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The technique operates on the principle that a positron or positronium will annihilate through interaction with electrons. This annihilation releases gamma rays that can be detected; the time between emission of positrons from a radioactive source and detection of gamma rays due to annihilation corresponds to the lifetime of positron or positronium.
When positrons are injected into a solid body, they interact in some manner with the electrons in that species. For solids containing free electrons (such as metals or semiconductors), the implanted positrons annihilate rapidly unless voids such as vacancy defects are present. If voids are available, positrons will reside in them and annihilate less rapidly than in the bulk of the material, on time scales up to ~1 ns. For insulators such as polymers or zeolites, implanted positrons interact with electrons in the material to form positronium.
Positronium is a metastable hydrogen-like bound state of an electron and a positron which can exist in two spin states. Para-positronium, p-Ps, is a singlet state (the positron and electron spins are anti-parallel) with a characteristic self-annihilation lifetime of 125 ps in vacuum. Ortho-positronium, o-Ps, is a triplet state (the positron and electron spins are parallel) with a characteristic self-annihilation lifetime of 142 ns in vacuum. In molecular materials, the lifetime of o-Ps is environment dependent and it delivers information pertaining to the size of the void in which it resides. Ps can pick up a molecular electron with an opposite spin to that of the positron, leading to a reduction of the o-Ps lifetime from 142 ns to 1-4 ns (depending on the size of the free volume in which it resides). The size of the molecular free volume can be derived from the o-Ps lifetime via the semi-empirical Tao-Eldrup model.
While the PALS is successful in examining local free volumes, it still needs to employ data from combined methods in order to yield free volume fractions. Even approaches to obtain fractional free volume from the PALS data that claim to be independent on other experiments, such as PVT measurements, they still do employ theoretical considerations, such as iso-free-volume amount from Simha-Boyer theory. A convenient emerging method for obtaining free volume amounts in an independent manner are computer simulations; these can be combined with the PALS measurements and help to interpret the PALS measurements.
Pore structure in insulators can be determined using the quantum mechanical Tao-Eldrup model and extensions thereof. By changing the temperature at which a sample is analyzed, the pore structure can be fit to a model where positronium is confined in one, two, or three dimensions. However, interconnected pores result in averaged lifetimes that cannot distinguish between smooth channels or channels having smaller, open, peripheral pores due to energetically favored positronium diffusion from small to larger pores.
The behavior of positrons in molecules or condensed matter is nontrivial due
to the strong correlation between electrons and positrons. Even the simplest
case, that of a single positron immersed in a homogeneous gas of electrons,
has proved to be a significant challenge for theory. The positron attracts
electrons to it, increasing the contact density and hence enhancing the
annihilation rate. Furthermore, the momentum density of annihilating
electron-positron pairs is enhanced near the Fermi surface. Theoretical
approaches used to study this problem have included the Tamm-Dancoff
approximation, Fermi and perturbed hypernetted chain approximations, density functional theory methods and quantum Monte Carlo. | 0 | Theoretical and Fundamental Chemistry |
* Ascorbic acid is easily oxidized and so is used as a reductant in photographic developer solutions (among others) and as a preservative.
* In fluorescence microscopy and related fluorescence-based techniques, ascorbic acid can be used as an antioxidant to increase fluorescent signal and chemically retard dye photobleaching.
* It is also commonly used to remove dissolved metal stains, such as iron, from fiberglass swimming pool surfaces.
* In plastic manufacturing, ascorbic acid can be used to assemble molecular chains more quickly and with less waste than traditional synthesis methods.
* Heroin users are known to use ascorbic acid as a means to convert heroin base to a water-soluble salt so that it can be injected.
* As justified by its reaction with iodine, it is used to negate the effects of iodine tablets in water purification. It reacts with the sterilized water, removing the taste, color, and smell of the iodine. This is why it is often sold as a second set of tablets in most sporting goods stores as Potable Aqua-Neutralizing Tablets, along with the potassium iodide tablets.
*Intravenous high-dose ascorbate is being used as a chemotherapeutic and biological response modifying agent. It is undergoing clinical trials.
* It is sometimes used as a urinary acidifier to enhance the antiseptic effect of methenamine. | 1 | Applied and Interdisciplinary Chemistry |
A globe valve, different from ball valve, is a type of valve used for regulating flow in a pipeline, consisting of a movable plug or disc element and a stationary ring seat in a generally spherical body.
Globe valves are named for their spherical body shape with the two halves of the body being separated by an internal baffle. This has an opening that forms a seat onto which a movable plug can be screwed in to close (or shut) the valve. The plug is also called a disc. In globe valves, the plug is connected to a stem which is operated by screw action using a handwheel in manual valves. Typically, automated globe valves use smooth stems rather than threaded and are opened and closed by an actuator assembly. | 1 | Applied and Interdisciplinary Chemistry |
Kerma ("kinetic energy released per unit mass") is used in radiation metrology as a measure of the liberated energy of ionisation due to irradiation, and is expressed in grays. Importantly, kerma dose is different from absorbed dose, depending on the radiation energies involved, partially because ionization energy is not accounted for. Whilst roughly equal at low energies, kerma is much higher than absorbed dose at higher energies, because some energy escapes from the absorbing volume in the form of bremsstrahlung (X-rays) or fast-moving electrons.
Kerma, when applied to air, is equivalent to the legacy roentgen unit of radiation exposure, but there is a difference in the definition of these two units. The gray is defined independently of any target material, however, the roentgen was defined specifically by the ionisation effect in dry air, which did not necessarily represent the effect on other media. | 0 | Theoretical and Fundamental Chemistry |
In some cases in the EU MRLs are also used for ornamental produce, and checked against MRLs for food crops. While this is a sound approach for the general environmental impact, it doesnt reflect potential exposure of people handling ornamentals. A swap test can eliminate this gap. MRLs for ornamental produce can sometimes result in a conflicting outcome because of the absence of pre harvest intervals (PHI) or withholding periods for ornamentals, specifically in crops where harvesting is continuous, like roses. This happens when a grower is following the label recommendations and the produce is sampled shortly after. | 1 | Applied and Interdisciplinary Chemistry |
PPS, available as PPS Silent Surfactant from Expedeon, is the abbreviation for sodium 3-(4-(1,1-bis(hexyloxy)ethyl)pyridinium-1-yl)propane-1-sulfonate. This acetalic detergent is split under acidic conditions into hexanol and the zwitterionic 3-acetyl-1-(3-sulfopropyl)pyridinium. | 0 | Theoretical and Fundamental Chemistry |
Electronic entropy is the entropy of a system attributable to electrons' probabilistic occupation of states. This entropy can take a number of forms. The first form can be termed a density of states based entropy. The Fermi–Dirac distribution implies that each eigenstate of a system, , is occupied with a certain probability, . As the entropy is given by a sum over the probabilities of occupation of those states, there is an entropy associated with the occupation of the various electronic states. In most molecular systems, the energy spacing between the highest occupied molecular orbital and the lowest unoccupied molecular orbital is usually large, and thus the probabilities associated with the occupation of the excited states are small. Therefore, the electronic entropy in molecular systems can safely be neglected. Electronic entropy is thus most relevant for the thermodynamics of condensed phases, where the density of states at the Fermi level can be quite large, and the electronic entropy can thus contribute substantially to thermodynamic behavior. A second form of electronic entropy can be attributed to the configurational entropy associated with localized electrons and holes. This entropy is similar in form to the configurational entropy associated with the mixing of atoms on a lattice.
Electronic entropy can substantially modify phase behavior, as in lithium ion battery electrodes, high temperature superconductors, and some perovskites. It is also the driving force for the coupling of heat and charge transport in thermoelectric materials, via the Onsager reciprocal relations. | 0 | Theoretical and Fundamental Chemistry |
Sulfuric acid was called oil of vitriol by medieval European alchemists because it was prepared by roasting iron(II) sulfate or green vitriol in an iron retort. The first allusions to it in works that are European in origin appear in the thirteenth century AD, as for example in the works of Vincent of Beauvais, in the Compositum de Compositis ascribed to Albertus Magnus, and in pseudo-Gebers Summa perfectionis'. | 0 | Theoretical and Fundamental Chemistry |
Colloid vibration current is an electroacoustic phenomenon that arises when ultrasound propagates through a fluid that contains ions and either solid particles or emulsion droplets.
The pressure gradient in an ultrasonic wave moves particles relative to the fluid. This motion disturbs the double layer that exists at the particle-fluid interface. The picture illustrates the mechanism of this distortion. Practically all particles in fluids carry a surface charge. This surface charge is screened with an equally charged diffuse layer; this structure is called the double layer. Ions of the diffuse layer are located in the fluid and can move with the fluid. Fluid motion relative to the particle drags these diffuse ions in the direction of one or the other of the particle's poles. The picture shows ions dragged towards the left hand pole. As a result of this drag, there is an excess of negative ions in the vicinity of the left hand pole and an excess of positive surface charge at the right hand pole. As a result of this charge excess, particles gain a dipole moment. These dipole moments generate an electric field that in turn generates measurable electric current. This phenomenon is widely used for measuring zeta potential in concentrated colloids. | 0 | Theoretical and Fundamental Chemistry |
The first study about submarine groundwater discharge was done by Sonrel (1868), who speculated on the risk of submarine springs for sailors. However, until the mid-1990s, SGD remained rather unrecognized by the scientific community because it was hard to detect and measure the freshwater discharge. The first elaborated method to study SGD was done by Moore (1996), who used radium-226 as a tracer for groundwater. Since then several methods and instruments have been developed to attempt to detect and quantify discharge rates. | 0 | Theoretical and Fundamental Chemistry |
An example of such an enantiomer is the sedative thalidomide, which was sold in a number of countries around the world from 1957 until 1961. It was withdrawn from the market when it was found to cause birth defects. One enantiomer caused the desirable sedative effects, while the other, unavoidably present in equal quantities, caused birth defects.
The herbicide mecoprop is a racemic mixture, with the (R)-(+)-enantiomer ("Mecoprop-P", "Duplosan KV") possessing the herbicidal activity.
