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A different perspective on Alzheimers is revealed by a mouse study that has found that APP possesses ferroxidase activity similar to ceruloplasmin, facilitating iron export through interaction with ferroportin; it seems that this activity is blocked by zinc trapped by accumulated Aβ in Alzheimers. It has been shown that a single nucleotide polymorphism in the 5'UTR of APP mRNA can disrupt its translation.
The hypothesis that APP has ferroxidase activity in its E2 domain and facilitates export of Fe(II) is possibly incorrect since the proposed ferroxidase site of APP located in the E2 domain does not have ferroxidase activity.
As APP does not possess ferroxidase activity within its E2 domain, the mechanism of APP-modulated iron efflux from ferroportin has come under scrutiny. One model suggests that APP acts to stabilize the iron efflux protein ferroportin in the plasma membrane of cells thereby increasing the total number of ferroportin molecules at the membrane. These iron-transporters can then be activated by known mammalian ferroxidases (i.e. ceruloplasmin or hephaestin). | 1 | Biochemistry |
Octahedral clusters are inorganic or organometallic cluster compounds composed of six metals in an octahedral array. Many types of compounds are known, but all are synthetic. | 7 | Physical Chemistry |
Examples of photochemical reactions are those between certain arenes and alkenes forming [2+2] and [2+4] cycloaddition adducts. | 0 | Organic Chemistry |
Glycoside hydrolases are typically named after the substrate that they act upon. Thus glucosidases catalyze the hydrolysis of glucosides and xylanases catalyze the cleavage of the xylose based homopolymer xylan. Other examples include lactase, amylase, chitinase, sucrase, maltase, neuraminidase, invertase, hyaluronidase and lysozyme. | 0 | Organic Chemistry |
From 1932 to 1937, Max Delbrück worked in Berlin as an assistant to Lise Meitner, who was collaborating with Otto Hahn on the results of irradiating uranium with neutrons. During this period he wrote a few papers, one of which turned out to be an important contribution on the scattering of gamma rays by a Coulomb field due to polarization of the vacuum produced by that field (1933). His conclusion proved to be theoretically sound but inapplicable to the case in point, but 20 years later Hans Bethe confirmed the phenomenon and named it "Delbrück scattering".
In 1953, Robert Wilson observed Delbrück scattering of 1.33 MeV gamma-rays by the electric fields of lead nuclei. | 7 | Physical Chemistry |
Silicon carbide is a semiconductor, which can be doped n-type by nitrogen or phosphorus and p-type by beryllium, boron, aluminium, or gallium. Metallic conductivity has been achieved by heavy doping with boron, aluminium or nitrogen.
Superconductivity has been detected in 3C-SiC:Al, 3C-SiC:B and 6H-SiC:B at similar temperatures ~1.5 K. A crucial difference is however observed for the magnetic field behavior between aluminium and boron doping: 3C-SiC:Al is type-II. In contrast, 3C-SiC:B is type-I, as is 6H-SiC:B. Thus the superconducting properties seem to depend more on dopant (B vs. Al) than on polytype (3C- vs 6H-). In an attempt to explain this dependence, it was noted that B substitutes at C sites in SiC, but Al substitutes at Si sites. Therefore, Al and B "see" different environments, in both polytypes. | 8 | Metallurgy |
Opportunity Rover found that the soil at Meridiani Planum was very similar to the soil at Gusev crater and Ares Vallis; however in many places at Meridiani the soil was covered with round, hard, gray spherules that were named "blueberries." These blueberries were found to be composed almost entirely of the mineral hematite. It was decided that the spectra signal spotted from orbit by Mars Odyssey was produced by these spherules. After further study it was decided that the blueberries were concretions formed in the ground by water. Over time, these concretions weathered from what was overlying rock, and then became concentrated on the surface as a lag deposit. The concentration of spherules in bedrock could have produced the observed blueberry covering from the weathering of as little as one meter of rock. Most of the soil consisted of olivine basalt sands that did not come from the local rocks. The sand may have been transported from somewhere else. | 9 | Geochemistry |
Structurally, rusticles contain channels which allow water to flow through, and they seem to build up in a ring structure similar to the growth rings of a tree. They are very delicate and can easily disintegrate into fine powder on even the slightest touch. | 8 | Metallurgy |
HCN channel was first identified in 1976 in the heart by Noma and Irisawa and characterized by Brown, Difrancesco and Weiss | 1 | Biochemistry |
Eschenmoser developed synthetic pathways for artificial nucleic acids, specifically modifying the sugar backbone of the polymer. Having developed a number of structural alternatives to the naturally occurring nucleic acids, Eschenmoser and his colleagues were able to contrast the properties of these synthetic nucleic acids with naturally occurring ones to effectively determine the properties of RNA and DNA vital to modern biochemical processes. This work demonstrated that hydrogen-bonding interactions between the base-paring surfaces of the nucleobases alone might not have provided sufficient selection pressure to lead to the eventual rise of ribose in the structure of modern nucleic acids. He determined that pentose sugars, particularly ribose, conform to a geometry that contributes significantly to the helical structure of DNA by optimizing base-pair stacking distances in naturally occurring oligonucleotides. These base-stacking interactions orient and stabilize the base-paring surfaces of the nucleobases (A, G, C, T or U in RNA) and give rise to the canonical Watson-Crick base-paring rules that are well understood today.
Threose nucleic acid is an artificial genetic polymer invented by Eschenmoser. TNA strings composed of repeating threose sugars linked together by phosphodiester bonds. Like DNA and RNA, the molecule TNA can store genetic information in strings of nucleotide sequences. John Chaput, a professor at UC Irvine, has theorized that issues concerning the prebiotic synthesis of ribose sugars and the non-enzymatic replication of RNA may provide circumstantial evidence of an earlier genetic system more readily produced under primitive earth conditions. TNA could have been an early pre-DNA genetic system. | 0 | Organic Chemistry |
It is known that most materials are polycrystalline and contain grain boundaries and that grain boundaries can act as sinks and transport pathways for point defects. However experimentally and theoretically determining what effect point defects have on a system is difficult. Interesting examples of the complications of how point defects behave has been manifested in the temperature dependence of the Seebeck effect. In addition the dielectric and piezoelectric response can be altered by the distribution of point defects near grain boundaries. Mechanical properties can also be significantly influenced with properties such as the bulk modulus and damping being influenced by changes to the distribution of point defects within a material. It has also been found that the Kondo effect within graphene can be tuned due to a complex relationship between grain boundaries and point defects. Recent theoretical calculations have revealed that point defects can be extremely favourable near certain grain boundary types and significantly affect the electronic properties with a reduction in the band gap. | 8 | Metallurgy |
Triglycerides are built from three fatty acids, esterified onto each of three hydroxy groups of glycerol, which is derived from glycerol 3-phosphate. In mammals, glycerol 3-phosphate is usually synthesized through glycolysis, a metabolic pathway that degrades glucose into fructose 1,6-bisphosphate and then into two molecules of dihydroxyacetone phosphate, which beget glycerol 3-phosphate and glyceraldehyde 3-phosphate. When an organism is deficient in glucose, from (for example) fasting or a low carbohydrate intake, glycerol 3-phosphate is generated by glyceroneogenesis instead. As well as synthesizing lipids for use in other metabolic processes, glyceroneogenesis regulates lipid levels in the cytosol. | 1 | Biochemistry |
The concept of the DNA of Things (DoT) was introduced in 2019 by a team of researchers from Israel and Switzerland, including Yaniv Erlich and Robert Grass. DoT encodes digital data into DNA molecules, which are then embedded into objects. This gives the ability to create objects that carry their own blueprint, similar to biological organisms. In contrast to Internet of things, which is a system of interrelated computing devices, DoT creates objects which are independent storage objects, completely off-grid.
As a proof of concept for DoT, the researcher 3D-printed a Stanford bunny which contains its blueprint in the plastic filament used for printing. By clipping off a tiny bit of the ear of the bunny, they were able to read out the blueprint, multiply it and produce a next generation of bunnies. In addition, the ability of DoT to serve for steganographic purposes was shown by producing non-distinguishable lenses which contain a YouTube video integrated into the material. | 1 | Biochemistry |
One of the most commonly used self-cleaning products, titanium dioxide, utilizes a unique self-cleaning mechanism that combines an initial photocatalytic step and subsequent superhydrophilicity. A titanium dioxide coating, typically on glass windows, when exposed to UV light, will generate free electrons that will interact with oxygen and water in the air to create free radicals. These free radicals will in turn breakdown any fouling organic matter deposited on the surface of the glass. Titanium dioxide also changes the normally hydrophobic glass to a superhydrophilic surface. Thus, when rainfall occurs, instead of water beading up on the window surface and instantly falling down the glass, rain drops will rapidly spread out on the hydrophilic surface. The water will then move down the surface of the window, as a film rather than a droplet, essentially acting like a squeegee to remove surface debris. | 7 | Physical Chemistry |
In step-growth polymerization, in order to achieve a high degree of polymerization (and hence molecular weight), , a high fractional monomer conversion, p, is required, according to Carothers equation For example, a monomer conversion of p' = 99% would be required to achieve .
For chain-growth free radical polymerization, however, Carothers' equation does not apply. Instead long chains are formed from the beginning of the reaction. Long reaction times increase the polymer yield, but have little effect on the average molecular weight. The degree of polymerization is related to the kinetic chain length, which is the average number of monomer molecules polymerized per chain initiated. However it often differs from the kinetic chain length for several reasons:
* chain termination may occur wholly or partly by recombination of two chain radicals, which doubles the degree of polymerization
* chain transfer to monomer starts a new macromolecule for the same kinetic chain (of reaction steps), corresponding to a decrease of the degree of polymerization
* chain transfer to solvent or to another solute (a modifier or regulator also decreases the degree of polymerization | 7 | Physical Chemistry |
Prior to Edwards developing his equation, other scientists were also working to define nucleophilicity quantitatively. Brønsted and Pederson first discovered the relationship between basicity, with respect to protons, and nucleophilicity in 1924:
:where
where k is the rate constant for nitramide decomposition by a base (B) and β is a parameter of the equation.
Swain and Scott later tried to define a more specific and quantitative relationship by correlating nucleophilic data with a single-parameter equation derived in 1953:
This equation relates the rate constant k, of a reaction, normalized to that of a standard reaction with water as the nucleophile (k), to a nucleophilic constant n for a given nucleophile and a substrate constant s that depends on the sensitivity of a substrate to nucleophilic attack (defined as 1 for methyl bromide). This equation was modeled after the Hammett equation.
