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Many of the usual methods are useful for determining physical and structural properties of Zintl phases. Some Zintl phases can be decomposed into a Zintl ion—the polyanion that composes the anionic substructure of the phase—and counter ion, which can be studied as described below. The heat of formation of these phases can be evaluated. Often their magnitude is comparable to those of salt formation, providing evidence for the ionic character of these phases. Density measurements indicate a contraction of the product compared to reactants, similarly indicating ionic bonding within the phase. X-ray spectroscopy gives additional information about the oxidation state of the elements, and correspondingly the nature of their bonding. Conductivity and magnetization measurements can also be taken. Finally, the structure of a Zintl phase or ion is most reliably confirmed via X-ray crystallography. | 0 | Theoretical and Fundamental Chemistry |
The Wigner–Seitz cell around a lattice point is defined as the locus of points in space that are closer to that lattice point than to any of the other lattice points.
It can be shown mathematically that a Wigner–Seitz cell is a primitive cell. This implies that the cell spans the entire direct space without leaving any gaps or holes, a property known as tessellation. | 0 | Theoretical and Fundamental Chemistry |
Many metal alkoxide compounds also feature oxo-ligands. Oxo-ligands typically arise via the hydrolysis, often accidentally, and via ether elimination:
Additionally, low valent metal alkoxides are susceptible to oxidation by air.
Characteristically, transition metal alkoxides are polynuclear, that is they contain more than one metal. Alkoxides are sterically undemanding and highly basic ligands that tend to bridge metals.
Upon the isomorphic substitution of metal atoms close in properties crystalline complexes of variable composition are formed. The metal ratio in such compounds can vary over a broad range. For instance, the substitution of molybdenum and tungsten for rhenium in the complexes allowed one to obtain complexes in the range and in the range . | 0 | Theoretical and Fundamental Chemistry |
The electron affinity (E) of an atom or molecule is defined as the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion.
::X(g) + e → X(g) + energy
This differs by sign from the energy change of electron capture ionization. The electron affinity is positive when energy is released on electron capture.
In solid state physics, the electron affinity for a surface is defined somewhat differently (see below). | 0 | Theoretical and Fundamental Chemistry |
All transcriptomic methods require RNA to first be isolated from the experimental organism before transcripts can be recorded. Although biological systems are incredibly diverse, RNA extraction techniques are broadly similar and involve mechanical disruption of cells or tissues, disruption of RNase with chaotropic salts, disruption of macromolecules and nucleotide complexes, separation of RNA from undesired biomolecules including DNA, and concentration of the RNA via precipitation from solution or elution from a solid matrix. Isolated RNA may additionally be treated with DNase to digest any traces of DNA. It is necessary to enrich messenger RNA as total RNA extracts are typically 98% ribosomal RNA. Enrichment for transcripts can be performed by poly-A affinity methods or by depletion of ribosomal RNA using sequence-specific probes. Degraded RNA may affect downstream results; for example, mRNA enrichment from degraded samples will result in the depletion of 5’ mRNA ends and an uneven signal across the length of a transcript. Snap-freezing of tissue prior to RNA isolation is typical, and care is taken to reduce exposure to RNase enzymes once isolation is complete. | 1 | Applied and Interdisciplinary Chemistry |
Lavoisier, together with Louis-Bernard Guyton de Morveau, Claude-Louis Berthollet, and Antoine François de Fourcroy, submitted a new program for the reforms of chemical nomenclature to the Academy in 1787, for there was virtually no rational system of chemical nomenclature at this time. This work, titled Méthode de nomenclature chimique (Method of Chemical Nomenclature, 1787), introduced a new system which was tied inextricably to Lavoisier's new oxygen theory of chemistry.
The classical elements of earth, air, fire, and water were discarded, and instead some 33 substances which could not be decomposed into simpler substances by any known chemical means were provisionally listed as elements. The elements included light; caloric (matter of heat); the principles of oxygen, hydrogen, and azote (nitrogen); carbon; sulfur; phosphorus; the yet unknown "radicals" of muriatic acid (hydrochloric acid), boric acid, and "fluoric" acid; 17 metals; 5 earths (mainly oxides of yet unknown metals such as magnesia, baria, and strontia); three alkalies (potash, soda, and ammonia); and the "radicals" of 19 organic acids.
The acids, regarded in the new system as compounds of various elements with oxygen, were given names which indicated the element involved together with the degree of oxygenation of that element, for example sulfuric and sulfurous acids, phosphoric and phosphorous acids, nitric and nitrous acids, the "ic" termination indicating acids with a higher proportion of oxygen than those with the "ous" ending.
Similarly, salts of the "ic" acids were given the terminal letters "ate," as in copper sulfate, whereas the salts of the "ous" acids terminated with the suffix "ite," as in copper sulfite.
The total effect of the new nomenclature can be gauged by comparing the new name "copper sulfate" with the old term "vitriol of Venus." Lavoisier's new nomenclature spread throughout Europe and to the United States and became common use in the field of chemistry. This marked the beginning of the anti-phlogistic approach to the field. | 1 | Applied and Interdisciplinary Chemistry |
Floral scent, or flower scent, is composed of all the volatile organic compounds (VOCs), or aroma compounds, emitted by floral tissue (e.g. flower petals). Other names for floral scent include, aroma, fragrance, floral odour or perfume. Flower scent of most flowering plant species encompasses a diversity of VOCs, sometimes up to several hundred different compounds. The primary functions of floral scent are to deter herbivores and especially folivorous insects (see Plant defense against herbivory), and to attract pollinators. Floral scent is one of the most important communication channels mediating plant-pollinator interactions, along with visual cues (flower color, shape, etc.). | 1 | Applied and Interdisciplinary Chemistry |
For many years the photocathode was the only practical method for converting light to an electron current. As such it tends to function as a form of electric film and shared many characteristics of photography. It was therefore the key element in opto-electronic devices, such as TV camera tubes like the orthicon and vidicon, and in image tubes such as intensifiers, converters, and dissectors. Simple phototubes were used for motion detectors and counters.
Phototubes have been used for years in movie projectors to read the sound tracks on the edge of movie film.
The more recent development of solid state optical devices such as photodiodes has reduced the use of photocathodes to cases where they still remain superior to semiconductor devices. | 0 | Theoretical and Fundamental Chemistry |
All skimmers have key features in common: water flows through a chamber and is brought into contact with a column of fine bubbles. The bubbles collect proteins and other substances and carry them to the top of the device where the foam, but not the water, collects in a cup. Here the foam condenses to a liquid, which can be easily removed from the system. The material that collects in the cup can range from pale greenish-yellow, watery liquid to a thick black tar.
Consider this summary of optimal protein skimmer design by Randy Holmes-Farley:
Also under considerable recent attention has been the general shape of a skimmer as well. In particular, much attention has been given to the introduction of cone shaped skimmer units. Originally designed by Klaus Jensen in 2004, the concept was founded on the principle that a conical body allows the foam to accumulate more steadily through a gently sloping transition. It was claimed that this reduces the overall turbulence, resulting in more efficient skimming. However, this design reduces the overall volume inside the skimmer, reducing dwell time. Cylindrical-shaped protein skimmers are the most popular design and allow for the largest volume of air and water.
Overall, protein skimmers can be classed in two ways depending on whether they operate by co-current flow or counter-current flow. In a co-current flow system, air is introduced at the bottom of the chamber and is in contact with the water as it rises upwards towards the collection chamber. In a counter-current system, air is forced into the system under pressure and moves against the flow of the water for a while before it rises up towards the collection cup. Because the air bubbles may be in contact with the water for a longer period in a counter-current flow system, protein skimmers of this type are considered by some to be more effective at removing organic wastes. | 0 | Theoretical and Fundamental Chemistry |
While tribocorrosion phenomena may affect many materials, they are most critical for metals, especially the normally corrosion resistant so-called passive metals. The vast majority of corrosion resistant metals and alloys used in engineering (stainless steels, titanium, aluminium etc.) fall into this category. These metals are thermodynamically unstable in the presence of oxygen or water, and they derive their corrosion resistance from the presence at the surface of a thin oxide film, called the passive film, which acts as a protective barrier between the metal and its environment. Passive films are usually just a few atomic layers thick. Nevertheless, they can provide excellent corrosion protection because if damaged accidentally they spontaneously self-heal by metal oxidation. However, when a metal surface is subjected to severe rubbing or to a stream of impacting particles the passive film damage becomes continuous and extensive. The self-healing process may no longer be effective and in addition it requires a high rate of metal oxidation. In other words, the underlying metal will strongly corrode before the protective passive film is reformed, if at all. In such a case, the total material loss due to tribocorrosion will be much higher than the sum of wear and corrosion one would measure in experiments with the same metal where only wear or only corrosion takes place. The example illustrates the fact that the rate of tribocorrosion is not simply the addition of the rate of wear and the rate of corrosion but it is strongly affected by synergistic and antagonistic effects between mechanical and chemical mechanisms. To study such effects in the laboratory, one most often uses mechanical wear testing rigs which are equipped with an electrochemical cell. This permits one to control independently the mechanical and chemical parameters. For example, by imposing a given potential to the rubbing metal one can simulate the oxidation potential of the environment and in addition, under certain conditions, the current flow is a measure of the instantaneous corrosion rate. Volume loss due to electrochemical dissolution can be measured by Faraday's laws of electrolysis and subtracted from total volume loss in tribocorrosion so the sum of mechanical wear loss and the synergies can be calculated. For a deeper understanding tribocorrosion experiments are supplemented by detailed microscopic and analytical studies of the contacting surfaces.
At high temperatures, the more rapid generation of oxide due to a combination of temperature and tribological action during sliding wear can generate potentially wear resistant oxide layers known as glazes. Under such circumstances, tribocorrosion can be used potentially in a beneficial way. | 1 | Applied and Interdisciplinary Chemistry |
While phases of matter are traditionally defined for systems in thermal equilibrium, work on quantum many-body localized (MBL) systems has provided a framework for defining phases out of equilibrium. MBL phases never reach thermal equilibrium, and can allow for new forms of order disallowed in equilibrium via a phenomenon known as localization protected quantum order. The transitions between different MBL phases and between MBL and thermalizing phases are novel dynamical phase transitions whose properties are active areas of research. | 0 | Theoretical and Fundamental Chemistry |
Scaffold proteins act in at least four ways: tethering signaling components, localizing these components to specific areas of the cell, regulating signal transduction by coordinating positive and negative feedback signals, and insulating correct signaling proteins from competing proteins. | 1 | Applied and Interdisciplinary Chemistry |
Isocyanates are electrophiles, and as such they are reactive toward a variety of nucleophiles including alcohols, amines, and even water having a higher reactivity compared to structurally analogous isothiocyanates.
Upon treatment with an alcohol, an isocyanate forms a urethane linkage:
where R and R' are alkyl or aryl groups.
If a diisocyanate is treated with a compound containing two or more hydroxyl groups, such as a diol or a polyol, polymer chains are formed, which are known as polyurethanes.
Isocyanates react with water to form carbon dioxide:
This reaction is exploited in tandem with the production of polyurethane to give polyurethane foams. The carbon dioxide functions as a blowing agent.
Isocyanates also react with amines to give ureas:
The addition of an isocyanate to a urea gives a biuret:
Reaction between a di-isocyanate and a compound containing two or more amine groups produces long polymer chains known as polyureas.
Carbodiimides are produced by the decarboxylation of alkyl and aryl isocyanate using phosphine oxides as a catalyst: | 0 | Theoretical and Fundamental Chemistry |
Oil of guaiac is a fragrance ingredient used in soap and perfumery. Despite its name it does not come from the Guaiacum tree, but from the palo santo tree (Bulnesia sarmientoi).
Oil of guaiac is produced through steam distillation of a mixture of wood and sawdust from palo santo. It is sometimes incorrectly called guaiac wood concrete. It is a yellow to greenish yellow semi-solid mass which melts around 40–50 °C. Once melted, it can be cooled back to room temperature yet remain liquid for a long time. Oil of guaiac has a soft roselike odour, similar to the odour of hybrid tea roses or violets. Because of this similarity, it has sometimes been used as an adulterant for rose oil.
