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The above technique can obviously not correct for a background with fine structure, as in this case the absorbance will be different at each of the correction pixels. In this case HR-CS AAS is offering the possibility to measure correction spectra of the molecule(s) that is (are) responsible for the background and store them in the computer. These spectra are then multiplied with a factor to match the intensity of the sample spectrum and subtracted pixel by pixel and spectrum by spectrum from the sample spectrum using a least-squares algorithm. This might sound complex, but first of all the number of di-atomic molecules that can exist at the temperatures of the atomizers used in AAS is relatively small, and second, the correction is performed by the computer within a few seconds. The same algorithm can actually also be used to correct for direct line overlap of two atomic absorption lines, making HR-CS AAS the only AAS technique that can correct for this kind of spectral interference. | 0 | Theoretical and Fundamental Chemistry |
Most plastics do not biodegrade readily, however, they do still degrade in the environment because of the effects of UV-light, oxygen, water and pollutants. This combination is often generalised as polymer weathering. Chain breaking by weathering causes increasing embrittlement of plastic items, which eventually causes them to break apart. Fragmentation then continues until eventually microplastics are formed. As the particle sizes get smaller, so their combined surface area increases. This facilitates the leaching of additives out of plastic and into the environment. Many controversies associated with plastics actually relate to these additives. | 0 | Theoretical and Fundamental Chemistry |
At the request of Ernest Lawrence, Gofman established the Medical Department at the Lawrence Livermore National Laboratory (LLNL) in early 1954 and acted as the medical director until 1957 roughly two days a week while teaching at Berkeley the rest of the time. | 0 | Theoretical and Fundamental Chemistry |
In the theory of many-particle systems, Jacobi coordinates often are used to simplify the mathematical formulation. These coordinates are particularly common in treating polyatomic molecules and chemical reactions, and in celestial mechanics. An algorithm for generating the Jacobi coordinates for N bodies may be based upon binary trees. In words, the algorithm is described as follows:
and m be the masses of two bodies that are replaced by a new body of virtual mass M = m + m. The position coordinates x and x are replaced by their relative position r = x − x and by the vector to their center of mass R = (m q + mq)/(m + m). The node in the binary tree corresponding to the virtual body has m as its right child and m as its left child. The order of children indicates the relative coordinate points from x to x. Repeat the above step for N − 1 bodies, that is, the N − 2 original bodies plus the new virtual body. </blockquote>
For the N-body problem the result is:
with
The vector is the center of mass of all the bodies and is the relative coordinate between the particles 1 and 2:
The result one is left with is thus a system of N-1 translationally invariant coordinates and a center of mass coordinate , from iteratively reducing two-body systems within the many-body system.
This change of coordinates has associated Jacobian equal to .
If one is interested in evaluating a free energy operator in these coordinates, one obtains
In the calculations can be useful the following identity | 0 | Theoretical and Fundamental Chemistry |
The first glycal was synthesized by Hermann Emil Fischer and Karl Zach in 1913. They synthesized this 1,2-unsaturated sugar from D-glucose and named their product D-glucal. Fischer believed he had synthesized an aldehyde, and therefore he gave the product a name that suggested this. By the time he discovered his mistake, the name "glycal" was adopted as a general name for all sugars with a double bond between carbon atoms 1 and 2. | 0 | Theoretical and Fundamental Chemistry |
The cost of sewerage - conventional or simplified - are always site-specific, and estimates are subject to controversies. Construction costs of simplified sewerage are up to half the costs of conventional sewerage. Investment cost savings come from various design features that may or may not be present in a particular simplified sewerage system. Cost-saving features of any simplified sewerage system are a smaller diameter of pipes, smaller and shallower trenches and simplified manholes. The two latter features are estimated to account for most of the cost savings. Other features that could further reduce costs may only be present in some systems, such as:
* shorter networks;
* avoidance of the need to damage pavements and sidewalks (if they already exist and if pipes are laid in front or back yards);
* decentralized, small-scale wastewater treatment, and consequently elimination of main collectors and sewage pumping stations.
An element that may slightly increase costs compared to conventional sewerage is the introduction of grease traps or of interceptor chambers for the settlement of sludge. The latter are more common in South Asia and are not used in the condominial model. A 2006 study of four countries showed cost savings of 31-57% from the use of simplified sewerage compared to conventional sewerage with unit costs varying from US$119 per connection in a neighborhood in Bolivia and to US$759 per connection in a small town in Paraguay. A detailed estimate gives the costs of simplified sewerage in Lima as at least US$700 per household (US$120–140 per person), including in-house sanitary facilities (US$100 per household) and including design, supervision and social intermediation costs (US$126 per household, which are common costs shared with water infrastructure), but excluding taxes.
In general, at higher population densities sewer systems are cheaper than on-site sanitation (such as septic tanks). The switching value at which sewerage becomes less costly is largely determined by the type of sewerage, conventional or simplified. A 1983 study in Natal showed that the investment costs for simplified sewerage were lower than for on-site systems at the quite low population density of about 160 people per hectare. Conventional sewerage, however, was cheaper only at densities above 400 people per hectare. | 1 | Applied and Interdisciplinary Chemistry |
The mechanisms of main group compounds of groups 13-18 are usually discussed in the context of organic chemistry (organic compounds are main group compounds, after all). Elements heavier than C, N, O, and F often form compounds with more electrons than predicted by the octet rule, as explained in the article on hypervalent molecules. The mechanisms of their reactions differ from organic compounds for this reason. Elements lighter than carbon (B, Be, Li) as well as Al and Mg often form electron-deficient structures that are electronically akin to carbocations. Such electron-deficient species tend to react via associative pathways. The chemistry of the lanthanides mirrors many aspects of chemistry seen for aluminium. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, the bicapped trigonal prismatic molecular geometry describes the shape of compounds where eight atoms or groups of atoms or ligands are arranged around a central atom defining the vertices of a biaugmented triangular prism. This shape has C symmetry and is one of the three common shapes for octacoordinate transition metal complexes, along with the square antiprism and the dodecahedron.
It is very similar to the square antiprismatic molecular geometry, and there is some dispute over the specific geometry exhibited by certain molecules. One example of the bicapped trigonal prismatic molecular geometry is the ion.
The bicapped trigonal prismatic coordination geometry is found in the plutonium(III) bromide crystal structure type, which is adopted by many of the bromides and iodides of the lanthanides and actinides. | 0 | Theoretical and Fundamental Chemistry |
An alternative quantitative approach to inorganic chemistry focuses on energies of reactions. This approach is highly traditional and empirical, but it is also useful. Broad concepts that are couched in thermodynamic terms include redox potential, acidity, phase changes. A classic concept in inorganic thermodynamics is the Born–Haber cycle, which is used for assessing the energies of elementary processes such as electron affinity, some of which cannot be observed directly. | 0 | Theoretical and Fundamental Chemistry |
Biodegradation has been well investigated because of its relevance to sewage plants with specialized microorganisms. Two microorganisms that have been studied in depth are the white rot fungus and the bacterium Nocardia Corallina. | 0 | Theoretical and Fundamental Chemistry |
Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important role in the cellular metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals. Urea is Neo-Latin, , , itself from Proto-Indo-European *h₂worsom.
It is a colorless, odorless solid, highly soluble in water, and practically non-toxic ( is 15 g/kg for rats). Dissolved in water, it is neither acidic nor alkaline. The body uses it in many processes, most notably nitrogen excretion. The liver forms it by combining two ammonia molecules () with a carbon dioxide () molecule in the urea cycle. Urea is widely used in fertilizers as a source of nitrogen (N) and is an important raw material for the chemical industry.
In 1828, Friedrich Wöhler discovered that urea can be produced from inorganic starting materials, which was an important conceptual milestone in chemistry. This showed for the first time that a substance previously known only as a byproduct of life could be synthesized in the laboratory without biological starting materials, thereby contradicting the widely held doctrine of vitalism, which stated that only living organisms could produce the chemicals of life. | 0 | Theoretical and Fundamental Chemistry |
The diffraction from a crystalline material, and thus the intensity of the diffracted beam, changes with the type and number of atoms inside the crystal unit cell. This fact is quantitatively expressed by the structure factor. Different materials have different structure factors, and similarly for different phases of the same material (e.g. for materials crystallizing in several different space groups). In samples composed of a mixture of materials/phases in spatially adjacent domains, the geometry of these domains can be resolved by topography. This is true, for example, also for twinned crystals, ferroelectric domains, and many others. | 0 | Theoretical and Fundamental Chemistry |
An airlift pump is a pump that has low suction and moderate discharge of liquid and entrained solids. The pump injects compressed air at the bottom of the discharge pipe which is immersed in the liquid. The compressed air mixes with the liquid causing the air-water mixture to be less dense than the rest of the liquid around it and therefore is displaced upwards through the discharge pipe by the surrounding liquid of higher density. Solids may be entrained in the flow and if small enough to fit through the pipe, will be discharged with the rest of the flow at a shallower depth or above the surface. Airlift pumps are widely used in aquaculture to pump, circulate and aerate water in closed, recirculating systems and ponds. Other applications include dredging, underwater archaeology, salvage operations and collection of scientific specimens. | 1 | Applied and Interdisciplinary Chemistry |
Arthur Charles Wahl (September 8, 1917 – March 6, 2006) was an American chemist who, as a doctoral student of Glenn T. Seaborg at the University of California, Berkeley, first isolated plutonium in February 1941. He was a worker on the Manhattan Project in Los Alamos until 1946, when he joined Washington University in St. Louis. Beginning in 1952, he was the Henry V. Farr Professor of Radiochemistry; he received the American Chemical Society Award in Nuclear Chemistry in 1966 and retired in 1983. He moved back to Los Alamos in 1991 and continued his scientific writing until 2005. He died in 2006 of Parkinson's disease and pneumonia. | 0 | Theoretical and Fundamental Chemistry |
Certain synthetic ion channels have conductances that can be modulated by additional of external chemicals. Both up-modulation (channels are turned on by ligand) and down-modulation (channels are turned off by ligands) are known: different mechanisms, including formation of supramolecular aggregates, as well as inter- and intramolecular blockage. | 0 | Theoretical and Fundamental Chemistry |
In magnetic resonance, a spin echo or Hahn echo is the refocusing of spin magnetisation by a pulse of resonant electromagnetic radiation. Modern nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) make use of this effect.
The NMR signal observed following an initial excitation pulse decays with time due to both spin relaxation and any inhomogeneous effects which cause spins in the sample to precess at different rates. The first of these, relaxation, leads to an irreversible loss of magnetisation. But the inhomogeneous dephasing can be removed by applying a 180° inversion pulse that inverts the magnetisation vectors. Examples of inhomogeneous effects include a magnetic field gradient and a distribution of chemical shifts. If the inversion pulse is applied after a period t of dephasing, the inhomogeneous evolution will rephase to form an echo at time 2t. In simple cases, the intensity of the echo relative to the initial signal is given by e is the time constant for spin–spin relaxation. The echo time (TE) is the time between the excitation pulse and the peak of the signal.
Echo phenomena are important features of coherent spectroscopy which have been used in fields other than magnetic resonance including laser spectroscopy and neutron scattering. | 0 | Theoretical and Fundamental Chemistry |
The Bionic Leaf is an artificial leaf that interfaces a triple-junction Si wafer with amorphous silicon photovoltaic with hydrogen- and oxygen-evolving catalysts made from a ternary alloy, nickel-molybdenum-zinc (NiMoZn) and a cobalt–phosphate cluster (Co-OEC). The Co-OEC is able to operate in natural water at room temperature. Accordingly, the Bionic Leaf can be immersed in water and when held up to sunlight, it can effect direct solar energy conversion via water-splitting.
The Bionic Leaf, by virtue of the Co-OEC, also exhibits self-assembling and self-healing properties. The Co-OEC self-assembles upon oxidation of an earth metal ion from 2+ to 3+. It also self-heals upon application of a potential, wherein the cluster reforms due to equilibrium between aqueous cobalt and phosphate.