Another example is the antidepressant drugs escitalopram and citalopram. Citalopram is a racemate [1:1 mixture of (S)-citalopram and (R)-citalopram]; escitalopram [(S)-citalopram] is a pure enantiomer. The dosages for escitalopram are typically 1/2 of those for citalopram. Here, (S)-citalopram is called a chiral switch of Citalopram. | 0 | Theoretical and Fundamental Chemistry |
The Blasius correlation is the simplest equation for computing the Darcy friction
factor. Because the Blasius correlation has no term for pipe roughness, it
is valid only to smooth pipes. However, the Blasius correlation is sometimes
used in rough pipes because of its simplicity. The Blasius correlation is valid
up to the Reynolds number 100000. | 1 | Applied and Interdisciplinary Chemistry |
T*-weighted imaging can be created as a postexcitation refocused gradient echo sequence with small flip angle. The sequence of a GRE T*WI requires high uniformity of the magnetic field. | 0 | Theoretical and Fundamental Chemistry |
In space plasmas where the electron density is relatively low, the Debye length may reach macroscopic values, such as in the magnetosphere, solar wind, interstellar medium and intergalactic medium. See the table here below: | 0 | Theoretical and Fundamental Chemistry |
The hydrogen ions displace metal from the salt so that metal, instead of hydrogen, is deposited on the positive plate. Examples:
* Silver oxide, used in the Silver-oxide battery
* Copper sulphate, used in the Daniell cell
* Mercurous sulphate, used in the Weston and Clark standard cells | 0 | Theoretical and Fundamental Chemistry |
A hydrogen bond is an extreme form of dipole-dipole bonding, referring to the attraction between a hydrogen atom that is bonded to an element with high electronegativity, usually nitrogen, oxygen, or fluorine. The hydrogen bond is often described as a strong electrostatic dipole–dipole interaction. However, it also has some features of covalent bonding: it is directional, stronger than a van der Waals force interaction, produces interatomic distances shorter than the sum of their van der Waals radii, and usually involves a limited number of interaction partners, which can be interpreted as a kind of valence. The number of Hydrogen bonds formed between molecules is equal to the number of active pairs. The molecule which donates its hydrogen is termed the donor molecule, while the molecule containing lone pair participating in H bonding is termed the acceptor molecule. The number of active pairs is equal to the common number between number of hydrogens the donor has and the number of lone pairs the acceptor has.
Though both not depicted in the diagram, water molecules have four active bonds. The oxygen atom’s two lone pairs interact with a hydrogen each, forming two additional hydrogen bonds, and the second hydrogen atom also interacts with a neighbouring oxygen. Intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C) compared to the other group 16 hydrides, which have little capability to hydrogen bond. Intramolecular hydrogen bonding is partly responsible for the secondary, tertiary, and quaternary structures of proteins and nucleic acids. It also plays an important role in the structure of polymers, both synthetic and natural. | 0 | Theoretical and Fundamental Chemistry |
The atoms that are used to build the purine nucleotides come from a variety of sources:
The de novo synthesis of purine nucleotides by which these precursors are incorporated into the purine ring proceeds by a 10-step pathway to the branch-point intermediate IMP, the nucleotide of the base hypoxanthine. AMP and GMP are subsequently synthesized from this intermediate via separate, two-step pathways. Thus, purine moieties are initially formed as part of the ribonucleotides rather than as free bases.
Six enzymes take part in IMP synthesis. Three of them are multifunctional:
* GART (reactions 2, 3, and 5)
* PAICS (reactions 6, and 7)
* ATIC (reactions 9, and 10)
The pathway starts with the formation of PRPP. PRPS1 is the enzyme that activates R5P, which is formed primarily by the pentose phosphate pathway, to PRPP by reacting it with ATP. The reaction is unusual in that a pyrophosphoryl group is directly transferred from ATP to C of R5P and that the product has the α configuration about C1. This reaction is also shared with the pathways for the synthesis of Trp, His, and the pyrimidine nucleotides. Being on a major metabolic crossroad and requiring much energy, this reaction is highly regulated.
In the first reaction unique to purine nucleotide biosynthesis, PPAT catalyzes the displacement of PRPP's pyrophosphate group (PP) by an amide nitrogen donated from either glutamine (N), glycine (N&C), aspartate (N), folic acid (C), or CO. This is the committed step in purine synthesis. The reaction occurs with the inversion of configuration about ribose C, thereby forming β-5-phosphorybosylamine (5-PRA) and establishing the anomeric form of the future nucleotide.
Next, a glycine is incorporated fueled by ATP hydrolysis, and the carboxyl group forms an amine bond to the NH previously introduced. A one-carbon unit from folic acid coenzyme N-formyl-THF is then added to the amino group of the substituted glycine followed by the closure of the imidazole ring. Next, a second NH group is transferred from glutamine to the first carbon of the glycine unit. A carboxylation of the second carbon of the glycin unit is concomitantly added. This new carbon is modified by the addition of a third NH unit, this time transferred from an aspartate residue. Finally, a second one-carbon unit from formyl-THF is added to the nitrogen group and the ring is covalently closed to form the common purine precursor inosine monophosphate (IMP).
Inosine monophosphate is converted to adenosine monophosphate in two steps. First, GTP hydrolysis fuels the addition of aspartate to IMP by adenylosuccinate synthase, substituting the carbonyl oxygen for a nitrogen and forming the intermediate adenylosuccinate. Fumarate is then cleaved off forming adenosine monophosphate. This step is catalyzed by adenylosuccinate lyase.
Inosine monophosphate is converted to guanosine monophosphate by the oxidation of IMP forming xanthylate, followed by the insertion of an amino group at C. NAD is the electron acceptor in the oxidation reaction. The amide group transfer from glutamine is fueled by ATP hydrolysis. | 1 | Applied and Interdisciplinary Chemistry |
Initially, the optical mapping system has been used to construct whole-genome restriction maps of bacteria, parasites, and fungi. It has also been used to scaffold and validate bacterial genomes. To serve as scaffolds for assembly, assembled sequence contigs can be scanned for restriction sites in silico using known sequence data and aligning them to the assembled genomic optical map. Commercial company, Opgen has provided optical mappings for microbial genomes. For larger eukaryotic genomes, only the David C. Schwartz lab (now at Madison-Wisconsin) has produced optical maps for mouse, human, rice, and maize. | 1 | Applied and Interdisciplinary Chemistry |
The occurrence of underpotential deposition is often interpreted as a result of a strong interaction between the electrodepositing metal M with the substrate S (of which the electrode is built). The M-S interaction needs to be energetically favoured to the M-M interaction in the crystal lattice of the pure metal M. This mechanism is deduced from the observation that UPD typically occurs only up to a monolayer of M (sometimes up to two monolayers). The electrodeposition of a metal on a substrate of the same metal occurs at an equilibrium potential, thus defining the reference point for the underpotential deposition. Underpotential deposition is much sharper on monocrystals than on polycrystalline materials. | 0 | Theoretical and Fundamental Chemistry |
GGT is elevated by ingestion of large quantities of alcohol (needs reference) However, determination of high levels of total serum GGT activity is not specific to alcohol intoxication, and the measurement of selected serum forms of the enzyme offer more specific information. Isolated elevation or disproportionate elevation compared to other liver enzymes (such as ALT or alanine transaminase) can indicate harmful alcohol use or alcoholic liver disease, and can indicate excess alcohol consumption up to 3 or 4 weeks prior to the test. The mechanism for this elevation is unclear. Alcohol might increase GGT production by inducing hepatic microsomal production, or it might cause the leakage of GGT from hepatocytes. | 1 | Applied and Interdisciplinary Chemistry |
Discrete dipole approximation (DDA), also known as coupled dipole approximation, is a method for computing scattering of radiation by particles of arbitrary shape and by periodic structures. Given a target of arbitrary geometry, one seeks to calculate its scattering and absorption properties by an approximation of the continuum target by a finite array of small polarizable dipoles. This technique is used in a variety of applications including nanophotonics, radar scattering, aerosol physics and astrophysics. | 0 | Theoretical and Fundamental Chemistry |
In aquatic organisms the most common form of nitrogen waste is ammonia, whereas land-dwelling organisms convert the toxic ammonia to either urea or uric acid. Urea is found in the urine of mammals and amphibians, as well as some fish. Birds and saurian reptiles have a different form of nitrogen metabolism that requires less water, and leads to nitrogen excretion in the form of uric acid. Tadpoles excrete ammonia, but shift to urea production during metamorphosis. Despite the generalization above, the urea pathway has been documented not only in mammals and amphibians, but in many other organisms as well, including birds, invertebrates, insects, plants, yeast, fungi, and even microorganisms. | 0 | Theoretical and Fundamental Chemistry |
Along with his interest in science, Fraser-Reid was an accomplished pianist and organist who gave recitals at notable venues such as St. George's Cathedral, Kingston, Jamaica (December 1986) and Cathedral de Seville, Spain (August 1995).
In the 1970s Fraser-Reid filed a lawsuit against a building contractor who had not followed municipal building codes. The case went all the way to the Supreme Court of Canada where Fraser-Reid prevailed, and "Fraser-Reid v Droumtsekas" is often cited in Canadian civil law. | 0 | Theoretical and Fundamental Chemistry |
Contour advection is another useful method for characterizing chaotic mixing.
In chaotic flows, advected contours will grow exponentially over time.
The figure above shows the frame-by-frame evolution of a contour advected over
several days. The figure to the right shows the length of this contour
as a function of time.
The link between exponential contour growth and positive Lyapunov exponents is
easy to see. The rate of contour growth is given as:
where is the path
and the integral is performed over the length of the contour.
Contour growth rates will approximate the average of the large Lyapunov exponents: | 1 | Applied and Interdisciplinary Chemistry |
1 July (14 July, New Style) 1900 was organized the Moscow Higher Women Courses (MHWC). Their structure originally consisted of two departments: History and Philosophy and Physics and Mathematics. On the last one were soon opened two offices: mathematical and natural, and after a few years two more – medical and chemical-pharmaceutical. The initiators and the first lecturers were outstanding scientists, academics subsequently S. A. Chaplygin, V. I. Vernadsky, N. D. Zelinsky (the inventor of the gas mask (1916)), Professors V. F. Davidov, B. K. Mlodzeevskii, A. N. Reformatsky, A. A. Eichenwald, S. G. Krapivin. The first director of MHWC was Professor V. I. Guerrier.
In 1905 as a director was elected S. A. Chaplygin, the leading scientist in the field of hydro- and aerodynamics, the organizer of the construction of school buildings on the Malaya Pirogovskaya street (formerly Devichie Pole). He remained in that post until 1918.
