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Cotransporters are found in all organisms and fall under the broader category of transport proteins, a diverse group of transmembrane proteins that includes uniporters, symporters, and antiporters. Each of them are responsible for providing a means of movement for water-soluble molecules that otherwise would not be able to pass through lipid-based plasma membrane. The simplest of these are the uniporters, which facilitate the movement of one type of molecule in the direction that follows its concentration gradient. In mammals, they are most commonly responsible for bringing glucose and amino acids into cells.
Symporters and antiporters are more complex because they move more than one ion and the movement of one of those ions is in an energetically unfavorable direction. As multiple molecules are involved, multiple binding processes must occur as the transporter undergoes a cycle of conformational changes to move them from one side of the membrane to the other. The mechanism used by these transporters limits their functioning to moving only a few molecules at a time. As a result, symporters and antiporters are characterized by a slower transport speed, moving between 10 and 10 molecules per second. Compare this to ion channels that provide a means for facilitated diffusion to occur and allow between 10 and 10 ions pass through the plasma membrane per second.
Though ATP-powered pumps also move molecules in an energetically unfavorable direction and undergo conformational changes to do so, they fall under a different category of membrane proteins because they couple the energy derived from ATP hydrolysis to transport their respective ions. These ion pumps are very selective, consisting of a double gating system where at least one of the gates is always shut. The ion is allowed to enter from one side of the membrane while one of the gates is open, after which it will shut. Only then will the second gate open to allow the ion to leave on the membrane's opposite side. The time between the alternating gate opening is referred to as the occluded state, where the ions are bound and both gates are shut. These gating reactions limit the speed of these pumps, causing them to function even slower than transport proteins, moving between 10 and 10 ions per second.
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Applied and Interdisciplinary Chemistry
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He then joined the Eveready Battery Co as a chemist where he was frustrated that his work to make longer lasting batteries was not well received by the marketing department. He then returned to teaching but now in tertiary education. During World War II he was a Gas Officer as the civil defence forces were very concerned that the likely Japanese invasion would include gas attacks. He was lecturer, then senior lecturer in Chemistry at Sydney Technical College from 1940 to 1951, although on leave in London from 1947. From 1952 to 1954 he was associate professor of Inorganic Chemistry at the New South Wales University of Technology. In 1954 he was elected President of the Royal Society of New South Wales. In 1955, Nyholm returned to England as Professor of Chemistry at University College London, where he worked until his death on 4 December 1971 as a result of a motorcar accident on the outskirts of Cambridge, England.
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Theoretical and Fundamental Chemistry
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Survivin is a member of the IAP family of antiapoptotic proteins. It is shown to be conserved in function across evolution as homologues of the protein are found both in vertebrates and invertebrates. The first members of the IAPs identified were from the baculovirus IAPs, Cp-IAP and Op-IAP, which bind to and inhibit caspases as a mechanism that contributes to its efficient infection and replication cycle in the host. Later, five more human IAPs that included XIAP, c-IAPl, C-IAP2, NAIP, and survivin were discovered. Survivin, like the others, was discovered by its structural homology to IAP family of proteins in human B-cell lymphoma. The human IAPs, XIAP, c-IAPl, C-IAP2 have been shown to bind to caspase-3 and -7, which are the effector caspases in the signaling pathway of apoptosis. It is not known with absolute certainty though, how the IAPs inhibit apoptosis mechanistically at the molecular level.
A common feature that is present in all IAPs in the presence of a BIR (Baculovirus IAP Repeat, a ~70 amino acid motif) in one to three copies. It was shown by Tamm et al. that knocking out BIR2 from XIAP was enough to cause a loss of function in terms of XIAPs ability to inhibit caspases. This gives the implication that it is within these BIR motifs that contains the anti-apoptotic function of these IAPs. Survivins one BIR domain shows a similar sequence compared to that of XIAPs BIR domains.
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Applied and Interdisciplinary Chemistry
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Ramboll Studio Dreiseitl are responsible for the waterscape on Potsdamer Platz in Berlin. Water was central to Renzo Piano and Christoph Kohlbecker's original design, but it was Ramboll Studio Dreiseitl that conceived and developed the scheme for rainwater recycling and created the many opportunities for public engagement with water. The scheme is one of the largest urban rainwater harvesting projects in the world and in 2011, it became one of the first city quarters to be retrospectively awarded the DGNB Certificate of the German Sustainable Building Council (DGNB) in silver.
Another major project in Germany is Arkadien Winnenden, the ecological city design which was named winner of the Green Dot Award ‘Build’ category in 2011. The firm turned the abandoned factory site into an eco-friendly development which combines dense layout with green space, includes permeable paving and waterways which provide natural flood control and a lake which filters rainwater.
In 2018, Ramboll Studio Dreiseitl was awarded the German Design Award in the category "Urban Space an Infrastructure" for their design and planning of the project Hafen Offenbach in Offenbach am Main, Germany. Studio Dreiseitl has transformed the initial urban plan by reconnecting public open spaces with their scenic context, creating a liveable as well as ecologically enriching neighbourhood.
In Asia, projects include the blue green infrastructure in the Tianjin Cultural Park near Beijing and the water strategy for the central catchment for the city of Singapore, together with the engineers CH2M Hill, as well as the design of the 60ha Bishan-Ang Mo Kio Park. The rehabilitation of the previously concreted Kallang River (which became a dangerous torrent in the rainy season) employed techniques of water collection and flood control which were entirely new to Singapore. Ramboll Studio Dreiseitl built a test area and held workshops to explain the concepts. The designers gave the river gentle banks and recycled the concrete from the old drainage channel to create stairs. Now Bishan Park is one of the most popular parks in Singapore, where people can have a new and direct connection to nature. In 2012, the design was awarded the Presidents Design Award Singapore and the World Architecture Festival “Landscape of the Year”.
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Applied and Interdisciplinary Chemistry
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Classical variables that time reversal negates include:
:, the time when an event occurs
:, velocity of a particle
:, linear momentum of a particle
:, angular momentum of a particle (both orbital and spin)
:, electromagnetic vector potential
:, magnetic field
:, magnetic auxiliary field
:, density of electric current
:, magnetization
:, Poynting vector
:, power (rate of work done).
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Theoretical and Fundamental Chemistry
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Anomerism is an identity for single bonded ring structures where "cis" or "Z" and "trans" or "E" (geometric isomerism) needs to name the substitutions on a carbon atom that also displays the identity of chirality; so anomers have carbon atoms that have geometric isomerism and optical isomerism (enantiomerism) on one or more of the carbons of the ring. Anomers are named "alpha" or "axial" and "beta" or "equatorial" when substituting a cyclic ring structure that has single bonds between the carbon atoms of the ring for example, a hydroxyl group, a methyl hydroxyl group, a methoxy group or another pyranose or furanose group which are typical single bond substitutions but not limited to these. Axial geometric isomerism will be perpendicular (90 degrees) to a reference plane and equatorial will be 120 degrees away from the axial bond or deviate 30 degrees from the reference plane.
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Theoretical and Fundamental Chemistry
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Opacity broadening is an example of a non-local broadening mechanism. Electromagnetic radiation emitted at a particular point in space can be reabsorbed as it travels through space. This absorption depends on wavelength. The line is broadened because the photons at the line center have a greater reabsorption probability than the photons at the line wings. Indeed, the reabsorption near the line center may be so great as to cause a self reversal in which the intensity at the center of the line is less than in the wings. This process is also sometimes called self-absorption.
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Theoretical and Fundamental Chemistry
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The rate of sequencing or imaging is dependent on the mechanical movement speed of the magnetic beads, which is limited by drag force. Currently, it is possible to measure 10 hairpin open-close cycle per second. Additional complications include the existence of a secondary hairpin structure in the DNA of interest. In such a case the DNA loop to be ligated must be designed such that it its closing is favored over the closing of the endogenous loop in the DNA of interest.
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Applied and Interdisciplinary Chemistry
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is synonymous to "the relative abundance of elements" in any object, either in weight ratio or in atomic (number of atoms) ratio, regardless of how "Earth's crust" is defined, and denotation is not restricted to percents.
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Theoretical and Fundamental Chemistry
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Compacted oxide layer glaze describes the often shiny, wear-protective layer of oxide formed when two metals (or a metal and ceramic) are slid against each other at high temperature in an oxygen-containing atmosphere. The layer forms on either or both of the surfaces in contact and can protect against wear.
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Applied and Interdisciplinary Chemistry
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Applications of thermal desorption were originally restricted to occupational health monitoring, but have since extended to cover a much wider range. Some of the most important are mentioned below – where available, examples of early reports, and more recent citations (including those of widely used standard methods) have been given:
*Outdoor environmental monitoring
*Workplace/occupational health monitoring
*Residual volatiles emitted from products and materials
*Studies of biological systems, including plant–herbivore interactions
*Breath analysis for disease diagnosis
*Aroma profiling of food and drink
*Defence/homeland security (detection of chemical agents)
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Theoretical and Fundamental Chemistry
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Friction loss takes place as a gas, say air, flows through duct work.
The difference in the character of the flow from the case of water in a pipe stems from the differing Reynolds number Re and the roughness of the duct.
The friction loss is customarily given as pressure loss for a given duct length, Δp / L, in units of (US) inches of water for 100 feet or (SI) kg / m / s.
For specific choices of duct material, and assuming air at standard temperature and pressure (STP), standard charts can be used to calculate the expected friction loss. The chart exhibited in this section can be used to graphically determine the required diameter of duct to be installed in an application where the volume of flow is determined and where the goal is to keep the pressure loss per unit length of duct S below some target value in all portions of the system under study. First, select the desired pressure loss Δp / L, say 1 kg / m / s (0.12 in HO per 100 ft) on the vertical axis (ordinate). Next scan horizontally to the needed flow volume Q, say 1 m / s (2000 cfm): the choice of duct with diameter D = 0.5 m (20 in.) will result in a pressure loss rate Δp / L less than the target value. Note in passing that selecting a duct with diameter D = 0.6 m (24 in.) will result in a loss Δp / L of 0.02 kg / m / s (0.02 in HO per 100 ft), illustrating the great gains in blower efficiency to be achieved by using modestly larger ducts.
The following table gives flow rate Q such that friction loss per unit length Δp / L (SI kg / m / s) is 0.082, 0.245, and 0.816, respectively, for a variety of nominal duct sizes. The three values chosen for friction loss correspond to, in US units inch water column per 100 feet, 0.01, .03, and 0.1. Note that, in approximation, for a given value of flow volume, a step up in duct size (say from 100mm to 120mm) will reduce the friction loss by a factor of 3.
Note that, for the chart and table presented here, flow is in the turbulent, smooth pipe domain, with R* < 5 in all cases.
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Applied and Interdisciplinary Chemistry
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Most methods for nucleic acid secondary structure prediction rely on a nearest neighbor thermodynamic model. A common method to determine the most probable structures given a sequence of nucleotides makes use of a dynamic programming algorithm that seeks to find structures with low free energy. Dynamic programming algorithms often forbid pseudoknots, or other cases in which base pairs are not fully nested, as considering these structures becomes computationally very expensive for even small nucleic acid molecules. Other methods, such as stochastic context-free grammars can also be used to predict nucleic acid secondary structure.