The Bionic Leaf can be used in artificial photosynthetic systems. One such system is a hybrid water-splitting-biosynthetic system that can operate at low driving voltages. The catalyst system of the Bionic Leaf is used in conjunction with bacterium Ralstonia eutropha. The bacterium is grown in contact with the catalysts and then consumes the produced H from the water-splitting reaction. After consumption, the bacterium synthesizes biomass and fuels or chemical products from low CO concentration in the presence of O. The usage of the bacterium requires a biocompatible catalyst system that is not toxic to the bacterium and that lowers the overpotential for water splitting. The original catalyst used, the nickel-molybdenum-zinc (NiMoZn) alloy, poisoned the microbes by destroying the bacteria's DNA. Accordingly, this hybrid system uses a cobalt-phosphorus (Co-P) alloy cathode that is resistant to reactive oxygen species. This in return leaves no excess metal and does not form oxygen radicals, leaving the microbes and DNA unharmed. This alloy drives the hydrogen evolution reaction while a cobalt-phosphate (CoP) anode drives the oxygen evolution reaction. This new catalyst can run up to 16 days at a time when compared to the nickel-molybdenum-zinc (NiMoZn) alloy. | 0 | Theoretical and Fundamental Chemistry |
CKLF like MARVEL transmembrane domain-containing 1 (i.e. CMTM1), formerly termed chemokine-like factor superfamily 1 (i.e. CKLFSF1), has 23 known isoforms, the CMTM1-v1 to CMTM1-v23 proteins. Protein isoforms are variant products that are made by alternative splicing of a single gene. The gene for these isoforms, CMTM1 (formerly termed CKLFSF1), is located in band 22 on the long (i.e. "q") arm of chromosome 16. The CMTM1 gene and its 23 isoforms belong to the CKLF-like MARVEL transmembrane domain-containing family of structurally and functionally related genes and proteins. CMTM1 (isoforms not specified) proteins are weakly express in a wide range of normal tissues but are far more highly expressed in normal testes as well as the malignant cells of certain types of cancer.
Studies have reported that the levels of CMTM1 (typically the CMTM1–v17 isoform) are more highly expressed in breast, kidney, lung, ovary, liver (i.e. hepatocellular carcinoma), and salivary gland adenoid cystic carcinoma malignant tissues than the nearby normal tissues of these respective organs. According to the Human Protein Atlas, higher levels of CMTM1 expression in hepatocellular carcinoma tissues are associated with shorter survival times. Another study found that the levels of CMTM1 mRNA (which directs the production of CMTM1 protein) were higher in stomach cancer compared to nearby normal stomach tissues. And, studies of glioblastoma found no significant difference between the levels of CMTM1 in this brain tumor's tissues versus nearby normal brain tissues but higher levels of tumor tissue CMTM1 were associated with poorer prognoses. In addition, the forced overexpression of CMTM1 in cultured glioblastoma cell lines increased their proliferation and invasiveness. These findings suggest that CMTM1 proteins may act to promote the cited cancers and support further studies to determine if these proteins contribute to the development and/or progression of the cited cancers, can be used as markers of disease severity and/or prognosis, or are targets for treating these cancers.
In contrast to the findings in the cancers just cited, cell culture studies indicated that the forced overexpression of the CMTM1-v5 isoform induced apoptosis (i.e. cell death due to the activation of cell death-inducing signaling pathways) in two types of lymphoma cell lines, Jurkat cells (a human T cell leukemia cell line) and Raji cells (a human non-Hodgkins lymphoma cell line). Simple addition of CMTM1-v5 protein to cultures of Daudi or Ramos cells (both are Burkitts lymphoma cell lines) or Jurkat cells likewise caused these cells to become apoptotic. Various other cultured hematological tumor cell lines had no such response to the CMTM1-v5 protein. Finally, the injection of CMTM1-v5 into mice containing Raji cell tumors in a xenotransplantation model of cancer inhibited the spread of these tumors and prolonged the survival of the mice. These findings suggest that CMTM1-v5 protein may act to suppress certain types of lymphoma in humans and support initial studies to define the CMTM1-v5 levels in the malignant cells of humans with these lymphomas. Further studies are also needed to determine the basis for the CMTM1 proteins promoting actions in the cited cancers versus' suppressing actions in the cited lymphomas. | 1 | Applied and Interdisciplinary Chemistry |
DNA encodes protein sequence by a series of three-nucleotide codons. Any given sequence of DNA can therefore be read in six different ways: Three reading frames in one direction (starting at different nucleotides) and three in the opposite direction. During transcription, the RNA polymerase read the template DNA strand in the 3′→5′ direction, but the mRNA is formed in the 5′ to 3′ direction. The mRNA is single-stranded and therefore only contains three possible reading frames, of which only one is translated. The codons of the mRNA reading frame are translated in the 5′→3′ direction into amino acids by a ribosome to produce a polypeptide chain. | 1 | Applied and Interdisciplinary Chemistry |
Sea salt is salt that is produced by the evaporation of seawater. It is used as a seasoning in foods, cooking, cosmetics and for preserving food. It is also called bay salt, solar salt, or simply salt. Like mined rock salt, production of sea salt has been dated to prehistoric times. | 0 | Theoretical and Fundamental Chemistry |
In 2017, the University of Maryland simulated an N-Body beam system to determine if recirculating ion-beams could reach fusion conditions. Models showed that the concept was fundamentally limited because it could not reach sufficient densities needed for fusion power. | 0 | Theoretical and Fundamental Chemistry |
Carboxylic acids often have strong sour odours. Esters of carboxylic acids tend to have fruity, pleasant odours, and many are used in perfume. | 0 | Theoretical and Fundamental Chemistry |
A simple lipid is a fatty acid ester of different alcohols and carries no other substance. These lipids belong to a heterogeneous class of predominantly nonpolar compounds, mostly insoluble in water, but soluble in nonpolar organic solvents such as chloroform and benzene.
"Simple lipid" can refer to many different types of lipid depending on the classification system used, but the most basic definitions usually classify simple lipids as those that do not contain acyl groups. The simple lipids are then divided further into glycerides, cholesteryl esters, and waxes. The term was first used by in 1947 to separate "simple" greases and waxes from "mixed" triglycerides found in animal fats. | 1 | Applied and Interdisciplinary Chemistry |
Some authors suggest the Le Bail technique exploits prior information more efficiently than Pawley method. This was an important consideration at the time of development when computing power was limited. Le Bail is also easily integrated into Rietveld analysis software, and is a part of a number of programs. Both methods improve subsequent structural refinements. | 0 | Theoretical and Fundamental Chemistry |
The economic importance of ultrapotassic rocks is wide and varied. Because kimberlites, lamproites and lamprophyres are all produced at depths of 120 km or greater, they are known to be a major source of diamond deposits and thus can bring diamonds to the surface as xenocrysts. Additionally, ultrapotassic granites are a known host for granite-hosted gold mineralization and well as significant porphyry-style mineralization. Ultrapotassic A-type intracontinental granites may also be associated with fluorite and columbite – tantalite mineralization. | 0 | Theoretical and Fundamental Chemistry |
Despite the low oxygen conditions, organisms have evolved to live in and around OMZs. For those organisms, like the vampire squid, special adaptations are needed to either make do with lesser amounts of oxygen or to extract oxygen from the water more efficiently. For example, the giant red mysid (Gnathophausia ingens) continues to live aerobically (using oxygen) in OMZs. They have highly developed gills with large surface area and thin blood-to-water diffusion distance that enables effective removal of oxygen from the water (up to 90% O removal from inhaled water) and an efficient circulatory system with high capacity and high blood concentration of a protein (hemocyanin) that readily binds oxygen.
Another strategy used by some classes of bacteria in the oxygen minimum zones is to use nitrate rather than oxygen, thus drawing down the concentrations of this important nutrient. This process is called denitrification. The oxygen minimum zones thus play an important role in regulating the productivity and ecological community structure of the global ocean. For example, giant bacterial mats floating in the oxygen minimum zone off the west coast of South America may play a key role in the region's extremely rich fisheries, as bacterial mats the size of Uruguay have been found there. | 0 | Theoretical and Fundamental Chemistry |
In chemistry and physics, LIESST (Light-Induced Excited Spin-State Trapping) is a method of changing the electronic spin state of a compound by means of irradiation with light.
Many transition metal complexes with electronic configuration d-d are capable of spin crossover (and d when molecular symmetry is lower than O). Spin crossover refers to where a transition from the high spin (HS) state to the low spin (LS) state or vice versa occurs. Alternatives to LIESST include using thermal changes and pressure to induce spin crossover. The metal most commonly exhibiting spin crossover is iron, with the first known example, an iron(III) tris(dithiocarbamato) complex, reported by Cambi et al. in 1931.
For iron complexes, LIESST involves excitation of the low spin complex with green light to a triplet state. Two successive steps of intersystem crossing result in the high spin complex. Movement from the high spin complex to the low spin complex requires excitation with red light. | 0 | Theoretical and Fundamental Chemistry |
With recent attention toward climate change, global warming, and sustainability, there has been a new wave of research regarding the creation and sustainability of biodegradable products. This research has evolved to include the creation of biodegradable biofoams, with the intention to replace other foams that may be environmentally harmful or whose production may be unsustainable. Following this vein, Gunawan et al. conducted research to developed “commercially-relevant polyurethane products that can biodegrade in the natural environment”. One such product includes flip-flops so as part of the research a flip-flop made from algae derived polyurethane was prototyped (see Figure 7). This research ultimately resulted in the conclusion that in both a compost and soil environment (different microorganisms present in each environment) significant degradation occurs in polyurethane foam formulated from algae oil.
Similarly, research has been done where algae oil (AO) and residual palm oil (RPO) have been formulated into foam polyurethane at different ratios to determine what ratio has the optimum biodegradability. RPO is recovered from the waste of palm oil mill and is a byproduct of that manufacturing process. After undergoing a tests to determine biodegradability as well as a thermogravimetric analysis, the team determined that the material could be utilized in applications such as insulation or fire retardants depending on the AO/RPO ratio.
Another focus of biofoam research is the development of biofoams that are not only biodegradable, but are also cost-effective and require less energy to produce. Luo et al. have conducted research in this area of biofoams and have ultimately developed a biofoam that is produced from a “higher content of nature bioresource materials” and using a “minimal [number of] processing steps”. The processing steps include the one-pot method of foam preparation published by F. Zhang and X. Luo in their paper about developing polyurethane biofoams as an alternative to petroleum based foams for specific applications. | 0 | Theoretical and Fundamental Chemistry |
When determining the F chemical shifts of aromatic fluorine atoms, specifically phenyl fluorides, there is another equation that allows for an approximation. Adopted from "Structure Determination of Organic Compounds," this equation is:where Z is the SSCS value for a substituent in a given position relative to the fluorine atom. Some representative values for use in this equation are provided in the table below:
The data shown above are only representative of some trends and molecules. Other sources and data tables can be consulted for a more comprehensive list of trends in F chemical shifts. Something to note is that, historically, most literature sources switched the convention of using negatives. Therefore, be wary of the sign of values reported in other sources. | 0 | Theoretical and Fundamental Chemistry |
A sacrificial coating forms a clear coat barrier over the wall or surface being protected. If the surface is vandalized the coating can be removed (sacrificed) using a high-pressure washer taking the graffiti with it. The coating then must be reapplied. The materials used to make a sacrificial coating are usually inexpensive optically clear polymers such as acrylates, biopolymers, and waxes. These polymers form weak bonds with the substrate to allow for easy removal. | 0 | Theoretical and Fundamental Chemistry |
IVF may be used to overcome female infertility when it is due to problems with the fallopian tubes, making in vivo fertilisation difficult. It can also assist in male infertility, in those cases where there is a defect in sperm quality; in such situations intracytoplasmic sperm injection (ICSI) may be used, where a sperm cell is injected directly into the egg cell. This is used when sperm has difficulty penetrating the egg. ICSI is also used when sperm numbers are very low. When indicated, the use of ICSI has been found to increase the success rates of IVF.
According to UK's National Institute for Health and Care Excellence (NICE) guidelines, IVF treatment is appropriate in cases of unexplained infertility for people who have not conceived after 2 years of regular unprotected sexual intercourse.
In people with anovulation, it may be an alternative after 7–12 attempted cycles of ovulation induction, since the latter is expensive and more easy to control. | 1 | Applied and Interdisciplinary Chemistry |
Paula Jefferson, head of Beachcroft LLP's Disease Group, said: "Any organisation involved in any activity in the future, where there is the potential for release of harmful substances in to the atmosphere, should ensure that they have taken all necessary steps to identify the potential contamination and to then ensure that they either employ, or have themselves the necessary skills, to deal with that contamination. The principles in the judgment apply not just when there is demolition in progress, but to any activity where there is potential for exposure in to the atmosphere. Where there is any known potential for such exposure, then regard should be had to not just the onsite workforce but also to those living and working in the surrounding area. In the Corby case the area of risk was 4km from the demolition site. The area for potential exposure will clearly vary depending on the circumstances of each case. In essence, the message remains the same - proper risk assessment is key and must include identifying the appropriate people to do the job and not cutting corners, which, as has been proved for Corby Borough Council, is likely to be false economy." | 1 | Applied and Interdisciplinary Chemistry |
Leslie Orgel was born in London, England, on . He received his Bachelor of Arts degree in chemistry with first-class honours from the University of Oxford in 1948. In 1951 he was elected a Fellow of Magdalen College, Oxford and in 1953 was awarded his PhD in chemistry.