By the beginning of World War I MHWC turned into one of the largest higher education institutions in the country. The number of trainees reached 710, and during the existence of courses released 5760 professionals. In turning into a first-class university MHWC paramount importance had an exceptional organizational skill of S. A. Chaplygin, later shown to them with equal brilliance in creating TsAGI. | 1 | Applied and Interdisciplinary Chemistry |
Aluminium hydroxide, , is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric, i.e., it has both basic and acidic properties. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide or alumina (), the latter of which is also amphoteric. These compounds together are the major components of the aluminium ore bauxite. Aluminium hydroxide also forms a gelatinous precipitate in water. | 0 | Theoretical and Fundamental Chemistry |
The electro-optic effect is a change in the optical properties of an optically active material in response to changes in an electric field. This interaction usually results in a change in the birefringence, and not simply the refractive index of the medium. In a Kerr cell, the change in birefringence is proportional to the square of the electric field, and the material is usually a liquid. In a Pockels cell, the change in birefringence varies linearly with the electric field, and the material is usually a crystal. Non-crystalline, solid electro-optical materials have generated interest because of their low cost of production. These organic, polymer-based materials are also known as organic EO material, plastic EO material, or polymer EO material. They consist of nonlinear optical chromophores in a polymer lattice. The nonlinear optical chromophores can produce Pockels effect. | 0 | Theoretical and Fundamental Chemistry |
Conjugated polymers offer the tantalizing possibility of organic molecules with a manipulable electronic band structure, but current methods for production have an uncontrolled topology. Sun, Lauher, and Goroff discovered that certain amides ensure a linear polymerization of poly(diiododiacetylene). The underlying mechanism is a self-organization of the amides via hydrogen bonds that then transfers to the diiododiacetylene monomers via halogen bonds. Although pure diiododiacetylene crystals do not polymerize spontaneously, the halogen-bond induced organization is sufficiently strong that the cocrystals do spontaneously polymerize. | 0 | Theoretical and Fundamental Chemistry |
The word solder comes from the Middle English word , via Old French and , from the Latin , meaning "to make solid". | 1 | Applied and Interdisciplinary Chemistry |
Anthocyanins are found in the cell vacuole, mostly in flowers and fruits, but also in leaves, stems, and roots. In these parts, they are found predominantly in outer cell layers such as the epidermis and peripheral mesophyll cells.
Most frequently occurring in nature are the glycosides of cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin. Roughly 2% of all hydrocarbons fixed in photosynthesis are converted into flavonoids and their derivatives, such as the anthocyanins. Not all land plants contain anthocyanin; in the Caryophyllales (including cactus, beets, and amaranth), they are replaced by betalains. Anthocyanins and betalains have never been found in the same plant.
Sometimes bred purposely for high anthocyanin content, ornamental plants such as sweet peppers may have unusual culinary and aesthetic appeal. | 0 | Theoretical and Fundamental Chemistry |
The desired enantiomer from resolution, allylic alcohol 5.1 (Scheme 5) was acetylated with acetic anhydride and 4-(dimethylamino)pyridine in methylene chloride to yield monoacetate 5.2. It is noteworthy that this reaction was exclusive for the allylic alcohol, and the adjacent hydroxyl group was not acetylated. Alcohol 5.2 was oxidized with tetrapropylammonium perruthenate and N-methylmorpholine N-oxide to give ketone 5.3. Alkene 5.3 underwent hydroboration in tetrahydrofuran. Oxidation with basic hydrogen peroxide and sodium bicarbonate gave alcohol 5.4 in 35% yield, with 15% yield of a regioisomer. The acetonide was removed, giving triol 5.5. This alcohol was monoacetylated, to give acetate 5.6. The benzyl group was removed and replaced with a triethylsilyl group. Diol 5.7 was selectively activated using methanesulfonyl chloride and 4-(dimethylamino)pyridine to give mesylate 5.8, in 78% yield.
The acetyl group in 6.1 (Scheme 6) was removed to give primary alcohol 6.2. The Taxol ring (D) was added by an intramolecular nucleophilic substitution involving this hydroxyl group to give oxetane 6.3. After acetylation, phenyllithium was used to open the carbonate ester ring to give alcohol 6.5. Allylic oxidation with pyridinium chlorochromate, sodium acetate, and celite gave ketone 6.6, which was subsequently reduced using sodium borohydride to give secondary alcohol 6.7. This was the last compound before the addition of the amide tail. | 0 | Theoretical and Fundamental Chemistry |
The highly reducing ferredoxins are reduced either by using another strong reducing agent, or by using some source of energy to "boost" electrons from less reducing sources to the ferredoxin. | 0 | Theoretical and Fundamental Chemistry |
With polymerase chain reaction (PCR) being among the most popular contexts in which DNA denaturation is desired, heating is the most frequent method of denaturation. Other than denaturation by heat, nucleic acids can undergo the denaturation process through various chemical agents such as formamide, guanidine, sodium salicylate, dimethyl sulfoxide (DMSO), propylene glycol, and urea. These chemical denaturing agents lower the melting temperature (T) by competing for hydrogen bond donors and acceptors with pre-existing nitrogenous base pairs. Some agents are even able to induce denaturation at room temperature. For example, alkaline agents (e.g. NaOH) have been shown to denature DNA by changing pH and removing hydrogen-bond contributing protons. These denaturants have been employed to make Denaturing Gradient Gel Electrophoresis gel (DGGE), which promotes denaturation of nucleic acids in order to eliminate the influence of nucleic acid shape on their electrophoretic mobility. | 1 | Applied and Interdisciplinary Chemistry |
Recognizing that approximately 50% of commercial pharmaceuticals are salts, ionic liquid forms of a number of pharmaceuticals have been investigated. Combining a pharmaceutically active cation with a pharmaceutically active anion leads to a Dual Active ionic liquid in which the actions of two drugs are combined.
ILs can extract specific compounds from plants for pharmaceutical, nutritional and cosmetic applications, such as the antimalarial drug artemisinin from the plant Artemisia annua. | 0 | Theoretical and Fundamental Chemistry |
A genomic library is a set of clones that together represents the entire genome of a given organism. The number of clones that constitute a genomic library depends on (1) the size of the genome in question and (2) the insert size tolerated by the particular cloning vector system. For most practical purposes, the tissue source of the genomic DNA is unimportant because each cell of the body contains virtually identical DNA (with some exceptions).
Applications of genomic libraries include:
* Determining the complete genome sequence of a given organism (see genome project)
* Serving as a source of genomic sequence for generation of transgenic animals through genetic engineering
* Study of the function of regulatory sequences in vitro
* Study of genetic mutations in cancer tissues | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, yield, also referred to as reaction yield, is a measure of the quantity of moles of a product formed in relation to the reactant consumed, obtained in a chemical reaction, usually expressed as a percentage. Yield is one of the primary factors that scientists must consider in organic and inorganic chemical synthesis processes. In chemical reaction engineering, "yield", "conversion" and "selectivity" are terms used to describe ratios of how much of a reactant was consumed (conversion), how much desired product was formed (yield) in relation to the undesired product (selectivity), represented as X, Y, and S.
The term yield also plays an important role in analytical chemistry, as individual compounds are recovered in purification processes in a range from quantitative yield (100 %) to low yield (< 50 %). | 0 | Theoretical and Fundamental Chemistry |
One of the most exciting and most studied uses of photocatalysis is the photo-oxidation of organics as it applies to environmental decontamination.
In contrast to gas phase interactions with the solid surface, the vast number of variables associated with the liquid solid interface (i.e. solution pH, photocatalyst concentration, solvent effects, diffusion rate, etc.) calls for greater care to be taken to control these variables to produce consistent experimental results. A greater variety of reactions also become possible due to the ability of solutions to stabilize charged species, making it possible to add an electron from the metal to a neutral species producing an anion that can go on to further react, or a hole to remove an electron, producing a cation that goes on to further react in solution. | 0 | Theoretical and Fundamental Chemistry |
Many industrial peroxides are produced using hydrogen peroxide. Reactions with aldehydes and ketones yield a series of compounds depending on conditions. Specific reactions include addition of hydrogen peroxide across the C=O double bond:
In some cases, these hydroperoxides convert to give cyclic diperoxides:
Addition of this initial adduct to a second equivalent of the carbonyl:
Further replacement of alcohol groups:
Triphenylmethanol reacts with hydrogen peroxide gives the unusually stable hydroperoxide, . | 0 | Theoretical and Fundamental Chemistry |
Carbonation is the chemical reaction of carbon dioxide to give carbonates, bicarbonates, and carbonic acid. In chemistry, the term is sometimes used in place of carboxylation, which refers to the formation of carboxylic acids.
In inorganic chemistry and geology, carbonation is common. Metal hydroxides (MOH) and metal oxides (M'O) react with CO to give bicarbonates and carbonates:
:MOH + CO → M(HCO)
:MO + CO → MCO | 0 | Theoretical and Fundamental Chemistry |
TTM has been studied in several use scenarios where it has not usually been found to be helpful, or is still under investigation, despite theoretical grounds for its usefulness. | 1 | Applied and Interdisciplinary Chemistry |
This method is similar to the previous method in that the glycosyl donor is protected at C-2 by an OAc group, which is converted into an enol ether by the Tebbe reagent. However, in this approach, N-iodosuccinimide (NIS) is used to tether the glycosyl acceptor to the enol ether, and in a second step, activation of the anomeric leaving group leads to intramolecular delivery of the aglycon to C-1 and formation of the 1,2-cis-glycoside product. | 0 | Theoretical and Fundamental Chemistry |
The study of extracellular metabolites has been prevalent in scientific literature. However, global exometabolite profiling was only realized with recent advances allowing for improved chromatographic separation and detection of hundreds to thousands of compounds by the mid-2000s. The first work to demonstrate the biological relevance of comparative profiling of exometabolite pools was not until 2003, when the term "metabolite footprinting" was coined by Jess Allen and coworkers. This work attracted a great deal of interest in the community, particularly for characterization of microbial metabolism. The idea of the "exometabolome" encompassing the components of the exometabolite pool was not introduced until 2005.
Recent advances in mass spectrometry imaging have allowed for spatial localization of released metabolites. As the field of microbiology becomes increasingly more centered on microbial community structure, exometabolomics has provided for rapid understanding of metabolic interactions between two or more species. Recently, exometabolomics has been used to design co-culture systems. Because the analysis of extracellular metabolites allows for the predictions and determinations of metabolite exchange, exometabolomics analyses can be used for understanding community ecological networks. | 1 | Applied and Interdisciplinary Chemistry |
The 5 UTR of prokaryotes consists of the Shine–Dalgarno sequence (5-AGGAGGU-3'). This sequence is found 3-10 base pairs upstream from the initiation codon. The initiation codon is the start site of translation into protein. | 1 | Applied and Interdisciplinary Chemistry |
Drill pipe, is hollow, thin-walled, steel or aluminium alloy piping that is used on drilling rigs. It is hollow to allow drilling fluid to be pumped down the hole through the bit and back up the annulus. It comes in a variety of sizes, strengths, and wall thicknesses, but is typically 27 to 32 feet in length (Range 2). Longer lengths, up to 45 feet, exist (Range 3). | 1 | Applied and Interdisciplinary Chemistry |
The free-surface boundary conditions and apply at the yet unknown free-surface elevation . They can be transformed into boundary conditions at a fixed elevation by use of Taylor series expansions of the flow field around that elevation.
