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Clay minerals can be incorporated in lime-metakaolin mortars to improve mechanical properties. Electrochemical separation helps to obtain modified saponite-containing products with high smectite-group minerals concentrations, lower mineral particles size, more compact structure, and greater surface area. These characteristics open possibilities for the manufacture of high-quality ceramics and heavy-metal sorbents from saponite-containing products.
Furthermore, tail grinding occurs during the preparation of the raw material for ceramics; this waste reprocessing is of high importance for the use of clay pulp as a neutralizing agent, as fine particles are required for the reaction. Experiments on the histosol deacidification with the alkaline clay slurry demonstrated that neutralization with the average pH level of 7.1 is reached at 30% of the pulp added and an experimental site with perennial grasses proved the efficacy of the technique. Moreover, the reclamation of disturbed lands is an integral part of the social and environmental responsibility of the mining company and this scenario addresses the community necessities at both local and regional levels. | 9 | Geochemistry |
Fluoroform is weakly acidic with a pK = 25–28 and quite inert. Attempted deprotonation results in defluorination to generate and difluorocarbene (). Some organocopper and organocadmium compounds have been developed as trifluoromethylation reagents.
Fluoroform is a precursor of the Ruppert-Prakash reagent Trifluoromethyltrimethylsilane|, which is a source of the nucleophilic anion. | 2 | Environmental Chemistry |
A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, molecule, or phenomenon – that provides scientific evidence of past or present life on a planet. Measurable attributes of life include its complex physical or chemical structures, its use of free energy, and the production of biomass and wastes.
The field of astrobiology uses biosignatures as evidence in the search for past or present extraterrestrial life. | 2 | Environmental Chemistry |
The lac operon of the model bacterium Escherichia coli was the first operon to be discovered and provides a typical example of operon function. It consists of three adjacent structural genes, a promoter, a terminator, and an operator. The lac operon is regulated by several factors including the availability of glucose and lactose. It can be activated by allolactose. Lactose binds to the repressor protein and prevents it from repressing gene transcription. This is an example of the derepressible (from above: negative inducible) model. So it is a negative inducible operon induced by presence of lactose or allolactose. | 1 | Biochemistry |
According to food chemist Udo Pollmer of the European Institute of Food and Nutrition Sciences in Munich, alcohol can be molecularly encapsulated in cyclodextrines, a sugar derivate. In this way, encapsuled in small capsules, the fluid can be handled as a powder. The cyclodextrines can absorb an estimated 60 percent of their own weight in alcohol. A US patent has been registered for the process as early as 1974. | 6 | Supramolecular Chemistry |
In addition to Cori Cycle, the lactate shuttle hypothesis proposes complementary functions of lactate in multiple tissues. Contrary to the long-held belief that lactate is formed as a result of oxygen-limited metabolism, substantial evidence exists that suggests lactate is formed under both aerobic and anaerobic conditions, as a result of substrate supply and equilibrium dynamics. | 1 | Biochemistry |
Endogenous gaseous mediators have shown anti-inflammatory and cytoprotective properties Combination nonsteroidal anti-inflammatory drugs featuring both a cyclooxygenase inhibitor and gaseous mediator releasing component are being investigated as a safer alternative to current anti-inflammatory drugs due to their potential reduction in risk for gastrointestinal ulcer formation. | 1 | Biochemistry |
The Diels-Alder reaction, also known as cycloaddition, combines a conjugated diene and an alkene to form cycloalkene. This is a concerted process, with bonds forming and breaking simultaneously. | 0 | Organic Chemistry |
Normal sound waves are fluctuations in the displacement and density of molecules in a substance;
second sound waves are fluctuations in the density of quasiparticle thermal excitations (rotons and phonons). Second sound can be observed in any system in which most phonon-phonon collisions conserve momentum, like superfluids and in some dielectric crystals when Umklapp scattering is small.
Contrary to molecules in a gas, quasiparticles are not necessarily conserved. Also gas molecules in a box conserve momentum (except at the boundaries of box), while quasiparticles can sometimes not conserve momentum in the presence of impurities or Umklapp scattering. Umklapp phonon-phonon scattering exchanges momentum with the crystal lattice, so phonon momentum is not conserved, but Umklapp processes can be reduced at low temperatures.
Normal sound in gases is a consequence of the collision rate between molecules being large compared to the frequency of the sound wave . For second sound, the Umklapp rate has to be small compared to the oscillation frequency for energy and momentum conservation. However analogous to gasses, the relaxation time describing the collisions has to be large with respect to the frequency , leaving a window:
for sound-like behaviour or second sound. The second sound thus behaves as oscillations of the local number of quasiparticles (or of the local energy carried by these particles). Contrary to the normal sound where energy is related to pressure and temperature, in a crystal the local energy density is purely a function of the temperature. In this sense, the second sound can also be considered as oscillations of the local temperature. Second sound is a wave-like phenomena which makes it very different from usual heat diffusion. | 7 | Physical Chemistry |
Aromatic acids are a type of aromatic compound. Included in that class are substances containing an aromatic ring and an organic acid functional group.
There are several categories of aromatic acids including:
*Phenolic acids: substances containing an aromatic ring and an organic carboxylic acid function (C6-C1 skeleton).
*Aromatic amino acids | 0 | Organic Chemistry |
The most common side effects of enalapril include increased serum creatinine (20%), dizziness (2–8%), low blood pressure (1–7%), syncope (2%), and dry cough (1–2%). The most serious common adverse event is angioedema (swelling) (0.68%) which often affects the face and lips, endangering the patient's airway. Angioedema can occur at any point during treatment with enalapril, but is most common after the first few doses. Angioedema and fatality therefrom are reportedly higher among black people. Agranulocytosis has been observed with Enalapril.
Some evidence suggests enalapril will cause injury and death to a developing fetus. In pregnancy, enalapril may result in damage to the fetus's kidneys and resulting oligohydramnios (not enough amniotic fluid). Enalapril is secreted in breast milk and is not recommended for use while breastfeeding. | 4 | Stereochemistry |
A grain boundary (GB) is the transition area or interface between adjacent crystallites (or grains) of the same chemical and lattice composition, not to be confused with a phase boundary. The adjacent grains do not have the same orientation of the lattice, thus giving the atoms in GB shifted positions relative to the lattice in the crystals. Due to the shifted positioning of the atoms in the GB they have a higher energy state when compared with the atoms in the crystal lattice of the grains. It is this imperfection that makes it possible to selectively etch the GBs when one wants the microstructure to be visible.
Striving to minimize its energy leads to the coarsening of the microstructure to reach a metastable state within the specimen. This involves minimizing its GB area and changing its topological structure to minimize its energy. This grain growth can either be normal or abnormal, a normal grain growth is characterized by the uniform growth and size of all the grains in the specimen. Abnormal grain growth is when a few grains grow much larger than the remaining majority. | 8 | Metallurgy |
Coward was born on 2 July 1885 in Blackburn, Lancashire. She studied Botany and graduated M.Sc. from University of Manchester. After a few years, she joined University College London to study biochemistry and perform research under J. C. Drummond on Vitamin A, paving the way for her to be nominated to the Fellow of the Chemical Society in 1923. | 3 | Analytical Chemistry |
As ozone in the atmosphere prevents most energetic ultraviolet radiation reaching the surface of the Earth, astronomical data in these wavelengths have to be gathered from satellites orbiting above the atmosphere and ozone layer. Most of the light from young hot stars is in the ultraviolet and so study of these wavelengths is important for studying the origins of galaxies. The Galaxy Evolution Explorer, GALEX, is an orbiting ultraviolet space telescope launched on April 28, 2003, which operated until early 2012. | 5 | Photochemistry |
The cycle comprises three enzyme-catalysed reactions. The first stage is the deamination of the purine nucleotide adenosine monophosphate (AMP) to form inosine monophosphate (IMP), catalysed by the enzyme AMP deaminase:
:AMP + HO + H → IMP + NH
The second stage is the formation of adenylosuccinate from IMP and the amino acid aspartate, which is coupled to the energetically favourable hydrolysis of GTP, and catalysed by the enzyme adenylosuccinate synthetase:
:Aspartate + IMP + GTP → Adenylosuccinate + GDP + P
Finally, adenylosuccinate is cleaved by the enzyme adenylosuccinate lyase to release fumarate and regenerate the starting material of AMP:
:Adenylosuccinate → AMP + Fumarate
A recent study showed that activation of HIF-1α allows cardiomyocytes to sustain mitochondrial membrane potential during anoxic stress by utilizing fumarate produced by adenylosuccinate lyase as an alternate terminal electron acceptor in place of oxygen. This mechanism should help provide protection in the ischemic heart. | 1 | Biochemistry |
Cyclamin can be extracted from cyclamen plants such as the species mirabile and trocopteranthum. Cyclamen are known houseplants; this raises concerns about the awareness of the toxicity of this flower. The compound cyclamin belongs to the family of triterpene saponins, which are derived from the saponin structure. Triterpenoid compounds contain one or more sugar moieties attached to triterpenoid aglycones. The large diversity of structures causes saponins to exhibit a wide range of biological and pharmacological properties. In China, cyclamin has been used as a traditional medicine for years. Cyclamen has been used against menstrual disorders, digestive disorders, and anxiety in women. However, this is only the case for the leaves, the roots of the plants are known to be harmful if ingested. In these roots, cyclamin is found, as well as in the bulbs. Therefore, cyclamin is suspected to be the compound which causes the toxicity of these roots and bulbs in cyclamen plants. | 0 | Organic Chemistry |
The four most common methods of transition metal catalyzed methane activation are the Shilov system, sigma bond metathesis, oxidative addition, and 1,2 addition reactions.
