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An older unit for the dose equivalent is the rem, still often used in the United States. One sievert is equal to 100 rem: | 0 | Theoretical and Fundamental Chemistry |
In this type of thermocell the electrolyte is some kind of salt with a relatively low melting point. Their use solves two problems. On one hand the temperature range of the cell is much larger. This is an advantage as these cells produce more power the larger the difference between the hot and cold sides. On the other hand, the liquid salt directly provides the anions and cations necessary for sustainment of a current through the cell. Therefore, no additional current-carrying compounds are necessary as the melted salt is the electrolyte itself. Typical hot source temperatures are between 600–900 K, but can get as high as 1730 K. Cold sink temperatures are in the 400–500 K range. | 0 | Theoretical and Fundamental Chemistry |
The second law of thermodynamics is a statement on the irreversibility of dynamics or, the breakup of time reversal symmetry (T-symmetry). This should be consistent with the empirical direct definition: heat will flow spontaneously from a hot source to a cold sink.
From a static viewpoint, for a closed quantum system, the 2nd law of thermodynamics is a consequence of the unitary evolution. In this approach, one accounts for the entropy change before and after a change in the entire system. A dynamical viewpoint is based on local accounting for the entropy changes
in the subsystems and the entropy generated in the baths. | 0 | Theoretical and Fundamental Chemistry |
Developing technologies include:
* Ion-trap mass spectrometry
* Laser-induced immunofluorometric biosensors
* Magnetic levitation
* Nuclear magnetic resonance spectroscopy | 0 | Theoretical and Fundamental Chemistry |
Glutaminolysis partially recruits reaction steps from the citric acid cycle and the malate-aspartate shuttle. | 1 | Applied and Interdisciplinary Chemistry |
The coenzyme Q : cytochrome c – oxidoreductase, sometimes called the cytochrome bc complex, and at other times complex III, is the third complex in the electron transport chain (), playing a critical role in biochemical generation of ATP (oxidative phosphorylation). Complex III is a multisubunit transmembrane protein encoded by both the mitochondrial (cytochrome b) and the nuclear genomes (all other subunits). Complex III is present in the mitochondria of all animals and all aerobic eukaryotes and the inner membranes of most eubacteria. Mutations in Complex III cause exercise intolerance as well as multisystem disorders. The bc1 complex contains 11 subunits, 3 respiratory subunits (cytochrome B, cytochrome C1, Rieske protein), 2 core proteins and 6 low-molecular weight proteins.
Ubiquinol—cytochrome-c reductase catalyzes the chemical reaction
:QH + 2 ferricytochrome c Q + 2 ferrocytochrome c + 2 H
Thus, the two substrates of this enzyme are quinol (QH) and ferri- (Fe) cytochrome c, whereas its 3 products are quinone (Q), ferro- (Fe) cytochrome c, and H.
This enzyme belongs to the family of oxidoreductases, specifically those acting on diphenols and related substances as donor with a cytochrome as acceptor. This enzyme participates in oxidative phosphorylation. It has four cofactors: cytochrome c, cytochrome b-562, cytochrome b-566, and a 2-Iron ferredoxin of the Rieske type. | 1 | Applied and Interdisciplinary Chemistry |
A special numbering system is to be used for fluorinated alkanes, prefixed with Freon-, R-, CFC- and HCFC-, where the rightmost value indicates the number of fluorine atoms, the next value to the left is the number of hydrogen atoms plus 1, and the next value to the left is the number of carbon atoms less one (zeroes are not stated), and the remaining atoms are chlorine.
Freon-12, for example, indicates a methane derivative (only two numbers) containing two fluorine atoms (the second 2) and no hydrogen (1-1=0). It is therefore CClF.
Another equation that can be applied to get the correct molecular formula of the CFC/R/Freon class compounds is to take the numbering and add 90 to it. The resulting value will give the number of carbons as the first numeral, the second numeral gives the number of hydrogen atoms, and the third numeral gives the number of fluorine atoms. The rest of the unaccounted carbon bonds are occupied by chlorine atoms. The value of this equation is always a three figure number. An easy example is that of CFC-12, which gives: 90+12=102 -> 1 carbon, 0 hydrogens, 2 fluorine atoms, and hence 2 chlorine atoms resulting in CClF. The main advantage of this method of deducing the molecular composition in comparison with the method described in the paragraph above is that it gives the number of carbon atoms of the molecule.
Freons containing bromine are signified by four numbers. Isomers, which are common for ethane and propane derivatives, are indicated by letters following the numbers: | 1 | Applied and Interdisciplinary Chemistry |
In the gas networks simulation and analysis, matrices turned out to be the natural way of expressing the problem. Any network can be described by set of matrices based on the network topology. Consider the gas network by the graph below. The network consists of one source node (reference node) L1, four load nodes (2, 3, 4 and 5) and seven pipes or branches. For network analysis it is necessary to select at least one reference node. Mathematically, the reference node is referred to as the independent node and all nodal and branch quantities are dependent on it. The pressure at source node is usually known, and this node is often used as the reference node. However, any node in the network may have its pressure defined and can be used as the reference node. A network may contain several sources or other pressure-defined nodes and these form a set of reference nodes for the network.<br />
The load nodes are points in the network where load values are known. These loads may be positive, negative or zero. A negative load represents a demand for gas from the network. This may consist in supplying domestic or commercial consumers, filling gas storage holders, or even accounting for leakage in the network. A positive load represents a supply of gas to the network. This may consist in taking gas from storage, source or from another network. A zero load is placed on nodes that do not have a load but are used to represent a point of change in the network topology, such as the junction of several branches. For steady state conditions, the total load on the network is balanced by the inflow into the network at the source node.<br />
The interconnection of a network can produce a closed path of branches, known as a loop. In figure, loop A consists of branches p12-p24-p14, loop B consists of p13-p34-p14, and loop C consists of p24-p25-p35-p34. A fourth loop may be defined as p12-p24-p34-p13, but it is redundant if loops A, B and C are also defined. Loops A, B and C are independent ones but the fourth one is not, as it can be derived from A, B and C by eliminating common branches.<br />
To define the network topology completely it is necessary to assign a direction to each branch. Each branch direction is assigned arbitrarily and is assumed to be positive direction of flow in the branch. If the flow has the negative value, then the direction of flow is opposite to branch direction. In the similar way, direction is assigned to each loop and flow in the loop.<br />
The solutions of problems involving gas network computation of any topology requires such a representation of the network to be found which enables the calculations to be performed in the most simple way. These requirements are met by the graph theory which permits representation of the network structure by means of the incidence properties of the network components and, in consequence, makes such a representation explicit. | 1 | Applied and Interdisciplinary Chemistry |
In 2010, Dunne was elected a Fellow of the Royal Academy of Engineering (FREng). In 2016, he was awarded the Institute of Materials, Minerals and Mining (IoM3) Harvey Flower Titanium Prize. In 2017, Dunnes Engineering Alloys team shared the Imperial Presidents Award for Outstanding Research Team with Professor Chris Phillips’s team. | 1 | Applied and Interdisciplinary Chemistry |
Kaede is a photoactivatable fluorescent protein naturally originated from a stony coral, Trachyphyllia geoffroyi. Its name means "maple" in Japanese. With the irradiation of ultraviolet light (350–400 nm), Kaede undergoes irreversible photoconversion from green fluorescence to red fluorescence.
Kaede is a homotetrameric protein with the size of 116 kDa. The tetrameric structure was deduced as its primary structure is only 28 kDa. This tetramerization possibly makes Kaede have a low tendency to form aggregates when fused to other proteins. | 1 | Applied and Interdisciplinary Chemistry |
* In the 2016 film Spectral, the US military battles mysterious enemy creatures fashioned out of Bose–Einstein condensates.
* In the 2003 novel Blind Lake, scientists observe sentient life on a planet 51 light-years away using telescopes powered by Bose–Einstein condensate-based quantum computers.
* The video game franchise Mass Effect has cryonic ammunition whose flavour text describes it as being filled with Bose–Einstein condensates. Upon impact, the bullets rupture and spray super-cold liquid on the enemy. | 0 | Theoretical and Fundamental Chemistry |
The alternative flatworm mitochondrial code (translation table 14) is a genetic code found in the mitochondria of Platyhelminthes and Nematodes. | 1 | Applied and Interdisciplinary Chemistry |
Fatty acids must be activated before they can be carried into the mitochondria, where fatty acid oxidation occurs. This process occurs in two steps catalyzed by the enzyme fatty acyl-CoA synthetase. | 1 | Applied and Interdisciplinary Chemistry |
Messenger RNA (mRNA) is a single-stranded RNA molecule that is complementary to one of the DNA strands of a gene. An mRNA molecule transfers a portion of the DNA code to other parts of the cell for making proteins. DNA therapeutics needs access to the nucleus to be transcribed into RNA, and its functionality depends on nuclear envelope breakdown during cell division. However, mRNA therapeutics do not need to enter into the nucleus to be functional since it will be translated immediately once it has reached to the cytoplasm. Moreover, unlike plasmids and viral vectors, mRNAs do not integrate into the genome and therefore do not have the risk of insertional mutagenesis, making them suitable for use in cancer vaccines, tumor immunotherapy and infectious disease prevention. | 1 | Applied and Interdisciplinary Chemistry |
The term pervaporation is a portmanteau of the two steps of the process: (a) permeation through the membrane by the permeate, then (b) its evaporation into the vapor phase. This process is used by a number of industries for several different processes, including purification and analysis, due to its simplicity and in-line nature.
The membrane acts as a selective barrier between the two phases: the liquid-phase feed and the vapor-phase permeate. It allows the desired components of the liquid feed to transfer through it by vaporization. Separation of components is based on a difference in transport rate of individual components through the membrane.
Typically, the upstream side of the membrane is at ambient pressure and the downstream side is under vacuum to allow the evaporation of the selective component after permeation through the membrane. Driving force for the separation is the difference in the partial pressures of the components on the two sides and not the volatility difference of the components in the feed.
The driving force for transport of different components is provided by a chemical potential difference between the liquid feed/retentate and vapor permeate at each side of the membrane. The retentate is the remainder of the feed leaving the membrane feed chamber, which is not permeated through the membrane.
The chemical potential can be expressed in terms of fugacity, given by Raoults law for a liquid and by Daltons law for (an ideal) gas. During operation, due to removal of the vapor-phase permeate, the actual fugacity of the vapor is lower than anticipated on basis of the collected (condensed) permeate.