However, both the Swain–Scott equation and the Brønsted relationship make the rather inaccurate assumption that all nucleophiles have the same reactivity with respect to a specific reaction site. There are several different categories of nucleophiles with different attacking atoms (e.g. oxygen, carbon, nitrogen) and each of these atoms has different nucleophilic characteristics. The Edwards equation attempts to account for this additional parameter by introducing a polarizability term. | 7 | Physical Chemistry |
In the environment, bacteria preferentially produce 5α-cholestan-3β-ol (5α-cholestanol) from cholesterol rather than the 5β isomer. This reaction occurs principally in anaerobic reducing sediments and the 5α-cholestanol / cholesterol ratio may be used as a secondary (process) biomarker for such conditions. No cut-off values have been suggested for this marker and so it is used in a relative sense; the greater the ratio, the more reducing the environment. Reducing environments are frequently associated with areas experiencing high organic matter input; this may include sewage derived discharges. The relationship between reducing conditions and the potential source can be seen in a cross plot with a sewage indicator.<br />
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It may be suggested from this relationship that sewage discharges are in part responsible for the anaerobic reducing conditions in the sediments. | 2 | Environmental Chemistry |
In the decades after the discovery of the Conia-ene reaction, several improvements allowed for milder reaction conditions and greater control of product stereo- and regiochemistry. For example, the carbonyl component, formerly a ketone or aldehyde, became a substituted β-ketoester or malonate ester. Such carbonyls enolize much more readily, yielding better access to the desired enol tautomer. Additionally, the alkene component was replaced with an alkyne, which not only gave better cyclization in accordance with Baldwin’s rules, but also furnished a product containing an alkene that served as a useful handle for further transformations. Finally, recent efforts have featured metal-mediated and metal-catalyzed Conia-ene reactions that can be rendered asymmetric using chiral ligands. | 0 | Organic Chemistry |
Two examples of boron-containing compounds that have been linked to porphyrin are BODIPY and diketonate.
The BODIPY chromophore acts as an antenna: it absorbs a broad range of UV-visible light, then emits at a wavelength compatible with porphyrin absorption, allowing for efficient energy transfer.
This work has been extended to triads and to porphyrins with various core transition metals, some displaying multiphoton excitation.
On the other hand, when boron difluoride β-diketonate is used for an antenna, the emission-absorption overlap is small and little change in the porphyrin's optical properties is observed. Though this chromophore is preferable to BODIPY in certain applications, it is not an effective antenna for porphyrin. | 5 | Photochemistry |
The main fuel stored in the bodies of animals is fat. A young adult human's fat stores average between about , but varies greatly depending on age, sex, and individual disposition. In contrast, the human body stores only about of glycogen, of which is locked inside the skeletal muscles and is unavailable to the body as a whole. The or so of glycogen stored in the liver is depleted within one day of starvation. Thereafter the glucose that is released into the blood by the liver for general use by the body tissues, has to be synthesized from the glucogenic amino acids and a few other gluconeogenic substrates, which do not include fatty acids.
Fatty acids are broken down to acetyl-CoA by means of beta oxidation inside the mitochondria, whereas fatty acids are synthesized from acetyl-CoA outside the mitochondrion, in the cytosol. The two pathways are distinct, not only in where they occur, but also in the reactions that occur, and the substrates that are used. The two pathways are mutually inhibitory, preventing the acetyl-CoA produced by beta-oxidation from entering the synthetic pathway via the acetyl-CoA carboxylase reaction. It can also not be converted to pyruvate as the pyruvate decarboxylation reaction is irreversible. Instead it condenses with oxaloacetate, to enter the citric acid cycle. During each turn of the cycle, two carbon atoms leave the cycle as in the decarboxylation reactions catalyzed by isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. Thus each turn of the citric acid cycle oxidizes an acetyl-CoA unit while regenerating the oxaloacetate molecule with which the acetyl-CoA had originally combined to form citric acid. The decarboxylation reactions occur before malate is formed in the cycle. Malate is the only substance that can be removed from the mitochondrion to enter the gluconeogenic pathway to form glucose or glycogen in the liver or any other tissue. There can therefore be no net conversion of fatty acids into glucose.
Only plants possess the enzymes to convert acetyl-CoA into oxaloacetate from which malate can be formed to ultimately be converted to glucose.
;Regulation
Acetyl-CoA is formed into malonyl-CoA by acetyl-CoA carboxylase, at which point malonyl-CoA is destined to feed into the fatty acid synthesis pathway. Acetyl-CoA carboxylase is the point of regulation in saturated straight-chain fatty acid synthesis, and is subject to both phosphorylation and allosteric regulation. Regulation by phosphorylation occurs mostly in mammals, while allosteric regulation occurs in most organisms. Allosteric control occurs as feedback inhibition by palmitoyl-CoA and activation by citrate. When there are high levels of palmitoyl-CoA, the final product of saturated fatty acid synthesis, it allosterically inactivates acetyl-CoA carboxylase to prevent a build-up of fatty acids in cells. Citrate acts to activate acetyl-CoA carboxylase under high levels, because high levels indicate that there is enough acetyl-CoA to feed into the Krebs cycle and conserve energy.
High plasma levels of insulin in the blood plasma (e.g. after meals) cause the dephosphorylation of acetyl-CoA carboxylase, thus promoting the formation of malonyl-CoA from acetyl-CoA, and consequently the conversion of carbohydrates into fatty acids, while epinephrine and glucagon (released into the blood during starvation and exercise) cause the phosphorylation of this enzyme, inhibiting lipogenesis in favor of fatty acid oxidation via beta-oxidation. | 1 | Biochemistry |
Many woody plants regrow around injuries, such as those caused by pruning. In time, such regrowth often completely covers the damaged area as the cambium growth layer produces new tissues. Well-pruned trees with undamaged branch collars often recover well, where poorly-pruned trees rot below the wound. | 1 | Biochemistry |
The simplest phase diagrams are pressure–temperature diagrams of a single simple substance, such as water. The axes correspond to the pressure and temperature. The phase diagram shows, in pressure–temperature space, the lines of equilibrium or phase boundaries between the three phases of solid, liquid, and gas.
The curves on the phase diagram show the points where the free energy (and other derived properties) becomes non-analytic: their derivatives with respect to the coordinates (temperature and pressure in this example) change discontinuously (abruptly). For example, the heat capacity of a container filled with ice will change abruptly as the container is heated past the melting point. The open spaces, where the free energy is analytic, correspond to single phase regions. Single phase regions are separated by lines of non-analytical behavior, where phase transitions occur, which are called phase boundaries.
In the diagram on the right, the phase boundary between liquid and gas does not continue indefinitely. Instead, it terminates at a point on the phase diagram called the critical point. This reflects the fact that, at extremely high temperatures and pressures, the liquid and gaseous phases become indistinguishable, in what is known as a supercritical fluid. In water, the critical point occurs at around T = , p = and ρ = 356 kg/m.
The existence of the liquid–gas critical point reveals a slight ambiguity in labelling the single phase regions. When going from the liquid to the gaseous phase, one usually crosses the phase boundary, but it is possible to choose a path that never crosses the boundary by going to the right of the critical point. Thus, the liquid and gaseous phases can blend continuously into each other. The solid–liquid phase boundary can only end in a critical point if the solid and liquid phases have the same symmetry group.
For most substances, the solid–liquid phase boundary (or fusion curve) in the phase diagram has a positive slope so that the melting point increases with pressure. This is true whenever the solid phase is denser than the liquid phase. The greater the pressure on a given substance, the closer together the molecules of the substance are brought to each other, which increases the effect of the substance's intermolecular forces. Thus, the substance requires a higher temperature for its molecules to have enough energy to break out of the fixed pattern of the solid phase and enter the liquid phase. A similar concept applies to liquid–gas phase changes.
Water is an exception which has a solid-liquid boundary with negative slope so that the melting point decreases with pressure. This occurs because ice (solid water) is less dense than liquid water, as shown by the fact that ice floats on water. At a molecular level, ice is less dense because it has a more extensive network of hydrogen bonding which requires a greater separation of water molecules. Other exceptions include antimony and bismuth.
At very high pressures above 50 GPa (500 000 atm), liquid nitrogen undergoes a liquid-liquid phase transition to a polymeric form and becomes denser than solid nitrogen at the same pressure. Under these conditions therefore, solid nitrogen also floats in its liquid.
The value of the slope dP/dT is given by the Clausius–Clapeyron equation for fusion (melting)
where ΔH is the heat of fusion which is always positive, and ΔV is the volume change for fusion. For most substances ΔV is positive so that the slope is positive. However for water and other exceptions, ΔV is negative so that the slope is negative. | 7 | Physical Chemistry |
In aquatic environments, oxygen saturation is a ratio of the concentration of "dissolved oxygen" (DO, O), to the maximum amount of oxygen that will dissolve in that water body, at the temperature and pressure which constitute stable equilibrium conditions. Well-aerated water (such as a fast-moving stream) without oxygen producers or consumers is 100% saturated.
It is possible for stagnant water to become somewhat supersaturated with oxygen (i.e. reach more than 100% saturation) either because of the presence of photosynthetic aquatic oxygen producers or because of a slow equilibration after a change of atmospheric conditions. Stagnant water in the presence of decaying matter will typically have an oxygen concentration much less than 100%, which is due to anaerobic bacteria being much less efficient at breaking down organic material. Similarly as in water, oxygen concentration also plays a key role in the breakdown of organic matter in soils. Higher oxygen saturation allows for aerobic bacteria to persist, which break down decaying organic material in soils much more efficiently than anaerobic bacteria. Thus soils with high oxygen saturation will have less organic matter per volume than those with low oxygen saturation.
Environmental oxygenation can be important to the sustainability of a particular ecosystem. The US Environmental Protection Agency has published a table of maximum equilibrium dissolved oxygen concentration versus temperature at atmospheric pressure. The optimal levels in an estuary for dissolved oxygen is higher than 6 ppm. Insufficient oxygen (environmental hypoxia), often caused by the decomposition of organic matter and/or nutrient pollution, may occur in bodies of water such as ponds and rivers, tending to suppress the presence of aerobic organisms such as fish. Deoxygenation increases the relative population of anaerobic organisms such as plants and some bacteria, resulting in fish kills and other adverse events. The net effect is to alter the balance of nature by increasing the concentration of anaerobic over aerobic species. | 3 | Analytical Chemistry |
A well-known thioamide is thioacetamide, which is used as a source of the sulfide ion and is a building block in heterocyclic chemistry.
