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Wetting is a measure of the thermodynamic compatibility of two surfaces. If the surfaces are well-matched, the surfaces will "desire" to interact with each other, minimizing the surface energy of both phases, and the surfaces will come into close contact. Because the intermolecular attractions strongly correlate with distance, the closer the interacting molecules are together, the stronger the attraction. Thus, two materials that wet well and have a large amount of surface area in contact will have stronger intermolecular attractions and a larger adhesive strength due to the dispersive mechanism. | 0 | Theoretical and Fundamental Chemistry |
#Rutile (TiO) frequently exhibits a prismatic or acicular growth habit. In the presence of alkali dopants or a solid-state ZrSiO dopant, rutile has been observed to crystallise from an anatase parent-phase in the form of abnormally large grains existing in a matrix of finer, equiaxed anatase or rutile grains.
# Alumina, AlO with silica and/or yttria dopants/impurities has been reported to exhibit undesirable AGG.
#BaTiO barium titanate with an excess of TiO is known to exhibit abnormal grain growth with profound consequences on piezoelectric performance.
#Tungsten carbide has been reported to exhibit AGG of faceted grains in the presence of a liquid cobalt-containing phase at grain boundaries
#Silicon nitride (SiN) may exhibit AGG depending on the size distribution of β-phase material in an α-SiN precursor. This type of grain growth is of importance in the toughening of silicon nitride materials
#Silicon carbide has been shown to exhibit improved fracture toughness as the result of AGG processes yielding elongated crack-tip/wake-bridging grains, with consequences for applications in ballistic armor. This enhancement of fracture toughness in ceramic materials via crack-bridging resulting from AGG is consistent with reported morphological effects on crack propagation in ceramics
#Strontium barium niobate, used for electro-optics and dielectric applications, is known to exhibit AGG with significant consequences on the electronic performance of the material
#Calcium titanate (CaTiO, perovskite) systems doped with BaO have been observed to exhibit AGG without the formation of liquid as the result of polytype interfaces between solid phases | 0 | Theoretical and Fundamental Chemistry |
Inner sphere complex is a type of surface complex that refers to the surface chemistry changing a water-surface interface to one without water molecules bridging a ligand to the metal ion. Formation of inner sphere complexes occurs when ions bind directly to the surface with no intervening water molecules. These types of surface complexes are restricted to ions that have a high affinity for surface sites and include specifically adsorbed ions that can bind to the surface through covalent bonding.
Inner sphere complexes describe active surface sites that are involved in nucleation, crystal growth, redox processes, soil chemistry, alongside other reactions taking place between a cation and surface. This affinity to surface sites can be attributed to covalent bonding.
When compared to outer sphere complexes that have water molecules separating ions from ligands, inner sphere complexes have surface hydroxyl groups that function as -donor ligands, increasing the coordinated metal ion's electron density. This is an example of competitive complex formation, in which ligands will compete for space on an activation site of a metal ion.
Surface structures are able to reduce and oxidize ligands, whereas transport phenomena do not. Therefore, surface structure serves an important role in surface reactivity, with the coordination environment at the solid-water interface changing intensity or rate of a reaction. | 0 | Theoretical and Fundamental Chemistry |
Since the early observations, several theoretical models have been proposed, to explain the experimental observation of the exclusion zone. | 1 | Applied and Interdisciplinary Chemistry |
The reaction has the following mechanism:
The rate of each species are:
These equations cannot be solved, because each one has values that change with time. For example, the first equation contains the concentrations of [Br], and , which depend on time, as can be seen in their respective equations.
To solve the rate equations the steady state approximation can be used. The reactants of this reaction are and , the intermediates are H and Br, and the product is HBr.
For solving the equations, the rates of the intermediates are set to 0 in the steady state approximation:
From the reaction rate of H, , so the reaction rate of Br can be simplified:
The reaction rate of HBr can also be simplifed, changing to , since both values are equal.
The concentration of H from equation 1 can be isolated:
The concentration of this intermediate is small and changes with time like the concentrations of reactants and product. It is inserted into the last differential equation to give
Simplifying the equation leads to
The experimentally observed rate is
The experimental rate law is very similar to the rate obtained with the steady state approximation, if is and is . | 0 | Theoretical and Fundamental Chemistry |
The above uses and effects are consequences of the fact that the solution is a source of effectively free elemental iodine, which is readily generated from the equilibrium between elemental iodine molecules and polyiodide ions in the solution. | 0 | Theoretical and Fundamental Chemistry |
Consider a column filled with a transporting medium and a balloon filled with a working fluid. Due to the hydrostatic pressure of the transporting medium, the pressure inside the column increases along the z axis (see figure). Initially, the balloon is inflated by the working fluid at temperature T and pressure P and located on top of the column. A thermogravitational cycle is decomposed into four ideal steps:
* 1→2: Descent of the balloon towards the bottom of the column. The working fluid undergoes adiabatic compression with its temperature increasing and its pressure reaching value P at the bottom (P>P).
* 2→3: While the ballon lays at the bottom, the working fluid receives heat from the hot source at temperature T and undergoes isobaric expansion at pressure P.
* 3→4: The balloon rises towards the column top. The working fluid undergoes adiabatic expansion with a drop in temperature and reaches pressure P after expansion when the balloon is on top.
* 4→1: Once arrived on top, the working fluid supplies heat to the cold source at temperature T while undergoing isobaric compression at pressure P.
For a thermogravitational cycle to occur, the balloon has to be denser than the transporting medium during 1→2 step and less dense during 3→4 step. If these conditions are not naturally satisfied by the working fluid, a weight can be attached to the balloon to increase its effective mass density. | 0 | Theoretical and Fundamental Chemistry |
Fluorescence in situ hybridization (FISH) is a laboratory method used to detect and locate a DNA sequence, often on a particular chromosome.
In the 1960s, researchers Joseph Gall and Mary Lou Pardue found that molecular hybridization could be used to identify the position of DNA sequences in situ (i.e., in their natural positions within a chromosome). In 1969, the two scientists published a paper demonstrating that radioactive copies of a ribosomal DNA sequence could be used to detect complementary DNA sequences in the nucleus of a frog egg. Since those original observations, many refinements have increased the versatility and sensitivity of the procedure to the extent that in situ hybridization is now considered an essential tool in cytogenetics. | 1 | Applied and Interdisciplinary Chemistry |
4,5-Dihydroorotic acid is a derivative of orotic acid which serves as an intermediate in pyrimidine biosynthesis. | 1 | Applied and Interdisciplinary Chemistry |
Visual phototransduction in invertebrates like the fruit fly differs from that of vertebrates, described up to now. The primary basis of invertebrate phototransduction is the PI(4,5)P cycle. Here, light induces the conformational change into rhodopsin and converts it into meta-rhodopsin. This helps in dissociation of G-protein complex. Alpha sub-unit of this complex activates the PLC enzyme (PLC-beta) which hydrolyze the PIP2 into DAG. This hydrolysis leads to opening of TRP channels and influx of calcium.
Invertebrate photoreceptor cells differ morphologically and physiologically from their vertebrate counterparts. Visual stimulation in vertebrates causes a hyperpolarization (weakening) of the photoreceptor membrane potential, whereas invertebrates experience a depolarization with light intensity. Single-photon events produced under identical conditions in invertebrates differ from vertebrates in time course and size. Likewise, multi-photon events are longer than single-photon responses in invertebrates. However, in vertebrates, the multi-photon response is similar to the single-photon response. Both phyla have light adaptation and single-photon events are smaller and faster. Calcium plays an important role in this adaptation. Light adaptation in vertebrates is primarily attributable to calcium feedback, but in invertebrates cyclic AMP is another control on dark adaptation. | 1 | Applied and Interdisciplinary Chemistry |
The regulation of translation in eukaryotes is more complex than in prokaryotes. Initially, the eIF4F complex is recruited to the 5′ cap, which in turn recruits the ribosomal complex to the 5′ UTR. Both eIF4E and eIF4G bind the 5′ UTR, which limits the rate at which translational initiation can occur. However, this is not the only regulatory step of translation that involves the 5′ UTR.
RNA-binding proteins sometimes serve to prevent the pre-initiation complex from forming. An example is regulation of the msl2 gene. The protein SXL attaches to an intron segment located within the 5′ UTR segment of the primary transcript, which leads to the inclusion of the intron after processing. This sequence allows the recruitment of proteins that bind simultaneously to both the 5′ and 3′ UTR, not allowing translation proteins to assemble. However, it has also been noted that SXL can also repress translation of RNAs that do not contain a poly(A) tail, or more generally, 3′ UTR. | 1 | Applied and Interdisciplinary Chemistry |
In 1962, Edwards and Pearson (the latter of HSAB theory) introduced the phrase alpha effect for this anomaly. He offered the suggestion that the effect was caused by a transition state (TS) stabilization effect: on entering the TS the free electron pair on the nucleophile moves away from the nucleus, causing a partial positive charge which can be stabilized by an adjacent lone pair as for instance happens in any carbocation. | 0 | Theoretical and Fundamental Chemistry |
Tritium for American nuclear weapons was produced in special heavy water reactors at the Savannah River Site until their closures in 1988. With the Strategic Arms Reduction Treaty (START) after the end of the Cold War, the existing supplies were sufficient for the new, smaller number of nuclear weapons for some time.
of tritium was produced in the United States from 1955 to 1996. Since it continually decays into helium-3, the total amount remaining was about at the time of the report,
and about as of 2023.
