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In 2014 based on their research on the northern United States Atlantic marine continental margins from Cape Hatteras to Georges Bank, a group of scientists from the US Geological Survey, the Department of Geosciences, Mississippi State University, Department of Geological Sciences, Brown University and Earth Resources Technology, found widespread leakage of methane from the seafloor, but they did not assign specific dates, beyond suggesting that some of the seeps were more than 1000 years old. In March 2017, a meta-analysis by the USGS Gas Hydrates Project concluded:
In June 2017, scientists from the Center for Arctic Gas Hydrate (CAGE), Environment and Climate at the University of Tromsø, published a study describing over a hundred ocean sediment craters, some 300 meters wide and up to 30 meters deep, formed due to explosive eruptions, attributed to destabilizing methane hydrates, following ice-sheet retreat during the last glacial period, around 15,000 years ago, a few centuries after the Bølling–Allerød warming. These areas around the Barents Sea, still seep methane today, and still existing bulges with methane reservoirs could eventually have the same fate. Later that same year, the Arctic Council published SWIPA 2017 report, where it cautioned "Arctic sources and sinks of greenhouse gases are still hampered by data and knowledge gaps."
In 2018, a perspective piece devoted to tipping points in the climate system suggested that the climate change contribution from methane hydrates would be "negligible" by the end of the century, but could amount to on the millennial timescales. In 2021, the IPCC Sixth Assessment Report no longer included methane hydrates in the list of potential tipping points, and says that "it is very unlikely that CH4 emissions from clathrates will substantially warm the climate system over the next few centuries." The report had also linked terrestrial hydrate deposites to gas emission craters discovered in the Yamal Peninsula in Siberia, Russia beginning in July 2014, but noted that since terrestrial gas hydrates predominantly form at a depth below 200 metres, a substantial response within the next few centuries can be ruled out. Likewise, a 2022 assessment of tipping points described methane hydrates as a "threshold-free feedback" rather than a tipping point. | 0 | Theoretical and Fundamental Chemistry |
The concept for an airborne LIFT instrument was developed by Zbigniew Kolber at Rutgers University in 1998. The first field test was conducted at Biosphere 2 in Arizona in 2002 using a stationary large LIFT setup equipped with a laser operating at a distance of up to 50 meters. The prototype instrument was later refined and improved at the Carnegie Institute, Stanford, and the Agricultural Research Center in Arizona, where the first attempt to operate it on a tractor frame was made. In 2010 several instruments were transferred from Carnegie to the Forschungszentrum Jülich where they are used for laboratory and field research in robotic positioning systems for non-invasive, high-throughput data acquisition. | 0 | Theoretical and Fundamental Chemistry |
Researchers prove that in the developing CNS, Nav1.2 is initially expressed at all forming nodes of Ranvier. Upon maturation, nodal Nav1.2 is down-regulated and replaced by Nav1.6. Nav1.2 is also expressed during PNS node formation, which suggests that the switching of Nav-channel subtypes is a general phenomenon in the CNS and PNS. In this same investigation, it was shown that Nav1.6 and Nav1.2 colocalize at many nodes of Ranvier during early myelination. This also led to the suggestion that early clusters of Nav1.2 and Nav1.6 channels are destined to later become nodes of Ranvier. Neurofascin is also reported to be one of the first proteins to accumulate at newly forming nodes of Ranvier. They are also found to provide the nucleation site for attachment of ankyrin G, Nav channels, and other proteins. The recent identification of the Schwann cell microvilli protein gliomedin as the likely binding partner of axonal neurofascin brings forward substantial evidence for the importance of this protein in recruiting Nav channels to the nodes of Ranvier. Furthermore, Lambert et al. and Eshed et al. also indicates that neurofascin accumulates before Nav channels and is likely to have crucial roles in the earliest events associated with node of Ranvier formation. Thus, multiple mechanisms may exist and work synergistically to facilitate clustering of Nav channels at nodes of Ranvier. | 1 | Applied and Interdisciplinary Chemistry |
Fully developed heat flow in a pipe can be considered in the following situation. If the wall of the pipe is constantly heated or cooled so that the heat flux from the wall to the fluid via convection is a fixed value, then the bulk temperature of the fluid steadily increases or decreases respectively at a fixed rate along the flow direction.
An example can be a pipe entirely covered by an electrical heating pad with the flow being introduced after a uniform heat flux from the pad is achieved. At some distance away from the entrance of the fluid, fully developed heat flow is achieved when the heat transfer coefficient of the fluid becomes constant and the temperature profile has the same shape along the flow. This distance is defined as the thermal entrance length, which is important for engineers to design efficient heat transfer processes. | 1 | Applied and Interdisciplinary Chemistry |
Actinides with odd neutron number are generally fissile (with thermal neutrons), whereas those with even neutron number are generally not, though they are fissionable with fast neutrons. All observationally stable odd-odd nuclides have nonzero integer spin. This is because the single unpaired neutron and unpaired proton have a larger nuclear force attraction to each other if their spins are aligned (producing a total spin of at least 1 unit), instead of anti-aligned. See deuterium for the simplest case of this nuclear behavior.
Only , , and have odd neutron number and are the most naturally abundant isotope of their element. | 0 | Theoretical and Fundamental Chemistry |
In case the following power-law conformal map is applied, from to :
then, writing in polar coordinates as , we have
In the figures to the right examples are given for several values of . The black line is the boundary of the flow, while the darker blue lines are streamlines, and the lighter blue lines are equi-potential lines. Some interesting powers are:
*: this corresponds with flow around a semi-infinite plate,
*: flow around a right corner,
*: a trivial case of uniform flow,
*: flow through a corner, or near a stagnation point, and
*: flow due to a source doublet
The constant is a scaling parameter: its absolute value determines the scale, while its argument introduces a rotation (if non-zero). | 1 | Applied and Interdisciplinary Chemistry |
Sperm banks make information available about the sperm donors whose donations they hold to enable customers to select the donor whose sperm they wish to use. This information is often available by way of an online catalog. Subscription fees to be able to view the sperm donor through California Cryobank, for example, start at $145. This cost could potentially be a barrier for many on limited income and may not have discretionary income to spend on sperm donor services.
A sperm bank will also usually have facilities to help customers to make their choice and they will be able to advise on the suitability of donors for individual donors and their partners.
Where the recipient has a partner, they may prefer to use sperm from a donor whose physical features are similar to those of their partner if they have one. In some cases, the choice of a donor with the correct blood group will be paramount, with particular considerations for the protection of recipients with negative blood groups. If a surrogate is to be used, such as where the customer is not intending to carry the child, considerations about their blood group etc. will also need to be taken into account. Similar considerations will apply where both partners in a lesbian couple intend to have a child using the same donor.
Information made available by a sperm bank will usually include the race, height, weight, blood group, health and eye color of the donor. Sometimes information about the donors age, family history and educational achievements will also be given. Some sperm banks make a personal profile of a donor available and occasionally more information may be purchased about a donor, either in the form of a DVD or in written form. Catalogs usually state whether samples supplied by a particular donor have already given rise to pregnancies, but this is not necessarily a guide to the fecundity of the sperm since a donor may not have been in the program long enough for any pregnancies to have been recorded. The donors educational qualification is also taken into account when choosing a donor.
If an individual intends to have more than one child, they may wish to have the additional child or children by the same donor. Sperm banks will usually advise whether sufficient stocks of sperm are available from a particular donor for subsequent pregnancies, and they normally have facilities available so that the woman may purchase and store additional vials from that donor on payment of an appropriate fee. These will be stored until required for subsequent pregnancies or they may be on-sold if they become surplus to the woman's requirements.
The catalogue will also state whether samples of sperm are available for ICI, IUI, or IVF use. | 1 | Applied and Interdisciplinary Chemistry |
Thigmonastic movements, those that occur in response to touch, are used as a defense in some plants. The leaves of the sensitive plant, Mimosa pudica, close up rapidly in response to direct touch, vibration, or even electrical and thermal stimuli. The proximate cause of this mechanical response is an abrupt change in the turgor pressure in the pulvini at the base of leaves resulting from osmotic phenomena. This is then spread via both electrical and chemical means through the plant; only a single leaflet need be disturbed. This response lowers the surface area available to herbivores, which are presented with the underside of each leaflet, and results in a wilted appearance. It may also physically dislodge small herbivores, such as insects. | 1 | Applied and Interdisciplinary Chemistry |
Endoglin (ENG) is a type I membrane glycoprotein located on cell surfaces and is part of the TGF beta receptor complex. It is also commonly referred to as CD105, END, FLJ41744, HHT1, ORW and ORW1. It has a crucial role in angiogenesis, therefore, making it an important protein for tumor growth, survival and metastasis of cancer cells to other locations in the body. | 1 | Applied and Interdisciplinary Chemistry |
Early fluctuations in oxygen concentration had little direct effect on life, with mass extinctions not observed until around the start of the Cambrian period, . The presence of provided life with new opportunities. Aerobic metabolism is more efficient than anaerobic pathways, and the presence of oxygen created new possibilities for life to explore. Since the start of the Cambrian period, atmospheric oxygen concentrations have fluctuated between 15% and 35% of atmospheric volume. 430-million-year-old fossilized charcoal produced by wildfires show that the atmospheric oxygen levels in the Silurian must have been equivalent to, or possibly above, present day levels. The maximum of 35% was reached towards the end of the Carboniferous period (about 300 million years ago), a peak which may have contributed to the large size of various arthropods, including insects, millipedes and scorpions. Whilst human activities, such as the burning of fossil fuels, affect relative carbon dioxide concentrations, their effect on the much larger concentration of oxygen is less significant.
The Great Oxygenation Event had the first major effect on the course of evolution. Due to the rapid buildup of oxygen in the atmosphere, many organisms not reliant on oxygen to live died.
The concentration of oxygen in the atmosphere is often cited as a possible contributor to large-scale evolutionary phenomena, such as the Avalon explosion, the Cambrian explosion, trends in animal body size, and other diversification and extinction events.
Data show an increase in biovolume soon after the Great Oxygenation Event by more than 100-fold and a moderate correlation between atmospheric oxygen and maximum body size later in the geological record. The large size of many arthropods in the Carboniferous period, when the oxygen concentration in the atmosphere reached 35%, has been attributed to the limiting role of diffusion in these organisms metabolism. But Haldanes essay points out that it would only apply to insects. However, the biological basis for this correlation is not firm, and many lines of evidence show that oxygen concentration is not size-limiting in modern insects. Ecological constraints can better explain the diminutive size of post-Carboniferous dragonflies – for instance, the appearance of flying competitors such as pterosaurs, birds and bats.
