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For most chain-growth polymerizations, the propagation steps are much faster than the initiation steps, so that each growing chain is formed in a short time compared to the overall polymerization reaction. During the formation of a single chain, the reactant concentrations and therefore the propagation rate remain effectively constant. Under these conditions, the ratio of the number of propagation steps to the number of initiation steps is just the ratio of reaction rates:
where is the rate of propagation, is the rate of initiation of polymerization, and is the rate of termination of the polymer chain. The second form of the equation is valid at steady-state polymerization, as the chains are being initiated at the same rate they are being terminated ().
An exception is the class of living polymerizations, in which propagation is much slower than initiation, and chain termination does not occur until a quenching agent is added. In such reactions the reactant monomer is slowly consumed and the propagation rate varies and is not used to obtain the kinetic chain length. Instead the length at a given time is usually written as:
where represents the number of monomer units consumed, and the number of radicals that initiate polymerization. When the reaction goes to completion, , and then the kinetic chain length is equal to the number average degree of polymerization of the polymer.
In both cases kinetic chain length is an average quantity, as not all polymer chains in a given reaction are identical in length. The value of ν depends on the nature and concentration of both the monomer and initiator involved. | 0 | Theoretical and Fundamental Chemistry |
*DNA sequencing
*Polymerase chain reaction
*Northern blotting
*Southern blotting
*Fusion proteins
*DNA microarray
*Bioinformatics
*Flow cytometry | 1 | Applied and Interdisciplinary Chemistry |
Spectroradiometers are used in many applications, and can be made to meet a wide variety of specifications. Example applications include:
*Solar UV and UVB radiation
*LED measurement
*Display measurement and calibration
*CFL testing
*Remote detection of oil slicks
*Plant research and development
*Earth and planetary remote sensing | 0 | Theoretical and Fundamental Chemistry |
Multi-layered systems containing the following functional layers: root barrier, protection layer, drainage layer, filter layer, growing medium and plant level. | 1 | Applied and Interdisciplinary Chemistry |
Tank and vat leaching involves placing ore, usually after size reduction and classification, into large tanks or vats at ambient operating conditions containing a leaching solution and allowing the valuable material to leach from the ore into solution.
In tank leaching the ground, classified solids are already mixed with water to form a slurry or pulp, and this is pumped into the tanks. Leaching reagents are added to the tanks to achieve the leaching reaction. In a continuous system the slurry will then either overflow from one tank to the next, or be pumped to the next tank. Ultimately the “pregnant” solution is separated from the slurry using some form of liquid/solid separation process, and the solution passes on to the next phase of recovery.
In vat leaching the solids are loaded into the vat, once full the vat is flooded with a leaching solution. The solution drains from the tank, and is either recycled back into the vat or is pumped to the next step of the recovery process.
. Vat leach units are rectangular containers (drums, barrels, tanks or vats), usually very big and made of wood or concrete, lined with material resistant to the leaching media. The treated ore is usually coarse.
The vats are usually run sequentially to maximize the contact time between the ore and the reagent. In such a series the leachate collected from one container is added to another vat with fresher ore
As mentioned previously tanks are equipped with agitators to keep the solids in suspension in the vats and improve the solid to liquid to gas contact. Agitation is further assisted by the use of tank baffles to increase the efficiency of agitation and prevent centrifuging of slurries in circular tanks... | 1 | Applied and Interdisciplinary Chemistry |
The site of former factory Nya Krokslätt is situated between a mountain and a stream. Danish engineers, Ramboll, have designed a concept of slowing down and guiding storm water in the area with methods such as vegetation combined with ponds, streams and soak-away pits as well as glazed green-blue climate zones surrounding the buildings which delay and clean roof water and greywater.
The design concept provides for a multifunctional, rich urban environment, which includes not only technical solutions for energy efficient buildings, but encompasses the implementation of blue-green infrastructure and ecosystem services in an urban area. | 1 | Applied and Interdisciplinary Chemistry |
The duration and intensity of pharmacological action of most lipophilic drugs are determined by the rate they are metabolized to inactive products. The Cytochrome P450 monooxygenase system is a crucial pathway in this regard. In general, anything that increases the rate of metabolism (e.g., enzyme induction) of a pharmacologically active metabolite will decrease the duration and intensity of the drug action. The opposite is also true, as in enzyme inhibition. However, in cases where an enzyme is responsible for metabolizing a pro-drug into a drug, enzyme induction can accelerate this conversion and increase drug levels, potentially causing toxicity.
Various physiological and pathological factors can also affect drug metabolism. Physiological factors that can influence drug metabolism include age, individual variation (e.g., pharmacogenetics), enterohepatic circulation, nutrition, sex differences or gut microbiota. This last factor has significance because gut microorganisms are able to chemically modify the structure of drugs through degradation and biotransformation processes, thus altering the activity and toxicity of drugs. These processes can decrease the efficacy of drugs, as is the case of digoxin in the presence of Eggerthella lenta in the microbiota. Genetic variation (polymorphism) accounts for some of the variability in the effect of drugs.
In general, drugs are metabolized more slowly in fetal, neonatal and elderly humans and animals than in adults. With N-acetyltransferases (involved in Phase II reactions), individual variation creates a group of people who acetylate slowly (slow acetylators) and those who acetylate quickly, split roughly 50:50 in the population of Canada.
This variation may have dramatic consequences, as the slow acetylators are more prone to dose-dependent toxicity.
Dose, frequency, route of administration, tissue distribution and protein binding of the drug affect its metabolism. Pathological factors can also influence drug metabolism, including liver, kidney, or heart diseases.
In silico modelling and simulation methods allow drug metabolism to be predicted in virtual patient populations prior to performing clinical studies in human subjects. This can be used to identify individuals most at risk from adverse reaction. | 1 | Applied and Interdisciplinary Chemistry |
The first coordination sphere refers to the molecules that are attached directly to the metal. The interactions between the first and second coordination spheres usually involve hydrogen-bonding. For charged complexes, ion pairing is important.
In hexamminecobalt(III) chloride ([Co(NH)]Cl), the cobalt cation plus the 6 ammonia ligands comprise the first coordination sphere. The coordination sphere of this ion thus consists of a central MN core "decorated" by 18 N−H bonds that radiate outwards. | 0 | Theoretical and Fundamental Chemistry |
Egg white ovalbumin: The unfolding of ovalbumin, a 45 kDa protein, as a function of guanidine hydrochloride (0-6M) occurred reversibly in one step. The protein fractions in native (N) and the denatured states (D) were characterized by UV spectrometry and viscosity measurements at defined temperatures in buffer pH 7.0. The thermodynamics of folding and possibly kinetics followed a two state transition (N->D). The data were consistent with the fact that the native state was stabilized by hydrophobic effect in aqueous solution; this effect was diminished by introducing Guanidine hydrochloride to protein solution with concomitant transition to denatured state, random coil conformation similar to a nascent polypeptide chain.
Egg white Ovomucoid: The unfolding of ovomucoid (N), a domain containing 28 kDa protein, by guanidine hydrochloride did not proceed in a single step but occurred in two steps; the transition at low denaturant was associated with an intermediate, native-like, structure (X), and at high denaturant, protein existed in random coil structure (D). The reversible unfolding at each step (N->X->D) followed a two state transition pattern, albeit with somewhat different folding rates for the intermediate and native structures (1978). The studies in his lab indicated that in vivo protein folding may not be explained by the amino acid sequence alone. Independently, the molecular biology of chaperones succeeded in the identification of additional folding factors in 1989. The latter studies marked the beginning of modern protein folding with manipulation in human health. | 1 | Applied and Interdisciplinary Chemistry |
Agricola addresses the book to prominent German aristocrats, the most important of whom were Maurice, Elector of Saxony and his brother Augustus, who were his main patrons. He then describes the works of ancient and contemporary writers on mining and metallurgy, the chief ancient source being Pliny the Elder. Agricola describes several books contemporary to him, the chief being a booklet by Calbus of Freiberg in German. The works of alchemists are then described. Agricola does not reject the idea of alchemy, but notes that alchemical writings are obscure and that we do not read of any of the masters who became rich. He then describes fraudulent alchemists, who deserve the death penalty. Agricola completes his introduction by explaining that, since no other author has described the art of metals completely, he has written this work, setting forth his scheme for twelve books. Finally, he again directly addresses his audience of German princes, explaining the wealth that can be gained from this art. | 1 | Applied and Interdisciplinary Chemistry |
Orthopoxviruses and some other nucleocytoplasmic large DNA viruses synthesize RNA using a virally encoded multi-subunit RNAP. They are most similar to eukaryotic RNAPs, with some subunits minified or removed. Exactly which RNAP they are most similar to is a topic of debate. Most other viruses that synthesize RNA use unrelated mechanics.
Many viruses use a single-subunit DNA-dependent RNAP (ssRNAP) that is structurally and mechanistically related to the single-subunit RNAP of eukaryotic chloroplasts (RpoT) and mitochondria (POLRMT) and, more distantly, to DNA polymerases and reverse transcriptases. Perhaps the most widely studied such single-subunit RNAP is bacteriophage T7 RNA polymerase. ssRNAPs cannot proofread.
B. subtilis prophage SPβ uses YonO, a homolog of the β+β′ subunits of msRNAPs to form a monomeric (both barrels on the same chain) RNAP distinct from the usual "right hand" ssRNAP. It probably diverged very long ago from the canonical five-unit msRNAP, before the time of the last universal common ancestor.
Other viruses use an RNA-dependent RNAP (an RNAP that employs RNA as a template instead of DNA). This occurs in negative strand RNA viruses and dsRNA viruses, both of which exist for a portion of their life cycle as double-stranded RNA. However, some positive strand RNA viruses, such as poliovirus, also contain RNA-dependent RNAP. | 1 | Applied and Interdisciplinary Chemistry |
Amine oxides with an average chain length of 12.6 have been measured to be water-soluble at ~410 g/L. They are considered to have low bioaccumulation potential in aquatic species based on log K data from chain lengths less than C14 (bioconcentration factor < 87%). Levels of AO in untreated influent were found to be 2.3–27.8 ug/L, while in effluent they were found to be 0.4–2.91 ug/L. The highest effluent concentrations were found in oxidation ditch and trickling filter treatment plants. On average, over 96% removal has been found with secondary activated sludge treatment. Acute toxicity in fish, as indicated by 96h LC50 tests, is in the range of 1,000–3,000 ug/L for carbon chain lengths less than C14. LC50 values for chain lengths greater than C14 range from 600 to 1400 ug/L. Chronic toxicity data for fish is 420 ug/L. When normalized to C12.9, the NOEC is 310 ug/L for growth and hatchability. | 0 | Theoretical and Fundamental Chemistry |
In most of the cases, agrochemicals refer to pesticides.
