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The COfertiliser effect has been greatly overestimated during Free-Air Carbon dioxide Enrichment (FACE) experiments where results show increased CO levels in the atmosphere enhances photosynthesis, reduce transpiration, and increase water use efficiency (WUE). Increased biomass is one of the effects with simulations from experiments predicting a 5–20% increase in crop yields at 550 ppm of CO. Rates of leaf photosynthesis were shown to increase by 30–50% in C3 plants, and 10–25% in C4 under doubled CO levels. The existence of a feedback mechanism results a phenotypic plasticity in response to [CO] that may have been an adaptive trait in the evolution of plant respiration and function.
Predicting how stomata perform during adaptation is useful for understanding the productivity of plant systems for both natural and agricultural systems. Plant breeders and farmers are beginning to work together using evolutionary and participatory plant breeding to find the best suited species such as heat and drought resistant crop varieties that could naturally evolve to the change in the face of food security challenges. | 0 | Theoretical and Fundamental Chemistry |
There are various applications for ASTM D1141-98 synthetic seawater including corrosion studies, ocean instrument calibration and chemical processing. Typically, laboratory-grade water is used when making synthetic salts. | 0 | Theoretical and Fundamental Chemistry |
Pines is a pioneer in the development and applications of nuclear magnetic resonance (NMR) spectroscopy of non-liquid samples. In his early work, he demonstrated time-reversal of dipole-dipole couplings in many-body spin systems, and introduced high sensitivity, cross polarization NMR of dilute spins such as carbon-13 in solids (Proton Enhanced Nuclear Induction Spectroscopy), thereby helping to launch the era of modern solid-state NMR in chemistry. He also developed the areas of multiple-quantum spectroscopy, adiabatic sech/tanh inversion pulses, zero-field NMR, double rotation and dynamic-angle spinning, iterative maps for pulse sequences and quantum control, and the quantum geometric phase. His combination of optical pumping and cross-polarization made it possible to observe enhanced NMR of surfaces and the selective "lighting up" of solution NMR and magnetic resonance imaging (MRI) by means of laser-polarized xenon.
Until he retired to emeritus status, his program was composed of two complementary components. The first is the establishment of new concepts and techniques in NMR and MRI, in order to extend their applicability and enhance their capability to investigate molecular structure, organization and function from materials to organisms. Examples of methodologies emanating from these efforts include: novel polarization and detection methods, ex-situ and mobile NMR and MRI, laser-polarized NMR and MRI, functionalized NMR biosensors and molecular imaging, ultralow and zero-field SQUID NMR and MRI, remote detection of NMR and MRI amplified by means of laser magnetometers, and miniaturization including fluid flow through porous materials and "microfluidic chemistry and NMR/MRI on a chip". The second component of his research program involves the application of such novel methods to problems in chemistry, materials science, and biomedicine. | 0 | Theoretical and Fundamental Chemistry |
Germann married Ida Helene Johanna Meinke (1884–1976) on November 26, 1914. They had four children: Luise Barbara Germann Pook (February 11, 1916 – January 27, 2012), Edith Germann Osborn (September 6, 1917 – March 31, 1990), Lucia May Germann Harley (May 28, 1920 – January 12, 1998), and Albert Fredrick Ottomar Germann II (born January 4, 1929).
Albert Sr. was raised as a member of the Lutheran Church (Missouri Synod) and as a youngster attended the Lutheran St. Johns Christian Day School in Peru. After moving to South Whitley, Ida and Albert joined St. Johns Lutheran Church (Missouri Synod), six miles east of South Whitley. Both were buried in the St. John's cemetery. | 0 | Theoretical and Fundamental Chemistry |
Bioenergetics is a field in biochemistry and cell biology that concerns energy flow through living systems. This is an active area of biological research that includes the study of the transformation of energy in living organisms and the study of thousands of different cellular processes such as cellular respiration and the many other metabolic and enzymatic processes that lead to production and utilization of energy in forms such as adenosine triphosphate (ATP) molecules. That is, the goal of bioenergetics is to describe how living organisms acquire and transform energy in order to perform biological work. The study of metabolic pathways is thus essential to bioenergetics. | 1 | Applied and Interdisciplinary Chemistry |
A nitrite test is a standard component of a urinary test strip. A positive test for nitrites in the urine is called nitrituria.
This test is commonly used in diagnosing urinary tract infections (UTIs). A positive nitrite test indicates that the cause of the UTI is a Gram-negative organism, most commonly Escherichia coli. The reason for nitrites' existence in the presence of a UTI is due to a bacterial conversion of endogenous nitrates to nitrites. This may be a sign of infection. However, other parameters, such as leukocyte esterase, urine white blood cell count, and symptoms such as dysuria, urinary urgency, fevers, and chills must be correlated to diagnose an infection.
False-negative nitrite tests in urinary tract infections occur in cases with a low colony forming unit (CFU) count, or in recently voided or dilute urine. In addition, a nitrite test does not detect organisms unable to reduce nitrate to nitrite, such as enterococci, staphylococci (Staphylococcus saprophyticus), Acinetobacter, or adenovirus. | 0 | Theoretical and Fundamental Chemistry |
Molecules containing an N-glycosidic bond are known as glycosylamines. Many authors in biochemistry call these compounds N-glycosides and group them with the glycosides; this is considered a misnomer and is discouraged by the International Union of Pure and Applied Chemistry. Glycosylamines and glycosides are grouped together as glycoconjugates; other glycoconjugates include glycoproteins, glycopeptides, peptidoglycans, glycolipids, and lipopolysaccharides. | 0 | Theoretical and Fundamental Chemistry |
McTaggart spent four months in 1962 on a working tour through the US, Buenos Aires and England. In 1963 he assembled and presented his papers for an honorary doctorate, which was granted in 1965, during which year he again traveled in Europe and presented in Belgrade at the VIIth International Conference on Phenomena in Ionized Gases, and commenced his monograph on plasma chemistry which he completed the following year.
In April 1967, he was invited by the United States Air Force to the American Chemical Society Conference at Miami, Florida, then addressed the Institution of Mining and Metallurgy Conference in London. In September the English edition of his monograph was published.
On the basis of his work in plasma chemistry, during July and August 1971, McTaggart was sponsored for a tour of the United States by its Office of Naval Research, to be flown by the US Airforce to the NASA-Ames Base to participate in a seminar on plasma chemistry. In Washington D.C. he presented the inaugural lecture at the IUPAC (International Union of Pure and Applied Chemistry) Conference on Plasma Chemistry, which appointed him a member of its steering committee. Following that, he lectured at the Gordon Research Conference on Plasma Chemistry, held at Beaver Dam. | 0 | Theoretical and Fundamental Chemistry |
Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms and small molecules. In practice, a tunable laser can be used to access an excited intermediate state. The selection rules associated with a two-photon or other multiphoton photoabsorption are different from the selection rules for a single photon transition. The REMPI technique typically involves a resonant single or multiple photon absorption to an electronically excited intermediate state followed by another photon which ionizes the atom or molecule. The light intensity to achieve a typical multiphoton transition is generally significantly larger than the light intensity to achieve a single photon photoabsorption. Because of this, subsequent photoabsorption is often very likely. An ion and a free electron will result if the photons have imparted enough energy to exceed the ionization threshold energy of the system. In many cases, REMPI provides spectroscopic information that can be unavailable to single photon spectroscopic methods, for example rotational structure in molecules is easily seen with this technique.
REMPI is usually generated by a focused frequency tunable laser beam to form a small-volume plasma. In REMPI, first m photons are simultaneously absorbed by an atom or molecule in the sample to bring it to an excited state. Other n photons are absorbed afterwards to generate an electron and ion pair. The so-called m+n REMPI is a nonlinear optical process, which can only occur within the focus of the laser beam. A small-volume plasma is formed near the laser focal region. If the energy of m photons does not match any state, an off-resonant transition can occur with an energy defect ΔE, however, the electron is very unlikely to remain in that state. For large detuning, it resides there only during the time Δt. The uncertainty principle is satisfied for Δt, where ћ=h/2π and h is the Planck constant (6.6261×10^-34 J∙s). Such transition and states are called virtual, unlike real transitions to states with long lifetimes. The real transition probability is many orders of magnitude higher than the virtual transition one, which is called resonance enhanced effect. | 0 | Theoretical and Fundamental Chemistry |
Casein kinase activity was found to be present in most cell types and to be associated with multiple enzymes. The type 1 casein kinase family of related gene products are now given designations such as "casein kinase 1 alpha" and "casein kinase 1 epsilon". | 1 | Applied and Interdisciplinary Chemistry |
RACE can be used to amplify unknown 5 (5-RACE) or 3 (3-RACE) parts of RNA molecules where part of the RNA sequence is known and targeted by a gene-specific primer. Combined with high-throughput sequencing for characterization of these amplified RACE products, it is possible to apply the approach to characterize any types of coding or non-coding RNA-molecules.
The idea of combining RACE with high-throughput sequencing was first introduced in 2009 as Deep-RACE to perform mapping of Transcription start sites (TSS) of 17 genes in a single cell-line. For example, In a study from 2014 to accurately map cleavage sites of target RNA directed by synthetic siRNAs, the approach was first named RACE-seq. Further, the methodology was used to characterize full-length unknown parts of novel transcripts and fusion transcripts in colorectal cancer.
In another study aiming to characterize unknown transcript structures of lncRNAs, RACE was used in combination with semi-long 454 sequencing. | 1 | Applied and Interdisciplinary Chemistry |
The isotopic resonance hypothesis (IsoRes) postulates that certain isotopic compositions of chemical elements affect kinetics of chemical reactions involving molecules built of these elements. The isotopic compositions for which this effect is predicted are called resonance isotopic compositions.
Fundamentally, the IsoRes hypothesis relies on a postulate that less complex systems exhibit faster kinetics than equivalent but more complex systems. Furthermore, system's complexity is affected by its symmetry (more symmetric systems are simpler), and symmetry (in general meaning) of reactants may be affected by their isotopic composition.
The term “resonance” relates to the use of this term in nuclear physics, where peaks in the dependence of a reaction cross section upon energy are called “resonances”. Similarly, a sharp increase (or decrease) in the reaction kinetics as a function of the average isotopic mass of a certain element is called here a resonance. | 0 | Theoretical and Fundamental Chemistry |
In steady state, the second order virial equation becomes
If the axis of rotation is chosen in direction, the equation becomes
and Chandrasekhar shows that in this case, the tensors can take only the following form | 1 | Applied and Interdisciplinary Chemistry |
Reduced oxygen levels are expected to lead to increased seawater concentrations of redox-sensitive metals. The reductive dissolution of iron–manganese oxyhydroxides in seafloor sediments under low-oxygen conditions would release those metals and associated trace metals. Sulfate reduction in such sediments could release other metals such as barium. When heavy-metal-rich anoxic deep water entered continental shelves and encountered increased O levels, precipitation of some of the metals, as well as poisoning of the local biota, would have occurred. In the late Silurian mid-Pridoli event, increases are seen in the Fe, Cu, As, Al, Pb, Ba, Mo and Mn levels in shallow-water sediment and microplankton; this is associated with a marked increase in the malformation rate in chitinozoans and other microplankton types, likely due to metal toxicity. Similar metal enrichment has been reported in sediments from the mid-Silurian Ireviken event. | 0 | Theoretical and Fundamental Chemistry |
Just like other short-affinity tags (His-tag, FLAG-tag), the Strep-tag can be easily fused to recombinant proteins during subcloning of its cDNA or gene. For its expression, various vectors for various host organisms (E. coli, yeast, insect, and mammalian cells) are available. A particular benefit of the Strep-tag is its rather small size and the fact that it is biochemically almost inert. Therefore, protein folding or secretion is not influenced and usually it does not interfere with protein function. Strep-tag is especially suited for analysis of functional proteins, because the purification procedure can be kept under physiological conditions. This not only allows the isolation of sensitive proteins in a native state, but it is also possible to purify intact protein complexes, even if just one subunit carries the tag.