For many RNA molecules, the secondary structure is highly important to the correct function of the RNA — often more so than the actual sequence. This fact aids in the analysis of non-coding RNA sometimes termed "RNA genes". One application of bioinformatics uses predicted RNA secondary structures in searching a genome for noncoding but functional forms of RNA. For example, microRNAs have canonical long stem-loop structures interrupted by small internal loops.
RNA secondary structure applies in RNA splicing in certain species. In humans and other tetrapods, it has been shown that without the U2AF2 protein, the splicing process is inhibited. However, in zebrafish and other teleosts the RNA splicing process can still occur on certain genes in the absence of U2AF2. This may be because 10% of genes in zebrafish have alternating TG and AC base pairs at the 3 splice site (3ss) and 5 splice site (5ss) respectively on each intron, which alters the secondary structure of the RNA. This suggests that secondary structure of RNA can influence splicing, potentially without the use of proteins like U2AF2 that have been thought to be required for splicing to occur.
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Theoretical and Fundamental Chemistry
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A sample is continuously extracted from the gas stream being monitored using a titanium probe, which is water-cooled to below 70 °C. The sample flow rate is automatically adjusted to ensure isokinetic sampling (the velocity of gas entering the sampling system is equal to the velocity of the gas in the system under test). The sample gas is drawn through a quartz wool pre-filter and then across a cartridge filled with resin, such as XAD 2. The sample gas is also cooled to below 5 °C to condense and remove water vapour. All system parameters are recorded digitally during sampling. The resin cartridge and the condensate are removed at the end of a monitoring period, and the contents are analysed to determine levels of dioxins and furans.
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Theoretical and Fundamental Chemistry
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Inexact differentials show up explicitly in the first law of thermodynamics,
where is the energy, is the differential change in heat and is the differential change in work. Based on the constants of the thermodynamic system, we are able to parameterize the average energy in several different ways. E.g., in the first stage of the Carnot cycle (which is isentropic) a gas is heated by a reservoir, giving us an isothermal expansion of that gas. During this stage, the volume is constant while some differential amount of heat enters the gas. During the second stage, the gas is allowed to freely expand, outputting some differential amount of work . The third stage is similar to the first stage, except the heat is lost by contact with a cold reservoir, while the fourth cycle is like the second except work is done onto the system by the surroundings to compress the gas. Because the overall changes in heat and work are different over different parts of the cycle, there is a nonzero net change in the heat and work, indicating that the differentials and must be inexact differentials.
Internal energy is a state function, meaning its change can be inferred just by comparing two different states of the system (independently of its transition path), which we can therefore indicate with and .
Since we can go from state to state either by providing heat or work , such a change of state does not uniquely identify the amount of work done to the system or heat transferred, but only the change in internal energy .
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Theoretical and Fundamental Chemistry
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This phenomenon describes damage to the metal (nearly always iron or steel) at low temperature by diffusible hydrogen.
Hydrogen can embrittle a number of metals and steel is one of them. It tends to happen to harder and higher tensile steels. Hydrogen cam also embrittle aluminum at high temperatures.). Titanium metal and alloys are also susceptible.
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Applied and Interdisciplinary Chemistry
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The closest competing method to IMHR is radical cyclization. Radical cyclizations are often reductive, which can cause undesired side reactions to occur if sensitive substrates are employed. The IMHR, on the other hand, can be run under reductive conditions if desired. Unlike the IMHR, radical cyclization does not require the coupling of two sp-hybridized carbons. In some cases, the results of radical cyclization and IMHR are complementary.
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Theoretical and Fundamental Chemistry
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Rachid Idrissi died on October 18, 1971, in Salé in a car accident after being hit by a truck on National Road 15 while crossing a bridge on Bou Regreg from Rabat on his way to his hometown of Outat El Haj. His sudden death immediately raised suspicion of a political assassination from his entourage. He was buried in the cemetery in Douar El Kchahda, near Outat El Haj.
During a speech at his funeral, engineer Mohamed Ait Kaddour, a colleague of Idrissi, stated that he fell victim to "his involvement in establishing a defense project in the Arab world based on his possession of science, knowledge, and ability". A scholar in Idrissis hometown, Hajj Mohamed Harmouche, blamed his death on "external parties". Newspaper Al Ittihad Al Ichtiraki' claimed that Idrissi had been surveilled by foreign intelligence agencies prior to his death, but this remains unconfirmed.
A posthumous Rachid Idrissi El Ouatati Prize for Criticism was created in May 2023 by the Oboure Cultural Publishing Association in Rabat, the prize crowns works of literary criticism in Morocco and commemorates Idrissi. In December 2023, a synopsium was held by the Moulay Rachid Idrissi Center for Studies and Research in Outat El Haj regarding Idrissi's life.
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Theoretical and Fundamental Chemistry
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BMR is a flexible trait (it can be reversibly adjusted within individuals), with, for example, lower temperatures generally resulting in higher basal metabolic rates for both birds and rodents. There are two models to explain how BMR changes in response to temperature: the variable maximum model (VMM) and variable fraction model (VFM). The VMM states that the summit metabolism (or the maximum metabolic rate in response to the cold) increases during the winter, and that the sustained metabolism (or the metabolic rate that can be indefinitely sustained) remains a constant fraction of the former. The VFM says that the summit metabolism does not change, but that the sustained metabolism is a larger fraction of it. The VMM is supported in mammals, and, when using whole-body rates, passerine birds. The VFM is supported in studies of passerine birds using mass-specific metabolic rates (or metabolic rates per unit of mass). This latter measurement has been criticized by Eric Liknes, Sarah Scott, and David Swanson, who say that mass-specific metabolic rates are inconsistent seasonally.
In addition to adjusting to temperature, BMR also may adjust before annual migration cycles. The red knot (ssp. islandica) increases its BMR by about 40% before migrating northward. This is because of the energetic demand of long-distance flights. The increase is likely primarily due to increased mass in organs related to flight. The end destination of migrants affects their BMR: yellow-rumped warblers migrating northward were found to have a 31% higher BMR than those migrating southward.
In humans, BMR is directly proportional to a persons lean body mass. In other words, the more lean body mass a person has, the higher their BMR; but BMR is also affected by acute illnesses and increases with conditions like burns, fractures, infections, fevers, etc. In menstruating females, BMR varies to some extent with the phases of their menstrual cycle. Due to the increase in progesterone, BMR rises at the start of the luteal phase and stays at its highest until this phase ends. There are different findings in research how much of an increase usually occurs. Small sample, early studies, found various figures, such as; a 6% higher postovulatory sleep metabolism, a 7% to 15% higher 24 hour expenditure following ovulation, and an increase and a luteal phase BMR increase by up to 12%. A study by the American Society of Clinical Nutrition found that an experimental group of female volunteers had an 11.5% average increase in 24 hour energy expenditure in the two weeks following ovulation, with a range of 8% to 16%. This group was measured via simultaneously direct and indirect calorimetry and had standardized daily meals and sedentary schedule in order to prevent the increase from being manipulated by change in food intake or activity level. A 2011 study conducted by the Mandya Institute of Medical Sciences found that during a womans follicular phase and menstrual cycle is no significant difference in BMR, however the calories burned per hour is significantly higher, up to 18%, during the luteal phase. Increased state anxiety (stress level) also temporarily increased BMR.
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Applied and Interdisciplinary Chemistry
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For a box of radiation, ignoring quantum mechanics, the energy of a classical field in thermal equilibrium is infinite, since equipartition demands that each field mode has an equal energy on average, and there are infinitely many modes. This is physically ridiculous, since it means that all energy leaks into high-frequency electromagnetic waves over time.
Still, without quantum mechanics, there are some things that can be said about the equilibrium distribution from thermodynamics alone, because there is still a notion of adiabatic invariance that relates boxes of different size.
When a box is slowly expanded, the frequency of the light recoiling from the wall can be computed from the Doppler shift. If the wall is not moving, the light recoils at the same frequency. If the wall is moving slowly, the recoil frequency is only equal in the frame where the wall is stationary. In the frame where the wall is moving away from the light, the light coming in is bluer than the light coming out by twice the Doppler shift factor v/c:
On the other hand, the energy in the light is also decreased when the wall is moving away, because the light is doing work on the wall by radiation pressure. Because the light is reflected, the pressure is equal to twice the momentum carried by light, which is E/c. The rate at which the pressure does work on the wall is found by multiplying by the velocity:
This means that the change in frequency of the light is equal to the work done on the wall by the radiation pressure. The light that is reflected is changed both in frequency and in energy by the same amount:
Since moving the wall slowly should keep a thermal distribution fixed, the probability that the light has energy E at frequency f must only be a function of E/f.
This function cannot be determined from thermodynamic reasoning alone, and Wien guessed at the form that was valid at high frequency. He supposed that the average energy in high-frequency modes was suppressed by a Boltzmann-like factor:
This is not the expected classical energy in the mode, which is by equipartition, but a new and unjustified assumption that fit the high-frequency data.
When the expectation value is added over all modes in a cavity, this is Wiens distribution, and it describes the thermodynamic distribution of energy in a classical gas of photons. Wiens law implicitly assumes that light is statistically composed of packets that change energy and frequency in the same way. The entropy of a Wien gas scales as the volume to the power N, where N is the number of packets. This led Einstein to suggest that light is composed of localizable particles with energy proportional to the frequency. Then the entropy of the Wien gas can be given a statistical interpretation as the number of possible positions that the photons can be in.
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Theoretical and Fundamental Chemistry
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Albert Rakoto Ratsimamanga (28 December 1907 – 16 September 2001) was a Malagasy physician, biochemist and diplomat. Born into a disgraced royal family; Ratsimamanga trained as a doctor of exotic medicine in French Madagascar and France, where he pioneered modern nutraceuticals. Ratsimamanga returned to Madagascar and, with his wife, Suzanne Urverg-Ratsimamanga, in 1957, established the which specialised in herbal medicine.
While in France, Ratsimamanga was involved in Madagascars independence efforts, and after independence, he became the Malagasy Republics first ambassador to France and helped shape its foreign affairs. Ratsimamanga is considered one of Madagascars most renowned scholars and bestowed upon him the highest orders of merits nationally and internationally. He was also one of the founders of The World Academy of Sciences (1983) and the African Academy of Sciences (1985), and was selected Madagascars Man of the Century.
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Applied and Interdisciplinary Chemistry
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Michael Faraday reported that the mass () of a substance deposited or liberated at an electrode is directly proportional to the charge (; SI units are ampere seconds or coulombs).
Here, the constant of proportionality, , is called the electro-chemical equivalent (ECE) of the substance. Thus, the ECE can be defined as the mass of the substance deposited or liberated per unit charge.
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Theoretical and Fundamental Chemistry
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Metallurgists throughout medieval Europe were generally free to move within different regions. For instance, German metallurgists in search of rich precious metal ores took the lead in mining and influenced the course of metal production, not only in East and South Germany but also in almost all of Central Europe and the Eastern Alps.
