text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
The minimum physiological requirement for sodium is between 115 and 500 mg per day depending on sweating due to physical activity, and whether the person is adapted to the climate. Sodium chloride is the principal source of sodium in the diet, and is used as seasoning and preservative, such as for pickling and jerky; most of it comes from processed foods. The Adequate Intake for sodium is 1.2 to 1.5 g per day, but on average people in the United States consume 3.4 g per day, the minimum amount that promotes hypertension. Note that salt contains about 39.3% sodium by massthe rest being chlorine and other trace chemicals; thus the Tolerable Upper Intake Level of 2.3 g sodium would be about 5.9 g of salt—about 1 teaspoon. The average daily excretion of sodium is between 40 and 220 mEq.
Normal serum sodium levels are between approximately 135 and 145 mEq/L (135 to 145 mmol/L). A serum sodium level of less than 135 mEq/L qualifies as hyponatremia, which is considered severe when the serum sodium level is below 125 mEq/L.
The renin–angiotensin system and the atrial natriuretic peptide indirectly regulate the amount of signal transduction in the human central nervous system, which depends on sodium ion motion across the nerve cell membrane, in all nerves. Sodium is thus important in neuron function and osmoregulation between cells and the extracellular fluid; the distribution of sodium ions are mediated in all animals by sodium–potassium pumps, which are active transporter solute pumps, pumping ions against the gradient, and sodium-potassium channels. Sodium channels are known to be less selective in comparison to potassium channels. Sodium is the most prominent cation in extracellular fluid: in the 15 L of extracellular fluid in a 70 kg human there is around 50 grams of sodium, 90% of the body's total sodium content.
Some potent neurotoxins, such as batrachotoxin, increase the sodium ion permeability of the cell membranes in nerves and muscles, causing a massive and irreversible depolarization of the membranes with potentially fatal consequences. However, drugs with smaller effects on sodium ion motion in nerves may have diverse pharmacological effects that range from anti-depressant to anti-seizure actions. | 1 | Biochemistry |
Under severe stress conditions the bacteria Escherichia coli protects its DNA from damage by sequestering it within a crystalline structure. This process is mediated by the stress response protein Dps and allows the bacteria to survive varied assaults such as oxidative stress, heat shock, ultraviolet light, gamma radiation and extremes of pH. | 1 | Biochemistry |
The concept first appeared in 1899 in Johannes Thieles "Partial Valence Hypothesis" to explain the unusual stability of benzene which would not be expected from August Kekulés structure proposed in 1865 with alternating single and double bonds. Benzene undergoes substitution reactions, rather than addition reactions as typical for alkenes. He proposed that the carbon-carbon bond in benzene is intermediate of a single and double bond.
The resonance proposal also helped explain the number of isomers of benzene derivatives. For example, Kekulés structure would predict four' dibromobenzene isomers, including two ortho isomers with the brominated carbon atoms joined by either a single or a double bond. In reality there are only three dibromobenzene isomers and only one is ortho, in agreement with the idea that there is only one type of carbon-carbon bond, intermediate between a single and a double bond.
The mechanism of resonance was introduced into quantum mechanics by Werner Heisenberg in 1926 in a discussion of the quantum states of the helium atom. He compared the structure of the helium atom with the classical system of resonating coupled harmonic oscillators. In the classical system, the coupling produces two modes, one of which is lower in frequency than either of the uncoupled vibrations; quantum mechanically, this lower frequency is interpreted as a lower energy. Linus Pauling used this mechanism to explain the partial valence of molecules in 1928, and developed it further in a series of papers in 1931-1933. The alternative term mesomerism popular in German and French publications with the same meaning was introduced by C. K. Ingold in 1938, but did not catch on in the English literature. The current concept of mesomeric effect has taken on a related but different meaning. The double headed arrow was introduced by the German chemist Fritz Arndt who preferred the German phrase zwischenstufe or intermediate stage.
Resonance theory dominated over competing Hückel method for two decades thanks to being relatively easier to understand for chemists without fundamental physics background, even if they couldnt grasp the concept of quantum superposition and confused it with tautomerism. Pauling and Wheland themselves characterized Erich Hückels approach as "cumbersome" at the time, and his lack of communication skills contributed: when Robert Robinson sent him a friendly request, he responded arrogantly that he is not interested in organic chemistry.
In the Soviet Union, resonance theory – especially as developed by Pauling – was attacked in the early 1950s as being contrary to the Marxist principles of dialectical materialism, and in June 1951 the Soviet Academy of Sciences under the leadership of Alexander Nesmeyanov convened a conference on the chemical structure of organic compounds, attended by 400 physicists, chemists, and philosophers, where "the pseudo-scientific essence of the theory of resonance was exposed and unmasked". | 7 | Physical Chemistry |
A large group of bacterial exotoxins are referred to as "A/B toxins", in essence because they are formed from two subunits. The "A" subunit possesses enzyme activity, and is transferred to the host cell following a conformational change in the membrane-bound transport "B" subunit. Pertussis toxin is an exotoxin with six subunits (named S1 through S5—each complex contains two copies of S4). The subunits are arranged in A-B structure: the A component is enzymatically active and is formed from the S1 subunit, while the B component is the receptor-binding portion and is made up of subunits S2–S5. The subunits are encoded by ptx genes encoded on a large PT operon that also includes additional genes that encode Ptl proteins. Together, these proteins form the PT secretion complex. | 1 | Biochemistry |
The number and organization of operons has been studied most critically in E. coli. As a result, predictions can be made based on an organism's genomic sequence.
One prediction method uses the intergenic distance between reading frames as a primary predictor of the number of operons in the genome. The separation merely changes the frame and guarantees that the read through is efficient. Longer stretches exist where operons start and stop, often up to 40–50 bases.
An alternative method to predict operons is based on finding gene clusters where gene order and orientation is conserved in two or more genomes.
Operon prediction is even more accurate if the functional class of the molecules is considered. Bacteria have clustered their reading frames into units, sequestered by co-involvement in protein complexes, common pathways, or shared substrates and transporters. Thus, accurate prediction would involve all of these data, a difficult task indeed.
Pascale Cossarts laboratory was the first to experimentally identify all operons of a microorganism, Listeria monocytogenes. The 517 polycistronic operons are listed in a 2009 study describing the global changes in transcription that occur in L. monocytogenes' under different conditions. | 1 | Biochemistry |
Giner-Delgado, Carla, et al. described a variant of MLPA combining it with iPCR. They call these new method iMLPA and its procedure is the same as MLPA but there are necessary two additional steps at the beginning:
# First, a DNA treatment with restriction enzymes that cut on both sides of the region of interest is necessary.
# The fragments obtained from digestion are recircularized and linked
The probe design is quite similar. Each probe will be formed by two parts that have at least: a target sequence, which is a region that contains the sequence complementary to the region of interest, so that the correct hybridization can occur. And a primer sequence at the end, it is a sequence whose design varies and is what will allow the design of primers and subsequent fragment amplification. In addition, one of the parts of the probe usually contains a stuffer between the target sequence and the primer sequence. The use of different stuffers allows the identification of probes with the same primer sequences but different target sequences, that is key for multiple amplification of several different fragments in a single reaction.
The next step continues with the typical MLPA protocol. | 1 | Biochemistry |
Applications of thermal desorption were originally restricted to occupational health monitoring, but have since extended to cover a much wider range. Some of the most important are mentioned below – where available, examples of early reports, and more recent citations (including those of widely used standard methods) have been given:
*Outdoor environmental monitoring
*Workplace/occupational health monitoring
*Residual volatiles emitted from products and materials
*Studies of biological systems, including plant–herbivore interactions
*Breath analysis for disease diagnosis
*Aroma profiling of food and drink
*Defence/homeland security (detection of chemical agents) | 3 | Analytical Chemistry |
The Comparative Toxicogenomics Database (CTD) is a public website and research tool launched in November 2004 that curates scientific data describing relationships between chemicals/drugs, genes/proteins, diseases, taxa, phenotypes, GO annotations, pathways, and interaction modules.
The database is maintained by the Department of Biological Sciences at North Carolina State University. | 1 | Biochemistry |
Ten communes border the Étang de Berre: Istres, Miramas, Saint-Chamas, Berre-l'Étang, Rognac, Vitrolles, Marignane, Châteauneuf-les-Martigues, Martigues and Saint-Mitre-les-Remparts. | 2 | Environmental Chemistry |
The hydroxyl HO radicals is one of the main chemical species controlling the oxidizing capacity of the global Earth atmosphere. This oxidizing reactive species has a major impact on the concentrations and distribution of greenhouse gases and pollutants in the Earth atmosphere. It is the most widespread oxidizer in the troposphere, the lowest part of the atmosphere. Understanding HO variability is important to evaluating human impacts on the atmosphere and climate. The HO species has a lifetime in the Earth atmosphere of less than one second. Understanding the role of HO in the oxidation process of methane (CH) present in the atmosphere to first carbon monoxide (CO) and then carbon dioxide (CO) is important for assessing the residence time of this greenhouse gas, the overall carbon budget of the troposphere, and its influence on the process of global warming. The lifetime of HO radicals in the Earth atmosphere is very short, therefore HO concentrations in the air are very low and very sensitive techniques are required for its direct detection. Global average hydroxyl radical concentrations have been measured indirectly by analyzing methyl chloroform (CHCCl) present in the air. The results obtained by Montzka et al. (2011) shows that the interannual variability in HO estimated from CHCCl measurements is small, indicating that global HO is generally well buffered against perturbations. This small variability is consistent with measurements of methane and other trace gases primarily oxidized by HO, as well as global photochemical model calculations. | 2 | Environmental Chemistry |
Westinghouse continued its manufacturing and research at the plant after the war. In 1964, Westinghouse was issued a permit from United States Atomic Energy Commission to conduct research using thorium and uranium to produce thorium-tungsten wire. In 1983, Westinghouse sold its lamp manufacturing operation to North American Phillips Lighting Corporation. The manufacturing of thorium-tungsten wire was continued at the plant until 1984. In 1986, North American Phillips Lighting Corporation returned the control of the plant back to Westinghouse. | 8 | Metallurgy |
In contrast to the paucity of evidence for , the corresponding arsenic ion, ortho-arsenite, is known. An example is AgAsO as well as the polymeric meta-arsenite . The iso-electronic sulfite ion, is known from its salts. | 0 | Organic Chemistry |
Hexamethylenetetramine is a versatile reagent in organic synthesis. It is used in the Duff reaction (formylation of arenes), the Sommelet reaction (converting benzyl halides to aldehydes), and in the Delepine reaction (synthesis of amines from alkyl halides). | 0 | Organic Chemistry |
The western meadow vole (Microtus drummondii) is a species of North American vole found in midwestern and western Canada and the United States, and formerly in Mexico. It was formerly considered conspecific with the eastern meadow vole (M. pennsylvanicus), but genetic studies indicate that it is a distinct species. | 2 | Environmental Chemistry |
Vitamin D content in typical foods is reduced variably by cooking. Boiled, fried and baked foods retained 6989% of original vitamin D. | 1 | Biochemistry |
The snRNAs (U1, U2, U4, U5, and the less abundant U11, U12 and U4atac) quickly interact with the SMN (survival of motor neuron protein); encoded by SMN1 gene) and Gemins 2-8 (Gem-associated proteins: GEMIN2, GEMIN3, GEMIN4, GEMIN5, GEMIN6, GEMIN7, GEMIN8) forming the SMN complex. It is here that the snRNA binds to the SmD1-SmD2-SmF-SmE-SmG pentamer, followed by addition of the SmD3-SmB dimer to complete the Sm ring around the so-called Sm site of the snRNA. This Sm site is a conserved sequence of nucleotides in these snRNAs, typically AUUUGUGG (where A, U and G represent the nucleosides adenosine, uridine and guanosine, respectively). After assembly of the Sm ring around the snRNA, the 5 terminal nucleoside (already modified to a 7-methylguanosine cap) is hyper-methylated to 2,2,7-trimethylguanosine and the other (3) end of the snRNA is trimmed. This modification, and the presence of a complete Sm ring, is recognized by the snurportin 1 protein. | 1 | Biochemistry |
When a hot steel work-piece is quenched, the area in contact with the water immediately cools and its temperature equilibrates with the quenching medium. The inner depths of the material however, do not cool so rapidly, and in work-pieces that are large, the cooling rate may be slow enough to allow the austenite to transform fully into a structure other than martensite or bainite. This results in a work-piece that does not have the same crystal structure throughout its entire depth; with a softer core and harder "shell". The softer core is some combination of ferrite and cementite, such as pearlite.
