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A scleroscope is a device used to measure rebound hardness. It consists of a steel ball dropped from a fixed height. The device was invented in 1907. As an improvement on this rough method, the Leeb Rebound Hardness Test, invented in the 1970s, uses the ratio of impact and rebound velocities (as measured by a magnetic inducer) to determine hardness. | 8 | Metallurgy |
People can be exposed to bitumen in the workplace by breathing in fumes or skin absorption. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit of 5 mg/m over a 15-minute period.
Bitumen is basically an inert material that must be heated or diluted to a point where it becomes workable for the production of materials for paving, roofing, and other applications. In examining the potential health hazards associated with bitumen, the International Agency for Research on Cancer (IARC) determined that it is the application parameters, predominantly temperature, that affect occupational exposure and the potential bioavailable carcinogenic hazard/risk of the bitumen emissions. In particular, temperatures greater than 199 °C (390 °F), were shown to produce a greater exposure risk than when bitumen was heated to lower temperatures, such as those typically used in asphalt pavement mix production and placement. IARC has classified paving asphalt fumes as a Class 2B possible carcinogen, indicating inadequate evidence of carcinogenicity in humans.
In 2020, scientists reported that bitumen currently is a significant and largely overlooked source of air pollution in urban areas, especially during hot and sunny periods.
A bitumen-like substance found in the Himalayas and known as shilajit is sometimes used as an Ayurveda medicine, but is not in fact a tar, resin or bitumen. | 7 | Physical Chemistry |
Additional evidence supporting the concept of an RNA world has resulted from research on viroids, the first representatives of a novel domain of "subviral pathogens".
Viroids infect plants, where most are pathogens, and consist of short stretches of highly complementary, circular, single-stranded and non-coding RNA without a protein coat. They are extremely small, ranging from 246 to 467 nucleobases, compared to the smallest known viruses capable of causing an infection, with genomes about 2,000 nucleobases in length.
Based on their characteristic properties, in 1989 plant biologist Theodor Diener argued that viroids are more plausible living relics of the RNA world than introns and other RNAs considered candidates at the time. Dieners hypothesis would be expanded by the research group of Ricardo Flores, and gained a broader audience when in 2014, a New York Times' science writer published a popularized version of the proposal.
The characteristics of viroids highlighted as consistent with an RNA world were their small size, high guanine and cytosine content, circular structure, structural periodicity, the lack of protein-coding ability and, in some cases, ribozyme-mediated replication. One aspect critics of the hypothesis have focused on is that the exclusive hosts of all known viroids, angiosperms, did not evolve until billions of years after the RNA world was replaced, making viroids more likely to have arisen through later evolutionary mechanisms unrelated to the RNA world than to have survived via a cryptic host over that extended period. Whether they are relics of that world or of more recent origin, their function as autonomous naked RNA is seen as analogous to that envisioned for an RNA world. | 9 | Geochemistry |
The development of fluorometers allowed chlorophyll fluorescence analysis to become a common method in plant research. Chlorophyll fluorescence analysis has been revolutionized by the invention of the Pulse-Amplitude-Modulation (PAM) technique and availability of the first commercial modulated chlorophyll fluorometer PAM-101 (Walz, Germany). By modulating the measuring light beam (microsecond-range pulses) and parallel detection of the excited fluorescence the relative fluorescence yield (Ft) can be determined in the presence of ambient light. Crucially, this means chlorophyll fluorescence can be measured in the field even in full sunlight.
Today, chlorophyll fluorometers are designed for measuring many different plant mechanisms. The measuring protocols: F/F and OJIP measure the efficiency of Photosystem II samples at a common and known dark adapted state. These protocols are useful in measuring many types of plant stress. Bernard Genty's light adapted measuring protocol ΔF/F’, or Y(II), is an effective and sensitive way to measure plant samples under ambient or artificial lighting conditions. However, since Y(II) values also change with light intensity, one should compare samples at the same light intensity unless light stress is the focus of the measurement. Y(II) can be more sensitive to some types of plant stress than F/F, such as heat stress.
Other plant mechanism measuring protocols have also been developed. When a chloroplast absorbs light, some of the light energy goes to photochemistry, some goes to regulated heat dissipation, and some goes to unregulated heat dissipation. Various chlorophyll fluorescence measuring parameters exist to measure all of these events. In the lake model, q measures photochemical quenching, Y(NYO) measures plant regulated heat dissipation, and Y(NO) measures unregulated heat dissipation. An older quenching protocol, called the puddle model, uses q for photochemical quenching, q for nonphotochemical quenching of both regulated and unregulated heat dissipation and NPQ for an estimate of nonphotochemical quenching. NPQ has also been resurrected to the lake model mathematically.
In addition, the parameters q, and pNPQ have been developed to measure the photoprotective xanthophyll cycle. q is a measure of state transitions. q is a measure of chloroplast migration, and q is a measure of plant photoinhibition.
At lower actinic light levels NPQ = qE+qT+qI
At high actinic light levels NPQ = qE+qM=qI
Some fluorometers are designed to be portable and operated in one hand.
Consistent further development into imaging fluorometers facilitate the visualization of spatial heterogeneities in photosynthetic activity of samples. These heterogeneities naturally occur in plant leaves for example during growths, various environmental stresses or pathogen infection. Thus knowledge about sample heterogeneities is important for correct interpretation of the photosynthetic performance of the plant sample. High performance imaging fluorometer systems provide options to analyze single cell/single chloroplast as well as sample areas covering whole leaves or plants. | 5 | Photochemistry |
Sequencing of nearly an entire human genome was first accomplished in 2000 partly through the use of shotgun sequencing technology. While full genome shotgun sequencing for small (4000–7000 base pair) genomes was already in use in 1979, broader application benefited from pairwise end sequencing, known colloquially as double-barrel shotgun sequencing. As sequencing projects began to take on longer and more complicated genomes, multiple groups began to realize that useful information could be obtained by sequencing both ends of a fragment of DNA. Although sequencing both ends of the same fragment and keeping track of the paired data was more cumbersome than sequencing a single end of two distinct fragments, the knowledge that the two sequences were oriented in opposite directions and were about the length of a fragment apart from each other was valuable in reconstructing the sequence of the original target fragment.
The first published description of the use of paired ends was in 1990 as part of the sequencing of the human HPRT locus, although the use of paired ends was limited to closing gaps after the application of a traditional shotgun sequencing approach. The first theoretical description of a pure pairwise end sequencing strategy, assuming fragments of constant length, was in 1991. In 1995 the innovation of using fragments of varying sizes was introduced, and demonstrated that a pure pairwise end-sequencing strategy would be possible on large targets. The strategy was subsequently adopted by The Institute for Genomic Research (TIGR) to sequence the entire genome of the bacterium Haemophilus influenzae in 1995, and then by Celera Genomics to sequence the entire fruit fly genome in 2000, and subsequently the entire human genome. Applied Biosystems, now called Life Technologies, manufactured the automated capillary sequencers utilized by both Celera Genomics and The Human Genome Project. | 1 | Biochemistry |
Human activities have also dramatically altered the global nitrogen cycle via production of nitrogenous gases, associated with the global atmospheric nitrogen pollution. There are multiple sources of atmospheric reactive nitrogen (Nr) fluxes. Agricultural sources of reactive nitrogen can produce atmospheric emission of ammonia (), nitrogen oxides () and nitrous oxide (). Combustion processes in energy production, transportation and industry can also result in the formation of new reactive nitrogen via the emission of , an unintentional waste product. When those reactive nitrogens are released to the lower atmosphere, they can induce the formation of smog, particulate matter and aerosols, all of which are major contributors to adverse health effects on human health from air pollution. In the atmosphere, can be oxidized to nitric acid (), and it can further react with to form ammonium nitrate (), which facilitates the formation of particulate nitrate. Moreover, can react with other acid gases (sulfuric and hydrochloric acids) to form ammonium-containing particles, which are the precursors for the secondary organic aerosol particles in photochemical smog. | 1 | Biochemistry |
The coordination of alkynes to transition metals is similar to that of alkenes. The bonding is described by the Dewar–Chatt–Duncanson model. Upon complexation the C-C bond elongates and the alkynyl carbon bends away from 180º. For example, in the phenylpropyne complex Pt(PPh)(MeCPh), the C-C distance is 1.277(25) vs 1.20 Å for a typical alkyne. The C-C-C angle distorts 40° from linearity upon complexation. Because the bending induced by complexation, strained alkynes such as cycloheptyne and cyclooctyne are stabilized by complexation.
The C≡C vibration of alkynes occurs near 2300 cm in the IR spectrum. This mode shifts upon complexation to around 1800 cm, indicating a weakening of the C-C bond. | 0 | Organic Chemistry |
Gerel Ochir was born in Moscow on 17 July 1941. She gained an interest in geology at the age of 10 after her mother gave her a book on geology by Russian geochemist Alexander Fersman. She graduated from secondary school in Ulaanbaatar in 1958.
From 1959, Ochir attended Charles University in Prague. She earned a bachelor's degree in geology and petrography in 1964. She then spent a year with the Department of Geological Survey at the Central Geological Laboratory before she started teaching at the Mongolian State University (now Mongolian University of Science and Technology) in 1965. She later returned to Charles University, earning her RNDr. in geology and geochemistry in 1980. Ochir earned her PhD in petrology from the Irkutsk Institute of Geochemistry of the Siberian Branch of the Russian Academy of Sciences in 1978. Her thesis was on the "Petrology and geochemistry of granite with crystal-bearing pegmatites of Eastern Mongolia." Ochir earned her ScD in geochemistry, petrology, and metallogeny from the Vinogradov Institute of Geochemistry of the Russian Academy of Sciences in 1990. | 9 | Geochemistry |
RMR is regularly used in ecology to study the response of individuals to changes in environmental conditions.