Oil of guaiac is primarily composed of 42–72% guaiol, bulnesol, δ-bulnesene, β-bulnesene, α-guaiene, guaioxide and β-patchoulene. It is considered non-irritating, non-sensitizing, and non-phototoxic to human skin.
Oil of guaiac was also a pre-Renaissance remedy to syphilis. | 1 | Applied and Interdisciplinary Chemistry |
Ceiling temperature () is a measure of the tendency of a polymer to revert to its constituent monomers. When a polymer is at its ceiling temperature, the rate of polymerization and depolymerization of the polymer are equal. Generally, the ceiling temperature of a given polymer is correlated to the steric hindrance of the polymer’s monomers. Polymers with high ceiling temperatures are often commercially useful. Polymers with low ceiling temperatures are more readily depolymerizable. | 0 | Theoretical and Fundamental Chemistry |
Lute was commonly used in distillation, which required airtight vessels and connectors to ensure that no vapours were lost; thus it was employed by chemists and alchemists, the latter being known to refer to it as "lutum sapientiae" or the "lute of Wisdom".
The earthen and glass vessels commonly employed in these processes were very vulnerable to cracking, both on heating and on cooling; one way of protecting them was by coating the vessels with lute and allowing it to set. One mixture for this purpose included "fat earth" (terra pinguis), Windsor loam, sand, iron filings or powdered glass, and cow's hair.
Another use for lute was to act as a safety valve, preventing the buildup of vapour pressure from shattering a vessel and possibly causing an explosion. For this purpose, a hole was bored in the flask and covered with luting material of a particular composition, which was kept soft so that excessive buildup of vapour would cause it to come away from the vessel, thus releasing the pressure safely. This process could also be performed manually by the operator removing and reaffixing the lute as required. Lute was also used to effect repairs to cracked glass vessels. In The Alchemist’s Experiment Takes Fire, 1687, one alembic is exploding; the luting used to seal a receiving bottle to another alembic can be seen behind the alchemist's upraised arm.
Lute was frequently applied to the joints between vessels (such as retorts and receivers), making them airtight and preventing vapour from escaping; this was especially important for more penetrating "spiritous" vapours and required a mixture that would set hard - such as a mix of quicklime and either egg white or size etc. However a stronger lute had to be used to confine acid vapours, and for this purpose fat earth and linseed oil were mixed to form "fat lute", which could be rolled into cylinders of convenient size, ready for use. Where the vapour was more "aqueous", and less penetrating, strips of paper affixed with sizing would suffice or "bladder long steeped in water".
Another related use for lute was for lining furnaces, and was described as far back as the 16th century by Georg Agricola in his "De re metallica". | 1 | Applied and Interdisciplinary Chemistry |
A room within a room (RWAR) is one method of isolating sound and preventing it from transmitting to the outside world where it may be undesirable.
Most sound transfer from a room to the outside occurs through mechanical means. The vibration passes directly through the brick, woodwork and other solid structural elements. When it meets with an element such as a wall, ceiling, floor or window, which acts as a sounding board, the vibration is amplified and heard in the second space. A mechanical transmission is much faster, more efficient and more readily amplified than an airborne transmission of the same initial strength.
The use of acoustic foam and other absorbent means is less effective against this transmitted vibration. The transmission can be stopped by breaking the connection between the room that contains the noise source and the outside world. This is called acoustic decoupling. | 1 | Applied and Interdisciplinary Chemistry |
These compounds form during the catabolism of carbohydrates and lipids in condensation reactions, and in some other metabolic reactions of the amino acids. Oxygen is produced by plants and some bacteria in photosynthesis, while CO is a waste product of all animals and plants. Nitrogen gases are produced by denitrifying bacteria and as a waste product, and bacteria for decaying yield ammonia, as do most invertebrates and vertebrates. Water is the only liquid waste from animals and photosynthesizing plants. | 1 | Applied and Interdisciplinary Chemistry |
Two main processes can explain the transfer of energy from the short wind waves to the long infragravity waves, and both are important in shallow water and for steep wind waves. The most common process is the subharmonic interaction of trains of wind waves which was first observed by Munk and Tucker and explained by Longuet-Higgins and Stewart. Because wind waves are not monochromatic they form groups. The Stokes drift induced by these groupy waves transports more water where the waves are highest. The waves also push the water around in a way that can be interpreted as a force: the divergence of the radiation stresses. Combining mass and momentum conservation, Longuet-Higgins and Stewart give, with three different methods, the now well-known result. Namely, the mean sea level oscillates with a wavelength that is equal to the length of the group, with a low level where the wind waves are highest and a high level where these waves are lowest. This oscillation of the sea surface is proportional to the square of the short wave amplitude and becomes very large when the group speed approaches the speed of shallow water waves. The details of this process are modified when the bottom is sloping, which is generally the case near the shore, but the theory captures the important effect, observed in most conditions, that the high water of this surf beat arrives with the waves of lowest amplitude.
Another process was proposed later by Graham Symonds and his collaborators. To explain some cases in which this phase of long and short waves were not opposed, they proposed that the position of the breaker line in the surf, moving towards deep water when waves are higher, could act like a wave maker. It appears that this is probably a good explanation for infragravity wave generation on a reef.
In the case of coral reefs, the infragravity periods are established by resonances with the reef itself. | 1 | Applied and Interdisciplinary Chemistry |
All of the following papers were published by
Scheele within a span of fifteen years.
Scheeles papers appeared first in the Transactions of the Swedish Academy of Sciences, and in various periodicals such as Lorenz Florenz Friedrich von Crells Chemische Annalen. Scheeles work was collected and published in four languages beginning with Mémoires de Chymie by Mme. Claudine Picardet in 1785 and Chemical Essays' by Thomas Beddoes in 1786, followed by Latin and German.
Another English translation was published by Dr Leonard Dobbin, in 1931. | 1 | Applied and Interdisciplinary Chemistry |
The insulin transduction pathway is a biochemical pathway by which insulin increases the uptake of glucose into fat and muscle cells and reduces the synthesis of glucose in the liver and hence is involved in maintaining glucose homeostasis. This pathway is also influenced by fed versus fasting states, stress levels, and a variety of other hormones.
When carbohydrates are consumed, digested, and absorbed the pancreas senses the subsequent rise in blood glucose concentration and releases insulin to promote uptake of glucose from the bloodstream. When insulin binds to the insulin receptor, it leads to a cascade of cellular processes that promote the usage or, in some cases, the storage of glucose in the cell. The effects of insulin vary depending on the tissue involved, e.g., insulin is most important in the uptake of glucose by muscle and adipose tissue.
This insulin signal transduction pathway is composed of trigger mechanisms (e.g., autophosphorylation mechanisms) that serve as signals throughout the cell. There is also a counter mechanism in the body to stop the secretion of insulin beyond a certain limit. Namely, those counter-regulatory mechanisms are glucagon and epinephrine. The process of the regulation of blood glucose (also known as glucose homeostasis) also exhibits oscillatory behavior.
On a pathological basis, this topic is crucial to understanding certain disorders in the body such as diabetes, hyperglycemia and hypoglycemia. | 1 | Applied and Interdisciplinary Chemistry |
Atmospheric concentration continued to fall after about 60 million years ago. About 34 million years ago, the time of the Eocene–Oligocene extinction event and when the Antarctic ice sheet started to take its current form, was about 760 ppm, and there is geochemical evidence that concentrations were less than 300 ppm by about 20 million years ago. Decreasing concentration, with a tipping point of 600 ppm, was the primary agent forcing Antarctic glaciation. Low concentrations may have been the stimulus that favored the evolution of C4 carbon fixation| plants, which increased greatly in abundance between 7 and 5 million years ago. | 1 | Applied and Interdisciplinary Chemistry |
In 1993, Schreiber and his co-workers reported the first total synthesis of the unnatural antipode (-)-discodermolide and determined the absolute stereochemistry of the natural product. The Schreiber team recognized three fragments of roughly equal complexity that are separated by olefinic units in discodermolide. The two starting materials, homoallylic alcohols, are both readily derived from 3-hydroxy-2-methylpropionate.
The trisubstituted (Z)-alkene of first fragment was generated by using the Still-Gennari reagent. Gilbert's reagent was then used to homologate it to an acetylene. Goekjian and Kishi method was then used to get the desired fragment, iodoacetylene. The same homoallylic alcohol was converted to diol in four steps. After oxidation to keto-aldehyde, it was homololated to dienes by a palladium-catalyzed coupling with vinylzinc bromide to generated the second fragment. The six-membered ring subunit was transformed from an acetal, which was obtained by an intramolecular 1,4-addition of a presumed hemiacetal intermediate.
The Schreiber team found that the NiCl and CrCl promoted addition of alkynyl iodide to aldehyde effectively. The reaction provides a 2:1 mixture of desired product and its isomer. However, the undesired isomer can be recycled to the desired epimer in three steps, including Swern oxidation and Corey's asymmetric reduction. Pd catalyzed partial hydrogenation of the alkyne to establish the Z-configuration at C(8)–C(9). The pivaloyloxy group was then converted to a bromide for the final coupling. A stereoselective enolate alkylation between the allylic bromide with the lithium enolate derived from the second fragment provided a 3:1 mixture of isomers and completed the backbone assembly of (-)-discodermolide. During the final conversion, the NaBH reduction of ketone provided a separable 2.5:1 mixture of isomers. The Schreiber synthesis of (-)-discodermolide has an overall yield of 3.2% with a longest linear sequence of 24 steps and 36 total steps. In 1996, the Schreiber group published the total synthesis of natural discodermolide with similar synthetic strategy (4.3% overall yield, 36 steps, 24 steps longest linear sequence. | 0 | Theoretical and Fundamental Chemistry |
If the incoming stream is perpendicular to the stagnation line, but approaches obliquely, the outer flow is not potential, but has a constant vorticity . The appropriate stream function for oblique stagnation point flow is given by
Viscous effects due to the presence of a solid wall was studied by Stuart (1959), Tamada (1979) and Dorrepaal (1986). In their approach, the streamfunction takes the form
where the function | 1 | Applied and Interdisciplinary Chemistry |
The Schoenflies (or Schönflies) notation, named after the German mathematician Arthur Moritz Schoenflies, is a notation primarily used to specify point groups in three dimensions. Because a point group alone is completely adequate to describe the symmetry of a molecule, the notation is often sufficient and commonly used for spectroscopy. However, in crystallography, there is additional translational symmetry, and point groups are not enough to describe the full symmetry of crystals, so the full space group is usually used instead. The naming of full space groups usually follows another common convention, the Hermann–Mauguin notation, also known as the international notation.
Although Schoenflies notation without superscripts is a pure point group notation, optionally, superscripts can be added to further specify individual space groups. However, for space groups, the connection to the underlying symmetry elements is much more clear in Hermann–Mauguin notation, so the latter notation is usually preferred for space groups. | 0 | Theoretical and Fundamental Chemistry |
Chemical materials developed to assist in the production of food, feed, and fiber include herbicides, insecticides, fungicides, and other pesticides. Pesticides are chemicals that play an important role in increasing crop yield and mitigating crop losses. These work to keep insects and other animals away from crops to allow them to grow undisturbed, effectively regulating pests and diseases.
Disadvantages of pesticides include contamination of the ground and water (see persistent organic pollutants). They may be toxic to non-target species, including birds, fish, pollinators, as well as the farmworkers themselves. | 1 | Applied and Interdisciplinary Chemistry |
A single nucleotide switch (polymorphism) in FRAS1 promoter region is associated with metastatic Prostate cancer. The promoter region is directly related to the NFkB pathway and has been shown to be associated with lethal prostate cancer.