Separation of components (e.g. water and ethanol) is based on a difference in transport rate of individual components through the membrane. This transport mechanism can be described using the solution-diffusion model, based on the rate/degree of dissolution of a component into the membrane and its velocity of transport (expressed in terms of diffusivity) through the membrane, which will be different for each component and membrane type leading to separation. | 0 | Theoretical and Fundamental Chemistry |
In the early 2000s, Zhao's group reported that visible light can accelerate the degradation of organic pollutants with aqueous
solutions of iron tetrasulfophthalocyanine ([Fe(PcS)]) and Hydrogen peroxide|. They also found out FeBR (Fe complex of 2,2′-bipyridine) is efficient in eliminating organic pollutants such as rhodamine B (RhB), malachite green (MG) and N, N-dimethylaniline (DMA). They did several control experiments, in the dark or under irradiation, with or without irradiation. They proposed that when light is introduced, excitation of [Fe(PcS)] can result in electron transfer from ligand(L) to Fe, then Fe can be reduced to Fe. The Fe-L complex can react with to produce HO, leading to the degradation of pollutants. | 1 | Applied and Interdisciplinary Chemistry |
The North Australian Pastoral Company (NAPCO) is an Australian cattle company founded in 1877. It was originally established in the Barkly Tableland in the Northern Territory before expanding to Queensland as the company developed. It is one of Australia's oldest cattle companies and is today, a leading national beef producer in the Australian cattle industry. The company has a variety of stations throughout the Northern Territory and Queensland. Northern Territory stations include those such as Alexandria and Mittiebah, whilst Queensland stations encompass those such as Boomarra, Kynuna and Portland Downs. The company is most well known for its development of the Alexandria and Kynuna cattle composites which are species of cattle that are distinct to NAPCO and separate it from others in the pastoral industry. | 1 | Applied and Interdisciplinary Chemistry |
A year after Oliver and Schafer, Władysław Szymonowicz (1869–1939) and Napoleon Cybulski of the Jagiellonian University in Kraków reported similar findings and conclusions. They found that blood from the adrenal veins caused hypertension when injected intravenously in a recipient dog, whereas blood from other veins did not, demonstrating that the adrenal pressor substance was in fact secreted into the blood and confirming Vulpian. The Polish authors freely acknowledged the priority of Oliver and Schäfer, and the British authors acknowledged the independence of Szymonowicz and Cybulski. The main difference was in the location of the action: to the periphery by Oliver and Schäfer but, erroneously, to the central nervous system by Szymonowicz and Cybulski.
Another year later, the US-American ophthalmologist William Bates, perhaps motivated like Oliver, instilled adrenal extracts into the eye and found that ″the conjunctiva of the globe and lids whitened in a few minutes″, correctly explained the effect by vasoconstriction, and administered the extracts in various eye diseases. | 1 | Applied and Interdisciplinary Chemistry |
The divergence theorem gives an equivalent integral definition of a solenoidal field; namely that for any closed surface, the net total flux through the surface must be zero:
where is the outward normal to each surface element.
The fundamental theorem of vector calculus states that any vector field can be expressed as the sum of an irrotational and a solenoidal field. The condition of zero divergence is satisfied whenever a vector field v has only a vector potential component, because the definition of the vector potential A as:
automatically results in the identity (as can be shown, for example, using Cartesian coordinates):
The converse also holds: for any solenoidal v there exists a vector potential A such that (Strictly speaking, this holds subject to certain technical conditions on v, see Helmholtz decomposition.) | 1 | Applied and Interdisciplinary Chemistry |
CAM photosynthesis is also found in aquatic species in at least 4 genera, including: Isoetes, Crassula, Littorella, Sagittaria, and possibly Vallisneria, being found in a variety of species e.g. Isoetes howellii, Crassula aquatica.
These plants follow the same nocturnal acid accumulation and daytime deacidification as terrestrial CAM species. However, the reason for CAM in aquatic plants is not due to a lack of available water, but a limited supply of . is limited due to slow diffusion in water, 10000x slower than in air. The problem is especially acute under acid pH, where the only inorganic carbon species present is , with no available bicarbonate or carbonate supply.
Aquatic CAM plants capture carbon at night when it is abundant due to a lack of competition from other photosynthetic organisms. This also results in lowered photorespiration due to less photosynthetically generated oxygen.
Aquatic CAM is most marked in the summer months when there is increased competition for , compared to the winter months. However, in the winter months CAM still has a significant role. | 0 | Theoretical and Fundamental Chemistry |
Δ-capnellene, also referred to simply as capnellene in the literature, is a monounsaturated hydrocarbon of the molecular formula CH. It features a tricyclic skeleton, a geminal dimethyl group, a tertiary methyl group, and an exocyclic methylene group.
Capnellene is also a sesquiterpene, a class of terpenes that are natural semiochemicals. However, it is a non-isoprenoid sesquiterpene, meaning that unlike most sesquiterpenes its structure is not based on a repeated isoprene unit. Capnellene is the presumed biosynthetic precursor to the capnellanols, a group of alcohols based on the capnellene skeleton that are also produced by Capnella imbricata, however the biosynthesis of these compounds has not yet been elucidated. | 0 | Theoretical and Fundamental Chemistry |
In combustion, Burke–Schumann limit, or large Damköhler number limit, is the limit of infinitely fast chemistry (or in other words, infinite Damköhler number), named after S.P. Burke and T.E.W. Schumann, due to their pioneering work on Burke–Schumann flame. One important conclusion of infinitely fast chemistry is the non-co-existence of fuel and oxidizer simultaneously except in a thin reaction sheet. The inner structure of the reaction sheet is described by Liñán's equation. | 1 | Applied and Interdisciplinary Chemistry |
A rusticle is a formation of rust similar to an icicle or stalactite in appearance that occurs deep underwater when iron-loving bacteria attack and oxidize wrought iron and steel. They may be familiar from underwater photographs of shipwrecks, such as the RMS Titanic and the German battleship Bismarck. They have also been found in the #3 turret, 8-inch gun turret on the stern remains in place of the USS Indianapolis. Rusticles are created by microbial organisms that consume iron.
The word rusticle is a portmanteau of the words rust and icicle and was coined by Robert Ballard, who first observed them on the wreck of the Titanic in 1986. Rusticles on the Titanic were first investigated in 1996 by Roy Cullimore, based at the University of Regina in Canada. A previously unknown species of bacteria living inside the Titanics rusticles called Halomonas titanicae was discovered in 2010 by Henrietta Mann.
Rusticles can form on any submerged steel object and have been seen on other subsea structures such as mooring chains and subsea equipment. They form more rapidly in warmer climates and can form in water with little to no dissolved oxygen. | 1 | Applied and Interdisciplinary Chemistry |
Biomedical implants should have low density for patient comfort and high porosity and surface area to facilitate vascularization and the ingrowth of new bone. Ideally, the implant will allow sufficiently easy fluid flow for cell nutrition and osteoblast multiplication as well as migration for cellular colonization of the implant to become uniform. The pores contained within the foam's cellular matrix mimic the extracellular matrix of bone, allowing the body to fixate with the implant. The porosity of the implant also promotes apposition and facilitates vascularization−as cells are able to attach, reproduce and form basic functions. It has been shown that a macropore size of 200–500 µm is preferred for ingrowths of new bone tissues and transportation of body fluids. The lower bound is controlled by the size of cells (~20 µm), and the upper bound is related to the specific surface area through the availability of binding sites. Finer pores further help in tissue growth and biofluid movement. Anisotropic, elongated pores (such as those attainable via the freeze-casting technique) may be beneficial in bone implants in that they can further mimic the structure of bone.
The porous surface geometry of the foam promotes bone in-growth, provides anchorage for fixation, and ensures stresses are transferred from the implant to the bone. Surface roughness in the pore can enhance bone in-growth, and coarser cell size facilitates faster tissue growth.
To optimize the implants functionality and ability to successfully fuse with bone, it may be necessary to manipulate the materials manufacturing methods in order to modify the foam's pore structure. Changes in pore structure can directly influence implant strength as well as other key properties. | 0 | Theoretical and Fundamental Chemistry |
Iron smelting—the extraction of usable metal from oxidized iron ores—is more difficult than tin and copper smelting. While these metals and their alloys can be cold-worked or melted in relatively simple furnaces (such as the kilns used for pottery) and cast into molds, smelted iron requires hot-working and can be melted only in specially designed furnaces. Iron is a common impurity in copper ores and iron ore was sometimes used as a flux, thus it is not surprising that humans mastered the technology of smelted iron only after several millennia of bronze metallurgy.
The place and time for the discovery of iron smelting is not known, partly because of the difficulty of distinguishing metal extracted from nickel-containing ores from hot-worked meteoritic iron. The archaeological evidence seems to point to the Middle East area, during the Bronze Age in the 3rd millennium BC. However, wrought iron artifacts remained a rarity until the 12th century BC.
The Iron Age is conventionally defined by the widespread replacement of bronze weapons and tools with those of iron and steel. That transition happened at different times in different places, as the technology spread. Mesopotamia was fully into the Iron Age by 900 BC. Although Egypt produced iron artifacts, bronze remained dominant until its conquest by Assyria in 663 BC. The Iron Age began in India about 1200 BC, in Central Europe about 800 BC, and in China about 300 BC. Around 500 BC, the Nubians, who had learned from the Assyrians the use of iron and were expelled from Egypt, became major manufacturers and exporters of iron. | 1 | Applied and Interdisciplinary Chemistry |
The GAIN domain (G-protein-coupled receptor (GPCR) autoproteolysis-inducing domain) is a protein domain found in a number of cell surface receptors, including adhesion-GPCRs and polycystic kidney disease proteins PKD1 and PKD2. The domain is involved in the self-cleavage of these transmembrane receptors, and has been shown to be crucial for their function . Point mutations within the GAIN domain of PKD1 and GPR56 are known to cause polycystic kidney disease and polymicrogyria, respectively. | 1 | Applied and Interdisciplinary Chemistry |
Restaurants, schools, office businesses, and healthcare facilities use architectural acoustics to reduce noise for their customers. In the United States, OSHA has requirements regulating the length of exposure of workers to certain levels of noise.
For educators and students, improving the sound quality of an environment will subsequently improve student learning, concentration, and teacher-student inter-communications. In 2014, a research study conducted by Applied Science revealed 86% of students perceived their instructors more intelligibly, while 66% of students reported experiencing higher concentration levels after sound-absorbing materials were incorporated into the classroom. | 1 | Applied and Interdisciplinary Chemistry |
Atmospheric-pressure plasmas have been used for a variety of industrial applications, including volatile organic compound (VOC) removal, exhaust gas emission treatment and polymer surface and food treatment. For decades, non-thermal plasmas have also been used to generate ozone for water purification. Atmospheric pressure plasmas can be characterized primarily by a large number of electrical discharges in which the majority of the electrical energy is used to generate energetic electrons. These energetic electrons produce chemically excited species - free radicals and ions - and additional electrons by dissociation, excitation and ionization of background gas molecules by electron impact. These excited species in turn oxidize, reduce or decompose the molecules, such as wastewater or biomethane, that are brought into contact with them. Part of the electrical energy is converted into chemical energy. Plasmalysis can thus be used to store energy, for example in the plasma analysis of ammonium from waste water or liquid fermentation residue, which produces hydrogen and nitrogen. The hydrogen thus produced can serve as an energy carrier for a hydrogen economy. | 0 | Theoretical and Fundamental Chemistry |
When the hydrogen atoms in an alkyl radical are displaced with deuterium, disproportionation proceeds at a slightly slower rate whereas the rate of recombination remains the same. Thus disproportionation is weakly affected by the kinetic isotope effect with k/k = 1.20 ± 0.15 for ethylene. Hydrogens and deuterons are not involved in recombination reactions. However, deuteron abstraction during disproportionation occurs more slowly than hydrogen abstraction due to the increased mass and reduced vibrational energy of deuterium, although the experimentally observed k/k is close to one. | 0 | Theoretical and Fundamental Chemistry |
Pseudogenes are mostly former genes that have become non-functional due to mutation but the term also refers to inactive DNA sequences that are derived from RNAs produced by functional genes (processed pseudogenes). Pseudogenes are only a small fraction of noncoding DNA in prokaryotic genomes because they are eliminated by negative selection. In some eukaryotes, however, pseudogenes can accumulate because selection is not powerful enough to eliminate them (see Nearly neutral theory of molecular evolution).