Rising oxygen concentrations have been cited as one of several drivers for evolutionary diversification, although the physiological arguments behind such arguments are questionable, and a consistent pattern between oxygen concentrations and the rate of evolution is not clearly evident. The most celebrated link between oxygen and evolution occurs at the end of the last of the Snowball Earth glaciations, where complex multicellular life is first found in the fossil record. Under low oxygen concentrations and before the evolution of nitrogen fixation, biologically-available nitrogen compounds were in limited supply and periodic "nitrogen crises" could render the ocean inhospitable to life. Significant concentrations of oxygen were just one of the prerequisites for the evolution of complex life. Models based on uniformitarian principles (i.e. extrapolating present-day ocean dynamics into deep time) suggest that such a concentration was only reached immediately before metazoa first appeared in the fossil record. Further, anoxic or otherwise chemically "inhospitable" oceanic conditions that resemble those supposed to inhibit macroscopic life re-occur at intervals through the early Cambrian, and also in the late Cretaceous – with no apparent effect on lifeforms at these times. This might suggest that the geochemical signatures found in ocean sediments reflect the atmosphere in a different way before the Cambrian – perhaps as a result of the fundamentally different mode of nutrient cycling in the absence of planktivory.
An oxygen-rich atmosphere can release phosphorus and iron from rock, by weathering, and these elements then become available for sustenance of new species whose metabolisms require these elements as oxides. | 0 | Theoretical and Fundamental Chemistry |
Biebrich scarlet (C.I. 26905) is a molecule used in Lillie's trichrome.
The dye was created in 1878 by the German chemist Rudolf Nietzki.
Biebrich scarlet dyes are used to color hydrophobic materials like fats and oils. The dye is an illegal dye for food additives because of its carcinogenic properties. Biebrich scarlet can have harmful effects on living and non-living organisms in natural water, therefore the pollutant must be removed. Removal of the pollutant involves absorption, membrane filtration, precipitation, ozonation, fungal detachment, and electrochemical separation. Hydrogel absorbents have active sites to which the dye is held using electrostatic interactions. Photocatalysis allows for almost total degradation of Biebrich scarlet azo dye bonds in less than 10 hours. Degradation of Biebrich scarlet is also observed using lignin peroxidase enzyme from wood rotting fungus in the presence of mediators like 2-chloro-1,4-dimethoxybenzene. | 1 | Applied and Interdisciplinary Chemistry |
* Math
* Chemistry
* Physics
* Fluid Mechanics
* Chemical Reaction Engineering
* Thermodynamics
* Chemical Thermodynamics
* Engineering Mechanics
* Fluid Dynamics
* Heat Transfer
* Mass Transfer
* Transport Phenomena
* Green Chemistry and Sustainability
* Process Control
* Process Instrumentation
* Process Safety
* Unit Operation
* Process Design
* Chemical Process Modeling and Simulation
* Engineering Economics | 1 | Applied and Interdisciplinary Chemistry |
Consider the element at radius r, shown in Fig. 1, which has the infinitesimal length dr and the width b. The motion of the element in an aircraft propeller in flight is along a helical path determined by the forward velocity V of the aircraft and the tangential velocity 2πrn of the element in the plane of the propeller disc, where n represents the revolutions per unit time. The velocity of the element with respect to the air Vr is then the resultant of the forward and tangential velocities, as shown in Fig. 2. Call the angle between the direction of motion of the element and the plane of rotation Φ, and the blade angle β. The angle of attack α of the element relative to the air is then .
Applying ordinary airfoil coefficients, the lift force on the element is:
Let γ be the angle between the lift component and the resultant force, or . Then the total resultant air force on the element is:
The thrust of the element is the component of the resultant force in the direction of the propeller axis (Fig. 2), or
and since
For convenience let
and
Then
and the total thrust for the propeller (of B blades) is:
Referring again to Fig. 2, the tangential or torque force is
and the torque on the element is
which, if , can be written
The expression for the torque of the whole propeller is therefore
The horsepower absorbed by the propeller, or the torque horse-power, is
and the efficiency is | 1 | Applied and Interdisciplinary Chemistry |
Most triptans were developed and introduced in the 1990s. Further studies have not shown much promise regarding the development of new triptans with better duration of action, efficacy and safety profile. Therefore, it is unlikely that further variations will be developed and new anti-migraine drugs are likely to have another mechanism of action. | 1 | Applied and Interdisciplinary Chemistry |
CAF formation is a process involving the transport of conductive chemistries across a nonmetallic substrate under the influence of an applied electric field. CAF is influenced by electric field strength, temperature (including soldering temperatures), humidity, laminate material, and the presence of manufacturing defects. The occurrence of CAF failures has been primarily driven by the electronics industry pushing for higher density circuit boards and the use of electronics in harsher environments for high reliability applications. | 0 | Theoretical and Fundamental Chemistry |
The mineral Chenevixite was named in his honour because of his earlier work analysing copper ferrate arsenates. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, the Knudsen equation is used to describe how gas flows through a tube in free molecular flow. When the mean free path of the molecules in the gas is larger than or equal to the diameter of the tube, the molecules will interact more often with the walls of the tube than with each other. For typical tube dimensions, this occurs only in high or ultrahigh vacuum.
The equation was developed by Martin Hans Christian Knudsen (1871–1949), a Danish physicist who taught and conducted research at the Technical University of Denmark. | 1 | Applied and Interdisciplinary Chemistry |
Iron has many important roles in animal biology, specifically when considering oxygen transport in the bloodstream, oxygen storage in muscles, and enzymes. Known isotope variations are shown in the figure below. Iron isotopes could be useful tracers of the iron biochemical pathways in animals, and also be indicative of trophic levels in a food chain.
Iron isotope variations in humans reflects a number of processes. Specifically, iron in the blood stream reflects dietary iron, which is isotopically lighter than iron in the geosphere. Iron isotopes are distributed heterogeneously throughout the body, primarily to red blood cells, the liver, muscle, skin, enzymes, nails, and hair. Iron losses in the body (intestinal bleeding, bile, sweat, etc.) favor the loss of isotopically heavy iron, with mean losses averaging a δFe of +10‰. Iron absorption in the intestine favors lighter iron isotopes. This is largely due to the fact that iron is carried by transport proteins and transferrin, both of which are kinetic processes, resulting in the preferential uptake of isotopically light iron.
The observed iron isotopic variations in humans and animals are particularly important as tracers. Iron isotopic signatures are utilized to determine the geographic origin of food. Additionally, anthropologists and paleontologists use iron isotope data in order to track the transfer of iron between the geosphere and the biosphere, specifically between plant foods and animals. This allows for the reconstruction of ancient dietary habits based on the variations in iron isotopes in food. | 0 | Theoretical and Fundamental Chemistry |
The enzyme rhodanase (thiosulfate sulfurtransferase) catalyzes the detoxification of cyanide ion by thiosulfate ion by transforming them into thiocyanate ion and sulfite ion:
Sodium thiosulfate has been considered as an empirical treatment for cyanide poisoning, along with hydroxocobalamin. It is most effective in a pre-hospital setting, since immediate administration by emergency personnel is necessary to reverse rapid intracellular hypoxia caused by the inhibition of cellular respiration, at complex IV.
It activates thiosulfate sulfurtransferase (TST) in mitochondria. TST is associated with protection against obesity and type II (insulin resistant) diabetes.
Thiosulfate can also work as electron donor for growth of bacteria oxidizing sulfur, such as Chlorobium limicola forma thiosulfatophilum. These bacteria use electrons from thiosulfate (and other sources) and carbon from carbon dioxide to synthesize carbon compounds through reverse Krebs cycle. | 1 | Applied and Interdisciplinary Chemistry |
The mathematical expression of the Langmuir adsorption isotherm involving only one sorbing species can be demonstrated in different ways: the kinetics approach, the thermodynamics approach, and the statistical mechanics approach respectively. In case of two competing adsorbed species, the competitive adsorption model is required, while when a sorbed species dissociates into two distinct entities, the dissociative adsorption model need to be used. | 0 | Theoretical and Fundamental Chemistry |
((N,N'-dimethylacrylamide)-co-4-phenylazophenyl acrylate) at the active site of endoglycanase creates a photoswitchable protein hybrid. The resulting hybrid catalyzes the hydrolysis of glycoside when irradiated by 350 nm UV light, but turns inactive under 420 nm visible light depending on the conformation of the conjugated polymer. | 1 | Applied and Interdisciplinary Chemistry |
tert-Butyllithium is produced commercially by treating tert-butyl chloride with lithium metal. Its synthesis was first reported by R. B. Woodward in 1941. | 0 | Theoretical and Fundamental Chemistry |
Work on alternatives for chlorofluorocarbons in refrigerants began in the late 1970s after the first warnings of damage to stratospheric ozone were published.
The hydrochlorofluorocarbons (HCFCs) are less stable in the lower atmosphere, enabling them to break down before reaching the ozone layer. Nevertheless, a significant fraction of the HCFCs do break down in the stratosphere and they have contributed to more chlorine buildup there than originally predicted. Later alternatives lacking the chlorine, the hydrofluorocarbons (HFCs) have an even shorter lifetimes in the lower atmosphere. One of these compounds, HFC-134a, were used in place of CFC-12 in automobile air conditioners. Hydrocarbon refrigerants (a propane/isobutane blend) were also used extensively in mobile air conditioning systems in Australia, the US and many other countries, as they had excellent thermodynamic properties and performed particularly well in high ambient temperatures. 1,1-Dichloro-1-fluoroethane (HCFC-141b) has replaced HFC-134a, due to its low ODP and GWP values. And according to the Montreal Protocol, HCFC-141b is supposed to be phased out completely and replaced with zero ODP substances such as cyclopentane, HFOs, and HFC-345a before January 2020.
Among the natural refrigerants (along with ammonia and carbon dioxide), hydrocarbons have negligible environmental impacts and are also used worldwide in domestic and commercial refrigeration applications, and are becoming available in new split system air conditioners.
Various other solvents and methods have replaced the use of CFCs in laboratory analytics.
In Metered-dose inhalers (MDI), a non-ozone effecting substitute was developed as a propellant, known as "hydrofluoroalkane." | 1 | Applied and Interdisciplinary Chemistry |
The definition of thermodynamic work is in terms of the changes of the system's extensive deformation (and chemical constitutive and certain other) state variables, such as volume, molar chemical constitution, or electric polarisation. Examples of state variables that are not extensive deformation or other such variables are temperature and entropy , as for example in the expression . Changes of such variables are not actually physically measureable by use of a single simple adiabatic thermodynamic process; they are processes that occur neither by thermodynamic work nor by transfer of matter, and therefore are said occur by heat transfer. The quantity of thermodynamic work is defined as work done by the system on its surroundings. According to the second law of thermodynamics, such work is irreversible. To get an actual and precise physical measurement of a quantity of thermodynamic work, it is necessary to take account of the irreversibility by restoring the system to its initial condition by running a cycle, for example a Carnot cycle, that includes the target work as a step. The work done by the system on its surroundings is calculated from the quantities that constitute the whole cycle. A different cycle would be needed to actually measure the work done by the surroundings on the system. This is a reminder that rubbing the surface of a system appears to the rubbing agent in the surroundings as mechanical, though not thermodynamic, work done on the system, not as heat, but appears to the system as heat transferred to the system, not as thermodynamic work. The production of heat by rubbing is irreversible; historically, it was a piece of evidence for the rejection of the caloric theory of heat as a conserved substance. The irreversible process known as Joule heating also occurs through a change of a non-deformation extensive state variable.