Parasites by definition have a negative impact on their hosts and it is thus expected that there might be effects on host RMR. Varying effects of parasite infection on host RMR have been found. Most studies indicate an increase in RMR with parasite infection, but others show no effect, or even a decrease in RMR. It is still unclear why such variation in the direction of change in RMR with parasite infection is seen. | 1 | Biochemistry |
Oxidative carbonylation is an alternative to phosgenation. The advantage is the avoidance of phosgene. Using copper catalysts, dimethylcarbonate is prepared in this way:
: 2 MeOH + CO + 1/2 O → MeOC(O)OMe + HO
Diphenyl carbonate is also prepared similarly, but using palladium catalysts. The Pd-catalyzed process requires a cocatalyst to reconvert the Pd(0) to Pd(II). Manganese(III) acetylacetonate has been used commercially. | 0 | Organic Chemistry |
Genome-wide CRISPR-Cas9 knockout screens aim to elucidate the relationship between genotype and phenotype by ablating gene expression on a genome-wide scale and studying the resulting phenotypic alterations. The approach utilises the CRISPR-Cas9 gene editing system, coupled with libraries of single guide RNAs (sgRNAs), which are designed to target every gene in the genome. Over recent years, the genome-wide CRISPR screen has emerged as a powerful tool for performing large-scale loss-of-function screens, with low noise, high knockout efficiency and minimal off-target effects. | 1 | Biochemistry |
During the formation of a crystalline structure, different impurities, irregularities, and other defects can form. These imperfections can form through deformation of the solid, rapid cooling, or high energy radiation. Types of defects include point defects, line defects, as well as edge dislocation. | 1 | Biochemistry |
Allyl thiocyanate isomerizes to the isothiocyanate:
Isothiocyanates can be prepared by degradation of dithiocarbamate salts, e.g. induced with lead nitrate.
A related method is tosyl chloride-mediated decomposition of dithiocarbamate salts.
Isothiocyanates may also be accessed by the fragmentation reactions of 1,4,2-oxathiazoles. This methodology has been applied to a polymer-supported synthesis of isothiocyanates. | 0 | Organic Chemistry |
Rigid unit modes (RUMs) represent a class of lattice vibrations or phonons that exist in network materials such as quartz, cristobalite or zirconium tungstate. Network materials can be described as three-dimensional networks of polyhedral groups of atoms such as SiO tetrahedra or TiO octahedra. A RUM is a lattice vibration in which the polyhedra are able to move, by translation and/or rotation, without distorting. RUMs in crystalline materials are the counterparts of floppy modes in glasses, as introduced by Jim Phillips and Mike Thorpe. | 3 | Analytical Chemistry |
* van der Waals Prize 2021 (awarded in 2022 by the 2nd International Conference on Noncovalent Interactions, ICNI-2022)
* RSC-SCI Award Lectureship in the Chemical Sciences (awarded in 2010 by Royal Society of Chemistry/Società Chimica Italiana)
* Intermolecular Interactions and Structural Aspects in Organic Chemistry Award (awarded in 2008 by Società Chimica Italiana)
* Corrado Fuortes award (awarded in 1986 by Istituto Lombardo Accademia di Scienze e Lettere)
* Member of the Academia Europaea (since 2012)
* Member of the International Advisory Board of the Journal of Fluorine Chemistry (Elsevier, 2001 onwards); of Crystals (MDPI, 2015 onwards); of Sustainable Chemistry & Pharmacy (Elsevier, 2017-2019)
* Topic Editor of Crystal Growth & Design (ACS) (2012 onwards)
* Member of the International Steering Committee of the: -International Conference on Noncovalent Intereactions (ICNI) from ICNI-1 (Lisbon, Portugal; 2019) onwards; -International Symposium on Fluorine Chemistry (ISFC) from ISFC-15 (Vancouver, Canada; 1997) onwards; -International Meeting on Halogen Chemistry (HalChem) from Halchem-V (Cagliari, Italy; 2010) onwards; -European Symposium on Fluorine Chemistry (ESFC) from ESFC-11 (Bled, Slovenia; 1995) to ESFC-19 (Warsaw, Poland; 2019)
* Chair of the: -21st International Symposium on Fluorine Chemistry (23-28 August 2015, Como, Italy); -1st International Symposium on Halogen Bonding (ISXB-1)(18-22 June 2014, Porto Cesareo, Lecce, Italy)
* Member of the National Organizing Committee of the 6th International IUPAC Conference on Green Chemistry (4-8 September 2016, Venice, Italy); member of the International Scientific Committee of the 2nd Green & Sustainable Chemistry Conference, 14–17 May 2017, Berlin, Germany; member of the Committee of the Faraday Discussion "Halogen Bonding in Supramolecular and Solid State Chemistry", 10–12 July 2017, Ottawa, Canada
* Coordinator of the UNESCO UNITWIN Network “GREENOMIcS - Green Chemistry Excellence from the Baltic See to the Mediterranean See and Beyond” (2017 onwards)
* Advisor of District 2050 Governor for starting Rotary Club Morimondo Abbazia (2012), Club charter member (2013) and president (2015–16)
* Knight of Magistral Grace of the Sovereign Military Order of Malta (2022); Knight Commander of the Equestrian Order of the Holy Sepulchre of Jerusalem (2020); Knight of Merit with Star of the Sacred Military Constantinian Order of Saint George (SMOCSG) (2020). | 0 | Organic Chemistry |
Many radical processes involve chain reactions or chain propagation with disproportionation and recombination occurring in the terminal step of the reaction. Terminating chain propagation is often most significant during polymerization as the desired chain propagation cannot take place if disproportionation and recombination reactions readily occur. Controlling termination products and regulating disproportionation and recombination reactions in the terminal step are important considerations in radical chemistry and polymerization. In some reactions (such as the one shown below) one or both of the termination pathways can be hindered by steric or solvent effects. | 0 | Organic Chemistry |
UNECE recognizes several rivers that cross international borders which flow into the Caspian Sea.
These are: | 2 | Environmental Chemistry |
HCN4 is the main isoform expressed in the sinoatrial node, but low levels of HCN1 and HCN2 have also been reported.
The current through HCN channels, called the pacemaker current (I), plays a key role in the generation and modulation of cardiac rhythmicity, as they are responsible for the spontaneous depolarization in pacemaker action potentials in the heart. HCN4 isoforms are regulated by cCMP and cAMP and these molecules are agonists at I. | 1 | Biochemistry |
Stopped-flow spectrometry allows chemical kinetics of fast reactions (with half times of the order of milliseconds) to be studied in solution. It was first used primarily to study enzyme-catalyzed reactions. Then the stopped-flow rapidly found its place in almost all biochemistry, biophysics, and chemistry laboratories with a need to follow chemical reactions in the millisecond time scale.
In its simplest form, a stopped-flow mixes two solutions. Small volumes of solutions are rapidly and continuously driven into a high-efficiency mixer. This mixing process then initiates an extremely fast reaction. The newly mixed solution travels to the observation cell and pushes out the contents of the cell (the solution remaining from the previous experiment or from necessary washing steps). The time required for this solution to pass from the mixing point to the observation point is known as dead time. The minimum injection volume will depend on the volume of the mixing cell. Once enough solution has been injected to completely remove the previous solution, the instrument reaches a stationary state and the flow can be stopped. Depending on the syringe drive technology, the flow stop is achieved by using a stop valve called the hard-stop or by using a stop syringe. The stopped-flow also sends a ‘start signal’ to the detector called the trigger so the reaction can be observed. The timing of the trigger is usually software controlled so the user can trigger at the same time the flow stops or a few milliseconds before the stop to check the stationary state has been reached. | 7 | Physical Chemistry |
The Van t Hoff equation relates the change in the equilibrium constant, , of a chemical reaction to the change in temperature, T, given the standard enthalpy change, , for the process. The subscript means "reaction" and the superscript means "standard". It was proposed by Dutch chemist Jacobus Henricus van t Hoff in 1884 in his book Études de Dynamique chimique (Studies in Dynamic Chemistry).
The Van t Hoff equation has been widely utilized to explore the changes in state functions in a thermodynamic system. The Van t Hoff plot, which is derived from this equation, is especially effective in estimating the change in enthalpy and entropy of a chemical reaction. | 7 | Physical Chemistry |
Polyclonal B cell response is a natural mode of immune response exhibited by the adaptive immune system of mammals. It ensures that a single antigen is recognized and attacked through its overlapping parts, called epitopes, by multiple clones of B cell.
In the course of normal immune response, parts of pathogens (e.g. bacteria) are recognized by the immune system as foreign (non-self), and eliminated or effectively neutralized to reduce their potential damage. Such a recognizable substance is called an antigen. The immune system may respond in multiple ways to an antigen; a key feature of this response is the production of antibodies by B cells (or B lymphocytes) involving an arm of the immune system known as humoral immunity. The antibodies are soluble and do not require direct cell-to-cell contact between the pathogen and the B-cell to function.
Antigens can be large and complex substances, and any single antibody can only bind to a small, specific area on the antigen. Consequently, an effective immune response often involves the production of many different antibodies by many different B cells against the same antigen. Hence the term "polyclonal", which derives from the words poly, meaning many, and clones from Greek klōn, meaning sprout or twig; a clone is a group of cells arising from a common "mother" cell. The antibodies thus produced in a polyclonal response are known as polyclonal antibodies. The heterogeneous polyclonal antibodies are distinct from monoclonal antibody molecules, which are identical and react against a single epitope only, i.e., are more specific.
Although the polyclonal response confers advantages on the immune system, in particular, greater probability of reacting against pathogens, it also increases chances of developing certain autoimmune diseases resulting from the reaction of the immune system against native molecules produced within the host. | 1 | Biochemistry |
The trihexagonal tiling exists in a sequence of symmetries of quasiregular tilings with vertex configurations (3.n), progressing from tilings of the sphere to the Euclidean plane and into the hyperbolic plane. With orbifold notation symmetry of *n32 all of these tilings are wythoff construction within a fundamental domain of symmetry, with generator points at the right angle corner of the domain. | 3 | Analytical Chemistry |
Unlike other endonucleases, the MmeI (type IIS) and EcoP15I (type III) restriction endonucleases cut downstream of their target binding sites. MmeI cuts 18/20 base pairs downstream and EcoP15I cuts 25/27 base pairs downstream. As these restriction enzymes bind at their target sequences located in the adaptors, they cut and release vectors that contain short sequences of the fragment or cDNA ligated to them, producing PETs. | 1 | Biochemistry |
Coupling reactions are routinely employed in the preparation of pharmaceuticals. Conjugated polymers are prepared using this technology as well. | 0 | Organic Chemistry |
The water-repelling liquid is applied:
* To provide the surface of materials with excellent water resistance properties - the surface does not absorb water;
* To make the material frost- and corrosion resistant;
* To reduce the pollution of surface;
In addition, the treated surface does not change its appearance, maintains air permeability - material is not sweated and retains the ability to output pairs.
The water-repelling liquid is applied:
* To provide the surface of materials with excellent water resistance properties - the surface does not absorb water;
* To make the material frost- and corrosion resistant;
* To reduce the pollution of surface;
In addition, the treated surface does not change its appearance, maintains air permeability - material is not sweated and retains the ability to output pairs.
* The liquid is methyl hydride siloxane polymer with low viscosity of light-yellow color or colorless.
