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There are many factors at play in even a basic melt spinning process. The quality and dimensions of the product are determined by how the machine is operated and configured. Consequently, there are many studies exploring the effects of variations in the melt spinner's configuration on specific alloys. For example, [https://www.jstage.jst.go.jp/article/matertrans1960/21/4/21_4_219/_article here] is an article about the specific conditions that were found to work well for melt spinning Fe-B and Fe-Si-B alloys.
In general, melt spinners will run with some variation in the following variables depending on the desired product.
* Nozzle gap: The distance between the nozzle and the cooled drum. Primarily affects ribbon thickness.
* Nozzle shape: The shape of the nozzle ejecting the molten material onto the drum. Nozzles allowing for a larger melt puddle on the drum's surface result in wider ribbons.
* Flow rate: The flow rate of melt onto the drum. The flow rate is usually closely related to the rotational speed of the drum. Mainly affects the width and thickness of the ribbons.
* Rotational speed: The speed at which the drum rotates. In general, a faster drum makes thinner ribbons.
* Drum temperature: The temperature at which the drum operates. Mainly affects the atomic structure of the resulting ribbon. Different alloys form best at specific temperatures.
Since every material acts differently, the exact cause-effect relationship between each of these variables and the resulting ribbon is usually determined experimentally. Other less commonly adjusted variables exist, but their effects on the final ribbon dimensions and structure aren't all documented. | 8 | Metallurgy |
The executive council of the Committee for Skeptical Inquiry (CSI) voted in April 2011 to include Walter McCrone in its "Pantheon of Skeptics". The Pantheon of Skeptics commemorates deceased distinguished fellows of CSI and their exceptional contributions to the cause of scientific skepticism. | 3 | Analytical Chemistry |
Since the method requires no binder, balsam or glue, the physical properties of the bound object are the same as the objects joined. Typically, glues and binders are more heat sensitive or have undesirable properties compared to the actual bodies being joined. The use of optical contact bonding allows the production of a final product with properties as good as the bulk solid. This can include temperature and chemical resistances, spectral absorption properties and reduced contamination from bonding materials. | 6 | Supramolecular Chemistry |
The term "ionic liquid" in the general sense was used as early as 1943.
The discovery date of the "first" ionic liquid is disputed, along with the identity of its discoverer. Ethanolammonium nitrate (m.p. 52–55 °C) was reported in 1888 by S. Gabriel and J. Weiner. In 1911 Ray and Rakshit, during preparation of the nitrite salts of ethylamine, dimethylamine, and trimethylamine observed that the reaction between ethylamine hydrochloride and silver nitrate yielded an unstable Ethylammonium nitrite ()· , a heavy yellow liquid which on immersion in a mixture of salt and ice could not be solidified and was probably the first report of room temperature ionic liquid. Later in 1914, Paul Walden reported one of the first stable room temperature ionic liquids ethylammonium nitrate ()· (m.p. 12 °C). In the 1970s and 1980s, ionic liquids based on alkyl-substituted imidazolium and pyridinium cations, with halide or tetrahalogenoaluminate anions, were developed as potential electrolytes in batteries.
For the imidazolium halogenoaluminate salts, their physical properties—such as viscosity, melting point, and acidity—could be adjusted by changing the alkyl substituents and the imidazolium/pyridinium and halide/halogenoaluminate ratios. Two major drawbacks for some applications were moisture sensitivity and acidity or basicity. In 1992, Wilkes and Zawarotko obtained ionic liquids with neutral weakly coordinating anions such as hexafluorophosphate () and tetrafluoroborate (), allowing a much wider range of applications. | 7 | Physical Chemistry |
A meter is a thermodynamic system which displays some aspect of its thermodynamic state to the observer. The nature of its contact with the system it is measuring can be controlled, and it is sufficiently small that it does not appreciably affect the state of the system being measured. The theoretical thermometer described below is just such a meter.
In some cases, the thermodynamic parameter is actually defined in terms of an idealized measuring instrument. For example, the zeroth law of thermodynamics states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This principle, as noted by James Maxwell in 1872, asserts that it is possible to measure temperature. An idealized thermometer is a sample of an ideal gas at constant pressure.
From the ideal gas law, the volume of such a sample can be used as an indicator of temperature; in this manner it defines temperature. Although pressure is defined mechanically, a pressure-measuring device called a barometer may also be constructed from a sample of an ideal gas held at a constant temperature. A calorimeter is a device which is used to measure and define the internal energy of a system.
Some common thermodynamic meters are:
* Thermometer - a device which measures temperature as described above
* Barometer - a device which measures pressure, most notably atmospheric pressure. An ideal gas barometer may be constructed by mechanically connecting an ideal gas to the system being measured, while thermally insulating it. The volume will then measure pressure, by the ideal gas equation P=NkT/V .
* Calorimeter - a device which measures the heat energy added to a system. A simple calorimeter is simply a thermometer connected to a thermally isolated system. | 7 | Physical Chemistry |
The IUPAC recommended name for phosphorous acid is phosphonic acid. Correspondingly, the IUPAC-recommended name for the ion is phosphonate. In the US the IUPAC naming conventions for inorganic compounds are taught at high school, but not as a required part of the curriculum. A well-known university-level textbook follows the IUPAC recommendations. In practice any reference to "phosphite" should be investigated to determine the naming convention being employed. | 0 | Organic Chemistry |
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems.
The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle. Human modification of the global nitrogen cycle can negatively affect the natural environment system and also human health. | 1 | Biochemistry |
Many possible applications have been suggested over years for LM and LB films. Their characteristics are extremely thin films and high degree of structural order. These films have different optical, electrical and biological properties which are composed of some specific organic compounds. Organic compounds usually have more positive responses than inorganic materials for outside factors (pressure, temperature or gas change). LM films can be used also as models for half a cellular membrane.
* LB films consisting of nanoparticles can be used for example to create functional coatings, sophisticated sensor surfaces and to coat silicon wafers.
* LB films can be used as passive layers in MIS (metal-insulator-semiconductor) which have more open structure than silicon oxide, and they allow gases to penetrate to the interface more effectively.
* LB films also can be used as biological membranes. Lipid molecules with the fatty acid moiety of long carbon chains attached to a polar group have received extended attention because of being naturally suited to the Langmuir method of film production. This type of biological membrane can be used to investigate: the modes of drug action, the permeability of biologically active molecules, and the chain reactions of biological systems.
* Also, it is possible to propose field effect devices for observing the immunological response and enzyme-substrate reactions by collecting biological molecules such as antibodies and enzymes in insulating LB films.
* Anti-reflective glass can be produced with successive layers of fluorinated organic film.
* The glucose biosensor can be made of poly(3-hexyl thiopene) as Langmuir–Blodgett film, which entraps glucose-oxide and transfers it to a coated indium-tin-oxide glass plate.
* UV resists can be made of poly(N-alkylmethacrylamides) Langmuir–Blodgett film.
* UV light and conductivity of a Langmuir–Blodgett film.
* Langmuir–Blodgett films are inherently 2D-structures and can be built up layer by layer, by dipping hydrophobic or hydrophilic substrates into a liquid sub-phase.
* Langmuir–Blodgett patterning is a new paradigm for large-area patterning with mesostructured features
* Recently, it has been demonstrated that Langmuir–Blodgett is an effective technique even to produce ultra-thin films of emerging two-dimensional layered materials on a large scale. | 7 | Physical Chemistry |
FSL Kode constructs have been used for research and development, diagnostic products, and are currently being investigated as potential therapeutic agents. | 1 | Biochemistry |
For the special case of simple cubic crystals, the lattice vectors are orthogonal and of equal length (usually denoted a), as are those of the reciprocal lattice. Thus, in this common case, the Miller indices (hkℓ) and [hkℓ] both simply denote normals/directions in Cartesian coordinates.
For cubic crystals with lattice constant a, the spacing d between adjacent (hkℓ) lattice planes is (from above)
Because of the symmetry of cubic crystals, it is possible to change the place and sign of the integers and have equivalent directions and planes:
*Indices in angle brackets such as ⟨100⟩ denote a family of directions which are equivalent due to symmetry operations, such as [100], [010], [001] or the negative of any of those directions.
*Indices in curly brackets or braces such as {100} denote a family of plane normals which are equivalent due to symmetry operations, much the way angle brackets denote a family of directions.
For face-centered cubic and body-centered cubic lattices, the primitive lattice vectors are not orthogonal. However, in these cases the Miller indices are conventionally defined relative to the lattice vectors of the cubic supercell and hence are again simply the Cartesian directions. | 3 | Analytical Chemistry |
In his last years, Walden focused on history of chemistry and collected a unique library of over 10,000 volumes. The library and his house were destroyed when the British bombed Rostock in 1942. Walden moved to Berlin and then to Frankfurt am Main, where he became a visiting professor of the history of chemistry at the local university. He met the end of World War II in the French Occupation Zone, cut off from Rostock University, located in the Soviet Zone, and thus left without any source of income.
Walden survived on a modest pension arranged by German chemists, giving occasional lectures in Tübingen and writing memoirs. In 1949, he published his best-known book, History of Chemistry. He died in Gammertingen in 1957, at the age of 93. His memoirs were published only in 1974. | 4 | Stereochemistry |
The non-random two-liquid model (abbreviated NRTL model) is an activity coefficient model introduced by Renon
and Prausnitz in 1968 that correlates the activity coefficients of a compound with its mole fractions in the liquid phase concerned. It is frequently applied in the field of chemical engineering to calculate phase equilibria. The concept of NRTL is based on the hypothesis of Wilson, who stated that the local concentration around a molecule in most mixtures is different from the bulk concentration. This difference is due to a difference between the interaction energy of the central molecule with the molecules of its own kind and that with the molecules of the other kind . The energy difference also introduces a non-randomness at the local molecular level. The NRTL model belongs to the so-called local-composition models. Other models of this type are the Wilson model, the UNIQUAC model, and the group contribution model UNIFAC. These local-composition models are not thermodynamically consistent for a one-fluid model for a real mixture due to the assumption that the local composition around molecule i is independent of the local composition around molecule j. This assumption is not true, as was shown by Flemr in 1976. However, they are consistent if a hypothetical two-liquid model is used. Models, which have consistency between bulk and the local molecular concentrations around different types of molecules are COSMO-RS, and COSMOSPACE. | 7 | Physical Chemistry |
A blank value in analytical chemistry is a measurement of a blank. The reading does not originate from a sample, but the matrix effects, reagents and other residues. These contribute to the sample value in the analytical measurement and therefore have to be subtracted.
The limit of blank is defined by the Clinical And Laboratory Standards Institute as the highest apparent analyte concentration expected to be found when replicates of a sample containing no analyte are tested. | 3 | Analytical Chemistry |
Noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) is an ultra-sensitive laser-based absorption technique that utilizes laser light to assess the concentration or the amount of a species in gas phase by absorption spectrometry (AS). | 7 | Physical Chemistry |
The product of layer thickness (d) and elevation height (h) is constant (d·h = constant), the two quantities are inversely proportional. The surface of the liquid between the planes is hyperbola. | 7 | Physical Chemistry |
Pre-computed results for biological assemblies
For a lot of proteins deposited in Protein Data Bank, the asymmetric unit might be different from biological unit, which would make the computational result biologically irrelevant. So the new CASTp 3.0 computed the topological features for biological assemblies, overcome the barriers between asymmetric unit and biological assemblies.