The Shilov system involves platinum based complexes to produce metal alkyls. It was first discovered when a hydrogen-deuterium exchanged was observed in a deuterated solution with the platinum tetrachloride anion. Shilov et al. then was able to catalytically convert methane into methanol or methyl chloride when a Pt(IV) salt was used as a stoichiometric oxidant. The process is simplified down into three main steps: (1) C-H activation, (2) a redox reaction to form an octahedral intermediate, followed by (3) the formation of the carbon-oxygen bond to form methanol ().
Sigma bond metathesis involves the formation of new C-H and metal-carbon bonds, where the metals are typically in the d configuration. Starting with a metal alkyl, a C-H bond coordinates with the metal complex via sigma bonding. A four-member transition state is created, where a new metal-carbon bond is formed, and the former C-H linkage is broken ().
In oxidative addition, the metal center's oxidation state increases by 2 units during the process. First, the metal center coordinates with a sigma C-H bond to form an intermediate called a sigma-methane complex. The C-H linkage is then broken, as the metal becomes covalently bonded each to the carbon and the hydrogen ().
Similar to sigma bond metathesis is the 1,2 addition reaction, where a four-membered transition state is also formed. However, a polarized double or triple metal-ligand bond is required in order to favor the formation of the desired product (). | 0 | Organic Chemistry |
Robert Travis Kennedy is an American chemist specializing in bioanalytical chemistry including liquid chromatography, capillary electrophoresis, and microfluidics. He is currently the Hobart H. Willard Distinguished University Professor of Chemistry and the chair of the department of chemistry at the University of Michigan. He holds joint appointments with the Department of Pharmacology and Department Macromolecular Science and Engineering. Kennedy is an Associate Editor of Analytical Chemistry and ACS Measurement Science AU. | 3 | Analytical Chemistry |
In the solid state, racemic mixtures may have different physical properties from either of the pure enantiomers because of the differential intermolecular interactions (see Biological Significance section). The change from a pure enantiomer to a racemate can change its density, melting point, solubility, heat of fusion, refractive index, and its various spectra. Crystallization of a racemate can result in separate (+) and (−) forms, or a single racemic compound. However, in liquid and gaseous states, racemic mixtures will behave with physical properties that are identical, or near identical, to their pure enantiomers. | 4 | Stereochemistry |
Laurie Ellen Locascio (born November 21, 1961) is an American biomedical engineer, analytical chemist, and former academic administrator serving as the under secretary of commerce for standards and technology and the director of National Institute of Standards and Technology. From 2017 to 2021, Locascio was vice president for research of University of Maryland, College Park and University of Maryland, Baltimore. | 3 | Analytical Chemistry |
Residence time distributions are measured by introducing a non-reactive tracer into the system at the inlet. Its input concentration is changed according to a known function and the output concentration measured. The tracer should not modify the physical characteristics of the fluid (equal density, equal viscosity) or the hydrodynamic conditions and it should be easily detectable.
In general, the change in tracer concentration will either be a pulse or a step. Other functions are possible, but they require more calculations to deconvolute the RTD curve. | 9 | Geochemistry |
The Takehara copper refinery of the Mitsui Mining & Smelting Company Limited of Japan commissioned a BBOC in its precious metals department in 1993.
Prior to the installation of the BBOC, the Takehara refinery refined a mixture of copper and lead anode slimes in a three reverberatory furnaces (two operating and one being rebricked) in a process that had a cycle time of 104 hours for refining 6 t of bullion.
The reverberatory furnaces were replaced with a single BBOC with a charge capacity of 6 t of feed. The cycle time was reduced to 50 hours. The use of the BBOC reduced the energy consumption from 74 GJ/t to 27 GJ/t and also had better bismuth elimination than the reverberatory furnaces. | 8 | Metallurgy |
Carbon-14 goes through radioactive beta decay:
: → + + + 156.5 keV
By emitting an electron and an electron antineutrino, one of the neutrons in the carbon-14 atom decays to a proton and the carbon-14 (half-life of 5,700 ± 30 years) decays into the stable (non-radioactive) isotope nitrogen-14.
As usual with beta decay, almost all the decay energy is carried away by the beta particle and the neutrino. The emitted beta particles have a maximum energy of about 156 keV, while their weighted mean energy is 49 keV. These are relatively low energies; the maximum distance traveled is estimated to be 22 cm in air and 0.27 mm in body tissue. The fraction of the radiation transmitted through the dead skin layer is estimated to be 0.11. Small amounts of carbon-14 are not easily detected by typical Geiger–Müller (G-M) detectors; it is estimated that G-M detectors will not normally detect contamination of less than about 100,000 disintegrations per minute (0.05 µCi). Liquid scintillation counting is the preferred method although more recently, accelerator mass spectrometry has become the method of choice; it counts all the carbon-14 atoms in the sample and not just the few that happen to decay during the measurements; it can therefore be used with much smaller samples (as small as individual plant seeds), and gives results much more quickly. The G-M counting efficiency is estimated to be 3%. The half-distance layer in water is 0.05 mm. | 9 | Geochemistry |
Exposure assessment is the process of estimating or measuring the magnitude, frequency and duration of exposure to an agent, along
with the number and characteristics of the population exposed. Ideally, it describes the sources, pathways, routes, and the uncertainties in the assessment. It is a necessary part of risk analysis and hence risk assessment.
Exposure analysis is the science that describes how an individual or population comes in contact with a contaminant, including quantification of the amount of contact across space and time. Exposure assessment and exposure analysis are often used as synonyms in many practical contexts. Risk is a function of exposure and hazard. For example, even for an extremely toxic (high hazard) substance, the risk of an adverse outcome is unlikely if exposures are near zero. Conversely, a moderately toxic substance may present substantial risk if an individual or a population is highly exposed. | 2 | Environmental Chemistry |
Hot baths of sodium hydroxide (NaOH), nitrates such as sodium nitrate (), and/or nitrites such as sodium nitrite (NaNO) at are used to convert the surface of the material into magnetite (FeO). Water must be periodically added to the bath, with proper controls to prevent a steam explosion.
Hot blackening involves dipping the part into various tanks. The workpiece is usually dipped by automated part carriers for transportation between tanks. These tanks contain, in order, alkaline detergent, water, sodium hydroxide at (the blackening compound), and finally the sealant, which is usually oil.
The NaOH (caustic soda) and elevated temperature cause FeO (black oxide) to form on the surface of the metal instead of FeO (red oxide; rust). While it is physically denser than red oxide, the fresh black oxide is porous, so oil is then applied as post treatment to the heated part, which seals it by "sinking" into it. The combination prevents corrosion of the workpiece. There are many advantages of blackening, including:
* Blackening can be done in large batches, which is ideal for small parts.
* There is no significant dimensional impact. The blacking process creates a layer about 1μm thick.
* It is far cheaper than similar corrosion protection systems, such as paint and electroplating.
The oldest and most widely used specification for hot black oxide is MIL-DTL-13924, which covers four classes of processes for different substrates. Alternate specifications include AMS 2485, ASTM D769, and ISO 11408.
Iron(III) chloride (FeCl) may also be used for steel blackening by dipping a piece of steel into a hot bath of 50% FeCl solution and then into a hot boiling water. The process is usually repeated several times. | 7 | Physical Chemistry |
The technique has been well utilized in studying carbon nanotubes to determine thermodynamic binding interactions with biological molecules and graphene composite interactions. Another notable use of ITC with carbon nanotubes is optimization of preparation of carbon nanotubes from graphene composite and polyvinyl alcohol (PVA). PVA assembly process can be measured thermodynamically as mixing of the two ingredients is an exothermic reaction, and its binding trend can be easily observed by ITC. | 7 | Physical Chemistry |
The first experimental evidence for the presence of 18 cm absorption lines of the hydroxyl (HO) radical in the radio absorption spectrum of Cassiopeia A was obtained by Weinreb et al. (Nature, Vol. 200, pp. 829, 1963) based on observations made during the period October 15–29, 1963. | 2 | Environmental Chemistry |
This reagent is inexpensively available for laboratory use. It is a by-product from the production of ortho-toluenesulfonyl chloride (a precursor for the synthesis of the common food additive and catalyst saccharin), via the chlorosulfonation of toluene:
: CHCH + SOCl → CHCHSOCl + HCl | 0 | Organic Chemistry |
Thermal treatment of milk by indirect heating (e.g. pasteurization) to reduce microbial load and increase shelf life is generally performed by a plate heat exchanger. Heat exchanger surfaces can become fouled by adsorbed milk protein deposits. Fouling is initiated by formation of a protein monolayer at room temperature, followed by heat induced aggregation and deposition of whey protein and calcium phosphate deposits. Adsorbed proteins decrease efficiency of heat transfer and potentially affect product quality by preventing adequate heating of milk. | 1 | Biochemistry |
Herman van Bekkum (26 September 1932 – 30 November 2020) was a Dutch organic chemist. He was professor of Catalysis in Organic Chemistry between 1971 and 1998 at Delft University of Technology. He served as rector magnificus of the university between 1975 and 1976. He was an expert in the field of carbohydrate chemistry and zeolites. | 0 | Organic Chemistry |
Ion chromatography (or ion-exchange chromatography) is a form of chromatography that separates ions and ionizable polar molecules based on their affinity to the ion exchanger. It works on almost any kind of charged molecule—including small inorganic anions, large proteins, small nucleotides, and amino acids. However, ion chromatography must be done in conditions that are one pH unit away from the isoelectric point of a protein.
