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We consider a polymer as a chain of monomers, each with its position vector and scattering amplitude . For simplicity, it is worthwhile considering identical monomers in the chain, such that all .
An incoming ray (of light/neutrons/X-ray etc.) has a wave vector (or momentum) , and is scattered by the polymer to the vector . This enables us to define the scattering vector .
By coherently summing the contributions of all monomers, we get the scattering intensity from a single polymer, as a function of : | 0 | Theoretical and Fundamental Chemistry |
Saturated hydronitrogens can be:
* linear (general formula ) wherein the nitrogen atoms are joined in a snakelike structure
* branched (general formula , n > 3) wherein the nitrogen backbone splits off in one or more directions
* cyclic (general formula , n > 2) wherein the nitrogen backbone is linked so as to form a loop.
According to IUPAC definitions, the former two are azanes, whereas the third group is called cycloazanes. Saturated hydronitrogens can also combine any of the linear, cyclic (e.g. polycyclic), and branching structures, and they are still azanes (no general formula) as long as they are acyclic (i.e., having no loops). They also have single covalent bonds between their nitrogens. | 0 | Theoretical and Fundamental Chemistry |
Copper is a biologically important metal to detect. It has many sensors developed for it including:
*CTAP-1, a sensor that shows a response in the UV region when Cu(I) binds to an azatetrathiacrown motif that in turn excites a pyrazoline-based dye that is attached. To use the probe, one excites it at 365 nm. If it is bound to Cu, then it will increase its fluorescence intensity. CTAP-1 is effective as it has a large modulation in its spectrum upon binding Cu, and is selective for the binding of Cu over other metals.
*Coppersensor-1 (CS1) that comprises a thioether rich motif that binds to Cu(I) causing the excitation of a boron-dipyrromethene (BODIPY) dye in the visible region. The probe has good selectivity for Cu(I) over alkaline earth metals, Cu(II), and d-block metals. | 0 | Theoretical and Fundamental Chemistry |
Catalysts for artificial photosynthesis are expected to effect turn over numbers in the millions. Catalysts often corrode in water, especially wen irradiated. Thus, they may be less stable than photovoltaics over long periods of time. Hydrogen catalysts are very sensitive to oxygen, being inactivated or degraded in its presence; also, photodamage may occur over time. | 0 | Theoretical and Fundamental Chemistry |
With the development of various next-generation sequencing platforms, there has been a substantial reduction in costs, and increase in throughput of DNA sequencing. However, the majority of the sequencing technologies rely on PCR-based clonal amplification of the DNA molecule in order to bring the signal to a detectable range. Sequencing of amplified clusters, or bulk sequencing in such a propose a read length-dependent phasing problem. During each cycle, not all of the molecules within the bulk have successful incorporation of an additional nucleotide. With increased sequencing cycle, the signal of the lagging molecules will eventually overwhelm the true signal. The phasing problem is a major limitation for the read lengths of the next-generation sequencing technologies. Therefore, there is an increased interest in developing single-molecule sequencing technologies, where no amplification is required. This not only shortens the preparation time for the sequencing libraries, it also has the potential to achieve much longer read lengths, as the lagging molecules with failed extensions can be ignored or considered separately. Previously known single-molecule sequencing technologies include Nanopore sequencing (Oxford Nanopore),
SMRT sequencing (Pacific Biosciences), and Heliscope single molecule sequencing (Helicos Biosciences). | 1 | Applied and Interdisciplinary Chemistry |
UV light, specifically non-ionizing shorter-wavelength radiation such as UVC and UVB, causes direct DNA damage by initiating a synthesis reaction between two thymine molecules. The resulting dimer is very stable. Although they can be removed through excision repairs, when UV damage is extensive, the entire DNA molecule breaks down and the cell dies. If the damage is not too extensive, precancerous or cancerous cells are created from healthy cells. | 1 | Applied and Interdisciplinary Chemistry |
A polymer shell is formed by conjugation of multiple molecules of polymers onto the protein core. The polymer shell can either protect the protein core from unwanted degradation or create desired interactive sites for guest molecules. The first generation of polymer shell protein core structures mainly used of Polyethylene glycol (PEG) chains to increase the hydrodynamic radius and reduce immune response to proteins. However, the PEG shell can reduce protein activity in the inner core. More advanced designs use biodegradable linkers to achieve programmed release of the protein core in specific tissues. Several therapeutic designs with biodegradable PEG shells are already being developed in vivo.
Direct conjugation of polymers ("grafting to" strategy) can efficiently construct a polymer shell with diverse polymer types, however, it has low polymer density, especially with large polymers. In contrast, "grafting from" strategy allows the formation of a dense and uniform polymer shell. The protein core can also function as a carrier for other therapeutic molecules, such as plasmid DNA.
Dendrite polymer shells have a high volume to molecular weight ratio compared with traditional polymer shells. Using branched carbohydrates can give unique biological properties while maintaining molecular definition. | 1 | Applied and Interdisciplinary Chemistry |
Pseudin-2 is the most abundant version of the pseudins found on the skin of the paradoxical frog. The primary sequence reads as GLNALKKVFQGIHEAIKLINNHVQ. Its secondary/tertiary structure consists of one cationic amphipathic α-helix. | 1 | Applied and Interdisciplinary Chemistry |
Prehistoric links between Mesoamerica and the Andes have been suggested on several occasions. Early Mesoamerican and Ecuadorian pottery style show some similarities, both in technique and motifs. Likewise, similarities in early burial styles (so-called "shaft tombs") present in Ecuador and western Mesoamerica have been pointed out. Even the origins of the Purépecha people in Michoacán have been suggested as lying in South America. However, none of these proposals are widely accepted by specialists. More widely accepted is the influence of South American metallurgy on Mesoamerica.
South American metallurgy itself can be divided into two traditions: one in Peru, southern Ecuador, and Bolivia, which used copper, tin, silver, gold, and arsenic in various alloys with a variety of uses; and a second in Colombia and southern Central America, the so-called Intermediate Area, which relied on gold and copper for largely artistic rather than utilitarian purposes. The metallurgical tradition of western Mesoamerica, though geographically closer to the Intermediate Zone, is much closer in form and function to the southern Ecuadorian tradition. The form and method of creating interlocking metal rings is identical in the two traditions, and even their archaeological context (placed around the cranium in burials) is remarkably similar. Fish-hooks, needles, and tweezers, also appear in both traditions. However, the wax-casting tradition of the Intermediate Area, which spread to other parts of Mesoamerica, also proved influential in the western Mesoamerican context, such as in the creation of copper-gold alloy bells. | 1 | Applied and Interdisciplinary Chemistry |
The Womersley number, usually denoted , is defined by the relation
where is an appropriate length scale (for example the radius of a pipe), is the angular frequency of the oscillations, and , , are the kinematic viscosity, density, and dynamic viscosity of the fluid, respectively. The Womersley number is normally written in the powerless form
In the cardiovascular system, the pulsation frequency, density, and dynamic viscosity are constant, however the Characteristic length, which in the case of blood flow is the vessel diameter, changes by three orders of magnitudes (OoM) between the aorta and fine capillaries. The Womersley number thus changes due to the variations in vessel size across the vasculature system. The Womersley number of human blood flow can be estimated as follows:
Below is a list of estimated Womersley numbers in different human blood vessels:
It can also be written in terms of the dimensionless Reynolds number (Re) and Strouhal number (St):
The Womersley number arises in the solution of the linearized Navier–Stokes equations for oscillatory flow (presumed to be laminar and incompressible) in a tube. It expresses the ratio of the transient or oscillatory inertia force to the shear force. When is small (1 or less), it means the frequency of pulsations is sufficiently low that a parabolic velocity profile has time to develop during each cycle, and the flow will be very nearly in phase with the pressure gradient, and will be given to a good approximation by Poiseuille's law, using the instantaneous pressure gradient. When is large (10 or more), it means the frequency of pulsations is sufficiently large that the velocity profile is relatively flat or plug-like, and the mean flow lags the pressure gradient by about 90 degrees. Along with the Reynolds number, the Womersley number governs dynamic similarity.
The boundary layer thickness that is associated with the transient acceleration is inversely related to the Womersley number. This can be seen by recognizing the Stokes number as the square root of the Womersley number.
where is a characteristic length. | 1 | Applied and Interdisciplinary Chemistry |
Nucleation in microcellular plastic is an important stage which decides the final cell size, cell density and cell morphology of the foam. In the recent past, numerous researchers have studied the cell nucleation phenomenon in microcellular polymers.
Studies were performed with ultrasound induced nucleation during microcellular foaming of Acrylonitrile butadiene styrene polymers. M.C.Guo studied nucleation under the shear action. As the shear enhanced, the cell size diminished and thereby increased the cell density in the foam. | 0 | Theoretical and Fundamental Chemistry |
The phase diagram explains why liquids do not exist in space or any other vacuum. Since the pressure is essentially zero (except on surfaces or interiors of planets and moons) water and other liquids exposed to space will either immediately boil or freeze depending on the temperature. In regions of space near the Earth, water will freeze if the sun is not shining directly on it and vaporize (sublime) as soon as it is in sunlight. If water exists as ice on the Moon, it can only exist in shadowed holes where the sun never shines and where the surrounding rock does not heat it up too much. At some point near the orbit of Saturn, the light from the Sun is too faint to sublime ice to water vapor. This is evident from the longevity of the ice that composes Saturn's rings. | 0 | Theoretical and Fundamental Chemistry |
An MPS gas is a mixture of two or more of propane, butane, butadiene, methylacetylene (propyne, CHC≡CH) and propadiene (CH=C=CH). They are marketed under different names including: "MPS", "Chem-O-Lean", "Apachi Gas", "FG-2 Gas", "Flamex" and "natural gas". The most commonly known type of MPS gas is the discontinued MAPP gas.
As a fuel gas, it burns hotter than propylene, propane or natural gas. | 0 | Theoretical and Fundamental Chemistry |
Nitric acid is subject to thermal or light decomposition and for this reason it was often stored in brown glass bottles:
This reaction may give rise to some non-negligible variations in the vapor pressure above the liquid because the nitrogen oxides produced dissolve partly or completely in the acid.
The nitrogen dioxide () and/or dinitrogen tetroxide () remains dissolved in the nitric acid coloring it yellow or even red at higher temperatures. While the pure acid tends to give off white fumes when exposed to air, acid with dissolved nitrogen dioxide gives off reddish-brown vapors, leading to the common names "red fuming nitric acid" and "white fuming nitric acid". Nitrogen oxides () are soluble in nitric acid. | 0 | Theoretical and Fundamental Chemistry |
HNF4 was originally classified as an orphan receptor that exhibits constitutive transactivation activity apparently by being continuously bound to a variety of fatty acids. The existence of a ligand for HNF4 has been somewhat controversial, but linoleic acid (LA) has been identified as the endogenous ligand of native HNF4 expressed in mouse liver; the binding of LA to HNF4 is reversible.
The ligand binding domain of HNF4, as with other nuclear receptors, adopts a canonical alpha helical sandwich fold and interacts with co-activator proteins.
HNF4 binds to the consensus sequence AGGTCAaAGGTCA in order to activate transcription. | 1 | Applied and Interdisciplinary Chemistry |
Coinage metals, such as copper and silver, slowly corrode through use.
A patina of green-blue copper carbonate forms on the surface of copper with exposure to the water and carbon dioxide in the air. Silver coins or cutlery that are exposed to high sulfur foods such as eggs or the low levels of sulfur species in the air develop a layer of black silver sulfide.
