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Gummed film refers to a technique used to measure nuclear fallout. It involves the use of a sheet of plastic (cellulose acetate) or paper substrate coated on one side with an adhesive (e.g., rubber cement). The sheet is exposed (adhesive-side up) to the environment to be monitored, where fallout particles land on (and thus adhere to) the gummed film. After some period, the films are collected and analyzed for radioactivity. | 0 | Theoretical and Fundamental Chemistry |
Amino acids are the building blocks of peptides and enzymes while sugar-peptide chains are the backbone of RNA and DNA. In biological organisms, amino acids appear almost exclusively in the left-handed form (-amino acids) and sugars in the right-handed form (R-sugars). Since the enzymes catalyze reactions, they enforce homochirality on a great variety of other chemicals, including hormones, toxins, fragrances and food flavors. Glycine is achiral, as are some other non-proteinogenic amino acids that are either achiral (such as dimethylglycine) or of the enantiomeric form.
Biological organisms easily discriminate between molecules with different chiralities. This can affect physiological reactions such as smell and taste. Carvone, a terpenoid found in essential oils, smells like mint in its L-form and caraway in its R-form. Limonene tastes like citrus when right-handed and pine when left-handed.
Homochirality also affects the response to drugs. Thalidomide, in its left-handed form, cures morning sickness; in its right-handed form, it causes birth defects. Unfortunately, even if a pure left-handed version is administered, some of it can convert to the right-handed form in the patient. Many drugs are available as both a racemic mixture (equal amounts of both chiralities) and an enantiopure drug (only one chirality). Depending on the manufacturing process, enantiopure forms can be more expensive to produce than stereochemical mixtures.
Chiral preferences can also be found at a macroscopic level. Snail shells can be right-turning or left-turning helices, but one form or the other is strongly preferred in a given species. In the edible snail Helix pomatia, only one out of 20,000 is left-helical. The coiling of plants can have a preferred chirality and even the chewing motion of cows has a 10% excess in one direction. | 0 | Theoretical and Fundamental Chemistry |
The Russian Navy developed the VA-111 Shkval supercavitation torpedo, which uses rocket propulsion and exceeds the speed of conventional torpedoes by at least a factor of five. NII-24 began development in 1960 under the code name "Шквал" (Squall). The VA-111 Shkval has been in service (exclusively in the Russian Navy) since 1977 with mass production starting in 1978. Several models were developed, with the most successful, the M-5, completed by 1972. From 1972 to 1977, over 300 test launches were conducted (95% of them on Issyk Kul lake).
In 2006, German weapons manufacturer Diehl BGT Defence announced their own supercavitating torpedo, the Barracuda, now officially named (). According to Diehl, it reaches speeds greater than .
In 1994, the United States Navy began development of the Rapid Airborne Mine Clearance System (RAMICS), a sea mine clearance system invented by C Tech Defense Corporation. The system is based on a supercavitating projectile stable in both air and water. RAMICS projectiles have been produced in diameters of , , and . The projectile's terminal ballistic design enables the explosive destruction of sea mines as deep as with a single round. In 2000 at Aberdeen Proving Ground, RAMICS projectiles fired from a hovering Sea Cobra gunship successfully destroyed a range of live underwater mines. As of March 2009, Northrop Grumman completed the initial phase of RAMICS testing for introduction into the fleet.
Iran claimed to have successfully tested its first supercavitation torpedo, the Hoot (Whale), on 2–3 April 2006. Some sources have speculated it is based on the Russian VA-111 Shkval supercavitation torpedo, which travels at the same speed. Russian Foreign Minister Sergey Lavrov denied supplying Iran with the technology.
In 2004, DARPA announced the Underwater Express program, a research and evaluation program to demonstrate the use of supercavitation for a high-speed underwater craft application. The US Navy's ultimate goal is a new class of underwater craft for littoral missions that can transport small groups of navy personnel or specialized military cargo at speeds up to 100 knots. DARPA awarded contracts to Northrop Grumman and General Dynamics Electric Boat in late 2006. In 2009, DARPA announced progress on a new class of submarine:
A prototype ship named the Ghost, uses supercavitation to propel itself atop two struts with sharpened edges. It was designed for stealth operations by Gregory Sancoff of Juliet Marine Systems. The vessel rides smoothly in choppy water and has reached speeds of 29 knots.
The Chinese Navy and US Navy are reportedly working on their own supercavitating submarines using technical information obtained on the Russian VA-111 Shkval supercavitation torpedo.
A supercavitating propeller uses supercavitation to reduce water skin friction and increase propeller speed. The design is used in military applications, high-performance racing boats, and model racing boats. It operates fully submerged with wedge-shaped blades to force cavitation on the entire forward face, starting at the leading edge. Since the cavity collapses well behind the blade, the supercavitating propeller avoids spalling damage caused by cavitation, which is a problem with conventional propellers.
Supercavitating ammunition is used with German (Heckler & Koch P11) and Russian underwater firearms, and other similar weapons. | 1 | Applied and Interdisciplinary Chemistry |
The runaway success of DNA microarrays has generated much enthusiasm for protein microarrays. However, protein microarrays have not quite taken off as expected, even with the necessary tools and know-how from DNA microarrays being in place and ready for adaptation. One major reason is that protein microarrays are much more laborious and technically challenging to construct than DNA microarrays.
The traditional methods of producing protein arrays require the separate in vivo expression of hundreds or thousands of proteins, followed by separate purification and immobilization of the proteins on a solid surface. Cell-free protein array technology attempts to simplify protein microarray construction by bypassing the need to express the proteins in bacteria cells and the subsequent need to purify them. It takes advantage of available cell-free protein synthesis technology which has demonstrated that protein synthesis can occur without an intact cell as long as cell extracts containing the DNA template, transcription and translation raw materials and machinery are provided. Common sources of cell extracts used in cell-free protein array technology include wheat germ, Escherichia coli, and rabbit reticulocyte. Cell extracts from other sources such as hyperthermophiles, hybridomas, Xenopus oocytes, insect, mammalian and human cells have also been used.
The target proteins are synthesized in situ on the protein microarray, directly from the DNA template, thus skipping many of the steps in traditional protein microarray production and their accompanying technical limitations. More importantly, the expression of the proteins can be done in parallel, meaning all the proteins can be expressed together in a single reaction. This ability to multiplex protein expression is a major time-saver in the production process. | 1 | Applied and Interdisciplinary Chemistry |
Organotantalum reagents arise via transmetalation of organotin compounds with tantalum(V) chloride. These organotantalum reagents promote the conjugate allylation of enones. Although the direct allylation of carbonyl groups is prevalent throughout the literature, little has been reported on the conjugate allylation of enones. | 0 | Theoretical and Fundamental Chemistry |
Mitochondrial abundant heat soluble (MAHS) proteins are localized in mitochondria and are responsible for protecting mitochondria during desiccation. Because of its role in metabolizing reactive oxygen species, the mitochondrion is an important organelle to protect in extreme environments. During dehydration, the mitochondria of tardigrades grow much smaller and lose their cristae. MAHS proteins may act to replace water in the membrane of the mitochondria, preventing uneven rehydration and membrane rupture. | 1 | Applied and Interdisciplinary Chemistry |
Applications involving dendrimers in general take advantage of either stuffing cargo into the interior of the dendrimer (sometimes referred to as the "dendritic box"), or attaching cargo onto the dendrimer surface. PAMAM dendrimer applications have generally focused on surface modification, taking advantage of both electrostatic and covalent methods for binding cargo. Currently, major areas of study using PAMAM dendrimers and their functionalized derivatives involve drug delivery and gene delivery. | 0 | Theoretical and Fundamental Chemistry |
The Van Slyke determination is a chemical test for the determination of amino acids containing a primary amine group. It is named after the biochemist Donald Dexter Van Slyke (1883-1971).
One of Van Slyke's first professional achievements was the quantification of amino acids by the Van Slyke determination reaction. To quantify aliphatic amino acids, the sample is diluted in glycerol and then treated with a solution of sodium nitrite, water and acetic acid. The resulting diazotisation reaction produces nitrogen gas which can be observed qualitatively or measured quantitatively.
Van Slyke Reaction:
In addition, Van Slyke developed the so-called Van Slyke apparatus, which can be used to determine the concentration of respiratory gases in the blood, especially the concentration of sodium bicarbonate. This was of high importance to be able to recognize a beginning acidosis in diabetic patients as early as possible, in order to start alkali treatment. The Van Slyke apparatus became a standard equipment in clinical laboratories around the world and the results of Van Slyke's research are still used today to determine abnormalities in the acid-base homeostasis. Later on, Van Slyke further improved his apparatus, increasing its accuracy and sensitivity. Using the new method, he was able to further investigate the role of gas and electrolyte equilibria in the blood and how they change in response to respiration. | 0 | Theoretical and Fundamental Chemistry |
The De Brouckere mean diameter is the mean of a particle size distribution weighted by the volume (also called volume-weighted mean diameter, volume moment mean diameter. or volume-weighted mean size). It is the mean diameter, which is directly obtained in particle size measurements, where the measured signal is proportional to the volume of the particles. The most prominent examples are laser diffraction and acoustic spectroscopy (Coulter counter).
The De Brouckere mean is defined in terms of the moment-ratio system as,
Where n is the frequency of occurrence of particles in size class i, having a mean D diameter. Usually in logarithmic spaced classes, the geometric mean size of the size class is taken | 1 | Applied and Interdisciplinary Chemistry |
The development of the classic theory of drug antagonism by Gaddum, Schild and Arunlakshana built on the work of Langley, Hill and Clark. Gaddum described a model for the competitive binding of two ligands to the same receptor in short communication to The Physiological Society in 1937. The description referred only to binding, it was not immediately useful for the analysis of experimental measurements of the effects of antagonists on the response to agonists. It was Heinz Otto Schild who made measurement of the equilibrium constant for the binding of an antagonist possible. He developed the Schild equation to determine a dose ratio, a measure of the potency of a drug. In Schild regression, the change in the dose ratio, the ratio of the EC of an agonist alone compared to the EC in the presence of a competitive antagonist as determined on a dose response curve used to determine the affinity of an antagonist for its receptor. | 1 | Applied and Interdisciplinary Chemistry |
In a narrow definition, harmful algal blooms are only those blooms that release toxins that affect other species. On the other hand, any algal bloom can cause dead zones due to low oxygen levels, and could therefore be called "harmful" in that sense. The usage of the term "harmful algal blooms" in the media and scientific literature is varied. In a broader definition, all "organisms and events are considered to be HABs if they negatively impact human health or socioeconomic interests or are detrimental to aquatic systems". A harmful algal bloom is "a societal concept rather than a scientific definition".