In the first step of the Strep-tag purification cycle, the cell lysate containing Strep-tag fusion protein is applied to a column with immobilized Strep-Tactin (step 1). After the tagged protein has specifically bound to Strep-Tactin, a short washing step with a physiological buffer (e.g. phosphate buffered saline, PBS) removes all other host proteins (step 2). This is due to Strep-Tactin's low tendency to bind proteins non specifically. Then, the purified Strep-tag fusion protein is gently eluted with a low concentration of desthiobiotin, which specifically competes for the biotin binding pocket (step 3). To regenerate the column, desthiobiotin is removed by application of a HABA containing solution (a yellow azo dye). The removal of desthiobiotin is indicated by a color change from yellow-orange to red (step 4+5).
Finally, the HABA solution is washed out with a small volume of running buffer, thus making the column ready to use for the next purification run. | 1 | Applied and Interdisciplinary Chemistry |
In 1881, George E. Davis proposed the formation of a Society of Chemical Engineers, but instead the Society of Chemical Industry (SCI) was formed.
The First World War required a huge increase in chemical production to meet the needs of the munitions and its supply industries, including a twenty-fold increase in explosives. This brought a number of chemical engineers into high positions within the Ministry of Munitions, notably K. B. Quinan, Frederic Nathan and Arthur Duckham.
The increased public perception of chemical engineers renewed the interest in a society, and in 1918 John Hinchley, who was a Council Member of the SCI, petitioned it to form a Chemical Engineers Group (CEG), which was done, with him as chairman and 510 members. In 1920 this group voted to form a separate Institution of Chemical Engineers,which was achieved in 1922 with Hinchley as the Secretary, a role he held until his death. The inaugural meeting was held on 2 May 1922, at the Hotel Cecil, London.
Despite opposition from the Institute of Chemistry and the Institution of Civil Engineers, it was formally incorporated with the Board of Trade on 21 December 1922 as a company not for profit and limited by guarantee. The first Corporate meeting was held 14 March 1923 and the first Annual General Meeting on 8 June 1923: Arthur Duckham was confirmed as President, Hinchley as Secretary and Quinan as Vice-President. At this time it had about 200 members. Nathan was the second President in 1925.
The American Institute of Chemical Engineers, which had been founded in 1908, served as a useful model. While suggestions of amalgamation were made and there was friendly but limited contact, the two organisations developed independently.
In 1926 an official Seal of the Institution was produced by Edith Mary Hinchley, wife of John Hinchley.
The same year the Institution set the first examinations for Associate (i.e. professionally qualified) membership, bringing it into line with the Civil and Mechanical Institutions. In addition to four set examinations of three hours each, there was a Home Paper requiring the candidate to gather information and data and design a chemical plant, accompanied by drawings and a written design proposal within a time limit of a month.
In 1938 the membership passed 1000.
In 1939 the first courses were recognised as granting exemption from the examinations for Associate Membership, being Manchester College of Technology and of the South Wales and Monmouthshire School of Mines. Others followed in subsequent years.
In 1942 Mrs Hilda Derrick (née Stroud) was the first female member, in the category Student, taking a correspondence course in chemical engineering during the war. She was active in promoting the Institution and profession to women.
In 1955 Canterbury University College, New Zealand, and University of Cape Town, South Africa, were the first overseas institutions to have their qualifications recognised.
On 8 April 1957 the IChemE was granted a Royal Charter, changing it from a limited company to a body incorporated by Royal Charter, a professional institution like the Civil and Mechanical ones, with HRH Prince Philip, Duke of Edinburgh as patron, a role he continued for over 63 years.
In 1971, the membership grades were changed: Associate became Member and Member became Fellow.
In 1976 the Institution moved its Headquarters from London to Rugby. | 1 | Applied and Interdisciplinary Chemistry |
In order to identify and quantify metabolites produced by the body, various detection methods have been employed. Most often, these involve the use of nuclear magnetic resonance (NMR) spectroscopy or mass spectrometry (MS), providing universal detection, identification and quantification of metabolites in individual patient samples. Although both processes are used in pharmacometabolomic analyses, there are advantages and disadvantages for using either nuclear magnetic resonance (NMR) spectroscopy- or mass spectrometry (MS)-based platforms in this application. | 1 | Applied and Interdisciplinary Chemistry |
Hot melt extrusion is utilized in pharmaceutical solid oral dose processing to enable delivery of drugs with poor solubility and bioavailability. Hot melt extrusion has been shown to molecularly disperse poorly soluble drugs in a polymer carrier increasing dissolution rates and bioavailability. The process involves the application of heat, pressure and agitation to mix materials together and extrude them through a die. Twin-screw high shear extruders blend materials and simultaneously break up particles. The extruded particles can then be blended and compressed into tablets or filled into capsules. | 1 | Applied and Interdisciplinary Chemistry |
Tissue engineered heart valves offer certain advantages over traditional biological and mechanical valves:
* Living valve – The option of a living heart valve replacement is highly optimal for children as the live valve has the ability to grow and respond to its biological environment, which is especially beneficial for children whose bodies are continually changing. This option would help reduce the number of reoperation needed in a child's life.
* Customized process – Since the scaffolds used in tissue engineering can be manufactured from scratch, there is a higher degree of flexibility and control. This allows the potential of tailoring tissue engineered heart valves and its properties such as the scaffold's shape and biomaterial makeup to be tailored specifically to the patient. | 1 | Applied and Interdisciplinary Chemistry |
Permeable pavements may not be appropriate when land surrounding or draining into the pavement exceeds a 20 percent slope, where pavement is down slope from buildings or where foundations have piped drainage at their footers. The key is to ensure that drainage from other parts of a site is intercepted and dealt with separately rather than being directed onto permeable surfaces. | 1 | Applied and Interdisciplinary Chemistry |
The principal mechanism of the epothilone class is the inhibition of the microtubule function. Microtubules are essential to cell division, and epothilones, therefore, stop cells from properly dividing. Epothilone B possesses the same biological effects as paclitaxel both in vitro and in cultured cells. This is because they share the same binding site, as well as binding affinity to the microtubule. Like paclitaxel, epothilone B binds to the αβ-tubulin heterodimer subunit. Once bound, the rate of αβ-tubulin dissociation decreases, thus stabilizing the microtubules. Furthermore, epothilone B has also been shown to induce tubulin polymerization into microtubules without the presence of GTP. This is caused by the formation of microtubule bundles throughout the cytoplasm. Finally, epothilone B also causes cell cycle arrest at the G2-M transition phase, thus leading to cytotoxicity and eventually cell apoptosis. The ability of epothilone to inhibit spindle function is generally attributed to its suppression of microtubule dynamics; but recent studies have demonstrated that suppression of dynamics occurs at concentrations lower than those needed to block mitosis. At higher antimitotic concentrations, paclitaxel appears to act by suppressing microtubule detachment from centrosomes, a process that is normally activated during mitosis. It is quite possible that epothilone can also act through a similar mechanism. | 0 | Theoretical and Fundamental Chemistry |
Benazepril, sold under the brand name Lotensin among others, is a medication used to treat high blood pressure, heart failure, and diabetic kidney disease. It is a reasonable initial treatment for high blood pressure. It is taken by mouth. Versions are available as the combinations benazepril/hydrochlorothiazide and benazepril/amlodipine.
Common side effects include feeling tired, dizziness, cough, and light-headedness with standing. Serious side effects may include kidney problems, low blood pressure, high blood potassium, and angioedema. Use in pregnancy may harm the baby, while use when breastfeeding may be safe. It is an ACE inhibitor and works by decreasing renin-angiotensin-aldosterone system activity.
Benazepril was patented in 1981 and came into medical use in 1990. It is available as a generic medication. In 2021, it was the 147th most commonly prescribed medication in the United States, with more than 3million prescriptions. | 0 | Theoretical and Fundamental Chemistry |
Sometime before 330 BC Aristotle asserted that the elements of fire, air, earth, and water were not made of atoms, but were continuous. Aristotle considered the existence of a void, which was required by atomic theories, to violate physical principles. Change took place not by the rearrangement of atoms to make new structures, but by transformation of matter from what it was in potential to a new actuality. A piece of wet clay, when acted upon by a potter, takes on its potential to be an actual drinking mug. Aristotle has often been criticized for rejecting atomism, but in ancient Greece the atomic theories of Democritus remained "pure speculations, incapable of being put to any experimental test".
Aristotle theorized minima naturalia as the smallest parts into which a homogeneous natural substance (e.g., flesh, bone, or wood) could be divided and still retain its essential character. Unlike the atomism of Democritus, these Aristotelian "natural minima" were not conceptualized as physically indivisible.
Instead, Aristotles concept was rooted in his hylomorphic worldview, which held that every physical thing is a compound of matter (Greek hyle) and of an immaterial substantial form (Greek morphe') that imparts its essential nature and structure. To use an analogy we could pose a rubber ball: we could imagine the rubber to be the matter that gives the ball the ability to take on another form, and the spherical shape to be the form that gives it its identity of "ball". Using this analogy, though, we should keep in mind that in fact rubber itself would already be considered a composite of form and matter, as it has identity and determinacy to a certain extent, pure or primary matter is completely unformed, unintelligible and with infinite potential to undergo change.
Aristotle's intuition was that there is some smallest size beyond which matter could no longer be structured as flesh, or bone, or wood, or some other such organic substance that for Aristotle (living before the invention of the microscope) could be considered homogeneous. For instance, if flesh were divided beyond its natural minimum, what would be left might be a large amount of the element water, and smaller amounts of the other elements. But whatever water or other elements were left, they would no longer have the "nature" of flesh: in hylomorphic terms, they would no longer be matter structured by the form of flesh; instead the remaining water, e.g., would be matter structured by the form of water, not by the form of flesh. | 1 | Applied and Interdisciplinary Chemistry |
Tacticity may be measured directly using proton or carbon-13 NMR. This technique enables quantification of the tacticity distribution by comparison of peak areas or integral ranges corresponding to known diads (r, m), triads (mm, rm+mr, rr) and/or higher order n-ads, depending on spectral resolution. In cases of limited resolution, stochastic methods such as Bernoullian or Markovian analysis may also be used to fit the distribution and predict higher n-ads and calculate the isotacticity of the polymer to the desired level.