Thioamides or anti-thyroid drugs are also a class of drugs that are used to control thyrotoxicosis. | 0 | Organic Chemistry |
Depending on the application, various types of working fluids are used. In a thermodynamic cycle it may be the case that the working fluid changes state from gas to liquid or vice versa. Certain gases such as helium can be treated as ideal gases. This is not generally the case for superheated steam and the ideal gas equation does not really hold. At much higher temperatures however it still yields relatively accurate results. The physical and chemical properties of the working fluid are extremely important when designing thermodynamic systems. For instance, in a refrigeration unit, the working fluid is called the refrigerant. Ammonia is a typical refrigerant and may be used as the primary working fluid. Compared with water (which can also be used as a refrigerant), ammonia makes use of relatively high pressures requiring more robust and expensive equipment.
In air standard cycles as in gas turbine cycles, the working fluid is air. In the open cycle gas turbine, air enters a compressor where its pressure is increased. The compressor therefore inputs work to the working fluid (positive work). The fluid is then transferred to a combustion chamber where this time heat energy is input by means of the burning of a fuel. The air then expands in a turbine thus doing work against the surroundings (negative work).
Different working fluids have different properties and in choosing one in particular the designer must identify the major requirements. In refrigeration units, high latent heats are required to provide large refrigeration capacities. | 7 | Physical Chemistry |
The mitochondria is believed to be important in controlling the supply of oxygen available for making light in fireflies. An increased rate of respiration decreases the intracellular oxygen concentration which reduces the amount available for light production. The mitochondria of the photocyte exists near the perimeter of the cell while the peroxisome is typically found closer to the middle of the cell. It is worth noting that not all bioluminescence in the firefly light organ occurs in the granules of the photocyte. Some fluorescent protein has been found to exist in the posterior region of the organ. | 1 | Biochemistry |
White fuming nitric acid, pure nitric acid or WFNA, is very close to anhydrous nitric acid. It is available as 99.9% nitric acid by assay. One specification for white fuming nitric acid is that it has a maximum of 2% water and a maximum of 0.5% dissolved . Anhydrous nitric acid has a density of 1.513 g/cm and has the approximate concentration of 24 molar. Anhydrous nitric acid is a colorless, low-viscosity (mobile) liquid with a density of 1.512 g/cm that solidifies at to form white crystals. As it decomposes to and water, it obtains a yellow tint. It boils at . It is usually stored in a glass shatterproof amber bottle with twice the volume of head space to allow for pressure build up, but even with those precautions the bottle must be vented monthly to release pressure. | 3 | Analytical Chemistry |
Melainabacteria is a phylum related to Cyanobacteria. Organisms belonging to this phylum have been found in the human gut and various aquatic habitats such as groundwater. By analyzing genomes of Melainabacteria, predictions are possible about the cell structure and metabolic abilities. The bacterial cell is similar to cyanobacteria in being surrounded by two membranes. It differs from cyanobacteria in its ability to move by flagella (like gram-negative flagella), though some members (e.g. Gastranaerophilales) lack flagella. Melainabacteria are not able to perform photosynthesis, but obtain energy by fermentation. | 2 | Environmental Chemistry |
Let and be two graphs. Graph is a sub-graph of graph (written as ) if and . If and contains all of the edges with , then is an induced sub-graph of . We call and isomorphic (written as ), if there exists a bijection (one-to-one correspondence) with for all . The mapping is called an isomorphism between and .
When and there exists an isomorphism between the sub-graph and a graph , this mapping represents an appearance of in . The number of appearances of graph in is called the frequency of in . A graph is called recurrent (or frequent) in when its frequency is above a predefined threshold or cut-off value. We use terms pattern and frequent sub-graph in this review interchangeably. There is an ensemble of random graphs corresponding to the null-model associated to . We should choose random graphs uniformly from and calculate the frequency for a particular frequent sub-graph in . If the frequency of in is higher than its arithmetic mean frequency in random graphs , where , we call this recurrent pattern significant and hence treat as a network motif for . For a small graph , the network , and a set of randomized networks , where , the Z-score of the frequency of is given by
where and stand for the mean and standard deviation of the frequency in set , respectively. The larger the , the more significant is the sub-graph as a motif. Alternatively, another measurement in statistical hypothesis testing that can be considered in motif detection is the p-value, given as the probability of (as its null-hypothesis), where indicates the frequency of G in a randomized network. A sub-graph with p-value less than a threshold (commonly 0.01 or 0.05) will be treated as a significant pattern. The p'-value for the frequency of is defined as
where indicates the number of randomized networks, is defined over an ensemble of randomized networks, and the Kronecker delta function is one if the condition holds. The concentration of a particular n-size sub-graph in network refers to the ratio of the sub-graph appearance in the network to the total n-size non-isomorphic sub-graphs' frequencies, which is formulated by
where index is defined over the set of all non-isomorphic n-size graphs. Another statistical measurement is defined for evaluating network motifs, but it is rarely used in known algorithms. This measurement is introduced by Picard et al. in 2008 and used the Poisson distribution, rather than the Gaussian normal distribution that is implicitly being used above.
In addition, three specific concepts of sub-graph frequency have been proposed. As the figure illustrates, the first frequency concept considers all matches of a graph in original network. This definition is similar to what we have introduced above. The second concept is defined as the maximum number of edge-disjoint instances of a given graph in original network. And finally, the frequency concept entails matches with disjoint edges and nodes. Therefore, the two concepts and restrict the usage of elements of the graph, and as can be inferred, the frequency of a sub-graph declines by imposing restrictions on network element usage. As a result, a network motif detection algorithm would pass over more candidate sub-graphs if we insist on frequency concepts and . | 1 | Biochemistry |
The 3rd analytical group of cations includes ions which form hydroxides that are insoluble even at low concentrations.
Cations in the 3rd group are, among others: Fe, Fe, Al, and Cr.
The group is determined by making a solution of the salt in water and adding ammonium chloride and ammonium hydroxide. Ammonium chloride is added to ensure low concentration of hydroxide ions.
The formation of a reddish-brown precipitate indicates Fe; a gelatinous white precipitate indicates Al; and a green precipitate indicates Cr or Fe. These last two are distinguished by adding sodium hydroxide in excess to the green precipitate. If the precipitate dissolves, Cr is indicated; otherwise, Fe is present. | 3 | Analytical Chemistry |
Carbohydrate-deficient transferrin is elevated in the blood of people with heavy alcohol consumption but elevated levels can also be found in a number of medical conditions. The limitations of the assay depend upon the methodology of the test. HPLC (High Performance Liquid Chromatography) can detect certain genetic variants and potential liver diseases affecting CDT.
Used with other tests, such as gamma glutamyl transferase (GGT), aspartate aminotransferase (AST), and alanine aminotransferase (ALT), carbohydrate-deficient transferrin can be a useful tool in identifying problem drinking, such as alcohol use disorder. However, it is less sensitive than phosphatidylethanol (PEth) in detecting current regular alcohol consumption. The ethanol conjugates ethyl glucuronide and ethyl sulfate remain positive for up to three days after ethanol consumption and are quite useful for detection of occult/denied alcohol use disorder. Both these substances are detectable clinically through urine drug testing by commercial toxicology labs.
CDT is measured by taking a sample of a patient's blood. Apparently healthy individuals with no or low reported alcohol consumption and a negative Alcohol Use Disorders Identification Test (AUDIT) will have a %CDT <1.7% (95th percentile for the social drinking population). Elevated levels of CDT suggest recent heavy alcohol consumption, especially if other liver-associated enzymes (such as GGT) are elevated. Although recent heavy alcohol use is most commonly associated with elevated CDT, certain rare liver disorders can also increase levels of CDT. CDT levels are less useful for detecting alcohol use disorder in people with other liver diseases. | 1 | Biochemistry |
Hemoglobin deficiency can be caused either by a decreased amount of hemoglobin molecules, as in anemia, or by decreased ability of each molecule to bind oxygen at the same partial pressure of oxygen. Hemoglobinopathies (genetic defects resulting in abnormal structure of the hemoglobin molecule) may cause both. In any case, hemoglobin deficiency decreases blood oxygen-carrying capacity. Hemoglobin deficiency is, in general, strictly distinguished from hypoxemia, defined as decreased partial pressure of oxygen in blood, although both are causes of hypoxia (insufficient oxygen supply to tissues).
Other common causes of low hemoglobin include loss of blood, nutritional deficiency, bone marrow problems, chemotherapy, kidney failure, or abnormal hemoglobin (such as that of sickle-cell disease).
The ability of each hemoglobin molecule to carry oxygen is normally modified by altered blood pH or CO, causing an altered oxygen–hemoglobin dissociation curve. However, it can also be pathologically altered in, e.g., carbon monoxide poisoning.
Decrease of hemoglobin, with or without an absolute decrease of red blood cells, leads to symptoms of anemia. Anemia has many different causes, although iron deficiency and its resultant iron deficiency anemia are the most common causes in the Western world. As absence of iron decreases heme synthesis, red blood cells in iron deficiency anemia are hypochromic (lacking the red hemoglobin pigment) and microcytic (smaller than normal). Other anemias are rarer. In hemolysis (accelerated breakdown of red blood cells), associated jaundice is caused by the hemoglobin metabolite bilirubin, and the circulating hemoglobin can cause kidney failure.
Some mutations in the globin chain are associated with the hemoglobinopathies, such as sickle-cell disease and thalassemia. Other mutations, as discussed at the beginning of the article, are benign and are referred to merely as hemoglobin variants.
There is a group of genetic disorders, known as the porphyrias that are characterized by errors in metabolic pathways of heme synthesis. King George III of the United Kingdom was probably the most famous porphyria sufferer.
To a small extent, hemoglobin A slowly combines with glucose at the terminal valine (an alpha aminoacid) of each β chain. The resulting molecule is often referred to as Hb A, a glycated hemoglobin. The binding of glucose to amino acids in the hemoglobin takes place spontaneously (without the help of an enzyme) in many proteins, and is not known to serve a useful purpose. However, as the concentration of glucose in the blood increases, the percentage of Hb A that turns into Hb A increases. In diabetics whose glucose usually runs high, the percent Hb A also runs high. Because of the slow rate of Hb A combination with glucose, the Hb A percentage reflects a weighted average of blood glucose levels over the lifetime of red cells, which is approximately 120 days. The levels of glycated hemoglobin are therefore measured in order to monitor the long-term control of the chronic disease of type 2 diabetes mellitus (T2DM). Poor control of T2DM results in high levels of glycated hemoglobin in the red blood cells. The normal reference range is approximately 4.0–5.9%. Though difficult to obtain, values less than 7% are recommended for people with T2DM. Levels greater than 9% are associated with poor control of the glycated hemoglobin, and levels greater than 12% are associated with very poor control. Diabetics who keep their glycated hemoglobin levels close to 7% have a much better chance of avoiding the complications that may accompany diabetes (than those whose levels are 8% or higher). In addition, increased glycated of hemoglobin increases its affinity for oxygen, therefore preventing its release at the tissue and inducing a level of hypoxia in extreme cases.