Imprints of negative volumes of topological features
In the 1st release of CASTp server in 2006, only geometric and topological features of those surface atoms participated in the formation of protein pockets, cavities, and channels. The new CASTp added the "negative volume" of the space, referred to the space encompassed by the atoms formed these geometric and topological features.
Comprehensive annotation on single amino-acid polymorphism
The latest CASTp integrated protein annotations aligned with the sequence, including the brief feature, positions, description, and reference of the domains, motifs, and single amino-acid polymorphisms.
Improved user interface & convenient visualization
The new CASTp now incorporated 3Dmol.js for structural visualization, made users able to browse, to interact the protein 3D model, and to examine the computational results in latest web-browsers including Chrome, Firefox, Safari, et al. Users can pick their own representation style of the atoms which form each topographic feature, and to edit the colors by their own preferences. | 1 | Biochemistry |
The process of organohalide respiration, uses reductive dehalogenation to produce energy that can be used by the respiring microorganism to carry out its growth and metabolism. Halogenated organic compounds are used as the terminal electron acceptor, which results in their dehalogenation. Reductive dehalogenation is the process by which this occurs. It involves the reduction of halogenated compounds by removing the halogen substituents, while simultaneously adding electrons to the compound. Hydrogenolysis and vicinal reduction are the two known processes of this mechanism that have been identified. In both processes, the removed halogen substituents are released as anions. Reductive dehalogenation is catalyzed by reductive dehalogenases, which are membrane-associated enzymes. A number of not only membrane-associated but also cytoplasmic hydrogenases, in some cases as part of the protein complexes, are predicted to play roles in the organohalide respiration process. Most of these enzymes contain iron-sulfur (Fe-S) clusters, and a corrinoid cofactor at their active sites. Although the exact mechanism is unknown, research suggests that these two components of the enzyme may be involved in the reduction. | 7 | Physical Chemistry |
The delocalization of electrons across the structure of a radical, also known as its ability to form one or more resonance structures, allows for the electron-deficiency to be spread over several atoms, minimizing instability. Delocalization usually occurs in the presence of electron-donating groups, such as hydroxyl groups (−OH), ethers (−OR), adjacent alkenes, and amines (−NH or −NR), or electron-withdrawing groups, such as C=O or C≡N.
Delocalization effects can also be understood using molecular orbital theory as a lens, more specifically, by examining the intramolecular interaction of the unpaired electron with a donating group's pair of electrons or the empty π* orbital of an electron-withdrawing group in the form of a molecular orbital diagram. The HOMO of a radical is singly-occupied hence the orbital is aptly referred to as the SOMO, or the Singly-Occupied Molecular Orbital. For an electron-donating group, the SOMO interacts with the lower energy lone pair to form a new lower-energy filled bonding-orbital and a singly-filled new SOMO, higher in energy than the original. While the energy of the unpaired electron has increased, the decrease in energy of the lone pair forming the new bonding orbital outweighs the increase in energy of the new SOMO, resulting in a net decrease of the energy of the molecule. Therefore, electron-donating groups help stabilize radicals.
With a group that is instead electron-withdrawing, the SOMO then interacts with the empty π* orbital. There are no electrons occupying the higher energy orbital formed, while a new SOMO forms that is lower in energy. This results in a lower energy and higher stability of the radical species. Both donating groups and withdrawing groups stabilize radicals.
Another well-known albeit weaker form of delocalization is hyperconjugation. In radical chemistry, radicals are stabilized by hyperconjugation with adjacent alkyl groups. The donation of sigma (σ) C−H bonds into the partially empty radical orbitals helps to differentiate the stabilities of radicals on tertiary, secondary, and primary carbons. Tertiary carbon radicals have three σ C-H bonds that donate, secondary radicals only two, and primary radicals only one. Therefore, tertiary radicals are the most stable and primary radicals the least stable. | 2 | Environmental Chemistry |
Description of the Mono Lake tufa dates back to the 1880s, when Edward S. Dana and Israel C. Russell made the first systematic descriptions of the Mono Lake tufa. The tufa occurs as "modern" tufa towers. There are tufa sections from old shorelines, when the lake levels were higher. These pioneering works in tufa morphology are referred to by researchers and were confirmed by James R. Dunn in 1953. The tufa types can roughly be divided into three main categories based on morphology:
*Lithoid tufa - massive and porous with a rock-like appearance
*Dendritic tufa - branching structures that look similar to small shrubs
*Thinolitic tufa - large well-formed crystals of several centimeters
Through time, many hypotheses were developed regarding the formation of the large thinolite crystals (also referred to as glendonite) in thinolitic tufa. It was relatively clear that the thinolites represented a calcite pseudomorph after some unknown original crystal. The original crystal was only determined when the mineral ikaite was discovered in 1963. Ikaite, or hexahydrated CaCO, is metastable and only crystallizes at near-freezing temperatures. It is also believed that calcite crystallization inhibitors such as phosphate, magnesium, and organic carbon may aid in the stabilization of ikaite. When heated, ikaite breaks down and becomes replaced by smaller crystals of calcite. In the Ikka Fjord of Greenland, ikaite was also observed to grow in columns similar to the tufa towers of Mono Lake. This has led scientists to believe that thinolitic tufa is an indicator of past climates in Mono Lake because they reflect very cold temperatures. | 2 | Environmental Chemistry |
Higher L1 copy numbers have been observed in the human brain compared to other organs. Studies of animal models and human cell lines have shown that L1s become active in neural progenitor cells (NPCs), and that experimental deregulation of or overexpression of L1 increases somatic mosaicism. This phenomenon is negatively regulated by Sox2, which is downregulated in NPCs, and by MeCP2 and methylation of the L1 5' UTR. Human cell lines modeling the neurological disorder Rett syndrome, which carry MeCP2 mutations, exhibit increased L1 transposition, suggesting a link between L1 activity and neurological disorders. Current studies are aimed at investigating the potential roles of L1 activity in various neuropsychiatric disorders including schizophrenia, autism spectrum disorders, epilepsy, bipolar disorder, Tourette syndrome, and drug addiction. L1s are also highly expressed in octopus brain, suggesting a convergent mechanism in complex cognition. | 1 | Biochemistry |
In semiconductor physics the Photo-Dember effect (named after its discoverer H. Dember) consists in the formation of a charge dipole in the vicinity of a semiconductor surface after ultra-fast photo-generation of charge carriers. The dipole forms owing to the difference of mobilities (or diffusion constants) for holes and electrons which combined with the break of symmetry provided by the surface lead to an effective charge separation in the direction perpendicular to the surface. | 7 | Physical Chemistry |
Several chemical factors affect the ionophore activity. The activity of an ionophore-metal complex depends on its geometric configuration and the coordinating sites and atoms which create coordination environment surrounding the metal center. This affects the selectivity and affinity towards a certain ion. Ionophores can be selective to a particular ion but may not be exclusive to it. Ionophores facilitate the transport of ions across biological membranes most commonly via passive transport, which is affected by lipophilicity of the ionophore molecule. The increase in lipophilicity of the ionophore-metal complex enhances its permeability through lipophilic membranes. The hydrophobicity and hydrophilicity of the complex also determines whether it will slow down or ease the transport of metal ions into cell compartments. The reduction potential of a metal complex influences its thermodynamic stability and affects its reactivity. The ability of an ionophore to transfer ions is also affected by the temperature. | 7 | Physical Chemistry |
In AFM, feedback loops control the operation of the microscope by keeping a fixed value a parameter of the tip's oscillation. If the main feedback loop operates with the amplitude, the AFM mode is called amplitude modulation (AM). If it operates with the frequency shift, the AFM mode is called frequency modulation (FM). Bimodal AFM might be operated with several feedback loops. This gives rise to a variety of bimodal configurations. The configurations are termed AM-open loop, AM-FM, FM-FM. For example, bimodal AM-FM means that the first mode is operated with an amplitude modulation loop while the 2nd mode is operated with a frequency modulation loop. The configurations might not be equivalent in terms of sensitivity, signal-to-noise ratio or complexity.
Let's consider the AM-FM configuration. The first mode is excited to reach free amplitude (no interaction) and the changes of its amplitude and phase shift are tracked by a lock-in amplifier. The main feedback loop keeps constant the amplitude, at a certain set-point by modifying the tip vertical position (AM). In a nanomechanical mapping experiment, must be kept below 90°, i.e., the AFM is operated in the repulsive regime. At the same time, an FM loop acts on the second eigenmode. A phase-lock-loop regulates the excitation frequency by keeping the phase shift of the second mode at 90°. An additional feedback loop might be used to maintain the amplitude constant. | 6 | Supramolecular Chemistry |
MMC Estates and Countryside Properties subsequently released statements in September 2005 acknowledging that there was significant contamination on the site. Michael Drogan, director of MMC, said: "Following the completion of investigations, which have now been published, we recognise there is significant asbestos contamination in areas of the woodland and have evidence of pockets of contamination in other parts of the site." Rochdale councillor Tom Stott responded: "In their initial reports they said there was little contamination. Now it is significant. I am shocked that it has taken so long for the companies to admit what we have known for over 12 months." | 2 | Environmental Chemistry |
(E,E)-2,4-Decadienal is an aromatic substance found in butter, cooked beef, fish, potato chips, roasted peanut, buckwheat and wheat bread crumb.
In an isolated state, it smells of deep fat flavor, characteristic of chicken aroma (at 10ppm). At lower concentration, it has the odor of citrus, orange or grapefruit.
It might be carcinogenic. It has been used as aroma in the EU, but use restrictions apply until the required data have been submitted. | 1 | Biochemistry |
In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural polymers (such as proteins).
In polymer chemistry "cross-linking" usually refers to the use of cross-links to promote a change in the polymers' physical properties.
When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies.
Although the term is used to refer to the "linking of polymer chains" for both sciences, the extent of crosslinking and specificities of the crosslinking agents vary greatly. | 7 | Physical Chemistry |
The pseudo-Voigt profile (or pseudo-Voigt function) is an approximation of the Voigt profile V(x) using a linear combination of a Gaussian curve G(x) and a Lorentzian curve L(x) instead of their convolution.
The pseudo-Voigt function is often used for calculations of experimental spectral line shapes.
The mathematical definition of the normalized pseudo-Voigt profile is given by
where now, is a function of Lorentz (), Gaussian () and total () Full width at half maximum (FWHM) parameters. The total FWHM () parameter is described by: | 7 | Physical Chemistry |
One can characterise a surface that has undergone certain finishing operations by three main properties of: roughness, waviness, and fractal dimension. Among these, roughness and fractality are of most importance, with roughness often indicated in terms of a rms value, and surface fractality denoted generally by D. The effect of surface structures on thermal conductivity at interfaces is analogous to the concept of electrical contact resistance, also known as ECR, involving contact patch restricted transport of phonons rather than electrons. | 7 | Physical Chemistry |
The oxygen blast furnace (OBF) process has been extensively studied theoretically because of the potentials of promising energy conservation and emission reduction. This type may be the most suitable for use with CCS. The main blast furnace has of three levels; the reduction zone (), slag formation zone (), and the combustion zone ().
Blast furnaces are currently rarely used in copper smelting, but modern lead smelting blast furnaces are much shorter than iron blast furnaces and are rectangular in shape. Modern lead blast furnaces are constructed using water-cooled steel or copper jackets for the walls, and have no refractory linings in the side walls. The base of the furnace is a hearth of refractory material (bricks or castable refractory). Lead blast furnaces are often open-topped rather than having the charging bell used in iron blast furnaces.
