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The Corey-correlation or Corey model has only one degree of freedom for the shape of each relative permeability curve, the shape parameter N.
The LET-correlation
adds more degrees of freedom in order to accommodate the shape of relative permeability curves in SCAL experiments and in 3D reservoir models that are adjusted to match historic production. These adjustments frequently includes relative permeability curves and endpoints.
The LET-type approximation is described by 3 parameters L, E, T. The correlation for water and oil relative permeability with water injection is thus
and
written using the same normalization as for Corey.
Only , , , and have direct physical meaning, while the parameters L, E and T are empirical. The parameter L describes the lower part of the curve, and by similarity and experience the L-values are comparable to the appropriate Corey parameter. The parameter T describes the upper part (or the top part) of the curve in a similar way that the L-parameter describes the lower part of the curve. The parameter E describes the position of the slope (or the elevation) of the curve. A value of one is a neutral value, and the position of the slope is governed by the L- and T-parameters. Increasing the value of the E-parameter pushes the slope towards the high end of the curve. Decreasing the value of the E-parameter pushes the slope towards the lower end of the curve. Experience using the LET correlation indicates the following reasonable ranges for the parameters L, E, and T: L ≥ 0.1, E > 0 and T ≥ 0.1.
In case of gas-water system or gas-oil system there are LET correlations similar to the oil-water relative permeabilities correlations shown above. | 1 | Applied and Interdisciplinary Chemistry |
The term "molecular tweezers" was first used by Whitlock. The class of hosts was developed and popularized by Zimmerman in the mid-1980s to early 1990s and later by Klärner. | 0 | Theoretical and Fundamental Chemistry |
The Zimmermann reagent is used as a simple spot-test used in chromatography to presumptively identify alkaloids, especially benzodiazepines, as well as other compounds. It is therefore used in drugs testing.
It is a two-component reagent, with the first component composed of 1,3-dinitrobenzene (1% w/v) in methanol and the second component composed of 15% potassium hydroxide in water.
One drop of each component is added to the sample being tested and the resulting colour change is observed to give an indication of the identity of the compound.
The reagent works by forming a reddish-purple Meisenheimer complex at C3 for diazepines with a carbonyl at C2 and an alkyl group at N1. Without these groups it is not possible to form the methylene compound which reacts with dinitrobenzene but triazolo compounds may react.
It is named for the American biochemist Robert Zimmermann (b.1937). | 0 | Theoretical and Fundamental Chemistry |
The typical process for creating ICCs in the lab involves ionisation of an elemental source, followed by confinement in an ion trap, where they are imaged via their fluorescence. Changing parameters such as the axial or radial confining potentials may lead to different observed geometries of the crystal, even if the number of ions does not change.
For measurements involving highly charged ions, these are typically observed as "dark" areas in the fluorescence of the Coulomb crystal, due to their different energy levels. This effect is also noticeable when ions in the Coulomb crystal appear to disappear, without changing the structure of the crystal, due to mixing with impurities in a non-ideal vacuum.
Heating effects are also important in the characterisation of Coulomb crystals, since thermal motion can cause the image to blur. This may be stimulated by the cooling laser being slightly off-resonance, and so needs to be carefully monitored. | 0 | Theoretical and Fundamental Chemistry |
Nuclear DNA is normally wrapped tightly around histones, making it hard or impossible for the transcription machinery to access the DNA. This association is due primarily to the electrostatic attraction between the DNA and histones as the DNA phosphate backbone is negatively charged and histones are rich in lysine residues, which are positively charged. The tight DNA-histone association prevents the transcription of DNA into RNA.
Many coactivators have histone acetyltransferase (HAT) activity meaning that they can acetylate specific lysine residues on the N-terminal tails of histones. In this method, an activator binds to an enhancer site and recruits a HAT complex that then acetylates nucleosomal promoter-bound histones by neutralizing the positively charged lysine residues. This charge neutralization causes the histones to have a weaker bond to the negatively charged DNA, which relaxes the chromatin structure, allowing other transcription factors or transcription machinery to bind to the promoter (transcription initiation). Acetylation by HAT complexes may also help keep chromatin open throughout the process of elongation, increasing the speed of transcription.
Acetylation of the N-terminal histone tail is one of the most common protein modifications found in eukaryotes, with about 85% of all human proteins being acetylated. Acetylation is crucial for synthesis, stability, function, regulation and localization of proteins and RNA transcripts.
HATs function similarly to N-terminal acetyltransferases (NATs) but their acetylation is reversible unlike in NATs. HAT mediated histone acetylation is reversed using histone deacetylase (HDAC), which catalyzes the hydrolysis of lysine residues, removing the acetyl group from the histones. This causes the chromatin to close back up from their relaxed state, making it difficult for the transcription machinery to bind to the promoter, thus repressing gene expression.
Examples of coactivators that display HAT activity include CARM1, CBP and EP300. | 1 | Applied and Interdisciplinary Chemistry |
WES was done with EPIC-seq and it detected a correlation between the biological signal and active genes' exonic regions; this shows that EPIC-seq can be generalized for expression of genes of interest rather than only cancer genes | 1 | Applied and Interdisciplinary Chemistry |
In a toroidal fusion power device, a plasma is confined within a donut-shaped cylinder. If the gas pressure of the plasma varies across the radius of the cylinder, a self-generated current will spontaneously arise within the plasma, due to collisions between trapped particles and passing particles. This current is called the bootstrap current, and is commonly found in tokamak fusion devices. The tokamak uses a combination of external magnets and a current driven in the plasma to create a stable confinement system. One goal of advanced tokamak designs is to maximize the bootstrap current, and thereby reduce or eliminate the need for an external current driver. This could dramatically reduce the cost and complexity of the device.
From a kinetic point of view, the bootstrap current is the effect of trapped particles (which practically lie on poloidal plane) and density gradient: the poloidal current due to trapped particles motion is unbalanced since the density is not constant, therefore the bootstrap current is needed to "close the circuit". | 0 | Theoretical and Fundamental Chemistry |
After the war, Seaborg and Ghiorso returned to Berkeley, where they and colleagues used the 60" Crocker cyclotron to produce elements of increasing atomic number by bombarding exotic targets with helium ions. In experiments during 1949–1950, they produced and identified elements 97 (berkelium) and 98 (californium). In 1953, in a collaboration with Argonne Lab, Ghiorso and collaborators sought and found elements 99 (einsteinium) and 100 (fermium), identified by their characteristic radiation in dust collected by airplanes from the first thermonuclear explosion (the Mike test). In 1955, the group used the cyclotron to produce 17 atoms of element 101 (mendelevium), the first new element to be discovered atom-by-atom. The recoil technique invented by Ghiorso was crucial to obtaining an identifiable signal from individual atoms of the new element.
In the mid-1950s it became clear that to extend the periodic chart any further, a new accelerator would be needed, and the Berkeley Heavy Ion Linear Accelerator (HILAC) was built, with Ghiorso in charge. That machine was used in the discovery of elements 102–106 (102, nobelium; 103, lawrencium; 104, rutherfordium; 105, dubnium and 106, seaborgium), each produced and identified on the basis of only a few atoms. The discovery of each successive element was made possible by the development of innovative techniques in robotic target handling, fast chemistry, efficient radiation detectors, and computer data processing. The 1972 upgrade of the HILAC to the superHILAC provided higher intensity ion beams, which was crucial to producing enough new atoms to enable detection of element 106.
With increasing atomic number, the experimental difficulties of producing and identifying a new element increase significantly. In the 1970s and 1980s, resources for new element research at Berkeley were diminishing, but the GSI laboratory at Darmstadt, Germany, under the leadership of Peter Armbruster and with considerable resources, was able to produce and identify elements 107–109 (107, bohrium; 108, hassium and 109, meitnerium). In the early 1990s, the Berkeley and Darmstadt groups made a collaborative attempt to create element 110. Experiments at Berkeley were unsuccessful, but eventually elements 110–112 (110, darmstadtium; 111, roentgenium and 112, copernicium) were identified at the Darmstadt laboratory. Subsequent work at the JINR laboratory at Dubna, led by Yuri Oganessian and a Russian-American team of scientists, was successful in identifying elements 113–118 (113, nihonium; 114, flerovium; 115, moscovium; 116, livermorium; 117, tennessine and 118, oganesson), thereby completing the Period 7 elements of the periodic table of the elements. | 1 | Applied and Interdisciplinary Chemistry |
The porous medium equation has been found to have a number of applications in gas flow, heat transfer, and groundwater flow. | 1 | Applied and Interdisciplinary Chemistry |
The per person organic matter load is a parameter used in the design of sewage treatment plants. This concept is known as population equivalent (PE). The base value used for PE can vary from one country to another. Commonly used definitions used worldwide are: 1 PE equates to 60 gram of BOD per person per day, and it also equals 200 liters of sewage per day. This concept is also used as a comparison parameter to express the strength of industrial wastewater compared to sewage. | 1 | Applied and Interdisciplinary Chemistry |
The halomethanes are produced on an industrial scale from abundant precursors such as natural gas or methanol, and from halogens or halides. They are usually prepared by one of three methods.
*Free radical chlorination of methane (under ultraviolet light):
This method is useful for the production of (n = 1, 2, 3, or 4). The main problems with this method are that it cogenerates HCl and it produces mixtures of different products. Using in large excess generates primarily and using in large excess generates primarily , but mixtures of other products will still be present.
*Halogenation of methanol. This method is used for the production of the mono-chloride, -bromide, and -iodide.
*Halogen exchange. The method is mainly used to produce fluorinated derivatives from the chlorides.
*Reaction of methane with hypochlorous acid, producing water.
*Reaction of methanol with hypochlorous acid, producing hydrogen peroxide.
Traces of halomethanes in the atmosphere arise through the introduction of other non-natural, industrial materials. | 1 | Applied and Interdisciplinary Chemistry |
In biology, abiogenesis (from Greek ἀ- a- not + βῐ́ος bios life + γένεσις genesis origin) or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities on Earth was not a single event, but a process of increasing complexity involving the formation of a habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. The transition from non-life to life has never been observed experimentally, but many proposals have been made for different stages of the process.
The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today. It primarily uses tools from biology and chemistry, with more recent approaches attempting a synthesis of many sciences. Life functions through the specialized chemistry of carbon and water, and builds largely upon four key families of chemicals: lipids for cell membranes, carbohydrates such as sugars, amino acids for protein metabolism, and nucleic acid DNA and RNA for the mechanisms of heredity. Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules. Many approaches to abiogenesis investigate how self-replicating molecules, or their components, came into existence. Researchers generally think that current life descends from an RNA world, although other self-replicating molecules may have preceded RNA.
The classic 1952 Miller–Urey experiment demonstrated that most amino acids, the chemical constituents of proteins, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. External sources of energy may have triggered these reactions, including lightning, radiation, atmospheric entries of micro-meteorites and implosion of bubbles in sea and ocean waves. Other approaches ("metabolism-first" hypotheses) focus on understanding how catalysis in chemical systems on the early Earth might have provided the precursor molecules necessary for self-replication.
While the last universal common ancestor (LUCA) is thought to have been quite different from the origin of life, investigations into LUCA can guide research into early universal characteristics. A genomics approach has sought to characterise LUCA of modern organisms by identifying the genes shared by Archaea and Bacteria, members of the two major branches of life (where the Eukaryotes belong to the archaean branch in the two-domain system). 355 genes appear to be common to all life; their nature implies that the LUCA was anaerobic with the Wood–Ljungdahl pathway, deriving energy by chemiosmosis, and maintaining its hereditary material with DNA, the genetic code, and ribosomes. Although the LUCA lived over 4 billion years ago (4 Gya), researchers do not believe it was the first form of life. Earlier cells might have had a leaky membrane and been powered by a naturally occurring proton gradient near a deep-sea white smoker hydrothermal vent.