As mining gradually became a task for specialized craftsmen, miners moved in large groups and formed settlements close to mines, each with their own customs. They were always welcomed by regional authorities, as the latter were interested in increasing revenue through the profitable exploitation of the mineral-rich subsurface. These authorities claimed a portion of the output, and smiths and miners were provided with land for cottages, mills, forges, farming, and pasture, while also being allowed to utilize streams and lumber. (Nef 1987, 706–715).
Advancing into the high and late Middle Ages, a notable shift occurred where smelting sites gained geographical independence from mines, leading to the separation of metalworking from ore smelting. The urban expansion that unfolded from the 10th century onwards, coupled with the pivotal influence of towns, afforded metallurgists an optimal setting to cultivate and refine their technological advancements. This era witnessed the systematic formation of metallurgical guilds, with their workshops often converging on the outskirts of these urban centers. (McLees 1996).
In medieval societies, liberal and mechanical arts were considered to be totally different disciplines. Metallurgists, like all craftsmen and artisans, almost always lacked the formal education that would inform a methodical intellectual background. Instead, they were the pioneers of causal thinking based on empirical observation and experimentation (Zilsel 2000).
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Applied and Interdisciplinary Chemistry
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For all but the simplest of velocity profiles , numerical or asymptotic methods are required to calculate solutions. Some typical flow profiles are discussed below. In general, the spectrum of the equation is discrete and infinite for a bounded flow, while for unbounded flows (such as boundary-layer flow), the spectrum contains both continuous and discrete parts.
For plane Poiseuille flow, it has been shown that the flow is unstable (i.e. one or more eigenvalues has a positive imaginary part) for some when and the neutrally stable mode at having , . To see the stability properties of the system, it is customary to plot a dispersion curve, that is, a plot of the growth rate as a function of the wavenumber .
The first figure shows the spectrum of the Orr–Sommerfeld equation at the critical values listed above. This is a plot of the eigenvalues (in the form ) in the complex plane. The rightmost eigenvalue is the most unstable one. At the critical values of Reynolds number and wavenumber, the rightmost eigenvalue is exactly zero. For higher (lower) values of Reynolds number, the rightmost eigenvalue shifts into the positive (negative) half of the complex plane. Then, a fuller picture of the stability properties is given by a plot exhibiting the functional dependence of this eigenvalue; this is shown in the second figure.
On the other hand, the spectrum of eigenvalues for Couette flow indicates stability, at all Reynolds numbers. However, in experiments, Couette flow is found to be unstable to small, but finite, perturbations for which the linear theory, and the Orr–Sommerfeld equation do not apply. It has been argued that the non-normality of the eigenvalue problem associated with Couette (and indeed, Poiseuille) flow might explain that observed instability. That is, the eigenfunctions of the Orr–Sommerfeld operator are complete but non-orthogonal. Then, the energy of the disturbance contains contributions from all eigenfunctions of the Orr–Sommerfeld equation. Even if the energy associated with each eigenvalue considered separately is decaying exponentially in time (as predicted by the Orr–Sommerfeld analysis for the Couette flow), the cross terms arising from the non-orthogonality of the eigenvalues can increase transiently. Thus, the total energy increases transiently (before tending asymptotically to zero). The argument is that if the magnitude of this transient growth is sufficiently large, it destabilizes the laminar flow, however this argument has not been universally accepted.
A nonlinear theory explaining transition, has also been proposed. Although that theory does include linear transient growth, the focus is on 3D nonlinear processes that are strongly suspected to underlie transition to turbulence in shear flows. The theory has led to the construction of so-called complete 3D steady states, traveling waves and time-periodic solutions of the Navier-Stokes equations that capture many of the key features of transition and coherent structures observed in the near wall region of turbulent shear flows. Even though "solution" usually implies the existence of an analytical result, it is common practice in fluid mechanics to refer to numerical results as "solutions" - regardless of whether the approximated solutions satisfy the Navier-Stokes equations in a mathematically satisfactory way or not. It is postulated that transition to turbulence involves the dynamic state of the fluid evolving from one solution to the next. The theory is thus predicated upon the actual existence of such solutions (many of which have yet to be observed in a physical experimental setup). This relaxation on the requirement of exact solutions allows a great deal of flexibility, since exact solutions are extremely difficult to obtain (contrary to numerical solutions), at the expense of rigor and (possibly) correctness. Thus, even though not as rigorous as previous approaches to transition, it has gained immense popularity.
An extension of the Orr–Sommerfeld equation to the flow in porous media has been recently suggested.
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Applied and Interdisciplinary Chemistry
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One way that Zero Carbon World aims to meet its objectives is the donation of Electric Vehicle Charging stations to various organisations around the UK. Sites that install donated chargers get added to the charity's ZeroNet EV charger map.
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Applied and Interdisciplinary Chemistry
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Solar cells degrade over time and lose their efficiency. Solar cells in extreme climates, such as desert or polar, are more prone to degradation due to exposure to harsh UV light and snow loads respectively. Usually, solar panels are given a lifespan of 25–30 years before they get decommissioned.
The International Renewable Energy Agency estimated that the amount of solar panel electronic waste generated in 2016 was 43,500–250,000 metric tons. This number is estimated to increase substantially by 2030, reaching an estimated waste volume of 60–78 million metric tons in 2050.
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Theoretical and Fundamental Chemistry
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Primary and secondary antibodies are two groups of antibodies that are classified based on whether they bind to antigens or proteins directly or target another (primary) antibody that, in turn, is bound to an antigen or protein.
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Applied and Interdisciplinary Chemistry
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Adenine and guanine are the two nucleotides classified as purines. In purine synthesis, PRPP is turned into inosine monophosphate, or IMP. Production of IMP from PRPP requires glutamine, glycine, aspartate, and 6 ATP, among other things. IMP is then converted to AMP (adenosine monophosphate) using GTP and aspartate, which is converted into fumarate. While IMP can be directly converted to AMP, synthesis of GMP (guanosine monophosphate) requires an intermediate step, in which NAD+ is used to form the intermediate xanthosine monophosphate, or XMP. XMP is then converted into GMP by using the hydrolysis of 1 ATP and the conversion of glutamine to glutamate. AMP and GMP can then be converted into ATP and GTP, respectively, by kinases that add additional phosphates.
ATP stimulates production of GTP, while GTP stimulates production of ATP. This cross regulation keeps the relative amounts of ATP and GTP the same. Excess of either nucleotide could increase the likelihood of DNA mutations, where the wrong purine nucleotide is inserted.
Lesch–Nyhan syndrome is caused by a deficiency in hypoxanthine-guanine phosphoribosyltransferase or HGPRT, the enzyme that catalyzes the reversible reaction of producing guanine from GMP. This is a sex-linked congenital defect that causes overproduction of uric acid along with mental retardation, spasticity, and an urge to self-mutilate.
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Applied and Interdisciplinary Chemistry
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Mutai grew up in Kericho, Kenya. She has stated that her love of science was stimulated by her love of nature and the serene natural environment she experienced in childhood.
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Applied and Interdisciplinary Chemistry
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A light-induced fluorescence transient (LIFT) is a device to remotely measure chlorophyll fluorescence in plants in a fast and non-destructive way. By using a series of excitation light pulses, LIFT combines chlorophyll fluorescence data with spectral and RGB information to provide insights into various photosynthetic traits and vegetation indices. LIFT combines the pump-probe method with the principle of laser-induced fluorescence.
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Theoretical and Fundamental Chemistry
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An icosahedral twin is a nanostructure appearing in atomic clusters and also nanoparticles with some thousands of atoms. These clusters are twenty-faced, with twenty interlinked tetrahedral crystals joined along triangular (e.g. cubic-(111)) faces having three-fold symmetry. A related, more common structure has five units similarly arranged with twinning, which were known as "fivelings" in the 19th century, more recently as "decahedral multiply twinned particles", "pentagonal particles" or "star particles". A variety of different methods (e.g. condensing argon, metal atoms, and virus capsids) lead to the icosahedral form at size scales where surface energies are more important than those from the bulk.
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Theoretical and Fundamental Chemistry
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Enzymatic browning affects the color, flavor, and nutritional value of foods, causing huge economic loss when not sold to consumers on time. It is estimated that more than 50% of produce is lost as a result of enzymatic browning. The increase in human population and consequential depletion in natural resources has prompted many biochemists and food engineers alike to find new or improved techniques to preserve food and for longer by using methods to inhibit the browning reaction. This effectively increases the shelf life of foods, solving this part of the waste problem. A better understanding of the enzymatic browning mechanisms, specifically, understanding the properties of the enzymes and substrates that are involved in the reaction may help food technologists to control certain stages in the mechanism and ultimately apply that knowledge to inhibit browning.
Apples are fruits commonly studied by researchers due to their high phenolic content, which make them highly susceptible to enzymatic browning. In accordance with other findings regarding apples and browning activity, a correlation has been found between higher phenolic quantities and increased enzymatic activity in apples. This provides a potential target and thus hope for food industries wishing to genetically modify foods to decrease polyphenol oxidase activity and thus decrease browning. An example of such accomplishments in food engineering is in the production of Arctic apples. These apples, engineered by Okanagan Specialty Fruits Inc, are a result of applying gene splicing, a laboratory technique that has allowed for the reduction in polyphenol oxidase.
Another type of issue that is closely studied is the browning of seafood. Seafood, in particular shrimp, is a staple consumed by people all over the world. The browning of shrimp, which is actually referred to as melanosis, creates a great concern for food handlers and consumers. Melanosis mainly occurs during postmortem handling and refrigerated storage. Recent studies have found a plant extract that acts as an anti-melatonin polyphenol oxidase inhibitor serves the same function as sulfites but without the health risks.
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Applied and Interdisciplinary Chemistry
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In UV-Vis absorption SEC, depending on the configuration of the light beam respect to the electrode/solution interface, two types of optical arrangements can be distinguished: normal and parallel configuration.
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Theoretical and Fundamental Chemistry
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CO absorbs the ground's thermal radiation mainly at wavelengths between 13 and 17 micron. At this wavelength range, it is almost solely responsible for the attenuation of radiation from the ground. The amount of ground radiation that is transmitted through the atmosphere in each wavelength is related to the optical depth of the atmosphere at this wavelength, OD, by:
The optical depth itself is given by Beer–Lambert law:
where σ is the absorption cross section of a single CO molecule, and n(y) is the
number density of these molecules at altitude y. Due to the high dependence of the cross section in wavelength, the OD changes from around 0.1 at 13 microns to ~10 at 14 microns and even higher beyond 100 at 15 microns, then dropping off to ~10 at 16 microns, ~1 at 17 microns and below 0.1 at 18 microns. Note that the OD depends on the total number of molecules per unit area in the atmosphere, and therefore rises linearly with its CO content.