Accordingly, in the opinion of Lavenda, work is not as primitive concept as is heat, which can be measured by calorimetry. This opinion does not negate the now customary thermodynamic definition of heat in terms of adiabatic work.
Known as a thermodynamic operation, the initiating factor of a thermodynamic process is, in many cases, a change in the permeability of a wall between the system and the surroundings. Rubbing is not a change in wall permeability. Kelvin's statement of the second law of thermodynamics uses the notion of an "inanimate material agency"; this notion is sometimes regarded as puzzling. The triggering of a process of rubbing can occur only in the surroundings, not in a thermodynamic system in its own state of internal thermodynamic equilibrium. Such triggering may be described as a thermodynamic operation. | 0 | Theoretical and Fundamental Chemistry |
Israel has the highest rate of IVF in the world, with 1,657 procedures performed per million people per year. Couples without children can receive funding for IVF for up to two children. The same funding is available for people without children who will raise up to two children in a single parent home. IVF is available for people aged 18 to 45. The Israeli Health Ministry says it spends roughly $3450 per procedure. | 1 | Applied and Interdisciplinary Chemistry |
Haifuki-ho (灰吹法; literally "ash-blowing method"), also known as Lead-silver separation method (Korean: 연은분리법; Hanja: 鉛銀分離法) is a method of silver mining developed in Joseon dynasty of Korea in the 16th century and spread to China and Feudal Japan. The industrial process involved cupellation, and was a contributing factor to the large amount of silver traditionally exported by Japan. | 1 | Applied and Interdisciplinary Chemistry |
By the time propranolol was launched, ICI was beginning to experience competition from other companies. This potential threat led to ongoing refinements in the pharmacologic structure of β-blockers and subsequent advances in drug delivery. ICI studied analogues further and in 1970 launched practolol (figure 4) under the trade name Eraldin. It was withdrawn from the market a few years later because of the severe side effects it caused, nevertheless it played a large role in the fundamental study of β-blockade and β-receptors.
The withdrawal of Eraldin gave ICI the nudge to launch another β-blocker, atenolol, which was launched in 1976 under the trade name Tenormin. Atenolol is a selective β1-receptor antagonist and was developed for the purpose of obtaining the “ideal β-blocker”. It soon became one of the best-selling heart drug. ICIs β-blocker project was based on Ahlquists dual receptor theory. The drugs that were the outcome of this project, from propranolol to atenolol, helped to establish the receptor theory among scientist and pharmaceutical companies.
The progress in β-blocker development led to the introduction of drugs with variety of properties. β-blockers were developed having a relative selectivity for cardiac β1-receptors (for example metoprolol and atenolol), partial adrenergic agonist activity (pindolol), concomitant α-adrenergic blocking activity (for example labetalol and carvedilol) and additional direct vasodilator activity (nebivolol). In addition, long-acting and ultra-short formulations of β-blockers were developed. In 1988, Sir James Black was awarded the Nobel Prize in Medicine for his work on drug development. | 1 | Applied and Interdisciplinary Chemistry |
When a fissile atom undergoes nuclear fission, it breaks into two or more fission fragments. Also, several free neutrons, gamma rays, and neutrinos are emitted, and a large amount of energy is released. The sum of the rest masses of the fission fragments and ejected neutrons is less than the sum of the rest masses of the original atom and incident neutron (of course the fission fragments are not at rest). The mass difference is accounted for in the release of energy according to the equation E=Δmc:
:mass of released energy =
Due to the extremely large value of the speed of light, c, a small decrease in mass is associated with a tremendous release of active energy (for example, the kinetic energy of the fission fragments). This energy (in the form of radiation and heat) carries the missing mass, when it leaves the reaction system (total mass, like total energy, is always conserved). While typical chemical reactions release energies on the order of a few eVs (e.g. the binding energy of the electron to hydrogen is 13.6 eV), nuclear fission reactions typically release energies on the order of hundreds of millions of eVs.
Two typical fission reactions are shown below with average values of energy released and number of neutrons ejected:
Note that these equations are for fissions caused by slow-moving (thermal) neutrons. The average energy released and number of neutrons ejected is a function of the incident neutron speed. Also, note that these equations exclude energy from neutrinos since these subatomic particles are extremely non-reactive and, therefore, rarely deposit their energy in the system. | 0 | Theoretical and Fundamental Chemistry |
The theory of diffusion-controlled reaction was originally utilized by R.A. Alberty, Gordon Hammes, and Manfred Eigen to estimate the upper limit of enzyme-substrate reaction. According to their estimation, the upper limit of enzyme-substrate reaction was 10 M s.
In 1972, it was observed that in the dehydration of HCO catalyzed by carbonic anhydrase, the second-order rate constant obtained experimentally was about 1.5 × 10 M s, which was one order of magnitude higher than the upper limit estimated by Alberty, Hammes, and Eigen based on a simplified model.
To address such a paradox, Kuo-Chen Chou and his co-workers proposed a model by taking into account the spatial factor and force field factor between the enzyme and its substrate and found that the upper limit could reach 10 M s, and can be used to explain some surprisingly high reaction rates in molecular biology.
The new upper limit found by Chou et al. for enzyme-substrate reaction was further discussed and analyzed by a series of follow-up studies.
A detailed comparison between the simplified Alberty-Hammes-Eigens model (a) and the Chous model (b) in calculating the diffusion-controlled reaction rate of enzyme with its substrate, or the upper limit of enzyme-substrate reaction, was elaborated in the paper. | 1 | Applied and Interdisciplinary Chemistry |
The current ACELL project began as APCELL (Australian Physical Chemistry Enhanced Laboratory Learning) in the late 1990s. Initially funded by the Australian Government through its Committee for University Teaching and Staff Development (CUTSD) program, the aim of APCELL was to build a database of tested, educationally-sound undergraduate level experiments in physical chemistry. APCELL ran several workshops at which experiments were tested by staff and students from Australian universities.
To be accepted to the APCELL database, an experiment had to be tested in a third-party laboratory (such as at a workshop), be judged to be educationally-sound, and to complete a peer review process. The educational analyses of experiments which completed this process were published in the Australian Journal of Education in Chemistry.
Additional funding was received from the Department of Education, Science and Training (Australia) through its Higher Education Innovation Program (HEIP) to enable the project to be extended to all areas of chemistry, which is the reason for the name change from APCELL to ACELL.
Whilst the ACELL project is run with the active support of its many contributors, the management team is spread across four universities: Macquarie University, the University of Adelaide, the University of Sydney, and Curtin University of Technology. | 1 | Applied and Interdisciplinary Chemistry |
The majority of these twintrons have been characterized within the Euglena chloroplast genome but these elements have also been found in cryptomonad algae (Pyrenomonas salina), and group I intron based twintrons (group I inserted within a group I intron) have been described in Didymium iridis. Since the discovery of the psbF twintron, several categories of twintrons have been characterized. A twintron can be simple (external intron interrupted by 1 internal intron), or complex (external intron interrupted by multiple internal introns). Most probably, the internal and external introns comprising the twintron element are from the same category; group I internal to group I, group II internal to group II, and group III internal to group III. Mixed twintrons (consisting of introns belonging to different categories) were characterized from the Euglena gracilis
rps3 gene in which an internal group II intron is found to interrupt an external group III intron. In Rhodomonas salina (=Pyrenomonas salina) twintrons (nested group II/group III introns) were identified where the internal intron lost its splicing capacity, essentially merging with the outer intron forming one splicing unit. Recently, two novel twintrons have been uncovered within the fungal mitochondrial genome, one at position mS917 of the Cryphonectria parasitica mt-rns gene, where a group ID intron encoding a LAGLIDADG ORF invaded another ORF-less group ID intron. Another twintron complex was detected at position mS1247 of the Chaetomium thermophilumhere mt-rns gene, a group IIA1 intron invaded the open reading frame embedded within a group IC2 intron. The mS1247 twintron represents the first recorded fungal mitochondrial mixed twintron consisting of group II intron as an internal intron and a group I intron as an external intron. In mS1247 twintron, splicing of the internal group IIA1 intron reconstitutes the open reading frame encoded within the group IC2 intron and thus facilitates the expression of the encoded homing endonuclease. The mS1247 twintron encod ORF have been biochemically characterized and the results showed that it is an active homing endonuclease that could potentially mobilize the twintron to rns genes that have not yet been invaded by this mobile composite element. | 1 | Applied and Interdisciplinary Chemistry |
Organisms may secrete bioadhesives for use in attachment, construction and obstruction, as well as in predation and defense. Examples include their use for:
* Colonization of surfaces (e.g. bacteria, algae, fungi, mussels, barnacles, rotifers)
* Mussel's byssal threads
* Tube building by polychaete worms, which live in underwater mounds
* Insect egg, larval or pupal attachment to surfaces (vegetation, rocks), and insect mating plugs
* Host attachment by blood-feeding ticks
* Nest-building by some insects, and also by some fish (e.g. the three-spined stickleback)
* Defense by Notaden frogs and by sea cucumbers
* Prey capture in spider webs and by velvet worms
Some bioadhesives are very strong. For example, adult barnacles achieve pull-off forces as high as 2 MPa (2 N/mm). A similarly strong, rapidly adhering glue - which contains 171 different proteins and can adhere to wet, moist and impure surfaces - is produced by the very hard limpet species Patella vulgata; this adhesive material is a very interesting subject of research in the development of surgical adhesives and several other applications. Silk dope can also be used as a glue by arachnids and insects. | 1 | Applied and Interdisciplinary Chemistry |
The eddy dissipation concept (EDC) model is an extension of the eddy dissipation model to include detailed chemical mechanism in turbulent flows. The EDC model attempts to incorporate the significance of fine structures in a turbulent reacting flow in which combustion is important. EDC has been proven efficient without the need for changing the constants for a great variety of premixed and diffusion controlled combustion problems, both where the chemical kinetics is faster than the overall fine structure mixing as well as in cases where the chemical kinetics has a dominating influence. | 1 | Applied and Interdisciplinary Chemistry |
A balance of magnesium is vital to the well-being of all organisms. Magnesium is a relatively abundant ion in Earth's crust and mantle and is highly bioavailable in the hydrosphere. This availability, in combination with a useful and very unusual chemistry, may have led to its utilization in evolution as an ion for signaling, enzyme activation, and catalysis. However, the unusual nature of ionic magnesium has also led to a major challenge in the use of the ion in biological systems. Biological membranes are impermeable to magnesium (and other ions), so transport proteins must facilitate the flow of magnesium, both into and out of cells and intracellular compartments. | 1 | Applied and Interdisciplinary Chemistry |
As a simplest approach to rotational coherence, one may define an elliptic LCS as a tubular material surface along which small material volumes complete the same net rotation over the time intervall of interest.
A challenge in that in each material volume element, all individual material fibers (tangent vectors to trajectories) perform different rotations.
To obtain a well-defined bulk rotation for each material element, one may employ the unique left and right polar decompositions of the flow gradient in the form
where the proper orthogonal tensor is called the rotation tensor and the symmetric, positive definite tensors are called the left stretch tensor and right stretch tensor, respectively.