The hardenability of ferrous alloys, i.e. steels, is a function of the carbon content and other alloying elements and the grain size of the austenite. The relative importance of the various alloying elements is calculated by finding the equivalent carbon content of the material.
The fluid used for quenching the material influences the cooling rate due to varying thermal conductivities and specific heats. Substances like brine and water cool the steel much more quickly than oil or air. If the fluid is agitated cooling occurs even more quickly. The geometry of the part also affects the cooling rate: of two samples of equal volume, the one with higher surface area will cool faster. | 8 | Metallurgy |
The immunomodulatory proteins, including virokines, in the poxvirus family have been extensively studied in the context of the evolution of the family. Virokines in this family are thought to have been acquired from host genes and from other viruses through horizontal gene transfer. Similar observations have been made in the herpesvirus family; for example, Epstein-Barr virus encodes an interleukin protein with high sequence identity to the human interleukin-10, suggesting a recent evolutionary origin. | 1 | Biochemistry |
Manganese deficiency in humans, which is rare, results in a number of medical problems. Many common vitamin and mineral supplement products fail to include manganese in their compositions. Relatively high dietary intake of other minerals such as iron, magnesium, and calcium may inhibit the proper intake of manganese. A deficiency of manganese causes skeletal deformation in animals and inhibits the production of collagen in wound healing. | 1 | Biochemistry |
Figure 4 shows the orbital array involved in the butadiene to cyclobutene interconversion. It is seen that there are four orbitals in this cyclic array. Thus in the interconversion reactions orbitals 1 and 4 overlap either in a conrotatory or a disrotatory fashion. Also, it is seen that the conrotation involves one plus-minus overlap as drawn while the disrotation involves zero plus-minus overlaps as drawn. Thus the conrotation uses a Möbius array while the disrotation uses a Hückel array.
But it is important to note, as described for the generalized orbital array in Figure 3, that the assignment of the basis-set p-orbitals is arbitrary. Were one p-orbital in either reaction mode to be written upside-down, this would change the number of sign inversions by two and not change the evenness or oddness of the orbital array.
With a conrotation giving a Möbius system, with butadiene's four electrons, we find an "allowed" reaction model. With disrotation giving a Hückel system, with the four electrons, we find a "forbidden" reaction model.
Although in these two examples symmetry is present, symmetry is not required or involved in determination of reaction allowedness versus forbiddenness. Hence a very large number of organic reactions can be understood. Even where symmetry is present, the Möbius–Hückel analysis proves simple to employ. | 7 | Physical Chemistry |
A further insight into the pre-equilibrium step and its equilibrium constant K comes from the Fuoss-Eigen equation proposed independently by Eigen and R. M. Fuoss:
:K = (4πa/3000) x Nexp(-V/RT)
Where a represents the minimum distance of approach between complex and ligand in solution (in cm), N is the Avogadro constant, R is the gas constant and T is the reaction temperature. V is the electrostatic potential energy of the ions at that distance:
:V = zze/4πaε
Where z is the charge number of each species and ε is the vacuum permittivity.
A typical value for K is 0.0202 dmmol for neutral particles at a distance of 200 pm. The result of the rate law is that at high concentrations of Y, the rate approximates k[M] while at low concentrations the result is kK[M][Y]. The Eigen-Fuoss equation shows that higher values of K (and thus a faster pre-equilibrium) are obtained for large, oppositely-charged ions in solution. | 0 | Organic Chemistry |
One of the more common cell-sorting systems makes use of flow cytometry through fluorescence imaging. In this method, a suspension of biologic cells is sorted into two or more containers, based upon specific fluorescent characteristics of each cell during an assisted flow. By using an electrical charge that the cell is "trapped" in, the cells are then sorted based on the fluorescence intensity measurements. The sorting process is undertaken by an electrostatic deflection system that diverts cells into containers based upon their charge.
In the optically actuated sorting process, the cells are flowed through into an optical landscape i.e. 2D or 3D optical lattices. Without any induced electrical charge, the cells would sort based on their intrinsic refractive index properties and can be re-configurability for dynamic sorting. An optical lattice can be created using diffractive optics and optical elements.
On the other hand, K. Ladavac et al. used a spatial light modulator to project an intensity pattern to enable the optical sorting process. K. Xiao and D. G. Grier applied holographic video microscopy to demonstrate that this technique can sort colloidal spheres with part-per-thousand resolution for size and refractive index.
The main mechanism for sorting is the arrangement of the optical lattice points. As the cell flow through the optical lattice, there are forces due to the particles drag force that is competing directly with the optical gradient force (See Physics of optical tweezers) from the optical lattice point. By shifting the arrangement of the optical lattice point, there is a preferred optical path where the optical forces are dominant and biased. With the aid of the flow of the cells, there is a resultant force that is directed along that preferred optical path. Hence, there is a relationship of the flow rate with the optical gradient force. By adjusting the two forces, one will be able to obtain a good optical sorting efficiency.
Competition of the forces in the sorting environment need fine tuning to succeed in high efficient optical sorting. The need is mainly with regards to the balance of the forces; drag force due to fluid flow and optical gradient force due to arrangement of intensity spot.
Scientists at the University of St. Andrews have received considerable funding from the UK Engineering and Physical Sciences Research Council (EPSRC) for an optical sorting machine. This new technology could rival the conventional fluorescence-activated cell sorting. | 1 | Biochemistry |
Induced metabolic bioluminescence imaging (imBI) is used to obtain a metabolic snapshot of biological tissues. Metabolites that may be quantified through imBI include glucose, lactate, pyruvate, ATP, glucose-6-phosphate, or D2-hydroxygluturate. imBI can be used to determine the lactate concentration of tumors or to measure the metabolism of the brain. | 1 | Biochemistry |
Common to all LOV proteins is the blue-light sensitive flavin chromophore, which in the signaling state is covalently linked to the protein core via an adjacent cysteine residue. LOV domains are e.g. encountered in phototropins, which are blue-light-sensitive protein complexes regulating a great diversity of biological processes in higher plants as well as in micro-algae. Phototropins are composed of two LOV domains, each containing a non-covalently bound flavin mononucleotide (FMN) chromophore in its dark-state form, and a C-terminal Ser-Thr kinase.
Upon blue-light absorption, a covalent bond between the FMN chromophore and an adjacent reactive cysteine residue of the apo-protein is formed in the LOV2 domain. This subsequently mediates the activation of the kinase, which induces a signal in the organism through phototropin autophosphorylation.
While the photochemical reactivity of the LOV2 domain has been found to be essential for the activation of the kinase, the in vivo functionality of the LOV1 domain within the protein complex still remains unclear. | 1 | Biochemistry |
Smelting involves more than just melting the metal out of its ore. Most ores are the chemical compound of the metal and other elements, such as oxygen (as an oxide), sulfur (as a sulfide), or carbon and oxygen together (as a carbonate). To extract the metal, workers must make these compounds undergo a chemical reaction. Smelting, therefore, consists of using suitable reducing substances that combine with those oxidizing elements to free the metal. | 8 | Metallurgy |
The channelosome (not to be confused with "channelome") is the collection of (usually) signalling proteins associated with an ion channel. The channelosome is frequently clustered within a lipid microdomain or caveolae. This collection of proteins may be involved with anchoring, phosphorylation or some other modulatory or support function. An example is neural KCNQ/M (Kv7) potassium channelosome (see Delmas & Brown, 2005). | 1 | Biochemistry |
Because of the specificity of toll-like receptors (and other innate immune receptors) they cannot easily be changed in the course of evolution, these receptors recognize molecules that are constantly associated with threats (i.e., pathogen or cell stress) and are highly specific to these threats (i.e., cannot be mistaken for self molecules that are normally expressed under physiological conditions). Pathogen-associated molecules that meet this requirement are thought to be critical to the pathogens function and difficult to change through mutation; they are said to be evolutionarily conserved. Somewhat conserved features in pathogens include bacterial cell-surface lipopolysaccharides (LPS), lipoproteins, lipopeptides, and lipoarabinomannan; proteins such as flagellin from bacterial flagella; double-stranded RNA of viruses; or the unmethylated CpG islands of bacterial and viral DNA; and also of the CpG islands found in the promoters of eukaryotic DNA; as well as certain other RNA and DNA molecules. As TLR ligands are present in most pathogens, they may also be present in pathogen-derived vaccines (e.g. MMR, influenza, polio vaccines) most commercially available vaccines have been assessed for their inherent TLR ligands capacity to activate distinct subsets of immune cells. For most of the TLRs, ligand recognition specificity has now been established by gene targeting (also known as "gene knockout"): a technique by which individual genes may be selectively deleted in mice. See the table above for a summary of known TLR ligands. | 1 | Biochemistry |
]In terms of thermodynamics, two types of polymorphic behaviour are recognized. For a monotropic system, plots of the free energies of the various polymorphs against temperature do not cross before all polymorphs melt. As a result, any transition from one polymorph to another below the melting point will be irreversible. For an enantiotropic system, a plot of the free energy against temperature shows a crossing point before the various melting points. It may also be possible to convert interchangeably between the two polymorphs by heating or cooling, or through physical contact with a lower energy polymorph.
A simple model of polymorphism is to model the Gibbs free energy of a ball-shaped crystal as . Here, the first term is the surface energy, and the second term is the volume energy. Both parameters . The function rises to a maximum before dropping, crossing zero at . In order to crystallize, a ball of crystal much overcome the energetic barrier to the part of the energy landscape.
Now, suppose there are two kinds of crystals, with different energies and , and if they have the same shape as in Figure 2, then the two curves intersect at some . Then the system has three phases:
* . Crystals tend to dissolve. Amorphous phase.
* . Crystals tend to grow as form 1.
* . Crystals tend to grow as form 2.
If the crystal is grown slowly, it could be kinetically stuck in form 1. | 3 | Analytical Chemistry |
Once the soluble compounds from the creosote preservative leach into the water, the compounds begin reacting with the external environment or are consumed by organisms. The reactions vary depending on the concentration of each compound that is released from the creosote, but major reactions are outlined below: | 7 | Physical Chemistry |
The negative charge of its phosphate backbone moves the DNA towards the positively charged anode during electrophoresis. However, the migration of DNA molecules in solution, in the absence of a gel matrix, is independent of molecular weight during electrophoresis, i.e. there is no separation by size without a gel matrix. Hydrodynamic interaction between different parts of the DNA are cut off by streaming counterions moving in the opposite direction, so no mechanism exists to generate a dependence of velocity on length on a scale larger than screening length of about 10 nm. This makes it different from other processes such as sedimentation or diffusion where long-ranged hydrodynamic interaction are important.
The gel matrix is therefore responsible for the separation of DNA by size during electrophoresis, however the precise mechanism responsible the separation is not entirely clear. A number of models exists for the mechanism of separation of biomolecules in gel matrix, a widely accepted one is the Ogston model which treats the polymer matrix as a sieve consisting of randomly distributed network of inter-connected pores. A globular protein or a random coil DNA moves through the connected pores large enough to accommodate its passage, and the movement of larger molecules is more likely to be impeded and slowed down by collisions with the gel matrix, and the molecules of different sizes can therefore be separated in this process of sieving.
The Ogston model however breaks down for large molecules whereby the pores are significantly smaller than size of the molecule. For DNA molecules of size greater than 1 kb, a reptation model (or its variants) is most commonly used. This model assumes that the DNA can crawl in a "snake-like" fashion (hence "reptation") through the pores as an elongated molecule. At higher electric field strength, this turned into a biased reptation model, whereby the leading end of the molecule become strongly biased in the forward direction, and this leading edge pulls the rest of the molecule along. In the fully biased mode, the mobility reached a saturation point and DNA beyond a certain size cannot be separated. Perfect parallel alignment of the chain with the field however is not observed in practice as that would mean the same mobility for long and short molecules. Further refinement of the biased reptation model takes into account of the internal fluctuations of the chain.
