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A proposed mechanism of ultrasensitivity, called allovalency, suggests that activity "derives from a high local concentration of interaction sites moving independently of each other"
Allovalency was first proposed when it was believed to occur in the pathway in which Sic1, is degraded in order for Cdk1-Clb (B-type cyclins) to allow entry into mitosis. Sic1 must be phosphorylated multiple times in order to be recognized and degraded by Cdc4 of the SCF Complex. Since Cdc4 only has one recognition site for these phosphorylated residues it was suggested that as the amount of phosphorylation increases, it exponentially increases the likelihood that Sic1 is recognized and degraded by Cdc4. This type of interaction was thought to be relatively immune to loss of any one site and easily tuned to any given threshold by adjusting the properties of individual sites. Assumptions for the allovalency mechanism were based on a general mathematical model that describes the interaction between a polyvalent disordered ligand and a single receptor site
It was later found that the ultrasensitivity in Cdk1 levels by degradation of Sic1 is in fact due to a positive feedback loop. | 1 | Applied and Interdisciplinary Chemistry |
PET scanning with the radiotracer [[Fluorodeoxyglucose (18F)|[F]fluorodeoxyglucose]] (FDG) is widely used in clinical oncology. FDG is a glucose analog that is taken up by glucose-using cells and phosphorylated by hexokinase (whose mitochondrial form is significantly elevated in rapidly growing malignant tumors). Metabolic trapping of the radioactive glucose molecule allows the PET scan to be utilized. The concentrations of imaged FDG tracer indicate tissue metabolic activity as it corresponds to the regional glucose uptake. FDG is used to explore the possibility of cancer spreading to other body sites (cancer metastasis). These FDG PET scans for detecting cancer metastasis are the most common in standard medical care (representing 90% of current scans). The same tracer may also be used for the diagnosis of types of dementia. Less often, other radioactive tracers, usually but not always labelled with fluorine-18 (F), are used to image the tissue concentration of different kinds of molecules of interest inside the body.
A typical dose of FDG used in an oncological scan has an effective radiation dose of 7.6 mSv. Because the hydroxy group that is replaced by fluorine-18 to generate FDG is required for the next step in glucose metabolism in all cells, no further reactions occur in FDG. Furthermore, most tissues (with the notable exception of liver and kidneys) cannot remove the phosphate added by hexokinase. This means that FDG is trapped in any cell that takes it up until it decays, since phosphorylated sugars, due to their ionic charge, cannot exit from the cell. This results in intense radiolabeling of tissues with high glucose uptake, such as the normal brain, liver, kidneys, and most cancers, which have a higher glucose uptake than most normal tissue due to the Warburg effect. As a result, FDG-PET can be used for diagnosis, staging, and monitoring treatment of cancers, particularly in Hodgkin lymphoma, non-Hodgkin lymphoma, and lung cancer.
A 2020 review of research on the use of PET for Hodgkin lymphoma found evidence that negative findings in interim PET scans are linked to higher overall survival and progression-free survival; however, the certainty of the available evidence was moderate for survival, and very low for progression-free survival.
A few other isotopes and radiotracers are slowly being introduced into oncology for specific purposes. For example, C-labelled metomidate (11C-metomidate) has been used to detect tumors of adrenocortical origin. Also, Fluorodopa (FDOPA) PET/CT (also called F-18-DOPA PET/CT) has proven to be a more sensitive alternative to finding and also localizing pheochromocytoma than the Iobenguane (MIBG) scan. | 1 | Applied and Interdisciplinary Chemistry |
Hellers test is a chemical test that shows that strong acids cause the denaturation of precipitated proteins. Concentrated nitric acid is added to a protein solution from the side of the test tube to form two layers. A white ring appears between the two layers if the test is positive. Hellers test is commonly used to test for the presence of proteins in urine. This test was discovered by the Austrian Chemist, Johann Florian Heller (1813-1871). | 0 | Theoretical and Fundamental Chemistry |
Again the geometry is widespread, particularly so for complexes where the metal has d or d configuration. Illustrative examples include tetrakis(triphenylphosphine)palladium(0) (), nickel carbonyl (), and titanium tetrachloride (). Many complexes with incompletely filled d-shells are often tetrahedral, e.g. the tetrahalides of iron(II), cobalt(II), and nickel(II). | 0 | Theoretical and Fundamental Chemistry |
mTOR promotes the protein synthesis required for synaptic plasticity. Studies in cell cultures and hippocampal slices indicate that mTOR inhibition reduces long-term potentiation. mTOR activation can protect against certain neurodegeneration associated with certain disease conditions. On the other hand, promotion of autophagy by mTOR inhibition may reduce cognitive decline associated with neurodegeneration.
Moderate reduction of mTOR activity by 25-30% has been shown to improve brain function, suggesting that the relation between mTOR and cognition is optimized with intermediate doses (2.24 mg/kg/day in mice, human equivalent about 0.19 mg/kg/day), where very high or very low doses impair cognition. Reduction of the inflammatory cytokine Interleukin 1 beta (IL-1β) in mice by mTOR inhibition (with rapamycin in doses of 20 mg/kg/day, human equivalent about 1.6 mg/kg/day) has been shown to enhance learning and memory. Although IL-1β is required for memory, IL-1β normally increases with age, impairing cognitive function. | 1 | Applied and Interdisciplinary Chemistry |
In 2016, some 90 organizations, representing over US$2.5 trillion of purchasing power, requested that their suppliers disclose information on how they are approaching climate and water risks and opportunities. Data was gathered from over 4,000 suppliers worldwide, who reported over US$12 billion worth of savings from emission reduction activities. | 1 | Applied and Interdisciplinary Chemistry |
Downs' process is an electrochemical method for the commercial preparation of metallic sodium, in which molten NaCl is electrolyzed in a special apparatus called the Downs cell. The Downs cell was invented in 1923 (patented: 1924) by the American chemist James Cloyd Downs (1885–1957). | 1 | Applied and Interdisciplinary Chemistry |
Fairings can be fitted to a structure to streamline the flow past the structure, such as on an aircraft wing.
Tall metal smokestacks or other tubular structures such as antenna masts or tethered cables can be fitted with an external corkscrew fin (a strake) to deliberately introduce turbulence, so the load is less variable and resonant load frequencies have negligible amplitudes. The effectiveness of helical strakes for reducing vortex induced vibration was discovered in 1957 by Christopher Scruton and D. E. J. Walshe at the National Physics Laboratory in Great Britain. They are therefore often described as Scruton strakes. For maximum effectiveness in suppression of vortices caused by air flow, each fin or strake should have a height of about 10 percent of the cylinder diameter. The pitch of each fin should be approximately 5 times the cylinder diameter.
A tuned mass damper can be used to mitigate vortex shedding in stacks and chimneys.
A Stockbridge damper is used to mitigate aeolian vibrations caused by vortex shedding on overhead power lines. | 1 | Applied and Interdisciplinary Chemistry |
In the IUPAC Nomenclature system, ethers are named using the general formula "alkoxyalkane", for example CH–CH–O–CH is methoxyethane. If the ether is part of a more-complex molecule, it is described as an alkoxy substituent, so –OCH would be considered a "methoxy-" group. The simpler alkyl radical is written in front, so CH–O–CHCH would be given as methoxy(CHO)ethane(CHCH). | 0 | Theoretical and Fundamental Chemistry |
It has been studied in AIDS-related Kaposis sarcoma, West Nile virus, and to inactivate Staphylococcus aureus', and HIV-1. Phenothiazine dyes and light have been known to have virucidal properties for over 70 years. | 0 | Theoretical and Fundamental Chemistry |
In most laboratory situations, the difference in behaviour between a real gas and an ideal gas is dependent only on the pressure and the temperature, not on the presence of any other gases. At a given temperature, the "effective" pressure of a gas is given by its fugacity : this may be higher or lower than its mechanical pressure. By historical convention, fugacities have the dimension of pressure, so the dimensionless activity is given by:
where is the dimensionless fugacity coefficient of the species, is its mole fraction in the gaseous mixture ( for a pure gas) and is the total pressure. The value is the standard pressure: it may be equal to 1 atm (101.325 kPa) or 1 bar (100 kPa) depending on the source of data, and should always be quoted. | 0 | Theoretical and Fundamental Chemistry |
Vaginal transplantation is procedure whereby donated or laboratory-grown vagina tissue is used to create a neovagina. It is most often used in women who have vaginal aplasia (the congenital absence of a vagina). | 1 | Applied and Interdisciplinary Chemistry |
Dynamic electrophoretic mobility is a parameter that determines intensity of electroacoustic phenomena, such as Colloid Vibration Current and Electric Sonic Amplitude in colloids. It is similar to electrophoretic mobility, but at high frequency, on a scale of megahertz. Usual electrophoretic mobility is the low frequency limit of the dynamic electrophoretic mobility. | 0 | Theoretical and Fundamental Chemistry |
Biomedical Materials is a peer-reviewed medical journal that covers research on tissue engineering and regenerative medicine. The editors-in-chief are Myron Spector (Harvard Medical School and VA Boston Healthcare System) and Joyce Wong (Boston University). | 1 | Applied and Interdisciplinary Chemistry |
This puckering leads to a total of 38 distinct basic pyranose conformations: 2 chairs, 6 boats, 6 skew-boats, 12 half-chairs, and 12 envelopes.
These conformers can interconvert with one another; however, each form may have very different relative energy, so a significant barrier to interconversion may be present. The energy of these conformations can be calculated from quantum mechanics; an example of possible glucopyranose interconversions is given.
The conformations of the pyranose ring are superficially similar to that of the cyclohexane ring. However, the specific nomenclature of pyranoses includes reference to the ring oxygen, and the presence of hydroxyls on the ring have distinct effects on its conformational preference. There are also conformational and stereochemical effects specific to the pyranose ring. | 0 | Theoretical and Fundamental Chemistry |
In some versions of the Schilling test, B can be given both with and without intrinsic factor at the same time, using different cobalt radioisotopes Co and Co, which have different radiation signatures, in order to differentiate the two forms of B. This is performed with the Dicopac kitset. This allows for only a single radioactive urine collection. | 1 | Applied and Interdisciplinary Chemistry |
Sclerotiorin is an antimicrobial Penicillium frequentans isolate. Sclerotiorin is an aldose reductase inhibitor (IC=0.4 μM) as well as a reversible lipoxygenase inhibitor (IC=4.2 μM). | 0 | Theoretical and Fundamental Chemistry |
Blue billy is a chemical or mineral deposit often encountered in contaminated land.
The name is a reference to its distinctive bright blue colour, which can make it immediately obvious in other mud or soil. Chemically it is a form of Prussian blue. Although several chemical industry processes could produce it, it is particularly associated with coal gasification and older town gasworks. It has been recognised as a problem effluent and land contaminant since the early industrial period and the first gasworks at the start of the 19th century.
As a visible proof of contamination, blue billy is an important signifier in contaminated land remediation projects and its discovery, especially if undisclosed, may be a cause of contract disputes. | 1 | Applied and Interdisciplinary Chemistry |
The preferential alignment is a criterion of an orientation of a molecule or atom. The preferential alignment can be related to the formation of the crystal structure of an amorphous structure.
