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Förster coupling is the resonant energy transfer between excitons within adjacent QD's (quantum dots). The first studies of Foerster were performed in the context of the sensitized luminescence of solids. Here, an excited sensitizer atom can transfer its excitation to a neighbouring acceptor atom, via an intermediate virtual photon. This same mechanism has also been shown to be responsible for exciton transfer between QD’s and within molecular systems and biosystems (though incoherently, as a mechanism for photosynthesis), all of which may be treated in a similar formulation. (See also Förster resonance energy transfer (FRET).) In the introductory lecture given by T. Förster, he considered the transfer of electronic excitation energy between otherwise well-separated atomic or molecular electronic systems, which exclude the trivial case of an excitation transfer that consists in the emission of one quantum of light by the first atom or molecule followed by re-absorption by the second one. It is only the non-radiative transfer of excitation occurring during the short lifetimes of excited electronic systems which he considered there. The first observation of energy transfer was made by Cario and Franck (1922) in their classical experiments on sensitized fluorescence of atoms in the vapour phase. A mixture of mercury and thallium vapour, when irradiated with the light of the mercury resonance line, shows the emission spectra of both atoms | https://en.wikipedia.org/wiki?curid=22976317 |
Förster coupling Since thallium atoms do not absorb the exciting light, they can get excited only indirectly by an excitation transfer from mercury atoms. A transfer by reabsorption is impossible here. Therefore, this transfer must be a non-radiative one with a mercury atom as the donor or sensitizer and the thallium atom as the acceptor. Unfortunately, in this case it cannot be decided whether the transfer occurs between distant atoms or during a normal collision or even in a labile molecule formed as an intermediate. This decision, however, was possible in similar cases, as in the mercury-sensitized fluorescence of sodium and in the mutual sensitization of the fluorescence of different mercury isotopes. In these cases, the transfer occurs over distances very much larger than those in normal collisional separations. Similar observations of sensitized fluorescence were made with molecular vapours and in solution. Further experiments have shown that in this case the transfer occurs not over collisional distances but over the mean intermolecular distances of sensitizer and acceptor, corresponding to a concentration of 10 to 10M. This is demonstrated by the fact that sensitization occurs with similar half-value concentrations in solution of very different viscosities and even in organic glasses at low temperature. The possibility of the formation of a complex between sensitizer and acceptor molecules was excluded by the additivity of the absorption spectra and the different dependence on concentration to be expected in this case | https://en.wikipedia.org/wiki?curid=22976317 |
Förster coupling It must be concluded, therefore, that excitation transfer of a non-trivial nature occurs over the mean distances between statistically distributed molecules which are about 40Å in this case. It differs from short-distance collisional transfer by its independence of solvent viscosity and from transfer within a molecular complex by the constancy of absorption spectra and the decrease in sensitizer fluorescence lifetime. Table 2 summarizes some qualitative features of this kind of long-range transfer and of some more or less trivial mechanisms. The non-trivial transfer differs from re-absorption transfer by its independence of the volume of the solution, by the decrease in sensitizer fluorescence lifetime, and by the invariability of the sensitizer fluorescence spectrum. It differs from short-distance collisional transfer by its independence of solvent viscosity and from transfer within a molecular complex by the constancy of absorption spectra and the decrease in sensitizer fluorescence lifetime. In most cases, some of these different properties allow a decision between trivial and non-trivial transfer mechanisms. Further discriminations may be made by quantitative studies of these properties. The electrons interact via the Coulomb interaction, given by the Hamiltonian where the Coulomb matrix element is given by Here, formula_3 is the dielectric constant of the medium | https://en.wikipedia.org/wiki?curid=22976317 |
Förster coupling To calculate the dynamics of two coupled QDs (each modeled as an interband two-level system with one conduction and one valence level formula_4and formula_5, respectively) which have no electronic overlap, an expansion of the potential is performed: (i) a long-range expansion about a reference point of each QD, varying on a mesoscopic scale and neglecting the variation on the scale of the elementary cell - this yields level diagonal contributions in the Hamiltonian formula_6 and formula_7 ; and (ii) a short-range expansion about an arbitrary lattice vector, taking into account the microscopic variation of the QD - this yields nondiagonal contributions formula_8 . On the dipole-dipole level, the level diagonal elements correspond to an electrostatic energetic shift of the system (biexcitonic shift formula_9), while the nondiagonal elements, the so-called elements formula_10, correspond to an excitation transfer between the different QDs. Here, we shall consider excitons in two coupled QD’s and the Coulomb interactions between them. More specifically, we shall derive an analytical expression for the strength of the inter-dot Foerster coupling. It can be also shown that this coupling is, under certain conditions, of dipole-dipole type and that it is responsible for resonant exciton exchange between adjacent QD’s. This is a transfer of energy only, not a tunnelling effect | https://en.wikipedia.org/wiki?curid=22976317 |
Förster coupling we write the Hamiltonian of two interacting QD’s in the computational basis formula_11 formula_12 where the off-diagonal Förster interaction is given by formula_10 , and the direct Coulomb binding energy between the two excitons, one on each dot, is on the diagonal and given by formula_14 . The ground state energy is denoted by formula_15 , and formula_16 is the difference between the excitation energy for dot I and that for dot II. These excitation energies and inter-dot interactions are all functions of the applied field F. It is also straightforward to see that an off-diagonal does indeed correspond to a resonant transfer of energy; if we begin in the state formula_17 (exciton on dot I, no exciton on dot II) this will naturally evolve to a state formula_18 | https://en.wikipedia.org/wiki?curid=22976317 |
Journal of Coatings Technology and Research The is a bimonthly peer-reviewed scientific journal. It is co-owned by the American Coatings Association and the Oil and Colour Chemists' Association and published on their behalf by Springer Science+Business Media. The editor-in-chief of the journal is Mark Nichols (Ford Motor Company). Areas of research covered in the "Journal of Coatings Technology and Research" include the manufacture of functional, protective and decorative coatings including paints, inks and related coatings and their raw materials. The journal publishes research papers describing chemistry, physics, materials science, and engineering studies relevant to surface coatings; Applications papers on experimental solutions for technological problems in the design, formulation, manufacture, application, use and performance of surface coatings; review articles offering broad, critical overviews of advances in coatings science; and brief communications, presenting notes and letters on research topics of limited scope or immediate impact. The journal is abstracted and indexed in: | https://en.wikipedia.org/wiki?curid=22976865 |
Nuclear magnetic resonance in porous media Nuclear magnetic resonance (NMR) in porous materials covers the application of using NMR as a tool to study the structure of porous media and various processes occurring in them. This technique allows the determination of characteristics such as the porosity and pore size distribution, the permeability, the water saturation, the wettability, etc. Microscopically the volume of a single pore in a porous media may be divided into two regions; surface area formula_1 and bulk volume formula_2 (Figure 1). The surface area is a thin layer with thickness formula_3 of a few molecules close to the pore wall surface. The bulk volume is the remaining part of the pore volume and usually dominates the overall pore volume. With respect to NMR excitations of nuclear states for hydrogen-containing molecules in these regions, different relaxation times for the induced excited energy states are expected. The relaxation time is significantly shorter for a molecule in the surface area, compared to a molecule in the bulk volume. This is an effect of paramagnetic centres in the pore wall surface that causes the relaxation time to be faster | https://en.wikipedia.org/wiki?curid=22977015 |
Nuclear magnetic resonance in porous media The inverse of the relaxation time formula_4, is expressed by contributions from the bulk volume formula_2, the surface area formula_1 and the self-diffusion formula_7: where formula_3 is the thickness of the surface area, formula_1 is the surface area, formula_2 is the pore volume, formula_13 is the relaxation time in the bulk volume, formula_14 is the relaxation time for the surface, formula_15 is the gyromagnetic ratio, formula_16 is the magnetic field gradient (assumed to be constant), formula_17 is the time between echoes and formula_18 is the self-diffusion coefficient of the fluid. The surface relaxation can be assumed as uniform or non-uniform. The NMR signal intensity in the formula_19 distribution plot reflected by the measured amplitude of the NMR signal is proportional to the total amount of hydrogen nuclei, while the relaxation time depends on the interaction between the nuclear spins and the surroundings. In a characteristic pore containing for an example, water, the bulk water exhibits a single exponential decay. The water close to the pore wall surface exhibits faster formula_19 relaxation time for this characteristic pore size. NMR techniques are typically used to predict permeability for fluid typing and to obtain formation porosity, which is independent of mineralogy. The former application uses a surface-relaxation mechanism to relate measured relaxation spectra with surface-to-volume ratios of pores, and the latter is used to estimate permeability | https://en.wikipedia.org/wiki?curid=22977015 |
Nuclear magnetic resonance in porous media The common approach is based on the model proposed by Brownstein and Tarr. They have shown that, in the fast diffusion limit, given by the expression: where formula_22 is the surface relaxivity of pore wall material, formula_23 is the radius of the spherical pore and formula_18 is the bulk diffusivity. The connection between NMR relaxation measurements and petrophysical parameters such as permeability stems from the strong effect that the rock surface has on promoting magnetic relaxation. For a single pore, the magnetic decay as a function of time is described by a single exponential: where formula_26 is the initial magnetization and the transverse relaxation time formula_27 is given by: formula_29 is the surface-to-volume ratio of the pore, formula_30 is bulk relaxation time of the fluid that fills the pore space, and formula_22 is the surface relaxation strength. For small pores or large formula_22, the bulk relaxation time is small and the equation can be approximated by: Real rocks contain an assembly of interconnected pores of different sizes. The pores are connected through small and narrow pore throats (i.e. links) that restrict interpore diffusion. If interpore diffusion is negligible, each pore can be considered to be distinct and the magnetization within individual pores decays independently of the magnetization in neighbouring pores. The decay can thus be described as: where formula_35 is the volume fraction of pores of size formula_36 that decays with relaxation time formula_37 | https://en.wikipedia.org/wiki?curid=22977015 |
Nuclear magnetic resonance in porous media The multi-exponential representation corresponds to a division of the pore space into formula_38 main groups based on formula_29 (surface-to-volume ratio) values. Due to the pore size variations, a non-linear optimization algorithm with multi-exponential terms is used to fit experimental data. Usually, a weighted geometric mean, formula_40, of the relaxation times is used for permeability correlations: formula_42 is thus related to an average formula_29 or pore size. Commonly used NMR permeability correlations as proposed by Dunn "et al." are of the form: where formula_45 is the porosity of the rock. The exponents formula_46 and formula_47 are usually taken as four and two, respectively. Correlations of this form can be rationalized from the Kozeny–Carman equation: by assuming that the tortuosity formula_49 is proportional to formula_50. However, it is well known that tortuosity is not only a function of porosity. It also depends on the formation factor formula_51. The formation factor can be obtained from resistivity logs and is usually readily available. This has given rise to permeability correlations of the form: Standard values for the exponents formula_53 and formula_54, respectively. Intuitively, correlations of this form are a better model since it incorporates tortuosity information through formula_55. The value of the surface relaxation strength formula_22 affects strongly the NMR signal decay rate and hence the estimated permeability | https://en.wikipedia.org/wiki?curid=22977015 |
Nuclear magnetic resonance in porous media Surface relaxivity data are difficult to measure, and most NMR permeability correlations assume a constant formula_22. However, for heterogeneous reservoir rocks with different mineralogy, formula_22 is certainly not constant and surface relaxivity has been reported to increase with higher fractions of microporosity. If surface relaxivity data are available it can be included in the NMR permeability correlation as For fully brine saturated porous media, three different mechanisms contribute to the relaxation: bulk fluid relaxation, surface relaxation, and relaxation due to gradients in the magnetic field. In the absence of magnetic field gradients, the equations describing the relaxation are: with the initial condition where formula_65 is the self-diffusion coefficient. The governing diffusion equation can be solved by a 3D random walk algorithm. Initially, the walkers are launched at random positions in the pore space. At each time step, formula_66, they advance from their current position, formula_67, to a new position, formula_68, by taking steps of fixed length formula_69 in a randomly chosen direction. The time step is given by: The new position is given by The angles formula_74 and formula_75 represent the randomly selected direction for each random walker in spherical coordinates. It can be noted that formula_76 must be distributed uniformly in the range (0,formula_77). If a walker encounters a pore-solid interface, it is killed with a finite probability formula_3 | https://en.wikipedia.org/wiki?curid=22977015 |
