text stringlengths 105 4.57k | label int64 0 1 | label_text stringclasses 2 values |
|---|---|---|
In fluid dynamics and thermodynamics, the Lewis number (denoted ) is a dimensionless number defined as the ratio of thermal diffusivity to mass diffusivity. It is used to characterize fluid flows where there is simultaneous heat and mass transfer. The Lewis number puts the thickness of the thermal boundary layer in relation to the concentration boundary layer. The Lewis number is defined as
where:
* is the thermal diffusivity,
* is the mass diffusivity,
* is the thermal conductivity,
* is the density,
* is the mixture-averaged diffusion coefficient,
* is the specific heat capacity at constant pressure.
In the field of fluid mechanics, many sources define the Lewis number to be the inverse of the above definition.
The Lewis number can also be expressed in terms of the Prandtl number () and the Schmidt number ():
It is named after Warren K. Lewis (1882–1975), who was the first head of the Chemical Engineering Department at MIT. Some workers in the field of combustion assume (incorrectly) that the Lewis number was named for Bernard Lewis (1899–1993), who for many years was a major figure in the field of combustion research. | 1 | Applied and Interdisciplinary Chemistry |
Site specific isotope enrichments of NO is measured in the environment to help disentangle microbial sources and sinks in the environment. Different isotopologues of N2O absorb light at different wavelengths. Laser spectroscopy converts these differences as it scans across wavelengths to measure the abundance of N-N-O vs. N-N-O, a distinction that is impossible on other instruments. These measurements have achieved very high precision, down to 0.2 per mille. | 0 | Theoretical and Fundamental Chemistry |
The Lowry protein assay is a biochemical assay for determining the total level of protein in a solution. The total protein concentration is exhibited by a color change of the sample solution in proportion to protein concentration, which can then be measured using colorimetric techniques. It is named for the biochemist Oliver H. Lowry who developed the reagent in the 1940s. His 1951 paper describing the technique is the most-highly cited paper ever in the scientific literature, cited over 300,000 times. | 1 | Applied and Interdisciplinary Chemistry |
There is great potential for RNA interference (RNAi) to be used therapeutically to reversibly silence any gene. For RNAi to realize its therapeutic potential, small interfering RNA (siRNA) must be delivered to the site of action in the cells of target tissues. But finding safe and efficient delivery mechanisms is a major obstacle to achieving the full potential of siRNA-based therapies. Unmodified siRNA is unstable in the bloodstream, has the potential to cause immunogenicity, and has difficulty readily navigating cell membranes. As a result, chemical alterations and/or delivery tools are needed to safely transfer siRNA to its site of action.
There are three main techniques of delivery for siRNA that differ on efficiency and toxicity. | 1 | Applied and Interdisciplinary Chemistry |
Pitting corrosion, or pitting, is extremely localized corrosion that leads to the creation of small holes in the material – nearly always a metal. The failures resulting from this form of corrosion can be catastrophic. With general corrosion it is easier to predict the amount of material that will be lost over time and this can be designed into the engineered structure. Pitting, like crevice corrosion can cause a catastrophic failure with very little loss of material. Pitting corrosion happens for passive materials. The classic reaction mechanism has been ascribed to Ulick Richardson Evans. | 1 | Applied and Interdisciplinary Chemistry |
Classical thermodynamics deals with states of dynamic equilibrium. The state of a system at thermodynamic equilibrium is the one for which some thermodynamic potential is minimized (in the absence of an applied voltage), or for which the entropy (S) is maximized, for specified conditions. One such potential is the Helmholtz free energy (A), for a closed system at constant volume and temperature (controlled by a heat bath):
Another potential, the Gibbs free energy (G), is minimized at thermodynamic equilibrium in a closed system at constant temperature and pressure, both controlled by the surroundings:
where T denotes the absolute thermodynamic temperature, P the pressure, S the entropy, V the volume, and U the internal energy of the system. In other words, is a necessary condition for chemical equilibrium under these conditions (in the absence of an applied voltage).
Thermodynamic equilibrium is the unique stable stationary state that is approached or eventually reached as the system interacts with its surroundings over a long time. The above-mentioned potentials are mathematically constructed to be the thermodynamic quantities that are minimized under the particular conditions in the specified surroundings. | 0 | Theoretical and Fundamental Chemistry |
Due to its size and complexity, the 43S PIC has eluded high resolution structural characterization. However, combined approaches including cryo-EM, cross-linking, and the structural characterization of individual components, has led to models for the complex organization. | 1 | Applied and Interdisciplinary Chemistry |
Gold clusters can be obtained in colloid form. Such colloids often occur with a surface coating of alkanethiols or proteins. Such clusters can be used in immunohistochemical staining. Gold metal nanoparticles (NPs) are characterized by an intense absorption in the visible region, which enhances the utility of these species for the development of completely optical devices. The wavelength of this surface plasmon resonance (SPR) band depends on the size and shape of the nanoparticles as well as their interactions with the surrounding medium. The presence of this band enhances the utility of gold nanoparticle as building blocks for devices for data storage, ultrafast switching, and gas sensors. Whilst plasmonic gold nanoparticles only exhibit electric moments, clusters of such particles can exhibit magnetic moments making them of great interest for use in optical metamaterials | 0 | Theoretical and Fundamental Chemistry |
The significance of CIA for astrophysics was recognized early-on, especially where dense atmospheres of mixtures of molecular hydrogen and helium gas exist. | 0 | Theoretical and Fundamental Chemistry |
In fluid dynamics, and oceanography, Langmuir turbulence is a turbulent flow with coherent Langmuir circulation structures that exist and evolve over a range of spatial and temporal scales. These structures arise through an interaction between the ocean surface waves and the currents.
In the upper ocean Langmuir circulations are a special case where the turbulent structures exhibit a dominant cell size. In general it is expected that Langmuir turbulence is a global ocean phenomenon and not confined to gentle wind conditions or shallow water ways (as with most observations of Langmuir circulation).
An important consequence of the Langmuir turbulence are deeply penetrating jets. These features occur between counter-rotating Langmuir circulations and can inject turbulent kinetic energy to depths well below the depth scale for the surface waves (Stokes drift depth scale). Langmuir turbulence could have an important impact on our understanding of climate. In particular, Langmuir turbulence could affect the global ocean's sea surface temperature as the deeply penetrating Langmuir jets modify the depth of the ocean mixed layer. | 1 | Applied and Interdisciplinary Chemistry |
The flow around a tropical cyclone is often well approximated as parallel to circular isobars, such as in a vortex. A strong pressure gradient draws air toward the center of the cyclone, a centripetal force nearly balanced by Coriolis and centrifugal forces in gradient wind balance. The viscous secondary flow near the Earths surface converges toward the center of the cyclone, ascending in the eyewall to satisfy mass continuity. As the secondary flow is drawn upward the air cools as its pressure falls, causing extremely heavy rainfall and releasing latent heat which is an important driver of the storms energy budget. | 1 | Applied and Interdisciplinary Chemistry |
Prompt-gamma neutron activation analysis (PGAA) is a very widely applicable technique for determining the presence and amount of many elements simultaneously in samples ranging in size from micrograms to many grams. It is a non-destructive method, and the chemical form and shape of the sample are relatively unimportant. Typical measurements take from a few minutes to several hours per sample.
The technique can be described as follows. The sample is continuously irradiated with a beam of neutrons. The constituent elements of the sample absorb some of these neutrons and emit prompt gamma rays which are measured with a gamma ray spectrometer. The energies of these gamma rays identify the neutron-capturing elements, while the intensities of the peaks at these energies reveal their concentrations. The amount of analyte element is given by the ratio of count rate of the characteristic peak in the sample to the rate in a known mass of the appropriate elemental standard irradiated under the same conditions.
Typically, the sample will not acquire significant long-lived radioactivity, and the sample may be removed from the facility and used for other purposes. One of the typical applications of PGAA is an online belt elemental analyzer or bulk material analyzer used in cement, coal and mineral industries. | 0 | Theoretical and Fundamental Chemistry |
Studies on the binding mechanism of selective COX-2 inhibitors show that they have two reversible steps with both COX-1 and COX-2, but the selectivity for COX-2 is due to another step that is slow and irreversible and is seen only in the inhibition of COX-2, not COX-1. The irreversible step has been attributed to the presence of the sulfonamide (or sulfone) that fits into the side-pocket of COX-2. This has been studied using SC-58125 (an analogue of celecoxib) and mutated COX-2, wherein the valine 523 residue was replaced by isoleucine 523. The irreversible inhibition did not happen, but reversible inhibition was noticed. A model has been made to explain this three-step mechanism behind the inhibitory effects of selective COX-2 inhibitors. The first step accounts for the contact of the inhibitor with the gate of the hydrophobic channel (called the lobby region). The second step could account for the movement of the inhibitor from the lobby region to the active site of the COX enzyme. The last step probably represents repositioning of the inhibitor at the active site, which leads to strong interactions of the phenylsulfonamide or phenylsulfone group of the inhibitor and the amino acids of the side pocket. It is directly inhibition to postaglanding | 1 | Applied and Interdisciplinary Chemistry |
Nujol is a brand of mineral oil by Plough Inc., cas number 8012-95-1, and density 0.838 g/mL at 25 °C, used in infrared spectroscopy. It is a heavy paraffin oil so it is chemically inert and has a relatively uncomplicated IR spectrum, with major peaks between 2950-2800, 1465-1450, and 1380–1300 cm. The empirical formula of Nujol is hard to determine exactly because it is a mixture but it is essentially the alkane formula where n is very large.
To obtain an IR spectrum of a solid, a sample is combined with Nujol in a mortar and pestle or some other device to make a mull (a very thick suspension), and is usually sandwiched between potassium- or sodium chloride plates before being placed in the spectrometer. For very reactive samples, the layer of Nujol can provide a protective coating, preventing sample decomposition during acquisition of the IR spectrum. When preparing the sample it is important to keep the sample from being saturated with Nujol, this will result in erroneous spectra since the Nujol peaks will dominate, silencing the actual sample's peaks. | 0 | Theoretical and Fundamental Chemistry |
The Laves graph has been suggested as an allotrope of carbon, analogous to the more common graphene and graphite carbon structure which also have three bonds per atom at 120° angles. In graphene, adjacent atoms have the same bonding planes as each other, whereas in the Laves graph structure the bonding planes of adjacent atoms are twisted by an angle of approximately 70.5° around the line of the bond. However, this hypothetical carbon allotrope turns out to be unstable.
