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Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α. Because they are identical to helium nuclei, they are also sometimes written as or indicating a helium ion with a +2 charge (missing its two electrons). Once the ion gains electrons from its environment, the alpha particle becomes a normal (electrically neutral) helium atom .
Alpha particles have a net spin of zero. When produced in standard alpha radioactive decay, alpha particles generally have a kinetic energy of about 5 MeV and a velocity in the vicinity of 4% of the speed of light. They are a highly ionizing form of particle radiation, with low penetration depth (stopped by a few centimetres of air, or by the skin).
However, so-called long-range alpha particles from ternary fission are three times as energetic and penetrate three times as far. The helium nuclei that form 10–12% of cosmic rays are also usually of much higher energy than those produced by nuclear decay processes, and thus may be highly penetrating and able to traverse the human body and also many metres of dense solid shielding, depending on their energy. To a lesser extent, this is also true of very high-energy helium nuclei produced by particle accelerators. | 0 | Theoretical and Fundamental Chemistry |
Alpha-aminoadipic and alpha-ketoadipic aciduria is an autosomal recessive metabolic disorder characterized by an increased urinary excretion of alpha-ketoadipic acid and alpha-aminoadipic acid. It is caused by mutations in DHTKD1, which encodes the E1 subunit of the oxoglutarate dehydrogenase complex (alpha-ketoglutarate dehydrogenase complex). | 1 | Applied and Interdisciplinary Chemistry |
Capsaicin (fig. 2), a naturally occurring vanilloid, is the best known TRPV1 agonist. Resiniferatoxin (RTX) is another naturally occurring vanilloid that exhibits TRPV1 agonistic activity. It is more potent than capsaicin and is currently in development as a sensory neuron desensitizing agent.
Initially, agonists were the major focus of the TRPV1 ligand development due to the analgesic effect resulting from desensitization of the receptor. However, because of an initial burning effect of all natural vanilloid receptor agonists, including capsaicin, therapy becomes complicated and perhaps ineffective. Attempts to make synthetic agonists with good separation between excitatory effects and the analgesic effects have not been successful. To avoid this persisting side effects of TRPV1 agonists, a focused consideration has been given to competitive antagonists as novel analgesic drugs. | 1 | Applied and Interdisciplinary Chemistry |
Construction of MOSE at the inlets necessitates complex logistical organisation. These are located in a highly delicate environmental context so as to avoid interfering with the surrounding area as far as possible. The sites have been set up on temporary areas of water in order to limit occupation of the land adjacent to the inlets and reduce as far as possible the effect on activities taking place there. Materials (for example, site supplies) and machines are also moved via sea to avoid overloading the road system along the coast. Since the sites opened, all work has been carried out without interrupting transit through the inlet channels.
Below is a description of the work underway and already completed at each inlet, listed in order from North to South. | 1 | Applied and Interdisciplinary Chemistry |
The process was invented in Hanau, Germany in 1917. Heraeus Vacuumschmelze and Dr. Wilhelm Rohn applied for a patent on vacuum melting on 12 January 1918 and were granted a German patent DE 345161.
Edwin Fitch Northrup built the first prototype of a vacuum induction furnace in the United States of America in 1920.
Medium frequency furnaces were seen soon afterwards in England and Sweden in 1927.
The process was initially developed to refine certain special metals such as cobalt and nickel. As these metals and alloys became more common, the process of VIM became more widely used.
VIM now helps to melt a variety of metals for aircraft and nuclear applications. | 1 | Applied and Interdisciplinary Chemistry |
For elements in the main groups of the periodic table, the valence can vary between 1 and 8.
Many elements have a common valence related to their position in the periodic table, and nowadays this is rationalised by the octet rule.
The Greek/Latin numeral prefixes (mono-/uni-, di-/bi-, tri-/ter-, and so on) are used to describe ions in the charge states 1, 2, 3, and so on, respectively. Polyvalence or multivalence refers to species that are not restricted to a specific number of valence bonds. Species with a single charge are univalent (monovalent). For example, the cation is a univalent or monovalent cation, whereas the cation is a divalent cation, and the cation is a trivalent cation. Unlike Cs and Ca, Fe can also exist in other charge states, notably 2+ and 4+, and is thus known as a multivalent (polyvalent) ion. Transition metals and metals to the right are typically multivalent but there is no simple pattern predicting their valency.
† The same adjectives are also used in medicine to refer to vaccine valence, with the slight difference that in the latter sense, quadri- is more common than tetra-.
‡ As demonstrated by hit counts in Google web search and Google Books search corpora (accessed 2017).
§ A few other forms can be found in large English-language corpora (for example, *quintavalent, *quintivalent, *decivalent), but they are not the conventionally established forms in English and thus are not entered in major dictionaries. | 0 | Theoretical and Fundamental Chemistry |
Black pepper contains the alkaloid guineesine, which is an anandamide reuptake inhibitor. It may therefore increase anandamide's physiological effects.
Low-dose anandamide has an anxiolytic effect, while in one study, high doses injected directly into the cerebral fluid of the brain of mice shows evident cell apoptosis (programmed cell death) in vitro as opposed to necrosis. That being said, another study conducted under similar conditions demonstrated neuronal growth both in vitro and in vivo.
Endocannabinoids may disturb homeostasis in several ways: by enhancing hunger sensations, encouraging increased food intake, and shifting energy balance towards energy storage. A resultant decrease in energy expenditure is observed.
Another study with rats found that reductions in AEA signaling through FAAH overexpression within the basolateral complex of amygdala (BLA) appeared to reliably reduce measurements of anxiety and overall levels of corticosterone, a primary glucocorticoid in animals like birds, rodents, reptiles and amphibians responsible for energy regulation, immune and stress responses. This is similar to the main glucocorticoid cortisol in humans. Reduction of AEA in the BLA has been shown to suppress fear behavior and promote fear extinction. This suggests possible involvement of AEA intervention in the future for the treatment of psychological disorders. However, further work in this area of study is needed, as reduced anandamide signaling is believed at this moment to involve CB1 receptors as well as GABAergic and glutamatergic interactions.
Cortical glutamatergic transmission may be modulated by endocannabinoids during stress and fear habituation. Glutamatergic interaction in the BLA believed to be responsible for changes in anxiety, appears to normalize stress-induced anxiety-like behavior. A study indicated that infusion of the GluK1 receptor agonist ATPA into the BLA enhanced GABAergic neurotransmission, which is currently believed to have a large role in the reduction of anxiety symptoms.
Additionally, the ECs, along with AEA, have been highlighted for their potential involvement in obesity development and harmful effects on lipid and glucose metabolism, which may contribute to insulin resistance and deficiency, both of which are major risk factors for developing type 2 diabetes mellitus. Blockade of CB1 receptors was found significantly to improve lipid resistance and lipid profile in obese subjects, but also has potential to increase fat accumulation through increased food intake, favored lipogenesis and reduced energy expenditure. This may affect downstream systems like the pancreas, liver, adipose tissue, and skeletal muscle, with inflammation and apoptosis in the case of the pancreas. CB1R inhibition with peripherally restricted antagonists and inverse agonists may aid in the treatment of diabetic neuropathy and neuropathy. CB2R agonists may show promise for the treatment of inflammation, which contributes to renal injury.
AEA was associated with nonalcoholic fatty liver disease, nonalcoholic steatohepatitis (NASH), and liver fibrosis. Data suggests AEA as a marker for cardiometabolic disease and NAFLD severity. NAFLD can progress to more severe diseases, like NASH, cirrhosis, and hepatocellular carcinoma.
A Scottish woman with a rare mutation in her FAAH gene that resulted in elevated anandamide levels was reported to be immune to anxiety, unable to experience fear, and insensitive to pain. The frequent burns and cuts she suffered due to her hypoalgesia healed more rapidly than was expected.
Topical Anandamide was found to reduce peripheral neuropathic pain by interaction with peripheral cannabinoid receptors.
The American Academy of Dermatology has named topical Anandamide a promising therapy for cutaneous lupus erythematosus. | 1 | Applied and Interdisciplinary Chemistry |
Spirotryprostatin B is an indolic alkaloid found in the Aspergillus fumigatus fungus that belongs to a class of naturally occurring 2,5-diketopiperazines. Spirotryprostatin B and several other indolic alkaloids (including Spirotryprostatin A, as well as other tryprostatins and cyclotryprostatins) have been found to have anti-mitotic properties, and as such they have become of great interest as anti-cancer drugs. Because of this, the total syntheses of these compounds is a major pursuit of organic chemists, and a number of different syntheses have been published in the chemical literature. | 0 | Theoretical and Fundamental Chemistry |
Gunpowder was also extensively used in railway construction. At first railways followed the contours of the land, or crossed low ground by means of bridges and viaducts, but later railways made extensive use of cuttings and tunnels. One 2400-ft stretch of the 5.4 mi Box Tunnel on the Great Western Railway line between London and Bristol consumed a ton of gunpowder per week for over two years. The 12.9 km long Mont Cenis Tunnel was completed in 13 years starting in 1857 but, even with black powder, progress was only 25 cm a day until the invention of pneumatic drills sped up the work. | 1 | Applied and Interdisciplinary Chemistry |
The first evidence for multiple isotopes of a stable (non-radioactive) element was found by J. J. Thomson in 1912 as part of his exploration into the composition of canal rays (positive ions). Thomson channelled streams of neon ions through parallel magnetic and electric fields, measured their deflection by placing a photographic plate in their path, and computed their mass to charge ratio using a method that became known as the Thomson's parabola method. Each stream created a glowing patch on the plate at the point it struck. Thomson observed two separate parabolic patches of light on the photographic plate (see image), which suggested two species of nuclei with different mass to charge ratios.
F. W. Aston subsequently discovered multiple stable isotopes for numerous elements using a mass spectrograph. In 1919 Aston studied neon with sufficient resolution to show that the two isotopic masses are very close to the integers 20 and 22 and that neither is equal to the known molar mass (20.2) of neon gas. This is an example of Aston's whole number rule for isotopic masses, which states that large deviations of elemental molar masses from integers are primarily due to the fact that the element is a mixture of isotopes. Aston similarly showed in 1920 that the molar mass of chlorine (35.45) is a weighted average of the almost integral masses for the two isotopes Cl and Cl. | 0 | Theoretical and Fundamental Chemistry |
β-Hydroxybutyryl-CoA (or 3-hydroxybutyryl-coenzyme A) is an intermediate in the fermentation of butyric acid, and in the metabolism of lysine and tryptophan. The L-3-hydroxybutyl-CoA (or (S)-3-hydroxybutanoyl-CoA) enantiomer is also the second to last intermediate in beta oxidation of even-numbered, straight chain, and saturated fatty acids. | 1 | Applied and Interdisciplinary Chemistry |
Lu was named an Outstanding Reviewer of the journal Chemical Society Reviews in 2018 and 2019, featured in a 2018 JACS Young Investigators Virtual Issue, and named a Kavli Frontiers of Science Fellow in 2013. She has been honored with invited speaking engagements, as she gave a plenary lecture at a Royal Society of Chemistry Dalton Conference in 2018, and the Association for Cultural Diversity in Chemistry Lecture at the University of Pennsylvania in 2016. In 2017, Lu was invited to be a speaker at the Indo-US Workshop on Organometallic Chemistry and a Inorganic Chemistry Young Outstanding Upcoming speaker at Symposium on Advanced Biological Inorganic Chemistry in Kolkata, India. | 0 | Theoretical and Fundamental Chemistry |
Progress in gas dynamics coincides with the developments of transonic and supersonic flights. As aircraft began to travel faster, the density of air began to change, considerably increasing the air resistance as the air speed approached the speed of sound. The phenomenon was later identified in wind tunnel experiments as an effect caused by the formation of shock waves around the aircraft. Major advances were made to describe the behavior during and after World War II, and the new understandings on compressible and high speed flows became theories of gas dynamics.