For a polymer material with liquid crystals, the liquid crystals are molecules shaped like rigid rods. Just as logs being floated down a river tend to travel parallel to the direction of the river, liquid crystals have a preferential alignment with each other. At high temperatures, this alignment is disrupted and the material is said to be in the isotropic state. At lower temperatures, the alignment will take place and the liquid crystals are said to be in the pneumatic state [Hoong.C.C]. | 0 | Theoretical and Fundamental Chemistry |
Some POMs exhibit unusual magnetic properties, which has prompted visions of many applications. One example is storage devices called qubits. non-volatile (permanent) storage components, also known as flash memory devices. | 0 | Theoretical and Fundamental Chemistry |
Residue storage methods have changed substantially since the original plants were built. The practice in early years was to pump the slurry, at a concentration of about 20% solids, into lagoons or ponds sometimes created in former bauxite mines or depleted quarries. In other cases, impoundments were constructed with dams or levees, while for some operations valleys were dammed and the residue deposited in these holding areas.
It was once common practice for the red mud to be discharged into rivers, estuaries, or the sea via pipelines or barges; in other instances the residue was shipped out to sea and disposed of in deep ocean trenches many kilometres offshore. From 2016, all disposal into the sea, estuaries and rivers was stopped.
As residue storage space ran out and concern increased over wet storage, since the mid-1980s dry stacking has been increasingly adopted. In this method, residues are thickened to a high density slurry (48–55% solids or higher), and then deposited in a way that it consolidates and dries.
An increasingly popular treatment process is filtration whereby a filter cake (typically resulting in 23–27% moisture) is produced. This cake can be washed with either water or steam to reduce alkalinity before being transported and stored as a semi-dried material. Residue produced in this form is ideal for reuse as it has lower alkalinity, is cheaper to transport, and is easier to handle and process. Another option for ensuring safe storage is to use amphirols to dewater the material once deposited and then conditioned using farming equipment such as harrows to accelerate carbonation and thereby reduce the alkalinity. Bauxite residue produced after press filtration and 'conditioning as described above are classified as non-hazardous under the EU Waste Framework Directive.
In 2013 Vedanta Aluminium, Ltd. commissioned a red mud powder-producing unit at its Lanjigarh refinery in Odisha, India, describing it as the first of its kind in the alumina industry, tackling major environmental hazards. | 1 | Applied and Interdisciplinary Chemistry |
Long intergenic Non-coding RNA (LincRNA) is defined as RNA transcripts that are longer than 200 nucleotides. These RNAs must not have open reading frames that encode proteins. The term “intergenic” refers to the identification of these transcripts from regions of the genome that do not contain protein-encoding genes. LncRNAs also contain promoter - or enhancer-associated RNAs that are gene proximal and can be either in the sense or antisense orientation. | 1 | Applied and Interdisciplinary Chemistry |
Bulat is a type of steel alloy known in Russia from medieval times; it was regularly mentioned in Russian legends as the material of choice for cold steel. The name булат is a Russian transliteration of the Persian word fulad, meaning steel. This type of steel was used by the armies of nomadic peoples. Bulat steel was the main type of steel used for swords in the armies of Genghis Khan. Bulat Steel is generally agreed to be a Russian name for wootz steel, the production method of which has been lost for centuries, and the bulat steel used today makes use of a more recently developed technique. | 1 | Applied and Interdisciplinary Chemistry |
A coating is a covering that is applied to the surface of an object, or substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. powder coatings.
Paints and lacquers are coatings that mostly have dual uses, which are protecting the substrate and being decorative, although some artists paints are only for decoration, and the paint on large industrial pipes is for identification (e.g. blue for process water, red for fire-fighting control) in addition to preventing corrosion. Along with corrosion resistance, functional coatings may also be applied to change the surface properties of the substrate, such as adhesion, wettability, or wear resistance. In other cases the coating adds a completely new property, such as a magnetic response or electrical conductivity (as in semiconductor device fabrication, where the substrate is a wafer), and forms an essential part of the finished product.
A major consideration for most coating processes is controlling coating thickness. Methods of achieving this range from a simple brush to expensive precision machinery in the electronics industry. Limiting coating area is crucial in some applications, such as printing.
"roll-to-roll" or "web-based" coating is the process of applying a thin film of functional material to a substrate on a roll, such as paper, fabric, film, foil, or sheet stock. | 1 | Applied and Interdisciplinary Chemistry |
Examples of amphiphilic compounds are the salts of fatty acids, phospholipids. Many simple amphiphiles are used as detergents. A mixture of soap and water is an everyday example of a lyotropic liquid crystal.
Biological structures such as fibrous proteins showings relatively long and well-defined hydrophobic and hydrophilic ‘‘blocks’’ of aminoacids can also show lyotropic liquid crystalline behaviour. | 0 | Theoretical and Fundamental Chemistry |
ATSDR is starting a new registry for people with amyotrophic lateral sclerosis (also known as ALS or Lou Gehrig's Disease). President George W. Bush signed the ALS Registry Act, which provided for establishment of the registry, on October 8, 2008. It is hoped that the registry will provide information on the prevalence of ALS and lead to a better understanding of factors that may be associated with the disease. The agency began registering people for the registry on October 20, 2010. | 1 | Applied and Interdisciplinary Chemistry |
In its earliest forms, most hardware was simple and hand-made – usually of readily available materials such as wood or leather. A patch of leather spanning between the stile and jamb and fastened with wooden pegs served to hinge a door or shutter. Hand-carved wooden hinges and pintles, slide bolts and lift-latches were whittled from a variety of woods.
The earliest examples of iron hardware were sponsored by the nobility. Iron itself was expensive and a valued resource for any kingdom and had many other more valuable uses in weaponry and tools.
In the post-Renaissance period industrial advances provided more iron and the emerging merchant/tradesman classes had money to purchase hardware for their homes and warehouses. Examples of hardware excavated from the Jamestown and Plymouth colonies of the 17th century were very ornate in design – typical of that being produced in England at the time.
In Colonial America, hardware was made in England and imported to the colonies. It was illegal for the colonials to produce manufactured goods. America sold iron and charcoal to the British, who used those raw materials and their resident labor force to produce hardware which was then sold back to the captive market in the colonies. Virtually all of the early hardware in New York, Philadelphia, Annapolis, Alexandria, Key West, or anyplace else where British ships could berth, was made in England. Away from the ports and cities where British authority was centered, many locally-made examples of early hardware can be found. Examples of German, French, and Dutch hardware remain in the inland river valleys – the homelands of the early settlers. English hardware, however, was the overwhelming standard in colonial America and set the pattern for all that evolved.
Virtually all of the shutters in colonial times were hung with strap hinges – following the examples in Britain. Strap hinges were strong and secure. The frames of windows were hewn from a single heavy piece of wood into which a heavy pintle could be driven. The rails of the shutter were often six or eight inches high and provided room to position the strap hinge across most of the width of the shutter. The hinges were fastened to the shutters with rivets or nails driven through and clinched on the inside of the closed shutter. Locks of the period followed the form of the strap hinges. The rolled barrel was replaced by a pin of about " in diameter and twice the length of the thickness of the shutter mounted perpendicular to the face of the lock. The lock would be nailed or riveted on the lock rail of one shutter with the pin positioned about two inches beyond the edge of the shutter. The opposite shutter would be drilled through with a hole to accept the pin protruding from the lock.
To close and secure the shutter: from the inside close the shutter with the hole then close the shutter with the lock. The lock pin passes through the hole and the user drops a simple nail-like key into the hole in the lock pin. The shutter is virtually impregnable from the exterior.
Tie-backs of the Colonial era were mostly of English origin and many were of the "Rattail" style. Variations are noted as different British manufacturers vied to produce a less expensive product. Inland, where local smiths were producing hardware on their own, a wide range of patterns have been noted. | 1 | Applied and Interdisciplinary Chemistry |
Some organic materials pass through intermediate states between solid and liquid; these states are called mesophases. Attention has been directed to mesophases because they enable display devices and have become commercially important through the so-called liquid-crystal technology. Phase diagrams are used to describe the occurrence of mesophases. | 0 | Theoretical and Fundamental Chemistry |
He subsequently joined the MRC Laboratory of Molecular Biology (LMB) in Cambridge to pursue post-doctoral research with Jan Löwe using cryo-EM to study proteins within bacterial cells. After his post-doctoral appointment concluded, he was recruited to the Sir William Dunn School of Pathology, University of Oxford as a Wellcome Trust and Royal Society Sir Henry Dale Fellow. After obtaining tenure at Oxford, he moved back to the LMB as a programme leader in 2022. His research investigates how bacteria and archaea use their surface molecules to form multicellular communities. For instance, during human infections bacteria form biofilms that help them evade antibiotics. The group also use electron tomography. | 1 | Applied and Interdisciplinary Chemistry |
There are two principal classes of fatty acid synthases.
* Type I systems utilise a single large, multifunctional polypeptide and are common to both animals and fungi (although the structural arrangement of fungal and animal syntheses differ). A Type I fatty acid synthase system is also found in the CMN group of bacteria (corynebacteria, mycobacteria, and nocardia). In these bacteria, the FAS I system produces palmitic acid, and cooperates with the FAS II system to produce a greater diversity of lipid products.
* Type II is found in archaea, bacteria and plant plastids, and is characterized by the use of discrete, monofunctional enzymes for fatty acid synthesis. Inhibitors of this pathway (FASII) are being investigated as possible antibiotics.
The mechanism of FAS I and FAS II elongation and reduction is the same, as the domains of the FAS II enzymes are largely homologous to their domain counterparts in FAS I multienzyme polypeptides. However, the differences in the organization of the enzymes - integrated in FAS I, discrete in FAS II - gives rise to many important biochemical differences.
The evolutionary history of fatty acid synthases are very much intertwined with that of polyketide synthases (PKS). Polyketide synthases use a similar mechanism and homologous domains to produce secondary metabolite lipids. Furthermore, polyketide synthases also exhibit a Type I and Type II organization. FAS I in animals is thought to have arisen through modification of PKS I in fungi, whereas FAS I in fungi and the CMN group of bacteria seem to have arisen separately through the fusion of FAS II genes. | 1 | Applied and Interdisciplinary Chemistry |
In 2000, EPA drafted plans to phase out the use of MTBE nationwide over four years. Some states enacted MTBE prohibitions without waiting for federal restrictions. California banned MTBE as a gasoline additive in 2002. The State of New York banned the use of MTBE as a "fuel additive", effective in 2004. However, MTBE is still legal in the state for other industrial uses.
