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* The monomer concentration is important for the synthesis of single chain cyclized/knotted polymers, but the kinetic chain length is the key determining factor for synthesis. | 0 | Theoretical and Fundamental Chemistry |
In contrast to the aforementioned odoriferous compounds, the levels of long straight-chain fatty acids such as hexadecanoic acid, octadecanoic acid, and linolic acid and short straight-chain fatty acids such as butyric acid, hexanoic acid, and octanoic acid in axillary sweat have not been found to be affected by the ABCC11 genotype, which suggests that their secretion is independent of ABCC11. These straight-chain fatty acids are odoriferous, but differently and to a much lesser extent compared to branched-chain fatty acids. In accordance, it has been said that it is very likely that these aliphatic straight-chain fatty acids are responsible for the faint sour acidic axillary odor that has previously been observed in most Japanese individuals. In addition to the secretion of straight-chain fatty acids, axillary microflora did not appear to differ between homozygous carriers of the 538G→A SNP and non-carriers.
The ABCC11 transporter appears to be involved both in the transport of androstane steroids into the secretory cells of apocrine glands and in the secretion of preodoriferous compounds from axillary apocrine glands. Specific steroids that ABCC11 has been found to transport include steroid sulfates like DHEA-S and estrone sulfate and steroid glucuronides like estradiol glucuronide. In accordance with its transport of compounds involved in axillary odor, ABCC11 alleles are strongly associated with axillary odor. Asians have little or faint axillary odor, whereas Caucasians and Africans have strong axillary odor, and this has been found to be due to genetic differences in the ABCC11 gene. | 1 | Applied and Interdisciplinary Chemistry |
The BVS apparatus consists of a specimen surrounded by Helmholtz coils and isolated from external vibrations by a framework constructed from insulating foam and either lead or brass. The specimen is affixed with both a permanent magnet and a mirror. The orientation of the coils with respect to the magnet when a current is driven through them determines whether the specimen undergoes bending or torsion. Angular displacement of the specimen is measured by an interferometer that detects the spatial movement of a reflected laser. This spatial waveform is converted to an electrical one by a light detector and read out on an oscilloscope. This oscilloscope also displays the torque or force waveform from the capacitor driving the current in the Helmholtz coils. Phase delay is determined by comparing these waveforms.
Resonance is minimized through the use of short specimens—which have higher resonant frequencies—and by reducing the inertia (magnetic and mass moments) of the magnet. Cubic samarium-cobalt magnets are ideal for high frequency studies. Due to the sample geometry being a short rectangular bar or cylinder, the equation governing the resonance of the BVS specimen geometry has an exact analytic solution, which allows the technique to yield results even for high loss materials. This exact solution provides a relationship between dynamic moduli, angular displacement, and geometric parameters. The inherent lack of drift and friction in the apparatus is responsible for its large range of operating frequencies. | 0 | Theoretical and Fundamental Chemistry |
The Kidd Metallurgical Site (or Met Site) is a metallurgical facility in Timmins, Ontario, Canada. It was built in 1980 and owned and operated by Xstrata Copper, following their 2006 takeover of Falconbridge Ltd. The site employs approximately 675 hourly employees.
The plant is southeast of the Kidd Mine, and houses a concentrator, copper smelter and refinery, zinc plant, cadmium plant, indium plant and a sulphuric acid plant. The Met Site was built away from the mine because of the muskeg-like terrain surrounding the mine.
The Met Site processes material from the Kidd Mine and outside sources, and employs 875 people. Of the 875 employees 125 work at the concentrator, 205 in the copper operations and 275 in the zinc facilities. The remainder of the employees are support staff.
Xstrata announced its plans to close the Metallurgical Site in May 2010. Only the concentrator will remain as the ore will now be shipped to Québec. The demolition of the rest of the plant started in February 2011. | 1 | Applied and Interdisciplinary Chemistry |
An analogous reaction with nitrogen as the heteroatom was described in 1984 for the synthesis of the antibiotic substance streptazolin. | 0 | Theoretical and Fundamental Chemistry |
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH). It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed with water. It has many names including hydrated lime, caustic lime, builders' lime, slaked lime, cal, and pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater, also called milk of lime, is the common name for a saturated solution of calcium hydroxide. | 0 | Theoretical and Fundamental Chemistry |
The level 1 destination vector determines the position and orientation of each gene in the final construct. There are fourteen available level 1 vectors, which differ only by the sequence of the flanking fusion sites while being identical in the internal fusion sites. Hence, all vectors can assemble the same level 0 parts.
As all level 1 vectors are binary plasmids, they are used for Agrobacterium mediated temporary expression in plants. | 1 | Applied and Interdisciplinary Chemistry |
The HNF6 subfamily members contain a cut-homeodomain (ONECUT) bind to DNA as monomers.
* HNF6α/OC-1/ONECUT1 ()
* HNF6β/OC-2/ONECUT2 () | 1 | Applied and Interdisciplinary Chemistry |
Surface nuclear magnetic resonance (SNMR), also known as magnetic resonance Sounding (MRS), is a geophysical technique specially designed for hydrogeology. It is based on the principle of nuclear magnetic resonance (NMR) and measurements can be used to indirectly estimate the water content of saturated and unsaturated zones in the earth's subsurface. SNMR is used to estimate aquifer properties, including the quantity of water contained in the aquifer, porosity, and hydraulic conductivity. | 0 | Theoretical and Fundamental Chemistry |
Free thyroxine (fT or free T4) is generally elevated in hyperthyroidism and decreased in hypothyroidism.
Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test. Example values are: | 1 | Applied and Interdisciplinary Chemistry |
Of the approximately three-thousand proteins found in chloroplasts, some 95% of them are encoded by nuclear genes. Many of the chloroplasts protein complexes consist of subunits from both the chloroplast genome and the hosts nuclear genome. As a result, protein synthesis must be coordinated between the chloroplast and the nucleus. The chloroplast is mostly under nuclear control, though chloroplasts can also give out signals regulating gene expression in the nucleus, called retrograde signaling. | 0 | Theoretical and Fundamental Chemistry |
A special case of a chemical synapse is the neuromuscular junction, in which the axon of a motor neuron terminates on a muscle fiber. In such cases, the released neurotransmitter is acetylcholine, which binds to the acetylcholine receptor, an integral membrane protein in the membrane (the sarcolemma) of the muscle fiber. However, the acetylcholine does not remain bound; rather, it dissociates and is hydrolyzed by the enzyme, acetylcholinesterase, located in the synapse. This enzyme quickly reduces the stimulus to the muscle, which allows the degree and timing of muscular contraction to be regulated delicately. Some poisons inactivate acetylcholinesterase to prevent this control, such as the nerve agents sarin and tabun, and the insecticides diazinon and malathion. | 0 | Theoretical and Fundamental Chemistry |
For small displacement hulls, such as sailboats or rowboats, wave-making resistance is the major source of the marine vessel drag.
A salient property of water waves is dispersiveness; i.e., the greater the wavelength, the faster it moves. Waves generated by a ship are affected by her geometry and speed, and most of the energy given by the ship for making waves is transferred to water through the bow and stern parts. Simply speaking, these two wave systems, i.e., bow and stern waves, interact with each other, and the resulting waves are responsible for the resistance. If the resulting wave is large, it carries much energy away from the ship, delivering it to the shore or wherever else the wave ends up or just dissipating it in the water, and that energy must be supplied by the ship's propulsion (or momentum), so that the ship experiences it as drag. Conversely, if the resulting wave is small, the drag experienced is small.
The amount and direction (additive or subtractive) of the interference depends upon the phase difference between the bow and stern waves (which have the same wavelength and phase speed), and that is a function of the length of the ship at the waterline. For a given ship speed, the phase difference between the bow wave and stern wave is proportional to the length of the ship at the waterline. For example, if the ship takes three seconds to travel its own length, then at some point the ship passes, a stern wave is initiated three seconds after a bow wave, which implies a specific phase difference between those two waves. Thus, the waterline length of the ship directly affects the magnitude of the wave-making resistance.
For a given waterline length, the phase difference depends upon the phase speed and wavelength of the waves, and those depend directly upon the speed of the ship. For a deepwater wave, the phase speed is the same as the propagation speed and is proportional to the square root of the wavelength. That wavelength is dependent upon the speed of the ship.
Thus, the magnitude of the wave-making resistance is a function of the speed of the ship in relation to its length at the waterline.
A simple way of considering wave-making resistance is to look at the hull in relation to bow and stern waves. If the length of a ship is half the length of the waves generated, the resulting wave will be very small due to cancellation, and if the length is the same as the wavelength, the wave will be large due to enhancement.
The phase speed of waves is given by the following formula:
where is the length of the wave and the gravitational acceleration. Substituting in the appropriate value for yields the equation:
or, in metric units:
These values, 1.34, 2.5 and very easy 6, are often used in the hull speed rule of thumb used to compare potential speeds of displacement hulls, and this relationship is also fundamental to the Froude number, used in the comparison of different scales of watercraft.