Earth remains the only place in the universe known to harbor life. Geochemical and fossil evidence from the Earth informs most studies of abiogenesis. The Earth was formed at 4.54 Gya, and the earliest evidence of life on Earth dates from at least 3.8 Gya from Western Australia. Fossil micro-organisms appear to have lived within hydrothermal vent precipitates dated 3.77 to 4.28 Gya from Quebec, soon after ocean formation 4.4 Gya during the Hadean. | 0 | Theoretical and Fundamental Chemistry |
Anodizing can produce yellowish integral colours without dyes if it is carried out in weak acids with high voltages, high current densities, and strong refrigeration. Shades of colour are restricted to a range which includes pale yellow, gold, deep bronze, brown, grey, and black. Some advanced variations can produce a white coating with 80% reflectivity. The shade of colour produced is sensitive to variations in the metallurgy of the underlying alloy and cannot be reproduced consistently.
Anodizing in some organic acids, for example malic acid, can enter a runaway situation, in which the current drives the acid to attack the aluminium far more aggressively than normal, resulting in huge pits and scarring. Also, if the current or voltage are driven too high, burning can set in; in this case, the supplies act as if nearly shorted and large, uneven and amorphous black regions develop.
Integral colour anodizing is generally done with organic acids, but the same effect has been produced in laboratories with very dilute sulfuric acid. Integral colour anodizing was originally performed with oxalic acid, but sulfonated aromatic compounds containing oxygen, particularly sulfosalicylic acid, have been more common since the 1960s. Thicknesses of up to 50 μm can be achieved. Organic acid anodizing is called Type IC by MIL-A-8625. | 1 | Applied and Interdisciplinary Chemistry |
Photochemical reduction of carbon dioxide harnesses solar energy to convert into higher-energy products. Environmental interest in producing artificial systems is motivated by recognition that CO is a greenhouse gas. The process has not been commercialized. | 0 | Theoretical and Fundamental Chemistry |
Goudar equation is the most accurate approximation to solve directly for the Darcy–Weisbach friction factor f for a full-flowing circular pipe. It is an approximation of the implicit Colebrook–White equation. Equation has the following form | 1 | Applied and Interdisciplinary Chemistry |
At one time, coordination compounds were used to identify the presence of metals in a sample. Qualitative inorganic analysis has largely been superseded by instrumental methods of analysis such as atomic absorption spectroscopy (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms substituent and functional group, as well as side chain and pendant group, are used almost interchangeably to describe those branches from the parent structure, though certain distinctions are made in polymer chemistry. In polymers, side chains extend from the backbone structure. In proteins, side chains are attached to the alpha carbon atoms of the amino acid backbone.)
The suffix -yl is used when naming organic compounds that contain a single bond replacing one hydrogen; -ylidene and -ylidyne are used with double bonds and triple bonds, respectively. In addition, when naming hydrocarbons that contain a substituent, positional numbers are used to indicate which carbon atom the substituent attaches to when such information is needed to distinguish between isomers. Substituents can be a combination of the inductive effect and the mesomeric effect. Such effects are also described as electron-rich and electron withdrawing. Additional steric effects result from the volume occupied by a substituent.
The phrases most-substituted and least-substituted are frequently used to describe or compare molecules that are products of a chemical reaction. In this terminology, methane is used as a reference of comparison. Using methane as a reference, for each hydrogen atom that is replaced or "substituted" by something else, the molecule can be said to be more highly substituted. For example:
* Markovnikov's rule predicts that the hydrogen atom is added to the carbon of the alkene functional group which has the greater number of hydrogen atoms (fewer alkyl substituents).
* Zaitsev's rule predicts that the major reaction product is the alkene with the more highly substituted (more stable) double bond. | 0 | Theoretical and Fundamental Chemistry |
Generally, in progression to cancer, hundreds of genes are silenced or activated. Although silencing of some genes in cancers occurs by mutation, a large proportion of carcinogenic gene silencing is a result of altered DNA methylation (see DNA methylation in cancer). DNA methylation causing silencing in cancer typically occurs at multiple CpG sites in the CpG islands that are present in the promoters of protein coding genes.
Altered expressions of microRNAs also silence or activate many genes in progression to cancer (see microRNAs in cancer). Altered microRNA expression occurs through hyper/hypo-methylation of CpG sites in CpG islands in promoters controlling transcription of the microRNAs.
Silencing of DNA repair genes through methylation of CpG islands in their promoters appears to be especially important in progression to cancer (see methylation of DNA repair genes in cancer). | 1 | Applied and Interdisciplinary Chemistry |
Mukaiyama has been recognized for his achievements in the form of seven honorary degrees and membership in the national academies of four nations. He is the namesake of the Mukaiyama Award, awarded by the Society of Synthetic Organic Chemistry, Japan since 2005. His major awards include:
* Chemical Society of Japan Award in 1973
* Imperial Prize and Academy Prize from the Japan Academy in 1983
* Nicholaus Copernicus Medal from the Polish Academy of Sciences in 1986
* Person of Cultural Merit from Japan in 1992
* Chevalier de l’Ordre National du Mérite from France in 1994
* ACS Award for Creative work in Synthetic Organic Chemistry from the American Chemical Society in 1996
* Order of Culture from Japan in 1997
* Tetrahedron Prize for Creativity in Organic Chemistry from Elsevier in 1998
* Sir Derek Barton Gold Medal from the Royal Society of Chemistry in 1998 | 0 | Theoretical and Fundamental Chemistry |
Urea was first discovered in urine in 1727 by the Dutch scientist Herman Boerhaave, although this discovery is often attributed to the French chemist Hilaire Rouelle as well as William Cruickshank.
Boerhaave used the following steps to isolate urea:
# Boiled off water, resulting in a substance similar to fresh cream
# Used filter paper to squeeze out remaining liquid
# Waited a year for solid to form under an oily liquid
# Removed the oily liquid
# Dissolved the solid in water
# Used recrystallization to tease out the urea
In 1828, the German chemist Friedrich Wöhler obtained urea artificially by treating silver cyanate with ammonium chloride.
This was the first time an organic compound was artificially synthesized from inorganic starting materials, without the involvement of living organisms. The results of this experiment implicitly discredited vitalism, the theory that the chemicals of living organisms are fundamentally different from those of inanimate matter. This insight was important for the development of organic chemistry. His discovery prompted Wöhler to write triumphantly to Jöns Jakob Berzelius:
:"I must tell you that I can make urea without the use of kidneys, either man or dog. Ammonium cyanate is urea."
In fact, his second sentence was incorrect. Ammonium cyanate and urea are two different chemicals with the same empirical formula , which are in chemical equilibrium heavily favoring urea under standard conditions. Regardless, with his discovery, Wöhler secured a place among the pioneers of organic chemistry.
Uremic frost was first described in 1865 by Harald Hirschsprung, the first Danish pediatrician in 1870 who also described the disease that carries his name in 1886. Uremic frost has become rare since the advent of dialysis. It is the classical pre-dialysis era description of crystallized urea deposits over the skin of patients with prolonged kidney failure and severe uremia. | 0 | Theoretical and Fundamental Chemistry |
Plants have mechanisms that protect against adverse effects of strong light. The most studied biochemical protective mechanism is non-photochemical quenching of excitation energy. Visible-light-induced photoinhibition is ~25% faster in an Arabidopsis thaliana mutant lacking non-photochemical quenching than in the wild type. It is also apparent that turning or folding of leaves, as occurs, e.g., in Oxalis species in response to exposure to high light, protects against photoinhibition. | 0 | Theoretical and Fundamental Chemistry |
Multiple companies have offered exome sequencing to consumers. Knome was the first company to offer exome sequencing services to consumers, at a cost of several thousand dollars. Later, 23andMe ran a pilot WES program that was announced in September 2011 and was discontinued in 2012. Consumers could obtain exome data at a cost of $999. The company provided raw data, and did not offer analysis.
In November 2012, DNADTC, a division of Gene by Gene started offering exomes at 80X coverage and introductory price of $695. This price per DNADTC web site is currently $895. In October 2013, BGI announced a promotion for personal whole exome sequencing at 50X coverage for $499.
In June 2016 Genos was able to achieve an even lower price of $399 with a CLIA-certified 75X consumer exome sequenced from saliva.
A 2018 review of 36 studies found the cost for exome sequencing to range from $555USD to $5,169USD, with a diagnostic yield ranging from 3% to 79% depending on patient groups. | 1 | Applied and Interdisciplinary Chemistry |
Non-destructive detectors in liquid chromatography:
*Ultraviolet light detectors, fixed or variable wavelength, which includes diode array detectors. The ultraviolet light absorption of the effluent is continuously measured at single or multiple wavelengths. These are by far most popular detectors for liquid chromatography.
* Fluorescence detector. Irradiates the effluent with a light of set wavelength and measure the fluorescence of the effluent at a single or multiple wavelength.
* Refractive index detector. Continuously measures the refractive index of the effluent. The lowest sensitivity of all detectors. Often used in size exclusion chromatography for polymer analysis.
* Radio flow detector. Measures radioactivity of the effluent. This detector can be destructive if a scintillation cocktail is continuously added to the effluent.
* Chiral detector continuously measures the optical angle of rotation of the effluent. It is used only when chiral compounds are being analyzed.
* Conductivity monitor. Continuously measures the conductivity of the effluent. Used only when conductive eluents (water or alcohols) are used.
Non-destructive detectors in gas chromatography:
* Thermal conductivity detector: measures the thermal conductivity of the eluent.
* Electron capture detector: the most sensitive detector known. Allows for the detection of organic molecules containing halogen, nitro groups etc.
* Photoionization detector measures the increase in conductivity achieved by ionizing the effluent gas with ultraviolet light radiation.
* Olfactometric detector: assesses the odor activity of the eluent using human assessors.
* Electronic nose detector which mimics human nose is emerging as a modern and advanced version of the olfactory detection is the electronic nose detector. | 0 | Theoretical and Fundamental Chemistry |
It is presumed that Chesapeake Bay was once inhabited by Paleoindians 11,000 years ago. For thousands of years, Native American societies lived in villages of wooden longhouses close to water bodies where they fished and farmed the land. Agricultural products included beans, corn, tobacco, and squash. Villages often lasted between 10 and 20 years before being abandoned due to local resources such as firewood running out or soil depleting. To produce enough food, labor was divided with men hunting while the women supervised the village's farming. All village members took part in the harvesting of fish and shellfish from the local bodies of water. As time went on, communities around Chesapeake Bay formed confederations such as the Powhatan, the Piscataway, and the Nanticoke. Each of these confederations consisted of a collection of smaller tribes falling under the leadership of a central chief. | 1 | Applied and Interdisciplinary Chemistry |
From 1991-1993 a group of investigators, headed by Zvi Shkedi, in the state of Massachusetts, USA, built well-insulated cells and calorimeters which included the capability to measure the actual Faraday efficiency in real-time during the experiments. The cells were of the light-water type; with a fine-wire nickel cathode; a platinum anode; and KCO electrolyte.
