleylacetoacetate (4-maleylacetoacetatic acid) is an intermediate in the metabolism of tyrosine. It is converted to fumarylacetoacetate by the enzyme 4-maleylacetoacetate cis-trans-isomerase. Gluthathione coenzymatically helps in conversion to fumarylacetoacetic acid. | 1 | Biochemistry |
Characterization of plant root exometabolites to determine how exometabolites affect Plant-growth promoting rhizobacteria.
Metabolic footprinting of yeast strains for identification of yeast strains optimal for enhancing fermentation performance and positive attributes in wine. | 1 | Biochemistry |
Hydroxide mineralizers are also used to control the alumina/silica ratio of zeolites. A typical recipe for the production of a zeolite includes the mineralizer, the solvent, the seed crystal, a nutrient consisting of silica (SiO) and alumina (AlO), and a template. Templates are cations that direct the polymerization of the anionic building blocks to form a certain zeolite structure. Different templating cations lead to different zeolite structures. Typical templates include tetramethylammonium (TMA), sodium (Na) and potassium (K). Different zeolites can also be formed by changing the ratios of the nutrient source, the type of mineralizer or the temperature and pH of the reaction. At high pH, zeolites with high alumina content are formed, because hydroxides prevent the ability of silica to condense and oligomerize through the reaction shown above. At lower pH, zeolites with high silica content are favored. | 7 | Physical Chemistry |
A computational comparative analysis of vertebrate genome sequences have identified a cluster of 6 conserved hairpin motifs in the 3'UTR of the MAT2A messenger RNA (mRNA) transcript. The predicted hairpins (named A-F) have strong evolutionary conservation and 3 of the predicted RNA structures (hairpins A, C and D) have been confirmed by in-line probing analysis. No structural changes were observed for any of the hairpins in the presence of metabolites SAM, S-adenosylhomocysteine or L-Methionine. They are proposed to be involved in transcript stability and their functionality is currently under investigation. | 1 | Biochemistry |
GLD-2 is a common and abundant, but yet quite unknown protein that has already been found in each of the five kingdoms. In the animal kingdom, it has been specially detected in Homo sapiens, Drosophila, Xenopus and Mus musculus. However, there has also been noticed the presence of GLD-2 in Arabidopsis thaliana which belongs in the plants kingdom; Escherichia Coli in monera and Candida albicans in fungi.
In human beings it is mostly expressed in the brain and within it, in the cerebellum, hippocampus and medulla. We can also find them in some other source tissues are the fibroblast, HeLa cell, MCF-7 cell, melanoma cell line and thymus. Inside those cells, it can be located in the nucleus and mitochondrion since its main function is related with DNA polyadenilation and these cell organelles are the only ones were DNA can be found. However, there are also GLD-2 in a soluble way in the cytosol, although the reason why they are there is still unsure.
In Escherichia Coli, this enzymatic protein can be found in the cell membrane and in the cytosol, whereas in Drosophila melanogaster, it predominates in the brains nucleus and cytoplasm, oocyte, ovary and testis’ cells. Finally, in the Arabidopsis thaliana, it is located in the flowers nucleus, root, stem and leaf cells. | 1 | Biochemistry |
There are several methods termed natural cycle IVF:
* IVF using no drugs for ovarian hyperstimulation, while drugs for ovulation suppression may still be used.
* IVF using ovarian hyperstimulation, including gonadotropins, but with a GnRH antagonist protocol so that the cycle initiates from natural mechanisms.
* Frozen embryo transfer; IVF using ovarian hyperstimulation, followed by embryo cryopreservation, followed by embryo transfer in a later, natural, cycle.
IVF using no drugs for ovarian hyperstimulation was the method for the conception of Louise Brown. This method can be successfully used when people want to avoid taking ovarian stimulating drugs with its associated side-effects. HFEA has estimated the live birth rate to be approximately 1.3% per IVF cycle using no hyperstimulation drugs for women aged between 40 and 42.
Mild IVF is a method where a small dose of ovarian stimulating drugs are used for a short duration during a natural menstrual cycle aimed at producing 2–7 eggs and creating healthy embryos. This method appears to be an advance in the field to reduce complications and side-effects for women, and it is aimed at quality, and not quantity of eggs and embryos. One study comparing a mild treatment (mild ovarian stimulation with GnRH antagonist co-treatment combined with single embryo transfer) to a standard treatment (stimulation with a GnRH agonist long-protocol and transfer of two embryos) came to the result that the proportions of cumulative pregnancies that resulted in term live birth after 1 year were 43.4% with mild treatment and 44.7% with standard treatment. Mild IVF can be cheaper than conventional IVF and with a significantly reduced risk of multiple gestation and OHSS. | 1 | Biochemistry |
Tripartite motif-containing 24 (TRIM24) also known as transcriptional intermediary factor 1α (TIF1α) is a protein that, in humans, is encoded by the TRIM24 gene. | 1 | Biochemistry |
Select filter cloth to obtain solid binding resistance and good cake release. Use coated fabric for more effective cake release and have a longer-lasting cloth media due to solid binding filter cloth. Both the discharge roll speed and drum speed must be the same. Adjust the scraper knife to leave a significant heal on discharge roll to produce a continuous cake transfer. | 3 | Analytical Chemistry |
Organic fluxes typically consist of four major components:
* Activators – chemicals disrupting/dissolving the metal oxides. Their role is to expose unoxidized, easily wettable metal surface and aid soldering by other means, e.g. by exchange reactions with the base metals.
** Highly active fluxes contain chemicals that are corrosive at room temperature. The compounds used include metal halides (most often zinc chloride or ammonium chloride), hydrochloric acid, phosphoric acid, citric acid, and hydrobromic acid. Salts of mineral acids with amines are also used as aggressive activators. Aggressive fluxes typically facilitate corrosion, require careful removal, and are unsuitable for finer work. Activators for fluxes for soldering and brazing aluminium often contain fluorides.