The human genome contains about 15,000 pseudogenes derived from protein-coding genes and an unknown number derived from noncoding genes. They may cover a substantial fraction of the genome (~5%) since many of them contain former intron sequences.
Pseudogenes are junk DNA by definition and they evolve at the neutral rate as expected for junk DNA. Some former pseudogenes have secondarily acquired a function and this leads some scientists to speculate that most pseudogenes are not junk because they have a yet-to-be-discovered function. | 1 | Applied and Interdisciplinary Chemistry |
In 2009, the Zimmerman group discovered a compound to target the trinucleotide repeat expanded RNA and DNA that cause DM1. Through rational design, they utilized a triaminotriazine recognition unit to target TT or UU mismatches through a Janus Wedge type binding mode, creating a base triplet with the mismatch. The combined use of an acridine intercalator to pi-pi stack on the target gave a nanomolar binding affinity for TT or UU mismatches over others. Along with high binding affinity, this molecule was shown to displace MBNL from the complex with r(CUG) with a micromolar K Additionally, HIV-1 RNA has been targeted extensively in vitro by RNA-binding small molecules. In 2007, Miller and coworkers used dynamic combinatorial chemistry to screen a compound library against HIV-1 frameshift regulatory stem-loop RNA. They identified a hit compound that was selective for the regulatory sequence with micromolar binding affinity.
In 2011, Butcher and colleagues discovered a frameshifting stimulator (DB213) which bound to HIV-1 FS RNA with moderate binding affinity. An NMR structure of the RNA in complex with DB213, showed that the small molecule bound to the major groove of the RNA duplex. [https://scholar.google.com/citations?hl=en&user=ViAlX_kAAAAJ Schneekloth] and Hargrove have taken a different approach by targeting the HIV-1 TAR RNA hairpin. In a small molecule microarray screening, the Schneekloth group identified a thienopyridine derivative that interacts with HIV-1 TAR RNA hairpin. Further SAR studies provided more information on the structure and binding mode. The lead analogue was found to bind to the 5’-UTR of HIV with an IC of 40 μM for displacing a Tat-derived peptide. The Hargrove group developed a small library of amiloride derivatives with changes at the C(5) and C(6) positions to improve the binding affinity of amiloride to the loop and bulge of the HIV-1 TAR RNA. Using in vitro studies and modeling, they found a hit compound whose inhibition activity was increased by more than 100x compared to the parent amiloride. This compound is reported to be one of the tightest non-aminoglycoside TAR ligands reported to date. | 1 | Applied and Interdisciplinary Chemistry |
R. R. Schmidt and co-workers have described the selective anomeric activation of O-protected hexopyranoses (glucose, galactose, mannose, glucosamine, galactosamine), hexofuranoses and pentopyranoses with trichloroacetonitrile in the presence of a base, as well as glycosylations under acid catalysis.
Under kinetic control with potassium carbonate as the base, β-trichloroacetimidates are formed selectively, whereas with sodium hydride, caesium carbonate or potassium hydroxide and in the presence of phase-transfer catalysts only α-trichloroacetimidates are obtained (thermodynamically controlled).
The trichloroacetimidates are reacted between −40 °C and room temperature with boron trifluoride etherate in dichloromethane with O-protected sugars. This method usually gives better results than the Koenigs–Knorr method using silver salts or the Helferich method which uses problematic mercury salts. Since an inversion occurs at the anomeric center, the reaction leads to β-O-glycosides (when using α-trichloroacetimidates). The trichloroacetimidate method often produces sterically uniform glycosides under mild reaction conditions in very good yields.
Thioacetic acid reacts with acetyl-protected α-galactosyl trichloroacetimidate even without additional acid catalysis to thioglycoside, from which (after cleavage of the protective groups) 1-thio-β--galactose is easily accessible, which is useful for the separation of racemates of amino acids.
Trichloroacetonitrile was an important fumigant in the first half of the 20th century, but today it has become obsolete for this application. | 0 | Theoretical and Fundamental Chemistry |
Side chain polyrotaxanes are formed by host–guest interactions of polymer side chains with cyclic molecules that are interlocked by bulky stoppers.
There are mainly three types of side chain polyrotaxanes:
(1) Polyaxis/rotor: Comb-like polymers assembled with the cyclic molecules that are not interlocked on the side chain.
(2) Polyrotor/axis: polymers possess cyclic molecules on the side chain, which assemble with guest molecules to form polypseudorotaxanes.
(3) Polyrotor/polyaxis: polymers possess covalently bonded cyclic molecule-moieties assembled with polymers possess guested in the side chain.
Similar to the synthesis routes to main chain polyrotaxanes, there are mainly six approaches to side chain polyrotaxane.
(1) Ring-threading of performed graft polymer
(2) Ring-grafting
(3) Rotaxane-grafting
(4) Polymerization of macromonomer with rings
(5) Polymerization of rotaxane-monomer
(6) Chemical conversion
Similarly, the positions of chain and rings can be switched, which results in corresponding side-chain polyrotaxanes. | 0 | Theoretical and Fundamental Chemistry |
When oxygen binds to the iron complex, it causes the iron atom to move back toward the center of the plane of the porphyrin ring (see moving diagram). At the same time, the imidazole side-chain of the histidine residue interacting at the other pole of the iron is pulled toward the porphyrin ring. This interaction forces the plane of the ring sideways toward the outside of the tetramer, and also induces a strain in the protein helix containing the histidine as it moves nearer to the iron atom. This strain is transmitted to the remaining three monomers in the tetramer, where it induces a similar conformational change in the other heme sites such that binding of oxygen to these sites becomes easier.
As oxygen binds to one monomer of hemoglobin, the tetramers conformation shifts from the T (tense) state to the R (relaxed) state. This shift promotes the binding of oxygen to the remaining three monomers heme groups, thus saturating the hemoglobin molecule with oxygen.
In the tetrameric form of normal adult hemoglobin, the binding of oxygen is, thus, a cooperative process. The binding affinity of hemoglobin for oxygen is increased by the oxygen saturation of the molecule, with the first molecules of oxygen bound influencing the shape of the binding sites for the next ones, in a way favorable for binding. This positive cooperative binding is achieved through steric conformational changes of the hemoglobin protein complex as discussed above; i.e., when one subunit protein in hemoglobin becomes oxygenated, a conformational or structural change in the whole complex is initiated, causing the other subunits to gain an increased affinity for oxygen. As a consequence, the oxygen binding curve of hemoglobin is sigmoidal, or S-shaped, as opposed to the normal hyperbolic curve associated with noncooperative binding.
The dynamic mechanism of the cooperativity in hemoglobin and its relation with low-frequency resonance has been discussed. | 0 | Theoretical and Fundamental Chemistry |
Dipen Sinha of the Los Alamos National Laboratory developed ARS in 1989. Most published work in acoustics has been in the ultrasonic region and their instrumentation has dealt with propagation through a medium and not a resonance effect. One of the first, if not the first publication related to acoustic resonance was in 1988 in the journal of Applied Spectroscopy. The researchers designed a V-shaped quartz rod instrument that utilized ultrasonic waves to obtain signatures of microliters of different liquids. The researchers did not have any type of classification statistics or identification protocols; the researchers simply observed ultrasonic resonance signatures with these different materials. Specifically, Sinha was working on developing an ARS instrument that can detect nuclear, chemical, and biological weapons. By 1996, he had successfully developed a portable ARS unit that can be used in a battlefield. The unit can detect and identify deadly chemicals that are stored in containers in matter of minutes. In addition, the instrument was further developed by a different research group (Dr. Robert Lodder, University of Kentucky) and their work was also published in Applied Spectroscopy. The researchers created a V-shaped instrument that could breach the sonic and ultrasonic regions creating more versatility. The term acoustic resonance spectrometer was coined for the V-shaped spectrometer as well. Since the study in 1994, the ARS has evolved and been used to differentiate wood species, differentiate pharmaceutical tablets, determine burn rates and determine dissolution rates of tablets. In 2007 Analytical Chemistry featured the past and current work of the lab of Dr. Lodder discussing the potential of acoustics in the analytical chemistry and engineering fields. | 0 | Theoretical and Fundamental Chemistry |
Many tools and concepts have been developed to exploit the advantages of intramolecular cyclizations. For example, installing large substituents exploits the Thorpe-Ingold effect. High dilution reactions suppress intermolecular processes. One set of tools involves tethering as discussed below. | 0 | Theoretical and Fundamental Chemistry |
At least one 1992 article suggests it is a slightly misconceived misconception to ascribe regelation to ice skating. The problem with matching the (large) magnitude of the water-ice p-V gradient above the triple point boundary with the magnitudes of prevailing temperature and pressure in the case of the ice skating context applies equally in the context of the classic lab experiment with a copper wire cutting through an 10cm ice block with say a 28 swg wire. The misconception is not that these observations fail to be regelation but that regelation can be explained (solely) in terms of the magnitude of p-V gradient above the triple point. There is much more going on. Regelation is empirical—it is a phenomenon as was, for example, Brownian Motion before, during, and arguably even after Einstein modelled it. It has been so widely observed and described that we generalise to describing it in terms of pressure causing increased surface melting. The recognition of this phenomenon in all the mentioned contexts is not in doubt. Car tyres work in snow even though there is some increased surface melting because they have tread which allows water to be liberated.
Ice skating is given as an example of regelation; however, the pressure required is much greater than the weight of a skater. Additionally, regelation does not explain how one can ice skate at sub-zero (0°C) temperatures.
Compaction and creation of snow balls is another example from old texts. Here, the pressure required is far greater than the pressure that can be applied by hand. A counter example is that cars do not melt snow as they run over it. | 0 | Theoretical and Fundamental Chemistry |
Future applications of this information could include:
* Constructing a more accurate and nuanced definition of the phenomenon of "death".
* Helping forensic pathologists (or biologists or veterinarians) establish a more precise time of death (for example, in an eco-health investigation, when the practitioner needs information on the time or cause of poisoning, without a case of zoonosis). With a better understanding of the steps of this phenomenon in the human thanatomicrobiome, a coroner could, via a "postmortem serology", establish with greater precision the time since death (by the hour, or even by the minute), which can be useful for investigations to reconstruct the conditions of death.
* Illuminating the phenomena of cell death, apoptosis, and in particular the phenomenon of ischemia (including myocardial ischemia) and the process of healing and resilience, perhaps even for the purpose of facilitating them. The post-mortem gene revival means that, for up to 48 hours following death, enough energy remains in the cells to activate some cellular machinery. At least some of these genes appear to be those involved in physiological healing, or "auto-resuscitation". Previous studies have shown that in people who have died by trauma, heart attack, or suffocation, various genes including those involved in cardiac muscle contraction and wound healing were active more than 12 hours after death. Similar genetic evidence has been found in dental pulp. Some authors in 2015 introduced the concept of "thanatotranscriptome apoptotic".
* Understanding cancer. It has been found that genes involved in carcinogenesis are among those reactivated soon after death, with a peak of activity about 24 hours post-mortem. A better understanding of this activity could shed light on the phenomenon of carcinogenesis and potentially lead to new tools to combat it.