A similarly broad definition of HABs was adopted by the US Environmental Protection Agency in 2008 who stated that HABs include "potentially toxic (auxotrophic, heterotrophic) species and high-biomass producers that can cause hypoxia and anoxia and indiscriminate mortalities of marine life after reaching dense concentrations, whether or not toxins are produced". | 0 | Theoretical and Fundamental Chemistry |
As MDCs contain low electrical conductivity in the desalination chamber and additional energy is not applied to the system, electron conductive-resins are applied to improve conductivity, decrease internal resistance and increase the desalination process of brackish waters. Brackish waters are low in salinity with a high amount of total dissolved solids, which results in difficulties in maintaining strong electrical currents due to increased internal resistance in the cell. MDCs also experience problems with the saturation of ions in the anode chamber which can be combatted by utilizing a microbial capacitive desalination cell (MCDC). MCDCs are analogous to MDCs with the exception of modification to the cation membrane by the addition of activate carbon cloth, permitting the free exchange of protons across both chambers of the cell and increasing the efficiency of desalination. | 0 | Theoretical and Fundamental Chemistry |
He studied chemistry in Berlin and Munich from 1929 to 1933, and then later received a doctorate in physical chemistry from the Kaiser Wilhelm Institute.
Havemann joined the Communist Party of Germany (KPD) in 1932 and was one of the founders of the resistance group, European Union. It was in connection with this group that he was arrested by the Gestapo in 1943. He received a death sentence for treason, but his execution was continually postponed because of the intervention of former colleagues, who insisted that Havemann was as important due to his work on chemical weapons and that he was still needed to explain the research. His execution was postponed so many times, he was able to survive until the Brandenburg-Görden Prison was liberated by the Red Army.
After the war, he became head of administration in the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry in Berlin, but in 1948 he was dismissed from this position due to political pressure from the American authorities in West Berlin. He continued his scientific work in the institute until he got barred from his laboratory in January 1950.
He then became a professor of physical chemistry at the Humboldt University of Berlin. He became a member of the Volkskammer in 1950 and won one of the GDRs national prizes in 1959. He published articles in Sinn und Form' criticizing modern socialism and revisionist works of the Western authors.
In 1963 he lectured on Scientific Aspects of Philosophical Problems (published as Dialectic without Dogmatism—Natural Sciences against Communistic Ideology) and was expelled from the ruling Socialist Unity Party and dismissed from the University—officially because he gave an interview to a newspaper from West Germany.
His son Florian Havemann (born 12 January 1952 in East Berlin) fled to West Germany in 1971.
Havemann was a victim of the Stasi's psychological warfare program.
He continued his work as a socialist critic and was put under house arrest in 1976, at his home in the village of Grünheide. This continued until his death in 1982, after a long time suffering from lung disease.
In 1989 he was politically rehabilitated by the Socialist Unity Party of Germany's Central Party Control Commission.
In 2005, Havemann was awarded the title Righteous among the Nations by the Israeli Holocaust memorial, Yad Vashem. | 0 | Theoretical and Fundamental Chemistry |
Alkaliphiles promise several interesting uses for biotechnology and future research. Alkaliphilic methods of regulating pH and producing ATP are of interest in the scientific community. However, perhaps the greatest area of interest from alkaliphiles lies in their enzymes: alkaline proteases; starch-degrading enzymes; cellulases; lipases; xylanases; pectinases; chitinases and their metabolites, including: 2-phenylamine; carotenoids; siderophores; cholic acid derivatives and organic acids. It is hoped that further research into alkaliphilic enzymes will allow scientists to harvest alkaliphiles' enzymes for use in basic conditions. Research aimed at discovering alkaliphile-produced antibiotics showed some success, yet has been held at bay by the fact that some products produced at high pH are unstable and unusable at a physiological pH range. | 1 | Applied and Interdisciplinary Chemistry |
The Morton number can also be expressed by using a combination of the Weber number, Froude number and Reynolds number,
The Froude number in the above expression is defined as
where V is a reference velocity and d is the equivalent diameter of the drop or bubble. | 1 | Applied and Interdisciplinary Chemistry |
The OCO-2 satellite was built by Orbital Sciences Corporation, based around the LEOStar-2 bus. The spacecraft is being used to study carbon dioxide concentrations and distributions in the atmosphere.
OCO-2 was ordered after the original OCO spacecraft failed to achieve orbit. During the first satellite's launch atop a Taurus-XL in February 2009, the payload fairing failed to separate from around the spacecraft and the rocket did not have sufficient power to enter orbit with its additional mass. Although a Taurus launch was initially contracted for the reflight, the launch contract was cancelled after the same malfunction occurred on the launch of the Glory satellite two years later.
United Launch Alliance launched OCO-2 using a Delta II rocket at the beginning of a 30-second launch window at 09:56 UTC (2:56 PDT) on 2 July 2014. Flying in the 7320-10C configuration, the rocket launched from Space Launch Complex 2W at Vandenberg Air Force Base. The initial launch attempt on 1 July at 09:56:44 UTC was scrubbed at 46 seconds on the countdown clock due to a faulty valve on the water suppression system, used to flow water on the launch pad to dampen the acoustic energy during launch.
OCO-2 joined the A-train satellite constellation, becoming the sixth satellite in the group. Members of the A-train fly very close together in Sun-synchronous orbit, to make nearly simultaneous measurements of Earth. A particularly short launch window of 30 seconds was necessary to achieve a proper position in the train. As of it was in an orbit with a perigee of , an apogee of and a 98.2° inclination.
The mission is expected to cost , including design, development, launch and operations. | 1 | Applied and Interdisciplinary Chemistry |
Heap leaching dates back to the second century BC in China, where iron was combined with copper sulfate. By the time of the Northern Song Dynasty, a copper alloy was able to be recovered by leaching.
Leaching can also be traced back to alchemy. Early examples of leaching performed by alchemists resembled mixing iron with copper sulfate, yielding a layer of metallic copper. In the 8th century, Jabir Ibn Hayyan, an Arab alchemist, discovered a substance he coined "aqua regia". Aqua regia, a combination of hydrochloric acid and nitric acid, was found to be effective in dissolving gold, which was previously thought to be insoluble. | 1 | Applied and Interdisciplinary Chemistry |
In terms of bonding, isocyanates are closely related to carbon dioxide (CO) and carbodiimides (C(NR)). The C−N=C=O unit that defines isocyanates is planar, and the N=C=O linkage is nearly linear. In phenyl isocyanate, the C=N and C=O distances are respectively 1.195 and 1.173 Å. The C−N=C angle is 134.9° and the N=C=O angle is 173.1°. | 0 | Theoretical and Fundamental Chemistry |
When considering whether a specific nuclear transmutation, a reaction or a decay, is energetically allowed, one only needs to sum the masses of the initial nucleus/nuclei and subtract from that value the sum of the masses of the product particles. If the result, or Q-value, is positive, then the transmutation is allowed, or exothermic because it releases energy, and if the Q-value is a negative quantity, then it is endothermic as at least that much energy must be added to the system before the transmutation may proceed. For example, to determine if C, the most common isotope of carbon, can undergo proton emission to B, one finds that about 16 MeV must be added to the system for this process to be allowed. While Q-values can be used to describe any nuclear transmutation, for particle decay, the particle separation energy quantity S, is also used, and it is equivalent to the negative of the Q-value. In other words, the proton separation energy S indicates how much energy must be added to a given nucleus to remove a single proton. Thus, the particle drip lines defined the boundaries where the particle separation energy is less than or equal to zero, for which the spontaneous emission of that particle is energetically allowed.
Although the location of the drip lines is well defined as the boundary beyond which particle separation energy becomes negative, the definition of what constitutes a nucleus or an unbound resonance is unclear. Some known nuclei of light elements beyond the drip lines decay with lifetimes on the order of 10 seconds; this is sometimes defined to be a limit of nuclear existence because several fundamental nuclear processes (such as vibration and rotation) occur on this timescale. For more massive nuclei, particle emission half-lives may be significantly longer due to a stronger Coulomb barrier and enable other transitions such as alpha and beta decay to instead occur. This renders unambiguous determination of the drip lines difficult, as nuclei with lifetimes long enough to be observed exist far longer than the timescale of particle emission and are most probably bound. Consequently, particle-unbound nuclei are difficult to observe directly, and are instead identified through their decay energy. | 0 | Theoretical and Fundamental Chemistry |
Several tissue banks have come into existence, including the "Frozen zoo" at the San Diego Zoo, to store frozen tissue from the world's rarest and most endangered species. This is also referred to as "Conservation cloning".
Engineers have proposed a "lunar ark" in 2021 – storing millions of seed, spore, sperm and egg samples from Earth's contemporary species in a network of lava tubes on the Moon as a genetic backup. Similar proposals have been made since at least 2008. These also include sending human customer DNA, and a proposal for "a lunar backup record of humanity" that includes genetic information by Avi Loeb et al.
Scientists at the University of Newcastle and University of New South Wales announced in March 2013 that the very recently extinct gastric-brooding frog would be the subject of a cloning attempt to resurrect the species.
Many such "De-extinction" projects are being championed by the non-profit Revive & Restore. | 1 | Applied and Interdisciplinary Chemistry |
In bacteria, the same enzyme catalyzes the synthesis of mRNA and non-coding RNA (ncRNA).
RNAP is a large molecule. The core enzyme has five subunits (~400 kDa):
; β′: The β′ subunit is the largest subunit, and is encoded by the rpoC gene. The β′ subunit contains part of the active center responsible for RNA synthesis and contains some of the determinants for non-sequence-specific interactions with DNA and nascent RNA. It is split into two subunits in Cyanobacteria and chloroplasts.
; β: The β subunit is the second-largest subunit, and is encoded by the rpoB gene. The β subunit contains the rest of the active center responsible for RNA synthesis and contains the rest of the determinants for non-sequence-specific interactions with DNA and nascent RNA.
