text stringlengths 105 4.57k | label int64 0 1 | label_text stringclasses 2
values |
|---|---|---|
The chlorophycean mitochondrial code (translation table 16) is a genetic code found in the mitochondria of Chlorophyceae. | 1 | Applied and Interdisciplinary Chemistry |
In addition to being used for their traditional properties, bioactive ceramics have seen specific use for due to their biological activity. Calcium phosphates, oxides, and hydroxides are common examples. Other natural materials — generally of animal origin — such as bioglass and other composites feature a combination of mineral-organic composite materials such as HAP, alumina, or titanium dioxide with the biocompatible polymers (polymethylmethacrylate): PMMA, poly(L-lactic) acid: PLLA, poly(ethylene). Composites can be differentiated as bioresorbable or non-bioresorbable, with the latter being the result of the combination of a bioresorbable calcium phosphate (HAP) with a non-bioresorbable polymer (PMMA, PE). These materials may become more widespread in the future, on account of the many combination possibilities and their aptitude at combining a biological activity with mechanical properties similar to those of the bone. | 0 | Theoretical and Fundamental Chemistry |
The expression for the magnetooptical absorption of a polaron is:
Here, is the cyclotron frequency for a rigid-band electron. The magnetooptical absorption Γ(Ω) at the frequency Ω takes the form Σ(Ω) is the so-called "memory function", which describes the dynamics of the polaron. Σ(Ω) depends also on α, β and .
In the absence of an external magnetic field () the optical absorption spectrum (3) of the polaron at weak coupling is determined by the absorption of radiation energy, which is reemitted in the form of LO phonons. At larger coupling, , the polaron can undergo transitions toward a relatively stable internal excited state called the "relaxed excited state" (RES) (see Fig. 2). The RES peak in the spectrum also has a phonon sideband, which is related to a Franck–Condon-type transition.
A comparison of the DSG results with the optical conductivity spectra given by approximation-free numerical and approximate analytical approaches is given in ref.
Calculations of the optical conductivity for the Fröhlich polaron performed within the Diagrammatic Quantum Monte Carlo method, see Fig. 3, fully confirm the results of the path-integral variational approach at In the intermediate coupling regime the low-energy behavior and the position of the maximum of the optical conductivity spectrum of ref. follow well the prediction of Devreese. There are the following qualitative differences between the two approaches in the intermediate and strong coupling regime: in ref., the dominant peak broadens and the second peak does not develop, giving instead rise to a flat shoulder in the optical conductivity spectrum at . This behavior can be attributed to the optical processes with participation of two or more phonons. The nature of the excited states of a polaron needs further study.
The application of a sufficiently strong external magnetic field allows one to satisfy the resonance condition , which {(for )} determines the polaron cyclotron resonance frequency. From this condition also the polaron cyclotron mass can be derived. Using the most accurate theoretical polaron models to evaluate , the experimental cyclotron data can be well accounted for.
Evidence for the polaron character of charge carriers in AgBr and AgCl was obtained through high-precision cyclotron resonance experiments in external magnetic fields up to 16 T. The all-coupling magneto-absorption calculated in ref., leads to the best quantitative agreement between theory and experiment for AgBr and AgCl. This quantitative interpretation of the cyclotron resonance experiment in AgBr and
AgCl by the theory of Peeters provided one of the most convincing and clearest demonstrations of Fröhlich polaron features in solids.
Experimental data on the magnetopolaron effect, obtained using far-infrared photoconductivity techniques, have been applied to study the energy spectrum of shallow donors in polar semiconductor layers of CdTe.
The polaron effect well above the LO phonon energy was studied through cyclotron resonance measurements, e. g., in II–VI semiconductors, observed in ultra-high magnetic fields. The resonant polaron effect manifests itself when the cyclotron frequency approaches the LO phonon energy in sufficiently high magnetic fields.
In the lattice models the optical conductivity is given by the formula:
Here is the activation energy of polaron, which is of the order of polaron binding energy . This formula was derived and extensively discussed in and was tested experimentally for example in photodoped parent compounds of high temperature superconductors. | 0 | Theoretical and Fundamental Chemistry |
Synthesis of the upper part of the NanoPutian chain begins with 1,3-dibromo-2,4-diiodobenzene as the starting material. Sonogashira coupling with 4-oxytrimethylsilylbut-1-yne produces 2,5-bis(4-tert-butyldimethylsiloxy-1′-butynyl)-1,4-di-bromobenzene. One of the bromine substituents is converted to an aldehyde through an S2 reaction with the strong base, n-BuLi, and THF in the aprotic polar solvent, DMF to produce 2,5-bis(4-tert-butyldimethylsiloxy-1′-butynyl)-4-bromobenzaldehyde. Another Sonogashira coupling with 3,5-(1′-Pentynyl)-1-ethynylbenzene attaches the lower body of the NanoPutian. The conversion of the aldehyde group to a diether “head” occurs in two steps. The first step involves addition of ethylene glycol and trimethylsilyl chloride (TMSCl) in CHCl solvent. Addition of TBAF in THF solvent removes the silyl protecting group. | 1 | Applied and Interdisciplinary Chemistry |
PSII also relies on light to drive the formation of proton gradients in chloroplasts, however, PSII utilizes vectorial redox chemistry to achieve this goal. Rather than physically transporting protons through the protein, reactions requiring the binding of protons will occur on the extracellular side while reactions requiring the release of protons will occur on the intracellular side. Absorption of photons of 680nm wavelength is used to excite two electrons in P to a higher energy level. These higher energy electrons are transferred to protein-bound plastoquinone (PQ) and then to unbound plastoquinone (PQ). This reduces plastoquinone (PQ) to plastoquinol (PQH) which is released from PSII after gaining two protons from the stroma. The electrons in P are replenished by oxidizing water through the oxygen-evolving complex (OEC). This results in release of O and H into the lumen, for a total reaction of
After being released from PSII, PQH travels to the cytochrome bf complex, which then transfers two electrons from PQH to plastocyanin in two separate reactions. The process that occurs is similar to the Q-cycle in Complex III of the electron transport chain. In the first reaction, PQH binds to the complex on the lumen side and one electron is transferred to the iron-sulfur center which then transfers it to cytochrome f which then transfers it to plastocyanin. The second electron is transferred to heme b which then transfers it to heme b which then transfers it to PQ. In the second reaction, a second PQH gets oxidized, adding an electron to another plastocyanin and PQ. Both reactions together transfer four protons into the lumen. | 0 | Theoretical and Fundamental Chemistry |
Qualitative filter paper is used in qualitative analytical techniques to determine materials. There are different grades of qualitative filter paper according to different pore size. There are total 13 different grades of qualitative filter paper. The largest pore size is grade 4; the smallest pore size is grade 602 h; the most commonly used grades are grade 1 to grade 4.
Grade 1 qualitative filter paper has the pore size of 11 μm. This grade of filter paper is widely used for many different fields in agricultural analysis, air pollution monitoring and other similar experiments.
Grade 2 qualitative filter paper has the pore size of 8 μm. This grade of filter paper requires more filtration time than Grade 1 filter paper. This filter paper is used for monitoring specific contaminants in the atmosphere and soil testing.
Grade 3 qualitative filter paper has the pore size of 6 μm. This grade of filter paper is very suitable for carrying samples after filtration.
Grade 4 qualitative filter paper has the pore size of 20~25 μm. This grade of filter paper has the largest pore size among all standard qualitative filter papers. It is very useful as rapid filter for cleanup of geological fluids or organic extracts during experiment.
Grade 602 h qualitative filter paper has the pore size of 2 μm. This grade of filter paper has the smallest pore size among all standard qualitative filter papers. It is used for collecting or removing fine particles. | 0 | Theoretical and Fundamental Chemistry |
A process for electrochemical production of titanium through the reduction of titanium oxide in a calcium chloride solution was first described in a 1904 German patent, and later in a US patent by Carl Marcus Olson.
The FFC Cambridge process was developed by George Chen, Derek Fray, and Thomas Farthing between 1996 and 1997 at the University of Cambridge. (The name FFC derives from the first letters of the last names of the inventors). The intellectual property relating to the technology has been acquired by Metalysis, (Sheffield, UK). | 0 | Theoretical and Fundamental Chemistry |
The pKa of the related acids can be guessed from the number of double bonds to oxygen. Thus perchloric acid is a very strong acid while hypochlorous acid is very weak. A simple rule usually works to within about 1 pH unit. | 0 | Theoretical and Fundamental Chemistry |
Impurities usually enter the solder reservoir by dissolving the metals present in the assemblies being soldered. Dissolving of process equipment is not common as the materials are usually chosen to be insoluble in solder.
* Aluminium – little solubility, causes sluggishness of solder and dull gritty appearance due to formation of oxides. Addition of antimony to solders forms Al-Sb intermetallics that are segregated into dross. Promotes embrittlement.
* Antimony – added intentionally, up to 0.3% improves wetting, larger amounts slowly degrade wetting. Increases melting point.
* Arsenic – forms thin intermetallics with adverse effects on mechanical properties, causes dewetting of brass surfaces
* Cadmium – causes sluggishness of solder, forms oxides and tarnishes
* Copper – most common contaminant, forms needle-shaped intermetallics, causes sluggishness of solders, grittiness of alloys, decreased wetting
* Gold – easily dissolves, forms brittle intermetallics, contamination above 0.5% causes sluggishness and decreases wetting. Lowers melting point of tin-based solders. Higher-tin alloys can absorb more gold without embrittlement.
* Iron – forms intermetallics, causes grittiness, but rate of dissolution is very low; readily dissolves in lead-tin above 427 °C.
* Lead – causes Restriction of Hazardous Substances Directive compliance problems at above 0.1%.
* Nickel – causes grittiness, very little solubility in Sn-Pb
* Phosphorus – forms tin and lead phosphides, causes grittiness and dewetting, present in electroless nickel plating
* Silver – often added intentionally, in high amounts forms intermetallics that cause grittiness and formation of pimples on the solder surface, potential for embrittlement
* Sulfur – forms lead and tin sulfides, causes dewetting
* Zinc – in melt forms excessive dross, in solidified joints rapidly oxidizes on the surface; zinc oxide is insoluble in fluxes, impairing repairability; copper and nickel barrier layers may be needed when soldering brass to prevent zinc migration to the surface; potential for embrittlement
Board finishes vs wave soldering bath impurities buildup:
* HASL, lead-free (Hot Air Level): usually virtually pure tin. Does not contaminate high-tin baths.
* HASL, leaded: some lead dissolves into the bath
* ENIG (Electroless Nickel Immersion Gold): typically 100-200 microinches of nickel with 3-5 microinches of gold on top. Some gold dissolves into the bath, but limits exceeding buildup is rare.
* Immersion silver: typically 10–15 microinches of silver. Some dissolves into the bath, limits exceeding buildup is rare.
* Immersion tin: does not contaminate high-tin baths.