** Milder activators begin to react with oxides only at elevated temperature. Typical compounds used are carboxylic acids (e.g. fatty acids (most often oleic acid and stearic acid), dicarboxylic acids) and sometimes amino acids. Some milder fluxes also contain halides or organohalides.
* Vehicles – high-temperature tolerant chemicals in the form of non-volatile liquids or solids with suitable melting point; they are generally liquid at soldering temperatures. Their role is to act as an oxygen barrier to protect the hot metal surface against oxidation, to dissolve the reaction products of activators and oxides and carry them away from the metal surface, and to facilitate heat transfer. Solid vehicles tend to be based on natural or modified rosin (mostly abietic acid, pimaric acid, and other resin acids) or natural or synthetic resins. Water-soluble organic fluxes tend to contain vehicles based on high-boiling polyols - glycols, diethylene glycol and higher polyglycols, polyglycol-based surfactants and glycerol.
* Solvents – added to facilitate processing and deposition to the joint. Solvents are typically dried out during preheating before the soldering operation; incomplete solvent removal may lead to boiling off and spattering of solder paste particles or molten solder.
* Additives – numerous other chemicals modifying the flux properties. Additives can be surfactants (especially nonionic), corrosion inhibitors, stabilizers and antioxidants, tackifiers, thickeners and other rheological modifiers (especially for solder pastes), plasticizers (especially for flux-cored solders), and dyes. | 8 | Metallurgy |
Methanesulfonyl chloride react with primary and secondary amines to give methanesulfonamides. Unlike methanesulfonates, methanesulfonamides are very resistant toward hydrolysis under both acidic and basic conditions. When used as a protecting group, they can be converted back to amines using lithium aluminium hydride or a dissolving metal reduction. | 0 | Organic Chemistry |
Nucleosomes are portions of double-stranded DNA (dsDNA) that are wrapped around protein complexes called histone cores. These histone cores are composed of 8 subunits, two each of H2A, H2B, H3 and H4 histones. This protein complex forms a cylindrical shape that dsDNA wraps around with approximately 147 base pairs. Nucleosomes are formed as a beginning step for DNA compaction that also contributes to structural support as well as serves functional roles. These functional roles are contributed by the tails of the histone subunits. The histone tails insert themselves in the minor grooves of the DNA and extend through the double helix, which leaves them open for modifications involved in transcriptional activation. Acetylation has been closely associated with increases in transcriptional activation while deacetylation has been linked with transcriptional deactivation. These reactions occur post-translation and are reversible.
The mechanism for acetylation and deacetylation takes place on the NH groups of lysine amino acid residues. These residues are located on the tails of histones that make up the nucleosome of packaged dsDNA. The process is aided by factors known as histone acetyltransferases (HATs). HAT molecules facilitate the transfer of an acetyl group from a molecule of acetyl-coenzyme A (Acetyl-CoA) to the NH group on lysine. When a lysine is to be deacetylated, factors known as histone deacetylases (HDACs) catalyze the removal of the acetyl group with a molecule of HO.
Acetylation has the effect of changing the overall charge of the histone tail from positive to neutral. Nucleosome formation is dependent on the positive charges of the H4 histones and the negative charge on the surface of H2A histone fold domains. Acetylation of the histone tails disrupts this association, leading to weaker binding of the nucleosomal components. By doing this, the DNA is more accessible and leads to more transcription factors being able to reach the DNA. Thus, acetylation of histones is known to increase the expression of genes through transcription activation. Deacetylation performed by HDAC molecules has the opposite effect. By deacetylating the histone tails, the DNA becomes more tightly wrapped around the histone cores, making it harder for transcription factors to bind to the DNA. This leads to decreased levels of gene expression and is known as gene silencing.
Acetylated histones, the octomeric protein cores of nucleosomes, represent a type of epigenetic marker within chromatin. Studies have shown that one modification has the tendency to influence whether another modification will take place. Modifications of histones can not only cause secondary structural changes at their specific points, but can cause many structural changes in distant locations which inevitably affects function. As the chromosome is replicated, the modifications that exist on the parental chromosomes are handed down to daughter chromosomes. The modifications, as part of their function, can recruit enzymes for their particular function and can contribute to the continuation of modifications and their effects after replication has taken place. It has been shown that, even past one replication, expression of genes may still be affected many cell generations later. A study showed that, upon inhibition of HDAC enzymes by Trichostatin A, genes inserted next to centric heterochromatin showed increased expression. Many cell generations later, in the absence of the inhibitor, the increased gene expression was still expressed, showing modifications can be carried through many replication processes such as mitosis and meiosis. | 0 | Organic Chemistry |
By chemically crosslinking the rings contained in the polyrotaxanes, sliding gels are obtained by being topologically interlocked by figure-of-eight crosslinks. Although it is a polymer network (gel), the rings are not fixed on the polyrotaxanes in the polymer network, the crosslinks of rings are able to freely move along the polymer chain. This can equalize the tension of the network, just like a pulley manner, which is referred to pulley effect. In chemical gels, the polymer chains are easy to be broken because the lengths of the heterogeneous polymer are limited or fixed. As a result, when the chemical gel is under a high pressure, the tension can not be equalized to the whole. On the opposite, the weakest part in the network will be broken easier, which leads to the damage of the gel. However, in the slide-ring materials, the polymer chain are able to pass through the figure-of-eight crosslinks which is like pulleys, and equalize the tension of network. As a result, slide-ring materials are applied to construct highly stretchable materials, up to 24 times its length when stretching and this process can be reversible. | 6 | Supramolecular Chemistry |
Columnar structures arise naturally in the context of dense hard sphere packings inside a cylinder. Mughal et al. studied such packings using simulated annealing up to the diameter ratio of for cylinder diameter to sphere diameter . This includes some structures with internal spheres that are not in contact with the cylinder wall.