As the construct that gases are small particles in Brownian motion became widely accepted and numerous quantitative studies verifying that the macroscopic properties of gases, such as temperature, pressure and density, are the results of collisions of moving particles, the study of kinetic theory of gases became increasingly an integrated part of gas dynamics. Modern books and classes on gas dynamics often began with an introduction to kinetic theory. The advent of the molecular modeling in computer simulation further made kinetic theory a highly relevant subject in today's research on gas dynamics. | 1 | Applied and Interdisciplinary Chemistry |
A small volume of PCBs has been detected throughout the Earth's atmosphere. The atmosphere serves as the primary route for global transport of PCBs, particularly for those congeners with one to four chlorine atoms.
In the atmosphere, PCBs may be degraded by hydroxyl radicals, or directly by photolysis of carbon–chlorine bonds (even if this is a less important process).
Atmospheric concentrations of PCBs tend to be lowest in rural areas, where they are typically in the picogram per cubic meter range, higher in suburban and urban areas, and highest in city centres, where they can reach 1 ng/m or more. In Milwaukee, an atmospheric concentration of 1.9 ng/m has been measured, and this source alone was estimated to account for 120 kg/year of PCBs entering Lake Michigan. In 2008, concentrations as high as 35 ng/m, 10 times higher than the EPA guideline limit of 3.4 ng/m, have been documented inside some houses in the U.S.
Volatilization of PCBs in soil was thought to be the primary source of PCBs in the atmosphere, but research suggests ventilation of PCB-contaminated indoor air from buildings is the primary source of PCB contamination in the atmosphere. | 1 | Applied and Interdisciplinary Chemistry |
Particulate inorganic carbon (PIC) usually takes the form of calcium carbonate (CaCO), and plays a key part in the ocean carbon cycle. This biologically fixed carbon is used as a protective coating for many planktonic species (coccolithophores, foraminifera) as well as larger marine organisms (mollusk shells). Calcium carbonate is also excreted at high rates during osmoregulation by fish, and can form in whiting events. While this form of carbon is not directly taken from the atmospheric budget, it is formed from dissolved forms of carbonate which are in equilibrium with CO and then responsible for removing this carbon via sequestration.
CO + HO → HCO → H + HCO
Ca + 2HCO → CaCO + CO + HO
While this process does manage to fix a large amount of carbon, two units of alkalinity are sequestered for every unit of sequestered carbon. The formation and sinking of CaCO therefore drives a surface to deep alkalinity gradient which serves to raise the pH of surface waters, shifting the speciation of dissolved carbon to raise the partial pressure of dissolved CO in surface waters, which actually raises atmospheric levels. In addition, the burial of CaCO in sediments serves to lower overall oceanic alkalinity, tending to raise pH and thereby atmospheric CO levels if not counterbalanced by the new input of alkalinity from weathering. The portion of carbon that is permanently buried at the sea floor becomes part of the geologic record. Calcium carbonate often forms remarkable deposits that can then be raised onto land through tectonic motion as in the case with the White Cliffs of Dover in Southern England. These cliffs are made almost entirely of the plates of buried coccolithophores. | 0 | Theoretical and Fundamental Chemistry |
Lattice models in biophysics represent a class of statistical-mechanical models which consider a biological macromacromolecule (such as DNA, protein, actin, etc.) as a lattice of units, each unit being in different states or conformations.
For example, DNA in chromatin can be represented as a one-dimensional lattice, whose elementary units are the nucleotide, base pair or nucleosome. Different states of the unit can be realized either by chemical modifications (e.g. DNA methylation or modifications of DNA-bound histones), or due to quantized internal degrees of freedom (e.g. different angles of the bond joining two neighboring units), or due to binding events involving a given unit (e.g. reversible binding of small ligands or proteins to DNA, or binding/unbinding of two complementary nucleotides in the DNA base pair). | 1 | Applied and Interdisciplinary Chemistry |
Warts, moles, skin tags, solar keratoses, molluscum, Mortons neuroma and small skin cancers are candidates for cryosurgical treatment. Several internal disorders are also treated with cryosurgery, including liver cancer, prostate cancer, lung cancer, oral cancers, cervical disorders and, more commonly in the past, hemorrhoids. Soft tissue conditions such as plantar fasciitis (joggers heel) and fibroma (benign excrescence of connective tissue) can be treated with cryosurgery.
Cryosurgery works by taking advantage of the destructive force of freezing temperatures on cells. When their temperature sinks beyond a certain level ice crystals begin forming inside the cells and, because of their lower density, eventually tear apart those cells. Further harm to malignant growth will result once the blood vessels supplying the affected tissue begin to freeze.
Cryosurgery is used to treat a variety of benign skin lesions including:
* Acne
* Dermatofibroma
* Hemangioma
* Keloid (hypertrophic scar)
* Molluscum contagiosum
* Myxoid cyst
* Pyogenic granuloma
* Seborrheic keratoses
* Skin tags
* Warts (including anogenital warts)
Cryosurgery may also be used to treat low risk skin cancers such as basal cell carcinoma and squamous cell carcinoma but a biopsy should be obtained first to confirm the diagnosis, determine the depth of invasion and characterize other high risk histologic features. | 1 | Applied and Interdisciplinary Chemistry |
A full description of non-linear inverse Compton scattering must include some effects related to the quantization of light and matter. The principal ones are listed below.
* Inclusion of the discretization of the emitted radiation, i.e. the introduction of photons with respect to the continuous description of the classical limit. This effect does not change quantitatively the emission features but changes how the emitted radiation is interpreted. A parameter equivalent to can be introduced for the photon of frequency and it is called photon quantum parameter:where is the photon four-wavevector and is the three-dimensional wavevector. In the limit in which the particle approaches the speed of light, the ratio between and is equal to:From the Frequency distribution of radiated energy one can get a rate of high-energy photon emission distributed in as a function of and but still valid in the classical limit:
where stands for the McDonald functions. The mean energy of the emitted photon is given by . Consequently, a large Lorentz factor and intense fields increase the chance of producing high-energy photons. goes as because of this formula.
* The effect of radiation reaction, due to photon recoil. The electron energy after the interaction process reduces because part of it is delivered to the emitted photon and the maximum energy achievable by the emitted photon cannot be higher than the electron kinetic energy. This effect is not taken into account in non-linear Thomson scattering in which the electron energy is supposed to remain almost unaltered in energy such as in elastic scattering. Quantum radiation reaction effects become important when the emitted photon energy approaches the electron energy. Since , if the classical limit of NICS is a valid description, while for the energy of the emitted photon is of the order of the electron energy and photon recoil is very relevant.
* The quantization of the motion of the electron and spin effects. An accurate description of non-linear inverse Compton scattering is made considering the electron dynamics described with the Dirac equation in presence of an electromagnetic field. | 0 | Theoretical and Fundamental Chemistry |
As an instance of adsorption, chemisorption follows the adsorption process. The first stage is for the adsorbate particle to come into contact with the surface. The particle needs to be trapped onto the surface by not possessing enough energy to leave the gas-surface potential well. If it elastically collides with the surface, then it would return to the bulk gas. If it loses enough momentum through an inelastic collision, then it "sticks" onto the surface, forming a precursor state bonded to the surface by weak forces, similar to physisorption. The particle diffuses on the surface until it finds a deep chemisorption potential well. Then it reacts with the surface or simply desorbs after enough energy and time.
The reaction with the surface is dependent on the chemical species involved. Applying the Gibbs energy equation for reactions:
General thermodynamics states that for spontaneous reactions at constant temperature and pressure, the change in free energy should be negative. Since a free particle is restrained to a surface, and unless the surface atom is highly mobile, entropy is lowered. This means that the enthalpy term must be negative, implying an exothermic reaction.
Physisorption is given as a Lennard-Jones potential and chemisorption is given as a Morse potential. There exists a point of crossover between the physisorption and chemisorption, meaning a point of transfer. It can occur above or below the zero-energy line (with a difference in the Morse potential, a), representing an activation energy requirement or lack of. Most simple gases on clean metal surfaces lack the activation energy requirement. | 0 | Theoretical and Fundamental Chemistry |
The development of UVGI traces back to 1878 when Arthur Downes and Thomas Blunt found that sunlight, particularly its shorter wavelengths, hindered microbial growth. Expanding upon this work, Émile Duclaux, in 1885, identified variations in sunlight sensitivity among different bacterial species. A few years later, in 1890, Robert Koch demonstrated the lethal effect of sunlight on Mycobacterium tuberculosis, hinting at UVGI's potential for combating diseases like tuberculosis.
Subsequent studies further defined the wavelengths most efficient for germicidal inactivation. In 1892, it was noted that the UV segment of sunlight had the most potent bactericidal effect. Research conducted in the early 1890s demonstrated the superior germicidal efficacy of UV-C compared to UV-A and UV-B.
The mutagenic effects of UV were first unveiled in a 1914 study that observed metabolic changes in Bacillus anthracis upon exposure to sublethal doses of UV. Frederick Gates, in the late 1920s, offered the first quantitative bactericidal action spectra for Staphylococcus aureus and Bacillus coli, noting peak effectiveness at 265 nm. This matched the absorption spectrum of nucleic acids, hinting at DNA damage as the key factor in bacterial inactivation. This understanding was solidified by the 1960s through research demonstrating the ability of UV-C to form thymine dimers, leading to microbial inactivation. These early findings collectively laid the groundwork for modern UVGI as a disinfection tool. | 0 | Theoretical and Fundamental Chemistry |
The Bluebelt program was initiated in the late 1980s by New York City’s Departments of Environmental Protection and City Planning, based on a suggestion made several decades earlier by Ian McHarg, a landscape architect. Acquisition of land began in 1991 for the project, one of the Northeast United States’ most ambitious stormwater management efforts. The overall goal is to provide the necessary stormwater drainage infrastructure for a region on the southern end of the island while at the same time preserving the last freshwater wetlands in New York City. The bluebelt uses a series of carefully placed BMPs at the storm sewer/wetland interface to reduce flooding and improve water quality. Creation of a self-regulating ecosystem that is native to the region is of primary importance to the program.
BMPs used in the bluebelt include stormwater wetlands, stream restoration, outlet stilling basins, and sand filters. Ninety-two stormwater wetlands were included as part of the Staten Island project. In order to integrate the wetlands into the natural ecology, the construction process is advised by restoration specialists since general contractors are typically not trained in proper plant selection and installation. The planting design focuses on quick establishment of the preferred successional communities that will complement the surrounding landscape, before invasive species take over the site.
The performance of the Bluebelt during the storms that battered the city in the early 21st century – including Hurricane Sandy – has been described as "brilliant". | 1 | Applied and Interdisciplinary Chemistry |
In microprocessors, graphics processors and other high-end chips, hotspots can occur as power densities vary significantly across a chip. These hotspots can severely limit the performance of the devices. Because of the small size of the thermal bumps and the relatively high density at which they can be placed on the active surface of the chip, these structures are ideally suited for cooling hotspots. In such a case, the distribution of the thermal bumps may not need to be even. Rather, the thermal bumps would be concentrated in the area of the hotspot while areas of lower heat density would have fewer thermal bumps per unit area. In this way, cooling from the thermal bumps is applied only where needed, thereby reducing the added power necessary to drive the cooling and reducing the general thermal overhead on the system. | 0 | Theoretical and Fundamental Chemistry |
Iron salt aerosols are one proposed method of enhanced atmospheric methane oxidation which involves lofting iron-based particles into the atmosphere (e.g. from planes or ships) to enhance atmospheric chlorine radicals, a natural methane sink.
Winds over the Sahara raise dust into the troposphere and disperse it over the Atlantic. A 2023 study suggests that this has contributed to natural atmospheric methane oxidation.
Iron salt aerosols are being studied for the potential of iron(III) chloride (FeCl) to catalyze chlorine radical production. Chlorine atoms are produced by photolysis from the FeCl stemming from iron-containing airborne dust aerosol particles in the oceanic boundary layer.