When the vessel exceeds a "speed–length ratio" (speed in knots divided by square root of length in feet) of 0.94, it starts to outrun most of its bow wave, the hull actually settles slightly in the water as it is now only supported by two wave peaks. As the vessel exceeds a speed-length ratio of 1.34, the wavelength is now longer than the hull, and the stern is no longer supported by the wake, causing the stern to squat, and the bow to rise. The hull is now starting to climb its own bow wave, and resistance begins to increase at a very high rate. While it is possible to drive a displacement hull faster than a speed-length ratio of 1.34, it is prohibitively expensive to do so. Most large vessels operate at speed-length ratios well below that level, at speed-length ratios of under 1.0. | 1 | Applied and Interdisciplinary Chemistry |
As with other metal foams, the properties of titanium foams depend mostly on the properties of the starting material and the relative density of the resultant foam. Thermal properties in foams – such as melting point, specific heat and expansion coefficient – remain constant for both the foams and the metals from which they are composed. However, the mechanical properties of foams are greatly influenced by microstructure, which include the aforementioned properties as well as anisotropy and defects within the foam's structure. | 0 | Theoretical and Fundamental Chemistry |
Temporally feathered radiation therapy (TFRT) is a radiation technique introduced in 2018 which aims to use the inherent non-linearities in normal tissue repair to allow for sparing of these tissues without affecting the dose delivered to the tumor. The application of this technique, which has yet to be automated, has been described carefully to enhance the ability of departments to perform it, and in 2021 it was reported as feasible in a small clinical trial, though its efficacy has yet to be formally studied. | 0 | Theoretical and Fundamental Chemistry |
Description of the Mono Lake tufa dates back to the 1880s, when Edward S. Dana and Israel C. Russell made the first systematic descriptions of the Mono Lake tufa. The tufa occurs as "modern" tufa towers. There are tufa sections from old shorelines, when the lake levels were higher. These pioneering works in tufa morphology are referred to by researchers and were confirmed by James R. Dunn in 1953. The tufa types can roughly be divided into three main categories based on morphology:
*Lithoid tufa - massive and porous with a rock-like appearance
*Dendritic tufa - branching structures that look similar to small shrubs
*Thinolitic tufa - large well-formed crystals of several centimeters
Through time, many hypotheses were developed regarding the formation of the large thinolite crystals (also referred to as glendonite) in thinolitic tufa. It was relatively clear that the thinolites represented a calcite pseudomorph after some unknown original crystal. The original crystal was only determined when the mineral ikaite was discovered in 1963. Ikaite, or hexahydrated CaCO, is metastable and only crystallizes at near-freezing temperatures. It is also believed that calcite crystallization inhibitors such as phosphate, magnesium, and organic carbon may aid in the stabilization of ikaite. When heated, ikaite breaks down and becomes replaced by smaller crystals of calcite. In the Ikka Fjord of Greenland, ikaite was also observed to grow in columns similar to the tufa towers of Mono Lake. This has led scientists to believe that thinolitic tufa is an indicator of past climates in Mono Lake because they reflect very cold temperatures. | 1 | Applied and Interdisciplinary Chemistry |
To achieve comparability of VOC measurements, reference standards traceable to SI-units are required. For a number of VOCs gaseous reference standards are available from specialty gas suppliers or national metrology institutes, either in the form of cylinders or dynamic generation methods. However, for many VOCs, such as oxygenated VOCs, monoterpenes, or formaldehyde, no standards are available at the appropriate amount of fraction due to the chemical reactivity or adsorption of these molecules. Currently, several national metrology institutes are working on the lacking standard gas mixtures at trace level concentration, minimising adsorption processes, and improving the zero gas. The final scopes are for the traceability and the long-term stability of the standard gases to be in accordance with the data quality objectives (DQO, maximum uncertainty of 20% in this case) required by the WMO/GAW program. | 0 | Theoretical and Fundamental Chemistry |
Histones are composed of mostly positively charged amino acid residues such as lysine and arginine. The positive charges allow them to closely associate with the negatively charged DNA through electrostatic interactions. Neutralizing the charges in the DNA allows it to become more tightly packed. | 1 | Applied and Interdisciplinary Chemistry |
Genes with uninterrupted coding sequences that are thousands of bases long - up to 90,000 bases - that occur in many bacterial organisms were practically impossible to have occurred. However, the bacterial genes could have originated from split genes by losing introns, the only proposed way to arrive at long coding sequences. It is also a better way than by increasing the lengths of ORFs from short random ORFs to long ORFs by specifically removing the stop codons by mutation.
According to the split gene theory, this process of intron loss could have happened from prebiotic random DNA. These contiguously coding genes could be tightly organized in the bacterial genomes without any introns and be more streamlined. According to Senapathy, the nuclear boundary that was required for a cell containing split genes would not be required for a cell containing only uninterrupted genes. Thus, the bacterial cells did not develop a nucleus. Based on split gene theory, the eukaryotic genomes and bacterial genomes could have independently originated from the split genes in primordial random DNA sequences. | 1 | Applied and Interdisciplinary Chemistry |
Members of the 2Fe–2S ferredoxin superfamily () have a general core structure consisting of beta(2)-alpha-beta(2), which includes putidaredoxin, terpredoxin, and adrenodoxin. They are proteins of around one hundred amino acids with four conserved cysteine residues to which the 2Fe–2S cluster is ligated. This conserved region is also found as a domain in various metabolic enzymes and in multidomain proteins, such as aldehyde oxidoreductase (N-terminal), xanthine oxidase (N-terminal), phthalate dioxygenase reductase (C-terminal), succinate dehydrogenase iron–sulphur protein (N-terminal), and methane monooxygenase reductase (N-terminal). | 0 | Theoretical and Fundamental Chemistry |
In 2017 Kimizuka reported a phthalocyanine based conductive MOF Cu-CuPc with an intrinsic conductivity in the range of 10 S cm. For the solvothermal synthesis of MOF, the organic linker Cu-octahydroxy phthalocyanine (CuPc) and metal ion is dissolved in a DMF/HO mixture at heated at 130 °C for 48 hours. Afterwards, Mirica and co-workers were able to enhance the conductivity to a range of 10 S cm by synthesizing a bimetallic phthalocyanine based MOF NiPc-Cu. | 0 | Theoretical and Fundamental Chemistry |
The development of Hydrofluoroolefins (HFOs) as replacements for Hydrochlorofluorocarbons and Hydrofluorocarbons began after the Kigali amendment to the Montreal Protocol in 2016, which called for the phase out of high global warming potential (GWP) refrigerants and to replace them with other refrigerants with a lower GWP, closer to that of carbon dioxide. HFOs have an ozone depletion potential of 0.0, compared to the 1.0 of principal CFC-11, and a low GWP which make them environmentally safer alternatives to CFCs, HCFCs and HFCs.
Hydrofluoroolefins serve as functional replacements for applications where high GWP hydrofluorocarbons were once used. In April 2022, the EPA signed a pre-published final rule Listing of HFO-1234yf under the Significant New Alternatives Policy (SNAP) Program for Motor Vehicle Air Conditioning in Nonroad Vehicles and Servicing Fittings for Small Refrigerant Cans. This ruling allows HFO-1234yf to take over in applications where ozone depleting CFCs such as R-12, and high GWP HFCs such as R-134a were once used. The phaseout and replacement of CFCs and HFCs in the automotive industry will ultimately reduce the release of these gases to atmosphere and intern have a positive contribution to the mitigation of climate change. | 1 | Applied and Interdisciplinary Chemistry |
Thylakoids are membrane-bound structures embedded in the chloroplast stroma. A stack of thylakoids is called a granum and resembles a stack of coins. | 0 | Theoretical and Fundamental Chemistry |
Asymmetric stereoinduction can be achieved with the use of chiral auxiliaries. Chiral auxiliaries may be reversibly attached to the substrate, inducing a diastereoselective reaction prior to cleavage, overall producing an enantioselective process. Examples of chiral auxiliaries include, Evans’ chiral oxazolidinone auxiliaries (for asymmetric aldol reactions) pseudoephedrine amides and tert-butanesulfinamide imines. | 0 | Theoretical and Fundamental Chemistry |
Despite the apparent lack of attention towards covalent inhibitor drug discovery by most pharmaceutical companies, there are several examples of covalent drugs that have been approved or are progressing to late-stage clinical development. | 1 | Applied and Interdisciplinary Chemistry |
Like intravenous immunoglobulin therapy, ZMapp contains a mixture of neutralizing antibodies that confer passive immunity to an individual, enhancing the normal immune response, and is designed to be administered after exposure to the Ebola virus. Such antibodies have been used in the treatment and prevention of various infectious diseases and are intended to attack the virus by interfering with its surface and neutralizing it to prevent further damage. | 1 | Applied and Interdisciplinary Chemistry |
*[https://web.archive.org/web/20080405110339/http://www.ipcc-nggip.iges.or.jp/public/2006gl/index.htm 2006 IPCC Guidelines for National Greenhouse Gas Inventories ]
*[https://web.archive.org/web/20080321094829/http://www.ipcc-nggip.iges.or.jp/public/gl/invs6.htm Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories (reference manual)].
*[http://www.ipcc-nggip.iges.or.jp/EFDB/main.php IPCC Emission Factor Database]
*[http://www.ec.gc.ca/pdb/ghg/inventory_report/2005_report/tdm-toc_eng.cfm National Inventory Report: Greenhouse Gas Sources and Sinks in Canada].
* [https://web.archive.org/web/20100707144526/http://www.naei.org.uk/emissions/index.php United Kingdom's emission factor database]. | 1 | Applied and Interdisciplinary Chemistry |
Regulatory sequences for the insulin gene are:
* A5
* Z
* negative regulatory element (NRE)
* C2
* E2
* A3
* cAMP response element
* A2
* CAAT enhancer binding (CEB)
* C1
* E1
* G1 | 1 | Applied and Interdisciplinary Chemistry |
When the motion is slow (in biology, for example, diffusion in a membrane), getting adequate statistics from a single-point FCS experiment may take a prohibitively long time. More data can be obtained by performing the experiment in multiple spatial points in parallel, using a laser scanning confocal microscope. This approach has been called Image Correlation Spectroscopy (ICS). The measurements can then be averaged together.