They calculated the packing fraction for all these structures as a function of the diameter ratio. At the peaks of this curve lie the uniform structures. In-between these discrete diameter ratios are the line slips at a lower packing density. Their packing fraction is significantly smaller than that of an unconfined lattice packing such as fcc, bcc, or hcp due to the free volume left by the cylindrical confinement.
The rich variety of such ordered structures can also be obtained by sequential depositioning the spheres into the cylinder. Chan reproduced all dense sphere packings up to using an algorithm, in which the spheres are placed sequentially dropped inside the cylinder.
Mughal et al. also discovered that such structures can be related to disk packings on a surface of a cylinder. The contact network of both packings are identical. For both packing types, it was found that different uniform structures are connected with each other by line slips.
Fu et al. extended this work to higher diameter ratios using linear programming and discovered 17 new dense structures with internal spheres that are not in contact with the cylinder wall.
A similar variety of dense crystalline structures have also been discovered for columnar packings of spheroids through Monte Carlo simulations. Such packings include achiral structures with specific spheroid orientations and chiral helical structures with rotating spheroid orientations. | 3 | Analytical Chemistry |
The formal standard reduction potential can be defined as the measured reduction potential of the half-reaction at unity concentration ratio of the oxidized and reduced species (i.e.', when 1) under given conditions.
Indeed:
as, , when ,
: , when ,
because , and that the term is included in .
The formal reduction potential makes possible to more simply work with molar or molal concentrations in place of activities. Because molar and molal concentrations were once referred as formal concentrations, it could explain the origin of the adjective formal in the expression formal potential.
The formal potential is thus the reversible potential of an electrode at equilibrium immersed in a solution where reactants and products are at unit concentration. If any small incremental change of potential causes a change in the direction of the reaction, i.e. from reduction to oxidation or vice versa, the system is close to equilibrium, reversible and is at its formal potential. When the formal potential is measured under standard conditions (i.e. the activity of each dissolved species is 1 mol/L, T = 298.15 K = 25 °C = 77 °F, = 1 bar) it becomes de facto a standard potential. According to Brown and Swift (1949), "A formal potential is defined as the potential of a half-cell, measured against the standard hydrogen electrode, when the total concentration of each oxidation state is one formal".
The activity coefficients and are included in the formal potential , and because they depend on experimental conditions such as temperature, ionic strength, and pH, cannot be referred as an immuable standard potential but needs to be systematically determined for each specific set of experimental conditions.
Formal reduction potentials are applied to simplify results interpretations and calculations of a considered system. Their relationship with the standard reduction potentials must be clearly expressed to avoid any confusion. | 1 | Biochemistry |
The point of zero charge is the pH for which the net surface charge of adsorbent is equal to zero. This concept has been introduced by an increase of interest in the pH of the solution during adsorption. The reason why pH has attracted much attention is that the adsorption of some substances is very dependent on pH. The pzc value is determined by the characteristics of an adsorbent. For example, the surface charge of adsorbent is described by the ion that lies on the surface of the particle (adsorbent) structure like image. At the lower pH, hydrogen ions (protons, H) would be adsorbed more than other cations (adsorbate) so that the other cations would be less adsorbed in the case of the negatively charged particle. On the other hand, if the surface is positively charged and pH is increased, anions will be less adsorbed as hydroxide ions are increased. From the view of the adsorbent, if the pH is below the pzc value, the surface charge of adsorbent would be positive so that the anions can be adsorbed. Conversely, if the pH is above the pzc value, the surface charge would be negative so that the cations can be adsorbed.
For example, the charge on the surface of silver iodide crystals may be determined by the concentration of iodide ions in the solution above the crystals. Then, the pzc value of the AgI surface will be described by the concentration of I in the solution (or negative decimal logarithm of this concentration, pI). | 7 | Physical Chemistry |
In the human ventricles, repolarization can be seen on an ECG (electrocardiogram) via the J-wave (Osborn), ST segment, T wave and U wave. Due to the complexity of the heart, specifically how it contains three layers of cells (endocardium, myocardium and epicardium), there are many physiological changes effecting repolarization that will also affect these waves. Apart from changes in the structure of the heart that effect repolarization, there are many pharmaceuticals that have the same effect.
On top of that, repolarization is also altered based on the location and duration of the initial action potential. In action potentials stimulated on the epicardium, it was found that the duration of the action potential needed to be 40–60 msec to give a normal, upright T-wave, whereas a duration of 20–40 msec would give an isoelectric wave and anything under 20 msec would result in a negative T-wave.
Early repolarization is a phenomenon that can be seen in ECG recordings of ventricular cells where there is an elevated ST segment, also known as a J wave. The J wave is prominent when there is a larger outward current in the epicardium compared to the endocardium. It has been historically considered to be a normal variant in cardiac rhythm but recent studies show that it is related to an increased risk of cardiac arrest. Early repolarization occurs mainly in males and is associated with a larger potassium current caused by the hormone testosterone. Additionally, although the risk is unknown, African American individuals seem more likely to have the early repolarization more often. | 7 | Physical Chemistry |
Cryosurgery is also used to treat internal and external tumors as well as tumors in the bone. To cure internal tumors, a hollow instrument called a cryoprobe is used, which is placed in contact with the tumor. Liquid nitrogen or argon gas is passed through the cryoprobe. Ultrasound or MRI is used to guide the cryoprobe and monitor the freezing of the cells. This helps in limiting damage to adjacent healthy tissues. A ball of ice crystals forms around the probe which results in freezing of nearby cells. When it is required to deliver gas to various parts of the tumor, more than one probe is used. After cryosurgery, the frozen tissue is either naturally absorbed by the body in the case of internal tumors, or it dissolves and forms a scab for external tumors. | 1 | Biochemistry |
Tris-buffered saline (TBS) is a buffer used in some biochemical techniques to maintain the pH within a relatively narrow range. Tris (with HCl) has a slightly alkaline buffering capacity in the 7–9.2 range. The conjugate acid of Tris has a pK of 8.07 at 25 °C. The pK declines approximately 0.03 units per degree Celsius rise in temperature. This can lead to relatively dramatic pH shifts when there are shifts in solution temperature. Sodium chloride concentration may vary from 100 to 200 mM, tris concentration from 5 to 100 mM and pH from 7.2 to 8.0. A common formulation of TBS is 150 mM NaCl, 50 mM Tris-HCl, pH 7.6. TBS can also be prepared by using commercially made TBS buffer tablets or pouches. | 1 | Biochemistry |
The methylglyoxal pathway is activated by the increased intercellular uptake of carbon containing molecules such as glucose, glucose-6-phosphate, lactate, or glycerol. Methylglyoxal is formed from dihydroxyacetone phosphate (DHAP) by the enzyme methylglyoxal synthase, giving off a phosphate group.