The calorimeters were calibrated to an accuracy of 0.02% of input power. The long-term stability of the calorimeters was verified over a period of 9 months of continuous operation. In their publication, the investigators show details of their calorimeters' design and teach the technology of achieving high calorimetric accuracy. | 0 | Theoretical and Fundamental Chemistry |
Plant-based digital data storage is a futuristic view that proposes storing digital data in plants and seeds. The first practical implication showed the possibility of using plants as storage media for digital data. New approaches for data archiving are required due to the constant increase in digital data production and the lack of a capacitive, low maintenance storage medium. | 1 | Applied and Interdisciplinary Chemistry |
The DrugWipe is a moist wipe used to detect drug residue on surfaces, or on the forehead, palm, or tongue of an individual. An integrated ampule is broken, which is the medium for transporting the collected analyte to the antigen-binding site. The DrugWipe can be configured to detect cannabis, cocaine, opiates, amphetamines, MDMA, and benzodiazepines. Immunoassay strips containing antibodies bind to components of the different drugs. | 0 | Theoretical and Fundamental Chemistry |
Lowe (born in Harrisburg, Arkansas) got his BA from Hendrix College and his PhD in organic chemistry from Duke University on synthesis of natural products, before spending time in Germany on a Humboldt Fellowship.
Lowe was one of the first people to blog from inside the pharmaceutical industry, with the approval of his supervisor and the company legal department, and one of the first science bloggers. By 2006, his blog had between 3,000 and 4,000 visitors per day during the workweek; he covered business matters, trends and issues in medicinal chemistry, and legal matters like patent law and regulation. At that time he was working at a pharmaceutical company doing hit to lead medical chemistry work. his blog received between 15,000 and 20,000 page views on a typical weekday. His response to a 2013 article in BuzzFeed that propagated chemophobia was widely cited.
He serves on the editorial board of ACS Medicinal Chemistry Letters and on the advisory board of Chemical & Engineering News.
he was working at Novartis; formerly he had worked for 10 years at Vertex, 9 years at Bayer, and 8 years at Schering-Plough. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, carbon tetrachloride serves as a source of chlorine in the Appel reaction.
Carbon tetrachloride made from heavy chlorine-37 has been used in the detection of neutrinos. | 1 | Applied and Interdisciplinary Chemistry |
In quantum mechanics, a shape resonance, in contrast to a Feshbach resonance, is a resonance which is not turned into a bound state if the coupling between some degrees of freedom and the degrees of freedom associated to the fragmentation (reaction coordinates) are set to zero. More simply, the shape resonance total energy is more than the separated fragment energy.
Practical implications of this difference for lifetimes and spectral widths are mentioned in works such as Zobel.
Related terms include a special kind of shape resonance, the core-excited shape resonance, and trap-induced shape resonance.
Of course in one-dimensional systems, resonances are shape resonances. In a system with more than one degree of freedom, this definition makes sense only if the separable model, which supposes the two groups of degrees of freedom uncoupled, is a meaningful approximation. When the coupling becomes large, the situation is much less clear.
In the case of atomic and molecular electronic structure problems, it is well known that the self-consistent field (SCF) approximation is relevant at least as a starting point of more elaborate methods. The Slater determinants built from SCF orbitals (atomic or molecular orbitals) are shape resonances if only one electronic transition is required to emit one electron.
Today, there is some debate about the definition and even existence of the shape resonance in some systems observed with molecular spectroscopy. It has been experimentally observed in the anionic yields from photofragmentation of small molecules to provide details of internal structure.
In nuclear physics the concept of "Shape Resonance" is described by Amos de-Shalit and Herman Feshbach in their book.
"It is well known that the scattering from a potential shows characteristics peaks, as a function of energy, for such values of E that make the integral number of wave lengths sit within the potential. The resulting shape resonances are rather broad, their width being of the order of ...."
The shape resonances were observed around the years 1949–54 in nuclear scattering experiments. They indicate broad asymmetric peaks in the scattering cross section of neutrons or protons scattered by nuclei. The name "shape resonance" has been introduced to describe the fact that the resonance in the potential scattering for the particle of energy E is controlled by the shape of the nucleus. In fact the shape resonance occurs where the integral number of wavelengths of the particle sit within the potential of the nucleus of radius R. Therefore, the measure of the energies of the shape resonances in the neutron-nucleus scattering have been used in the years from 1947 to 1954 to measure the radii R of the nuclei with the precision of ±1×10 cm as it can be seen in the chapter "Elastic Cross Sections" of A Textbook in Nuclear Physics by R. D. Evans.
The "shape resonances" are discussed in general introductory academic courses of quantum mechanics in the frame of potential scattering phenomena.
The shape resonances arise from the quantum interference between closed and an open scattering channels. At the resonance energy a quasi bound state is degenerate with a continuum. This quantum interference in many body system has been described using quantum mechanics by Gregor Wentzel, for the interpretation of the Auger effect, by Ettore Majorana for the dissociation processes and quasi bound states, by Ugo Fano for the atomic auto-ionization states in the continuum of helium atomic spectrum and by Victor Frederick Weisskopf. J. M. Blatt and Herman Feshbach for nuclear scattering experiments.
The shape resonances are related with the existence of nearly stable bound states (that is, resonances) of two objects that dramatically influences how those two objects interact when their total energy is near that of the bound state. When the total energy of the objects is close to the energy of the resonance they interact strongly, and their scattering cross-section becomes very large.
A particular type of "shape resonance" occurs in multiband or two-band superconducting heterostructures at atomic limit called superstripes due to quantum interference of a first pairing channel in a first wide band and a second pairing channel in a second band where the chemical potential is tuned near a Lifshitz transition at the band edge or at the topological electronic transitions of the Fermi surface type "neck-collapsing" or "neck-disrupting" | 0 | Theoretical and Fundamental Chemistry |
* A commercial, high purity (non-recycled) polymer sample with known molecular mass distribution can be obtained or synthesized according to standard procedures.
* Common properties such as elastic modulus, tan δ, crystallinity, viscosity, density should be characterized.
* Anchor points, physical or chemical (chain entanglement, crystallinity or vulcanization), must be decided.
If crosslinking with slight vulcanization is desired, standardized methods for each polymer must be taken into account. In the case of PCO, for example, it is a polymer without shape-shape-memory effect because it does not present a clear "plateau", but the addition of a minimum amount of peroxide (~1%) provides PCO with all the requirements to present this effect.
# A permanent stress-free shape with known dimensions is prepared by conventional methods.
# The system is programmed, i.e. it is heated up to T and at that temperature the shape is modified by applying pressure or stress. Then the material is cooled and finally the pressure or stress is removed.
# After heating the sample again to T, the stresses are released and the permanent shape is recovered.
Some polymers fatigue first, so each system can be evaluated with a simple experiment that consists of programming the system 10 or 20 times in a row and measuring the recovery in % and time. | 0 | Theoretical and Fundamental Chemistry |
Liquid level floats, also known as float balls, are spherical, cylindrical, oblong or similarly shaped objects, made from either rigid or flexible material, that are buoyant in water and other liquids. They are non-electrical hardware frequently used as visual sight-indicators for surface demarcation and level measurement. They may also be incorporated into switch mechanisms or translucent fluid-tubes as a component in monitoring or controlling liquid level.
Liquid level floats, or float switches, use the principle of material buoyancy (differential densities) to follow fluid levels. Solid floats are often made of plastics with a density less than water or other application liquid, and so they float. Hollow floats filled with air are much less dense than water or other liquids, and are appropriate for some applications.
Stainless Steel Magnetic floats are tubed magnetic floats, used for reed switch activation; they have a hollow tubed connection running through them. These magnetic floats have become standard equipment where strength, corrosion resistance and buoyancy are necessary. They are manufactured by welding two drawn half shells together. The welding process is critical for the strength and durability of the float. The weld is a full penetration weld providing a smoothly finished seam, hardly distinguishable from the rest of the float surface.
Liquid level floats can also be constructed with thermoplastic corrosion-resistant materials. These materials include PVC, Polypropylene and PVDF. An example of an application that would require such materials would be if a manufacturer of metal plating and metal finishing lines required continuous level measurement of their chromic acid tanks. Stainless Steel would rapidly corrode in chromic acid, which is why one would have the option to go with a PVDF float, which is a material with great chemical resistance to chromic acid.
Thermoplastic level floats are a great alternative to some other forms of level sensors such as ultrasonic or radar when dealing with corrosive chemical applications. This is because some chemicals create vapor blankets or corrosive fumes inside of tanks. Liquid level floats are unaffected by any foam, vapor, turbulence or condensate inside of the tanks that would normally cause issues with an ultrasonic or radar level sensor. | 1 | Applied and Interdisciplinary Chemistry |
In the 1960s and 1970s it was speculated that aluminium was related to various neurological disorders, including Alzheimer's disease. Since then, multiple epidemiological studies have found no connection between exposure to environmental or swallowed aluminium and neurological disorders, though injected aluminium was not looked at in these studies.
Neural disorders were found in experiments on mice motivated by Gulf War illness (GWI). Aluminium hydroxide injected in doses equivalent to those administered to the United States military, showed increased reactive astrocytes, increased apoptosis of motor neurons and microglial proliferation within the spinal cord and cortex. | 0 | Theoretical and Fundamental Chemistry |
The application of transformations to retrosynthetic analysis can lead to powerful reductions in molecular complexity. Unfortunately, powerful transform-based retrons are rarely present in complex molecules, and additional synthetic steps are often needed to establish their presence. | 0 | Theoretical and Fundamental Chemistry |
The process involves an electron (hole) incident on the interface from the normal state material at energies less than the superconducting energy gap. The incident electron (hole) forms a Cooper pair in the superconductor with the retroreflection of a hole (electron) of opposite spin and velocity but equal momentum to the incident electron (hole), as seen in the figure. The barrier transparency is assumed to be high, with no oxide or tunnel layer which reduces instances of normal electron-electron or hole-hole scattering at the interface. Since the pair consists of an up and down spin electron, a second electron (hole) of opposite spin to the incident electron (hole) from the normal state forms the pair in the superconductor, and hence the retroreflected hole (electron). Through time-reversal symmetry, the process with an incident electron will also work with an incident hole (and retroreflected electron).
The process is highly spin-dependent – if only one spin band is occupied by the conduction electrons in the normal-state material (i.e. it is fully spin-polarized), Andreev reflection will be inhibited due to inability to form a pair in the superconductor and impossibility of single-particle transmission. In a ferromagnet or material where spin-polarization exists or may be induced by a magnetic field, the strength of the Andreev reflection (and hence conductance of the junction) is a function of the spin-polarization in the normal state.
The spin-dependence of AR gives rise to the Point Contact Andreev Reflection (or PCAR) technique, whereby a narrow superconducting tip (often niobium, antimony or lead) is placed into contact with a normal material at temperatures below the critical temperature of the tip. By applying a voltage to the tip, and measuring differential conductance between it and the sample, the spin polarization of the normal metal at that point (and magnetic field) may be determined. This is of use in such tasks as measurement of spin-polarized currents or characterizing spin polarization of material layers or bulk samples, and the effects of magnetic fields on such properties.