Other techniques sensitive to tacticity include x-ray powder diffraction, secondary ion mass spectrometry (SIMS), vibrational spectroscopy (FTIR) and especially two-dimensional techniques. Tacticity may also be inferred by measuring another physical property, such as melting temperature, when the relationship between tacticity and that property is well-established. | 0 | Theoretical and Fundamental Chemistry |
Kocienski has made contributions to the design and development of new organometallic reagents in synthesis, and the applications of synthetic methods to complex natural products. Early work with Basil Lythgoe on the scope and stereochemistry of the Julia olefination with alpha-metallated sulphone reagents emphasised the value of this method in organic chemistry. His major contribution has been to research the synthesis and chemistry of novel metallated (lithium, copper and nickel) enol ethers, and to develop the uses of these intermediates in the synthesis of oxacyclic and geometrically defined alkene units in natural products of biological significance. Kocienski has synthesised the insecticide milbemycin beta 3, the potassium channel blocker talaromycin B, the hypotensive agent lacrimin, and the antihypertensive agent zoapatanol. His total synthesis of the insect toxin pederin, and his synthetic work toward the immunosuppressant FK 506, have made him regarded as one of the leading organic chemists in the field. | 0 | Theoretical and Fundamental Chemistry |
In January 2018 darunavir was still the most recent HIV protease inhibitor to reach the market.
In 2006, GlaxoSmithKline discontinued the phase II clinical development of brecanavir, an investigational protease inhibitor for the treatment of HIV, due to insurmountable issues regarding formulation.
In the summer of 2009, GlaxoSmithKline and Concert Pharmaceuticals announced their collaboration to develop and commercialise deuterium-containing medicines. One of them is CTP-518, a protease inhibitor for the treatment of HIV, expected to enter phase I clinical trials in the second half of 2009. CTP-518 is a novel HIV protease inhibitor developed by replacing certain key hydrogen atoms of atazanavir with deuterium. Pre-clinical studies have demonstrated that this modification fully retains the antiviral potency but can evidently slow hepatic metabolism and thereby increase the half life and plasma trough levels. CTP-518, therefore, has the potential to be the first HIV protease inhibitor to eliminate the need to co-dose with a boosting agent, such as ritonavir. | 1 | Applied and Interdisciplinary Chemistry |
The Bulletin for the History of Chemistry is a peer-reviewed scientific journal that publishes articles on the history of chemistry. The journal is published by the History of Chemistry Division of the American Chemical Society. | 1 | Applied and Interdisciplinary Chemistry |
Temperatures throughout the Jurassic and Cretaceous are generally thought to have been relatively warm, and consequently dissolved oxygen levels in the ocean were lower than today—making anoxia easier to achieve. However, more specific conditions are required to explain the short-period (less than a million years) oceanic anoxic events. Two hypotheses, and variations upon them, have proved most durable.
One hypothesis suggests that the anomalous accumulation of organic matter relates to its enhanced preservation under restricted and poorly oxygenated conditions, which themselves were a function of the particular geometry of the ocean basin: such a hypothesis, although readily applicable to the young and relatively narrow Cretaceous Atlantic (which could be likened to a large-scale Black Sea, only poorly connected to the World Ocean), fails to explain the occurrence of coeval black shales on open-ocean Pacific plateaus and shelf seas around the world. There are suggestions, again from the Atlantic, that a shift in oceanic circulation was responsible, where warm, salty waters at low latitudes became hypersaline and sank to form an intermediate layer, at depth, with a temperature of .
The second hypothesis suggests that oceanic anoxic events record a major change in the fertility of the oceans that resulted in an increase in organic-walled plankton (including bacteria) at the expense of calcareous plankton such as coccoliths and foraminifera. Such an accelerated flux of organic matter would have expanded and intensified the oxygen minimum zone, further enhancing the amount of organic carbon entering the sedimentary record. Essentially this mechanism assumes a major increase in the availability of dissolved nutrients such as nitrate, phosphate and possibly iron to the phytoplankton population living in the illuminated layers of the oceans.
For such an increase to occur would have required an accelerated influx of land-derived nutrients coupled with vigorous upwelling, requiring major climate change on a global scale. Geochemical data from oxygen-isotope ratios in carbonate sediments and fossils, and magnesium/calcium ratios in fossils, indicate that all major oceanic anoxic events were associated with thermal maxima, making it likely that global weathering rates, and nutrient flux to the oceans, were increased during these intervals. Indeed, the reduced solubility of oxygen would lead to phosphate release, further nourishing the ocean and fuelling high productivity, hence a high oxygen demand—sustaining the event through a positive feedback.
Another way to explain anoxic events is that the Earth releases a huge volume of carbon dioxide during an interval of intense volcanism; global temperatures rise due to the greenhouse effect; global weathering rates and fluvial nutrient flux increase; organic productivity in the oceans increases; organic-carbon burial in the oceans increases (OAE begins); carbon dioxide is drawn down due to both burial of organic matter and weathering of silicate rocks (inverse greenhouse effect); global temperatures fall, and the ocean–atmosphere system returns to equilibrium (OAE ends).
In this way, an oceanic anoxic event can be viewed as the Earth's response to the injection of excess carbon dioxide into the atmosphere and hydrosphere. One test of this notion is to look at the age of large igneous provinces (LIPs), the extrusion of which would presumably have been accompanied by rapid effusion of vast quantities of volcanogenic gases such as carbon dioxide. The age of three LIPs (Karoo-Ferrar flood basalt, Caribbean large igneous province, Ontong Java Plateau) correlates well with that of the major Jurassic (early Toarcian) and Cretaceous (early Aptian and Cenomanian–Turonian) oceanic anoxic events, indicating that a causal link is feasible. | 0 | Theoretical and Fundamental Chemistry |
SMA actuators are typically actuated electrically by Joule heating. If the SMA is used in an environment where the ambient temperature is uncontrolled, unintentional actuation by ambient heating may occur. | 1 | Applied and Interdisciplinary Chemistry |
If the solvent is a solid, then gases, liquids, and solids can be dissolved.
* Gas in solids:
** Hydrogen dissolves rather well in metals, especially in palladium; this is studied as a means of hydrogen storage.
* Liquid in solid:
** Mercury in gold, forming an amalgam
** Water in solid salt or sugar, forming moist solids
** Hexane in paraffin wax
** Polymers containing plasticizers such as phthalate (liquid) in PVC (solid)
* Solid in solid:
** Steel, basically a solution of carbon atoms in a crystalline matrix of iron atoms
** Alloys like bronze and many others
** Radium sulfate dissolved in barium sulfate: a true solid solution of Ra in BaSO | 0 | Theoretical and Fundamental Chemistry |
Sprinkler fitting is an occupation consisting of the installing, testing, inspecting, and certifying of automatic fire suppression systems in all types of structures. Sprinkler systems installed by sprinkler fitters can include the underground supply as well as integrated systems and standpipes. The fire suppression piping may contain water, air (in a dry system), antifreeze, gas or chemicals as in a hood system, or a mixture producing fire retardant foam.
Sprinkler fitters work with a variety of pipe and tubing materials including several types of plastic, copper, steel, cast iron, and ductile iron.
Sprinkler fitters specialize in piping associated with fire sprinkler systems. The piping within these types of systems are required to be installed and maintained in accordance with strict guidelines in order to maintain compliance with the local building code and the fire code. This type of fire protection is considered a part of active fire protection rather than passive fire protection. | 1 | Applied and Interdisciplinary Chemistry |
Peter Day (20 August 1938 – 19 May 2020) was a British inorganic chemist and Professor of Chemistry at Oxford University and later at University College London (UCL). | 0 | Theoretical and Fundamental Chemistry |
In hot and dry conditions, plants close their stomata to prevent water loss. Under these conditions, will decrease and oxygen gas, produced by the light reactions of photosynthesis, will increase, causing an increase of photorespiration by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and decrease in carbon fixation. Some plants have evolved mechanisms to increase the concentration in the leaves under these conditions.
Plants that use the C carbon fixation process chemically fix carbon dioxide in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalyzed by an enzyme called PEP carboxylase, creating the four-carbon organic acid oxaloacetic acid. Oxaloacetic acid or malate synthesized by this process is then translocated to specialized bundle sheath cells where the enzyme RuBisCO and other Calvin cycle enzymes are located, and where released by decarboxylation of the four-carbon acids is then fixed by RuBisCO activity to the three-carbon 3-phosphoglyceric acids. The physical separation of RuBisCO from the oxygen-generating light reactions reduces photorespiration and increases fixation and, thus, the photosynthetic capacity of the leaf. plants can produce more sugar than plants in conditions of high light and temperature. Many important crop plants are plants, including maize, sorghum, sugarcane, and millet. Plants that do not use PEP-carboxylase in carbon fixation are called C plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle. Over 90% of plants use carbon fixation, compared to 3% that use carbon fixation; however, the evolution of in over sixty plant lineages makes it a striking example of convergent evolution. C photosynthesis, which involves carbon-concentration by selective breakdown of photorespiratory glycine, is both an evolutionary precursor to and a useful carbon-concentrating mechanism in its own right.
Xerophytes, such as cacti and most succulents, also use PEP carboxylase to capture carbon dioxide in a process called Crassulacean acid metabolism (CAM). In contrast to metabolism, which spatially separates the fixation to PEP from the Calvin cycle, CAM temporally separates these two processes. CAM plants have a different leaf anatomy from plants, and fix the at night, when their stomata are open. CAM plants store the mostly in the form of malic acid via carboxylation of phosphoenolpyruvate to oxaloacetate, which is then reduced to malate. Decarboxylation of malate during the day releases inside the leaves, thus allowing carbon fixation to 3-phosphoglycerate by RuBisCO. CAM is used by 16,000 species of plants.
Calcium-oxalate-accumulating plants, such as Amaranthus hybridus and Colobanthus quitensis, show a variation of photosynthesis where calcium oxalate crystals function as dynamic carbon pools, supplying carbon dioxide (CO) to photosynthetic cells when stomata are partially or totally closed. This process was named alarm photosynthesis. Under stress conditions (e.g., water deficit), oxalate released from calcium oxalate crystals is converted to CO by an oxalate oxidase enzyme, and the produced CO can support the Calvin cycle reactions. Reactive hydrogen peroxide (HO), the byproduct of oxalate oxidase reaction, can be neutralized by catalase. Alarm photosynthesis represents a photosynthetic variant to be added to the well-known C4 and CAM pathways. However, alarm photosynthesis, in contrast to these pathways, operates as a biochemical pump that collects carbon from the organ interior (or from the soil) and not from the atmosphere. | 0 | Theoretical and Fundamental Chemistry |
Although dialyzing a sample is relatively simple, a universal dialysis procedure for all applications cannot be provided due to the following variables:
* The sample volume
* The size of the molecules being separated
* The membrane used
* The geometry of the membrane, which affects the diffusion distance
Additionally, the dialysis endpoint is somewhat subjective and application specific. Therefore, the general procedure might require optimization. | 1 | Applied and Interdisciplinary Chemistry |
The Fanning friction factor, named after John Thomas Fanning, is a dimensionless number used as a local parameter in continuum mechanics calculations. It is defined as the ratio between the local shear stress and the local flow kinetic energy density:
where:
* is the local Fanning friction factor (dimensionless)
* is the local shear stress (unit in or or Pa)
* is the bulk dynamic pressure (unit in or )
where the dynamic pressure is given by:
where:
* is the density of the fluid (unit in or )
* is the bulk flow velocity (unit in or )
In particular the shear stress at the wall can, in turn, be related to the pressure loss by multiplying the wall shear stress by the wall area ( for a pipe with circular cross section) and dividing by the cross-sectional flow area ( for a pipe with circular cross section). Thus | 1 | Applied and Interdisciplinary Chemistry |
A chelating agent is the main component of some rust removal formulations.