* Improving the quality of organ transplants. The fact that cancer-related genes are activated following death can shed light on the timing of organ transplantation to reduce the incidence of cancer in transplant recipients. Liver transplant recipients have been shown to be more prone to cancers after treatment than would be statistically normal. This phenomenon has been attributed to their post-operative diet, or to the immunosuppressive drugs administered to prevent their body from rejecting the transplant. One hypothesis (yet to be verified) is that post-mortem cancer genes activated in the liver of the donor may also play a role.
* Testing the hypothesis that after death, a rapid decrease of "suppressor gene" activity (which normally inhibit the activation of other genes, including those no longer needed after the fetal stage) would allow dormant genes wake up, at least for a short period of time. | 1 | Applied and Interdisciplinary Chemistry |
Sodium amide is mainly used as a strong base in organic chemistry, often in liquid ammonia solution. It is the reagent of choice for the drying of ammonia (liquid or gaseous). One of the main advantages to the use of sodium amide is its relatively low nucleophilicity. In the industrial production of indigo, sodium amide is a component of the highly basic mixture that induces cyclisation of N-phenylglycine. The reaction produces ammonia, which is recycled typically. | 0 | Theoretical and Fundamental Chemistry |
Perennial plants whose leaves are shed annually are said to have deciduous leaves, while leaves that remain through winter are evergreens.
Leaves attached to stems by stalks (known as petioles) are called petiolate, and if attached directly to the stem with no petiole they are called sessile.
* Ferns have fronds.
* Conifer leaves are typically needle- or awl-shaped or scale-like, they are usually evergreen, but can sometimes be deciduous. Usually, they have a single vein.
* Flowering plant (Angiosperm) leaves: the standard form includes stipules, a petiole, and a lamina.
* Lycophytes have microphylls.
* Sheath leaves are the type found in most grasses and many other monocots.
* Other specialized leaves include those of Nepenthes, a pitcher plant.
Dicot leaves have blades with pinnate venation (where major veins diverge from one large mid-vein and have smaller connecting networks between them). Less commonly, dicot leaf blades may have palmate venation (several large veins diverging from petiole to leaf edges). Finally, some exhibit parallel venation.
Monocot leaves in temperate climates usually have narrow blades, and usually parallel venation converging at leaf tips or edges. Some also have pinnate venation. | 0 | Theoretical and Fundamental Chemistry |
Most of the codes apply to arbitrary-shaped inhomogeneous nonmagnetic particles and particle systems in free space or homogeneous dielectric host medium. The calculated quantities typically include the Mueller matrices, integral cross-sections (extinction, absorption, and scattering), internal fields and angle-resolved scattered fields (phase function). There are some published comparisons of existing DDA codes. | 0 | Theoretical and Fundamental Chemistry |
John William Gofman (21 September 1918 – 15 August 2007) was an American scientist and advocate. He was Professor Emeritus of Molecular and Cell Biology at the University of California at Berkeley.
Gofman pioneered the field of clinical lipidology, and in 2007 was honored by the Journal of Clinical Lipidology with the title of "Father of Clinical Lipidology". With Frank T. Lindgren and other research associates, Gofman discovered and described three major classes of plasma lipoproteins, fat molecules that carry cholesterol in the blood. The team he led at the Donner Laboratory went on to demonstrate the role of lipoproteins in the causation of heart disease.
Gofman was instrumental in inducing the health-physics scientific community both to acknowledge the cancer risks of ionizing radiation and to adopt the Linear No-Threshold (LNT) model as a means of estimating actual cancer risks from low-level radiation and as the foundation of the international guidelines for radiation protection. However, his conclusions were that the dose-response relationship was not linear, but supra-linear.
Gofmans earliest research was in nuclear physics and chemistry, in close connection with the Manhattan Project. He codiscovered several radioisotopes, notably uranium-233 and its fissionability; he was the third person ever to work with plutonium and, having devised an early process for separating plutonium from fission products at J. Robert Oppenheimers request, he was the first chemist ever to try and isolate milligram quantities of plutonium.
In 1963 Gofman established the Biomedical Research Division for the Livermore National Laboratory, where he was on the cutting edge of research into the connection between chromosomal abnormalities and cancer.
Later in life, Gofman took on a role as an advocate warning of dangers involved with nuclear power. From 1971 on, he was Chairman of the Committee for Nuclear Responsibility. He was awarded the Right Livelihood Award for "his pioneering work in exposing the health effects of low-level radiation" on the Chernobyl disaster's area population.
In his 1996 book Gofman claimed that exposure to medical x-rays was responsible for about 75 percent of breast cancers in the United States. This order of magnitude appears to correlate with the increase in breast-cancer incidence following mammography screening in the US and France. | 0 | Theoretical and Fundamental Chemistry |
Several points of high symmetry are of special interest – these are called critical points.
Other lattices have different types of high-symmetry points. They can be found in the illustrations below. | 0 | Theoretical and Fundamental Chemistry |
DDM was introduced in 2008 and it was applied for characterizing the dynamics of colloidal particles in Brownian motion. More recently it has been successfully applied also to the study of aggregation processes of colloidal nanoparticles, of bacterial motions, of the dynamics of anisotropic colloids and of motile cilia. | 0 | Theoretical and Fundamental Chemistry |
The genes that encode both the dihydroxy acid dehydrase used in the creation of α-ketoisovalerate and Transaminase E, as well as other enzymes are encoded on the ilvEDA operon. This operon is bound and inactivated by valine, leucine, and isoleucine. (Isoleucine is not a direct derivative of pyruvate, but is produced by the use of many of the same enzymes used to produce valine and, indirectly, leucine.) When one of these amino acids is limited, the gene furthest from the amino-acid binding site of this operon can be transcribed. When a second of these amino acids is limited, the next-closest gene to the binding site can be transcribed, and so forth. | 1 | Applied and Interdisciplinary Chemistry |
Halohydrins react with base to give epoxides. The reaction is spontaneous because the energetic cost of introducing the ring strain (13 kcal/mol) is offset by the larger bond enthalpy of the newly introduced C-O bond (when compared to that of the cleaved C-halogen bond).
Formation of epoxides from secondary halohydrins is predicted to occur faster than from primary halohydrins due to increased entropic effects in the secondary halohydrin, and tertiary halohydrins react (if at all) extremely slowly due to steric crowding.
Starting with propylene chlorohydrin, most of the world's supply of propylene oxide arises via this route.
An intramolecular epoxide formation reaction is one of the key steps in the Darzens reaction.
In the Johnson–Corey–Chaykovsky reaction epoxides are generated from carbonyl groups and sulfonium ylides. In this reaction, a sulfonium is the leaving group instead of chloride. | 0 | Theoretical and Fundamental Chemistry |
For two-dimensional potential flow, streamlines are perpendicular to equipotential lines. Taken together with the velocity potential, the stream function may be used to derive a complex potential. In other words, the stream function accounts for the solenoidal part of a two-dimensional Helmholtz decomposition, while the velocity potential accounts for the irrotational part. | 1 | Applied and Interdisciplinary Chemistry |
In 1990, Waters was awarded the New Zealand 1990 Commemoration Medal. In the 1995 Queen's Birthday Honours, he was appointed a Knight Bachelor, for services to tertiary education.
Waters was conferred with honorary Doctor of Science degrees by the University of East Asia in 1986, and Massey University in 1996. He was elected a Fellow of the New Zealand Institute of Chemistry in 1977, Fellow of the Australian and New Zealand Association for the Advancement of Science in 1979, and Fellow of the Royal Society of New Zealand in 1992. | 0 | Theoretical and Fundamental Chemistry |
* Fossil-fuel power stations may also use a steam turbine generator or in the case of natural gas-fired power plants may use a combustion turbine. A coal-fired power station produces heat by burning coal in a steam boiler. The steam drives a steam turbine and generator that then produces electricity. The waste products of combustion include ash, sulfur dioxide, nitrogen oxides, and carbon dioxide. Some of the gases can be removed from the waste stream to reduce pollution.
* Nuclear power plants use the heat generated in a nuclear reactor's core (by the fission process) to create steam which then operates a steam turbine and generator. About 20 percent of electric generation in the USA is produced by nuclear power plants.
* Geothermal power plants use steam extracted from hot underground rocks. These rocks are heated by the decay of radioactive material in the Earth's core.
* Biomass-fuelled power plants may be fuelled by waste from sugar cane, municipal solid waste, landfill methane, or other forms of biomass.
* In integrated steel mills, blast furnace exhaust gas is a low-cost, although low-energy-density, fuel.
* Waste heat from industrial processes is occasionally concentrated enough to use for power generation, usually in a steam boiler and turbine.
* Solar thermal electric plants use sunlight to boil water and produce steam which turns the generator.
* Hydrogen power plants can use green hydrogen from electrolysis to help balance supply and demand from Variable renewable energy sources. | 1 | Applied and Interdisciplinary Chemistry |
Solute flow is driven by a difference in hydraulic pressure created from the unloading of solutes in the sink tissues. That is, as solutes are off-loaded into sink cells (by active or passive transport), the density of the phloem liquid decreases locally, creating a pressure gradient. | 1 | Applied and Interdisciplinary Chemistry |
In 1944, Margaret Jennings determined how penicillin acts, and showed that it has no lytic effects on mature organisms, including staphylococci; lysis occurs only if penicillin acts on bacteria during their initial stages of division and growth, when it interferes with the metabolic process that forms the cell wall. This brought Flemings explanation into question, for the mould had to have been there before the staphylococci. Over the next twenty years, all attempts to replicate Flemings results failed. In 1964, Ronald Hare took up the challenge. Like those before him, he found he could not get the mould to grow properly on a plate containing staphylococci colonies. He re-examined Fleming's paper and images of the original Petri dish. He attempted to replicate the original layout of the dish so there was a large space between the staphylococci. He was then able to get the mould to grow, but it had no effect on the bacteria.
Finally, on 1 August 1966, Hare was able to duplicate Flemings results. However, when he tried again a fortnight later, the experiment failed. He considered whether the weather had anything to do with it, for Penicillium' grows well in cold temperatures, but staphylococci do not. He conducted a series of experiments with the temperature carefully controlled, and found that penicillin would be reliably "rediscovered" when the temperature was below , but never when it was above . He consulted the weather records for 1928, and found that, as in 1966, there was a heat wave in mid-August followed by nine days of cold weather starting on 28 August that greatly favoured the growth of the mould. | 1 | Applied and Interdisciplinary Chemistry |
Methyl red displays pH dependent photochromism, with protonation causing it to adopt a hydrazone/quinone structure.
Methyl Red has a special use in histopathology for showing acidic nature of tissue and presence of organisms with acidic natured cell walls.
Methyl Red is detectably fluorescent in 1:1 water:methanol (pH 7.0), with an emission maximum at 375 nm (UVA) upon excitation with 310 nm light (UVB). | 0 | Theoretical and Fundamental Chemistry |
Gregorio Baró (June 19, 1928 - May 28, 2012) was an Argentine scientist. He was born in Santiago Temple, Córdoba and died in Buenos Aires. | 0 | Theoretical and Fundamental Chemistry |
A wide range of metals may be found in rivers from natural sources where metal ores are present in the rocks over which the river flows or in the aquifers feeding water into the river. However many rivers have an increased load of metals because of industrial activities which include mining and quarrying and the processing and use of metals. | 1 | Applied and Interdisciplinary Chemistry |
Carbonyl allylation has been employed in the synthesis of polyketide natural products and other oxygenated molecules with a contiguous array of stereocenters. For example, allylstannanation of a threose-derived aldehyde affords the macrolide antascomicin B, which structurally resembles FK506 and rapamycin, and is a potent binder of FKBP12. The Krische allylation was used to prepare the polyketide (+)-SCH 351448, a macrodiolide ionophore bearing 14 stereogenic centers. | 0 | Theoretical and Fundamental Chemistry |
Transketolase is widely expressed in a wide range of organisms including bacteria, plants, and mammals. The following human genes encode proteins with transketolase activity:
* TKT (transketolase)
* TKTL1 (transketolase-like protein 1)
* TKTL2 (transketolase-like protein 2) | 0 | Theoretical and Fundamental Chemistry |
Racivir is a racemic mixture of the two β-enantiomers of emtricitabine (FTC), (-)-FTC and (+)-FTC. Racivir has excellent oral bioavailability and has the advantage of needing to be taken only once a day. Racivir can be considered to be used in combination of two NRTIs and has shown promising antiviral activity when used in combination. Racivir is currently in phase II clinical trials.
