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In addition to LaNi, there are other alloys such as LaNi, LaNi, LaNi, LaNi, LaNi, and LaNi, and nonstoichiometric alloys such as LaNi (tetragonal, space group I4̄2m). The nickel atoms in LaNi can also be replaced by other atoms, such as LaNiCo. | 1 | Applied and Interdisciplinary Chemistry |
The sample (fruits, vegetables, tobacco, etc.) is homogenized and centrifuged with a reagent and agitated for 1 minute. The reagents used depend on the type of sample to be analyzed. Following this, the sample is put through a dispersive solid phase extraction cleanup prior to analysis by gas-liquid chromatography or liquid-liquid chromatography.
Samples prepared using the QuEChERS method can be processed more quickly using a homogenization instrument. Such instruments can homogenize the food sample in a centrifuge tube, then agitate the sample with the reagent of choice, before moving the extracted sample for centrifuging. By using such an instrument, the samples can be moved through the QuEChERS method more quickly.
Some modifications to the original QuEChERS method had to be introduced to ensure efficient extraction of pH-dependent compounds (e.g., phenoxyalkanoic acids), to minimize degradation of susceptible compounds (e.g., base and acid labile pesticides) and to expand the spectrum of matrices covered. | 0 | Theoretical and Fundamental Chemistry |
Certain gases, when mixed with dry water, combine with the water, which then traps them in a solid clathrate hydrate cage. This presents the possibility that explosive gases could be transported in dry water with a reduced risk of detonation. Dry water is currently being considered for use as a carbon sequestration agent to capture and seal away greenhouse gases from the atmosphere. It can trap four times more carbon dioxide than ordinary water over a similar length of time. Dry water also has applications for the transportation and storage of many dangerous materials. It can be used as a medium for volatile compounds, as materials stored within the dry water can be reduced to powder and stabilized – reducing not only the volatility of the substance, but also its weight for transport. It has also been theorized that dry water could have potential uses in the construction of fuel cells for automobiles due to its ability to store and stabilize very large amounts of volatile gases and materials without permanently binding them. Due to its nature, dry water is classified as an adsorbent material. It has many potential uses in fields where emulsions are used. Recent studies have also found dry water can act as a catalyst. | 0 | Theoretical and Fundamental Chemistry |
Energy accounting is a system used to measure, analyze and report the energy consumption of different activities on a regular basis. This is done to improve energy efficiency, and to monitor the environment impact of energy consumption. | 0 | Theoretical and Fundamental Chemistry |
This derivation is a slight simplification of Curzon & Ahlborn.
Consider a heat engine, with a single working fluid cycling around the engine. On one side, the working fluid has temperature , and is in direct contact with the hot heat bath. On the other side, it has temperature , and is in direct contact with the cold heat bath.
The heat flow into the engine is , where is the heat conduction coefficient. The heat flow out of the engine is . The power output of the engine is .
Side note: if one cycle of the engine takes time , and during this time, it is in contact with the hot side only for a time , then we can reduce to this case by replacing with . Similar comments apply to the cold side.
By Carnot theorem, we have . This then gives us a problem of constraint optimization:<math display="block">\begin{cases}
\max_{T_H, T_L} \dot W \\
\frac{\dot W}{\dot Q_H} \leq 1 - \frac{T_L}{T_H}
\end{cases} at which point the engine is operating at efficiency .
In particular, if , then we have This is often the case with practical heat engines in power generation plants, where the work fluid can only spend a small amount of time with the hot bath (nuclear reactor core, coal furnance, etc), but a much larger amount of time with the cold bath (open atmosphere, a large body of water, etc). | 0 | Theoretical and Fundamental Chemistry |
In chromatography substances are separated by partition between a stationary phase and a mobile phase. The analyte is dissolved in the mobile phase, and passes over the stationary phase. Separation occurs because of differing affinities of the analytes for the stationary phase. A distribution constant, K can be defined as
where a and a are the equilibrium activities in the stationary and mobile phases respectively. It can be shown that the rate of migration, , is related to the distribution constant by
f is a factor which depends on the volumes of the two phases. Thus, the higher the affinity of the solute for the stationary phase, the slower the migration rate.
There is a wide variety of chromatographic techniques, depending on the nature of the stationary and mobile phases. When the stationary phase is solid, the analyte may form a complex with it. A water softener functions by selective complexation with a sulfonate ion exchange resin. Sodium ions form relatively weak complexes with the resin. When hard water is passed through the resin, the divalent ions of magnesium and calcium displace the sodium ions and are retained on the resin, R.
: RNa + M RM + Na
The water coming out of the column is relatively rich in sodium ions and poor in calcium and magnesium which are retained on the column. The column is regenerated by passing a strong solution of sodium chloride through it, so that the resin–sodium complex is again formed on the column. Ion-exchange chromatography utilizes a resin such as chelex 100 in which iminodiacetate residues, attached to a polymer backbone, form chelate complexes of differing strengths with different metal ions, allowing the ions such as Cu and Ni to be separated chromatographically.
Another example of complex formation is in chiral chromatography in which is used to separate enantiomers from each other. The stationary phase is itself chiral and forms complexes selectively with the enantiomers. In other types of chromatography with a solid stationary phase, such as thin-layer chromatography the analyte is selectively adsorbed onto the solid.
In gas–liquid chromatography (GLC) the stationary phase is a liquid such as polydimethylsiloxane, coated on a glass tube. Separation is achieved because the various components in the gas have different solubility in the stationary phase. GLC can be used to separate literally hundreds of components in a gas mixture such as cigarette smoke or essential oils, such as lavender oil. | 0 | Theoretical and Fundamental Chemistry |
For vessels which are not symmetric about the center (for example rectangular vessel), the problem involves solving a nonlinear partial differential equation instead of a nonlinear ordinary differential equation, which can be solved only through numerical methods in most cases. The equation is
with boundary condition on the bounding surfaces. | 1 | Applied and Interdisciplinary Chemistry |
Levonorgestrel is a progestogen with weak androgenic activity. It has no other important hormonal activity, including no estrogenic, glucocorticoid, or antimineralocorticoid activity. The lack of significant mineralocorticoid or antimineralocorticoid activity with levonorgestrel is in spite of it having relatively high affinity for the mineralocorticoid receptor, which is as much as 75% of that of aldosterone. | 0 | Theoretical and Fundamental Chemistry |
Oxidative addition is the main route to metal boryl complexes. Both B-H and B-B bonds add to low-valent metal complexes. For example, catecholborane oxidatively adds to Pt(0) to give the boryl hydride.
:CHOBH + Pt(PR) → CHOB Pt(PR)H
Addition of diboron tetrafluoride to Vaska's complex gives the triboryl iridium(III) derivative:
:2BF + IrCl(CO)(PPh) → Ir(BF)(CO)(PPh) + ClBF | 0 | Theoretical and Fundamental Chemistry |
Melt spinning is used to manufacture thin metal sheets or ribbons that are near amorphous or non-crystalline. The unique resulting electric and magnetic properties of melt-spun metals are a consequence of this structure as well as the composition of the alloy or metal that was used to form the ribbon. | 1 | Applied and Interdisciplinary Chemistry |
Hydrological models are simplified, conceptual representations of a part of the hydrologic cycle. They are primarily used for hydrological prediction and for understanding hydrological processes, within the general field of scientific modeling. Two major types of hydrological models can be distinguished:
* Models based on data. These models are black box systems, using mathematical and statistical concepts to link a certain input (for instance rainfall) to the model output (for instance runoff). Commonly used techniques are regression, transfer functions, and system identification. The simplest of these models may be linear models, but it is common to deploy non-linear components to represent some general aspects of a catchment's response without going deeply into the real physical processes involved. An example of such an aspect is the well-known behavior that a catchment will respond much more quickly and strongly when it is already wet than when it is dry.
* Models based on process descriptions. These models try to represent the physical processes observed in the real world. Typically, such models contain representations of surface runoff, subsurface flow, evapotranspiration, and channel flow, but they can be far more complicated. Within this category, models can be divided into conceptual and deterministic. Conceptual models link simplified representations of the hydrological processes in an area, whereas deterministic models seek to resolve as much of the physics of a system as possible. These models can be subdivided into single-event models and continuous simulation models.
Recent research in hydrological modeling tries to have a more global approach to the understanding of the behavior of hydrologic systems to make better predictions and to face the major challenges in water resources management. | 1 | Applied and Interdisciplinary Chemistry |
Stevens' research has contributed to understanding how changes in the levels of nitrogen compounds in the soil, deposited from the atmosphere, have had significant effects on the composition of the UK flora. This has shown that the number of different species of plants present is reduced as soils receive more inorganic nitrogen compounds from the atmosphere. Stevens has been involved with a long-term project at Tadmore Moor that started in 1986 following the effects of nitrogen fertiliser on this wetland. No fertiliser was added after 1990 but she could still find effects in 2005.
Stevens is part of the Nutrient Network, an international collaboration investigating how grasslands are affected by global climate change, specifically how anthropogenic increases in nitrogen and phosphorus levels affect plant productivity and diversity and the interaction of the plants with grazing animals. This research involves the partners setting up the same experiment in their location so that global comparisons can readily be made. It started in 2005 and had grown to 130 sites by 2021.
She is a trustee of the Ecological Continuity Trust that maintains long-term ecological field experiments and their data in the UK. | 0 | Theoretical and Fundamental Chemistry |
In general, SEC is considered a low-resolution chromatography as it does not discern similar species very well, and is therefore often reserved for the final step of a purification. The technique can determine the quaternary structure of purified proteins that have slow exchange times, since it can be carried out under native solution conditions, preserving macromolecular interactions. SEC can also assay protein tertiary structure, as it measures the hydrodynamic volume (not molecular weight), allowing folded and unfolded versions of the same protein to be distinguished. For example, the apparent hydrodynamic radius of a typical protein domain might be 14 Å and 36 Å for the folded and unfolded forms, respectively. SEC allows the separation of these two forms, as the folded form elutes much later due to its smaller size. | 1 | Applied and Interdisciplinary Chemistry |
As studied mainly on cisplatin, but presumably for other members as well, platinum-based antineoplastic agents cause crosslinking of DNA as monoadduct, interstrand crosslinks, intrastrand crosslinks or DNA protein crosslinks. Mostly they act on the adjacent N-7 position of guanine, forming a 1, 2 intrastrand crosslink. The resultant crosslinking inhibits DNA repair and/or DNA synthesis. This mechanism leads to specific patterns of damage in DNA, which can kill cancer cells but can also increase the risk of secondary tumors developing.