The Laves graph may also give a crystal structure for boron, one which computations predict should be stable. Other chemicals that may form this structure include SrSi (from which the "srs net" name derives) and elemental nitrogen, as well as certain metal–organic frameworks and cyclic hydrocarbons.
The electronic band structure for the tight-binding model of the Laves graph has been studied, showing the existence of Dirac and Weyl points in this structure. | 0 | Theoretical and Fundamental Chemistry |
In biogeochemistry, remineralisation (or remineralization) refers to the breakdown or transformation of organic matter (those molecules derived from a biological source) into its simplest inorganic forms. These transformations form a crucial link within ecosystems as they are responsible for liberating the energy stored in organic molecules and recycling matter within the system to be reused as nutrients by other organisms.
Remineralisation is normally viewed as it relates to the cycling of the major biologically important elements such as carbon, nitrogen and phosphorus. While crucial to all ecosystems, the process receives special consideration in aquatic settings, where it forms a significant link in the biogeochemical dynamics and cycling of aquatic ecosystems. | 0 | Theoretical and Fundamental Chemistry |
An international subculture has grown up around the exploration of stormwater drains. Societies such as the Cave Clan regularly explore the drains underneath cities. This is commonly known as "urban exploration", but is also known as draining when in specific relation to storm drains. | 1 | Applied and Interdisciplinary Chemistry |
Strutt was born on 12 November 1842 at Langford Grove in Maldon, Essex. In his early years he suffered from frailty and poor health. He attended Eton College and Harrow School (each for only a short period), before going on to the University of Cambridge in 1861 where he studied mathematics at Trinity College, Cambridge. He obtained a Bachelor of Arts degree (Senior Wrangler and 1st Smith's Prize) in 1865, and a Master of Arts in 1868. He was subsequently elected to a fellowship of Trinity. He held the post until his marriage to Evelyn Balfour, daughter of James Maitland Balfour, in 1871. He had three sons with her. In 1873, on the death of his father, John Strutt, 2nd Baron Rayleigh, he inherited the Barony of Rayleigh.
He was the second Cavendish Professor of Physics at the University of Cambridge (following James Clerk Maxwell), from 1879 to 1884. He first described dynamic soaring by seabirds in 1883, in the British journal Nature. From 1887 to 1905 he was professor of Natural Philosophy at the Royal Institution.
Around the year 1900 Rayleigh developed the duplex (combination of two) theory of human sound localisation using two binaural cues, interaural phase difference (IPD) and interaural level difference (ILD) (based on analysis of a spherical head with no external pinnae). The theory posits that we use two primary cues for sound lateralisation, using the difference in the phases of sinusoidal components of the sound and the difference in amplitude (level) between the two ears.
In 1904 he was awarded the Nobel Prize for Physics "for his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies".
During the First World War, he was president of the government's Advisory Committee for Aeronautics, which was located at the National Physical Laboratory, and chaired by Richard Glazebrook.
In 1919, Rayleigh served as president of the Society for Psychical Research. As an advocate that simplicity and theory be part of the scientific method, Rayleigh argued for the principle of similitude.
Rayleigh was elected fellow of the Royal Society on 12 June 1873, and served as president of the Royal Society from 1905 to 1908. From time to time he participated in the House of Lords; however, he spoke up only if politics attempted to become involved in science.
Many of the papers that he wrote on lubrication are now recognized as early classical contributions to the field of tribology. For these contributions, he was named as one of the 23 "Men of Tribology" by Duncan Dowson.
He died on 30 June 1919, at his home in Witham, Essex. He was succeeded, as the 4th Lord Rayleigh, by his son Robert John Strutt, another well-known physicist. Lord Rayleigh was buried in the graveyard of All Saints Church in Terling in Essex. There is a memorial to him by Derwent Wood in St Andrews Chapel at Westminster Abbey. | 1 | Applied and Interdisciplinary Chemistry |
Alternate land use, deforestation, afforestation and different types of river engineering have also led to changes in hydrologic processes, such as runoff. Mushrooming illegal mining activity can, for example, change the soil structure, the pressure-gradient between stream flow and groundwater and the vegetation cover and therefore lead to increased or decreased runoff. In southern Ghana in the Lower Pra River Basin, the percentage of runoff change, which is linked to human activity is approximately up to 66%.
Human presence and infrastructure has benefited from river management, by changing and straightening rivers to make the valuable land around them more live-able. | 1 | Applied and Interdisciplinary Chemistry |
Ocean acidification not only has impacts on aquatic life, but also on human communities and the overall livelihood of people living near these waters. For example, as a result of crustaceans being unable to produce their shells and skeletons due to reduced amounts of carbonate ions, populations such as crabs have significantly decreased in some areas in the Northern hemisphere. This has resulted in numerous fisheries in these areas to close down as a result of multi-million dollar losses. In addition, increased temperatures have caused a swift increase in toxic algal blooms, which are known to produce a neurotoxin called domoic acid that can accumulate inside the bodies of certain shellfish. If ingested by humans this toxin can cause severe health issues, which has forced many additional fisheries to close down. | 0 | Theoretical and Fundamental Chemistry |
Sample thickness can be estimated using twoBeamGUI from a convergent beam electron diffraction pattern (CBED) in two beam approximation. The procedure is based on an automated extraction of the intensity profile across the diffracted disk in the following steps:
# diffraction disk radius is determined using multi-scale Hough transform,
# the transmitted and diffracted disks are localized and the reflection is indexed,
# the disks are horizontally aligned, cropped out and profiles are measured across the disks,
# the profile across the diffracted disk is matched with a series of profiles automatically simulated for given material, reflection and specified thickness range.
Once the procedure is completed, the measured profile and the most similar simulated profile are displayed with the diffracted disk on the background. This allows the user to verify correctness of the automated estimate and easily check the similarity of other intensity profiles within the specified thickness range. | 0 | Theoretical and Fundamental Chemistry |
There is no known antidote against MFA, but there are some suggestions regarding the treatment of MFA poisoning. Advised is to use an intravenous injection of fast-acting anesthetics directly after poisoning. The anesthetic should be pentothal sodium or evipan sodium followed by an intramuscular injection of long-acting cortical depressants like sodium phenobarbitone or rectal avertin. Afterward, careful supervision of oxygen supply is necessary together with a BLB mask and the use of artificial respiration. Possibly, the use of hypertonic glucose intravenously is required as in status epilepticus. At last, careful use of tubocurarine chloride should be applied to control any convulsions. If any vomiting occurs, lean the patient forward to maintain an open airway.
Alternatively, there is a therapy aimed at the prevention of fluorocitrate synthesis, the blocking of aconitase within the mitochondria, and to provide a citrate outflow from the mitochondria to keep the TCA cycle going. For now, ethanol has proven to be the most effective against FC formation. When ethanol is oxidized, it increases blood acetate levels which inhibits FC production. In humans, an oral dose of 40-60 mL 96% ethanol is advised followed by 1.0-1.5 g/kg of 5-10% ethanol intravenously during the first hour and 0.1 g/kg during the following 6–8 hours. This therapy is meant for fluoroacetate (FA) poisoning which is highly related MFA, so this therapy aimed at MFA may result in other outcomes.
Treatment with monoacetin (glycerol monoacetate) helped against FA poisoning. It aids in increasing acetate levels of the blood and it decreases citrate levels in the heart, brain, and kidneys. However, this is only tested experimentally. In monkeys, monoacetin even reverses the effects of FA: all biological effects normalized. As with ethanol, monoacetin is effective against FA poisoning.
There is up until now, no proven treatment against MFA. However, the beforementioned treatments can provide starting points for therapy aimed at MFA since FA and MFA are closely related compounds. | 1 | Applied and Interdisciplinary Chemistry |
Oxophilicity is the tendency of certain chemical compounds to form oxides by hydrolysis or abstraction of an oxygen atom from another molecule, often from organic compounds. The term is often used to describe metal centers, commonly the early transition metals such as titanium, niobium, and tungsten. Oxophilicity is often stated to be related to the hardness of the element, within the HSAB theory (hard and soft (Lewis) acids and bases), but it has been shown that oxophilicity depends more on the electronegativity and effective nuclear charge of the element than on its hardness. This explains why the early transition metals, whose electronegativities and effective nuclear charges are low, are very oxophilic. Many main group compounds are also oxophilic, such as derivatives of aluminium, silicon, and phosphorus(III). The handling of oxophilic compounds often requires air-free techniques. | 0 | Theoretical and Fundamental Chemistry |
Further splitting in the fluorescence spectrum may occur due to the hyperfine interaction which leads to further resonance conditions and corresponding spectral lines. In NV ODMR, this detailed structure usually originates from nitrogen and carbon-13 atoms near to the defect. These atoms have small magnetic fields which interact with the spectral lines from the NV, causing further splitting. | 0 | Theoretical and Fundamental Chemistry |
A dilution series of a sample or extract is prepared and assessed for presence of odour. The result can be described as the odour potency of a compound.
One kind of analysis is to measure the maximum dilution in the series in which odour is still perceived. The resulting value is called the flavour dilution (FD) factor in the aroma extraction dilution analysis (AEDA) developed in 1987 by Schieberle and Grosch. On the other hand, another kind of analysis is to also measure the duration of the perceived odour to compute peak areas. The peak areas are known as Charm values in the CharmAnalysis developed in 1984 by Acree and co-workers. The former can then be interpreted as the peak height of the latter. Because the odour threshold of a compound is intended to be measured from a prepared series of dilution (commonly by a factor of 2–3 with 8–10 dilutions), the precision and variation in data can be determined from the dilution factors used.
Due to time demand requirements from this method and the general requirement for multiple assessors to minimise errors, having the column split into multiple odour ports would be beneficial for the method. | 0 | Theoretical and Fundamental Chemistry |
The formation of multiple native disulfides remains challenging of native peptide synthesis by solid-phase methods. Random chain combination typically results in several products with nonnative disulfide bonds. Stepwise formation of disulfide bonds is typically the preferred method, and performed with thiol protecting groups. Different thiol protecting groups provide multiple dimensions of orthogonal protection. These orthogonally protected cysteines are incorporated during the solid-phase synthesis of the peptide. Successive removal of these groups, to allow for selective exposure of free thiol groups, leads to disulfide formation in a stepwise manner. The order of removal of the groups must be considered so that only one group is removed at a time.
