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Dross is a mass of solid impurities floating on a molten metal or dispersed in the metal, such as in wrought iron. It forms on the surface of low-melting-point metals such as tin, lead, zinc or aluminium or alloys by oxidation of the metal. For higher melting point metals and alloys such as steel and silver, oxidized impurities melt and float making them easy to pour off.
With wrought iron, hammering and later rolling remove some dross.
With tin and lead the dross can be removed by adding sodium hydroxide pellets, which dissolve the oxides and form a slag. If floating, dross can also be skimmed off.
Dross, as a solid, is distinguished from slag, which is a liquid. Dross product is not entirely waste material; for example, aluminium dross can be recycled and is also used in secondary steelmaking for slag deoxidation. | 8 | Metallurgy |
Pyroglutamyl-histidyl-glycine (pEHG) is an endogenous tripeptide that acts as a tissue-specific antimitotic and selectively inhibits the proliferation of colon epithelial cells. Early research indicated that pEHG had anorectic effects in mice and was possibly involved in the pathophysiology of anorexia nervosa. However, subsequent studies have found that pEHG lacks anorectic effects and does not alter food intake in mice. | 1 | Biochemistry |
Total organic carbon (TOC) is an analytical parameter representing the concentration of organic carbon in a sample. TOC determinations are made in a variety of application areas. For example, TOC may be used as a non-specific indicator of water quality, or TOC of source rock may be used as one factor in evaluating a petroleum play. For marine surface sediments average TOC content is 0.5% in the deep ocean, and 2% along the eastern margins.
A typical analysis for total carbon (TC) measures both the total organic carbon (TOC) present and the complementing total inorganic carbon (TIC), the latter representing the amount of non-organic carbon, like carbon in carbonate minerals. Subtracting the inorganic carbon from the total carbon yields TOC. Another common variant of TOC analysis involves removing the TIC portion first and then measuring the leftover carbon. This method involves purging an acidified sample with carbon-free air or nitrogen prior to measurement, and so is more accurately called non-purgeable organic carbon (NPOC). | 3 | Analytical Chemistry |
Examples are numerous: combustion, the thermite reaction, combining strong acids and bases, polymerizations. As an example in everyday life, hand warmers make use of the oxidation of iron to achieve an exothermic reaction:
:4Fe  + 3O  → 2FeO  ΔH⚬ = - 1648 kJ/mol
A particularly important class of exothermic reactions is combustion of a hydrocarbon fuel, e.g. the burning of natural gas:
:CH  + 2O  → CO  + 2HO  ΔH⚬ = - 890 kJ/mol
These sample reactions are strongly exothermic.
Uncontrolled exothermic reactions, those leading to fires and explosions, are wasteful because it is difficult to capture the released energy. Nature effects combustion reactions under highly controlled conditions, avoiding fires and explosions, in aerobic respiration so as to capture the released energy, e.g. for the formation of ATP. | 7 | Physical Chemistry |
Development of theoretical models describing grain growth is an active field of research. Many models have been proposed for grain growth, but no theory has yet been put forth that has been independently validated to apply across the full range of conditions and many questions remain open. By no means is the following a comprehensive review. One recent theory of grain growth posits that normal grain growth only occurs in the polycrystalline systems with grain boundaries which have undergone roughening transitions, and abnormal and/or stagnant grain growth can only occur in the polycrystalline systems with non-zero GB (grain boundary) step free energy of grains. Other models explaining grain coarsening assert that disconnections are responsible for the motion of grain boundaries, and provide limited experimental evidence suggesting that they govern grain boundary migration and grain growth behavior. Other models have indicated that triple junctions play an important role in determining the grain growth behavior in many systems. | 8 | Metallurgy |
Another purpose of this titration is determination of the optimum dose of surfactant for achieving stabilization or flocculation of a heterogeneous system. | 7 | Physical Chemistry |
In neuroscience and anatomy, nodes of Ranvier ( ), also known as myelin-sheath gaps, occur along a myelinated axon where the axolemma is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, allowing them to participate in the exchange of ions required to regenerate the action potential. Nerve conduction in myelinated axons is referred to as saltatory conduction () due to the manner in which the action potential seems to "jump" from one node to the next along the axon. This results in faster conduction of the action potential. | 1 | Biochemistry |
Human polypeptide C5a contains 74 amino acids and has 11kDa. NMR spectroscopy proved that the molecule is composed of four helices and connected by peptide loops with three disulphide bonds between helix IV and II, III. There is a short 1.5 turn helix on N-terminus but all agonist activity take place in the C-terminus. C5a is rapidly metabolised by a serum enzyme carboxypeptidase B to a 72 amino acid form C5a des-Arg without C terminal arginine. | 1 | Biochemistry |
According to popular legend, Galvani discovered the effects of electricity on muscle tissue when investigating an unrelated phenomenon which required skinned frogs in the 1780s and 1790s. His assistant is claimed to have accidentally touched a scalpel to the sciatic nerve of the frog and this resulted in a spark and animation of its legs. This was building on the theories of Giovanni Battista Beccaria, Felice Fontana, Leopoldo Marco Antonio Caldani, and . Galvani was investigating the effects of distant atmospheric electricity (lightning) on prepared frog legs when he discovered the legs convulsed not only when lightning struck but also when he pressed the brass hooks attached to the frogs spinal cord to the iron railing they were suspended from. In his laboratory, Galvani later discovered that he could replicate this phenomenon by touching metal electrodes of brass connected to the frogs spinal cord to an iron plate. He concluded that this was proof of "animal electricity," the electric power which animated living things. | 7 | Physical Chemistry |
Complex metallic alloys (CMAs) or complex intermetallics (CIMs) are intermetallic compounds characterized by the following structural features:
#large unit cells, comprising some tens up to thousands of atoms,
#the presence of well-defined atom clusters, frequently of icosahedral point group symmetry,
#the occurrence of inherent disorder in the ideal structure. | 8 | Metallurgy |
Single nucleotide polymorphisms (SNPs) in TCF7L2 gene have shown an increase in susceptibility to schizophrenia in Arab, European and Chinese Han populations. In the Chinese Han population, SNP rs12573128 in TCF7L2 is the variant that was associated with an increase in schizophrenia risk. This marker is used as a pre-diagnostic marker for schizophrenia. TCF7L2 has also been reported as a risk gene in autism spectrum disorder and has been linked to it in recent large-scale genetic studies.
The mechanism behind TCF7L2s involvement in the emergence of neurodevelopmental disorders is not fully understood, as there have been few studies characterizing its role in brain development in detail. It was shown that during embryogenesis TCF7L2 is involved in the development of fish-specific habenula asymmetry in Danio rerio, and that the dominant negative TCF7L2 isoform influences cephalic separation in the embryo by inhibiting the posteriorizing effect of the Wnt pathway. It was also shown that in Tcf7l2' knockout mice the number of proliferating cells in cortical neural progenitor cells is reduced. In contrast, no such effect was found in the midbrain.