The biased reptation model has also been used to explain the mobility of DNA in PFGE. The orientation of the DNA is progressively built up by reptation after the onset of a field, and the time it reached the steady state velocity is dependent on the size of the molecule. When the field is changed, larger molecules take longer to reorientate, it is therefore possible to discriminate between the long chains that cannot reach its steady state velocity from the short ones that travel most of the time in steady velocity. Other models, however, also exist.
Real-time fluorescence microscopy of stained molecules showed more subtle dynamics during electrophoresis, with the DNA showing considerable elasticity as it alternately stretching in the direction of the applied field and then contracting into a ball, or becoming hooked into a U-shape when it gets caught on the polymer fibres. This observation may be termed the "caterpillar" model. Other model proposes that the DNA gets entangled with the polymer matrix, and the larger the molecule, the more likely it is to become entangled and its movement impeded. | 1 | Biochemistry |
Butyric acid reacts as a typical carboxylic acid: it can form amide, ester, anhydride, and chloride derivatives. The latter, butyryl chloride, is commonly used as the intermediate to obtain the others. | 1 | Biochemistry |
With the rise of the environmentalist movement has also come an increased appreciation for social justice, and mining has showed similar trends lately. Societies located near potential mining sites are at increased risk to be subjected to injustices as their environment is affected by the changes made to mined lands—either public or private—that could eventually lead to problems in social structure, identity, and physical health (Franks 2009). Many have argued that by cycling mine power through local citizens, this disagreement can be alleviated, since both interest groups would have shared and equal voice and understanding in future goals. However, it is often difficult to match corporate mining interests with local social interests, and money is often a deciding factor in the successes of any disagreements. If communities are able to feel like they have a valid understanding and power in issues concerning their local environment and society, they are more likely to tolerate and encourage the positive benefits that come with mining, as well as more effectively promote alternative methods to heap leach mining using their intimate knowledge of the local geography (Franks 2009). | 8 | Metallurgy |
Boundary scattering is particularly important for low-dimensional nanostructures and its relaxation rate is given by:
where is the characteristic length of the system and represents the fraction of specularly scattered phonons. The parameter is not easily calculated for an arbitrary surface. For a surface characterized by a root-mean-square roughness , a wavelength-dependent value for can be calculated using
where is the angle of incidence. An extra factor of is sometimes erroneously included in the exponent of the above equation. At normal incidence, , perfectly specular scattering (i.e. ) would require an arbitrarily large wavelength, or conversely an arbitrarily small roughness. Purely specular scattering does not introduce a boundary-associated increase in the thermal resistance. In the diffusive limit, however, at the relaxation rate becomes
This equation is also known as Casimir limit.
These phenomenological equations can in many cases accurately model the thermal conductivity of isotropic nano-structures with characteristic sizes on the order of the phonon mean free path. More detailed calculations are in general required to fully capture the phonon-boundary interaction across all relevant vibrational modes in an arbitrary structure. | 7 | Physical Chemistry |
The main limitation in the use of MLC is the reduction in efficiency (peak broadening) that is observed when purely aqueous micellar mobile phases are used. Several explanations for the poor efficiency have been theorized. Poor wetting of the stationary phase by the micellar aqueous mobile phase, slow mass transfer between the micelles and the stationary phase, and poor mass transfer within the stationary phase have all been postulated as possible causes. To enhance efficiency, the most common approaches have been the addition of small amounts of isopropyl alcohol and increase in temperature. A review by Berthod studied the combined theories presented above and applied the Knox equation to independently determine the cause of the reduced efficiency. The Knox equation is commonly used in HPLC to describe the different contributions to overall band broadening of a solute. The Knox equation is expressed as:
:h = An^(1/3)+ B/n + Cn
Where:
*h = the reduced plate height count (plate height/stationary phase particle diameter)
*n = the reduced mobile phase linear velocity (velocity times stationary phase particle diameter/solute diffusion coefficient in the mobile phase)
*A, B, and C are constants related to solute flow anisotropy (eddy diffusion), molecular longitudinal diffusion, and mass transfer properties respectively.
Berthod's use of the Knox equation to experimentally determine which of the proposed theories was most correct led him to the following conclusions. The flow anisotropy in micellar phase seems to be much greater than in traditional hydro-organic mobile phases of similar viscosity. This is likely due to the partial clogging of the stationary phase pores by adsorbed surfactant molecules. Raising the column temperature served to both decrease viscosity of the mobile phase and the amount of adsorbed surfactant. Both results reduce the A term and the amount of eddy diffusion, and thereby increase efficiency.
The increase in the B term, as related to longitudinal diffusion, is associated with the decrease in the solute diffusion coefficient in the mobile phase, DM, due to the presence of the micelles, and an increase in the capacity factor, k¢. Again, this is related to surfactant adsorption on the stationary phase causing a dramatic decrease in the solute diffusion coefficient in the stationary phase, DS. Again an increase in temperature, now coupled with an addition of alcohol to the mobile phase, drastically decreases the amount of the absorbed surfactant. In turn, both actions reduce the C term caused by a slow mass transfer from the stationary phase to the mobile phase. Further optimization of efficiency can be gained by reducing the flow rate to one closely matched to that derived from the Knox equation. Overall, the three proposed theories seemed to have contributing effects of the poor efficiency observed, and can be partially countered by the addition of organic modifiers, particularly alcohol, and increasing the column temperature. | 3 | Analytical Chemistry |
There are several types of screen media manufactured with different types of material that use the two common types of screen media attachment systems, tensioned and modular. | 8 | Metallurgy |
NUT carcinoma is a rare, highly aggressive malignancy. Initially, it was regarded as occurring in the midline areas of the upper respiratory tract, upper digestive tract, and mediastinum (i.e. central compartment of the thoracic cavity) of young adults and to lesser extents children and infants. It was therefore termed NUT midline granuloma. However, subsequent studies defined these carcinomas based on the presence of a NUT fusion gene in their malignant cells. As so defined, this malignancy occurs in individuals of all ages and, while most commonly developing in the cited respiratory, gastrointestinal, and mediastinal areas, occasionally develops in the salivary glands, pancreas, urinary bladder, retroperitoneum (i.e. space behind the peritoneum of the abdominal cavity), endometrium, kidneys, ovaries, and other organs. Consequently, the name of this disorder was changed form NUT midline carcinoma to NUT carcinoma by the World Health Organization, 2015. NUT carcinomas are characterized histologically as tumors containing
primitive epithelioid cells (i.e. derived from activated macrophages and resembling epithelial cells) admixed with foci of keratinization (i.e. tissue areas that are rich in keratin fibers); NUT carcinomas are considered variants of squamous cell carcinomas. Studies have found that ~66 tp 80% of NUT carcinomas harbor a BRD4-NUTM1 fusion gene while the remaining NUT carcinomas, sometimes termed NUT variant carcinomas, involve the BRD3-NUTM1 (~10 to 25% of cases) or, rarely, the NSD3-NUTM1, ZNF532-NUTM1,, or ZNF592-NUTM1 fusion gene. It is thought that the latter fusions genes promote NUT carcinomas in manners at least somewhat similar to the BRD4-NUTM1 fusion gene. | 1 | Biochemistry |
In plasma spraying process, the material to be deposited (feedstock)—typically as a powder, sometimes as a liquid, suspension or wire—is introduced into the plasma jet, emanating from a plasma torch. In the jet, where the temperature is on the order of 10,000 K, the material is melted and propelled towards a substrate. There, the molten droplets flatten, rapidly solidify and form a deposit. Commonly, the deposits remain adherent to the substrate as coatings; free-standing parts can also be produced by removing the substrate. There are a large number of technological parameters that influence the interaction of the particles with the plasma jet and the substrate and therefore the deposit properties. These parameters include feedstock type, plasma gas composition and flow rate, energy input, torch offset distance, substrate cooling, etc. | 8 | Metallurgy |
By raster scanning the sample, making measurements at several points across the surface, multi-megapixel images of the SAW velocity can be built up - providing rich microstructural maps. On samples with a good surface finish measurements can be made without averaging, allowing samples to be rapidly scanned. In-theory, means the acquisition rate is limited only by the repetition rate of the pump laser; modern laser repetition rates can exceed 10 kHz. As the measurements do not require a vacuum chamber or acoustic couplant there is little restriction, beyond the limit of scanning stages, to the size of sample which can be interrogated. The elastic anisotropy of most engineering materials means the acoustic response is a function of the loading direction. Hence, a unique velocity map exists for each propagation direction of the SAW direction. It is possible to combine multiple velocity maps to improve contrast between grains. | 7 | Physical Chemistry |
There are several other reliable tests and V̇O max calculators to estimate V̇O max, most notably the multi-stage fitness test (or beep test). | 1 | Biochemistry |
Nutrients dissolved in seawater are essential for the survival of marine life. Nitrogen and phosphorus are particularly important. They are regarded as limiting nutrients in many marine environments, because primary producers, like algae and marine plants, cannot grow without them. They are critical for stimulating primary production by phytoplankton. Other important nutrients are silicon, iron, and zinc.
The process of cycling nutrients in the sea starts with biological pumping, when nutrients are extracted from surface waters by phytoplankton to become part of their organic makeup. Phytoplankton are either eaten by other organisms, or eventually die and drift down as marine snow. There they decay and return to the dissolved state, but at greater ocean depths. The fertility of the oceans depends on the abundance of the nutrients, and is measured by the primary production, which is the rate of fixation of carbon per unit of water per unit time. "Primary production is often mapped by satellites using the distribution of chlorophyll, which is a pigment produced by plants that absorbs energy during photosynthesis. The distribution of chlorophyll is shown in the figure above. You can see the highest abundance close to the coastlines where nutrients from the land are fed in by rivers. The other location where chlorophyll levels are high is in upwelling zones where nutrients are brought to the surface ocean from depth by the upwelling process..."
"Another critical element for the health of the oceans is the dissolved oxygen content. Oxygen in the surface ocean is continuously added across the air-sea interface as well as by photosynthesis; it is used up in respiration by marine organisms and during the decay or oxidation of organic material that rains down in the ocean and is deposited on the ocean bottom. Most organisms require oxygen, thus its depletion has adverse effects for marine populations. Temperature also affects oxygen levels as warm waters can hold less dissolved oxygen than cold waters. This relationship will have major implications for future oceans, as we will see... The final seawater property we will consider is the content of dissolved . is nearly opposite to oxygen in many chemical and biological processes; it is used up by plankton during photosynthesis and replenished during respiration as well as during the oxidation of organic matter. As we will see later, content has importance for the study of deep-water aging." | 9 | Geochemistry |
Nucleation can be either homogeneous, without the influence of foreign particles, or heterogeneous, with the influence of foreign particles. Generally, heterogeneous nucleation takes place more quickly since the foreign particles act as a scaffold for the crystal to grow on, thus eliminating the necessity of creating a new surface and the incipient surface energy requirements.
Heterogeneous nucleation can take place by several methods. Some of the most typical are small inclusions, or cuts, in the container the crystal is being grown on. This includes scratches on the sides and bottom of glassware. A common practice in crystal growing is to add a foreign substance, such as a string or a rock, to the solution, thereby providing nucleation sites for facilitating crystal growth and reducing the time to fully crystallize.