Thiol protecting groups used in peptide synthesis requiring later regioselective disulfide bond formation must possess multiple characteristics. First, they must be reversible with conditions that do not affect the unprotected side chains. Second, the protecting group must be able to withstand the conditions of solid-phase synthesis. Third, the removal of the thiol protecting group must be such that it leaves intact other thiol protecting groups, if orthogonal protection is desired. That is, the removal of PG A should not affect PG B. Some of the thiol protecting groups commonly used include the acetamidomethyl (Acm), tert-butyl (But), 3-nitro-2-pyridine sulfenyl (NPYS), 2-pyridine-sulfenyl (Pyr), and trityl (Trt) groups. Importantly, the NPYS group can replace the Acm PG to yield an activated thiol.
Using this method, Kiso and coworkers reported the first total synthesis of insulin in 1993. In this work, the A-chain of insulin was prepared with following protecting groups in place on its cysteines: CysA6(But), CysA7(Acm), and CysA11(But), leaving CysA20 unprotected. | 1 | Applied and Interdisciplinary Chemistry |
In igneous petrology the term more specifically refers to the volatile components of magma (mostly water vapor and carbon dioxide) that affect the appearance and explosivity of volcanoes. Volatiles in a magma with a high viscosity, generally felsic with a higher silica (SiO) content, tend to produce eruptions that are explosive eruption. Volatiles in a magma with a low viscosity, generally mafic with a lower silica content, tend to vent as effusive eruption and can give rise to a lava fountain. | 0 | Theoretical and Fundamental Chemistry |
Acid-base extraction works on the fundamental principle that salts are ionic compounds with a high solubility in water, while neutral molecules typically lack solubility in water.
Consider a mixture of acidic and basic compounds dissolved in an organic solvent. Adding aqueous acid will cause the acidic component to stay uncharged, while the basic component will be protonated to form a salt. The uncharged acid component will remain dissolved in the organic solvent, while the highly charged basic salt will migrate to the aqueous solvent. Since the acidic and basic components are now in two different layers, they can easily be separated.
Alternatively, adding aqueous base will cause the acidic component to be deprotonated and form a salt, while the basic component will remain uncharged. In this case, the uncharged base will stay in the organic layer, while the highly charged acidic salt will migrate to the aqueous layer.
If the organic acid component is relatively weak and has a pK value of ~5 (such as a carboxylic acid), adding additional acid can further improve separation by lowering the pH of the solution. This minimizes the self ionization of the organic acid component and limits its tendency to enter the aqueous layer. This principle is also applicable to an organic base when it is a relatively weak base.
Although acid-base extractions are most commonly used to separate acids from bases, they can be used to separate two acids or two bases from each other. However, the acids and bases must differ greatly in strength, e.g. one strong acid and one very weak acid. Therefore, the two acids must have a pK (or pK) difference that is as large as possible. For example, the following can be separated:
* Very weak acids like phenols (pK around 10) from stronger acids like carboxylic acids (pK around 4–5).
* Very weak bases (pK around 13–14) from stronger bases (pK around 3–4). This is frequently used in purifying soil to determine trace metal concentration.
When separating two acids or two bases, the pH is usually adjusted to a value roughly between the pK (or pK) constants. Separation occurs at this intermediate pH because one component is fully ionized, while the other is fully in its neutral form. Often, the solutions used to extract the acids or bases can also be used to control the pH. When separating two acids, the mixture is first washed with a weak base (e.g. sodium bicarbonate) to extract the strong acid, then washed with a strong base (e.g. sodium hydroxide) to extract the weak acid. For separating basic components, weak acid (e.g. dilute acetic acid) is first used to extract the stronger base, then more concentrated acid (e.g. hydrochloric acid or nitric acid) is used to create strongly acidic pH values and separate the weaker base. | 0 | Theoretical and Fundamental Chemistry |
TFA interacts with the TBP subunit of TFD and aids in the binding of TBP to TATA-box containing promoter DNA. Interaction of TFA with TBP facilitates formation of and stabilizes the preinitiation complex. Interaction of TFA with TBP also results in the exclusion of negative (repressive) factors that might otherwise bind to TBP and interfere with PIC formation. TFA also acts as a coactivator for some transcriptional activators, assisting with their ability to increase, or activate, transcription. The requirement for TFA in vitro transcription systems has been variable, and it can be considered either as a GTF and/or a loosely associated TAF-like coactivator. Genetic analysis in yeast has shown that TFA is essential for viability. | 1 | Applied and Interdisciplinary Chemistry |
Favre averaging is the density-weighted averaging method, used in variable density or compressible turbulent flows, in place of the Reynolds averaging. The method was introduced formally by the French scientist A. J. Favre in 1965, although Osborne Reynolds has also already introduced the density-weighted averaging in 1895. The averaging results a simplistic form for the nonlinear convective terms of the Navier-Stokes equations, at the expense of making the diffusion terms complicated. | 1 | Applied and Interdisciplinary Chemistry |
Paired receptors transduce extracellular signals through opposing intracellular signaling pathways. Canonically, inhibitory receptors recruit phosphatases through their ITIM motifs, inhibiting the function of cells in which they are expressed. By contrast, activating receptors interact with adaptor proteins such as DAP-12 bearing an ITAM motif, which in turn recruit kinases such as Syk and ZAP70.
Ligands for paired receptors can be very diverse. They are often proteins; the best-characterized are the MHC class I molecules, but a number of other endogenous molecules have been described as ligands for at least one family of paired receptors, and in a few cases in the LILR family, even intact bacteria or viruses can serve as ligands. Lipids such as phosphatidylethanolamine and phosphatidylserine, sugars and sialylated glycans, and nucleic acids can all serve as ligands for some paired receptors.
The binding affinity of paired receptors' extracellular domains for their ligands is generally fairly weak, with dissociation constants (K) in the micromolar (μM) range. However, the inhibitory member of a pair usually binds with higher affinity than the activating member. This can produce a competitive inhibition effect, in which the inhibitory member of the pair out-competes its activating counterpart for ligand binding; other mechanisms of interference with activation, such as disrupting dimerization, have also been described. Thus the net baseline signal from the pair is usually inhibitory, but may be modulated through differences in expression, surface density, subcellular localization, or other factors.
In NK cells, ligands for inhibitory receptors are often MHC class I (MHC-I) molecules, while those for activating receptors may include signals of abnormality or infection such as proteins from pathogens or tumors, or molecules associated with cell stress. Endogenous ligands for inhibitory receptors are better characterized than those for activating receptors. Paired receptor signaling may represent maintenance of homeostasis such that immune responses to normal host cells are inhibited, while responses to abnormal or pathogenic molecules in the environment are activating. NK activation in the absence of inhibitory receptor signals from endogenous ligands is a molecular mechanism for the missing-self hypothesis of NK activation. | 1 | Applied and Interdisciplinary Chemistry |
In biochemistry, intercalation is the insertion of molecules between the planar bases of deoxyribonucleic acid (DNA). This process is used as a method for analyzing DNA and it is also the basis of certain kinds of poisoning.
There are several ways molecules (in this case, also known as ligands) can interact with DNA. Ligands may interact with DNA by covalently binding, electrostatically binding, or intercalating. Intercalation occurs when ligands of an appropriate size and chemical nature fit themselves in between base pairs of DNA. These ligands are mostly polycyclic, aromatic, and planar, and therefore often make good nucleic acid stains. Intensively studied DNA intercalators include berberine, ethidium bromide, proflavine, daunomycin, doxorubicin, and thalidomide. DNA intercalators are used in chemotherapeutic treatment to inhibit DNA replication in rapidly growing cancer cells. Examples include doxorubicin (adriamycin) and daunorubicin (both of which are used in treatment of Hodgkins lymphoma), and dactinomycin (used in Wilms tumour, Ewing's Sarcoma, rhabdomyosarcoma).
Metallointercalators are complexes of a metal cation with polycyclic aromatic ligands. The most commonly used metal ion is ruthenium(II), because its complexes are very slow to decompose in the biological environment. Other metallic cations that have been used include rhodium(III) and iridium(III). Typical ligands attached to the metal ion are dipyridine and terpyridine whose planar structure is ideal for intercalation.
In order for an intercalator to fit between base pairs, the DNA must dynamically open a space between its base pairs by unwinding. The degree of unwinding varies depending on the intercalator; for example, ethidium cation (the ionic form of ethidium bromide found in aqueous solution) unwinds DNA by about 26°, whereas proflavine unwinds it by about 17°. This unwinding causes the base pairs to separate, or "rise", creating an opening of about 0.34 nm (3.4 Å). This unwinding induces local structural changes to the DNA strand, such as lengthening of the DNA strand or twisting of the base pairs. These structural modifications can lead to functional changes, often to the inhibition of transcription and replication and DNA repair processes, which makes intercalators potent mutagens. For this reason, DNA intercalators are often carcinogenic, such as the exo (but not the endo) 8,9 epoxide of aflatoxin B and acridines such as proflavine or quinacrine.