More recently it was shown that TCF7L2 plays a crucial role in both the embryonic development and postnatal maturation of the thalamus through direct and indirect regulation of many genes previously reported to be important for both processes. In late gestation TCF7L2 regulates the expression of many thalamus-enriched transcription factors (e.g. Foxp2, Rora, Mef2a, Lef1, Prox1), axon guidance molecules (e.g. Epha1, Epha4, Ntng1, Epha8) and cell adhesion molecules (e.g. Cdh6, Cdh8, Cdhr1). Accordingly, a total knockout of Tcf7l2 in mice leads to improper growth of thalamocortical axons, changed anatomy and improper sorting of the cells in the thalamo-habenular region. In the early postnaral period TCF7L2 starts to regulate the expression of many genes necessary for the acquisition of characteristic excitability patterns in the thalamus, mainly ion channels, neurotransmitters and their receptors and synaptic vescicle proteins (e.g. Cacna1g, Kcnc2, Slc17a7, Grin2b), and an early postnatal knockout of Tcf7l2 in mouse thalamus leads to significant reduction in the number and frequency of action potentials generated by the thalamocortical neurons. The mechanism that leads to the change in TCF7L2 target genes between gestation and early postnatal period is unknown. It is likely that a perinatal change in the proportion of TCF7L2 isoforms expressed in the thalamus is partially responsible. Abnormalities in the anatomy of the thalamus and the activity of its connections to the cerebral cortex are frequently detected in patients with schizophrenia and autism. Such abnormalities could arise from developmental aberrations in patients with unfavorable mutations of TCF7L2, further strengthening the link between TCF7L2 and neurodevelopmental disorders. | 1 | Biochemistry |
The refrigeration industry has been seeking replacements for R-410A because of its high global warming potential. R-454B, formerly known as DL-5A, has been selected by several manufacturers, including Mitsubishi Electric, Carrier, Johnson Controls, and others.
R-454B was developed at and is manufactured by Chemours. Carrier first announced introduction of R-454B in ducted residential and light commercial packaged refrigeration and air conditioning products in 2018, with R-454B-based products launches starting in 2023. | 2 | Environmental Chemistry |
Water may be tested by a bioassay comparing survival of an aquatic test species in the wastewater in comparison to water from some other source. Water may also be evaluated to determine the approximate biological population of the wastewater. Pathogenic micro-organisms using water as a means of moving from one host to another may be present in sewage. Coliform index measures the population of an organism commonly found in the intestines of warm-blooded animals as an indicator of the possible presence of other intestinal pathogens.
Aquatic toxicology tests are used to provide qualitative and quantitative data on adverse effects on aquatic organisms from a toxicant. Testing types include acute (short-term exposure), chronic (life span) and bioaccumulation tests. Many industrial facilities in the US conduct "whole effluent toxicity" (WET) tests on their wastewater discharges, typically in combination with chemical tests for selected pollutants. | 3 | Analytical Chemistry |
The intrinsic hydrophobicity of a surface can be enhanced by being textured with different length scales of roughness. The red rose takes advantage of this by using a hierarchy of micro- and nanostructures on each petal to provide sufficient roughness for superhydrophobicity. More specifically, each rose petal has a collection of micropapillae on the surface and each papilla, in turn, has many nanofolds. The term "petal effect" describes the fact that a water droplet on the surface of a rose petal is spherical in shape, but cannot roll off even if the petal is turned upside down. The water drops maintain their spherical shape due to the superhydrophobicity of the petal (contact angle of about 152.4°), but do not roll off because the petal surface has a high adhesive force with water.
When comparing the "petal effect" to the "lotus effect", it is important to note some striking differences. The surface structure of the lotus leaf and the rose petal, as seen in Figure 9, can be used to explain the two different effects.
The lotus leaf has a randomly rough surface and low contact angle hysteresis, which means the water droplet is not able to wet the microstructure spaces between the spikes. This allows air to remain inside the texture, causing a heterogeneous surface composed of both air and solid. As a result, the adhesive force between the water and the solid surface is extremely low, allowing the water to roll off easily (i.e. "self-cleaning" phenomenon).
The rose petal's micro- and nanostructures are larger in scale than those of the lotus leaf, which allows the liquid film to impregnate the texture. However, as seen in Figure 9, the liquid can enter the larger-scale grooves, but it cannot enter into the smaller grooves. This is known as the Cassie impregnating wetting regime. Since the liquid can wet the larger-scale grooves, the adhesive force between the water and solid is very high. This explains why the water droplet will not fall off even if the petal is tilted at an angle or turned upside down. This effect will fail if the droplet has a volume larger than 10 µl because the balance between weight and surface tension is surpassed. | 7 | Physical Chemistry |
The Harbor Branch Oceanographic Institution licensed (+)-discodermolide to Novartis, which began a phase 1 clinical trial in 2004. The trial concluded that the drug resulted in minimal toxicities and represents a novel mechanism of action. Amos B. Smith's research group, in collaboration with Kosan Biosciences, has a preclinical drug development program ongoing. | 0 | Organic Chemistry |
The Rabi frequency is the frequency at which the probability amplitudes of two atomic energy levels fluctuate in an oscillating electromagnetic field. It is proportional to the transition dipole moment of the two levels and to the amplitude (not intensity) of the electromagnetic field. Population transfer between the levels of such a 2-level system illuminated with light exactly resonant with the difference in energy between the two levels will occur at the Rabi frequency; when the incident light is detuned from this energy difference (detuned from resonance) then the population transfer occurs at the generalized Rabi frequency. The Rabi frequency is a semiclassical concept since it treats the atom as an object with quantized energy levels and the electromagnetic field as a continuous wave.
In the context of a nuclear magnetic resonance experiment, the Rabi frequency is the nutation frequency of a sample's net nuclear magnetization vector about a radio-frequency field. (Note that this is distinct from the Larmor frequency, which characterizes the precession of a transverse nuclear magnetization about a static magnetic field.) | 7 | Physical Chemistry |
The standards are listed in . Primary standards are designed to protect human health, with an adequate margin of safety, including sensitive populations such as children, the elderly, and individuals suffering from respiratory diseases. Secondary standards are designed to protect public welfare, damage to property, transportation hazards, economic values, and personal comfort and well-being from any known or anticipated adverse effects of a pollutant. A district meeting a given standard is known as an "attainment area" for that standard, and otherwise a "non-attainment area".
Standards are required to "accurately reflect the latest scientific knowledge," and are reviewed every five years by a Clean Air Scientific Advisory Committee (CASAC), consisting of "seven members appointed by the EPA administrator."
EPA has set NAAQS for six major pollutants listed as below. These six are also the criteria air pollutants.
* Each standard has its own criteria for how many times it may be exceeded
* As of June 15, 2005, the 1-hour ozone standard no longer applies to areas designated with respect to the 8-hour ozone standard (which includes most of the United States, except for portions of 10 states).
* Source: [https://www.epa.gov/criteria-air-pollutants/naaqs-table USEPA] | 2 | Environmental Chemistry |
A coccolithophore is a unicellular, eukaryotic phytoplankton (alga). Understanding calcification changes in coccolithophores may be particularly important because a decline in the coccolithophores may have secondary effects on climate: it could contribute to global warming by decreasing the Earth's albedo via their effects on oceanic cloud cover. A study in 2008 examined a sediment core from the North Atlantic and found that the species composition of coccolithophorids remained unchanged over the past 224 years (1780 to 2004). But the average coccolith mass had increased by 40% during the same period. | 9 | Geochemistry |
*J. D. Bjorken, S. D. Drell, Relativistic Quantum Mechanics, 1964
*P. Roman, Introduction to Quantum Theory, 1969
*W. Greiner, J. Reinhardt, Quantum Electrodynamics, 1994
*R. G. Newton. Scattering Theory of Waves and Particles. McGraw Hill, 1966. | 7 | Physical Chemistry |
Wootz is characterized by a pattern caused by bands of clustered particles made by melting of low levels of carbide-forming elements. Wootz contains greater carbonaceous matter than common qualities of cast steel.
The distinct patterns of Wootz steel that can be made through forging are wave, ladder, and rose patterns with finely spaced bands. However, with hammering, dyeing, and etching further customized patterns were made.