*Pesticides
**Insecticides
**Herbicides
**Fungicides
**Algaecides
**Rodenticides
**Molluscicides
**Nematicides
*Fertilisers
*Soil conditioners
*Liming and acidifying agents
*Plant growth regulators | 1 | Applied and Interdisciplinary Chemistry |
Where there is no β-hydrogen to be eliminated, cyclic compounds may be formed, as in the preparation of methylenecyclopropane below.
Cyclopropenes, aziridines
and cyclobutanes may be formed in a similar manner. | 0 | Theoretical and Fundamental Chemistry |
The Laves graph is a cubic graph, meaning that there are exactly three edges at each vertex. Every pair of a vertex and adjacent edge can be transformed into every other such pair by a symmetry of the graph, so it is a symmetric graph. More strongly, for every two vertices and , every one-to-one correspondence between the three edges incident to and the three edges incident to can be realized by a symmetry. However, the overall structure is chiral: no sequence of translations and rotations can make it coincide with its mirror image. The symmetry group of the Laves graph is the space group .
The girth of this structure is 10—the shortest cycles in the graph have 10 vertices—and 15 of these cycles pass through each vertex. The numbers of vertices at distance 0, 1, 2, ... from any vertex (forming the coordination sequence of the Laves graph) are:
If the surrounding space is partitioned into the regions nearest each vertex—the cells of the Voronoi diagram of this structure—these form heptadecahedra with 17 faces each. They are plesiohedra, polyhedra that tile space isohedrally. Experimenting with the structures formed by these polyhedra led physicist Alan Schoen to discover the gyroid minimal surface, which is topologically equivalent to the surface obtained by thickening the edges of the Laves graph to cylinders and taking the boundary of their union.
The Laves graph is the unique shortest triply-periodic network, in the following sense. Triply-periodic means repeating infinitely in all three dimensions of space, so a triply-periodic network is a connected geometric graph with a three-dimensional lattice of translational symmetries. A fundamental domain is any shape that can tile space with its translated copies under these symmetries. Any lattice has infinitely many choices of fundamental domain, of varying shapes, but they all have the same volume . One can also measure the length of the edges of the network within a single copy of the fundamental domain; call this number . Similarly to , does not depend on the choice of fundamental domain, as long as the domain boundary only crosses the edges, rather than containing parts of their length. The Laves graph has four symmetry classes of vertices (orbits), because the symmetries considered here are only translations, not the rotations needed to map these four classes into each other. Each symmetry class has one vertex in any fundamental domain, so the fundamental domain contains twelve half-edges, with total length . The volume of its fundamental domain is 32. From these two numbers, the ratio (a dimensionless quantity) is therefore . This is in fact the minimum possible value: All triply-periodic networks have with equality only in the case of the Laves graph. | 0 | Theoretical and Fundamental Chemistry |
Deuterium has been shown to lengthen the period of oscillation of the circadian clock when dosed in rats, hamsters, and Gonyaulax dinoflagellates. In rats, chronic intake of 25% DO disrupts circadian rhythmicity by lengthening the circadian period of suprachiasmatic nucleus-dependent rhythms in the brain's hypothalamus. Experiments in hamsters also support the theory that deuterium acts directly on the suprachiasmatic nucleus to lengthen the free-running circadian period. | 0 | Theoretical and Fundamental Chemistry |
The society holds a biennial International Congress. These congresses are an open platform for research presentations and also discussions about history of pharmacy in an truly international context. | 1 | Applied and Interdisciplinary Chemistry |
Melting is effected at approximately 2200 °C (4000 °F) using either an electrically heated furnace (electrically fused) or a gas/oxygen-fuelled furnace (flame-fused). Fused silica can be made from almost any silicon-rich chemical precursor, usually using a continuous process which involves flame oxidation of volatile silicon compounds to silicon dioxide, and thermal fusion of the resulting dust (although alternative processes are used). This results in a transparent glass with an ultra-high purity and improved optical transmission in the deep ultraviolet. One common method involves adding silicon tetrachloride to a hydrogen–oxygen flame. | 1 | Applied and Interdisciplinary Chemistry |
The theory is based on the assumption that the reaction can be described by a reaction coordinate, and that we can apply Boltzmann distribution at least in the reactant state.
A new, especially reactive segment of the reactant, called the saddle domain, is introduced, and the rate constant is factored:
where α is the conversion factor between the reactant state and saddle domain, while k is the rate constant from the saddle domain. The first can be simply calculated from the free energy surface, the latter is easily accessible from short molecular dynamics simulations | 0 | Theoretical and Fundamental Chemistry |
Although the risks of low-level radiation exposures are not well understood, a cautious approach has been universally adopted that all human radiation exposures should be kept As Low As Reasonably Practicable, "ALARP". (Originally, this was known as "As Low As Reasonably Achievable" (ALARA), but this has changed in modern draftings of the legislation to add more emphasis on the "Reasonably" and less on the "Achievable".)
Working with the ALARP principle, before a patient is exposed for a nuclear medicine examination, the benefit of the examination must be identified. This needs to take into account the particular circumstances of the patient in question, where appropriate. For instance, if a patient is unlikely to be able to tolerate a sufficient amount of the procedure to achieve a diagnosis, then it would be inappropriate to proceed with injecting the patient with the radioactive tracer.
When the benefit does justify the procedure, then the radiation exposure (the amount of radiation given to the patient) should also be kept as low as reasonably practicable. This means that the images produced in nuclear medicine should never be better than required for confident diagnosis. Giving larger radiation exposures can reduce the noise in an image and make it more photographically appealing, but if the clinical question can be answered without this level of detail, then this is inappropriate.
As a result, the radiation dose from nuclear medicine imaging varies greatly depending on the type of study. The effective radiation dose can be lower than or comparable to or can far exceed the general day-to-day environmental annual background radiation dose. Likewise, it can also be less than, in the range of, or higher than the radiation dose from an abdomen/pelvis CT scan.
Some nuclear medicine procedures require special patient preparation before the study to obtain the most accurate result. Pre-imaging preparations may include dietary preparation or the withholding of certain medications. Patients are encouraged to consult with the nuclear medicine department prior to a scan. | 1 | Applied and Interdisciplinary Chemistry |
The most common magnetic sensing devices are solid-state Hall effect sensors. These sensors produce a voltage proportional to the applied magnetic field and also sense polarity. They are used in applications where the magnetic field strength is relatively large, such as in anti-lock braking systems in cars, which sense wheel rotation speed via slots in the wheel disks. | 0 | Theoretical and Fundamental Chemistry |
The coenzyme NAD was first discovered by the British biochemists Arthur Harden and William John Young in 1906. They noticed that adding boiled and filtered yeast extract greatly accelerated alcoholic fermentation in unboiled yeast extracts. They called the unidentified factor responsible for this effect a coferment. Through a long and difficult purification from yeast extracts, this heat-stable factor was identified as a nucleotide sugar phosphate by Hans von Euler-Chelpin. In 1936, the German scientist Otto Heinrich Warburg showed the function of the nucleotide coenzyme in hydride transfer and identified the nicotinamide portion as the site of redox reactions.
Vitamin precursors of NAD were first identified in 1938, when Conrad Elvehjem showed that liver has an "anti-black tongue" activity in the form of nicotinamide. Then, in 1939, he provided the first strong evidence that niacin is used to synthesize NAD. In the early 1940s, Arthur Kornberg was the first to detect an enzyme in the biosynthetic pathway. In 1949, the American biochemists Morris Friedkin and Albert L. Lehninger proved that NADH linked metabolic pathways such as the citric acid cycle with the synthesis of ATP in oxidative phosphorylation. In 1958, Jack Preiss and Philip Handler discovered the intermediates and enzymes involved in the biosynthesis of NAD; salvage synthesis from nicotinic acid is termed the Preiss-Handler pathway. In 2004, Charles Brenner and co-workers uncovered the nicotinamide riboside kinase pathway to NAD.
The non-redox roles of NAD(P) were discovered later. The first to be identified was the use of NAD as the ADP-ribose donor in ADP-ribosylation reactions, observed in the early 1960s. Studies in the 1980s and 1990s revealed the activities of NAD and NADP metabolites in cell signaling – such as the action of cyclic ADP-ribose, which was discovered in 1987.
The metabolism of NAD remained an area of intense research into the 21st century, with interest heightened after the discovery of the NAD-dependent protein deacetylases called sirtuins in 2000, by Shin-ichiro Imai and coworkers in the laboratory of Leonard P. Guarente. In 2009 Imai proposed the "NAD World" hypothesis that key regulators of aging and longevity in mammals are sirtuin 1 and the primary NAD synthesizing enzyme nicotinamide phosphoribosyltransferase (NAMPT). In 2016 Imai expanded his hypothesis to "NAD World 2.0", which postulates that extracellular NAMPT from adipose tissue maintains NAD in the hypothalamus (the control center) in conjunction with myokines from skeletal muscle cells. In 2018, Napa Therapeutics was formed to develop drugs against a novel aging related target based on the research in NAD metabolism conducted in the lab of Eric Verdin. | 0 | Theoretical and Fundamental Chemistry |
In the interest of national and global public health, C-Path develops large databases of aggregated clinical trial data that can be used to study disease progression. These data are also used to develop and qualify biomarkers and clinical outcome assessment instruments that are shared with the greater community for use in drug development. C-Path also develops quantitative models to facilitate the design of efficient clinical trials. | 1 | Applied and Interdisciplinary Chemistry |
Hyperconjugation is also found in acyclic molecules containing heteroatoms, another form of the anomeric effect. If a molecule has an atom with a lone pair of electrons and the adjacent atom is able to accept electrons into the σ* orbital, hyperconjugation occurs, stabilizing the molecule. This forms a "no bond" resonance form. For this orbital overlap to occur, the trans, trans conformation is preferred for most heteroatoms, however for the stabilization to occur in dimethoxymethane, the gauche, gauche conformation is about 3–5 kcal/mol lower in energy (more stable) than the trans,trans conformation—this is about two times as big as the effect in sugars because there are two rotatable bonds (hence it is trans around both bonds or gauche around both) that are affected. | 0 | Theoretical and Fundamental Chemistry |
Memory foam was developed in 1966 under a contract by NASA's Ames Research Center to improve the safety of aircraft cushions. The temperature-sensitive memory foam was initially referred to as "slow spring back foam"; most called it "temper foam". Created by feeding gas into a polymer matrix, it had an open-cell solid structure that matched pressure against it, yet slowly returned to its original shape.