; α (α and α): Two copies of the α subunit, being the third-largest subunit, are present in a molecule of RNAP: α and α (one and two). Each α subunit contains two domains: αNTD (N-terminal domain) and αCTD (C-terminal domain). αNTD contains determinants for assembly of RNAP. αCTD (C-terminal domain) contains determinants for interaction with promoter DNA, making non-sequence-non-specific interactions at most promoters and sequence-specific interactions at upstream-element-containing promoters, and contains determinants for interactions with regulatory factors.
; ω: The ω subunit is the smallest subunit. The ω subunit facilitates assembly of RNAP and stabilizes assembled RNAP.
In order to bind promoters, RNAP core associates with the transcription initiation factor sigma (σ) to form RNA polymerase holoenzyme. Sigma reduces the affinity of RNAP for nonspecific DNA while increasing specificity for promoters, allowing transcription to initiate at correct sites. The complete holoenzyme therefore has 6 subunits: β′βα and αωσ (~450 kDa). | 1 | Applied and Interdisciplinary Chemistry |
In fluid mechanics, plug flow is a simple model of the velocity profile of a fluid flowing in a pipe. In plug flow, the velocity of the fluid is assumed to be constant across any cross-section of the pipe perpendicular to the axis of the pipe. The plug flow model assumes there is no boundary layer adjacent to the inner wall of the pipe.
The plug flow model has many practical applications. One example is in the design of chemical reactors. Essentially no back mixing is assumed with "plugs" of fluid passing through the reactor. This results in differential equations that need to be integrated to find the reactor conversion and outlet temperatures. Other simplifications used are perfect radial mixing and a homogeneous bed structure.
An advantage of the plug flow model is that no part of the solution of the problem can be perpetuated "upstream". This allows one to calculate the exact solution to the differential equation knowing only the initial conditions. No further iteration is required. Each "plug" can be solved independently provided the previous plug's state is known.
The flow model in which the velocity profile consists of the fully developed boundary layer is known as pipe flow. In laminar pipe flow, the velocity profile is parabolic. | 1 | Applied and Interdisciplinary Chemistry |
Beam attenuation is measured with a device called a transmissometer that has a light source at one end and a detector at the other end, in one plane. The amount of light transmitted to the detector through the water is the beam transmission, and the amount of light lost is the beam attenuation. Beam attenuation is essentially the opposite of light transmission. Clearer water with a low beam attenuation coefficient will have high light transmission, and more turbid water with a high beam attenuation coefficient will have low light transmission. Beam attenuation is used as a proxy for particulate organic carbon in oligotrophic waters like the open ocean. | 0 | Theoretical and Fundamental Chemistry |
Release of other organisms that fight the pest is another example of an alternative to pesticide use. These organisms can include natural predators or parasites of the pests. Biological pesticides based on entomopathogenic fungi, bacteria and viruses causing disease in the pest species can also be used. | 1 | Applied and Interdisciplinary Chemistry |
After his arrival at Oxford and during World War II, Cornforth significantly influenced the work on penicillin, particularly in purifying and concentrating it. Penicillin is usually very unstable in its crude form; as a consequence of this, researchers at the time were building upon Howard Floreys work on the drug. In 1940, Cornforth and other chemists measured the yield of penicillin in arbitrary units to understand the conditions that favoured penicillin production and activity, and he contributed to the writing of The Chemistry of Penicillin'.
In 1946, the Cornforths, who had by now married, left Oxford and joined the Medical Research Council (MRC), working at the National Institute for Medical Research (NIMR), where they continued on earlier work in synthesising sterols, including cholesterol. The Cornforths' collaboration with Robinson continued and flourished. In 1951, they completed, simultaneously with Robert Burns Woodward, the first total synthesis of the non-aromatic steroids. At the NIMR, Cornforth collaborated with numerous biological scientists, including George Popják, with whom he shared an interest in cholesterol. Together, they received the Davy Medal in 1968 in recognition of their distinguished joint work on the elucidation of the biosynthetic pathway to polyisoprenoids and steroids.
While working at the MRC, Cornforth was appointed a professor at the University of Warwick and was employed there from 1965 to 1971.
In 1975, Cornforth was awarded a share of the Nobel Prize in Chemistry, alongside Vladimir Prelog. In his acceptance speech, Cornforth said:
Also in 1975, he moved to the University of Sussex in Brighton as a Royal Society Research Professor. Cornforth remained there as a professor and was active in research until his death. | 0 | Theoretical and Fundamental Chemistry |
The lac operon in the prokaryote E. coli consists of genes that produce enzymes to break down lactose. Its operon is an example of a prokaryotic silencer. The three functional genes in this operon are lacZ, lacY, and lacA. The repressor gene, lacI, will produce the repressor protein LacI which is under allosteric regulation. These genes are activated by the presence of lactose in the cell which acts as an effector molecule that binds to LacI. When the repressor is bound to lactose, it will not bind to the operator, which allows RNA polymerase to bind to the promoter to initiate transcription of the operon. When the repressors allosteric site is not bound to lactose, its active site will bind to the operator to prevent RNA polymerase from transcribing the genes of the lac' operon. | 1 | Applied and Interdisciplinary Chemistry |
A Penning trap stores charged particles using a strong homogeneous axial magnetic field to confine particles radially and a quadrupole electric field to confine the particles axially. Penning traps are well suited for measurements of the properties of ions and stable charged subatomic particles. Precision studies of the electron magnetic moment by Dehmelt and others are an important topic in modern physics.
Penning traps can be used in quantum computation and quantum information processing and are used at CERN to store antimatter. Penning traps form the basis of Fourier-transform ion cyclotron resonance mass spectrometry for determining the mass-to-charge ratio of ions.
The Penning Trap was invented by Frans Michel Penning and Hans Georg Dehmelt, who built the first trap in the 1950s. | 0 | Theoretical and Fundamental Chemistry |
In the following section XH stands for any hydrogen compound, e.g. CH- and NH-compounds.
* Thermal dissociation: gaseous hydrogen molecules are being dissociated at temperatures above 3000 K e.g. in a plasma. At temperatures above 3500 K H und O are dissociated.
* electron impact dissociation:
The density of radicals scales with the electron density and higher gas and electron temperatures (thermal dissociation and electron impact).
* ion impact dissociation: <br />
* dissociative electron attachment:
This process generates negative ions as well as neutral particles. The collision electron is captured by collision excitation. The energy difference between the ground state and the excited state dissociates the molecule. The electron-induced dissociation of water depends on the electron temperature, which influences the ratio of the OH density (n_OH) to the electron density (n_e) significantly. The maximum OH density is reached in the early afterglow when the electron temperature (T_e) is low.
* Photoionisation:<br> High-energy photons dissociate molecules
* Solvated electrons:<br> Reducing agent in liquid | 0 | Theoretical and Fundamental Chemistry |
Project 523 also resulted in the discovery of synthetic drugs such as pyronaridine in 1973, lumefantrine in 1976 and naphthoquine in 1986. These are all antimalarial drugs and are still used in artemisinin-combination therapy. | 1 | Applied and Interdisciplinary Chemistry |
Calamine brass is brass produced by a particular alloying technique using the zinc ore calamine directly, rather than first refining it to metallic zinc. Direct zinc smelting appears to have been unknown in Europe until the mid-18th century, even though the alloyed calamine brass was in use for centuries, and metallic zinc was produced directly via reducing-atmosphere smelting in India and China from the 12th century CE onwards.
Brass is an alloy of copper and zinc and, when it was first developed, methods for producing metallic zinc were unknown. Metallurgists wishing to produce brass thus used calamine (actually a mixture of the virtually indistinguishable zinc ores smithsonite and hemimorphite) as the zinc component of brass. The resulting brasses, produced by heating a mixture of copper and calamine to a high temperature for several hours (allowing zinc vapor to distill from the ores and permeate the metallic copper), contained a significant amount of slag material resulting from the non-zinc components of calamine. The use of ore rather than metallic zinc also made it difficult to accurately produce the desired final proportion of copper to zinc. This process is known as cementation.
Calamine brass was produced using proportions of two-sevenths fine copper, four-sevenths calamine, and one-seventh shruff (old plate brass). Calamine brass was the first type of brass produced, probably starting during the 1st millennium BC, and was not replaced in Europe by other brass manufactures until the 18th century. It is likely that Indian brass manufacturers had developed more advanced techniques some centuries earlier.
The area around La Calamine, now Kelmis, in Belgium, was the source of much of the medieval brass of northern Europe. Brass production was introduced to England in 1587 when several members of the Company of Mineral and Battery Works obtained a licence from the company (within whose monopoly it was) to build a brass works at Isleworth. However a decade later the company obstructed the owners from mining calamine. A plaque at Tintern Abbey claims that the well-known brassworks at this site began in 1568.
New brass works were built by a German immigrant in 1649 at Esher, probably using Swedish copper. After the passing of the Mines Royal Act in 1689, further works were built near Bristol, where brass production became a major industry in the 18th century. Later brass production sites in England included Cheadle and Birmingham.
Calamine brass was slowly phased out as zinc smelting techniques were developed in Europe, which produced metallic zinc more suitable for brass production than calamine. However, the conversion away from calamine brass manufacture was slow; a British patent was awarded to William Champion in 1738, but the alloying of metallic zinc and copper to produce brass was not patented until 1781 (by James Emerson), and calamine brass mills persisted in South Wales until as late as 1858. The slow diffusion of this technology was probably the result of economic factors. | 1 | Applied and Interdisciplinary Chemistry |
For reactions in aqueous solution, such as an acid dissociation reaction
:AH + HO A + HO
the concentration of water may be taken as being constant and the formation of the hydronium ion is implicit.
:AH A + H
Water concentration is omitted from expressions defining equilibrium constants, except when solutions are very concentrated.
: (K defined as a dissociation constant)
Similar considerations apply to metal ion hydrolysis reactions. | 0 | Theoretical and Fundamental Chemistry |
Cyclooxygenases are enzymes that take part in a complex biosynthetic cascade that results in the conversion of polyunsaturated fatty acids to prostaglandins and thromboxane(s).
Their main role is to catalyze the transformation of arachidonic acid into the intermediate prostaglandin H2, which is the precursor of a variety of prostanoids with diverse and potent biological actions.