Another variation of ICS performs a spatial autocorrelation on images, which gives information about the concentration of particles. The correlation is then averaged in time. While camera white noise does not autocorrelate over time, it does over space - this creates a white noise amplitude in the spatial autocorrelation function which must be accounted for when fitting the autocorrelation amplitude in order to find the concentration of fluorescent molecules.
A natural extension of the temporal and spatial correlation versions is spatio-temporal ICS (STICS). In STICS there is no explicit averaging in space or time (only the averaging inherent in correlation). In systems with non-isotropic motion (e.g. directed flow, asymmetric diffusion), STICS can extract the directional information. A variation that is closely related to STICS (by the Fourier transform) is k-space Image Correlation Spectroscopy (kICS).
There are cross-correlation versions of ICS as well, which can yield the concentration, distribution and dynamics of co-localized fluorescent molecules. Molecules are considered co-localized when individual fluorescence contributions are indistinguishable due to overlapping point-spread functions of fluorescence intensities. | 0 | Theoretical and Fundamental Chemistry |
Hormone transport and the involvement of binding proteins is an essential aspect when considering the function of hormones.
The formation of a complex with a binding protein has several benefits: the effective half-life of the bound hormone is increased, and a reservoir of bound hormones is created, which evens the variations in concentration of unbound hormones (bound hormones will replace the unbound hormones when these are eliminated). An example of the usage of hormone-binding proteins is in the thyroxine-binding protein which carries up to 80% of all thyroxine in the body, a crucial element in regulating the metabolic rate. | 1 | Applied and Interdisciplinary Chemistry |
Heat transfer coefficient due to nucleate boiling increases with wall superheat until they reach a certain point. When the applied heat flux exceeds the certain limit, heat transfer capability of the flow decreases or significantly drops. Normally, the critical heat flux corresponds to DNB in PWR and dryout in BWR. The reduced heat transfer coefficient seen in post-DNB or post-dryout is likely to result in damaging of the boiling surface. Understanding of the exact point and triggering mechanism related to critical heat flux is a topic of interest. | 0 | Theoretical and Fundamental Chemistry |
Plasma protein binding refers to the degree to which medications attach to blood proteins within the blood plasma. A drug's efficacy may be affected by the degree to which it binds. The less bound a drug is, the more efficiently it can traverse or diffuse through cell membranes. Common blood proteins that drugs bind to are human serum albumin, lipoprotein, glycoprotein, and α, β‚ and γ globulins. | 1 | Applied and Interdisciplinary Chemistry |
While surface energy is conventionally defined as the work required to build a unit of area of a given surface, when it comes to its measurement by the sessile drop technique, the surface energy is not quite as well defined. The values obtained through the sessile drop technique depend not only on the solid sample in question, but equally on the properties of the probe liquid being used, as well as the particular theory relating the parameters mathematically to one another.
There are numerous such theories developed by various researchers. These methods differ in several regards, such as derivation and convention, but most importantly they differ in the number of components or parameters which they are equipped to analyze. The simpler methods containing fewer components simplify the system by lumping surface energy into one number, while more rigorous methods with more components are derived to distinguish between various components of the surface energy. Again, the total surface energy of solids and liquids depends on different types of molecular interactions, such as dispersive (van der Waals), polar, and acid/base interactions, and is considered to be the sum of these independent components. Some theories account for more of these phenomena than do other theories. These distinctions are to be considered when deciding which method is appropriate for the experiment at hand. The following are a few commonly used such theories. | 0 | Theoretical and Fundamental Chemistry |
Transcriptional modification or co-transcriptional modification is a set of biological processes common to most eukaryotic cells by which an RNA primary transcript is chemically altered following transcription from a gene to produce a mature, functional RNA molecule that can then leave the nucleus and perform any of a variety of different functions in the cell. There are many types of post-transcriptional modifications achieved through a diverse class of molecular mechanisms.
One example is the conversion of precursor messenger RNA transcripts into mature messenger RNA that is subsequently capable of being translated into protein. This process includes three major steps that significantly modify the chemical structure of the RNA molecule: the addition of a 5 cap, the addition of a 3 polyadenylated tail, and RNA splicing. Such processing is vital for the correct translation of eukaryotic genomes because the initial precursor mRNA produced by transcription often contains both exons (coding sequences) and introns (non-coding sequences); splicing removes the introns and links the exons directly, while the cap and tail facilitate the transport of the mRNA to a ribosome and protect it from molecular degradation.
Post-transcriptional modifications may also occur during the processing of other transcripts which ultimately become transfer RNA, ribosomal RNA, or any of the other types of RNA used by the cell. | 1 | Applied and Interdisciplinary Chemistry |
Sodium/glucose co-transporter (SGLT) proteins are bound to the cell membrane and have the role of transporting glucose through the membrane into the cells, against the concentration gradient of glucose. This is done by using the sodium gradient, produced by sodium/potassium ATPase pumps, so at the same time glucose is transported into the cells, the sodium is too. Since it is against the gradient, it requires energy to work. SGLT proteins cause the glucose reabsorption from the glomerular filtrate, independent of insulin.
SGLT-2 is a member of the glucose transporter family and is a low-affinity, high-capacity glucose transporter. SGLT-2 is mainly expressed in the S-1 and S-2 segments of the proximal renal tubules where the majority of filtered glucose is absorbed. SGLT-2 has a role in regulation of glucose and is responsible for most glucose reabsorption in the kidneys.
In diabetes, extracellular glucose concentration increases and this high glucose level leads to upregulation of SGLT-2, leading in turn to more absorption of glucose in the kidneys. These effects cause maintenance of hyperglycemia. Because sodium is absorbed at the same time as glucose via SGLT-2, the upregulation of SGLT-2 probably leads to development or maintenance of hypertension. In study where rats were given either ramipril or losartan, levels of SGLT-2 protein and mRNA were significantly reduced. In patients with diabetes, hypertension is a common problem so this may have relevance in this disease.
Drugs that inhibit sodium/glucose cotransporter 2 inhibit renal glucose reabsorption which leads to enhanced urinary glucose excretion and lower glucose in blood. They work independently of insulin and can reduce glucose levels without causing hypoglycemia or weight gain. | 1 | Applied and Interdisciplinary Chemistry |
Many new monomeric versions of EosFP have been developed that offer advantages over wild type EosFP. Developed by a team at the Janelia Farm Research Campus at Howard Hughes Medical Institute, mEos4 has higher photostability and longer imaging abilities than EosFP. It is also highly resistant to chemical fixatives such as PFA, gluteraldehyde and OsO4 which are used to preserve samples. mEos4 is effective at higher temperatures than EosFP, phot-converts at an increased rate and has a higher emission amplitude in both green and red fluorescent states. Applications for the mEos4 protein include photoactivation localization microscopy (PALM), correlative light/ electron microscopy (CLEM), protein activity indication and activity integration (post-hoc imaging for protein activity over time). | 1 | Applied and Interdisciplinary Chemistry |
Changing the volume of the system changes the partial pressures of the products and reactants and can affect the equilibrium concentrations. With a pressure increase due to a decrease in volume, the side of the equilibrium with fewer moles is more favorable and with a pressure decrease due to an increase in volume, the side with more moles is more favorable. There is no effect on a reaction where the number of moles of gas is the same on each side of the chemical equation.
Considering the reaction of nitrogen gas with hydrogen gas to form ammonia:
: ⇌ ΔH = −92kJ mol
Note the number of moles of gas on the left-hand side and the number of moles of gas on the right-hand side. When the volume of the system is changed, the partial pressures of the gases change. If we were to decrease pressure by increasing volume, the equilibrium of the above reaction will shift to the left, because the reactant side has a greater number of moles than does the product side. The system tries to counteract the decrease in partial pressure of gas molecules by shifting to the side that exerts greater pressure. Similarly, if we were to increase pressure by decreasing volume, the equilibrium shifts to the right, counteracting the pressure increase by shifting to the side with fewer moles of gas that exert less pressure. If the volume is increased because there are more moles of gas on the reactant side, this change is more significant in the denominator of the equilibrium constant expression, causing a shift in equilibrium.
would be as follow:
If we double the pressure of the above situation, by halving the volume of both sides then would now be as follow: | 0 | Theoretical and Fundamental Chemistry |
The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. The gas emerging from the hot end can reach temperatures of , and the gas emerging from the cold end can reach . It has no moving parts and is considered an environmentally friendly technology because it can work solely on compressed air and does not use Freon. Its efficiency is low, however, counteracting its other environmental advantages.
Pressurised gas is injected tangentially into a swirl chamber near one end of a tube, leading to a rapid rotation—the first vortex—as it moves along the inner surface of the tube to the far end. A conical nozzle allows gas specifically from this outer layer to escape at that end through a valve. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex. Gas from the inner vortex transfers energy to the gas in the outer vortex, so the outer layer is hotter at the far end than it was initially. The gas in the central vortex is likewise cooler upon its return to the starting-point, where it is released from the tube. | 0 | Theoretical and Fundamental Chemistry |
Nucleophilic alkylating agents deliver the equivalent of an alkyl anion (carbanion). The formal "alkyl anion" attacks an electrophile, forming a new covalent bond between the alkyl group and the electrophile. The counterion, which is a cation such as lithium, can be removed and washed away in the work-up. Examples include the use of organometallic compounds such as Grignard (organomagnesium), organolithium, organocopper, and organosodium reagents. These compounds typically can add to an electron-deficient carbon atom such as at a carbonyl group. Nucleophilic alkylating agents can displace halide substituents on a carbon atom through the SN2 mechanism. With a catalyst, they also alkylate alkyl and aryl halides, as exemplified by Suzuki couplings.
