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The iso-electric point is one such property. The iso-electric point is the pH value at which the zeta potential is approximately zero. At a pH near the iso-electric point (± 2 pH units), colloids are usually unstable; the particles tend to coagulate or flocculate. Such titrations use acids or bases as titration reagents. Tables of iso-electric points for different materials are available. The attached figure illustrates results of such titrations for concentrated dispersions of alumina (4% v/v) and rutile (7% v/v). It is seen that iso-electric point of alumina is around pH 9.3, whereas for rutile it is around pH 4. Alumina is unstable in the pH range from 7 to 11. Rutile is unstable in the pH range from 2 to 6. | 7 | Physical Chemistry |
Environmental Chemistry is a peer-reviewed scientific journal published by CSIRO Publishing. It covers all aspects of environmental chemistry, including atmospheric chemistry, (bio)geochemistry, climate change, marine chemistry, water chemistry, polar chemistry, fire chemistry, astrochemistry, earth and geochemistry, soil and sediment chemistry, and chemical toxicology. The editor-in-chief is Jamie Lead (University of South Carolina). | 9 | Geochemistry |
Ligand efficacy refers to the ability of the ligand to produce a biological response upon binding to the target receptor and the quantitative magnitude of this response. This response may be as an agonist, antagonist, or inverse agonist, depending on the physiological response produced. | 1 | Biochemistry |
Steroid 21-hydroxylase, is a member of the cytochrome P450 family of monooxygenase enzymes, the protein has 494 amino acid residues with a molecular weight of 55,000. This enzyme is at most 28% homologous to other P-450 enzymes that have been studied.
Structurally, the protein contains an evolutionarily conserved core of four α-helix bundles (the importance of such genetic conservation is in demonstrating the functional importance of this aspect of this protein's structure). In addition, it has two additional alpha helices, two sets of β-sheets, and a heme cofactor binding loop. Each subunit in the human enzyme consists of a total of 13 α-helices and 9 β-strands that folds into a triangular prism-like tertiary structure.
The iron(III) heme group that defines the active site resides in the center of each subunit. The human enzyme binds one substrate at a time. In contrast, the well-characterized bovine enzyme can bind two substrates. The human and bovine enzyme share 80% amino acid sequence identity, but are structurally different, particularly in loop regions, and also evident in secondary structure elements. | 1 | Biochemistry |
In molecular biology, the presence of amylase can serve as an additional method of selecting for successful integration of a reporter construct in addition to antibiotic resistance. As reporter genes are flanked by homologous regions of the structural gene for amylase, successful integration will disrupt the amylase gene and prevent starch degradation, which is easily detectable through iodine staining. | 1 | Biochemistry |
Given two signals and , each of which possess power spectral densities and , it is possible to define a cross power spectral density (CPSD) or cross spectral density (CSD). To begin, let us consider the average power of such a combined signal.
Using the same notation and methods as used for the power spectral density derivation, we exploit Parseval's theorem and obtain
where, again, the contributions of and are already understood. Note that , so the full contribution to the cross power is, generally, from twice the real part of either individual CPSD. Just as before, from here we recast these products as the Fourier transform of a time convolution, which when divided by the period and taken to the limit becomes the Fourier transform of a cross-correlation function.
where is the cross-correlation of with and is the cross-correlation of with . In light of this, the PSD is seen to be a special case of the CSD for . If and are real signals (e.g. voltage or current), their Fourier transforms and are usually restricted to positive frequencies by convention. Therefore, in typical signal processing, the full CPSD is just one of the CPSDs scaled by a factor of two.
For discrete signals and , the relationship between the cross-spectral density and the cross-covariance is | 7 | Physical Chemistry |
The Australasian Institute of Mining and Metallurgy (AusIMM) provides services to professionals engaged in all facets of the global minerals sector and is based in Carlton, Victoria, Australia. | 8 | Metallurgy |
Ketones and aldehydes with electron-withdrawing substituents react more readily with diazoalkanes than those bearing electron-donating substituents (Table 2). In addition to accelerating the reaction, electron-withdrawing substituents typically increase the amount of epoxide produced (Table 2).
The effects of substituents on the diazoalkanes is reversed relative to the carbonyl reactants: electron-withdrawing substituents decrease the rate of reaction while electron-donating substituents accelerate it. For example, diazomethane is significantly more reactive than ethyl diazoacetate, though less reactive than its higher alkyl homologs (e.g. diazoethane). Reaction conditions may also affect the yields of carbonyl product and epoxide product. In the reactions of o-nitrobenzaldehyde, p-nitrobenzaldehyde, and phenylacetaldehyde with diazomethane, the ratio of epoxide to carbonyl is increased by the inclusion of methanol in the reaction mixture. The opposite influence has also been observed in the reaction of piperonal with diazomethane, which exhibits increased carbonyl yield in the presence of methanol. | 0 | Organic Chemistry |
The dispersion of a monochromator is characterized as the width of the band of colors per unit of slit width, 1 nm of spectrum per mm of slit width for instance. This factor is constant for a grating, but varies with wavelength for a prism. If a scanning prism monochromator is used in a constant bandwidth mode, the slit width must change as the wavelength changes. Dispersion depends on the focal length, the grating order and grating resolving power. | 7 | Physical Chemistry |
In organic chemistry, 1-propenyl (or simply propenyl) has the formula CH=CHCH and 2-propenyl (isopropenyl) has the formula CH=C-CH. These groups are found in many compounds. Propenyl compounds are isomeric with allyl compounds, which have the formula CH-CH=CH. | 0 | Organic Chemistry |
Key adaptations are adaptations that allow a group of organisms to diversify. Daphnia lumholtzi is a water flea that is able to form rigid head spines in response to chemicals released when fish are present. These phenotypically plastic traits serve as an induced defense against these predators. A study showed that Daphnia pulicaria is competitively superior to D. lumholtzi in the absence of predators. However, in the presence of fish predation the invasive species formed its defenses and became the dominant water flea in the region. This switch in dominance suggests that the induced defense against fish predation could represent a key adaptation for the invasion success of D. lumholtzi. A defensive trait that qualifies as a key adaptation is most likely an example of escape and radiate coevolution. | 1 | Biochemistry |
Retinyl esters from animal-sourced foods (or synthesized for dietary supplements for humans and domesticated animals) are acted upon by retinyl ester hydrolases in the lumen of the small intestine to release free retinol. Retinol enters intestinal absorptive cells by passive diffusion. Absorption efficiency is in the range of 70 to 90%. Humans are at risk for acute or chronic vitamin A toxicity because there are no mechanisms to suppress absorption or excrete the excess in urine. Within the cell, retinol is there bound to retinol binding protein 2 (RBP2). It is then enzymatically reesterified by the action of lecithin retinol acyltransferase and incorporated into chylomicrons that are secreted into the lymphatic system.
Unlike retinol, β-carotene is taken up by enterocytes by the membrane transporter protein scavenger receptor B1 (SCARB1). The protein is upregulated in times of vitamin A deficiency. If vitamin A status is in the normal range, SCARB1 is downregulated, reducing absorption. Also downregulated is the enzyme beta-carotene 15,15-dioxygenase (formerly known as beta-carotene 15,15-monooxygenase) coded for by the BCMO1 gene, responsible for symmetrically cleaving β-carotene into retinal. Absorbed β-carotene is either incorporated as such into chylomicrons or first converted to retinal and then retinol, bound to RBP2. After a meal, roughly two-thirds of the chylomicrons are taken up by the liver with the remainder delivered to peripheral tissues. Peripheral tissues also can convert chylomicron β-carotene to retinol.
The capacity to store retinol in the liver means that well-nourished humans can go months on a vitamin A deficient diet without manifesting signs and symptoms of deficiency. Two liver cell types are responsible for storage and release: hepatocytes and hepatic stellate cells (HSCs). Hepatocytes take up the lipid-rich chylomicrons, bind retinol to retinol-binding protein 4 (RBP4), and transfer the retinol-RBP4 to HSCs for storage in lipid droplets as retinyl esters. Mobilization reverses the process: retinyl ester hydrolase releases free retinol which is transferred to hepatocytes, bound to RBP4, and put into blood circulation. Other than either after a meal or when consumption of large amounts exceeds liver storage capacity, more than 95% of retinol in circulation is bound to RBP4. | 1 | Biochemistry |
Hattori and De Hoog, after considering the debate surrounding the cause of varying oxidation conditions in igneous rocks at shallow crustal levels, documented that highly oxidized conditions of rocks are an intrinsic character of the source magma in the mantle. They emphasized the capability of oxidized magmas to transport large quantities of sulfur and metals as well.
In her 1995 work, Hattori provided the initial documentation of oxidized arsenic in the overall reduced mantle, as arsenic is present by replacing Si. One of her PhD students, Jian Wangm, evaluated the redox state of mantle rocks and discovered that carbon is the primary control for the oxidation conditions of the mantle in subduction zones. | 9 | Geochemistry |
Of all the radiation-based chemical reactions that have been studied, the most important is the decomposition of water. When exposed to radiation, water undergoes a breakdown sequence into hydrogen peroxide, hydrogen radicals, and assorted oxygen compounds, such as ozone, which when converted back into oxygen releases great amounts of energy. Some of these are explosive. This decomposition is produced mainly by alpha particles, which can be entirely absorbed by very thin layers of water.
Summarizing, the radiolysis of water can be written as: | 5 | Photochemistry |
For any 2-dimensional lattice, the unit cells are parallelograms, which in special cases may have orthogonal angles, equal lengths, or both. Four of the five two-dimensional Bravais lattices are represented using conventional primitive cells, as shown below.
The centered rectangular lattice also has a primitive cell in the shape of a rhombus, but in order to allow easy discrimination on the basis of symmetry, it is represented by a conventional cell which contains two lattice points. | 3 | Analytical Chemistry |
Physiological ketosis is the non-pathological (normal functioning) elevation of ketone bodies that can result from any state of increased fatty acid oxidation including fasting, prolonged exercise, or very low-carbohydrate diets such as the ketogenic diet. In physiological ketosis, serum ketone levels generally remain below 3 mM. | 1 | Biochemistry |
The first version of PCLake (by then called PCLoos) was built in the early 1990s at the Netherlands National Institute for Public Health and the Environment (RIVM), within the framework of a research and restoration project on Lake Loosdrecht. It has been extended and improved since then. Parallel to PCLake, PCDitch was created, which is an ecosystem model for ditches and other linear water bodies. The models were further developed by dr. Jan H. Janse and colleagues at the Netherlands Environmental Assessment Agency (PBL), formerly part of the RIVM. Since 2009, the model is jointly owned by PBL and the Netherlands Institute of Ecology, where further development and application of PCLake is taking place, related to aquatic-ecological research. | 2 | Environmental Chemistry |
Stable nucleic acid lipid particles (SNALPs) are microscopic particles approximately 120 nanometers in diameter, smaller than the wavelengths of visible light. They have been used to deliver siRNAs therapeutically to mammals in vivo. In SNALPs, the siRNA is surrounded by a lipid bilayer containing a mixture of cationic and fusogenic lipids, coated with diffusible polyethylene glycol. | 1 | Biochemistry |
1 g/cm is equivalent to:
: = 1000 g/L (exactly)
: = 1000 kg/m (exactly)
: ≈ (approximately)
: ≈ (approximately)
1 kg/m = 0.001 g/cm(exactly)
1 lb/cu ft ≈ (approximately)
1 oz/US gal ≈ (approximately) | 3 | Analytical Chemistry |
There is no standardized list of metallurgical failure modes and different metallurgists might use a different name for the same failure mode. The failure mode terms listed below are those accepted by ASTM, ASM, and/or NACE as distinct metallurgical failure mechanisms. | 8 | Metallurgy |
The reciprocal lattice to an FCC lattice is the body-centered cubic (BCC) lattice, with a cube side of .