Fras1 related extracellular matrix (FREM1) directly relates to congenital diaphragmatic hernia in developing fetuses. Decreased expression of FREM1 may be linked with disruptions in the growth of diaphragm cells. Both FRAS1 and FREM1 are among the proteins that are primarily interacting during embryonic development. It is shown that a decrease in these two proteins lead to an increase of congenital diaphragmatic hernia in both humans and mice. | 1 | Applied and Interdisciplinary Chemistry |
In eastern Washington and northern Idaho, meadow voles are found in relative abundance in sedge (Carex sp.) fens, but not in adjacent cedar (Thuja sp.)-hemlock (Tsuga sp.), Douglas-fir (Pseudotsuga menziesii), or ponderosa pine (Pinus ponderosa) forests. Meadow voles are also absent from fescue (Festuca sp.)-snowberry (Symphoricarpos sp.) associations. Moisture may be a major factor in habitat use; possibly the presence of free water is a deciding factor.
In southeastern Montana, western meadow voles were the second-most abundant small mammal (after deer mice, Peromyscus maniculatus) in riparian areas within big sagebrush (Artemisia tridentata)-buffalo grass (Bouteloua dactyloides) habitats. Western meadow voles are listed as riparian-dependent vertebrates in the Snake River drainage of Wyoming. In a compilation of 11 studies on small mammals, western meadow voles were reported in only three of 29 sites in subalpine forests of the central Rocky Mountains. Their range extensions were likely to be related to irrigation practices. They are now common in hayfields, pastures, and along ditches in the Rocky Mountain states. In Pipestone National Monument, Minnesota, western meadow voles were present in riparian shrublands, tallgrass prairie, and other habitats. | 1 | Applied and Interdisciplinary Chemistry |
Bioadhesives are of commercial interest because they tend to be biocompatible, i.e. useful for biomedical applications involving skin or other body tissue. Some work in wet environments and under water, while others can stick to low surface energy – non-polar surfaces like plastic. In recent years, the synthetic adhesives industry has been impacted by environmental concerns and health and safety issues relating to hazardous ingredients, volatile organic compound emissions, and difficulties in recycling or re mediating adhesives derived from petrochemical feedstocks. Rising oil prices may also stimulate commercial interest in biological alternatives to synthetic adhesives.
Shellac is an early example of a bioadhesive put to practical use. Additional examples now exist, with others in development:
* Commodity wood adhesive based on a bacterial exopolysaccharide
* USB PRF/Soy 2000, a commodity wood adhesive that is 50% soy hydrolysate and excels at finger-jointing green lumber
* Mussel adhesive proteins can assist in attaching cells to plastic surfaces in laboratory cell and tissue culture experiments (see External Links)
* The Notaden frog glue is under development for biomedical uses, e.g. as a surgical glue for orthopedic applications or as a hemostat
* Mucosal drug delivery applications. For example, films of mussel adhesive protein give comparable mucoadhesion to polycarbophil, a synthetic hydrogel used to achieve effective drug delivery at low drug doses. An increased residence time through adhesion to the mucosal surface, such as in the eye or the nose can lead to an improved absorption of the drug.
* Long-duration continuous imaging of diverse organs (via a wearable bioadhesive stretchable high-resolution ultrasound imaging patch, potentially enabling novel diagnostic and monitoring tools)
Several commercial methods of production are being researched:
* Direct chemical synthesis, e.g. incorporation of L-DOPA groups in synthetic polymers
* Fermentation of transgenic bacteria or yeasts that express bioadhesive protein genes
* Farming of natural organisms (small and large) that secrete bioadhesive materials | 1 | Applied and Interdisciplinary Chemistry |
Another use for FRET is in the study of metabolic or signaling pathways. For example, FRET and BRET have been used in various experiments to characterize G-protein coupled receptor activation and consequent signaling mechanisms. Other examples include the use of FRET to analyze such diverse processes as bacterial chemotaxis and caspase activity in apoptosis. | 1 | Applied and Interdisciplinary Chemistry |
Alpha-substitution reactions occur at the position next to the carbonyl group,
the α-position, and involve the substitution of an α hydrogen atom
by an electrophile, E, through either an enol or enolate ion intermediate. | 0 | Theoretical and Fundamental Chemistry |
In sporadic cancers, a DNA repair deficiency is occasionally found to be due to a mutation in a DNA repair gene. However, much more frequently, reduced or absent expression of a DNA repair gene in cancer is due to methylation of its promoter. For example, of 113 colorectal cancers examined, only four had a missense mutation in the DNA repair gene MGMT, while the majority had reduced MGMT expression due to methylation of the MGMT promoter region. Similarly, among 119 cases of mismatch repair-deficient colorectal cancers that lacked DNA repair gene PMS2 expression, 6 had a mutation in the PMS2 gene, while for 103 PMS2 was deficient because its pairing partner MLH1 was repressed due to promoter methylation (PMS2 protein is unstable in the absence of MLH1). In the remaining 10 cases, loss of PMS2 expression was likely due to epigenetic overexpression of the microRNA, miR-155, which down-regulates MLH1. | 1 | Applied and Interdisciplinary Chemistry |
The structure of tetrakis(dimethylamino)ethylene (TDAE) is highly distorted. The dihedral angle for the two NC ends is 28º although the C=C distance is normal 135 pm. The nearly isostructural tetraisopropylethylene also has a C=C distance of 135 pm, but its C core is planar. | 0 | Theoretical and Fundamental Chemistry |
The Sommelet reaction is an organic reaction in which a benzyl halide is converted to an aldehyde by action of hexamine and water. It is named after the French chemist Marcel Sommelet, who first reported the reaction in 1913.
One example, thiophene-2-carboxaldehyde is prepared by the reaction of hexamine with 2-chloromethylthiophene. The reaction is formally an oxidation of the carbon. | 0 | Theoretical and Fundamental Chemistry |
The mathematical formula can be derived from first principles. It reads:where the population density is a function of age and time , and is the death function. When , we have:
It relates that a population ages, and that fact is the only one that influences change in population density; the negative sign shows that time flows in just one direction, that there is no birth and the population is going to die out. | 1 | Applied and Interdisciplinary Chemistry |
The development of rapamycin as an anticancer agent began again in the 1990s with the discovery of temsirolimus (CCI-779). This novel soluble rapamycin derivative had a favorable toxicological profile in animals. More rapamycin derivatives with improved pharmacokinetics and reduced immunosuppressive effects have since then been developed for the treatment of cancer. These rapalogs include temsirolimus (CCI-779), everolimus (RAD001), and ridaforolimus (AP-23573) which are being evaluated in cancer clinical trials. Rapamycin analogs have similar therapeutic effects as rapamycin. However they have improved hydrophilicity and can be used for oral and intravenous administration. In 2012 National Cancer Institute listed more than 200 clinical trials testing the anticancer activity of rapalogs both as monotherapy or as a part of combination therapy for many cancer types.
Rapalogs, which are the first generation mTOR inhibitors, have proven effective in a range of preclinical models. However, the success in clinical trials is limited to only a few rare cancers. Animal and clinical studies show that rapalogs are primarily cytostatic, and therefore effective as disease stabilizers rather than for regression. The response rate in solid tumors where rapalogs have been used as a single-agent therapy have been modest. Due to partial mTOR inhibition as mentioned before, rapalogs are not sufficient for achieving a broad and robust anticancer effect, at least when used as monotherapy.
Another reason for the limited success is that there is a feedback loop between mTORC1 and AKT in certain tumor cells. It seems that mTORC1 inhibition by rapalogs fails to repress a negative feedback loop that results in phosphorylation and activation of AKT. These limitations have led to the development of the second generation of mTOR inhibitors. | 1 | Applied and Interdisciplinary Chemistry |
Dynamic vapor sorption (DVS) is a gravimetric technique that measures how quickly and how much of a solvent is absorbed by a sample such as a dry powder absorbing water. It does this by varying the vapor concentration surrounding the sample and measuring the change in mass which this produces. The technique is mostly used for water vapor, but is suitable for a wide range of organic solvents.
Daryl Williams, founder of Surface Measurement Systems Ltd, developed Dynamic Vapor Sorption in 1991; the first instrument was delivered to Pfizer UK in 1992. DVS was originally developed to replace the time and labor-intensive desiccators and saturated salt solutions used to measure water vapor sorption isotherms. | 0 | Theoretical and Fundamental Chemistry |
Wohl model may refer to:
* Wohl equation of state: an empirical model for a real gas proposed by A. Wohl
* an empirical model for the excess Gibbs free energy of mixing which has been formulated for ternary solutions by K. Wohl (1946, 1953) | 0 | Theoretical and Fundamental Chemistry |
In geology, a deformation mechanism is a process occurring at a microscopic scale that is responsible for changes in a material's internal structure, shape and volume. The process involves planar discontinuity and/or displacement of atoms from their original position within a crystal lattice structure. These small changes are preserved in various microstructures of materials such as rocks, metals and plastics, and can be studied in depth using optical or digital microscopy. | 1 | Applied and Interdisciplinary Chemistry |
Cold fusion is a hypothesized type of nuclear reaction that would occur at, or near, room temperature. It would contrast starkly with the "hot" fusion that is known to take place naturally within stars and artificially in hydrogen bombs and prototype fusion reactors under immense pressure and at temperatures of millions of degrees, and be distinguished from muon-catalyzed fusion. There is currently no accepted theoretical model that would allow cold fusion to occur.
In 1989, two electrochemists, Martin Fleischmann and Stanley Pons, reported that their apparatus had produced anomalous heat ("excess heat") of a magnitude they asserted would defy explanation except in terms of nuclear processes. They further reported measuring small amounts of nuclear reaction byproducts, including neutrons and tritium. The small tabletop experiment involved electrolysis of heavy water on the surface of a palladium (Pd) electrode. The reported results received wide media attention and raised hopes of a cheap and abundant source of energy.
Many scientists tried to replicate the experiment with the few details available. Hopes faded with the large number of negative replications, the withdrawal of many reported positive replications, the discovery of flaws and sources of experimental error in the original experiment, and finally the discovery that Fleischmann and Pons had not actually detected nuclear reaction byproducts. By late 1989, most scientists considered cold fusion claims dead, and cold fusion subsequently gained a reputation as pathological science. In 1989 the United States Department of Energy (DOE) concluded that the reported results of excess heat did not present convincing evidence of a useful source of energy and decided against allocating funding specifically for cold fusion. A second DOE review in 2004, which looked at new research, reached similar conclusions and did not result in DOE funding of cold fusion. Presently, since articles about cold fusion are rarely published in peer-reviewed mainstream scientific journals, they do not attract the level of scrutiny expected for mainstream scientific publications.
Nevertheless, some interest in cold fusion has continued through the decades—for example, a Google-funded failed replication attempt was published in a 2019 issue of Nature. A small community of researchers continues to investigate it, often under the alternative designations low-energy nuclear reactions (LENR) or condensed matter nuclear science (CMNS). | 0 | Theoretical and Fundamental Chemistry |
Refer to the figure on the bottom right plotting the heat capacity as a function of temperature. In this context, T is the temperature corresponding to point A on the curve.
Different operational definitions of the glass transition temperature T are in use, and several of them are endorsed as accepted scientific standards. Nevertheless, all definitions are arbitrary, and all yield different numeric results: at best, values of T for a given substance agree within a few kelvins. One definition refers to the viscosity, fixing T at a value of 10 poise (or 10 Pa·s). As evidenced experimentally, this value is close to the annealing point of many glasses.
In contrast to viscosity, the thermal expansion, heat capacity, shear modulus, and many other properties of inorganic glasses show a relatively sudden change at the glass transition temperature. Any such step or kink can be used to define T. To make this definition reproducible, the cooling or heating rate must be specified.
The most frequently used definition of T uses the energy release on heating in differential scanning calorimetry (DSC, see figure). Typically, the sample is first cooled with 10 K/min and then heated with that same speed.
Yet another definition of T uses the kink in dilatometry (a.k.a. thermal expansion): refer to the figure on the top right. Here, heating rates of are common. The linear sections below and above T are colored green. T is the temperature at the intersection of the red regression lines.