The SN2 mechanism is not available for aryl substituents, where the trajectory to attack the carbon atom would be inside the ring. Thus, only reactions catalyzed by organometallic catalysts are possible. | 0 | Theoretical and Fundamental Chemistry |
The specific protein glomalin has not yet been isolated and described. What has been described is an extraction process involving heat and citrate, producing a mixture containing a substance that is reactive to a monoclonal antibody Mab32B11 raised against crushed AM fungi spores. The substance is then provisionally named "glomalin". As many laboratories do not have the equipment to perform an antibody-based isolation (ELISA), a crude mixture called glomalin-related soil proteins (GRSP) is used to refer to the extract portion reactive to the Bradford protein assay. There is significant confusion between the ideal glomalin protein, the antibody-reactive extract portion termed "glomalin", and GRSP.
"Glomalin" was first detected by the Mab32B11 ELISA assay in 1987. According to the scientist that proposed the hypothetical protein, Sarah F. Wright, it eluded extraction until 1996 because "It requires an unusual effort to dislodge glomalin for study: a bath in citrate combined with heating at 250 °F (121 °C) for at least an hour.... No other soil glue found to date required anything as drastic as this." However, using advanced analytical methods in 2010, the citrate-heating extraction procedure for GRSP was proven to co-extract humic substances, so it is still not clear if this "glue effect" comes from glomalin or the other substances that are co-extracted using that method. | 0 | Theoretical and Fundamental Chemistry |
In Vitis vinifera grape, trans-resveratrol is a phytoalexin produced against the growth of fungal pathogens such as Botrytis cinerea and delta-viniferin is another grapevine phytoalexin produced following fungal infection by Plasmopara viticola. Pinosylvin is a pre-infectious stilbenoid toxin (i.e. synthesized prior to infection), contrary to phytoalexins, which are synthesized during infection. It is present in the heartwood of Pinaceae. It is a fungitoxin protecting the wood from fungal infection.
Sakuranetin is a flavanone, a type of flavonoid. It can be found in Polymnia fruticosa and rice, where it acts as a phytoalexin against spore germination of Pyricularia oryzae. In Sorghum, the SbF3H2 H? --> gene, encoding a flavonoid 3-hydroxylase, seems to be expressed in pathogen-specific 3-deoxyanthocyanidin phytoalexins synthesis, for example in Sorghum-Colletotrichum' interactions.
6-Methoxymellein is a dihydroisocoumarin and a phytoalexin induced in carrot slices by UV-C, that allows resistance to Botrytis cinerea and other microorganisms.
Danielone is a phytoalexin found in the papaya fruit. This compound showed high antifungal activity against Colletotrichum gloesporioides, a pathogenic fungus of papaya.
Stilbenes are produced in Eucalyptus sideroxylon in case of pathogens attacks. Such compounds can be implied in the hypersensitive response of plants. High levels of phenolics in some woods can explain their natural preservation against rot.
In plants, VirA is a protein histidine kinase which senses certain sugars and phenolic compounds. These compounds are typically found from wounded plants, and as a result VirA is used by Agrobacterium tumefaciens to locate potential host organisms for infection. | 0 | Theoretical and Fundamental Chemistry |
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement. Commonly used are parts-per-million (ppm, ), parts-per-billion (ppb, ), parts-per-trillion (ppt, ) and parts-per-quadrillion (ppq, ). This notation is not part of the International System of Units (SI) system and its meaning is ambiguous. | 1 | Applied and Interdisciplinary Chemistry |
Branca Edmée Marques de Sousa Torres (Lisbon, 14 April 1899 - Lisbon, 19 July 1986) was a leading Portuguese specialist in the peaceful applications of nuclear technology who obtained a doctorate in Paris under the guidance of Marie Curie. Returning to Lisbon she founded the Radiochemistry Laboratory, where she continued her research for three decades. | 0 | Theoretical and Fundamental Chemistry |
Throughout the clinical trial, the sponsor is responsible for accurately informing the local site investigators of the true historical safety record of the drug, device or other medical treatments to be tested, and of any potential interactions of the study treatment(s) with already approved treatments. This allows the local investigators to make an informed judgment on whether to participate in the study or not. The sponsor is also responsible for monitoring the results of the study as they come in from the various sites as the trial proceeds. In larger clinical trials, a sponsor will use the services of a data monitoring committee (DMC, known in the US as a data safety monitoring board). This independent group of clinicians and statisticians meets periodically to review the unblinded data the sponsor has received so far. The DMC has the power to recommend termination of the study based on their review, for example if the study treatment is causing more deaths than the standard treatment, or seems to be causing unexpected and study-related serious adverse events. The sponsor is responsible for collecting adverse event reports from all site investigators in the study, and for informing all the investigators of the sponsor's judgment as to whether these adverse events were related or not related to the study treatment.
The sponsor and the local site investigators are jointly responsible for writing a site-specific informed consent that accurately informs the potential subjects of the true risks and potential benefits of participating in the study, while at the same time presenting the material as briefly as possible and in ordinary language. FDA regulations state that participating in clinical trials is voluntary, with the subject having the right not to participate or to end participation at any time. | 1 | Applied and Interdisciplinary Chemistry |
* Liepmann, H. W., and Z. O. Bleviss. "The effects of dissociation and ionization on compressible couette flow." Douglas Aircraft Co. Rept. SM-19831 130 (1956).
* Liepmann, Hans Wolfgang, and Anatol Roshko. Elements of gasdynamics. Courier Corporation, 1957.
* Richard Feynman (1964) The Feynman Lectures on Physics: Mainly Electromagnetism and Matter, § 41–6 [https://feynmanlectures.caltech.edu/II_41.html#Ch41-S6 Couette flow], Addison–Wesley | 1 | Applied and Interdisciplinary Chemistry |
In the high and low temperature limits, viscous flow in amorphous materials (e.g. in glasses and melts) has the Arrhenius form:
where is a relevant activation energy, given in terms of molecular parameters; is temperature; is the molar gas constant; and is approximately a constant. The activation energy takes a different value depending on whether the high or low temperature limit is being considered: it changes from a high value at low temperatures (in the glassy state) to a low value at high temperatures (in the liquid state).
For intermediate temperatures, varies nontrivially with temperature and the simple Arrhenius form fails. On the other hand, the two-exponential equation
where , , , are all constants, provides a good fit to experimental data over the entire range of temperatures, while at the same time reducing to the correct Arrhenius form in the low and high temperature limits. This expression can be motivated from various theoretical models of amorphous materials at the atomic level.
A two-exponential equation for the viscosity can be derived within the Dyre shoving model of supercooled liquids, where the Arrhenius energy barrier is identified with the high-frequency shear modulus times a characteristic shoving volume. Upon specifying the temperature dependence of the shear modulus via thermal expansion and via the repulsive part of the intermolecular potential, another two-exponential equation is retrieved:
where denotes the high-frequency shear modulus of the material evaluated at a temperature equal to the glass transition temperature , is the so-called shoving volume, i.e. it is the characteristic volume of the group of atoms involved in the shoving event by which an atom/molecule escapes from the cage of nearest-neighbours, typically on the order of the volume occupied by few atoms. Furthermore, is the thermal expansion coefficient of the material, is a parameter which measures the steepness of the power-law rise of the ascending flank of the first peak of the radial distribution function, and is quantitatively related to the repulsive part of the interatomic potential. Finally, denotes the Boltzmann constant. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, vortex shedding is an oscillating flow that takes place when a fluid such as air or water flows past a bluff (as opposed to streamlined) body at certain velocities, depending on the size and shape of the body. In this flow, vortices are created at the back of the body and detach periodically from either side of the body forming a Kármán vortex street. The fluid flow past the object creates alternating low-pressure vortices on the downstream side of the object. The object will tend to move toward the low-pressure zone.
If the bluff structure is not mounted rigidly and the frequency of vortex shedding matches the resonance frequency of the structure, then the structure can begin to resonate, vibrating with harmonic oscillations driven by the energy of the flow. This vibration is the cause for overhead power line wires humming in the wind, and for the fluttering of automobile whip radio antennas at some speeds. Tall chimneys constructed of thin-walled steel tubes can be sufficiently flexible that, in air flow with a speed in the critical range, vortex shedding can drive the chimney into violent oscillations that can damage or destroy the chimney.
Vortex shedding was one of the causes proposed for the failure of the original Tacoma Narrows Bridge (Galloping Gertie) in 1940, but was rejected because the frequency of the vortex shedding did not match that of the bridge. The bridge actually failed by aeroelastic flutter.
A thrill ride, "VertiGo" at Cedar Point in Sandusky, Ohio suffered vortex shedding during the winter of 2001, causing one of the three towers to collapse. The ride was closed for the winter at the time. In northeastern Iran, the Hashemi-Nejad natural gas refinery's flare stacks suffered vortex shedding seven times from 1975 to 2003. Some simulation and analyses were done, which revealed that the main cause was the interaction of the pilot flame and flare stack. The problem was solved by removing the pilot. | 1 | Applied and Interdisciplinary Chemistry |
A separation process is a method that converts a mixture or a solution of chemical substances into two or more distinct product mixtures, a scientific process of separating two or more substances in order to obtain purity. At least one product mixture from the separation is enriched in one or more of the source mixture's constituents. In some cases, a separation may fully divide the mixture into pure constituents. Separations exploit differences in chemical properties or physical properties (such as size, shape, mass, density, or chemical affinity) between the constituents of a mixture.