The number of nucleating sites can also be controlled in this manner. If a brand-new piece of glassware or a plastic container is used, crystals may not form because the container surface is too smooth to allow heterogeneous nucleation. On the other hand, a badly scratched container will result in many lines of small crystals. To achieve a moderate number of medium-sized crystals, a container which has a few scratches works best. Likewise, adding small previously made crystals, or seed crystals, to a crystal growing project will provide nucleating sites to the solution. The addition of only one seed crystal should result in a larger single crystal. | 3 | Analytical Chemistry |
Arsaalkynes are produced by dehydrohalogenation or related base-induced elimination reactions. The case of HCAs is illustrative:
Owing to the principles of the double bond rule, arsaalkynes tend to oligomerize more readily than the phosphorus analogues. Thus attempts to prepare AsCCMe produce the tetramer, which has a cubane structure. The very bulky substituent CH-2,4,6-(t-Bu) does however allow the crystallization of the monomeric arsaalkyne. Its As-C bond length is 1.657(7) Å. | 0 | Organic Chemistry |
Iron has many important roles in animal biology, specifically when considering oxygen transport in the bloodstream, oxygen storage in muscles, and enzymes. Known isotope variations are shown in the figure below. Iron isotopes could be useful tracers of the iron biochemical pathways in animals, and also be indicative of trophic levels in a food chain.
Iron isotope variations in humans reflects a number of processes. Specifically, iron in the blood stream reflects dietary iron, which is isotopically lighter than iron in the geosphere. Iron isotopes are distributed heterogeneously throughout the body, primarily to red blood cells, the liver, muscle, skin, enzymes, nails, and hair. Iron losses in the body (intestinal bleeding, bile, sweat, etc.) favor the loss of isotopically heavy iron, with mean losses averaging a δFe of +10‰. Iron absorption in the intestine favors lighter iron isotopes. This is largely due to the fact that iron is carried by transport proteins and transferrin, both of which are kinetic processes, resulting in the preferential uptake of isotopically light iron.
The observed iron isotopic variations in humans and animals are particularly important as tracers. Iron isotopic signatures are utilized to determine the geographic origin of food. Additionally, anthropologists and paleontologists use iron isotope data in order to track the transfer of iron between the geosphere and the biosphere, specifically between plant foods and animals. This allows for the reconstruction of ancient dietary habits based on the variations in iron isotopes in food. | 9 | Geochemistry |
The elementary reaction responsible for water quantification in the Karl Fischer titration is oxidation of sulfur dioxide () with iodine:
This elementary reaction consumes exactly one molar equivalent of water vs. iodine. Iodine is added to the solution until it is present in excess, marking the end point of the titration, which can be detected by potentiometry. The reaction is run in an alcohol solution containing a base, which consumes the sulfur trioxide and hydroiodic acid produced. | 3 | Analytical Chemistry |
Although the targets of CK2 are predominantly nucleus-based the protein itself is localized to both the nucleus and cytoplasm. Casein kinase 2 activity has been reported to be activated following Wnt signaling pathway activation. A Pertussis toxin-sensitive G protein and Dishevelled appear to be an intermediary between Wnt-mediated activation of the Frizzled receptor and activation of CK2. Further studies need to be done on the regulation of this protein due to the complexity of CK2 function and localization.
Phosphorylation of CK2α T344 has been shown to inhibit its proteasomal degradation and support binding to Pin1. O-GlcNAcylation at S347 antagonizes this phosphorylation and accelerates CK2α degradation. O-GlcNAcylation of CK2α has also been shown to alter the phosphoproteome, notably including many chromatin regulators such as HDAC1, HDAC2, and HCFC1. | 1 | Biochemistry |
Cryoprotectants operate by increasing the solute concentration in cells. However, in order to be biologically viable they must easily penetrate and must not be toxic to cells. | 1 | Biochemistry |
ASF/SF2 is an integral part of numerous components of the splicing process. ASF/SF2 is required for 5’ splice site cleavage and selection, and is capable of discriminating between cryptic and authentic splice sites. Subsequent lariat formation during the first chemical step of pre-mRNA splicing also requires ASF/SF2. ASF/SF2 promotes recruitment of the U1 snRNP to the 5’ splice site, and bridges the 5’ and 3’ splice sites to facilitate splicing reactions. ASF/SF2 also associates with the U2 snRNP. During the reaction, ASF/SF2 promotes the use of intron proximal sites and hinders the use of intron distal sites, affecting alternative splicing. Alternative splicing is affected by ASF/SF2 in a concentration-dependent manner; differing concentrations of ASF/SF2 is a mechanism for alternative splicing regulation, and will result in differing amounts of product isoforms. ASF/SF2 accomplishes this regulation through direct or indirect binding to exonic splicing enhancer (ESE) sequences. | 1 | Biochemistry |
A small volume of PCBs has been detected throughout the Earth's atmosphere. The atmosphere serves as the primary route for global transport of PCBs, particularly for those congeners with one to four chlorine atoms.
In the atmosphere, PCBs may be degraded by hydroxyl radicals, or directly by photolysis of carbon–chlorine bonds (even if this is a less important process).
Atmospheric concentrations of PCBs tend to be lowest in rural areas, where they are typically in the picogram per cubic meter range, higher in suburban and urban areas, and highest in city centres, where they can reach 1 ng/m or more. In Milwaukee, an atmospheric concentration of 1.9 ng/m has been measured, and this source alone was estimated to account for 120 kg/year of PCBs entering Lake Michigan. In 2008, concentrations as high as 35 ng/m, 10 times higher than the EPA guideline limit of 3.4 ng/m, have been documented inside some houses in the U.S.
Volatilization of PCBs in soil was thought to be the primary source of PCBs in the atmosphere, but research suggests ventilation of PCB-contaminated indoor air from buildings is the primary source of PCB contamination in the atmosphere. | 2 | Environmental Chemistry |
Chromatin remodeling provides fine-tuning at crucial cell growth and division steps, like cell-cycle progression, DNA repair and chromosome segregation, and therefore exerts tumor-suppressor function. Mutations in such chromatin remodelers and deregulated covalent histone modifications potentially favor self-sufficiency in cell growth and escape from growth-regulatory cell signals - two important hallmarks of cancer.
* Inactivating mutations in SMARCB1, formerly known as hSNF5/INI1 and a component of the human SWI/SNF remodeling complex have been found in large number of rhabdoid tumors, commonly affecting pediatric population. Similar mutations are also present in other childhood cancers, such as choroid plexus carcinoma, medulloblastoma and in some acute leukemias. Further, mouse knock-out studies strongly support SMARCB1 as a tumor suppressor protein. Since the original observation of SMARCB1 mutations in rhabdoid tumors, several more subunits of the human SWI/SNF chromatin remodeling complex have been found mutated in a wide range of neoplasms.
* The SWI/SNF ATPase BRG1 (or SMARCA4) is the most frequently mutated chromatin remodeling ATPase in cancer. Mutations in this gene were first recognized in human cancer cell lines derived from lung. In cancer, mutations in BRG1 show an unusually high preference for missense mutations that target the ATPase domain. Mutations are enriched at highly conserved ATPase sequences, which lie on important functional surfaces such as the ATP pocket or DNA-binding surface. These mutations act in a genetically dominant manner to alter chromatin regulatory function at enhancers and promoters.
* Inactivating mutations in BCL7A in Diffuse large B-cell lymphoma (DLBCL) and in other haematological malignancies
* PML-RARA fusion protein in acute myeloid leukemia recruits histone deacetylases. This leads to repression of genes responsible for myelocytes to differentiate, leading to leukemia.
* Tumor suppressor Rb protein functions by the recruitment of the human homologs of the SWI/SNF enzymes BRG1, histone deacetylase and DNA methyltransferase. Mutations in BRG1 are reported in several cancers causing loss of tumor suppressor action of Rb.
* Recent reports indicate DNA hypermethylation in the promoter region of major tumor suppressor genes in several cancers. Although few mutations are reported in histone methyltransferases yet, correlation of DNA hypermethylation and histone H3 lysine-9 methylation has been reported in several cancers, mainly in colorectal and breast cancers.
* Mutations in Histone Acetyl Transferases (HAT) p300 (missense and truncating type) are most commonly reported in colorectal, pancreatic, breast and gastric carcinomas. Loss of heterozygosity in coding region of p300 (chromosome 22q13) is present in large number of glioblastomas.
* Further, HATs have diverse role as transcription factors beside having histone acetylase activity, e.g., HAT subunit, hADA3 may act as an adaptor protein linking transcription factors with other HAT complexes. In the absence of hADA3, TP53 transcriptional activity is significantly reduced, suggesting role of hADA3 in activating TP53 function in response to DNA damage.
* Similarly, TRRAP, the human homolog to yeast Tra1, has been shown to directly interact with c-Myc and E2F1, known oncoproteins. | 1 | Biochemistry |
A colloidal crystal is a highly ordered array of particles that can be formed over a very long range (typically on the order of a few millimeters to one centimeter) and that appear analogous to their atomic or molecular counterparts. One of the finest natural examples of this ordering phenomenon can be found in precious opal, in which brilliant regions of pure spectral color result from close-packed domains of amorphous colloidal spheres of silicon dioxide (or silica, SiO). These spherical particles precipitate in highly siliceous pools in Australia and elsewhere, and form these highly ordered arrays after years of sedimentation and compression under hydrostatic and gravitational forces. The periodic arrays of submicrometre spherical particles provide similar arrays of interstitial voids, which act as a natural diffraction grating for visible light waves, particularly when the interstitial spacing is of the same order of magnitude as the incident lightwave.
Thus, it has been known for many years that, due to repulsive Coulombic interactions, electrically charged macromolecules in an aqueous environment can exhibit long-range crystal-like correlations with interparticle separation distances, often being considerably greater than the individual particle diameter. In all of these cases in nature, the same brilliant iridescence (or play of colors) can be attributed to the diffraction and constructive interference of visible lightwaves that satisfy Bragg’s law, in a matter analogous to the scattering of X-rays in crystalline solids.
The large number of experiments exploring the physics and chemistry of these so-called "colloidal crystals" has emerged as a result of the relatively simple methods that have evolved in the last 20 years for preparing synthetic monodisperse colloids (both polymer and mineral) and, through various mechanisms, implementing and preserving their long-range order formation. | 7 | Physical Chemistry |
Hund's coupling cases are idealizations. The appropriate case for a given situation can be found by comparing three strengths: the electrostatic coupling of to the internuclear axis, the spin-orbit coupling, and the rotational coupling of and to the total angular momentum .
For Σ states the orbital and spin angular momenta are zero and the total angular momentum is just the nuclear rotational angular momentum. For other states, Hund proposed five possible idealized modes of coupling.
The last two rows are degenerate because they have the same good quantum numbers.
In practice there are also many molecular states which are intermediate between the above limiting cases. | 7 | Physical Chemistry |
Several natural ingredients are certified by the United States Environmental Protection Agency as insect repellents, namely catnip oil, oil of lemon eucalyptus (OLE) (and its active ingredient p-Menthane-3,8-diol), oil of citronella, and 2-Undecanone, which is usually produced synthetically but has also been isolated from many plant sources.
Many other studies have also investigated the potential of natural compounds from plants as insect repellents. Moreover, there are many preparations from naturally occurring sources that have been used as a repellent to certain insects. Some of these act as insecticides while others are only repellent. Below is a list of some natural products with repellent activity:
* Achillea alpina (mosquitos)
* alpha-terpinene (mosquitos)
* Andrographis paniculata extracts (mosquito)
* Basil
** Sweet basil (Ocimum basilicum)
* Breadfruit (Insect repellent, including mosquitoes)
* Callicarpa americana (beautyberry)
* Camphor (mosquitoes)
* Carvacrol (mosquitos)
* Castor oil (Ricinus communis) (mosquitos)
* Catnip oil (Nepeta species) (nepetalactone against mosquitos)
* Cedar oil (mosquitos, moths)
* Celery extract (Apium graveolens) (mosquitos) In clinical testing an extract of celery was demonstrated to be at least equally effective to 25% DEET, although the commercial availability of such an extract is not known.
* Cinnamon (leaf oil kills mosquito larvae)
* Citronella oil (repels mosquitos) (contains insect repelling substances, such as citronellol and geraniol)
* Clove oil (mosquitos)
* D-Limonene (ticks, fleas, flies, mosquitoes, and other insects) (widely used in insect repellents for pets)
* Eucalyptus oil (70%+ eucalyptol), (cineol is a synonym), mosquitos, flies, dust mites In the U.S., eucalyptus oil was first registered in 1948 as an insecticide and miticide.
