text stringlengths 105 4.57k | label int64 0 1 | label_text stringclasses 2
values |
|---|---|---|
*Hattori, K. (1993). High-sulfur magma, a product of fluid discharge from underlying mafic magma: evidence from Mount Pinatubo, Philippines. Geology, 21(12), 1083–1086.
*Hattori, K. H., & Keith, J. D. (2001). Contribution of mafic melt to porphyry copper mineralization: evidence from Mount Pinatubo, Philippines, and Bingham Canyon, Utah, USA. Mineralium Deposita, 36, 799–806.
*Hattori, K. H., & Guillot, S. (2003, April). Volcanic fronts as a consequence of serpentinite dehydration in the mantle wedge. In EGS-AGU-EUG Joint Assembly.
*Takahashi, Y., Minamikawa, R., Hattori, K. H., Kurishima, K., Kihou, N., & Yuita, K. (2004). Arsenic behavior in paddy fields during the cycle of flooded and non-flooded periods. Environmental Science & Technology, 38(4), 1038–1044.
*Guillot, S., Hattori, K., 2013. Serpentinites: Essential roles in geodynamics, arc volcanism, sustainable development, and the origin of life. Elements, 9 (2),. 95-98. Doi: 10.2113/gselements.9.2.25
*Hattori, K. H., & Guillot, S. (2003l). Volcanic fronts as a consequence of serpentinite dehydration in the mantle wedge.Geology, 31 (6), 525-528.
*Hattori, K., Takahashi, Y., Guillot, S., & Johanson, B. (2005). Occurrence of arsenic (V) in forearc mantle serpentinites based on X-ray absorption spectroscopy study. Geochimica et Cosmochimica Acta, 69(23), 5585–5596.
*Pagé, L., & Hattori, K. (2017). Tracing halogen and B cycling in subduction zones based on obducted, subducted and forearc serpentinites of the Dominican Republic. Scientific Reports, 7(1), 17776. | 0 | Theoretical and Fundamental Chemistry |
The flux control summation theorem was discovered independently by the Kacser/Burns group and the Heinrich/Rapoport group in the early 1970s and late 1960s. The flux control summation theorem implies that metabolic fluxes are systemic properties and that their control is shared by all reactions in the system. When a single reaction changes its control of the flux this is compensated by changes in the control of the same flux by all other reactions. | 1 | Applied and Interdisciplinary Chemistry |
A governing equation which describes the atom concentration evolution throughout some interconnect segment, is the conventional mass balance (continuity) equation
where is the atom concentration at the point with a coordinates at the moment of time , and is the total atomic flux at this location. The total atomic flux is a combination of the fluxes caused by the different atom migration forces. The major forces are induced by the electric current, and by the gradients of temperature, mechanical stress and concentration. .
To define the fluxes mentioned above:
Here is the electron charge, is the effective charge of the migrating atom, the resistivity of the conductor where atom migration takes place, is the local current density, is the Boltzmann constant, is the absolute temperature. is the time and position dependent atom diffusivity.
: .  We use the heat of thermal diffusion.
here is the atomic volume and is initial atomic concentration, is the hydrostatic stress and are the components of principal stress.
Assuming a vacancy mechanism for atom diffusion we can express <math>
D where is the effective activation energy of the thermal diffusion of metal atoms. The vacancy concentration represents availability of empty lattice sites, which might be occupied by a migrating atom. | 0 | Theoretical and Fundamental Chemistry |
An internal control region is a sequence of DNA located with the coding region of eukaryotic genes that binds regulatory elements such as activators or repressors. This region can recruit RNA Polymerase or contribute to splicing. | 1 | Applied and Interdisciplinary Chemistry |
To effect dual activation by a single metal, the same metal species that activates the enolate also interacts with the alkyne. Though the precise mechanisms are poorly understood and likely vary from case to case, metals such as In, Zn, Fe, and Cu are proposed to operate via this mode. One reaction system thought to proceed via one-metal dual activation is that developed by Shaw et al. in 2014. Using a catalytic Fe(III)-(Salen) complex, Shaw and coworkers were able to access chiral cyclopentanes from an array of alkynyl-tethered β-ketoesters and analogs thereof. The reaction tolerated a wide range of ketones (phenyl, homoallyl, cyclopropyl, 2-furyl, etc.), esters (ethyl, tert-butyl, etc.), and ester analogs (nitro, , cyano, sulfonyl, etc.). | 0 | Theoretical and Fundamental Chemistry |
Knockouts are accomplished through a variety of techniques. Originally, naturally occurring mutations were identified and then gene loss or inactivation had to be established by DNA sequencing or other methods. | 1 | Applied and Interdisciplinary Chemistry |
Gold cyanidation (also known as the cyanide process or the MacArthur–Forrest process) is a hydrometallurgical technique for extracting gold from low-grade ore by converting the gold to a water-soluble coordination complex. It is the most commonly used leaching process for gold extraction. Cyanidation is also widely used in the extraction of silver, usually after froth flotation.
Production of reagents for mineral processing to recover gold represents more than 70% of cyanide consumption globally. Other metals are recovered from the process include copper, zinc, and silver, but gold is the main driver of this technology. Due to the highly poisonous nature of cyanide, the process is controversial and its use is even banned in some parts of the world. Cyanide can be safely used in the gold mining industry. A key feature for safe use of cyanide is to ensure adequate pH control at an alkaline pH level above 10.5. At industrial scale, pH control is mainly achieved using lime, as an important enabling reagent in gold processing. | 1 | Applied and Interdisciplinary Chemistry |
The absorbance of an object quantifies how much of the incident light is absorbed by it (instead of being reflected or refracted). This may be related to other properties of the object through the Beer–Lambert law.
Precise measurements of the absorbance at many wavelengths allow the identification of a substance via absorption spectroscopy, where a sample is illuminated from one side, and the intensity of the light that exits from the sample in every direction is measured. A few examples of absorption are ultraviolet–visible spectroscopy, infrared spectroscopy, and X-ray absorption spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
Green roofs can be categorized as intensive, semi-intensive, or extensive, depending on the depth of planting medium and the amount of maintenance they need. Extensive green roofs traditionally support of vegetation while intensive roofs support of vegetation. Traditional roof gardens, which require a reasonable depth of soil to grow large plants or conventional lawns, are considered intensive because they are labour-intensive, requiring irrigation, feeding, and other maintenance. Intensive roofs are more park-like with easy access and may include anything from kitchen herbs to shrubs and small trees.
Extensive green roofs, by contrast, are designed to be virtually self-sustaining and should require only a minimum of maintenance, perhaps a once-yearly weeding or an application of slow-release fertiliser to boost growth. Extensive roofs are usually only accessed for maintenance. They can be established on a very thin layer of soil (most use specially formulated composts): even a thin layer of rockwool laid directly onto a watertight roof can support a planting of Sedum species and mosses. Some green roof designs incorporate both intensive and extensive elements. To protect the roof, a waterproofing membrane is often used, which is manufactured to remain watertight in extreme conditions including constant dampness, ponding water, high and low alkaline conditions and exposure to plant roots, fungi and bacterial organisms.
Advances in green roof technology have led to the development of new systems that do not fit into the traditional classification of green roof types. Comprehensive green roofs bring the most advantageous qualities of extensive and intensive green roofs together. Comprehensive green roofs support plant varieties typically seen in intensive green roofs at the depth and weight of an extensive green roof system.
Another important distinction is between pitched green roofs and flat green roofs. Pitched sod roofs, a traditional feature of many Scandinavian buildings, tend to be of a simpler design than flat green roofs. This is because the pitch of the roof reduces the risk of water penetrating through the roof structure, allowing the use of fewer waterproofing and drainage layers. | 1 | Applied and Interdisciplinary Chemistry |
A real polymer is not freely-jointed. A -C-C- single bond has a fixed tetrahedral angle of 109.5 degrees. The value of L is well-defined for, say, a fully extended polyethylene or nylon, but it is less than N x l because of the zig-zag backbone. There is, however, free rotation about many chain bonds. The model above can be enhanced. A longer, "effective" unit length can be defined such that the chain can be regarded as freely-jointed, along with a smaller N, such that the constraint L = N x l is still obeyed. It, too, gives a Gaussian distribution. However, specific cases can also be precisely calculated. The average end-to-end distance for freely-rotating (not freely-jointed) polymethylene (polyethylene with each -C-C- considered as a subunit) is l times the square root of 2N, an increase by a factor of about 1.4. Unlike the zero volume assumed in a random walk calculation, all real polymers' segments occupy space because of the van der Waals radii of their atoms, including bulky substituent groups that interfere with bond rotations. This can also be taken into account in calculations. All such effects increase the mean end-to-end distance.
Because their polymerization is stochastically driven, chain lengths in any real population of synthetic polymers will obey a statistical distribution. In that case, we should take N to be an average value. Also, many polymers have random branching.
Even with corrections for local constraints, the random walk model ignores steric interference between chains, and between distal parts of the same chain. A chain often cannot move from a given conformation to a closely related one by a small displacement because one part of it would have to pass through another part, or through a neighbor. We may still hope that the ideal-chain, random-coil model will be at least a qualitative indication of the shapes and dimensions of real polymers in solution, and in the amorphous state, as long as there are only weak physicochemical interactions between the monomers. This model, and the Flory-Huggins Solution Theory, for which Paul Flory received the Nobel Prize in Chemistry in 1974, ostensibly apply only to ideal, dilute solutions. But there is reason to believe (e.g., neutron diffraction studies) that excluded volume effects may cancel out, so that, under certain conditions, chain dimensions in amorphous polymers have approximately the ideal, calculated size
When separate chains interact cooperatively, as in forming crystalline regions in solid thermoplastics, a different mathematical approach must be used.
Stiffer polymers such as helical polypeptides, Kevlar, and double-stranded DNA can be treated by the worm-like chain model.
Even copolymers with monomers of unequal length will distribute in random coils if the subunits lack any specific interactions. The parts of branched polymers may also assume random coils.
Below their melting temperatures, most thermoplastic polymers (polyethylene, nylon, etc.) have amorphous regions in which the chains approximate random coils, alternating with regions that are crystalline. The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity.
More complex polymers such as proteins, with various interacting chemical groups attached to their backbones, self-assemble into well-defined structures. But segments of proteins, and polypeptides that lack secondary structure, are often assumed to exhibit a random-coil conformation in which the only fixed relationship is the joining of adjacent amino acid residues by a peptide bond. This is not actually the case, since the ensemble will be energy weighted due to interactions between amino acid side-chains, with lower-energy conformations being present more frequently. In addition, even arbitrary sequences of amino acids tend to exhibit some hydrogen bonding and secondary structure. For this reason, the term "statistical coil" is occasionally preferred. The conformational entropy of the random-coil stabilizes the unfolded protein state and represents main free energy contribution that opposes to protein folding. | 0 | Theoretical and Fundamental Chemistry |
Carbomethoxymethylenetriphenylphosphorane reacts with aldehydes to give a two carbon atom extension. The carbomethoxymethylene group replaces the oxygen of the aldehyde to give a trans- double bond. | 0 | Theoretical and Fundamental Chemistry |
Substitution, nucleophilic bimolecular reactions are concerted reactions where both the nucleophile and substrate are involved in the rate limiting step. Since this reaction is concerted, the reaction occurs in one step, where the bonds are broken, while new bonds are formed. Therefore, to interpret this reaction, it is important to look at the transition state, which resembles the concerted rate limiting step. In the "Depiction of S2 Reaction" figure, the nucleophile forms a new bond to the carbon, while the halide (L) bond is broken. | 0 | Theoretical and Fundamental Chemistry |
The competition method may be used when a stability constant value is too large to be determined by a direct method. It was first used by Schwarzenbach in the determination of the stability constants of complexes of EDTA with metal ions.