Summarized below are T values characteristic of certain classes of materials. | 0 | Theoretical and Fundamental Chemistry |
The pedosphere () is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere (air in and above the soil), biosphere (living organisms), lithosphere (unconsolidated regolith and consolidated bedrock) and the hydrosphere (water in, on and below the soil). The pedosphere is the foundation of terrestrial life on Earth.
The pedosphere acts as the mediator of chemical and biogeochemical flux into and out of these respective systems and is made up of gaseous, mineralic, fluid and biologic components. The pedosphere lies within the Critical Zone, a broader interface that includes vegetation, pedosphere, aquifer systems, regolith and finally ends at some depth in the bedrock where the biosphere and hydrosphere cease to make significant changes to the chemistry at depth. As part of the larger global system, any particular environment in which soil forms is influenced solely by its geographic position on the globe as climatic, geologic, biologic and anthropogenic changes occur with changes in longitude and latitude.
The pedosphere lies below the vegetative cover of the biosphere and above the hydrosphere and lithosphere. The soil forming process (pedogenesis) can begin without the aid of biology but is significantly quickened in the presence of biologic reactions, where it forms a soil carbon sponge. Soil formation begins with the chemical and/or physical breakdown of minerals to form the initial material that overlies the bedrock substrate. Biology quickens this by secreting acidic compounds that help break rock apart. Particular biologic pioneers are lichen, mosses and seed bearing plants, but many other inorganic reactions take place that diversify the chemical makeup of the early soil layer. Once weathering and decomposition products accumulate, a coherent soil body allows the migration of fluids both vertically and laterally through the soil profile, causing ion exchange between solid, fluid and gaseous phases. As time progresses, the bulk geochemistry of the soil layer will deviate away from the initial composition of the bedrock and will evolve to a chemistry that reflects the type of reactions that take place in the soil. | 0 | Theoretical and Fundamental Chemistry |
Frogs acquire the toxins needed for chemical defense by either producing them through glands on their skin or through their diet. The source of toxins in their diet are primarily arthropods, ranging from beetles to millipedes. When the required dietary components are absent, such as in captivity, the frog is no longer able to produce the toxins, making them nonpoisonous. The profile of toxins may even change with the season, as is the case for the Climbing Mantella, whose diet and feeding behavior differ between wet and dry seasons
The evolutionary advantage of producing such toxins is the deterrence of predators. There is evidence to suggest that the ability to produce toxins evolved along with aposematic coloration, acting as a visual cue to predators to remember which species are not palatable.
While the toxins produced by frogs are frequently referred to as poisonous, the doses of toxins are low enough that they are more noxious than poisonous. However, components of the toxins, namely the alkaloids, are very active in ion channels. Therefore, they disrupt the victim's nervous system, making them much more effective. Within the frogs themselves, the toxins are accumulated and delivered through small, specialized transport proteins.
Besides providing defense from predators, the toxins that poison frogs secrete interest medical researchers. Poison dart frogs, of the Dendrobatidae family, secrete batrachotoxin. This toxin has the potential to act as a muscle relaxant, heart stimulant, or anesthetic. Multiple species of frogs secrete epibatidine, whose study has yielded several important results. It was discovered that the frogs resist poisoning themselves through a single amino acid replacement that desensitizes the targeted receptors to the toxin, but still maintains the function of the receptor. This finding gives insight to the roles of proteins, the nervous system, and the mechanics of chemical defense, all of which promote future biomedical research and innovation. | 1 | Applied and Interdisciplinary Chemistry |
Metabolic imprinting refers to the long-term physiological and metabolic effects that an offsprings prenatal and postnatal environments have on them. Perinatal nutrition has been identified as a significant factor in determining an offsprings likelihood of it being predisposed to developing cardiovascular disease, obesity, and type 2 diabetes amongst other conditions.
During pregnancy, maternal glucose can cross the blood-placental barrier meaning maternal hyperglycaemia is associated with foetal hyperglycaemia. Despite maternal glucose being able to cross the blood-placental barrier, maternal insulin is not able and the foetus has to make its own. As a result, if a mother is hyperglycaemic the foetus is likely to be hyperinsulinaemic which leads to it having increased levels of growth and adiposity. | 1 | Applied and Interdisciplinary Chemistry |
Thermoplastic polymers like polyolefins can be remelted and reformed into new items. This approach is referred to as mechanical recycling and is usually the simplest and most economical form of recovery. Post-consumer plastic will usually already bare a degree of degradation. Another round of melt-processing will exacerbate this, with the result being that mechanically recycled plastic will usually have poorer mechanical properties than virgin plastic. Degradation can be enhanced by high concentrations of hydroperoxides, cross-contamination between different types of plastic and by additives present within the plastic. Technologies developed to enhance the biodegradation of plastic can also conflict with its recycling, with oxo-biodegradable additives, consisting of metallic salts of iron, magnesium, nickel, and cobalt, increasing the rate of thermal degradation. Depending on the polymer in question, an amount of virgin material may be added to maintain the quality of the product. | 0 | Theoretical and Fundamental Chemistry |
Self-assembly is the most common term in use in the modern scientific community to describe the spontaneous aggregation of particles (atoms, molecules, colloids, micelles, etc.) without the influence of any external forces. Large groups of such particles are known to assemble themselves into thermodynamically stable, structurally well-defined arrays, quite reminiscent of one of the 7 crystal systems found in metallurgy and mineralogy (e.g. face-centered cubic, body-centered cubic, etc.). The fundamental difference in equilibrium structure is in the spatial scale of the unit cell (or lattice parameter) in each particular case.
Molecular self-assembly is found widely in biological systems and provides the basis of a wide variety of complex biological structures. This includes an emerging class of mechanically superior biomaterials based on microstructural features and designs found in nature. Thus, self-assembly is also emerging as a new strategy in chemical synthesis and nanotechnology. Molecular crystals, liquid crystals, colloids, micelles, emulsions, phase-separated polymers, thin films and self-assembled monolayers all represent examples of the types of highly ordered structures which are obtained using these techniques. The distinguishing feature of these methods is self-organization. | 0 | Theoretical and Fundamental Chemistry |
* Progesterone also has a role in skin elasticity and bone strength, in respiration, in nerve tissue and in female sexuality, and the presence of progesterone receptors in certain muscle and fat tissue may hint at a role in sexually dimorphic proportions of those.
* During pregnancy, progesterone is said to decrease uterine irritability.
* During pregnancy, progesterone helps to suppress immune responses of the mother to fetal antigens, which prevents rejection of the fetus.
* Progesterone raises epidermal growth factor-1 (EGF-1) levels, a factor often used to induce proliferation, and used to sustain cultures, of stem cells.
* Progesterone increases core temperature (thermogenic function) during ovulation.
* Progesterone reduces spasm and relaxes smooth muscle. Bronchi are widened and mucus regulated. (PRs are widely present in submucosal tissue.)
* Progesterone acts as an antiinflammatory agent and regulates the immune response.
* Progesterone reduces gall-bladder activity.
* Progesterone normalizes blood clotting and vascular tone, zinc and copper levels, cell oxygen levels, and use of fat stores for energy.
* Progesterone may affect gum health, increasing risk of gingivitis (gum inflammation).
* Progesterone appears to prevent endometrial cancer (involving the uterine lining) by regulating the effects of estrogen.
* Progesterone plays an important role in the signaling of insulin release and pancreatic function, and may affect the susceptibility to diabetes or gestational diabetes.
* Progesterone levels in the blood were found to be lower in women who had higher weight and higher BMI among those who became pregnant through in vitro fertilization.
* Current data shows that micronized progesterone, which is chemically identical to the progesterone produced in women's bodies, in combination with estrogen in menopausal hormone therapy does not seem to have significant effects on venous thromboembolism (blood clots in veins) and ischemic stroke (lack of blood flow to the brain due to blockage of a blood vessel that supplies the brain). However, more studies need to be conducted to see whether or not micronized progesterone alone or in combined menopausal hormone therapy changes the risk of myocardial infarctions (heart attacks).
* There have not been any studies done yet on the effects of micronized progesterone on hair loss due to menopause.
* Despite suggestions for using hormone therapy to prevent loss of muscle mass in post-menopausal women (50 and older), menopausal hormone therapy involving either estrogen alone or estrogen and progesterone has not been found to preserve muscle mass. Menopausal hormone therapy also does not result in body weight reduction, BMI reduction, or change in glucose metabolism. | 0 | Theoretical and Fundamental Chemistry |
Gas lasers, laser diodes, and solid-state lasers can be manufactured to emit ultraviolet rays, and lasers are available that cover the entire UV range. The nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at 337.1 nm and 357.6 nm in wavelength. Another type of high-power gas lasers are excimer lasers. They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV argon-fluoride excimer lasers operating at 193 nm are routinely used in integrated circuit production by photolithography. The current wavelength limit of production of coherent UV is about 126 nm, characteristic of the Ar* excimer laser.
Direct UV-emitting laser diodes are available at 375 nm. UV diode-pumped solid state lasers have been demonstrated using cerium-doped lithium strontium aluminum fluoride crystals (Ce:LiSAF), a process developed in the 1990s at Lawrence Livermore National Laboratory. Wavelengths shorter than 325 nm are commercially generated in diode-pumped solid-state lasers. Ultraviolet lasers can also be made by applying frequency conversion to lower-frequency lasers.
Ultraviolet lasers have applications in industry (laser engraving), medicine (dermatology, and keratectomy), chemistry (MALDI), free-air secure communications, computing (optical storage), and manufacture of integrated circuits. | 0 | Theoretical and Fundamental Chemistry |
Sildenafil has been shown to be at least as effective as calcium channel blockers in treating severe Raynauds phenomenon (RP) associated with systemic sclerosis and digital ulceration. When given sildenafil for 4 weeks subjects had reduced mean frequency and duration of Raynaud attacks and a significantly lowered mean Raynauds condition score. The capillary blood flow velocity also increased in each individual patient and the mean capillary flow velocity of all patients increased significantly. These results came without significant reductions of the systemic blood pressure. However, the therapeutic effects of PDE5 inhibitors in primary (idiopathic) RP are less well defined. | 1 | Applied and Interdisciplinary Chemistry |
There are multiple conventions for naming polymer substances. Many commonly used polymers, such as those found in consumer products, are referred to by a common or trivial name. The trivial name is assigned based on historical precedent or popular usage rather than a standardized naming convention. Both the American Chemical Society (ACS) and IUPAC have proposed standardized naming conventions; the ACS and IUPAC conventions are similar but not identical. Examples of the differences between the various naming conventions are given in the table below:
In both standardized conventions, the polymers names are intended to reflect the monomer(s) from which they are synthesized (source based nomenclature) rather than the precise nature of the repeating subunit. For example, the polymer synthesized from the simple alkene ethene is called polyethene, retaining the -ene' suffix even though the double bond is removed during the polymerization process:
:→
However, IUPAC structure based nomenclature is based on naming of the preferred constitutional repeating unit. | 0 | Theoretical and Fundamental Chemistry |
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
Some examples of facultatively anaerobic bacteria are Staphylococcus spp., Escherichia coli, Salmonella, Listeria spp., Shewanella oneidensis and Yersinia pestis. Certain eukaryotes are also facultative anaerobes, including fungi such as Saccharomyces cerevisiae and many aquatic invertebrates such as nereid polychaetes.
It has been observed that in mutants of Salmonella typhimurium that underwent mutations to be either obligate aerobes or anaerobes, there were varying levels of chromatin-remodeling proteins. The obligate aerobes were later found to have a defective DNA gyrase subunit A gene (gyrA), while obligate anaerobes were defective in topoisomerase I (topI). This indicates that topoisomerase I and its associated relaxation of chromosomal DNA is required for transcription of genes required for aerobic growth, while the opposite is true for DNA gyrase. Additionally, in Escherichia coli K-12 it has been noted that phosphofructokinase (PFK) exists as a dimer under aerobic conditions and as a tetramer under anaerobic conditions. Given PFK’s role in glycolysis, this has implications for the effect of oxygen on the glucose metabolism of E. coli K-12 in relation to the mechanism of the Pasteur effect.
