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Thermoporometry and cryoporometry Then on re-cooling the equilibrium freezing event can be measured, as the external ice will then grow into the pores. This is in effect an "ice intrusion" measurement (c.f. Mercury Intrusion Porosimetry), and as such in part may provide information on pore throat properties. The melting event was then previously expected to provide more accurate information on the pore body. However, a new melting mechanism has been proposed which means the melting event does not provide accurate information on the pore body. The melting mechanism has been termed advanced melting and is described below. The melting process for the frozen phase is initiated from existing molten phase, such as the liquid-like layer that is retained at the pore wall. This is shown in Figure 1 for a through ink bottle pore model (position A); the arrows show how the liquid-like layer initiates the melting process and this melting mechanism is said to occur via sleeve shaped menisci. For such a melting mechanism, the smaller necks will melt first and as the temperature is raised the large pore will then melt. Therefore, the melting event would give an accurate description of the necks and body. However, in cylindrical pores, melting would occur at a lower temperature via a hemispherical meniscus (between solid and molten phases), than it would via a sleeve-shaped meniscus. Scanning curves and loops have been used to show that cryoporometry melting curves are prone to pore-pore cooperative effects and this is demonstrated by position B in Figure 1 | https://en.wikipedia.org/wiki?curid=30950746 |
Thermoporometry and cryoporometry For the through ink bottle pore, melting is initiated in the outer necks from the thin cylindrical sleeve of permanently unfrozen liquid-like fluid that exists at the pore wall. Once the necks have become molten via the cylindrical sleeve meniscus mechanism, a hemispherical meniscus will be formed at both ends of the larger pore body. The hemispherical menisci can then initiate the melting process in the large pore. Moreover, if the larger pore radius is smaller than the critical size for melting via a hemispherical meniscus at the current temperature, then the larger pore will melt at the same temperature as the smaller pore. Therefore, the melting event will not give accurate information on the pore body. If the incorrect melting mechanism is assumed when deriving a PSD (pore size distribution) there will be "at least" a 100% error in the PSD. Moreover, it has been shown that advanced melting effects can lead to a dramatic skew towards smaller pores in PSDs for mesoporous sol-gel silicas, determined from cryoporometry melting curves. NMR cryoporometry (external cryoporometry website) is a very useful nano- through meso- to micro-metrology technique (nanometrology, nano-science.co.uk/nano-metrology) that has been used to study many materials, and has particularly been used to study porous rocks (i.e. sandstone, shale and chalk/carbonate rocks), with a view to improving oil extraction, shale gas extraction and water abstraction | https://en.wikipedia.org/wiki?curid=30950746 |
Thermoporometry and cryoporometry Also very useful for studying porous building materials such as wood, cement and concrete. A currently exciting application for NMR Cryoporometry is the measurement of porosity and pore-size distributions, in the study of carbon, charcoal and biochar. Biochar is regarded as an important soil enhancer (used since pre-history), and offers great possibilities for carbon dioxide removal from the biosphere. Materials studied by NMR cryoporometry include: Possible future application include measuring porosity and pore-size distributions in porous medical implants. | https://en.wikipedia.org/wiki?curid=30950746 |
Carbene dimerization is a type of organic reaction in which two carbene or carbenoid precursors react in a formal dimerization to an alkene. This reaction is often considered an unwanted side-reaction but it is also investigated as a synthetic tool. In this reaction type either the two carbenic intermediates react or a carbenic intermediate reacts with a carbene precursor. An early pioneer was Christoph Grundmann reporting on a carbene dimerisation in 1938. In the domain of persistent carbenes the Wanzlick equilibrium describes an equilibrium between a carbene and its alkene. A reoccurring substrate is a diazo compound and more specifically an alpha-carbonyl diazo compound. For example, ethyl diazoacetate is converted to diethyl maleate using the ruthenium catalyst chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium: Grubbs' catalyst is also effective In this reaction type the active intermediate is a transition metal carbene complex. A diazo cross-coupling reaction has also been reported between ethyl diazoacetate and "methyl phenyldiazoacetate" using the rhodium catalyst [Rh(OPiv)]. A direct metal carbene dimerization has been used in the synthesis of novel Polyalkynylethenes | https://en.wikipedia.org/wiki?curid=30953451 |
Neutron moisture gauge A neutron moisture meter is a moisture meter utilizing neutron scattering. The meters are most frequently used to measure the water content in soil or rock. The technique is non-destructive, and is sensitive to moisture in the bulk of the target material, not just at the surface. Water, due to its hydrogen content, is an effective neutron moderator, slowing high-energy neutrons. With a source of high-energy neutrons and a detector sensitive to low-energy neutrons (thermal neutrons), the detection rate will be governed by the water content of the soil between the source and the detector. The neutron source typically contains a small amount of a radionuclide. Sources may emit neutrons during spontaneous fission, as with californium; alternatively, an alpha emitter may be mixed with a light element for a nuclear reaction yielding excess neutrons, as with americium in a beryllium matrix. | https://en.wikipedia.org/wiki?curid=30953521 |
Peter Rheinstein Peter Howard Rheinstein (born September 7, 1943) is an American physician, lawyer, author, and administrator (both private and governmental). He was an official of the Food and Drug Administration (FDA) 1974-1999. Rheinstein, a General Motors Scholar, received a B.A. with high honors from Michigan State University in 1963, an M.S. in mathematics from Michigan State University in 1964, an M.D. from Johns Hopkins University in 1967, and a J.D. from the University of Maryland School of Law in 1973. At Michigan State University Rheinstein was noted for his facility in mathematics. Rheinstein was director of the Drug Advertising and Labeling Division, Food and Drug Administration, Rockville, 1974-1982; he was acting deputy director Office of Drugs, 1982–83, acting director Office of Drugs; 1983–84, director Office of Drug Standards, 1984–90, director medicine staff Office Health Affairs, 1990-99. While at FDA Rheinstein developed precedents for Food and Drug Administration regulation of prescription drug promotion, initiated FDA’s first patient medication information program; implemented the Drug Price Competition and Patent Term Restoration Act of 1984, and authored medication goals for Healthy People 2000 and 2010. Judy Woodruff interviewed Rheinstein about generic drug safety on the McNeil-Lehrer NewsHour, 11 Dec 1985. Stone Phillips interviewed Rheinstein about drug labeling on Dateline NBC, March 31, 1992. From 1999 – 2004, Rheinstein was senior vice president for medical and clinical affairs, Cell Works, Inc | https://en.wikipedia.org/wiki?curid=30954342 |
Peter Rheinstein , Baltimore. Among other projects, Cell Works wanted to develop a blood test for anthrax, similar to a system for cancer cells it produced. "It's something that companies like ours can incorporate into our diagnostic technology," Rheinstein told the Washington Times. Biodefense projects "create new technologies, the spin-offs of which can be commercialized into some pretty good things." In 2000 Rheinstein became president of Severn Health Solutions in Severna Park, Maryland. In 2010 Rheinstein was named president of the Academy of Physicians in Clinical Research and in 2011 was named chairman of the American Board of Legal Medicine. Rheinstein was named chairman of the United States Adopted Names Council in 2012. Rheinstein is a member of Phi Kappa Phi, and vice-president of the Intercultural Friends Foundation. Rheinstein is publisher of Discovery Medicine and chairman of MedData Foundation. He is president-elect of the Academy of Medicine of Washington, DC. | https://en.wikipedia.org/wiki?curid=30954342 |
C1QL1 The complement component 1, q subcomponent-like 1 (or C1QL1) is encoded by a gene located at chromosome 17q21.31. It is a secreted protein and is 258 amino acids in length. The protein is widely expressed but its expression is highest in the brain and may also be involved in regulation of motor control. The pre-mRNA of this protein is subject to RNA editing. Its physiological function is unknown. It is a member of the C1Q domain proteins which have important signalling roles in inflammation and in adaptive immunity. The pre-mRNA of this protein is subject to A to I RNA editing, which is catalyzed by a family of adenosine deaminases acting on RNA (ADARs) that specifically recognize adenosines within double-stranded regions of pre-mRNAs and deaminate them to inosine. Inosines are recognised as guanosine by the cell's translational machinery. There are three members of the ADAR family: ADARs 1-3, with ADAR 1 and ADAR 2 being the only enzymatically active members. ADAR 3 is thought to have a regulatory role in the brain. ADAR 1 and ADAR 2 are widely expressed in tissues while ADAR 3 is restricted to the brain. The double-stranded regions of RNA are formed by base-pairing between residues in a region complementary to the region of the editing site. This complementary region is usually found in a neighbouring intron but can also be located in an exonic sequence. The region that pairs with the editing region is known as an Editing Complementary Sequence (ECS) | https://en.wikipedia.org/wiki?curid=30960309 |
C1QL1 The candidate editing sites were determined experimentally by comparison of cDNA sequences and genomically encoded DNA from the same individual to avoid single nucleotide polymorphisms (SNPs). Two of the three editing sites found in mouse gene were found in the human transcript. However, only the Q/R site was detected in all RNA, with the T/A site detected just once. Both sites are found within exon 1. Q/R site This site is found in exon 1 at position 66. Editing results in a codon change from a Glutamine codon to an Arginine codon. T/A site This site is also found in exon 1, at position 63. It was only detected in one genomic sample indicating that the edited residue may be an SNP. However, the secondary structure of the RNA is predicted, around the editing site, to be highly conserved in mice and humans. This indicates that the T/A site may still be shown to be a site of A to I RNA editing. Editing at this site would result in an amino acid change from a Threonine to an Alanine. The ECS is also predicted to be found within exon 1 at a location 5' to the editing region. Editing is differentially expressed in the cerebellum and cortex. This regulation is also present in mice suggesting conservation of editing regulation. No editing has been detected in human lung, heart, kidney or spleen tissue. The sequence of exon 1 is highly conserved in mammalian species and editing of the pre-mRNA of this protein is likely to occur in mice, rat, dog and cow as well as humans | https://en.wikipedia.org/wiki?curid=30960309 |
C1QL1 Even though the ECS is not conserved in non-mammals, an alternative ECS has been predicted in Zebrafish with a similar structure but in a different location. The Ecs is found downstram of the editing sites. These predicted editing sites result in the translation of an Arginine instead of a Glutamine at the Q/R site and an Alanine instead of a Threonine at the T/A site. These codon changes are nonsynomonous. Since the editing sites are located just before a collagen like trimerization domain, editing may effect protein oligomerization. This region is also likely to be a protease domain. It is not known if the amino acid changes caused by editing could have an effect on these domains. | https://en.wikipedia.org/wiki?curid=30960309 |
Chemotronics is an intersection field of chemistry (especially electrochemistry) and electronics dealing with the design of electrochemical and optical chemical sensors. One of pioneers of this field was Alexander Frumkin. | https://en.wikipedia.org/wiki?curid=30961750 |
Human-transcriptome database for alternative splicing The Human-transcriptome DataBase for Alternative Splicing (H-DBAS) is a database of alternatively spliced human transcripts based on H-Invitational. | https://en.wikipedia.org/wiki?curid=30962412 |
Ion semiconductor sequencing is a method of DNA sequencing based on the detection of hydrogen ions that are released during the polymerization of DNA. This is a method of "sequencing by synthesis", during which a complementary strand is built based on the sequence of a template strand. A microwell containing a template DNA strand to be sequenced is flooded with a single species of deoxyribonucleotide triphosphate (dNTP). If the introduced dNTP is complementary to the leading template nucleotide, it is incorporated into the growing complementary strand. This causes the release of a hydrogen ion that triggers an ISFET ion sensor, which indicates that a reaction has occurred. If homopolymer repeats are present in the template sequence, multiple dNTP molecules will be incorporated in a single cycle. This leads to a corresponding number of released hydrogens and a proportionally higher electronic signal. This technology differs from other sequencing-by-synthesis technologies in that no modified nucleotides or optics are used. may also be referred to as Ion Torrent sequencing, pH-mediated sequencing, silicon sequencing, or semiconductor sequencing. The technology was licensed from DNA Electronics Ltd, developed by Ion Torrent Systems Inc. and was released in February 2010. Ion Torrent have marketed their machine as a rapid, compact and economical sequencer that can be utilized in a large number of laboratories as a bench top machine | https://en.wikipedia.org/wiki?curid=30965725 |