For simplicity consider the determination of the stability constant of a binary complex, AB, of a reagent A with another reagent B.
where the [X] represents the concentration, at equilibrium, of a species X in a solution of given composition.
A ligand C is chosen which forms a weaker complex with A The stability constant, K, is small enough to be determined by a direct method. For example, in the case of EDTA complexes A is a metal ion and C may be a polyamine such as diethylenetriamine.
The stability constant, K for the competition reaction
can be expressed as
It follows that
where K is the stability constant for the competition reaction. Thus, the value of the stability constant may be derived from the experimentally determined values of K and . | 0 | Theoretical and Fundamental Chemistry |
Because it contains free iodine, Lugol's solution at 2% or 5% concentration without dilution is irritating and destructive to mucosa, such as the lining of the esophagus and stomach. Doses of 10 mL of undiluted 5% solution have been reported to cause gastric lesions when used in endoscopy. The LD50 for 5% Iodine is 14,000 mg/kg (14 g/kg) in rats, and 22,000 mg/kg (22 g/kg) in mice.
The World Health Organization classifies substances taken orally with an LD50 of 5–50 mg/kg as the second highest toxicity class, Class Ib (Highly Hazardous). The Global Harmonized System of Classification and Labeling of Chemicals categorizes this as Category 2 with a hazard statement "Fatal if swallowed". Potassium iodide is not considered hazardous. | 0 | Theoretical and Fundamental Chemistry |
TFIIB is a single 33kDa polypeptide consisting of 316 amino acids. TFIIB is made up of four functional regions: the C-terminal core domain; the B linker; the B reader and the amino terminal zinc ribbon.
TFIIB makes protein-protein interactions with the TATA-binding protein (TBP) subunit of transcription factor IID, and the RPB1 subunit of RNA polymerase II.
TFIIB makes sequence-specific protein-DNA interactions with the B recognition element (BRE), a promoter element flanking the TATA element. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, Howarth–Dorodnitsyn transformation (or Dorodnitsyn-Howarth transformation) is a density-weighted coordinate transformation, which reduces variable-density flow conservation equations to simpler form (in most cases, to incompressible form). The transformation was first used by Anatoly Dorodnitsyn in 1942 and later by Leslie Howarth in 1948. The transformation of coordinate (usually taken as the coordinate normal to the predominant flow direction) to is given by
where is the density and is the density at infinity. The transformation is extensively used in boundary layer theory and other gas dynamics problems. | 1 | Applied and Interdisciplinary Chemistry |
:Direct methods in crystallography are a collection of mathematical techniques that seek to determine crystal structure based on measurements of diffraction patterns and potentially other a priori knowledge (constraints). The central challenge of inverting measured diffraction intensities (i.e. applying an inverse Fourier Transform) to determine the original crystal potential is that phase information is lost in general since intensity is a measurement of the square of the modulus of the amplitude of any given diffracted beam. This is known as the phase problem of crystallography.
:If the diffraction can be considered kinematical, constraints may be used to probabilistically relate the phases of the reflections to their amplitudes, and the original structure can be solved via direct methods (see Sayre equation as an example). Kinematical diffraction is often the case in x-ray diffraction, and is one of the primary reasons that technique has been so successful at solving crystal structures. However, in electron diffraction, the probing wave interacts much more strongly with the electrostatic crystal potential, and complex dynamical diffraction effects can dominate the measured diffraction patterns. This makes application of direct methods much more challenging without a priori knowledge of the structure in question. | 0 | Theoretical and Fundamental Chemistry |
In continuum mechanics, the material derivative describes the time rate of change of some physical quantity (like heat or momentum) of a material element that is subjected to a space-and-time-dependent macroscopic velocity field. The material derivative can serve as a link between Eulerian and Lagrangian descriptions of continuum deformation.
For example, in fluid dynamics, the velocity field is the flow velocity, and the quantity of interest might be the temperature of the fluid. In which case, the material derivative then describes the temperature change of a certain fluid parcel with time, as it flows along its pathline (trajectory). | 1 | Applied and Interdisciplinary Chemistry |
This style is traditional to suburbs of Philadelphia, Pennsylvania, including Chester, Bucks, and Montgomery Counties. The amount of the required offset is divided evenly between the hinge and the pintle. | 1 | Applied and Interdisciplinary Chemistry |
The string-net model is claimed to show the derivation of photons, electrons, and U(1) gauge charge, small (relative to the Planck mass) but nonzero masses, and suggestions that the leptons, quarks, and gluons can be modeled in the same way. In other words, string-net condensation provides a unified origin for photons and electrons (or gauge bosons and fermions). It can be viewed as an origin of light and electron (or gauge interactions and Fermi statistics).
However, their model does not account for the chiral coupling between the fermions and the SU(2) gauge bosons in the standard model.
For strings labeled by the positive integers, string-nets are the spin networks studied in loop quantum gravity. This has led to the proposal by Levin and Wen, and Smolin, Markopoulou and Konopka that loop quantum gravitys spin networks can give rise to the standard model of particle physics through this mechanism, along with fermi statistics and gauge interactions. To date, a rigorous derivation from LQGs spin networks to Levin and Wen's spin lattice has yet to be done, but the project to do so is called quantum graphity, and in a more recent paper, Tomasz Konopka, Fotini Markopoulou, Simone Severini argued that there are some similarities to spin networks (but not necessarily an exact equivalence) that gives rise to U(1) gauge charge and electrons in the string net mechanism.
Herbertsmithite may be an example of string-net matter. | 0 | Theoretical and Fundamental Chemistry |
A DTA curve can be used only as a finger print for identification purposes but usually the applications of this method are the determination of phase diagrams, heat change measurements and decomposition in various atmospheres.
DTA is widely used in the pharmaceutical and food industries.
DTA may be used in cement chemistry, mineralogical research and in environmental studies.
DTA curves may also be used to date bone remains or to study archaeological materials.
Using DTA one can obtain liquidus & solidus lines of phase diagrams. | 0 | Theoretical and Fundamental Chemistry |
Flow rate of the liquid phase and molar fractions of the desired compound in it are and .
Flow rate of the vapour phase and molar fractions of the desired compound in it are and . | 0 | Theoretical and Fundamental Chemistry |
Isostructural chemical compounds have similar chemical structures. "Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous substances crystallise in the same space group and have the same unit cell dimensions. The IUCR definition used by crystallographers is:
Examples include:
*I-Gold(I) bromide is isostructural with gold(I) chloride
*Borazine is isostructural with benzene
*Indium(I) bromide is isostructural with β-thallium(I) iodide and has a distorted rock salt structure.
Many minerals are isostructural when they differ only in the nature of a cation.
Compounds which are isoelectronic usually have similar chemical structures. For example, methane, CH, and the ammonium ion, NH, are isoelectric and are isostructural
as both have a tetrahedral structure. The C-H and N-H bond lengths are different and crystal structures are completely different because the ammonium ion only occurs in salts. | 0 | Theoretical and Fundamental Chemistry |
An instance where hyperconjugation may be overlooked as a possible chemical explanation is in rationalizing the rotational barrier of ethane (CH). It had been accepted as early as the 1930s that the staggered conformations of ethane were more stable than the eclipsed conformation. Wilson had proven that the energy barrier between any pair of eclipsed and staggered conformations is approximately 3 kcal/mol, and the generally accepted rationale for this was the unfavorable steric interactions between hydrogen atoms.
In their 2001 paper, however, Pophristic and Goodman revealed that this explanation may be too simplistic. Goodman focused on three principal physical factors: hyperconjugative interactions, exchange repulsion defined by the Pauli exclusion principle, and electrostatic interactions (Coulomb interactions). By comparing a traditional ethane molecule and a hypothetical ethane molecule with all exchange repulsions removed, potential curves were prepared by plotting torsional angle versus energy for each molecule. The analysis of the curves determined that the staggered conformation had no connection to the amount of electrostatic repulsions within the molecule. These results demonstrate that Coulombic forces do not explain the favored staggered conformations, despite the fact that central bond stretching decreases electrostatic interactions.
Goodman also conducted studies to determine the contribution of vicinal (between two methyl groups) vs. geminal (between the atoms in a single methyl group) interactions to hyperconjugation. In separate experiments, the geminal and vicinal interactions were removed, and the most stable conformer for each interaction was deduced.
From these experiments, it can be concluded that hyperconjugative effects delocalize charge and stabilize the molecule. Further, it is the vicinal hyperconjugative effects that keep the molecule in the staggered conformation. Thanks to this work, the following model of the stabilization of the staggered conformation of ethane is now more accepted:
Hyperconjugation can also explain several other phenomena whose explanations may also not be as intuitive as that for the rotational barrier of ethane.
The matter of the rotational barrier of ethane is not settled within the scientific community. An analysis within quantitative molecular orbital theory shows that 2-orbital-4-electron (steric) repulsions are dominant over hyperconjugation. A valence bond theory study also emphasizes the importance of steric effects. | 0 | Theoretical and Fundamental Chemistry |
Oxoammonium cations are isoelectronic with carbonyls and structurally related to aldoximes (hydroxylamines), and aminoxyl (nitroxide) radicals, with which they can interconvert via a series of redox steps. According to X-ray crystallography, the N–O distance in [TEMPO]BF is 1.184 Å, 0.1 Å shorter than the N–O distance of 1.284 Å in the charge-neutral TEMPO. Similarly, the N in [TEMPO] is nearly planar, but the O moves 0.1765 Å out of the plane in the neutral TEMPO.
The N-oxoammonium salts are used for oxidation of alcohols to carbonyl groups, as well as other forms of oxoammonium-catalyzed oxidations. The nitroxyl TEMPO reacts via its N-oxoammonium salt. | 0 | Theoretical and Fundamental Chemistry |
The mouse sperm genome is 80–90% methylated at its CpG sites in DNA, amounting to about 20 million methylated sites. After fertilization, early in the first day of embryogenesis, the paternal chromosomes are almost completely demethylated in six hours by an active TET-dependent process, before DNA replication begins (blue line in Figure).