:FeCl + hv → FeCl + Cl
The chlorine atoms initiate methane oxidation:
:CH + Cl → HCl + CH
The resulting methyl radical is unstable and oxidises naturally to CO and water:
:3.5O + 2CH → 2CO + 3HO | 1 | Applied and Interdisciplinary Chemistry |
Matrix notation differs from Wood's notation in the second term, which is replaced by the matrix that describes the overlayer primitive vectors in terms of the substrate primitive vectors:
:, where
and so hence matrix notation has the form | 0 | Theoretical and Fundamental Chemistry |
The Boltzmann constant is named after its 19th century Austrian discoverer, Ludwig Boltzmann. Although Boltzmann first linked entropy and probability in 1877, the relation was never expressed with a specific constant until Max Planck first introduced , and gave a more precise value for it (, about 2.5% lower than todays figure), in his derivation of the law of black-body radiation in 1900–1901. Before 1900, equations involving Boltzmann factors were not written using the energies per molecule and the Boltzmann constant, but rather using a form of the gas constant , and macroscopic energies for macroscopic quantities of the substance. The iconic terse form of the equation on Boltzmanns tombstone is in fact due to Planck, not Boltzmann. Planck actually introduced it in the same work as his eponymous .
In 1920, Planck wrote in his Nobel Prize lecture:
This "peculiar state of affairs" is illustrated by reference to one of the great scientific debates of the time. There was considerable disagreement in the second half of the nineteenth century as to whether atoms and molecules were real or whether they were simply a heuristic tool for solving problems. There was no agreement whether chemical molecules, as measured by atomic weights, were the same as physical molecules, as measured by kinetic theory. Planck's 1920 lecture continued:
In versions of SI prior to the 2019 redefinition of the SI base units, the Boltzmann constant was a measured quantity rather than a fixed value. Its exact definition also varied over the years due to redefinitions of the kelvin (see ) and other SI base units (see ).
In 2017, the most accurate measures of the Boltzmann constant were obtained by acoustic gas thermometry, which determines the speed of sound of a monatomic gas in a triaxial ellipsoid chamber using microwave and acoustic resonances. This decade-long effort was undertaken with different techniques by several laboratories; it is one of the cornerstones of the 2019 redefinition of SI base units. Based on these measurements, the CODATA recommended to be the final fixed value of the Boltzmann constant to be used for the International System of Units. | 0 | Theoretical and Fundamental Chemistry |
Although NPP primarily catalyzes phosphodiester hydrolysis, the enzyme will also catalyze the hydrolysis of phosphate monoesters, though to a much smaller extent. NPP preferentially hydrolyzes phosphate diesters over monoesters by factors of 10-10, depending on the identity of the diester substrate. This ability to catalyze a reaction with a secondary substrate is known as enzyme promiscuity, and may have played a role in NPP's evolutionary history.
NPP's promiscuity enables the enzyme to share substrates with alkaline phosphatase (AP), another member of the alkaline phosphate superfamily. Alkaline phosphatase primarily hydrolyzes phosphate monoester bonds, but it shows some promiscuity towards hydrolyzing phosphate diester bonds, making it a sort of opposite to NPP. The active sites of these two enzymes show marked similarities, namely in the presence of nearly superimposable Zn bimetallo catalytic centers. In addition to the bimetallo core, AP also has an Mg ion in its active site. | 1 | Applied and Interdisciplinary Chemistry |
A lead compound may arise from a variety of different sources. Lead compounds are found by characterizing natural products, employing combinatorial chemistry, or by molecular modeling as in rational drug design. Chemicals identified as hits through high-throughput screening may also become lead compounds. Once a lead compound is selected it must undergo lead optimization, which involves making the compound more "drug-like." This is where Lipinski's rule of five comes into play, sometimes also referred to as the "Pfizer rule" or simply as the "rule of five." Other factors, such as the ease of scaling up the manufacturing of the chemical, must be taken into consideration. | 1 | Applied and Interdisciplinary Chemistry |
Flashover is one of the most feared phenomena among firefighters. Firefighters are taught to recognize the signs of imminent rollovers and flashovers and to avoid backdrafts. For example, there are certain routines for opening closed doors to buildings and compartments on fire, known as door entry procedures, ensuring fire crew safety where possible. | 0 | Theoretical and Fundamental Chemistry |
Diisopinocampheylborane is an organoborane that is useful for asymmetric synthesis of secondary alcohols. It is derived by hydroboration of α-pinene, a common diterpene member of the chiral pool. | 0 | Theoretical and Fundamental Chemistry |
Apoptotic DNA fragmentation is a key feature of apoptosis, a type of programmed cell death. Apoptosis is characterized by the activation of endogenous endonucleases, particularly the caspase-3 activated DNase (CAD), with subsequent cleavage of nuclear DNA into internucleosomal fragments of roughly 180 base pairs (bp) and multiples thereof (360, 540 etc.). The apoptotic DNA fragmentation is being used as a marker of apoptosis and for identification of apoptotic cells either via the DNA laddering assay, the TUNEL assay, or the by detection of cells with fractional DNA content ("sub G cells") on DNA content frequency histograms e.g. as in the Nicoletti assay. | 1 | Applied and Interdisciplinary Chemistry |
For each particular lattice, a conventional cell has been chosen on a case-by-case basis by crystallographers based on convenience of calculation. These conventional cells may have additional lattice points located in the middle of the faces or body of the unit cell. The number of lattice points, as well as the volume of the conventional cell is an integer multiple (1, 2, 3, or 4) of that of the primitive cell. | 0 | Theoretical and Fundamental Chemistry |
Layered sedimentary deposits are widespread on Mars. These deposits probably consist of both sedimentary rock and poorly indurated or unconsolidated sediments. Thick sedimentary deposits occur in the interior of several canyons in Valles Marineris, within large craters in Arabia and Meridiani Planum (see Henry Crater for example), and probably comprise much of the deposits in the northern lowlands (e.g., Vastitas Borealis Formation). The Mars Exploration Rover Opportunity landed in an area containing cross-bedded (mainly eolian) sandstones (Burns formation). Fluvial-deltaic deposits are present in Eberswalde Crater and elsewhere, and photogeologic evidence suggests that many craters and low lying intercrater areas in the southern highlands contain Noachian-aged lake sediments.
While the possibility of carbonates on Mars has been of great interest to astrobiologists and geochemists alike, there was little evidence for significant quantities of carbonate deposits on the surface. In the summer of 2008, the TEGA and WCL experiments on the 2007 Phoenix Mars lander found between 3–5wt% (percent by weight) calcite (CaCO) and an alkaline soil. In 2010, analyses by the Mars Exploration Rover Spirit identified outcrops rich in magnesium-iron carbonate (16–34 wt%) in the Columbia Hills of Gusev crater. The magnesium-iron carbonate most likely precipitated from carbonate-bearing solutions under hydrothermal conditions at near-neutral pH in association with volcanic activity during the Noachian Period.
Carbonates (calcium or iron carbonates) were discovered in a crater on the rim of Huygens Crater, located in the Iapygia quadrangle. The impact on the rim exposed material that had been dug up from the impact that created Huygens. These minerals represent evidence that Mars once had a thicker carbon dioxide atmosphere with abundant moisture, since these kind of carbonates only form when there is a lot of water. They were found with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter. Earlier, the instrument had detected clay minerals. The carbonates were found near the clay minerals. Both of these minerals form in wet environments. It is supposed that billions of years ago Mars was much warmer and wetter. At that time, carbonates would have formed from water and the carbon dioxide-rich atmosphere. Later the deposits of carbonate would have been buried. The double impact has now exposed the minerals. Earth has vast carbonate deposits in the form of limestone. | 0 | Theoretical and Fundamental Chemistry |
A meta-analysis of observational studies showed that children with ADHD have lower vitamin D levels, and that there was a small association between low vitamin D levels at the time of birth and later development of ADHD. Several small, randomized controlled trials of vitamin D supplementation indicated improved ADHD symptoms such as impulsivity and hyperactivity. | 1 | Applied and Interdisciplinary Chemistry |
NAA can detect up to 74 elements depending upon the experimental procedure, with minimum detection limits ranging from 0.1 to 1x10 ng g depending on element under investigation. Heavier elements have larger nuclei, therefore they have a larger neutron capture cross-section and are more likely to be activated. Some nuclei can capture a number of neutrons and remain relatively stable, not undergoing transmutation or decay for many months or even years. Other nuclei decay instantaneously or form only stable isotopes and can only be identified by PGNAA. | 0 | Theoretical and Fundamental Chemistry |
RATs are immunochromatographic assays which give results that can be seen with the naked eye (with or without special illumination, such as a UV lamp). They are qualitative in nature, although within a certain range it is possible to make rough order of magnitude estimates of viral load from the results. RATs are generally screening tests, with relatively low sensitivity and specificity, thus results should be evaluated on the basis of confirmatory tests like PCR testing or western blot.
One inherent advantage of an antigen test over an antibody test (such as antibody-detecting rapid HIV tests) is that it can take time for the immune system to develop antibodies after infection begins, but the foreign antigen is present right away. Although any diagnostic test may have false negatives, this latency period can open an especially wide avenue for false negatives in antibody tests, although the particulars depend on which disease and which test are involved. A rapid antigen test typically costs around US$5 to manufacture. | 1 | Applied and Interdisciplinary Chemistry |
The exhaled human breath contains a few thousand volatile organic compounds and is used in breath biopsy to serve as a VOC biomarker to test for diseases, such as lung cancer. One study has shown that "volatile organic compounds ... are mainly blood borne and therefore enable monitoring of different processes in the body." And it appears that VOC compounds in the body "may be either produced by metabolic processes or inhaled/absorbed from exogenous sources" such as environmental tobacco smoke. Chemical fingerprinting and breath analysis of volatile organic compounds has also been demonstrated with chemical sensor arrays, which utilize pattern recognition for detection of component volatile organics in complex mixtures such as breath gas. | 0 | Theoretical and Fundamental Chemistry |
Many routes for the synthesis of TMP have been reported. One method starts with a conjugate addition reaction of ammonia to phorone. The intermediate triacetone amine is then reduced in a Wolff-Kishner reaction. | 0 | Theoretical and Fundamental Chemistry |
There are many different materials and fabrication methods that can be used to produce gated drug delivery scaffolding. In general, porous materials, such as mesoporous silica nanoparticles are used because of their expansive surface area, large loading capacity, and porous structures. These characteristics make it possible to load a variety of molecules that vary greatly in size. | 1 | Applied and Interdisciplinary Chemistry |
Omeprazole showed an inter-individual variability and therefore a significant number of patients with acid-related disorders required higher or multiple doses to achieve symptom relief and healing. Astra started a new research program in 1987 to identify a new analogue to omeprazole with less interpatient variability. Only one compound proved superior to omeprazole and that was the (S)-(−)-isomer, esomeprazole, which was developed as the magnesium salt. Esomeprazole magnesium (brand name Nexium) received its first approval in 2000 and provided more pronounced inhibition of acid secretion and less inter-patient variation compared to omeprazole. In 2004, Nexium had already been used to treat over 200 million patients. | 1 | Applied and Interdisciplinary Chemistry |
SERS can be used to target specific DNA and RNA sequences using a combination of gold and silver nanoparticles and Raman-active dyes, such as Cy3. Specific single nucleotide polymorphisms (SNP) can be identified using this technique. The gold nanoparticles facilitate the formation of a silver coating on the dye-labelled regions of DNA or RNA, allowing SERS to be performed. This has several potential applications: For example, Cao et al. report that gene sequences for HIV, Ebola, Hepatitis, and Bacillus Anthracis can be uniquely identified using this technique. Each spectrum was specific, which is advantageous over fluorescence detection; some fluorescent markers overlap and interfere with other gene markers. The advantage of this technique to identify gene sequences is that several Raman dyes are commercially available, which could lead to the development of non-overlapping probes for gene detection. | 0 | Theoretical and Fundamental Chemistry |
Murray studied chemistry at St. Marys University in Halifax, Nova Scotia, Canada from 1985, graduating with a Bachelors Degree with Honors in Chemistry in 1988. He spent a year as a Rotary International Fellow at the University of Auckland in 1989. From 1990 he studied at the Massachusetts Institute of Technology (MIT), where he received his doctorate in chemistry in 1995. | 0 | Theoretical and Fundamental Chemistry |
Azanes with more than three nitrogen atoms can be arranged in various different ways, forming structural isomers. The simplest isomer of an azane is the one in which the nitrogen atoms are arranged in a single chain with no branches. This isomer is sometimes called the n-isomer (n for "normal", although it is not necessarily the most common). However the chain of nitrogen atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of nitrogen atoms.