Ion semiconductor sequencing Roche's 454 Life Sciences is partnering with DNA Electronics on the development of a long-read, high-density semiconductor sequencing platform using this technology. In nature, the incorporation of a deoxyribonucleoside triphosphate (dNTP) into a growing DNA strand involves the formation of a covalent bond and the release of pyrophosphate and a positively charged hydrogen ion. A dNTP will only be incorporated if it is complementary to the leading unpaired template nucleotide. exploits these facts by determining if a hydrogen ion is released upon providing a single species of dNTP to the reaction. Microwells on a semiconductor chip that each contain many copies of one single-stranded template DNA molecule to be sequenced and DNA polymerase are sequentially flooded with unmodified A, C, G or T dNTP. If an introduced dNTP is complementary to the next unpaired nucleotide on the template strand it is incorporated into the growing complementary strand by the DNA polymerase. If the introduced dNTP is not complementary there is no incorporation and no biochemical reaction. The hydrogen ion that is released in the reaction changes the pH of the solution, which is detected by an ISFET. The unattached dNTP molecules are washed out before the next cycle when a different dNTP species is introduced. Beneath the layer of microwells is an ion sensitive layer, below which is an ISFET ion sensor. All layers are contained within a CMOS semiconductor chip, similar to that used in the electronics industry | https://en.wikipedia.org/wiki?curid=30965725 |
Ion semiconductor sequencing Each chip contains an array of microwells with corresponding ISFET detectors. Each released hydrogen ion then triggers the ISFET ion sensor. The series of electrical pulses transmitted from the chip to a computer is translated into a DNA sequence, with no intermediate signal conversion required. Because nucleotide incorporation events are measured directly by electronics, the use of labeled nucleotides and optical measurements are avoided. Signal processing and DNA assembly can then be carried out in software. The per base accuracy achieved in house by Ion Torrent on the Ion Torrent Ion semiconductor sequencer as of February 2011 was 99.6% based on 50 base reads, with 100 Mb per run. The read-length as of February 2011 was 100 base pairs. The accuracy for homopolymer repeats of 5 repeats in length was 98%. Later releases show a read length of 400 base pairs These figures have not yet been independently verified outside of the company. The major benefits of ion semiconductor sequencing are rapid sequencing speed and low upfront and operating costs. This has been enabled by the avoidance of modified nucleotides and optical measurements. Because the system records natural polymerase-mediated nucleotide incorporation events, sequencing can occur in real-time. In reality, the sequencing rate is limited by the cycling of substrate nucleotides through the system. Ion Torrent Systems Inc | https://en.wikipedia.org/wiki?curid=30965725 |
Ion semiconductor sequencing , the developer of the technology, claims that each incorporation measurement takes 4 seconds and each run takes about one hour, during which 100-200 nucleotides are sequenced. If the semiconductor chips are improved (as predicted by Moore’s law), the number of reads per chip (and therefore per run) should increase. The cost of acquiring a pH-mediated sequencer from Ion Torrent Systems Inc. at time of launch was priced at around $50,000 USD, excluding sample preparation equipment and a server for data analysis. The cost per run is also significantly lower than that of alternative automated sequencing methods, at roughly $1,000. If homopolymer repeats of the same nucleotide (e.g. ) are present on the template strand (strand to be sequenced) then multiple introduced nucleotides are incorporated and more hydrogen ions are released in a single cycle. This results in a greater pH change and a proportionally greater electronic signal. This is a limitation of the system in that it is difficult to enumerate long repeats. This limitation is shared by other techniques that detect single nucleotide additions such as pyrosequencing. Signals generated from a high repeat number are difficult to differentiate from repeats of a similar but different number; "e.g.", homorepeats of length 7 are difficult to differentiate from those of length 8. Another limitation of this system is the short read length compared to other sequencing methods such as Sanger sequencing or pyrosequencing | https://en.wikipedia.org/wiki?curid=30965725 |
Ion semiconductor sequencing Longer read lengths are beneficial for "de novo" genome assembly. Ion Torrent semiconductor sequencers produce an average read length of approximately 400 nucleotides per read. The throughput is currently lower than that of other high-throughput sequencing technologies, although the developers hope to change this by increasing the density of the chip. The developers of Ion Torrent semiconductor sequencing have marketed it as a rapid, compact and economical sequencer that can be utilized in a large number of laboratories as a bench top machine. The company hopes that their system will take sequencing outside of specialized centers and into the reach of hospitals and smaller laboratories. A January 2011 New York Times article, "Taking DNA Sequencing to the Masses", underlines these ambitions. Due to the ability of alternative sequencing methods to achieve a greater read length (and therefore being more suited to whole genome analysis) this technology may be best suited to small scale applications such as microbial genome sequencing, microbial transcriptome sequencing, targeted sequencing, amplicon sequencing, or for quality testing of sequencing libraries. | https://en.wikipedia.org/wiki?curid=30965725 |
Specim Specim, Spectral Imaging Ltd is a European technology firm headquartered in Oulu, Finland. manufactures and sells imaging spectrographs, hyperspectral cameras and systems. Specim's airborne AISA hyperspectral cameras have been utilized for example in monitoring the environmental effects of major industrial catastrophes such as Deepwater Horizon oil spill and Red mud spill. In 2010, was widely credited for its Thermal Infrared Hyperspectral Cameras, including a position as a Prism Awards for Photonics Innovation finalist. The credited Owl is world's first Thermal Hyperspectral Camera that can efficiently be used for outdoor surveillance and UAV applications without an external light source such as the Sun or the Moon. In 2013, together with Germany’s Forschungszentrum Jülich research centre, developed and thoroughly tested the novel Hyplant airborne hyperspectral sensor. This was the first airborne sensor to map the fluorescence over large areas. Since then it has been used to map various types of vegetation all over Europe and also in the USA. This project is one step in assessing feasibility of possible new ESA satellite instrument that could provide global maps of vegetation fluorescence called the Fluorescence Explorer (FLEX). | https://en.wikipedia.org/wiki?curid=30968333 |
Phaseolin may refer to: | https://en.wikipedia.org/wiki?curid=30971683 |
C20H18O4 The molecular formula CHO may refer to: | https://en.wikipedia.org/wiki?curid=30971879 |
Bloch wave – MoM method Bloch wave – MoM is a first principles technique for determining the photonic band structure of triply-periodic electromagnetic media such as photonic crystals. It is based on the 3-dimensional spectral domain method (Kastner [1987]), specialized to triply-periodic media. This technique uses the method of moments (MoM) in combination with a Bloch wave expansion of the electromagnetic field to yield a matrix eigenvalue equation for the propagation bands. The eigenvalue is the frequency (for a given propagation constant) and the eigenvector is the set of current amplitudes on the surface of the scatterers. Bloch wave - MoM is similar in principle to the plane wave expansion method, but since it additionally employs the method of moments to produce a surface integral equation, it is significantly more efficient both in terms of the number of unknowns and the number of plane waves needed for good convergence. Bloch wave - MoM is the extension to 3 dimensions of the spectral domain MoM method commonly used for analyzing 2D periodic structures such as frequency selective surfaces (FSS). In both cases, the field is expanded as a set of eigenfunction modes (either a Bloch wave in 3D or a discrete plane wave - aka Floquet mode - spectrum in 2D), and an integral equation is enforced on the surface of the scatterers in each unit cell. In the FSS case, the unit cell is 2-dimensional and in the photonic crystal case, the unit cell is 3-dimensional | https://en.wikipedia.org/wiki?curid=30975689 |
Bloch wave – MoM method The Bloch wave - MoM approach will be illustrated here for the case of perfectly electrically conducting (PEC) structures admitting only electric current sources, J. However, it can also be readily expanded to dielectric structures, using the well-known interior and exterior equivalent problems commonly employed in ordinary spatial domain method of moments formulations (Harrington [1961]). In dielectric problems, there are twice as many unknowns - J & M - and also twice as many equations to enforce - continuity of tangential E & H - at the dielectric interfaces (Scott [1998]). For PEC structures, the electric field E is related to the vector magnetic potential A via the well-known relation: and the vector magnetic potential is in turn related to the source currents via: where To solve equations (1.1) and (1.2) within the infinite periodic volume, we may assume a Bloch wave expansion for all currents, fields and potentials: where for simplicity, we assume an orthogonal lattice in which α only depends on "m", β only depends on "n" and γ only depends on "p". With this assumption, and, where "l", "l", "l" are the unit cell dimensions in the "x","y","z" directions respectively, λ is the effective wavelength in the crystal and θ, φ are the directions of propagation in spherical coordinates. The quantity "k" in equations (1.1) and (1 | https://en.wikipedia.org/wiki?curid=30975689 |
Bloch wave – MoM method 2) comes originally from the time derivative in Maxwell's equations and is the "free space" propagation constant (actually, the propagation constant of whatever dielectric medium the metallic scatterers are embedded in), proportional to frequency as in equation (1.3). On the other hand, "k" in the equations above comes from the "assumed Bloch wave solution" given by equations (2.1) & (2.2). As a result, it represents the propagation constant inside the periodic medium, inversely proportional to wavelength. These two "k's", i.e. the free space propagation constant (proportional to frequency) and the propagation constant of the Bloch wave (inversely proportional to wavelength), are in general different thereby allowing for dispersion in the solution. The band diagram is essentially a plot of "k" as a function of "k". The Bloch wave expansions in equations (2.1) are nothing more than exponential Fourier series multiplied by the cell-to-cell propagation factor: formula_11 The Bloch wave expansions are chosen since any field solution within an infinite periodic volume must have the same periodicity as the medium itself, or stated another way, the fields in neighboring cells must be identical up to a (real or complex) propagation factor. In passbands the propagation factor is an exponential function with purely imaginary argument and in the stop bands (or band gaps) it is a decaying exponential function whose argument has a real component | https://en.wikipedia.org/wiki?curid=30975689 |
Bloch wave – MoM method The wave numbers α, β and γ satisfy the relations: formula_12 and outside of these ranges, the bands are periodic. The Bloch waves are periodic functions of space, with periods "l", "l", "l" and the bands are periodic functions of wavenumber, with periods: formula_13, formula_14 and formula_15 Substituting equations (2.1) into (1.1) and (1.2) yields the spectral domain Greens function relating the radiated electric field to its source currents: where, is the tensor Green's function in the spectral domain. Note that the spatial domain convolution has been transformed into a simple multiplication in the spectral domain, consistent with the convolution theorem for Fourier transforms. With this equation for the electric field, the electric field boundary condition (requiring that the total tangential electric field be zero on the surface of PEC scatterer) becomes: Since we are seeking characteristic modes (eigenmodes) of the structure, there is no impressed E-field on the RHS of this electric field integral equation (EFIE). Equation (3.3) is not strictly correct however, since it is only the tangential components of electric field that are actually zero on the surface of the PEC scatterer. This inexactness will be resolved presently, when we test this equation with the electric current basis functions - defined as residing on the surface of the scatterer | https://en.wikipedia.org/wiki?curid=30975689 |
Bloch wave – MoM method As is usual in the method of moments, the source currents are now expanded in terms of a sum over some known set of basis functions with unknown weighting coefficients "J" : Different structures will have different sets of basis functions for representing the currents on the elements and as in the ordinary spatial domain method of moments, the solution (in this case, the band diagram) "is a function of the set of basis functions used". Substituting (4.1) into (3.3) and then testing the resulting equation with the "i"-th current basis function (i.e., dotting from the left and integrating over the domain of the "i"-th current basis function, thereby completing the quadratic form) produces the "i"-th row of the matrix eigenvalue equation for a 3-dimensional array of PEC scatterers as: As in all MoM formulations, the reaction concept in electromagnetics (Rumsey [1954], Harrington [1961]) was used in obtaining this equation. The electric field boundary/continuity conditions are "tested" (or enforced) by being integrated against electric current basis functions (for dielectric structures, the magnetic field continuity conditions are additionally tested by being integrated against magnetic current basis functions), and this is how the electric (and magnetic) field boundary conditions are converted into a matrix equation via the method of moments | https://en.wikipedia.org/wiki?curid=30975689 |