Nuclear magnetic resonance in porous media The killing probability formula_3 is related to the surface relaxation strength by: If the walker survives, it simply bounces off the interface and its position does not change. At each time step, the fraction formula_81 of the initial walkers that are still alive is recorded. Since the walkers move with equal probability in all directions, the above algorithm is valid as long as there is no magnetic gradient in the system. When protons are diffusing, the sequence of spin echo amplitudes is affected by inhomogeneities in the permanent magnetic field. This results in an additional decay of the spin echo amplitudes that depends on the echo spacing formula_82. In the simple case of a uniform spatial gradient formula_16, the additional decay can be expressed as a multiplicative factor: where formula_15 is the ratio of the Larmor frequency to the magnetic field intensity. The total magnetization amplitude as a function of time is then given as: The wettability conditions in a porous media containing two or more immiscible fluid phases determine the microscopic fluid distribution in the pore network. Nuclear magnetic resonance measurements are sensitive to wettability because of the strong effect that the solid surface has on promoting magnetic relaxation of the saturating fluid. The idea of using NMR as a tool to measure wettability was presented by Brown and Fatt in 1956. The magnitude of this effect depends upon the wettability characteristics of the solid with respect to the liquid in contact with the surface | https://en.wikipedia.org/wiki?curid=22977015 |
Nuclear magnetic resonance in porous media Their theory is based on the hypothesis that molecular movements are slower in the bulk liquid than at the solid-liquid interface. In this solid-liquid interface the diffusion coefficient is reduced, which correspond to a zone of higher viscosity. In this higher viscosity zone, the magnetically aligned protons can more easily transfer their energy to their surroundings. The magnitude of this effect depends upon the wettability characteristics of the solid with respect to the liquid in contact with the surface. NMR Cryoporometry (NMRC) is a recent technique for measuring total porosity and pore size distributions. It makes use of the Gibbs-Thomson effect : small crystals of a liquid in the pores melt at a lower temperature than the bulk liquid : The melting point depression is inversely proportional to the pore size. The technique is closely related to that of the use of gas adsorption to measure pore sizes (Kelvin equation). Both techniques are particular cases of the Gibbs Equations (Josiah Willard Gibbs): the Kelvin Equation is the constant temperature case, and the Gibbs-Thomson Equation is the constant pressure case. To make a Cryoporometry measurement, a liquid is imbibed into the porous sample, the sample cooled until all the liquid is frozen, and then warmed slowly while measuring the quantity of the liquid that has melted | https://en.wikipedia.org/wiki?curid=22977015 |
Nuclear magnetic resonance in porous media Thus it is similar to DSC thermoporosimetry, but has higher resolution, as the signal detection does not rely on transient heat flows, and the measurement can be made arbitrarily slowly. It is suitable for measuring pore diameters in the range 2 nm–2 μm. Nuclear Magnetic Resonance (NMR) may be used as a convenient method of measuring the quantity of liquid that has melted, as a function of temperature, making use of the fact that the formula_19 relaxation time in a frozen material is usually much shorter than that in a mobile liquid. The technique was developed at the University of Kent in the UK. | https://en.wikipedia.org/wiki?curid=22977015 |
Streptamer The technology allows the reversible isolation and staining of antigen-specific T cells. This technology combines a current T cell isolation method with the Strep-tag technology. In principle, the T cells are separated by establishing a specific interaction between the T cell of interest and a molecule that is conjugated to a marker, which enables the isolation. The reversibility of this interaction and the fact that it is performed at low temperatures is the reason for the successful isolation and characterization of functional T cells. Because T cells remain phenotypically and functionally indistinguishable from untreated cells, this method offers new strategies in clinical and basic T cell research. T cells play an important role in the adaptive immune system. They are capable of orchestrating, regulating and coordinating complex immune responses. A wide array of clinically relevant aspects are associated with the function or malfunction of T-cells: Autoimmune diseases, control of viral or bacterial pathogens, development of cancer or graft versus host responses. Over the past years, various methods (ELISpot Assay, intracellular cytokine staining, secretion assay) have been developed for the identification of T cells, but only major histocompatibility complex (MHC) procedures allow identification and purification of antigen-specific T cells independent of their functional status. In principle, MHC procedures are using the T cell receptor (TCR) ligand, which is the MHC-peptide complex, as a staining probe | https://en.wikipedia.org/wiki?curid=22977267 |
Streptamer The MHC interacts with the TCR, which in turn is expressed on the T cells. Because TCR-MHC interactions have only a very weak affinity towards each other, monomeric MHC-epitope complexes cannot provide stable binding. This problem can be solved by using multimerized MHC-epitopes, which increases the binding avidity and therefore allows stable binding. Fluorochromes conjugated to the MHC-multimers then can be used for identification of T cells by flow cytometry. Nowadays, MHC molecules can be produced recombinantly together with the antigenic peptides which are known for a fast-growing number of diseases. The staining principle combines the classic method of T cell isolation by MHC-multimers with the Strep-tag/Strep-Tactin technology. The "Strep"-tag is a short peptide sequence that displays moderate binding affinity for the biotin-binding site of a mutated streptavidin molecule, called Strep-Tactin. For the technology, the Strep-Tactin molecules are multimerized and form the "backbone", thus creating a platform for binding to strep-tagged proteins. Further, the Strep-Tactin backbone has a fluorescent label to allow flow cytometry analysis. Incubation of MHC-Strep-tag fusion proteins with the Strep-Tactin backbone results in the formation of a MHC-multimer, which is capable for antigen-specific staining of T cells. Because the molecule d-biotin has a much higher affinity to Strep-Tactin than Strep-tag, it can effectively compete for the binding site | https://en.wikipedia.org/wiki?curid=22977267 |
Streptamer Therefore, a MHC multimer based on the interaction of Strep-tag with Strep-Tactin is easily disrupted in the presence of relatively low concentrations of d-biotin. Without the Strep-Tactin backbone, the single MHC-Strep-tag fusion proteins spontaneously detach from the TCR of the T cell, because of weak binding affinities (monomeric MHC-epitope complexes cannot provide stable binding, see above). | https://en.wikipedia.org/wiki?curid=22977267 |
Venturi flume A venturi flume is a critical-flow open flume with a constricted flow which causes a drop in the hydraulic grade line, creating a critical depth. It is used in flow measurement of very large flow rates, usually given in millions of cubic units. A venturi meter would normally measure in millimetres, whereas a venturi flume measures in metres. Measurement of discharge with venturi flumes requires two measurements, one upstream and one at the throat (narrowest cross-section), if the flow passes in a subcritical state through the flume. If the flumes are designed so as to pass the flow from sub critical to supercritical state while passing through the flume, a single measurement at the throat (which in this case becomes a critical section) is sufficient for computation of discharge. To ensure the occurrence of critical depth at the throat, the flumes are usually designed in such way as to form a hydraulic jump on the downstream side of the structure. These flumes are called 'standing wave flumes' Venturi flumes have two advantages over weirs where the critical depth is created by a vertical constriction. First, the hydraulic head loss is smaller in flumes than in weirs. Second, there is no dead zone in flumes where sediment and debris can accumulate; such a dead zone exists upstream of the weirs. what is Cd value ? | https://en.wikipedia.org/wiki?curid=22984567 |
Endoreversible thermodynamics is a subset of irreversible thermodynamics aimed at making more realistic assumptions about heat transfer than are typically made in reversible thermodynamics. It gives an upper bound on the energy that can be derived from a real process that is "lower" than that predicted by Carnot for a Carnot cycle, and accommodates the exergy destruction occurring as heat is transferred irreversibly. was discovered in simultaneous work by Novikov and Chambadal, although sometimes mistakenly attributed to Curzon & Ahlborn. An equation for the efficiency of a semi-ideal heat engine operating at maximum power output in which "heat transfer is irreversible" but other components are ideal can be shown to have the following form, which is the Chambadal-Novikov efficiency: In the limit of infinitesimally small power output, the standard Carnot result for efficiency is recovered. For some typical cycles, the above equation (note that absolute temperatures must be used) gives the following results: As shown, the endoreversible efficiency much more closely models the observed data. However, such an engine violates Carnot's principle which states that work can be done any time there is a difference in temperature. The fact that the hot and cold reservoirs are not at the same temperature as the working fluid they are in contact with means that work can and is done at the hot and cold reservoirs. The result is tantamount to coupling the high and low temperature parts of the cycle, so that the cycle collapses | https://en.wikipedia.org/wiki?curid=22987859 |
Endoreversible thermodynamics In the Carnot cycle there is strict necessity that the working fluid be at the same temperatures as the heat reservoirs they are in contact with and that they are separated by adiabatic transformations which prevent thermal contact. The efficiency was first derived by William Thomson in his study of an unevenly heated body in which the adiabatic partitions between bodies at different temperatures are removed and maximum work is performed. It is well known that the final temperature is the geometric mean temperature formula_2 so that the efficiency is the Carnot efficiency for an engine working between formula_3 and formula_2. Due to occasional confusion about the origins of the above equation, it is sometimes named the Chambadal-Novikov-Curzon-Ahlborn efficiency. An introduction to endoreversible thermodynamics is given in the thesis by Katharina Wagner. It is also introduced by Hoffman et al. A thorough discussion of the concept, together with many applications in engineering, is given in the book by Hans Ulrich Fuchs. | https://en.wikipedia.org/wiki?curid=22987859 |
Physica Status Solidi Physica Status Solidi, often stylized "physica status solidi" or "pss", is a family of international peer-reviewed, scientific journals, publishing research on all aspects of solid state physics, and materials science. It is owned and published by Wiley–VCH. These journals publish over 2000 articles per year, making it one of the largest international publications in condensed matter physics. The current editor in chief is Stefan Hildebrandt at the Editorial Office based in Berlin. This office also manages the peer-review process. "Physica Status Solidi" was founded by Karl Wolfgang Böer (then at Humboldt University of Berlin) in East Berlin and published its first issue in July 1961. Shortly after the journal was founded, the construction of the Berlin Wall in August 1961 exacerbated the distances between scientists from the Eastern and Western blocs. Throughout the cold war "Physica Status Solidi" maintained political independence and English as publication language and, as such, it became a major platform for the scientists behind the Iron Curtain to disseminate their results in the Western world (and vice versa) and thus a forum of international exchange for scientists from the East and the West. In 1970 the journal was divided into series A ("Applications and Materials Science") and B ("Basic Solid State Physics"). In 2003, series C ("Current Topics in Solid State Physics") was created to accommodate the publication of conference proceedings | https://en.wikipedia.org/wiki?curid=22988737 |
Physica Status Solidi Following the reunification of Germany in 1990 the journal's original publisher Akademie Verlag became part of the VCH Publishing group, which again was merged into John Wiley & Sons, leading to the formation of Wiley-VCH Verlag in 1997. A fourth series, RRL ("Rapid Research Letters"), was launched in 2007 to publish short articles of broader and immediate interest to the solid state physics and materials science community. Publication times are typically two weeks from submission to online publication. | https://en.wikipedia.org/wiki?curid=22988737 |
Journal of Microscopy The is the monthly peer-reviewed scientific journal of the Royal Microscopical Society which covers all aspects of microscopy including spatially resolved spectroscopy, compositional mapping, and image analysis. This includes technology and applications in physics, chemistry, material science, and the life sciences. It is published by Wiley-Blackwell on behalf of the Society. The editor-in-chief is Pete Nellist, a Materials Science professor at Oxford University. The journal publishes review articles, original research papers, short communications, and letters to the editor. It was established in 1841 as the "Transactions of the Microscopical Society of London", obtaining its current name in 1869, with volume numbering restarting at 1. The journals is abstracted and indexed in: According to the "Journal Citation Reports", the journal has a 2017 impact factor of 1.693. | https://en.wikipedia.org/wiki?curid=22993228 |