Platinum-based antineoplastic agents are sometimes described as "alkylating-like" due to similar effects as alkylating antineoplastic agents, although they do not have an alkyl group. | 1 | Applied and Interdisciplinary Chemistry |
An Extraordinary General Meeting was held on 27 March 1906, under the direction of president Edward Divers and secretary C. G. Cresswell, to discuss a motion to apply for incorporation under a royal charter. The resolution was formally proposed by Sir (Thomas) Boverton Redwood. After some discussion, the motion was unanimously supported.
The society was formally incorporated, by Royal Charter, as of 17 June 1907, and its bylaws were published in the Journal of the Society of Chemical Industry. By that time, it had expanded to include a number of satellite chapters, including Canada, New South Wales, New York and New England as well as locations within Great Britain. | 1 | Applied and Interdisciplinary Chemistry |
Nitric acid is a corrosive acid and a powerful oxidizing agent. The major hazard posed by it is chemical burns, as it carries out acid hydrolysis with proteins (amide) and fats (ester), which consequently decomposes living tissue (e.g. skin and flesh). Concentrated nitric acid stains human skin yellow due to its reaction with the keratin. These yellow stains turn orange when neutralized. Systemic effects are unlikely, and the substance is not considered a carcinogen or mutagen.
The standard first-aid treatment for acid spills on the skin is, as for other corrosive agents, irrigation with large quantities of water. Washing is continued for at least 10–15 minutes to cool the tissue surrounding the acid burn and to prevent secondary damage. Contaminated clothing is removed immediately and the underlying skin washed thoroughly.
Being a strong oxidizing agent, nitric acid can react violently with many compounds. | 0 | Theoretical and Fundamental Chemistry |
Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana (singular: granum). Grana are connected by intergranal or stromal thylakoids, which join granum stacks together as a single functional compartment.
In thylakoid membranes, chlorophyll pigments are found in packets called quantasomes. Each quantasome contains 230 to 250 chlorophyll molecules. | 0 | Theoretical and Fundamental Chemistry |
Despite the widespread classification of genes as either structural or regulatory, these categories are not an absolute division. Recent genetic discoveries call into question the distinction between regulatory and structural genes.
The distinction between regulatory and structural genes can be attributed to the original 1959 work on Lac operon protein expression. In this instance, a single regulatory protein was detected that affected the transcription of the other proteins now known to compose the Lac operon. From this point forward, the two types of coding sequences were separated.
However, increasing discoveries of gene regulation suggest greater complexity. Structural gene expression is regulated by numerous factors including epigenetics (e.g. methylation), RNAi, and more. Regulatory and structural genes can be epigenetically regulated identically, so not all regulation is coded for by “regulatory genes”.
There are also examples of proteins that do not decidedly fit either category, such as chaperone proteins. These proteins aid in the folding of other proteins, a seemingly regulatory role. Yet these same proteins also aid in the movement of their chaperoned proteins across membranes, and have now been implicated in immune responses (see Hsp60) and in the apoptotic pathway (see Hsp70).
More recently, microRNAs were found to be produced from the internal transcribed spacers of rRNA genes. Thus an internal component of a structural gene is, in fact, regulatory. Binding sites for microRNAs were also detected within coding sequences of genes. Typically interfering RNAs target the 3’UTR, but inclusion of binding sites within the sequence of the protein itself allows the transcripts of these proteins to effectively regulate the microRNAs within the cell. This interaction was demonstrated to have an effect on expression, and thus again a structural gene contains a regulatory component. | 1 | Applied and Interdisciplinary Chemistry |
The final peptide is often modified, e.g., by glycosylation, acylation, halogenation, or hydroxylation. The responsible enzymes are usually associated to the synthetase complex and their genes are organized in the same operons or gene clusters. | 1 | Applied and Interdisciplinary Chemistry |
In organic and physical organic chemistry, Clars rule is an empirical rule that relates the chemical stability of a molecule with its aromaticity. It was introduced in 1972 by the Austrian organic chemist Erich Clar in his book The Aromatic Sextet'. The rule states that given a polycyclic aromatic hydrocarbon, the resonance structure most important to characterize its properties is that with the largest number of aromatic π-sextets i.e. benzene-like moieties. | 0 | Theoretical and Fundamental Chemistry |
5-Diphosphomevalonic acid (or mevalonate-5-pyrophosphate, or 5-pyrophosphomevalonate) is an intermediate in the mevalonate pathway. | 1 | Applied and Interdisciplinary Chemistry |
The idea of interstitial compounds was started in the late 1930s and they are often called Hagg phases after Hägg. Transition metals generally crystallise in either the hexagonal close packed or face centered cubic structures, both of which can be considered to be made up of layers of hexagonally close packed atoms. In both of these very similar lattices there are two sorts of interstice, or hole:
*Two tetrahedral holes per metal atom, i.e. the hole is between four metal atoms
*One octahedral hole per metal atom, i.e. the hole is between six metal atoms
It was suggested by early workers that:
*the metal lattice was relatively unaffected by the interstitial atom
*the electrical conductivity was comparable to that of the pure metal
*there was a range of composition
*the type of interstice occupied was determined by the size of the atom
These were not viewed as compounds, but rather as solutions, of say carbon, in the metal lattice, with a limiting upper “concentration” of the smaller atom that was determined by the number of interstices available. | 1 | Applied and Interdisciplinary Chemistry |
In 1953, Strassmann gave up the directorship, choosing instead to focus on his research and scholarship at the University of Mainz. He succeeded in building up the departments capabilities, and he worked directly with students. Strassmann began these undertakings at the University of Mainz with a few scattered rooms and very little money. He negotiated with the university and with Badische Anilin- und Soda-Fabriken (B.A.S.F.) to fund an institute for the chemical sciences at the university with a focus on nuclear chemistry. He also lobbied the German federal government to fund a neutron generator, a nuclear reactor for research purposes, and a special institute for nuclear chemistry. Strassmans creation, the Institute for Nuclear Chemistry, officially opened on 3 April 1967.
In 1957 Strassmann was one of the Göttinger Achtzehn (Göttingen eighteen), a group of leading nuclear researchers of the Federal Republic of Germany who wrote a manifesto (Göttinger Manifest, Göttinger Erklärung) opposing chancellor Konrad Adenauer and defense secretary Franz-Josef Straußs plans to equip the Bundeswehr, Western Germanys army, with tactical nuclear weapons.
Strassmann retired in 1970. He died on 22 April 1980 in Mainz. | 0 | Theoretical and Fundamental Chemistry |
He was born at High Close Hall near Plumbland, the son of local gentry, George Brownrigg. William's mother, Mary Brownrigg, was from Ireland.
William was educated in Latin and Greek by a local clergyman from the age of 13 and by the age of 15 was an apprentice to an apothecary in Carlisle. Then followed two years studying under a surgeon in London before going to Leiden where he studied under Boerhaave, 's Gravesande, van Royen and Albinus. He graduated in 1737 with his thesis "De Praxi Medica Ineunda" – about the environment where the clinician practises medicine. He gained the degree of Doctor of Medicine (MD). | 1 | Applied and Interdisciplinary Chemistry |
Chemistry determines the optimum relationship between the fuel and the material, among other variables. The reverberatory furnace can be contrasted on the one hand with the blast furnace, in which fuel and material are mixed in a single chamber, and, on the other hand, with crucible, muffling, or retort furnaces, in which the subject material is isolated from the fuel and all of the products of combustion including gases and flying ash. There are, however, a great many furnace designs, and the terminology of metallurgy has not been very consistently defined, so it is difficult to categorically contradict other views.
The applications of these devices fall into two general categories, metallurgical melting furnaces, and lower temperature processing furnaces typically used for metallic ores and other minerals.
A reverberatory furnace is at a disadvantage from the standpoint of efficiency compared to a blast furnace due to the separation of the burning fuel and the subject material, and it is necessary to effectively utilize both reflected radiant heat and direct contact with the exhaust gases (convection) to maximize heat transfer. Historically these furnaces have used solid fuel, and bituminous coal has proven to be the best choice. The brightly visible flames, due to the substantial volatile component, give more radiant heat transfer than anthracite coal or charcoal.
Contact with the products of combustion, which may add undesirable elements to the subject material, is used to advantage in some processes. Control of the fuel/air balance can alter the exhaust gas chemistry toward either an oxidizing or a reducing mixture, and thus alter the chemistry of the material being processed. For example, cast iron can be puddled in an oxidizing atmosphere to convert it to the lower-carbon mild steel or bar iron. The Siemens-Martin oven in open hearth steelmaking is also a reverberatory furnace.
Reverberatory furnaces (in this context, usually called air furnaces) were formerly also used for melting brass, bronze, and pig iron for foundry work. They were also, for the first 75 years of the 20th century, the dominant smelting furnace used in copper production, treating either roasted calcine or raw copper sulfide concentrate. While they have been supplanted in this role, first by flash furnaces and more recently also by the Ausmelt and ISASMELT furnaces, they are very effective at producing slags with low copper losses. | 1 | Applied and Interdisciplinary Chemistry |
Different phases of digestion take place including: the cephalic phase, gastric phase, and intestinal phase.
The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex. Taste and smell stimuli are sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal (secretes acid) and G cell (secretes gastrin) activity via D cell secretion of somatostatin.
The gastric phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes. This activates the release of acetylcholine, which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0.5% hydrochloric acid, which lowers the pH to the desired pH of 1–3. Acid release is also triggered by acetylcholine and histamine.
