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Direct carbon-proton coupling constants are used to study the anomeric configuration of a sugar.
Vicinal proton-proton coupling constants are used to study stereo orientation of protons relatively to the other protons within a sugar ring, thus identifying a monosaccharide.
Vicinal heteronuclear H-C-O-C coupling constants are used to study torsional angles along glycosidic bond between sugars or along exocyclic fragments, thus revealing a molecular conformation.
Sugar rings are relatively rigid molecular fragments, thus vicinal proton-proton couplings are characteristic:
*Equatorial to axial: 1–4 Hz
*Equatorial to equatorial: 0–2 Hz
*Axial to axial non-anomeric: 9–11 Hz
*Axial to axial anomeric: 7–9 Hz
*Axial to exocyclic hydroxymethyl: 5 Hz, 2 Hz
*Geminal between hydroxymethyl protons: 12 Hz | 0 | Theoretical and Fundamental Chemistry |
For the past years, researchers have been trying to reduce the price of solar cells while maximizing efficiency. Thin-film solar cell is a cost-effective second generation solar cell with much reduced thickness at the expense of light absorption efficiency. Efforts to maximize light absorption efficiency with reduced thickness have been made. Surface texturing is one of techniques used to reduce optical losses to maximize light absorbed. Currently, surface texturing techniques on silicon photovoltaics are drawing much attention. Surface texturing could be done in multiple ways. Etching single crystalline silicon substrate can produce randomly distributed square based pyramids on the surface using anisotropic etchants. Recent studies show that c-Si wafers could be etched down to form nano-scale inverted pyramids. Multicrystalline silicon solar cells, due to poorer crystallographic quality, are less effective than single crystal solar cells, but mc-Si solar cells are still being used widely due to less manufacturing difficulties. It is reported that multicrystalline solar cells can be surface-textured to yield solar energy conversion efficiency comparable to that of monocrystalline silicon cells, through isotropic etching or photolithography techniques. Incident light rays onto a textured surface do not reflect back out to the air as opposed to rays onto a flat surface. Rather some light rays are bounced back onto the other surface again due to the geometry of the surface. This process significantly improves light to electricity conversion efficiency, due to increased light absorption. This texture effect as well as the interaction with other interfaces in the PV module is a challenging optical simulation task. A particularly efficient method for modeling and optimization is the OPTOS formalism. In 2012, researchers at MIT reported that c-Si films textured with nanoscale inverted pyramids could achieve light absorption comparable to 30 times thicker planar c-Si. In combination with anti-reflective coating, surface texturing technique can effectively trap light rays within a thin film silicon solar cell. Consequently, required thickness for solar cells decreases with the increased absorption of light rays. | 0 | Theoretical and Fundamental Chemistry |
Elisabeth Ivanova Kara-Michailova (), alternatively Elisabeth Karamichailova was a Bulgarian physicist of a Bulgarian father and an English mother. She was among the handful of female nuclear physics pioneers at the beginning of the 20th century, established the first practical courses of particle physics in Bulgaria and was the first woman to hold a professorial title in the country. | 0 | Theoretical and Fundamental Chemistry |
High-gradient magnetic separator is to separate magnetic and non-magnetic particles (concentrate and tails) from the feed slurry. This feed comes from intermediate thickener underflow pump through Linear Screen & Passive Matrix. Tailings go to tailing thickener & product goes to throw launder through vacuum tanks. | 0 | Theoretical and Fundamental Chemistry |
Biological signaling networks incorporate a wide array of reversible interactions, post-translational modifications and conformational changes. Furthermore, it is common for a protein to be composed of several - identical or nonidentical - subunits, and for several proteins and/or nucleic acid species to assemble into larger complexes. A molecular species with several of those features can therefore exist in a large number of possible states.
For instance, it has been estimated that the yeast scaffold protein Ste5 can be a part of 25666 unique protein complexes. In E. coli, chemotaxis receptors of four different kinds interact in groups of three, and each individual receptor can exist in at least two possible conformations and has up to eight methylation sites, resulting in billions of potential states. The protein kinase CaMKII is a dodecamer of twelve catalytic subunits, arranged in two hexameric rings. Each subunit can exist in at least two distinct conformations, and each subunit features various phosphorylation and ligand binding sites. A recent model incorporated conformational states, two phosphorylation sites and two modes of binding calcium/calmodulin, for a total of around one billion possible states per hexameric ring. A model of coupling of the EGF receptor to a MAP kinase cascade presented by Danos and colleagues accounts for distinct molecular species, yet the authors note several points at which the model could be further extended. A more recent model of ErbB receptor signalling even accounts for more than one googol () distinct molecular species. The problem of combinatorial explosion is also relevant to synthetic biology, with a recent model of a relatively simple synthetic eukaryotic gene circuit featuring 187 species and 1165 reactions.
Of course, not all of the possible states of a multi-state molecule or complex will necessarily be populated. Indeed, in systems where the number of possible states is far greater than that of molecules in the compartment (e.g. the cell), they cannot be. In some cases, empirical information can be used to rule out certain states if, for instance, some combinations of features are incompatible. In the absence of such information, however, all possible states need to be considered a priori. In such cases, computational modeling can be used to uncover to what extent the different states are populated.
The existence (or potential existence) of such large numbers of molecular species is a combinatorial phenomenon: It arises from a relatively small set of features or modifications (such as post-translational modification or complex formation) that combine to dictate the state of the entire molecule or complex, in the same way that the existence of just a few choices in a coffee shop (small, medium or large, with or without milk, decaf or not, extra shot of espresso) quickly leads to a large number of possible beverages (24 in this case; each additional binary choice will double that number). Although it is difficult for us to grasp the total numbers of possible combinations, it is usually not conceptually difficult to understand the (much smaller) set of features or modifications and the effect each of them has on the function of the biomolecule. The rate at which a molecule undergoes a particular reaction will usually depend mainly on a single feature or a small subset of features. It is the presence or absence of those features that dictates the reaction rate. The reaction rate is the same for two molecules that differ only in features which do not affect this reaction. Thus, the number of parameters will be much smaller than the number of reactions. (In the coffee shop example, adding an extra shot of espresso will cost 40 cent, no matter what size the beverage is and whether or not it has milk in it). It is such "local rules" that are usually discovered in laboratory experiments. Thus, a multi-state model can be conceptualised in terms of combinations of modular features and local rules. This means that even a model that can account for a vast number of molecular species and reactions is not necessarily conceptually complex. | 1 | Applied and Interdisciplinary Chemistry |
A drug in blood exists in two forms: bound and unbound. Depending on a specific drug's affinity for plasma proteins, a proportion of the drug may become bound to the proteins, with the remainder being unbound. If the protein binding is reversible, then a chemical equilibrium will exist between the bound and unbound states, such that:
:Protein + drug ⇌ Protein-drug complex
Notably, it is the unbound fraction which exhibits pharmacologic effects. It is also the fraction that may be metabolized and/or excreted. For example, the "fraction bound" of the anticoagulant warfarin is 97%. This means that out of the amount of warfarin in the blood, 97% is bound to plasma proteins. The remaining 3% (the fraction unbound) is the fraction that is actually active and may be excreted.
Protein binding can influence the drug's biological half-life. The bound portion may act as a reservoir or depot from which the drug is slowly released as the unbound form. Since the unbound form is being metabolized and/or excreted from the body, the bound fraction will be released in order to maintain equilibrium.
Since albumin is alkalotic, acidic and neutral drugs will primarily bind to albumin. If albumin becomes saturated, then these drugs will bind to lipoprotein. Basic drugs will bind to the acidic alpha-1 acid glycoprotein. This is significant because various medical conditions may affect the levels of albumin, alpha-1 acid glycoprotein, and lipoproteins. | 1 | Applied and Interdisciplinary Chemistry |
One example of Ostwald ripening is the re-crystallization of water within ice cream which gives old ice cream a gritty, crunchy texture. Larger ice crystals grow at the expense of smaller ones within the ice cream, creating a coarser texture.
Another gastronomical example is the ouzo effect, where the droplets in the cloudy microemulsion grow by Ostwald ripening.
In geology, it is the textural coarsening, aging or growth of phenocrysts and crystals in solid rock which is below the solidus temperature. It is often ascribed as a process in the formation of orthoclase megacrysts, as an alternative to the physical processes governing crystal growth from nucleation and growth rate thermochemical limitations.
In aqueous solution chemistry and precipitates ageing, the term refers to the growth of larger crystals from those of smaller size which have a higher solubility than the larger ones. In the process, many small crystals formed initially (nuclei) slowly disappear, except for a few that grow larger, at the expense of the small crystals (crystal growth). The smaller crystals act as fuel for the growth of bigger crystals. Limiting Ostwald ripening is fundamental in modern technology for the solution synthesis of quantum dots. Ostwald ripening is also the key process in the digestion and aging of precipitates, an important step in gravimetric analysis. The digested precipitate is generally purer, and easier to wash and filter.
Ostwald ripening can also occur in emulsion systems, with molecules diffusing from small droplets to large ones through the continuous phase. When a miniemulsion is desired, an extremely hydrophobic compound is added to stop this process from taking place.
Diffusional growth of larger drops in liquid water clouds in the atmosphere at the expense of smaller drops is also characterized as Ostwald ripening. | 0 | Theoretical and Fundamental Chemistry |
The van der Waals volume, V, also called the atomic volume or molecular volume, is the atomic property most directly related to the van der Waals radius. It is the volume "occupied" by an individual atom (or molecule).
The van der Waals volume may be calculated if the van der Waals radii (and, for molecules, the inter-atomic distances, and angles) are known. For a single atom, it is the volume of a sphere whose radius is the van der Waals radius of the atom:
For a molecule, it is the volume enclosed by the van der Waals surface.
The van der Waals volume of a molecule is always smaller than the sum of the van der Waals volumes of the constituent atoms: the atoms can be said to "overlap" when they form chemical bonds.
The van der Waals volume of an atom or molecule may also be determined by experimental measurements on gases, notably from the van der Waals constant b, the polarizability α, or the molar refractivity A.
In all three cases, measurements are made on macroscopic samples and it is normal to express the results as molar quantities.
To find the van der Waals volume of a single atom or molecule, it is necessary to divide by the Avogadro constant N.
The molar van der Waals volume should not be confused with the molar volume of the substance.
In general, at normal laboratory temperatures and pressures, the atoms or molecules of gas only occupy about of the volume of the gas, the rest is empty space.
Hence the molar van der Waals volume, which only counts the volume occupied by the atoms or molecules, is usually about times smaller than the molar volume for a gas at standard temperature and pressure. | 0 | Theoretical and Fundamental Chemistry |
* Relative entropy is always non-negative, a result known as Gibbs' inequality, with equals zero if and only if as measures.
In particular, if and , then -almost everywhere. The entropy thus sets a minimum value for the cross-entropy , the expected number of bits required when using a code based on rather than ; and the Kullback–Leibler divergence therefore represents the expected number of extra bits that must be transmitted to identify a value drawn from , if a code is used corresponding to the probability distribution , rather than the "true" distribution .
* No upper-bound exists for the general case. However, it is shown that if and are two discrete probability distributions built by distributing the same discrete quantity, then the maximum value of can be calculated.
* Relative entropy remains well-defined for continuous distributions, and furthermore is invariant under parameter transformations. For example, if a transformation is made from variable to variable , then, since and where is the absolute value of the derivative or more generally of the Jacobian, the relative entropy may be rewritten:
* The Taylor expansion is . | 0 | Theoretical and Fundamental Chemistry |
Plants that contribute to nitrogen fixation include those of the legume family—Fabaceae— with taxa such as kudzu, clover, soybean, alfalfa, lupin, peanut and rooibos. They contain symbiotic rhizobia bacteria within nodules in their root systems, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants; this helps to fertilize the soil. The great majority of legumes have this association, but a few genera (e.g., Styphnolobium) do not. In many traditional farming practices, fields are rotated through various types of crops, which usually include one consisting mainly or entirely of clover.