C12H16N2 The molecular formula CHN (molar mass : 188.26 g/mol, exact mass : 188.131349) may refer to: | https://en.wikipedia.org/wiki?curid=22996459 |
C20H20 The molecular formula CH may refer to: | https://en.wikipedia.org/wiki?curid=22998776 |
4,4'-Dinitro-3,3'-diazenofuroxan 4,4’-Dinitro-3,3’-diazenofuroxan (DDF) is a powerful experimental high explosive with performance comparable to that of other high-density high-explosives such as octanitrocubane. It is synthesised by oxidative coupling of 4-amino-3-(azidocarbonyl)furoxan followed by Curtius rearrangement and further oxidation. | https://en.wikipedia.org/wiki?curid=23000019 |
Diffusing-wave spectroscopy (DWS) is an optical technique derived from dynamic light scattering (DLS) that studies the dynamics of scattered light in the limit of strong multiple scattering. It has been widely used in the past to study colloidal suspensions, emulsions, foams, gels, biological media and other forms of soft matter. If carefully calibrated, DWS allows the quantitative measurement of microscopic motion in a soft material, from which the rheological properties of the complex medium can be extracted via the microrheology approach. Laser light is sent to the sample and the outcoming transmitted or backscattered light is detected by an optoelectric sensor. The light intensity detected is the result of the interference of all the optical waves coming from the different light paths. The signal is analysed by calculating the intensity autocorrelation function called g. formula_1 For the case of non-interacting particles suspended in a (complex) fluid a direct relation between g-1 and the mean squared displacement of the particles <Δr> can be established. Let's note P(s) the probability density function (PDF) of the photon path length s. The relation can be written as follows: formula_2 with formula_3 and formula_4 is the transport mean free path of scattered light. For simple cell geometries, it is thus possible to calculate the mean squared displacement of the particles <Δr> from the measured g-1 values analytically | https://en.wikipedia.org/wiki?curid=23001219 |
Diffusing-wave spectroscopy For example, for the backscattering geometry, an infinitely thick cell, large laser spot illumination and detection of photons coming from the center of the spot, the relationship between g-1 and <Δr> is: formula_5, γ value is around 2. For less thick cells and in transmission, the relationship depends also on l* (the transport length). This technique either uses a camera to detect many speckle grains (see speckle pattern) or a ground glass to create a large number of speckle realizations (Echo-DWS ). In both cases an average over a large number of statistically independent intensity values is obtained, allowing a much faster data acquisition time. formula_6 MSDWS is particularly adapted for the study of slow dynamics and non ergodic media. Echo-DWS allows seamless integration of MSDWS in a traditional DWS-scheme with superior temporal resolution down to 12 ns. Camera based adaptive image processing allows online measurement of particle dynamics for example during drying. | https://en.wikipedia.org/wiki?curid=23001219 |
Lurgi–Ruhrgas process The is an above-ground coal liquefaction and shale oil extraction technology. It is classified as a hot recycled solids technology. The was originally invented in the 1940s and further developed in the 1950s for a low-temperature liquefaction of lignite (brown coal). The technology is named after its developers Lurgi Gesellschaft für Wärmetechnik G.m.b.H. and Ruhrgas AG. Over a time, the process was used for coal processing in Japan, Germany, the United Kingdom, Argentina, and former Yugoslavia. The plant in Japan processed also cracking petroleum oils to olefins. In 1947–1949, the was used in Germany for shale oil production. In Lukavac, Bosnia and Herzegovina, two retorts for liquefaction of lignite were in operation from 1963 to 1968. The capacity of the plant was 850 tons of lignite per day. The plant in Lincolnshire, the United Kingdom, operated in 1978–1979 with capacity of 900 tons of coal per day. In late 1960s and early 1970s oil shales from different European countries and from the Green River Formation of Colorado, the United States, were tested at the Lurgi's pilot plant in Frankfurt. In the United States, the technology was promoted in cooperation with Dravo Corporation. In the 1970s, the technology was licensed to the Rio Blanco Shale Oil Project for construction of a modular retort in combination with the modified "in situ" process. However, this plan was terminated | https://en.wikipedia.org/wiki?curid=23001725 |
Lurgi–Ruhrgas process In 1980, the Natural Resources Authority of Jordan commissioned from the Klöckner-Lurgi consortium a pre-feasibility study of construction of an oil shale retorting complex in Jordan using the Lurgi–Ruhrgas process. However, although the study found the technology feasible, it was never implemented. The is a hot recycled solids technology, which processes fine particles of coal or oil shale sized . As a heat carrier, it uses spent char or spent oil shale (oil shale ash), mixed with sand or other more durable materials. In this process, crushed coal or oil shale is fed into the top of the retort. In retort, coal or oil shale is mixed with the heated char or spent oil shale particles in the mechanical mixer (screw conveyor). The heat is transferred from the heated char or spent oil shale to the coal or raw oil shale causing pyrolysis. As a result, oil shale decomposes to shale oil vapors, oil shale gas and spent oil shale. The oil vapor and product gases pass through a hot cyclone for cleaning before sending to a condenser. In the condenser, shale oil is separated from product gases. The spent oil shale, still including residual carbon (char), is burnt at a lift pipe combustor to heat the process. If necessary, additional fuel oil is used for combustion. During the combustion process, heated solid particles in the pipe are moved to the surge bin by pre-heated air that is introduced from the bottom of the pipe | https://en.wikipedia.org/wiki?curid=23001725 |
Lurgi–Ruhrgas process At the surge bin, solids and gases are separated, and solid particles are transferred to the mixer unit to conduct the pyrolysis of the raw oil shale. One of the disadvantages of this technology is the fact that produced shale oil vapors are mixed with shale ash causing impurities in shale oil. Ensuring the quality of produced shale oil is complicated as compared with other mineral dusts the shale ash is more difficult to collect. | https://en.wikipedia.org/wiki?curid=23001725 |
Charge transfer coefficient Charge transfer coefficient, and symmetry factor (symbols "α" and "β", respectively) are two related parameters used in description of the kinetics of electrochemical reactions. They appear in the Butler–Volmer equation and related expressions. The symmetry factor and the charge transfer coefficient are dimensionless. According to an IUPAC definition, for a reaction with a single rate-determining step, the charge transfer coefficient for a cathodic reaction (the cathodic transfer coefficient, "α") is defined as: The anodic transfer coefficient ("α") is defined by analogy: where: The charge transfer coefficient signifies the fraction of the interfacial potential at an electrode-electrolyte interface that helps in lowering the free energy barrier for the electrochemical reaction. The electroactive ion present in the interfacial region experiences the interfacial potential and electrostatic work is done on the ion by "a part" of the interfacial electric field. It is charge transfer coefficient that signifies "this part" that is utilized in activating the ion to the top of the free energy barrier. In operating batteries and fuel cells, charge transfer coefficient is the parameter that signifies the fraction of overpotential that affects the current density. This parameter has had a mysterious significance in electrochemical kinetics for over three quarters of the previous century. It can also be said that charge transfer coefficient is the heart of electrode kinetics | https://en.wikipedia.org/wiki?curid=23002479 |
Charge transfer coefficient The symmetry factor (or barrier symmetry factor) is a coefficient similar to the transfer coefficient, but applicable only to single-step reactions. The sum of anodic symmetry factor and cathodic symmetry factor is equal to one: | https://en.wikipedia.org/wiki?curid=23002479 |
Transport length The transport length in a strongly diffusing medium (noted l*) is the length over which the direction of propagation of the photon is randomized. It is related to the mean free path l by the relation: formula_1 with: g: the asymmetry coefficient. formula_2 or averaging of the scattering angle θ over a high number of scattering events. g can be evaluated with the Mie theory. If g=0, l=l*. A single scattering is already isotropic. If g→1, l*→infinite. A single scattering doesn't deviate the photons. Then the scattering never gets isotropic. This length is useful for renormalizing a non-isotropic scattering problem into an isotropic one in order to use classical diffusion laws (Fick law and Brownian motion). The transport length might be measured by transmission experiments and backscattering experiments. | https://en.wikipedia.org/wiki?curid=23003504 |
Tripartite Commission for the Restitution of Monetary Gold The Tripartite Commission for the Restitution of Monetary Gold, also known as the Tripartite Gold Commission, was a panel established in September 1946 by the United Kingdom, United States and France to recover gold stolen by Nazi Germany from other nations and eventually return it to the rightful owners. The Commission was headquartered in Brussels. After recovering gold and receiving claims for it, the Commission found that it had insufficient resources to pay back all of the countries in full. Thus, each country received about 65% of its claim from the gold reserves recovered by the Commission. The Commission completed its work and was formally dissolved on September 9, 1998. | https://en.wikipedia.org/wiki?curid=23005379 |
Metallurgical assay A metallurgical assay is a compositional analysis of an ore, metal, or alloy. Some assay methods are suitable for raw materials; others are more appropriate for finished goods. Raw precious metals (bullion) are assayed by an assay office. Silver is assayed by titration, gold by cupellation and platinum by inductively coupled plasma optical emission spectrometry (ICP OES). Precious metal items of art or jewelry are frequently hallmarked (depending upon the requirements of the laws of either the place of manufacture or the place of import). Where required to be hallmarked, semi-finished precious metal items of art or jewelry pass through the official testing channels where they are analyzed or assayed for precious metal content. While different nations permit a variety of legally acceptable finenesses, the assayer is actually testing to determine that the fineness of the product conforms with the statement or claim of fineness that the maker has claimed (usually by stamping a number such as 750 for 18k gold) on the item. In the past the assay was conducted by using the touchstone method but currently (most often) it is done using X-ray fluorescence (XRF). XRF is used because this method is more exacting than the touchstone test. The most exact method of assay is known as fire assay or cupellation. This method is better suited for the assay of bullion and gold stocks rather than works of art or jewelry because it is a completely destructive method | https://en.wikipedia.org/wiki?curid=23008816 |
Metallurgical assay The age-old touchstone method is particularly suited to the testing of very valuable pieces, for which sampling by destructive means, such as scraping, cutting or drilling is unacceptable. A rubbing of the item is made on a special stone, treated with acids and the resulting color compared to references. Red radiolarian chert or black siliceous slate were used to view the resultant treated streak of the sample. Differences in precious metal content as small as 10 to 20 parts per thousand can often be established with confidence by the test. However, it is not useful with white gold, for example, because the color variation among white gold alloys is almost imperceptible. The modern X-ray fluorescence is also a non-destructive technique that is suitable for normal assaying requirements. It typically has an accuracy of 2 to 5 parts per thousand and is well-suited to relatively flat and large surfaces. It is a quick technique taking about three minutes, and the results can be automatically printed out by computer. It also measures the content of the other alloying metals present. It is not indicated, however, for articles with chemical surface treatment or electroplating. The process for X-ray fluorescence assay involves melting the material in a furnace and stirring to make a homogeneous mix. Following this, a sample is taken from the centre of the molten sample. Samples are typically taken using a vacuum pin tube. The sample is then tested by X-ray fluorescence spectroscopy | https://en.wikipedia.org/wiki?curid=23008816 |
Metallurgical assay is typically completed in this way to ensure that an accurate assay is performed. X-ray fluorescence assay is not as accurate as fire assay but depending on the spectrometer used, can achieve results of within 1 percent. The most elaborately accurate, but totally destructive, precious metal assay is fire assay. (It may also be called by the critical cupellation step that separates precious metal from lead.) If performed on bullion (high purity precious metal alloy) to international standards, the method can be accurate on gold metal to 1 part in 10,000. If performed on ore materials using fusion followed by cupellation separation, detection may be in parts per billion. However, accuracy on ore material is typically limited to 3 to 5% of reported value. Although time consuming, the method is the accepted standard applied for valuing gold ore as well as gold and silver bullion at major refineries and gold mining companies. In the case of fire assaying of gold and platinum ores, the lengthy time required to carry out an assay is generally offset by carrying out large numbers of assays simultaneously, and a typical laboratory will be equipped with several fusion and cupellation furnaces, each capable of taking multiple samples, so that several hundred analyses per day can be carried out. The principal advantage of fire assay is that large samples can be used, and these increase the accuracy in analyzing low-yield ores in the <1g/T range of concentration | https://en.wikipedia.org/wiki?curid=23008816 |