Demethylation of the maternal genome occurs by a different process. In the mature oocyte, about 40% of its CpG sites in DNA are methylated. In the pre-implantation embryo up to the blastocyst stage (see Figure), the only methyltransferase present is an isoform of DNMT1 designated DNMT1o. It appears that demethylation of the maternal chromosomes largely takes place by blockage of the methylating enzyme DNMT1o from entering the nucleus except briefly at the 8 cell stage (see DNA demethylation). The maternal-origin DNA thus undergoes passive demethylation by dilution of the methylated maternal DNA during replication (red line in Figure). The morula (at the 16 cell stage), has only a small amount of DNA methylation (black line in Figure). | 1 | Applied and Interdisciplinary Chemistry |
It is still not fully understood how salts are transported from the ocean and oxidized to become reactive halogen species in the air. Other halogens (chlorine and iodine) are also activated through mechanisms coupled to bromine chemistry. The main consequence of halogen activation is chemical destruction of ozone, which removes the primary precursor of atmospheric oxidation, and generation of reactive halogen atoms/oxides that become the primary oxidizing species. The oxidation ability originally influenced by ozone is weakened, while the halogen species now holds the oxidation ability. This changes the reaction cycles and final products of many atmospheric reactions. During ozone depletion events, the enhanced halogen chemistry can effectively oxidize reactive gaseous elements. | 1 | Applied and Interdisciplinary Chemistry |
Based on current evidence, the term of endothelium-derived hyperpolarising factor should represent a mechanism rather than a specific factor. The mechanism(s) of endothelium-dependent hyperpolarization (i.e., EDHF-mediated relaxation) seems to be heterogeneous depending on several factors (e.g., size and vascular bed), surrounding environment (oxidative stress, hypercholesterolemia) and demand (compensatory). Different endothelial mediators or pathways involved in EDHF-mediated relaxation may also work simultaneously and/or substitute each other. It implies a reasonable physiological sense, although to some extent and when EDHF acts as backup mechanism for endothelium-dependent relaxation in the present of compromised NO contribution. Thus, alternatives for EDHF-typed responses (HO, K etc.) will provide a guarantee for compensation of endothelial function. However, once the involvement of a certain endothelium-derived vasodilator for a given vascular bed is confirmed, it is preferred that they be described by their proper name (i.e., endothelium-derived HO, or CNP), and no longer be termed as “EDHF”. Although the role of EDHF in the genesis of Cardiovascular Disease remains to be further elucidated, the EDHF contribution and its importance at the level of small arteries delivers a theoretical opportunity to control systemic blood pressure. There is an increasing experimental evidence to suggest that treatment of the EDHF system could provide a means to control blood pressure and blood flow to target organs in compatible way achieved by manipulations of NO system.
Since “EDHF story” is particularly heterogeneous and based mainly on animal studies, the most important and demanding current task is to strengthen our knowledge about EDHF action in human arteries in health and disease. | 1 | Applied and Interdisciplinary Chemistry |
Conventional sewage treatment utilises bioreactors to undertake the main purification processes. In some of these systems, a chemically inert medium with very high surface area is provided as a substrate for the growth of biological film. Separation of excess biological film takes place in settling tanks or cyclones. In other systems aerators supply oxygen to the sewage and biota to create activated sludge in which the biological component is freely mixed in the liquor in "flocs". In these processes, the liquid's biochemical oxygen demand (BOD) is reduced sufficiently to render the contaminated water fit for reuse. The biosolids can be collected for further processing, or dried and used as fertilizer. An extremely simple version of a sewage bioreactor is a septic tank whereby the sewage is left in situ, with or without additional media to house bacteria. In this instance, the biosludge itself is the primary host for the bacteria. | 1 | Applied and Interdisciplinary Chemistry |
Bromothymol blue acts as a weak acid in a solution. It can thus be in protonated or deprotonated form, appearing yellow or blue, respectively. It is bright aquamarine by itself, and greenish-blue in a neutral solution. The deprotonation of the neutral form results in a highly conjugated structure, accounting for the difference in color. An intermediate of the deprotonation mechanism is responsible for the greenish color in neutral solution.
The protonated form of bromothymol blue has its peak absorption at 427 nm thus transmitting yellow light in acidic solutions, and the deprotonated form has its peak absorption at 602 nm thus transmitting blue light in more basic solutions. Highly acidic Bromothymol blue is magenta in color.
The general carbon skeleton of bromothymol blue is common to many indicators including chlorophenol red, thymol blue, and bromocresol green.
The presence of one moderate electron-withdrawing group (bromine atom) and two moderate donating groups (alkyl substituents) are responsible for bromothymol blues active indication range from a pH of 6.0 to 7.6. While the conjugation is responsible for the length and nature of the color change range, these substituent groups are ultimately responsible for the indicators active range.
Bromothymol blue is sparingly soluble in oil, but soluble in water, ether, and aqueous solutions of alkalis. It is less soluble in nonpolar solvents such as benzene, toluene, and xylene, and practically insoluble in petroleum ether. | 0 | Theoretical and Fundamental Chemistry |
In 1971, Eric Wood implemented the first cured-in-place pipe technology in London, England. He called the CIPP process insitu form, derived from the Latin meaning "form in place". Wood applied for U.S. patent no. 4009063 on January 29, 1975. The patent was granted February 22, 1977, and was commercialized by Insituform Technologies until it entered the public domain on February 22, 1994. | 1 | Applied and Interdisciplinary Chemistry |
Germanenes electronic and optical properties have been determined from ab initio' calculations, and structural and electronic properties from first principles. These properties make the material suitable for use in the channel of a high-performance field-effect transistor and have generated discussion regarding the use of elemental monolayers in other electronic devices. The electronic properties of germanene are unusual, and provide a rare opportunity to test the properties of Dirac fermions. Germanene has no band gap, but attaching a hydrogen atom to each germanium atom creates one. These unusual properties are generally shared by graphene, silicene, germanene, stanene, and plumbene. | 0 | Theoretical and Fundamental Chemistry |
A record-long of human transplant organ preservation with machine perfusion of a liver for 3 days rather than usually <12 hours was reported in 2022. It could possibly be extended to 10 days and prevent substantial cell damage by low temperature preservation methods. Alternative approaches include novel cryoprotectant solvents.
There is a novel organ perfusion system under development that can restore, i.e. on the cellular level, multiple vital (pig) organs one hour after death (during which the body had a prolonged warm ischaemia), and a similar method/system for reviving (pig) brains hours after death. The system for cellular recovery could be used to preserve donor organs or for revival-treatments in medical emergencies. | 1 | Applied and Interdisciplinary Chemistry |
Domain walls are spatially extended regions of transition mediating the transfer of the order parameter from one domain to another. In comparison to the domains the domain walls are not homogeneous and they can have a lower symmetry. This may modify the properties of a multiferroic and the coupling of its order parameters. Multiferroic domain walls may display particular static and dynamic properties.
Static properties refer to stationary walls. They can result from
*The reduced dimensionality
*The finite width of the wall
*The different symmetry of the wall
*The inherent chemical, electronic, or order-parameter inhomogeneity within the walls and the resulting gradient effects. | 0 | Theoretical and Fundamental Chemistry |
Omega-alicyclic fatty acids typically contain an omega-terminal propyl or butyryl cyclic group and are some of the major membrane fatty acids found in several species of bacteria. The fatty acid synthetase used to produce omega-alicyclic fatty acids is also used to produce membrane branched-chain fatty acids. In bacteria with membranes composed mainly of omega-alicyclic fatty acids, the supply of cyclic carboxylic acid-CoA esters is much greater than that of branched-chain primers. The synthesis of cyclic primers is not well understood but it has been suggested that mechanism involves the conversion of sugars to shikimic acid which is then converted to cyclohexylcarboxylic acid-CoA esters that serve as primers for omega-alicyclic fatty acid synthesis | 1 | Applied and Interdisciplinary Chemistry |
Brown dwarfs have greater internal heating than gas giants but not as great as stars. The internal heating within brown dwarfs (initially generated by gravitational contraction) is great enough to ignite and sustain fusion of deuterium with hydrogen to helium; for the largest brown dwarfs, it is also enough to ignite and sustain fusion of lithium with hydrogen, but not fusion of hydrogen with itself. Like gas giants, brown dwarfs can have weather and wind powered by internal heating. Brown dwarfs are substellar objects not massive enough to sustain hydrogen-1 fusion reactions in their cores, unlike main-sequence stars. Brown dwarfs occupy the mass range between the heaviest gas giants and the lightest stars, with an upper limit around 75 to 80 Jupiter masses (MJ). Brown dwarfs heavier than about 13 MJ are thought to fuse deuterium and those above ~65 MJ, fuse lithium as well. | 0 | Theoretical and Fundamental Chemistry |
The Graduate Institute of Ferrous Technology has nine laboratories with key areas of expertise:
* [https://web.archive.org/web/20110728031933/http://www.postech.ac.kr/mse/axal/ Alternative Technology Lab]:
**Continuous casting-related innovation
**Texture control
**Alternative alloying and processing
* [https://web.archive.org/web/20100325004541/http://controllab.postech.ac.kr/ Control and Automation Lab]:
**Computer control system
**Process automation
**Control theory & Applications
**Measurement
* [http://gift.webteem.co.kr/jdboard/club/main.php?page=club&code=csl&group_a=csl Clean Steel Lab]:
**Thermochemistry
**Physico-chemical properties
**Fluid dynamics
**Solidification and casting
* Environmental Metallurgy Lab:
**Reduction of CO emission
**Improvement of energy efficiency
**Gas alloying technology
* [http://cml.postech.ac.kr/ Computational Metallurgy Lab]:
**Classical modeling and experiments
**Phase field modeling and experiments
**First principle calculation, quantum mechanical modeling
* Microstructure Control Lab:
**Phase transformation / electron microscopy
**Microscopic deformation behavior
**Toughness enhancement via microstructure control
**Innovative processing (e.g., twin-roll casting)
* Materials Design Lab:
**[http://www.worldsteel.org/?action=storypages&id=242 Automotive Steels], Galvanized/Galvannealed Products
**Electrical Steels
**Stainless steels
**Steel grades related to power generation
* [http://mml.postech.ac.kr/ Materials Mechanics Lab]:
**Net Shape Forming (sheet forming, other forming)
**Performance in service (fracture, crashworthiness, fatigue)
* [http://sel.postech.ac.kr/ Surface Engineering Lab]:
**Composite coatings
** Corrosion mechanism & lifetime prediction
**Corrosion resistant alloy design
**Metallic coatings | 1 | Applied and Interdisciplinary Chemistry |
Variations in the DNA sequences of humans can affect how humans develop diseases and respond to pathogens, chemicals, drugs, vaccines, and other agents. SNPs are also critical for personalized medicine. Examples include biomedical research, forensics, pharmacogenetics, and disease causation, as outlined below. | 1 | Applied and Interdisciplinary Chemistry |
The presence of these two genes was first suspected when Nelson and Kennedy (1972) showed that there were Mg-repressible and non-repressible Mg uptake systems in E. coli. The non-repressible uptake of Mg is mediated by the CorA protein. In S. typhimurium the repressible Mg uptake was eventually shown to be via the MgtA and MgtB proteins.
Both MgtA and MgtB are regulated by the PhoPQ system and are actively transcribed during the process of infection of human patients by S. typhimurium. Although neither gene is required for pathogenicity, the MgtB protein does enhance the long-term survival of the pathogen in the cell. The genes are also upregulated in vitro when the Mg concentration falls below 50 μM (Snavely et al., 1991a). Although the proteins have km values similar to CorA and transport rates approximately 10 times less, the genes may be part of a Mg scavenging system. Chamnongpol and Groisman (2002) presents evidence that the role of these proteins may be to compensate for the inactivation of the CorA protein by the PhoPQ regulon. The authors suggest that the CorA protein is inactivated to allow the avoidance of metal toxicity via the protein in the low Mg environments S. typhimurium is subjected to by cells after infection.