Cyclooxygenases have two main isoforms that are called COX-1 and COX-2 (as well as a COX-3). COX-1 is responsible for the synthesis of prostaglandin and thromboxane in many types of cells, including the gastro-intestinal tract and blood platelets. COX-2 plays a major role in prostaglandin biosynthesis in inflammatory cells and in the central nervous system. Prostaglandin synthesis in these sites is a key factor in the development of inflammation and hyperalgesia.
COX-2 inhibitors have analgesic and anti-inflammatory activity by blocking the transformation of arachidonic acid into prostaglandin H2 selectively. | 1 | Applied and Interdisciplinary Chemistry |
Plants and yeasts have no known endogenous AMPylating enzymes, but animal genomes are endowed with a single copy of a gene encoding a Fic-domain AMPylase, that was likely acquired by an early ancestor of animals via horizontal gene transfer from a prokaryote. The human protein referred to commonly as FICD, had been previously identified as Huntingtin associated protein E (HypE; an assignment arising from a yeast two-hybrid screen, but of questionable relevance, as Huntingtin and HypE/FICD are localised to different cellular compartments). CG9523 Homologues in Drosophila melanogaster (CG9523) and C. elegans (Fic-1) have also received attention. In all animals FICD has a similar structure. It is a type II transmembrane domain protein, with a short cytoplasmic domain followed by membrane anchor that holds the protein in the endoplasmic reticulum (ER) and long C-terminal portion that resides in ER and encompasses tetratricopeptide repeats (TPRs) followed by a catalytic Fic domain. | 1 | Applied and Interdisciplinary Chemistry |
While such diagrams can be drawn for any chemical system, it is important to note that the addition of a metal binding agent (ligand) will often modify the diagram. For instance, carbonate () has a great effect upon the diagram for uranium. (See diagrams at right). The presence of trace amounts of certain species such as chloride ions can also greatly affect the stability of certain species by destroying passivating layers. | 0 | Theoretical and Fundamental Chemistry |
In a handful of cases, a woman with vaginal aplasia has received a successful vagina transplant donated by her mother. The first such case is believed to have occurred in 1970, with no signs of rejection taking place after three years. In at least one case, a woman who received such a transplant was able to conceive and give birth. In 1981, a 12-year-old girl with vaginal aplasia received a vaginal wall implant from her mother. She became sexually active seven years later, without incident. At age 24, she conceived and carried a child to term. The child was born via cesarean section. | 1 | Applied and Interdisciplinary Chemistry |
Just because a radioisotope lands on the surface of the soil, does not mean it will enter the human food chain. After release into the environment, radioactive materials can reach humans in a range of different routes, and the chemistry of the element usually dictates the most likely route. | 0 | Theoretical and Fundamental Chemistry |
The Clinical Pharmacogenetics Implementation Consortium (CPIC) is "an international consortium of individual volunteers and a small dedicated staff who are interested in facilitating use of pharmacogenetic tests for patient care. CPIC’s goal is to address barriers to clinical implementation of pharmacogenetic tests by creating, curating, and posting freely available, peer-reviewed, evidence-based, updatable, and detailed gene/drug clinical practice guidelines. CPIC guidelines follow standardized formats, include systematic grading of evidence and clinical recommendations, use standardized terminology, are peer-reviewed, and are published in a journal (in partnership with Clinical Pharmacology and Therapeutics) with simultaneous posting to cpicpgx.org, where they are regularly updated."
The CPIC guidelines are "designed to help clinicians understand HOW available genetic test results should be used to optimize drug therapy, rather than WHETHER tests should be ordered. A key assumption underlying the CPIC guidelines is that clinical high-throughput and pre-emptive (pre-prescription) genotyping will become more widespread, and that clinicians will be faced with having patients’ genotypes available even if they have not explicitly ordered a test with a specific drug in mind. CPIC's guidelines, processes and projects have been endorsed by several professional societies." | 1 | Applied and Interdisciplinary Chemistry |
In prokaryotes, the term corepressor is used to denote the activating ligand of a repressor protein. For example, the E. coli tryptophan repressor (TrpR) is only able to bind to DNA and repress transcription of the trp operon when its corepressor tryptophan is bound to it. TrpR in the absence of tryptophan is known as an aporepressor and is inactive in repressing gene transcription. Trp operon encodes enzymes responsible for the synthesis of tryptophan. Hence TrpR provides a negative feedback mechanism that regulates the biosynthesis of tryptophan.
In short tryptophan acts as a corepressor for its own biosynthesis. | 1 | Applied and Interdisciplinary Chemistry |
According to a research study conducted Hutton, M et al, a missense mutation occurring on the 5 region of the RNA associated with the tau protein was found to be correlated with inherited dementia (known as FTDP-17). The splice-site mutations all destabilize a potential stem–loop structure which is most likely involved in regulating the alternative splicing of exon10 in chromosome 17. Consequently, more usage occurs on the 5 splice site and an increased proportion of tau transcripts that include exon 10 are created. Such drastic increase in mRNA will increase the proportion of Tau containing four microtubule-binding repeats, which is consistent with the neuropathology described in several families with FTDP-17, a type inherited dementia. | 1 | Applied and Interdisciplinary Chemistry |
Criticism of cold fusion claims generally take one of two forms: either pointing out the theoretical implausibility that fusion reactions have occurred in electrolysis setups or criticizing the excess heat measurements as being spurious, erroneous, or due to poor methodology or controls. There are several reasons why known fusion reactions are an unlikely explanation for the excess heat and associated cold fusion claims. | 0 | Theoretical and Fundamental Chemistry |
Artificial nanoparticles can be created from any solid or liquid material, including metals, dielectrics, and semiconductors. They may be internally homogeneous or heterogenous, e.g. with a core–shell structure.
There are several methods for creating nanoparticles, including gas condensation, attrition, chemical precipitation, ion implantation, pyrolysis, hydrothermal synthesis, and biosynthesis. | 0 | Theoretical and Fundamental Chemistry |
Homofermentative bacteria convert glucose to two molecules of lactate and use this reaction to perform substrate-level phosphorylation to make two molecules of ATP:
:Glucose + 2 ADP + 2 P → 2 Lactate + 2 ATP | 1 | Applied and Interdisciplinary Chemistry |
In mathematics and solid state physics, the first Brillouin zone (named after Léon Brillouin) is a uniquely defined primitive cell in reciprocal space. In the same way the Bravais lattice is divided up into Wigner–Seitz cells in the real lattice, the reciprocal lattice is broken up into Brillouin zones. The boundaries of this cell are given by planes related to points on the reciprocal lattice. The importance of the Brillouin zone stems from the description of waves in a periodic medium given by Bloch's theorem, in which it is found that the solutions can be completely characterized by their behavior in a single Brillouin zone.
The first Brillouin zone is the locus of points in reciprocal space that are closer to the origin of the reciprocal lattice than they are to any other reciprocal lattice points (see the derivation of the Wigner–Seitz cell). Another definition is as the set of points in k-space that can be reached from the origin without crossing any Bragg plane. Equivalently, this is the Voronoi cell around the origin of the reciprocal lattice.
There are also second, third, etc., Brillouin zones, corresponding to a sequence of disjoint regions (all with the same volume) at increasing distances from the origin, but these are used less frequently. As a result, the first Brillouin zone is often called simply the Brillouin zone. In general, the n-th Brillouin zone consists of the set of points that can be reached from the origin by crossing exactly n − 1 distinct Bragg planes. A related concept is that of the irreducible Brillouin zone, which is the first Brillouin zone reduced by all of the symmetries in the point group of the lattice (point group of the crystal).
The concept of a Brillouin zone was developed by Léon Brillouin (1889–1969), a French physicist.
Within the Brillouin zone, a constant-energy surface represents the loci of all the -points (that is, all the electron momentum values) that have the same energy. Fermi surface is a special constant-energy surface that separates the unfilled orbitals from the filled ones at zero kelvin. | 0 | Theoretical and Fundamental Chemistry |
The facultative lagoon may be replaced by an aerated lagoon as the first pond of the series. Aerated lagoons have mechanical aerators which minimize anaerobic zones by completely mixing the lagoon to achieve catabolism through a process called extended aeration. | 1 | Applied and Interdisciplinary Chemistry |
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The spacer is an integral part of the FSL Kode construct and gives it several important characteristics including water dispersibility.
* Length – the spacer can be varied in length, for example 1.9 nm (Ad), 7.2 nm (CMG2), 11.5 nm (CMG4), allowing for enhanced presentation of Functional groups at the biosurface.
* Optimizes F presentation – The presentation of the bioactive (functional group) on a spacer reduces steric hindrance and increases the bioactive surfaces exposed and available for interactions
* Rigidity – the spacer can be modified to be either flexible or rigid depending upon desired characteristics
* Substitutions (represented by the leaves on the stalk) – the spacer can be modified both in charge, and polarity.
* Branches – usually the spacer is linear, but it can also be branched including specific spacing of the branches to optimize presentation and interaction of the F group.
* Inert – important to the design of FSL Kode constructs is the biologically inert nature of the spacer. Importantly this feature means the S-L components of the constructs are unreactive with undiluted serum. Consequently, the constructs are compatible in vivo use, and can improve diagnostic assay sensitivity by allowing for the use of undiluted serum. | 1 | Applied and Interdisciplinary Chemistry |
In the recent past the problem of removing the deleterious iron particles from a process stream had a few alternatives. Magnetic separation was typically limited and moderately effective. Magnetic separators that used permanent magnets could generate fields of low intensity only. These worked well in removing ferrous tramp but not fine paramagnetic particles. Thus high-intensity magnetic separators that were effective in collecting paramagnetic particles came into existence. These focus on the separation of very fine particles that are paramagnetic.