There may exist a core network of transcription factors (TFs) that includes the major oxygen-responsive ArcA and FNR control the adaptation of Escherichia coli to changes in oxygen availability. Activities of these two regulators are indicative of spatial effects that may affect gene expression in the microaerobic range. It has also been observed that these oxygen-sensitive proteins are protected within the cytoplasm by oxygen consumers within the cell membrane, known as terminal oxidases. | 1 | Applied and Interdisciplinary Chemistry |
A metallic microlattice is composed of a network of interconnecting hollow struts. In the least-dense microlattice sample reported, each strut is about 100 micrometres in diameter, with a wall 100 nanometres thick. The completed structure is about 99.99% air by volume, and by convention, the mass of air is excluded when the microlattice density is calculated. Allowing for the mass of the interstitial air, the true density of the structure is approximately 2.1 mg/cm (2.1 kg/m), which is only about 1.76 times the density of air itself at 25 °C. The material is described as being 100 times lighter than Styrofoam. Microlattices can also be 100 times stronger than regular polymers.
Metallic microlattices are characterized by very low densities, with the 2011 record of 0.9 mg/cm being among the lowest values of any known solid. The previous record of 1.0 mg/cm was held by silica aerogels, and aerographite is claimed to have a density of 0.2 mg/cm. Mechanically, these microlattices are behaviorally similar to elastomers and almost completely recover their shape after significant compression. This gives them a significant advantage over earlier aerogels, which are brittle, glass-like substances. This elastomeric property in metallic microlattices furthermore results in efficient shock absorption. Their Young's modulus E exhibits different scaling, with the density ρ, E ~ ρ, compared to E ~ ρ in aerogels and carbon nanotube foams. | 0 | Theoretical and Fundamental Chemistry |
Under the auspices of the Manhattan Project, Rafferty directed Union Carbide's efforts to enrich uranium (some of which was mined by another Union Carbide subsidiary: the United States Vanadium Corporation) for use in an atomic bomb. This effort culminated in Union Carbide designing (along with the Kellex Corporation), building, and operating the massive K-25 gaseous diffusion plant at Oak Ridge.
General Leslie Groves wrote of Rafferty:
Stéphane Groueff, in his book chronicling the Manhattan Project, had this to say about Rafferty:On June 1, 1945, prominent industrialists, including Rafferty, were invited to the second meeting of the Interim Committee. The industrialists were introduced to the committee as follows:Tennessee Eastman also managed and operated the Y-12 facility at Oak Ridge. In 1947 Union Carbide took over the operation of Y-12.
The graphite for the Hanford B Reactor as well as the Oak Ridge X-10 Reactor was produced by another Union Carbide subsidiary National Carbon Company. | 1 | Applied and Interdisciplinary Chemistry |
A Ramachandran plot can be used in two somewhat different ways. One is to show in theory which values, or conformations, of the ψ and φ angles are possible for an amino-acid residue in a protein (as at top right). A second is to show the empirical distribution of datapoints observed in a single structure (as at right, here) in usage for structure validation, or else in a database of many structures (as in the lower 3 plots at left). Either case is usually shown against outlines for the theoretically favored regions. | 1 | Applied and Interdisciplinary Chemistry |
The Römpp Encyclopedia Natural Products is an encyclopedia of natural products written by German chemists who specialize in this area of science. It is published by Thieme Medical Publishers. | 1 | Applied and Interdisciplinary Chemistry |
The electrical field of terahertz pulses is measured in a detector simultaneously illuminated with an ultrashort laser pulse. Two common detection schemes are used in THz-TDS: photoconductive sampling and electro-optical sampling. The power of THz pulses can be detected by bolometers (heat detectors cooled to liquid-helium temperatures), but since bolometers can only measure the total energy of a terahertz pulse rather than its electric field over time, they are unsuitable for THz-TDS.
Because the measurement technique is coherent, it naturally rejects incoherent radiation. Additionally, because the time slice of the measurement is extremely narrow, the noise contribution to the measurement is extremely low.
The signal-to-noise ratio (S/N) of the resulting time-domain waveform depends on experimental conditions (e.g., averaging time). However due to the coherent sampling techniques described, high S/N values (>70 dB) are routinely observed with 1 minute averaging times. | 0 | Theoretical and Fundamental Chemistry |
Antiquarian interest in the gold artefacts of prehistory emerged in the British Isles during the Early Modern period. In 1696, the Ashmolean Museum in Oxford, southern England obtained the Ballyshannon Disk, the first such artefact of its type in their collection, although in ensuing centuries they would gain a number of other items to accompany it. The British Museum in London would follow suit almost a century later, gaining its first Bronze Age gold artefact, a disk from Kirk Andrews on the Isle of Man, in 1782. | 1 | Applied and Interdisciplinary Chemistry |
Amylolytic process or amylolysis is the conversion of starch into sugar by the action of acids or enzymes such as amylase.
Starch begins to pile up inside the leaves of plants during times of light when starch is able to be produced by photosynthetic processes. This ability to make starch disappears in the dark due to the lack of illumination; there is insufficient amount of light produced during the dark needed to carry this reaction forward. Turning starch into sugar is done by the enzyme amylase. | 0 | Theoretical and Fundamental Chemistry |
In 1977 J.M Whatley proposed a plastid development cycle which said that plastid development is not always unidirectional but is instead a complicated cyclic process. Proplastids are the precursor of the more differentiated forms of plastids, as shown in the diagram to the right. | 0 | Theoretical and Fundamental Chemistry |
By using the first law of thermodynamics, this internal energy can be expressed as a pressure, that is
where this expression remains valid for temperatures much smaller than the Fermi temperature. This pressure is known as the degeneracy pressure. In this sense, systems composed of fermions are also referred as degenerate matter.
Standard stars avoid collapse by balancing thermal pressure (plasma and radiation) against gravitational forces. At the end of the star lifetime, when thermal processes are weaker, some stars may become white dwarfs, which are only sustained against gravity by electron degeneracy pressure. Using the Fermi gas as a model, it is possible to calculate the Chandrasekhar limit, i.e. the maximum mass any star may acquire (without significant thermally generated pressure) before collapsing into a black hole or a neutron star. The latter, is a star mainly composed of neutrons, where the collapse is also avoided by neutron degeneracy pressure.
For the case of metals, the electron degeneracy pressure contributes to the compressibility or bulk modulus of the material. | 0 | Theoretical and Fundamental Chemistry |
Referring to conduction, Partington writes: "If a hot body is brought in conducting contact with a cold body, the temperature of the hot body falls and that of the cold body rises, and it is said that a quantity of heat has passed from the hot body to the cold body."
Referring to radiation, Maxwell writes: "In Radiation, the hotter body loses heat, and the colder body receives heat by means of a process occurring in some intervening medium which does not itself thereby become hot."
Maxwell writes that convection as such "is not a purely thermal phenomenon". In thermodynamics, convection in general is regarded as transport of internal energy. If, however, the convection is enclosed and circulatory, then it may be regarded as an intermediary that transfers energy as heat between source and destination bodies, because it transfers only energy and not matter from the source to the destination body.
In accordance with the first law for closed systems, energy transferred solely as heat leaves one body and enters another, changing the internal energies of each. Transfer, between bodies, of energy as work is a complementary way of changing internal energies. Though it is not logically rigorous from the viewpoint of strict physical concepts, a common form of words that expresses this is to say that heat and work are interconvertible.
Cyclically operating engines that use only heat and work transfers have two thermal reservoirs, a hot and a cold one. They may be classified by the range of operating temperatures of the working body, relative to those reservoirs. In a heat engine, the working body is at all times colder than the hot reservoir and hotter than the cold reservoir. In a sense, it uses heat transfer to produce work. In a heat pump, the working body, at stages of the cycle, goes both hotter than the hot reservoir, and colder than the cold reservoir. In a sense, it uses work to produce heat transfer. | 0 | Theoretical and Fundamental Chemistry |
The structure–correlation principle states that structural changes that occur along the reaction coordinate can reveal themselves in the ground state as deviations of bond distances and angles from normal values along the reaction coordinate. According to this theory if one particular bond length on reaching the transition state increases then this bond is already longer in its ground state compared to a compound not sharing this transition state. One demonstration of this principle is found in the two bicyclic compounds depicted below. The one on the left is a bicyclo[2.2.2]octene, which, at 200 °C, extrudes ethylene in a retro-Diels–Alder reaction.
Compared to the compound on the right (which, lacking an alkene group, is unable to give this reaction) the bridgehead carbon-carbon bond length is expected to be shorter if the theory holds, because on approaching the transition state this bond gains double bond character. For these two compounds the prediction holds up based on X-ray crystallography. | 0 | Theoretical and Fundamental Chemistry |
NaK containing 40% to 90% potassium by mass is liquid at room temperature. The eutectic mixture consists of 77% potassium and 23% sodium by mass (NaK-77), and it is a liquid from , and has a density of 0.866 g/cm at and 0.855 g/cm at , making it less dense than water. It is highly reactive with water and is stored usually under hexane or other hydrocarbons, or under an inert gas (usually dry nitrogen or argon) if high purity and low levels of oxidation are required.
A solid compound, , exists at low temperatures, containing 46 percent potassium by mass.
NaK has a very high surface tension, which makes large amounts of it pull into a bun-like shape. Its specific heat capacity is 982 J/(kg⋅K), which is roughly one quarter of that for water, but heat transfer is higher over a temperature gradient due to higher thermal conductivity. | 1 | Applied and Interdisciplinary Chemistry |
The second major application of pharmacometabolomics is the analysis of a patient's metabolic profile following the administration of a specific therapy. This process is often secondary to a pre-treatment metabolic analysis, allowing for the comparison of pre- and post-treatment metabolite concentrations. This allows for the identification of the metabolic processes and pathways that are being altered by the treatment either intentionally as a designated target of the compound, or unintentionally as a side effect. Furthermore, the concentration and variety of metabolites produced from the compound itself can also be identified, providing information on the rate of metabolism and potentially leading to development of a related compound with increased efficacy or decreased side effects. An example of this approach was used to investigate the effect of several antipsychotic drugs on lipid metabolism in patients treated for schizophrenia. It was hypothesized that these antipsychotic drugs may be altering lipid metabolism in treated patients with schizophrenia, contributing to the weight gain and hypertriglyceridemia. The study monitored lipid metabolites in patients both before and after treatment with antipsychotics. The compiled pre- and post-treatment profiles were then compared to examine the effect of these compounds on lipid metabolism. The researchers found correlations between treatment with antipsychotic drugs and lipid metabolism, in both a lipid-class-specific and drug-specific manner, establishing new foundations around the concept that pharmacometabolomics provides powerful tools for enabling detailed mapping of drug effects. Additional studies by the Pharmacometabolomics Research Network enabled mapping in ways not possible before effects of statins, atenolol and aspirin. Totally new insights were gained about effect of these drugs on metabolism and they highlighted pathways implicated in response and side effects. | 1 | Applied and Interdisciplinary Chemistry |
The other function of retromer is the recycling of protein cargo directly back to the plasma membrane. Dysfunction of this branch of the retromer recycling pathway causes endosomal protein traffic jams that are linked to Alzheimer’s disease. It has been suggested that recycling dysfunction is the “fire” that drives the common form of Alzheimer’s, leading to the production of amyloid and tau tangle “smoke”. | 1 | Applied and Interdisciplinary Chemistry |
The ability to inhibit or modify enzyme function absent a catalytic pocket binding site target greatly expands the potentially druggable portion of the proteome. Furthermore, most classes of chimeric small molecules can act on many targets over their life cycle, lowering the effective dose compared to traditional inhibitors that act only on one protein at a time. These therapeutics provide an alternative mechanism of action that may be useful as a combination therapy in diseases where drug resistance is a concern. Chimeric drug activity is also highly dependent on distance between targeted proteins allowing effect to be effectively tuned through optimization of the linker structure. | 1 | Applied and Interdisciplinary Chemistry |
A decrease in pH (increase in ion concentration) shifts the standard curve to the right, while an increase shifts it to the left. This occurs because at greater ion concentration, various amino acid residues, such as Histidine 146 exist predominantly in their protonated form allowing them to form ion pairs that stabilize deoxyhemoglobin in the T state. The T state has a lower affinity for oxygen than the R state, so with increased acidity, the hemoglobin binds less O for a given P (and more H). This is known as the Bohr effect. A reduction in the total binding capacity of hemoglobin to oxygen (i.e. shifting the curve down, not just to the right) due to reduced pH is called the root effect. This is seen in bony fish. The binding affinity of hemoglobin to O is greatest under a relatively high pH. | 1 | Applied and Interdisciplinary Chemistry |
As polymers get longer and their molecular weight increases, their viscosity tend to increase. Thus, the measured viscosity of polymers can provide valuable information about the average length of the polymer, the progress of reactions, and in what ways the polymer branches. | 0 | Theoretical and Fundamental Chemistry |
This page discusses each of the main elements in the mixture of fission products produced by nuclear fission of the common nuclear fuels uranium and plutonium. The isotopes are listed by element, in order by atomic number.