The proteins are both P-type ATPases
and neither gene shows any similarity to CorA. The MgtA and MgtB proteins are 75% similar (50% identical), although it seems that MgtB may have been acquired by horizontal gene transfer as part of Salmonella Pathogenicity Island 3. The TM topology of the MgtB protein has been experimentally determined, showing that the protein has ten TM-spanning helices with the termini of the protein in the cytoplasm (see figure
). MgtA is present in widely divergent bacteria, but is not nearly as common as CorA, while MgtB appears to have a quite restricted distribution. No hypotheses for the unusual distribution have been suggested.
The figure, adapted from Smith et al. (1993b), shows the experimentally determined membrane topology of the MgtB protein in S. typhimurium. The TM domains are shown in light blue and the orientation in the membrane and the positions of the N- and C-termini are indicated. The figure is not drawn to scale.
While the MgtA and MgtB proteins are very similar, they do show some minor differences in activity. MgtB is very sensitive to temperature, losing all activity (with regard to Mg transport) at a temperature of 20 °C. Additionally, MgtB and MgtA are inhibited by different ranges of cations (Table A10.1).
The table lists cation transport characteristics of the MgtA and MgtB proteins in S. typhimurium as well as the kinetic data for the MgtA and MgtB transport proteins at 37 °C. The Vmax numbers listed in parentheses are those for uptake at 20 °C. The inhibition of Mg transport by Mn via MgtA showed unusual kinetics (see Figure 1 of Snavely et al., 1989b)
The MgtA and MgtB proteins are ATPases, using one molecule of ATP per transport cycle, whereas the Mg uptake via CorA is simply electrochemically favourable. Chamnongpol and Groisman (2002) have suggested that the MgtA and MgtB proteins form part of a metal toxicity avoidance system. Alternatively, as most P-type ATPases function as efflux mediating transporters, it has been suggested that the MgtA and MgtB proteins act as efflux proteins for a currently unidentified cation, and Mg transport is either non-specific or exchanged to maintain the electro-neutrality of the transport process. Further experiments will be required to define the physiological function of these proteins. | 1 | Applied and Interdisciplinary Chemistry |
There are several extensions of the dual-plane stereoscopic PIV idea available. There is an option to create several parallel laser sheets using a set of beamsplitters and quarter-wave plates, providing three or more planes, using a single laser unit and stereoscopic PIV setup, called XPIV. | 1 | Applied and Interdisciplinary Chemistry |
Nucleic acid was first discovered by Friedrich Miescher in 1869 at the University of Tübingen, Germany. He gave its first name as nuclein.
In the early 1880s Albrecht Kossel further purified the substance and discovered its highly acidic properties. He later also identified the nucleobases.
In 1889 Richard Altmann created the term nucleic acid – at that time DNA and RNA were not differentiated.
In 1938 Astbury and Bell published the first X-ray diffraction pattern of DNA.
In 1944 the Avery–MacLeod–McCarty experiment showed that DNA is the carrier of genetic information and in 1953 Watson and Crick proposed the double-helix structure of DNA.
Experimental studies of nucleic acids constitute a major part of modern biological and medical research, and form a foundation for genome and forensic science, and the biotechnology and pharmaceutical industries. | 1 | Applied and Interdisciplinary Chemistry |
DPVweb is a database for virologists working on plant viruses combining taxonomic, bioinformatic and symptom data. | 1 | Applied and Interdisciplinary Chemistry |
Since the Palm Island outbreak, several other species of cyanobacteria have been identified as producing CYN: Anabaena bergii, Anabaena lapponica , Aphanizomenon ovalisporum, Umezakia natans, Raphidiopsis curvata. and Aphanizomenon issatschenkoi. In Australia, three main toxic cyanobacteria exist: Anabaena circinalis, Microcystis species and C. raciborskii. Of these the latter, which produces CYN, has attracted considerable attention, not only due to the Palm Island outbreak, but also as the species is spreading to more temperate areas. Previously, the algae was classed as only tropical, however it has recently been discovered in temperate regions of Australia, Europe, North and South America, and also New Zealand.
In August 1997, three cows and ten calves died from cylindrospermopsin poisoning on a farm in northwest Queensland. A nearby dam containing an algal bloom was tested, and C. raciborskii was identified. Analysis by HPLC/mass spectrometry revealed the presence of CYN in a sample of the biomass. An autopsy of one of the calves reported a swollen liver and gall bladder, along with haemorrhages of the heart and small intestine. Histological examination of the hepatic tissue was consistent with that reported in CYN-affected mice. This was the first report of C. raciborskii causing mortality in animals in Australia.
The effect of a bloom of C. raciborskii on an aquaculture pond in Townsville, Australia was assessed in 1997. The pond contained Redclaw crayfish, along with a population of Lake Eacham Rainbowfish to control the excess food. Analysis revealed that the water contained both extracellular and intracellular CYN, and that the crayfish had accumulated this primarily in the liver but also in the muscle tissue. Examination of the gut contents revealed cyanobacterial cells, indicating that the crayfish had ingested intracellular toxin. An experiment using an extract of the bloom showed that it was also possible to uptake extracellular toxin directly into the tissues. Such bioaccumulation, particularly in the aquaculture industry, was of concern, especially when humans were the end users of the product.
The impact of cyanobacterial blooms has been assessed in economic terms. In December 1991, the world's largest algal bloom occurred in Australia, where 1000 km of the Darling-Barwon River was affected. One million people-days of drinking water were lost, and the direct costs incurred totalled more than A$1.3 million. Moreover, 2000 site-days of recreation were also lost, and the economic cost was estimated at A$10 million, after taking into account indirectly affected industries such as tourism, accommodation and transport. | 0 | Theoretical and Fundamental Chemistry |
Microscale thermophoresis (MST) measures the size, charge and hydration entropy of molecules/substrates at equilibrium. The thermophoretic movement of a fluorescently labeled substrate changes significantly as it is modified by an enzyme. This enzymatic activity can be measured with high time resolution in real time. The material consumption of the all optical MST method is very low, only 5 μl sample volume and 10nM enzyme concentration are needed to measure the enzymatic rate constants for activity and inhibition. MST allows analysts to measure the modification of two different substrates at once (multiplexing) if both substrates are labeled with different fluorophores. Thus substrate competition experiments can be performed. | 1 | Applied and Interdisciplinary Chemistry |
Foams are materials formed by trapping pockets of gas in a liquid or solid.
A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the regions of gas. Soap foams are also known as suds.
Solid foams can be closed-cell or open-cell. In closed-cell foam, the gas forms discrete pockets, each completely surrounded by the solid material. In open-cell foam, gas pockets connect to each other. A bath sponge is an example of an open-cell foam: water easily flows through the entire structure, displacing the air. A sleeping mat is an example of a closed-cell foam: gas pockets are sealed from each other so the mat cannot soak up water.
Foams are examples of dispersed media. In general, gas is present, so it divides into gas bubbles of different sizes (i.e., the material is polydisperse)—separated by liquid regions that may form films, thinner and thinner when the liquid phase drains out of the system films. When the principal scale is small, i.e., for a very fine foam, this dispersed medium can be considered a type of colloid.
Foam can also refer to something that is analogous to foam, such as quantum foam. | 0 | Theoretical and Fundamental Chemistry |
Besides chemical bonds, compliance constants are also useful for determining non-covalent bonds, such as H-bonds in Watson-Crick base pairs. Grunenberg calculated the compliance constant for each of the donor-H⋯acceptor linkages in AT and CG base pairs and found that the central N-H⋯N bond in CG base pair is the strongest one with the compliance constant value of 2.284 Å/mdyn. (Note that the unit is reported in a reverse unit.) In addition, one of the three hydrogen bonding interactions in a AT base pair shows an extremely large compliance value of >20 Å/mdyn indicative of a weak interaction. | 0 | Theoretical and Fundamental Chemistry |
The term "half-life" is almost exclusively used for decay processes that are exponential (such as radioactive decay or the other examples above), or approximately exponential (such as biological half-life discussed below). In a decay process that is not even close to exponential, the half-life will change dramatically while the decay is happening. In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc., where the first half-life is defined as the time required for decay from the initial value to 50%, the second half-life is from 50% to 25%, and so on. | 0 | Theoretical and Fundamental Chemistry |
The oxoeicosanoids are nonclassic eicosanoids, derived from arachidonic acid (AA).
For example, Lipoxygenase produces 5-HETE from AA; a dehydrogenase then produces 5-oxo-eicosatetraenoic acid, an oxoeicosanoid, from 5-HETE.
They are similar to the leukotrienes in their actions, but they act via a different receptor. | 1 | Applied and Interdisciplinary Chemistry |
Leaching is a process widely used in extractive metallurgy where ore is treated with chemicals to convert the valuable metals within the ore, into soluble salts while the impurity remains insoluble. These can then be washed out and processed to give the pure metal; the materials left over are commonly known as tailings. Compared to pyrometallurgy, leaching is easier to perform, requires less energy and is potentially less harmful as no gaseous pollution occurs. Drawbacks of leaching include its lower efficiency and the often significant quantities of waste effluent and tailings produced, which are usually either highly acidic or alkali as well as toxic (e.g. bauxite tailings).
There are four types of leaching:
# Cyanide leaching (e.g. gold ore)
# Ammonia leaching (e.g. crushed ore)
# Alkali leaching (e.g. bauxite ore)
# Acid leaching (e.g. sulfide ore)
Leaching is also notable in the extraction of rare earth elements, which consists of lanthanides, yttrium and scandium. | 1 | Applied and Interdisciplinary Chemistry |
The process of activation and binding in eukaryotes is different from bacteria in the way that specific DNA elements bind the factors for a functional pre-initiation complex. In bacteria there is a single polymerase, that contain catalytic subunits and a single regulatory subunits known as sigma, which transcribe for different type of genes.
In eukaryotes, the transcription is performed by three different RNA polymerase, RNA pol I for ribosomal RNAs (rRNAs), RNA polymerase II for messenger RNAs (mRNAs) and some small regulatory RNAs, and the RNA polymerase III for small RNAs such as transfer RNAs (tRNAs). The process of positioning of the RNA polymerase II and the transcriptional machinery require the recognition of a region known as "core promoter". The elements that could be found in the core promoter include the TATA element, the TFIIB recognition element (BRE), the initiator (Inr), and the downstream core promoter element (DPE). Promoters in eukaryotes contain one or more of these core promotes elements (but any of them are absolutely essential for promoter function), these elements are binding sites for subunits of the transcriptional machinery and are involve in the initiation of the transcription, but also they have some specific enhancer functions. In addition, the promoter activity in eukaryotes include some complexities in the way of how they integrate signals from distal factors with the core promoter. | 1 | Applied and Interdisciplinary Chemistry |
The project was not continued with the change in administrations after the 1980 United States elections. The Office of Technology Assessment concluded that "Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture."
In 1997, NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility. In assessing "What has changed" since the DOE study, NASA asserted that the "US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO [Earth to Orbit] transportation down dramatically. This is, of course, an absolute requirement of space solar power."
Conversely, Pete Worden of NASA claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Worden referred to possible solutions as speculative and not available for decades at the earliest.
On November 2, 2012, China proposed a space collaboration with India that mentioned SBSP, "may be Space-based Solar Power initiative so that both India and China can work for long term association with proper funding along with other willing space faring nations to bring space solar power to earth." | 0 | Theoretical and Fundamental Chemistry |
It is prepared by electrofluorination of tributylamine using hydrogen fluoride as solvent and source of fluorine: | 1 | Applied and Interdisciplinary Chemistry |
Common adverse drug reactions are nausea and vomiting. People who are allergic to penicillin and other β-lactam antibiotics should take caution if taking imipenem, as cross-reactivity rates are high. At high doses, imipenem is seizurogenic. | 0 | Theoretical and Fundamental Chemistry |
*Photosynthesis: Plants use solar energy to convert carbon dioxide and water into glucose and oxygen.