The current is passed through the coil, which creates a magnetic field, which magnetizes the expanded steel matrix ring. The paramagnetic matrix material behaves like a magnet in the magnetic field and thereby attracts the fines. The ring is rinsed when it is in the magnetic field and all the non-magnetic particles are carried with the rinse water. Next as the ring leaves the magnetic zone the ring is flushed and a vacuum of about – 0.3 bars is applied to remove the magnetic particles attached to the matrix ring. | 0 | Theoretical and Fundamental Chemistry |
Erich Clar (23 August 1902 – 27 March 1987) was an Austrian organic chemist, born in Hřensko, who studied polycyclic aromatic hydrocarbon chemistry. He is considered as the father of that field. In 1941, he authored "Aromatische Kohlenwasserstoffe" (Springer-Verlag) and in 1964 the greatly expanded two-volume Polycyclic Hydrocarbons, which described the syntheses, properties, and UV-visible absorption spectra of hundreds of PAHs. He discovered the Clar reaction of the cyclic ketone perinaphthenone to form dibenzo[cd,lm]perylene in a 400 C melt of zinc dust, zinc (II) chloride, and sodium chloride. He created the Sextet Theory, now eponymously called Clars rule, to describe the behavior of polycyclic aromatic hydrocarbon isomers. This was described in his book The Aromatic Sextet'. He was awarded the August Kekulé Medal by the Chemical Society of the GDR in 1965, the highest award given by that society to foreign scientists, and the first Polycyclic Aromatic Hydrocarbon Research Award of the International Symposium on Polynuclear Aromatic Hydrocarbons in 1987. He died aged 84 in 1987 at Estepona. | 0 | Theoretical and Fundamental Chemistry |
The LAL test is a major source of animal product dependence in the biomedical industry, and a challenge to the Three Rs of science in relation to the use of animals in testing. With reports of higher-than anticipated mortality rates it has been considered more ethical to devise alternatives to the test. Since 2003, a recombinant protein substitute for use in the LAL test has been commercially available. Named the recombinant factor C (rFC) assay, it is based on the same Limulus clotting factor C protein, but produced by genetically modified insect cells (the specific factor C sequence used does not necessarily come from the Atlantic horseshoe crab).
Instead of emulating the whole clotting pathway, rFC tests let factor C cleave a synthetic fluorogenic substrate, so that the sample lights up when endotoxin activates the factor. Since it does not contain factor G, (1,3)-β-D-glucan will not cause false-positives. As of 2018, available evidence shows that the rFC test is no worse than the LAL test.
The adoption of the rFC test was slow, which began to change in 2012 when the US FDA and the European health ministry acknowledged it as an accepted alternative. Its lack of mention in Pharmacopeias remained an issue, as there was no good standard for running the test in production. In 2016, it was added to the European Pharmacopoeia. A patent on rFC also limited adoption until its expiration in 2018.
On 1 June 2020, the United States Pharmacopeia (USP) decided to cancel the proposal to include recombinant technology for endotoxin testing in chapter 85, Bacterial Endotoxins, and start the development of a separate chapter that expands on the use, validation, and comparability of endotoxin tests based on recombinantly derived reagents. A separate guidance-only chapter 1085.1 was proposed by the USP, though comments and feedback published on 11 December 2020 show that pharmaceutical companies and the FDA do not support this chapter, and request for compendial status. | 0 | Theoretical and Fundamental Chemistry |
Huizenga married Dorothy Koeze in 1946. They had two sons and two daughters. One son, Dr. Robert Huizenga, is a prominent physician whose career has included a stint as team physician for the Los Angeles Raiders American football team.
Following his retirement from Rochester, Huizenga and his wife moved to North Carolina, where he continued to serve on advisory committees at major accelerator laboratories, worked to debunk cold fusion, and wrote his memoirs. Dolly Huizenga died in 1999. John Huizenga died of heart failure in San Diego, California, in January 2014, aged 92. | 0 | Theoretical and Fundamental Chemistry |
An alternative to the ensemble-based method described above is the voltage-clamp experiment. In a voltage-clamp experiment, two compartments of electrolyte are divided by an aperture, usually between 5-250 micrometres in diameter. A lipid bilayer is painted across this aperture, thus electrically separating the compartments; the molecular nature can be ascertained by measuring its capacitance.
Upon the addition of an (ideal) ion channel, a defined path between the two compartments is formed. Through this pore, ions flow down the potential and electrochemical gradient rapidly (>10/second), the maximum flux limited by the geometry and dimensions of the pore. At some later instant the pore may close or collapse, whereupon the current returns to zero. This open-state current, originating and amplified from a single-molecule event, is typically on the order of pA to nA, with time-resolution of approx. millisecond. Ideal or close-to-ideal events is termed "square-tops" in the literature, and have been considered as signature for a channel-based mechanism.
It is notable that the events observed at this scale are truly stochastic - that is, they are the result of random molecular collision and conformation changes. As the membrane area is much larger than that of a pore, multiple copies may open and close independently of one another, giving rise to the staircase like appearance (Panel C in figure); these ideal events are often modelled as Markov processes.
By using the activity grid notation, synthetic ion channels studied with the voltage-clamp method during the period 1982-2010 have been critically reviewed. While the ideal traces are most frequently analyzed and reported in the literature, many records are decidedly non-ideal, with a subset was shown to be fractal. Developing methods for analyzing these non-ideal traces and clarifying their relationship to transport mechanism is an area of contemporary research. | 0 | Theoretical and Fundamental Chemistry |
Smiths contributions to engineering education encompass work in cooperative learning and knowledge engineering applications. He published a paper in the Journal of Engineering Education', in 1981, introducing cooperative learning in engineering literature. During the early 1980s, he conducted some of the first randomized design empirical studies on cooperative learning in engineering classes. Subsequently, in the late 1980s, he transitioned from engineering research to education research, particularly focusing on cooperative learning and structured controversy, as his emphasis shifted towards teaching and research on project and knowledge management. This research addressed the critical needs of enhancing student learning, deepening understanding, and fostering collaborative skills. Beyond cooperative learning, his work included structured academic controversy, aimed at facilitating comprehensive understanding of complex issues through argument development and cooperative learning strategies.
Smith published books on this topic, including Active Learning: Cooperation in the College Classroom with David W. Johnson and Roger T. Johnson, providing strategies for college faculty to implement cooperative learning. They also co-authored Cooperative learning: Increasing College Faculty Instructional Productivity, in which they delved into the basics of cooperative learning, and he discussed how cooperative learning changed college teaching in New Paradigms for College Teaching that he co-edited with William E. Campbell. Later, in 2000, he wrote Teamwork and Project Management, where he emphasized key skills for engineering success, including teamwork, problem-solving, and project management. | 1 | Applied and Interdisciplinary Chemistry |
Amine-borane dehydrogenation can be coupled with hydride transfer to unsaturated functional groups, usually olefins in an anti-Markovnikov fashion. Hydroboration of the olefin and release of H from the amine-borane occur in parallel reactions, reducing the percent of olefin reduced. | 0 | Theoretical and Fundamental Chemistry |
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HMB is synthesized in the human body through the metabolism of leucine|, a branched-chain amino acid.
The vast majority of metabolism is initially catalyzed by the branched-chain amino acid aminotransferase enzyme, producing (α-KIC). α-KIC is mostly metabolized by the mitochondrial enzyme branched-chain dehydrogenase, which converts it to isovaleryl-CoA. Isovaleryl-CoA is subsequently metabolized by isovaleryl-CoA dehydrogenase and converted to , which is used in the synthesis of acetyl-CoA and other compounds. During biotin deficiency, HMB can be synthesized from via enoyl-CoA hydratase and an unknown thioesterase enzyme, which convert into and into HMB respectively. A relatively small amount of α-KIC is metabolized in the liver by the cytosolic enzyme 4-hydroxyphenylpyruvate dioxygenase (KIC dioxygenase), which converts α-KIC to HMB. In healthy individuals, this minor pathway – which involves the conversion of to α-KIC and then HMB – is the predominant route of HMB synthesis. | 1 | Applied and Interdisciplinary Chemistry |
An emerging stream restoration technique is the installation of engineered log jams. Because of channelization and removal of beaver dams and woody debris, many streams lack the hydraulic complexity that is necessary to maintain bank stabilization and healthy aquatic habitats. Reintroduction of large woody debris into streams is a method that is being experimented in streams such as Lagunitas Creek in Marin County, California and Thornton Creek, in Seattle, Washington. Log jams add diversity to the water flow by creating riffles, pools, and temperature variations. Large wood pieces, both living and dead, play an important role in the long-term stability of engineered log jams. However, individual pieces of wood in log jams are rarely stable over long periods and are naturally transported downstream, where they can get trapped in further log jams, other stream features or human infrastructures, which can generate nuisances for human use. | 1 | Applied and Interdisciplinary Chemistry |
Perhaps the most prevalent carbamate is the one involved in the capture of CO by plants. This process is necessary for their growth. The enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) fixes a molecule of carbon dioxide as phosphoglycerate in the Calvin cycle. At the active site of the enzyme, a Mg ion is bound to glutamate and aspartate residues as well as a lysine carbamate. The carbamate is formed when an uncharged lysine side chain near the ion reacts with a carbon dioxide molecule from the air (not the substrate carbon dioxide molecule), which then renders it charged, and, therefore, able to bind the Mg ion. | 0 | Theoretical and Fundamental Chemistry |
If is height of the orifice above the ground and is height of the liquid column from the ground (height of liquid's surface), then the horizontal distance covered by the jet of liquid to reach the same level as the base of the liquid column can be easily derived. Since be the vertical height traveled by a particle of jet stream, we have from the laws of falling body
where is the time taken by the jet particle to fall from the orifice to the ground. If the horizontal efflux velocity is , then the horizontal distance traveled by the jet particle during the time duration is
Since the water level is above the orifice, the horizontal efflux velocity as given by Torricelli's law. Thus, we have from the two equations
The location of the orifice that yields the maximum horizontal range is obtained by differentiating the above equation for with respect to , and solving . Here we have
Solving we obtain
and the maximum range | 1 | Applied and Interdisciplinary Chemistry |
PSDs can be measured microscopically by sizing against a graticule and counting, but for a statistically valid analysis, millions of particles must be measured. This is impossibly arduous when done manually, but automated analysis of electron micrographs is now commercially available. It is used to determine the particle size within the range of 0.2 to 100 micrometers. | 0 | Theoretical and Fundamental Chemistry |
Polishing refers to treatments made in further advanced treatment steps after the above methods (also called "fourth stage" treatment). These treatments may also be used independently for some industrial wastewater. Chemical reduction or pH adjustment minimizes chemical reactivity of wastewater following chemical oxidation. Carbon filtering removes remaining contaminants and impurities by chemical absorption onto activated carbon. Filtration through sand (calcium carbonate) or fabric filters is the most common method used in municipal wastewater treatment. | 1 | Applied and Interdisciplinary Chemistry |
It has already been mentioned that in HR-CS AAS lamp flicker noise is eliminated using correction pixels. In fact, any increase or decrease in radiation intensity that is observed to the same extent at all pixels chosen for correction is eliminated by the correction algorithm. This obviously also includes a reduction of the measured intensity due to radiation scattering or molecular absorption, which is corrected in the same way. As measurement of total and background absorption, and correction for the latter, are strictly simultaneous (in contrast to LS AAS), even the fastest changes of background absorption, as they may be observed in ET AAS, do not cause any problem. In addition, as the same algorithm is used for background correction and elimination of lamp noise, the background corrected signals show a much better signal-to-noise ratio compared to the uncorrected signals, which is also in contrast to LS AAS. | 0 | Theoretical and Fundamental Chemistry |
Calcineurin inhibitors are prescribed for adult rheumatoid arthritis (RA) as a single drug or in combination with methotrexate. The microemulsion formulation is approved by the U.S. Food and Drug Administration for treatment of severely active RA. It is also prescribed for: psoriatic arthritis, psoriasis, acute ocular Behçets disease, juvenile idiopathic arthritis, adult and juvenile polymyositis and dermatomyositis, adult and juvenile systemic lupus erythematosus, adult lupus membranous nephritis, systemic sclerosis, aplastic anemia, steroid-resistant nephrotic syndrome, atopic dermatitis, severe corticosteroid-dependent asthma, severe ulcerative colitis, pemphigus vulgaris, myasthenia gravis, and dry eye disease, with or without Sjögrens syndrome (administered as ophthalmic emulsion). | 1 | Applied and Interdisciplinary Chemistry |
Hydrogen damage is caused by hydrogen atoms (as opposed to hydrogen molecules in the gaseous state), interacting with metal. | 1 | Applied and Interdisciplinary Chemistry |
Knowles was awarded a Fellowship of the Institute of Materials, Minerals and Mining (FIMMM) in 2004 in recognition of his contributions to the field of materials science. In 2015, he was also made Fellow of the Royal Academy of Engineering (FREng). He holds two European patents and has authored over 100 academic papers - five of which have been cited over 100 times - and he has also given a number of invited lectures and conference keynotes | 1 | Applied and Interdisciplinary Chemistry |
As explained by Gibbs and appreciated by Maxwell, the advantage of a U-V-S (energy-volume-entropy) surface over the usual P-V-T (pressure-volume-temperature) surface was that it allowed to geometrically explain sharp, discontinuous phase transitions as emerging from a purely continuous and smooth state function ; Maxwell's surface demonstrated the generic behaviour for a substance that can exist in solid, liquid, and gaseous phases. The basic geometrical operation involved simply placing a tangent plane (such as a flat sheet of glass) on the surface and rolling it around, observing where it touches the surface. Using this operation, it was possible to explain phase coexistence, the triple point, to identify the boundary between absolutely stable and metastable phases (e.g., superheating and supercooling), the spinodal boundary between metastable and unstable phases, and to illustrate the critical point.