Later commercialisation of the foam included use in medical equipment such as X-ray table pads, and sports equipment such as American / Canadian football helmet liners.
When NASA released memory foam to the public domain in the early 1980s, Fagerdala World Foams was one of the few companies willing to work with it, as the manufacturing process remained difficult and unreliable. Their 1991 product, the Tempur-Pedic Swedish Mattress eventually led to the mattress and cushion company Tempur World.
Memory foam was subsequently used in medical settings. For example, when patients were required to lie immobile in bed, on a firm mattress, for an unhealthy period of time, the pressure on some of their body regions impaired blood flow, causing pressure sores or gangrene. Memory foam mattresses significantly decreased such events, as well as alternating pressure air mattresses.
Memory foam was initially too expensive for widespread use, but became cheaper. Its most common domestic uses are mattresses, pillows, shoes, and blankets. It has medical uses, such as wheelchair seat cushions, hospital bed pillows and padding for people suffering long-term pain or postural problems. | 0 | Theoretical and Fundamental Chemistry |
For more than 35 years, AWWA has set aside a week in the spring to recognize the importance of safe drinking water throughout North America. In 1988, AWWA brought the event to the attention of the US government and formed a coalition along with the League of Women Voters, the Association of State Drinking Water Administrators and the US Environmental Protection Agency. Subsequently, AWWA worked with Representative Robert Roe and Senator Dennis DeConcini to sponsor a resolution naming the first week of May as "Drinking Water Week." In 1988, a joint congressional resolution declaration was passed and signed by President Ronald Reagan. | 1 | Applied and Interdisciplinary Chemistry |
Herman's academic awards include the Ian Marcus Marci Medal (Czech Spectroscopic Society, 1989), the Alexander von Humboldt Research Prize (awarded in Germany in 1992, the first time the prize was awarded to a Czech natural scientist), the Česká hlava ("Czech Head") National Prize for lifetime achievements (2003), an Honorary Degree from the Leopold-Franzens University in Innsbruck (2007), and honorary membership of the Czech Mass Spectrometric Society.
Special honorary issues of The Journal of Physical Chemistry (1995) and The International Journal of Mass Spectrometry (2009) were issued to celebrate his 60th and 75th birthdays respectively. Since 2014 the Resonance Foundation awards "The Zdeněk Herman Prize" for the best PhD thesis in chemical physics and mass spectrometry. Since 2016 the international conference MOLEC (Dynamics of Molecular Systems) awards the "Zdeněk Herman Young Scientist Prize".
In his free time, Herman painted and sculpted, and has exhibited his work on several occasions. Busts by Herman of founders of several institutes of the Academy of Sciences are on display at those institutes. Three statues sculpted by Herman stand in the countryside around Rakovník (e.g., in the park in Pavlíkov). | 0 | Theoretical and Fundamental Chemistry |
The sample of a material (analyte) is brought into the flame as a gas, sprayed solution, or directly inserted into the flame by use of a small loop of wire, usually platinum. The heat from the flame evaporates the solvent and breaks intramolecular bonds to create free atoms. The thermal energy also excites the atoms into excited electronic states that subsequently emit light when they return to the ground electronic state. Each element emits light at a characteristic wavelength, which is dispersed by a grating or prism and detected in the spectrometer.
A frequent application of the emission measurement with the flame is the regulation of alkali metals for pharmaceutical analytics. | 0 | Theoretical and Fundamental Chemistry |
NASAs Dragonfly' lander/aircraft concept is proposed to launch in 2025 and would seek evidence of biosignatures on the organic-rich surface and atmosphere of Titan, as well as study its possible prebiotic primordial soup. Titan is the largest moon of Saturn and is widely believed to have a large subsurface ocean consisting of a salty brine. In addition, scientists believe that Titan may have the conditions necessary to promote prebiotic chemistry, making it a prime candidate for biosignature discovery. | 1 | Applied and Interdisciplinary Chemistry |
The current American regulation for organ matching is centered on the national registry of organ donors after the National Organ Transplant Act was passed in 1984. This act was set in place to ensure equal and honest distribution, although it has been proven insufficient due to the large demand for organ transplants. Organ printing can assist in diminishing the imbalance between supply and demand by printing patient-specific organ replacements, all of which is unfeasible without regulation. The Food and Drug Administration (FDA) is responsible for regulation of biologics, devices, and drugs in the United States. Due to the complexity of this therapeutic approach, the location of organ printing on the spectrum has not been discerned. Studies have characterized printed organs as multi-functional combination products, meaning they fall between the biologics and devices sectors of the FDA; this leads to more extensive processes for review and approval. In 2016, the FDA issued draft guidance on the Technical Considerations for Additive Manufactured Devices and is currently evaluating new submissions for 3D printed devices. However, the technology itself is not advanced enough for the FDA to mainstream it directly. Currently, the 3D printers, rather than the finished products, are the main focus in safety and efficacy evaluations in order to standardize the technology for personalized treatment approaches. From a global perspective, only South Korea and Japan's medical device regulation administrations have provided guidelines that are applicable to 3D bio-printing.
There are also concerns with intellectual property and ownership. These can have a large impact on more consequential matters such as piracy, quality control for manufacturing, and unauthorized use on the black market. These considerations are focused more on the materials and fabrication processes; they are more extensively explained in the legal aspects subsection of 3D printing. | 1 | Applied and Interdisciplinary Chemistry |
Compared to normal analyses methods, microanalysis:
* Can resolve fine-scale variations in chemical elements.
* Can be used to identify the presence and distribution of different phases in materials.
* Requires less sample material and therefore can provide information on microscopic objects. | 0 | Theoretical and Fundamental Chemistry |
In 1970, Eckelman and Richards presented the first "kit" containing all the ingredients required to release the Tc, "milked" from the generator, in the chemical form to be administered to the patient.
Technetium-99m is used in 20 million diagnostic nuclear medical procedures every year. Approximately 85% of diagnostic imaging procedures in nuclear medicine use this isotope as radioactive tracer. Klaus Schwochaus book Technetium' lists 31 radiopharmaceuticals based on Tc for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood, and tumors. A more recent review is also available.
Depending on the procedure, the Tc is tagged (or bound to) a pharmaceutical that transports it to its required location. For example, when Tc is chemically bound to exametazime (HMPAO), the drug is able to cross the blood–brain barrier and flow through the vessels in the brain for cerebral blood-flow imaging. This combination is also used for labeling white blood cells (Tc labeled WBC) to visualize sites of infection. Tc sestamibi is used for myocardial perfusion imaging, which shows how well the blood flows through the heart. Imaging to measure renal function is done by attaching Tc to mercaptoacetyl triglycine (MAG3); this procedure is known as a MAG3 scan.
Technetium-99m (Tc-99m) can be readily detected in the body by medical equipment because it emits 140.5 keV gamma rays (these are about the same wavelength as emitted by conventional X-ray diagnostic equipment), and its half-life for gamma emission is six hours (meaning 94% of it decays to Tc in 24 hours). Besides, it emits virtually no beta radiation, thus keeping radiation dosage low. Its decay product, Tc, has a relatively long half-life (211,000 years) and emits little radiation. The short physical half-life of Tc and its biological half-life of 1 day with its other favourable properties allows scanning procedures to collect data rapidly and keep total patient radiation exposure low. Chemically, technetium is selectively concentrated in thyroid, salivary glands, and stomach and excluded from cerebrospinal fluid. Combination with perchlorate abolishes its selectiveness. | 0 | Theoretical and Fundamental Chemistry |
Phosphine is an attractive fumigant because it is lethal to insects and rodents, but degrades to phosphoric acid, which is non-toxic. As sources of phosphine, for farm use, pellets of aluminium phosphide (AlP), calcium phosphide (), or zinc phosphide () are used. These phosphides release phosphine upon contact with atmospheric water or rodents' stomach acid. These pellets also contain reagents to reduce the potential for ignition or explosion of the released phosphine.
An alternative is the use of phosphine gas itself which requires dilution with either or or even air to bring it below the flammability point. Use of the gas avoids the issues related with the solid residues left by metal phosphide and results in faster, more efficient control of the target pests.
One problem with phosphine fumigants is the increased resistance by insects. | 0 | Theoretical and Fundamental Chemistry |
Although bitumen typically makes up only 4 to 5 percent (by weight) of the pavement mixture, as the pavement's binder, it is also the most expensive part of the cost of the road-paving material.
During bitumen's early use in modern paving, oil refiners gave it away. However, bitumen is a highly traded commodity today. Its prices increased substantially in the early 21st Century. A U.S. government report states:
:"In 2002, asphalt sold for approximately $160 per ton. By the end of 2006, the cost had doubled to approximately $320 per ton, and then it almost doubled again in 2012 to approximately $610 per ton."
The report indicates that an "average" 1-mile (1.6-kilometer)-long, four-lane highway would include "300 tons of asphalt," which, "in 2002 would have cost around $48,000. By 2006 this would have increased to $96,000 and by 2012 to $183,000... an increase of about $135,000 for every mile of highway in just 10 years." | 0 | Theoretical and Fundamental Chemistry |
Hydrogen gas porosity is an aluminium casting defect in the form of a porosity or void in an aluminium casting caused by a high level of hydrogen gas (H) dissolved in the aluminium at liquid phase. The solubility of hydrogen in solid aluminium is much smaller than in liquid aluminium. As the aluminium freezes, some of the hydrogen comes out of solution and forms bubbles, creating porosity in the solid aluminium.