Elevated levels of hemoglobin are associated with increased numbers or sizes of red blood cells, called polycythemia. This elevation may be caused by congenital heart disease, cor pulmonale, pulmonary fibrosis, too much erythropoietin, or polycythemia vera. High hemoglobin levels may also be caused by exposure to high altitudes, smoking, dehydration (artificially by concentrating Hb), advanced lung disease and certain tumors.
A recent study done in Pondicherry, India, shows its importance in coronary artery disease. | 7 | Physical Chemistry |
To illustrate how choices of coordinate systems for calculations of chemical bonds can immensely affect the results and consequently engender ill-defined descriptors of the bonds, sample calculations for n-butane and cyclobutane are shown in this section. Note that it is known that the all the four equivalent C-C bonds in cyclobutane are weaker than any of the two distinct C-C bonds in n-butane; therefore, juxtaposition and evaluation of the strength of the C-C bonds in this C4 system can exemplify how force constants fail and how compliance constants do not. The tables immediately below are results that are calculated at MP2/aug-cc-pvtz level of theory based on typical force constants calculation.
Tables 1 and 2 display a force constant in N/cm between each pair of carbon atoms (diagonal) as well as the coupling (off-diagonal). Considering natural internal coordinates on the left, the results make chemical sense. Firstly, the C-C bonds are n-butane are generally stronger than those in cyclobutane, which is in line with what is expected. Secondly, the C-C bonds in cyclobutane are equivalent with the force constant values of 4.173 N/cm. Lastly, there is little coupling between the force constants as seen as the small compliance coupling constants in the off-diagonal terms.
However, when z-matrix coordinates are used, the results are different from those obtained from natural internal coordinates and become erroneous. The four C-C bonds all have distinct values in cyclobutane, and the coupling becomes much more pronounced. Significantly, the force constants of the C-C bonds in cyclobutane here are also larger than those of n-butane, which is in conflict with chemical intuition. Clearly for cyclobutane—and numerous other molecules, using force constants therefore gives rise to inaccurate bond descriptors due to its dependence on coordinate systems. | 6 | Supramolecular Chemistry |
Electrons can be scattered by other charged particles through the electrostatic Coulomb forces. Furthermore, if a magnetic field is present, a traveling electron will be deflected by the Lorentz force. An extremely accurate description of all electron scattering, including quantum and relativistic aspects, is given by the theory of quantum electrodynamics. | 7 | Physical Chemistry |
In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an organyl group () or hydrogen in the case of formyl group (). In organic chemistry, the acyl group (IUPAC name alkanoyl if the organyl group is alkyl) is usually derived from a carboxylic acid, in which case it has the formula , where R represents an organyl group or hydrogen. Although the term is almost always applied to organic compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids and phosphonic acids. In the most common arrangement, acyl groups are attached to a larger molecular fragment, in which case the carbon and oxygen atoms are linked by a double bond. | 0 | Organic Chemistry |
MgCu can be prepared by hydrogenation of MgCu or the reaction of magnesium hydride and metallic copper at elevated temperature and pressure:
: 2 MgCu + 3 H → 3 MgH + MgCu
: MgH + 2 Cu → MgCu + H
MgCu can also be prepared by reacting of stoichiometric amounts of metals at about 380 °C in the presence of excess copper. | 8 | Metallurgy |
Vinegar, petroleum jelly, milk and lemon juice solutions have also been used by activists. It is unclear how effective these remedies are. In particular, vinegar itself can burn the eyes and prolonged inhalation can also irritate the airways. Vegetable oil and vinegar have been reported as helping relieve burning caused by pepper spray, Kräuter suggests the usage of baking soda or toothpaste, stating that they trap the particles emanating from the gas near the airways that are more feasible to inhale. A small trial of baby shampoo for washing out the eyes did not show any benefit. | 1 | Biochemistry |
There are various treatments to combat the effects of nonivamide. One popular method includes administering a one to one solution of milk of magnesia, and water to the eyes. Doctors also recommend not using oils or creams on the skin, and to not wear contact lenses, if one is planning to minimise the effects of nonivamide. | 1 | Biochemistry |
Adding scalar quarks (squarks) and fermionic gluons (gluinos) to the theory makes it more tractable, but the thermodynamics of quark matter depends crucially on the fact that only fermions can carry quark number, and on the number of degrees of freedom in general. | 7 | Physical Chemistry |
Bilirubin in plasma is mostly produced by the destruction of erythrocytes. Heme is metabolized into biliverdin (via heme oxygenase) and then into bilirubin (via biliverdin reductase) inside the macrophages.
Bilirubin is then released into the plasma and transported to the liver bound by albumin, since it is insoluble in water in this state. In this state, bilirubin is called unconjugated (despite being bound by albumin).
In the liver, unconjugated bilirubin is up-taken by the hepatocytes and subsequently conjugated with glucuronic acid (via the enzyme uridine diphosphate–glucuronyl transferase). In this state, bilirubin is soluble in water and it is called conjugated bilirubin.
Conjugated bilirubin is excreted into the bile ducts and enters the duodenum. During its transport to the colon, it is converted into urobilinogen by the bacterial enzyme bilirubin reductase. Most of the urobilinogen is further reduced into stercobilinogen and is excreted through feces (air oxidizes stercobilinogen to stercobilin, which gives feces their characteristic brown color).
A lesser amount of urobilinogen is re-absorbed into portal circulation and transferred to the liver. For the most part, this urobilinogen is recycled to conjugated bilirubin and this process closes the enterohepatic circle. There is also an amount of urobilinogen which is not recycled, but rather enters the systemic circulation and subsequently the kidneys, where it is excreted. Air oxidizes urobilinogen into urobilin, which gives urine its characteristic color.
In parallel, a small amount of conjugated billirubin can also enter the systemic circulation and get excreted through urine. This is exaggerated in various pathological situations. | 1 | Biochemistry |
Levan can be used for hair care and skin whitening. In hair care products, levan acts to form a film which creates a hair holding effect utilized in various gels and mousses. Levan is used as a skin whitener as well because it has been tested to show inhibition on melanin production by decreasing the activity of the enzyme tyrosinase which is responsible for melanogenesis. | 1 | Biochemistry |
1,1'-Carbonyldiimidazole (CDI) is an organic compound with the molecular formula (CHN)CO. It is a white crystalline solid. It is often used for the coupling of amino acids for peptide synthesis and as a reagent in organic synthesis. | 0 | Organic Chemistry |
The topology of an interactome makes certain predictions how a network reacts to the perturbation (e.g. removal) of nodes (proteins) or edges (interactions). Such perturbations can be caused by mutations of genes, and thus their proteins, and a network reaction can manifest as a disease. A network analysis can identify drug targets and biomarkers of diseases. | 1 | Biochemistry |
The analytical solutions for these equations (supposing that initial concentrations of every substance except for A are zero) are: | 7 | Physical Chemistry |
Stage heating is the process of heating a melt inclusion on a microscope-mounted stage and flowing either helium gas (Vernadsky stage) or argon gas (Linkam TS1400XY) over the stage and then rapidly quenching the melt inclusion after it has reached its original melt temperature to form a homogenous glass phase. Use of a heating stage allows for observation of changing phases of the melt inclusion as it is reheated to its original melt temperature. | 9 | Geochemistry |
Some of the furnaces burned at . Factory tours were discontinued due to liability concerns attendant to the "very high temperatures and extremely bright light" and the unavailability of affordable insurance to cover the risk.
The gems were synthesized in a furnace. The Shelby Gem Factory's diamonds were simulants. The factory also manufactured simulated citrine and topaz, along with other birthstone substitutes. | 7 | Physical Chemistry |
Wetlands are areas of land submerged in water near both terrestrial and aquatic systems. They are highly diverse and are classified by the United States Fish and Wildlife Service into five categories: “The term wetland includes a variety of areas that fall into one of five categories: (1) areas with hydrophytes and hydric soils, such as those commonly known as marshes, swamps, and bogs; (2) areas without hydrophytes but with hydric soils - for example, flats where drastic fluctuation in water level, wave action, turbidity, or high concentration of salts may prevent the growth of hydrophytes; (3) areas with hydrophytes but nonhydric soils, such as margins of impoundments or excavations where hydrophytes have become established but hydric soils have not yet developed; (4) areas without soils but with hydrophytes such as the seaweed-covered portion of rocky shores; and (5) wetlands without soil and without hydrophytes, such as gravel beaches or rocky shores without vegetation”.
Wetlands can also be classified based on salinity, a type of classification often referenced in research where salinity is a major factor. These classifications are often referred to in parts per thousand (ppt) and include freshwater (0-2 ppt), intermediate (2-10 ppt), brackish (10-20 ppt), and saltwater (20+ ppt). | 9 | Geochemistry |
Pyruvate dehydrogenase deficiency (PDCD) can result from mutations in any of the enzymes or cofactors used to build the complex. Its primary clinical finding is lactic acidosis. Such PDCD mutations, leading to subsequent deficiencies in NAD and FAD production, hinder oxidative phosphorylation processes that are key in aerobic respiration. Thus, acetyl-CoA is instead reduced via anaerobic mechanisms into other molecules like lactate, leading to an excess of bodily lactate and associated neurological pathologies.
While pyruvate dehydrogenase deficiency is rare, there are a variety of different genes when mutated or nonfunctional that can induce this deficiency. First, the E1 subunit of pyruvate dehydrogenase contains four different subunits: two alpha subunits designated as E1-alpha and two beta subunits designated as E1-beta. The PDHA1 gene found in the E1-alpha subunits, when mutated, causes 80% of the cases of pyruvate dehydrogenase deficiency because this mutation abridges the E1-alpha protein. Decreased functional E1 alpha prevents pyruvate dehydrogenase from sufficiently binding to pyruvate, thus reducing the activity of the overall complex. When the PDHB gene found in the E1 beta subunit of the complex is mutated, this also leads to pyruvate dehydrogenase deficiency. Likewise, mutations found on other subunits of the complex, like the DLAT gene found on the E2 subunit, the PDHX gene found on the E3 subunit, as well as a mutation on a pyruvate dehydrogenase phosphatase gene, known as PDP1, have all been traced back to pyruvate dehydrogenase deficiency, while their specific contribution to the disease state is unknown. | 1 | Biochemistry |
In analytical chemistry, potentiometric titration is a technique similar to direct titration of a redox reaction. It is a useful means of characterizing an acid. No indicator is used; instead the electric potential is measured across the analyte, typically an electrolyte solution. To do this, two electrodes are used, an indicator electrode (the glass electrode and metal ion indicator electrode) and a reference electrode. Reference electrodes generally used are hydrogen electrodes, calomel electrodes, and silver chloride electrodes. The indicator electrode forms an electrochemical half-cell with the interested ions in the test solution. The reference electrode forms the other half-cell.