Methylglyoxal is then converted into two different products, either D-lactate, and L-lactate. Methylglyoxal reductase and aldehyde dehydrogenase convert methylglyoxal into lactaldehyde and, eventually, L-lactate. If methylglyoxal enters the glyoxylase pathway, it is converted into lactoylguatathione and eventually D-lactate. Both D-lactate, and L-lactate are then converted into pyruvate. The pyruvate that is created most often goes on to enter the Krebs cycle ([http://mic.sgmjournals.org/cgi/reprint/151/3/707 Weber] 711–13). | 1 | Biochemistry |
Isocyanides have a very disagreeable odour. To quote from Lieke, "Es besitzt einen penetranten, höchst unangenehmen Geruch; das Oeffnen eines Gefässes mit Cyanallyl reicht hin, die Luft eines Zimmers mehrere Tage lang zu verpesten, ..." (It has a penetrating, extremely unpleasant odour; the opening of a flask of allyl [iso]cyanide is enough to foul up the air in a room for several days). Note that in Lieke's day, the difference between isocyanide and nitrile was not fully appreciated.
Ivar Karl Ugi states that "The development of the chemistry of isocyanides has probably suffered only little delay through the characteristic odor of volatile isonitriles, which has been described by Hofmann and Gautier as highly specific, almost overpowering, horrible, and extremely distressing. It is true that many potential workers in this field have been turned away by the odour, but this is heavily outweighed by the fact that isonitriles can be detected even in traces, and that most of the routes leading to the formation of isonitriles were discovered through the odor of these compounds." Isocyanides have been investigated as potential non-lethal weapons.
Some isocyanides convey less offensive odours such as malt, natural rubber, creosote, cherry or old wood. Non-volatile derivatives such as tosylmethyl isocyanide do not have an odor. | 0 | Organic Chemistry |
A superconductor is generally considered high-temperature if it reaches a superconducting state above a temperature of 30 K (−243.15 °C); as in the initial discovery by Georg Bednorz and K. Alex Müller. It may also reference materials that transition to superconductivity when cooled using liquid nitrogen – that is, at only T > 77 K, although this is generally used only to emphasize that liquid nitrogen coolant is sufficient. Low temperature superconductors refer to materials with a critical temperature below 30 K, and are cooled mainly by liquid helium (T > 4.2 K). One exception to this rule is the iron pnictide group of superconductors which display behaviour and properties typical of high-temperature superconductors, yet some of the group have critical temperatures below 30 K. | 7 | Physical Chemistry |
The issue of limit of detection, or limit of quantification, is encountered in all scientific disciplines. This explains the variety of definitions and the diversity of juridiction specific solutions developed to address preferences. In the simplest cases as in nuclear and chemical measurements, definitions and approaches have probably received the clearer and the simplest solutions. In biochemical tests and in biological experiments depending on many more intricate factors, the situation involving false positive and false negative responses is more delicate to handle. In many other disciplines such as geochemistry, seismology, astronomy, dendrochronology, climatology, life sciences in general, and in many other fields impossible to enumerate extensively, the problem is wider and deals with signal extraction out of a background of noise. It involves complex statistical analysis procedures and therefore it also depends on the models used, the hypotheses and the simplifications or approximations to be made to handle and manage uncertainties. When the data resolution is poor and different signals overlap, different deconvolution procedures are applied to extract parameters. The use of different phenomenological, mathematical and statistical models may also complicate the exact mathematical definition of limit of detection and how it is calculated. This explains why it is not easy to come to a general consensus, if any, about the precise mathematical definition of the expression of limit of detection. However, one thing is clear: it always requires a sufficient number of data (or accumulated data) and a rigorous statistical analysis to render better signification statistically. | 3 | Analytical Chemistry |
Herman was born on 24 March 1934 in Libušín. He studied physical chemistry and radiochemistry at the School of Mathematics and Physics of Charles University, Prague (1952–1957). He then joined the Institute of Physical Chemistry of the Czech Academy of Sciences, to which he remained affiliated.
Herman's early work, with Vladimír Čermák concerned mass spectrometric studies of the kinetics of collision and ionization processes of ions (chemical reaction of ions, Penning and associative ionization). During his post-doctoral years (1964–1965), with Richard Wolfgang at Yale University, Herman built one of the first crossed beam machines to study ion-molecule processes.
Herman also built an improved crossed beam machine that was used in Prague with colleagues to investigate the dynamics of ion-molecule and charge transfer reactions of cations and dications, and ion-surface collisions by the scattering method (1970–2010).
Herman has published over 240 scientific articles in this field. | 7 | Physical Chemistry |
Photaki was born in Corinth in 1921 and finished her secondary education at the 2nd Girls Gymnasium of Athens in 1938. In the same year she enrolled at the Department of Chemistry in the University of Athens, where she specialised in Organic chemistry under the mentorship of Leonidas Zervas. Her studies were interrupted during the Axis occupation of Greece when the Laboratory of Organic Chemistry was destroyed and Zervas was imprisoned as a member of the Greek Resistance. Photaki was finally awarded her degree summa cum laude' in 1946 and subsequently continued her postgraduate studies under Zervas, earning her PhD in 1950 with a dissertation regarding glucosamine. Concurrently, she held a paid laboratory assistant position at the university already from 1943, carrying on as a research assistant until 1953.
