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The proper identification of splice sites has to be highly precise as the consensus splice sequences are very short and there are many other sequences similar to the authentic splice sites within gene sequences, which are known as cryptic, non-canonical, or pseudo splice sites. When an authentic or real splice site is mutated, any cryptic splice sites present close to the original real splice site could be erroneously used as authentic site, resulting in an aberrant mRNA. The erroneous mRNA may include a partial sequence from the neighboring intron or lose a partial exon, which may result in a premature stop codon. The result may be a truncated protein that would have lost its function completely.
Shapiro–Senapathy algorithm can identify the cryptic splice sites, in addition to the authentic splice sites. Cryptic sites can often be stronger than the authentic sites, with a higher S&S score. However, due to the lack of an accompanying complementary donor or acceptor site, this cryptic site will not be active or used in a splicing reaction. When a neighboring real site is mutated to become weaker than the cryptic site, then the cryptic site may be used instead of the real site, resulting in a cryptic exon and an aberrant transcript.
Numerous diseases have been caused by cryptic splice site mutations or usage of cryptic splice sites due to the mutations in authentic splice sites. | 1 | Biochemistry |
The US Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for selenium in 2000. If there is not sufficient information to establish EARs and RDAs, an estimate designated Adequate Intake (AI) is used instead. The current EAR for selenium for people ages 14 and up is 45 μg/day. The RDA is 55 μg/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 60 μg/day. RDA for lactation is 70 μg/day. For children ages 1–13 years the RDA increases with age from 20 to 40 μg/day. As for safety, the IOM sets Tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of selenium the UL is 400 μg/day. Collectively the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes (DRIs).
The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For women and men ages 15 and older the AI is set at 70 μg/day. AI for pregnancy is 70 μg/day, for lactation 85 μg/day. For children ages 1–14 years the AIs increase with age from 15 to 55 μg/day. These AIs are higher than the U.S. RDAs. The European Food Safety Authority reviewed the same safety question and set its UL at 300 μg/day, which is lower than the U.S. value.
In the United States, selenium deficiency is not common. A federal survey of food consumption determined that for women and men over the age of 19, average consumption from foods and beverages was 89 and 125 μg/day, respectively. For women and men of all ages fewer than 3% consumed less than the EAR. | 1 | Biochemistry |
Triplet-triplet annihilation combines the energy of two triplet-excited molecules onto one molecule to produce a higher excited state. Since the higher excited state is an emissive singlet state, TTA can be used to achieve photon upconversion which is a process that converts the energy of two photons into one photon of higher energy.
To achieve photon upconversion through triplet-triplet annihilation two types of molecules are often combined: a sensitizer and an emitter (annihilator). The sensitizer absorbs the low energy photon and populates its first excited triplet state (T) through intersystem crossing. The sensitizer then transfers the excitation energy to the emitter, resulting in a triplet excited emitter and a ground state sensitizer. Two triplet-excited emitters can then undergo triplet-triplet annihilation to produce a singlet excited state (S) of the emitter, which can emit an upconverted photon. | 7 | Physical Chemistry |
Minimotif Miner is a program and database designed to identify minimotifs in any protein. Minimotifs are short, contiguous peptide sequences that are known to have a function in at least one protein. Minimotifs are also called sequence motifs or short linear motifs or SLiMs. These are generally restricted to one secondary structure element and are less than 15 amino acids in length. | 1 | Biochemistry |
Pioneering structural studies in the 1980s by Aaron Klug's group provided the first evidence that an octamer of histone proteins wraps DNA around itself in about 1.7 turns of a left-handed superhelix. In 1997 the first near atomic resolution crystal structure of the nucleosome was solved by the Richmond group, showing the most important details of the particle. The human alpha satellite palindromic DNA critical to achieving the 1997 nucleosome crystal structure was developed by the Bunick group at Oak Ridge National Laboratory in Tennessee. The structures of over 20 different nucleosome core particles have been solved to date, including those containing histone variants and histones from different species. The structure of the nucleosome core particle is remarkably conserved, and even a change of over 100 residues between frog and yeast histones results in electron density maps with an overall root mean square deviation of only 1.6Å. | 1 | Biochemistry |
In thermodynamics, the particle number (symbol ) of a thermodynamic system is the number of constituent particles in that system. The particle number is a fundamental thermodynamic property which is conjugate to the chemical potential. Unlike most physical quantities, the particle number is a dimensionless quantity, specifically a countable quantity. It is an extensive property, as it is directly proportional to the size of the system under consideration and thus meaningful only for closed systems.
A constituent particle is one that cannot be broken into smaller pieces at the scale of energy involved in the process (where is the Boltzmann constant and is the temperature). For example, in a thermodynamic system consisting of a piston containing water vapour, the particle number is the number of water molecules in the system. The meaning of constituent particles, and thereby of particle numbers, is thus temperature-dependent. | 7 | Physical Chemistry |
Racemic tartaric acid can be prepared in a multistep reaction from maleic acid. In the first step, the maleic acid is epoxidized by hydrogen peroxide using potassium tungstate as a catalyst.
:HOCCHCOH + HO → OCH(COH)
In the next step, the epoxide is hydrolyzed.
:OCH(COH) + HO → (HOCH)(COH) | 4 | Stereochemistry |
Similar to a western blot, the far-western blot uses protein–protein interactions to detect the presence of a specific protein immobilized on a blotting matrix. Antibodies are then used to detect the presence of the protein–protein complex, making the Far-Western blot a specific case of the Western blot. | 1 | Biochemistry |
Explosive boiling can be best described by a p-T phase diagram. Figure on right shows a typical p-T phase diagram of a substance. The binodal line or the coexistence curve is a thermodynamic state where at that specific temperature and pressure, liquid and vapor can coexist. The spinodal line on right is the boundary of absolute instability of a solution to decomposition into multiple phases. A typical heating process is shown using red ink.
If the heating process is relatively slow, the liquid has enough time to relax to an equilibrium state and the liquid follows the binodal curve, the Clausius–Clapeyron relation is still valid. During this time heterogeneous evaporation occurs in the substance with bubbles nucleating from impurity sites, surfaces, grain boundaries etc.
On the other hand, if the heating process is fast enough that the substance cannot reach binodal curve through heterogeneous boiling, the liquid becomes superheated with its temperature above boiling point at a given pressure. System then shifts away from the binodal and continues to follow the red curve and thus approaches towards spinodal. Near the critical temperature thermodynamic properties like specific heat, density varies rapidly as shown on the figure at right. Density and entropy undergoes largest fluctuation. During this time it is possible to have a large density fluctuation in a very small volume. This fluctuation of density results in the nucleation of a bubble. The bubble nucleation process occurs homogeneously everywhere in the substance. The rate of bubble nucleation and vapor sphere growth rate increases exponentially closer to the critical temperature. The increasing nucleation prevents the system from going to the spinodal. When the bubble radius reaches the critical size it continues to expand and eventually explodes resulting a mixture of gas and droplets which is termed as explosive boiling or phase explosion.
At the beginning, explosive boiling was used by Martynyuk to calculate the critical temperature of metals. He used electric resistance to heat up metal wire. Later explosive boiling was found to occur while using ultra fast femtosecond laser ablation. Although this kind of explosive boiling should occur by any mechanism whereby the temperature of the liquid is rapidly raised close to the critical temperature of the substance. | 7 | Physical Chemistry |
Numerous drugs can raise GGT levels, including barbiturates and phenytoin. GGT elevation has also been occasionally reported following nonsteroidal anti-inflammatory drugs (including aspirin), St. John's wort and kava. | 1 | Biochemistry |
Enediynes are organic compounds containing two triple bonds and one double bond.
Enediynes are most notable for their limited use as antitumor antibiotics (known as enediyne anticancer antibiotics). They are efficient at inducing apoptosis in cells, but cannot differentiate cancerous cells from healthy cells. Consequently, research is being conducted to increase the specificity of enediyne toxicity. | 0 | Organic Chemistry |
Ca is required to activate the binding. Ca binds to the protein and carbohydrate by non covalent bond. Mannose-binding protein (MBP) contains the C-type CRD. | 0 | Organic Chemistry |
β-Glycerophosphate is an inhibitor of the enzyme serine-threonine phosphatase. It is often used in combination with other phosphatase/protease inhibitors for broad spectrum inhibition.
β-Glycerophosphate is also used to drive osteogenic differentiation of bone marrow stem cells in vitro.
β-Glycerophosphate is used to buffer M17 media for Lactococcus culture in recombinant protein expression. | 1 | Biochemistry |
EBSD is conducted using an SEM equipped with an EBSD detector containing at least a phosphor screen, compact lens and low-light Charge-coupled device (CCD) or Complementary metal–oxide–semiconductor (CMOS) camera. , commercially available EBSD systems typically come with one of two different CCD cameras: for fast measurements, the CCD chip has a native resolution of 640×480 pixels; for slower, and more sensitive measurements, the CCD chip resolution can go up to 1600×1200 pixels.
The biggest advantage of the high-resolution detectors is their higher sensitivity, and therefore the information within each diffraction pattern can be analysed in more detail. For texture and orientation measurements, the diffraction patterns are binned to reduce their size and computational times. Modern CCD-based EBSD systems can index patterns at a speed of up to 1800 patterns/second. This enables rapid and rich microstructural maps to be generated. | 7 | Physical Chemistry |
The spacing, and the energy of a typical spectroscopic transition, between vibrational energy levels is about 100 times greater than that of a typical transition between rotational energy levels. | 4 | Stereochemistry |
The United Nations, through the World Health Organization (WHO) together with the International Labour Organization (ILO) and United Nations Environment Programme (UNEP), collaborate on the International Programme on Chemical Safety (IPCS) to publish summary documents on chemicals. The IPCS published one such document in 2000 summarizing the status of scientific knowledge on MDI.
