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G protein can refer to two distinct families of proteins. Heterotrimeric G proteins, sometimes referred to as the "large" G proteins, are activated by G protein-coupled receptors and are made up of alpha (α), beta (β), and gamma (γ) subunits. "Small" G proteins (20-25kDa) belong to the Ras superfamily of small GTPases. These proteins are homologous to the alpha (α) subunit found in heterotrimers, but are in fact monomeric, consisting of only a single unit. However, like their larger relatives, they also bind GTP and GDP and are involved in signal transduction. | 1 | Applied and Interdisciplinary Chemistry |
Metal complexes are known to catalyze alkyne trimerization to give arenes. These reactions have been used to prepare arene complexes. Illustrative is the reaction of [Co(mesitylene)] with 2-butyne to give [Co(CMe)]. | 0 | Theoretical and Fundamental Chemistry |
The Water Sanitation and Hygiene Institute of India has developed a truck based mobile treatment unit that is able to treat fecal sludge on site. The MTUs were evaluated in a technical paper authored by Aaron Forbis-Stokes. The system was evaluated for operational and treatment performance while processing septage in the field at 108 sites in Tamil Nadu, India. This option is preferable as it does not require transport of the septage and avoids the common practice of illegal disposal of untreated septage into the environment. Six mobile septage treatment units have been built to date using readily available filters and membranes (mesh fabric, sand, granular activated carbon (GAC), microfilter, ultrafilter) and installed on the bed of a small truck. The target application is emptying of septic or sewage holding tanks and concentration of suspended solids while generating a liquid that could be safely discharged. With support from a USAID grant, the WASH Institute is working to scale the MTU solution as the preferred option over traditional vacuum trucks that discharge wastes into the environment. | 1 | Applied and Interdisciplinary Chemistry |
Soluble uranium salts are toxic, though less so than those of other heavy metals such as lead or mercury. The organ which is most affected is the kidney. Soluble uranium salts are readily excreted in the urine, although some accumulation in the kidneys does occur in the case of chronic exposure. The World Health Organization has established a daily "tolerated intake" of soluble uranium salts for the general public of 0.5 μg/kg body weight (or 35 μg for a 70 kg adult): exposure at this level is not thought to lead to any significant kidney damage.
Tiron may be used to remove uranium from the human body, in a form of chelation therapy. Bicarbonate may also be used as uranium (VI) forms complexes with the carbonate ion. | 0 | Theoretical and Fundamental Chemistry |
In the past, heterogeneous gold catalysts have found preliminary commercial applications for the industrial production of vinyl chloride (precursor to polyvinyl chloride or PVC) and methyl methacrylate. Traditionally, PVC production uses mercury catalysts and leads to serious environmental concerns. China accounts for 50% of worlds mercury emissions and 60% of Chinas mercury emission is caused by PVC production. Although gold catalysts are slightly expensive, overall production cost is affected by only ~1%. Therefore, green gold catalysis is considered valuable. The price fluctuation in gold has later led to cease the operations based on their use in catalytic converters. Very recently, there has been a lot of developments in gold catalysis for the synthesis of organic molecules including the C-C bond forming homocoupling or cross-coupling reactions and it has been speculated that some of these catalysts could find applications in various fields. | 0 | Theoretical and Fundamental Chemistry |
T characterizes the rate at which the longitudinal M component of the magnetization vector recovers exponentially towards its thermodynamic equilibrium, according to equation
Or, for the specific case that
It is thus the time it takes for the longitudinal magnetization to recover approximately 63% [1-(1/e)] of its initial value after being flipped into the magnetic transverse plane by a 90° radiofrequency pulse.
Nuclei are contained within a molecular structure, and are in constant vibrational and rotational motion, creating a complex magnetic field. The magnetic field caused by thermal motion of nuclei within the lattice is called the lattice field. The lattice field of a nucleus in a lower energy state can interact with nuclei in a higher energy state, causing the energy of the higher energy state to distribute itself between the two nuclei. Therefore, the energy gained by nuclei from the RF pulse is dissipated as increased vibration and rotation within the lattice, which can slightly increase the temperature of the sample. The name spin-lattice relaxation refers to the process in which the spins give the energy they obtained from the RF pulse back to the surrounding lattice, thereby restoring their equilibrium state. The same process occurs after the spin energy has been altered by a change of the surrounding static magnetic field (e.g. pre-polarization by or insertion into high magnetic field) or if the nonequilibrium state has been achieved by other means (e.g., hyperpolarization by optical pumping).
The relaxation time, T (the average lifetime of nuclei in the higher energy state) is dependent on the gyromagnetic ratio of the nucleus and the mobility of the lattice. As mobility increases, the vibrational and rotational frequencies increase, making it more likely for a component of the lattice field to be able to stimulate the transition from high to low energy states. However, at extremely high mobilities, the probability decreases as the vibrational and rotational frequencies no longer correspond to the energy gap between states.
Different tissues have different T values. For example, fluids have long Ts (1500-2000 ms), and water-based tissues are in the 400-1200 ms range, while fat based tissues are in the shorter 100-150 ms range. The presence of strongly magnetic ions or particles (e.g., ferromagnetic or paramagnetic) also strongly alter T values and are widely used as MRI contrast agents. | 0 | Theoretical and Fundamental Chemistry |
According to a 2015 report published by EvaluatePharma, the economics of orphan drugs mirrors the economics of the pharmaceutical market as a whole but has a few very large differences. The market for orphan drugs is by definition very small, but while the customer base is drastically smaller the cost of research and development is very much the same as for non orphan drugs. This, the producers have claimed, causes them to charge extremely high amounts for treatment, sometimes as high as $700,000 a year, as in the case of Spinraza (Biogen), FDA approved in December 2016 for spinal muscular atrophy, placing a large amount of stress on insurance companies and patients. An analysis of 12 orphan drugs that were approved in the US between 1990 and 2000 estimated a price reduction of on average 50% upon loss of marketing exclusivity, with a range of price reductions from 14% to 95%.
Governments have implemented steps to reduce high research and development cost with subsidies and other forms of financial assistance. The largest assistance are tax breaks which can be as high as 50% of research and development costs. Orphan drug manufacturers are also able to take advantage of the small customer base to cut cost on clinical trials due to the small number of cases to have smaller trials which reduces cost. These smaller clinical trials also allow orphan drugs to move to market faster as the average time to receive FDA approval for an orphan drug is 10 months compared to 13 months for non-orphan drugs. This is especially true in the market for cancer drugs, as a 2011 study found that between 2004 and 2010 orphan drug trials were more likely to be smaller and less randomized than their non-orphan counterparts, but still had a higher FDA approval rate, with 15 orphan cancer drugs being approved, while only 12 non-orphan drugs were approved. This allows manufactures to get cost to the point that it is economically feasible to produce these treatments. The subsidies can total up to $30 million per fiscal year in the United States alone.
By 2015, industry analysts and academic researchers agreed, that the sky-high price of orphan drugs, such as eculizumab, was not related to research, development and manufacturing costs. Their price is arbitrary and they have become more profitable than traditional medicines. | 1 | Applied and Interdisciplinary Chemistry |
Additive interaction or additive effect can be found in the treatment of the majority of common diseases. The combination of drugs with different effects has the benefit of using each drug at its optimal dose. This decreases the possibility of using a higher dose of a single medication if the previous dose is ineffective in treating diseases or relieving symptoms. The significance of using drugs with optimal dose is lowering the occurrence of intolerable side effects, adverse reactions, and possible drug toxicity in patient's body. This increases the safe use of drugs and increases patient compliance with the therapy.
One of the examples is the use of calcium channel blocker and beta-blocker. They are drugs that can be used to treat stable angina. They can both decrease the frequency of angina, aiming to relieve the symptoms of angina. There are controlled, double blind clinical trials and studies involving patients with preserved left ventricular function demonstrating that the combination of calcium channel blocker and beta blocker has an additive cardio depressant effects when comparing with either drug class alone. The combination therapy is used when a single medication fails to produce a therapeutic effect. Choosing the optimal dose of the two medications in the combination therapy prevents the use of an extreme high dose of a single medication alone, leading to adverse effects. | 1 | Applied and Interdisciplinary Chemistry |
The direct cost of electric energy produced by a thermal power station is the result of cost of fuel, capital cost for the plant, operator labour, maintenance, and such factors as ash handling and disposal. Indirect social or environmental costs, such as the economic value of environmental impacts, or environmental and health effects of the complete fuel cycle and plant decommissioning, are not usually assigned to generation costs for thermal stations in utility practice, but may form part of an environmental impact assessment. Those indirect costs belong to the broader concept of externalities. | 1 | Applied and Interdisciplinary Chemistry |
This first strategy involves locally depositing self-assembled monolayers on the surface only where the nanostructure will later be located. This strategy is advantageous because it involves high throughput methods that generally involve fewer steps than the other two strategies. The major techniques that use this strategy are:
* Micro-contact printing
:Micro-contact printing or soft lithography is analogous to printing ink with a rubber stamp. The SAM molecules are inked onto a pre-shaped elastomeric stamp with a solvent and transferred to the substrate surface by stamping. The SAM solution is applied to the entire stamp but only areas that make contact with the surface allow transfer of the SAMs. The transfer of the SAMs is a complex diffusion process that depends on the type of molecule, concentration, duration of contact, and pressure applied. Typical stamps use PDMS because its elastomeric properties, E = 1.8 MPa, allow it to fit the contour of micro surfaces and its low surface energy, γ = 21.6 dyn/cm². This is a parallel process and can thus place nanoscale objects over a large area in a short time.
* Dip-pen nanolithography
:Dip-pen nanolithography is a process that uses an atomic force microscope to transfer molecules on the tip to a substrate. Initially the tip is dipped into a reservoir with an ink. The ink on the tip evaporates and leaves the desired molecules attached to the tip. When the tip is brought into contact with the surface a water meniscus forms between the tip and the surface resulting in the diffusion of molecules from the tip to the surface. These tips can have radii in the tens of nanometers, and thus SAM molecules can be very precisely deposited onto a specific location of the surface. This process was discovered by Chad Mirkin and co-workers at Northwestern University. | 0 | Theoretical and Fundamental Chemistry |
Filamentous fungi, especially Aspergillus and Trichoderma, have long been used to produce diverse industrial enzymes from their own genomes ("native", "homologous") and from recombinant DNA ("heterologous").
More recently, Myceliophthora thermophila C1 has been developed into an expression platform for screening and production of native and heterologous proteins.The expression system C1 shows a low viscosity morphology in submerged culture, enabling the use of complex growth and production media. C1 also does not "hyperglycosylate" heterologous proteins, as Aspergillus and Trichoderma tend to do. | 1 | Applied and Interdisciplinary Chemistry |
The quantitative response of neutron tool to gas or light hydrocarbon depends primarily on hydrogen index and "excavation effect". The hydrogen index can be estimated from the composition and density of the hydrocarbons
Given a fixed volume, gas has considerably lower hydrogen concentration. When pore spaces in the rock are excavated and replaced with gas, the formation has smaller neutron-slowing characteristic, hence the terms "Excavation Effect". If this effect is ignored, a neutron log will show a low porosity value. This characteristic allows a neutron porosity log to be used with other porosity logs (such as a density log) to detect gas zones and identify gas-liquid contacts. | 0 | Theoretical and Fundamental Chemistry |
Hemodynamic stress overrides fatty acid inhibition of glucose metabolism. During this time there is a decrease in substrate supply and an increase in the substrate demand. This leads to an activation of AMP-activated protein kinase (AMPK) as the AMP concentration rises in intracellular fluids and the ATP concentration decreases. The stress-induced activation of AMPK provides an immediate metabolic adaptation and protects the heart from ischemic stress. | 1 | Applied and Interdisciplinary Chemistry |
As a background to this change of ownership, the general climate for science and technology was becoming less favourable. Faith in scientific and technological solutions was diminished by some spectacular failures: the de Havilland Comet suffered catastrophic in-flight failures; thalidomide caused tragic birth defects. Government procurement projects were frequently out of control: the BAC TSR-2 was cancelled after enormous overspend in development and only 24 test flights; the de Havilland Blue Streak missile was also abandoned in 1960 after great expense.