* OSP (Organic solderability preservative): usually imidazole-class compounds forming a thin layer on the copper surface. Copper readily dissolves in high-tin baths. | 1 | Applied and Interdisciplinary Chemistry |
Experiments and calculations generally agree that the methenium ion is planar, with threefold symmetry. The carbon atom is a prototypical (and exact) example of sp hybridization. | 0 | Theoretical and Fundamental Chemistry |
The Allen–Millar–Trippett rearrangement is a ring expansion reaction in which a cyclic phosphine is transformed into a cyclic phosphine oxide. This name reaction, first reported in the 1960s by David W. Allen, Ian T. Millar, and Stuart Trippett, occurs by alkylation or acylation of the phosphorus, followed by reaction with hydroxide to give a rearranged product. The hydroxide first attacks the phosphonium atom, followed by collapse to the phosphine oxide with one of the groups migrating off of the phosphorus. | 0 | Theoretical and Fundamental Chemistry |
The leukocyte immunoglobulin-like receptors (LILR) are a family of receptors possessing extracellular immunoglobulin domains.
They are also known as CD85, ILTs and LIR, and can exert immunomodulatory effects on a wide range of immune cells. The human genes encoding these receptors are found in a gene cluster at chromosomal region 19q13.4.
They include
* LILRA1
* LILRA2
* LILRA3
* LILRA4
* LILRA5
* LILRA6
* LILRB1
* LILRB2
* LILRB3
* LILRB4
* LILRB5
* LILRB6 or LILRA6
* LILRB7 or LILRA5
A subset of LILR recognise MHC class I (also known as HLA class I in humans). The LILR family is a cluster of paired receptors with both activating and inhibitory functions. Of these, the inhibitory receptors LILRB1 and LILRB2 show a broad specificity for classical and non-classical MHC alleles with preferential binding to b2m-associated complexes. In contrast, the activating receptors LILRA1 and LILRA3 prefer b2m-independent free heavy chains of MHC class I, and in particular HLA-C alleles. | 1 | Applied and Interdisciplinary Chemistry |
Laser-induced breakdown spectroscopy (LIBS) is a type of atomic emission spectroscopy which uses a highly energetic laser pulse as the excitation source. The laser is focused to form a plasma, which atomizes and excites samples. The formation of the plasma only begins when the focused laser achieves a certain threshold for optical breakdown, which generally depends on the environment and the target material. | 0 | Theoretical and Fundamental Chemistry |
The carbonate–silicate geochemical cycle, also known as the inorganic carbon cycle, describes the long-term transformation of silicate rocks to carbonate rocks by weathering and sedimentation, and the transformation of carbonate rocks back into silicate rocks by metamorphism and volcanism. Carbon dioxide is removed from the atmosphere during burial of weathered minerals and returned to the atmosphere through volcanism. On million-year time scales, the carbonate-silicate cycle is a key factor in controlling Earth's climate because it regulates carbon dioxide levels and therefore global temperature.
The rate of weathering is sensitive to factors that change how much land is exposed. These factors include sea level, topography, lithology, and vegetation changes. Furthermore, these geomorphic and chemical changes have worked in tandem with solar forcing, whether due to orbital changes or stellar evolution, to determine the global surface temperature. Additionally, the carbonate-silicate cycle has been considered a possible solution to the faint young Sun paradox. | 0 | Theoretical and Fundamental Chemistry |
The partial order with respect to a given reactant can be evaluated by the method of flooding (or of isolation) of Ostwald. In this method, the concentration of one reactant is measured with all other reactants in large excess so that their concentration remains essentially constant. For a reaction with rate law the partial order with respect to is determined using a large excess of . In this case
with
and may be determined by the integral method. The order with respect to under the same conditions (with in excess) is determined by a series of similar experiments with a range of initial concentration so that the variation of can be measured. | 0 | Theoretical and Fundamental Chemistry |
Leukocytes or white blood cells destroy abnormal cells and also provide protection against bacteria and other foreign matter. These interactions are transitory in nature but are crucial as an immediate immune response. To fight infection, leukocytes must move from the blood into the affected tissues. This movement into tissues is called extravasation. It requires successive forming and breaking of cell-cell interactions between the leukocytes and the endothelial cells that line blood vessels. These cell-cell interactions are mediated mainly by a group of Cell Adhesion Molecules (CAMs) called selectins.
T helper cells, central to the immune system, interact with other leukocytes by releasing signals known as cytokines which activate and stimulate the proliferation of B cells and killer T cells. T helper cells also directly interact with macrophages, cells that engulf foreign matter and display antigens on its surface. T-helper cells that possess the appropriate receptors can bind to these antigens and proliferate resulting in T-helper cells that have the ability to identify the same antigens. | 1 | Applied and Interdisciplinary Chemistry |
Characterization of microstructures has also been performed using x-ray diffraction (XRD) techniques for many years. XRD can be used to determine the percentages of various phases present in a specimen if they have different crystal structures. For example, the amount of retained austenite in a hardened steel is best measured using XRD (ASTM E 975). If a particular phase can be chemically extracted from a bulk specimen, it can be identified using XRD based on the crystal structure and lattice dimensions. This work can be complemented by EDS and/or WDS analysis where the chemical composition is quantified. But EDS and WDS are difficult to apply to particles less than 2-3 micrometers in diameter. For smaller particles, diffraction techniques can be performed using the TEM for identification and EDS can be performed on small particles if they are extracted from the matrix using replication methods to avoid detection of the matrix along with the precipitate. | 1 | Applied and Interdisciplinary Chemistry |
Backscattering can occur in quite different physical situations, where the incoming waves or particles are deflected from their original direction by different mechanisms:
*Diffuse reflection from large particles and Mie scattering, causing alpenglow and gegenschein, and showing up in weather radar;
*Inelastic collisions between electromagnetic waves and the transmitting medium (Brillouin scattering and Raman scattering), important in fiber optics, see below;
*Elastic collisions between accelerated ions and a sample (Rutherford backscattering)
*Bragg diffraction from crystals, used in inelastic scattering experiments (neutron backscattering, X-ray backscattering spectroscopy);
*Compton scattering, used in Backscatter X-ray imaging.
* Stimulated backscatter, observed in non-linear optics, and described by a class of solutions to the three-wave equation.
Sometimes, the scattering is more or less isotropic, i.e. the incoming particles are scattered randomly in various directions, with no particular preference for backward scattering. In these cases, the term "backscattering" just designates the detector location chosen for some practical reasons:
*in X-ray imaging, backscattering means just the opposite of transmission imaging;
*in inelastic neutron or X-ray spectroscopy, backscattering geometry is chosen because it optimizes the energy resolution;
*in astronomy, backscattered light is that which is reflected with a phase angle of less than 90°.
In other cases, the scattering intensity is enhanced in backward direction. This can have different reasons:
*In alpenglow, red light prevails because the blue part of the spectrum is depleted by Rayleigh scattering.
*In gegenschein, constructive interference might play a role.
*Coherent backscattering is observed in random media; for visible light most typically in suspensions like milk. Due to weak localization, enhanced multiple scattering is observed in back direction.
** The Back Scattering Alignment (BSA) coordinate system is often used in radar applications
** The Forward Scattering Alignment (FSA) coordinate system is primarily used in optical applications
Backscattering properties of a target are wavelength dependent and can also be polarization dependent. Sensor systems using multiple wavelengths or polarizations can thus be used to infer additional information about target properties. | 0 | Theoretical and Fundamental Chemistry |
The local solidification time can be calculated using Chvorinov's rule, which is:
Where t is the solidification time, V is the volume of the casting, A is the surface area of the casting that contacts the mold, n is a constant, and B is the mold constant. It is most useful in determining if a riser will solidify before the casting, because if the riser does solidify first then it is worthless. | 1 | Applied and Interdisciplinary Chemistry |
The angles used for each facet play a crucial role in the outcome of a gem. While the general facet arrangement of a particular gemstone cut may appear the same in any given gem material, the angles of each facet must be carefully adjusted to maximize the optical performance. The angles used will vary based on the refractive index of the gem material. When light passes through a gemstone and strikes a polished facet, the minimum angle possible for the facet to reflect the light back into the gemstone is called the critical angle. If the ray of light strikes a surface lower than this angle, it will leave the gem material instead of reflecting through the gem as brilliance. These lost light rays are sometimes referred to as "light leakage", and the effect caused by it is called "windowing" as the area will appear transparent and without brilliance. This is especially common in poorly cut commercial gemstones. Gemstones with higher refractive indexes generally make more desirable gemstones, the critical angle decreases as refractive indices increase, allowing for greater internal reflections as the light is less likely to escape. | 0 | Theoretical and Fundamental Chemistry |
The ortho effect occurs in Diels-Alder reactions when the Z-substituted dienophiles react with 1-substituted butadienes to give 3,4-disubstituted cyclohexenes, independent of the nature of diene substituents. | 0 | Theoretical and Fundamental Chemistry |
In general, amino radicals are highly reactive and short lived; however, this is not the case when reacted with some organic molecules. Relative reactivities of the amino radical with several organic compounds have been reported, but the absolute rate constants for such reactions remain unknown. In reaction 1, it was hypothesized that the amino radical might possibly react with NH more rapidly than OH and might oxidize to produce the amino radical in acid solutions, given that radicals are stronger oxidants than OH. In order to test this, sulfate and phosphate radical anions were used. The sulfate and phosphate radical anions were found to react more slowly with NH than does the amino radical and they react with ammonia by hydrogen abstraction and not by electron transfer oxidation.
When the amino radical is reacted with benzoate ions, the rate constant is very low and only a weak absorption in the UV spectra is observed, indicating that amino radicals do not react with benzene rapidly. Phenol, on the other hand, was found to react more rapidly with the amino radical. In experiments at pH 11.3 and 12, using 1.5 M NH and varying concentrations of phenol between 4 and 10 mM, the formation of the phenoxyl radical absorption was observed with a rate constant of . This reaction can produce phenoxyl radicals via two possible mechanisms:
# Addition to the ring followed by elimination of NH, or
# Oxidation by direct electron transfer
While the amino radical is known to be weakly reactive, the recombination process of two amino radicals to form hydrazine appears to be one of the fastest. As a result, it often competes with other NH reactions.