In an AR process, the phase difference between the electron and hole is −π/2 plus the phase of the superconducting order parameter. | 0 | Theoretical and Fundamental Chemistry |
As oxygen levels decrease, fish may at first increase movements in an attempt to escape the hypoxic zone, but eventually they greatly reduce their activity levels, thus reducing their energetic (and therefore oxygen) demands. Atlantic herring show this exact pattern. Other examples of fishes that reduce their activity levels under hypoxia include the common sole, the guppy, the small-spotted catshark, and the viviparous eelpout. Some sharks that ram-ventilate their gills may understandably increase their swimming speeds under hypoxia, to bring more water to the gills. | 0 | Theoretical and Fundamental Chemistry |
The IPF Dresden was founded on January 1, 1992, emerging from the largest polymer research center of the former GDR, which was at the time already internationally acknowledged. Since then the IPF Dresden developed into a leading institute in selected topics of polymer science.
As all Leibniz institutes, the IPF is evaluated at least every seven years. The last successful evaluation took place in 2022. | 1 | Applied and Interdisciplinary Chemistry |
Transplatin, the trans-stereoisomer of cisplatin, has formula trans-[PtCl(NH)] and does not exhibit a comparably useful pharmacological effect. Two mechanisms have been suggested to explain the reduced anticancer effect of transplatin. Firstly, the trans arrangement of the chloro ligands is thought to confer transplatin with greater chemical reactivity, causing transplatin to become deactivated before it reaches the DNA, where cisplatin exerts its pharmacological action. Secondly, the stereo-conformation of transplatin is such that it is unable to form the characteristic 1,2-intrastrand d(GpG) adducts formed by cisplatin in abundance. | 1 | Applied and Interdisciplinary Chemistry |
;Surrounding animals
:Although the pheromone may diffuse off as a territorial representation of the foraging organism, that does not secure the safety of the organism. In fact, this act may do the opposite and attract competing wildlife. With more surrounding predators, or competitors, comes more difficulty with foraging for a food source. Especially in cases were food is scarce, surrounding organism. Depending on the cost vs benefits tradeoff, an organism, in a situation where it may need the food supply, may be willing to risk the dangers to obtain it. Also, with more predators or competitors out there, the risks of foraging increase.
;Surrounding plants
:Factors such as type and abundance of surrounding plants in an environment may certainly affect the degree of trail pheromone potency. Plants residing in close proximity to the odor trail may emit an abundance of chemicals which can either mask, change, or possibly even help propagate the signal. Additionally, areas saturated with plant life may block or alter trail pheromone diffusion. | 1 | Applied and Interdisciplinary Chemistry |
Plutonium selenide forms black crystals of a cubic system, space group Fmm, cell parameters a = 0.57934 nm, Z = 4, structure of the NaCl type.
With increasing pressure, two phase transitions occur: at 20 GPa into the trigonal system and at 35 GPa into the cubic system, a structure of the CsCl type.
Its magnetic susceptibility follows the Curie-Weiss law. | 0 | Theoretical and Fundamental Chemistry |
The inorganic cycle begins with the production of carbonic acid (HCO) from rainwater and gaseous carbon dioxide. Due to this process, normal rain has a pH of around 5.6. Carbonic acid is a weak acid, but over long timescales, it can dissolve silicate rocks (as well as carbonate rocks). Most of the Earth's crust (and mantle) is composed of silicates. These substances break down into dissolved ions as a result. For example, calcium silicate (CaSiO), or wollastonite, reacts with carbon dioxide and water to yield a calcium ion, Ca, a bicarbonate ion, HCO, and dissolved silica. This reaction structure is representative of general silicate weathering of calcium silicate minerals. The chemical pathway is as follows:
River runoff carries these products to the ocean, where marine calcifying organisms use Ca and HCO to build their shells and skeletons, a process called carbonate precipitation:
Two molecules of CO are required for silicate rock weathering; marine calcification releases one molecule back to the atmosphere. The calcium carbonate (CaCO) contained in shells and skeletons sinks after the marine organism dies and is deposited on the ocean floor.
The final stage of the process involves the movement of the seafloor. At subduction zones, the carbonate sediments are buried and forced back into the mantle. Some carbonate may be carried deep into the mantle where high pressure and temperature conditions allow it to combine metamorphically with SiO to form CaSiO and CO, which is released from the interior into the atmosphere via volcanism, thermal vents in the ocean, or soda springs, which are natural springs that contain carbon dioxide gas or soda water:
This final step returns the second CO molecule to the atmosphere and closes the inorganic carbon budget. 99.6% of all carbon on Earth (equating to roughly 10 billion tons of carbon) is sequestered in the longterm rock reservoir. And essentially all carbon has spent time in the form of carbonate. By contrast, only 0.002% of carbon exists in the biosphere. | 0 | Theoretical and Fundamental Chemistry |
Flutamide has been found to be effective in the treatment of hirsutism (excessive body/facial hair growth) in numerous studies. It possesses moderate effectiveness for this indication, and the overall quality of the evidence is considered to be moderate. The medication shows equivalent or superior effectiveness to other antiandrogens including spironolactone, cyproterone acetate, and finasteride in the treatment of hirsutism, although its relatively high risk of hepatotoxicity makes it unfavorable compared to these other options. It has been used to treat hirsutism at dosages ranging from 62.5 mg/day to 750 mg/day. A study found that multiple dosages of flutamide significantly reduced hirsutism in women with polycystic ovary syndrome and that there were no significant differences in the effectiveness for dosages of 125 mg/day, 250 mg/day, and 375 mg/day. In addition, a study found that combination of 125 mg/day flutamide with finasteride was no more effective than 125 mg/day flutamide alone in the treatment of hirsutism. These findings support the use of flutamide at lower doses for hirsutism without loss of effectiveness, which may help to lower the risk of hepatotoxicity. However, the risk has been found to remain even at very low doses. | 0 | Theoretical and Fundamental Chemistry |
Molecular recognition plays an important role in biological systems and is observed in between receptor-ligand, antigen-antibody, DNA-protein, sugar-lectin, RNA-ribosome, etc. An important example of molecular recognition is the antibiotic vancomycin that selectively binds with the peptides with terminal D-alanyl-D-alanine in bacterial cells through five hydrogen bonds. The vancomycin is lethal to the bacteria since once it has bound to these particular peptides they are unable to be used to construct the bacteria's cell wall. | 0 | Theoretical and Fundamental Chemistry |
Although the most common class of pincer ligands features PCP donor sets, variations have been developed where the phosphines are replaced by thioethers and tertiary amines. Many pincer ligands also feature nitrogenous donors at the central coordinating group position (see figure), such as pyridines.
An easily prepared pincer ligand is POCOP. Many tridentate ligands types occupy three contiguous, coplanar coordination sites. The most famous such ligand is terpyridine (“terpy”). Terpy and its relatives lack the steric bulk of the two terminal donor sites found in traditional pincer ligands.
Metal pincer complexes are often prepared through C-H bond activation.
Ni(II) N,N,N pincer complexes are active in Kumada, Sonogashira, and Suzuki-Miyaura coupling reactions with unactivated alkyl halides. | 0 | Theoretical and Fundamental Chemistry |
The main functions of detonation spray coatings are to protect against corrosion (due to low oxygen content), abrasion and adhesion under low load. This means that detonation spraying produces hard durable coatings that are suitable for:
* Various components of general machinery: shafts, seals, bushings, bearings, seals
* Aviation:
** rotor and stator blades
**engine components
** guide rails
* Oil and gas industry:
** bushings and sealing rings of ESP units
** gate valves
** shut-off valves
** working surface of drill tools
* Space rocket industry
* Electronic and radio industry
* Engineering of instruments
* Tools industry
** Tubular drills
** Skiving knives for rubber and plastic
* Shipbuilding industry
* D-gun plated plug and ring gauges | 1 | Applied and Interdisciplinary Chemistry |
As particles and droplets in an aerosol collide with one another, they may undergo coalescence or aggregation. This process leads to a change in the aerosol particle-size distribution, with the mode increasing in diameter as total number of particles decreases. On occasion, particles may shatter apart into numerous smaller particles; however, this process usually occurs primarily in particles too large for consideration as aerosols. | 0 | Theoretical and Fundamental Chemistry |
The column used for GPC is filled with a microporous packing material. The column is filled with the gel. Since the total penetration volume is the maximum volume permeated by the analytes, and there is no retention on the surface of the stationary phase, the total column volume is usually large, relatively to the sample volume. | 0 | Theoretical and Fundamental Chemistry |
Without loss of generality, we can consider only centered profiles, which peak at zero. The Voigt profile is then
where x is the shift from the line center, is the centered Gaussian profile:
and is the centered Lorentzian profile:
The defining integral can be evaluated as:
where Re[w(z)] is the real part of the Faddeeva function evaluated for
In the limiting cases of and then simplifies to and , respectively. | 0 | Theoretical and Fundamental Chemistry |
Reinforced thermoplastic pipe (RTP) is a type of pipe reinforced using a high strength synthetic fibre such as glass, aramid or carbon. It was initially developed in the early 1990s by Wavin Repox, Akzo Nobel and by Tubes d'Aquitaine from France, who developed the first pipes reinforced with synthetic fibre to replace medium pressure steel pipes in response to growing demand for non-corrosive conduits for application in the onshore oil and gas industry, particularly in the Middle East. Typically, the materials used in the construction of the pipe might be Polyethylene (PE), Polyamide-11 or PVDF and may be reinforced with Aramid or Polyester fibre although other combinations are used. More recently the technology of producing such pipe, including the marketing, rests with a few key companies, where it is available in coils up to length. These pipes are available in pressure ratings from . Over the last few years this type of pipe has been acknowledged as a standard alternative solution to steel for oilfield flowline applications by certain oil companies and operators. An advantage of this pipe is also its very fast installation time compared to steel pipe when considering the welding time as average speeds up to /day have been reached installing RTP in ground surface.
Primarily, the pipe provides benefit to applications where steel may rupture due to corrosion and installation time is an issue. | 1 | Applied and Interdisciplinary Chemistry |
The configuration index is a single digit which is the priority number of the ligand trans to the highest priority ligand. (If there are two possibilities the principle of trans difference is applied). As an example, (acetonitrile)dichlorido(pyridine)platinum(II) complex where the Cl ligands may be trans or cis to one another.<br />
The ligand priority numbers are, applying the CIP rules:
*two chlorides of priority number 1
*acetonitrile priority 2
*pyridine priority 3
In the trans case the configuration index is 1 giving the name(SP-4-1)-(acetonitrile)dichlorido(pyridine)platinum(II).<br />
In the cis case both of the organic ligands are trans to a chloride so to choose the trans difference is considered and the greater is between 1 and three therefore the name is (SP-4-3)-(acetonitrile)dichlorido(pyridine)platinum(II). | 0 | Theoretical and Fundamental Chemistry |
It has been found that Arc may have been acquired by animals more than once. While Arc seems to be closely related among all tetrapods, the versions of Arc found in fruit flies (Drosophila melanogaster), silkworms (Bombyx mori), and Argentine ants (Linepithema humile) may have been transferred to a common ancestor of these insects by another event. | 1 | Applied and Interdisciplinary Chemistry |
Laser Doppler velocimetry is often chosen over other forms of flow measurement because the equipment can be outside of the flow being measured and therefore has no effect on the flow. Some typical applications include the following:
*Wind tunnel velocity experiments for testing aerodynamics of aircraft, missiles, cars, trucks, trains, and buildings and other structures
*Velocity measurements in water flows (research in general hydrodynamics, ship hull design, rotating machinery, pipe flows, channel flow, etc.)
*Fuel injection and spray research where there is a need to measure velocities inside engines or through nozzles
*Environmental research (combustion research, wave dynamics, coastal engineering, tidal modeling, river hydrology, etc.).