Metallurgical assay Fusion: the process requires a self-generating reducing atmosphere, and so the crushed ore sample is mixed with fluxes and a carbon source (e.g. coal dust, ground charcoal, flour, etc.) mixed with powdered lead oxide (litharge) in a refractory crucible. In general, multiple crucibles will be placed inside an electric furnace fitted with silicon carbide heating elements, and heated to between 1000–1200 °C. The temperature required, and the type of flux used, are dependent on the composition of the rock in which the precious metals are concentrated, and in many laboratories an empirical approach based on long experience is used. A complex reaction takes place, whereby the carbon source reduces the lead oxide to lead, which alloys with the precious metals: at the same time, the fluxes combine with the crushed rock, reducing its melting point and forming a glassy slag. When fusion is complete, the sample is tipped into a mold (usually iron) where the slag floats to the top, and the lead, now alloyed with the precious metals, sinks to the bottom, forming a 'button'. After solidification, the samples are knocked out, and the lead bullets recovered for cupellation, or for analysis by other means. Method details for various fire assay procedures vary, but concentration and separation chemistry typically comply with traditions set by Bugby or Shepard & Dietrich in the early 20th century. Method advancements since that time primarily automate material handling and final finish measurements (i.e | https://en.wikipedia.org/wiki?curid=23008816 |
Metallurgical assay , instrument finish rather than physical gold product weighing). Arguably, even these texts are largely an extension of traditions that were detailed in "De re metallica" by Agricola in 1556. Variation from skills taught in modern standard adaptions of fire assay methodology should be viewed with caution. The standard traditions have a long history of reliability; "special" new methods frequently associate with reduced assay accuracy. Cupellation: the lead bullets are placed in porous crucibles (cupels) of bone ash or magnesium oxide and heated in air to about 1000 °C. This is usually carried out in a 'muffle' furnace, containing a refractory muffle (usually nitride-bonded silicon carbide) heated externally by silicon carbide heating elements. A flow of air through the muffle assists oxidation of the lead, and carries the fumes for safe collection outside the furnace unit. The lead melts and oxidises to lead oxide, which in turn melts and is drawn into the pores of the cupel by capillary attraction. The precious metals remain in the base of the cupel as a 'prill' which is sent for final analysis of precious metal content. In the bullion fire assay process, a sample from the article is wrapped in a lead foil with copper and silver. The wrapped sample, along with prepared control samples, heated at 1650 F (temperature varies with exact method) in a cupel made of compressed bone ash or magnesium oxide powder. Base metals oxidize and absorb into the cupel | https://en.wikipedia.org/wiki?curid=23008816 |
Metallurgical assay The product of this cupellation (doré) is flattened and treated in nitric acid to remove silver. Precision weighing of metal content of samples and process controls (proofs) at each process stage is the basis of the extreme method precision. European assayers follow bullion traditions based in hallmarking regulations. Reputable North American bullion assayers conform closely to ASTM method E1335-04e1. Only bullion methods validated and traceable to accepted international standards obtain genuine accuracies of 1 part in 10,000. Cupellation alone can only remove a limited quantity of impurities from a sample. Fire assay, as applied to ores, concentrates, or less pure metals, adds a fusion or scorification step before cupellation. A coin assayer is often assigned to each mint or assay office to determine and assure that all coins produced at the mint have the correct content or purity of each metal specified, usually by law, to be contained in them. This was particularly important when gold and silver coins were produced for circulation and used in daily commerce. Few nations, however, persist in minting silver or gold coins for general circulation. For example, the U.S. discontinued the use of gold in coinage in 1933. The U.S. was one of the last nations to discontinue the use of silver in circulating coins after its 1970 half dollar coin, although the amount of silver used in smaller denomination coins was ended after 1964 | https://en.wikipedia.org/wiki?curid=23008816 |
Metallurgical assay Even with the half dollar, the amount of silver used in the coins was reduced from 90% in 1964 and earlier to 40% between 1965 and 1970. Copper, nickel, cupro-nickel and brass alloys now predominate in coin making. Notwithstanding, several national mints, including the Perth Mint in Australia, the Austrian Mint, the British Royal Mint, the Royal Canadian Mint, the South African Mint, and the U.S. Mint continue to produce precious metal bullion coins for collectors and investors. The precious metal purity and content of these coins is guaranteed by the respective mint or government, and, therefore, the assay of the raw materials and finished coins is an important quality control. In the UK, the Trial of the Pyx is a ceremonial procedure for ensuring that newly minted coins conform to required standards. | https://en.wikipedia.org/wiki?curid=23008816 |
Sulfenyl chloride A sulfenyl chloride is a functional group with the connectivity R–S–Cl, where R is alkyl or aryl. Sulfenyl chlorides are reactive compounds that behave as sources of RS. They are used in the formation of RS–N and RS–O bonds. According to IUPAC nomenclature they are named as alkyl thiohypochlorites, i.e. esters of thiohypochlorous acid. Sulfenyl chlorides are typically prepared by chlorination of disulfides: This reaction is sometimes called the Zincke disulfide reaction, in recognition of Theodor Zincke. Typically, sulfenyl halides are stabilized by electronegative substituents. This trend is illustrated by the stability of CClSCl obtained by chlorination of carbon disulfide. Perchloromethyl mercaptan (CClSCl) reacts with N-H-containing compounds in the presence of base to give the sulfenamides: This method is used in the production of the fungicides Captan and Folpet. Sulfenyl chlorides add across alkenes: They undergo chlorination to the trichlorides: Sulfenyl chlorides can be converted to sulfinyl chlorides (RS(O)Cl). In one approach, the sulfinyl chloride is generated in two steps starting with reaction of a thiol with sulfuryl chloride, In some cases the sulfenyl chloride results instead, as happens with 2,2,2-trifluoro-1,1-diphenylethanethiol. A trifluoroperacetic acid oxidation then provides a general approach to formation of sulfinyl chlorides from sulfenyl chlorides: Sulfenyl bromides are also known | https://en.wikipedia.org/wiki?curid=23020713 |
Sulfenyl chloride Simple sulfenyl iodides are unknown because they are unstable with respect to the disulfide and iodine: Sulfenyl iodides can be isolated as stable compounds if they bear alkyl steric protecting groups as part of a cavity-shaped framework, illustrating the technique of kinetic stabilization of a reactive functionality, as in the case of sulfenic acids. A related class of compounds are the alkylsulfur trichlorides, as exemplified by methylsulfur trichloride, CHSCl. The corresponding selenenyl halides, e.g. CHSeCl, are more commonly encountered in the laboratory. Sulfenyl chlorides are used in the production of agents used in the vulcanization of rubber. | https://en.wikipedia.org/wiki?curid=23020713 |
Osmotic dehydration is an operation used for the partial removal of water from plant tissues by immersion in a hypertonic (osmotic) solution. Sugar or salt solutions are used to reduce the moisture content of foods before actual drying process. This technique is used to give the product quality improvement over conventional drying process. Mild heat treatment after osmotic dehydration favours colour and flavour retention resulting in the product having superior organoleptic characteristics. It also increases resistance to heat treatment, prevents enzymatic browning and inhibits activities of polyphenol oxidase. The process is economical. depends on: 1) Temperature of osmotic solution. 2) Concentration of the osmotic solution. 3) Osmotic agent used. 4) Process duration. 5) Geometry of food material. Water removal is based on the natural and non-destructive phenomenon of osmosis across cell membranes. The driving force for the diffusion of water from the tissue into the solution is provided by the higher osmotic pressure of the hyper-tonic solution. The diffusion of water is accompanied by the simultaneous counter diffusion of solutes from the osmotic solution into the tissue. Since the cell membrane responsible for osmotic transport is not perfectly selective, solutes present in the cells (organic acids, reducing sugars, minerals, flavors and pigment compounds) can also be leaked into the osmotic solution, which affects the organoleptic and nutritional characteristics of the product | https://en.wikipedia.org/wiki?curid=23021180 |
Osmotic dehydration The rate of diffusion of water from any material made up of such tissues depends upon factors such as temperature and concentration of the osmotic solution, the size and geometry of the material, the solution-to-material mass ratio and, to a certain level, agitation of the solution. | https://en.wikipedia.org/wiki?curid=23021180 |
Aluminium(II) oxide or aluminium monoxide is a compound of aluminium and oxygen with the chemical formula AlO. It has been detected in the gas phase after explosion of aluminized grenades in the upper atmosphere and in stellar absorption spectra. | https://en.wikipedia.org/wiki?curid=23022498 |
Aluminium oxides or aluminum oxides are a group of inorganic compounds with formulas including aluminium (Al) and oxygen (O). | https://en.wikipedia.org/wiki?curid=23022534 |
Vesicle fusion is the merging of a vesicle with other vesicles or a part of a cell membrane. In the latter case, it is the end stage of secretion from secretory vesicles, where their contents are expelled from the cell through exocytosis. Vesicles can also fuse with other target cell compartments, such as a lysosome. Exocytosis occurs when secretory vesicles transiently dock and fuse at the base of cup-shaped structures at the cell plasma membrane called porosome, the universal secretory machinery in cells. may depend on SNARE proteins in the presence of increased intracellular calcium (Ca) concentration. Stimuli that trigger vesicle fusion act by increasing intracellular Ca. Model systems consisting of a single phospholipid or a mixture have been studied by physical chemists. Cardiolipin is found mainly in mitochondrial membranes, and calcium ions play an important role in the respiratory processes mediated by the mitochondrion. The forces involved have been postulated to explain this process in terms of nucleation for agglomeration of smaller supramolecular entities or phase changes in the structure of the biomembranes. In synaptic vesicle fusion, the vesicle must be within a few nanometers of the target membrane for the fusion process to begin. This closeness allows the cell membrane and the vesicle to exchange lipids which is mediated by certain proteins which remove water that comes between the forming junction | https://en.wikipedia.org/wiki?curid=23022763 |
Vesicle fusion Once the vesicle is in position it must wait until Ca enters the cell by the propagation of an action potential to the presynaptic membrane. Ca binds to specific proteins, one of which is Synaptotagmin, in neurons which triggers the complete fusion of the vesicle with the target membrane. SNARE proteins are also thought to help mediate which membrane is the target of which vesicle. Assembly of the SNAREs into the "trans" complexes likely bridges the opposing lipid bilayers of membranes belonging to cell and secretory granule, bringing them in proximity and inducing their fusion. The influx of calcium into the cell triggers the completion of the assembly reaction, which is mediated by an interaction between the putative calcium sensor, synaptotagmin, with membrane lipids and/or the partially assembled SNARE complex. One hypothesis implicates the molecule Complexin within the SNARE complex and its interaction with the molecule synaptotagmin. Known as the "clamp" hypothesis, the presence of complexin normally inhibits the fusion of the vesicle to the cell membrane. However, binding of calcium ions to synaptotagmin triggers the complexin to be released or inactivated, so that the vesicle is then free to fuse. According to the "zipper" hypothesis, the complex assembly starts at the N-terminal parts of SNARE motifs and proceeds towards the C-termini that anchor interacting proteins in membranes | https://en.wikipedia.org/wiki?curid=23022763 |
Vesicle fusion Formation of the "trans"-SNARE complex proceeds through an intermediate complex composed of SNAP-25 and syntaxin-1, which later accommodates synaptobrevin-2 (the quoted syntaxin and synaptobrevin isotypes participate in neuronal neuromediator release). Based on the stability of the resultant "cis-SNARE complex", it has been postulated that energy released during the assembly process serves as a means for overcoming the repulsive forces between the membranes. There are several models that propose explanation of a subsequent step – the formation of stalk and fusion pore, but the exact nature of these processes remains debated. Two of the most prominent models on fusion pore formation are the lipid-lined and protein-lined fusion pore theories. One possible model for fusion pore formation is the lipid-line pore theory. In this model, once the membranes have been brought into sufficiently close proximity via the "zipper" mechanism of the SNARE complex, membrane fusion occurs spontaneously. It has been shown that when the two membranes are brought within a critical distance, it is possible for hydrophilic lipid headgroups of one membrane to merge with the opposing membrane. In the lipid-lined fusion pore model, the SNARE complex acts as a scaffold, pulling on the membrane, causing both membranes to pucker so they may reach the critical fusion distance. As the two membranes begin to fuse, a lipid-lined stalk is produced, expanding radially outward as fusion proceeds | https://en.wikipedia.org/wiki?curid=23022763 |