Gold and platinum are extremely difficult to oxidize under normal circumstances, and require exposure to a powerful chemical oxidizing agent such as aqua regia.
Some common metals oxidize extremely rapidly in air. Titanium and aluminium oxidize instantaneously in contact with the oxygen in the air. These metals form an extremely thin layer of oxidized metal on the surface, which bonds with the underlying metal. This thin oxide layer protects the underlying bulk of the metal from the air preventing the entire metal from oxidizing. These metals are used in applications where corrosion resistance is important. Iron, in contrast, has an oxide that forms in air and water, called rust, that does not bond with the iron and therefore does not stop the further oxidation of the iron. Thus iron left exposed to air and water will continue to rust until all of the iron is oxidized. | 0 | Theoretical and Fundamental Chemistry |
UV pinning enhances the management of drop size and image integrity, minimizing the unwanted mixing of drops and providing the highest possible image quality and the sharpest colour rendering.
Challenge:
Overcome the wetting problems that were causing UV-Curable inks to spread and cause ink droplets to bleed into each other before full curing single-pass digital printing of narrow web labels.
Solution:
A UV pinning system that uses high power UV light emitting diodes(LEDs) installed next to the inkjet array (print head). The UV light from the pinning system, typically lower than that of the full cure UV system, causes the UV ink to thicken, also known as gelling, but not fully cure. This ink thickening stops dot gain and holds the ink droplet pattern in place until it reaches the full cure UV system. | 0 | Theoretical and Fundamental Chemistry |
The coat of arms is a shield with two figures. On the left a helmeted woman, Pallas Athene, the goddess of wisdom, and on the right, a bearded man with a large hammer, Hephaestus the god of technology and of fire. The shield itself shows a salamander as the symbol of chemistry, and a corn grinding mill as a symbol of continuous processes. Between these is a diagonal stripe in red and blue in steps to indicate the cascade nature of many chemical engineering processes. The shield is surmounted by helmet on which is a dolphin, which is in heraldry associated with intellectual activity, and also represents the importance of fluid mechanics. Just below the dolphin are two Integral signs to illustrate the necessity of mathematics and in particular calculus.
The Latin motto is "Findendo Fingere Disco" or "I learn to make by separating". | 1 | Applied and Interdisciplinary Chemistry |
The increasing of the mean value of AoA leads to more evident flow separation, higher overshoots of lift and pitch moment, and larger airloads hysteresis, which may ultimately result in deep dynamic stall. | 1 | Applied and Interdisciplinary Chemistry |
Other than for vision, the metabolic functions of vitamin A are mediated by all-trans-retinoic acid (RA). The formation of RA from retinal is irreversible. To prevent accumulation of RA it is oxidized and eliminated fairly quickly, i.e., has a short half-life. Three cytochromes catalyze the oxidation of retinoic acid. The genes for Cyp26A1, Cyp26B1 and Cyp26C1 are induced by high levels of RA, providing a self-regulating feedback loop. | 1 | Applied and Interdisciplinary Chemistry |
The most prominent roles of mitochondria are to produce the energy currency of the cell, ATP (i.e., phosphorylation of ADP), through respiration and to regulate cellular metabolism. The central set of reactions involved in ATP production are collectively known as the citric acid cycle, or the Krebs cycle, and oxidative phosphorylation. However, the mitochondrion has many other functions in addition to the production of ATP. | 1 | Applied and Interdisciplinary Chemistry |
While a simple siphon cannot output liquid at a level higher than the source reservoir, a more complicated device utilizing an airtight metering chamber at the crest and a system of automatic valves, may discharge liquid on an ongoing basis, at a level higher than the source reservoir, without outside pumping energy being added. It can accomplish this despite what initially appears to be a violation of conservation of energy because it can take advantage of the energy of a large volume of liquid dropping some distance, to raise and discharge a small volume of liquid above the source reservoir. Thus it might be said to "require" a large quantity of falling liquid to power the dispensing of a small quantity. Such a system typically operates in a cyclical or start/stop but ongoing and self-powered manner. Ram pumps do not work in this way. These metering pumps are true siphon pumping devices which use siphons as their power source. | 1 | Applied and Interdisciplinary Chemistry |
Methylene blue is used in endoscopic polypectomy as an adjunct to saline or epinephrine, and is used for injection into the submucosa around the polyp to be removed. This allows the submucosal tissue plane to be identified after the polyp is removed, which is useful in determining if more tissue needs to be removed, or if there has been a high risk for perforation. Methylene blue is also used as a dye in chromoendoscopy, and is sprayed onto the mucosa of the gastrointestinal tract in order to identify dysplasia, or pre-cancerous lesions. Intravenously injected methylene blue is readily released into the urine and thus can be used to test the urinary tract for leaks or fistulas.
In surgeries such as sentinel lymph node dissections, methylene blue can be used to visually trace the lymphatic drainage of tested tissues. Similarly, methylene blue is added to bone cement in orthopedic operations to provide easy discrimination between native bone and cement. Additionally, methylene blue accelerates the hardening of bone cement, increasing the speed at which bone cement can be effectively applied. Methylene blue is used as an aid to visualisation/orientation in a number of medical devices, including a Surgical sealant film, TissuePatch. In fistulas and pilonidal sinuses it is used to identify the tract for complete excision. It can also be used during gastrointestinal surgeries (such as bowel resection or gastric bypass) to test for leaks.
It is sometimes used in cytopathology, in mixtures including Wright-Giemsa and Diff-Quik. It confers a blue color to both nuclei and cytoplasm, and makes the nuclei more visible. When methylene blue is "polychromed" (oxidized in solution or "ripened" by fungal metabolism, as originally noted in the thesis of Dr. D. L. Romanowsky in the 1890s), it gets serially demethylated and forms all the tri-, di-, mono- and non-methyl intermediates, which are Azure B, Azure A, Azure C, and thionine, respectively. This is the basis of the basophilic part of the spectrum of Romanowski-Giemsa effect. If only synthetic Azure B and Eosin Y is used, it may serve as a standardized Giemsa stain; but, without methylene blue, the normal neutrophilic granules tend to overstain and look like toxic granules. On the other hand, if methylene blue is used it might help to give the normal look of neutrophil granules and may also enhance the staining of nucleoli and polychromatophilic RBCs (reticulocytes).
A traditional application of methylene blue is the intravital or supravital staining of nerve fibers, an effect first described by Paul Ehrlich in 1887. A dilute solution of the dye is either injected into tissue or applied to small freshly removed pieces. The selective blue coloration develops with exposure to air (oxygen) and can be fixed by immersion of the stained specimen in an aqueous solution of ammonium molybdate. Vital methylene blue was formerly much used for examining the innervation of muscle, skin and internal organs. The mechanism of selective dye uptake is incompletely understood; vital staining of nerve fibers in skin is prevented by ouabain, a drug that inhibits the Na/K-ATPase of cell membranes. | 0 | Theoretical and Fundamental Chemistry |
Desulfonylation reactions are chemical reactions leading to the removal of a sulfonyl group from organic compounds. As the sulfonyl functional group is electron-withdrawing, methods for cleaving the sulfur–carbon bonds of sulfones are typically reductive in nature. Olefination or replacement with hydrogen may be accomplished using reductive desulfonylation methods. | 0 | Theoretical and Fundamental Chemistry |
A deuterated drug is a small molecule medicinal product in which one or more of the hydrogen atoms contained in the drug molecule have been replaced by deuterium. Because of the kinetic isotope effect, deuterium-containing drugs may have significantly lower rates of metabolism, and hence a longer half-life. In 2017, deutetrabenazine became the first deuterated drug to receive FDA approval. | 0 | Theoretical and Fundamental Chemistry |
Glycosylation-dependent cell adhesion molecule-1 (GLYCAM1) is a proteoglycan ligand expressed on cells of the high endothelial venules in lymphoid tissues. It is the ligand for the receptor L-selectin allowing for naive lymphocytes to exit the bloodstream into lymphoid tissues.
GLYCAM1 binds to L-selectin by presenting one or more O-linked carbohydrates to the lectin domain of the leukocyte cell surface selectin.
Data suggests that GLYCAM1 is a hormone-regulated milk protein that is part of the milk mucin complex.
GlyCAM-1 is expressed exclusively on high endothelial venules. It is unclear how GlyCAM-1 is attached to the membrane as it lacks a transmembrane region. | 1 | Applied and Interdisciplinary Chemistry |
William Webster (1855–1910) was an English chemical engineer credited with developments in gas detection, sewage treatment and medical use of x-rays. A gifted artist and musician, Webster also helped found the Blackheath Concert Halls and the adjacent Conservatoire in Blackheath in south-east London during the 1890s. | 1 | Applied and Interdisciplinary Chemistry |
The freezing from liquid state to amorphous solid - glass transition - is considered one of the very important and unsolved problems of physics. | 0 | Theoretical and Fundamental Chemistry |
By combining microfluidics with landscape ecology and nanofluidics, a nano/micro fabricated fluidic landscape can be constructed by building local patches of bacterial habitat and connecting them by dispersal corridors. The resulting landscapes can be used as physical implementations of an adaptive landscape, by generating a spatial mosaic of patches of opportunity distributed in space and time. The patchy nature of these fluidic landscapes allows for the study of adapting bacterial cells in a metapopulation system. The evolutionary ecology of these bacterial systems in these synthetic ecosystems allows for using biophysics to address questions in evolutionary biology. | 1 | Applied and Interdisciplinary Chemistry |
In February 2017, DuPont and Chemours (a DuPont spin-off) agreed to pay $671 million to settle lawsuits arising from 3,550 personal injury claims related to releasing of PFASs from their Parkersburg, West Virginia, plant into the drinking water of several thousand residents. This was after a court-created independent scientific panel—the C8 Science Panel—found a "probable link" between C8 exposure and six illnesses: kidney and testicular cancer, ulcerative colitis, thyroid disease, pregnancy-induced hypertension and high cholesterol.