The presence of cementite nanowires and carbon nanotubes has been identified by Peter Pepler of TU Dresden in the microstructure of wootz steel. There is a possibility of an abundance of ultrahard metallic carbides in the steel matrix precipitating out in bands.Wootz swords were renowned for their sharpness and toughness. | 8 | Metallurgy |
The outer portion of a SLMD consists of a section of sealed, flat, semi-permeable polyethylene tubing. Sealed inside this tubing is a 1:1 mixture of a hydrophobic metal complexing agent and a long chain organic acid. The organic acid diffuses through the tubing to the outer surface, where the carboxylic acid portion can form stable complexes with calcium and magnesium ions in the water. This allows a waxy layer to slowly accumulate on the outside of the tube. the metal complexing agent continuously mobilizes into this waxy layer, where it can sequester metal ions from the water. The hydrophobic metal complexing agent most commonly used in SLMDs is an alkylated 8-hydroxyquinoline. Oleic acid is commonly used as the other half of the 1:1 hydrophobic reagent mixture, as it readily forms calcium oleates in the aqueous sampling media. In addition to the base device, hydrophobic plastic sheaths are sometimes used to house SLMDs in the field. Variable water flow can alter the sampling rates of metals by SLMDs, making a time-averaged concentration difficult to determine. By allowing liable metal analytes to diffuse to the SLMD's surface while limiting the diffusion of particulate, colloidal, or humic substances, these hydrophobic sheaths help reduce variability of SLMD uptake in faster moving waters.
After being deployed for a known time interval, SLMDs can be recovered from the field for analysis. Washing with 20% nitric acid allows for the extraction of accumulated metals, and by using analytical techniques like inductively coupled plasma mass spectroscopy (ICP-MS) or atomic absorption spectroscopy (flame AAS) to measure the concentration of metal in the extract, the amount of metal accumulated by the SLMD can be determined. | 3 | Analytical Chemistry |
-homoserine product bound at the dizinc metal center. The zinc ions are shown as cyan spheres. All ligand molecules are shown in ball-and-stick form. Carbon, oxygen, and nitrogen atoms are colored white, red, and blue, respectively. -->
A dinuclear zinc binding site is conserved in all known lactonases and essential for enzyme activity and protein folding.
Zn1 is tetracoordinated by His104, His106, His169, and the bridging hydroxide ion. Zn2 has five ligands, including Asp191, His235, His109, Asp108, and the bridging hydroxide ion. The metal ions assist in polarizing the lactone bond, increasing the electrophilicity of the lactone ring’s carbonyl carbon. Isotopic labeling studies indicated that the ring opening occurs via an addition elimination reaction with water addition shown below. | 1 | Biochemistry |
Although E varies greatly across the periodic table, some patterns emerge. Generally, nonmetals have more positive E than metals. Atoms whose anions are more stable than neutral atoms have a greater E. Chlorine most strongly attracts extra electrons; neon most weakly attracts an extra electron. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values.
E generally increases across a period (row) in the periodic table prior to reaching group 18. This is caused by the filling of the valence shell of the atom; a group 17 atom releases more energy than a group 1 atom on gaining an electron because it obtains a filled valence shell and therefore is more stable. In group 18, the valence shell is full, meaning that added electrons are unstable, tending to be ejected very quickly.
Counterintuitively, E does not decrease when progressing down most columns of the periodic table. For example, E actually increases consistently on descending the column for the group 2 data. Thus, electron affinity follows the same "left-right" trend as electronegativity, but not the "up-down" trend.
The following data are quoted in kJ/mol. | 7 | Physical Chemistry |
β-Hydroxybutyric acid is the precursor to polyesters, which are biodegradable plastics. This polymer, poly(3-hydroxybutyrate), is also naturally produced by the bacteria Alcaligenes eutrophus.
β-Hydroxybutyrate can be extracted from poly(3-hydroxybutyrate) by acid hydrolysis.
The concentration of in blood plasma is measured through a test that uses β-hydroxybutyrate dehydrogenase, with NAD as an electron-accepting cofactor. The conversion of to acetoacetate, which is catalyzed by this enzyme, reduces the NAD to NADH, generating an electrical change; the magnitude of this change can then be used to extrapolate the amount of in the sample. | 1 | Biochemistry |
Ultrasensitivity can be achieved through several mechanisms:
#Multistep mechanisms (examples: cooperativity) and multisite phosphorylation
#Buffering mechanisms (examples: decoy phosphorylation sites) or stoichiometric inhibitors
#Changes in localisation (such as translocation across the nuclear envelope)
#Saturation mechanisms (also known as zero-order ultrasensitivity)
#Positive feedback
#Allovalency
#Non-Zero-Order Ultrasensitivity in Membrane Proteins
#Dissipative Allostery | 1 | Biochemistry |
In a laminar flow reactor, the fluid flows through a long tube or parallel plate reactor and the flow is in layers parallel to the walls of the tube. The velocity of the flow is a parabolic function of radius. In the absence of molecular diffusion, the RTD is
The variance is infinite. In a real reactor, diffusion will eventually mix the layers so that the tail of the RTD becomes exponential and the variance finite; but laminar flow reactors can have variance greater than 1, the maximum for CTSD reactors. | 9 | Geochemistry |
* Fructone (fruity, apple-like)
* Ethyl methylphenylglycidate (Strawberry)
* alpha-Methylbenzyl acetate (Gardenia) | 0 | Organic Chemistry |
Colloid vibration potential measures the AC potential difference generated between two identical relaxed electrodes, placed in the dispersion, if the latter is subjected to an ultrasonic field. When a sound wave travels through a colloidal suspension of particles whose density differs from that of the surrounding medium, inertial forces induced by the vibration of the suspension give rise to a motion of the charged particles relative to the liquid, causing an alternating electromotive force. The manifestations of this electromotive force may be measured, depending on the relation between the impedance of the suspension and that of the measuring instrument, either as colloid vibration potential or as colloid vibration current.
Colloid vibration potential and current was first reported by Hermans and then independently by Rutgers in 1938. It is widely used for characterizing the ζ-potential of various dispersions and emulsions. The effect, theory, experimental verification and multiple applications are discussed in the book by Dukhin and Goetz. | 7 | Physical Chemistry |
Used as drugs, compounds with different configuration normally have different physiological activity, including the desired pharmacological effect, the toxicology and the metabolism. Enantiomeric ratios and purity is an important factor in clinical assessments. Racemic mixtures are those that contain equimolar amounts of both enantiomers of a compound. Racemate and single enantiomer actions differ in most cases. | 4 | Stereochemistry |
A systematic review of clinical studies found an association between low vitamin D levels with cognitive impairment and a higher risk of developing Alzheimer's disease. However, lower vitamin D concentrations are also associated with poor nutrition and spending less time outdoors. Therefore, alternative explanations for the increase in cognitive impairment exist and hence a direct causal relationship between vitamin D levels and cognition could not be established. | 1 | Biochemistry |
Murexide is prepared by treating alloxantin with ammonia to 100 °C, or by treating uramil (5-aminobarbituric acid) with mercury oxide. It may also be prepared by digesting alloxan with alcoholic ammonia. | 3 | Analytical Chemistry |
An important occurrence of phosphates in biological systems is as the structural material of bone and teeth. These structures are made of crystalline calcium phosphate in the form of hydroxyapatite. The hard dense enamel of mammalian teeth may contain fluoroapatite, a hydroxy calcium phosphate where some of the hydroxyl groups have been replaced by fluoride ions. | 0 | Organic Chemistry |
Modafinil was developed in France by neurophysiology professor Michel Jouvet and Lafon Laboratories. It is part of a series of benzhydryl sulfinyl compounds, including adrafinil, initially used as a treatment for narcolepsy in France in 1986. Modafinil, the primary metabolite of adrafinil, has been prescribed in France since 1994 under the name Modiodal, and in the United States since 1998 as Provigil. Unlike modafinil, adrafinil does not have FDA approval and was withdrawn from the French market in 2011.