Fixation efficiency in soil is dependent on many factors, including the legume and air and soil conditions. For example, nitrogen fixation by red clover can range from . | 1 | Applied and Interdisciplinary Chemistry |
The dry ice color show is a demonstration of the chemical formation of carbonic acid () by the dissolution of dry ice (the solid or frozen form of carbon dioxide – ) in water (). The dry ice color show is usually performed in classrooms to demonstrate the properties of acids and bases, their effect on pH indicators, and the sublimation of dry ice. Setup is simple and generally involves only minor hazards, the main one being the low temperature of dry ice, which can cause frostbite upon skin contact. The carbonic acid formed in the demonstration is a weak acid and is not hazardous, being present in numerous consumer products including tonic water, soda, and beer. | 1 | Applied and Interdisciplinary Chemistry |
Mansfield married Jean Margaret Kibble (b. 1935) on 1 September 1962. He had two daughters.
Mansfield died in Nottingham on 8 February 2017, aged 83. | 0 | Theoretical and Fundamental Chemistry |
The field of building-integrated photovoltaics (BIPV) has gained attention from the scientific community due to its potential to reduce pollution and materials and electricity costs, as well as to improve the aesthetics of a building. In recent years, scientists have looked at ways to incorporate DSSC’s in BIPV applications, since the dominant Si-based PV systems in the market have a limited presence in this field due to their energy-intensive manufacturing methods, poor conversion efficiency under low light intensities, and high maintenance requirements. In 2021, a group of researchers from the Silesian University of Technology in Poland developed a DSSC in which the classic glass counter electrode was replaced by an electrode based on a ceramic tile and nickel foil. The motivation for this change was that, despite that glass substrates have resulted in the highest recorded efficiencies for DSSC’s, for BIPV applications like roof tiles or building facades, lighter and more flexible materials are essential. This includes plastic films, metals, steel, or paper, which may also reduce manufacturing costs. The team found that the cell had an efficiency of 4% (close to that of a solar cell with a glass counter electrode), demonstrated the potential for creating building-integrated DSSC’s that are stable and low-cost. | 0 | Theoretical and Fundamental Chemistry |
mTOR Complex 2 (mTORC2) is composed of MTOR, rapamycin-insensitive companion of MTOR (RICTOR), MLST8, and mammalian stress-activated protein kinase interacting protein 1 (mSIN1). mTORC2 has been shown to function as an important regulator of the actin cytoskeleton through its stimulation of F-actin stress fibers, paxillin, RhoA, Rac1, Cdc42, and protein kinase C α (PKCα). mTORC2 also phosphorylates the serine/threonine protein kinase Akt/PKB on serine residue Ser473, thus affecting metabolism and survival. Phosphorylation of Akt's serine residue Ser473 by mTORC2 stimulates Akt phosphorylation on threonine residue Thr308 by PDK1 and leads to full Akt activation. In addition, mTORC2 exhibits tyrosine protein kinase activity and phosphorylates the insulin-like growth factor 1 receptor (IGF-1R) and insulin receptor (InsR) on the tyrosine residues Tyr1131/1136 and Tyr1146/1151, respectively, leading to full activation of IGF-IR and InsR. | 1 | Applied and Interdisciplinary Chemistry |
The Rayleigh number above is for convection in a bulk fluid such as air or water, but convection can also occur when the fluid is inside and fills a porous medium, such as porous rock saturated with water. Then the Rayleigh number, sometimes called the Rayleigh-Darcy number, is different. In a bulk fluid, i.e., not in a porous medium, from the Stokes equation, the falling speed of a domain of size of liquid . In porous medium, this expression is replaced by that from Darcy's law , with the permeability of the porous medium. The Rayleigh or Rayleigh-Darcy number is then
This also applies to A-segregates, in the mushy zone of a solidifying alloy. | 1 | Applied and Interdisciplinary Chemistry |
The boiler is a rectangular furnace about on a side and tall. Its walls are made of a web of high pressure steel tubes about in diameter.
Fuel such as pulverized coal is air-blown into the furnace through burners located at the four corners, or along one wall, or two opposite walls, and it is ignited to rapidly burn, forming a large fireball at the center. The thermal radiation of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter. The water circulation rate in the boiler is three to four times the throughput. As the water in the boiler circulates it absorbs heat and changes into steam. It is separated from the water inside a drum at the top of the furnace. The saturated steam is introduced into superheat pendant tubes that hang in the hottest part of the combustion gases as they exit the furnace. Here the steam is superheated to to prepare it for the turbine.
Plants that use gas turbines to heat the water for conversion into steam use boilers known as heat recovery steam generators (HRSG). The exhaust heat from the gas turbines is used to make superheated steam that is then used in a conventional water-steam generation cycle, as described in the gas turbine combined-cycle plants section. | 1 | Applied and Interdisciplinary Chemistry |
*Allègre C.J., 2008. Isotope Geology (Cambridge University Press).
*Dickin A.P., 2005. Radiogenic Isotope Geology (Cambridge University Press).
*Faure G., Mensing T. M. (2004), Isotopes: Principles and Applications (John Wiley & Sons).
*Hoefs J., 2004. Stable Isotope Geochemistry (Springer Verlag).
*Sharp Z., 2006. Principles of Stable Isotope Geochemistry (Prentice Hall). | 0 | Theoretical and Fundamental Chemistry |
Many additional tests have since been run to apply and compare Hoffman's principles to reality. Among the experiments done, some of the more notable secondary nucleation tests are briefly explained in the table below. | 0 | Theoretical and Fundamental Chemistry |
Homoepitaxy is a kind of epitaxy performed with only one material, in which a crystalline film is grown on a substrate or film of the same material. This technology is often used to grow a more pure film than the substrate and to fabricate layers with different doping levels. In academic literature, homoepitaxy is often abbreviated to "homoepi".
Homotopotaxy is a process similar to homoepitaxy except that the thin-film growth is not limited to two-dimensional growth. Here the substrate is the thin-film material.
Heteroepitaxy is a kind of epitaxy performed with materials that are different from each other. In heteroepitaxy, a crystalline film grows on a crystalline substrate or film of a different material. This technology is often used to grow crystalline films of materials for which crystals cannot otherwise be obtained and to fabricate integrated crystalline layers of different materials. Examples include silicon on sapphire, gallium nitride (GaN) on sapphire, aluminium gallium indium phosphide (AlGaInP) on gallium arsenide (GaAs) or diamond or iridium, and graphene on hexagonal boron nitride (hBN).
Heteroepitaxy occurs when a film of different composition and/or crystalline films grown on a substrate. In this case, the amount of strain in the film is determined by the lattice mismatch Ԑ:
Where and are the lattice constants of the film and the substrate. The film and substrate could have similar lattice spacings but also different thermal expansion coefficients. If a film is grown at a high temperature, it can experience large strains upon cooling to room temperature. In reality, is necessary for obtaining epitaxy. If is larger than that, the film experiences a volumetric strain that builds with each layer until a critical thickness. With increased thickness, the elastic strain in the film is relieved by the formation of dislocations, which can become scattering centers that damage the quality of the structure. Heteroepitaxy is commonly used to create so-called bandgap systems thanks to the additional energy caused by de deformation. A very popular system with great potential for microelectronic applications is that of Si–Ge.
Heterotopotaxy is a process similar to heteroepitaxy except that thin-film growth is not limited to two-dimensional growth; the substrate is similar only in structure to the thin-film material.
Pendeo-epitaxy is a process in which the heteroepitaxial film is growing vertically and laterally simultaneously.
In 2D crystal heterostructure, graphene nanoribbons embedded in hexagonal boron nitride give an example of pendeo-epitaxy.
Grain-to-grain epitaxy involves epitaxial growth between the grains of a multicrystalline epitaxial and seed layer. This can usually occur when the seed layer only has an out-of-plane texture but no in-plane texture. In such a case, the seed layer consists of grains with different in-plane textures. The epitaxial overlayer then creates specific textures along each grain of the seed layer, due to lattice matching. This kind of epitaxial growth doesn't involve single-crystal films.
Epitaxy is used in silicon-based manufacturing processes for bipolar junction transistors (BJTs) and modern complementary metal–oxide–semiconductors (CMOS), but it is particularly important for compound semiconductors such as gallium arsenide. Manufacturing issues include control of the amount and uniformity of the depositions resistivity and thickness, the cleanliness and purity of the surface and the chamber atmosphere, the prevention of the typically much more highly doped substrate wafers diffusion of dopant to the new layers, imperfections of the growth process, and protecting the surfaces during manufacture and handling. | 0 | Theoretical and Fundamental Chemistry |
Particle image velocimetry (PIV) is an optical method of flow visualization used in education and research. It is used to obtain instantaneous velocity measurements and related properties in fluids. The fluid is seeded with tracer particles which, for sufficiently small particles, are assumed to faithfully follow the flow dynamics (the degree to which the particles faithfully follow the flow is represented by the Stokes number). The fluid with entrained particles is illuminated so that particles are visible. The motion of the seeding particles is used to calculate speed and direction (the velocity field) of the flow being studied.
Other techniques used to measure flows are laser Doppler velocimetry and hot-wire anemometry. The main difference between PIV and those techniques is that PIV produces two-dimensional or even three-dimensional vector fields, while the other techniques measure the velocity at a point. During PIV, the particle concentration is such that it is possible to identify individual particles in an image, but not with certainty to track it between images. When the particle concentration is so low that it is possible to follow an individual particle it is called particle tracking velocimetry, while laser speckle velocimetry is used for cases where the particle concentration is so high that it is difficult to observe individual particles in an image.
Typical PIV apparatus consists of a camera (normally a digital camera with a charge-coupled device (CCD) chip in modern systems), a strobe or laser with an optical arrangement to limit the physical region illuminated (normally a cylindrical lens to convert a light beam to a line), a synchronizer to act as an external trigger for control of the camera and laser, the seeding particles and the fluid under investigation. A fiber-optic cable or liquid light guide may connect the laser to the lens setup. PIV software is used to post-process the optical images. | 1 | Applied and Interdisciplinary Chemistry |
Transcriptional bursting, also known as transcriptional pulsing, is a fundamental property of genes in which transcription from DNA to RNA can occur in "bursts" or "pulses", which has been observed in diverse organisms, from bacteria to mammals. | 1 | Applied and Interdisciplinary Chemistry |
A second class of Ziegler–Natta catalysts are soluble in the reaction medium. Traditionally such homogeneous catalysts were derived from metallocenes, but the structures of active catalysts have been significantly broadened to include nitrogen-based ligands. | 0 | Theoretical and Fundamental Chemistry |
The arrangement of leaves on the stem is known as phyllotaxis. A large variety of phyllotactic patterns occur in nature:
;Alternate: One leaf, branch, or flower part attaches at each point or node on the stem, and leaves alternate direction, to a greater or lesser degree, along the stem.
;Basal: Arising from the base of the plant.
;Cauline: Attached to the aerial stem.
;Opposite: Two leaves, branches, or flower parts attach at each point or node on the stem. Leaf attachments are paired at each node.
;Decussate: An opposite arrangement in which each successive pair is rotated 90° from the previous.
;Whorled, or verticillate: Three or more leaves, branches, or flower parts attach at each point or node on the stem. As with opposite leaves, successive whorls may or may not be decussate, rotated by half the angle between the leaves in the whorl (i.e., successive whorls of three rotated 60°, whorls of four rotated 45°, etc.). Opposite leaves may appear whorled near the tip of the stem. Pseudoverticillate describes an arrangement only appearing whorled, but not actually so.
;Rosulate: Leaves form a rosette.
;Rows: The term, distichous, literally means two rows. Leaves in this arrangement may be alternate or opposite in their attachment. The term, 2-ranked, is equivalent. The terms, tristichous and tetrastichous, are sometimes encountered. For example, the "leaves" (actually microphylls) of most species of Selaginella are tetrastichous, but not decussate.
In the simplest mathematical models of phyllotaxis, the apex of the stem is represented as a circle. Each new node is formed at the apex, and it is rotated by a constant angle from the previous node. This angle is called the divergence angle. The number of leaves that grow from a node depends on the plant species. When a single leaf grows from each node, and when the stem is held straight, the leaves form a helix.