Orgel started his career as a theoretical inorganic chemist and continued his studies in this field at Oxford, the California Institute of Technology, and the University of Chicago.
Together with Sydney Brenner, Jack Dunitz, Dorothy Hodgkin, and Beryl M. Oughton he was one of the first people in April 1953 to see the model of the structure of DNA, constructed by Francis Crick and James Watson, at the time he and the other scientists were working at Oxford University's Chemistry Department. According to the late Dr. Beryl Oughton, later Rimmer, they all travelled together in two cars once Dorothy Hodgkin announced to them that they were off to Cambridge to see the model of the structure of DNA. All were impressed by the new DNA model, especially Brenner who subsequently worked with Crick; Orgel himself also worked with Crick at the Salk Institute for Biological Studies.
In 1955 he joined the chemistry department at Cambridge University. There he did work in transition metal chemistry and ligand field theory, published several peer-reviewed journal articles, and wrote a textbook entitled Transition Metal Chemistry: Ligand Field Theory (1960). He developed the Orgel diagram showing the energies of electronic terms in transition metal complexes.
Orgel formulated his protein-translation error-catastrophe theory of aging in 1963, (prior to the use of the term by Manfred Eigen for mutational error catastrophe) which has since been experimentally challenged.
In 1964, Orgel was appointed senior fellow and research professor at the Salk Institute for Biological Studies in La Jolla, California, where he directed the Chemical Evolution Laboratory. He was also an adjunct professor in the Department of Chemistry and Biochemistry at the University of California, San Diego, and he was one of five principal investigators in the NASA-sponsored NSCORT program in exobiology. Orgel also participated in NASA's Viking Mars Lander Program as a member of the Molecular Analysis Team that designed the gas chromatography mass spectrometer instrument that robots took to the planet Mars.
Orgels lab came across an economical way to make cytarabine, a compound that is one of todays most commonly used anti-cancer agents.
Together with Stanley Miller, Orgel also suggested that peptide nucleic acids – rather than ribonucleic acids – constituted the first pre-biotic systems capable of self-replication on early Earth.
His name is popularly known because of Orgels rules, credited to him, particularly Orgels Second Rule: "Evolution is cleverer than you are."
In his book The Origins of Life, Orgel coined the concept of specified complexity, to describe the criterion by which living organisms are distinguished from non-living matter. He published over three hundred articles in his research areas.
In 1993, Orgel presented at the "What is Life?" Conference at Trinity College in Dublin, Ireland along with many other prominent scientists exploring the origin of life research such as Manfred Eigen, John Maynard Smith and Stephen Jay Gould. Orgel's talk was on "Molecular Structure and Disordered Crystals."
Orgel died of pancreatic cancer on 27 October 2007 at the San Diego Hospice & Palliative Care in San Diego, California. | 0 | Theoretical and Fundamental Chemistry |
In molecular biology, the term double helix refers to the structure formed by double-stranded molecules of nucleic acids such as DNA. The double helical structure of a nucleic acid complex arises as a consequence of its secondary structure, and is a fundamental component in determining its tertiary structure. The structure was discovered by Rosalind Franklin and her student Raymond Gosling, but the term "double helix" entered popular culture with the publication in 1968 of The Double Helix: A Personal Account of the Discovery of the Structure of DNA by James Watson.
The DNA double helix biopolymer of nucleic acid is held together by nucleotides which base pair together. In B-DNA, the most common double helical structure found in nature, the double helix is right-handed with about 10–10.5 base pairs per turn. The double helix structure of DNA contains a major groove and minor groove. In B-DNA the major groove is wider than the minor groove. Given the difference in widths of the major groove and minor groove, many proteins which bind to B-DNA do so through the wider major groove. | 0 | Theoretical and Fundamental Chemistry |
1,1’-Binaphthyl-2,2’-diol, or BINOL, has been used as chiral auxiliary for the asymmetric synthesis since 1983.
Hisashi Yamamoto first utilized (R)-BINOL as a chiral auxiliary in the asymmetric synthesis of limonene, which is an example of cyclic mono-terpenes. (R)-BINOL mononeryl ether was prepared by the monosilylation and alkylation of (R)-BINOL as the chiral auxiliary. Followed with the reduction by organoaluminum reagent, limonene was synthesized with low yields (29% yield) and moderate enantiomeric excesses up to 64% ee.
The preparation of a variety of enantiomerically pure uncommon R-amino acids can be achieved by the alkylation of chiral glycine derivatives possessing axially chiral BINOL as an auxiliary. It has been depicted by Fuji et al. Based on different electrophile, the diastereomeric excess varied from 69% to 86.
Protected at the aldehyde function with (R)-BINOL, reacted diastereoselectively with Grignard reagents to afford protected atrolactaldehyde with moderate to excellent diastereomeric excess and high yields.
BINOL was also used as a chiral auxiliary to control the formation of a P-stereocenter in an asymmetric metal-catalyzed C-P coupling process. Mondal et al. discovered that the Pd-catalysed C-P cross-coupling reaction between axially chiral BINOL-based phosphoramidites and aryl halides or triflates proceeds with excellent stereoselectivity due to the presence of BINOL near the reacting P center. | 0 | Theoretical and Fundamental Chemistry |
The first known use of metals in the Southern Levant is during the Chalcolithic period (end of 5th–most of the 4th millennium BCE). More than 500 metal objects were found, mainly in hoards, burials, and habitation
remains. Most of the metals originate from sites in the southern part of Israel and Jordan; very rarely do they occur beyond the center of Israel and north of Wadi Qana. The metal findings from this period were separated into three groups; most of them belong to the following first two groups:
Prestige/cult-elaborated and complex-shaped objects made of copper (Cu) alloyed (a deliberate
choice of complex minerals that could be reduced to a mixture of metals with specific recognizable
and desirable properties, totally different from unalloyed copper) with distinct amounts of antimony
(Sb) or nickel (Ni) and arsenic (As). They were cast using a “lost wax” technique into single closed clay moulds and then polished into their final shining gray or gold-like colors depending on the amount of antimony or nickel and arsenic in the copper. The Nahal Mishmar hoard was the biggest hoard (416 metal objects comprising mainly artistically complex-shaped objects), found hidden in a cave by Nahal Mishmar, Judean Desert, Israel.
They were wrapped in a straw mat (e.g., Shalev; Tadmor). Carbon-14 dating of the reed mat in which the objects were wrapped suggests that it dates to at least 3500 B.C.
The origin of the complex source material for the production of these objects is currently unknown. The nearest suitable ore is in Trans-Caucasus and Azerbaijan — more than 1500 km from the finding sites of the objects. Several clay and stone cores and clay
mould remains were petrographically analyzed and the results point to a possible local
production in the area of the Judean Desert, within the metals distribution zone in Israel, which is concentrated mainly in the southern part of the country: between Giv’at Oranit and Wadi Qana (east of
modern Tel Aviv) in the north and the Be’er Sheva valley sites in the south. Currently, no production
remains or production sites of these prestige/cult objects were found.
Unalloyed copper tools comprising mainly relatively thick- and short-bladed objects (axes, adzes,
and chisels) and points (awls and/or drills) made from a smelted copper ore, cast into an open mould and then hammered and annealed into their final shape. The copper tools were produced in the Chalcolithic villages on the banks of the Be’er Sheva valley where slag fragments, clay crucibles, some possible furnace lining pieces, copper prills, and amorphous lumps were found, in addition to high-grade carbonated copper ore (cuprite). The ore was collected and selected in the area of Feinan in Trans-Jordan and transported to northern Negev villages some 150 km to the north, to be smelted for the local production of these copper objects.
A third group of eight gold (Au) and electrum (Au + up to 30% Ag) solid rings was found in Wadi Qanah cave.
This unique find, with no dated parallels, is attributed by the excavators to the Chalcolithic period based on local stratigraphic and geological evidence and 14C dating of ground samples from the vicinity of the finds in the cave. Surface analyses of these objects revealed a surface
gold enrichment caused by the depletion of silver and the copper traces. This effect could be caused naturally by deposition but could have been achieved intentionally at the time of production in
order to achieve a yellow color for the electrum rings rich in silver, as well. During the Chalcolithic
(copper and stone) era at least two, if not three distinct industries of different metals were operating
and their products were found in the Southern Levant. | 1 | Applied and Interdisciplinary Chemistry |
Blue carbon is defined by the IPCC as: "Biologically driven carbon fluxes and storage in marine systems that are amenable to management."
Another definition states: "Blue carbon refers to organic carbon that is captured and stored by the oceans and coastal ecosystems, particularly by vegetated coastal ecosystems: seagrass meadows, tidal marshes, and mangrove forests."
Coastal blue carbon focuses on "rooted vegetation in the coastal zone, such as tidal marshes, mangroves and seagrasses". Seagrass, salt marshes and mangroves are sometimes referred to as "blue forests" in contrast to land-based "green forests".
Deep blue carbon is located in the high seas beyond national jurisdictions. It includes carbon contained in "continental shelf waters, deep-sea waters and the sea floor beneath them" and makes up 90% of all ocean carbon. Deep blue carbon is generally seen as "less amenable to management" and challenging due to lack of data "relating to the permanence of their carbon stores". | 0 | Theoretical and Fundamental Chemistry |
Squalene is an organic compound. It is a triterpene with the formula CH. It is a colourless oil, although impure samples appear yellow. It was originally obtained from shark liver oil (hence its name, as Squalus is a genus of sharks). An estimated 12% of bodily squalene in humans is found in sebum. Squalene has a role in topical skin lubrication and protection.
Most plants, fungi, and animals produce squalene as biochemical precursor in sterol biosynthesis, including cholesterol and steroid hormones in the human body. It is also an intermediate in the biosynthesis of hopanoids in many bacteria.
Squalene is an important ingredient in some vaccine adjuvants: The Novartis and GlaxoSmithKline adjuvants are called MF59 and AS03, respectively. | 1 | Applied and Interdisciplinary Chemistry |
When disposed, PHBV degrades into carbon dioxide and water. PHBV undergo bacterial degradation. PHBV, just like fats to human, is an energy source to microorganisms. Enzymes produced by them degrade it and are consumed.
PHBV has a low thermal stability and the cleavage occurs at the ester bond by β elimination reaction.
Hydrolytic degradation occurs only slowly making it usable in medical applications. | 1 | Applied and Interdisciplinary Chemistry |
The precise mechanism of action for thalidomide was not known until the twenty-first century, although efforts to identify thalidomide's teratogenic action generated more than 2,000 research papers and the proposal of 15 or 16 plausible mechanisms by 2000. The primary mechanism of action of thalidomide and its analogs in both their anti-cancer and teratogenic effects is now known to be as cereblon E3 ligase modulators.
Thalidomide also binds to and acts as an antagonist of the androgen receptor and hence is a nonsteroidal antiandrogen of some capacity. In accordance, it can produce gynecomastia and sexual dysfunction as side effects in men. | 0 | Theoretical and Fundamental Chemistry |
Lower division coursework in this field requires the student to take several laboratory-based classes in calculus-based physics, chemistry, biology, programming and analysis. This is intended to give the student background information in order to introduce them to the engineering fields and to prepare them for more technical information in their upper division coursework. | 1 | Applied and Interdisciplinary Chemistry |
Electron diffraction is a generic term for phenomena associated with changes in the direction of electron beams due to elastic interactions with atoms. It occurs due to elastic scattering, when there is no change in the energy of the electrons. The negatively charged electrons are scattered due to Coulomb forces when they interact with both the positively charged atomic core and the negatively charged electrons around the atoms. The resulting map of the directions of the electrons far from the sample is called a diffraction pattern, see for instance Figure 1. Beyond patterns showing the directions of electrons, electron diffraction also plays a major role in the contrast of images in electron microscopes.
This article provides an overview of electron diffraction and electron diffraction patterns, collective referred to by the generic name electron diffraction. This includes aspects of how in a general way electrons can act as waves, and diffract and interact with matter. It also involves the extensive history behind modern electron diffraction, how the combination of developments in the 19th century in understanding and controlling electrons in vacuum and the early 20th century developments with electron waves were combined with early instruments, giving birth to electron microscopy and diffraction in 1920–1935. While this was the birth, there have been a large number of further developments since then.