* Fennel oil (Foeniculum vulgare) (mosquitos)
* Garlic (Allium sativum) (Mosquito, rice weevil, wheat flour beetle)
* Geranium oil (also known as Pelargonium graveolens)
* Hinokitiol (ticks, mosquitos, larvae)
* Lavender (ineffective alone, but measurable effect in certain repellent mixtures)
* Lemon eucalyptus (Corymbia citriodora) essential oil and its active ingredient p-menthane-3,8-diol (PMD)
* Lemongrass oil (Cymbopogon species) (mosquitos)
** East-Indian lemon grass (Cymbopogon flexuosus)
* Linalool (ticks, fleas, mites, mosquitoes, spiders, cockroach)
* Marjoram (spider mites Tetranychus urticae and Eutetranychus orientalis)
* Mint (menthol is active chemical.) (Mentha sp.)
* Neem oil (Azadirachta indica) (Repels or kills mosquitos, their larvae and a plethora of other insects including those in agriculture)
* Nootkatone (ticks, mosquitoes and other insects)
* Oleic acid, repels bees and ants by simulating the "smell of death" produced by their decomposing corpses.
* Pennyroyal (Mentha pulegium) (mosquitos, fleas,) but very toxic to pets
* Peppermint (Mentha x piperita) (mosquitos)
* Pyrethrum (from Chrysanthemum species, particularly C. cinerariifolium and C. coccineum)
* Rosemary (Rosmarinus officinalis) (mosquitos)
* Spanish Flag (Lantana camara) (against Tea Mosquito Bug, Helopeltis theivora)
* Tea tree oil from the leaves of Melaleuca alternifolia
* Thyme (Thymus species) (mosquitos)
* Yellow nightshade (Solanum villosum), berry juice (against Stegomyia aegypti mosquitos) | 1 | Biochemistry |
The terms "endothermic" and "endotherm" are both derived from Greek "within" and "heat", but depending on context, they can have very different meanings.
In physics, thermodynamics applies to processes involving a system and its surroundings, and the term "endothermic" is used to describe a reaction where energy is taken "(with)in" by the system (vs. an "exothermic" reaction, which releases energy "outwards").
In biology, thermoregulation is the ability of an organism to maintain its body temperature, and the term "endotherm" refers to an organism that can do so from "within" by using the heat released by its internal bodily functions (vs. an "ectotherm", which relies on external, environmental heat sources) to maintain an adequate temperature. | 7 | Physical Chemistry |
Polymer brushes can be used in Area-selective deposition. Area-selective deposition is a promising technique for positional self-alignment of materials at a prepatterned surface. | 7 | Physical Chemistry |
Formate can be converted to hydrogen gas and carbon dioxide in E. coli. This reaction requires the enzyme [http://biocyc.org/ECOLI/NEW-IMAGE?type=ENZYME&object=FHLMULTI-CPLX formate-hydrogen lyase]. It can be used to prevent the conditions inside the cell becoming too acidic.
formate → H and CO | 1 | Biochemistry |
Somatic fusion, also called protoplast fusion, is a type of genetic modification in plants by which two distinct species of plants are fused together to form a new hybrid plant with the characteristics of both, a somatic hybrid. Hybrids have been produced either between different varieties of the same species (e.g. between non-flowering potato plants and flowering potato plants) or between two different species (e.g. between wheat Triticum and rye Secale to produce Triticale).
Uses of somatic fusion include developing plants resistant to disease, such as making potato plants resistant to potato leaf roll disease. Through somatic fusion, the crop potato plant Solanum tuberosum – the yield of which is severely reduced by a viral disease transmitted on by the aphid vector – is fused with the wild, non-tuber-bearing potato Solanum brevidens, which is resistant to the disease. The resulting hybrid has the chromosomes of both plants and is thus similar to polyploid plants.
Somatic hybridization was first introduced by Carlson et al. in Nicotiana glauca. | 1 | Biochemistry |
Carboxypeptidases hydrolyze peptides at the first amide or polypeptide bond on the C-terminal end of the chain. Carboxypeptidases act by replacing the substrate water with a carbonyl (C=O) group. The carboxypeptidase A hydrolysis reaction has two mechanistic hypotheses, via a nucleophilic water and via an anhydride.
In the first proposed mechanism, a promoted-water pathway is favoured as Glu270 deprotonates the nucleophilic water. The Zn ion, along with positively charged residues, decreases the pKa of the bound water to approximately 7. Glu 270 has a dual role in this mechanism as it acts as a base to allow for the attack at the amide carbonyl group during nucleophilic addition. It acts as an acid during elimination when the water proton is transferred to the leaving nitrogen group. The oxygen on the amide carbonyl group does not coordinate to the Zn until the addition of the water. The deprotonation of the Zn coordinated water by Glu 270 provides an activated hydroxide nucleophile which attacks the amide carbonyl group in the peptide bond in a nucleophilic addition. The negatively charged intermediates that are formed during hydrolysis are stabilized by the Zn ion. The interaction between the carbonyl group and the neighbouring arginine, Arg 217, also stabilizes the negatively charged intermediates. The zinc-bound hydroxide interacts with the amide with the electrostatic stabilization of the transition state provided by the Zn ion and the neighbouring arginine.
The second proposed mechanism via an anhydride has similar steps but there is a direct attack of Glu270 on the carbonyl group, and then the interaction of Glu270 on the Zn-bound amide forms an anhydride instead which can subsequently be hydrolyzed by water. | 1 | Biochemistry |
Nikolay Bogoliubov considered perturbations on the limit of dilute gas, finding a finite pressure at zero temperature and positive chemical potential. This leads to corrections for the ground state. The Bogoliubov state has pressure (T = 0): .
The original interacting system can be converted to a system of non-interacting particles with a dispersion law. | 7 | Physical Chemistry |
Plant and fungal cells are also electrically excitable. The fundamental difference from animal action potentials is that the depolarization in plant cells is not accomplished by an uptake of positive sodium ions, but by release of negative chloride ions. In 1906, J. C. Bose published the first measurements of action potentials in plants, which had previously been discovered by Burdon-Sanderson and Darwin. An increase in cytoplasmic calcium ions may be the cause of anion release into the cell. This makes calcium a precursor to ion movements, such as the influx of negative chloride ions and efflux of positive potassium ions, as seen in barley leaves.
The initial influx of calcium ions also poses a small cellular depolarization, causing the voltage-gated ion channels to open and allowing full depolarization to be propagated by chloride ions.
Some plants (e.g. Dionaea muscipula) use sodium-gated channels to operate movements and essentially "count". Dionaea muscipula, also known as the Venus flytrap, is found in subtropical wetlands in North and South Carolina. When there are poor soil nutrients, the flytrap relies on a diet of insects and animals. Despite research on the plant, there lacks an understanding behind the molecular basis to the Venus flytraps, and carnivore plants in general.
However, plenty of research has been done on action potentials and how they affect movement and clockwork within the Venus flytrap. To start, the resting membrane potential of the Venus flytrap (-120mV) is lower than animal cells (usually -90mV to -40mV). The lower resting potential makes it easier to activate an action potential. Thus, when an insect lands on the trap of the plant, it triggers a hair-like mechanoreceptor. This receptor then activates an action potential which lasts around 1.5 ms. Ultimately, this causes an increase of positive Calcium ions into the cell, slightly depolarizing it.
However, the flytrap does not close after one trigger. Instead, it requires the activation of 2 or more hairs. If only one hair is triggered, it throws the activation as a false positive. Further, the second hair must be activated within a certain time interval (0.75 s - 40 s) for it to register with the first activation. Thus, a buildup of calcium starts and slowly falls from the first trigger. When the second action potential is fired within the time interval, it reaches the Calcium threshold to depolarize the cell, closing the trap on the prey within a fraction of a second.
Together with the subsequent release of positive potassium ions the action potential in plants involves an osmotic loss of salt (KCl). Whereas, the animal action potential is osmotically neutral because equal amounts of entering sodium and leaving potassium cancel each other osmotically. The interaction of electrical and osmotic relations in plant cells appears to have arisen from an osmotic function of electrical excitability in a common unicellular ancestors of plants and animals under changing salinity conditions. Further, the present function of rapid signal transmission is seen as a newer accomplishment of metazoan cells in a more stable osmotic environment. It is likely that the familiar signaling function of action potentials in some vascular plants (e.g. Mimosa pudica) arose independently from that in metazoan excitable cells.
Unlike the rising phase and peak, the falling phase and after-hyperpolarization seem to depend primarily on cations that are not calcium. To initiate repolarization, the cell requires movement of potassium out of the cell through passive transportation on the membrane. This differs from neurons because the movement of potassium does not dominate the decrease in membrane potential; In fact, to fully repolarize, a plant cell requires energy in the form of ATP to assist in the release of hydrogen from the cell – utilizing a transporter commonly known as H+-ATPase. | 7 | Physical Chemistry |
Phosphoryl transfer only occurs on closing of the open lid. This causes an exclusion of water molecules that brings the substrates in proximity to each other, lowering the energy barrier for the nucleophilic attack by the α-phosphoryl of AMP on the γ-phosphoryl group of ATP resulting in formation of ADP by transfer of the γ-phosphoryl group to AMP. In the crystal structure of the ADK enzyme from E. coli with inhibitor Ap5A, the Arg88 residue binds the Ap5A at the α-phosphate group. It has been shown that the mutation R88G results in 99% loss of catalytic activity of this enzyme, suggesting that this residue is intimately involved in the phosphoryl transfer. Another highly conserved residue is Arg119, which lies in the adenosine binding region of the ADK, and acts to sandwich the adenine in the active site. It has been suggested that the promiscuity of these enzymes in accepting other NTPs is due to this relatively inconsequential interactions of the base in the ATP binding pocket. A network of positive, conserved residues (Lys13, Arg123, Arg156, and Arg167 in ADK from E. coli') stabilize the buildup of negative charge on phosphoryl group during the transfer. Two distal aspartate residues bind to the arginine network, causing the enzyme to fold and reduces its flexibility. A magnesium cofactor is also required, essential for increasing the electrophilicity of the phosphate on AMP, though this magnesium ion is only held in the active pocket by electrostatic interactions and dissociates easily. | 1 | Biochemistry |
This method is similar to the previous method in that the glycosyl donor is protected at C-2 by an OAc group, which is converted into an enol ether by the Tebbe reagent. However, in this approach, N-iodosuccinimide (NIS) is used to tether the glycosyl acceptor to the enol ether, and in a second step, activation of the anomeric leaving group leads to intramolecular delivery of the aglycon to C-1 and formation of the 1,2-cis-glycoside product. | 0 | Organic Chemistry |
* L.I. Mandelstam, Zh. Russ. Fiz-Khim., Ova. 58, 381 (1926).
*B.Ya. Zel’dovich, V.I.Popovichev, V.V.Ragulskii and F.S.Faisullov, "Connection between the wavefronts of the reflected and exciting light in stimulated Mandel’shtam Brillouin scattering," Sov. Phys. JETP, 15, 109 (1972) | 7 | Physical Chemistry |
Trefonas joined MEMC Electronic Materials in late 1984. In 1986, he and others co-founded Aspect Systems Inc., utilizing photolithography technology acquired from MEMC. Trefonas worked at Aspect from 1986-1989. Then, through a succession of company acquisitions, he moved to Shipley Company (1990-2000), Rohm and Haas (1997-2008), to The Dow Chemical Company (2008-2019), and finally to DuPont (2019-current).