In 1953, Photaki was awarded a scholarship to conduct research in Basel after examinations by the Greek State Scholarships Foundation. At the University of Basel she worked in the Laboratory of Organic Chemistry, at the time headed by Nobel laureate Tadeusz Reichstein. For the first two years of her stay (1953–1955) she was part of the Max Brenner research group, later moving as an independent scientific associate of Hans Erlenmeyer. Upon returning to Greece, she initially worked at the biochemical lab of the Evangelismos Hospital before being invited by Zervas to the nascent National Hellenic Research Foundation (NHRF) which he had helped found. | 0 | Organic Chemistry |
In addition to LaNi, there are other alloys such as LaNi, LaNi, LaNi, LaNi, LaNi, and LaNi, and nonstoichiometric alloys such as LaNi (tetragonal, space group I4̄2m). The nickel atoms in LaNi can also be replaced by other atoms, such as LaNiCo. | 8 | Metallurgy |
Unlike the hormones with which it competes, flutamide is not a steroid; rather, it is a substituted anilide. Hence, it is described as nonsteroidal in order to distinguish it from older steroidal antiandrogens such as cyproterone acetate and megestrol acetate. | 4 | Stereochemistry |
The first suggestion of ADP-ribosylation surfaced during the early 1960s. At this time, Pierre Chambon and coworkers observed the incorporation of ATP into hen liver nuclei extract. After extensive studies on the acid insoluble fraction, several different research laboratories were able to identify ADP-ribose, derived from NAD, as the incorporated group. Several years later, the enzymes responsible for this incorporation were identified and given the name poly(ADP-ribose)polymerase. Originally, this group was thought to be a linear sequence of ADP-ribose units covalently bonded through a ribose glycosidic bond. It was later reported that branching can occur every 20 to 30 ADP residues.
The first appearance of mono(ADP-ribosyl)ation occurred a year later during a study of toxins: the diphtheria toxin of Corynebacterium diphtheriae was shown to be dependent on NAD in order for it to be completely effective, leading to the discovery of enzymatic conjugation of a single ADP-ribose group by mono(ADP-ribosyl)transferase.
It was initially thought that ADP-ribosylation was a post translational modification involved solely in gene regulation. However, as more enzymes with the ability to ADP-ribosylate proteins were discovered, the multifunctional nature of ADP-ribosylation became apparent. The first mammalian enzyme with poly(ADP-ribose)transferase activity was discovered during the late 1980s. For the next 15 years, it was thought to be the only enzyme capable of adding a chain of ADP-ribose in mammalian cells. During the late 1980s, ADP-ribosyl cyclases, which catalyze the addition of cyclic-ADP-ribose groups to proteins, were discovered. Finally, sirtuins, a family of enzymes that also possess NAD-dependent deacylation activity, were discovered to also possess mono(ADP-ribosyl)transferase activity. | 1 | Biochemistry |
More than 80 sponsors support the NADP: Private companies and other non-governmental organizations, universities, local and state government agencies (i.e. state agricultural experiment stations), national laboratories, Native American environmental organizations, [http://www.ec.gc.ca/ Canadian government agencies], the National Oceanic and Atmospheric Administration, the U.S. Environmental Protection Agency, the U.S. Geological Survey, the National Park Service, the U.S. Fish & Wildlife Service, the Bureau of Land Management, the U.S. Forest Service, the U.S. Department of Agriculture-Agricultural Research Service, the National Science Foundation, and the U.S. Department of Energy. | 2 | Environmental Chemistry |
There are three different replication systems during the life cycle of a retrovirus. The first process is the reverse transcriptase synthesis of viral DNA from viral RNA, which then forms newly made complementary DNA strands. The second replication process occurs when host cellular DNA polymerase replicates the integrated viral DNA. Lastly, RNA polymerase II transcribes the proviral DNA into RNA, which will be packed into virions. Mutation can occur during one or all of these replication steps.
Reverse transcriptase has a high error rate when transcribing RNA into DNA since, unlike most other DNA polymerases, it has no proofreading ability. This high error rate allows mutations to accumulate at an accelerated rate relative to proofread forms of replication. The commercially available reverse transcriptases produced by Promega are quoted by their manuals as having error rates in the range of 1 in 17,000 bases for AMV and 1 in 30,000 bases for M-MLV.
Other than creating single-nucleotide polymorphisms, reverse transcriptases have also been shown to be involved in processes such as transcript fusions, exon shuffling and creating artificial antisense transcripts. It has been speculated that this template switching activity of reverse transcriptase, which can be demonstrated completely in vivo, may have been one of the causes for finding several thousand unannotated transcripts in the genomes of model organisms. | 1 | Biochemistry |
Sediment chemistry provides information on contamination, however it does not provide information of biological effects (Chapman, 1990). Sediment chemistry is used as a screening tool to determine the contaminants that are most likely to be destructive to organisms present in the benthic community at a specific site. During analysis, sediment chemistry data does not depend strictly on comparisons to sediment quality guidelines when utilizing the triad approach. Rather, sediment chemistry data, once collected for the specific site, is compared to the most relevant guide values, based on site characteristics, to assess which chemicals are of the greatest concern. This technique is used because no one set of data is adequate for all situations. This allows you to identify the chemicals of concern, which most frequently exceed effects-based guidelines. Once the chemical composition of the sediment is determined and the most concerning contaminants have been identified, toxicity tests are conducted to link environmental concentrations to potential adverse effects. | 2 | Environmental Chemistry |
Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or phase changes such as melting and boiling. A reaction may release or absorb energy, and a phase change may do the same. Thermochemistry focuses on the energy exchange between a system and its surroundings in the form of heat. Thermochemistry is useful in predicting reactant and product quantities throughout the course of a given reaction. In combination with entropy determinations, it is also used to predict whether a reaction is spontaneous or non-spontaneous, favorable or unfavorable.