The intestinal phase has two parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes. | 1 | Applied and Interdisciplinary Chemistry |
Pure Togni reagent II is metastable at room temperature. Heating it above the melting point will lead to strong exothermic decomposition, in which trifluoroiodomethane (CFI) is released. The heat of composition at a temperature of 149 °C and higher has been determined to be 502 J·g. From recrystallization in acetonitrile, small amounts of trifluoromethyl-2-iodobenzoate and 2-iodobenzyl fluoride were observed as decomposition products. Togni reagent II reacts violently with strong bases and acids, as well as reductants. In tetrahydrofuran, the compound polymerizes. | 0 | Theoretical and Fundamental Chemistry |
The Fermi function that appears in the beta spectrum formula accounts for the Coulomb attraction / repulsion between the emitted beta and the final state nucleus. Approximating the associated wavefunctions to be spherically symmetric, the Fermi function can be analytically calculated to be:
where is the final momentum, Γ the Gamma function, and (if is the fine-structure constant and the radius of the final state nucleus) , (+ for electrons, − for positrons), and .
For non-relativistic betas (), this expression can be approximated by:
Other approximations can be found in the literature. | 0 | Theoretical and Fundamental Chemistry |
Under the free electron model, the electrons in a metal can be considered to form a uniform Fermi gas. The number density of conduction electrons in metals ranges between approximately 10 and 10 electrons per m, which is also the typical density of atoms in ordinary solid matter. This number density produces a Fermi energy of the order:
where m is the electron rest mass. This Fermi energy corresponds to a Fermi temperature of the order of 10 kelvins, much higher than the temperature of the Suns surface. Any metal will boil before reaching this temperature under atmospheric pressure. Thus for any practical purpose, a metal can be considered as a Fermi gas at zero temperature as a first approximation (normal temperatures are small compared to T'). | 0 | Theoretical and Fundamental Chemistry |
A frequency comb or spectral comb is a spectrum made of discrete and regularly spaced spectral lines.
In optics, a frequency comb can be generated by certain laser sources.
A number of mechanisms exist for obtaining an optical frequency comb, including periodic modulation (in amplitude and/or phase) of a continuous-wave laser, four-wave mixing in nonlinear media, or stabilization of the pulse train generated by a mode-locked laser. Much work has been devoted to this last mechanism, which was developed around the turn of the 21st century and ultimately led to one half of the Nobel Prize in Physics being shared by John L. Hall and Theodor W. Hänsch in 2005.
The frequency domain representation of a perfect frequency comb is like a Dirac comb, a series of delta functions spaced according to
where is an integer, is the comb tooth spacing (equal to the mode-locked laser's repetition rate or, alternatively, the modulation frequency), and is the carrier offset frequency, which is less than .
Combs spanning an octave in frequency (i.e., a factor of two) can be used to directly measure (and correct for drifts in) . Thus, octave-spanning combs can be used to steer a piezoelectric mirror within a carrier–envelope phase-correcting feedback loop. Any mechanism by which the combs' two degrees of freedom ( and ) are stabilized generates a comb that is useful for mapping optical frequencies into the radio frequency for the direct measurement of optical frequency. | 0 | Theoretical and Fundamental Chemistry |
Core histones are four proteins called H2A, H2B, H3 and H4 and they are all found in equal parts in the cell. All four of the core histone amino acid sequences contain between 20 and 24% of lysine and arginine and the size or the protein ranges between 11400 and 15400 daltons, making them relatively small, yet highly positively charged proteins. High content of positively charged amino acids allow them to closely associate with negatively charged DNA. Heterodimers, or histone-only intermediates are formed from histone-fold domains. The formation of histone only-intermediates proceeds when core histones are paired into the interlocked crescent shape quasi-symmetric heterodimer. Each histone fold domain is composed of 3 α-helix regions that are separated by disordered loops. The histone fold domain is responsible for formation of head-to-tail heterodimers of two histones: H2A-H2B and H3-H4. However, H3 and H4 histones first form a heterodimer and then in turn the heterodimer dimerizes to form a tetramer (H3-H4). The heterodimer formation is based on the interaction of hydrophobic amino acid residue interactions between the two proteins.
Quasi symmetry allows the heterodimer to be superimposed on itself by a 180 degree rotation around this symmetry axis. As a result of the rotation, two ends of histones involved in DNA binding of the crescent shape H3-H4 are equivalent, yet they organize different stretches of DNA. The H2A-H2B dimer also folds similarly. The (H3-H4) tetramer is wrapped with DNA around it as a first step of nucleosome formation. Then two H2A-H2B dimers are connected to the DNA-(H3-H4) complex to form a nucleosome.
Each of the four core histones, in addition to their histone-fold domains, also contain flexible, unstructured extensions called histone “tails”. Treatment of nucleosomes with protease trypsin indicates that after histone tails are removed, DNA is able to stay tightly bound to the nucleosome. Histone tails are subject to a wide array of modifications which includes phosphorylation, acetylation, and methylation of serine, lysine and arginine residues. | 1 | Applied and Interdisciplinary Chemistry |
A noble metal is ordinarily regarded as a metallic chemical element that is generally resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals (ruthenium, rhodium, palladium, osmium, iridium) are most often so classified. Silver, copper, and mercury are sometimes included as noble metals, but each of these usually occurs in nature combined with sulfur.
In more specialized fields of study and applications the number of elements counted as noble metals can be smaller or larger. In physics, there are only three noble metals: copper, silver, and gold. In dentistry, silver is not always considered a noble metal because it is subject to corrosion when present in the mouth. In chemistry, the term noble metal is sometimes applied more broadly to any metallic or semimetallic element that does not react with a weak acid and give off hydrogen gas in the process. This broader set includes copper, mercury, technetium, rhenium, arsenic, antimony, bismuth, polonium, gold, the six platinum group metals, and silver.
__TOC__ | 1 | Applied and Interdisciplinary Chemistry |
While the number of possible nuclear reactions is immense, there are several types that are more common, or otherwise notable. Some examples include:
*Fusion reactions – two light nuclei join to form a heavier one, with additional particles (usually protons or neutrons) emitted subsequently.
*Spallation – a nucleus is hit by a particle with sufficient energy and momentum to knock out several small fragments or smash it into many fragments.
*Induced gamma emission belongs to a class in which only photons were involved in creating and destroying states of nuclear excitation.
*Fission reactions – a very heavy nucleus, after absorbing additional light particles (usually neutrons), splits into two or sometimes three pieces. This is an induced nuclear reaction. Spontaneous fission, which occurs without assistance of a neutron, is usually not considered a nuclear reaction. At most, it is not an induced nuclear reaction. | 0 | Theoretical and Fundamental Chemistry |
Inside eukaryotic cells, there is a balance between the processes of translation and mRNA decay. Messages that are being actively translated are bound by ribosomes, the eukaryotic initiation factors eIF-4E and eIF-4G, and poly(A)-binding protein. eIF-4E and eIF-4G block the decapping enzyme (DCP2), and poly(A)-binding protein blocks the exosome complex, protecting the ends of the message. The balance between translation and decay is reflected in the size and abundance of cytoplasmic structures known as P-bodies. The poly(A) tail of the mRNA is shortened by specialized exonucleases that are targeted to specific messenger RNAs by a combination of cis-regulatory sequences on the RNA and trans-acting RNA-binding proteins. Poly(A) tail removal is thought to disrupt the circular structure of the message and destabilize the cap binding complex. The message is then subject to degradation by either the exosome complex or the decapping complex. In this way, translationally inactive messages can be destroyed quickly, while active messages remain intact. The mechanism by which translation stops and the message is handed-off to decay complexes is not understood in detail. | 1 | Applied and Interdisciplinary Chemistry |
DBT has been shown to physically interact with PER in vitro and in vivo, and to create a stable complex with PER throughout the circadian cycle. PER that has been phosphorylated by DBT is recognized by the Slimb protein. Slimb is a component of the Skp1/Cullin/F-box protein (SCF) ubiquitin ligase complex, which marks proteins for proteosomal degradation in a phosphorylation-dependent manner. Enhanced PER degradation in the cytoplasm is predicted to delay nuclear translocation of both PER and TIM, and to thus affect the period of circadian rhythms.
The mutation dbtS, associated with a proline to serine substitution at residue 47 [P47S], shortens period length by about 6 h. dbtL contains an amino acid substitution of isoleucine for methionine at residue 80 (M80I) and lengthens period to 29 h. A third mutation, dbtAR, is associated with a change from histidine 126 to tyrosine and causes arrhythmia. PER protein in this mutant is hypophosphorylated. Each of these mutations maps to the kinase domain of DBT gene. The short- and long-period alleles of DBT enhance or attenuate, respectively, PER degradation in the nucleus, further demonstrating the importance of timely PER degradation as a critical determinant in establishing 24-h rhythmicity. In addition to influencing protein degradation, DBT affects the timing of nuclear accumulation of PER. The short-period mutant dbtS delays PER nuclear accumulation, which is independent of PER protein stability, and arrhythmic alleles of dbt cause nuclear accumulation of PER in clock-containing cells of larval and adult Drosophila.
Both mammalian CK1δ and CK1ε contain closely related 123-amino-acid carboxy-terminal domains that can auto-regulate kinase activity. CK1δ and CK1ε are 53% identical. These domains are not related to the carboxy-terminal domain of double-time, suggesting a split in the evolution of the mammalian and fly homologs.
A similar function for casein kinase 2 has been reported in Arabidopsis thaliana, Drosophila, and Neurospora. | 1 | Applied and Interdisciplinary Chemistry |
Aluminium smelting is highly energy intensive, and in some countries is economical only if there are inexpensive sources of electricity. In some countries, smelters are given exemptions to energy policy like renewable energy targets.
To reduce the energy cost of the smelting process, alternative electrolytes such as Na3AlF6 are being investigated that can operate at a lower temperature. However, changing the electrolyte changes the kinetics of the liberated oxygen from the AlO ore. This change in bubble formation can alter the rate the anode reacts with Oxygen or the electrolyte and effectively change the efficiency of the reduction process.
Inert anodes, used in tandem with vertical electrode cells, can also reduce the energy cost of aluminum reduction up to 30% by lowering the voltage needed for reduction to occur. Applying these two technologies at the same times allows the anode-cathode distance to be minimized which decreases restive losses. | 1 | Applied and Interdisciplinary Chemistry |
The known cases up to 2015 are discussed in a review article by Bučar, Lancaster, and Bernstein.
