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By the 1890s, the profound effect of adrenal extracts on many different tissue types had been discovered, setting off a search both for the mechanism of chemical signalling and efforts to exploit these observations for the development of new drugs. The blood pressure raising and vasoconstrictive effects of adrenal extracts were of particular interest to surgeons as hemostatic agents and as treatment for shock, and a number of companies developed products based on adrenal extracts containing varying purities of the active substance. In 1897, John Abel of Johns Hopkins University identified the active principle as epinephrine, which he isolated in an impure state as the sulfate salt. Industrial chemist Jōkichi Takamine later developed a method for obtaining epinephrine in a pure state, and licensed the technology to Parke-Davis. Parke-Davis marketed epinephrine under the trade name Adrenalin. Injected epinephrine proved to be especially efficacious for the acute treatment of asthma attacks, and an inhaled version was sold in the United States until 2011 (Primatene Mist). By 1929 epinephrine had been formulated into an inhaler for use in the treatment of nasal congestion.
While highly effective, the requirement for injection limited the use of epinephrine and orally active derivatives were sought. A structurally similar compound, ephedrine, was identified by Japanese chemists in the Ma Huang plant and marketed by Eli Lilly as an oral treatment for asthma. Following the work of Henry Dale and George Barger at Burroughs-Wellcome, academic chemist Gordon Alles synthesized amphetamine and tested it in asthma patients in 1929. The drug proved to have only modest anti-asthma effects but produced sensations of exhilaration and palpitations. Amphetamine was developed by Smith, Kline and French as a nasal decongestant under the trade name Benzedrine Inhaler. Amphetamine was eventually developed for the treatment of narcolepsy, post-encephalitic parkinsonism, and mood elevation in depression and other psychiatric indications. It received approval as a New and Nonofficial Remedy from the American Medical Association for these uses in 1937, and remained in common use for depression until the development of tricyclic antidepressants in the 1960s. | 1 | Applied and Interdisciplinary Chemistry |
Pyridine crystallizes in an orthorhombic crystal system with space group Pna2 and lattice parameters a = 1752 pm, b = 897 pm, c = 1135 pm, and 16 formula units per unit cell (measured at 153 K). For comparison, crystalline benzene is also orthorhombic, with space group Pbca, a = 729.2 pm, b = 947.1 pm, c = 674.2 pm (at 78 K), but the number of molecules per cell is only 4. This difference is partly related to the lower symmetry of the individual pyridine molecule (C vs D for benzene). A trihydrate (pyridine·3HO) is known; it also crystallizes in an orthorhombic system in the space group Pbca, lattice parameters a = 1244 pm, b = 1783 pm, c = 679 pm and eight formula units per unit cell (measured at 223 K). | 0 | Theoretical and Fundamental Chemistry |
A particularly common α-substitution reaction in the laboratory is the halogenation of aldehydes and ketones at their α positions by reaction Cl, Br or I in acidic solution. Bromine in acetic acid solvent is often used.
Remarkably, ketone halogenation also occurs in biological systems, particularly in marine alga, where , bromoacetone, , and other related compounds have been found.
The halogenation is a typical α-substitution reaction that proceeds by acid catalyzed formation of an enol intermediate. | 0 | Theoretical and Fundamental Chemistry |
Both formulas are widely taught and used in modern times. Since both equations reference a single control volume location along the channel, neither address friction factor nor head loss directly, but the change in pressure head may be calculated by combining them with other formulas such as the Darcy–Weisbach equation. The empirical aspect to the coefficient indirectly addresses friction factor and Reynold's number and is the reason why the Chézy formula remains most accurate in certain conditions, such as river channels with non-uniform channel dimensions. Additionally, both equations are explicitly used with uniform or "steady-state" flow where the hydraulic depth is constant, due to their derivation from the conservation of momentum. In contrast, if the hydraulic conditions fluctuate in open channel flow, they are then described as gradually or rapidly varied flow, and will require further analyses beyond these two formula methods.
As partially full pipes are by definition open channels, so long as they aren't pressurized, the Manning and Chézy formulas may also be used to calculate partially full pipe flow; however, these formulas are intended for uniform and turbulent flow. Many other formulas that have been developed since these two may produce more accurate pipe flow results, such as the Darcy–Weisbach equation or the Hazen–Williams equation, but lack the simplicity of the Manning or Chézy formulas.
Both formulas continue to be broadly taught and are used in open channel and fluid dynamics research. Today, the Manning formula is likely the most globally used formula for open channel uniform flow analysis, due to its simplicity, proven efficacy, and the fact that most open channel studies are concerned with turbulent flow. Chézy's formula is one of the oldest in the field of fluid mechanics, it applies to a wider range of flows than the Manning equation, and its influence continues to this day. | 1 | Applied and Interdisciplinary Chemistry |
Dutch engineer Piet Bergveld studied the MOSFET and realized it could be adapted into a sensor for chemical and biological applications.
In 1970, Bergveld invented the ion-sensitive field-effect transistor (ISFET). He described the ISFET as "a special type of MOSFET with a gate at a certain distance". In the ISFET structure, the metal gate of a standard MOSFET is replaced by an ion-sensitive membrane, electrolyte solution and reference electrode.
ChemFETs are based on a modified ISFET, a concept developed by Bergveld in the 1970s. There is some confusion as to the relationship between ChemFETs and ISFETs. Whereas an ISFET only detects ions, a ChemFET detects any chemical (including ions). | 0 | Theoretical and Fundamental Chemistry |
where M is the molecular weight.
The method uses a two-parameter equation to describe the temperature dependency of the dynamic viscosity. The authors state that the parameters are valid from the melting temperature up to 0.7 of the critical temperature (T < 0.7). | 0 | Theoretical and Fundamental Chemistry |
In cases where the diameter of a trapped particle is significantly smaller than the wavelength of light, the conditions for Rayleigh scattering are satisfied and the particle can be treated as a point dipole in an inhomogeneous electromagnetic field. The force applied on a single charge in an electromagnetic field is known as the Lorentz force,
The force on the dipole can be calculated by substituting two terms for the electric field in the equation above, one for each charge. The polarization of a dipole is where is the distance between the two charges. For a point dipole, the distance is infinitesimal, Taking into account that the two charges have opposite signs, the force takes the form
Notice that the cancel out. Multiplying through by the charge, , converts position, , into polarization, ,
where in the second equality, it has been assumed that the dielectric particle is linear (i.e. ).
In the final steps, two equalities will be used: (1) a vector analysis equality, (2) Faraday's law of induction.
First, the vector equality will be inserted for the first term in the force equation above. Maxwell's equation will be substituted in for the second term in the vector equality. Then the two terms which contain time derivatives can be combined into a single term.
The second term in the last equality is the time derivative of a quantity that is related through a multiplicative constant to the Poynting vector, which describes the power per unit area passing through a surface. Since the power of the laser is constant when sampling over frequencies much longer than the frequency of the laser's light ~10 Hz, the derivative of this term averages to zero and the force can be written as
where in the second part we have included the induced dipole moment (in MKS units) of a spherical dielectric particle: , where is the particle radius, is the index of refraction of the particle and is the relative refractive index between the particle and the medium. The square of the magnitude of the electric field is equal to the intensity of the beam as a function of position. Therefore, the result indicates that the force on the dielectric particle, when treated as a point dipole, is proportional to the gradient along the intensity of the beam. In other words, the gradient force described here tends to attract the particle to the region of highest intensity. In reality, the scattering force of the light works against the gradient force in the axial direction of the trap, resulting in an equilibrium position that is displaced slightly downstream of the intensity maximum. Under the Rayleigh approximation, we can also write the scattering force as
Since the scattering is isotropic, the net momentum is transferred in the forward direction. On the quantum level, we picture the gradient force as forward Rayleigh scattering in which identical photons are created and annihilated concurrently, while in the scattering (radiation) force the incident photons travel in the same direction and ‘scatter’ isotropically. By conservation of momentum, the particle must accumulate the photons' original momenta, causing a forward force in the latter. | 1 | Applied and Interdisciplinary Chemistry |
The eddy dissipation model or the Magnussen model, based on the work of Magnussen and Hjertager, is a turbulent-chemistry reaction model. Most fuels are fast burning and the overall rate of reaction is controlled by turbulence mixing. In the non-premixed flames, turbulence slowly mixes the fuel and oxidizer into the reaction zones where they burn quickly. In premixed flames the turbulence slowly mixes cold reactants and hot products into the reaction zones where reaction occurs rapidly. In such cases the combustion is said to be mixing-limited, and the complex and often unknown chemical kinetics can be safely neglected. In this model, the chemical reaction is governed by large eddy mixing time scale. Combustion initiates whenever there is turbulence present in the flow. It does not need an ignition source to initiate the combustion. This type of model is valid for the non-premixed combustion, but for the premixed flames the reactant is assumed to burn at the moment it enters the computation model, which is a shortcoming of this model as in practice the reactant needs some time to get to the ignition temperature to initiate the combustion. | 1 | Applied and Interdisciplinary Chemistry |
ATP is one of four monomers required in the synthesis of RNA. The process is promoted by RNA polymerases. A similar process occurs in the formation of DNA, except that ATP is first converted to the deoxyribonucleotide dATP. Like many condensation reactions in nature, DNA replication and DNA transcription also consume ATP. | 1 | Applied and Interdisciplinary Chemistry |
Numerous experimental techniques have been developed to study particle
aggregation. Most frequently used are time-resolved optical techniques that are based on transmittance or scattering of light.
Light transmission. The variation of transmitted light through an aggregating suspension can be studied with a regular spectrophotometer in the visible region. As aggregation proceeds, the medium becomes more turbid, and its absorbance increases. The increase of the absorbance can be related to the aggregation rate constant k and the stability ratio can be estimated from such measurements. The advantage of this
technique is its simplicity.
Light scattering. These techniques are based on probing the scattered light from an aggregating suspension in a time-resolved fashion. Static light scattering yields the change in the scattering intensity, while dynamic light scattering the variation in the apparent hydrodynamic radius. At early-stages of aggregation, the variation of each of these quantities is directly proportional to the aggregation rate constant
k.