Due to the low energy of inversion, unsubstituted branched azanes cannot be chiral. In addition to these isomers, the chain of nitrogen atoms may form one or more loops. Such compounds are called cycloazanes. | 0 | Theoretical and Fundamental Chemistry |
In the United Kingdom there are three principal regulations that mandate the marking of equipment and piping:
* Classification, Labelling and Packaging of Chemicals (Amendments to Secondary Legislation) Regulations 2015,
* Health and Safety (Safety Signs and Signals) Regulations 1996,
* Provision and Use of Work Equipment Regulations 1998,
The regulations require that vessels containing hazardous substances together with the pipes containing or transporting such substances must be labelled or marked with the relevant hazard pictograms or pipe marking. The labels used on pipes must be positioned visibly in the vicinity of the most hazardous points, such as valves and joints; at both sides of bulkheads and floor penetrations; and at reasonable intervals.
The regulations do not specify a specific marking system, but BS EN ISO 1710 Graphical symbols — Safety colours and safety signs is often used. | 1 | Applied and Interdisciplinary Chemistry |
Cell Surface Peptides provide one way to introduce drug delivery into a target cell. This method is accomplished by the peptide binding to a target cells surface receptors, in a way that bypasses immune defenses that would otherwise compromise a slower delivery, without causing harm to the host. In particular, peptides, such as intercellular adhesion molecule-1, have shown a great deal of binding ability in a target cell. This method has shown a degree of efficacy in treating both autoimmune diseases as well as forms of cancer as a result of this binding affinity. Peptide mediated delivery is also of promise due to the low cost of creating the peptides as well as the simplicity of their structure. | 1 | Applied and Interdisciplinary Chemistry |
The Monod equation is a mathematical model for the growth of microorganisms. It is named for Jacques Monod (1910–1976, a French biochemist, Nobel Prize in Physiology or Medicine in 1965), who proposed using an equation of this form to relate microbial growth rates in an aqueous environment to the concentration of a limiting nutrient. The Monod equation has the same form as the Michaelis–Menten equation, but differs in that it is empirical while the latter is based on theoretical considerations.
The Monod equation is commonly used in environmental engineering. For example, it is used in the activated sludge model for sewage treatment. | 0 | Theoretical and Fundamental Chemistry |
Paul Christian Lauterbur (May 6, 1929 – March 27, 2007) was an American chemist who shared the Nobel Prize in Physiology or Medicine in 2003 with Peter Mansfield for his work which made the development of magnetic resonance imaging (MRI) possible.
Lauterbur was a professor at Stony Brook University from 1963 until 1985, where he conducted his research for the development of the MRI. In 1985 he became a professor along with his wife Joan at the University of Illinois at Urbana-Champaign for 22 years until his death in Urbana. He never stopped working with undergraduates on research, and he served as a professor of chemistry, with appointments in bioengineering, biophysics, the College of Medicine at Urbana-Champaign and computational biology at the Center for Advanced Study. | 0 | Theoretical and Fundamental Chemistry |
The mechanism of chemotaxis that eukaryotic cells employ is quite different from that in the bacteria E. coli; however, sensing of chemical gradients is still a crucial step in the process. Due to their small size and other biophysical constraints, E. coli cannot directly detect a concentration gradient. Instead, they employ temporal gradient sensing, where they move over larger distances several times their own width and measure the rate at which perceived chemical concentration changes.
Eukaryotic cells are much larger than prokaryotes and have receptors embedded uniformly throughout the cell membrane. Eukaryotic chemotaxis involves detecting a concentration gradient spatially by comparing the asymmetric activation of these receptors at the different ends of the cell. Activation of these receptors results in migration towards chemoattractants, or away from chemorepellants. In mating yeast, which are non-motile, patches of polarity proteins on the cell cortex can relocate in a chemotactic fashion up pheromone gradients.
It has also been shown that both prokaryotic and eukaryotic cells are capable of chemotactic memory. In prokaryotes, this mechanism involves the methylation of receptors called methyl-accepting chemotaxis proteins (MCPs). This results in their desensitization and allows prokaryotes to "remember" and adapt to a chemical gradient. In contrast, chemotactic memory in eukaryotes can be explained by the Local Excitation Global Inhibition (LEGI) model. LEGI involves the balance between a fast excitation and delayed inhibition which controls downstream signaling such as Ras activation and PIP3 production.
Levels of receptors, intracellular signalling pathways and the effector mechanisms all represent diverse, eukaryotic-type components. In eukaryotic unicellular cells, amoeboid movement and cilium or the eukaryotic flagellum are the main effectors (e.g., Amoeba or Tetrahymena). Some eukaryotic cells of higher vertebrate origin, such as immune cells also move to where they need to be. Besides immune competent cells (granulocyte, monocyte, lymphocyte) a large group of cells—considered previously to be fixed into tissues—are also motile in special physiological (e.g., mast cell, fibroblast, endothelial cells) or pathological conditions (e.g., metastases). Chemotaxis has high significance in the early phases of embryogenesis as development of germ layers is guided by gradients of signal molecules. | 1 | Applied and Interdisciplinary Chemistry |
The CaBER is a capillary breakup rheometer. A small quantity of material is placed between plates, which are rapidly stretched to a fixed level of strain. The midpoint diameter is monitored as a function of time as the fluid filament necks and breaks up under the combined forces of surface tension, gravity, and viscoelasticity. The extensional viscosity can be extracted from the data as a function of strain and strain rate. This system is useful for low viscosity fluids, inks, paints, adhesives, and biological fluids. | 1 | Applied and Interdisciplinary Chemistry |
Many cells and tissues, especially mammalian ones, must have a surface or other structural support in order to grow, and agitated environments are often destructive to these cell types and tissues. Higher organisms, being auxotrophic, also require highly specialized growth media. This poses a challenge when the goal is to culture larger quantities of cells for therapeutic production purposes, and a significantly different design is needed compared to industrial bioreactors used for growing protein expression systems such as yeast and bacteria.
Many research groups have developed novel bioreactors for growing specialized tissues and cells on a structural scaffold, in attempt to recreate organ-like tissue structures in-vitro. Among these include tissue bioreactors that can grow heart tissue, skeletal muscle tissue, ligaments, cancer tissue models, and others. Currently, scaling production of these specialized bioreactors for industrial use remains challenging and is an active area of research.
For more information on artificial tissue culture, see tissue engineering. | 1 | Applied and Interdisciplinary Chemistry |
LINE1 (also L1 and LINE-1) is a family of related class I transposable elements in the DNA of some organisms, classified with the long interspersed elements (LINEs). L1 transposons comprise approximately 17% of the human genome. These active L1s can interrupt the genome through insertions, deletions, rearrangements, and copy number variations. L1 activity has contributed to the instability and evolution of genomes and is tightly regulated in the germline by DNA methylation, histone modifications, and piRNA. L1s can further impact genome variation through mispairing and unequal crossing over during meiosis due to its repetitive DNA sequences.
L1 gene products are also required by many non-autonomous Alu and SVA SINE retrotransposons. Mutations induced by L1 and its non-autonomous counterparts have been found to cause a variety of heritable and somatic diseases.
In 2011, human L1 was reportedly discovered in the genome of the gonorrhea bacteria, evidently having arrived there by horizontal gene transfer. | 1 | Applied and Interdisciplinary Chemistry |
There are three main G-protein-mediated signaling pathways, mediated by four sub-classes of G-proteins distinguished from each other by sequence homology (G, G, G, and G). Each sub-class of G-protein consists of multiple proteins, each the product of multiple genes or splice variations that may imbue them with differences ranging from subtle to distinct with regard to signaling properties, but in general they appear reasonably grouped into four classes. Because the signal transducing properties of the various possible βγ combinations do not appear to radically differ from one another, these classes are defined according to the isoform of their α-subunit.
While most GPCRs are capable of activating more than one Gα-subtype, they also show a preference for one subtype over another. When the subtype activated depends on the ligand that is bound to the GPCR, this is called functional selectivity (also known as agonist-directed trafficking, or conformation-specific agonism). However, the binding of any single particular agonist may also initiate activation of multiple different G-proteins, as it may be capable of stabilizing more than one conformation of the GPCRs GEF domain, even over the course of a single interaction. In addition, a conformation that preferably activates one isoform of Gα may activate another if the preferred is less available. Furthermore, feedback pathways may result in receptor modifications (e.g., phosphorylation) that alter the G-protein preference. Regardless of these various nuances, the GPCRs preferred coupling partner is usually defined according to the G-protein most obviously activated by the endogenous ligand under most physiological or experimental conditions. | 1 | Applied and Interdisciplinary Chemistry |
The methods to prevent and treat lipotoxicity are divided into three main groups.
The first strategy focuses on decreasing the lipid content of non-adipose tissues. This can be accomplished by either increasing the oxidation of the lipids, or increasing their secretion and transport. Current treatments involve extreme weight loss and leptin treatment.
Another strategy is focusing on diverting excess lipids away from non-adipose tissues, and towards adipose tissues. This is accomplished with thiazolidinediones, a group of medications that activate nuclear receptor proteins responsible for lipid metabolism.
The final strategy focuses on inhibiting the apoptotic pathways and signaling cascades. This is accomplished by using drugs that inhibit production of specific chemicals required for the pathways to be functional. While this may prove to the most effective protection against cell death, it will also require the most research and development due to the specificity required of the medications. | 1 | Applied and Interdisciplinary Chemistry |
The term is known as the asymmetry term (or Pauli term).
The theoretical justification for this term is more complex. The Pauli exclusion principle states that no two identical fermions can occupy exactly the same quantum state in an atom. At a given energy level, there are only finitely many quantum states available for particles. What this means in the nucleus is that as more particles are "added", these particles must occupy higher energy levels, increasing the total energy of the nucleus (and decreasing the binding energy). Note that this effect is not based on any of the fundamental forces (gravitational, electromagnetic, etc.), only the Pauli exclusion principle.
Protons and neutrons, being distinct types of particles, occupy different quantum states. One can think of two different "pools" of states one for protons and one for neutrons. Now, for example, if there are significantly more neutrons than protons in a nucleus, some of the neutrons will be higher in energy than the available states in the proton pool. If we could move some particles from the neutron pool to the proton pool, in other words, change some neutrons into protons, we would significantly decrease the energy. The imbalance between the number of protons and neutrons causes the energy to be higher than it needs to be, for a given number of nucleons. This is the basis for the asymmetry term.
The actual form of the asymmetry term can again be derived by modeling the nucleus as a Fermi ball of protons and neutrons. Its total kinetic energy is
where and are the Fermi energies of the protons and neutrons. Since these are proportional to and respectively, one gets
: for some constant C.
The leading terms in the expansion in the difference are then
At the zeroth order in the expansion the kinetic energy is just the overall Fermi energy multiplied by . Thus we get
The first term contributes to the volume term in the semi-empirical mass formula, and the second term is minus the asymmetry term (remember, the kinetic energy contributes to the total binding energy with a negative sign).
is 38 MeV, so calculating from the equation above, we get only half the measured value. The discrepancy is explained by our model not being accurate: nucleons in fact interact with each other and are not spread evenly across the nucleus. For example, in the shell model, a proton and a neutron with overlapping wavefunctions will have a greater strong interaction between them and stronger binding energy. This makes it energetically favourable (i.e. having lower energy) for protons and neutrons to have the same quantum numbers (other than isospin), and thus increase the energy cost of asymmetry between them.