The FDA approved modafinil in 1998 for narcolepsy treatment, and later for shift work sleep disorde and obstructive sleep apnea in 2003. It was approved in the UK in December 2002. In the United States, modafinil is marketed by Cephalon, who acquired the rights from Lafon and purchased the company in 2001.
Cephalon introduced armodafinil, the (R)-enantiomer of modafinil, in the United States in 2007. Generic versions of modafinil became available in the US in 2012 after extensive patent litigation. | 4 | Stereochemistry |
Chemical-based transfection can be divided into several kinds: cyclodextrin, polymers, liposomes, or nanoparticles (with or without chemical or viral functionalization. See below).
*One of the cheapest methods uses calcium phosphate, originally discovered by F. L. Graham and A. J. van der Eb in 1973 (see also). HEPES-buffered saline solution (HeBS) containing phosphate ions is combined with a calcium chloride solution containing the DNA to be transfected. When the two are combined, a fine precipitate of the positively charged calcium and the negatively charged phosphate will form, binding the DNA to be transfected on its surface. The suspension of the precipitate is then added to the cells to be transfected (usually a cell culture grown in a monolayer). By a process not entirely understood, the cells take up some of the precipitate, and with it, the DNA. This process has been a preferred method of identifying many oncogenes.
*Another method is the use of cationic polymers such as DEAE-dextran or polyethylenimine (PEI). The negatively charged DNA binds to the polycation and the complex is taken up by the cell via endocytosis.
*Lipofection (or liposome transfection) is a technique used to inject genetic material into a cell by means of liposomes, which are vesicles that can easily merge with the cell membrane since they are both made of a phospholipid bilayer. Lipofection generally uses a positively charged (cationic) lipid (cationic liposomes or mixtures) to form an aggregate with the negatively charged (anionic) genetic material. This transfection technology performs the same tasks as other biochemical procedures utilizing polymers, DEAE-dextran, calcium phosphate, and electroporation. The efficiency of lipofection can be improved by treating transfected cells with a mild heat shock.
* Fugene is a series of widely used proprietary non-liposomal transfection reagents capable of directly transfecting a wide variety of cells with high efficiency and low toxicity.
*Dendrimer is a class of highly branched molecules based on various building blocks and synthesized through a convergent or a divergent method. These dendrimers bind the nucleic acids to form dendriplexes that then penetrate the cells. | 1 | Biochemistry |
Spermine synthase (, spermidine aminopropyltransferase, spermine synthetase) is an enzyme that converts spermidine into spermine. This enzyme catalyses the following chemical reaction
: S-adenosylmethioninamine + spermidine S-methyl-5'-thioadenosine + spermine
Spermine synthase is an enzyme involved in polyamine biosynthesis. It is present in all eukaryotes and plays a role in a variety of biological functions in plants Its structure consists of two identical monomers of 41 kDa with three domains each, creating a homodimer formed via dimerization. The interactions between one of the three domains, the N-terminals of the monomers, is responsible for dimerization as that is where the active site is located; the central terminal consisting of four β- strands structurally forming a lid for the third domain, the C-terminal domain. | 1 | Biochemistry |
Electrochlorination is the process of producing hypochlorite by passing electric current through salt water. This disinfects the water and makes it safe for human use, such as for drinking water or swimming pools. | 7 | Physical Chemistry |
BEI is very hazardous since it attacks nucleic acids and proteins as described above. It can be neutralised by sodium thiosulfate; the thiosulfate is a nucleophile which opens the three-membered ring.
The presence of BEI can be tested for using silver nitrate solution. | 0 | Organic Chemistry |
Lipid bilayers are structures of lipid molecules consisting of a hydrophobic tail and a hydrophilic head group. Therefore, these structures experience all the characteristic Interbilayer forces involved in that regime. | 6 | Supramolecular Chemistry |
Aliphatic nitro compounds can be synthesized by various methods; notable examples include:
*Free radical nitration of alkanes. The reaction produces fragments from the parent alkane, creating a diverse mixture of products; for instance, nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane are produced by treating propane with nitric acid in the gas phase (e.g. 350–450 °C and 8–12 atm).
*Nucleophilic substitution reactions between halocarbons or organosulfates with silver or alkali nitrite salts.
*Nitromethane can be produced in the laboratory by treating sodium chloroacetate with sodium nitrite.
*Oxidation of oximes or primary amines.
*Reduction of β-nitro alcohols or nitroalkenes.
*By decarboxylation of α-nitro carboxylic acids formed from nitriles and ethyl nitrate. | 0 | Organic Chemistry |
The complete quantum mechanical description was first performed by Bethe and Heitler. They assumed plane waves for electrons which scatter at the nucleus of an atom, and derived a cross section which relates the complete geometry of that process to the frequency of the emitted photon. The quadruply differential cross section, which shows a quantum mechanical symmetry to pair production, is
where is the atomic number, the fine-structure constant, the reduced Planck's constant and the speed of light. The kinetic energy of the electron in the initial and final state is connected to its total energy or its momenta via
where is the mass of an electron. Conservation of energy gives
where is the photon energy. The directions of the emitted photon and the scattered electron are given by
where is the momentum of the photon.
The differentials are given as
The absolute value of the virtual photon between the nucleus and electron is
The range of validity is given by the Born approximation
where this relation has to be fulfilled for the velocity of the electron in the initial and final state.
For practical applications (e.g. in Monte Carlo codes) it can be interesting to focus on the relation between the frequency of the emitted photon and the angle between this photon and the incident electron. Köhn and Ebert integrated the quadruply differential cross section by Bethe and Heitler over and and obtained:
with
and
However, a much simpler expression for the same integral can be found in (Eq. 2BN) and in (Eq. 4.1).
An analysis of the doubly differential cross section above shows that electrons whose kinetic energy is larger than the rest energy (511 keV) emit photons in forward direction while electrons with a small energy emit photons isotropically. | 7 | Physical Chemistry |
Thiamine triphosphate (ThTP) is a biomolecule found in most organisms including bacteria, fungi, plants and animals. Chemically, it is the triphosphate derivative of the vitamin thiamine. | 1 | Biochemistry |
Hydroxylamine-O-sulfonic acid (HOSA) or aminosulfuric acid is the inorganic compound with molecular formula HNOS that is formed by the sulfonation of hydroxylamine with oleum. It is a white, water-soluble and hygroscopic, solid, commonly represented by the condensed structural formula HNOSOH, though it actually exists as a zwitterion and thus is more accurately represented as HNOSO. It is used as a reagent for the introduction of amine groups (–NH), for the conversion of aldehydes into nitriles and alicyclic ketones into lactams (cyclic amides), and for the synthesis of variety of nitrogen-containing heterocycles. | 0 | Organic Chemistry |
Ocean salinity has been constant at about 3.5% for a very long time. Salinity stability in oceanic environments is important as most cells require a rather constant salinity and do not generally tolerate values above 5%. The constant ocean salinity was a long-standing mystery, because no process counterbalancing the salt influx from rivers was known. Recently it was suggested that salinity may also be strongly influenced by seawater circulation through hot basaltic rocks, and emerging as hot water vents on mid-ocean ridges. However, the composition of seawater is far from equilibrium, and it is difficult to explain this fact without the influence of organic processes. One suggested explanation lies in the formation of salt plains throughout Earth's history. It is hypothesized that these are created by bacterial colonies that fix ions and heavy metals during their life processes.