Citric acid is used to soften water in soaps and laundry detergents. A common synthetic chelator is EDTA. Phosphonates are also well-known chelating agents. Chelators are used in water treatment programs and specifically in steam engineering. Although the treatment is often referred to as "softening," chelation has little effect on the waters mineral content, other than to make it soluble and lower the waters pH level. | 0 | Theoretical and Fundamental Chemistry |
If substantial differences are detected between one or more acquired signals and the reference spectral models, these samples are identified, classified as unreliable and automatically discarded: for instance, spectra which are not clearly associated to bone portions but to osteophytes or calcifications. Hence, this approach natively identifies and eliminates outliers, bringing significant advantages with respect to the clinical reliability of the obtained results. | 0 | Theoretical and Fundamental Chemistry |
According to the historical registers of the pharmacy, a contract redacted in 1778 mentions that the Genoese surgeon and chemist Lorenzo Robello was tasked to procure ingredients for the pharmacy, prepare the medicines and administer them "to the friars and to external patients". At that time it was not possible to find a friar with the necessary qualifications; the resolve of the Carmelite Order, however, remained that the pharmacy was to be run primarily by friars and, by 1792, the fully-qualified chemist friar Giovanni della Croce assumed the direction of the pharmacy, updated its equipment and furnished the dispensary room with the boiserie which is still visible today. | 1 | Applied and Interdisciplinary Chemistry |
Attosecond physics, also known as attophysics, or more generally attosecond science, is a branch of physics that deals with light-matter interaction phenomena wherein attosecond (10 s) photon pulses are used to unravel dynamical processes in matter with unprecedented time resolution.
Attosecond science mainly employs pump–probe spectroscopic methods to investigate the physical process of interest. Due to the complexity of this field of study, it generally requires a synergistic interplay between state-of-the-art experimental setup and advanced theoretical tools to interpret the data collected from attosecond experiments.
The main interests of attosecond physics are:
# Atomic physics: investigation of electron correlation effects, photo-emission delay and ionization tunneling.
# Molecular physics and molecular chemistry: role of electronic motion in molecular excited states (e.g. charge-transfer processes), light-induced photo-fragmentation, and light-induced electron transfer processes.
# Solid-state physics: investigation of exciton dynamics in advanced 2D materials, petahertz charge carrier motion in solids, spin dynamics in ferromagnetic materials.
One of the primary goals of attosecond science is to provide advanced insights into the quantum dynamics of electrons in atoms, molecules and solids with the long-term challenge of achieving real-time control of the electron motion in matter.
The advent of broadband solid-state titanium-doped sapphire based (Ti:Sa) lasers (1986), chirped pulse amplification (CPA) (1988), spectral broadening of high-energy pulses (e.g. gas-filled hollow-core fiber via self-phase modulation) (1996), mirror-dispersion-controlled technology (chirped mirrors) (1994), and carrier envelop offset stabilization (2000) had enabled the creation of isolated-attosecond light pulses (generated by the non-linear process of high harmonic generation in a noble gas) (2004, 2006), which have given birth to the field of attosecond science.
The current world record for the shortest light-pulse generated by human technology is 43 as.
In 2022, Anne LHuillier, Paul Corkum, Ferenc Krausz were awarded with the Wolf prize in physics for their pioneering contributions to ultrafast laser science and attosecond physics. This was followed by the 2023 Nobel Prize in Physics, where LHuillier, Krausz and Pierre Agostini were rewarded “for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.” | 0 | Theoretical and Fundamental Chemistry |
Dendrites form in unary (one-component) systems as well as multi-component systems. The requirement is that the liquid (the molten material) be undercooled, aka supercooled, below the freezing point of the solid. Initially, a spherical solid nucleus grows in the undercooled melt. As the sphere grows, the spherical morphology becomes unstable and its shape becomes perturbed. The solid shape begins to express the preferred growth directions of the crystal. This growth direction may be due to anisotropy in the surface energy of the solid–liquid interface, or to the ease of attachment of atoms to the interface on different crystallographic planes, or both (for an example of the latter, see hopper crystal). In metallic systems, interface attachment kinetics is usually negligible (for non-negligible cases, see dendrite (crystal)). In metallic systems, the solid then attempts to minimize the area of those surfaces with the highest surface energy. The dendrite thus exhibits a sharper and sharper tip as it grows. If the anisotropy is large enough, the dendrite may present a faceted morphology. The microstructural length scale is determined by the interplay or balance between the surface energy and the temperature gradient (which drives the heat/solute diffusion) in the liquid at the interface.
As solidification proceeds, an increasing number of atoms lose their kinetic energy, making the process exothermic. For a pure material, latent heat is released at the solid–liquid interface so that the temperature remains constant until the melt has completely solidified. The growth rate of the resultant crystalline substance will depend on how fast this latent heat can be conducted away. A dendrite growing in an undercooled melt can be approximated as a parabolic needle-like crystal that grows in a shape-preserving manner at constant velocity. Nucleation and growth determine the grain size in equiaxed solidification while the competition between adjacent dendrites decides the primary spacing in columnar growth. Generally, if the melt is cooled slowly, nucleation of new crystals will be less than at large undercooling. The dendritic growth will result in dendrites of a large size. Conversely, a rapid cooling cycle with a large undercooling will increase the number of nuclei and thus reduce the size of the resulting dendrites (and often lead to small grains).
Smaller dendrites generally lead to higher ductility of the product. One application where dendritic growth and resulting material properties can be seen is the process of welding. The dendrites are also common in cast products, where they may become visible by etching of a polished specimen.
As dendrites develop further into the liquid metal, they get hotter because they continue to extract heat. If they get too hot, they will remelt. This remelting of the dendrites is called recalescence. Dendrites usually form under non-equilibrium conditions. | 1 | Applied and Interdisciplinary Chemistry |
TaqMan probes are hydrolysis probes that are designed to increase the specificity of quantitative PCR. The method was first reported in 1991 by researcher Kary Mullis at Cetus Corporation, and the technology was subsequently developed by Hoffmann-La Roche for diagnostic assays and by Applied Biosystems (now part of Thermo Fisher Scientific) for research applications.
The TaqMan probe principle relies on the 5´–3´ exonuclease activity of Taq polymerase to cleave a dual-labeled probe during hybridization to the complementary target sequence and fluorophore-based detection. As in other quantitative PCR methods, the resulting fluorescence signal permits quantitative measurements of the accumulation of the product during the exponential stages of the PCR; however, the TaqMan probe significantly increases the specificity of the detection. TaqMan probes were named after the videogame Pac-Man (Taq Polymerase + PacMan = TaqMan) as its mechanism is based on the Pac-Man principle. | 1 | Applied and Interdisciplinary Chemistry |
Cold fusion setups utilize an input power source (to ostensibly provide activation energy), a platinum group electrode, a deuterium or hydrogen source, a calorimeter, and, at times, detectors to look for byproducts such as helium or neutrons. Critics have variously taken issue with each of these aspects and have asserted that there has not yet been a consistent reproduction of claimed cold fusion results in either energy output or byproducts. Some cold fusion researchers who claim that they can consistently measure an excess heat effect have argued that the apparent lack of reproducibility might be attributable to a lack of quality control in the electrode metal or the amount of hydrogen or deuterium loaded in the system. Critics have further taken issue with what they describe as mistakes or errors of interpretation that cold fusion researchers have made in calorimetry analyses and energy budgets. | 0 | Theoretical and Fundamental Chemistry |
If the liquid and vapor are pure, in that they consist of only one molecular component and no impurities, then the equilibrium state between the two phases is described by the following equations:
:; and
where and are the pressures within the liquid and vapor, and are the temperatures within the liquid and vapor, and and are the molar Gibbs free energies (units of energy per amount of substance) within the liquid and vapor, respectively. In other words, the temperature, pressure and molar Gibbs free energy are the same between the two phases when they are at equilibrium.
An equivalent, more common way to express the vapor–liquid equilibrium condition in a pure system is by using the concept of fugacity. Under this view, equilibrium is described by the following equation:
where and are the fugacities of the liquid and vapor, respectively, at the system temperature and pressure . It is often convenient to use the quantity , the dimensionless fugacity coefficient, which is 1 for an ideal gas. | 0 | Theoretical and Fundamental Chemistry |
Decantation is frequently used to purify a liquid by separating it from a suspension of insoluble particles (e.g. in red wine, where the wine is decanted from the potassium bitartrate crystals to avoid unsavory taste). This makes the wine more tonic and astringent.
Cream accelerates to the top of milk, allowing the separation of milk and cream. This is used in the cheese industry. Fat is determined in butter by decantation.
To obtain a sample of clear water from muddy water, muddy water is poured into another container, which separates the water from the mud.
In the sugar industry, the processing of sugar beets into granular sugar involves many liquid–solid separations; e.g. separation of syrups from crystals.
Decantation is also present in nanotechnology. In the synthesis of high quality silver nanowire (AgNW) solutions and fabrication process of high performance electrodes, decantation is also being applied which greatly simplifies the purification process.
After using a desiccant to absorb water from an organic liquid, the organic liquid can often be decanted away from the desiccant.
The process of deriving vinegar also requires decantation to remove fats and biomolecular antioxidants from the raw substance.
Plasma can be separated from blood through decantation by using a centrifuge.
Mercury is disposed of in water bodies during mining, turning the water unfit and toxic. The mercury can be removed through decantation. | 0 | Theoretical and Fundamental Chemistry |
Juan José Elhuyar Lubize (15 June 1754 – 20 September 1796) was a Spanish chemist and mineralogist, who was best known for being first to isolate tungsten with his brother Fausto Elhuyar in 1783.
He was born in Logroño, in northern Spain and died in Santafé de Bogotá, New Granada (present-day Colombia) at 42. | 1 | Applied and Interdisciplinary Chemistry |
Ferrallitisation is the process in which rock is changed into a soil consisting of clay (kaolinite) and sesquioxides, in the form of hydrated oxides of iron and aluminium. In humid tropical areas, with consistently high temperatures and rainfall for all or most of the year, chemical weathering rapidly breaks down the rock. This at first produces clays which later also break down to form silica. The silica is removed by leaching and the sesquioxides of iron and aluminium remain, giving the characteristic red colour of many tropical soils. Ferrallitisation is the reverse of podsolisation, where silica remains and the iron and aluminum are removed. In tropical rain forests with rain throughout the year, ferrallitic soils develop. In savanna areas, with altering dry and wet climates, ferruginous soils occur. | 0 | Theoretical and Fundamental Chemistry |
Only a small minority of enzyme-catalysed reactions have just one substrate, and even the number is increased by treating two-substrate reactions in which one substrate is water as one-substrate reactions the number is still small. One might accordingly suppose that the Michaelis–Menten equation, normally written with just one substrate, is of limited usefulness. This supposition is misleading, however. One of the common equations for a two-substrate reaction can be written as follows to express in terms of two substrate concentrations and :
the other symbols represent kinetic constants. Suppose now that is varied with held constant. Then it is convenient to reorganize the equation as follows:
This has exactly the form of the Michaelis–Menten equation
with apparent values and defined as follows: | 0 | Theoretical and Fundamental Chemistry |
In a short-jump library, 3 kb genomic DNA fragments are ligated with biotinylate ends and circularized. The circular segments are then sheared into small fragments and the biotinylated fragments are selected by affinity assay for paired-end sequencing.