Processes are often classified according to the particular properties they exploit to achieve separation. If no single difference can be used to accomplish the desired separation, multiple operations can often be combined to achieve the desired end.
With a few exceptions, elements or compounds exist in nature in an impure state. Often these raw materials must go through a separation before they can be put to productive use, making separation techniques essential for the modern industrial economy.
The purpose of separation may be:
* analytical: to identify the size of each fraction of a mixture is attributable to each component without attempting to harvest the fractions.
* preparative: to "prepare" fractions for input into processes that benefit when components are separated.
Separations may be performed on a small scale, as in a laboratory for analytical purposes, or on a large scale, as in a chemical plant. | 0 | Theoretical and Fundamental Chemistry |
As shown below, the SCODA principle applies to any particle driven by a force field in which the particle's mobility is altered in sync with the driving field. | 1 | Applied and Interdisciplinary Chemistry |
Amorphous polymers do not have a crystallization temperature (Tm) like semi-crystalline polymers and have only a glass transition temperature (Tg). This has a decisive influence on the behavior of shape-shape-memory polymer systems.
A crystalline copolymer system alone can result in the crosslinker-treated copolymer losing its crystallinity and becoming practically amorphous.
An amorphous polymer depends on the level of crosslinking or the degree of polymerization to exhibit this effect. In the case of poly(norbornene), which is a linear, amorphous polymer, with a content of 70 to 80% of trans bonds in commercial products, molecular mass of approximately 3x106 g mol and Tg of approximately 35 to 45°C. Because it achieves an unusually high degree of polymerization, chain entanglements can be relied upon as anchor points to achieve the thermally induced shape-memory effect. Therefore, this polymer relies solely on physical anchor points. When heated up to Tg, the material abruptly changes from a rigid state to a tapered state (softens). To achieve the effect, the shape must be changed rapidly to avoid rearrangement of the segments of the polymer chains and immediately cool the material also very rapidly below Tg. Reheating the material back to Tg will show the recovery of the original shape. | 0 | Theoretical and Fundamental Chemistry |
At Cambridge University George Liveing and James Dewar set out to systematically measure spectra of elements from groups I, II and III in visible light and longer wave ultraviolet that would transmit through air. They noticed that lines for sodium were alternating sharp and diffuse. They were the first to use the term "diffuse" for the lines. They classified alkali metal spectral lines into sharp and diffuse categories. In 1890 the lines that also appeared in the absorption spectrum were termed the principal series. Rydberg continued the use of sharp and diffuse for the other lines, whereas Kayser and Runge preferred to use the term first subordinate series for the diffuse series.
Arno Bergmann found a fourth series in infrared in 1907, and this became known as Bergmann Series or fundamental series.
Heinrich Kayser, Carl Runge and Johannes Rydberg found mathematical relations between the wave numbers of emission lines of the alkali metals.
Friedrich Hund introduced the s, p, d, f notation for subshells in atoms. Others followed this use in the 1930s and the terminology has remained to this day. | 0 | Theoretical and Fundamental Chemistry |
Virilization can occur in childhood in both males and females due to excessive amounts of androgens. Typical effects of virilization in children are pubic hair, accelerated growth and bone maturation, increased muscle strength, acne, and adult body odor. In males, virilization may signal precocious puberty, while congenital adrenal hyperplasia and androgen producing tumors (usually) of the gonads or adrenals are occasional causes in both sexes. | 1 | Applied and Interdisciplinary Chemistry |
Conjugation increases the allylic strain because it forces substituents into a configuration that causes their atoms to be in closer proximity, increasing the strength of repulsive Van der Waals forces. This situation occurs most noticeably when carboxylic acid or ketone is involved as a substituent of the allylic group. Resonance effect on the carboxylic group shifts the CO double bond to a hydroxy group. The carboxylic group will thus function as a hydroxyl group that will cause a large allylic strain to form and cancel the stabilization effects of the extended conjugation. This is very common in enolization reactions and can be viewed in the figure below under "Acidic Conditions."
In situations where the molecule can either be in a conjugated system or avoid allylic strain, it has been shown that the molecule's major form will be the one that avoids strain. This has been found via the cyclization in the figure below. Under treatment of perchloric acid, molecule A cyclizes into the conjugated system show in molecule B. However, the molecule will rearrange (due to allylic strain) into molecule C, causing molecule C to be the major species. Thus, the magnitude of destabilization via the allylic strain outweighs the stabilization caused by the conjugated system. | 0 | Theoretical and Fundamental Chemistry |
When polymers are oxidized, unstable alkyl radicals are formed which react further with oxygen to form peroxy bonds. The excitation and stabilization of the peroxy radical causes chemiluminescence. The light produced by this reaction is typically low wavelength infrared light. The amount of light emitted is used to determine the oxidation rate of an adhesive.
Chemiluminescence (CL) light intensity can be measured at various isothermal oxidation cycles; however, the temperature need not be raised to high levels. Correlation of light intensity is made to oxidation process parameters such as Oxidation Induction Temperature (OIT). By obtaining measurements at different temperatures, an accelerated oxidation progression correlation can be established. The prediction of oxidation during service life can then be carried out. | 0 | Theoretical and Fundamental Chemistry |
At high temperatures in air, it decomposes or burns to produce poisonous phosgene. This was a common problem when carbon tetrachloride was used as a fire extinguisher: there have been deaths due to its conversion to phosgene reported.
Carbon tetrachloride is a suspected human carcinogen based on sufficient evidence of carcinogenicity from studies in experimental animals. The World Health Organization reports carbon tetrachloride can induce hepatocellular carcinomas (hepatomas) in mice and rats. The doses inducing hepatic tumours are higher than those inducing cell toxicity. The International Agency for Research on Cancer (IARC) classified this compound in Group 2B, "possibly carcinogenic to humans". Carbon tetrachloride is one of the most potent hepatotoxins (toxic to the liver), so much so that it is widely used in scientific research to evaluate hepatoprotective agents. Exposure to high concentrations of carbon tetrachloride (including vapor) can affect the central nervous system and degenerate the liver and kidneys, and prolonged exposure may lead to coma or death. Chronic exposure to carbon tetrachloride can cause liver and kidney damage and could result in cancer.
Consumption of alcohol increases the toxic effects of carbon tetrachloride and may cause more severe organ damage, such as acute renal failure, in heavy drinkers. The doses that can cause mild toxicity to non-drinkers can be fatal to drinkers.
The effects of carbon tetrachloride on human health and the environment have been assessed under REACH in 2012 in the context of the substance evaluation by France.
In 2008, a study of common cleaning products found the presence of carbon tetrachloride in "very high concentrations" (up to 101 mg/m) as a result of manufacturers' mixing of surfactants or soap with sodium hypochlorite (bleach).
Carbon tetrachloride is also both ozone-depleting and a greenhouse gas. However, since 1992 its atmospheric concentrations have been in decline for the reasons described above (see atmospheric concentration graphs in the gallery). CCl has an atmospheric lifetime of 85 years. | 1 | Applied and Interdisciplinary Chemistry |
Fluoride is naturally present in groundwater, fresh and saltwater sources, as well as in rainwater, particularly in urban areas. Seawater fluoride levels are usually in the range of 0.86 to 1.4 mg/L, and average 1.1 mg/L (milligrams per litre). For comparison, chloride concentration in seawater is about 19 g/L. The low concentration of fluoride reflects the insolubility of the alkaline earth fluorides, e.g., CaF.
Concentrations in fresh water vary more significantly. Surface water such as rivers or lakes generally contains between 0.01 and 0.3 mg/L. Groundwater (well water) concentrations vary even more, depending on the presence of local fluoride-containing minerals. For example, natural levels of under 0.05 mg/L have been detected in parts of Canada but up to 8 mg/L in parts of China; in general levels rarely exceed 10 mg/litre
* In parts of Asia the groundwater can contain dangerously high levels of fluoride, leading to serious health problems.
* Worldwide, 50 million people receive water from water supplies that naturally have close to the "optimal level".
* In other locations the level of fluoride is very low, sometimes leading to fluoridation of public water supplies to bring the level to around 0.7–1.2 ppm.
*Mining can increase local fluoride levels
Fluoride can be present in rain, with its concentration increasing significantly upon exposure to volcanic activity or atmospheric pollution derived from burning fossil fuels or other sorts of industry, particularly aluminium smelters. | 1 | Applied and Interdisciplinary Chemistry |
Case hardening processes harden only the exterior of the steel part, creating a hard, wear-resistant skin (the "case") but preserving a tough and ductile interior. Carbon steels are not very hardenable meaning they can not be hardened throughout thick sections. Alloy steels have a better hardenability, so they can be through-hardened and do not require case hardening. This property of carbon steel can be beneficial, because it gives the surface good wear characteristics but leaves the core flexible and shock-absorbing. | 1 | Applied and Interdisciplinary Chemistry |
The expression vector is transformed or transfected into the host cell for protein synthesis. Some expression vectors may have elements for transformation or the insertion of DNA into the host chromosome, for example the vir genes for plant transformation, and integrase sites for chromosomal integration .
Some vectors may include targeting sequence that may target the expressed protein to a specific location such as the periplasmic space of bacteria. | 1 | Applied and Interdisciplinary Chemistry |
Frank Winton (1894–1985) held the Chair of Pharmacology from 1938 to 1961. His main scientific interest was in the control of blood flow to the kidney. Winton ran the department through the difficult war years when the Medical School was evacuated to Leatherhead, Surrey.