* It is readily dissoluble in aromatic and chlorinated hydrocarbons, and is undergone to gelation in the presence of amines, amino alcohols, strong acids and alkalis.
* No dissolution in lower alcohols and water.
The positive effects of the application of methyl hydride siloxane:
* Improved water resistance of various building materials - water remains on the surface in the form of droplets and does not penetrate the material;
* Increases frost resistance and improves thermal insulation materials;
* Does not prevent air exchange – the construction outputs pair outside and does not accumulate moisture;
* Prevents UV and infrared radiation;
* Preserves the appearance of the material;
* Extends the service life of materials;
* Prevents surface mosses and lichens.
Water emulsion of organo silicon the methyl hydride siloxane with additives of emulsifier, biocides and stabilizers
Solids content in the emulsion SE 50-94M is 50%. The color is from white to light gray.
Application:
The emulsion oligo methyl hydride siloxane has properties and characteristics similar with the methyl hydride siloxane. The emulsion is also used to provide various materials with water repellency properties.
However, as oligo methyl hydride siloxane is the water emulsion, it can be applied as an additive in the production of solutions and mixtures that is by the volumetric method.
* for concrete, asbestos, gypsum, ceramic, porcelain
* in the production of waterproof papers and leather;
* in the production of water-resistant fabrics;
* by volumetric method in the manufacture of paving tiles, slabs, curbs, fences of different silicate materials;
* as plasticizer in the preparation of plaster, lime and cement solutions;
* as an air involving admixture in the preparation of cement solution
Liquid is a mixture of tetra ethoxy silane and polyethoxy siloxanes.
Application
* Metal manufacture: binding agent in the manufacture of ceramic molds for precision core-mold casting; manufacture of rods exposed to high temperatures; manufacture of non-stick paints;
* Textile industry: feltproofing of woolen cloths; abatement of carpet shrinkage; antirot and antidust protection of carpets; impregnating compound for filter cloths;
* Construction engineering: hydrophobization of construction materials, treatment of coated surfaces; porosity decreasing impregnation of concrete; manufacture of acid-resistant cement;
* Glasswork and cerarnics: antireflection treatment of optical glass; application of light-diffusing coat to electric light bulbs; binding agent for ceramic mixtures, resistant to strongly corrosive mediums, with high manufacture of fireproof material standing temperatures of about 1750 °C and stress of above 127 kg/cm3;
* Coating industry: paint additives forming quick-drying, thermostable and water-resistant coats with constant gloss. | 6 | Supramolecular Chemistry |
In 1955, biologists Britton Chance and G. R. Williams were the first to propose the idea that respiratory enzymes assemble into larger complexes, although the fluid state model remained the standard. However, as early as 1985, researchers had begun isolating complex III/complex IV supercomplexes from bacteria and yeast. Finally, in 2000 Hermann Schägger and Kathy Pfeiffer used Blue Native PAGE to isolate bovine mitochondrial membrane proteins, showing Complex I, III, and IV arranged in supercomplexes. | 1 | Biochemistry |
Solvents with a dielectric constant (more accurately, relative static permittivity) greater than 15 (i.e. polar or polarizable) can be further divided into protic and aprotic. Protic solvents, such as water, solvate anions (negatively charged solutes) strongly via hydrogen bonding. Polar aprotic solvents, such as acetone or dichloromethane, tend to have large dipole moments (separation of partial positive and partial negative charges within the same molecule) and solvate positively charged species via their negative dipole. In chemical reactions the use of polar protic solvents favors the S1 reaction mechanism, while polar aprotic solvents favor the S2 reaction mechanism. These polar solvents are capable of forming hydrogen bonds with water to dissolve in water whereas non-polar solvents are not capable of strong hydrogen bonds. | 2 | Environmental Chemistry |
Some sucrose esters, such as sucrose distearate, sucrose dilaurate, sucrose palmitate, etc. are added in cosmetics products as an emulsifier. Some have a function in skin conditioning and emollient. Cosmetics products that might have sucrose esters as an ingredient includes eyelash products, hair treatments, oil gels, skin products and deodorants. | 0 | Organic Chemistry |
Solid diazonium halides are often dangerously explosive, and fatalities and injuries have been reported.
The nature of the anions affects stability of the salt. Arenediazonium perchlorates, such as nitrobenzenediazonium perchlorate, have been used to initiate explosives. | 0 | Organic Chemistry |
The RNA-editing system seen in the animal may have evolved from mononucleotide deaminases, which have led to larger gene families that include the apobec-1 and adar genes. These genes share close identity with the bacterial deaminases involved in nucleotide metabolism. The adenosine deaminase of E. coli cannot deaminate a nucleoside in the RNA; the enzymes reaction pocket is too small for the RNA strand to bind to. However, this active site is widened by amino acid changes in the corresponding human analog genes, APOBEC1 and ADAR', allowing deamination.
The gRNA-mediated pan-editing in trypanosome mitochondria, involving templated insertion of U residues, is an entirely different biochemical reaction. The enzymes involved have been shown in other studies to be recruited and adapted from different sources. But the specificity of nucleotide insertion via the interaction between the gRNA and mRNA is similar to the tRNA editing processes in the animal and Acanthamoeba mitochondria. Eukaryotic ribose methylation of rRNAs by guide RNA molecules is a similar form of modification.
Thus, RNA editing evolved more than once. Several adaptive rationales for editing have been suggested. Editing is often described as a mechanism of correction or repair to compensate for defects in gene sequences. However, in the case of gRNA-mediated editing, this explanation does not seem possible because if a defect happens first, there is no way to generate an error-free gRNA-encoding region, which presumably arises by duplication of the original gene region. A more plausible alternative for the evolutionary origins of this system is through constructive neutral evolution, where the order of steps is reversed, with the gratuitous capacity for editing preceding the "defect". | 1 | Biochemistry |
Microscopically, liquids consist of a dense, disordered packing of molecules. This contrasts with the other two common phases of matter, gases and solids. Although gases are disordered, the molecules are well-separated in space and interact primarily through molecule-molecule collisions. Conversely, although the molecules in solids are densely packed, they usually fall into a regular structure, such as a crystalline lattice (glasses are a notable
exception). | 7 | Physical Chemistry |
The charge modulation spectroscopy signal can be defined as the differential transmission divided by the total transmission . By modulating the mobile carriers, an increase transmission and decrease transmission features could be both observed. The former relates to the bleaching and the latter to the charge absorption and electrically induced absorption (electro-absorption). The charge modulation spectroscopy spectra is an overlap of charge-induced and electro-absorption features. In transistors, the electro-absorption is more significant during the high voltage drop. There are several ways to identify the electro-absorption contribution, such as get the second harmonic , or probe it at the depletion region. | 7 | Physical Chemistry |
Polar liquids have a tendency to be more viscous than nonpolar liquids. For example, nonpolar hexane is much less viscous than polar water. However, molecule size is a much stronger factor on viscosity than polarity, where compounds with larger molecules are more viscous than compounds with smaller molecules. Thus, water (small polar molecules) is less viscous than hexadecane (large nonpolar molecules). | 7 | Physical Chemistry |
The photocytes of Renilla köllikeri were found to have a diameter of eight to ten micrometers. The mitochondria of the photocytes were found to be very large with abnormally organized cristae surrounding the nucleus of the cell. The rough endoplasmic reticulum of the photocytes were found to exist close to the cell membrane. Several small vesicles, on the order of 0.25 micrometers, were found in the cell, and differently shaped granules containing diverse contents were also observed. | 1 | Biochemistry |
The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Archibald Scott Couper in 1858 and Johann Josef Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but in these years very little was known about aromatic chemistry, and so chemists were unable to adduce appropriate evidence to favor any particular formula.
But many chemists had begun to work on aromatic substances, especially in Germany, and relevant data was coming fast. In 1865, the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German on the same subject. Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every disubstituted derivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure. Kekulés symmetrical ring could explain these curious facts, as well as benzenes 1:1 carbon-hydrogen ratio.
The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulés honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory. He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake biting its own tail (a symbol in ancient cultures known as the ouroboros). This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. This was seven years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. Curiously, a similar, humorous depiction of benzene had appeared in 1886 in a pamphlet entitled Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft, only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulés anecdote. Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if it had not yet appeared in print. Kekulé's 1890 speech in which this anecdote appeared has been translated into English. If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862.
In 1929, the cyclic nature of benzene was finally confirmed by the crystallographer Kathleen Lonsdale using X-ray diffraction methods. Using large crystals of hexamethylbenzene, a benzene derivative with the same core of six carbon atoms, Lonsdale obtained diffraction patterns. Through calculating more than thirty parameters, Lonsdale demonstrated that the benzene ring could not be anything but a flat hexagon, and provided accurate distances for all carbon-carbon bonds in the molecule. | 2 | Environmental Chemistry |
Increasing the yield of succinate from mixed acid fermentation was first done by overexpressing the enzyme PEP carboxylase. This produced a succinate yield that was approximately 3 times greater than normal. Several experiments using a similar approach have followed.
Alternative approaches have altered the redox and ATP balance to optimize the succinate yield. | 1 | Biochemistry |
Dissimilatory nitrate reduction to ammonium is similar to the process of denitrification, though NO is reduced farther to NH rather than to N, transferring eight electrons. Both denitrifiers and nitrate ammonifiers are competing for NO in the environment. Despite the redox potential of dissimilatory nitrate reduction to ammonium being lower than denitrification and producing less Gibbs free energy, energy yield of denitrification may not be efficiently conserved in its series of enzymatic reactions and nitrate ammonifiers may achieve higher growth rates and outcompete denitrifiers. This is may be especially pronounced when NO is limiting compared to organic carbon, as organic carbon is oxidised more efficiently per NO (as each molecule NO is reduced farther). The balance of denitrification and DNRA is important to the nitrogen cycle of an environment as both use NO but, unlike denitrification, which produces gaseous, non-bioavailable N (a sink of nitrogen), DNRA produces bioavailable, soluble NH. | 1 | Biochemistry |
Phenoxymethylpenicillin is usually well tolerated but may occasionally cause transient nausea, vomiting, epigastric distress, diarrhea, constipation, acidic smell to urine and black hairy tongue. A previous hypersensitivity reaction to any penicillin is a contraindication. | 4 | Stereochemistry |
Carpanone is a naturally occurring lignan-type natural product most widely known for the remarkably complex way nature prepares it, and the similarly remarkable success that an early chemistry group, that of Orville L. Chapman, had at mimicking natures pathway. Carpanone is an organic compound first isolated from the carpano trees (Cinnamomum sp.') of Bougainville Island by Brophy and coworkers, trees from which the natural product derives its name. The hexacyclic lignan is one of a class of related diastereomers isolated from carpano bark as mixtures of equal proportion of the "handedness" of its components (i.e., racemic mixtures), and is notable in its stereochemical complexity, because it contains five contiguous stereogenic centers. The route by which this complex structure is achieved through biosynthesis involves a series of reactions that, almost instantly, take a molecule with little three-dimensionality to the complex final structure. Notably, Brophy and coworkers isolated the simpler carpacin, a phenylpropanoid with a 9-carbon framework, recognized its substructure as being dimerized within the complex carpanone structure, and proposed a hypothesis of how carpacin was converted to carpanone in plant cells:
* carpacin underwent loss of a methyl (-CH) group from the ring methoxy (-OCH) group to provide the phenol, desmethylcarpacin,
* this phenol intermediate then underwent a phenolic coupling to generate a dimeric intermediate, which was
* followed immediately by a Diels-Alder (4+2) cycloaddition reaction to create 2 new rings, to give the final carpanone product.