There are two issues related to short-jump libraries. First, a read can pass through the biotinylated circularization junction and reduce the effective read length. Second, reads from non-jumped fragments (i.e. fragments without the circularization junction) are sequenced and reduce genomic coverage. It has been reported that non-jumped fragments range from 4% to 13%, depending on the size of selection. The first problem might be solved by shearing circles into a larger size and select for those larger fragments. The second problem can be addressed by using a custom barcoded jumping library. | 1 | Applied and Interdisciplinary Chemistry |
Inelastic scattering of light caused by acoustic phonons was first predicted by Léon Brillouin in 1914
. Leonid Mandelstam is believed to have recognised the possibility of such scattering as early as 1918, but he published his idea only in 1926.
In order to credit Mandelstam, the effect is also called Brillouin-Mandelstam scattering (BMS). Other commonly used names are Brillouin light scattering (BLS) and Brillouin-Mandelstam light scattering (BMLS).
The process of stimulated Brillouin scattering (SBS) was first observed by Chiao et al. in 1964. The optical phase conjugation aspect of the SBS process was discovered by Boris Yakovlevich Zeldovich et al. in 1972. | 0 | Theoretical and Fundamental Chemistry |
Immunosequencing, sometimes referred to as repertoire sequencing or Rep-Seq, is a method for analyzing the genetic makeup of an individual's immune system. | 1 | Applied and Interdisciplinary Chemistry |
The aim of virtual screening is to identify molecules of novel chemical structure that bind to the macromolecular target of interest. Thus, success of a virtual screen is defined in terms of finding interesting new scaffolds rather than the total number of hits. Interpretations of virtual screening accuracy should, therefore, be considered with caution. Low hit rates of interesting scaffolds are clearly preferable over high hit rates of already known scaffolds.
Most tests of virtual screening studies in the literature are retrospective. In these studies, the performance of a VS technique is measured by its ability to retrieve a small set of previously known molecules with affinity to the target of interest (active molecules or just actives) from a library containing a much higher proportion of assumed inactives or decoys. There are several distinct ways to select decoys by matching the properties of the corresponding active molecule and more recently decoys are also selected in a property-unmatched manner. The actual impact of decoy selection, either for training or testing purposes, has also been discussed.
By contrast, in prospective applications of virtual screening, the resulting hits are subjected to experimental confirmation (e.g., IC measurements). There is consensus that retrospective benchmarks are not good predictors of prospective performance and consequently only prospective studies constitute conclusive proof of the suitability of a technique for a particular target. | 1 | Applied and Interdisciplinary Chemistry |
In thermodynamics, the fundamental thermodynamic relation are four fundamental equations which demonstrate how four important thermodynamic quantities depend on variables that can be controlled and measured experimentally. Thus, they are essentially equations of state, and using the fundamental equations, experimental data can be used to determine sought-after quantities like G (Gibbs free energy) or H (enthalpy). The relation is generally expressed as a microscopic change in internal energy in terms of microscopic changes in entropy, and volume for a closed system in thermal equilibrium in the following way.
Here, U is internal energy, T is absolute temperature, S is entropy, P is pressure, and V is volume.
This is only one expression of the fundamental thermodynamic relation. It may be expressed in other ways, using different variables (e.g. using thermodynamic potentials). For example, the fundamental relation may be expressed in terms of the enthalpy H as
in terms of the Helmholtz free energy F as
and in terms of the Gibbs free energy G as | 0 | Theoretical and Fundamental Chemistry |
One way to theoretically derive the capillary length, is to imagine a liquid droplet at the point where surface tension balances gravity.
Let there be a spherical droplet with radius ,
The characteristic Laplace pressure , due to surface tension, is equal to
where is the surface tension. The pressure due to gravity (hydrostatic pressure) of a column of liquid is given by
where is the droplet density, the gravitational acceleration, and is the height of the droplet.
At the point where the Laplace pressure balances out the pressure due to gravity , | 1 | Applied and Interdisciplinary Chemistry |
Polybutene is an organic polymer made from a mixture of 1-butene, 2-butene, and isobutylene. Ethylene steam cracker C4s are also used as supplemental feed for polybutene. It is similar to polyisobutylene (PIB), which is produced from essentially pure isobutylene made in a C4 complex of a major refinery. The presence of isomers other than isobutylene can have several effects including: 1) lower reactivity due to steric hindrance at the terminal carbon in, e.g., manufacture of polyisobutenyl succinic anhydride (PIBSA) dispersant manufacture; 2) the molecular weight—viscosity relationships of the two materials may also be somewhat different. | 0 | Theoretical and Fundamental Chemistry |
# The citrate binds to citrate transporters.
# The shuttle delivers the citrate from the inner membrane to the intermembrane space.
# There is a net movement of the citrate from the intermembrane space to the cytosol across the outer membrane, following the concentration gradient. | 1 | Applied and Interdisciplinary Chemistry |
As a gemstone used in jewelry, silicon carbide is called "synthetic moissanite" or just "moissanite" after the mineral name. Moissanite is similar to diamond in several important respects: it is transparent and hard (9–9.5 on the Mohs scale, compared to 10 for diamond), with a refractive index between 2.65 and 2.69 (compared to 2.42 for diamond). Moissanite is somewhat harder than common cubic zirconia. Unlike diamond, moissanite can be strongly birefringent. For this reason, moissanite jewels are cut along the optic axis of the crystal to minimize birefringent effects. It is lighter (density 3.21 g/cm vs. 3.53 g/cm), and much more resistant to heat than diamond. This results in a stone of higher luster, sharper facets, and good resilience. Loose moissanite stones may be placed directly into wax ring moulds for lost-wax casting, as can diamond, as moissanite remains undamaged by temperatures up to . Moissanite has become popular as a diamond substitute, and may be misidentified as diamond, since its thermal conductivity is closer to diamond than any other substitute. Many thermal diamond-testing devices cannot distinguish moissanite from diamond, but the gem is distinct in its birefringence and a very slight green or yellow fluorescence under ultraviolet light. Some moissanite stones also have curved, string-like inclusions, which diamonds never have. | 1 | Applied and Interdisciplinary Chemistry |
Formate can be converted to hydrogen gas and carbon dioxide in E. coli. This reaction requires the enzyme [http://biocyc.org/ECOLI/NEW-IMAGE?type=ENZYME&object=FHLMULTI-CPLX formate-hydrogen lyase]. It can be used to prevent the conditions inside the cell becoming too acidic.
formate → H and CO | 1 | Applied and Interdisciplinary Chemistry |
Anhydrous iron(II) oxalate is unknown among minerals as of 2020. However, the dihydrate is known as humboldtine. A related, though much more complex mineral is stepanovite,<br>
Na[Mg(HO)] [Fe(CO)]·3HO - an example of trioxalatoferrate(III). | 0 | Theoretical and Fundamental Chemistry |
In igneous petrology, an intermediate composition refers to the chemical composition of a rock that has 51.563 wt% SiO being an intermediate between felsic and mafic compositions. Typical intermediate rocks include andesite and trachyandesite among volcanic rocks and diorite and granodiorite among plutonic rocks. | 0 | Theoretical and Fundamental Chemistry |
Hydrogen is the simplest solar fuel. Its formation involves only the transference of two electrons to two protons:
The hydrogenase enzymes effect this conversion
Dirhodium photocatalyst and cobalt catalysts. | 0 | Theoretical and Fundamental Chemistry |
He was born in Balsall Heath, Birmingham, Warwickshire, (now the West Midlands), England, the son of Joseph Henry Pickard, a tool maker, and Alice his wife, the daughter of Robert Howson of Birmingham. From 1883-1891 he attended King Edward VIs Grammar School. In 1891 he studied chemistry at Mason Science College (which later became the University of Birmingham), under Percy F. Frankland and obtained a first class BSc, then awarded by the University of London. In 1896 he attended the University of Munich as an 1851 Exhibitioner being awarded a PhD summa cum laude' in 1898. | 0 | Theoretical and Fundamental Chemistry |
The discovery of mRNA modifications dates back to 1957 with the discovery of the pseudouridine modification. Many of these modifications were found in the noncoding regions of cellular RNA. Once these modifications were discovered in mRNA, discoveries in viral transcripts soon followed. Detections have been aided with the advancement and use of new techniques such as mA seq. | 1 | Applied and Interdisciplinary Chemistry |
Depolarization occurs in the four chambers of the heart: both atria first, and then both ventricles.
# The sinoatrial (SA) node on the wall of the right atrium initiates depolarization in the right and left atria, causing contraction, which corresponds to the P wave on an electrocardiogram.
# The SA node sends the depolarization wave to the atrioventricular (AV) node which—with about a 100 ms delay to let the atria finish contracting—then causes contraction in both ventricles, seen in the QRS wave. At the same time, the atria re-polarize and relax.
# The ventricles are re-polarized and relaxed at the T wave.
This process continues regularly, unless there is a problem in the heart. | 0 | Theoretical and Fundamental Chemistry |
Previous analysis focused only on diffraction from a perfectly flat surface of a crystal surface. However, non-flat surfaces add additional diffraction conditions to RHEED analysis.
Streaked or elongated spots are common to RHEED patterns. As Fig 3 shows, the reciprocal lattice rods with the lowest orders intersect the Ewald sphere at very small angles, so the intersection between the rods and sphere is not a singular point if the sphere and rods have thickness. The incident electron beam diverges and electrons in the beam have a range of energies, so in practice, the Ewald sphere is not infinitely thin as it is theoretically modeled. The reciprocal lattice rods have a finite thickness as well, with their diameters dependent on the quality of the sample surface. Streaks appear in the place of perfect points when broadened rods intersect the Ewald sphere. Diffraction conditions are fulfilled over the entire intersection of the rods with the sphere, yielding elongated points or ‘streaks’ along the vertical axis of the RHEED pattern. In real cases, streaky RHEED patterns indicate a flat sample surface while the broadening of the streaks indicate small area of coherence on the surface.
Surface features and polycrystalline surfaces add complexity or change RHEED patterns from those from perfectly flat surfaces. Growing films, nucleating particles, crystal twinning, grains of varying size and adsorbed species add complicated diffraction conditions to those of a perfect surface. Superimposed patterns of the substrate and heterogeneous materials, complex interference patterns and degradation of the resolution are characteristic of complex surfaces or those partially covered with heterogeneous materials. | 0 | Theoretical and Fundamental Chemistry |
Intensification of technological processes and chemical reactions is achieved due to intensive mixing and dispersion, acoustic and electromagnetic treatment, high local pressure and electrolysis of processed components. Electromagnetic devices with a vortex layer with ferromagnetic elements accelerate the reactions 1.5-2 times; reduce the consumption of reagents and electricity by 20%. The grinding effect is achieved by the motion of ferromagnetic particles and their free collision with each other, and a constrained collision between the particles and a body. The degree of grinding is 0.5 μm (with an initial size of 20 mm).
At present, the electromagnetic devices with a vortex layer with ferromagnetic elements actually exist (D.D. Logvinenko himself designed and produced more than 2000 pieces), their principle is also implemented in some technological lines. | 1 | Applied and Interdisciplinary Chemistry |
In animal communication, an alarm signal is an antipredator adaptation in the form of signals emitted by social animals in response to danger. Many primates and birds have elaborate alarm calls for warning conspecifics of approaching predators. For example, the alarm call of the blackbird is a familiar sound in many gardens. Other animals, like fish and insects, may use non-auditory signals, such as chemical messages. Visual signs such as the white tail flashes of many deer have been suggested as alarm signals; they are less likely to be received by conspecifics, so have tended to be treated as a signal to the predator instead.
Different calls may be used for predators on the ground or from the air. Often, the animals can tell which member of the group is making the call, so that they can disregard those of little reliability.