Bloch wave – MoM method This process is wholly analogous to that used to decompose a periodic function into its Fourier sine & cosine components, the only difference being that in this case the basis functions are not necessarily orthogonal, merely linearly independent. This matrix equation is easy to implement and requires only that the 3D Fourier transform (FT) of the basis functions be computed, preferably in closed form (see Scott [1998], available on researchgate.net). In fact, computing bands of a 3D photonic crystal with this method is no more difficult than computing reflection and transmission from a 2D periodic surface using the spectral domain method . This is because equation (4.2) is identical to the basic EFIE for a freestanding PEC FSS (Scott [1989] or Frequency selective surface eq. (4.2)), the only difference being the stronger singularity in 3D which significantly accelerates convergence of the triple sums, and of course the fact that the vectors are now 3-dimensional. As a result, an ordinary PC is sufficient to compute bands of many types of photonic crystals. It's evident from (4.2) that the EFIE could become singular whenever the free space wavenumber is exactly equal to one of the wave numbers in any of the 3 periodic coordinate directions. This can happen for example when the free space wavelength exactly equals the lattice spacing. This is a statistically rare occurrence in computational practice and corresponds to a propagation anomaly similar to a Wood's reflection anomaly for gratings | https://en.wikipedia.org/wiki?curid=30975689 |
Bloch wave – MoM method To compute bands of the crystal (i.e. "k"-"k" diagrams), successive values of frequency ("k") are tried - in conjunction with pre-selected values of propagation constant ("k") and propagation direction (θ & φ) - until a combination is found which drives the determinant of the matrix to zero. Equation (4.2) has been used to compute bands in various types of doped and undoped photonic crystals (Scott [1998], Scott [2002], both available on researchgate.net). Not surprisingly, doping photonic crystals with defects provides a means for designing photonic passbands, in just the same way that doping semiconductors with chemical impurities provides a means for designing electronic passbands. For many subsectional basis functions, such as those having a half-sine or triangular shape along a round wire, the FT of the basis function for negative wave numbers -α, -β, -γ is the complex conjugate of the basis function FT for positive wave numbers. As a result, the matrix in eqn. (4.2) is Hermitian. And as a result of that, only half the matrix needs to be computed. And a second result is that the determinant is a purely real function of the real-valued wavenumber "k". Zeroes generally occur at zero-crossings (inflection points, where curvature is zero), so a simple root-finding algorithm such as Newton's method is usually sufficient to find the roots to a very high degree of accuracy. If may still be useful however to plot the determinant as a function of "k", to observe its behavior near the zeros | https://en.wikipedia.org/wiki?curid=30975689 |
Bloch wave – MoM method As a matter of computational convenience, whenever the matrix is larger than 2x2 it's vastly more efficient to compute the determinant either by reducing the matrix to upper triangular form using QR decomposition or to compute the determinant by reducing to echelon form using Gaussian elimination, rather than trying to actually compute the determinant of the matrix directly. | https://en.wikipedia.org/wiki?curid=30975689 |
Sodium ethyl xanthate (SEX) is an organosulfur compound with the chemical formula CHCHOCSNa. It is a pale yellow powder, which is usually obtained as the dihydrate. is used in the mining industry as a flotation agent. A closely related potassium ethyl xanthate (KEX) is obtained as the anhydrous salt. As with most xanthates, sodium ethyl xanthate can be prepared by treating sodium ethoxide with carbon disulfide: is a pale yellow powder. It is relatively stable in water at high pH if not heated. It rapidly hydrolyses at pH <9 at 25 °C. It is the conjugate base of the unknown strong acid with p"K" of 1.6 and p"K" estimated as 12.4 for the conjugate base. easily adsorbs on the surface of solid sulfides. Xanthate are susceptible to hydrolysis and oxidation: These reactions require acidic conditions. can be identified through optical absorption peaks in the infrared (1179, 1160, 1115, 1085 cm) and ultraviolet (300 nm) ranges. There are at least six chemical detection methods: can also be quantified using gravimetry, by weighing the lead xanthate residue obtained after reacting SEX with 10% solution of lead nitrate. There are also several electrochemical detection methods, which can be combined with some of the above chemical techniques. is predominantly used in the mining industry as flotation agent for recovery of metals, such as copper, nickel, silver or gold, as well as solid metal sulfides or oxides from ore slurries. This application was introduced by Cornelius H. Keller in 1925 | https://en.wikipedia.org/wiki?curid=30977268 |
Sodium ethyl xanthate Other applications include defoliant, herbicide and an additive to rubber to protect it against oxygen and ozone. The mechanism of flotation enhancement is as follows. The polar part of xanthate molecule attaches to the ore particles with the non-polar hydrocarbon part sticking out and forming a hydrophobic layer. Then the particles are brought to the water surface by air bubbles. Only a small amount of about 300 g/tonne of ore is required for efficient separation. The efficiency of the hydrophobic action increases, but the selectivity to ore type decreases with increasing length of the hydrocarbon chain in xanthates. The chain is shortest in sodium ethyl xanthate that makes it highly selective to copper, nickel, lead, gold and zinc ores. Aqueous solutions (10%) with pH=7–11 are normally used in the process. In 2000, Australia produced up to 10,000 tonnes of sodium ethyl xanthate and imported about 6,000 tonnes, mostly from China. The material produced in Australia is the so-called 'liquid sodium ethyl xanthate' that refers to a 40% aqueous solution of the solid. It is obtained by reacting carbon disulfide with sodium hydroxide and ethanol in a closed process. Its density is 1.2 g/cm and the freezing point is −6 °C. has moderate oral and dermal toxicity in animals and is irritating to eyes and skin. It is especially toxic to aquatic life and therefore its disposal is strictly controlled | https://en.wikipedia.org/wiki?curid=30977268 |
Sodium ethyl xanthate Median lethal dose for (male albino mice, oral, 10% solution at pH~11) is 730 mg/kg of body weight, with most deaths occurring in the first day. The most affected organs were the central nervous system, liver and spleen. Since 1993, sodium ethyl xanthate is classified as a Priority Existing Chemical in Australia, meaning that its manufacture, handling, storage, use or disposal may result in adverse health or environment effects. This decision was justified by the widespread use of the chemical in industry and its decomposition to the toxic and flammable carbon disulfide gas. From two examples of sodium ethyl xanthate spillage in Australia, one resulted in evacuation of 100 people and hospitalization of 6 workers who were exposed to the fumes. In another accident, residents of the spillage area complained of headache, dizziness and nausea. Consequently, during high-risk sodium ethyl xanthate handling operations, workers are required by the Australian regulations to be equipped with protective clothing, anti-static gloves, boots and full-face respirators or self-contained breathing apparatus. | https://en.wikipedia.org/wiki?curid=30977268 |
Thallous acetate is a salt of thallium and acetate with the chemical formula TlCHCOO. It is used in microbiology as a selective growth medium. It is poisonous. | https://en.wikipedia.org/wiki?curid=30983523 |
TRH stimulation test Prior to the availability of sensitive TSH assays, thyrotropin releasing hormone or TRH stimulation tests were relied upon for confirming and assessing the degree of suppression in suspected hyperthyroidism. Typically, this stimulation test involves determining basal TSH levels and levels 15 to 30 minutes after an intravenous bolus of TRH. Normally, TSH would rise into the concentration range measurable with less sensitive TSH assays. Third generation TSH assays do not have this limitation and thus TRH stimulation is generally not required when third generation TSH assays are used to assess degree of suppression. TRH-stimulation testing however continues to be useful for the differential diagnosis of secondary (pituitary disorder) and tertiary (hypothalamic disorder) hypothyroidism. Patients with these conditions appear to have physiologically inactive TSH in their circulation that is recognized by TSH assays to a degree such that they may yield misleading, "euthyroid" TSH results. Use and Interpretation: • Helpful in diagnosis in patients with confusing TFTs | https://en.wikipedia.org/wiki?curid=22836654 |
TRH stimulation test In primary hyperthyroidism TSH are low and TRH administration induces little or no change in TSH levels • In hypothyroidism due to end organ failure, administration of TRH produces a prompt increase in TSH • In hypothyroidism due to pituitary disease (secondary hypothyroidism)administration of TRH does not produce an increase in TSH • In hypothyroidism due to hypothalamic disease (tertiary hypothyroidism), administration of TRH produces a delayed (60–120 minutes, rather than 15–30 minutes) increase in TSH The TRH test involves administration of a small amount of TRH intravenously, following which levels of TSH will be measured at several subsequent time points using samples of blood taken from a peripheral vein. The test is used in the differential diagnosis of secondary and tertiary hypothyroidism. First, blood is drawn and a baseline TSH level is measured. Then, TRH is administered via a vein. After 30 minutes blood is drawn again and the levels of TSH are measured and compared to the baseline. Some authors recommend additional blood sampling at 15 minutes. In children, late blood sampling at 60 to 120 minutes is necessary. An increase in the serum TSH level following TRH administration means that the cause of the hypothyroidism is in the hypothalamus (tertiary hypothyroidism), i.e. the hypothalamus is not producing TRH. Therefore, when TRH is given exogenously, TSH levels increase | https://en.wikipedia.org/wiki?curid=22836654 |
TRH stimulation test If the increase in serum TSH level following TRH administration is absent or very slight, then the cause of the hypothyroidism is in the anterior pituitary gland, i.e. the pituitary is not secreting TSH. Therefore, even when TRH is given exogenously, TSH levels do not rise as the pituitary is diseased. TRH may cause nausea, vomiting and some patients experience an urge to urinate. Rarely, TRH may cause blood vessel constriction leading to hemorrhage in patients with pre-existing pituitary tumors. Accordingly, patients should be advised about the risks, albeit rare, of TRH testing. 3. http://www.auburn.edu/~deruija/endo_thyroidfts.pdf | https://en.wikipedia.org/wiki?curid=22836654 |
Slater integrals In mathematics and mathematical physics, are certain integrals of products of three spherical harmonics. They occur naturally when applying an orthonormal basis of functions on the unit sphere that transform in a particular way under rotations in three dimensions. Such integrals are particularly useful when computing properties of atoms which have natural spherical symmetry. These integrals are defined below along with some of their mathematical properties. In connection with the quantum theory of atomic structure, John C. Slater defined the integral of three spherical harmonics as a coefficient formula_1. These coefficients are essentially the product of two Wigner 3jm symbols. These integrals are useful and necessary when doing atomic calculations of the Hartree–Fock variety where matrix elements of the Coulomb operator and Exchange operator are needed. For an explicit formula, one can use Gaunt's formula for associated Legendre polynomials. Note that the product of two spherical harmonics can be written in terms of these coefficients. By expanding such a product over a spherical harmonic basis with the same order one may then multiply by formula_4 and integrate, using the conjugate property and being careful with phases and normalisations: Hence These coefficient obey a number of identities. They include | https://en.wikipedia.org/wiki?curid=22843059 |
Blue Obelisk is an informal group of chemists who promote open data, open source, and open standards; it was initiated by Peter Murray-Rust and others in 2005. Multiple open source cheminformatics projects associate themselves with the Blue Obelisk, among which, in alphabetical order, Avogadro, Bioclipse, cclib, Chemistry Development Kit, GaussSum, JChemPaint, JOELib, Kalzium, Openbabel, OpenSMILES, and UsefulChem. The project has handed out personal awards for achievements in promoting Open Data, Open Source and Open Standards. Among those who received a Award are: | https://en.wikipedia.org/wiki?curid=22844503 |
Lunar regolith simulant A lunar regolith simulant is a terrestrial material synthesized in order to approximate the chemical, mechanical, or engineering properties of, and the mineralogy and particle size distributions of, lunar regolith. Lunar regolith simulants are used by researchers who wish to research the materials handling, excavation, transportation, and uses of lunar regolith. Samples of actual lunar regolith are too scarce, and too small, for such research. In the run-up to the Apollo program, crushed terrestrial rocks were first used to simulate the anticipated soils that astronauts would encounter on the lunar surface. In some cases the properties of these early simulants were substantially different from actual lunar soil, and the issues associated with the pervasive, fine-grained sharp dust grains on the Moon came as a surprise. After Apollo and particularly during the development of the Constellation program, there was a large proliferation of lunar simulants produced by different organizations and researchers. Many of these were given three-letter acronyms to distinguish them (e.g., MLS-1, JSC-1), and numbers to designate subsequent versions. These simulants were broadly divided into highlands or mare soils, and were usually produced by crushing and sieving analogous terrestrial rocks (anorthosite for highlands, basalt for mare). Returned Apollo and Luna samples were used as reference materials in order to target specific properties such as elemental chemistry or particle size distribution | https://en.wikipedia.org/wiki?curid=22861361 |