The overall electric potential is calculated as
is the potential drop over the test solution between the two electrodes. is recorded at intervals as the titrant is added. A graph of potential against volume added can be drawn and the end point of the reaction is halfway between the jump in voltage.
depends on the concentration of the interested ions with which the indicator electrode is in contact. For example, the electrode reaction may be
As the concentration of changes, the changes correspondingly. Thus the potentiometric titration involve measurement of with the addition of titrant. Types of potentiometric titration include acid–base titration (total alkalinity and total acidity), redox titration (HI/HY and cerate), precipitation titration (halides), and complexometric titration (free EDTA and Antical #5). | 3 | Analytical Chemistry |
The Earth, as a system, is open to radiation from the sun and space, but is practically closed with regard to matter. As all closed systems, it follows the law of conservation of mass which states that matter cannot be created nor destroyed, thus, the matter, although transformed and migrated, remains the same as when the Earth was formed. The Earth system contains seven different reservoirs that are separated into surface reservoirs, which include atmosphere, hydrosphere, biosphere, pedosphere, and lithosphere and the isolated reservoirs that include deep Earth and outer space. Geochemical cycles are concerned with the interactions between deep earth which consists of Earths mantle and core, and the lithosphere which consists of the Earths crust. | 9 | Geochemistry |
Silt particles range in size (about 0.002–0.5 mm). Silt pores are considered a medium in size compared with the other particle groups. Silt has a texture consistency of flour. Silt particles allow water and air to pass readily, yet retain moisture for crop growth. Silty soil contains sufficient quantities of nutrients, both organic and inorganic. | 9 | Geochemistry |
* bicarbonate derived from carbonic anhydrase (CA)-dependent hydration.
* CO metabolism
* Enters through membrane-transporting proteins or cystic fibrosis transmembrane conductance regulators.
* Calcium enters by voltage-dependent Ca channels or by release from the endoplasmic reticulum.
* Hydrogencarbonate and calcium activates sAC in the nucleus.
* sAC inside mitochondria is activated by metabolically generated CO through carbonic anhydrase. | 1 | Biochemistry |
Juvenile retinoschisis is a disease that affects the nerve tissue in the eye. This disease is an X-linked recessive degenerative disease of the central macula region, and it is caused by mutation in the RSI gene encoding the protein retinoschisin. Retinoschisin is produced in the photoreceptor and bipolar cells and it is critical in maintaining the synaptic integrity of the retina.
Specifically the AAV 5 vector containing the wild-type human RSI cDNA driven by a mouse opsin promoter showed long-term retinal functional and structural recovery. Also the retinal structural reliability improved greatly after the treatment, characterized by an increase in the outer nuclear layer thickness. | 1 | Biochemistry |
In the context of biochemistry and drug development, a hybridization assay is a type of Ligand Binding Assay (LBA) used to quantify nucleic acids in biological matrices. Hybridization assays can be in solution or on a solid support such as 96-well plates or labelled beads.
Hybridization assays involve labelled nucleic acid probes to identify related DNA or RNA molecules (i.e. with significantly high degree of sequence similarity) within a complex mixture of unlabelled nucleic acid molecules. Antisense therapy, siRNA, and other oligonucleotide and nucleic acid based biotherapeutics can be quantified with hybridization assays.
Signalling of hybridization methods can be performed using oligonucleotide probes modified in-synthesis with haptens and small molecule ligands which act homologous to the capture and detection antibodies. As with traditional ELISA, conjugates to horse radish peroxidase (HRP) or alkaline phosphatase (AP) can be used as secondary antibodies. | 1 | Biochemistry |
Acid phosphatase (EC 3.1.3.2, systematic name phosphate-monoester phosphohydrolase (acid optimum)) is an enzyme that frees attached phosphoryl groups from other molecules during digestion. It can be further classified as a phosphomonoesterase. It is stored in lysosomes and functions when these fuse with endosomes, which are acidified while they function; therefore, it has an acid pH optimum. This enzyme is present in many animal and plant species.
Different forms of acid phosphatase are found in different organs, and their serum levels are used to evaluate the success of the surgical treatment of prostate cancer. In the past, they were also used to diagnose this type of cancer.
It's also used as a cytogenetic marker to distinguish the two different lineages of acute lymphoblastic leukemia (ALL) : B-ALL (a leukemia of B lymphocytes) is acid-phosphatase negative , T-ALL (originating instead from T Lymphocytes) is acid-phosphatase positive .
Acid phosphatase catalyzes the following reaction at an optimal acidic pH (below 7):
: a phosphate monoester + HO = an alcohol + phosphate
Phosphatase enzymes are also used by soil microorganisms to access organically bound phosphate nutrients. An assay on the rates of activity of these enzymes may be used to ascertain biological demand for phosphates in the soil.
Some plant roots, especially cluster roots, exude carboxylates that perform acid phosphatase activity, helping to mobilise phosphorus in nutrient-deficient soils.
Certain bacteria, such as Nocardia, can degrade this enzyme and utilize it as a carbon source. | 1 | Biochemistry |
Deficiencies in vitamin A have been linked to an increased susceptibility to skin infection and inflammation. Vitamin A appears to modulate the innate immune response and maintains homeostasis of epithelial tissues and mucosa through its metabolite, retinoic acid (RA). As part of the innate immune system, toll-like receptors in skin cells respond to pathogens and cell damage by inducing a pro-inflammatory immune response which includes increased RA production. The epithelium of the skin encounters bacteria, fungi and viruses. Keratinocytes of the epidermal layer of the skin produce and secrete antimicrobial peptides (AMPs). Production of AMPs resistin and cathelicidin, are promoted by RA. | 1 | Biochemistry |
The lac repressor (LacI) operates by a helix-turn-helix motif in its DNA-binding domain, binding base-specifically to the major groove of the operator region of the lac operon, with base contacts also made by residues of symmetry-related alpha helices, the "hinge" helices, which bind deeply in the minor groove. This bound repressor can reduce transcription of the Lac proteins by occluding the RNA polymerase binding site or by prompting DNA looping. When lactose is present, allolactose binds to the lac repressor, causing an allosteric change in its shape. In its changed state, the lac repressor is unable to bind tightly to its cognate operator. Thus, the gene is mostly off in the absence of inducer and mostly on in the presence of inducer, although the degree of gene expression depends on the number of repressors in the cell and on the repressors DNA-binding affinity. Isopropyl β-D-1-thiogalactopyranoside (IPTG) is a commonly used allolactose mimic which can be used to induce transcription of genes being regulated by lac' repressor. | 1 | Biochemistry |
The Pfeiffer effect is an optical phenomenon whereby the presence of an optically active compound influences the optical rotation of a racemic mixture of a second compound.
Racemic mixtures do not rotate plane polarized light, but the equilibrium concentration of the two enantiomers can shift from unity in the presence of a strongly interacting chiral species. Paul Pfeiffer, a student of Alfred Werner and inventor of the salen ligand, reported this phenomenon. The first example of the effect is credited to Eligio Perucca, who observed optical rotations in the visible part of the spectrum when crystals of sodium chlorate, which are chiral and colourless, were stained with a racemic dye. The effect is attributed to the interaction of the optically pure substance with the second coordination sphere of the racemate. | 4 | Stereochemistry |
In the field of photometry (optics), the luminous transmittance of a filter is a measure of the amount of luminous flux or intensity transmitted by an optical filter. It is generally defined in terms of a standard illuminant (e.g. Illuminant A, Iluminant C, or Illuminant E). The luminous transmittance with respect to the standard illuminant is defined as:
where:
* is the spectral radiant flux or intensity of the standard illuminant (unspecified magnitude).
* is the spectral transmittance of the filter
* is the luminous efficiency function
The luminous transmittance is independent of the magnitude of the flux or intensity of the standard illuminant used to measure it, and is a dimensionless quantity. | 7 | Physical Chemistry |
Besides de novo synthesis, PA can be formed in three ways:
* By phospholipase D (PLD), via the hydrolysis of the P-O bond of phosphatidylcholine (PC) to produce PA and choline.
* By the phosphorylation of diacylglycerol (DAG) by DAG kinase (DAGK).
* By the acylation of lysophosphatidic acid by lysoPA-acyltransferase (LPAAT); this is the most common pathway.
The glycerol 3-phosphate pathway for de novo synthesis of PA is shown here:
In addition, PA can be converted into DAG by lipid phosphate phosphohydrolases (LPPs) or into lyso-PA by phospholipase A (PLA). | 1 | Biochemistry |
In more common usage, an oxidizing agent transfers oxygen atoms to a substrate. In this context, the oxidizing agent can be called an oxygenation reagent or oxygen-atom transfer (OAT) agent. Examples include (permanganate), (chromate), OsO (osmium tetroxide), and especially (perchlorate). Notice that these species are all oxides.
In some cases, these oxides can also serve as electron acceptors, as illustrated by the conversion of to ,ie permanganate to manganate. | 7 | Physical Chemistry |
Cell-specific DamID can also be achieved using recombination mediated excision of a transcriptional terminator cassette upstream of the Dam-fusion protein. The terminator cassette is flanked by FRT recombination sites which can be removed when combined with tissue specific expression of FLP recombinase. Upon removal of the cassette, the Dam-fusion is expressed at low levels under the control of a basal promoter. | 1 | Biochemistry |
* Classed as a restricted weapon.
** A permit is required to obtain or carry pepper spray.
** Front-line police officers have routinely carried pepper spray since 1997. New Zealand Prison Service made OC spray available for use in approved situations in 2013.
** New Zealand Defence Force Military Police are permitted to carry OC spray under a special agreement due to the nature of their duties.