Evidently, alarm signals promote survival by allowing the receivers of the alarm to escape from the source of peril; this can evolve by kin selection, assuming the receivers are related to the signaller. However, alarm calls can increase individual fitness, for example by informing the predator it has been detected.
Alarm calls are often high-frequency sounds because these sounds are harder to localize. | 1 | Applied and Interdisciplinary Chemistry |
Carotenoid synthesis takes place in plants, certain fungi, and bacteria. Structurally carotenes are tetraterpenes, meaning that they are synthesized biochemically from four 10-carbon terpene units, which in turn were formed from eight 5-carbon isoprene units. Intermediate steps are the creation of a 40-carbon phytoene molecule, conversion to lycopene via desaturation, and then creation of ionone rings at both ends of the molecule. β-carotene has a β-ionone ring at both ends, meaning that the molecule can be divided symmetrically to yield two retinol molecules. α-Carotene has a β-ionone ring at one end and an Ɛ-ionone ring at the other, so it has half the retinol conversion capacity.
In most animal species, retinol is synthesized from the breakdown of the plant-formed provitamin, β-carotene. First, the enzyme beta-carotene 15,15'-dioxygenase (BCO-1) cleaves β-carotene at the central double bond, creating an epoxide. This epoxide is then attacked by water creating two hydroxyl groups in the center of the structure. The cleavage occurs when these alcohols are oxidized to the aldehydes using NAD. The resultant retinal is then quickly reduced to retinol by the enzyme retinol dehydrogenase. Omnivore species such as dogs, wolves, coyotes and foxes in general are low producers of BCO-1. The enzyme is lacking in felids (cats), meaning that vitamin A requirements are met from the retinyl ester content of prey animals. | 1 | Applied and Interdisciplinary Chemistry |
The method is currently being developed and was applied to investigate translation dynamics in live yeast cells and is extending, rather than simply combining, the capabilities of the previous techniques. The only other transcriptome-wide method for mapping ribosome positions over mRNA with nucleotide precision is ribosome (translation) profiling. However, it captures positions of only elongating ribosomes, and most dynamic and functionally important intermediates of translation at the initiation stage are not detected.
TCP-seq was designed to specifically target these blind spots. It can essentially provide the same level of details for elongation phase as ribosome (translation) profiling, but also includes recording of initiation, termination and recycling intermediates (and basically any other possible translation complexes as long as the ribosome or its subunits are contacting and protecting the mRNA) of protein synthesis that previously remained out of the reach. Therefore, TCP-seq provides a single approach for a complete insight into the translation process of a biological sample. This particular aspect of the method can be expected to be developed further as the dynamics of ribosomal scanning on mRNA during translation initiation is generally unknown for the most of life. Current dataset containing TCP-seq data for translation initiation is available for yeast Saccharomyces cerevisiae, and likely to be extended for other organisms in the future. | 1 | Applied and Interdisciplinary Chemistry |
Hydrodimerization is an organic reaction that couples two alkenes to give a symmetrical hydrocarbon. The reaction is often implemented electrochemically; in that case the reaction is called electrodimerization. The reaction can also be induced with samarium diiodide, a one-electron reductant.
Hydrodimerization is the basis of the Monsanto adiponitrile synthesis:
:2CH=CHCN + 2e + 2H → NCCHCHCHCHCN
The reaction applies to a number electrophilic alkenes (Michael acceptors). | 0 | Theoretical and Fundamental Chemistry |
* Several arthropods translate the codon AGG as lysine instead of serine (as in the Pterobranchia Mitochondrial Code) or arginine (as in the standard genetic code).
* GUG may possibly function as an initiator in Drosophila. AUU is not used as an initiator in Mytilus
* "An exceptional mechanism must operate for initiation of translation of the cytochrome oxidase subunit I mRNA in both D. melanogaster and D. yakuba, since its only plausible initiation codon, AUA, is out of frame with the rest of the gene. Initiation appears to require the "reading" of an AUAA quadruplet, which would be equivalent to initiation at AUA followed immediately by a specific ribosomal frameshift. Another possible mechanism ... is that the mRNA is "edited" to bring the AUA initiation into frame." | 1 | Applied and Interdisciplinary Chemistry |
Deriving the Gibbs–Duhem equation from the fundamental thermodynamic equation is straightforward. The total differential of the extensive Gibbs free energy in terms of its natural variables is
Since the Gibbs free energy is the Legendre transformation of the internal energy, the derivatives can be replaced by their definitions, transforming the above equation into:
The chemical potential is simply another name for the partial molar Gibbs free energy (or the partial Gibbs free energy, depending on whether N is in units of moles or particles). Thus the Gibbs free energy of a system can be calculated by collecting moles together carefully at a specified T, P and at a constant molar ratio composition (so that the chemical potential doesn't change as the moles are added together), i.e.
The total differential of this expression is
Combining the two expressions for the total differential of the Gibbs free energy gives
which simplifies to the Gibbs–Duhem relation: | 0 | Theoretical and Fundamental Chemistry |
Typically the reaction to form Grignard reagents involves the use of magnesium ribbon. All magnesium is coated with a passivating layer of magnesium oxide, which inhibits reactions with the organic halide. Many methods have been developed to weaken this passivating layer, thereby exposing highly reactive magnesium to the organic halide. Mechanical methods include crushing of the Mg pieces in situ, rapid stirring, and sonication. Iodine, methyl iodide, and 1,2-dibromoethane are common activating agents. The use of 1,2-dibromoethane is advantageous as its action can be monitored by the observation of bubbles of ethylene. Furthermore, the side-products are innocuous:
The amount of Mg consumed by these activating agents is usually insignificant. A small amount of mercuric chloride will amalgamate the surface of the metal, enhancing its reactivity. Addition of preformed Grignard reagent is often used as the initiator.
Specially activated magnesium, such as Rieke magnesium, circumvents this problem.The oxide layer can also be broken up using ultrasound, using a stirring rod to scratch the oxidized layer off, or by adding a few drops of iodine or 1,2-Diiodoethane. Another option is to use sublimed magnesium or magnesium anthracene.
"Rieke magnesium" is prepared by a reduction of an anhydrous magnesium chloride with an potassium: | 0 | Theoretical and Fundamental Chemistry |
Ideal grain growth is a special case of normal grain growth where boundary motion is driven only by local curvature of the grain boundary. It results in the reduction of the total amount of grain boundary surface area i.e. total energy of the system. Additional contributions to the driving force by e.g. elastic strains or temperature gradients are neglected. If it holds that the rate of growth is proportional to the driving force and that the driving force is proportional to the total amount of grain boundary energy, then it can be shown that the time t required to reach a given grain size is approximated by the equation
where d is the initial grain size, d is the final grain size and k is a temperature dependent constant given by an exponential law:
where k is a constant, T is the absolute temperature and Q is the activation energy for boundary mobility. Theoretically, the activation energy for boundary mobility should equal that for self-diffusion but this is often found not to be the case.
In general these equations are found to hold for ultra-high purity materials but rapidly fail when even tiny concentrations of solute are introduced. | 1 | Applied and Interdisciplinary Chemistry |
A fourth international conference on the Gaia hypothesis, sponsored by the Northern Virginia Regional Park Authority and others, was held in October 2006 at the Arlington, VA campus of George Mason University.
Martin Ogle, Chief Naturalist, for NVRPA, and long-time Gaia hypothesis proponent, organized the event. Lynn Margulis, Distinguished University Professor in the Department of Geosciences, University of Massachusetts-Amherst, and long-time advocate of the Gaia hypothesis, was a keynote speaker. Among many other speakers: Tyler Volk, co-director of the Program in Earth and Environmental Science at New York University; Dr. Donald Aitken, Principal of Donald Aitken Associates; Dr. Thomas Lovejoy, President of the Heinz Center for Science, Economics and the Environment; Robert Corell, Senior Fellow, Atmospheric Policy Program, American Meteorological Society and noted environmental ethicist, J. Baird Callicott. | 0 | Theoretical and Fundamental Chemistry |
A blank solution is a solution containing little to no analyte of interest, usually used to calibrate instruments such as a colorimeter. According to the EPA, the "primary purpose of blanks is to trace sources of artificially introduced contamination." Different types of blanks are used to identify the source of contamination in the sample. The types of blanks include equipment blank, field blank, trip blank, method blank, and instrument blank. | 0 | Theoretical and Fundamental Chemistry |
Proteomics permits the quantitative analysis and detection of changes to proteins or protein biomarkers. Protein biomarkers detect a variety of biological changes, such as protein-protein interactions, post-translational modifications and immunological responses. | 1 | Applied and Interdisciplinary Chemistry |
A dialdehyde is an organic chemical compound with two aldehyde groups. The nomenclature of dialdehydes have the ending -dial or sometimes -dialdehyde. Short aliphatic dialdehydes are sometimes named after the diacid from which they can be derived. An example is butanedial, which is also called succinaldehyde (from succinic acid). | 0 | Theoretical and Fundamental Chemistry |
Various signalling pathways, as FGF, WNT and TGF-β pathways, regulate the processes involved in embryogenesis.
FGF (Fibroblast Growth Factor) ligands bind to receptors tyrosine kinase, FGFR (Fibroblast Growth Factor Receptors), and form a stable complex with co-receptors HSPG (Heparan Sulphate Proteoglycans) that will promote autophosphorylation of the intracellular domain of FGFR and consequent activation of four main pathways: MAPK/ERK, PI3K, PLCγ and JAK/STAT.
* MAPK/ERK (Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase) regulates gene transcription through successive kinase phosphorylation and in human embryonic stem cells it helps maintaining pluripotency. However, in the presence of Activin A, a TGF-β ligand, it causes the formation of mesoderm and neuroectoderm.
* Phosphorylation of membrane phospholipids by PI3K (Phosphatidylinositol 3-Kinase) results in activation of AKT/PKB (Protein Kinase B). This kinase is involved in cell survival and inhibition of apoptosis, cellular growth and maintenance of pluripotency, in embryonic stem cells.
* PLCγ (Phosphoinositide Phospholipase C γ) hydrolyzes membrane phospholipids to form IP3 (Inositoltriphosphate) and DAG (Diacylglycerol), leading to activation of kinases and regulating morphogenic movements during gastrulation and neurulation.
* STAT (Signal Trandsducer and Activator of Transcription) is phosphorylated by JAK (Janus Kinase) and regulates gene transcription, determining cell fates. In mouse embryonic stem cells, this pathway helps maintaining pluripotency.
The WNT pathway allows β-catenin function in gene transcription, once the interaction between WNT ligand and G protein-coupled receptor Frizzled inhibits GSK-3 (Glycogen Synthase Kinase-3) and thus formation of β-catenin destruction complex. Although there is some controversy about the effects of this pathway in embryogenesis, it is thought that WNT signalling induces primitive streak, mesoderm and endoderm formation.
In TGF-β (Transforming Growth Factor β) pathway, BMP (Bone Morphogenic Protein), Activin and Nodal ligands bind to their receptors and activate Smads that bind to DNA and promote gene transcription. Activin is necessary for mesoderm and specially endoderm differentiation, and Nodal and BMP are involved in embryo patterning. BMP is also responsible for formation of extra-embryonic tissues before and during gastrulation, and for early mesoderm differentiation, when Activin and FGF pathways are activated. | 0 | Theoretical and Fundamental Chemistry |
Xing enjoyed collecting crafts relevant the tortoise.