Endothermic reactions absorb heat, while exothermic reactions release heat. Thermochemistry coalesces the concepts of thermodynamics with the concept of energy in the form of chemical bonds. The subject commonly includes calculations of such quantities as heat capacity, heat of combustion, heat of formation, enthalpy, entropy, and free energy.
Thermochemistry is one part of the broader field of chemical thermodynamics, which deals with the exchange of all forms of energy between system and surroundings, including not only heat but also various forms of work, as well the exchange of matter. When all forms of energy are considered, the concepts of exothermic and endothermic reactions are generalized to exergonic reactions and endergonic reactions. | 7 | Physical Chemistry |
Fretting damage in steel can be identified by the presence of a pitted surface and fine red iron oxide dust resembling cocoa powder. Strictly this debris is not rust as its production requires no water. The particles are much harder than the steel surfaces in contact, so abrasive wear is inevitable; however, particulates are not required to initiate fret. | 8 | Metallurgy |
The Golden Gate Cloning principle can also be applied to perform mutagenesis termed Golden Mutagenesis. The technology is easy to implement as a web tool is available for primer design (https://msbi.ipb-halle.de/GoldenMutagenesisWeb/) and the vectors are deposited at addgene (http://www.addgene.org/browse/article/28196591/). | 1 | Biochemistry |
Single nucleotide polymorphism annotation (SNP annotation) is the process of predicting the effect or function of an individual SNP using SNP annotation tools. In SNP annotation the biological information is extracted, collected and displayed in a clear form amenable to query. SNP functional annotation is typically performed based on the available information on nucleic acid and protein sequences. | 1 | Biochemistry |
The first protected peptide was synthesised by Theodor Curtius in 1882 and the first free peptide was synthesised by Emil Fischer in 1901. | 1 | Biochemistry |
Typically bainite manifests as aggregates, termed sheaves, of ferrite plates (sub-units) separated by retained austenite, martensite or cementite. While the sub-units appear separate when viewed on a 2-dimensional section they are in fact interconnected in 3-dimensions and usually take on a lenticular plate or lath morphology. The sheaves themselves are wedge-shaped with the thicker end associated with the nucleation site.
The thickness of the ferritic plates is found to increase with the transformation temperature. Neural network models have indicated that this is not a direct effect of the temperature per se but rather a result of the temperature dependence of the driving force for the reaction and the strength of the austenite surrounding the plates. At higher temperatures, and hence lower undercooling, the reduced thermodynamic driving force causes a decrease in the nucleation rate which allows individual plates to grow larger before they physically impinge on each other. Further, the growth of the plates must be accommodated by plastic flow in the surrounding austenite which is difficult if the austenite is strong and resists the plate's growth. | 8 | Metallurgy |
Despite being a powerful model organism for biology and the study of transcriptional enhancers, the tissue specific activity of less than 5% of the estimated 50,000 transcriptional enhancers in Drosophila melanogaster have been discovered. Over the past decade, the main method for detection of tissue- or cell-type specific activities of enhancers in Drosophila melanogaster was to test candidate enhancers by traditional reporter assays, which are low-throughput and costly. Over the past few years, even though enhancer discovery has been improved and other parallel reporter assays have been developed, none so far allowed the direct identification of enhancer activity in a genomic context in cell types of interest in a whole embryo. | 1 | Biochemistry |
Thylakoids can be purified from plant cells using a combination of differential and gradient centrifugation. Disruption of isolated thylakoids, for example by mechanical shearing, releases the lumenal fraction. Peripheral and integral membrane fractions can be extracted from the remaining membrane fraction. Treatment with sodium carbonate (NaCO) detaches peripheral membrane proteins, whereas treatment with detergents and organic solvents solubilizes integral membrane proteins. | 5 | Photochemistry |
CK1ε and CK1δ are essential in the genetic transcription-translation (and post-translation) feedback loops that generate circadian rhythm in mammals.
The previously-characterized CK1ε isoform was first implicated as a clock gene when its Drosophila homolog, double-time (Doubletime (gene)), was discovered in 1998. Double-time is 86% identical to human CK1ε. Kloss et al and Price et al showed that mutations in double-time altered circadian rhythm. They found two DBT mutants that had abnormal free-running periods and one that was pupal-lethal but resulted in accumulations of hypophosphorylated PER protein. Since then, double-time's protein product DBT has been well characterized for its role in phosphorylating PER, the protein product of clock gene period in Drosophila, and its mammalian homologs appear to play a similar role.
In 2021, scientists reported the development of a light-responsive days-lasting modulator of circadian rhythms of tissues via Ck1 inhibition. Such modulators may be useful for chronobiology research and repair of organs that are "out of sync". | 1 | Biochemistry |
In general, carboxylic acids () are named with the suffix -oic acid (etymologically a back-formation from benzoic acid). As with aldehydes, the carboxyl functional group must take the "1" position on the main chain and so the locant need not be stated. For example, (lactic acid) is named 2-hydroxypropanoic acid with no "1" stated. Some traditional names for common carboxylic acids (such as acetic acid) are in such widespread use that they are retained in IUPAC nomenclature, though systematic names like ethanoic acid are also used. Carboxylic acids attached to a benzene ring are structural analogs of benzoic acid () and are named as one of its derivatives.