Consider an FCC compound unit cell. Locate a primitive unit cell of the FCC; i.e., a unit cell with one lattice point. Now take one of the vertices of the primitive unit cell as the origin. Give the basis vectors of the real lattice. Then from the known formulae, you can calculate the basis vectors of the reciprocal lattice. These reciprocal lattice vectors of the FCC represent the basis vectors of a BCC real lattice. The basis vectors of a real BCC lattice and the reciprocal lattice of an FCC resemble each other in direction but not in magnitude. | 3 | Analytical Chemistry |
Inherent within this model, the following assumptions are valid specifically for the simplest case: the adsorption of a single adsorbate onto a series of equivalent sites onto the surface of the solid.
# The surface containing the adsorbing sites is a perfectly flat plane with no corrugations (assume the surface is homogeneous). However, chemically heterogeneous surfaces can be considered to be homogeneous if the adsorbate is bound to only one type of functional groups on the surface.
# The adsorbing gas adsorbs into an immobile state.
# All sites are energetically equivalent, and the energy of adsorption is equal for all sites.
# Each site can hold at most one molecule (mono-layer coverage only).
# No (or ideal) interactions between adsorbate molecules on adjacent sites. When the interactions are ideal, the energy of side-to-side interactions is equal for all sites regardless of the surface occupancy. | 7 | Physical Chemistry |
A peptide library is a tool for studying proteins. Peptide libraries typically contain a large number of peptides that have a systematic combination of amino acids. Usually, solid phase synthesis, e.g. resin as a flat surface or beads, is used for peptide library generation. Peptide libraries are a popular tool for experiments in drug design, protein–protein interactions, and other biochemical and pharmaceutical applications.
Synthetic peptide libraries are synthesized without utilizing biological systems such as phage or in vitro translation. There are at least five subtypes of synthetic peptide libraries that differ from each other by the design of the library and/or the method used for the synthesis of the library. The subtypes include:
* Overlapping peptide libraries - in which the entirety of a larger protein is used to produce a library of 8-20 amino acid peptides which overlap; these libraries can be used to identify the specific regions of a larger protein which participate in a given interaction or to provide pre-digested versions of a larger protein for binding.
* Truncation peptide libraries - in which a given peptide is produced with various or all N or C terminal truncations, these smaller fragments can be used to identify the minimal required region of a peptide for a given interaction being studied.
* Random libraries - randomly generated peptides of a set length, or range of lengths, can be used to identify novel binding partners of a target of interest.
* Alanine scanning libraries - in which each amino acid of a given protein or peptide is replaced with an alanine sequentially such that each peptide contains only one alanine mutations but all possible mutations to alanine are present; this can be used to identify critical residues for binding
* Positional or scrambled peptide libraries - in which specific positions in the peptide are substituted for many or all other amino acids such that the affect of each amino acid at that position in the peptide on the binding or other activity of the peptide can be tested. Scrambled libraries are often random peptides and used as negative controls.
Solid phase peptide synthesis is limited to a peptide chain length of approximately 70 amino acids and is generally unsuitable for the study of larger proteins. Many libraries utilize peptide chains much shorter than 70 amino acids. For 20 encoded amino acids at maximally 70 positions, this results in an upper limit of 20, or more than 10 quindecillion (1x10), possible combinations, not accounting for the potential use of amino acids with post-translational modifications or amino acids not encoded in the genetic code, such as selenocysteine and pyrrolysine. Peptide libraries generally encompass only a fraction of this diversity, selected for depending on the needs of the experiment, for instance keeping some amino acids constant at certain positions.
Large random peptide libraries are often used for the synthesis of certain peptide molecules, such as ultra-large chemical libraries for the discovery of high-affinity peptide binders. Any increase in the library size severely affects parameters, such as the synthesis scale, the number of library members, the sequence deconvolution and peptide structure elucidation. To mitigate these technical challenges, an algorithm-supported approach to peptide library design may use molecular mass and amino acid diversity to simplify the laborious permutation identification in complex mixtures when using mass spectrometry. This approach is used to avoid mass redundancy.
Biological reagent companies, such as Pepscan, ProteoGenix, Mimotopes, GenScript and many others, manufacture customized peptide libraries. | 1 | Biochemistry |
Capsaicin is not soluble in water, and even large volumes of water will not wash it off, only dilute it. In general, victims are encouraged to blink vigorously in order to encourage tears, which will help flush the irritant from the eyes.
A study of five often-recommended treatments for skin pain (Maalox, 2% lidocaine gel, baby shampoo, milk, or water) concluded that: "...there was no significant difference in pain relief provided by five different treatment regimens. Time after exposure appeared to be the best predictor for a decrease in pain...".
Many ambulance services and emergency departments carry saline to remove the spray. Some of the OC and CS will remain in the respiratory system, but a recovery of vision and the coordination of the eyes can be expected within 7 to 15 minutes.
Some "triple-action" pepper sprays also contain "tear gas" (CS gas), which can be neutralized with sodium metabisulfite (Campden tablets), though it is not for use on a person, only for area clean up. | 1 | Biochemistry |
Instead of the differential symbol , the symbol is used, a convention which originated in the 19th century work of German mathematician Carl Gottfried Neumann, indicating that (heat) and (work) are path-dependent, while (internal energy) is not. | 7 | Physical Chemistry |
In dodecaborate(12) anion, twelve boron atoms covalently link to each other to form an icosahedral structure. Various other similar motifs are also well studied, such as boranes, carboranes and metal dicarbollides. | 0 | Organic Chemistry |
Typical genera include:
* Citrobacter are peritrichous facultative anaerobic bacilli between 0.6–6 μm in length. Citrobacter species inhabit intestinal flora without causing harm, but can lead to urinary tract infections, bacteremia, brain abscesses, pneumonia, intra abdominal sepsis, meningitis, and joint infections if they are given the opportunity. Infections of a Citrobacter species has a mortality rate between 33–48%, with infants and immunocompromised individuals being more susceptible.
* Enterobacter are motile, flagellated bacilli known for causing infections such as bacteremia, respiratory tract infections, urinary tract infections, infections of areas where surgery occurred, and in extreme cases meningitis, sinusitis and osteomyelitis. To determine the presence of Enterobacter in a sample, they are first grown on MacConkey agar to confirm they are lactose fermenting. An indole test will differentiate Enterobacter from Escherichia, as Enterobacter are indole negative and Escherichia is positive. Enterobacter are distinguished from Klebsiella because of their differences in motility.
* Klebsiella are non-motile, Gram-negative bacilli ranging from 1–2 μm in length. They are facultative anaerobes with a capsule composed of complex acid polysaccharides that allows them to withstand drying for several months. Klebsiella pneumoniae is the most common Klebsiella species found in humans, the gastrointestinal tracts of animals, in sewage and in soil. On carbohydrate-rich media, Klebsiella colonies appear greyish-white in colour with a mucosal outer surface. The media used for selecting for Klebsiella species in a mixed sample is an agar including ornithine, raffinose, and Koser citrate, where members of this genus will form yellow, wet-looking colonies.
* Escherichia species normally inhabit the human intestine and those of other warm-blooded animals, and are the most commonly responsible for causing disease in humans. E. coli specifically is the most common organism seen in the human intestine and are known to cause a variety of diseases in humans. Most E. coli strains are motile and have obtained many of their virulence features from horizontal gene transfer. There are several different pathotypes of E. coli causing gastrointestinal syndromes: diarrheagenic E. coli (DEC), enterotoxigenic E. coli (ETEC); EPEC; Shiga toxin–producingE. coli (STEC), which includes EHEC; enteroaggregative E. coli (EAEC); and enteroinvasive E. coli (EIEC). There are different ways to identify E. coli based on variation of their O, H and K polysaccharides on their cell surface or by using selective medias.
Escherichia coli (E. coli) can be distinguished from most other coliforms by its ability to ferment lactose at 44 °C in the fecal coliform test, and by its growth and color reaction on certain types of culture media. When cultured on an eosin methylene blue (EMB) plate, a positive result for E. coli is metallic green colonies on a dark purple medium. Also can be cultured on Tryptone Bile X-Glucuronide (TBX) to appear as blue or green colonies after incubation period of 24 hours. Escherichia coli have an incubation period of 12–72 hours with the optimal growth temperature being 37 °C. Unlike the general coliform group, E. coli are almost exclusively of fecal origin and their presence is thus an effective confirmation of fecal contamination. Most strains of E. coli are harmless, but some can cause serious illness in humans. Infection symptoms and signs include bloody diarrhea, stomach cramps, vomiting and occasionally, fever. The bacteria can also cause pneumonia, other respiratory illnesses and urinary tract infections.
An easy way to differentiate between different types of coliform bacteria is by using an eosin methylene blue agar plate. This plate is partially inhibitory to Gram (+) bacteria, and will produce a color change in the Gram (-) bacterial colonies based on lactose fermentation abilities. Strong lactose fermenters will appear as dark blue/purple/black, and E.coli (which also ferments lactose) colonies will be dark colored, but will also appear to have a metallic green sheen. Other coliform bacteria will appear as thick, slimy colonies, with non-fermenters being colorless, and weak fermenters being pink. | 3 | Analytical Chemistry |
The Cystic Fibrosis Transport Regulator (CFTR) works by binding two ATP to the A1 and A2, ATP-binding domain. This opens the CFTR channel and allows chloride ions to flow into the lungs and airway lumen. This influx of negatively charged chloride ions into the airway lumen causes sodium to move into the airway lumen to balance the negative charge. Water then moves in with the sodium to balance the osmotic pressure and ultimately leads to the thinning of mucus. In cases of Cystic Fibrosis, the CFTR is defective and only binds a single ATP, leading to the channel failing to open and preventing chloride ions from diffusing into the airway lumen. Since chloride ions cannot diffuse in, there is no movement of sodium into the airway lumen, and no need for water to move into the lumen, leading to thick mucus that clogs and infects the airway lumen. | 1 | Biochemistry |
A melt inclusion is a small parcel or "blobs" of melt(s) that is entrapped by crystals growing in magma and eventually forming igneous rocks. In many respects it is analogous to a fluid inclusion within magmatic hydrothermal systems. Melt inclusions tend to be microscopic in size and can be analyzed for volatile contents that are used to interpret trapping pressures of the melt at depth. | 9 | Geochemistry |
Full-field displacement, elastic strain, and the GND density provide quantifiable information about the material's elastic and plastic behaviour at the microscale. Measuring strain at the microscale requires careful consideration of other key details besides the change in length/shape (e.g., local texture, individual grain orientations). These micro-scale features can be measured using different techniques, e.g., hole drilling, monochromatic or polychromatic energy-dispersive X-ray diffraction or neutron diffraction (ND). EBSD has a high spatial resolution and is relatively sensitive and easy to use compared to other techniques. Strain measurements using EBSD can be performed at a high spatial resolution, allowing researchers to study the local variation in strain within a material. This information can be used to study the deformation and mechanical behaviour of materials, to develop models of material behaviour under different loading conditions, and to optimise the processing and performance of materials. Overall, strain measurement using EBSD is a powerful tool for studying the deformation and mechanical behaviour of materials, and is widely used in materials science and engineering research and development. | 7 | Physical Chemistry |
Precipitation in grasslands is equal to or less than evapotranspiration and causes soil development to operate in relative drought. Leaching and migration of weathering products is therefore decreased. Large amounts of evaporation causes buildup of calcium (Ca) and other large cations flocculate clay minerals and fulvic acids in the upper soil profile. Low amounts of precipitation and high levels of evapotranspiration limit the downward percolation of water and organic acids, reducing chemical weathering and soil development. The depth to the maximum concentration of clay increases in areas of increased precipitation and leaching. When leaching is decreased, the calcium precipitates as calcite (CaCO) in the lower soil levels, a layer known as caliche.