There are several more NRTIs in development. Either the sponsors have filed for an Investigational New Drug (IND) application, the application has been approved by the FDA or the drugs are in different phases of clinical trials. Some of the NRTIs that are in development exhibit various attractive pharmacological properties that could make them desirable for the treatment of patients in need of new agents. | 1 | Applied and Interdisciplinary Chemistry |
Lavoisier's fundamental contributions to chemistry were a result of a conscious effort to fit all experiments into the framework of a single theory. He established the consistent use of the chemical balance, used oxygen to overthrow the phlogiston theory, and developed a new system of chemical nomenclature which held that oxygen was an essential constituent of all acids (which later turned out to be erroneous).
Lavoisier also did early research in physical chemistry and thermodynamics in joint experiments with Laplace. They used a calorimeter to estimate the heat evolved per unit of carbon dioxide produced, eventually finding the same ratio for a flame and animals, indicating that animals produced energy by a type of combustion reaction.
Lavoisier also contributed to early ideas on composition and chemical changes by stating the radical theory, believing that radicals, which function as a single group in a chemical process, combine with oxygen in reactions. He also introduced the possibility of allotropy in chemical elements when he discovered that diamond is a crystalline form of carbon.
He was also responsible for the construction of the gasometer, an expensive instrument he used at his demonstrations. While he used his gasometer exclusively for these, he also created smaller, cheaper, more practical gasometers that worked with a sufficient degree of precision that more chemists could recreate.
Overall, his contributions are considered the most important in advancing chemistry to the level reached in physics and mathematics during the 18th century.
Following his death, a collection comprising most of his scientific manuscripts and instruments was established by his relatives at the Château de la Canière in Puy-de-Dôme.
Mount Lavoisier in New Zealand's Paparoa Range was named after him in 1970 by the Department of Scientific and Industrial Research. | 1 | Applied and Interdisciplinary Chemistry |
Non-classical bioisosteres may differ in a multitude of ways from classical bioisosteres, but retain the focus on providing similar sterics and electronic profile to the original functional group. Whereas classical bioisosteres commonly conserve much of the same structural properties, nonclassical bioisosteres are much more dependent on the specific binding needs of the ligand in question and may substitute a linear functional group for a cyclic moiety, an alkyl group for a complex heteroatom moiety, or other changes that go far beyond a simple atom-for-atom switch.
For example, a chloride -Cl group may often be replaced by a trifluoromethyl -CF group or by a cyano -C≡N group. Depending on the particular molecule used, the substitution may result in little change in activity, or either increased or decreased affinity or efficacy - depending on what factors are important for ligand binding to the target protein. Another example is aromatic rings, where a phenyl -CH ring can often be replaced by a different aromatic ring such as thiophene or naphthalene which may improve efficacy, change specificity of binding or reduce metabolically labile sites on the molecule, resulting in better pharmacokinetic properties.
*Alloxanthine is an inhibitor of xanthine oxidase. It is also an isostere of xanthine, the normal substrate for the enzyme. Alloxanthine is considered a non-classical bioisostere because of the scaffold change.
*Silafluofen is an organosilicon analogue of pyrethroid insecticide Etofenprox, wherein a carbon center has been replaced by isosteric silicon, and in addition, one hydrogen atom is replaced by isosteric fluorine atom. | 1 | Applied and Interdisciplinary Chemistry |
The N-terminal amino groups of valine residues in the α- and β-chains of deoxyhemoglobin exist as carbamates. They help to stabilise the protein when it becomes deoxyhemoglobin, and increases the likelihood of the release of remaining oxygen molecules bound to the protein. This stabilizing effect should not be confused with the Bohr effect (an indirect effect caused by carbon dioxide). | 0 | Theoretical and Fundamental Chemistry |
Hess’ law of constant heat summation, also known simply as Hess' law, is a relationship in physical chemistry named after Germain Hess, a Swiss-born Russian chemist and physician who published it in 1840. The law states that the total enthalpy change during the complete course of a chemical reaction is independent of the sequence of steps taken.
Hess law is now understood as an expression of the fact that the enthalpy of a chemical process is independent of the path taken from the initial to the final state (i.e. enthalpy is a state function). According to the first law of thermodynamics, the enthalpy change in a system due to a reaction at constant pressure is equal to the heat absorbed (or the negative of the heat released), which can be determined by calorimetry for many reactions. The values are usually stated for reactions with the same initial and final temperatures and pressures (while conditions are allowed to vary during the course of the reactions). Hesss law can be used to determine the overall energy required for a chemical reaction that can be divided into synthetic steps that are individually easier to characterize. This affords the compilation of standard enthalpies of formation, which may be used to predict the enthalpy change in complex synthesis. | 0 | Theoretical and Fundamental Chemistry |
A symmetry of a pattern is, loosely speaking, a way of transforming the pattern so that it looks exactly the same after the transformation. For example, translational symmetry is present when the pattern can be translated (in other words, shifted) some finite distance and appear unchanged. Think of shifting a set of vertical stripes horizontally by one stripe. The pattern is unchanged. Strictly speaking, a true symmetry only exists in patterns that repeat exactly and continue indefinitely. A set of only, say, five stripes does not have translational symmetry—when shifted, the stripe on one end "disappears" and a new stripe is "added" at the other end. In practice, however, classification is applied to finite patterns, and small imperfections may be ignored.
The types of transformations that are relevant here are called Euclidean plane isometries. For example:
* If one shifts example B one unit to the right, so that each square covers the square that was originally adjacent to it, then the resulting pattern is exactly the same as the starting pattern. This type of symmetry is called a translation. Examples A and C are similar, except that the smallest possible shifts are in diagonal directions.
* If one turns example B clockwise by 90°, around the centre of one of the squares, again one obtains exactly the same pattern. This is called a rotation. Examples A and C also have 90° rotations, although it requires a little more ingenuity to find the correct centre of rotation for C.
* One can also flip example B across a horizontal axis that runs across the middle of the image. This is called a reflection. Example B also has reflections across a vertical axis, and across two diagonal axes. The same can be said for A.
However, example C is different. It only has reflections in horizontal and vertical directions, not across diagonal axes. If one flips across a diagonal line, one does not get the same pattern back, but the original pattern shifted across by a certain distance. This is part of the reason that the wallpaper group of A and B is different from the wallpaper group of C.
Another transformation is "Glide", a combination of reflection and translation parallel to the line of reflection. | 0 | Theoretical and Fundamental Chemistry |
All syntheses start from the perxenates, which are accessible from the xenates through two methods. One is the disproportionation of xenates to perxenates and xenon:
: 2 + 2 OH → + Xe + O + 2 HO
The other is oxidation of the xenates with ozone in basic solution:
: + O + 3 OH → + O + 2 HO
Barium perxenate is reacted with sulfuric acid and the unstable perxenic acid is dehydrated to give xenon tetroxide:
Any excess perxenic acid slowly undergoes a decomposition reaction to xenic acid and oxygen: | 0 | Theoretical and Fundamental Chemistry |
Homocitric acid is an organic compound with the formula HOC(COH)(CHCOH)(CHCOH). This tricarboxylic acid occurs naturally as a component of the iron-molybdenum cofactor of certain nitrogenase proteins. Biochemists often refer to this cofactor as homocitrate, which is the conjugate bases that predominate in neutral aqueous solutions of this species.
The molecule is related to citric acid by the addition of one methylene unit, hence the prefix "homo." Unlike citric acid, homocitric acid is chiral. The acid exists in equilibrium with the lactone. | 1 | Applied and Interdisciplinary Chemistry |
When comparing initiation in eukaryotes to prokaryotes, perhaps one of the first noticeable differences is the use of a larger 80S ribosome. Regulation of this process begins with the supply of methionine by a tRNA anticodon that basepairs AUG. This base pairing comes about by the scanning mechanism that ensues once the small 40S ribosomal subunit binds the 5 untranslated region (UTR) of mRNA. The usage of this scanning mechanism, in opposition to the Shine-Dalgarno sequence that was referenced in prokaryotes, is the ability to regulate translation through upstream RNA secondary structures. This inhibition of initiation through complex RNA structures may be circumvented in some cases by way of internal ribosomal entry sites (IRESs) that localize pre-initiation complexes (PIC) to the start site. In addition to this, the guidance of the PIC to the 5 UTR is coordinated by subunits of the PIC, known as eukaryotic initiation factors (eIFs). When some of these proteins are down-regulated through stresses, translation initiation is reduced by inhibiting cap dependent initiation, the activation of translation by binding eIF4E to the 5' 7-methylguanylate cap. eIF2 is responsible for coordinating the interaction between the Met-tRNA and the P-site of the ribosome. Regulation by phosphorylation of eIF2 is largely associated with the termination of translation initiation. Serine kinases, GCN2, PERK, PKR, and HRI are examples of detection mechanisms for differing cellular stresses that respond by slowing translation through eIF2 phosphorylation. | 1 | Applied and Interdisciplinary Chemistry |
Transition metals can serve as pro-oxidants. For example, chronic manganism is a classic "pro-oxidant" disease. Another disease associated with the chronic presence of a pro-oxidant transition-series metal is hemochromatosis, associated with elevated iron levels. Similarly, Wilsons disease is associated with elevated tissue levels of copper. Such syndromes tend to be associated with common symptomology. Thus, all are occasional symptoms of (e.g) hemochromatosis, another name for which is "bronze diabetes". The pro-oxidant herbicide paraquat, Wilsons disease, and striatal iron have similarly been linked to human Parkinsonism. Paraquat also produces Parkinsonian-like symptoms in rodents. | 1 | Applied and Interdisciplinary Chemistry |
The plasmon resonance displayed by nanoparticles, gold particles are most often used as an example, can be altered using the interfacial layer. When either anionic or cationic ligands bound to a nanoparticle made of gold for example are increased in length, the wavelength of the plasmon resonance will shift to red.
An example of another effect, that has recently been observed by Amendola et al. on small gold nanoparticles, of 10 nm or less, is that dense monolayers that consist of certain specific short chain ligands tend to dampen the surface plasmon resonance effects.
Plasmon resonance can be used to analyze the surfactants of the nanoparticle. This principle is based on the so-called Fröhlich condition which states that the refractive index of the surrounding medium of a nanoparticle can be used to tune or alter the frequency of the surface plasmon resonance. The equation that relates both properties is as follows:
In which is the wavelength at which the plasmon resonance frequency peaks, is the refractive index of the environment, which relates to the dielectric constant of the medium as follows: . Furthermore is the frequency of the plasmon resonance and is the speed of light in vacuum.