If there are multiple carboxyl groups on the same parent chain, multiplying prefixes are used: Malonic acid, , is systematically named propanedioic acid. Alternatively, the suffix can be used in place of "oic acid", combined with a multiplying prefix if necessary – mellitic acid is benzenehexacarboxylic acid, for example. In the latter case, the carbon atoms in the carboxyl groups do not count as being part of the main chain, a rule that also applies to the prefix form "carboxy-". Citric acid serves as an example: it is formally named rather than . | 0 | Organic Chemistry |
In n-pentane, the terminal methyl groups experience additional pentane interference.
Replacing hydrogen by fluorine in polytetrafluoroethylene changes the stereochemistry from the zigzag geometry to that of a helix due to electrostatic repulsion of the fluorine atoms in the 1,3 positions. Evidence for the helix structure in the crystalline state is derived from X-ray crystallography and from NMR spectroscopy and circular dichroism in solution. | 4 | Stereochemistry |
In particle physics, (; ) is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic energy, which is converted into radiation (i.e., photons), thus satisfying the law of conservation of energy. The term is also used to refer to the process of producing the radiation. has a continuous spectrum, which becomes more intense and whose peak intensity shifts toward higher frequencies as the change of the energy of the decelerated particles increases.
Broadly speaking, or braking radiation is any radiation produced due to the acceleration (positive or negative) of a charged particle, which includes synchrotron radiation (i.e., photon emission by a relativistic particle), cyclotron radiation (i.e. photon emission by a non-relativistic particle), and the emission of electrons and positrons during beta decay. However, the term is frequently used in the more narrow sense of radiation from electrons (from whatever source) slowing in matter.
Bremsstrahlung emitted from plasma is sometimes referred to as free–free radiation. This refers to the fact that the radiation in this case is created by electrons that are free (i.e., not in an atomic or molecular bound state) before, and remain free after, the emission of a photon. In the same parlance, bound–bound radiation refers to discrete spectral lines (an electron "jumps" between two bound states), while free–bound radiation refers to the radiative combination process, in which a free electron recombines with an ion.
This article uses SI units, along with the scaled single-particle charge . | 7 | Physical Chemistry |
Secondary (indirect) immunofluorescence (SIF) is similar to direct immunofluorescence, however the technique utilizes two types of antibodies whereas only one of them have a conjugated fluorophore. The antibody with the conjugated fluorophore is referred to as the secondary antibody, while the unconjugated is referred to as the primary antibody.
The principle of this technique is that the primary antibody specifically binds to the epitope on the target molecule, whereas the secondary antibody, with the conjugated fluorophore, recognizes and binds to the primary antibody.
This technique is considered to be more sensitive than primary immunofluorescence, because multiple secondary antibodies can bind to the same primary antibody. The increased number of fluorophore molecules per antigen increases the amount of emitted light, and thus amplifies the signal. There are different methods for attaining a higher fluorophore-antigen ratio such as the Avidin-Biotin Complex (ABC method) and Labeled Streptavidin-Biotin (LSAB method). | 1 | Biochemistry |
Certain materials especially refractories which are processed at high temperatures end up with excessively large grain size and poor mechanical properties at room temperature. To mitigate this problem in a common sintering procedure, a variety of dopants are often used to inhibit grain growth. | 8 | Metallurgy |
If the β phase is replaced by a flat rigid surface, as shown in Figure 5, then β = π, and the second net force equation simplifies to the Young equation,
which relates the surface tensions between the three phases: solid, liquid and gas. Subsequently, this predicts the contact angle of a liquid droplet on a solid surface from knowledge of the three surface energies involved. This equation also applies if the "gas" phase is another liquid, immiscible with the droplet of the first "liquid" phase. | 7 | Physical Chemistry |
Electrochemical migration (ECM) is the dissolution and movement of metal ions in presence of electric potential, which results in the growth of dendritic structures between anode and cathode. The process is most commonly observed in printed circuit boards where it may significantly decrease the insulation between conductors.
The main factor facilitating the ECM is humidity. In the presence of water, ECM can go very quickly. Usually the process involves several stages: water adsorption, anode metal dissolution, ion accumulation, ion migration to cathode, and dendritic growth. The growth of the dendrite takes fraction of a second, during which time the resistance between anode and cathode drops almost to zero. | 7 | Physical Chemistry |
75% of plant viruses have genomes that consist of single stranded RNA (ssRNA). 65% of plant viruses have +ssRNA, meaning that they are in the same sense orientation as messenger RNA but 10% have -ssRNA, meaning they must be converted to +ssRNA before they can be translated. 5% are double stranded RNA and so can be immediately translated as +ssRNA viruses. 3% require a reverse transcriptase enzyme to convert between RNA and DNA. 17% of plant viruses are ssDNA and very few are dsDNA, in contrast a quarter of animal viruses are dsDNA and three-quarters of bacteriophage are dsDNA. Viruses use the plant ribosomes to produce the 4-10 proteins encoded by their genome. However, since many of the proteins are encoded on a single strand (that is, they are polycistronic) this will mean that the ribosome will either only produce one protein, as it will terminate translation at the first stop codon, or that a polyprotein will be produced. Plant viruses have had to evolve special techniques to allow the production of viral proteins by plant cells. | 1 | Biochemistry |
* [https://www.rickallmendinger.net/stereonet Stereonet], a software tool for structural geology by Rick Allmendinger.
* [http://sourceforge.net/projects/tclab/ PTCLab], the phase transformation crystallography lab
* [http://sourceforge.net/projects/sphaerica Sphaerica], software tool for straightedge and compass construction on the sphere, including a stereographic projection display option
* [http://estereo.reyuntec.ar/ Estereografica Web], a web application for stereographic projection in structural geology and fault kinematics by Ernesto Cristallini. | 3 | Analytical Chemistry |
Among the earlier uses of bitumen in the United Kingdom was for etching. William Salmons Polygraphice' (1673) provides a recipe for varnish used in etching, consisting of three ounces of virgin wax, two ounces of mastic, and one ounce of asphaltum. By the fifth edition in 1685, he had included more asphaltum recipes from other sources.