Aluminium foundries want to produce high-quality aluminum castings with minimum porosity. Hydrogen porosity can be reduced by reducing the amount of hydrogen in the liquid aluminium alloy, by degassing or sparging. (Sometimes a small hydrogen concentration is intentionally maintained; some very fine hydrogen porosity can be preferable to internal voids caused by shrinkage.) Directional solidification can drive impurities to one end of the casting. | 1 | Applied and Interdisciplinary Chemistry |
Sala was the son of the spinner Bernardino Sala. He probably first learned the profession of pharmacy in Venice. A Calvinist, he left Italy and his career as a doctor without academic studies led him to Dresden (1602), Sondrio (1604), Nuremberg (1606), Frauenfeld (1607) and settled in Geneva (1609). From 1607 to 1609 he was a city doctor in Winterthur. | 1 | Applied and Interdisciplinary Chemistry |
Acute beryllium poisoning is acute chemical pneumonitis resulting from the toxic effect of beryllium in its elemental form or in various chemical compounds, and is distinct from berylliosis (also called chronic beryllium disease). After occupational safety procedures were put into place following the realization that the metal caused berylliosis around 1950, acute beryllium poisoning became extremely rare. | 1 | Applied and Interdisciplinary Chemistry |
A blastoid is an embryoid, a stem cell-based embryo model which, morphologically and transcriptionally resembles the early, pre-implantation, mammalian conceptus, called the blastocyst. The first blastoids were created by the Nicolas Rivron laboratory by combining mouse embryonic stem cells and mouse trophoblast stem cells. Upon in vitro development, blastoids generate analogs of the primitive endoderm cells, thus comprising analogs of the three founding cell types of the conceptus (epiblast, trophoblast and primitive endoderm), and recapitulate aspects of implantation on being introduced into the uterus of a compatible female. Mouse blastoids have not shown the capacity to support the development of a foetus and are thus generally not considered as an embryo but rather as a model. As compared to other stem cell-based embryo models (e.g., Gastruloids), blastoids model the preimplantation stage and the integrated development of the conceptus including the embryo proper and the two extraembryonic tissues (trophectoderm and primitive endoderm). The blastoid is a model system for the study of mammalian development and disease. It might be useful for the identification of therapeutic targets and preclinical modelling. | 1 | Applied and Interdisciplinary Chemistry |
Low-volume/high-velocity (LVHV) capture systems are specialised types of LEV that use an extractor hood designed as an integral part of the tool or positioned very close to the operating point of the cutting tool. The hood is designed to provide high capture velocities, often greater than 50 m/s (10,000 fpm) at the contaminant release point. This high velocity is accompanied by airflows often less than 0.02m3/s (50 cfm) resulting from the small face area of the hood that is used. These systems have come into favour for portable power tools, although adoption of the technology is not widespread. Festool is one manufacturer of portable power tools using LVHV ventilation integrated into the tool design. | 1 | Applied and Interdisciplinary Chemistry |
The LINE-1/L1-element is one of the elements that are still active in the human genome today. It is found in all therian mammals except megabats. | 1 | Applied and Interdisciplinary Chemistry |
The M and H subunits are encoded by two different genes:
* The M subunit is encoded by LDHA, located on chromosome 11p15.4 ().
* The H subunit is encoded by LDHB, located on chromosome 12p12.2-p12.1 ().
* A third isoform, LDHC or LDHX, is expressed only in the testis (); its gene is likely a duplicate of LDHA and is also located on the eleventh chromosome (11p15.5-p15.3).
* The fourth isoform is localized in the peroxisome. It is tetramer containing one LDHBx subunit, which is also encoded by the LDHB gene. The LDHBx protein is seven amino acids longer than the LDHB (LDH-H) protein. This amino acid extension is generated by functional translational readthrough.
Mutations of the M subunit have been linked to the rare disease exertional myoglobinuria (see OMIM article), and mutations of the H subunit have been described but do not appear to lead to disease. | 1 | Applied and Interdisciplinary Chemistry |
Some communities have begun stream restoration projects in an attempt to correct the problems caused by alteration, using techniques such as daylighting and fixing stream bank erosion caused by heavy stormwater runoff. Streamflow augmentation to restore habitat and aesthetics is also an option, and recycled water can be used for this purpose. | 1 | Applied and Interdisciplinary Chemistry |
The diagnosis of sepiapterin reductase deficiency in a patient at the age of 14 years was delayed by an earlier diagnosis of an initially unclassified form of methylmalonic aciduria at the age of 2. At that time the hypotonia and delayed development were not considered to be suggestive of a neurotransmitter defect. The clinically relevant diagnosis was only made following the onset of dystonia with diurnal variation, when the patient was a teenager. Variability in occurrence and severity of other symptoms of the condition, such as hypotonia, ataxia, tremors, spasticity, bulbar involvement, oculogyric crises, and cognitive impairment, is comparable with autosomal dominant GTPCH and tyrosine hydroxylase deficiency, which are both classified as forms of DOPA-responsive dystonia. | 1 | Applied and Interdisciplinary Chemistry |
AFM-IR (atomic force microscope-infrared spectroscopy) or infrared nanospectroscopy is one of a family of techniques that are derived from a combination of two parent instrumental techniques. AFM-IR combines the chemical analysis power of infrared spectroscopy and the high-spatial resolution of scanning probe microscopy (SPM). The term was first used to denote a method that combined a tuneable free electron laser with an atomic force microscope (AFM, a type of SPM) equipped with a sharp probe that measured the local absorption of infrared light by a sample with nanoscale spatial resolution.
Originally the technique required the sample to be deposited on an infrared-transparent prism and be less than 1μm thick. This early setup improved the spatial resolution and sensitivity of photothermal AFM-based techniques from microns to circa 100 nm. Then, the use of modern pulsed optical parametric oscillators and quantum cascade lasers, in combination with top-illumination, have enabled to investigate samples on any substrate and with increase sensitivity and spatial resolution. As most recent advances, AFM-IR has been proved capable to acquire chemical maps and nanoscale resolved spectra at the single-molecule scale from macromolecular self-assemblies and biomolecules with circa 10 nm diameter, as well as to overcome limitations of IR spectroscopy and measure in aqueous liquid environments.
Recording the amount of infrared absorption as a function of wavelength or wavenumber, AFM-IR creates an infrared absorption spectra that can be used to chemically characterize and even identify unknown samples. Recording the infrared absorption as a function of position can be used to create chemical composition maps that show the spatial distribution of different chemical components. Novel extensions of the original AFM-IR technique and earlier techniques have enabled the development of bench-top devices capable of nanometer spatial resolution, that do not require a prism and can work with thicker samples, and thereby greatly improving ease of use and expanding the range of samples that can be analysed. AFM-IR has achieved lateral spatial resolutions of ca. 10 nm, with a sensitivity down to the scale of molecular monolayer and single protein molecules with molecular weight down to 400-600 kDa.
AFM-IR is related to techniques such as tip-enhanced Raman spectroscopy (TERS), scanning near-field optical microscopy (SNOM), nano-FTIR and other methods of vibrational analysis with scanning probe microscopy. | 0 | Theoretical and Fundamental Chemistry |
Dimitar Ivanov Popov () (October 13, 1894 – October 25, 1975) was a Bulgarian organic chemist and an academician of the Bulgarian Academy of Sciences.
Prof. D. Ivanov is known by his fathers name Ivanov rather than his familys name Popov.
He is the namesake of the Ivanov reaction in chemistry. | 0 | Theoretical and Fundamental Chemistry |
The following outline is provided as an overview of and topical guide to fluid dynamics:
Below is a structured list of topics in fluid dynamics. | 1 | Applied and Interdisciplinary Chemistry |
In Brazil, the prices are regulated through legislation under the name of Medicamento Genérico (generic drugs) since 1999. | 1 | Applied and Interdisciplinary Chemistry |
For nucleoside (nucleobase + ribose sugar) synthesis, Orgel suggested an almost opposite approach, heating a mixture of ribose and the purine nucleobases hypoxanthine, adenine, and guanine to dryness in the presence of magnesium ions. This reaction puts the glycosidic bond in the correct position in two ways: the nucleobase attaches to the correct carbon on ribose, and in the correct orientation (the beta anomer).
However, the synthesis was later criticised because it only worked most with hypoxanthine, a nucleobase that is not relevant to current life on Earth, and because it was not specific for the ribose sugar and could instead be applied to other sugars. | 0 | Theoretical and Fundamental Chemistry |
Many metabolites are chemically reactive and unstable, and thus prone to chemical damage. In general, any reaction that occurs in vitro under physiological conditions can also occur in vivo. Some metabolites are so reactive that their half-life in a cell is measured in minutes. For example, the glycolytic intermediate 1,3-bisphosphoglyceric acid has a half-life of 27 minutes in vivo. Typical types of chemical damage reactions that can occur to metabolites are racemization, rearrangement, elimination, photodissociation, addition, and condensation. | 1 | Applied and Interdisciplinary Chemistry |
Molecular intermixing tends to broaden the glass transition regions of some IPN materials compared to their component polymers. This unique characteristic provides excellent mechanical damping properties over a wide range of temperatures and frequencies due to a relatively constant and high phase angle. In IPNs composed of both rubbery and glassy polymers, considerable toughening is observed compared to the constituent polymers. When the glassy component forms a discrete, discontinuous phase, the elastomeric nature of the continuous rubbery phase can be preserved while increasing the overall toughness of the material and its elongation at break. On the other hand, when the glassy polymer forms a bicontinuous phase within the rubbery network, the IPN material can behave like an impact-resistant plastic. | 0 | Theoretical and Fundamental Chemistry |
Stripping is mainly conducted in trayed towers (plate columns) and packed columns, and less often in spray towers, bubble columns, and centrifugal contactors.