Intercalation as a mechanism of interaction between cationic, planar, polycyclic aromatic systems of the correct size (on the order of a base pair) was first proposed by Leonard Lerman in 1961. One proposed mechanism of intercalation is as follows: In aqueous isotonic solution, the cationic intercalator is attracted electrostatically to the surface of the polyanionic DNA. The ligand displaces a sodium and/or magnesium cation present in the "condensation cloud" of such cations that surrounds DNA (to partially balance the sum of the negative charges carried by each phosphate oxygen), thus forming a weak electrostatic association with the outer surface of DNA. From this position, the ligand diffuses along the surface of the DNA and may slide into the hydrophobic environment found between two base pairs that may transiently "open" to form an intercalation site, allowing the ethidium to move away from the hydrophilic (aqueous) environment surrounding the DNA and into the intercalation site. The base pairs transiently form such openings due to energy absorbed during collisions with solvent molecules. | 0 | Theoretical and Fundamental Chemistry |
Extensive studies relating to the establishment of the presence of radium, uranium, and decay products of the thorium series in natural brines of the Soviet Union were carried out under the direction of V. G. Khlopin; numerous expeditions revealed a new form of accumulation in nature of radium and its isotopes in brine waters of the Na, Ca, and Cl types. The following of his students and colleagues participated in these studies: V. I. Baranov, L. V. Komlev, M. S. Merkulov, B. A. Nikitin, V. P. Savchenko, A. G. Samartseva, N. V. Tageev, and others. | 0 | Theoretical and Fundamental Chemistry |
Coenzyme A is produced commercially via extraction from yeast, however this is an inefficient process (yields approximately 25 mg/kg) resulting in an expensive product. Various ways of producing CoA synthetically, or semi-synthetically have been investigated although none are currently operating at an industrial scale. | 1 | Applied and Interdisciplinary Chemistry |
Born in Aarberg, Switzerland, Wüthrich was educated in chemistry, physics, and mathematics at the University of Bern before pursuing his PhD supervised by Silvio Fallab at the University of Basel, awarded in 1964. | 0 | Theoretical and Fundamental Chemistry |
Vicinal difunctionalization reactions, most generally, lead to new bonds at two adjacent carbon atoms. Often this takes place in a stereocontrolled fashion, particularly if both bonds are formed simultaneously, as in the Diels-Alder reaction. Activated double bonds represent a useful handle for vicinal difunctionalization because they can act as both nucleophiles and electrophiles—one carbon is necessarily electron poor, and the other electron rich. In the presence of a nucleophile and an electrophile, then, the two carbons of a double bond can act as a "relay," mediating electron flow from the nucleophile to the electrophile with the formation of two, rather than the usual one, chemical bonds.
Most often, the nucleophile employed in this context is an organometallic compound and the electrophile is an alkyl halide. | 0 | Theoretical and Fundamental Chemistry |
*Receptors must possess structural and steric specificity.
*Receptors are saturable and finite (limited number of binding sites)
*Receptors must possess high affinity for its endogenous ligand at physiological concentrations
*Once the endogenous ligand binds to the receptor, some early recognizable chemical event must occur | 1 | Applied and Interdisciplinary Chemistry |
The chemical components of orcein were elucidated only in the 1950s by Hans Musso. The structures are shown below. A paper originally published in 1961, embodying most of Musso's work on components of orcein and litmus, was translated into English and published in 2003 in a special issue of the journal Biotechnic & Histochemistry (Vol 78, No. 6) devoted to the dye. A single alternative structural formula for orcein, possibly incorrect, is given by the National Library of Medicine and Emolecules.
Orcein is a reddish-brown dye, orchil is a purple-blue dye. Orcein is also used as a stain in microscopy to visualize chromosomes, elastic fibers, Hepatitis B surface antigens, and copper-associated proteins.
Orcein is not approved as a food dye (banned in Europe since January 1977), with E number E121 before 1977 and E182 after. Its CAS number is . Its chemical formula is CHNO. It forms dark brown crystals. It is a mixture of phenoxazone derivates - hydroxyorceins, aminoorceins, and aminoorceinimines. | 0 | Theoretical and Fundamental Chemistry |
The role of endoglin plays in angiogenesis and the modulation of TGF beta receptor signaling, which mediates cellular localization, cellular migration, cellular morphology, cell proliferation, cluster formation, etc., makes endoglin an important player in tumor growth and metastasis. Being able to target and efficiently reduce or halt neoangiogenesis in tumors would prevent metastasis of primary cancer cells into other areas of the body. Also, it has been suggested that endoglin can be used for tumor imaging and prognosis.
The role of endoglin in cancer can be contradicting at times since it is needed for neoangiogenesis in tumors, which is needed for tumor growth and survival, yet the reduction in expression of endoglin has in many cancers correlated with a negative outcome of that cancer. In breast cancer, for example, the reduction of the full form of endoglin, and the increase of the soluble form of endoglin correlate with metastasis of cancer cells. The TGF beta receptor-endoglin complex relay contradicting signals from TGF beta as well. TGF beta can act as a tumor suppressor in the premalignant stage of the benign neoplasm by inhibiting its growth and inducing apoptosis. However, once the cancer cells have gone through the Hallmarks of Cancer and lost inhibitory growth responses, TGF beta mediates cell invasion, angiogenesis (with the help of endoglin), immune system evasion, and their ECM composition, allowing them to become malignant. | 1 | Applied and Interdisciplinary Chemistry |
The intercalation compounds graphite bisulfate and graphite perchlorate can be prepared by treating graphite with strong oxidizing agents in the presence of strong acids. In contrast to the potassium and calcium graphites, the carbon layers are oxidized in this process:
:48 C + 0.25 O + 3 HSO → [C][HSO]·2HSO + 0.5 HO
In graphite perchlorate, planar layers of carbon atoms are 794 picometers apart, separated by ions. Cathodic reduction of graphite perchlorate is analogous to heating , which leads to a sequential elimination of .
Both graphite bisulfate and graphite perchlorate are better conductors as compared to graphite, as predicted by using a positive-hole mechanism.
Reaction of graphite with affords the salt . | 0 | Theoretical and Fundamental Chemistry |
Large quantities of fecal coliform bacteria in water are not harmful according to some authorities, but may indicate a higher risk of pathogens being present in the water. Some waterborne pathogenic diseases that may coincide with fecal coliform contamination include ear infections, dysentery, typhoid fever, viral and bacterial gastroenteritis, and hepatitis A. | 0 | Theoretical and Fundamental Chemistry |
Hydrodynamic theories describe liquids in terms of space- and time-dependent macroscopic fields, such as density, velocity, and temperature. These fields obey partial differential equations, which can be linear or nonlinear. Hydrodynamic theories are more general than equilibrium thermodynamic descriptions, which assume that liquids are approximately homogeneous and time-independent. The Navier-Stokes equations are a well-known example: they are partial differential equations giving the time evolution of density, velocity, and temperature of a viscous fluid. There are numerous methods for numerically solving the Navier-Stokes equations and its variants. | 0 | Theoretical and Fundamental Chemistry |
Reversible non-covalent reactions, such as metal-ligand coordination, has also been applied in protein-directed DCC. This strategy is useful for the investigation of the optimal ligand stereochemistry to the binding site of the target protein. | 1 | Applied and Interdisciplinary Chemistry |
Technomimetics are molecular systems that can mimic man-made devices. The term was first introduced in 1997. The current set of technomimetic molecules includes motors, rotors, gears, gyroscopes, tweezers, and other molecular devices. Technomimetics can be considered as the essential components of molecular machines and have the primary use in molecular nanotechnology. | 0 | Theoretical and Fundamental Chemistry |
Richard Llewellyns novel How Green Was My Valley (1939) describes the social and environmental effects of coal mining in Wales at the turn of the 20th century. The local mines spoil tip, which he calls a slag heap, is the central figure of devastation. Eventually the pile overtakes the entire valley and crushes Huw Morgan's house: | 1 | Applied and Interdisciplinary Chemistry |
In 1972, Friedmann and Roblin authored a paper in Science titled "Gene therapy for human genetic disease?". Rogers (1970) was cited for proposing that exogenous good DNA be used to replace the defective DNA in those with genetic defects. | 1 | Applied and Interdisciplinary Chemistry |
Mirror life (also called mirror-image life) is a hypothetical form of life with mirror-reflected molecular building blocks. The possibility of mirror life was first discussed by Louis Pasteur. Although this alternative life form has not been discovered in nature, efforts to build a mirror-image version of biology's molecular machinery are already underway. | 0 | Theoretical and Fundamental Chemistry |
First eliminate the pressure p from the momentum flux S by use of the Bernoulli equation:
The streamfunction Ψ is expanded as a Maclaurin series around the bed at z = 0, and using that the impermeable bed is a streamline and the irrotationality of the flow: Ψ = 0 and ∂Ψ = 0 at z = 0:
with u the horizontal velocity at the bed z = 0. Because the waves are long, h ≫ λ, only terms up to z and ζ are retained in the approximations to Q and S. The momentum flux S then becomes:
The discharge Q becomes, since it is the value of the streamfunction Ψ at the free surface z = ζ:
As can be seen, the discharge Q is an O(ζ) quantity. From this, the bed velocity is seen to be
Note that Q / ζ is an order one quantity. This relation will be used to replace the bed velocity u by Q and ζ in the momentum flux S. The following terms can be derived from it:
Consequently, the momentum flux S becomes, again retaining only terms up to proportional to ζ:
Which can directly be recast in the form of equation (). | 1 | Applied and Interdisciplinary Chemistry |
Spinor condensates are degenerate Bose gases that have degrees of freedom arising from the internal spin of the constituent particles
They are described by a multi-component (spinor) order parameter.
Since their initial experimental realisation,
a wealth of studies have appeared, both
experimental and theoretical, focusing
on the physical properties of spinor condensates, including their
ground states, non-equilibrium dynamics, and
vortices. | 0 | Theoretical and Fundamental Chemistry |
Only the unbound fraction of the drug undergoes metabolism in the liver and other tissues. As the drug dissociates from the protein, more and more drug undergoes metabolism. Changes in the levels of free drug change the volume of distribution because free drug may distribute into the tissues leading to a decrease in plasma concentration profile. For the drugs which rapidly undergo metabolism, clearance is dependent on the hepatic blood flow. For drugs which slowly undergo metabolism, changes in the unbound fraction of the drug directly change the clearance of the drug.
The most commonly used methods for measuring drug concentration levels in the plasma measure bound as well as unbound fractions of the drug.