Without loss of generality the mean surface elevation – around which the Taylor series are developed – can be taken at . This assures the expansion is around an elevation in the proximity of the actual free-surface elevation. Convergence of the Taylor series for small-amplitude steady-wave motion was proved by .
The following notation is used: the Taylor series of some field around – and evaluated at – is:
with subscript zero meaning evaluation at , e.g.: .
Applying the Taylor expansion to free-surface boundary condition in terms of the potential Φ gives:
showing terms up to triple products of η, Φ and u, as required for the construction of the Stokes expansion up to third-order ((ka)). Here, ka is the wave steepness, with k a characteristic wavenumber and a a characteristic wave amplitude for the problem under study. The fields η, Φ and u are assumed to be (ka).
The dynamic free-surface boundary condition can be evaluated in terms of quantities at as:
The advantages of these Taylor-series expansions fully emerge in combination with a perturbation-series approach, for weakly non-linear waves . | 1 | Applied and Interdisciplinary Chemistry |
Fretting refers to wear and sometimes corrosion damage of loaded surfaces in contact while they encounter small oscillatory movements tangential to the surface. Fretting is caused by adhesion of contact surface asperities, which are subsequently broken again by the small movement. This breaking causes wear debris to be formed.
If the debris and/or surface subsequently undergo chemical reaction, i.e., mainly oxidation, the mechanism is termed fretting corrosion. Fretting degrades the surface, leading to increased surface roughness and micropits, which reduces the fatigue strength of the components.
The amplitude of the relative sliding motion is often in the order of micrometers to millimeters, but can be as low as 3 nanometers.
Typically fretting is encountered in shrink fits, bearing seats, bolted parts, splines, and dovetail connections. | 1 | Applied and Interdisciplinary Chemistry |
The mechanism proceeds in two stages: β-nucleophilic addition to the unsaturated carbonyl compound, followed by electrophilic substitution at the α-carbon of the resulting enolate.
When the nucleophile is an organometallic reagent, the mechanisms of the first step can vary. Whether reactions take place by ionic or radical mechanisms is unclear in some cases. Research has shown that the second step may even proceed via single-electron transfers when the reduction potential of the electrophile is low. A general scheme involving ionic intermediates is shown below.
Lithium organocuprates undergo oxidative addition to enones to give, after reductive elimination of an organocopper(III) species, β-substituted lithium enolates.
In any case, the second step is well described in all cases as the reaction of an enolate with an electrophile. The two steps may be carried out as distinct experimental operations if the initially formed enolate is protected after β-addition. If the two steps are not distinct, however, the counterion of the enolate is determined by the counterion of the nucleophilic starting material and can influence the reactivity of the enolate profoundly. | 0 | Theoretical and Fundamental Chemistry |
The compound was first described by Carl Wilhelm Scheele in 1780, who obtained it by the dry distillation of mucic acid. For this reason it was initially known as pyromucic acid. This was the first known synthesis of a furan compound, the second being furfural in 1821.
Despite this, it was furfural which came to set naming conventions for later furans. | 0 | Theoretical and Fundamental Chemistry |
The corium (molten core) will cool and change to a solid with time. It is thought that the solid is weathering with time. The solid can be described as Fuel Containing Mass, it is a mixture of sand, zirconium and uranium dioxide which had been heated at a very high temperature until it has melted. The chemical nature of this FCM has been the subject of some research. The amount of fuel left in this form within the plant has been considered. A silicone polymer has been used to fix the contamination.
The Chernobyl melt was a silicate melt which did contain inclusions of Zr/U phases, molten steel and high uranium zirconium silicate. The lava flow consists of more than one type of material—a brown lava and a porous ceramic material have been found.
The uranium to zirconium for different parts of the solid differs a lot, in the brown lava a uranium rich phase with a U:Zr ratio of 19:3 to about 38:10 is found. The uranium poor phase in the brown lava has a U:Zr ratio of about 1:10. It is possible from the examination of the Zr/U phases to know the thermal history of the mixture. It can be shown that before the explosion that in part of the core the temperature was higher than 2000 °C, while in some areas the temperature was over 2400–2600 °C. | 0 | Theoretical and Fundamental Chemistry |
Journal of Molecular Structure is a scientific journal published by Elsevier ScienceDirect since 1968. Its articles discuss molecular structure in chemistry.
After the 2022 Russian invasion of Ukraine it said that it would no longer consider manuscripts written by scientists at Russian institutions. Rui Fausto, the journal's editor and a chemist at the University of Coimbra in Portugal, said: "Our decision will be in force until international legality is restored." | 0 | Theoretical and Fundamental Chemistry |
In a solid, inelastic scattering events also contribute to the photoemission process, generating electron-hole pairs which show up as an inelastic tail on the high BE side of the main photoemission peak. In fact this allows the calculation of electron inelastic mean free path (IMFP). This can be modeled based on the Beer–Lambert law, which states
where is the IMFP and is the axis perpendicular to the sample. In fact it is generally the case that the IMFP is only weakly material dependent, but rather strongly dependent on the photoelectron kinetic energy. Quantitatively we can relate to IMFP by
where is the mean atomic diameter as calculated by the density so . The above formula was developed by Seah and Dench. | 0 | Theoretical and Fundamental Chemistry |
Another difference between eukaryotes and prokaryotes is mRNA transport. Because eukaryotic transcription and translation is compartmentally separated, eukaryotic mRNAs must be exported from the nucleus to the cytoplasm—a process that may be regulated by different signaling pathways. Mature mRNAs are recognized by their processed modifications and then exported through the nuclear pore by binding to the cap-binding proteins CBP20 and CBP80, as well as the transcription/export complex (TREX). Multiple mRNA export pathways have been identified in eukaryotes.
In spatially complex cells, some mRNAs are transported to particular subcellular destinations. In mature neurons, certain mRNA are transported from the soma to dendrites. One site of mRNA translation is at polyribosomes selectively localized beneath synapses. The mRNA for Arc/Arg3.1 is induced by synaptic activity and localizes selectively near active synapses based on signals generated by NMDA receptors. Other mRNAs also move into dendrites in response to external stimuli, such as β-actin mRNA. For export from the nucleus, actin mRNA associates with ZBP1 and later with 40S subunit. The complex is bound by a motor protein and is transported to the target location (neurite extension) along the cytoskeleton. Eventually ZBP1 is phosphorylated by Src in order for translation to be initiated. In developing neurons, mRNAs are also transported into growing axons and especially growth cones. Many mRNAs are marked with so-called "zip codes", which target their transport to a specific location. mRNAs can also transfer between mammalian cells through structures called tunneling nanotubes. | 1 | Applied and Interdisciplinary Chemistry |
Robert W. Bussard (August 11, 1928 – October 6, 2007) was an American physicist who worked primarily in nuclear fusion energy research. He was the recipient of the Schreiber-Spence Achievement Award for STAIF-2004. He was also a fellow of the International Academy of Astronautics and held a Ph.D. from Princeton University. | 0 | Theoretical and Fundamental Chemistry |
A large number of currently prescribed drugs have been either directly derived from or inspired by natural products.
Some of the oldest natural product based drugs are analgesics. The bark of the willow tree has been known from antiquity to have pain relieving properties. This is due to presence of the natural product salicin which in turn may be hydrolyzed into salicylic acid. A synthetic derivative acetylsalicylic acid better known as aspirin is a widely used pain reliever. Its mechanism of action is inhibition of the cyclooxygenase (COX) enzyme. Another notable example is opium is extracted from the latex from Papaver somniferous (a flowering poppy plant). The most potent narcotic component of opium is the alkaloid morphine which acts as an opioid receptor agonist. A more recent example is the N-type calcium channel blocker ziconotide analgesic which is based on a cyclic peptide cone snail toxin (ω-conotoxin MVIIA) from the species Conus magus.
A significant number of anti-infectives are based on natural products. The first antibiotic to be discovered, penicillin, was isolated from the mold Penicillium. Penicillin and related beta lactams work by inhibiting DD-transpeptidase enzyme that is required by bacteria to cross link peptidoglycan to form the cell wall.
Several natural product drugs target tubulin, which is a component of the cytoskeleton. These include the tubulin polymerization inhibitor colchicine isolated from the Colchicum autumnale (autumn crocus flowering plant), which is used to treat gout. Colchicine is biosynthesized from the amino acids phenylalanine and tryptophan. Paclitaxel, in contrast, is a tubulin polymerization stabilizer and is used as a chemotherapeutic drug. Paclitaxel is based on the terpenoid natural product taxol, which is isolated from Taxus brevifolia (the pacific yew tree).
A class of drugs widely used to lower cholesterol are the HMG-CoA reductase inhibitors, for example atorvastatin. These were developed from mevastatin, a polyketide produced by the fungus Penicillium citrinum. Finally, a number natural product drugs are used to treat hypertension and congestive heart failure. These include the angiotensin-converting enzyme inhibitor captopril. Captopril is based on the peptidic bradykinin potentiating factor isolated from venom of the Brazilian arrowhead viper (Bothrops jararaca). | 1 | Applied and Interdisciplinary Chemistry |
A glacier can exert a sufficient amount of pressure on its lower surface to lower the melting point of its ice. The melting of the ice at the glacier's base allows it to move from a higher elevation to a lower elevation. Liquid water may flow from the base of a glacier at lower elevations when the temperature of the air is above the freezing point of water. | 0 | Theoretical and Fundamental Chemistry |
A rotor ship uses one or more Flettner rotors mounted upright. They are rotated by the ship's engines, and act like sails to propel the ship under wind power. A conventionally-powered underwater propeller may be provided for additional operational flexibility.
An early prototype, the Baden Baden (formerly the Buckau), crossed the Atlantic in 1925, but interest was not revived until energy saving became a major concern in the new millennium. The E-Ship 1 was launched in 2008, and new vessels continue to appear. Since then, multiple rotor installations have been completed, including tilting rotors to allow passage beneath bridges. Typically, rotor sails have been reported to generate 5-20% fuel savings. | 1 | Applied and Interdisciplinary Chemistry |
Cicadia wings have a surface of hexagonally close packed nanopillars that have been shown to have self-cleaning properties. Similarly templated nanopatterned silica arrays have been shown to have hydrophobic, anti-reflective, and self-cleaning properties. These silica arrays begin as non-close packed monolayers, and are patterned in a series of etching steps involving chlorine and oxygen reactive ion etching, and a hydrofluoric acid wash. These properties have implicated that this surface pattern may prove to be useful in solar cell applications. Biomimetic materials based on the cicadia wing have also been made from polytetrafluoroethylene films with carbon/epoxy supports treated with argon and oxygen ion beams. A nanoimprint patterned surface based on the cicadia wings has been made by electrochemically templating and aluminum sheet with alumina oxide, and using this template to pattern a polymer surface. | 0 | Theoretical and Fundamental Chemistry |
Stamp sand is a coarse sand left over from the processing of ore in a stamp mill. In the United States, the most well-known deposits of stamp sand are in the Copper Country of northern Michigan, where it is black or dark gray, and may contain hazardous concentrations of trace metals.