The production of tritium was resumed with irradiation of rods containing lithium (replacing the usual control rods containing boron, cadmium, or hafnium), at the reactors of the commercial Watts Bar Nuclear Plant from 2003 to 2005 followed by extraction of tritium from the rods at the Tritium Extraction Facility at the Savannah River Site beginning in November 2006. Tritium leakage from the rods during reactor operations limits the number that can be used in any reactor without exceeding the maximum allowed tritium levels in the coolant. | 0 | Theoretical and Fundamental Chemistry |
Standard reduction potentials in aqueous solution are also a useful way of predicting the non-aqueous chemistry of the metals involved. Thus, metals with high negative potentials, such as sodium, or potassium, will ignite in air, forming the respective oxides. These fires cannot be extinguished with water, which also react with the metals involved to give hydrogen, which is itself explosive. Noble metals, in contrast, are disinclined to react with oxygen and, for that reason (as well as their scarcity) have been valued for millennia, and used in jewellery and coins.
The adjacent table lists standard reduction potential in volts; electronegativity (revised Pauling); and electron affinity values (kJ/mol), for some metals and metalloids.
The simplified entries in the reaction column can be read in detail from the Pourbaix diagrams of the considered element in water. Noble metals have large positive potentials; elements not in this table have a negative standard potential or are not metals.
Electronegativity is included since it is reckoned to be, "a major driver of metal nobleness and reactivity".
On account of their high electron affinity values, the incorporation of a noble metal in the electrochemical photolysis process, such as platinum and gold, among others, can increase photoactivity.
Arsenic and antimony are usually considered to be metalloids rather than noble metals. However, physically speaking their most stable allotropes are metallic. Semiconductors, such as selenium and tellurium, have been excluded.
The black tarnish commonly seen on silver arises from its sensitivity to hydrogen sulfide:
:2 Ag + HS + O → AgS + HO.
Rayner-Canham contends that, "silver is so much more chemically-reactive and has such a different chemistry, that it should not be considered as a noble metal." In dentistry, silver is not regarded as a noble metal due to its tendency to corrode in the oral environment.
The relevance of the entry for water is addressed by Li et al. in the context of galvanic corrosion. Such a process will only occur when:
:"(1) two metals which have different electrochemical potentials are...connected, (2) an aqueous phase with electrolyte exists, and (3) one of the two metals has...potential lower than the potential of the reaction ( + 4e + = 4 OH</sup>)."
The superheavy elements from hassium (element 108) to livermorium (116) inclusive are expected to be "partially very noble metals"; chemical investigations of hassium has established that it behaves like its lighter congener osmium, and preliminary investigations of nihonium and flerovium have suggested but not definitively established noble behavior. Copernicium's behaviour seems to partly resemble both its lighter congener mercury and the noble gas radon. | 1 | Applied and Interdisciplinary Chemistry |
It is possible to scrub sulfur dioxide by using a cold solution of sodium sulfite; this forms a sodium hydrogen sulfite solution. By heating this solution it is possible to reverse the reaction to form sulfur dioxide and the sodium sulfite solution. Since the sodium sulfite solution is not consumed, it is called a regenerative treatment. The application of this reaction is also known as the Wellman–Lord process.
In some ways this can be thought of as being similar to the reversible liquid–liquid extraction of an inert gas such as xenon or radon (or some other solute which does not undergo a chemical change during the extraction) from water to another phase. While a chemical change does occur during the extraction of the sulfur dioxide from the gas mixture, it is the case that the extraction equilibrium is shifted by changing the temperature rather than by the use of a chemical reagent. | 1 | Applied and Interdisciplinary Chemistry |
ELS is useful for characterizing information about the surface of proteins. Ware and Flygare (1971) demonstrated that electrophoretic techniques can be combined with laser beat spectroscopy in order to simultaneously determine the electrophoretic mobility and diffusion coefficient of bovine serum albumin. The width of a Doppler shifted spectrum of light that is scattered from a solution of macromolecules is proportional to the diffusion coefficient. The Doppler shift is proportional to the electrophoretic mobility of a macromolecule. From studies that have applied this method to poly (L-lysine), ELS is believed to monitor fluctuation mobilities in the presence of solvents with varying salt concentrations. It has also been shown that electrophoretic mobility data can be converted to zeta potential values, which enables the determination of the isoelectric point of proteins and the number of electrokinetic charges on the surface.
Other biological macromolecules that can be analyzed with ELS include polysaccharides. pKa values of chitosans can be calculated from the dependency of electrophoretic mobility values on pH and charge density. Like proteins, the size and zeta potential of chitosans can be determined through ELS.
ELS has also been applied to nucleic acids and viruses. The technique can be extended to measure electrophoretic mobilities of large bacteria molecules at low ionic strengths. | 0 | Theoretical and Fundamental Chemistry |
Monothiophosphate is the anion [POS], which has C symmetry. A common salt is sodium monothiophosphate (NaPOS). Monothiophosphate is used in research as an analogue of phosphate in biochemistry. Monothiophosphate esters are biochemical reagents used in the study of transcription, substitution interference assays. Sometimes, "monothiophosphate" refers to esters such as (CHO)POS. | 0 | Theoretical and Fundamental Chemistry |
A three-step mechanism was derived in 1987 by Peters and Forman A. Williams by assuming steady-state approximation for the hydrogen radical. Then, | 0 | Theoretical and Fundamental Chemistry |
can be expressed as follows:
where:
, so that .
The vector Laplacian of a vector of the type reads:
It can thus be calculated that:
Therefore:
Thus the vorticity is:
where we have used the vanishing of the divergence of to relate the vector laplacian and a double curl.
The equation of motion's left hand side is the curl of the following:
We calculate the derivative separately for each term in .
Note that:
And also:
We thus have:
Combining all the terms we have:
Taking the curl, we find an expression that is equal to times the gradient of the following function, which is the pressure:
where is the pressure at infinity, .is the polar angle originated from the opposite side of the front stagnation point ( where is the front stagnation point).
Also, the velocity is derived by taking the curl of :
These p and u satisfy the equation of motion and thus constitute the solution to Oseen's approximation. | 1 | Applied and Interdisciplinary Chemistry |
NCoR (nuclear receptor co-repressor) directly binds to the D and E domains of nuclear receptors and represses their transcriptional activity. Class I histone deacetylases are recruited by NCoR through SIN3, and NCoR directly binds to class II histone deacetylases. | 1 | Applied and Interdisciplinary Chemistry |
Terephthalaldehyde (TA) is an organic compound with the formula CH(CHO). It is one of three isomers of benzene dicarboxaldehyde, in which the aldehyde moieties are positioned in the para conformation on the benzene ring. Terephthalaldehyde appears as a white to beige solid, typically in the form of a powder. It is soluble in many organic solvents, such as alcohols (e.g., methanol or ethanol) and ethers (e.g., tetrahydrofuran or diethylether). | 0 | Theoretical and Fundamental Chemistry |
Sunset yellow is used in foods, condoms, cosmetics, and drugs. Sunset yellow FCF is used as an orange or yellow-orange dye. For example, it is used in candy, desserts, snacks, sauces, and preserved fruits.
Sunset yellow is often used in conjunction with E123, amaranth, to produce a brown colouring in both chocolates and caramel. | 0 | Theoretical and Fundamental Chemistry |
The energy required to break the base-base hydrogen bonding between two strands of DNA is dependent on their length, GC content and their complementarity. By heating a reaction-mixture that contains double-stranded DNA sequences and measuring dissociation against temperature, these attributes can be inferred.
Originally, strand dissociation was observed using UV absorbance measurements, but techniques based on fluorescence measurements are now the most common approach.
The temperature-dependent dissociation between two DNA-strands can be measured using a DNA-intercalating fluorophore such as SYBR green, EvaGreen or fluorophore-labelled DNA probes. In the case of SYBR green (which fluoresces 1000-fold more intensely while intercalated in the minor groove of two strands of DNA), the dissociation of the DNA during heating is measurable by the large reduction in fluorescence that results. Alternatively, juxtapositioned probes (one featuring a fluorophore and the other, a suitable quencher) can be used to determine the complementarity of the probe to the target sequence.
The graph of the negative first derivative of the melting-curve may make it easier to pin-point the temperature of dissociation (defined as 50% dissociation), by virtue of the peaks thus formed.
SYBR Green enabled product differentiation in the LightCycler in 1997. Hybridization probes (or FRET probes) were also demonstrated to provide very specific melting curves from the single-stranded (ss) probe-to-amplicon hybrid. Idaho Technology and Roche have done much to popularize this use on the LightCycler instrument. | 1 | Applied and Interdisciplinary Chemistry |
Regenerative medicine deals with the "process of replacing, engineering or regenerating human or animal cells, tissues or organs to restore or establish normal function". This field holds the promise of engineering damaged tissues and organs by stimulating the body's own repair mechanisms to functionally heal previously irreparable tissues or organs.
Regenerative medicine also includes the possibility of growing tissues and organs in the laboratory and implanting them when the body cannot heal itself. When the cell source for a regenerated organ is derived from the patient's own tissue or cells, the challenge of organ transplant rejection via immunological mismatch is circumvented. This approach could alleviate the problem of the shortage of organs available for donation.
Some of the biomedical approaches within the field of regenerative medicine may involve the use of stem cells. Examples include the injection of stem cells or progenitor cells obtained through directed differentiation (cell therapies); the induction of regeneration by biologically active molecules administered alone or as a secretion by infused cells (immunomodulation therapy); and transplantation of in vitro grown organs and tissues (tissue engineering). | 1 | Applied and Interdisciplinary Chemistry |
Changes in animal populations, whether increases or decreases, can indicate pollution. For example, if pollution causes depletion of a plant, animal species that depend on that plant will experience population decline. Conversely, overpopulation may be opportunistic growth of a species in response to loss of other species in an ecosystem. On the other hand, stress-induced sub-lethal effects can be manifested in animal physiology, morphology, and behaviour of individuals long before responses are expressed and observed at the population level. Such sub-lethal responses can be very useful as "early warning signals" to predict how populations will further respond.