The fraction unbound can be altered by a number of variables, such as the concentration of drug in the body, the amount and quality of plasma protein, and other drugs that bind to plasma proteins. Higher drug concentrations would lead to a higher fraction unbound, because the plasma protein would be saturated with drug and any excess drug would be unbound. If the amount of plasma protein is decreased (such as in catabolism, malnutrition, liver disease, renal disease), there would also be a higher fraction unbound. Additionally, the quality of the plasma protein may affect how many drug-binding sites there are on the protein. | 1 | Applied and Interdisciplinary Chemistry |
*[http://www.ciml.univ-mrs.fr/software/cocas/index.html] CoCAS: a free Analysis software for Agilent ChIP-on-Chip experiments
*[http://www.bioconductor.org/packages/2.4/bioc/html/rMAT.html] rMAT: R implementation from MAT program to normalize and analyze tiling arrays and ChIP-chip data. | 1 | Applied and Interdisciplinary Chemistry |
Single fluorophores can be chemically attached to biomolecules, such as proteins or DNA, and the dynamics of individual molecules can be tracked by monitoring the fluorescent probe. Spatial movements within the Rayleigh limit can be tracked, along with changes in emission intensity and/or radiative lifetime, which often indicate changes in local environment. For instance, single-molecule labeling has yielded a vast quantity of information on how kinesin motor proteins move along microtubule strands in muscle cells. Single-molecule imaging in live cells reveals interesting information about protein dynamics under its physiological environment. Several biophysical parameters about protein dynamics can be quantified such as diffusion coefficient, mean squared displacements, residence time, the fraction of bound and unbound molecules, and target-search mechanism of protein binding to its target site in the live cell. | 0 | Theoretical and Fundamental Chemistry |
Although the network is completely described by only two parameters (the number of network nodes per unit volume and the statistical de-correlation length of the polymer, the Kuhn length), the way in which the chains are connected is actually quite complicated. There is a wide variation in the lengths of the chains and most of them are not connected to the nearest neighbor network node. Both the chain length and its end-to-end distance are described by probability distributions. The term ‘morphology’ refers to this complexity. If the cross-linking agent is thoroughly mixed, there is an equal probability for any isoprene unit to become a network node. For dicumyl peroxide, the cross linking efficiency in natural rubber is unity, but this is not the case for sulfur. The initial morphology of the network is dictated by two random processes: the probability for a cross-link to occur at any isoprene unit and the Markov random walk nature of a chain conformation. The probability distribution function for how far one end of a chain end can ‘wander’ from the other is generated by a Markov sequence. This conditional probability density function relates the chain length in units of the Kuhn length to the end-to-end distance :
The probability that any isoprene unit becomes part of a cross-link node is proportional to the ratio of the concentrations of the cross-linker molecules (e.g., dicumyl-peroxide) to the isoprene units: The factor of two comes about because two isoprene units (one from each chain) participate in the cross-link. The probability for finding a chain containing isoprene units is given by:
where .
The equation can be understood as simply the probability that an isoprene unit is NOT a cross-link (1−p) in N−1 successive units along a chain. Since P(N) decreases with N, shorter chains are more probable than longer ones. Note that the number of statistically independent backbone segments is not the same as the number of isoprene units. For natural rubber networks, the Kuhn length contains about 2.2 isoprene units, so . It is the product of equations () and () (the joint probability distribution) that relates the network chain length () and end-to-end distance () between its terminating cross-link nodes:
The complex morphology of a natural rubber network can be seen in Fig. 3, which shows the probability density vs. end-to-end distance (in units of mean node spacing) for an ‘average’ chain. For the common experimental cross-link density of 4x10 cm, an average chain contains about 116 isoprene units (52 Kuhn lengths) and has a contour length of about 50 nm. Fig. 3 shows that a significant fraction of chains span several node spacings, i.e., the chain ends overlap other network chains. Natural rubber, cross-linked with dicumyl peroxide, has tetra-functional cross-links, i.e. each cross-link node has 4 network chains emanating from it. Depending on their initial tortuosity and the orientation of their endpoints with respect to the strain axis, each chain associated with an active cross-link node can have a different elastic force constant as it resists the applied strain. To preserve force equilibrium (zero net force) on each cross-link node, a node may be forced to move in tandem with the chain having the highest force constant for chain extension. It is this complex node motion, arising from the random nature of the network morphology, that makes the study of the mechanical properties of rubber networks so difficult. As the network is strained, paths composed of these more extended chains emerge that span the entire sample, and it is these paths that carry most of the stress at high strains. | 0 | Theoretical and Fundamental Chemistry |
Metal sulfides are usually prepared by heating mixtures of the two elements, but in the case of scandium, this method yields scandium monosulfide, ScS. ScS can be prepared by heating scandium(III) oxide under flowing hydrogen sulfide in a graphite crucible to 1550 °C or above for 2–3 hours. The crude product is then purified by chemical vapor transport at 950 °C using iodine as the transport agent.
:ScO + 3HS → ScS + 3HO
Scandium(III) sulfide can be prepared by reacting scandium(III) chloride with dry hydrogen sulfide at elevated temperature:
:2 ScCl + 3 HS → ScS + 6 HCl | 0 | Theoretical and Fundamental Chemistry |
A relation between the apparent molar of a component of a mixture and molar mixing ratio can be obtained by dividing the definition relation
to the number of moles of one component. This gives the following relation: | 0 | Theoretical and Fundamental Chemistry |
The Mountain Pass Rare Earth Mine and Processing Facility, owned by MP Materials, is an open-pit mine of rare-earth elements on the south flank of the Clark Mountain Range in California, southwest of Las Vegas, Nevada. In 2020 the mine supplied 15.8% of the world's rare-earth production. It is the only rare-earth mining and processing facility in the United States.
As of 2022, work is ongoing to restore processing capabilities for domestic light rare-earth elements (LREEs) and work has been funded by the United States Department of Defense to restore processing capabilities for heavy rare-earth metals (HREEs) to alleviate supply chain risk. | 1 | Applied and Interdisciplinary Chemistry |
Whereas promiscuity is mainly studied in terms of standard enzyme kinetics, drug binding and subsequent reaction is a promiscuous activity as the enzyme catalyses an inactivating reaction towards a novel substrate it did not evolve to catalyse. This could be because of the demonstration that there are only a small number of distinct ligand binding pockets in proteins.
Mammalian xenobiotic metabolism, on the other hand, was evolved to have a broad specificity to oxidise, bind and eliminate foreign lipophilic compounds which may be toxic, such as plant alkaloids, so their ability to detoxify anthropogenic xenobiotics is an extension of this. | 1 | Applied and Interdisciplinary Chemistry |
Pigulevsky was married to Nina Viktorovna Pigulevskaya (1894-1970), a soviet historian, corresponding member of the Academy of Sciences of the USSR, specialist in the history of Byzantium, the Near and Middle East in the early Middle Ages. | 0 | Theoretical and Fundamental Chemistry |
For strong electrolytes, a single reaction arrow shows that the reaction occurs completely in one direction, in contrast to the dissociation of weak electrolytes, which both ionize and re-bond in significant quantities.
Strong electrolytes conduct electricity only when molten or in aqueous solutions.
Strong electrolytes break apart into ions completely.
The stronger an electrolyte the greater the voltage produced when used in a galvanic cell. | 0 | Theoretical and Fundamental Chemistry |
Nutrient bioextraction is bioremediation involving cultured plants and animals. Nutrient bioextraction or bioharvesting is the practice of farming and harvesting shellfish and seaweed for the purpose of removing nitrogen and other nutrients from natural water bodies. | 1 | Applied and Interdisciplinary Chemistry |
For the simplest AH molecular system, Walsh produced the first angular correlation diagram by plotting the ab initio orbital energy curves for the canonical molecular orbitals while changing the bond angle from 90° to 180°. As the bond angle is distorted, the energy for each of the orbitals can be followed along the lines, allowing a quick approximation of molecular energy as a function of conformation. It is still unclear whether or not the Walsh ordinate considers nuclear repulsion, and this remains a topic of debate. A typical prediction result for water is a bond angle of 90°, which is not even close to the experimental derived value of 104°. At best the method is able to differentiate between a bent and linear molecule.
This same concept can be applied to other species including non-hydride AB and BAC molecules, HAB and HAAH molecules, tetraatomic hydride molecules (AH), tetraatomic nonhydride molecules (AB), HAB molecules, acetaldehyde, pentaatomic molecules (CH3I), hexatomic molecules (ethylene), and benzene. | 0 | Theoretical and Fundamental Chemistry |
DLVO theory is the combined effect of van der Waals and double layer force. For the derivation, different conditions must be taken into account and different equations can be obtained. But some useful assumptions can effectively simplify the process, which are suitable for ordinary conditions. The simplified way to derive it is to add the two parts together. | 0 | Theoretical and Fundamental Chemistry |
Froth flotation efficiency is determined by a series of probabilities: those of particle–bubble contact, particle–bubble attachment, transport between the pulp and the froth, and froth collection into the product launder. In a conventional mechanically-agitated cell, the void fraction (i.e. volume occupied by air bubbles) is low (5 to 10 percent) and the bubble size is usually greater than 1 mm. This results in a relatively low interfacial area and a low probability of particle–bubble contact. Consequently, several cells in series are required to increase the particle residence time, thus increasing the probability of particle–bubble contact. | 1 | Applied and Interdisciplinary Chemistry |
Originally, the FRAP technique was intended for use as a means to characterize the mobility of individual lipid molecules within a cell membrane. While providing great utility in this role, current research leans more toward investigation of artificial lipid membranes. Supported by hydrophilic or hydrophobic substrates (to produce lipid bilayers or monolayers respectively) and incorporating membrane proteins, these biomimetic structures are potentially useful as analytical devices for determining the identity of unknown substances, understanding cellular transduction, and identifying ligand binding sites. | 1 | Applied and Interdisciplinary Chemistry |
Health Canada has investigated the risks and benefits of pseudoephedrine and ephedrine/Ephedra. Near the end of the study, Health Canada issued a warning on their website stating that those who are under the age of 12, or who have heart disease and may have strokes, should avoid taking pseudoephedrine and ephedrine. Also, they warned that everyone should avoid taking ephedrine or pseudoephrine with other stimulants like caffeine. They also banned all products that contain both ephedrine (or pseudoephedrine) and caffeine.
Products whose only medicinal ingredient is pseudoephedrine must be kept behind the pharmacy counter. Products containing pseudoephedrine along with other medicinal ingredients may be displayed on store shelves but may be sold only in a pharmacy when a pharmacist is present. | 0 | Theoretical and Fundamental Chemistry |
The experimental archaeometallurgy of iron is more recent then that of copper in that for the most part was not widely studied until the mid-20th century. This can be attributed to the modern smelting of wrought iron still being produced as an industry up until 1900, when the last of the large-scale production shut down, along with the belief among researchers that many of the same techniques had been passed down since the inception of bloomery iron. A static technique simply was not the case as the technology used to make Roman Era iron showed the use of a technology that had long since disappeared. That being said research in iron has progressed beyond that of copper due to the greater amount of historic text and surviving remains of iron production.