Deserts behave similarly to grasslands but operate in constant drought as precipitation is less than evapotranspiration. Chemical weathering proceeds more slowly than in grasslands and beneath the caliche layer may be a layer of gypsum and halite. To study soils in deserts, pedologists have used the concept of chronosequences to relate timing and development of the soil layers. It has been shown that phosphorus is leached very quickly from the system and therefore decreases with increasing age. Furthermore, carbon buildup in the soils is decreased due to slower decomposition rates. As a result, the rates of carbon circulation in the biogeochemical cycle is decreased. | 9 | Geochemistry |
Although it is a relatively immature area of research, it appears that heterotrimeric G-proteins may also take part in non-GPCR signaling. There is evidence for roles as signal transducers in nearly all other types of receptor-mediated signaling, including integrins, receptor tyrosine kinases (RTKs), cytokine receptors (JAK/STATs), as well as modulation of various other "accessory" proteins such as GEFs, guanine-nucleotide dissociation inhibitors (GDIs) and protein phosphatases. There may even be specific proteins of these classes whose primary function is as part of GPCR-independent pathways, termed activators of G-protein signalling (AGS). Both the ubiquity of these interactions and the importance of Gα vs. Gβγ subunits to these processes are still unclear. | 1 | Biochemistry |
Fischer glycosidation (or Fischer glycosylation) refers to the formation of a glycoside by the reaction of an aldose or ketose with an alcohol in the presence of an acid catalyst. The reaction is named after the German chemist, Emil Fischer, winner of the Nobel Prize in chemistry, 1902, who developed this method between 1893 and 1895.
Commonly, the reaction is performed using a solution or suspension of the carbohydrate in the alcohol as the solvent. The carbohydrate is usually completely unprotected. The Fischer glycosidation reaction is an equilibrium process and can lead to a mixture of ring size isomers, and anomers, plus in some cases, small amounts of acyclic forms. With hexoses, short reactions times usually lead to furanose ring forms, and longer reaction times lead to pyranose forms. With long reaction times the most thermodynamically stable product will result which, owing to the anomeric effect, is usually the alpha anomer. | 0 | Organic Chemistry |
Schlögl was born October 5, 1924, in Vienna. Schlögl's first contact with organic chemistry happened during his middle-school education, when his father - the principal and teacher for natural sciences - took young Karl to school after hours to do experiments together.
Schlögl graduated from high-school in 1943 and was declared unfit for service by the Wehrmacht due to his asthma.
He started studying chemistry at the University of Vienna under Ernst Späth, where he completed his dissertation in 1950.
From 1954 to 1955 Schlögl began working on ferrocenes at the University of Manchester during a British council scholarship.
After his return to the University of Vienna he achieved the habilitation for organic chemistry in 1959.
In 1970 Schlögl was promoted to associate professor and in 1971 to full professor for organic chemistry.
Since 1974 he was director, and since 1978 chairman of the [http://www.univie.ac.at/orgchem/ Institute of Organic Chemistry] at the University of Vienna. From 1977 through 1979 he was the first elected Dean of the Faculty of Formal and Natural Sciences at the University of Vienna.
The Austrian Academy of Sciences elected Schlögl as a corresponding member in 1978 and as a full member in 1982. From 1991 to 1995 Schlögl was general secretary of the academy, and from 1997 to 2000 he was vice-president of the Austrian Academy of Sciences. Furthermore, Schlögl was a corresponding member of the Nordrhein-Westfälische Akademie der Wissenschaften as well as the New York Academy of Sciences. | 0 | Organic Chemistry |
Despite the occasional use in pharmaceuticals, the nitro group is associated with mutagenicity and genotoxicity and therefore is often regarded as a liability in the drug discovery process. | 0 | Organic Chemistry |
In the 15th century, the finery process, another process which shares the air-blowing principle with the Bessemer process, was developed in Europe. In 1740, Benjamin Huntsman developed the crucible technique for steel manufacture, at his workshop in the district of Handsworth in Sheffield. This process had an enormous impact on the quantity and quality of steel production, but it was unrelated to the Bessemer-type process employing decarburization.
The Japanese may have made use of a Bessemer-type process, which was observed by European travellers in the 17th century. The adventurer Johan Albrecht de Mandelslo describes the process in a book published in English in 1669. He writes, "They have, among others, particular invention for the melting of iron, without the using of fire, casting it into a tun done about on the inside without about half a foot of earth, where they keep it with continual blowing, take it out by ladles full, to give it what form they please." According to historian Donald Wagner, Mandelslo did not personally visit Japan, so his description of the process is likely derived from accounts of other Europeans who had traveled to Japan. Wagner believes that the Japanese process may have been similar to the Bessemer process, but cautions that alternative explanations are also plausible. | 8 | Metallurgy |
During the fading, colourant molecules undergo various chemical processes which result in fading.
When a UV-photon reacts with a molecule acting as colourant, the molecule is excited from the ground state to an excited state. The excited molecule is highly reactive and unstable. During the quenching of the molecule from excited state to ground state, atmospheric triplet oxygen reacts with the colourant molecule to form singlet oxygen and superoxide oxygen radical. The oxygen atom and the superoxide radical resulting from the reaction are both highly reactive and capable of destroying the colourants. | 5 | Photochemistry |
Hash oil is produced by solvent extraction (maceration, infusion or percolation) of marijuana or hashish. After filtering and evaporating the solvent, a sticky resinous liquid with a strong herbal odor (remarkably different from the odor of hemp) remains.
Fresh, undried plant material is less suited for hash oil production, because much THC and CBD will be present in their carboxylic acid forms (THCA and CBDA), which may not be highly soluble in some solvents. The acids are decarboxylated during drying and heating (smoking).
A wide variety of solvents can be used for extraction, such as chloroform, dichloromethane, petroleum ether, naphtha, benzene, butane, methanol, ethanol, isopropanol, and olive oil. Currently, resinoids are often obtained by extraction with supercritical carbon dioxide. The alcohols extract undesirable water-soluble substances such as chlorophyll and sugars (which can be removed later by washing with water). Non-polar solvents such as benzene, chloroform and petroleum ether will not extract the water-soluble constituents of marijuana or hashish while still producing hash oil. In general, non-polar cannabis extracts taste much better than polar extracts. Alkali washing further improves the odor and taste.
The oil may be further refined by 1) alkali washing, or removing the heavy aromatic carboxylic acids with antibiotic properties, which may cause heartburn, gallbladder and pancreas irritation, and resistance to hemp antibiotics; 2) conversion of CBD to THC. Process 1) consists of dissolving the oil in a non-polar solvent such as petroleum ether, repeatedly washing (saponifying) with a base such as sodium carbonate solution until the yellow residue disappears from the watery phase, decanting, and washing with water to remove the base and the saponified components (and evaporating the solvents). This process reduces the oil yield, but the resulting oil is less acidic, more easily digestible and much more potent (almost pure THC). Process 2) consists of dissolving the oil in a suitable solvent such as absolute ethanol containing 0.05% hydrochloric acid, and boiling the mixture for 2 hours.
The majority of ready to consume extract products are produced via "Closed Loop Systems.". These systems typically entail: a vessel that holds the solvent, material columns to hold the plant material, a [https://www.aBHOutit.com flow meter] to measure the volume of solvent entering the plant material, a recovery vessel(where heat is applied via an external jacket) to convert the liquid solvent into a vapor and separate it from the THC, CBD, or other cannabinoids/byproducts, and some form of a heat exchanger to then convert the hydrocarbon vapors back into a liquid form prior to returning to the original vessel.
Ten grams of marijuana yields one to two grams of hash oil. The oil may retain considerable residual solvent: oil extracted with longer-chain volatile hydrocarbons (such as naphtha) is less viscous (thinner) than oil extracted with short-chain hydrocarbons (such as butane).
Colored impurities from the oil can be removed by adding activated charcoal to about one third to one half the weight or volume of the solvent containing the dissolved oil, mixing well, filtering, and evaporating the solvent. When decolorizing fatty oils, oil retention can be up to 50 wt % on bleaching earths and nearly 100 wt % on activated charcoal. The many different textures/types of hydrocarbon extracts include:
* shatter (solid, breaks easily, glass like oil)
* pull and snap (solid, bendable, but still breakable, taffy-like oil)
* diamonds/live resin (rock hard THCA isolated diamonds drenched in terpene sauce)
* crumble (solid oil that will break into small crumbs)
* budder/wax (soft, pliable, peanut butter-like consistency) | 7 | Physical Chemistry |
The Mecke reagent is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It is composed of a mixture of selenous acid and concentrated sulfuric acid, which is dripped onto the substance being tested.
The United States Department of Justice method for producing the reagent is the addition of 100 mL of concentrated (95–98%) sulfuric acid to 1 g of selenous acid. While sale to the general public is legal, it is not recommended as strong corrosives can cause permanent skin and eye damage and require extensive safety ratings. | 3 | Analytical Chemistry |
In humans, can be synthesized in the liver via the metabolism of fatty acids (e.g., butyrate), , and ketogenic amino acids through a series of reactions that metabolize these compounds into acetoacetate, which is the first ketone body that is produced in the fasting state. The biosynthesis of from acetoacetate is catalyzed by the β-hydroxybutyrate dehydrogenase enzyme.
Butyrate can also be metabolized into via a second metabolic pathway that does not involve acetoacetate as a metabolic intermediate. This metabolic pathway is as follows:
:butyrate→butyryl-CoA→crotonyl-CoA→β-hydroxybutyryl-CoA→poly-β-hydroxybutyrate→()→
The last reaction in this metabolic pathway, which involves the conversion of () into , is catalyzed by the hydroxybutyrate-dimer hydrolase enzyme.
The concentration of β-hydroxybutyrate in human blood plasma, as with other ketone bodies, increases through ketosis. This elevated β-hydroxybutyrate level is naturally expected, as β-hydroxybutyrate is formed from acetoacetate. The compound can be used as an energy source by the brain and skeletal muscle when blood glucose is low. Diabetic patients can have their ketone levels tested via urine or blood to indicate diabetic ketoacidosis. In alcoholic ketoacidosis, this ketone body is produced in greatest concentration. Ketogenesis occurs if oxaloacetate in the liver cells is depleted, a circumstance created by reduced carbohydrate intake (through diet or starvation); prolonged, excessive alcohol consumption; and/or insulin deficiency. Because oxaloacetate is crucial for entry of acetyl-CoA into the TCA cycle, the rapid production of acetyl-CoA from fatty acid oxidation in the absence of ample oxaloacetate overwhelms the decreased capacity of the TCA cycle, and the resultant excess of acetyl-CoA is shunted towards ketone body production. | 1 | Biochemistry |
;Disconnection: A retrosynthetic step involving the breaking of a bond to form two (or more) synthons.