Pollution and other stress agents can be monitored by measuring any of several variables in animals: the concentration of toxins in animal tissues; the rate at which deformities arise in animal populations; behaviour in the field or in the laboratory; and by assessing changes in individual physiology. | 1 | Applied and Interdisciplinary Chemistry |
Micellar solubilization is widely utilized, e.g. in laundry washing using detergents, in the pharmaceutical industry, for formulations of poorly soluble drugs in solution form, and in cleanup of oil spills using dispersants. | 0 | Theoretical and Fundamental Chemistry |
In electrophilic aromatic substitution reactions, existing substituent groups on the aromatic ring influence the overall reaction rate or have a directing effect on positional isomer of the products that are formed.
An electron donating group (EDG) or electron releasing group (ERG, Z in structural formulas) is an atom or functional group that donates some of its electron density into a conjugated π system via resonance (mesomerism) or inductive effects (or induction)—called +M or +I effects, respectively—thus making the π system more nucleophilic. As a result of these electronic effects, an aromatic ring to which such a group is attached is more likely to participate in electrophilic substitution reaction. EDGs are therefore often known as activating groups, though steric effects can interfere with the reaction.
An electron withdrawing group (EWG) will have the opposite effect on the nucleophilicity of the ring. The EWG removes electron density from a π system, making it less reactive in this type of reaction, and therefore called deactivating groups.
EDGs and EWGs also determine the positions (relative to themselves) on the aromatic ring where substitution reactions are most likely to take place. Electron donating groups are generally ortho/para directors for electrophilic aromatic substitutions, while electron withdrawing groups (except the halogens) are generally meta directors. The selectivities observed with EDGs and EWGs were first described in 1892 and have been known as the Crum Brown–Gibson rule. | 0 | Theoretical and Fundamental Chemistry |
There is a strong scientific consensus that greenhouse effect due to carbon dioxide is a main driver of climate change. Following is an illustrative model meant for a pedagogical purpose, showing the main physical determinants of the effect.
Under this understanding, global warming is determined by a simple energy budget: In the long run, Earth emits radiation in the same amount as it receives from the sun. However, the amount emitted depends both on Earths temperature and on its albedo: The more reflective the Earth in a certain wavelength, the less radiation it would both receive and emit in this wavelength; the warmer the Earth, the more radiation it emits. Thus changes in the albedo may have an effect on Earths temperature, and the effect can be calculated by assuming a new steady state would be arrived at.
In most of the electromagnetic spectrum, atmospheric carbon dioxide either blocks the radiation emitted from the ground almost completely, or is almost transparent, so that increasing the amount of carbon dioxide in the atmosphere, e.g. doubling the amount, will have negligible effects. However, in some narrow parts of the spectrum this is not so; doubling the amount of atmospheric carbon dioxide will make Earth's atmosphere relatively opaque to in these wavelengths, which would result in Earth emitting light in these wavelengths from the upper layers of the atmosphere, rather from lower layers or from the ground. Since the upper layers are colder, the amount emitted would be lower, leading to warming of Earth until the reduction in emission is compensated by the rise in temperature.
Furthermore, such warming may cause a feedback mechanism due to other changes in Earth's albedo, e.g. due to ice melting. | 1 | Applied and Interdisciplinary Chemistry |
Sea salt aerosols are mainly constituted of sodium chloride (NaCl), but other chemical ions which are common in sea water, such as K, Mg, Ca, SO and so on, can also be found. A recent study revealed that sea salt aerosols also contain a substantial amount of organic matter. Mostly, organic materials are internally mixed due to the drying of air bubbles at the organic-rich sea surface. The fraction of organic components increases with the decreasing particle size. The contained organic materials change the optical properties of sea salt as well as the hygroscopicity, especially when some insoluble organic matter is induced. | 0 | Theoretical and Fundamental Chemistry |
The presence of ptaquiloside has been detected in a variety of ferns, including the species in the genera Pteridium (bracken), Pteris, Microlepia, and Hypolepis. Pteridium aquilinum (commonly known as bracken fern) is the most common ptaquiloside-containing fern with a wide geographical and ecological distribution. It is present in all continents from subtropic to subarctic areas. Bracken fern is a very adaptable plant and is capable of forming dense, rapidly expanding populations in course of the first phases of the ecological succession in forest cleanings and other disturbed rural areas. Its aggressive growth, characterized by an extensive rhizome system and rapidly growing fronds, sometimes enables it to be a dominant species in certain plant communities.
The ptaquiloside content of bracken varies widely across species and changes with the part of the plant, the plant growing site and the collecting season. According to previous studies, the concentrations of ptaquiloside in bracken varied between 0 to 1% of the dry weight of the plant. Generally, ptaquiloside is found to occur in the highest concentrations in the young developing parts of bracken, such as the croziers and unfolding parts during the spring and early summer, while the concentrations of ptaquiloside in the rhizomes are rather low. However, studies on the concentrations of ptaquiloside in Danish bracken by Rasmussen et al. showed that the concentrations of ptaquiloside in the rhizomes were significantly higher than the previously reported values.
Ptaquiloside can pass into the milk produced by bracken-fed cows and sheep. In 1996, Alonso-Amelot, Smith and co-workers found that ptaquiloside was excreted in milk at a concentration of 8.6 ± 1.2% of the amount ingested by a cow from bracken, and was linearly dose-dependent. On the basis of their experiments and the assumption that a person drinks 0.5 litres of milk daily, they estimated that this person might ingest about 10 mg of ptaquiloside per day, although only some of that amount will be absorbed. Ptaquiloside can also leach from the bracken leaves into water and soil. Numerous studies have reported the presence of ptaquiloside in the underground/surface water, and soil near bracken vegetation. The degradation speed of ptaquiloside in the soil is affected by the acidity, clay content, carbon content, temperature and presumably microbioactivity. Acidic condition (pH<4) and high temperature (at least 25°C) facilitate ptaquiloside degradation, while the half-life of ptaquiloside in less acidic sandy soil is reported to be between 150 and 180 hours. | 0 | Theoretical and Fundamental Chemistry |
Polyunsaturated aldehydes (PUAs) are a group of allelopathic chemicals typically associated with diatom-copepod predator-prey interactions. These compounds are classified by an aldehyde group covalently bound to long carbon chains containing two or more carbon-carbon double bonds. Examples include isomers of heptadienal, octadienal, octatrienal, and decatrienal. | 1 | Applied and Interdisciplinary Chemistry |
PDE3 enzymes are involved in regulation of cardiac and vascular smooth muscle contractility. Molecules that inhibit PDE3 were originally investigated for the treatment of heart failure, but, because of unwanted arrhythmic side-effects, they are not studied for that indication any longer. Nonetheless, the PDE3 inhibitor milrinone is approved for use in heart failure in intravenous form.
Both PDE3A and PDE3B are expressed in vascular smooth muscle cells and are likely to modulate contraction. Their expression in vascular smooth muscle is altered under specific conditions such as elevated cAMP and hypoxia. | 1 | Applied and Interdisciplinary Chemistry |
Ab initio or first principles calculations are any of a number of software packages making use of density functional theory to solve for the quantum mechanical state of a system. Perfect crystals are an ideal subject for such calculations because of their high periodicity. Since every simulation package will vary in the details of its algorithms and implementations, this page will focus on a methodological overview. | 0 | Theoretical and Fundamental Chemistry |
The objective of environmental risk assessment is to protect the environment from adverse effects. Researchers are further developing QSAR models with the ultimate goal providing a clear insight about a mode of toxic action, but also about what the actual target site is, the concentration of the chemical at this target site, and the interaction occurring at the target site, as well as to predict the modes of toxic action in mixtures. Information on the mode of toxic action is crucial not only in understanding joint toxic effects and potential interactions between chemicals in mixtures, but also for developing assays for the evaluation of complex mixtures in the field. | 1 | Applied and Interdisciplinary Chemistry |
Mutations in super-enhancers have been noted in various diseases, including cancers, type 1 diabetes, Alzheimer’s disease, lupus, rheumatoid arthritis, multiple sclerosis, systemic scleroderma, primary biliary cirrhosis, Crohn’s disease, Graves disease, vitiligo, and atrial fibrillation. A similar enrichment in disease-associated sequence variation has also been observed for stretch enhancers.
Super-enhancers may play important roles in the misregulation of gene expression in cancer. During tumor development, tumor cells acquire super-enhancers at key oncogenes, which drive higher levels of transcription of these genes than in healthy cells. Altered super-enhancer function is also induced by mutations of chromatin regulators. Acquired super-enhancers may thus be biomarkers that could be useful for diagnosis and therapeutic intervention.