Since the Cauchy–Green strain tensor can be written as
the local material straining described by the eigenvalues and eigenvectors of are fully captured by the singular values and singular vectors of the stretch tensors. The remaining factor in the deformation gradient is represented by , interpreted as the bulk solid-body rotation component of volume elements. In planar motions, this rotation is defined relative to the normal of the plane. In three dimensions, the rotation is defined relative to the axis defined by the eigenvector of corresponding to its unit eigenvalue. In higher-dimensional flows, the rotation tensor cannot be viewed as a rotation about a single axis.
In two and three dimensions, therefore, there exists a polar rotation angle (PRA) that characterises the material rotation generated by for a volume element centered at the initial condition . This PRA is well-defined up to multiples of . For two-dimensional flows, the PRA can be computed from the invariants of using the formulas
which yield a four-quadrant version of the PRA via the formula
For three-dimensional flows, the PRA can again be computed from the invariants of from the formulas
where is the Levi-Civita symbol, is the eigenvector corresponding to the unit eigenvector of the matrix .
The time positions of elliptic LCSs are visualized as tubular level sets of the PRA distribution . In two-dimensions, therefore, (polar) elliptic LCSs are simply closed level curves of the PRA, which turn out to be objective. In three dimensions, (polar) elliptic LCSs are toroidal or cylindrical level surfaces of the PRA, which are, however, not objective and hence will generally change in rotating frames. Coherent Lagrangian vortex boundaries can be visualized as outermost members of nested families of elliptic LCSs. Two- and three-dimensional examples of elliptic LCS revealed by tubular level surfaces of the PRA are shown in Fig. 10a-b. | 1 | Applied and Interdisciplinary Chemistry |
In general, the analysis of the capacitance transients in the DLTS measurements assumes that the concentration of investigated traps is much smaller than the material doping concentration. In cases when this assumption is not fulfilled then the constant capacitance DLTS (CCDLTS) method is used for more accurate determination of the trap concentration. When the defects recharge and their concentration is high then the width of the device space region varies making the analysis of the capacitance transient inaccurate. The additional electronic circuitry maintaining the total device capacitance constant by varying the device bias voltage helps to keep the depletion region width constant. As a result, the varying device voltage reflects the defect recharge process. An analysis of the CCDLTS system using feedback theory was provided by Lau and Lam in 1982. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, a nitrile is any organic compound that has a functional group. The name of the compound is composed of a base, which includes the carbon of the , suffixed with "nitrile", so for example is called "propionitrile" (or propanenitrile). The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile rubber, a nitrile-containing polymer used in latex-free laboratory and medical gloves. Nitrile rubber is also widely used as automotive and other seals since it is resistant to fuels and oils. Organic compounds containing multiple nitrile groups are known as cyanocarbons.
Inorganic compounds containing the group are not called nitriles, but cyanides instead. Though both nitriles and cyanides can be derived from cyanide salts, most nitriles are not nearly as toxic. | 0 | Theoretical and Fundamental Chemistry |
Permanent gas is a term used for a gas which has a critical temperature below the range of normal human-habitable temperatures and therefore cannot be liquefied by pressure within this range. Historically such gases were thought to be impossible to liquefy and would therefore permanently remain in the gaseous state. The term is relevant to ambient temperature storage and transport of gases at high pressure. | 0 | Theoretical and Fundamental Chemistry |
Day was married to Frances, who died in 2018, and had two children, Alison and Christopher, and five grandchildren. Day died on 19 May 2020, at his home in Marsh Baldon, Oxfordshire, at the age of 81. | 0 | Theoretical and Fundamental Chemistry |
Additives are also used to overturn conformational preferences, increase reaction concentration, and chelate highly polar groups, such as esters or amides, which can bind to the catalyst. Titanium isopropoxide (Ti(OPr)) is commonly used to chelate polar groups to prevent catalyst poisoning and in the case of an ester, the titanium Lewis acid binds the carbonyl oxygen. Once the oxygen is chelated with the titanium it can no longer bind to the ruthenium metal of the catalyst, which would result in catalyst deactivation. This also allows the reaction to be run at a higher effective concentration without dimerization of starting material.
Another classic example is the use of a bulky Lewis acid to form the E-isomer of an ester over the preferred Z-isomer for cyclolactonization of medium rings. In one study, the addition of aluminum tris(2,6-diphenylphenoxide) (ATPH) was added to form a 7-membered lactone. The aluminum binds with the carbonyl oxygen forcing the bulky diphenylphenoxide groups in close proximity to the ester compound. As a result, the ester adopts the E-isomer to minimize penalizing steric interactions. Without the Lewis acid, only the 14-membered dimer ring was observed.
By orienting the molecule in such a way that the two reactive alkenes are in close proximity, the risk of intermolecular cross-metathesis is minimized. | 0 | Theoretical and Fundamental Chemistry |
In addition to its use in recovering silver in lead refineries, the BBOC has been used to treat anode slimes from copper electrolytic refineries.
Anode slimes are composed of solid particles that do not dissolve in the electrolyte in the refining cells. This includes the gold and silver present in the copper anodes that are being refined. As with recovering silver in lead smelting, reverberatory furnaces are often used in the copper refining industry for the purification and recovery of gold and silver from anode slimes. However, the reverberatory furnaces suffer from similar disadvantages in copper anode doré production as they do in lead refineries, including resulting in a large inventory of gold in the system. Other furnace types used, include top-blown rotary converters and short rotary furnaces. | 1 | Applied and Interdisciplinary Chemistry |
The mechanism of fluorination by SF is assumed to resemble chlorination by phosphorus pentachloride. Hydrogen fluoride, a useful solvent for these reactions, activates SF:
Species of the type ROSF are often invoked as intermediates. In the case of aldehydes and ketones, SF4 is thought to initially add across the double bond to give R2CFOSF. | 0 | Theoretical and Fundamental Chemistry |
Reactive flows are flows that are chemically reactive, which finds its applications in many areas, including combustion (IC engine), propulsion devices (rockets, jet engines, and so on), detonations, fire and safety hazards, and astrophysics. In addition to conservation of mass, momentum and energy, conservation of individual species (for example, mass fraction of methane in methane combustion) need to be derived, where the production/depletion rate of any species are obtained by simultaneously solving the equations of chemical kinetics. | 1 | Applied and Interdisciplinary Chemistry |
In crystallography, a Strukturbericht designation or Strukturbericht type is a system of detailed crystal structure classification by analogy to another known structure. The designations were intended to be comprehensive but are mainly used as supplement to space group crystal structures designations, especially historically. Each Strukturbericht designation is described by a single space group, but the designation includes additional information about the positions of the individual atoms, rather than just the symmetry of the crystal structure. While Strukturbericht symbols exist for many of the earliest observed and most common crystal structures, the system is not comprehensive, and is no longer being updated. Modern databases such as Inorganic Crystal Structure Database index thousands of structure types directly by the prototype compound (i.e. "the NaCl structure" instead of "the B1 structure"). These are essentially equivalent to the old Stukturbericht designations. | 0 | Theoretical and Fundamental Chemistry |
While α-galactose as a part of glycoprotein glycans from vertebrates other than higher apes was known for a long time as being a prominent xeno-antigen, its implication in allergy only began to materialize when complications during treatment with a recombinant monoclonal antibody (Erbitux) were attributed to IgE directed against α-Gal containing N-glycans on this antibody. The incidencies of anaphylaxis due to Erbitux were confined to a certain area in the eastern United States, which raised speculations about the involvement of a particular type of tick endemic in this area. However, IgE antibodies against the α-Gal epitope should be taken into account in the diagnosis of milk and meat allergy. It is currently largely unexplored whether this type of CCD is generally also clinically irrelevant such as the plant/insect CCDs. The very localized case of Erbitux complications points at a possible if rare clinical significance of α-Gal.
Yet other potentially immunogenic carbohydrates with widespread occurrence such as N-Glycolylneuraminic acid, which does not occur in humans, or plant O-glycans (arabinogalactans and arabinans) may be mentioned but have so far not qualified as either IgE or as cross-reactive determinants.
Literature: | 0 | Theoretical and Fundamental Chemistry |
The micelle packing parameter equation is utilized to help "predict molecular self-assembly in surfactant solutions":
where is the surfactant tail volume, is the tail length, and is the equilibrium area per molecule at the aggregate surface. | 0 | Theoretical and Fundamental Chemistry |
The NNT is an important measure in pharmacoeconomics. If a clinical endpoint is devastating enough (e.g. death, heart attack), drugs with a high NNT may still be indicated in particular situations. If the endpoint is minor, health insurers may decline to reimburse drugs with a high NNT. NNT is significant to consider when comparing possible side effects of a medication against its benefits. For medications with a high NNT, even a small incidence of adverse effects may outweigh the benefits. Even though NNT is an important measure in a clinical trial, it is infrequently included in medical journal articles reporting the results of clinical trials. There are several important problems with the NNT, involving bias and lack of reliable confidence intervals, as well as difficulties in excluding the possibility of no difference between two treatments or groups.
NNT may vary substantially over time, and hence convey different information as a function of the specific time-point of its calculation. Snapinn and Jiang showed examples where the information conveyed by the NNT may be incomplete or even contradictory compared to the traditional statistics of interest in survival analysis. A comprehensive research on adjustment of the NNT for explanatory variables and accommodation to time-dependent outcomes was conducted by Bender and Blettner, Austin, and Vancak et al. | 1 | Applied and Interdisciplinary Chemistry |
Söllner was the son of lawyer Anton Maria Söllner and his wife Julie ( Karplus). He grew up in Vienna and began studying chemistry and philosophy at the University of Vienna in 1921. From his third semester he was a student assistant (Demonstrator) at the university. He completed his dissertation with Alfons Klemenc. In 1928 he entered the service of the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry in Berlin, where he worked as a scientific assistant alongside Herbert Freundlich. In May 1933, Söllner began a habilitation thesis in the field of osmosis which was reviewed by Fritz Haber, Max Bodenstein and Herbert Freundlich.
Unfortunately, in the same year the Nazi party seized power. According to the national socialist definition he was of Jewish heritage and was therefore forced him to leave his position at the institute in June 1933. He then emigrated to Great Britain, where he found a position in the chemistry department of University College London, where he worked from 1933 to 1937. He was also a visiting researcher and consultant at Imperial Chemical Industries.
In 1937 Söllner moved to the United States. There he took a position as a chemist with the Department of Agronomy at Cornell University in Ithaca with support from the “Emergency Committee in Aid of Displaced German Scholars“. In 1938 he moved to the Department of Physiological Chemistry at the University of Minnesota School of Medicine in Minneapolis. There he was initially employed as an Associate Chemist. He was promoted to "Regular Chemist" in 1939, Associate Professor in 1943 and Full Professor in 1947.
Söllner was labelled as an enemy of the state by Nazi authorities. In the spring of 1940, the Reich Security Main Office in Berlin put him on a special Great Britain wanted list, a list of people who, in the event of a successful invasion and occupation of the British Isles by the Wehrmacht, should be identified and arrested as a priority by the SS special forces that followed the occupation forces.