Remarkably, within two years, Chapman and coworkers were able to chemically design a route to mimic this proposed biosynthetic route, and achieved the synthesis of carpanone from carpacin in a single "pot", in about 50% yield.
Carpanone itself is limited in its pharmacologic and biologic activities, but related analogs arrived at by variations of the Brophy-Chapman approach have shown activities as tool compounds relevant to mammalian exocytosis and vesicular traffic, and provided therapeutic "hits" in antiinfective, antihypertensive, and hepatoprotective areas.
The original Chapman design and synthesis is considered a classic in total synthesis, and one that highlights the power of biomimetic synthesis. | 0 | Organic Chemistry |
(LAP-A), a product of the octadecanoid pathway in some solanaceous plants, has been shown by Fowler et al. to have a regulatory role in the late wound response of tomato. Experiments were conducted using three genotypes of tomato plants: wildtype (WT), (LapA-SI) plants that were silenced for LAP-A, and LapA-OX that constitutively expressed LAP-A. Late-gene expression was inhibited in wounded LapA-SI plants, and the LapA-SI plants were also more susceptible to tobacco hornworm feeding, relative to wildtype (WT) plants. In comparison, the wounded LapA-OX leaves exhibited heightened levels of late gene RNA accumulation, an increased resistance to herbivory, and extended expression of late wound-response genes. These data suggest that LAP-A functions in regulating both the intensity and the persistence of the late wound response. However, unwounded LapA-OX did not accumulate late gene RNA transcripts, suggesting that presence of LAP-A alone is not sufficient to induce late gene expression. LAP-A is the first plant aminopeptidase shown to have a regulatory role in signal transduction pathway. | 1 | Biochemistry |
Modern-day boilers, such as those in coal-fired power stations, are still fitted with economizers which are descendants of Green's original design. In this context they are often referred to as feedwater heaters and heat the condensate from turbines before it is pumped to the boilers.
Economizers are commonly used as part of a heat recovery steam generator (HRSG) in a combined cycle power plant. In an HRSG, water passes through an economizer, then a boiler and then a superheater. The economizer also prevents flooding of the boiler with liquid water that is too cold to be boiled given the flow rates and design of the boiler.
A common application of economizers in steam power plants is to capture the waste heat from boiler stack gases (flue gas) and transfer it to the boiler feedwater. This raises the temperature of the boiler feedwater, lowering the needed energy input, in turn reducing the firing rates needed for the rated boiler output. Economizers lower stack temperatures which may cause condensation of acidic combustion gases and serious equipment corrosion damage if care is not taken in their design and material selection. | 7 | Physical Chemistry |
The Sharpless epoxidation, developed by K. Barry Sharpless in 1980, has been utilized for the kinetic resolution of a racemic mixture of allylic alcohols. While extremely effective at resolving a number of allylic alcohols, this method has a number of drawbacks. Reaction times can run as long as 6 days, and the catalyst is not recyclable. However, the Sharpless asymmetric epoxidation kinetic resolution remains one of the most effective synthetic kinetic resolutions to date. A number of different tartrates can be used for the catalyst; a representative scheme is shown below utilizing diisopropyl tartrate. This method has seen general use on a number of secondary allylic alcohols.
Sharpless asymmetric dihydroxylation has also seen use as a method for kinetic resolution. This method is not widely used, however, since the same resolution can be accomplished in different manners that are more economical. Additionally, the Shi epoxidation has been shown to affect kinetic resolution of a limited selection of olefins. This method is also not widely used, but is of mechanistic interest. | 4 | Stereochemistry |
The so-called carbamate insecticides feature the carbamate ester functional group. Included in this group are aldicarb (Temik), carbofuran (Furadan), carbaryl (Sevin), ethienocarb, fenobucarb, oxamyl, and methomyl. These insecticides kill insects by reversibly inactivating the enzyme acetylcholinesterase (AChE inhibition) (IRAC mode of action 1a). The organophosphate pesticides also inhibit this enzyme, although irreversibly, and cause a more severe form of cholinergic poisoning (the similar IRAC MoA 1b).
Fenoxycarb has a carbamate group but acts as a juvenile hormone mimic, rather than inactivating acetylcholinesterase.
The insect repellent icaridin is a substituted carbamate.
Besides their common use as arthropodocides/insecticides, they are also nematicidal. One such is Oxamyl.
Sales have declined dramatically over recent decades. | 0 | Organic Chemistry |
Planar Flow Casting (PFC) is a commonly used melt spinning process for the industrial fabrication of wide metallic glass sheets. In this process, the primary modification is that a much wider nozzle is used to eject the melt from the crucible. As a result, the melt puddle covers a larger area of the drum, which in turn forms a larger area of ribbon. PFC is commonly cast in a vacuum to avoid oxidation of the molten material, which would affect the quality of the resulting product. Ribbons up to 200 mm wide have been industrially achieved using PFC. | 8 | Metallurgy |
Annual Review of Physical Chemistry is a peer-reviewed scientific journal published by Annual Reviews. It covers all topics pertaining to physical chemistry. The editors are Todd J. Martínez (Stanford University) and Anne McCoy (University of Washington). As of 2023, Annual Review of Physical Chemistry is being published as open access, under the Subscribe to Open model. The journal is indexed in the Science Citation Index Expanded and Chemical Abstracts Service. As of 2023, Journal Citation Reports gives it a 2022 impact factor of 14.7. | 7 | Physical Chemistry |
His lectures frequently lasted for three or four hours. His longest known lecture defined the unit of time known as the "Woodward", after which his other lectures were deemed to be so many "milli-Woodwards" long. In many of these, he eschewed the use of slides and drew structures by using multicolored chalk. Typically, to begin a lecture, Woodward would arrive and lay out two large white handkerchiefs on the countertop. Upon one would be four or five colors of chalk (new pieces), neatly sorted by color, in a long row. Upon the other handkerchief would be placed an equally impressive row of cigarettes. The previous cigarette would be used to light the next one. His Thursday seminars at Harvard often lasted well into the night. He had a fixation with blue, and many of his suits, his car, and even his parking space were coloured in blue.
In one of his laboratories, his students hung a large black and white photograph of the master from the ceiling, complete with a large blue "tie" appended. There it hung for some years (early 1970s), until scorched in a minor laboratory fire. He detested exercise, could get along with only a few hours of sleep every night, was a heavy smoker, and enjoyed Scotch whisky and martinis. | 4 | Stereochemistry |
Four members of 2A peptides family are frequently used in life science research. They are P2A, E2A, F2A, and T2A. F2A is derived from foot-and-mouth disease virus 18; E2A is derived from equine rhinitis A virus; P2A is derived from porcine teschovirus-1 2A; T2A is derived from thosea asigna virus 2A.
The following table shows the sequences of four members of 2A peptides. Adding the optional linker “GSG” (Gly-Ser-Gly) on the N-terminal of a 2A peptide helps with efficiency. | 1 | Biochemistry |
A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input. The name is from the Greek roots mono-, "single", and chroma, "colour", and the Latin suffix -ator, denoting an agent. | 7 | Physical Chemistry |
Late transition metals from groups 10, 11, and 12 when placed at the anomeric carbon show strong axial preferences. This phenomenon termed as the metallo-anomeric effect originates from stabilizing hyperconjugative interactions between oxygen or other heteroatoms with lone pairs and C-M anti-bonding orbitals that act as good acceptors. The generalized metallo-anomeric effect refers to thermodynamic stabilization of synclinal conformers of compounds with the general formula M-CH-OR. Axial/equatorial preferences can be influenced by ligands attached to the metal and electronic configuration. In general terms, moving from a lighter to a heavier element in the group, the magnitude of the metallo-anomeric effect increases. Furthermore, higher oxidation states favor axial/synclinal conformers. | 7 | Physical Chemistry |
Trifluoromethylsulfur pentafluoride, CFSF, is a rarely used industrial greenhouse gas. It was first identified in the atmosphere in 2000. Trifluoromethylsulfur pentafluoride is considered to be one of the several "super-greenhouse gases". | 2 | Environmental Chemistry |
The hexahydrate consists of octahedral cation centers and chloride anions () as counterions. Hydrogen bonds link the cation and anions.
The hydrated form of aluminium chloride has an octahedral molecular geometry, with the central aluminium ion surrounded by six water ligand molecules. Being coordinatively saturated, the hydrate is of little value as a catalyst in Friedel-Crafts alkylation and related reactions. | 0 | Organic Chemistry |
Ethyl bromoacetate is listed by the World Health Organization as a riot control agent, and was first employed for that purpose by French police in 1912. The French army used rifle grenades grenades lacrymogènes filled with this gas against the Germans beginning in August 1914, but the weapons were largely ineffective, even though ethyl bromoacetate is twice as toxic as chlorine. In the early months of the war the British also used the weaponized use of tear gas agents and more toxic gasses including sulfur dioxide. The German army then used these attacks to justify their subsequent employment of it as odorant or warning agent in odorless, toxic gases and chemical weapons in 1915 under the German code Weisskreuz (White Cross).
In organic synthesis, it is a versatile alkylating agent. Its major application involves the Reformatsky reaction, wherein it reacts with zinc to form a zinc enolate. The resulting condenses with carbonyl compounds to give a β-hydroxy-esters.