Proteins enriched at super-enhancers include the targets of small molecules that target transcription-regulating proteins and have been deployed against cancers. For instance, super-enhancers rely on exceptional amounts of CDK7, and, in cancer, multiple papers report the loss of expression of their target genes when cells are treated with the CDK7 inhibitor THZ1. Similarly, super-enhancers are enriched in the target of the JQ1 small molecule, BRD4, so treatment with JQ1 causes exceptional losses in expression for super-enhancer—associated genes. | 1 | Applied and Interdisciplinary Chemistry |
Neutron capture nucleosynthesis describes two nucleosynthesis pathways: the r-process and the s-process, for rapid and slow neutron captures, respectively. R-process describes neutron capture in a region of high neutron flux, such as during supernova nucleosynthesis after core-collapse, and yields neutron-rich nuclides. S-process describes neutron capture that is slow relative to the rate of beta decay, as for stellar nucleosynthesis in some stars, and yields nuclei with stable nuclear shells. Each process is responsible for roughly half of the observed abundances of elements heavier than iron. The importance of neutron capture to the observed abundance of the chemical elements was first described in 1957 in the BFH paper. | 0 | Theoretical and Fundamental Chemistry |
Since its inception as a tool of analytical chemistry, LC-MS/MS spread rapidly and indeed continues to do so in (amongst others) bioanalytical fields. One of the advantages of the technique is its selectivity for many analytes of interest. However, this high selectivity could lead to a misconception that it is always possible to simplify or (on occasion) almost completely remove the necessity for extensive sample preparation. However, during and after uptake by bioanalytical laboratories worldwide, it became apparent that there were inherent problems with detection of relatively small analyte concentrations in the complex sample matrices associated with biological fluids (e.g. blood and urine). | 0 | Theoretical and Fundamental Chemistry |
Spectral line shape or spectral line profile describes the form of an electromagnetic spectrum in the vicinity of a spectral line – a region of stronger or weaker intensity in the spectrum. Ideal line shapes include Lorentzian, Gaussian and Voigt functions, whose parameters are the line position, maximum height and half-width. Actual line shapes are determined principally by Doppler, collision and proximity broadening. For each system the half-width of the shape function varies with temperature, pressure (or concentration) and phase. A knowledge of shape function is needed for spectroscopic curve fitting and deconvolution. | 0 | Theoretical and Fundamental Chemistry |
Copepods are sometimes found in public main water supplies, especially systems where the water is not mechanically filtered, such as New York City, Boston, and San Francisco. This is not usually a problem in treated water supplies. In some tropical countries, such as Peru and Bangladesh, a correlation has been found between copepods presence and cholera in untreated water, because the cholera bacteria attach to the surfaces of planktonic animals. The larvae of the guinea worm must develop within a copepods digestive tract before being transmitted to humans. The risk of infection with these diseases can be reduced by filtering out the copepods (and other matter), for example with a cloth filter.
Copepods have been used successfully in Vietnam to control disease-bearing mosquitoes such as Aedes aegypti that transmit dengue fever and other human parasitic diseases.
The copepods can be added to water-storage containers where the mosquitoes breed. Copepods, primarily of the genera Mesocyclops and Macrocyclops (such as Macrocyclops albidus), can survive for periods of months in the containers, if the containers are not completely drained by their users. They attack, kill, and eat the younger first- and second-instar larvae of the mosquitoes. This biological control method is complemented by community trash removal and recycling to eliminate other possible mosquito-breeding sites. Because the water in these containers is drawn from uncontaminated sources such as rainfall, the risk of contamination by cholera bacteria is small, and in fact no cases of cholera have been linked to copepods introduced into water-storage containers. Trials using copepods to control container-breeding mosquitoes are underway in several other countries, including Thailand and the southern United States. The method, though, would be very ill-advised in areas where the guinea worm is endemic.
The presence of copepods in the New York City water supply system has caused problems for some Jewish people who observe kashrut. Copepods, being crustaceans, are not kosher, nor are they quite small enough to be ignored as nonfood microscopic organisms, since some specimens can be seen with the naked eye. Hence, large specimens are certainly non-Kosher. However, some species are visible to the naked eye, but are small enough that they only appear as little white specks. These are problematic, as it is a question as to whether they are considered visible enough to be non-Kosher.
When a group of rabbis in Brooklyn, New York, discovered these copepods in the summer of 2004, they triggered such debate in rabbinic circles that some observant Jews felt compelled to buy and install filters for their water. The water was ruled kosher by posek Yisrael Belsky, chief posek of the OU and one of the most scientifically literate poskim of his time. Meanwhile, Rabbi Dovid Feinstein, based on the ruling of Rabbi Yosef Shalom Elyashiv - the two widely considered to be the greatest poskim of their time - ruled it was not kosher until filtered. Several major kashrus organizations (e.g OU Kashrus and Star-K) require tap water to have filters. | 1 | Applied and Interdisciplinary Chemistry |
Trimethylsilylpropanoic acid (TMSP or TSP) is a chemical compound containing a trimethylsilyl group. It is used as internal reference in nuclear magnetic resonance for aqueous solvents (e.g. DO). For that use it is often deuterated (3-(trimethylsilyl)-2,2,3,3-tetradeuteropropionic acid or TMSP-d). Other internal references that are frequently used in NMR experiments are DSS and tetramethylsilane. | 0 | Theoretical and Fundamental Chemistry |
Besides the individual toxic effects of each metal, a wide range of metals are nephrotoxic in humans and/or in animals. Some metals and their compounds are carcinogenic to humans. A few metals, such as lead and mercury, can cross the placental barrier and adversely affect fetal development. Several (cadmium, zinc, copper, and mercury) can induce special protein complexes called metallothioneins. | 1 | Applied and Interdisciplinary Chemistry |
Health Canada classifies VOCs as organic compounds that have boiling points roughly in the range of . The emphasis is placed on commonly encountered VOCs that would have an effect on air quality. | 0 | Theoretical and Fundamental Chemistry |
A quantitative method to determine the amount of phosphate present in samples, such as boiler feedwater, is as follows. A measured amount of boiler water is poured into a mixing tube and ammonium heptamolybdate reagent is added. The tube is then stoppered and vigorously shaken. The next step is to add dilute stannous chloride reagent, which has been freshly prepared from concentrated stannous chloride reagent and distilled water, to the mixture in the tube. This will produce a blue colour (due to the formation of molybdenum blue) and the depth of the blue colour indicates the amount of phosphate in the boiler water. The absorbance of the blue solution can be measured with a colorimeter and the concentration of phosphate in the original solution can be calculated. Alternatively, a direct (but approximate) reading of phosphate concentration can be obtained by using a Lovibond comparator. This method for phosphate determination is known as Denigés' method. | 0 | Theoretical and Fundamental Chemistry |
The model calculates the ground water levels and the incoming and outgoing ground water flows between the polygons by a numerical solution of the well-known Boussinesq equation. The levels and flows influence each other mutually.
The ground water situation is further determined by the vertical groundwater recharge that is calculated from the agronomic water balance. These depend again on the levels of the ground water.
When semi-confined aquifers are present, the resistance to vertical flow in the slowly permeable top-layer and the overpressure in the aquifer, if any, are taken into account.
Hydraulic boundary conditions are given as hydraulic heads in the external nodes in combination with the hydraulic conductivity between internal and external nodes. If one wishes to impose a zero flow condition at the external nodes, the conductivity can be set at zero.
Further, aquifer flow conditions can be given for the internal nodes. These are required when a geological fault is present at the bottom of the aquifer or when flow occurs between the main aquifer and a deeper aquifer separated by a semi-confining layer.
The depth of the water table, the rainfall and salt concentrations of the deeper layers are assumed to be the same over the whole polygon. Other parameters can very within the polygons according to type of crops and cropping rotation schedule. | 0 | Theoretical and Fundamental Chemistry |
Viruses can be spread by direct transfer of sap by contact of a wounded plant with a healthy one. Such contact may occur during agricultural practices, as by damage caused by tools or hands, or naturally, as by an animal feeding on the plant. Generally TMV, potato viruses and cucumber mosaic viruses are transmitted via sap. | 1 | Applied and Interdisciplinary Chemistry |
Lake surface temperatures fluctuate between in winter, and in summer. From 1979 to 2011 annual rainfall was at the lake, and at Cerro La Laguna, the highest part of the catchment. The residence time of water in the lake is therefore 35 ± 6 days assuming homogeneous water mixing. In actuality the lake is strongly stratified and dimictic, being composed of a highly turbid and poorly mineralized epilimnion, over a 5 °C cooler, highly mineralized hypolimnion. Most of the water therefore only restrict its circulation to the epilimnion, with an average residence time of 18 ± 3 days, assuming a constant mean depth of the termocline of . The lake usually homogenizes in January or February, sometimes very rapidly.
The lake is fed by several streams, most noticeably by the Paná River in the west, which is born from the junction of Chijuljá and Requenzal creeks. Other streams (Los Lavaderos, Chicojgual, Cerro Caj Coj) contribute very little to the lake water budget. Some springs feed the lake either directly near the shoreline (for example near Panconsul cave), or through the extensive marshlands that surround the lake. Lake Chichoj drains to Río El Desagüe, a tributary of the Cahabón River, which it joins after sinking into a cave for several hundreds of meters. Some of the sewage of San Cristál Verapaz is rerouted away from the lake and flows in a pipe through the marshlands before being emptied into Río El Desagüe, downstream of lake Chichoj.
The lake results from the coalescence of at least three dolines, likely resulting from the dissolution of gypsum at depth. The occurrence of gypsum is evidenced by a cluster of sulfate-bearing springs that dot the active trace of the Chixoy Polochic fault, 2 km south of the lake in the chixoy river valley, where they form large travertine fans. Discharge at these springs is much larger than what their upslope catchments can provide. The catchment of Lake Chichój is the closest catchment susceptible to provide water to these springs, and it lies above the springs. | 1 | Applied and Interdisciplinary Chemistry |
A large number of variant annotation tools are available for variant annotation. The annotation by different tools does not alway agree amongst each other, as the defined rules for data handling differ between applications. It is frankly impossible to perform a perfect comparison of the available tools. Not all tools have the same input and output nor the same functionality. Below is a table of major annotation tools and their functional area. | 1 | Applied and Interdisciplinary Chemistry |
In order for a molecule (or crystal) to exhibit circular birefringence and circular dichroism, it must be distinguishable from its mirror image. An object that cannot be superimposed on its mirror image is said to be chiral, and optical rotatory dispersion and circular dichroism are known as chiroptical properties.
Most biological molecules have one or more chiral centers and undergo enzyme-catalyzed transformations that either maintain or invert the chirality at one or more of these centers. Still other enzymes produce new chiral centers, always with a high specificity. These properties account for the fact that optical rotatory dispersion and circular dichroism are widely used in organic and inorganic chemistry and in biochemistry.