The relation between the wavelength and the refractive index of the environment is not strictly linear but for small values of the theoretical predictions align with experimental results.
This relation can thus be used to analyse the environment of the nanoparticle, i.e. the interfacial layer, by measuring the wavelength of the plasmon resonance. | 0 | Theoretical and Fundamental Chemistry |
The suffix -yl is used in organic chemistry to form names of radicals, either separate species (called free radicals) or chemically bonded parts of molecules (called moieties). It can be traced back to the old name of methanol, "methylene" (from , wine and , wood, forest), which became shortened to "methyl" in compound names, from which -yl was extracted. Several reforms of chemical nomenclature eventually generalized the use of the suffix to other organic substituents.
The use of the suffix is determined by the number of hydrogen atoms that the substituent replaces on a parent compound (and also, usually, on the substituent). According to the 1993 IUPAC recommendations:
* -yl means that one hydrogen is replaced.
* -ylidene means that two hydrogens are replaced by a double bond between parent and substituent.
* -ylidyne means that three hydrogens are replaced by a triple bond between parent and substituent.
The suffix -ylidine is encountered sporadically, and appears to be a variant spelling of "-ylidene"; it is not mentioned in the IUPAC guidelines.
For multiple bonds of the same type, which link the substituent to the parent group, the infixes -di-, -tri-, -tetra-, etc., are used: -diyl (two single bonds), -triyl (three single bonds), -tetrayl (four single bonds), -diylidene (two double bonds).
For multiple bonds of different types, multiple suffixes are concatenated: -ylylidene (one single and one double), -ylylidyne (one single and one triple), -diylylidene (two single and one double).
The parent compound name can be altered in two ways:
* For many common compounds the substituent is linked at one end (the 1 position) and historically not numbered in the name. The IUPAC 2013 Rules however do require an explicit locant for most substituents in a preferred IUPAC name. The substituent name is modified by stripping -ane (see alkane) and adding the appropriate suffix. This is "recommended only for saturated acyclic and monocyclic hydrocarbon substituent groups and for the mononuclear parent hydrides of silicon, germanium, tin, lead, and boron". Thus, if there is a carboxylic acid called "X-ic acid", an alcohol ending "X-anol" (or "X-yl alcohol"), or an alkane called "X-ane", then "X-yl" typically denotes the same carbon chain lacking these groups but modified by attachment to some other parent molecule.
* The more general method omits only the terminal "e" of the substituent name, but requires explicit numbering of each yl prefix, even at position 1 (except for -ylidyne, which as a triple bond must terminate the substituent carbon chain). Pentan-1-yl is an example of a name by this method, and is synonymous with pentyl from the previous guideline.
Note that some popular terms such as "vinyl" (when used to mean "polyvinyl") represent only a portion of the full chemical name. | 0 | Theoretical and Fundamental Chemistry |
Factors IIa, Xa, VIIa, IXa and XIa are all proteolytic enzymes that have a specific role in the coagulation cascade. Factor Xa (FXa) is the most promising one due to its position at the intersection of the intrinsic and extrinsic pathway as well as generating around 1000 thrombin molecules for each Xa molecule which results in a potent anticoagulant effect. FXa is generated from FX by cleavage of a 52 amino acid activation peptide, as the "a" in factor Xa means activated. FXa consists of 254 amino acid catalytic domain and is also linked to a 142 amino acid light chain. The chain contains both GLA domain and two epidermal growth factor domains (EGF like domains).
The active site of FXa is structured to catalyze the cleavage of physiological substrates and cleaves PhePheAsnProArg-ThrPhe and TyrIleAspGlyArg-IleVal in prothrombin. FXa has four so-called pockets which are targets for substrates to bind to factor Xa. These pockets are lined up by different amino acids and Xa inhibitors target these pocket when binding to factor Xa. The two most relevant pockets regarding affinity and selectivity for the Xa inhibitors are S1 and S4.
S1: The S1 pocket is a hydrophobic pocket and contains an aspartic acid residue (Asp-189) which can serve as a recognition site for a basic group. FXa has a residual space in the S1 pocket and is lined by residues Tyr-228, Asp-189 and Ser-195.
S2: The S2 pocket is a small and shallow pocket. It merges with the S4 pocket and has room for small amino acids. Tyr-99 seems to block access to this pocket, so this pocket is not as important as S1 and S4.
S3: The S3 pocket is located on the rim of the S1 pocket and is flat and exposed to the solvent. This pocket is not as important as S1 and S4.
S4: The S4 pocket is hydrophobic in nature and the floor of the pocket is formed by Trp-215 residue. The residues Phe-174 and Tyr-99 of FXa join Trp-215 to form an aromatic box that is able to bind aliphatic, aromatic and positively charged fragments. Because of the binding to positively charged entities, it can be described as a cation hole. | 1 | Applied and Interdisciplinary Chemistry |
The extent to which a solid is crystalline (crystallinity) has important effects on its physical properties. Sulfur, while usually polycrystalline, may also occur in other allotropic forms with completely different properties. Although crystallites are referred to as grains, powder grains are different, as they can be composed of smaller polycrystalline grains themselves. Generally, polycrystals cannot be superheated; they will melt promptly once they are brought to a high enough temperature. This is because grain boundaries are amorphous, and serve as nucleation points for the liquid phase. By contrast, if no solid nucleus is present as a liquid cools, it tends to become supercooled. Since this is undesirable for mechanical materials, alloy designers often take steps against it (by grain refinement).
Material fractures can be either intergranular or a transgranular fracture. There is an ambiguity with powder grains: a powder grain can be made of several crystallites. Thus, the (powder) "grain size" found by laser granulometry can be different from the "grain size" (rather, crystallite size) found by X-ray diffraction (e.g. Scherrer method), by optical microscopy under polarised light, or by scanning electron microscopy (backscattered electrons).
If the individual crystallites are oriented completely at random, a large enough volume of polycrystalline material will be approximately isotropic. This property helps the simplifying assumptions of continuum mechanics to apply to real-world solids. However, most manufactured materials have some alignment to their crystallites, resulting in texture that must be taken into account for accurate predictions of their behavior and characteristics. When the crystallites are mostly ordered with a random spread of orientations, one has a mosaic crystal. Abnormal grain growth, where a small number of crystallites are significantly larger than the mean crystallite size, is commonly observed in diverse polycrystalline materials, and results in mechanical and optical properties that diverge from similar materials having a monodisperse crystallite size distribution with a similar mean crystallite size.
Coarse grained rocks are formed very slowly, while fine grained rocks are formed quickly, on geological time scales. If a rock forms very quickly, such as from the solidification of lava ejected from a volcano, there may be no crystals at all. This is how obsidian forms. | 1 | Applied and Interdisciplinary Chemistry |
Concentrated fluoride solutions are corrosive. Gloves made of nitrile rubber are worn when handling fluoride compounds. The hazards of solutions of fluoride salts depend on the concentration. In the presence of strong acids, fluoride salts release hydrogen fluoride, which is corrosive, especially toward glass. | 1 | Applied and Interdisciplinary Chemistry |
The efficiency of duplex sequencing depends on the final number of DCSs which is directly related to the number of reads in each family (family size). If the family size is too small then the DCS can not be assembled and if too many reads are sharing the same tag, the data yield will be low. Family size is determined by the amount of DNA template needed for PCR amplification and the dedicated sequencing lane fraction. The optimal tag family size is between 6 and 12 members. To obtain the optimal family size, the amounts of DNA template and the dedicated sequencing lane fraction need to be adjusted. The following formula takes into account the most important variables that can affect depth of coverage (N=40DG÷R) where "N" is the number of reads, "D" is the desired depth of coverage, "G" is the size of DNA target in base pair, and "R" is final read length. | 1 | Applied and Interdisciplinary Chemistry |
Since then, biochemistry has advanced, especially since the mid-20th century, with the development of new techniques such as chromatography, X-ray diffraction, NMR spectroscopy, radioisotopic labelling, electron microscopy and molecular dynamics simulations. These techniques allowed for the discovery and detailed analysis of many molecules and metabolic pathways of the cell, such as glycolysis and the Krebs cycle (citric acid cycle). The example of an NMR instrument shows that some of these instruments, such as the HWB-NMR, can be very large in size and can cost anywhere from a few thousand dollars to millions of dollars ($16 million for the one shown here). | 1 | Applied and Interdisciplinary Chemistry |
Benzene, toluene, and xylenes can be made by various processes. However, most BTX production is based on the recovery of aromatics derived from the catalytic reforming of naphtha in a petroleum refinery.
Catalytic reforming usually utilizes a feedstock naphtha that contains non-aromatic hydrocarbons with 6 to 12 carbon atoms and typically produces a reformate product containing C to C aromatics (benzene, toluene, xylenes) as well as paraffins and heavier aromatics containing 9 to 12 carbon atoms.
Another process for producing BTX aromatics involves the steam cracking of hydrocarbons which typically produces a cracked naphtha product commonly referred to as pyrolysis gasoline, pyrolysis gas or pygas. The pyrolysis gasoline typically consists of C to C aromatics, heavier aromatics containing 9 to 12 carbon atoms, and non-aromatic cyclic hydrocarbons (naphthenes) containing 6 or more carbon atoms.
The adjacent table compares the BTX content of pyrolysis gasoline produced at standard cracking severity or at medium cracking severity with the BTX content of catalytic reformate produced by either a continuous catalytic regenerative (CCR) reformer or by a semi-regenerative catalytic reformer. About 70 percent of the global production of benzene is by extraction from either reformate or pyrolysis gasoline.
The BTX aromatics can be extracted from catalytic reformate or from pyrolysis gasoline by many different methods. Most of those methods, but not all, involve the use of a solvent either for liquid-liquid extraction or extractive distillation. Many different solvents are suitable, including sulfolane (CHOS), furfural (CHO), tetraethylene glycol (CHO), dimethylsulfoxide (CHOS), and N-methyl-2-pyrrolidone (CHNO).
Below is a schematic flow diagram of one method, involving extractive distillation, for extraction of the BTX aromatics from a catalytic reformate:<br />
<br /> | 0 | Theoretical and Fundamental Chemistry |
Capturing and reusing stormwater as a resource helps maintain a site's predevelopment hydrology while creating an additional supply of water for irrigation or other purposes. Rainwater harvesting is an LID practice that facilitates the reuse of stormwater. | 1 | Applied and Interdisciplinary Chemistry |
A pragmatic, if not scientific, knowledge of fluid flow was exhibited by ancient civilizations, such as in the design of arrows, spears, boats, and particularly hydraulic engineering projects for flood protection, irrigation, drainage, and water supply. The earliest human civilizations began near the shores of rivers, and consequently coincided with the dawn of hydrology, hydraulics, and hydraulic engineering. | 1 | Applied and Interdisciplinary Chemistry |
In the Greek school at Alexandria, which flourished under the auspices of the Ptolemies, attempts were made at the construction of hydraulic machinery, and about 120 BC the fountain of compression, the siphon, and the forcing-pump were invented by Ctesibius and Hero. The siphon is a simple instrument; but the forcing-pump is a complicated invention, which could scarcely have been expected in the infancy of hydraulics. It was probably suggested to Ctesibius by the Egyptian wheel or Noria, which was common at that time, and which was a kind of chain pump, consisting of a number of earthen pots carried round by a wheel. In some of these machines the pots have a valve in the bottom which enables them to descend without much resistance, and diminishes greatly the load upon the wheel; and, if we suppose that this valve was introduced so early as the time of Ctesibius, it is not difficult to perceive how such a machine might have led to the invention of the forcing-pump. | 1 | Applied and Interdisciplinary Chemistry |
eOn was a volunteer computing project running on the Berkeley Open Infrastructure for Network Computing (BOINC) platform, which uses theoretical chemistry techniques to solve problems in condensed matter physics and materials science. It was a project of the Institute for Computational Engineering and Sciences at the University of Texas.