The two types of ion chromatography are anion-exchange and cation-exchange. Cation-exchange chromatography is used when the molecule of interest is positively charged. The molecule is positively charged because the pH for chromatography is less than the pI (also known as pH(I)). In this type of chromatography, the stationary phase is negatively charged and positively charged molecules are loaded to be attracted to it. Anion-exchange chromatography is when the stationary phase is positively charged and negatively charged molecules (meaning that pH for chromatography is greater than the pI) are loaded to be attracted to it. It is often used in protein purification, water analysis, and quality control. The water-soluble and charged molecules such as proteins, amino acids, and peptides bind to moieties which are oppositely charged by forming ionic bonds to the insoluble stationary phase. The equilibrated stationary phase consists of an ionizable functional group where the targeted molecules of a mixture to be separated and quantified can bind while passing through the column—a cationic stationary phase is used to separate anions and an anionic stationary phase is used to separate cations. Cation exchange chromatography is used when the desired molecules to separate are cations and anion exchange chromatography is used to separate anions. The bound molecules then can be eluted and collected using an eluant which contains anions and cations by running a higher concentration of ions through the column or by changing the pH of the column.
One of the primary advantages for the use of ion chromatography is that only one interaction is involved the separation, as opposed to other separation techniques; therefore, ion chromatography may have higher matrix tolerance. Another advantage of ion exchange is the predictability of elution patterns (based on the presence of the ionizable group). For example, when cation exchange chromatography is used, certain cations will elute out first and others later. A local charge balance is always maintained. However, there are also disadvantages involved when performing ion-exchange chromatography, such as constant evolution of the technique which leads to the inconsistency from column to column. A major limitation to this purification technique is that it is limited to ionizable group. | 3 | Analytical Chemistry |
The oldest and most widely used expression systems are cell-based and may be defined as the "combination of an expression vector, its cloned DNA, and the host for the vector that provide a context to allow foreign gene function in a host cell, that is, produce proteins at a high level". Overexpression is an abnormally and excessively high level of gene expression which produces a pronounced gene-related phenotype.
There are many ways to introduce foreign DNA to a cell for expression, and many different host cells may be used for expression — each expression system has distinct advantages and liabilities. Expression systems are normally referred to by the host and the DNA source or the delivery mechanism for the genetic material. For example, common hosts are bacteria (such as E. coli, B. subtilis), yeast (such as S. cerevisiae) or eukaryotic cell lines. Common DNA sources and delivery mechanisms are viruses (such as baculovirus, retrovirus, adenovirus), plasmids, artificial chromosomes and bacteriophage (such as lambda). The best expression system depends on the gene involved, for example the Saccharomyces cerevisiae is often preferred for proteins that require significant posttranslational modification. Insect or mammal cell lines are used when human-like splicing of mRNA is required. Nonetheless, bacterial expression has the advantage of easily producing large amounts of protein, which is required for X-ray crystallography or nuclear magnetic resonance experiments for structure determination.
Because bacteria are prokaryotes, they are not equipped with the full enzymatic machinery to accomplish the required post-translational modifications or molecular folding. Hence, multi-domain eukaryotic proteins expressed in bacteria often are non-functional. Also, many proteins become insoluble as inclusion bodies that are difficult to recover without harsh denaturants and subsequent cumbersome protein-refolding.
To address these concerns, expressions systems using multiple eukaryotic cells were developed for applications requiring the proteins be conformed as in, or closer to eukaryotic organisms: cells of plants (i.e. tobacco), of insects or mammalians (i.e. bovines) are transfected with genes and cultured in suspension and even as tissues or whole organisms, to produce fully folded proteins. Mammalian in vivo expression systems have however low yield and other limitations (time-consuming, toxicity to host cells,..). To combine the high yield/productivity and scalable protein features of bacteria and yeast, and advanced epigenetic features of plants, insects and mammalians systems, other protein production systems are developed using unicellular eukaryotes (i.e. non-pathogenic <nowiki/>Leishmania<nowiki/> cells). | 1 | Biochemistry |
Marion Katherine Blight was born in Watford in 1921. Her mother worked in domestic service while her father was a shop assistant. McQuillan attended Wycombe High School before getting a scholarship to Henrietta Barnett’s School. McQuillan went to University in 1939 where she graduated from Girton College, Cambridge with a degree in metallurgy and natural sciences. She got her first job in 1942 in the Royal Aircraft Establishment Farnborough (RAE) in 1942. McQuillan researched jet engine metals and was a member of the first team to research titanium.
In 1946 she travelled through Germany and Austria as member of one of the many teams sent by the British Intelligence Objectives Sub-Committee, collecting technical information from universities, research establishments and factories.
She also worked at the Atomic Energy Research Establishment at Harwell, working on some of the early metallurgical problems of nuclear energy. From 1948-1951 she was at the Australian Royal Aircraft Establishment in Melbourne.
McQuillan returned to the UK where she began to work for ICI Metals (also known as IMI), in the Titanium Alloy Research Department where, within two years later she was head of the section. With her husband McQuillan published the seminal book “Titanium” in 1956. During the 1960s McQuillan registered 8 titanium alloy patents. In 1967 McQuillan was appointed technical director of the New Metals Division and by 1978 she became the first woman managing director of Imperial Metal Industries subsidiary, Enots. | 8 | Metallurgy |
To date, many studies have been conducted on the benefits of selenium intake in reducing the risk of cancer incidence at the nutritional level, indicating that likely selenium functions as an immunostimulator, i.e. reversing the immunosuppression in tumour microenvironment towards antitumour immunity by activating immune cells (e.g. M1 macrophages and CD8+ T-lymphocytes, the elevated number of neutrophils and activated cytotoxic NK cells) and releasing pro-inflammatory cytokines such as IFNγ and TNFα. | 1 | Biochemistry |
Relative entropy can also be interpreted as the expected discrimination information for over : the mean information per sample for discriminating in favor of a hypothesis against a hypothesis , when hypothesis is true. Another name for this quantity, given to it by I. J. Good, is the expected weight of evidence for over to be expected from each sample.
The expected weight of evidence for over is not the same as the information gain expected per sample about the probability distribution of the hypotheses,
Either of the two quantities can be used as a utility function in Bayesian experimental design, to choose an optimal next question to investigate: but they will in general lead to rather different experimental strategies.
On the entropy scale of information gain there is very little difference between near certainty and absolute certainty—coding according to a near certainty requires hardly any more bits than coding according to an absolute certainty. On the other hand, on the logit scale implied by weight of evidence, the difference between the two is enormous – infinite perhaps; this might reflect the difference between being almost sure (on a probabilistic level) that, say, the Riemann hypothesis is correct, compared to being certain that it is correct because one has a mathematical proof. These two different scales of loss function for uncertainty are both useful, according to how well each reflects the particular circumstances of the problem in question. | 7 | Physical Chemistry |
In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. The etymology stems from Latin ligare, which means to bind. In protein-ligand binding, the ligand is usually a molecule which produces a signal by binding to a site on a target protein. The binding typically results in a change of conformational isomerism (conformation) of the target protein. In DNA-ligand binding studies, the ligand can be a small molecule, ion, or protein which binds to the DNA double helix. The relationship between ligand and binding partner is a function of charge, hydrophobicity, and molecular structure.
Binding occurs by intermolecular forces, such as ionic bonds, hydrogen bonds and Van der Waals forces. The association or docking is actually reversible through dissociation. Measurably irreversible covalent bonding between a ligand and target molecule is atypical in biological systems. In contrast to the definition of ligand in metalorganic and inorganic chemistry, in biochemistry it is ambiguous whether the ligand generally binds at a metal site, as is the case in hemoglobin. In general, the interpretation of ligand is contextual with regards to what sort of binding has been observed.
Ligand binding to a receptor protein alters the conformation by affecting the three-dimensional shape orientation. The conformation of a receptor protein composes the functional state. Ligands include substrates, inhibitors, activators, signaling lipids, and neurotransmitters. The rate of binding is called affinity, and this measurement typifies a tendency or strength of the effect. Binding affinity is actualized not only by host–guest interactions, but also by solvent effects that can play a dominant, steric role which drives non-covalent binding in solution. The solvent provides a chemical environment for the ligand and receptor to adapt, and thus accept or reject each other as partners.
Radioligands are radioisotope labeled compounds used in vivo as tracers in PET studies and for in vitro binding studies. | 1 | Biochemistry |
MTBE gives water an unpleasant taste at very low concentrations. MTBE often is introduced into water-supply aquifers by leaking underground storage tanks (USTs) at gasoline stations or by gasoline containing MTBE being spilled onto the ground. The higher water solubility and persistence of MTBE cause it to travel faster and farther than many other components of gasoline when released into an aquifer.
MTBE is biodegraded by the action of bacteria. In the proper type of bioreactor, such as a fluidized bed bioreactor, MTBE may be removed rapidly and economically from water to undetectable levels. Activated carbon produced from coconut shells and optimized for MTBE adsorption may reduce MTBE to undetectable levels, although this level of reduction is likely to occur only in the most ideal circumstances. There are currently no known published cases of any in-situ treatment method that has been capable of reducing contaminant concentrations to baseline (pre-development) conditions within the aquifer soil matrix.
According to the International Agency for Research on Cancer (IARC), a cancer research agency of the World Health Organization, MTBE is not classified as a human carcinogen. MTBE may be tasted in water at concentrations of 5–15 µg/L (5-15ppb).
As of 2007, researchers have limited data about the health effects of ingestion of MTBE. The United States Environmental Protection Agency (EPA) has concluded that available data are inadequate to quantify health risks of MTBE at low exposure levels in drinking water, but the data support the conclusion that MTBE is a potential human carcinogen at high doses. | 2 | Environmental Chemistry |
In thermodynamics, the volume of a system is an important extensive parameter for describing its thermodynamic state. The specific volume, an intensive property, is the system's volume per unit mass. Volume is a function of state and is interdependent with other thermodynamic properties such as pressure and temperature. For example, volume is related to the pressure and temperature of an ideal gas by the ideal gas law.