With Government budgets under severe pressure, contracts from government agencies were becoming harder to obtain,
Thus most of Fulmers markets were becoming difficult and Fulmers long term viability was in doubt. | 1 | Applied and Interdisciplinary Chemistry |
Rietti began studying chemistry in 1948 after she had finished her secondary education, graduating in 1954 with her degree in nuclear chemistry. She took her last course at the National Atomic Energy Commission in 1953, a fact that by chance allowed her to be the first nuclear chemist in Argentina. Her thesis was titled Study of the reaction between diboron tetrachloride and diborane. Boranes are chemical compounds known as boron hydrides. These materials cannot receive air or humidity. Because they have to always remain cold, she had to constantly monitor her compounds, including on weekends when she went to her laboratory with her children. In 1963, she finally obtained her doctorate from UBA. | 0 | Theoretical and Fundamental Chemistry |
Squalene is biosynthesised by coupling two molecules of farnesyl pyrophosphate. The condensation requires NADPH and the enzyme squalene synthase. | 1 | Applied and Interdisciplinary Chemistry |
While at Harvard, Woodward took on the directorship of the
Woodward Research Institute, based at Basel, Switzerland, in 1963. He also became a trustee of his alma mater, MIT, from 1966 to 1971, and of the Weizmann Institute of Science in Israel.
Woodward died in Cambridge, Massachusetts, from a heart attack in his sleep. At the time, he was working on the synthesis of an antibiotic, erythromycin. A student of his said about him:
:I owe a lot to R. B. Woodward. He showed me that one could attack difficult problems without a clear idea of their outcome, but with confidence that intelligence and effort would solve them. He showed me the beauty of modern organic chemistry, and the relevance to the field of detailed careful reasoning. He showed me that one does not need to specialize. Woodward made great contributions to the strategy of synthesis, to the deduction of difficult structures, to the invention of new chemistry, and to theoretical aspects as well. He taught his students by example the satisfaction that comes from total immersion in our science. I treasure the memory of my association with this remarkable chemist. | 0 | Theoretical and Fundamental Chemistry |
Members of the signal transducer and activator of transcription (STAT) protein family are intracellular transcription factors that mediate many aspects of cellular immunity, proliferation, apoptosis and differentiation. They are primarily activated by membrane receptor-associated Janus kinases (JAK). Dysregulation of this pathway is frequently observed in primary tumors and leads to increased angiogenesis which enhances the survival of tumors and immunosuppression. Gene knockout studies have provided evidence that STAT proteins are involved in the development and function of the immune system and play a role in maintaining immune tolerance and tumor surveillance. | 1 | Applied and Interdisciplinary Chemistry |
Raychelle Burks is an associate professor of analytical chemistry at American University in Washington, D.C., and science communicator, who has regularly appeared on the Science Channel. In 2020, the American Chemical Society awarded her the Grady-Stack award for her public engagement excellence. | 0 | Theoretical and Fundamental Chemistry |
Chemaxon was founded in 1998 by two brothers, Ferenc and Péter-Csizmadia. The company name was created by combining the words chem, indicating chemistry, and axon referring to a vast network of connections between the scientific and informatic domains. Initially, Chemaxon offered consultancy services and later moved into product development. As a startup company, Chemaxon had strong ties with local universities engaged in software development projects with PhD students. Emerging technologies and software languages were studied, and as a result, a platform-independent back-end product line reliant on Java started to come together. The first Chemaxon software product was Marvin, a chemical editor. Its first version was released in January 1999. Marvin was followed by the development of the JChem technology, adding chemical intelligence to common database management systems with the first release in early 2000 and providing the first company sale that same year. Chemaxon's first software developments were presented in scientific articles and posters presented in cheminformatics journals and conferences. Company revenue and user number increased rapidly in the early 2000s, which resulted in the first user meeting in 2005.
In 2004, Chemaxon began to offer a free software license package. Chemaxon also established representatives in the US from 2000 and in Japan via an official distributor company in 2005. Growing user requests led to the development and release of more software products. The company's product portfolio expanded with physical and chemical calculations and predictions, desktop-based chemical database management applications, and chemical naming intelligence. The growing trend affected employee numbers and required a larger head office space.
The first official office headquarters was opened in 2003 in Máramaros köz, Budapest, Hungary. A software development office opened in Prague, Czech Republic, in 2006. Chemaxon's desktop-based, cheminformatics product portfolio saturated in the late 2000s. GlaxoSmithKline contracted with them in late 2009. The company started to experiment with agile software development approach in 2010, eventually adopting scrum methodology in the following year.
Chemaxon encourages an agile office environment with cross-functional teams. This philosophy is supported by a publicly available online company culture guide. With the wave of change came new product development directions that mimicked the trends in the industry at the end of the 2000s. The demand for online services has emerged in research to allow lab colleagues to access chemical applications from all devices, enabling contract research organizations and other suppliers to collaborate with chemical data and cut IT costs at the same time.
Chemaxon started to build its cloud-based software systems in 2008 – the first one being Chemicalize – and continuously expanded in this area. On the other hand, the rise of biologics within newly developed pharmaceutical drugs influenced Chemaxon to start developing its biopolymer informatics portfolio in 2015. In 2011, Chemaxon moved its office headquarters to Graphisoft Park, one of Budapest's tech hubs, where the company is currently located. More offices were established: in 2014, a US East Coast headquarters opened in Cambridge, Massachusetts, followed by an office opening in San Diego in 2018. | 1 | Applied and Interdisciplinary Chemistry |
Insulin affects ACC in a similar way to PDH. It leads to its dephosphorylation via activation of PP2A phosphatase whose activity results in the activation of the enzyme. Glucagon has an antagonistic effect and increases phosphorylation, deactivation, thereby inhibiting ACC and slowing fat synthesis.
Affecting ACC affects the rate of acetyl-CoA conversion to malonyl-CoA. Increased malonyl-CoA level pushes the equilibrium over to increase production of fatty acids through biosynthesis. Long chain fatty acids are negative allosteric regulators of ACC and so when the cell has sufficient long chain fatty acids, they will eventually inhibit ACC activity and stop fatty acid synthesis.
AMP and ATP concentrations of the cell act as a measure of the ATP needs of a cell. When ATP is depleted, there is a rise in 5'AMP. This rise activates AMP-activated protein kinase, which phosphorylates ACC and thereby inhibits fat synthesis. This is a useful way to ensure that glucose is not diverted down a storage pathway in times when energy levels are low.
ACC is also activated by citrate. When there is abundant acetyl-CoA in the cell cytoplasm for fat synthesis, it proceeds at an appropriate rate. | 1 | Applied and Interdisciplinary Chemistry |
In volatilization methods, removal of the analyte involves separation by heating or chemically decomposing a volatile sample at a suitable temperature. In other words, thermal or chemical energy is used to precipitate a volatile species. For example, the water content of a compound can be determined by vaporizing the water using thermal energy (heat). Heat can also be used, if oxygen is present, for combustion to isolate the suspect species and obtain the desired results.
The two most common gravimetric methods using volatilization are those for water and carbon dioxide. An example of this method is the isolation of sodium hydrogen bicarbonate (the main ingredient in most antacid tablets) from a mixture of carbonate and bicarbonate. The total amount of this analyte, in whatever form, is obtained by addition of an excess of dilute sulfuric acid to the analyte in solution.
In this reaction, nitrogen gas is introduced through a tube into the flask which contains the solution. As it passes through, it gently bubbles. The gas then exits, first passing a drying agent (here CaSO, the common desiccant Drierite). It then passes a mixture of the drying agent and sodium hydroxide which lies on asbestos or Ascarite II, a non-fibrous silicate containing sodium hydroxide. The mass of the carbon dioxide is obtained by measuring the increase in mass of this absorbent. This is performed by measuring the difference in weight of the tube in which the ascarite contained before and after the procedure.
The calcium sulfate (CaSO) in the tube retains carbon dioxide selectively as it's heated, and thereby, removed from the solution. The drying agent absorbs any aerosolized water and/or water vapor (reaction 3.). The mix of the drying agent and NaOH absorbs the CO and any water that may have been produced as a result of the absorption of the NaOH (reaction 4.).
The reactions are:
Reaction 3 - absorption of water
NaHCO + HSO → CO) + HO + NaHSO
Reaction 4. Absorption of CO and residual water
CO + 2 NaOH NaCO + HO | 0 | Theoretical and Fundamental Chemistry |
Epoxide hydrolases (EHs), also known as epoxide hydratases, are enzymes that metabolize compounds that contain an epoxide residue; they convert this residue to two hydroxyl residues through an epoxide hydrolysis reaction to form diol products. Several enzymes possess EH activity. Microsomal epoxide hydrolase (epoxide hydrolase 1, EH1, or mEH), soluble epoxide hydrolase (sEH, epoxide hydrolase 2, EH2, or cytoplasmic epoxide hydrolase), and the more recently discovered but not as yet well defined functionally, epoxide hydrolase 3 (EH3) and epoxide hydrolase 4 (EH4) are structurally closely related isozymes. Other enzymes with epoxide hydrolase activity include leukotriene A4 hydrolase, Cholesterol-5,6-oxide hydrolase, MEST (gene) (Peg1/MEST), and Hepoxilin-epoxide hydrolase. The hydrolases are distinguished from each other by their substrate preferences and, directly related to this, their functions. | 1 | Applied and Interdisciplinary Chemistry |
Christopher Alexander Hunter, FRS (born 19 February 1965) is a British chemist and academic. Since 2014, he has been Herchel Smith Professor of Organic Chemistry in the Department of Chemistry at the University of Cambridge. His research is currently focused on molecular recognition. He was previously a lecturer at the University of Otago and a lecturer then professor at the University of Sheffield. | 0 | Theoretical and Fundamental Chemistry |
The omni processor initiative for processing fecal sludge is being complemented by an effort to develop new technologies for improved pit latrine emptying (called by the Gates Foundation the "omni ingestor") and by the Reinvent the Toilet Challenge. The latter is a long-term research and development effort to develop a hygienic, stand-alone toilet. It is focused on "reinventing the flush toilet". The aim is to create a toilet that not only removes pathogens from human excreta, but also recovers resources such as energy, clean water, and nutrients (a concept also known as reuse of excreta). It should operate "off the grid" without connections to water, sewer, or electrical networks. Finally, it should cost less than 5 US-cents per user per day. | 1 | Applied and Interdisciplinary Chemistry |
Nanofluidic devices have been built for application in chemistry, molecular biology and medicine. The main purposes to use nanofluidic devices are separation and measurement of solutions containing nanoparticles for drug delivery, gene therapy and nanoparticle toxicology on a micro-total-analysis system. An important advantage of micro- and nano-scaled systems is the small amount of sample or reagent used in analysis. This reduces the time required for sample processing. It is also possible to achieve analysis in an array, which further speeds up processes and increases throughput of analysis.