The first British patent for the use of asphalt was "Cassell's patent asphalte or bitumen" in 1834. Then on 25 November 1837, Richard Tappin Claridge patented the use of Seyssel asphalt (patent #7849), for use in asphalte pavement, having seen it employed in France and Belgium when visiting with Frederick Walter Simms, who worked with him on the introduction of asphalt to Britain. Dr T. Lamb Phipson writes that his father, Samuel Ryland Phipson, a friend of Claridge, was also "instrumental in introducing the asphalte pavement (in 1836)".
Claridge obtained a patent in Scotland on 27 March 1838, and obtained a patent in Ireland on 23 April 1838. In 1851, extensions for the 1837 patent and for both 1838 patents were sought by the trustees of a company previously formed by Claridge. Claridges Patent Asphalte Companyformed in 1838 for the purpose of introducing to Britain "Asphalte in its natural state from the mine at Pyrimont Seysell in France","laid one of the first asphalt pavements in Whitehall". Trials were made of the pavement in 1838 on the footway in Whitehall, the stable at Knightsbridge Barracks, "and subsequently on the space at the bottom of the steps leading from Waterloo Place to St. James Park". "The formation in 1838 of Claridges Patent Asphalte Company (with a distinguished list of aristocratic patrons, and Marc and Isambard Brunel as, respectively, a trustee and consulting engineer), gave an enormous impetus to the development of a British asphalt industry". "By the end of 1838, at least two other companies, Robinsons and the Bastenne company, were in production", with asphalt being laid as paving at Brighton, Herne Bay, Canterbury, Kensington, the Strand, and a large floor area in Bunhill-row, while meantime Claridges Whitehall paving "continue(d) in good order". The Bonnington Chemical Works manufactured asphalt using coal tar and by 1839 had installed it in Bonnington.
In 1838, there was a flurry of entrepreneurial activity involving bitumen, which had uses beyond paving. For example, bitumen could also be used for flooring, damp proofing in buildings, and for waterproofing of various types of pools and baths, both of which were also proliferating in the 19th century. One of the earliest surviving examples of its use can be seen at Highgate Cemetery where it was used in 1839 to seal the roof of the terrace catacombs. On the London stockmarket, there were various claims as to the exclusivity of bitumen quality from France, Germany and England. And numerous patents were granted in France, with similar numbers of patent applications being denied in England due to their similarity to each other. In England, "Claridge's was the type most used in the 1840s and 50s".
In 1914, Claridges Company entered into a joint venture to produce tar-bound macadam, with materials manufactured through a subsidiary company called Clarmac Roads Ltd. Two products resulted, namely Clarmac, and Clarphalte, with the former being manufactured by Clarmac Roads and the latter by Claridges Patent Asphalte Co., although Clarmac was more widely used. However, the First World War ruined the Clarmac Company, which entered into liquidation in 1915. The failure of Clarmac Roads Ltd had a flow-on effect to Claridge's Company, which was itself compulsorily wound up, ceasing operations in 1917, having invested a substantial amount of funds into the new venture, both at the outset and in a subsequent attempt to save the Clarmac Company.
Bitumen was thought in 19th century Britain to contain chemicals with medicinal properties. Extracts from bitumen were used to treat catarrh and some forms of asthma and as a remedy against worms, especially the tapeworm. | 7 | Physical Chemistry |
Metallic hydrogen is a phase of hydrogen in which it behaves like an electrical conductor. This phase was predicted in 1935 on theoretical grounds by Eugene Wigner and Hillard Bell Huntington.
At high pressure and temperatures, metallic hydrogen can exist as a partial liquid rather than a solid, and researchers think it might be present in large quantities in the hot and gravitationally compressed interiors of Jupiter and Saturn, as well as in some exoplanets. | 7 | Physical Chemistry |
The projectile is usually sold to be used with a launcher or gun by the same company, to provide best reliability. The different companies usually also sell other types of projectiles for non-lethal use or projectiles with combined effects. Such effects may include:
*break glass and disperse barricades
*mark suspects for later round-ups
*force of impact effect | 1 | Biochemistry |
In a Compton scattering process, an incident photon collides with an electron in a material. The amount of energy exchanged varies with angle, and is given by the formula:
or
* E is the energy of the incident photon.
* E ' is the energy of the outgoing photon, which escapes the material.
* is the mass of the electron.
* c is the speed of light.
* is the angle of deflection for the photon.
The amount of energy transferred to the material varies with the angle of deflection. As approaches zero, none of the energy is transferred. The maximum amount of energy is transferred when approaches 180 degrees.
It is impossible for the photon to transfer any more energy via this process; thus, there is a sharp cutoff at this energy, leading to the name Compton edge. If an isotope has multiple photopeaks, each inflection point will have its own Compton edge.
The region between zero energy transfer and the Compton edge is known as the Compton continuum. | 7 | Physical Chemistry |
In the electronics industry, deionized water is used to rinse components during manufacturing. This is necessary to avoid potential short circuits that could destroy electronic chips. As electronic chips are very small, there is little free space between component elements and unwanted electricity may conduct across components via even a small number of ions, causing a short circuit. Using deionized water to clean the components helps minimize the ions on their surfaces and thus minimizes short circuits.
In the pharmaceutical industry, the presence of unwanted ions in water used in drug development can lead to unwanted side reactions and introduce harmful impurities.
In power generation, the presence of ions in boiler feedwater can lead to the buildup of solids or the degradation of boiler walls, both of which can lower boiler efficiency and present safety hazards.
Due to the large financial and safety concerns present in these three industries, their economic demand for highly pure water provides the bulk of the demand for EDI devices and development.
Electrodeionization systems have also been applied to the removal of heavy metals from different types of wastewater from mining, electroplating, and nuclear processes. The primary ions removed in these processes are chromium, copper, cobalt, and caesium, though EDI sees use in the removal of others as well. | 7 | Physical Chemistry |
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