Traditional molecular dynamics can accurately model events that occur within a fraction of a millisecond. In order to model events that take place on much longer timescales, Eon combines transition state theory with kinetic Monte Carlo. The result is a combination of classical mechanics and quantum methods like density functional theory.
Since the generation of new work units depended on the results of previous units, the project could only give each host a few units at a time.
On May 26, 2014, it was announced that eOn would be retiring from BOINC. | 0 | Theoretical and Fundamental Chemistry |
The galvanic series (or electropotential series) determines the nobility of metals and semi-metals. When two metals are submerged in an electrolyte, while also electrically connected by some external conductor, the less noble (base) will experience galvanic corrosion. The rate of corrosion is determined by the electrolyte, the difference in nobility, and the relative areas of the anode and cathode exposed to the electrolyte. The difference can be measured as a difference in voltage potential: the less noble metal is the one with a lower (that is, more negative) electrode potential than the nobler one, and will function as the anode (electron or anion attractor) within the electrolyte device functioning as described above (a galvanic cell). Galvanic reaction is the principle upon which batteries are based.
See the table of standard electrode potentials for more details. | 1 | Applied and Interdisciplinary Chemistry |
The term supramolecular chemistry is defined by Jean-Marie Lehn as "the chemistry of intermolecular bond, covering structures and functions of the entities formed by association of two or more chemical species" in his Nobel lecture in 1987, but the concept of supramolecular catalysis was started way earlier in 1946 by Linus Pauling when he founded the theory of enzymatic catalysis in which rate acceleration is the result of non-covalent stabilization of the transition state by the enzymes. Nevertheless, it was not until a few decades later that an artificial enzyme was developed. The first simple enzyme mimics were based on crown ether and cryptand. In 1976, less than ten years after the discovery of crown ether, Cram et al. developed a functionalized binapthyl crown ether that catalyze transacylation. The catalyst makes use the crown ether motif's ability to capture cation to bind to the ammonium ion part of the substrate and subsequently employs the nearby thiol motif to cleave the ester.
From the early 1970s, cyclodextrins have been extensively studied for its encapsulation properties and used as binding sites in supramolecular catalyst. Cyclodextrins have rigid ring structure, hydrophilic surface, and hydrophobic cavity on the inside; therefore, they are capable of binding organic molecules in aqueous solution. In 1978, with the background knowledge that the hydrolysis of m-tert-butylphenyl acetate is accelerated in the presence of 2-benzimidazoleacetic acid and alpha-cyclodextrin, Brewslow et al. developed a catalyst based on a beta-cyclodextrin carrying two imidazole groups. This cyclodextrin catalytic system mimics ribonuclease A by its use of a neutral imidazole and an imidazolium cation to selective cleave cyclic phosphate substrates. The rate of the reaction is catalyzed 120 times faster, and unlike a hydrolysis by simple base NaOH that gives a 1:1 mixture of the products, this catalysts yield a 99:1 selectivity for one compound.
In 1993, Rebek et al. developed the first self-assemble capsule and in 1997 the so-called "tennis ball" structure was used to catalyze a Diels-Alder reaction. Self-assembled molecules have an advantage over crown ether and cyclodextrin in that they can capture significant larger molecules or even two molecules at the same time. In the following decades, many research groups, such as Makoto Fujita, Ken Raymond, and Jonathan Nitschke, developed cage-like catalysts also from molecular self-assembly principle.
In 2002, Sanders and coworkers published the use of dynamic combinatorial library technique to construct a receptor and in 2003 they employed the technique to develop a catalyst for Diels-Alder reaction. | 0 | Theoretical and Fundamental Chemistry |
# The slope ds/dT of the saturated vapour line in T–s diagram (see Chapter Classification of pure (single-component) working fluids) should be nearly zero, but never positive in the applied pressure ratio of the compressor. This prevents significant moisture (liquid droplet) formation or excessive superheat occurring during the compression. Compressors are very sensitive to liquid droplets.
# The saturation pressure at the temperature of evaporation should not be lower than atmospheric pressure. This mainly corresponds to open-type compressors.
# The saturation pressure at the temperature of condensation should not be high.
# The ratio of condensation and evaporation pressures should be low. | 0 | Theoretical and Fundamental Chemistry |
The rotary kilns maximum temperature ranges between 1,230 and 1,260 °C, which significantly exceeds the 1,000 to 1,050 °C threshold for iron oxide reduction. The main objective is to achieve a paste-like consistency of the ore gangue. The reduced iron agglomerates into 3 to 8 mm metal nodules called . If the infusibility of the gangue is high, the temperature must be increased, up to 1,400 °C for a basic charge. It is crucial to control the gangues hot viscosity. Among rotary drum direct reduction processes, it stands out for using high temperatures.
Another distinctive attribute of the procedure involves introducing powdered coal to the furnace outlet. Furthermore, the process has evolved to enable terminating the supply of coal and running exclusively on the coal dust or coke dust introduced with the ore. In this situation, solely combustion air is injected at the furnace outlet. Thermal efficiency is improved in shaft furnaces such as blast furnaces compared to rotary furnaces due to the air absorbing some of the Luppen heat. However, the oxygen in the air partially re-oxidizes the product, meaning that the Luppen is still altered by contact with air at the end or after leaving the furnace, despite complete reduction of iron in the furnace.
The hot assembly is discharged from the furnace and then rapidly cooled and crushed. The iron is separated from the slag via magnetic separation. Magnetically intermediate fines make up 5–15% of the charge. While partial melting of the charge leads to the increased density of the prereducts, it also requires significant energy consumption. | 1 | Applied and Interdisciplinary Chemistry |
For 1,2- and 1,4-disubstituted cyclohexanes, a cis configuration leads to one axial and one equatorial group. Such species undergo rapid, degenerate chair flipping. For 1,2- and 1,4-disubstituted cyclohexane, a trans configuration, the diaxial conformation is effectively prevented by its high steric strain. For 1,3-disubstituted cyclohexanes, the cis form is diequatorial and the flipped conformation suffers additional steric interaction between the two axial groups. trans-1,3-Disubstituted cyclohexanes are like cis-1,2- and cis-1,4- and can flip between the two equivalent axial/equatorial forms.
Cis-1,4-Di-tert-butylcyclohexane has an axial tert-butyl group in the chair conformation and conversion to the twist-boat conformation places both groups in more favorable equatorial positions. As a result, the twist-boat conformation is more stable by at as measured by NMR spectroscopy.
Also, for a disubstituted cyclohexane, as well as more highly substituted molecules, the aforementioned A values are additive for each substituent. For example, if calculating the A value of a dimethylcyclohexane, any methyl group in the axial position contributes 1.70 kcal/mol- this number is specific to methyl groups and is different for each possible substituent. Therefore, the overall A value for the molecule is 1.70 kcal/mol per methyl group in the axial position. | 0 | Theoretical and Fundamental Chemistry |
In fluid dynamics, Janzen–Rayleigh expansion represents a regular perturbation expansion using the relevant mach number as the small parameter of expansion for the velocity field that possess slight compressibility effects. The expansion was first studied by O. Janzen in 1913 and Lord Rayleigh in 1916. | 1 | Applied and Interdisciplinary Chemistry |
In late 1920s von Neergaard identified the function of the pulmonary surfactant in increasing the compliance of the lungs by reducing surface tension. However the significance of his discovery was not understood by the scientific and medical community at that time. He also realized the importance of having low surface tension in lungs of newborn infants. Later, in the middle of the 1950s, Pattle and Clements rediscovered the importance of surfactant and low surface tension in the lungs. At the end of that decade it was discovered that the lack of surfactant caused infant respiratory distress syndrome (IRDS). | 0 | Theoretical and Fundamental Chemistry |
SIMS is used to determine volatile and trace element concentrations by aiming an ion beam (O or Cs) at the melt inclusion to produce secondary ions that can be measured by a mass spectrometer. | 0 | Theoretical and Fundamental Chemistry |
A simple example illustrates the principle. Ozone (O) dissociates following ultraviolet excitation to yield an oxygen atom and an oxygen molecule. Although there are (at least) two possible channels, the principle products are O(D) and O(Δ); that is, both the atom and the molecule are in their first excited electronic state (see atomic term symbol and molecular term symbol for further explanation). At a wavelength of 266 nm, the photon has enough energy to dissociate ozone to these two products, to excite the O(Δ) vibrationally to a maximum level of v = 3, and to provide some energy to the recoil velocity between the two fragments. Of course, the more energy that is used to excite the O vibrations, the less will be available for the recoil. The O(1D) atom's REMPI, combined with the product imaging technique, yields an image that can be used to calculate the O(1D) three-dimensional velocity distribution. A slice through this cylindrically symmetric distribution is shown in the figure, where an O(D) atom that has zero velocity in the center-of-mass frame would arrive at the center of the figure.D) three-dimensional velocity distribution -->
Note that there are four rings, corresponding to four main groups of O(D) speeds. These [https://www.tilakastro.com/which-planet-is-responsible-for-fame-in-astrology/ correspond] to O2(1) production at vibrational levels v = 0, 1, 2, and 3. The ring corresponding to v = 0 is the outer one, since production of the O(Δ) in this level leaves the most energy for recoil between the O(D) and O(Δ). Thus, the product imaging technique immediately shows the vibrational distribution of the O(Δ).
Note that the angular distribution of the O(D) is not uniform – more of the atoms fly toward the north or south pole than to the equator. In this case, the north-south axis is parallel to the polarization direction of the light that dissociated the ozone. Ozone molecules that absorb the polarized light are those in a particular alignment distribution, with a line connecting the end oxygen atoms in O roughly parallel to the polarization. Because the ozone dissociates more rapidly than it rotates, the O and O products recoil predominantly along this polarization axis. But there is more detail as well. A close examination shows that the peak in the angular distribution is not actually exactly at the north or south pole, but rather at an angle of about 45 degrees. This has to do with the polarization of the laser that ionizes the O(D), and can be analyzed to show that the angular momentum of this atom (which has 2 units) is aligned relative to the velocity of recoil. More detail can be found elsewhere.
There are other dissociation channels available to ozone following excitation at this wavelength. One produces O(P) and O(Σ), indicating that both the atom and molecule are in their ground electronic state. The image above has no information on this channel, since only the O(D) is probed. However, by tuning the ionization laser to the REMPI wavelength of O(P) one finds a completely different image that provides information about the internal energy distribution of O(Σ). | 0 | Theoretical and Fundamental Chemistry |
Fish generally use bioluminescence for camouflage to hide from predators. Endogenous photocytes are more commonly used for bioluminescence than other means like bacteria. Some fish may use the bioluminescence produced by their photocytes as a means of communication. | 1 | Applied and Interdisciplinary Chemistry |
A charge density wave (CDW) is an ordered quantum fluid of electrons in a linear chain compound or layered crystal. The electrons within a CDW form a standing wave pattern and sometimes collectively carry an electric current. The electrons in such a CDW, like those in a superconductor, can flow through a linear chain compound en masse, in a highly correlated fashion. Unlike a superconductor, however, the electric CDW current often flows in a jerky fashion, much like water dripping from a faucet due to its electrostatic properties. In a CDW, the combined effects of pinning (due to impurities) and electrostatic interactions (due to the net electric charges of any CDW kinks) likely play critical roles in the CDW current's jerky behavior, as discussed in sections 4 & 5 below.