The IARC evaluates the hazard data on chemicals and assigns a rating on the risk of carcinogenesis. In the case of TDI, the final evaluation is possibly carcinogenic to humans (Group 2B). For MDI, the final evaluation is not classifiable as to its carcinogenicity to humans (Group 3).
The International Isocyanate Institute is an international industry consortium that seeks promote the safe utilization of isocyanates by promulgating best practices. | 0 | Organic Chemistry |
The development of the winnowing barn allowed rice plantations in South Carolina to increase their yields dramatically. | 3 | Analytical Chemistry |
Oxaziridines undergo cycloaddition reactions with heterocumulenes to afford a number of unique five membered heterocycles, as shown in the figure below. This reactivity is due to the strained three membered ring and weak N-O bond. | 0 | Organic Chemistry |
Nicolas Dauphas (born December 10, 1975) is a planetary scientist and isotope geochemist. He is a professor of geochemistry and cosmochemistry in the Department of the Geophysical Sciences and Enrico Fermi Institute at the University of Chicago. Within cosmochemistry, his research focus is on isotope geochemistry. He studies the origin and evolution of planets and other objects in the solar system by analyzing the natural distributions of elements and their isotopes using mass spectrometers. | 9 | Geochemistry |
The inner mitochondrial membrane contains proteins with three types of functions:
# Those that perform the electron transport chain redox reactions
# ATP synthase, which generates ATP in the matrix
# Specific transport proteins that regulate metabolite passage into and out of the mitochondrial matrix
It contains more than 151 different polypeptides, and has a very high protein-to-phospholipid ratio (more than 3:1 by weight, which is about 1 protein for 15 phospholipids). The inner membrane is home to around 1/5 of the total protein in a mitochondrion. Additionally, the inner membrane is rich in an unusual phospholipid, cardiolipin. This phospholipid was originally discovered in cow hearts in 1942, and is usually characteristic of mitochondrial and bacterial plasma membranes. Cardiolipin contains four fatty acids rather than two, and may help to make the inner membrane impermeable, and its disruption can lead to multiple clinical disorders including neurological disorders and cancer. Unlike the outer membrane, the inner membrane does not contain porins, and is highly impermeable to all molecules. Almost all ions and molecules require special membrane transporters to enter or exit the matrix. Proteins are ferried into the matrix via the translocase of the inner membrane (TIM) complex or via OXA1L. In addition, there is a membrane potential across the inner membrane, formed by the action of the enzymes of the electron transport chain. Inner membrane fusion is mediated by the inner membrane protein OPA1. | 1 | Biochemistry |
The termination of translation requires coordination between release factor proteins, the mRNA sequence, and ribosomes. Once a termination codon is read, release factors RF-1, RF-2, and RF-3 contribute to the hydrolysis of the growing polypeptide, which terminates the chain. Bases downstream the stop codon affect the activity of these release factors. In fact, some bases proximal to the stop codon suppress the efficiency of translation termination by reducing the enzymatic activity of the release factors. For instance, the termination efficiency of a UAAU stop codon is near 80% while the efficiency of UGAC as a termination signal is only 7%. | 1 | Biochemistry |
Isofurans are nonclassic eicosanoids formed nonenzymatically by free radical mediated peroxidation of arachidonic acid. The isofurans are similar to the isoprostanes and are formed under similar conditions, but contain a substituted tetrahydrofuran ring. The concentration of oxygen affects this process; at elevated oxygen concentrations, the formation of isofurans is favored whereas the formation of isoprostanes is disfavored. | 1 | Biochemistry |
The advantages of chromosome jumping are:
* Allows more rapid movement through the genome compared to other techniques, such as chromosome walking.
* Able to travel across chromosomal regions containing unclonable sequences in bacterial hosts.
* Thirdly, this technique can be used to generate genomic markers with known chromosomal locations.
*Combination of jumping and linking jumping libraries to walking offers possibility of directional walking and might allow the analysis of longer regions in parallel mapping strategies.
*Reduces the complexity of libraries to be screened and constructed of mammalian genome.
However, despite these advantages, chromosome jumping is still restricted by the capacity of the cloning vector which is the distance of the ends of the two fragments which can be approximately hundreds of kilobases. Additionally, because the jump does not clone the intervening DNA, chromosome walking would have to be done to identify all the genes present in the DNA. Regardless, it is still deemed to be beneficial due to the possibility to jump over hundred kilobases in comparison to chromosome walking. | 1 | Biochemistry |
Plastid differentiation is not permanent, in fact many interconversions are possible. Chloroplasts may be converted to chromoplasts, which are pigment-filled plastids responsible for the bright colors seen in flowers and ripe fruit. Starch storing amyloplasts can also be converted to chromoplasts, and it is possible for proplastids to develop straight into chromoplasts. Chromoplasts and amyloplasts can also become chloroplasts, like what happens when a carrot or a potato is illuminated. If a plant is injured, or something else causes a plant cell to revert to a meristematic state, chloroplasts and other plastids can turn back into proplastids. Chloroplast, amyloplast, chromoplast, proplastid are not absolute; state—intermediate forms are common. | 5 | Photochemistry |
The MG-RAST application provides a comprehensive suite of services, including automated quality control, annotation, comparative analysis, and archiving for metagenomic and amplicon sequences. It utilizes a combination of various bioinformatics tools to achieve these functionalities. Originally designed for metagenomic data analysis, MG-RAST also extends support to amplicon sequences (16S, 18S, and ITS) and metatranscriptome (RNA-seq) sequences processing. However, it's important to note that MG-RAST currently lacks the capability to predict coding regions from eukaryotes, limiting its utility for eukaryotic metagenome analysis.
The MG-RAST pipeline can be segmented into five distinct stages: | 1 | Biochemistry |
Solar-specific feed-in tariffs vary by country and within countries. Such tariffs encourage the development of solar power projects. Widespread grid parity, the point at which photovoltaic electricity is equal to or cheaper than grid power without subsidies, likely requires advances on all three fronts. Proponents of solar hope to achieve grid parity first in areas with abundant sun and high electricity costs such as in California and Japan. In 2007 BP claimed grid parity for Hawaii and other islands that otherwise use diesel fuel to produce electricity. George W. Bush set 2015 as the date for grid parity in the US. The Photovoltaic Association reported in 2012 that Australia had reached grid parity (ignoring feed in tariffs).
The price of solar panels fell steadily for 40 years, interrupted in 2004 when high subsidies in Germany drastically increased demand there and greatly increased the price of purified silicon (which is used in computer chips as well as solar panels). The recession of 2008 and the onset of Chinese manufacturing caused prices to resume their decline. In the four years after January 2008 prices for solar modules in Germany dropped from €3 to €1 per peak watt. During that same time production capacity surged with an annual growth of more than 50%. China increased market share from 8% in 2008 to over 55% in the last quarter of 2010. In December 2012 the price of Chinese solar panels had dropped to $0.60/Wp (crystalline modules). (The abbreviation Wp stands for watt peak capacity, or the maximum capacity under optimal conditions.)
As of the end of 2016, it was reported that spot prices for assembled solar panels (not cells) had fallen to a record-low of US$0.36/Wp. The second largest supplier, Canadian Solar Inc., had reported costs of US$0.37/Wp in the third quarter of 2016, having dropped $0.02 from the previous quarter, and hence was probably still at least breaking even. Many producers expected costs would drop to the vicinity of $0.30 by the end of 2017. It was also reported that new solar installations were cheaper than coal-based thermal power plants in some regions of the world, and this was expected to be the case in most of the world within a decade. | 7 | Physical Chemistry |
Most LFTs are intended to operate on a purely qualitative basis. However, it is possible to measure the intensity of the test line to determine the quantity of analyte in the sample. Handheld diagnostic devices known as lateral flow readers are used by several companies to provide a fully quantitative assay result. By utilizing unique wavelengths of light for illumination in conjunction with either CMOS or CCD detection technology, a signal rich image can be produced of the actual test lines. Using image processing algorithms specifically designed for a particular test type and medium, line intensities can then be correlated with analyte concentrations. One such handheld lateral flow device platform is made by Detekt Biomedical L.L.C. Alternative non-optical techniques are also able to report quantitative assays results. One such example is a magnetic immunoassay (MIA) in the LFT form also allows for getting a quantified result. Reducing variations in the capillary pumping of the sample fluid is another approach to move from qualitative to quantitative results. Recent work has, for example, demonstrated capillary pumping with a constant flow rate independent from the liquid viscosity and surface energy. | 1 | Biochemistry |
IHC staining has been shown to be a useful diagnostic tool for prioritizing patients for SDH mutation testing in early stages of cancer. The absence of SDHB in IHC staining would be linked to the presence of SDH oncogene mutations. The already commercialized drug decitabine (Dacogen®) could be an effective therapy to repress the migration capacities of SDHB-mutant cells, | 1 | Biochemistry |
Radiation is the evolutionary process of diversification of a single species into multiple forms. It includes the physiological and ecological diversity within a rapidly multiplying lineage. There are many types of radiation including adaptive, concordant, and discordant radiation however escape and radiate coevolution does not always follow those specific types.