Trayed towers consist of a vertical column with liquid flowing in the top and out the bottom. The vapor phase enters in the bottom of the column and exits out of the top. Inside of the column are trays or plates. These trays force the liquid to flow back and forth horizontally while the vapor bubbles up through holes in the trays. The purpose of these trays is to increase the amount of contact area between the liquid and vapor phases.
Packed columns are similar to trayed columns in that the liquid and vapor flows enter and exit in the same manner. The difference is that in packed towers there are no trays. Instead, packing is used to increase the contact area between the liquid and vapor phases. There are many different types of packing used and each one has advantages and disadvantages. | 0 | Theoretical and Fundamental Chemistry |
The movement of grain boundaries (HAGB) has implications for recrystallization and grain growth while subgrain boundary (LAGB) movement strongly influences recovery and the nucleation of recrystallization.
A boundary moves due to a pressure acting on it. It is generally assumed that the velocity is directly proportional to the pressure with the constant of proportionality being the mobility of the boundary. The mobility is strongly temperature dependent and often follows an Arrhenius type relationship:
The apparent activation energy (Q) may be related to the thermally activated atomistic processes that occur during boundary movement. However, there are several proposed mechanisms where the mobility will depend on the driving pressure and the assumed proportionality may break down.
It is generally accepted that the mobility of low-angle boundaries is much lower than that of high-angle boundaries. The following observations appear to hold true over a range of conditions:
* The mobility of low-angle boundaries is proportional to the pressure acting on it.
* The rate controlling process is that of bulk diffusion
* The boundary mobility increases with misorientation.
Since low-angle boundaries are composed of arrays of dislocations and their movement may be related to dislocation theory. The most likely mechanism, given the experimental data, is that of dislocation climb, rate limited by the diffusion of solute in the bulk.
The movement of high-angle boundaries occurs by the transfer of atoms between the neighbouring grains. The ease with which this can occur will depend on the structure of the boundary, itself dependent on the crystallography of the grains involved, impurity atoms and the temperature. It is possible that some form of diffusionless mechanism (akin to diffusionless phase transformations such as martensite) may operate in certain conditions. Some defects in the boundary, such as steps and ledges, may also offer alternative mechanisms for atomic transfer.
Since a high-angle boundary is imperfectly packed compared to the normal lattice it has some amount of free space or free volume where solute atoms may possess a lower energy. As a result, a boundary may be associated with a solute atmosphere that will retard its movement. Only at higher velocities will the boundary be able to break free of its atmosphere and resume normal motion.
Both low- and high-angle boundaries are retarded by the presence of particles via the so-called Zener pinning effect. This effect is often exploited in commercial alloys to minimise or prevent recrystallization or grain growth during heat-treatment. | 1 | Applied and Interdisciplinary Chemistry |
The first protected peptide was synthesised by Theodor Curtius in 1882 and the first free peptide was synthesised by Emil Fischer in 1901. | 1 | Applied and Interdisciplinary Chemistry |
The complete mathematical model describing electromigration consists of several partial differential equations (PDEs) which need to be solved for three-dimensional geometrical domains representing segments of an interconnect structure. Such a mathematical model forms the basis for simulation of electromigration in modern technology computer aided design (TCAD) tools.
Use of TCAD tools for detailed investigations of electromigration induced interconnect degradation is gaining importance. Results of TCAD studies in combination with reliability tests lead to modification of design rules improving the interconnect resistance to electromigration. | 0 | Theoretical and Fundamental Chemistry |
A prismatic surface is a surface generated by all the lines that are parallel to a given line and intersect a broken line that is not in the same plane as the given line. The broken line is the directrix of the surface; the parallel lines are its generators (or elements). If the broken line is closed (i.e., a closed polygon), then the surface is a closed prismatic surface.
With regards to crystallography, a prismatic surface is a single face of a prismatic form, which is an open form consisting of three, four, or six identical faces related by a symmetry operator. | 0 | Theoretical and Fundamental Chemistry |
In February 1967, he started working with Dudley Herschbach at Harvard University on reactions between hydrogen atoms and diatomic alkali molecules and the construction of a universal crossed molecular beams apparatus. After the postdoctoral year with Herschbach he joined the University of Chicago faculty in 1968. In 1974, he returned to Berkeley as professor of chemistry and principal investigator at the Lawrence Berkeley National Laboratory, becoming a U.S. citizen the same year. Lee is a University Professor Emeritus of the University of California system. | 0 | Theoretical and Fundamental Chemistry |
Initial desensitization due to rapid phosphorylation of activated receptors by kinases, which increases affinity for arrestin. Arrestin prevents protein-receptor interaction and the receptor becomes dephosphorylated and inhibited from signaling. This is a sufficient and rapid form of termination of PAR signaling. Irreversibly activated PAR1 is internalized and terminated from further signaling by clathrin-mediated endocytosis and lysosome degradation, preventing replenishment at the cell surface. | 1 | Applied and Interdisciplinary Chemistry |
The biosynthesis of the Fe–S clusters has been well studied.
The biogenesis of iron sulfur clusters has been studied most extensively in the bacteria E. coli and A. vinelandii and yeast S. cerevisiae. At least three different biosynthetic systems have been identified so far, namely nif, suf, and isc systems, which were first identified in bacteria. The nif system is responsible for the clusters in the enzyme nitrogenase. The suf and isc systems are more general.
The yeast isc system is the best described. Several proteins constitute the biosynthetic machinery via the isc pathway. The process occurs in two major steps:
(1) the Fe/S cluster is assembled on a scaffold protein followed by (2) transfer of the preformed cluster to the recipient proteins.
The first step of this process occurs in the cytoplasm of prokaryotic organisms or in the mitochondria of eukaryotic organisms. In the higher organisms the clusters are therefore transported out of the mitochondrion to be incorporated into the extramitochondrial enzymes. These organisms also possess a set of proteins involved in the Fe/S clusters transport and incorporation processes that are not homologous to proteins found in prokaryotic systems. | 0 | Theoretical and Fundamental Chemistry |
Fluorosurfactants such as PFOS, PFOA, and PFNA have caught the attention of regulatory agencies because of their persistence, toxicity, and widespread occurrence in the blood of general populations and wildlife. In 2009, PFOS, its salts, and perfluorooctanesulfonyl fluoride were listed as persistent organic pollutants under the Stockholm Convention due to their ubiquitous, persistent, bioaccumulative, and toxic nature. PFAS chemicals were dubbed "forever chemicals" in a 2018 op-ed in the Washington Post. The nickname was derived by combining the two dominant attributes of this class of chemicals: PFAS chemicals are characterized by a carbon-fluorine backbone (the "F-C" in "forever chemicals"), and the carbon-fluorine bond is one of the strongest bonds in organic chemistry, which gives these chemicals an extremely long environmental half-life. The term forever chemicals is commonly used in media outlets in addition to the more technical name of per- and polyfluorinated alkyl substances. Their production has been regulated or phased out by manufacturers, such as 3M, DuPont, Daikin, and Miteni in the U.S., Japan, and Europe. In 2006 3M replaced PFOS and PFOA with short-chain PFASs, such as perfluorohexanoic acid (PFHxA) and perfluorobutanesulfonic acid (PFBS). Shorter fluorosurfactants may be less prone to accumulating in mammals; there is still some concern that they may be harmful to both humans and the environment, though the EPA states, "...research is still ongoing to determine how different levels of exposure to different PFAS can lead to a variety of health effects." Many PFASs are either not covered by European legislation or are excluded from registration obligations under the EU REACH chemical regulation. Several PFASs have been detected in drinking water, municipal wastewater, and landfill leachates worldwide.
It had been thought that PFAAs would eventually end up in the oceans, where they would be diluted over decades, but a field study published in 2021 by researchers at Stockholm University found that they are significantly transferred from water to air when waves break on land, and are a significant source of air pollution, and eventually get into the rain. The researchers concluded that pollution "may impact large areas of inland Europe and other continents, in addition to coastal areas". | 0 | Theoretical and Fundamental Chemistry |
Products of carotenoid degradation such as ionones, damascones and damascenones are also important fragrance chemicals that are used extensively in the perfumes and fragrance industry. Both β-damascenone and β-ionone although low in concentration in rose distillates are the key odor-contributing compounds in flowers. In fact, the sweet floral smells present in black tea, aged tobacco, grape, and many fruits are due to the aromatic compounds resulting from carotenoid breakdown. | 0 | Theoretical and Fundamental Chemistry |
ASF/SF2 is involved in genomic stability; it is thought that RNA Polymerase recruits ASF/SF2 to nascent RNA transcripts to impede formation of mutagenic DNA:RNA hybrid R-loop structures between the transcript and the template DNA. In this way, ASF/SF2 is protecting cells from the potential deleterious effects of transcription itself. ASF/SF2 is also implicated in cellular mechanisms to hinder exon skipping and to ensure splicing is occurring accurately and correctly. | 1 | Applied and Interdisciplinary Chemistry |
Many specialized methods also yield amides. A variety of reagents, e.g. tris(2,2,2-trifluoroethyl) borate have been developed for specialized applications. | 0 | Theoretical and Fundamental Chemistry |
Surface-enhanced Raman spectroscopy or surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces or by nanostructures such as plasmonic-magnetic silica nanotubes. The enhancement factor can be as much as 10 to 10, which means the technique may detect single molecules. | 0 | Theoretical and Fundamental Chemistry |
Maritime New Zealand used the oil dispersant Corexit 9500 to help in the cleanup process. The dispersant was applied for only a week, after results proved inconclusive. | 1 | Applied and Interdisciplinary Chemistry |
Salt spalling is a specific type of weathering which occurs in porous building materials, such as brick, natural stone, tiles and concrete. Dissolved salt is carried through the material in water and crystallizes inside the material near the surface as the water evaporates. As the salt crystals expand this builds up shear stresses which break away spall from the surface.
Some engineers believe that porous building materials can be protected against salt spalling by treatment with penetrating sealants which are hydrophobic (water repellent) and will penetrate deeply enough to keep water with dissolved salts well away from the surface. Great care and expert advice must be consulted, however, to ensure that any coating is compatible with the substrate in terms of breathability (ability to allow the release of vapours from inside while preventing water intrusion), or other serious problems can be created.