In October 2018, a class action suit was filed by an Ohio firefighter against several producers of fluorosurfactants, including the 3M and DuPont corporations, on behalf of all U.S. residents who may have adverse health effects from exposure to PFASs. The story is told in the film Dark Waters. | 0 | Theoretical and Fundamental Chemistry |
Surfactant behavior is highly dependent on the hydrophilic-lipophilic balance (HLB) value. The HLB is a coding scale from 0 to 20 for non-ionic surfactants, and takes into account the chemical structure of the surfactant molecule. A zero value corresponds to the most lipophilic and a value of 20 is the most hydrophilic for a non-ionic surfactant. In general, compounds with an HLB between one and four will not mix with water. Compounds with an HLB value above 13 will form a clear solution in water. Oil dispersants usually have HLB values from 8–18. | 1 | Applied and Interdisciplinary Chemistry |
In interfacial synthesis, the polymerization happens at the interface between an aqueous and an organic layer. A typical reaction involves an aqueous solution of acid and oxidant and an organic layer of aniline together. This creates the reactive interface for polymerization to occur. As polymerization proceeds, the polyaniline nanofibers will diffuse into the water layer, leaving the reactive interface. This prevents overgrowth onto the existing wires, allowing for homogeneous nucleation to continue occurring. Conditions in the interfacial synthesis can be tuned, such as the type of acid used as well as the oxidant used. | 0 | Theoretical and Fundamental Chemistry |
Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman transport is a component of wind-driven ocean current. Ekman transport occurs when ocean surface waters are influenced by the friction force acting on them via the wind. As the wind blows it casts a friction force on the ocean surface that drags the upper 10-100m of the water column with it. However, due to the influence of the Coriolis effect, the ocean water moves at a 90° angle from the direction of the surface wind. The direction of transport is dependent on the hemisphere: in the northern hemisphere, transport occurs at 90° clockwise from wind direction, while in the southern hemisphere it occurs at 90° anticlockwise. This phenomenon was first noted by Fridtjof Nansen, who recorded that ice transport appeared to occur at an angle to the wind direction during his Arctic expedition of the 1890s. Ekman transport has significant impacts on the biogeochemical properties of the world's oceans. This is because it leads to upwelling (Ekman suction) and downwelling (Ekman pumping) in order to obey mass conservation laws. Mass conservation, in reference to Ekman transfer, requires that any water displaced within an area must be replenished. This can be done by either Ekman suction or Ekman pumping depending on wind patterns. | 1 | Applied and Interdisciplinary Chemistry |
Bimodal AFM is widely used to provide high-spatial resolution maps of material properties, in particular, mechanical properties. Elastic and/or viscoelastic property maps of polymers, DNA, proteins, protein fibers, lipids or 2D materials were generated. Non-mechanical properties and interactions including crystal magnetic garnets, electrostatic strain, superparamagnetic particles and high-density disks were also mapped. Quantitative property mapping requires the calibration of the force constants of the excited modes. | 0 | Theoretical and Fundamental Chemistry |
The nitrogen vacancy defect in diamond consists of a single substitutional nitrogen atom (replacing one carbon atom) and an adjacent gap, or vacancy, in the lattice where normally a carbon atom would be located.
The nitrogen vacancy occurs in three possible charge states: positive (NV), neutral (NV) and negative (NV). As NV is the only one of these charge states which has shown to be ODMR active, it is often referred to simply as the NV.
The energy level structure of the NV consists of a triplet ground state, a triplet excited state and two singlet states. Under resonant optical excitation, the NV may be raised from the triplet ground state to the triplet excited state. The centre may then return to the ground state via two routes; by the emission of a photon of 637 nm in the zero phonon line (ZPL) (or longer wavelength from the phonon sideband) or alternatively via the aforementioned singlet states through intersystem crossing and the emission of a 1042 nm photon. A return to the ground state via the latter route will preferentially result in the state.
Relaxation to the state necessarily results in a decrease in visible wavelength fluorescence (as the emitted photon is in the infrared range). Microwave pumping at a resonant frequency of places the centre in the degenerate state. The application of a magnetic field lifts this degeneracy, causing Zeeman splitting and the decrease of fluorescence at two resonant frequencies, given by , where is the Planck constant, is the electron g-factor and is the Bohr magneton. Sweeping the microwave field through these frequencies results in two characteristic dips in the observed fluorescence, the separation between which enables determination of the strength of the magnetic field . | 0 | Theoretical and Fundamental Chemistry |
Transketolase (abbreviated as TK) is an enzyme that, in humans, is encoded by the TKT gene. It participates in both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis. Transketolase catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the non-oxidative pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose (D-xylulose-5-P), then transfers this fragment to a 5-carbon aldose (D-ribose-5-P) to form a 7-carbon ketose (sedoheptulose-7-P). The abstraction of two carbons from D-xylulose-5-P yields the 3-carbon aldose glyceraldehyde-3-P. In the Calvin cycle, transketolase catalyzes the reverse reaction, the conversion of sedoheptulose-7-P and glyceraldehyde-3-P to pentoses, the aldose D-ribose-5-P and the ketose D-xylulose-5-P.
The second reaction catalyzed by transketolase in the pentose phosphate pathway involves the same thiamine diphosphate-mediated transfer of a 2-carbon fragment from D-xylulose-5-P to the aldose erythrose-4-phosphate, affording fructose 6-phosphate and glyceraldehyde-3-P. Again, in the Calvin cycle exactly the same reaction occurs, but in the opposite direction. Moreover, in the Calvin cycle this is the first reaction catalyzed by transketolase, rather than the second.
In mammals, transketolase connects the pentose phosphate pathway to glycolysis, feeding excess sugar phosphates into the main carbohydrate metabolic pathways. Its presence is necessary for the production of NADPH, especially in tissues actively engaged in biosyntheses, such as fatty acid synthesis by the liver and mammary glands, and for steroid synthesis by the liver and adrenal glands. Thiamine diphosphate is an essential cofactor, along with calcium.
Transketolase is abundantly expressed in the mammalian cornea by the stromal keratocytes and epithelial cells and is reputed to be one of the corneal crystallins. | 0 | Theoretical and Fundamental Chemistry |
With these technologies, cold water circulates through a blanket, or torso wraparound vest and leg wraps. To lower temperature with optimal speed, 70% of a persons surface area should be covered with water blankets. The treatment represents the most well studied means of controlling body temperature. Water blankets lower a persons temperature exclusively by cooling a person's skin and accordingly require no invasive procedures.
Water blankets possess several undesirable qualities. They are susceptible to leaking, which may represent an electrical hazard since they are operated in close proximity to electrically powered medical equipment. The Food and Drug Administration also has reported several cases of external cooling blankets causing significant burns to the skin of person. Other problems with external cooling include overshoot of temperature (20% of people will have overshoot), slower induction time versus internal cooling, increased compensatory response, decreased patient access, and discontinuation of cooling for invasive procedures such as the cardiac catheterization.
If therapy with water blankets is given along with two litres of cold intravenous saline, people can be cooled to in 65 minutes. Most machines now come with core temperature probes. When inserted into the rectum, the core body temperature is monitored and feedback to the machine allows changes in the water blanket to achieve the desired set temperature. In the past some of the models of cooling machines have produced an overshoot in the target temperature and cooled people to levels below , resulting in increased adverse events. They have also rewarmed patients at too fast a rate, leading to spikes in intracranial pressure. Some of the new models have more software that attempt to prevent this overshoot by utilizing warmer water when the target temperature is close and preventing any overshoot. Some of the new machines now also have 3 rates of cooling and warming; a rewarming rate with one of these machines allows a patient to be rewarmed at a very slow rate of just an hour in the "automatic mode", allowing rewarming from to over 24 hours. | 1 | Applied and Interdisciplinary Chemistry |
The cyano group usually cannot be introduced by nucleophilic substitution of haloarenes, but such compounds can be easily prepared from diazonium salts. Illustrative is the preparation of benzonitrile using the reagent cuprous cyanide:
This reaction is a special type of Sandmeyer reaction. | 0 | Theoretical and Fundamental Chemistry |
According to a story collected by the erudite Francesco Cancellieri in 1802, a pilgrim named "Stibeum" (from Latin: stibium, which means "antimony") was hosted in the villa for a night. That night, the pilgrim, identified later by some as the alchemist Giuseppe Francesco Borri—known as Giustiniano Bono—, searched the gardens of the villa overnight in search of a mysterious herb capable of concocting gold. Legend held that the next morning he was seen to disappear forever through a door, but left behind a few flakes of gold, the fruits of a successful alchemical transmutation, and a mysterious paper full of puzzling symbols and equations, putatively describing the ingredients and process required. The marquis had these symbols engraved on the five gates of the villa Palombara and on the walls of the mansion, hoping that one day they would be translated.
A second legend holds that between 1678 and 1680, the same Giuseppe Francesco Borri along with Athanasius Kircher and Gian Lorenzo Bernini designed and built the gate for the marquis. The marquis Palombara developed a passion for alchemy in 1656, when he visited the alchemical laboratory in Riario Palace, now known as Palazzo Corsini. Patronized by the exiled queen Christina of Sweden, the laboratory was supervised by Pietro Antonio Bandiera and had been visited by Borri and Kircher. This tradition holds the gate was built to memorialize a successful alchemical transmutation that occurred in the Riario Palace. It was rumored that Palombara, Bernini and Kircher were all poisoned on 28 November 1680, probably by Borri, for having revealed the secret formulas through the inscriptions on the gate.
Cancellieri published his semi-fanciful account in 1806, including his interpretation of the inscriptions on the Porta Alchimica. His work was published in June 1895 in French by Pietro Bornia as an issue of the periodical LInitiation'. | 1 | Applied and Interdisciplinary Chemistry |
Christian Alfred Elie Janot (January 4, 1936 – February 23, 2022) was a French physicist and materials scientist known for his work on materials characterization using Mössbauer spectroscopy and his physical metallurgy studies of quasicrystals and noncrystalline materials using neutron scattering techniques. | 1 | Applied and Interdisciplinary Chemistry |
Pest management in the home begins with restricting the availability to insects of three vital commodities: shelter, water and food. If insects become a problem despite such measures, it may become necessary to control them using chemical methods, targeting the active ingredient to the particular pest.
Insect repellent, referred to as "bug spray", comes in a plastic bottle or aerosol can. Applied to clothing, arms, legs, and other extremities, the use of these products will tend to ward off nearby insects. This is not an insecticide.
Insecticide used for killing pests—most often insects, and arachnids—primarily comes in an aerosol can, and is sprayed directly on the insect or its nest as a means of killing it. Fly sprays will kill house flies, blowflies, ants, cockroaches and other insects and also spiders. Other preparations are granules or liquids that are formulated with bait that is eaten by insects. For many household pests bait traps are available that contain the pesticide and either pheromone or food baits. Crack and crevice sprays are applied into and around openings in houses such as baseboards and plumbing. Pesticides to control termites are often injected into and around the foundations of homes.
Active ingredients of many household insecticides include permethrin and tetramethrin, which act on the nervous system of insects and arachnids.
Bug sprays should be used in well ventilated areas only, as the chemicals contained in the aerosol and most insecticides can be harmful or deadly to humans and pets. All insecticide products including solids, baits and bait traps should be applied such that they are out of reach of wildlife, pets and children. | 1 | Applied and Interdisciplinary Chemistry |
External covers or shrouds should be used to protect the internal bellows from being damaged. They also serve a purpose as insulation of the bellows. Covers can either be designed as removable or permanent accessories. | 1 | Applied and Interdisciplinary Chemistry |
Carbonate esters can be converted to other carbonates by transesterification. A more nucleophilic alcohol will displace a less nucleophilic alcohol. In other words, aliphatic alcohols will displace phenols from aryl carbonates. If the departing alcohol is more volatile, the equilibrium may be driven by distilling that off. | 0 | Theoretical and Fundamental Chemistry |
In the 1990s, the Chinese government decided to increase the efficiency of the Chinese economy and reduce the environmental effects of heavy industry by modernising plants. As a response, the Yunnan Copper Corporation ("YCC") upgraded its existing plant, which was based on a sinter plant and an electric furnace, with a copper ISASMELT furnace. As with the Miami smelter, the electric furnace was converted from smelting duty to separation of matte and slag and providing matte surge capacity for the converters, and again, the small footprint of the ISASMELT furnace was very important in retrofitting it to the existing smelter.
The YCC ISASMELT plant had a design capacity of 600,000 dry t/y of copper concentrate and started smelting concentrate on 15 May 2002. YCC placed a lot of emphasis on training its operators, sending people to Mount Isa for training over a seven-month period during 2001 ahead of the ISASMELT commissioning. The total cost of the smelter modernisation program, including the ISASMELT furnace, was 640 million yuan (approximately US$80 million) and the smelter's concentrate treatment rate increased from 470,000 t/y to 800,000 t/y as a result.