** The Scoville rating of these sprays are 500,000 (sabre MK9 HVS unit) and 2,000,000 (Sabre, cell buster fog delivery). This was as a result of excessive staff assaults and a two-year trial in ten prisons throughout the country. | 1 | Biochemistry |
Förster resonance energy transfer is named after the German scientist Theodor Förster. When both chromophores are fluorescent, the term "fluorescence resonance energy transfer" is often used instead, although the energy is not actually transferred by fluorescence. In order to avoid an erroneous interpretation of the phenomenon that is always a nonradiative transfer of energy (even when occurring between two fluorescent chromophores), the name "Förster resonance energy transfer" is preferred to "fluorescence resonance energy transfer"; however, the latter enjoys common usage in scientific literature. FRET is not restricted to fluorescence and occurs in connection with phosphorescence as well. | 1 | Biochemistry |
The grain macrostructure in ingots and most castings have three distinct regions or zones: the chill zone, columnar zone, and equiaxed zone. The image below depicts these zones.
The chill zone is named so because it occurs at the walls of the mold where the wall chills the material. Here is where the nucleation phase of the solidification process takes place. As more heat is removed the grains grow towards the center of the casting. These are thin, long columns that are perpendicular to the casting surface, which are undesirable because they have anisotropic properties. Finally, in the center the equiaxed zone contains spherical, randomly oriented crystals. These are desirable because they have isotropic properties. The creation of this zone can be promoted by using a low pouring temperature, alloy inclusions, or inoculants. | 8 | Metallurgy |
Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that is used to relieve pain, fever, and inflammation. This includes painful menstrual periods, migraines, and rheumatoid arthritis. It may also be used to close a patent ductus arteriosus in a premature baby. It can be used orally (by mouth) or intravenously. It typically begins working within an hour.
Common side effects include heartburn and a rash. Compared to other NSAIDs, it may have other side effects such as gastrointestinal bleeding. It increases the risk of heart failure, kidney failure, and liver failure. At low doses, it does not appear to increase the risk of heart attack; however, at higher doses it may. Ibuprofen can also worsen asthma. While its safety in early pregnancy is unclear, it appears to be harmful in later pregnancy, so it is not recommended during that period. Like other NSAIDs, it works by inhibiting the production of prostaglandins by decreasing the activity of the enzyme cyclooxygenase (COX). Ibuprofen is a weaker anti-inflammatory agent than other NSAIDs.
Ibuprofen was discovered in 1961 by Stewart Adams and John Nicholson while working at Boots UK Limited and initially marketed as Brufen. It is available under a number of brand names, including Nurofen, Advil, and Motrin. Ibuprofen was first marketed in 1969 in the United Kingdom and in 1974 in the United States. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2021, it was the 36th-most commonly prescribed medication in the United States, with more than 17million prescriptions. | 4 | Stereochemistry |
In the case of sulfides and carbonates, a process called "roasting" removes the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment. A few practical examples:
* Malachite, a common ore of copper is primarily copper carbonate hydroxide Cu(CO)(OH). This mineral undergoes thermal decomposition to 2CuO, CO, and HO in several stages between 250 °C and 350 °C. The carbon dioxide and water are expelled into the atmosphere, leaving copper(II) oxide, which can be directly reduced to copper as described in the following section titled Reduction.
* Galena, the most common mineral of lead, is primarily lead sulfide (PbS). The sulfide is oxidized to a sulfite (PbSO), which thermally decomposes into lead oxide and sulfur dioxide gas (PbO and SO). The sulfur dioxide is expelled (like the carbon dioxide in the previous example), and the lead oxide is reduced as below. | 8 | Metallurgy |
A dialdehyde is an organic chemical compound with two aldehyde groups. The nomenclature of dialdehydes have the ending -dial or sometimes -dialdehyde. Short aliphatic dialdehydes are sometimes named after the diacid from which they can be derived. An example is butanedial, which is also called succinaldehyde (from succinic acid). | 0 | Organic Chemistry |
The clearest waters occur in oligotrophic ocean regions such as the South Pacific Gyre, tropical coastal waters, glacially-formed lakes with low sediment inputs, and lakes with some kind of natural filtration occurring at the inflow point. Blue Lake in New Zealand holds the record for the highest water clarity of any lake, with a Secchi depth of 230 to 260 feet. Blue Lake is fed by an underground passage from a nearby lake, which acts as a natural filter. Some other very clear water bodies are Lake Tahoe between California and Nevada in the United States, Lake Baikal in Russia, and Crater Lake in Oregon in the United States.
In tropical coastal waters, the water is clear thanks to low nutrient inputs, low primary production, and coral reefs acting as a natural buffer that keep sediments from getting resuspended.
The clearest recorded water on Earth is either Blue Lake, New Zealand or the Weddell Sea near Antarctica, both of which claim Secchi depths of 80 meters (230 to 260 feet). | 3 | Analytical Chemistry |
The abstract definition of chemical potential given above—total change in free energy per extra mole of substance—is more specifically called total chemical potential. If two locations have different total chemical potentials for a species, some of it may be due to potentials associated with "external" force fields (electric potential energy, gravitational potential energy, etc.), while the rest would be due to "internal" factors (density, temperature, etc.) Therefore, the total chemical potential can be split into internal chemical potential and external chemical potential:
where
i.e., the external potential is the sum of electric potential, gravitational potential, etc. (where q and m are the charge and mass of the species, V and h are the electric potential and height of the container, respectively, and g is the acceleration due to gravity). The internal chemical potential includes everything else besides the external potentials, such as density, temperature, and enthalpy. This formalism can be understood by assuming that the total energy of a system, , is the sum of two parts: an internal energy, , and an external energy due to the interaction of each particle with an external field, . The definition of chemical potential applied to yields the above expression for .
The phrase "chemical potential" sometimes means "total chemical potential", but that is not universal. In some fields, in particular electrochemistry, semiconductor physics, and solid-state physics, the term "chemical potential" means internal chemical potential, while the term electrochemical potential is used to mean total chemical potential. | 7 | Physical Chemistry |
The only approved indication for oral vancomycin therapy is in the treatment of pseudomembranous colitis, where it must be given orally to reach the site of infection in the colon. Following oral administration, the fecal concentration of vancomycin is around 500 µg/mL (sensitive strains of Clostridium difficile have a mean inhibitory concentration of ≤2 µg/mL) | 0 | Organic Chemistry |
The Brønsted catalysis equation or law of correlation, after Johannes Nicolaus Brønsted, gives the relationship between acid strength and catalytic activity in general acid catalysis.
A plot of the common logarithm of the reaction rate constant k versus the logarithm of the ionization constant K for a series of acids (for example a group of substituted phenols or carboxylic acids) gives a straight line with slope α and intercept C. The Brønsted equation is a free-energy relationship. The relationship implies that the Gibbs free energy for proton dissociation is proportional to the activation energy for the catalytic step. When the relationship is not linear, the chosen group of catalysts do not operate through the same reaction mechanism.
Specific and general catalysis is also found in base catalysed reactions and base Brønsted equation also exists with constant β.
The Brønsted equation gives information about a reaction mechanism. Reactions that have low values for proportionality constants α or β are considered to have a transition state closely resembling the reactant with little proton transfer. With a high value, proton transfer in the transition state is almost complete. In a study of a group of phenalene compounds it was concluded from Brønsted analysis that phenalene acidity is very different from either indene acidity or phenylene acidity. | 7 | Physical Chemistry |
It is still not fully understood how salts are transported from the ocean and oxidized to become reactive halogen species in the air. Other halogens (chlorine and iodine) are also activated through mechanisms coupled to bromine chemistry. The main consequence of halogen activation is chemical destruction of ozone, which removes the primary precursor of atmospheric oxidation, and generation of reactive halogen atoms/oxides that become the primary oxidizing species. The oxidation ability originally influenced by ozone is weakened, while the halogen species now holds the oxidation ability. This changes the reaction cycles and final products of many atmospheric reactions. During ozone depletion events, the enhanced halogen chemistry can effectively oxidize reactive gaseous elements. | 2 | Environmental Chemistry |
Indoline 9 was acetylated to N-acetyl compound 10 (acetic anhydride, pyridine) and then the veratryl group was then ring-opened with ozone in aqueous acetic acid to muconic ester 11 (made possible by the two electron-donating methoxide groups). This is an example of bioinspired synthesis already proposed by Woodward in 1948. Cleavage of the acetyl group and ester hydrolysis with HCl in methanol resulted in formation of pyridone ester 12 with additional isomerization of the exocyclic double bond to an endocyclic double bond (destroying one asymmetric center). Subsequent treatment with hydrogen iodide and red phosphorus removed the tosyl group and hydrolysed both remaining ester groups to form diacid 13. Acetylation and esterification (diazomethane) produced acetyl diester 14 which was then subjected to a Dieckman condensation with sodium methoxide in methanol to enol 15. | 0 | Organic Chemistry |
Five of the crystal systems are essentially the same as five of the lattice systems. The hexagonal and trigonal crystal systems differ from the hexagonal and rhombohedral lattice systems. These are combined into the hexagonal crystal family.
The relation between three-dimensional crystal families, crystal systems and lattice systems is shown in the following table:
:Note: there is no "trigonal" lattice system. To avoid confusion of terminology, the term "trigonal lattice" is not used. | 3 | Analytical Chemistry |
ASF/SF2 is involved in genomic stability; it is thought that RNA Polymerase recruits ASF/SF2 to nascent RNA transcripts to impede formation of mutagenic DNA:RNA hybrid R-loop structures between the transcript and the template DNA. In this way, ASF/SF2 is protecting cells from the potential deleterious effects of transcription itself. ASF/SF2 is also implicated in cellular mechanisms to hinder exon skipping and to ensure splicing is occurring accurately and correctly. | 1 | Biochemistry |
Spot tests are performed by placing a small amount of the desired reagent on the portion of the lichen to be tested. Often, both the cortex and medulla of the lichen are tested, and at times it is useful to test other structures such as soralia. One method is to draw up a small amount of the chemical into a glass capillary and touch it to the lichen thallus; a small paint brush is also used for this purpose. Reactions are best visualised with a hand lens or a stereo microscope. A razor blade may be used to remove the cortex and access the medulla. Alternatively, the solution can be applied to lichen features that lack a cortex or that leave the medulla exposed, such as soralia, pseudocyphellae, or the underside of squamules.
In a variation of this technique, suggested by the Swedish chemist Johan Santesson, a piece of filter paper is used to try to make the colour reaction more readily observable. The lichen fragment is pressed on the paper, and lichen substances are extracted with 10–20 drops of acetone. After evaporating the acetone, the lichen substances are left on the paper in a ring around the lichen fragment. The filter paper can then be spot tested in the usual way. In cases where the results of a spot test on the thallus are uncertain, it is possible to squash a thin section of the tissue on a microscope slide in a minimal amount of water and reagent under a cover slip. A colour change is visible under a low-power microscope objective, or when the slide placed against a white background. This technique is useful when testing lichens with dark pigments, such as Bryoria.