Chimneys show spalling damage before other portions of buildings because they are more exposed to the elements. | 1 | Applied and Interdisciplinary Chemistry |
In biochemistry, a Janin plot, like a Ramachandran plot, is a way to visualize dihedral angle distributions in protein structures. While a Ramachandran plot relates the two backbone dihedral angles, a Janin plot relates the first side chain dihedral angle χ-1 against χ-2. Because not all amino acids have these dihedral angles, a Janin plot is not applicable to all such acids.
This correlation is different for the various amino acids and can depend on the type of secondary structure (Helix, Sheet, etc.) local to that residue. The plot is named for Joël Janin, who studied these correlations in 1978 with Shoshana Wodak. | 1 | Applied and Interdisciplinary Chemistry |
Despite having only four choices for each monomer unit (nucleotides), compared to 20 amino acid side chains found in proteins, ribozymes have diverse structures and mechanisms. In many cases they are able to mimic the mechanism used by their protein counterparts. For example, in self cleaving ribozyme RNAs, an in-line SN2 reaction is carried out using the 2’ hydroxyl group as a nucleophile attacking the bridging phosphate and causing 5’ oxygen of the N+1 base to act as a leaving group. In comparison, RNase A, a protein that catalyzes the same reaction, uses a coordinating histidine and lysine to act as a base to attack the phosphate backbone.
Like many protein enzymes, metal binding is also critical to the function of many ribozymes. Often these interactions use both the phosphate backbone and the base of the nucleotide, causing drastic conformational changes. There are two mechanism classes for the cleavage of a phosphodiester backbone in the presence of metal. In the first mechanism, the internal 2’- OH group attacks the phosphorus center in a SN mechanism. Metal ions promote this reaction by first coordinating the phosphate oxygen and later stabling the oxyanion. The second mechanism also follows a SN displacement, but the nucleophile comes from water or exogenous hydroxyl groups rather than RNA itself. The smallest ribozyme is UUU, which can promote the cleavage between G and A of the GAAA tetranucleotide via the first mechanism in the presence of Mn. The reason why this trinucleotide (rather than the complementary tetramer) catalyzes this reaction may be because the UUU-AAA pairing is the weakest and most flexible trinucleotide among the 64 conformations, which provides the binding site for Mn.
Phosphoryl transfer can also be catalyzed without metal ions. For example, pancreatic ribonuclease A and hepatitis delta virus (HDV) ribozymes can catalyze the cleavage of RNA backbone through acid-base catalysis without metal ions. Hairpin ribozyme can also catalyze the self-cleavage of RNA without metal ions, but the mechanism for this is still unclear.
Ribozyme can also catalyze the formation of peptide bond between adjacent amino acids by lowering the activation entropy. | 0 | Theoretical and Fundamental Chemistry |
Located within the , the Institute of Analytical Sciences (UMR 5280) is a French research, training and expertise center specializing in analytical chemistry. It is a Joint Research Unit (French: Unité mixte de recherche or UMR) affiliated with the National Centre for Scientific Research (CNRS), Claude Bernard University Lyon 1, and École normale supérieure de Lyon. | 0 | Theoretical and Fundamental Chemistry |
2,2-Dimethoxypropane (DMP) is an organic compound with the formula (CH)C(OCH). A colorless liquid, it is the product of the condensation of acetone and methanol. DMP is used as a water scavenger in water-sensitive reactions. Upon acid-catalyzed reaction, DMP reacts quantitatively with water to form acetone and methanol. This property can be used to accurately determine the amount of water in a sample, alternatively to the Karl Fischer method.
DMP is specifically used to prepare acetonides:
:RCHOHCHOHCH + (MeO)CMe → RCHCHCHOCMe + 2 MeOH
Dimethoxypropane is an intermediate for the synthesis of 2-methoxypropene.
In histology, DMP is used for the dehydration of animal tissue. | 0 | Theoretical and Fundamental Chemistry |
The New Zealand Institute of Chemistry (NZIC) was founded in 1931 and is the professional membership organisation for professionals working in the field of chemistry across the education and industry sectors in New Zealand. It is organised into six geographical branches (Auckland, Waikato, Manawatu, Wellington, Canterbury, and Otago) and a number of specialist groups.
In 2019 it formed the group Secondary Chemistry Educators of NZ (SCENZ) as the national chemistry teachers’ subject association.
The NZIC publishes its own quarterly journal Chemistry in New Zealand. It has been a co-owner society of Chemistry: An Asian Journal since 2008, and is a co-owner of Physical Chemistry Chemical Physics published by the Royal Society of Chemistry (UK).
The NZIC holds a national conference every two years with the branches taking turns to host. It is also a co-sponsor of the Pacifichem Congress which is held in Hawaii every five years.
The Council of the NZIC consists of an Executive (President, Vice President or Past President and Treasurer), Student Representative, Secretary, and delegates from each of the Branch Committees. Members of the executive are elected annually at the Annual General Meeting. | 1 | Applied and Interdisciplinary Chemistry |
Also during Phase II, copper and arsenical bronze production was practiced at the site.
Norşuntepe provides first clear and unambiguous evidence of arsenical bronze production in this general area before the 4th millennium. It demonstrates that some form of arsenic alloying was being deliberately practised. Since the slag identified at Norşuntepe contains no arsenic, this means that arsenic-bearing materials were added separately. The evidence was discovered at the levels with Ubaid style ceramics, where also were found a number of structures related to the Mesopotamian architectural traditions. A related site in the area from the same time period is Değirmentepe, where arsenic-bronze was also produced around 4200 BC.
The final Chalcolithic phases were characterized by small-scale single-room houses. Radiocarbon dating from the different Chalcolithic levels provided dates between 4300-3800 BC. | 1 | Applied and Interdisciplinary Chemistry |
The so-called depth-averaged or shallow-water models are initially introduced for compositional gravity currents
and then later extended to turbidity currents. The typical assumptions used along with the shallow-water models are: hydrostatic pressure field, clear fluid is not entrained (or detrained), and particle concentration does not depend on the vertical location. Considering the ease of implementation, these models can typically predict flow characteristic such as front location or front speed in simplified geometries, e.g. rectangular channels, fairly accurately. | 1 | Applied and Interdisciplinary Chemistry |
DNA base flipping, or nucleotide flipping, is a mechanism in which a single nucleotide base, or nucleobase, is rotated outside the nucleic acid double helix. This occurs when a nucleic acid-processing enzyme needs access to the base to perform work on it, such as its excision for replacement with another base during DNA repair. It was first observed in 1994 using X-ray crystallography in a methyltransferase enzyme catalyzing methylation of a cytosine base in DNA. Since then, it has been shown to be used by different enzymes in many biological processes such as DNA methylation, various DNA repair mechanisms, and DNA replication. It can also occur in RNA double helices or in the DNA:RNA intermediates formed during RNA transcription.
DNA base flipping occurs by breaking the hydrogen bonds between the bases and unstacking the base from its neighbors. This could occur through an active process, where an enzyme binds to the DNA and then facilitates rotation of the base, or a passive process, where the
base rotates out spontaneously, and this state is recognized and bound by an enzyme. It can be detected using
X-ray crystallography, NMR spectroscopy, fluorescence spectroscopy, or hybridization probes. | 1 | Applied and Interdisciplinary Chemistry |
The hypothesis was postulated by the Nobel laureate Otto Heinrich Warburg in 1924. He hypothesized that cancer, malignant growth, and tumor growth are caused by the fact that tumor cells mainly generate energy (as e.g., adenosine triphosphate / ATP) by non-oxidative breakdown of glucose (a process called glycolysis). This is in contrast to healthy cells which mainly generate energy from oxidative breakdown of pyruvate. Pyruvate is an end-product of glycolysis, and is oxidized within the mitochondria. Hence, according to Warburg, carcinogenesis stems from the lowering of mitochondrial respiration. Warburg regarded the fundamental difference between normal and cancerous cells to be the ratio of glycolysis to respiration; this observation is also known as the Warburg effect.
In the somatic mutation theory of cancer, malignant proliferation is caused by mutations and altered gene expression, in a process called malignant transformation, resulting in an uncontrolled growth of cells. The metabolic difference observed by Warburg adapts cancer cells to the hypoxic (oxygen-deficient) conditions inside solid tumors, and results largely from the same mutations in oncogenes and tumor suppressor genes that cause the other abnormal characteristics of cancer cells. Therefore, the metabolic change observed by Warburg is not so much the cause of cancer, as he claimed, but rather, it is one of the characteristic effects of cancer-causing mutations.
Warburg articulated his hypothesis in a paper entitled The Prime Cause and Prevention of Cancer which he presented in lecture at the meeting of the Nobel-Laureates on June 30, 1966 at Lindau, Lake Constance, Germany. In this speech, Warburg presented additional evidence supporting his theory that the elevated anaerobiosis seen in cancer cells was a consequence of damaged or insufficient respiration. Put in his own words, "the prime cause of cancer is the replacement of the respiration of oxygen in normal body cells by a fermentation of sugar."
The body often kills damaged cells by apoptosis, a mechanism of self-destruction that involves mitochondria, but this mechanism fails in cancer cells where the mitochondria are shut down. The reactivation of mitochondria in cancer cells restarts their apoptosis program. | 1 | Applied and Interdisciplinary Chemistry |
A transition metal thiosulfate complex is a coordination complex containing one or more thiosulfate ligands. Thiosulfate occurs in nature and is used industrially, so its interactions with metal ions are of some practical interest. Three binding modes are common: monodentate (κ-), O,S-bidentate (κ-),and bridging (μ-). Typically, thiosulfate complexes are prepared from thiosulfate salts. In some cases, they arise by oxidation of polysulfido complexes, or by binding of sulfur trioxide to sulfido ligands. | 0 | Theoretical and Fundamental Chemistry |
The Saffman–Taylor instability is usually seen in an axisymmetric context as opposed to the simple planar case derived above. The mechanisms for the instability remain the same in this case, and the selection of the most unstable wavenumber in this case corresponds to a given number of fingers (an integer). | 1 | Applied and Interdisciplinary Chemistry |
Antigenic specificity is the ability of the host cells to recognize an antigen specifically as a unique molecular entity and distinguish it from another with exquisite precision. Antigen specificity is due primarily to the side-chain conformations of the antigen. It is measurable and need not be linear or of a rate-limited step or equation. Both T cells and B cells are cellular components of adaptive immunity. | 1 | Applied and Interdisciplinary Chemistry |
The various global temperatures that may be theoretically conceived for any planet in general can be computed. Such temperatures include the planetary equilibrium temperature, equivalent blackbody temperature or effective radiation emission temperature of the planet. For a planet with an atmosphere, these temperatures can be different than the mean surface temperature, which may be measured as the global-mean surface air temperature, or as the global-mean surface skin temperature.