The Energy Policy Act of 2005, as approved by the U.S. House of Representatives, did not include a provision for shielding MTBE manufacturers from water contamination lawsuits. This provision was first proposed in 2003 and had been thought by some to be a priority of Tom DeLay and Rep. Joe Barton, then chairman of the Energy and Commerce Committee. This bill did include a provision that gave MTBE makers, including some major oil companies, $2 billion in transition assistance while MTBE was phased out over the following nine years. Due to opposition in the Senate, the conference report dropped all MTBE provisions. The final bill was signed into law by President George W. Bush. The lack of MTBE liability protection is resulting in a switchover to the use of ethanol as a gasoline additive. | 1 | Applied and Interdisciplinary Chemistry |
An electric field pointing from left to right, for example, tends to pull nuclei to the right and electrons to the left. In another way of viewing it, if an electronic state has its electron disproportionately to the left, its energy is lowered, while if it has the electron disproportionately to the right, its energy is raised.
Other things being equal, the effect of the electric field is greater for outer electron shells, because the electron is more distant from the nucleus, so it travels farther left and farther right.
The Stark effect can lead to splitting of degenerate energy levels. For example, in the Bohr model, an electron has the same energy whether it is in the 2s state or any of the 2p states. However, in an electric field, there will be hybrid orbitals (also called quantum superpositions) of the 2s and 2p states where the electron tends to be to the left, which will acquire a lower energy, and other hybrid orbitals where the electron tends to be to the right, which will acquire a higher energy. Therefore, the formerly degenerate energy levels will split into slightly lower and slightly higher energy levels. | 0 | Theoretical and Fundamental Chemistry |
The National Science Foundation (NSF) funded Wiki project Open Wetware (OWW) provides a resource for reagent, project and laboratory notebook sharing.
A somewhat related NSF consortium Synthetic Biology Engineering Research Center (SynBERC) constructs and distributes wetware. | 1 | Applied and Interdisciplinary Chemistry |
VOCs are also found in hospital and health care environments. In these settings, these chemicals are widely used for cleaning, disinfection, and hygiene of the different areas. Thus, health professionals such as nurses, doctors, sanitation staff, etc., may present with adverse health effects such as asthma; however, further evaluation is required to determine the exact levels and determinants that influence the exposure to these compounds.
Studies have shown that the concentration levels of different VOCs such as halogenated and aromatic hydrocarbons differ substantially between areas of the same hospital. However, one of these studies reported that ethanol, isopropanol, ether, and acetone were the main compounds in the interior of the site. Following the same line, in a study conducted in the United States, it was established that nursing assistants are the most exposed to compounds such as ethanol, while medical equipment preparers are most exposed to 2-propanol.
In relation to exposure to VOCs by cleaning and hygiene personnel, a study conducted in 4 hospitals in the United States established that sterilization and disinfection workers are linked to exposures to d-limonene and 2-propanol, while those responsible for cleaning with chlorine-containing products are more likely to have higher levels of exposure to α-pinene and chloroform. Those who perform floor and other surface cleaning tasks (e.g., floor waxing) and who use quaternary ammonium, alcohol, and chlorine-based products are associated with a higher VOC exposure than the two previous groups, that is, they are particularly linked to exposure to acetone, chloroform, α-pinene, 2-propanol or d-limonene.
Other healthcare environments such as nursing and age care homes have been rarely a subject of study, even though the elderly and vulnerable populations may spend considerable time in these indoor settings where they might be exposed to VOCs, derived from the common use of cleaning agents, sprays and fresheners. In a study conducted in France, a team of researchers developed an online questionnaire for different social and age care facilities, asking about cleaning practices, products used, and the frequency of these activities. As a result, more than 200 chemicals were identified, of which 41 are known to have adverse health effects, 37 of them being VOCs. The health effects include skin sensitization, reproductive and organ-specific toxicity, carcinogenicity, mutagenicity, and endocrine-disrupting properties. Furthermore, in another study carried out in the same European country, it was found that there is a significant association between breathlessness in the elderly population and elevated exposure to VOCs such as toluene and o-xylene, unlike the remainder of the population. | 0 | Theoretical and Fundamental Chemistry |
Consider a system of particles in a volume (for an average number density ) and at a temperature (let us also define ; is Boltzmann’s constant). The particle coordinates are , with . The potential energy due to the interaction between particles is and we do not consider the case of an externally applied field.
The appropriate averages are taken in the canonical ensemble , with the configurational integral, taken over all possible combinations of particle positions. The probability of an elementary configuration, namely finding particle 1 in , particle 2 in , etc. is given by
The total number of particles is huge, so that in itself is not very useful. However, one can also obtain the probability of a reduced configuration, where the positions of only particles are fixed, in , with no constraints on the remaining particles. To this end, one has to integrate () over the remaining coordinates :
If the particles are non-interacting, in the sense that the potential energy of each particle does not depend on any of the other particles, , then the partition function factorizes, and the probability of an elementary configuration decomposes with independent arguments to a product of single particle probabilities,
Note how for non-interacting particles the probability is symmetric in its arguments. This is not true in general, and the order in which the positions occupy the argument slots of matters. Given a set of positions, the way that the particles can occupy those positions is The probability that those positions ARE occupied is found by summing over all configurations in which a particle is at each of those locations. This can be done by taking every permutation, , in the symmetric group on objects, , to write . For fewer positions, we integrate over extraneous arguments, and include a correction factor to prevent overcounting,
In fact, for this special case every n-particle density is independent of coordinates, and can be computed explicitlywhere it is clear that the n-point correlation function is dimensionless. | 0 | Theoretical and Fundamental Chemistry |
It was discovered that bioluminescent snails are able to exercise a great deal of control over light emission, but the way in which they exercise control over it is still unknown. Phuphania have even been shown to be able to preserve their ability to produce light even after long periods of hibernation. It is currently unknown how these snails are able to maintain their ability to produce light for long periods of time, but theories have been proposed possibly relating it to the way certain fungi are able to maintain their bioluminescence. | 1 | Applied and Interdisciplinary Chemistry |
Commercial-grade fuming nitric acid contains 98% and has a density of 1.50 g/cm. This grade is often used in the explosives industry. It is not as volatile nor as corrosive as the anhydrous acid and has the approximate concentration of 21.4 M.
Red fuming nitric acid, or RFNA, contains substantial quantities of dissolved nitrogen dioxide () leaving the solution with a reddish-brown color. Due to the dissolved nitrogen dioxide, the density of red fuming nitric acid is lower at 1.490 g/cm.
An inhibited fuming nitric acid, either White Inhibited Fuming Nitric Acid (IWFNA), or Red Inhibited Fuming Nitric Acid (IRFNA), can be made by the addition of 0.6 to 0.7% hydrogen fluoride (HF). This fluoride is added for corrosion resistance in metal tanks. The fluoride creates a metal fluoride layer that protects the metal. | 0 | Theoretical and Fundamental Chemistry |
Since directing groups are ligands, their effectiveness correlates with their affinities for metals. Common functional groups such as ketones usually are only weak ligands and thus often are poor DGs. This problem is solved by the use of a transient directing group. Transient DGs reversibly convert weak DGs (e.g., ketones) into strong DG's (e.g., imines) via a Schiff base condensation. Subsequent to serving their role as DGs, the imine can hydrolyze, regenerating the ketone and amine. | 0 | Theoretical and Fundamental Chemistry |
The sodium diffuse series has wave numbers given by:
The sharp series has wave numbers given by:
when n tends to infinity the diffuse and sharp series end up with the same limit. | 0 | Theoretical and Fundamental Chemistry |
This category groups pages related to Internal ribosome entry sites (IRESs) of RNA. IRESs are a nucleotide sequence that directs translation initiation in the middle of a messenger RNA (mRNA) as opposed to the usual process where initiation occurs at the five-prime end. | 1 | Applied and Interdisciplinary Chemistry |
Polymer degradation by galvanic action was first described in the technical literature in 1990 by Michael C. Faudree, an employee at General Dynamics, Fort Worth Division. The phenomenon has been referred to as the "Faudree Effect", and can possibly be used as a sustainable process to degrade non-recyclable thermoset plastics, and also has had implications for preventing corrosion on aircraft for safety such as changes in design. When carbon-fiber-reinforced polymer is attached to a metal surface, the carbon fiber can act as a cathode if exposed to water or sufficient humidity, resulting in galvanic corrosion. This has been seen in engineering when carbon-fiber polymers have been used to reinforce weakened steel structures. Reactions have also been seen in aluminium and magnesium alloys, polymers affected include bismaleimides (BMI), and polyimides. The mechanism of degradation is believed to involve the electrochemical generation of hydroxide ions, which then cleave the amide bonds. | 0 | Theoretical and Fundamental Chemistry |
Putative genes can be identified by scanning a genome for regions likely to encode proteins, based on characteristics such as long open reading frames, transcriptional initiation sequences, and polyadenylation sites. A sequence identified as a putative gene must be confirmed by further evidence, such as similarity to cDNA or EST sequences from the same organism, similarity of the predicted protein sequence to known proteins, association with promoter sequences, or evidence that mutating the sequence produces an observable phenotype. | 1 | Applied and Interdisciplinary Chemistry |
E. coli is one of the most widely used expression hosts, and DNA is normally introduced in a plasmid expression vector. The techniques for overexpression in E. coli are well developed and work by increasing the number of copies of the gene or increasing the binding strength of the promoter region so assisting transcription.
For example, a DNA sequence for a protein of interest could be cloned or subcloned into a high copy-number plasmid containing the lac (often LacUV5) promoter, which is then transformed into the bacterium E. coli. Addition of IPTG (a lactose analog) activates the lac promoter and causes the bacteria to express the protein of interest.
E. coli strain BL21 and BL21(DE3) are two strains commonly used for protein production. As members of the B lineage, they lack lon and OmpT proteases, protecting the produced proteins from degradation. The DE3 prophage found in BL21(DE3) provides T7 RNA polymerase (driven by the LacUV5 promoter), allowing for vectors with the T7 promoter to be used instead. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics the Borda–Carnot equation is an empirical description of the mechanical energy losses of the fluid due to a (sudden) flow expansion. It describes how the total head reduces due to the losses. This is in contrast with Bernoulli's principle for dissipationless flow (without irreversible losses), where the total head is a constant along a streamline. The equation is named after Jean-Charles de Borda (1733–1799) and Lazare Carnot (1753–1823).