The transfer of operating knowledge from MIM to YCC was sufficient for the first ISASMELT furnace refractory lining to last for two years, a marked improvement on the life of the initial lining of other plants.
YCC described the modernisation project as "a great success, achieving all that was expected." Energy consumption per tonne of blister copper produced decreased by 34% as a result of installing the ISASMELT furnace, and YCC estimated that during the first 38 months of operation, it saved approximately US$31.4 million through reduced energy costs alone, giving the modernisation a very short payback by industry standards.
In 2004, YCC's management was presented with awards for Innovation in Project Management and the National Medal for High Quality Projects by the Chinese government to mark the success of the smelter modernisation project.
Xstrata subsequently licensed YCC to build three more ISASMELT plants, one in Chuxiong in Yunnan Province, China to treat 500,000 t/y of copper concentrate, one in Liangshan in Sichuan Province, China and the other in Chambishi in Zambia to treat 350,000 t/y of concentrate. Chuxiong and Chambishi were commissioned in 2009. Liangshan was commissioned in 2012.
*Mopani Copper Mines, as part of Zambia Consolidated Copper Mines Limited | 1 | Applied and Interdisciplinary Chemistry |
Chemical imaging shares the fundamentals of vibrational spectroscopic techniques, but provides additional information by way of the simultaneous acquisition of spatially resolved spectra. It combines the advantages of digital imaging with the attributes of spectroscopic measurements. Briefly, vibrational spectroscopy measures the interaction of light with matter. Photons that interact with a sample are either absorbed or scattered; photons of specific energy are absorbed, and the pattern of absorption provides information, or a fingerprint, on the molecules that are present in the sample.
On the other hand, in terms of the observation setup, chemical imaging can be carried out in one of the following modes: (optical) absorption, emission (fluorescence), (optical) transmission or scattering (Raman). A consensus currently exists that the fluorescence (emission) and Raman scattering modes are the most sensitive and powerful, but also the most expensive.
In a transmission measurement, the radiation goes through a sample and is measured by a detector placed on the far side of the sample. The energy transferred from the incoming radiation to the molecule(s) can be calculated as the difference between the quantity of photons that were emitted by the source and the quantity that is measured by the detector. In a diffuse reflectance measurement, the same energy difference measurement is made, but the source and detector are located on the same side of the sample, and the photons that are measured have re-emerged from the illuminated side of the sample rather than passed through it. The energy may be measured at one or multiple wavelengths; when a series of measurements are made, the response curve is called a spectrum.
A key element in acquiring spectra is that the radiation must somehow be energy selected – either before or after interacting with the sample. Wavelength selection can be accomplished with a fixed filter, tunable filter, spectrograph, an interferometer, or other devices. For a fixed filter approach, it is not efficient to collect a significant number of wavelengths, and multispectral data are usually collected. Interferometer-based chemical imaging requires that entire spectral ranges be collected, and therefore results in hyperspectral data. Tunable filters have the flexibility to provide either multi- or hyperspectral data, depending on analytical requirements.
Spectra are typically measured with an imaging spectrometer, based on a Focal Plane Array. | 0 | Theoretical and Fundamental Chemistry |
With the insurgence in the usage of PPA during the past few years for various applications, the need to ameliorate the transient properties and enhance the mechanical features of this polymer has come to surface. PPA is known to be brittle; it possesses a large storage modulus, and a glass transition temperature that is above its thermal degradation point, which renders the polymer unsuitable for a broad range of applications. One way to ameliorate its intrinsic properties is via the addition of a plasticizing agent that can disrupt the polymer's intermolecular packing, and thus making it more flexible, decreasing its storage modulus, depressing its glass transition temperature, and increasing its shear strength. A few examples of plasticizers that have been used with PPA include dimethyl phthalate, bis(2-ethylhexyl) phthalate, diethyl adipate, and tri-isononyl trimellitate (TINTM). In a recent study, the effect of two ether-ester plasticizers on the mechanical flexibility and photo-transience speed of cyclic PPA was investigated. The authors were able to show that the addition of these additives broadened the storage modulus range and decreased it from 2300 MPa in the case of pure PPA down to 19 MPa in the PPA/plasticizer mixture, hence making the polymer more flexible and in need of less energy to be distorted. In another study published by the same research group, the effect of diethyl adipate (DEA) plasticizer on the glass transition temperature of cyclic PPA was investigated. After determining the glass transition temperature of pure PPA to be 187 °C, PPA films with various DEA concentrations were prepared. By varying DEA concentration, the authors were able depress T to 12.5 °C demonstrating the importance of plasticizers in enhancing the mechanical flexibility and thermal properties of PPA. Similar results were previously observed where the thermal transitions were depressed from 95 °C for cPPA to 24 °C for diethyl phthalate (DEP)-plasticized cPPA. Among the few studies that have been reported on the usage of plasticizers with PPA, it has been noted that the usage of plasticizers results in a decrease in the tensile stress of the polymers which indicate that PPA is becoming more flexible and hence the film can fold more easily. Nevertheless, a control on the amount of plasticizer used is important. For instance, in the study discussed above, it has been reported that the usage of a large amount of plasticizer (more than 50% w/w in comparison with PPA polymer) results in phase segregation and a decrease in the flexibility of the PPA film. Furthermore, the nature of the used solvent can highly affect the mechanical properties of PPA as well. In particular, in another study published in 2019, both the elastic modulus and tensile strength increase when dichloromethane was used as a solvent to drop-cast PPA in comparison to dioxane and chloroform. | 0 | Theoretical and Fundamental Chemistry |
The boundaries of the valley of stability, that is, the upper limits of the valley walls, are the neutron drip line on the neutron-rich side, and the proton drip line on the proton-rich side. The nucleon drip lines are at the extremes of the neutron-proton ratio. At neutron–proton ratios beyond the drip lines, no nuclei can exist. The location of the neutron drip line is not well known for most of the Segrè chart, whereas the proton and alpha drip lines have been measured for a wide range of elements. Drip lines are defined for protons, neutrons, and alpha particles, and these all play important roles in nuclear physics.
The difference in binding energy between neighboring nuclides increases as the sides of the valley of stability are ascended, and correspondingly the nuclide half-lives decrease, as indicated in the figure above. If one were to add nucleons one at a time to a given nuclide, the process will eventually lead to a newly formed nuclide that is so unstable that it promptly decays by emitting a proton (or neutron). Colloquially speaking, the nucleon has leaked or dripped out of the nucleus, hence giving rise to the term "drip line".
Proton emission is not seen in naturally occurring nuclides. Proton emitters can be produced via nuclear reactions, usually utilizing linear particle accelerators (linac). Although prompt (i.e. not beta-delayed) proton emission was observed from an isomer in cobalt-53 as early as 1969, no other proton-emitting states were found until 1981, when the proton radioactive ground states of lutetium-151 and thulium-147 were observed at experiments at the GSI in West Germany. Research in the field flourished after this breakthrough, and to date more than 25 nuclides have been found to exhibit proton emission. The study of proton emission has aided the understanding of nuclear deformation, masses and structure, and it is an example of quantum tunneling.
Two examples of nuclides that emit neutrons are beryllium-13 (mean life ) and helium-5 (). Since only a neutron is lost in this process, the atom does not gain or lose any protons, and so it does not become an atom of a different element. Instead, the atom will become a new isotope of the original element, such as beryllium-13 becoming beryllium-12 after emitting one of its neutrons.
In nuclear engineering, a prompt neutron is a neutron immediately emitted by a nuclear fission event. Prompt neutrons emerge from the fission of an unstable fissionable or fissile heavy nucleus almost instantaneously. Delayed neutron decay can occur within the same context, emitted after beta decay of one of the fission products. Delayed neutron decay can occur at times from a few milliseconds to a few minutes. The U.S. Nuclear Regulatory Commission defines a prompt neutron as a neutron emerging from fission within 10 seconds. | 0 | Theoretical and Fundamental Chemistry |
A positive balance is a result of energy intake being higher than what is consumed in external work and other bodily means of energy expenditure.
The main preventable causes are:
*Overeating, resulting in increased energy intake
*Sedentary lifestyle, resulting in decreased energy expenditure through external work
A positive balance results in energy being stored as fat and/or muscle, causing weight gain. In time, overweight and obesity may develop, with resultant complications. | 1 | Applied and Interdisciplinary Chemistry |
Periphyton communities are used in aquaculture food production systems for the removal of solid and dissolved pollutants. Their performance in filtration is established and their application as aquacultural feed is being researched.
Periphyton serves as an indicator of water quality because:
:*It has a naturally high number of species.
:*It has a fast response to changes.
:*It is easy to sample.
:*It is known for tolerance/sensitivity to change. | 1 | Applied and Interdisciplinary Chemistry |
Aquasomes can be characterized by a variety of techniques that analyze the properties of their three functional units: the ceramic core, carbohydrate coating, and bioactive drug. Characterization of aquasomes after synthesis is done to gain a better understanding of each of the facets that provide or contribute to their functionality. Analyzing characteristics of aquasomes such as size distribution, the carbohydrate coat-to-core ratio, and electrical potential between the nanoparticles can be important in understanding an aquasome’s function.
Solution precipitation as a core synthesis technique produces homogenous-sized nanoparticles, which can be advantageous in controlling specific physical properties such as surface tension and packing density of the atoms in a crystalline lattice structure. The most common methods of characterizing nanoparticle size distribution and morphology of the core in aquasomes include scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In a study by Kommimeni et al. in 2012, researchers employed TEM to verify that the ceramic particles were spherical and also in the acceptable nano-range for aquasomes. The carbohydrate coating size can also be characterized using SEM and TEM, but a Fourier Transform Infrared Spectroscopy (FTIR) is commonly utilized to check for the presence of the coat. In a study by Kommimeni et al. in 2020, FTIR was used to confirm the presence of the coating by analyzing the IR spectra bands that correspond to the functional groups of either the core or the sugar coat.
The bioactive drug loaded onto the aquasome can be characterized in a variety of ways depending on the molecular classification of the drug. In Kossovsky et al. in 1996, which studied the effect of insulin as the bioactive drug of interest, immunogold labeling was employed. Through this technique, the different binding efficiencies of carbohydrate coatings for insulin were able to be observed.