There are many types and techniques of electron diffraction. The most common approach is where the electrons transmit through a thin sample, from 1 nm to 100 nm (10 atoms to 1000 thick), where the results depending upon how the atoms are arranged in the material, for instance a single crystal, many crystals or different types of solids. Other cases such as larger repeats, no periodicity or disorder have their own characteristic patterns. There are many different ways of collecting diffraction information, from parallel illumination to a converging beam of electrons or where the beam is rotated or scanned across the sample which produce information that is often easier to interpret. There are also many other types of instruments. For instance, in a scanning electron microscope (SEM), electron backscatter diffraction can be used to determine crystal orientation across the sample. Electron diffraction patterns can also be used to characterize molecules using gas electron diffraction, liquids, surfaces using lower energy electrons, a technique called LEED, and by reflecting electrons off surfaces, a technique called RHEED.
There are also many levels of analysis of electron diffraction, including:
# The simplest approximation using the de Broglie wavelength for electrons, where only the geometry is considered and often Bragg's law is invoked. This approach only considers the electrons far from the sample, a far-field or Fraunhofer approach.
# The first level of more accuracy where it is approximated that the electrons are only scattered once, which is called kinematical diffraction and is also a far-field or Fraunhofer approach.
# More complete and accurate explanations where multiple scattering is included, what is called dynamical diffraction (e.g. refs). These involve more general analyses using relativistically corrected Schrödinger equation methods, and track the electrons through the sample, being accurate both near and far from the sample (both Fresnel and Fraunhofer diffraction).
Electron diffraction is similar to x-ray and neutron diffraction. However, unlike x-ray and neutron diffraction where the simplest approximations are quite accurate, with electron diffraction this is not the case. Simple models give the geometry of the intensities in a diffraction pattern, but dynamical diffraction approaches are needed for accurate intensities and the positions of diffraction spots. | 0 | Theoretical and Fundamental Chemistry |
Leiv Kristen Sydnes (born 9 July 1948) is a Norwegian chemist, specializing in organic chemistry.
He was born in Haugesund, and took his education at the University of Oslo. He has the dr.philos. degree from 1978. He was hired as an associate professor at the University of Tromsø in 1978, and was later promoted to professor. In 1993 he moved to the University of Bergen. He presided over the Norwegian Chemical Society from 1992 to 1996 and the International Union of Pure and Applied Chemistry (IUPAC) from 2004 to 2005. He is a member of the Norwegian Academy of Science and Letters and the Norwegian Academy of Technological Sciences.
Sydnes stood for election as rector of the University of Bergen in 2005, but lost the election to Sigmund Grønmo. In 2009 he applied for the position as rector of the Norwegian University of Science and Technology; here the rectors are hired rather than elected. | 0 | Theoretical and Fundamental Chemistry |
Carbon dioxide () from air and bicarbonate () or carbonate () anions dissolved in water react with the calcium hydroxide (, portlandite) produced by Portland cement hydration in concrete to form calcium carbonate () while releasing a water molecule in the following reaction:
Exception made of the water molecule, the carbonation reaction is essentially the reverse of the process of calcination of limestone taking place in a cement kiln:
Carbonation of concrete is a slow and continuous process of atmospheric diffusing from the outer surface of concrete exposed to air into its mass and chemically reacting with the mineral phases of the hydrated cement paste. Carbonation slows down with increasing diffusion depth.
Carbonation has two antagonist effects for (1) the concrete strength, and (2) its durability:
# The precipitation of calcite filling the microscopic voids in the concrete pore space decreases the concrete matrix porosity: so, it increases the mechanical strength of concrete;
# At the same time carbonation consumes portlandite and therefore decreases the concrete alkalinity reserve buffer. Hyper-alkaline conditions (i.e., basic chemical conditions) characterized by a high pH (typically 12.5 – 13.5) are needed to passivate the steel surface of the reinforcement bars (rebar) and to protect them from corrosion. Below a pH of 10, the solubility of the iron oxides forming a protective thin coating at the surface of carbon steel increases. The thin protective oxide layer starts to dissolve, and corrosion is then promoted. As the volumetric mass of iron oxides can be as high as 6 – 7 times that of metallic iron (Fe), a detrimental consequence is the expansion of the corrosion products around the rebar. This causes the development of a tensile stress in the concrete matrix around the rebar. When the tensile strength of concrete is exceeded in the concrete cover above the rebar, concrete starts to spall. Cracks appear in the concrete cover protecting the rebar against corrosion and constitute preferential pathways for direct ingress towards the rebar. This accelerates the carbonation reaction and in turn the corrosion process speeds up.
This explain why the carbonation reaction of reinforced concrete is an undesirable process in concrete chemistry. Concrete carbonation can be visually revealed by applying a phenolphthalein solution over the fresh surface of a concrete samples (concrete core, prism, freshly fractured bar). Phenolphthalein is a pH indicator, whose color turns from colorless at pH < 8.5 to pink-fuchsia at pH > 9.5. A violet color indicates still alkaline areas and thus non-carbonated concrete. Carbonated zones favorable for steel corrosion and concrete degradation are colorless.
The presence of water in carbonated concrete is necessary to lower the pH of concrete pore water around rebar and to depassivate the carbon steel surface at low pH. Water is central to corrosion processes. Without water, the steel corrosion is very limited and rebar present in dry carbonated concrete structures, or components, not affected by water infiltration do not suffer from significant corrosion. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, the Oseen equations (or Oseen flow) describe the flow of a viscous and incompressible fluid at small Reynolds numbers, as formulated by Carl Wilhelm Oseen in 1910. Oseen flow is an improved description of these flows, as compared to Stokes flow, with the (partial) inclusion of convective acceleration.
Oseens work is based on the experiments of G.G. Stokes, who had studied the falling of a sphere through a viscous fluid. He developed a correction term, which included inertial factors, for the flow velocity used in Stokes calculations, to solve the problem known as Stokes paradox. His approximation leads to an improvement to Stokes calculations. | 1 | Applied and Interdisciplinary Chemistry |
Homologous paired receptors are located in the same gene cluster and are thought to have evolved through gene duplication. Sequence features such as the presence of an ITIM-like sequence in the 3' untranslated region of some activating receptors imply that the activating members of the pair likely evolved from the inhibitory members. A number of pathogens interact with the inhibitory member of a pair as a means of immune evasion or viral entry, suggesting that activating members with similar binding competencies may be an evolutionary response to this mechanism. This hypothesis is known as the "counterbalance theory" and these evolutionary dynamics represent an evolutionary arms race between pathogens and the host immune system. The evolutionary pressures on some paired-receptor families have been described as examples of the "Red Queen" effect.
Including non-paired examples, over 300 potential immune inhibitory receptors have been identified in the human genome. There are strong indications that paired receptors are rapidly and recently evolving. These genetic regions have high levels of gene polymorphism, and the gene repertoires found in the genomes of closely related lineages vary significantly. The selective pressure experienced by the host from pathogens is thought to underlie this rapid evolution.
Although paired receptors are best characterized as part of the human and mouse immune systems, they have also been studied in other organisms. The chicken (Gallus gallus domesticus) genome contains a number of examples including a very large family, the chicken Ig-like receptors (CHIR) with over 100 members. Paired receptor evolution has also been studied in Xenopus (clawed frog) species. The adaptive immune system is unique to jawed vertebrates, but an example of a paired receptor family has been identified in a jawless vertebrate, termed agnathan paired receptors resembling Ag receptors (APAR) in the hagfish. | 1 | Applied and Interdisciplinary Chemistry |
The working fluid can be used to output useful work if used in a turbine. Also, in thermodynamic cycles energy may be input to the working fluid by means of a compressor. The mathematical formulation for this may be quite simple if we consider a cylinder in which a working fluid resides. A piston is used to input useful work to the fluid. From mechanics, the work done from state 1 to state 2 of the process is given by:
where ds is the incremental distance from one state to the next and F is the force applied. The negative sign is introduced since in this case a decrease in volume is being considered. The situation is shown in the following figure:
The force is given by the product of the pressure in the cylinder and its cross sectional area such that
Where A⋅ds = dV is the elemental change of cylinder volume. If from state 1 to 2 the volume increases then the working fluid actually does work on its surroundings and this is commonly denoted by a negative work. If the volume decreases the work is positive. By the definition given with the above integral the work done is represented by the area under a pressure–volume diagram. If we consider the case where we have a constant pressure process then the work is simply given by | 0 | Theoretical and Fundamental Chemistry |
The Nepenthes carnivorous pitcher, widespread in a lot of countries such as India, Indonesia, Malaysia and Australia, possesses a superhydrophilic surface, on which wetting angle approaches to zero to create uniform water film. Therefore, it increases the slipperiness of the surface and the prey slides off from its rims (peristome). Surface topography of Nepenthes rim demonstrates multiple scale radial ridges. The second order ridges are quite small in size and generated by straight rows of overlapping epidermidis cells. The surface of epidermidis cells are smooth and wax-free. The absence of wax crystals and microscopic roughness enhance the hydrophilicity and capillary forces, in doing so, water can swiftly wet the surface of rim. | 0 | Theoretical and Fundamental Chemistry |
Since all the A functional groups are from the trifunctional monomer, ρ = 1 and
Therefore, gelation occurs when
or when,
Similarly, gelation occurs when | 0 | Theoretical and Fundamental Chemistry |
DSSCs are currently the most efficient third-generation (2005 Basic Research Solar Energy Utilization 16) solar technology available. Other thin-film technologies are typically between 5% and 13%, and traditional low-cost commercial silicon panels operate between 14% and 17%. This makes DSSCs attractive as a replacement for existing technologies in "low density" applications like rooftop solar collectors, where the mechanical robustness and light weight of the glass-less collector is a major advantage. They may not be as attractive for large-scale deployments where higher-cost higher-efficiency cells are more viable, but even small increases in the DSSC conversion efficiency might make them suitable for some of these roles as well.
There is another area where DSSCs are particularly attractive. The process of injecting an electron directly into the TiO is qualitatively different from that occurring in a traditional cell, where the electron is "promoted" within the original crystal. In theory, given low rates of production, the high-energy electron in the silicon could re-combine with its own hole, giving off a photon (or other form of energy) which does not result in current being generated. Although this particular case may not be common, it is fairly easy for an electron generated by another atom to combine with a hole left behind in a previous photoexcitation.
In comparison, the injection process used in the DSSC does not introduce a hole in the TiO, only an extra electron. Although it is energetically possible for the electron to recombine back into the dye, the rate at which this occurs is quite slow compared to the rate that the dye regains an electron from the surrounding electrolyte. Recombination directly from the TiO to species in the electrolyte is also possible although, again, for optimized devices this reaction is rather slow. On the contrary, electron transfer from the platinum coated electrode to species in the electrolyte is necessarily very fast.
As a result of these favorable "differential kinetics", DSSCs work even in low-light conditions. DSSCs are therefore able to work under cloudy skies and non-direct sunlight, whereas traditional designs would suffer a "cutout" at some lower limit of illumination, when charge carrier mobility is low and recombination becomes a major issue. The cutoff is so low they are even being proposed for indoor use, collecting energy for small devices from the lights in the house.
A practical advantage which DSSCs share with most thin-film technologies, is that the cell's mechanical robustness indirectly leads to higher efficiencies at higher temperatures. In any semiconductor, increasing temperature will promote some electrons into the conduction band "mechanically". The fragility of traditional silicon cells requires them to be protected from the elements, typically by encasing them in a glass box similar to a greenhouse, with a metal backing for strength. Such systems suffer noticeable decreases in efficiency as the cells heat up internally. DSSCs are normally built with only a thin layer of conductive plastic on the front layer, allowing them to radiate away heat much easier, and therefore operate at lower internal temperatures. | 0 | Theoretical and Fundamental Chemistry |
Spin crossover (SCO) is a phenomenon that occurs in some metal complexes wherein the spin state of the complex changes due to an external stimulus. The stimuli can include temperature or pressure. Spin crossover is sometimes referred to as spin transition or spin equilibrium behavior. The change in spin state usually involves interchange of low spin (LS) and high spin (HS) configuration.