Nanochannels are utilized to achieve single-molecule sensing and diagnosis, as well as DNA separation. In many cases, nanofluidic devices are integrated within a microfluidic system to facilitate logic operation of fluids. The future of nanofluidic systems will be focused on several areas such as analytical chemistry and biochemistry, liquid transport and metering, and energy conversion.
In nanofluidics, the valence numbers of the ions determines their net electrophoretic velocities. In other words, the velocity of an ion in the nano-channel is related not only to its ion mobility but also its ion valence. This enables the sorting function of nanofluidics, which cannot be done in a micro-channel. Therefore, it is possible to do sorting and separation for short strand DNA by using a nanochannel. For the single-molecule DNA application, the final goal is to sequence a strand of genomic DNA in a reproducible and precise result. Similar application can also be found in chromatography, or separation of various ingredients in the solution.
Application also can be found in synthesis of fibers. Polymer fibers can be created by electrospinning the monomers at an interface between liquid and vacuum. An organized polymer structure is formed from a flow of monomers aligning on a substrate.
There is also an attempt to bring nanofluidic technology into energy conversion. In this case, the electrical charged wall behaves as the stator, while the flowing solution as the rotor. It is observed that when the pressure-driven solvent flowing through a charged nanochannel, it can generate a streaming current and a streaming potential. This phenomenon can be used in electrical energy harvesting.
Advances in nanofabrication techniques and concerns about energy shortage make people interested in this idea. The main challenge is to increase efficiency, which is now only a few percent, compared with efficiencies of up to about 95 per cent for standard rotational electromagnetic generators. | 0 | Theoretical and Fundamental Chemistry |
Peatlands store an enormous amount of carbon. Covering only 3% of the land surface, they store more than 450 gigatonnes of carbon - more than stored by forests (which cover 30% of the land surface). Drained peatlands cause numerous negative environmental impacts such as greenhouse gas emission, nutrient leaching, subsidence and loss of biodiversity. Although only 0.3% of all peatlands are drained, peatland drainage is estimated to be responsible for 6% of all human greenhouse gas emission. By making soils waterlogged when re-wetting peatlands, decomposition of organic matter (~50% carbon) will almost cease, and hence carbon will no longer escape into the atmosphere as carbon dioxide. Peatland rewetting can significantly reduce environmental impacts caused by drainage by restoring hydrological buffering and reducing the water table's sensitivity to atmospheric evaporative demand. Due to the drainage of soils for agriculture in many areas, the peat soil depth and water quality has dropped significantly over the years. These problems are mitigated by re-wetting peatlands. As such, they can also make installations against rising sea levels (levees, pumps) unnecessary. Wet bogs act as nitrogen sinks, whereas mineralisation and fertilisation from agriculture on drained bogs produces nitrogen run-off into nearby waters. | 1 | Applied and Interdisciplinary Chemistry |
The Air Movement and Control Association, International was founded in 1955 when the National Association of Fan Manufacturers (NAFM) combined with the Power Fan Manufacturers Association (PFMA) and the Industrial Unit Heater Association (IUHA). Originally known as the Air Moving and Conditioning Association, AMCA was retitled in 1960 to its current name. In 1996, the AMCA Board of Directors added the term International to AMCAs name in order to better indicate the global scope of AMCAs membership.
In 1923, the first edition of the Fan Test Codes was developed as a result of problems encountered by the U.S. Navy in regards to performance ratings of fans being procured during World War 1. To resolve the issue of variations in testing methods and performance ratings, a joint committee of NAFM and the American Society of Heating and Ventilating Engineers (ASHVE) was formed to develop a standard test code for fans.
When NAFM combined with PFMA and IUHA, the organizations major concern was the accuracy and practicality of the pitot traverse method of testing, and a committee was formed to study various test methods and develop a new test code. To aid in the study, AMCA sponsored research by the Battelle Memorial Institute to compare the test results using the pitot tube test methods and nozzle test methods. The result of this effort was a new revision of the test code, which was published in 1960 as AMCA Standard Test Code for Air Moving Devices, Bulletin 210'. Standard 210 became widely accepted and known as virtually the only standard used in the United States and Canada.
In 1985, AMCA expanded its scope to include air control devices, such as louvers, dampers, and airflow measurement stations.
In 1996, AMCAs first accredited laboratory, ITRI, began testing in Taiwan. In 2008, AMCAs second independent accredited laboratory, AFMA, began testing in Singapore. | 1 | Applied and Interdisciplinary Chemistry |
The limiting current in electrochemistry is the limiting value of a faradaic current that is approached as the rate of charge transfer to an electrode is increased. The limiting current can be approached, for example, by increasing the electric potential or decreasing the rate of mass transfer to the electrode. It is independent of the applied potential over a finite range, and is usually evaluated by subtracting the appropriate residual current from the measured total current. A limiting current can have the character of an adsorption, catalytic, diffusion, or kinetic current, and may include a migration current. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, hexol is a cation with formula {[Co(NH)(OH)]Co} — a coordination complex consisting of four cobalt cations in oxidation state +3, twelve ammonia molecules , and six hydroxy anions , with a net charge of +6. The hydroxy groups act as bridges between the central cobalt atom and the other three, which carry the ammonia ligands.
Salts of hexol, such as the sulfate {[Co(NH)(OH)]Co}(SO)(HO), are of historical significance as the first synthetic non-carbon-containing chiral compounds. | 0 | Theoretical and Fundamental Chemistry |
Prior to the introduction of diethylaminosulfur trifluoride (DAST) in 1970 for the replacement of hydroxyl groups with fluoride, sulfur tetrafluoride was the reagent most commonly used to accomplish this transformation. However, sulfur tetrafluoride only reacts with the most acidic hydroxyl groups (its substrate scope is limited), and is difficult to handle, toxic, and capable of generating hydrogen fluoride upon hydrolysis. Thus, aminosulfurane reagents such as diethylaminosulfur trifluoride have largely replaced SF as the reagents of choice for replacement of hydroxyl groups with fluoride.
Aminosulfuranes are usually prepared by reaction of the corresponding dialkylamino(trialkyl)silanes with SF. When the aminosulfurane is exposed to a second equivalent of aminosilane, bis(dialkylamino)sulfur difluorides result. Tris(dialkylamino)sulfonium difluorotrimethylsilicates such as tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF) have achieved synthetic utility as reagents for the fluorination of halides. These form when three equivalents of aminosilane are exposed to sulfur tetrafluoride. | 0 | Theoretical and Fundamental Chemistry |
The initial use of racemic dopa for the treatment of Parkinson's disease resulted in a number of adverse effects viz. nausea, vomiting, anorexia, involuntary movements and granulocytopenia. The use of L-dopa [the (S)-enantiomer] resulted in reducing the required dose, and adverse effects. The granulocytopenia was not observed with the single enantiomer. | 0 | Theoretical and Fundamental Chemistry |
Molecular oxygen is a good terminal electron acceptor because it is a strong oxidizing agent. The reduction of oxygen does involve potentially harmful intermediates. Although the transfer of four electrons and four protons reduces oxygen to water, which is harmless, transfer of one or two electrons produces superoxide or peroxide anions, which are dangerously reactive.
These reactive oxygen species and their reaction products, such as the hydroxyl radical, are very harmful to cells, as they oxidize proteins and cause mutations in DNA. This cellular damage may contribute to disease and is proposed as one cause of aging.
The cytochrome c oxidase complex is highly efficient at reducing oxygen to water, and it releases very few partly reduced intermediates; however small amounts of superoxide anion and peroxide are produced by the electron transport chain. Particularly important is the reduction of coenzyme Q in complex III, as a highly reactive ubisemiquinone free radical is formed as an intermediate in the Q cycle. This unstable species can lead to electron "leakage" when electrons transfer directly to oxygen, forming superoxide. As the production of reactive oxygen species by these proton-pumping complexes is greatest at high membrane potentials, it has been proposed that mitochondria regulate their activity to maintain the membrane potential within a narrow range that balances ATP production against oxidant generation. For instance, oxidants can activate uncoupling proteins that reduce membrane potential.
To counteract these reactive oxygen species, cells contain numerous antioxidant systems, including antioxidant vitamins such as vitamin C and vitamin E, and antioxidant enzymes such as superoxide dismutase, catalase, and peroxidases, which detoxify the reactive species, limiting damage to the cell. | 1 | Applied and Interdisciplinary Chemistry |
In this example we will use the five liquids in the Table 2 (Liquid Data) to find the critical wetting surface tension needed to effectively wet PC (polycarbonate) using the Zisman Plot.
The data of the liquids given from the table above is then graphed on the Zisman Plot (Figure 2) with the independent variable as the surface tension of the liquid in dynes/cm and the dependent variable as 1-cos(θ). There also are different variations of the Zisman plot since the Y-axis is unitless as seen in Table 1 and as mentioned above.
Liquids 1 and 2 fully wet the surface as shown by their low contact angles, so they should be neglected when first drawing the line of best fit to find the critical liquid surface tension needed to effectively wet the PC surface, γ, which is simply the x-intercept of the best fit line for the Zisman Plot. To find the best fit line a least squares regression is recommended by using a computer program such as Microsoft Excel, Minitab, Matlab, or it can also be done using a modern graphing calculator such as a TI-84. This was done with the data from Table 1 and the fit data for liquids 3,4, and 5 can be seen on Figure 3.
The x-intercept lands at 39.5 dynes per centimeter (This can be calculated by setting y equal to zero and solving for x) which is less than that of liquid 2, 42.9 dynes per centimeter; therefore, a more accurate measurement of the critical liquid surface tension needed to effectively wet the surface of PC can be obtained by including liquid 2 when making the line of best fit, as seen in Figure 4.
The x-intercept here lands at 42.1 dynes per centimeter (This can be calculated by setting y equal to zero and solving for x), indicating the critical liquid surface tension for PC. | 0 | Theoretical and Fundamental Chemistry |
A mass analysis is done by representing the purity and flowrate for each stream from the hydrogen consumers (sinks), such as hydrotreaters, hydrocrackers, isomerization units and lubricant plants and the hydrogen producers (sources), such as hydrogen plants and naphtha reformers, streams from hydrogen purifiers, membrane reactors, pressure swing adsorption and continuous distillation and off-gas streams from low- or high-pressure separators. The source-demand diagram shows bottlenecks, surplus or shortages. The hydrogen pinch is the purity at which the hydrogen network has neither hydrogen surplus nor deficit.
After the analysis REFOPT from the Centre for Process Integration at The University of Manchester is used as a tool for process integration with which the process is optimized. The methodology was also developed into commercial software by companies such as Linnhoff March and AspenTech. The Aspen product incorporated the work of Nick Hallale (formerly a lecturer at University of Manchester) and was the first method to consider multiple components, rather than a pseudo-binary mixture of hydrogen and methane. | 1 | Applied and Interdisciplinary Chemistry |
Andrés Manuel del Río y Fernández (10 November 1764 – 23 March 1849) was a Spanish scientist, naturalist and engineer, nationalized Mexican, who discovered compounds of vanadium in 1801. He proposed that the element be given the name panchromium, or later, erythronium, but his discovery was not credited at the time, and his names were not used. | 1 | Applied and Interdisciplinary Chemistry |
In geochemistry, the primitive mantle (also known as the bulk silicate Earth) is the chemical composition of the Earth's mantle during the developmental stage between core-mantle differentiation and the formation of early continental crust. The chemical composition of the primitive mantle contains characteristics of both the crust and the mantle. | 0 | Theoretical and Fundamental Chemistry |
Although the SI unit of total cross sections is m, smaller units are usually used in practice.