Neutron capture by the nuclear fuel in nuclear reactors and atomic bombs also produces actinides and transuranium elements (not listed here). These are found mixed with fission products in spent nuclear fuel and nuclear fallout.
Neutron capture by materials of the nuclear reactor (shielding, cladding, etc.) or the environment (seawater, soil, etc.) produces activation products (not listed here). These are found in used nuclear reactors and nuclear fallout. A small but non-negligible proportion of fission events produces not two, but three fission products (not counting neutrons or subatomic particles). This ternary fission usually produces a very light nucleus such as helium (about 80% of ternary fissions produce an alpha particle) or hydrogen (most of the rest produce tritium or to a lesser extent deuterium and protium) as the third product. This is the main source of tritium from light water reactors. Another source of tritium is Helium-6 which immediately decays to (stable) Lithium-6. Lithium-6 produces tritium when hit by neutrons and is one of the main sources of commercially or militarily produced tritium. If the first or only step of nuclear reprocessing is an aqueous solution (as is the case in PUREX) this poses a problem as tritium contamination cannot be removed from water other than by costly isotope separation. Furthermore, a tiny fraction of the free neutrons involved in the operation of a nuclear reactor decay to a proton and a beta particle before they can interact with anything else. Given that protons from this source are indistinguishable from protons from ternary fission or radiolysis of coolant water, their overall proportion is hard to quantify. | 0 | Theoretical and Fundamental Chemistry |
Ferrier was born in Edinburgh on 7 August 1932. Following the family's idiosyncratic naming tradition, although he was named Robert John, he was always known as Robin. Likewise his father Edward was known as William and his mother Sophia was known as Rita. William was a policeman and became head of Edinburgh CID, while Rita was a housewife.
His only sibling was a fraternal twin sister Dr Barbara M. Ferrier (d. 2006), known as Ray, who likewise became an organic chemist, becoming professor emeritus of the Department of Biochemistry and Biomedical Sciences at McMaster University. A polycyclic ketone "barbaralone", related to bullvalene was named after her.
Ferrier attended George Heriot's School for all of his schooling, apart from a brief time in Traquair, to where he was evacuated during the war with his mother and sister.
He gained a Bachelor of Science with first class honours in 1954 and a PhD in plant polysaccharides in 1957, under Professor Gerald Aspinall. | 0 | Theoretical and Fundamental Chemistry |
First, ion-specific microelectrodes can be used to measure the internal free ion concentration of cells and organelles. The major advantages are that readings can be made from cells over relatively long periods of time, and that unlike dyes very little extra ion buffering capacity is added to the cells.
Second, the technique of two-electrode voltage-clamp allows the direct measurement of the ion flux across the membrane of a cell. The membrane is held at an electric potential and the responding current is measured. All ions passing across the membrane contribute to the measured current.
Third, the technique of patch-clamp uses isolated sections of natural or artificial membrane in much the same manner as voltage-clamp but without the secondary effects of a cellular system. Under ideal conditions the conductance of individual channels can be quantified. This methodology gives the most direct measurement of the action of ion channels. | 1 | Applied and Interdisciplinary Chemistry |
A more complex, specific example of crosstalk between two major signaling pathways can be observed with the interaction of the cAMP and MAPK signaling pathways in the activation of lymphocytes. In this case, components of the cAMP pathway directly and indirectly affect MAPK signaling pathway meant to activate genes involving immunity and lymphocytes.
Newly formed cAMP is released from the membrane and diffuses across the intracellular space where it serves to activate PKA. The catalytic subunit of PKA must bind four molecules of cAMP to be activated, whereupon activation consists of cleavage between the regulatory and catalytic subunits. This cleavage in turn activates PKA by exposing the catalytic sites of the C subunits, which can then phosphorylate an array of proteins in the cell.
In lymphocytes, the intracellular levels of cAMP increase upon antigen-receptor stimulation and even more so in response to prostaglandin E and other immunosuppression agents. In this case, cAMP serves to inhibit immunity players. PKA type I colocalizes with the T-cell and B-cell antigen receptors and causes inhibition of T- and B-cell activation. PKA has even been highlighted as a direct inducer of genes contributing to immunosuppression.
Additionally, the cAMP pathway also interacts with the MAPK pathway in a more indirect manner through its interaction with hematopoietic PTPase (HePTP). HePTP is expressed in all leukocytes. When overexpressed in T-cells, HePTP reduces the transcriptional activation of the interleukin-2 promoter typically induced by the activated T-cell receptor through a MAPK signaling cascade. The way that HePTP effectively inhibits the MAPK signaling is by interacting with the MAP kinases Erk1, Erk2, and p38 through a short sequence in HePTP's non-catalytic N terminus termed the kinase interaction motif (KIM)., The highly-specific binding of Erk and p38 to this subunit of HePTP results in rapid inactivation of the signaling cascade (see figure 3).
Yet, since both HePTP and Erk are cytosolic enzymes, it is reasonable to conclude that there exists a mechanism for the inhibition of Erk by HePTP to cease in order to allow for the translocation of activated Erk to the nucleus. Indeed, like in many other cases of protein-protein interaction, HePTP appears to be phosphorylated by Erk and p38 at the sites Thr45 and Ser72. Importantly though, a third phosphorylation site in the non-catalytic N terminus (the KIM region) of HePTP has been found—one that is phosphorylated to a much higher stoichiometry by the cAMP pathway, in yet another instance of crosstalk between the cAMP and MAPK pathways.
Phosphorylation of this third site by PKAs from the cAMP pathway inhibits binding of MAP kinases to HePTP and thereby upregulates the MAPK/ERK signaling cascade. The MAPK pathway, through Ras, Raf, Mek, and Erk, shows low activity in the presence of unphosphorylated (active) HePTP. However, activation the cAMP pathway stimulates the activation of PKA, which in turn phosphorylates HePTP at Ser23. This prevents HePTP from binding to Erk and frees the MAPK pathway from inhibition, allowing downstream signaling to continue (see figure 4).
Moreover, studies involving smooth muscle cells from the atrium of the heart have shown that PKA can reduce the activation of MAP kinases in response to platelet-derived growth factor (PDGF) by phosphorylating the kinase c-Raf. Thus, it seems plausible that PKA in the cAMP pathway could even be further involved in the regulation of lymphocyte activation not only by inhibiting the antigen-receptor MAPK signal pathway at its final stage, but even further upstream. | 1 | Applied and Interdisciplinary Chemistry |
Generally, and except for specific continuous-filtering or continuous-cultivating versions, algae scrubbers require the algae to be removed ("harvested") periodically from the scrubber. This removal of algae has the effect of removing undesired nutrients from the water because the algae used the nutrients in order to grow. The algae is generally removed either:
*Every 7 to 21 days, or
*When it is black, or
*When it fills up the scrubber, or
*When it starts letting go, or
*When nutrients start to rise in the water.
For waterfall versions, the screen is removed from the pipe and cleaned in a sink with running water. The pipe is removed also, and the slot is cleaned with a toothbrush, to remove any algae that have grown up into it. After the algae are removed, the screen and pipe are put back in the scrubber. For upflow versions, the cleaning method depends on the type:
Glass-attached version: The magnet portion outside the glass is removed, and the inside portion is lifted out of the water. If the growth is thick green hair algae, then it is just removed by hand. If the growth is thin green hair (as occurs in freshwater) or dark slime, then the inside unit is taken to the sink and cleaned with a toothbrush. After cleaning, the inside and outside parts are put back into place on the glass.
Floating-surface version: If the growth is thick green hair algae then it is just removed by hand by lifting the LED lid up and pulling the growth out. If the growth is thin green hair or dark slime, then the floating portion is taken to the sink and cleaned with a toothbrush.
Drop-in version: The entire unit is lifted out of the water, and the lid is removed. If the growth is thick green hair algae then it is just removed by hand. If the growth is thin green hair or dark slime, then the whole unit is taken to the sink and cleaned with a toothbrush.
If the screen is not cleaned like this periodically, the algae will get too thick and block light and flow from reaching the "roots" of the algae, and these areas will die and let go, putting nutrients back into the water. | 0 | Theoretical and Fundamental Chemistry |
The lower limit of the hot working temperature is determined by its recrystallization temperature. As a guideline, the lower limit of the hot working temperature of a material is 60% its melting temperature (on an absolute temperature scale). The upper limit for hot working is determined by various factors, such as: excessive oxidation, grain growth, or an undesirable phase transformation. In practice materials are usually heated to the upper limit first to keep forming forces as low as possible and to maximize the amount of time available to hot work the workpiece.
The most important aspect of any hot working process is controlling the temperature of the workpiece. 90% of the energy imparted into the workpiece is converted into heat. Therefore, if the deformation process is quick enough the temperature of the workpiece should rise, however, this does not usually happen in practice. Most of the heat is lost through the surface of the workpiece into the cooler tooling. This causes temperature gradients in the workpiece, usually due to non-uniform cross-sections where the thinner sections are cooler than the thicker sections. Ultimately, this can lead to cracking in the cooler, less ductile surfaces. One way to minimize the problem is to heat the tooling. The hotter the tooling the less heat lost to it, but as the tooling temperature rises, the tool life decreases. Therefore the tooling temperature must be compromised; commonly, hot working tooling is heated to 500–850 °F (325–450 °C). | 1 | Applied and Interdisciplinary Chemistry |
The Reststrahlen effect (German: “residual rays”) is a reflectance phenomenon in which electromagnetic radiation within a narrow energy band cannot propagate within a given medium due to a change in refractive index concurrent with the specific absorbance band of the medium in question; this narrow energy band is termed the Reststrahlen band.
As a result of this inability to propagate, normally incident Reststrahlen band radiation experiences strong-reflection or total-reflection from that medium. The energies at which Reststrahlen bands occur vary and are particular to the individual compound. Numerous physical attributes of a compound will have an effect on the appearance of the Reststrahlen band. These include phonon band-gap, particle/grain size, strongly absorbing compounds, compounds with optically opaque bands in the infrared. | 0 | Theoretical and Fundamental Chemistry |
A nuclear chain reaction was proposed by Leo Szilard in 1933, shortly after the neutron was discovered, yet more than five years before nuclear fission was first discovered. Szilárd knew of chemical chain reactions, and he had been reading about an energy-producing nuclear reaction involving high-energy protons bombarding lithium, demonstrated by John Cockcroft and Ernest Walton, in 1932. Now, Szilárd proposed to use neutrons theoretically produced from certain nuclear reactions in lighter isotopes, to induce further reactions in light isotopes that produced more neutrons. This would in theory produce a chain reaction at the level of the nucleus. He did not envision fission as one of these neutron-producing reactions, since this reaction was not known at the time. Experiments he proposed using beryllium and indium failed.