The divergence angle is often represented as a fraction of a full rotation around the stem. A rotation fraction of 1/2 (a divergence angle of 180°) produces an alternate arrangement, such as in Gasteria or the fan-aloe Kumara plicatilis. Rotation fractions of 1/3 (divergence angles of 120°) occur in beech and hazel. Oak and apricot rotate by 2/5, sunflowers, poplar, and pear by 3/8, and in willow and almond the fraction is 5/13. These arrangements are periodic. The denominator of the rotation fraction indicates the number of leaves in one period, while the numerator indicates the number of complete turns or gyres made in one period. For example:
* 180° (or ): two leaves in one circle (alternate leaves)
* 120° (or ): three leaves in one circle
* 144° (or ): five leaves in two gyres
* 135° (or ): eight leaves in three gyres.
Most divergence angles are related to the sequence of Fibonacci numbers . This sequence begins 1, 1, 2, 3, 5, 8, 13; each term is the sum of the previous two. Rotation fractions are often quotients of a Fibonacci number by the number two terms later in the sequence. This is the case for the fractions 1/2, 1/3, 2/5, 3/8, and 5/13. The ratio between successive Fibonacci numbers tends to the golden ratio . When a circle is divided into two arcs whose lengths are in the ratio , the angle formed by the smaller arc is the golden angle, which is . Because of this, many divergence angles are approximately .
In plants where a pair of opposite leaves grows from each node, the leaves form a double helix. If the nodes do not rotate (a rotation fraction of zero and a divergence angle of 0°), the two helices become a pair of parallel lines, creating a distichous arrangement as in maple or olive trees. More common in a decussate pattern, in which each node rotates by 1/4 (90°) as in the herb basil. The leaves of tricussate plants such as Nerium oleander form a triple helix.
The leaves of some plants do not form helices. In some plants, the divergence angle changes as the plant grows. In orixate phyllotaxis, named after Orixa japonica, the divergence angle is not constant. Instead, it is periodic and follows the sequence 180°, 90°, 180°, 270°. | 0 | Theoretical and Fundamental Chemistry |
Passive daytime radiative cooling can be used in various power plant condensers, including thermoelectric power plants and concentrated solar plants (CSP) to cool water for effective use within the heat exchanger. A generalized study of "a covered pond with radiative cooler revealed that 150 W/m2 flux could be achieved without loss of water." PDRC application for power plant condensers can reduce high water use and thermal pollution caused by water cooling.
For a thermoelectric power plant condenser, one study found that supplementing the air-cooled condenser for radiative cooling panels "get a 4096 kWhth/day cooling effect with a pump energy consumption of 11 kWh/day." For a concentrated solar plant (CSP) "on the supercritical cycle at 550ᵒC can be improved in 5% net output over an air-cooled system by integration with 14 m2 /kWe capacity radiative cooler." | 0 | Theoretical and Fundamental Chemistry |
Chemiluminescence is the emission of light by a chemical reaction. Some enzyme reactions produce light and this can be measured to detect product formation. These types of assay can be extremely sensitive, since the light produced can be captured by photographic film over days or weeks, but can be hard to quantify, because not all the light released by a reaction will be detected.
The detection of horseradish peroxidase by enzymatic chemiluminescence (ECL) is a common method of detecting antibodies in western blotting. Another example is the enzyme luciferase, this is found in fireflies and naturally produces light from its substrate luciferin. | 1 | Applied and Interdisciplinary Chemistry |
The concept of pressure is central to the study of fluids. A pressure can be identified for every point in a body of fluid, regardless of whether the fluid is in motion. Pressure can be measured using an aneroid, Bourdon tube, mercury column, or various other methods.
The concepts of total pressure and dynamic pressure arise from Bernoullis equation and are significant in the study of all fluid flows. These two pressures are not pressures in the usual sense - they cannot be measured using a pressure sensor. To avoid potential ambiguity when referring to pressure in fluid dynamics, many authors use the term static pressure to distinguish it from total pressure and dynamic pressure; the term static pressure is identical to the term pressure', and can be identified for every point in a fluid flow field.
In Aerodynamics, L.J. Clancy writes: "To distinguish it from the total and dynamic pressures, the actual pressure of the fluid, which is associated not with its motion but with its state, is often referred to as the static pressure, but where the term pressure alone is used it refers to this static pressure."
Bernoullis equation is foundational to the dynamics of incompressible fluids. In many fluid flow situations of interest, changes in elevation are insignificant and can be ignored. With this simplification, Bernoullis equation for incompressible flows can be expressed as
where:
* is static pressure,
* is dynamic pressure, usually denoted by ,
* is the density of the fluid,
* is the flow velocity, and
* is total pressure which is constant along any streamline. It is also known as the stagnation pressure.
Every point in a steadily flowing fluid, regardless of the fluid speed at that point, has its own static pressure , dynamic pressure , and total pressure . Static pressure and dynamic pressure are likely to vary significantly throughout the fluid but total pressure is constant along each streamline. In irrotational flow, total pressure is the same on all streamlines and is therefore constant throughout the flow.
The simplified form of Bernoulli's equation can be summarised in the following memorable word equation:
:static pressure + dynamic pressure = total pressure.
This simplified form of Bernoulli's equation is fundamental to an understanding of the design and operation of ships, low speed aircraft, and airspeed indicators for low speed aircraft – that is aircraft whose maximum speed will be less than about 30% of the speed of sound.
As a consequence of the widespread understanding of the term static pressure in relation to Bernoullis equation, many authors in the field of fluid dynamics also use static pressure rather than pressure in applications not directly related to Bernoullis equation.
The British Standards Institution, in its Standard Glossary of Aeronautical Terms, gives the following definition:
:4412 Static pressure The pressure at a point on a body moving with the fluid. | 1 | Applied and Interdisciplinary Chemistry |
* Epoxy resin used as the matrix component in many fiber reinforced plastics such as glass-reinforced plastic and graphite-reinforced plastic; casting; electronics encapsulation; construction; protective coatings; adhesives; sealing and joining.
* Polyimides and Bismaleimides used in printed circuit boards and in body parts of modern aircraft, aerospace composite structures, as a coating material and for glass reinforced pipes.
* Cyanate esters or polycyanurates for electronics applications with need for dielectric properties and high glass temperature requirements in aerospace structural composite components.
* Polyester resin fiberglass systems: sheet molding compounds and bulk molding compounds; filament winding; wet lay-up lamination; repair compounds and protective coatings.
* Polyurethanes: insulating foams, mattresses, coatings, adhesives, car parts, print rollers, shoe soles, flooring, synthetic fibers, etc. Polyurethane polymers are formed by combining two bi- or higher functional monomers/oligomers.
* Polyurea/polyurethane hybrids used for abrasion resistant waterproofing coatings.
* Vulcanized rubber.
* Bakelite, a phenol-formaldehyde resin used in electrical insulators and plasticware.
* Duroplast, light but strong material, similar to Bakelite formerly used in the manufacture of the Trabant automobile, currently used for household objects
* Urea-formaldehyde foam used in plywood, particleboard and medium-density fibreboard.
* Melamine resin used on worktop surfaces.
* Diallyl-phthalate (DAP) used in high temperature and mil-spec electrical connectors and other components. Usually glass filled.
* Epoxy novolac resins used for printed circuit boards, electrical encapsulation, adhesives and coatings for metal.
* Benzoxazines, used alone or hybridised with epoxy and phenolic resins, for structural prepregs, liquid molding and film adhesives for composite construction, bonding and repair.
* Mold or mold runners (the black plastic part in integrated circuits or semiconductors).
* Furan resins used in the manufacture of sustainable biocomposite construction, cements, adhesives, coatings and casting/foundry resins.
* Silicone resins used for thermoset polymer matrix composites and as ceramic matrix composite precursors.
* Thiolyte, an electrical insulating thermoset phenolic laminate material.
* Vinyl ester resins used for wet lay-up laminating, molding and fast setting industrial protection and repair materials. | 0 | Theoretical and Fundamental Chemistry |
Potable water is not well distributed in the world. 1.8 million deaths are attributed to unsafe water supplies every year, according to the WHO. Many people do not have any access, or do not have access to quality and quantity of potable water, though water itself is abundant. Poor people in developing countries can be close to major rivers, or be in high rainfall areas, yet not have access to potable water at all. There are also people living where lack of water creates millions of deaths every year.
Where the water supply system cannot reach the slums, people manage to use hand pumps, to reach the pit wells, rivers, canals, swamps and any other source of water. In most cases the water quality is unfit for human consumption. The principal cause of water scarcity is the growth in demand. Water is taken from remote areas to satisfy the needs of urban areas. Another reason for water scarcity is climate change: precipitation patterns have changed; rivers have decreased their flow; lakes are drying up; and aquifers are being emptied. | 1 | Applied and Interdisciplinary Chemistry |
The hallmark difference of elongation in eukaryotes in comparison to prokaryotes is its separation from transcription. While prokaryotes are able to undergo both cellular processes simultaneously, the spatial separation that is provided by the nuclear membrane prevents this coupling in eukaryotes. Eukaryotic elongation factor 2 (eEF2) is a regulateable GTP-dependent translocase that moves nascent polypeptide chains from the A-site to the P-site in the ribosome. Phosphorylation of threonine 56 is inhibitory to the binding of eEF2 to the ribosome. Cellular stressors, such as anoxia have proven to induce translational inhibition through this biochemical interaction. | 1 | Applied and Interdisciplinary Chemistry |
Aryl sulfonic acids are produced by the process of sulfonation. Usually the sulfonating agent is sulfur trioxide. A large scale application of this method is the production of alkylbenzenesulfonic acids:
In this reaction, sulfur trioxide is an electrophile and the arene is the nucleophile. The reaction is an example of electrophilic aromatic substitution.
Alkylsulfonic acids can be prepared by many methods. In sulfoxidation, alkanes are irradiated with a mixture of sulfur dioxide and oxygen. This reaction is employed industrially to produce alkyl sulfonic acids, which are used as surfactants.
Direct reaction of alkanes with sulfur trioxide is not generally useful, except for the conversion methanesulfonic acid to methanedisulfonic acid.
Many alkane sulfonic acids can be obtained by the addition of bisulfite to terminal alkenes. Bisulfite can also be alkylated by alkyl halides:
Sulfonic acids can be prepared by oxidation of thiols:
This pathway is the basis of the biosynthesis of taurine. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus pentachloride (), sulfur hexafluoride (), chlorine trifluoride (), the chlorite () ion, and the triiodide () ion are examples of hypervalent molecules. | 0 | Theoretical and Fundamental Chemistry |
Using the specific values of in matrix , it can be shown that the fourth-rank elasticity stiffness tensor may be written in 2-index Voigt notation as the matrix
The elasticity stiffness matrix has 5 independent constants, which are related to well known engineering elastic moduli in the following way. These engineering moduli are experimentally determined.
The compliance matrix (inverse of the elastic stiffness matrix) is
where . In engineering notation,
Comparing these two forms of the compliance matrix shows us that the longitudinal Young's modulus is given by
Similarly, the transverse Young's modulus is
The inplane shear modulus is
and the Poisson's ratio for loading along the polar axis is
Here, L represents the longitudinal (polar) direction and T represents the transverse direction. | 0 | Theoretical and Fundamental Chemistry |
Chromatographic assays measure product formation by separating the reaction mixture into its components by chromatography. This is usually done by high-performance liquid chromatography (HPLC), but can also use the simpler technique of thin layer chromatography. Although this approach can need a lot of material, its sensitivity can be increased by labelling the substrates/products with a radioactive or fluorescent tag. Assay sensitivity has also been increased by switching protocols to improved chromatographic instruments (e.g. ultra-high pressure liquid chromatography) that operate at pump pressure a few-fold higher than HPLC instruments (see High-performance liquid chromatography#Pump pressure). | 1 | Applied and Interdisciplinary Chemistry |
Grant McDonald Wilson (May 24, 1931 – September 10, 2012) was a notable American thermodynamicist. He is widely known to the fields of chemical engineering and physical chemistry for having developed the Wilson equation, one of the first attempts of practical importance to model nonideal behavior in liquid mixtures as observed in practice with common polar compounds such as alcohols, amines, etc. The equation has been in use in all commercial chemical process simulators to predict phase behavior and produce safe process designs of commercial and environmental protection importance to the chemical industry. He founded the company Wilco (now Wiltec) in 1977 to research, measure, commercialize, and publish thermophysical property data for numerous chemical mixtures of interest to the industry. The Journal of Chemical & Engineering Data published a posthumous issue in honor of Wilson in April 2014 in recognition of his extensive contributions to the field. | 0 | Theoretical and Fundamental Chemistry |
The mean generation time, Λ, is the average time from a neutron emission to a capture that results in fission. The mean generation time is different from the prompt neutron lifetime because the mean generation time only includes neutron absorptions that lead to fission reactions (not other absorption reactions). The two times are related by the following formula:
In this formula, k is the effective neutron multiplication factor, described below. | 0 | Theoretical and Fundamental Chemistry |
If the flow is steady and conservative, the mean residence time equals the ratio between the amount of fluid contained in the control volume and the flow rate through it:
This ratio is commonly known as the turnover time or flushing time. When applied to liquids, it is also known as the hydraulic retention time (HRT), hydraulic residence time or hydraulic detention time. In the field of chemical engineering this is also known as space time.