Maxwell drew lines of equal pressure (isopiestics) and of equal temperature (isothermals) on his plaster cast by placing it in the sunlight, and "tracing the curve when the rays just grazed the surface." He sent sketches of these lines to a number of colleagues. For example, his letter to Thomas Andrews of 15 July 1875 included sketches of these lines. Maxwell provided a more detailed explanation and a clearer drawing of the lines (pictured) in the revised version of his book Theory of Heat, and a version of this drawing appeared on a 2005 US postage stamp in honour of Gibbs.
As well as being on display in two countries, Maxwells model lives on in the literature of thermodynamics, and books on the subject often mention it, though not always with complete historical accuracy. For example, the thermodynamic surface represented by the sculpture is often reported to be that of water, contrary to Maxwells own statement. | 0 | Theoretical and Fundamental Chemistry |
The most common types of π-interactions involve:
*Metal–π interactions: involves interaction of a metal and the face of a π system, the metal can be a cation (known as cation–π interactions) or neutral
*Polar–π interactions: involves interaction of a polar molecule and quadrupole moment a π system.
*Aromatic–aromatic interactions (π stacking): involves interactions of aromatic molecules with each other.
**Arene–perfluoroarene interaction: electron-rich benzene ring interacts with electron-poor hexafluorobenzene.
*π donor–acceptor interactions: interaction between low energy empty orbital (acceptor) and a high-energy filled orbital (donor).
*Anion–π interactions: interaction of anion with π system
*Cation–π interactions: interaction of a cation with a π system
*C–H–π interactions: interaction of C-H with π system: These interactions are well studied using experimental as well as computational techniques. | 0 | Theoretical and Fundamental Chemistry |
The kinetic process of destabilisation can be rather long (up to several months or years for some products). Thus, it is often required for the formulator to use further accelerating methods to reach reasonable development time for new product design. Thermal methods are the most commonly used and consist of increasing temperature to accelerate destabilisation (below critical temperatures of phase inversion or chemical degradation). Temperature affects not only viscosity, but also interfacial tension in the case of non-ionic surfactants or more generally interactions forces inside the system. Storing a dispersion at high temperatures enables to simulate real life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times.
Mechanical acceleration including vibration, centrifugation and agitation are sometimes used. They subject the product to different forces that pushes the particles / droplets against one another, hence helping in the film drainage. Some emulsions would never coalesce in normal gravity, while they do under artificial gravity. Segregation of different populations of particles have been highlighted when using centrifugation and vibration. | 0 | Theoretical and Fundamental Chemistry |
Several pseudo-response regulators have been found in Selaginella, but their function has not yet been explored. | 1 | Applied and Interdisciplinary Chemistry |
Thermocouples of platinum/molybdenum-alloy (95%Pt/5%Mo–99.9%Pt/0.1%Mo, by weight) are sometimes used in nuclear reactors, since they show a low drift from nuclear transmutation induced by neutron irradiation, compared to the platinum/rhodium-alloy types. | 1 | Applied and Interdisciplinary Chemistry |
Like other β-lactam antibiotics, dicloxacillin acts by inhibiting the synthesis of bacterial cell walls. It inhibits cross-linkage between the linear peptidoglycan polymer chains that make up a major component of the cell wall of Gram-positive bacteria. | 0 | Theoretical and Fundamental Chemistry |
A yeast commonly used for protein production is Pichia pastoris. Examples of yeast expression vector in Pichia are the pPIC series of vectors, and these vectors use the AOX1 promoter which is inducible with methanol. The plasmids may contain elements for insertion of foreign DNA into the yeast genome and signal sequence for the secretion of expressed protein. Proteins with disulphide bonds and glycosylation can be efficiently produced in yeast. Another yeast used for protein production is Kluyveromyces lactis and the gene is expressed, driven by a variant of the strong lactase LAC4 promoter.
Saccharomyces cerevisiae is particularly widely used for gene expression studies in yeast, for example in yeast two-hybrid system for the study of protein-protein interaction. The vectors used in yeast two-hybrid system contain fusion partners for two cloned genes that allow the transcription of a reporter gene when there is interaction between the two proteins expressed from the cloned genes. | 1 | Applied and Interdisciplinary Chemistry |
The ACB is responsible for determining the specific content for courses related to certification as a clinical biochemist in the UK. Normally this is a three or four year academic sequence followed by qualification examinations. Because of the competitive admission criteria, many applicants have advanced degrees before beginning the biochemistry program.
Papers published by ACB members are related to the use of laboratories by doctors and patient health diagnostic testing in the UK.
* Blood draw procedures and tests by junior doctors and nurses in the A&E department of a Birmingham hospital were frequently performed with the wrong collection equipment or were mishandled afterward. The College of Emergency Medicine said the issue identified by the audit at Birmingham is "universally relevant".
* A 2008 study emphasized issues with junior doctors who were not being trained in pathology and laboratory testing. Eighteen percent of junior doctors in the sample were not confident they could interpret the results of tests they ordered for patients. More than 70% felt a need for more training in clinical biochemistry.
The ACB was part of a 2008 effort by a consortium to support a Scottish government initiative aimed at emphasizing the need for quality laboratory services to the practice of medicine. | 1 | Applied and Interdisciplinary Chemistry |
According to IUPAC convention, by precedence (stylized electronegativity), hydrogen falls between group 15 and group 16 elements. Therefore, we have NH, "nitrogen hydride" (ammonia), versus HO, "hydrogen oxide" (water). This convention is sometimes broken for polonium, which on the grounds of polonium's metallicity is often referred to as "polonium hydride" instead of the expected "hydrogen polonide". | 0 | Theoretical and Fundamental Chemistry |
Activation of the ERK1/2 pathway by aberrant RAS/RAF signalling, DNA damage, and oxidative stress leads to cellular senescence. Low doses of DNA damage resulting from cancer therapy cause ERK1/2 to induce senescence, whereas higher doses of DNA damage fail to activate ERK1/2, and thus induce cell death by apoptosis. | 1 | Applied and Interdisciplinary Chemistry |
In molecular biology and genetics, transcriptional regulation is the means by which a cell regulates the conversion of DNA to RNA (transcription), thereby orchestrating gene activity. A single gene can be regulated in a range of ways, from altering the number of copies of RNA that are transcribed, to the temporal control of when the gene is transcribed. This control allows the cell or organism to respond to a variety of intra- and extracellular signals and thus mount a response. Some examples of this include producing the mRNA that encode enzymes to adapt to a change in a food source, producing the gene products involved in cell cycle specific activities, and producing the gene products responsible for cellular differentiation in multicellular eukaryotes, as studied in evolutionary developmental biology.
The regulation of transcription is a vital process in all living organisms. It is orchestrated by transcription factors and other proteins working in concert to finely tune the amount of RNA being produced through a variety of mechanisms. Bacteria and eukaryotes have very different strategies of accomplishing control over transcription, but some important features remain conserved between the two. Most importantly is the idea of combinatorial control, which is that any given gene is likely controlled by a specific combination of factors to control transcription. In a hypothetical example, the factors A and B might regulate a distinct set of genes from the combination of factors A and C. This combinatorial nature extends to complexes of far more than two proteins, and allows a very small subset (less than 10%) of the genome to control the transcriptional program of the entire cell. | 1 | Applied and Interdisciplinary Chemistry |
Single-molecule real-time sequencing (SMRT) is used in the epigenomic and epitranscriptomic fields. As regards epigenomics, thousands of zero-mode waveguides (ZMWs) are used to capture the DNA polymerase: when a modified base is present, the biophysical dynamics of its movement changes, creating a unique kinetic signature before, during, and after the base incorporation.