In the 19th and early 20th centuries, many metal mines used stamp mills to process ore-bearing rock. The rock was brought to a stamp mill to be crushed. After crushing the material was mechanically separated to extract metals, or chemically treated by acids if the metal could be leached out. The size of the crushed material depended on the nature of the ore found in each mining district. | 1 | Applied and Interdisciplinary Chemistry |
The choice of aryl halide or pseudohalide substrate (sp-carbon) is one of the factors that mainly influence the reactivity of the Sonogashira catalytic system. The reactivity of halides is higher towards iodine, and vinyl halides are more reactive than analogous aryl halides. The coupling of aryl iodides proceeds at room temperature, while aryl bromides require heating.
This difference in reactivity can be exploited to selectively couple an aryl iodide but not an aryl bromide, by performing the reaction at room temperature. An example is the symmetrical Sonogashira coupling of two equivalents of 1-bromo-4-iodobenzene with trimethylsilylacetylene (with the trimethylsilyl group removed in-situ) to form bis(4-bromophenyl)acetylene.
Aryl triflates can also be employed instead of aryl halides. | 0 | Theoretical and Fundamental Chemistry |
GTPases are enzymes capable of binding and hydrolyzing guanosine triphosphate (GTP). Small GTPases, such as Ran and Ras, can exist in either a GTP-bound form (active) or a GDP-bound form (inactive), and the conversion between these two forms grants them a switch-like behavior. As such, small GTPases are involved in multiple cellular events, including nuclear translocation and signaling. The transition between the active and inactive states is facilitated by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs).
Computational studies on the switching behavior of GTPases have revealed that the GTPase-GAP-GEF system displays ultrasensitivity. In their study, Lipshtat et al. simulated the effects of the levels of GEF and GAP activation on the Rap activation signaling network in response to signals from activated α2-adrenergic (α2R) receptors, which lead to degradation of the activated Rap GAP. They found that the switching behavior of Rap activation was ultrasensitive to changes in the concentration (i.e. amplitude) and the duration of the α2R signal, yielding Hill coefficients of nH=2.9 and nH=1.7, respectively (a Hill coefficient greater than nH=1 is characteristic of ultrasensitivity ). The authors confirmed this experimentally by treating neuroblasts with HU-210, which activates RAP through degradation of Rap GAP. Ultrasensitivity was observed both in a dose-dependent manner (nH=5±0.2), by treating cells with different HU-210 concentrations for a fixed time, and in a duration-dependent manner (nH=8.6±0.8), by treating cells with a fixed HU-210 concentration during varying times.
By further studying system, the authors determined that (the degree of responsiveness and ultrasensitivity) was heavily dependent on two parameters: the initial ratio of , where the k's incorporate both the concentration of active GAP or GEF and their corresponding kinetic rates; and the signal impact, which is the product of the degradation rate of activated GAP and either the signal amplitude or the signal duration. The parameter affects the steepness of the transition from the two states of the GTPase switch, with higher values (~10) leading to ultrasensitivity. The signal impact affects the switching point. Therefore, by depending on the ratio of concentrations rather than on individual concentrations, the switch-like behavior of the system can also be displayed outside of the zero-order regime. | 1 | Applied and Interdisciplinary Chemistry |
Lupeol has a complex pharmacology, displaying antiprotozoal, antimicrobial, antiinflammatory, antitumor and chemopreventive properties.
Animal models suggest lupeol may act as an anti-inflammatory agent. A 1998 study found lupeol to decrease paw swelling in rats by 39%, compared to 35% for the standardized control compound indomethacin.
One study has also found some activity as a Dipeptidyl peptidase-4 inhibitor and prolyl oligopeptidase inhibitor at high concentrations (in the millimolar range).
It is an effective inhibitor in laboratory models of prostate and skin cancers.
As an anti-inflammatory agent, lupeol functions primarily on the interleukin system. Lupeol to decreases IL-4 (interleukin 4) production by T-helper type 2 cells.
Lupeol has been found to have a contraceptive effect due to its inhibiting effect on the calcium channel of sperm (CatSper).
Lupeol has also been shown to exert anti-angiogenic and anti-cancer effects via the downregulation of TNF-alpha and VEGFR-2.
Famous anti-inflammatory ethno-medicinal plant Camellia japonica contains anti-inflammatory component lupeol in its leaf. | 0 | Theoretical and Fundamental Chemistry |
The biosynthesis of benzoxazinone, a cyclic hydroxamate and a natural insecticide, has been well-characterized in maize and related grass species. In maize, genes in the pathway are named using the symbol bx. Maize Bx-genes are tightly linked, a feature that has been considered uncommon for plant genes of a biosynthetic pathways. Especially notable are genes encoding the different enzymatic functions BX1, BX2 and BX8 and which are found within about 50 kilobases. Results from wheat and rye indicate that the cluster is an ancient feature. In wheat the cluster is split into two parts. The wheat genes Bx1 and Bx2 are located in close proximity on chromosome 4 and wheat Bx3, Bx4 and Bx5 map to the short arm of chromosome 5; an additional Bx3 copy was detected on the long arm of chromosome 5B. Recently, additional biosynthetic clusters have been detected in other plants for other biosynthetic pathways and this organization might be common in plants. | 1 | Applied and Interdisciplinary Chemistry |
Based on mammalian median lethal dose (LD) rating of 2,660 mg/kg body mass, boric acid is only poisonous if taken internally or inhaled in large quantities. The Fourteenth Edition of the Merck Index indicates that the LD of boric acid is 5.14 g/kg for oral dosages given to rats, and that 5 to 20 g/kg has produced death in adult humans. For a 70 kg adult, at the lower 5 g/kg limit, 350 g could produce death in humans. For comparisons sake, the LD of salt is reported to be 3.75 g/kg in rats according to the Merck Index'. According to the Agency for Toxic Substances and Disease Registry, "The minimal lethal dose of ingested boron (as boric acid) was reported to be 2–3 g in infants, 5–6 g in children, and 15–20 g in adults. [...] However, a review of 784 human poisonings with boric acid (10–88 g) reported no fatalities, with 88% of cases being asymptomatic."
Long-term exposure to boric acid may be of more concern, causing kidney damage and eventually kidney failure (see links below). Although it does not appear to be carcinogenic, studies in dogs have reported testicular atrophy after exposure to 32 mg/(kg⋅day) for 90 days. This level, were it applicable to humans at like dose, would equate to a cumulative dose of 202 g over 90 days for a 70 kg adult, not far lower than the above LD.
According to the CLH report for boric acid published by the Bureau for Chemical Substances Lodz, Poland, boric acid in high doses shows significant developmental toxicity and teratogenicity in rabbit, rat, and mouse fetuses, as well as cardiovascular defects, skeletal variations, and mild kidney lesions. As a consequence in the 30th ATP to EU directive 67/548/EEC of August 2008, the European Commission decided to amend its classification as reprotoxic category 2 and to apply the risk phrases R60 (may impair fertility) and R61 (may cause harm to the unborn child).
At a 2010 European Diagnostics Manufacturing Association (EDMA) Meeting, several new additions to the substance of very high concern (SVHC) candidate list in relation to the Registration, Evaluation, Authorisation and Restriction of Chemicals Regulations 2007 (REACH) were discussed. Following the registration and review completed as part of REACH, the classification of boric acid CAS 10043-35-3 / 11113-50-1 is listed from 1 December 2010 is H360FD (May damage fertility. May damage the unborn child). | 0 | Theoretical and Fundamental Chemistry |
The cristae greatly increase the surface area of the inner membrane on which the above-mentioned reactions may take place. A widely accepted hypothesis for the function of the cristae is that the high surface area allows an increased capacity for ATP generation. However, the current model is that active ATP synthase complexes localize preferentially in dimers to the narrow edges of the cristae. Thus, the surface area of mitochondrial membranes allocated to ATP syntheses is actually quite modest.
Mathematical modelling suggested that the optical properties of the cristae in filamentous mitochondria may affect the generation and propagation of light within the tissue. | 1 | Applied and Interdisciplinary Chemistry |
The AFM can be used to image and manipulate atoms and structures on a variety of surfaces. The atom at the apex of the tip "senses" individual atoms on the underlying surface when it forms incipient chemical bonds with each atom. Because these chemical interactions subtly alter the tips vibration frequency, they can be detected and mapped. This principle was used to distinguish between atoms of silicon, tin and lead on an alloy surface, by comparing these "atomic fingerprints" with values obtained from density functional theory (DFT) simulations.
The trick is to first measure these forces precisely for each type of atom expected in the sample, and then to compare with forces given by DFT simulations. The team found that the tip interacted most strongly with silicon atoms, and interacted 24% and 41% less strongly with tin and lead atoms, respectively. Thus, each different type of atom can be identified in the matrix as the tip is moved across the surface. | 0 | Theoretical and Fundamental Chemistry |
In heap leaching processes, crushed (and sometimes agglomerated) ore is piled in a heap which is lined with an impervious layer. Leach solution is sprayed over the top of the heap, and allowed to percolate downward through the heap. The heap design usually incorporates collection sumps, which allow the "pregnant" leach solution (i.e. solution with dissolved valuable metals) to be pumped for further processing. An example is gold cyanidation, where pulverized ores are extracted with a solution of sodium cyanide, which, in the presence of air, dissolves the gold, leaving behind the nonprecious residue. | 1 | Applied and Interdisciplinary Chemistry |
In in vivo systems it is often used to quantify the binding of a test molecule to the binding site of radioligand. The higher the affinity of the molecule the more radioligand is displaced from the binding site and the increasing radioactive decay can be measured by scintillography. This assay is commonly used to calculate binding constant of molecules to receptors. Due to the probable injuries of PET-radiotracers, they could not be administered in the normal doses of the medications. Therefore, the binding affinity (P) of the PET-tracers must be high. In addition, since via the PET imaging technique is desired to investigate a function accurately, the selectivity of bindings to the specific targets is very important. | 1 | Applied and Interdisciplinary Chemistry |
William Crookes was born in London in 1832, the eldest of eight surviving children (eight others died young) of Joseph Crookes (1792–1889), a wealthy tailor and real estate investor of north-country origin, and his second wife, Mary (née Scott; 1806–1884). Joseph Crookes's father, William (1734-–814), was also a tailor, and his grandfather, John Crookes (b. 1660), had been Mayor of Hartlepool, County Durham on three occasions.