In nuclear and particle physics, the conventional unit is the barn b, where 1 b = 10 m = 100 fm. Smaller prefixed units such as mb and μb are also widely used. Correspondingly, the differential cross section can be measured in units such as mb/sr.
When the scattered radiation is visible light, it is conventional to measure the path length in centimetres. To avoid the need for conversion factors, the scattering cross section is expressed in cm, and the number concentration in cm. The measurement of the scattering of visible light is known as nephelometry, and is effective for particles of 2–50 µm in diameter: as such, it is widely used in meteorology and in the measurement of atmospheric pollution.
The scattering of X-rays can also be described in terms of scattering cross sections, in which case the square ångström is a convenient unit: 1 Å = 10 m = = 10 b. The sum of the scattering, photoelectric, and pair-production cross-sections (in barns) is charted as the "atomic attenuation coefficient" (narrow-beam), in barns. | 0 | Theoretical and Fundamental Chemistry |
When the soil is saturated and the depression storage filled, and rain continues to fall, the rainfall will immediately produce surface runoff. The level of antecedent soil moisture is one factor affecting the time until soil becomes saturated. This runoff is called saturation excess overland flow, saturated overland flow, or Dunne runoff. | 1 | Applied and Interdisciplinary Chemistry |
A tarball is a blob of crude oil (not to be confused with tar, which is a human-made product derived from pine trees or refined from petroleum) which has been weathered after floating in the ocean. Tarballs are an aquatic pollutant in most environments, although they can occur naturally, for example in the Santa Barbara Channel of California or in the Gulf of Mexico off Texas. Their concentration and features have been used to assess the extent of oil spills. Their composition can be used to identify their sources of origin, and tarballs themselves may be dispersed over long distances by deep sea currents. They are slowly decomposed by bacteria, including Chromobacterium violaceum, Cladosporium resinae, Bacillus submarinus, Micrococcus varians, Pseudomonas aeruginosa, Candida marina and Saccharomyces estuari. | 0 | Theoretical and Fundamental Chemistry |
In theoretical chemistry, Marcus theory is a theory originally developed by Rudolph A. Marcus, starting in 1956, to explain the rates of electron transfer reactions – the rate at which an electron can move or jump from one chemical species (called the electron donor) to another (called the electron acceptor). It was originally formulated to address outer sphere electron transfer reactions, in which the two chemical species only change in their charge with an electron jumping (e.g. the oxidation of an ion like Fe/Fe), but do not undergo large structural changes. It was extended to include inner sphere electron transfer contributions, in which a change of distances or geometry in the solvation or coordination shells of the two chemical species is taken into account (the Fe-O distances in Fe(HO) and Fe(HO) are different).
For electron transfer reactions without making or breaking bonds Marcus theory takes the place of Eyrings transition state theory which has been derived for reactions with structural changes. Both theories lead to rate equations of the same exponential form. However, whereas in Eyring theory the reaction partners become strongly coupled in the course of the reaction to form a structurally defined activated complex, in Marcus theory they are weakly coupled and retain their individuality. It is the thermally induced reorganization of the surroundings, the solvent (outer sphere) and the solvent sheath or the ligands (inner sphere) which create the geometrically favourable situation prior' to and independent of the electron jump.
The original classical Marcus theory for outer sphere electron transfer reactions demonstrates the importance of the solvent and leads the way to the calculation of the Gibbs free energy of activation, using the polarization properties of the solvent, the size of the reactants, the transfer distance and the Gibbs free energy of the redox reaction. The most startling result of Marcus' theory was the "inverted region": whereas the reaction rates usually become higher with increasing exergonicity of the reaction, electron transfer should, according to Marcus theory, become slower in the very negative domain. Scientists searched the inverted region for proof of a slower electron transfer rate for 30 years until it was unequivocally verified experimentally in 1984.
R. A. Marcus received the Nobel Prize in Chemistry in 1992 for this theory. Marcus theory is used to describe a number of important processes in chemistry and biology, including photosynthesis, corrosion, certain types of chemiluminescence, charge separation in some types of solar cells and more. Besides the inner and outer sphere applications, Marcus theory has been extended to address heterogeneous electron transfer. | 0 | Theoretical and Fundamental Chemistry |
The Earths night sky is illuminated by diffuse light, called airglow, that is produced by radiative transitions of atoms and molecules. Among the most intense such features observed in the Earths night sky is a group of infrared transitions at wavelengths between 700 nanometers and 900 nanometers. In 1950, Aden Meinel showed that these were transitions of the hydroxyl molecule, OH. | 0 | Theoretical and Fundamental Chemistry |
A check dam is a small, sometimes temporary, dam constructed across a swale, drainage ditch, or waterway to counteract erosion by reducing water flow velocity. Check dams themselves are not a type of new technology; rather, they are an ancient technique dating from the second century AD. Check dams are typically, though not always, implemented in a system of several dams situated at regular intervals across the area of interest. | 1 | Applied and Interdisciplinary Chemistry |
Hot (> 300 °C) hydrothermal fluids from mid ocean ridges are isotopically light, with δFe between -0.2 and -0.8‰. Particles in hydrothermal plumes are isotopically heavy relative to the hydrothermal fluids, with δFe between 0.1 and 1.1‰. Hydrothermal deposits have average δFe between -1.6 and 0.3‰. The sulfide minerals within these deposits have δFe between -2.0 and 1.1‰. | 0 | Theoretical and Fundamental Chemistry |
Collision in diluted gas or liquid solution is regulated by diffusion instead of direct collisions, which can be calculated from Fick's laws of diffusion. Theoretical models to calculate the collision frequency in solutions have been proposed by Marian Smoluchowski in a seminal 1916 publication at the infinite time limit, and Jixin Chen in 2022 at a finite-time approximation. A scheme of comparing the rate equations in pure gas and solution is shown in the right figure.
For a diluted solution in the gas or the liquid phase, the collision equation developed for neat gas is not suitable when diffusion takes control of the collision frequency, i.e., the direct collision between the two molecules no longer dominates. For any given molecule A, it has to collide with a lot of solvent molecules, let's say molecule C, before finding the B molecule to react with. Thus the probability of collision should be calculated using the Brownian motion model, which can be approximated to a diffusive flux using various boundary conditions that yield different equations in the Smoluchowski model and the JChen Model.
For the diffusive collision, at the infinite time limit when the molecular flux can be calculated from the Fick's laws of diffusion, in 1916 Smoluchowski derived a collision frequency between molecule A and B in a diluted solution:
where:
* is the collision frequency, unit #collisions/s in 1 m of solution.
* is the radius of the collision cross-section, unit m.
* is the relative diffusion constant between A and B, unit m/s, and .
* and are the number concentrations of molecules A and B in the solution respectively, unit #molecule/m.
or
where:
* is in unit mole collisions/s in 1 L of solution.
* is the Avogadro constant.
* is the radius of the collision cross-section, unit m.
* is the relative diffusion constant between A and B, unit m/s.
* and are the molar concentrations of A and B respectively, unit mol/L.
* is the diffusive collision rate constant, unit L mol s.
There have been a lot of extensions and modifications to the Smoluchowski model since it was proposed in 1916.
In 2022, Chen rationales that because the diffusive flux is evolving over time and the distance between the molecules has a finite value at a given concentration, there should be a critical time to cut off the evolution of the flux that will give a value much larger than the infinite solution Smoluchowski has proposed. So he proposes to use the average time for two molecules to switch places in the solution as the critical cut-off time, i.e., first neighbor visiting time. Although an alternative time could be the mean free path time or the average first passenger time, it overestimates the concentration gradient between the original location of the first passenger to the target. This hypothesis yields a fractal reaction kinetic rate equation of diffusive collision in a diluted solution:
where:
* is in unit mole collisions/s in 1 L of solution.
* is the Avogadro constant.
* is the area of the collision cross-section in unit m.
* is the product of the unitless fractions of reactive surface area on A and B. is the effective adsorption cross-section area.
* is the relative diffusion constant between A and B, unit m/s, and .
* and are the molar concentrations of A and B respectively, unit mol/L.
* is the diffusive collision rate constant, unit L mol s. | 0 | Theoretical and Fundamental Chemistry |
During quiescence, the DREAM complex represses G1/S and G2/M gene expression. In mammalian systems, chromatin-immunoprecipitation (ChIP) studies have revealed that DREAM components are found together at promoters of genes that peak in G1/S or G2/M phase. Abrogation of the DREAM complex on the other hand, led to increased expression of E2F regulated genes normally repressed in the G0 phase. Contrary to mammalian cells, the fly dREAM complex was found at almost one-third of all promoters, which may reflect a broader role for dREAM in gene regulation, such as programmed cell death of neural precursor cells.
Docking of the DREAM complex to promoters is achieved by binding of LIN-54 to regions known as cell cycle genes homology region (CHR). These are specific sequence of nucleotides that are commonly found in the promoters of genes expressed during late S phase or G2/M phase. Docking can also be achieved via E2F proteins binding to sequences known as cell cycle-dependent element sites (CDEs). Some cell cycle dependent genes have been found where both CHRs and CDEs are in proximity to one another. Because p130-E2F4 can form stable associations with the MuvB complex, the proximity of CHRs to CDEs suggests that affinity of binding of the DREAM complex to target genes is cooperatively improved by association with both the binding sites.
When DREAM is docked onto the promoter, p130 is bound to LIN52, and this association inhibits LIN52 binding to chromatin modifier proteins. Therefore, unlike RB-E2F, the DREAM complex is unlikely to directly recruit chromatin modifiers to repress gene expression, although some associations have been suggested. DREAM complex may instead down-regulate gene expression by affecting nucleosome positioning. Compacted DNA at transcription start sites inhibit gene expression by blocking the docking of RNA polymerase. In worms for example, loss of a MuvB complex protein, LIN35, leads to loss of repressive histone associations and high expression of cell cycle dependent genes. However, direct evidence for the link between repressive histones and the DREAM complex remains to be elucidated. | 1 | Applied and Interdisciplinary Chemistry |
Adolf Hitler was sworn in as the Chancellor of Germany on 30 January 1933, as his Nazi Party (NSDAP) was now the largest party in the Reichstag (Weimar Republic). The 7 April 1933 Law for the Restoration of the Professional Civil Service removed Jews from the civil service, which included academia. Meitner never tried to conceal her Jewish descent, but initially was exempt from its impact on multiple grounds: she had been employed before 1914, had served in the military during the World War, was an Austrian rather than a German citizen, and the Kaiser Wilhelm Institute was a government-industry partnership. However, she was dismissed from her adjunct professorship on 6 September on the grounds that her World War I service was not at the front, and she had not completed her habilitation until 1922. This had no effect on her salary or work at the KWI for Chemistry. Carl Bosch, the director of IG Farben, a major sponsor of the KWI for Chemistry, assured Meitner that her position there was safe. Although Hahn and Meitner remained in charge, their assistants, Otto Erbacher and Kurt Philipp respectively, who were both NSDAP members, were given increasing influence over the day-to-day running of the institute.