He appointed the first two female academics in the department. Mary Lockett (1911–1982) was a lecturer in the department from 1945 - 1950. Hannah Steinberg arrived in the UK from Vienna on a Kindertransport train while still a schoolgirl, and she eventually became Professor of Psychopharmacology.
Winton also worked hard and successfully to ensure that pharmacology had an appropriate place in the preclinical curriculum. He oversaw the extension of the department, including the Pharmacology Lecture Theatre (now the Schild Theatre).
He was the author, with [https://www.ucl.ac.uk/current-students/money/scholarships/life/bayliss Leonard Bayliss], of a widely used textbook Human Physiology, first published in 1932. The 6th edition, 1968 was written by Olof J.C. Lippold and F.R Winton | 1 | Applied and Interdisciplinary Chemistry |
3D-printing techniques have been used in a variety of industries for the overall goal of fabricating a product. Organ printing, on the other hand, is a novel industry that utilizes biological components to develop therapeutic applications for organ transplants. Due to the increased interest in this field, regulation and ethical considerations desperately need to be established. Specifically, there can be legal complications from pre-clinical to clinical translation for this treatment method. | 1 | Applied and Interdisciplinary Chemistry |
Penicillium rubens is a species of fungus in the genus Penicillium and was the first species known to produce the antibiotic penicillin. It was first described by Philibert Melchior Joseph Ehi Biourge in 1923. For the discovery of penicillin from this species Alexander Fleming shared the Nobel Prize in Physiology or Medicine in 1945. The original penicillin-producing type has been variously identified as Penicillium rubrum, P. notatum, and P. chrysogenum among others, but genomic comparison and phylogenetic analysis in 2011 resolved that it is P. rubens. It is the best source of penicillins and produces benzylpenicillin (G), phenoxymethylpenicillin (V) and octanoylpenicillin (K). It also produces other important bioactive compounds such as andrastin, chrysogine, fungisporin, roquefortine, and sorbicillins. | 1 | Applied and Interdisciplinary Chemistry |
There are two main types of blowing agents: gases at the temperature that the foam is formed, and gases generated by chemical reaction. Carbon dioxide, pentane, and chlorofluorocarbons are examples of the former. Blowing agents that produce gas via chemical reactions include baking powder, azodicarbonamide, titanium hydride, and isocyanates (when they react with water). | 0 | Theoretical and Fundamental Chemistry |
Nanodiamonds can self-assemble and a wide range of small molecules, proteins antibodies, therapeutics, and nucleic acids can bind to its surface allowing for drug delivery, protein-mimicking, and surgical implants. Other potential biomedical applications are the use of nanodiamonds as support for solid-phase peptide synthesis and as sorbents for detoxification and separation and fluorescent nanodiamonds for biomedical imaging. Nanodiamonds are capable of biocompatibility, the ability to carry a broad range of therapeutics, dispersibility in water and scalability, and the potential for targeted therapy all properties needed for a drug delivery platform. The small size, stable core, rich surface chemistry, ability to self-assemble, and low cytotoxicity of nanodiamonds have led to suggestions that they could be used to mimic globular proteins. Nanodiamonds have been mostly studied as potential injectable therapeutic agents for generalized drug delivery, but it has also been shown that films of Parylene nanodiamond composites can be used for localized sustained release of drugs over periods ranging from two days to one month. | 0 | Theoretical and Fundamental Chemistry |
This comparison is approximate. The actual relative strengths will vary depending on the molecules involved. For instance, the presence of water creates competing interactions that greatly weaken the strength of both ionic and hydrogen bonds. We may consider that for static systems, Ionic bonding and covalent bonding will always be stronger than intermolecular forces in any given substance. But it is not so for big moving systems like enzyme molecules interacting with substrate molecules. Here the numerous intramolecular (most often - hydrogen bonds) bonds form an active intermediate state where the intermolecular bonds cause some of the covalent bond to be broken, while the others are formed, in this way proceeding the thousands of enzymatic reactions, so important for living organisms. | 0 | Theoretical and Fundamental Chemistry |
Chimie ParisTech, officially École nationale supérieure de chimie de Paris (National Chemical Engineering Institute in Paris) and also known as ENSCP or Chimie Paris, is an engineering school and a constituent college of PSL Research University specialised in chemical science. It was founded in 1896 within the University of Paris and is located in the 5th arrondissement of Paris.
Most of the students enter the school after highly competitive exams known as the Concours commun Mines-Ponts, following at least two years of classes préparatoires. There is also a small number of excellent students from French universities admitted to the school. Chimie ParisTech is known as France's most selective chemical engineering college
The school is a research center hosting ten laboratories which conduct high level research in various fields of chemistry. | 1 | Applied and Interdisciplinary Chemistry |
The prediction of crystal properties by numerical simulation has become commonplace in the last 20 years as computers have grown more powerful and theoretical techniques more sophisticated. High accuracy prediction of elastic, electronic, transport and phase properties is possible with modern methods. | 0 | Theoretical and Fundamental Chemistry |
The small size of nanoparticles affects their magnetic and electric properties. The ferromagnetic materials in the micrometer range is a good example: widely used in magnetic recording media, for the stability of their magnetization state, those particles smaller than 10 nm are unstable and can change their state (flip) as the result of thermal energy at ordinary temperatures, thus making them unsuitable for that application. | 0 | Theoretical and Fundamental Chemistry |
The species MoCl feature Mo(II) (d) centers. Six Mo(II) centers gives rise to a total of 24 valence electrons, or 2e/Mo-Mo vector. More electron-deficient derivatives such as TaCl have fewer d-electrons. For example, the naked cluster Ta, the core of TaCl would have 5(6) - 14 = 16 valence electrons. Fewer d-electrons result in weakened M-M bonding and the extended Ta---Ta distances accommodate doubly bridging halides. | 0 | Theoretical and Fundamental Chemistry |
Pressure head is a component of hydraulic head, in which it is combined with elevation head. When considering dynamic (flowing) systems, there is a third term needed: velocity head. Thus, the three terms of velocity head, elevation head, and pressure head appear in the head equation derived from the Bernoulli equation for incompressible fluids:
where
: is velocity head,
: is elevation head,
: is pressure head, and
: is a constant for the system | 1 | Applied and Interdisciplinary Chemistry |
The elimination half-life of levomethamphetamine is between 13.3 and 15 hours, whereas dextromethamphetamine has a half-life of about 10.5 hours. | 0 | Theoretical and Fundamental Chemistry |
In order to get a good quality product, removing the inclusion becomes necessary. Liquid metal filtration through a ceramic medium is an efficient way to clean the metal. Different types of ceramic media are used in-line in foundries, such as ceramic foam filters, porous tube filters, bonded ceramic filters, and deep bed filters. | 1 | Applied and Interdisciplinary Chemistry |
The preparation of stable carbenes free from metal cations has been keenly sought to allow further study of the carbene species in isolation from these metals. Separating a carbene from a carbene-metal complex can be problematic due to the stability of the complex. Accordingly, it is preferable to make the carbene free from these metals in the first place. Indeed, some metal ions, rather than stabilising the carbene, have been implicated in the catalytic dimerisation of unhindered examples.
Shown right is an X-ray structure showing a complex between a diaminocarbene and potassium HMDS. This complex was formed when excess KHMDS was used as a strong base to deprotonate the formamidinium salt. Removing lithium ions resulting from deprotonation with reagents such as lithium diisopropylamide (LDA) can be especially problematic. Potassium and sodium salt by-products tend to precipitate from solution and can be removed. Lithium ions may be chemically removed by binding to species such as cryptands or crown ethers.
Metal free carbenes have been prepared in several ways as outlined below: | 0 | Theoretical and Fundamental Chemistry |
Another useful coordinate system is 3D cylindrical coordinates (typically where a pumping well is a line source located at the origin — parallel to the z axis — causing converging radial flow). Under these conditions the above equation becomes (r being radial distance and θ being angle), | 1 | Applied and Interdisciplinary Chemistry |
Researchers have investigated the role of surface plasmon resonances present on gold nanorods in the performance of dye-sensitized solar cells. They found that with an increase nanorod concentration, the light absorption grew linearly; however, charge extraction was also dependent on the concentration. With an optimized concentration, they found that the overall power conversion efficiency improved from 5.31 to 8.86% for Y123 dye-sensitized solar cells.
The synthesis of one-dimensional TiO nanostructures directly on fluorine-doped tin oxide glass substrates was successful demonstrated via a two-stop solvothermal reaction. Additionally, through a TiO sol treatment, the performance of the dual TiO nanowire cells was enhanced, reaching a power conversion efficiency of 7.65%.
Stainless steel based counter-electrodes for DSSCs have been reported which further reduce cost compared to conventional platinum based counter electrode and are suitable for outdoor application.
Researchers from EPFL have advanced the DSSCs based on copper complexes redox electrolytes, which have achieved 13.1% efficiency under standard AM1.5G, 100 mW/cm conditions and record 32% efficiency under 1000 lux of indoor light.
Researchers from Uppsala University have used n-type semiconductors instead of redox electrolyte to fabricate solid state p-type dye sensitized solar cells. | 0 | Theoretical and Fundamental Chemistry |
The sulfochlorination first described by Cortes F. Reed in 1936 proceeds under almost identical conditions as the conventional photochlorination. In addition to chlorine, sulfur dioxide is also introduced into the reaction mixture. The products formed are alkylsulfonyl chlorides, which are further processed into surfactants.