Vesicle fusion While a lipid-lined pore is possible and can achieve all the same properties observed in early pore formation, sufficient data does not exist to prove it is the sole method of formation. There is not currently a proposed mechanism on inter-cellular regulation for fluctuation of lipid-lined pores, and they would have a substantially more difficult time producing effects such as the "kiss-and-run" when compared with their protein-lined counterparts. Lipid-lined pores effectiveness would also be highly dependent on the composition of both membranes, and its success or failure could vary wildly with changes in elasticity and rigidity. Another possible model for fusion pore formation is the protein-lined pore theory. In this model, after activation of synaptotagmin by calcium, several SNARE complexes come together to form a ring structure, with synaptobrevin forming the pore in the vesicle membrane and Syntaxin forming the pore in the cell membrane. As the initial pore expands it incorporates lipids from both bilayers, eventually resulting in complete fusion of the two membranes. The SNARE complex has a much more active role in the protein-lined pore theory; because the pore consists initially entirely of SNARE proteins, the pore is easily able to undergo intercellular regulation, making fluctuation and "kiss-and-run" mechanisms easily attainable | https://en.wikipedia.org/wiki?curid=23022763 |
Vesicle fusion A protein-lined pore perfectly meets all the observed requirements of the early fusion pore, and while some data does support this theory, sufficient data does not exist to pronounce it the primary method of fusion. A protein-lined pore requires at least five copies of the SNARE complex while fusion has been observed with as few as two. In both theories the function of the SNARE complex remains largely unchanged, and the entire SNARE complex is necessary to initiate fusion. It has, however, been proven that "in vitro" Syntaxin "per se" is sufficient to drive spontaneous calcium independent fusion of synaptic vesicles containing v-SNAREs. This suggests that in Ca-dependent neuronal exocytosis synaptotagmin is a dual regulator, in absence of Ca ions to inhibit SNARE dynamics, while in presence of Ca ions to act as agonist in the membrane fusion process. In synaptic vesicles, some neurochemists have suggested that vesicles occasionally may not completely fuse with presynaptic membranes in neurotransmitter release into the synaptic cleft. The controversy lies in whether or not endocytosis always occurs in vesicle reforming after release of the neurotransmitter. Another proposed mechanism for release of vesicle contents into extracellular fluid is called kiss-and-run fusion. There is some indication that vesicles may only form a small pore in the presynaptic membrane allowing contents to be released by standard diffusion for a short while before retreating back into the presynaptic cell | https://en.wikipedia.org/wiki?curid=23022763 |
Vesicle fusion This mechanism may be a way around clathrin-mediated endocytosis. It is also proposed that the vesicle does not need to return to an endosome to refill, though it is not thoroughly understood by which mechanism it would refill. This does not exclude full vesicle fusion, but only states that both mechanisms may operate in synaptic clefts. "Kiss and run" has been shown to occur in endocrine cells, though it has not been directly witnessed in synaptic gaps. | https://en.wikipedia.org/wiki?curid=23022763 |
Lead-based paint in the United States Lead-based paint was widely used in the United States, because of its durability. The United States banned the manufacture of lead-based house paint in 1978 due to health concerns. Lead has long been considered to be a harmful environmental pollutant. Cited cases of lead poisoning date back to the early 20th century. In the July 1904 edition of its monthly publication, paint manufacturer Sherwin-Williams reported the dangers of paint containing lead, noting that a French expert had deemed lead paint "poisonous in a large degree, both for the workmen and for the inhabitants of a house painted with lead colors." Congress banned the use of lead-based paint in residential structures and environments, in 1971, in residential projects constructed by, or with the assistance of, the federal government, and the Consumer Product Safety Commission followed with implementing regulations, effective in 1978. Additional regulations regarding lead abatement, testing and related issues have been issued by the Environmental Protection Agency (EPA). Much of the government's response to the lead public health problems in the 1970s can be credited to the work of epidemiologist and pediatrician Philip J. Landrigan, who conducted detailed studies of lead poisoning near lead refineries, as well as the effects of lead in gasoline. In 1991, the Secretary of the Department of Health and Human Services, Louis Wade Sullivan, called lead the "number one environmental threat to the health of children in the United States | https://en.wikipedia.org/wiki?curid=23034778 |
Lead-based paint in the United States " Humans are exposed to lead in many ways. These can be through air, drinking water, food, contaminated soil, deteriorating paint, and dust. Airborne lead enters the body by breathing or swallowing lead particles or dust once it has settled. Old lead-based paint is the most significant source of lead exposure in the U.S. Most homes built before 1960 contain heavily leaded paint. Some homes built as recently as 1978 may also contain lead paint. The U.S. Centers for Disease Control and Prevention’s (CDC) National Center for Health Statistics monitors blood lead levels in the United States. Experts use a new level based on the U.S. population of children ages 1-5 years who are in the top 2.5% of children when tested for lead in their blood (when compared to children who are exposed to more lead than most children). Currently that is 5 micrograms of lead per deciliter of blood. The U.S. government defines "lead-based paint" as any "paint, surface coating that contains lead equal to or exceeding one milligram per square centimeter (1.0 mg/cm2) or 0.5% by weight." Some states have adopted this or similar definitions of "lead-based paint." These definitions are used to enforce regulations that apply to certain activities conducted in housing constructed prior to 1978, such as abatement, or the permanent elimination of a "lead-based paint hazard." The U.S. government and many states have regulations regarding lead-based paint. Many of them apply to evaluating a property for lead-based paint | https://en.wikipedia.org/wiki?curid=23034778 |
Lead-based paint in the United States There are two different testing procedures that are similar but yield different information. Lead-based paint inspections will evaluate all painted surfaces in a complex to determine where lead-based paint, if any, is present. The procedures for lead inspections is outlined in the United States Department of Housing and Urban Development (HUD) Guidelines, Chapter 7, 1997 Revision. The other testing is a lead-based paint risk assessment. In this testing, only deteriorated painted surfaces are tested and dust wipe samples are collected. This information will help the risk assessor determine if there are any "lead hazards". Many property owners decided to get a combination of both tests to determine where the lead-based paint is present and what hazards are present as well. Risk assessments are outlined in the HUD Guidelines, Chapter 5. In addition, if a child is poisoned in a property, the owner may be required to perform abatement (permanent elimination of the lead hazard). In 1996, the Department of Housing and Urban Development and the Environmental Protection Agency enacted the Lead-Based Paint Disclosure Regulation. It requires owners of pre-1978 "target housing" to disclose to potential buyers or renters all known information about the presence of lead-based paint and/or lead-based paint hazards in the property | https://en.wikipedia.org/wiki?curid=23034778 |
Lead-based paint in the United States It requires that the potential buyer or tenant be given the lead information pamphlet, "Protect Your Family From Lead In Your Home," or other EPA-approved pamphlet as well as a specific disclosure statement. The option of whether to test for the presence of lead-based paint is left to the owner, so long as a decision not to test is disclosed. The EPA issued a new regulation called 'Renovation, Repair and Painting' (RRP) regarding the renovation of residential housing and child-occupied buildings built before 1978 on April 22, 2008. The rule (Federal Register: July 15, 2009 (Volume 74, Number 134)) became effective April 22, 2010. Under the rule, contractors performing renovation, repair and painting projects that disturb lead-based coatings (including lead paint, shellac or varnish) in child-occupied facilities built before 1978 must be certified and must follow specific work practices to prevent lead contamination. EPA’s RRP rule impacts many construction trades, including general contractors and special trade contractors, painters, plumbers, carpenters, glaziers, wood floor refinishers and electricians. Activities performed by all of these trades can disturb lead-based paint and have the potential to create hazardous lead dust. For most individuals, eight hours of training is required | https://en.wikipedia.org/wiki?curid=23034778 |
Lead-based paint in the United States However, individuals who have successfully completed renovation courses developed by HUD or EPA, or an abatement worker or supervisor course accredited by EPA or an authorized State or Tribal program, can become certified renovators by taking a four-hour EPA-accredited renovator refresher training. The RRP rule is controversial, primarily due to the increased cost remodelers incur as a result of having to set up dust containment apparatuses, including sealing off doorways and HVAC ducts with plastic. Various national trade associations have been very vocal in their opposition, some going so far as to sue the EPA. Though the EPA considered expanding the rule to require contractors to pass a third-party dust wipe clearance exam these revisions were rejected in July, 2011. Although the rule was not fully implemented until April 2010, certain elements were required before, and others required attention well before April 2010. The state of Rhode Island filed a public nuisance lawsuit in 1999 ("State of Rhode Island v. Lead Industries Association") to force the former manufacturers of lead paint to pay for the cleanup of current lead hazards in Rhode Island. After a trial that ended in a hung jury in 2002, the state refiled the case. In February 2006, the jury decided in favor of the state and said that Sherwin-Williams, NL Industries and Millennium Holdings would have to pay for the clean-up of lead paint in the state | https://en.wikipedia.org/wiki?curid=23034778 |
Lead-based paint in the United States On July 1, 2008, the Rhode Island Supreme Court in a landmark decision overturned the verdict, dismissing the case stating that "the State of Rhode Island 'cannot allege' facts sufficient to state a claim for common law public nuisance against lead pigment manufacturers." In 2007, the Missouri Supreme Court and the New Jersey Supreme Court also rejected the use of the public nuisance theory in lead paint lawsuits, leaving Ohio and California as the only two remaining public nuisance cases. The California Supreme Court has reviewed the contingency fee agreement between the municipalities and private counsel. A briefing schedule is currently being set. But in recent rulings the Supreme Court held the contingent fee agreement is improper stating that “When a government attorney has a personal interest in the litigation, the neutrality so essential to the system is violated.” While the City of Columbus, Ohio voluntarily dropped its lawsuit against the paint industry after the Rhode Island decision, the State of Ohio's suit remains. Humans can be poisoned during unsafe renovations or repainting jobs on housing that has lead paint. Therefore, homeowners are encouraged to carefully stabilize any deteriorated (peeling, chipping, cracking, etc.) paint in a lead-safe manner. More than 250,000 children in the United States have significantly harmful levels of lead in their bodies. There is no safe level of exposure | https://en.wikipedia.org/wiki?curid=23034778 |
Lead-based paint in the United States Dry sanding, dry scraping, removing paint by torching and burning, the use of heat guns over 1100°F, and machine-sanding or grinding without a HEPA filtered dust collection system or a HEPA-filtered vacuum are all prohibited by the United States Department of Housing and Urban Development (HUD) as methods of removing lead-based-paint. HUD prohibits these methods because they have been proven to create significant levels of lead dust during remodeling, renovation and painting. The use of these methods should be avoided because they significantly increase the chance to become lead poisoned. Paint strippers are also often used to remove lead-based-paint from walls. There are specialized paint strippers for use with lead paint which render lead non-hazardous decreasing the risks associated with lead paint removal. HUD requires a dust test for "clearance" at the end of any remodeling or repainting job be performed by a third-party professional who is independent of the entity performing the work. Lead evaluations of paint are usually performed by a field testing method known as X-Ray fluorescence (XRF) using equipment which can effectively detect lead. XRF is the preferred method because it is not destructive and a reading is usually obtained in about 4–8 seconds with a 95% accuracy at the 2-sigma level. Instruments of this sort have an inconclusive range, and when a reading falls in this range (range is different for each instrument and model), a paint chip may be taken and sent for laboratory analysis | https://en.wikipedia.org/wiki?curid=23034778 |
Lead-based paint in the United States Testing for lead in dust, water, and air also require laboratory analysis. Although there are commercially available lead test kits, they are not reliable and are not authorized by HUD for the use of determining if a property is lead-based-paint free. The home's year of construction can be a clue as to the likelihood that lead is present in its paint. As of April 2011, 87% of homes built before 1940 contain at least some lead paint, homes built between 1940 and 1960 have a 69% chance of containing such paint, homes built between 1960 and 1978 have a 24% chance of containing lead paint, while homes built after 1978 are unlikely to have lead-based paint. The U.S. Department of Housing and Urban Development's Office of Healthy Homes and Lead Hazard Control performs regular studies of housing-based health hazards in the U.S. | https://en.wikipedia.org/wiki?curid=23034778 |