In the absence of magnetic fields, only chiral substances exhibit optical rotatory dispersion and circular dichroism. In a magnetic field, even substances that lack chirality rotate the plane of polarized light, as shown by Michael Faraday. Magnetic optical rotation is known as the Faraday effect, and its wavelength dependence is known as magnetic optical rotatory dispersion. In regions of absorption, magnetic circular dichroism is observable. | 0 | Theoretical and Fundamental Chemistry |
Traditionally metal nitrito complexes are prepared by salt metathesis or ligand substitution reactions using alkali metal nitrite salts, such as sodium nitrite. At neutral pH, nitrite exists predominantly as the anion, not nitrous acid.
Metal nitrosyl complexes undergo base hydrolysis, yielding nitrite complexes. This pattern is manifested in the behavior of nitroprusside: | 0 | Theoretical and Fundamental Chemistry |
The non-pathogenic and gram-negative bacteria, Pseudomonas fluorescens, is used for high level production of recombinant proteins; commonly for the development bio-therapeutics and vaccines. P. fluorescens is a metabolically versatile organism, allowing for high throughput screening and rapid development of complex proteins. P. fluorescens is most well known for its ability to rapid and successfully produce high titers of active, soluble protein. | 1 | Applied and Interdisciplinary Chemistry |
Bioluminescent bacteria are light-producing bacteria that are predominantly present in sea water, marine sediments, the surface of decomposing fish and in the gut of marine animals. While not as common, bacterial bioluminescence is also found in terrestrial and freshwater bacteria. These bacteria may be free living (such as Vibrio harveyi) or in symbiosis with animals such as the Hawaiian Bobtail squid (Aliivibrio fischeri) or terrestrial nematodes (Photorhabdus luminescens). The host organisms provide these bacteria a safe home and sufficient nutrition. In exchange, the hosts use the light produced by the bacteria for camouflage, prey and/or mate attraction. Bioluminescent bacteria have evolved symbiotic relationships with other organisms in which both participants benefit close to equally. Another possible reason bacteria use luminescence reaction is for quorum sensing, an ability to regulate gene expression in response to bacterial cell density. | 1 | Applied and Interdisciplinary Chemistry |
AQC processes are of particular importance in laboratories analysing environmental samples where the concentration of chemical species present may be extremely low and close to the detection limit of the analytical method. In well managed laboratories, AQC processes are built into the routine operations of the laboratory often by the random introduction of known standards into the sample stream or by the use of spiked samples.
Quality control begins with sample collection and ends with the reporting of data. AQC is achieved through laboratory control of analytical performance. Initial control of the complete system can be achieved through specification of laboratory services, instrumentation, glassware, reagents, solvents, and gases. However, evaluation of daily performance must be documented to ensure continual production of valid data. A check should first be done to ensure that the data should be seen is precise and accurate. Next, systematic daily checks such as analysing blanks, calibration standards, quality control check samples, and references must be performed to establish the reproducibility of the data. The checks help certify that the methodology is measuring what is in the sample.
The quality of individual AQC efforts can be variable depending on the training, professional pride, and importance of a particular project to a particular analyst. The burden of an individual analyst originating AQC efforts can be lessened through the implementation of quality assurance programs. Through the implementation of established and routine quality assurance programs, two primary functions are fulfilled: the determination of quality, and the control of quality. By monitoring the accuracy and precision of results, the quality assurance program should increase confidence in the reliability of the reported analytical results, thereby achieving adequate AQC. | 1 | Applied and Interdisciplinary Chemistry |
Ostwald ripening is a process in which large particles grow at the expense of the smaller particles as a result of dissolution of small particles and deposition of the dissolved molecules on the surfaces of the larger particles. It occurs because smaller particles have a higher surface energy than larger particles. This process is typically undesirable in nanoparticle synthesis as it negatively impacts the functionality of nanoparticles. | 0 | Theoretical and Fundamental 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. | 0 | Theoretical and Fundamental Chemistry |
The definition employed by Lieb and Yngvason is rather different since the state changes considered can be the result of arbitrarily complicated, possibly violent, irreversible processes and there is no mention of heat or differential forms. In the example of the water given above, if the stirring is done slowly, the transition from cool water to warm water will be quasistatic. However, a system containing an exploded firecracker is adiabatically accessible from a system containing an unexploded firecracker (but not vice versa), and this transition is far from quasistatic. Lieb and Yngvasons definition of adiabatic accessibility is: A state is adiabatically accessible from a state , in symbols (pronounced X precedes' Y), if it is possible to transform into in such a way that the only net effect of the process on the surroundings is that a weight has been raised or lowered (or a spring is stretched/compressed, or a flywheel is set in motion). | 0 | Theoretical and Fundamental Chemistry |
Both dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) measure the Brownian motion of nanoparticles whose speed of motion, or diffusion constant, Dt, is related to particle size through the Stokes–Einstein equation.
where
*Dt is the diffusion constant, a product of diffusion coefficient D and time t
* is Boltzmann's constant,
*T is the absolute temperature,
*η is viscosity
*d is the diameter of the spherical particle.
In NTA this motion is analyzed by video – individual particle positional changes are tracked in two dimensions from which the particle diffusion is determined. Knowing Dt, the particle hydrodynamic diameter can be then determined.
In contrast, DLS does not visualize the particles individually but analyzes, using a digital correlator, the time dependent scattering intensity fluctuations. These fluctuations are caused by interference effects arising from the relative Brownian movements of an ensemble of a large number of particles within a sample. Through analysis of the resultant exponential autocorrelation function, average particle size can be calculated as well as a polydispersity index. For multi-exponential autocorrelation functions arising from polydisperse samples, deconvolution can give limited information about the particle size distribution profile. | 0 | Theoretical and Fundamental Chemistry |
A brass mill is a mill which processes brass. Brass mills are common in England; many date from long before the Industrial Revolution.
;Examples of brass mills include:
*Brassmill (Ross on Wye)
*Saltford Brass Mill | 1 | Applied and Interdisciplinary Chemistry |
The creation of the Society of Chemical Industry (SCI) in London in 1881 led to the eventual formation of a number of satellite groups. A number of informal meetings were held in 1894, with the goal of organizing a New York section of the Society of Chemical Industry. On May 2, 1894, analytical chemist Arthur McGeorge met with seven other members of London's Society of Chemical Industry who were active in New York. At a second meeting, with Alfred H. Mason as chairman and McGeorge as secretary, it was decided to invite all New York-based members of the London society to an organizational meeting. At this third meeting, at the College of Pharmacy, 36 members of the Society of Chemical Industry signed a petition requesting the London organization to form a New York section, the first section to be created overseas. Their proposal was enthusiastically received by London president E. C. C. Stanford, who wrote "We are pleased to add the stars and stripes to our highly respectable old colours."
The first official meeting of the new New York Section was held in November 1894. The new section had a membership of 350 members, about one-tenth of the entire organization. The London group's president Thomas Tyrer and foreign secretary Ludwig Mond attended the October 1895 fall meeting in New York, which was rescheduled so that they could participate.
In contrast to the American Chemical Society, which required its members to hold university degrees, the Society of Chemical Industry was open to a broad range of working chemists in industry, manufacturing and pharmaceuticals. Mason emphasized that the new organization did not intend to compete with the ACS, but rather to bring together academic and manufacturing chemists:
Members of the America section benefited from the activities of the parent society, which held scientific conferences and published The Journal of the Society of Chemical Industry to inform chemists throughout the world about development in the field. From the beginning, the America Sections focus was networking, engaging its members in collegial activities. The second chairman, Charles F. Chandler, said "It serves to bring us together, to make us acquainted, and it enables us to help each other." Members of the New York section helped to establish The Chemists Club in New York City in 1898, using it for lectures and meetings, and establishing a members' library. In the beginning, talks were presented at the monthly meetings and published in the parent journal. Guest speakers included important international figures like Leo Baekeland, Carl Duisberg, and Jōkichi Takamine. In 1904, the New York Section hosted the first annual meeting of its parent organization to be held in the United States.
The New York section was briefly involved in practical work on standardization in 1902–03, when they established a Subcommittee on Uniformity of Analysis of Materials. Two samples of Portland cement were analyzed by 14 chemists, and 3 samples of zinc ore were analyzed by 42 chemists. The results were critiqued by William Francis Hillebrand, who became chief chemist at the National Bureau of Standards. The committee dissolved and was replaced in 1904 by a new committee formed by the ACS. The American section also engaged in early lobbying efforts, as in 1907, when they passed a resolution protesting that Rules and Regulations published by the Department of Agriculture displayed a "lack of expert knowledge." However, such activities never became a major focus of the organization.
In 1919, the New York group was renamed the America Section. | 1 | Applied and Interdisciplinary Chemistry |
The main threat of beta radiation exposure comes from hot particles in contact with or close to the skin of a person. Also, swallowed or inhaled hot particles could cause beta burns. As it is important to avoid bringing hot particles into the shelter, one option is to remove one's outer clothing, or follow other decontamination procedures, on entry. Fallout particles will cease to be radioactive enough to cause beta burns within a few days following a nuclear explosion. The danger of gamma radiation will persist for far longer than the threat of beta burns in areas with heavy fallout exposure. | 0 | Theoretical and Fundamental Chemistry |
Levetiracetam has not been found to be useful for treatment of neuropathic pain, nor for treatment of essential tremors. Levetiracetam has not been found to be useful for treating all developmental disorders within the autism spectrum; studies have only proven to be an effective treatment for partial, myoclonic, or tonic-clonic seizures associated with autism spectrum disorder. | 0 | Theoretical and Fundamental Chemistry |
Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes but also in tamarinds, bananas, avocados, and citrus. Its salt, potassium bitartrate, commonly known as cream of tartar, develops naturally in the process of fermentation. Potassium bitartrate is commonly mixed with sodium bicarbonate and is sold as baking powder used as a leavening agent in food preparation. The acid itself is added to foods as an antioxidant E334 and to impart its distinctive sour taste. Naturally occurring tartaric acid is a useful raw material in organic chemical synthesis. Tartaric acid, an alpha-hydroxy-carboxylic acid, is diprotic and aldaric in acid characteristics and is a dihydroxyl derivative of succinic acid. | 0 | Theoretical and Fundamental Chemistry |
Deuterium and tritium are both considered first-generation fusion fuels; they are the easiest to fuse, because the electrical charge on their nuclei is the lowest of all elements. The three most commonly cited nuclear reactions that could be used to generate energy are:
:H + H → n (14.07 MeV) + He (3.52 MeV)
:H + H → n (2.45 MeV) + He (0.82 MeV)
:H + H → p (3.02 MeV) + H (1.01 MeV) | 0 | Theoretical and Fundamental Chemistry |
Erwin Hahn first used inversion recovery technique to determine the value of T1 (the time taken for longitudinal magnetisation to recover 63% of its maximum value) for water in 1949, 3 years after the nuclear magnetic resonance was discovered. | 0 | Theoretical and Fundamental Chemistry |
The value is defined as the total energy released in a given nuclear decay. In beta decay, is therefore also the sum of the kinetic energies of the emitted beta particle, neutrino, and recoiling nucleus. (Because of the large mass of the nucleus compared to that of the beta particle and neutrino, the kinetic energy of the recoiling nucleus can generally be neglected.) Beta particles can therefore be emitted with any kinetic energy ranging from 0 to . A typical is around 1 MeV, but can range from a few keV to a few tens of MeV.