Others were not so fortunate; her nephew Otto Frisch was dismissed from his post in the Institute for Physical Chemistry at the University of Hamburg, as was Otto Stern, the director of the institute. Stern found Frisch a position with Patrick Blackett at Birkbeck College in England, and he later worked at the Niels Bohr Institute in Copenhagen from 1934 to 1939. Fritz Strassman had come to the Kaiser Wilhelm Institute for Chemistry to study under Hahn to improve his employment prospects. He declined a lucrative offer of employment because it required political training and Nazi Party membership, and resigned from the Society of German Chemists when it became part of the Nazi German Labour Front rather than become a member of a Nazi-controlled organisation. As a result, he could neither work in the chemical industry nor receive his habilitation. Meitner persuaded Hahn to hire him as an assistant. Soon he would be credited as a third collaborator on the papers they produced, and would sometimes even be listed first. Between 1933 and 1935, Meitner published exclusively in Naturwissenschaften, as its editor Arnold Berliner was Jewish, and continued to accept submissions from Jewish scientists. This generated a boycott of the publication, and in August 1935 publisher Springer-Verlag fired Berliner. | 1 | Applied and Interdisciplinary Chemistry |
When two miscible liquids are brought into contact, and diffusion takes place, the macroscopic (or average) concentration evolves following Ficks law. On a mesoscopic scale, that is, between the macroscopic scale described by Ficks law and molecular scale, where molecular random walks take place, fluctuations cannot be neglected. Such situations can be successfully modeled with Landau-Lifshitz fluctuating hydrodynamics. In this theoretical framework, diffusion is due to fluctuations whose dimensions range from the molecular scale to the macroscopic scale.
In particular, fluctuating hydrodynamic equations include a Ficks flow term, with a given diffusion coefficient, along with hydrodynamics equations and stochastic terms describing fluctuations. When calculating the fluctuations with a perturbative approach, the zero order approximation is Ficks law. The first order gives the fluctuations, and it comes out that fluctuations contribute to diffusion. This represents somehow a tautology, since the phenomena described by a lower order approximation is the result of a higher approximation: this problem is solved only by renormalizing the fluctuating hydrodynamics equations. | 0 | Theoretical and Fundamental Chemistry |
In the history of chemistry, the chemical revolution, also called the first chemical revolution, was the reformulation of chemistry during the seventeenth and eighteenth centuries, which culminated in the law of conservation of mass and the oxygen theory of combustion.
During the 19th and 20th century, this transformation was credited to the work of the French chemist Antoine Lavoisier (the "father of modern chemistry"). However, recent work on the history of early modern chemistry considers the chemical revolution to consist of gradual changes in chemical theory and practice that emerged over a period of two centuries. The so-called scientific revolution took place during the sixteenth and seventeenth centuries whereas the chemical revolution took place during the seventeenth and eighteenth centuries. | 1 | Applied and Interdisciplinary Chemistry |
Flow rate of the liquid phase and mole fraction of the desired compound in it are and .
Flow rate of the vapour phase and mole fraction of the desired compound in it are and . | 0 | Theoretical and Fundamental Chemistry |
Seismic methods are preferred to magnetometers as the primary survey method for oil exploration although magnetic methods can give additional information about the underlying geology and in some environments evidence of leakage from traps. Magnetometers are also used in oil exploration to show locations of geologic features that make drilling impractical, and other features that give geophysicists a more complete picture of stratigraphy. | 0 | Theoretical and Fundamental Chemistry |
Bacteriorhodopsin is a 27 kDa integral membrane protein usually found in two-dimensional crystalline patches known as "purple membrane", which can occupy almost 50% of the surface area of the archaeal cell. The repeating element of the hexagonal lattice is composed of three identical protein chains, each rotated by 120 degrees relative to the others. Each monomer has seven transmembrane alpha helices and an extracellular-facing, two-stranded beta sheet.
Bacteriorhodopsin is synthesized as a protein precursor, known as bacterio-opsin, which is extensively modified after translation. The modifications are:
* Covalent conjugation of a retinal molecule to residue Lys216, via a Schiff base, to create the retinylidene chromophore.
* Cleavage of the signal peptide, the first 13 amino acids at the N-terminus, and the conversion of residue Gln14 to pyroglutamate
* Removal of residue Asp262 at the C-terminus | 0 | Theoretical and Fundamental Chemistry |
Maxwell-Wagner polarization processes should be taken into account during the investigation of inhomogeneous materials like suspensions or colloids, biological materials, phase separated polymers, blends, and crystalline or liquid crystalline polymers. | 0 | Theoretical and Fundamental Chemistry |
The isochore theory purported that the genome of "warm-blooded" vertebrates (mammals and birds) are mosaics of long isochoric regions of alternating GC-poor and GC-rich composition, as opposed to the genome of "cold-blooded" vertebrates (fishes and amphibians) that were supposed to lack GC-rich isochores.
These findings were explained by the thermodynamic stability hypothesis, attributing genomic structure to body temperature. GC-rich isochores were purported to be a form of adaptation to environmental pressures, as an increase in genomic GC-content could protect DNA, RNA, and proteins from degradation by heat.
Despite its attractive simplicity, the thermodynamic stability hypothesis has been repeatedly shown to be in error
Many authors showed the absence of a relationship between temperature and GC-content in vertebrates, while others showed the existence of GC-rich domains in "cold-blooded" vertebrates such as crocodiles, amphibians, and fish. | 1 | Applied and Interdisciplinary Chemistry |
The Science Based Targets initiative (SBTi) is a collaboration between the CDP (it was the Carbon Disclosure Project), the United Nations Global Compact, World Resources Institute (WRI) and the World Wide Fund for Nature (WWF). Since 2015, more than 1,000 companies have joined the initiative to set a science-based climate target. | 1 | Applied and Interdisciplinary Chemistry |
If major depressive disorder symptoms fail to respond to standard treatment (such as selective serotonin reuptake inhibitors [SSRIs]), a second agent is sometimes added. A recent systematic review found some evidence of the clinical utility of adjunctive lithium, but the majority of supportive evidence is dated. The same review found no evidence to support the use of lithium for monotherapy. | 1 | Applied and Interdisciplinary Chemistry |
Arterial damage results from white blood cell invasion and inflammation within the wall. CRP is a general marker for inflammation and infection, so it can be used as a very rough proxy for heart disease risk. Since many things can cause elevated CRP, this is not a very specific prognostic indicator. Nevertheless, a level above 2.4 mg/L has been associated with a doubled risk of a coronary event compared to levels below 1 mg/L; however, the study group in this case consisted of patients who had been diagnosed with unstable angina pectoris; whether elevated CRP has any predictive value of acute coronary events in the general population of all age ranges remains unclear. Currently, C-reactive protein is not recommended as a cardiovascular disease screening test for average-risk adults without symptoms.
The American Heart Association and U.S. Centers for Disease Control and Prevention have defined risk groups as follows:
* Low Risk: less than 1.0 mg/L
* Average risk: 1.0 to 3.0 mg/L
* High risk: above 3.0 mg/L
But hs-CRP is not to be used alone and should be combined with elevated levels of cholesterol, LDL-C, triglycerides, and glucose level. Smoking, hypertension and diabetes also increase the risk level of cardiovascular disease. | 1 | Applied and Interdisciplinary Chemistry |
Holmes is a keen hillwalker and an enthusiastic aficionado of classical music, from baroque to romantic opera. During his time in Cambridge he was a member and regular volunteer at St Columba's United Reformed Church. He lives in Melbourne and Lorne, Victoria with his wife Jennifer. | 0 | Theoretical and Fundamental Chemistry |
The Schilling test was a medical investigation used for patients with vitamin B (cobalamin) deficiency. The purpose of the test was to determine how well a patient is able to absorb B12 from their intestinal tract. The test is now considered obsolete and is rarely performed, and is no longer available at many medical centers. It is named for Robert F. Schilling. | 1 | Applied and Interdisciplinary Chemistry |
The laser peening process using computer control is described in AMS 2546. Like many other surface enhancement technologies, direct measuring of the results of the process on the workpiece during processing is not practical. Therefore, the process parameters of pulse energy and duration, water and opaque overlays are closely monitored during processing. Other quality control systems are also available that rely on pressure measurements such as electromagnetic acoustic transducers (EMAT), Velocity Interferometer System for Any Reflector (VISAR) and PVDF gauges, and plasma radiometers. Almen strips are also used, but they function as a comparison tool and do not provide a definitive measure of laser peening intensity. The resultant residual stresses imparted by the laser peening process are routinely measured by industry using x-ray diffraction techniques for the purposes of process optimization and quality assurance. | 1 | Applied and Interdisciplinary Chemistry |
Utako Okamoto was married to Shosuke Okamoto and at her death was survived by one daughter, Kumi Nakamura.
She had one miscarriage, which she said was not related to overworking but "coming home late from work".
Ian Roberts, Professor of Epidemiology and Public Health at the London School of Hygiene & Tropical Medicine who had been coordinating the 2010 trauma trial visited Okamoto, then about 92 in Japan. He said that he "found a fascinating character, really lively and vigorous and still very much engaged with research, meeting with researchers, and reading journal articles". | 1 | Applied and Interdisciplinary Chemistry |
In environmental management, water analysis is frequently deployed when pollution is suspected to identify the pollutant in order to take remedial action. The analysis can often enable the polluter to be identified. Such forensic work can examine the ratios of various components and can "type" samples of oils or other mixed organic contaminants to directly link the pollutant with the source.
In drinking water supplies the cause of unacceptable quality can similarly be determined by carefully targeted chemical analysis of samples taken throughout the distribution system.
In manufacturing, off-spec products may be directly tied back to unexpected changes in wet processing stages and analytical chemistry can identify which stages may be at fault and for what reason. | 0 | Theoretical and Fundamental Chemistry |
To date, PAMPA models have been developed that exhibit a high degree of correlation with permeation across a variety of barriers, including Caco-2 cultures, the gastrointestinal tract, blood–brain barrier and skin.
The donor and/or acceptor compartments may contain solubilizing agents, or additives that bind the drugs as they permeate. To improve the in vitro - in vivo correlation and performance of the PAMPA method, the lipid, pH and chemical composition of the system is often designed with biomimetic considerations in mind.
Although active transport is not modeled by the artificial PAMPA membrane, up to 95% of known drugs are absorbed by passive transport. Some experts support a lower figure, so the amount is open to some interpretation. Microtiter plates with 96 wells can be used for the assay which increases the speed and lowers the per sample cost. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, alpha elimination refers to particular types of elimination reactions. The definition of alpha elimination differs for organometallic and organic chemistry. | 0 | Theoretical and Fundamental Chemistry |
Volatile matter in coal refers to the components of coal, except for moisture, which are liberated at high temperature in the absence of air. This is usually a mixture of short- and long-chain hydrocarbons, aromatic hydrocarbons and some sulfur. Volatile matter also evaluate the adsorption application of an activated carbon. The volatile matter of coal is determined under rigidly controlled standards. In Australian and British laboratories this involves heating the coal sample to 900 ± 5 °C (1650 ±10 °F) for 7 min. Also as the rank of coal increases the volatile matter decreases (AMK). | 0 | Theoretical and Fundamental Chemistry |
Determining chirality based on Fischer Projections is effectively the same as the standard method. The primary difference is the benefit that Fischer Projections provide in depicting the orientation of substituents with the vertical and horizontal lines. Considering that orientation of these molecules is already known, it may be properly depicted with wedges and dashes if needed. After this, the priority of each of the groups bonded to the carbon are ranked and the chirality is determined in the standard fashion. While there is no significant difference in the actual process of determining chirality, Fischer Projections allow one to better visualize where substituents are in space making it convenient to assign S or R chirality based on this model. In certain cases, it can be helpful to draw a Fischer Projection from a larger molecule to visualize and determine the chirality of a specific carbon. | 0 | Theoretical and Fundamental Chemistry |
DABCO (1,4-diazabicyclo[2.2.2]octane), also known as triethylenediamine or TEDA, is a bicyclic organic compound with the formula N(CH). This colorless solid is a highly nucleophilic tertiary amine base, which is used as a catalyst and reagent in polymerization and organic synthesis.