The physical region covered by a system may or may not coincide with a control volume used to analyze the system. | 7 | Physical Chemistry |
Amine oxides are used as protecting group for amines and as chemical intermediates. Long-chain alkyl amine oxides are used as amphoteric surfactants and foam stabilizers.
Amine oxides are highly polar molecules and have a polarity close to that of quaternary ammonium salts. Small amine oxides are very hydrophilic and have an excellent water solubility and a very poor solubility in most organic solvents.
Amine oxides are weak bases with a pK of around 4.5 that form , cationic hydroxylamines, upon protonation at a pH below their pK. | 0 | Organic Chemistry |
The dominant industrial method for producing ammonia is the Haber process also known as the Haber-Bosch process. Fertilizer production is now the largest source of human-produced fixed nitrogen in the terrestrial ecosystem. Ammonia is a required precursor to fertilizers, explosives, and other products. The Haber process requires high pressures (around 200 atm) and high temperatures (at least 400 °C), which are routine conditions for industrial catalysis. This process uses natural gas as a hydrogen source and air as a nitrogen source. The ammonia product has resulted in an intensification of nitrogen fertilizer globally and is credited with supporting the expansion of the human population from around 2 billion in the early 20th century to roughly 8 billion people now. | 1 | Biochemistry |
Organolithium reagents are sensitive to moisture and thus should be handled under inert atmosphere in anhydrous conditions. Tetrahydrofuran is the most common solvent employed for lateral lithiation reactions. Measurement of the concentration of commercial or prepared alkyllithium solutions may be accomplished using well-established titration methods.
A useful indicator for the progress of lateral lithiations is the color of the reaction mixture. Benzyllithium compounds range in color from red to deep purple, and in many cases the lack of a color change upon addition of an organolithium reagent to the substrate may indicate the presence of an undesired proton source in solution. | 0 | Organic Chemistry |
In the presence of an appropriate transition metal (typically copper or rhodium), α-diazocarbonyl compounds are converted to transition metal carbenes, which undergo addition reactions in the presence of carbon–carbon double bonds to form cyclopropanes. Insertion into carbon–carbon or carbon–hydrogen bonds is possible in substrates lacking a double bond. The intramolecular version of this reaction forms fused carbocycles, although yields of reactions mediated by copper are typically moderate. For enantioselective cyclopropanations and insertions, both copper- and rhodium-based catalysts are employed, although the latter have been more heavily studied in recent years. | 0 | Organic Chemistry |
White etching cracks (WEC), or white structure flaking or brittle flaking, is a type of rolling contact fatigue (RCF) damage that can occur in bearing steels under certain conditions, such as hydrogen embrittlement, high stress, inadequate lubrication, and high temperature. WEC is characterised by the presence of white areas of microstructural alteration in the material, which can lead to the formation of small cracks that can grow and propagate over time, eventually leading to premature failure of the bearing. WEC has been observed in a variety of applications, including wind turbine gearboxes, automotive engines, and other heavy machinery. The exact mechanism of WEC formation is still a subject of research, but it is believed to be related to a combination of microstructural changes, such as phase transformations and grain boundary degradation, and cyclic loading. | 8 | Metallurgy |
The evolution of interactome complexity is delineated in a study published in Nature. In this study it is first noted that the boundaries between prokaryotes, unicellular eukaryotes and multicellular eukaryotes are accompanied by orders-of-magnitude reductions in effective population size, with concurrent amplifications of the effects of random genetic drift. The resultant decline in the efficiency of selection seems to be sufficient to influence a wide range of attributes at the genomic level in a nonadaptive manner. The Nature study shows that the variation in the power of random genetic drift is also capable of influencing phylogenetic diversity at the subcellular and cellular levels. Thus, population size would have to be considered as a potential determinant of the mechanistic pathways underlying long-term phenotypic evolution. In the study it is further shown that a phylogenetically broad inverse relation exists between the power of drift and the structural integrity of protein subunits. Thus, the accumulation of mildly deleterious mutations in populations of small size induces secondary selection for protein–protein interactions that stabilize key gene functions, mitigating the structural degradation promoted by inefficient selection. By this means, the complex protein architectures and interactions essential to the genesis of phenotypic diversity may initially emerge by non-adaptive mechanisms. | 1 | Biochemistry |
In some cases, such as the decay of , the bremsstrahlung produced by shielding the beta radiation with the normally used dense materials (e.g. lead) is itself dangerous; in such cases, shielding must be accomplished with low density materials, such as Plexiglas (Lucite), plastic, wood, or water; as the atomic number is lower for these materials, the intensity of bremsstrahlung is significantly reduced, but a larger thickness of shielding is required to stop the electrons (beta radiation). | 7 | Physical Chemistry |
Those rocks that contain the most silica, and on crystallizing yield free quartz, form a group generally designated the "felsic" rocks. Those again that contain the least silica and most magnesia and iron, so that quartz is absent while olivine is usually abundant, form the "mafic" group. The "intermediate" rocks include those characterized by the general absence of both quartz and olivine. An important subdivision of these contains a very high percentage of alkalis, especially soda, and consequently has minerals such as nepheline and leucite not common in other rocks. It is often separated from the others as the "alkali" or "soda" rocks, and there is a corresponding series of mafic rocks. Lastly, a small sub-group rich in olivine and without feldspar has been called the "ultramafic" rocks. They have very low percentages of silica but much iron and magnesia.
Except these last, practically all rocks contain felspars or feldspathoid minerals. In the acid rocks, the common feldspars are orthoclase, perthite, microcline, and oligoclase—all having much silica and alkalis. In the mafic rocks labradorite, anorthite, and bytownite prevail, being rich in lime and poor in silica, potash, and soda. Augite is the most common ferromagnesian in mafic rocks, but biotite and hornblende are on the whole more frequent in felsic rocks.
Rocks that contain leucite or nepheline, either partly or wholly replacing felspar, are not included in this table. They are essentially of intermediate or of mafic character. We might in consequence regard them as varieties of syenite, diorite, gabbro, etc., in which feldspathoid minerals occur, and indeed there are many transitions between syenites of ordinary type and nepheline — or leucite — syenite, and between gabbro or dolerite and theralite or essexite. But, as many minerals develop in these "alkali" rocks that are uncommon elsewhere, it is convenient in a purely formal classification like that outlined here to treat the whole assemblage as a distinct series.
This classification is based essentially on the mineralogical constitution of the igneous rocks. Any chemical distinctions between the different groups, though implied, are relegated to a subordinate position. It is admittedly artificial, but it has grown up with the growth of the science and is still adopted as the basis on which more minute subdivisions are erected. The subdivisions are by no means of equal value. The syenites, for example, and the peridotites, are far less important than the granites, diorites, and gabbros. Moreover, the effusive andesites do not always correspond to the plutonic diorites but partly also to the gabbros. As the different kinds of rock, regarded as aggregates of minerals, pass gradually into one another, transitional types are very common and are often so important as to receive special names. The quartz-syenites and nordmarkites may be interposed between granite and syenite, the tonalites and adamellites between granite and diorite, the monzonites between syenite and diorite, norites and hyperites between diorite and gabbro, and so on. | 9 | Geochemistry |
Minerals produced through hydrothermal alteration and weathering of primary basaltic minerals are also present on Mars. Secondary minerals include hematite, phyllosilicates (clay minerals), goethite, jarosite, iron sulfate minerals, opaline silica, and gypsum. Many of these secondary minerals require liquid water to form (aqueous minerals).
Opaline silica and iron sulphate minerals form in acidic (low pH) solutions. Sulphates have been found in a variety of locations, including near Juventae Chasma, Ius Chasma, Melas Chasma, Candor Chasma, and Ganges Chasma. These sites all contain fluvial landforms indicating that abundant water was once present. Spirit rover discovered sulfates and goethite in the Columbia Hills.
Some of the mineral classes detected may have formed in environments suitable (i.e., enough water and the proper pH) for life. The mineral smectite (a phyllosilicate) forms in near-neutral waters. Phyllosilicates and carbonates are good for preserving organic matter, so they may contain evidence of past life. Sulfate deposits preserve chemical and morphological fossils, and fossils of microorganisms form in iron oxides like hematite. The presence of opaline silica points toward a hydrothermal environment that could support life. Silica is also excellent for preserving evidence of microbes. | 9 | Geochemistry |
Hypersensitive sites are found on every active gene, and many of these genes often have more than one hypersensitive site. Most often, hypersensitive sites are found only in chromatin of cells in which the associated gene is being expressed, and do not occur when the gene is inactive.
In DNA being transcribed, 5'hypersensitive sites appear before transcription begins, and the DNA sequences within the hypersensitive sites are required for gene expression. Note: hypersensitive sites precede active promoters.
Hypersensitive sites are generated as a result of the binding of transcription factors that displace histone octamers.
They can also be located by indirect end labelling. A fragment of DNA is cut once at the hypersensitive site with DNase and at another site with a restriction enzyme. The distance from the known restriction site to the DNase cut is then measured to give the location. | 1 | Biochemistry |
Typical type II restriction enzymes differ from type I restriction enzymes in several ways. They form homodimers, with recognition sites that are usually undivided and palindromic and 4–8 nucleotides in length. They recognize and cleave DNA at the same site, and they do not use ATP or AdoMet for their activity—they usually require only Mg as a cofactor. These enzymes cleave the phosphodiester bond of double helix DNA. It can either cleave at the center of both strands to yield a blunt end, or at a staggered position leaving overhangs called sticky ends. These are the most commonly available and used restriction enzymes. In the 1990s and early 2000s, new enzymes from this family were discovered that did not follow all the classical criteria of this enzyme class, and new subfamily nomenclature was developed to divide this large family into subcategories based on deviations from typical characteristics of type II enzymes. These subgroups are defined using a letter suffix.