One can also understand the asymmetry term intuitively as follows. It should be dependent on the absolute difference , and the form is simple and differentiable, which is important for certain applications of the formula. In addition, small differences between Z and N do not have a high energy cost. The A in the denominator reflects the fact that a given difference is less significant for larger values of A. | 0 | Theoretical and Fundamental Chemistry |
Yttria-stabilized zirconia (YSZ) is a ceramic in which the cubic crystal structure of zirconium dioxide is made stable at room temperature by an addition of yttrium oxide. These oxides are commonly called "zirconia" (ZrO) and "yttria" (YO), hence the name. | 0 | Theoretical and Fundamental Chemistry |
With the rise of mechanization and mass production, new modes of medication-delivery, among them the tablet (1884), the enteric-coated pill (1884) and the gelatin capsule (first produced on a large scale in 1875 by Parke, Davis & Company, Detroit) became practicable. By 1900, most pharmacies stocked the shelves, partially or predominantly, with medicines prefabricated en masse by the growing pharmaceutical industry instead of custom-produced by individual pharmacisti, and the traditional role of the scientifically trained pharmacist to produce medicines increasingly eroded. This shift worried many, raising concerns of quality control, professional irrelevance and more. William Procter lamented that, "If the pharmacist becomes a mere dispenser of medicines, he relapses into a simple shopkeeper.” | 1 | Applied and Interdisciplinary Chemistry |
Geometric dynamic recrystallization occurs in grains with local serrations. Upon deformation, grains undergoing GDRX elongate until the thickness of the grain falls below a threshold (below which the serration boundaries intersect and small grains pinch off into equiaxed grains). The serrations may predate stresses being exerted on the material, or may result from the material’s deformation.
Geometric Dynamic Recrystallization has 6 main characteristics:
* It generally occurs with deformation at elevated temperatures, in materials with high stacking fault energy
* Stress increases and then declines to a steady state
* Subgrain formation requires a critical deformation
* Subgrain misorientation peaks at 2˚
* There is little texture change
* Pinning of grain boundaries causes an increase in the required strain
While GDRX is primarily affected by the initial grain size and strain (geometry-dependent), other factors that occur during the hot working process complicate the development of predictive modeling (which tend to oversimplify the process) and can lead to incomplete recrystallization. The equiaxed grain formation does not occur immediately and uniformly along the entire grain once the threshold stress is reached, as individual regions are subjected to different strains/stresses. In practice, a generally sinusoidal edge (as predicted by Martorano et al.) gradually forms as the grains begin to pinch off as they each reach the threshold. More sophisticated models consider complex initial grain geometries, local pressures along grain boundaries, and hot working temperature, but the models are unable to make accurate predictions throughout the entire stress regime and the evolution of the overall microstructure. Additionally, grain boundaries may migrate during GDRX at high temperatures and GB curvatures, dragging along subgrain boundaries and resulting in unwanted growth of the original grain. This new, larger grain will require far more deformation for GDRX to occur, and the local area will be weaker rather than strengthened. Lastly, recrystallization can be accelerated as grains are shifted and stretched, causing subgrain boundaries to become grain boundaries (angle increases). The affected grains are thinner and longer, and thus more easily undergo deformation. | 1 | Applied and Interdisciplinary Chemistry |
The PECT effect is also present in typical ion-insertion-based battery electrodes (e.g. Li-ion). The electrodes expand and contract when inserted with ions, which is one of the issues that leads to battery ageing and capacity loss over time. The PECT effect in battery electrodes could be an issue in situations where battery electrodes are mechanically stressed (e.g. in structural batteries), causing a change in electrical potential when the stress-state changes.
It has been proposed that the PECT effect in Li-ion batteries could be exploited to measure battery health., and to harvest mechanical energy. | 0 | Theoretical and Fundamental Chemistry |
The kinetic theory of gases is a simple classical model of the thermodynamic behavior of gases. It treats a gas as composed of numerous particles, too small to see with a microscope, which are constantly in random motion. Their collisions with each other and with the walls of their container are used to explain physical properties of the gas—for example the relationship between its temperature, pressure and volume. The particles are now known to be the atoms or molecules of the gas.
The basic version of the model describes an ideal gas. It treats the collisions as perfectly elastic and as the only interaction between the particles, which are additionally assumed to be much smaller than their average distance apart.
The theory's introduction allowed many principal concepts of thermodynamics to be established. It explains the macroscopic properties of gases, such as volume, pressure, and temperature, as well as transport properties such as viscosity, thermal conductivity and mass diffusivity. Due to the time reversibility of microscopic dynamics (microscopic reversibility), the kinetic theory is also connected to the principle of detailed balance, in terms of the fluctuation-dissipation theorem (for Brownian motion) and the Onsager reciprocal relations.
The theory was historically significant as the first explicit exercise of the ideas of statistical mechanics. | 0 | Theoretical and Fundamental Chemistry |
The process of electrochlorination is a simple application based on the chloralkali process (in an unpartitioned cell).
It is the electrolysis of saltwater to produce a chlorinated solution. The first step is removing any solids from the saltwater. Next, the saltwater streams through an electrolyzer cell's channel of decreasing thickness. One side of the channel is a cathode, the other is an anode. A low voltage DC current is applied, electrolysis happens producing sodium hypochlorite and hydrogen gas (H). The solution travels to a tank that separates the hydrogen gas based on its low density. Only water and sodium chloride are used. The simplified chemical reaction is:
:NaCl + HO + energy → NaOCl + H
That is, energy is added to sodium chloride (table salt) in water, producing sodium hypochlorite and hydrogen gas.
Because the reaction takes place in an unpartitioned cell and NaOH is present in the same solution as the Cl:
:2 NaCl + 2 HO → 2 NaOH + H + Cl
any Cl disproportionates to hypochlorite and chloride
:Cl + 2 NaOH → NaCl + NaClO + HO
resulting in a hypochlorite solution. | 0 | Theoretical and Fundamental Chemistry |
Another purpose of this titration is determination of the optimum dose of surfactant for achieving stabilization or flocculation of a heterogeneous system. | 0 | Theoretical and Fundamental Chemistry |
In 1986, the N-end rule was elucidated, and it states that the identity of the amino acid at the N-terminus of the protein's amino acid sequence determines the half-life of the protein. In an effort to determine the effects of arginylation on the half-life of proteins, several studies were performed using modified yeast proteins. These studies revealed that when proteins were engineered to include N-termini which had been arginylated, the modified proteins were metabolically unstable. Furthermore, it was also discovered that protein ubiquitination and degradation become more likely to occur when a protein is arginylated. The evidence gathered from these experiments make it clear that arginylation in vivo leads to the degradation of proteins with asparagine and glutamine residues at their N-termini.
However, there have also been several recent studies which have shown that protein degradation may not be the prevalent function of arginylation, but that this modification may also be important for certain proteins to function correctly. For instance, when arginylation occurs on beta amyloid proteins, the proteins are guided into their proper alpha helical shape and are also prevented from misfolding and aggregating. Another protein which benefits from arginylation is calreticulin because when modified, its role during endoplasmic reticulum stress is facilitated, rather than it being removed from cells entirely. As both degradation and facilitation effects of arginylation have been identified and studied, it is clear that arginylation has an important role in protein regulation within cells. | 1 | Applied and Interdisciplinary Chemistry |
Nucleotide excision repair is one of the main mechanisms used to remove bulky adducts from DNA lesions caused by chemotherapy drugs, environmental mutagens, and most importantly UV radiation. This mechanism functions by releasing a short damage containing oligonucleotide from the DNA site, and then that gap is filled in and repaired by NER. NER recognizes a variety of structurally unrelated DNA lesions due to the flexibility of the mechanism itself, as NER is highly sensitive to changes in the DNA helical structure. Bulky adducts seem to trigger NER. The XPC-RAD23-CETN2 heterotrimer involved with NER has a critical role in DNA lesion recognition. In addition to other general lesions in the genome, UV damaged DNA binding protein complex (UV-DDB) also has an important role in both recognition and repair of UV-induced DNA photolesions.
Mismatch repair (MMR) mechanisms within the cell correct base mispairs that occur during replication using a variety of pathways. It has a high affinity for targeting DNA lesions with specificity, as alternations in base pair stacking that occur at DNA lesion sites affect the helical structure. This is likely one of many signals that triggers MMR. | 1 | Applied and Interdisciplinary Chemistry |
The degree of homogeneity in pore distribution of the final product is primarily dependent on the adequacy of mixing of the precursor. The difference in particle size between the titanium powders and the spacers directly impacts the ability to adequately mix the preform. The greater the size difference, the more difficult it is to control this process. Nonhomogeneous mixing resulting from the use of spacers considerably larger than the titanium particles employed and has shown adverse effects in the stability of the precursor after removal of spacer and in the distribution of porosity.
Spacer size has been investigated. It was shown that the use of a coarse spacer results in thicker pore walls while the use of finer spacers results in enhanced compaction, leading to increased densification. Increased densification is evidenced by a monomodal pore distribution with the employment of fine spacers and a bimodal distribution using coarse spacers. Further, finer spacers result in a more homogeneous pore distribution. Sharma et al. utilized acicular spacers and achieved porosities up to 60% where pores were undistorted. In samples employing fine particles, porosities up to 70% were achievable before noting distortion in the pores. However, the bimodal pore distribution observed in coarse-spacer samples showed to be beneficial in terms of mechanical properties in that higher compressive strengths were observed, beyond those that might exist due to the inverse relationship of porosity and compressive strength alone. | 0 | Theoretical and Fundamental Chemistry |
Cyclamin is an organic compound that has been used by the pharmaceutical industry as an ingredient for nasal sprays. | 0 | Theoretical and Fundamental Chemistry |
RuBisCO is important biologically because it catalyzes the primary chemical reaction by which inorganic carbon enters the biosphere. While many autotrophic bacteria and archaea fix carbon via the reductive acetyl CoA pathway, the 3-hydroxypropionate cycle, or the reverse Krebs cycle, these pathways are relatively small contributors to global carbon fixation compared to that catalyzed by RuBisCO. Phosphoenolpyruvate carboxylase, unlike RuBisCO, only temporarily fixes carbon. Reflecting its importance, RuBisCO is the most abundant protein in leaves, accounting for 50% of soluble leaf protein in plants (20–30% of total leaf nitrogen) and 30% of soluble leaf protein in plants (5–9% of total leaf nitrogen). Given its important role in the biosphere, the genetic engineering of RuBisCO in crops is of continuing interest (see below). | 0 | Theoretical and Fundamental Chemistry |
The mined ore is usually crushed into small chunks and heaped on an impermeable plastic or clay lined leach pad where it can be irrigated with a leach solution to dissolve the valuable metals. While sprinklers are occasionally used for irrigation, more often operations use drip irrigation to minimize evaporation, provide more uniform distribution of the leach solution, and avoid damaging the exposed mineral. The solution then percolates through the heap and leaches both the target and other minerals. This process, called the "leach cycle," generally takes from one or two months for simple oxide ores (e.g. most gold ores) to two years for nickel laterite ores. The leach solution containing the dissolved minerals is then collected, treated in a process plant to recover the target mineral and in some cases precipitate other minerals, and recycled to the heap after reagent levels are adjusted. Ultimate recovery of the target mineral can range from 30% of contained run-of-mine dump leaching sulfide copper ores to over 90% for the ores that are easiest to leach, some oxide gold ores.
The essential questions to address during the process of the heap leaching are:
* Can the investment of crushing the ore be justified by the potential increase in recovery and rate of recovery?
* How should the concentration of acid be altered over time in order to produce a solution that can be economically treated?
* How does the form of a heap affect the recovery and solution grade?
* Under any given set of circumstances, what type of recovery can be expected before the leach solution quality drops below a critical limit?
* What recovery (quantifiable measure) can be expected?
In recent years, the addition of an agglomeration drum has improved on the heap leaching process by allowing for a more efficient leach. The rotary drum agglomerator works by taking the crushed ore fines and agglomerating them into more uniform particles. This makes it much easier for the leaching solution to percolate through the pile, making its way through the channels between particles.
The addition of an agglomeration drum also has the added benefit of being able to pre-mix the leaching solution with the ore fines to achieve a more concentrated, homogeneous mixture and allow the leach to begin prior to the heap.