It is similar in structure to quinuclidine, but the latter has one of the nitrogen atoms replaced by a carbon atom. Regarding their structures, both DABCO and quinuclidine are unusual in that the methylene hydrogen atoms are eclipsed within each of the three ethylene linkages. Furthermore, the diazacyclohexane rings, of which there are three, adopt the boat conformations, not the usual chair conformations. | 0 | Theoretical and Fundamental Chemistry |
The resorcinarenes are typically prepared by condensation of resorcinol and an aldehyde in acid solution. This reaction was first described by Adolf von Baeyer who described the condensation of resorcinol and benzaldehyde but was unable to elucidate the nature of the product(s). The methods have since been refined. Recrystallization typically gives the desired isomer in quite pure form. However, for certain aldehydes, the reaction conditions lead to significant by-products. Alternative condensation conditions have been developed, including the use of Lewis acid catalysts.
A green chemistry procedure uses solvent-free conditions: resorcinol, an aldehyde, and p-toluenesulfonic acid are ground together in a mortar and pestle at low temperature. | 0 | Theoretical and Fundamental Chemistry |
Histones H3 and H4 from disassembled old nucleosomes are kept in the vicinity and randomly distributed on the newly synthesized DNA. They are assembled by the chromatin assembly factor 1 (CAF-1) complex, which consists of three subunits (p150, p60, and p48). Newly synthesized H3 and H4 are assembled by the replication coupling assembly factor (RCAF). RCAF contains the subunit Asf1, which binds to newly synthesized H3 and H4 proteins. The old H3 and H4 proteins retain their chemical modifications which contributes to the passing down of the epigenetic signature. The newly synthesized H3 and H4 proteins are gradually acetylated at different lysine residues as part of the chromatin maturation process. It is also thought that the old H3 and H4 proteins in the new nucleosomes recruit histone modifying enzymes that mark the new histones, contributing to epigenetic memory. | 1 | Applied and Interdisciplinary Chemistry |
The following is a sample recipe for TBST:
*20 mM Tris
*150 mM NaCl
*0.1% Tween 20
Adjust pH with HCl to pH 7.4–7.6
The simplest way to prepare a TBS-Tween solution is to use TBS-T tablets. They are formulated to give a ready to use TBST solution upon dissolution in 500 ml of deionized water. | 1 | Applied and Interdisciplinary Chemistry |
Ischemic cell death, or oncosis, is a form of accidental cell death. The process is characterized by an ATP depletion within the cell leading to impairment of ionic pumps, cell swelling, clearing of the cytosol, dilation of the endoplasmic reticulum and golgi apparatus, mitochondrial condensation, chromatin clumping, and cytoplasmic bleb formation. Oncosis refers to a series of cellular reactions following injury that precedes cell death. The process of oncosis is divided into three stages. First, the cell becomes committed to oncosis as a result of damage incurred to the plasma membrane through toxicity or ischemia, resulting in the leak of ions and water due to ATP depletion. The ionic imbalance that occurs subsequently causes the cell to swell without a concurrent change in membrane permeability to reverse the swelling. In stage two, the reversibility threshold for the cell is passed and the cell becomes committed to cell death. During this stage the membrane becomes abnormally permeable to trypan blue and propidium iodide, indicating membrane compromise. The final stage is cell death and removal of the cell via phagocytosis mediated by an inflammatory response. | 1 | Applied and Interdisciplinary Chemistry |
Sorption is a physical and chemical process by which one substance becomes attached to another. Specific cases of sorption are treated in the following articles:
; Absorption: "the incorporation of a substance in one state into another of a different state" (e.g., liquids being absorbed by a solid or gases being absorbed by a liquid);
; Adsorption: The physical adherence or bonding of ions and molecules onto the surface of another phase (e.g., reagents adsorbed to a solid catalyst surface);
; Ion exchange: An exchange of ions between two electrolytes or between an electrolyte solution and a complex.
The reverse of sorption is desorption. | 0 | Theoretical and Fundamental Chemistry |
Not much is known about archaeal termination. Euryarchaeal RNAPs seem to terminate on their own when poly-U stretches appear. | 1 | Applied and Interdisciplinary Chemistry |
The earliest reference to waterproof sand is in the 1915 book The Boy Mechanic Book 2 published by Popular Mechanics. The Boy Mechanic states waterproof sand was invented by East Indian magicians. The sand was made by mixing heated sand with melted wax. The wax would repel water when the sand was exposed to water.
Magic sand was originally developed to trap ocean oil spills near the shore. This was done by sprinkling magic sand on floating petroleum, which would then mix with the oil and make it heavy enough to sink. Due to the expense of production, however, it is no longer used for this purpose.
Hydrophobic sand has also been tested by utility companies in Arctic regions as a foundation for junction boxes, as it never freezes. It is also used as an aerating medium for potted plants. | 1 | Applied and Interdisciplinary Chemistry |
Antibody diversity is produced by genetic rearrangement after shuffling and rejoining one of each of the various gene segments for the heavy and light chains. Due to mixing and random recombination of the gene segments errors can occur at the sites where gene segments join with each other. These errors are one of the sources of the antibody diversity that is commonly observed in both the light and heavy chains. Moreover, when B cells continue to proliferate, mutations accumulate at the variable regions through a process called somatic hypermutation. The high concentrations of these mutations at the variable region also produce high antibody diversity. | 1 | Applied and Interdisciplinary Chemistry |
Microorganisms are the earliest form of life on earth, first evolving more than three billion years ago. Our ancestors discovered how to harness the power of microorganisms to make new foods, even if they did not know the science behind what they were doing.
Milestones
1665—Robert Hooke and Antoni Van Leeuwenhoek first observe and describe microorganisms.
1857–1876—Louis Pasteur proves the function of microorganisms in lactic and alcoholic fermentation.
1881—Emil Christian Hansen isolates Saccharomyces carlsbergensis, a pure yeast culture, which is today widely used in brewing of lager beers.
1889–1896—Herbert William Conn, Vilhelm Storch and Hermann Weigmann demonstrate that bacteria are responsible for the acidification of milk and of cream.
1897—Eduard von Freudenreich isolates Lactobacillus brevis.
1919—Sigurd Orla-Jensen classifies lactic acid bacteria on the basis of the bacteria's physiological response patterns.
Starting from 1970s—production of first industrial concentrated cultures, frozen or freeze-dried cultures, for the direct inoculation of processed milk, improving the regularity of production processes. | 1 | Applied and Interdisciplinary Chemistry |
Pesticides can save farmers' money by preventing crop losses to insects and other pests; in the U.S., farmers get an estimated fourfold return on money they spend on pesticides. One study found that not using pesticides reduced crop yields by about 10%. Another study, conducted in 1999, found that a ban on pesticides in the United States may result in a rise of food prices, loss of jobs, and an increase in world hunger.
There are two levels of benefits for pesticide use, primary and secondary. Primary benefits are direct gains from the use of pesticides and secondary benefits are effects that are more long-term. | 1 | Applied and Interdisciplinary Chemistry |
Natural products containing acid anhydrides have been isolated from animals, bacteria and fungi. Examples include cantharidin from species of blister beetle, including the Spanish fly, Lytta vesicatoria, and tautomycin, from the bacterium Streptomyces spiroverticillatus. The maleidride family of fungal secondary metabolites, which possess a wide range of antibiotic and antifungal activity, are alicyclic compounds with maleic anhydride functional groups.
A number of proteins in prokaryotes and eukaryotes undergo spontaneous cleavage between the amino acid residues aspartic acid and proline via an acid anhydride intermediate. In some cases, the anhydride may then react with nucleophiles of other cellular components, such as at the surface of the bacterium Neisseria meningitidis or on proteins localized nearby. | 0 | Theoretical and Fundamental Chemistry |
T7 RNA polymerase - taq polymerase - TATA box - taurochenodeoxycholate 6α-hydroxylase - taxadiene 5alpha-hydroxylase - taxane 10beta-hydroxylase - TAZ zinc finger - Tbf5 protein domain - technology transfer - template - termination codon - terminator - tertiary structure - tet resistance - TGF beta Activation - thymine - tissue-specific expression - tm - trans - trans-feruloyl-CoA hydratase - transcript - transcription - transcription factor - transcription/translation reaction - transcriptional start site - transfection - transformation (genetics) - transformation (with respect to bacteria) - transfection (with respect to cultured cells) - transgene - transgenic - transient transfection - transition - translation - transposition - transposon - transversion - triplet - trisomy - tRNA - tRNA (adenine-N1-)-methyltransferase - tRNA (guanine-N1-)-methyltransferase - TUG-UBL1 protein domain - tumor suppressor - tumor suppressor gene - | 1 | Applied and Interdisciplinary Chemistry |
Enzymes are proteins that act as biological catalysts by accelerating chemical reactions. Enzymes act on small molecules called substrates, which an enzyme converts into products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. The study of how fast an enzyme can transform a substrate into a product is called enzyme kinetics.
The rate of reaction of many chemical reactions shows a linear response as function of the concentration of substrate molecules. Enzymes however display a saturation effect where,, as the substrate concentration is increased the reaction rate reaches a maximum value. Standard approaches to describing this behavior are based on models developed by Michaelis and Menten as well and Briggs and Haldane. Most elementary formulations of these models assume that the enzyme reaction is irreversible, that is product is not converted back to substrate. However, this is unrealistic when describing the kinetics of enzymes in an intact cell because there is product available. Reversible Michaelis–Menten kinetics, using the reversible form of the Michaelis–Menten equation, is therefore important when developing computer models of cellular processes involving enzymes.
In enzyme kinetics, the Michaelis–Menten kinetics kinetic rate law that describes the conversion of one substrate to one product, is often commonly depicted in its irreversible form as:
where is the reaction rate, is the maximum rate when saturating levels of the substrate are present, is the Michaelis constant and the substrate concentration.
In practice, this equation is used to predict the rate of reaction when little or no product is present. Such situations arise in enzyme assays. When used to model enzyme rates , for example, to model a metabolic pathway, this representation is inadequate because under these conditions product is present. As a result, when building computer models of metabolism or other enzymatic processes, it is better to use the reversible form of the Michaelis–Menten equation.
To model the reversible form of the Michaelis–Menten equation, the following reversible mechanism is considered:
To derive the rate equation, it is assumed that the concentration of enzyme-substrate complex is at steady-state, that is .
Following current literature convention, we will be using lowercase Roman lettering to indicate concentrations (this avoids cluttering the equations with square brackets). Thus indicates the concentration of enzyme-substrate complex, ES.
The net rate of change of product (which is equal to ) is given by the difference in forward and reverse rates:
The total level of enzyme moiety is the sum total of free enzyme and enzyme-complex, that is . Hence the level of free is given by the difference in the total enzyme concentration, and the concentration of complex, that is:
Using mass conservation we can compute the rate of change of using the balance equation:
where has been replaced using . This leaves as the only unknown. Solving for gives:
Inserting into the rate equation and rearranging gives:
The following substitutions are now made:
and
after rearrangement, we obtain the reversible Michaelis–Menten equation in terms of four constants: | 0 | Theoretical and Fundamental Chemistry |
The Stanton number is a useful measure of the rate of change of the thermal energy deficit (or excess) in the boundary layer due to heat transfer from a planar surface. If the enthalpy thickness is defined as:
Then the Stanton number is equivalent to
for boundary layer flow over a flat plate with a constant surface temperature and properties. | 1 | Applied and Interdisciplinary Chemistry |
Both families in Group VII have DNA genomes contained within the invading virus particles. The DNA genome is transcribed into both mRNA, for use as a transcript in protein synthesis, and pre-genomic RNA, for use as the template during genome replication. Virally encoded reverse transcriptase uses the pre-genomic RNA as a template for the creation of genomic DNA.