In the biogeochemical processes of Earth, sources and sinks are the movement of elements. The composition of salt ions within our oceans and seas is: sodium (Na), chlorine (Cl), sulfate (SO), magnesium (Mg), calcium (Ca) and potassium (K). The elements that comprise salinity do not readily change and are a conservative property of seawater. There are many mechanisms that change salinity from a particulate form to a dissolved form and back. Considering the metallic composition of iron sources across a multifaceted grid of thermomagnetic design, not only would the movement of elements hypothetically help restructure the movement of ions, electrons, and the like, but would also potentially and inexplicably assist in balancing the magnetic bodies of the Earth's geomagnetic field. The known sources of sodium i.e. salts are when weathering, erosion, and dissolution of rocks are transported into rivers and deposited into the oceans.
The Mediterranean Sea as being Gaia's kidney is found ([http://scimar.icm.csic.es/scimar/index.php/secId/6/IdArt/209/ here]) by Kenneth J. Hsu, a correspondence author in 2001. Hsu suggests the "desiccation" of the Mediterranean is evidence of a functioning Gaia "kidney". In this and earlier suggested cases, it is plate movements and physics, not biology, which performs the regulation. Earlier "kidney functions" were performed during the "deposition of the Cretaceous (South Atlantic), Jurassic (Gulf of Mexico), Permo-Triassic (Europe), Devonian (Canada), and Cambrian/Precambrian (Gondwana) saline giants." | 9 | Geochemistry |
Ouabain is a highly toxic compound, however, it has a low bioavailability and is absorbed poorly from the alimentary tract as so much of the oral dose is destroyed. Intravenous administration results in greater available concentrations. After intravenous administration, the onset of action occurs within 2–10 minutes in humans with the maximum effect enduring for 1.5 hours.
Ouabain is eliminated by renal excretion, largely unchanged. | 0 | Organic Chemistry |
S. Finch and R. H. Collier, in a paper entitled "Insects can see clearly now the weeds have gone", showed experimentally that flying pests are far less successful if their host-plants are surrounded by other plants or even "decoy-plants" coloured green. Pests find hosts in stages, first detecting plant odours which induce it to try to land on the host plant, avoiding bare soil. If the plant is isolated, then the insect simply lands on the patch of green near the odour, making an "appropriate landing". If it finds itself on the wrong plant, an "inappropriate landing", it takes off and flies to another plant; it eventually leaves the area if there are too many "inappropriate" landings. Companion planting of clover as ground cover was equally disruptive to eight pest species from four different insect orders. In a test, 36% of cabbage root flies laid eggs beside cabbages growing in bare soil (destroying the crop), compared to only 7% beside cabbages growing in clover (which allowed a good crop). Simple decoys of green cardboard worked just as well as the live ground cover. | 1 | Biochemistry |
Second sound has been observed in solid He and He,
and in some dielectric solids such as Bi in the temperature
range of 1.2 to 4.0 K with a velocity of 780 ± 50 m/s,
or solid sodium fluoride (NaF) around 10 to 20 K. In 2021 this effect was observed in a BKT superfluid as well as in a germanium semiconductor | 7 | Physical Chemistry |
In (forward) osmosis, the solvent moves from an area of low solute concentration (high water potential), through a membrane, to an area of high solute concentration (low water potential). The driving force for the movement of the solvent is the reduction in the Gibbs free energy of the system in which the difference in solvent concentration between the sides of a membrane is reduced. This is called osmotic pressure. It reduces as the solvent moves into the more concentrated solution. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications.
RO differs from filtration in that the mechanism of fluid flow is reversed, as the solvent crosses membrane, leaving the solute behind. The predominant removal mechanism in membrane filtration is straining, or size exclusion, where the pores are 0.01 micrometers or larger, so the process can theoretically achieve perfect efficiency regardless of parameters such as the solution's pressure and concentration. RO instead involves solvent diffusion across a membrane that is either nonporous or uses nanofiltration with pores 0.001 micrometers in size. The predominant removal mechanism is from differences in solubility or diffusivity, and the process is dependent on pressure, solute concentration, and other conditions.
RO requires pressure between 2–17 bar (30–250 psi) for fresh and brackish water, and 40–82 bar (600–1200 psi) for seawater. Seawater has around 27 bar (390 psi) natural osmotic pressure that must be overcome.
Membrane pore sizes vary from 0.1 to 5,000 nm. Particle filtration removes particles of 1 µm or larger. Microfiltration removes particles of 50 nm or larger. Ultrafiltration removes particles of roughly 3 nm or larger. Nanofiltration removes particles of 1 nm or larger. RO is in the final category of membrane filtration, hyperfiltration, and removes particles larger than 0.1 nm. | 3 | Analytical Chemistry |
Prior to, and during the 1920s, refrigerators used toxic gases as refrigerants, including ammonia, sulphur dioxide, and chloromethane. Later in the 1920s after a series of fatal accidents involving the leaking of chloromethane from refrigerators, a major collaborative effort began between American corporations Frigidaire, General Motors, and DuPont to develop a safer, non-toxic alternative. Thomas Midgley Jr. of General Motors is credited for synthesizing the first chlorofluorocarbons. The Frigidaire corporation was issued the first patent, number 1,886,339, for the formula for CFCs on December 31, 1928. In a demonstration for the American Chemical Society, Midgley flamboyantly demonstrated all these properties by inhaling a breath of the gas and using it to blow out a candle in 1930.
By 1930, General Motors and Du Pont formed the Kinetic Chemical Company to produce Freon, and by 1935, over 8 million refrigerators utilizing R-12 were sold by Frigidaire and its competitors. In 1932, Carrier began using R-11 in the worlds first self-contained home air conditioning unit known as the "atmospheric cabinet". As a result of CFCs being largely non-toxic, they quickly became the coolant of choice in large air-conditioning systems. Public health codes in cities were revised to designate chlorofluorocarbons as the only gases that could be used as refrigerants in public buildings.
Growth in CFCs continued over the following decades leading to peak annual sales of over 1 billion USD with greater than 1 million metric tonnes being produced annually. It wasn't until 1974 that it was first discovered by two University of California chemists, Professor F. Sherwood Rowland and Dr. Mario Molina, that the use of chlorofluorocarbons were causing a significant depletion in atmospheric ozone concentrations. This initiated the environmental effort which eventually resulted in the enactment of the Montreal Protocol. | 2 | Environmental Chemistry |
In the region close to the minimum of the objective function, , the system approximates to a linear least-squares system, for which
Therefore, the parameter values are (approximately) linear combinations of the observed data values and the errors on the parameters, , can be obtained by error propagation from the observations, , using the linear formula. Let the variance-covariance matrix for the observations be denoted by and that of the parameters by . Then,
When , this simplifies to
In most cases the errors on the observations are un-correlated, so that is diagonal.
If so, each weight should be the reciprocal of the variance of the corresponding observation. For example, in a potentiometric titration, the weight at a titration point, , can be given by
where is the error in electrode potential or pH, is the slope of the titration curve and is the error on added volume.
When unit weights are used (, ) it is implied that the experimental errors are uncorrelated and all equal: , where is known as the variance of an observation of unit weight, and is an identity matrix. In this case is approximated by
where is the minimum value of the objective function and and are the number of data and parameters, respectively.
In all cases, the variance of the parameter is given by and the covariance between parameters and is given by . Standard deviation is the square root of variance. These error estimates reflect only random errors in the measurements. The true uncertainty in the parameters is larger due to the presence of systematic errors—which, by definition, cannot be quantified.
Note that even though the observations may be uncorrelated, the parameters are always correlated. | 7 | Physical Chemistry |
Tre recombinase is an experimental enzyme that in lab tests has removed DNA inserted by HIV from infected cells. Through selective mutation, Cre recombinase which recognizes loxP sites are modified to identify HIV long terminal repeats (loxLTR) instead. As a result, instead of performing Cre-Lox recombination, the new enzyme performs recombination at HIV provirus sites.