The blast furnace used at the Nyrstar Port Pirie lead smelter differs from most other lead blast furnaces in that it has a double row of tuyeres rather than the single row normally used. The lower shaft of the furnace has a chair shape with the lower part of the shaft being narrower than the upper. The lower row of tuyeres being located in the narrow part of the shaft. This allows the upper part of the shaft to be wider than the standard. | 8 | Metallurgy |
The tin belt of Southeast Asia extends all the way down to Tasmania, but metals were not exploited in Australia until the arrival of Europeans in the 1780s. | 8 | Metallurgy |
A more complex use of reporter genes on a large scale is in two-hybrid screening, which aims to identify proteins that natively interact with one another in vivo. | 1 | Biochemistry |
Nucleotidomimetics do not generally qualify as foldamers. Most are designed to mimic single DNA bases, nucleosides, or nucleotides in order to nonspecifically target DNA. These have several different medicinal uses including anti-cancer, anti-viral, and anti-fungal applications. | 6 | Supramolecular Chemistry |
In organic chemistry, acyloins or α-hydroxy ketones are a class of organic compounds of the general form , composed of a hydroxy group () adjacent to a ketone group (). The name acyloin is derived from the fact that they are formally derived from reductive coupling of carboxylic acyl groups (). They are one of the two main classes of hydroxy ketones, distinguished by the position of the hydroxy group relative to the ketone; in this form, the hydroxy is on the alpha carbon, explaining the secondary name of α-hydroxy ketone. | 0 | Organic Chemistry |
The GPCR superfamily is the largest gene family in the human genome containing approximately 800 genes. As the vertebrate superfamily can be phylogenetically grouped into five main families, the GRAFS classification system has been proposed, which includes the glutamate, rhodopsin, adhesion, Frizzled/Taste2, and secretin GPCR families.
There are 33 human adhesion GPCRs that can be broken down into eight groups, with two independent receptors. Group I consists of LPHN1, LPHN2, LPHN3, and ETL. Group II consists of CD97, EMR1, EMR2, EMR3, and EMR4. Group III consists of GPR123, GPR124, and GPR125. Group IV consists of CELSR1, CELSR2, and CELSR3. Group V consists of GPR133 and GPR144. Group VI consists of GPR110, GPR111, GPR113, GPR115, and GPR116. Group VII consists of BAI1, BAI2, and BAI3. Group VIII consists of GPR56, GPR97, GPR112, GPR114, GPR126, and GPR64. Two additional adhesion GPCRs do not fit into these groups: VLGR1 and GPR128. | 1 | Biochemistry |
The Procellarum KREEP Terrane, or PKT, is a large province on the near side of the Moon that has high abundances of KREEP. KREEP is an acronym built from the letters K (the atomic symbol for potassium), REE (rare-earth elements) and P (for phosphorus), and is a geochemical component of some lunar impact breccia and basaltic rocks. Notably, it is high in the KREEP element thorium, at a level of 4.8 ppm. This is a major factor distinguishing it from the other terranes. The PKT is on the near side of the moon, and covers 10% of the lunar surface, or 16% if one includes the maria lying within the FHT. Despite this, it contains 60% of all basaltic flows. KREEP has been shown to lower the melting point of rocks similar to those found on the Moon, and is expected to have contributed to volcanism in the region.
The Oceanus Procellarum and Mare Imbrium regions lie within the PKT. In general, many maria, such as (but not limited to) Mare Frigoris and Mare Cognitum are members of the PKT. Not all maria are in the PKT, however - Mare Crisium and Mare Orientale are located within the outer Feldspathic Highlands.
The PKT is the only terrane to lie exclusively in the near side of the Moon. Human and robotic missions have been done to this terrane, and samples have been returned to Earth for further study. | 9 | Geochemistry |
P700, or photosystem I primary donor, is the reaction-center chlorophyll a molecular dimer associated with photosystem I in plants, algae, and cyanobacteria. | 5 | Photochemistry |
Convection can be "forced" by movement of a fluid by means other than buoyancy forces (for example, a water pump in an automobile engine). Thermal expansion of fluids may also force convection. In other cases, natural buoyancy forces alone are entirely responsible for fluid motion when the fluid is heated, and this process is called "natural convection". An example is the draft in a chimney or around any fire. In natural convection, an increase in temperature produces a reduction in density, which in turn causes fluid motion due to pressures and forces when the fluids of different densities are affected by gravity (or any g-force). For example, when water is heated on a stove, hot water from the bottom of the pan is displaced (or forced up) by the colder denser liquid, which falls. After heating has stopped, mixing and conduction from this natural convection eventually result in a nearly homogeneous density, and even temperature. Without the presence of gravity (or conditions that cause a g-force of any type), natural convection does not occur, and only forced-convection modes operate.
The convection heat transfer mode comprises two mechanism. In addition to energy transfer due to specific molecular motion (diffusion), energy is transferred by bulk, or macroscopic, motion of the fluid. This motion is associated with the fact that, at any instant, large numbers of molecules are moving collectively or as aggregates. Such motion, in the presence of a temperature gradient, contributes to heat transfer. Because the molecules in aggregate retain their random motion, the total heat transfer is then due to the superposition of energy transport by random motion of the molecules and by the bulk motion of the fluid. It is customary to use the term convection when referring to this cumulative transport and the term advection when referring to the transport due to bulk fluid motion. | 7 | Physical Chemistry |
Robert Emerson described the eponymous effect in 1957. In his paper he observed that:
# When plants are exposed to light having wavelength greater than 680 nm, then only one photosystem is activated; i.e. PS700 resulting in formation of ATP only.
# When plants are exposed to light having wavelength less than 680 nm, the rate of photosynthesis was very low.
# On giving both shorter and higher wavelengths of light, the efficiency of the process increased, because both photosystems were working together at the same time, resulting in higher yield. | 5 | Photochemistry |
Queuine (Q) is a modified nucleotide at position 34 in tRNA (queuosine is the name of the nucleoside, while queuine is the name of the nucleotide). Nucleotide modifications in tRNA are not uncommon, as tRNA is one of the most heavily modified types of RNA, and nearly 80 types of modified nucleotides have been identified. Queuosine is a very heavily modified version of guanosine (G). Modifications in tRNA have the well-known ability to control and modulate gene expression. The regulation of gene expression typically comes from some structural changes to the stem-loop structure of the tRNA. The editing that tRNA undergoes may have developed as a response to rare codons, and tRNA counteracts frameshifts by utilizing the modified bases. Other similar modifications to nucleotides impact the ability of tRNA to initiate translation, thus impeding gene expression.
This modification is particularly widespread and found amongst a variety of organisms, indicating that perhaps convergent evolution took place in the development of this nucleoside. Eukaryotic cells cannot synthesize queuosine, so they must rely on prokaryotes of the microbiome to produce and increase the availability of it within the body. Depleted levels of Q34 (queuine at position 34) are associated with the development of tumors. | 1 | Biochemistry |
The Tn7 transposon is a mobile genetic element found in many prokaryotes such as Escherichia coli (E. coli), and was first discovered as a DNA sequence in bacterial chromosomes and naturally occurring plasmids that encoded resistance to the antibiotics trimethoprim and streptomycin. Specifically classified as a transposable element (transposon), the sequence can duplicate and move itself within a genome by utilizing a self-encoded recombinase enzyme called a transposase, resulting in effects such as creating or reversing mutations and changing genome size. The Tn7 transposon has developed two mechanisms to promote its propagation among prokaryotes. Like many other bacterial transposons, Tn7 transposes at low-frequency and inserts into many different sites with little to no site-selectivity. Through this first pathway, Tn7 is preferentially directed into conjugable plasmids, which can be replicated and distributed between bacteria. However, Tn7 is unique in that it also transposes at high-frequency into a single specific site in bacterial chromosomes called attTn7. This specific sequence is an essential and highly conserved gene found in many strains of bacteria. However, the recombination is not deleterious to the host bacterium as Tn7 actually transposes downstream of the gene after recognizing it, resulting in a safe way to propagate the transposon without killing the host. This highly evolved and sophisticated target-site selection pathway suggests this pathway evolved to promote coexistence between the transposon and it host, as well as Tn7's successful transmission into future generations of bacterium.
The Tn7 transposon is 14 kb long and codes for five enzymes. The ends of the DNA sequence consists of two segments that the Tn7 transposase interacts with during recombination. The left segment (Tn7-L) is 150 bp long and the right sequence (Tn7-R) is 90 bp long. Both ends of the transposon contain a series of 22 bp binding sites that the Tn7 transposase recognizes and binds to. Within the transposon are five discrete genes encoding for proteins that make up the transposition machinery. In addition, the transposon contains an integron, a DNA segment containing several cassettes of genes encoding for antibiotic-resistance.
The Tn7 transposon codes for five proteins: TnsA, TnsB, TnsC, TnsD, and TnsE. TnsA and TnsB interact together to form the Tn7 transposase enzyme TnsAB. The enzyme specifically recognizes and binds to the ends of the DNA sequence of the transposon, and excises it by introducing double-stranded DNA breaks to each end. The excised sequence is then inserted to another target DNA site. Much like other characterized transposons, the mechanism for Tn7 transposition involves cleavage of the 3 ends from the donating DNA by the TnsA protein of the TnsAB transposase. However, Tn7 is also uniquely cleaved near the 5 ends, about 5 bp from the 5 end towards the Tn7 transposon, by the TnsB protein of TnsAB. After the insertion of the transposon into the target DNA site, the 3 ends are covalently linked to the target DNA, but the 5 bp gaps are still present at the 5 ends. As a result, repair of these gaps leads to a further 5 bp duplication at the target site. The TnsC protein interacts with the transposase enzyme and the target DNA to promote the excision and insertion processes. The ability of TnsC to activate the transposase depends on its interaction with a target DNA along with its appropriate targeting protein, TnsD or TnsE. The TnsD and TnsE proteins are alternative target selectors that are also DNA binding activators that promote excision and insertion of Tn7. Their ability to interact with a particular target DNA is key to the target-site selection of Tn7. The proteins TnsA, TnsB, and TnsC thus form the core machinery of Tn7: TnsA and TnsB interact together to form the transposase, while TnsC functions as a regulator of the transposases activity, communicating between the transposase and TnsD and TnsE. When the TnsE protein interacts with the TnsABC core machinery, Tn7 preferentially directs insertions into conjugable plasmids. When the TnsD protein interacts with TnsABC, Tn7 preferentially directs insertions downstream into a single essential and highly conserved site in the bacterial chromosome. This site, attTn7, is specifically recognized by TnsD. | 1 | Biochemistry |
At equilibrium the rate of the forward reaction is equal to the backward reaction rate. A simple reaction, such as ester hydrolysis
has reaction rates given by expressions
According to Guldberg and Waage, equilibrium is attained when the forward and backward reaction rates are equal to each other. In these circumstances, an equilibrium constant is defined to be equal to the ratio of the forward and backward reaction rate constants
The concentration of water may be taken to be constant, resulting in the simpler expression
This particular concentration quotient, , has the dimension of concentration, but the thermodynamic equilibrium constant, , is always dimensionless. | 7 | Physical Chemistry |
Michael Polanyi, FRS (11 March 1891 – 22 February 1976) was a Hungarian polymath, who made theoretical contribution to physical chemistry, economics, and philosophy. Polanyi was a well known theoretical chemist who contributed to the chemistry field through three main areas of study: adsorption of gases on solids, x-ray structure analysis of the properties of solids, and the rate of chemical reactions. However, Polanyi was active in both theoretical and experimental studies within the Chemistry field. Polanyi obtained a degree in medicine in 1913 as well as a Ph.D. in physical chemistry in 1917 from the University of Budapest. Later in his life, he taught as a chemistry professor at the Kaiser Wilhelm Institute in Berlin as well as the University of Manchester in Manchester, England. | 7 | Physical Chemistry |
In bipolar disorder, one commonly identified endophenotype is a deficit in face emotion labeling, which is found in both individuals with bipolar disorder and in individuals who are "at risk" (i.e., have a first degree relative with bipolar disorder). Using fMRI, this endophenotype has been linked to dysfunction in the dorsolateral and ventrolateral prefrontal cortex, anterior cingulate cortex, striatum, and amygdala. A polymorphism in the CACNA1C gene coding for the voltage-dependent calcium channel Ca1.2 has been found to be associated with deficits in facial emotion recognition. | 2 | Environmental Chemistry |
While the exact epistasis of Imd pathway signalling components is continually scrutinized, the mechanistic order of many key components of the pathway is well-established. The following sections discuss Imd signalling as it is found in Drosophila melanogaster, where it is exceptionally well-characterized. Imd signalling is activated by a series of steps from recognition of a bacterial substance (e.g. peptidoglycan) to the transmission of that signal leading to activation of the NF-κB transcription factor Relish. Activated Relish then forms dimers that move into the nucleus and bind to DNA leading to the transcription of antimicrobial peptides and other effectors. | 1 | Biochemistry |
The Gaia hypothesis continues to be broadly skeptically received by the scientific community. For instance, arguments both for and against it were laid out in the journal Climatic Change in 2002 and 2003. A significant argument raised against it are the many examples where life has had a detrimental or destabilising effect on the environment rather than acting to regulate it. Several recent books have criticised the Gaia hypothesis, expressing views ranging from "... the Gaia hypothesis lacks unambiguous observational support and has significant theoretical difficulties" to "Suspended uncomfortably between tainted metaphor, fact, and false science, I prefer to leave Gaia firmly in the background" to "The Gaia hypothesis is supported neither by evolutionary theory nor by the empirical evidence of the geological record". The CLAW hypothesis, initially suggested as a potential example of direct Gaian feedback, has subsequently been found to be less credible as understanding of cloud condensation nuclei has improved. In 2009 the Medea hypothesis was proposed: that life has highly detrimental (biocidal) impacts on planetary conditions, in direct opposition to the Gaia hypothesis.