*Human formation of vitamin D by exposure to sunlight.
*Bioluminescence: e.g. In fireflies, an enzyme in the abdomen catalyzes a reaction that produces light.
*Polymerizations started by photoinitiators, which decompose upon absorbing light to produce the free radicals for radical polymerization.
*Photodegradation of many substances, e.g. polyvinyl chloride and Fp. Medicine bottles are often made from darkened glass to protect the drugs from photodegradation.
*Photochemical rearrangements, e.g. photoisomerization, hydrogen atom transfer, and photochemical electrocyclic reactions.
*Photodynamic therapy: Light is used to destroy tumors by the action of singlet oxygen generated by photosensitized reactions of triplet oxygen. Typical photosensitizers include tetraphenylporphyrin and methylene blue. The resulting singlet oxygen is an aggressive oxidant, capable of converting C–H bonds into C–OH groups.
*Diazo printing process
*Photoresist technology, used in the production of microelectronic components.
*Vision is initiated by a photochemical reaction of rhodopsin.
*Toray photochemical production of ε-caprolactame.
*Photochemical production of artemisinin, an anti-malaria drug.
*Photoalkylation, used for the light-induced addition of alkyl groups to molecules.
*DNA: photodimerization leading to cyclobutane pyrimidine dimers. | 0 | Theoretical and Fundamental Chemistry |
Common sphere packings taken on by atomic systems are listed below with their corresponding packing fraction.
* Hexagonal close-packed (HCP): 0.74
* Face-centered cubic (FCC): 0.74 (also called cubic close-packed, CCP)
* Body-centered cubic (BCC): 0.68
* Simple cubic: 0.52
* Diamond cubic: 0.34
The majority of metals take on either the HCP, FCC, or BCC structure. | 0 | Theoretical and Fundamental Chemistry |
Some cryoprotectants function by lowering the glass transition temperature of a solution or of a material. In this way, the cryoprotectant prevents actual freezing, and the solution maintains some flexibility in a glassy phase. Many cryoprotectants also function by forming hydrogen bonds with biological molecules as water molecules are displaced. Hydrogen bonding in aqueous solutions is important for proper protein and DNA function. Thus, as the cryoprotectant replaces the water molecules, the biological material retains its native physiological structure and function, although they are no longer immersed in an aqueous environment. This preservation strategy is most often utilized in anhydrobiosis. | 1 | Applied and Interdisciplinary Chemistry |
The model permits a maximum of 240 internal and 120 external polygons with a minimum of 3 and a maximum of 6 sides each. The subdivision of the area into polygons, based on nodal points with known coordinates, should be governed by the characteristics of the distribution of the cropping, irrigation, drainage and groundwater characteristics over the study area.
The nodes must be numbered, which can be done at will. With an index one indicates whether the node is internal or external. Nodes can be added and removed at will or changed from internal to external or vice versa. Through another index one indicates whether the internal nodes have an unconfined or semi-confined aquifer. This can also be changed at will.
Nodal network relations are to be given indicating the neighboring polygon numbers of each node. The program then calculates the surface area of each polygon, the distance between the nodes and the length of the sides between them using the Thiessen principle.
The hydraulic conductivity can vary for each side of the polygons.
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 |
In the late 1840s, the German chemist developed a modification of the puddling process to produce not iron but steel at the Haspe Iron Works in Hagen; it was subsequently commercialized in Germany, France and the UK in the 1850s, and puddled steel was the main raw material for Krupp cast steel even in the 1870s. Before the development of the basic refractory lining (with magnesium oxide, MgO) and the wide-scale adoption of the Gilchrist–Thomas process ca. 1880 it complemented acidic Bessemer converters (with a refractory material made of ) and open hearths because unlike them, the puddling furnace could utilize phosphorous ores abundant in Continental Europe. | 1 | Applied and Interdisciplinary Chemistry |
We thus have two new kinds of isometry subgroups: all translations, and rotations sharing a fixed point. Both are subgroups of the even subgroup, within which translations are normal. Because translations are a normal subgroup, we can factor them out leaving the subgroup of isometries with a fixed point, the orthogonal group. | 0 | Theoretical and Fundamental Chemistry |
In Fourier transform nuclear magnetic resonance spectroscopy, free induction decay (FID) is the observable NMR signal generated by non-equilibrium nuclear spin magnetization precessing about the magnetic field (conventionally along z). This non-equilibrium magnetization can be created generally by applying a pulse of radio-frequency close to the Larmor frequency of the nuclear spins.
If the magnetization vector has a non-zero component in the xy plane, then the precessing magnetisation will induce a corresponding oscillating voltage in a detection coil surrounding the sample. This time-domain signal (a sinusoid) is typically digitised and then Fourier transformed in order to obtain a frequency spectrum of the NMR signal i.e. the NMR spectrum.
The duration of the NMR signal is ultimately limited by T relaxation, but mutual interference of the different NMR frequencies present also causes the signal to be damped more quickly.
When NMR frequencies are well-resolved, as is typically the case in the NMR of samples in solution, the overall decay of the FID is relaxation-limited and the FID is approximately exponential (with the time constant T changed, indicated by T). FID durations will then be of the order of seconds for nuclei such as H.
Particularly if a limited number of frequency components are present, the FID may be analysed directly for quantitative determinations of physical properties, such as hydrogen content in aviation fuel, solid and liquid ratio in dairy products (time-domain NMR).
Advances in the development of quantum-scale sensors, particularly NV centres, have enabled the observation of the FID of single nuclei. When measuring the precession of a single nucleus, quantum mechanical measurement back action has to be considered. In this special case, also the measurement itself contributes to the decay as predicted by quantum mechanics. | 0 | Theoretical and Fundamental Chemistry |
When embedded in an atomic nucleus, neutrons are (usually) stable particles. Outside the nucleus, free neutrons are unstable and have a mean lifetime of or (about and or , respectively). Therefore, the half-life for this process (which differs from the mean lifetime by a factor of ) is (about , ).
The beta decay of the neutron described in this article can be notated at four slightly different levels of detail, as shown in four layers of Feynman diagrams in a section below.
The hard-to-observe quickly decays into an electron and its matching antineutrino. The subatomic reaction shown immediately above depicts the process as it was first understood, in the first half of the 20th century. The boson () vanished so quickly that it was not detected until much later.
Later, beta decay was understood to occur by the emission of a weak boson (), sometimes called a charged weak current. Beta decay specifically involves the emission of a boson from one of the down quarks hidden within the neutron, thereby converting the down quark into an up quark and consequently the neutron into a proton. The following diagram gives a summary sketch of the beta decay process according to the present level of understanding.
For diagrams at several levels of detail, see § Decay process, below. | 0 | Theoretical and Fundamental Chemistry |
Thermal expansion changes the space between particles of a substance, which changes the volume of the substance while negligibly changing its mass (the negligible amount comes from mass–energy equivalence), thus changing its density, which has an effect on any buoyant forces acting on it. This plays a crucial role in convection of unevenly heated fluid masses, notably making thermal expansion partly responsible for wind and ocean currents. | 0 | Theoretical and Fundamental Chemistry |
Mach stem formation occurs when a blast wave reflects off the ground and the reflection catches up with the original shock front, therefore creating a high pressure zone that extends from the ground up to a certain point called the triple point at the edge of the blast wave. Anything in this area experiences peak pressures that can be several times higher than the peak pressure of the original shock front. | 1 | Applied and Interdisciplinary Chemistry |
A solubility equilibrium exists when a chemical compound in the solid state is in chemical equilibrium with a solution containing the compound. This type of equilibrium is an example of dynamic equilibrium in that some individual molecules migrate between the solid and solution phases such that the rates of dissolution and precipitation are equal to one another. When equilibrium is established and the solid has not all dissolved, the solution is said to be saturated. The concentration of the solute in a saturated solution is known as the solubility. Units of solubility may be molar (mol dm) or expressed as mass per unit volume, such as μg mL. Solubility is temperature dependent. A solution containing a higher concentration of solute than the solubility is said to be supersaturated. A supersaturated solution may be induced to come to equilibrium by the addition of a "seed" which may be a tiny crystal of the solute, or a tiny solid particle, which initiates precipitation.
There are three main types of solubility equilibria.
# Simple dissolution.
# Dissolution with dissociation reaction. This is characteristic of salts. The equilibrium constant is known in this case as a solubility product.
# Dissolution with ionization reaction. This is characteristic of the dissolution of weak acids or weak bases in aqueous media of varying pH.
In each case an equilibrium constant can be specified as a quotient of activities. This equilibrium constant is dimensionless as activity is a dimensionless quantity. However, use of activities is very inconvenient, so the equilibrium constant is usually divided by the quotient of activity coefficients, to become a quotient of concentrations. See Equilibrium chemistry#Equilibrium constant for details. Moreover, the activity of a solid is, by definition, equal to 1 so it is omitted from the defining expression.
For a chemical equilibrium
the solubility product, K for the compound AB is defined as follows
where [A] and [B] are the concentrations of A and B in a saturated solution. A solubility product has a similar functionality to an equilibrium constant though formally K has the dimension of (concentration). | 0 | Theoretical and Fundamental Chemistry |
A covalent bond joining atoms in an organic molecule consists of a group of two electrons. Such a group is referred to as an electron pair. Reactions in organic chemistry proceed through the sequential breaking and formation of such bonds. Organic chemists recognize two processes for the breaking of a chemical bond. These processes are known as homolytic cleavage and heterolytic cleavage. | 0 | Theoretical and Fundamental Chemistry |
Electrochlorination is the process of producing hypochlorite by passing electric current through salt water. This disinfects the water and makes it safe for human use, such as for drinking water or swimming pools. | 0 | Theoretical and Fundamental Chemistry |
Routine tests for surface dealkalization in the glass container industry all generally aim to evaluate the amount of alkali extracted from the glass when it is rinsed with or exposed to purified water. For example, dealkalization can be quickly checked by introducing a small volume of distilled water to a freshly made bottle and rolling the bottle gently to pass the water completely over its inside surface. The pH of the rinse water is then measured; untreated containers will tend to yield a slightly alkaline pH in the 8-9 range due to extracted alkali, while dealkalized containers tend to yield a pH that remains approximately neutral.
A much more thorough version of this test is outlined in various international and domestic testing standards for glass containers, all with comparable methodologies. These tests evaluate the hydrolytic stability of the containers under more severe conditions, wherein containers, filled close to capacity with purified water, are covered and then heat-cycled in an autoclave at 121 °C for 1 hour. After cooling to room temperature, the water is titrated with acid to evaluate the pH of the water, and therefore the equivalent amount of alkali extracted during the heat cycle. The alkali content of the rinse water can also be evaluated more directly by chemical analysis of the rinse water, as outlined in more recent versions of the European Pharmacopoeia. According to the Pharmacopoeia standards, internally treated or dealkalized soda-lime glass containers are designated as "Type II" containers, thus setting them apart from their untreated counterparts due to their improved resistance to product interactions (as opposed to "Type III", which is standard, untreated soda-lime glass, or "Type I", which is reserved for highly resistant borosilicate glass).