It is also the starting point for the preparation of several other reagents. For example, the related Wittig reagent (prepared by reaction with triphenylphosphine) is commonly used to prepare alpha,beta-unsaturated esters from carbonyl compounds such as benzaldehyde: | 0 | Organic Chemistry |
Crystalline structure is the composition of ions, atoms, and molecules that are held together and ordered in a 3D shape. The main difference between a crystalline structure and an amorphous structure is the order of the components. Crystalline has the highest level of order possible in the material where amorphous structure consists of irregularities in the ordering pattern. One way to describe crystalline structures is through the crystal lattice, which is a three-dimensional representation of the location of a repeating factor (unit cell) in the structure denoted with lattices. There are 14 different configurations of atom arrangement in a crystalline structure, and are all represented under Bravais lattices. | 1 | Biochemistry |
At equilibrium, the sum of the chemical potentials of the reactants is equal to the sum of the chemical potentials of the products. The Gibbs free energy change for the reactions, ΔG, is equal to the difference between these sums and therefore, at equilibrium, is equal to zero. Thus, for an equilibrium such as
Substitute in the expressions for the chemical potential of each reactant:
Upon rearrangement this expression becomes
The sum
is the standard free energy change for the reaction, .
Therefore,
where is the equilibrium constant. Note that activities and equilibrium constants are dimensionless numbers.
This derivation serves two purposes. It shows the relationship between standard free energy change and equilibrium constant. It also shows that an equilibrium constant is defined as a quotient of activities. In practical terms this is inconvenient. When each activity is replaced by the product of a concentration and an activity coefficient, the equilibrium constant is defined as
where [S] denotes the concentration of S, etc. In practice equilibrium constants are determined in a medium such that the quotient of activity coefficient is constant and can be ignored, leading to the usual expression
which applies under the conditions that the activity quotient has a particular (constant) value. | 7 | Physical Chemistry |
Like the photo-oxidation method, UV light is the oxidizer but the oxidation power of the reaction is magnified by the addition of a chemical oxidizer, which is usually a persulfate compound. The mechanisms of the reactions are as follows:
Free radical oxidants formed:
Excitation of organics:
Oxidation of organics:
The UV–chemical oxidation method offers a relatively low maintenance, high sensitivity method for a wide range of applications. However, there are oxidation limitations of this method. Limitations include the inaccuracies associated with the addition of any foreign substance into the analyte and samples with high amounts of particulates. Performing "system blank" analysis, which is to analyze then subtract the amount of carbon contributed by the chemical additive, inaccuracies are lowered. However, analyses of levels below 200 ppb TOC are still difficult. | 3 | Analytical Chemistry |
As the slag becomes enriched with iron oxide during the reaction in air, it becomes basic and then combines with the siliceous refractory lining, which is very acidic. A basic refractory lining would not react and would therefore lower the cost of production. The adoption of a lining inspired by one developed by Sidney Thomas and Percy Gilchrist in 1877 was suggested by Hollway during his last tests in the early 1800s. However, the idea was not tested, as fundamental problems related to the air blowing were more of a problem than refractory optimization.
In 1890, a basic refractory lining was tested on one of Parrot Smelter's Manhès-David converters, in Butte, under the direction of Herman A. Keller. The tests did not result in a lining compatible with industrial operation. In 1906, Ralph Baggaley, still in Montana, succeeded, after a number of tests, in industrializing a basic coating at Pittsmont Smelter, which was abandoned in 1908 after he left the factory. After all that, the Norwegian Kudsen succeeded as of 1908 in using a basic coating with the Sulitjelma Mines. He carried out two successive blowings there, initially in a small converter with a basic coating, and then in a second traditional converter with an acidic coating.
Finally, in 1909, at the Baltimore Copper Company's Smelter, the Americans William H. Peirce and Elias A.C. Smith succeeded in addressing the main drawbacks of basic refractories; basic refractories were more fragile, and, above all, they dissipated more heat than acidic refractories. By developing a masonry suitable for the cylindrical converter and increasing the amount of metal fed into the furnace, they solved the remaining problems.
Peirce and Smith's converter proved much more advantageous than that of Manhès and David. The basic refractory, which did not react with slag, lasted much longer. This improvement eliminated the need for replacement of the converters, the construction of masonry installations, and replacement converters (there were two masonry converters for every one in service in 1897 at Anaconda Copper). It also reduced the risk of piercings due to poor control of wearing of the refractory. The refractory layer could then be thinner, increasing the capacity of the converter. The capacity was not dependent on wearing of the refractory, thus simplifying the management of the flows of molten metal in factories.
If the material used to prepare the acid refractory contains copper, or even silver or gold (frequently associated with copper in gold-bearing quartz), these metals join the matte as the lining is removed. Considering the refractory's rapid destruction, the economic advantage of an acidic refractory is therefore only realized if its consumption adds value to the process. This situation is however rather rare and, even if this is the case, silica rich in precious metals can be made by other economically viable means. Therefore, in 1921, the basic refractory was considered the main factor in the cost reduction in the extraction of copper ores. In some cases, a reduction in conversion costs from $15–20 to $4–5 was reported. | 8 | Metallurgy |
Previously called "ideal ATM" and "polarization-varying ATM," stationary sample ATM (SSATM) involves rotation of the linearly polarized state of the THz beam in a time-domain spectroscopy (TDS) configuration parallel to the interrogated material sample. In a SSATM configuration, the THz beam polarization is rotated through 360° in a plane perpendicular to the propagation direction of the beam. Measurements of the sample's anisotropy is measured at several THz polarization angles.
At least two methods to achieve THz polarization rotation for SSATM have been demonstrated: 1) by using a THz quarter waveplate (THz-QWP) together with an infrared polarizer and 2) by rotating the photoconductive antenna.
In the case of employing a THz-QWP and an infrared polarizer, the magnitude of the measured signal, , where is a time delay between THz generation and the detected pulses in a THz-TDS system is dependent on the relative polarization angle of the THz light, and the polarization angle of the ultrafast near-infrared (NIR) probe beam, , at the sample by the relationship
The objective is to maintain equal magnitude of the THz electric field at the sample for all measurement angles, . This requires adjustment of for every . | 7 | Physical Chemistry |
As early as 1976 a short-term, relatively small, dead zone off the coasts of New York and New Jersey cost commercial and recreational fisheries over $500 million. In 1998 a HAB in Hong Kong killed over $10 million in high-value fish.
In 2009, the economic impact for the state of Washington's coastal counties dependent on its fishing industry was estimated to be $22 million. In 2016, the U.S. seafood industry expected future lost revenue could amount to $900 million annually.
NOAA has provided a few cost estimates for various blooms over the past few years: $10.3 million in 2011 due to a HAB at Texas oyster landings; $2.4 million lost income by tribal commerce from 2015 fishery closures in the pacific northwest; $40 million from Washington state's loss of tourism from the same fishery closure.
Along with damage to businesses, the toll from human sickness results in lost wages and damaged health. The costs of medical treatment, investigation by health agencies through water sampling and testing, and the posting of warning signs at effected locations is also costly.
The closures applied to areas where this algae bloom occurs has a big negative impact of the fishing industries, add to that the high fish mortality that follows, the increase in price due to the shortage of fish available and decrease in the demand for seafood due to the fear of contamination by toxins. This causes a big economic loss for the industry.
Economic costs are estimated to rise. In June 2015, for instance, the largest known toxic HAB forced the shutdown of the west coast shellfish industry, the first time that has ever happened. One Seattle NOAA expert commented, "This is unprecedented in terms of the extent and magnitude of this harmful algal bloom and the warm water conditions we're seeing offshore...." The bloom covered a range from Santa Barbara, California northward to Alaska.
The negative impact on fish can be even more severe when they are confined to pens, as they are in fish farms. In 2007 a fish farm in British Columbia lost 260 tons of salmon as a result of blooms, and in 2016 a farm in Chile lost 23 million salmon after an algal bloom. | 3 | Analytical Chemistry |
After the first bond is synthesized, the RNA polymerase must clear the promoter. During this time, there is a tendency to release the RNA transcript and produce truncated transcripts. This is called abortive initiation and is common for both eukaryotes and prokaryotes. Abortive initiation continues to occur until the σ factor rearranges, resulting in the transcription elongation complex (which gives a 35 bp-moving footprint). The σ factor is released before 80 nucleotides of mRNA are synthesized. Once the transcript reaches approximately 23 nucleotides, it no longer slips and elongation can occur. | 1 | Biochemistry |
Polymerized ionic liquids, poly(ionic liquid)s or polymeric ionic liquids, all abbreviated as PIL is the polymeric form of ionic liquids. They have half of the ionicity of ionic liquids since one ion is fixed as the polymer moiety to form a polymeric chain. PILs have a similar range of applications, comparable with those of ionic liquids but the polymer architecture provides a better chance for controlling the ionic conductivity. They have extended the applications of ionic liquids for designing smart materials or solid electrolytes. | 7 | Physical Chemistry |
Atmospheric carbon dioxide has risen from 280 to 409 ppm since the industrial revolution. This increase in carbon dioxide has led to a 0.1 decrease in pH, and it could decrease by 0.5 by 2100. When carbon dioxide meets seawater, it forms carbonic acid; the molecules dissociate into hydrogen, bicarbonate, and carbonate, and they lower the pH of the ocean. Sea surface temperature, ocean acidity, and dissolved inorganic carbon are also positively correlated with atmospheric carbon dioxide. Ocean acidification can cause hypercapnia and increase stress in marine organisms, thereby leading to decreased biodiversity. Coral reefs themselves can also be negatively affected by ocean acidification, as calcification rates decrease and acidity increases.
Aragonite is impacted by the process of ocean acidification because it is a form of calcium carbonate. It is essential in coral viability and health because it is found in coral skeletons and is more readily soluble than calcite. Increasing carbon dioxide levels can reduce coral growth rates from 9 to 56% due to the lack of available carbonate ions needed for the calcification process.Other calcifying organisms, such as bivalves and gastropods, experience negative effects due to ocean acidification as well. The excess hydrogen ions in the acidic water dissolve their shells, limiting their shelter and reproduction rates.
As a biodiversity hotspot, the many taxa of the Great Barrier Reef are threatened by ocean acidification. Rare and endemic species are in greater danger due to ocean acidification, because they rely upon the Great Barrier Reef more extensively. Additionally, the risk of coral reefs collapsing due to acidification poses a threat to biodiversity. The stress of ocean acidification could also negatively affect other biological processes, such as reducing photosynthesis or reproduction and allowing organisms to become vulnerable to disease. | 9 | Geochemistry |
The equation describing the fluorescence as a function of time is particularly simple in another limit. If a large number of proteins bind to sites in a small volume such that there the fluorescence signal is dominated by the signal from bound proteins, and if this binding is all in a single state with an off rate k, then the fluorescence as a function of time is given by
Note that the recovery depends on the rate constant for unbinding, k, only. It does not depend on the on rate for binding. Although it does depend on a number of assumptions
#The on rate must be sufficiently large in order for the local concentration of bound protein to greatly exceed the local concentration of free protein, and so allow us to neglect the contribution to f of the free protein.