Later Söllner moved to the Institute of Health in Bethesda, Maryland where he worked in the laboratory of National Institute of Arthritis Metabolism and Digestive Diseases, initially at the rank of Principal Research Analyst, from 1948 as a senior physical biochemist and from 1965 as head of the section for electrochemistry and colloid chemistry. In 1973 he officially retired, but continued to work as a consultant and visiting researcher for the institute until 1975.
Söllner was a specialist in ultrasound for colloid systems. In this context, he focused his research on the study of membranes and their electrophysical properties and on "Studies of Dispersion of Solids, Coagulation, and Fog Formation". Söllner published about 120 scientific papers in specialist journals. He was also a member of the American Association for the Advancement of Science, the American Institute of Chemistry and the New York Academy of Sciences, the American Chemical Society, the Society of General Physiologists and the Electrochemical Society. | 0 | Theoretical and Fundamental Chemistry |
TFH is a ten‐subunit complex; seven of these subunits comprise the “core” whereas three comprise the dissociable “CAK” (CDK Activating Kinase) module. The core consists of subunits XPB, XPD, p62, p52, p44, p34 and p8 while CAK is composed of CDK7, cyclin H, and MAT1. | 1 | Applied and Interdisciplinary Chemistry |
Most naturally occurring nuclides on earth are beta stable. Nuclides that are not beta stable have half-lives ranging from under a second to periods of time significantly greater than the age of the universe. One common example of a long-lived isotope is the odd-proton odd-neutron nuclide , which undergoes all three types of beta decay (, and electron capture) with a half-life of . | 0 | Theoretical and Fundamental Chemistry |
Fundamentally, pressure-based meters measure kinetic energy density. Bernoulli's equation (used above) relates this to mass density and volumetric flow:
where constant terms are absorbed into k. Using the definitions of density (), molar concentration (), and molar mass (), one can also derive mass flow or molar flow (i.e. standard volume flow):
However, measurements outside the design point must compensate for the effects of temperature, pressure, and molar mass on density and concentration. The ideal gas law is used to relate actual values to design values:
Substituting these two relations into the pressure-flow equations above yields the fully compensated flows:
Q, m, or n are easily isolated by dividing and taking the square root. Note that pressure-, temperature-, and mass-compensation is required for every flow, regardless of the end units or dimensions. Also we see the relations: | 1 | Applied and Interdisciplinary Chemistry |
The thermal expansion coefficients depends on the modification of zirconia as follows:
* Monoclinic: 7·10/K
* Tetragonal: 12·10/K
* YO stabilized: 10,5·10/K | 0 | Theoretical and Fundamental Chemistry |
The hydraulic jump is the most commonly used choice of design engineers for energy dissipation below spillways and outlets. A properly designed hydraulic jump can provide for 60-70% energy dissipation of the energy in the basin itself, limiting the damage to structures and the streambed. Even with such efficient energy dissipation, stilling basins must be carefully designed to avoid serious damage due to uplift, vibration, cavitation, and abrasion. An extensive literature has been developed for this type of engineering. | 1 | Applied and Interdisciplinary Chemistry |
Odd-chain fatty acids (OCFAs) are those fatty acids that contain an odd number of carbon atoms. The most common OCFAs are the saturated C15 and C17 derivatives, respectively pentadecanoic acid and heptadecanoic acid. The synthesis of even-chained fatty acid synthesis is done by assembling acetyl-CoA precursors, however, propionyl-CoA instead of acetyl-CoA is used as the primer for the biosynthesis of long-chain fatty acids with an odd number of carbon atoms.
;Regulation
In B. subtilis, this pathway is regulated by a two-component system: DesK and DesR. DesK is a membrane-associated kinase and DesR is a transcriptional regulator of the des gene. The regulation responds to temperature; when there is a drop in temperature, this gene is upregulated. Unsaturated fatty acids increase the fluidity of the membrane and stabilize it under lower temperatures. DesK is the sensor protein that, when there is a decrease in temperature, will autophosphorylate. DesK-P will transfer its phosphoryl group to DesR. Two DesR-P proteins will dimerize and bind to the DNA promoters of the des gene and recruit RNA polymerase to begin transcription.
Pseudomonas aeruginosa
In general, both anaerobic and aerobic unsaturated fatty acid synthesis will not occur within the same system, however Pseudomonas aeruginosa and Vibrio ABE-1 are exceptions.
While P. aeruginosa undergoes primarily anaerobic desaturation, it also undergoes two aerobic pathways. One pathway utilizes a Δ-desaturase (DesA) that catalyzes a double bond formation in membrane lipids. Another pathway uses two proteins, DesC and DesB, together to act as a Δ-desaturase, which inserts a double bond into a saturated fatty acid-CoA molecule. This second pathway is regulated by repressor protein DesT. DesT is also a repressor of fabAB expression for anaerobic desaturation when in presence of exogenous unsaturated fatty acids. This functions to coordinate the expression of the two pathways within the organism. | 1 | Applied and Interdisciplinary Chemistry |
Ships and marine facilities must conform to an international standard for piping systems identification. This is ISO 14726:2008 Ships and marine technology — Identification colours for the content of piping systems.
This is a two-colour banded marking system. The main colour shows what the fluid is being used for. This is on either side of the secondary colour which indicates what the substance actually is. The main colours are as follows:
* Black - Waste media
* Blue - Fresh water
* Brown - Fuel
* Green – Sea water
* Grey - Non-flammable gases
* Maroon - Air and sounding pipes
* Orange - Oils other than fuels
* Silver - Steam
* Red - Fire fighting
* Violet - Acids, alkalis
* White - Air in ventilation systems
* Yellow - Flammable gases | 1 | Applied and Interdisciplinary Chemistry |
Esomeprazole can be used as a parasiticide. Gokmen et al., 2016 screen for efficacy against Trichomonas vaginalis isolates from horses. They found esomeprazole to be effective as a veterinary antiparasitic. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, a diamino acid, also called a diamino carboxylic acid, is a molecule including a carboxylic acid and two amine functional groups. Diamino acids belong to the class of amino acids. | 1 | Applied and Interdisciplinary Chemistry |
Monoclinic phosphorus, or violet phosphorus, is also known as Hittorfs metallic phosphorus. In 1865, Johann Wilhelm Hittorf heated red phosphorus in a sealed tube at 530 °C. The upper part of the tube was kept at 444 °C. Brilliant opaque monoclinic, or rhombohedral, crystals sublimed as a result. Violet phosphorus can also be prepared by dissolving white phosphorus in molten lead in a sealed tube at 500 °C for 18 hours. Upon slow cooling, Hittorfs allotrope crystallises out. The crystals can be revealed by dissolving the lead in dilute nitric acid followed by boiling in concentrated hydrochloric acid. In addition, a fibrous form exists with similar phosphorus cages. The lattice structure of violet phosphorus was presented by Thurn and Krebs in 1969. Imaginary frequencies, indicating the irrationalities or instabilities of the structure, were obtained for the reported violet structure from 1969. The single crystal of violet phosphorus was also produced. The lattice structure of violet phosphorus has been obtained by single‐crystal x‐ray diffraction to be monoclinic with space group of P2/n (13) (a = 9.210, b = 9.128, c = 21.893 Å, β = 97.776°, [https://www.ccdc.cam.ac.uk/structures/Search?Doi=10.1002%2Fanie.201912761&DatabaseToSearch=Published CSD-1935087]). The optical band gap of the violet phosphorus was measured by diffuse reflectance spectroscopy to be around 1.7 eV. The thermal decomposition temperature was 52 °C higher than its black phosphorus counterpart. The violet phosphorene was easily obtained from both mechanical and solution exfoliation. | 0 | Theoretical and Fundamental Chemistry |
Enzymatically active lactate dehydrogenase is consisting of four subunits (tetramer). The two most common subunits are the LDH-M and LDH-H peptides, named for their discovery in muscle and heart tissue, and encoded by the LDHA and LDHB genes, respectively. These two subunits can form five possible tetramers (isoenzymes): LDH-1 (4H), LDH-5 (4M), and the three mixed tetramers (LDH-2/3H1M, LDH-3/2H2M, LDH-4/1H3M). These five isoforms are enzymatically similar but show different tissue distribution.
* LDH-1 (4H)—in the heart and in RBC (red blood cells), as well as the brain
* LDH-2 (3H1M)—in the reticuloendothelial system
* LDH-3 (2H2M)—in the lungs
* LDH-4 (1H3M)—in the kidneys, placenta, and pancreas
* LDH-5 (4M)—in the liver and striated muscle, also present in the brain
LDH-2 is usually the predominant form in the serum. An LDH-1 level higher than the LDH-2 level (a "flipped pattern") suggests myocardial infarction (damage to heart tissues releases heart LDH, which is rich in LDH-1, into the bloodstream). The use of this phenomenon to diagnose infarction has been largely superseded by the use of Troponin I or T measurement.
There are two more mammalian LDH subunits that can be included in LDH tetramers: LDHC and LDHBx. LDHC is a testes-specific LDH protein, that is encoded by the LDHC gene. LDHBx is a peroxisome-specific LDH protein. LDHBx is the readthrough-form of LDHB. LDHBx is generated by translation of the LDHB mRNA, but the stop codon is interpreted as an amino acid-encoding codon. In consequence, translation continues to the next stop codon. This leads to the addition of seven amino acid residues to the normal LDH-H protein. The extension contains a peroxisomal targeting signal, so that LDHBx is imported into the peroxisome. | 1 | Applied and Interdisciplinary Chemistry |
The formation of the link between the glycan and the protein is key element of the synthesis of glycoproteins. The most common method of glycosylation of N-linked glycoproteins is through the reaction between a protected glycan and a protected Asparagine. Similarly, an O-linked glycoprotein can be formed through the addition of a glycosyl donor with a protected Serine or Threonine. These two methods are examples of natural linkage. However, there are also methods of unnatural linkages. Some methods include ligation and a reaction between a serine-derived sulfamidate and thiohexoses in water. Once this linkage is complete, the amino acid sequence can be expanded upon using solid-phase peptide synthesis. | 0 | Theoretical and Fundamental Chemistry |
The Pacific Proving Grounds was the name used to describe a number of sites in the Marshall Islands and a few other sites in the Pacific Ocean, used by the United States to conduct nuclear testing at various times between 1946 and 1962. In July 1947, after the first atomic weapons testing at Bikini Atoll, the United States entered into an agreement with the United Nations to govern the Trust Territory of the Pacific Islands as a strategic trusteeship territory. The Trust Territory is composed of 2,000 islands spread over of the North Pacific Ocean. On July 23, 1947, the United States Atomic Energy Commission announced the establishment of the Pacific Proving Grounds.
105 atmospheric (i.e., not underground) nuclear tests were conducted there, many of which were of extremely high yield. While the Marshall Islands testing composed 14% of all U.S. tests, it composed nearly 80% of the total yields of those detonated by the U.S., with an estimated total yield of around 210 megatons, with the largest being the 15 Mt Castle Bravo shot of 1954 which spread considerable nuclear fallout on many of the islands, including several which were inhabited, and some that had not been evacuated.