A radiative equilibrium temperature is calculated for the case that the supply of energy from within the planet (for example, from chemical or nuclear sources) is negligibly small; this assumption is reasonable for Earth, but fails, for example, for calculating the temperature of Jupiter, for which internal energy sources are larger than the incident solar radiation, and hence the actual temperature is higher than the theoretical radiative equilibrium. | 0 | Theoretical and Fundamental Chemistry |
AGEs affect nearly every type of cell and molecule in the body and are thought to be one factor in aging and some age-related chronic diseases. They are also believed to play a causative role in the vascular complications of diabetes mellitus.
AGEs arise under certain pathologic conditions, such as oxidative stress due to hyperglycemia in patients with diabetes. AGEs play a role as proinflammatory mediators in gestational diabetes as well.
In the context of cardiovascular disease, AGEs can induce crosslinking of collagen, which can cause vascular stiffening and entrapment of low-density lipoprotein particles (LDL) in the artery walls. AGEs can also cause glycation of LDL which can promote its oxidation. Oxidized LDL is one of the major factors in the development of atherosclerosis. Finally, AGEs can bind to RAGE (receptor for advanced glycation end products) and cause oxidative stress as well as activation of inflammatory pathways in vascular endothelial cells. | 1 | Applied and Interdisciplinary Chemistry |
Solasonine is a glycoalkaloid that is found in Solanum plants of the family Solanaceae. Solasonine is a poisonous chemical compound when used at high levels. It is a glycoside of solasodine. Glycoalkaloids such as Solasonine have various applications including pharmacology, cancer treatments and even a role as a pesticide.
High levels of glycoalkaloids are toxic to humans due to their ability to disrupt cell-membrane function. There is a loss of membrane integrity which puts the cell at risk for apoptosis (cell death) due to the ability of any chemical coming into contact with the cell.
Solasonine was one component of the unsuccessful experimental cancer drug candidate Coramsine. | 1 | Applied and Interdisciplinary Chemistry |
The Governing Board of the Eastern Analytical Symposium presents awards each year for outstanding contributions and achievements in general analytical chemistry and in five specific areas of analysis. The award inscriptions read, "In Recognition of Outstanding Achievements in the Field of -----".
*Analytical Chemistry
*Magnetic Resonance
*Vibrational spectroscopy
*Chemometrics
*Mass Spectrometry
*Separation Science or Chromatography
The Governing Board each year also honors a Young Investigator who is making an impact on the field of analytical chemistry. The [http://easinc.org/wordpress/?page_id=2142 2017 Awardee] will be Prof. Dwight R. Stoll.
In addition to the EAS Awards, awards presented by sponsoring organizations at the Symposium include:
* The Benedetti-Pichler Award of the American Microchemical Society
* The Ernst Abbe Award of the New York Microscopical Society
* The Gold Medal of the New York Society for Applied Spectroscopy
From 2012 to 2014, an award was also presented to a New Faculty active in NMR.
Past award recipients can be found [https://eas.org/2021/?page_id=811 here]. | 0 | Theoretical and Fundamental Chemistry |
The Dean number is typically denoted by De (or Dn). For a flow in a pipe or tube it is defined as:
where
* is the density of the fluid
* is the dynamic viscosity
* is the axial velocity scale
* is the diameter (for non-circular geometry, an equivalent diameter is used; see Reynolds number)
* is the radius of curvature of the path of the channel.
* is the Reynolds number.
The Dean number is therefore the product of the Reynolds number (based on axial flow through a pipe of diameter ) and the square root of the curvature ratio. | 1 | Applied and Interdisciplinary Chemistry |
The resulting solution for solving the final equations listed above for both the Eulerian and Lagrangian models for analyzing the statistics of species in turbulent flow, both result in very similar expressions for calculating the average concentration at a location from a continuous source. Both solutions develop a [http://www.shodor.org/master/environmental/air/plume/index.html Gaussian Plume] and are virtually identical under the assumption that the variances in the x,y,z directions are related to the eddy diffusivity:
where
q= species emission rate, u = wind speed, σ = variance in i direction.
Under various external conditions such as directional flow speed (wind) and environmental conditions, the variances and diffusivities of turbulent diffusion are measured and used to calculate a good estimate of concentrations at a specific point from a source. This model is very useful in atmospheric sciences, especially when dealing with concentrations of contaminants in air pollution that emanate from sources such as combustion stacks, rivers, or strings of automobiles on a road. | 1 | Applied and Interdisciplinary Chemistry |
To date there have been nine human ADK protein isoforms identified. While some of these are ubiquitous throughout the body, some are localized into specific tissues. For example, ADK7 and ADK8 are both only found in the cytosol of cells; and ADK7 is found in skeletal muscle whereas ADK8 is not. Not only do the locations of the various isoforms within the cell vary, but the binding of substrate to the enzyme and kinetics of the phosphoryl transfer are different as well. ADK1, the most abundant cytosolic ADK isozyme, has a K about a thousand times higher than the K of ADK7 and 8, indicating a much weaker binding of ADK1 to AMP. Sub-cellular localization of the ADK enzymes is done by including a targeting sequence in the protein. Each isoform also has different preference for NTP's. Some will only use ATP, whereas others will accept GTP, UTP, and CTP as the phosphoryl carrier.
Some of these isoforms prefer other NTP's entirely. There is a mitochondrial GTP:AMP phosphotransferase, also specific for the phosphorylation of AMP, that can only use GTP or ITP as the phosphoryl donor. ADK has also been identified in different bacterial species and in yeast. Two further enzymes are known to be related to the ADK family, i.e. yeast uridine monophosphokinase and slime mold UMP-CMP kinase. Some residues are conserved across these isoforms, indicating how essential they are for catalysis. One of the most conserved areas includes an Arg residue, whose modification inactivates the enzyme, together with an Asp that resides in the catalytic cleft of the enzyme and participates in a salt bridge. | 1 | Applied and Interdisciplinary Chemistry |
The Wilfley Table was built to solve a problem common in the recovery of heavy ore minerals; approximately 90% of gold grains, platinum group minerals, sulphides, arsenides/antimonides and tellurides, in source rocks are silt-sized (<). Concentration of these minerals requires preconcentration techniques that include recovery of this fraction. Preconcentration may involve any number of methods including jigs, spirals, shaking tables, Knelson concentration, dense media separation, panning and hydroseparation. The Wilfley Table exploits preconcentration on the basis of density to separate minerals. It can recover silt to coarse sand-sized heavy minerals for a broad spectrum of commodities including diamonds, precious and base metals, and uranium. | 1 | Applied and Interdisciplinary Chemistry |
Simply add the name of the attached halide to the end of the acyl group. For example, is ethanoyl chloride. An alternate suffix is "-carbonyl halide" as opposed to "-oyl halide". The prefix form is "halocarbonyl-". | 0 | Theoretical and Fundamental Chemistry |
Depending on the expected level and volume of rainwater or runoff, French drains can be widened or also fitted on two or three underground drainpipes. Multiple pipes also provide for redundancy, in case one pipe becomes overfilled or clogged by a rupture or defect in the piping. A pipe might become overfilled if it is on a side of the drain which receives a much larger volume of water, such as one pipe being closer to an uphill slope, or closer to a roofline that drips near the French drain. When a pipe becomes overfilled, water can seep sideways into a parallel pipe, as a form of load-balancing, so that neither pipe becomes slowed by air bubbles, as might happen in a full-pipe with no upper air space. | 1 | Applied and Interdisciplinary Chemistry |
Porous absorbers, typically open cell rubber foams or melamine sponges, absorb noise by friction within the cell structure. Porous open cell foams are highly effective noise absorbers across a broad range of medium-high frequencies. Performance can be less impressive at lower frequencies. The exact absorption profile of a porous open-cell foam will be determined by a number of factors including cell size, tortuosity, porosity, thickness, and density.
The absorption aspect in soundproofing should not be confused with sound-absorbing panels used in acoustic treatments. Absorption in this sense refers to reducing a resonating frequency in a cavity by installing insulation between walls, ceilings or floors. Acoustic panels can play a role in treatment reducing reflections that make the overall sound in the source room louder, after walls, ceilings, and floors have been soundproofed. | 1 | Applied and Interdisciplinary Chemistry |
Briefly, when sheared genomic DNA in solution is heated to near boiling temperature, the molecular forces holding complementary base pairs together are disrupted, and the two strands of each double-helix dissociate or ‘denature.’ If the denatured DNA is then slowly returned to a cooler temperature, sequences will begin to ‘reassociate’ (renature) with complementary strands.
The temperature at which renaturation occurs can be regulated so that little or no sequence mismatch is tolerated. The rate at which a sequence finds a complementary strand with which to hybridize is directly related to how common that sequence is in the genome. In other words, those sequences that are extremely abundant (on average) find complementary strands with which to pair relatively quickly while single-copy sequences take much longer to find complements.
In CF, genomic DNA is heat-denatured and allowed to renature to a Cot value (Cot = DNA concentration x time x a factor based on the cation concentration of the buffer) at which the majority of repetitive elements have reassociated but single and low-copy elements remain single stranded. Double-stranded, repetitive DNA is separated from single-stranded, low-copy DNA by hydroxyapatite chromatography or other means. | 1 | Applied and Interdisciplinary Chemistry |
Magnetorheological dampers are utilized in semi-active human prosthetic legs. Much like those used in military and commercial helicopters, a damper in the prosthetic leg decreases the shock delivered to the patients leg when jumping, for example. This results in an increased mobility and agility for the patient. | 1 | Applied and Interdisciplinary Chemistry |
Phosphonate groups in the chemical structure are important for the binding of the drug to the target enzyme. Studies have showed that removal or replacement of the phosphonate group with a carboxylic acid causes drastic loss in potency of the drug and the enzyme inhibitor no longer goes into an isomerized state. | 1 | Applied and Interdisciplinary Chemistry |
Simple permutation-based estimation is used to determine how likely a given RP value or better is observed in a random experiment.