Although heap leach design has made significant progress over the last few years through the use of new materials and improved analytical tools, industrial experience shows that there are significant benefits from extending the design process beyond the liner and into the rock pile itself. Characterization of the physical and hydraulic (hydrodynamic) properties of ore-for-leach focuses on the direct measurement of the key properties of the ore, namely:
* The relationship between heap height and ore bulk density (density profile)
* The relationship between bulk density and percolation capacity (conductivity profile)
* The relationship between the bulk density, porosity and its components (micro and macro)
* The relationship between the moisture content and percolation capacity (conductivity curve)
* The relationship between the aforementioned parameters and the ore preparation practices (mining, crushing, agglomeration, curing, and method of placement)
Theoretical and numerical analysis, and operational data show that these fundamental mechanisms are controlled by scale, dimensionality, and heterogeneity, all of which adversely affect the scalability of metallurgical and hydrodynamic properties from the lab to the field. The dismissal of these mechanisms can result in a number of practical and financial problems that will resonate throughout the life of the heap impacting the financial return of the operation. Through procedures that go beyond the commonly employed metallurgical testing and the integration of data gleaned through real time 3D monitoring, a more complete representative characterization of the physicochemical properties of the heap environment is obtained. This improved understanding results in a significantly higher degree of accuracy in terms of creating a truly representative sample of the environment within the heap.
By adhering to the characterization identified above, a more comprehensive view of heap leach environments can be realized, allowing the industry to move away from the de facto black-box approach to a physicochemically inclusive industrial reactor model. | 1 | Applied and Interdisciplinary Chemistry |
The conversion of biomass into energy is perhaps more challenging to the technologist than energy from fossil fuels. Water, dissolved organic and inorganic compounds, and solid particulates of various size can be present in biomass processes. It is perhaps the development of microbial fuel cells where the philosophical thinking of process miniaturization will play a wider role. Distribution of knowledge, in a fashionable, intriguing style through miniaturized devices, can be substantially enhanced (accelerated) by low power consuming devices (such as smart phones). A rethinking of "what is a powerplant?" can create enormous innovations, given recent advances in membrane materials of construction, immobilized whole cell methodologies, metabolic engineering, and nanotechnology.
The challenges of microbial fuel cells relate mainly to finding lower cost manufacturing methods, materials of construction, and systems design. [http://www.engr.psu.edu/ce/enve/logan/journal_publications.htm Bruce Logan] from the Penn State University has described in several research articles and reviews these challenges.
However, even with existing designs which generate low power, there are applications in [http://www.technologyreview.com/business/21332/page1/ distribution of electrical recharging] systems to remote areas of Africa, where smart phone, can enable access to the vast information of the internet, and to provide lighting. These systems can run on agricultural, animal and human waste streams using naturally occurring bacteria. | 1 | Applied and Interdisciplinary Chemistry |
Since their introduction in the early 1980s, CDSs have also generated considerable research work, especially for brain and eye targeting of various therapeutic agents, including those that cannot cross the blood–brain barrier or the blood–retinal barrier on their own. Within this approach, three major general CDS classes have been identified:
:* Enzymatic physicochemical-based (e.g., brain-targeting) CDSs: exploit site-specific traffic properties by sequential metabolic conversions that result in considerably altered properties
:* Site-specific enzyme-activated (e.g., eye-targeting) CDSs: exploit specific enzymes found primarily, exclusively, or at higher activity at the site of action
:* Receptor-based transient anchor-type (e.g., lung-targeting) CDSs: provide enhanced selectivity and activity through transient, reversible binding at the receptor
This concept has been extended to many drugs and peptides, its importance illustrated by the fact that its first applications and uses were published in Science in 1975, 1981 and 1983. Its extension to the targeted brain-delivery of neuropeptides was included by the Harvard Health Letter as one of the top 10 medical advances of 1992. Several compounds have reached advanced clinical development phase, such as
:* E-CDS (Estredox) for the brain-targeted delivery of estradiol and
:* betaxoxime for the eye-targeted delivery of betaxolol
In the first example above, brain-targeted CDSs employ a sequential metabolic conversion of a redox-based targetor moiety, which is closely related to the ubiquitous NAD(P)H ⇌ NAD(P) coenzyme system, to exploit the unique properties of the blood–brain barrier (BBB). After enzymatic oxidation of the NADH type drug conjugate to its corresponding NAD- drug, the still inactive precursor, "locks-in" behind the BBB to provide targeted and sustained CNS-delivery of the compound of interest.
The second example involves eye-specific delivery of betaxoxime, the oxime derivative of betaxolol. The administered, inactive β-amino-ketoxime is converted to the corresponding ketone via oxime hydrolase, an enzyme recently identified with preferential activity in the eye, and then stereospecifically reduced to its alcohol form. IOP-lowering activity is demonstrated without producing the active β-blockers systemically, making them void of any cardiovascular activity, a major drawback of classical antiglaucoma agents. Because of the advantages provided by this unique eye-targeting profile, oxime-based eye-targeting CDSs could replace the β-blockers currently used for ophthalmic applications. | 1 | Applied and Interdisciplinary Chemistry |
In 2011, the Vanderwal group reported a concise, longest linear sequence of 6 steps, total synthesis of strychnine. It featured a Zincke aldehyde followed by an anionic bicyclization reaction and a tandem Brook rearrangement / conjugate addition. | 0 | Theoretical and Fundamental Chemistry |
Most people think of waves as a surface phenomenon, which acts between water (as in lakes or oceans) and the air. Where low density water overlies high density water in the ocean, internal waves propagate along the boundary. They are especially common over the continental shelf regions of the world oceans and where brackish water overlies salt water at the outlet of large rivers. There is typically little surface expression of the waves, aside from slick bands that can form over the trough of the waves.
Internal waves are the source of a curious phenomenon called dead water, first reported in 1893 by the Norwegian oceanographer Fridtjof Nansen, in which a boat may experience strong resistance to forward motion in apparently calm conditions. This occurs when the ship is sailing on a layer of relatively fresh water whose depth is comparable to the ship's draft. This causes a wake of internal waves that dissipates a huge amount of energy. | 1 | Applied and Interdisciplinary Chemistry |
Pipes are commonly joined by welding, using threaded pipe and fittings; sealing the connection with a pipe thread compound, Polytetrafluoroethylene (PTFE) Thread seal tape, oakum, or PTFE string, or by using a mechanical coupling. Process piping is usually joined by welding using a TIG or MIG process. The most common process pipe joint is the butt weld. The ends of pipe to be welded must have a certain weld preparation called an End Weld Prep (EWP) which is typically at an angle of 37.5 degrees to accommodate the filler weld metal. The most common pipe thread in North America is the National Pipe Thread (NPT) or the Dryseal (NPTF) version. Other pipe threads include the British Standard Pipe Thread (BSPT), the garden hose thread (GHT), and the fire hose coupling (NST).
Copper pipes are typically joined by soldering, brazing, compression fittings, flaring, or crimping.
Plastic pipes may be joined by solvent welding, heat fusion, or elastomeric sealing.
If frequent disconnection will be required, gasketed pipe flanges or union fittings provide better reliability than threads. Some thin-walled pipes of ductile material, such as the smaller copper or flexible plastic water pipes found in homes for ice makers and humidifiers, for example, may be joined with compression fittings.
typically uses a "push-on" gasket style of pipe that compresses a gasket into a space formed between the two adjoining pieces. Push-on joints are available on most types of pipe. A pipe joint lubricant must be used in the assembly of the pipe. Under buried conditions, gasket-joint pipes allow for lateral movement due to soil shifting as well as expansion/contraction due to temperature differentials. Plastic MDPE and HDPE gas and water pipes are also often joined with Electrofusion fittings.
Large above ground pipe typically uses a flanged joint, which is generally available in ductile iron pipe and some others. It is a gasket style where the flanges of the adjoining pipes are bolted together, compressing the gasket into a space between the pipe.
Mechanical grooved couplings or Victaulic joints are also frequently used for frequent disassembly and assembly. Developed in the 1920s, these mechanical grooved couplings can operate up to working pressures and available in materials to match the pipe grade. Another type of mechanical coupling is a flareless tube fitting (Major brands include Swagelok, Ham-Let, Parker); this type of compression fitting is typically used on small tubing under in diameter.
When pipes join in chambers where other components are needed for the management of the network (such as valves or gauges), dismantling joints are generally used, in order to make mounting/dismounting easier. | 1 | Applied and Interdisciplinary Chemistry |
Glass solder is used to join glasses to other glasses, ceramics, metals, semiconductors, mica, and other materials, in a process called glass frit bonding. The glass solder has to flow and wet the soldered surfaces well below the temperature where deformation or degradation of either of the joined materials or nearby structures (e.g., metallization layers on chips or ceramic substrates) occurs. The usual temperature of achieving flowing and wetting is between . | 1 | Applied and Interdisciplinary Chemistry |
MCAT is also involved in bacterial polyketide biosynthesis. The enzyme MCAT together with an acyl carrier protein (ACP), and a polyketide synthase (PKS) and chain-length factor heterodimer, constitutes the minimal PKS of type II polyketides. | 1 | Applied and Interdisciplinary Chemistry |
This form factor is useful for applications where the spectrum analyzer can be plugged into AC power, which generally means in a lab environment or production/manufacturing area. Bench top spectrum analyzers have historically offered better performance and specifications than the portable or handheld form factor. Bench top spectrum analyzers normally have multiple fans (with associated vents) to dissipate heat produced by the processor. Due to their architecture, bench top spectrum analyzers typically weigh more than . Some bench top spectrum analyzers offer optional battery packs, allowing them to be used away from AC power. This type of analyzer is often referred to as a "portable" spectrum analyzer. | 0 | Theoretical and Fundamental Chemistry |
During his time in the Soviet Union, Liu married a Russian woman named Mara Fedotova. The couple had two children; a son named Alexei (Russian: Алексей Климович Федото, Alexei Klimovich Fedotov; Chinese: 刘维宁, Liu Weining) and a daughter named Sonya.
After Liu returned to China in 1957, Mara also moved to China with the children in 1959, which would be the last time the couple would see each other. Due to the tensions between China and Soviet Union, Mara divorced Liu and returned to Moscow with her two children. Liu later married Li Miaoxiu, with whom he had two sons, Liu Weidong and Liu Weize.
Alexei, who is also known by nickname Alyosha, did not publicly reveal himself as grandson of Liu Shaoqi due to fear of being spied on by the KGB when Sino-Soviet relations further deteriorated. After graduating from Moscow Aviation Institute, he worked at the national aviation space center of the Soviet Union and Roscosmos for a number of years with his identity not known until he was invited by the Government of China to attend the commemoration of the 100th anniversary of Liu Shaoqi's birthday in 1998.
His request to travel to China was rejected as his occupation involved military secrecy. The denial of his request led him to grow anxious to travel to China and therefore to retire from the Russian military early. When his request to travel to China was refused again he filed a lawsuit and in 2003 managed to visit China for the first time, where he met with Liu Shaoqi's living family members, including his wife Wang Guangmei.
He decided to settle in China, where he presently manages an organization called Russian-Asian Union of Industrialists and Entrepreneurs that facilitates trade between China and Russia in Guangzhou. Alexei and his wife have two children, including a daughter named Margarita who is currently serving as the vice chairman of the Russian-Asian Industrial Entrepreneurs Association and Russia-Philippine Business Council.