Lunar regolith simulant Many of these simulants were criticized by prominent lunar scientist Larry Taylor for a lack of quality control and wasted money on features like nanophase iron that had no documented purpose. JSC-1 (Johnson Space Center Number One) was a lunar regolith simulant that was developed in 1994 by NASA and the Johnson Space Center. Its developers intended it to approximate the lunar soil of the maria. It was sourced from a basaltic ash with a high glass content. In 2005, NASA contracted with Orbital Technologies Corporation (ORBITEC) for a second batch of simulant in three grades: NASA received 14 metric tons of JSC-1A, and one ton each of AF and AC in 2006. Another 15 tons of JSC-1A and 100 kg of JSC-1F were produced by ORBITEC for commercial sale, but ORBITEC is no longer selling simulants and was acquired by the Sierra Nevada Corporation. An 8-ton sand box of commercial JSC‐1A is available for daily rental from the NASA Solar System Exploration Research Virtual Institute (SSERVI). JSC-1A can geopolymerize in an alkaline solutions resulting in a hard, rock-like, material. Tests show that the maximum compressive and flexural strength of the 'lunar' geopolymer is comparable to that of conventional cements. JSC-1 and JSC-1A are now no longer available outside of NASA centers. Two lunar highlands simulants, the NU-LHT (lunar highlands type) series and OB-1 (olivine-bytownite) were developed and produced in anticipation of the Constellation activities | https://en.wikipedia.org/wiki?curid=22861361 |
Lunar regolith simulant Both of these simulants are sourced mostly from rare anorthosite deposits on the Earth. For NU-LHT the anorthosite came from the Stillwater complex, and for OB-1 it came from the Shawmere Anorthosite in Ontario. Neither of these simulants were widely distributed. Most of the previously developed lunar simulants are no longer being produced or distributed outside of NASA. Multiple companies have tried to sell regolith simulants for profit, including Zybek Advanced Products, ORBITEC, and Deep Space Industries. None of these efforts have seen much success. NASA is unable to sell simulants, or distribute unlimited amounts for free; however, NASA can award set amounts of simulant to grant winners. Several lunar simulants have been developed recently and are either being sold commercially or are available for rent inside large regolith bins. These include the "OPRL2N Standard Representative Lunar Mare Simulant" and "Standard Representative Lunar Highland Simulant". Off Planet Research also produces customized simulants for specific locations on the Moon including lunar polar icy regolith simulants that include the volatiles identified in the LCROSS mission. Other simulants include "Lunar Highlands Simulant (LHS-1)" and "Lunar Mare Simulant (LMS-1)" produced and distributed by the not-for-profit Exolith Lab run out of the University of Central Florida. | https://en.wikipedia.org/wiki?curid=22861361 |
Red heat The practice of using colours to determine the temperature of a piece of (usually) ferrous metal comes from blacksmithing. Long before thermometers were widely available it was necessary to know what state the metal was in for heat treating it and the only way to do this was to heat it up to a colour which was known to be best for the work. According to Chapman's "Workshop Technology", the colours which can be observed in steel are: In 1905, Stirling Consolidated Boiler Company published a slightly different set of values: | https://en.wikipedia.org/wiki?curid=22862812 |
Composite fermion A composite fermion is the topological bound state of an electron and an even number of quantized vortices, sometimes visually pictured as the bound state of an electron and, attached, an even number of magnetic flux quanta. Composite fermions were originally envisioned in the context of the fractional quantum Hall effect, but subsequently took on a life of their own, exhibiting many other consequences and phenomena. Vortices are an example of topological defect, and also occur in other situations. Quantized vortices are found in type II superconductors, called Abrikosov vortices. Classical vortices are relevant to the Berezenskii–Kosterlitz–Thouless transition in two-dimensional XY model. When electrons are confined to two dimensions, cooled to very low temperatures, and subjected to a strong magnetic field, their kinetic energy is quenched due to Landau level quantization. Their behavior under such conditions is governed by the Coulomb repulsion alone, and they produce a strongly correlated quantum liquid. Experiments have shown that electrons minimize their interaction by capturing quantized vortices to become composite fermions. The interaction between composite fermions themselves is often negligible to a good approximation, which makes them the physical quasiparticles of this quantum liquid. The signature quality of composite fermions, which is responsible for the otherwise unexpected behavior of this system, is that they experience a much smaller magnetic field than electrons | https://en.wikipedia.org/wiki?curid=22863481 |
Composite fermion The magnetic field seen by composite fermions is given by where formula_2 is the external magnetic field, formula_3 is the number of vortices bound to composite fermion (also called the vorticity or the vortex charge of the composite fermion), formula_4 is the particle density in two dimensions, and formula_5 is called the “flux quantum” (which differs from the superconducting flux quantum by a factor of two). The effective magnetic field is a direct manifestation of the existence of composite fermions, and also embodies a fundamental distinction between electrons and composite fermions. Sometimes it is said that electrons "swallow" formula_3 flux quanta each to transform into composite fermions, and the composite fermions then experience the residual magnetic field formula_7 More accurately, the vortices bound to electrons produce their own geometric phases which partly cancel the Aharonov–Bohm phase due to the external magnetic field to generate a net geometric phase that can be modeled as an Aharonov–Bohm phase in an effective magnetic field formula_8 The behavior of composite fermions is similar to that of electrons in an effective magnetic field formula_7 Electrons form Landau levels in a magnetic field, and the number of filled Landau levels is called the filling factor, given by the expression formula_10 Composite fermions form Landau-like levels in the effective magnetic field formula_11 which are called composite fermion Landau levels or formula_12 levels | https://en.wikipedia.org/wiki?curid=22863481 |
Composite fermion One defines the filling factor for composite fermions as formula_13 This gives the following relation between the electron and composite fermion filling factors The minus sign occurs when the effective magnetic field is antiparallel to the applied magnetic field, which happens when the geometric phase from the vortices overcompensate the Aharonov–Bohm phase. The central statement of composite fermion theory is that the strongly correlated electrons at a magnetic field formula_15 (or filling factor formula_16) turn into weakly interacting composite fermions at a magnetic field formula_17 (or composite fermion filling factor formula_18). This allows an effectively single-particle explanation of the otherwise complex many-body behavior, with the interaction between electrons manifesting as an effective kinetic energy of composite fermions. Here are some of the phenomena arising from composite fermions: The effective magnetic field for composite fermions vanishes for formula_19, where the filling factor for electrons is formula_20. Here, composite fermions make a Fermi sea. This Fermi sea has been observed at half filled Landau level in a number of experiments, which also measure the Fermi wave vector. As the magnetic field is moved slightly away from formula_21, composite fermions execute semiclassical cyclotron orbits. These have been observed by coupling to surface acoustic waves, resonance peaks in antidot superlattice, and magnetic focusing | https://en.wikipedia.org/wiki?curid=22863481 |
Composite fermion The radius of the cyclotron orbits is consistent with the effective magnetic field formula_21 and is sometimes an order of magnitude or more larger than the radius of the cyclotron orbit of an electron at the externally applied magnetic field formula_15. Also, the observed direction of trajectory is opposite to that of electrons when formula_17 is anti-parallel to formula_15. In addition to the cyclotron orbits, cyclotron resonance of composite fermions has also been observed by photoluminescence. As the magnetic field is moved further away from formula_21, quantum oscillations are observed that are periodic in formula_27 These are Shubnikov–de Haas oscillations of composite fermions. These oscillations arise from the quantization of the semiclassical cyclotron orbits of composite fermions into composite fermion Landau levels. From the analysis of the Shubnikov–de Haas experiments, one can deduce the effective mass and the quantum lifetime of composite fermions. With further increase in formula_28 or decrease in temperature and disorder, composite fermions exhibit integer quantum Hall effect. The integer fillings of composite fermions, formula_29, correspond to the electrons fillings Combined with which are obtained by attaching vortices to holes in the lowest Landau level, these constitute the prominently observed sequences of fractions. Examples are The fractional quantum Hall effect of electrons is thus explained as the integer quantum Hall effect of composite fermions | https://en.wikipedia.org/wiki?curid=22863481 |
Composite fermion It results in fractionally quantized Hall plateaus at with formula_36 given by above quantized values. These sequences terminate at the composite fermion Fermi sea. Note that the fractions have odd denominators, which follows from the even vorticity of composite fermions. The above sequences account for most, but not all, observed fractions. Other fractions have been observed, which arise from a weak residual interaction between composite fermions, and are thus more delicate. A number of these are understood as fractional quantum Hall effect of composite fermions. For example, the fractional quantum Hall effect of composite fermions at formula_37 produces the fraction 4/11, which does not belong to the primary sequences. An even denominator fraction, formula_38 has been observed. Here the second Landau level is half full, but the state cannot be a Fermi sea of composite fermions, because the Fermi sea is gapless and does not show quantum Hall effect. This state is viewed as a "superconductor" of composite fermion, arising from a weak attractive interaction between composite fermions at this filling factor. The pairing of composite fermions opens a gap and produces a fractional quantum Hall effect. The neutral excitations of various fractional quantum Hall states are excitons of composite fermions, that is, particle hole pairs of composite fermions. The energy dispersion of these excitons has been measured by light scattering and phonon scattering | https://en.wikipedia.org/wiki?curid=22863481 |
Composite fermion At high magnetic fields the spin of composite fermions is frozen, but it is observable at relatively low magnetic fields. The fan diagram of the composite fermion Landau levels has been determined by transport, and shows both spin-up and spin-down composite fermion Landau levels. The fractional quantum Hall states as well as composite fermion Fermi sea are also partially spin polarized for relatively low magnetic fields. The effective magnetic field of composite fermions has been confirmed by the similarity of the fractional and the integer quantum Hall effects, observation of Fermi sea at half filled Landau level, and measurements of the cyclotron radius. The mass of composite fermions has been determined from the measurements of: the effective cyclotron energy of composite fermions; the temperature dependence of Shubnikov–de Haas oscillations; energy of the cyclotron resonance; spin polarization of the Fermi sea; and quantum phase transitions between states with different spin polarizations. Its typical value in GaAs systems is on the order of the electron mass in vacuum. (It is unrelated to the electron band mass in GaAs, which is 0.07 of the electron mass in vacuum.) Much of the experimental phenomenology can be understood from the qualitative picture of composite fermions in an effective magnetic field. In addition, composite fermions also lead to a detailed and accurate microscopic theory of this quantum liquid. Two approaches have proved useful | https://en.wikipedia.org/wiki?curid=22863481 |
Composite fermion The following trial wave functions embody the composite fermion physics: formula_39 Here formula_40 is the wave function of interacting electrons at filling factor formula_16; formula_42 is the wave function for weakly interacting electrons at formula_18; formula_44 is the number of electrons or composite fermions; formula_45 is the coordinate of the formula_46th particle; and formula_47 is an operator that projects the wave function into the lowest Landau level. This provides an explicit mapping between the integer and the fractional quantum Hall effects. Multiplication by formula_48 attaches formula_49 vortices to each electron to convert it into a composite fermion. The right hand side is thus interpreted as describing composite fermions at filling factor formula_18. The above mapping gives wave functions for both the ground and excited states of the fractional quantum Hall states in terms of the corresponding known wave functions for the integral quantum Hall states. The latter do not contain any adjustable parameters for formula_29, so the FQHE wave functions do not contain any adjustable parameters at formula_52. Comparisons with exact results show that these wave functions are quantitatively accurate. They can be used to compute a number of measurable quantities, such as the excitation gaps and exciton dispersions, the phase diagram of composite fermions with spin, the composite fermion mass, etc. For formula_53 they reduce to the Laughlin wavefunction at fillings formula_54 | https://en.wikipedia.org/wiki?curid=22863481 |
Composite fermion Another formulation of the composite fermion physics is through a Chern–Simons field theory, wherein flux quanta are attached to electrons by a singular gauge transformation. At the mean field approximation the physics of free fermions in an effective field is recovered. Perturbation theory at the level of the random phase approximation captures many of the properties of composite fermions. | https://en.wikipedia.org/wiki?curid=22863481 |