Spin crossover is commonly observed with first row transition metal complexes with a d through d electron configuration in an octahedral ligand geometry. Spin transition curves typically plot the high-spin molar fraction against temperature. Often a gradual spin transition is followed by an abrupt (ΔT = 10K) transition with hysteresis and a two-step transition. The abruptness with hysteresis indicates cooperativity, or “communication”, between neighboring metal complexes. In the latter case, the material is bistable and can exist in the two different spin states with a different range of external stimuli (temperature in this case) for the two phenomena, namely LS → HS and HS → LS. The two-step transition is relatively rare but is observed, for example, with dinuclear SCO complexes for which the spin transition in one metal center renders the transition in the second metal center less favorable. Several types of spin crossover have been identified; some of them are light induced excited spin-state trapping (LIESST), ligand-driven light induced spin change (LD-LISC), and charge transfer induced spin transition (CTIST). | 0 | Theoretical and Fundamental Chemistry |
The original example proceeded via sequential loss of two equivalents of H from decamethyltungstocene dihydride, Cp*WH. The first dehydrogenation step affords a simple tuck-in complex:
:(CMe)WH → (CMe)(η-CMeCH)WH + H
The second dehydrogenation step affords a double tuck-in complex:
:(CMe)(η-CMeCH)WH → (CMe)(η-CMe(CH))W + H
In organouranium chemistry, both tuck-in and tuck-over complexes are recognized, for example in the dihydrido diuranium complex [Cp*(η-CMe(CH))UH]. In this complex the two methylene groups bind to different uranium centers. The tuck-over mode is binding of the Cp* methylene to a metal center elsewhere in the molecule rather than the one coordinated to that Cp* ligand. | 0 | Theoretical and Fundamental Chemistry |
Invented by and named for Alexander Dounce
, a Dounce homogenizer or "Douncer", is a cylindrical glass tube, closed at one end, with two glass pestles of carefully specified outer diameters, intended for the gentle homogenization of eukaryotic cells (e.g. mammalian cells). Dounce homogenizers are still commonly used today to isolate cellular organelles.
The two Dounce homogenizer pestles (known as the "loose" or "A" and "tight" or "B" pestles), have a carefully specified outer diameter, relative to the inner diameter of the cylinder. The "A" (loose) pestle has a clearance from the cylinder wall of (~0.0025 - 0.0055 in.) while the "B" (tight) pestle has a clearance of (~0.0005 - 0.0025 in.). This allows for tissue and cells to be lysed by shear stress with minimal (if any) degree of heating, thereby leaving extracted organelles or heat-sensitive enzyme complexes largely intact.
Typically, a soft tissue (e.g. mammalian liver) is cut or broken into smaller pieces and placed into the glass cylinder, alongside a suitable volume of an appropriate lysis buffer. Homogenization is performed by a defined number of "passes" of the pestles, first with the loose pestle, then with the tight pestle, up and down the cylinder. Five to ten passes are typical. Dounce homogenizers are typically produced from borosilicate glass, but are still fragile, and should be used with care. Especially hard or tough tissues should be pre-homogenized before use in a dounce homogenizer.
Eukaryotic cells with tough cell walls, such as Saccharomyces cerevisiae, cannot be directly lysed with a dounce homogenizer, unless the cell wall is first broken down (e.g. with lyticase, or zymolyase in the case of S. cerevisiae). | 1 | Applied and Interdisciplinary Chemistry |
Mikhail Usanovich developed a general theory that does not restrict acidity to hydrogen-containing compounds, but his approach, published in 1938, was even more general than Lewis theory. Usanovich's theory can be summarized as defining an acid as anything that accepts negative species or donates positive ones, and a base as the reverse. This defined the concept of redox (oxidation-reduction) as a special case of acid–base reactions.
Some examples of Usanovich acid–base reactions include: | 0 | Theoretical and Fundamental Chemistry |
Each phycobiliprotein has a specific absorption and fluorescence emission maximum in the visible range of light. Therefore, their presence and the particular arrangement within the phycobilisomes allow absorption and unidirectional transfer of light energy to chlorophyll a of the photosystem II. In this way, the cells take advantage of the available wavelengths of light (in the 500–650 nm range), which are inaccessible to chlorophyll, and utilize their energy for photosynthesis. This is particularly advantageous deeper in the water column, where light with longer wavelengths is less transmitted and therefore less available directly to chlorophyll.
The geometrical arrangement of a phycobilisome is very elegant in an antenna-like assembly. It results in 95% efficiency of energy transfer. | 0 | Theoretical and Fundamental Chemistry |
Several metal consolidation techniques are used to produce the final product. Metal injection moulding (MIM) otherwise known as powder injection moulding is a well-established and cost-effective method of fabricating small-to-moderate size metal components in large quantities. It is derived from the method plastic injection moulding, whereby mixing of a metal powder with a polymer binder forms the feedstock, which is then injected into a mould, after which the binder is removed via heat treatment under vacuum before final sintering. With titanium however, the binders used in MIM results in the introduction of carbon into the matrix due to insufficient binder removal prior to sintering and/or deleterious reactions between the decomposing binder, the debinding atmosphere, and the metal phase. This results in titanium parts with mechanical properties unsuited for critical aerospace applications, but suitable for parts where tensile and impact properties are less important. Recently, work has been carried out to reduce the binder to < 8% volume fraction, resulting in the complete removal of the binder from the moulded component during heat treatment.
In the direct powder rolling (DPR) process BE powder is used to produce sheet and plate and composite multilayered sheet and plates. Sheets between 1.27 and 2.54 mm and 50 to 99+% dense of single layer CP titanium, Ti Grade 5, TiAl (Ti-48Al-2Cr-2Nb) and composite Ti/Grade 5/Ti and Grade 5/TiAl/Grade 5 have been produced by DPR and sintering.
Laser engineered net shaping (LENS) is an additive manufacturing technique for rapidly fabricating, enhancing and repairing metal components directly from CAD data. The processes use a high power solid state laser focused onto a metal substrate to create a ~1 mm diameter melt pool. Metal powder is then injected into the melt pool to increase the material volume and build up the component layer by layer. Experimental gas thrusters (build time 8 hours) and automotive brackets have been manufactured in Ti-Grade 5. Selective Laser Sintering (SLS) is similar, except that the laser selectively fuses powdered material by scanning on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed.
In hot isostatic pressing high temperature and pressure are used to consolidate powders to close to their maximum theoretical densities.
Electric current assisted sintering, also known as spark plasma sintering (SPS) relies on fast application of resistive heating and pressure to consolidate powders close to their maximum theoretical densities, without the undesired grain growth effect, thereby retaining close to original grain size and achieving improved mechanical properties in the final product. | 1 | Applied and Interdisciplinary Chemistry |
Biocatalysis makes use of biological compounds, ranging from isolated enzymes to living cells, to perform chemical transformations.
The advantages of these reagents include very high e.e.s and reagent specificity, as well as mild operating conditions and low environmental impact. Biocatalysts are more commonly used in industry than in academic research; for example in the production of statins.
The high reagent specificity can be a problem, however, as it often requires that a wide range of biocatalysts be screened before an effective reagent is found. | 0 | Theoretical and Fundamental Chemistry |
The cobalt-containing Vitamin B (also known as cobalamin) catalyzes the transfer of methyl (−CH) groups between two molecules, which involves the breaking of C−C bonds, a process that is energetically expensive in organic reactions. The metal ion lowers the activation energy for the process by forming a transient Co−CH bond. The structure of the coenzyme was famously determined by Dorothy Hodgkin and co-workers, for which she received a Nobel Prize in Chemistry. It consists of a cobalt(II) ion coordinated to four nitrogen atoms of a corrin ring and a fifth nitrogen atom from an imidazole group. In the resting state there is a Co−C sigma bond with the 5′ carbon atom of adenosine. This is a naturally occurring organometallic compound, which explains its function in trans-methylation reactions, such as the reaction carried out by methionine synthase. | 1 | Applied and Interdisciplinary Chemistry |
The elementary formula of a simple monosaccharide is CHO, where the integer n is at least 3 and rarely greater than 7. Simple monosaccharides may be named generically based on the number of carbon atoms n: trioses, tetroses, pentoses, hexoses, etc.
Every simple monosaccharide has an acyclic (open chain) form, which can be written as ; that is, a straight chain of carbon atoms, one of which is a carbonyl group, all the others bearing a hydrogen -H and a hydroxyl -OH each, with one extra hydrogen at either end. The carbons of the chain are conventionally numbered from 1 to n, starting from the end which is closest to the carbonyl.
If the carbonyl is at the very beginning of the chain (carbon 1), the monosaccharide is said to be an aldose, otherwise it is a ketose. These names can be combined with the chain length prefix, as in aldohexose or ketopentose. Most ketoses found in nature have the carbonyl in position 2; when that is not the case, one uses a numeric prefix to indicate the carbonyl's position. Thus for example, aldohexose means H(C=O)(CHOH)H, ketopentose means H(CHOH)(C=O)(CHOH)H, and 3-ketopentose means H(CHOH)(C=O)(CHOH)H.
An alternative nomenclature uses the suffix -ose only for aldoses, and -ulose for ketoses. The position of the carbonyl (when it is not 1 or 2) is indicated by a numerical infix. For example, hexose in this nomenclature means H(C=O)(CHOH)H, pentulose means H(CHOH)(C=O)(CHOH)H, and hexa-3-ulose means H(CHOH)(C=O)(CHOH)H. | 0 | Theoretical and Fundamental Chemistry |
Polycrystalline silicon carbide (SiC) is the most commonly used emitter for burner TPVs. SiC is thermally stable to ~1700 °C. However, SiC radiates much of its energy in the long wavelength regime, far lower in energy than even the narrowest bandgap photovoltaic. Such radiation is not converted into electrical energy. However, non-absorbing selective filters in front of the PV, or mirrors deposited on the back side of the PV can be used to reflect the long wavelengths back to the emitter, thereby recycling the unconverted energy. In addition, polycrystalline SiC is inexpensive. | 0 | Theoretical and Fundamental Chemistry |
Real-time PCR technique can be classified by the chemistry used to detect the PCR product, specific or non-specific fluorochromes. | 1 | Applied and Interdisciplinary Chemistry |
IR near-field scanning optical microscopy (IR-NSOM) is a powerful spectroscopic tool because it allows subwavelength resolution in IR spectroscopy. Previously, IR-NSOM was realized by applying a solid immersion lens with a refractive index of n, which shortens wavelength (λ) to (λ/n), compared to FTIR-based IR microscopy. In 2004, an IR-SNOM achieved a spatial resolution ~λ/7 that is less than 1 μm. This resolution was further improved to about λ/60 that is 50–150 nm for a boron nitride thin film sample.
IR-NSOM uses an AFM to detect the absorption response of a material to the modulated infrared radiation from an FTIR spectrometer and therefore is also referred to as AFM/FTIR spectroscopy. Two approaches have been used to measure the response of polymer systems to infrared absorption. The first mode relies on the AFM contact mode, and the second mode of operation employs a scanning thermal microscopy probe (invented in 1986) to measure the polymer's temperature increase. In 2007, AFM was combined with infrared attenuated total reflection (IR-ATR) spectroscopy to study the dissolution process of urea in a cyclohexane/butanol solution with a high spatial resolution. | 0 | Theoretical and Fundamental Chemistry |
Time-resolved mass spectrometry (TRMS) is a strategy in analytical chemistry that uses mass spectrometry platform to collect data with temporal resolution. Implementation of TRMS builds on the ability of mass spectrometers to process ions within sub-second duty cycles. It often requires the use of customized experimental setups. However, they can normally incorporate commercial mass spectrometers. As a concept in analytical chemistry, TRMS encompasses instrumental developments (e.g. interfaces, ion sources, mass analyzers), methodological developments, and applications. | 1 | Applied and Interdisciplinary Chemistry |
Dielectrophoresis can be used to manipulate, transport, separate and sort different types of particles. DEP is being applied in fields such as medical diagnostics, drug discovery, cell therapeutics, and particle filtration.
DEP has been also used in conjunction with semiconductor chip technology for the development of DEP array technology for the simultaneous management of thousands of cells in microfluidic devices. Single microelectrodes on the floor of a flow cell are managed by a CMOS chip to form thousands of dielectrophoretic "cages", each capable of capturing and moving one single cell under control of routing software.
As biological cells have dielectric properties, dielectrophoresis has many biological and medical applications. Instruments capable of separating cancer cells from healthy cells have been made as well as isolating single cells from forensic mixed samples. Platelets have been separated from whole blood with a DEP-activated cell sorter.
DEP has made it possible to characterize and manipulate biological particles like blood cells, stem cells, neurons, pancreatic β cells, DNA, chromosomes, proteins and viruses.
DEP can be used to separate particles with different sign polarizabilities as they move in different directions at a given frequency of the AC field applied. DEP has been applied for the separation of live and dead cells, with the remaining live cells still viable after separation or to force contact between selected single cells to study cell-cell interaction.
DEP has been used to separate strains of bacteria and viruses. DEP can also be used to detect apoptosis soon after drug induction measuring the changes in electrophysiological properties. | 0 | Theoretical and Fundamental Chemistry |
Photooxygenation reactions are easily confused with a number of processes baring similar names (i.e. photosensitized oxidation). Clear distinctions can be made based on three attributes: oxidation, the involvement of light, and the incorporation of molecular oxygen into the products: | 0 | Theoretical and Fundamental Chemistry |
Describing them to the French Academy of Sciences on 27 February 1896, he said:
But further experiments led him to doubt and then abandon this hypothesis. On 2 March 1896 he reported: | 0 | Theoretical and Fundamental Chemistry |
The separation of compounds is due to the differences in their attraction to the stationary phase and because of differences in solubility in the solvent. As a result, the compounds and the mobile phase compete for binding sites on the stationary phase. Different compounds in the sample mixture travel at different rates due to the differences in their partition coefficients. Different solvents, or different solvent mixtures, gives different separation. The retardation factor (R), or retention factor, quantifies the results. It is the distance traveled by a given substance divided by the distance traveled by the mobile phase.