;Retron: A minimal molecular substructure that enables certain transformations.
;Retrosynthetic tree: A directed acyclic graph of several (or all) possible retrosyntheses of a single target.
;Synthon: A fragment of a compound that assists in the formation of a synthesis, derived from that target molecule. A synthon and the corresponding commercially available synthetic equivalent are shown below:
;Target: The desired final compound.
;Transform: The reverse of a synthetic reaction; the formation of starting materials from a single product. | 0 | Organic Chemistry |
Properly designed copper roofs minimize movements due to thermal changes. Coppers low thermal expansion, 40% less than zinc and lead, helps to prevent deterioration and failure. Also, coppers high melting point ensures that it will not creep or stretch as some other metals do.
On small gable roofs, thermal movement is relatively minor and usually is not an issue. On wide-span buildings over and when long panels are used, an allowance for thermal expansion may be necessary. This enables the roof to "float" over supporting substructures while remaining secure. | 8 | Metallurgy |
The non-fluorescent acetomethoxy derivate of calcein (calcein AM, AM = acetoxymethyl) is used in biology as it can be transported through the cellular membrane into live cells, which makes it useful for testing of cell viability and for short-term labeling of cells. Alternatively, Fura-2 , Furaptra , Indo-1 and aequorin may be used. An acetomethoxy group obscures the part of the molecule that chelates Ca, Mg, Zn and other ions. After transport into the cells, intracellular esterases remove the acetomethoxy group, the molecule gets trapped inside and gives out strong green fluorescence. As dead cells lack active esterases, only live cells are labeled and counted by flow cytometry.
Calcein is now rarely used as a Ca or Mg indicator because its fluorescence is directly sensitive to these ions only at strongly alkaline pH, and thus it is not particularly useful for measuring Ca or Mg in cells. Fluorescence of calcein is quenched strongly by Co, Ni and Cu and appreciably by Fe and Mn at physiological pH. This fluorescence quenching response can be exploited for detecting the opening of the mitochondrial permeability transition pore (mPTP) and for measuring cell volume changes. Calcein is commonly used for cell tracing and in studies of endocytosis, cell migration, and gap junctions.
The acetoxymethyl ester of calcein is also used to detect drug interactions with multidrug resistance proteins (ABC transporters ATP-binding cassette transporter genes) in intact cells as it is an excellent substrate of the multidrug resistance transporter 1 (MDR1) P-glycoprotein and the Multidrug Resistance-Associated Protein (MRP1). The calcein AM assay can be used as a model for drug-drug interactions, for screening transporter substrates and/or inhibitors; and also to determine in vitro drug resistance of cells, including samples from patients.
Calcein is also used for marking freshly hatched fish and for labeling of bones in live animals. | 3 | Analytical Chemistry |
Biochemical detection is the science and technology of detecting biochemicals and their concentration where trace analysis is concerned this is usually done by using a quartz crystal microbalance, which measures a mass per unit area by measuring the change in frequency of a quartz crystal resonator. Another method is with nanoparticles. | 1 | Biochemistry |
Mathematically, the points of the diamond cubic structure can be given coordinates as a subset of a three-dimensional integer lattice by using a cubic unit cell four units across. With these coordinates, the points of the structure have coordinates satisfying the equations
There are eight points (modulo 4) that satisfy these conditions:
All of the other points in the structure may be obtained by adding multiples of four to the coordinates of these eight points. Adjacent points in this structure are at distance apart in the integer lattice; the edges of the diamond structure lie along the body diagonals of the integer grid cubes. This structure may be scaled to a cubical unit cell that is some number of units across by multiplying all coordinates by .
Alternatively, each point of the diamond cubic structure may be given by four-dimensional integer coordinates whose sum is either zero or one. Two points are adjacent in the diamond structure if and only if their four-dimensional coordinates differ by one in a single coordinate. The total difference in coordinate values between any two points (their four-dimensional Manhattan distance) gives the number of edges in the shortest path between them in the diamond structure. The four nearest neighbors of each point may be obtained, in this coordinate system, by adding one to each of the four coordinates, or by subtracting one from each of the four coordinates, accordingly as the coordinate sum is zero or one. These four-dimensional coordinates may be transformed into three-dimensional coordinates by the formula
Because the diamond structure forms a distance-preserving subset of the four-dimensional integer lattice, it is a partial cube.
Yet another coordinatization of the diamond cubic involves the removal of some of the edges from a three-dimensional grid graph. In this coordinatization, which has a distorted geometry from the standard diamond cubic structure but has the same topological structure, the vertices of the diamond cubic are represented by all possible 3d grid points and the edges of the diamond cubic are represented by a subset of the 3d grid edges.
The diamond cubic is sometimes called the "diamond lattice" but it is not, mathematically, a lattice: there is no translational symmetry that takes the point (0,0,0) into the point (3,3,3), for instance. However, it is still a highly symmetric structure: any incident pair of a vertex and edge can be transformed into any other incident pair by a congruence of Euclidean space. Moreover, the diamond crystal as a network in space has a strong isotropic property. Namely, for any two vertices of the crystal net, and for any ordering of the edges adjacent to and any ordering of the edges adjacent to , there is a net-preserving congruence taking to and each -edge to the similarly ordered -edge. Another (hypothetical) crystal with this property is the Laves graph (also called the K crystal, (10,3)-a, or the diamond twin). | 3 | Analytical Chemistry |
The four-dimensional unit cell is defined by four edge lengths (a, b, c, d) and six interaxial angles (α, β, γ, δ, ε, ζ). The following conditions for the lattice parameters define 23 crystal families
The names here are given according to Whittaker. They are almost the same as in Brown et al., with exception for names of the crystal families 9, 13, and 22. The names for these three families according to Brown et al. are given in parentheses.
The relation between four-dimensional crystal families, crystal systems, and lattice systems is shown in the following table. Enantiomorphic systems are marked with an asterisk. The number of enantiomorphic pairs is given in parentheses. Here the term "enantiomorphic" has a different meaning than in the table for three-dimensional crystal classes. The latter means, that enantiomorphic point groups describe chiral (enantiomorphic) structures. In the current table, "enantiomorphic" means that a group itself (considered as a geometric object) is enantiomorphic, like enantiomorphic pairs of three-dimensional space groups P3 and P3, P422 and P422. Starting from four-dimensional space, point groups also can be enantiomorphic in this sense. | 3 | Analytical Chemistry |
As the temperature in the joint increases, polymer begins to melt and a fusion zone is formed. The molten polymer in the fusion zone exerts an outward force on the surrounding solid polymer material, referred to as "cold zones". These cold zones cause a pressure to develop in the molten fusion zone. The pressure in the fusion zone takes some time to reach its maximum value, usually not reaching the peak until about a quarter of the way into the joining process. After the current is shut off and cooling begins, the pressure slowly decreases until the joint is uniform temperature. | 7 | Physical Chemistry |
The hydrosphere is 33% oxygen by volume present mainly as a component of water molecules, with dissolved molecules including free oxygen and carbolic acids (HCO). | 5 | Photochemistry |
A diglyceride, or diacylglycerol (DAG), is a glyceride consisting of two fatty acid chains covalently bonded to a glycerol molecule through ester linkages. Two possible forms exist, 1,2-diacylglycerols and 1,3-diacylglycerols. Diglycerides are natural components of food fats, though minor in comparison to triglycerides. DAGs can act as surfactants and are commonly used as emulsifiers in processed foods. DAG-enriched oil (particularly 1,3-DAG) has been investigated extensively as a fat substitute due to its ability to suppress the accumulation of body fat; with total annual sales of approximately USD 200 million in Japan since its introduction in the late 1990s till 2009. | 1 | Biochemistry |
The initiation of gene transcription in eukaryotes occurs in specific steps. First, an RNA polymerase along with general transcription factors binds to the promoter region of the gene to form a closed complex called the preinitiation complex. The subsequent transition of the complex from the closed state to the open state results in the melting or separation of the two DNA strands and the positioning of the template strand to the active site of the RNA polymerase. Without the need of a primer, RNA polymerase can initiate the synthesis of a new RNA chain using the template DNA strand to guide ribonucleotide selection and polymerization chemistry. However, many of the initiated syntheses are aborted before the transcripts reach a significant length (~10 nucleotides). During these abortive cycles, the polymerase keeps making and releasing short transcripts until it is able to produce a transcript that surpasses ten nucleotides in length. Once this threshold is attained, RNA polymerase passes the promoter and transcription proceeds to the elongation phase. | 1 | Biochemistry |
If a reaction occurs through these steps:
: A + S ⇌ AS → Products
where A is the reactant and S is an adsorption site on the surface and the respective rate constants for the adsorption, desorption and reaction are k, k and k, then the global reaction rate is:
where:
* r is the rate, mol·m·s
*is the concentration of adsorbate, mol·m
* is the surface concentration of occupied sites, mol·m
* is the concentration of all sites (occupied or not), mol·m
* is the surface coverage, (i.e. ) defined as the fraction of sites which are occupied, which is dimensionless
* is time, s
* is the rate constant for the surface reaction, s.
*is the rate constant for surface adsorption, m·mol·s
*is the rate constant for surface desorption, s
is highly related to the total surface area of the adsorbent: the greater the surface area, the more sites and the faster the reaction. This is the reason why heterogeneous catalysts are usually chosen to have great surface areas (in the order of a hundred m/gram)
If we apply the steady state approximation to AS, then:
: so
and
The result is equivalent to the Michaelis–Menten kinetics of reactions catalyzed at a site on an enzyme. The rate equation is complex, and the reaction order is not clear. In experimental work, usually two extreme cases are looked for in order to prove the mechanism. In them, the rate-determining step can be:
*Limiting step: adsorption/desorption
The order respect to A is 1. Examples of this mechanism are NO on gold and HI on platinum
*Limiting step: reaction of adsorbed species
The last expression is the Langmuir isotherm for the surface coverage. The adsorption equilibrium constant , and the numerator and denominator have each been divided by . The overall reaction rate becomes .
Depending on the concentration of the reactant the rate changes:
:* Low concentrations, then , that is to say a first order reaction in component A.