Many of the islands which were part of the Pacific Proving Grounds continue to be contaminated by nuclear fallout, and many of those who were living on the islands at the time of testing has suffered from an increased incidence of various health problems. Through the Radiation Exposure Compensation Act of 1990, at least $759 million has been paid to Marshall Islanders as compensation for their exposure to U.S. nuclear testing. Following the Castle Bravo accident, $15.3 million was paid to Japan. | 1 | Applied and Interdisciplinary Chemistry |
A cannulated cow or fistulated cow refers to a cow that has been surgically fitted with a cannula. A cannula acts as a porthole-like device that allows access to the rumen of a cow, to perform research and analysis of the digestive system and to allow veterinarians to transplant rumen contents from one cow to another.
The practice of rumen cannulation was first documented in 1928 by Arthur Frederick Schalk and R.S. Amadon of North Dakota Agricultural College. | 1 | Applied and Interdisciplinary Chemistry |
:Protein enzymes catalyze various chemical reactions, but over half of them incorporate cofactors to facilitate and diversify their catalytic activities. Cofactors are essential in biology, as they are based largely on nucleotides rather than amino acids. Ribozymes use nucleotide cofactors to create metabolism, with two basic choices: non-covalent binding or covalent attachment. Both approaches have been demonstrated using directed evolution to reinvent RNA dupes of protein-catalyzed processes. Lorsch and Szostak investigated ribozymes that could phosphorylate themselves and use ATP-γS as a substrate. However, only one of the seven classes of selected ribozymes had detectable ATP affinity, indicating that the ability to bind ATP was compromised. NAD- dependent redox ribozymes were also evaluated. The select ribozyme had a rate of enhancement of more than 10 fold and was proven to catalyze the reverse reaction - benzaldehyde reduction by NADH. Since the usage of adenosine as a cofactor is prevalent in current metabolism and is likely to have been common in the RNA world, these discoveries are essential for the evolution of metabolism in the RNA world. | 0 | Theoretical and Fundamental Chemistry |
Arctic sea ice has experienced an extreme reduction over the past few decades, with the minimum area of sea ice being 4.32 million km in 2019, a sharp 38% decrease from 1980, when the minimum area was 7.01 million km. Sea ice plays an important role in the health of the Arctic Ocean, and its decline has had detrimental effects on Arctic Ocean chemistry. All oceans equilibrate with the atmosphere by pulling carbon dioxide out of the atmosphere and into the ocean, which lowers the pH of the water. Sea ice limits the air-sea gas exchange with carbon dioxide by protecting the water from being completely exposed to the atmosphere. Low carbon dioxide levels are important to the Arctic Ocean due to intense cooling, fresh water runoff, and photosynthesis from marine organisms. Reductions in sea ice have allowed more carbon dioxide to equilibrate with the arctic water, resulting in increased acidification. The decrease in sea ice has also allowed more Pacific Ocean water to flow into in the Arctic Ocean during the winter, called Pacific winter water. Pacific Ocean water is high in carbon dioxide, and with decreased amounts of sea ice, more Pacific Ocean water has been able to enter the Arctic Ocean, carrying carbon dioxide with it. This Pacific winter water has further acidified the Arctic Ocean, as well as increased the depth of acidified water. | 0 | Theoretical and Fundamental Chemistry |
When water flows over a dam spillway, the irregularities on the spillway surface will cause small areas of flow separation in a high-speed flow, and, in these regions, the pressure will be lowered. If the flow velocities are high enough the pressure may fall to below the local vapor pressure of the water and vapor bubbles will form. When these are carried downstream into a high pressure region the bubbles collapse giving rise to high pressures and possible cavitation damage.
Experimental investigations show that the damage on concrete chute and tunnel spillways can start at clear water flow velocities of between , and, up to flow velocities of , it may be possible to protect the surface by streamlining the boundaries, improving the surface finishes or using resistant materials.
When some air is present in the water the resulting mixture is compressible and this damps the high pressure caused by the bubble collapses. If the flow velocities near the spillway invert are sufficiently high, aerators (or aeration devices) must be introduced to prevent cavitation. Although these have been installed for some years, the mechanisms of air entrainment at the aerators and the slow movement of the air away from the spillway surface are still challenging.
The spillway aeration device design is based upon a small deflection of the spillway bed (or sidewall) such as a ramp and offset to deflect the high flow velocity flow away from the spillway surface. In the cavity formed below the nappe, a local subpressure beneath the nappe is produced by which air is sucked into the flow. The complete design includes the deflection device (ramp, offset) and the air supply system. | 1 | Applied and Interdisciplinary Chemistry |
The law is amended to include a contribution by the volume viscosity :
The volume viscosity coefficient is relevant when the fluid's compressibility cannot be ignored, such as in the case of ultrasound in water. The volume viscosity of water at 15 C is 3.09 centipoise. | 1 | Applied and Interdisciplinary Chemistry |
Neurotransmitters bind to ionotropic receptors on postsynaptic neurons, either causing their opening or closing. The variations in the quantities of neurotransmitters released from the presynaptic neuron may play a role in regulating the effectiveness of synaptic transmission. In fact, the concentration of cytoplasmic calcium is involved in regulating the release of neurotransmitters from presynaptic neurons.
The chemical transmission involves several sequential processes:
# Synthesizing neurotransmitters within the presynaptic neuron.
# Loading the neurotransmitters into secretory vesicles.
# Controlling the release of neurotransmitters into the synaptic cleft.
# Binding of neurotransmitters to postsynaptic receptors.
# Ceasing the activity of the released neurotransmitters. | 1 | Applied and Interdisciplinary Chemistry |
Grignard reactions and reagents were discovered by and are named after the French chemist François Auguste Victor Grignard (University of Nancy, France), who described them in 1900. He was awarded the 1912 Nobel Prize in Chemistry for this work.
The reaction of an organic halide with magnesium is not a Grignard reaction, but provides a Grignard reagent.
Classically, the Grignard reaction refers to the reaction between a ketone or aldehyde group with a Grignard reagent to form a primary or tertiary alcohol. However, some chemists understand the definition to mean all reactions of any electrophiles with Grignard reagents. Therefore, there is some dispute about the modern definition of the Grignard reaction. In the Merck Index, published online by the Royal Society of Chemistry, the classical definition is acknowledged, followed by "A more modern interpretation extends the scope of the reaction to include the addition of Grignard reagents to a wide variety of electrophilic substrates." This variety of definitions illustrates that there is some dispute within the chemistry community about the definition of a Grignard reaction.
Shown below are some reactions involving Grignard reagents, but they themselves are not classically understood as Grignard reactions. | 0 | Theoretical and Fundamental Chemistry |
Mutations in the coding region can have very diverse effects on the phenotype of the organism. While some mutations in this region of DNA/RNA can result in advantageous changes, others can be harmful and sometimes even lethal to an organism's survival. In contrast, changes in the non-coding region may not always result in detectable changes in phenotype. | 1 | Applied and Interdisciplinary Chemistry |
Monomer 1 is consumed with reaction rate:
with the concentration of all the active chains terminating in monomer 1, summed over chain lengths. is defined similarly for monomer 2.
Likewise the rate of disappearance for monomer 2 is:
Division of both equations by followed by division of the first equation by the second yields:
The ratio of active center concentrations can be found using the steady state approximation, meaning that the concentration of each type of active center remains constant.
The rate of formation of active centers of monomer 1 () is equal to the rate of their destruction () so that
or
Substituting into the ratio of monomer consumption rates yields the Mayo–Lewis equation after rearrangement: | 0 | Theoretical and Fundamental Chemistry |
CDw17 antigen is a lactosylceramide, a class of glycosphingolipids found in microdomains on the plasma layers of numerous cells.
The enzyme A4GALT acts upon it, aiding transfer of galactose to lactosylceramide to form globotriaosylceramide. | 1 | Applied and Interdisciplinary Chemistry |
Archimedes principle (also spelled Archimedess principle) states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' principle is a law of physics fundamental to fluid mechanics. It was formulated by Archimedes of Syracuse. | 1 | Applied and Interdisciplinary Chemistry |
Ancestral sequence reconstruction (ASR) – also known as ancestral gene/sequence reconstruction/resurrection – is a technique used in the study of molecular evolution. The method uses related sequences to reconstruct an "ancestral" gene from a multiple sequence alignment.
The method can be used to resurrect ancestral proteins and was suggested in 1963 by Linus Pauling and Emile Zuckerkandl. In the case of enzymes, this approach has been called paleoenzymology (British: palaeoenzymology). Some early efforts were made in the 1980s and 1990s, led by the laboratory of Steven A. Benner, showing the potential of this technique. Thanks to the improvement of algorithms and of better sequencing and synthesis techniques, the method was developed further in the early 2000s to allow the resurrection of a greater variety of and much more ancient genes. Over the last decade, ancestral protein resurrection has developed as a strategy to reveal the mechanisms and dynamics of protein evolution. | 1 | Applied and Interdisciplinary Chemistry |
Ding was born in March 1966 in Yongcheng, Henan, China. He earned his bachelor's degree from Zhengzhou University in 1985 and his Ph.D. from the Department of Chemistry of Nanjing University in 1990. His doctoral advisor was Wu Yangjie.
Ding became a faculty member of Zhengzhou University in 1990. He conducted postdoctoral research at Ryukoku University in Japan from 1993 to 1994, and was promoted to full professor of Zhengzhou University in 1995. From 1997 to 1998, he was a UNESCO fellow at Tokyo Institute of Technology.
In December 1998, he became a research professor at the Shanghai Institute of Organic Chemistry. He served as President of the institute from 2009 to 2018. In October 2018, he was appointed Executive Vice President of Shanghai Jiao Tong University.
Ding's research interests are asymmetric catalysis and organometallics. He developed multiple chiral phosphine ligands that have been produced by chemical companies. He has received many awards, including the State Natural Science Award (Second Class), the Eli Lilly Scientific Excellence Award, the Yoshida Prize, and the Humboldt Prize. He serves as an editor of more than ten international chemistry journals. He was elected an academician of the Chinese Academy of Sciences in 2013. | 0 | Theoretical and Fundamental Chemistry |
In rheology, the Farris Effect describes the decrease of the viscosity of a suspension upon increasing the dispersity of the solid additive, at constant volume fraction of the solid additive. That is, that a broader particle size distribution yields a lower viscosity than a narrow particle size distribution, for the same concentration of particles. The phenomenon is names after Richard J. Farris, who modeled the effect. The effect is relevant whenever suspensions are flowing, particularly for suspensions with high loading fractions. Examples include hydraulic fracturing fluids, metal injection molding feedstocks, cosmetics, and various geological processes including sedimentation and lava flows. | 0 | Theoretical and Fundamental Chemistry |
Stream restoration is gradually being introduced in the legislative framework of various states. Examples include the European water framework's commitment to restoring surface water bodies, the adoption of the concept of freedom space in the French legislation, the inclusion in the Swiss legislation of the notion of space reserved for watercourses and of the requirement to restore streams to a state close to their natural state, and the inclusion of river corridors in land use planning in the American states of Vermont and Washington. Although this evolution is generally viewed positively by the scientific community, a concern expressed by some is that it could lead to less flexibility and less room for innovation in a field that is still in development. | 1 | Applied and Interdisciplinary Chemistry |
Some Marshallese have alleged that the exposure of the Marshallese was premeditated. In 1972, Micronesian Representative Ataji Balos charged at the Congress of Micronesia that the exposure during Bravo was purposeful so that the AEC could develop medical capabilities for treating those exposed to fallout during nuclear war, and charged that the Marshallese were chosen because of their marginal status in the world at large. According to a U.S. internal transcription of Balos' talk, Balos alleged that "The U.S. chose to make guinea pigs out of our people because they are not white but some brown natives in some remote Pacific islands. Medical treatment that Rongelapese and Utrikese have been receiving is also highly questionable." The AEC issued a staff comment denying these charges.