In normal-phase TLC, the stationary phase is polar. Silica gel is very common in normal-phase TLC. More polar compounds in a sample mixture interact more strongly with the polar stationary phase. As a result, more-polar compounds move less (resulting in smaller R) while less-polar compounds move higher up the plate (higher R). A more-polar mobile phase also binds more strongly to the plate, competing more with the compound for binding sites; a more-polar mobile phase also dissolves polar compounds more. As such, all compounds on the TLC plate move higher up the plate in polar solvent mixtures. "Strong" solvents move compounds higher up the plate, whereas "weak" solvents move them less.
If the stationary phase is non-polar, like C18-functionalized silica plates, it is called reverse-phase TLC. In this case, non-polar compounds move less and polar compounds move more. The solvent mixture will also be much more polar than in normal-phase TLC. | 0 | Theoretical and Fundamental Chemistry |
The material matrix has a symmetry with respect to a given orthogonal transformation () if it does not change when subjected to that transformation.
For invariance of the material properties under such a transformation we require
Hence the condition for material symmetry is (using the definition of an orthogonal transformation)
Orthogonal transformations can be represented in Cartesian coordinates by a matrix given by
Therefore, the symmetry condition can be written in matrix form as
For a transversely isotropic material, the matrix has the form
where the -axis is the axis of symmetry. The material matrix remains invariant under rotation by any angle about the -axis. | 0 | Theoretical and Fundamental Chemistry |
Brain cytoplasmic 200 long-noncoding RNA (or BC200 lncRNA) is a 200 nucleotide RNA transcript found predominantly in the brain with a primary function of regulating translation by inhibiting its initiation. As a long non-coding RNA, it belongs to a family of RNA transcripts that are not translated into protein (ncRNAs). Of these ncRNAs, lncRNAs are transcripts of 200 nucleotides or longer and are almost three times more prevalent than protein-coding genes. Nevertheless, only a few of the almost 60,000 lncRNAs have been characterized, and little is known about their diverse functions (transcriptional interference, chromatin remodeling, splicing, translation regulation, interaction with miRNAs and siRNAs, and mRNA degradation). BC200 is one lncRNA that has given insight into their specific role in translation regulation, and implications in various forms of cancer as well as Alzheimer's disease.
The accepted gene symbol for the BC200-coding gene is BCYRN1, for Brain cytoplasmic RNA 1. | 1 | Applied and Interdisciplinary Chemistry |
Butyric acid is metabolized by various human XM-ligases (ACSM1, ACSM2B, ASCM3, ACSM4, ACSM5, and ACSM6), also known as butyrate–CoA ligase. The metabolite produced by this reaction is butyryl–CoA, and is produced as follows:
:Adenosine triphosphate + butyric acid + coenzyme A → adenosine monophosphate + pyrophosphate + butyryl-CoA
As a short-chain fatty acid, butyrate is metabolized by mitochondria as an energy (i.e., adenosine triphosphate or ATP) source through fatty acid metabolism. In particular, it is an important energy source for cells lining the mammalian colon (colonocytes). Without butyrates, colon cells undergo autophagy (i.e., self-digestion) and die.
In humans, the butyrate precursor tributyrin, which is naturally present in butter, is metabolized by triacylglycerol lipase into dibutyrin and butyrate through the reaction:
:Tributyrin + dibutyrin + butyric acid | 1 | Applied and Interdisciplinary Chemistry |
The basic principles of SNP array are the same as the DNA microarray. These are the convergence of DNA hybridization, fluorescence microscopy, and solid surface DNA capture. The three mandatory components of the SNP arrays are:
# An array containing immobilized allele-specific oligonucleotide (ASO) probes.
# Fragmented nucleic acid sequences of target, labelled with fluorescent dyes.
# A detection system that records and interprets the hybridization signal.
The ASO probes are often chosen based on sequencing of a representative panel of individuals: positions found to vary in the panel at a specified frequency are used as the basis for probes. SNP chips are generally described by the number of SNP positions they assay. Two probes must be used for each SNP position to detect both alleles; if only one probe were used, experimental failure would be indistinguishable from homozygosity of the non-probed allele. | 1 | Applied and Interdisciplinary Chemistry |
*1992 C E H Morris
*1991 Frank Fitzgerald
*1990 J S Pennington
*1989 Gerald R Heffernan
*1988 Sir R Scholey
*1987 Tae-Joon Park
*1986 J.R.D. Tata
*1985 Viscount E Davignon | 1 | Applied and Interdisciplinary Chemistry |
The greater part of the worlds peatlands occur in the northern hemisphere, encompassing both boreal and temperate regions. Global estimates indicate that northern peatlands cover 3,794,000 km2, storing about 450 Gt of C at a density of approximately 118,318 t C km−2 . Peatlands form in poorly drained areas under conditions of high precipitation and low temperature . 66% of northern peatlands are found in Eurasia and 34% in North America. About 60% of these peatlands (2718×103 km2) are perennially frozen, with approximately 2152×103 km2 occurring in Eurasia and 565×103 km2 in North America . In the European Union (25 countries in Europe), peatlands cover approximately 291×103 km2, of which nearly 55% are in Finland and Sweden . Peatlands are more common in Belarus and Ukraine, where they occupy approximately 497×103 km2. Both boreal and temperate peatlands are primarily formed from bryophytes and graminoids, displaying slower rates of accumulation and decomposition comparative to the tropics . Northern peatlands have been drained for agriculture, forestry, and peat mining for fuel and horticulture. Historical uses of intact northern peatlands include fishing, hunting, grazing and gathering berries. Paludiculture is not widely established commercially in northern peatlands and most research projects identified below are ongoing. Many have not yet published peer-reviewed results. Most are focused on Sphagnum and reed farming. Rather than excavating decomposed Sphagnum as peat, non-decomposed reed fibres are harvested in cycles, as a renewable source of biomass. Sphagnum' fibres can be used as a growing substrate, packaging to protect plants in transport, or to reintroduce moss when restoring other peatlands. | 1 | Applied and Interdisciplinary Chemistry |
Modular Cloning, or MoClo, is an assembly method introduced in 2011 by Ernst Weber et al., whereby using Type IIS restriction sites, the user can ligate at least six DNA parts together into a backbone in a one-pot reaction. It is a method based on Golden Gate Assembly, where Type IIS restriction enzymes cleave outside of their recognition site to one side, allowing for removal of those restriction sites from the design. This helps eliminate excess base pairs, or scars, from forming between DNA Parts. However, in order to ligate together properly, MoClo utilizes a set of 4-base pair fusion sites, which remain between parts after ligation, forming 4-base pair scars between DNA parts in the final DNA sequence following ligation of two or more parts.
MoClo utilizes a parallel approach, where all constructs from tier-one(level 0 modules) have restriction sites for BpiI on both sides of the inserts. The vector(also known as "destination vector"), where genes will be added, has an outward-facing BsaI restriction site with a drop-out screening cassette. LacZ is a common screening cassette, where it is replaced by the multigene construct on the destination vector. Each tier-one construct and the vector have different overhangs on them yet complementary to the overhang of the next segment, and this determines the layout of the final multigene construct. Golden Gate Cloning usually starts with level 0 modules. However, if the level 0 module is too large, cloning will start from level -1 fragments, which have to be sequenced, to help cloning the large construct. If starting from level -1 fragments, the level 0 modules do not need to be sequenced again, whereas if starting from level 0 modules, the modules must be sequenced. | 1 | Applied and Interdisciplinary Chemistry |
The Kroll process was invented in 1940 by William J. Kroll in Luxembourg. After moving to the United States, Kroll further developed the method for the production of zirconium.
Many methods had been applied to the production of titanium metal, beginning with a report in 1887 by Nilsen and Pettersen using sodium, which was optimized into the commercial Hunter process. In the 1920s van Arkel had described the thermal decomposition of titanium tetraiodide to give highly pure titanium. Titanium tetrachloride was found to reduce with hydrogen at high temperatures to give hydrides that can be thermally processed to the pure metal. With this background, Kroll developed both new reductants and new apparatus for the reduction of titanium tetrachloride. Its high reactivity toward trace amounts of water and other metal oxides presented challenges. Significant success came with the use of calcium as a reductant, but the resulting mixture still contained significant oxide impurities. Major success using magnesium at 1000 °C using a molybdenum clad reactor, as reported to the Electrochemical Society in Ottawa. Krolls titanium was highly ductile reflecting its high purity. The Kroll process displaced the Hunter process and continues to be the dominant technology for the production of titanium metal, as well as driving the majority of the worlds production of magnesium metal. | 1 | Applied and Interdisciplinary Chemistry |
Primary role of EpoR is to promote proliferation of erythroid progenitor cells and rescue erythroid progenitors from cell death. EpoR induced Jak2-Stat5 signaling, together with transcriptional factor GATA-1, induces the transcription of pro-survival protein Bcl-xL. Additionally, EpoR has been implicated in suppressing expression of death receptors Fas, Trail and TNFa that negatively affect erythropoiesis.
Based on current evidence, it is still unknown whether Epo/EpoR directly cause "proliferation and differentiation" of erythroid progenitors in vivo, although such direct effects have been described based on in vitro work. | 1 | Applied and Interdisciplinary Chemistry |
The term friction loss (or frictional loss) has a number of different meanings, depending on its context.
* In fluid flow it is the head loss that occurs in a containment such as a pipe or duct due to the effect of the fluid's viscosity near the surface of the containment.
* In mechanical systems such as internal combustion engines, the term refers to the power lost in overcoming the friction between two moving surfaces.
* In economics, frictional loss is natural and irrecoverable loss in a transaction or the cost(s) of doing business too small to account for. Contrast with tret in shipping, which made a general allowance for otherwise unaccounted for factors. | 1 | Applied and Interdisciplinary Chemistry |
These depend upon analysis of the "halo" of diffracted light produced when a laser beam passes through a dispersion of particles in air or in a liquid. The angle of diffraction increases as particle size decreases, so that this method is particularly good for measuring sizes between 0.1 and 3,000 μm. Advances in sophisticated data processing and automation have allowed this to become the dominant method used in industrial PSD determination. This technique is relatively fast and can be performed on very small samples. A particular advantage is that the technique can generate a continuous measurement for analyzing process streams.
Laser diffraction measures particle size distributions by measuring the angular variation in intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles. The angular scattering intensity data is then analyzed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory or Fraunhofer approximation of light scattering. The particle size is reported as a volume equivalent sphere diameter. | 0 | Theoretical and Fundamental Chemistry |
Thermally stimulated current (TSC) spectroscopy (not to be confused with thermally stimulated depolarization current) is an experimental technique which is used to study energy levels in semiconductors or insulators (organic or inorganic). Energy levels are first filled either by optical or electrical injection usually at a relatively low temperature, subsequently electrons or holes are emitted by heating to a higher temperature. A curve of emitted current will be recorded and plotted against temperature, resulting in a TSC spectrum. By analyzing TSC spectra, information can be obtained regarding energy levels in semiconductors or insulators.
A driving force is required for emitted carriers to flow when the sample temperature is being increased. This driving force can be an electric field or a temperature gradient. Usually, the driving force adopted is an electric field; however, electron traps and hole traps cannot be distinguished. If the driving force adopted is a temperature gradient, electron traps and hole traps can be distinguished by the sign of the current. TSC based on a temperature gradient is also known as "Thermoelectric Effect Spectroscopy" (TEES) according to 2 scientists (Santic and Desnica) from ex-Yugoslavia; they demonstrated their technique on semi-insulating gallium arsenide (GaAs). (Note: TSC based on a temperature gradient was invented before Santic and Desnica and applied to the study of organic plastic materials. However, Santic and Desnica applied TSC based on a temperature gradient to study a technologically important semiconductor material and coined a new name, TEES, for it.)
Historically, Frei and Groetzinger published a paper in German in 1936 with the title "Liberation of electrical energy during the fusion of electrets" (English translation of the original title in German). This may be the first paper on TSC. Before the invention of deep-level transient spectroscopy (DLTS), thermally stimulated current (TSC) spectroscopy was a popular technique to study traps in semiconductors. Nowadays, for traps in Schottky diodes or p-n junctions, DLTS is the standard method to study traps. However, there is an important shortcoming for DLTS: it cannot be used for an insulating material while TSC can be applied to such a situation. (Note: an insulator can be considered as a very large bandgap semiconductor.) In addition, the standard transient capacitance based DLTS method may not be very good for the study of traps in the i-region of a p-i-n diode while the transient current based DLTS (I-DLTS) may be more useful.