In a 2013 book-length evaluation of the Gaia hypothesis considering modern evidence from across the various relevant disciplines, Toby Tyrrell concluded that: "I believe Gaia is a dead end. Its study has, however, generated many new and thought provoking questions. While rejecting Gaia, we can at the same time appreciate Lovelock's originality and breadth of vision, and recognize that his audacious concept has helped to stimulate many new ideas about the Earth, and to champion a holistic approach to studying it". Elsewhere he presents his conclusion "The Gaia hypothesis is not an accurate picture of how our world works". This statement needs to be understood as referring to the "strong" and "moderate" forms of Gaia—that the biota obeys a principle that works to make Earth optimal (strength 5) or favourable for life (strength 4) or that it works as a homeostatic mechanism (strength 3). The latter is the "weakest" form of Gaia that Lovelock has advocated. Tyrrell rejects it. However, he finds that the two weaker forms of Gaia—Coeveolutionary Gaia and Influential Gaia, which assert that there are close links between the evolution of life and the environment and that biology affects the physical and chemical environment—are both credible, but that it is not useful to use the term "Gaia" in this sense and that those two forms were already accepted and explained by the processes of natural selection and adaptation. | 9 | Geochemistry |
Chlorprothixene was the first of the thioxanthene antipsychotics to be synthesized. It was introduced in 1959 by Lundbeck.
Lometraline, tametraline, and sertraline were reportedly derived via structural modification of chlorprothixene. | 4 | Stereochemistry |
The journal is abstracted and indexed in:
*Chemical Abstracts
*Current Contents/Engineering, Computing & Technology
*Inspec
*Materials Science Citation Index
*Scopus
According to the Journal Citation Reports, the journal has a 2020 impact factor of 7.205. | 8 | Metallurgy |
Markovnikov married Lyubov Dmitrievna Rychkova. They had two sons, Vladimir, a politician and Nikolai, an architect. | 0 | Organic Chemistry |
Brown was born Herbert Brovarnik in London, to Ukrainian Jewish immigrants from Zhitomir, Pearl (née Gorinstein) and Charles Brovarnik, a hardware store manager and carpenter. His family moved to Chicago in June 1914, when he was two years old. Brown attended Crane Junior College in Chicago, where he met Sarah Baylen, whom he would later marry. The college was under threat of closing, and Brown and Baylen transferred to Wright Junior College. In 1935 he left Wright Junior College and that autumn entered the University of Chicago, completed two years of studies in three quarters, and earned a B.S. in 1936. That same year, he became a naturalized United States citizen. On February 6, 1937, Brown married Baylen, the person he credits with making him interested in hydrides of boron, a topic related to the work in which he, together with Georg Wittig, won the Nobel prize in Chemistry in 1979. Two years after starting graduate studies, he earned a Ph.D. in 1938, also from the University of Chicago.
Unable to find a position in industry, he decided to accept a postdoctoral position. This became the beginning of his academic career. He became an instructor at the University of Chicago in 1939, and held the position for four years before moving to Wayne University in Detroit as an assistant professor. In 1946, he was promoted to associate professor. He became a professor of inorganic chemistry at Purdue University in 1947 and joined the Beta Nu chapter of Alpha Chi Sigma there in 1960. He held the position of Professor Emeritus from 1978 until his death in 2004. The Herbert C. Brown Laboratory of Chemistry was named after him on Purdue University's campus. He was an honorary member of the International Academy of Science, Munich.
During World War II, while working with Hermann Irving Schlesinger, Brown discovered a method for producing sodium borohydride (NaBH), which can be used to produce boranes, compounds of boron and hydrogen. His work led to the discovery of the first general method for producing asymmetric pure enantiomers. The elements found as initials of his name H, C and B were his working field.
In 1969, he was awarded the National Medal of Science.
Brown was quick to credit his wife Sarah with supporting him and allowing him to focus on creative efforts by handling finances, maintaining the house and yard, etc. According to Brown, after receiving the Nobel prize in Stockholm, he carried the medal and she carried the US$100,000 award.
In 1971, he received the Golden Plate Award of the American Academy of Achievement.
He was inducted into the Alpha Chi Sigma Hall of Fame in 2000.
He died December 19, 2004, at a hospital in Lafayette, Indiana after a heart attack. His wife died May 29, 2005, aged 89. | 4 | Stereochemistry |
The dangerous goods definition of an oxidizing agent is a substance that can cause or contribute to the combustion of other material. By this definition some materials that are classified as oxidizing agents by analytical chemists are not classified as oxidizing agents in a dangerous materials sense. An example is potassium dichromate, which does not pass the dangerous goods test of an oxidizing agent.
The U.S. Department of Transportation defines oxidizing agents specifically. There are two definitions for oxidizing agents governed under DOT regulations. These two are Class 5; Division 5.1(a)1 and Class 5; Division 5.1(a)2. Division 5.1 "means a material that may, generally by yielding oxygen, cause or enhance the combustion of other materials." Division 5.(a)1 of the DOT code applies to solid oxidizers "if, when tested in accordance with the UN Manual of Tests and Criteria (IBR, see § 171.7 of this subchapter), its mean burning time is less than or equal to the burning time of a 3:7 potassium bromate/cellulose mixture." 5.1(a)2 of the DOT code applies to liquid oxidizers "if, when tested in accordance with the UN Manual of Tests and Criteria, it spontaneously ignites or its mean time for a pressure rise from 690 kPa to 2070 kPa gauge is less than the time of a 1:1 nitric acid (65 percent)/cellulose mixture." | 7 | Physical Chemistry |
If the gas is ideal, both the initial (, , ) and final (, , ) conditions follow the Ideal Gas Law, so that initially
and then, after the tap is opened,
Here is the number of moles of gas and is the molar ideal gas constant. Because the internal energy does not change and the internal energy of an ideal gas is solely a function of temperature, the temperature of the gas does not change; therefore . This implies that
Therefore if the volume doubles, the pressure halves.
The fact that the temperature does not change makes it easy to compute the change in entropy of the universe for this process. | 7 | Physical Chemistry |
In chemistry, an open-chain compound (or open chain compound) or acyclic compound (Greek prefix α without and κύκλος cycle) is a compound with a linear structure, rather than a cyclic one.
An open-chain compound having no side groups is called a straight-chain compound (also spelled as straight chain compound). Many of the simple molecules of organic chemistry, such as the alkanes and alkenes, have both linear and ring isomers, that is, both acyclic and cyclic. For those with 4 or more carbons, the linear forms can have straight-chain or branched-chain isomers. The lowercase prefix n- denotes the straight-chain isomer; for example, n-butane is straight-chain butane, whereas i-butane is isobutane. Cycloalkanes are isomers of alkenes, not of alkanes, because the ring's closure involves a C-C bond. Having no rings (aromatic or otherwise), all open-chain compounds are aliphatic.
Typically in biochemistry, some isomers are more prevalent than others. For example, in living organisms, the open-chain isomer of glucose usually exists only transiently, in small amounts; D-glucose is the usual isomer; and L-glucose is rare.
Straight-chain molecules are often not literally straight, in the sense that their bond angles are often not 180°, but the name reflects that they are schematically straight. For example, the straight-chain alkanes are wavy or "puckered", as the models below show. | 4 | Stereochemistry |
Function-Spacer-Lipid (FSL) Kode constructs (Kode Technology) are amphiphatic, water dispersible biosurface engineering constructs that can be used to engineer the surface of cells, viruses and organisms, or to modify solutions and non-biological surfaces with bioactives. FSL Kode constructs spontaneously and stably incorporate into cell membranes. FSL Kode constructs with all these aforementioned features are also known as Kode Constructs. The process of modifying surfaces with FSL Kode constructs is known as "koding" and the resultant "koded" cells, viruses and liposomes are respectively known as kodecytes, and kodevirions. | 1 | Biochemistry |
In thermodynamics, enthalpy–entropy compensation is a specific example of the compensation effect. The compensation effect refers to the behavior of a series of closely related chemical reactions (e.g., reactants in different solvents or reactants differing only in a single substituent), which exhibit a linear relationship between one of the following kinetic or thermodynamic parameters for describing the reactions:
# Between the logarithm of the pre-exponential factors (or prefactors) and the activation energies where the series of closely related reactions are indicated by the index , are the preexponential factors, are the activation energies, is the gas constant, and are constants.
# Between enthalpies and entropies of activation (enthalpy–entropy compensation) where are the enthalpies of activation and are the entropies of activation.
# Between the enthalpy and entropy changes of a series of similar reactions (enthalpy–entropy compensation) where are the enthalpy changes and are the entropy changes.
When the activation energy is varied in the first instance, we may observe a related change in pre-exponential factors. An increase in tends to compensate for an increase in , which is why we call this phenomenon a compensation effect. Similarly, for the second and third instances, in accordance with the Gibbs free energy equation, with which we derive the listed equations, scales proportionately with . The enthalpy and entropy compensate for each other because of their opposite algebraic signs in the Gibbs equation.