Several experiments have taken place to reproduce bloomery iron. Clough presents an average example of experimental ironwork with the reproduction possible Roman bowl furnaces. Clough found the reproduction bowl furnaces to be inefficient by producing small amounts of poor quality iron, which, when compared to excavated findings of much larger better quality blooms of iron led to the conclusion that bowl furnaces were not used by the Romans. | 1 | Applied and Interdisciplinary Chemistry |
Expression of genetic code in all life forms consists of two major processes, synthesis of copies of the genetic code recorded in DNA into the form of mRNA (transcription), and protein synthesis itself (translation), whereby the code copies in mRNA are decoded into amino acid sequences of the respective proteins. Both transcription and translation are highly regulated processes essentially controlling everything of what happens in live cells (and multicellular organisms, consequently).
Control of translation is especially important in eukaryotic cells where it forms part of post-transcriptional regulatory networks of genes expression. This additional functionality is reflected in the increased complexity of the translation process, making it a hard object to investigate. Yet details on when and what mRNA is translated and what mechanisms are responsible for this control are key to understanding of normal and pathological cell functionality. TCP-seq can be used to obtain this information. | 1 | Applied and Interdisciplinary Chemistry |
Optical tweezers are capable of manipulating nanometer and micron-sized dielectric particles, and even individual atoms, by exerting extremely small forces via a highly focused laser beam. The beam is typically focused by sending it through a microscope objective. Near the narrowest point of the focused beam, known as the beam waist, the amplitude of the oscillating electric field varies rapidly in space. Dielectric particles are attracted along the gradient to the region of strongest electric field, which is the center of the beam. The laser light also tends to apply a force on particles in the beam along the direction of beam propagation. This is due to conservation of momentum: photons that are absorbed or scattered by the tiny dielectric particle impart momentum to the dielectric particle. This is known as the scattering force and results in the particle being displaced slightly downstream from the exact position of the beam waist, as seen in the figure.
Optical traps are very sensitive instruments and are capable of the manipulation and detection of sub-nanometer displacements for sub-micron dielectric particles. For this reason, they are often used to manipulate and study single molecules by interacting with a bead that has been attached to that molecule. DNA and the proteins and enzymes that interact with it are commonly studied in this way.
For quantitative scientific measurements, most optical traps are operated in such a way that the dielectric particle rarely moves far from the trap center. The reason for this is that the force applied to the particle is linear with respect to its displacement from the center of the trap as long as the displacement is small. In this way, an optical trap can be compared to a simple spring, which follows Hooke's law. | 1 | Applied and Interdisciplinary Chemistry |
In 1781, processes for preparing highly concentrated forms of yeast were established. Research on Single Cell Protein Technology started a century ago when Max Delbrück and his colleagues found out the high value of surplus brewer’s yeast as a feeding supplement for animals. During World War I and World War II, yeast-SCP was employed on a large scale in Germany to counteract food shortages during the war. Inventions for SCP production often represented milestones for biotechnology in general: for example, in 1919, Sak in Denmark and Hayduck in Germany invented a method named, “Zulaufverfahren”, (fed-batch) in which sugar solution was fed continuously to an aerated suspension of yeast instead of adding yeast to diluted sugar solution once (batch). In post war period, the Food and Agriculture Organization of the United Nations (FAO) emphasized on hunger and malnutrition problems of the world in 1960 and introduced the concept of protein gap, showing that 25% of the world population had a deficiency of protein intake in their diet. It was also feared that agricultural production would fail to meet the increasing demands of food by humanity. By the mid 60’s, almost quarter of a million tons of food yeast were being produced in different parts of the world and Soviet Union alone produced some 900,000 tons by 1970 of food and fodder yeast.
In the 1960s, researchers at British Petroleum developed what they called "proteins-from-oil process": a technology for producing single-cell protein by yeast fed by waxy n-paraffins, a byproduct of oil refineries. Initial research work was done by Alfred Champagnat at BP's Lavera Oil Refinery in France; a small pilot plant there started operations in March 1963, and the same construction of the second pilot plant, at Grangemouth Oil Refinery in Britain, was authorized.
The term SCP was coined in 1966 by Carroll L. Wilson of MIT.
The "food from oil" idea became quite popular by the 1970s, with Champagnat being awarded the UNESCO Science Prize in 1976, and paraffin-fed yeast facilities being built in a number of countries. The primary use of the product was as poultry and cattle feed.
The Soviets were particularly enthusiastic, opening large "BVK" (belkovo-vitaminny kontsentrat, i.e., "protein-vitamin concentrate") plants next to their oil refineries in Kstovo (1973) and Kirishi (1974). The Soviet Ministry of Microbiological Industry had eight plants of this kind by 1989. However, due to concerns of toxicity of alkanes in SCP and pressured by the environmentalist movements, the government decided to close them down, or convert to some other microbiological processes.
Quorn is a range of vegetarian and vegan meat-substitutes made from Fusarium venenatum mycoprotein, sold in Europe and North America.
Another type of single cell protein-based meat analogue (which does not use fungi however but rather bacteria) is Calysta. Other producers are Unibio (Denmark) Circe Biotechnologie (Austria) and String Bio (India).
SCP has been argued to be a source of alternative or resilient food. | 1 | Applied and Interdisciplinary Chemistry |
Sodium methylsulfinylmethylide is prepared by heating sodium hydride or sodium amide in DMSO
:CHSOCH + NaH → CHSOCHNa + H
:CHSOCH + NaNH → CHSOCHNa + NH | 0 | Theoretical and Fundamental Chemistry |
Optodes can apply various optical measurement schemes such as reflection, absorption, evanescent wave, luminescence (fluorescence and phosphorescences), chemiluminescence, surface plasmon resonance. By far the most popular methodology is luminescence.
Luminescence in solution obeys the linear Stern–Volmer relationship. Fluorescence of a molecule is quenched by specific analytes, e.g., ruthenium complexes are quenched by oxygen. When a fluorophore is immobilised within a polymer matrix myriad micro-environments are created. The micro-environments reflect varying diffusion co-efficients for the analyte. This leads to a non-linear relationship between the fluorescence and the quencher (analyte). This relationship is modelled in various ways, the most popular model is the two site model created by James Demas (University of Virginia).
The signal (fluorescence) to oxygen ratio is not linear, and an optode is most sensitive at low oxygen concentration, i.e., the sensitivity decreases as oxygen concentration increases. The optode sensors can however work in the whole region 0–100% oxygen saturation in water, and the calibration is done the same way as with the Clark type sensor. No oxygen is consumed and hence the sensor is stirring insensitive, but the signal will stabilize more quickly if the sensor is stirred after being put into the sample. | 0 | Theoretical and Fundamental Chemistry |
Due to its surface property, sucrose esters are used in pharmaceutical research as a stabilizer or a surfactant on vesicles for drug delivery systems. | 0 | Theoretical and Fundamental Chemistry |
He is the author of numerous books including Foundations of Solid Mechanics, Continuum Mechanics, and a series of books on Biomechanics. He is also one of the principal founders of the Journal of Biomechanics and was a past chair of the ASME International Applied Mechanics Division. In 1972, Fung established the Biomechanics Symposium under the American Society of Mechanical Engineers. This biannual summer meeting, first held at the Georgia Institute of Technology, became the annual Summer Bioengineering Conference. Fung and colleagues were also the first to recognize the importance of residual stress on arterial mechanical behavior. | 1 | Applied and Interdisciplinary Chemistry |
A photobioreactor (PBR) is a bioreactor which incorporates some type of light source (that may be natural sunlight or artificial illumination). Virtually any translucent container could be called a PBR, however the term is more commonly used to define a closed system, as opposed to an open storage tank or pond.
Photobioreactors are used to grow small phototrophic organisms such as cyanobacteria, algae, or moss plants. These organisms use light through photosynthesis as their energy source and do not require sugars or lipids as energy
source. Consequently, risk of contamination with other organisms like bacteria or fungi is lower in photobioreactors when compared to bioreactors for heterotroph organisms. | 1 | Applied and Interdisciplinary Chemistry |
Public Analyst Laboratories in Cork, Dublin and Galway provide an analytical service to the Food Safety Authority. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers, flows tend to be turbulent. The turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents). These eddy currents begin to churn the flow, using up energy in the process, which for liquids increases the chances of cavitation.
The Reynolds number has wide applications, ranging from liquid flow in a pipe to the passage of air over an aircraft wing. It is used to predict the transition from laminar to turbulent flow and is used in the scaling of similar but different-sized flow situations, such as between an aircraft model in a wind tunnel and the full-size version. The predictions of the onset of turbulence and the ability to calculate scaling effects can be used to help predict fluid behavior on a larger scale, such as in local or global air or water movement, and thereby the associated meteorological and climatological effects.
The concept was introduced by George Stokes in 1851, but the Reynolds number was named by Arnold Sommerfeld in 1908 after Osborne Reynolds (1842–1912), who popularized its use in 1883. | 1 | Applied and Interdisciplinary Chemistry |
Imaging mass cytometry (IMC) is a relatively new imaging technique, emerged from previously available CyTOF technology (cytometry by time of flight), that combines mass spectrometry with UV laser ablation to generate pseudo images of tissue samples. This approach adds spatial resolution to the data, which enables simultaneous analysis of multiple cell markers at subcellular resolution and their spatial distribution in tissue sections. The IMC approach, in the same way as CyTOF, relies on detection of metal-tagged antibodies using time-of-flight mass spectrometry, allowing for quantification of up to 40 markers simultaneously. | 0 | Theoretical and Fundamental Chemistry |
In Europe, the Water Framework Directive (WFD) went into effect on October 23, 2000. It requires all EU member states to show that all surface and groundwater bodies are in good status. The WFD requires member states to implement monitoring systems to estimate the integrity of biological stream components for specific sub-surface water categories. This requirement increased the incidence of biometrics applied to ascertain stream health in Europe A remote online biomonitoring system was designed in 2006. It is based on bivalve molluscs and the exchange of real-time data between a remote intelligent device in the field (able to work for more than 1 year without in-situ human intervention) and a data centre designed to capture, process and distribute the web information derived from the data. The technique relates bivalve behaviour, specifically shell gaping activity, to water quality changes. This technology has been successfully used for the assessment of coastal water quality in various countries (France, Spain, Norway, Russia, Svalbard (Ny-Ålesund) and New Caledonia).
In the United States, the Environmental Protection Agency (EPA) published Rapid Bioassessment Protocols, in 1999, based on measuring macroinvertebrates, as well as periphyton and fish for assessment of water quality.