# generate p permutations of k rank lists of length n.
# calculate the rank products of the n genes in the p permutations.
# count how many times the rank products of the genes in the permutations are smaller or equal to the observed rank product. Set c to this value.
# calculate the average expected value for the rank product by: .
# calculate the percentage of false positives as : where is the rank of gene g in a list of all n genes sorted by increasing . | 1 | Applied and Interdisciplinary Chemistry |
Living organisms are composed of organic compounds. In life, they secrete or excrete organic material into their environment, shed body parts such as leaves and roots and after organisms die, their bodies are broken down by bacterial and fungal action. Larger molecules of organic matter can be formed from the polymerization of different parts of already broken down matter. The composition of natural organic matter depends on its origin, transformation mode, age, and existing environment, thus its bio-physicochemical functions vary with different environments. | 0 | Theoretical and Fundamental Chemistry |
In thermodynamic terms, all organic tissues are composed of chemical energy, which, when not maintained by the constant biochemical maintenance of the living organism, begin to chemically break down due to the reaction with water into amino acids, known as hydrolysis. The breakdown of the proteins of a decomposing body is a spontaneous process. Protein hydrolysis is accelerated as the anaerobic bacteria of the digestive tract consume, digest, and excrete the cellular proteins of the body.
The bacterial digestion of the cellular proteins weakens the tissues of the body. As the proteins are continuously broken down to smaller components, the bacteria excrete gases and organic compounds, such as the functional-group amines putrescine (from ornithine) and cadaverine (from lysine), which carry the noxious odor of rotten flesh. Initially, the gases of putrefaction are constrained within the body cavities, but eventually diffuse through the adjacent tissues, and then into the circulatory system. Once in the blood vessels, the putrid gases infiltrate and diffuse to other parts of the body and the limbs.
The visual result of gaseous tissue-infiltration is notable bloating of the torso and limbs. The increased internal pressure of the continually rising volume of gas further stresses, weakens, and separates the tissues constraining the gas. In the course of putrefaction, the skin tissues of the body eventually rupture and release the bacterial gas. As the anaerobic bacteria continue consuming, digesting, and excreting the tissue proteins, the body's decomposition progresses to the stage of skeletonization. This continued consumption also results in the production of ethanol by the bacteria, which can make it difficult to determine the blood alcohol content (BAC) in autopsies, particularly in bodies recovered from water.
Generally, the term decomposition encompasses the biochemical processes that occur from the physical death of the person (or animal) until the skeletonization of the body. Putrefaction is one of seven stages of decomposition; as such, the term putrescible identifies all organic matter (animal and human) that is biochemically subject to putrefaction. In the matter of death by poisoning, the putrefaction of the body is chemically delayed by poisons such as antimony, arsenic, carbolic acid (phenol), nux vomica (plant), strychnine (pesticide), and zinc chloride. | 1 | Applied and Interdisciplinary Chemistry |
The first practical application of superconductivity was developed in 1954 with Dudley Allen Buck's invention of the cryotron. Two superconductors with greatly different values of the critical magnetic field are combined to produce a fast, simple switch for computer elements.
Soon after discovering superconductivity in 1911, Kamerlingh Onnes attempted to make an electromagnet with superconducting windings but found that relatively low magnetic fields destroyed superconductivity in the materials he investigated. Much later, in 1955, G. B. Yntema succeeded in constructing a small 0.7-tesla iron-core electromagnet with superconducting niobium wire windings. Then, in 1961, J. E. Kunzler, E. Buehler, F. S. L. Hsu, and J. H. Wernick made the startling discovery that, at 4.2 kelvin, niobium–tin, a compound consisting of three parts niobium and one part tin, was capable of supporting a current density of more than 100,000 amperes per square centimeter in a magnetic field of 8.8 tesla. Despite being brittle and difficult to fabricate, niobium–tin has since proved extremely useful in supermagnets generating magnetic fields as high as 20 tesla. In 1962, T. G. Berlincourt and R. R. Hake discovered that more ductile alloys of niobium and titanium are suitable for applications up to 10 tesla. Promptly thereafter, commercial production of niobium–titanium supermagnet wire commenced at Westinghouse Electric Corporation and at Wah Chang Corporation. Although niobium–titanium boasts less-impressive superconducting properties than those of niobium–tin, niobium–titanium has, nevertheless, become the most widely used "workhorse" supermagnet material, in large measure a consequence of its very high ductility and ease of fabrication. However, both niobium–tin and niobium–titanium find wide application in MRI medical imagers, bending and focusing magnets for enormous high-energy-particle accelerators, and a host of other applications. Conectus, a European superconductivity consortium, estimated that in 2014, global economic activity for which superconductivity was indispensable amounted to about five billion euros, with MRI systems accounting for about 80% of that total.
In 1962, Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator. This phenomenon, now called the Josephson effect, is exploited by superconducting devices such as SQUIDs. It is used in the most accurate available measurements of the magnetic flux quantum Φ = h/(2e), where h is the Planck constant. Coupled with the quantum Hall resistivity, this leads to a precise measurement of the Planck constant. Josephson was awarded the Nobel Prize for this work in 1973.
In 2008, it was proposed that the same mechanism that produces superconductivity could produce a superinsulator state in some materials, with almost infinite electrical resistance. The first development and study of superconducting Bose–Einstein condensate (BEC) in 2020 suggests that there is a "smooth transition between" BEC and Bardeen-Cooper-Shrieffer regimes. | 0 | Theoretical and Fundamental Chemistry |
Amidines are organic compounds with the functional group RC(NR)NR, where the R groups can be the same or different. They are the imine derivatives of amides (RC(O)NR). The simplest amidine is formamidine, HC(=NH)NH.
Examples of amidines include:
* DBU
* diminazene
* benzamidine
* Pentamidine
* Paranyline | 0 | Theoretical and Fundamental Chemistry |
Consider a nucleus with a non-zero quadrupole moment and charge density , which is surrounded by a potential . This potential may be produced by the electrons as stated above, whose probability distribution might be non-isotropic in general. The potential energy in this system equals to the integral over the charge distribution and the potential within a domain :
One can write the potential as a Taylor-expansion at the center of the considered nucleus. This method corresponds to the multipole expansion in cartesian coordinates (note that the equations below use the Einstein sum-convention):
The first term involving will not be relevant and can therefore be omitted. Since nuclei do not have an electric dipole moment , which would interact with the electric field , the first derivatives can also be neglected. One is therefore left with all nine combinations of second derivatives. However if one deals with a homogeneous oblate or prolate nucleus the matrix will be diagonal and elements with vanish. This leads to a simplification because the equation for the potential energy now contains only the second derivatives in respect to the same variable:
The remaining terms in the integral are related to the charge distribution and hence the quadrupole moment. The formula can be simplified even further by introducing the electric field gradient , choosing the z-axis as the one with the maximal principal component and using the Laplace equation to obtain the proportionality written above. For an nucleus one obtains with the frequency-energy relation : | 0 | Theoretical and Fundamental Chemistry |
Expendable mold casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) moldings. This method of mold casting involves the use of temporary, non-reusable molds. | 1 | Applied and Interdisciplinary Chemistry |
When two or more sites in an asymmetrical molecule may be involved in an equilibrium reaction there are more than one possible equilibrium constants. For example, the molecule -DOPA has two non-equivalent hydroxyl groups which may be deprotonated. Denoting -DOPA as LH, the following diagram shows all the species that may be formed (X = ).
The concentration of the species LH is equal to the sum of the concentrations of the two micro-species with the same chemical formula, labelled LH and LH. The constant K is for a reaction with these two micro-species as products, so that [LH] = [LH] + [LH] appears in the numerator, and it follows that this macro-constant is equal to the sum of the two micro-constants for the component reactions.
:K = k + k
However, the constant K is for a reaction with these two micro-species as reactants, and [LH] = [LH] + [LH] in the denominator, so that in this case
:1/K =1/ k + 1/k,
and therefore K =k k / (k + k).
Thus, in this example there are four micro-constants whose values are subject to two constraints; in consequence, only the two macro-constant values, for K and K can be derived from experimental data.
Micro-constant values can, in principle, be determined using a spectroscopic technique, such as infrared spectroscopy, where each micro-species gives a different signal. Methods which have been used to estimate micro-constant values include
* Chemical: blocking one of the sites, for example by methylation of a hydroxyl group, followed by determination of the equilibrium constant of the related molecule, from which the micro-constant value for the "parent" molecule may be estimated.
* Mathematical: applying numerical procedures to C NMR data.
Although the value of a micro-constant cannot be determined from experimental data, site occupancy, which is proportional to the micro-constant value, can be very important for biological activity. Therefore, various methods have been developed for estimating micro-constant values. For example, the isomerization constant for -DOPA has been estimated to have a value of 0.9, so the micro-species LH and LH have almost equal concentrations at all pH values. | 0 | Theoretical and Fundamental Chemistry |
To produce nanolattice materials, polymer templates are manufactured by high-resolution 3D printing processes, such as multiphoton lithography, self-assembly, self-propagating photopolymer waveguides, and direct laser writing techniques. Those methods can synthesize the structure with a unit cell size down to the order of 50 nanometers. Genetic engineering also has the potential in synthesizing nanolattice. Ceramic, metal or composite material nanolattices are formed by post-treatment of the polymer templates with techniques including pyrolysis, atomic layer deposition, electroplating and electroless plating. Pyrolysis, which additionally shrinks the lattices by up to 90%, creates the smallest-size structures, whereby the polymeric template material transforms into carbon, or other ceramics and metals, through thermal decomposition in inert atmosphere or vacuum. | 0 | Theoretical and Fundamental Chemistry |
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