At later stages, one can obtain information on the clusters formed (e.g., fractal dimension). Light scattering works well for a wide range of particle sizes. Multiple scattering effects may have to be considered, since scattering becomes increasingly important for larger particles or larger aggregates. Such effects can be neglected in weakly turbid suspensions. Aggregation processes in strongly scattering systems have been studied with transmittance, backscattering techniques or diffusing-wave spectroscopy.
Single particle counting. This technique offers excellent resolution, whereby clusters made out of tenths of particles can be resolved individually. The aggregating suspension is forced through a narrow capillary particle counter and the size of each aggregate is being analyzed by light scattering. From the scattering intensity, one can deduce the size of each aggregate, and construct a detailed aggregate size distribution. If the suspensions contain high amounts of salt, one could equally use a Coulter counter. As time proceeds, the size distribution shifts towards larger aggregates, and from this variation aggregation and breakup rates involving different clusters can be deduced. The disadvantage of the technique is that the aggregates are forced through a narrow capillary under high shear, and the aggregates may disrupt under these conditions.
Indirect techniques. As many properties of colloidal suspensions depend on the state of aggregation of the suspended particles, various indirect techniques have been used to monitor particle aggregation too. While it can be difficult to obtain quantitative information on aggregation rates or cluster properties from such experiments, they can be most valuable for practical applications. Among these techniques settling tests are most relevant. When one inspects a series of test tubes with suspensions prepared at different concentration of the flocculant, stable suspensions often remain dispersed, while the unstable ones settle. Automated instruments based on light scattering/transmittance to monitor suspension settling have been developed, and they can be used to probe particle aggregation. One must realize, however, that these techniques may not always reflect the actual aggregation state of a suspension correctly. For example, larger primary particles may settle even in the absence of aggregation, or aggregates that have formed a colloidal gel will remain in suspension. Other indirect techniques capable to monitor the state of aggregation include, for example, filtration, rheology, absorption of ultrasonic waves, or dielectric properties. | 0 | Theoretical and Fundamental Chemistry |
Co-based superalloys depend on carbide precipitation and solid solution strengthening for mechanical properties. While these strengthening mechanisms are inferior to gamma prime (γ') precipitation strengthening, cobalt has a higher melting point than nickel and has superior hot corrosion resistance and thermal fatigue. As a result, carbide-strengthened Co-based superalloys are used in lower stress, higher temperature applications such as stationary vanes in gas turbines.
Cos γ/γ microstructure was rediscovered and published in 2006 by Sato et al. That γ phase was Co(Al, W). Mo, Ti, Nb, V, and Ta partition to the γ phase, while Fe, Mn, and Cr partition to the matrix γ.
The next family of Co-based superalloys was discovered in 2015 by Makineni et al. This family has a similar γ/γ microstructure, but is W-free and has a γ phase of Co(Al,Mo,Nb). Since W is heavy, its elimination makes Co-based alloys increasingly viable in turbines for aircraft, where low density is especially valued.
The most recently discovered family of superalloys was computationally predicted by Nyshadham et al. in 2017, and demonstrated by Reyes Tirado et al. in 2018. This γ' phase is W free and has the composition Co(Nb,V) and Co(Ta,V). | 1 | Applied and Interdisciplinary Chemistry |
The single cell gel electrophoresis assay (SCGE, also known as comet assay) is an uncomplicated and sensitive technique for the detection of DNA damage at the level of the individual eukaryotic cell. It was first developed by Östling & Johansson in 1984 and later modified by Singh et al. in 1988. It has since increased in popularity as a standard technique for evaluation of DNA damage/repair, biomonitoring and genotoxicity testing. It involves the encapsulation of cells in a low-melting-point agarose suspension, lysis of the cells in neutral or alkaline (pH>13) conditions, and electrophoresis of the suspended lysed cells. The term "comet" refers to the pattern of DNA migration through the electrophoresis gel, which often resembles a comet.
The comet assay (single-cell gel electrophoresis) is a simple method for measuring deoxyribonucleic acid (DNA) strand breaks in eukaryotic cells. Cells embedded in agarose on a microscope slide are lysed with detergent and high salt to form nucleoids containing supercoiled loops of DNA linked to the nuclear matrix. Electrophoresis at high pH results in structures resembling comets, observed by fluorescence microscopy; the intensity of the comet tail relative to the head reflects the number of DNA breaks. The likely basis for this is that loops containing a break lose their supercoiling and become free to extend toward the anode. This is followed by visual analysis with staining of DNA and calculating fluorescence to determine the extent of DNA damage. This can be performed by manual scoring or automatically by imaging software. | 1 | Applied and Interdisciplinary Chemistry |
P-Chiral phosphines are organophosphorus compounds of the formula PRR′R″, where R, R′, R″ = H, alkyl, aryl, etc. They are a subset of chiral phosphines, a broader class of compounds where the stereogenic center can reside at sites other than phosphorus. P-chirality exploits the high barrier for inversion of phosphines, which ensures that enantiomers of PRR'R" do not racemize readily. The inversion barrier is relatively insensitive to substituents for triorganophosphines. By contrast, most amines of the type NRR′R″ undergo rapid pyramidal inversion. | 0 | Theoretical and Fundamental Chemistry |
Galileo Galilei (1564–1642) was an advocate of atomism in his 1612 Discourse on Floating Bodies (Redondi 1969). In The Assayer, Galileo offered a more complete physical system based on a corpuscular theory of matter, in which all phenomena—with the exception of sound—are produced by "matter in motion". | 1 | Applied and Interdisciplinary Chemistry |
Accelerated testing may induce reaction kinetics that is not applicable to the actual service environment of an adhesive, which could cause greater concern than is necessary for certain adhesives. High temperatures are often avoided because it frequently causes new reactions to occur. | 0 | Theoretical and Fundamental Chemistry |
vaccine - vacuole - valence - valine - van der Waals force - van der Waals radius - vapor pressure - vapour pressure - vasoactive intestinal peptide - vasoactive intestinal peptide receptor - vasopressin - vasopressin receptor - venom - vertebrate photoreceptor - vesicle - vestibular system - vimentin - viral envelope protein - viral oncogene protein - viral protein - virology - virus (biology) - vitamin - vitamin D-dependent calcium-binding protein - vitellogenin - vitronectin - von Willebrand factor | 1 | Applied and Interdisciplinary Chemistry |
Catalysts for the lower temperature WGS reaction are commonly based on copper or copper oxide loaded ceramic phases, While the most common supports include alumina or alumina with zinc oxide, other supports may include rare earth oxides, spinels or perovskites. A typical composition of a commercial LTS catalyst has been reported as 32-33% CuO, 34-53% ZnO, 15-33% AlO. The active catalytic species is CuO. The function of ZnO is to provide structural support as well as prevent the poisoning of copper by sulfur. The AlO prevents dispersion and pellet shrinkage. The LTS shift reactor operates at a range of 200–250 °C. The upper temperature limit is due to the susceptibility of copper to thermal sintering. These lower temperatures also reduce the occurrence of side reactions that are observed in the case of the HTS. Noble metals such as platinum, supported on ceria, have also been used for LTS. | 0 | Theoretical and Fundamental Chemistry |
Except for very common sizes, liners are not usually stocked and must be made specifically for each project. CIPP requires bypass of the flow in the existing pipeline while the liner is being installed. The curing may take from one hour to 30 hours depending on pipe diameter and curing system (steam, water or uv) and must be carefully monitored, inspected, and tested. Obstructions in the existing pipeline, such as protruding laterals, must be removed prior to installation. Cost should be compared with similar methods such as Shotcrete, thermoformed pipe, close-fit pipe, spiral wound pipe and sliplining as these other methods can provide a similar design solution for similar or less cost in certain situations. CIPP must also be carefully monitored for release of chemical agents utilized in the reaction process for contamination downstream of rehabilitated pipes. The liner material used for common sizes is normally a felted fabric (non-woven) and does not go around bends well without wrinkling and going out of round on corners. Liners used for pipes with bends (particularly 100 mm pipes) are made from a woven fabric allowing it to go around bends with minimal wrinkling. The more flexible the liner, the more care needs to be taken during inversion to ensure the liner remains on the correct alignment. Once a line is repaired with the CIPP method, that line can no longer be cabled or snaked with a machine, it must be cleaned by method of Hydro jetting (AKA high-pressure water blasting) | 1 | Applied and Interdisciplinary Chemistry |
Analogous to the process leading to novae, degenerate matter can also accumulate on the surface of a neutron star that is accreting gas from a close companion. If a sufficiently thick layer of hydrogen accumulates, ignition of runaway hydrogen fusion can then lead to an X-ray burst. As with novae, such bursts tend to repeat and may also be triggered by helium or even carbon fusion. It has been proposed that in the case of "superbursts", runaway breakup of accumulated heavy nuclei into iron group nuclei via photodissociation rather than nuclear fusion could contribute the majority of the energy of the burst. | 1 | Applied and Interdisciplinary Chemistry |
Nüchter et al. (2001) have shown a new approach to Fischer glycosidation. Employing a microwave oven equipped with refluxing apparatus in a rotor reactor with pressure bombs, Nüchter et al. (2001) were able to achieve 100% yield of α- and β-D-glucosides. This method can be performed on a multi-kilogram scale. | 0 | Theoretical and Fundamental Chemistry |
If the hull is designed to operate at speeds substantially lower than hull speed then it is possible to refine the hull shape along its length to reduce wave resistance at one speed. This is practical only where the block coefficient of the hull is not a significant issue. | 1 | Applied and Interdisciplinary Chemistry |
Holthusen (1921) first quantified the oxygen effect finding 2.5 to 3.0-fold less hatching eggs of the nematode Ascaris in oxygenated compared to anoxic conditions, which was incorrectly assigned to changes in cell division. However, two years later, Petry (1923) first attributed oxygen tension as affecting ionizing radiation effects on vegetable seeds. Later, the implications of the effects of oxygen on radiotherapy were discussed by Mottram (1936).