Type IIB restriction enzymes (e.g., BcgI and BplI) are multimers, containing more than one subunit. They cleave DNA on both sides of their recognition to cut out the recognition site. They require both AdoMet and Mg cofactors. Type IIE restriction endonucleases (e.g., NaeI) cleave DNA following interaction with two copies of their recognition sequence. One recognition site acts as the target for cleavage, while the other acts as an allosteric effector that speeds up or improves the efficiency of enzyme cleavage. Similar to type IIE enzymes, type IIF restriction endonucleases (e.g. NgoMIV) interact with two copies of their recognition sequence but cleave both sequences at the same time. Type IIG restriction endonucleases (e.g., RM.Eco57I) do have a single subunit, like classical Type II restriction enzymes, but require the cofactor AdoMet to be active. Type IIM restriction endonucleases, such as DpnI, are able to recognize and cut methylated DNA. Type IIS restriction endonucleases (e.g. FokI) cleave DNA at a defined distance from their non-palindromic asymmetric recognition sites; this characteristic is widely used to perform in-vitro cloning techniques such as Golden Gate cloning. These enzymes may function as dimers. Similarly, Type IIT restriction enzymes (e.g., Bpu10I and BslI) are composed of two different subunits. Some recognize palindromic sequences while others have asymmetric recognition sites. | 1 | Biochemistry |
NAD-dependent formate dehydrogenases are important in methylotrophic yeast and bacteria, being vital in the catabolism of C1 compounds such as methanol. The cytochrome-dependent enzymes are more important in anaerobic metabolism in prokaryotes. For example, in E. coli, the formate:ferricytochrome-b1 oxidoreductase is an intrinsic membrane protein with two subunits and is involved in anaerobic nitrate respiration.
NAD-dependent reaction
Formate + NAD CO + NADH + H
Cytochrome-dependent reaction
Formate + 2 ferricytochrome b1 CO + 2 ferrocytochrome b1 + 2 H | 1 | Biochemistry |
Metal-catalyzed cyclopropanations are chemical reactions that result in the formation of a cyclopropane ring from a metal carbenoid species and an alkene. In the Simmons–Smith reaction the metal involved is zinc. Metal carbenoid species can be generated through the reaction of a diazo compound with a transition metal). The intramolecular variant of this reaction was first reported in 1961. Rhodium carboxylate complexes, such as dirhodium tetraacetate, are common catalysts. Enantioselective cyclopropanations have been developed. | 0 | Organic Chemistry |
An example due to photodissociation is triphenylsulfonium triflate. This colourless salt consists of a sulfonium cation and the triflate anion. Many related salts are known including those with other noncoordinating anions and those with diverse substituents on the phenyl rings.
The triphenylsulfonium salts absorb at a wavelength of 233 nm, which induces a dissociation of one of the three phenyl rings. This dissociated phenyl radical then re-combines with remaining diphenylsulfonium to liberate an H ion. The second reaction is irreversible, and therefore the entire process is irreversible, so triphenylsulfonium triflate is a photoacid generator. The ultimate products are thus a neutral organic sulfide and the strong acid triflic acid.
:[(CH)S][CFSO] + hν → [(CH)S][CFSO] + CH
:[(CH)S][CFSO] + CH → (CHCH)(CH)S + [[Triflic acid|[CFSO][H]]]
Applications of these photoacids include photolithography and catalysis of the polymerization of epoxides. | 5 | Photochemistry |
Asymmetric Heck reactions establish quaternary or tertiary stereocenters. If migratory insertion generates a quaternary center adjacent to the palladium-carbon bond (as in reactions of trisubstituted or 1,1-disubstituted alkenes), β-hydride elimination toward that center is not possible and it is retained in the product. Similarly, β-hydride elimination is not possible if a hydrogen syn to the palladium-carbon bond is not available. Thus, tertiary stereocenters can be established in conformationally restricted systems. | 0 | Organic Chemistry |
Amorphous brazing foils are typically used for brazing, a metallurgy process by which two pieces of metal are joined by melting and cooling a third "fill metal" at their joint. The use of preforms increases the capability of ABFs for use on an industrial scale, even being able to be assembled by machine. | 8 | Metallurgy |
Endohedral fullerenes, also called endofullerenes, are fullerenes that have additional atoms, ions, or clusters enclosed within their inner spheres. The first lanthanum C complex called La@C was synthesized in 1985. The @ (at sign) in the name reflects the notion of a small molecule trapped inside a shell. Two types of endohedral complexes exist: endohedral metallofullerenes and non-metal doped fullerenes. | 6 | Supramolecular Chemistry |
In 1956 a heterogeneous catalyst made of palladium deposited on silk was shown to effect asymmetric hydrogenation. Later, in 1968, the groups of William Knowles and Leopold Horner independently published the examples of asymmetric hydrogenation using a homogeneous catalysts. While exhibiting only modest enantiomeric excesses, these early reactions demonstrated feasibility. By 1972, enantiomeric excess of 90% was achieved, and the first industrial synthesis of the Parkinson's drug L-DOPA commenced using this technology.
The field of asymmetric hydrogenation continued to experience a number of notable advances. Henri Kagan developed DIOP, an easily prepared C-symmetric diphosphine that gave high ees in certain reactions. Ryōji Noyori introduced the ruthenium-based catalysts for the asymmetric hydrogenated polar substrates, such as ketones and aldehydes. Robert H. Crabtree demonstrated the ability for Iridium compounds to catalyse asymmetric hydrogenation reactions in 1979 with the invention of Crabtrees catalyst. In the early 1990's, the introduction of P,N ligands by several groups independently then further expanded the scope of the C-symmetric ligands, although they are not fundamentally superior to chiral ligands lacking rotational symmetry.
Today, asymmetric hydrogenation is a routine methodology in laboratory and industrial scale organic chemistry. The importance of asymmetric hydrogenation was recognized by the 2001 Nobel Prize in Chemistry awarded to William Standish Knowles and Ryōji Noyori. | 0 | Organic Chemistry |
Biotic material or biological derived material is any material that originates from living organisms. Most such materials contain carbon and are capable of decay.
The earliest life on Earth arose at least 3.5 billion years ago. Earlier physical evidences of life include graphite, a biogenic substance, in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland, as well as, "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia. Earth's biodiversity has expanded continually except when interrupted by mass extinctions. Although scholars estimate that over 99 percent of all species of life (over five billion) that ever lived on Earth are extinct, there are still an estimated 10–14 million extant species, of which about 1.2 million have been documented and over 86% have not yet been described.
Examples of biotic materials are wood, straw, humus, manure, bark, crude oil, cotton, spider silk, chitin, fibrin, and bone.
The use of biotic materials, and processed biotic materials (bio-based material) as alternative natural materials, over synthetics is popular with those who are environmentally conscious because such materials are usually biodegradable, renewable, and the processing is commonly understood and has minimal environmental impact. However, not all biotic materials are used in an environmentally friendly way, such as those that require high levels of processing, are harvested unsustainably, or those that are used to produce carbon emissions.
When the source of the recently living material has little importance to the product produced, such as in the production of biofuels, biotic material is simply called biomass. Many fuel sources may have biological sources, and may be divided roughly into fossil fuels, and biofuel.
In soil science, biotic material is often referred to as organic matter. Biotic materials in soil include glomalin, Dopplerite and humic acid. Some biotic material may not be considered to be organic matter if it is low in organic compounds, such as a clam's shell, which is an essential component of the living organism, but contains little organic carbon.
Examples of the use of biotic materials include:
*Alternative natural materials
*Building material, for a stylistic reasons, or to reduce allergic reactions
*Clothing
*Energy production
*Food
*Medicine
*Ink
*Composting and mulch | 1 | Biochemistry |
A column is prepared by packing a solid adsorbent into a cylindrical glass or plastic tube. The size will depend on the amount of compound being isolated. The base of the tube contains a filter, either a cotton or glass wool plug, or glass frit to hold the solid phase in place. A solvent reservoir may be attached at the top of the column.
Two methods are generally used to prepare a column: the dry method and the wet method. For the dry method, the column is first filled with dry stationary phase powder, followed by the addition of mobile phase, which is flushed through the column until it is completely wet, and from this point is never allowed to run dry. For the wet method, a slurry is prepared of the eluent with the stationary phase powder and then carefully poured into the column. The top of the silica should be flat, and the top of the silica can be protected by a layer of sand. Eluent is slowly passed through the column to advance the organic material.
The individual components are retained by the stationary phase differently and separate from each other while they are running at different speeds through the column with the eluent. At the end of the column they elute one at a time. During the entire chromatography process the eluent is collected in a series of fractions. Fractions can be collected automatically by means of fraction collectors. The productivity of chromatography can be increased by running several columns at a time. In this case multi stream collectors are used. The composition of the eluent flow can be monitored and each fraction is analyzed for dissolved compounds, e.g. by analytical chromatography, UV absorption spectra, or fluorescence. Colored compounds (or fluorescent compounds with the aid of a UV lamp) can be seen through the glass wall as moving bands. | 3 | Analytical Chemistry |
To begin HPTLC, a stationary phase has to be determined to separate different compounds within a mixture. Around 90% of all pharmaceutical separations are performed on normal phase silica gel; however, other stationary phases such as alumina can be used for samples with dissociating compounds and cellulose for ionic compounds. The reverse-phase HPTLC method (similar methodology to reverse-phase TLC) is used for compounds with high polarity. After the selection of the stationary phase, plates are generally washed with methanol and dried in an oven to remove excess solvent.