TSC has been used to study traps in semi-insulating gallium arsenide (GaAs) substrates. It has also been applied to materials used for particle detectors or semiconductor detectors used in nuclear research, for example, high-resistivity silicon, cadmium telluride (CdTe), etc. TSC has also been applied to various organic insulators. TSC is useful for electret research. More advanced modifications of TSC have been applied to study traps in ultrathin high-k dielectric thin films. W. S. Lau (Lau Wai Shing, Republic of Singapore) applied zero-bias thermally stimulated current or zero-temperature-gradient zero-bias thermally stimulated current to ultrathin tantalum pentoxide samples. For samples with some shallow traps which can be filled at low temperature and some deep traps which can be filled only at high temperature, a two-scan TSC may be useful as suggested by Lau in 2007. TSC has also been applied to hafnium oxide.
TSC technique is used to study dielectric materials and polymers. Different theories was made to describe the response curve for this technique in order to calculate the peak parameters which are, the activation energy and the relaxation time. | 0 | Theoretical and Fundamental Chemistry |
Like other alchemists of the time, Brand searched for the "philosopher's stone", a substance which supposedly transformed base metals (like lead) into gold. By the time his first wife died he had exhausted her money on this pursuit. He then married his second wife Margaretha, a wealthy widow whose financial resources allowed him to continue the search.
Like many before him, he was interested in urine and tried combining it with various other materials, in hundreds of combinations. He had seen for instance a recipe in a book 400 Auserlensene Chemische Process, by F. T. Kessler of Strasbourg, published in 1630, for using alum, saltpetre (potassium nitrate) and concentrated urine to turn base metals into silver (a recipe which did not work).
Around 1669 he heated residues from boiled-down urine on his furnace until the retort was red hot, where all of a sudden glowing fumes filled it and liquid dripped out, bursting into flames. He could catch the liquid in a jar and cover it, where it solidified and continued to give off a pale-green glow. What he collected was phosphorus, which he named from the Greek word for "light-bearing" or "light-bearer."
Phosphorus must have been awe-inspiring to an alchemist: it was a product of man, and seeming to glow with a "life force" that did not diminish over time (and did not need re-exposure to light like the previously discovered Bologna Stone). Brand kept his discovery secret, as alchemists of the time did, and worked with the phosphorus trying unsuccessfully to use it to produce gold.
His recipe was:
* Let urine stand for days until it gives off a pungent smell. (This step was not necessary, as later scientists discovered that fresh urine yielded the same amount of phosphorus).
*Boil urine to reduce it to a thick syrup.
* Heat until a red oil distills up from it, and draw that off.
* Allow the remainder to cool, where it consists of a black spongy upper part and a salty lower part.
* Discard the salt, mix the red oil back into the black material.
* Heat that mixture strongly for 16 hours.
* First white fumes come off, then an oil, then phosphorus.
* The phosphorus may be passed into cold water to solidify.
The chemical reaction Brand stumbled on was as follows. Urine contains phosphates PO, as sodium phosphate (i.e. with Na) in the form of microcosmic salt, and various carbon-based organics. Under strong heat the oxygen atoms from the phosphate react with carbon to produce carbon monoxide CO, leaving elemental phosphorus P, which comes off as a gas. Phosphorus condenses to a liquid below about 280°C and then solidifies (to the white phosphorus allotrope) below about 44°C (depending on purity). This same essential reaction is still used today (but with mined phosphate ores, coke for carbon, and electric furnaces).
Brand's process yielded far less phosphorus than it could have. The salt part he discarded contained most of the phosphate. He used about of urine to produce just 120 grams of phosphorus. If he had ground up the entire residue he could have obtained many times more than this (1 litre of adult human urine contains about 1.4g of phosphorus salts, which amounts to around 0.11 grams of pure white phosphorus).
Though Brand initially kept his process for producing phosphorus from urine a secret, he later sold the recipe for 200 thalers to a Johann Daniel Kraft from Dresden. Subsequently, both Swedish chemist Johann Kunckel (in 1678) and English chemist Robert Boyle (in 1680) were able to independently discover phosphorus; the latter's assistant, Ambrose Godfrey-Hanckwitz, later made a business of manufacturing phosphorus from 1707 onwards. | 1 | Applied and Interdisciplinary Chemistry |
Examples of intermetallics through history include:
# Roman yellow brass, CuZn
# Chinese high tin bronze, CuSn
# Type metal, SbSn
# Chinese white copper, CuNi
German type metal is described as breaking like glass, not bending, softer than copper but more fusible than lead. The chemical formula does not agree with the one above; however, the properties match with an intermetallic compound or an alloy of one. | 1 | Applied and Interdisciplinary Chemistry |
The process of separating mixtures of chemical compounds by passing them through a column that contains a solid stationary phase that was eluted with a mobile phase (column chromatography) was well known at that time. Chromatographic separation was considered to occur by an adsorption process whereby compounds adhered to a solid media and were washed off the column with a solvent, mixture of solvents, or solvent gradient. In contrast, Martin and Synge developed and described a chromatographic separation process whereby compounds were partitioned between two liquid phases similar to the separatory funnel liquid-liquid separation dynamic. This was an important departure, both in theory and inder equilibrium conditions. Martin and Synge initially attempted to devise a method of performing a sequential liquid-liquid extraction with serially connected glass vessels that functioned as separatory funnels. The seminal article presenting their early studies described a rather complicated instrument that allowed partitioning of amino acids between water and chloroform phases. The process was termed "counter-current liquid-liquid extraction." Martin and Synge described the theory of this technique in reference to continuous fractional distillation described by Randall and Longtin. This approach was deemed too cumbersome, so they developed a method of absorbing water onto silica gel as the stationary phase and using a solvent, such as chloroform, as the mobile phase. This work was published in 1941 as "a new form of chromatogram employing two liquid phases." The article describes both the theory in terms of the partition coefficient of a compound, and the application of the process to the separation of amino acids on a water-impregnated silica column eluted with a water:chloroform:n-butanol solvent mixture. | 0 | Theoretical and Fundamental Chemistry |
*Vibration - either sinusoidal vibration or gyratory vibration.
**Sinusoidal Vibration occurs at an angled plane relative to the horizontal. The vibration is in a wave pattern determined by frequency and amplitude.
**Gyratory Vibration occurs at near level plane at low angles in a reciprocating side to side motion.
*Gravity - This physical interaction is after material is thrown from the screen causing it to fall to a lower level. Gravity also pulls the particles through the screen media.
*Density - The density of the material relates to material stratification.
*Electrostatic Force - This force applies to screening when particles are extremely dry or is wet. | 1 | Applied and Interdisciplinary Chemistry |
Phytomining was first proposed in 1983 by Rufus Chaney, a USDA agronomist. He and Alan Baker, a University of Melbourne professor, first tested it in 1996. They, as well as Jay Scott Angle and Yin-Ming Li, filed a patent on the process in 1995 which expired in 2015. | 1 | Applied and Interdisciplinary Chemistry |
K. C. Nicolaous group successfully synthesized endiandric acid, 1, in 1982 as a test of Blacks biosynthetic conjecture, using a biomimetic strategy involving series of stereocontrolled electrocyclic reactions. Specifically, they observed that the natural products endiandric acids A and C could have arisen from a common precursor, via slightly different 6π [4s+2s] cycloaddition (Diels-Alder) reactions. This key precursor was in turn accessible biosynthetically via two further thermally allowed sequential 6π electron and 8π electron electrocyclizations.
The Nicolaou group therefore sought to synthesize endiandric acid C from an acyclic symmetric diacetylenic diol precursor, 14 (as shown); they began with "mild hydrogenation" in the presence of Lindlar catalyst and quinoline, anticipating tetraene diol 15, cyclooctatriene 16, or the fully cyclized bicyclo[4.2.0]octadiene (bicyclic diol) 17. Remarkably, following this 3-6 hour, 25 °C process, a 45-55% yield of bicyclic diol 17 could be isolated. Hence, it was not necessary to do anything specific to promote the required sequence of 8π conrotatory and 6π disrotatory cyclizations (further highlighted in supplementary image); they occurred spontaneously on generation of tetraene-diol 15. Protection of a single alcohol moiety (as TBDPS) was accomplished using the silyl chloride via the corresponding tricyclic iodoether intermediate (not shown), with the internally masked remaining hydroxyl group being released on treatment with zinc dust in acetic acid (giving 18 in 70-80% yield). Bromination of the alcohol under Appel conditions followed by its displacement on treatment with sodium cyanide in HMPA gave nitrile 20, the key intermediate in all of this groups endiandric acid syntheses.'
The title compound was then pursued via DIBAL reduction of the nitrile at low temperature, followed by mild acidic hydrolysis to release aldehyde 21. A series of 7 further steps—condensation to form trans-butenoate 22, thermal intramolecular Diels-Alder reaction to create the tetracyclic endiantric core structure 23, desilylation to unmask alcohol 24, bromination and nitrile formation (as described above) to give 25 and 26, respectively, then hydrolysis of the methyl ester and repeat of the earlier DIBAL/acid hydrolysis sequence—generated the endiantric core structure with pendant aldehyde, 28, that was poised for the final step. Its treatment with diethyl cinnamylphosphonate and LDA at low temperature in THF (generating en route the anionic olefination reagent) formed the desired diene in good yield in a "geometrically controlled manner", thus providing the desired endiandric acid C product. | 0 | Theoretical and Fundamental Chemistry |
* ABS (acrylonitrile butadiene styrene)
* CPVC (chlorinated polyvinyl chloride)
* HDPE (high-density polyethylene)
* PB-1 (polybutylene)
* PE (polyethylene) of various densities, also abbreviated to LDPE, MDPE and HDPE (low, medium and high density polyethylene; the medium density version is at times referred to as "black alkathene" in the UK)
* PE-RT (polyethylene of raised temperature (RT))
* PEX (cross-linked polyethylene)
* PP (polypropylene)
* PVDF (polyvinylidene difluoride)
* UPVC (unplasticized polyvinyl chloride) | 1 | Applied and Interdisciplinary Chemistry |
In electromagnetism, Brillouin scattering (also known as Brillouin light scattering or BLS), named after Léon Brillouin, refers to the interaction of light with the material waves in a medium (e.g. electrostriction and magnetostriction). It is mediated by the refractive index dependence on the material properties of the medium; as described in optics, the index of refraction of a transparent material changes under deformation (compression-distension or shear-skewing).
The result of the interaction between the light-wave and the carrier-deformation wave is that a fraction of the transmitted light-wave changes its momentum (thus its frequency and energy) in preferential directions, as if by diffraction caused by an oscillating 3-dimensional diffraction grating.
If the medium is a solid crystal, a macromolecular chain condensate or a viscous liquid or gas, then the low frequency atomic-chain-deformation waves within the transmitting medium (not the transmitted electro-magnetic wave) in the carrier (represented as a quasiparticle) could be for example:
# mass oscillation (acoustic) modes (called phonons);
# charge displacement modes (in dielectrics, called polarons);
# magnetic spin oscillation modes (in magnetic materials, called magnons). | 0 | Theoretical and Fundamental Chemistry |
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. | 0 | Theoretical and Fundamental Chemistry |
Dendrimers are highly ordered, branched polymeric molecules. Synonymous terms for dendrimer include arborols and cascade molecules. Typically, dendrimers are symmetric about the core, and often adopt a spherical three-dimensional morphology. The word dendron is also encountered frequently. A dendron usually contains a single chemically addressable group called the focal point or core. The difference between dendrons and dendrimers is illustrated in the top figure, but the terms are typically encountered interchangeably.
The first dendrimers were made by divergent synthesis approaches by Fritz Vögtle in 1978, R.G. Denkewalter at Allied Corporation in 1981, Donald Tomalia at Dow Chemical in 1983 and in 1985, and by George R. Newkome in 1985. In 1990 a convergent synthetic approach was introduced by Craig Hawker and Jean Fréchet. Dendrimer popularity then greatly increased, resulting in more than 5,000 scientific papers and patents by the year 2005. | 0 | Theoretical and Fundamental Chemistry |
A regular solution can also be described by Raoult's law modified with a Margules function with only one parameter :
where the Margules function is
Notice that the Margules function for each component contains the mole fraction of the other component. It can also be shown using the Gibbs-Duhem relation that if the first Margules expression holds, then the other one must have the same shape. A regular solutions internal energy will vary during mixing or during process.