A key observation limiting hypotheses to explain the biological mechanisms of the oxygen effect is that the gas nitric oxide is a radiosensitizer with similar effects to oxygen observed in tumour cells. Another important observation is that oxygen must be present at irradiation or within milliseconds afterward for the oxygen effect to take place.
The best known explanation of the oxygen effect is the oxygen fixation hypothesis developed by Alexander in 1962, which posited that radiation-induced non-restorable or "fixed" nuclear DNA lesions are lethal to cells in the presence of diatomic oxygen. Recent hypotheses include one based on oxygen-enhanced damage from first principles. Another hypothesis posits that ionizing radiation provokes mitochondria to produce reactive oxygen (and nitrogen species), which are leakage during oxidative phosphorylation that varies with a hyperbolic saturation relationship observed with both the oxygen and nitric oxide effects. | 1 | Applied and Interdisciplinary Chemistry |
The following table shows the characteristics of various HIV-1 bNAbs
In addition to targeting conserved epitopes, bNAbs are known to have long variable regions on their immunoglobulin (Ig) isotypes and subclasses. When compared to non-bNAbs, sequence variability from the germline immunoglobulin isotype is 7 fold. This implies that bNAbs develop from intense affinity maturation in the germinal centers hence the reason for high sequence variability on the variable Ig domain. Indeed HIV-1 patients who develop bNAbs have been shown to have high germinal center activity as exhibited by their comparatively higher levels of plasma CXCL13, which is a biomarker of germinal center activity.
Online databases like bNAber and LANL constantly report and update the discovery of new HIV bNAbs. | 1 | Applied and Interdisciplinary Chemistry |
Wiggins was appointed a Fellow of the Royal Society Te Apārangi in 1991. She received a medal for her research from the Health Research Council of New Zealand.
In 2017 Wiggins was featured as one of the Royal Society Te Apārangi's 150 women in 150 words. | 0 | Theoretical and Fundamental Chemistry |
The low dielectric constant of COC, even at high frequency, has led to its use in certain antenna applications as well as capacitors requiring higher temperature resistance than polypropylene can provide. | 0 | Theoretical and Fundamental Chemistry |
Based on the special chemical properties of formed free radicals, ABTS assay has been used to determine the antioxidant capacity of food products. For example, polyphenol compounds, which widely exist in fruit, can quench free radicals inside human body, thus prevent oxidative damage by free radicals. The antioxidant potency of plant extract or food product has been measured by ABTS assay. One example with detailed method is the antioxidant activity analysis of Hibiscus products. | 1 | Applied and Interdisciplinary Chemistry |
* – edited by James Clerk Maxwell and revised by Joseph Larmor
* – edited by James Clerk Maxwell and revised by Joseph Larmor | 1 | Applied and Interdisciplinary Chemistry |
Magnetofection has been tested on a broad range of cell lines, hard-to-transfect and primary cells. Several optimized and efficient magnetic nanoparticle formulations have been specifically developed for several types of applications such as DNA, siRNA, and primary neuron transfection as well as viral applications.
Magnetofection research is currently in the preclinical stage. This technique has primarily been tested in vivo using plasmid DNA in mouse, rat, and rabbit models for applications in the hippocampus, subcutaneous tumors, lungs, spinal cord, and muscle.
Some applications include:
* Delivery of GFP gene into primary neural stem cells, which are typically difficult to transfect, with 18% efficacy with a static magnetic field and 32% efficacy with an oscillating field.
* Delivery of oligodesoxynucleotides (ODN) into human umbilical vein endothelial cells with 84% efficiency.
* Delivery of siRNA to HeLa cells to knock down luciferase reporter gene.
* Delivery of adenoviral vectors to primary human peripheral blood lymphocytes. | 1 | Applied and Interdisciplinary Chemistry |
Spinodal decomposition is a mechanism by which a single thermodynamic phase spontaneously separates into two phases (without nucleation). Decomposition occurs when there is no thermodynamic barrier to phase separation. As a result, phase separation via decomposition does not require the nucleation events resulting from thermodynamic fluctuations, which normally trigger phase separation.
Spinodal decomposition is observed when mixtures of metals or polymers separate into two co-existing phases, each rich in one species and poor in the other. When the two phases emerge in approximately equal proportion (each occupying about the same volume or area), characteristic intertwined structures are formed that gradually coarsen (see animation). The dynamics of spinodal decomposition is commonly modeled using the Cahn–Hilliard equation.
Spinodal decomposition is fundamentally different from nucleation and growth. When there is a nucleation barrier to the formation of a second phase, time is taken by the system to overcome that barrier. As there is no barrier (by definition) to spinodal decomposition, some fluctuations (in the order parameter that characterizes the phase) start growing instantly. Furthermore, in spinodal decomposition, the two distinct phases start growing in any location uniformly throughout the volume, whereas a nucleated phase change begins at a discrete number of points.
Spinodal decomposition occurs when a homogenous phase becomes thermodynamically unstable. An unstable phase lies at a maximum in free energy. In contrast, nucleation and growth occur when a homogenous phase becomes metastable. That is, another biphasic system becomes lower in free energy, but the homogenous phase remains at a local minimum in free energy, and so is resistant to small fluctuations. J. Willard Gibbs described two criteria for a metastable phase: that it must remain stable against a small change over a large area. | 0 | Theoretical and Fundamental Chemistry |
Hemolithin is the name given to a protein molecule isolated from two CV3 meteorites, Allende and Acfer-086. Its deuterium to hydrogen ratio is 26 times terrestrial which is consistent with it having formed in an interstellar molecular cloud, or later in the protoplanetary disk at the start of the Solar System 4.567 billion years ago. The elements hydrogen, lithium, carbon, oxygen, nitrogen and iron that it is composed of, were all available for the first time 13 billion years ago after the first generation of massive stars ended in nucleosynthetic events.
The research leading to the discovery of Hemolithin started in 2007 when another protein, one of the first to form on Earth, was observed to entrap water. That property being useful to chemistry before biochemistry on earth developed, theoretical enthalpy calculations on the condensation of amino acids were performed in gas phase space asking: "whether amino acids could polymerize to protein in space?" - they could, and their water of condensation aided their polymerization. This led to several manuscripts of isotope and mass information on Hemolithin. | 0 | Theoretical and Fundamental Chemistry |
Usually, an enzyme molecule has only one active site, and the active site fits with one specific type of substrate. An active site contains a binding site that binds the substrate and orients it for catalysis. The orientation of the substrate and the close proximity between it and the active site is so important that in some cases the enzyme can still function properly even though all other parts are mutated and lose function.
Initially, the interaction between the active site and the substrate is non-covalent and transient. There are four important types of interaction that hold the substrate in a defined orientation and form an enzyme-substrate complex (ES complex): hydrogen bonds, van der Waals interactions, hydrophobic interactions and electrostatic force interactions. The charge distribution on the substrate and active site must be complementary, which means all positive and negative charges must be cancelled out. Otherwise, there will be a repulsive force pushing them apart. The active site usually contains non-polar amino acids, although sometimes polar amino acids may also occur. The binding of substrate to the binding site requires at least three contact points in order to achieve stereo-, regio-, and enantioselectivity. For example, alcohol dehydrogenase which catalyses the transfer of a hydride ion from ethanol to NAD interacts with the substrate methyl group, hydroxyl group and the pro-(R) hydrogen that will be abstracted during the reaction.
In order to exert their function, enzymes need to assume their correct protein fold (native fold) and tertiary structure. To maintain this defined three-dimensional structure, proteins rely on various types of interactions between their amino acid residues. If these interactions are interfered with, for example by extreme pH values, high temperature or high ion concentrations, this will cause the enzyme to denature and lose its catalytic activity.
A tighter fit between an active site and the substrate molecule is believed to increase the efficiency of a reaction. If the tightness between the active site of DNA polymerase and its substrate is increased, the fidelity, which means the correct rate of DNA replication will also increase. Most enzymes have deeply buried active sites, which can be accessed by a substrate via access channels.
There are three proposed models of how enzymes fit their specific substrate: the lock and key model, the induced fit model, and the conformational selection model. The latter two are not mutually exclusive: conformational selection can be followed by a change in the enzyme's shape. Additionally, a protein may not wholly follow either model. Amino acids at the binding site of ubiquitin generally follow the induced fit model, whereas the rest of the protein generally adheres to conformational selection. Factors such as temperature likely influences the pathway taken during binding, with higher temperatures predicted to increase the importance of conformational selection and decrease that of induced fit. | 1 | Applied and Interdisciplinary Chemistry |
An important technique for characterizing metal carbonyls is infrared spectroscopy. The C–O vibration, typically denoted ν, occurs at 2143 cm for carbon monoxide gas. The energies of the ν band for the metal carbonyls correlates with the strength of the carbon–oxygen bond, and inversely correlated with the strength of the π-backbonding between the metal and the carbon. The π-basicity of the metal center depends on a lot of factors; in the isoelectronic series (titanium to iron) at the bottom of this section, the hexacarbonyls show decreasing π-backbonding as one increases (makes more positive) the charge on the metal. π-Basic ligands increase π-electron density at the metal, and improved backbonding reduces ν. The Tolman electronic parameter uses the Ni(CO) fragment to order ligands by their π-donating abilities.