In 1994, a 1953 Castle Bravo program prospectus was found which included reference to Project 4.1 apparently written before the Bravo shot had occurred. The U.S. government responded that someone had gone back into the project list after the Bravo test to insert Project 4.1; thus, according to the U.S. government, the acts were not premeditated. All other U.S. documents point to Project 4.1 having been established after the Bravo test—most sources point to its having been organized on March 7, 1954. The final Project 4.1 report began in its preface with the statement that "Operation CASTLE did not include a biomedical program" (it mentions this in discussing the ad hoc nature by which the project personnel were assembled). All official and mainstream historical accounts of the Bravo test indicate that its high level of fallout was a result of a miscalculation in relation to its design and was not deliberate (see the Castle Bravo article for more information on the alleged accident).
Barton C. Hacker, the official historian of U.S. nuclear testing exposures (who is, in the end, very critical of the U.S. handling of the Bravo incident), characterized the controversy in the following way:
Controversy continues however, fed by the legacy of mistrust sown by American nuclear testing in the Marshall Islands, which involved relocating hundreds of people and rendering several atolls uninhabitable. While most sources do not think that the exposure was intentional, there is no dispute that the United States did carefully study the exposed Marshallese, but never obtained informed consent from the study subjects. This study of the Marshallese was in some cases beneficial for their treatment, and in other cases not. In these ways, the study of the exposed Marshallese reflects the same ethical lapses as were undertaken in other aspects of the secret human radiation experiments conducted by the Atomic Energy Commission in the 1940s and 1950s, which came to light only after the end of the Cold War. | 0 | Theoretical and Fundamental Chemistry |
Burgers' equation or Bateman–Burgers equation is a fundamental partial differential equation and convection–diffusion equation occurring in various areas of applied mathematics, such as fluid mechanics, nonlinear acoustics, gas dynamics, and traffic flow. The equation was first introduced by Harry Bateman in 1915 and later studied by Johannes Martinus Burgers in 1948.
For a given field and diffusion coefficient (or kinematic viscosity, as in the original fluid mechanical context) , the general form of Burgers equation (also known as viscous Burgers equation) in one space dimension is the dissipative system:
When the diffusion term is absent (i.e. ), Burgers equation becomes the inviscid Burgers equation:
which is a prototype for conservation equations that can develop discontinuities (shock waves).
In conservative form, the Burgers' equation becomes | 1 | Applied and Interdisciplinary Chemistry |
Avogadros hypothesis (as it was known originally) was formulated in the same spirit of earlier empirical gas laws like Boyles law (1662), Charless law (1787) and Gay-Lussacs law (1808). The hypothesis was first published by Amadeo Avogadro in 1811, and it reconciled Dalton atomic theory with the "incompatible" idea of Joseph Louis Gay-Lussac that some gases were composite of different fundamental substances (molecules) in integer proportions. In 1814, independently from Avogadro, André-Marie Ampère published the same law with similar conclusions. As Ampère was more well known in France, the hypothesis was usually referred there as Ampère's hypothesis, and later also as Avogadro–Ampère hypothesis or even Ampère–Avogadro hypothesis.
Experimental studies carried out by Charles Frédéric Gerhardt and Auguste Laurent on organic chemistry demonstrated that Avogadros law explained why the same quantities of molecules in a gas have the same volume. Nevertheless, related experiments with some inorganic substances showed seeming exceptions to the law. This apparent contradiction was finally resolved by Stanislao Cannizzaro, as announced at Karlsruhe Congress in 1860, four years after Avogadros death. He explained that these exceptions were due to molecular dissociations at certain temperatures, and that Avogadro's law determined not only molecular masses, but atomic masses as well. | 0 | Theoretical and Fundamental Chemistry |
The Bellini–Tosi direction finder was a type of radio direction finder that was widely used from World War I to World War II. It used the signals from two crossed antennas, or four individual antennas simulating two crossed ones, to re-create the radio signal in a small area between two loops of wire. The operator could then measure the angle to the target radio source by performing direction finding within this small area. The advantage to the Bellini–Tosi system is that the antennas do not move, allowing them to be built at any required size.
The basic technique remains in use, although the equipment has changed dramatically. Goniometers are widely used for military and civil purposes, e.g. interception of satellite and naval communications on the French warship Dupuy de Lôme uses multiple goniometers. | 0 | Theoretical and Fundamental Chemistry |
Underpotential deposition (UPD), in electrochemistry, is a phenomenon of electrodeposition of a species (typically reduction of a metal cation to a solid metal) at a potential less negative than the equilibrium (Nernst) potential for the reduction of this metal. The equilibrium potential for the reduction of a metal in this context is the potential at which it will deposit onto itself. Underpotential deposition can then be understood to be when a metal can deposit onto another material more easily than it can deposit onto itself. | 0 | Theoretical and Fundamental Chemistry |
Neutron scattering techniques particularly profit from availability of deuterated samples: The H and H cross sections are very distinct and different in sign, which allows contrast variation in such experiments. Further, a nuisance problem of ordinary hydrogen is its large incoherent neutron cross section, which is nil for H. The substitution of deuterium atoms for hydrogen atoms thus reduces scattering noise.
Hydrogen is an important and major component in all materials of organic chemistry and life science, but it barely interacts with X-rays. As hydrogen atoms (including deuterium) interact strongly with neutrons, neutron scattering techniques, together with a modern deuteration facility, fills a niche in many studies of macromolecules in biology and many other areas. | 0 | Theoretical and Fundamental Chemistry |
Cu is strongly cycled in the surface and deep ocean. In the deep ocean, Cu concentrations are ~5 nM in the Pacific and ~1.5 nM in the Atlantic. The deep/surface ratio of Cu in the ocean is typically <10, and vertical concentration profiles for Cu are roughly linear due to biological recycling and scavenging processes as well as adsorption to particles.
Due to equilibrium and biological processes that fractionate Cu isotopes in the marine environment, the bulk copper isotopic composition (δCu = +0.6 to +1.5‰) is different from the δCu values of the riverine input (δCu = +0.02 to +1.45‰, with discharge-weighted average δCu = +0.68‰) to the oceans. δCu values of the surface layers of FeMn-nodules are fairly homogenous throughout the oceans (average = 0.31‰), suggesting low biological demand for Cu in the marine environment compared to that of Fe or Zn. Additionally, δCu values in the Atlantic ocean do not markedly vary with depth, ranging from +0.56 to +0.72‰. However, Cu isotope compositions of material collected on sediment traps at depths of 1,000 and 2,500 m in the central Atlantic ocean show seasonal variation with heaviest δCu values in the spring and summer seasons suggesting seasonal preferential uptake of Cu by biological processes.
Equilibrium processes that fractionate Cu isotopes include high temperature ion exchange and redox speciation between mineral phases, and low temperature ion exchange between aqueous species or redox speciation between inorganic species. In riverine and marine environments, Cu/Cu ratios are driven by preferential adsorption of Cu to particulate matter and preferential binding of Cu to organic complexes. As a net result, ocean sediments tend to be depleted in Cu relative to the bulk ocean. For example, the downcore δCu values of a 760 cm sedimentary core taken from the Central Pacific ocean varied from -0.94 to -2.83‰, significantly lighter than the bulk ocean. | 0 | Theoretical and Fundamental Chemistry |
In 1953, Charles Frank proposed a model to demonstrate that homochirality is a consequence of autocatalysis. In his model the and enantiomers of a chiral molecule are autocatalytically produced from an achiral molecule A
while suppressing each other through a reaction that he called mutual antagonism
In this model the racemic state is unstable in the sense that the slightest enantiomeric excess will be amplified to a completely homochiral state. This can be shown by computing the reaction rates from the law of mass action:
where is the rate constant for the autocatalytic reactions, is the rate constant for mutual antagonism reaction, and the concentration of A is kept constant for simplicity.
The analytical solutions for are found to be
Linear stability analysis of this equation shows that the racemic state is unstable. Starting from almost everywhere in the concentration space, the system evolves to a homochiral state.
It is generally understood that autocatalysis alone does not yield to homochirality, and the presence of the mutually antagonistic relationship between the two enantiomers is necessary for the instability of the racemic mixture. However, recent studies show that homochirality could be achieved from autocatalysis in the absence of the mutually antagonistic relationship, but the underlying mechanism for symmetry-breaking is different. | 0 | Theoretical and Fundamental Chemistry |
In 2008, the submission was announced of a registration dossier to the European Medicines Agency and the FDA for Yondelis when administered in combination with pegylated liposomal doxorubicin (Doxil, Caelyx) for the treatment of women with relapsed ovarian cancer. In 2011, Johnson & Johnson voluntarily withdrew the submission in the United States following a request by the FDA for an additional phase III study to be done in support of the submission.
Trabectedin is also in phase II trials for prostate, breast, and paediatric cancers. | 0 | Theoretical and Fundamental Chemistry |
Laminar flow is encountered in practice with very viscous fluids, such as motor oil, flowing through small-diameter tubes, at low velocity. Friction loss under conditions of laminar flow follow the Hagen–Poiseuille equation, which is an exact solution to the Navier-Stokes equations. For a circular pipe with a fluid of density ρ and viscosity μ, the hydraulic slope S can be expressed
In laminar flow (that is, with Re < ~2000), the hydraulic slope is proportional to the flow velocity. | 1 | Applied and Interdisciplinary Chemistry |
A single-molecule electrically operated motor made from a single molecule of n-butyl methyl sulfide (CHS) has been reported. The molecule is adsorbed onto a copper (111) single-crystal piece by chemisorption. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, the pentagonal planar molecular geometry describes the shape of compounds where five atoms, groups of atoms, or ligands are arranged around a central atom, defining the vertices of a pentagon. | 0 | Theoretical and Fundamental Chemistry |
Splat quenching is a metallurgical, metal morphing technique used for forming metals with a particular crystal structure by means of extremely rapid quenching, or cooling.
A typical technique for splat quenching involves casting molten metal by pouring it between two massive, cooled copper rollers that are constantly chilled by the circulation of water. These provide a near-instant quench because of the large surface area in close contact with the melt. The thin sheet formed has a low ratio of volume relative to the area used for cooling.