Hydrochloric acid is formed as a coupling product, as is the case with photochlorination. Since direct sulfonation of the alkanes is hardly possible, this reaction has proven to be useful. Due to chlorine, which is bound directly to the sulfur, the resulting products are highly reactive. As secondary products there are alkyl chlorides formed by pure photochlorination, as well as several sulfochlorinated products in the reaction mixture. | 0 | Theoretical and Fundamental Chemistry |
If the plasma is optically thin, the bremsstrahlung radiation leaves the plasma, carrying part of the internal plasma energy. This effect is known as the bremsstrahlung cooling. It is a type of radiative cooling. The energy carried away by bremsstrahlung is called bremsstrahlung losses and represents a type of radiative losses. One generally uses the term bremsstrahlung losses in the context when the plasma cooling is undesired, as e.g. in fusion plasmas. | 0 | Theoretical and Fundamental Chemistry |
Residues from the oil and gas industry often contain radium and its decay products. The sulfate scale from an oil well can be very radium rich, while the water, oil, and gas from a well often contain radon. The radon decays to form solid radioisotopes which form coatings on the inside of pipework. In an oil processing plant, the area of the plant where propane is processed is often one of the more contaminated areas of the plant as radon has a similar boiling point to propane.
Radioactive elements are an industrial problem in some oil wells where workers operating in direct contact with the crude oil and brine can be actually exposed to doses having negative health effects. Due to the relatively high concentration of these elements in the brine, its disposal is also a technological challenge. In the United States, the brine is however exempt from the dangerous waste regulations and can be disposed of regardless of radioactive or toxic substances content since the 1980s. | 0 | Theoretical and Fundamental Chemistry |
Amylases are used in breadmaking and to break down complex sugars, such as starch (found in flour), into simple sugars. Yeast then feeds on these simple sugars and converts it into the waste products of ethanol and carbon dioxide. This imparts flavour and causes the bread to rise. While amylases are found naturally in yeast cells, it takes time for the yeast to produce enough of these enzymes to break down significant quantities of starch in the bread. This is the reason for long fermented doughs such as sourdough. Modern breadmaking techniques have included amylases (often in the form of malted barley) into bread improver, thereby making the process faster and more practical for commercial use.
α-Amylase is often listed as an ingredient on commercially package-milled flour. Bakers with long exposure to amylase-enriched flour are at risk of developing dermatitis or asthma. | 1 | Applied and Interdisciplinary Chemistry |
SiGe has been used as a material in RTGs since 1976. Each mission that has used RTG technology involves exploration of far-reaching regions of the solar system. The most recent mission, New Horizons (2005), was originally set for a 3-year exploration, but was extended to 17 years. | 0 | Theoretical and Fundamental Chemistry |
Sedoheptulose-bisphosphatase (also sedoheptulose-1,7-bisphosphatase or SBPase, EC number 3.1.3.37; systematic name sedoheptulose-1,7-bisphosphate 1-phosphohydrolase) is an enzyme that catalyzes the removal of a phosphate group from sedoheptulose 1,7-bisphosphate to produce sedoheptulose 7-phosphate. SBPase is an example of a phosphatase, or, more generally, a hydrolase. This enzyme participates in the Calvin cycle. | 0 | Theoretical and Fundamental Chemistry |
Isotopes with extremely long half-lives and their decay products can be used to study multi-million year processes, such as tectonics and extreme climate change. For example, in rubidium–strontium dating, the isotopic ratio of strontium (Sr/Sr) can be analyzed within ice cores to examine changes over the earths lifetime. Differences in this ratio within the ice core would indicate significant alterations in the earths geochemistry. | 0 | Theoretical and Fundamental Chemistry |
Historically a cesium chloride (CsCl) solution was often used, but more commonly used density gradients are sucrose or Percoll. The sample is put on top of the solution, and then the tube is spun at a very high speed for an extended time, at times lasting days. The CsCl molecules become densely packed toward the bottom, so a continuous gradient of layers of different densities (and CsCl concentrations) form. Since the original solution was approximately the same density, they go to a level where their density and the CsCl density are the same, to which they form a sharp, distinctive band. | 0 | Theoretical and Fundamental Chemistry |
Autologous mitochondria extracted from healthy tissue and supplied to damaged tissue has been used to treat cardiac-compromised newborns. Alternatives to the approach include use of an extracorporeal membrane oxygenator (ECMO) or tissue or organ transplantation. | 1 | Applied and Interdisciplinary Chemistry |
Isoaspartic acid (isoaspartate, isoaspartyl, β-aspartate) is an aspartic acid residue isomeric to the typical α peptide linkage. It is a β-amino acid, with the side chain carboxyl moved to the backbone. Such a change is caused by a chemical reaction in which the nitrogen atom on the N+1 following peptide bond (in black at top right of Figure 1) nucleophilically attacks the γ-carbon of the side chain of an asparagine or aspartic acid residue, forming a succinimide intermediate (in red). Hydrolysis of the intermediate results in two products, either aspartic acid (in black at left) or isoaspartic acid, which is a β-amino acid (in green at bottom right). The reaction also results in the deamidation of the asparagine residue. Racemization may occur leading to the formation of D-aminoacids. | 1 | Applied and Interdisciplinary Chemistry |
*PDB molecule of the month:
**[http://www.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb72_1.html ATP synthase]
**[http://www.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb36_1.html Cytochrome c]
**[http://www.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb5_1.html Cytochrome c oxidase]
*Interactive molecular models at Universidade Fernando Pessoa:
**[https://web.archive.org/web/20090112031333/http://www2.ufp.pt/~pedros/anim/2frame-ien.htm NADH dehydrogenase]
**[https://web.archive.org/web/20090111212436/http://www2.ufp.pt/~pedros/anim/2frame-iien.htm succinate dehydrogenase]
**[https://web.archive.org/web/20090112035125/http://www2.ufp.pt/~pedros/anim/2frame-iiien.htm Coenzyme Q - cytochrome c reductase]
**[https://web.archive.org/web/20090111220321/http://www2.ufp.pt/~pedros/anim/2frame-iven.htm cytochrome c oxidase] | 1 | Applied and Interdisciplinary Chemistry |
In the realms of toxicology and pathology, the Irwin screen is utilised to determine whether the subject(s) show adverse effects from a course of pharmaceutical treatment or environmental pollution. It is an observational methodology. | 1 | Applied and Interdisciplinary Chemistry |
The rate expressions given in Guldberg and Waage's 1864 paper could not be differentiated, so they were simplified as follows. The chemical force was assumed to be directly proportional to the product of the active masses of the reactants.
This is equivalent to setting the exponents a and b of the earlier theory to one. The proportionality constant was called an affinity constant, k. The equilibrium condition for an "ideal" reaction was thus given the simplified form
[A], [B] etc. are the active masses at equilibrium. In terms of the initial amounts reagents p,q etc. this becomes
The ratio of the affinity coefficients, k'/k, can be recognized as an equilibrium constant. Turning to the kinetic aspect, it was suggested that the velocity of reaction, v, is proportional to the sum of chemical affinities (forces). In its simplest form this results in the expression
where is the proportionality constant. Actually, Guldberg and Waage used a more complicated expression which allowed for interaction between A and A', etc. By making certain simplifying approximations to those more complicated expressions, the rate equation could be integrated and hence the equilibrium quantity could be calculated. The extensive calculations in the 1867 paper gave support to the simplified concept, namely,
:The rate of a reaction is proportional to the product of the active masses of the reagents involved.
This is an alternative statement of the law of mass action. | 0 | Theoretical and Fundamental Chemistry |
According to Stokes’ law, a perfect sphere traveling through a viscous liquid feels a drag force proportional to the frictional coefficient :
where is the liquids viscosity, is the spheres drift speed, and is its radius. Because ionic mobility is directly proportional to drift speed, it is inversely proportional to the frictional coefficient:
where represents ionic charge in integer multiples of electron charges.
In 1905, Albert Einstein found the diffusion coefficient of an ion to be proportional to its mobility constant:
where is the Boltzmann constant and is electrical charge. This is known as the Einstein relation. Substituting in the frictional coefficient of a perfect sphere from Stokes’ law yields
which can be rearranged to solve for , the radius:
In non-spherical systems, the frictional coefficient is determined by the size and shape of the species under consideration. | 1 | Applied and Interdisciplinary Chemistry |
In the post-genomic age, high-throughput sequencing and gene/protein profiling techniques have transformed biological research by enabling comprehensive monitoring of a biological system, yielding a list of differentially expressed genes or proteins, which is useful in identifying genes that may have roles in a given phenomenon or phenotype. With DNA microarrays and genome-wide gene engineering, it is possible to screen global gene expression profiles to contribute a wealth of genomic data to the public domain. With RNA interference, it is possible to distill the inferences contained in the experimental literature and primary databases into knowledge bases that consist of annotated representations of biological pathways. In this case, individual genes and proteins are known to be involved in biological processes, components, or structures, as well as how and where gene products interact with each other. Pathway-oriented approaches for analyzing microarray data, by grouping long lists of individual genes, proteins, and/or other biological molecules according to the pathways they are involved in into smaller sets of related genes or proteins, which reduces the complexity, have proven useful for connecting genomic data to specific biological processes and systems. Identifying active pathways that differ between two conditions can have more explanatory power than a simple list of different genes or proteins. In addition, a large number of pathway analytic methods exploit pathway knowledge in public repositories such as Gene Ontology (GO) or Kyoto Encyclopedia of Genes and Genomes (KEGG), rather than inferring pathways from molecular measurements. Furthermore, different research focuses have given the word "pathway" different meanings. For example, pathway can denote a metabolic pathway involving a sequence of enzyme-catalyzed reactions of small molecules, or a signaling pathway involving a set of protein phosphorylation reactions and gene regulation events. Therefore, the term "pathway analysis" has a very broad application. For instance, it can refer to the analysis physical interaction networks (e.g., protein–protein interactions), kinetic simulation of pathways, and steady-state pathway analysis (e.g., flux-balance analysis), as well as its usage in the inference of pathways from expression and sequence data. Several functional enrichment analysis tools and algorithms have been developed to enhance data interpretation. The existing knowledge base–driven pathway analysis methods in each generation have been summarized in recent literature. | 0 | Theoretical and Fundamental Chemistry |
The color triangles formed by velocity vectors u,c and w are called velocity triangles and are helpful in explaining how pumps work.