:* High concentration, then . It is a zeroth order reaction in component A. | 7 | Physical Chemistry |
Oligosaccharides that participate in O-linked glycosylation are attached to threonine or serine on the hydroxyl group of the side chain. O-linked glycosylation occurs in the Golgi apparatus, where monosaccharide units are added to a complete polypeptide chain. Cell surface proteins and extracellular proteins are O-glycosylated. Glycosylation sites in O-linked oligosaccharides are determined by the secondary and tertiary structures of the polypeptide, which dictate where glycosyltransferases will add sugars. | 0 | Organic Chemistry |
Several domains of PCAF can act independently or in unison to enable its functions. PCAF has separate acetyltransferase and E3 ubiquitin ligase domains as well as a bromodomain for interaction with other proteins. PCAF also possesses sites for its own acetylation and ubiquitination. | 1 | Biochemistry |
The word "emulsion" comes from the Latin emulgere "to milk out", from ex "out" + mulgere "to milk", as milk is an emulsion of fat and water, along with other components, including colloidal casein micelles (a type of secreted biomolecular condensate). | 7 | Physical Chemistry |
A Wahrhaftig diagram (named after Austin L. Wahrhaftig) illustrates the relative contributions in unimolecular ion decomposition of direct fragmentation and fragmentation following rearrangement. The x-axis of the diagram represents the internal energy of the ion. The lower part of the diagram shows the logarithm of the rate constant k for unimolecular dissociation whereas the upper portion of the diagram indicates the probability of forming a particular product ion. The green trace in the lower part of the diagram indicates the rate of the rearrangement reaction given by
and the blue trace indicates the direct cleavage reaction
A rate constant of 10 s is sufficiently fast for ion decomposition within the ion source of a typical mass spectrometer. Ions with rate constants less than 10 s and greater than approximately 10 s (lifetimes between 10 and 10 s) have a high probability of decomposing in the mass spectrometer between the ion source and the detector. These rate constants are indicated in the Wahrhaftig diagram by the log k = 5 and log k = 6 dashed lines.
Indicated on the rate constant plot are the reaction critical energy (also called the activation energy) for the formation of AD, E(AD) and AB, E(AB). These represent the minimum internal energy of ABCD required to form the respective product ions: the difference in the zero point energy of ABCD and that of the activated complex.
When the internal energy of ABCD is greater than E(AD), the ions are metastable (indicated by m); this occurs near log k > 5. A metastable ion has sufficient internal energy to dissociate prior to detection. The energy E(AD) is defined as the internal energy of ABCD that results in an equal probability that ABCDand AD leave the ion source, which occurs at near log k = 6. When the precursor ion has an internal energy equal to E(AB), the rates of formation of AD and AB are equal. | 7 | Physical Chemistry |
Haploid yeast switch mating type by replacing the information present at the MAT locus. For example, an a cell will switch to an α cell by replacing the MATa allele with the MATα allele. This replacement of one allele of MAT for the other is possible because yeast cells carry an additional silenced copy of both the MATa and MATα alleles: the HML (homothallic mating left) locus typically carries a silenced copy of the MATα allele, and the HMR (homothallic mating right) locus typically carries a silenced copy of the MATa allele. The silent HML and HMR loci are often referred to as the silent mating cassettes, as the information present there is read into the active MAT locus.
These additional copies of the mating type information do not interfere with the function of whatever allele is present at the MAT locus because they are not expressed, so a haploid cell with the MATa allele present at the active MAT locus is still an a cell, despite also having a (silenced) copy of the MATα allele present at HML. Only the allele present at the active MAT locus is transcribed, and thus only the allele present at MAT will influence cell behaviour. Hidden mating type loci are epigenetically silenced by SIR proteins, which form a heterochromatin scaffold that prevents transcription from the silent mating cassettes. | 1 | Biochemistry |
As the first Ph.D. and full-time professor of biochemistry in Korea, Lee contributed to the establishment of biochemistry as a newly organized field of study in Korea.
He began with a study of glycolysis. In the late 1920s, the role of phosphorylated compounds in glycolysis had not yet been fully explained. Lee's work touched on early aspects of intermediary carbohydrate metabolism, which was also the subject of Nobel Prize-winning research by Otto Fritz Meyerhof, Otto Heinrich Warburg, and Hans Adolf Krebs.
Lee maintained an interest in factors affecting glucose metabolism upon his return to Korea, where he continued his research with published studies of the Korean diet. Building upon work begun in 1928, he investigated the problem of identifying and quantifying the nutritional elements of the staple Korean diet and its effects on metabolism. He identified nutritional sources in these foods for the healthy development of Korean children and adults during the Japanese occupation of Korea.
In addition to teaching and editing, Lee authored and co-authored at least 10 scientific papers and articles in several languages throughout his brief career. He did all of this despite working under conditions of widespread rationing at the end of World War II. | 1 | Biochemistry |
Bioceramics and bioglasses are ceramic materials that are biocompatible. Bioceramics are an important subset of biomaterials. Bioceramics range in biocompatibility from the ceramic oxides, which are inert in the body, to the other extreme of resorbable materials, which are eventually replaced by the body after they have assisted repair. Bioceramics are used in many types of medical procedures. Bioceramics are typically used as rigid materials in surgical implants, though some bioceramics are flexible. The ceramic materials used are not the same as porcelain type ceramic materials. Rather, bioceramics are closely related to either the body's own materials or are extremely durable metal oxides. | 7 | Physical Chemistry |
Many methods have been developed for the restriction of microbial corrosion. The primary challenge has been finding ways to prevent or stop microbial growth without negatively impacting the surrounding environment. The list below provides an overview of some of the tactics that have been used or that are in development.
* Using biocide (any chemical that inhibits life) to kill microorganisms. Because biofilms are so resistant, a lot of biocide must be used. This is expensive, has negative effects on the surrounding environment, and can actually cause more corrosion of the surface due to its toxicity. Biocides and other chemical treatments against microbes also tend to be dangerous for the people preparing and applying them.
Rao and Mulky developed an extensive list of methods to limit the growth of microbes and therefore microbial corrosion.
* Plant products could aid in restricting microbial growth. These would be biodegradable and safe for the people applying them, but have not yet been widely tested.
* Surfactants, specifically ones generated by organisms as secondary metabolites. They’re useful because they get between the corrosive liquid and the surface and keep them apart.
* Putting a superhydrophobic coating on a surface. This keeps a biofilm from being able to develop, but is sensitive and can easily lose its superhydrophobic qualities.
* Using self-healing surfaces can prevent corrosion in cracks or faults. This could be used with a superhydrophobic surface, to mitigate its sensitivity.
* Using hydrophilic surfaces to create a region that deters the development of proteins into a film covering a surface.
* Using synthetically-created substances that deter corrosion because of their chemical structures. This may have a smaller negative effect on the environment than other options.
* Using biofilms that are grown intentionally to inhibit microbial corrosion. This is done by growing a biofilm on a surface made of a bacteria that can release compounds that kill other microbes and that prevent corrosion.
* Using essential oils. The effectiveness of essential oils against microbial corrosion has not been widely tested.
* Coating a surface with various nanomaterials or ozone to prevent microbial corrosion. | 8 | Metallurgy |
In genetic epidemiology, endophenotype (or intermediate phenotype) is a term used to separate behavioral symptoms into more stable phenotypes with a clear genetic connection. By seeing the EP notion as a special case of a larger collection of multivariate genetic models, which may be fitted using currently accessible methodology, it is possible to maximize its valuable potential lessons for etiological study in psychiatric disorders.
The concept was coined by Bernard John and Kenneth R. Lewis in a 1966 paper attempting to explain the geographic distribution of grasshoppers. They claimed that the particular geographic distribution could not be explained by the obvious and external "exophenotype" of the grasshoppers, but instead must be explained by their microscopic and internal "endophenotype". The endophenotype idea represents the influence of two important conceptual currents in biology and psychology research. An adequate technology would be required to perceive the endophenotype, which represents an unobservable latent entity that cannot be directly observed with the unaided naked eye. In the investigation of anxiety and affective disorders, the endophenotype idea has gained popularity.
The next major use of the term was in psychiatric genetics, to bridge the gap between high-level symptom presentation and low-level genetic variability, such as single nucleotide polymorphisms. It is therefore more applicable to more heritable disorders, such as bipolar disorder and schizophrenia. Through their impact on the growth and operation of the vital components of the nervous system, such as neurons, transmitter systems, and neural networks, genes have an impact on complex behavior. Therefore, heritable differences in mental abilities may be caused by changes in the code describing the shape and operation of the underlying neural network. One significant expression of this idea is believed to be the many cognitive deficiencies seen in ADHD, making them ideal candidates for an endophenotype approach. Since then, the concept has expanded to many other fields, such as the study of ADHD, addiction, Alzheimer's disease, obesity and cystic fibrosis. Some other terms which have a similar meaning but do not stress the genetic connection as highly are "intermediate phenotype", "biological marker", "subclinical trait", "vulnerability marker", and "cognitive marker". The strength of an endophenotype is its ability to differentiate between potential diagnoses that present with similar symptoms. | 2 | Environmental Chemistry |
In 2013, researchers reported their discovery of bacteria living in the rock of the oceanic crust below the thick layers of sediment, and apart from the hydrothermal vents that form along the edges of the tectonic plates. Preliminary findings are that these bacteria subsist on the hydrogen produced by chemical reduction of olivine by seawater circulating in the small veins that permeate the basalt that comprises oceanic crust. The bacteria synthesize methane by combining hydrogen and carbon dioxide. | 1 | Biochemistry |
In the early 1970s, Alexey Olovnikov first recognized that chromosomes cannot completely duplicate their ends during cell division. This is known as the "end replication problem". Olovnikov proposed that every time a cell divides, a part of the DNA sequence is lost, and if this loss reaches a certain level, cell division will stop at the end. According to his "marginotomy" theory, there are sequences at the end of the DNA (telomeres) that are placed in tandem repeats and create a buffer zone that determines the number of divisions a particular cell can undergo.
Many organisms have a ribonucleoprotein enzyme called telomerase, which is responsible for adding repetitive nucleotide sequences to the ends of DNA. Telomerase replicates the telomere head and does not require ATP. In most multicellular eukaryotic organisms, telomerase is active only in germ cells, some types of stem cells such as embryonic stem cells, and certain white blood cells. Telomerase can be reactivated and telomeres restored to the embryonic state by somatic cell nuclear transfer. The continuous shortening of telomeres with each replication in somatic (body) cells may play a role in aging and in cancer prevention. This is because telomeres act as a kind of "delayed fuse" and eventually run out after a certain number of cell divisions. This action results in the loss of vital genetic information from the cell's chromosome after multiple divisions. Research on telomerase is extremely important in understanding its role in maintaining telomere length and its potential implications for aging and cancer. | 1 | Biochemistry |
In carbon capture an effective absorbent is one which demonstrates a high selectivity, meaning that CO will preferentially dissolve in the absorbent compared to other gaseous components. In post-combustion carbon capture the most salient separation is CO from N, whereas in pre-combustion separation CO is primarily separated from H. Other components and impurities may be present in the flue gas, such as hydrocarbons, SO, or HS. Before selecting the appropriate solvent to use for carbon capture it is critical to ensure that at the given process conditions and flue gas composition CO maintains a much higher solubility in the solvent than the other species in the flue gas and thus has a high selectivity.
The selectivity of CO in ionic liquids has been widely studied by researchers. Generally, polar molecules and molecules with an electric quadrupole moment are highly soluble in liquid ionic substances. It has been found that at high process temperatures the solubility of CO decreases, while the solubility of other species, such as CH and H, may increase with increasing temperature, thereby reducing the effectiveness of the solvent. However, the solubility of N in ionic liquids is relatively low and does not increase with increasing temperature so the use of ionic liquids in post-combustion carbon capture may be appropriate due to the consistently high CO/N selectivity. The presence of common flue gas impurities such as HS severely inhibits CO solubility in ionic liquids and should be carefully considered by engineers when choosing an appropriate solvent for a particular flue gas. | 7 | Physical Chemistry |
Preliminary research indicates that disease risk in aging may be associated with telomere shortening, senescent cells, or SASP (senescence-associated secretory phenotype). | 1 | Biochemistry |
In physical and analytical chemistry, colorimetry or colourimetry is a technique used to determine the concentration of colored compounds in solution.