To characterize the loading of the bioactive drug, it is common to employ mathematical equations that use theoretical estimations for drug concentrations entrapped in the aquasome. One such parameter is entrapment efficiency, which is the amount of drug added that was adsorbed onto aquasomes. Another parameter of interest is drug loading, which is the percentage of the aquasome’s weight that is composed of the drug. In a study done by Kutlehria et al. in 2018, the following equations were used to quantify the entrapment efficiency and drug loading::
Finally, measuring the mechanism of action of the formulated aquasomes is important for understanding their potential therapeutic effect. Several studies have carried out in vitro drug release studies that place the aquasomes in a dissolution media and measure the subsequent release of drug into the solution. By obtaining these values, a release profile of the aquasome can be postulated and further optimizations can be determined for aquasomes to meet specific therapeutic indices or pharmacological outcomes. | 0 | Theoretical and Fundamental Chemistry |
Macroscopic viscous flow fields can direct self-assembly of a random solution of particles into ordered crystals. However, the assembled particles tend to disassemble when the flow is stopped or removed. Shear flows are useful for jammed suspensions or random close packing. As these systems begin in nonequilibrium, flow fields are useful in that they help the system relax towards ordered equilibrium. Flow fields are also useful when dealing with complex matrices that themselves have rheological behavior. Flow can induce anisotropic viseoelastic stresses, which helps to overcome the matrix and cause self-assembly. | 0 | Theoretical and Fundamental Chemistry |
Researchers are attempting to eliminate the problem of blinking nanocrystals. One common solution is to suppress nanocrystal ionization. This could be done, for example, by growing a very thick semiconductor shell around the nanocrystal core. However, blinking was reduced, not eliminated, because the fundamental processes responsible for blinking - the non-radiative Auger recombination- were still present. | 0 | Theoretical and Fundamental Chemistry |
Discoveries of the microwave spectra of a considerable number of molecules prove the existence of rather complex molecules in the interstellar clouds, and provides the possibility to study dense clouds, which are obscured by the dust they contain. The HO molecule has been observed in the interstellar medium since 1963 through its 18-cm transitions. In the subsequent years HO was observed by its rotational transitions at far infrared wavelengths, mainly in the Orion region. Because each rotational level of HO is split in by lambda doubling, astronomers can observe a wide variety of energy states from the ground state. | 1 | Applied and Interdisciplinary Chemistry |
The atmosphere of Early Earth is widely speculated to have been reducing. The Miller–Urey experiment, related to some hypotheses for the origin of life, entailed reactions in a reducing atmosphere composed of a mixed atmosphere of methane, ammonia and hydrogen sulfide. Some hypotheses for the origin of life invoke a reducing atmosphere consisting of hydrogen cyanide (HCN). Experiments show that HCN can polymerize in the presence of ammonia to give a variety of products including amino acids. The same principle applies to Mars, Venus and Titan.
Cyanobacteria are suspected to be the first photoautotrophs that evolved oxygenic photosynthesis, which over the latter half of the Archaen eon eventually depleted all reductants in the Earth's oceans, terrestrial surface and atmsophere, gradually increasing the oxygen concentration in the atmosphere, changing it to what is known as an oxidizing atmosphere. This rising oxygen initially led to a 300 million-year-long ice age that devastated the then-mostly anaerobe-dominated biosphere, forcing the surviving anaerobic colonies to evolve into symbiotic microbial mats with the newly evolved aerobes. Some aerobic bacteria eventually became endosymbiont within other anaerobes (likely archaea), and the resultant symbiogenesis led to the evolution of a completely new lineage of life — the eukaryotes, who took advantage of mitochondrial aerobic respiration to power their cellular activities, allowing life to thrive and evolve into ever more complex forms. The increased oxygen in the atmosphere also eventually created the ozone layer, which shielded away harmful ionizing ultraviolet radiation that otherwise would have photodissociated away surface water and rendered life impossible on land and the ocean surface.
In contrast to the hypothesized early reducing atmosphere, evidence exists that Hadean atmospheric oxygen levels were similar to those of today. These results suggests prebiotic building blocks were delivered from elsewhere in the galaxy. The results however do not run contrary to existing theories on life's journey from anaerobic to aerobic organisms. The results quantify the nature of gas molecules containing carbon, hydrogen, and sulphur in the earliest atmosphere, but they shed no light on the much later rise of free oxygen in the air. | 1 | Applied and Interdisciplinary Chemistry |
Tool compounds are an important class of reagent in biology. They are small molecules or biochemicals like siRNA or antibodies that are known to affect a given biomolecule—for example a drug target—but are unlikely to be useful as drugs themselves, and are often starting points in the drug discovery process.
However, many natural substances are hits in almost any assay in which they are tested, and therefore not useful as tool compounds. Medicinal chemists class them instead as pan-assay interference compounds. One example is curcumin. | 0 | Theoretical and Fundamental Chemistry |
For over two millennia, texts in Chinese herbology and traditional Chinese medicine have recorded medicinal plants that are also hallucinogens and psychedelics. Some are familiar psychoactive plants in Western herbal medicine (e.g., , i.e. Hyoscyamus niger), but several Chinese plants have not been noted as hallucinogens in modern works (e.g.,, i.e. Caesalpinia decapetala). Chinese herbals are an important resource for the history of botany, for instance, Zhang Huas c. 290 Bowuzhi is the earliest record of the psilocybin mushroom xiàojùn (lit. "laughing mushroom", i.e. Gymnopilus junonius'). | 1 | Applied and Interdisciplinary Chemistry |
Insensitive nuclei enhanced by polarization transfer (INEPT) is a signal resolution enhancement method. Because N has a gyromagnetic ratio that is small in magnitude, the resolution is quite poor. A common pulse sequence which dramatically improves the resolution for N is INEPT. The INEPT is an elegant solution in most cases because it increases the Boltzmann polarization and lowers T values (thus scans are shorter). Additionally, INEPT can accommodate negative gyromagnetic ratios, whereas the common nuclear Overhauser effect (NOE) cannot. | 0 | Theoretical and Fundamental Chemistry |
A whiting event is a phenomenon that occurs when a suspended cloud of fine-grained calcium carbonate precipitates in water bodies, typically during summer months, as a result of photosynthetic microbiological activity or sediment disturbance. The phenomenon gets its name from the white, chalky color it imbues to the water. These events have been shown to occur in temperate waters as well as tropical ones, and they can span for hundreds of meters. They can also occur in both marine and freshwater environments. The origin of whiting events is debated among the scientific community, and it is unclear if there is a single, specific cause. Generally, they are thought to result from either bottom sediment re-suspension or by increased activity of certain microscopic life such as phytoplankton. Because whiting events affect aquatic chemistry, physical properties, and carbon cycling, studying the mechanisms behind them holds scientific relevance in various ways. | 0 | Theoretical and Fundamental Chemistry |
Effluent in the artificial sense is in general considered to be water pollution, such as the outflow from a sewage treatment facility or an industrial wastewater discharge. An effluent sump pump, for instance, pumps waste from toilets installed below a main sewage line. In the context of waste water treatment plants, effluent that has been treated is sometimes called secondary effluent, or treated effluent. This cleaner effluent is then used to feed the bacteria in biofilters.
In the context of a thermal power station and other industrial facilities, the output of the cooling system may be referred to as the effluent cooling water, which is noticeably warmer than the environment and is called thermal pollution. In chemical engineering practice, effluent is the stream exiting a chemical reactor.
Effluent may carry pollutants such as fats, oils and greases; solvents, detergents and other chemicals; heavy metal; other solids; and food waste. Possible sources include a wide range of manufacturing industries, mining industries, oil and gas extraction, and service industries. | 1 | Applied and Interdisciplinary Chemistry |
The calibration of magnetometers is usually performed by means of coils which are supplied by an electrical current to create a magnetic field. It allows to characterize the sensitivity of the magnetometer (in terms of V/T). In many applications the homogeneity of the calibration coil is an important feature. For this reason, coils like Helmholtz coils are commonly used either in a single axis or a three axis configuration. For demanding applications a high homogeneity magnetic field is mandatory, in such cases magnetic field calibration can be performed using a Maxwell coil, cosine coils, or calibration in the highly homogenous Earth's magnetic field. | 0 | Theoretical and Fundamental Chemistry |
With cyclopropylketones, transition metal can coordinate to the ketone to direct oxidative addition into the proximal C-C bond. The resulting metallacyclobutane intermediate can be in equilibrium with the six-membered alkyl metal enolate depending on presence of a Lewis acid (e.g. dimethylaluminum chloride).
With the metallacyclobutane intermediate, 1,2-migratory insertion into an alkyne followed by reductive elimination yields a substituted cyclopentene product. Examples of intramolecular reactions with a tethered alkyne and intermolecular reactions with a nontethered alkyne both exist with use of a nickel or rhodium catalyst. With the six-membered alkyl metal enolate intermediate, dimerization or reaction with an added alpha-beta unsaturated ketone yields a 1,3-substituted cyclopentane product. | 0 | Theoretical and Fundamental Chemistry |
The first transition metal complexes of nontrigonal pnictogen compounds have been reported in the 1980s and '90s. Up to now, several complexes have been successfully synthesized, but they have not yet been applied in secondary processes, such as catalytic cycles.
In 2018, the synthesis and reactivity of a chelating ligand containing a nontrigonal phosphorus center was reported. It is worth noting that, apart from direct metalation of this ligand with RuCl(PPh), metalation with a ruthenium hydride compound RuHCl(CO)(PPh) yields a complex with net insertion into the Ru−H bond. These ligands, along with recent developments for higher valent states of Sb ligands, may possess rich potential in the field of catalysis and sensing. | 0 | Theoretical and Fundamental Chemistry |
The Strouhal number is most commonly used for assessing oscillating flow as a result of an objects motion through a fluid. The Strouhal number reflects the difficulty for animals to travel efficiently through a fluid with their cyclic propelling motions. The number relates to propulsive efficiency, which peaks between when within the optimal Strouhal number range of . Through the use of factors such as the stroke frequency, the amplitude of each stroke, and velocity, the Strouhal number is able to analyze the efficiency and impact of an animals propulsive forces through a fluid, such as those from swimming or flying. For instance, the value represents the constraints to achieve greater propulsive efficiency, which affects motion when cruising and aerodynamic forces when hovering.
Greater reactive forces and properties that act against the object, such as viscosity and density, reduce the ability of an animal's motion to fall within the ideal Strouhal number range when swimming. Through the assessment of different species that fly or swim, it was found that the motion of many species of birds and fish falls within the optimal Strouhal range. However, the Strouhal number varies more within the same species than other species based on the method of how they move in a constrained manner in response to aerodynamic forces. | 1 | Applied and Interdisciplinary Chemistry |
Because the energy of an X-ray with particular wavelength is known (for Al K X-rays, E = 1486.7 eV), and because the emitted electrons' kinetic energies are measured, the electron binding energy of each of the emitted electrons can be determined by using the photoelectric effect equation,
where E is the binding energy (BE) of the electron measured relative to the chemical potential, E is the energy of the X-ray photons being used, E is the kinetic energy of the electron as measured by the instrument and is a work function-like term for the specific surface of the material, which in real measurements includes a small correction by the instrument's work function because of the contact potential. This equation is essentially a conservation of energy equation. The work function-like term can be thought of as an adjustable instrumental correction factor that accounts for the few eV of kinetic energy given up by the photoelectron as it gets emitted from the bulk and absorbed by the detector. It is a constant that rarely needs to be adjusted in practice. | 0 | Theoretical and Fundamental Chemistry |
There are many biologically active chemicals which elicit an effect on the nervous system. Neurotransmitters and similarly functioning biochemical messengers elicit effects on postsynaptic neurons at neuronal synapses. Excitatory Amino Acids include Glutamate, whereas inhibitory Amino Acids include GABA and Glycine. Additionally, catecholamines, serotonin, acetylcholine, histamine, and orexins have widely-projecting effects and are often referred to as neuromodulators. Neuropeptides include bradykinin, cholecystokinin, corticotropin-releasing factor (CRF), galanin, MCH, MSH, Neuropeptide Y (NPY), Neurotensin, Opioids, orexin, oxytocin, somatostatin, tachykinins, TRH, CUP, and vasopressin. Purines, endogenous cannabinoids, gasses, neurotrophic factors, chemokines, and VEGF are all classified as atypical neurotransmitters. Major receptors of neurotransmitters include AMPA receptors, NMDA receptors, and Kainate Receptors. | 1 | Applied and Interdisciplinary Chemistry |
In aqueous solution, oxyanions with high charge can undergo condensation reactions, such as in the formation of the dichromate ion, :
The driving force for this reaction is the reduction of electrical charge density on the anion and the elimination of the hydronium () ion. The amount of order in the solution is decreased, releasing a certain amount of entropy which makes the Gibbs free energy more negative and favors the forward reaction. It is an example of an acid–base reaction with the monomeric oxyanion acting as a base and the condensed oxyanion acting as its conjugate acid. The reverse reaction is a hydrolysis reaction, as a water molecule, acting as a base, is split. Further condensation may occur, particularly with anions of higher charge, as occurs with adenosine phosphates.