The value of can be interpreted as W/RT, where W = 2U - U - U represents the difference in interaction energy between like and unlike neighbors.
In contrast to ideal solutions, regular solutions do possess a non-zero enthalpy of mixing, due to the W term. If the unlike interactions are more unfavorable than the like ones, we get competition between an entropy of mixing term that produces a minimum in the Gibbs free energy at x = 0.5 and the enthalpy term that has a maximum there. At high temperatures, the entropic term in the free energy of mixing dominates and the system is fully miscible, but at lower temperatures the G(x) curve will have two minima and a maximum in between. This results in phase separation. In general there will be a temperature where the three extremes coalesce and the system becomes fully miscible. This point is known as the upper critical solution temperature or the upper consolute temperature.
In contrast to ideal solutions, the volumes in the case of regular solutions are no longer strictly additive but must be calculated from partial molar volumes that are a function of x.
The term was introduced in 1927 by the American physical chemist Joel Henry Hildebrand. | 0 | Theoretical and Fundamental Chemistry |
Carboxylation of the 2,3-enediolate results in the intermediate 3-keto-2-carboxyarabinitol-1,5-bisphosphate and Lys334 is positioned to facilitate the addition of the substrate as it replaces the third -coordinated water molecule and add directly to the enediol. No Michaelis complex is formed in this process. Hydration of this ketone results in an additional hydroxy group on C3, forming a gem-diol intermediate. Carboxylation and hydration have been proposed as either a single concerted step or as two sequential steps. Concerted mechanism is supported by the proximity of the water molecule to C3 of RuBP in multiple crystal structures. Within the spinach structure, other residues are well placed to aid in the hydration step as they are within hydrogen bonding distance of the water molecule. | 0 | Theoretical and Fundamental Chemistry |
The biorheological approach applies in particular to molecular studies where changes of physical properties and conformation are investigated without reference to how the process actually takes place. Biorheological analyses include study of pathological processes through clinical research in the related fields of hemodynamics and hemorheology, and may have clinical implications in aiding the treatment of specific diseases. | 1 | Applied and Interdisciplinary Chemistry |
On a microscopic scale, conduction occurs within a body considered as being stationary; this means that the kinetic and potential energies of the bulk motion of the body are separately accounted for. Internal energy diffuses as rapidly moving or vibrating atoms and molecules interact with neighbouring particles, transferring some of their microscopic kinetic and potential energies, these quantities being defined relative to the bulk of the body considered as being stationary. Heat is transferred by conduction when adjacent atoms or molecules collide, or as several electrons move backwards and forwards from atom to atom in a disorganized way so as not to form a macroscopic electric current, or as phonons collide and scatter. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact, occurring more readily than in liquids or gases since the network of relatively close fixed spatial relationships between atoms helps to transfer energy between them by vibration.
Thermal contact conductance is the study of heat conduction between solid bodies in contact. A temperature drop is often observed at the interface between the two surfaces in contact. This phenomenon is said to be a result of a thermal contact resistance existing between the contacting surfaces. Interfacial thermal resistance is a measure of an interface's resistance to thermal flow. This thermal resistance differs from contact resistance, as it exists even at atomically perfect interfaces. Understanding the thermal resistance at the interface between two materials is of primary significance in the study of its thermal properties. Interfaces often contribute significantly to the observed properties of the materials.
The inter-molecular transfer of energy could be primarily by elastic impact, as in fluids, or by free-electron diffusion, as in metals, or phonon vibration, as in insulators. In insulators, the heat flux is carried almost entirely by phonon vibrations.
Metals (e.g., copper, platinum, gold, etc.) are usually good conductors of thermal energy. This is due to the way that metals bond chemically: metallic bonds (as opposed to covalent or ionic bonds) have free-moving electrons that transfer thermal energy rapidly through the metal. The electron fluid of a conductive metallic solid conducts most of the heat flux through the solid. Phonon flux is still present but carries less of the energy. Electrons also conduct electric current through conductive solids, and the thermal and electrical conductivities of most metals have about the same ratio. A good electrical conductor, such as copper, also conducts heat well. Thermoelectricity is caused by the interaction of heat flux and electric current. Heat conduction within a solid is directly analogous to diffusion of particles within a fluid, in the situation where there are no fluid currents.
In gases, heat transfer occurs through collisions of gas molecules with one another. In the absence of convection, which relates to a moving fluid or gas phase, thermal conduction through a gas phase is highly dependent on the composition and pressure of this phase, and in particular, the mean free path of gas molecules relative to the size of the gas gap, as given by the Knudsen number .
To quantify the ease with which a particular medium conducts, engineers employ the thermal conductivity, also known as the conductivity constant or conduction coefficient, k. In thermal conductivity, k is defined as "the quantity of heat, Q, transmitted in time (t) through a thickness (L), in a direction normal to a surface of area (A), due to a temperature difference (ΔT) [...]". Thermal conductivity is a material property that is primarily dependent on the medium's phase, temperature, density, and molecular bonding. Thermal effusivity is a quantity derived from conductivity, which is a measure of its ability to exchange thermal energy with its surroundings. | 1 | Applied and Interdisciplinary Chemistry |
Within the electrocoagulation reactor, several distinct electrochemical reactions are produced independently. These are:
* Seeding, resulting from the anode reduction of metal ions that become new centers for larger, stable, insoluble complexes that precipitate as complex metal ions.
* Emulsion Breaking, resulting from the oxygen and hydrogen ions that bond into the water receptor sites of emulsified oil molecules creating a water-insoluble complex separating water from oil, driller's mud, dyes, inks, fatty acids, etc.
* Halogen Complexing, as the metal ions bind themselves to chlorines in a chlorinated hydrocarbon molecule resulting in a large insoluble complex separating water from pesticides, herbicides, chlorinated PCBs, etc.
* Bleaching by the oxygen ions produced in the reaction chamber oxidizes dyes, cyanides, bacteria, viruses, biohazards, etc. Electron flooding of electrodes forced ions to be formed to carry charge into the water, thereby eliminating the polar effect of the water complex, allowing colloidal materials to precipitate and the current controlled ion transport between the electrodes creates an osmotic pressure that typically ruptures bacteria, cysts, and viruses.
* Oxidation and Reduction reactions are forced to their natural end point within the reaction tank which speeds up the natural process of nature that occurs in wet chemistry, where concentration gradients and solubility products (KsP) are the chief determinants to enable reactions to reach stoichiometric completion.
* Electrocoagulation Induced pH swings toward neutral. | 1 | Applied and Interdisciplinary Chemistry |
The Ruhr Valley provided an excellent location for the German iron and steel industry because of the availability of raw materials, coal, transport, a skilled labor force, nearby markets, and an entrepreneurial spirit that led to the creation of many firms, often in close conjunction with coal mines. By 1850 the Ruhr had 50 iron works with 2,813 full-time employees. The first modern furnace was built in 1849. The unification of Germany in 1871 gave further impetus to rapid growth, as the German Empire started to catch up with Britain. From 1880 to World War I, the industry of the Ruhr area consisted of numerous enterprises, each working on a separate level of production. Mixed enterprises could unite all levels of production through vertical integration, thus lowering production costs. Technological progress brought new advantages as well. These developments set the stage for the creation of combined business concerns.
The leading firm was Friedrich Krupp AG run by the Krupp family. Many diverse, large-scale family firms such as Krupps reorganized in order to adapt to the changing conditions and meet the economic depression of the 1870s, which reduced the earnings in the German iron and steel industry. Krupp reformed his accounting system to better manage his growing empire, adding a specialized bureau of calculation as well as a bureau for the control of times and wages. The rival firm GHH quickly followed, as did Thyssen AG, which had been founded by August Thyssen in 1867. Germany became Europes leading steel-producing nation in the late 19th century, thanks in large part to the protection from American and British competition afforded by tariffs and cartels.
By 1913 American and German exports dominated the world steel market, and Britain slipped to third place. German steel production grew explosively from 1 million metric tons in 1885 to 10 million in 1905 and peaked at 19 million in 1918. In the 1920s Germany produced about 15 million tons, but output plunged to 6 million in 1933. Under Nazi rule, steel output peaked at 22 million tons in 1940, then dipped to 18 million in 1944 under Allied bombing.
The merger of four major firms into the German Steel Trust (Vereinigte Stahlwerke) in 1926 was modeled on the U.S. Steel corporation in the U.S. The goal was to move beyond the limitations of the old cartel system by incorporating advances simultaneously inside a single corporation. The new company emphasized rationalization of management structures and modernization of the technology; it employed a multi-divisional structure and used return on investment as its measure of success. It represented the "Americanization" of the German steel industry because its internal structure, management methods, use of technology, and emphasis on mass production. The chief difference was that consumer capitalism as an industrial strategy did not seem plausible to German steel industrialists.
In iron and steel and other industries, German firms avoided cut-throat competition and instead relied on trade associations. Germany was a world leader because of its prevailing "corporatist mentality", its strong bureaucratic tradition, and the encouragement of the government. These associations regulated competition and allowed small firms to function in the shadow of much larger companies.
With the need to rebuild the bombed-out infrastructure after the Second World War, Marshall Plan (1948–51) enabled West Germany to rebuild and modernize its mills. It produced 3 million tons of steel in 1947, 12 million in 1950, 34 million in 1960 and 46 million in 1970. East Germany produced about a tenth as much. | 1 | Applied and Interdisciplinary Chemistry |
Sutherland and collaborators proposed a geochemical scenario to argue that cyanosulfidic synthesis was a plausible process on the early Earth. Their scenario starts following a meteorite impact leads to the production of HCN and phosphate. The meteorite fragments also supply the necessary sulfide for the reaction. As ponds and lakes containing these reagents experience wet dry cycles, ferrocyanide, sodium, and potassium salts precipitate out of solution into evaporites, concentrating and storing reactants for future chemistry. These evaporites can then be thermally altered through additional impacts or geothermal heating, producing all necessary components for the proposed syntheses. Rain and runoff create streams that transport compounds along geochemical gradients, introducing new reactants along the way which causes new syntheses to occur. The streams are also exposed to ultraviolet radiation, providing energy for the reactions. The conditions described here support an evaporative lake or terrestrial hydrothermal pond scenario for the origin of life. The proposed geochemical scenario also relies on flow chemistry concepts to introduce new reactants throughout the process to cause additional chemical reactions and syntheses to occur. | 0 | Theoretical and Fundamental Chemistry |
The convection–diffusion equation is a relatively simple equation describing flows, or alternatively, describing a stochastically-changing system. Therefore, the same or similar equation arises in many contexts unrelated to flows through space.
*It is formally identical to the Fokker–Planck equation for the velocity of a particle.
*It is closely related to the Black–Scholes equation and other equations in financial mathematics.
*It is closely related to the Navier–Stokes equations, because the flow of momentum in a fluid is mathematically similar to the flow of mass or energy. The correspondence is clearest in the case of an incompressible Newtonian fluid, in which case the Navier–Stokes equation is:
where is the momentum of the fluid (per unit volume) at each point (equal to the density multiplied by the velocity ), is viscosity, is fluid pressure, and is any other body force such as gravity. In this equation, the term on the left-hand side describes the change in momentum at a given point; the first term on the right describes the diffusion of momentum by viscosity; the second term on the right describes the advective flow of momentum; and the last two terms on the right describes the external and internal forces which can act as sources or sinks of momentum. | 1 | Applied and Interdisciplinary Chemistry |
Fausto de Elhuyar (11 October 1755 – 6 February 1833) was a Spanish chemist, and the first to isolate tungsten with his brother Juan José Elhuyar in 1783. He was in charge, under a King of Spain commission, of organizing the School of Mines in México City and so was responsible for building the Palacio de Minería, a structure that would house the school. Elhuyar left Mexico after the Mexican War of Independence, when most of the Spanish residents in Mexico were expelled. | 1 | Applied and Interdisciplinary Chemistry |
From the commercial perspective, the most important phosphite salt is basic lead phosphite. Many salts containing the phosphite ion have been investigated structurally, these include sodium phosphite pentahydrate (NaHPO·5HO). (NH)HPO·HO, CuHPO·HO, SnHPO and Al(HPO)·4HO. The structure of is approximately tetrahedral.
has a number of canonical resonance forms making it isoelectronic with bisulfite ion, , which has a similar structure. | 0 | Theoretical and Fundamental Chemistry |
One of the best-known ironmasters of the early part of the industrial revolution was John Wilkinson (1728–1808), who was considered to have "iron madness", extending even to making cast iron coffins. Wilkinsons patented method for boring iron cylinders was first used to create cannons, but later provided the precision needed to create James Watts first steam engines. | 1 | Applied and Interdisciplinary Chemistry |
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