Ehrlich and Raven's original paper did not clearly answer why ecological escape leads to increased diversification, however several explanations have been proposed. Once a novel defense has been acquired, the attacking organism which had evolved adaptations that allowed it to predate is now up against a new defense that it has not yet been evolved to encounter. This gives the defending organism the advantage, and therefore time to rapidly multiply unopposed by the previously attacking organism. This ultimately leads to the physiological and ecological diversity within the rapidly multiplying lineage, hence radiation. | 1 | Biochemistry |
Ores mined for their base metal content often contain precious metals, usually gold and silver. These have to be removed from the base metals as part of the refining processes used to purify the metals. In the case of copper electrolytic refining, the gold and silver fall to the bottom of the electrolytic refining cell as “slimes” that are subsequently treated to recover gold and silver as byproducts. In the case of lead refining, silver, gold, and other precious metals are typically removed using the Parkes process, in which zinc is added to the impure lead bullion to collect the silver, gold and other precious metals.
The BRM lead refinery at Northfleet in England uses the Parkes process followed by liquation and a vacuum induction retort to recover precious metals. The product of this process is a feed for the BBOC consisting of a mixture of lead, silver (60–75%), zinc (2–3%) and copper (2–3%), with trace amounts of gold. Prior to the development of the BBOC, BRM used cupellation in a 15 tonne (“t”) reverberatory cupellation furnace to recover the precious metals from this mixture. Three of these furnaces were used to produce 450 t of silver per year.
Cupellation works by exposing the mixture at high temperature to air or oxygen. The base metals, being less noble than silver and gold, react with the oxygen to form their oxides, which separate from the noble metals to form a slag that floats on the top of the residual metals (or “doré”). At BRM, the doré contains 99.7% silver.
To maximize the oxygen transfer from the blast air in the reverberatory furnace, a shallow bath is used, thus increasing the surface-area-to-volume ratio of the furnace.
A problem with using reverberatory furnaces for cupellation is that the zinc oxidizes first, forming a crust across the top of the molten material. This crust prevents the penetration of oxygen to the rest of the material, and so it has to be manually broken up and removed using a rabble bar. This is both labor-intensive and also results in the loss of some of the silver. Similarly, the oxidized lead slag has to be removed when it forms to maintain the operation, and its removal also results in loss of silver.
The BBOC was developed by BRM personnel as a way of reducing these and other problems, such as low energy efficiency and low oxygen utilization, associated with the reverberatory cupellation process. | 8 | Metallurgy |
* N-Iodosuccinimide (NIS), the iodine analog of N-chlorosuccinimide.
* N-bromosuccinimide (NBS), the bromine analog of N-chlorosuccinimide.
* Other N-chloro compounds that are commercially available include chloramine-T, trichloroisocyanuric acid ((OCNCl)), 1,3-dichloro-5,5-dimethylhydantoin. | 0 | Organic Chemistry |
Reverse transcriptase is commonly used in research to apply the polymerase chain reaction technique to RNA in a technique called reverse transcription polymerase chain reaction (RT-PCR). The classical PCR technique can be applied only to DNA strands, but, with the help of reverse transcriptase, RNA can be transcribed into DNA, thus making PCR analysis of RNA molecules possible. Reverse transcriptase is used also to create cDNA libraries from mRNA. The commercial availability of reverse transcriptase greatly improved knowledge in the area of molecular biology, as, along with other enzymes, it allowed scientists to clone, sequence, and characterise RNA. | 1 | Biochemistry |
The terms resin flux and rosin flux are ambiguous and somewhat interchangeable, with different vendors using different assignments. Generally, fluxes are labeled as rosin if the vehicle they are based on is primarily natural rosin. Some manufactures reserve "rosin" designation for military fluxes based on rosin (R, RMA and RA compositions) and label others as "resin".
Rosin has good flux properties. A mixture of organic acids (resin acids, predominantly abietic acid, with pimaric acid, isopimaric acid, neoabietic acid, dihydroabietic acid, and dehydroabietic acid), rosin is a glassy solid, virtually nonreactive and noncorrosive at normal temperature, but liquid, ionic and mildly reactive to metal oxides at molten state. Rosin tends to soften between 60–70 °C and is fully fluid at around 120 °C; molten rosin is weakly acidic and is able to dissolve thinner layers of surface oxides from copper without further additives. For heavier surface contamination or improved process speed, additional activators can be added.
There are several possible activator groups for rosins:
* halide activators (organic halide salts, e.g. dimethylammonium chloride and diethylammonium chloride)
* organic acids (monocarboxylic, e.g. formic acid, acetic acid, propionic acid, and dicarboxylic, e.g. oxalic acid, malonic acid, sebacic acid)
There are three types of rosin: gum rosin (from pine tree oleoresin), wood rosin (obtained by extraction of tree stumps), and tall oil rosin (obtained from tall oil, a byproduct of kraft paper process). Gum rosin has a milder odor and lower tendency to crystallize from solutions than wood rosin, and is therefore preferred for flux applications. Tall oil rosin finds increased use due to its higher thermal stability and therefore lower tendency to form insoluble thermal decomposition residues. The composition and quality of rosin differs by the tree type, and also by location and even by year. In Europe, rosin for fluxes is usually obtained from a specific type of Portuguese pine; in America a North Carolina variant is used.
Natural rosin can be used as is, or can be chemically modified by e.g. esterification, polymerization, or hydrogenation. The properties being altered are increased thermal stability, better cleanability, altered solution viscosity, and harder residue (or conversely, softer and more tacky residue). Rosin can be also converted to a water-soluble rosin flux, by formation of an ethoxylated rosin amine, an adduct with a polyglycol and an amine.
One of the early fluxes was a mixture of equal amounts of rosin and vaseline. A more aggressive early composition was a mixture of saturated solution of zinc chloride, alcohol, and glycerol.
Fluxes can be also prepared from synthetic resins, often based on esters of polyols and fatty acids. Such resins have improved fume odor and lower residue tack, but their fluxing activity and solubility tend to be lower than that of natural resins. | 8 | Metallurgy |
For a mixture of two materials with permittivities and with corresponding volume fractions and , D.A.G. Bruggeman proposed a formula of the following form:
Here the positive sign before the square root must be altered to a negative sign in some cases in order to get the correct imaginary part of effective complex permittivity which is related with electromagnetic wave attenuation. The formula is symmetric with respect to swapping the d and m roles. This formula is based on the equality
where is the jump of electric displacement flux all over the integration surface, is the component of microscopic electric field normal to the integration surface, is the local relative complex permittivity which takes the value inside the picked metal particle, the value inside the picked dielectric particle and the value outside the picked particle, is the normal component of the macroscopic electric field. Formula (4) comes out of Maxwells equality . Thus only one picked particle is considered in Bruggemans approach. The interaction with all the other particles is taken into account only in a mean field approximation described by . Formula (3) gives a reasonable resonant curve for plasmon excitations in metal nanoparticles if their size is 10 nm or smaller. However, it is unable to describe the size dependence for the resonant frequency of plasmon excitations that are observed in experiments | 7 | Physical Chemistry |
It has been noted that radial distribution functions alone are insufficient to characterize structural information. Distinct point processes may possess identical or practically indistinguishable radial distribution functions, known as the degeneracy problem. In such cases, higher order correlation functions are needed to further describe the structure.
Higher-order distribution functions with were less studied, since they are generally less important for the thermodynamics of the system; at the same time, they are not accessible by conventional scattering techniques. They can however be measured by coherent X-ray scattering and are interesting insofar as they can reveal local symmetries in disordered systems. | 7 | Physical Chemistry |
The following table gives the five-dimensional reflection groups (excluding those that are lower-dimensional reflection groups), by listing them as Coxeter groups. Related chiral groups exist for each with half the order, and can be represented by the bracket Coxeter notation with a + exponent, for example [3,3,3,3] has four 3-fold gyration points and symmetry order 360. | 4 | Stereochemistry |
Jinhua Ye is a Chinese chemist who is a professor at the National Institute for Materials Science in Tsukuba. Her research considers high-temperature superconductors for photocatalysis. She was elected Fellow of the Royal Society of Chemistry in 2016 and has been included in the Clarivate Analytics Highly Cited Researcher every year since then. | 5 | Photochemistry |
The risks of isocyanates was brought to the world's attention with the 1984 Bhopal disaster, which caused the death of nearly 4000 people from the accidental release of methyl isocyanate. In 2008, the same chemical was involved in an explosion at a pesticide manufacturing plant in West Virginia.
LD50s for isocyanates are typically several hundred milligrams per kilogram. Despite this low acute toxicity, an extremely low short-term exposure limit (STEL) of 0.07 mg/m is the legal limit for all isocyanates (except methyl isocyanate: 0.02 mg/m) in the United Kingdom. These limits are set to protect workers from chronic health effects such as occupational asthma, contact dermatitis, or irritation of the respiratory tract.
Since they are used in spraying applications, the properties of their aerosols have attracted attention. In the U.S., OSHA conducted a National Emphasis Program on isocyanates starting in 2013 to make employers and workers more aware of the health risks.
Polyurethanes have variable curing times, and the presence of free isocyanates in foams vary accordingly.
Both the US National Toxicology Program (NTP) and International Agency for Research on Cancer (IARC) have evaluated TDI as a potential human carcinogen and Group 2B "possibly carcinogenic to humans". MDI appears to be relatively safer and is unlikely a human carcinogen. The IARC evaluates MDI as Group 3 "not classifiable as to its carcinogenicity in humans".
All major producers of MDI and TDI are members of the International Isocyanate Institute, which promotes the safe handling of MDI and TDI. | 0 | Organic Chemistry |
The midbody structure contains bundles of microtubules derived from the mitotic spindle which compacts during the final stages of cell division. It has a typical diameter of 1 micrometre and a length of 3 to 5 micrometres. Aside from microtubules it also contains various proteins involved in cytokinesis, asymmetric cell division, and chromosome segregation.