A colorimeter is a device used to test the magnitude of a solution by measuring its absorbance of a specific wavelength of light (not to be confused with the tristimulus colorimeter used to measure colors in general).
To use the colorimeter, different solutions must be made, including a control or reference of known concentration. With a visual colorimeter, for example the Duboscq colorimeter illustrated, the length of the light path through the solutions can be varied while filtered light transmitted through them is compared for a visual match. The concentration times path length is taken to be equal when the colors match, so the concentration of the unknown can be determined by simple proportions. Nessler tubes work on the same principle.
There are also electronic automated colorimeters; before these machines are used, they must be calibrated with a cuvette containing the control solution. The concentration of a sample can be calculated from the intensity of light before and after it passes through the sample by using the Beer–Lambert law. Photoelectric analyzers came to dominate in the 1960s.
The color or wavelength of the filter chosen for the colorimeter is extremely important, as the wavelength of light that is transmitted by the colorimeter has to be the same as that absorbed by the substance being measured. For example, the filter on a colorimeter might be set to red if the liquid is blue. | 3 | Analytical Chemistry |
Plants rich in anthocyanins are Vaccinium species, such as blueberry, cranberry, and bilberry; Rubus berries, including black raspberry, red raspberry, and blackberry; blackcurrant, cherry, eggplant (aubergine) peel, black rice, ube, Okinawan sweet potato, Concord grape, muscadine grape, red cabbage, and violet petals. Red-fleshed peaches and apples contain anthocyanins. Anthocyanins are less abundant in banana, asparagus, pea, fennel, pear, and potato, and may be totally absent in certain cultivars of green gooseberries.
The highest recorded amount appears to be specifically in the seed coat of black soybean (Glycine max L. Merr.) containing approximately 2 g per 100 g, in purple corn kernels and husks, and in the skins and pulp of black chokeberry (Aronia melanocarpa L.) (see table). Due to critical differences in sample origin, preparation, and extraction methods determining anthocyanin content, the values presented in the adjoining table are not directly comparable.
Nature, traditional agriculture methods, and plant breeding have produced various uncommon crops containing anthocyanins, including blue- or red-flesh potatoes and purple or red broccoli, cabbage, cauliflower, carrots, and corn. Garden tomatoes have been subjected to a breeding program using introgression lines of genetically modified organisms (but not incorporating them in the final purple tomato) to define the genetic basis of purple coloration in wild species that originally were from Chile and the Galapagos Islands. The variety known as "Indigo Rose" became available commercially to the agricultural industry and home gardeners in 2012. Investing tomatoes with high anthocyanin content doubles their shelf-life and inhibits growth of a post-harvest mold pathogen, Botrytis cinerea.
Some tomatoes also have been modified genetically with transcription factors from snapdragons to produce high levels of anthocyanins in the fruits. Anthocyanins also may be found in naturally ripened olives, and are partly responsible for the red and purple colors of some olives. | 3 | Analytical Chemistry |
In aerosol mass spectrometry, one of the ionization techniques consists in firing a laser to individual droplets. These systems are called single particle mass spectrometers (SPMS). The sample may optionally be mixed with a MALDI matrix prior to aerosolization. | 1 | Biochemistry |
While many of the proteins involved in NMD are not conserved between species, in Saccharomyces cerevisiae (yeast), there are three main factors in NMD: UPF1, UPF2 and UPF3 (UPF3A and UPF3B in humans), that make up the conserved core of the NMD pathway. All three of these factors are trans-acting elements called up-frameshift (UPF) proteins. In mammals, UPF2 and UPF3 are part of the exon-exon junction complex (EJC) bound to mRNA after splicing along with other proteins, eIF4AIII, MLN51, and the Y14/MAGOH heterodimer, which also function in NMD. UPF1 phosphorylation is controlled by the proteins SMG-1, SMG-5, SMG-6 and SMG-7.
The process of detecting aberrant transcripts occurs during translation of the mRNA. A popular model for the detection of aberrant transcripts in mammals suggests that during the first round of translation, the ribosome removes the exon-exon junction complexes bound to the mRNA after splicing occurs. If after this first round of translation, any of these proteins remain bound to the mRNA, NMD is activated. Exon-exon junction complexes located downstream of a stop codon are not removed from the transcript because the ribosome is released before reaching them. Termination of translation leads to the assembly of a complex composed of UPF1, SMG1 and the release factors, eRF1 and eRF3, on the mRNA. If an EJC is left on the mRNA because the transcript contains a premature stop codon, then UPF1 comes into contact with UPF2 and UPF3, triggering the phosphorylation of UPF1. In vertebrates, the location of the last exon-junction complex relative to the termination codon usually determines whether the transcript will be subjected to NMD or not. If the termination codon is downstream of or within about 50 nucleotides of the final exon-junction complex then the transcript is translated normally. However, if the termination codon is further than about 50 nucleotides upstream of any exon-junction complexes, then the transcript is down regulated by NMD. The phosphorylated UPF1 then interacts with SMG-5, SMG-6 and SMG-7, which promote the dephosphorylation of UPF1. SMG-7 is thought to be the terminating effector in NMD, as it accumulates in P-bodies, which are cytoplasmic sites for mRNA decay. In both yeast and human cells, the major pathway for mRNA decay is initiated by the removal of the 5’ cap followed by degradation by XRN1, an exoribonuclease enzyme. The other pathway by which mRNA is degraded is by deadenylation from 3’-5'.
In addition to the well recognized role of NMD in removing aberrant transcripts, there are transcripts that contain introns within their 3'UTRs. These messages are predicted to be NMD-targets yet they (e.g., activity-regulated cytoskeleton-associated protein, known as Arc) can play crucial biologic functions suggesting that NMD may have physiologically relevant roles. | 1 | Biochemistry |
In healthy persons, the intra-individual variation of TSH and thyroid hormones is considerably smaller than the inter-individual variation. This results from a personal set point of thyroid homeostasis. In hypothyroidism, it is impossible to directly access the set point, but it can be reconstructed with methods of systems theory.
A computerised algorithm, called Thyroid-SPOT, which is based on this mathematical theory, has been implemented in software applications. In patients undergoing thyroidectomy it could be demonstrated that this algorithm can be used to reconstruct the personal set point with sufficient precision. | 1 | Biochemistry |
Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming from the Sun. Extremely short or vacuum UV (10–100 nm) is screened out by nitrogen. UV radiation capable of penetrating nitrogen is divided into three categories, based on its wavelength; these are referred to as UV-A (400–315 nm), UV-B (315–280 nm), and UV-C (280–100 nm).
UV-C, which is very harmful to all living things, is entirely screened out by a combination of dioxygen (< 200 nm) and ozone (> about 200 nm) by around altitude. UV-B radiation can be harmful to the skin and is the main cause of sunburn; excessive exposure can also cause cataracts, immune system suppression, and genetic damage, resulting in problems such as skin cancer. The ozone layer (which absorbs from about 200 nm to 310 nm with a maximal absorption at about 250 nm) is very effective at screening out UV-B; for radiation with a wavelength of 290 nm, the intensity at the top of the atmosphere is 350 million times stronger than at the Earths surface. Nevertheless, some UV-B, particularly at its longest wavelengths, reaches the surface, and is important for the skins production of vitamin D in mammals.
Ozone is transparent to most UV-A, so most of this longer-wavelength UV radiation reaches the surface, and it constitutes most of the UV reaching the Earth. This type of UV radiation is significantly less harmful to DNA, although it may still potentially cause physical damage, premature aging of the skin, indirect genetic damage, and skin cancer. | 5 | Photochemistry |
Stamp sand is a coarse sand left over from the processing of ore in a stamp mill. In the United States, the most well-known deposits of stamp sand are in the Copper Country of northern Michigan, where it is black or dark gray, and may contain hazardous concentrations of trace metals.
In the 19th and early 20th centuries, many metal mines used stamp mills to process ore-bearing rock. The rock was brought to a stamp mill to be crushed. After crushing the material was mechanically separated to extract metals, or chemically treated by acids if the metal could be leached out. The size of the crushed material depended on the nature of the ore found in each mining district. | 8 | Metallurgy |
The application of electric fields to ceramics can give rise to plasticity in materials that traditionally exhibit no plastic deformation. High homologous temperatures are, however, typically necessary to achieve significant plastic deformation in ceramic materials. Plastic deformation ceramic oxides was found by Conrad et al. to occur under relatively modest electric field strengths (0.02-0.32 ). Strain-mediating defects such as vacancies and dislocations tend to be charged in ceramic materials due to the ionic or covalent nature of bonding. Thus, the movement of electrons can have a direct impact on the mobility of these defects in ceramics and subsequent plastic deformation. The primary effect of the electric field in the deformation of fine-grained ceramic oxides is to shift the diffusion pathway from bulk diffusion to grain boundary diffusion, resulting in greater diffusion and easier grain boundary sliding. | 7 | Physical Chemistry |
A western blot is a technique by which specific proteins can be detected from a mixture of proteins. Western blots can be used to determine the size of isolated proteins, as well as to quantify their expression. In western blotting, proteins are first separated by size, in a thin gel sandwiched between two glass plates in a technique known as SDS-PAGE. The proteins in the gel are then transferred to a polyvinylidene fluoride (PVDF), nitrocellulose, nylon, or other support membrane. This membrane can then be probed with solutions of antibodies. Antibodies that specifically bind to the protein of interest can then be visualized by a variety of techniques, including colored products, chemiluminescence, or autoradiography. Often, the antibodies are labeled with enzymes. When a chemiluminescent substrate is exposed to the enzyme it allows detection. Using western blotting techniques allows not only detection but also quantitative analysis. Analogous methods to western blotting can be used to directly stain specific proteins in live cells or tissue sections. | 1 | Biochemistry |
ATSDR is an agency within the US Department of Health and Human Services concerned with the effects of hazardous substances on human health. ATSDR is charged with assessing the presence and nature of health hazards at specific Superfund sites, as well as helping prevent or reduce further exposure and the illnesses that can result from such exposures. ATSDR is an oversight agency created to ensure that public health protection and environmental regulation work hand in hand.
ATSDR functions include public health assessments of National Priority List (NPL or Superfund) hazardous waste sites; petitioned health consultations or assessments concerning specific waste sites or industrial facilities that US citizens have requested further action upon; the conduct of health studies (including surveillance and registries) to determine the long-term impact of these facilities; response to emergency releases of hazardous substances, applied research in support of public health assessments, information development and dissemination, and education and training concerning hazardous substances. ATSDR also prepares [https://wwwn.cdc.gov/TSP/index.aspx toxicological profiles] for hazardous substances found at National Priorities List sites, as well as at federal sites administered by the Department of Defense and Department of Energy. | 1 | Biochemistry |
Ions of opposite charge are naturally attracted to each other by the electrostatic force. This is described by Coulomb's law:
where is the force of attraction, and are the magnitudes of the electrical charges, is the dielectric constant of the medium and is the distance between the ions. For ions in solution this is an approximation because the ions exert a polarizing effect on the solvent molecules that surround them, which attenuates the electric field somewhat. Nevertheless, some general conclusions can be inferred.