The structure of Tre in complex with loxLTR has been resolved (), allowing for analyzing the roles of individual mutations. | 1 | Biochemistry |
When first invented, the Haber process competed against another industrial process, the cyanamide process. However, the cyanamide process consumed large amounts of electrical power and was more labor-intensive than the Haber process.
As of 2018, the Haber process produces 230 million tonnes of anhydrous ammonia per year. The ammonia is used mainly as a nitrogen fertilizer as ammonia itself, in the form of ammonium nitrate, and as urea. The Haber process consumes 3–5% of the worlds natural gas production (around 1–2% of the worlds energy supply). In combination with advances in breeding, herbicides, and pesticides, these fertilizers have helped to increase the productivity of agricultural land:
The energy-intensity of the process contributes to climate change and other environmental problems such as the leaching of nitrates into groundwater, rivers, ponds, and lakes; expanding dead zones in coastal ocean waters, resulting from recurrent eutrophication; atmospheric deposition of nitrates and ammonia affecting natural ecosystems; higher emissions of nitrous oxide (NO), now the third most important greenhouse gas following CO and CH. The Haber–Bosch process is one of the largest contributors to a buildup of reactive nitrogen in the biosphere, causing an anthropogenic disruption to the nitrogen cycle.
Since nitrogen use efficiency is typically less than 50%, farm runoff from heavy use of fixed industrial nitrogen disrupts biological habitats.
Nearly 50% of the nitrogen found in human tissues originated from the Haber–Bosch process. Thus, the Haber process serves as the "detonator of the population explosion", enabling the global population to increase from 1.6 billion in 1900 to 7.7 billion by November 2018.
Reverse fuel cell technology converts electric energy, water and air into ammonia without a separate hydrogen electrolysis process. | 7 | Physical Chemistry |
The word polyurea is derived from the Greek words πολυ- - poly- meaning "many"; and ουρίας - oûron meaning "to urinate" (referring to the substance urea, found in urine). Urea or carbamide is an organic compound with the chemical formula (NH)CO. The molecule has two amine groups (–NH) joined by a carbonyl functional group (C=O). In a polyurea, alternating monomer units of isocyanates and amines react with each other to form urea linkages. Ureas can also be formed from the reaction of isocyanates and water which forms a carbamic acid intermediate. This acid quickly decomposes by splitting off carbon dioxide and leaving behind an amine. This amine then reacts with another isocyanate group to form the polyurea linkage. This two step reaction is used to make what is commonly but improperly called polyurethane foam. The carbon dioxide that is liberated in this reaction is the primary blowing (foaming) agent especially in many polyurethane foams which more precisely should be called polyurethane/urea foams. | 7 | Physical Chemistry |
The following advantages have been reported for the BBOC:
* very high oxygen efficiency – the injection of oxygen directly into the reaction zone within the furnace results in much greater oxygen efficiency (close to 100%) than with reverberatory furnaces (8% for the Niihama furnace) or top-blown rotary converters (about 30%)
* reduced off-gas volume – the use of industrial oxygen and the high oxygen efficiency of the process means that excess air is not required to achieve the results. This reduces the off-gas volume and thus the cost of the off-gas train and handling equipment. Rand Refinery reported that the off-gas volume of the BBOC was about 75% of that of a TBRC with a special lance conversion and only 19% of that of top-submerged lance smelting. Niihama refinery reported that its BBOC had 15% of the off-gas volume of its reverberatory furnace while producing 1.8 times the product
* higher reaction rates – by injecting the oxygen directly into the reaction zone, the reaction rates are much higher than in reverberatory furnaces where the oxygen has first to penetrate the slag layer. BRM reported a reaction rate per unit of furnace volume of 10–20 times that of the reverberatory furnace
* lower refractory wear – Rand Refinery reported that the refractory linings of its TBRC furnaces needed replacing after approximately two weeks, while the linings of its BBOC furnace lasted about 14 weeks
* lower precious metal inventories – a consequence of the higher reaction rates is that smaller furnace volumes are required and there are smaller cycle times. This results in lower precious metal inventories. In lead slimes bullion processing, the silver inventory was reduced from 4.5 t to 1.25 t after replacing a reverberatory furnace with a BBOC and at BRM the silver inventory fell from 11.5 t to 3.1 t with the introduction of the BBOC furnace
* better energy efficiency – a supplementary burner is needed only during heating the charge and doré casting operations. During cupellation, the oxidation reactions provide sufficient heat to maintain temperature. There was a 92% reduction in fuel consumption per tonne of doré treated reported for the BBOC at the Niihama refinery
* better product quality – BHAS reported that lead and copper levels in silver produced from the BBOC of 0.01% and 0.1% respectively were possible when the furnace was operating under design conditions, compared to 0.04% and 0.2% for the old reverberatory furnace, and 0.8% and 0.4% for the Sirosmelt furnace. Rand Refinery reported that a doré bullion of 99.2% was achievable. BRM reported that its doré is 99.7% silver
* higher recoveries of precious metals – due to changes in the way the BBOC is operated compare to reverberatory furnaces, notably in being able to use deeper layers of slag, there is an increase in the recovery of precious metals compared to the reverberatory furnaces. Replacement of reverberatory furnaces with BBOC furnaces saw the direct silver recovery increase from 92.5% to 97.5% at BRM and from 70% to over 95% at Niihama
* simple vessel design – the BBOC has a relatively simple vessel design, without the complex moving parts of TBRCs
* good process control – the high oxygen utilization allows good process control, particularly when combined with an oxygen sensor in the off-gas system
* lower labor requirements – the BBOC has a lower labor requirement than reverberatory furnaces, top-submerged lance furnaces and TBRCs
* lower operating costs – lower labor requirements, lower fuel requirements and longer refractory life contributed to a 28.3% reduction in overall operating costs when the BBOC was installed at the Rand Refinery
* lower capital cost – the BBOC is a simpler furnace than TBRC or top-submerged lance furnaces. Rand Refinery reported a capital cost comparison indicating that its BBOC option was 67% of the cost of a top-submerged lance option. | 8 | Metallurgy |
Certain materials, such as glass and glycerol, may harden without crystallizing; these are called amorphous solids. Amorphous materials, as well as some polymers, do not have a freezing point, as there is no abrupt phase change at any specific temperature. Instead, there is a gradual change in their viscoelastic properties over a range of temperatures. Such materials are characterized by a glass transition that occurs at a glass transition temperature, which may be roughly defined as the "knee" point of the material's density vs. temperature graph. Because vitrification is a non-equilibrium process, it does not qualify as freezing, which requires an equilibrium between the crystalline and liquid state. | 1 | Biochemistry |
The Edinburgh Handedness Inventory is a measurement scale used to assess the dominance of a person's right or left hand in everyday activities, sometimes referred to as laterality. The inventory can be used by an observer assessing the person, or by a person self-reporting hand use. The latter method tends to be less reliable due to a person over-attributing tasks to the dominant hand.
The Edinburgh Handedness Inventory was published in 1971 by Richard Carolus Oldfieldand has been used in various scientific studies as well as popular literature. According to Google Scholar it has been cited tens of thousands of times. Within the very substantial literature on handedness it is used far more than any rival, such as FLANDERS, or the Annett Hand Preference Questionnaire, which is not good at eliciting either-hand responses.
Nevertheless, profound dissatisfaction with the Inventory has been expressed and statistical analysis of the Inventory has shown that the two-handed items broom and box are poorly correlated with the other eight items, while drawing is too highly correlated with writing to add information. A major revision has been published. | 4 | Stereochemistry |
RNA Pol II-mediated gene transcription induces a local opening of chromatin state through the recruitment of histone acetyltransferases and other histone modifiers that promote euchromatin formation. It was proposed that the presence of these enzymes could also induce an opening of chromatin at enhancer regions, which are usually present at distant locations but can be recruited to target genes through looping of DNA. In this model, eRNAs are therefore expressed in response to RNA Pol II transcription and therefore carry no biological function. | 1 | Biochemistry |
In quantum physics, the scattering amplitude is the probability amplitude of the outgoing spherical wave relative to the incoming plane wave in a stationary-state scattering process.