Environmental impact of paint The environmental impact of paint is diverse. Traditional painting materials and processes can have harmful effects on the environment, including those from the use of lead and other additives. Measures can be taken to reduce environmental impact, including accurately estimating paint quantities so waste is minimized, and use of environmentally preferred paints, coating, painting accessories, and techniques. The United States Environmental Protection Agency guidelines and Green Star standards can be applied. Volatile organic compounds are gases emitted by various solids or liquids, many of which have short- and long-term adverse health effects. Solvents in traditional paints often contain high quantities of VOCs. Low VOC paints improve indoor air quality and reduce urban smog. The beneficial characteristics of such paints include low odor, clean air, and safer technology, as well as excellent durability and a washable finish. Low-VOC paint types include latex (water-based), recycled latex (water-based), acrylic, and milk paint. The labels of paint cans can be checked for the following information: In the US, items containing toxic ingredients have registration numbers with either the: Antifouling paint (or bottom paint) is used to protect the hulls of boats from fouling by marine organisms. Antifouling paint protects the surface from corrosion and prevents drag on the ship from any build-up of marine organisms | https://en.wikipedia.org/wiki?curid=23035042 |
Environmental impact of paint These paints have contained organotin compounds such as tributyltin, which are considered to be toxic chemicals with negative effects on humans and the environment. Tributyltin compounds are moderately to highly persistent organic pollutants that bioconcentrate up the marine predators' food chain. One common example is it leaching from marine paints into the aquatic environment, causing irreversible damage to the aquatic life. Tributyltin has also been linked to obesity in humans, as it triggers genes that cause the growth of fat cells. Tributyltin is harmful to some marine organisms, including the dog whelk, it causes dog whelks to suffer from imposex; females develop male sexual characteristics such as a penis. This causes them to become infertile or even die. In severe cases, males can develop egg sacs. Alternatives include biomimetic antifouling coatings. Heavy metals are used in paints and have raised concerns due to their toxicity at high levels of exposure and since they build up in the food chain. Lead paint contains lead as pigment. Lead is also added to paint to speed drying, increase durability, retain a fresh appearance, and resist moisture that causes corrosion. Paint with significant lead content is still used in industry and by the military. For example, leaded paint is sometimes used to paint roadways and parking lot lines. Lead, a poisonous metal, can damage nerve connections (especially in young children) and cause blood and brain disorders | https://en.wikipedia.org/wiki?curid=23035042 |
Environmental impact of paint Because of lead's low reactivity and solubility, lead poisoning usually only occurs in cases when it is dispersed, such as when sanding lead-based paint prior to repainting. Primer paint containing hexavalent chromium is still widely used for aerospace and automobile refinishing applications. Zinc chromate has been used as a pigment for artists' paint, known as zinc yellow or yellow 36. It is highly toxic and now rarely used. As a response to the environmental and health concerns, some paint manufacturers now offer environmentally friendly alternatives. Also, in some countries, paint recycling is carried out on surplus paints and resold. Products like ECOBOND LBP are available to treat lead. Ecobond can chemically change lead to make it less leechable and, therefore, easier on the environment. | https://en.wikipedia.org/wiki?curid=23035042 |
Fibrin scaffold A fibrin scaffold is a network of protein that holds together and supports a variety of living tissues. It is produced naturally by the body after injury, but also can be engineered as a tissue substitute to speed healing. The scaffold consists of naturally occurring biomaterials composed of a cross-linked fibrin network and has a broad use in biomedical applications. Fibrin consists of the blood proteins fibrinogen and thrombin which participate in blood clotting. Fibrin glue or fibrin sealant is also referred to as a fibrin based scaffold and used to control surgical bleeding, speed wound healing, seal off hollow body organs or cover holes made by standard sutures, and provide slow-release delivery of medications like antibiotics to tissues exposed. use is helpful in repairing injuries to the urinary tract, liver lung, spleen, kidney, and heart. In biomedical research, fibrin scaffolds have been used to fill bone cavities, repair neurons, heart valves, vascular grafts and the surface of the eye. The complexity of biological systems requires customized care to sustain their function. When they are no longer able to perform their purpose, interference of new cells and biological cues is provided by a scaffold material. has many aspects like being biocompatible, biodegradable and easily processable. Furthermore, it has an autologous nature and it can be manipulated in various size and shape. Inherent role in wound healing is helpful in surgical applications | https://en.wikipedia.org/wiki?curid=23037879 |
Fibrin scaffold Many factors can be bound to fibrin scaffold and those can be released in a cell-controlled manner. Its stiffness can be managed by changing the concentration according to needs of surrounding or encapsulated cells. Additional mechanical properties can be obtained by combining fibrin with other suitable scaffolds. Each biomedical application has its own characteristic requirement for different kinds of tissues and recent studies with fibrin scaffold are promising towards faster recovery, less complications and long-lasting solutions. is an important element in tissue engineering approaches as a scaffold material. It is advantageous opposed to synthetic polymers and collagen gels when cost, inflammation, immune response, toxicity and cell adhesion are concerned. When there is a trauma in a body, cells at site start the cascade of blood clotting and fibrin is the first scaffold formed normally. To achieve in clinical use of a scaffold, fast and entire incorporation into host tissue is essential. Regeneration of the tissue and the degradation of the scaffold should be balanced in terms of rate, surface area and interaction so that ideal templating can be achieved. Fibrin satisfies many requirements of scaffold functions. Biomaterials made up of fibrin can attach many biological surfaces with high adhesion. Its biocompatibility comes from being not toxic, allergenic or inflammatory. By the help of fibrinolysis inhibitors or fiber cross-linkers, biodegradation can be managed | https://en.wikipedia.org/wiki?curid=23037879 |
Fibrin scaffold Fibrin can be provided from individuals to be treated many times so that gels from autologous fibrin have no undesired immunogenic reactions in addition to be reproducible. Inherently, structure and biochemistry of fibrin has an important role in wound healing. Although there are limitations due to diffusion, exceptional cellular growth and tissue development can be achieved. According to the application, fibrin scaffold characteristics can be adjustable by manipulating concentrations of components. Long-lasting durable fibrin hydrogels are enviable in many applications. Polymerization time of fibrinogen and thrombin is affected primarily by concentration of thrombin and temperature, while fibrinogen concentration has a minor effect. Fibrin gel characterization by scanning electron microscopy reveals that thick fibers make up a dense structure at lower fibrinogen concentrations (5 mg/ml) and thinner fibers and looser gel can be obtained as fibrinogen concentration (20 mg/ml) increases whereas increase in thrombin concentration (from 0.5 U/ml to 5 U/ml) has no such significant result although the fibers steadily get thinner. Fibrin gels can be enriched by addition of other extracellular matrix (ECM) components such as fibronectin, vitronectin, laminin and collagen. These can be linked covalently to fibrin scaffold by reactions catalyzed by transglutaminase. Laminin originated substrate amino acid sequences for transglutaminase can be IKVAV, YIGSR or RNIAEIIKDI | https://en.wikipedia.org/wiki?curid=23037879 |
Fibrin scaffold Collagen originated sequence is DGEA and many other ECM protein originated RGD sequence can be given as other examples. Heparin binding sequences KβAFAKLAARLYRKA, RβAFARLAARLYRRA, KHKGRDVILKKDVR, YKKIIKKL are from antithrombin III, modified antithrombin III, neural cell adhesion molecule and platelet factor 4, respectively. Heparin-binding growth factors can be attached to heparin binding domains via heparin. As a result, a reservoir can be provided instead of passive diffusion by liberation of growth factors in extended time. Acidic and basic fibroblast growth factor, neurotrophin 3, transforming growth factor beta 1, transforming growth factor beta 2, nerve growth factor, brain derived neurotrophic factor can be given as examples for such growth factors. For some tissues like cartilage, highly dense polymeric scaffolds such as polyethylene glycol (PEG) are essential due to mechanical stress and that can be achieved by combining them with natural biodegradable cell-adhesive scaffolds since cells can not attach to synthetic polymers and take proper signals for normal cell function. Various scaffold combinations with PEG-based hydrogels are studied to assess the chondrogenic response to dynamic strain stimulation in a recent study. PEG-Proteoglycan, PEG-Fibrinogen, PEG-Albumin conjugates and only PEG including hydrogels are used to evaluate the mechanical effect on bovine chondrocytes by using a pneumatic reactor system | https://en.wikipedia.org/wiki?curid=23037879 |
Fibrin scaffold The most substantial increase in stiffness is observed in PEG-Fibrinogen conjugated hydrogel after 28 days of mechanical stimulation. In orthopedics, methods with minimum invasion are desired and improving injectable systems is a leading aim. Bone cavities can be filled by polymerizing materials when injected and adaptation to the shape of the cavity can be provided. Shorter surgical operation time, minimum large muscle retraction harm, smaller scar size, less pain after operation and consequently faster recovery can be obtained by using such systems. In a study to evaluate if injectable fibrin scaffold is helpful for transplantation of bone marrow stromal cell (BMSC) when central nervous system (CNS) tissue is damaged, Yasuda et al. found that BMSC has extended survival, migration and differentiation after transplantation to rat cortical lesion although there is complete degradation of fibrin matrix after four weeks. Another study to assess if fibrin glue enriched with platelet is better than just platelet rich plasma (PRP) on bone formation was conducted. Each combined with bone marrow mesenchymal stem cells and bone morphogenetic protein 2 (BMP-2) are injected into the subcutaneous space. Results shows that fibrin glue enriched with platelet has better osteogenic properties when compared to PRP. To initiate and speed up tissue repair and regeneration, platelet-rich fibrin gels are ideal since they have a high concentration of platelet releasing growth factors and bioactive proteins | https://en.wikipedia.org/wiki?curid=23037879 |
Fibrin scaffold Addition of fibrin glue to calcium phosphate granules has promising results leading to faster bone repair by inducing mineralization and possible effects of fibrin on angiogenesis, cell attachment and proliferation. Valvular heart disease is a major cause of death globally. Both mechanical valves and fixed biological xenograft or homografts used clinically have many drawbacks. One study focused on fibrin-based heart valves to assess structure and mechanical durability on sheep revealed promising potential for patient originated valve replacements. From autologous arterial-derived cells and fibrin scaffold, tissue engineered heart valves are formed, then mechanically conditioned and transplanted into the pulmonary trunk of the same animals. The preliminary result are potentially hopeful towards autologous heart valve production. In atherosclerosis, a severe disease in modern society, coronary blood vessels occlude. These vessels have to be freed and held open i.e. by stents. Unfortunately after certain time these vessels close again and have to be bypassed to allow for upkeep of circulation. Usually autologous vessels from the patient or synthetic polymer grafts are used for this purpose. Both options have disadvantages. Firstly there are only few autologous vessels available in a human body that might be of low quality, considering the health status of the patient | https://en.wikipedia.org/wiki?curid=23037879 |
Fibrin scaffold The synthetic polymer based grafts on the other hand often have insufficient haemocompatibility and thus rapidly occlude - a problem that is especially prone in small calibre grafts. In this context the fibrin-gel-based tissue engineering of autologous vessel substitutes is a very promising approach to overcome the current problems. Cells and fibrin are isolated by a low invasive procedure from the patient and shaped in individual moulds to meet the required dimensions. Additional pre-cultivation in a specialized bioreactor is inevitable to ensure appropriate properties of the graft. Bullous keratopathy that is characterized by corneal stromal edema related to cell loss and endothelial decompensation as well as subepithelial fibrosis and corneal vascularization in further cases, results vision problems due to loss of corneal transparency. Fibrin glue is used as a sutureless method onto the corneal surface to fix amniotic membrane that is cryopreserved. Complete re-epithelialization on the ocular surface with no symptom is achieved in 3 weeks. Results show that fibrin glue fixation is easy, reliable and efficient with the corneal surface. Because fibrin fulfills the mechanical aspects of neuronal growth without initiation of glial proliferation, it can be potentially used in neuronal wound healing even with no need of growth factors or such constituents. Neurons and astrocytes, two major cell type of central nervous system, can show various responses to differences in matrix stiffness | https://en.wikipedia.org/wiki?curid=23037879 |