Dibenzoxazepines
Multidisciplinary studies involving experimental and computational approaches were applied to pharmaceutical molecules to facilitate the comparison of their solid-state structures. Specifically, this study has focused on exploring how changes in molecular structure affect the molecular conformation, packing motifs, interactions in the resultant crystal lattices and the extent of solid-state diversity of these compounds. The results highlight the value of crystal structure prediction studies and PIXEL calculations in the interpretation of the observed solid-state behaviour and quantifying the intermolecular interactions in the packed structures and identifying the key stabilising interactions. An experimental screen yielded 4 physical forms for clozapine as compared to 60 distinct physical forms for olanzapine. The experimental screening results of clozapine are consistent with its crystal energy landscape which confirms that no alternate packing arrangement is thermodynamically competitive to the experimentally obtained structure. Whilst in case of olanzapine, crystal energy landscape highlights that the extensive experimental screening has probably not found all possible polymorphs of olanzapine, and further solid form diversity could be targeted with a better understanding of the role of kinetics in its crystallisation. CSP studies were able to offer an explanation for the absence of the centrosymmetric dimer in anhydrous clozapine. PIXEL calculations on all the crystal structures of clozapine revealed that similar to olanzapine, the intermolecular interaction energy in each structure is also dominated by the Ed. Despite the molecular structure similarity between amoxapine and loxapine (molecules in group 2), the crystal packing observed in polymorphs of loxa differs significantly from the amoxapine. A combined experimental and computational study demonstrated that the methyl group in loxapine has a significant influence in increasing the range of accessible solid forms and favouring various alternate packing arrangements. CSP studies have again helped in explaining the observed solid-state diversity of loxapine and amoxapine. PIXEL calculations showed that in absence of strong H-bonds, weak H-bonds such as C–H...O, C–H...N and dispersion interactions play a key role in stabilising the crystal lattice of both the molecules. Efficient crystal packing of amoxapine seems to be contributing towards its monomorphic behaviour as compared to the comparatively less efficient packing of loxapine molecules in both polymorphs. The combination of experimental and computational approaches has provided a deeper understanding of the factors influencing the solid-state structure and diversity in these compounds. Hirshfeld surfaces using Crystal Explorer represent another way of exploring packing modes and intermolecular interactions in molecular crystals. The influence of changes in the small substituents on shape and electron distribution can also be investigated by mapping the total electron density on the electrostatic potential for molecules in the gas phase. This allows straightforward visualisation and comparison of overall shape, electron-rich and electron-deficient regions within molecules. The shape of these molecules can be further investigated to study its influence on diverse solid-state diversity.
Posaconazole
The original formulations of posaconazole on the market licensed as Noxafil were formulated utilising form I of posaconazole. The discovery of polymorphs of posaconazole increased rapidly and resulted in much research in crystallography of posaconazole. A methanol solvate and a 1,4-dioxane co-crystal were added to the Cambridge Structural Database (CSD). | 0 | Theoretical and Fundamental Chemistry |
Electrocatalysis for CO reduction is not practiced commercially but remains a topic of research. The reduction of CO into useable products is a potential way to combat climate change. Electrocatalysts can promote the reduction of carbon dioxide into methanol and other useful fuel and stock chemicals. The most valuable reduction products of CO are those that have a higher energy content, meaning that they can be reused as fuels. Thus, catalyst development focuses on the production of products such as methane and methanol. Homogeneous catalysts, such as enzymes and synthetic coordination complexes have been employed for this purpose. A variety of nanomaterials have also been studied for CO reduction, including carbon-based materials and framework materials. | 0 | Theoretical and Fundamental Chemistry |
Organoids offer researchers an exceptional model to study developmental biology. Since the identification of pluripotent stem cells, there have been great advancements in directing pluripotent stem cells fate in vitro using 2D cultures. These advancements in PSC fate direction, coupled with the advancements in 3D culturing techniques allowed for the creation of organoids that recapitulate the properties of various specific subregions of a multitude of organs. The use of these organoids has thus greatly contributed to expanding our understanding of the processes of organogenesis, and the field of developmental biology. In central nervous system development, for example, organoids have contributed to our understanding of the physical forces that underlie retinal cup formation. More recent work has extended cortical organoid growth periods extensively and at nearly a year under specific differentiation conditions, the organoids persist and have some features of human fetal development stages. | 1 | Applied and Interdisciplinary Chemistry |
Gallium arsenide (GaAs) transistors are used in the RF power amplifiers for cell phones and wireless communicating. | 0 | Theoretical and Fundamental Chemistry |
Some, but not all, carboxypeptidases are initially produced in an inactive form; this precursor form is referred to as a procarboxypeptidase. In the case of pancreatic carboxypeptidase A, the inactive zymogen form - pro-carboxypeptidase A - is converted to its active form - carboxypeptidase A - by the enzyme trypsin. This mechanism ensures that the cells wherein pro-carboxypeptidase A is produced are not themselves digested. | 1 | Applied and Interdisciplinary Chemistry |
In order to perform a dynamic simulation with such a network it is necessary to construct an ordinary differential equation
system that describes the rates of change in each metabolite's concentration or amount. To this end, a rate law, i.e., a kinetic equation that determines the rate of reaction based on the concentrations of all reactants is required for each reaction. Software packages that include numerical integrators, such as COPASI or [http://www.cogsys.cs.uni-tuebingen.de/software/SBMLsimulator SBMLsimulator], are then able to simulate the system dynamics given an initial condition. Often these rate laws contain kinetic parameters with uncertain values. In many cases it is desired to estimate these parameter values with respect to given time-series data of metabolite concentrations. The system is then supposed to reproduce the given data. For this purpose the distance between the given data set and the result of the simulation, i.e., the numerically or in few cases analytically obtained solution of the differential equation system is computed. The values of the parameters are then estimated to minimize this distance. One step further, it may be desired to estimate the mathematical structure of the differential equation system because the real rate laws are not known for the reactions within the system under study. To this end, the program [http://www.cogsys.cs.uni-tuebingen.de/software/SBMLsqueezer SBMLsqueezer] allows automatic creation of appropriate rate laws for all reactions with the network. | 1 | Applied and Interdisciplinary Chemistry |
The city of Toronto approved a by-law in May 2009 mandating green roofs on residential and industrial buildings. There is criticism from Green Roofs for Healthy Cities that the new laws are not stringent enough, since they will only apply to residential building that are a minimum of six stories high. By 31 January 2011, industrial buildings were required to render 10% or of their roofs green. Toronto City Hall's Podium roof was renovated to include a rooftop garden, the largest publicly accessible roof in the city. The green roof was opened to the public in June 2010. Many green roofs in Canada also use sustainable rainwater harvesting practices.
In 2008, the Vancouver Convention Centre installed a living roof of indigenous plants and grasses on its West building, making it the largest green roof in Canada.
The new Canadian War Museum in Ottawa, opened in 2005, also features a grass-covered roof.
During the renovation of the Hamilton City Hall in Hamilton, Ontario that spanned from 2007 to 2010, many efforts were taken to enhance the environmentally friendly nature of the structure, which included the addition of a grass-covered roof.
Simon Fraser University's Burnaby campus contains a substantial number of green roofs.
Canadas first LEED Platinum V4 Home in Wakefield QC, EcoHomes Edelweiss House, has a living Green Roof which is sloped at 12 degrees. | 1 | Applied and Interdisciplinary Chemistry |
Paired receptors are membrane proteins with extracellular domains that interact with extracellular ligands. The extracellular region may contain multiple repeating protein domains and may be members of either the immunoglobulin or C-type lectin families. The extracellular domains of homologous paired receptors are typically very similar in sequence but have different binding affinity for their shared ligands, with the inhibitory member of the pair binding more tightly.
Homologous paired receptors have characteristic differences in their transmembrane and cytoplasmic regions that distinguish the activating and inhibiting members of the pair. Inhibitory receptors have a cytoplasmic sequence typically containing at least one immunoreceptor tyrosine-based inhibitory motif (ITIM). Activating receptors have a truncated cytoplasmic sequence compared to their corresponding inhibitory receptor and feature a positively charged amino acid residue in their transmembrane domain, enabling protein-protein interaction with an adaptor protein that possesses a immunoreceptor tyrosine-based activation motif (ITAM). | 1 | Applied and Interdisciplinary Chemistry |
All enzyme assays measure either the consumption of substrate or production of product over time. A large number of different methods of measuring the concentrations of substrates and products exist and many enzymes can be assayed in several different ways. Biochemists usually study enzyme-catalysed reactions using four types of experiments:
* Initial rate experiments. When an enzyme is mixed with a large excess of the substrate, the enzyme-substrate intermediate builds up in a fast initial transient. Then the reaction achieves a steady-state kinetics in which enzyme substrate intermediates remains approximately constant over time and the reaction rate changes relatively slowly. Rates are measured for a short period after the attainment of the quasi-steady state, typically by monitoring the accumulation of product with time. Because the measurements are carried out for a very short period and because of the large excess of substrate, the approximation that the amount of free substrate is approximately equal to the amount of the initial substrate can be made. The initial rate experiment is the simplest to perform and analyze, being relatively free from complications such as back-reaction and enzyme degradation. It is therefore by far the most commonly used type of experiment in enzyme kinetics.
* Progress curve experiments. In these experiments, the kinetic parameters are determined from expressions for the species concentrations as a function of time. The concentration of the substrate or product is recorded in time after the initial fast transient and for a sufficiently long period to allow the reaction to approach equilibrium. Progress curve experiments were widely used in the early period of enzyme kinetics, but are less common now.
* Transient kinetics experiments. In these experiments, reaction behaviour is tracked during the initial fast transient as the intermediate reaches the steady-state kinetics period. These experiments are more difficult to perform than either of the above two classes because they require specialist techniques (such as flash photolysis of caged compounds) or rapid mixing (such as stopped-flow, quenched flow or continuous flow).
* Relaxation experiments. In these experiments, an equilibrium mixture of enzyme, substrate and product is perturbed, for instance by a temperature, pressure or pH jump, and the return to equilibrium is monitored. The analysis of these experiments requires consideration of the fully reversible reaction. Moreover, relaxation experiments are relatively insensitive to mechanistic details and are thus not typically used for mechanism identification, although they can be under appropriate conditions.