One disadvantage has been that laser Doppler velocimetry sensors are range-dependent; they have to be calibrated minutely and the distances where they measure has to be precisely defined. This distance restriction has recently been at least partially overcome with a new sensor that is range independent. | 1 | Applied and Interdisciplinary Chemistry |
DLI affects many plant traits. Generalised dose-response curves show that DLI is particularly limiting individual plant growth and functioning below 5 mol·m·d, whereas most traits approach saturation beyond a DLI of 20 mol·m·d. Although not all plants respond in the same way and different wavelengths have various effects, a range of general trends are found: | 0 | Theoretical and Fundamental Chemistry |
The marine biological pump depends on a number of key pools, components and processes that influence its functioning. There are four main pools of carbon in the ocean.
* Dissolved inorganic carbon (DIC) is the largest pool. It constitutes around 38,000 Pg C and includes dissolved carbon dioxide (CO), bicarbonate (), carbonate (), and carbonic acid (). The equilibrium between carbonic acid and carbonate determines the pH of the seawater. Carbon dioxide dissolves easily in water and its solubility is inversely related to temperature. Dissolved CO is taken up in the process of photosynthesis, and can reduce the partial pressure of CO in the seawater, favouring drawdown from the atmosphere. The reverse process respiration, releases CO back into the water, can increase partial pressure of CO in the seawater, favouring release back to the atmosphere. The formation of calcium carbonate by organisms such as coccolithophores has the effect of releasing CO into the water.
* Dissolved organic carbon (DOC) is the next largest pool at around 662 Pg C. DOC can be classified according to its reactivity as refractory, semi-labile or labile. The labile pool constitutes around 0.2 Pg C, is bioavailable, and has a high production rate (~ 15−25 Pg C y). The refractory component is the biggest pool (~642 Pg C ± 32; but has a very low turnover rate (0.043 Pg C y). The turnover time for refractory DOC is thought to be greater than 1000 years.
* Particulate organic carbon (POC) constitutes around 2.3 Pg C, and is relatively small compared with DIC and DOC. Though small in size, this pool is highly dynamic, having the highest turnover rate of any organic carbon pool on the planet. Driven by primary production, it produces around 50 Pg C y globally. It can be separated into living (e.g. phytoplankton, zooplankton, bacteria) and non-living (e.g. detritus) material. Of these, the phytoplankton carbon is particularly important, because of its role in marine primary production, and also because it serves as the food resource for all the larger organisms in the pelagic ecosystem.
* Particulate inorganic carbon (PIC) is the smallest of the pools at around 0.03 Pg C. It is present in the form of calcium carbonate (CaCO) in particulate form, and impacts the carbonate system and pH of the seawater. Estimates for PIC production are in the region of 0.8–1.4 Pg C y, with at least 65% of it being dissolved in the upper water column, the rest contributing to deep sediments. Coccolithophores and foraminifera are estimated to be the dominant sources of PIC in the open ocean. The PIC pool is of particular importance due to its role in the ocean carbonate system, and in facilitating the export of carbon to the deep ocean through the carbonate pump, whereby PIC is exported out of the photic zone and deposited in the bottom sediments. | 0 | Theoretical and Fundamental Chemistry |
For a two-jet final state, a useful measure of acoplanarity is
where are the azimuthal angles of the final state jets with respect to the beam line.
An alternative measure of acoplanarity which is infrared safe and which works for broad jets of many particles is given by
where are the momenta of the final state particles and are the components of these momenta perpendicular to a plane chosen such that A is minimized.
In the case of two coplanar final state particles, the plane which minimizes A would contain the paths of both particles and the beamline, and A would equal 0. | 0 | Theoretical and Fundamental Chemistry |
The simplest application of this technique is to assess whether a given protein binds to a region of interest within a DNA molecule. Polymerase chain reaction (PCR) amplify and label region of interest that contains a potential protein-binding site, ideally amplicon is between 50 and 200 base pairs in length. Add protein of interest to a portion of the labeled template DNA; a portion should remain separate without protein, for later comparison. Add a cleavage agent to both portions of DNA template. The cleavage agent is a chemical or enzyme that will cut at random locations in a sequence independent manner. The reaction should occur just long enough to cut each DNA molecule in only one location. A protein that specifically binds a region within the DNA template will protect the DNA it is bound to from the cleavage agent. Run both samples side by side on a polyacrylamide gel electrophoresis. The portion of DNA template without protein will be cut at random locations, and thus when it is run on a gel, will produce a ladder-like distribution. The DNA template with the protein will result in ladder distribution with a break in it, the "footprint", where the DNA has been protected from the cleavage agent.
Note: Maxam-Gilbert chemical DNA sequencing can be run alongside the samples on the polyacrylamide gel to allow the prediction of the exact location of ligand binding site. | 1 | Applied and Interdisciplinary Chemistry |
According to the school, a paramanu (atom) is an indestructible particle of matter. The atom is indivisible because it is a state at which no measurement can be attributed. They used invariance arguments to determine properties of the atoms. It also stated that anu can have two states—absolute rest and a state of motion.
They postulated four different kinds of atoms: two with mass, and two without. Each substance is supposed to consist of all four kinds of atoms. Atoms can be combined into s (triads) and (dyad)before they aggregate into bodies of a kind that can be perceived. Each (atom) possesses its own distinct (individuality)
The measure of the partless atoms is known as parimaṇḍala parimāṇa. It is eternal and it cannot generate the measure of any other substance. Its measure is its own absolutely. | 1 | Applied and Interdisciplinary Chemistry |
Two of the main functions of carbohydrates are energy storage and providing structure. One of the common sugars known as glucose is a carbohydrate, but not all carbohydrates are sugars. There are more carbohydrates on Earth than any other known type of biomolecule; they are used to store energy and genetic information, as well as play important roles in cell to cell interactions and communications.
The simplest type of carbohydrate is a monosaccharide, which among other properties contains carbon, hydrogen, and oxygen, mostly in a ratio of 1:2:1 (generalized formula CHO, where n is at least 3). Glucose (CHO) is one of the most important carbohydrates; others include fructose (CHO), the sugar commonly associated with the sweet taste of fruits, and deoxyribose (CHO), a component of DNA. A monosaccharide can switch between acyclic (open-chain) form and a cyclic form. The open-chain form can be turned into a ring of carbon atoms bridged by an oxygen atom created from the carbonyl group of one end and the hydroxyl group of another. The cyclic molecule has a hemiacetal or hemiketal group, depending on whether the linear form was an aldose or a ketose.
In these cyclic forms, the ring usually has 5 or 6 atoms. These forms are called furanoses and pyranoses, respectively—by analogy with furan and pyran, the simplest compounds with the same carbon-oxygen ring (although they lack the carbon-carbon double bonds of these two molecules). For example, the aldohexose glucose may form a hemiacetal linkage between the hydroxyl on carbon 1 and the oxygen on carbon 4, yielding a molecule with a 5-membered ring, called glucofuranose. The same reaction can take place between carbons 1 and 5 to form a molecule with a 6-membered ring, called glucopyranose. Cyclic forms with a 7-atom ring called heptoses are rare.
Two monosaccharides can be joined by a glycosidic or ester bond into a disaccharide through a dehydration reaction during which a molecule of water is released. The reverse reaction in which the glycosidic bond of a disaccharide is broken into two monosaccharides is termed hydrolysis. The best-known disaccharide is sucrose or ordinary sugar, which consists of a glucose molecule and a fructose molecule joined. Another important disaccharide is lactose found in milk, consisting of a glucose molecule and a galactose molecule. Lactose may be hydrolysed by lactase, and deficiency in this enzyme results in lactose intolerance.
When a few (around three to six) monosaccharides are joined, it is called an oligosaccharide (oligo- meaning "few"). These molecules tend to be used as markers and signals, as well as having some other uses. Many monosaccharides joined form a polysaccharide. They can be joined in one long linear chain, or they may be branched. Two of the most common polysaccharides are cellulose and glycogen, both consisting of repeating glucose monomers. Cellulose is an important structural component of plants cell walls and glycogen' is used as a form of energy storage in animals.
Sugar can be characterized by having reducing or non-reducing ends. A reducing end of a carbohydrate is a carbon atom that can be in equilibrium with the open-chain aldehyde (aldose) or keto form (ketose). If the joining of monomers takes place at such a carbon atom, the free hydroxy group of the pyranose or furanose form is exchanged with an OH-side-chain of another sugar, yielding a full acetal. This prevents opening of the chain to the aldehyde or keto form and renders the modified residue non-reducing. Lactose contains a reducing end at its glucose moiety, whereas the galactose moiety forms a full acetal with the C4-OH group of glucose. Saccharose does not have a reducing end because of full acetal formation between the aldehyde carbon of glucose (C1) and the keto carbon of fructose (C2). | 1 | Applied and Interdisciplinary Chemistry |
Research has shown that cells undergoing rapid growth have shown changes in their metabolism. These changes are observed with regards to glucose metabolism. The changes in metabolism occur because the rate of metabolism controls various signal transduction pathways that coordinate the activation of transcription factors as well as determining cell-cycle progress.
Growing cells require synthesis of new nucleotides, membranes and protein components. These materials can be obtained from carbon metabolism (e.g. glucose metabolism) or from peripheral metabolism. The enhanced flux observed in abnormally growing cells is brought about by high glucose uptake. | 1 | Applied and Interdisciplinary Chemistry |
A gaur that died of natural causes had some skin cells frozen and added to the San Diego Frozen Zoo. Eight years later, DNA from these cells was inserted into a domestic-cow egg to create an embryo (trans-species cloning), which was then implanted in a domestic cow (Bos taurus). On 8 January 2001, the gaur, named Noah, was born in Sioux Center, Iowa. Noah was initially healthy, but the next day, he came down with clostridial enteritis, and died of dysentery within 48 hours of birth. This is not uncommon in uncloned animals, and the researchers did not think it was due to the cloning. | 1 | Applied and Interdisciplinary Chemistry |
To capture genomic regions of interest using in-solution capture, a pool of custom oligonucleotides (probes) is synthesized and hybridized in solution to a fragmented genomic DNA sample. The probes (labeled with beads) selectively hybridize to the genomic regions of interest after which the beads (now including the DNA fragments of interest) can be pulled down and washed to clear excess material. The beads are then removed and the genomic fragments can be sequenced allowing for selective DNA sequencing of genomic regions (e.g., exons) of interest.
This method was developed to improve on the hybridization capture target-enrichment method. In solution capture (as opposed to hybrid capture) there is an excess of probes to target regions of interest over the amount of template required. The optimal target size is about 3.5 megabases and yields excellent sequence coverage of the target regions. The preferred method is dependent on several factors including: number of base pairs in the region of interest, demands for reads on target, equipment in house, etc. | 1 | Applied and Interdisciplinary Chemistry |
There has been controversy over energy-balance messages that downplay energy intake being promoted by food industry groups. | 1 | Applied and Interdisciplinary Chemistry |
Interplanetary contamination occurs when a planetary body is biologically contaminated by a space probe or spacecraft, either deliberately or unintentionally. This can work both on arrival to the foreign planetary body and upon return to Earth. | 0 | Theoretical and Fundamental Chemistry |
Halocarbons are less prolific compounds developed for diverse uses throughout industry; for example as solvents and refrigerants. Nevertheless, the buildup of relatively small concentrations (parts per trillion) of chlorofluorocarbon, hydrofluorocarbon, and perfluorocarbon gases in the atmosphere is responsible for about 10% of the total direct radiative forcing from all long-lived greenhouse gases (year 2019); which includes forcing from the much larger concentrations of carbon dioxide and methane. Chlorofluorocarbons also cause stratospheric ozone depletion. International efforts are ongoing under the Montreal Protocol and Kyoto Protocol to control rapid growth in the industrial manufacturing and use of these environmentally potent gases. For some applications more benign alternatives such as hydrofluoroolefins have been developed and are being gradually introduced. | 0 | Theoretical and Fundamental Chemistry |
In the sandwich hybridization ELISA assay format, the antigen ligand and antibodies in ELISA are replaced with a nucleic acid analyte, complementary oligonucleotide capture and detection probes.