Trefonas has published at least 132 journal articles and technical publications. He has received 107 American patents, and has more than 15 active patent applications pending. | 5 | Photochemistry |
Vitamin D supplementation is not associated with a reduced risk of stroke, cerebrovascular disease, myocardial infarction, or ischemic heart disease. Supplementation does not lower blood pressure in the general population. | 1 | Biochemistry |
This pathway is also called the “Xylose Reductase-Xylitol Dehydrogenase” or XR-XDH pathway. Xylose reductase (XR) and xylitol dehydrogenase (XDH) are the first two enzymes in this pathway. XR is reducing D-xylose to xylitol using NADH or NADPH. Xylitol is then oxidized to D-xylulose by XDH, using the cofactor NAD. In the last step D-xylulose is phosphorylated by an ATP utilising kinase, XK, to result in D-xylulose-5-phosphate which is an intermediate of the pentose phosphate pathway. | 1 | Biochemistry |
Due to their invasive nature, and their potentially disruptive production of ncRNAs, most transposons are dangerous to plants and metazoans alike. Given the lack of distinction between germ-line and somatic cells in the plant kingdom, this is doubly so, since alterations to the genetic and epigenetic code will be more easily inherited. While transposable elements may affect any number of different cell-types in an animal, be a skin cell, a liver cell, a brain cell, these changes are not heritable, due to the fact that an animal inherits only a parents gametic genetic code. In plants, however, there is no such distinction; a flower develops from a meristem, which is a form of somatic cell, and which will pass down to the flower, and thus to the offspring, any genetic or epigenetic alteration. Since each meristem will have developed differently, each different flower from each meristem of the same plant will potentially possess different modifications. In contrast to animals, however, plants do not undergo chromatin remodeling between generations, making the maintenance and inheritance of silencing an entirely different process. There are distinct and identifiable mechanisms on the maintenance of transposon inactivation in plants but, unfortunately, there is significantly less information on initiation of said inactivation. | 1 | Biochemistry |
When a shape-memory alloy is in its cold state (below M), the metal can be bent or stretched and will hold those shapes until heated above the transition temperature. Upon heating, the shape changes to its original. When the metal cools again, it will retain the shape, until deformed again.
With the one-way effect, cooling from high temperatures does not cause a macroscopic shape change. A deformation is necessary to create the low-temperature shape. On heating, transformation starts at A and is completed at A (typically 2 to 20 °C or hotter, depending on the alloy or the loading conditions). A is determined by the alloy type and composition and can vary between and . | 8 | Metallurgy |
Since the diameter of the probing convergent beam is smaller than in the case of a parallel beam, most of the information in the CBED pattern is obtained from very small regions, which other methods cannot reach. For example, in Selected Area Electron Diffraction (SAED), where a parallel beam illumination is used, the smallest area that can be selected is 0.5 µm at 100 kV, whereas in CBED, it is possible to go to areas smaller than 100 nm. Also, the amount of information that is obtained from a CBED pattern is larger than that from a SAED pattern.
Nonetheless, CBED also has its disadvantages. The focused probe may generate contamination, which can cause localized stresses. But this was more of a problem in the past, and now, with the high vacuum conditions, one should be able to probe a clean region of the specimen in minutes to hours. Another disadvantage is that the convergent beam may heat or damage the chosen region of the specimen.
Since 1939, CBED has been mainly used to study thicker materials. | 3 | Analytical Chemistry |
Digestion is the breakdown of carbohydrates to yield an energy-rich compound called ATP. The production of ATP is achieved through the oxidation of glucose molecules. In oxidation, the electrons are stripped from a glucose molecule to reduce NAD+ and FAD. NAD+ and FAD possess a high energy potential to drive the production of ATP in the electron transport chain. ATP production occurs in the mitochondria of the cell. There are two methods of producing ATP: aerobic and anaerobic.
In aerobic respiration, oxygen is required. Using oxygen increases ATP production from 4 ATP molecules to about 30 ATP molecules.
In anaerobic respiration, oxygen is not required. When oxygen is absent, the generation of ATP continues through fermentation. There are two types of fermentation: alcohol fermentation and lactic acid fermentation.
There are several different types of carbohydrates: polysaccharides (e.g., starch, amylopectin, glycogen, cellulose), monosaccharides (e.g., glucose, galactose, fructose, ribose) and the disaccharides (e.g., sucrose, maltose, lactose).
[https://www.ncbi.nlm.nih.gov/books/NBK459280/ Monosaccharides], also known as simple sugars, are the most basic, fundamental unit of a carbohydrate. These are simple sugars with the general chemical structure of C6H12O6.
[https://www.ncbi.nlm.nih.gov/books/NBK459280/ Disaccharides] are a type of carbohydrate. Disaccharides consist of compound sugars containing two monosaccharides with the elimination of a water molecule with the general chemical structure C12H22O11.
[https://www.ncbi.nlm.nih.gov/books/NBK459280/ Oligosaccharides] are carbohydrates that consist of a polymer that contains three to ten monosaccharides linked together by glycosidic bonds.
Glucose reacts with oxygen in the following reaction, CHO + 6O → 6CO + 6HO. Carbon dioxide and water are waste products, and the overall reaction is exothermic.
The reaction of glucose with oxygen releasing energy in the form of molecules of ATP is therefore one of the most important biochemical pathways found in living organisms. | 1 | Biochemistry |
In 2009, India's Chandrayaan-1 satellite and the National Aeronautics and Space Administration (NASA) Cassini spacecraft and Deep Impact probe each detected evidence of water by evidence of hydroxyl fragments on the Moon. As reported by Richard Kerr, "A spectrometer [the Moon Mineralogy Mapper, also known as "M3"] detected an infrared absorption at a wavelength of 3.0 micrometers that only water or hydroxyl—a hydrogen and an oxygen bound together—could have created." NASA also reported in 2009 that the LCROSS probe revealed an ultraviolet emission spectrum consistent with hydroxyl presence.
On 26 October 2020, NASA reported definitive evidence of water on the sunlit surface of the Moon, in the vicinity of the crater Clavius (crater), obtained by the Stratospheric Observatory for Infrared Astronomy (SOFIA). The SOFIA Faint Object infrared Camera for the SOFIA Telescope (FORCAST) detected emission bands at a wavelength of 6.1 micrometers that are present in water but not in hydroxyl. The abundance of water on the Moon's surface was inferred to be equivalent to the contents of a 12-ounce bottle of water per cubic meter of lunar soil.
The Chang'e 5 probe, which landed on the Moon on 1 December 2020, carried a mineralogical spectrometer that could measure infrared reflectance spectra of lunar rock and regolith. The reflectance spectrum of a rock sample at a wavelength of 2.85 micrometers indicated localized water/hydroxyl concentrations as high as 180 parts per million. | 0 | Organic Chemistry |
The development of the Lemieux–Johnson oxidation was preceded by an analogous process, developed by Lemieux and Ernst Von Rudloff (sometimes called the Lemieux-Von Rudloff reaction), which used an aqueous solution of sodium periodate with a low (catalytic) concentration of potassium permanganate. This mixture became known as Lemieux reagent and has been used to determine the position of double bonds and for preparing carbonyl compounds. Unlike the Lemieux–Johnson oxidation, which normally stops at the aldehyde, this older method could continue to give a mixture of aldehydes and carboxylic acids. | 0 | Organic Chemistry |
The intrinsic color of liquid water may be demonstrated by looking at a white light source through a long pipe that is filled with purified water and closed at both ends with a transparent window. The light cyan color is caused by weak absorption in the red part of the visible spectrum.
Absorptions in the visible spectrum are usually attributed to excitations of electronic energy states in matter. Water is a simple three-atom molecule, HO, and all its electronic absorptions occur in the ultraviolet region of the electromagnetic spectrum and are therefore not responsible for the color of water in the visible region of the spectrum. The water molecule has three fundamental modes of vibration. Two stretching vibrations of the O–H bonds in the gaseous state of water occur at = 3650 cm and = 3755 cm. Absorption due to these vibrations occurs in the infrared region of the spectrum. The absorption in the visible spectrum is due mainly to the harmonic = 14,318 cm, which is equivalent to a wavelength of 698 nm. In liquid state at 20°C these vibrations are red-shifted by hydrogen bonding, resulting in red absorption at 740 nm, other harmonics such as giving red absorption at 660 nm. The absorption curve for heavy water (DO) is of a similar shape, but is shifted further towards the infrared end of the spectrum, because the vibrational transitions have a lower energy. For this reason, heavy water does not absorb red light and thus large bodies of DO would lack the characteristic cyan color of the more commonly found light water (HO).
Absorption intensity decreases markedly with each successive overtone, resulting in very weak absorption for the third overtone. For this reason, the pipe needs to have a length of a meter or more and the water must be purified by microfiltration to remove any particles that could produce Mie scattering. | 3 | Analytical Chemistry |
Pure copper. Unlike other metals, copper is frequently used in its pure (99.9% Cu) unalloyed form for sheet and strip applications in roofing, exterior cladding, and flashing.
Tempering is a heat treatment technique used to increase the toughness of metals. Tempers determine the ductility of the metal, and therefore how well it forms and will hold its shape without additional support. In the U.S., copper is available in six tempers: 060 soft, hard cold rolled, cold rolled high yield, half hard, three quarter hard, and hard. In the U.K., only three designations exist: soft, half-hard, and hard. Copper and its alloys are defined in the U.S. in Standard Designations for Copper and Copper Alloys by ASTM; in Europe by BS EN 1172: 1997 - Copper and Copper Alloys in Europe; and in the U.K. by the British Standard Code of Practice CP143: Part12: 1970.
Cold rolled copper temper is by far the most popular in building construction in the U.S. It is less malleable than soft copper but is far stronger. Cold rolled hard tempered copper is often recommended for roofing and flashing installations. Roof sheets with higher tempers may be specified for certain applications.
Soft tempered copper is extremely malleable and offers far less resistance than cold rolled copper to the stresses induced by expansion and contraction. It is used for intricate ornamental work and where extreme forming is required, such as in complicated thru-wall flashing conditions.
The major use for high-yield copper is in flashing products, where malleability and strength are both important.
The thickness of sheet and strip copper is measured in the U.S. by its weight in ounces per square foot. Thicknesses commonly used in construction in the U.S. are between and . Since the industry often uses gauge numbers or actual thicknesses for sheet metal or other building materials, it is necessary to convert between the different measurement systems.
In Europe, phosphorus de-oxidized non-arsenical copper is used with the designation C106. The copper is rolled to thicknesses ranging between ( for curtain walling) but a thickness is usually used for roofing.
Alloyed copper. Copper alloys, such as brass and bronze, are also used in residential and commercial building structures. Variations in color stem primarily from differences in the alloy chemical composition.
Some of the more popular copper alloys and their associated Unified Numbering System (UNS) numbers developed by ASTM and SAE are as follows:
In practice, the term bronze may be used for a variety of copper alloys with little or no tin if they resemble true bronzes in color.
Further information on architectural copper alloys is available. | 8 | Metallurgy |
A Bland–Altman plot (difference plot) in analytical chemistry or biomedicine is a method of data plotting used in analyzing the agreement between two different assays. It is identical to a Tukey mean-difference plot, the name by which it is known in other fields, but was popularised in medical statistics by J. Martin Bland and Douglas G. Altman. | 3 | Analytical Chemistry |
The monocyte activation test (MAT) is another proposed method to test for endotoxins based on monocytes in human blood. It measures the release of cytokines from these due to the presence of pyrogens, basically mirroring the process by which these toxins cause fever in humans (and rabbits, as in the original pyrogen test). A protocol for the MAT test, using cultured cells, is described in the European Pharmacopoeia.
A recent study employing genetically engineered monocytes was able to significantly enhance the sensitivity of monocyte-based detection assays by bringing down the assay-completion time from more than 20 hours to 2–3 hours. | 3 | Analytical Chemistry |
In chemistry, a molecular knot is a mechanically interlocked molecular architecture that is analogous to a macroscopic knot. Naturally-forming molecular knots are found in organic molecules like DNA, RNA, and proteins. It is not certain that naturally occurring knots are evolutionarily advantageous to nucleic acids or proteins, though knotting is thought to play a role in the structure, stability, and function of knotted biological molecules. The mechanism by which knots naturally form in molecules, and the mechanism by which a molecule is stabilized or improved by knotting, is ambiguous. The study of molecular knots involves the formation and applications of both naturally occurring and chemically synthesized molecular knots. Applying chemical topology and knot theory to molecular knots allows biologists to better understand the structures and synthesis of knotted organic molecules.