:Ion association will increase as:
:*the magnitude(s) of the electrical charge(s) and increase,
:*the magnitude of the dielectric constant decreases,
:*the size of the ions decreases so that the distance between cation and anion decreases.
The equilibrium constant for ion-pair formation, like all equilibrium constants, is related to the standard free-energy change:
where is the gas constant and is the temperature in kelvins. Free energy is made up of an enthalpy term and an entropy term:
The coulombic energy released when ions associate contributes to the enthalpy term, . In the case of contact ion pairs, the covalent interaction energy also contributes to the enthalpy, as does the energy of displacing a solvent molecule from the solvation shell of the cation or anion. The tendency to associate is opposed by the entropy term, which results from the fact that the solution containing unassociated ions is more disordered than a solution containing associates. The entropy term is similar for electrolytes of the same type, with minor differences due to solvation effects. Therefore, it is the magnitude of the enthalpy term that mostly determines the extent of ion association for a given electrolyte type. This explains the general rules given above. | 7 | Physical Chemistry |
Both photosystem I and II are required for oxygenic photosynthesis. Oxygenic photosynthesis can be performed by plants and cyanobacteria; cyanobacteria are believed to be the progenitors of the photosystem-containing chloroplasts of eukaryotes. Photosynthetic bacteria that cannot produce oxygen have only one photosystem, which is similar to either PSI or PSII.
At the core of photosystem II is P680, a special chlorophyll to which incoming excitation energy from the antenna complex is funneled. One of the electrons of excited P680* will be transferred to a non-fluorescent molecule, which ionizes the chlorophyll and boosts its energy further, enough that it can split water in the oxygen evolving complex (OEC) of PSII and recover its electron. At the heart of the OEC are 4 Mn atoms, each of which can trap one electron. The electrons harvested from the splitting of two waters fill the OEC complex in its highest-energy state, which holds 4 excess electrons.
Electrons travel through the cytochrome b6f complex to photosystem I via an electron transport chain within the thylakoid membrane. Energy from PSI drives this process and is harnessed (the whole process is termed chemiosmosis) to pump protons across the membrane, into the thylakoid lumen space from the chloroplast stroma. This will provide a potential energy difference between lumen and stroma, which amounts to a proton-motive force that can be utilized by the proton-driven ATP synthase to generate ATP. If electrons only pass through once, the process is termed noncyclic photophosphorylation, but if they pass through PSI and the proton pump multiple times it is called cyclic photophosphorylation.
When the electron reaches photosystem I, it fills the electron deficit of light-excited reaction-center chlorophyll P700 of PSI. The electron may either continue to go through cyclic electron transport around PSI or pass, via ferredoxin, to the enzyme NADP reductase. Electrons and protons are added to NADP to form NADPH.
This reducing (hydrogenation) agent is transported to the Calvin cycle to react with glycerate 3-phosphate, along with ATP to form glyceraldehyde 3-phosphate, the basic building block from which plants can make a variety of substances. | 5 | Photochemistry |
In 2008, Hunter married Rosaleen Theresa McHugh. Together they have three children; two sons and one daughter. | 0 | Organic Chemistry |
From 1955 until 1977, the Sangamo Weston plant in Pickens, South Carolina, used PCBs to manufacture capacitors, and dumped 400,000 pounds of PCB contaminated wastewater into the Twelve Mile Creek. In 1990, the EPA declared the site of the capacitor plant, its landfills and the polluted watershed, which stretches nearly downstream to Lake Hartwell as a Superfund site. Two dams on the Twelve Mile Creek are to be removed and on Feb. 22, 2011 the first of two dams began to be dismantled. Some contaminated sediment is being removed from the site and hauled away, while other sediment is pumped into a series of settling ponds.
In 2013, the state environmental regulators issued a rare emergency order, banning all sewage sludge from being land applied or deposited on landfills, as it contained very high levels of PCBs. The problem had not been discovered until thousands of acres of farm land in the state had been contaminated by the hazardous sludge. A criminal investigation to determine the perpetrator of this crime was launched. | 2 | Environmental Chemistry |
As with any functional group, the hazards of halohydrins are difficult to generalize as they may form part of an almost limitless series of compounds, with each structure having different pharmacology. In general, simpler low molecular weight compounds are often toxic and carcinogenic (e.g. 2-chloroethanol, 3-MCPD) by virtue of being alkylating agents. This reactivity can be put to good use, for instance in the anti-cancer drug mitobronitol. A number of synthetic corticosteroids exist bearing a fluorohydrin motif (triamcinolone, dexamethasone). | 0 | Organic Chemistry |
Beginning in about 3000 BC arsenic was mined and added to copper in the alloying of bronze, but the adverse health effects of working with arsenic led to it being abandoned when a viable alternative, tin, was discovered.
In addition to its presence as a poison, for centuries arsenic was used medicinally. It has been used for over 2,400 years as a part of traditional Chinese medicine. In the western world, arsenic compounds, such as salvarsan, were used extensively to treat syphilis before penicillin was introduced. It was eventually replaced as a therapeutic agent by sulfa drugs and then by other antibiotics. Arsenic was also an ingredient in many tonics (or "patent medicines").
In addition, during the Elizabethan era, some women used a mixture of vinegar, chalk, and arsenic applied topically to whiten their skin. This use of arsenic was intended to prevent aging and creasing of the skin, but some arsenic was inevitably absorbed into the blood stream.
During the Victorian era (late 19th century) in the United States, U.S. newspapers advertised "arsenic complexion wafers" that promised to remove facial blemishes such as moles and pimples.
Some pigments, most notably the popular Emerald Green (known also under several other names), were based on arsenic compounds. Overexposure to these pigments was a frequent cause of accidental poisoning of artists and craftsmen.
Arsenic became a favored method for murder of the Middle Ages and Renaissance, particularly among ruling classes in Italy allegedly. Because the symptoms are similar to those of cholera, which was common at the time, arsenic poisoning often went undetected. By the 19th century, it had acquired the nickname "inheritance powder," perhaps because impatient heirs were known or suspected to use it to ensure or accelerate their inheritances. It was also a common murder technique in the 19th century in domestic violence situations, such as the case of Rebecca Copin, who attempted to poison her husband by "putting arsenic in his coffee".
In post-WW1 Hungary, arsenic extracted by boiling fly paper was used in an estimated 300 murders by the Angel Makers of Nagyrév.
In imperial China, arsenic trioxide and sulfides were used in murder, as well as for capital punishment for members of the royal family or aristocracy. Forensic studies have determined that the Guangxu Emperor (d. 1908) was murdered by arsenic, most likely ordered by the Empress Dowager Cixi or Generalissimo Yuan Shikai. Likewise, in ancient Korea, and particularly in the Joseon Dynasty, arsenic-sulfur compounds had been used as a major ingredient of sayak (사약; 賜藥), which was a poison cocktail used in capital punishment of high-profile political figures and members of the royal family. Due to social and political prominence of the condemned, many of these events were well-documented, often in the Annals of Joseon Dynasty; they are sometimes portrayed in historical television miniseries because of their dramatic nature.
One of the worst incidents of arsenic poisoning via well water occurred in Bangladesh, which the World Health Organization called the "largest mass poisoning of a population in history" recognized as a major public health concern. The contamination in the Ganga-Brahmaputra fluvial plains in India and Padma-Meghna fluvial plains in Bangladesh demonstrated adverse impacts on human health.
Arsenic poisoning from exposure to groundwater is believed to be responsible for the illness experienced by those that witnessed the 2007 Carancas impact event in Peru, as local residents inhaled steam which was contaminated with arsenic, produced from groundwater which boiled from the intense heat and pressure produced by a chondrite meteorite impacting the ground. | 1 | Biochemistry |
Adjusting for inflation, it cost $96 per watt for a solar module in the mid-1970s. Process improvements and a very large boost in production have brought that figure down more than 99%, to 30¢ per watt in 2018
and as low as 20¢ per watt in 2020.
Swansons law is an observation similar to Moores Law that states that solar cell prices fall 20% for every doubling of industry capacity. It was featured in an article in the British weekly newspaper The Economist in late 2012. Balance of system costs were then higher than those of the panels. Large commercial arrays could be built, as of 2018, at below $1.00 a watt, fully commissioned.
As the semiconductor industry moved to ever-larger boules, older equipment became inexpensive. Cell sizes grew as equipment became available on the surplus market; ARCO Solar's original panels used cells in diameter. Panels in the 1990s and early 2000s generally used 125 mm wafers; since 2008, almost all new panels use 156 mm cells. The widespread introduction of flat screen televisions in the late 1990s and early 2000s led to the wide availability of large, high-quality glass sheets to cover the panels.
During the 1990s, polysilicon ("poly") cells became increasingly popular. These cells offer less efficiency than their monosilicon ("mono") counterparts, but they are grown in large vats that reduce cost. By the mid-2000s, poly was dominant in the low-cost panel market, but more recently the mono returned to widespread use.
Manufacturers of wafer-based cells responded to high silicon prices in 2004–2008 with rapid reductions in silicon consumption. In 2008, according to Jef Poortmans, director of IMEC's organic and solar department, current cells use of silicon per watt of power generation, with wafer thicknesses in the neighborhood of 200 microns. Crystalline silicon panels dominate worldwide markets and are mostly manufactured in China and Taiwan. By late 2011, a drop in European demand dropped prices for crystalline solar modules to about $1.09 per watt down sharply from 2010. Prices continued to fall in 2012, reaching $0.62/watt by 4Q2012.
Solar PV is growing fastest in Asia, with China and Japan currently accounting for half of worldwide deployment. Global installed PV capacity reached at least 301 gigawatts in 2016, and grew to supply 1.3% of global power by 2016.
It was anticipated that electricity from PV will be competitive with wholesale electricity costs all across Europe and the energy payback time of crystalline silicon modules can be reduced to below 0.5 years by 2020.
Falling costs are considered one of the biggest factors in the rapid growth of renewable energy, with the cost of solar photovoltaic electricity falling by ~85% between 2010 (when solar and wind made up 1.7% of global electricity generation) and 2021 (where they made up 8.7%). In 2019 solar cells accounted for ~3 % of the world's electricity generation. | 7 | Physical Chemistry |
In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, three and four hydroxyl groups are diols, triols, and tetrols, respectively. | 7 | Physical Chemistry |
DEAD is toxic, shock and light sensitive; it can violently explode when its undiluted form is heated above 100 °C. Shipment by air of pure diethyl azodicarboxylate is prohibited in the United States and is carried out in solution, typically about 40% DEAD in toluene. Alternatively, DEAD is transported and stored on 100–300 mesh polystyrene particles at a concentration of about 1 mmol/g. The time-weighed average threshold limit value for exposure to DEAD over a typical 40-hour working week is 50 parts per million; that is, DEAD is half as toxic as, e.g., carbon monoxide. Safety hazards have resulted in rapid decline of DEAD usage and replacement with DIAD and other similar compounds. | 0 | Organic Chemistry |
The C−H bond in general is very strong, so it is relatively unreactive. In several compound classes, collectively called carbon acids, the C−H bond can be sufficiently acidic for proton removal. Unactivated C−H bonds are found in alkanes and are not adjacent to a heteroatom (O, N, Si, etc.). Such bonds usually only participate in radical substitution. Many enzymes are known, however, to effect these reactions.