Liu's daughter Sonya married a Russian American and is currently settled in the United States. | 0 | Theoretical and Fundamental Chemistry |
Fitness in this model is the probability that an individual survives to reproduce. In the simplest implementation of the model, developmentally stable genotypes survive (i.e. their fitness is ) and developmentally unstable ones do not (i.e. their fitness is ). | 1 | Applied and Interdisciplinary Chemistry |
Retention treatment basins or large concrete tanks that store and treat combined sewage are another solution. These underground structures can range in storage and treatment capacity from to of combined sewage. While each facility is unique, a typical facility operation is as follows. Flows from the overloaded sewers are pumped into a basin that is divided into compartments. The first flush compartment captures and stores flows with the highest level of pollutants from the first part of a storm. These pollutants include motor oil, sediment, road salt, and lawn chemicals (pesticides and fertilizers) that are picked up by the stormwater as it runs off roads and lawns. The flows from this compartment are stored and sent to the wastewater treatment plant when there is capacity in the interceptor sewer after the storm. The second compartment is a treatment or flow-through compartment. The flows are disinfected by injecting sodium hypochlorite, or bleach, as they enter this compartment. It then takes about 20‑30 minutes for the flows to move to the end of the compartment. During this time, bacteria are killed and large solid materials settle out. At the end of the compartment, any remaining sanitary trash is skimmed off the top and the treated flows are discharged into the river or lake.
The City of Detroit, Michigan, utilizes a system of nine CSO retention basins and screening/disinfection facilities that are owned and operated by the Great Lakes Water Authority. These basins are located at original combined sewer outfalls located along the Detroit River and Rouge River within metropolitan Detroit. These facilities are generally designed to contain two inches of stormwater runoff, with the ability to disinfect overflows during extreme wet-weather rainfall events. | 1 | Applied and Interdisciplinary Chemistry |
In order of increasing cost and decreasing product moisture the most common dewatering options are a thickener, deep bed thickening, belt presses and membrane filter presses. In general centrifuges and other competing technologies do not show a significant cost advantage compared to the belt press filter, for the same cake dryness. The cost of flocculant is often a major operating cost of dewatering equipment. Belt press filters in general have the lowest flocculant consumption for any of the listed processes excluding membrane filter presses and centrifuges.
Increasing the feed solid concentration increases the solid filtration rate, minimises cake moisture content and produces a more homogeneous cake all of which are desirable outcomes. If increasing the feed solid concentration is not practical the addition of flocculants in a pre-treatment step has a similar result. The optimum dosage level of flocculant can be found by monitoring the viscosity of the slurry.
Homogeneous cakes are desirable as if the feed slurry is too dilute the filter cake will contain higher moisture content as a result of stratification. The minimum feed concentration that results in a homogeneous cake is determined by observing a sample of the slurry. If rapid settling occurs the filter cake formed will not be homogeneous and the filtration rate is decreased.
The minimum cake discharge thickness for horizontal belt press filters is in the region of 5 mm.
The choice of belt is critical to the function of the belt press filter and a wide variety of materials and weaves are available. The filter cloth for a belt press filter should be as open as possible while maintaining the desired filtrate clarity or, if precoat is used, to prevent the loss of precoat. Lighter cloths produce a clearer filtrate and do not block as rapidly however their durability and life span is significantly shorter than heavier cloths. Both seamless and seamed belts are available. Seamed belts wear faster at the seam and cause wear at the rollers and the doctor blade. Zipper-type and clipper-type seamed belts are also available with the zipper-type having a longer life span as they provide less discontinuity. Seamless belts have the longest life span but are more expensive. Also it should be ensured that the belt press is compatible with a seamless belt.
Increasing the temperature of the feed slurry decreases the viscosity of the liquid phase. This is beneficial as it increases the filtration rate and decreases the cake moisture. The same advantages can be obtained by other drying methods such as passing dry steam through the deliquored cake to raise the temperature of the remaining moisture, or other drying methods can be utilised.
Cake thickness may have to be controlled or restricted when cake washing is required or the final cake moisture is a critical parameter. When cake washing time is a dominating factor the maximum filtration rate will occur when the minimum cake thickness for discharge is achieved. The time required for washing is increased by the square of the ratio of cake thicknesses. For example, if the thickness of the cake is doubled the washing time will increase roughly by a factor of 4. | 1 | Applied and Interdisciplinary Chemistry |
These mechanistic mimetics do not directly recapitulate the side chains or conformation of a peptide but mimic its mode-of-action. Class D peptidomimetics can be directly designed from a small peptide sequence or identified the screening of compound libraries. For example, Nirmatrelvir is an orally-active small molecule drug derived from lufotrelvir, a modified L-peptide. | 0 | Theoretical and Fundamental Chemistry |
Alcohol is absorbed throughout the gastrointestinal tract, but more slowly in the stomach than in the small or large intestine. For this reason, alcohol consumed with food is absorbed more slowly, because it spends a longer time in the stomach. Furthermore, alcohol dehydrogenase is present in the stomach lining. After absorption, the alcohol passes to the liver through the hepatic portal vein, where it undergoes a first pass of metabolism before entering the general bloodstream.
Alcohol is removed from the bloodstream by a combination of metabolism, excretion, and evaporation. Alcohol is metabolized mainly by the group of six enzymes collectively called alcohol dehydrogenase. These convert the ethanol into acetaldehyde (an intermediate more toxic than ethanol). The enzyme acetaldehyde dehydrogenase then converts the acetaldehyde into non-toxic acetic acid.
Many physiologically active materials are removed from the bloodstream (whether by metabolism or excretion) at a rate proportional to the current concentration, so that they exhibit exponential decay with a characteristic half-life (see pharmacokinetics). This is not true for alcohol, however. Typical doses of alcohol actually saturate the enzymes capacity, so that alcohol is removed from the bloodstream at an approximately constant rate. This rate varies considerably between individuals. Another sex-based difference is in the elimination of alcohol. For females, the concentration of alcohol in breast milk produced during lactation is closely correlated to the individuals blood alcohol content. People under 25, women, or people with liver disease may process alcohol more slowly. Falsely high BAC readings may be seen in patients with kidney or liver disease or failure.
Such persons also have impaired acetaldehyde dehydrogenase, which causes acetaldehyde levels to peak higher, producing more severe hangovers and other effects such as flushing and tachycardia. Conversely, members of certain ethnicities that traditionally did not use alcoholic beverages have lower levels of alcohol dehydrogenases and thus "sober up" very slowly but reach lower aldehyde concentrations and have milder hangovers. The rate of detoxification of alcohol can also be slowed by certain drugs which interfere with the action of alcohol dehydrogenases, notably aspirin, furfural (which may be found in fusel alcohol), fumes of certain solvents, many heavy metals, and some pyrazole compounds. Also suspected of having this effect are cimetidine, ranitidine, and acetaminophen (paracetamol).
Currently, the only known substance that can increase the rate of alcohol metabolism is fructose. The effect can vary significantly from person to person, but a 100 g dose of fructose has been shown to increase alcohol metabolism by an average of 80%. Fructose also increases false positives of high BAC readings in anyone with proteinuria and hematuria, due to kidney-liver metabolism.
The peak of blood alcohol level (or concentration of alcohol) is reduced after a large meal. | 1 | Applied and Interdisciplinary Chemistry |
Flammability of furniture is of concern as cigarettes and candle accidents can trigger domestic fires. In 1975, California began implementing Technical Bulletin 117 (TB 117), which required that materials such as polyurethane foam used to fill furniture be able to withstand a small open flame, equivalent to a candle, for at least 12 seconds. In polyurethane foam, furniture manufacturers typically meet TB 117 with additive halogenated organic flame retardants. No other U.S. states had similar standards, but because California has such a large market, manufacturers meet TB 117 in products that they distribute across the United States. The proliferation of flame retardants, and especially halogenated organic flame retardants, in furniture across the United States is strongly linked to TB 117. When it became apparent that the risk-benefit ratio of this approach was unfavorable and industry had used falsified documentation (i.e. see David Heimbach) for the use of flame retardants, California modified TB 117 to require that fabric covering upholstered furniture meet a smolder test replacing the open flame test. Gov. Jerry Brown signed the modified TB117-2013, which became effective in 2014. | 0 | Theoretical and Fundamental Chemistry |
Azlocillin is an acyl ampicillin antibiotic with an extended spectrum of activity and greater in vitro potency than the carboxy penicillins.
Azlocillin is similar to mezlocillin and piperacillin. It demonstrates antibacterial activity against a broad spectrum of bacteria, including Pseudomonas aeruginosa and, in contrast to most cephalosporins, exhibits activity against enterococci. | 0 | Theoretical and Fundamental Chemistry |
The most obvious characteristic of flatfish, other than their flatness, is their asymmetric morphology: both eyes are on the same side of the head in the adult fish. In some families of flatfish, the eyes are always on the right side of the body (dextral or right-eyed flatfish), and in others, they are always on the left (sinistral or left-eyed flatfish). Primitive spiny turbots include equal numbers of right- and left-sided individuals, and are generally more symmetric than other families. | 0 | Theoretical and Fundamental Chemistry |
Spliced leader sequences are short sequences of non coding RNA, not found within a gene itself, that are attached to the 5’ end of all, or a portion of, mRNAs transcribed in an organism. They have been found in several species to be responsible for separating polycistronic transcripts into single gene mRNAs, and in others to splice onto monocistronic transcripts. The major role of trans-splicing on monocistronic transcripts is largely unknown. It has been proposed that they may act as an independent promoter that aids in tissue specific expression of independent protein isoforms. Spliced leaders have been seen in trypanosomatids, Euglena, flatworms, Caenorhabditis. Some species contain only one spliced leader sequence found on all mRNAs. In C. elegans two are seen and are labeled SL1 and SL2. | 1 | Applied and Interdisciplinary Chemistry |
Enzyme-based cleaners are especially useful for biofilm removal. Bacteria are somewhat difficult to remove with traditional alkaline or acid cleaners. Enzyme cleaners are more effective on biofilms since they work as proteases by breaking down proteins at bacterial attachment sites. They work at maximum efficiency at high pH and at temperatures below 60 °C. Enzyme cleaners are an increasingly attractive alternative to traditional chemical cleaners because of biodegradability and other environmental factors, such as reduced wastewater generation and energy savings from using cold water. However, they are typically more expensive than alkaline or acid cleaners. | 1 | Applied and Interdisciplinary Chemistry |
When a photon is absorbed, 11-cis-retinal is transformed to all-trans-retinal, and it moves to the exit site of rhodopsin. It will not leave the opsin protein until another fresh chromophore comes to replace it, except for in the ABCR pathway. Whilst still bound to the opsin, all-trans-retinal is transformed into all-trans-retinol by all-trans-Retinol Dehydrogenase. It then proceeds to the cell membrane of the rod, where it is chaperoned to the Retinal Pigment Epithelium (RPE) by Interphotoreceptor retinoid-binding protein (IRBP). It then enters the RPE cells, and is transferred to the Cellular Retinol Binding Protein (CRBP) chaperone.
When inside the RPE cell, bound to CRBP, the all-trans-retinol is esterified by Lecithin Retinol Acyltransferase (LRAT) to form a retinyl ester. The retinyl esters of the RPE are chaperoned by a protein known as RPE65. It is in this form that the RPE stores most of its retinoids, as the RPE stores 2-3 times more retinoids than the neural retina itself. When further chromophore is required, the retinyl esters are acted on by isomerohydrolase to produce 11-cis-retinol, which is transferred to the Cellular retinaldehyde binding protein (CRALBP). 11-cis-Retinol is transformed into 11-cis retinal by 11-cis-retinol dehydrogenase, then it is shipped back to the photoreceptor cells via IRBP. There, it replaces the spent chromophore in opsin molecules, rendering the opsin photosensitive. | 1 | Applied and Interdisciplinary Chemistry |
If the fluid domain is bounded by an upper, stationary wall, located at a height , the flow velocity is given by
where . | 1 | Applied and Interdisciplinary Chemistry |
*2020 Laura Gagliardi
*2019 Daniel M. Neumark
*2016 Mark A. Ratner
*2015 Xiaoliang Sunney Xie
*2014 Henry F. Schaefer III
*2013 William E. Moerner
*2012 David Chandler
*2011 Louis E. Brus
*2010 George Schatz
*2009 Richard J. Saykally
*2008 Michael L. Klein
*2007 John T. Yates, Jr.