:NH + NH → NH
At low pressures, this reaction is the fastest and therefore the principal mode of NH disappearance. | 0 | Theoretical and Fundamental Chemistry |
Many pesticides are enzyme inhibitors. Acetylcholinesterase (AChE) is an enzyme found in animals, from insects to humans. It is essential to nerve cell function through its mechanism of breaking down the neurotransmitter acetylcholine into its constituents, acetate and choline. This is somewhat unusual among neurotransmitters as most, including serotonin, dopamine, and norepinephrine, are absorbed from the synaptic cleft rather than cleaved. A large number of AChE inhibitors are used in both medicine and agriculture. Reversible competitive inhibitors, such as edrophonium, physostigmine, and neostigmine, are used in the treatment of myasthenia gravis and in anaesthesia to reverse muscle blockade. The carbamate pesticides are also examples of reversible AChE inhibitors. The organophosphate pesticides such as malathion, parathion, and chlorpyrifos irreversibly inhibit acetylcholinesterase. | 1 | Applied and Interdisciplinary Chemistry |
The standard state for a gas is the hypothetical state it would have as a pure substance obeying the ideal gas equation at standard pressure. IUPAC recommends using a standard pressure p or P° equal to , or 1 bar. No real gas has perfectly ideal behavior, but this definition of the standard state allows corrections for non-ideality to be made consistently for all the different gases. | 0 | Theoretical and Fundamental Chemistry |
Although the apertureless mode is more promising than the aperture mode, the latter is more widely used because of easier instrumental setup and operation. To obtain a high resolution Raman micrograph/spectrum, the following conditions should be met: (1) the size of the aperture must be on the order of the wavelength of the excitation light. (2) The distance from the tip of the probe to the sample must be smaller than excitation wavelength. (3) The instrument must remain stable over a long time. An important AFM feature is the ability to accurately control the distance between the sample and probe tip, which is the reason why the AFM-Raman combination is preferred for realizing Raman-NSOM. | 0 | Theoretical and Fundamental Chemistry |
He was born at the Trewarthenick Estate in Cornwall, the son of Francis Gregor and Mary Copley and the brother of Francis Gregor, MP for Cornwall. He was educated at Bristol Grammar School, where he became interested in chemistry, then after two years with a private tutor entered St Johns College, Cambridge, graduating BA in 1784 and MA in 1787. He was ordained in the Church of England. He became vicar of St Marys Church Diptford near Totnes, Devon. He married Charlotte Anne Gwatkin in 1790 and they had one daughter. | 1 | Applied and Interdisciplinary Chemistry |
In a water-cooled reactor the action of radiation on the water (radiolysis) forms hydrogen peroxide and oxygen. These can cause stress corrosion cracking of metal parts which include fuel cladding and other pipework. To mitigate this hydrazine and hydrogen are injected into a BWR or PWR primary cooling circuit as corrosion inhibitors to adjust the redox properties of the system. A review of recent developments on this topic has been published. | 0 | Theoretical and Fundamental Chemistry |
Several other scales have been proposed for the ranking of the donor properties of ligands. The HEP scale ranks ligands on the basis of the C NMR shift of a reference ligand. Lever's electronic parameter ranking is related to the Ru(II/III) couple. Another scale evaluated ligands on the basis of the redox couples of [Cr(CO)L].
In a treatment akin to the TEP analysis, the donor properties of N-heterocyclic carbene (NHC) ligands have been ranked according to IR data recorded on cis-[RhCl(NHC)(CO)] complexes. | 0 | Theoretical and Fundamental Chemistry |
sAC is encoded in a single Homo sapiens gene identified as ADCY10 or Adenylate cyclase 10 (soluble). This gene packed down 33 exons that comprise greater than 100kb; though, it seems to utilize multiple promoters, and its mRNA undergoes extensive alternative splicing. | 1 | Applied and Interdisciplinary Chemistry |
Huang was born in Putian, Fujian, China on December 15, 1921. He graduated from Fukien Christian University in 1943 with a bachelor's degree in chemistry. After earning his MS in 1949 from Lingnan University in Guangzhou, he entered Harvard University and received his Ph.D. in 1952. His graduate advisor was the organic chemist Louis Fieser. | 0 | Theoretical and Fundamental Chemistry |
A biological target is anything within a living organism to which some other entity (like an endogenous ligand or a drug) is directed and/or binds, resulting in a change in its behavior or function. Examples of common classes of biological targets are proteins and nucleic acids. The definition is context-dependent, and can refer to the biological target of a pharmacologically active drug compound, the receptor target of a hormone (like insulin), or some other target of an external stimulus. Biological targets are most commonly proteins such as enzymes, ion channels, and receptors. | 1 | Applied and Interdisciplinary Chemistry |
Biosensors have the potential for "high sensitivity, selectivity, reliability, simplicity, low-cost and real-time response". For instance, bionanotechnologists reported the development of , that can detect levels of diverse water pollutants. | 0 | Theoretical and Fundamental Chemistry |
Valves are quite diverse and may be classified into a number of basic types. Valves may also be classified by how they are actuated:
*Hydraulic
*Pneumatic
*Manual
*Solenoid valve
*Motor | 1 | Applied and Interdisciplinary Chemistry |
This form factor is useful for any applications where the spectrum analyzer needs to be taken outside to make measurements or simply carried while in use. Attributes that contribute to a useful portable spectrum analyzer include:
*Optional battery-powered operation to allow the user to move freely outside.
*Clearly viewable display to allow the screen to be read in bright sunlight, darkness or dusty conditions.
*Light weight (usually less than ). | 0 | Theoretical and Fundamental Chemistry |
Electric companies often prefer to use cooling water from the ocean or a lake, river, or cooling pond instead of a cooling tower. This single pass or once-through cooling system can save the cost of a cooling tower and may have lower energy costs for pumping cooling water through the plant's heat exchangers. However, the waste heat can cause thermal pollution as the water is discharged. Power plants using natural bodies of water for cooling are designed with mechanisms such as fish screens, to limit intake of organisms into the cooling machinery. These screens are only partially effective and as a result billions of fish and other aquatic organisms are killed by power plants each year. For example, the cooling system at the Indian Point Energy Center in New York kills over a billion fish eggs and larvae annually. A further environmental impact is that aquatic organisms which adapt to the warmer discharge water may be injured if the plant shuts down in cold weather.
Water consumption by power stations is a developing issue.
In recent years, recycled wastewater, or grey water, has been used in cooling towers. The Calpine Riverside and the Calpine Fox power stations in Wisconsin as well as the Calpine Mankato power station in Minnesota are among these facilities. | 1 | Applied and Interdisciplinary Chemistry |
Deaths have resulted from accidental exposure to fumigation materials containing aluminium phosphide or phosphine. It can be absorbed either by inhalation or transdermally. As a respiratory poison, it affects the transport of oxygen or interferes with the utilization of oxygen by various cells in the body. Exposure results in pulmonary edema (the lungs fill with fluid). Phosphine gas is heavier than air so it stays near the floor.
Phosphine appears to be mainly a redox toxin, causing cell damage by inducing oxidative stress and mitochondrial dysfunction. Resistance in insects is caused by a mutation in a mitochondrial metabolic gene.
Phosphine can be absorbed into the body by inhalation. The main target organ of phosphine gas is the respiratory tract. According to the 2009 U.S. National Institute for Occupational Safety and Health (NIOSH) pocket guide, and U.S. Occupational Safety and Health Administration (OSHA) regulation, the 8 hour average respiratory exposure should not exceed 0.3 ppm. NIOSH recommends that the short term respiratory exposure to phosphine gas should not exceed 1 ppm. The Immediately Dangerous to Life or Health level is 50 ppm. Overexposure to phosphine gas causes nausea, vomiting, abdominal pain, diarrhea, thirst, chest tightness, dyspnea (breathing difficulty), muscle pain, chills, stupor or syncope, and pulmonary edema. Phosphine has been reported to have the odor of decaying fish or garlic at concentrations below 0.3 ppm. The smell is normally restricted to laboratory areas or phosphine processing since the smell comes from the way the phosphine is extracted from the environment. However, it may occur elsewhere, such as in industrial waste landfills. Exposure to higher concentrations may cause olfactory fatigue. | 0 | Theoretical and Fundamental Chemistry |
The fact that radon is present in indoor air has been known since at least the 1950s and research into its effects on human health started in the early 1970s. The danger of radon exposure in dwellings received more widespread public awareness after 1984, as a result of a case of Stanley Watras, an employee at the Limerick nuclear power plant in Pennsylvania. Mr. Watras set off the radiation alarms (see Geiger counter) on his way into work for two weeks straight while authorities searched for the source of the contamination. They were shocked to find that the source was astonishingly high levels of radon in his basement and it was not related to the nuclear plant. The risks associated with living in his house were estimated to be equivalent to smoking 135 packs of cigarettes every day.
Depending how houses are built and ventilated, radon may accumulate in basements and dwellings. The European Union recommends that mitigation should be taken starting from concentrations of 400 Bq/m for old houses, and 200 Bq/m for new ones.
The National Council on Radiation Protection and Measurements (NCRP) recommends action for any house with a concentration higher than 8 pCi/L (300 Bq/m).
The United States Environmental Protection Agency recommends action for any house with a concentration higher than 148 Bq/m (given as 4 pCi/L). Nearly one in 15 homes in the U.S. has a high level of indoor radon according to their statistics. The U.S. Surgeon General and EPA recommend all homes be tested for radon. Since 1985, millions of homes have been tested for radon in the U.S.
By adding a crawl space under the ground floor, which is subject to forced ventilation the radon level in the house can be lowered. | 0 | Theoretical and Fundamental Chemistry |
The primary convention for expressing tacticity is in terms of the relative weight fraction of triad or higher-order components, as described above. An alternative expression for tacticity is the average length of meso and racemo sequences within the polymer molecule. The average meso sequence length may be approximated from the relative abundance of pentads as follows: | 0 | Theoretical and Fundamental Chemistry |
Septage or "septic tank sludge" is fecal sludge that is accumulated and stored in a septic tank. Septage tends to be more dilute, as septic tanks are typically used with flush toilets (blackwater) and can also include grey water. Septic tanks also tend to have less solid waste, as they only receive things that can be flushed down a toilet (e.g. toilet paper). When operating as designed, a sludge blanket layer accumulates on the bottom of the tank, a scum layer that contains fats, oil and grease accumulates at the top, and the effluent or supernatant contains less solids.
Septage is periodically removed (with a frequency depending on tank capacity, system efficiency, and usage level, but typically less often than annually) from the septic tanks by specialized vehicles known as vacuum trucks. They pump the septage out of the tank, and transport it to a local fecal sludge treatment plant. It can also be used by farmers for fertilizer, or stored in large septage waste storage facilities for later treatment or use on crops.
The term "septage" has been used in the United States since at least 1992. It has also been used in projects by the United States Agency for International Development in Asia. Another definition of septage is: "A historical term to define sludge removed from septic tanks."
In India some government policy documents are using the term FSSM for "Fecal sludge and septage management". | 1 | Applied and Interdisciplinary Chemistry |
The Radiological Response and Emergency Management System (RREMS) is a system managed by the Department for Energy Security and Net Zero and used by the Government of the United Kingdom which records and analyses the level of radioactivity across the United Kingdom. A reading is taken from each of the over 200 stations every hour and an alert triggered if radiation levels for specific isotopes rise significantly above normal background radiation levels at one or more stations. RREMS replaced the older Radioactive Incident Monitoring Network (RIMNET) system in September 2022.
Stations are distributed across the UK, but are more concentrated at coastal areas. Many monitoring sites are also located at or nearby airports, including Gatwick, Heathrow, Stansted and Lydd.