Xings father Duan () was a member of Hanlin Academy in the Late Qing dynasty, he once studied in Japan and used to be an officer at the Beiyang government. Xings mother, Zhang Xian (), was a housewife. Xing and his wife Qian Cunrou (), a microbiologist, had two sons. | 0 | Theoretical and Fundamental Chemistry |
Different factors have been proposed to be related to codon usage bias, including gene expression level (reflecting selection for optimizing the translation process by tRNA abundance), guanine-cytosine content (GC content, reflecting horizontal gene transfer or mutational bias), guanine-cytosine skew (GC skew, reflecting strand-specific mutational bias), amino acid conservation, protein hydropathy, transcriptional selection, RNA stability, optimal growth temperature, hypersaline adaptation, and dietary nitrogen. | 1 | Applied and Interdisciplinary Chemistry |
Calcium is a necessary ion in the formation of the mitotic spindle. Without the mitotic spindle, cellular division cannot occur. Although young leaves have a higher need for calcium, older leaves contain higher amounts of calcium because calcium is relatively immobile through the plant. It is not transported through the phloem because it can bind with other nutrient ions and precipitate out of liquid solutions. | 1 | Applied and Interdisciplinary Chemistry |
The quantum tunneling may be calculated either by extending fission theory to a larger mass asymmetry or by heavier emitted particle from alpha decay theory.
Both fission-like and alpha-like approaches are able to express the decay constant , as a product of three model-dependent quantities
where is the frequency of assaults on the barrier per second, S is the preformation probability of the cluster at the nuclear surface, and P is the penetrability of the external barrier. In alpha-like theories S is an overlap integral of the wave function of the three partners (parent, daughter, and emitted cluster). In a fission theory the preformation probability is the penetrability of the internal part of the barrier from the initial turning point R to the touching point R.
Very frequently it is calculated by using the Wentzel-Kramers-Brillouin (WKB) approximation.
A very large number, of the order 10, of parent-emitted cluster combinations were considered in a systematic search for new decay modes. The large amount of computations could be performed in a reasonable time by using the ASAF model developed by Dorin N Poenaru, Walter Greiner, et al. The model was the first to be used to predict measurable quantities in cluster decay. More than 150 cluster decay modes have been predicted before any other kind of half-lives calculations have been reported. Comprehensive tables of half-lives, branching ratios, and kinetic energies have been published, e.g.
Potential barrier shapes similar to that considered within the ASAF model have been calculated by using the macroscopic-microscopic method.
Previously
it was shown that even alpha decay may be considered a particular case of cold fission. The ASAF model may be used to describe in a unified manner cold alpha decay, cluster decay, and cold fission (see figure 6.7, p. 287 of the Ref. [2]).
One can obtain with good approximation one universal curve (UNIV) for any kind of cluster decay mode with a mass number Ae, including alpha decay
In a logarithmic scale the equation log T = f(log P) represents a single straight line which can be conveniently used to estimate the half-life. A single universal curve for alpha decay and cluster decay modes results by expressing log T + log S = f(log P).
The experimental data on cluster decay in three groups of even-even, even-odd, and odd-even parent nuclei are reproduced with comparable accuracy by both types of universal curves, fission-like UNIV and UDL
derived using alpha-like R-matrix theory.
In order to find the released energy
one can use the compilation of measured masses
M, M, and M of the parent, daughter, and emitted nuclei, c is the light velocity. The mass excess is transformed into energy according to the Einstein's formula E = mc. | 0 | Theoretical and Fundamental Chemistry |
The main effect of chloride ions on reinforced concrete is to cause pitting corrosion of the steel reinforcement bars (rebar). It is a surreptitious and dangerous form of localized corrosion because the rebar sections can be decreased to the point that the steel reinforcement are no longer capable to withstand to the tensile efforts they are supposed to resist by design. When the rebar sections are too small or the rebar are locally broken, the reinforcements are lost, and concrete is no longer reinforced concrete.
Chlorides, particularly calcium chloride, have been used to shorten the setting time of concrete.
However, calcium chloride and (to a lesser extent) sodium chloride have been shown to leach calcium hydroxide and cause chemical changes in Portland cement, leading to loss of strength, as well as attacking the steel reinforcement present in most concrete. The ten-storey Queen Elizabeth hospital in Kota Kinabalu contained a high percentage of chloride causing early failure. | 1 | Applied and Interdisciplinary Chemistry |
Periodic copolymers have units arranged in a repeating sequence. For two monomers A and B, for example, they might form the repeated pattern (A-B-A-B-B-A-A-A-A-B-B-B). | 0 | Theoretical and Fundamental Chemistry |
There are several COF single crystals synthesized to date. There are a variety of techniques employed to improve crystallinity of COFs. The use of modulators, monofunctional version of precursors, serve to slow the COF formation to allow for more favorable balance between kinetic and thermodynamic control, hereby enabling crystalline growth. This was employed by Yaghi and coworkers for 3D imine-based COFs (COF-300, COF 303, LZU-79, and LZU-111). However, the vast majority of COFs are not able to crystallize into single crystals but instead are insoluble powders. The improvement of crystallinity of these polycrystalline materials can be improved through tuning the reversibility of the linkage formation to allow for corrective particle growth and self-healing of defects that arise during COF formation. | 0 | Theoretical and Fundamental Chemistry |
Nitrogen-15, or N, is often used in agricultural and medical research, for example in the Meselson–Stahl experiment to establish the nature of DNA replication. An extension of this research resulted in development of DNA-based stable-isotope probing, which allows examination of links between metabolic function and taxonomic identity of microorganisms in the environment, without the need for culture isolation. Proteins can be isotopically labelled by cultivating them in a medium containing N as the only source of nitrogen, e.g., in quantitative proteomics such as SILAC.
Nitrogen-15 is extensively used to trace mineral nitrogen compounds (particularly fertilizers) in the environment. When combined with the use of other isotopic labels, N is also a very important tracer for describing the fate of nitrogenous organic pollutants. Nitrogen-15 tracing is an important method used in biogeochemistry.
The ratio of stable nitrogen isotopes, N/N or δN, tends to increase with trophic level, such that herbivores have higher nitrogen isotope values than plants, and carnivores have higher nitrogen isotope values than herbivores. Depending on the tissue being examined, there tends to be an increase of 3-4 parts per thousand with each increase in trophic level. The tissues and hair of vegans therefore contain significantly lower δN than the bodies of people who eat mostly meat. Similarly, a terrestrial diet produces a different signature than a marine-based diet. Isotopic analysis of hair is an important source of information for archaeologists, providing clues about the ancient diets and differing cultural attitudes to food sources.
A number of other environmental and physiological factors can influence the nitrogen isotopic composition at the base of the food web (i.e. in plants) or at the level of individual animals. For example, in arid regions, the nitrogen cycle tends to be more open and prone to the loss of N, increasing δN in soils and plants. This leads to relatively high δN values in plants and animals in hot and arid ecosystems relative to cooler and moister ecosystems. Furthermore, elevated δN have been linked to the preferential excretion of 14N and reutilization of already enriched 15N tissues in the body under prolonged water stress conditions or insufficient protein intake.
δN also provides a diagnostic tool in planetary science as the ratio exhibited in atmospheres and surface materials "is closely tied to the conditions under which materials form". | 0 | Theoretical and Fundamental Chemistry |
Debye forces, or dipole–induced dipole interactions, can also play a role in dispersive adhesion. These come about when a nonpolar molecule becomes temporarily polarized due to interaction with a nearby polar molecule. This "induced dipole" in the nonpolar molecule then is attracted to the permanent dipole, yielding a Debye attraction. | 0 | Theoretical and Fundamental Chemistry |
EPA supported the city of Emeryville, California in the development of "Stormwater Guidelines for Green, Dense Redevelopment." Emeryville, which is a suburb of San Francisco, began in the 1990s reclaiming, remediating and redeveloping the many brownfields within its borders. These efforts sparked a successful economic rebound. The city did not stop there, and decided in the 2000s to harness the redevelopment progress for even better environmental outcomes, in particular that related to stormwater runoff, by requiring in 2005 the use of on-site GI practices in all new private development projects. The city faced several challenges, including a high water table, tidal flows, clay soils, contaminated soil and water, and few absorbent natural areas among the primarily impervious, paved parcels of existing and redeveloped industrial sites. The guidelines, and an accompanying spreadsheet model, were developed to make as much use of redevelopment sites as possible for handling stormwater. The main strategies fell into several categories:
* Reducing the need, space and stormwater impact of motor vehicle parking by way of increased densities, height limits and floor area ratios; shared, stacked, indoor and unbundled automobile parking; making the best use of on-street parking and pricing strategies; car-sharing; free citywide mass transit; requiring one secure indoor bicycle parking space per bedroom and better bicycle and pedestrian roadway infrastructure.
* Sustainable landscape design features, such as tree preservation and minimum rootable soil volumes for new tree planting, use of structural soils, suspended paving systems, bioretention and biofiltration strategies and requiring the use of the holistic practices of Bay-Friendly Landscaping.
* Water storage and harvesting through cisterns and rooftop containers.
* Other strategies to handle or infiltrate water on development and redevelopment sites. | 1 | Applied and Interdisciplinary Chemistry |
Zero- to ultralow-field (ZULF) NMR is the acquisition of nuclear magnetic resonance (NMR) spectra of chemicals with magnetically active nuclei (spins 1/2 and greater) in an environment carefully screened from magnetic fields (including from the Earth's field). ZULF NMR experiments typically involve the use of passive or active shielding to attenuate Earth’s magnetic field. This is in contrast to the majority of NMR experiments which are performed in high magnetic fields provided by superconducting magnets. In ZULF experiments the dominant interactions are nuclear spin-spin couplings, and the coupling between spins and the external magnetic field is a perturbation to this. There are a number of advantages to operating in this regime: magnetic-susceptibility-induced line broadening is attenuated which reduces inhomogeneous broadening of the spectral lines for samples in heterogeneous environments. Another advantage is that the low frequency signals readily pass through conductive materials such as metals due to the increased skin depth; this is not the case for high-field NMR for which the sample containers are usually made of glass, quartz or ceramic.
High-field NMR employs inductive detectors to pick up the radiofrequency signals, but this would be inefficient in ZULF NMR experiments since the signal frequencies are typically much lower (on the order of hertz to kilohertz). The development of highly sensitive magnetic sensors in the early 2000s including SQUIDs, magnetoresistive sensors, and SERF atomic magnetometers made it possible to detect NMR signals directly in the ZULF regime. Previous ZULF NMR experiments relied on indirect detection where the sample had to be shuttled from the shielded ZULF environment into a high magnetic field for detection with a conventional inductive pick-up coil. One successful implementation was using atomic magnetometers at zero magnetic field working with rubidium vapor cells to detect zero-field NMR.
Without a large magnetic field to induce nuclear spin polarization, the nuclear spins must be polarized externally using hyperpolarization techniques. This can be as simple as polarizing the spins in a magnetic field followed by shuttling to the ZULF region for signal acquisition, and alternative chemistry-based hyperpolarization techniques can also be used.
It is sometimes but inaccurately referred to as nuclear quadrupole resonance (NQR). | 0 | Theoretical and Fundamental Chemistry |
The beginning of carbochemistry goes back to the 16th century. At that time, large quantities of charcoal were needed for the smelting of iron ores. Since the production of charcoal required large amounts of slowly-regenerating wood, the use of coal was studied. The use of pure coal was difficult because of the amount of liquid and solid by-products that were generated. In order to improve the handling the coal was initially treated as wood in kilns to produce coke.