The conversion of ATP to ADP is a hydrolysis reaction and is an important source of energy in biological systems.
The formation of most silicate minerals can be viewed as the result of a de-condensation reaction in which silica reacts with a basic oxide, an acid–base reaction in the Lux–Flood sense. | 0 | Theoretical and Fundamental Chemistry |
Many proteins and hormones are synthesized in the form of their precursors - zymogens, proenzymes, and prehormones. These proteins are cleaved to form their final active structures. Insulin, for example, is synthesized as preproinsulin, which yields proinsulin after the signal peptide has been cleaved. The proinsulin is then cleaved at two positions to yield two polypeptide chains linked by two disulfide bonds. Removal of two C-terminal residues from the B-chain then yields the mature insulin. Protein folding occurs in the single-chain proinsulin form which facilitates formation of the ultimate inter-peptide disulfide bonds, and the ultimate intra-peptide disulfide bond, found in the native structure of insulin.
Proteases in particular are synthesized in the inactive form so that they may be safely stored in cells, and ready for release in sufficient quantity when required. This is to ensure that the protease is activated only in the correct location or context, as inappropriate activation of these proteases can be very destructive for an organism. Proteolysis of the zymogen yields an active protein; for example, when trypsinogen is cleaved to form trypsin, a slight rearrangement of the protein structure that completes the active site of the protease occurs, thereby activating the protein.
Proteolysis can, therefore, be a method of regulating biological processes by turning inactive proteins into active ones. A good example is the blood clotting cascade whereby an initial event triggers a cascade of sequential proteolytic activation of many specific proteases, resulting in blood coagulation. The complement system of the immune response also involves a complex sequential proteolytic activation and interaction that result in an attack on invading pathogens. | 1 | Applied and Interdisciplinary Chemistry |
Consider two points and in the plane, and a curve , also in the plane, that connects them. Then every point on the curve has coordinate . Let the total length of the curve be .
Suppose a ribbon-shaped surface is created by extending the curve upward to the horizontal plane , where is the thickness of the flow. Then the surface has length , width , and area . Call this the test surface. | 1 | Applied and Interdisciplinary Chemistry |
Stringing is perhaps the most crucial of these effects, and is often seen on adhesive tapes. Stringing occurs when a separation of two surfaces is beginning and molecules at the interface bridge out across the gap, rather than cracking like the interface itself. The most significant consequence of this effect is the restraint of the crack. By providing the otherwise brittle interfacial bonds with some flexibility, the molecules that are stringing across the gap can stop the crack from propagating. Another way to understand this phenomenon is by comparing it to the stress concentration at the point of failure mentioned earlier. Since the stress is now spread out over some area, the stress at any given point has less of a chance of overwhelming the total adhesive force between the surfaces. If failure does occur at an interface containing a viscoelastic adhesive agent, and a crack does propagate, it happens by a gradual process called “fingering”, rather than a rapid, brittle fracture.
Stringing can apply to both the diffusive bonding regime and the chemical bonding regime. The strings of molecules bridging across the gap would either be the molecules that had earlier diffused across the interface or the viscoelastic adhesive, provided that there was a significant volume of it at the interface. | 0 | Theoretical and Fundamental Chemistry |
PKA has always been considered important in formation of a memory. In the fruit fly, reductions in expression activity of DCO (PKA catalytic subunit encoding gene) can cause severe learning disabilities, middle term memory and short term memory. Long term memory is dependent on the CREB transcription factor, regulated by PKA. A study done on drosophila reported that an increase in PKA activity can affect short term memory. However, a decrease in PKA activity by 24% inhibited learning abilities and a decrease by 16% affected both learning ability and memory retention. Formation of a normal memory is highly sensitive to PKA levels. | 1 | Applied and Interdisciplinary Chemistry |
In Prinzbach's optimized route from pagodane to dodecahedrane, the original low-yielding isomerization of parent pagodane to dodecahedrane is replaced by a longer but higher yielding sequence - which nevertheless still relies heavily on pagodane derivatives. In the scheme below, the divergence from the original happens after compound 16. | 0 | Theoretical and Fundamental Chemistry |
It is still not clear on how to find the linear range of the BET plot for microporous materials in a way that reduces any subjectivity in the assessment of the monolayer capacity. A crowd-sourced study involving 61 research groups has shown that reproducibility of BET area determination from identical isotherms is, in some cases, problematic. Rouquerol et al. suggested a procedure that is based on two criteria:
* C must be positive implying that any negative intercept on the BET plot indicates that one is outside the valid range of the BET equation.
* Application of the BET equation must be limited to the range where the term V(1-P/P) continuously increases with P/P.
These corrections are an attempt to salvage the BET theory, which is restricted to type II isotherms. Even while using this type, use of the data itself is restricted to 0.05 to 0.35 of , routinely discarding 70% of the data. This restriction must be modified depending upon conditions. | 0 | Theoretical and Fundamental Chemistry |
García Mancheño is head of a research group at the University of Münster that focuses on developing new catalysts to accomplish organic chemical transformations. She has authored several review articles in peer-reviewed journals on topics in organocatalytic chemistry, and is the editor of a textbook on anion-binding catalysts. | 0 | Theoretical and Fundamental Chemistry |
MAP4 was previously not thought to exist in neuronal tissue however the MAP-SP has been found in certain mammalian brain tissue. MAP4 is not confined to just nerve cells, but rather can be found in nearly all types of cells. | 1 | Applied and Interdisciplinary Chemistry |
Translation in plants is tightly regulated as in animals, however, it is not as well understood as transcriptional regulation. There are several levels of regulation including translation initiation, mRNA turnover and ribosome loading. Recent studies have shown that translation is also under the control of the circadian clock. Like transcription, the translation state of numerous mRNAs changes over the diel cycle (day night period). | 1 | Applied and Interdisciplinary Chemistry |
* 1941: Isaac Asimov published the science fiction short story "Reason," in which a space station transmits energy collected from the sun to various planets using microwave beams. "Reason" was published in the "Astounding Science Fiction" magazine.
*1968: Peter Glaser introduces the concept of a "solar power satellite" system with square miles of solar collectors in high geosynchronous orbit for collection and conversion of sun's energy into a microwave beam to transmit usable energy to large receiving antennas (rectennas) on Earth for distribution.
* 1973: Peter Glaser is granted United States patent number 3,781,647 for his method of transmitting power over long distances using microwaves from a large (one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
* 1978–1981: The United States Department of Energy and NASA examine the solar power satellite (SPS) concept extensively, publishing design and feasibility studies.
* 1987: Stationary High Altitude Relay Platform a Canadian experiment
* 1995–1997: NASA conducts a "Fresh Look" study of space solar power (SSP) concepts and technologies.
* 1998: The Space Solar Power Concept Definition Study (CDS) identifies credible, commercially viable SSP concepts, while pointing out technical and programmatic risks.
* 1998: Japan's space agency begins developing a space solar power system (SSPS), a program that continues to the present day.
* 1999: NASAs Space Solar Power Exploratory Research and Technology program (SERT, see below') begins.
* 2000: John Mankins of NASA testifies in the U.S. House of Representatives, saying "Large-scale SSP is a very complex integrated system of systems that requires numerous significant advances in current technology and capabilities. A technology roadmap has been developed that lays out potential paths for achieving all needed advances — albeit over several decades. | 0 | Theoretical and Fundamental Chemistry |
* J. Day and R. F. Tylecote, The Industrial Revolution in Metals (The Institute of Metals, London 1991).
* Söderberg, A. 2011. [http://web.comhem.se/vikingbronze/soderberg_situne_dei_2011.pdf Eyvind Skáldaspillir's silver - refining and standards in pre-monetary economies in the light of finds from Sigtuna and Gotland]. Situne Dei 2011. Edberg, R. Wikström, A. (eds). Sigtuna.
* R. F. Tylecote, A history of metallurgy (Institute of materials, London 1992).
* [http://www.ncl.ac.uk/library/specialcollections/collections/daguerreotypes/pattinson.php Newcastle University: Hugh Lee Pattinson] | 1 | Applied and Interdisciplinary Chemistry |
An alternative method to assess DNA and RNA concentration is to tag the sample with a Fluorescent tag, which is a fluorescent dye used to measure the intensity of the dyes that bind to nucleic acids and selectively fluoresce when bound (e.g. Ethidium bromide). This method is useful for cases where concentration is too low to accurately assess with spectrophotometry and in cases where contaminants absorbing at 260 nm make accurate quantitation by that method impossible. The benefit of fluorescence quantitation of DNA and RNA is the improved sensitivity over spectrophotometric analysis. Although, that increase in sensitivity comes at the cost of a higher price per sample and a lengthier sample preparation process.
There are two main ways to approach this. "Spotting" involves placing a sample directly onto an agarose gel or plastic wrap. The fluorescent dye is either present in the agarose gel, or is added in appropriate concentrations to the samples on the plastic film. A set of samples with known concentrations are spotted alongside the sample. The concentration of the unknown sample is then estimated by comparison with the fluorescence of these known concentrations. Alternatively, one may run the sample through an agarose or polyacrylamide gel, alongside some samples of known concentration. As with the spot test, concentration is estimated through comparison of fluorescent intensity with the known samples.
If the sample volumes are large enough to use microplates or cuvettes, the dye-loaded samples can also be quantified with a fluorescence photometer. Minimum sample volume starts at 0.3 μl.
To date there is no fluorescence method to determine protein contamination of a DNA sample that is similar to the 260 nm/280 nm spectrophotometric version. | 0 | Theoretical and Fundamental Chemistry |
Glycogen is cleaved from the nonreducing ends of the chain by the enzyme glycogen phosphorylase to produce monomers of glucose-1-phosphate:
In vivo, phosphorolysis proceeds in the direction of glycogen breakdown because the ratio of phosphate and glucose-1-phosphate is usually greater than 100. Glucose-1-phosphate is then converted to glucose 6 phosphate (G6P) by phosphoglucomutase. A special debranching enzyme is needed to remove the α(1→6) branches in branched glycogen and reshape the chain into a linear polymer. The G6P monomers produced have three possible fates:
* G6P can continue on the glycolysis pathway and be used as fuel.
* G6P can enter the pentose phosphate pathway via the enzyme glucose-6-phosphate dehydrogenase to produce NADPH and 5 carbon sugars.
* In the liver and kidney, G6P can be dephosphorylated back to glucose by the enzyme glucose 6-phosphatase. This is the final step in the gluconeogenesis pathway. | 1 | Applied and Interdisciplinary Chemistry |
Grand potential is defined by
where U is the internal energy, T is the temperature of the system, S is the entropy, μ is the chemical potential, and N is the number of particles in the system.