As well as being of use in an emergency, the stations also serve to record historical data on radiation levels. | 0 | Theoretical and Fundamental Chemistry |
There is significant correlation of phosphorylated mTOR with the survival rate for patients with stages I and II TNBC. A patient-derived xenograft TNBC model testing the mTOR inhibitor rapamycin showed 77–99% tumor-growth inhibition, which is significantly more than has been seen with doxorubicin; protein phosphorylation studies indicated that constitutive activation of the mTOR pathway decreased with treatment. | 1 | Applied and Interdisciplinary Chemistry |
The first three have similar half-lives, between 200 thousand and 300 thousand years; the last four have longer half-lives, in the low millions of years.
#Technetium-99 produces the largest amount of LLFP radioactivity. It emits beta particles of low to medium energy but no gamma rays, so has little hazard on external exposure, but only if ingested. However, technetium's chemistry allows it to form anions (pertechnetate, TcO) that are relatively mobile in the environment.
#Tin-126 has a large decay energy (due to its following short half-life decay product) and is the only LLFP that emits energetic gamma radiation, which is an external exposure hazard. However, this isotope is produced in very small quantities in fission by thermal neutrons, so the energy per unit time from Sn is only about 5% as much as from Tc for U-235 fission, or 20% as much for 65% U-235+35% Pu-239. Fast fission may produce higher yields. Tin is an inert metal with little mobility in the environment, helping to limit health risks from its radiation.
#Selenium-79 is produced at low yields and emits only weak radiation. Its decay energy per unit time should be only about 0.2% that of Tc-99.
#Zirconium-93 is produced at a relatively high yield of about 6%, but its decay is 7.5 times slower than Tc-99, and its decay energy is only 30% as great; therefore its energy production is initially only 4% as great as Tc-99, though this fraction will increase as the Tc-99 decays. Zr does produce gamma radiation, but of a very low energy, and zirconium is relatively inert in the environment.
#Caesium-135s predecessor xenon-135 is produced at a high rate of over 6% of fissions, but is an extremely potent absorber of thermal neutrons (neutron poison), so that most of it is transmuted to almost-stable xenon-136 before it can decay to caesium-135. If 90% of Xe is destroyed, then the remaining Css decay energy per unit time is initially only about 1% as great as that of the Tc. In a fast reactor, less of the Xe-135 may be destroyed.Cs is the only alkaline or electropositive LLFP; in contrast, the main medium-lived fission products and the minor actinides other than neptunium are all alkaline and tend to stay together during reprocessing; with many reprocessing techniques such as salt solution or salt volatilization, Cs will also stay with this group, although some techniques such as high-temperature volatilization can separate it. Often the alkaline wastes are vitrified to form high level waste, which will include the Cs.Cs but also stable but neutron-absorbing Cs (which wastes neutrons and forms Cs which is radioactive with a half-life of 2 years) as well as the common fission product Cs which does not absorb neutrons but is highly radioactive, making handling more hazardous and complicated; for all these reasons, transmutation disposal of Cs would be more difficult.
#Palladium-107 has a very long half-life, a low yield (though the yield for plutonium fission is higher than the yield from uranium-235 fission), and very weak radiation. Its initial contribution to LLFP radiation should be only about one part in 10000 for U fission, or 2000 for 65% U+35% Pu. Palladium is a noble metal and extremely inert.
#Iodine-129 has the longest half-life, 15.7 million years, and due to its higher half life, lower fission fraction and decay energy it produces only about 1% the intensity of radioactivity as Tc. However, radioactive iodine is a disproportionate biohazard because the thyroid gland concentrates iodine. I has a half-life nearly a billion times as long as its more hazardous sister isotope I; therefore, with a shorter half-life and a higher decay energy, I is approximately a billion times more radioactive than the longer-lived I. (What relevance I has in this coverage of LLFPs is debatable.) | 0 | Theoretical and Fundamental Chemistry |
Disjoining pressure can be expressed as:
where (in SI units):
* - disjoining pressure (N/m)
* - the surface area of the interacting surfaces (m)
* - total Gibbs energy of the interaction of the two surfaces (J)
* - distance (m)
* indices and signify that the temperature, volume, and the surface area remain constant in the derivative.
Using the concept of the disjoining pressure, the pressure in a film can be viewed as:
where:
* - pressure in a film (Pa)
* - pressure in the bulk of the same phase as that of the film (Pa)
Disjoining pressure is interpreted as a sum of several interactions: dispersion forces, electrostatic forces between charged surfaces, interactions due to layers of neutral molecules adsorbed on the two surfaces, and the structural effects of the solvent.
Classic theory predicts that the disjoining pressure of a thin liquid film on a flat surface as follows,
where:
* - Hamaker constant (J)
* - liquid film thickness (m)
For a solid-liquid-vapor system where the solid surface is structured, the disjoining pressure is affected by the solid surface profile, , and the meniscus shape,
where:
* - solid-liquid potential (J/m)
The meniscus shape can be by minimization of total system free energy as follows
where:
* - total system free energy including surface excess energy and free energy due to solid-liquid interactions (J/m)
* - meniscus shape (m)
* - slope of meniscus shape (1)
In the theory of liquid drops and films, the disjoining pressure can be shown to be related to the equilibrium liquid-solid contact angle through the relation
where is the liquid-vapor surface tension and is the precursor film thickness. | 0 | Theoretical and Fundamental Chemistry |
The heat distortion temperature is determined by the following test procedure outlined in ASTM D648. The test specimen is loaded in three-point bending in the edgewise direction. The outer fiber stress used for testing is either 0.455 MPa or 1.82 MPa, and the temperature is increased at 2 °C/min until the specimen deflects 0.25 mm. This is similar to the test procedure defined in the ISO 75 standard.
Limitations that are associated with the determination of the HDT is that the sample is not thermally isotropic and, in thick samples in particular, will contain a temperature gradient. The HDT of a particular material can also be very sensitive to stress experienced by the component which is dependent on the component’s dimensions. The selected deflection of 0.25 mm (which is 0.2% additional strain) is selected arbitrarily and has no particular physical significance. | 0 | Theoretical and Fundamental Chemistry |
Well-defined, molecular clusters are known, invariably containing organic ligands on their exteriors. Two examples are and . In order to generate naked gold clusters for catalytic applications, the ligands must be removed, which is typically done via a high-temperature ( or higher) calcination process, but can also be achieved chemically at low temperatures (below ), e.g. using a peroxide-assisted route. | 0 | Theoretical and Fundamental Chemistry |
Mass-independent fractionation of sulfur can be observed in ancient sediments, where it preserves a signal of the prevailing environmental conditions. The creation and transfer of the mass-independent signature into minerals would be unlikely in an atmosphere containing abundant oxygen, constraining the Great Oxygenation Event to some time after . Prior to this time, the MIS record implies that sulfate-reducing bacteria did not play a significant role in the global sulfur cycle, and that the MIS signal is due primarily to changes in volcanic activity. | 0 | Theoretical and Fundamental Chemistry |
Inorganic atoms form cyclic compounds as well. Examples include sulfur and nitrogen (e.g. heptasulfur imide , trithiazyl trichloride , tetrasulfur tetranitride ), silicon (e.g., cyclopentasilane ), phosphorus and nitrogen (e.g., hexachlorophosphazene ), phosphorus and oxygen (e.g., metaphosphates and other cyclic phosphoric acid derivatives), boron and oxygen (e.g., sodium metaborate , borax), boron and nitrogen (e.g. borazine ). When carbon in benzene is "replaced" by other elements, e.g., as in borabenzene, silabenzene, germanabenzene, stannabenzene, and phosphorine, aromaticity is retained, and so aromatic inorganic cyclic compounds are also known and well-characterized. | 0 | Theoretical and Fundamental Chemistry |
Triethyloxonium tetrafluoroborate is the organic oxonium compound with the formula . It is often called Meerweins reagent or Meerweins salt after its discoverer Hans Meerwein. Also well known and commercially available is the related trimethyloxonium tetrafluoroborate. The compounds are white solids that dissolve in polar organic solvents. They are strong alkylating agents. Aside from the tetrafluoroborate| salt, many related derivatives are available. | 0 | Theoretical and Fundamental Chemistry |
In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers. The name is composed of Greek elements oligo-, "a few" and -mer, "parts". An adjective form is oligomeric.
The oligomer concept is contrasted to that of a polymer, which is usually understood to have a large number of units, possibly thousands or millions. However, there is no sharp distinction between these two concepts. One proposed criterion is whether the molecule's properties vary significantly with the removal of one or a few of the units.
An oligomer with a specific number of units is referred to by the Greek prefix denoting that number, with the ending -mer: thus dimer, trimer, tetramer, pentamer, and hexamer refer to molecules with two, three, four, five, and six units, respectively. The units of an oligomer may be arranged in a linear chain (as in melam, a dimer of melamine); a closed ring (as in 1,3,5-trioxane, a cyclic trimer of formaldehyde); or a more complex structure (as in tellurium tetrabromide, a tetramer of with a cube-like core). If the units are identical, one has a homo-oligomer; otherwise one may use hetero-oligomer. An example of a homo-oligomeric protein is collagen, which is composed of three identical protein chains.
Some biologically important oligomers are macromolecules like proteins or nucleic acids; for instance, hemoglobin is a protein tetramer. An oligomer of amino acids is called an oligopeptide or just a peptide. An oligosaccharide is an oligomer of monosaccharides (simple sugars). An oligonucleotide is a short single-stranded fragment of nucleic acid such as DNA or RNA, or similar fragments of analogs of nucleic acids such as peptide nucleic acid or Morpholinos.
The units of an oligomer may be connected by covalent bonds, which may result from bond rearrangement or condensation reactions, or by weaker forces such as hydrogen bonds.
The term multimer () is used in biochemistry for oligomers of proteins that are not covalently bound. The major capsid protein VP1 that comprises the shell of the polio virus is a self-assembling multimer of 72 pentamers held together by local electric charges.
Many oils are oligomeric, such as liquid paraffin. Plasticizers are oligomeric esters widely used to soften thermoplastics such as PVC. They may be made from monomers by linking them together, or by separation from the higher fractions of crude oil. Polybutene is an oligomeric oil used to make putty.
Oligomerization is a chemical process that converts monomers to macromolecular complexes through a finite degree of polymerization. Telomerization is an oligomerization carried out under conditions that result in chain transfer, limiting the size of the oligomers. (This concept is not to be confused with the formation of a telomere, a region of highly repetitive DNA at the end of a chromosome.) | 0 | Theoretical and Fundamental Chemistry |
Ingold married Dr. Edith Hilda Ingold (Usherwood) in 1923. She was a fellow chemist with whom he collaborated. They had two daughters and a son, the chemist Keith Ingold. | 0 | Theoretical and Fundamental Chemistry |
In very strong magnetic fields, (around 750,000 Tesla) and low enough temperatures, helium atoms attract, and can even form linear chains. This may happen in white dwarfs and neutron stars. The bond length and dissociation energy both increase as the magnetic field increases. | 0 | Theoretical and Fundamental Chemistry |
Mill scale, often shortened to just scale, is the flaky surface of hot rolled steel, consisting of the mixed iron oxides iron(II) oxide (, wüstite), iron(III) oxide (, hematite), and iron(II,III) oxide (, magnetite).