The midbody is important for completing the final stages of cytokinesis, a process called abscission. During symmetric abscission, the midbody is severed at each end and released into the cellular environment. | 1 | Biochemistry |
Cryptophanes are a class of organic supramolecular compounds studied and synthesized primarily for molecular encapsulation and recognition. One possible noteworthy application of cryptophanes is encapsulation and storage of hydrogen gas for potential use in fuel cell automobiles. Cryptophanes can also serve as containers in which organic chemists can carry out reactions that would otherwise be difficult to run under normal conditions. Due to their unique molecular recognition properties, cryptophanes also hold great promise as a potentially new way to study the binding of organic molecules with substrates, particularly as pertaining to biological and biochemical applications. | 6 | Supramolecular Chemistry |
Smooth muscle cells cultured from the myometrium showed no significant induction of SFRP1 mRNA in response to treatment with E2 and/or progesterone. Conversely, cells cultured from leiomyomas showed significant dose-dependent induction of SFRP1 mRNA in response to treatment with E2; however, progesterone had no effect on SFRP1 even when coapplied with E2. | 1 | Biochemistry |
Before performing any kind of immobilization techniques, some factors should be in mind. It is necessary to understand the chemical and physical effects on an enzyme following immobilization. Enzyme stability and kinetic characteristics can be altered due to changes in the microenvironment conditions of the enzyme after entrapment, support material attachment, or products of enzymatic actions for instance. Additionally, it is important to consider maintaining the tertiary structure of an enzyme prior to immobilizing to have a functional enzyme. Similarly, another crucial site for the functionality of an enzyme is the active-site, which should also be maintained while enzyme is being attached to a surface for immobilization, it is a must to have a selective method for the attachment of surface/material to not end up with an immobilized, but dysfunctional enzyme. Consequently, there are three foundational factors to be thought of for the production of functional immobilized enzymes: immobilization supports selection, conditions and methods of immobilization. | 4 | Stereochemistry |
The contact angle (symbol ) is the angle between a liquid surface and a solid surface where they meet. More specifically, it is the angle between the surface tangent on the liquid–vapor interface and the tangent on the solid–liquid interface at their intersection.
It quantifies the wettability of a solid surface by a liquid via the Young equation.
A given system of solid, liquid, and vapor at a given temperature and pressure has a unique equilibrium contact angle. However, in practice a dynamic phenomenon of contact angle hysteresis is often observed, ranging from the advancing (maximal) contact angle to the receding (minimal) contact angle. The equilibrium contact is within those values, and can be calculated from them. The equilibrium contact angle reflects the relative strength of the liquid, solid, and vapour molecular interaction.
The contact angle depends upon the medium above the free surface of the liquid, and the nature of the liquid and solid in contact. It is independent of the inclination of solid to the liquid surface. It changes with surface tension and hence with the temperature and purity of the liquid. | 7 | Physical Chemistry |
The raw materials are different paper pulps. The pulp may be from softwood, hardwood, fiber crops, mineral fibers. For high quality filters, dissolving pulp and mercerised pulp are used. Most filter papers are made using small paper machines. For laboratory filters, the machines may be as small as 50 cm in width. The paper is often crêped to improve porosity. The filter papers may also be treated with reagents or impregnation to get the right properties. | 3 | Analytical Chemistry |
The dietary reference intake for vitamin D issued in 2010 by the Institute of Medicine (IoM) (renamed National Academy of Medicine in 2015), superseded previous recommendations which were expressed in terms of adequate intake. The recommendations were formed assuming the individual has no skin synthesis of vitamin D because of inadequate sun exposure. The reference intake for vitamin D refers to total intake from food, beverages and supplements, and assumes that calcium requirements are being met. The tolerable upper intake level (UL) is defined as "the highest average daily intake of a nutrient that is likely to pose no risk of adverse health effects for nearly all persons in the general population." Although ULs are believed to be safe, information on the long-term effects is incomplete and these levels of intake are not recommended for long-term consumption.
For US food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For vitamin D labeling purposes, 100% of the daily value was 400IU (10μg), but in May 2016, it was revised to 800IU (20μg) to bring it into agreement with the recommended dietary allowance (RDA). Compliance with the updated labeling regulations was required by 1 January 2020 for manufacturers with or more in annual food sales, and by 1 January 2021 for manufacturers with lower volume food sales. A table of the old and new adult daily values is provided at Reference Daily Intake. | 1 | Biochemistry |
In physics, sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface, after the material is itself bombarded by energetic particles of a plasma or gas. It occurs naturally in outer space, and can be an unwelcome source of wear in precision components. However, the fact that it can be made to act on extremely fine layers of material is utilised in science and industry—there, it is used to perform precise etching, carry out analytical techniques, and deposit thin film layers in the manufacture of optical coatings, semiconductor devices and nanotechnology products. It is a physical vapor deposition technique. | 7 | Physical Chemistry |
NOEs are sensitive to interatomic distances, allowing their usage as a conformational probe, or proof of a glycoside bond formation. It's a common practice to compare calculated to experimental proton-proton NOEs in oligosaccharides to confirm a theoretical conformational map. Calculation of NOEs implies an optimization of molecular geometry. | 0 | Organic Chemistry |
Titer (American English) or titre (British English) is a way of expressing concentration. Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure that inherently only evaluates as positive or negative. The titer corresponds to the highest dilution factor that still yields a positive reading. For example, positive readings in the first 8 serial, twofold dilutions translate into a titer of 1:256 (i.e., 2). Titres are sometimes expressed by the denominator only, for example 1:256 is written 256.
The term also has two other, conflicting meanings. In titration, the titer is the ratio of actual to nominal concentration of a titrant, e.g. a titer of 0.5 would require 1/0.5 = 2 times more titrant than nominal. This is to compensate for possible degradation of the titrant solution. Second, in textile engineering, titre is also a synonym for linear density. | 1 | Biochemistry |
Clarkes father had been the European representative of US photographic pioneer company Kodak for several years, and was a personal friend of founder George Eastman. After Hans graduated in Chemistry, Eastman consulted with him a few times regarding chemistry-related processes. When World War I erupted, Eastman was forced to look for other sources of the chemicals that he had been obtaining from Germany, and he turned to Hans Clarke for assistance. At Eastmans request, Clarke moved to Rochester, New York in 1914 to assist what he assumed to be the company's considerable chemical engineering department. He was shocked to discover that he was the sole organic chemist there.
Clarke stayed with Kodak until 1928, when he was invited to become the Professor of Biological Chemistry in the Columbia University College of Physicians and Surgeons. His administrative skills and ability to recognize talent contributed to the growth of Columbia's biochemistry department, which by the 1940s had become one of the largest and most influential in the United States.
As the dark events foreshadowing World War II pushed eminent Jewish scientists out of Europe, Clarke opened his laboratory to refugee biochemists, among them E. Brand, Erwin Chargaff, Zacharias Dische, K. Meyer, David Nachmansohn, Rudolph Schoenheimer, and Heinrich Waelsch.
As head of Columbia's Biochemistry Department, Clarke took a personal interest in graduate students, of whom he demanded rigorous qualifications prior to admission. As time went on he devoted less time to his own research, becoming inundated with departmental and professional responsibilities.
Clarke's time at Kodak resulted in few publications in the chemical literature, but he aided the preparation of 26 substances to the Organic Syntheses series, and checked some 65 others. He stayed associated with Kodak for the rest of his life, only retiring as a consultant in 1969. Among other researches, he was involved in the production of penicillin in the United States.
Clarke retired from Columbia in 1956 due to its mandatory retirement policy, but was able to move to Yale University, where he spent eight years in full-time research. When Yale required the space that he was occupying he moved again, and did another seven years work at the Childrens Cancer Relief Foundation in Boston, Massachusetts. | 0 | Organic Chemistry |
The calcite compensation depth (CCD) occurs at the depth that the rate of calcite to the sediments is balanced with the dissolution flux, the depth at which the CaCO content are values 2–10%. Hence, the lysocline and CCD are not equivalent. The lysocline and compensation depth occur at greater depths in the Atlantic (5000–6000 m) than in the Pacific (4000–5000 m), and at greater depths in equatorial regions than in polar regions.
The depth of the CCD varies as a function of the chemical composition of the seawater and its temperature. Specifically, it is the deep waters that are undersaturated with calcium carbonate primarily because its solubility increases strongly with increasing pressure and salinity and decreasing temperature. As the atmospheric concentration of carbon dioxide continues to increase, the CCD can be expected to decrease in depth, as the ocean's acidity rises. | 9 | Geochemistry |
Schellman loops (also called Schellman motifs or paperclips) are commonly occurring structural features of proteins and polypeptides. Each has six amino acid residues (labelled residues i to i+5) with two specific inter-mainchain hydrogen bonds (as in lower figure, i) and a characteristic main chain dihedral angle conformation. The CO group of residue i is hydrogen-bonded to the NH of residue i+5 (colored orange in upper figure), and the CO group of residue i+1 is hydrogen-bonded to the NH of residue i+4 (beta turn, colored purple). Residues i+1, i+2, and i+3 have negative φ (phi) angle values and the phi value of residue i+4 is positive. Schellman loops incorporate a three amino acid residue RL nest (protein structural motif), in which three mainchain NH groups (from Schellman loop residues i+3 to i+5) form a concavity for hydrogen bonding to carbonyl oxygens. About 2.5% of amino acids in proteins belong to Schellman loops. Two websites are available for examining small motifs in proteins, Motivated Proteins: [http://motif.gla.ac.uk/motif/index.html]; or PDBeMotif: [http://www.ebi.ac.uk/pdbe-site/pdbemotif/].
The majority of Schellman loops (82%) occur at the C-terminus of an alpha-helix such that residues i, i+1, i+2 and i+3 are part of the helix. Over a quarter of helices (28%) have a C-terminal Schellman loop.