Group VII includes:
* Family Caulimoviridae — e.g. Cauliflower mosaic virus
* Family Hepadnaviridae — e.g. Hepatitis B virus
The latter family is closely related to the newly proposed
* Family Nackednaviridae — e.g. African cichlid nackednavirus (ACNDV), formerly named African cichlid hepatitis B virus (ACHBV).
whilst families Belpaoviridae, Metaviridae, Pseudoviridae, Retroviridae, and Caulimoviridae constitute the order Ortervirales. | 1 | Applied and Interdisciplinary Chemistry |
Continuous dynamic recrystallization is common in materials with high stacking-fault energies. It occurs when low angle grain boundaries form and evolve into high angle boundaries, forming new grains in the process. For continuous dynamic recrystallization there is no clear distinction between nucleation and growth phases of the new grains.
Continuous Dynamic Recrystallization has 4 main characteristics:
* As strain increases, stress increases
* As strain increases, subgrain boundary misorientation increases
* As low angle grain boundaries evolve into high angle grain boundaries, the misorientation increases homogeneously
* As deformation increases, crystallite size decreases
There are three main mechanisms of continuous dynamic recrystallization:
First, continuous dynamic recrystallization can occur when low angle grain boundaries are assembled from dislocations formed within the grain. When the material is subjected to continued stress, the misorientation angle increases until the critical angle is achieved, creating a high angle grain boundary. This evolution can be promoted by the pinning of subgrain boundaries.
Second, continuous dynamic recrystallization can occur through subgrain rotation recrystallization; subgrains rotate increasing the misorientation angle. Once the misorientation angle exceeds the critical angle, the former subgrains qualify as independent grains.
Third, continuous dynamic recrystallization can occur due to deformation caused by microshear bands. Subgrains are assembled by dislocations within the grain formed during work hardening. If microshear bands are formed within the grain, the stress they introduce rapidly increases the misorientation of low angle grain boundaries, transforming them into high angle grain boundaries. However, the impact of microshear bands are localized, so this mechanism preferentially impacts regions which deform heterogeneously, such as microshear bands or areas near pre-existing grain boundaries. As recrystallization proceeds, it spreads out from these zones, generating a homogenous, equiaxed microstructure. | 1 | Applied and Interdisciplinary Chemistry |
Blood pH and concentrations of several chemicals are tested in a corpse to help determine the time of death of the victim, also known as the post-mortem interval. These chemicals include lactic acid, hypoxanthine, uric acid, ammonia, NADH and formic acid.
The decrease in the concentration of oxygen because of the lack of circulation causes a dramatic switch from aerobic to anaerobic metabolism
This type of analysis can be used to help diagnose various different types of deaths such as: drowning, anaphylactic shock, hypothermia or any deaths related to alcohol or diabetes. Although these types of diagnosis become very difficult because of the changes to the body and biochemical measurements vary after death. | 1 | Applied and Interdisciplinary Chemistry |
The most common powder X-ray diffraction (XRD) refinement technique used today is based on the method proposed in the 1960s by Hugo Rietveld. The Rietveld method fits a calculated profile (including all structural and instrumental parameters) to experimental data. It employs the non-linear least squares method, and requires the reasonable initial approximation of many free parameters, including peak shape, unit cell dimensions and coordinates of all atoms in the crystal structure. Other parameters can be guessed while still being reasonably refined. In this way one can refine the crystal structure of a powder material from PXRD data. The successful outcome of the refinement is directly related to the quality of the data, the quality of the model (including initial approximations), and the experience of the user.
The Rietveld method is an incredibly powerful technique which began a remarkable era for powder XRD and materials science in general. Powder XRD is at heart a very basic experimental technique with diverse applications and experimental options. Despite being slightly limited by the one-dimensionality of PXRD data and limited resolution, powder XRD's power is astonishing. It is possible to determine the accuracy of a crystal structure model by fitting a profile to a 1D plot of observed intensity vs angle. It is important to remember that Rietveld refinement requires a crystal structure model and offers no way to come up with such a model on its own. However, it can be used to find structural details missing from a partial or complete ab initio structure solution, such as unit cell dimensions, phase quantities, crystallite sizes/shapes, atomic coordinates/bond lengths, micro strain in crystal lattice, texture, and vacancies. | 0 | Theoretical and Fundamental Chemistry |
An example demonstrating how drug combination with additive effect can cause adverse effects is the co-administration of ACEI and potassium-sparing diuretics. Despite having different mechanisms of action, the drugs are able to reduce potassium excretion from the body. Hence, both ACEI and potassium-sparing diuretics have the side effect of hyperkalemia. When two drugs are used together, the risk of having hyperkalemia is doubled. Since hyperkalemia has the potential to cause arrhythmia and metabolic acidosis, the combination of ACEI and potassium-sparing diuretics is avoided. | 1 | Applied and Interdisciplinary Chemistry |
Rewarming can be done with a number of methods including passive external rewarming, active external rewarming, and active internal rewarming. Passive external rewarming involves the use of a person's own ability to generate heat by providing properly insulated dry clothing and moving to a warm environment. Passive external rewarming is recommended for those with mild hypothermia.
Active external rewarming involves applying warming devices externally, such as a heating blanket. These may function by warmed forced air (Bair Hugger is a commonly used device), chemical reactions, or electricity. In wilderness environments, hypothermia may be helped by placing hot water bottles in both armpits and in the groin. Active external rewarming is recommended for moderate hypothermia. Active core rewarming involves the use of intravenous warmed fluids, irrigation of body cavities with warmed fluids (the chest or abdomen), use of warm humidified inhaled air, or use of extracorporeal rewarming such as via a heart lung machine or extracorporeal membrane oxygenation (ECMO). Extracorporeal rewarming is the fastest method for those with severe hypothermia. When severe hypothermia has led to cardiac arrest, effective extracorporeal warming results in survival with normal mental function about 50% of the time. Chest irrigation is recommended if bypass or ECMO is not possible.
Rewarming shock (or rewarming collapse) is a sudden drop in blood pressure in combination with a low cardiac output which may occur during active treatment of a severely hypothermic person. There was a theoretical concern that external rewarming rather than internal rewarming may increase the risk. These concerns were partly believed to be due to afterdrop, a situation detected during laboratory experiments where there is a continued decrease in core temperature after rewarming has been started. Recent studies have not supported these concerns, and problems are not found with active external rewarming. | 1 | Applied and Interdisciplinary Chemistry |
Acid–base titrations depend on the neutralization between an acid and a base when mixed in solution. In addition to the sample, an appropriate pH indicator is added to the titration chamber, representing the pH range of the equivalence point. The acid–base indicator indicates the endpoint of the titration by changing color. The endpoint and the equivalence point are not exactly the same because the equivalence point is determined by the stoichiometry of the reaction while the endpoint is just the color change from the indicator. Thus, a careful selection of the indicator will reduce the indicator error. For example, if the equivalence point is at a pH of 8.4, then the phenolphthalein indicator would be used instead of Alizarin Yellow because phenolphthalein would reduce the indicator error. Common indicators, their colors, and the pH range in which they change color are given in the table above. When more precise results are required, or when the reagents are a weak acid and a weak base, a pH meter or a conductance meter are used.
For very strong bases, such as organolithium reagent, metal amides, and hydrides, water is generally not a suitable solvent and indicators whose pKa are in the range of aqueous pH changes are of little use. Instead, the titrant and indicator used are much weaker acids, and anhydrous solvents such as THF are used.
The approximate pH during titration can be approximated by three kinds of calculations. Before beginning of titration, the concentration of is calculated in an aqueous solution of weak acid before adding any base. When the number of moles of bases added equals the number of moles of initial acid or so called equivalence point, one of hydrolysis and the pH is calculated in the same way that the conjugate bases of the acid titrated was calculated. Between starting and end points, is obtained from the Henderson-Hasselbalch equation and titration mixture is considered as buffer. In Henderson-Hasselbalch equation the and are said to be the molarities that would have been present even with dissociation or hydrolysis. In a buffer, can be calculated exactly but the dissociation of , the hydrolysis of and self-ionization of water must be taken into account. Four independent equations must be used:
In the equations, and are the moles of acid () and salt ( where X is the cation), respectively, used in the buffer, and the volume of solution is . The law of mass action is applied to the ionization of water and the dissociation of acid to derived the first and second equations. The mass balance is used in the third equation, where the sum of and must equal to the number of moles of dissolved acid and base, respectively. Charge balance is used in the fourth equation, where the left hand side represents the total charge of the cations and the right hand side represents the total charge of the anions: is the molarity of the cation (e.g. sodium, if sodium salt of the acid or sodium hydroxide is used in making the buffer). | 0 | Theoretical and Fundamental Chemistry |
As aromatic compounds have been exhausted to a large extent as building blocks for life science products, N-heterocyclic structures prevail nowadays. They are found in many natural products, such as chlorophyll, hemoglobin, and the vitamins biotin, folic acid, niacin (PP), pyridoxine (vitamin B), riboflavin (vitamin B), and thiamine (vitamin B). In synthetic life science products, N-heterocyclic moieties are widely used in both pharmaceuticals and agrochemicals.
Thus, β-lactams are structural elements of penicillin and cephalosporin antibiotics, imidazoles are found both in modern herbicides, e.g. Arsenal (imazapyr) and pharmaceuticals, e.g. the antiulcerants Tagamet (cimetidine. see above) and Nexium (omeprazole), the antimycotics Daktarin (miconazole), Fungarest (ketoconazole) and Travogen (isoconazole). Tetrazoles and tetrazolidines are pivotal parts of the "sartan" class of hypertensives, e.g. Candesartan cilexetil (candesartan), Avapro (irbesartan), Cozaar (losartan) and Diovan (valsartan).
A vast array of pharmaceuticals and agrochemicals are based on pyrimidines, such as Vitamin B1 (thiamine), the sulfonamide antibiotics, e.g. Madribon (sulfadimethoxime) and –half a century later– the sulfonyl urea herbicides, e.g. Eagle (amidosulfuron) and Londax (bensulfuron-methyl). Benzodiazepine derivatives are the pivotal structural elements of breakthrough CNS Drugs, such as Librium (chlordiazepoxide) and Valium (diazepam). Pyridine derivatives are found in both well-known Diquat and Chlorpyrifos herbicides, and in modern nicotinoid insecticides, such as Imidacloprid.
Even modern pigments, such as diphenylpyrazolopyrazoles, quinacridones, and engineering plastics, such as polybenzimidazoles, polyimides, and triazine resins, exhibit an N-heterocyclic structure. | 0 | Theoretical and Fundamental Chemistry |
Vervet monkeys (Chlorocebus Pygerythus) are some of the most studied monkeys when it comes to vocalization and alarm calls within the nonhuman primates. They are most known for making alarm calls in the presence of their most common predators (leopards, eagles, and snakes). The alarm calls of the Vervet monkey are considered arbitrary in relation to the predator that it signifies. In the sense that the calls may be distinct to the threat that the monkeys are seeing but arbitrary in that it does not mimic the sounds of the predator. This is like yelling "Danger!" when seeing an angry dog instead of making barking sounds. This type of alarm calls is seen as the earliest example of symbolic communication (the relationship between signifier and signified is arbitrary and purely conventional) in nonhuman primates.