Generally, in the case of nucleic acid hybridization, monovalent salt concentration and temperature are controlled for hybridization and wash stringency, contrary to a traditional ELISA, where the salt concentration will usually be fixed for the binding and wash steps (i.e. PBS or TBS). Thus, optimal salt concentration in hybridization assays varies dependent upon the length and base composition of the analyte, capture and detection probes. | 1 | Applied and Interdisciplinary Chemistry |
From 1761 onwards, copper plating had been fitted to the undersides of Royal Navy ships to protect the wood from attack by shipworms. However, the copper bottoms were gradually corroded by exposure to the salt water. Between 1823 and 1825, Davy, assisted by Michael Faraday, attempted to protect the copper by electrochemical means. He attached to the copper sacrificial pieces of zinc or iron, which provided cathodic protection to the host metal. It was discovered, however, that protected copper became foul quickly, i.e. pieces of weed and/or marine creatures became attached to the hull, which had a detrimental effect on the handling of the ship.
The Navy Board approached Davy in 1823, asking for help with the corrosion. Davy conducted a number of tests in Portsmouth Dockyard, which led to the Navy Board adopting the use of Davys "protectors". By 1824, it had become apparent that fouling of the copper bottoms was occurring on the majority of protected ships. By the end of 1825, the Admiralty ordered the Navy Board to cease fitting the protectors to sea-going ships, and to remove those that had already been fitted. Davys scheme was seen as a public failure, despite success of the corrosion protection as such. As Frank A. J. L. James explains, "[Because] the poisonous salts from [corroding] copper were no longer entering the water, there was nothing to kill the barnacles and the like in the vicinity of a ship. This meant that barnacles [and the like] could now attach themselves to the bottom of a vessel, thus impeding severely its steerage, much to the anger of the captains who wrote to the Admiralty to complain about Davy's protectors." | 1 | Applied and Interdisciplinary Chemistry |
Moving wire IRMS is useful for analyzing carbon-13 ratios of compounds in a solution, such as after purification by liquid chromatography. The solution (or outflow from the chromatography) is dried onto a nickel or stainless steel wire. After the residue is deposited on the wire, it enters a furnace where the sample is converted to CO and water by combustion. The gas stream finally enters a capillary, is dried, ionized, and analyzed. This process allows a mixture of compounds to be purified and analyzed continuously, which can decrease the analysis time by a factor of four. Moving wire IRMS is quite sensitive, and samples containing as little as 1 nanomole of carbon can yield precise (within 1‰) results. | 0 | Theoretical and Fundamental Chemistry |
The starting of Townsend discharge sets the upper limit to the blocking voltage a glow discharge gas-filled tube can withstand. This limit is the Townsend discharge breakdown voltage, also called ignition voltage of the tube.
The occurrence of Townsend discharge, leading to glow discharge breakdown shapes the current–voltage characteristic of a gas-discharge tube such as a neon lamp in a way such that it has a negative differential resistance region of the S-type. The negative resistance can be used to generate electrical oscillations and waveforms, as in the relaxation oscillator whose schematic is shown in the picture on the right. The sawtooth shaped oscillation generated has frequency
:where
:* is the glow discharge breakdown voltage,
:* is the Townsend discharge breakdown voltage,
:*, and are respectively the capacitance, the resistance and the supply voltage of the circuit.
:Since temperature and time stability of the characteristics of gas diodes and neon lamps is low, and also the statistical dispersion of breakdown voltages is high, the above formula can only give a qualitative indication of what the real frequency of oscillation is. | 0 | Theoretical and Fundamental Chemistry |
Vertebrate genes and proteins have names (typically strings of words) and symbols, which are short identifiers (typically 3 to 8 characters). For example, the gene cytotoxic T-lymphocyte-associated protein 4 has the HGNC symbol CTLA4. These symbols are usually, but not always, coined by contraction or acronymic abbreviation of the name. They are pseudo-acronyms, however, in the sense that they are complete identifiers by themselves—short names, essentially. They are synonymous with (rather than standing for) the gene/protein name (or any of its aliases), regardless of whether the initial letters "match". For example, the symbol for the gene v-akt murine thymoma viral oncogene homolog 1, which is AKT1, cannot be said to be an acronym for the name, and neither can any of its various synonyms, which include AKT, PKB, PRKBA, and RAC. Thus, the relationship of a gene symbol to the gene name is functionally the relationship of a nickname to a formal name (both are complete identifiers)—it is not the relationship of an acronym to its expansion. In this sense they are similar to the symbols for units of measurement in the SI system (such as km for the kilometre), in that they can be viewed as true logograms rather than just abbreviations. Sometimes the distinction is academic, but not always. Although it is not wrong to say that "VEGFA" is an acronym standing for "vascular endothelial growth factor A", just as it is not wrong that "km" is an abbreviation for "kilometre", there is more to the formality of symbols than those statements capture.
The root portion of the symbols for a gene family (such as the "SERPIN" root in SERPIN1, SERPIN2, SERPIN3, and so on) is called a root symbol. | 1 | Applied and Interdisciplinary Chemistry |
The Emeritus Group at MPI-Marburg is headed by renowned biochemist and Gottfried Wilhelm Leibniz Prize recipient, Rudolf K. Thauer, who was also the founding director of the institute when it was established in 1991. The scientific focus of the group is on the biochemistry of methanogenic archaea, methanotrophic archaea and saccharolytic clostridia. The following specific topics are being addressed:
* Hydrogen activation
* Methane formation and anaerobic methane oxidation
* Ferredoxin reduction | 0 | Theoretical and Fundamental Chemistry |
Significant nonspecific protein adsorption during implantation can cause adverse effects. However, some proteins can be beneficial in stabilizing the implant by reducing micro-motion and implant migration, as well as improving the signal quality through increased neuron connection; improving the long-term performance. Instead of relying on the native cells to secrete these proteins, they can be added to the surface of the material prior to implantation. The surface modification of biomaterials with proteins has been done with great success in various regions of the body. However, since the anatomy of the brain is different from the rest of the body, the types of proteins that must be used in these applications vary from those used elsewhere. Proteins like laminin that promotes neuronal outgrowth and L1 that promotes axonal outgrowth have shown great promise in surface modification applications; L1 more so than laminin because of the decreased attachment associated with astrocytes – the cells responsible for glial scar formation.
Proteins are typically added to the material surface via self-assembled monolayer (SAM) formation. | 0 | Theoretical and Fundamental Chemistry |
More powerful gamma rays from very distant quasars and closer active galaxies are thought to have a gamma ray production source similar to a particle accelerator. High energy electrons produced by the quasar, and subjected to inverse Compton scattering, synchrotron radiation, or bremsstrahlung, are the likely source of the gamma rays from those objects. It is thought that a supermassive black hole at the center of such galaxies provides the power source that intermittently destroys stars and focuses the resulting charged particles into beams that emerge from their rotational poles. When those beams interact with gas, dust, and lower energy photons they produce X-rays and gamma rays. These sources are known to fluctuate with durations of a few weeks, suggesting their relatively small size (less than a few light-weeks across). Such sources of gamma and X-rays are the most commonly visible high intensity sources outside the Milky Way galaxy. They shine not in bursts (see illustration), but relatively continuously when viewed with gamma ray telescopes. The power of a typical quasar is about 10 watts, a small fraction of which is gamma radiation. Much of the rest is emitted as electromagnetic waves of all frequencies, including radio waves. | 0 | Theoretical and Fundamental Chemistry |
1) The elastic modulus of the implant is decreased, allowing the implant to better match the elastic modulus of the bone. The elastic modulus of cortical bone (~18 GPa) is significantly lower than typical solid titanium or steel implants (110 GPa and 210 GPa, respectively), causing the implant take up a disproportionate amount of the load applied to the appendage, leading to an effect called stress shielding.
2) Porosity enables osteoblastic cells to grow into the pores of implants. Cells can span gaps of smaller than 75 microns and grow into pores larger than 200 microns. Bone ingrowth is a favorable effect, as it anchors the cells into the implant, increasing the strength of the bone-implant interface. More load is transferred from the implant to the bone, reducing stress shielding effects. The density of the bone around the implant is likely to be higher due to the increased load applied to the bone. Bone ingrowth reduces the likelihood of the implant loosening over time because stress shielding and corresponding bone resorption over extended timescales is avoided. Porosity of greater than 40% is favorable to facilitate sufficient anchoring of the osteoblastic cells. | 1 | Applied and Interdisciplinary Chemistry |
Metabolic control analysis (MCA) is a mathematical framework for describing
metabolic, signaling, and genetic pathways. MCA quantifies how variables, such as fluxes and species concentrations, depend on network parameters.
In particular, it is able to describe how network-dependent properties,
called control coefficients, depend on local properties called elasticities or Elasticity Coefficients.
MCA was originally developed to describe the control in metabolic pathways
but was subsequently extended to describe signaling and genetic networks. MCA has sometimes also been referred to as Metabolic Control Theory, but this terminology was rather strongly opposed by Henrik Kacser, one of the founders.
More recent work has shown that MCA can be mapped directly on to classical control theory and are as such equivalent.
Biochemical systems theory (BST) is a similar formalism, though with rather different objectives. Both are evolutions of an earlier theoretical analysis by Joseph Higgins.
Chemical reaction network theory is another theoretical framework that has overlap with both MCA and BST but is considerably more mathematically formal in its approach. It's emphasis is primarily on dynamic stability criteria and related theorems associated with mass-action networks. In more recent years the field has also developed a sensitivity analysis which is similar if not identical to MCA and BST. | 1 | Applied and Interdisciplinary Chemistry |
In pattern comparison the general shapes of electropherograms of different samples are compared for changes such as presence-absence of peaks between treatments, their relative size, etc. | 1 | Applied and Interdisciplinary Chemistry |
Calcium hydroxide is typically added to a bundle of areca nut and betel leaf called "paan" to keep the alkaloid stimulants chemically available to enter the bloodstream via sublingual absorption.
It is used in making naswar (also known as nass or niswar), a type of dipping tobacco made from fresh tobacco leaves, calcium hydroxide (chuna or soon), and wood ash. It is consumed most in the Pathan diaspora, Afghanistan, Pakistan, India and Bangladesh. Villagers also use calcium hydroxide to paint their mud houses in Afghanistan, Pakistan and India. | 0 | Theoretical and Fundamental Chemistry |
Fluorescence polarization immunoassay (FPIA) is a class of in vitro biochemical test used for rapid detection of antibody or antigen in sample. FPIA is a competitive homogenous assay, that consists of a simple prepare and read method, without the requirement of separation or washing steps.
The basis of the assay is fluorescence anisotropy, also known as fluorescence polarization. If a fluorescent molecule is stationary and exposed to plane-polarized light, it will become excited and consequently emit radiation back to the polarized-plane. However, if the excited fluorescent molecule is in motion (rotational or translational) during the fluorescent lifetime, it will emit light in a different direction than the excitation plane. The fluorescent lifetime is the amount of time between the absorption moment and the fluorescent emission moment.