Looked upon from outer space into the atmosphere at a specific wavelength, one would see to different degrees different layers of the atmosphere, but on average one would see down to an altitude such that the part of the atmosphere from this altitude and up has an optical depth of ~1. Earth will therefore radiate at this wavelength approximately according to the temperature of that altitude. The effect of increasing CO atmospheric content means that the optical depth increases, so that the altitude seen from outer space increases; as long as it increases within the troposphere, the radiation temperature drops and the radiation decreases. When it reaches the tropopause, any further increase in CO levels will have no noticeable effect, since the temperature no longer depends there on the altitude.
At wavelengths of 14 to 16 microns, even the tropopause, having ~0.12 of the amount of CO of the whole atmosphere, has OD>1. Therefore, at these wavelengths Earth radiates mainly in the tropopause temperature, and addition of CO does not change this. At wavelengths smaller than 13 microns or larger than 18 microns, the atmospheric absorption is negligible, and addition of CO hardly changes this. Therefore, the effect of CO increase on radiation is relevant in wavelengths 13–14 and 16–18 microns, and addition on CO mainly contributes to the opacity of the troposphere, changing the altitude that is effectively seen from outer space within the troposphere.
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Applied and Interdisciplinary Chemistry
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Over the years, for example in his 1879 thesis, but particularly in 1926, Planck advocated regarding the generation of heat by rubbing as the most specific way to define heat. Planck criticised Carathéodory for not attending to this. Carathéodory was a mathematician who liked to think in terms of adiabatic processes, and perhaps found friction to tricky to think about, while Planck was a physicist.
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Theoretical and Fundamental Chemistry
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The drag coefficient is a dimensionless quantity which quantifies the resistance of the water surface. Due to the fact that the drag coefficient depends on the past of the wind, the drag coefficient is expressed differently for different time and spatial scales. A general expression for the drag coefficient does not yet exist and the value is unknown for unsteady and non-ideal conditions. In general, the drag coefficient increases with increasing wind speed and is greater for shallower waters.
The geostrophic drag coefficient is expressed as:
where is the geostrophic wind which is given by:
In global climate models, often a drag coefficient appropriate for a spatial scale of 1° by 1° and a monthly time scale is used. In such a timescale, the wind can strongly fluctuate. The monthly mean shear stress can be expressed as:
where is the density, is the drag coefficient, is the monthly mean wind and U' is the fluctuation from the monthly mean.
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Applied and Interdisciplinary Chemistry
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At this time, physician and scientific writer Thomas Beddoes and geologist John Hailstone were engaged in a geological controversy on the rival merits of the Plutonian and Neptunist hypotheses. They travelled together to examine the Cornish coast accompanied by Giddy—an intimate friend of Beddoes—and made Davys acquaintance. Beddoes, who had established at Bristol the medical research facility the Pneumatic Institution, needed an assistant to superintend the laboratory. Giddy recommended Davy, and in 1798 Gregory Watt showed Beddoes Davys Young mans Researches on Heat and Light, which were subsequently published by him in the first volume of West-Country Contributions. After prolonged negotiations, mainly by Giddy, Mrs Davy and Borlase consented to Davys departure, but Tonkin wished him to remain in his native town as a surgeon, and altered his will when he found that Davy insisted on going to Dr Beddoes.
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Applied and Interdisciplinary Chemistry
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Pictets experiment is the demonstration of the reflection of heat and the apparent reflection of cold in a series of experiments performed in 1790 (reported in English in 1791 in An Essay on Fire') by Marc-Auguste Pictet—ten years before the discovery of infrared heating of the Earth by the Sun. The apparatus for most of the experiments used two concave mirrors facing one another at a distance. An object placed at the focus of one mirror would have heat and light reflected by the mirror and focused. An object at the focus of the counterpart mirror would do the same. Placing a hot object at one focus and a thermometer at the other would register an increase in temperature on the thermometer. This was sometimes demonstrated with the explosion of a flammable mix of gasses in a blackened balloon, as described and depicted by John Tyndall in 1863.
After "demonstrating that radiant heat, even when it was not accompanied by any light, could be reflected and focused like light", Pictet used the same apparatus to demonstrate the apparent reflection of cold in a similar manner. This demonstration was important to Benjamin Thompson, Count Rumford who argued for the existence of "frigorific rays" conveying cold. Rumford's continuation of the experiments and promotion of the topic caused the name to be attached to the experiment.
The apparent reflection of cold if a cold object is placed in one focus surprised Pictet and two scholars writing about the experiment in 1985 noted "most physicists, on seeing it demonstrated for the first time, find it surprising and even puzzling." The confusion may be resolved by understanding that all objects in the system—including the thermometer—are constantly radiating heat. Pictet described this as "the thermometer acts the same part relatively to the snow as the bullet [heat source] in relation to the thermometer." Addition of a very cold object adds an effective heat sink versus a room temperature object which would not, in the net, cool or warm a thermometer in the other focus.
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Theoretical and Fundamental Chemistry
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A compressed fluid (also called a compressed or unsaturated liquid, subcooled fluid or liquid) is a fluid under mechanical or thermodynamic conditions that force it to be a liquid.
At a given pressure, a fluid is a compressed fluid if it is at a temperature lower than the saturation temperature. This is the case, for example, for liquid water at atmospheric pressure and room temperature. In a plot that compares pressure and specific volume (commonly called a p-v diagram), compressed fluid is the state to the left of the saturation curve.
Conditions that cause a fluid to be compressed include:
* Specific volume and enthalpy inferior to that of a saturated liquid;
* Temperature below the saturation temperature;
* Pressure above the saturation pressure.
The term compressed liquid emphasizes that the pressure is greater than the saturation pressure for the given temperature. Compressed liquid properties are relatively independent of pressure.
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Applied and Interdisciplinary Chemistry
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The first step of SELEX involves the synthesis of fully or partially randomized oligonucleotide sequences of some length flanked by defined regions which allow PCR amplification of those randomized regions and, in the case of RNA SELEX, in vitro transcription of the randomized sequence. While Ellington and Szostak demonstrated that chemical synthesis is capable of generating ~10 unique sequences for oligonucleotide libraries in their 1990 paper on in vitro selection, they found that amplification of these synthesized oligonucleotides led to significant loss of pool diversity due to PCR bias and defects in synthesized fragments. The oligonucleotide pool is amplified and a sufficient amount of the initial library is added to the reaction so that there are numerous copies of each individual sequence to minimize the loss of potential binding sequences due to stochastic events. Before the library is introduced to target for incubation and selective retention, the sequence library must be converted to single stranded oligonucleotides to achieve structural conformations with target binding properties.
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Applied and Interdisciplinary Chemistry
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During nuclear magnetic resonance observations, spin–lattice relaxation is the mechanism by which the longitudinal component of the total nuclear magnetic moment vector (parallel to the constant magnetic field) exponentially relaxes from a higher energy, non-equilibrium state to thermodynamic equilibrium with its surroundings (the "lattice"). It is characterized by the spin–lattice relaxation time, a time constant known as T.
There is a different parameter, T, the spin-spin relaxation time, which concerns the exponential relaxation of the transverse component of the nuclear magnetization vector ( to the external magnetic field). Measuring the variation of T and T in different materials is the basis for some magnetic resonance imaging techniques.
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Theoretical and Fundamental Chemistry
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N NMR is used in a wide array of areas from biological to inorganic techniques. A famous application in organic synthesis is to utilize N to monitor tautomerization equilibria in heteroaromatics because of the dramatic change in N shifts between tautomers.
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Theoretical and Fundamental Chemistry
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The pressure–volume conjugate pair is concerned with the transfer of mechanical energy as the result of work.
* An isobaric process occurs at constant pressure. An example would be to have a movable piston in a cylinder, so that the pressure inside the cylinder is always at atmospheric pressure, although it is separated from the atmosphere. In other words, the system is dynamically connected, by a movable boundary, to a constant-pressure reservoir.
* An isochoric process is one in which the volume is held constant, with the result that the mechanical PV work done by the system will be zero. On the other hand, work can be done isochorically on the system, for example by a shaft that drives a rotary paddle located inside the system. It follows that, for the simple system of one deformation variable, any heat energy transferred to the system externally will be absorbed as internal energy. An isochoric process is also known as an isometric process or an isovolumetric process. An example would be to place a closed tin can of material into a fire. To a first approximation, the can will not expand, and the only change will be that the contents gain internal energy, evidenced by increase in temperature and pressure. Mathematically, . The system is dynamically insulated, by a rigid boundary, from the environment.
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Theoretical and Fundamental Chemistry
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Atmospheric science is the study of the Earth's atmosphere and its various inner-working physical processes. Meteorology includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. Climatology is the study of atmospheric changes (both long and short-term) that define average climates and their change over time climate variability. Aeronomy is the study of the upper layers of the atmosphere, where dissociation and ionization are important. Atmospheric science has been extended to the field of planetary science and the study of the atmospheres of the planets and natural satellites of the Solar System.
Experimental instruments used in atmospheric science include satellites, rocketsondes, radiosondes, weather balloons, radars, and lasers.
The term aerology (from Greek ἀήρ, aēr, "air"; and -λογία, -logia) is sometimes used as an alternative term for the study of Earth's atmosphere; in other definitions, aerology is restricted to the free atmosphere, the region above the planetary boundary layer.
Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann.
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Applied and Interdisciplinary Chemistry
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Abū Bakr ibn Zakariyā’ al-Rāzī (Latin: Rhazes), born around 865 in Rayy, was mainly known as a Persian physician. He wrote a number of alchemical works, including the Sirr al-asrār (Latin: Secretum secretorum; English: Secret of Secrets.)
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Applied and Interdisciplinary Chemistry
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Pressure drop is related inversely to pipe diameter to the fifth power. For example, halving a pipe's diameter would increase the pressure drop by a factor of (e.g. from 2 psi to 64 psi), assuming no change in flow.
Pressure drop in piping is directly proportional to the length of the piping—for example, a pipe with twice the length will have twice the pressure drop, given the same flow rate. Piping fittings (such as elbow and tee joints) generally lead to greater pressure drop than straight pipe. As such, a number of correlations have been developed to calculate equivalent length of fittings.
Certain valves are provided with an associated flow coefficient, commonly known as or . The flow coefficient relates pressure drop, flow rate, and specific gravity for a given valve.
Many empirical calculations exist for calculation of pressure drop, including:
* Darcy–Weisbach equation, to calculate pressure drop in a pipe
* Hagen–Poiseuille equation
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Applied and Interdisciplinary Chemistry
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Kinetic binding experiments differ from saturation and competition experiments in that they are not done at equilibrium. Instead, they measure the course of binding of the radioligand during the experiment as well as the dissociation to determine calculation of the Kd, and rate constants of binding and dissociation. Kinetic binding experiments are also called dissociation binding experiments and can help evaluate the interaction of the radioligand and the targeted receptor.
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Applied and Interdisciplinary Chemistry
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Photographic film responds to ultraviolet radiation but the glass lenses of cameras usually block radiation shorter than 350 nm. Slightly yellow UV-blocking filters are often used for outdoor photography to prevent unwanted bluing and overexposure by UV rays. For photography in the near UV, special filters may be used. Photography with wavelengths shorter than 350 nm requires special quartz lenses which do not absorb the radiation.