Mallory metal is proprietary name for an alloy of tungsten, with other metallic elements added to improve machining. Its primary use is as a balance weight which is added to the crankshaft of an automotive engine, where the existing counterweight is not large enough to compensate for the weight of the reciprocating and rotating components attached to the crankshaft's connecting rod journals. Rather than add to the counterweight by welding or fabrication, holes are drilled in structurally safe positions in the counterweights, and "slugs" (cylindrical dowels) of are inserted and fastened securely. The difference in density between the replacement and the original steel is about 2:1, so the counterweight is heavier without changing its shape or size. | https://en.wikipedia.org/wiki?curid=22877891 |
Allotropes of boron Boron can be prepared in several crystalline and amorphous forms. Well known crystalline forms are α-rhombohedral, β-rhombohedral, and β-tetragonal. In special circumstances, boron can also be synthesized in the form of its α-tetragonal and γ-orthorhombic allotropes. Two amorphous forms, one a finely divided powder and the other a glassy solid, are also known. Although at least 14 more allotropes have been reported, these other forms are based on tenuous evidence or have not been experimentally confirmed, or are thought to represent mixed allotropes, or boron frameworks stabilized by impurities. Whereas the β-rhombohedral phase is the most stable and the others are metastable, the transformation rate is negligible at room temperature, and thus all five phases can exist at ambient conditions. Amorphous powder boron and polycrystalline rhombohedral β-boron are the most common forms. The latter allotrope is a very hard grey material, about ten percent lighter than aluminium and with a melting point (2080 °C) several hundred degrees higher than that of steel. Elemental boron has been found in star dust and meteorites but does not exist in the high oxygen environment of Earth. It is difficult to extract from its compounds. The earliest methods involved reduction of boric oxide with metals such as magnesium or aluminium. However, the product is almost always contaminated with metal borides. Pure boron can be prepared by reducing volatile boron halides with hydrogen at high temperatures | https://en.wikipedia.org/wiki?curid=22878312 |
Allotropes of boron Very pure boron, for use in semiconductor industry, is produced by the decomposition of diborane at high temperatures, followed by purification via zone melting or the Czochralski process. Even more difficult to prepare are single crystals of pure boron phases, due to polymorphism and the tendency of boron to react with impurities; typical crystal size is ~0.1 mm. α-rhombohedral boron has a unit cell of twelve boron atoms. The structure consists of icosahedra in which each boron atom has five nearest neighbors within the icosahedron. If the bonding were the conventional covalent type then each boron would have donated five electrons. However, boron has only three valence electrons, and it is thought that the bonding in the icosahedra is achieved by the so-called 3-center electron-deficient bonds where the electron charge is accumulated at the center of a triangle formed by three adjacent atoms. The isolated icosahedra are not stable, due to the nonuniformity of the honeycomb; thus boron is not a molecular solid, but the icosahedra in it are connected by strong covalent bonds. Pure α-tetragonal can only be synthesized as thin layers deposited on an underlying substrate of isotropic boron carbide (BC) or nitride (BN). Most examples of α-tetragonal boron are in fact boron-rich carbide or nitrides. β-rhombohedral boron has a unit cell containing 105–108 atoms. Most atoms form B discrete icosahedra; a few form partially interpenetrating icosahedra, and there are two deltahedral B units, and a single central B atom | https://en.wikipedia.org/wiki?curid=22878312 |
Allotropes of boron For a long time, it was unclear whether the α or β phase is most stable at ambient conditions; however, gradually a consensus was reached that the β phase is the most thermodynamically stable allotrope. The β phase was produced in 1960 by hydrogen reduction of BBr on hot tungsten, rhenium or tantalum filaments at temperatures 1270–1550 °C (i.e. chemical vapor deposition). Further studies have reproduced the synthesis and confirmed the absence of impurities in this phase. The γ-phase can be described as a NaCl-type arrangement of two types of clusters, B icosahedra and B pairs. It can be produced by compressing other boron phases to 12–20 GPa and heating to 1500–1800 °C, and remains stable at ambient conditions. There is evidence of significant charge transfer from B pairs to the B icosahedra in this structure; in particular, lattice dynamics suggests the presence of significant long-range electrostatic interactions. This phase was reported by Wentorf in 1965, however neither structure nor chemical composition were established. The structure was solved using "ab initio" crystal structure prediction calculations and confirmed using single crystal X-ray diffraction. Sullenger "et al." (1969) and McConville "et al." (1976) reported a cubic allotrope of boron, obtained in argon plasma experiments, with a unit cell of 1705±3 atoms and a density of 2.367 g/cm | https://en.wikipedia.org/wiki?curid=22878312 |
Allotropes of boron While this allotrope is occasionally mentioned in the literature, no subsequent work appears to have been published either confirming or discrediting its existence. Donohue (1982) commented that the number of atoms in the unit cell did not appear to be icosahedrally related (the icosahedron being a motif common to boron structures). Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure. Contrary to other phases, which are semiconductors, this phase is a metal and becomes a superconductor with a critical temperature increasing from 4 K at 160 GPa to 11 K at 250 GPa. This structural transformation occurs at pressures at which theory predicts the icosahedra will dissociate. Speculation as to the structure of this phase has included face-centred cubic (analogous to Al); α-Ga, and body-centred tetragonal (analogous to In). It has also been suggested that the nonmetal-metal transition is simply the result of a band gap closure, as occurs with iodine, rather than a structural transition. There exist several two-dimensional forms of boron (together called borophenes), and even more are predicted theoretically. The discovery of the quasispherical allotropic molecule borospherene (B) was announced in July 2014. Amorphous boron contains B regular icosahedra that are randomly bonded to each other without long range order. Pure amorphous boron can be produced by thermal decomposition of diborane at temperatures below 1000 °C | https://en.wikipedia.org/wiki?curid=22878312 |
Allotropes of boron Annealing at 1000 °C converts amorphous boron to β-rhombohedral boron. Amorphous boron nanowires (30–60 nm thick) or fibers can be produced by magnetron sputtering and laser-assisted chemical vapor deposition, respectively; and they also convert to β-rhombohedral boron nanowires upon annealing at 1000 °C. | https://en.wikipedia.org/wiki?curid=22878312 |
Electron-longitudinal acoustic phonon interaction The electron-LA phonon interaction is an interaction that can take place between an electron and a longitudinal acoustic (LA) phonon in a material such as a semiconductor. The equations of motion of the atoms of mass M which locates in the periodic lattice is where formula_2 is the displacement of the "n"th atom from their equilibrium positions. Defining the displacement formula_3 of the formula_4th atom by formula_5, where formula_6 is the coordinates of the formula_4th atom and formula_8 is the lattice constant, the displacement is given by formula_9 Then using Fourier transform: and Since formula_3 is a Hermite operator, From the definition of the creation and annihilation operator formula_14 Then formula_3 expressed as Hence, using the continuum model, the displacement operator for the 3-dimensional case is where formula_20 is the unit vector along the displacement direction. The electron-longitudinal acoustic phonon interaction Hamiltonian is defined as formula_21 where formula_23 is the deformation potential for electron scattering by acoustic phonons. Inserting the displacement vector to the Hamiltonian results to The scattering probability for electrons from formula_25 to formula_26 states is Replace the integral over the whole space with a summation of unit cell integrations where formula_30, formula_31 is the volume of a unit cell. | https://en.wikipedia.org/wiki?curid=22883373 |
Docosatetraenoylethanolamide (DEA) is an endogenous ethanolamide that has been shown to act on the cannabinoid (CB) receptor. DEA is similar in structure to anandamide (AEA, a recognized endogenous ligand for the CB receptor), containing docosatetraenoic acid in place of arachidonic acid. While DEA has been shown to bind to the CB receptor with similar potency and efficacy as AEA, its role as a cannabinergic neurotransmitter is not well understood. | https://en.wikipedia.org/wiki?curid=22884190 |
Exchange current density In electrochemistry, exchange current density is a parameter used in the Tafel equation, Butler–Volmer equation and other electrochemical kinetics expressions. The Tafel equation describes the dependence of current for an electrolytic process to overpotential. The exchange current density is the current in the absence of net electrolysis and at zero overpotential. The exchange current can be thought of as a background current to which the net current observed at various overpotentials is normalized. For a redox reaction written as a reduction at the equilibrium potential, electron transfer processes continue at electrode/solution interface in both directions. The cathodic current is balanced by the anodic current. This ongoing current in both directions is called the exchange current density. When the potential is set more negative than the formal potential, the cathodic current is greater than the anodic current. Written as a reduction, cathodic current is positive. The net current density is the difference between the cathodic and anodic current density. Exchange current densities reflect intrinsic rates of electron transfer between an analyte and the electrode. Such rates provide insights into the structure and bonding in the analyte and the electrode. For example, the exchange current densities for platinum and mercury electrodes for reduction of protons differ by a factor of 10, indicative of the excellent catalytic properties of platinum | https://en.wikipedia.org/wiki?curid=22888578 |
Exchange current density Owing to this difference, mercury is preferred electrode material at reducing (cathodic) potentials in aqueous solution. The exchange current density depends critically on the nature of the electrode, not only its structure, but also physical parameters such as surface roughness. Of course, factors that change the composition of the electrode, including passivating oxides and adsorbed species on the surface, also influences the electron transfer. The nature of the electroactive species (the analyte) in the solution also critically affects the exchange current densities, both the reduced and oxidized form. Less important but still relevant are the environment of the solution including the solvent, nature of other electrolyte, and temperature. For the concentration dependence of the exchange current density, the following expression is given for a one-electron reaction: | https://en.wikipedia.org/wiki?curid=22888578 |
Facility for Rare Isotope Beams The Facility for Rare Isotopes Beams (FRIB) will be a new scientific accelerator facility for nuclear science, funded by the U.S. Department of Energy Office of Science (DOE-SC), Michigan State University (MSU), and the State of Michigan. Under construction on the MSU campus and to be operated by MSU as a DOE-SC national user facility, FRIB will provide intense beams of rare isotopes (that is, short-lived atomic nuclei not normally found on Earth). FRIB will enable scientists to make discoveries about the properties of rare isotopes to advance knowledge in nuclear physics, nuclear astrophysics, fundamental interactions of nuclei, and applications of rare isotopes for society. Construction of the FRIB conventional facilities began in spring 2014 and was completed in 2017. Final design of the technical systems is complete and technical construction is underway, having started in the fall of 2014. The total project cost is baselined at $730M with project completion in June 2022. FRIB is expected to provide research opportunities for an international community of university and laboratory scientists, postdoctoral associates, and graduate students. FRIB will provide researchers with the technical capabilities to study the properties of rare isotopes, and to put this knowledge to use in various applications, including in materials science, nuclear medicine, and the fundamental understanding of nuclear material important to nuclear weapons stockpile stewardship | https://en.wikipedia.org/wiki?curid=22897257 |
Facility for Rare Isotope Beams More than 20 working groups specializing in experimental equipment and scientific topics have been organized through the FRIB Users Organization. DOE-SC determined that the establishment of a (FRIB) is a high priority for the future of U.S. nuclear science research. It is the first recommendation in the 2012 National Academies Decadal Study of Nuclear Physics: "Nuclear Physics: Exploring the Heart of the Matter". The priority for completion is listed in the 2015 Long Range Plan for Nuclear Science: "Implementing Reaching for the Horizon" by the DOE/NSF Nuclear Science Advisory Committee. DOE-SC announced the selection of Michigan State University to design and establish FRIB on December 11, 2008 after a rigorous merit review process including a written application, oral presentations, and site visits. The project earned Critical Decision 1 (CD-1) approval in September 2010 which established a preferred alternative and the associated established cost and schedule ranges. On August 1, 2013, DOE-SC approved the project baseline (CD-2) and the start of civil construction (CD-3a), pending a notice to proceed. Civil construction could not start under the continuing appropriations resolution, which disallowed new construction starts. January 18, 2014 the appropriations bill passed both houses of congress. Following the passage of the FY2014 appropriation, DOE-SC issued a notice to proceed on January 22, 2014, allowing the start of civil construction | https://en.wikipedia.org/wiki?curid=22897257 |