Typically, the rate at which a molecule rotates is indicative of its size. When a fluorescent-labelled molecule (tracer) binds to another molecule the rotational motion will change, resulting in an altered intensity of plane-polarized light, which results in altered fluorescence polarization. Fluorescence polarization immunoassays employ a fluorophore bound antigen that when bound to the antibody of interest, will increase fluorescence polarization. The change in polarization is proportional to the amount of antigen in sample, and is measured by a fluorescence polarization analyzer. | 1 | Applied and Interdisciplinary Chemistry |
A quantity of radioactive waste typically consists of a number of radionuclides, which are unstable isotopes of elements that undergo decay and thereby emit ionizing radiation, which is harmful to humans and the environment. Different isotopes emit different types and levels of radiation, which last for different periods of time. | 0 | Theoretical and Fundamental Chemistry |
Aerobic desaturation is the most widespread pathway for the synthesis of unsaturated fatty acids. It is utilized in all eukaryotes and some prokaryotes. This pathway utilizes desaturases to synthesize unsaturated fatty acids from full-length saturated fatty acid substrates. All desaturases require oxygen and ultimately consume NADH even though desaturation is an oxidative process. Desaturases are specific for the double bond they induce in the substrate. In Bacillus subtilis, the desaturase, Δ-Des, is specific for inducing a cis-double bond at the Δ position. Saccharomyces cerevisiae contains one desaturase, Ole1p, which induces the cis-double bond at Δ.
In mammals the aerobic desaturation is catalyzed by a complex of three membrane-bound enzymes (NADH-cytochrome b reductase, cytochrome b, and a desaturase). These enzymes allow molecular oxygen, , to interact with the saturated fatty acyl-CoA chain, forming a double bond and two molecules of water, . Two electrons come from NADH + and two from the single bond in the fatty acid chain. These mammalian enzymes are, however, incapable of introducing double bonds at carbon atoms beyond C-9 in the fatty acid chain..) Hence mammals cannot synthesize linoleate or linolenate (which have double bonds at the C-12 (= Δ), or the C-12 and C-15 (= Δ and Δ) positions, respectively, as well as at the Δ position), nor the polyunsaturated, 20-carbon arachidonic acid that is derived from linoleate. These are all termed essential fatty acids, meaning that they are required by the organism, but can only be supplied via the diet. (Arachidonic acid is the precursor the prostaglandins which fulfill a wide variety of functions as local hormones.) | 1 | Applied and Interdisciplinary Chemistry |
Exemestane is indicated for the adjuvant treatment of postmenopausal women with estrogen-receptor positive early breast cancer who have received two to three years of tamoxifen and are switched to it for completion of a total of five consecutive years of adjuvant hormonal therapy.
US FDA approval was in October 1999.
Exemestane is also indicated for the treatment of advanced breast cancer in postmenopausal women whose disease has progressed following tamoxifen therapy.
For premenopausal women with hormone-receptor–positive breast cancer, adjuvant treatment with ovarian suppression plus the aromatase inhibitor exemestane, as compared with ovarian suppression plus tamoxifen, provides a new treatment option that reduces the risk of recurrence. The TEXT and SOFT trials demonstrated improved disease free survival in patients treated with exemestane and ovarian suppression compared to the tamoxifen and ovarian suppression group. Premenopausal women who receive ovarian suppression may now benefit from an aromatase inhibitor, a class of drugs that until now has been recommended only for postmenopausal women. | 0 | Theoretical and Fundamental Chemistry |
Transcription fidelity is achieved through multiple mechanisms. RNA polymerases select correct nucleoside triphosphate (NTP) substrate to prevent transcription errors. Only the NTP which correctly base pairs with the coding base in the DNA is admitted to the active center. RNA polymerase performs two known proof reading functions to detect and remove misincorporated nucleotides: pyrophosphorylytic editing and hydrolytic editing. The former removes the incorrectly inserted ribonucleotide by a simple reversal of the polymerization reaction, while the latter involves backtracking of the polymerase and cleaving of a segment of error-containing RNA product. Elongation factor TFIIS (; TCEA1, TCEA2, TCEA3) stimulates an inherent ribonuclease activity in the polymerase, allowing the removal of misincorporated bases through limited local RNA degradation. Note that all reactions (phosphodiester bond synthesis, pyrophosphorolysis, phosphodiester bond hydrolysis) are performed by RNA polymerase by using a single active center. | 1 | Applied and Interdisciplinary Chemistry |
Stokes law is the basis of the falling-sphere viscometer, in which the fluid is stationary in a vertical glass tube. A sphere of known size and density is allowed to descend through the liquid. If correctly selected, it reaches terminal velocity, which can be measured by the time it takes to pass two marks on the tube. Electronic sensing can be used for opaque fluids. Knowing the terminal velocity, the size and density of the sphere, and the density of the liquid, Stokes law can be used to calculate the viscosity of the fluid. A series of steel ball bearings of different diameters are normally used in the classic experiment to improve the accuracy of the calculation. The school experiment uses glycerine or golden syrup as the fluid, and the technique is used industrially to check the viscosity of fluids used in processes. Several school experiments often involve varying the temperature and/or concentration of the substances used in order to demonstrate the effects this has on the viscosity. Industrial methods include many different oils, and polymer liquids such as solutions.
The importance of Stokes' law is illustrated by the fact that it played a critical role in the research leading to at least three Nobel Prizes.
Stokes' law is important for understanding the swimming of microorganisms and sperm; also, the sedimentation of small particles and organisms in water, under the force of gravity.
In air, the same theory can be used to explain why small water droplets (or ice crystals) can remain suspended in air (as clouds) until they grow to a critical size and start falling as rain (or snow and hail). Similar use of the equation can be made in the settling of fine particles in water or other fluids. | 1 | Applied and Interdisciplinary Chemistry |
Many different color reagents have been developed for determining the concentrations of different substances. For example, Nessler's reagent can be used to determine the concentration of a solution of ammonia. | 0 | Theoretical and Fundamental Chemistry |
In scientific visualization a streamlet is used to visualize flows. It is essentially a short streamline segment. Normally the length of a streamlet is proportional to the flow magnitude at its seed point. | 1 | Applied and Interdisciplinary Chemistry |
The Kursk submarine disaster was initially thought to have been caused by a faulty Shkval supercavitating torpedo, though later evidence points to a faulty 65-76 torpedo. | 1 | Applied and Interdisciplinary Chemistry |
Passive ventilation is the process of supplying air to and removing air from an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure differences arising from natural forces.
There are two types of natural ventilation occurring in buildings: wind driven ventilation and buoyancy-driven ventilation. Wind driven ventilation arises from the different pressures created by wind around a building or structure, and openings being formed on the perimeter which then permit flow through the building. Buoyancy-driven ventilation occurs as a result of the directional buoyancy force that results from temperature differences between the interior and exterior.
Since the internal heat gains which create temperature differences between the interior and exterior are created by natural processes, including the heat from people, and wind effects are variable, naturally ventilated buildings are sometimes called "breathing buildings". | 1 | Applied and Interdisciplinary Chemistry |
A list of nuclear medicine radiopharmaceuticals follows. Some radioisotopes are used in ionic or inert form without attachment to a pharmaceutical; these are also included. There is a section for each radioisotope with a table of radiopharmaceuticals using that radioisotope. The sections are ordered alphabetically by the English name of the radioisotope. Sections for the same element are then ordered by atomic mass number. | 0 | Theoretical and Fundamental Chemistry |
If the carbon in freshwater is partly acquired from aged carbon, such as rocks, then the result will be a reduction in the / ratio in the water. For example, rivers that pass over limestone, which is mostly composed of calcium carbonate, will acquire carbonate ions. Similarly, groundwater can contain carbon derived from the rocks through which it has passed. These rocks are usually so old that they no longer contain any measurable , so this carbon lowers the / ratio of the water it enters, which can lead to apparent ages of thousands of years for both the affected water and the plants and freshwater organisms that live in it. This is known as the hard water effect because it is often associated with calcium ions, which are characteristic of hard water; other sources of carbon such as humus can produce similar results, and can also reduce the apparent age if they are of more recent origin than the sample. The effect varies greatly and there is no general offset that can be applied; additional research is usually needed to determine the size of the offset, for example by comparing the radiocarbon age of deposited freshwater shells with associated organic material.
Volcanic eruptions eject large amounts of carbon into the air. The carbon is of geological origin and has no detectable , so the / ratio in the vicinity of the volcano is depressed relative to surrounding areas. Dormant volcanoes can also emit aged carbon. Plants that photosynthesize this carbon also have lower / ratios: for example, plants in the neighbourhood of the Furnas caldera in the Azores were found to have apparent ages that ranged from 250 years to 3320 years. | 0 | Theoretical and Fundamental Chemistry |
The study of action potentials has required the development of new experimental methods. The initial work, prior to 1955, was carried out primarily by Alan Lloyd Hodgkin and Andrew Fielding Huxley, who were, along John Carew Eccles, awarded the 1963 Nobel Prize in Physiology or Medicine for their contribution to the description of the ionic basis of nerve conduction. It focused on three goals: isolating signals from single neurons or axons, developing fast, sensitive electronics, and shrinking electrodes enough that the voltage inside a single cell could be recorded.
The first problem was solved by studying the giant axons found in the neurons of the squid (Loligo forbesii and Doryteuthis pealeii, at the time classified as Loligo pealeii). These axons are so large in diameter (roughly 1 mm, or 100-fold larger than a typical neuron) that they can be seen with the naked eye, making them easy to extract and manipulate. However, they are not representative of all excitable cells, and numerous other systems with action potentials have been studied.
The second problem was addressed with the crucial development of the voltage clamp, which permitted experimenters to study the ionic currents underlying an action potential in isolation, and eliminated a key source of electronic noise, the current I associated with the capacitance C of the membrane. Since the current equals C times the rate of change of the transmembrane voltage V, the solution was to design a circuit that kept V fixed (zero rate of change) regardless of the currents flowing across the membrane. Thus, the current required to keep V at a fixed value is a direct reflection of the current flowing through the membrane. Other electronic advances included the use of Faraday cages and electronics with high input impedance, so that the measurement itself did not affect the voltage being measured.
The third problem, that of obtaining electrodes small enough to record voltages within a single axon without perturbing it, was solved in 1949 with the invention of the glass micropipette electrode, which was quickly adopted by other researchers. Refinements of this method are able to produce electrode tips that are as fine as 100 Å (10 nm), which also confers high input impedance. Action potentials may also be recorded with small metal electrodes placed just next to a neuron, with neurochips containing EOSFETs, or optically with dyes that are sensitive to Ca or to voltage.
While glass micropipette electrodes measure the sum of the currents passing through many ion channels, studying the electrical properties of a single ion channel became possible in the 1970s with the development of the patch clamp by Erwin Neher and Bert Sakmann. For this discovery, they were awarded the Nobel Prize in Physiology or Medicine in 1991. Patch-clamping verified that ionic channels have discrete states of conductance, such as open, closed and inactivated.