Enzyme assays can be split into two groups according to their sampling method: continuous assays, where the assay gives a continuous reading of activity, and discontinuous assays, where samples are taken, the reaction stopped and then the concentration of substrates/products determined. | 1 | Applied and Interdisciplinary Chemistry |
Pore formation following ultrasound application was first reported in 1999 in a study that observed cell membrane craters following ultrasound application at 255 kHz. Later, sonoporation mediated microinjection of dextran molecules showed that membrane permeability mechanisms differ depending on the size of dextran molecules. Microinjection of dextran molecules from 3 to 70 kDa was reported to have crossed the cellular membrane via transient pores. In contrast, dextran molecules of 155 and 500 kDa were predominantly found in vesicle-like structures, likely indicating the mechanism of endocytosis. This variability in membrane behavior has led to other studies investigating membrane rupture and resealing characteristics depending on ultrasound amplitude and duration. | 1 | Applied and Interdisciplinary Chemistry |
NOEs are sensitive to interatomic distances, allowing their usage as a conformational probe, or proof of a glycoside bond formation. It's a common practice to compare calculated to experimental proton-proton NOEs in oligosaccharides to confirm a theoretical conformational map. Calculation of NOEs implies an optimization of molecular geometry. | 0 | Theoretical and Fundamental Chemistry |
Shamoo currently resides in Columbia, MD with his wife and occasional co-author, Bonnie Bricker; his daughter, and stepdaughter. He has two sons and another stepdaughter who also all reside in the Washington Metropolitan Area. | 1 | Applied and Interdisciplinary Chemistry |
If soap bubbles are blown into air that is below a temperature of , they will freeze when they touch a surface. The air inside will gradually diffuse out, causing the bubble to crumble under its own weight. At temperatures below about , bubbles will freeze in the air and may shatter when hitting the ground. When a bubble is blown with warm air, the bubble will freeze to an almost perfect sphere at first, but when the warm air cools, and a reduction in volume occurs, there will be a partial collapse of the bubble. A bubble, created successfully at this low temperature, will always be rather small; it will freeze quickly and will shatter if increased further.
Freezing of small soap bubbles happens within 2 seconds after setting on snow (at air temperature around –10...–14 °C). | 1 | Applied and Interdisciplinary Chemistry |
Most photosynthetic, oxygen-producing organisms contain the positive chlorophyll biosynthesis regulator GENOMES UNCOUPLED 4 (GUN4). Research suggests that GUN4 regulates chlorophyll synthesis, by activating the enzyme Magnesium chelatase, which catalyzes the insertion of Mg into Protoporphyrin IX. Bilins noncovalently bind to CrGUN4, an algal GUN4 from Chlamydomonas reinhardtii, which has been shown to participate in retrograde signaling. | 1 | Applied and Interdisciplinary Chemistry |
Photopharmacology is an emerging multidisciplinary field that combines photochemistry and pharmacology. Built upon the ability of light to change the pharmacokinetics and pharmacodynamics of bioactive molecules, it aims at regulating the activity of drugs in vivo by using light. The light-based modulation is achieved by incorporating molecular photoswitches such as azobenzene and diarylethenes or photocages such as o-nitrobenzyl, coumarin, and BODIPY compounds into the pharmacophore. This selective activation of the biomolecules helps prevent or minimize off-target activity and systemic side effects. Moreover, light being the regulatory element offers additional advantages such as the ability to be delivered with high spatiotemporal precision, low to negligible toxicity, and the ability to be controlled both qualitatively and quantitatively by tuning its wavelength and intensity.
Though photopharmacology is a relatively new field, the concept of using light in therapeutic applications came into practice a few decades ago. Photodynamic therapy (PTD) is a well-established clinically practiced protocol in which photosensitizers are used to produce singlet oxygen for destroying diseased or damaged cells or tissues. Optogenetics is another method that relies on light for dynamically controlling biological functions especially brain and neural. Though this approach has proven useful as a research tool, its clinical implementation is limited by the requirement for genetic manipulation. Mainly, these two techniques laid the foundation for photopharmacology. Today, it is a rapidly evolving field with diverse applications in both basic research and clinical medicine which has the potential to overcome some of the challenges limiting the range of applications of the other light-guided therapies.
Figure 1. Schematic representation of the mechanism of (a) photopharmacology (b) photodynamic therapy, and (c) optogenetics
The discovery of natural photoreceptors such as rhodopsins in the eye inspired the biomedical and pharmacology research community to engineer light-sensitive proteins for therapeutic applications. The development of synthetic photoswitchable molecules is the most significant milestone in the history of light-delivery systems. Scientists are continuing with their efforts to explore new photoswitches and delivery strategies with enhanced performance to target different biological molecules such as ion channels, nucleic acid, and enzyme receptors. Photopharmacology research progressed from in vitro to in vivo studies in a significantly short period of time yielding promising results in both forms. Clinical trials are underway to assess the safety and efficacy of these photopharmacological therapies further and validate their potential as an innovative drug delivery approach. | 1 | Applied and Interdisciplinary Chemistry |
Chibaite is a rare silicate mineral. It is a silica clathrate with formula (n = 3/17 (max)). The mineral is cubic (diploidal class, m) and the silica hosts or traps various hydrocarbon molecules, such as methane, ethane, propane and isobutane.
Chibaite was first described for specimens collected from Arakawa, Minamibōsō, Chiba Prefecture, Honshu Island, Japan. The mineral was approved by the IMA in 2009. | 0 | Theoretical and Fundamental Chemistry |
Oligomer Restriction (abbreviated OR) is a procedure to detect an altered DNA sequence in a genome. A labeled oligonucleotide probe is hybridized to a target DNA, and then treated with a restriction enzyme. If the probe exactly matches the target, the restriction enzyme will cleave the probe, changing its size. If, however, the target DNA does not exactly match the probe, the restriction enzyme will have no effect on the length of the probe. The OR technique, now rarely performed, was closely associated with the development of the popular polymerase chain reaction (PCR) method. | 1 | Applied and Interdisciplinary Chemistry |
Streaming currents in well-defined geometries are a sensitive method to characterize the zeta potential of surfaces, which is important in the fields of colloid and interface science. In geology, measurements of related spontaneous potential are used for evaluations of formations. Streaming potential has to be considered in design for flow of poorly conductive fluids (e.g., gasoline lines) because of the danger of buildup of high voltages. The streaming current monitor (SCM) is a fundamental tool for monitoring coagulation in wastewater treatment plants. The degree of coagulation of raw water may be monitored by the use of an SCM to provide a positive feedback control of coagulant injection. As the streaming current of the wastewater increases, more coagulant agent is injected into the stream. The higher levels of coagulant agent cause the small colloidal particles to coagulate and sediment out of the stream. Since less colloid particles are in the wastewater stream, the streaming potential decreases. The SCM recognizes this and subsequently reduces the amount of coagulant agent injected into the wastewater stream. The implementation of SCM feedback control has led to a significant materials cost reduction, one that was not realized until the early 1980s. In addition to monitoring capabilities, the streaming current could, in theory, generate usable electrical power. This process, however, has yet to be applied as typical streaming potential mechanical to electrical efficiencies are around 1%. | 0 | Theoretical and Fundamental Chemistry |
The term polyol is used for various chemistries of the molecular backbone. Polyols may be reacted with diisocyanates or polyisocyanates to produce polyurethanes. MDI finds considerable use in PU foam production. Polyurethanes are used to make flexible foam for mattresses and seating, rigid foam insulation for refrigerators and freezers, elastomeric shoe soles, fibers (e.g. Spandex), coatings, sealants and adhesives.
The term polyol is also attributed to other molecules containing hydroxyl groups. For instance, polyvinyl alcohol is (CHCHOH) with n hydroxyl groups where n can be in the thousands. Cellulose is a polymer with many hydroxyl groups, but it is not referred to as a polyol. | 0 | Theoretical and Fundamental Chemistry |
For equibiaxial extension in the and directions, the principal stretches are . From incompressibility . Hence .
Therefore,
The left Cauchy–Green deformation tensor can then be expressed as
If the directions of the principal stretches are oriented with the coordinate basis vectors, we have
The engineering strain is . The engineering stress is | 0 | Theoretical and Fundamental Chemistry |
In a report by the Nordic Council of Ministers, the total annual health-related costs associated with human exposure to PFASs were estimated to be at least €52–84 billion in the European Economic Area (EEA) countries. Aggregated annual costs covering environmental screening, monitoring where contamination is found, water treatment, soil remediation and health assessment total €821 million – 170 billion in the EEA plus Switzerland.
In the United States, estimated PFAS-attributable disease costs amount to 6–62 billion US$. Studies have estimated the annual healthcare costs in the United States of each of some of the major diseases attributed to PFAS. | 0 | Theoretical and Fundamental Chemistry |
A bypass transition is a laminar–turbulent transition in a fluid flow over a surface. It occurs when a laminar boundary layer transitions to a turbulent one through some secondary instability mode, bypassing some of the pre-transitional events that typically occur in a natural laminar–turbulent transition. | 1 | Applied and Interdisciplinary Chemistry |
From 1993 to 2007, the cDNA library was maintained by the IMAGE Consortium, a joint effort of four academic groups led by Drs. Greg Lennon, Charles Auffray, Mihael Polymeropoulos, and Marcelo Bento Soares. At the end of 2007, the consortium handed over operations and stocks to a company associated with Open Biosystems. | 1 | Applied and Interdisciplinary Chemistry |
Ste5 is involved in the following biological processes:
*Invasive growth in response to glucose limitation
*Negative regulation of the MAPK cascade
*Pheromone-dependent signal transduction involved in conjugation with cellular fusion
*Positive regulation of protein phosphorylation
*Regulation of RNA-mediated transposition | 1 | Applied and Interdisciplinary Chemistry |
Flory–Stockmayer theory is a theory governing the cross-linking and gelation of step-growth polymers. The Flory–Stockmayer theory represents an advancement from the Carothers equation, allowing for the identification of the gel point for polymer synthesis not at stoichiometric balance. The theory was initially conceptualized by Paul Flory in 1941 and then was further developed by Walter Stockmayer in 1944 to include cross-linking with an arbitrary initial size distribution.