The number of vibrational modes of a metal carbonyl complex can be determined by group theory. Only vibrational modes that transform as the electric dipole operator will have nonzero direct products and are observed. The number of observable IR transitions (but not their energies) can thus be predicted. For example, the CO ligands of octahedral complexes, such as Cr(CO), transform as a, e, and t, but only the t mode (antisymmetric stretch of the apical carbonyl ligands) is IR-allowed. Thus, only a single ν band is observed in the IR spectra of the octahedral metal hexacarbonyls. Spectra for complexes of lower symmetry are more complex. For example, the IR spectrum of Fe(CO) displays CO bands at 2082, 2019 and 1829 cm. The number of IR-observable vibrational modes for some metal carbonyls are shown in the table. Exhaustive tabulations are available. These rules apply to metal carbonyls in solution or the gas phase. Low-polarity solvents are ideal for high resolution. For measurements on solid samples of metal carbonyls, the number of bands can increase owing in part to site symmetry. | 0 | Theoretical and Fundamental Chemistry |
The first description of an approximately 6.4 kb long LINE-derived sequence was published by J. Adams et al. in 1980. | 1 | Applied and Interdisciplinary Chemistry |
One important factor in gene delivery is developing altered cell tropisms to narrow or broaden rAAV-mediated gene delivery and to increase its efficiency in tissues. Specific properties like capsid conformation, cell targeting strategies can determine which cell types are affected and also the efficiency of the gene transfer process. Different kinds of modification can be undertaken. For example, modification by chemical, immunological or genetic changes that enables the AAV2 capsid to interact with specific cell surface molecules.
Initial studies with AAV in the retina have utilized AAV serotype 2. Researchers are now beginning to develop new variants of AAV, based on naturally-occurring AAV serotypes and engineered AAV variants.
Several naturally-occurring serotypes of AAV have been isolated that can transduce retinal cells. Following intravitreal injection, only AAV serotypes 2 and 8 were capable of transducing retinal ganglion cells. Occasional Muller cells were transduced by AAV serotypes 2, 8, and 9. Following subretinal injection, serotypes 2, 5, 7, and 8 efficiently transduced photoreceptors, and serotypes 1, 2, 5, 7, 8, and 9 efficiently transduce RPE cells.
One example of an engineered variant has recently been described that efficiently transduces Muller glia following intravitreal injection, and has been used to rescue an animal model of aggressive, autosomal-dominant retinitis pigmentosa. | 1 | Applied and Interdisciplinary Chemistry |
As the name suggests, trishomoaromatics are defined as containing one additional methylene bridge compared to bishomoaromatics, therefore containing three of these homoconjugate bridges in total. Just like semibullvalene, there is still much debate as to the extent of the homoaromatic character of trishomoaromatics. While theoretically they are homoaromatic, these compounds show a stabilization of no more than 5% of benzene due to delocalization. | 0 | Theoretical and Fundamental Chemistry |
The usual method of industrial production is the peroxide process, starting from the ketone, ammonia, and hydrogen peroxide.
In the laboratory, azines are typically prepared by condensation of hydrazine with two equivalents of a carbonyl.
Azines are also produced when chalcone reacts with a hydrazone to produce 3,5-diphenyl-1H-pyrazole, in a conversion also carried out with hydrazine hydrate. | 0 | Theoretical and Fundamental Chemistry |
Deoxydehydration (DODH) is a chemical reaction for removing two adjacent hydroxyl groups in a vicinal diol to form an alkene. In contrast to hydrodeoxygenation which uses hydrogen as a reductant, deoxydehydration is able to use a variety of other reductants such as alcohols and organic phosphines. In research, the most common homogeneous catalysts for this reaction use rhenium.
Recently, research has focused on the use of vanadium heterogeneous catalysts for deoxydehydration, such as the conversion of 2,3-butanediol to butene. Although deoxydehydration over vanadium catalysts requires higher temperatures than over rhenium catalysts, the reaction can proceed without the need for hydrogen or external reductants, which can reduce waste products. | 0 | Theoretical and Fundamental Chemistry |
Soil acidification is a common issue in long-term crop production which can be reduced by lime, organic amendments (e.g., straw and manure) and biochar application. In sugarcane, soybean and corn crops grown in acidic soils, lime application resulted in nutrient restoration, increase in soil pH, increase in root biomass, and better plant health.
Different management strategies may also be applied to prevent further acidification: using less acidifying fertilizers, considering fertilizer amount and application timing to reduce nitrate-nitrogen leaching, good irrigation management with acid-neutralizing water, and considering the ratio of basic nutrients to nitrogen in harvested crops. Sulfur fertilizers should only be used in responsive crops, with a high rate of crop recovery.
Through reduction of anthropogenic sources of sulfur dioxides, nitrogen oxides, and with air-pollution control measures, let us try to reduce acid rain and soil acidification all over the world.
This has been observed in Ontario, Canada, over their several lakes and demonstrated improvements in water pH and alkalinity. | 0 | Theoretical and Fundamental Chemistry |
Lithotrophs participate in many geological processes, such as the formation of soil and the biogeochemical cycling of carbon, nitrogen, and other elements. Lithotrophs also associate with the modern-day issue of acid mine drainage. Lithotrophs may be present in a variety of environments, including deep terrestrial subsurfaces, soils, mines, and in endolith communities. | 1 | Applied and Interdisciplinary Chemistry |
The formal naming of haloalkanes should follow IUPAC nomenclature, which put the halogen as a prefix to the alkane. For example, ethane with bromine becomes bromoethane, methane with four chlorine groups becomes tetrachloromethane. However, many of these compounds have already an established trivial name, which is endorsed by the IUPAC nomenclature, for example chloroform (trichloromethane) and methylene chloride (dichloromethane). But nowadays, IUPAC nomenclature is used. To reduce confusion this article follows the systematic naming scheme throughout. | 0 | Theoretical and Fundamental Chemistry |
Another use for affinity chromatography is the purification of specific proteins using a gel matrix that is unique to a specific protein. For example, the purification of E. coli β-galactosidase is accomplished by affinity chromatography using p-aminobenyl-1-thio-β-D-galactopyranosyl agarose as the affinity matrix. p-aminobenyl-1-thio-β-D-galactopyranosyl agarose is used as the affinity matrix because it contains a galactopyranosyl group, which serves as a good substrate analog for E. coli β-Galactosidase. This property allows the enzyme to bind to the stationary phase of the affinity matrix and β-Galactosidase is eluted by adding increasing concentrations of salt to the column. | 0 | Theoretical and Fundamental Chemistry |
In biochemistry and pharmacology, the Hill equation refers to two closely related equations that reflect the binding of ligands to macromolecules, as a function of the ligand concentration. A ligand is "a substance that forms a complex with a biomolecule to serve a biological purpose" (ligand definition), and a macromolecule is a very large molecule, such as a protein, with a complex structure of components (macromolecule definition). Protein-ligand binding typically changes the structure of the target protein, thereby changing its function in a cell.
The distinction between the two Hill equations is whether they measure occupancy or response. The Hill equation reflects the occupancy of macromolecules: the fraction that is saturated or bound by the ligand. This equation is formally equivalent to the Langmuir isotherm. Conversely, the Hill equation proper reflects the cellular or tissue response to the ligand: the physiological output of the system, such as muscle contraction.
The Hill equation was originally formulated by Archibald Hill in 1910 to describe the sigmoidal O binding curve of haemoglobin.
The binding of a ligand to a macromolecule is often enhanced if there are already other ligands present on the same macromolecule (this is known as cooperative binding). The Hill equation is useful for determining the degree of cooperativity of the ligand(s) binding to the enzyme or receptor. The Hill coefficient provides a way to quantify the degree of interaction between ligand binding sites.
The Hill equation (for response) is important in the construction of dose-response curves. | 1 | Applied and Interdisciplinary Chemistry |
*Leslie E. Orgel, An Introduction to Transition-Metal Chemistry. The Ligand Field Theory, 1961
*Leslie E. Orgel, The Origins of Life: Molecules and Natural Selection, 1973
*Leslie E. Orgel and Stanley L. Miller, The Origins of Life on the Earth, 1974 | 0 | Theoretical and Fundamental Chemistry |
adopts an unusual “extreme cradle” structure, with D point group symmetry. It can be viewed as a derivative of a (hypothetical) eight-membered ring (or more simply a deformed eight-membered ring) of alternating sulfur and nitrogen atoms. The pairs of sulfur atoms across the ring are separated by 2.586 Å, resulting in a cage-like structure as determined by single crystal X-ray diffraction. The nature of the transannular S–S interactions remains a matter of investigation because it is significantly shorter than the sum of the van der Waal's distances but has been explained in the context of molecular orbital theory. One pair of the transannular S atoms have valence 4, and the other pair of the transannular S atoms have valence 2. The bonding in is considered to be delocalized, which is indicated by the fact that the bond distances between neighboring sulfur and nitrogen atoms are nearly identical. has been shown to co-crystallize with benzene and the fullerene| molecule. | 0 | Theoretical and Fundamental Chemistry |
Between 1978 and 1986, the Congress authorized the Department of Energy (DoE) and NASA to jointly investigate the concept. They organized the Satellite Power System Concept Development and Evaluation Program. The study remains the most extensive performed to date (budget $50 million). Several reports were published investigating the engineering feasibility of such a project. They include:
* Resource Requirements (Critical Materials, Energy, and Land)
* Financial/Management Scenarios
* Public Acceptance
* State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities
* Student Participation
* Potential of Laser for SBSP Power Transmission
* International Agreements
* Centralization/Decentralization
* Mapping of Exclusion Areas For Rectenna Sites
* Economic and Demographic Issues Related to Deployment
* Some Questions and Answers
* Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers
* Public Outreach Experiment
* Power Transmission and Reception Technical Summary and Assessment
* Space Transportation | 0 | Theoretical and Fundamental Chemistry |
Mitsubishi Chemical Holdings was reported to be developing its own artificial photosynthesis research by using sunlight, water and carbon dioxide to "create the carbon building blocks from which resins, plastics and fibers can be synthesized." This was confirmed with the establishment of the KAITEKI Institute later that year, with carbon dioxide reduction through artificial photosynthesis as one of the main goals. | 0 | Theoretical and Fundamental Chemistry |
Past winners of the Martin Medal are:
* Robert Kennedy (2019)
* Jean-Luc Veuthey (2018)
* Andreas Manz (2017)
* Ian Wilson & Peter Myers (2016)
* Pavel Jandera (2015)
* Nobuo Tanaka (2014)
* Günther Bonn & Frantisek Svec (2013)
* Edward S. Yeung (2012)
* Peter J. Schoenmakers (2011)
* Peter Carr (2010)
* Wolfgang F. Lindner (2009)
* Ron Majors & Johan Roeraade (2007)
* Jim Waters (2006)
* Vadim A. Davankov (2005)
* Terry Berger (2004)
* Jack Henion (2003)
* Paul R. Haddad & Werner Engewald (2002)
* John Michael Ramsey (2001)
* Klaus Mosbach & William S. Hancock (2000)
* Hans Poppe & Geoffrey Eglinton, FRS (1999)
* Albert Zlatkis (1998, awarded posthumously)
* Will Jennings & Joseph Jack Kirkland (1997)
* Milton L. Lee (1996)
* Milos Novotny & Shigeru Terabe (1995)
* Pat Sandra & Csaba Horvath (1994)
* Hans Engelhardt, Fred E. Regnier, & Klaus K. Unger (1993)
* Irving Wainer & James W. Jorgenson (1992)
* Dai E. Games, Barry L. Karger, Daniel W. Armstrong, & Dennis H. Desty (1991)
* Egil Jellum, William Pirkle, & Carl A. Cramers (1990)
* Jon Calvin Giddings, Udo. A Th Brinkman, J. F. K. Huber, Rudolf E. Kaiser, & Lloyd R. Snyder (1986)
* Ervin Kovats & John Knox (1985)
* C. E. Roland Jones & Arnaldo L. Liberti (1984)
* Gerhard Schomburg & Ralph Stock (1983)
* Edward R. Adlard, Leslie S. Ettre, Courtney S. G. Phillips, & Raymond P. W. Scott (1982)
* G. A. Peter Tuey & Georges Guiochon (1980)
* Ernst Bayer & C. E. H. Knapman (1978) | 0 | Theoretical and Fundamental Chemistry |
Unidirectional spreading of mTEC-derived TRAs onto additional APCs via antigen transfer increases the probability of encounter between potential autoreactive T cell and its corresponding TRA and therefore enhances processes of central tolerance. Furthermore, antigen transfer enables TRA processing and presentation by different cellular microenvironments.