Most CDW's in metallic crystals form due to the wave-like nature of electrons – a manifestation of quantum mechanical wave–particle duality – causing the electronic charge density to become spatially modulated, i.e., to form periodic "bumps" in charge. This standing wave affects each electronic wave function, and is created by combining electron states, or wavefunctions, of opposite momenta. The effect is somewhat analogous to the standing wave in a guitar string, which can be viewed as the combination of two interfering, traveling waves moving in opposite directions (see interference (wave propagation)).
The CDW in electronic charge is accompanied by a periodic distortion – essentially a superlattice – of the atomic lattice. The metallic crystals look like thin shiny ribbons (e.g., quasi-1-D NbSe crystals) or shiny flat sheets (e.g., quasi-2-D, 1T-TaS crystals). The CDWs existence was first predicted in the 1930s by Rudolf Peierls. He argued that a 1-D metal would be unstable to the formation of energy gaps at the Fermi wavevectors ±k, which reduce the energies of the filled electronic states at ±k as compared to their original Fermi energy E. The temperature below which such gaps form is known as the Peierls transition temperature, T'.
The electron spins are spatially modulated to form a standing spin wave in a spin density wave (SDW). A SDW can be viewed as two CDWs for the spin-up and spin-down subbands, whose charge modulations are 180° out-of-phase. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, diazirines are a class of organic molecules consisting of a carbon bound to two nitrogen atoms, which are double-bonded to each other, forming a cyclopropene-like ring, 3H-diazirine (). They are isomeric with diazocarbon groups (), and like them can serve as precursors for carbenes by loss of a molecule of dinitrogen. For example, irradiation of diazirines with ultraviolet light leads to carbene insertion into various , , and bonds. Hence, diazirines have grown in popularity as small, photo-reactive, crosslinking reagents. They are often used in photoaffinity labeling studies to observe a variety of interactions, including ligand-receptor, ligand-enzyme, protein-protein, and protein-nucleic acid interactions. | 0 | Theoretical and Fundamental Chemistry |
In 2012, scientists at the University of New South Wales were able to use phosphine to precisely, deterministically eject a single silicon atom onto a surface of epitaxial silicon. This resulting adatom created what is described as a single-atom transistor. Thus, inasmuch as chemical empirical formulas pinpoint the locations of branching ions that are attached to a particular molecule, the dopant of silicon based transistors and other such electronic components will have the location identified of each dopant atom or molecule, along with the associated characteristic of the device based on the named locations. Thus, the mapping of the dopant substances will give exact characteristics of any given semiconductor device, once all is known.
With the technology available nowadays it is possible to create a linear chain of adatoms on top of an epitaxial film. With this, one can analyse theoretical situations.
Furthermore, Usami et al. were able to create quantum wells by adding Si atoms to a SiGe bulk crystal. Within these wells they observed photoluminescence of excitons that were confined in these wells. | 0 | Theoretical and Fundamental Chemistry |
To form an A-B-A-B-... hexagonal close packing of spheres, the coordinate points of the lattice will be the spheres centers. Suppose, the goal is to fill a box with spheres according to HCP. The box would be placed on the x-y-z' coordinate space.
First form a row of spheres. The centers will all lie on a straight line. Their x-coordinate will vary by 2r since the distance between each center of the spheres are touching is 2r. The y-coordinate and z-coordinate will be the same. For simplicity, say that the balls are the first row and that their y- and z-coordinates are simply r, so that their surfaces rest on the zero-planes. Coordinates of the centers of the first row will look like (2r, r, r), (4r, r, r), (6r ,r, r), (8r ,r, r), ... .
Now, form the next row of spheres. Again, the centers will all lie on a straight line with x-coordinate differences of 2r, but there will be a shift of distance r in the x-direction so that the center of every sphere in this row aligns with the x-coordinate of where two spheres touch in the first row. This allows the spheres of the new row to slide in closer to the first row until all spheres in the new row are touching two spheres of the first row. Since the new spheres touch two spheres, their centers form an equilateral triangle with those two neighbors centers. The side lengths are all 2r, so the height or y-coordinate difference between the rows is r'. Thus, this row will have coordinates like this:
The first sphere of this row only touches one sphere in the original row, but its location follows suit with the rest of the row.
The next row follows this pattern of shifting the x-coordinate by r and the y-coordinate by . Add rows until reaching the x and y maximum borders of the box.
In an A-B-A-B-... stacking pattern, the odd numbered planes of spheres will have exactly the same coordinates save for a pitch difference in the z-coordinates and the even numbered planes of spheres will share the same x- and y-coordinates. Both types of planes are formed using the pattern mentioned above, but the starting place for the first row's first sphere will be different.
Using the plane described precisely above as plane #1, the A plane, place a sphere on top of this plane so that it lies touching three spheres in the A-plane. The three spheres are all already touching each other, forming an equilateral triangle, and since they all touch the new sphere, the four centers form a regular tetrahedron. All of the sides are equal to 2r because all of the sides are formed by two spheres touching. The height of which or the z-coordinate difference between the two "planes" is . This, combined with the offsets in the x and y-coordinates gives the centers of the first row in the B plane:
The second row's coordinates follow the pattern first described above and are:
The difference to the next plane, the A plane, is again in the z-direction and a shift in the x and y to match those x- and y-coordinates of the first A plane.
In general, the coordinates of sphere centers can be written as:
where i, j and k are indices starting at 0 for the x-, y- and z-coordinates. | 0 | Theoretical and Fundamental Chemistry |
In 1950–1951 in the Soviet Union, Igor Tamm and Andrei Sakharov first discussed a tokamak-like approach. Experimental research on those designs began in 1956 at the Moscow Kurchatov Institute by a group of Soviet scientists led by Lev Artsimovich. The tokamak essentially combined a low-power pinch device with a low-power stellarator. The notion was to combine the fields in such a way that the particles orbited within the reactor a particular number of times, today known as the "safety factor". The combination of these fields dramatically improved confinement times and densities, resulting in huge improvements over existing devices. | 0 | Theoretical and Fundamental Chemistry |
Activation of PKC-θ by diacylglycerol may cause insulin resistance in muscle by decreasing IRS1-associated PI3K activity. Similarly, activation of PKCε by diacyglycerol may cause insulin resistance in the liver. | 1 | Applied and Interdisciplinary Chemistry |
Xenin is a peptide hormone secreted from the chromogranin A-positive enteroendocrine cells called the K-cells in the mucous membrane of the duodenum and stomach of the upper gut. The peptide has been found in humans, dogs, pigs, rats, and rabbits.
In humans, xenin circulates in the blood plasma. There is a relationship between peaks of xenin concentration in the plasma and the third phase of the Migrating Motor Complex. For example, infusion of synthetic xenin in fasting volunteers will cause phase III activity. After a meal (the postprandial state), infusion of xenin increases both frequency and the percentage of aborally propagated contractions. In higher concentrations xenin stimulates exocrine pancreatic secretion and inhibits the gastrin-stimulated secretion of acid in dogs. Xenin is also produced in neuroendocrine tumors of the duodenal mucosa.
In vitro, xenin interacts with the neurotensin receptor 1. | 1 | Applied and Interdisciplinary Chemistry |
Since returning to Glasgow in 2007, Paul Braterman has concentrated on educational activities, writing for a broad audience, and campaigning in defence of science education. He is on the board of the British Centre for Science Education, and scientific adviser to the Scottish Secular Society His work with these organisations led to the blocking of teaching of creationism as science in both English and Scottish schools.
His first popular science book, From Stars to Stalagmites, was a Scientific American book club choice.
He has been a regular contributor to 3 Quarks Daily, and his writing has appeared in The Conversation, Scientific American, Newsweek, International Business Times, and Massimo Pigliucci’s Scientia Salon.
Braterman has also contributed to The Panda's Thumb (blog) in an article entitled Creationism and climate - Birth of a new Pseudoscience.[https://pandasthumb.org/archives/2022/10/creationclimate.html] | 0 | Theoretical and Fundamental Chemistry |
The conversion of aldehydes to nitriles via aldoximes is a popular laboratory route. Aldehydes react readily with hydroxylamine salts, sometimes at temperatures as low as ambient, to give aldoximes. These can be dehydrated to nitriles by simple heating, although a wide range of reagents may assist with this, including triethylamine/sulfur dioxide, zeolites, or sulfuryl chloride. The related hydroxylamine-O-sulfonic acid reacts similarly.
In specialised cases the Van Leusen reaction can be used. Biocatalysts such as aliphatic aldoxime dehydratase are also effective. | 0 | Theoretical and Fundamental Chemistry |
Large and fast-moving turbidity currents can carve gulleys and ravines into the ocean floor of continental margins and cause damage to artificial structures such as telecommunication cables on the seafloor. Understanding where turbidity currents flow on the ocean floor can help to decrease the amount of damage to telecommunication cables by avoiding these areas or reinforcing the cables in vulnerable areas.
When turbidity currents interact with regular ocean currents, such as contour currents, they can change their direction. This ultimately shifts submarine canyons and sediment deposition locations. One example of this is located in the western part of the Gulf of Cadiz, where the ocean current leaving the Mediterranean Sea (also known as the Mediterranean outflow water) pushes turbidity currents westward. This has changed the shape of submarine valleys and canyons in the region to also curve in that direction. | 1 | Applied and Interdisciplinary Chemistry |
According to the safety data sheet of PPA, it should not be allowed in contact with the skin or eyes as it may lead to skin, eye, and respiratory irritations or allergic reactions. In addition, as some unfunctionalized PPA are unstable at temperatures even lower than room temperature, it is important to note that PPA should be stored at temperatures below -10 °C under inert atmosphere and away from sunlight, moisture, and heat, but with proper ventilation.
Since the depolymerization of PPA is greatly studied in its applications, it is important to also note the possible safety concerns of its monomer. In addition to the abovementioned hazards of PPA, phthalaldehyde is very toxic if swallowed and for aquatic life. | 0 | Theoretical and Fundamental Chemistry |
Francis Hauksbee performed some of the earliest observations and experiments in 1709 and these were repeated in 1718 by James Jurin who observed that the height of fluid in a capillary column was a function only of the cross-sectional area at the surface, not of any other dimensions of the column.
Thomas Young laid the foundations of the equation in his 1804 paper An Essay on the Cohesion of Fluids where he set out in descriptive terms the principles governing contact between fluids (along with many other aspects of fluid behaviour). Pierre Simon Laplace followed this up in Mécanique Céleste with the formal mathematical description given above, which reproduced in symbolic terms the relationship described earlier by Young.
Laplace accepted the idea propounded by Hauksbee in his book Physico-mechanical Experiments (1709), that the phenomenon was due to a force of attraction that was insensible at sensible distances. The part which deals with the action of a solid on a liquid and the mutual action of two liquids was not worked out thoroughly, but ultimately was completed by Carl Friedrich Gauss. Franz Ernst Neumann (1798-1895) later filled in a few details. | 1 | Applied and Interdisciplinary Chemistry |
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