The change in the grand potential is given by
where P is pressure and V is volume, using the fundamental thermodynamic relation (combined first and second thermodynamic laws);
When the system is in thermodynamic equilibrium, Φ is a minimum. This can be seen by considering that dΦ is zero if the volume is fixed and the temperature and chemical potential have stopped evolving. | 0 | Theoretical and Fundamental Chemistry |
Svante Arrhenius (1889) equation is often used to characterize the effect of temperature on the rates of chemical reactions. The Arrhenius formula gave a simple and powerful law, which in a vast generality of cases describes the dependence on absolute temperature of the rate constant as following,
where is the absolute temperature, is the gas constant and the factor varies only slightly with temperature. The meaning attached to the energy of activation is as the minimum energy, which molecules need have to overcome the threshold to reaction. Therefore, the year 1889 can be considered as the birth date of reactive dynamics as the study of the motion of atoms and molecules in a reactive event. Eq. (1) was motivated by the 1884 discovery by vant Hoff of the exponential dependence from the temperature of the equilibrium constants for most reactions: Eq.(1), when used for both a reaction and its inverse, agrees with vant Hoff's equation interpreting chemical equilibrium as dynamical at the microscopic level. In case of a single rate-limited thermally activated process, an Arrhenius plot gives a straight line, from which the activation energy and the pre-exponential factor can both be determined.
However, advances in experimental and theoretical methods have revealed the existence of deviation from Arrhenius behavior (Fig.1).
To overcome this problem, Aquilanti and Mundim proposed (2010) a generalized Arrhenius law based on algebraic deformation of the usual exponential function. Starting from the Euler exponential definition given by,
defining the deformed exponential function as,
Identifying the deformation parameter as a continuous generalization of . At the limit the d-exponential function, , coincides with the usual exponential according to the well-known limit due to Euler, that is,
This definition was first used in thermodynamics and statistical mechanics by Landau. In the most recent scientific literature, there is a variety of deformed algebras with applications in different areas of science. Considering the d-exponential function, we introduce the deformed reaction rate coefficient, , in the following way,
and at the limit the usual Arrhenius reaction law is recovered (Figs.1 and 1a). is pre-exponential factor. Taking the logarithm of , Eq.(5), we obtain the following expression for the non-Arrhenius plot,
The logarithm of the reaction rate coefficient against reciprocal temperature shows a curvature, rather than the straight-line behavior described by the usual Arrhenius law (Figs.1 and 1a).
In Tolman’s definition the barrier or activation energy is a phenomenological quantity defined in terms of the slope of an Arrhenius law; it is usually assumed to be independent of absolute temperature (T), requires only local equilibrium and in general is given by
where is constant and is the ideal gas constant.
To generalize Tolman´s definition, in the case chemical reactions, we assume that the barrier or activation energy is a function of the temperature given by the following differential equation,
or → (8)
where (constant) at limit and the usual activation energy law is recovered as a constant. Noticeably, on the contrary of the usual Arrhenius case, the barrier or activation energy is temperature dependent and has different concavities depending on the value of the d parameter (see Figs.1 and 1a). Thus, a positive convexity means that decreases with increasing temperature. This general result is explained by a new Tolman-like interpretation of the activation energy through Eq.(8).
In the recent literature, it is possible to find different applications to verify the applicability of this new chemical reaction formalism | 0 | Theoretical and Fundamental Chemistry |
Vitamin B, CHCoNOP, is the most complex of all known vitamins. Its chemical structure had been determined by x-ray crystal structure analysis in 1956 by the research group of Dorothy Hodgkin (Oxford University) in collaboration with Kenneth N. Trueblood at UCLA and John G. White at Princeton University.
Core of the molecule is the corrin structure, a nitrogenous tetradentate ligand system. This is biogenetically related to porphyrins and chlorophylls, yet differs from them in important respects: the carbon skeleton lacks one of the four meso carbons between the five-membered rings, two rings (A and D, fig. 1) being directly connected by a carbon-carbon single bond. The corrin chromophore system is thus non-cyclic and expands over three meso positions only, incorporating three vinylogous amidine units. Lined up at the periphery of the macrocyclic ring are eight methyl groups and four propionic and three acetic acid side chains. Nine carbon atoms on the corrin periphery are chirogenic centers. The tetradentate, monobasic corrin ligand is equatorially coordinated with a trivalent cobalt ion which bears two additional axial ligands.
Several natural variants of the B structure exist that differ in these axial ligands. In the vitamin itself, the cobalt bears a cyano group on the top side of the corrin plane (cyanocobalamin), and a nucleotide loop on the other. This loop is connected on its other end to the peripheral propionic amide group at ring D and consists of structural elements derived from aminopropanol, phosphate, ribose, and 5,6-dimethylbenzimidazole. One of the nitrogen atoms of the imidazole ring is axially coordinated to the cobalt, the nucleotide loop thus forming a nineteen-membered ring. All side chain carboxyl groups are amides.
Cobyric acid, one of the natural derivatives of vitamin B, lacks the nucleotide loop; depending on the nature of the two axial ligands, it displays instead its propionic acid function at ring D as carboxylate (as shown in fig. 1), or carboxylic acid (with two cyanide ligands at cobalt). | 0 | Theoretical and Fundamental Chemistry |
Dilution of sample or reducing the volume of sample injected may give a reduction of ion suppression by reducing the quantity of interfering species present, although the quantity of analyte of interest will also be reduced, making this an undesirable approach for trace analysis.
Similar is the effect of reducing the mobile phase flow rate to the nanolitre-per-minute range since, in addition to resulting in improved desolvation, the smaller droplets formed are more tolerant to the presence of non-volatile species in the sample matrix. | 0 | Theoretical and Fundamental Chemistry |
Since PECT materials expand and contract upon ion-insertion it is possible to use this effect for actuation. Several different materials have been proposed for this, including: carbon fibers inserted with lithium, sodium, and potassium; lithium cobalt oxide; and vanadium oxide nanofibers inserted with lithium and sodium. Applications for PECT-based actuation range from microelectromechanical systems (MEMS), to large morphing structures.
Different materials exhibit different amounts of expansion/contraction, with a response that is dependent on the type of ion, as well as the amount of charge. For example, silicon expands by more than 300% when inserted with lithium, whereas graphite expands by around 13%. Carbon fibres expand by up to 1% when inserted with lithium, but only around 0.2% when inserted with potassium. | 0 | Theoretical and Fundamental Chemistry |
Sulfuric acid contains not only molecules, but is actually an equilibrium of many other chemical species, as it is shown in the table below.
Sulfuric acid is a colorless oily liquid, and has a vapor pressure of <0.001 mmHg at 25 °C and 1 mmHg at 145.8 °C, and 98% sulfuric acid has a vapor pressure of <1 mmHg at 40 °C.
In the solid state, sulfuric acid is a molecular solid that forms monoclinic crystals with nearly trigonal lattice parameters. The structure consists of layers parallel to the (010) plane, in which each molecule is connected by hydrogen bonds to two others. Hydrates are known for n = 1, 2, 3, 4, 6.5, and 8, although most intermediate hydrates are stable against disproportionation. | 0 | Theoretical and Fundamental Chemistry |
A doublet can be thought of as a combination of a source and a sink of equal strengths kept at an infinitesimally small distance apart. Thus the streamlines can be seen to start and end at the same point.
The strength of a doublet made by a source and sink of strength kept a distance is given by –
The velocity of fluid flow can be expressed as –
The equations and the plot are for the limiting condition of
The concept of a doublet is very similar to that of electric dipoles and magnetic dipoles in electrodynamics. | 1 | Applied and Interdisciplinary Chemistry |
Substances that have the ability to reduce other substances (cause them to gain electrons) are said to be reductive or reducing and are known as reducing agents, reductants, or reducers. The reductant transfers electrons to another substance and is thus itself oxidized. Because it donates electrons, the reducing agent is also called an electron donor. Electron donors can also form charge transfer complexes with electron acceptors. The word reduction originally referred to the loss in weight upon heating a metallic ore such as a metal oxide to extract the metal. In other words, ore was "reduced" to metal. Antoine Lavoisier demonstrated that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the metal atom gains electrons in this process. The meaning of reduction then became generalized to include all processes involving a gain of electrons. Reducing equivalent refers to chemical species which transfer the equivalent of one electron in redox reactions. The term is common in biochemistry. A reducing equivalent can be an electron or a hydrogen atom as a hydride ion.
Reductants in chemistry are very diverse. Electropositive elemental metals, such as lithium, sodium, magnesium, iron, zinc, and aluminium, are good reducing agents. These metals donate electrons relatively readily.
Hydride transfer reagents, such as NaBH and LiAlH, reduce by atom transfer: they transfer the equivalent of hydride or H. These reagents are widely used in the reduction of carbonyl compounds to alcohols. A related method of reduction involves the use of hydrogen gas (H) as sources of H atoms. | 0 | Theoretical and Fundamental Chemistry |
Plant cells are surrounded by cell walls which are barriers for cell-cell communication. This barrier is overcome by specialized junctions called plasmodesmata. They are similar to gap junctions, connecting the cytosol of adjacent cells. Small molecules (<1000 Da), such as ions, amino acids, and sugars, can diffuse freely through plasmodesmata. These small molecules include signaling molecule and transcription factors. The size of the channel is also regulated to allow molecules up to 10,000 Da in size. The permeability of these channels is dependent on many factors, including Ca2+ concentration. An increase in cytosolic Ca2+ concentration will reversibly limit passage through the plasmodesmata. Unlike gap junctions, the cell membranes of adjacent cells merge to form a continuous channel called an annulus. Additionally, within the channel, there is an extension of the endoplasmic reticulum, called a desmotubule, which spans between the cells. The cell-cell interactions facilitated by plasmodesmata play an important role in development of plant cells and tissues and defense against viral infection. | 1 | Applied and Interdisciplinary Chemistry |
The history of acid-base titration dates back to the late 19th century when advancements in analytical chemistry fostered the development of systematic techniques for quantitative analysis. The origins of titration methods can be linked to the work of chemists such as Karl Friedrich Mohr in the mid-1800s. His contributions laid the groundwork for understanding titrations involving acids and bases.
Theoretical progress came with the research of Swedish chemist Svante Arrhenius, who in the late 19th century, introduced the Arrhenius theory, providing a theoretical framework for acid-base reactions. This theoretical foundation, along with ongoing experimental refinements, contributed to the evolution of acid-base titration as a precise and widely applicable analytical method.
Over time, the method has undergone further refinements and adaptations, establishing itself as an essential tool in laboratories across various scientific disciplines. | 0 | Theoretical and Fundamental Chemistry |
Pharmacological cardiotoxicity is a cardiac damage under the action of drugs and it can occur both affecting the performances of the cardiac muscle and by altering the ion channels/currents of the functional cardiac cells, named the cardiomyocytes.
Two distinct case in which can occur are related to anti-cancer drugs and antiarrhythmic drugs. From early observations, some of the first ones which go under the name of anthracycline. It has emerged that such drugs cause a progressive form of heart failure leading to cardiac death. The mechanism of cell injury is thought to account for iron-dependent generation of reactive oxygen species with a spreading of oxidative damage to the cardiomyocytes. On the other hand, related to the antiarrhythmic drugs, the cardiotoxicity is associated to the risk of induce a potential fatal arrhythmias due to an imbalance in the amount of ion currents that flows in/out the cell membrane of the cardiomyocytes. | 1 | Applied and Interdisciplinary Chemistry |
After the sample has been processed, the extract can be analysed using a variety of data analysis techniques. The chemical analysis and analytical instrumentation used depends on the goal of the study. Many analyses require multiple samples, although in some cases a single POCIS sample can be used for multiple analyses.