Spot tests may be used individually or in combination. The results of a spot tests are typically represented with a short code that includes, in order, (1) a letter indicating the reagent used, (2) a "+" or "−" sign indicating a colour change or lack of colour change, respectively, and (3) a letter or word indicating the colour observed. In addition, care should be taken to indicate which part of the lichen was tested. For example, "Cortex K+ orange, C−, P−" means the cortex of the test specimen turned orange with application of KOH and did not change under bleach or para-phenylenediamine. Similarly, "Medulla K−, KC+R" would indicate the medulla of the lichen was insensitive to application of KOH, but application of KOH followed immediately by bleach caused the medulla to turn red.
Occasionally, it takes some time for the colour reaction to develop. For example, in certain Cladonia species, the PD reaction with fumarprotocetraric acid can take up to half a minute. In contrast, the reactions with C and KC are usually fleeting and occur within a second of applying the reagent, so a colour change can easily be missed. There are several possible reasons that an anticipated test result does not occur. Causes include old and chemically inactive reagents, and low concentrations of lichen substances in the sample. If the colour of the thallus is dark, a colour change might be obscured, and other techniques are more appropriate, like the filter paper technique. | 3 | Analytical Chemistry |
The following formula is used to calculate COD:
where b is the volume of FAS used in the blank sample, s is the volume of FAS in the original sample, and n is the normality of FAS. If milliliters are used consistently for volume measurements, the result of the COD calculation is given in mg/L.
The COD can also be estimated from the concentration of oxidizable compound in the sample, based on its stoichiometric reaction with oxygen to yield CO (assume all C goes to CO), HO (assume all H goes to HO), and NH (assume all N goes to NH), using the following formula:
:COD = (C/FW)·(RMO)·32
Where
:C = Concentration of oxidizable compound in the sample,
:FW = Formula weight of the oxidizable compound in the sample,
:RMO = Ratio of the # of moles of oxygen to # of moles of oxidizable compound in their reaction to CO, water, and ammonia
For example, if a sample has 500 Wppm (Weight Parts per Million) of phenol:
:CHOH + 7O → 6CO + 3HO
:COD = (500/94)·7·32 = 1191 Wppm | 9 | Geochemistry |
immunoblot - immunoprecipitation - immunotherapy - IMPDH/GMPR family - in situ hybridization - in vitro translation - indoleacetaldoxime dehydratase - inducer - infologs - inherited - initiation codon - insert - insertion - insertion sequence - intellectual property rights - intergenic - interleukin 40 - intron - inverted repeat - IscR stability element - isopiperitenol dehydrogenase - | 1 | Biochemistry |
The regioselectivity of water elimination is highly influenced by ring size. When water is eliminated from cyclic tertiary alcohols by an E1 route, three major products are formed. The semicyclic isomer (so-called because the double bond is shared by a ring atom and an exocyclic atom) and the (E) endocyclic isomer are expected to predominate; the (Z) endocyclic isomer is not expected to be formed until the ring size is large enough to accommodate the awkward angles of the trans configuration. The exact population of each product relative to the others differs considerably depending upon the size of the ring involved. As the ring size increases, the semicyclic isomer decreases rapidly and the (E) endocyclic isomer increases, but after a certain point, the semicyclic isomer begins to increase again. This can be attributed to transannular strain; this strain is significantly reduced in the (E) endocyclic isomer because it has one less substituent in the ring than the semicyclic isomer. | 4 | Stereochemistry |
The armed/disarmed approach to glycosylation is an effective way to prevent sugar molecules from self-glycosylation when synthesizing disaccharides. This approach was first recognized when acetylated sugars only acted as glycosyl acceptors when reacted with benzylated sugars. The acetylated sugars were termed “disarmed” while the benzylated sugars were termed “armed”. | 0 | Organic Chemistry |
In combustion, the Karlovitz number is defined as the ratio of chemical time scale to Kolmogorov time scale , named after Béla Karlovitz. The number reads as
In premixed turbulent combustion, the chemical time scale can be defined as , where is the thermal diffusivity and is the laminar flame speed and the flame thickness is given by , in which case,
where is the Kolmogorov scale. The Karlovitz number is related to Damköhler number as
if the Damköhler number is defined with Kolmogorov scale. If , the premixed turbulent flame falls into the category of corrugated flamelets and wrinkled flamelets, otherwise into the thin reaction zone or broken reaction zone flames. | 7 | Physical Chemistry |
The silencing of genes created by abnormal DNA methylation is a major contributor to the formation of cancerous tumors. Variations in DNA methylation of normal cells compared to malignant cells shows a prominent mechanism in how cancerous cells proliferate. Those variations are particularly prevalent in cell cycle regulation, DNA repair, and natural tumor suppression mechanisms. A leading therapeutic strategy in treating solid tumors stems from the use of demethylating agents to suppress DNA methylation in cancerous growths. Azacitidine and decitabine are both frequently used demethylating agents while decitabine is significantly more potent in its demethylating abilities. Both of these drugs are inhibitors of DNA Methyltransferases (DNMT) which are enzymes that are responsible for methylating DNA. In the 1970’s, these drugs have shown promising results in hematological cancers in organisms such as mice. The FDA initially rejected the use of azacitidine clinically due to negative side effects caused by elevated toxicity levels. However, in later clinical trials performed on patients with MDS, myelodysplastic syndromes, azacitidine provided effective and exhibited consistent results which led to FDA approval in 2004. The commercial name of azacitidine became Vidaza. Decitabine, with the commercial name Dacogen, followed with FDA approval in 2006. As more research is completed in the field of genetic mutations, specifically involving DNA Methylation, these drugs can be utilized to their maximum efficiency to clinically treat cancerous tumors. As of 2017, there were no approved demethylating agents for the treatment of solid tumors which can be a focus of research in the future. Treatment utilizing demethylating agents can have further clinical use by targeting cancer stem cells and triggering apoptosis. Demethylating agents and their relevance in clinical studies as therapy to treat lymphocytic leukemia can be seen in. Procaine can also be used as therapeutic development to inhibit the growth of cancer cells in humans. There is a new world of possibilities of using demethylating agents to treat different diseases such as leukemia and cancer as therapeutic treatment.
Procaine (PCA) is a demethylating agent considered to be effective in inhibiting the growth of human cancer cells. Several studies have explored and elucidated the effects of procaine on human liver cancer cells and breast cancer cells. Studies have shown that procaine, as an inhibitor of DNA methylation in breast cancer cells, can effectively cause hypomethylation and demethylation of the entire group of breast cancer cell DNA genomes by reducing 5-methylcytosine DNA content. In addition, procaine can effectively restore the gene expression of tumor suppressor genes by demethylating densely hypermethylated CpG-enriched DNA. For human liver cancer cells, procaine is capable of reducing tumor volume by suppressing the cell viability of HLE, HuH7, and HuH6 cells, and it has shown effective inhibition of S/G2/M transition in HLE cells. | 1 | Biochemistry |
*1968–2008 - Institute of Biochemistry and Biotechnology, Georgian Academy of Sciences
*1968–1999 - Professor at Tbilisi State University, Georgia
*2008–2010 - Professor at Ilia State University, Tbilisi, Georgia
*2010–2011 - Professor at Free University of Tbilisi, Georgia
*2012–2021- Director of Institute of Molecular Genetics, Agricultural University of Georgia
*2012–present - Professor at Agricultural University of Georgia, Tbilisi, Georgia | 1 | Biochemistry |
The term "library" can refer to a population of organisms, each of which carries a DNA molecule inserted into a cloning vector, or alternatively to the collection of all of the cloned vector molecules. | 1 | Biochemistry |
DNA damage appears to be the primary underlying cause of cancer. If accurate DNA repair is deficient, DNA damages tend to accumulate. Unrepaired DNA damage can increase mutational errors during DNA replication due to error-prone translesion synthesis. DNA damage can also increase epigenetic alterations due to errors during DNA repair. Such mutations and epigenetic alterations can give rise to cancer (see malignant neoplasms). Investigation of epigenetic down- or upregulation of repaired DNA genes as possibly central to progression of cancer has been regularly undertaken since 2000.
As described in Regulation of transcription in cancer, epigenetic downregulation of the DNA repair gene MGMT occurs in 93% of bladder cancers, 88% of stomach cancers, 74% of thyroid cancers, 40–90% of colorectal cancers and 50% of brain cancers. Similarly, epigenetic downregulation of LIG4 occurs in 82% of colorectal cancers and epigenetic downregulation of NEIL1 occurs in 62% of head and neck cancers and in 42% of non-small-cell lung cancers.
Epigenetic upregulation of the DNA repair genes PARP1 and FEN1 occurs in numerous cancers (see Regulation of transcription in cancer). PARP1 and FEN1 are essential genes in the error-prone and mutagenic DNA repair pathway microhomology-mediated end joining. If this pathway is upregulated, the excess mutations it causes can lead to cancer. PARP1 is over-expressed in tyrosine kinase-activated leukemias, in neuroblastoma, in testicular and other germ cell tumors, and in Ewing's sarcoma. FEN1 is upregulated in the majority of cancers of the breast, prostate, stomach, neuroblastomas, pancreas, and lung. | 1 | Biochemistry |
The method of combination differences uses differences of wavenumbers in the P- and R- branches to obtain data that depend only on rotational constants in the vibrational ground or excited state. For the excited state
This function can be fitted, using the method of least-squares to data for carbon monoxide, from Harris and Bertolucci. The data calculated with the formula
in which centrifugal distortion is ignored, are shown in the columns labelled with (1). This formula implies that the data should lie on a straight line with slope 2B′′ and intercept zero. At first sight the data appear to conform to this model, with a root mean square residual of 0.21 cm. However, when centrifugal distortion is included, using the formula
the least-squares fit is improved markedly, with ms residual decreasing to 0.000086 cm. The calculated data are shown in the columns labelled with (2). | 7 | Physical Chemistry |
SB buffer is a buffer solution used in agarose and polyacrylamide gel electrophoresis for the separation of nucleic acids such as DNA and RNA. "SB" is a commercial trademark of Faster Better Media LLC for their sodium boric acid-based conductive medium (US Patent # 7811437), which is based on the publications of Brody and Kern.