The residence time of a specific compound in a mixture equals the turnover time (that of the compound, as well as that of the mixture) only if the compound does not take part in any chemical reaction (otherwise its flow is not conservative) and its concentration is uniform.
Although the equivalence between the residence time and the ratio does not hold if the flow is not stationary or it is not conservative, it does hold on average if the flow is steady and conservative on average, and not necessarily at any instant. Under such conditions, which are common in queueing theory and supply chain management, the relation is known as Little's Law. | 0 | Theoretical and Fundamental Chemistry |
Submarine outfalls exist, existed or have been considered in the following locations, among many others:
;Africa
* Casablanca (Morocco).
* Cape Town (South Africa).
;Asia
* Manila Bay (Philippines).
* Mumbai (India).
* Mutwall ( Sri Lanka).
* Wellawaththa (Sri Lanka).
* Lunawa (Sri Lanka).
;Oceania
* Anglesea, Victoria.
* Geelong, Victoria.
* Sydney (e.g., Bondi Ocean Outfall Sewer)
;Europe
* Barcelona, Spain
* Costa do Estoril (Portugal)
* Marmara Sea near Istanbul (Turkey)
* San Sebastián (Spain)
* Split (Croatia)
* Thames Estuary downstream of London (UK)
* Edinburgh, Scotland.
;North America
* Honolulu (USA)
* New York Bight (USA)
* Southern California Bight (USA). and
* Victoria, British Columbia, (Canada).
* Santa Monica, United States (world's first)
* Boston, United States (world's largest)
* The city of San Diego used Pacific Ocean dilution of primary treated effluent into the 21st century.
;Latin America and the Caribbean
* Cartagena, Colombia
* Ipanema Beach beach from Rio de Janeiro (Brazil). This outfall, built in 1975, discharges untreated wastewater through a pipe with a diameter of 2.4m and a length of 4,775m at a depth of 27m.
* Sosua (Dominican Republic). | 1 | Applied and Interdisciplinary Chemistry |
Bacteria of the genera Chromobacterium, Janthinobacterium, and Pseudoalteromonas produce a toxic secondary metabolite, violacein, to deter protozoan predation. Violacein is released when bacteria are consumed, killing the protozoan. Another bacteria, Pseudomonas aeruginosa, aggregates into quorum sensing biofilms which may aid the coordinated release of toxins to protect against predation by protozoans. Flagellates were allowed to grow and were present in a biofilm of P. aeruginosa grown for three days, but no flagellates were detected after seven days. This suggests that concentrated and coordinated release of extracellular toxins by biofilms has a greater effect than unicellular excretions. Bacterial growth is inhibited not only by bacterial toxins, but also by secondary metabolites produced by fungi as well. The most well-known of these, first discovered and published by Alexander Fleming in 1929, described the antibacterial properties of a "mould juice" isolated from Penicillium notatum. He named the substance penicillin, and it became the worlds first broad-spectrum antibiotic. Many fungi are either pathogenic saprophytic, or live within plants without harming them as endophytes, and many of these have been documented to produce chemicals with antagonistic effects against a variety of organisms, including fungi, bacteria, and protozoa. Studies of coprophilous fungi have found antifungal agents which reduce the fitness of competing fungi. In addition, sclerotia of Aspergillus flavus contained a number of previously unknown aflavinines which were much more effective at reducing predation by the fungivorous beetle, Carpophilus hemipterus, than aflatoxins which A. flavus also produced and it has been hypothesized that ergot alkaloids, mycotoxins produced by Claviceps purpurea', may have evolved to discourage herbivory of the host plant. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, chemical stability is the thermodynamic stability of a chemical system.
Thermodynamic stability occurs when a system is in its lowest energy state, or in chemical equilibrium with its environment. This may be a dynamic equilibrium in which individual atoms or molecules change form, but their overall number in a particular form is conserved. This type of chemical thermodynamic equilibrium will persist indefinitely unless the system is changed. Chemical systems might undergo changes in the phase of matter or a set of chemical reactions.
State A is said to be more thermodynamically stable than state B if the Gibbs free energy of the change from A to B is positive. | 0 | Theoretical and Fundamental Chemistry |
An elbow is installed between two lengths of pipe (or tubing) to allow a change of direction, usually a 90° or 45° angle; 22.5° elbows are also available. The ends may be machined for butt welding, threaded (usually female), or socketed. When the ends differ in size, it is known as a reducing (or reducer) elbow.
Elbows are also categorized by length. The radius of curvature of a long-radius (LR) elbow is 1.5 times the pipe diameter, but a short-radius (SR) elbow has a radius equal to the pipe diameter. Wide available short elbows are typically used in pressurized systems and physically tight locations.
Long elbows are used in low-pressure gravity-fed systems and other applications where low turbulence and minimum deposition of entrained solids are of concern. They are available in acrylonitrile butadiene styrene (ABS plastic), polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), and copper, and are used in DWV systems, sewage, and central vacuum systems. | 1 | Applied and Interdisciplinary Chemistry |
In 2006, the Australian military deemed mefloquine "a third-line drug" alternative, and over the five years from 2011 only 25 soldiers had been prescribed the drug, and only in cases of their intolerance for other alternatives. Between 2001 and 2012, 16,000 Canadian soldiers sent to Afghanistan were given the drug as a preventative measure. In 2013, the US Army banned mefloquine from use by its special forces such as the Green Berets. In autumn 2016, the UK military followed suit with their Australian peers after a parliamentary inquiry into the matter revealed that it can cause permanent side effects and brain damage.
In early December 2016, the German defence ministry removed mefloquine from the list of medications it would provide to its soldiers.
In autumn 2016, Canadian Surgeon General Brigadier General Hugh Colin MacKay told a parliamentary committee that faulty science supported the assertion that the drug has indelible noxious side effects. An expert from Health Canada named Barbara Raymond told the same committee that the evidence she had read failed to support the conclusion of indelible side effects. Canadian soldiers who took mefloquine when deployed overseas have claimed they have been left with ongoing mental health problems.
In 2020 the UK Ministry of Defence (MoD) admitted to a breach of duty regarding the use of Mefloquine. by acknowledging numerous instances of failure to assess the risks and warn of potential side effects of the drug. | 0 | Theoretical and Fundamental Chemistry |
In crystalline materials, Umklapp scattering (also U-process or Umklapp process) is a scattering process that results in a wave vector (usually written k) which falls outside the first Brillouin zone. If a material is periodic, it has a Brillouin zone, and any point outside the first Brillouin zone can also be expressed as a point inside the zone. So, the wave vector is then mathematically transformed to a point inside the first Brillouin zone. This transformation allows for scattering processes which would otherwise violate the conservation of momentum: two wave vectors pointing to the right can combine to create a wave vector that points to the left. This non-conservation is why crystal momentum is not a true momentum.
Examples include electron-lattice potential scattering or an anharmonic phonon-phonon (or electron-phonon) scattering process, reflecting an electronic state or creating a phonon with a momentum k-vector outside the first Brillouin zone. Umklapp scattering is one process limiting the thermal conductivity in crystalline materials, the others being phonon scattering on crystal defects and at the surface of the sample.
The left panel of Figure 1 schematically shows the possible scattering processes of two incoming phonons with wave-vectors (k-vectors) k and k (red) creating one outgoing phonon with a wave vector k (blue). As long as the sum of k and k stay inside the first Brillouin zone (grey squares), k is the sum of the former two, thus conserving phonon momentum. This process is called normal scattering (N-process).
With increasing phonon momentum and thus larger wave vectors k and k, their sum might point outside the first Brillouin zone (k). As shown in the right panel of Figure 1, k-vectors outside the first Brillouin zone are physically equivalent to vectors inside it and can be mathematically transformed into each other by the addition of a reciprocal lattice vector G'. These processes are called Umklapp scattering and change the total phonon momentum.
Umklapp scattering is the dominant process for electrical resistivity at low temperatures for low defect crystals (as opposed to phonon-electron scattering, which dominates at high temperatures, and high-defect lattices which lead to scattering at any temperature.)
Umklapp scattering is the dominant process for thermal resistivity at high temperatures for low defect crystals. The thermal conductivity for an insulating crystal where the U-processes are dominant has 1/T dependence. | 0 | Theoretical and Fundamental Chemistry |
Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year being produced during the early 1990s, but is occasionally also used as a solvent. It is toxic, reacts with water, and is also listed under the Chemical Weapons Convention as it may be used for the production of chemical weapons.
Thionyl chloride is sometimes confused with sulfuryl chloride, , but the properties of these compounds differ significantly. Sulfuryl chloride is a source of chlorine whereas thionyl chloride is a source of chloride ions. | 0 | Theoretical and Fundamental Chemistry |
In the following reaction network, A is irreversibly converted to an intermediate B, which irreversibly reacts to form C.
The pools of A, B, and C have delta values defined as δ, δ, and δ respectively. These values are related to the ratio of heavy to light isotopes in each pool, and are the conventional means by which scientists express the isotopic composition of materials. Importantly, δ is distinct from δ listed on the diagram, as δ is the isotopic composition of B produced from A before it mixes with the pool of B. The isotopic compositions of the pools and products are related through fractionation factors that reflect the kinetic isotope effects (KIEs) associated with each reaction. For A → B,
Rearranging for δ gives in which . In many cases, and . This is consistent with a normal kinetic isotope effect in which the product is slightly depleted in a heavy isotope relative to the reactant. If the isotope effect is small, as is typical for C and N, and . From this, we can see that the product produced from A will be depleted by roughly ‰ relative to the starting material.
At steady state, the mass flux of material entering pool B must equal the flux leaving pool B. In other words, the amounts of heavy and light isotopes entering and exiting the pool must be identical, so . Since there is no flux of material out of pool C, its delta value is also equal to . This analysis shows that the end product of a linear, irreversible reaction network has an isotopic composition determined solely by the composition of the starting material and the KIE of the first reaction in the network. | 0 | Theoretical and Fundamental Chemistry |
Glycoside hydrolases are typically named after the substrate that they act upon. Thus glucosidases catalyze the hydrolysis of glucosides and xylanases catalyze the cleavage of the xylose based homopolymer xylan. Other examples include lactase, amylase, chitinase, sucrase, maltase, neuraminidase, invertase, hyaluronidase and lysozyme. | 0 | Theoretical and Fundamental Chemistry |
Education in Chemistry (often referred to by its brand EiC) is a print and online magazine covering all areas of chemistry education, mainly concentrating on the teaching of chemistry in secondary schools and universities. It is published by the Royal Society of Chemistry, which also publishes Chemistry Education Research and Practice, a peer-reviewed academic journal on the same topic. | 1 | Applied and Interdisciplinary Chemistry |
Sir William Herschel was one of the first to advocate the use of fingerprinting in the identification of criminal suspects. While working for the Indian Civil Service, he began to use thumbprints on documents as a security measure to prevent the then-rampant repudiation of signatures in 1858.
In 1877 at Hooghly (near Kolkata), Herschel instituted the use of fingerprints on contracts and deeds, and he registered government pensioners fingerprints to prevent the collection of money by relatives after a pensioners death.
In 1880, Henry Faulds, a Scottish surgeon in a Tokyo hospital, published his first paper on the subject in the scientific journal Nature, discussing the usefulness of fingerprints for identification and proposing a method to record them with printing ink. He established their first classification and was also the first to identify fingerprints left on a vial. Returning to the UK in 1886, he offered the concept to the Metropolitan Police in London, but it was dismissed at that time.