In South Africa, the Southern African Scoring System (SASS) method is based on benthic macroinvertebrates, and is used for the assessment of water quality in South African rivers. The SASS aquatic biomonitoring tool has been refined over the past 30 years and is now on the fifth version (SASS5) in accordance with the ISO/IEC 17025 protocol. The SASS5 method is used by the South African Department of Water Affairs as a standard method for River Health Assessment, which feeds the national River Health Programme and the national Rivers Database.
The imposex phenomenon in the dog conch species of sea snail leads to the abnormal development of a penis in females, but does not cause sterility. Because of this, the species has been suggested as a good indicator of pollution with organic man-made tin compounds in Malaysian ports. | 1 | Applied and Interdisciplinary Chemistry |
Large aggregates can become anoxic which gives rise to anaerobic metabolisms. Typically anaerobic metabolisms are confined to areas where it is more energetically favorable. Given the abundance of denitrifying and sulfate-reducing bacteria, it is thought that these metabolisms are able to thrive within marine snow aggregates. In a model developed by Bianchi et al., it shows the various redox potentials within an aggregate. | 0 | Theoretical and Fundamental Chemistry |
Garnet-Garnet reaction can be used to estimate the redox state of transition zone.
A recent study showed that the oxygen fugacity of transition referred from Garnet-Garnet reaction is -0.26 to +3 relative to the Fe-FeO (IW, iron- wütstite) oxygen buffer. | 0 | Theoretical and Fundamental Chemistry |
Experimental study of any supramolecular structures in bulk water is difficult because of their short lifetime: the hydrogen bonds are continually breaking and reforming at timescales faster than 200 femtoseconds.
Nevertheless, water clusters have been observed in the gas phase and in dilute mixtures of water and non-polar solvents like benzene and liquid helium. The experimental detection and characterization of the clusters has been achieved with the following methods: far-infrared spectroscopy|far-infrared (FIR), vibration-rotation-tunneling spectroscopy|vibration-rotation-tunneling (VRT), Н-NMR, and neutron diffraction. The hexamer is found to have planar geometry in liquid helium, a chair conformation in organic solvents, and a cage structure in the gas phase. Experiments combining IR spectroscopy with mass spectrometry reveal cubic configurations for clusters in the range n=(8-10).
When the water is part of a crystal structure as in a hydrate, x-ray diffraction can be used. Conformation of a water heptamer was determined (cyclic twisted nonplanar) using this method. Further, multi-layered water clusters with formulae (HO) trapped inside cavities of several polyoxometalate clusters were also reported by Mueller et al. | 0 | Theoretical and Fundamental Chemistry |
The "tuck-in" process is related to ortho-metalation in the sense that it is an intramolecular cyclometalation. Tuck-in complexes derived from Cp* ligands are derivatives of tetramethylfulvene, sometimes abbreviated MeFv. A variety of complexes are known for MeFv and related ligands. In these complexes, the Fv can serve as a 4-electron or as a 6-electron ligand. | 0 | Theoretical and Fundamental Chemistry |
Rogue waves can occur in media other than water. They appear to be ubiquitous and have also been reported in liquid helium, in quantum mechanics, in nonlinear optics, in microwave cavities, in Bose–Einstein condensate, in heat and diffusion, and in finance. | 1 | Applied and Interdisciplinary Chemistry |
A number of bacterial mRNAs have no 5'UTR whatsoever, or a very short one. The complete 70S ribosome, with the help of IF2 (recruiting fMet-tRNA), can simply start translating such a "leaderless" mRNA.
A number of factors modify the efficiency of leaderless initiation. A 5 phosphate group attached to the start codon seems near-essential. AUG is strongly preferred in E. coli, but not necessarily in other species. IF3 inhibits leaderless initiation. A longer 5UTR or one with significant secondary structure also inhibits leaderless initiation. | 1 | Applied and Interdisciplinary Chemistry |
The Shine-Dalgarno sequence, of the prokaryotic RBS, was discovered by John Shine and Lynne Dalgarno in 1975. The Kozak consensus sequence was first identified by Marilyn Kozak in 1984 while she was in the Department of Biological Sciences at the University of Pittsburgh. | 1 | Applied and Interdisciplinary Chemistry |
The localization of ADAM17 is speculated to be an important determinant of shedding activity. TNF-α processing has classically been understood to occur in the trans-Golgi network, and be closely connected to transport of soluble TNF-α to the cell surface. Shedding is also associated with clustering of ADAM17 with its substrate, membrane bound TNF, in lipid rafts. The overall process is called substrate presentation and regulated by cholesterol. Research also suggests that the majority of mature, endogenous ADAM17 may be localized to a perinuclear compartment, with only a small amount of TACE being present on the cell surface. The localization of mature ADAM17 to a perinuclear compartment, therefore, raises the possibility that ADAM17-mediated ectodomain shedding may also occur in the intracellular environment, in contrast with the conventional model.
Functional ADAM17 has been documented to be ubiquitously expressed in the human colon, with increased activity in the colonic mucosa of patients with ulcerative colitis, a main form of inflammatory bowel disease. Other experiments have also suggested that expression of ADAM17 may be inhibited by ethanol. | 1 | Applied and Interdisciplinary Chemistry |
Histamine N-methyltransferase belongs to methyltransferases, a superfamily of enzymes present in every life form, including archaeans.
These enzymes catalyze methylation, which is a chemical process that involves the addition of a methyl group to a molecule, which can affect its biological function.
To facilitate methylation, methyltransferases transfer a methyl group (-CH) from a cosubstrate (donor) to a substrate molecule (acceptor), leading to the formation of a methylated molecule. Most methyltransferases use S-adenosyl--methionine (SAM-e) as a donor, converting it into S-adenosyl--homocysteine (SAH). In various species, members of the methyltransferase superfamily of enzymes methylate a wide range of molecules, including small molecules, proteins, nucleic acids, and lipids. These enzymes are involved in numerous cellular processes such as signaling, protein repair, chromatin regulation, and gene regulation. More than 230 families of methyltransferases have been described in various species.
This specific protein, histamine N-methyltransferase, is found in vertebrates, including mammals, birds, reptiles, amphibians, and fishes, but not in invertebrates and plants.
The complementary DNA (cDNA) of Hnmt was initially cloned from a rat kidney and has since been cloned from human, mouse, and guinea pig sources. Human HNMT shares 55.37% similarity with that of zebrafish, 86.76% with that of mouse, 90.53% with that of dog, and 99.54% with that of chimpanzee. Moreover, expressed sequence tags from cow, pig, and gorilla, as well as genome survey sequences from pufferfish, also exhibit strong similarity to human HNMT, suggesting that it is a highly conserved protein among vertebrates. To understand the role of histamine N-methyltransferase in brain function, researchers have studied Hnmt-deficient (knockout) mice, that were genetically modified to have the Hnmt gene "knocked out", i.e., deactivated. Scientists discovered that disrupting the gene led to a significant rise in histamine levels in the mouse brain that highlighted the role of the gene in the brains histamine system and suggested that HNMT' genetic variations in humans could be linked to brain disorders. | 1 | Applied and Interdisciplinary Chemistry |
TSEs, or prion diseases, are infectious neurodegenerative diseases of mammals that include bovine spongiform encephalopathy, chronic wasting disease of deer and elk, scrapie in sheep, and Creutzfeldt–Jakob disease (CJD) in humans. TSEs may be passed from host to host by ingestion of infected tissues or blood transfusions. Clinical symptoms of TSEs include loss of movement and coordination and dementia in humans. They have incubation periods of months to years, but after the appearance of clinical signs, they progress rapidly, are untreatable and invariably are fatal. Attempts at TSE risk-reduction have led to significant changes in the production and trade of agricultural goods, medicines, cosmetics, blood and tissue donations, and biotechnology products. Post mortem neuropathological examination of brain tissue from an animal or human has remained the ‘gold standard’ of TSE diagnosis and is very specific, but not as sensitive as other techniques.
To improve food safety, it would be levels are very low in presymptomatic hosts. In addition, PrPs are generally unevenly distributed in body tissues, with highest concentration consistently found in nervous system tissues and very low concentrations in easily accessible body fluids such as blood or urine. Therefore, any such test would be required to detect extremely small amounts of PrP and would have to differentiate PrP and PrP.
Current PrP detection methods are time-consuming and employ post mortem analysis after suspicious animals manifest one or more symptoms of the disease. Current diagnostic methods are based mainly on detection of physiochemical differences between PrP and PrP which, to date, are the only reliable markers for TSEs. For example, the most widely used diagnostic tests exploit the relative protease resistance of PrP in brain samples to discriminate between PrP and PrP, in combination with antibody-based detection of the PK-resistant portion of PrP. It has as yet not been possible to detect prion diseases by using conventional methods, such as polymerase chain reaction, serology, or cell culture assays. An agent-specific nucleic acid has not yet been identified, and the infected host does not elicit an antibody response.
The conformationally altered form of PrP is PrP. Some groups believe PrP is the infectious agent (prion agent) in TSEs, while other groups do not. PrP could be a neuropathological product of the disease process, a component of the infectious agent, the infectious agent itself, or something else altogether. Regardless of what its actual function in the disease state is, PrP is clearly specifically associated with the disease process, and detection of it indicates infection with the agent causing prion diseases. | 1 | Applied and Interdisciplinary Chemistry |
Drought poses negative impacts to growth and yield of hemp, therefore, hemp has evolved survival mechanisms for abiotic stress. Plant cells will discontinue normal growth rates when exposed to drought stress along with other physiological processes such as photosynthesis. Down regulating certain gene's expressions or transcription factors can assist in this response. For example, photosynthesis–antenna proteins and differentially expressed genes (DEGs) in the jasmonic acid pathway were demonstrated as being down-regulated during drought stress. In a 2018 research article by Gao, they attribute the down regulation to reduced photosynthesis in the plant. Up regulating genes can also occur, such as transcriptional factors from the NAC gene family, which were demonstrated to be over expressed in response to drought treatments, possibly contributing to tolerance. Numerous regulation genes involved in the biosynthesis of abscisic acid (ABA), a plant hormone linked to stress response, are over expressed during times of drought stress. Some of these genes are from the PP2C and SnPK gene families, linked to drought tolerance because of their intrinsic roles of ABA signaling. ABA signaling, controlled by changes in ABA metabolic pathways, assist in stomata closure and changes in the photosynthesis processes in hemp plants to combat water loss during drought stress.