Occasional Schellman loops occur with seven instead of six residues. In these, the CO group of residue i is hydrogen-bonded to the NH of residue i+6, and the CO group of residue i+1 is hydrogen-bonded to the NH of residue i+5. Rare “left-handed” six-residue Schellman loops occur; these have the same hydrogen bonds, but residues i+1, i+2, and i+3 have positive φ values while the φ value of residue i+4 is negative; the nest is of the LR, rather than the RL, kind.
Amino acid propensities for the residues of the common type of Schellman loop have been described. Residue i+4 is the one most-highly conserved; it has positive φ values; 70% of amino acids are glycine and none are proline.
Consideration of the hydrogen bonding in the nests of Schellman loops bound to mainchain oxygens reveals two main types of arrangement: 1,3-bridged or not. In one (lower figure, ii) the first and third nest NH groups are bridged by an oxygen atom. In the other (lower figure, iv) the first NH group is hydrogen bonded to the CO group of an amino acid four residues behind in the sequence, and none of the nest NH groups are bridged. It seems that Schellman loops are less homogeneous than might have been expected.
The original Schellman criteria result in the inclusion of features not now regarded as Schellman loops. A newer set of criteria is given in the first paragraph. | 0 | Organic Chemistry |
Global steel production grew enormously in the 20th century from a mere 28 million tonnes at the beginning of the century to 781 million tons at the end. Per-capita steel consumption in the US peaked in 1977, then fell by half before staging a modest recovery to levels well below the peak. | 8 | Metallurgy |
Glide operations combine mirroring with translation. The operation involves choosing a translation vector →U of the object and acts by mirroring through a plane parallel to vector, of →U. The plane through which the mirror part of the glide operation occurs is called a glide plane. The unit cell is almost al- ways chosen so that the glide plane is per- pendicular to a unit cell edge.
In crystals, screw rotations and/or glide reflections are additionally possible. These are rotations or reflections together with partial translation. These operations may change based on the dimensions of the crystal lattice.
The Bravais lattices may be considered as representing translational symmetry operations. Combinations of operations of the crystallographic point groups with the addition symmetry operations produce the 230 crystallographic space groups. | 7 | Physical Chemistry |
The DNA sequence of the fd genome has 6408 nucleotide comprising 9 genes, but the genome has 11 open reading frames producing 11 proteins, since two genes, gene 2 and gene 1, have internal in-frame translation starts, generating two additional proteins, p10 and p11. The genome also contains a short non-coding intergenic sequence. M13 and f1 sequences are slightly different from fd. They both have only 6407 nucleotides; f1 differs from fd in 180 positions (only 10 of these changes are reflected in amino-acid changes in gene products) and M13 has only 59 nucleotide differences from f1. For many purposes the phages in the Ff group can be considered as interchangeable.
Five gene products are part of the virion: the major coat protein (p8) and the minor proteins capping the two ends, p3 and p6 at one end, and p7 and p9 at the other end. Three gene products (p2, p5, and p10) are cytoplasmic proteins needed for DNA synthesis and the rest are membrane proteins involved in assembly of the virion.
The gene encoding p1 has been used as a conserved marker gene, along with three other features specific for inovirus genomes, in an automatic machine-learning approach to identify over 10000 inovirus-like sequences from microbial genomes. | 1 | Biochemistry |
*When a reaction is reversed, the magnitude of ΔH stays the same, but the sign changes.
*When the balanced equation for a reaction is multiplied by an integer, the corresponding value of ΔH must be multiplied by that integer as well.
*The change in enthalpy for a reaction can be calculated from the enthalpies of formation of the reactants and the products
*Elements in their standard states make no contribution to the enthalpy calculations for the reaction, since the enthalpy of an element in its standard state is zero. Allotropes of an element other than the standard state generally have non-zero standard enthalpies of formation. | 7 | Physical Chemistry |
A monatomic ion (also called simple ion) is an ion consisting of exactly one atom. If, instead of being monatomic, an ion contains more than one atom, even if these are of the same element, it is called a polyatomic ion. For example, calcium carbonate consists of the monatomic cation Ca and the polyatomic anion ; both pentazenium () and azide () are polyatomic as well. | 7 | Physical Chemistry |
The area thermal expansion coefficient relates the change in a material's area dimensions to a change in temperature. It is the fractional change in area per degree of temperature change. Ignoring pressure, one may write:
where is some area of interest on the object, and is the rate of change of that area per unit change in temperature.
The change in the area can be estimated as:
This equation works well as long as the area expansion coefficient does not change much over the change in temperature , and the fractional change in area is small . If either of these conditions does not hold, the equation must be integrated. | 7 | Physical Chemistry |
In oxidizing environment, green rust generally turns into oxyhydroxides, namely α- (goethite) and γ- (lepidocrocite).
Oxidation of the carbonate variety can be retarded by wetting the material with hydroxyl-containing compounds such as glycerol or glucose, even though they do not penetrate the structure. Some variety of green rust is stabilized also by an atmosphere with high partial pressure.
Sulfate green rust has been shown to reduce nitrate and nitrite in solution to ammonium , with concurrent oxidation of to . Depending on the cations in the solution, the nitrate anions replaced the sulfate in the intercalation layer, before the reduction. It was conjectured that green rust may be formed in the reducing alkaline conditions below the surface of marine sediments and may be connected to the disappearance of oxidized species like nitrate in that environment.
Suspensions of carbonate green rust and orange γ- in water will react over a few days produce a black precipitate of magnetite . | 8 | Metallurgy |
Amagat's law or the law of partial volumes describes the behaviour and properties of mixtures of ideal (as well as some cases of non-ideal) gases. It is of use in chemistry and thermodynamics. It is named after Emile Amagat. | 7 | Physical Chemistry |
The [https://cran.r-project.org/web/packages/caroline/index.html caroline CRAN R package] contains the only known implementation of an RA plot. However, the meta-transcriptomics [http://bioconductor.org/packages/devel/bioc/html/manta.html "manta" R package] provides a wrapper around this RA plot implementation and is used for assessing fold change in transcription of genes (the points) while simultaneously visualizing each gene's taxonomic distributions as individual pie chart points. | 1 | Biochemistry |
In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms substituent and functional group, as well as side chain and pendant group, are used almost interchangeably to describe those branches from the parent structure, though certain distinctions are made in polymer chemistry. In polymers, side chains extend from the backbone structure. In proteins, side chains are attached to the alpha carbon atoms of the amino acid backbone.)
The suffix -yl is used when naming organic compounds that contain a single bond replacing one hydrogen; -ylidene and -ylidyne are used with double bonds and triple bonds, respectively. In addition, when naming hydrocarbons that contain a substituent, positional numbers are used to indicate which carbon atom the substituent attaches to when such information is needed to distinguish between isomers. Substituents can be a combination of the inductive effect and the mesomeric effect. Such effects are also described as electron-rich and electron withdrawing. Additional steric effects result from the volume occupied by a substituent.
The phrases most-substituted and least-substituted are frequently used to describe or compare molecules that are products of a chemical reaction. In this terminology, methane is used as a reference of comparison. Using methane as a reference, for each hydrogen atom that is replaced or "substituted" by something else, the molecule can be said to be more highly substituted. For example:
* Markovnikov's rule predicts that the hydrogen atom is added to the carbon of the alkene functional group which has the greater number of hydrogen atoms (fewer alkyl substituents).
* Zaitsev's rule predicts that the major reaction product is the alkene with the more highly substituted (more stable) double bond. | 0 | Organic Chemistry |
Doping fullerenes with electropositive metals takes place in an arc reactor or via laser evaporation. The metals can be transition metals like scandium, yttrium as well as lanthanides like lanthanum and cerium. Also possible are endohedral complexes with elements of the alkaline earth metals like barium and strontium, alkali metals like potassium and tetravalent metals like uranium, zirconium and hafnium. The synthesis in the arc reactor is however unspecific. Besides unfilled fullerenes, endohedral metallofullerenes develop with different cage sizes like La@C or La@C and as different isomer cages. Aside from the dominant presence of mono-metal cages, numerous di-metal endohedral complexes and the tri-metal carbide fullerenes like ScC@C were also isolated.
In 1999 a discovery drew large attention. With the synthesis of the ScN@C by Harry Dorn and coworkers, the inclusion of a molecule fragment in a fullerene cage had succeeded for the first time. This compound can be prepared by arc-vaporization at temperatures up to 1100 °C of graphite rods packed with scandium(III) oxide iron nitride and graphite powder in a K-H generator in a nitrogen atmosphere at 300 Torr.
Endohedral metallofullerenes are characterised by the fact that electrons will transfer from the metal atom to the fullerene cage and that the metal atom takes a position off-center in the cage. The size of the charge transfer is not always simple to determine. In most cases it is between 2 and 3 charge units, in the case of the La@C however it can be even about 6 electrons such as in ScN@C which is better described as [ScN]@[C]. These anionic fullerene cages are very stable molecules and do not have the reactivity associated with ordinary empty fullerenes. They are stable in air up to very high temperatures (600 to 850 °C).
The lack of reactivity in Diels-Alder reactions is utilised in a method to purify [C] compounds from a complex mixture of empty and partly filled fullerenes of different cage size. In this method Merrifield resin is modified as a cyclopentadienyl resin and used as a solid phase against a mobile phase containing the complex mixture in a column chromatography operation. Only very stable fullerenes such as [ScN]@[C] pass through the column unreacted.
In Ce@C the two metal atoms exhibit a non-bonded interaction. Since all the six-membered rings in C-I are equal the two encapsulated Ce atoms exhibit a three-dimensional random motion. This is evidenced by the presence of only two signals in the C-NMR spectrum. It is possible to force the metal atoms to a standstill at the equator as shown by x-ray crystallography when the fullerene is exahedrally functionalized by an electron donation silyl group in a reaction of Ce@C with 1,1,2,2-tetrakis(2,4,6-trimethylphenyl)-1,2-disilirane.