#The reaction is a simple bimolecular reaction, where the protein binds to localised sites that do not move significantly during recovery
#Exchange is much slower than diffusion (or whatever transport mechanism is responsible for mobility), as only then does the diffusing fraction recovery rapidly and then acts as the source of fluorescent protein that binds and replaces the bound bleached protein and so increases the fluorescence. With r the radius of the bleached spot, this means that the equation is only valid if the bound lifetime .
If all these assumptions are satisfied, then fitting an exponential to the recovery curve will give the off rate constant, k. However, other dynamics can give recovery curves similar to exponentials, so fitting an exponential does not necessarily imply that recovery is dominated by a simple bimolecular reaction. One way to distinguish between recovery with a rate determined by unbinding and recovery that is limited by diffusion, is to note that the recovery rate for unbinding-limited recovery is independent of the size of the bleached area r, while it scales as , for diffusion-limited recovery. Thus if a small and a large area are bleached, if recovery is limited by unbinding then the recovery rates will be the same for the two sizes of bleached area, whereas if recovery is limited by diffusion then it will be much slower for the larger bleached area. | 1 | Biochemistry |
While the presence of any symmetry element within a ligand intended for asymmetric induction might appear counterintuitive, asymmetric induction only requires that the ligand be chiral (i.e. have no improper rotation axis). Asymmetry (i.e. absence of any symmetry elements) is not required. C symmetry improves the enantioselectivity of the complex by reducing the number of unique geometries in the transition states. Steric and kinetic factors then usually favor the formation of a single product. | 4 | Stereochemistry |
Aqueous samples, lysed cells, or homogenised tissue are mixed with equal volumes of a phenol:chloroform mixture. This mixture is then centrifuged. Because the phenol:chloroform mixture is immiscible with water, the centrifuge will cause two distinct phases to form: an upper aqueous phase, and a lower organic phase. The aqueous phase rises to the top because it is less dense than the organic phase containing the phenol:chloroform. This difference in density is why phenol, which only has a slightly higher density than water, must be mixed with chloroform to form a mixture with a much higher density than water.
The hydrophobic lipids will partition into the lower organic phase, and the proteins will remain at the interphase between the two phases, while the nucleic acids (as well as other contaminants such as salts, sugars, etc.) remain in the upper aqueous phase. The upper aqueous phase can then be pipetted off. Care must be taken to avoid pipetting any of the organic phase or material at the interface. This procedure is often performed multiple times to increase the purity of the DNA. This procedure yields large double stranded DNA that can be used in PCR or RFLP.
If the mixture is acidic, DNA will precipitate into the organic phase while RNA remains in the aqueous phase. This is because DNA is more readily neutralized than RNA.
There are some disadvantages of this technique in forensic use. It is time-consuming and uses hazardous reagents. Also, because it is a two-step process involving transfer of reagents between tubes, it is at a greater risk of contamination. | 1 | Biochemistry |
Gamma helix (or γ-helix) is a type of secondary structure in proteins that has been predicted by Pauling, Corey, and Branson, but has never been observed in natural proteins. The hydrogen bond in this type of helix was predicted to be between N-H group of one amino acid and the C=O group of the amino acid six residues earlier (or, as described by Pauling, Corey, Branson, "to the fifth amide group beyond it"). This can also be described as i + 6 → i bond and would be a continuation of the series (3 helix, alpha helix, pi helix and gamma helix). This theoretical helix contains 5.1 residues per turn.However, a fully developed gamma helix has characteristics of a structure that has 2.2 amino acid residues per turn, a rise of 2.75Å per residue, and a pseudo-cyclic (C7) structure closed by intramolecular H-bond. Depending on the amino acid's side chain (R) involved in this main-chain reversal motif, two stereoisomers can occur with their Cα-substituent located either in the axial or in the equatorial position relative to the H-bonded pseudo-cycle. | 1 | Biochemistry |
For iron rust to occur the metal has to be in contact with oxygen and water. The chemical reactions for this process are relatively complex and not all of them are completely understood. It is believed the causes are the following:
Electron transfer (reduction-oxidation)
:One area on the surface of the metal acts as the anode, which is where the oxidation (corrosion) occurs. At the anode, the metal gives up electrons.
::Fe → Fe + 2 e
:Electrons are transferred from iron, reducing oxygen in the atmosphere into water on the cathode, which is placed in another region of the metal.
::O + 4 H + 4 e → 2 HO
:Global reaction for the process:
::2 Fe + O + 4 H → 2 Fe + 2 HO
:Standard emf for iron rusting:
::E° = E° (cathode) − E° (anode)
::E° = 1.23V − (−0.44 V) = 1.67 V
Iron corrosion takes place in an acid medium; H ions come from reaction between carbon dioxide in the atmosphere and water, forming carbonic acid. Fe ions oxidize further, following this equation:
: 4 Fe + O + (4+2) HO → 2 FeO·HO + 8 H
Iron(III) oxide hydrate is known as rust. The concentration of water associated with iron oxide varies, thus the chemical formula is represented by FeO·HO.
An electric circuit is formed as passage of electrons and ions occurs; thus if an electrolyte is present it will facilitate oxidation, explaining why rusting is quicker in salt water. | 7 | Physical Chemistry |
In molecular biology, protein catabolism is the breakdown of proteins into smaller peptides and ultimately into amino acids. Protein catabolism is a key function of digestion process. Protein catabolism often begins with pepsin, which converts proteins into polypeptides. These polypeptides are then further degraded. In humans, the pancreatic proteases include trypsin, chymotrypsin, and other enzymes. In the intestine, the small peptides are broken down into amino acids that can be absorbed into the bloodstream. These absorbed amino acids can then undergo amino acid catabolism, where they are utilized as an energy source or as precursors to new proteins.
The amino acids produced by catabolism may be directly recycled to form new proteins, converted into different amino acids, or can undergo amino acid catabolism to be converted to other compounds via the Krebs cycle. | 1 | Biochemistry |
For small-scale hydrogen production, RO is sometimes used to prevent formation of mineral deposits on the surface of electrodes. | 3 | Analytical Chemistry |
Solder bumping technology (the process of joining a chip to a substrate without shorting using solder) was first conceived and implemented by IBM in the early 1960s. Three versions of this type of solder joining were developed. The first was to embed copper balls in the solder bumps to provide a positive stand-off. The second solution, developed by Delco Electronics (General Motors) in the late 1960s, was similar to embedding copper balls except that the design employed a rigid silver bump. The bump provided a positive stand-off and was attached to the substrate by means of solder that was screen-printed onto the substrate. The third solution was to use a screened glass dam near the electrode tips to act as a ‘‘stop-off’’ to prevent the ball solder from flowing down the electrode. By then the Ball Limiting Metallurgy (BLM) with a high-lead (Pb) solder system and a copper ball had proven to work well. Therefore, the ball was simply removed and the solder evaporation process extended to form pure solder bumps that were approximately 125μm high. This system became known as the controlled collapse chip connection (C3 or C4).
Until the mid-1990s, this type of flip-chip assembly was practiced almost exclusively by IBM and Delco. Around this time, Delco sought to commercialize its technology and formed Flip Chip Technologies with Kulicke & Soffa Industries as a partner. At the same time, MCNC (which had developed a plated version of IBM’s C4 process) received funding from DARPA to commercialize its technology. These two organizations, along with APTOS (Advanced Plating Technologies on Silicon), formed the nascent out-sourcing market.
During this same time, companies began to look at reducing or streamlining their packaging, from the earlier multi-chip-on-ceramic packages that IBM had originally developed C4 to support, to what were referred to as Chip Scale Packages (CSP). There were a number of companies developing products in this area. These products could usually be put into one of two camps: either they were scaled down versions of the multi-chip on ceramic package (of which the Tessera package would be one example); or they were the streamlined versions developed by Unitive Electronics, et al. (where the package wiring had been transferred to the chip, and after bumping, they were ready to be placed).
One of the issues with the CSP type of package (which was intended to be soldered directly to an FR4 or flex circuit) was that for high-density interconnects, the soft solder bump provided less of a stand-off as the solder bump diameter and pitch were decreased. Different solutions were employed including one developed by Focus Interconnect Technology (former APTOS engineers), which used a high aspect ratio plated copper post to provide a larger fixed standoff than was possible for a soft solder collapse joint.
Today, flip chip is a well established technology and collapsed soft solder connections are used in the vast majority of assemblies. The copper post stand-off developed for the CSP market has found a home in high-density interconnects for advanced micro-processors and is used today by IBM for its CPU packaging. | 7 | Physical Chemistry |
Genetic disorders are often an issue within captive populations due to the fact that the populations are usually established from a small number of founders. In large, outbreeding populations, the frequencies of most deleterious alleles are relatively low, but when a population undergoes a bottleneck during the founding of a captive population, previously rare alleles may survive and increase in number. Further inbreeding within the captive population may also increase the likelihood that deleterious alleles will be expressed due to increasing homozygosity within the population. The high occurrence of genetic disorders within a captive population can threaten both the survival of the captive population and its eventual reintroduction back into the wild. If the genetic disorder is dominant, it may be possible to eliminate the disease completely in a single generation by avoiding breeding of the affected individuals. However, if the genetic disorder is recessive, it may not be possible to completely eliminate the allele due to its presence in unaffected heterozygotes. In this case, the best option is to attempt to minimize the frequency of the allele by selectively choosing mating pairs. In the process of eliminating genetic disorders, it is important to consider that when certain individuals are prevented from breeding, alleles and therefore genetic diversity are removed from the population; if these alleles are not present in other individuals, they may be lost completely. Preventing certain individuals from the breeding also reduces the effective population size, which is associated with problems such as the loss of genetic diversity and increased inbreeding. | 1 | Biochemistry |
Thermodynamic scale differs from empirical scales in that it is absolute. It is based on the fundamental laws of thermodynamics or statistical mechanics instead of some arbitrary chosen working material. Besides it covers full range of temperature and has simple relation with microscopic quantities like the average kinetic energy of particles (see equipartition theorem). In experiments ITS-90 is used to approximate thermodynamic scale due to simpler realization. | 7 | Physical Chemistry |
Selective leaching can be used to produce powdered materials with extremely high surface area, such as Raney nickel and other heterogeneous catalysts. Selective leaching can be the pre-final stage of depletion gilding. | 8 | Metallurgy |
One method for synthesizing ynones is the acyl substitution reaction of an alkynyldimethylaluminum with an acyl chloride. An alkynyldimethylaluminum compound is the reaction product of trimethylaluminum and a terminal alkyne.