Facility for Rare Isotope Beams On February 25, 2014 the board of the Michigan Strategic Fund met at Michigan State University and approved nearly $91 million to support the construction of FRIB. FRIB marked the official start of civil construction with a groundbreaking ceremony March 17, 2014. In attendance were representatives from the Michigan delegation, State of Michigan, Michigan State University, and the U.S. Department of Energy Office of Science. Technical construction started in October 2014, following a CD-3b approval by DOE-SC. In March 2017, FRIB achieved beneficial occupancy of civil construction, and technical installation activities escalated as a result. In September/October 2017, the front end with the ion source and low-energy beam transport were completed. The FRIB cryogenic plant made its first liquid helium at 4.5 Kelvin (K) in November 2017. Liquid helium makes FRIB's accelerator cavities superconducting and is needed to operate FRIB's superconducting linear accelerator. The 4 K cryogenic plant was completed in December 2017, and in July 2018, following two days of commissioning, beams of argon and krypton were accelerated in the first three superconducting cryomodules to the Key Performance Parameters required at project completion.Cryomodule production is now at peak capacity, with the project team building nine cryomodules per six months. | https://en.wikipedia.org/wiki?curid=22897257 |
Thermodynamics of nanostructures As the devices continue to shrink further into the sub-100 nm range following the trend predicted by Moore’s law, the topic of thermal properties and transport in such nanoscale devices becomes increasingly important. Display of great potential by nanostructures for thermoelectric applications also motivates the studies of thermal transport in such devices. These fields, however, generate two contradictory demands: high thermal conductivity to deal with heating issues in sub-100 nm devices and low thermal conductivity for thermoelectric applications. These issues can be addressed with phonon engineering, once nanoscale thermal behaviors have been studied and understood. In general two carrier types can contribute to thermal conductivity - electrons and phonons. In nanostructures phonons usually dominate and the phonon properties of the structure become of a particular importance for thermal conductivity. These phonon properties include: phonon group velocity, phonon scattering mechanisms, heat capacity, Grüneisen parameter. Unlike bulk materials, nanoscale devices have thermal properties which are complicated by boundary effects due to small size. It has been shown that in some cases phonon-boundary scattering effects dominate the thermal conduction processes, reducing thermal conductivity. Depending on the nanostructure size, the phonon mean free path values (Λ) may be comparable or larger than the object size, formula_1 | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures When formula_1 is larger than the phonon mean free path, Umklapp scattering process limits thermal conductivity (regime of diffusive thermal conductivity). When formula_1 is comparable to or smaller than the mean free path (which is of the order 1 µm for carbon nanostructures), the continuous energy model used for bulk materials no longer applies and nonlocal and nonequilibrium aspects to heat transfer also need to be considered. In this case phonons in defectless structure could propagate without scattering and thermal conductivity becomes ballistic (similar to ballistic conductivity). More severe changes in thermal behavior are observed when the feature size formula_1 shrinks further down to the wavelength of phonons. The first measurement of thermal conductivity in silicon nanowires was published in 2003. Two important features were pointed out: 1) The measured thermal conductivities are significantly lower than that of the bulk Si and, as the wire diameter is decreased, the corresponding thermal conductivity is reduced. 2) As the wire diameter is reduced, the phonon boundary scattering dominates over phonon–phonon Umklapp scattering, which decreases the thermal conductivity with an increase in temperature. For 56 nm and 115 nm wires "k ~ T" dependence was observed, while for 37 nm wire "k ~ T" dependence and for 22 nm wire "k ~ T" dependence were observed. Chen "et al | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures " has shown that the one-dimensional cross-over for 20 nm Si nanowire occurs around 8K, while the phenomenon was observed for temperature values greater than 20K. Therefore, the reason of such behaviour is not in the confinement experienced by phonons so that three-dimensional structures display two-dimensional or one-dimensional behavior. Assuming that Boltzmann transport equation is valid, thermal conductivity can be written as: where C is the heat capacity, v is the group velocity and formula_6 is the relaxation time. Note that this assumption breaks down when the dimensions of the system are comparable to or smaller than the wavelength of the phonons responsible for thermal transport. In our case, phonon wavelengths are generally in the 1 nm range and the nanowires under consideration are within tens of nanometers range, the assumption is valid. Different phonon mode contributions to heat conduction can be extracted from analysis of the experimental data for silicon nanowires of different diameters to extract the "C·v" product for analysis. It was shown that all phonon modes contributing to thermal transport are excited well below the Si Debye temperature (645 K). From the thermal conductivity equation, one can write the product "C·v" for each isotropic phonon branch "i". where formula_8 and formula_9 is the phonon phase velocity, which is less sensitive to phonon dispersions than the group velocity "v" | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures Many models of phonon thermal transport ignores the effects of transverse acoustic phonons (TA) at high frequency due to their small group velocity. (Optical phonon contributions are also ignored for the same reason.) However, upper branch of TA phonons have non-zero group velocity at the Brillouin zone boundary along the Γ-Κ direction and, in fact, behave similarly to the longitudinal acoustic phonons (LA) and can contribute to the heat transport. Then, the possible phonon modes contributing to heat conduction are both LA and TA phonons at low and high frequencies. Using the corresponding dispersion curves, the "C·v" product can then be calculated and fitted to the experimental data. The best fit was found when contribution of high-frequency TA phonons is accounted as 70% of the product at room temperature. The remaining 30% is contributed by the LA and TA phonons at low-frequency. Thermal conductivity in nanowires can be computed based on complete phonon dispersions instead of the linearlized dispersion relations commonly used to calculate thermal conductivity in bulk materials | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures Assuming the phonon transport is diffusive and Boltzmann transport equation (BTE) is valid, nanowire thermal conductance "G(T)" can be defined as: where the variable α represents discrete quantum numbers associated with sub-bands found in one-dimensional phonon dispersion relations, "f" represents the Bose-Einstein distribution, "v" is the phonon velocity in the "z" direction and λ is the phonon relaxation length along the direction of the wire length. Thermal conductivity is then expressed as: where "S" is the cross sectional area of the wire, "a" is the lattice constant. It was shown that, using this formula and atomistically computed phonon dispersions (with interatomic potentials developed in ), it is possible to predictively calculate lattice thermal conductivity curves for nanowires, in good agreement with experiments. On the other hand, it was not possible to obtain correct results with the approximated Callaway formula. These results are expected to apply to ”nanowhiskers” for which phonon confinement effects are unimportant. Si nanowires wider than ~35 nm are within this category. For large diameter nanowires, theoretical models assuming the nanowire diameters are comparable to the mean free path and that the mean free path is independent of phonon frequency have been able to closely match the experimental results. But for very thin nanowires whose dimensions are comparable to the dominant phonon wavelength, a new model is required | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures The study in has shown that in such cases, the phonon-boundary scattering is dependent on frequency. The new mean free path is then should be used: Here, "l" is the mean free path (same as Λ). The parameter "h" is length scale associated with the disordered region, "d" is the diameter, "N(ω)" is number of modes at frequency ω, and "B" is a constant related to the disorder region. Thermal conductance is then calculated using the Landauer formula: As nanoscale graphitic structures, carbon nanotubes are of great interest for their thermal properties. The low-temperature specific heat and thermal conductivity show direct evidence of 1-D quantization of the phonon band structure. Modeling of the low-temperature specific heat allows determination of the on-tube phonon velocity, the splitting of phonon subbands on a single tube, and the interaction between neighboring tubes in a bundle. Measurements show a single-wall carbon nanotubes (SWNTs) room-temperature thermal conductivity about 3500 W/(m·K), and over 3000 W/(m·K) for individual multiwalled carbon nanotubes (MWNTs). It is difficult to replicate these properties on the macroscale due to imperfect contact between individual CNTs, and so tangible objects from CNTs such as films or fibres have reached only up to 1500 W/(m·K) so far. Addition of nanotubes to epoxy resin can double the thermal conductivity for a loading of only 1%, showing that nanotube composite materials may be useful for thermal management applications | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures Thermal conductivity in CNT is mainly due to phonons rather than electrons so the Wiedemann–Franz law is not applicable. In general, the thermal conductivity is a tensor quality, but for this discussion, it is only important to consider the diagonal elements: where C is the specific heat, and "v" and formula_6 are the group velocity and relaxation time of a given phonon state. At low temperatures (T is far less than Debye temperature), the relaxation time is determined by scattering of fixed impurities, defects, sample boundaries, etc. and is roughly constant. Therefore, in ordinary materials, the low-temperature thermal conductivity has the same temperature dependence as the specific heat. However, in anisotropic materials, this relationship does not strictly hold. Because the contribution of each state is weighted by the scattering time and the square of the velocity, the thermal conductivity preferentially samples states with large velocity and scattering time. For instance, in graphite, the thermal conductivity parallel to the basal planes is only weakly dependent on the interlayer phonons. In SWNT bundles, it is likely that "k(T)" depends only on the on-tube phonons, rather than the intertube modes. Thermal conductivity is of particular interest in low-dimensional systems | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures For CNT, represented as 1-D ballistic electronic channel, the electronic conductance is quantized, with a universal value of Similarly, for a single ballistic 1-D channel, the thermal conductance is independent of materials parameters, and there exists a quantum of thermal conductance, which is linear in temperature: Possible conditions for observation of this quantum were examined by Rego and Kirczenow. In 1999, Keith Schwab, Erik Henriksen, John Worlock, and Michael Roukes carried out a series of experimental measurements that enabled first observation of the thermal conductance quantum. The measurements employed suspended nanostructures coupled to sensitive dc SQUID measurement devices. In 2008, a colorized electron micrograph of one of the Caltech devices was acquired for the permanent collection of the Museum of Modern Art in New York. At high temperatures, three-phonon Umklapp scattering begins to limit the phonon relaxation time. Therefore, the phonon thermal conductivity displays a peak and decreases with increasing temperature. Umklapp scattering requires production of a phonon beyond the Brillouin zone boundary; because of the high Debye temperature of diamond and graphite, the peak in the thermal conductivity of these materials is near 100 K, significantly higher than for most other materials. In less crystalline forms of graphite, such as carbon fibers, the peak in "k(T)" occurs at higher temperatures, because defect scattering remains dominant over Umklapp scattering to higher temperature | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures In low-dimensional systems, it is difficult to conserve both energy and momentum for Umklapp processes, and so it may be possible that Umklapp scattering is suppressed in nanotubes relative to 2-D or 3-D forms of carbon. Berber "et al." have calculated the phonon thermal conductivity of isolated nanotubes. The value "k(T)" peaks near 100 K, and then decreases with increasing temperature. The value of "k(T)" at the peak (37,000 W/(m·K)) is comparable to the highest thermal conductivity ever measured (41,000 W/(m·K) for an isotopically pure diamond sample at 104 K). Even at room temperature, the thermal conductivity is quite high (6600 W/(m·K)), exceeding the reported room-temperature thermal conductivity of isotopically pure diamond by almost a factor of 2. In graphite, the interlayer interactions quench the thermal conductivity by nearly 1 order of magnitude . It is likely that the same process occurs in nanotube bundles . Thus it is significant that the coupling between tubes in bundles is weaker than expected . It may be that this weak coupling, which is problematic for mechanical applications of nanotubes, is an advantage for thermal applications. The phonon density of states is to calculated through band structure of isolated nanotubes, which is studied in Saito "et al." and Sanchez-Portal "et al." When a graphene sheet is ‘‘rolled’’ into a