Gd@C(OH), an endohedral metallofluorenol, can competitively inhibit the WW domain in the oncogene YAP1 from activating. It was originally developed as an MRI contrast agent. | 6 | Supramolecular Chemistry |
The International Energy Agency reports the following typical higher heating values per Standard cubic metre of gas:
* Algeria: 39.57MJ/Sm
* Bangladesh: 36.00MJ/Sm
* Canada: 39.00MJ/Sm
* China: 38.93MJ/Sm
* Indonesia: 40.60MJ/Sm
* Iran: 39.36MJ/Sm
* Netherlands: 33.32MJ/Sm
* Norway: 39.24MJ/Sm
* Pakistan: 34.90MJ/Sm
* Qatar: 41.40MJ/Sm
* Russia: 38.23MJ/Sm
* Saudi Arabia: 38.00MJ/Sm
* Turkmenistan: 37.89MJ/Sm
* United Kingdom: 39.71MJ/Sm
* United States: 38.42MJ/Sm
* Uzbekistan: 37.89MJ/Sm
The lower heating value of natural gas is normally about 90% of its higher heating value. This table is in Standard cubic metres (1atm, 15°C), to convert to values per Normal cubic metre (1atm, 0°C), multiply above table by 1.0549. | 7 | Physical Chemistry |
Some people experience persistent sexual side effects when taking SSRIs or after discontinuing them. Symptoms of medication-induced sexual dysfunction from antidepressants include difficulty with orgasm, erection, or ejaculation. Other symptoms may be genital anesthesia, anhedonia, decreased libido, vaginal lubrication issues, and nipple insensitivity in women. Rates are unknown, and there is no established treatment. | 4 | Stereochemistry |
In contact with ambient air, liquid aluminium reacts with the oxygen and form an oxide film layer (gamma-AlO). This layer becomes thicker with time. When molten aluminium is disturbed, this oxide film gets mixed inside the melt. | 8 | Metallurgy |
In autumn 1806, he was welcomed into the family home of Ørsted, where he was given a position as an Assistant, helping Ørsted prepare his university lectures. His stay with Ørsted lasted several years and was certainly of the greatest importance for his development. Ørsted himself recounted how he influenced Zeise through conversations and encouraged him when he expressed the desire to take the university entrance examination (Examen artium). Ørsted spoke fondly of Zeise's independent spirit. Zeise became a university student in 1809.
Zeise had at first intended to study medicine, but while attending lectures it became clear that his interests had a broader scientific base; and chemistry remained his favourite subject. He still experimented in Ørsteds Laboratory, but since at that time there was no prospect for a teaching position at the university, he took the pharmacist exam in 1815, later a masters degree (magisterkonferens) and on 21 October 1817 he defended his doctoral dissertation on The effect of Alkalies upon organic substances. The experimental part of this work he performed in a small laboratory, which in 1816 he had converted from the pharmacy in Slagelse.
As the university had no separate lecturing chair in chemistry and no scientific laboratory, Zeise decided to work and study abroad. In 1818 he managed to get travelling money. Zeise arrived in Göttingen, where he spent four months working in Friedrich Stromeyers laboratory, one of the few experimental laboratories in Germany at that time. He was trained particularly in analytical chemistry, in which he would become a great master. Zeise next spent nearly a year in Paris. His diary entries reflect how diligent he was, and depict vividly the impression he got of the famous French scientists he came in contact with. In August 1818, while in Paris, Zeise became personally acquainted with the distinguished Swedish chemist Jöns Jacob Berzelius. Berzelius received the young Danish chemist with great benevolence, expressing his admiration for Zeises Doctoral thesis. They continued a respectful friendship thereafter, despite Zeise being ten years younger than Berzelius. | 0 | Organic Chemistry |
An example of artificial ratchets is the work by Serreli et al. (2007). Serreli et al. constructed a nanomachine, a rotaxane, that consists of a ring-shaped molecule, that moves along a tiny molecular axle between two different equal compartments, A and B. The normal, random movement of molecules sends the ring back and forth. Since the rings move freely, half of the rotaxanes have the ring on site B and the other half on site A. But the system used by Serreli et al. has a chemical gate on the rotaxane molecule and the axle contains two sticky parts, one at either side of the gate. This gate opens when the ring is close by. The sticky part in B is close to the gate and the rings pass more readily to A than from A to B. They obtained a deviation from equilibrium of 70:50 for A and B respectively, a bit like the demon of Maxwell. But this system works only when light is shone on it and thus needs external energy, just like molecular demons. | 6 | Supramolecular Chemistry |
Bachrach earned a Bachelor of Science degree from the University of Illinois Urbana-Champaign and a PhD from the University of California, Berkeley. | 0 | Organic Chemistry |
In the field of genomics, GeneCalling is an open-platform mRNA transcriptional profiling technique. The GeneCalling protocol measures levels of cDNA, which are correlated with gene expression levels of specific transcripts. Differences between gene expression in healthy tissues and disease or drug responsive tissues are examined and compared in this technology. The technique has been applied to the study of human tissues and plant tissues. | 1 | Biochemistry |
An emulator for the APEXC series has been developed by MESS. They describe its functioning as follows:
<blockquote>The APEXC is an incredibly simple machine.
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Instruction and data words are always 32 bits long. The processor uses integer arithmetic with 2's complement representation. Addresses are 10 bits long. The APEXC has no RAM, except for a 32-bit accumulator and a 32-bit data register (used along with the 32-bit accumulator to implement 64-bit shift instructions and hold the 64-bit result of a multiplication). Instructions and data are stored in two magnetic drums, for a total of 32 circular magnetic tracks of 32 words. Since the rotation rate is 3750rpm (62.5 rotations per second), the program execution speed can go from as high as the theoretical maximum of 1 kIPS to lower than 100IPS if program instructions and data are not contiguous. Nowadays, many say a pocket calculator is faster.
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One oddity is that there is no program counter: each machine instruction includes the address of the next instruction. This design may sound weird, but it is the only way to achieve optimal performance with this cylinder-based memory.
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The machine code is made of 15 instructions only, namely addition, subtraction, multiplication, load (3 variants), store (2 variants), conditional branch, right arithmetic bit shift, right bit rotation, punched-card input, punched-card output, machine stop, and bank-switching (which is never used on the APEXC, since it only has 1024 words of storage, and addresses are 10-bit-long). A so-called vector mode enables to repeat the same operation 32 times with 32 successive memory locations. Note the lack of bitwise and/or/xor and division. Also, note the lack of indirect addressing modes: dynamic modification of opcodes is the only way one may simulate it.
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Another oddity is that the memory bus and the ALU are 1-bit-wide. There is a 64 kHz bit-clock and a 2 kHz word-clock, and each word memory and arithmetic operation is decomposed into 32 1-bit memory and arithmetic operations: this takes 32 bit cycles, for a total of 1 word cycle.
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The processor is fairly efficient: most instructions take only 2 word cycles (1 for fetch, 1 for read operand and execute), with the exception of stores, shifts and multiplications. The APEXC CPU qualifies as RISC; there is no other adequate word.
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Note there is no read-only memory (ROM), and therefore no bootstrap loader or default start-up program whatsoever. It is believed that no executive or operating system was ever written for the APEXC, although there were subroutine libraries of sorts for common arithmetic, I/O and debug tasks.
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Operation of the machine is normally done through a control panel which allows the user to start, stop and resume the central processing unit, and to alter registers and memory when the CPU is stopped. When starting the machine, the address of the first instruction of the program to be executed must be entered in the control panel, then the run switch must be pressed. Most programs end with a stop instruction, which enables the operator to check the state of the machine, possibly run some post-mortem debugging procedures (a core dump routine is described in an APEXC programming book), then enter the address of another program and run it.
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Two I/O devices were supported: a paper tape reader, and a paper tape puncher. The puncher output could be fed to a printer (teletyper) unit when desirable. Printer output is emulated and is displayed on screen. Tape input was either computer-generated by the APEXC, or hand-typed with a special 32-key keyboard (each tape row had 5 data holes ( | 3 | Analytical Chemistry |
In chemistry and fluid mechanics, the volume fraction is defined as the volume of a constituent V divided by the volume of all constituents of the mixture V prior to mixing:
Being dimensionless, its unit is 1; it is expressed as a number, e.g., 0.18. It is the same concept as volume percent (vol%) except that the latter is expressed with a denominator of 100, e.g., 18%.
The volume fraction coincides with the volume concentration in ideal solutions where the volumes of the constituents are additive (the volume of the solution is equal to the sum of the volumes of its ingredients).