Despite relevance of antigen transfer, seminal study was published, showing mTECs to form fully established central tolerance without support of additional APCs. | 1 | Applied and Interdisciplinary Chemistry |
Standards and handbooks stipulate a well-developed flow profile; velocities will be lower at the pipe wall than in the centre but not eccentric or jetting. Similarly the flow downstream of the plate must be unobstructed, otherwise the downstream pressure will be affected. To achieve this, the pipe must be acceptably circular, smooth and straight for stipulated distances. Sometimes when it is impossible to provide enough straight pipe, flow conditioners such as tube bundles or plates with multiple holes are inserted into the pipe to straighten and develop the flow profile, but even these require a further length of straight pipe before the orifice itself. Some standards and handbooks also provide for flows from or into large spaces rather than pipes, stipulating that the region before or after the plate is free of obstruction and abnormalities in the flow. | 1 | Applied and Interdisciplinary Chemistry |
DIC has largely replaced the older oblique illumination (OI) technique, which was available on reflected light microscopes prior to about 1975. In OI, the vertical illuminator is offset from perpendicular, producing shading effects that reveal height differences. This procedure reduces resolution and yields uneven illumination across the field of view. Nevertheless, OI was useful when people needed to know if a second phase particle was standing above or was recessed below the plane-of-polish, and is still available on a few microscopes. OI can be created on any microscope by placing a piece of paper under one corner of the mount so that the plane-of-polish is no longer perpendicular to the optical axis. | 1 | Applied and Interdisciplinary Chemistry |
Forced degradation studies are used to identify reactions which may occur to degrade a processed product. Usually conducted before final formulation, forced degradation uses external stresses to rapidly screen material stabilities.
Longer-term storage tests are usually used to measure similar properties when final formulations are involved because of the stringent FDA regulations. These tests are generally more expensive (because of the time involved) than forced degradation which is therefore used for rapid selection and elimination tests. | 1 | Applied and Interdisciplinary Chemistry |
Anhydrous aluminium chloride is a powerful Lewis acid, capable of forming Lewis acid-base adducts with even weak Lewis bases such as benzophenone and mesitylene. It forms tetrachloroaluminate () in the presence of chloride ions.
Aluminium chloride reacts with calcium and magnesium hydrides in tetrahydrofuran forming tetrahydroaluminates. | 0 | Theoretical and Fundamental Chemistry |
A titration curve is a curve in graph the x-coordinate of which represents the volume of titrant added since the beginning of the titration, and the y-coordinate of which represents the concentration of the analyte at the corresponding stage of the titration (in an acid–base titration, the y-coordinate usually represents the pH of the solution).
In an acid–base titration, the titration curve represents the strength of the corresponding acid and base. For a strong acid and a strong base, the curve will be relatively smooth and very steep near the equivalence point. Because of this, a small change in titrant volume near the equivalence point results in a large pH change and many indicators would be appropriate (for instance litmus, phenolphthalein or bromothymol blue).
If one reagent is a weak acid or base and the other is a strong acid or base, the titration curve is irregular and the pH shifts less with small additions of titrant near the equivalence point. For example, the titration curve for the titration between oxalic acid (a weak acid) and sodium hydroxide (a strong base) is pictured. The equivalence point occurs between pH 8-10, indicating the solution is basic at the equivalence point and an indicator such as phenolphthalein would be appropriate. Titration curves corresponding to weak bases and strong acids are similarly behaved, with the solution being acidic at the equivalence point and indicators such as methyl orange and bromothymol blue being most appropriate.
Titrations between a weak acid and a weak base have titration curves which are very irregular. Because of this, no definite indicator may be appropriate and a pH meter is often used to monitor the reaction.
The type of function that can be used to describe the curve is termed a sigmoid function. | 0 | Theoretical and Fundamental Chemistry |
The Davies equation is an empirical extension of Debye–Hückel theory which can be used to calculate activity coefficients of electrolyte solutions at relatively high concentrations at 25 °C. The equation, originally published in 1938, was refined by fitting to experimental data. The final form of the equation gives the mean molal activity coefficient of an electrolyte that dissociates into ions having charges and as a function of ionic strength :
The second term, , goes to zero as the ionic strength goes to zero, so the equation reduces to the Debye–Hückel equation at low concentration. However, as concentration increases, the second term becomes increasingly important, so the Davies equation can be used for solutions too concentrated to allow the use of the Debye–Hückel equation. For 1:1 electrolytes the difference between measured values and those calculated with this equation is about 2% of the value for 0.1 M solutions. The calculations become less precise for electrolytes that dissociate into ions with higher charges. Further discrepancies will arise if there is association between the ions, with the formation of ion pairs, such as . | 0 | Theoretical and Fundamental Chemistry |
Many aquatic animals feed extensively on periphyton. The mbuna cichlids from Lake Malawi are particularly well known examples of fish adapted for feeding on periphyton. Examples include Labeotropheus trewavasae and Pseudotropheus zebra. They have scraper-like teeth that allow them to rasp the periphyton from rocks. In marine communities, periphyton food sources are important for animals such as limpets and sea urchins. Another amphibian that feasts on periphyton are spring peepers, small chorus frogs that occupy many ponds throughout Canada and the eastern United States. Spring peepers filter periphyton from the environmental surfaces of their habitat. | 1 | Applied and Interdisciplinary Chemistry |
A supersonic airfoil is a cross-section geometry designed to generate lift efficiently at supersonic speeds. The need for such a design arises when an aircraft is required to operate consistently in the supersonic flight regime.
Supersonic airfoils generally have a thin section formed of either angled planes or opposed arcs (called "double wedge airfoils" and "biconvex airfoils" respectively), with very sharp leading and trailing edges. The sharp edges prevent the formation of a detached bow shock in front of the airfoil as it moves through the air. This shape is in contrast to subsonic airfoils, which often have rounded leading edges to reduce flow separation over a wide range of angle of attack. A rounded edge would behave as a blunt body in supersonic flight and thus would form a bow shock, which greatly increases wave drag. The airfoils' thickness, camber, and angle of attack are varied to achieve a design that will cause a slight deviation in the direction of the surrounding airflow. | 1 | Applied and Interdisciplinary Chemistry |
For iron rust to occur the metal has to be in contact with oxygen and water. The chemical reactions for this process are relatively complex and not all of them are completely understood. It is believed the causes are the following:
Electron transfer (reduction-oxidation)
:One area on the surface of the metal acts as the anode, which is where the oxidation (corrosion) occurs. At the anode, the metal gives up electrons.
::Fe → Fe + 2 e
:Electrons are transferred from iron, reducing oxygen in the atmosphere into water on the cathode, which is placed in another region of the metal.
::O + 4 H + 4 e → 2 HO
:Global reaction for the process:
::2 Fe + O + 4 H → 2 Fe + 2 HO
:Standard emf for iron rusting:
::E° = E° (cathode) − E° (anode)
::E° = 1.23V − (−0.44 V) = 1.67 V
Iron corrosion takes place in an acid medium; H ions come from reaction between carbon dioxide in the atmosphere and water, forming carbonic acid. Fe ions oxidize further, following this equation:
: 4 Fe + O + (4+2) HO → 2 FeO·HO + 8 H
Iron(III) oxide hydrate is known as rust. The concentration of water associated with iron oxide varies, thus the chemical formula is represented by FeO·HO.
An electric circuit is formed as passage of electrons and ions occurs; thus if an electrolyte is present it will facilitate oxidation, explaining why rusting is quicker in salt water. | 0 | Theoretical and Fundamental Chemistry |
* At the University of Technology in Xian, China, a rain garden was built to observe and study over four years. This study showed that over four years, there were 28 large storm events in Xian. Within these 28 storms, the rain garden was able to retain the rainfall from a majority of the storms. Only 5 of these storms caused the rain garden to overflow.
* Rain Gardens in this sub-humid loess region of Xi'an China, are Low Impact Developments (LID).
* China plans to implement a sponge city program in response to urban flooding. This program will prioritize the natural environment and will include rain gardens, green roofs, wetlands and more permeable surfaces to slow down storm water retention. | 1 | Applied and Interdisciplinary Chemistry |
The design of covalent drugs requires careful optimization of both the non-covalent binding affinity (which is reflected in K) and the reactivity of the electrophilic warhead (which is reflected in k).