nanotube, the 2-D band structure folds into a large number of 1-D subbands | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures In a (10,10) tube, for instance, the six phonon bands (three acoustic and three optical) of the graphene sheet become 66 separate 1-D subbands. A direct result of this folding is that the nanotube density of states has a number of sharp peaks due to 1-D van Hove singularities, which are absent in graphene and graphite. Despite the presence of these singularities, the overall density of states is similar at high energies, so that the high temperature specific heat should be roughly equal as well. This is to be expected: the high-energy phonons are more reflective of carbon–carbon bonding than the geometry of the graphene sheet. Thin films are prevalent in the micro and nanoelectronics industry for the fabrication of sensors, actuators and transistors; thus, thermal transport properties affect the performance and reliability of many structures such as transistors, solid-state lasers, sensors, and actuators. Although these devices are traditionally made from bulk crystalline material (silicon), they often contain thin films of oxides, polysilicon, metal, as well as superlattices such as thin-film stacks of GaAs/AlGaAs for lasers. Silicon-on-insulator (SOI) films with silicon thicknesses of 0 | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures 05 µm to 10 µm above a buried silicon dioxide layer are increasingly popular for semiconductor devices due to the increased dielectric isolation associated with SOI/ SOI wafers contain a thin-layer of silicon on an oxide layer and a thin-film of single-crystal silicon, which reduces the effective thermal conductivity of the material by up to 50% as compared to bulk silicon, due to phonon-interface scattering and defects and dislocations in the crystalline structure. Previous studies by Asheghi "et al.", show a similar trend. Other studies of thin-films show similar thermal effects . Thermal properties associated with superlattices are critical in the development of semiconductor lasers. Heat conduction of superlattices is less understood than homogeneous thin films. It is theorized that superlattices have a lower thermal conductivity due to impurities from lattice mismatches and at the heterojunctions. Phonon-interface scattering at heterojunctions needs to be considered in this case; fully elastic scattering underestimates the heat conduction, while fully inelastic scattering overestimates the heat conduction. For example, a Si/Ge thin-film superlattice has a greater decrease in thermal conductivity than an AlAs/GaAs film stack due to increased lattice mismatch | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures A simple estimate of heat conduction of superlattices is: where "C" and "C" are the corresponding heat capacity of film1 and film2 respectively, "v" and "v" are the acoustic propagation velocities in film1 and film2, and "d1" and "d2" are the thicknesses of film1 and film2. This model neglects scattering within the layers and assumes fully diffuse, inelastic scattering. Polycrystalline films are common in semiconductor devices, as the gate electrode of a field-effect transistor is often made of polycrystalline silicon. If the polysilicon grain sizes are small, internal scattering from grain boundaries can overwhelm the effects of film-boundary scattering. Also, grain boundaries contain more impurities, which result in impurity scattering. Likewise, disordered or amorphous films will experience a severe reduction of thermal conductivity, since the small grain size results in numerous grain-boundary scattering effects. Different deposition methods of amorphous films will result in differences in impurities and grain sizes. The simplest approach to modeling phonon scattering at grain boundaries is to increase the scattering rate by introducing this equation: where B is a dimensionless parameter that correlates with the phonon reflection coefficient at the grain boundaries, "d" is the characteristic grain size, and "v" is the phonon velocity through the material | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures A more formal approach to estimating the scattering rate is: where "v" is the dimensionless grain-boundary scattering strength, defined as Here formula_22 is the cross-section of a grain-boundary area, and "ν" is the density of the grain boundary area. There are two approaches to experimentally determine the thermal conductivity of thin films. The goal of experimental metrology of thermal conductivity of thin films is to attain an accurate thermal measurement without disturbing the properties of the thin-film. Electrical heating is used for thin films which have a lower thermal conductivity than the substrate; it is fairly accurate in measuring out-of-plane conductivity. Often, a resistive heater and thermistor is fabricated on the sample film using a highly conductive metal, such as aluminium. The most straightforward approach would be to apply a steady-state current and measure the change in temperature of adjacent thermistors. A more versatile approach uses an AC signal applied to the electrodes. The third harmonic of the AC signal reveals heating and temperature fluctuations of the material. Laser heating is a non-contact metrology method, which uses picosecond and nanosecond laser pulses to deliver thermal energy to the substrate. Laser heating uses a pump-probe mechanism; the pump beam introduces energy to the thin-film, as the probe beam picks up the characteristics of how the energy propagates through the film | https://en.wikipedia.org/wiki?curid=22898551 |
Thermodynamics of nanostructures Laser heating is advantageous because the energy delivered to the film can be precisely controlled; furthermore, the short heating duration decouples the thermal conductivity of the thin film from the substrate . | https://en.wikipedia.org/wiki?curid=22898551 |
Aminoisobutyric acid may refer to either of two isomeric chemical compounds: | https://en.wikipedia.org/wiki?curid=22905329 |
Volute (pump) A volute is a curved funnel that increases in area as it approaches the discharge port. The volute of a centrifugal pump is the casing that receives the fluid being pumped by the impeller, maintaining the velocity of the fluid through to the diffuser. As liquid exits the impeller it has high kinetic energy and the volute directs this flow through to the discharge. As the fluid travels along the volute it is joined by more and more fluid exiting the impeller but, as the cross sectional area of the volute increases, the velocity is maintained if the pump is running close to the design point. If the pump has a low flow rate then the velocity will decrease across the volute leading to a pressure rise causing a cross thrust across the impeller that we see as vibration. If the pump flow is higher than design the velocity will increase across the volute and the pressure will decrease according to the first law of thermodynamics. This will cause a side thrust in the opposite direction to that caused by low flow but the result is the same - vibration with resultant short bearing and seal life. The volute does not convert kinetic energy into pressure - that is done at the diffuser by reducing liquid velocity while increasing pressure. The name "volute" is inspired by the resemblance of this kind of casing to the scroll-like part near the top of an ionic order column in classical architecture, called a volute | https://en.wikipedia.org/wiki?curid=22917401 |
Volute (pump) In a split volute or double volute pump, the path along the volute is partitioned, providing two distinct discharge paths. The streams start out 180 degrees from each other, and merge by the time they reach the discharge port. This arrangement helps to balance the radial force on the bearings. | https://en.wikipedia.org/wiki?curid=22917401 |
Trifluoromethyltrimethylsilane (known as Ruppert-Prakash reagent, TMSCF) is an organosilicon compound with the formula CFSi(CH). It is a colorless liquid. The compound is a reagent used in organic chemistry for the introduction of the trifluoromethyl group. The compound was first prepared in 1984 by Ingo Ruppert and further developed as a reagent by G. K. Surya Prakash. The reagent is prepared from trimethylsilyl chloride and bromotrifluoromethane in the presence of a phosphorus(III) reagent that serves as a halogen acceptor. In the presence of an anionic initiator (M X), the reagent reacts with aldehydes and ketones to give a trimethylsilyl ether, the net product of insertion of the carbonyl into the Si-CF bond. Hydrolysis gives trifluoromethyl methanols. The reagent also converts esters to trifluoromethyl ketones. A typical initiator is a soluble fluoride-containing species such as tetrabutylammonium fluoride, however simple alkoxides, e.g. KOtBu, are also effective. The mechanism begins by generation of Si(CH)X and a highly reactive [CF] (trifluoromethide) intermediate. The [CF] attacks the carbonyl to generate an alkoxide anion. The alkoxide is silylated by the reagent to give the overall addition product, plus [CF], thus propagating an anionic chain reaction. The reagent competes with the carbonyl for the reactive intermediate, rapidly sequestering [CF] in a reversibly-generated -ate complex [(CF)Si(CH)] | https://en.wikipedia.org/wiki?curid=22919086 |
Trifluoromethyltrimethylsilane This -ate complex is unable to react directly with the carbonyl, resulting in powerful inhibition of the chain reaction by the reagent. This inhibitory process is common to all anion-initiated reactions of the reagent, with the identity of the counter-cation (M) playing a major role in controlling the overall rate. The reagent has largely supplanted trifluoromethyllithium, which is not isolable and rapidly decomposes to yield lithium fluoride and difluorocarbene. | https://en.wikipedia.org/wiki?curid=22919086 |
MTBE controversy Methyl tert-butyl ether (MTBE) is a gasoline additive used as an oxygenate and to raise the octane number. Its use has declined in the United States in response to environmental and health concerns. It has polluted groundwater due to MTBE-containing gasoline being spilled or leaked at gas stations. MTBE spreads more easily underground than other gasoline components due to its higher solubility in water. Cost estimates for removing MTBE from groundwater and contaminated soil range from $1 billion to $30 billion, including removing the compound from aquifers and municipal water supplies, and replacing leaky underground oil tanks. Who will pay for remediation is controversial. In one case, the cost to oil companies to clean up the MTBE in wells belonging to the city of Santa Monica, California is estimated to exceed $200 million. Some U.S. states have enacted laws to ban MTBE in certain areas. California and New York, which together accounted for 40% of U.S. MTBE consumption, banned usage of the chemical in gasoline, effective 2002 and 2004, respectively. As of 2007, 25 states had issued complete or partial bans on the use of MTBE. The Energy Policy Act of 2005 prompted gasoline refiners to transition to the use of ethanol as a gasoline additive, in place of MTBE. Harford County, Maryland, found MTBE in wells near several of its filling stations beginning in 2004. This led the state of Maryland to make moves to ban MTBE | https://en.wikipedia.org/wiki?curid=22928693 |
MTBE controversy In 2005, an Exxon-Mobil station in Fallston, Maryland, was found to be leaking MTBE into the local wells. The discovery resulted in the station being abruptly closed. Exxon-Mobil referred to the closure as a "business decision". Following the closure, MTBE levels in the area dropped. In September 2004, Harford County placed a six-month moratorium on construction of filling stations. In 2006, the wells of a neighborhood in Jacksonville, Maryland, were contaminated by a spill of 26,000 gallons of gasoline from an Exxon-Mobil station in the area, resulting in an ongoing court battle. The suit has been filed by the state of Maryland's Department of the Environment on behalf of the area's residents, seeking millions of dollars in damages from Exxon-Mobil. Many residents also filed their own separate lawsuits. The case began in 2006, when a gasoline tank sprang a leak that was not detected for 34 days. Testing of 120 wells resulted in dangerously high levels of MTBE being found. Residents were put in danger by the spill, and in order to prevent further health problems, they required bottled water for cooking, drinking, and brushing teeth. Residents of Jacksonville continue to use bottled water for all activities despite having MTBE filters and alarms installed in their homes. Home values also dropped as a result of the spill | https://en.wikipedia.org/wiki?curid=22928693 |
MTBE controversy In September 2008, Exxon-Mobil settled the case with the state by agreeing to pay a $4 million fine, and face an additional $1 million in penalties annually if they did not work to clean up the spill. In March 2009, a jury awarded $150 million in damages to some of the area's residents. The jury did not assess any punitive damages in the case, finding that Exxon Mobil did not act fraudulently. A separate case including over 150 property owners as plaintiffs began in early 2011. Punitive damages were awarded to the second group of plaintiffs, on the basis that Exxon acted fraudulently, however this decision was later reversed. In 1995 high levels of MTBE were unexpectedly discovered in the water wells of Santa Monica, California, and the U.S. Geological Survey reported detections.<ref name="https://pubs.er.usgs.gov/pubs/fs/fs11495"></ref> Subsequent U.S. findings indicate tens of thousands of contaminated sites in water wells distributed across the country. As per toxicity alone, MTBE is not classified as a hazard for the environment, but it imparts an unpleasant taste to water even at very low concentrations. The maximum contaminant level of MTBE in drinking water has not yet been established by the United States Environmental Protection Agency (EPA). The leakage problem is partially attributed to the lack of effective regulations for underground storage tanks, but spillage from overfilling is also a contributor. As an ingredient in unleaded gasoline, MTBE is the most water-soluble component | https://en.wikipedia.org/wiki?curid=22928693 |