A correlation between enthalpy and entropy has been observed for a wide variety of reactions. The correlation is significant because, for linear free-energy relationships (LFERs) to hold, one of three conditions for the relationship between enthalpy and entropy for a series of reactions must be met, with the most common encountered scenario being that which describes enthalpy–entropy compensation. The empirical relations above were noticed by several investigators beginning in the 1920s, since which the compensatory effects they govern have been identified under different aliases. | 7 | Physical Chemistry |
Bronze disease is an irreversible and nearly inexorable corrosion process that occurs when chlorides come into contact with bronze or other copper-bearing alloys. It can occur as both a dark green coating, or as a much lighter whitish fuzzy or furry green coating. It is not a bacterial infection, but the result of a chemical reaction with the chlorides that usually occurs due to contamination of the bronze object by saltwater or from burial in specific types of soil where chloride salts are present. If not treated, complete destruction of the affected artifact is possible. Treatment is very difficult, costly and not always effective. Transfer of chlorides from the contaminated artefact to other artefacts can spread the condition. | 8 | Metallurgy |
In electrophilic aromatic substitution reactions, existing substituent groups on the aromatic ring influence the overall reaction rate or have a directing effect on positional isomer of the products that are formed.
An electron donating group (EDG) or electron releasing group (ERG, Z in structural formulas) is an atom or functional group that donates some of its electron density into a conjugated π system via resonance (mesomerism) or inductive effects (or induction)—called +M or +I effects, respectively—thus making the π system more nucleophilic. As a result of these electronic effects, an aromatic ring to which such a group is attached is more likely to participate in electrophilic substitution reaction. EDGs are therefore often known as activating groups, though steric effects can interfere with the reaction.
An electron withdrawing group (EWG) will have the opposite effect on the nucleophilicity of the ring. The EWG removes electron density from a π system, making it less reactive in this type of reaction, and therefore called deactivating groups.
EDGs and EWGs also determine the positions (relative to themselves) on the aromatic ring where substitution reactions are most likely to take place. Electron donating groups are generally ortho/para directors for electrophilic aromatic substitutions, while electron withdrawing groups (except the halogens) are generally meta directors. The selectivities observed with EDGs and EWGs were first described in 1892 and have been known as the Crum Brown–Gibson rule. | 0 | Organic Chemistry |
*Gilmore G, Hemingway J. Practical Gamma-Ray Spectrometry. John Wiley & Sons, Chichester: 1995, .
*Knoll G, Radiation Detection and Measurement. John Wiley & Sons, Inc. NY:2000, .
*Nucleonica Wiki. [https://web.archive.org/web/20120226211611/http://www.nucleonica.net/wiki/index.php/Help:Gamma_Spectrum_Generator Gamma Spectrum Generator]. Accessed 8 October 2008. | 7 | Physical Chemistry |
The elasticity coefficient measures the local response of an enzyme or other chemical reaction to changes in its environment. Such changes include factors such as substrates, products, or effector concentrations. For further information, please refer to the dedicated page at elasticity coefficients. | 1 | Biochemistry |
In organic chemistry, the Cahn–Ingold–Prelog (CIP) sequence rules (also the CIP priority convention; named after Robert Sidney Cahn, Christopher Kelk Ingold, and Vladimir Prelog) are a standard process to completely and unequivocally name a stereoisomer of a molecule. The purpose of the CIP system is to assign an R or S descriptor to each stereocenter and an E or Z descriptor to each double bond so that the configuration of the entire molecule can be specified uniquely by including the descriptors in its systematic name. A molecule may contain any number of stereocenters and any number of double bonds, and each usually gives rise to two possible isomers. A molecule with an integer describing the number of stereocenters will usually have stereoisomers, and diastereomers each having an associated pair of enantiomers. The CIP sequence rules contribute to the precise naming of every stereoisomer of every organic molecule with all atoms of ligancy of fewer than 4 (but including ligancy of 6 as well, this term referring to the "number of neighboring atoms" bonded to a center).
The key article setting out the CIP sequence rules was published in 1966, and was followed by further refinements, before it was incorporated into the rules of the International Union of Pure and Applied Chemistry (IUPAC), the official body that defines organic nomenclature, in 1974. The rules have since been revised, most recently in 2013, as part of the IUPAC book Nomenclature of Organic Chemistry. The IUPAC presentation of the rules constitute the official, formal standard for their use, and it notes that "the method has been developed to cover all compounds with ligancy up to 4... and… [extended to the case of] ligancy 6… [as well as] for all configurations and conformations of such compounds." Nevertheless, though the IUPAC documentation presents a thorough introduction, it includes the caution that "it is essential to study the original papers, especially the 1966 paper, before using the sequence rule for other than fairly simple cases."
A recent paper argues for changes to some of the rules (sequence rules 1b and 2) to address certain molecules for which the correct descriptors were unclear. However, a different problem remains: in rare cases, two different stereoisomers of the same molecule can have the same CIP descriptors, so the CIP system may not be able to unambiguously name a stereoisomer, and other systems may be preferable. | 4 | Stereochemistry |
A hydrogen bond (H-bond), is a specific type of interaction that involves dipole–dipole attraction between a partially positive hydrogen atom and a highly electronegative, partially negative oxygen, nitrogen, sulfur, or fluorine atom (not covalently bound to said hydrogen atom). It is not a covalent bond, but instead is classified as a strong non-covalent interaction. It is responsible for why water is a liquid at room temperature and not a gas (given water's low molecular weight). Most commonly, the strength of hydrogen bonds lies between 0–4 kcal/mol, but can sometimes be as strong as 40 kcal/mol In solvents such as chloroform or carbon tetrachloride one observes e.g. for the interaction between amides additive values of about 5 kJ/mol. According to Linus Pauling the strength of a hydrogen bond is essentially determined by the electrostatic charges. Measurements of thousands of complexes in chloroform or carbon tetrachloride have led to additive free energy increments for all kind of donor-acceptor combinations. | 6 | Supramolecular Chemistry |
Optical particle measurements are emerging as an important technique for understanding the ocean carbon cycle, including contributions to estimates of their downward flux, which sequesters carbon dioxide in the deep sea. Optical instruments can be used from ships or installed on autonomous platforms, delivering much greater spatial and temporal coverage of particles in the mesopelagic zone of the ocean than traditional techniques, such as sediment traps. Technologies to image particles have advanced greatly over the last two decades, but the quantitative translation of these immense datasets into biogeochemical properties remains a challenge. In particular, advances are needed to enable the optimal translation of imaged objects into carbon content and sinking velocities. In addition, different devices often measure different optical properties, leading to difficulties in comparing results. | 9 | Geochemistry |
The limiting current in electrochemistry is the limiting value of a faradaic current that is approached as the rate of charge transfer to an electrode is increased. The limiting current can be approached, for example, by increasing the electric potential or decreasing the rate of mass transfer to the electrode. It is independent of the applied potential over a finite range, and is usually evaluated by subtracting the appropriate residual current from the measured total current. A limiting current can have the character of an adsorption, catalytic, diffusion, or kinetic current, and may include a migration current. | 7 | Physical Chemistry |
The mechanisms of embrittlement are similar to those of metals. Inorganic glass embrittlement can be manifested via static fatigue. Embrittlement in glasses, such as Pyrex, is a function of humidity. Growth rate of cracks vary linearly with humidity, suggesting a first-order kinetic relationship. The static fatigue of Pyrex by this mechanism requires dissolution to be concentrated at the tip of the crack. If the dissolution is uniform along the crack flat surfaces, the crack tip will be blunted. This blunting can actually increase the fracture strength of the material by 100 times.
The embrittlement of SiC/alumina composites serves as an instructive example. The mechanism for this system is primarily the diffusion of oxygen into the material through cracks in the matrix. The oxygen reaches the SiC fibers and produces silicate. Stress concentrates around the newly formed silicate and the fibers strength is degraded. This ultimately leads to fracture at stresses less than the materials typical fracture stress. | 8 | Metallurgy |
Depending on ring size, the three-dimensional shapes of particular cyclic structures—typically rings of 5-atoms and larger—can vary and interconvert such that conformational isomerism is displayed. Indeed, the development of this important chemical concept arose, historically, in reference to cyclic compounds. For instance, cyclohexanes—six membered carbocycles with no double bonds, to which various substituents might be attached, see image—display an equilibrium between two conformations, the chair and the boat, as shown in the image.
The chair conformation is the favored configuration, because in this conformation, the steric strain, eclipsing strain, and angle strain that are otherwise possible are minimized. Which of the possible chair conformations predominate in cyclohexanes bearing one or more substituents depends on the substituents, and where they are located on the ring; generally, "bulky" substituents—those groups with large volumes, or groups that are otherwise repulsive in their interactions—prefer to occupy an equatorial location. An example of interactions within a molecule that would lead to steric strain, leading to a shift in equilibrium from boat to chair, is the interaction between the two methyl groups in cis-1,4-dimethylcyclohexane. In this molecule, the two methyl groups are in opposing positions of the ring (1,4-), and their cis stereochemistry projects both of these groups toward the same side of the ring. Hence, if forced into the higher energy boat form, these methyl groups are in steric contact, repel one another, and drive the equilibrium toward the chair conformation. | 4 | Stereochemistry |
Polymer-bonded explosives, also called PBX or plastic-bonded explosives, are explosive materials in which explosive powder is bound together in a matrix using small quantities (typically 5–10% by weight) of a synthetic polymer. PBXs are normally used for explosive materials that are not easily melted into a casting, or are otherwise difficult to form.
PBX was first developed in 1952 at Los Alamos National Laboratory, as RDX embedded in polystyrene with dioctyl phthalate plasticizer. HMX compositions with teflon-based binders were developed in 1960s and 1970s for gun shells and for Apollo Lunar Surface Experiments Package (ALSEP) seismic experiments, although the latter experiments are usually cited as using hexanitrostilbene (HNS). | 7 | Physical Chemistry |
The Tishchenko reaction is an organic chemical reaction that involves disproportionation of an aldehyde in the presence of an alkoxide. The reaction is named after Russian organic chemist Vyacheslav Tishchenko, who discovered that aluminium alkoxides are effective catalysts for the reaction.
In the related Cannizzaro reaction, the base is sodium hydroxide and then the oxidation product is a carboxylic acid and the reduction product is an alcohol. | 0 | Organic Chemistry |
One characteristic of adhesion GPCRs is their extended extracellular region. This region is modular in nature, often possessing a variety of structurally defined protein domains and a membrane proximal GAIN domain. In the aptly named Very Large G protein-coupled Receptor 1 VLGR1 the extracellular region extends up to almost 6000 amino acids. Human adhesion GPCRs possess domains including EGF-like (), Cadherin (), thrombospondin (), Immunoglobulin (), Pentraxin (), Calx-beta () and Leucine-rich repeats (). In non-vertebrate species multiple other structural motifs including Kringle, Somatomedin B (), SRCR () may be contained with the extracellular region. Since many of these domains have been demonstrated to mediate protein-protein interactions within other proteins, they are believed to play the same role in adhesion GPCRs. Indeed, many ligands have been discovered for adhesion GPCRs (see ligands section). Many of the adhesion GPCR possess long stretches of amino acids with little homology to known protein domains suggesting the possibility of new structural domains being elucidated within their extracellular regions. | 1 | Biochemistry |
In 2013, the Fujita group rediscovered that the molecular structure of liquids can be elucidated by X-ray crystallography in the presence of [(ZnI)(TPT)] crystalline sponges. The guest compounds, such as cyclohexanone, cinnamaldehyde were dropped onto the pre-made single crystal of crystalline sponges. The liquid samples would penetrate into the crystalline sponges, and occupy the sponges’ cavities. As crystalline sponges provide a well-organized structure, the guests in sponges’ cavities would also have organized distribution in the space. As a result, the structure of guest can be characterized by X-ray crystallography .