The initial design of TCIs involves three key steps. First, bioinformatics analysis is used to identify a nucleophilic amino acid (for example, cysteine) that is either inside or near to a functionally relevant binding site on a drug target, but is rare in that protein family. Next, a reversible inhibitor is identified for which the binding mode is known. Finally, structure-based computational methods are used to guide the design of modified ligands that have electrophilic functionality, and are positioned to react specifically with the nucleophilic amino acid in the target protein.
Targeted covalent photoisomerizable ligands (photoswitches) have been developed to remotely and reversibly control the activity of receptor proteins with light. They have been used as molecular prostheses to restore visual input in the retina and auditory input in the cochlea via glutamate receptors. Ligand conjugation is targeted to specific lysine residues via an affinity labeling mechanism. | 1 | Applied and Interdisciplinary Chemistry |
The inductive effect can be explained with Bents rule. The inductive effect is the transmission of charge through covalent bonds and Bents rule provides a mechanism for such results via differences in hybridisation. In the table below, as the groups bonded to the central carbon become more electronegative, the central carbon becomes more electron-withdrawing as measured by the polar substituent constant. The polar substituent constants are similar in principle to σ values from the Hammett equation, as an increasing value corresponds to a greater electron-withdrawing ability. Bent's rule suggests that as the electronegativity of the groups increase, more p character is diverted towards those groups, which leaves more s character in the bond between the central carbon and the R group. As s orbitals have greater electron density closer to the nucleus than p orbitals, the electron density in the C−R bond will more shift towards the carbon as the s character increases. This will make the central carbon more electron-withdrawing to the R group. Thus, the electron-withdrawing ability of the substituents has been transferred to the adjacent carbon, as the inductive effect predicts. | 0 | Theoretical and Fundamental Chemistry |
Sea foam is formed under conditions that are similar to the formation of sea spray. One of the main distinctions from sea spray formation is the presence of higher concentrations of dissolved organic matter from macrophytes and phytoplankton. The dissolved organic matter in the surface water, which can be derived from the natural environment or human-made sources, provides stability to the resulting sea foam.
The physical processes that contribute to sea foam formation are breaking surface waves, bubble entrainment, a process of bubbles being incorporated or captured within a liquid such as sea water and whitecap formation. Breaking of surface waves injects air from the atmosphere into the water column, leading to bubble creation. These bubbles get transported around the top few meters of the surface ocean due to their buoyancy. The smallest bubbles entrained in the water column dissolve entirely, leading to higher ratios of dissolved gases in the surface ocean. The bubbles that do not dissolve eventually make it back to the surface. As they rise, these bubbles accumulate hydrophobic substances. Presence of dissolved organic matter stabilizes the bubbles, aggregating together as sea foam. Some studies on sea foam report that breaking of algal cells in times of heavy swells makes sea foam production more likely.
Falling rain drops on the sea surface can also contribute to sea foam formation and destruction. There have been some non-mechanistic studies demonstrating increased sea foam formation due to high rainfall events. Turbulence in the surface mixed layer can affect the concentration of dissolved organic matter and aids in the formation of nutrient-dense foam. | 0 | Theoretical and Fundamental Chemistry |
The human CCR4-Not complex is composed of structural (non-catalytic) subunits and those that have exonuclease and E3 ligase activity. Some but not all of the human subunits are conserved in budding yeast. In yeast the complex has nine core subunits, comprising Ccr4 (carbon catabolite repression), Caf proteins (Ccr4 associated factor) (Caf1, Caf40, Caf130) and Not proteins (Not1, Not2, Not3, Not4, and Not5).
Molecular weight of human subunits from Uniprot. | 1 | Applied and Interdisciplinary Chemistry |
Other software tools which help to model pharmacophores include:
*Molecular Operating Environment] (MOE) – by the Chemical Computing Group
*Phase – by Schrödinger
*Discovery Studio – by Accelrys
*SYBYL-X – by Tripos
*Pharao by [https://github.com/gertthijs/pharao/ Silicos-It][https://doi.org/10.1016/j.jmgm.2008.04.003] | 1 | Applied and Interdisciplinary Chemistry |
Consider the case of a nuclide that decays into another by some process (emission of other particles, like electron neutrinos and electrons e as in beta decay, are irrelevant in what follows). The decay of an unstable nucleus is entirely random in time so it is impossible to predict when a particular atom will decay. However, it is equally likely to decay at any instant in time. Therefore, given a sample of a particular radioisotope, the number of decay events expected to occur in a small interval of time is proportional to the number of atoms present , that is
Particular radionuclides decay at different rates, so each has its own decay constant . The expected decay is proportional to an increment of time, :
The negative sign indicates that decreases as time increases, as the decay events follow one after another. The solution to this first-order differential equation is the function:
where is the value of at time = 0, with the decay constant expressed as
We have for all time :
where is the constant number of particles throughout the decay process, which is equal to the initial number of nuclides since this is the initial substance.
If the number of non-decayed nuclei is:
then the number of nuclei of (i.e. the number of decayed nuclei) is
The number of decays observed over a given interval obeys Poisson statistics. If the average number of decays is , the probability of a given number of decays is | 0 | Theoretical and Fundamental Chemistry |
The development of MBBR technology is attributed to Professor Hallvard Ødegaard and his colleagues at Norwegian University of Science and Technology (NTNU). This is traced back to the late 1970s to early 1980s. The first MBBR pilot plant was installed at NTNU in the early 1980s in which its success lead to the construction and start-up of the first full-scale MBBR plant in Norway in 1985. It was commercialized by Kaldnes Miljöteknologi (now called AnoxKaldnes and owned by Veolia Water Technologies). Since then, MBBR technology has been widely adopted throughout the world, mainly in Europe and Asia. Now, there are over 700 wastewater treatment systems (both municipal and industrial) installed in over 50 countries. | 1 | Applied and Interdisciplinary Chemistry |
Viral RNA modifications play important roles in interactions with the immune system of host cells. The mA modification of viral RNAs allows for the viruses to escape recognition by the retinoic acid inducible gene-I receptor (RIG-I), in the type 1 IFN response, a crucial pathway of innate immunity. 5' N-7methylguanisone capping and 2-O-methylation also play vital roles for the viral infections. The cap structures help viral RNA to blend in among modified cellular mRNA and avoid triggering immune response systems. | 1 | Applied and Interdisciplinary Chemistry |
OA was first used after World War II by the US railroad industry to monitor the health of locomotives. In 1946 the Denver and Rio Grande Railroad's research laboratory successfully detected diesel engine problems through wear metal analysis of used oils. A key factor in their success was the development of the spectrograph, an instrument which replaced several wet chemical methods for detecting and measuring individual chemical element such as iron or copper. This practice was soon accepted and used extensively throughout the railroad industry.
By 1955 OA had matured to the point that the United States Bureau of Naval Weapons began a major research program to adopt wear metal analysis for use in aircraft component failure prediction. These studies formed the basis for a Joint Oil Analysis Program (JOAP) involving all branches of the U.S. Armed Forces. The JOAP results proved conclusively that increases in component wear could be confirmed by detecting corresponding increases in the wear metal content of the lubricating oil. In 1958 Pacific Intermountain Express (P.I.E.) was the first trucking company to set up an in-house used oil analysis laboratory to control vehicle maintenance costs which was managed by Bob Herguth. In 1960 the first independent commercial oil analysis laboratory was started by Edward Forgeron in Oakland, CA. | 0 | Theoretical and Fundamental Chemistry |
Tin oxide with antimony and arsenic oxides produce an opaque white glass (milk glass), first used in Venice to produce an imitation porcelain, very often then painted with enamels. Similarly, some smoked glasses may be based on dark-colored inclusions, but with ionic coloring it is also possible to produce dark colors (see above). | 0 | Theoretical and Fundamental Chemistry |
PCBs are technically attractive because of their inertness, which includes their resistance to combustion. Nonetheless, they can be effectively destroyed by incineration at 1000 °C. When combusted at lower temperatures, they convert in part to more hazardous materials, including dibenzofurans and dibenzodioxins. When conducted properly, the combustion products are water, carbon dioxide, and hydrogen chloride. In some cases, the PCBs are combusted as a solution in kerosene. PCBs have also been destroyed by pyrolysis in the presence of alkali metal carbonates.
Thermal desorption is highly effective at removing PCBs from soil. | 1 | Applied and Interdisciplinary Chemistry |
In this approach, an enantiomerically pure compound, the chiral selector, is added to the mobile phase and separation happens on a conventional achiral column. When a mixture of enantiomers is introduced into the chromatographic system, the individual enantiomers form transient diastereomeric complexes with the chiral mobile phase additive. In the chiral mobile phase additive technique, two possible mechanisms may operate: one possibility is that CMPA and the enantiomers may form diastereomers in the mobile phase. Another is that the stationary phase may be coated with the CMPA, leading to diastereomeric interactions with the enantiomeric pairs during chromatographic separation process. It is observed that both the mechanisms may happen depending on the characteristic of the stationary phase and mobile phase employed. Of late this method finds limited application. | 0 | Theoretical and Fundamental Chemistry |
Professor Harald Christian Pederson founded the A/S Ila and Lilleby smelteverk melting facilities in the 1920s. He worked with a chemical process which later has been called the Pederson-2 process. It consists of melting ironmalm which gives ferrosilicon as a by-product. | 1 | Applied and Interdisciplinary Chemistry |
Fried became a member of the National Academy of Sciences in 1971. He became a member of the American Academy of Arts and Sciences in 1981. He received the Medicinal Chemistry Award in 1974 from the American Chemical Society. He also received the Alfred Burger Award in Medicinal Chemistry in 1996.
He also received the Gregory Pincus Medal from the Worcester Foundation for Experimental Biology and the Roussel Prize from the Roussel Scientific Institute in Paris in 1994.