Since the rest mass of the electron is 511 keV, the most energetic beta particles are ultrarelativistic, with speeds very close to the speed of light.
In the case of Re, the maximum speed of the beta particle is only 9.8% of the speed of light.
The following table gives some examples: | 0 | Theoretical and Fundamental Chemistry |
A descaling agent or chemical descaler is a liquid chemical substance used to remove limescale from metal surfaces in contact with hot water, such as in boilers, water heaters, and kettles. Limescale is either white or brown in colour due to the presence of iron compounds. Glass surfaces may also exhibit scaling stains, as can many ceramic surfaces present in bathrooms and kitchen, and descaling agents can be used safely to remove those stains without affecting the substrate since both ceramics and glass are unreactive to most acids. | 1 | Applied and Interdisciplinary Chemistry |
In the spring of 2012, the Molecularium Project launched NanoSpace, an online molecular theme park. Visitors to NanoSpace learn scientific concepts with games, activities and movies. Areas within Nanospace include the Hall of Atoms and Molecules, H2O park (the water cycle), Sizes in the Universe (scale and scientific notation), Material Boulevard (Materials Science), and DNA Land (Molecular Biology). | 1 | Applied and Interdisciplinary Chemistry |
The feed water to the IGF float tank is often (but not always) dosed with a coagulant (such as ferric chloride or aluminum sulfate) to flocculate the suspended matter.
The bubbles may be generated by an impeller, eductors or a sparger. The bubbles adhere to the suspended matter, causing the suspended matter to float to the surface and form a froth layer which is then removed by a skimmer. The froth-free water exits the float tank as the clarified effluent from the IGF unit.
Some IGF unit designs utilize parallel plate packing material to provide more separation surface and therefore to enhance the separation efficiency of the unit. | 1 | Applied and Interdisciplinary Chemistry |
Intrinsic viscosity is a measure of a solute's contribution to the viscosity of a solution. It should not be confused with inherent viscosity, which is the ratio of the natural logarithm of the relative viscosity to the mass concentration of the polymer.
Intrinsic viscosity is defined as
where is the viscosity in the absence of the solute, is (dynamic or kinematic) viscosity of the solution and is the volume fraction of the solute in the solution. As defined here, the intrinsic viscosity is a dimensionless number. When the solute particles are rigid spheres at infinite dilution, the intrinsic viscosity equals , as shown first by Albert Einstein.
In practical settings, is usually solute mass concentration (c, g/dL), and the units of intrinsic viscosity are deciliters per gram (dL/g), otherwise known as inverse concentration. | 1 | Applied and Interdisciplinary Chemistry |
The use of crucibles in the Iron Age remains very similar to that of the Bronze Age with copper and tin smelting being used to produce bronze. The Iron Age crucible designs remain the same as the Bronze Age.
The Roman period shows technical innovations, with crucibles for new methods used to produce new alloys. The smelting and melting process also changed with both the heating technique and the crucible design. The crucible changed into rounded or pointed bottom vessels with a more conical shape; these were heated from below, unlike prehistoric types which were irregular in shape and were heated from above. These designs gave greater stability within the charcoal. These crucibles in some cases have thinner walls and have more refractory properties.
During the Roman period a new process of metalworking started, cementation, used in the production of brass. This process involves the combination of a metal and a gas to produce an alloy. Brass is made by mixing solid copper metal with zinc oxide or carbonate which comes in the form of calamine or smithsonite. This is heated to about 900 °C, the zinc oxide vaporizes into a gas, and the zinc gas bonds with the molten copper. This reaction has to take place in a part-closed or closed container otherwise the zinc vapor would escape before it can react with the copper. Cementation crucibles, therefore, have a lid or cap which limits the amount of gas loss from the crucible. The crucible design is similar to the smelting and melting crucibles of the period utilizing the same material as the smelting and melting crucibles. The conical shape and smallmouth allowed the lid to be added. These small crucibles are seen in Colonia Ulpia Trajana (modern-day Xanten), Germany, where the crucibles are around 4 cm in size, however, these are small examples. There are examples of larger vessels such as cooking pots and amphorae being used for cementation to process larger amounts of brass; since the reaction takes place at low temperatures lower fired ceramics could be used. The ceramic vessels which are used are important as the vessel must be able to lose gas through the walls otherwise the pressure would break the vessel. Cementation vessels are mass-produced due to crucibles having to be broken open to remove the brass once the reaction has finished as in most cases the lid would have baked hard to the vessel or the brass might have adhered to the vessel walls. | 0 | Theoretical and Fundamental Chemistry |
Hybrid hydrogels combine synthetic and biological materials and take advantage of the best properties of each. Synthetic polymers are easily customizable and can be tailored for specific functions such as biocompatibility. Biological polymers such as peptides also have adventitious properties such as specificity of binding and high affinity for certain cells and molecules. A hybrid of these two polymer types allows for the creation of hydrogels with novel properties. An example of a hybrid hydrogel would include a synthetically created polymer with several peptide domains. | 0 | Theoretical and Fundamental Chemistry |
Clumped isotope analyses have recently been used to constrain the paleoaltitude or uplift history of a region. Air temperature decreases systematically with altitude throughout the troposphere (see lapse rate). Due to the close coupling between lake water temperature and air temperature, there is a similar decrease in lake water temperature as altitude increases. Thus, variation in water temperature implied by Δ47 could indicate changes in lake altitude, driven by tectonic uplift or subsidence. Two recent studies derive the timing of the uplift of the Andes Mountains and the Altiplano Plateau, citing sharp decreases in Δ47-derived temperatures as evidence of rapid tectonic uplift. | 0 | Theoretical and Fundamental Chemistry |
Although 1,3-dipolar cycloaddition is a useful method for the generation of five-membered heterocyclic compounds, few methods exist to synthesize five-membered carbocyclic rings in a single step via annulation. Most of these, like TMM cycloaddition, rely on the generation of a suitable three-atom component for combination with a stable two-atom partner such as an alkene or alkyne. When heated, cyclopropene acetals rearrange to vinylcarbenes, which can serve as the three-atom component in cycloadditions with highly electron-deficient alkenes. Zinc homoenolates can also serve as indirect three-atom components, and undergo cyclization to cyclopentenones in the presence of an unsaturated ester. Tandem intermolecular-intramolecular cyclization of homopropargylic radicals leads to methylenecyclopropanes. | 0 | Theoretical and Fundamental Chemistry |
Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically-conducting phase (typically an external electrical circuit, but not necessarily, as in electroless plating) between electrodes separated by an ionically conducting and electronically insulating electrolyte (or ionic species in a solution).
When a chemical reaction is driven by an electrical potential difference, as in electrolysis, or if a potential difference results from a chemical reaction as in an electric battery or fuel cell, it is called an electrochemical reaction. Unlike in other chemical reactions, in electrochemical reactions electrons are not transferred directly between atoms, ions, or molecules, but via the aforementioned electronically-conducting circuit. This phenomenon is what distinguishes an electrochemical reaction from a conventional chemical reaction. | 0 | Theoretical and Fundamental Chemistry |
Tyrosine phosphorylation sites in growth factor receptors serve two major purposes—to control the state of activity of the kinase and to create binding sites for downstream signal transduction molecules, which in many cases also are substrates for the kinase. The second part of the tyrosine kinase domain in the PDGFβ receptor is phosphorylated at Tyr-857, and mutant receptors carrying phenylalanine at this position have reduced kinase activity. Tyr-857 has therefore been assigned a role in positive regulation of kinase activity. Sites of tyrosine phosphorylation involved in binding signal transduction molecules have been identified in the juxtamembrane domain, the kinase insert, and in the C-terminal tail in the PDGFβ receptor. The phosphorylated tyrosine residue and in general three adjacent C-terminal amino acid residues form specific binding sites for signal transduction molecules. Binding to these sites involves a common conserved stretches, denoted the Src homology (SH) 2 domain and/or Phosphotyrosine Binding Domains (PTB). The specificity of these interactions appears to be very high, since mutant receptors carrying phenylalanine residues in one or several of the different phosphorylation sites generally lack the capacity to bind the targeted signal transduction molecule. The signal transduction molecules are either equipped with different enzymatic activities, or they are adaptor molecules, which in some but not all cases are found in complexes with subunits that carry a catalytic activity. Upon interaction with the activated receptor, the catalytic activities become up-regulated, through tyrosine phosphorylation or other mechanisms, generating a signal that may be unique for each type of signal transduction molecule.