Some of the structures of liquid natural products which are difficult to differentiate by NMR spectroscopy can be easily characterized by crystalline sponges techniques. Elatenyne is a liquid molecule isolated from Laurencia elata, marine red algae. Due to its pseudo-C symmetry, the difference of NMR spectrum between elatenyne and its stereoisomer is hard to differentiate. However, with the crystalline sponges, the Fujita group easily elucidated the chirality in the elatenyne.
Cycloelatanene A and B are a pair of diastereomers isolated from Laurencia elata. Both compounds are liquid, so the traditional X-ray diffraction analysis cannot elucidate their absolute chirality. After the crystalline sponges assisted X-ray crystallography, the Fujita group revised the chirality of C4 position reported by precedent NMR analysis. | 0 | Organic Chemistry |
Enantiomer self-disproportionation is a process in stereochemistry describing the separation of a non-racemic mixture of enantiomers in an enantioenriched fraction and a more racemic fraction as a result of the formation of heterochiral or homochiral aggregates. This process is known to occur in achiral column chromatography.
The phenomenon was first reported in 1983 in the separation of an excess of
carbon-14 labeled (S)-(−)-nicotine enantiomer and its isomer. Two fractions were recorded, one containing racemic nicotine and the other pure (S) enantiomer.
In 2006, Vadim A. Soloshonok introduced the term Enantiomer self-disproportionation or self-disproportionation of enantiomers. He investigated achiral separations of several trifluoromethyl compounds.
By column chromatography on regular silica gel with a hexane / ethyl acetate eluent (5:1), a 66.6% ee sample of a trifluoromethyl substrate is separated into several fractions ranging from 8.1% ee for the first fraction collected to > 99.9% ee for the last fraction collected. A presence of a strong electronegative group in the substrate such as the trifluoromethyl group is a prerequisite. The effect disappears when a more polar eluent is selected. A possible explanation is offered. Compounds with large electronegative groups such as trifluoromethyl can form supramolecular associations or aggregates or clusters in which these groups are separated from each other as much as possible with minimized electrostatic repulsions. When these associations are stacks of alternating (R) and (S) molecules (as in syndiotactic polymers) this can be accomplished very efficiently. This association will form a racemic fraction of relatively high molecular weight eluting more slowly than the non-associating enantiopure fraction. | 4 | Stereochemistry |
The first proposed mechanism for a thermal rearrangement of an aromatic compound was for the automerization of naphthalene. It was suggested that the rearrangement of naphthalene occurred due to reversibility of the isomerization of azulene to naphthalene. This mechanism would therefore involve an azulene intermediate and is depicted below:
Subsequent work showed that the isomerization of azulene to naphthalene is not readily reversible ( the free energy of a naphthalene to azulene isomerization was too high - approximately 90 kcal/mol). A new reaction mechanism was suggested that involved a carbene intermediate and consecutive 1,2-hydrogen and 1,2-carbon shifts across the same C-C bond but in opposite directions. This is currently the preferred mechanism and is as follows: | 5 | Photochemistry |
The tog is a measure of thermal insulance of a unit area, also known as thermal resistance. It is commonly used in the textile industry and often seen quoted on, for example, duvets and carpet underlay.
The Shirley Institute in Manchester, England developed the tog as an easy-to-follow alternative to the SI unit of m⋅K/W. The name comes from the informal word togs for clothing, which itself was probably derived from the word toga, a Roman garment. The backronym thermal overall grade is also attested.
The basic unit of insulation coefficient is the R, (1 m⋅K/W). 1 tog = 0.1 R. There is also a US clothing unit, the clo, equivalent to 0.155 R or 1.55 tog, described in ASTM D-1518.
A tog is 0.1⋅m⋅K/W. In other words, the thermal resistance in togs is equal to ten times the temperature difference (in °C) between the two surfaces of a material, when the flow of heat is equal to one watt per square metre.
British duvets are sold in steps of 1.5 tog from 3.0 tog (summer) to 16.5 tog (extra-warm). The stated values are a minimum; actual values may be up to 3 tog higher. Also, these values assume there is no added duvet cover that can trap air.
A few manufacturers have marketed combined duvet sets consisting of two duvets; one of approximately 4.5 tog and one of approximately 9.0 tog. These can be used individually as summer (4.5 tog) and spring/autumn (9.0 tog). When joined together using press studs around the edges, or Velcro strips across each of the corners, they become a 13.5 tog winter duvet and as such can be made to suit all seasons. | 7 | Physical Chemistry |
Rapid fentanyl test strips are decriminalized in Tennessee. Representative William Lamberth, R-Portland, introduced HB2177 in the Tennessee General Assembly on January 31, 2022, followed by the introduction of SB2427 by Senator Jack Johnson, R-Franklin, the following day. The bill was eventually passed by Governor Bill Lee on March 31. Fentanyl test strips were previously considered drug paraphernalia by Tennessee Code Annotated §39-17-402, which defines terms such as controlled substance and drug paraphernalia in Tennessee state law. Per TCA §39-17-425, possession of fentanyl test strips was previously a Class A misdemeanor, punishable by up to 11 months, 29 days in jail and fines of up to $2,500; distributing them was previously a Class E felony, punishable by prison sentences of one to six years and fines of up to $3,000. | 3 | Analytical Chemistry |
Passive daytime radiative cooling surfaces can mitigate extreme heat from the urban heat island effect which occurs in over 450 cities worldwide, where it can be as much as hotter in urban areas in comparison to surrounding rural areas. On an average hot summer day, the roofs of buildings can be hotter than the surrounding air, warming air temperatures further through convection. Well-insulated dark rooftops are significantly hotter than all other urban surfaces, including asphalt pavements, further expanding air conditioning demand (which further accelerates global warming and urban heat island through the release of waste heat into the ambient air) and increasing risks of heat-related disease and fatal health effects.
PDRCs can be applied to building roofs and urban shelters to significantly lower surface temperatures with zero energy consumption by reflecting heat out of the urban environment and into outer space. The primary obstacle of PDRC implementation in urban areas is the glare that may be caused through the reflectance of visible light onto surrounding buildings. Colored PDRC surfaces may mitigate glare issues, such as Zhai et al. "Super-white paints with commercial high-index (n~1.9) retroreflective spheres," as per Mandal et al., or the use of retroreflective materials (RRM) may also mitigate glare, although further research and development is needed. Surrounding buildings without PDRC application may weaken the cooling power of PDRCs.
Even when installed on roofs in highly dense urban areas, broadband radiative cooling panels have been shown to lower surface temperatures at the sidewalk level. A study by Khan et al. published in 2022 assessed the effects of PDRC surfaces in winter, including for both non-modulated and modulated PDRCs, in the Kolkata metropolitan area. A non-modulated PDRC with a reflectance of 0.95 and emissivity of 0.93 decreased ground surface temperatures by nearly and with an average daytime reduction of .
While in summer the cooling effects of broadband non-modulated PDRCs may be desirable, they could present an uncomfortable "overcooling" effect for city populations in winter and thus increase energy use for heating. This can be mitigated by broadband modulated PDRCs, which they found could increase daily ambient urban temperatures by in winter. While in the tropical metropolitan area of Kolkata, for instance, "overcooling" is unlikely, elsewhere it could impact the willingness to apply PDRCs in urban spaces. Therefore, modulated PDRCs may be preferred in cities with warm summers and cold winters for controlled cooling, while non-modulated PDRCs may be more beneficial for cities with hot summers and moderate winters. The authors expected "low-cost optically modulated passive systems" to be commercially available soon.
In a study on urban bus shelters, it was found that most shelters fail at providing thermal comfort for commuters, noting that, on average, a tree could provide more cooling. Other methods to cool shelters often resort to air conditioning or other energy intensive measures that can crowd commuters in an enclosed space for cooling. Urban shelters with PDRC roofing can significantly reduce temperatures with zero added costs or energy input, while adding "a non-reciprocal mid-infrared cover" can increase benefits by reducing incoming atmospheric radiation as well as reflecting radiation from surrounding buildings, as per Mokharti et al.
For outdoor urban space cooling, it is recommended that PDRC implementation in urban areas primarily focus on increasing albedo so long as heat emissivity can be maintained at the standard of 90%, as per Anand et al. This can rapidly and significantly lower temperatures while reducing energy demand and costs for cooling in urban environments. | 7 | Physical Chemistry |
Strong spectral lines in the visible part of the electromagnetic spectrum often have a unique Fraunhofer line designation, such as K for a line at 393.366 nm emerging from singly-ionized calcium atom, Ca, though some of the Fraunhofer "lines" are blends of multiple lines from several different species.
In other cases, the lines are designated according to the level of ionization by adding a Roman numeral to the designation of the chemical element. Neutral atoms are denoted with the Roman numeral I, singly ionized atoms with II, and so on, so that, for example:
Cu II copper ion with +1 charge, Cu
Fe III iron ion with +2 charge, Fe
More detailed designations usually include the line wavelength and may include a multiplet number (for atomic lines) or band designation (for molecular lines). Many spectral lines of atomic hydrogen also have designations within their respective series, such as the Lyman series or Balmer series. Originally all spectral lines were classified into series: the principal series, sharp series, and diffuse series. These series exist across atoms of all elements, and the patterns for all atoms are well-predicted by the Rydberg-Ritz formula. These series were later associated with suborbitals. | 7 | Physical Chemistry |
Quantitative RT-PCR assay is considered to be the gold standard for measuring the number of copies of specific cDNA targets in a sample but it is poorly standardized. As a result, while there are numerous publications utilizing the technique, many provide inadequate experimental detail and use unsuitable data analysis to draw inappropriate conclusions. Due to the inherent variability in the quality of any quantitative PCR data, not only do reviewers have a difficult time evaluating these manuscripts, but the studies also become impossible to replicate. Recognizing the need for the standardization of the reporting of experimental conditions, the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE, pronounced mykee) guidelines have been published by an international consortium of academic scientists. The MIQE guidelines describe the minimum information necessary for evaluating quantitative PCR experiments that should be required for publication for encouraging better experimental practice and ensuring the relevance, accuracy, correct interpretation, and repeatability of quantitative PCR data.
Besides reporting guidelines, the MIQE stresses the need to standardize the nomenclature associated with quantitative PCR to avoid confusion; for example, the abbreviation qPCR should be used for quantitative real-time PCR, while RT-qPCR should be used for reverse transcription-qPCR, and genes used for normalisation should be referred to as reference genes instead of housekeeping genes. It also proposes that commercially derived terms like TaqMan probes should not be used, but instead referred to as hydrolysis probes. Additionally, it is proposed that quantification cycle (Cq) be used to describe the PCR cycle used for quantification instead of threshold cycle (Ct), crossing point (Cp), and takeoff point (TOP), which refer to the same value but were coined by different manufacturers of real-time instruments.