This equation is used both for open channel flow as well as in pipe flows. In parts of the flow where the irreversible energy losses are negligible, Bernoulli's principle can be used. | 1 | Applied and Interdisciplinary Chemistry |
According to a recent investigation by Wong, Liang, Kwon, Bai, Alper and Gropman, TGGE can be utilized to examine the mitochondrial DNA of an individual. According to these authors, TGGE was utilized to determine two novel mutations in the mitochondrial genome: "A 21-year-old woman who has been suspected of mitochondrial cytopathy, but negative for common mitochondrial DNA (mtDNA) point mutations and deletions, was screened for unknown mutations in the entire mitochondrial genome by temperature gradient gel electrophoresis". | 1 | Applied and Interdisciplinary Chemistry |
The role of vitamin A in the visual cycle is specifically related to the retinal compound. Retinol is converted by the enzyme RPE65 within the retinal pigment epithelium into 11-cis-retinal. Within the eye, 11-cis-retinal is bound to the protein opsin to form rhodopsin in rod cells and iodopsin in cone cells. As light enters the eye, the 11-cis-retinal is isomerized to the all-trans form. The all-trans-retinal dissociates from the opsin in a series of steps called photo-bleaching. This isomerization induces a nervous signal along the optic nerve to the visual center of the brain. After separating from opsin, the all-trans-retinal is recycled and converted back to the 11-cis-retinal form by a series of enzymatic reactions, which then completes the cycle by binding to opsin to reform rhodopsin in the retina. In addition, some of the all-trans-retinal may be converted to all-trans-retinol form and then transported with an interphotoreceptor retinol-binding protein to the retinal pigmented epithelial cells. Further esterification into all-trans-retinyl esters allow for storage of all-trans-retinol within the pigment epithelial cells to be reused when needed. It is for this reason that a deficiency in vitamin A will inhibit the reformation of rhodopsin, and will lead to one of the first symptoms, night blindness. | 1 | Applied and Interdisciplinary Chemistry |
A particular use of a stepwise constant is in the determination of stability constant values outside the normal range for a given method. For example, EDTA complexes of many metals are outside the range for the potentiometric method. The stability constants for those complexes were determined by competition with a weaker ligand.
:ML + L′ ML′ + L
The formation constant of [[Palladium(II) cyanide|[Pd(CN)]]] was determined by the competition method. | 0 | Theoretical and Fundamental Chemistry |
β-Hematin crystals are made of dimers of hematin molecules that are, in turn, joined together by hydrogen bonds to form larger structures. In these dimers, an iron-oxygen coordinate bond links the central iron of one hematin to the oxygen of the carboxylate side-chain of the adjacent hematin. These reciprocal iron–oxygen bonds are highly unusual and have not been observed in any other porphyrin dimer. β-Hematin can be either a cyclic dimer or a linear polymer, a polymeric form has never been found in hemozoin, disproving the widely held idea that hemozoin is produced by the enzyme heme-polymerase.
Hemozoin crystals have a distinct triclinic structure and are weakly magnetic. The difference between diamagnetic low-spin oxyhemoglobin and paramagnetic hemozoin can be used for isolation. They also exhibit optical dichroism, meaning they absorb light more strongly along their length than across their width, enabling the automated detection of malaria. Hemozoin is produced in a form that, under the action of an applied magnetic field, gives rise to an induced optical dichroism characteristic of the hemozoin concentration; and precise measurement of this induced dichroism (Magnetic circular dichroism) may be used to determine the level of malarial infection. | 1 | Applied and Interdisciplinary Chemistry |
There are seemingly two independent formulations of the third law of thermodynamics both originally were stated by Walther Nernst. The first formulation is known as the Nernst heat theorem, and can be phrased as:
*The entropy of any pure substance in thermodynamic equilibrium approaches zero as the temperature approaches zero.
The second formulation is dynamical, known as the unattainability principle:
*It is impossible by any procedure, no matter how idealized, to reduce any assembly to absolute zero temperature in a finite number of operations.
At steady state the second law of thermodynamics implies that the total entropy production is non-negative.
When the cold bath approaches the absolute zero temperature,
it is necessary to eliminate the entropy production divergence at the cold side
when , therefore
For the fulfillment of the second law depends on the entropy production of the other baths,
which should compensate for the negative entropy production of the cold bath.
The first formulation of the third law modifies this restriction.
Instead of the third law imposes ,
guaranteeing that at absolute zero the entropy production at the cold bath is zero: .
This requirement leads to the scaling condition of the heat current .
The second formulation, known as the unattainability principle can be rephrased as;
*No refrigerator can cool a system to absolute zero temperature at finite time.
The dynamics of the cooling process is governed by the equation
where is the heat capacity of the bath. Taking and with , we can quantify this formulation by evaluating the characteristic exponent of the cooling process,
This equation introduce the relation between the characteristic exponents and . When then the bath is cooled to zero temperature in a finite time, which implies a violation of the third law. It is apparent from the last equation, that the unattainability principle is more restrictive than the Nernst heat theorem. | 0 | Theoretical and Fundamental Chemistry |
There are three major wind patterns that lead to Ekman suction or pumping. The first are wind patterns that are parallel to the coastline. Due to the Coriolis effect, surface water moves at a 90° angle to the wind current. If the wind moves in a direction causing the water to be pulled away from the coast then Ekman suction will occur. On the other hand, if the wind is moving in such a way that surface waters move towards the shoreline then Ekman pumping will take place.
The second mechanism of wind currents resulting in Ekman transfer is the Trade Winds both north and south of the equator pulling surface waters towards the poles. There is a great deal of upwelling Ekman suction at the equator because water is being pulled northward north of the equator and southward south of the equator. This leads to a divergence in the water, resulting in Ekman suction, and therefore, upwelling.
The third wind pattern influencing Ekman transfer is large-scale wind patterns in the open ocean. Open ocean wind circulation can lead to gyre-like structures of piled up sea surface water resulting in horizontal gradients of sea surface height. This pile up of water causes the water to have a downward flow and suction, due to gravity and mass balance. Ekman pumping downward in the central ocean is a consequence of this convergence of water. | 1 | Applied and Interdisciplinary Chemistry |
As of 2020, YwIE is the only known active PAP in B.Subtilis, although Fuhrmann et al. (2013). identified a YwIE homolog in Drosophila, but its role in the specie is still unknown. In contrast, Suzuki et al. (2013) identified the presence of McsB in over 150 bacteria species | 1 | Applied and Interdisciplinary Chemistry |
Warm water corals are clearly in decline, with losses of 50% over the last 30–50 years due to multiple threats from ocean warming, ocean acidification, pollution and physical damage from activities such as fishing, and these pressures are expected to intensify.
The fluid in the internal compartments (the coelenteron) where corals grow their exoskeleton is also extremely important for calcification growth. When the saturation state of aragonite in the external seawater is at ambient levels, the corals will grow their aragonite crystals rapidly in their internal compartments, hence their exoskeleton grows rapidly. If the saturation state of aragonite in the external seawater is lower than the ambient level, the corals have to work harder to maintain the right balance in the internal compartment. When that happens, the process of growing the crystals slows down, and this slows down the rate of how much their exoskeleton is growing. Depending on the aragonite saturation state in the surrounding water, the corals may halt growth because pumping aragonite into the internal compartment will not be energetically favorable. Under the current progression of carbon emissions, around 70% of North Atlantic cold-water corals will be living in corrosive waters by 2050–60.
Acidified conditions primarily reduce the coral's capacity to build dense exoskeletons, rather than affecting the linear extension of the exoskeleton. The density of some species of corals could be reduced by over 20% by the end of this century.
An in situ experiment, conducted on a 400 m2 patch of the Great Barrier Reef, to decrease seawater CO level (raise pH) to near the preindustrial value showed a 7% increase in net calcification. A similar experiment to raise in situ seawater CO level (lower pH) to a level expected soon after the 2050 found that net calcification decreased 34%.
However, a field study of the coral reef in Queensland and Western Australia from 2007 to 2012 found that corals are more resistant to the environmental pH changes than previously thought, due to internal homeostasis regulation; this makes thermal change (marine heatwaves), which leads to coral bleaching, rather than acidification, the main factor for coral reef vulnerability due to climate change. | 0 | Theoretical and Fundamental Chemistry |
The Organismic Interactions Department, headed by Regine Kahmann, is focused on the biology of phytopathogenic fungi and in particular the mechanisms that underlie morphological differentiation and communication of these fungi with their plant hosts. Furthermore, the department is focused on the mechanisms that enable fungi to colonize plants successfully and on the processes accounting for variations in host preference and fungal lifestyles. There are three research groups:
* Molecular phytopathology (Regine Kahmann)
* Establishment of compatibility in biotrophic interactions (Gunther Döhlemann)
* Functional genomics and molecular biology of symbiotic fungi (Alga Zuccaro) | 0 | Theoretical and Fundamental Chemistry |
The core principle behind microarrays is hybridization between two DNA strands, the property of complementary nucleic acid sequences to specifically pair with each other by forming hydrogen bonds between complementary nucleotide base pairs. A high number of complementary base pairs in a nucleotide sequence means tighter non-covalent bonding between the two strands. After washing off non-specific bonding sequences, only strongly paired strands will remain hybridized. Fluorescently labeled target sequences that bind to a probe sequence generate a signal that depends on the hybridization conditions (such as temperature), and washing after hybridization. Total strength of the signal, from a spot (feature), depends upon the amount of target sample binding to the probes present on that spot. Microarrays use relative quantitation in which the intensity of a feature is compared to the intensity of the same feature under a different condition, and the identity of the feature is known by its position. | 1 | Applied and Interdisciplinary Chemistry |
In a typical double beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted. The process can be thought as two simultaneous beta minus decays. In order for (double) beta decay to be possible, the final nucleus must have a larger binding energy than the original nucleus. For some nuclei, such as germanium-76, the isobar one atomic number higher (arsenic-76) has a smaller binding energy, preventing single beta decay. However, the isobar with atomic number two higher, selenium-76, has a larger binding energy, so double beta decay is allowed.
The emission spectrum of the two electrons can be computed in a similar way to beta emission spectrum using Fermi's golden rule. The differential rate is given by
where the subscripts refer to each electron, is kinetic energy, is total energy, is the Fermi function with Z the charge of the final-state nucleus, is momentum, is velocity in units of , is the angle between the electrons, and is the Q value of the decay.
For some nuclei, the process occurs as conversion of two protons to neutrons, emitting two electron neutrinos and absorbing two orbital electrons (double electron capture). If the mass difference between the parent and daughter atoms is more than 1.022 MeV/c (two electron masses), another decay is accessible, capture of one orbital electron and emission of one positron. When the mass difference is more than 2.044 MeV/c (four electron masses), emission of two positrons is possible. These theoretical decay branches have not been observed. | 0 | Theoretical and Fundamental Chemistry |
An S2 reaction occurs when a nucleophile displaces a leaving group residing on a molecule from the backside of the leaving group. This displacement or substitution results in the formation of a substitution product with inversion of stereochemical configuration. The nucleophile forms a bond with its lone pair as the electron source. The electron sink which ultimately accepts the electron density is the nucleofuge (leaving group), with bond forming and bond breaking occurring simultaneously at the transition state (marked with a double-dagger). The rates of S2 reactions are dependent on the concentration of the haloalkane and the nucleophile.