Around 1684, John Clayton discovered that coal gas generated from coal was combustible. He described his discovery in the Philosophical Transactions of the Royal Society. | 1 | Applied and Interdisciplinary Chemistry |
Two mechanisms of fractionation occur that alter sulfur stable isotope ratios: kinetic effects, especially due to the metabolism of sulfate-reducing bacteria, and isotope exchange reactions that occur between sulfide phases based on temperature. With VCDT as the reference standard, natural δS value variations have been recorded between -72‰ and +147‰.
The presence of sulfate-reducing bacteria, which reduce sulfate () to hydrogen sulfide (HS), has played a significant role in the oceanic δS value throughout the earth's history. Sulfate-reducing bacteria metabolize S more readily than S, resulting in an increase in the value of the δS in the remaining sulfate in the seawater. Archean pyrite found in barite in the Warrawoona Group, Western Australia, with sulfur fractionations as great as 21.1‰ hint at the presence of sulfate-reducers as early as .
It is now better known that the degree of isotope fractionation during microbial sulfate reduction depends on the cell-specific sulfate reduction rate of the sulfate-reducing microorganism. The relative extent of sulfur isotope fractionating activities, including sulfate reduction, sulfide reoxidation and disproportionation, determines the isotopic compositions of the minerals or fluid measured. Other than microbial activities and environmental conditions, isotopic compositions also change due to diffusion, accumulation and mixing after burial.
The δS value, recorded by sulfate in marine evaporites, can be used to chart the sulfur cycle throughout earths history. The Great Oxygenation Event around altered the sulfur cycle radically, as increased atmospheric oxygen permitted an increase in the mechanisms that could fractionate sulfur isotopes, leading to an increase in the δS value from ~0‰ pre-oxygenation. Approximately , the δS values in seawater sulfates began to vary more and those in sedimentary sulfates grew more negative. Researchers have interpreted this excursion as indicative of an increase in water column oxygenation with continued periods of anoxia in the deepest waters. Modern seawater sulfate δS values are consistently 21.0 ± 0.2‰ across the worlds oceans, while sedimentary sulfides vary widely. Seawater sulfate δS and δO values exhibit similar trends not seen in sedimentary sulfide minerals. | 0 | Theoretical and Fundamental Chemistry |
SEC is used primarily for the analysis of large molecules such as proteins or polymers. SEC works by trapping smaller molecules in the pores of the adsorbent ("stationary phase"). This process is usually performed within a column, which typically consists of a hollow tube tightly packed with micron-scale polymer beads containing pores of different sizes. These pores may be depressions on the surface or channels through the bead. As the solution travels down the column some particles enter into the pores. Larger particles cannot enter into as many pores. The larger the particles, the faster the elution. The larger molecules simply pass by the pores because those molecules are too large to enter the pores. Larger molecules therefore flow through the column more quickly than smaller molecules, that is, the smaller the molecule, the longer the retention time.
One requirement for SEC is that the analyte does not interact with the surface of the stationary phases, with differences in elution time between analytes ideally being based solely on the solute volume the analytes can enter, rather than chemical or electrostatic interactions with the stationary phases. Thus, a small molecule that can penetrate every region of the stationary phase pore system can enter a total volume equal to the sum of the entire pore volume and the interparticle volume. This small molecule elutes late (after the molecule has penetrated all of the pore- and interparticle volume—approximately 80% of the column volume). At the other extreme, a very large molecule that cannot penetrate any the smaller pores can enter only the interparticle volume (~35% of the column volume) and elutes earlier when this volume of mobile phase has passed through the column. The underlying principle of SEC is that particles of different sizes elute (filter) through a stationary phase at different rates. This results in the separation of a solution of particles based on size. Provided that all the particles are loaded simultaneously or near-simultaneously, particles of the same size should elute together.
However, as there are various measures of the size of a macromolecule (for instance, the radius of gyration and the hydrodynamic radius), a fundamental problem in the theory of SEC has been the choice of a proper molecular size parameter by which molecules of different kinds are separated. Experimentally, Benoit and co-workers found an excellent correlation between elution volume and a dynamically based molecular size, the hydrodynamic volume, for several different chain architecture and chemical compositions. The observed correlation based on the hydrodynamic volume became accepted as the basis of universal SEC calibration.
Still, the use of the hydrodynamic volume, a size based on dynamical properties, in the interpretation of SEC data is not fully understood. This is because SEC is typically run under low flow rate conditions where hydrodynamic factor should have little effect on the separation. In fact, both theory and computer simulations assume a thermodynamic separation principle: the separation process is determined by the equilibrium distribution (partitioning) of solute macromolecules between two phases: a dilute bulk solution phase located at the interstitial space and confined solution phases within the pores of column packing material. Based on this theory, it has been shown that the relevant size parameter to the partitioning of polymers in pores is the mean span dimension (mean maximal projection onto a line). Although this issue has not been fully resolved, it is likely that the mean span dimension and the hydrodynamic volume are strongly correlated.
Each size exclusion column has a range of molecular weights that can be separated. The exclusion limit defines the molecular weight at the upper end of the column working range and is where molecules are too large to get trapped in the stationary phase. The lower end of the range is defined by the permeation limit, which defines the molecular weight of a molecule that is small enough to penetrate all pores of the stationary phase. All molecules below this molecular mass are so small that they elute as a single band.
The filtered solution that is collected at the end is known as the eluate. The void volume includes any particles too large to enter the medium, and the solvent volume is known as the column volume.
Following are the materials which are commonly used for porous gel beads in size exclusion chromatography | 1 | Applied and Interdisciplinary Chemistry |
The M muscarinic receptors are located in the heart and lungs. In the heart, they act to slow the heart rate down below the normal baseline sinus rhythm, by slowing the speed of depolarization. In humans, under resting conditions, vagal activity dominates over sympathetic activity. Hence, inhibition of M receptors (e.g. by atropine) will cause a raise in heart rate. They also moderately reduce contractile forces of the atrial cardiac muscle, and reduce conduction velocity of the atrioventricular node (AV node). It also serves to slightly decrease the contractile forces of the ventricular muscle.
M muscarinic receptors act via a G type receptor, which causes a decrease in cAMP in the cell, inhibition of voltage-gated Ca channels, and increasing efflux of K, in general, leading to inhibitory-type effects. | 1 | Applied and Interdisciplinary Chemistry |
Electrophilic fluorinating reagents could in principle operate by electron transfer pathways or an S2 attack at fluorine. This distinction has not been decided. By using a charge-spin separated probe, it was possible to show that the electrophilic fluorination of stilbenes with Selectfluor proceeds through an SET/fluorine atom transfer mechanism.
In certain cases Selectfluor can transfer fluorine to alkyl radicals. | 0 | Theoretical and Fundamental Chemistry |
Lateral adhesion is the adhesion associated with sliding one object on a substrate such as sliding a drop on a surface. When the two objects are solids, either with or without a liquid between them, the lateral adhesion is described as friction. However, the behavior of lateral adhesion between a drop and a surface is tribologically very different from friction between solids, and the naturally adhesive contact between a flat surface and a liquid drop makes the lateral adhesion in this case, an individual field. Lateral adhesion can be measured using the centrifugal adhesion balance (CAB), which uses a combination of centrifugal and gravitational forces to decouple the normal and lateral forces in the problem. | 0 | Theoretical and Fundamental Chemistry |
Not all neutrons are emitted as a direct product of fission; some are instead due to the radioactive decay of some of the fission fragments. The neutrons that occur directly from fission are called "prompt neutrons", and the ones that are a result of radioactive decay of fission fragments are called "delayed neutrons". The fraction of neutrons that are delayed is called β, and this fraction is typically less than 1% of all the neutrons in the chain reaction.
The delayed neutrons allow a nuclear reactor to respond several orders of magnitude more slowly than just prompt neutrons would alone. Without delayed neutrons, changes in reaction rates in nuclear reactors would occur at speeds that are too fast for humans to control.
The region of supercriticality between k = 1 and k = 1/(1 − β) is known as delayed supercriticality (or delayed criticality). It is in this region that all nuclear power reactors operate. The region of supercriticality for k > 1/(1 − β) is known as prompt supercriticality (or prompt criticality), which is the region in which nuclear weapons operate.
The change in k needed to go from critical to prompt critical is defined as a dollar. | 0 | Theoretical and Fundamental Chemistry |
G-quadruplexes, also known as G4 DNA are secondary structures found in nucleic acids that are rich in guanine. These structures are normally located at the telomeres (the ends of the chromosomes). The G-quadruplex can either be parallel or antiparallel depending on the loop configuration, which is a component of the structure. If all the DNA strands run in the same direction, it is termed to be a parallel quadruplex, and is known as a strand-reversal/propeller, connecting adjacent parallel strands. If one or more of the DNA strands run in opposite direction, it is termed as an anti-parallel quadruplex, and can either be in a form of a lateral/edgewise, connecting adjacent anti-parallel strands, or a diagonal, joining two diagonally opposite strands. The structure of these G-quadruplexes can be determined by a cation. | 1 | Applied and Interdisciplinary Chemistry |
The Gross-Pitaevskii equation is a partial differential equation in space and time variables. Usually it does not have analytic solution and
different numerical methods, such as split-step
Crank-Nicolson
and Fourier spectral methods, are used for its solution. There are different Fortran and C programs for its solution for contact interaction
and long-range dipolar interaction which can be freely used. | 0 | Theoretical and Fundamental Chemistry |
By chemical modifications certain properties of polysaccharides can be improved. Various ligands can be covalently attached to their hydroxyl groups. Due to the covalent attachment of methyl-, hydroxyethyl- or carboxymethyl- groups on cellulose, for instance, high swelling properties in aqueous media can be introduced. Another example are thiolated polysaccharides ( see thiomers). Thiol groups are covalently attached to polysaccharides such as hyaluronic acid or chitosan. As thiolated polysaccharides can crosslink via disulfide bond formation, they form stable three-dimensional networks. Furthermore, they can bind to cysteine subunits of proteins via disulfide bonds. Because of these bonds polysaccharides can be covalently attached to endogenous proteins such as mucins or keratins. | 0 | Theoretical and Fundamental Chemistry |
The emission directly after the excitation is spectrally very broad, yet still centered in the vicinity of the strongest exciton resonance. As the carrier distribution relaxes and cools, the width of the PL peak decreases and the emission energy shifts to match the ground state of the exciton (such as an electron) for ideal samples without disorder. The PL spectrum approaches its quasi-steady-state shape defined by the distribution of electrons and holes. Increasing the excitation density will change the emission spectra. They are dominated by the excitonic ground state for low densities. Additional peaks from higher subband transitions appear as the carrier density or lattice temperature are increased as these states get more and more populated. Also, the width of the main PL peak increases significantly with rising excitation due to excitation-induced dephasing and the emission peak experiences a small shift in energy due to the Coulomb-renormalization and phase-filling.
In general, both exciton populations and plasma, uncorrelated electrons and holes, can act as sources for photoluminescence as described in the semiconductor-luminescence equations. Both yield very similar spectral features which are difficult to distinguish; their emission dynamics, however, vary significantly. The decay of excitons yields a single-exponential decay function since the probability of their radiative recombination does not depend on the carrier density. The probability of spontaneous emission for uncorrelated electrons and holes, is approximately proportional to the product of electron and hole populations eventually leading to a non-single-exponential decay described by a hyperbolic function. | 0 | Theoretical and Fundamental Chemistry |
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