An alternative is the direct coupling of an acyl chloride with a terminal alkyne, using a copper-based nanocatalyst:
Other methods utilize an oxidative cleavage of an aldehyde, followed by reaction with a hypervalent alkynyl iodide, using a gold catalyst.
An alternative but longer synthetic method involves the reaction of an alkynyllithium compound with an aldehyde. The reaction produces a secondary alcohol that then can be oxidized via the Swern oxidation. | 0 | Organic Chemistry |
Vitamin A deficiency is common in developing countries, especially in Sub-Saharan Africa and Southeast Asia. Deficiency can occur at any age, but is most common in pre-school-age children and pregnant women, the latter due to a need to transfer retinol to the fetus. The causes are low intake of retinol-containing, animal-sourced foods and low intake of carotene-containing, plant-sourced foods. Vitamin A deficiency is estimated to affect approximately one third of children under the age of five around the world, possibly leading to the deaths of 670,000 children under five annually.
Between 250,000 and 500,000 children in developing countries become blind each year owing to vitamin A deficiency. Vitamin A deficiency is "the leading cause of preventable childhood blindness", according to UNICEF. It also increases the risk of death from common childhood conditions, such as diarrhea. UNICEF regards addressing vitamin A deficiency as critical to reducing child mortality, the fourth of the United Nations' Millennium Development Goals.
During diagnosis, night blindness and dry eyes are signs of vitamin A deficiency that can be recognized without requiring biochemical tests. Plasma retinol is used to confirm vitamin A status. A plasma concentration of about 2.0 μmol/L is normal; less than 0.70 μmol/L (equivalent to 20 μg/dL) indicates moderate vitamin A deficiency, and less than 0.35 μmol/L (10 μg/dL) indicates severe vitamin A deficiency. Breast milk retinol of less than 8 μg/gram milk fat is considered insufficient. One weakness of these measures is that they are not good indicators of liver vitamin A stores as retinyl esters in hepatic stellate cells. The amount of vitamin A leaving the liver, bound to retinol binding protein (RBP), is under tight control as long as there are sufficient liver reserves. Only when liver content of vitamin A drops below approximately 20 μg/gram will concentration in the blood decline. | 1 | Biochemistry |
The construction of large-scale microalgae cultivation facilities would inevitably result in negative environmental impacts related to land use change, such as the destruction of existing natural habitats. Microalgae can also under certain conditions emit greenhouse gases, like methane or nitrous oxide, or foul-smelling gases, like hydrogen sulfide, although this has not been widely studied to date. If poorly managed, toxins naturally produced by microalgae may leak into the surrounding soil or ground water. | 0 | Organic Chemistry |
A pigment termed molybdenum blue is recorded in 1844 as a mixture of molybdenum with "oxyde of tin or phosphate of lime". An alternative formulation involves "digesting" molybdenum sulfide with nitric acid to form molybdic acid, which is then mixed with tin filings and a little muriatic acid (HCl). This is evaporated and heated with alumina. A 1955 paper states that molybdenum blue is unstable and is not used commercially as a pigment. The chemistry of these pigments has not been investigated. | 7 | Physical Chemistry |
Precondition for the applicability of sensor-based ore sorting is the presence of liberation at the particle size of interest. Before entering into sensor-based ore sorting testing procedures there is the possibility to assess the degree of liberation through the inspection of drill cores, hand-counting and washability analysis. The quantification of liberation does not include any process efficiencies, but gives an estimate of the possible sorting result and can thus be applied for desktop financial feasibility analysis.
Drill core analysis
Both for green-field and brown-field applications, inspection of drill core in combination with the grade distribution and mineralogical description is a good option for estimation of the liberation characteristics and the possible success of sensor-based ore sorting. In combination with the mining method and mine plan, an estimation of possible grade distribution in coarse particles can be done. | 3 | Analytical Chemistry |
Maternal overnutrition can have detrimental effects on the health of the offspring later in life. This area is less well studied and understood but some progress has been made in identifying specific genes that are affected. Studies have investigated hypermethylation of DNA and found it to be higher in obese mothers to those of a healthy BMI. More specific studies have investigated Leptin (LEP) as a possible gene which is altered via metabolic imprinting in response to overnutrition in utero, and found hypermethylation of LEP in the placenta of those born to overly nourished mothers. This hypermethylation has been found to cause changes in the levels of circulating Leptin, as well as to leptin sensitivity and the development of neural circuits involved in the control of homeostasis which causes the higher risk of metabolic disease.
Upon investigation it was found that a mother who was obese before conception was likely to have a higher level of placental LEP than the placenta of a mother of a healthy weight. One strategy for overcoming obesity is the use of gastric bypass and other such surgeries, while this does not entirely alleviate the risk of altered metabolic imprinting it has been found that siblings born post maternal surgery are less likely to have as high body fat percentages than over nutrition as siblings born before the surgery.
Paternal overnutrition can also have a detrimental effect and new-borns have shown changes in methylation of DNA generally, with substantial hypomethylation at the gene Insulin-like Growth factor 2 (IGF2). However, this topic is much less studied than maternal nutrition. | 1 | Biochemistry |
Levels of phosphatidylethanols in blood are used as markers of previous alcohol consumption.
An increase of alcohol intake by ~20 g ethanol/day will raise the PEth 16:0/18:1 concentration by ~0.10 μmol/L, and vice versa if the alcohol consumption has decreased. However, it has been demonstrated that there can be significant inter-personal variation, leading to potential misclassification between moderate and heavy drinkers.
After cessation of alcohol intake, the half-life of PEth is between 4.5 and 10 days in the first week and between 5 and 12 days in the second week. As a blood marker PEth is more sensitive than carbohydrate deficient transferrin (CDT), urinary ethyl glucuronide (EtG) and ethyl sulfate (EtS). | 1 | Biochemistry |
Drinking water which has been chlorinated to kill microbes may contain trace levels of chlorine. The World Health Organization recommends an upper limit of 5 ppm.
Although low, 5 ppm is enough to slowly attack certain types of plastic, particularly when the water is heated, as it is for washing.
Polyethylene, polybutylene and acetal resin (polyoxymethylene) pipework and fittings are all susceptible. Attack leads to hardening of pipework, which can leave it brittle and more susceptible to mechanical failure. | 7 | Physical Chemistry |
An organic compound is a chemical whose molecules contain carbon. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets. Organic compounds are relatively common in space, formed by "factories of complex molecular synthesis" which occur in molecular clouds and circumstellar envelopes, and chemically evolve after reactions are initiated mostly by ionizing radiation. Purine and pyrimidine nucleobases including guanine, adenine, cytosine, uracil, and thymine have been found in meteorites. These could have provided the materials for DNA and RNA to form on the early Earth. The amino acid glycine was found in material ejected from comet Wild 2; it had earlier been detected in meteorites. Comets are encrusted with dark material, thought to be a tar-like organic substance formed from simple carbon compounds under ionizing radiation. A rain of material from comets could have brought such complex organic molecules to Earth. It is estimated that during the Late Heavy Bombardment, meteorites may have delivered up to five million tons of organic prebiotic elements to Earth per year. | 9 | Geochemistry |
Recent work suggests that molecular recognition elements can be synthetically produced at the nano-scale, circumventing the need for naturally occurring molecular recognition elements for the development of sensing tools for small molecules. Bio-mimetic polymers such as molecular imprinted polymers and peptoids can be used to recognize larger biological targets such as proteins and the conjugation of polymers to synthetic fluorescent nanomaterials can generate synthetic macromolecular structures that serve as synthetic antibodies for optical protein recognition and detection. | 6 | Supramolecular Chemistry |
Plants under horticultural care in a constructed landscape, typically a botanic garden or arboreta. This technique is similar to a field gene bank in that plants are maintained in the ambient environment, but the collections are typically not as genetically diverse or extensive. These collections are susceptible to hybridization, artificial selection, genetic drift, and disease transmission. Species that cannot be conserved by other ex situ techniques are often included in cultivated collections. | 1 | Biochemistry |
Secondary standards are compounds with a concentration determined by a primary standard. Secondary standards do not satisfy the requirements for a primary standard. | 3 | Analytical Chemistry |
Coactivators are promising targets for drug therapies in the treatment of cancer, metabolic disorder, cardiovascular disease and type 2 diabetes, along with many other disorders. For example, the steroid receptor coactivator (SCR) NCOA3 is often overexpressed in breast cancer, so the development of an inhibitor molecule that targets this coactivator and decreases its expression could be used as a potential treatment for breast cancer.
Because transcription factors control many different biological processes, they are ideal targets for drug therapy. The coactivators that regulate them can be easily replaced with a synthetic ligand that allows for control over an increase or decrease in gene expression.
Further technological advances will provide new insights into the function and regulation of coactivators at a whole-organism level and elucidate their role in human disease, which will hopefully provide better targets for future drug therapies. | 1 | Biochemistry |
Ambident is a molecule or group that has two alternative and interacting reaction sites, to either of which a bond may be made during a reaction, in Chemistry. | 7 | Physical Chemistry |
E.coli are shown to be more sensitive to accumulations of guanosine tetraphosphate than guanosine pentaphosphate. A complete absence of (p)ppGpp causes multiple amino acid requirements, poor survival of aged cultures, aberrant cell division, morphology, and immotility, as well as being locked in a growth mode during entry into starvation. | 1 | Biochemistry |
SELDI is often criticized for its reproducibility due to differences in the mass spectra obtained when using different batches of chip surfaces. While the method has been successful with analyzing low molecular weight proteins, consistent results have not been obtained when analyzing high molecular weight proteins. There also exists a potential for sample bias, as nonspecific absorption matrices favor the binding of analytes with higher abundances in the sample at the expense of less abundant analytes. While SELDI-TOF-MS has detection limits in the femtomolar range, the baseline signal in the spectra varies and noise due to the matrix is maximal below 2000 Da, with Ciphergen Biosystems suggesting to ignore spectral peaks below 2000 Da. | 1 | Biochemistry |
If we attempt to build a densely packed collection of spheres, we will be tempted to always place the next sphere in a hollow between three packed spheres. If five spheres are assembled in this way, they will be consistent with one of the regularly packed arrangements described above. However, the sixth sphere placed in this way will render the structure inconsistent with any regular arrangement. This results in the possibility of a random close packing of spheres which is stable against compression. Vibration of a random loose packing can result in the arrangement of spherical particles into regular packings, a process known as granular crystallisation. Such processes depend on the geometry of the container holding the spherical grains.