Joseph Crookes had had five children with his first wife; two sons from that marriage, Joseph and Alfred, took over the tailoring business, leaving William free to choose his own path. In 1848, at age 16, Crookes entered the Royal College of Chemistry (now the Imperial College chemistry department) to study organic chemistry. Crookes lived with his parents about three miles from the College in Oxford Street. His fathers shop was about half a mile away. Crookes paid £25 for his first years tuition and had to provide his own apparatus and some of the more expensive chemicals. At the end of his first year, Crookes won the Ashburton scholarship which covered his second year's tuition. At the end of his second year, Crookes became a junior assistant to August Wilhelm von Hofmann, doing laboratory demonstrations and helping with research and commercial analysis. In October 1851, Crookes was promoted to senior assistant, a position he held until 1854.
Although Crookes revered Hofmann, he did not share his primary interest in organic chemistry.
One of Crookes's students was the Reverend John Barlow, Secretary of the Royal Institution, who chose to take a course in analytical chemistry. Through Barlow, Crookes met scientists such as George Gabriel Stokes and Michael Faraday.
Such friends reinforced Crookes's interest in optical physics which was respected by Hofmann.
By 1851, Crookes's interest in photography and optics caused his father to build him a laboratory in the garden at home for his research.
When Crookes embarked upon original work, it wasn't in organic chemistry, but rather into new compounds of selenium. These were the subject of his first published papers, in 1851. He worked with Manuel Johnson at the Radcliffe Observatory in Oxford in 1854, where he adapted the recent innovation of wax paper photography to machines built by Francis Ronalds to continuously record meteorological parameters. In 1855 he was appointed lecturer in chemistry at the Chester Diocesan Training College.
In April 1856 Crookes married Ellen, daughter of William Humphrey of Darlington. Since staff at Chester were required to be bachelors, he had to resign his position. Williams father, Joseph Crookes, gave the couple a house at 15 Stanley Street, Brompton. Ellens mother, Mrs. Humphrey, lived with them for the rest of her life, nearly forty years. A devoted couple, William and Ellen Crookes had six sons and three daughters. Their first child, Alice Mary (born 1857, later Mrs. Cowland) remained unmarried for forty years, living with her parents and working as an assistant to her father. Two of Crookes's sons became engineers, and two lawyers.
Married and living in London, Crookes sought to support his new family through independent work as a photographic chemist. In 1859, he founded the Chemical News, a science magazine which he edited for many years and conducted on much less formal lines than was usual for the journals of scientific societies. Between 1864 and 1869, he was also involved with the Quarterly Journal of Science. At various times he edited the Journal of the Photographic Society and the Photographic News. | 1 | Applied and Interdisciplinary Chemistry |
Dithionite () can also be used as a reductant. It is usually used in addition to iron reduce contaminants. A number of reactions take place and eventually the contaminant is removed. In the process, ditionite is consumed and the final product of all the reactions is 2 sulfur dioxide anions. The dithionite is not stable for a long period of time. | 1 | Applied and Interdisciplinary Chemistry |
The ion vibration current (IVI) and the associated ion vibration potential is an electric signal that arises when an acoustic wave propagates through a homogeneous fluid.
Historically, the IVI was the first known electroacoustic phenomenon. It was predicted by Peter Debye in 1933.
When a longitudinal sound wave travels through a solvent, the associated pressure gradients push the fluid particles back and forth, and it is easy in practice to create such accelerations that measure thousands or millions of gs. If a solute molecule is more dense or less dense than the surrounding liquid, then in this accelerating environment, the molecule will move relative to the surrounding liquid. This relative motion is essentially the same phenomenon that occurs in a centrifuge, or more simply, it is essentially the same phenomenon that occurs when low-density objects float to the top of a glass of water, and high-density particles sink to the bottom (see the equivalence principle, which states that gravity is just like any other acceleration). The amount of relative motion depends on the balance between the molecules effective mass (which includes both the mass of the molecule itself and any solvent molecules that are so tightly bound to the molecule that they follow along with the molecule's motion), its effective volume (related to buoyant force), and the viscous drag (friction) between the molecule and the surrounding fluid.
IVI concerns the case where the particles in question are anions and cations. In general, they will have different amounts of motion relative to the fluid during the sound wave oscillations, and that discrepancy creates an alternating electric potential between various points in a sound wave.
This effect was extensively used in the 1950s and 1960s for characterizing ion solvation. These works are mostly associated with the names of Zana and Yaeger, who published a review of their studies in 1982.
This effect can be studied with modern devices that employ electroacoustics for studying zeta potential, as described in the book. | 0 | Theoretical and Fundamental Chemistry |
Degenerate matter occurs when the Pauli exclusion principle significantly alters a state of matter at low temperature. The term is used in astrophysics to refer to dense stellar objects such as white dwarfs and neutron stars, where thermal pressure alone is not enough to avoid gravitational collapse. The term also applies to metals in the Fermi gas approximation.
Degenerate matter is usually modelled as an ideal Fermi gas, an ensemble of non-interacting fermions. In a quantum mechanical description, particles limited to a finite volume may take only a discrete set of energies, called quantum states. The Pauli exclusion principle prevents identical fermions from occupying the same quantum state. At lowest total energy (when the thermal energy of the particles is negligible), all the lowest energy quantum states are filled. This state is referred to as full degeneracy. This degeneracy pressure remains non-zero even at absolute zero temperature. Adding particles or reducing the volume forces the particles into higher-energy quantum states. In this situation, a compression force is required, and is made manifest as a resisting pressure. The key feature is that this degeneracy pressure does not depend on the temperature but only on the density of the fermions. Degeneracy pressure keeps dense stars in equilibrium, independent of the thermal structure of the star.
A degenerate mass whose fermions have velocities close to the speed of light (particle kinetic energy larger than its rest mass energy) is called relativistic degenerate matter.
The concept of degenerate stars, stellar objects composed of degenerate matter, was originally developed in a joint effort between Arthur Eddington, Ralph Fowler and Arthur Milne. Eddington had suggested that the atoms in Sirius B were almost completely ionised and closely packed. Fowler described white dwarfs as composed of a gas of particles that became degenerate at low temperature; he also pointed out that ordinary atoms broadly similar in regards to the filling of energy levels by fermions. Milne proposed that degenerate matter is found in most of the nuclei of stars, not only in compact stars. | 0 | Theoretical and Fundamental Chemistry |
DNA repair genes are frequently repressed in cancers due to hypermethylation of CpG islands within their promoters. In head and neck squamous cell carcinomas at least 15 DNA repair genes have frequently hypermethylated promoters; these genes are XRCC1, MLH3, PMS1, RAD51B, XRCC3, RAD54B, BRCA1, SHFM1, GEN1, FANCE, FAAP20, SPRTN, SETMAR, HUS1, and PER1. About seventeen types of cancer are frequently deficient in one or more DNA repair genes due to hypermethylation of their promoters. As summarized in one review article, promoter hypermethylation of the DNA repair gene MGMT occurs in 93% of bladder cancers, 88% of stomach cancers, 74% of thyroid cancers, 40%-90% of colorectal cancers and 50% of brain cancers. Promoter hypermethylation of LIG4 occurs in 82% of colorectal cancers. This review article also indicates promoter hypermethylation of NEIL1 occurs in 62% of head and neck cancers and in 42% of non-small-cell lung cancers; promoter hypermetylation of ATM occurs in 47% of non-small-cell lung cancers; promoter hypermethylation of MLH1 occurs in 48% of squamous cell carcinomas; and promoter hypermethylation of FANCB occurs in 46% of head and neck cancers.
On the other hand, the promoters of two genes, PARP1 and FEN1, were hypomethylated and these genes were over-expressed in numerous cancers. PARP1 and FEN1 are essential genes in the error-prone and mutagenic DNA repair pathway microhomology-mediated end joining. If this pathway is over-expressed, the excess mutations it causes can lead to cancer. PARP1 is over-expressed in tyrosine kinase-activated leukemias, in neuroblastoma, in testicular and other germ cell tumors, and in Ewing's sarcoma, FEN1 is over-expressed in the majority of cancers of the breast, prostate, stomach, neuroblastomas, pancreatic, and lung.
DNA damage appears to be the primary underlying cause of cancer. If accurate DNA repair is deficient, DNA damages tend to accumulate. Such excess DNA damage can increase mutational errors during DNA replication due to error-prone translesion synthesis. Excess DNA damage can also increase epigenetic alterations due to errors during DNA repair. Such mutations and epigenetic alterations can give rise to cancer (see malignant neoplasms). Thus, CpG island hyper/hypo-methylation in the promoters of DNA repair genes are likely central to progression to cancer. | 1 | Applied and Interdisciplinary Chemistry |
August 2023 research, drawing from 176 flux stations globally, reveals a climate trade-off: increased carbon uptake from afforestation results in reduced albedo. Initially, this reduction may lead to moderate global warming over a span of approximately 20 years, but it is expected to transition into significant cooling thereafter. | 0 | Theoretical and Fundamental Chemistry |
One of the largest application areas is thin films, which can be produced on a piece of substrate by spin coating or dip-coating. Protective and decorative coatings, and electro-optic components can be applied to glass, metal and other types of substrates with these methods. Cast into a mold, and with further drying and heat-treatment, dense ceramic or glass articles with novel properties can be formed that cannot be created by any other method. Other coating methods include spraying, electrophoresis, inkjet printing, or roll coating. | 0 | Theoretical and Fundamental Chemistry |
Another important property which can be deduced from the stress strain curve is the energy that the foam is able to absorb. The area under the curve (specified to be before rapid densification at the peak stress), represents the energy in the foam in units of energy per unit volume. The maximum energy stored by the foam prior to rupture is described by the equation:
This equation is derived from assuming an idealized foam with engineering approximations from experimental results. Most energy absorption occurs at the plateau stress region after the steep linear elastic regime. | 0 | Theoretical and Fundamental Chemistry |
Acetone is fragmented in two different groups, one carbonyl group and two methyl groups. For the critical volume the following calculation results:
V = 40 + 60.0 + 2 * 55.0 = 210 cm
In the literature (such as in the Dortmund Data Bank) the values 215.90 cm, 230.5 cm and 209.0 cm are published. | 0 | Theoretical and Fundamental Chemistry |
A medical isotope is an isotope used in medicine.
The first uses of isotopes in medicine were in radiopharmaceuticals, and this is still the most common use. However more recently, separated stable isotopes have also come into use.