Faulds wrote to Charles Darwin with a description of his method, but, too old and ill to work on it, Darwin gave the information to his cousin, Francis Galton, who was interested in anthropology. Having been thus inspired to study fingerprints for ten years, Galton published a detailed statistical model of fingerprint analysis and identification and encouraged its use in forensic science in his book Finger Prints. He had calculated that the chance of a "false positive" (two different individuals having the same fingerprints) was about 1 in 64 billion.
Juan Vucetich, an Argentine chief police officer, created the first method of recording the fingerprints of individuals on file. In 1892, after studying Galtons pattern types, Vucetich set up the worlds first fingerprint bureau. In that same year, Francisca Rojas of Necochea was found in a house with neck injuries whilst her two sons were found dead with their throats cut. Rojas accused a neighbour, but despite brutal interrogation, this neighbour would not confess to the crimes. Inspector Alvarez, a colleague of Vucetich, went to the scene and found a bloody thumb mark on a door. When it was compared with Rojas' prints, it was found to be identical with her right thumb. She then confessed to the murder of her sons.
A Fingerprint Bureau was established in Calcutta (Kolkata), India, in 1897, after the Council of the Governor General approved a committee report that fingerprints should be used for the classification of criminal records. Working in the Calcutta Anthropometric Bureau, before it became the Fingerprint Bureau, were Azizul Haque and Hem Chandra Bose. Haque and Bose were Indian fingerprint experts who have been credited with the primary development of a fingerprint classification system eventually named after their supervisor, Sir Edward Richard Henry. The Henry Classification System, co-devised by Haque and Bose, was accepted in England and Wales when the first United Kingdom Fingerprint Bureau was founded in Scotland Yard, the Metropolitan Police headquarters, London, in 1901. Sir Edward Richard Henry subsequently achieved improvements in dactyloscopy.
In the United States, Henry P. DeForrest used fingerprinting in the New York Civil Service in 1902, and by December 1905, New York City Police Department Deputy Commissioner Joseph A. Faurot, an expert in the Bertillon system and a fingerprint advocate at Police Headquarters, introduced the fingerprinting of criminals to the United States. | 0 | Theoretical and Fundamental Chemistry |
This mechanism is similar to the hydrolysis of esters, the ammonia attacks the electrophilic carbonyl carbon forming a tetrahedral intermediate. The reformation of the C-O double bond ejects the ester. The alkoxide deprotonates the ammonia forming an alcohol and amide as products. | 1 | Applied and Interdisciplinary Chemistry |
Assume a fluid enters an internally contracting nozzle at cross-section 0, and passes through a throat of smaller area at cross-section 4. A normal shock is assumed to start at the beginning of the nozzle contraction, and this point in the nozzle is referred to as cross-section 2. Due to conservation of mass within the nozzle, the mass flow rate at each cross section must be equal:
For an ideal compressible gas, the mass flow rate at each cross-section can be written as,
where is the cross-section area at the specified point, is the Isentropic expansion factor of the gas, is the Mach number of the flow at the specified cross-section, is the ideal gas constant, is the stagnation pressure, and is the stagnation temperature.
Setting the mass flow rates equal at the inlet and throat, and recognizing that the total temperature, ratio of specific heats, and gas constant are constant, the conservation of mass simplifies to,
Solving for A/A,
Three assumptions will be made: the flow from behind the normal shock in the inlet is isentropic, or p = p , the flow at the throat (point 4) is sonic such that M = 1, and the pressures between the various point are related through normal shock relations, resulting in the following relation between inlet and throat pressures,
And since M = 1, shock relations at the throat simplify to,
Substituting for and in the area ratio expression gives,
This can also be written as, | 1 | Applied and Interdisciplinary Chemistry |
Fluorescence spectroscopy is used in, among others, biochemical, medical, and chemical research fields for analyzing organic compounds. There has also been a report of its use in differentiating malignant skin tumors from benign.
Atomic Fluorescence Spectroscopy (AFS) techniques are useful in other kinds of analysis/measurement of a compound present in air or water, or other media, such as CVAFS which is used for heavy metals detection, such as mercury.
Fluorescence can also be used to redirect photons, see fluorescent solar collector.
Additionally, Fluorescence spectroscopy can be adapted to the microscopic level using microfluorimetry
In analytical chemistry, fluorescence detectors are used with HPLC.
In the field of water research, fluorescence spectroscopy can be used to monitor water quality by detecting organic pollutants. Recent advances in computer science and machine learning have even enabled detection of bacterial contamination of water | 0 | Theoretical and Fundamental Chemistry |
Following multiphoton or tunnel ionization the electron is being accelerated by inverse Bremsstrahlung and can collide with the nearby molecules and generate new electrons through collisions. If the pulse duration is long, the newly ionized electrons can be accelerated and eventually avalanche or cascade ionization follows. Once the density of the electrons reaches a critical value, breakdown occurs and high density plasma is created which has no memory of the laser pulse. So, the criterion for the shortness of a pulse in dense media is as follows: A pulse interacting with a dense matter is considered to be short if during the interaction the threshold for the avalanche ionization is not reached. At the first glance this definition may appear to be too limiting. Fortunately, due to the delicately balanced behavior of the pulses in dense media, the threshold cannot be reached easily. The phenomenon responsible for the balance is the intensity clamping through the onset of filamentation process during the propagation of strong laser pulses in dense media.
A potentially important development to LIBS involves the use of a short laser pulse as a spectroscopic source. In this method, a plasma column is created as a result of focusing ultrafast laser pulses in a gas. The self-luminous plasma is far superior in terms of low level of continuum and also smaller line broadening. This is attributed to the lower density of the plasma in the case of short laser pulses due to the defocusing effects which limits the intensity of the pulse in the interaction region and thus prevents further multiphoton/tunnel ionization of the gas. | 0 | Theoretical and Fundamental Chemistry |
Silicon carbide, dissolved in a basic oxygen furnace used for making steel, acts as a fuel. The additional energy liberated allows the furnace to process more scrap with the same charge of hot metal. It can also be used to raise tap temperatures and adjust the carbon and silicon content. Silicon carbide is cheaper than a combination of ferrosilicon and carbon, produces cleaner steel and lower emissions due to low levels of trace elements, has a low gas content, and does not lower the temperature of steel. | 1 | Applied and Interdisciplinary Chemistry |
Aluminium smelting is the process of extracting aluminium from its oxide, alumina, generally by the Hall-Héroult process. Alumina is extracted from the ore bauxite by means of the Bayer process at an alumina refinery.
This is an electrolytic process, so an aluminium smelter uses huge amounts of electric power; smelters tend to be located close to large power stations, often hydro-electric ones, in order to hold down costs and reduce the overall carbon footprint. Smelters are often located near ports, since many smelters use imported alumina. | 1 | Applied and Interdisciplinary Chemistry |
A primer dimer (PD) is a potential by-product in the polymerase chain reaction (PCR), a common biotechnological method. As its name implies, a PD consists of two primer molecules that have attached (hybridized) to each other because of strings of complementary bases in the primers. As a result, the DNA polymerase amplifies the PD, leading to competition for PCR reagents, thus potentially inhibiting amplification of the DNA sequence targeted for PCR amplification. In quantitative PCR, PDs may interfere with accurate quantification. | 1 | Applied and Interdisciplinary Chemistry |
Also known as luminophors, these compounds absorb the scintillation of the base and then emit at larger wavelength, effectively converting the ultraviolet radiation of the base into the more easily transferred visible light. Further increasing the attenuation length can be accomplished through the addition of a second fluor, referred to as a spectrum shifter or converter, often resulting in the emission of blue or green light.
Common fluors include polyphenyl hydrocarbons, oxazole and oxadiazole aryls, especially, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), 1,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD), and 2-(4’-tert-butylphenyl)-5-(4’’-biphenylyl)-1,3,4-oxadiazole (B-PBD). | 0 | Theoretical and Fundamental Chemistry |
Clemens Alexander Winkler (December 26, 1838 – October 8, 1904) was a German chemist who discovered the element germanium in 1886, solidifying Dmitri Mendeleev's theory of periodicity. | 1 | Applied and Interdisciplinary Chemistry |
GPCRs downstream signals have been shown to possibly interact with integrin signals, such as FAK. Integrin signaling will phosphorylate FAK, which can then decrease GPCR G activity. | 1 | Applied and Interdisciplinary Chemistry |
Many lichens reproduce asexually, either by a piece breaking off and growing on its own (vegetative reproduction) or through the dispersal of diaspores containing a few algal cells surrounded by fungal cells. Because of the relative lack of differentiation in the thallus, the line between diaspore formation and vegetative reproduction is often blurred. Fruticose lichens can fragment, and new lichens can grow from the fragment (vegetative reproduction). Many lichens break up into fragments when they dry, dispersing themselves by wind action, to resume growth when moisture returns. Soredia (singular: "soredium") are small groups of algal cells surrounded by fungal filaments that form in structures called soralia, from which the soredia can be dispersed by wind. Isidia (singular: "isidium") are branched, spiny, elongated, outgrowths from the thallus that break off for mechanical dispersal. Lichen propagules (diaspores) typically contain cells from both partners, although the fungal components of so-called "fringe species" rely instead on algal cells dispersed by the "core species". | 1 | Applied and Interdisciplinary Chemistry |
For laminar flow, the thermal entrance length is a function of pipe diameter and the dimensionless Reynolds number and Prandtl number.
where
* is the Reynolds number (based on the pipe diameter) and
* is the Prandtl number.
The Prandtl number modifies the hydrodynamic entrance length to determine thermal entrance length. The Prandtl number is the dimensionless number for the ratio of momentum diffusivity to thermal diffusivity. The thermal entrance length for a fluid with a Prandtl number greater than one will be longer than the hydrodynamic entrance length, and shorter if the Prandtl number is less than one. For example, molten sodium has a low Prandtl number of 0.004, so the thermal entrance length will be significantly shorter than the hydraulic entrance length.
For turbulent flows, thermal entrance length may be approximated solely based on pipe diameter.
where
* is the thermal entrance length and
* is the pipe inner diameter. | 1 | Applied and Interdisciplinary Chemistry |
Samarium(II) iodide is a reagent for carbon-carbon bond formation, for example in a Barbier reaction (similar to the Grignard reaction) between a ketone and an alkyl iodide to form a tertiary alcohol:
:RI + RCOR → RRC(OH)R
Typical reaction conditions use SmI in THF in the presence of catalytic NiI.
Esters react similarly (adding two R groups), but aldehydes give by-products. The reaction is convenient in that it is often very rapid (5 minutes or less in the cold). Although samarium(II) iodide is considered a powerful single-electron reducing agent, it does display remarkable chemoselectivity among functional groups. For example, sulfones and sulfoxides can be reduced to the corresponding sulfide in the presence of a variety of carbonyl-containing functionalities (such as esters, ketones, amides, aldehydes, etc.). This is presumably due to the considerably slower reaction with carbonyls as compared to sulfones and sulfoxides. Furthermore, hydrodehalogenation of halogenated hydrocarbons to the corresponding hydrocarbon compound can be achieved using samarium(II) iodide. Also, it can be monitored by the color change that occurs as the dark blue color of SmI in THF discharges to a light yellow once the reaction has occurred. The picture shows the dark colour disappearing immediately upon contact with the Barbier reaction mixture.
Work-up is with dilute hydrochloric acid, and the samarium is removed as aqueous Sm.
Carbonyl compounds can also be coupled with simple alkenes to form five, six or eight membered rings.
Tosyl groups can be removed from N-tosylamides almost instantaneously, using SmI in conjunction with distilled water and an amine base. The reaction is even effective for deprotection of sensitive substrates such as aziridines:
In the Markó-Lam deoxygenation, an alcohol could be almost instantaneously deoxygenated by reducing their toluate ester in presence of SmI.
The applications of SmI have been reviewed. The book Organic Synthesis Using Samarium Diiodide, published in 2009, gives a detailed overview of reactions mediated by SmI. | 0 | Theoretical and Fundamental Chemistry |
Arthur W. Thomas, then an instructor in Food Chemistry at Columbia University, volunteered for military service in the spring of 1917 and was mustered in as a First Lieutenant in the newly formed Sanitary Corps in the U.S. National Army in September 1917. He was assigned to the Food and Nutrition Section or Division of the Sanitary Corps under the command of the Surgeon General. Thomas took part in food surveys at army cantonments in the Northeast and also served in the Office of the Surgeon General in Washington. The officers in the Food and Nutrition Section included those who in civilian life were professors in chemistry and biochemistry.