Examination of the different signaling cascades induced by RTKs established Ras/mitogen-activated protein kinase (MAPK), PI-3 kinase, and phospholipase-γ (PLCγ) pathways as key downstream mediators of PDGFR signaling. In addition, reactive oxygen species (ROS)-dependent STAT3 activation has been established to be a key downstream mediator of PDGFR signaling in vascular smooth muscle cells. | 1 | Applied and Interdisciplinary Chemistry |
A colloid has a dispersed phase and a continuous phase, whereas in a solution, the solute and solvent constitute only one phase. A solute in a solution are individual molecules or ions, whereas colloidal particles are bigger. For example, in a solution of salt in water, the sodium chloride (NaCl) crystal dissolves, and the Na and Cl ions are surrounded by water molecules. However, in a colloid such as milk, the colloidal particles are globules of fat, rather than individual fat molecules. Because colloid is multiple phases, it has very different properties compared to fully mixed, continuous solution. | 0 | Theoretical and Fundamental Chemistry |
Some drug classes have been amalgamated from these three principles to meet practical needs. The class of nonsteroidal anti-inflammatory drugs (NSAIDs) is one such example. Strictly speaking, and also historically, the wider class of anti-inflammatory drugs also comprises steroidal anti-inflammatory drugs. These drugs were in fact the predominant anti-inflammatories during the decade leading up to the introduction of the term "nonsteroidal anti-inflammatory drugs." Because of the disastrous reputation that the corticosteroids had got in the 1950s, the new term, which offered to signal that an anti-inflammatory drug was not a steroid, rapidly gained currency. The drug class of "nonsteroidal anti-inflammatory drugs" (NSAIDs) is thus composed by one element ("anti-inflammatory") that designates the mechanism of action, and one element ("nonsteroidal") that separates it from other drugs with that same mechanism of action. Similarly, one might argue that the class of disease-modifying anti-rheumatic drugs (DMARD) is composed by one element ("disease-modifying") that albeit vaguely designates a mechanism of action, and one element ("anti-rheumatic drug") that indicates its therapeutic use.
* Disease-modifying antirheumatic drug (DMARD)
* Nonsteroidal anti-inflammatory drug (NSAID) | 1 | Applied and Interdisciplinary Chemistry |
The IX Brigade, led by Okladnikov, worked in the Greater Balkan region of Turkmenistan, and in the plateau of Krasnovodsk. The finds at the Jebel rock shelter site near the Caspian Sea on the southwestern end of the Uly Balkan massif was a stratigraphic sequence of Mesolithic and Neolithic deposits, considered a model for the Turkmenistan Caspian Mesolithic period.
Two other sites, located in the southern escarpments of the Greater Balkan, were examined in great detail by G. E. Markov of Moscow State University; these were the Mesolithic sites of Dam-Dam Cheshme 1 and 2.
The XIV Brigade occurred in 1952 and researched primitive settled-agriculturalist settlement attributed to the Copper and Bronze periods. | 1 | Applied and Interdisciplinary Chemistry |
The haloacid dehalogenase (HAD) superfamily is a further PP group that uses Asp as a nucleophile and was recently shown to have dual-specificity. These PPs can target both Ser and Tyr, but are thought to have greater specificity towards Tyr. A subfamily of HADs, the Eyes Absent Family (Eya), are also transcription factors and can therefore regulate their own phosphorylation and that of transcriptional cofactor/s, and contribute to the control of gene transcription. The combination of these two functions in Eya reveals a greater complexity of transcriptional gene control than previously thought . A further member of this class is the RNA polymerase II C-terminal domain phosphatase. While this family remains poorly understood, it is known to play important roles in development and nuclear morphology. | 1 | Applied and Interdisciplinary Chemistry |
Benzyl chloroformate is commonly used in organic synthesis for the introduction of the benzyloxycarbonyl (formerly called carboxybenzyl) protecting group for amines. The protecting group is abbreviated Cbz or Z (in honor of discoverer Zervas), hence the alternative shorthand designation for benzyl chloroformate as Cbz-Cl or Z-Cl.
Benzyloxycarbonyl is a key protecting group for amines, suppressing the nucleophilic and basic properties of the N lone pair. This "reactivity masking" property, along with the ability to prevent racemization of Z-protected amines, made the Z group the basis of the Begmann-Zervas synthesis of oligopeptides (1932) where the following general reaction is performed to protect the N-terminus of a serially growing oligopeptide chain:
This reaction was hailed as a "revolution" and essentially started the distinct field of synthetic peptide chemistry. It remained unsurpassed in utility for peptide synthesis until the early 1950s when mixed anhydride and active ester methodologies were developed.
Although the reaction is no longer commonly used for peptides, it is nonetheless very widespread for amine protection in other applications within organic synthesis and total synthesis. Common procedures to achieve protection starting from benzyl chloroformate include:
* Benzyl chloroformate and a base, such as sodium carbonate in water at 0 °C
* Benzyl chloroformate and magnesium oxide in ethyl acetate at 70 °C to reflux
* Benzyl chloroformate, DIPEA, acetonitrile and scandium trifluoromethanesulfonate (Sc(OTf))
Alternatively, the Cbz group can be generated by the reaction of an isocyanate with benzyl alcohol (as in the Curtius rearrangement). | 0 | Theoretical and Fundamental Chemistry |
This concept of clone assumes importance as all the cells that form a clone share common ancestry, which has a very significant consequence: shared genotype.
# One of the most prominent usage is in describing a clone of B cells. The B cells in the body have two important phenotypes (functional forms)—the antibody secreting, terminally differentiated (that is, they cannot divide further) plasma cells, and the memory and the naive cells—both of which retain their proliferative potential.
# Another important area where one can talk of "clones" of cells is neoplasms. Many of the tumors derive from one (sufficiently) mutated cell, so they are technically a single clone of cells. However, during course of cell division, one of the cells can get mutated further and acquire new characteristics to diverge as a new clone. However, this view of cancer onset has been challenged in recent years and many tumors have been argued to have polyclonal origin, i.e. derived from two or more cells or clones, including malignant mesothelioma.
# All the granulosa cells in a Graafian follicle are in fact clones.
# Paroxysmal nocturnal hemoglobinuria is a disorder of bone marrow cells resulting in shortened life of red blood cells, which is also a result of clonal expansion, i.e., all the altered cells are originally derived from a single cell, which also somewhat compromises the functioning of other "normal" bone marrow cells. | 1 | Applied and Interdisciplinary Chemistry |
EmBiology was originally launched as EMBiology in 2005 as a life science bibliographic database in a partnership with Ovid Technologies as a smaller version of Embase. | 1 | Applied and Interdisciplinary Chemistry |
In these glycosides, the aglycone part is a steroid nucleus. These glycosides are found in the plant genera Digitalis, Scilla, and Strophanthus. They are used in the treatment of heart diseases, e.g., congestive heart failure (historically as now recognised does not improve survivability; other agents are now preferred) and arrhythmia. | 0 | Theoretical and Fundamental Chemistry |
The clay hypothesis for the origin of life was proposed by Graham Cairns-Smith in 1985. It postulates that complex organic molecules arose gradually on pre-existing, non-organic replication surfaces of silicate crystals in contact with an aqueous solution. The clay mineral montmorillonite has been shown to catalyze the polymerization of RNA in aqueous solution from nucleotide monomers, and the formation of membranes from lipids. In 1998, Hyman Hartman proposed that "the first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic acid and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hot spring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids." | 0 | Theoretical and Fundamental Chemistry |
The MAP2 family is involved in the development of neurons, mostly present during early stages of axon formation then disappear later. However they exist in mature dendrites as well. Different forms of MAP2s are formed by different post-translational modifications of the mRNA. | 1 | Applied and Interdisciplinary Chemistry |
Homologous recombination is the exchange of genes between two DNA strands that include extensive regions of base sequences that are identical to one another. In eukaryotic species, bacteria, and some viruses, homologous recombination happens spontaneously and is a useful tool in genetically engineered. Homologous recombination, which takes place during meiosis in eukaryotes, is essential for the repair of double-stranded DNA breaks and promotes genetic variation by allowing the movement of genetic information during chromosomal crossing. Homologous recombination, a key DNA repair mechanism in bacteria, enables the insertion of genetic material acquired through horizontal transfer of genes and transformation into DNA. Homologous recombination in viruses influences the course of viral evolution. Homologous recombination, a type of gene targeting used in genetic engineering, involves the introduction of an engineered mutation into a particular gene in order to learn more about the function of that gene. This method involves inserting foreign DNA into a cell that has a sequence similar to the target gene while being flanked by sequences that are the same upstream and downstream of the target gene. The target genes DNA is substituted with the foreign DNA sequence during replication when the cell detects the similar flanking regions as homologues. The target gene is "knocked out" by the exchange. By using this technique to target particular alleles in embryonic stem cells in mice, it is possible to create knockout mice. With the aid of gene targeting, numerous mouse genes have been shut down, leading to the creation of hundreds of distinct mouse models of various human diseases, such as cancer, diabetes, cardiovascular diseases, and neurological disorders. Mario Capecchi, Sir Martin J. Evans, and Oliver Smithies performed groundbreaking research on homologous recombination in mouse stem cells, and they shared the 2007 Nobel Prize in Physiology or Medicine for their findings. Traditionally, homologous recombination was the main method for causing a gene knockout. This method involves creating a DNA construct containing the desired mutation. For knockout purposes, this typically involves a drug resistance marker in place of the desired knockout gene. The construct will also contain a minimum of 2kb of homology to the target sequence. The construct can be delivered to stem cells either through microinjection or electroporation. This method then relies on the cells own repair mechanisms to recombine the DNA construct into the existing DNA. This results in the sequence of the gene being altered, and most cases the gene will be translated into a nonfunctional protein, if it is translated at all. However, this is an inefficient process, as homologous recombination accounts for only 10 to 10 of DNA integrations. Often, the drug selection marker on the construct is used to select for cells in which the recombination event has occurred.