The term knotane was coined by Vögtle et al. in 2000 to describe molecular knots by analogy with rotaxanes and catenanes, which are other mechanically interlocked molecular architectures. The term has not been broadly adopted by chemists and has not been adopted by IUPAC. | 6 | Supramolecular Chemistry |
Massively parallel reporter assays is a technology to test the cis-regulatory activity of DNA sequences. MPRAs use a plasmid with a synthetic cis-regulatory element upstream of a promoter driving a synthetic gene such as Green Fluorescent Protein. A library of cis-regulatory elements is usually tested using MPRAs, a library can contain from hundreds to thousands of cis-regulatory elements. The cis-regulatory activity of the elements is assayed by using the downstream reporter activity. The activity of all the library members is assayed in parallel using barcodes for each cis-regulatory element. One limitation of MPRAs is that the activity is assayed on a plasmid and may not capture all aspects of gene regulation observed in the genome. | 1 | Biochemistry |
Gibbs considered the following difficulty that arises if the ideal gas entropy is not extensive. Two containers of an ideal gas sit side-by-side. The gas in container #1 is identical in every respect to the gas in container #2 (i.e. in volume, mass, temperature, pressure, etc). Accordingly, they have the same entropy S. Now a door in the container wall is opened to allow the gas particles to mix between the containers. No macroscopic changes occur, as the system is in equilibrium. But if the formula for entropy is not extensive, the entropy of the combined system will not be 2S. In fact, the particular non-extensive entropy quantity considered by Gibbs predicts additional entropy (more than 2S). Closing the door then reduces the entropy again to S per box, in apparent violation of the Second Law of Thermodynamics.
As understood by Gibbs, and reemphasized more recently, this is a misuse of Gibbs non-extensive entropy quantity. If the gas particles are distinguishable, closing the doors will not return the system to its original state – many of the particles will have switched containers. There is a freedom in defining what is "ordered", and it would be a mistake to conclude that the entropy has not increased. In particular, Gibbs non-extensive entropy quantity for an ideal gas is not intended for situations where the number of particles changes.
The paradox is averted by assuming the indistinguishability (at least effective indistinguishability) of the particles in the volume. This results in the extensive Sackur–Tetrode equation for entropy, as derived next. | 7 | Physical Chemistry |
A calorimeter constant (denoted C) is a constant that quantifies the heat capacity of a calorimeter. It may be calculated by applying a known amount of heat to the calorimeter and measuring the calorimeters corresponding change in temperature. In SI units, the calorimeter constant is then calculated by dividing the change in enthalpy (ΔH) in joules by the change in temperature (ΔT') in kelvins or degrees Celsius:
The calorimeter constant is usually presented in units of joules per degree Celsius (J/°C) or joules per kelvin (J/K). Every calorimeter has a unique calorimeter constant. | 7 | Physical Chemistry |
According to textbook knowledge, it is possible to transform a liquid continuously into a gas, without undergoing a phase transition, by heating and compressing strongly enough to go around the critical point. However, different criteria still allow to distinguish liquid-like and more gas-like states of a supercritical fluid. These criteria result in different boundaries in the pT plane. These lines emanate either from the critical point, or from the liquid–vapor boundary (boiling curve) somewhat below the critical point. They do not correspond to first or second order phase transitions, but to weaker singularities.
The Fisher–Widom line is the boundary between monotonic and oscillating asymptotics of the pair correlation function .
The Widom line is a generalization thereof, apparently so named by H. Eugene Stanley. However, it was first measured experimentally in 1956 by Jones and Walker, and subsequently named the hypercritical line by Bernal in 1964, who suggested a structural interpretation. The Frenkel line is a boundary between "rigid" and "non-rigid" fluids characterized by the onset of transverse sound modes.
One of the above mentioned criteria is based on the velocity autocorrelation function (vacf): below the Frenkel line the vacf demonstrates oscillatory behaviour, while above it the vacf monotonically decays to zero. The second criterion is based on the fact that at moderate temperatures liquids can sustain transverse excitations, which disappear upon heating. One further criterion is based on isochoric heat capacity measurements. The isochoric heat capacity per particle of a monatomic liquid near to the melting line is close to (where is the Boltzmann constant). The contribution to the heat capacity due to the potential part of transverse excitations is . Therefore at the Frenkel line, where transverse excitations vanish, the isochoric heat capacity per particle should be , a direct prediction from the phonon theory of liquid thermodynamics.
Another criterion for the Widom line is a peak in the isobaric heat capacity. In the subcritical region, the phase transition is associated with an effective spike in the heat capacity (i.e., the latent heat). Approaching the critical point, the latent heat falls to zero but this is accompanied by a gradual rise in heat capacity in the pure phases near phase transition. At the critical point, the latent heat is zero but the heat capacity shows a diverging singularity. Beyond the critical point, there is no divergence, but rather a smooth peak in the heat capacity; the highest point of this peak identifies the Widom line.
Anisimov et al. (2004), without referring to Frenkel, Fisher, or Widom, reviewed thermodynamic derivatives (specific heat, expansion coefficient, compressibility) and transport coefficients (viscosity, speed of sound) in supercritical water, and found pronounced extrema as function of pressure up to 100 K above T. | 7 | Physical Chemistry |
Surface ocean waters generally have oxygen concentrations close to equilibrium with the Earth's atmosphere. In general, colder waters hold more oxygen than warmer waters. As water moves out of the mixed layer into the thermocline, it is exposed to a rain of organic matter from above. Aerobic bacteria feed on this organic matter; oxygen is used as part of the bacterial metabolic process, lowering its concentration within the water. Therefore, the concentration of oxygen in deep water is dependent on the amount of oxygen it had when it was at the surface, minus depletion by deep sea organisms.
The downward flux of organic matter decreases sharply with depth, with 80–90% being consumed in the top . The deep ocean thus has higher oxygen because rates of oxygen consumption are low compared with the supply of cold, oxygen-rich deep waters from polar regions. In the surface layers, oxygen is supplied by photosynthesis of phytoplankton. Depths in between, however, have higher rates of oxygen consumption and lower rates of advective supply of oxygen-rich waters. In much of the ocean, mixing processes enable the resupply of oxygen to these waters (see upwelling).
A distribution of the open-ocean oxygen minimum zones is controlled by the large-scale ocean circulation as well as local physical as well as biological processes. For example, wind blowing parallel to the coast causes Ekman transport that upwells nutrients from deep water. The increased nutrients support phytoplankton blooms, zooplankton grazing, and an overall productive food web at the surface. The byproducts of these blooms and the subsequent grazing sink in the form of particulate and dissolved nutrients (from phytodetritus, dead organisms, fecal pellets, excretions, shed shells, scales, and other parts). This "rain" of organic matter (see the biological pump) feeds the microbial loop and may lead to bacterial blooms in water below the euphotic zone due to the influx of nutrients. Since oxygen is not being produced as a byproduct of photosynthesis below the euphotic zone, these microbes use up what oxygen is in the water as they break down the falling organic matter thus creating the lower oxygen conditions.
Physical processes then constrain the mixing and isolate this low oxygen water from outside water. Vertical mixing is constrained due to the separation from the mixed layer by depth. Horizontal mixing is constrained by bathymetry and boundaries formed by interactions with sub-tropical gyres and other major current systems. Low oxygen water may spread (by advection) from under areas of high productivity up to these physical boundaries to create a stagnant pool of water with no direct connection to the ocean surface even though (as in the Eastern Tropical North Pacific) there may be relatively little organic matter falling from the surface. | 9 | Geochemistry |
Fermionic condensates are attained at lower temperatures than Bose–Einstein condensates. Fermionic condensates are a type of superfluid. As the name suggests, a superfluid possesses fluid properties similar to those possessed by ordinary liquids and gases, such as the lack of a definite shape and the ability to flow in response to applied forces. However, superfluids possess some properties that do not appear in ordinary matter. For instance, they can flow at high velocities without dissipating any energy—i.e. zero viscosity. At lower velocities, energy is dissipated by the formation of quantized vortices, which act as "holes" in the medium where superfluidity breaks down. Superfluidity was originally discovered in liquid helium-4 whose atoms are bosons, not fermions. | 7 | Physical Chemistry |
The AFM-IR technique can simultaneously provide complementary measurements of the mechanical stiffness and dissipation of a sample surface. When infrared light is absorbed by the sample the resulting rapid thermal expansion excites a "contact resonance" of the AFM cantilever, i.e. a coupled resonance resulting from the properties of both the cantilever and the stiffness and damping of the sample surface. Specifically, the resonance frequency shifts to higher frequencies for stiffer materials and to lower frequencies for softer material. Additionally, the resonance becomes broader for materials with larger dissipation. These contact resonances have been studied extensively by the AFM community (see, for example, atomic force acoustic microscopy). Traditional contact resonance AFM requires an external actuator to excite the cantilever contact resonances. In AFM-IR these contact resonances are automatically excited every time an infrared pulse is absorbed by the sample. So the AFM-IR technique can measure the infrared absorption by the amplitude of the cantilever oscillation response and the mechanical properties of the sample via the contact resonance frequency and quality factor. | 3 | Analytical Chemistry |
Polysialic acid (polySia) is polymer of linearly repeating monomer units of α2,8- and α2,9-glycosidic linked sialic acid residues. Sialic acid refers to carboxylated 9-carbon sugars, 2-keto-3-dexoxy-D-glycero-nononic acids. An unusual property of this sugar is that it often polymerizes into polySia. This is accomplished by attaching the monomers to the nonreducing end of the glycan. This mostly consists of Neu5Ac subunits. It is polyanionic and bulky, meaning there is little ability to reach its central molecules. polySia is useful in signaling in vertebrates and on the cell surface of few glycoproteins and glycolipids causing modifications, and it has been recently found that the function of polySia relates almost directly to its degree of polymerization. The number of units can range from 8 to greater than 400. This vast range causes differences in the polySias ability to adhere different cells, assist in cellular migration, synapse formation, and regulate adhesion in nerve cells by modeling and formating them. polySias most prominent role is in post-translational modifications in a few proteins, with the main one being NCAM. polySia links to adhesion molecules causing their adhesive properties to be subdued allowing for the detailed control of cell migration and cell to cell relations. This is caused by polySia's bulky and polyanionic properties.
The human body produces polySia naturally and attaches it to a various number of proteins. This is done by linking polySia on the α2,3- or α2,6- terminal of the glycoprotein. O-linked glycosylation through threonine or N-linked glycosylation through asparagine is employed. This polySia linkage is found in proteins such as NCAM, E-selectin ligand 1 (ESL-1), C–C chemokine receptor type 7 (CCR7), synaptic cell adhesion molecule-1 (SynCAM-1), neuropilin-2 (NRP-2), the CD36 scavenger receptor found in the milk of humans, and the α-subunit of the voltage-sensitive sodium channel. The synthesis of polySia is enzymatically formed by α2,8-sialyltransferase (ST8Sia) in a Type II transmembrane protein located on the Golgi Apparatus membrane. ST8Sia does this by adding sialic acids to the terminal end of the glycan through the CMP-sialic acid donor at various lengths depending on necessity. The length is controlled extensively by the expression of polysialyltransferase enzymes, once again controlling the function of polySia. | 1 | Biochemistry |
Transition metal complexes of aldehydes and ketones describes coordination complexes with aldehyde (RCHO) and ketone ligands. Because aldehydes and ketones are common, the area is of fundamental interest. Some reactions that are useful in organic chemistry involve such complexes. | 0 | Organic Chemistry |
In thermodynamics, a diathermal wall between two thermodynamic systems allows heat transfer but does not allow transfer of matter across it.