Bristol-Myers Squibb and the University of Chicago launched in 1990 the first of a series of annual Josef Fried Symposia of Bioorganic Chemistry. Fried is a member of the Medicinal Chemistry Hall of Fame. | 0 | Theoretical and Fundamental Chemistry |
In 1950, the US Public Health service began a comprehensive study of uranium miners, leading to the first publication of a statistical correlation between cancer and uranium mining, released in 1962. The federal government eventually regulated the standard amount of radon in mines, setting the level at 0.3 WL on January 1, 1969.
Out of 69 present and former uranium milling sites in 12 states, 24 have been abandoned, and are the responsibility of the US Department of Energy. Accidental releases from uranium mills include the 1979 Church Rock uranium mill spill in New Mexico, called the largest accident of nuclear-related waste in US history, and the 1986 Sequoyah Corporation Fuels Release in Oklahoma.
In 1990, Congress passed the Radiation Exposure Compensation Act (RECA), granting reparations for those affected by mining, with amendments passed in 2000 to address criticisms with the original act. | 0 | Theoretical and Fundamental Chemistry |
In theoretical electrolysis of water, a voltage of only 1.23 V is required to split water into hydrogen and oxygen, The formation of an EDL increases this to its thermo-neutral voltage of 1.45 V. Minimising the EDL formed during pulse electrolysis is advantageous, as it can reduce the thermo-neutral voltage and the energy input required, increasing energy efficiency. | 0 | Theoretical and Fundamental Chemistry |
The short timescale of interconversion precludes the separation of conformational isomers in most cases. Atropisomers are conformational isomers which can be separated due to restricted rotation. The equilibrium between conformational isomers can be observed using a variety of spectroscopic techniques.
Protein folding also generates stable conformational isomers which can be observed. The Karplus equation relates the dihedral angle of vicinal protons to their J-coupling constants as measured by NMR. The equation aids in the elucidation of protein folding as well as the conformations of other rigid aliphatic molecules. Protein side chains exhibit rotamers, whose distribution is determined by their steric interaction with different conformations of the backbone. This is evident from statistical analysis of the conformations of protein side chains in the Backbone-dependent rotamer library.
In cyclohexane derivatives, the two chair conformers interconvert with rapidly at room temperature, with cyclohexane itself undergoing the ring-flip at a rates of approximately 10 ring-flips/sec, with an overall energy barrier of 10 kcal/mol (42 kJ/mol), which precludes their separation at ambient temperatures. However, at low temperatures below the coalescence point one can directly monitor the equilibrium by NMR spectroscopy and by dynamic, temperature dependent NMR spectroscopy the barrier interconversion.
The dynamics of conformational (and other kinds of) isomerism can be monitored by NMR spectroscopy at varying temperatures. The technique applies to barriers of 8–14 kcal/mol, and species exhibiting such dynamics are often called "fluxional".
Besides NMR spectroscopy, IR spectroscopy is used to measure conformer ratios. For the axial and equatorial conformer of bromocyclohexane, ν differs by almost 50 cm. | 0 | Theoretical and Fundamental Chemistry |
*Nucleobase analogues
**Fluorouracil (5FU), which inhibits thymidylate synthase
**Floxuridine (FUDR)
**6-azauracil (6-AU)
*Nucleoside analogues
**Cytarabine (Cytosine arabinoside)
**Gemcitabine
*Nucleotide analogues | 1 | Applied and Interdisciplinary Chemistry |
Cannon started her academic career in 1974 at Stockholm University, where she held various positions, including a research associate at the Wenner-Grenn Institute from 1974 to 1980. Subsequently, she served as an associate professor from 1980 to 1983 and then as a professor of physiology from 1983 to 2013. Since 2013, she has held the title of emeritus professor at Stockholm University.
Cannon's involvement with the Royal Swedish Academy of Sciences included a tenure as vice president from 2003 to 2008 and subsequently as president from 2012 to 2015. Furthermore, she played an important role in the Nobel Foundation, serving as a member of the Trustees from 2006 to 2011 and taking on the role of chairman from 2008 to 2011. | 1 | Applied and Interdisciplinary Chemistry |
To broaden distribution of information on water and related subjects, AWWA publishes the periodicals Journal AWWA and Opflow. AWWA also publishes a variety of books, training manuals, standards, reports and videos for use by water professionals and others. The Association also hosts an annual conference and exposition for the entire organization each summer in North America. Section conferences are also held in all parts of North America. Specialty conferences are held throughout the year on topics including water quality, distribution systems and utility management. Proceedings of the annual and specialty conferences are published by AWWA. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, dehalogenation is a set of chemical reactions that involve the cleavage of carbon-halogen bonds; as such, it is the inverse reaction of halogenation. Dehalogenations come in many varieties, including defluorination (removal of fluorine), dechlorination (removal of chlorine), debromination (removal of bromine), and deiodination (removal of iodine). Incentives to investigate dehalogenations include both constructive and destructive goals. Complicated organic compounds such as pharmaceutical drugs are occasionally generated by dehalogenation. Many organohalides are hazardous, so their dehalogenation is one route for their detoxification. | 0 | Theoretical and Fundamental Chemistry |
The dynamically, or inelastically, scattered electrons provide several types of information about the sample as well. The brightness or intensity at a point on the detector depends on dynamic scattering, so all analysis involving the intensity must account for dynamic scattering. Some inelastically scattered electrons penetrate the bulk crystal and fulfill Bragg diffraction conditions. These inelastically scattered electrons can reach the detector to yield Kikuchi diffraction patterns, which are useful for calculating diffraction conditions. Kikuchi patterns are characterized by lines connecting the intense diffraction points on a RHEED pattern. Figure 6 shows a RHEED pattern with visible Kikuchi lines. | 0 | Theoretical and Fundamental Chemistry |
For SNP annotation, many kinds of genetic and genomic information are used. Based on the different features used by each annotation tool, SNP annotation methods may be split roughly into the following categories: | 1 | Applied and Interdisciplinary Chemistry |
CW occurs after the polymer chain has grown somewhat on the metal catalyst. The precursor is a 16 e complex with the general formula [ML(CH)(chain)]. The ethylene ligand (the monomer) dissociates to produce a highly unsaturated 14 e cation. This cation is stabilized by an agostic interaction. β-Hydride elimination then occurs to give a hydride-alkene complex. Subsequent reinsertion of the M-H into the C=C bond, but in the opposite sense gives a metal-alkyl complex.
This process, a step in the chain walk, moves the metal from the end of a chain to a secondary carbon center. At this stage, two options are available: (1) chain walking can continue or (2) a molecule of ethylene can bind to reform the 16e complex. At this second resting state, the ethylene molecule can insert to grow the polymer or dissociate inducing further chain walking. If many branches can form, a hyperbranched topology results. Therefore, ethene only homopolymerization can provide branched polymer whereas the same mechanism leads to chain straightening in α-olefin polymerization. The variation of CW by changing T, monomer concentration, or catalyst switch can be used to produce block copolymer with amorphous and semi-crystalline blocks or with blocks of different topology. | 0 | Theoretical and Fundamental Chemistry |
According to the "Green Infrastructure Master Plan" developed by Hawkins Partners, civil engineers use GIS to analyze the modeling of impervious surfaces with historical Nashville rainfall data within the CSS (combined sewer system) to find the current rates of runoff. GIS systems are able to help planning teams analyze potential volume reductions at the specific region for green infrastructures, including water harvesting, green roofs, urban trees, and structural control measures. | 1 | Applied and Interdisciplinary Chemistry |
The Gibbs–Duhem equation is useful because it relates individual chemical potentials. For example, in a binary mixture, at constant temperature and pressure, the chemical potentials of the two participants A and B are related by
where is the number of moles of A and is the number of moles of B. Every instance of phase or chemical equilibrium is characterized by a constant. For instance, the melting of ice is characterized by a temperature, known as the melting point at which solid and liquid phases are in equilibrium with each other. Chemical potentials can be used to explain the slopes of lines on a phase diagram by using the Clapeyron equation, which in turn can be derived from the Gibbs–Duhem equation. They are used to explain colligative properties such as melting-point depression by the application of pressure. Henrys law for the solute can be derived from Raoults law for the solvent using chemical potentials. | 0 | Theoretical and Fundamental Chemistry |
Phillips began his career doing postdoctoral research at the University of Texas at Austin and the Academy of Sciences of the USSR. He was appointed a lecturer in chemistry at the University of Southampton, rising to the status of Reader then becoming Wolfson Professor of Natural Philosophy, at the Royal Institution. In 1981, Phillips became a founding member of the World Cultural Council. In 1989 he moved to Imperial College, London as professor of physical chemistry and held a number of senior posts there.
In 1987 he gave the Royal Institution Christmas Lectures on television. He was appointed Officer of the Order of the British Empire (OBE) in 1999 and Commander of the Order of the British Empire (CBE) in the 2012 New Year Honours for services to chemistry. In May 2011 he was the guest on Desert Island Discs and in June 2012 was Michael Berkeley's guest on Private Passions. | 0 | Theoretical and Fundamental Chemistry |
Depending on the field of literature being surveyed, one might encounter the same compound referred to with different chemical formulas. An example of the most common difference is XYZ versus XYZ, where the labels of the two transition metals X and Y in the compound are swapped. The traditional convention XYZ arises from the interpretation of Heuslers as intermetallics and is used predominantly in literature studying magnetic applications of Heuslers compounds. The XYZ convention on the other hand is used mostly in thermoelectric materials and transparent conducting applications literature where semiconducting Heuslers (most half-Heuslers are semiconductors) are used. This convention, in which the left-most element on the periodic table comes first, uses the Zintl interpretation of semiconducting compounds where the chemical formula XYZ is written in order of increasing electronegativity. In well-known compounds such as FeVAl which were historically thought of as metallic (semi-metallic) but were more recently shown to be small-gap semiconductors one might find both styles being used. In the present article semiconducting compounds might sometimes be mentioned in the XYZ style. | 1 | Applied and Interdisciplinary Chemistry |
Pathogens synthesize proteins that can serve as "recognizable" antigens; they may express the molecules on their surface or release them into the surroundings (body fluids). What makes these substances recognizable is that they bind very specifically and somewhat strongly to certain host proteins called antibodies. The same antibodies can be anchored to the surface of cells of the immune system, in which case they serve as receptors, or they can be secreted in the blood, known as soluble antibodies. On a molecular scale, the proteins are relatively large, so they cannot be recognized as a whole; instead, their segments, called epitopes, can be recognized. An epitope comes in contact with a very small region (of 15–22 amino acids) of the antibody molecule; this region is known as the paratope. In the immune system, membrane-bound antibodies are the B-cell receptor (BCR). Also, while the T-cell receptor is not biochemically classified as an antibody, it serves a similar function in that it specifically binds to epitopes complexed with major histocompatibility complex (MHC) molecules. The binding between a paratope and its corresponding antigen is very specific, owing to its structure, and is guided by various noncovalent bonds, not unlike the pairing of other types of ligands (any atom, ion or molecule that binds with any receptor with at least some degree of specificity and strength). The specificity of binding does not arise out of a rigid lock and key type of interaction, but rather requires both the paratope and the epitope to undergo slight conformational changes in each other's presence. | 1 | Applied and Interdisciplinary Chemistry |
For Couette flow, it is possible to make mathematical progress in the solution of the Orr–Sommerfeld equation. In this section, a demonstration of this method is given for the case of free-surface flow, that is, when the upper lid of the channel is replaced by a free surface. Note first of all that it is necessary to modify upper boundary conditions to take account of the free surface. In non-dimensional form, these conditions now read
at ,
at .