The Flory–Stockmayer theory was the first theory investigating percolation processes. Flory–Stockmayer theory is a special case of random graph theory of gelation. | 0 | Theoretical and Fundamental Chemistry |
It may be necessary to repair a concrete structure following damage (e.g. due to age, chemical attack, fire, impact, movement or reinforcement corrosion). Strengthening may be necessary if the structure is weakened (e.g. due to design or construction errors, excessive loading, or because of a change of use). | 1 | Applied and Interdisciplinary Chemistry |
YeTFaSCo (The Yeast Transcription Factor Specificity Compendium) is a database of transcription factors for Saccharomyces cerevisiae. | 1 | Applied and Interdisciplinary Chemistry |
Applications:
* The rotary filter is most suitable for continuous operation on large quantities of slurry.
* If the slurry contains considerable amount of solids, that is, in the range of 15-30%.
* Examples of pharmaceutical applications include the collection of calcium carbonate, magnesium carbonate and starch.
* The separation of the mycelia from the fermentation liquor in the manufacture of antibiotics.
* block and instant yeast production. | 0 | Theoretical and Fundamental Chemistry |
CDAs are used with NMR spectroscopic analysis to determine enantiomeric excess and the absolute configuration of a substrate. Chiral discriminating agents are sometimes difficult to distinguish from chiral solvating agents (CSA) and some agents can be used as both. The speed of the exchange between the substrate and the metal center is the most important determining factor to differentiate between the use of a compound as a CDA or CSA. Generally, a CDA has a slow exchange whereas a CSA has a fast exchange. CDAs are more widely used than CSAs to determine absolute configurations because the covalent bonding to the substrate and auxiliary reagent produce species with greater conformational rigidity which creates greater differences in the NMR spectra. CDAs and CSAs can be used together to improve chiral recognition, although this is not a common.
NMR shift reagents such as EuFOD, Pirkle's alcohol, and TRISPHAT take advantage of the formation of diastereomeric complexes between the shift reagent and the analytical sample. | 0 | Theoretical and Fundamental Chemistry |
Significant progress in chemical shift prediction has been made through continuous improvements in our understanding of the key physico-chemical factors contributing to chemical shift changes. These improvements have also been helped along through significant computational advancements
and the rapid expansion of biomolecular chemical shift databases
. Over the past four decades, at least three different methods for calculating or predicting protein chemical shifts have emerged. The first is based on using sequence/structure alignment against protein chemical shift databases, the second is based on directly calculating shifts from atomic coordinates, and the third is based on using a combination of the two approaches.
*Predicting shifts via sequence homology: these are based on the simple observation that similar protein sequences share similar structures and similar chemical shifts
*Predicting shifts from coordinate data / structure:
**Semi-classical methods: employ empirical equations derived from classical physics and experimental data
**Quantum mechanical (QM) methods: employ density functional theory (DFT)
**Empirical methods: rely on using chemical shift ‘‘hypersurfaces" or related "structure/shift" tables
*Hybrid Methods: combining the above two methods | 0 | Theoretical and Fundamental Chemistry |
Sintering is generally considered successful when the process reduces porosity and enhances properties such as strength, electrical conductivity, translucency and thermal conductivity. In some special cases, sintering is carefully applied to enhance the strength of a material while preserving porosity (e.g. in filters or catalysts, where gas absorbency is a priority). During the firing process, atomic diffusion drives powder surface elimination in different stages, starting at the formation of necks between powders to final elimination of small pores at the end of the process.
The driving force for densification is the change in free energy from the decrease in surface area and lowering of the surface free energy by the replacement of solid-vapor interfaces. It forms new but lower-energy solid-solid interfaces with a net decrease in total free energy. On a microscopic scale, material transfer is affected by the change in pressure and differences in free energy across the curved surface. If the size of the particle is small (and its curvature is high), these effects become very large in magnitude. The change in energy is much higher when the radius of curvature is less than a few micrometers, which is one of the main reasons why much ceramic technology is based on the use of fine-particle materials.
The ratio of bond area to particle size is a determining factor for properties such as strength and electrical conductivity. To yield the desired bond area, temperature and initial grain size are precisely controlled over the sintering process. At steady state, the particle radius and the vapor pressure are proportional to (p) and to (p), respectively.
The source of power for solid-state processes is the change in free or chemical potential energy between the neck and the surface of the particle. This energy creates a transfer of material through the fastest means possible; if transfer were to take place from the particle volume or the grain boundary between particles, particle count would decrease and pores would be destroyed. Pore elimination is fastest in samples with many pores of uniform size because the boundary diffusion distance is smallest. during the latter portions of the process, boundary and lattice diffusion from the boundary become important.
Control of temperature is very important to the sintering process, since grain-boundary diffusion and volume diffusion rely heavily upon temperature, particle size, particle distribution, material composition, and often other properties of the sintering environment itself. | 1 | Applied and Interdisciplinary Chemistry |
Malaria and vitamin A deficiency are both common among young children in sub-Saharan Africa. Vitamin A supplementation to children in regions where vitamin A deficiency is common has repeatedly been shown to reduce overall mortality rates, especially from measles and diarrhea. For malaria, clinical trial results are mixed, either showing that vitamin A treatment did not reduce the incidence of probable malarial fever, or else did not affect incidence, but did reduce slide-confirmed parasite density and reduced the number of fever episodes. The question was raised as to whether malaria causes vitamin A deficiency, or vitamin A deficiency contributes to the severity of malaria, or both. Researchers proposed several mechanisms by which malaria (and other infections) could contribute to vitamin A deficiency, including a fever-induced reduction in synthesis of retinal-binding protein (RBP) responsible for transporting retinol from liver to plasma and tissues, but reported finding no evidence for a transient depression or restoration of plasma RBP or retinol after a malarial infection was eliminated. | 1 | Applied and Interdisciplinary Chemistry |
Time resolved crystallography utilizes X-ray crystallography imaging to visualize reactions in four dimensions (x, y, z and time). This enables the studies of dynamical changes that occur in for example enzymes during their catalysis. The time dimension is incorporated by triggering the reaction of interest in the crystal prior to X-ray exposure, and then collecting the diffraction patterns at different time delays. In order to study these dynamical properties of macromolecules three criteria must be met;
* The macromolecule must be biologically active in the crystalline state
* It must be possible to trigger the reaction in the crystal
* The intermediate of interest must be detectable, i.e. it must have a reasonable amount of concentration in the crystal (preferably over 25%).
This has led to the development of several techniques that can be divided into two groups, the pump-probe method and diffusion-trapping methods. | 0 | Theoretical and Fundamental Chemistry |
Heterotopic groups are those that when substituted are structurally different. They are neither diastereotopic or enantiotopic nor homotopic. | 0 | Theoretical and Fundamental Chemistry |
Many mechanically interlocked molecules have been studied to construct molecular machines. Because the molecules are linked by mechanical bonds instead of conventional covalent bonds, a component can move (shuttle) or rotate around the other parent component, which results in the large amount of freedom of mechanically interlocked molecules. Polyrotaxanes, as the polymer form of corresponding rotaxanes, are also applied in molecular machines.
For example, the shuttling behavior of the molecular shuttle can be controlled by the solvent or temperature. Due to the hydrophobic interaction between rings and strings, and the repulsive interaction between rings and linkers, conditions that are capable of influencing these interactions can be used to control the mobility of the rings in the molecular shuttle. In addition, if cationic or anionic units are employed to form the polyrotaxanes, the salts or pH in the solution also will influence the charge interactions between rings and strings, which is an alternative method to control the ring motion of the molecular shuttle.
Poly[2]rotaxane "daisy chains" (like a string of daisies with stems linked to form a chain)is an example of a molecule that can be used to form a molecular muscle. Poly[2]rotaxane can expand or shrink in response to external stimulus, which is similar to behaviors of muscle, an ideal model to construct a "molecular muscle". The ring stations on the chain can be controlled by pH or light. Due to "daisy chain" structure, two rings on the daisy chain will shift from one station to another station, which changes the distance between two rings as well as the state of the whole daisy chain. When the rings come close, the whole size of the daisy chain will increase, which is the "expand" state. As the rings get to the further station, the molecule become the "shrink" state as the decreased size. | 0 | Theoretical and Fundamental Chemistry |
Closing methods can be categorized into two principal groups: gradual closures and sudden closures. Within gradual closures, four distinct methods are identified: horizontal closure without a significant sill (a), vertical closure (b), horizontal closure with a sill (c), and sand closures. Sand closures further differentiate into horizontal and vertical types. Sudden closures are typically achieved through the deployment of (sluice) caissons, often positioned on a sill (d). | 1 | Applied and Interdisciplinary Chemistry |
Fecal sludge management refers to the storage, collection, transport, treatment, and safe end use or disposal of fecal sludge. Collectively, the collection, transport, treatment and end use or reuse of excreta constitute the "value chain" of fecal sludge management. | 1 | Applied and Interdisciplinary Chemistry |
The Reynolds number (Re) is a dimensionless quantity that is commonly used in fluid dynamics and engineering. Originally described by George Gabriel Stokes in 1850, it became popularized by Osborne Reynolds after whom the concept was named by Arnold Sommerfeld in 1908. The Reynolds number is calculated as:
The value represents the ratio of inertial forces to viscous forces in a fluid, and is useful in determining the relative importance of viscosity. In inviscid flow, since the viscous forces are zero, the Reynolds number approaches infinity. When viscous forces are negligible, the Reynolds number is much greater than one. In such cases (Re>>1), assuming inviscid flow can be useful in simplifying many fluid dynamics problems. | 1 | Applied and Interdisciplinary Chemistry |
This can be the case when studying a bimolecular reaction and a simultaneous hydrolysis (which can be treated as pseudo order one) takes place: the hydrolysis complicates the study of the reaction kinetics, because some reactant is being "spent" in a parallel reaction. For example, A reacts with R to give our product C, but meanwhile the hydrolysis reaction takes away an amount of A to give B, a byproduct: and . The rate equations are: and , where is the pseudo first order constant.