In January 1918 Thomas was promoted to captain; In March 1918 he was sent to England where he participated in food surveys at US Army cantonments in southern England.
From April 1918 to June 1919 Thomas served in France where he was stationed in Base Section No. 1 in the northwest, in the front lines with the 26th (Yankee) and 89th (Middle West) Divisions in the Toul sector, and at the Sanitary Corps laboratory station at Dijon where he worked with other offices in the updating of army food rations. In the summer of 1918 he also gave instruction at the Second Army Corps school. In June 1919 he was involved in inspections of the adequacies of ship bakeries and galleys of three dozen Army and Navy troop transports returning thousands of men to America. | 0 | Theoretical and Fundamental Chemistry |
A percolation trench, also called an infiltration trench, is a type of best management practice (BMP) that is used to manage stormwater runoff, prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. It is a shallow excavated trench filled with gravel or crushed stone that is designed to infiltrate stormwater though permeable soils into the groundwater aquifer.
A percolation trench is similar to a dry well, which is typically an excavated hole filled with gravel. Another similar drainage structure is a French drain, which directs water away from a building foundation, but is usually not designed to protect water quality. | 1 | Applied and Interdisciplinary Chemistry |
In recent years, there has been increasing recognition that methylmercury affects fish and wildlife health, both in acutely polluted ecosystems and ecosystems with modest methylmercury levels. Two reviews document numerous studies of diminished reproductive success of fish, fish-eating birds, and mammals due to methylmercury contamination in aquatic ecosystems. | 0 | Theoretical and Fundamental Chemistry |
Metabolomics is the scientific study of chemical processes involving metabolites, the small molecule substrates, intermediates, and products of cell metabolism. Specifically, metabolomics is the "systematic study of the unique chemical fingerprints that specific cellular processes leave behind", the study of their small-molecule metabolite profiles. The metabolome represents the complete set of metabolites in a biological cell, tissue, organ, or organism, which are the end products of cellular processes. Messenger RNA (mRNA), gene expression data, and proteomic analyses reveal the set of gene products being produced in the cell, data that represents one aspect of cellular function. Conversely, metabolic profiling can give an instantaneous snapshot of the physiology of that cell, and thus, metabolomics provides a direct "functional readout of the physiological state" of an organism. There are indeed quantifiable correlations between the metabolome and the other cellular ensembles (genome, transcriptome, proteome, and lipidome), which can be used to predict metabolite abundances in biological samples from, for example mRNA abundances. One of the ultimate challenges of systems biology is to integrate metabolomics with all other -omics information to provide a better understanding of cellular biology. | 1 | Applied and Interdisciplinary Chemistry |
In evolutionary biology, sequence space is a way of representing all possible sequences (for a protein, gene or genome). The sequence space has one dimension per amino acid or nucleotide in the sequence leading to highly dimensional spaces.
Most sequences in sequence space have no function, leaving relatively small regions that are populated by naturally occurring genes. Each protein sequence is adjacent to all other sequences that can be reached through a single mutation. It has been estimated that the whole functional protein sequence space has been explored by life on the Earth. Evolution by natural selection can be visualised as the process of sampling nearby sequences in sequence space and moving to any with improved fitness over the current one. | 1 | Applied and Interdisciplinary Chemistry |
The Flippin-Lodge and Bürgi-Dunitz angles were central, practically, to the development of a clearer understanding of asymmetric induction during nucleophilic attack at hindered carbonyl centers in synthetic organic chemistry. It was in this area that was first defined by Heathcock, and has been primarily used. Larger substituents around the electrophilic center, such as tert-butyls, lead to higher stereoselectivities in asymmetric induction than smaller substituents like methyls. The trajectory of the nucleophile approaching a center flanked by two large substituents is more limited, i.e. the Flippin–Lodge angle is smaller. For example, in Mukaiyama aldol addition, the bulkier phenyl tert-butyl ketone has a higher selectivity for the syn isomer than the smaller phenyl methyl ketone. Likewise, if bulky a nucleophile, such as a t-butylmethylsilyl enolate, is used, the selectivity is higher than for a small nucleophile like a lithium enolate.
Given a reaction system of a given nucleophile with a carbonyl having the two substituents R and R, where substituent R is sterically small relative to substituent R (e.g., R = hydrogen atom, R = phenyl), the values that are inferred from the reaction outcomes and theoretical studies tend to be larger; alternatively, if the hydrocarbon substituents are nearer or equal in steric size, the inferred values diminish and may approach zero (e.g., R = tert-butyl, R = phenyl). Thus, from the perspective of simpler electrophile systems where only steric bulk come into play, the attack trajectories of the classes of nucleophiles studied makes clear that as the disparity in size between the substituent increase, there is a perturbation in the FL angle that can be used to provide higher stereoselectivities in designed reaction systems; while the patterns become more complex when factors other than steric bulk come into play (see section above on orbital contributions), Flippin, Lodge, and Heathcock were able to show that generalizations could be made that were useful to reaction design.
A surpassing area of application has been in studies of various aldol reactions, the addition of ketone-derived enol/enolate nucleophiles to electrophilic aldehydes, each with functional groups varying in size and group polarity; the way that features on the nucleophile and electrophile impact the stereochemistry seen in reaction products, and in particular, the diastereoselection exhibited, has been carefully mapped (see the steric and orbital description above, the aldol reaction article, and David Evans related Harvard teaching materials on the aldol). These studies have improved the chemists abilities to design enantioselective and diastereoselective reactions needed in the construction of complex molecules, such as the natural product spongistatins and modern drugs. It remains to be seen whether a particular range of values contributes similarly to the arrangement of functional groups within proteins and so to their conformational stabilities (as has been reported in relation to the BD trajectory), or to other BD-correlated stabilizations of conformation important to structure and reactivity. | 0 | Theoretical and Fundamental Chemistry |
Kujawinski was an undergraduate student at Massachusetts Institute of Technology (MIT). She was awarded the undergraduate teaching award from the Department of Chemistry. She moved to the Woods Hole Oceanographic Institution (WHOI) as a doctoral researcher, where she worked in chemical oceanography. Her doctoral research considered the effect of protozoan grazers on polychlorinated biphenyl cycling. After graduating Kujawinski joined the Ohio State University as a postdoctoral scholar. | 0 | Theoretical and Fundamental Chemistry |
The function of liver glycogen is to maintain glucose homeostasis, generating glucose via glycogenolysis to compensate for the decrease of glucose levels that can occur between meals. Thanks to the presence of the glucose-6-phosphatase enzyme, the hepatocytes are capable of turning glycogen to glucose, releasing it into blood to prevent hypoglycemia.
In skeletal muscle, glycogen is used as an energy source for muscle contraction during exercise. The different functions of glycogen in muscle or liver make the regulation mechanisms of its metabolism differ in each tissue. These mechanisms are based mainly on the differences on structure and on the regulation of the enzymes that catalyze synthesis, glycogen synthase (GS), and degradation, glycogen phosphorylase (GF). | 1 | Applied and Interdisciplinary Chemistry |
In the Arrhenius model of reaction rates, activation energy is the minimum amount of energy that must be available to reactants for a chemical reaction to occur. The activation energy (E) of a reaction is measured in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol). Activation energy can be thought of as the magnitude of the potential barrier (sometimes called the energy barrier) separating minima of the potential energy surface pertaining to the initial and final thermodynamic state. For a chemical reaction to proceed at a reasonable rate, the temperature of the system should be high enough such that there exists an appreciable number of molecules with translational energy equal to or greater than the activation energy. The term "activation energy" was introduced in 1889 by the Swedish scientist Svante Arrhenius. | 0 | Theoretical and Fundamental Chemistry |
Edward Roberts FRSC., is a British-born American scientist with expertise in biochemistry and synthetic organic chemistry. He is recognized for his significant contributions to medicinal chemistry, the design and discovery of new medicines in the development of novel therapeutics. | 0 | Theoretical and Fundamental Chemistry |
Barrier activity has been linked to the disruption of specific processes in the heterochromatin formation pathway. These types of insulators modify the nucleosomal substrate in the reaction cycle that is central to heterochromatin formation. Modifications are achieved through various mechanisms including nucleosome removal, in which nucleosome-excluding elements disrupt heterochromatin from spreading and silencing (chromatin-mediated silencing). Modification can also be done through recruitment of histone acetyltransferase(s) and ATP-dependent nucleosome remodelling complexes. | 1 | Applied and Interdisciplinary Chemistry |
Aldol condensation of acetone and ethyl acetoacetate gave β-keto-ester 3. A Grignard reaction involving methylmagnesium bromide provided alcohol 4, which was subjected to acid catalyzed elimination to give diene 5. Reduction and acetylation gave diene 7 (Scheme 3, compound 1). | 0 | Theoretical and Fundamental Chemistry |
Claire Jane Carmalt is a British chemist who is a Professor of Inorganic Chemistry and Head of the Department of Chemistry at University College London. Her research considers the synthesis of molecular precursors and the development of thin film deposition techniques. | 0 | Theoretical and Fundamental Chemistry |
Quick clay has a remolded strength which is much less than its strength upon initial loading. This is caused by its highly unstable clay particle structure.
Quick clay is originally deposited in a marine environment. Clay mineral particles are always negatively charged because of the presence of permanent negative charges and pH dependent charges at their surface. Because of the need to respect electro-neutrality and a net zero electrical charge balance, these negative electrical charges are always compensated by the positive charges born by cations (such as Na) adsorbed onto the surface of the clay, or present in the clay pore water. Exchangeable cations are present in the clay minerals interlayers and on the external basal planes of clay platelets. Cations also compensate the negative charges on the clay particle edges caused by the protolysis of silanol and aluminol groups (pH dependent charges). So, clay platelets are always surrounded by an electrical double layer (EDL), or diffuse double layer (DDL). The thickness of EDL depends on the salinity of water. Under salty conditions (at high ionic strength) EDL is compressed (or said to be collapsed). It facilitates the aggregation of clay platelets which flocculate and stick together in a more stable aggregates structure. After the marine clay deposit is uplifted and is no longer exposed to salt water conditions, rainwater can slowly infiltrate the poorly compacted clay layer and the excess of NaCl present in seawater can also diffuse out of the clay. As a result, the EDL is less compressed and can expand. It results in a stronger electrostatic repulsion between negatively charged clay platelets which can more easily become dispersed and form stable suspensions in water (peptization phenomenon). The effect leads to a destabilization of the clay aggregates structure.
In case of insufficient mechanical compaction of the clay layer, and with a shear stress, the weaker EDL compression by the salts in the quick clay results in clay particle repulsion and leads to their realignment in a structure that is weaker and unstable. Quick clay regains strength rapidly when salt is again added (compression of the EDL), which allows clay particles to restore their cohesion with one another. | 0 | Theoretical and Fundamental Chemistry |
There are no d-d electron transitions in d metal complexes because the d orbitals are completely filled. Thus, UV-vis absorption bands are not observed and a Tanabe–Sugano diagram does not exist. | 0 | Theoretical and Fundamental Chemistry |
Non-uniform pore geometries often lead to differences in adsorption and desorption pathways within a capillary. This deviation in the two is called a hysteresis and is characteristic of many path dependent processes. For example, if a capillary's radius increases sharply, then capillary condensation (adsorption) will cease until an equilibrium vapor pressure is reached which satisfies the larger pore radius. However, during evaporation (desorption), liquid will remain filled to the larger pore radius until an equilibrium vapor pressure that satisfies the smaller pore radius is reached. The resulting plot of adsorbed volume versus relative humidity yields a hysteresis "loop." This loop is seen in all hysteresis governed processes and gives direct meaning the term "path dependent." The concept of hysteresis was explained indirectly in the curvature section of this article; however, here we are speaking in terms of a single capillary instead of a distribution of random pore sizes.