Digital cameras sensors may have internal filters that block UV to improve color rendition accuracy. Sometimes these internal filters can be removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography. A few cameras are designed for use in the UV.
Photography by reflected ultraviolet radiation is useful for medical, scientific, and forensic investigations, in applications as widespread as detecting bruising of skin, alterations of documents, or restoration work on paintings. Photography of the fluorescence produced by ultraviolet illumination uses visible wavelengths of light.
In ultraviolet astronomy, measurements are used to discern the chemical composition of the interstellar medium, and the temperature and composition of stars. Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space.
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Theoretical and Fundamental Chemistry
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In the summer of 1981 the acquired immunodeficiency syndrome (AIDS) was first reported. Two years later the etiological link to AIDS, the human immunodeficiency virus (HIV) was identified. Since the identification of HIV the development of effective antiretroviral drugs and the scientific achievements in HIV research has been enormous. Antiretroviral drugs for the treatment of HIV infections belong to six categories: Nucleoside and nucleotide reverse-transcriptase inhibitors, Non-nucleoside reverse-transcriptase inhibitors, protease inhibitors, entry inhibitors, co-receptor inhibitors and integrase inhibitors. The reverse transcriptase of HIV-1 has been the main foundation for the development of anti-HIV drugs. The first nucleoside reverse-transcriptase inhibitor with in vitro anti-HIV activity was zidovudine. Since zidovudine was approved in 1987, six nucleosides and one nucleotide reverse-transcriptase inhibitor (NRTI) have been approved by FDA. NRTIs approved by the FDA are zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir and emtricitabine and the only nucleotide reverse-transcriptase inhibitor (NtRTI) approved is tenofovir (see table 4).
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Applied and Interdisciplinary Chemistry
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There are two distinct uniform colorings of a trihexagonal tiling. Naming the colors by indices on the 4 faces around a vertex (3.6.3.6): 1212, 1232. The second is called a cantic hexagonal tiling, h{6,3}, with two colors of triangles, existing in p3m1 (*333) symmetry.
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Theoretical and Fundamental Chemistry
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The above standard treatment of a macroscopic Bose gas is straightforward, but the inclusion of the ground state is somewhat inelegant. Another approach is to include the ground state explicitly (contributing a term in the grand potential, as in the section below), this gives rise to an unrealistic fluctuation catastrophe: the number of particles in any given state follow a geometric distribution, meaning that when condensation happens at T and most particles are in one state, there is a huge uncertainty in the total number of particles. This is related to the fact that the compressibility becomes unbounded for T . Calculations can instead be performed in the canonical ensemble, which fixes the total particle number, however the calculations are not as easy.
Practically however, the aforementioned theoretical flaw is a minor issue, as the most unrealistic assumption is that of non-interaction between bosons. Experimental realizations of boson gases always have significant interactions, i.e., they are non-ideal gases. The interactions significantly change the physics of how a condensate of bosons behaves: the ground state spreads out, the chemical potential saturates to a positive value even at zero temperature, and the fluctuation problem disappears (the compressibility becomes finite). See the article Bose–Einstein condensate.
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Theoretical and Fundamental Chemistry
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Commonly three types of silicate paints are distinguished: Pure silicate paint consisting of two components, a color powder in dry or water-paste form and the liquid binder water glass. (DIN 18363 Painting and coating work Section 2.4.1). The processing of pure silicate paints require great experience and know-how. These are especially common for the historic area.
Around the middle of the 20th century the first single-component silicate paint was developed. The addition of up to 5 mass percent of organic additives (e.g. acrylate dispersion, hydrophobisers, thickeners or similar) makes ready-to-use paint in containers possible. These are also called "dispersion silicate paints" (DIN 18363 Painting and coating work Section 2.4.1). The range of application for such silicate paints is significantly higher than for pure silicate paints as the dispersion allows coats for less solid substrates and/or organic composition. Above that handling and processing is simpler than pure silicate paint.
Since 2002 a third category of silicate paints is known: sol-silicate paint. The binder is a combination of silica sol and water glass. The organic fraction is limited to 5 mass percent similar to dispersion silicate paint allowing for chemical setting and retaining of the silicate specific advantages. The sol silicate paint allows use on non-mineral plaster. For these the bonding occurs chemically and physically. The sol-silicate paint has revolutionized the field of application of silicate paints. These paints can be applied easily and safely to nearly all common substrates.
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Theoretical and Fundamental Chemistry
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* 1983 — Member of the National Academy of Sciences
* 1985–1987 — President of the Geochemical Society
* 1992 — V. M. Goldschmidt Award, Geochemical Society
* 1997 — Harry Hess Medal, American Geophysical Union
* 2005 — Fellow of the American Academy of Arts and Sciences
* 2008 — Arthur L. Day Prize and Lectureship
* 2016 — William Bowie Medal
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Theoretical and Fundamental Chemistry
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One of the first substances that was reported to produce an oxygen diffusion-enhancing effect was crocetin, a carotenoid that occurs naturally in plants such as crocus sativus, and is related to another carotenoid, saffron. Saffron has been used culturally (e.g., as a dye) and medicinally since ancient times.
Trans sodium crocetinate (TSC), a synthetic drug containing the carotenoid structure of trans crocetin has been extensively investigated in animal disease models and in human clinical trials. Clinical trials of TSC have focused on testing the compound's effectiveness in sensitizing hypoxic cancer cells to radiation therapy in patients with glioblastoma, an aggressive form of brain cancer.
TSC, which is being developed by Diffusion Pharmaceuticals, has been shown to enhance the oxygenation of hypoxic tumor tissue and belongs to a subclass of oxygen diffusion-enhancing compounds known as bipolar trans carotenoid salts. Diffusion Pharmaceuticals is currently investigating the use of trans sodium crocetinate in the treatment of COVID-19, acute stroke, and solid cancerous tumors.
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Applied and Interdisciplinary Chemistry
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Dielectric constant is the most important factor in determining the occurrence of ion association. A table of some typical values can be found under dielectric constant.
Water has a relatively high dielectric constant value of 78.7 at 298K (25 °C), so in aqueous solutions at ambient temperatures 1:1 electrolytes such as NaCl do not form ion pairs to an appreciable extent except when the solution is very concentrated. 2:2 electrolytes (q = 2, q = 2) form ion pairs more readily. Indeed, the solvent-shared ion pair [Mg(HO)]SO was famously discovered to be present in seawater, in equilibrium with the contact ion pair [Mg(HO)(SO)] Trivalent ions such as Al, Fe and lanthanide ions form weak complexes with monovalent anions.
The dielectric constant of water decreases with increasing temperature to about 55 at 100 °C and about 5 at the critical temperature (217.7 °C). Thus ion pairing will become more significant in superheated water.
Solvents with a dielectric constant in the range, roughly, 20–40, show extensive ion-pair formation. For example, in acetonitrile both contact and solvent-shared ion pairs of Li(NCS) have been observed. In methanol the 2:1 electrolyte Mg(NCS) is partially dissociated into a contact ion pair, [Mg(NCS)] and the thiocyanate ion.
The dielectric constant of liquid ammonia decreases from 26 at its freezing point (−80 °C) to 17 at 20 °C (under pressure). Many simple 1:1 electrolytes form contact ion pairs at ambient temperatures. The extent of ion pairing decreases as temperature decreases. With lithium salts there is evidence to show that both inner-sphere and outer-sphere complexes exist in liquid-ammonia solutions.
Of the solvents with dielectric constant of 10 or less, tetrahydrofuran (THF) is particularly relevant in this context, as it solvates cations strongly with the result that simple electrolytes have sufficient solubility to make the study of ion association possible. In this solvent ion association is the rule rather than the exception. Indeed, higher associates such as tetramers are often formed. Triple cations and triple anions have also been characterized in THF solutions.
Ion association is an important factor in phase-transfer catalysis, since a species such as RPCl is formally neutral and so can dissolve easily in a non-polar solvent of low dielectric constant. In this case it also helps that the surface of the cation is hydrophobic.
In S1 reactions the carbocation intermediate may form an ion pair with an anion, particularly in solvents of low dielectric constant, such as diethylether. This can affect both the kinetic parameters of the reaction and the stereochemistry of the reaction products.
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Theoretical and Fundamental Chemistry
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Addition (or removal) of CO to a solution does not change its alkalinity, since the net reaction produces the same number of equivalents of positively contributing species (H) as negative contributing species ( and/or ). Adding CO to the solution lowers its pH, but does not affect alkalinity.
At all pH values:
:CO + HO ⇌ + H
Only at high (basic) pH values:
: + H ⇌ + 2 H
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Theoretical and Fundamental Chemistry
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YAC (yeast artificial chromosome) - Ycf9 protein domain - YchF-GTPase C terminal protein domain - Ydc2 protein domain - YDG SRA protein domain - YecM bacterial protein domain - YjeF N terminal protein domain - YopH, N-terminal - YopR bacterial protein domain - Y Y Y -
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Applied and Interdisciplinary Chemistry
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A number of related compounds are known, with a similar structure but having the indole core flipped and/or replaced with related cores such as indoline, indazole, benzothiophene, or benzofuran. These similarly are primarily active as agonists at the 5-HT family of serotonin receptors, with applications in the treatment of glaucoma, cluster headaches or as anorectics.
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Theoretical and Fundamental Chemistry
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Consider nuclei with a spin of one-half, like , or . Each nucleus has two linearly independent spin states, with m = or m = − (also referred to as spin-up and spin-down, or sometimes α and β spin states, respectively) for the z-component of spin. In the absence of a magnetic field, these states are degenerate; that is, they have the same energy. Hence the number of nuclei in these two states will be essentially equal at thermal equilibrium.
If a nucleus is placed in a magnetic field, however, the two states no longer have the same energy as a result of the interaction between the nuclear magnetic dipole moment and the external magnetic field. The energy of a magnetic dipole moment in a magnetic field B is given by:
Usually the z-axis is chosen to be along B, and the above expression reduces to:
or alternatively:
As a result, the different nuclear spin states have different energies in a non-zero magnetic field. In less formal language, we can talk about the two spin states of a spin as being aligned either with or against the magnetic field. If γ is positive (true for most isotopes used in NMR) then is the lower energy state.
The energy difference between the two states is:
and this results in a small population bias favoring the lower energy state in thermal equilibrium. With more spins pointing up than down, a net spin magnetization along the magnetic field B results.
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Theoretical and Fundamental Chemistry
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Besides the oxygen ligand, which binds to hemoglobin in a cooperative manner, hemoglobin ligands also include competitive inhibitors such as carbon monoxide (CO) and allosteric ligands such as carbon dioxide (CO) and nitric oxide (NO). The carbon dioxide is bound to amino groups of the globin proteins to form carbaminohemoglobin; this mechanism is thought to account for about 10% of carbon dioxide transport in mammals. Nitric oxide can also be transported by hemoglobin; it is bound to specific thiol groups in the globin protein to form an S-nitrosothiol, which dissociates into free nitric oxide and thiol again, as the hemoglobin releases oxygen from its heme site. This nitric oxide transport to peripheral tissues is hypothesized to assist oxygen transport in tissues, by releasing vasodilatory nitric oxide to tissues in which oxygen levels are low.