The integrated rate equation for the main product [C] is , which is equivalent to . Concentration of B is related to that of C through
The integrated equations were analytically obtained but during the process it was assumed that . Therefore, previous equation for [C] can only be used for low concentrations of [C] compared to [A] | 0 | Theoretical and Fundamental Chemistry |
Body composition may be analyzed in various ways. This can be done in terms of the chemical elements present, or by molecular structure e.g., water, protein, fats (or lipids), hydroxylapatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, connective tissue, muscle, bone, etc. In terms of cell type, the body contains hundreds of different types of cells, but notably, the largest number of cells contained in a human body (though not the largest mass of cells) are not human cells, but bacteria residing in the normal human gastrointestinal tract. | 1 | Applied and Interdisciplinary Chemistry |
*A helper strain, carrying a conjugative plasmid (such as the F-plasmid) that codes for genes required for conjugation and DNA transfer.
*A donor strain, carrying a mobilizable plasmid that can utilize the transfer functions of the conjugative plasmid.
*A recipient strain, you wish to introduce the mobilizable plasmid into.
Five to seven days are required to determine if the
plasmid was successfully introduced into the new bacterial
strain and confirm that there is no carryover of the helper or
donor strain.
In contrast, electroporation does not require a helper or
donor strain. This helps
avoid possible contamination with other strains. The introduction
of the plasmid can be verified in the recipient
strain in two days, making electroporation a faster and
more efficient method of transformation. Electroporation however does not work with all bacteria and is mostly limited to well-characterized model organisms. | 1 | Applied and Interdisciplinary Chemistry |
An advantage is silent operation, with none of the fan noise of current resistive grid designs.
Disadvantages include:
* corrosion to the copper connection cables and to the wire rope
* lack of insulation from ground which may trip a ground detection system | 0 | Theoretical and Fundamental Chemistry |
As T-RFLP is a fingerprinting technique its advantages and drawbacks are often discussed in comparison with other similar techniques, mostly DGGE. | 1 | Applied and Interdisciplinary Chemistry |
Though hypothesized that vitamin D supplementation may be an effective treatment for obesity apart from calorie restriction, one systematic review found no association of supplementation with body weight or fat mass. A 2016 meta-analysis found that circulating vitamin D status was improved by weight loss, indicating that fat mass may be inversely associated with blood levels of vitamin D. | 1 | Applied and Interdisciplinary Chemistry |
Butler studied at Reed College, graduating in 1977. She started in immunology, but moved into chemistry to work with transition metals. She worked with Professor Tom Dunne on An intramolecular electron transfer study: the reduction of pyrazinepentaaminecobalt (III) by chromium (II). She earned her PhD at University of California, San Diego in 1982 under Robert G. Linck and Teddy G. Traylor. | 0 | Theoretical and Fundamental Chemistry |
AFPs create a difference between the melting point and freezing point (busting temperature of AFP bound ice crystal) known as thermal hysteresis. The addition of AFPs at the interface between solid ice and liquid water inhibits the thermodynamically favored growth of the ice crystal. Ice growth is kinetically inhibited by the AFPs covering the water-accessible surfaces of ice.
Thermal hysteresis is easily measured in the lab with a nanolitre osmometer. Organisms differ in their values of thermal hysteresis. The maximum level of thermal hysteresis shown by fish AFP is approximately −3.5 °C (Sheikh Mahatabuddin et al., SciRep)(29.3 °F). In contrast, aquatic organisms are exposed only to −1 to −2 °C below freezing. During the extreme winter months, the spruce budworm resists freezing at temperatures approaching −30 °C.
The rate of cooling can influence the thermal hysteresis value of AFPs. Rapid cooling can substantially decrease the nonequilibrium freezing point, and hence the thermal hysteresis value. Consequently, organisms cannot necessarily adapt to their subzero environment if the temperature drops abruptly. | 1 | Applied and Interdisciplinary Chemistry |
English physicist and mathematician Isaac Newton produced works exploring chronology, and biblical interpretation (especially of the Apocalypse), and alchemy. Some of this could be considered occult. Newtons scientific work may have been of lesser personal importance to him, as he placed emphasis on rediscovering the wisdom of the ancients. Historical research on Newtons occult studies in relation to his science have also been used to challenge the disenchantment narrative within critical theory.
In the Early Modern Period of Newton's lifetime, the educated embraced a world view different from that of later centuries. Distinctions between science, superstition, and pseudoscience were still being formulated, and a devoutly Christian biblical perspective permeated Western culture. | 1 | Applied and Interdisciplinary Chemistry |
Soldering is a joining process that occurs at temperatures below . It is similar to brazing in the way that a filler is melted and drawn into a capillary to form a joint, although at a lower temperature. Because of this lower temperature and different alloys used as fillers, the metallurgical reaction between filler and work piece is minimal, resulting in a weaker joint. | 1 | Applied and Interdisciplinary Chemistry |
As a hybrid technique, GISAS combines concepts from transmission small-angle scattering (SAS), from grazing-incidence diffraction (GID), and from diffuse reflectometry. From SAS it uses the form factors and structure factors. From GID it uses the scattering geometry close to the critical angles of substrate and film, and the two-dimensional character of the scattering, giving rise to diffuse rods of scattering intensity perpendicular to the surface. With diffuse (off-specular) reflectometry it shares phenomena like the Yoneda/Vinyard peak at the critical angle of the sample, and the scattering theory, the distorted wave Born approximation (DWBA). However, while diffuse reflectivity remains confined to the incident plane (the plane given by the incident beam and the surface normal), GISAS explores the whole scattering from the surface in all directions, typically utilizing an area detector. Thus GISAS gains access to a wider range of lateral and vertical structures and, in particular, is sensitive to the morphology and preferential alignment of nanoscale objects at the surface or inside the thin film.
As a particular consequence of the DWBA, the refraction of x-rays or neutrons has to be always taken into account in the case of thin film studies, due to the fact that scattering angles are small, often less than 1 deg. The refraction correction applies to the perpendicular component of the scattering vector with respect to the substrate while the parallel component is unaffected. Thus parallel scattering can often be interpreted within the kinematic theory of SAS, while refractive corrections apply to the scattering along perpendicular cuts of the scattering image, for instance along a scattering rod.
In the interpretation of GISAS images some complication arises in the scattering from low-Z films e.g. organic materials on silicon wafers, when the incident angle is in between the critical angles of the film and the substrate. In this case, the reflected beam from the substrate has a similar strength as the incident beam and thus the scattering from the reflected beam from the film structure can give rise to a doubling of scattering features in the perpendicular direction. This as well as interference between the scattering from the direct and the reflected beam can be fully accounted for by the DWBA scattering theory.
These complications are often more than offset by the fact that the dynamic enhancement of the scattering intensity is significant. In combination with the straightforward scattering geometry, where all relevant information is contained in a single scattering image, in-situ and real-time experiments are facilitated. Specifically self-organization during MBE growth and re-organization processes in block copolymer films under the influence of solvent vapor have been characterized on the relevant timescales ranging from seconds to minutes. Ultimately the time resolution is limited by the x-ray flux on the samples necessary to collect an image and the read-out time of the area detector. | 0 | Theoretical and Fundamental Chemistry |
Indoor tanning is most popular with white females, 16–25 years old, with low-to-moderate skin sensitivity, who know other tanners. Studies seeking to link indoor tanning to education level and income have returned inconsistent results. Prevalence was highest in one German study among those with a moderate level of education (neither high nor low).
The late teens to early–mid 20s is the highest-prevalence age group. In a national survey of white teenagers in 2003 in the US (aged 13–19), 24% had used a tanning facility. Indoor-tanning prevalence figures in the US vary from 30 million each year to just under 10 million (7.8 million women and 1.9 million men).
The figures in the US are in decline: according to the Centres for Disease Control and Prevention, usage in the 18–29 age group fell from 11.3 percent in 2010 to 8.6 percent in 2013, perhaps attributable in part to a 10% "tanning tax" introduced in 2010. Attitudes toward tanning vary across states; in one study, doctors in the northeast and midwest of the country were more likely than those in the south or west to recommend tanning beds to treat vitamin D deficiency and depression.
Tanning bed use is more prevalent in northern countries. In Sweden in 2001, 44% said they had used one (in a survey of 1,752 men and women aged 18–37). Their use increased in Denmark between 1994 and 2002 from 35% to 50% (reported use in the previous two years). In Germany, between 29% and 47% had used one, and one survey found that 21% had done so in the previous year. In France, 15% of adults in 1994–1995 had tanned indoors; the practice was more common in the north of France. In 2006, 12% of grade 9–10 students in Canada had used a tanning bed in the last year. In 2004, 7% of 8–11-year-olds in Scotland said they had used one. Tanning bed use is higher in the UK in the north of England. One study found that the prevalence was lower in London than in less urban areas of the country. | 0 | Theoretical and Fundamental Chemistry |
Molecular hydrogen, H, contains two different spin isomers, para-hydrogen and ortho-hydrogen, with a ratio of 25:75 at room temperature. Creating para-hydrogen induced polarization (PHIP) means that this ratio is increased, in other words that para-hydrogen is enriched. This can be accomplished by cooling hydrogen gas and then inducing ortho-to-para conversion via an iron-oxide or charcoal catalyst. When performing this procedure at ≈70 K (i.e. with liquid nitrogen), para-hydrogen is enriched from 25% to ca. 50%. When cooling to below 20 K and then inducing the ortho-to-para conversion, close to 100% parahydrogen can be obtained.
For practical applications, the PHIP is most commonly transferred to organic molecules by reacting the hyperpolarized hydrogen with precursor molecules in the presence of a transition metal catalyst. Proton NMR signals with ca. 10,000-fold increased intensity can be obtained compared to NMR signals of the same organic molecule without PHIP and thus only "thermal" polarization at room temperature. | 0 | Theoretical and Fundamental Chemistry |
ASF/SF2 has been shown to interact with:
* CDC5L,
* CLK1,
* PSIP1,
* SFRS2,
* SRPK1,
* SRPK2,
* TOP1,
* U2 small nuclear RNA auxiliary factor 1, and
* snRNP70. | 1 | Applied and Interdisciplinary Chemistry |
Ferric iron () is a widespread anaerobic terminal electron acceptor both for autotrophic and heterotrophic organisms. Electron flow in these organisms is similar to those in electron transport, ending in oxygen or nitrate, except that in ferric iron-reducing organisms the final enzyme in this system is a ferric iron reductase. Model organisms include Shewanella putrefaciens and Geobacter metallireducens. Since some ferric iron-reducing bacteria (e.g. G. metallireducens) can use toxic hydrocarbons such as toluene as a carbon source, there is significant interest in using these organisms as bioremediation agents in ferric iron-rich contaminated aquifers.