Examples of non-radioactive medical isotopes are:
* Deuterium in deuterated drugs
* Carbon-13 used in liver function and metabolic tests | 1 | Applied and Interdisciplinary Chemistry |
Other methods of laser cooling include:
* Sisyphus cooling
* Resolved sideband cooling
* Raman sideband cooling
* Velocity selective coherent population trapping (VSCPT)
* Gray molasses
* Optical molasses
* Cavity-mediated cooling
* Use of a Zeeman slower
* Electromagnetically induced transparency (EIT) cooling
* Anti-Stokes cooling in solids
* Polarization gradient cooling | 0 | Theoretical and Fundamental Chemistry |
There are many proteins capable of binding to glycans, including lectins, antibodies, microbial adhesins, viral agglutinins, etc. | 1 | Applied and Interdisciplinary Chemistry |
A depsipeptide is a peptide in which one or more of its amide, -C(O)NHR-, groups are replaced by the corresponding ester, -C(O)OR-. Many depsipeptides have both peptide and ester linkages. Elimination of the N–H group in a peptide structure results in a decrease of H-bonding capability, which is responsible for secondary structure and folding patterns of peptides, thus inducing structural deformation of the helix and β-sheet structures. Because of decreased resonance delocalization in esters relative to amides, depsipeptides have lower rotational barriers for cis-trans isomerization and therefore they have more flexible structures than their native analogs. They are mainly found in marine and microbial natural products. | 1 | Applied and Interdisciplinary Chemistry |
The majority of eukaryotic genes are transcribed by RNA polymerase II, proceeding in the 5 to 3 direction. In eukaryotes, specific subunits within the RNA polymerase II complex allow it to carry out multiple functions. General transcription factors help binding RNA polymerase II to DNA. Promoters are cites where RNA polymerase II binds to start transcription and, in eukaryotes, transcription starting point is positioned at +1 nucleotide. Like all RNA polymerases, it travels along the template DNA, in the 3 to 5 direction and synthesizes a new RNA strand in the 5 to 3 direction, by adding new bases to the 3' end of the new RNA. A transcription bubble occurs as a result of the double stranded DNA unwinding. After about 25 base pairs of the DNA double strand are unwound, RNA synthesis takes place within the transcription bubble region. Supercoiling is also part of this process since DNA regions in front of the RNA polymerase II are unwinding, while DNA regions behind it are rewinding, forming a double helix again.
The RNA polymerase carries out the majority of the steps during the transcription cycle, especially in maintaining the transcription bubble open for the complementary base pairing. There are some steps of the transcription cycle that require more proteins, such as the Rpb4/7 complex and the RNA polymerase attached to the elongation factor transcription factor IIS (TFIIS). | 1 | Applied and Interdisciplinary Chemistry |
In elution mode, solutes are applied to the column as narrow bands and, at low concentration, move down the column as approximately Gaussian peaks. These peaks continue to broaden as they travel, in proportion to the square root of the distance traveled. For two substances to be resolved, they must migrate down the column at sufficiently different rates to overcome the effects of band spreading. Operating at high concentration, where the isotherm is curved, is disadvantageous in elution chromatography because the rate of travel then depends on concentration, causing the peaks to spread and distort.
Retention in elution chromatography is usually controlled by adjusting the composition of the mobile phase (in terms of solvent composition, pH, ionic strength, and so forth) according to the type of stationary phase employed and the particular solutes to be separated. The mobile phase components generally have lower affinity for the stationary phase than do the solutes being separated, but are present at higher concentration and achieve their effects due to mass action. Resolution in elution chromatography is generally better when peaks are strongly retained, but conditions that give good resolution of early peaks lead to long run-times and excessive broadening of later peaks unless gradient elution is employed. Gradient equipment adds complexity and expense, particularly at large scale. | 0 | Theoretical and Fundamental Chemistry |
Scintillons are small structures in cytoplasm that produce light. Among bioluminescent organisms, only dinoflagellates have scintillons. | 1 | Applied and Interdisciplinary Chemistry |
Pigmentation patterns provide one of the most striking and easily scored differences between different species of animals. Pigmentation of the Drosophila wing has proven to be a particularly amenable system for studying the development of complex pigmentation phenotypes. The Drosophila guttifera wing has 12 dark pigmentation spots and 4 lighter gray intervein patches. Pigment spots arise from expression of the yellow gene, whose product produces black melanin. Recent work has shown that two enhancers in the yellow gene produce gene expression in precisely this pattern – the vein spot enhancer drives reporter gene expression in the 12 spots, and the intervein shade enhancer drives reporter expression in the 4 distinct patches. These two enhancers are responsive to the Wnt signaling pathway, which is activated by wingless expression at all of the pigmented locations. Thus, in the evolution of the complex pigmentation phenotype, the yellow pigment gene evolved enhancers responsive to the wingless signal and wingless expression evolved at new locations to produce novel wing patterns. | 1 | Applied and Interdisciplinary Chemistry |
Deterministic theories can be divided into two subgroups: if the initial chiral influence took place in a specific space or time location (averaging zero over large enough areas of observation or periods of time), the theory is classified as local deterministic; if the chiral influence is permanent at the time the chiral selection occurred, then it is classified as universal deterministic. The classification groups for local determinist theories and theories based on chance mechanisms can overlap. Even if an external chiral influence produced the initial chiral imbalance in a deterministic way, the outcome sign could be random since the external chiral influence has its enantiomeric counterpart elsewhere.
In deterministic theories, the enantiomeric imbalance is created due to an external chiral field or influence, and the ultimate sign imprinted in biomolecules will be due to it. Deterministic mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the electroweak interaction (via cosmic rays) or asymmetric environments, such as those caused by circularly polarized light, quartz crystals, or the Earth's rotation, β-Radiolysis or the magnetochiral effect. The most accepted universal deterministic theory is the electroweak interaction. Once established, chirality would be selected for.
One supposition is that the discovery of an enantiomeric imbalance in molecules in the Murchison meteorite supports an extraterrestrial origin of homochirality: there is evidence for the existence of circularly polarized light originating from Mie scattering on aligned interstellar dust particles which may trigger the formation of an enantiomeric excess within chiral material in space. Interstellar and near-stellar magnetic fields can align dust particles in this fashion. Another speculation (the Vester-Ulbricht hypothesis) suggests that fundamental chirality of physical processes such as that of the beta decay (see Parity violation) leads to slightly different half-lives of biologically relevant molecules. | 0 | Theoretical and Fundamental Chemistry |
The abstract definition of chemical potential given above—total change in free energy per extra mole of substance—is more specifically called total chemical potential. If two locations have different total chemical potentials for a species, some of it may be due to potentials associated with "external" force fields (electric potential energy, gravitational potential energy, etc.), while the rest would be due to "internal" factors (density, temperature, etc.) Therefore, the total chemical potential can be split into internal chemical potential and external chemical potential:
where
i.e., the external potential is the sum of electric potential, gravitational potential, etc. (where q and m are the charge and mass of the species, V and h are the electric potential and height of the container, respectively, and g is the acceleration due to gravity). The internal chemical potential includes everything else besides the external potentials, such as density, temperature, and enthalpy. This formalism can be understood by assuming that the total energy of a system, , is the sum of two parts: an internal energy, , and an external energy due to the interaction of each particle with an external field, . The definition of chemical potential applied to yields the above expression for .
The phrase "chemical potential" sometimes means "total chemical potential", but that is not universal. In some fields, in particular electrochemistry, semiconductor physics, and solid-state physics, the term "chemical potential" means internal chemical potential, while the term electrochemical potential is used to mean total chemical potential. | 0 | Theoretical and Fundamental Chemistry |
The F number is calculated using the formula:
where:
: B is the number of double bonds
: C is the number of primary carbon and secondary carbon atoms
: R is the number of non-aromatic rings. | 0 | Theoretical and Fundamental Chemistry |
is a computer program that simulates inundation for rivers, flood plains and urban drainage systems. It dynamically couples 1D (MIKE 11 and Mouse) and 2D (MIKE 21) modeling techniques into one single tool. MIKE FLOOD is developed by DHI.
MIKE FLOOD is accepted by US Federal Emergency Management Agency (FEMA) for use in the National Flood Insurance Program (NFIP).
MIKE FLOOD can be expanded with a range of modules and methods including a flexible mesh overland flow solver, MIKE URBAN, Rainfall-runoff modeling and dynamic operation of structures. | 1 | Applied and Interdisciplinary Chemistry |
In theory, any complexation reaction can be used as a volumetric technique provided that:
# The reaction reaches equilibrium rapidly after each portion of titrant is added.
# Interfering situations do not arise. For instance, the stepwise formation of several different complexes of the metal ion with the titrant, resulting in the presence of more than one complex in solution during the titration process.
# A complexometric indicator capable of locating equivalence point with fair accuracy is available.
In practice, the use of EDTA as a titrant is well established. | 0 | Theoretical and Fundamental Chemistry |
Drug development is the process of bringing a new drug to the market once a lead compound has been identified through the process of drug discovery. It includes pre-clinical research (microorganisms/animals) and clinical trials (on humans) and may include the step of obtaining regulatory approval to market the drug.
[https://www.fda.gov/patients/learn-about-drug-and-device-approvals/drug-development-process Drug Development Process]
Discovery: The Drug Development process starts with Discovery, a process of identifying a new medicine.
Development: Chemicals extracted from natural products are used to make pills, capsules, or syrups for oral use. Injections for direct infusion into the blood drops for eyes or ears.
Preclinical research: Drugs go under laboratory or animal testing, to ensure that they can be used on Humans.
Clinical testing: The drug is used on people to confirm that it is safe to use.
FDA Review: drug is sent to FDA before launching the drug into the market.
FDA post-Market Review: The drug is reviewed and monitored by FDA for the safety once it is available to the public. | 1 | Applied and Interdisciplinary Chemistry |
Showy Indian clover, Trifolium amoenum, is an example of a species that was thought to be extinct, but was rediscovered in 1993 in the form of a single plant at a site in western Sonoma County. Seeds were harvested and the species grown in ex situ facilities.
The Wollemi pine is another example of a plant that is being preserved via ex situ conservation, as they are being grown in nurseries to be sold to the general public.
The Orange-bellied parrot, with a wild population of 14 birds as of early February 2017, are being bred in a captive breeding program. The captive population consists of around 300 birds. | 1 | Applied and Interdisciplinary Chemistry |
The oldest known blast furnaces in the West were built in Durstel in Switzerland, the Märkische Sauerland in Germany, and at Lapphyttan in Sweden, where the complex was active between 1205 and 1300. At Noraskog in the Swedish parish of Järnboås, traces of even earlier blast furnaces have been found, possibly from around 1100. These early blast furnaces, like the Chinese examples, were very inefficient compared to those used today. The iron from the Lapphyttan complex was used to produce balls of wrought iron known as osmonds, and these were traded internationally – a possible reference occurs in a treaty with Novgorod from 1203 and several certain references in accounts of English customs from the 1250s and 1320s. Other furnaces of the 13th to 15th centuries have been identified in Westphalia.