The sum of all volume fractions of a mixture is equal to 1:
The volume fraction (percentage by volume, vol%) is one way of expressing the composition of a mixture with a dimensionless quantity; mass fraction (percentage by weight, wt%) and mole fraction (percentage by moles, mol%) are others. | 7 | Physical Chemistry |
In polymer chemistry, materials science, and food science, bloom refers to the migration of one component of a solid mixture to the surface of an article. The process is an example of phase separation or phase aggregation. | 7 | Physical Chemistry |
Instead of light, this method employs ultrasound for collecting information on the particles that are dispersed in fluid. Dispersed particles absorb and scatter ultrasound similarly to light. This has been known since Lord Rayleigh developed the first theory of ultrasound scattering and published a book "The Theory of Sound" in 1878. There have been hundreds of papers studying ultrasound propagation through fluid particulates in the 20th century. It turns out that instead of measuring scattered energy versus angle, as with light, in the case of ultrasound, measuring the transmitted energy versus frequency is a better choice. The resulting ultrasound attenuation frequency spectra are the raw data for calculating particle size distribution. It can be measured for any fluid system with no dilution or other sample preparation. This is a big advantage of this method. Calculation of particle size distribution is based on theoretical models that are well verified for up to 50% by volume of dispersed particles on micron and nanometer scales. However, as concentration increases and the particle sizes approach the nanoscale, conventional modelling gives way to the necessity to include shear-wave re-conversion effects in order for the models to accurately reflect the real attenuation spectra. | 7 | Physical Chemistry |
For cases where the molecule is un-ionized:
For other cases, estimation of log D at a given pH, from log P and the known mole fraction of the un-ionized form, , in the case where partition of ionized forms into non-polar phase can be neglected, can be formulated as
The following approximate expressions are valid only for monoprotic acids and bases:
Further approximations for when the compound is largely ionized:
* for acids with , ,
* for bases with , .
For prediction of pK, which in turn can be used to estimate log D, Hammett type equations have frequently been applied. | 7 | Physical Chemistry |
Hot black oxide for stainless steel is a mixture of caustic, oxidizing, and sulfur salts. It blackens 300 and 400 series and the precipitation-hardened 17-4 PH stainless steel alloys. The solution can be used on cast iron and mild low-carbon steel. The resulting finish complies with military specification MIL-DTL–13924D Class 4 and offers abrasion resistance. Black oxide finish is used on surgical instruments in light-intensive environments to reduce eye fatigue.
Room-temperature blackening for stainless steel occurs by auto-catalytic reaction of copper-selenide depositing on the stainless-steel surface. It offers less abrasion resistance and the same corrosion protection as the hot blackening process. | 7 | Physical Chemistry |
Paracetamol powder has poor compression properties, which poses difficulty in making tablets. A second polymorph was found with more suitable compressive properties. | 3 | Analytical Chemistry |
In mammals, malic enzyme 2 (ME2) is allosterically activated by fumarate. The Krebs cycle intermediate fumarate links metabolism to mitobiogenesis through binding to malic enzyme 2 (ME2). Mechanistically, fumarate binds ME2 with two complementary consequences. First, promoting the formation of ME2 dimers, which activate deoxyuridine 5'-triphosphate nucleotidohydrolase (DUT). DUT fosters thymidine generation and an increase of mtDNA. Second, fumarate-induced ME2 dimers abrogate ME2 monomer binding to mitochondrial ribosome protein L45, freeing it for mitoribosome assembly and mtDNA-encoded protein production. Methylation of the ME2-fumarate binding site by protein arginine methyltransferase-1 inhibits fumarate signaling to constrain mitobiogenesis. Notably, acute myeloid leukemia is highly dependent on mitochondrial function and is sensitive to targeting of the fumarate-ME2 axis. | 1 | Biochemistry |
The equilibrium constant K for a base is usually defined as the association constant for protonation of the base, B, to form the conjugate acid, .
Using similar reasoning to that used before
K is related to K for the conjugate acid. In water, the concentration of the hydroxide ion, , is related to the concentration of the hydrogen ion by , therefore
Substitution of the expression for into the expression for K gives
When K, K and K are determined under the same conditions of temperature and ionic strength, it follows, taking cologarithms, that pK = pK − pK. In aqueous solutions at 25 °C, pK is 13.9965, so
with sufficient accuracy for most practical purposes. In effect there is no need to define pK separately from pK, but it is done here as often only pK values can be found in the older literature.
For an hydrolyzed metal ion, K can also be defined as a stepwise dissociation constant
This is the reciprocal of an association constant for formation of the complex. | 7 | Physical Chemistry |
Receptor desensitization is mediated through a combination phosphorylation, β-arr binding, and endocytosis as described above. Downregulation occurs when endocytosed receptor is embedded in an endosome that is trafficked to merge with an organelle called a lysosome. Because lysosomal membranes are rich in proton pumps, their interiors have low pH (≈4.8 vs. the pH≈7.2 cytosol), which acts to denature the GPCRs. In addition, lysosomes contain many degradative enzymes, including proteases, which can function only at such low pH, and so the peptide bonds joining the residues of the GPCR together may be cleaved. Whether or not a given receptor is trafficked to a lysosome, detained in endosomes, or trafficked back to the plasma membrane depends on a variety of factors, including receptor type and magnitude of the signal.
GPCR regulation is additionally mediated by gene transcription factors. These factors can increase or decrease gene transcription and thus increase or decrease the generation of new receptors (up- or down-regulation) that travel to the cell membrane. | 1 | Biochemistry |
Iron is also the most abundant transition metal in the human body and it is used in various processes like oxygen transport and ATP production. It plays a key role in the function of enzymes like cytochrome a, b and c as well as iron-sulfur complexes which play an important role in ATP production. It is present in every type of cell in the brain as the brain itself has a very high energy requirement and by extension a very high iron requirement. In animals, iron plays a very important role in transporting oxygen from the lungs to tissues and CO from tissues to the lungs. It does this via two important transport proteins called hemoglobin and myoglobin. Hemoglobin in the blood transports oxygen from the lungs to myoglobin in tissues. Both proteins are tetramer complexes with iron protein complexes called hemes built into each subunit of the tetramer. The oxygen binds to the iron in the heme via affinity-based binding or liganding and dissociates from the protein once it has reached its destination. Iron can also be a potential carcinogen in three ways; first being the production of hydroxyl radicals. Ferric ions can be reduced via superoxide and the product can be reoxidized via peroxide to form hydroxyl radicals. Hydroxyl radicals and other reactive oxygen species when generated near DNA can cause point mutations, cross-linkage and breaks. The second being the bolstering of the growth of neoplastic cells by suppressing host defenses. Excessive iron inhibits the activity of CD lymphocytes and suppresses the tumoricidal activity of macrophages. The third way it can act as a carcinogen is by functioning as an essential nutrient for unrestricted proliferation of tumor cells. | 1 | Biochemistry |
The revival of the woolly mammoth is a proposed hypothetical that frozen soft-tissue remains and DNA from extinct woolly mammoths could be a means of regenerating the species. Several methods have been proposed to achieve this goal, including cloning, artificial insemination, and genome editing. Whether or not it is ethical to create a live mammoth is debated.
In 2003, the Pyrenean ibex was briefly revived, giving credence to the idea that the mammoth could be successfully revived. | 1 | Biochemistry |
Enzymes are proteins that act as biological catalysts by accelerating chemical reactions. Enzymes act on small molecules called substrates, which an enzyme converts into products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. The study of how fast an enzyme can transform a substrate into a product is called enzyme kinetics.
The rate of reaction of many chemical reactions shows a linear response as function of the concentration of substrate molecules. Enzymes however display a saturation effect where,, as the substrate concentration is increased the reaction rate reaches a maximum value. Standard approaches to describing this behavior are based on models developed by Michaelis and Menten as well and Briggs and Haldane. Most elementary formulations of these models assume that the enzyme reaction is irreversible, that is product is not converted back to substrate. However, this is unrealistic when describing the kinetics of enzymes in an intact cell because there is product available. Reversible Michaelis–Menten kinetics, using the reversible form of the Michaelis–Menten equation, is therefore important when developing computer models of cellular processes involving enzymes.
In enzyme kinetics, the Michaelis–Menten kinetics kinetic rate law that describes the conversion of one substrate to one product, is often commonly depicted in its irreversible form as:
where is the reaction rate, is the maximum rate when saturating levels of the substrate are present, is the Michaelis constant and the substrate concentration.
In practice, this equation is used to predict the rate of reaction when little or no product is present. Such situations arise in enzyme assays. When used to model enzyme rates , for example, to model a metabolic pathway, this representation is inadequate because under these conditions product is present. As a result, when building computer models of metabolism or other enzymatic processes, it is better to use the reversible form of the Michaelis–Menten equation.
To model the reversible form of the Michaelis–Menten equation, the following reversible mechanism is considered:
To derive the rate equation, it is assumed that the concentration of enzyme-substrate complex is at steady-state, that is .
Following current literature convention, we will be using lowercase Roman lettering to indicate concentrations (this avoids cluttering the equations with square brackets). Thus indicates the concentration of enzyme-substrate complex, ES.
The net rate of change of product (which is equal to ) is given by the difference in forward and reverse rates:
The total level of enzyme moiety is the sum total of free enzyme and enzyme-complex, that is . Hence the level of free is given by the difference in the total enzyme concentration, and the concentration of complex, that is:
Using mass conservation we can compute the rate of change of using the balance equation:
where has been replaced using . This leaves as the only unknown. Solving for gives:
Inserting into the rate equation and rearranging gives:
The following substitutions are now made:
and
after rearrangement, we obtain the reversible Michaelis–Menten equation in terms of four constants: | 7 | Physical Chemistry |
In the quantum mechanical framework, this scattering is most noticeable in confined systems, in which the energies for charge carriers are determined by the locations of interfaces. An example of such a system is a quantum well, which may be constructed from a sandwich of different layers of semiconductor. Variations in the thickness of these layers therefore causes the energy of particles to be dependent on their in-plane location in the layer. Classification of the roughness at a given position, , is complex, but as in the classical models, it has been modeled as a Gaussian distribution by some researchers
This assumption may be formulated in terms of the ensemble average for some given characteristic height, , and correlation length, , such that | 7 | Physical Chemistry |
Georgy Vasilyevich Pigulevsky (; – 19 September 1964) was a soviet organic chemist, specializing in natural product chemistry. He studied essential oils and resins of plants, as well as terpene compounds extracted from them. | 0 | Organic Chemistry |
The compressibility factor is defined in thermodynamics and engineering frequently as:
where p is the pressure, is the density of the gas and is the specific gas constant, being the molar mass, and the is the absolute temperature (kelvin or Rankine scale).