Because an S2 reaction proceeds with the substitution of a leaving group with a nucleophile, the S designation is used. Because this mechanism proceeds with the interaction of two species at the transition state, it is referred to as a bimolecular process, resulting in the S2 designation. An S2 reaction is a concerted process, which means that the bonds are breaking and forming concurrently. Thus, the electron movement shown by the arrow pushing is happening simultaneously. An S2 reaction has one step. | 0 | Theoretical and Fundamental Chemistry |
Some assembly methods also make use of type IIs restriction endonucleases. These differ from other type II endonucleases as they cut several base pairs away from the recognition site. As a result, the overhang sequence can be modified to contain the desired sequence. This provides Type IIs assembly methods with two advantages – it enables "scar-less" assembly, and allows for one-pot, multi-part assembly. Assembly methods that use type IIs endonucleases include Golden Gate and its associated variants. | 1 | Applied and Interdisciplinary Chemistry |
Both anti-glycoprotein-210 (anti-gp210) and anti-nucleoporin 62 (anti-p62) antibodies are antibodies to components of the nuclear membrane and are found in primary biliary cirrhosis (PBC). Each antibody is present in approximately 25–30% of PBC. The antigens of both antibodies are constituents of the nuclear membrane. gp210 is a 200kDa protein involved in anchoring components of the nuclear pore to the nuclear membrane. The p62 antigen is a 60kDa nuclear pore complex. | 1 | Applied and Interdisciplinary Chemistry |
"Litigation science" describes analysis or data developed or produced expressly for use in a trial versus those produced in the course of independent research. This distinction was made by the U.S. 9th Circuit Court of Appeals when evaluating the admissibility of experts.
This uses demonstrative evidence, which is evidence created in preparation of trial by attorneys or paralegals. | 0 | Theoretical and Fundamental Chemistry |
Growth EPDs measure the amount of weight a given offspring will gain due to the parent's genetics.
Calving ease predicts the level of difficulty first time heifers will have during birth. These are determined by the percentage of unassisted births for that particular animal.
Birth weight measures how much above or below the breed's average an offspring will gain due to the parent. It does not necessarily predict the exact weight of all offspring, but instead gives a general prediction of how much extra or less weight an offspring will weigh compared to if it had been sired by another bull. High birth weight is the biggest cause of difficulty in calving, so having a bull with a low birth weight EPD is high beneficial.
Weaning and yearling weight measure the amount of weight an offspring has gained by the time it is weaned and at the one year mark. Typically the weaning weight is measured at the 205-day mark and the yearling weight is taken at the 365-day mark. Typically a larger number is favored for both of these traits.
Milk EPDs give an estimate for the maternal portion of the weaning weight that determined by milk production of the dam. It is measured in pounds of weaning weight of a bulls grandprogeny due to the milk production of the bulls daughters. | 1 | Applied and Interdisciplinary Chemistry |
For Stokes waves under the action of gravity, the third-order dispersion relation is – according to Stokes's first definition of celerity:
This third-order dispersion relation is a direct consequence of avoiding secular terms, when inserting the second-order Stokes solution into the third-order equations (of the perturbation series for the periodic wave problem).
In deep water (short wavelength compared to the depth):
and in shallow water (long wavelengths compared to the depth):
As shown above, the long-wave Stokes expansion for the dispersion relation will only be valid for small enough values of the Ursell parameter: . | 1 | Applied and Interdisciplinary Chemistry |
The decay of the positive muon into a positron and two neutrinos occurs via the weak interaction process after a mean lifetime of
τ = 2.197034(21) μs:
Parity violation in the weak interaction leads in this more complicated case (three body decay) to an anisotropic distribution of the positron emission with respect to the spin direction of the μ at the decay time. The positron emission probability is given by
where is the angle between the positron trajectory and the μ-spin, and is an intrinsic asymmetry parameter determined by the weak decay mechanism. This anisotropic emission constitutes in fact the basics for the μSR technique.
The average asymmetry is measured over a statistical ensemble of implanted muons and it depends on further experimental parameters, such as the beam spin polarization , close to one, as already mentioned. Theoretically =1/3 is obtained if all emitted positrons are detected with the same efficiency, irrespective of their energy. Practically, values of ≈ 0.25 are routinely obtained.
The muon spin motion may be measured over a time scale dictated by the muon decay, i.e. a few times τ, roughly 10 µs. The asymmetry in the muon decay correlates the positron emission and the muon spin directions. The simplest example is when the spin direction of all muons remains constant in time after implantation (no motion). In this case the asymmetry shows up as an imbalance between the positron counts in two equivalent detectors placed in front and behind the sample, along the beam axis. Each of them records an exponentially decaying rate as a function of the time t elapsed from implantation, according to
with for the detector looking towards and away from the spin arrow, respectively. Considering that the huge muon spin polarization is completely outside thermal equilibrium, a dynamical relaxation towards the equilibrium unpolarized state typically shows up in the count rate, as an additional decay factor in front of the experimental asymmetry parameter, A. A magnetic field parallel to the initial muon spin direction probes the dynamical relaxation rate as a function of the additional muon Zeeman energy, without introducing additional coherent spin dynamics. This experimental arrangement is called Longitudinal Field (LF) μSR.
A special case of LF μSR is Zero Field (ZF) μSR, when the external magnetic field is zero. This experimental condition is particularly important since it allows to probe any internal quasi-static (i.e. static on the muon time-scale) magnetic field of field distribution at the muon site. Internal quasi-static fields may appear spontaneously, not induced by the magnetic response of the sample to an external field They are produced by disordered nuclear magnetic moments or, more importantly, by ordered electron magnetic moments and orbital currents.
Another simple type of μSR experiment is when implanted all muon spins precess coherently around the external magnetic field of modulus , perpendicular to the beam axis, causing the count unbalance to oscillate at the corresponding Larmor frequency between the same two detectors, according to
Since the Larmor frequency is , with a gyromagnetic ratio Mrad(sT), the frequency spectrum obtained by means of this experimental arrangement provides a direct measure of the internal magnetic field intensity distribution. The distribution produces an additional decay factor of the experimental asymmetry A. This method is usually referred to as Transverse Field (TF) μSR.
A more general case is when the initial muon spin direction (coinciding with the detector axis) forms an angle with the field direction. In this case the muon spin precession describes a cone which results in both a longitudinal component, , and a transverse precessing component, , of the total asymmetry. ZF μSR experiments in the presence of a spontaneous internal field fall into this category as well. | 0 | Theoretical and Fundamental Chemistry |
The effective absolute limit of the range of the nuclear force (also known as residual strong force) is represented by halo nuclei such as lithium-11 or boron-14, in which dineutrons, or other collections of neutrons, orbit at distances of about (roughly similar to the radius of the nucleus of uranium-238). These nuclei are not maximally dense. Halo nuclei form at the extreme edges of the chart of the nuclides—the neutron drip line and proton drip line—and are all unstable with short half-lives, measured in milliseconds; for example, lithium-11 has a half-life of .
Halos in effect represent an excited state with nucleons in an outer quantum shell which has unfilled energy levels "below" it (both in terms of radius and energy). The halo may be made of either neutrons [NN, NNN] or protons [PP, PPP]. Nuclei which have a single neutron halo include Be and C. A two-neutron halo is exhibited by He, Li, B, B and C. Two-neutron halo nuclei break into three fragments, never two, and are called Borromean nuclei because of this behavior (referring to a system of three interlocked rings in which breaking any ring frees both of the others). He and Be both exhibit a four-neutron halo. Nuclei which have a proton halo include B and P. A two-proton halo is exhibited by Ne and S. Proton halos are expected to be more rare and unstable than the neutron examples, because of the repulsive electromagnetic forces of the halo proton(s). | 0 | Theoretical and Fundamental Chemistry |
In science, a process that is not reversible is called irreversible. This concept arises frequently in thermodynamics. All complex natural processes are irreversible, although a phase transition at the coexistence temperature (e.g. melting of ice cubes in water) is well approximated as reversible.
In thermodynamics, a change in the thermodynamic state of a system and all of its surroundings cannot be precisely restored to its initial state by infinitesimal changes in some property of the system without expenditure of energy. A system that undergoes an irreversible process may still be capable of returning to its initial state. Because entropy is a state function, the change in entropy of the system is the same whether the process is reversible or irreversible. However, the impossibility occurs in restoring the environment to its own initial conditions. An irreversible process increases the total entropy of the system and its surroundings. The second law of thermodynamics can be used to determine whether a hypothetical process is reversible or not.
Intuitively, a process is reversible if there is no dissipation. For example, Joule expansion is irreversible because initially the system is not uniform. Initially, there is part of the system with gas in it, and part of the system with no gas. For dissipation to occur, there needs to be such a non uniformity. This is just the same as if in a system one section of the gas was hot, and the other cold. Then dissipation would occur; the temperature distribution would become uniform with no work being done, and this would be irreversible because you couldn't add or remove heat or change the volume to return the system to its initial state. Thus, if the system is always uniform, then the process is reversible, meaning that you can return the system to its original state by either adding or removing heat, doing work on the system, or letting the system do work. As another example, to approximate the expansion in an internal combustion engine as reversible, we would be assuming that the temperature and pressure uniformly change throughout the volume after the spark. Obviously, this is not true and there is a flame front and sometimes even engine knocking. One of the reasons that Diesel engines are able to attain higher efficiency is that the combustion is much more uniform, so less energy is lost to dissipation and the process is closer to reversible.
The phenomenon of irreversibility results from the fact that if a thermodynamic system, which is any system of sufficient complexity, of interacting molecules is brought from one thermodynamic state to another, the configuration or arrangement of the atoms and molecules in the system will change in a way that is not easily predictable. Some "transformation energy" will be used as the molecules of the "working body" do work on each other when they change from one state to another. During this transformation, there will be some heat energy loss or dissipation due to intermolecular friction and collisions. This energy will not be recoverable if the process is reversed.
Many biological processes that were once thought to be reversible have been found to actually be a pairing of two irreversible processes. Whereas a single enzyme was once believed to catalyze both the forward and reverse chemical changes, research has found that two separate enzymes of similar structure are typically needed to perform what results in a pair of thermodynamically irreversible processes. | 0 | Theoretical and Fundamental Chemistry |
* ACE observations. The [http://www.ace.uwaterloo.ca/ Atmospheric Chemistry Experiment] (ACE) satellite, also known as SCISAT-1, is a Canadian satellite that makes measurements of the Earth's atmosphere and follows in heritage of ATMOS.
* Aura observations. [http://aura.gsfc.nasa.gov/ Aura] flies in formation with the NASA EOS "A Train," a collection of several other satellites (Aqua, CALIPSO, CloudSat and the French PARASOL). Aura carries four instruments for studies of atmospheric chemistry: MLS, HIRDLS, TES and OMI.
* ILAS observations. [https://web.archive.org/web/20070205195349/http://www-ilas.nies.go.jp/index.html ILAS] (Improved Limb Atmospheric Spectrometer) developed by MOE (the Ministry of the Environment) (formerly EA - Environment Agency of Japan) is boarded on ADEOS (Advanced Earth Observing Satellite). On August 17, 1996, ADEOS was launched by the H-II rocket from the Tanegashima Space Center of Japan (ADEOS was renamed as "MIDORI") and stopped its operation on June 30, 1997. Data obtained by ILAS are processed, archived, and distributed by NIES (National Institute for Environmental Studies).
* POAM observations. The [https://web.archive.org/web/20070301180400/http://wvms.nrl.navy.mil/POAM/poam.html Polar Ozone and Aerosol Measurement] II (POAM II) instrument was developed by the Naval Research Laboratory (NRL) to measure the vertical distribution of atmospheric ozone, water vapor, nitrogen dioxide, aerosol extinction, and temperature. POAM II measures solar extinction in nine narrow band channels, covering the spectral range from approximately 350 to 1060 nm.