Selection for the mobile phase is one of the most important processes of HPTLC and follows a trial and error pathway. However, the PRISMA system stands as a guideline for finding the optimal mobile phase. The mobile phase is dependent on the absorptivity of the stationary phase and the composition of the compound of interest. The compound is first tested with solutions such as diethyl ether, ethanol, dichloromethane, chloroform for normal phase HPTLC, or solutions such as methanol, acetonitrile, and tetrahydrofuran for reverse phase HPTLC. The retardation factors (Rf) of the compounds with the selected solvent are then analyzed and the solvent that gives the largest Rf is chosen to be the mobile phase for the compound. Then, the mobile solvent strength is tested against hexane (for normal HPTLC) and water (for reverse-phase HPTLC) to determine the need for adjustment.
Notable HPTLC devices such as the Linomat 5 and the Automatic TLC Sampler 4 (ATS 4) by CAMAG function very similarly by having the automated spray-on sample application technique. This automated spray-on technique is useful to overcome the uncertainty in droplet size and position when the sample is applied to the TLC plate by hand. Additionally, automation provides high resolution and narrow bands since the solvent evaporates immediately as the sample makes contact with the plate. One approach to automation has been the use of piezoelectric devices and inkjet printers for applying the sample. Alternatively, the Nanomat 4 and ATS 4 by CAMAG are manually operated where the sample is applied via spot application using a capillary pipette.
Upon chromatographic detection, HPTLC plates are usually developed in saturated twin-trough chambers with filter paper for optimal outcomes. However, flat-bottom chambers and horizontal-development chambers are also used for specific compounds. A general mechanism for the HPTLC device goes as follows. A fitted filter paper is placed in the rear trough of the chamber and the mobile phase is poured through the rear trough to ensure complete solvent absorption of the filter paper. The chamber is then tilted to ~45° so both troughs are equal in solvent volume and left alone to equilibrate for ~20 mins. Finally, the HPTLC plate is placed in the chamber to develop. Between each sample reading, the mobile phase and filter paper are changed to ensure the best outcomes.
The spot capacity (analogous to peak capacity in HPLC) can be increased by developing the plate with two different solvents, using two-dimensional chromatography. The procedure begins with development of a sample loaded plate with first solvent. After removing it, the plate is rotated 90° and developed with a second solvent. | 3 | Analytical Chemistry |
Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (ground tissue) or chlorenchyma tissue called the mesophyll (Greek for "middle leaf"). This assimilation tissue is the primary location of photosynthesis in the plant. The products of photosynthesis are called "assimilates".
In ferns and most flowering plants, the mesophyll is divided into two layers:
* An upper palisade layer of vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis, with intercellular air spaces between them. Its cells contain many more chloroplasts than the spongy layer. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil are single-layered.
* Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more branched and not so tightly packed, so that there are large intercellular air spaces between them. The pores or stomata of the epidermis open into substomatal chambers, which are connected to the intercellular air spaces between the spongy and palisade mesophyll cell, so that oxygen, carbon dioxide and water vapor can diffuse into and out of the leaf and access the mesophyll cells during respiration, photosynthesis and transpiration.
Leaves are normally green, due to chlorophyll in chloroplasts in the mesophyll cells. Some plants have leaves of different colours due to the presence of accessory pigments such as carotenoids in their mesophyll cells. | 5 | Photochemistry |
Gas chromatography-olfactometry (GC-O) is a technique that integrates the separation of volatile compounds using a gas chromatograph with the detection of odour using an olfactometer (human assessor). It was first invented and applied in 1964 by Fuller and co-workers. While GC separates volatile compounds from an extract, human olfaction detects the odour activity of each eluting compound. In this olfactometric detection, a human assessor may qualitatively determine whether a compound has odour activity or describe the odour perceived, or quantitatively evaluate the intensity of the odour or the duration of the odour activity. The olfactometric detection of compounds allows the assessment of the relationship between a quantified substance and the human perception of its odour, without instrumental detection limits present in other kinds of detectors. Compound identification still requires use of other detectors, such as mass spectrometry, with analytical standards. | 3 | Analytical Chemistry |
FRET in lanthanide probes is a widely used technique to measure the distance between two points separated by approximately 15–100 Angstrom. Measurements can be done under physiological conditions in vitro with genetically encoded dyes, and often in vivo as well. The technique relies on a distant- dependent transfer of energy from a donor fluorophore to an acceptor dye. Lanthanide probes has been used to study DNA-protein interactions (using a terbium chelate complex) to measure distances in DNA complexes bent by the CAP protein. | 1 | Biochemistry |
There are three distinct groups of Complex III inhibitors.
* Antimycin A binds to the Q site and inhibits the transfer of electrons in Complex III from heme b to oxidized Q (Qi site inhibitor).
* Myxothiazol and stigmatellin binds to the Q site and inhibits the transfer of electrons from reduced QH to the Rieske Iron sulfur protein. Myxothiazol and stigmatellin bind to distinct but overlapping pockets within the Q site.
** Myxothiazol binds nearer to cytochrome bL (hence termed a "proximal" inhibitor).
** Stigmatellin binds farther from heme bL and nearer the Rieske Iron sulfur protein, with which it strongly interacts.
Some have been commercialized as fungicides (the strobilurin derivatives, best known of which is azoxystrobin; QoI inhibitors) and as anti-malaria agents (atovaquone).
Also propylhexedrine inhibits cytochrome c reductase. | 1 | Biochemistry |
A parallel relationship can easily be drawn between halogen bonding and hydrogen bonding. Both interactions revolve around an electron donor/electron acceptor relationship, between a halogen-like atom and an electron-dense one. But halogen bonding is both much stronger and more sensitive to direction than hydrogen bonding. A typical hydrogen bond has energy of formation ; known halogen bond energies range from 10–200 kJ/mol.
The σ-hole concept readily extends to pnictogen, chalcogen and aerogen bonds, corresponding to atoms of Groups 15, 16 and 18 (respectively). | 6 | Supramolecular Chemistry |
The widespread application of passive daytime radiative cooling (PDRC) technologies that use the infrared window (8–13 µm) to dissipate heat through longwave infrared (LWIR) thermal radiation heat transfer with outer space, has been proposed as a method of reducing temperature increases caused by climate change. The installation of passive radiative heat emission technologies has been proposed as necessary to lower the temperature of Earth at a fast enough rate for human survivability. Munday summarized the global implementation of such technologies: more than it is emitting, which leads to an overall warming of the climate. By covering the Earth with a small fraction of thermally emitting materials, the heat flow away from the Earth can be increased, and the net radiative flux can be reduced to zero (or even made negative), thus stabilizing (or cooling) the Earth (...) If only 1%–2% of the Earth’s surface were instead made to radiate at this rate rather than its current average value, the total heat fluxes into and away from the entire Earth would be balanced and warming would cease. with a diffuse component between 50-100 W/m. The average PDRC has an estimated cooling power of ~100-150 W/m. The cooling power of PDRCs is proportional to the exposed surface area of the installation. | 7 | Physical Chemistry |
Thermal mass is ideally placed within the building and situated where it still can be exposed to low-angle winter sunlight (via windows) but insulated from heat loss. In summer the same thermal mass should be obscured from higher-angle summer sunlight in order to prevent overheating of the structure.
The thermal mass is warmed passively by the sun or additionally by internal heating systems during the day. Thermal energy stored in the mass is then released back into the interior during the night. It is essential that it be used in conjunction with the standard principles of passive solar design.
Any form of thermal mass can be used. A concrete slab foundation either left exposed or covered with conductive materials, e.g. tiles, is one easy solution. Another novel method is to place the masonry facade of a timber-framed house on the inside (reverse-brick veneer). Thermal mass in this situation is best applied over a large area rather than in large volumes or thicknesses. 7.5–10 cm (3″–4″) is often adequate.
Since the most important source of thermal energy is the Sun, the ratio of glazing to thermal mass is an important factor to consider. Various formulas have been devised to determine this. As a general rule, additional solar-exposed thermal mass needs to be applied in a ratio from 6:1 to 8:1 for any area of sun-facing (north-facing in Southern Hemisphere or south-facing in Northern Hemisphere) glazing above 7% of the total floor area. For example, a 200 m house with 20 m of sun-facing glazing has 10% of glazing by total floor area; 6 m of that glazing will require additional thermal mass. Therefore, using the 6:1 to 8:1 ratio above, an additional 36–48 m of solar-exposed thermal mass is required. The exact requirements vary from climate to climate. | 7 | Physical Chemistry |
The trifluoromethyl group occurs in certain pharmaceuticals, drugs, and abiotically synthesized natural fluorocarbon based compounds. The medicinal use of the trifloromethyl group dates from 1928, although research became more intense in the mid-1940s. The trifluoromethyl group is often used as a bioisostere to create derivatives by replacing a chloride or a methyl group. This can be used to adjust the steric and electronic properties of a lead compound, or to protect a reactive methyl group from metabolic oxidation. Some notable drugs containing trifluoromethyl groups include efavirenz (Sustiva), an HIV reverse transcriptase inhibitor; fluoxetine (Prozac), an antidepressant; and celecoxib (Celebrex), a nonsteroidal anti-inflammatory drug. Sulfoxaflor is used as a systemic insecticide.