Although ferric iron is the most prevalent inorganic electron acceptor, a number of organisms (including the iron-reducing bacteria mentioned above) can use other inorganic ions in anaerobic respiration. While these processes may often be less significant ecologically, they are of considerable interest for bioremediation, especially when heavy metals or radionuclides are used as electron acceptors. Examples include:
* Manganic ion () reduction to manganous ion ()
* Selenate () reduction to selenite () and selenite reduction to inorganic selenium (Se)
* Arsenate () reduction to arsenite ()
* Uranyl ion () reduction to uranium dioxide () | 1 | Applied and Interdisciplinary Chemistry |
Dallol mountain has an area of about , and rises about above the surrounding salt plains. A circular depression near the centre is probably a collapsed crater. The southwestern slopes have water-eroded salt canyons, pillars, and blocks. There are numerous saline springs and fields of small fumaroles.
Numerous hot springs discharge brine and acidic liquid here. Small, widespread, temporary geysers produce cones of salt. The Dallol deposits include significant bodies of potash found directly at the surface. The yellow, ochre and brown colourings are the result of the presence of iron and other impurities. Older, inactive springs tend to be dark brown because of oxidation processes. | 0 | Theoretical and Fundamental Chemistry |
Ørsted was born in Rudkøbing in 1777. As a young boy he developed an interest in science while working for his father, who was a pharmacist in the towns pharmacy. He and his brother Anders received most of their early education through self-study at home, going to Copenhagen in 1793 to take entrance exams for the University of Copenhagen, where both brothers excelled academically. By 1796, Ørsted had been awarded honors for his papers in both aesthetics and physics. He earned his doctorate in 1799 for a dissertation based on the works of Kant entitled The Architectonics of Natural Metaphysics'.
In 1800, Alessandro Volta reported his invention of the voltaic pile, which inspired Ørsted to investigate the nature of electricity and to conduct his first electrical experiments. In 1801, Ørsted received a travel scholarship and public grant which enabled him to spend three years traveling across Europe. He toured science headquarters throughout the continent, including in Berlin and Paris.
In Germany Ørsted met Johann Wilhelm Ritter, a physicist who believed there was a connection between electricity and magnetism. This idea made sense to Ørsted as he subscribed to Kantian thought regarding the unity of nature. Ørsted's conversations with Ritter drew him into the study of physics. He became a professor at the University of Copenhagen in 1806 and continued research on electric currents and acoustics. Under his guidance the university developed a comprehensive physics and chemistry program and established new laboratories.
Ørsted welcomed William Christopher Zeise to his family home in autumn 1806. He granted Zeise a position as his lecturing assistant and took the young chemist under his tutelage. In 1812, Ørsted again visited Germany and France after publishing and (1811).
Ørsted was the first modern thinker to explicitly describe and name the thought experiment. He used the Latin-German term circa 1812 and the German term in 1820.
In 1819 Ørsted was the first to extract piperine and subsequently name it. He extracted it from Piper nigrum, the plant from which both white and black pepper comes from.
Ørsted designed a new type of piezometer to measure the compressibility of liquids in 1822. | 1 | Applied and Interdisciplinary Chemistry |
Valves vary widely in form and application. Sizes typically range from 0.1 mm to 60 cm. Special valves can have a diameter exceeding 5 meters.
Valve costs range from simple inexpensive disposable valves to specialized valves which cost thousands of dollars (US) per inch of the diameter of the valve.
Disposable valves may be found in common household items including mini-pump dispensers and aerosol cans.
A common use of the term valve refers to the poppet valves found in the vast majority of modern internal combustion engines such as those in most fossil fuel powered vehicles which are used to control the intake of the fuel-air mixture and allow exhaust gas venting. | 1 | Applied and Interdisciplinary Chemistry |
Similar assays can be performed for research purposes, detecting concentrations of potential clinical candidates like anti-fungal and asthma drugs. This technique is obviously useful in observing multiple species in collected samples, as well, but requires the use of standard solutions when information about species identity is sought out. It is used as a method to confirm results of synthesis reactions, as purity is essential in this type of research. However, mass spectrometry is still the more reliable way to identify species. | 0 | Theoretical and Fundamental Chemistry |
Racemic Photo-Methionine is synthesized from 4,4'-azi-pentanal by the Strecker amino acid synthesis. The enantiomer is separated by enzymatic resolution of the acetamide. | 0 | Theoretical and Fundamental Chemistry |
The same reaction can be described with the GEBIK and GEBIF equations under the BFEI and QSS approximations as
where has been substituted with because the rate
constants in the third reaction have been assumed to equal those
of the second reaction. | 0 | Theoretical and Fundamental Chemistry |
The amount of light transmitted through a material diminishes exponentially as it travels through the material, according to the Beer–Lambert law (). Since the absorbance of a sample is measured as a logarithm, it is directly proportional to the thickness of the sample and to the concentration of the absorbing material in the sample. Some other measures related to absorption, such as transmittance, are measured as a simple ratio so they vary exponentially with the thickness and concentration of the material. | 0 | Theoretical and Fundamental Chemistry |
While the secretion of glucocorticoids in response to stressful stimuli is an adaptive response necessary for an organism to respond appropriately to a stressor, persistent secretion may be harmful. The endocannabinoid system has been implicated in the habituation of the hypothalamic-pituitary-adrenal axis (HPA axis) to repeated exposure to restraint stress. Studies have demonstrated differential synthesis of anandamide and 2-AG during tonic stress. A decrease of anandamide was found along the axis that contributed to basal hypersecretion of corticosterone; in contrast, an increase of 2-AG was found in the amygdala after repeated stress, which was negatively correlated to magnitude of the corticosterone response. All effects were abolished by the CB antagonist AM251, supporting the conclusion that these effects were cannabinoid-receptor dependent. These findings show that anandamide and 2-AG divergently regulate the HPA axis response to stress: while habituation of the stress-induced HPA axis via 2-AG prevents excessive secretion of glucocorticoids to non-threatening stimuli, the increase of basal corticosterone secretion resulting from decreased anandamide allows for a facilitated response of the HPA axis to novel stimuli. | 1 | Applied and Interdisciplinary Chemistry |
Polyrotaxane is a type of mechanically interlocked molecule consisting of strings and rings, in which multiple rings are threaded onto a molecular axle and prevented from dethreading by two bulky end groups. As oligomeric or polymeric species of rotaxanes, polyrotaxanes are also capable of converting energy input to molecular movements because the ring motions can be controlled by external stimulus. Polyrotaxanes have attracted much attention for decades, because they can help build functional molecular machines with complicated molecular structure.
Although there are no covalent bonds between the axes and rings, polyrotaxanes are stable due to the high free activation energy (Gibbs energy) needed to be overcome to withdraw rings from the axes. Also, rings are capable of shuttling along and rotating around the axes freely, which leads to a huge amount of internal degree of freedom of polyrotaxanes. Due to this topologically interlocked structure, polyrotaxanes have many different mechanical, electrical, and optical properties compared to conventional polymers.
Additionally the mechanically interlocked structures can be maintained in slide-ring materials, which are a type supramolecular network synthesized by crosslinking the rings (called figure-of-eight crosslinking) in different polyrotaxanes. In slide-ring materials, crosslinks of rings can pass along the axes freely to equalize the tension of the threading polymer networks, which is similar to pulleys. With this specific structure, slide-ring materials can be fabricated highly stretchable engineering materials due to their different mechanical properties.
If the rings and axes are biodegradable and biocompatible, the polyrotaxanes can also be used for biomedical application, such as gene/drug delivery. The advantage of polyrotaxanes over other biomedical polymers, such as polysaccharides, is that because the interlocked structures are maintained by bulky stoppers at the ends of the strings, if the bulky stoppers are removed, such as removed by a chemical stimulus, rings dethread from the axes. The drastic structural change can be used for programmed drug or gene delivery, in which the drug or gene can be released with the rings when the stoppers are cut off at the specific destination. | 0 | Theoretical and Fundamental Chemistry |
The van der Waals binding energy can be analyzed by another simple physical picture: modeling the motion of an electron around its nucleus by a three-dimensional simple harmonic oscillator with a potential energy V:
where m and ω are the mass and vibrational frequency of the electron, respectively.
As this atom approaches the surface of a metal and forms adsorption, this potential energy V will be modified due to the image charges by additional potential terms which are quadratic in the displacements:
: (from the Taylor expansion above.)
Assuming
the potential is well approximated as
where
If one assumes that the electron is in the ground state, then the van der Waals binding energy is essentially the change of the zero-point energy:
This expression also shows the nature of the Z dependence of the van der Waals interaction.
Furthermore, by introducing the atomic polarizability,
the van der Waals potential can be further simplified:
where
is the van der Waals constant which is related to the atomic polarizability.
Also, by expressing the fourth-order correction in the Taylor expansion above as (aCZ) / (Z), where a is some constant, we can define Z as the position of the dynamical image plane and obtain
The origin of Z comes from the spilling of the electron wavefunction out of the surface. As a result, the position of image plane representing the reference for the space coordinate is different from the substrate surface itself and modified by Z.
Table 1 shows the jellium model calculation for van der Waals constant C and dynamical image plane Z of rare gas atoms on various metal surfaces. The increasing of C from He to Xe for all metal substrates is caused by the larger atomic polarizability of the heavier rare gas atoms. For the position of the dynamical image plane, it decreases with increasing dielectric function and is typically on the order of 0.2 Å. | 0 | Theoretical and Fundamental Chemistry |
Molecular tweezers, and molecular clips, are host molecules with open cavities capable of binding guest molecules. The open cavity of the molecular tweezers may bind guests using non-covalent bonding, which includes hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, π–π interactions, and/or electrostatic effects. These complexes are a subset of macrocyclic molecular receptors and their structure is that the two "arms" that bind the guest molecule between them are only connected at one end leading to a certain flexibility of these receptor molecules (induced fit model). | 0 | Theoretical and Fundamental Chemistry |
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