The guideline consists of the following elements: 1) experimental design, 2) sample, 3) nucleic acid extraction, 4) reverse transcription, 5) qPCR target information, 6) oligonucleotides, 7) protocol, 8) validation, and 9) data analysis. Specific items within each element carry a label of either E (essential) or D (desirable). Those labelled E are considered critical and indispensable while those labelled D are considered peripheral yet important for best-practices. | 1 | Biochemistry |
It is important to note that while all non-competitive inhibitors bind the enzyme at allosteric sites (i.e. locations other than its active site)—not all inhibitors that bind at allosteric sites are non-competitive inhibitors. In fact, allosteric inhibitors may act as competitive, non-competitive, or uncompetitive inhibitors.
Many sources continue to conflate these two terms, or state the definition of allosteric inhibition as the definition for non-competitive inhibition. | 1 | Biochemistry |
Mobility and access to medical care are one of the major challenges for many disabled Iranian veterans. In Tehran alone there are very few wheelchair-accessible ramps, elevators and parking spots and the problem is more serious in smaller cities. This is while by 2018 over 5,000 disabled Iranian veterans, mostly living in the capital, are reliant on wheelchairs for mobility. According to the Tehran Metro Group many more elevators are needed in Tehran's subway system. To provide better services for disabled veterans, the Iranian government has announced that around $5 million has been dedicated to constructing ramps and wheelchair-accessible paths throughout Tehran. No similar official plans are dedicated for other cities in Iran.
In Tehran, chemical weapons victims are often referred to the Sasan Hospital.
The Tehran Peace Museum plans to focus on the enduring human consequences of Iran–Iraq War and serves as a centre for surviving victims of the war, especially chemical warfare veterans attacked by Saddam Hussein's forces.
In addition to numerous laws and regulations the Iranian government has passed to address disability related issues, the Disability Protect Act, including 16 articles
providing legal protections for disabled persons in areas such as public building access, education, housing and finance, has been Iran's
most progressive and comprehensive legislation concerning disabled persons which was passed in 2003.
The Janbazan Foundation is created by Iran government for the assistance of Iranian disabled veterans and for giving them special treatment. They also receive services such as financial loan from Foundation of Martyrs and Veterans Affairs. | 1 | Biochemistry |
Some metal carbonyls are prepared by the reduction of metal halides in the presence of high pressure of carbon monoxide. A variety of reducing agents are employed, including copper, aluminum, hydrogen, as well as metal alkyls such as triethylaluminium. Illustrative is the formation of chromium hexacarbonyl from anhydrous chromium(III) chloride in benzene with aluminum as a reducing agent, and aluminum chloride as the catalyst:
:CrCl + Al + 6 CO → Cr(CO) + AlCl
The use of metal alkyls, such as triethylaluminium and diethylzinc, as the reducing agent leads to the oxidative coupling of the alkyl radical to form the dimer alkane:
:WCl + 6 CO + 2 Al(CH) → W(CO) + 2 AlCl + 3 CH
Tungsten, molybdenum, manganese, and rhodium salts may be reduced with lithium aluminium hydride. Vanadium hexacarbonyl is prepared with sodium as a reducing agent in chelating solvents such as diglyme.
:VCl + 4 Na + 6 CO + 2 diglyme → Na(diglyme)[V(CO)] + 3 NaCl
:[V(CO)] + H → H[V(CO)] → H + V(CO)
In the aqueous phase, nickel or cobalt salts can be reduced, for example by sodium dithionite. In the presence of carbon monoxide, cobalt salts are quantitatively converted to the tetracarbonylcobalt(−1) anion:
:Co + + 6 OH + 4 CO → + 3 + 3 HO
Some metal carbonyls are prepared using CO directly as the reducing agent. In this way, Hieber and Fuchs first prepared dirhenium decacarbonyl from the oxide:
:ReO + 17 CO → Re(CO) + 7 CO
If metal oxides are used carbon dioxide is formed as a reaction product. In the reduction of metal chlorides with carbon monoxide phosgene is formed, as in the preparation of osmium carbonyl chloride from the chloride salts. Carbon monoxide is also suitable for the reduction of sulfides, where carbonyl sulfide is the byproduct. | 0 | Organic Chemistry |
In mineralogy, crystal habit is the characteristic external shape of an individual crystal or aggregate of crystals. The habit of a crystal is dependent on its crystallographic form and growth conditions, which generally creates irregularities due to limited space in the crystallizing medium (commonly in rocks). | 3 | Analytical Chemistry |
An ambident nucleophile is one that can attack from two or more places, resulting in two or more products. For example, the thiocyanate ion (SCN) may attack from either the sulfur or the nitrogen. For this reason, the S2 reaction of an alkyl halide with SCN often leads to a mixture of an alkyl thiocyanate (R-SCN) and an alkyl isothiocyanate (R-NCS). Similar considerations apply in the Kolbe nitrile synthesis. | 7 | Physical Chemistry |
Fluorescence correlation spectroscopy (FCS) is a statistical analysis, via time correlation, of stationary fluctuations of the fluorescence intensity. Its theoretical underpinning originated from L. Onsager's regression hypothesis. The analysis provides kinetic parameters of the physical processes underlying the fluctuations. One of the interesting applications of this is an analysis of the concentration fluctuations of fluorescent particles (molecules) in solution. In this application, the fluorescence emitted from a very tiny space in solution containing a small number of fluorescent particles (molecules) is observed. The fluorescence intensity is fluctuating due to Brownian motion of the particles. In other words, the number of the particles in the sub-space defined by the optical system is randomly changing around the average number. The analysis gives the average number of fluorescent particles and average diffusion time, when the particle is passing through the space. Eventually, both the concentration and size of the particle (molecule) are determined. Both parameters are important in biochemical research, biophysics, and chemistry.
FCS is such a sensitive analytical tool because it observes a small number of molecules (nanomolar to picomolar concentrations) in a small volume (~1 μm). In contrast to other methods (such as HPLC analysis) FCS has no physical separation process; instead, it achieves its spatial resolution through its optics. Furthermore, FCS enables observation of fluorescence-tagged molecules in the biochemical pathway in intact living cells. This opens a new area, "in situ or in vivo biochemistry": tracing the biochemical pathway in intact cells and organs.
Commonly, FCS is employed in the context of optical microscopy, in particular confocal microscopy or two-photon excitation microscopy. In these techniques light is focused on a sample and the measured fluorescence intensity fluctuations (due to diffusion, physical or chemical reactions, aggregation, etc.) are analyzed using the temporal autocorrelation. Because the measured property is essentially related to the magnitude and/or the amount of fluctuations, there is an optimum measurement regime at the level when individual species enter or exit the observation volume (or turn on and off in the volume). When too many entities are measured at the same time the overall fluctuations are small in comparison to the total signal and may not be resolvable – in the other direction, if the individual fluctuation-events are too sparse in time, one measurement may take prohibitively too long. FCS is in a way the fluorescent counterpart to dynamic light scattering, which uses coherent light scattering, instead of (incoherent) fluorescence.
When an appropriate model is known, FCS can be used to obtain quantitative information such as
* diffusion coefficients
* hydrodynamic radii
* average concentrations
* kinetic chemical reaction rates
* singlet-triplet dynamics
Because fluorescent markers come in a variety of colors and can be specifically bound to a particular molecule (e.g. proteins, polymers, metal-complexes, etc.), it is possible to study the behavior of individual molecules (in rapid succession in composite solutions). With the development of sensitive detectors such as avalanche photodiodes the detection of the fluorescence signal coming from individual molecules in highly dilute samples has become practical. With this emerged the possibility to conduct FCS experiments in a wide variety of specimens, ranging from materials science to biology. The advent of engineered cells with genetically tagged proteins (like green fluorescent protein) has made FCS a common tool for studying molecular dynamics in living cells. | 7 | Physical Chemistry |
Metabonomics is defined as "the quantitative measurement of the dynamic multiparametric metabolic response of living systems to pathophysiological stimuli or genetic modification". The word origin is from the Greek μεταβολή meaning change and nomos meaning a rule set or set of laws. This approach was pioneered by Jeremy Nicholson at Murdoch University and has been used in toxicology, disease diagnosis and a number of other fields. Historically, the metabonomics approach was one of the first methods to apply the scope of systems biology to studies of metabolism.
There has been some disagreement over the exact differences between metabolomics and metabonomics. The difference between the two terms is not related to choice of analytical platform: although metabonomics is more associated with NMR spectroscopy and metabolomics with mass spectrometry-based techniques, this is simply because of usages amongst different groups that have popularized the different terms. While there is still no absolute agreement, there is a growing consensus that metabolomics places a greater emphasis on metabolic profiling at a cellular or organ level and is primarily concerned with normal endogenous metabolism. Metabonomics extends metabolic profiling to include information about perturbations of metabolism caused by environmental factors (including diet and toxins), disease processes, and the involvement of extragenomic influences, such as gut microflora. This is not a trivial difference; metabolomic studies should, by definition, exclude metabolic contributions from extragenomic sources, because these are external to the system being studied. However, in practice, within the field of human disease research there is still a large degree of overlap in the way both terms are used, and they are often in effect synonymous. | 1 | Biochemistry |
The trivial name carbyne is the preferred IUPAC name.
Following the substitutive nomenclature, the molecule is viewed as methane with three hydrogen atoms removed, yielding the systematic name "methylidyne".
Following the additive nomenclature, the molecule is viewed as a hydrogen atom bonded to a carbon atom, yielding the name "hydridocarbon".
By default, these names pay no regard to the excitation state of the molecule. When that attribute is considered, the states with one unpaired electron are named "methylylidene" or "hydridocarbon(•)", whereas the excited states with three unpaired electrons are named "methanetriyl" or "hydridocarbon(3•)". | 0 | Organic Chemistry |
Mollapour completed his postdoctoral research at the University of Sheffield and in 2006 he received the Federation of European Societies (FEBS) fellowship.
He joined the laboratory of Dr Len Neckers in Urological Oncology Branch, (Chief Dr. W. Marston Linehan), at the National Cancer Institute as a research fellow in 2007.
In 2013 he joined the Department of Urology at the Upstate Medical University as an Assistant Professor. He became the Director of the Kidney Cancer Program within the same department in 2015.
In 2018 he became the Professor of Urology and Adjunct Professor of Biochemistry and Molecular Biology at SUNY Upstate Medical University. He was also named the Vice Chair for Translational Research for the Department of Urology in the same year. In 2023, Mollapour was elected the president-elect for the Cell Stress Society International; his term at president will begin in 2025. Mollapour’s h-index is 45, based on 7,751 citations. | 1 | Biochemistry |
Hexafluoroethane's solid phase has two polymorphs. In the scientific literature, different phase transition temperatures have been stated. The latest works assign it at 103 K (−170 °C). Below 103 K it has a slightly disordered structure, and over the transition point, it has a body centered cubic structure. The critical point is at 19.89 °C (293.04 K) and 30.39 bar.