Optical imaging technologies have been developed in recent years to measure action potentials, either via simultaneous multisite recordings or with ultra-spatial resolution. Using voltage-sensitive dyes, action potentials have been optically recorded from a tiny patch of cardiomyocyte membrane. | 0 | Theoretical and Fundamental Chemistry |
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Low-energy electron diffraction (LEED) is a technique for the determination of the surface structure of single-crystalline materials by bombardment with a collimated beam of low-energy electrons (30–200 eV). In this case the Ewald sphere leads to approximately back-reflection, as illustrated in Figure 20, and diffracted electrons as spots on a fluorescent screen as shown in Figure 21; see the main page for more information and references. It has been used to solve a very large number of relatively simple surface structures of metals and semiconductors, plus cases with simple chemisorbants. For more complex cases transmission electron diffraction or surface x-ray diffraction have been used, often combined with scanning tunneling microscopy and density functional theory calculations.
LEED may be used in one of two ways:
# Qualitatively, where the diffraction pattern is recorded and analysis of the spot positions gives information on the symmetry of the surface structure. In the presence of an adsorbate the qualitative analysis may reveal information about the size and rotational alignment of the adsorbate unit cell with respect to the substrate unit cell.
# Quantitatively, where the intensities of diffracted beams are recorded as a function of incident electron beam energy to generate the so-called I–V curves. By comparison with theoretical curves, these may provide accurate information on atomic positions on the surface. | 0 | Theoretical and Fundamental Chemistry |
Joanna V. Clark is an American geoscientist working for Geocontrols Systems Inc on the JETS Contract at NASA Johnson Space Center. She is collaborator on the Sample Analysis at Mars (SAM) and Mars Science Lab (MSL) science teams. Her research includes oxychlorines, chlorides, phyllosilicates, manganese oxides and has also been involved with martian simulant development for In-Situ Resource Utilization. | 0 | Theoretical and Fundamental Chemistry |
Significant ERH technological advancements have occurred over the last five years. Three areas of focus have been: bedrock remediation, 1,4-dioxane and other emerging contaminants, and controlled low temperature heat to enhance other remedial or natural processes. | 1 | Applied and Interdisciplinary Chemistry |
To quantitatively assess changes in the composition of biologic communities, IBIs are developed to accurately reflect the ecological complexity from statistical analysis. There is no one universal IBI, and developing metrics that consistently give accurate assessment of the monitored population requires rigorous testing to confirm its validity for a given subject. Often IBIs are region-specific and require experienced professionals to provide sufficient quality data to correctly assess a score. Because communities naturally vary as do samples collected from a larger population, identifying robust statistics with acceptable variance is an area of active and important research.
This can be a powerful tool to identify systemic impacts on the health of biological systems. IBIs are increasingly involved in the identification of impairment, and confirmation of recovery of impaired waters, in the total maximum daily load process required by the Clean Water Act in the USA.
Unlike chemical testing of water samples, which gives brief snap-shots of chemical concentrations, an IBI captures an integrated net impact on a biological community structure. While the complete absence, particularly sudden disappearance of, suites of indicator species can constitute powerful evidence of a specific pollutant or stress factor, IBIs generally do not resolve a specific cause of impairment.
The IBI concept was formulated by James Karr in 1981. To date IBIs have been developed for fish, algae, macroinvertebrates, pupal exuvia (shed skins of chironomidae), vascular plants, and combinations of these. Comparatively little work has been done to develop IBIs for terrestrial ecosystems. | 1 | Applied and Interdisciplinary Chemistry |
* Bowen, H. J. M., A standard biological material for elementary analysis. In P. W. Sallis (ed.), Proc. of the SAC Conference, Nottingham, UK, pp. 25–31. Cambridge: W. Heffer and Sons, 1965.
* Bowen, H. J. M., Kale as a reference material. In W. R. Wolf (ed.), Biological Reference Materials: Availability, uses and need for validation of nutrient measurement, pp. 3–17. John Wiley & Sons, 1984.
* Stoeppler, M., Wolf, W. R. and Jenks, P. J. (eds.), Reference Materials for Chemical Analysis: Certification, Availability and Proper Usage. Weinheim: Wiley-VCH, 2001. . (See pages 4, 26, 59 & 216.) | 1 | Applied and Interdisciplinary Chemistry |
To perform SCODA concentration of DNA molecules, the sample must be embedded in the separation media (gel) in locations where the electrophoretic field is of optimal intensity. This initial translocation of the sample into the optimal concentration position is referred to as "injection". The optimal position is determined by the gel geometry and location of the SCODA driving electrodes. Initially the sample is located in a buffer solution in the sample chamber, adjacent to the concentration gel. Injection is achieved by the application of a controlled DC electrophoretic field across the sample chamber which results in all charged particles being transferred into the concentration gel. To obtain a good stacking of the sample (i.e. tight DNA band) multiple methods can be employed. One example is to exploit the conductivity ratio between the sample chamber buffer and the concentration gel buffer. If the sample chamber buffer has a low conductivity and the concentration gel buffer has a high conductivity this results in a sharp drop off in electric field at the gel-buffer interface which promotes stacking. | 1 | Applied and Interdisciplinary Chemistry |
The electrochemical reduction of carbon dioxide to various products is usually described as:
The redox potentials for these reactions are similar to that for hydrogen evolution in aqueous electrolytes, thus electrochemical reduction of CO is usually competitive with hydrogen evolution reaction.
Electrochemical methods have gained significant attention:
# at ambient pressure and room temperature;
# in connection with renewable energy sources (see also solar fuel)
# competitive controllability, modularity and scale-up are relatively simple.
The electrochemical reduction or electrocatalytic conversion of CO can produce value-added chemicals such methane, ethylene, ethanol, etc., and the products are mainly dependent on the selected catalysts and operating potentials (applying reduction voltage). A variety of homogeneous and heterogeneous catalysts have been evaluated.
Many such processes are assumed to operate via the intermediacy of metal carbon dioxide complexes. Many processes suffer from high overpotential, low current efficiency, low selectivity, slow kinetics, and/or poor catalyst stability.
The composition of the electrolyte can be decisive. Gas-diffusion electrodes are beneficial. | 1 | Applied and Interdisciplinary Chemistry |
There are three types of reactions that clinopyroxene is involved in and can be used for thermobarometry.
Univariant reactions or displaced equilibria reactions either create or destroy phases within the magma. Each phase will eventually crystalize as a unique mineral. Based on the temperature and pressure conditions, different proportions of these phases will emerge in the final rock. An example reaction is jadeite and quartz reacting to make analbite. Jadeite is a type of pyroxene, so this reaction is used for clinopyroxene barometry.
This particular reaction involves a large change in volume between the reactants and the products, so the reaction is very sensitive to pressure changes.
Exchange Reactions occur when there are minerals with similar structures, and ions switch places with each other within that structure. This is a common method to calculate the temperature because most exchange reactions have a high enthalpy. One example reaction is an exchange of Fe and Mg within garnet and clinopyroxene. That causes pyrope and hedenbergite (pyroxene) to change into almandine and diopside (pyroxene).
Solvus Equilibria reactions occur when two phases dissolve into each other based on the temperature, so it is usually useful for geothermometry. One such reaction is when clinopyroxene and orthopyroxene dissolve into each other. This changes the distribution of calcium and magnesium throughout the mineral. | 0 | Theoretical and Fundamental Chemistry |
Alkaline tide (mal del puerco) refers to a condition, normally encountered after eating a meal, where during the production of hydrochloric acid by the parietal cells in the stomach, the parietal cells secrete bicarbonate ions across their basolateral membranes and into the blood, causing a temporary increase in blood pH.
During hydrochloric acid secretion in the stomach, the gastric parietal cells extract chloride anions, carbon dioxide, water and sodium cations from the blood plasma and in turn release bicarbonate back into the plasma after forming it from carbon dioxide and water constituents. This is to maintain the plasma's electrical balance, as the chloride anions have been extracted. The bicarbonate content causes the venous blood leaving the stomach to be more alkaline than the arterial blood delivered to it.
The alkaline tide is neutralised by a secretion of Hinto the blood during HCO secretion in the pancreas.
Postprandial (i.e., after a meal) alkaline tide lasts until the acids in food absorbed in the small intestine reunite with the bicarbonate that was produced when the food was in the stomach. Thus, alkaline tide is self-limited and normally lasts less than two hours.
Postprandial alkaline tide has also been shown to be a causative agent of calcium oxalate urinary stones in cats, and potentially in other species.
A more pronounced alkaline tide results from vomiting, which stimulates hyperactivity of gastric parietal cells to replace lost stomach acid. Thus, protracted vomiting can result in metabolic alkalosis. | 1 | Applied and Interdisciplinary Chemistry |
Soil biota (soil microflora, soil animals) are sensitive to soil pH, either directly upon contact or after soil ingestion or indirectly through the various soil properties to which pH contributes (e.g. nutrient status, metal toxicity, humus form). According to the various physiological and behavioural adaptations of soil biota, the species composition of soil microbial and animal communities varies with soil pH. Along altitudinal gradients, changes in the species distribution of soil animal and microbial communities can be at least partly ascribed to variation in soil pH. The shift from toxic to non-toxic forms of aluminium around pH5 marks the passage from acid-tolerance to acid-intolerance, with few changes in the species composition of soil communities above this threshold, even in calcareous soils. Soil animals exhibit distinct pH preferences when allowed to exert a choice along a range of pH values, explaining that various field distributions of soil organisms, motile microbes included, could at least partly result from active movement along pH gradients. Like for plants, competition between acido-tolerant and acido-intolerant soil-dwelling organisms was suspected to play a role in the shifts in species composition observed along pH ranges.
The opposition between acido-tolerance and acido-intolerance is commonly observed at species level within a genus or at genus level within a family, but it also occurs at much higher taxonomic rank, like between soil fungi and bacteria, here too with a strong involvement of competition.
It has been suggested that soil organisms more tolerant of soil acidity, and thus living mainly in soils at pH less than 5, were more primitive than those intolerant of soil acidity. A cladistic analysis on the collembolan genus Willemia showed that tolerance to soil acidity was correlated with tolerance of other stress factors and that stress tolerance was an ancestral character in this genus. However the generality of these findings remains to be established.
At low pH, the oxidative stress induced by aluminium (Al) affects soil animals the body of which is not protected by a thick chitinous exoskeleton like in arthropods, and thus are in more direct contact with the soil solution, e.g. protists, nematodes, rotifers (microfauna), enchytraeids (mesofauna) and earthworms (macrofauna).
Effects of pH on soil biota can be mediated by the various functional interactions of soil foodwebs. It has been shown experimentally that the collembolan Heteromurus nitidus, commonly living in soils at pH higher than 5, could be cultured in more acid soils provided that predators were absent. Its attraction to earthworm excreta (mucus, urine, faeces), mediated by ammonia emission, provides food and shelter within earthworm burrows in mull humus forms associated with less acid soils. | 0 | Theoretical and Fundamental Chemistry |
Integrating equation over the control volume containing node N, and using Gauss’ theorem i.e.,
Yields the following result,
Where, A is the cross-sectional area of the control volume.
The equation must also satisfy the continuity equation, i.e.,
Now let us define variables F and D to represent the convection mass flux and diffusion conductance at cell faces,
: and ()
Hence, equations () and () transform into the following equations:
Where, the lower case letters denote the values at the faces and the upper case letters denote that at the nodes.
We also define a non-dimensional parameter Péclet number (Pe) as a measure of the relative strengths of convection and diffusion,
For a low Peclet number (|Pe|<2) the flow is characterized as dominated by diffusion. For large Peclet number the flow is dominated by convection. | 1 | Applied and Interdisciplinary Chemistry |
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