SMRT sequencing can be used to detect modified bases in RNA, including m6A sites. In this case, a reverse transcriptase is used as enzyme with ZMWs to observe the cDNA synthesis in real time. The incorporation of synthetically designed m6A sites leaves a kinetic signature and increases the interpulse duration (IPD).
There are some issues concerning the reading of homonucleotide stretches and the base resolution of m6A therein, due to the stuttering of reverse transcriptase. Secondly, the throughput is too low for transcriptome-wide approaches.
One of the most commonly used platform is the SMRT sequencing technology by Pacific Biosciences. | 1 | Applied and Interdisciplinary Chemistry |
The operator prepares a series of standards across a range of concentrations near the expected concentration of analyte in the unknown. The concentrations of the standards must lie within the working range of the technique (instrumentation) they are using. Analyzing each of these standards using the chosen technique will produce a series of measurements. For most analyses a plot of instrument response vs. concentration will show a linear relationship. The operator can measure the response of the unknown and, using the calibration curve, can interpolate to find the concentration of analyte.
The data - the concentrations of the analyte and the instrument response for each standard - can be fit to a straight line, using linear regression analysis. This yields a model described by the equation y = mx + y, where y is the instrument response, m represents the sensitivity, and y is a constant that describes the background. The analyte concentration (x) of unknown samples may be calculated from this equation.
Many different variables can be used as the analytical signal. For instance, chromium (III) might be measured using a chemiluminescence method, in an instrument that contains a photomultiplier tube (PMT) as the detector. The detector converts the light produced by the sample into a voltage, which increases with intensity of light. The amount of light measured is the analytical signal. | 1 | Applied and Interdisciplinary Chemistry |
A Woods lamp may be used to rapidly assess whether an individual is suffering from ethylene glycol poisoning as a consequence of antifreeze ingestion. Manufacturers of ethylene glycol-containing antifreezes commonly add fluorescein, which causes the patients urine to fluoresce under Wood's lamp. | 0 | Theoretical and Fundamental Chemistry |
He married Ethel Marian Wood in 1901. She died in 1944. They had a daughter, who predeceased her father, and a son. He died at his son's home in Headley, Surrey. | 0 | Theoretical and Fundamental Chemistry |
DEAD is an efficient component in Diels-Alder reactions and in click chemistry, for example the synthesis of bicyclo[2.1.0]pentane, which originates from Otto Diels. It has also been used to generate aza-Baylis-Hillman adducts with acrylates.
DEAD can be used for synthesis of heterocyclic compounds. Thus, pyrazoline derivatives convert by condensation to α,β-unsaturated ketones:
Another application is the use of DEAD as an enophile in ene reactions: | 0 | Theoretical and Fundamental Chemistry |
One common criticism of the hyperconjugation theory is that it fails to explain why the anomeric effect is not observed when substituted tetrahydropyran molecules are placed in polar solvents, and the equatorial position is once again preferred. It has been shown, however, that hyperconjugation does depend on the solvent in the system. Each of the substituted systems described above were tested in the gas phase (i.e. with no solvent) and in aqueous solution (i.e. polar solvent). When X=F, the anomeric effect was observed in both media, and the axial position was always preferred. This is attributed to hyperconjugation. When X=OH or CN, the anomeric effect was seen in the gas phase, when the axial position was preferred. However, in aqueous solutions, both substituents preferred the equatorial position. This is attributed to the fact that there are more electrostatic repulsions with the axial positioned substituent and the polar solvent, causing the equatorial position to be preferred. When X=NH, again, no anomeric effect was observed and the equatorial position was always preferred. | 0 | Theoretical and Fundamental Chemistry |
In photolithography, HMDS is often used as an adhesion promoter for photoresists. Best results are obtained by applying HMDS from the gas phase on heated substrates.
In electron microscopy, HMDS can be used as an alternative to critical point drying during sample preparation.
In pyrolysis-gas chromatography-mass spectrometry, HMDS is added to the analyte to create silylated diagnostic products during pyrolysis, in order to enhance detectability of compounds with polar functional groups.
In plasma-enhanced chemical vapor deposition (PECVD), HMDS is used as a molecular precursor as a replacement to highly flammable and corrosive gasses like SiH, CH, NH as it can be easily handled. HMDS is used in conjunction with a plasma of various gases such as argon, helium and nitrogen to deposit SiCN thin films/coatings with excellent mechanical, optical and electronic properties. | 0 | Theoretical and Fundamental Chemistry |
A diet with insufficient vitamin D in conjunction with inadequate sun exposure causes vitamin D deficiency, which is defined as a blood 25(OH)D level below 12ng/mL (30nmol/liter), whereas vitamin D insufficiency is a blood 25(OH)D level of 12–20ng/mL (30–50nmol/liter). An estimated one billion adults worldwide are either vitamin D insufficient or deficient, including in developed countries in Europe. Severe vitamin D deficiency in children, a rare disease in the developed world, causes a softening and weakening of growing bones, and a condition called rickets.
Vitamin D deficiency is found worldwide in the elderly and remains common in children and adults. Deficiency results in impaired bone mineralization and bone damage which leads to bone-softening diseases, including rickets in children and osteomalacia in adults. Low blood calcifediol (25-hydroxy-vitamin D) can result from avoiding the sun. Being deficient in Vitamin D can cause the absorption of dietary calcium to fall from the normal fraction (between 60 and 80 percent) to as little as 15 percent.
Dark-skinned people living in temperate climates have been shown to have low vitamin D levels. Dark-skinned people are less efficient at making vitamin D because melanin in the skin hinders vitamin D synthesis. Vitamin D deficiency is common in Hispanic and African-Americans in the United States, with levels dropping significantly in the winter. This is due to the levels of melanin in the skin, as it acts as a natural protectant from sun exposure. | 1 | Applied and Interdisciplinary Chemistry |
In generic terms, electrochemical potential is the mechanical work done in bringing 1 mole of an ion from a standard state to a specified concentration and electrical potential. According to the IUPAC definition, it is the partial molar Gibbs energy of the substance at the specified electric potential, where the substance is in a specified phase. Electrochemical potential can be expressed as
where:
* is the electrochemical potential of species i, in J/mol,
* μ is the chemical potential of the species i, in J/mol,
* z is the valency (charge) of the ion i, a dimensionless integer,
* F is the Faraday constant, in C/mol,
* Φ is the local electrostatic potential, in V.
In the special case of an uncharged atom, z = 0, and so = μ.
Electrochemical potential is important in biological processes that involve molecular diffusion across membranes, in electroanalytical chemistry, and industrial applications such as batteries and fuel cells. It represents one of the many interchangeable forms of potential energy through which energy may be conserved.
In cell membranes, the electrochemical potential is the sum of the chemical potential and the membrane potential. | 0 | Theoretical and Fundamental Chemistry |
Homolytic bond cleavage is a process where the electron pair comprising a bond is split, causing the bond to break. This is denoted by two single barbed curved arrows pointing away from the bond. The consequence of this process is the retention of a single unpaired electron denoted by a dot on each of the atoms that were formerly joined by a bond. The single electron movement can be denoted by a curved arrow commonly referred to as a fish hook. These single electron species are known as free radicals. Heat or light are required to provide enough energy for this process to occur.
For example, Ultraviolet light causes the chlorine-chlorine bond to break homolytically. The pair of electrons become split, denoted by the two fish hook arrows between both atoms pointing to both chlorine atoms. After the reaction occurs, it leads to both chlorine molecules left with a single unpaired electron. This is the initiation stage of free radical halogenation. | 0 | Theoretical and Fundamental Chemistry |
In fluid dynamics the Milne-Thomson circle theorem or the circle theorem is a statement giving a new stream function for a fluid flow when a cylinder is placed into that flow. It was named after the English mathematician L. M. Milne-Thomson.
Let be the complex potential for a fluid flow, where all singularities of lie in . If a circle is placed into that flow, the complex potential for the new flow is given by
with same singularities as in and is a streamline. On the circle , , therefore | 1 | Applied and Interdisciplinary Chemistry |
Room-temperature ionic liquids (RTILs) are dominated by salts derived from 1-methylimidazole, i.e., 1-alkyl-3-methylimidazolium. Examples include 1-ethyl-3-methyl- (EMIM), 1-butyl-3-methyl- (BMIM), 1-octyl-3 methyl (OMIM), 1-decyl-3-methyl-(DMIM), 1-dodecyl-3-methyl- (dodecylMIM). Other imidazolium cations are 1-butyl-2,3-dimethylimidazolium (BMMIM or DBMIM) and 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium (DAMI). Other N-heterocyclic cations are derived from pyridine: 4-methyl-N-butyl-pyridinium (MBPy) and N-octylpyridinium (C8Py). Conventional quaternary ammonium cations also form ILs, e.g. tetraethylammonium (TEA) and tetrabutylammonium (TBA). | 0 | Theoretical and Fundamental Chemistry |
With the help of two biotechnologists, they encoded a basic computer program in Python Programming language into Nicotiana benthamiana.
They first encoded a “Hello World” computer program into a DNA code, synthesized it and cloned this coded DNA into a plasmid-vector to be used further for transformation into Nicotiana benthamiana plants. The encoded program was reconstructed from the resulting seedlings with 100% accuracy by showing “Hello World” on the computer screen.
Their approach demonstrated that artificially encoded data can be stored and multiplied within plants without affecting their vigor and fertility. It also takes a step forward from storing data into a naked DNA molecule.
It is inherent in progeny and authentically reproducible while the reduced metabolism of the seeds provides an additional protection for encoded DNA archives.