The technology required for blast furnaces may have either been transferred from China, or may have been an indigenous innovation. Al-Qazvini in the 13th century and other travellers subsequently noted an iron industry in the Alburz Mountains to the south of the Caspian Sea. This is close to the silk route, so that the use of technology derived from China is conceivable. Much later descriptions record blast furnaces about three metres high. As the Varangian Rus' people from Scandinavia traded with the Caspian (using their Volga trade route), it is possible that the technology reached Sweden by this means. The Vikings are known to have used double bellows, which greatly increases the volumetric flow of the blast.
The Caspian region may also have been the source for the design of the furnace at Ferriere, described by Filarete, involving a water-powered bellows at Semogo in Valdidentro in northern Italy in 1226. In a two-stage process the molten iron was tapped twice a day into water, thereby granulating it. | 1 | Applied and Interdisciplinary Chemistry |
APDS monitors air and water for the three types of biological threat agents: bacteria, viruses, and toxins. The autonomous detection system is capable of (1) rapidly processing and accurately analyzing aerosol or water samples with a high level of confidence; (2) automating and integrating the major system functions into the detector, including sample collection, preparation, analysis, and analytical results reporting; (3) operating in its intended indoor and outdoor environments; and (4) disseminating and archiving analysis results and system operational data via the C3 network, known as the BioWatch Gen-3 Operations Support Service.
APDS operates continuously; the system can detect low concentrations of bioagents that might go undetected by a system that is triggered only when the overall number of particles in the air is high. APDS collects samples, prepares them for analysis, and tests for multiple biological agents. This automation reduces the cost and staffing that would be required to manually analyze samples.
As APDS collects air or water samples, it first runs them through an immunoassay detector. If that detector returns a positive result, APDS performs a second assay based on nucleic-acid amplification and detection. Having two different assay systems increases system reliability and minimizes the possibility of false positives.
The immunoassay detector incorporates liquid arrays, a multiplexed assay that uses small-diameter polystyrene beads (microbeads) coated with thousands of antibodies. Each microbead is colored with a unique combination of red- and orange-emitting dyes. The number of agents that can be detected in a sample is limited only by the number of colored bead sets. When the sample is exposed to the beads, a bioagent, if present, binds to the bead with the appropriate antibody. A second fluorescently labeled antibody is then added to the sample, resulting in a highly fluorescent target for flow analysis. Preparing the sample and performing this first analysis takes less than 30 minutes.
Nucleic acid assays require amplification of one or more target sequences of nucleic acid. Short strands of single-stranded DNA are synthesized in known sequences and attached to spots in the array in a predetermined way Detection of these spots that contain hybridized target DNA allows one to the sequence of DNA in the unknown target. RNA readily hybridizes to form double-stranded structures to its complementary sequence (A-T, C-G, G-C, U-A). Thus, arrays of single-stranded DNA can be used to detect RNA via hybridization.
TABLE 1.1 Centers for Disease Control and Prevention (CDC) Prioritized List of Biological Threat Agents
Research Internationals sells standalone and portable systems for use in mailrooms, called ASAP II. ASAP II gives real time detection of bio-warfare agents, chemical agents and toxic industrial chemicals, explosives in particulate and vapor form and nuclear materials. The system can be customised according to the need of the mailroom.
ASAP II is an automated chemical, biological and nuclear detection and identification system. The system can detect and identify from four (RAPTOR module) to eight (BioHawk module) bio-agents in real time. Periodically or on demand, a concentrated sample is sent to the modules and within fifteen minutes these systems will identify the presence of any bioagents and notify the operator if a hazardous agent is detected.
The systems need to be in a negative pressure room on a downward draft table. An air sampling module within the systems draws air into the downward draft table for analysis. Sampling is continuous until the batch of mail is complete, which may take a few minutes, hours or days. The systems are able to handle thousands of pieces of mail per hour. | 0 | Theoretical and Fundamental Chemistry |
Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (ground tissue) or chlorenchyma tissue called the mesophyll (Greek for "middle leaf"). This assimilation tissue is the primary location of photosynthesis in the plant. The products of photosynthesis are called "assimilates".
In ferns and most flowering plants, the mesophyll is divided into two layers:
* An upper palisade layer of vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis, with intercellular air spaces between them. Its cells contain many more chloroplasts than the spongy layer. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil are single-layered.
* Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more branched and not so tightly packed, so that there are large intercellular air spaces between them. The pores or stomata of the epidermis open into substomatal chambers, which are connected to the intercellular air spaces between the spongy and palisade mesophyll cell, so that oxygen, carbon dioxide and water vapor can diffuse into and out of the leaf and access the mesophyll cells during respiration, photosynthesis and transpiration.
Leaves are normally green, due to chlorophyll in chloroplasts in the mesophyll cells. Some plants have leaves of different colours due to the presence of accessory pigments such as carotenoids in their mesophyll cells. | 0 | Theoretical and Fundamental Chemistry |
TRH may cause nausea, vomiting and some patients experience an urge to urinate.
Rarely, TRH may cause blood vessel constriction leading to hemorrhage in patients with pre-existing pituitary tumors. Accordingly, patients should be advised about the risks, albeit rare, of TRH testing. | 1 | Applied and Interdisciplinary Chemistry |
Phenol extraction is a laboratory technique that purifies nucleic acid samples using a phenol solution. Phenol is common reagent in extraction because its properties allow for effective nucleic acid extraction, particularly as it strongly denatures proteins, it is a nucleic acid preservative, and it is immiscible in water.
It may also refer to the process of extracting and isolating phenols from raw materials such as coal tar. These purified phenols are used in many industrial and medical compounds and are used as precursors in some synthesis reactions. | 1 | Applied and Interdisciplinary Chemistry |
The idea of the International Chemistry Olympiad was developed in the former Czechoslovakia in 1968. It was designed with the aim to increase the number of international contacts and the exchange of information between nations. Invitations were sent by the Czechoslovak national committee to all Warsaw Pact countries, except Romania (due to political issues between Romania and USSR). However, in May 1968, relations between Czechoslovakia and the Soviet Union became so delicate that only Poland and Hungary participated in the first international competition.
The first International Chemistry Olympiad took place in Prague between 18 and 21 June 1968. Each of the three participating countries sent a team of six students, and four theoretical tasks were to be solved. Guidelines for the next competitions were already suggested. The second chemistry Olympiad took place in 1969 in Poland, and Bulgaria also participated, with USSR and GDR only sending observers. Each team consisted of five pupils, and an experimental competition was added. The decision was made to invite more socialist countries to future competitions and to limit the number of pupils to four. The third Olympiad in 1970 was organized in Hungary with the GDR, Romania and the Soviet Union as new countries. In this competition, more than three prizes were distributed for the first time.
There was no Olympiad held in 1971, as at the end of the competition in 1970, an organizer and host for the next event could not be agreed on. This was solved for the next three years by diplomatically agreeing on the Soviet Union to host 1972, Bulgaria in 1973, and Romania in 1974, starting the tradition to decide the host years in advance. 1972 was the first time where preparation tasks for the International Chemistry Olympiad were created. Also, at a jury session, it was suggested that invitations should be sent to Vietnam, Mongolia, and Cuba. Unfortunately though, these invitations were not sent, leaving seven to compete in 1973.
In 1974, Romania invited Sweden and Yugoslavia to the Olympiad in Bucharest and Germany and Austria sent observers. The Federal Republic of Germany was the first NATO-country with an observer present and this was only able to occur because the Brandt government had contracts in the East. Thus, in 1975, West Germany, Austria, and Belgium also participated in the International Chemistry Olympiad.
The first Olympiad in a non-socialist country took place 1980 in Linz in Austria, although the Soviet Union did not participate. Since then the number of the participating countries has increased steadily. In 1980, only 13 nations took part but this number increased to 21 by the 1984 Olympiad in Frankfurt/Main. With the fall of the Iron Curtain and the break-up of the Soviet Union into independent states in the early 1990s, the number of participants increased again. In addition, the increasing interest of Asian and Latin American countries became apparent with the numbers of participants. Altogether 47 delegations participated in 1998. Presently, 88 countries are invited to the International Chemistry Olympiads. | 1 | Applied and Interdisciplinary Chemistry |
Woods lamp is useful in diagnosing conditions such as tuberous sclerosis and erythrasma (caused by Corynebacterium minutissimum, see above). Additionally, detection of porphyria cutanea tarda can sometimes be made when urine turns pink upon illumination with Woods lamp. Woods lamps have also been used to differentiate hypopigmentation from depigmentation such as with vitiligo. A vitiligo patients skin will appear yellow-green or blue under the Wood's lamp. Its use in detecting melanoma has been reported. | 0 | Theoretical and Fundamental Chemistry |
An antichlor is a substance used to decompose residual hypochlorite or chlorine after chlorine-based bleaching, in order to prevent ongoing reactions with, and therefore damage to, the material that has been bleached. Sodium bisulfite is an example of an antichlor. Historically, sodium bisulfite has been used in the textile industry, cosmetic industry, food industry, and more.
Antichlors are very useful in the textile industry because bleaching of compounds using chlorine is a standard practice. However, the use of sodium bisulfite in the decomposition of excess hypochlorite can lead to harmful byproducts when it comes into contact with water at the concentrations present for industrial use. Contact with these dangerous byproducts or even strong concentrations of sodium bisulfite can be harmful to the environment and contact with the skin. Strong concentrations of these compounds can contaminate ecosystems, harm animals, and cause contact dermatitis with industrial workers. The concentrations that could result in these outcomes are much stronger than the concentrations discussed in the cosmetic and food industry. | 0 | Theoretical and Fundamental Chemistry |
Copper can be found in the active sites of most enzymes that catalyze redox reactions (i.e., oxidoreductases), as it facilitates single electron transfers while reversibly oscillating between the Cu and Cu redox states. Enzymes typically contain between one (mononuclear) and four (tetranuclear) copper centers, which enable enzymes to catalyze different reactions. These copper centers coordinate with different ligands depending on the Cu redox state. Oxidized Cu preferentially coordinates with "hard donor" ligands (e.g., N- or O-containing ligands such as histidine, aspartic acid, glutamic acid or tyrosine), while reduced Cu preferentially coordinates with "soft donor" ligands (e.g., S-containing ligands such as cysteine or methionine). Copper's powerful redox capability makes it critically important for biology, but comes at a cost: Cu is a highly toxic metal to cells because it readily abstracts single electrons from organic compounds and cellular material, leading to production of free radicals. Thus, cells have evolved specific strategies for carefully controlling the activity of Cu while exploiting its redox behavior. | 0 | Theoretical and Fundamental Chemistry |
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