These stem cells now lacking the gene could be used in vivo, for instance in mice, by inserting them into early embryos. If the resulting chimeric mouse contained the genetic change in their germline, this could then be passed on offspring.
In diploid organisms, which contain two alleles for most genes, and may as well contain several related genes that collaborate in the same role, additional rounds of transformation and selection are performed until every targeted gene is knocked out. Selective breeding may be required to produce homozygous knockout animals. | 1 | Applied and Interdisciplinary Chemistry |
Electrode potential and other environmental factors such as temperature, pH and degree of aeration can greatly impact the results off this accelerated stress corrosion cracking test, as can the specimen surface finish and metallurgical condition. | 1 | Applied and Interdisciplinary Chemistry |
AB chromosome translocation analyses place on short arm of chromosome 4 (4S; Simcox and Weber 1985 ). There is close linkage to other genes in the benzoxazinoid synthesis pathway [bx2, bx3, bx4, bx5 Frey et al. 1995, 1997 ). Gene bx1 is 2490 bp from bx2 (Frey et al. 1997 ); between umc123 and agrc94 on 4S (Melanson et al. 1997 ). Mapping probes: SSR p-umc1022 (Sharopova et al. 2002 ); Overgo (physical map probe) PCO06449 (Gardiner et al. 2004 ). | 1 | Applied and Interdisciplinary Chemistry |
Ammonia is explosive when mixed with air (15 – 25%). Other lower azanes can also form explosive mixtures with air. The lighter liquid azanes are highly flammable; this risk increases with the length of the nitrogen chain. One consideration for detection and risk control is that ammonia is lighter than air, creating the possibility of accumulation on ceilings. | 0 | Theoretical and Fundamental Chemistry |
Galactogen is a polysaccharide of galactose that functions as energy storage in pulmonate snails and some Caenogastropoda. This polysaccharide is exclusive of the reproduction and is only found in the albumen gland from the female snail reproductive system and in the perivitelline fluid of eggs. Furthermore, galactogen serves as an energy reserve for developing embryos and hatchlings, which is later replaced by glycogen in juveniles and adults.
Formed by crosslinking polysaccharide-based nanoparticles and functional polymers, galactogens have applications within hydrogel structures. These hydrogel structures can be designed to release particular nanoparticle pharmaceuticals and/or encapsulated therapeutics over time or in response to environmental stimuli.
Galactogens are polysaccharides with binding affinity for bioanalytes. With this, by end-point attaching galactogens to other polysaccharides constituting the surface of medical devices, galactogens have use as a method of capturing bioanalytes (e.g., CTC's), a method for releasing the captured bioanalytes and an analysis method. | 0 | Theoretical and Fundamental Chemistry |
Langmuir is indexed in Chemical Abstracts Service, Scopus, EBSCOhost, British Library, PubMed, Web of Science, and SwetsWise. | 0 | Theoretical and Fundamental Chemistry |
Recent works have shown that plants can respond to airborne sounds at audible frequencies and that they also produce airborne sounds at the ultrasonic range, presumably audible to multiple organisms including bats, mice, moths and other insects. | 1 | Applied and Interdisciplinary Chemistry |
Cancer cells lack or have reduced ferrochelatase activity and this results in accumulation of Protoporphyrin IX, a fluorescent substance that can easily be visualized. | 1 | Applied and Interdisciplinary Chemistry |
Fas ligand has been shown to interact with:
* CASP8,
* EZR,
* FADD,
* FNBP1,
* FYN,
* FAS,
* Grb2,
* PACSIN2, and
* TNFRSF6B. | 1 | Applied and Interdisciplinary Chemistry |
Lamb and Batchelor define the stream function as follows.
Using the expression derived above for the total volumetric flux, , this can be written as
In words, the stream function is the volumetric flux through the test surface per unit thickness, where thickness is measured perpendicular to the plane of flow.
The point is a reference point that defines where the stream function is identically zero. Its position is chosen more or less arbitrarily and, once chosen, typically remains fixed.
An infinitesimal shift in the position of point results in the following change of the stream function:
From the exact differential
so the flow velocity components in relation to the stream function must be
Notice that the stream function is linear in the velocity. Consequently if two incompressible flow fields are superimposed, then the stream function of the resultant flow field is the algebraic sum of the stream functions of the two original fields. | 1 | Applied and Interdisciplinary Chemistry |
Single 20 to 40mg oral doses generally give rise to peak plasma esomeprazole concentrations of 0.5-1.0mg/L within 1–4 hours, but after several days of once-daily administration, these levels may increase by about 50%. A 30-minute intravenous infusion of a similar dose usually produces peak plasma levels on the order of 1–3mg/L. The drug is rapidly cleared from the body, largely by urinary excretion of pharmacologically inactive metabolites such as 5-hydroxymethylesomeprazole and 5-carboxyesomeprazole. Esomeprazole and its metabolites are analytically indistinguishable from omeprazole and the corresponding omeprazole metabolites unless chiral techniques are employed. | 0 | Theoretical and Fundamental Chemistry |
Multiscale turbulence is a class of turbulent flows in which the chaotic motion of the fluid is forced at different length and/or time scales. This is usually achieved by immersing in a moving fluid a body with a multiscale, often fractal-like, arrangement of length scales. This arrangement of scales can be either passive or active
As turbulent flows contain eddies with a wide range of scales, exciting the turbulence at particular scales (or range of scales) allows one to fine-tune the properties of that flow. Multiscale turbulent flows have been successfully applied in different fields., such as:
* Reducing acoustic noise from wings by modifying the geometry of spoilers;
* Enhancing heat transfer from impinging jets passing through grids;
* Reducing the vortex shedding intensity of flows past normal plates without changing the shedding frequency;
* Enhancing mixing by energy-efficient stirring;
* Improving flow metering and flow conditioning in pipes;
* Improving combustion.
Multiscale turbulence has also played an important role into probing the internal structure of turbulence. This sort of turbulence allowed researchers to unveil a novel dissipation law in which the parameter in
is not constant, as required by the Richardson-Kolmogorov energy cascade. This new law can be expressed as , with , where and are Reynolds numbers based, respectively, on initial/global conditions (such as free-stream velocity and the object's length scale) and local conditions (such as the rms velocity and integral length scale). This new dissipation law characterises non-equilibrium turbulence apparently universally in various flows (not just multiscale turbulence) and results from non-equilibrium unsteady energy cascade. This imbalance implies that new mean flow scalings exist for free shear turbulent flows, as already observed in axisymmetric wakes | 1 | Applied and Interdisciplinary Chemistry |
The acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction; the pK value is directly proportional to the standard Gibbs free energy change for the reaction. The value of the pK changes with temperature and can be understood qualitatively based on Le Châteliers principle: when the reaction is endothermic, K increases and pK' decreases with increasing temperature; the opposite is true for exothermic reactions.
The value of pK also depends on molecular structure of the acid in many ways. For example, Pauling proposed two rules: one for successive pK of polyprotic acids (see Polyprotic acids below), and one to estimate the pK of oxyacids based on the number of =O and −OH groups (see Factors that affect pK values below). Other structural factors that influence the magnitude of the acid dissociation constant include inductive effects, mesomeric effects, and hydrogen bonding. Hammett type equations have frequently been applied to the estimation of pK.
The quantitative behaviour of acids and bases in solution can be understood only if their pK values are known. In particular, the pH of a solution can be predicted when the analytical concentration and pK values of all acids and bases are known; conversely, it is possible to calculate the equilibrium concentration of the acids and bases in solution when the pH is known. These calculations find application in many different areas of chemistry, biology, medicine, and geology. For example, many compounds used for medication are weak acids or bases, and a knowledge of the pK values, together with the octanol-water partition coefficient, can be used for estimating the extent to which the compound enters the blood stream. Acid dissociation constants are also essential in aquatic chemistry and chemical oceanography, where the acidity of water plays a fundamental role. In living organisms, acid–base homeostasis and enzyme kinetics are dependent on the pK values of the many acids and bases present in the cell and in the body. In chemistry, a knowledge of pK values is necessary for the preparation of buffer solutions and is also a prerequisite for a quantitative understanding of the interaction between acids or bases and metal ions to form complexes. Experimentally, pK values can be determined by potentiometric (pH) titration, but for values of pK less than about 2 or more than about 11, spectrophotometric or NMR measurements may be required due to practical difficulties with pH measurements. | 0 | Theoretical and Fundamental Chemistry |
Unsaturated fluorocarbons are far more reactive than fluoroalkanes. Although difluoroacetylene is unstable (as is typical for related alkynes, see dichloroacetylene), hexafluoro-2-butyne and related fluorinated alkynes are well known. | 1 | Applied and Interdisciplinary Chemistry |
A general [p+q]-cycloaddition is a concerted addition reaction between two components, one with p π-electrons, and one with q π-electrons. This reaction is symmetry allowed under the following conditions:
* For a supra/supra or antara/antara cycloaddition, it is thermally allowed if p + q = 4n + 2 and photochemically allowed if p + q = 4n
* For a supra/antara cycloaddition, it is thermally allowed if p + q = 4n and photochemically allowed if p + q = 4n + 2
This is summarized in the following table: | 0 | Theoretical and Fundamental Chemistry |
A heterocyclic compound is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Cyclic compounds that have both carbon and non-carbon atoms present are heterocyclic carbon compounds, and the name refers to inorganic cyclic compounds as well (e.g., siloxanes, which contain only silicon and oxygen in the rings, and borazines, which contain only boron and nitrogen in the rings). Hantzsch–Widman nomenclature is recommended by the IUPAC for naming heterocycles, but many common names remain in regular use. | 0 | Theoretical and Fundamental Chemistry |
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