MTBE controversy When dissolved in groundwater, MTBE will lead the contaminant plume with the remaining components such as benzene and toluene following. Thus the discovery of MTBE in public groundwater wells indicates that the contaminant source was a gasoline release. Its criticism and subsequent decreased usage, some claim, is more a product of its easy detectability (taste) in extremely low concentrations (ppb) than its toxicity. The MTBE concentrations used in the EU (usually 1.0–1.6%) and allowed (maximum 5%) in Europe are lower than in California. Chevron, BP, and other oil companies agreed to settle with Santa Monica for $423 million on May 7, 2008. "This was a significant collision causing significant damage to both vessels," said Capt. Brian Penoyer with the U.S. Coast Guard. The Carla Maersk was damaged and leaked MTBE, which is a fuel additive in gasoline. The Carla Maersk was reportedly carrying 216,000 barrels of MTBE, but the Coast Guard is unsure at this time how much chemical leaked. In 2000, EPA drafted plans to phase out the use of MTBE nationwide over four years.. Some states enacted MTBE prohibitions without waiting for federal restrictions. California banned MTBE as a gasoline additive in 2002. The State of New York banned the use of MTBE as a "fuel additive", effective in 2004. MTBE use is still legal in the state for other industrial uses. The federal Energy Policy Act of 2005 removed the oxygenate requirement for reformulated gasoline and established a renewable fuel standard | https://en.wikipedia.org/wiki?curid=22928693 |
MTBE controversy The lack of MTBE liability protection in the law also prompted refiners to substitute ethanol for MTBE as a gasoline additive. EPA issued a drinking water health advisory for MTBE, a guidance document for water utilities and the public, in 1997. The Agency first listed MTBE in 1998 as a candidate for development of a national Maximum Contaminant Level (MCL) standard in drinking water. As of 2018 EPA has not announced whether it will develop an MCL. EPA uses toxicity data in developing MCLs for public water systems. California established a state-level MCL for MTBE in 2000. | https://en.wikipedia.org/wiki?curid=22928693 |
Paraho process The is an above ground retorting technology for shale oil extraction. The name "Paraho" is delivered from the words ""para homem"", which means in Portuguese "for mankind". The was invented by John B. Jones, Jr., later president of the Paraho Development Corporation, and developed by Development Engineering, Inc., in the late 1960s. Its design was based on a gas combustion retort developed by the United States Bureau of Mines and the earlier Nevada–Texas–Utah Retort. In the late 1940s, these retorts were tested in the Oil Shale Experiment Station at Anvil Points in Rifle, Colorado. In 1971, the Standard Oil of Ohio started to cooperate with Mr. John B. Jones providing financial support for obtaining an oil shale lease at Anvil Points. In May 1972, the lease was approved. Before leasing a track at Anvil Points, a test of using the Paraho Direct process for limestone calcination in cement kilns was carried out. The consortium for developing the Anvil Points lease – the Paraho Development Corporation – was formed in 1973. In addition to the Standard Oil of Ohio, other participants of the consortium were Atlantic Richfield, Carter Oil, Chevron Research, Cleveland-Cliffs Iron, Gulf Oil, Kerr-McKee, Marathon Oil, Arthur G. McKee, Mobil Research, Phillips Petroleum Company, Shell Development, Southern California Edison, Standard Oil Company (Indiana), Sun Oil, Texaco, and the Webb-Chambers-Gary-McLoraine Group | https://en.wikipedia.org/wiki?curid=22929865 |
Paraho process Shale oil retorting started in 1974 when two operational retorts – pilot plant and semiworks – were put into operation. The semiworks unit achieved a maximum throughput capacity of 290 tons (263 tonnes) of raw oil shale per day. In March 1976, the Paraho Development Corporation tested a modification of its technology – the Paraho Indirect process. The Anvil Points lease was closed in 1978. In 1976–1978, under the contracts with the United States Navy, Paraho technology was used for production of 100,000 barrels of crude shale oil. It was tested for using as military transportation fuels. The Gary Western Refinery in Fruita, Colorado, refined the Paraho shale oil for production of gasoline, jet fuels, diesel fuel marine, and heavy fuel oil. Paraho JP-4 aviation fuel was tested by the United States Air Force in the T-39 jet aircraft flight, which took a place between the Wright Patterson Air Force Base (Dayton, Ohio) and the Carswell Air Force Base (Fort Worth, Texas). In addition, the Paraho heavy fuel oil was used for fueling a Cleveland-Cliffs Iron ore carrier during its 7-day cruise on Great Lakes. On 13 June 1980, the Department of Energy awarded $4.4 million contract (participants providing additional $3.7 million) for an 18-month study to construct an 18,000 TPD modular demonstration shale oil plant producing 10,000 BPD on a lease 40 miles southeast of Vernal, Utah. The demonstration module was never built | https://en.wikipedia.org/wiki?curid=22929865 |
Paraho process In 1982, Paraho’s semi-works plant was torn down when the Anvil Points station was decommissioned, but the pilot plant was moved to an adjacent plot of private land. In 1987, Paraho reorganized as New Paraho and began production of SOMAT asphalt additive used in test strips in 5 States. In 1991, New PARAHO reported successful tests of SOMAT shale oil asphalt additive. On 28 June 2000, Shale Technologies purchased Paraho Development Corporation and became owner of the proprietary information relating to the Paraho oil shale retorting technologies. On 14 August 2008, Queensland Energy Resources announced that it will use the Paraho Indirect technology for its Stuart Oil Shale Project. The can be operated in two different heating modes, which are direct and indirect. The Paraho Direct process evolved from gas combustion retort technology and is classified as an internal combustion method. Accordingly, the Paraho Direct retort is a vertical shaft retort similar to the Kiviter and Fushun retorts, used correspondingly in Estonia and China. However, compared to the earlier gas combustion retorts the Paraho retort's raw oil shale feeding mechanism, gas distributor, and discharge grate have different designs. In the Paraho Direct process, the crushed and screened raw oil shale is fed into the top of the retort through a rotating distributor. The oil shale descends the retort as a moving bed | https://en.wikipedia.org/wiki?curid=22929865 |
Paraho process The oil shale is heated by the rising combustion gases from the lower part of the retort and the kerogen in the shale decomposes at about to oil vapour, shale oil gas and spent shale. Heat for pyrolysis comes from the combustion of char in the spent shale. The combustion takes place where air is injected at two levels in the middle of the retort below the pyrolysis section raising the temperature of the shale and the gas to to . Collecting tubes at the top of the retort carry shale oil mist, evolved gases and combustion gases into the product separation unit, where oil, water and dust are separated from the gases. For combined removal of liquid droplets and particulates, a wet electrostatic precipitator is used. Cleaned gases from the precipitator are compressed in a compressor. Part of the gas from the compressor is recycled to the bottom of the retort to cool the combusted shale (shale ash) and carry the recovered heat back up the retort. Cooled shale ash exits the retort through the discharge grate in the bottom of the retort. After processing, shale ash is disposed of. The liquid oil is separated from produced water and may be further refined into high quality products. The mixture of evolved gases and combustions gases is available for use as a low quality fuel gas for drying or power generation. The Paraho Indirect is classified as an externally generated hot gas technology | https://en.wikipedia.org/wiki?curid=22929865 |
Paraho process The Paraho Indirect retort configuration is similar to the Paraho Direct except that a part of the gas from the compressor is heated to between to in a separate furnace and injected into the retort instead of air. No combustion occurs in the Paraho Indirect retort itself. As a result, the fuel gas from the Paraho Indirect is not diluted with combustion gases and the char remains on the disposed spent shale. The main advantage of the is simplicity in process and design; it has few moving parts and therefore low construction and operating costs compared with more sophisticated technologies. The Paraho retort also consumes no water, which is especially important for oil shale extraction in areas with water scarcity. A disadvantage common to both the Paraho Direct and Paraho Indirect is that neither are able to process oil shale particles smaller than about . These fines may account for 10 to 30 per cent of the crushed feed. | https://en.wikipedia.org/wiki?curid=22929865 |
Diboride may refer to: | https://en.wikipedia.org/wiki?curid=22930206 |
Hose barb Hose barbs are cylindrical pieces or parts for attaching and securing of hoses (tubing). The barb-like rings on the cylindrical piece allow for an easy push-connection of flexible-plastic or rubber tubing that is not so easily disconnected. Hose barbs are used in machine perfusion and chemistry laboratory equipment. fittings are small curved, bent or T-shaped pipes, hoses or tubes with hose barbs on at least one side used to join two or more pieces of piping (hosing, tubing) together. Hose barbs are commonly used in the agriculture industry to connect anhydrous ammonia (NH3) hoses. | https://en.wikipedia.org/wiki?curid=22943237 |
Adolf Martin Pleischl (born 10 October 1787, in Hossenreith, Bohemia; died 31 July 1867, in Dorf an der Enns) was a chemist and medical doctor. In 1815 he obtained his medical doctorate from the University of Prague, where he later served as a professor of general and pharmaceutical chemistry (1821–38). At Prague he is credited with improvement and redevelopment of the chemical-pharmaceutical institute. In 1838 he relocated to the University of Vienna, where he also redeveloped and modernized its chemical and pharmaceutical facilities. As an instructor, two of his better-known students were Johann Florian Heller (1813-1871) and Johann August Natterer (1821-1900). While at Prague he performed the first scientific analysis of its water (the Moldau River, city fountains, drinking water). He also analyzed the thermal springs of Bohemian spa sites, and was an enthusiastic recruiter for spa treatment at Karlsbad, Marienbad, Franzensbad and Teplitz. His endorsement of Karlsbad water helped lead to a lucrative source of income through the export of bottled water and soda products. Pleischl is credited with the creation of a safe non-metallic enamel for coating metal dishes. Also, he attempted to liquefy carbon dioxide by means of pressure and low temperature, a process that was later successfully achieved by his pupil, Johann August Natterer. In his later years, he was awarded with the Knight's Cross of the Order of Franz Joseph. In 1949 the "Pleischlgasse" in Simmering (11th District- Vienna) was named in his honour | https://en.wikipedia.org/wiki?curid=22948278 |
Adolf Martin Pleischl His daughter Mary, was married to physician Johann von Oppolzer (1808-1871). | https://en.wikipedia.org/wiki?curid=22948278 |
Magnetation (iron ore) Magnetation is the processing of iron ore tailings, the waste product of iron ore mines, to recover hematite. Crushed mine tailings are mixed with water to create a slurry; the slurry is then pumped through magnetic separation chambers to extract hematite. Commercial interest in this process stems from the possibility of extracting additional iron from tailings supplied by existing mines, increasing their yield. | https://en.wikipedia.org/wiki?curid=22956808 |
William J. A. Bailey William John Aloysius Bailey (May 25, 1884 – May 17, 1949) was an American patent medicine inventor and salesman. A Harvard University dropout, Bailey falsely claimed to be a doctor of medicine and promoted the use of radioactive radium as a cure for coughs, flu, and other common ailments. Although Bailey's Radium Laboratories in East Orange, New Jersey was continually investigated by the Federal Trade Commission, he died wealthy from his many devices and products, including an aphrodisiac called Arium, marketed as a restorative that "renewed happiness and youthful thrill into the lives of married peoples whose attractions to each other had weakened." Bailey was born on May 25, 1884 in Boston, Massachusetts and attended Boston Latin School. He was later accepted to Harvard University but did not graduate. In 1918, Bailey claimed that radium added to drinking water could be used to treat dozens of conditions, from mental illness and headaches to diabetes, anemia, constipation, and asthma. Bailey became rich from the sale of Radithor, a well known patent medicine/snake oil that is possibly the best known example of radioactive quackery. Bailey created Radithor by dissolving radium salts in water to deliver 1 microcurie of radiation from each of Ra and Ra, claiming its curative properties were due to stimulation of the endocrine system | https://en.wikipedia.org/wiki?curid=22964649 |
William J. A. Bailey Radithor was advertised as "A Cure for the Living Dead" as well as "Perpetual Sunshine" In fact, Radithor was a lethal mixture, and was responsible for the death of Eben Byers in 1932, who died of radiation-induced cancer after drinking about 1,400 bottles of Radithor. Bailey also invented the Radiendocrinator around 1930. This was a cased source, intended to be worn against the skin. During World War II, Bailey was the wartime manager of the electronic division of International Business Machines. Bailey died of bladder cancer on May 17, 1949. When his body was exhumed nearly 20 years later, it was found to be "ravaged by radiation". | https://en.wikipedia.org/wiki?curid=22964649 |
C10H14 The molecular formula CH may refer to: | https://en.wikipedia.org/wiki?curid=22965315 |
Nitrosonium octafluoroxenate(VI) is a chemical compound of xenon with nitrogen, oxygen, and fluorine, having formula . It is an ionic compound containing well-separated nitrosonium cations (NO) and octafluoroxenate(VI) anions (). The molecular geometry of the octafluoroxenate(VI) ion is square antiprismatic, having Xe–F bond lengths of 1.971 Å, 1.946 Å, 1.958 Å, 2.052 Å, and 2.099 Å. It is synthesized by the reaction of xenon hexafluoride () with nitrosyl fluoride (NOF): Other compounds containing the octafluoroxenate(VI) ion include its alkali metal salts, including CsXeF and RbXeF, which are stable up to 400 °C. | https://en.wikipedia.org/wiki?curid=22965963 |
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