At large distances from the centrally symmetric scattering center, the plane wave is described by the wavefunction
where is the position vector; ; is the incoming plane wave with the wavenumber along the axis; is the outgoing spherical wave; is the scattering angle (angle between the incident and scattered direction); and is the scattering amplitude. The dimension of the scattering amplitude is length. The scattering amplitude is a probability amplitude; the differential cross-section as a function of scattering angle is given as its modulus squared,
The asymptotic form of the wave function in arbitrary external field takes the form
where is the direction of incidient particles and is the direction of scattered particles. | 7 | Physical Chemistry |
Ali Akbar Moosavi-Movahedi (born in Shiraz, Iran, February 1953) is an Iranian Biophysicist, and Biophysical Chemist at the Institute of Biochemistry and Biophysics, University of Tehran. He is the founder of the [http://isobc.com/ Iran Society of Biophysical Chemistry] . He is the fellow of The World Academy of Sciences (TWAS), fellow of Islamic World Academy of Sciences (IAS), and a member of the Islamic Republic of Iran Academy of Sciences. | 7 | Physical Chemistry |
Homolytic bond cleavage is a process where the electron pair comprising a bond is split, causing the bond to break. This is denoted by two single barbed curved arrows pointing away from the bond. The consequence of this process is the retention of a single unpaired electron denoted by a dot on each of the atoms that were formerly joined by a bond. The single electron movement can be denoted by a curved arrow commonly referred to as a fish hook. These single electron species are known as free radicals. Heat or light are required to provide enough energy for this process to occur.
For example, Ultraviolet light causes the chlorine-chlorine bond to break homolytically. The pair of electrons become split, denoted by the two fish hook arrows between both atoms pointing to both chlorine atoms. After the reaction occurs, it leads to both chlorine molecules left with a single unpaired electron. This is the initiation stage of free radical halogenation. | 0 | Organic Chemistry |
The substituents on the diazirine affect which carbene species is generated upon irradiation and subsequent photolytic cleavage. Diazirine substituents that are electron donating in nature can donate electron density to the empty p-orbital of the carbene that will be formed, and hence can stabilize the singlet state. For example, phenyldiazirine produces phenylcarbene in the singlet carbene state whereas p-nitrophenylchlorodiazirine or trifluorophenyldiazirine produce the respective triplet carbene products.
Electron donating substituents can also encourage photoisomerization to the linear diazo compound , rather than the singlet carbene, and hence these compounds are unfavorable for use in biological assays. On the other hand, trifluoroaryldiazirines in particular show favorable stability and photolytic qualities and are most commonly used in biological applications. Carbenes produced from diazirines are quickly quenched by reaction with water molecules, and hence yields for photoreactive crosslinking assays are often low. Yet, as this feature minimizes unspecific labeling, it is actually an advantage of using diazirines. | 5 | Photochemistry |
The ground state is believed to be a bent triplet, with two orthogonal sp hybrid orbitals singly occupied by unpaired spins. One electron occupies an orbital of sigma symmetry in the plane of the rings, while the other occupies an orbital of pi symmetry, which interacts with the pi systems of the adjacent aromatic rings (delocalization into the rings is minimal, since zero-field parameter D is high). The zero field splitting parameters predict a bond angle greater than 135°, and since the ideal bond geometry for cyclopentane carbons is about 109°, considerable ring strain causes the methylene sigma bonds to be bent. In the singlet state, the spin-paired electrons occupy the sp hybrid orbital, orthogonal to an empty p-orbital. Conversion of singlet to triplet fluorenylidene is achieved through intersystem crossing (ISC). | 0 | Organic Chemistry |
Xing enjoyed collecting crafts relevant the tortoise.
Xings father Duan () was a member of Hanlin Academy in the Late Qing dynasty, he once studied in Japan and used to be an officer at the Beiyang government. Xings mother, Zhang Xian (), was a housewife. Xing and his wife Qian Cunrou (), a microbiologist, had two sons. | 0 | Organic Chemistry |
The cell cycle is a four-stage process that a cell goes through as it develops and divides. It includes Gap 1 (G1), synthesis (S), Gap 2 (G2), and mitosis (M).The cell either restarts the cycle from G1 or leaves the cycle through G0 after completing the cycle. The cell can progress from G0 through terminal differentiation.
The interphase refers to the phases of the cell cycle that occur between one mitosis and the next, and includes G1, S, and G2. | 1 | Biochemistry |
The disaster prompted many countries to introduce tougher rules for the testing and licensing of drugs, such as the 1962 Kefauver Harris Amendment (US), 1965 Directive 65/65/EEC1 (EU), and the Medicines Act 1968 (UK). In the United States, the new regulations strengthened the FDA, among other ways, by requiring applicants to prove efficacy and to disclose all side effects encountered in testing. The FDA subsequently initiated the Drug Efficacy Study Implementation to reclassify drugs already on the market. | 4 | Stereochemistry |
The heteronuclear single quantum coherence or heteronuclear single quantum correlation experiment, normally abbreviated as HSQC, is used frequently in NMR spectroscopy of organic molecules and is of particular significance in the field of protein NMR. The experiment was first described by Geoffrey Bodenhausen and D. J. Ruben in 1980. The resulting spectrum is two-dimensional (2D) with one axis for proton (H) and the other for a heteronucleus (an atomic nucleus other than a proton), which is usually C or N. The spectrum contains a peak for each unique proton attached to the heteronucleus being considered. The 2D HSQC can also be combined with other experiments in higher-dimensional NMR experiments, such as NOESY-HSQC or TOCSY-HSQC. | 7 | Physical Chemistry |
3-Carboxy-cis,cis-muconic acid is a metabolite of the catechin degradation by Bradyrhizobium japonicum.
The enzyme 3-carboxy-cis,cis-muconate cycloisomerase uses 2-carboxy-2,5-dihydro-5-oxofuran-2-acetate to produce 3-carboxy-cis,cis-muconate.
The enzyme carboxy-cis,cis-muconate cyclase uses 3-carboxy-2,5-dihydro-5-oxofuran-2-acetate to produce 3-carboxy-cis,cis-muconate.
The enzyme protocatechuate 3,4-dioxygenase uses 3,4-dihydroxybenzoate and O to produce 3-carboxy-cis,cis-muconate. | 1 | Biochemistry |
A variety of complexes - a subset of metallaborane - are known with one or two dicarbollide ligands. An example of a 1:1 complex is [Mn(CO)(η-7,8-CBH)].
Most heavily studied are complexes with two dicarbollide ligands, especially sandwich complexes. Thus, these are prepared by salt metathesis reactions, as illustrated by the synthesis of the ferrocene analogue:
:2 NaCBH + FeCl → Na[Fe(CBH)] + 2 NaCl
These bisdicarbollide dianions are often readily oxidized. Fe(III), Co(III), Ni(III), and Ni(IV) derivatives are known. In some cases, the oxidation induces rearrangement of the CB cage to give complexes where the carbon centers are nonadjacent. | 7 | Physical Chemistry |
Polyunsaturated aldehydes are oxylipins that are formed from lipids (specifically the fatty acid portion of lipids) when diatoms are exposed to environmental stresses. Stresses can include nutrient limitations, grazing by predators, and wounding.