While not routine, dealkalization can also be measured in a variety of other ways. Since dealkalized surfaces are more chemically durable, they are also more resistant to weathering reactions, and appropriate evaluation of this parameter can give indirect evidence of a previously dealkalized surface. It is also possible to evaluate dealkalization through the use of advanced, surface analytical techniques such as SIMS or XPS, which give direct measurements of glass surface composition. | 0 | Theoretical and Fundamental Chemistry |
Promoters are DNA segments near the 5' end of the gene where transcription begins. They are the sites where RNA polymerase binds to initiate RNA synthesis. Every gene has a noncoding promoter.
Regulatory elements are sites that control the transcription of a nearby gene. They are almost always sequences where transcription factors bind to DNA and these transcription factors can either activate transcription (activators) or repress transcription (repressors). Regulatory elements were discovered in the 1960s and their general characteristics were worked out in the 1970s by studying specific transcription factors in bacteria and bacteriophage.
Promoters and regulatory sequences represent an abundant class of noncoding DNA but they mostly consist of a collection of relatively short sequences so they do not take up a very large fraction of the genome. The exact amount of regulatory DNA in mammalian genome is unclear because it is difficult to distinguish between spurious transcription factor binding sites and those that are functional. The binding characteristics of typical DNA-binding proteins were characterized in the 1970s and the biochemical properties of transcription factors predict that in cells with large genomes, the majority of binding sites will not be biologically functional.
Many regulatory sequences occur near promoters, usually upstream of the transcription start site of the gene. Some occur within a gene and a few are located downstream of the transcription termination site. In eukaryotes, there are some regulatory sequences that are located at a considerable distance from the promoter region. These distant regulatory sequences are often called enhancers but there is no rigorous definition of enhancer that distinguishes it from other transcription factor binding sites. | 1 | Applied and Interdisciplinary Chemistry |
Many thiols have strong odors resembling that of garlic. The odors of thiols, particularly those of low molecular weight, are often strong and repulsive. The spray of skunks consists mainly of low-molecular-weight thiols and derivatives. These compounds are detectable by the human nose at concentrations of only 10 parts per billion. Human sweat contains (R)/(S)-3-methyl-3-mercapto-1-ol (MSH), detectable at 2 parts per billion and having a fruity, onion-like odor. (Methylthio)methanethiol (MeSCHSH; MTMT) is a strong-smelling volatile thiol, also detectable at parts per billion levels, found in male mouse urine. Lawrence C. Katz and co-workers showed that MTMT functioned as a semiochemical, activating certain mouse olfactory sensory neurons, attracting female mice. Copper has been shown to be required by a specific mouse olfactory receptor, MOR244-3, which is highly responsive to MTMT as well as to various other thiols and related compounds. A human olfactory receptor, OR2T11, has been identified which, in the presence of copper, is highly responsive to the gas odorants (see below) ethanethiol and t-butyl mercaptan as well as other low molecular weight thiols, including allyl mercaptan found in human garlic breath, and the strong-smelling cyclic sulfide thietane.
Thiols are also responsible for a class of wine faults caused by an unintended reaction between sulfur and yeast and the "skunky" odor of beer that has been exposed to ultraviolet light.
Not all thiols have unpleasant odors. For example, furan-2-ylmethanethiol contributes to the aroma of roasted coffee, whereas grapefruit mercaptan, a monoterpenoid thiol, is responsible for the characteristic scent of grapefruit. The effect of the latter compound is present only at low concentrations. The pure mercaptan has an unpleasant odor.
In the United States, natural gas distributors were required to add thiols, originally ethanethiol, to natural gas (which is naturally odorless) after the deadly New London School explosion in New London, Texas, in 1937. Many gas distributors were odorizing gas prior to this event. Most currently-used gas odorants contain mixtures of mercaptans and sulfides, with t-butyl mercaptan as the main odor constituent in natural gas and ethanethiol in liquefied petroleum gas (LPG, propane). In situations where thiols are used in commercial industry, such as liquid petroleum gas tankers and bulk handling systems, an oxidizing catalyst is used to destroy the odor. A copper-based oxidation catalyst neutralizes the volatile thiols and transforms them into inert products. | 0 | Theoretical and Fundamental Chemistry |
AOAC International is a 501(c) non-profit scientific association with headquarters in Rockville, Maryland. It was founded in 1884 as the Association of Official Agricultural Chemists (AOAC) and became AOAC International in 1991. It publishes standardized, chemical analysis methods designed to increase confidence in the results of chemical and microbiological analyses. Government agencies and civil organizations often require that laboratories use official AOAC methods. AOAC is headquartered in Rockville, Maryland, and has approximately 3,000 members based in over 90 countries. | 0 | Theoretical and Fundamental Chemistry |
Porphine or porphin is an organic compound of empirical formula . It is heterocyclic and aromatic. The molecule is a flat macrocycle, consisting of four pyrrole-like rings joined by four methine bridges, which makes it the simplest of the tetrapyrroles.
The nonpolar tetrapyrrolic ring structure of porphine means it is poorly soluble in most organic solvents and hardly water soluble. As a result, porphine is mostly of theoretical interest. It has been detected in GC-MS of certain fractions of Piper betle. | 1 | Applied and Interdisciplinary Chemistry |
myo-Inositol trispyrophosphate (ITPP) is an inositol phosphate, a pyrophosphate, a drug candidate, and a putative performance-enhancing substance, which exerts its biological effects by increasing tissue oxygenation. | 1 | Applied and Interdisciplinary Chemistry |
The most recent and most clear cut example of enzyme evolution is the rise of bioremediating enzymes in the past 60 years. Due to the very low number of amino acid changes, these provide an excellent model to investigate enzyme evolution in nature. However, using extant enzymes to determine how the family of enzymes evolved has the drawback that the newly evolved enzyme is compared to paralogues without knowing the true identity of the ancestor before the two genes diverged. This issue can be resolved thanks to ancestral reconstruction.
First proposed in 1963 by Linus Pauling and Emile Zuckerkandl, ancestral reconstruction is the inference and synthesis of a gene from the ancestral form of a group of genes, which has had a recent revival thanks to improved inference techniques and low-cost artificial gene synthesis, resulting in several ancestral enzymes—dubbed "stemzymes" by some—to be studied.
Evidence gained from reconstructed enzyme suggests that the order of the events where the novel activity is improved and the gene is duplication is not clear cut, unlike what the theoretical models of gene evolution suggest.
One study showed that the ancestral gene of the immune defence protease family in mammals had a broader specificity and a higher catalytic efficiency than the contemporary family of paralogues, whereas another study showed that the ancestral steroid receptor of vertebrates was an oestrogen receptor with slight substrate ambiguity for other hormones—indicating that these probably were not synthesised at the time.
This variability in ancestral specificity has not only been observed between different genes, but also within the same gene family.
In light of the large number of paralogous fungal α-glucosidase genes with a number of specific maltose-like (maltose, turanose, maltotriose, maltulose and sucrose) and isomaltose-like (isomaltose and palatinose) substrates, a study reconstructed all key ancestors and found that the last common ancestor of the paralogues was mainly active on maltose-like substrates with only trace activity for isomaltose-like sugars, despite leading to a lineage of iso-maltose glucosidases and a lineage that further split into maltose glucosidases and iso-maltose glucosidases. Antithetically, the ancestor before the latter split had a more pronounced isomaltose-like glucosidase activity. | 1 | Applied and Interdisciplinary Chemistry |
The most important operating parameters of disc filters are the height of the slurry tank, agitation and the intensity and rotation speed of the disc as these will determine the cake formation and drying times. It is important to continuously agitate the slurry in order to prevent sedimentation of the solids. Excessively high agitation intensity may affect cake formation or change the particle size distribution of the product. One of the most commonly used agitators for filtration using vacuum disc filters is an oscillating cradle-type agitator located in the bottom of the basin, which requires fairly high rotation speeds to form homogeneous slurry. For processing rapidly settling high concentration slurries, bottom-feed rotary disc filters are usually used.
Stage 1: Filtration
The filtrate from the internal passages of the discs is removed by the low vacuum used in the filter, while the small pressure differential across the disc causes cake formation. With a thicker cake produced in this stage, more effective washing is achieved at higher wash liquor flows. However, this causes larger air volumes to be consumed at discharge due to reduced resistance and marginally lower cake moisture.
Stage 2: Dewatering
In rare cases, due to the even structure of the cakes formed, the steady flow profile of the ceramic filter media and the gas free filtrate flow cake, washing has proved to be efficient in ceramic disc filters. The formation of thicker cakes during filtration and higher vacuum level leads to greater removal of solute.
Stage 3: Discharge
The basic scraper works well when the cakes are relatively thick and non-sticky. The final cakes are discharged by blade or wire scrapers on either side of the discs However, other types of agitators should be considered and installed if the cake is sticky or thin. An air blow-back system is often employed to aid cake removal where wetter cakes are discharged from disc filter. | 0 | Theoretical and Fundamental Chemistry |
Stable isotope labeling by/with amino acids in cell culture (SILAC) is a technique based on mass spectrometry that detects differences in protein abundance among samples using non-radioactive isotopic labeling. It is a popular method for quantitative proteomics. | 1 | Applied and Interdisciplinary Chemistry |
An example of undesirable work hardening is during machining when early passes of a cutter inadvertently work-harden the workpiece surface, causing damage to the cutter during the later passes. Certain alloys are more prone to this than others; superalloys such as Inconel require machining strategies that take it into account.
For metal objects designed to flex, such as springs, specialized alloys are usually employed in order to avoid work hardening (a result of plastic deformation) and metal fatigue, with specific heat treatments required to obtain the necessary characteristics. | 1 | Applied and Interdisciplinary Chemistry |
These relief structures, called "storm-water regulators" (in American English - or "combined sewer overflows" in British English) are constructed in combined sewer systems to divert flows in excess of the peak design flow of the sewage treatment plant. Combined sewers are built with control sections establishing stage-discharge or pressure differential-discharge relationships which may be either predicted or calibrated to divert flows in excess of sewage treatment plant capacity. A leaping weir may be used as a regulating device allowing typical dry-weather sewage flow rates to fall into an interceptor sewer to the sewage treatment plant, but causing a major portion of higher flow rates to leap over the interceptor into the diversion outfall. Alternatively, an orifice may be sized to accept the sewage treatment plant design capacity and cause excess flow to accumulate above the orifice until it overtops a side-overflow weir to the diversion outfall.
CSO statistics may be confusing because the term may describe either the number of events or the number of relief structure locations at which such events may occur. A CSO event, as the term is used in American English, occurs when mixed sewage and stormwater are bypassed from a combined sewer system control section into a river, stream, lake, or ocean through a designed diversion outfall, but without treatment. Overflow frequency and duration varies both from system to system, and from outfall to outfall, within a single combined sewer system. Some CSO outfalls discharge infrequently, while others activate every time it rains.