When spheres are randomly added to a container and then compressed, they will generally form what is known as an "irregular" or "jammed" packing configuration when they can be compressed no more. This irregular packing will generally have a density of about 64%. Recent research predicts analytically that it cannot exceed a density limit of 63.4% This situation is unlike the case of one or two dimensions, where compressing a collection of 1-dimensional or 2-dimensional spheres (that is, line segments or circles) will yield a regular packing. | 3 | Analytical Chemistry |
Each dislocation is associated with a strain field which contributes some small but finite amount to the materials stored energy. When the temperature is increased - typically below one-third of the absolute melting point - dislocations become mobile and are able to glide, cross-slip and climb. If two dislocations of opposite sign meet then they effectively cancel out and their contribution to the stored energy is removed. When annihilation is complete then only excess dislocation of one kind will remain. | 8 | Metallurgy |
Pseudoknots are common structural motifs found in RNA. They are formed by two nested stem-loops such that the stem of one structure is formed from the loop of the other. There are multiple folding topologies among pseudoknots and great variation in loop lengths, making them a structurally diverse group.
Inverted repeats are a key component of pseudoknots as can be seen in the illustration of a naturally occurring pseudoknot found in the human telomerase RNA component. Four different sets of inverted repeats are involved in this structure. Sets 1 and 2 are the stem of stem-loop A and are part of the loop for stem-loop B. Similarly, sets 3 and 4 are the stem for stem-loop B and are part of the loop for stem-loop A.
Pseudoknots play a number of different roles in biology. The telomerase pseudoknot in the illustration is critical to that enzymes activity. The ribozyme for the hepatitis delta virus (HDV)' folds into a double-pseudoknot structure and self-cleaves its circular genome to produce a single-genome-length RNA. Pseudoknots also play a role in programmed ribosomal frameshifting found in some viruses and required in the replication of retroviruses. | 1 | Biochemistry |
The density of saltwater depends on the dissolved salt content as well as the temperature. Ice still floats in the oceans, otherwise, they would freeze from the bottom up. However, the salt content of oceans lowers the freezing point by about 1.9 °C (due to freezing-point depression of a solvent containing a solute) and lowers the temperature of the density maximum of water to the former freezing point at 0 °C. This is why, in ocean water, the downward convection of colder water is not blocked by an expansion of water as it becomes colder near the freezing point. The oceans' cold water near the freezing point continues to sink. So creatures that live at the bottom of cold oceans like the Arctic Ocean generally live in water 4 °C colder than at the bottom of frozen-over fresh water lakes and rivers.
As the surface of saltwater begins to freeze (at −1.9 °C for normal salinity seawater, 3.5%) the ice that forms is essentially salt-free, with about the same density as freshwater ice. This ice floats on the surface, and the salt that is "frozen out" adds to the salinity and density of the seawater just below it, in a process known as brine rejection. This denser saltwater sinks by convection and the replacing seawater is subject to the same process. This produces essentially freshwater ice at −1.9 °C on the surface. The increased density of the seawater beneath the forming ice causes it to sink towards the bottom. On a large scale, the process of brine rejection and sinking cold salty water results in ocean currents forming to transport such water away from the Poles, leading to a global system of currents called the thermohaline circulation. | 2 | Environmental Chemistry |
In 1980, Staden wrote: In order to make it easier to talk about our data gained by the shotgun method of sequencing we have invented the word "contig". A contig is a set of gel readings that are related to one another by overlap of their sequences. All gel readings belong to one and only one contig, and each contig contains at least one gel reading. The gel readings in a contig can be summed to form a contiguous consensus sequence and the length of this sequence is the length of the contig. | 1 | Biochemistry |
cAMP is a signaling molecule important for a variety of cellular functions. cAMP exerts its effects by activating the cAMP-dependent protein kinase A (PKA), which transduces the signal through phosphorylation of different target proteins. The inactive holoenzyme of PKA is a tetramer composed of two regulatory and two catalytic subunits. cAMP causes the dissociation of the inactive holoenzyme into a dimer of regulatory subunits bound to four cAMP and two free monomeric catalytic subunits. Four different regulatory subunits and three catalytic subunits of PKA have been identified in humans. The protein encoded by this gene is one of the regulatory subunits. This protein was found to be a tissue-specific extinguisher that down-regulates the expression of seven liver genes in hepatoma x fibroblast hybrids Three alternatively spliced transcript variants encoding the same protein have been observed. | 1 | Biochemistry |
Many kinds of diketones are known, some with unusual properties. The simplest is diacetyl , once used as butter-flavoring in popcorn. Acetylacetone (pentane-2,4-dione) is virtually a misnomer (inappropriate name) because this species exists mainly as the monoenol . Its enolate is a common ligand in coordination chemistry. | 0 | Organic Chemistry |
Dextroamphetamine is the active metabolite of the prodrug lisdexamfetamine (L-lysine-dextroamphetamine), available by the brand name Vyvanse (Elvanse in the European market) (Venvanse in the Brazil market) (lisdexamfetamine dimesylate). Dextroamphetamine is liberated from lisdexamfetamine enzymatically following contact with red blood cells. The conversion is rate-limited by the enzyme, which prevents high blood concentrations of dextroamphetamine and reduces lisdexamfetamine's drug liking and abuse potential at clinical doses. Vyvanse is marketed as once-a-day dosing as it provides a slow release of dextroamphetamine into the body. Vyvanse is available as capsules, and chewable tablets, and in seven strengths; 10 mg, 20 mg, 30 mg, 40 mg, 50 mg, 60 mg, and 70 mg. The conversion rate between lisdexamfetamine dimesylate (Vyvanse) to dextroamphetamine base is 29.5%. | 4 | Stereochemistry |
For typical three-dimensional metals, the temperature-dependence of the electrical resistivity ρ(T) due to the scattering of electrons by acoustic phonons changes from a high-temperature regime in which ρ ∝ T to a low-temperature regime in which ρ ∝ T at a characteristic temperature known as the Debye temperature. For low density electron systems, however, the Fermi surface can be substantially smaller than the size of the Brillouin zone, and only a small fraction of acoustic phonons can scatter off electrons. This results in a new characteristic temperature known as the Bloch–Grüneisen temperature that is lower than the Debye temperature. The Bloch–Grüneisen temperature is defined as 2ħvk/k, where ħ is the Planck constant, v is the velocity of sound, ħk is the Fermi momentum, and k is the Boltzmann constant.
When the temperature is lower than the Bloch–Grüneisen temperature, the most energetic thermal phonons have a typical momentum of kT/v which is smaller than ħk, the momentum of the conducting electrons at the Fermi surface. This means that the electrons will only scatter in small angles when they absorb or emit a phonon. In contrast when the temperature is higher than the Bloch–Grüneisen temperature, there are thermal phonons of all momenta and in this case electrons will also experience large angle scattering events when they absorb or emit a phonon. In many cases, the Bloch–Grüneisen temperature is approximately equal to the Debye temperature (usually written ), which is used in modeling specific heat capacity. However, in particular circumstances these temperatures can be quite different.
The theory was initially put forward by Felix Bloch and Eduard Grüneisen. The Bloch–Grüneisen temperature has been observed experimentally in a two-dimensional electron gas and in graphene.
Mathematically, the Bloch–Grüneisen model produces a resistivity given by:
Here, is a characteristic temperature (typically matching well with the Debye temperature). Under Bloch's original assumptions for simple metals, . For , this can be approximated as dependence. In contrast, the so called Bloch–Wilson limit, where works better for s-d inter-band scattering, such as with transition metals. The second limit gives at low temperatures. In practice, which model is more applicable depends on the particular material. | 7 | Physical Chemistry |
Bees can use trail pheromones to mark food sources and the entrance of their hives. Oftentimes, when finding a source, bees will mark that exact location as well as secreting pheromones along the flight back to their hives. Employment of trail pheromones is extensively studied in honey bees and stingless bees, for both are highly social.
The trail pheromone of the stingless bee Trigona recursa is produced by its labial glands. One of its key compounds is hexyl decanoate, and when secreted, the pheromone will recruit other bees towards the source. The stingless bee Scaptotrigona pectoralis, like ants, can utilize another colonys food trail. Specifically, they can learn foreign pheromone trails at a source, broadening their options for foraging. However, in some cases of aggressive bees, like Trigona corvina', encounters between individuals from different colonies at a food source will result in fights and ultimately death amongst both parties. | 1 | Biochemistry |
The E1 subunit, called the pyruvate dehydrogenase subunit, is either a homodimer (comprising two “ɑ” chains, e.g. in Escherichia coli) or a heterotetramer of two different chains (two “ɑ” and two “ꞵ” chains). A magnesium ion forms a 4-coordinate complex with three, polar amino acid residues (Asp, Asn, and Tyr) located on the alpha chain, and the thiamine diphosphate (TPP) cofactor directly involved in decarboxylation of the pyruvate. | 1 | Biochemistry |
The retinoic acid receptor (RAR) is a type of nuclear receptor which can also act as a ligand-activated transcription factor that is activated by both all-trans retinoic acid and 9-cis retinoic acid, retinoid active derivatives of Vitamin A. They are typically found within the nucleus. There are three retinoic acid receptors (RAR), RAR-alpha, RAR-beta, and RAR-gamma, encoded by the , , genes, respectively. Within each RAR subtype there are various isoforms differing in their N-terminal region A. Multiple splice variants have been identified in human RARs: four for , five for , and two for . As with other type II nuclear receptors, RAR heterodimerizes with RXR and in the absence of ligand, the RAR/RXR dimer binds to hormone response elements known as retinoic acid response elements (RAREs) complexed with corepressor protein. Binding of agonist ligands to RAR results in dissociation of corepressor and recruitment of coactivator protein that, in turn, promotes transcription of the downstream target gene into mRNA and eventually protein. In addition, the expression of RAR genes is under epigenetic regulation by promoter methylation. Both the length and magnitude of the retinoid response is dependent of the degradation of RARs and RXRs through the ubiquitin-proteasome. This degradation can lead to elongation of the DNA transcription through disruption of the initiation complex or to end the response to facilitate further transcriptional programs. Due to RAR/RXR heterodimers acting as subtrates to the non steroid hormone ligand retinoid they are extensively involved in cell differentiation, proliferation, and apoptosis. | 1 | Biochemistry |
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