* Sulfate aerosol observations from SAGE and HALOE. The SAGE II (Stratospheric Aerosol and Gas Experiment II) sensor was launched into a 57 degree inclination orbit aboard the Earth Radiation Budget Satellite (ERBS) in October 1984. During each sunrise and sunset encountered by the orbiting spacecraft, the instrument uses the solar occultation technique to measure attenuated solar radiation through the Earth's limb in seven channels centered at wavelengths ranging from 0.385 to 1.02 micrometers. The retrieval of stratospheric aerosol size distributions based on HALOE multi-wavelength particle extinction measurements was described by Hervig et al. [1998]. That approach yields unimodal lognormal size distributions, which describe the aerosol concentration versus radius using three parameters: total aerosol concentration, median radius, and distribution width. This [https://web.archive.org/web/20061208105210/http://haloedata.larc.nasa.gov/home/index.php?p=noframe_home.html site] offers results based on the Hervig et al. [1998] technique, with one exception. The retrieval results reported here are based on sulfate refractive indices for 215 K, where Hervig et al. [1998] used room temperature indices adjusted to stratospheric temperatures using the Lorentz-Lorenz rule. Size distributions were only retrieved at altitudes above tropospheric cloud tops. Clouds were identified using techniques described by Hervig and McHugh [1999]. The HALOE size distributions are offered in NetCDF files containing data for a single year. The results are reported on a uniform altitude grid ranging from 6 to 33 km at 0.3 km spacing. The native HALOE altitude spacing is 0.3 km, so this interpolation has little or no effect on the data. The files report profile data including: altitude, pressure, temperature, aerosol concentration, median radius, distribution width, aerosol composition. Aerosol surface area and volume densities can be easily calculated from the size distribution parameters using the relationships given [http://gwest.gats-inc.com/haloe_aerosols/HALOE_size_distribution_data.html here].
* Upper Atmosphere Research Satellite (UARS) observations. Data from the UARS is available from the [https://web.archive.org/web/20030210093521/http://daac.gsfc.nasa.gov/data/ GES Distributed Active Archive Center] (DAAC). The UARS satellite was launched in 1991 by the Space Shuttle Discovery. It is long, in diameter, weighs 13,000 pounds, and carries 10 instruments. UARS orbits at an altitude of with an orbital inclination of 57 degrees. UARS measured ozone and chemical compounds found in the ozone layer which affect ozone chemistry and processes. UARS also measured winds and temperatures in the stratosphere as well as the energy input from the Sun. Together, these helped define the role of the upper atmosphere in climate and climate variability. | 1 | Applied and Interdisciplinary Chemistry |
Wilhelm Roentgen is credited with the discovery of radioactivity in 1895 with many others such as Antoine Henri Becquerel, Pierre Curie, and Marie Curie following closely behind to further advance the field of radioactivity. John Lawrence, a physicist at The University of California Berkeley, first used nuclear medicine in humans came in 1936 after extensive use of radioactive phosphorus in mouse models. Often called the father of nuclear medicine, Lawrence treated a leukemia patient with radiophosphorus, which was the first time a radioactive isotope has been used to treat human patients. Another pioneer in the field, Sam Seidlin, in partnership with Saul Hertz, treated a case of thyroid cancer with radioactive iodine (I-131) 1946. In the 1950s, nuclear medicine began to gain traction as a medical specialty with the Society of Nuclear Medicine forming in 1954 and later releasing the first copy of the Journal of Nuclear Medicine in 1960. The use of radioligands and nuclear tagging started to gain popularity in in the early 1960s when Elwood Jensen and Herbert Jacobsen (1962) and later Jack Gorksi, David Toft, G, Shymala, Donald Smith, and Angelo Notides (1968) attempted to identify the estrogen receptor. The American Medical Association (AMA) officially recognized Nuclear Medicine as a medical specialty in 1970 and the American Board of Nuclear Medicine was established in 1972. Progress came quickly in 1973 when Edward Hoffman, Michael M. Ter-Pogossian, and Michael E. Phelps invented the first PET camera for human use. The 1980s brought early radioligand studies for neuroendocrine tumors (NETs) which continued into the early 2000s. In 2017 the European Union (EU) approved the use of radioligand therapy for NETs with the U.S. following close behind in 2018. | 1 | Applied and Interdisciplinary Chemistry |
The complex changes that the Schwann cell undergoes during the process of myelination of peripheral nerve fibers have been observed and studied by many. The initial envelopment of the axon occurs without interruption along the entire extent of the Schwann cell. This process is sequenced by the in-folding of the Schwann cell surface so that a double membrane of the opposing faces of the in-folded Schwann cell surface is formed. This membrane stretches and spirally wraps itself over and over as the in-folding of the Schwann cell surface continues. As a result, the increase in the thickness of the extension of the myelin sheath in its cross-sectional diameter is easily ascertained. It is also evident that each of the consecutive turns of the spiral increases in size along the length of the axon as the number of turns increase. However, it is not clear whether or not the increase in length of the myelin sheath can be accounted solely by the increase in length of axon covered by each successive turn of the spiral, as previously explained.
At the junction of two Schwann cells along an axon, the directions of the lamellar overhang of the myelin endings are of opposite sense. This junction, adjacent of the Schwann cells, constitutes the region designated as the node of Ranvier. | 1 | Applied and Interdisciplinary Chemistry |
The rate of carboxylation (V) is the rate that RuBisCO fixes CO to RuBP under substrate saturated conditions. A higher value of V corresponds to a higher rate of carboxylation. This rate of carboxylation can also be represented through its Michaelis-Menten constant K, with a higher value of K corresponding to a higher rate of carboxylation. V is represented by V, and K is represented as K in the generalized Michaelis-Menten curve. Although the rate of carboxylation varies among RuBisCO types, RuBisCO on average fixes only three molecules of CO per second. This is remarkably slow compared to typical enzyme catalytic rates, which usually catalyze reactions at the rate of thousands of molecules per second. | 0 | Theoretical and Fundamental Chemistry |
FISH is a very general technique. The differences between the various FISH techniques are usually due to variations in the sequence and labeling of the probes; and how they are used in combination. Probes are divided into two generic categories: cellular and acellular. In fluorescent "in situ" hybridization refers to the cellular placement of the probe
Probe size is important because shorter probes hybridize less specifically than longer probes, so that long enough strands of DNA or RNA (often 10–25 nucleotides) which are complementary to a given target sequence are often used to locate a target. The overlap defines the resolution of detectable features. For example, if the goal of an experiment is to detect the breakpoint of a translocation, then the overlap of the probes — the degree to which one DNA sequence is contained in the adjacent probes — defines the minimum window in which the breakpoint may be detected.
The mixture of probe sequences determines the type of feature the probe can detect. Probes that hybridize along an entire chromosome are used to count the number of a certain chromosome, show translocations, or identify extra-chromosomal fragments of chromatin. This is often called "whole-chromosome painting." If every possible probe is used, every chromosome, (the whole genome) would be marked fluorescently, which would not be particularly useful for determining features of individual sequences. However, it is possible to create a mixture of smaller probes that are specific to a particular region (locus) of DNA; these mixtures are used to detect deletion mutations. When combined with a specific color, a locus-specific probe mixture is used to detect very specific translocations. Special locus-specific probe mixtures are often used to count chromosomes, by binding to the centromeric regions of chromosomes, which are distinctive enough to identify each chromosome (with the exception of Chromosome 13, 14, 21, 22.)
A variety of other techniques uses mixtures of differently colored probes. A range of colors in mixtures of fluorescent dyes can be detected, so each human chromosome can be identified by a characteristic color using whole-chromosome probe mixtures and a variety of ratios of colors. Although there are more chromosomes than easily distinguishable fluorescent dye colors, ratios of probe mixtures can be used to create secondary colors. Similar to comparative genomic hybridization, the probe mixture for the secondary colors is created by mixing the correct ratio of two sets of differently colored probes for the same chromosome. This technique is sometimes called M-FISH.
The same physics that make a variety of colors possible for M-FISH can be used for the detection of translocations. That is, colors that are adjacent appear to overlap; a secondary color is observed. Some assays are designed so that the secondary color will be present or absent in cases of interest. An example is the detection of BCR/ABL translocations, where the secondary color indicates disease. This variation is often called double-fusion FISH or D-FISH. In the opposite situation—where the absence of the secondary color is pathological—is illustrated by an assay used to investigate translocations where only one of the breakpoints is known or constant. Locus-specific probes are made for one side of the breakpoint and the other intact chromosome. In normal cells, the secondary color is observed, but only the primary colors are observed when the translocation occurs. This technique is sometimes called "break-apart FISH". | 1 | Applied and Interdisciplinary Chemistry |
The Darcy friction factor for fully turbulent flow (Reynolds number greater than 4000) in rough conduits can be modeled by the Colebrook–White equation. | 1 | Applied and Interdisciplinary Chemistry |
Experimentally, it is hard to map the phase diagram of quark matter because it has been rather difficult to learn how to tune to high enough temperatures and density in the laboratory experiment using collisions of relativistic heavy ions as experimental tools. However, these collisions ultimately will provide information about the crossover from hadronic matter to QGP. It has been suggested that the observations of compact stars may also constrain the information about the high-density low-temperature region. Models of the cooling, spin-down, and precession of these stars offer information about the relevant properties of their interior. As observations become more precise, physicists hope to learn more.
One of the natural subjects for future research is the search for the exact location of the chiral critical point. Some ambitious lattice QCD calculations may have found evidence for it, and future calculations will clarify the situation. Heavy-ion collisions might be able to measure its position experimentally, but this will require scanning across a range of values of μ and T. | 0 | Theoretical and Fundamental Chemistry |
Azobenzenes are a class of photoswitchable molecules and are used in photopharmalogical applications for their reversible photoisomerization, as described in the previous section. An example of a photoswitchable molecule that uses azobenzene is phototrexate. Phototrexate is an inhibitor of human dihydrofolate reductase and is an analogue of methotrexate, a chemotherapy agent. When in its photoactive cis form, phototrexate has been shown to be a potent antifolate and is relatively inactive when in the trans form. The azologization, or incorporation of azobenzene, of methotrexate allows for control of cytotoxic activity and is considered a step forward in developing targeted anticancer drugs with localized efficacy. | 1 | Applied and Interdisciplinary Chemistry |
The Potential of Mean Force of a system with N particles is by construction the potential that gives the average force over all the configurations of all the n+1...N particles acting on a particle j at any fixed configuration keeping fixed a set of particles 1...n
Above, is the averaged force, i.e. "mean force" on particle j. And is the so-called potential of mean force. For , is the average work needed to bring the two particles from infinite separation to a distance . It is also related to the radial distribution function of the system, , by: | 0 | Theoretical and Fundamental Chemistry |
Philip Joseph Kocienski (born 23 December 1946) is a British organic chemist. He is an Emeritus Professor at the University of Leeds. | 0 | Theoretical and Fundamental Chemistry |
Chemotactic drug delivery systems are an emerging field of drug delivery that aims to apply the natural phenomenon of chemotaxis in guiding and delivering a drug to a specific tissue or cell within the body. Thus, similar to how organisms use chemotaxis, researchers have designed drug delivery systems to detect, maneuver, and react to chemical molecules released by a desired cell or its surrounding area. | 1 | Applied and Interdisciplinary Chemistry |
As a ligand, NS acts as a σ-donor and π-acceptor, forming metal-thionitrosyl complexes. Transition-metal thionitrosyl complexes have been prepared by the following procedures:
* Sulfur transfer to metal nitrido complexes
** Example: Reflux of (PhP)[OsNCl] and (PhP)NCS yields green-brown solid [PhP][Os(NS)(NCS)]
* Reaction of trithiazyltrichloride with transition metal complexes
** NSCl + OsCl > [Os(NS)Cl]
* Halide abstraction from coordinated thiazyl complexes
** Abstraction of sulfur-bonded fluorine from [(ηCH)Cr(NO)(NSF)]-[AsF] by AsF > [(η-CH)Cr(NO)(NS)]-[AsF]
* Reaction of NS salts with transition metal complexes
** NSSbF + [M(CO)Br] > [M(CO)(NS)], M=Mn, Re
** NSAsF + [(η-CH)Fe(CO)(SO)] > [(η-CH)Fe(CO)(NS)] [AsF]
* Reaction of tetrasulfur tetranitride with metal halides or nitrides
From X-ray crystallography of many of such metal-thionitrosyl complexes, one can observe that the M-N-S bond angle is nearly linear, suggesting sp hybridization about N. Short M-N distances and long N-S distances reflect the resonance structure of M=N=S having greater contribution than M-N≡S.