It is vital to use quality control (QC) procedures when using passive samplers. It is common practice for 10% to 50% of the total number of samples to be used for QC purposes. The number of QC samples depends on the study objectives. The QC samples are used to address issues such as sample contamination and analyte recovery. The types of QC samples commonly used include; reagent blanks, field blanks, matrix spikes, and procedural spikes.
A large number of studies have been performed in which POCIS data was combined with bioassays to measure biological endpoints. Testing POCIS extracts in biological assays is useful as a POCIS device samples over its entire deployment period, and biologically active compounds can be effectively monitored. It can also be argued that the use of POCIS is a more relevant from an ecotoxicological perspective as the use of a passive sampler mimics the uptake of compounds by organisms. Another strength in using bioassays to test environmental samples is that they can provide an integrative measure of the toxic potential of a group of chemical compounds, rather than a single contaminant. | 0 | Theoretical and Fundamental Chemistry |
The common feature of early kilns was an egg-cup shaped burning chamber, with an air inlet at the base (the "eye"), constructed of brick. Limestone was crushed (often by hand) to fairly uniform lumps – fine stone was rejected. Successive dome-shaped layers of limestone and wood or coal were built up in the kiln on grate bars across the eye. When loading was complete, the kiln was kindled at the bottom, and the fire gradually spread upwards through the charge. When burnt through, the lime was cooled and raked out through the base. Fine ash dropped out and was rejected with the "riddlings".
Only lump stone could be used, because the charge needed to "breathe" during firing. This also limited the size of kilns and explains why kilns were all much the same size. Above a certain diameter, the half-burned charge would be likely to collapse under its own weight, extinguishing the fire. So kilns always made 25–30 tonnes of lime in a batch. Typically the kiln took a day to load, three days to fire, two days to cool and a day to unload, so a one-week turnaround was normal. The degree of burning was controlled by trial and error from batch to batch by varying the amount of fuel used. Because there were large temperature differences between the center of the charge and the material close to the wall, a mixture of underburned (i.e. high loss on ignition), well-burned and dead-burned lime was normally produced. Typical fuel efficiency was low, with 0.5 tonnes or more of coal being used per tonne of finished lime (15 MJ/kg). | 1 | Applied and Interdisciplinary Chemistry |
For a normal crystalline ice far below its melting point, there will be some relaxation of the atoms near the surface. Simulations of ice near to its melting point show that there is significant melting of the surface layers rather than a symmetric relaxation of atom positions. Nuclear magnetic resonance provided evidence for a liquid layer on the surface of ice. In 1998, using atomic force microscopy, Astrid Döppenschmidt and Hans-Jürgen Butt measured the thickness of the liquid-like layer on ice to be roughly 32 nm at −1 °C, and 11 nm at −10 °C.
The surface melting can account for the following:
*Low coefficient of friction of ice, as experienced by skaters.
*Ease of compaction of ice
*High adhesion of ice surfaces | 0 | Theoretical and Fundamental Chemistry |
a cells produce a-factor, a mating pheromone which signals the presence of an a cell to neighbouring α cells. a cells respond to α-factor, the α cell mating pheromone, by growing a projection (known as a shmoo, due to its distinctive shape resembling the Al Capp cartoon character Shmoo) towards the source of α-factor. Similarly, α cells produce α-factor, and respond to a-factor by growing a projection towards the source of the pheromone. The response of haploid cells only to the mating pheromones of the opposite mating type allows mating between a and α cells, but not between cells of the same mating type.
These phenotypic differences between a and α cells are due to a different set of genes being actively transcribed and repressed in cells of the two mating types. a cells activate genes which produce a-factor and produce a cell surface receptor (Ste2) which binds to α-factor and triggers signaling within the cell. a cells also repress the genes associated with being an α cell. Similarly, α cells activate genes which produce α-factor and produce a cell surface receptor (Ste3) which binds and responds to a-factor, and α cells repress the genes associated with being an a cell. | 1 | Applied and Interdisciplinary Chemistry |
James Derek Birchall (usually known as Derek) was born in Leigh, the son of David Birchall, who managed a butcher's shop, and Valetta (née Marsh), who died in childbirth, aged 25. David Birchall remarried four years later, to Dora Mary Leather. In the meantime, Derek had been brought up by his grandparents.
Birchall left primary school, aged 14, and joined an industrial firm in his area, Sutcliffe Speakman as a general laboratory assistant. He was promoted to assistant in the research laboratory, and worked on activated carbon and flame. From an internal company report in 1947 it was evident that Birchall had done a lot of experimental work “with great care and precision”.
After a period of time with John Kerr & Co, and doing his National Service in the army, Birchall joined ICI Salt Division in 1957, as assistant technical officer. Much of his early work there was on the nucleation of sodium chloride solutions and the improved formation of dendritic crystals. He was then transferred to ICI Cassel Works to apply his expertise to help commission a sodium cyanide plant, and increase the size of the crystals produced.
After the formation of the Mond Division in 1964, and further promotion, Birchall had his own team and could return to his first love: the extinction of fire. It resulted in the invention and commercialising of Monnex, a dry powder extinguisher still in use today. He later worked on new composite materials, and on silica and its hydrates.
There then followed a period of outside appointments:
* 1976–1985 Visiting Professor in Materials Science, University of Surrey
* 1977–1979 Visiting Fellow of Wolfson College, Oxford
* 1984–1986 Visiting Professor at MIT
* 1985 Professorial Associate of Brunel University
* 1986–1988 Visiting Professor of Biochemistry, University of Surrey
* 1988-ca 1991 Visiting Professor at Durham University
In 1992, Birchall took up the post of Professor of Inorganic Chemistry at the University of Keele, where he became interested in the role of silicon in biology. | 0 | Theoretical and Fundamental Chemistry |
In chronobiology, an ultradian rhythm is a recurrent period or cycle repeated throughout a 24-hour day. In contrast, circadian rhythms complete one cycle daily, while infradian rhythms such as the menstrual cycle have periods longer than a day. The Oxford English Dictionarys definition of Ultradian' specifies that it refers to cycles with a period shorter than a day but longer than an hour.
The descriptive term ultradian is used in sleep research in reference to the 90–120 minute cycling of the sleep stages during human sleep.
There is a circasemidian rhythm in body temperature and cognitive function which is technically ultradian. However, this appears to be the first harmonic of the circadian rhythm of each and not an endogenous rhythm with its own rhythm generator.
Other ultradian rhythms include blood circulation, blinking, pulse, hormonal secretions such as growth hormone, heart rate, thermoregulation, micturition, bowel activity, nostril dilation, appetite, and arousal. Ultradian rhythms of appetite require antiphasic release of neuropeptide Y (NPY) and corticotropin-releasing hormone (CRH), stimulating and inhibiting appetite ultradian rhythms. Recently, ultradian rhythms of arousal lasting approximately 4 hours were attributed to the dopaminergic system in mammals. When the dopaminergic system is perturbed either by use of drugs or by genetic disruption, these 4-hour rhythms can lengthen significantly into the infradian (> 24 h) range, sometimes even lasting for days (> 110 h) when methamphetamine are provided.
According to a study published in 1996: Ultradian mood states in bipolar disorder cycle much faster than rapid cycling; the latter is defined as four or more mood episodes in one year, sometimes occurring within a few weeks. Ultradian mood cycling is characterized by cycles shorter than 24 hours. | 1 | Applied and Interdisciplinary Chemistry |
In 1843, Louis Pasteur discovered optical activity in paratartaric, or racemic, acid found in grape wine. He was able to separate two enantiomer crystals that rotated polarized light in opposite directions. | 0 | Theoretical and Fundamental Chemistry |
Modern artificially-constructed vectors contain essential components found in all vectors, and may contain other additional features found only in some vectors:
*Origin of replication: Necessary for the replication and maintenance of the vector in the host cell.
*Promoter: Promoters are used to drive the transcription of the vector's transgene as well as the other genes in the vector such as the antibiotic resistance gene. Some cloning vectors need not have a promoter for the cloned insert but it is an essential component of expression vectors so that the cloned product may be expressed.
* Cloning site: This may be a multiple cloning site or other features that allow for the insertion of foreign DNA into the vector through ligation.
*Genetic markers: Genetic markers for viral vectors allow for confirmation that the vector has integrated with the host genomic DNA.
*Antibiotic resistance: Vectors with antibiotic-resistance open reading frames allow for survival of cells that have taken up the vector in growth media containing antibiotics through antibiotic selection.
*Epitope: Some vectors may contain a sequence for a specific epitope that can be incorporated into the expressed protein. It allows for antibody identification of cells expressing the target protein.
*Reporter genes: Some vectors may contain a reporter gene that allow for identification of plasmid that contains inserted DNA sequence. An example is lacZ-α which codes for the N-terminus fragment of β-galactosidase, an enzyme that digests galactose. A multiple cloning site is located within lacZ-α, and an insert successfully ligated into the vector will disrupt the gene sequence, resulting in an inactive β-galactosidase. Cells containing vector with an insert may be identified using blue/white selection by growing cells in media containing an analogue of galactose (X-gal). Cells expressing β-galactosidase (therefore does not contain an insert) appear as blue colonies. White colonies would be selected as those that may contain an insert. Other commonly used reporters include green fluorescent protein and luciferase.
*Targeting sequence: Expression vectors may include encoding for a targeting sequence in the finished protein that directs the expressed protein to a specific organelle in the cell or specific location such as the periplasmic space of bacteria.
*Protein purification tags: Some expression vectors include proteins or peptide sequences that allows for easier purification of the expressed protein. Examples include polyhistidine-tag, glutathione-S-transferase, and maltose binding protein. Some of these tags may also allow for increased solubility of the target protein. The target protein is fused to the protein tag, but a protease cleavage site positioned in the polypeptide linker region between the protein and the tag allows the tag to be removed later. | 1 | Applied and Interdisciplinary Chemistry |
Within the CH group, commonly found in organic compounds, the two low mass hydrogens can vibrate in six different ways which can be grouped as 3 pairs of modes: 1. symmetric and asymmetric stretching, 2. scissoring and rocking, 3. wagging and twisting. These are shown here:
(These figures do not represent the "recoil" of the C atoms, which, though necessarily present to balance the overall movements of the molecule, are much smaller than the movements of the lighter H atoms). | 0 | Theoretical and Fundamental Chemistry |
A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, pulse jet, or scramjet. In general, jet engines are internal combustion engines.
Air-breathing jet engines typically feature a rotating air compressor powered by a turbine, with the leftover power providing thrust through the propelling nozzle—this process is known as the Brayton thermodynamic cycle. Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines that were relatively inefficient for subsonic flight. Most modern subsonic jet aircraft use more complex high-bypass turbofan engines. They give higher speed and greater fuel efficiency than piston and propeller aeroengines over long distances. A few air-breathing engines made for high-speed applications (ramjets and scramjets) use the ram effect of the vehicle's speed instead of a mechanical compressor.
The thrust of a typical jetliner engine went from (de Havilland Ghost turbojet) in the 1950s to (General Electric GE90 turbofan) in the 1990s, and their reliability went from 40 in-flight shutdowns per 100,000 engine flight hours to less than 1 per 100,000 in the late 1990s. This, combined with greatly decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century, where previously a similar journey would have required multiple fuel stops. | 1 | Applied and Interdisciplinary Chemistry |
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