Mill scale is formed on the outer surfaces of plates, sheets or profiles when they are produced by passing red hot iron or steel billets through rolling mills. Mill scale is bluish-black in color. It is usually less than thick, and initially adheres to the steel surface and protects it from atmospheric corrosion provided no break occurs in this coating.
Because it is electrochemically cathodic to steel, any break in the mill scale coating will cause accelerated corrosion of steel exposed at the break. Mill scale is thus a boon for a while, until its coating breaks due to handling of the steel product or due to any other mechanical cause.
Mill scale becomes a nuisance when the steel is to be processed. Any paint applied over it is wasted, since it will come off with the scale as moisture-laden air gets under it. Thus mill scale can be removed from steel surfaces by flame cleaning, pickling, or abrasive blasting, which are all tedious operations that consume energy. This is why shipbuilders and steel fixers used to leave steel and rebar delivered freshly rolled from mills out in the open to allow it to weather until most of the scale fell off due to atmospheric action. Nowadays, most steel mills can supply their product with mill scale removed and steel coated with shop primers over which welding or painting can be done safely.
Mill scale generated in rolling mills will be collected and sent to a sinter plant for recycling. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, the sulfonamide functional group (also spelled sulphonamide) is an organosulfur group with the structure . It consists of a sulfonyl group () connected to an amine group (). Relatively speaking this group is unreactive. Because of the rigidity of the functional group, sulfonamides are typically crystalline; for this reason, the formation of a sulfonamide is a classic method to convert an amine into a crystalline derivative which can be identified by its melting point. Many important drugs contain the sulfonamide group.
A sulfonamide (compound) is a chemical compound that contains this group. The general formula is or , where each R is some organic group; for example, "methanesulfonamide" (where R = methane, R' = R" = hydrogen) is . Any sulfonamide can be considered as derived from a sulfonic acid by replacing a hydroxyl group () with an amine group.
In medicine, the term "sulfonamide" is sometimes used as a synonym for sulfa drug, a derivative or variation of sulfanilamide. The first sulfonamide was discovered in Germany in 1932. | 0 | Theoretical and Fundamental Chemistry |
Steam cracking is the process for producing ethylene and other alkenes from aliphatic hydrocarbons. Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid by-product called pyrolysis gasoline. Pyrolysis gasoline can be blended with other hydrocarbons as a gasoline additive, or routed through an extraction process to recover BTX aromatics (benzene, toluene and xylenes). | 1 | Applied and Interdisciplinary Chemistry |
An α,β-unsaturated acid is a type of α,β-unsaturated carbonyl compound that consists of an alkene conjugated to a carboxylic acid. The simplest example is acrylic acid (CH=CHCOH). These compounds are prone to polymerization, giving rise to the large area of polyacrylate plastics. Acrylate polymers are derived from but do not contain the acrylate group. The carboxyl group of acrylic acid can react with ammonia to form acrylamide, or with an alcohol to form an acrylate ester. Acrylamide and methyl acrylate are commercially important examples of α,β-unsaturated amides and α,β-unsaturated esters, respectively. They also polymerize readily. Acrylic acid, its esters, and its amide derivatives feature the acryloyl group.
α,β-Unsaturated dicarbonyls are also common. The parent compounds are maleic acid and the isomeric fumaric acid. Maleic acid forms esters, an imide, and an anhydride, i.e. diethyl maleate, maleimide, and maleic anhydride. Fumaric acid, as fumarate, is an intermediate in the Krebs citric acid cycle, which is of great importance in bioenergy. | 0 | Theoretical and Fundamental Chemistry |
Chiral inversion is a very important part of designing and making drugs. Because this process can change how chiral drugs work in the body and can cause side effects that can be serious or even fatal. Traditionally, chiral inversions have been studied with NMR spectroscopy at different temperatures and chiroptical methods like polarimetry. But strong, complementary methods based on dynamic chromatography (GC, HPLC, SFC, CEC, and MEKC) and electrophoresis have been made and used to figure out how the enantiomeric composition of stereo-labile chiral compounds changes over time. Most of the time, liquid chromatographic methods are used to do enantioselective analysis of chiral drugs. When an analyte with one stereogenic center or axis is separated well, the chromatogram will show two peaks. But if the analyte is stereo-labile, the peaks tend to merge. How much coalescence there is will depend on how fast chiral inversion and enantioresolution happen. Over time, the peaks will merge into a flat area. Dynamic chromatography shows how the elution profile changes over time. This makes it useful for figuring out how pH, temperature, and solvents affect chiral inversion, which can happen on the stationary phase, in the injector, or in the detector.
Multidimensional approaches have been used to improve separation and detection. Table below shows a list of common methods and experiments used to figure out chiral inversion. Any of these methods can then be used to determine chiral inversion. Which instrument is used to analyze a chiral compound depends on its physical and chemical properties (i.e., the solubility, vapor pressure, thermal and solvent stability, and detection).
For example, capillary electrophoresis or liquid chromatography could be used if the analyte can be ionized and has a high vapor pressure, but it is also soluble in polar solvents. On the other hand, gas chromatography is the best way to test a substance that is stable at high temperatures but has a low vapor pressure. When compared to gas or liquid chromatography, supercritical fluid chromatography is a better way to measure chiral inversion because it uses mass spectrometers and a green method. | 0 | Theoretical and Fundamental Chemistry |
The Hazen–Williams equation is an empirical relationship which relates the flow of water in a pipe with the physical properties of the pipe and the pressure drop caused by friction. It is used in the design of water pipe systems such as fire sprinkler systems, water supply networks, and irrigation systems. It is named after Allen Hazen and Gardner Stewart Williams.
The Hazen–Williams equation has the advantage that the coefficient C is not a function of the Reynolds number, but it has the disadvantage that it is only valid for water. Also, it does not account for the temperature or viscosity of the water, and therefore is only valid at room temperature and conventional velocities. | 1 | Applied and Interdisciplinary Chemistry |
Hexachlorophosphazene has a core with six equivalent P–N bonds, for which the adjacent P–N distances are 157 pm. This is characteristically shorter than the ca. 177 pm P–N bonds in the valence saturated phosphazane analogues.
The molecule possesses D symmetry, and each phosphorus center is tetrahedral with a Cl–P–Cl angle of 101°.
The ring in hexachlorophosphazene deviates from planarity and is slightly ruffled (see chair conformation). By contrast, the ring in the related hexafluorophosphazene species is completely planar. | 0 | Theoretical and Fundamental Chemistry |
Common laboratory conductivity meters employ a potentiometric method and four electrodes. Often, the electrodes are cylindrical and arranged concentrically. The electrodes are usually made of platinum metal. An alternating current is applied to the outer pair of the electrodes. The potential between the inner pair is measured. Conductivity could in principle be determined using the distance between the electrodes and their surface area using Ohm's law but generally, for accuracy, a calibration is employed using electrolytes of well-known conductivity.
Industrial conductivity probes often employ an inductive method, which has the advantage that the fluid does not wet the electrical parts of the sensor. Here, two inductively-coupled coils are used. One is the driving coil producing a magnetic field and it is supplied with accurately-known voltage. The other forms a secondary coil of a transformer. The liquid passing through a channel in the sensor forms one turn in the secondary winding of the transformer. The induced current is the output of the sensor.
Another way is to use four-electrode conductivity sensors that are made from corrosion-resistant materials. A benefit of four-electrode conductivity sensors compared to inductive sensors is scaling compensation and the ability to measure low (below 100 μS/cm) conductivities (a feature especially important when measuring near-100% hydrofluoric acid). | 0 | Theoretical and Fundamental Chemistry |
Spectrometer can determine chemical composition through its measure of spectrums. The common spectrometer used in analytical chemistry is Mass spectrometry. In a mass spectrometer, a small amount of sample is ionized and converted to gaseous ions, where they are separated and analyzed according to their mass-to-charge ratios.
NMR Spectroscopy involves exciting a NMR-active sample and then measuring the effects of this magnetic excitation. From this, the bonds present in a sample can be determined. | 0 | Theoretical and Fundamental Chemistry |
The Röntgen equivalent physical or rep (symbol rep) of tissue.
At the time, this was thought to be the amount of energy deposited by 1 roentgen. Improved measurements have since found that one roentgen of air kerma deposits 8.77 mGy in dry air, or 9.6 mGy in soft tissue, but the rep was defined as a fixed number of ergs per unit gram.
A 1952 handbook from the US National Bureau of Standards affirms that "The numerical coefficient of the rep has been deliberately changed to 93, instead of the earlier 83, to agree with L. H. Grays energy-unit." Grays energy unit was " one roentgen of hard gamma resulted in about 93 ergs per gram energy absorption in water". The lower range value of 83.8 ergs was the value in air corresponding to wet tissue. The rep was commonly used until the 1960s, but was gradually displaced by the rad starting in 1954 and later the gray starting in 1977. | 0 | Theoretical and Fundamental Chemistry |
Typically, for free convection, the average Nusselt number is expressed as a function of the Rayleigh number and the Prandtl number, written as:
Otherwise, for forced convection, the Nusselt number is generally a function of the Reynolds number and the Prandtl number, or
Empirical correlations for a wide variety of geometries are available that express the Nusselt number in the aforementioned forms. | 1 | Applied and Interdisciplinary Chemistry |
The French iron industry lagged behind Britain and Belgium in the early 19th century. After 1850 it also lagged behind Germany and Luxembourg. Its industry comprised too many small, inefficient firms. 20th century growth was not robust, due more to traditional social and economic attitudes than to inherent geographic, population, or resource factors. Despite a high national income level, the French steel industry remained laggard. The industry was based on large supplies of coal and iron ore, and was dispersed across the country. The greatest output came in 1929, at 10.4 million metric tons. The industry suffered sharply during the Great Depression and World War II. Prosperity returned by mid-1950s, but profits came largely from strong domestic demand rather than competitive capacity. Late modernization delayed the development of powerful unions and collective bargaining. | 1 | Applied and Interdisciplinary Chemistry |
To gather relevant statistical data higher sample masses are needed in some cases. Thus, transportation of the sample into the mini-bulk testing facility becomes unviable and the equipment is set up in the field. Containerised units in conjunction with Diesel-powered crushing and screening equipment are often applied and used for production test runs under full scale operating conditions. | 0 | Theoretical and Fundamental Chemistry |
A base metal, such as iron (Fe) goes into aqueous solution as positively charged cation, Fe. As the metal is oxidized under anaerobic conditions by the protons of water, H ions are reduced to form molecular H. This can be written in the following ways under acidic and neutral conditions respectively:
:Fe + 2 H → Fe + H
:Fe + 2 HO → Fe(OH) + H
Usually, a thin film of molecular hydrogen forms on the metal. Sulfate-reducing bacteria oxidize the molecular hydrogen to produce hydrogen sulfide ions (HS) and water:
:4 H + SO → HS + 3 HO + OH
The iron ions partly precipitate to form iron (II) sulfide. Another reaction occurs between iron and water producing iron hydroxide.