Hysteresis in capillary condensation has been shown to be minimized at higher temperatures. | 1 | Applied and Interdisciplinary Chemistry |
Homeostatic control can change the PCO2| and hence the pH of the arterial plasma within a few seconds. The partial pressure of carbon dioxide in the arterial blood is monitored by the central chemoreceptors of the medulla oblongata. These chemoreceptors are sensitive to the levels of carbon dioxide and pH in the cerebrospinal fluid.
The central chemoreceptors send their information to the respiratory centers in the medulla oblongata and pons of the brainstem. The respiratory centres then determine the average rate of ventilation of the alveoli of the lungs, to keep the in the arterial blood constant. The respiratory center does so via motor neurons which activate the muscles of respiration (in particular, the diaphragm). A rise in the in the arterial blood plasma above reflexly causes an increase in the rate and depth of breathing. Normal breathing is resumed when the partial pressure of carbon dioxide has returned to 5.3 kPa. The converse happens if the partial pressure of carbon dioxide falls below the normal range. Breathing may be temporally halted, or slowed down to allow carbon dioxide to accumulate once more in the lungs and arterial blood.
The sensor for the plasma HCO concentration is not known for certain. It is very probable that the renal tubular cells of the distal convoluted tubules are themselves sensitive to the pH of the plasma. The metabolism of these cells produces CO, which is rapidly converted to H and HCO through the action of carbonic anhydrase. When the extracellular fluids tend towards acidity, the renal tubular cells secrete the H ions into the tubular fluid from where they exit the body via the urine. The HCO ions are simultaneously secreted into the blood plasma, thus raising the bicarbonate ion concentration in the plasma, lowering the carbonic acid/bicarbonate ion ratio, and consequently raising the pH of the plasma. The converse happens when the plasma pH rises above normal: bicarbonate ions are excreted into the urine, and hydrogen ions into the plasma. These combine with the bicarbonate ions in the plasma to form carbonic acid (H + HCO HCO), thus raising the carbonic acid:bicarbonate ratio in the extracellular fluids, and returning its pH to normal.
In general, metabolism produces more waste acids than bases. Urine produced is generally acidic and is partially neutralized by the ammonia (NH) that is excreted into the urine when glutamate and glutamine (carriers of excess, no longer needed, amino groups) are deaminated by the distal renal tubular epithelial cells. Thus some of the "acid content" of the urine resides in the resulting ammonium ion (NH) content of the urine, though this has no effect on pH homeostasis of the extracellular fluids. | 0 | Theoretical and Fundamental Chemistry |
Cannabis (/ˈkænəbɪs/) is commonly known as marijuana or hemp and has two known strains: Cannabis sativa and Cannabis indica, both of which produce chemicals to deter herbivory. The chemical composition includes specialized terpenes and cannabinoids, mainly tetrahydrocannabinol (THC), and cannabidiol (CBD). These substances play a role in defending the plant from pathogens including insects, fungi, viruses and bacteria. THC and CBD are stored mostly in the trichomes of the plant, and can cause psychological and physical impairment in the user, via the endocannabinoid system and unique receptors. THC increases dopamine levels in the brain, which attributes to the euphoric and relaxed feelings cannabis provides. As THC is a secondary metabolite, it poses no known effects towards plant development, growth, and reproduction. However, some studies show secondary metabolites such as cannabinoids, flavonoids, and terpenes are used as defense mechanisms against biotic and abiotic environmental stressors. | 1 | Applied and Interdisciplinary Chemistry |
Bisulfite sequencing relies on the conversion of every single unmethylated cytosine residue to uracil. If conversion is incomplete, the subsequent analysis will incorrectly interpret the unconverted unmethylated cytosines as methylated cytosines, resulting in false positive results for methylation. Only cytosines in single-stranded DNA are susceptible to attack by bisulfite, therefore denaturation of the DNA undergoing analysis is critical. It is important to ensure that reaction parameters such as temperature and salt concentration are suitable to maintain the DNA in a single-stranded conformation and allow for complete conversion. Embedding the DNA in agarose gel has been reported to improve the rate of conversion by keeping strands of DNA physically separate. Incomplete conversion rates can be estimated and adjusted-for after sequencing by including an internal control in the sequencing library, such as lambda phage DNA (which is known to be unmethylated) or by aligning bisulfite sequencing reads to a known unmethylated region in the organism, such as the chloroplast genome. | 1 | Applied and Interdisciplinary Chemistry |
Thermomechanical mechanisms involve stresses by thermal expansion (namely differential thermal expansions, as thermal gradients tend to be involved), melting/freezing or sublimation/condensation of components, and phase transitions of crystals (e.g. transition of HMX from beta phase to delta phase at 175 °C involves a large change in volume and causes extensive cracking of its crystals). | 0 | Theoretical and Fundamental Chemistry |
Within the field of fluid dynamics, Homogeneous isotropic turbulence is an idealized version of the realistic turbulence, but amenable to analytical studies. The concept of isotropic turbulence was first introduced by G.I. Taylor in 1935. The meaning of the turbulence is given below,
* homogeneous, the statistical properties are invariant under arbitrary translations of the coordinate axes
* isotropic, the statistical properties are invariant over a full rotation group, which includes rotations and reflections of the coordinate axes.
G.I. Taylor also suggested a way of obtaining almost homogeneous isotropic turbulence by passing fluid over a uniform grid. The theory was further developed by Theodore von Kármán and Leslie Howarth (Kármán–Howarth equation) under dynamical considerations. Kolmogorovs theory of 1941 was developed using Taylors idea as a platform. | 1 | Applied and Interdisciplinary Chemistry |
Almost all proteins that are destined to the secretory pathway have a sequence consisting of 5-30 hydrophobic amino acids on the N-terminus, which is commonly referred to as the signal peptide, signal sequence or leader peptide. Signal peptides form alpha-helical structures. Proteins that contain such signals are destined for either extra-cellular secretion, the plasma membrane, the lumen or membrane of either the (ER), Golgi or endosomes. Certain membrane-bound proteins are targeted to the secretory pathway by their first transmembrane domain, which resembles a typical signal peptide.
In prokaryotes, signal peptides direct the newly synthesized protein to the SecYEG protein-conducting channel, which is present in the plasma membrane. A homologous system exists in eukaryotes, where the signal peptide directs the newly synthesized protein to the Sec61 channel, which shares structural and sequence similarity with SecYEG, but is present in the endoplasmic reticulum. Both the SecYEG and Sec61 channels are commonly referred to as the translocon, and transit through this channel is known as translocation. While secreted proteins are threaded through the channel, transmembrane domains may diffuse across a lateral gate in the translocon to partition into the surrounding membrane. | 1 | Applied and Interdisciplinary Chemistry |
In 1973, the use of PCBs in "open" or "dissipative" sources (such as plasticisers in paints and cements, casting agents, fire retardant fabric treatments and heat stabilizing additives for PVC electrical insulation, adhesives, paints and waterproofing, railroad ties) was banned in Sweden. | 1 | Applied and Interdisciplinary Chemistry |
* 1.D.1 The Gramicidin A Channel Family
* 1.D.2 The Channel-forming Syringomycin Family
* 1.D.3 The Channel-Forming Syringopeptin Family
* 1.D.4 The Tolaasin Channel-forming Family
* 1.D.5 The Alamethicin or Peptaibol Antibiotic Channel-forming Family
* 1.D.6 The Complexed Poly 3-Hydroxybutyrate Ca Channel (cPHB-CC) Family
* 1.D.7 The Beticolin Family
* 1.D.8 The Saponin Family
* 1.D.9 The Polyglutamine Ion Channel (PG-IC) Family
* 1.D.10 The Ceramide-forming Channel Family
* 1.D.11 The Surfactin Family
* 1.D.12 The Beauvericin (Beauvericin) Family
* 1.D.13 DNA-delivery Amphipathic Peptide Antibiotics (DAPA)
* 1.D.14 The Synthetic Leu/Ser Amphipathic Channel-forming Peptide (l/S-SCP) Family
* 1.D.15 The Daptomycin (Daptomycin) Family
* 1.D.16 The Synthetic Amphipathic Pore-forming Heptapeptide (SAPH) Family
* 1.D.17 Combinatorially-designed, Pore-forming, β-sheet Peptide Family
* 1.D.18 The Pore-forming Guanosine-Bile Acid Conjugate Family
* 1.D.19 Ca Channel-forming Drug, Digitoxin Family
* 1.D.20 The Pore-forming Polyene Macrolide Antibiotic/fungal Agent (PMAA) Family
* 1.D.21 The Lipid Nanopore (LipNP) Family
* 1.D.22 The Proton-Translocating Carotenoid Pigment, Zeaxanthin Family
* 1.D.23 Phenylene Ethynylene Pore-forming Antimicrobial (PEPA) Family
* 1.D.24 The Marine Sponge Polytheonamide B (pTB) Family
* 1.D.25 The Arylamine Foldamer (AAF) Family
* 1.D.26 The Dihydrodehydrodiconiferyl alcohol 9'-O-β-D-glucoside (DDDC9G) Family
* 1.D.27 The Thiourea isosteres Family
* 1.D.28 The Lipopeptaibol Family
* 1.D.29 The Macrocyclic Oligocholate Family
* 1.D.30 The Artificial Hydrazide-appended pillar[5]arene Channels (HAPA-C) Family
* 1.D.31 The Amphotericin B Family
* 1.D.32 The Pore-forming Novicidin Family
* 1.D.33 The Channel-forming Polytheonamide B Family
* 1.D.34 The Channel-forming Oligoester Bolaamphiphiles
* 1.D.35 The Pore-forming cyclic Lipodepsipeptide Family
* 1.D.36 The Oligobornene Ion Channel Family
* 1.D.37 The Hibicuslide C Family
* 1.D.38 The Cyclic Peptide Nanotube (cPepNT) Family
* 1.D.39 The Light-controlled Azobenzene-based Amphiphilic Molecular Ion Channel (AAM-IC) Family
* 1.D.40 The Protein-induced Lipid Toroidal Pore Family
* 1.D.41 The Sprotetonate-type Ionophore (Spirohexanolide) Family
* 1.D.42 The Phe-Arg Tripeptide-Pillar[5]Arene Channel (TPPA-C) Family
* 1.D.43 The Triazole-tailored Guanosine Dinucleoside Channel (TT-GDN-C) Family
* 1.D.44 The Synthetic Ion Channel with Redox-active Ferrocene (ICRF) Family
* 1.D.45 The Sonoporation and Electroporation Membrane Pore (SEMP) Family
* 1.D.46 The DNA Nanopore (DnaNP) Family
* 1.D.47 The Pore-forming Synthetic Cyclic Peptide (PSCP) Family
* 1.D.48 The Pore-forming Syringomycin E Family
* 1.D.49 The Transmembrane Carotenoid Radical Channel (CRC) Family
* 1.D.50 The Amphiphilic bis-Catechol Anion Transporter (AC-AT) Family
* 1.D.51 The Protein Nanopore (ProNP) Family
* 1.D.52 The Aromatic Oligoamide Macrocycle Nanopore (OmnNP) Family
* 1.D.53 The alpha, gamma-Peptide Nanotube (a,gPepNT) Family
* 1.D.54 The potassium-selective Hexyl-Benzoureido-15-Crown-5-Ether Ion Channel (HBEC) Family
* 1.D.55 The Porphyrin-based Nanopore (PorNP) Family
* 1.D.56 The Alpha-Aminoisobutyrate (Aib) Oligomeric Nanopore (AibNP) Family
* 1.D.57 The Lipid Electro-Pore (LEP) Family
* 1.D.58 The Anion Transporting Prodigiosene (Prodigiosene) Family
* 1.D.59 The Anion Transporting Perenosin (Perenosin) Family
* 1.D.60 The Alpha,Gamma-Cyclic Peptide (AGCP) Family
* 1.D.61 The Anionophoric (ABBP) Family
* 1.D.62 The Bis-Triazolyl DiGuanosine Derivative Channel-forming (TDG) Family
* 1.D.63 The Peptide-based Nanopore (PepNP) Family
* 1.D.64 The Carbon Nanotube (CarNT) Family
* 1.D.65 The Pore-forming Amphidinol (Amphidinol) Family
* 1.D.66 The Helical Macromolecule Nanopore (HmmNP) Family
* 1.D.67 The Crown Ether-modified Helical Peptide Ion Channel (CEHP) Family
* 1.D.68 The Pore-forming Pleuronic Block Polymer (PPBP) Family
* 1.D.69 The Conical Nanopore (ConNP) Family
* 1.D.70 The Metallic (Au/Ag/Pt/graphene) Nanopore (MetNP) Family
* 1.D.71 The Synthetic TP359 Peptide (TP359) Family
* 1.D.72 The Chloride Carrier Triazine-based Tripodal Receptor (CCTTR) Family
* 1.D.73 The Mesoporous Silica Nanopore (SilNP) Family
* 1.D.74 The Stimulus-responsive Synthetic Rigid p-Octiphenyl Stave Pore (SSROP) Family | 1 | Applied and Interdisciplinary Chemistry |
The criteria by which copper and copper alloys are selected for architectural projects include color, strength, hardness, resistance to fatigue and corrosion, electrical and thermal conductivity, and ease of fabrication. Appropriate thicknesses and tempers for specific applications are essential; substitutions can lead to inadequate performance.