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Theoretical and Fundamental Chemistry
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The high electronegativity of fluorine (4.0 for fluorine vs. 2.5 for carbon) gives the carbon–fluorine bond a significant polarity or dipole moment. The electron density is concentrated around the fluorine, leaving the carbon relatively electron poor. This introduces ionic character to the bond through partial charges (C—F). The partial charges on the fluorine and carbon are attractive, contributing to the unusual bond strength of the carbon–fluorine bond. The bond is labeled as "the strongest in organic chemistry," because fluorine forms the strongest single bond to carbon. Carbon–fluorine bonds can have a bond dissociation energy (BDE) of up to 130 kcal/mol. The BDE (strength of the bond) of C–F is higher than other carbon–halogen and carbon–hydrogen bonds. For example, the BDEs of the C–X bond within a CH–X molecule is 115, 104.9, 83.7, 72.1, and 57.6 kcal/mol for X = fluorine, hydrogen, chlorine, bromine, and iodine, respectively.
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Theoretical and Fundamental Chemistry
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The du Noüy Padday rod consists of a rod usually on the order of a few millimeters square making a small ring. The rod is often made from a composite metal material that may be roughened to ensure complete wetting at the interface. The rod is cleaned with water, alcohol and a flame or with strong acid to ensure complete removal of surfactants. The rod is attached to a scale or balance via a thin metal hook. The Padday method uses the maximum pull force method, i.e. the maximum force due to the surface tension is recorded as the probe is first immersed ca. one mm into the solution and then slowly withdrawn from the interface. The main forces acting on a probe are the buoyancy (due to the volume of liquid displaced by the probe) and the mass of the meniscus adhering to the probe. This is an old, reliable, and well-documented technique.
An important advantage of the maximum pull force technique is that the receding contact angle on the probe is effectively zero. The maximum pull force is obtained when the buoyancy force reaches its minimum,
The surface tension measurement used in the Padday devices based on the du Noüy ring/maximum pull force method is explained further here:
The force acting on the probe can be divided into two components:
: i) Buoyancy stemming from the volume displaced by the probe, and
: ii) the mass of the meniscus of the liquid adhering to the probe.
The latter is in equilibrium with the surface tension force, i.e.
where
:* is the perimeter of the probe,
:* is the surface tension and the weight of the meniscus under the probe. In the situation considered here the volume displaced by the probe is included in the meniscus.
:* is the contact angle between the probe and the solution that is measured, and is negligible for the majority of solutions with Kibron’s probes.
Thus, the force measured by the balance is given by
where
:* is the force acting on the probe and
:* is the force due to buoyancy.
At the point of detachment the volume of the probe immersed in the solution vanishes, and thus, also the buoyancy term. This is observed as a maximum in the force curve, which relates to the surface tension through
The above derivation holds for ideal conditions. Non-idealities, e.g. from defect probe shape, are partly compensated in the calibration routine using a solution with known surface tension.
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Theoretical and Fundamental Chemistry
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A western blot is used for the detection of specific proteins in complex samples. Proteins are first separated by size using electrophoresis before being transferred to an appropriate blotting matrix (usually polyvinylidene fluoride or nitrocellulose) and subsequent detection with antibodies.
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Applied and Interdisciplinary Chemistry
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Gene expression in mammals is regulated by many cis-regulatory elements, including core promoters and promoter-proximal elements that are located near the transcription start sites of genes. Core promoters are sufficient to direct transcription
initiation, but generally have low basal activity. Other important cis-regulatory modules are localized in DNA regions that are distant from the transcription start sites. These include enhancers, silencers, insulators and tethering elements. Among this constellation of elements, enhancers and their associated transcription factors have a leading role in the regulation of gene expression. An enhancer localized in a DNA region distant from the promoter of a gene can have a very large effect on gene expression, with some genes undergoing up to 100-fold increased expression due to an activated enhancer.
Enhancers are regions of the genome that are major gene-regulatory elements. Enhancers control cell-type-specific gene expression programs, most often by looping through long distances to come in physical proximity with the promoters of their target genes. While there are hundreds of thousands of enhancer DNA regions, for a particular type of tissue only specific enhancers are brought into proximity with the promoters that they regulate. In a study of brain cortical neurons, 24,937 loops were found, bringing enhancers to their target promoters. Multiple enhancers, each often at tens or hundreds of thousands of nucleotides distant from their target genes, loop to their target gene promoters and can coordinate with each other to control the expression of their common target gene.
The schematic illustration in this section shows an enhancer looping around to come into close physical proximity with the promoter of a target gene. The loop is stabilized by a dimer of a connector protein (e.g. dimer of CTCF or YY1), with one member of the dimer anchored to its binding motif on the enhancer and the other member anchored to its binding motif on the promoter (represented by the red zigzags in the illustration). Several cell function specific transcription factors (there are about 1,600 transcription factors in a human cell) generally bind to specific motifs on an enhancer and a small combination of these enhancer-bound transcription factors, when brought close to a promoter by a DNA loop, govern level of transcription of the target gene. Mediator (a complex usually consisting of about 26 proteins in an interacting structure) communicates regulatory signals from enhancer DNA-bound transcription factors directly to the RNA polymerase II (pol II) enzyme bound to the promoter.
Enhancers, when active, are generally transcribed from both strands of DNA with RNA polymerases acting in two different directions, producing two Enhancer RNAs (eRNAs) as illustrated in the Figure. Like mRNAs, these eRNAs are usually protected by their 5′ cap. An inactive enhancer may be bound by an inactive transcription factor. Phosphorylation of the transcription factor may activate it and that activated transcription factor may then activate the enhancer to which it is bound (see small red star representing phosphorylation of transcription factor bound to enhancer in the illustration). An activated enhancer begins transcription of its RNA before activating transcription of messenger RNA from its target gene.
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Applied and Interdisciplinary Chemistry
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Through research done on nicotinic acetylcholine receptors it has been determined that the channels are activated through allosteric interactions between the binding and gating domains. Once the agonist binds it brings about conformational changes (including moving a beta sheet of the amino-terminal domain, and outward movement from loops 2, F and cys-loop which are tied to the M2-M3 linker and pull the channel open). Electron microscopy (at 9 Å) shows that the opening is caused by rotation at the M2 domain, but other studies on crystal structures of these receptors has shown that the opening could be a result from a M2 tilt which leads to pore dilation and a quaternary turn of the entire pentameric receptor.
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Applied and Interdisciplinary Chemistry
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The material derivative is defined for any tensor field y that is macroscopic, with the sense that it depends only on position and time coordinates, :
where is the covariant derivative of the tensor, and is the flow velocity. Generally the convective derivative of the field , the one that contains the covariant derivative of the field, can be interpreted both as involving the streamline tensor derivative of the field , or as involving the streamline directional derivative of the field , leading to the same result.
Only this spatial term containing the flow velocity describes the transport of the field in the flow, while the other describes the intrinsic variation of the field, independent of the presence of any flow. Confusingly, sometimes the name "convective derivative" is used for the whole material derivative , instead for only the spatial term . The effect of the time-independent terms in the definitions are for the scalar and tensor case respectively known as advection and convection.
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Applied and Interdisciplinary Chemistry
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The operating costs are typically much greater for aerobic digestion than for anaerobic digestion because of energy used by the blowers, pumps and motors needed to add oxygen to the process. However, recent technological advances include non-electrically aerated filter systems that use natural air currents for the aeration instead of electrically operated machinery.
The digested sludge is relatively low in residual energy and although it can be dried and incinerated to produce heat, the energy yield is very much lower than that produced by anaerobic digestion.
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Applied and Interdisciplinary Chemistry
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The majority of prostaglandin signaling occurs via GPCRs (see above) although certain prostaglandins activate nuclear receptors in the PPAR family. (See article eicosanoid receptors for more information).
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Applied and Interdisciplinary Chemistry
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In the first half of 1926, building on de Broglie's hypothesis, Erwin Schrödinger developed the equation that describes the behavior of a quantum-mechanical wave. The mathematical model, called the Schrödinger equation after its creator, is central to quantum mechanics, defines the permitted stationary states of a quantum system, and describes how the quantum state of a physical system changes in time. The wave itself is described by a mathematical function known as a "wave function". Schrödinger said that the wave function provides the "means for predicting the probability of measurement results".
Schrödinger was able to calculate the energy levels of hydrogen by treating a hydrogen atom's electron as a classical wave, moving in a well of the electrical potential created by the proton. This calculation accurately reproduced the energy levels of the Bohr model.
In May 1926, Schrödinger proved that Heisenbergs matrix mechanics and his own wave mechanics made the same predictions about the properties and behavior of the electron; mathematically, the two theories had an underlying common form. Yet the two men disagreed on the interpretation of their mutual theory. For instance, Heisenberg accepted the theoretical prediction of jumps of electrons between orbitals in an atom, but Schrödinger hoped that a theory based on continuous wave-like properties could avoid what he called (as paraphrased by Wilhelm Wien) "this nonsense about quantum jumps". In the end, Heisenbergs approach won out, and quantum jumps were confirmed.
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Applied and Interdisciplinary Chemistry
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After a cell has established a resting potential, that cell has the capacity to undergo depolarization. Depolarization is the process by which the membrane potential becomes less negative, facilitating the generation of an action potential. For this rapid change to take place within the interior of the cell, several events must occur along the plasma membrane of the cell. While the sodium–potassium pump continues to work, the voltage-gated sodium and calcium channels that had been closed while the cell was at resting potential are opened in response to an initial change in voltage. As a change in the neuronal charge leads to the opening of voltage-gated sodium channels, this results in an influx of sodium ions down their electrochemical gradient. Sodium ions enter the cell, and they contribute a positive charge to the cell interior, causing a change in the membrane potential from negative to positive. The initial sodium ion influx triggers the opening of additional sodium channels (positive-feedback loop), leading to further sodium ion transfer into the cell and sustaining the depolarization process until the positive equilibrium potential is reached. Sodium channels possess an inherent inactivation mechanism that prompts rapid reclosure, even as the membrane remains depolarized. During this equilibrium, the sodium channels enter an inactivated state, temporarily halting the influx of sodium ions until the membrane potential becomes negatively charged again.Once the cell's interior is sufficiently positively charged, depolarization concludes, and the channels close once more.
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Theoretical and Fundamental Chemistry
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The microprocessor complex consists minimally of two proteins: Drosha, a ribonuclease III enzyme; and DGCR8, a double-stranded RNA binding protein. (DGCR8 is the name used in mammalian genetics, abbreviated from "DiGeorge syndrome critical region 8"; the homologous protein in model organisms such as flies and worms is called Pasha, for Partner of Drosha.) The stoichiometry of the minimal complex was at one point experimentally difficult to determine, but it has been demonstrated to be a heterotrimer of two DGCR8 proteins and one Drosha.