The storm water component contributes pollutants to CSO; but a major faction of pollution is the first foul flush of accumulated biofilm and sanitary solids scoured from the dry weather wetted perimeter of combined sewers during peak flow turbulence. Each storm is different in the quantity and type of pollutants it contributes. For example, storms that occur in late summer, when it has not rained for a while, have the most pollutants. Pollutants like oil, grease, fecal coliform from pet and wildlife waste, and pesticides get flushed into the sewer system. In cold weather areas, pollutants from cars, people and animals also accumulate on hard surfaces and grass during the winter and then are flushed into the sewer systems during heavy spring rains. | 1 | Applied and Interdisciplinary Chemistry |
*In the hydrodynamic interpretation of the behaviour of electromagnetic fields, the acceleration of electric fluid in a particular direction creates a positive vortex of magnetic fluid. This in turn creates around itself a corresponding negative vortex of electric fluid. Exact solutions to classical nonlinear magnetic equations include the Landau–Lifshitz equation, the continuum Heisenberg model, the Ishimori equation, and the nonlinear Schrödinger equation.
*Vortex rings are torus-shaped vortices where the axis of rotation is a continuous closed curve. Smoke rings and bubble rings are two well-known examples.
*The lifting force of aircraft wings, propeller blades, sails, and other airfoils can be explained by the creation of a vortex superimposed on the flow of air past the wing.
*Aerodynamic drag can be explained in large part by the formation of vortices in the surrounding fluid that carry away energy from the moving body.
*Large whirlpools can be produced by ocean tides in certain straits or bays. Examples are Charybdis of classical mythology in the Straits of Messina, Italy; the Naruto whirlpools of Nankaido, Japan; and the Maelstrom at Lofoten, Norway.
*Vortices in the Earths atmosphere are important phenomena for meteorology. They include mesocyclones on the scale of a few miles, tornadoes, waterspouts, and hurricanes. These vortices are often driven by temperature and humidity variations with altitude. The sense of rotation of hurricanes is influenced by the Earths rotation. Another example is the Polar vortex, a persistent, large-scale cyclone centered near the Earth's poles, in the middle and upper troposphere and the stratosphere.
*Vortices are prominent features of the atmospheres of other planets. They include the permanent Great Red Spot on Jupiter, the intermittent Great Dark Spot on Neptune, the polar vortices of Venus, the Martian dust devils and the North Polar Hexagon of Saturn.
*Sunspots are dark regions on the Sun's visible surface (photosphere) marked by a lower temperature than its surroundings, and intense magnetic activity.
*The accretion disks of black holes and other massive gravitational sources.
*Taylor–Couette flow occurs in a fluid between two nested cylinders, one rotating, the other fixed. | 1 | Applied and Interdisciplinary Chemistry |
Indolyl-3-acryloylglycine, also known as trans-indolyl-3-acryloylglycine, or IAG for short, is a compound consisting of an indole group attached to an acrylic acid moiety, which is in turn attached to a glycine molecule. This compound has been shown to isomerize when exposed to light. It is likely a metabolic intermediate in the biosynthesis of tryptophan, and is synthesized from tryptophan via indolepropionic acid and indoleacrylicacid (IAcrA). It is also likely that IAcrA is converted into IAG in the gut wall. It may also be produced by certain elements of the mammalian gut microbiota by phenylalanine ammonia-lyase. Identifiable in the urine by high-performance liquid chromatography, it may be a biomarker for autism spectrum disorders, as demonstrated by the research of Paul Shattock and other researchers from Australia. These researchers have reported that urinary levels of IAG are much higher in autistic children than in controls; however, other researchers have found no association between IAG concentrations in the urine and autism. Its excretion in the urine may also be changed in Hartnup disease and celiac disease, as well as photodermatosis, muscular dystrophy, and liver cirrhosis. | 0 | Theoretical and Fundamental Chemistry |
Effectively, the postulate states that the structure of a transition state resembles that of the species nearest to it in free energy. This can be explained with reference to potential energy diagrams:
In case (a), which is an exothermic reaction, the energy of the transition state is closer in energy to that of the reactant than that of the intermediate or the product. Therefore, from the postulate, the structure of the transition state also more closely resembles that of the reactant. In case (b), the energy of the transition state is close to neither the reactant nor the product, making none of them a good structural model for the transition state. Further information would be needed in order to predict the structure or characteristics of the transition state. Case (c) depicts the potential diagram for an endothermic reaction, in which, according to the postulate, the transition state should more closely resemble that of the intermediate or the product.
Another significance of Hammond's postulate is that it permits us to discuss the structure of the transition state in terms of the reactants, intermediates, or products. In the case where the transition state closely resembles the reactants, the transition state is called “early” while a “late” transition state is the one that closely resembles the intermediate or the product.
An example of the “early” transition state is chlorination. Chlorination favors the products because it is an exothermic reaction, which means that the products are lower in energy than the reactants. When looking at the adjacent diagram (representation of an "early" transition state), one must focus on the transition state, which is not able to be observed during an experiment. To understand what is meant by an “early” transition state, the Hammond postulate represents a curve that shows the kinetics of this reaction. Since the reactants are higher in energy, the transition state appears to be right after the reaction starts.
An example of the “late” transition state is bromination. Bromination favors the reactants because it is an endothermic reaction, which means that the reactants are lower in energy than the products. Since the transition state is hard to observe, the postulate of bromination helps to picture the “late” transition state (see the representation of the "late" transition state). Since the products are higher in energy, the transition state appears to be right before the reaction is complete.
One other useful interpretation of the postulate often found in textbooks of organic chemistry is the following:
:Assume that the transition states for reactions involving unstable intermediates can be closely approximated by the intermediates themselves.
This interpretation ignores extremely exothermic and endothermic reactions which are relatively unusual and relates the transition state to the intermediates which are usually the most unstable. | 0 | Theoretical and Fundamental Chemistry |
Lewis formulae are rule-based approximations of chemical reality, as are Allen electronegativities. Still, oxidation states may seem ambiguous when their determination is not straightforward. If only an experiment can determine the oxidation state, the rule-based determination is ambiguous (insufficient). There are also truly dichotomous values that are decided arbitrarily. | 0 | Theoretical and Fundamental Chemistry |
In his book Chance and Necessity, Jacques Monod described the functions of proteins and other molecules capable of recognizing with elective discrimination a substrate or ligand or other molecule. In describing these molecules he introduced the term cognitive functions, the same cognitive functions that Maxwell attributed to his demon. Werner Loewenstein goes further and names these molecules molecular demon<nowiki/> or demon in short.
Naming the biological molecular machines in this way makes it easier to understand the similarities between these molecules and Maxwell's demon.
Because of this real discriminative if not cognitive property, Jacques Monod attributed a teleonomic function to these biological complexes. Teleonomy implies the idea of an oriented, coherent and constructive activity. Proteins therefore must be considered essential molecular agents in the teleonomic performances of all living beings. | 0 | Theoretical and Fundamental Chemistry |
In physics, the signal might be a wave, such as an electromagnetic wave, an acoustic wave, or the vibration of a mechanism. The power spectral density (PSD) of the signal describes the power present in the signal as a function of frequency, per unit frequency. Power spectral density is commonly expressed in watts per hertz (W/Hz).
When a signal is defined in terms only of a voltage, for instance, there is no unique power associated with the stated amplitude. In this case "power" is simply reckoned in terms of the square of the signal, as this would always be proportional to the actual power delivered by that signal into a given impedance. So one might use units of V Hz for the PSD. Energy spectral density (ESD) would have units of V s Hz, since energy has units of power multiplied by time (e.g., watt-hour).
In the general case, the units of PSD will be the ratio of units of variance per unit of frequency; so, for example, a series of displacement values (in meters) over time (in seconds) will have PSD in units of meters squared per hertz, m/Hz.
In the analysis of random vibrations, units of g Hz are frequently used for the PSD of acceleration, where g denotes the g-force.
Mathematically, it is not necessary to assign physical dimensions to the signal or to the independent variable. In the following discussion the meaning of x(t) will remain unspecified, but the independent variable will be assumed to be that of time. | 0 | Theoretical and Fundamental Chemistry |
According to Arab bibliographer Ibn al-Nadim, al-Kindi wrote at least two hundred and sixty books, contributing heavily to geometry (thirty-two books), medicine and philosophy (twenty-two books each), logic (nine books), and physics (twelve books). Although most of his books have been lost over the centuries, a few have survived in the form of Latin translations by Gerard of Cremona, and others have been rediscovered in Arabic manuscripts; most importantly, twenty-four of his lost works were located in the mid-twentieth century in a Turkish library. | 1 | Applied and Interdisciplinary Chemistry |
The compressive properties of syntactic foams, in most cases, strongly depend on the properties of the filler particle material. In general, the compressive strength of the material is proportional to its density. Cementitious syntactic foams are reported to achieve compressive strength values greater than while maintaining densities lower than .
The matrix material has more influence on the tensile properties. Tensile strength may be highly improved by a chemical surface treatment of the particles, such as silanization, which allows the formation of strong bonds between glass particles and epoxy matrix. Addition of fibrous materials can also increase the tensile strength. | 0 | Theoretical and Fundamental Chemistry |
Slip-joint fittings are frequently used in kitchen, bathroom and tub drainage systems. They include a detached (movable) slip nut and slip-joint washer; the washer is made of rubber or nylon. An advantage of this type of fitting is that the pipe it is connecting to does not need to be cut to a precise length; the slip joint can attach within a range of the end of the inserting pipe. Many slip fittings may be tightened or loosened by hand for easier access to residential drainpipe systems (for example, to clean out a trap or access a drain line past a trap). | 1 | Applied and Interdisciplinary Chemistry |
Roses metal, Rose metal or Roses alloy is a fusible alloy with a low melting point.
Rose's metal consists of 50% bismuth, 25–28% lead and 22–25% tin. Its melting point is between . The alloy does not appreciably contract or expand on solidification, this characteristic being a function of its bismuth percentage, but does slightly contract on cooling. | 1 | Applied and Interdisciplinary Chemistry |
Usually called RTD – Riverine Tailings Disposal. In most environments, not a particularly environmentally sound practice, it has seen significant utilisation in the past, leading to such spectacular environmental damage as done by the Mount Lyell Mining and Railway Company in Tasmania to the King River, or the poisoning from the Panguna mine on Bougainville Island, which led to large-scale civil unrest on the island, and the eventual permanent closing of the mine.
As of 2005, only three mines operated by international companies continued to use river disposal: The Ok Tedi mine, the Grasberg mine and the Porgera mine, all on New Guinea. This method is used in these cases due to seismic activity and landslide dangers which make other disposal methods impractical and dangerous. | 1 | Applied and Interdisciplinary Chemistry |
Nuclear magnetic resonance chemical shift re-referencing is a chemical analysis method for chemical shift referencing in biomolecular nuclear magnetic resonance (NMR). It has been estimated that up to 20% of 13C and up to 35% of 15N shift assignments are improperly referenced. Given that the structural and dynamic information contained within chemical shifts is often quite subtle, it is critical that protein chemical shifts be properly referenced so that these subtle differences can be detected. Fundamentally, the problem with chemical shift referencing comes from the fact that chemical shifts are relative frequency measurements rather than absolute frequency measurements. Because of the historic problems with chemical shift referencing, chemical shifts are perhaps the most precisely measurable but the least accurately measured parameters in all of NMR spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
Albert Strickler (25 July 1887 – 1 February 1963) was a Swiss mechnical engineer recognized for contributions to our understanding of hydraulic roughness in open channel and pipe flow. Strickler proposed that hydraulic roughness could be characterized as a function of measurable surface roughness and described the concept of relative roughness, the ratio of hydraulic radius to surface roughness. He applied these concepts to the development of a dimensionally homogeneous form of the Manning formula. | 1 | Applied and Interdisciplinary Chemistry |
Photofission is a process in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission and splits into two or more fragments.