:Fe + HS → FeS + H
:3 Fe + 6 HO → 3 Fe(OH) + 6 H
The net equation comes to:
:4 Fe + SO + H + 3 HO → FeS + 3 Fe(OH) + OH
This form of corrosion by sulfate-reducing bacteria can, in this way, be far more harmful than anaerobic corrosion. | 1 | Applied and Interdisciplinary Chemistry |
In polymer chemistry and materials science, the term "polymer" refers to large molecules whose structure is composed of multiple repeating units. Supramolecular polymers are a new category of polymers that can potentially be used for material applications beyond the limits of conventional polymers. By definition, supramolecular polymers are polymeric arrays of monomeric units that are connected by reversible and highly directional secondary interactions–that is, non-covalent bonds. These non-covalent interactions include van der Waals interactions, hydrogen bonding, Coulomb or ionic interactions, π-π stacking, metal coordination, halogen bonding, chalcogen bonding, and host–guest interaction. The direction and strength of the interactions are precisely tuned so that the array of molecules behaves as a polymer (that is, it behaves in a way that can be described by the theories of polymer physics) in dilute and concentrated solution, as well as in the bulk.
In conventional polymers, monomeric units are linked by strong covalent bonds and have excellent properties as materials; however, high temperatures and pressures are typically required for processing due to polymer entanglement in the highly viscous melt. Supramolecular polymers combine good material properties with low-viscosity melts that are easy to handle. Additionally, some supramolecular polymers have unique characteristics, such as the ability to self-heal fractures. Although covalent polymers can be recycled, their strong covalent bonds never disintegrate, and go on to negatively affect the environment as plastic wastes. Thus, supramolecular polymers are increasingly getting attention because of their potential for the design of responsive, adaptive, self-healing, and environmentally friendly materials. | 0 | Theoretical and Fundamental Chemistry |
Not all reactions have a single rate-determining step. In particular, the rate of a chain reaction is usually not controlled by any single step. | 0 | Theoretical and Fundamental Chemistry |
The borax method is a technique of artisanal gold mining, which uses borax as a flux to purify gold concentrates. By using borax, no mercury flour is produced, hence gold recovery increases. | 1 | Applied and Interdisciplinary Chemistry |
Under certain conditions the Beer–Lambert law fails to maintain a linear relationship between attenuation and concentration of analyte. These deviations are classified into three categories:
# Real—fundamental deviations due to the limitations of the law itself.
# Chemical—deviations observed due to specific chemical species of the sample which is being analyzed.
# Instrument—deviations which occur due to how the attenuation measurements are made.
There are at least six conditions that need to be fulfilled in order for the Beer–Lambert law to be valid. These are:
# The attenuators must act independently of each other.
# The attenuating medium must be homogeneous in the interaction volume.
# The attenuating medium must not scatter the radiation—no turbidity—unless this is accounted for as in DOAS.
# The incident radiation must consist of parallel rays, each traversing the same length in the absorbing medium.
# The incident radiation should preferably be monochromatic, or have at least a width that is narrower than that of the attenuating transition. Otherwise a spectrometer as detector for the power is needed instead of a photodiode which cannot discriminate between wavelengths.
# The incident flux must not influence the atoms or molecules; it should only act as a non-invasive probe of the species under study. In particular, this implies that the light should not cause optical saturation or optical pumping, since such effects will deplete the lower level and possibly give rise to stimulated emission.
If any of these conditions are not fulfilled, there will be deviations from the Beer–Lambert law. | 0 | Theoretical and Fundamental Chemistry |
Crude oil and refined fuel spills from tanker ship accidents have damaged natural ecosystems and human livelihoods in Alaska, the Gulf of Mexico, the Galápagos Islands, France and many other places.
The quantity of oil spilled during accidents has ranged from a few hundred tons to several hundred thousand tons (e.g., Deepwater Horizon oil spill, SS Atlantic Empress, Amoco Cadiz). Smaller spills have already proven to have a great impact on ecosystems, such as the Exxon Valdez oil spill.
Oil spills at sea are generally much more damaging than those on land, since they can spread for hundreds of nautical miles in a thin oil slick which can cover beaches with a thin coating of oil. This can kill sea birds, mammals, shellfish and other organisms it coats. Oil spills on land are more readily containable if a makeshift earth dam can be rapidly bulldozed around the spill site before most of the oil escapes, and land animals can avoid the oil more easily.
Control of oil spills is difficult, requires ad hoc methods, and often a large amount of manpower. The dropping of bombs and incendiary devices from aircraft on the wreck produced poor results; modern techniques would include pumping the oil from the wreck, like in the Prestige oil spill or the Erika oil spill.
Though crude oil is predominantly composed of various hydrocarbons, certain nitrogen heterocyclic compounds, such as pyridine, picoline, and quinoline are reported as contaminants associated with crude oil, as well as facilities processing oil shale or coal, and have also been found at legacy wood treatment sites. These compounds have a very high water solubility, and thus tend to dissolve and move with water. Certain naturally occurring bacteria, such as Micrococcus, Arthrobacter, and Rhodococcus have been shown to degrade these contaminants.
Because petroleum is a naturally occurring substance, its presence in the environment need not be the result of human causes such as accidents and routine activities (seismic exploration, drilling, extraction, refining and combustion). Phenomena such as seeps and tar pits are examples of areas that petroleum affects without man's involvement. | 0 | Theoretical and Fundamental Chemistry |
By analyzing the emissivity of ground surfaces, multispectral imaging can detect the presence of underground missiles. Surface and sub-surface soil possess different physical and chemical properties that appear in spectral analysis. Disturbed soil has increased emissivity in the wavelength range of 8.5 to 9.5 micrometers while demonstrating no change in wavelengths greater than 10 micrometers. The US Army Research Laboratorys dual MWIR/LWIR FPA used "red" and "blue" detectors to search for areas with enhanced emissivity. The red detector acts as a backdrop, verifying realms of undisturbed soil areas, as it is sensitive to the 10.4 micrometer wavelength. The blue detector is sensitive to wavelengths of 9.3 micrometers. If the intensity of the blue image changes when scanning, that region is likely disturbed.' The scientists reported that fusing these two images increased detection capabilities. | 0 | Theoretical and Fundamental Chemistry |
In general, the most important requisite is to calibrate the incubation time of the assay both to the model cell and the ligand to be evaluated. Too short incubation time results in no cells in the sample, while too long time perturbs the concentration gradients and measures more chemokinetic than chemotactic responses.
The most commonly used techniques are grouped into two main groups: | 1 | Applied and Interdisciplinary Chemistry |
An enantiomer can be named by the direction in which it rotates the plane of polarized light. Clockwise rotation of the light traveling toward the viewer is labeled (+) enantiomer. Its mirror-image is labeled (−). The (+) and (−) isomers have been also termed d- and l- (for dextrorotatory and levorotatory); but, naming with d- and l- is easy to confuse with - and - labeling and is therefore discouraged by IUPAC. | 0 | Theoretical and Fundamental Chemistry |
The physical state (solid, liquid, or gas) of a reactant is also an important factor of the rate of change. When reactants are in the same phase, as in aqueous solution, thermal motion brings them into contact. However, when they are in separate phases, the reaction is limited to the interface between the reactants. Reaction can occur only at their area of contact; in the case of a liquid and a gas, at the surface of the liquid. Vigorous shaking and stirring may be needed to bring the reaction to completion. This means that the more finely divided a solid or liquid reactant the greater its surface area per unit volume and the more contact it with the other reactant, thus the faster the reaction. To make an analogy, for example, when one starts a fire, one uses wood chips and small branches — one does not start with large logs right away. In organic chemistry, on water reactions are the exception to the rule that homogeneous reactions take place faster than heterogeneous reactions ( are those reactions in which solute and solvent not mix properly) | 0 | Theoretical and Fundamental Chemistry |
As the environment is altered through physical means (dredging), the occurring reactions change resulting in a decrease of the availability of nutrients and chemical species to plant species and the ecosystem. This then further changes the physical environment as these species are no longer able to survive. The loss of species then results in further changes to the chemical environment, as they are no longer present to remove excess nutrients. This also changes the physical environment further as the lack of survival of plant species results in open land and increased erosion. The change of the chemical environment also affects the mitigation techniques to be applied for rebuilding of wetlands as the survival of plant species that could potentially be planted depends on the chemical environment, and changes must be monitored for effective mitigation to take place. | 0 | Theoretical and Fundamental Chemistry |
tert-Butyllithium is renowned for deprotonation of carbon acids (C-H bonds). One example is the double deprotonation of allyl alcohol. Other examples are the deprotonation of vinyl ethers.
In combination with n-butyllithiium, tert-butylllithium monolithiates ferrocene. tert-Butyllithium deprotonates dichloromethane:
Similar to n-butyllithium, tert-butyllithium can be used for lithium–halogen exchange reactions. | 0 | Theoretical and Fundamental Chemistry |
Schott systematized the chemical composition of a significant range of glass compositions. Representative examples are summarized in the table. | 0 | Theoretical and Fundamental Chemistry |
Mass spectrometric immunoassay (MSIA) is a rapid method is used to detect and/ or quantify antigens and or antibody analytes. This method uses an analyte affinity (either through antigens or antibodies) isolation to extract targeted molecules and internal standards from biological fluid in preparation for matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS). This method allows for "top down" and "bottom up" analysis. This sensitive method allows for a new and improved process for detecting multiple antigens and antibodies in a single assay. This assay is also capable of distinguishing mass shifted forms of the same molecule via a panantibody, as well as distinguish point mutations in proteins. Each specific form is detected uniquely based on their characteristic molecular mass. MSIA has dual specificity because of the antibody-antigen reaction coupled with the power of a mass spectrometer.
There are various other immunoassy techniques that have been used previously such as radioimmunoassay (RIA) and enzyme immunoassay (EIA and ELISA). These techniques are extremely sensitive however, there are many limitations to these methods. For example, quantification for ELISA and EIA require several hours because the binding has to reach equilibrium. RIA's disadvantage is that you need radioactive particles which are universally known to be carcinogens.
The creation of MSIA fulfilled the need to determine the presence of one or more antigens in a specimen as well as the quantification of those said species. | 1 | Applied and Interdisciplinary Chemistry |
The European Journal of Medicinal Chemistry is a monthly peer-reviewed scientific journal covering medicinal chemistry and published by Elsevier. It was established in 1966 as Chimica Therapeutica (CODEN: CHTPBA) and obtained its current title in 1974. From 1974 to 1981 the journal was still subtitled as Chimica Therapeutica and from 1982 to 1986 the subtitle was Chimie Thérapeutique, indicating its French origin. And now it is the journal of the French Société de Chimie Thérapeutique.