: and are the absolute velocities of the fluid at the inlet and outlet respectively.
: and are the relative velocities of the fluid with respect to the blade at the inlet and outlet respectively.
: and are the velocities of the blade at the inlet and outlet respectively.
: is angular velocity.
Figures a and b show impellers with backward and forward-curved vanes respectively. | 1 | Applied and Interdisciplinary Chemistry |
Iron is also potentially toxic. Its ability to donate and accept electrons means that it can catalyze the conversion of hydrogen peroxide into free radicals. Free radicals can cause damage to a wide variety of cellular structures, and ultimately kill the cell.
Iron bound to proteins or cofactors such as heme is safe. Also, there are virtually no truly free iron ions in the cell, since they readily form complexes with organic molecules. However, some of the intracellular iron is bound to low-affinity complexes, and is termed labile iron or "free" iron. Iron in such complexes can cause damage as described above.
To prevent that kind of damage, all life forms that use iron bind the iron atoms to proteins. This binding allows cells to benefit from iron while also limiting its ability to do harm. Typical intracellular labile iron concentrations in bacteria are 10-20 micromolar, though they can be 10-fold higher in anaerobic environment, where free radicals and reactive oxygen species are scarcer. In mammalian cells, intracellular labile iron concentrations are typically smaller than 1 micromolar, less than 5 percent of total cellular iron. | 1 | Applied and Interdisciplinary Chemistry |
Liver of sulfur was once used to counteract poisoning with several metals, including arsenic, copper, lead, and antimony. A lump was dissolved in warm water and the patient was instructed to drink the solution three or four times over the course of an hour. At one time sulfurated potash was used to combat arthritis. It eventually fell into disfavor for medical purposes because sulfides and polysulfides were discovered to be toxic in their own right. | 0 | Theoretical and Fundamental Chemistry |
The most common application for spontaneous fission is as neutron source for further use. These neutrons may be used for applications such as neutron imaging, or may drive additional nuclear reactions, including initiating induced fission of a target as is common in nuclear reactors and nuclear weapons.
In crystals containing high proportions of uranium, fission products generated via spontaneous fission produce damage trails as the fragments recoil through the crystal structure. The number of trails, or fission tracks, may be used to estimate the age of a sample via fission track dating. | 0 | Theoretical and Fundamental Chemistry |
The bronze-colored material is one of the strongest reducing agents known. It has also been used as a catalyst in polymerizations and as a coupling reagent for aryl halides to biphenyls. In one study, freshly prepared was treated with 1-iodododecane delivering a modification (micrometre scale carbon platelets with long alkyl chains sticking out providing solubility) that is soluble in chloroform. Another potassium graphite compound, , has been used as a neutron monochromator. A new essential application for potassium graphite was introduced by the invention of the potassium-ion battery. Like the lithium-ion battery, the potassium-ion battery should use a carbon-based anode instead of a metallic anode. In this circumstance, the stable structure of potassium graphite is an important advantage. | 0 | Theoretical and Fundamental Chemistry |
Clay bricks expand as they absorb heat and moisture. This places compression stress on the bricks and mortar, encouraging bulging or flaking. A joint replacing mortar with elastomeric sealant will absorb the compressive forces without damage. Concrete decking (most typically in sidewalks) can suffer similar horizontal issues, which is usually relieved by adding a wooden spacer between the slabs. The wooden expansion joint compresses as the concrete expands. Dry, rot-resistant cedar is typically used, with a row of nails protruding out that will embed into the concrete and hold the spacer in place. | 1 | Applied and Interdisciplinary Chemistry |
The Henry solubility can also be expressed as the dimensionless ratio between the aqueous-phase concentration of a species and its gas-phase concentration :
For an ideal gas, the conversion is:
where is the gas constant, and is the temperature.
Sometimes, this dimensionless constant is called the water–air partitioning coefficient . It is closely related to the various, slightly different definitions of the Ostwald coefficient , as discussed by Battino (1984). | 0 | Theoretical and Fundamental Chemistry |
This method was developed by British physicists Oliver Lodge in 1886 and William Cecil Dampier in 1893. It depends on the movement of the boundary between two adjacent electrolytes under the influence of an electric field. If a colored solution is used and the interface stays reasonably sharp, the speed of the moving boundary can be measured and used to determine the ion transference numbers.
The cation of the indicator electrolyte should not move faster than the cation whose transport number is to be determined, and it should have same anion as the principle electrolyte. Besides the principal electrolyte (e.g., HCl) is kept light so that it floats on indicator electrolyte. serves best because is less mobile than and is common to both and the principal electrolyte HCl.
For example, the transport numbers of hydrochloric acid (HCl(aq)) may be determined by electrolysis between a cadmium anode and an Ag-AgCl cathode. The anode reaction is so that a cadmium chloride () solution is formed near the anode and moves toward the cathode during the experiment. An acid-base indicator such as bromophenol blue is added to make visible the boundary between the acidic HCl solution and the near-neutral solution. The boundary tends to remain sharp since the leading solution HCl has a higher conductivity that the indicator solution , and therefore a lower electric field to carry the same current. If a more mobile ion diffuses into the solution, it will rapidly be accelerated back to the boundary by the higher electric field; if a less mobile ion diffuses into the HCl solution it will decelerate in the lower electric field and return to the solution. Also the apparatus is constructed with the anode below the cathode, so that the denser solution forms at the bottom.
The cation transport number of the leading solution is then calculated as
where is the cation charge, the concentration, the distance moved by the boundary in time , the cross-sectional area, the Faraday constant, and the electric current. | 0 | Theoretical and Fundamental Chemistry |
Many commercial elastomers contain polysulfides as crosslinks. These crosslinks interconnect neighboring polymer chains, thereby conferring rigidity. The degree of rigidity is related to the number of crosslinks. Elastomers, therefore, have a characteristic ability to return to their original shape after being stretched or compressed. Because of this memory for their original cured shape, elastomers are commonly referred to as rubbers. The process of crosslinking the polymer chains in these polymers with sulfur is called vulcanization. The sulfur chains attach themselves to the allylic carbon atoms, which are adjacent to C=C linkages. Vulcanization is a step in the processing of several classes of rubbers, including polychloroprene (Neoprene), styrene-butadiene, and polyisoprene, which is chemically similar to natural rubber. Charles Goodyear's discovery of vulcanization, involving the heating of polyisoprene with sulfur, was revolutionary because it converted a sticky and almost useless material into an elastomer that could be fabricated into useful products. | 1 | Applied and Interdisciplinary Chemistry |
He was born in Nafplio, the first capital of Greece and his paternal family home. During World War II, he accompanied his parents to Egypt, South Africa, and finally the United States (U.S.), where his father held ministerial posts in the Greek Government in exile. The family stayed in the U.S. until 1944, when, following the liberation of Greece after the defeat of Nazi Germany, they returned permanently to Greece.
After his secondary education at the 8th Gymnasium of Athens, he graduated from the Medical School of the National and Kapodistrian University of Athens in 1956. After completion of Army service he joined the team of Prof. Peter Karlson at the Institut für Physiologische Chemie of the Ludwig Maximilian University of Munich. He completed his doctoral degree in biochemistry in 1962 from the Medical School of the Ludwig Maximilian University of Munich. | 1 | Applied and Interdisciplinary Chemistry |
The performance and capabilities of magnetometers are described through their technical specifications. Major specifications include
*Sample rate is the number of readings given per second. The inverse is the cycle time in seconds per reading. Sample rate is important in mobile magnetometers; the sample rate and the vehicle speed determine the distance between measurements.
*Bandwidth or bandpass characterizes how well a magnetometer tracks rapid changes in magnetic field. For magnetometers with no onboard signal processing, bandwidth is determined by the Nyquist limit set by sample rate. Modern magnetometers may perform smoothing or averaging over sequential samples, achieving a lower noise in exchange for lower bandwidth.
*Resolution is the smallest change in a magnetic field the magnetometer can resolve. A magnetometer should have a resolution a good deal smaller than the smallest change one wishes to observe. This includes quantization error which is caused by recording roundoff and truncation of digital expressions of the data.
*Absolute error is the difference between the readings of a magnetometer true magnetic field.
*Drift is the change in absolute error over time.
*Thermal stability is the dependence of the measurement on temperature. It is given as a temperature coefficient in units of nT per degree Celsius.
*Noise is the random fluctuations generated by the magnetometer sensor or electronics. Noise is given in units of , where frequency component refers to the bandwidth.
*Sensitivity is the larger of the noise or the resolution.
*Heading error is the change in the measurement due to a change in orientation of the instrument in a constant magnetic field.
*The dead zone is the angular region of magnetometer orientation in which the instrument produces poor or no measurements. All optically pumped, proton-free precession, and Overhauser magnetometers experience some dead zone effects.
*Gradient tolerance is the ability of a magnetometer to obtain a reliable measurement in the presence of a magnetic field gradient. In surveys of unexploded ordnance or landfills, gradients can be large. | 0 | Theoretical and Fundamental Chemistry |
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