Typical v(NS) IR stretching frequencies are approximately 1065 cm for low-valent transition metal complexes and around 1390 cm in the high valent cases, whereas the free gas-phase radical exhibits a 1204 cm signal. | 0 | Theoretical and Fundamental Chemistry |
Above the theoretical shear strength of the material, a type of defect-less flow can still occur, shearing the material. Dislocation motion through glide (any temperature) or dislocation creep (at high temperatures) is a typical mechanism found at high stresses in deformation maps. | 1 | Applied and Interdisciplinary Chemistry |
When translating a polycistronic mRNA, a 70S ribosome ends translation at a stop codon. It is now shown that instead of immediately splitting into its two halves, the ribosome can "scan" forward until it hits another Shine–Dalgarno sequence and the downstream initiation codon, initiating another translation with the help of IF2 and IF3. This mode is thought to be important for the translation of genes that are clustered in poly-cistronic operons, where the canonical binding mode can be disruptive due to small distances between neighboring genes on the same mRNA molecule. | 1 | Applied and Interdisciplinary Chemistry |
The retromer complex has been shown to mediate retrieval of various transmembrane receptors, such as the cation-independent mannose 6-phosphate receptor, functional mammalian counterparts of Vps10 such as SORL1, and the Wnt receptor Wntless. Retromer is required for the recycling of Kex2p and DPAP-A, which also cycle between the trans-Golgi network and a pre-vacuolar (yeast endosome equivalent) compartment in yeast. It is also required for the recycling of the cell surface receptor CED-1, which is necessary for phagocytosis of apoptotic cells.
Retromer plays a central role in the retrieval of several different cargo proteins from the endosome to the trans-Golgi network, or for direct recycling back to the cell surface. However, it is clear that there are other complexes and proteins that act in this retrieval process. So far it is not clear whether some of the other components that have been identified in the retrieval pathway act with retromer in the same pathway or are involved in alternative pathways. Recent studies have implicated retromer sorting defects in Alzheimer's disease and late-onset Parkinson disease
Retromer also seems to play a role in Hepatitis C Virus replication. | 1 | Applied and Interdisciplinary Chemistry |
An amagat is a practical unit of volumetric number density. Although it can be applied to any substance at any conditions, it is defined as the number of ideal gas molecules per unit volume at 1 atm (101.325 kPa) and 0 °C (273.15 K). It is named after Émile Amagat, who also has Amagat's law named after him. The abbreviated form of amagat is "amg". The abbreviation "Am" has also been used. | 0 | Theoretical and Fundamental Chemistry |
The NV center has a ground-state triplet (A), an excited-state triplet (E) and two intermediate-state singlets (A and E). Both A and E contain m = ±1 spin states, in which the two electron spins are aligned (either up, such that m = +1 or down, such that m = -1), and an m = 0 spin state where the electron spins are antiparallel. Due to the magnetic interaction, the energy of the m = ±1 states is higher than that of the m = 0 state. A and E only contain a spin state singlet each with m = 0.
If an external magnetic field is applied along the defect axis (the axis which aligns with the nitrogen atom and the vacancy) of the NV center, it does not affect the m = 0 states, but it splits the m = ±1 levels (Zeeman effect). Similarly the following other properties of the environment influence the energy level diagram :
# Amplitude and orientation of a static magnetic field splits the m = ±1 levels in the ground and excited states.
# Amplitude and orientation of elastic (strain) or electric fields have a much smaller but also more complex effects on the different levels.
# Continuous-wave microwave radiation (applied in resonance with the transition between m = 0 and (one of the) m = ±1 states) changes the population of the sublevels within the ground and excited state.
# A tunable laser can selectively excite certain sublevels of the ground and excited states.
# Surrounding spins and spin–orbit interaction will modulate the magnetic field experienced by the NV center.
# Temperature and pressure affect different parts of the spectrum including the shift between ground and excited states.
The above-described energy structure is by no means exceptional for a defect in diamond or other semiconductor. It was not this structure alone, but a combination of several favorable factors (previous knowledge, easy production, biocompatibility, simple initialisation, use at room temperature etc.) which suggested the use of the NV center as a qubit and quantum sensor. | 0 | Theoretical and Fundamental Chemistry |
In oceanography, the Richardson number has a more general form which takes stratification into account. It is a measure of relative importance of mechanical and density effects in the water column, as described by the Taylor–Goldstein equation, used to model Kelvin–Helmholtz instability which is driven by sheared flows.
where N is the Brunt–Väisälä frequency and u the wind speed.
The Richardson number defined above is always considered positive. A negative value of N² (i.e. complex N) indicates unstable density gradients with active convective overturning. Under such circumstances the magnitude of negative Ri is not generally of interest. It can be shown that Ri < 1/4 is a necessary condition for velocity shear to overcome the tendency of a stratified fluid to remain stratified, and some mixing (turbulence) will generally occur. When Ri is large, turbulent mixing across the stratification is generally suppressed. | 1 | Applied and Interdisciplinary Chemistry |
Multi-substrate analogue inhibitors are high affinity selective inhibitors that can be prepared for enzymes that catalyse reactions with more than one substrate by capturing the binding energy of each of those substrate into one molecule. For example, in the formyl transfer reactions of purine biosynthesis, a potent Multi-substrate Adduct Inhibitor (MAI) to glycinamide ribonucleotide (GAR) TFase was prepared synthetically by linking analogues of the GAR substrate and the N-10-formyl tetrahydrofolate cofactor together to produce thioglycinamide ribonucleotide dideazafolate (TGDDF), or enzymatically from the natural GAR substrate to yield GDDF. Here the subnanomolar dissociation constant (KD) of TGDDF was greater than predicted presumably due to entropic advantages gained and/or positive interactions acquired through the atoms linking the components. MAIs have also been observed to be produced in cells by reactions of pro-drugs such as isoniazid or enzyme inhibitor ligands (for example, PTC124) with cellular cofactors such as nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP) respectively. | 1 | Applied and Interdisciplinary Chemistry |
Water movement is a significant means by which other materials, such as soil, gravel, boulders or pollutants, are transported from place to place. Initial input to receiving waters may arise from a point source discharge or a line source or area source, such as surface runoff. Since the 1960s rather complex mathematical models have been developed, facilitated by the availability of high-speed computers. The most common pollutant classes analyzed are nutrients, pesticides, total dissolved solids and sediment. | 1 | Applied and Interdisciplinary Chemistry |
The May 2014 IEEE Spectrum magazine carried a lengthy article "Its Always Sunny in Space" by Susumu Sasaki. The article stated, "Its been the subject of many previous studies and the stuff of sci-fi for decades, but space-based solar power could at last become a reality—and within 25 years, according to a proposal from researchers at the Tokyo-based Japan Aerospace Exploration Agency (JAXA)."
JAXA announced on 12 March 2015 that they wirelessly beamed 1.8 kilowatts 50 meters to a small receiver by converting electricity to microwaves and then back to electricity. This is the standard plan for this type of power. On 12 March 2015 Mitsubishi Heavy Industries demonstrated transmission of 10 kilowatts (kW) of power to a receiver unit located at a distance of 500 meters (m) away. | 0 | Theoretical and Fundamental Chemistry |
Bärnighausen studied Chemistry at Leipzig University and received his diploma after a diploma thesis with Leopold Wolf in 1955. In May 1958, he flew from East Germany to University of Freiburg, where he worked with Georg Brauer. He finished his doctorate in the group of Georg Brauer in 1959. In 1967, he received his habilitation. From 1967 to 1998, he was a professor for inorganic chemistry at the University of Karlsruhe. | 0 | Theoretical and Fundamental Chemistry |
Anodizing can be carried out in phosphoric acid, usually as a surface preparation for adhesives. This is described in standard ASTM D3933. | 1 | Applied and Interdisciplinary Chemistry |
1H-NMR (300 MHz, CDCl3): δ 7.59 (d, J = 9.5 Hz, 1H, aromatic), 7.22 (s, 1H, aromatic), 6.75 (d, J = 21.6 Hz, 1H, aromatic), 6.20 (d, J = 9.5 Hz, 1H, aromatic), 4.74 (t, J = 8.8 Hz, 1H, CH), 3.28-3.15 (m, 2H, CH2), 1.87 (s, 1H, OH), 1.37 (s, 3H, CH3), 1.24 (s, 3H, CH3) ppm. | 1 | Applied and Interdisciplinary Chemistry |
Plasma was first identified in laboratory by Sir William Crookes. Crookes presented a lecture on what he called "radiant matter" to the British Association for the Advancement of Science, in Sheffield, on Friday, 22 August 1879.
Systematic studies of plasma began with the research of Irving Langmuir and his colleagues in the 1920s. Langmuir also introduced the term "plasma" as a description of ionized gas in 1928:
Lewi Tonks and Harold Mott-Smith, both of whom worked with Langmuir in the 1920s, recall that Langmuir first used the term by analogy with the blood plasma. Mott-Smith recalls, in particular, that the transport of electrons from thermionic filaments reminded Langmuir of "the way blood plasma carries red and white corpuscles and germs." | 0 | Theoretical and Fundamental Chemistry |
In biological research, the Van t Hoff plot is also called Van t Hoff analysis. It is most effective in determining the favored product in a reaction. It may obtain results different from direct calorimetry such as differential scanning calorimetry or isothermal titration calorimetry due to various effects other than experimental error.
Assume two products B and C form in a reaction:
:a A + d D → b B,
:a A + d D → c C.