The journal covers research on all aspects of medicinal chemistry and publishes original papers, laboratory notes, short or preliminary communications, and invited reviews.
The European Journal of Medicinal Chemistry is abstracted and indexed in the Index medicus and MEDLINE since 2000. | 1 | Applied and Interdisciplinary Chemistry |
Around one-third of the human population drinks water from groundwater resources. Of this, about 10%, approximately three hundred million people, obtain water from groundwater resources that are heavily contaminated with arsenic or fluoride. These trace elements derive mainly from minerals. Maps locating potential problematic wells are available. | 1 | Applied and Interdisciplinary Chemistry |
Fatty acids are preferentially oxidized because of the inactivation of PDH by fatty acid oxidation inhibiting glucose oxidation. This suggests that mitochondrial metabolism may control fuel selection. Cellular respiration is stimulated by fatty acids and this relates to an increase in the mitochondrial NADH to NAD+ ratio, suggesting that energy provision overtakes energy consumption. Switching from glucose to fatty acid oxidation leads to a bigger proportion of electrons being transported to complex 2 rather than complex 1 of the respiratory chain. This difference leads to a less efficient oxidative phosphorylation. By oxidizing fatty acids, mitochondria increase their respiration while increasing the production of ROS. | 1 | Applied and Interdisciplinary Chemistry |
To use electron affinities properly, it is essential to keep track of sign. For any reaction that releases energy, the change ΔE in total energy has a negative value and the reaction is called an exothermic process. Electron capture for almost all non-noble gas atoms involves the release of energy and thus is exothermic. The positive values that are listed in tables of E are amounts or magnitudes. It is the word "released" within the definition "energy released" that supplies the negative sign to ΔE. Confusion arises in mistaking E for a change in energy, ΔE, in which case the positive values listed in tables would be for an endo- not exo-thermic process. The relation between the two is E = −ΔE(attach).
However, if the value assigned to E is negative, the negative sign implies a reversal of direction, and energy is required to attach an electron. In this case, the electron capture is an endothermic process and the relationship, E = −ΔE(attach) is still valid. Negative values typically arise for the capture of a second electron, but also for the nitrogen atom.
The usual expression for calculating E when an electron is attached is
This expression does follow the convention ΔX = X(final) − X(initial) since −ΔE = −(E(final) − E(initial)) = E(initial) − E(final).
Equivalently, electron affinity can also be defined as the amount of energy required to detach an electron from the atom while it holds a single-excess-electron thus making the atom a negative ion, i.e. the energy change for the process
:X → X + e
If the same table is employed for the forward and reverse reactions, without switching signs, care must be taken to apply the correct definition to the corresponding direction, attachment (release) or detachment (require). Since almost all detachments (require +) an amount of energy listed on the table, those detachment reactions are endothermic, or ΔE(detach) > 0. | 0 | Theoretical and Fundamental Chemistry |
In thermodynamics and fluid mechanics, the stagnation enthalpy of a fluid is the static enthalpy of the fluid at a stagnation point. The stagnation enthalpy is also called total enthalpy. At a point where the flow does not stagnate, it corresponds to the static enthalpy of the fluid at that point assuming it was brought to rest from velocity isentropically. That means all the kinetic energy was converted to internal energy without losses and is added to the local static enthalpy. When the potential energy of the fluid is negligible, the mass-specific stagnation enthalpy represents the total energy of a flowing fluid stream per unit mass.
Stagnation enthalpy, or total enthalpy, is the sum of the static enthalpy (associated with the temperature and static pressure at that point) plus the enthalpy associated with the dynamic pressure, or velocity. This can be expressed in a formula in various ways. Often it is expressed in specific quantities, where specific means mass-specific, to get an intensive quantity:
where:
: mass-specific total enthalpy, in [J/kg]
: mass-specific static enthalpy, in [J/kg]
: fluid velocity at the point of interest, in [m/s]
: mass-specific kinetic energy, in [J/kg]
The volume-specific version of this equation (in units of energy per volume, [J/m^3] is obtained by multiplying the equation with the fluid density :
where:
: volume-specific total enthalpy, in [J/m^3]
: volume-specific static enthalpy, in [J/m^3]
: fluid velocity at the point of interest, in [m/s]
: fluid density at the point of interest, in [kg/m^3]
: volume-specific kinetic energy, in [J/m^3]
The non-specific version of this equation, that means extensive quantities are used, is:
where:
: total enthalpy, in [J]
: static enthalpy, in [J]
: fluid mass, in [kg]
: fluid velocity at the point of interest, in [m/s]
: kinetic energy, in [J]
The suffix ‘0’ usually denotes the stagnation condition and is used as such here.
Enthalpy is the energy associated with the temperature plus the energy associated with the pressure. The stagnation enthalpy adds a term associated with the kinetic energy of the fluid mass.
The total enthalpy for a real or ideal gas does not change across a shock. The total enthalpy can not be measured directly. Instead, the static enthalpy and the fluid velocity can be measured. Static enthalpy is often used in the energy equation for a fluid. | 1 | Applied and Interdisciplinary Chemistry |
The radiometric description of the electromagnetic radiative field at a point in space and time is completely represented by the spectral radiance (or specific intensity) at that point. In a region in which the material is uniform and the radiative field is isotropic and homogeneous, let the spectral radiance (or specific intensity) be denoted by , a scalar-valued function of its arguments , , , and , where denotes a unit vector with the direction and sense of the geometrical vector from the source point to the detection point , where denotes the coordinates of , at time and wave frequency . Then, in the region, takes a constant scalar value, which we here denote by . In this case, the value of the vector flux density at is the zero vector, while the scalar or hemispheric flux density at in every direction in both senses takes the constant scalar value . The reason for the value is that the hemispheric integral is half the full spherical integral, and the integrated effect of the angles of incidence of the radiation on the detector requires a halving of the energy flux according to Lambert's cosine law; the solid angle of a sphere is .
The vector definition is suitable for the study of general radiative fields. The scalar or hemispheric spectral flux density is convenient for discussions in terms of the two-stream model of the radiative field, which is reasonable for a field that is uniformly stratified in flat layers, when the base of the hemisphere is chosen to be parallel to the layers, and one or other sense (up or down) is specified. In an inhomogeneous non-isotropic radiative field, the spectral flux density defined as a scalar-valued function of direction and sense contains much more directional information than does the spectral flux density defined as a vector, but the full radiometric information is customarily stated as the spectral radiance (or specific intensity). | 0 | Theoretical and Fundamental Chemistry |
In a homogeneous environment, all U nuclei are in the same conditions with respect to the resonant neutron flux. In a heterogeneous environment uranium is separated from the moderator, which significantly affects the resonant neutron absorption. Firstly, some of the resonant neutrons become thermal neutrons in the moderator without colliding with uranium nuclei; secondly, resonant neutrons hitting the surface of the fuel elements are almost all absorbed by the thin surface layer. The inner U nuclei are shielded by the surface nuclei and participate less in the resonant neutron absorption, and the shielding increases with the increase of the fuel element diameter d. Therefore, the effective U resonance integral in a heterogeneous reactor depends on the fuel element diameter d:
The constant a characterizes the absorption of resonance neutrons by surface and the constant b - by inner U nuclei. For each type of nuclear fuel (natural uranium, uranium dioxide, etc.) the constants a and b are measured experimentally. For natural uranium rods a=4.15, b=12.35.
U for a rod from natural uranium with diameter d=3 cm:
: barns.
Comparison of the last two examples shows that the separation of
uranium and moderator noticeably decreases neutron absorption in the
resonance region. | 0 | Theoretical and Fundamental Chemistry |
Underground stormwater detention allows for high volume storage of runoff in a small footprint area. The storage vessels can be made from a variety of materials, including corrugated metal pipe, aluminum, steel, plastic, fiberglass, pre-cast or poured-in-place concrete.
The vault is typically buried under a parking lot or other open land on the site. In the latter case, this underground vault may be preferable to a surface detention pond if other uses are intended for the land (e.g. a pedestrian plaza or park). In other situations, a vault is used because installing a pond might pose other problems, such as attracting unwanted waterfowl or other animals. In some sites, a vault may be installed in the basement of a building, such as a parking garage. Tunnels may be bored to serve as detention vaults. Tunnels may be cheaper than basins, as they do not require pumps to move the water.
The outlet is generally a restricted-flow drain from the detention vessel, with a weir for containing detritus. Detention vessels delay water's delivery downstream, and possibly creates a later water level peak post-rainfall. It is important to consider timing of water release and the types of reservoirs feeding a waterway. | 1 | Applied and Interdisciplinary Chemistry |
In 1967, Charles Pedersen, who was a chemist working at DuPont, discovered a simple method of synthesizing a crown ether when he was trying to prepare a complexing agent for divalent cations. His strategy entailed linking two catecholate groups through one hydroxyl on each molecule. This linking defines a polydentate ligand that could partially envelop the cation and, by ionization of the phenolic hydroxyls, neutralize the bound dication. He was surprised to isolate a by-product that strongly complexed potassium cations. Citing earlier work on the dissolution of potassium in 16-crown-4, he realized that the cyclic polyethers represented a new class of complexing agents that were capable of binding alkali metal cations. He proceeded to report systematic studies of the synthesis and binding properties of crown ethers in a seminal series of papers. The fields of organic synthesis, phase transfer catalysts, and other emerging disciplines benefited from the discovery of crown ethers. Pedersen particularly popularized the dibenzo crown ethers.
Pedersen shared the 1987 Nobel Prize in Chemistry for the discovery of the synthetic routes to, and binding properties of, crown ethers. | 0 | Theoretical and Fundamental Chemistry |
The measurement approaches of end-point RT-PCR requires the detection of gene expression levels by the use of fluorescent dyes like ethidium bromide, P32 labeling of PCR products using phosphorimager, or by scintillation counting. End-point RT-PCR is commonly achieved using three different methods: relative, competitive and comparative.
; Relative RT-PCR: Relative quantifications of RT-PCR involves the co-amplification of an internal control simultaneously with the gene of interest. The internal control is used to normalize the samples. Once normalized, a direct comparison of relative transcript abundances across multiple samples of mRNA can be made. One precaution to note is that the internal control must be chosen so that it is not affected by the experimental treatment. The expression level should be constant across all samples and with the mRNA of interest for the results to be accurate and meaningful. Because the quantification of the results are analyzed by comparing the linear range of the target and control amplification, it is crucial to take into consideration the starting target molecules concentration and their amplification rate prior to starting the analysis. The results of the analysis are expressed as the ratios of gene signal to internal control signal, which the values can then be used for the comparison between the samples in the estimation of relative target RNA expression.