It is made up of sodium borate, usually 1–10 mM at pH 8.0. It has a lower conductivity, produces sharper bands, and can be run at higher speeds than can gels made from TBE buffer or TAE buffer (5–35 V/cm as compared to 5–10 V/cm). At a given voltage, heat will be generated and thus the gel will be heated. However, SB buffer has lower conductivity than TBE and TAE, and thus the gel temperature is much lower than with TBE or TAE buffers. Therefore, the voltage can be increased to speed up electrophoresis so that a gel run takes only a fraction of the usual time. Downstream applications, such as isolation of DNA from a gel slice or southern blot analysis, work as expected with sodium borate gels.
LB buffer containing lithium borate is similar to sodium borate and has all of its advantages, but permits use of even higher voltages due to the lower conductivity of lithium ions as compared to sodium ions. However, lithium borate is somewhat more expensive. | 1 | Biochemistry |
General scenario The Le Chatelier–Braun principle analyzes the qualitative behaviour of a thermodynamic system when a particular one of its externally controlled state variables, say changes by an amount the driving change, causing a change the response of prime interest, in its conjugate state variable all other externally controlled state variables remaining constant. The response illustrates moderation in ways evident in two related thermodynamic equilibria. Obviously, one of has to be intensive, the other extensive. Also as a necessary part of the scenario, there is some particular auxiliary moderating state variable , with its conjugate state variable For this to be of interest, the moderating variable must undergo a change or in some part of the experimental protocol; this can be either by imposition of a change , or with the holding of constant, written For the principle to hold with full generality, must be extensive or intensive accordingly as is so. Obviously, to give this scenario physical meaning, the driving variable and the moderating variable must be subject to separate independent experimental controls and measurements. | 7 | Physical Chemistry |
Sometimes adding an ion other than the ones that are part of the precipitated salt itself can increase the solubility of the salt. This "salting in" is called the "uncommon-ion effect" (also "salt effect" or the "diverse-ion effect"). It occurs because as the total ion concentration increases, inter-ion attraction within the solution can become an important factor. This alternate equilibrium makes the ions less available for the precipitation reaction. This is also called odd ion effect. | 7 | Physical Chemistry |
In dual-mode, the mobile and stationary phases are reversed part way through the separation experiment. This requires changing the phase being pumped through the column as well as the direction of flow. Dual-mode operation is likely to elute the entire sample from the column but the order of elution is disrupted by switching the phase and direction of flow. | 3 | Analytical Chemistry |
Erwin Hiebert died in Waltham, Massachusetts in November 2012, shortly after his wife of 69 years died in September 2012. He was survived by their two daughters, Catherine and Margaret, a son Thomas, and seven grandchildren. Catherine Hiebert Beissinger became a professor of Slavic languages and literatures at Princeton University. Thomas Hiebert became a professor of music at California State University, Fresno. | 7 | Physical Chemistry |
Froth flotation depends on the selective adhesion of air bubbles to mineral surfaces in a mineral/water slurry. The air bubbles attach to more hydrophobic particles, as determined by the interfacial energies between the solid, liquid, and gas phases. This energy is determined by the Young–Dupré equation:
where:
* γ is the surface energy of the liquid/vapor interface
* γ is the surface energy of the solid/vapor interface
* γ is the surface energy of the solid/liquid interface,
* θ is the contact angle, the angle formed at the junction between vapor, solid, and liquid phases.
Minerals targeted for separation may be chemically surface-modified with collectors so that they are more hydrophobic. Collectors are a type of surfactant that increase the natural hydrophobicity of the surface, increasing the separability of the hydrophobic and hydrophilic particles. Collectors either chemically bond via chemisorption to the mineral or adsorb onto the surface via physisorption. | 8 | Metallurgy |
There are over 16 million dams in the world that alter carbon transport from rivers to oceans. Using data from the Global Reservoirs and Dams database, which contains approximately 7000 reservoirs that hold 77% of the total volume of water held back by dams (8000 km), it is estimated that the delivery of carbon to the ocean has decreased by 13% since 1970 and is projected to reach 19% by 2030. The excess carbon contained in the reservoirs may emit an additional ~0.184 Gt of carbon to the atmosphere per year and an additional ~0.2 GtC will be buried in sediment. Prior to 2000, the Mississippi, the Niger, and the Ganges River basins account for 25 – 31% of all reservoir carbon burial. After 2000, the Paraná (home to 70 dams) and the Zambezi (home to the largest reservoir) River basins exceeded the burial by the Mississippi. Other large contributors to carbon burial caused by damming occur on the Danube, the Amazon, the Yangtze, the Mekong, the Yenisei, and the Tocantins Rivers. | 9 | Geochemistry |
As water reaches the temperature where it begins to crystallize and form ice, salt ions are rejected from the lattices within the ice and are either forced out into the surrounding water, or trapped among the ice crystals in pockets called brine cells. Generally, sea ice has a salinity ranging from 0 psu at the surface to 4 psu at the base. The faster that this freezing process occurs, the more brine cells are left in the ice. Once the ice reaches a critical thickness, roughly 15 cm, the concentration of salt ions in the liquid around the ice begins to increase, as leftover brine is rejected from the cells. This increase is associated with the appearance of strong convective plumes, which flow from channels and within the ice and carry a significant salt flux. The brine that drains from the newly-formed ice is replaced by a weak flow of relatively fresh water from the liquid region below it. The new water partially freezes within the pores of the ice, increasing the solidity of the ice.
As sea ice ages and thickens, the initial salinity of the ice decreases due to the rejection of brine over time. While the sea ice ages, desalinization occurs to such a degree that some multiyear ice has a salinity of less than 1 PSU. This occurs in three different ways:
*solute diffusion: this depends on the fact that brine inclusions trapped in ice will begin to migrate toward the warmer end of the ice block. The ice block is warmest at the water-ice interface, thus pushing the brine out into the water surrounding the ice.
*gravity drainage: gravity drainage involves the movement of brine due to differences in density between brine in the interior of the ice and brine in the seawater outside of the ice, which occurs due to the development of a buoyancy-driven convection system.
*expulsion: the migration of brine due to cracking produced by thermal expansion of the ice, or pressure caused by the increased volume of the newly formed ice. | 9 | Geochemistry |
A simple container (U-tube) is filled with a solid or catalyst. This sample vessel is positioned in a furnace with temperature control equipment. A thermocouple is placed in the solid for temperature measurement. The air originally present in the container is flushed out with an inert gas (nitrogen, argon). Flow controllers are used to add hydrogen (for example, 10% hydrogen in nitrogen). The composition of the gaseous mixture is measured at the exit of the sample container with appropriate detectors (thermal conductivity detector, mass spectrometer). Now, the sample in the oven is heated up on predefined values. Heating rates are usually between 1 K/min and 20 K/min. If a reduction takes place at a certain temperature, hydrogen is consumed, which is recorded by the detector. In practice the production of water is a more accurate way of measuring the reduction. This is due to the potential for varying hydrogen concentrations at the inlet, so the decrease in this number may not be precise, however as the starting concentration of water will be zero, any increase can be measured more accurately. | 7 | Physical Chemistry |
Monsanto manufactured PCBs at its chemical plant in Newport, South Wales, until the mid- to late-1970s. During this period, waste matter, including PCBs, from the Newport site was dumped at a disused quarry near Groes-faen, west of Cardiff, and Penhros landfill site from where it continues to be released in waste water discharges. | 2 | Environmental Chemistry |
The sphere packing problem is the three-dimensional version of a class of ball-packing problems in arbitrary dimensions. In two dimensions, the equivalent problem is packing circles on a plane. In one dimension it is packing line segments into a linear universe.
In dimensions higher than three, the densest lattice packings of hyperspheres are known up to 8 dimensions. Very little is known about irregular hypersphere packings; it is possible that in some dimensions the densest packing may be irregular. Some support for this conjecture comes from the fact that in certain dimensions (e.g. 10) the densest known irregular packing is denser than the densest known regular packing.
In 2016, Maryna Viazovska announced a proof that the E lattice provides the optimal packing (regardless of regularity) in eight-dimensional space, and soon afterwards she and a group of collaborators announced a similar proof that the Leech lattice is optimal in 24 dimensions. This result built on and improved previous methods which showed that these two lattices are very close to optimal.
The new proofs involve using the Laplace transform of a carefully chosen modular function to construct a radially symmetric function such that and its Fourier transform both equal 1 at the origin, and both vanish at all other points of the optimal lattice, with negative outside the central sphere of the packing and positive. Then, the Poisson summation formula for is used to compare the density of the optimal lattice with that of any other packing. Before the proof had been formally refereed and published, mathematician Peter Sarnak called the proof "stunningly simple" and wrote that "You just start reading the paper and you know this is correct."
Another line of research in high dimensions is trying to find asymptotic bounds for the density of the densest packings. It is known that for large , the densest lattice in dimension has density between (for some constant ) and . to | 3 | Analytical Chemistry |
This is an outline of an example mechanism of yeast cells by which chromatin structure and histone post-translational modification help regulate and record the transcription of genes by RNA polymerase II.
This pathway gives examples of regulation at these points of transcription:
* Pre-initiation (promotion by Bre1, histone modification)
* Initiation (promotion by TFIIH, Pol II modification and promotion by COMPASS, histone modification)
* Elongation (promotion by Set2, Histone Modification)
This refers to various stages of the process as regulatory steps. It has not been proven that they are used for regulation, but is very likely they are.
RNA Pol II elongation promoters can be summarised in 3 classes.
#Drug/sequence-dependent arrest-affected factors (Various interfering proteins)
#Chromatin structure-oriented factors (Histone posttranscriptional modifiers, e.g., Histone Methyltransferases)
#RNA Pol II catalysis-improving factors (Various interfering proteins and Pol II cofactors; see RNA polymerase II). | 1 | Biochemistry |
TSE or Tris/Saline/EDTA, is a buffer solution containing a mixture of Tris base, Sodium chloride and EDTA.
In molecular biology, TSE buffers are often used in procedures involving nucleic acids. Tris-acid solutions are effective buffers for slightly basic conditions, which keep DNA deprotonated and soluble in water. The concentration of tris in the solution is kept near 25 mM. EDTA is a chelator of divalent cations, particularly of magnesium (Mg). As these ions are necessary co-factors for many enzymes, including contaminant nucleases, the role of the EDTA is to protect the nucleic acids against enzymatic degradation. But since Mg is also a co-factor for many useful DNA-modifying enzymes such as restriction enzymes and DNA polymerases, its concentration in TSE buffers is generally kept low (typically at around 2.5 mM). The sodium chloride is generally kept at a concentration of 0.05 M. | 1 | Biochemistry |
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