In statistical mechanics the description is:
where p is the pressure, n is the number of moles of gas, is the absolute temperature, and is the gas constant, V is unit Volume
For an ideal gas the compressibility factor is per definition. In many real world applications requirements for accuracy demand that deviations from ideal gas behaviour, i.e., real gas behaviour, be taken into account. The value of generally increases with pressure and decreases with temperature. At high pressures molecules are colliding more often. This allows repulsive forces between molecules to have a noticeable effect, making the molar volume of the real gas () greater than the molar volume of the corresponding ideal gas (), which causes to exceed one. When pressures are lower, the molecules are free to move. In this case attractive forces dominate, making . The closer the gas is to its critical point or its boiling point, the more deviates from the ideal case. | 7 | Physical Chemistry |
The light reactions take place on the thylakoid membranes. They take light energy and store it in NADPH, a form of NADP, and ATP to fuel the dark reactions. | 5 | Photochemistry |
Ideal materials for thermal mass are those materials that have:
* high specific heat capacity,
* high density
Any solid, liquid, or gas that has mass will have some thermal mass. A common misconception is that only concrete or earth soil has thermal mass; even air has thermal mass (although very little).
A table of volumetric heat capacity for building materials is available, but note that their definition of thermal mass is slightly different. | 7 | Physical Chemistry |
THz-TDS measures the electric field of a pulse and not just the power. Thus, THz-TDS measures both the amplitude and phase information of the frequency components it contains. In contrast, measuring only the power at each frequency is essentially a photon counting technique; information regarding the phase of the light is not obtained. Thus, the waveform is not uniquely determined by such a power measurement.
Even when measuring only the power reflected from a sample, the complex optical response constant of the material can be obtained. This is so because the complex nature of an optical constant is not arbitrary. The real and imaginary parts of an optical constant are related by the Kramers–Kronig relations. There is a difficulty in applying the Kramers-Kronig relations as written, because information about the sample (reflected power, for example) must be obtained at all frequencies. In practice, far separated frequency regions do not have significant influence on each other, and reasonable limiting conditions can be applied at high and low frequency, outside of the measured range.
THz-TDS, in contrast, does not require use of Kramers-Kronig relations. By measuring the electric field of a THz pulse in the time-domain, the amplitude and phase of each frequency component of the THz pulse are known (in contrast to the single piece of information known by a power measurement). Thus the real and imaginary parts of an optical constant can be known at every frequency within the usable bandwidth of a THz pulse, without need of frequencies outside the usable bandwidth or Kramers-Kronig relations. | 7 | Physical Chemistry |
This is a special category of chain-growth supramolecular polymerization, where the monomer nucleates only in an early stage of polymerization to generate "seeds" and becomes active for polymer chain elongation upon further addition of a new batch of monomer. A secondary nucleation is suppressed in most of the case and thus possible to realize a narrow polydispersity of the resulting supramolecular polymer. In 2007, Ian Manners and Mitchell A. Winnik introduced this concept using a polyferrocenyldimethylsilane–polyisoprene diblock copolymer as the monomer, which assembles into cylindrical micelles. When a fresh feed of the monomer is added to the micellar "seeds" obtained by sonication, the polymerization starts in a living polymerization manner. They named this method as crystallization-driven self-assembly (CDSA) and is applicable to construct micron-scale supramolecular anisotropic structures in 1D–3D. A conceptually different seeded supramolecular polymerization was shown by Kazunori Sugiyasu in a porphyrin-based monomer bearing amide-appended long alkyl chains. At low temperature, this monomer preferentially forms spherical J-aggregates while fibrous H-aggregates at higher temperature. By adding a sonicated mixture of the J-aggregates ("seeds") into a concentrated solution of the J-aggregate particles, long fibers can be prepared via living seeded supramolecular polymerization. Frank Würthner achieved similar seeded supramolecular polymerization of amide functionalized perylene bisimide as monomer. Importantly, the seeded supramolecular polymerization is also applicable to prepare supramolecular block copolymers. | 6 | Supramolecular Chemistry |
To relate the orientation of a crystal, much like in X-ray diffraction (XRD), the geometry of the system must be known. In particular, the pattern centre describes the distance of the interaction volume to the detector and the location of the nearest point between the phosphor and the sample, on the phosphor screen. Early work used a single crystal of known orientation being inserted into the SEM chamber, and a particular feature of the EBSP was known to correspond to the pattern centre. Later developments involved exploiting various geometric relationships between the generation of an EBSP and the chamber geometry (shadow casting and phosphor movement).
Unfortunately, each of these methods is cumbersome and can be prone to some systematic errors for a general operator. Typically they cannot be easily used in modern SEMs with multiple designated uses. Thus, most commercial EBSD systems use the indexing algorithm combined with an iterative movement of crystal orientation and suggested pattern centre location. Minimising the fit between bands located within experimental patterns and those in look-up tables tends to converge on the pattern centre location to an accuracy of ~0.5–1% of the pattern width.
The recent development of AstroEBSD and PCGlobal, open-source MATLAB codes, increased the precision of determining the pattern centre (PC) and – consequently – elastic strains by using a pattern matching approach which simulates the pattern using EMSoft. | 7 | Physical Chemistry |
Nucleic acid sequence-based amplification, commonly referred to as NASBA, is a method in molecular biology which is used to produce multiple copies of single stranded RNA. NASBA is a two-step process that takes RNA and anneals specially designed primers, then utilizes an enzyme cocktail to amplify it. | 1 | Biochemistry |
While water acts as a catalyst in the reaction, other catalysts can be added to the reaction vessel to optimize the conversion. Previously used catalysts include water-soluble inorganic compounds and salts, including KOH and NaCO, as well as transition metal catalysts using nickel, palladium, platinum and ruthenium supported on either carbon, silica or alumina. The addition of these catalysts can lead to an oil yield increase of 20% or greater, due to the catalysts converting the protein, cellulose, and hemicellulose into oil. This ability for catalysts to convert biomaterials other than fats and oils to bio-oil allows for a wider range of feedstock to be used. | 0 | Organic Chemistry |
Loam is a combination of sand, silt and clay that encompasses soils. It can be named based on the primary particles in the soil composition, ex. sandy loam, clay loam, silt loam, etc. | 9 | Geochemistry |
With homeostasis the pH of a biological solution is maintained at a constant value by adjusting the position of the equilibria
where is the bicarbonate ion and is carbonic acid.
However, the solubility of carbonic acid in water may be exceeded. When this happens carbon dioxide gas is liberated and the following equation may be used instead.
represents the carbon dioxide liberated as gas. In this equation, which is widely used in biochemistry, is a mixed equilibrium constant relating to both chemical and solubility equilibria. It can be expressed as
where is the molar concentration of bicarbonate in the blood plasma and is the partial pressure of carbon dioxide in the supernatant gas. | 7 | Physical Chemistry |
Compounds that contain phosphorus exhibit unique chemistry due to the ability of phosphorus to form more bonds than nitrogen, its lighter analogue on the periodic table. | 0 | Organic Chemistry |
The number density (symbol: n or ρ) is an intensive quantity used to describe the degree of concentration of countable objects (particles, molecules, phonons, cells, galaxies, etc.) in physical space: three-dimensional volumetric number density, two-dimensional areal number density, or one-dimensional linear number density. Population density is an example of areal number density. The term number concentration (symbol: lowercase n, or C, to avoid confusion with amount of substance indicated by uppercase N) is sometimes used in chemistry for the same quantity, particularly when comparing with other concentrations. | 3 | Analytical Chemistry |
As the 5′ UTR has high GC content, secondary structures often occur within it. Hairpin loops are one such secondary structure that can be located within the 5′ UTR. These secondary structures also impact the regulation of translation. | 1 | Biochemistry |
Everyday examples of heat engines include the thermal power station, internal combustion engine, firearms, refrigerators and heat pumps. Power stations are examples of heat engines run in a forward direction in which heat flows from a hot reservoir and flows into a cool reservoir to produce work as the desired product. Refrigerators, air conditioners and heat pumps are examples of heat engines that are run in reverse, i.e. they use work to take heat energy at a low temperature and raise its temperature in a more efficient way than the simple conversion of work into heat (either through friction or electrical resistance). Refrigerators remove heat from within a thermally sealed chamber at low temperature and vent waste heat at a higher temperature to the environment and heat pumps take heat from the low temperature environment and vent it into a thermally sealed chamber (a house) at higher temperature.
In general heat engines exploit the thermal properties associated with the expansion and compression of gases according to the gas laws or the properties associated with phase changes between gas and liquid states. | 7 | Physical Chemistry |
Piano stool complexes of the type (η-CH)M(CO) are typically synthesized by heating the appropriate metal carbonyl compound with benzene. Alternately, the same compounds can be obtained by carbonylation of the bis(arene) sandwich compounds, such as (η-CH)M compound with the metal carbonyl compound. This second approach may be more appropriate for arene ligands containing thermally fragile substituents. | 0 | Organic Chemistry |
Lysergic acid is generally produced by hydrolysis of natural lysergamides, but can also be synthesized in the laboratory by a complex total synthesis, for example by Robert Burns Woodward's team in 1956. An enantioselective total synthesis based on a palladium-catalyzed domino cyclization reaction has been described in 2011 by Fujii and Ohno. Lysergic acid monohydrate crystallizes in very thin hexagonal leaflets when recrystallized from water. Lysergic acid monohydrate, when dried (140 °C at ) forms anhydrous lysergic acid. | 0 | Organic Chemistry |
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