However, there is much debate on whether the vervet monkeys alarm calls are actual "words" in the sense of purposely manipulating sounds to communicate specific meaning or are unintentional sounds that are made when interacting with an outside stimulus. Like small children who cannot communicate words effectively make random noises when being played with or are stimulated by something in their immediate environment. As children grow and begin learning how to communicate the noises, they make are very broad in relation to their environment. They begin to recognize the things in their environment but there more things than known words or noises so a certain sound may reference multiple things. As children get older, they can become more specific about the noises and words made in relation to the things in their environment. It is thought that as Vervet monkeys get older they are able to learn and break the broad categories into more specific sub categories to a specific context.
In an experiment conducted by Dr. Tabitha Price, they used custom software to gather the acoustic sounds of male and female Vervet monkeys from East Africa and male Vervet monkey from South Africa. The point of the experiment was to gather the acoustic sounds of these monkeys when stimulated by the presence of snakes (mainly Python), raptors, terrestrial animals (mostly Leopards), and aggression. Then to determine if the calls could be distinguished with a known context.
The experiment determined that while the Vervet monkeys were able to categorize different predators and members of different social groups, however their ability to communicate specific threats is not proven. The chirps and barks that Vervet monkeys make as an eagle swoops in are the same chirps and barks that are made in moments of high arousal. Similarly, the barks made for leopards are the same that are made during aggressive interactions. The environment that they exist in is too complex for their ability to communicate about everything in their environment specifically..
In an experiment conducted by Dr. Julia Fischer, a drone was flown over Vervet monkeys and recorded the sounds produced. The Vervet monkeys made alarm calls that were almost identical to the eagle calls of East African Vervets. When a sound recording of the drone was played back a few days later to a monkey that was alone and away from the main group it looked up and scanned the sky. Dr. Fischer concluded that Vervet monkeys can be exposed to a new threat once and understand what it means.
It is still debated whether or not Vervet monkeys are actually aware of what the alarm calls mean. One side of the argument is that the monkeys give alarm calls because they are simply excited. The other side of the argument is that the alarm calls create mental representation of predators in the listeners minds. The common middle ground argument is that they give alarm calls because they want others to elicit a certain response, not necessarily because they want the group to think that there is a specific threat near.
Ultimately there is not enough evidence to support whether or not the calls are simply identifying a threat or calling for specific action due to the threat. | 1 | Applied and Interdisciplinary Chemistry |
A slosh baffle is a device used to dampen the adverse effects of liquid slosh in a tank. Slosh baffles have been implemented in a variety of applications including tanker trucks, and liquid rockets, although any moving tank containing liquid may employ them. | 1 | Applied and Interdisciplinary Chemistry |
In type I reactions, the photoactivated Sens* interacts with the substrate to yield a radical substrate, usually through the homolytic bond breaking of a hydrogen bond on the substrate. This substrate radical then interacts with O (ground state) to yield a substrate-O radical. Such a radical is generally quenched by abstracting a hydrogen from another substrate molecule or from the solvent. This process allows for chain propagation of the reaction. | 0 | Theoretical and Fundamental Chemistry |
A Phase 3 clinical trial of LMTM (TauRx0237 or LMT-X), a derivative of methylene blue, failed to show any benefit against cognitive or functional decline in people with mild to moderate Alzheimer's disease. Disease progression for both the drug and the placebo were practically identical. | 0 | Theoretical and Fundamental Chemistry |
In general the product distribution of hydrocarbons formed during the Fischer–Tropsch process follows an Anderson–Schulz–Flory distribution, which can be expressed as:
: = (1 − α)α
where W is the weight fraction of hydrocarbons containing n carbon atoms, and α is the chain growth probability or the probability that a molecule will continue reacting to form a longer chain. In general, α is largely determined by the catalyst and the specific process conditions.
Examination of the above equation reveals that methane will always be the largest single product so long as α is less than 0.5; however, by increasing α close to one, the total amount of methane formed can be minimized compared to the sum of all of the various long-chained products. Increasing α increases the formation of long-chained hydrocarbons. The very long-chained hydrocarbons are waxes, which are solid at room temperature. Therefore, for production of liquid transportation fuels it may be necessary to crack some of the FT products. In order to avoid this, some researchers have proposed using zeolites or other catalyst substrates with fixed sized pores that can restrict the formation of hydrocarbons longer than some characteristic size (usually n < 10). This way they can drive the reaction so as to minimize methane formation without producing many long-chained hydrocarbons. Such efforts have had only limited success. | 0 | Theoretical and Fundamental Chemistry |
The term self-siphon is used in a number of ways. Liquids that are composed of long polymers can "self-siphon" and these liquids do not depend on atmospheric pressure. Self-siphoning polymer liquids work the same as the siphon-chain model where the lower part of the chain pulls the rest of the chain up and over the crest. This phenomenon is also called a tubeless siphon.
"Self-siphon" is also often used in sales literature by siphon manufacturers to describe portable siphons that contain a pump. With the pump, no external suction (e.g. from a person's mouth/lungs) is required to start the siphon and thus the product is described as a "self-siphon".
If the upper reservoir is such that the liquid there can rise above the height of the siphon crest, the rising liquid in the reservoir can "self-prime" the siphon and the whole apparatus be described as a "self-siphon". Once primed, such a siphon will continue to operate until the level of the upper reservoir falls below the intake of the siphon. Such self-priming siphons are useful in some rain gauges and dams. | 1 | Applied and Interdisciplinary Chemistry |
Like methane itself, halomethanes are tetrahedral molecules. The halogen atoms differ greatly in size and charge from hydrogen and from each other. Consequently, most halomethanes deviate from the perfect tetrahedral symmetry of methane.
The physical properties of halomethanes depend on the number and identity of the halogen atoms in the compound. In general, halomethanes are volatile but less so than methane because of the polarizability of the halides. The polarizability of the halides and the polarity of the molecules makes them useful as solvents. The halomethanes are far less flammable than methane. Broadly speaking, reactivity of the compounds is greatest for the iodides and lowest for the fluorides. | 1 | Applied and Interdisciplinary Chemistry |
With knowledge of substituent constants it is now possible to obtain reaction constants for a wide range of organic reactions. The archetypal reaction is the alkaline hydrolysis of ethyl benzoate (R=R'=H) in a water/ethanol mixture at 30 °C. Measurement of the reaction rate k combined with that of many substituted ethyl benzoates ultimately result in a reaction constant of +2.498.
Reaction constants are known for many other reactions and equilibria. Here is a selection of those provided by Hammett himself (with their values in parentheses):
* the hydrolysis of substituted cinnamic acid ester in ethanol/water (+1.267)
* the ionization of substituted phenols in water (+2.008)
* the acid catalyzed esterification of substituted benzoic esters in ethanol (-0.085)
* the acid catalyzed bromination of substituted acetophenones (Ketone halogenation) in an acetic acid/water/hydrochloric acid (+0.417)
* the hydrolysis of substituted benzyl chlorides in acetone-water at 69.8 °C (-1.875).
The reaction constant, or sensitivity constant, ρ, describes the susceptibility of the reaction to substituents, compared to the ionization of benzoic acid. It is equivalent to the slope of the Hammett plot. Information on the reaction and the associated mechanism can be obtained based on the value obtained for ρ. If the value of:
# ρ>1, the reaction is more sensitive to substituents than benzoic acid and negative charge is built during the reaction (or positive charge is lost).
# 0<ρ<1, the reaction is less sensitive to substituents than benzoic acid and negative charge is built (or positive charge is lost).
# ρ=0, no sensitivity to substituents, and no charge is built or lost.
# ρ<0, the reaction builds positive charge (or loses negative charge).
These relations can be exploited to elucidate the mechanism of a reaction. As the value of ρ is related to the charge during the rate determining step, mechanisms can be devised based on this information. If the mechanism for the reaction of an aromatic compound is thought to occur through one of two mechanisms, the compound can be modified with substituents with different σ values and kinetic measurements taken. Once these measurements have been made, a Hammett plot can be constructed to determine the value of ρ. If one of these mechanisms involves the formation of charge, this can be verified based on the ρ value. Conversely, if the Hammett plot shows that no charge is developed, i.e. a zero slope, the mechanism involving the building of charge can be discarded.
Hammett plots may not always be perfectly linear. For instance, a curve may show a sudden change in slope, or ρ value. In such a case, it is likely that the mechanism of the reaction changes upon adding a different substituent. Other deviations from linearity may be due to a change in the position of the transition state. In such a situation, certain substituents may cause the transition state to appear earlier (or later) in the reaction mechanism. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, mechanically interlocked molecular architectures (MIMAs) are molecules that are connected as a consequence of their topology. This connection of molecules is analogous to keys on a keychain loop. The keys are not directly connected to the keychain loop but they cannot be separated without breaking the loop. On the molecular level, the interlocked molecules cannot be separated without the breaking of the covalent bonds that comprise the conjoined molecules; this is referred to as a mechanical bond. Examples of mechanically interlocked molecular architectures include catenanes, rotaxanes, molecular knots, and molecular Borromean rings. Work in this area was recognized with the 2016 Nobel Prize in Chemistry to Bernard L. Feringa, Jean-Pierre Sauvage, and J. Fraser Stoddart.
The synthesis of such entangled architectures has been made efficient by combining supramolecular chemistry with traditional covalent synthesis, however mechanically interlocked molecular architectures have properties that differ from both "supramolecular assemblies" and "covalently bonded molecules". The terminology "mechanical bond" has been coined to describe the connection between the components of mechanically interlocked molecular architectures. Although research into mechanically interlocked molecular architectures is primarily focused on artificial compounds, many examples have been found in biological systems including: cystine knots, cyclotides or lasso-peptides such as microcin J25 which are proteins, and a variety of peptides. | 0 | Theoretical and Fundamental Chemistry |
A gas network is in the steady state when the values of gas flow characteristics are independent of time and system described by the set of nonlinear equations. The goal of simple simulation of a gas network is usually that of computing the values of nodes pressures, loads and the values of flows in the individual pipes. The pressures at the nodes and the flow rates in the pipes must satisfy the flow equations, and together with nodes loads must fulfill the first and second Kirchhoff's laws.
There are many methods of analyzing the mathematical models of gas networks but they can be divided into two types as the networks, the solvers for low pressure networks and solvers for high pressure networks.<br />
The networks equations are nonlinear and are generally solved by some of Newton iteration; rather than use the full set of variables it is possible to eliminate some of them. Based on the type of elimination we can get solution techniques are termed either nodal or loop methods. | 1 | Applied and Interdisciplinary Chemistry |
Eukaryotic RNA must undergo a series of modifications in order to be exported from the nucleus and successfully translated into function proteins, many of which are dependent on mRNA capping, the first mRNA modification to take place. 5 capping is essential for mRNA stability, enhancing mRNA processing, mRNA export and translation. After successful capping, an additional phosphorylation event initiates the recruitment of machinery necessary for RNA splicing, a process by which introns are removed to produce a mature mRNA. The addition of the cap onto mRNA confers protection to the transcript from exonucleases that degrade unprotected RNA and assist in the nuclear export transport process so that the mRNA can be translated to form proteins. The function of the 5 cap is essential to the ultimate expression of the RNA. | 1 | Applied and Interdisciplinary Chemistry |
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