In addition to the minimal catalytically active microprocessor components, other cofactors such as DEAD box RNA helicases and heterogeneous nuclear ribonucleoproteins may be present in the complex to mediate the activity of Drosha. Some miRNAs are processed by microprocessor only in the presence of specific cofactors.
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Applied and Interdisciplinary Chemistry
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The kappa and lambda light chains undergo rearrangements of the V and J gene segments. In this process, a functional Vlambda can combine with four functional Jλ –Cλ combinations. On the other hands, Vk gene segments can join with either one of the Jk functional gene segments. The overall rearrangements result in a gene segment order from 5 prime to 3 prime end. These are a short leader (L) exon, a noncoding sequence (intron), a joined VJ segment, a second intron, and the constant region. There is a promoter upstream from each leader gene segment. The leader exon is important in the transcription of light chain by the RNA polymerase. To remain with coding sequence only, the introns are removed during RNA- processing and repairing. In summary,
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Applied and Interdisciplinary Chemistry
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A collision between reactant molecules may or may not result in a successful reaction.
The outcome depends on factors such as the relative kinetic energy, relative orientation and internal energy of the molecules.
Even if the collision partners form an activated complex they are not bound to go on and form
products, and instead the complex may fall apart back to the reactants.
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Theoretical and Fundamental Chemistry
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Pre-B-cell leukemia homeobox (PBX) refers to a family of transcription factors.
Types include:
* PBX1
* PBX2
* PBX3
* PBX4
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Applied and Interdisciplinary Chemistry
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Gustavo R. Paz-Pujalt (born 1954) is a Peruvian American scientist and inventor. He holds 45 US patents and 59 international patents mainly in the areas of remote sensing, thin films, sensors, and upconversion materials.
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Theoretical and Fundamental Chemistry
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N-Bromosuccinimide or NBS is a chemical reagent used in radical substitution, electrophilic addition, and electrophilic substitution reactions in organic chemistry. NBS can be a convenient source of Br, the bromine radical.
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Theoretical and Fundamental Chemistry
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A "refractory" gold ore is an ore that has ultra-fine gold particles disseminated throughout its gold occluded minerals. These ores are naturally resistant to recovery by standard cyanidation and carbon adsorption processes. These refractory ores require pre-treatment in order for cyanidation to be effective in recovery of the gold. A refractory ore generally contains sulphide minerals, organic carbon, or both. Sulphide minerals are impermeable minerals that occlude gold particles, making it difficult for the leach solution to form a complex with the gold. Organic carbon present in gold ore may adsorb dissolved gold-cyanide complexes in much the same way as activated carbon. This so-called "preg-robbing" carbon is washed away because it is significantly finer than the carbon recovery screens typically used to recover activated carbon.
Pre-treatment options for refractory ores include:
# Roasting
# Bio-oxidation, such as bacterial oxidation
# Pressure oxidation
# Albion process
The refractory ore treatment processes may be preceded by concentration (usually sulphide flotation). Roasting is used to oxidize both the sulphur and organic carbon at high temperatures using air and/or oxygen. Bio-oxidation involves the use of bacteria that promote oxidation reactions in an aqueous environment. Pressure oxidation is an aqueous process for sulphur removal carried out in a continuous autoclave, operating at high pressures and somewhat elevated temperatures. The Albion process utilises a combination of ultrafine grinding and atmospheric, auto-thermal, oxidative leaching.
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Applied and Interdisciplinary Chemistry
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Ethyl 3-bromopropionate is the organobromine compound with the formula BrCHCHCOCH. It is a colorless liquid and an alkylating agent. It is prepared by the esterification of 3-bromopropionic acid. Alternatively, it can be prepared by hydrobromination of ethyl acrylate, a reaction that proceeds in an anti-Markovnikov sense.
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Theoretical and Fundamental Chemistry
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In surface vibrational spectroscopy, the surface selection rule is applied to identify the peaks observed in vibrational spectra. When a molecule is adsorbed on a substrate, the molecule induces opposite image charges in the substrate. The dipole moment of the molecule and the image charges perpendicular to the surface reinforce each other. In contrast, the dipole moments of the molecule and the image charges parallel to the surface cancel out. Therefore, only molecular vibrational peaks giving rise to a dynamic dipole moment perpendicular to the surface will be observed in the vibrational spectrum.
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Theoretical and Fundamental Chemistry
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The Hill's spherical vortex with a swirling motion is provided by Keith Moffatt in 1969. Earlier discussion of similar problems are provided by William Mitchinson Hicks in 1899. The solution was also discovered by Kelvin H. Pendergast in 1956, in the context of plasma physics, as there exists a direct connection between these fluid flows and plasma physics (see the connection between Hicks equation and Grad–Shafranov equation). The motion in the axial (or, meridional) plane is described by the Stokes stream function as before. The azimuthal motion is given by
where
where and are the Bessel functions of the first kind. Unlike the Hills spherical vortex without any swirling motion, the problem here contains an arbitrary parameter . A general class of solutions of the Eulers equation describing propagating three-dimensional vortices without change of shape is provided by Keith Moffatt in 1986.
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Applied and Interdisciplinary Chemistry
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The following is a list of human hepatocyte nuclear factors (see also boxes to the right for additional information about these proteins):
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Applied and Interdisciplinary Chemistry
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* The spectral centroid of a signal is the midpoint of its spectral density function, i.e. the frequency that divides the distribution into two equal parts.
* The spectral edge frequency (SEF), usually expressed as "SEF x", represents the frequency below which x percent of the total power of a given signal are located; typically, x is in the range 75 to 95. It is more particularly a popular measure used in EEG monitoring, in which case SEF has variously been used to estimate the depth of anesthesia and stages of sleep.
* A spectral envelope is the envelope curve of the spectrum density. It describes one point in time (one window, to be precise). For example, in remote sensing using a spectrometer, the spectral envelope of a feature is the boundary of its spectral properties, as defined by the range of brightness levels in each of the spectral bands of interest.
* The spectral density is a function of frequency, not a function of time. However, the spectral density of a small window of a longer signal may be calculated, and plotted versus time associated with the window. Such a graph is called a spectrogram. This is the basis of a number of spectral analysis techniques such as the short-time Fourier transform and wavelets.
* A "spectrum" generally means the power spectral density, as discussed above, which depicts the distribution of signal content over frequency. For transfer functions (e.g., Bode plot, chirp) the complete frequency response may be graphed in two parts: power versus frequency and phase versus frequency—the phase spectral density, phase spectrum, or spectral phase. Less commonly, the two parts may be the real and imaginary parts of the transfer function. This is not to be confused with the frequency response of a transfer function, which also includes a phase (or equivalently, a real and imaginary part) as a function of frequency. The time-domain impulse response cannot generally be uniquely recovered from the power spectral density alone without the phase part. Although these are also Fourier transform pairs, there is no symmetry (as there is for the autocorrelation) forcing the Fourier transform to be real-valued. See Ultrashort pulse#Spectral phase, phase noise, group delay.
* Sometimes one encounters an amplitude spectral density (ASD), which is the square root of the PSD; the ASD of a voltage signal has units of V Hz. This is useful when the shape of the spectrum is rather constant, since variations in the ASD will then be proportional to variations in the signal's voltage level itself. But it is mathematically preferred to use the PSD, since only in that case is the area under the curve meaningful in terms of actual power over all frequency or over a specified bandwidth.
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Theoretical and Fundamental Chemistry
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Phosphohydroxypyruvic acid is an organic acid most widely known as an intermediate in the synthesis of serine.
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Applied and Interdisciplinary Chemistry
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The three oxygen atoms form a trigonal planar geometry around the boron. The B-O bond length is 136 pm and the O-H is 97 pm. The molecular point group is C.
Two crystalline forms of orthoboric acid are known: triclinic and hexagonal. The former is the most common; the second, which is a bit more stable thermodynamically, can be obtained with a special preparation method.
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Theoretical and Fundamental Chemistry
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For a face-centered cubic unit cell, the number of atoms is four. A line can be drawn from the top corner of a cube diagonally to the bottom corner on the same side of the cube, which is equal to 4r. Using geometry, and the side length, a can be related to r as:
Knowing this and the formula for the volume of a sphere, it becomes possible to calculate the APF as follows:
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Theoretical and Fundamental Chemistry
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Hydrogenolysis in the presence of a variety of palladium-based catalysts is the usual method for deprotection. Palladium on charcoal is typical.
Alternatively, HBr and strong Lewis acids have been used, provided that a trap is provided for the released benzyl carbocation.
When the protected amine is treated by either of the above methods (i.e. by catalytic hydrogenation or acidic workup), it yields a terminal carbamic acid which then readily decarboxylates to give the free amine.
2-Mercaptoethanol can also be used, in the presence of potassium phosphate in dimethylacetamide.
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Theoretical and Fundamental Chemistry
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Arusi is a member of the American Association of Corrosion Engineers and a member of the British Institute of Corrosion.
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Applied and Interdisciplinary Chemistry
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In the 1920s there was an outbreak of a mysterious haemorrhagic cattle disease in Canada and the northern United States. The disease was named sweet clover disease because the cattle had grazed on sweet clover hay. It wasnt until ten years after the outbreak, that a local investigator, Karl P. Link and his student Wilhelm Schoeffel started an intense investigation to find the substance causing the internal bleeding. It took them 6 years to discover dicoumarol, the causing agent. They patented the right for the substance and in 1945 Link started selling a coumarin derivative as a rodenticide. He and his colleagues worked on several variations and ended up with a substance they named warfarin in 1948. It wasnt until 1954 that it was approved for medicinal use in humans making warfarin the first oral anticoagulant drug.
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Applied and Interdisciplinary Chemistry
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Many universities and seats of learning honored Heyrovský. He was elected Fellow of University College, London, in 1927, and received honorary doctorates from the Technical University, Dresden in 1955, the University of Warsaw in 1956, the University Aix-Marseille in 1959, and the University of Paris in 1960. He was granted honorary membership in the American Academy of Arts and Sciences in 1933; in the Hungarian Academy of Sciences in 1955; the Indian Academy of Sciences, Bangalore, in 1955; the Polish Academy of Sciences, Warsaw, in 1962; was elected Corresponding Member of the German Academy of Sciences, Berlin, in 1955; member of the German Academy of Natural Scientists, Leopoldina (Halle-Saale) in 1956; Foreign Member of the Royal Danish Academy of Sciences, Copenhagen, in 1962; Vice-President of the International Union of Physics from 1951 to 1957; President and first honorary member of the Polarographic Society, London; honorary member of the Polarographic Society of Japan; honorary member of the Chemical Societies of Czechoslovakia, Austria, Poland, England and India. In 1965, Heyrovský was elected a Foreign Member of the Royal Society (ForMemRS) in 1965.
In Czechoslovakia Heyrovský was awarded the State Prize, First Grade, in 1951, and in 1955 the Order of the Czechoslovak Republic.
Heyrovský lectured on polarography in the United States in 1933, the USSR in 1934, England in 1946, Sweden in 1947, the People's Republic of China in 1958, and in U.A.R. (Egypt) in 1960 and 1961.