The diathermal wall is important because, in thermodynamics, it is customary to assume a priori, for a closed system, the physical existence of transfer of energy across a wall that is impermeable to matter but is not adiabatic, transfer which is called transfer of energy as heat, though it is not customary to label this assumption separately as an axiom or numbered law. | 7 | Physical Chemistry |
In order to infect a cell, the envelope glycoprotein GP120 of the HIV virus interacts with CD4 (acting as the primary receptor) and a co-receptor: either CCR5 or CXCR4. This binding results in membrane fusion and the subsequent intracellular signaling that facilitates viral invasion. In approximately half of all HIV cases, the viruses using the CCR5 co-receptor seem to favor immediate infection and transmission while those using the CXCR4 receptor do not present until later in the immunologically suppressed stage of the disease. The virus will often switch from using CCR5 to CXCR4 during the course of the infection, which serves as an indicator for the progression of the disease. Recent evidence suggests that some forms of HIV also use the large integrin a4b7 receptor to facilitate increased binding efficiency in mucosal tissues. | 1 | Biochemistry |
The mechanism of carboboration depends highly on the substrate and reagents utilized in the reaction. Shown below are examples of two types of Pd-catalyzed alkene 1,2 carboborations, Heck-type and the Wacker-type. However, the Cu- and Ni-catalyzed reactions can proceed through similar mechanisms. These two mechanisms mainly differ in the oxidation state of the active catalyst and how the carbon group is delivered to the substrate: whether the C–C bond is formed via migratory insertion from the catalyst (inner sphere) or attack by an external nucleophile (outer sphere). Wacker-type carboborations, catalyzed by Pd, are much rarer than Heck-type. The first example of a Wacker-type 1,2 carboboration was reported by the Engle group in 2019.
Despite the common trend of utilizing transition metals, transition metal-free processes have also been developed, such as utilizing boronic acids or light-mediated radical initiation. These reactions usually lead to the boron substituent being at the terminus or less substituted side of the substrate, but anti-carborborations have also been developed which produce reverse regioselectivity. Much work has also been done to render 1,2 carboboration enantioselective using various ligands on transition metal catalysts. | 0 | Organic Chemistry |
Capsular exopolysaccharides can protect pathogenic bacteria against desiccation and predation, and contribute to their pathogenicity. Sessile bacteria fixed and aggregated in biofilms are less vulnerable compared to drifting planktonic bacteria, as the EPS matrix is able to act as a protective diffusion barrier. The physical and chemical characteristics of bacterial cells can be affected by EPS composition, influencing factors such as cellular recognition, aggregation, and adhesion in their natural environments. Furthermore, the EPS layer acts as a nutrient trap, facilitating bacterial growth. The exopolysaccharides of some strains of lactic acid bacteria, e.g., Lactococcus lactis subsp. cremoris, contribute a gelatinous texture to fermented milk products (e.g., Viili), and these polysaccharides are also digestible. An example of the industrial use of exopolysaccharides is the application of dextran in panettone and other breads in the bakery industry.
Apart from negative contributions of EPS in biofilms, EPS can also contribute to some beneficial functions. For example, B. subtilis has gained interest for its probiotic properties due to its biofilm which allows it to effectively maintain a favorable microenvironment in the gastrointestinal tract. In order to survive the passage through the upper gastrointestinal tract, B. subtilis produces an extracellular matrix that protects it from stressful environments such as the highly acidic environment in the stomach. In B. subtilis, the protein matrix component, TasA, and the exopolysaccharide have both been shown to be essential for effective plant-root colonization in Arabidopsis and tomato plants. It was also suggested that TasA plays an important role in mediating interspecies aggregation with streptococci. | 1 | Biochemistry |
The cold work produced from this process is typically minimal, similar to the cold work produced by laser peening, only a few percent, but a great deal less than shot peening, gravity peening or, deep rolling. Cold work is particularly important because the higher the cold work at the surface of a component, the more vulnerable to elevated temperatures and mechanical overload that component will be and the easier the beneficial surface residual compression will relax, rendering the treatment pointless. In other words, a component that has been highly cold worked will not hold the compression if it comes into contact with extreme heat, like an engine, and will be just as vulnerable as it was to start. Therefore, LPB and laser peening stand out in the surface enhancement industry because they are both thermally stable at high temperatures. The reason LPB produces such low percentages of cold work is because of the aforementioned closed-loop process control. Conventional shot peening processes have some guesswork involved and are not exact at all, causing the procedure to have to be performed multiple times on one component. For example, shot peening, in order to make sure every spot on the component is treated, typically specifies coverage of between 200% (2T) and 400% (4T). This means that at 200% coverage (2T), 5 or more impacts occur at 84% of locations and at 400% coverage (4T), it is significantly more. The problem is that one area will be hit several times while the area next to it is hit fewer times, leaving uneven compression at the surface. This uneven compression results in the whole process being easily "undone", as was mentioned above. LPB requires only one pass with the tool and leaves a deep, even, beneficial compressive stress.
The LPB process can be performed on-site in the shop or in situ on aircraft using robots, making it easy to incorporate into everyday maintenance and manufacturing procedures. The method is applied under continuous closed loop process control (CLPC), creating accuracy within 0.1% and alerting the operator and QA immediately if the processing bounds are exceeded. The limitation of this process is that different CNC processing codes need to be developed for each application, just like any other machining task. The other issue is that because of dimensional restrictions, it may not be possible to create the tools necessary to work on certain geometries, although that has yet to be a problem. | 8 | Metallurgy |
The United States Department of Agriculture (USDA) web site has a very complete searchable table of calcium content (in milligrams) in foods, per common measures such as per 100 grams or per a normal serving. | 1 | Biochemistry |
Promoters are DNA segments near the 5' end of the gene where transcription begins. They are the sites where RNA polymerase binds to initiate RNA synthesis. Every gene has a noncoding promoter.
Regulatory elements are sites that control the transcription of a nearby gene. They are almost always sequences where transcription factors bind to DNA and these transcription factors can either activate transcription (activators) or repress transcription (repressors). Regulatory elements were discovered in the 1960s and their general characteristics were worked out in the 1970s by studying specific transcription factors in bacteria and bacteriophage.
Promoters and regulatory sequences represent an abundant class of noncoding DNA but they mostly consist of a collection of relatively short sequences so they do not take up a very large fraction of the genome. The exact amount of regulatory DNA in mammalian genome is unclear because it is difficult to distinguish between spurious transcription factor binding sites and those that are functional. The binding characteristics of typical DNA-binding proteins were characterized in the 1970s and the biochemical properties of transcription factors predict that in cells with large genomes, the majority of binding sites will not be biologically functional.
Many regulatory sequences occur near promoters, usually upstream of the transcription start site of the gene. Some occur within a gene and a few are located downstream of the transcription termination site. In eukaryotes, there are some regulatory sequences that are located at a considerable distance from the promoter region. These distant regulatory sequences are often called enhancers but there is no rigorous definition of enhancer that distinguishes it from other transcription factor binding sites. | 1 | Biochemistry |
Non exhaustive list of microorganisms.
Bacteria (Gram-positive and -negative)
*Acinetobacter spp.
*Aeromonas hydrophila
*Bacillus brevis
*Bacillus cereus
*Bacillus megaterium
*Bacillus subtilis
*Burkholderia cepacia
*Campylobacter jejuni
*Capnocytophaga ochracea
*Corynebacterium xerosis
*Enterobacter cloacae
*Escherichia coli
*Haemophilus influenzae
*Helicobacter pylori
*Klebsiella oxytoca
*Klebsiella pneumoniae
*Legionella spp.
*Listeria monocytogenes
*Micrococcus luteus
*Mycobacterium smegmatis
*Mycobacterium abscessus
*Neisseria spp.
*Pseudomonas aeruginosa
*Pseudomonas pyocyanea
*Salmonella spp.
*Selenomonas sputigena
*Shigella sonnei
*Staphylococcus aerogenes
*Staphylococcus aureus
*Streptococcus agalactiae
*Streptococcus faecalis
*Streptococcus mutans
*Wolinella recta
*Xanthomonas campestris
*Yersinia enterocolitica
Viruses
*Echovirus 11
*Herpes simplex virus, HSV
*Influenza virus
*Human immunodeficiency virus, HIV
*Respiratory syncytial virus, RSV
Yeasts and moulds
*Aspergillus niger
*Botryodiplodia theobromae
*Byssochlamys fulva
*Candida albicans
*Colletotrichum gloeosporioide
*Colletotrichum musae
*Fusarium monoliforme
*Fusarium oxysporum
*Rhodotula rubra
*Sclerotinia spp. | 1 | Biochemistry |
Testosterone sulfate is an endogenous, naturally occurring steroid and minor urinary metabolite of testosterone. | 1 | Biochemistry |
Physical exercise has well established beneficial effects on learning and memory (see Neurobiological effects of physical exercise). BDNF is a particularly important regulator of learning and memory. As reviewed by Fernandes et al., in rats, exercise enhances the hippocampus expression of the gene Bdnf, which has an essential role in memory formation. Enhanced expression of Bdnf occurs through demethylation of its CpG island promoter at exon IV and this demethylation depends on steps illustrated in the two figures. | 1 | Biochemistry |
Macrocycles are very useful in supramolecular chemistry, as they provide whole cavities that can completely surround guest molecules and may be chemically modified to fine-tune their properties.
*Cyclodextrins, calixarenes, cucurbiturils and crown ethers are readily synthesized in large quantities, and are therefore convenient for use in supramolecular systems.
*More complex cyclophanes, and cryptands can be synthesised to provide more tailored recognition properties.
*Supramolecular metallocycles are macrocyclic aggregates with metal ions in the ring, often formed from angular and linear modules. Common metallocycle shapes in these types of applications include triangles, squares, and pentagons, each bearing functional groups that connect the pieces via "self-assembly."
*Metallacrowns are metallomacrocycles generated via a similar self-assembly approach from fused chelate-rings. | 6 | Supramolecular Chemistry |
Carbohydrate chemistry is a subdiscipline of chemistry primarily concerned with the detection, synthesis, structure, and function of carbohydrates. Due to the general structure of carbohydrates, their synthesis is often preoccupied with the selective formation of glycosidic linkages and the selective reaction of hydroxyl groups; as a result, it relies heavily on the use of protecting groups. | 0 | Organic Chemistry |
In the Kroll process, the TiCl is reduced by liquid magnesium to give titanium metal:
The reduction is conducted at 800–850 °C in a stainless steel retort. Complications result from partial reduction of the TiCl, giving to the lower chlorides TiCl and TiCl. The MgCl can be further refined back to magnesium. The resulting porous metallic titanium sponge is purified by leaching or vacuum distillation. The sponge is crushed, and pressed before it is melted in a consumable carbon electrode vacuum arc furnace. The melted ingot is allowed to solidify under vacuum. It is often remelted to remove inclusions and ensure uniformity. These melting steps add to the cost of the product. Titanium is about six times as expensive as stainless steel.
In the earlier Hunter process, which ceased to be commercial in the 1990s, the TiCl from the chloride process is reduced to the metal by sodium. | 8 | Metallurgy |
Volumetric water content, θ, is defined mathematically as:
where is the volume of water and is equal to the total volume of the wet material, i.e. of the sum of the volume of solid host material (e.g., soil particles, vegetation tissue) , of water , and of air .
Gravimetric water content is expressed by mass (weight) as follows:
where is the mass of water and is the mass of the solids.
For materials that change in volume with water content, such as coal, the gravimetric water content, u, is expressed in terms of the mass of water per unit mass of the moist specimen (before drying):
However, woodworking, geotechnics and soil science require the gravimetric moisture content to be expressed with respect to the sample's dry weight:
And in food science, both and are used and called respectively moisture content wet basis (MC) and moisture content dry basis (MC).
Values are often expressed as a percentage, i.e. u×100%.
To convert gravimetric water content to volumetric water content, multiply the gravimetric water content by the bulk specific gravity of the material: | 7 | Physical Chemistry |
The four-dimensional point groups (chiral as well as achiral) are listed in Conway and Smith, Section 4, Tables 4.1–4.3.
The following list gives the four-dimensional reflection groups (excluding those that leave a subspace fixed and that are therefore lower-dimensional reflection groups). Each group is specified as a Coxeter group, and like the polyhedral groups of 3D, it can be named by its related convex regular 4-polytope. Related pure rotational groups exist for each with half the order, and can be represented by the bracket Coxeter notation with a + exponent, for example [3,3,3] has three 3-fold gyration points and symmetry order 60. Front-back symmetric groups like [3,3,3] and [3,4,3] can be doubled, shown as double brackets in Coxeter's notation, for example with its order doubled to 240. | 4 | Stereochemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.