That was the first practical implication of utilizing a multi-cellular, eukaryotic organism for storing digital data in the world. It goes beyond plant genome manipulations for biotechnological research and plant breeding. It takes the advantage of multi-cellular organisms and serves to propagate the encoded information in daughter cells. The host organism is able to grow and multiply with the embedded information, and every cell of the organism contains a copy of the encoded information; therefore, it avoids the costs of synthetic production of multiple copies of the same encoded information. Moreover, in contrast to naked DNA, which can be affected by unfavorable environmental conditions like excessive temperature, in desiccation/re-hydration conditions, DNA stored in a seed is protected against alterations and degradation over time without the need of any active maintenance. Insertion of short computer programs into plants could also serve to provide a detailed description of a given variety, since the need for such labeling has already been expressed.
As for manipulating and storing archives, their approach leverages a new look at accessing, browsing and reading information. 1g of DNA could store exabytes of data and it is a huge, capacitive storage medium. DNA protected within a seed of a living plant could be easy to access when hand-held readers will become a reality. | 1 | Applied and Interdisciplinary Chemistry |
Toxic hotspots are locations where emissions from specific sources such as water or air pollution may expose local populations to elevated health risks, such as cancer. These emissions contribute to cumulative health risks of emissions from other sources nearby. Urban, highly populated areas around pollutant emitters such as old factories and waste storage sites are often toxic hotspots. | 1 | Applied and Interdisciplinary Chemistry |
Advanced photonic materials and structures, such as multilayer thin films, micro/nanoparticles, photonic crystals, metamaterials, metasurfaces, have been tested to significantly facilitate radiative cooling. However, while multilayer and complex nano-photonic structures have proven successful in experimental scenarios and simulations, widespread application "is severely restricted because of the complex and expensive processes of preparation," as per Cui et al. Similarly, Zhang et al. noted that "scalable production of artificial photonic radiators with complex structures, outstanding properties, high throughput, and low cost is still challenging." This has advanced research of simpler structures for PDRC materials that are more suited for mass production. | 0 | Theoretical and Fundamental Chemistry |
Drugs that inhibit PDE5, sildenafil, tadalafil and vardenafil, have been used as treatment for erectile dysfunction. These inhibitors increase the cGMP, smooth muscle relaxation and consequently cause penis erection during sexual stimulation. | 1 | Applied and Interdisciplinary Chemistry |
* Therapeutic T cell engineering: altering T cells to target cancer-related antigens for treatment
* Monoclonal antibody production: improving monoclonal antibody production using engineered cells
* In vivo cell factories: engineering cells to produce therapeutics within the patient's body
* Directed stem cell differentiation: using external factors to direct stem cell differentiation
* Antibody Drug Conjugates: engineering antibody and cytotoxic drug linkages for disease treatment | 1 | Applied and Interdisciplinary Chemistry |
Nanocomposite hydrogels or hybrid hydrogels, are highly hydrated polymeric networks, either physically or covalently crosslinked with each other and/or with nanoparticles or nanostructures. Nanocomposite hydrogels can mimic native tissue properties, structure and microenvironment due to their hydrated and interconnected porous structure. A wide range of nanoparticles, such as carbon-based, polymeric, ceramic, and metallic nanomaterials can be incorporated within the hydrogel structure to obtain nanocomposites with tailored functionality. Nanocomposite hydrogels can be engineered to possess superior physical, chemical, electrical, thermal, and biological properties. | 0 | Theoretical and Fundamental Chemistry |
The pressure coefficient can be estimated for irrotational and isentropic flow by introducing the potential and the perturbation potential , normalized by the free-stream velocity
Using Bernoulli's equation,
which can be rewritten as
where is the sound speed.
The pressure coefficient becomes
where is the far-field sound speed. | 1 | Applied and Interdisciplinary Chemistry |
The crosslinks which bond the polymers of a hydrogel fall under two general categories: physical hydrogels and chemical hydrogels. Chemical hydrogels have covalent cross-linking bonds, whereas physical hydrogels have non-covalent bonds. Chemical hydrogels can result in strong reversible or irreversible gels due to the covalent bonding. Chemical hydrogels that contain reversible covalent cross-linking bonds such as hydrogels of thiomers being cross-linked via disulfide bonds are non-toxic and are used in numerous medicinal products. Physical hydrogels usually have high biocompatibility, are not toxic, and are also easily reversible by simply changing an external stimulus such as pH, ion concentration (alginate) or temperature (gelatine); they are also used for medical applications. Physical crosslinks consist of hydrogen bonds, hydrophobic interactions, and chain entanglements (among others). A hydrogel generated through the use of physical crosslinks is sometimes called a reversible hydrogel. Chemical crosslinks consist of covalent bonds between polymer strands. Hydrogels generated in this manner are sometimes called permanent hydrogels.
Hydrogels are prepared using a variety of polymeric materials, which can be divided broadly into two categories according to their origin: natural or synthetic polymers. Natural polymers for hydrogel preparation include hyaluronic acid, chitosan, heparin, alginate, gelatin and fibrin. Common synthetic polymers include polyvinyl alcohol, polyethylene glycol, sodium polyacrylate, acrylate polymers and copolymers thereof. Whereas natural hydrogels are usually non-toxic, and often provides other advantages for medical use, such as biocompatibility, biodegradability, antibiotic/antifungal effect and improve regeneration of nearby tissue, their stability and strength is usually much lower than synthetic hydrogels. There are also synthetic hydrogels than can be used for medical applications, such as polyethylene glycol (PEG), polyacrylate, and polyvinylpyrrolidone (PVP). | 0 | Theoretical and Fundamental Chemistry |
Red edge refers to the region of rapid change in reflectance of vegetation in the near infrared range of the electromagnetic spectrum. Chlorophyll contained in vegetation absorbs most of the light in the visible part of the spectrum but becomes almost transparent at wavelengths greater than 700 nm. The cellular structure of the vegetation then causes this infrared light to be reflected because each cell acts something like an elementary corner reflector. The change can be from 5% to 50% reflectance going from 680 nm to 730 nm. This is an advantage to plants in avoiding overheating during photosynthesis. For a more detailed explanation and a graph of the photosynthetically active radiation (PAR) spectral region, see .
The phenomenon accounts for the brightness of foliage in infrared photography and is extensively utilized in the form of so-called vegetation indices (e.g. Normalized difference vegetation index). It is used in remote sensing to monitor plant activity, and it has been suggested that it could be useful to detect light-harvesting organisms on distant planets. | 0 | Theoretical and Fundamental Chemistry |
Stress corrosion cracking is a phenomenon where a synergistic action of corrosion and tensile stress leads to brittle fracture of normally ductile materials at generally lower stress levels. During stress corrosion cracking, the material is relatively unattacked by the corrosive agent (no general corrosion, only localized corrosion), but fine cracks form within it. This process has serious implications on the utilisation of the material because the applicable safe stress levels are drastically reduced in the corrosive medium. Season cracking and caustic embrittlement are two stress corrosion cracking processes which affected the serviceability of brass cartridge cases and riveted steel boilers respectively. | 1 | Applied and Interdisciplinary Chemistry |
RA regulates gene transcription by binding to nuclear receptors known as retinoic acid receptors (RARs; RARα, RARβ, RARγ) which are bound to DNA as heterodimers with retinoid "X" receptors (RXRs; RXRα, RXRβ, RXRγ). RARs and RXRs must dimerize before they can bind to the DNA. Expression of more than 500 genes is responsive to retinoic acid. The process is that RAR-RXR heterodimers recognize retinoic acid response elements on DNA. The receptors undergo a conformational change that causes co-repressors to dissociate from the receptors. Coactivators can then bind to the receptor complex, which may help to loosen the chromatin structure from the histones or may interact with the transcriptional machinery. This response upregulates or downregulates the expression of target genes, including the genes that encode for the receptors themselves. To prevent excess accumulation of RA it must be metabolized and eliminated. Three cytochromes (Cyp26A1, Cyp26B1 Cyp26C1) catalyze the oxidation of RA. The genes for these proteins are induced by high concentrations of RA, thus providing a regulatory feedback mechanism. | 1 | Applied and Interdisciplinary Chemistry |
In a highly basic solution, phenolphthalein's slow change from pink to colorless as it is converted to its Ph(OH) form is used in chemistry classes for the study of reaction kinetics. | 0 | Theoretical and Fundamental Chemistry |
Institute of Geochemistry (), which is located in Guiyang, the capital of Guizhou Province of China, was founded in 1966 by the Beijing Institute of Geology, Chinese Academy of Sciences (now Institute of Geology and Geophysics, Chinese Academy of Sciences). | 0 | Theoretical and Fundamental Chemistry |
In mathematics and physics, surface growth refers to models used in the dynamical study of the growth of a surface, usually by means of a stochastic differential equation of a field. | 0 | Theoretical and Fundamental Chemistry |
Fluoroantimonic acid is the strongest superacid based on the measured value of its Hammett acidity function (H), which has been determined for various ratios of HF:SbF. The H of HF is −15. A solution of HF containing 1 mol % of SbF is −20. The H is −21 for 10 mol%. For > 50 mol % SbF, the H is between −21 and −23. The lowest attained H is about -28. The following H values show that fluoroantimonic acid is stronger than other superacids. Increased acidity is indicated by smaller (in this case, more negative) values of H.
* Fluoroantimonic acid (−23 > H > −28)
* Magic acid (H = −23)
* Carborane acid (H < −18)
* Fluorosulfuric acid (H = −15)
* Triflic acid (H = −15)
* Perchloric acid (H = −13)
Of the above, only the carborane acids, whose H could not be directly determined due to their high melting points, may be stronger acids than fluoroantimonic acid.
The H value measures the protonating ability of the bulk, liquid acid, and this value has been directly determined or estimated for various compositions of the mixture. The pK on the other hand, measures the equilibrium of proton dissociation of a discrete chemical species when dissolved in a particular solvent. Since fluoroantimonic acid is not a single chemical species, its pK value is not well-defined.
The gas-phase acidity (GPA) of individual species present in the mixture have been calculated using density functional theory methods. (Solution-phase pKs of these species can, in principle, be estimated by taking into account solvation energies, but do not appear to be reported in the literature as of 2019.) For example, the ion-pair [HF]· was estimated to have a GPA of 254 kcal/mol. For comparison, the commonly encountered superacid triflic acid, TfOH, is a substantially weaker acid by this measure, with a GPA of 299 kcal/mol. However, certain carborane superacids have GPAs lower than that of [HF]·. For example, H(CHBCl) has an experimentally determined GPA of 241 kcal/mol. | 0 | Theoretical and Fundamental Chemistry |
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