Products that are formed through this process have a crystal structure that is near-amorphous, or non-crystalline. They are commonly used for their valuable magnetic properties, specifically high magnetic permeability. This makes them useful for magnetic shielding and for low-loss transformer cores in electrical grids. | 1 | Applied and Interdisciplinary Chemistry |
Experimental work by White and Brantley (2003) highlighted some of the limitations of the Goldich dissolution series, most notably that some variations in weathering rates of different minerals are not as pronounced as Goldich argues. According to the Goldich dissolution series, anorthite, a plagioclase feldspar, should weather quickly, with a lifetime of 10 years quantified by Kowalski and Rimstidt. Conversely, the lifetime of K-feldspar should be much longer, at 10 years based again on Kowalski and Rimstidt’s work. However, White and Brantley’s experimental results demonstrate that the relative weathering rates of K-feldspar and plagioclase feldspar are quite similar, and mainly moderated by the extent to which the minerals had already been weathered (in an exponentially decreasing function). This demonstrates that the Goldich series may not apply across all kinds of weathering processes, and likewise does not take into account the effect of exponential decay in weathering rate of a surface. | 0 | Theoretical and Fundamental Chemistry |
Systemic ablation of dendritic cells (DCs) was shown to cause fatal manifestations of autoimmunity which points to their importance in central tolerance. Indeed, as mTECs represent exclusive donors of TRAs, experiments with first antigen transfer mouse models discovered thymic dendritic cells (DCs) to be so far the only known TRAs acceptors involved in antigen transfer. Indispensability of DCs for the establishment of central tolerance was further verified by recent analysis, which revealed that DCs mediate both recessive and dominant tolerance, with preference for the latter, via presentation of more common TRAs. | 1 | Applied and Interdisciplinary Chemistry |
An encryption system constructed by pillar[5]arene, spiropyran and pentanenitrile (free state and grafted to polymer) was constructed by Wang et al. After UV irradiation, spiropyran would transform into merocyanine. When the visible light was shined on the material, the merocyanine close to the pillar[5]arene-free pentanenitrile complex had faster transformation to spiropyran; on the contrary, the one close to pillar[5]arene-grafted pentanenitrile complex has much slower transformation rate. This spiropyran-merocyanine transformation can be used for message encryption. Another strategy is based on the metallacages and polycyclic aromatic hydrocarbons. Because of the fluorescnece emission differences between the complex and the cages, the information could be encrypted. | 0 | Theoretical and Fundamental Chemistry |
An interesting aspect of particle-laden flows is preferential migration of particles to certain regions within the fluid flow. This is often characterized by the Stokes number (St) of the particles. At low St, particles tend to act as tracers and are uniformly distributed. At high St, particles are heavy and are influenced less by the fluid and more by its inertia. At intermediate St, particles are affected by both the fluid motion and its inertia, which gives rise to several interesting behaviors. This is especially true in wall-bounded flows where there is a velocity gradient near the wall.
One of the earliest works describing preferential migration is the experimental work of Segre and Silberberg. They showed that a neutrally buoyant particle in a laminar pipe flow comes to an equilibrium position between the wall and the axis. This is referred to as the Segré–Silberberg effect. Saffman explained this in terms of the force acting on the particle when it experiences a velocity gradient across it. Feng et al. have studied this through detailed direct numerical simulations and have elaborated on the physical mechanism of this migration.
Recently it was found that even for non-neutrally buoyant particles similar preferential migration occurs
. At low St, the particles tend to settle at an equilibrium position while for high St, the particles begin to oscillate about the center of the channel.
The behavior becomes even interesting in turbulent flows. Here, the turbophoretic force (transport of particles down gradients of turbulent kinetic energy) causes a high concentration of particles near the walls. Experimental and particle-resolved DNS studies have explained the mechanism of this migration in terms of the Saffman lift and the turbophoretic force
. These preferential migration are of significant importance to several applications where wall-bounded particle-laden flows are encountered and is an active area of research. | 1 | Applied and Interdisciplinary Chemistry |
Scintillation counters are usually not ideal for the detection of heavy ions for three reasons:
# the very high ionizing power of heavy ions induces quenching effects which result in a reduced light output (e.g. for equal energies, a proton will produce 1/4 to 1/2 the light of an electron, while alphas will produce only about 1/10 the light);
# the high stopping power of the particles also results in a reduction of the fast component relative to the slow component, increasing detector dead-time;
# strong non-linearities are observed in the detector response especially at lower energies.
The reduction in light output is stronger for organics than for inorganic crystals. Therefore, where needed, inorganic crystals, e.g. , (typically used in thin sheets as α-particle monitors), , should be preferred to organic materials. Typical applications are α-survey instruments, dosimetry instruments, and heavy ion dE/dx detectors. Gaseous scintillators have also been used in nuclear physics experiments. | 0 | Theoretical and Fundamental Chemistry |
Drug titration is the process of adjusting the dose of a medication for the maximum benefit without adverse effects.
When a drug has a narrow therapeutic index, titration is especially important, because the range between the dose at which a drug is effective and the dose at which side effects occur is small. Some examples of the types of drugs commonly requiring titration include insulin, anticonvulsants, blood thinners, anti-depressants, and sedatives.
Titrating off of a medication instead of stopping abruptly is recommended in some situations. Glucocorticoids should be tapered after extended use to avoid adrenal insufficiency.
Drug titration is also used in phase I of clinical trials. The experimental drug is given in increasing dosages until side effects become intolerable. A clinical trial in which a suitable dose is found is called a dose-ranging study. | 1 | Applied and Interdisciplinary Chemistry |
Oxyhydrogen is associated with various exaggerated claims. It is often called "Brown's gas" or "HHO gas", a term popularized by fringe physicist Ruggero Santilli, who claimed that his HHO gas, produced by a special apparatus, is "a new form of water", with new properties, based on his fringe theory of "magnecules".
Many other pseudoscientific claims have been made about oxyhydrogen, like an ability to neutralize radioactive waste, help plants to germinate, and more.
Oxyhydrogen is often mentioned in conjunction with vehicles that claim to use water as a fuel. The most common and decisive counter-argument against producing this gas on board to use as a fuel or fuel additive is that more energy is always needed to split water molecules than is recouped by burning the resulting gas. Additionally, the volume of gas that can be produced for on-demand consumption through electrolysis is very small in comparison to the volume consumed by an internal combustion engine.
An article in Popular Mechanics in 2008 reported that oxyhydrogen does not increase the fuel economy in automobiles.
"Water-fueled" cars should not be confused with hydrogen-fueled cars, where the hydrogen is produced elsewhere and used as fuel or where it is used as fuel enhancement. | 0 | Theoretical and Fundamental Chemistry |
nc-AFM was the first form of AFM to achieve true atomic resolution images, rather than averaging over multiple contacts, both on non-reactive and reactive surfaces.
nc-AFM was the first form of microscopy to achieve subatomic resolution images, initially on tip atoms and later on single iron adatoms on copper.
nc-AFM was the first technique to directly image chemical bonds in real space, see inset image. This resolution was achieved by picking up a single CO molecule on the apex of the tip.
nc-AFM has been used to probe the force interaction between a single pair of molecules. | 0 | Theoretical and Fundamental Chemistry |
As a recently created program, environmental engineering science has not yet been incorporated into the terminology found among environmentally focused professionals. In the few engineering colleges that offer this major, the curriculum shares more classes in common with environmental engineering than it does with environmental science. Typically, EES students follow a similar course curriculum with environmental engineers until their fields diverge during the last year of college. The majority of the environmental engineering students must take classes designed to connect their knowledge of the environment to modern building materials and construction methods. This is meant to direct the environmental engineer into a field where they will more than likely assist in building treatment facilities, preparing environmental impact assessments or helping to mitigate air pollution from specific point sources.
Meanwhile, the environmental engineering science student will choose a direction for their career. From the range of electives they have to choose from, these students can move into a fields such as the design of nuclear storage facilities, bacterial bioreactors or environmental policies. These students combine the practical design background of an engineer with the detailed theory found in many of the biological and physical sciences. | 1 | Applied and Interdisciplinary Chemistry |
A bioprocessor is a miniaturized bioreactor capable of culturing mammalian, insect and microbial cells. Bioprocessors are capable of mimicking performance of large-scale bioreactors, hence making them ideal for laboratory scale experimentation of cell culture processes. Bioprocessors are also used for concentrating bioparticles (such as cells) in bioanalytical systems. Microfluidic processes such as electrophoresis can be implemented by bioprocessors to aid in DNA isolation and purification. | 1 | Applied and Interdisciplinary Chemistry |
Gregory Fu and colleagues have developed a methodology utilizing a chiral DMAP analogue to achieve excellent kinetic resolution of secondary alcohols. Initial studies utilizing ether as a solvent, low catalyst loadings (2 mol %), acetic anhydride as the acylating agent, and triethylamine at room temperature gave selectivities ranging from 14-52, corresponding to ee's of the recovered alcohol product as high as 99.2%. However, solvent screening proved that the use of tert-amyl alcohol increased both the reactivity and selectivity.
With the benchmark substrate 1-phenylethanol, this corresponded to 99% ee of the unreacted alcohol at 55% conversion when run at 0 °C. This system proved to be adept at resolution of a number of arylalkylcarbinols, with selectivities as high as 95 and low catalyst loadings of 1%, as shown below utilizing the (-)-enantiomer of the catalyst. This resulted in highly enantioenriched alcohols at very low conversions, giving excellent yields as well. In addition, the high selectivities result in highly enantioenriched acylated products, with a 90% ee sample of acylated alcohol for o-tolylmethylcarbinol, with s=71.
In addition, Fu reported the first highly selective acylation of racemic diols (as well as desymmetrization of meso diols). With low catalyst loading of 1%, enantioenriched diol was recovered in 98% ee and 43% yield, with the diacetate in 39% yield and 99% ee. The remainder of the material was recovered as a mixture of monoacetate.
The planar-chiral DMAP catalyst was also shown to be effective at kinetically resolving propargylic alcohols. In this case, though, selectivities were found to be highest without any base present. When run with 1 mol% of the catalyst at 0 °C, selectivities as high as 20 could be attained. The limitations of this method include the requirement of an unsaturated functionality, such as carbonyl or alkenes, at the remote alkynyl position. Alcohols resolved using the (+)-enantiomer of the DMAP catalyst are shown below.
Fu also showed his chiral DMAP catalyst's ability to resolve allylic alcohols.
Effective selectivity was dependent upon the presence of either a geminal or cis substituent to the alcohol-bearing group, with a notable exception of a trans-phenyl alcohol which exhibited the highest selectivity. Using 1-2.5 mol% of the (+)-enantiomer of the DMAP catalyst, the alcohols shown below were resolved in the presence of triethylamine.
While Fu's DMAP analogue catalyst worked exceptionally well to kinetically resolve racemic alcohols, it was not successful in use for the kinetic resolution of amines. A similar catalyst, PPY*, was developed that, in use with a novel acylating agent, allowed for the successful kinetic resolution acylation of amines. With 10 mol% (-)-PPY* in chloroform at –50 °C, good to very good selectivities were observed in the acylation of amines, shown below. A similar protocol was developed for the kinetic resolution of indolines. | 0 | Theoretical and Fundamental Chemistry |
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