Another stress hormone, auxin, may be important in drought tolerance by means of the gene GH3. A hemp GH3 homolog gene has been shown to increase drought resistance in rice by decreasing expression of Indole-3-Acetic Acid (IAA), which decreases photosynthesis and cell growth. | 1 | Applied and Interdisciplinary Chemistry |
One of the problems of both the glutamate–glutamine cycle and the GABA-glutamine cycle is ammonia homeostasis. When one molecule of glutamate or GABA is converted to glutamine in the astrocytes, one molecule of ammonia is absorbed. Also, for each molecule of glutamate or GABA cycled into the astrocytes from the synapse, one molecule of ammonia will be produced in the neurons. This ammonia will obviously have to be transported out of the neurons and back into the astrocytes for detoxification, as an elevated ammonia concentration has detrimental effects on a number of cellular functions and can cause a spectrum of neuropsychiatric and neurological symptoms (impaired memory, shortened attention span, sleep-wake inversions, brain edema, intracranial hypertension, seizures, ataxia and coma). | 1 | Applied and Interdisciplinary Chemistry |
*Saves time for preparation and clear away
*Reduces waste at the source
*More safety
*Lower costs for chemical substances and equipment
*Smaller storage area
*Reduced reliance on intensive ventilation systems
*Pleasant working atmosphere
*Shorter reaction times
*More time for evaluation and communication. | 1 | Applied and Interdisciplinary Chemistry |
Urine bilirubin may also be clinically significant. Bilirubin is not normally detectable in the urine of healthy people. If the blood level of conjugated bilirubin becomes elevated, e.g. due to liver disease, excess conjugated bilirubin is excreted in the urine, indicating a pathological process. Unconjugated bilirubin is not water-soluble and so is not excreted in the urine. Testing urine for both bilirubin and urobilinogen can help differentiate obstructive liver disease from other causes of jaundice.
As with billirubin, under normal circumstances, only a very small amount of urobilinogen is excreted in the urine. If the liver's function is impaired or when biliary drainage is blocked, some of the conjugated bilirubin leaks out of the hepatocytes and appears in the urine, turning it dark amber. However, in disorders involving hemolytic anemia, an increased number of red blood cells are broken down, causing an increase in the amount of unconjugated bilirubin in the blood. Because the unconjugated bilirubin is not water-soluble, one will not see an increase in bilirubin in the urine. Because there is no problem with the liver or bile systems, this excess unconjugated bilirubin will go through all of the normal processing mechanisms that occur (e.g., conjugation, excretion in bile, metabolism to urobilinogen, reabsorption) and will show up as an increase of urobilinogen in the urine. This difference between increased urine bilirubin and increased urine urobilinogen helps to distinguish between various disorders in those systems. | 1 | Applied and Interdisciplinary Chemistry |
Of particular concern in nuclear waste management are two long-lived fission products, Tc-99 (half-life 220,000 years) and I-129 (half-life 15.7 million years), which dominate spent fuel radioactivity after a few thousand years. The most troublesome transuranic elements in spent fuel are Np-237 (half-life two million years) and Pu-239 (half-life 24,000 years). Nuclear waste requires sophisticated treatment and management to successfully isolate it from interacting with the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving storage, disposal or transformation of the waste into a non-toxic form. Governments around the world are considering a range of waste management and disposal options, though there has been limited progress toward long-term waste management solutions.
In the second half of the 20th century, several methods of disposal of radioactive waste were investigated by nuclear nations, which are :
* "Long-term above-ground storage", not implemented.
* "Disposal in outer space" (for instance, inside the Sun), not implemented—as it would be currently too expensive.
* "Deep borehole disposal", not implemented.
* "Rock melting", not implemented.
* "Disposal at subduction zones", not implemented.
* Ocean disposal, by the USSR, the United Kingdom, Switzerland, the United States, Belgium, France, the Netherlands, Japan, Sweden, Russia, Germany, Italy and South Korea (1954–93). This is no longer permitted by international agreements.
* "Sub-seabed disposal", not implemented, not permitted by international agreements.
* "Disposal in ice sheets", rejected in Antarctic Treaty
* "Deep well injection", by USSR and USA.
* Nuclear transmutation, using lasers to cause beta decay to convert the unstable atoms to those with shorter half-lives.
In the United States, waste management policy completely broke down with the ending of work on the incomplete Yucca Mountain Repository. At present there are 70 nuclear power plant sites where spent fuel is stored. A Blue Ribbon Commission was appointed by President Obama to look into future options for this and future waste. A deep geological repository seems to be favored. 2018 Nobel Prize for Physics-winner Gérard Mourou has proposed using Chirped pulse amplification to generate high-energy and low-duration laser pulses to transmute highly radioactive material (contained in a target) to significantly reduce its half-life, from thousands of years to only a few minutes. | 0 | Theoretical and Fundamental Chemistry |
Libby's original exchange reservoir hypothesis assumed that the / ratio in the exchange reservoir is constant all over the world, but it has since been discovered that there are several causes of variation in the ratio across the reservoir. | 0 | Theoretical and Fundamental Chemistry |
Virtually all TOC analysers measure the CO formed when organic carbon is oxidized and/or when inorganic carbon is acidified. Oxidation is performed either through Pt-catalyzed combustion, by heated persulfate, or with a UV/persulfate reactor. Once the CO is formed, it is measured by a detector: either a conductivity cell (if the CO is aqueous) or a non-dispersive infrared cell (after purging the aqueous CO into the gaseous phase). Conductivity detection is only desirable in the lower TOC ranges in deionized waters, whereas NDIR detection excels in all TOC ranges. A variation described as "membrane conductometric detection can allow for measurement of TOC across a wide analytical range in both deionized and non-deionized water samples. Modern high-performance TOC instruments are capable of detecting carbon concentrations well below 1 µg/L (1 part per billion or ppb).
A total organic carbon analyser determines the amount of carbon in a water sample. By acidifying the sample and flushing with nitrogen or helium the sample removes inorganic carbon, leaving only organic carbon sources for measurement. There are two types of analysers. One uses combustion and the other chemical oxidation. This is used as a water purity test, as the presence of bacteria introduces organic carbon. | 0 | Theoretical and Fundamental Chemistry |
Goldschmidt was born in Zürich, Switzerland on 27 January 1888. His father, Heinrich Jacob Goldschmidt, (1857–1937) was a physical chemist at the Eidgenössisches Polytechnikum and his mother, Amelie Koehne (1864–1929), was the daughter of a lumber merchant. They named him Viktor after a colleague of Heinrich, Victor Meyer. His fathers family was Jewish back to at least 1600 and mostly highly educated, with rabbis, judges, lawyers and military officers among their numbers. As his fathers career progressed, the family moved first to Amsterdam in 1893, to Heidelberg in 1896, and finally to Kristiania (later Oslo), Norway in 1901, where he took over the physical chemistry chair at the university. The family became Norwegian citizens in 1905.
Goldschmidt entered the University of Kristiana (later the University of Oslo) in 1906 and studied inorganic and physical chemistry, geology, mineralogy, physics, mathematics, zoology and botany. He secured a fellowship for his doctoral studies from the university at the age of 21 (1909). He worked on his thesis with the noted geologist Waldemar Christofer Brøgger and obtained his Norwegian doctor’s degree when he was 23 years old (1911). For his dissertation titled Die Kontaktmetamorphose im Kristianiagebiet ("The Contact Metamorphism in the Kristiania Region"), the Norwegian Academy of Sciences awarded him the Fridtjof Nansen award in 1912. The same year he was made Docent (Associate Professor) of Mineralogy and Petrography at the university. | 0 | Theoretical and Fundamental Chemistry |
The simplest method of manufacturing the molding of a disk in one piece is a possibility for some systems. A more complex method of media manufacturing is for the media to be constructed layer by layer. This is required if the data is to be physically created during manufacture. However, layer-by-layer construction need not mean the sandwiching of many layers together. Another alternative is to create the medium in a form analogous to a roll of adhesive tape. | 0 | Theoretical and Fundamental Chemistry |
DNA recombinases are widely used in multicellular organisms to manipulate the structure of genomes, and to control gene expression. These enzymes, derived from bacteria (bacteriophages) and fungi, catalyze directionally sensitive DNA exchange reactions between short (30–40 nucleotides) target site sequences that are specific to each recombinase. These reactions enable four basic functional modules: excision/insertion, inversion, translocation and cassette exchange, which have been used individually or combined in a wide range of configurations to control gene expression.
Types include:
* Cre recombinase
* Hin recombinase
* Tre recombinase
* FLP recombinase | 1 | Applied and Interdisciplinary Chemistry |
In order to define a good DPN application, it is important to understand what DPN can do that other techniques cannot. Direct-write techniques, like contact printing, can pattern multiple biological materials but it cannot create features with subcellular resolution. Many high-resolution lithography methods can pattern at sub-micrometre resolution, but these require high-cost equipment that were not designed for biomolecule deposition and cell culture. Microcontact printing can print biomolecules at ambient conditions, but it cannot pattern multiple materials with nanoscale registry. | 1 | Applied and Interdisciplinary Chemistry |
In recognition of his eminent contributions in the field of organic chemistry, he has been conferred with many civil awards, including:
* Nishan-e-Imtiaz (2002) (highest national civil award)
* Hilal-e-Imtiaz (1998)
* Sitara-e-Imtiaz (1991)
* Tamgha-e-Imtiaz (1983)
* UNESCO Science Prize (1999)
* Grosse Goldene Ehrenzeischen am Bande(2007) high civil award by the Austrian government (2007)
* China, International Science and Technology Cooperation Award (2020) bestowed by Chinese President Xi Jinping in Beijing on January 7, 2020
* Academician, Chinese Academy of Sciences (2015)
* Friendship Award of China (2014)
* Vice President, The World Academy of Science (TWAS)
* Prescient, Network of Academies of Science of Organising of Islamic Conference (NASIC)
* Member, Korean Academy of Science and Technology
* Einstein Professorship, Chinese Academy of Sciences
* Babai Urdu Award (1994)
* Scientist of the Year Award (for 1985)/Prize Rs. 200,000 (1987)
* FPCCI Prize for Technological Innovation (1985)
* Engro Excellence Award (2010)
* HEC, National Distinguished Professor (2011–present)
* Professor Emeritus, University of Karachi (2011–present)
* Lifetime Achievement Award by University of Management and Technology, Lahore (2012) | 0 | Theoretical and Fundamental Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.