The trifluoromethyl group can also be added to change the solubility of molecules containing other groups of interest. | 0 | Organic Chemistry |
Photosynthesis is a process where light is absorbed or harvested by pigment protein complexes which are able to turn sunlight into energy. Absorption of a photon by a molecule takes place when pigment protein complexes harvest sunlight leading to electronic excitation delivered to the reaction centre where the process of charge separation can take place. when the energy of the captured photon matches that of an electronic transition. The fate of such excitation can be a return to the ground state or another electronic state of the same molecule. When the excited molecule has a nearby neighbour molecule, the excitation energy may also be transferred, through electromagnetic interactions, from one molecule to another. This process is called resonance energy transfer, and the rate depends strongly on the distance between the energy donor and energy acceptor molecules. Before an excited molecule can transition back to ground state, the energy needs to be harvested. This excitation is transferred among chromophores where it is delivered to the reaction centre. Light-harvesting complexes have their pigments specifically positioned to optimize these rates. | 5 | Photochemistry |
Moexipril is generally well tolerated in elderly patients with hypertension.
Hypotension, dizziness, increased cough, diarrhea, flu syndrome, fatigue, and flushing have been found to affect less than 6% of patients who were prescribed moexipril. | 4 | Stereochemistry |
* Chromium carbonyl
* Ferrocyanide
* Iron pentacarbonyl
* Nickel carbonyl
* Tetrakis(triphenylphosphine)palladium(0)
* Ferrocene
* Uranium hexafluoride
* tetraethyl lead
* tetramethyl lead
* tetrabutyl tin
* trimethylaluminium
* dimethylmercury
* Diethylzinc
* triethylborane
* Chromate
* Permanganate
* Ferroin
* bis(terpyridine)iron(II) | 0 | Organic Chemistry |
It is indicated for intraocular pressure reduction in patients with open-angle glaucoma or ocular hypertension. | 4 | Stereochemistry |
High-carbon steel has approximately 0.6 to 1.0% carbon content. It is very strong, used for springs, edged tools, and high-strength wires. | 8 | Metallurgy |
No applications have been identified for ferrocene-containing dendrimers. They exhibit multielectron redox indicating that the ferrocenyl moieties are essentially noninteracting redox centers. | 6 | Supramolecular Chemistry |
miRNAs, microRNA, are short RNA sequences that are complementary to regions of a transcribed gene and have regulatory functions. Current research indicates that circulating miRNA may be utilized as novel biomarkers, hence show promising evidence to be utilized in disease diagnostics. MiRNAs are formed from longer sequences of RNA that are cut free by a Dicer enzyme from an RNA sequence that is from a regulator gene. These short strands bind to a RISC complex. They match up with sequences in the upstream region of a transcribed gene due to their complementarity to act as a silencer for the gene in three ways. One is by preventing a ribosome from binding and initiating translation. Two is by degrading the mRNA that the complex has bound to. And three is by providing a new double-stranded RNA (dsRNA) sequence that Dicer can act upon to create more miRNA to find and degrade more copies of the gene. Small interfering RNAs (siRNAs) are similar in function to miRNAs; they come from other sources of RNA, but serve a similar purpose to miRNAs.
Given their short length, the rules for complementarity means that they can still be very discriminating in their targets of choice. Given that there are four choices for each base in the strand and a 20bp - 22bp length for a mi/siRNA, that leads to more than possible combinations. Given that the human genome is ~3.1 billion bases in length, this means that each miRNA should only find a match once in the entire human genome by accident. | 1 | Biochemistry |
Under the light microscope, eyespots appear as dark, orange-reddish spots or stigmata. They get their color from carotenoid pigments contained in bodies called pigment granules. The photoreceptors are found in the plasma membrane overlaying the pigmented bodies.
The eyespot apparatus of Euglena comprises the paraflagellar body connecting the eyespot to the flagellum. In electron microscopy, the eyespot apparatus appears as a highly ordered lamellar structure formed by membranous rods in a helical arrangement.
In Chlamydomonas, the eyespot is part of the chloroplast and takes on the appearance of a membranous sandwich structure. It is assembled from chloroplast membranes (outer, inner, and thylakoid membranes) and carotenoid-filled granules overlaid by plasma membrane. The stacks of granules act as a quarter-wave plate, reflecting incoming photons back to the overlying photoreceptors, while shielding the photoreceptors from light coming from other directions. It disassembles during cell division and reforms in the daughter cells in an asymmetric fashion in relation to the cytoskeleton. This asymmetric positioning of the eyespot in the cell is essential for proper phototaxis. | 1 | Biochemistry |
Amoxicillin is effective for treatment of early cutaneous Lyme borreliosis; the effectiveness and safety of oral amoxicillin is neither better nor worse than common alternatively-used antibiotics. | 4 | Stereochemistry |
Desmodium also enhances soil quality by increasing soil organic matter, nitrogen content, and soil biodiversity, as well as conserving moisture, moderating soil temperature and preventing erosion. | 1 | Biochemistry |
In the late 1940s at the University of California, Berkeley, the details of photosynthetic carbon metabolism were sorted out by the chemists Melvin Calvin, Andrew Benson, James Bassham and a score of students and researchers utilizing the carbon-14 isotope and paper chromatography techniques. The pathway of CO fixation by the algae Chlorella in a fraction of a second in light resulted in a three carbon molecule called phosphoglyceric acid (PGA). For that original and ground-breaking work, a Nobel Prize in Chemistry was awarded to Melvin Calvin in 1961. In parallel, plant physiologists studied leaf gas exchanges using the new method of infrared gas analysis and a leaf chamber where the net photosynthetic rates ranged from 10 to 13 μmol CO·m·s, with the conclusion that all terrestrial plants have the same photosynthetic capacities, that are light saturated at less than 50% of sunlight.
Later in 1958–1963 at Cornell University, field grown maize was reported to have much greater leaf photosynthetic rates of 40 μmol CO·m·s and not be saturated at near full sunlight. This higher rate in maize was almost double of those observed in other species such as wheat and soybean, indicating that large differences in photosynthesis exist among higher plants. At the University of Arizona, detailed gas exchange research on more than 15 species of monocots and dicots uncovered for the first time that differences in leaf anatomy are crucial factors in differentiating photosynthetic capacities among species. In tropical grasses, including maize, sorghum, sugarcane, Bermuda grass and in the dicot amaranthus, leaf photosynthetic rates were around 38−40 μmol CO·m·s, and the leaves have two types of green cells, i.e. outer layer of mesophyll cells surrounding a tightly packed cholorophyllous vascular bundle sheath cells. This type of anatomy was termed Kranz anatomy in the 19th century by the botanist Gottlieb Haberlandt while studying leaf anatomy of sugarcane. Plant species with the greatest photosynthetic rates and Kranz anatomy showed no apparent photorespiration, very low CO compensation point, high optimum temperature, high stomatal resistances and lower mesophyll resistances for gas diffusion and rates never saturated at full sun light. The research at Arizona was designated a Citation Classic in 1986. These species were later termed C4 plants as the first stable compound of CO fixation in light has four carbons as malate and aspartate. Other species that lack Kranz anatomy were termed C3 type such as cotton and sunflower, as the first stable carbon compound is the three-carbon PGA. At 1000 ppm CO in measuring air, both the C3 and C4 plants had similar leaf photosynthetic rates around 60 μmol CO·m·s indicating the suppression of photorespiration in C3 plants. | 5 | Photochemistry |
Fats are broken down by conversion to acyl-CoA. This conversion is one response to high energy demands such as exercise.
The oxidative degradation of fatty acids is a two-step process, catalyzed by acyl-CoA synthetase. Fatty acids are converted to their acyl phosphate, the precursor to acyl-CoA. The latter conversion is mediated by acyl-CoA synthase"
:acyl-P + HS-CoA → acyl-S-CoA + P + H
Three types of acyl-CoA synthases are employed, depending on the chain length of the fatty acid. For example, the substrates for medium chain acyl-CoA synthase are 4-11 carbon fatty acids. The enzyme acyl-CoA thioesterase takes of the acyl-CoA to form a free fatty acid and coenzyme A. | 1 | Biochemistry |
Carboxypeptidases are usually classified into one of several families based on their active site mechanism.
* Enzymes that use a metal in the active site are called "metallo-carboxypeptidases" (EC number 3.4.17).
* Other carboxypeptidases that use active site serine residues are called "serine carboxypeptidases" (EC number 3.4.16).
* Those that use an active site cysteine are called "cysteine carboxypeptidase" (or "thiol carboxypeptidases")(EC number 3.4.18).
These names do not refer to the selectivity of the amino acid that is cleaved. | 1 | Biochemistry |
Norvaline and norleucine (one hydrocarbon group longer) both possess the nor- prefix for historical reason, despite current conventional usage of the prefix to denote a missing hydrocarbon group (under which they would theoretically be called "dihomoalanine" and "trihomoalanine"). The name is not systematic, and the IUPAC/IUB Joint Commission on Nomenclature recommends that this name should be abandoned and the systematic name should be used. | 1 | Biochemistry |
In the presence of very reactive dienes (for example 1,3-diphenylisobenzofuran) butadienesulfone behaves as a dienophile and forms the corresponding Diels-Alder adduct.