; Competitive RT-PCR: Competitive RT-PCR technique is used for absolute quantification. It involves the use of a synthetic “competitor” RNA that can be distinguished from the target RNA by a small difference in size or sequence. It is important for the design of the synthetic RNA be identical in sequence but slightly shorter than the target RNA for accurate results. Once designed and synthesized, a known amount of the competitor RNA is added to experimental samples and is co-amplified with the target using RT-PCR. Then, a concentration curve of the competitor RNA is produced and it is used to compare the RT-PCR signals produced from the endogenous transcripts to determine the amount of target present in the sample.
; Comparative RT-PCR: Comparative RT-PCR is similar to the competitive RT-PCR in that the target RNA competes for amplification reagents within a single reaction with an internal standard of unrelated sequence. Once the reaction is complete, the results are compared to an external standard curve to determine the target RNA concentration. In comparison to the relative and competitive quantification methods, comparative RT-PCR is considered to be the more convenient method to use since it does not require the investigator to perform a pilot experiment; in relative RT-PCR, the exponential amplification range of the mRNA must be predetermined and in competitive RT-PCR, a synthetic competitor RNA must be synthesized. | 1 | Applied and Interdisciplinary Chemistry |
Legumes such as clover provide nitrogen compounds to neighbouring plants such as grasses by fixing nitrogen from the air with symbiotic bacteria in their root nodules. These enable the grasses or other neighbours to produce more protein (with lower inputs of artificial fertiliser) and hence to grow more. | 1 | Applied and Interdisciplinary Chemistry |
Diffusion hardening can be done in many different ways to achieve different hardnesses and different surface finishes on metal parts. Some of the different diffusion hardening operations include: Carburizing, Nitriding, Carbonitriding, Nitrocarburizing, Boriding, Titanium-carbon diffusion, and Toyota diffusion. While diffusion hardening is performed mainly on steel parts and carbon is mainly the element used for diffusion, diffusion hardening can also be performed with other diffusion elements and with other metals. In nitriding, nitrogen is diffused into the surface of steel, but can also be used with metals such as Aluminum, Chromium, Molybdenum, and Vanadium. Besides metals and diffusion elements used, diffusion hardening processes differ in the temperature required for diffusion, the phase of the diffusion element, and additional treatments such as quenching and tempering. These different factors greatly affect surface finish and dimensional accuracy of a part. A quenched and tempered part does not have the same dimensional accuracy as a part that has not undergone such a process. Also, they can affect the efficiency of the overall process. In carburizing, the carbon can be in any of the solid, liquid, or gas phases. Although using carbon in the solid phase is usually the safest and easiest of these to work with, the process is difficult to control and the heating is inefficient. All these things must come into consideration when choosing a diffusion hardening process. | 1 | Applied and Interdisciplinary Chemistry |
Putting foreign molecules or atoms between hexagon graphite sheets leads to ordered structures and to superconductivity even if neither the foreign molecule or atom nor the graphite layers are metallic. Several stoichiometries have been synthesized using mainly alkali atoms as anions. | 0 | Theoretical and Fundamental Chemistry |
Drospirenone is the generic name of the drug and its , , , and , while drospirénone is its . Its name is a shortened form of the name 1,2-dihydrospirorenone or dihydrospirenone. Drospirenone is also known by its developmental code names SH-470 and ZK-30595 (alone), BAY 86-5300, BAY 98-7071, and SH-T-00186D (in combination with ethinylestradiol), BAY 86-4891 (in combination with estradiol), and FSN-013 (in combination with estetrol). | 0 | Theoretical and Fundamental Chemistry |
If a specular reflection from a hard flat surface is giving a problematic echo then an acoustic diffuser may be applied to the surface. It will scatter sound in all directions. | 1 | Applied and Interdisciplinary Chemistry |
The extended double-stranded adapters are cleaved by HpyCH4III at a specific restriction site located at 3’ side of the tag sequence and will result in a 3’-dT overhang that will be ligated to the 3’-dA overhang on DNA libraries in the adapter ligation step (Figure 1). | 1 | Applied and Interdisciplinary Chemistry |
Extended aeration is a method of sewage treatment using modified activated sludge procedures. It is preferred for relatively small waste loads, where lower operating efficiency is offset by mechanical simplicity. | 1 | Applied and Interdisciplinary Chemistry |
The nonlinear nature of ferroelectric materials can be used to make capacitors with adjustable capacitance. Typically, a ferroelectric capacitor simply consists of a pair of electrodes sandwiching a layer of ferroelectric material. The permittivity of ferroelectrics is not only adjustable but commonly also very high, especially when close to the phase transition temperature. Because of this, ferroelectric capacitors are small in physical size compared to dielectric (non-tunable) capacitors of similar capacitance.
The spontaneous polarization of ferroelectric materials implies a hysteresis effect which can be used as a memory function, and ferroelectric capacitors are indeed used to make ferroelectric RAM for computers and RFID cards. In these applications thin films of ferroelectric materials are typically used, as this allows the field required to switch the polarization to be achieved with a moderate voltage. However, when using thin films a great deal of attention needs to be paid to the interfaces, electrodes and sample quality for devices to work reliably.
Ferroelectric materials are required by symmetry considerations to be also piezoelectric and pyroelectric. The combined properties of memory, piezoelectricity, and pyroelectricity make ferroelectric capacitors very useful, e.g. for sensor applications. Ferroelectric capacitors are used in medical ultrasound machines (the capacitors generate and then listen for the ultrasound ping used to image the internal organs of a body), high quality infrared cameras (the infrared image is projected onto a two dimensional array of ferroelectric capacitors capable of detecting temperature differences as small as millionths of a degree Celsius), fire sensors, sonar, vibration sensors, and even fuel injectors on diesel engines.
Another idea of recent interest is the ferroelectric tunnel junction (FTJ) in which a contact is made up by nanometer-thick ferroelectric film placed between metal electrodes. The thickness of the ferroelectric layer is small enough to allow tunneling of electrons. The piezoelectric and interface effects as well as the depolarization field may lead to a giant electroresistance (GER) switching effect.
Yet another burgeoning application is multiferroics, where researchers are looking for ways to couple magnetic and ferroelectric ordering within a material or heterostructure; there are several recent reviews on this topic.
Catalytic properties of ferroelectrics have been studied since 1952 when Parravano observed anomalies in CO oxidation rates over ferroelectric sodium and potassium niobates near the Curie temperature of these materials. Surface-perpendicular component of the ferroelectric polarization can dope polarization-dependent charges on surfaces of ferroelectric materials, changing their chemistry. This opens the possibility of performing catalysis beyond the limits of the Sabatier principle. Sabatier principle states that the surface-adsorbates interaction has to be an optimal amount: not too weak to be inert toward the reactants and not too strong to poison the surface and avoid desorption of the products: a compromise situation. This set of optimum interactions is usually referred to as "top of the volcano" in activity volcano plots. On the other hand, ferroelectric polarization-dependent chemistry can offer the possibility of switching the surface—adsorbates interaction from strong adsorption to strong desorption, thus a compromise between desorption and adsorption is no longer needed. Ferroelectric polarization can also act as an energy harvester. Polarization can help the separation of photo-generated electron-hole pairs, leading to enhanced photocatalysis. Also, due to pyroelectric and piezoelectric effects under varying temperature (heating/cooling cycles) or varying strain (vibrations) conditions extra charges can appear on the surface and drive various (electro)chemical reactions forward.
Photoferroelectric imaging is a technique to record optical information on pieces of ferroelectric material. The images are nonvolatile and selectively erasable. | 0 | Theoretical and Fundamental Chemistry |
Rain can generally help clean PDRC surfaces that have been covered with dust, dirt, or other debris and improve their reflectivity. However, in humid areas, consistent rain can result in heavy water accumulation on PDRC surfaces which can hinder performance. In response, porous PDRCs have been developed. Another response is to make hydrophobic PDRCs which are "self-cleaning." Scalable and sustainable hydrophobic PDRCs that avoid VOCs have been developed that repel rainwater and other liquids. | 0 | Theoretical and Fundamental Chemistry |
The Sumerians are said to have cultivated and harvested the opium poppy (Papaver somniferum) in lower Mesopotamia as early as 3400 BC, though this has been disputed. The most ancient testimony concerning the opium poppy found to date was inscribed in cuneiform script on a small white clay tablet at the end of the third millennium BC. This tablet was discovered in 1954 during excavations at Nippur, and is currently kept at the University of Pennsylvania Museum of Archaeology and Anthropology. Deciphered by Samuel Noah Kramer and Martin Leve, it is considered to be the most ancient pharmacopoeia in existence. Some Sumerian tablets of this era have an ideogram inscribed upon them, "hul gil", which translates to "plant of joy", believed by some authors to refer to opium. The term gil is still used for opium in certain parts of the world. The Sumerian goddess Nidaba is often depicted with poppies growing out of her shoulders. About 2225 BC, the Sumerian territory became a part of the Babylonian empire. Knowledge and use of the opium poppy and its euphoric effects thus passed to the Babylonians, who expanded their empire eastwards to Persia and westwards to Egypt, thereby extending its range to these civilizations. British archaeologist and cuneiformist Reginald Campbell Thompson writes that opium was known to the Assyrians in the 7th century BC. The term "Arat Pa Pa" occurs in the Assyrian Herbal, a collection of inscribed Assyrian tablets dated to c. 650 BC. According to Thompson, this term is the Assyrian name for the juice of the poppy and it may be the etymological origin of the Latin "papaver".
The ancient Egyptians had some surgical instruments, as well as crude analgesics and sedatives, including possibly an extract prepared from the mandrake fruit. The use of preparations similar to opium in surgery is recorded in the Ebers Papyrus, an Egyptian medical papyrus written in the Eighteenth Dynasty. However, it is questionable whether opium itself was known in ancient Egypt. The Greek gods Hypnos (Sleep), Nyx (Night), and Thanatos (Death) were often depicted holding poppies.
Prior to the introduction of opium to ancient India and China, these civilizations pioneered the use of cannabis incense and aconitum. c. 400 BC, the Sushruta Samhita (a text from the Indian subcontinent on Ayurvedic medicine and surgery) advocates the use of wine with incense of cannabis for anesthesia. By the 8th century AD, Arab traders had brought opium to India and China. | 1 | Applied and Interdisciplinary Chemistry |
Monte Carlo and molecular dynamic approaches became useful tools for theoretical calculations aiming at predictions of adsorption equilibria and diffusivities in small pores of various simple geometries. The interactions between adsorbate molecules are represented by the Lenard-Jones potential:
where r is the interparticle distance, is the point at which the potential is zero, and is the well depth. | 0 | Theoretical and Fundamental Chemistry |
SCS facilitates the flux of molecules into other metabolic pathways by controlling the interconversion between succinyl CoA and succinate. This is important because succinyl CoA is an intermediate necessary for porphyrin, heme, and ketone body biosynthesis. | 1 | Applied and Interdisciplinary Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.