Architectural copper is generally used in sheet and strip. Strip is or less in width, while sheet is over in width, up to in width by in length, plus in coil form. | 1 | Applied and Interdisciplinary Chemistry |
Rust is a commonly used metaphor for slow decay due to neglect, since it gradually converts robust iron and steel metal into a soft crumbling powder. A wide section of the industrialized American Midwest and American Northeast, once dominated by steel foundries, the automotive industry, and other manufacturers, has experienced harsh economic cutbacks that have caused the region to be dubbed the "Rust Belt".
In music, literature, and art, rust is associated with images of faded glory, neglect, decay, and ruin. | 1 | Applied and Interdisciplinary Chemistry |
The Freundlich isotherm is the most important multi-site adsorption isotherm for rough surfaces.
where α and C are fitting parameters. This equation implies that if one makes a log–log plot of adsorption data, the data will fit a straight line. The Freundlich isotherm has two parameters, while Langmuirs equations has only one: as a result, it often fits the data on rough surfaces better than the Langmuirs equations. However, the Freundlich equation is unique; consequently, if the data fit the equation, it is only likely, but not proved, that the surface is heterogeneous. The heterogeneity of the surface can be confirmed with calorimetry. Homogeneous surfaces (or heterogeneous surfaces that exhibit homogeneous adsorption (single-site)) have a constant of adsorption as a function of the occupied-sites fraction. On the other hand, heterogeneous adsorption (multi-site) have a variable of adsorption depending on the sites occupation. When the adsorbate pressure (or concentration) are low, high-energy sites are occupied, and as the pressure (or concentration) increases, the lesser-energy sites become occupied, resulting in a lower of adsorption.
A related equation is the Toth equation. Rearranging the Langmuir equation, one can obtain
Toth modified this equation by adding two parameters α</sub> to formulate the Toth equation: | 0 | Theoretical and Fundamental Chemistry |
Protease inhibitors were designed to mimic the transition state of the proteases actual substrates. A peptide linkage consisting of –NH-CO- is replaced by an hydroxyethylen group (-CH-CH(OH)-) which the protease is unable to cleave. HIV protease inhibitors fit the active site of the HIV aspartic protease and were rationally designed utilizing knowledge of the aspartyl proteases mode of action. The most promising transition state mimic was hydroxyethylamine which led to the discovery of the first protease inhibitor, saquinavir. Following that discovery, other HIV protease inhibitors were designed using the same principle. | 1 | Applied and Interdisciplinary Chemistry |
Hele-Shaw flow is an example of a geometry for which inertia forces are negligible. It is defined by two parallel plates arranged very close together with the space between the plates occupied partly by fluid and partly by obstacles in the form of cylinders with generators normal to the plates. | 1 | Applied and Interdisciplinary Chemistry |
All equilibrium constants vary with temperature according to the Van 't Hoff equation
Alternatively
R is the gas constant and T is the thermodynamic temperature. Thus, for exothermic reactions, where the standard enthalpy change, ΔH, is negative, K decreases with temperature, but for endothermic reactions, where ΔH is positive, K increases with temperature. | 0 | Theoretical and Fundamental Chemistry |
The trihexagonal tiling exists in a sequence of symmetries of quasiregular tilings with vertex configurations (3.n), progressing from tilings of the sphere to the Euclidean plane and into the hyperbolic plane. With orbifold notation symmetry of *n32 all of these tilings are wythoff construction within a fundamental domain of symmetry, with generator points at the right angle corner of the domain. | 0 | Theoretical and Fundamental Chemistry |
Epigenetic instability caused by deregulation in chromatin remodeling is studied in several cancers, including breast cancer, colorectal cancer, pancreatic cancer. Such instability largely cause widespread silencing of genes with primary impact on tumor-suppressor genes. Hence, strategies are now being tried to overcome epigenetic silencing with synergistic combination of HDAC inhibitors or HDI and DNA-demethylating agents.
HDIs are primarily used as adjunct therapy in several cancer types. HDAC inhibitors can induce p21 (WAF1) expression, a regulator of p53's tumor suppressoractivity. HDACs are involved in the pathway by which the retinoblastoma protein (pRb) suppresses cell proliferation. Estrogen is well-established as a mitogenic factor implicated in the tumorigenesis and progression of breast cancer via its binding to the estrogen receptor alpha (ERα). Recent data indicate that chromatin inactivation mediated by HDAC and DNA methylation is a critical component of ERα silencing in human breast cancer cells.
* Approved usage:
**Vorinostat was licensed by the U.S. FDA in October 2006 for the treatment of cutaneous T cell lymphoma (CTCL).
**Romidepsin (trade name Istodax) was licensed by the US FDA in Nov 2009 for cutaneous T-cell lymphoma (CTCL).
* Phase III Clinical trials:
** Panobinostat (LBH589) is in clinical trials for various cancers including a phase III trial for cutaneous T cell lymphoma (CTCL).
** Valproic acid (as Mg valproate) in phase III trials for cervical cancer and ovarian cancer.
* Started pivotal phase II clinical trials:
** Belinostat (PXD101) has had a phase II trial for relapsed ovarian cancer, and reported good results for T cell lymphoma.
** HDAC inhibitors.
Current front-runner candidates for new drug targets are Histone Lysine Methyltransferases (KMT) and Protein Arginine Methyltransferases (PRMT). | 1 | Applied and Interdisciplinary Chemistry |
Performance, maintenance, service life, and recovery costs from recycling are factors that determine the cost effectiveness of building components. While copper's initial cost is higher than some other architectural metals, it usually does not need to be replaced during the life of a building. Due to its durability, low maintenance, and ultimate salvage value, the additional cost for copper may be insignificant over the life of a roofing system.
Copper roofing is considerably less expensive than lead, slate, or hand-made clay tiles. Its costs are comparable with zinc, stainless steel, aluminium and even some clay and concrete tiles when considering overall roofing costs (including structure).
Some studies indicate that copper is a more cost-effective material on a life cycle basis than other roof materials with a lifetime of 30 years or more. A European study comparing roofing costs of copper with other metals, concrete and clay tiles, slate, and bitumen found that in the medium to long-term (for lives of 60 to 80 years and 100 years and over), copper and stainless steel were the most cost effective roofing materials of all materials examined.
Installation techniques such as prefabrication, in-situ machine forming, mechanized seaming, and the long-strip system help to reduce the installation costs of copper roofing. By lowering installation costs, these techniques permit designers to specify copper into a wider array of building types, not just large prestigious projects as had been common in the past.
Since scrap copper retains much of its primary value, copper's life cycle costs are reduced when accounting for its salvage value. For more information, see Recyclability section in this article. | 1 | Applied and Interdisciplinary Chemistry |
Rather than starting from "naked" gold ions in solution, template reactions can be used for directed synthesis of clusters. The high affinity of the gold ions to electronegative and (partially) charged atoms of functional groups yields potential seeds for cluster formation. The interface between the metal and the template can act as a stabilizer and steer the final size of the cluster. Some potential templates are dendrimers, oligonucleotides, proteins, polyelectrolytes and polymers. | 0 | Theoretical and Fundamental Chemistry |
Food Standards Australia New Zealand develops the standards for levels of pesticide residues in foods through a consultation process. The New Zealand Food Safety Authority publishes the maximum limits of pesticide residues for foods produced in New Zealand. | 1 | Applied and Interdisciplinary Chemistry |
Gravity separation is an industrial method of separating two components, either a suspension, or dry granular mixture where separating the components with gravity is sufficiently practical: i.e. the components of the mixture have different specific weight. Every gravitational method uses gravity as the primary force for separation. One type of gravity separator lifts the material by vacuum over an inclined vibrating screen covered deck.
This results in the material being suspended in air while the heavier impurities are left behind on the screen and are discharged from the stone outlet. Gravity separation is used in a wide variety of industries, and can be most simply differentiated by the characteristics of the mixture to be separated - principally that of wet i.e. - a suspension versus dry -a mixture of granular product. Often other methods are applied to make the separation faster and more efficient, such as flocculation, coagulation and suction. The most notable advantages of the gravitational methods are their cost effectiveness and in some cases excellent reduction. Gravity separation is an attractive unit operation as it generally has low capital and operating costs, uses few if any chemicals that might cause environmental concerns and the recent development of new equipment enhances the range of separations possible. | 0 | Theoretical and Fundamental Chemistry |
The use of equivalent weights in general chemistry has largely been superseded by the use of molar masses. Equivalent weights may be calculated from molar masses if the chemistry of the substance is well known:
*sulfuric acid has a molar mass of 98.078(5) , and supplies two moles of hydrogen ions per mole of sulfuric acid, so its equivalent weight is 98.078(5) /2 = 49.039(3) .
*potassium permanganate has a molar mass of 158.034(1) , and reacts with five moles of electrons per mole of potassium permanganate, so its equivalent weight is 158.034(1) /5 = 31.6068(3) .
Historically, the equivalent weights of the elements were often determined by studying their reactions with oxygen. For example, 50 g of zinc will react with oxygen to produce 62.24 g of zinc oxide, implying that the zinc has reacted with 12.24 g of oxygen (from the Law of conservation of mass): the equivalent weight of zinc is the mass which will react with eight grams of oxygen, hence 50 g × 8 g/12.24 g = 32.7 g.
Some contemporary general chemistry textbooks make no mention of equivalent weights. Others explain the topic, but point out that it is merely an alternate method of doing calculations using moles. | 0 | Theoretical and Fundamental Chemistry |
The first experimental evidence for the presence of 18 cm absorption lines of the hydroxyl (HO) radical in the radio absorption spectrum of Cassiopeia A was obtained by Weinreb et al. (Nature, Vol. 200, pp. 829, 1963) based on observations made during the period October 15–29, 1963. | 1 | Applied and Interdisciplinary Chemistry |
This is the oldest and still most commonly used technique, particularly for flame AAS. In this case, a separate source (a deuterium lamp) with broad emission is used to measure the background absorption over the entire width of the exit slit of the spectrometer. The use of a separate lamp makes this technique the least accurate one, as it cannot correct for any structured background. It also cannot be used at wavelengths above about 320 nm, as the emission intensity of the deuterium lamp becomes very weak. The use of deuterium HCL is preferable compared to an arc lamp due to the better fit of the image of the former lamp with that of the analyte HCL. | 0 | Theoretical and Fundamental Chemistry |
Human cloning is the creation of a genetically identical copy of a human. The term is generally used to refer to artificial human cloning, which is the reproduction of human cells and tissues. It does not refer to the natural conception and delivery of identical twins. The possibility of human cloning has raised controversies. These ethical concerns have prompted several nations to pass legislation regarding human cloning and its legality. As of right now, scientists have no intention of trying to clone people and they believe their results should spark a wider discussion about the laws and regulations the world needs to regulate cloning.
Two commonly discussed types of theoretical human cloning are therapeutic cloning and reproductive cloning. Therapeutic cloning would involve cloning cells from a human for use in medicine and transplants, and is an active area of research, but is not in medical practice anywhere in the world, . Two common methods of therapeutic cloning that are being researched are somatic-cell nuclear transfer and, more recently, pluripotent stem cell induction. Reproductive cloning would involve making an entire cloned human, instead of just specific cells or tissues. | 1 | Applied and Interdisciplinary Chemistry |
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