Later, after fission was discovered in 1938, Szilárd immediately realized the possibility of using neutron-induced fission as the particular nuclear reaction necessary to create a chain-reaction, so long as fission also produced neutrons. In 1939, with Enrico Fermi, Szilárd proved this neutron-multiplying reaction in uranium. In this reaction, a neutron plus a fissionable atom causes a fission resulting in a larger number of neutrons than the single one that was consumed in the initial reaction. Thus was born the practical nuclear chain reaction by the mechanism of neutron-induced nuclear fission.
Specifically, if one or more of the produced neutrons themselves interact with other fissionable nuclei, and these also undergo fission, then there is a possibility that the macroscopic overall fission reaction will not stop, but continue throughout the reaction material. This is then a self-propagating and thus self-sustaining chain reaction. This is the principle for nuclear reactors and atomic bombs.
Demonstration of a self-sustaining nuclear chain reaction was accomplished by Enrico Fermi and others, in the successful operation of Chicago Pile-1, the first artificial nuclear reactor, in late 1942. | 0 | Theoretical and Fundamental Chemistry |
The main advantage of FbFPs over GFP is their independence of molecular oxygen. Since all GFP derivatives and homologues require molecular oxygen for the maturation of their chromophore, these fluorescent proteins are of limited use under anaerobic or hypoxic conditions.
Since FbFPs bind FMN as chromophore, which is synthesized independently of molecular oxygen, their fluorescence signal does not differ between aerobic and anaerobic conditions.<br />
Another advantage is the small size of FbFPs, which is typically between 100 and 150 amino acids. This is about half the size of GFP (238 amino acids). It could for example be shown that this renders them superior tags for monitoring tobacco mosaic virus infections in tobacco leaves.<br />
Due to their extraordinary long average fluorescence lifetime of up to 5.7 ns they are also very well suited for the use as donor domains in FRET systems in conjunction with e.g. YFP (see photophysical properties). A fusion of EcFbFP and YFP was e.g. used to develop the first genetically encoded fluorescence biosensor for oxygen (FluBO)
The main disadvantage compared to GFP variants is their lower brightness (the product of ε and Φ). The commonly used EGFP (ε = 55,000 Mcm; Φ = 0.60 ) for example is approximately five times as bright as EcFbFP.<br />
Another disadvantage of the FbFPs is the lack of color variants to tag and distinguish multiple proteins in a single cell or tissue. The largest spectral shift reported for FbFPs so far is 10 nm. Although this variant (Pp2FbFP Q116V) can be visually distinguished from the others with the human eye, the spectral differences are too small for fluorescence microscopy filters. | 1 | Applied and Interdisciplinary Chemistry |
Monomeric metal carbyne complexes exhibit fairly linear M–C–R linkages according to X-ray crystallography. The M–C distances are typically shorter than the M–C bonds found in metal carbenes. The bond angle is generally between 170° and 180° Analogous to Fischer and Schrock carbenes; Fischer and Schrock carbynes are also known. Fischer carbynes usually have lower oxidation state metals and the ligands are π-accepting/electron-withdrawing ligands. Schrock carbynes on the other hand typically have higher oxidation state metals and electron-donating/anionic ligands. In a Fischer carbyne the C-carbyne exhibits electrophilic behavior while Schrock carbynes display nucleophilic reactivity on the carbyne carbon Carbyne complexes have also been characterized by many methods including infrared Spectroscopy, Raman spectroscopy. Bond lengths, bond angles and structures can be inferred from these and other analytical techniques.
Metal carbyne complexes also exhibit a large trans effect, where the ligand opposite the carbyne is typically labile. | 0 | Theoretical and Fundamental Chemistry |
Ultraviolet radiation is helpful in the treatment of skin conditions such as psoriasis and vitiligo. Exposure to UVA, while the skin is hyper-photosensitive, by taking psoralens is an effective treatment for psoriasis. Due to the potential of psoralens to cause damage to the liver, PUVA therapy may be used only a limited number of times over a patient's lifetime.
UVB phototherapy does not require additional medications or topical preparations for the therapeutic benefit; only the exposure is needed. However, phototherapy can be effective when used in conjunction with certain topical treatments such as anthralin, coal tar, and vitamin A and D derivatives, or systemic treatments such as methotrexate and Soriatane. | 0 | Theoretical and Fundamental Chemistry |
In order to have a practical microscope or diffractometer, just having an electron beam was not enough, it needed to be controlled. Many developments laid the groundwork of electron optics; see the paper by Chester J. Calbick for an overview of the early work. One significant step was the work of Heinrich Hertz in 1883 who made a cathode-ray tube with electrostatic and magnetic deflection, demonstrating manipulation of the direction of an electron beam. Others were focusing of electrons by an axial magnetic field by Emil Wiechert in 1899, improved oxide-coated cathodes which produced more electrons by Arthur Wehnelt in 1905 and the development of the electromagnetic lens in 1926 by Hans Busch.
Building an electron microscope involves combining these elements, similar to an optical microscope but with magnetic or electrostatic lenses instead of glass ones. To this day the issue of who invented the transmission electron microscope is controversial, as discussed by Thomas Mulvey and more recently by Yaping Tao. Extensive additional information can be found in the articles by Martin Freundlich, Reinhold Rüdenberg and Mulvey.
One effort was university based. In 1928, at the Technical University of Berlin, (Professor of High Voltage Technology and Electrical Installations) appointed Max Knoll to lead a team of researchers to advance research on electron beams and cathode-ray oscilloscopes. The team consisted of several PhD students including Ernst Ruska. In 1931, Max Knoll and Ernst Ruska successfully generated magnified images of mesh grids placed over an anode aperture. The device, a replicate of which is shown in Figure 5, used two magnetic lenses to achieve higher magnifications, the first electron microscope. (Max Knoll died in 1969, so did not receive a share of the Nobel Prize in Physics in 1986.)
Apparently independent of this effort was work at Siemens-Schuckert by Reinhold Rudenberg. According to patent law (U.S. Patent No. 2058914 and 2070318, both filed in 1932), he is the inventor of the electron microscope, but it is not clear when he had a working instrument. He stated in a very brief article in 1932 that Siemens had been working on this for some years before the patents were filed in 1932, so his effort was parallel to the university effort. He died in 1961, so similar to Max Knoll, was not eligible for a share of the Nobel Prize.
These instruments could produce magnified images, but were not particularly useful for electron diffraction; indeed, the wave nature of electrons was not exploited during the development. Key for electron diffraction in microscopes was the advance in 1936 where showed that they could be used as micro-diffraction cameras with an aperture—the birth of selected area electron diffraction.
Less controversial was the development of LEED—the early experiments of Davisson and Germer used this approach. As early as 1929 Germer investigated gas adsorption, and in 1932 Harrison E. Farnsworth probed single crystals of copper and silver. However, the vacuum systems available at that time were not good enough to properly control the surfaces, and it took almost forty years before these became available. Similarly, it was not until about 1965 that Peter B. Sewell and M. Cohen demonstrated the power of RHEED in a system with a very well controlled vacuum. | 0 | Theoretical and Fundamental Chemistry |
Experiments in atomic physics are often done with a laser of a specific frequency (meaning the photons have a specific energy), so they only couple one set of states with a particular energy to another set of states with an energy . However, the atom can still decay spontaneously into a third state by emitting a photon of a different frequency. The new state with energy of the atom no longer interacts with the laser simply because no photons of the right frequency are present to induce a transition to a different level. In practice, the term dark state is often used for a state that is not accessible by the specific laser in use even though transitions from this state are in principle allowed. | 0 | Theoretical and Fundamental Chemistry |
Human endogenous retroviruses (HERV) comprise a significant part of the human genome, with approximately 98,000 ERV elements and fragments making up 5–8%. According to a study published in 2005, no HERVs capable of replication had been identified; all appeared to be defective, containing major deletions or nonsense mutations (not true for HERV-K). This is because most HERVs are merely traces of original viruses, having first integrated millions of years ago. An analysis of HERV integrations is ongoing as part of the 100,000 Genomes Project.
A 2023 study found HERV can become awakened from dormant states and contribute to aging which could be blocked by neutralizing antibodies.
Human endogenous retroviruses were originally discovered when human genomic libraries were screened under low-stringency conditions using either probes from animal retroviruses or by using oligonucleotides with similarity to virus sequences. | 1 | Applied and Interdisciplinary Chemistry |
Calorimetry may be used to monitor the course of a reaction, since the instantaneous heat flux of the reaction, which is directly related to the enthalpy change for the reaction, is monitored. Reaction calorimetry may be classified as a differential technique since the primary data collected are proportional to rate vs. time. From these data, the starting material or product concentration over time may be obtained by simply taking the integral of a polynomial fit to the experimental curve.
While reaction calorimetry is less frequently employed than a number of other techniques, it has found use as an effective tool for catalyst screening. Reaction calorimetry has also been applied as an efficient method for mechanistic study of individual reactions including the prolinate-catalyzed α-amination of aldehydes and the palladium catalyzed Buchwald-Hartwig amination reaction. | 0 | Theoretical and Fundamental Chemistry |
Penicillamine is a trifunctional organic compound, consisting of a thiol, an amine, and a carboxylic acid. It is an amino acid structurally similar to cysteine, but with geminal dimethyl substituents α to the thiol. Like most amino acids, it is a colorless solid that exists in the zwitterionic form at physiological pH.
Penicillamine is a chiral drug with one stereogenic center and exist as a pair of enantiomers. Refer the image for the structure of penicillamine enantiomers. The (S)-enantiomer, the eutomer, is antiarthritic while the distomer (R)-penicillamine is extremely toxic. Of its two enantiomers, -penicillamine (having R absolute configuration) is toxic because it inhibits the action of pyridoxine (also known as vitamin B). That enantiomer is a metabolite of penicillin but has no antibiotic properties itself. A variety of penicillamine–copper complex structures are known. | 0 | Theoretical and Fundamental Chemistry |
A photochemical logic gate is based on the photochemical intersystem crossing and molecular electronic transition between photochemically active molecules, leading to logic gates that can be produced. | 0 | Theoretical and Fundamental Chemistry |
Despite having a lower than optimum drug penetration into bone ratio of 10–20%, flucloxacillin appears effective in treating osteomyelitis.
Depending on local guidance it may be used in the treatment of infection of joints while waiting for culture results. | 0 | Theoretical and Fundamental Chemistry |
Microbial superantigens are molecules expressed by bacteria and other microorganisms that have the power to stimulate a strong immune response by activation of T-cells. These molecules generally have regions that resemble self-antigens that promote a residual autoimmune response – this is the theory of molecular mimicry. Staphylococcal and streptococcal superantigens have been characterized in autoimmune diseases – the classical example in post group A streptococcal rheumatic heart disease, where there is similarity between M proteins of Streptococcus pyogenes to cardiac myosin and laminin. It has also been shown that up to 70% of patients with granulomatosis with polyangiitis are chronic nasal carriers of Staphylococcus aureus, with carriers having an eight times increased risk of relapse. This would therefore be considered a type II hypersensitivity reaction. | 1 | Applied and Interdisciplinary Chemistry |
The European Union (EU) was the first to issue regulations for biosolids land application; this aimed to put a limit to the pathogen and pollution risk. These risks come from the fact that some metabolites remain intact after waste water treatment processes. Debates over biosolid use vary in severity across the EU. | 1 | Applied and Interdisciplinary Chemistry |
Submolecular resolution can be achieved in constant height mode. In this case it is crucial to operate the cantilever at small, even sub-Ångström oscillation amplitudes. The frequency shift is then independent of the amplitude and is most sensitive to short-range forces, possibly yielding atomic scale contrast within a short tip-sample distance. The requirement for small amplitude is fulfilled with the qplus sensor. The qplus sensor-based cantilevers are much stiffer than regular silicon cantilevers, allowing stable operation in the negative force regime without instabilities. An added benefit of the stiff cantilever is the possibility to measure STM tunneling current while performing the AFM experiment, thus providing complementary data for the AFM images.