In this case, can be defined as ratio of B to C rather than the equilibrium constant.
When > 1, B is the favored product, and the data on the Van 't Hoff plot will be in the positive region.
When < 1, C is the favored product, and the data on the Van 't Hoff plot will be in the negative region.
Using this information, a Van 't Hoff analysis can help determine the most suitable temperature for a favored product.
In 2010, a Van t Hoff analysis was used to determine whether water preferentially forms a hydrogen bond with the C-terminus or the N-terminus of the amino acid proline. The equilibrium constant for each reaction was found at a variety of temperatures, and a Van t Hoff plot was created. This analysis showed that enthalpically, the water preferred to hydrogen bond to the C-terminus, but entropically it was more favorable to hydrogen bond with the N-terminus. Specifically, they found that C-terminus hydrogen bonding was favored by 4.2–6.4 kJ/mol. The N-terminus hydrogen bonding was favored by 31–43 J/(K mol).
This data alone could not conclude which site water will preferentially hydrogen-bond to, so additional experiments were used. It was determined that at lower temperatures, the enthalpically favored species, the water hydrogen-bonded to the C-terminus, was preferred. At higher temperatures, the entropically favored species, the water hydrogen-bonded to the N-terminus, was preferred. | 0 | Theoretical and Fundamental Chemistry |
Some articles reported that rapamycin can inhibit mTORC1 so that the phosphorylation of GS (glycogen synthase) can be increased in skeletal muscle. This discovery represents a potential novel therapeutic approach for glycogen storage disease that involve glycogen accumulation in muscle. | 1 | Applied and Interdisciplinary Chemistry |
For an electrode in a solution with a particular size and geometry, the reversible charge injection limit is the amount of charge that can move from the electrode to the surroundings without causing a chemical reaction that is irreversible. | 0 | Theoretical and Fundamental Chemistry |
The case of an ideal chain whose two ends are attached to fixed points will be considered in this sub-section. The vector joining these two points characterizes the macroscopic state (or macro-state) of the ideal chain. Each macro-state corresponds a certain number of micro-states, that we will call (micro-states are defined in the introduction to this section). Since the ideal chain's energy is constant, each of these micro-states is equally likely to occur. The entropy associated to a macro-state is thus equal to:
where is Boltzmann's constant
The above expression gives the absolute (quantum) entropy of the system. A precise determination of would require a quantum model for the ideal chain, which is beyond the scope of this article. However, we have already calculated the probability density associated with the end-to-end vector of the unconstrained ideal chain, above. Since all micro-states of the ideal chain are equally likely to occur, is proportional to . This leads to the following expression for the classical (relative) entropy of the ideal chain:
where is a fixed constant. Let us call the force exerted by the chain on the point to which its end is attached. From the above expression of the entropy, we can deduce an expression of this force. Suppose that, instead of being fixed, the positions of the two ends of the ideal chain are now controlled by an operator. The operator controls the evolution of the end to end vector . If the operator changes by a tiny amount , then the variation of internal energy of the chain is zero, since the energy of the chain is constant. This condition can be written as:
is defined as the elementary amount of mechanical work transferred by the operator to the ideal chain, and is defined as the elementary amount of heat transferred by the solvent to the ideal chain. Now, if we assume that the transformation imposed by the operator on the system is quasistatic (i.e., infinitely slow), then the system's transformation will be time-reversible, and we can assume that during its passage from macro-state to macro-state , the system passes through a series of thermodynamic equilibrium macro-states. This has two consequences:
# first, the amount of heat received by the system during the transformation can be tied to the variation of its entropy: where is the temperature of the chain.
# second, in order for the transformation to remain infinitely slow, the mean force exerted by the operator on the end points of the chain must balance the mean force exerted by the chain on its end points. Calling the force exerted by the operator and the force exerted by the chain, we have:
We are thus led to:
The above equation is the equation of state of the ideal chain. Since the expression depends on the central limit theorem, it is only exact in the limit of polymers containing a large number of monomers (that is, the thermodynamic limit). It is also only valid for small end-to-end distances, relative to the overall polymer contour length, where the behavior is like a hookean spring. Behavior over larger force ranges can be modeled using a canonical ensemble treatment identical to magnetization of paramagnetic spins. For the arbitrary forces the extension-force dependence will be given by Langevin function :
where the extension is .
For the arbitrary extensions the force-extension dependence can be approximated by:
where is the inverse Langevin function, is the number of bonds in the molecule (therefore if the molecule has bonds it has monomers making up the molecule.).
Finally, the model can be extended to even larger force ranges by inclusion of a stretch modulus along the polymer contour length. That is, by allowing the length of each unit of the chain to respond elastically to the applied force. | 0 | Theoretical and Fundamental Chemistry |
As previously mentioned 1,3BPG is a metabolic intermediate in the glycolytic pathway. It is created by the exergonic oxidation of the aldehyde in G3P. The result of this oxidation is the conversion of the aldehyde group into a carboxylic acid group which drives the formation of an acyl phosphate bond. This is incidentally the only step in the glycolytic pathway in which NAD is converted into NADH. The formation reaction of 1,3BPG requires the presence of an enzyme called glyceraldehyde-3-phosphate dehydrogenase.
The high-energy acyl phosphate bond of 1,3BPG is important in respiration as it assists in the formation of ATP. The molecule of ATP created during the following reaction is the first molecule produced during respiration. The reaction occurs as follows;
:1,3-bisphosphoglycerate + ADP ⇌ 3-phosphoglycerate + ATP
The transfer of an inorganic phosphate from the carboxyl group on 1,3BPG to ADP to form ATP is reversible due to a low ΔG. This is as a result of one acyl phosphate bond being cleaved whilst another is created. This reaction is not naturally spontaneous and requires the presence of a catalyst. This role is performed by the enzyme phosphoglycerate kinase. During the reaction phosphoglycerate kinase undergoes a substrate induced conformational change similar to another metabolic enzyme called hexokinase.
Because two molecules of glyceraldehyde-3-phosphate are formed during glycolysis from one molecule of glucose, 1,3BPG can be said to be responsible for two of the ten molecules of ATP produced during the entire process. Glycolysis also uses two molecules of ATP in its initial stages as a committed and irreversible step. For this reason glycolysis is not reversible and has a net produce of 2 molecules of ATP and two of NADH. The two molecules of NADH themselves go on to produce approximately 3 molecules of ATP each. | 0 | Theoretical and Fundamental Chemistry |
The two enantiomers of a molecule possess many of the same physical properties (e.g. melting point, boiling point, polarity etc.) and so behave identically to each other. As a result, they will migrate with an identical R in thin layer chromatography and have identical retention times in HPLC and GC. Their NMR and IR spectra are identical.
This can make it very difficult to determine whether a process has produced a single enantiomer (and crucially which enantiomer it is) as well as making it hard to separate enantiomers from a reaction which has not been 100% enantioselective. Fortunately, enantiomers behave differently in the presence of other chiral materials and this can be exploited to allow their separation and analysis.
Enantiomers do not migrate identically on chiral chromatographic media, such as quartz or standard media that has been chirally modified. This forms the basis of chiral column chromatography, which can be used on a small scale to allow analysis via GC and HPLC, or on a large scale to separate chirally impure materials. However this process can require large amount of chiral packing material which can be expensive. A common alternative is to use a chiral derivatizing agent to convert the enantiomers into a diastereomers, in much the same way as chiral auxiliaries. These have different physical properties and hence can be separated and analysed using conventional methods. Special chiral derivitizing agents known as chiral resolution agents are used in the NMR spectroscopy of stereoisomers, these typically involve coordination to chiral europium complexes such as Eu(fod) and Eu(hfc).
The separation and analysis of component enantiomers of a racemic drugs or pharmaceutical substances are referred to as chiral analysis. or enantioselective analysis. The most frequently employed technique to carry out chiral analysis involves separation science procedures, specifically chiral chromatographic methods.
The enantiomeric excess of a substance can also be determined using certain optical methods. The oldest method for doing this is to use a polarimeter to compare the level of optical rotation in the product against a standard of known composition. It is also possible to perform ultraviolet-visible spectroscopy of stereoisomers by exploiting the Cotton effect.
One of the most accurate ways of determining the chirality of compound is to determine its absolute configuration by X-ray crystallography. However this is a labour-intensive process which requires that a suitable single crystal be grown. | 0 | Theoretical and Fundamental Chemistry |
The most common type of frameshifting is −1 frameshifting or programmed −1 ribosomal frameshifting (−1 PRF). Other, rarer types of frameshifting include +1 and −2 frameshifting. −1 and +1 frameshifting are believed to be controlled by different mechanisms, which are discussed below. Both mechanisms are kinetically driven. | 1 | Applied and Interdisciplinary Chemistry |
In inner-sphere ET, the two redox centers are covalently linked during the ET. This bridge can be permanent, in which case the electron transfer event is termed intramolecular electron transfer. More commonly, however, the covalent linkage is transitory, forming just prior to the ET and then disconnecting following the ET event. In such cases, the electron transfer is termed intermolecular electron transfer. A famous example of an inner sphere ET process that proceeds via a transitory bridged intermediate is the reduction of [CoCl(NH)] by [Cr(HO)]. In this case, the chloride ligand is the bridging ligand that covalently connects the redox partners. | 0 | Theoretical and Fundamental Chemistry |
The photochlorination of toluene is selective for the methyl group. Mono- to trichlorinated products are obtained. The most important of which is the mono-substituted benzyl chloride, which is hydrolyzed to benzyl alcohol. Benzyl chloride can also be converted via benzyl cyanide with subsequent hydrolysis into phenylacetic acid. The disubstituted benzal chloride is converted to benzaldehyde, a popular flavorant and intermediate for the production of malachite green and other dyes. The trisubstituted benzotrichloride is used for the hydrolysis of the synthesis of benzoyl chloride:
By reaction with alcohols, benzoyl chloride can be converted into the corresponding esters. With sodium peroxide it turns into dibenzoyl peroxide, a radical initiator for polymerizations. However, the atom economy of these syntheses is poor, since stoichiometric amounts of salts are obtained. | 0 | Theoretical and Fundamental Chemistry |
When an antigen-presenting cell interacts with a T cell receptor on T cells, there is an increase in the cytoplasmic level of calcium, which activates calcineurin by binding a regulatory subunit and activating calmodulin binding. Calcineurin induces transcription factors (NFATs) that are important in the transcription of IL-2 genes. IL-2 activates T-helper lymphocytes and induces the production of other cytokines. In this way, it governs the action of cytotoxic lymphocytes. The amount of IL-2 being produced by the T-helper cells is believed to influence the extent of the immune response significantly. | 1 | Applied and Interdisciplinary Chemistry |
Drospirenone stimulates the proliferation of MCF-7 breast cancer cells in vitro, an action that is independent of the classical PRs and is instead mediated via the progesterone receptor membrane component-1 (PGRMC1). Certain other progestins act similarly in this assay, whereas progesterone acts neutrally. It is unclear if these findings may explain the different risks of breast cancer observed with progesterone and progestins in clinical studies. | 0 | Theoretical and Fundamental Chemistry |
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