As early as 1938, Kurt Alder and co-workers reported Diels-Alder adducts from the isomeric 2-sulfolene with 1,3-butadiene and 2-sulfolene with cyclopentadiene. | 0 | Organic Chemistry |
The first iron-cased and metal-cylinder rockets (Mysorean rockets) were developed by the Mysorean army of the South Indian Kingdom of Mysore in the 1780s. The Mysoreans successfully used these iron-cased rockets against the Presidency armies of the East India Company during the Anglo-Mysore Wars. | 8 | Metallurgy |
hMeRIP-seq is an immunoprecipitation method, in which RNA–protein complexes are crosslinked for stability, and antibodies specific to hm5C are added. Using this method, over 3,000 hm5C peaks have been called in Drosophila melanogaster S2 cells. | 1 | Biochemistry |
In organic chemistry, alkylimino-de-oxo-bisubstitution is the organic reaction of carbonyl compounds with amines to imines. The reaction name is based on the IUPAC Nomenclature for Transformations. The reaction is acid catalyzed and the reaction type is nucleophilic addition of the amine to the carbonyl compound followed by transfer of a proton from nitrogen to oxygen to a stable hemiaminal or carbinolamine. With primary amines water is lost in an elimination reaction to an imine. With aryl amines especially stable Schiff bases are formed. | 0 | Organic Chemistry |
There are two broad causes of nucleic acid lesions, endogenous and exogenous factors. Endogenous factors, or endogeny, refer to the resulting conditions that develop within an organism. This is in contrast with exogenous factors which originate from outside the organism. DNA and RNA lesions caused by endogenous factors generally occur more frequently than damage caused by exogenous ones. | 1 | Biochemistry |
Monophosphine-type ligands were among the first to appear in asymmetric hydrogenation, e.g., the ligand CAMP. Continued research into these types of ligands has explored both P-alkyl and P-heteroatom bonded ligands, with P-heteroatom ligands like the phosphites and phosphoramidites generally achieving more impressive results. Structural classes of ligands that have been successful include those based on the binapthyl structure of MonoPHOS or the spiro ring system of SiPHOS. Notably, these monodentate ligands can be used in combination with each other to achieve a synergistic improvement in enantioselectivity; something that is not possible with the diphosphine ligands. | 0 | Organic Chemistry |
When implanted on a surface, gold clusters catalyze oxidation of at ambient temperatures. Similarly gold clusters implanted on can oxidize at temperatures as low as 40K. Catalytic activity correlated with the structure of gold nanoclusters. A strong relationship between energetic and electronic properties with size and structure of gold nanoclusters. | 7 | Physical Chemistry |
The urea cycle is a metabolic pathway that results in the formation of urea using one ammonium molecule from degraded amino acids, another ammonium group from aspartate and one bicarbonate molecule. This route commonly occurs in hepatocytes. The reactions related to the urea cycle produce NADH, and NADH can be produced in two different ways. One of these uses oxaloacetate. In the cytosol there are fumarate molecules. Fumarate can be transformed into malate by the actions of the enzyme fumarase. Malate is acted on by malate dehydrogenase to become oxaloacetate, producing a molecule of NADH. After that, oxaloacetate will be recycled to aspartate, as transaminases prefer these keto acids over the others. This recycling maintains the flow of nitrogen into the cell. | 1 | Biochemistry |
Reagent testing is one of the processes used to identify substances contained within a pill, usually illicit substances.
With the increased prevalence of drugs being available in their pure forms, the terms "drug checking" or "pill testing" may also be used, although these terms usually refer to testing with a wider variety of techniques covered by drug checking. | 3 | Analytical Chemistry |
Peroxisomes (microbodies) were first described by a Swedish doctoral student, J. Rhodin in 1954. They were identified as organelles by the Belgian cytologist Christian de Duve in 1967. De Duve and co-workers discovered that peroxisomes contain several oxidases involved in the production of hydrogen peroxide (HO) as well as catalase involved in the decomposition of HO to oxygen and water. Due to their role in peroxide metabolism, De Duve named them “peroxisomes”, replacing the formerly used morphological term “microbodies”. Later, it was described that firefly luciferase is targeted to peroxisomes in mammalian cells, allowing the discovery of the import targeting signal for peroxisomes, and triggering many advances in the peroxisome biogenesis field. | 1 | Biochemistry |
The Thyroid Feedback Quantile-based Index (TFQI) is another parameter for thyrotropic pituitary function. It was defined to be more robust to distorted data than JTI and TTSI. It is calculated with
from quantiles of FT4 and TSH concentration (as determined based on cumulative distribution functions). Per definition the TFQI has a mean of 0 and a standard deviation of 0.37 in a reference population. Higher values of TFQI are associated with obesity, metabolic syndrome, impaired renal function, diabetes, and diabetes-related mortality. TFQI results are also elevated in takotsubo syndrome, potentially reflecting type 2 allostatic load in the situation of psychosocial stress. Reductions have been observed in subjects with schizophrenia after initiation of therapy with oxcarbazepine, potentially reflecting declining allostatic load. | 1 | Biochemistry |
Several monoclonal antibodies, such as bevacizumab and cetuximab, can cause different kinds of side effects. These side effects can be categorized into common and serious side effects.
Some common side effects include:
* Dizziness
* Headaches
* Allergies
* Diarrhea
* Cough
* Fever
* Itching
* Back pain
* General weakness
* Loss of appetite
* Insomnia
* Constipation
Among the possible serious side effects are:
* Anaphylaxis
* Bleeding
* Arterial and venous blood clots
* Autoimmune thyroiditis
* Hypothyroidism
* Hepatitis
* Heart failure
* Cancer
* Anemia
* Decrease in white blood cells
* Stomatitis
* Enterocolitis
* Gastrointestinal perforation
* Mucositis | 1 | Biochemistry |
A bioindicator is an organism or biological response that reveals the presence of pollutants by the occurrence of typical symptoms or measurable responses and is, therefore, more qualitative.
These organisms (or communities of organisms) can be used to deliver information on alterations in the environment or the quantity of environmental pollutants by changing in one of the following ways: physiologically, chemically or behaviourally.
The information can be deduced through the study of:
# their content of certain elements or compounds
# their morphological or cellular structure
# metabolic biochemical processes
# behaviour
# population structure(s).
The importance and relevance of biomonitors, rather than man-made equipment, are justified by the observation that the best indicator of the status of a species or system is itself. Bioindicators can reveal indirect biotic effects of pollutants when many physical or chemical measurements cannot. Through bioindicators, scientists need to observe only the single indicating species to check on the environment rather than monitor the whole community. Small sets of indicator species can also be used to predict species richness for multiple taxonomic groups.
The use of a biomonitor is described as biological monitoring and is the use of the properties of an organism to obtain information on certain aspects of the biosphere. Biomonitoring of air pollutants can be passive or active. Experts use passive methods to observe plants growing naturally within the area of interest. Active methods are used to detect the presence of air pollutants by placing test plants of known response and genotype into the study area.
The use of a biomonitor is described as biological monitoring. This refers to the measurement of specific properties of an organism to obtain information on the surrounding physical and chemical environment.
Bioaccumulative indicators are frequently regarded as biomonitors. Depending on the organism selected and their use, there are several types of bioindicators. | 2 | Environmental Chemistry |
There are fourteen naturally occurring enediynes. The other existing classes of enediynes have been synthesized in the lab.
Enediynes have been split into two sub-families: those with nine members in the core enediyne ring and those with ten-membered rings. | 0 | Organic Chemistry |
Alain-Edgard Berton (1912–1979) was a French chemical engineer who specialized in toxicology and in the analysis of air components in industrial environments. In the late 1950s he invented the "Osmopile", a measuring device, dubbed "the first artificial nose," which initiated, through the use of highly sensitive galvanic cells, the electrochemical analysis of air to detect dangerous components. | 3 | Analytical Chemistry |
NURF was first purified from the model organism Drosophila melanogaster by Toshio Tsukiyama and Carl Wu in 1995. Tsukiyama and Wu described NURF’s chromatin remodeling activity on the hsp70 promoter. It was later discovered that NURF regulates transcription in this manner for hundreds of genes. A human ortholog of NURF, called hNURF, was isolated in 2003. | 1 | Biochemistry |
According to Beer–Lambert law, the intensity of an electromagnetic wave inside a material falls off exponentially from the surface as
If denotes the penetration depth, we have
Penetration depth is one term that describes the decay of electromagnetic waves inside of a material. The above definition refers to the depth at which the intensity or power of the field decays to 1/e of its surface value. In many contexts one is concentrating on the field quantities themselves: the electric and magnetic fields in the case of electromagnetic waves. Since the power of a wave in a particular medium is proportional to the square of a field quantity, one may speak of a penetration depth at which the magnitude of the electric (or magnetic) field has decayed to 1/e of its surface value, and at which point the power of the wave has thereby decreased to or about 13% of its surface value:
Note that is identical to the skin depth, the latter term usually applying to metals in reference to the decay of electrical currents (which follow the decay in the electric or magnetic field due to a plane wave incident on a bulk conductor). The attenuation constant is also identical to the (negative) real part of the propagation constant, which may also be referred to as using a notation inconsistent with the above use. When referencing a source one must always be careful to note whether a number such as or refers to the decay of the field itself, or of the intensity (power) associated with that field. It can also be ambiguous as to whether a positive number describes attenuation (reduction of the field) or gain; this is usually obvious from the context. | 7 | Physical Chemistry |
The amplification reaction initiates when multiple primer hexamers anneal to the template. When DNA synthesis proceeds to the next starting site, the polymerase displaces the newly produced DNA strand and continues its strand elongation. The strand displacement generates a newly synthesized single-stranded DNA template for more primers to anneal. Further primer annealing and strand displacement on the newly synthesized template results in a hyper-branched DNA network. The sequence debranching during amplification results in a high yield of the products. To separate the DNA branching network, S1 nucleases are used to cleave the fragments at displacement sites. The nicks on the resulting DNA fragments are repaired by DNA polymerase I. | 1 | Biochemistry |
The following result, due to Donsker and Varadhan, is known as Donsker and Varadhan's variational formula.
For alternative proof using measure theory, see. | 7 | Physical Chemistry |
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