To enhance the resolution to a truly atomic scale, the cantilever tip apex can be functionalized with atom or molecule of a well-known structure and suitable characteristics. The functionalization of the tip is done by picking up a chosen particle to the end of the tip apex. CO molecule has shown to be a prominent option for the tip functionalization, but also other possibilities have been studied, such as Xe atoms. Reactive atoms and molecules, such as halogens Br and Cl or metals have been shown not to perform as well for imaging purposes. With inert tip apex, it is possible to get closer to the sample with still stable conditions whereas a reactive tip has a greater chance to accidentally move or pick up an atom from the sample. The atomic contrast is attained in the repulsive force domain close to the sample, where the frequency shift is generally attributed to Pauli repulsion due to overlapping wave functions between the tip and the sample. Van der Waals interaction, on the other hand, merely adds a diffuse background to the total force.
During the pick-up, the CO molecule orients itself such that the carbon atom attaches to the metal probe tip. The CO molecule, due to its linear structure, can bend while experiencing varying forces during the scanning, as shown in the figure. This bending appears to be a major cause for the contrast improvement, although it is not a general requirement for atomic resolution for different tip terminations such as a single oxygen atom, which exhibits negligible bending. Additionally, the bending of the CO molecule adds its contribution to the images, which may cause bond-like features in locations where no bonds exist. Thus, one should be careful while interpreting the physical meaning of the image obtained with a bending tip molecule such as CO. | 0 | Theoretical and Fundamental Chemistry |
In natural optical activity, the difference between the LCP light and the RCP light is caused by the asymmetry of the molecules (i.e. chiral molecules). Because of the handedness of the molecule, the absorption of the LCP light would be different from the RCP light. However, in MCD in the presence of a magnetic field, LCP and RCP no longer interact equivalently with the absorbing medium. Thus, there is not the same direct relation between magnetic optical activity and molecular stereochemistry which would be expected, because it is found in natural optical activity. So, natural CD is much more rare than MCD which does not strictly require the target molecule to be chiral.
Although there is much overlap in the requirements and use of instruments, ordinary CD instruments are usually optimized for operation in the ultraviolet, approximately 170–300 nm, while MCD instruments are typically required to operate in the visible to near infrared, approximately 300–2000 nm. The physical processes that lead to MCD are substantively different from those of CD. However, like CD, it is dependent on the differential absorption of left and right hand circularly polarized light. MCD will only exist at a given wavelength if the studied sample has an optical absorption at that wavelength. This is distinctly different from the related phenomenon of optical rotatory dispersion (ORD), which can be observed at wavelengths far from any absorption band. | 0 | Theoretical and Fundamental Chemistry |
Asphalt modification through nanoparticles can be considered as an interesting low-cost technique in asphalt pavement engineering providing novel perspectives in making asphalt materials more durable. | 0 | Theoretical and Fundamental Chemistry |
The circumstances of Brands birth are unknown but he was born in 1630 and died or 1710. Some sources describe his origins as humble and indicate that he had been an apprentice glassmaker as a young man. However, correspondence by his second wife Margaretha states that he was of high social standing. In any case he held a post as a junior army officer during the Thirty Years War and his first wife's dowry was substantial, allowing him to pursue alchemy on leaving the army.
He was one of the many searchers for the philosopher's stone. In the process, he accidentally discovered phosphorus. | 1 | Applied and Interdisciplinary Chemistry |
When a shape-memory alloy is in its cold state (below M), the metal can be bent or stretched and will hold those shapes until heated above the transition temperature. Upon heating, the shape changes to its original. When the metal cools again, it will retain the shape, until deformed again.
With the one-way effect, cooling from high temperatures does not cause a macroscopic shape change. A deformation is necessary to create the low-temperature shape. On heating, transformation starts at A and is completed at A (typically 2 to 20 °C or hotter, depending on the alloy or the loading conditions). A is determined by the alloy type and composition and can vary between and . | 1 | Applied and Interdisciplinary Chemistry |
The European Congress on Molecular Spectroscopy (EUCMOS) is held every two years. The first Congress in this series was held in Basel (Switzerland) in 1951. It focuses on all aspects of spectroscopic methods and techniques (including applications), as well as computational and theoretical approaches for the investigation of structure, dynamics, and properties of molecular systems.
This Congress covers various scientific topics including vibrational, electronic and rotational spectroscopies, spectroscopy of surfaces and interfaces, spectroscopy of biological molecules, computational methods in spectroscopy, applied spectroscopies (archaeology, geology, mineralogy, arts, environmental analysis, food analysis, and processing), new materials, and time-resolved spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
Dibenzo-18-crown-6 is the organic compound with the formula [OCHOCHCHOCHCH]. It is a white solid that is soluble in organic solvents. As one of the most popular crown ethers, it facilitates the dissolution of many salts in organic solvents. It is related to the non-benzannulated 18-crown-6.
Dibenzo-18-crown-6 can be synthesized from catechol and bis(chloroethyl) ether.
In contrast to those of 18-crown-6, complexes of the dibenzo crown are flattened, which often allows higher coordination numbers at the encapsulated metal cation. | 0 | Theoretical and Fundamental Chemistry |
A typical action potential begins at the axon hillock with a sufficiently strong depolarization, e.g., a stimulus that increases V. This depolarization is often caused by the injection of extra sodium cations into the cell; these cations can come from a wide variety of sources, such as chemical synapses, sensory neurons or pacemaker potentials.
For a neuron at rest, there is a high concentration of sodium and chloride ions in the extracellular fluid compared to the intracellular fluid, while there is a high concentration of potassium ions in the intracellular fluid compared to the extracellular fluid. The difference in concentrations, which causes ions to move from a high to a low concentration, and electrostatic effects (attraction of opposite charges) are responsible for the movement of ions in and out of the neuron. The inside of a neuron has a negative charge, relative to the cell exterior, from the movement of K out of the cell. The neuron membrane is more permeable to K than to other ions, allowing this ion to selectively move out of the cell, down its concentration gradient. This concentration gradient along with potassium leak channels present on the membrane of the neuron causes an efflux of potassium ions making the resting potential close to E ≈ –75 mV. Since Na ions are in higher concentrations outside of the cell, the concentration and voltage differences both drive them into the cell when Na channels open. Depolarization opens both the sodium and potassium channels in the membrane, allowing the ions to flow into and out of the axon, respectively. If the depolarization is small (say, increasing V from −70 mV to −60 mV), the outward potassium current overwhelms the inward sodium current and the membrane repolarizes back to its normal resting potential around −70 mV. However, if the depolarization is large enough, the inward sodium current increases more than the outward potassium current and a runaway condition (positive feedback) results: the more inward current there is, the more V increases, which in turn further increases the inward current. A sufficiently strong depolarization (increase in V) causes the voltage-sensitive sodium channels to open; the increasing permeability to sodium drives V closer to the sodium equilibrium voltage E≈ +55 mV. The increasing voltage in turn causes even more sodium channels to open, which pushes V still further towards E. This positive feedback continues until the sodium channels are fully open and V is close to E. The sharp rise in V and sodium permeability correspond to the rising phase of the action potential.
The critical threshold voltage for this runaway condition is usually around −45 mV, but it depends on the recent activity of the axon. A cell that has just fired an action potential cannot fire another one immediately, since the Na channels have not recovered from the inactivated state. The period during which no new action potential can be fired is called the absolute refractory period. At longer times, after some but not all of the ion channels have recovered, the axon can be stimulated to produce another action potential, but with a higher threshold, requiring a much stronger depolarization, e.g., to −30 mV. The period during which action potentials are unusually difficult to evoke is called the relative refractory period. | 0 | Theoretical and Fundamental Chemistry |
After recognizing an antigen, an antigen-presenting cell such as the macrophage or B lymphocyte engulfs it completely by a process called phagocytosis. The engulfed particle, along with some material surrounding it, forms the endocytic vesicle (the phagosome), which fuses with lysosomes. Within the lysosome, the antigen is broken down into smaller pieces called peptides by proteases (enzymes that degrade larger proteins). The individual peptides are then complexed with major histocompatibility complex class II (MHC class II) molecules located in the lysosome – this method of "handling" the antigen is known as the exogenous or endocytic pathway of antigen processing in contrast to the endogenous or cytosolic pathway, which complexes the abnormal proteins produced within the cell (e.g. under the influence of a viral infection or in a tumor cell) with MHC class I molecules.
An alternate pathway of endocytic processing had also been demonstrated wherein certain proteins like fibrinogen and myoglobin can bind as a whole to MHC-II molecules after they are denatured and their disulfide bonds are reduced (breaking the bond by adding hydrogen atoms across it). The proteases then degrade the exposed regions of the protein-MHC II-complex. | 1 | Applied and Interdisciplinary Chemistry |
The so-called "Heidelberg-Moscow collaboration" (HDM; 1990–2003) of the German Max-Planck-Institut für Kernphysik and the Russian science center Kurchatov Institute in Moscow famously claimed to have found "evidence for neutrinoless double beta decay" (Heidelberg-Moscow controversy). Initially, in 2001 the collaboration announced a 2.2σ, or a 3.1σ (depending on the used calculation method) evidence. The decay rate was found to be around years. This result has been topic of discussions between many scientists and authors. To this day, no other experiment has ever confirmed or approved the result of the HDM group. Instead, recent results from the GERDA experiment for the lifetime limit clearly disfavor and reject the values of the HDM collaboration.
Neutrinoless double beta decay has not yet been found. | 0 | Theoretical and Fundamental Chemistry |
Sulfation is a relatively slow reaction (several hours) compared with carbonation ( will come into contact with CaCO than CaO. However, both reactions are possible, and are shown below.
:Indirect sulfation: CaO + SO + 1/2 O → CaSO
:Direct sulfation: CaCO + + 1/2 O → CaSO + CO
Because calcium sulfate has a greater molar volume than either CaO or CaCO a sulfated layer will form on the outside of the particle, which can prevent the uptake of CO by the CaO further inside the particle. Furthermore, the temperature at which calcium sulfate dissociates to CaO and SO is relatively high, precluding sulfation's reversibility at the conditions present in CaL. | 1 | Applied and Interdisciplinary Chemistry |
Lightweighting is a concept in the auto industry about building cars and trucks that are less heavy as a way to achieve better fuel efficiency, battery range, acceleration, braking and handling. In addition, lighter vehicles can tow and haul larger loads because the engine is not carrying unnecessary weight. Excessive vehicle weight is also a contributing factor to particulate emissions from tyre and brake wear.
Carmakers make body structure parts from aluminium sheet, aluminium extrusions,press hardening steel, carbon fibers, windshields from plastic, and bumpers out of aluminum foam, as ways to lessen vehicle load. Replacing car parts with lighter materials does not lessen overall safety for drivers, according to one view, since many grades of aluminium and plastics have a high strength-to-weight ratio; and aluminum has high energy absorption properties for its weight.
The search to replace car parts with lighter ones is not limited to any one type of part; according to a spokesman for Ford Motor Company, engineers strive for lightweighting "anywhere we can." Using lightweight materials such as plastics, high strength steels and aluminium can mean less strain on the engine and better gas mileage as well as improved handling. One material sometimes used to reduce weight for structures that can accept the cost premium is carbon fiber. The auto industry has used the term for many years, as the effort to keep making cars lighter is ongoing.
Another common material used for lightweighting is aluminum. Incorporating aluminum has grown continuously to not only meet CAFE standards but to also improve automotive performance. A light
weighting magazine finds: "Even though aluminum is light, it does not sacrifice strength. Aluminum body structure is equal in strength to steel and can absorb twice as much crash-induced energy." The use of aluminium for lightweighting can be limited for the higher strength grades by their low formability - and in response to this forming challenge new techniques such as roll forming and hot forming (Hot Form Quench) have been introduced in recent years.
Many other materials are used to meet lightweighting goals. Cost of lightweighting, and increasingly sustainability of materials, is becoming an issue in solution selection - with the viable cost increase of a part per kilogram saved being between $5 and $15, depending on the price point and performance needs of the vehicle. | 1 | Applied and Interdisciplinary Chemistry |
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