The crater Heyrovský on the Moon is named in his honour.
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Theoretical and Fundamental Chemistry
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In fluid dynamics, shear flow is the flow induced by a force in a fluid. In solid mechanics, shear flow is the shear stress over a distance in a thin-walled structure.
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Applied and Interdisciplinary Chemistry
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Cold water pitting of copper tube occurs in only a minority of installations. Copper water tubes are usually guaranteed by the manufacturer against manufacturing defects for a period of 50 years. The vast majority of copper systems far exceed this time period but a small minority may fail after a comparatively short time.
The majority of failures seen are the result of poor installation or operation of the water system. The most common failure seen in the last 20 years is pitting corrosion in cold water tubes, also known as Type 1 pitting. These failures are usually the result of poor commissioning practice although a significant number are initiated by flux left in the bore after assembly of soldered joints. Prior to about 1970 the most common cause of Type 1 pitting was carbon films left in the bore by the manufacturing process.
Research and manufacturing improvements in the 1960s virtually eliminated carbon as a cause of pitting with the introduction of a clause in the 1971 edition of BS 2871 requiring tube bores to be free of deleterious films. Despite this, carbon is still regularly blamed for tube failures without proper investigation.
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Applied and Interdisciplinary Chemistry
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Fructo-oligosaccharides (FOS), which are found in many vegetables, are short chains of fructose molecules. They differ from fructans such as inulin, which as polysaccharides have a much higher degree of polymerization than FOS and other oligosaccharides, but like inulin and other fructans, they are considered soluble dietary fibre. Using fructo-oligosaccharides (FOS) as fiber supplementations is shown to have an effect on glucose homeostasis quite similar to insulin. These (FOS) supplementations can be considered prebiotics which produce short-chain fructo-oligosaccharides (scFOS). Galacto-oligosaccharides (GOS) in particular are used to create a prebiotic effect for infants that are not being breastfed.
Galactooligosaccharides (GOS), which also occur naturally, consist of short chains of galactose molecules. Human milk is an example of this and contains oligosaccharides, known as human milk oligosaccharides (HMOs), which are derived from lactose. These oligosaccharides have biological function in the development of the gut flora of infants. Examples include lacto-N-tetraose, lacto-N-neotetraose, and lacto-N-fucopentaose. These compounds cannot be digested in the human small intestine, and instead pass through to the large intestine, where they promote the growth of Bifidobacteria, which are beneficial to gut health.
HMOs can also protect infants by acting as decoy receptors against viral infection. HMOs accomplish this by mimicking viral receptors which draws the virus particles away from host cells. Experimentation has been done to determine how glycan-binding occurs between HMOs and many viruses such as influenza, rotavirus, human immunodeficiency virus (HIV), and respiratory syncytial virus (RSV). The strategy HMOs employ could be used to create new antiviral drugs.
Mannan oligosaccharides (MOS) are widely used in animal feed to improve gastrointestinal health. They are normally obtained from the yeast cell walls of Saccharomyces cerevisiae. Mannan oligosaccharides differ from other oligosaccharides in that they are not fermentable and their primary mode of action includes agglutination of type-1 fimbria pathogens and immunomodulation.
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Theoretical and Fundamental Chemistry
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Among children and adolescents, the most common health effect post-flooding was lower respiratory tract symptoms, though there was a lack of association with measurements of total fungi. Another study found that these respiratory symptoms were positively associated with exposure to water damaged homes, exposure included being inside without participating in clean up. Despite lower respiratory effects among all children, there was a significant difference in health outcomes between children with pre-existing conditions and children without. Children with pre-existing conditions were at greater risk that can likely be attributed to the greater disruption of care in the face of flooding and natural disaster.
Although mold is the primary focus post flooding for residents, the effects of dampness alone must also be considered. According to the Institute of Medicine, there is a significant association between dampness in the home and wheeze, cough, and upper respiratory symptoms. A later analysis determined that 30% to 50% of asthma-related health outcomes are associated with not only mold, but also dampness in buildings. Another health effect associated with dampness and mold is Sick Building Syndrome (SBS), which is defined by manifestations of symptomatic illness as a result of poor indoor air quality and pollutant exposures. Signs of potentially illness-causing buildings include condensation on the windows, high humidity in the bathrooms, a moldy odor, or water leakage.
While there is a proven correlation between mold exposure and the development of upper and lower respiratory syndromes, there are still fewer incidences of negative health effects than one might expect. Barbeau and colleagues suggested that studies do not show a greater impact from mold exposure for several reasons: 1) the types of health effects are not severe and are therefore not caught; 2) people whose homes have flooded find alternative housing to prevent exposure; 3) self-selection, the healthier people participated in mold clean-up and were less likely to get sick; 4) exposures were time-limited as result of remediation efforts and; 5) the lack of access to health care post-flooding may result in fewer illnesses being discovered and reported for their association with mold. There are also certain notable scientific limitations in studying the exposure effects of dampness and molds on individuals because there are currently no known biomarkers that can prove that a person was exclusively exposed to molds. Thus, it is currently impossible to prove correlation between mold exposure and symptoms.
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Applied and Interdisciplinary Chemistry
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An ideal Bose gas is a quantum-mechanical phase of matter, analogous to a classical ideal gas. It is composed of bosons, which have an integer value of spin and abide by Bose–Einstein statistics. The statistical mechanics of bosons were developed by Satyendra Nath Bose for a photon gas and extended to massive particles by Albert Einstein, who realized that an ideal gas of bosons would form a condensate at a low enough temperature, unlike a classical ideal gas. This condensate is known as a Bose–Einstein condensate.
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Theoretical and Fundamental Chemistry
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Diphenylchlorarsine was used as a chemical weapon on the Western front during the trench warfare of World War I. It belongs to the class of chemicals classified as vomiting agents. Other such agents are diphenylcyanoarsine (DC) and diphenylaminechlorarsine (DM, Adamsite). Diphenylchlorarsine was sometimes believed to penetrate the gas masks of the time and to cause violent sneezing, forcing removal of the protecting device. The Germans called it (mask breaker), together with other substances with similar effects, such as Adamsite, diphenylarsincyanide, and diphenylaminarsincyanide. This gas did not actually penetrate masks any better than other gases.
DA (military code and acronym for diphenylchloroarsine) is a precursor to DC (diphenylcyanoarsine), generated by the reaction of an aqueous solution of sodium cyanide and DA (DC process, NaCN method), with cyanide being used in excess of 5%, for military purposes.
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Applied and Interdisciplinary Chemistry
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A relaxase is a single-strand DNA transesterase enzyme produced by some prokaryotes and viruses. Relaxases are responsible for site- and strand-specific nicks in unwound double-stranded DNA . Known relaxases belong to the rolling circle replication (RCR) initiator superfamily of enzymes and fall into two broad classes: replicative (Rep) and mobilization (Mob). The nicks produced by Rep relaxases initiate plasmid or virus RCR. Mob relaxases nick at origin of transfer (oriT) to initiate the process of DNA mobilization and transfer known as bacterial conjugation. Relaxases are so named because the single-stranded DNA nick that they catalyze lead to relaxation of helical tension.
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Applied and Interdisciplinary Chemistry
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Only a small fraction of the light incident on the ocean will be reflected and received by the satellite. The probability for a photon to reflect and exit the ocean decreases exponentially with length of its path through the water because the ocean is an absorbing medium. The more ocean a photon must travel through, the greater its chances of being absorbed by something. After absorption, it will eventually become part of the ocean's heat reservoir. The absorption and scattering characteristics of a water body determine the rate of vertical light attenuation and set a limit to the depths contributing to a satellite signal. A reasonable rule of thumb is that 90 percent of the signal coming from the water that is seen by the satellite is from the first attenuation length. How deep this is depends on the absorption and scattering properties of both the water itself and other constituents in the water. For wavelengths in the near infrared and longer, the penetration depth varies from a metre to a few micrometres. For band 1, the penetration depth will usually be between 1 and 10 metres. If the water has a large turbidity spike below 10 metres, the spike is unlikely to be seen by a satellite.
For very shallow clear water there is a good chance the bottom may be seen. For example, in the Bahamas, the water is quite clear and only a few metres deep, resulting in an apparent high turbidity because the bottom reflects much band 1 light. For areas with consistently high turbidity signals, particularly areas with relatively clear water, part of the signal may be due to bottom reflection. Normally this will not be a problem with a post-hurricane turbidity image since the storm easily resuspends enough sediment such that bottom reflection is negligible.
Clouds are also problematic for the interpretation of satellite derived turbidity. Cloud removal algorithms perform a satisfactory job for pixels that are fully cloudy. Partially cloudy pixels are much harder to identify and typically result in false high turbidity estimates. High turbidity values near clouds are suspect.
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Theoretical and Fundamental Chemistry
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Settling basins are designed to retain water long enough so that suspended solids can settle to obtain a high purity water in the outlet and to provide the opportunity for pH adjustment. Other processes that could be used: thickeners, clarifiers, hydro cyclones and membrane filtration are highly used techniques in the field. Compared to those processes, settling basins have a simpler and cheaper design, with fewer moving parts, demanding less maintenance, despite requiring cleaning and vacuuming of the quiescent zones at least once every two weeks.
However, settling basins can introduce new kinds of water contamination, particularly if the water supply is from a well. The basin can catch windblown contaminants, and if the water is retained for a long period, algae grows in the pool, leading to greater filtration problems. Settling ponds may also be ineffective at reducing turbidity caused by small particles with specific gravity low enough to be suspended by Brownian motion. Usually, it can only remove particles ranging from sand (2 mm in diameter) to silt (0.002 mm in diameter).
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Applied and Interdisciplinary Chemistry
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Froth flotation is applied to a wide range of separations. An estimated 1B tons of materials are processed in this manner annually.
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Applied and Interdisciplinary Chemistry
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Two systems exist for the asymmetric hydrogenation of 2-substituted quinolines with isolated yields generally greater than 80% and ee values generally greater than 90%. The first is an iridium(I)/chiral phosphine/I system, first reported by Zhou et al.. While the first chiral phosphine used in this system was MeOBiPhep, newer iterations have focused on improving the performance of this ligand. To this end, systems use phosphines (or related ligands) with improved air stability, recyclability, ease of preparation, lower catalyst loading and the potential role of achiral phosphine additives. As of October 2012 no mechanism appears to have been proposed, although both the necessity of I or a halogen surrogate and the possible role of the heteroaromatic N in assisting reactivity have been documented.
The second is an organocatalytic transfer hydrogenation system based on Hantzsch esters and a chiral Brønsted acid. In this case, the authors envision a mechanism where the isoquinoline is alternately protonated in an activating step, then reduced by conjugate addition of hydride from the Hantzsch ester.
<br />
Much of the asymmetric hydrogenation chemistry of quinoxalines is closely related to that of the structurally similar quinolines. Effective (and efficient) results can be obtained with an Ir(I)/phophinite/I system and a Hantzsh ester-based organocatalytic system, both of which are similar to the systems discussed earlier with regards to quinolines.
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Theoretical and Fundamental Chemistry
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