*2006 Donald Truhlar
*2005 Stephen Leone
*2004 William Carl Lineberger
*2003 William H. Miller
*2002 Giacinto Scoles
*2001 John Ross
*2000 Peter G. Wolynes
*1999 Jesse L. Beauchamp
*1998 Graham R. Fleming
*1997 Robin M. Hochstrasser
*1996 Ahmed Zewail
*1995 John C. Tully
*1994 William A. Klemperer
*1993 F. Sherwood Rowland
*1992 Frank H. Stillinger
*1991 Richard N. Zare
*1990 Harden M. McConnell
*1989 Gabor A. Somorjai
*1988 Rudolph A. Marcus
*1987 Harry G. Drickamer
*1986 Yuan T. Lee
*1985 Stuart A. Rice
*1984 B. Seymour Rabinovitch
*1983 George C. Pimentel
*1982 Peter M. Rentzepis
*1981 Richard B. Bernstein
*1976 Robert W. Zwanzig
*1975 Herbert S. Gutowsky
*1974 Walter H. Stockmayer
*1973 William N. Lipscomb, Jr.
*1972 Clyde A. Hutchison, Jr.
*1971 Norman Davidson
*1969 Paul J. Flory
*1968 George B. Kistiakowsky
*1967 Joseph E. Mayer
*1966 Joseph O. Hirschfelder
*1965 Lars Onsager
*1964 Henry Eyring
*1963 Robert S. Mulliken
*1962 E. Bright Wilson, Jr. | 0 | Theoretical and Fundamental Chemistry |
Lenses can first be designed using paraxial theory to position images and pupils, then real surfaces inserted and optimized. Paraxial theory can be skipped in simpler cases and the lens directly optimized using real surfaces. Lenses are first designed using average index of refraction and dispersion (see Abbe number) properties published in the glass manufacturer's catalog and through glass model calculations. However, the properties of the real glass blanks will vary from this ideal; index of refraction values can vary by as much as 0.0003 or more from catalog values, and dispersion can vary slightly. These changes in index and dispersion can sometimes be enough to affect the lens focus location and imaging performance in highly corrected systems.
The lens blank manufacturing process is as follows:
#The glass batch ingredients for a desired glass type are mixed in a powder state,
#the powder mixture is melted in a furnace,
#the fluid is further mixed while molten to maximize batch homogeneity,
#poured into lens blanks and
#annealed according to empirically determined time-temperature schedules.
The glass blank pedigree, or "melt data", can be determined for a given glass batch by making small precision prisms from various locations in the batch and measuring their index of refraction on a spectrometer, typically at five or more wavelengths. Lens design programs have curve fitting routines that can fit the melt data to a selected dispersion curve, from which the index of refraction at any wavelength within the fitted wavelength range can be calculated. A re-optimization, or "melt re-comp", can then be performed on the lens design using measured index of refraction data where available. When manufactured, the resulting lens performance will more closely match the desired requirements than if average glass catalog values for index of refraction were assumed.
Delivery schedules are impacted by glass and mirror blank availability and lead times to acquire, the amount of tooling a shop must fabricate prior to starting on a project, the manufacturing tolerances on the parts (tighter tolerances mean longer fab times), the complexity of any optical coatings that must be applied to the finished parts, further complexities in mounting or bonding lens elements into cells and in the overall lens system assembly, and any post-assembly alignment and quality control testing and tooling required. Tooling costs and delivery schedules can be reduced by using existing tooling at any given shop wherever possible, and by maximizing manufacturing tolerances to the extent possible. | 0 | Theoretical and Fundamental Chemistry |
BN-PAGE is a native PAGE technique, where the Coomassie brilliant blue dye provides the necessary charges to the protein complexes for the electrophoretic separation. The disadvantage of Coomassie is that in binding to proteins it can act like a detergent causing complexes to dissociate. Another drawback is the potential quenching of chemoluminescence (e.g. in subsequent western blot detection or activity assays) or fluorescence of proteins with prosthetic groups (e.g. heme or chlorophyll) or labelled with fluorescent dyes. | 1 | Applied and Interdisciplinary Chemistry |
N mers form the polymer, whose total unfolded length is:
where N is the number of mers.
In this very simple approach where no interactions between mers are considered, the energy of the polymer is taken to be independent of its shape, which means that at thermodynamic equilibrium, all of its shape configurations are equally likely to occur as the polymer fluctuates in time, according to the Maxwell–Boltzmann distribution.
Let us call the total end to end vector of an ideal chain and the vectors corresponding to individual mers. Those random vectors have components in the three directions of space. Most of the expressions given in this article assume that the number of mers N is large, so that the central limit theorem applies. The figure below shows a sketch of a (short) ideal chain.
The two ends of the chain are not coincident, but they fluctuate around each other, so that of course:
Throughout the article the brackets will be used to denote the mean (of values taken over time) of a random variable or a random vector, as above.
Since are independent, it follows from the Central limit theorem that is distributed according to a normal distribution (or gaussian distribution): precisely, in 3D, and are distributed according to a normal distribution of mean 0 and of variance:
So that . The end to end vector of the chain is distributed according to the following probability density function:
The average end-to-end distance of the polymer is:
A quantity frequently used in polymer physics is the radius of gyration:
It is worth noting that the above average end-to-end distance, which in the case of this simple model is also the typical amplitude of the system's fluctuations, becomes negligible compared to the total unfolded length of the polymer at the thermodynamic limit. This result is a general property of statistical systems.
Mathematical remark: the rigorous demonstration of the expression of the density of probability is not as direct as it appears above: from the application of the usual (1D) central limit theorem one can deduce that , and are distributed according to a centered normal distribution of variance . Then, the expression given above for is not the only one that is compatible with such distribution for , and . However, since the components of the vectors are uncorrelated for the random walk we are considering, it follows that , and are also uncorrelated. This additional condition can only be fulfilled if is distributed according to . Alternatively, this result can also be demonstrated by applying a multidimensional generalization of the central limit theorem, or through symmetry arguments. | 0 | Theoretical and Fundamental Chemistry |
Using the KRAKEN autonomous qPCR device, Kraken Sense monitored airport wastewater for the presence of SARS-CoV-2 variants, such as Omicron, and Monkeypox to act as an early warning system for infectious diseases entering the country. This program was funded in part by the National Research Council Canada Industrial Research Assistance Program (NRC IRAP). | 0 | Theoretical and Fundamental Chemistry |
Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation. | 1 | Applied and Interdisciplinary Chemistry |
Cerrosafe is a fusible alloy with a low melting point. It is a non-eutectic mixture consisting of 42.5% bismuth, 37.7% lead, 11.3% tin, and 8.5% cadmium that melts between and . It is useful for making reference castings whose dimensions can be correlated to those of the mold or other template due to its well-known thermal expansion properties during cooling. The alloy contracts during the first 30 minutes, allowing easy removal from a mold, then expands during the next 30 minutes to return to the exact original size. It then continues expanding at a known rate for 200 hours, allowing conversion of measurements of the casting back to those of the mold. | 1 | Applied and Interdisciplinary Chemistry |
During mania, there is an increase in neurotransmission of dopamine that causes a secondary homeostatic down-regulation, resulting in decreased neurotransmission of dopamine, which can cause depression. Additionally, the post-synaptic actions of dopamine are mediated through G-protein coupled receptors. Once dopamine is coupled to the G-protein receptors, it stimulates other secondary messenger systems that modulate neurotransmission. Studies found that in autopsies (which do not necessarily reflect living people), people with bipolar disorder had increased G-protein coupling compared to people without bipolar disorder. Lithium treatment alters the function of certain subunits of the dopamine associated G-protein, which may be part of its mechanism of action. | 1 | Applied and Interdisciplinary Chemistry |
The mouse sperm genome is 80–90% methylated at its CpG sites in DNA, amounting to about 20 million methylated sites. After fertilization, the paternal chromosome is almost completely demethylated in six hours by an active process, before DNA replication (blue line in Figure).
Demethylation of the maternal genome occurs by a different process. In the mature oocyte, about 40% of its CpG sites in DNA are methylated. While somatic cells of mammals have three main DNA methyltransferases (which add methyl groups to cytosines at CpG sites), DNMT1, DNMT3A, and DNMT3B, in the pre-implantation embryo up to the blastocyst stage (see Figure), the only methyltransferase present is an isoform of DNMT1 designated DNMT1o. DNMT1o has an alternative oocyte-specific promoter and first exon (exon 1o) located 5' of the somatic and spermatocyte promoters. As reviewed by Howell et al., DNMT1o is sequestered in the cytoplasm of mature oocytes and in 2-cell and 4-cell embryos, but at the 8-cell stage is only present in the nucleus. At the 16 cell stage (the morula) DNMT1o is again found only in the cytoplasm. It appears that demethylation of the maternal chromosomes largely takes place by blockage of the methylating enzyme DNMT1o from entering the nucleus except briefly at the 8 cell stage. The maternal-origin DNA thus undergoes passive demethylation by dilution of the methylated maternal DNA during replication (red line in Figure). The morula (at the 16 cell stage), has only a small amount of DNA methylation (black line in Figure).
DNMT3b begins to be expressed in the blastocyst. Methylation begins to increase at 3.5 days after fertilization in the blastocyst, and a large wave of methylation then occurs on days 4.5 to 5.5 in the epiblast, going from 12% to 62% methylation, and reaching maximum level after implantation in the uterus. By day seven after fertilization, the newly formed primordial germ cells (PGC) in the implanted embryo segregate from the remaining somatic cells. At this point the PGCs have about the same level of methylation as the somatic cells. | 1 | Applied and Interdisciplinary Chemistry |
random primed synthesis - reading frame - recessive - recognition sequence - recombinant DNA - recombination - recombination-repair - relaxed DNA - repetitive DNA - replica plating - reporter gene - repression - repressor - residue - response element - restriction - restriction endonuclease - restriction enzyme - restriction fragment - restriction fragment length polymorphism (RFLP) - restriction fragments - restriction map - restriction site - reticulocyte lysate - retrovirus - reverse transcriptase - reverse transcription - revertant - ribonuclease - ribonuclease - ribonucleic acid - riboprobe - ribosomal-protein-alanine N-acetyltransferase - ribosomal binding sequence - ribosome - ribosyldihydronicotinamide dehydrogenase (quinone) - ribozyme - risk communication - RNA polymerase - RNA splicing - RNAi - RNase - RNase protection assay - rRNA - rRNA (guanine-N2-)-methyltransferase - RT-PCR - Run-on - runoff transcript | 1 | Applied and Interdisciplinary Chemistry |
Prenatal virilization of a genetically female fetus can occur when an excessive amount of androgen is produced by the fetal adrenal glands or is present in maternal blood. In the severest form of congenital adrenal hyperplasia, complete masculinization of a genetically female fetus results in an apparently normal male anatomy with no palpable testes. More often, the virilization is partial and the genitalia are ambiguous.
It can also be associated with progestin-induced virilisation. | 1 | Applied and Interdisciplinary Chemistry |
Macrocyclic rings containing sp centers display a conformational preference for the sp centers to avoid transannular nonbonded interactions by orienting perpendicular to the plan of the ring. Clark W. Still proposed that the ground state conformations of macrocyclic rings, containing the energy minimized orientation of the sp center, display one face of an olefin outwards from the ring. Addition of reagents from the outside the olefin face and the ring (peripheral attack) is thus favored, while attack from across the ring on the inward diastereoface is disfavored. Ground state conformations dictate the exposed face of the reactive site of the macrocycle, thus both local and distant stereocontrol elements must be considered. The peripheral attack model holds well for several classes of macrocycles, though relies on the assumption that ground state geometries remain unperturbed in the corresponding transition state of the reaction. | 0 | Theoretical and Fundamental Chemistry |
Biocrystallization is the formation of crystals from organic macromolecules by living organisms. This may be a stress response, a normal part of metabolism such as processes that dispose of waste compounds, or a pathology. Template mediated crystallization is qualitatively different from in vitro crystallization. Inhibitors of biocrystallization are of interest in drug design efforts against lithiasis and against pathogens that feed on blood, since many of these organisms use this process to safely dispose of heme. | 1 | Applied and Interdisciplinary Chemistry |
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