The first free-surface condition is the statement of continuity of tangential stress, while the second condition relates the normal stress to the surface tension. Here
are the Froude and Weber numbers respectively.
For Couette flow , the four linearly independent solutions to the non-dimensional Orr–Sommerfeld equation are,
where is the Airy function of the first kind. Substitution of the superposition solution into the four boundary conditions gives four equations in the four unknown constants . For the equations to have a non-trivial solution, the determinant condition
must be satisfied. This is a single equation in the unknown c, which can be solved numerically or by asymptotic methods. It can be shown that for a range of wavenumbers and for sufficiently large Reynolds numbers, the growth rate is positive. | 1 | Applied and Interdisciplinary Chemistry |
Alkylated diphenylamines function as antioxidants in lubricants, approved for use in machines, in which contact with food is not ruled out. Alkylated diphenylamines and other derivatives are used as anti-ozonants in the manufacture of rubber products, reflecting the antioxidant nature of aniline derivatives. | 0 | Theoretical and Fundamental Chemistry |
Tehshik Peter Yoon (born 20 June 1975) is a Canadian-born chemist who studies the new reaction methods for organic synthesis with the use of catalysis. Yoon currently is a professor at the University of Wisconsin–Madison in the chemistry department. For his contributions to science, he has received numerous awards including the Beckman Young Investigator Award and National Science Foundation CAREER Award. | 0 | Theoretical and Fundamental Chemistry |
Proton gradients in particular are important in many types of cells as a form of energy storage. The gradient is usually used to drive ATP synthase, flagellar rotation, or metabolite transport. This section will focus on three processes that help establish proton gradients in their respective cells: bacteriorhodopsin and noncyclic photophosphorylation and oxidative phosphorylation. | 0 | Theoretical and Fundamental Chemistry |
Most photoluminescent events, in which a chemical substrate absorbs and then re-emits a photon of light, are fast, in the order of 10 nanoseconds. Light is absorbed and emitted at these fast time scales in cases where the energy of the photons involved matches the available energy states and allowed transitions of the substrate. In the special case of phosphorescence, the electron which absorbed the photon (energy) undergoes an unusual intersystem crossing into an energy state of different (usually higher) spin multiplicity (see term symbol), usually a triplet state. As a result, the excited electron can become trapped in the triplet state with only "forbidden" transitions available to return to the lower energy singlet state. These transitions, although "forbidden", will still occur in quantum mechanics but are kinetically unfavored and thus progress at significantly slower time scales. Most phosphorescent compounds are still relatively fast emitters, with triplet decay-times in the order of milliseconds.
Common examples include the phosphor coatings used in fluorescent lamps, where phosphorescence on the order of milliseconds or longer is useful for filling in the "off-time" between AC current cycles, helping to reduce "flicker". Phosphors with faster decay times are used in applications like the pixels excited by free electrons (cathodoluminescence) in cathode-ray tube television-sets, which are slow enough to allow the formation of a picture as the electron beam scans the screen, but fast enough to prevent the frames from blurring together. Even substances commonly associated with fluorescence may in fact be prone to phosphorescence, such as the liquid dyes found in highlighter pens, which is a common problem in liquid dye lasers. The onset of phosphorescence in this case can sometimes be reduced or delayed significantly by the use of triplet-quenching agents. | 0 | Theoretical and Fundamental Chemistry |
The School of Chemistry has a node of the Centre of Excellence in Exciton Science which is a research collaboration between the University of Melbourne, University of New South Wales, RMIT University, University of Sydney, and Monash University.
The Centre of Excellence in Exciton Science is focused on novel materials for the development of low-cost, high efficiency, light-harvesting devices. The research programme utilises high-throughput screening, single molecule photochemistry, and ultrafast spectroscopy. | 1 | Applied and Interdisciplinary Chemistry |
The majority of sperm donors who donate their sperm through a sperm bank receive some kind of payment, although this is rarely a significant amount. A review including 29 studies from nine countries came to the result that the amount of money actual donors received for their donation varied from $10 to €70 per donation or sample. The payments vary from the situation in the United Kingdom where donors are only entitled to their expenses in connection with the donation, to the situation with some US sperm banks where a donor receives a set fee for each donation plus an additional amount for each vial stored. At one prominent California sperm bank for example, TSBC, donors receive roughly $50 for each donation (ejaculation) which has acceptable motility/survival rates both at donation and at a test-thaw a couple of days later. Because of the requirement for the two-day celibacy period before donation, and geographical factors which usually require the donor to travel, it is not a viable way to earn a significant income—and is far less lucrative than selling human eggs. Some private donors may seek remuneration although others donate for altruistic reasons. According to the EU Tissue Directive donors in EU may only receive compensation, which is strictly limited to making good the expenses and inconveniences related to the donation. | 1 | Applied and Interdisciplinary Chemistry |
AGA and AGG were thought to have become mitochondrial stop codons early in vertebrate evolution. However, at least in humans it has now been shown that AGA and AGG sequences are not recognized as termination codons. A -1 mitoribosome frameshift occurs at the AGA and AGG codons predicted to terminate the CO1 and ND6 open reading frames (ORFs), and consequently both ORFs terminate in the standard UAG codon. | 1 | Applied and Interdisciplinary Chemistry |
For steelmaking, direct current (DC) arc furnaces are used, with a single electrode in the roof and the current return through a conductive bottom lining or conductive pins in the base. The advantage of DC is lower electrode consumption per ton of steel produced, since only one electrode is used, as well as less electrical harmonics and other similar problems. The size of DC arc furnaces is limited by the current carrying capacity of available electrodes, and the maximum allowable voltage. Maintenance of the conductive furnace hearth is a bottleneck in extended operation of a DC arc furnace.
In a steel plant, a ladle furnace (LF) is used to maintain the temperature of liquid steel during processing after tapping from EAF or to change the alloy composition. The ladle is used for the first purpose when there is a delay later in the steelmaking process. The ladle furnace consists of a refractory roof, a heating system, and, when applicable, a provision for injecting argon gas into the bottom of the melt for stirring. Unlike a scrap melting furnace, a ladle furnace does not have a tilting or scrap-charging mechanism.
Electric arc furnaces are also used for production of calcium carbide, ferroalloys, and other non-ferrous alloys, and for production of phosphorus. Furnaces for these services are physically different from steel-making furnaces and may operate on a continuous, rather than batch, basis. Continuous-process furnaces may also use paste-type, Søderberg electrodes to prevent interruptions from electrode changes.
Such a furnace is known as a submerged arc furnace, because the electrode tips are buried in the slag/charge, and arcing occurs through the slag, between the matte and the electrode. The casing and casing fins of the electrode melt the electrode paste through electrical current passing through the electrode casing and heat from the furnace. A steelmaking arc furnace, by comparison, arcs in the open. The key is the electrical resistance, which is what generates the heat required: the resistance in a steelmaking furnace is the atmosphere, while in a submerged-arc furnace, the slag (or charge) supplies the resistance. The liquid metal formed in either furnace is too conductive to form an effective heat-generating resistance.
Amateurs have constructed a variety of arc furnaces, often based on electric arc welding kits contained by silica blocks or flower pots. Though crude, these simple furnaces can melt a wide range of materials, create calcium carbide, and more. | 1 | Applied and Interdisciplinary Chemistry |
In geological applications, detecting the presence of calcite or other forms of calcium carbonate in alkaline soils or during lithological analysis involves using dilute hydrochloric acid and observing effervescence. | 0 | Theoretical and Fundamental Chemistry |
Karen Dale Williams Morse is a inorganic chemist. She was president of Western Washington University from 1993 until 2008, and was named the Bowman Distinguished Professor in 2014. She is an elected fellow of the American Association for the Advancement of Science. | 0 | Theoretical and Fundamental Chemistry |
In astrophysics, Chandrasekhar's white dwarf equation is an initial value ordinary differential equation introduced by the Indian American astrophysicist Subrahmanyan Chandrasekhar, in his study of the gravitational potential of completely degenerate white dwarf stars. The equation reads as
with initial conditions
where measures the density of white dwarf, is the non-dimensional radial distance from the center and is a constant which is related to the density of the white dwarf at the center. The boundary of the equation is defined by the condition
such that the range of becomes . This condition is equivalent to saying that the density vanishes at . | 1 | Applied and Interdisciplinary Chemistry |
Bases (e.g. sodium bicarbonate) or acids (e.g. citric acid) are sometimes used as cutting agents. An individual base solution and acid solution can help determine if the substance contains an acid or base respectively, if an acid–base reaction will occur. | 0 | Theoretical and Fundamental Chemistry |
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