Fibrin scaffold Neuronal development of precursor cells is maintained by gels with low elastic modulus. When stiffness of the matrix is more than that of a normal brain, extension of spinal cord and cortical brain neurons is inhibited since neurite extension and branch forming take place on soft materials (<1000Pa). In a study, fibrins from different species are used to compare the effects on neurite growth of mouse spinal cord neurons. Among salmon, bovine and human fibrin in addition to Matrigel, salmon fibrin promotes the neurite growth best and it is more proteolysis resistant than mammalian fibrins. Because down to 0 °C, salmon fibrinogen can clot whereas polymerization of human fibrinogen occurs slowly below 37 °C, this can be taken as an advantage in surgical settings that are cooler. Therefore, for treatment of central nervous system damages, salmon fibrin can be a useful biomaterial. For sciatic nerve regeneration, fibrin scaffold is used with glial derived neurotrophic factor (GDNF) in a recent study. Survival of both sensory and motor neurons is promoted by glial-derived neurotrophic factor and its delivery to peripheral nervous system improves regeneration after an injury. GDNF and nerve growth factor (NGF) is sequestered in the gel via a bi-domain peptide. This peptide is composed of heparin binding domain and transglutaminase substrate domain which can be cross-linked into the fibrin matrix by polymerization via transglutaminase activity of factor XIIIa | https://en.wikipedia.org/wiki?curid=23037879 |
Fibrin scaffold Many neurotrophic factors can bind to heparin through its sulfated domains. This is the affinity-based delivery system in which growth factors are released by cell-based degradation control. After a 13 mm rat sciatic nerve defect is made, the fibrin matrix delivery system is applied to the gap as a nerve guiding channel. Results show that such a delivery system is efficient to enhance maturity and promote organized architecture of nerve regenerating in presence of GDNF, in addition to expressing the promising treatment variations for peripheral nerve injuries. The use of fibrin hydrogel in gene delivery (transfection) is studied to address essential factors controlling the delivery process such as fibrinogen and pDNA concentration in addition to significance of cell-mediated fibrin degradation for pursuing the potential of cell-transfection microarray engineering or in vivo gene transfer. Gene transfer is more successful in-gel than on-gel probably because of proximity of lipoplexes and target cells. Less cytotoxicity is observed due to less use of transfection agents like lipofectamine and steady degradation of fibrin. Consequently, each cell type requires optimization of fibrinogen and pDNA concentrations for higher transfection yields and studies towards high-throughput transfection microarray experiments are promising. | https://en.wikipedia.org/wiki?curid=23037879 |
SrCO3 SrCO may refer to: | https://en.wikipedia.org/wiki?curid=23042642 |
Nicking enzyme amplification reaction Nicking Enzyme Amplification Reaction (NEAR) is a method for "in vitro" DNA amplification like the polymerase chain reaction (PCR). NEAR is isothermal, replicating DNA at a constant temperature using a polymerase (and nicking enzyme) to exponentially amplify the DNA at a temperature range of 55 °C to 59 °C. One disadvantage of PCR is that it consumes time uncoiling the double-stranded DNA with heat into single strands (a process called denaturation) . This leads to amplification times typically thirty minutes or more for significant production of amplified products. Potential advantages of NEAR over PCR are increased speed and lower energy requirements, characteristics that are shared with other isothermal amplification schemes. A major disadvantage of NEAR relative to PCR is that production of nonspecific amplification products is a common issue with isothermal amplification reactions. The NEAR reaction uses naturally occurring or engineered endonucleases that introduce a strand break on only one strand of a double-stranded DNA cleavage site. The ability of several of these enzymes to catalyze isothermal DNA amplification was disclosed but not claimed in the patents issued for the enzymes themselves. | https://en.wikipedia.org/wiki?curid=23046982 |
2-Acetylaminofluorene (AAF, 2-AAF) is a carcinogenic and mutagenic derivative of fluorene. It is used as a biochemical tool in the study of carcinogenesis. It induces tumors in a number of species in the liver, bladder and kidney. The metabolism of this compound in the body by means of biotransformation reactions is the key to its carcinogenicity. 2-AAF is a substrate for cytochrome P-450 (CYP) enzyme, which is a part of a super family found in almost all organisms. This reaction results in the formation of hydroxyacetylaminofluorene which is a proximal carcinogen and is more potent than the parent molecule. The "N"-hydroxy metabolite undergoes several enzymatic and non-enzymatic rearrangements. It can be O-acetylated by cytosolic N-acetyltransferase enzyme to yield "N"-acetyl-"N"-acetoxyaminofluorene. This intermediate can spontaneously rearrange to form the arylamidonium ion and a carbonium ion which can interact directly with DNA to produce DNA adducts. In addition to esterification by acetylation, the "N"-hydroxy derivative can be "O"-sulfated by cytosolic sulfur transferase enzyme giving rise to the "N"-acetyl-"N"-sulfoxy product. In addition, the cytosolic "N","O"-aryl hydroxamic acid acyltransferase enzyme catalyzes the transfer of the acetyl group from the N atom of the N-OH-2-AAF to the O atom of the N-OH group to produce N-acetoxy-2-aminofluorene (N-OH-2-AF). This reactive metabolite spontaneously decomposes to form a nitrenium ion which will also react with DNA | https://en.wikipedia.org/wiki?curid=23047742 |
2-Acetylaminofluorene However, the product of this latter reaction is the deacetylated aminofluorene adduct. The interconversion of amide and amine metabolites of 2-AAF can further occur via the microsomal enzyme deacetylase producing the "N"-hydroxy metabolite of the amine derivative. Subsequent esterification of the aryl hydroxylamine by sulfur transferase yields the sulfate ester which also spontaneously decompose to form nitrenium ion. The reactive nitrenium, carbonium and arylamidonium ion metabolites of 2-AAF react with the nucleophilic groups in DNA, proteins and endogenous thiols like glutathione. Other metabolites such as the "N","O"-glucuronide, although not directly activated products, can be important in the carcinogenic process because they are capable of degradation to proximal "N"-hydroxy metabolites. This metabolite is presumed to be involved in formation of bladder tumors. The mechanism for this is thought to involve degradation of glucuronide in the bladder due to acidic pH of urine. | https://en.wikipedia.org/wiki?curid=23047742 |
Nicking enzyme A nicking enzyme (or nicking endonuclease) is an enzyme that cuts one strand of a double-stranded DNA at a specific recognition nucleotide sequences known as a restriction site. Such enzymes hydrolyse (cut) only one strand of the DNA duplex, to produce DNA molecules that are “nicked”, rather than cleaved. They can be used for strand-displacement amplification, Nicking Enzyme Amplification Reaction, exonucleotyic degradation, the creation of small gaps, or nick translation. The latter process has been successfully used to incorporate both radioactively labelled nucleotides and fluorescent nucleotides allowing specific regions on a double stranded DNA to be studied. Over 200 nicking enzymes have been studied, and 13 of these are available commercially and are routinely used for research and in commercial products. | https://en.wikipedia.org/wiki?curid=23048210 |
Avogadro (software) Avogadro is a molecule editor and visualizer designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science, and related areas. It is extensible via a plugin architecture. | https://en.wikipedia.org/wiki?curid=23057806 |
Extensible Computational Chemistry Environment The (ECCE, pronounced "etch-ā") provides a sophisticated graphical user interface, scientific visualization tools, and the underlying data management framework enabling scientists to efficiently set up calculations and store, retrieve, and analyze the rapidly growing volumes of data produced by computational chemistry studies. | https://en.wikipedia.org/wiki?curid=23058094 |
Glyoxylate and dicarboxylate metabolism describes a variety of reactions involving glyoxylate or dicarboxylates. Glyoxylate is the conjugate base of glyoxylic acid, and within a buffered environment of known pH such as the cell cytoplasm these terms can be used almost interchangeably, as the gain or loss of a hydrogen ion is all that distinguishes them, and this can occur in the aqueous environment at any time. Likewise dicarboxylates are the conjugate bases of dicarboxylic acids, a general class of organic compounds containing two carboxylic acid groups, such as oxalic acid or succinic acid. A compact graphical description of major biochemical reactions involved can be found at KEGG This provides information on the relevant enzymes and details the relationship with several other metabolic processes: glycine, serine, and threonine metabolism which provides hydroxypyruvate and glyoxylate, purine metabolism which provides glyoxylate, pyruvate metabolism which provides (S)-malate and formate, carbon fixation which consumes 3-phospho-D-glycerate and provides D-ribulose 1,5-P2, ascorbate and aldarate metabolism which shares tartronate-semialdehyde, nitrogen metabolism which shares formate, pyruvate metabolism and the citrate cycle which share oxaloacetate, and vitamin B metabolism which consumes glycolaldehyde. The glyoxylate cycle describes an important subset of these reactions involved in biosynthesis of carbohydrates from fatty acids or two-carbon precursors which enter the system as acetyl-coenzyme A | https://en.wikipedia.org/wiki?curid=23060790 |
Glyoxylate and dicarboxylate metabolism Its crucial enzymes are isocitrate lyase and malate synthase. However, alternate pathways have been proposed in organisms lacking isocitrate lyase. | https://en.wikipedia.org/wiki?curid=23060790 |
Optical modulators using semiconductor nano-structures An optical modulator is an optical device which is used to modulate a beam of light with a perturbation device. It is a kind of transmitter to convert information to optical binary signal through optical fiber (optical waveguide) or transmission medium of optical frequency in fiber optic communication. There are several methods to manipulate this device depending on the parameter of a light beam like amplitude modulator (majority), phase modulator, polarization modulator etc. The easiest way to obtain modulation is modulation of intensity of a light by the current driving the light source (laser diode). This sort of modulation is called direct modulation, as opposed to the external modulation performed by a light modulator. For this reason, light modulators are called external light modulators. According to manipulation of the properties of material modulators are divided into two groups, absorptive modulators (absorption coefficient) and refractive modulators (refractive index of the material). Absorption coefficient can be manipulated by Franz-Keldysh effect, Quantum-Confined Stark Effect, excitonic absorption, or changes of free carrier concentration. Usually, if several such effects appear together, the modulator is called electro-absorptive modulator. Refractive modulators most often make use of electro-optic effect (amplitude & phase modulation), other modulators are made with acousto-optic effect, magneto-optic effect such as Faraday and Cotton-Mouton effects | https://en.wikipedia.org/wiki?curid=23079699 |
Optical modulators using semiconductor nano-structures The other case of modulators is spatial light modulator (SLM) which is modified two dimensional distribution of amplitude & phase of an optical wave. Optical modulators can be implemented using Semiconductor Nano-structures to increase the performance like high operation, high stability, high speed response, and highly compact system. Highly compact electro-optical modulators have been demonstrated in compound semiconductors. However, in silicon photonics, electro-optical modulation has been demonstrated only in large structures, and is therefore inappropriate for effective on-chip integration. Electro-optical control of light on silicon is challenging owing to its weak electro-optical properties. The large dimensions of previously demonstrated structures were necessary to achieve a significant modulation of the transmission in spite of the small change of refractive index of silicon. Liu et al. have recently demonstrated a high-speed silicon optical modulator based on a metal–oxide–semiconductor (MOS) configuration. Their work showed a high-speed optical active device on silicon—a critical milestone towards optoelectronic integration on silicon. An electro-optic modulator is a device which can be used for controlling the power, phase or polarization of a laser beam with an electrical control signal. It typically contains one or two Pockels cells, and possibly additional optical elements such as polarizers | https://en.wikipedia.org/wiki?curid=23079699 |
Optical modulators using semiconductor nano-structures The principle of operation is based on the linear electro-optic effect (the Pockels effect, the modification of the refractive index of a nonlinear crystal by an electric field in proportion to the field strength). The crystal which is covered by electrode may be considered to be a voltage-variable wave-plate. When a voltage is applied, the retardation of laser polarization of the light would be changed while a beam passes through an ADP crystal. This variation in polarization results in intensity modulation downstream from the output polarizer. The output polarizer converts the phase shift into an amplitude modulation. Micrometre-scale silicon electro-optic modulator This device was fabricated a shape of the p-i-n ring resonator on a silicon-on-insulator substrate with a 3-mm-thick buried oxide layer. Both the waveguide coupling to the ring and that forming the ring have awidth of 450 nm and a height of 250 nm. The diameter of the ring is 12 mm, and the spacing between the ring and the straight waveguide is 200 nm. Acousto-optic modulators are used to vary and control laser beam intensity. A Bragg configuration gives a single first order output beam, whose intensity is directly linked to the power of RF control signal. The rise time of the modulator is simply deduced by the necessary time for the acoustic wave to travel through the laser beam. For highest speeds the laser beam will be focused down, forming a beam waist as it passes through the modulator | https://en.wikipedia.org/wiki?curid=23079699 |