Table of densities:
Vapor density is 4.823 (air = 1), specific gravity at 21 °C is 4.773 (air = 1) and specific volume at 21 °C is 0.1748 m/kg. | 2 | Environmental Chemistry |
Decarbonylation of aldehydes, the reverse of CO insertion, is a well-recognized reaction:
:RCHO → RH + CO
The reaction is not widely practiced in part because the alkanes are less useful materials than are the aldehyde precursors. Furthermore, the reaction is not often conducted catalytically because the extruded CO can be slow to dissociate. Extrusion of CO from an organic aldehyde is most famously demonstrated using Wilkinson's catalyst:
:RhCl(PPh) + RCHO → RhCl(CO)(PPh) + RH + PPh
Please see Tsuji-Wilkinson Decarbonylation Reaction for an example of this elementary organometallic step in synthesis | 0 | Organic Chemistry |
Snow and ice sublime gradually at temperatures below the solid-liquid boundary (melting point) (generally 0 °C), and at partial pressures below the triple point pressure of , at a low rate. In freeze-drying, the material to be dehydrated is frozen and its water is allowed to sublime under reduced pressure or vacuum. The loss of snow from a snowfield during a cold spell is often caused by sunshine acting directly on the upper layers of the snow. Sublimation of ice is a factor to the erosive wear of glacier ice, also called ablation in glaciology. | 3 | Analytical Chemistry |
The Institute for Problems of Cryobiology and Cryomedicine in Kharkiv is one of the institutes of the National Academy of Science of Ukraine, and is the largest institute devoted to cryobiology research in the world. | 1 | Biochemistry |
MALDI-TOF spectra are often used for the identification of microorganisms such as bacteria or fungi. A portion of a colony of the microbe in question is placed onto the sample target and overlaid with matrix. The mass spectra of expressed proteins generated are analyzed by dedicated software and compared with stored profiles for species determination in what is known as biotyping. It offers benefits to other immunological or biochemical procedures and has become a common method for species identification in clinical microbiological laboratories. Benefits of high resolution MALDI-MS performed on a Fourier transform ion cyclotron resonance mass spectrometry (also known as FT-MS) have been demonstrated for typing and subtyping viruses though single ion detection known as proteotyping, with a particular focus on influenza viruses.
One main advantage over other microbiological identification methods is its ability to rapidly and reliably identify, at low cost, a wide variety of microorganisms directly from the selective medium used to isolate them. The absence of the need to purify the suspect or "presumptive" colony allows for a much faster turn-around times. For example, it has been demonstrated that MALDI-TOF can be used to detect bacteria directly from blood cultures.
Another advantage is the potential to predict antibiotic susceptibility of bacteria. A single mass spectral peak can predict methicillin resistance of Staphylococcus aureus. MALDI can also detect carbapenemase of carbapenem-resistant enterobacteriaceae, including Acinetobacter baumannii and Klebsiella pneumoniae. However, most proteins that mediate antibiotic resistance are larger than MALDI-TOFs 2000–20,000 Da range for protein peak interpretation and only occasionally, as in the 2011 Klebsiella pneumoniae' carbapenemase (KPC) outbreak at the NIH, a correlation between a peak and resistance conferring protein can be made. | 1 | Biochemistry |
Machine learning is a powerful tool that can be used in metabolomics analysis. Recently, scientists have developed retention time prediction software. These tools allow researchers to apply artificial intelligence to the retention time prediction of small molecules in complex mixture, such as human plasma, plant extracts, foods, or microbial cultures. Retention time prediction increases the identification rate in liquid chromatography and can lead to an improved biological interpretation of metabolomics data. | 1 | Biochemistry |
Light scattering spectroscopy has been applied for detection of precancer in many organs including esophagus, colon, urinary bladder, oral cavity, cervix, pancreatic cyst, stomach, skin, and bile duct. | 7 | Physical Chemistry |
Debye forces, or dipole–induced dipole interactions, can also play a role in dispersive adhesion. These come about when a nonpolar molecule becomes temporarily polarized due to interaction with a nearby polar molecule. This "induced dipole" in the nonpolar molecule then is attracted to the permanent dipole, yielding a Debye attraction. | 6 | Supramolecular Chemistry |
The N terminal domain is well conserved across different species. This may be due to its important function in substrate and cation binding. The residues involved in methionine binding are found in the N-terminal domain. | 1 | Biochemistry |
When writing the chemical formula for an ion, its net charge is written in superscript immediately after the chemical structure for the molecule/atom. The net charge is written with the magnitude before the sign; that is, a doubly charged cation is indicated as 2+ instead of +2. However, the magnitude of the charge is omitted for singly charged molecules/atoms; for example, the sodium cation is indicated as and not .
An alternative (and acceptable) way of showing a molecule/atom with multiple charges is by drawing out the signs multiple times, this is often seen with transition metals. Chemists sometimes circle the sign; this is merely ornamental and does not alter the chemical meaning. All three representations of , , and shown in the figure, are thus equivalent.
Monatomic ions are sometimes also denoted with Roman numerals, particularly in spectroscopy; for example, the (positively doubly charged) example seen above is referred to as , or Fe III (Fe I for a neutral Fe atom, Fe II for a singly ionized Fe ion). The Roman numeral designates the formal oxidation state of an element, whereas the superscripted Indo-Arabic numerals denote the net charge. The two notations are, therefore, exchangeable for monatomic ions, but the Roman numerals cannot be applied to polyatomic ions. However, it is possible to mix the notations for the individual metal centre with a polyatomic complex, as shown by the uranyl ion example. | 7 | Physical Chemistry |
Wiggins was appointed a Fellow of the Royal Society Te Apārangi in 1991. She received a medal for her research from the Health Research Council of New Zealand.
In 2017 Wiggins was featured as one of the Royal Society Te Apārangi's 150 women in 150 words. | 7 | Physical Chemistry |
The first use of bitumen in the New World was by aboriginal peoples. On the west coast, as early as the 13th century, the Tongva, Luiseño and Chumash peoples collected the naturally occurring bitumen that seeped to the surface above underlying petroleum deposits. All three groups used the substance as an adhesive. It is found on many different artifacts of tools and ceremonial items. For example, it was used on rattles to adhere gourds or turtle shells to rattle handles. It was also used in decorations. Small round shell beads were often set in asphaltum to provide decorations. It was used as a sealant on baskets to make them watertight for carrying water, possibly poisoning those who drank the water. Asphalt was used also to seal the planks on ocean-going canoes.
Asphalt was first used to pave streets in the 1870s. At first naturally occurring "bituminous rock" was used, such as at Ritchie Mines in Macfarlan in Ritchie County, West Virginia from 1852 to 1873. In 1876, asphalt-based paving was used to pave Pennsylvania Avenue in Washington DC, in time for the celebration of the national centennial.
In the horse-drawn era, US streets were mostly unpaved and covered with dirt or gravel. Especially where mud or trenching often made streets difficult to pass, pavements were sometimes made of diverse materials including wooden planks, cobble stones or other stone blocks, or bricks. Unpaved roads produced uneven wear and hazards for pedestrians. In the late 19th century with the rise of the popular bicycle, bicycle clubs were important in pushing for more general pavement of streets. Advocacy for pavement increased in the early 20th century with the rise of the automobile. Asphalt gradually became an ever more common method of paving. St. Charles Avenue in New Orleans was paved its whole length with asphalt by 1889.
In 1900, Manhattan alone had 130,000 horses, pulling streetcars, wagons, and carriages, and leaving their waste behind. They were not fast, and pedestrians could dodge and scramble their way across the crowded streets. Small towns continued to rely on dirt and gravel, but larger cities wanted much better streets. They looked to wood or granite blocks by the 1850s. In 1890, a third of Chicago's 2000 miles of streets were paved, chiefly with wooden blocks, which gave better traction than mud. Brick surfacing was a good compromise, but even better was asphalt paving, which was easy to install and to cut through to get at sewers. With London and Paris serving as models, Washington laid 400,000 square yards of asphalt paving by 1882; it became the model for Buffalo, Philadelphia and elsewhere. By the end of the century, American cities boasted 30 million square yards of asphalt paving, well ahead of brick. The streets became faster and more dangerous so electric traffic lights were installed. Electric trolleys (at 12 miles per hour) became the main transportation service for middle class shoppers and office workers until they bought automobiles after 1945 and commuted from more distant suburbs in privacy and comfort on asphalt highways. | 7 | Physical Chemistry |
The settlement was mediated by retired judge Sir Henry Brooke. Before settlement had been reached, Chris Mallender explained: "We have reached a view that there are going to be no outright winners in this. In the circumstances we feel that its better that we try and find a middle ground, we settle in a way thats fair to the families, but is also fair in terms of the residual burden on the council tax payer."
On 16 April 2010 the council released a joint statement with the families solicitors announcing it was dropping its appeal and had agreed a financial settlement with 19 families. Chris Mallender said: "The council recognises that it made mistakes in its clean-up of the former British Steel site years ago and extends its deepest sympathy to the children and their families. Although I accept that money cannot properly compensate these young people for their disabilities and for all that they have suffered to date and their problems in the future, the council sincerely hopes that this apology coupled with todays agreement will mean that they can now put their legal battle behind them and proceed with their lives with a greater degree of financial certainty." The financial terms of the settlement remained confidential, and the agreement forbids disclosure of the financial arrangements. On the subject of cost, Mallender said: "Every £1m of cost involves a payment £5 per household in Corby on average, per year, for the next 20 years. So, simple maths: if the overall bill is £5m, it's £25 per household for 20 years."
The settlement also encompassed three children not covered by the original ruling, including India Harrison and Ashleigh Custance. | 2 | Environmental Chemistry |
Poly(pentafluorophenyl acrylate) finds application in the synthesis of functional polymers by post-polymerization modification. Applications of the resulting polyacrylamides can be found in drug delivery, functional surfaces, and nanoparticles. | 7 | Physical Chemistry |
In crystallography, a crystallographic point group is a three dimensional point group whose symmetry operations are compatible with a three dimensional crystallographic lattice. According to the crystallographic restriction it may only contain one-, two-, three-, four- and sixfold rotations or rotoinversions. This reduces the number of crystallographic point groups to 32 (from an infinity of general point groups). These 32 groups are one-and-the-same as the 32 types of morphological (external) crystalline symmetries derived in 1830 by Johann Friedrich Christian Hessel from a consideration of observed crystal forms.
In the classification of crystals, to each space group is associated a crystallographic point group by "forgetting" the translational components of the symmetry operations. That is, by turning screw rotations into rotations, glide reflections into reflections and moving all symmetry elements into the origin. Each crystallographic point group defines the (geometric) crystal class of the crystal.
The point group of a crystal determines, among other things, the directional variation of physical properties that arise from its structure, including optical properties such as birefringency, or electro-optical features such as the Pockels effect. | 3 | Analytical Chemistry |
Nuclear matter is an idealized system of interacting nucleons (protons and neutrons) that exists in several phases of exotic matter that, as of yet, are not fully established. It is not matter in an atomic nucleus, but a hypothetical substance consisting of a huge number of protons and neutrons held together by only nuclear forces and no Coulomb forces. Volume and the number of particles are infinite, but the ratio is finite. Infinite volume implies no surface effects and translational invariance (only differences in position matter, not absolute positions).
A common idealization is symmetric nuclear matter, which consists of equal numbers of protons and neutrons, with no electrons.
When nuclear matter is compressed to sufficiently high density, it is expected, on the basis of the asymptotic freedom of quantum chromodynamics, that it will become quark matter, which is a degenerate Fermi gas of quarks.
Some authors use "nuclear matter" in a broader sense, and refer to the model described above as "infinite nuclear matter", and consider it as a "toy model", a testing ground for analytical techniques. However, the composition of a neutron star, which requires more than neutrons and protons, is not necessarily locally charge neutral, and does not exhibit translation invariance, often is differently referred to, for example, as neutron star matter or stellar matter and is considered distinct from nuclear matter. In a neutron star, pressure rises from zero (at the surface) to an unknown large value in the center.
Methods capable of treating finite regions have been applied to stars and to atomic nuclei. One such model for finite nuclei is the liquid drop model, which includes surface effects and Coulomb interactions. | 7 | Physical Chemistry |
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