The reaction was discovered in 1940 by a small team of engineers and scientists operating the Westinghouse Atom Smasher at the company's Research Laboratories in Forest Hills, Pennsylvania. They used a 5 MeV proton beam to bombard fluorine and generate high-energy photons, which then irradiated samples of uranium and thorium.
Gamma radiation of modest energies, in the low tens of MeV, can induce fission in traditionally fissile elements such as the actinides thorium, uranium, plutonium, and neptunium. Experiments have been conducted with much higher energy gamma rays, finding that the photofission cross section varies little within ranges in the low GeV range.
Baldwin et al made measurements of the yields of photo-fission in uranium and thorium together with a search for photo-fission in other heavy elements, using continuous x-rays from a 100-MeV betatron. Fission was detected in the presence of an intense background of x-rays by a differential ionization chamber and linear amplifier, the substance investigated being coated on an electrode of one chamber. They deduced the maximum cross section being of the order of 5×10 cm for uranium and half that for thorium. In the other elements studied, the cross section must be below 10 cm. | 0 | Theoretical and Fundamental Chemistry |
Coenzyme A is naturally synthesized from pantothenate (vitamin B), which is found in food such as meat, vegetables, cereal grains, legumes, eggs, and milk. In humans and most living organisms, pantothenate is an essential vitamin that has a variety of functions. In some plants and bacteria, including Escherichia coli, pantothenate can be synthesised de novo and is therefore not considered essential. These bacteria synthesize pantothenate from the amino acid aspartate and a metabolite in valine biosynthesis.
In all living organisms, coenzyme A is synthesized in a five-step process that requires four molecules of ATP, pantothenate and cysteine (see figure):
# Pantothenate (vitamin B) is phosphorylated to 4′-phosphopantothenate by the enzyme pantothenate kinase (PanK; CoaA; CoaX). This is the committed step in CoA biosynthesis and requires ATP.
# A cysteine is added to 4′-phosphopantothenate by the enzyme phosphopantothenoylcysteine synthetase (PPCS; CoaB) to form 4'-phospho-N-pantothenoylcysteine (PPC). This step is coupled with ATP hydrolysis.
# PPC is decarboxylated to 4′-phosphopantetheine by phosphopantothenoylcysteine decarboxylase (PPC-DC; CoaC)
# 4′-phosphopantetheine is adenylated (or more properly, AMPylated) to form dephospho-CoA by the enzyme phosphopantetheine adenylyl transferase (COASY; PPAT; CoaD)
# Finally, dephospho-CoA is phosphorylated to coenzyme A by the enzyme dephosphocoenzyme A kinase (COASY, DPCK; CoaE). This final step requires ATP.
Enzyme nomenclature abbreviations in parentheses represent mammalian, other eukaryotic, and prokaryotic enzymes respectively. In mammals steps 4 and 5 are catalyzed by a bifunctional enzyme called COASY. This pathway is regulated by product inhibition. CoA is a competitive inhibitor for Pantothenate Kinase, which normally binds ATP. Coenzyme A, three ADP, one monophosphate, and one diphosphate are harvested from biosynthesis.
Coenzyme A can be synthesized through alternate routes when intracellular coenzyme A level are reduced and the de novo pathway is impaired. In these pathways, coenzyme A needs to be provided from an external source, such as food, in order to produce 4′-phosphopantetheine. Ectonucleotide pyrophosphates (ENPP) degrade coenzyme A to 4′-phosphopantetheine, a stable molecule in organisms. Acyl carrier proteins (ACP) (such as ACP synthase and ACP degradation) are also used to produce 4′-phosphopantetheine. This pathway allows for 4′-phosphopantetheine to be replenished in the cell and allows for the conversion to coenzyme A through enzymes, PPAT and PPCK.
A 2024 article detailed a plausible chemical synthesis mechanism for the pantetheine component (the main functional part) of coenzyme A in a primordial prebiotic world. | 1 | Applied and Interdisciplinary Chemistry |
The information collected from these studies is vital so that safe human testing can begin. Typically, in drug development studies animal testing involves two species. The most commonly used models are murine and canine, although primate and porcine are also used. | 1 | Applied and Interdisciplinary Chemistry |
Antioxidants are an important group of anticarcinogenic compounds that may help remove ROS or potentially harmful chemicals. These may be found naturally in fruits and vegetables. Examples of antioxidants are vitamin A and its carotenoid precursors, vitamin C, vitamin E, polyphenols, and various other compounds. β-Carotene is the red-orange colored compounds found in vegetables like carrots and tomatoes. Vitamin C may prevent some cancers by inhibiting the formation of mutagenic N-nitroso compounds (nitrosamine). Flavonoids, such as EGCG in green tea, have also been shown to be effective antioxidants and may have anti-cancer properties. Epidemiological studies indicate that a diet rich in fruits and vegetables is associated with lower incidence of some cancers and longer life expectancy, however, the effectiveness of antioxidant supplements in cancer prevention in general is still the subject of some debate.
Other chemicals may reduce mutagenesis or prevent cancer via other mechanisms, although for some the precise mechanism for their protective property may not be certain. Selenium, which is present as a micronutrient in vegetables, is a component of important antioxidant enzymes such as gluthathione peroxidase. Many phytonutrients may counter the effect of mutagens; for example, sulforaphane in vegetables such as broccoli has been shown to be protective against prostate cancer. Others that may be effective against cancer include indole-3-carbinol from cruciferous vegetables and resveratrol from red wine.
An effective precautionary measure an individual can undertake to protect themselves is by limiting exposure to mutagens such as UV radiations and tobacco smoke. In Australia, where people with pale skin are often exposed to strong sunlight, melanoma is the most common cancer diagnosed in people aged 15–44 years.
In 1981, human epidemiological analysis by Richard Doll and Richard Peto indicated that smoking caused 30% of cancers in the US. Diet is also thought to cause a significant number of cancer, and it has been estimated that around 32% of cancer deaths may be avoidable by modification to the diet. Mutagens identified in food include mycotoxins from food contaminated with fungal growths, such as aflatoxins which may be present in contaminated peanuts and corn; heterocyclic amines generated in meat when cooked at high temperature; PAHs in charred meat and smoked fish, as well as in oils, fats, bread, and cereal; and nitrosamines generated from nitrites used as food preservatives in cured meat such as bacon (ascorbate, which is added to cured meat, however, reduces nitrosamine formation). Overly-browned starchy food such as bread, biscuits and potatoes can generate acrylamide, a chemical shown to cause cancer in animal studies. Excessive alcohol consumption has also been linked to cancer; the possible mechanisms for its carcinogenicity include formation of the possible mutagen acetaldehyde, and the induction of the cytochrome P450 system which is known to produce mutagenic compounds from promutagens.
For certain mutagens, such as dangerous chemicals and radioactive materials, as well as infectious agents known to cause cancer, government legislations and regulatory bodies are necessary for their control. | 0 | Theoretical and Fundamental Chemistry |
Building on his earlier pioneering research on the surface passivation and thermal oxidation processes, Atalla developed the metal–oxide–semiconductor (MOS) process. Atalla then proposed that a field effect transistor–a concept first envisioned in the 1920s and confirmed experimentally in the 1940s, but not achieved as a practical device—be built of metal-oxide-silicon. Atalla assigned the task of assisting him to Dawon Kahng, a Korean scientist who had recently joined his group. That led to the invention of the MOSFET (metal–oxide–semiconductor field-effect transistor) by Atalla and Kahng, in November 1959. Atalla and Kahng first demonstrated the MOSFET in early 1960. With its high scalability, and much lower power consumption and higher density than bipolar junction transistors, the MOSFET made it possible to build high-density integrated circuit (IC) chips. | 0 | Theoretical and Fundamental Chemistry |
In double knockout STAT2 mice, an increased proliferation of M1, M2, and M1/M2 coexpressing macrophages during influenza-bacterial super-infection is observed. The bacterial clearance was also impaired by neutralization of IFN-γ (M1) and Arginase-1 (M2) what suggests that pulmonary macrophages expressing a mixed M1/M2 phenotype promote bacterial control during influenza-bacterial super-infection. Therefore the STAT2 signaling is associated with suppressing macrophage activation and bacterial control during influenza-bacterial super-infection. These mice demonstrate no developmental defects. The knockout STAT2 and double knockout STAT mice in Vesicular stromatitis Indiana virus (VSV) model produce at least 10 times more virus plaque-forming units than the wild type (WT). IFN-α pretreatment supplied protection in WT and STAT2 cells but not in double knockout STAT2 cells. IFN-γ pretreatment did not provide any antiviral response during infection of VSV. This finding could be explained by the reduced level of STAT1 in cells of STAT2 knockout mice. Additionally, the double knockout STAT2 mice are more sensitive to mouse cytomegalovirus (MCMV), severe fever thrombocytopenia syndrome virus, influenza virus, dengue virus (DNV) and Zika virus than control mice, which suggests that STAT2 plays a critical role in the suppression of virus replication in mice. | 1 | Applied and Interdisciplinary Chemistry |
Gels consist of a solid three-dimensional network that spans the volume of a liquid medium and ensnares it through surface tension effects. This internal network structure may result from physical bonds such as polymer chain entanglements (see polymers) (physical gels) or chemical bonds such as disulfide bonds (see thiomers) (chemical gels), as well as crystallites or other junctions that remain intact within the extending fluid. Virtually any fluid can be used as an extender including water (hydrogels), oil, and air (aerogel). Both by weight and volume, gels are mostly fluid in composition and thus exhibit densities similar to those of their constituent liquids. Edible jelly is a common example of a hydrogel and has approximately the density of water. | 0 | Theoretical and Fundamental Chemistry |
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst. Heat is not necessarily applied externally, and is often generated by the reaction of the resin with a curing agent (catalyst, hardener). Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.
The starting material for making thermosets is usually malleable or liquid prior to curing, and is often designed to be molded into the final shape. It may also be used as an adhesive. Once hardened, a thermoset cannot be melted for reshaping, in contrast to thermoplastic polymers which are commonly produced and distributed in the form of pellets, and shaped into the final product form by melting, pressing, or injection molding. | 0 | Theoretical and Fundamental Chemistry |
Available data suggests that mefloquine is safe and effective for use by pregnant women during all trimesters of pregnancy, and it is widely used for this indication. In pregnant women, mefloquine appears to pose minimal risk to the fetus, and is not associated with increased risk of birth defects or miscarriages. Compared to other malaria chemoprophylaxis regimens, however, mefloqinone may produce more side effects in non-pregnant travelers.
Mefloquine is also safe and effective for use during breastfeeding, though it appears in breast milk in low concentrations. The World Health Organization (WHO) gives approval for the use of mefloquine in the second and third trimesters of pregnancy and use in the first trimester does not mandate termination of pregnancy. | 0 | Theoretical and Fundamental Chemistry |
Tetra-n-butylammonium fluoride, commonly abbreviated to TBAF and n-BuNF, is a quaternary ammonium salt with the chemical formula (CHCHCHCH)NF. It is commercially available as the white solid trihydrate and as a solution in tetrahydrofuran. TBAF is used as a source of fluoride ion in organic solvents. | 0 | Theoretical and Fundamental Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.