Optical modulators using semiconductor nano-structures In an AOM a laser beam is caused to interact with a high frequency ultrasonic sound wave inside an optically polished block of crystal or glass (the interaction medium). By carefully orientating the laser with respect to the sound waves the beam can be made to reflect off the acoustic wave-fronts (Bragg diffraction). Therefore, when the sound field is present the beam is deflected and when it is absent the beam passes through undeviated. By switching the sound field on and off very rapidly the deflected beam appears and disappears in response (digital modulation). By varying the amplitude of the acoustic waves the intensity of the deflected beam can similarly be modulated (analogue modulation). Acoustic solitons in semiconductor nanostructures Acoustic solitons strongly influence the electron states in a semiconductor nanostructure. The amplitude of soliton pulses is so high that the electron states in a quantum well make temporal excursions in energy up to 10 meV. The subpicosecond duration of the solitons is less than the coherence time of the optical transition between the electron states and a frequency modulation of emitted light during the coherence time (chirping effect) is observed. This system is for an ultrafast control of electron states in semiconductor nanostructures. A dc magnetic field Hdc is applied perpendicular to the light propagation direction to produce a single domain, transverse directed 4~Ms | https://en.wikipedia.org/wiki?curid=23079699 |
Optical modulators using semiconductor nano-structures The rf modulation field Hrf, applied by means of a coil along the light propagation direction, wobbles 4~Ms through an angle of @ and produces a time varying magnetization component in the longitudinal direction. This component then produces an ac variation in the plane of polarization via the longitudinal Faraday effect. Conversion to amplitude modulation is accomplished by the indicated analyzer. Wideband magneto-optic modulation in a bismuth-substituted yttrium iron garnet waveguide The current transient creates a time-varying magnetic field that has a component along the direction of optical propagation. This component (underneath the microstrip line) acts to tip the magnetization, M, along the propagation direction of the optical beam. A static in-plane magnetic field, by, is applied perpendicular to the light propagation direction, thus ensuring the return of M to its initial orientation after the passage of the current transient. Depending on the component of the magnetization along the z-direction, Mz, the optical beam experiences a rotation of its polarization due to the Faraday effect. The polarization modulation is converted into an intensity modulation via a polarization analyzer, which is detected by a high-speed photodiode. MODULATION OF THz RADIATION BY SEMICONDUCTOR NANOSTRUCTURES As a result of increased demand for bandwidth, wireless short-range communication systems are expected to extend into the THz frequency range | https://en.wikipedia.org/wiki?curid=23079699 |
Optical modulators using semiconductor nano-structures Therefore, the fundamental interactions between THz radiation and semiconductors are receiving increasing attention. This new quantum structure is based on the well-established technology for producing high electron mobility transistors where an electron gas is confined at a GaAs/AlxGa1 xAs interface. The electron density at the hetero-interface can be controlled by the application of an external gate voltage, which in turn will alter the transmission/reflection characteristics of the device to an incident THz beam. 40 Gbit/s Phase Modulator The 40 Gbit/s Phase Modulator is a high performance, low drive voltage External Optical Modulator designed for customers developing next generation 40G transmission systems. The increased bandwidth allows for chirp control in high-speed data communications. Applications ; Chirp Control for High-Speed Communications (SONET OC-768 Interfaces, SDH STM-256 Interfaces), Coherent communications, C & L Band Operation, Optical Sensing, All-optical frequency shifting. Applications ; acousto-optic modulators include laser printing, video disk recording, laser projection systems. | https://en.wikipedia.org/wiki?curid=23079699 |
CataCXium F sulf is a water-soluble organophosphorus compound derived from fluorene. The palladium complexes of the respective phosphine show an excellent activity in various palladium-catalyzed coupling reactions, including Suzuki reactions, Sonogashira couplings and Buchwald–Hartwig reactions. | https://en.wikipedia.org/wiki?curid=23079724 |
Stopping and Range of Ions in Matter (SRIM) is a group of computer programs which calculate interaction of ions with matter; the core of SRIM is a program Transport of ions in matter (TRIM). SRIM is popular in the ion implantation research and technology community and also used widely in other branches of radiation material science. SRIM originated in 1980 as a DOS based program then called TRIM. The DOS version was upgraded until 1998 and is still available for download. It will run on a Unix PC having a DOS emulator. SRIM-2000 requires a computer with any Windows operating system. The program may work with Unix or Macintosh based systems through Wine. The programs were developed by James F. Ziegler and Jochen P. Biersack around 1983 and are being continuously upgraded with the major changes occurring approximately every five years. SRIM is based on a Monte Carlo simulation method, namely the binary collision approximation with a random selection of the impact parameter of the next colliding ion. As the input parameters, it needs the ion type and energy (in the range 10 eV – 2 GeV) and the material of one or several target layers | https://en.wikipedia.org/wiki?curid=23080387 |
Stopping and Range of Ions in Matter As the output, it lists or plots the three-dimensional distribution of the ions in the solid and its parameters, such as penetration depth, its spread along the ion beam (called straggle) and perpendicular to it, all target atom cascades in the target are followed in detail; concentration of vacancies, sputtering rate, ionization, and phonon production in the target material; energy partitioning between the nuclear and electron losses, energy deposition rate; The programs are made so they can be interrupted at any time, and then resumed later. They have an easy-to-use user interface and built-in default parameters for all ions and materials. Another part of the software allows calculating the electronic stopping power of any ion in any material (including gaseous targets) based on an averaging parametrization of a vast range of experimental data. Those features made SRIM immensely popular. However, it doesn't take account of the crystal structure nor dynamic composition changes in the material that severely limits its usefulness in some cases. Other approximations of the program include binary collision (i.e. the influence of neighboring atoms is neglected); the material is fully amorphous, i.e | https://en.wikipedia.org/wiki?curid=23080387 |
Stopping and Range of Ions in Matter description of ion channeling effects is not possible, recombination of knocked off atoms (interstitials) with the vacancies, an effect known to be very important in heat spikes in metals, is neglected; There is no description of defect clustering and irradiation-induced amorphization, even though the former occurs in most materials and the latter is very important in semiconductors. The electronic stopping power is an averaging fit to a large number of experiments. and the interatomic potential as a universal form which is an averaging fit to quantum mechanical calculations, the target atom which reaches the surface can leave the surface (be sputtered) if it has momentum and energy to pass the surface barrier, which is a simplifying assumption that does not work well e.g. at energies below the surface penetration energy or if chemical effects are present. The system is layered, i.e. simulation of materials with composition differences in 2D or 3D is not possible. The threshold displacement energy is a step function for each element, even though in reality it is crystal-direction dependent. | https://en.wikipedia.org/wiki?curid=23080387 |
Random hexamer A random hexamer or random hexonucleotides are for various PCR applications such as rolling circle amplification to prime the DNA. They are oligonucleotide sequences of 6 bases which are synthesised entirely randomly to give a numerous range of sequences that have the potential to anneal at many random points on a DNA sequence and act as a primer to commence first strand cDNA synthesis. | https://en.wikipedia.org/wiki?curid=23081873 |
Bismuth fluoride may refer to: | https://en.wikipedia.org/wiki?curid=23088025 |
Spin crossover Spin Crossover (SCO) is a phenomenon that occurs in some metal complexes wherein the spin state of the complex changes due to an external stimulus. The stimulus include temperature, pressure, is sometimes referred to as spin transition or spin equilibrium behavior. The change in spin state usually involves interchange of low spin (LS) and high spin (HS) configuration. is commonly observed with first row transition metal complexes with a d through d electron configuration in an octahedral ligand geometry. Spin transition curves typically plot the high-spin molar fraction vs. T. Often a gradual spin transition is followed by an abrupt (ΔT = 10K) transition with hysteresis and a two-step transition. The abruptness with hysteresis indicates cooperativity, or “communication”, between neighboring metal complexes. In the latter case, the material is bistable and can exist in the two different spin states with a different range of external stimuli (temperature in this case) for the two phenomena, namely LS → HS and HS → LS. The two-step transition is relatively rare but is observed, for example, with dinuclear SCO complexes for which the spin transition in one metal center renders the transition in the second metal center less favorable. Several types of spin crossover have been identified; some of them are light induced excited spin-state trapping (LIESST), ligand-driven light induced spin change (LD-LISC), and charge transfer induced spin transition (CTIST). SCO was first observed in 1931 by Cambi "et al | https://en.wikipedia.org/wiki?curid=23089179 |
Spin crossover " who discovered anomalous magnetic behavior for the tris(N,N-dialkyldithiocarbamatoiron(III) complexes. The spin states of these complexes were sensitive to the nature of the amine substituents. In the 1960s, the first Co SCO complex was reported. Magnetic measurements and Mössbauer spectroscopic studies established the nature of the spin transition in iron(II) SCO complexes. Building on those early studies, there is now interest in applications of SCO in electronic and optical displays. Due to the changes in magnetic properties that occur from a spin transition - the complex being less magnetic in a LS state and more magnetic in a HS state - magnetic susceptibility measurements are key to characterization of spin crossover compounds. The magnetic susceptibility as a function of temperature, (χT) is the principal technique used to characterize SCO complexes. Fe Mössbauer Spectroscopy is another technique employed to characterize SCO in iron complexes, especially since this technique is sensitive to magnetism. Another very useful technique for characterizing SCO complexes is Fe Mössbauer Spectroscopy. When spectra are recorded as a function of temperature, the areas under the curves of the absorption peaks are proportional to the fraction of HS and LS states in the sample. SCO induces changes in metal-to-ligand bond distances due to the population or depopulation of the e orbitals that have a slight antibonding character | https://en.wikipedia.org/wiki?curid=23089179 |
Spin crossover Consequently X-ray crystallography above and below transition temperatures will generally reveal changes in metal-ligand bond lengths. Transitions from a HS to a LS state cause a decrease in and a strengthening of the metal-ligand bond. These changes are also manifested in FT-IR and Raman spectra. The spin crossover phenomenon is very sensitive to grinding, milling and pressure, but Raman spectroscopy has the advantage that the sample does not require further preparation, in contrast to Fourier Transform Infrared spectroscopy, FT-IR, techniques; highly colored samples may affect the measurements however. Raman spectroscopy is also advantageous because it allows perturbation of the sample with external stimuli to induce SCO. Thermally induced spin crossover is due to the higher electronic degeneracies of the LS form and lower vibrational frequencies of the HS form, thus increasing the entropy. The Raman spectrum of an iron(II) complex in the HS and LS state, emphasizing the changes in the M-L vibrational modes, where a shift from 2114 cm to 2070 cm corresponds to changes in the stretching vibrational modes of the thiocyanate ligand from a LS state to a HS state, respectively. SCO behavior can be followed with UV-vis spectroscopy. In some cases, the absorption bands obscured due to the high intensity absorption bands caused by the Metal-to-Ligand Charge Transfer (MLCT) absorption bands. Thermal perturbations are the most common type of external stimulus used to induce SCO | https://en.wikipedia.org/wiki?curid=23089179 |
Spin crossover One example is [Fe(tmphen)][Co(CN)] trigonal bipyramid (TBP), with the Fe centers in the equatorial positions. The HS Fe remains under 20% i the range of 4.2 K to 50 K, but at room temperature about two-thirds of the Fe ions in the sample are HS, as shown by the absorption band at 2.1 mm/s, while the other third of the ions remain in the LS state. SCO is also influenced by the application of pressure, which changes the population of the HS and LS states. Upon application of pressure, a conversion from the HS state to the LS state and a shift from T, (the temperature at which half of the complex is in a LS state), to higher temperatures will occur. This effect results from an increase in the zero point energy difference, ΔE°, caused by an increase in the relative vertical displacement of the potential wells and a decrease in the activation energy, ΔW°, which favors the LS state. The complex Fe(phen)(SCN) exhibits this effect. At high pressures the LS state predominates and the transition temperature increases. At high pressures the compound is almost entirely transformed to the LS state at room temperature. As a result of the application of pressure on the Fe(phen)(SCN) compound, the bond lengths are affected. The difference in M-L bond lengths in both HS and LS states changes the entropy of the system | https://en.wikipedia.org/wiki?curid=23089179 |
Spin crossover The change in spin transition temperature, T and pressure obeys the Clausius-Clapeyron relationship: formula_1 The increase in pressure will decrease the volume of the unit cell of the Fe(phen)(SCN) and increase the T of the system. A linear relationship between T and pressure for Fe(phen)(SCN), where the slope of the line is <math>\frac{\partial | https://en.wikipedia.org/wiki?curid=23089179 |
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