Although the C−H bond is one of the strongest, it varies over 30% in magnitude for fairly stable organic compounds, even in the absence of heteroatoms. | 0 | Organic Chemistry |
Various clinical studies have shown that levamlodipine has more selectivity and better efficacy than (R)-amlodipine. In pooled data, from three comparative studies conducted in 200 patients with mild to moderate hypertension, 2.5 mg of levamlodipine was found to be equivalent in its blood pressure lowering efficacy to 5 mg of amlodipine. The average reduction in systolic BP was 19±3 vs 19±4, 20±2 vs 19±3 and 20±2 vs 19±3 mm of Hg recorded in standing, supine and sitting position respectively for levamlodipine compared to racemic amlodipine. The studies also reported a significant reduction in total cholesterol and triglyceride levels with levamlodipine, which was not seen with amlodipine.
Efficacy and safety of levamlodipine (2.5 mg, once daily) has been evaluated in the patients with isolated systolic hypertension (ISH). Levamlodipine effectively reduced the systolic BP (mean reduction 22±14 mm of Hg) in all grades of ISH. After 28 days of the treatment, overall responder rate was 73%. It significantly reduced the systolic and diastolic BP within 4 weeks with a responder rate of 96.5%.
Elderly hypertensives with diabetes mellitus exhibits higher response to levamlodipine therapy than non-diabetic patients. Levamlodipine is an effective switch-over option for the elderly patients who experience oedema and other adverse events with racemic amlodipine. | 4 | Stereochemistry |
In this situation RNA polymerase is dependent on (lagging) ribosome activity; if the ribosome pauses due to insufficient charged tRNA then the anti-terminator structure is favoured. The canonical attenuator example of the trp operon uses this mechanism in E. coli. Similar regulatory mechanisms have been found in many amino acid biosynthetic operons. | 1 | Biochemistry |
For almost 50 years molecular biology was based on two dogmas: (i) equating biological function of the protein with a unique three-dimensional structure and (ii) assuming exquisite specificity in protein complexes. Specificity/selectivity is ensured by unambiguous set of interactions formed between the protein and its ligand (another protein, DNA, RNA or small molecule). Many protein complexes however, contain functionally important/critical regions, which remain highly dynamic in the complex or adopt different conformations. This phenomenon is defined fuzziness. The most pertinent example is the cyclin-dependent kinase inhibitor Sic1, which binds to the SCF subunit of Cdc4 in a phosphorylation dependent manner. No regular secondary structures are gained upon phosphorylation and the different phosphorylation sites interchange in the complex. | 4 | Stereochemistry |
In soldering metals, flux serves a threefold purpose: it removes any oxidized metal from the surfaces to be soldered, seals out air thus preventing further oxidation, and improves the wetting characteristics of the liquid solder. Some fluxes are corrosive, so the parts have to be cleaned with a damp sponge or other absorbent material after soldering to prevent damage. Several types of flux are used in electronics.
A number of standards exist to define the various flux types. The principal standard is J-STD-004.
Various tests, including the ROSE test, may be used after soldering to check for the presence of ionic or other contaminants that could cause short circuits or other problems. | 8 | Metallurgy |
Numerous chemical targets have distinct stereochemical demands. Stereochemical transformations (such as the Claisen rearrangement and Mitsunobu reaction) can remove or transfer the desired chirality thus simplifying the target. | 0 | Organic Chemistry |
Currently, the stability of most ionic liquids under practical electrochemical conditions is unknown, and the fundamental choice of ionic fluid is still empirical as there is almost no data on metal ion thermodynamics to feed into solubility and speciation models. Also, there are no Pourbaix diagrams available, no standard redox potentials, and bare knowledge of speciation or pH-values. It must be noticed that most processes reported in the literature involving ionic fluids have a Technology Readiness Level (TRL) 3 (experimental proof-of-concept) or 4 (technology validated in the lab), which is a disadvantage for short-term implementation. However, ionometallurgy has the potential to effectively recover metals in a more selective and sustainable way, as it considers environmentally benign solvents, reduction of greenhouse gas emissions and avoidance of corrosive and harmful reagents. | 8 | Metallurgy |
The ETS family is present throughout the body and is involved in a wide variety of functions including the regulation of cellular differentiation, cell cycle control, cell migration, cell proliferation, apoptosis (programmed cell death) and angiogenesis.
Multiple ETS factors have been found to be associated with cancer, such as through gene fusion. For example, the ERG ETS transcription factor is fused to the EWS gene, resulting in a condition called Ewing's sarcoma. The fusion of TEL to the JAK2 protein results in early pre-B acute lymphoid leukaemia. ERG and ETV1 are known gene fusions found in prostate cancer.
In addition, ETS factors, e.g. the vertebrate Etv1 and the invertebrate Ast-1, have been shown to be important players in the specification and differentiation of dopaminergic neurons in both C. elegans and olfactory bulbs of mice. | 1 | Biochemistry |
Classically radicals form by one-electron reductions. Typically one-electron reduced organic compounds are unstable. Stability is conferred to the radical anion when the charge can be delocalized. Examples include alkali metal naphthenides, anthracenides, and ketyls. | 2 | Environmental Chemistry |
Autapses can be either glutamate-releasing (excitatory) or GABA-releasing (inhibitory), just like their traditional synapse counterparts. Similarly, autapses can be electrical or chemical by nature.
Broadly speaking, negative feedback in autapses tends to inhibit excitable neurons whereas positive feedback can stimulate quiescent neurons.
Although the stimulation of inhibitory autapses did not induce hyperpolarizing inhibitory post-synaptic potentials in interneurons of layer V of neocortical slices, they have been shown to impact excitability. Upon using a GABA-antagonist to block autapses, the likelihood of an immediate subsequent second depolarization step increased following a first depolarization step. This suggests that autapses act by suppressing the second of two closely timed depolarization steps and therefore, they may provide feedback inhibition onto these cells. This mechanism may also potentially explain shunting inhibition.
In cell culture, autapses have been shown to contribute to the prolonged activation of B31/B32 neurons, which significantly contribute food-response behavior in Aplysia. This suggests that autapses may play a role in mediating positive feedback. The B31/B32 autapse was unable to play a role in initiating the neurons activity, although it is believed to have helped sustain the neurons depolarized state. The extent to which autapses maintain depolarization remains unclear, particularly since other components of the neural circuit (i.e. B63 neurons) are also capable of providing strong synaptic input throughout the depolarization. Additionally, it has been suggested that autapses provide B31/B32 neurons with the ability to quickly repolarize. Bekkers (2009) has proposed that specifically blocking the contribution of autapses and then assessing the differences with or without blocked autapses could better illuminate the function of autapses.
Hindmarsh–Rose (HR) model neurons have demonstrated chaotic, regular spiking, quiescent, and periodic patterns of burst firing without autapses. Upon the introduction of an electrical autapse, the periodic state switches to the chaotic state and displays an alternating behavior that increases in frequency with a greater autaptic intensity and time delay. On the other hand, excitatory chemical autapses enhanced the overall chaotic state. The chaotic state was reduced and suppressed in the neurons with inhibitory chemical autapses. In HR model neurons without autapses, the pattern of firing altered from quiescent to periodic and then to chaotic as DC current was increased. Generally, HR model neurons with autapses have the ability to swap into any firing pattern, regardless of the prior firing pattern. | 1 | Biochemistry |
Due to the potential for wear protection at high temperatures beyond which conventional lubricants can be used, possible uses have been speculated in applications such as car engines, power generation and even aerospace, where there is an increasing demand for ever higher efficiency and thus operating temperature. | 8 | Metallurgy |
Good flow properties of granules and powders are important in the manufacturing of tablets and capsules. The distribution of particles should be uniform in terms of number and weight. Very small particle size causes attraction, which in turn destabilises the suspension by coagulating. | 7 | Physical Chemistry |
In astronomy, hyperspectral imaging is used to determine a spatially-resolved spectral image. Since a spectrum is an important diagnostic, having a spectrum for each pixel allows more science cases to be addressed. In astronomy, this technique is commonly referred to as integral field spectroscopy, and examples of this technique include FLAMES and SINFONI on the Very Large Telescope, but also the Advanced CCD Imaging Spectrometer on Chandra X-ray Observatory uses this technique. | 7 | Physical Chemistry |
β-Carbon elimination (beta-carbon elimination) is a type of reaction in organometallic chemistry wherein an allyl ligand bonded to a metal center is broken into the corresponding metal-bonded alkyl (aryl) ligand and an alkene. It is a subgroup of elimination reactions. Though less common and less understood than β-hydride elimination, it is an important step involved in some olefin polymerization processes and transition-metal-catalyzed organic reactions. | 0 | Organic Chemistry |
Neoglycorandomization is a chemoselective glycodiversification method inspired by the alkoxyamine-based ‘neoglycosylation’ reaction first described Peri and Dumy. This reaction proceeds via an oxy-iminium intermediate to ultimately provide the more thermodynamically-favored closed ring neoglycoside. The neoglycosylation reaction is compatible with a wide range of saccharide and aglycon functionality where neoglycoside anomeric stereospecificity is a thermodynamically-driven. Importantly, structural and functional studies reveal neoglycosides to serve as good mimics of their O-glycosidic comparators. The first neoglycorandomization proof of concept focused upon digitoxin where the rapid generation and cancer cell line cytotoxicity screening of 78 digitoxigenin neoglycosides revealed unique analogs with improved anticancer activity and reduced potential for cardiotoxicity. This platform has since been automated and used as an effective medicinal chemistry tool to modulate the properties of a range of natural products and pharmaceutical drugs. | 0 | Organic Chemistry |
Pulsatile secretion is a biochemical phenomenon observed in a wide variety of cell and tissue types, in which chemical products are secreted in a regular temporal pattern. The most common cellular products observed to be released in this manner are intercellular signaling molecules such as hormones or neurotransmitters. Examples of hormones that are secreted pulsatilely include insulin, thyrotropin, TRH, gonadotropin-releasing hormone (GnRH) and growth hormone (GH). In the nervous system, pulsatility is observed in oscillatory activity from central pattern generators. In the heart, pacemakers are able to work and secrete in a pulsatile manner. A pulsatile secretion pattern is critical to the function of many hormones in order to maintain the delicate homeostatic balance necessary for essential life processes, such as development and reproduction. Variations of the concentration in a certain frequency can be critical to hormone function, as evidenced by the case of GnRH agonists, which cause functional inhibition of the receptor for GnRH due to profound downregulation in response to constant (tonic) stimulation. Pulsatility may function to sensitize target tissues to the hormone of interest and upregulate receptors, leading to improved responses. This heightened response may have served to improve the animal's fitness in its environment and promote its evolutionary retention.
Pulsatile secretion in its various forms is observed in:
*Hypothalamic-pituitary-gonadal axis (HPG) related hormones
*Glucocorticoids
*Insulin
*Growth hormone
*Parathyroid hormone | 1 | Biochemistry |
As of November 2007, the database contained 59 pathways (comprising 3309 molecular interactions) curated by the NCI-Nature editorial team. New pathways are added each month. The database also contains 254 pathways (comprising 3003 interactions) imported from the June 2004 edition of the BioCarta pathway database.
The NCI-Nature curated data is gathered from published research literature and reviewed by expert scientists before publication. Evidence codes are assigned to each molecular interaction, which allows users to evaluate the reliability of the interactions or to search for interactions identified by particular experimental techniques. | 1 | Biochemistry |
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