In particular, damage to diatom cells as a result of grazing by zooplankton invokes a chemical defense mechanism that produces PUA’s as secondary metabolites from fatty acids. The production mechanism is as follows:
# Grazing by predators results in diatom cell membrane disruption.
# Enzymes (lipases) are produced in response to the damaged membranes. These enzymes make contact with newly freed phospholipids (from cell membranes) and catalyze the formation of polyunsaturated fatty acids.
# The enzyme lipoxygenase then catalyzes the reaction of fatty acids to polyunsaturated aldehydes, which are then directly exposed to the grazing zooplankton.
Thalassiosira rotula represents the most well-studied diatom species in terms of polyunsaturated aldehyde production. Wichard et al. determined that only 30% of PUA precursor molecules remain in T. rotula within minutes of cell membrane wounding, indicating a fast rate of response by diatoms to zooplankton grazing. | 1 | Biochemistry |
In elementary applications, Raoults law is generally valid when the liquid phase is either nearly pure or a mixture of similar substances. Raoults law may be adapted to non-ideal solutions by incorporating two factors that account for the interactions between molecules of different substances. The first factor is a correction for gas non-ideality, or deviations from the ideal-gas law. It is called the fugacity coefficient (). The second, the activity coefficient , is a correction for interactions in the liquid phase between the different molecules.
This modified or extended Raoult's law is then written as | 7 | Physical Chemistry |
The process is commonly used in control of the morphology of polymer blends, for applications in thermoelectrics, solid-state lighting, polymer electrolytes, composites, membrane formation, and surface pattern formations. | 7 | Physical Chemistry |
To be effective on a given ore slurry, the collectors are chosen based upon their selective wetting of the types of particles to be separated. A good collector will adsorb, physically or chemically, with one of the types of particles. The wetting activity of a surfactant on a particle can in principle be quantified by measuring the contact angles of the liquid/bubble interface. Another important measure for attachment of bubbles to particles is induction time, the time required for the particle and bubble to rupture the thin film separating the particle and bubble. This rupturing is achieved by the surface forces between the particle and bubble.
The mechanisms for the bubble-particle attachment is complex but is viewed as consisting of three steps: collision, attachment, and detachment. The collision is achieved by particles being within the collision tube of a bubble and this is affected by the velocity of the bubble and radius of the bubble. The collision tube corresponds to the region in which a particle will collide with the bubble, with the perimeter of the collision tube corresponding to the grazing trajectory.
The attachment of the particle to the bubble is controlled by the induction time of the particle and bubble. The particle and bubble need to bind and this occurs if the time in which the particle and bubble are in contact with each other is larger than the required induction time. This induction time is affected by the fluid viscosity, particle and bubble size and the forces between the particle and bubbles.
The detachment of a particle and bubble occurs when the force exerted by the surface tension is exceeded by shear forces and gravitational forces. These forces are complex and vary within the cell. High shear will be experienced close to the impeller of a mechanical flotation cell and mostly gravitational force in the collection and cleaning zone of a flotation column.
Significant issues of entrainment of fine particles occurs as these particles experience low collision efficiencies as well as sliming and degradation of the particle surfaces. Coarse particles show a low recovery of the valuable mineral due to the low liberation and high detachment efficiencies. | 8 | Metallurgy |
Palliser and Parry have examined about 100 scales and found that they can use them for locating B-strands on the surface of proteins. Hydrophobicity scales were also used to predict the preservation of the genetic code. Trinquier observed a new order of the bases that better reflect the conserved character of the genetic code. They believed new ordering of the bases was uracil-guanine-cystosine-adenine (UGCA) better reflected the conserved character of the genetic code compared to the commonly seen ordering UCAG. | 6 | Supramolecular Chemistry |
The electrolyte for this process is a mixture of lead fluorosilicate ("PbSiF") and hexafluorosilicic acid (HSiF) operating at 45 °C (113 °F). Cathodes are thin sheets of pure lead and anodes are cast from the impure lead to be purified. A potential of 0.5 volts is applied. At the anode, lead dissolves, as do metal impurities that are less noble than lead. Impurities that are more noble than lead, such as silver, gold, and bismuth, flake from the anode as it dissolves and settle to the bottom of the vessel as "anode mud." Pure metallic lead plates onto the cathode, with the less noble metals remaining in solution. Because of its high cost, electrolysis is used only when very pure lead is needed. Otherwise pyrometallurgical methods are preferred, such as the Parkes process followed by the Betterton-Kroll process. | 8 | Metallurgy |
The purpose of using RNA FISH is to detect target mRNA transcripts in cells, tissue sections, or even whole-mounts. The process is done in 3 main procedures: tissue preparation (pre-hybridization), hybridization, and washing (post-hybridization).
The tissue preparation starts by collecting the appropriate tissue sections to perform RNA FISH. First, cells, circulating tumor cells (CTCs), formalin-fixed paraffin-embedded (FFPE), or frozen tissue sections are fixed. Some commonly used fixatives are 4% formaldehyde or paraformaldehyde (PFA) in phosphate buffered saline (PBS). FISH has also been successfully done on unfixed cells. After fixation, samples are permeabilized to allow the penetration of hybridization reagents. The use of detergents at a 0.1% concentration is commonly used to enhance the tissue permeability such as Tween-20 or Triton X-100.
It is critical for the hybridization process to have all optimal conditions to have a successful in situ result, including temperature, pH, salt concentration, and time of the hybridization reaction. After checking all the necessary conditions, hybridization steps can be started by first adding a target-specific probe, composed of 20 oligonucleotide pairs, hybridizes to the target RNA(s). Separate but compatible signal amplification systems enable the multiplex assay (up to two targets per assay). Signal amplification is achieved via series of sequential hybridization steps.
After the hybridization steps, washing steps are performed. These steps aim to remove nonspecific hybrids and get rid of unbound probe molecules from the samples to reduce any background signaling. The use of ethanol washes are typically used at this stage to reduce autofluorescence in tissues or cells. At the end of the assay the tissue samples are visualized under a fluorescence microscope such as the confocal fluorescence microscope and the Keyence microscope. | 1 | Biochemistry |
Under lab conditions, xDNA orients itself in the syn conformation. This unfortunately does not expose the binding face of the xDNA nucleotides to face the neighbouring strand for binding, meaning that extra measures must be applied to alter the conformation of xDNA before attempting to form helices. However, the anti and syn orientations are practically identical energetically in expanded bases. This conformational preference is seen primarily in pyrimidines, and purines display minimal preference for orientation. | 1 | Biochemistry |
Kathlyn Ann Parker is a chemist known for her work on synthesis of compounds, especially organic compounds with biological roles. She is an elected fellow of the American Chemical Society and a recipient of the Garvan–Olin Medal in chemistry. | 0 | Organic Chemistry |
Therapy is supportive and includes removal from further beryllium exposure. For very severe cases mechanical ventilation may be required. | 1 | Biochemistry |
In food chemistry and medicinal chemistry, the term "contamination" is used to describe harmful intrusions, such as the presence of toxins or pathogens in food or pharmaceutical drugs. | 9 | Geochemistry |
Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe hypothermia, there may be hallucinations and paradoxical undressing, in which a person removes their clothing, as well as an increased risk of the heart stopping.
Hypothermia has two main types of causes. It classically occurs from exposure to cold weather and cold water immersion. It may also occur from any condition that decreases heat production or increases heat loss. Commonly, this includes alcohol intoxication but may also include low blood sugar, anorexia and advanced age. Body temperature is usually maintained near a constant level of through thermoregulation. Efforts to increase body temperature involve shivering, increased voluntary activity, and putting on warmer clothing. Hypothermia may be diagnosed based on either a persons symptoms in the presence of risk factors or by measuring a persons core temperature.
The treatment of mild hypothermia involves warm drinks, warm clothing, and voluntary physical activity. In those with moderate hypothermia, heating blankets and warmed intravenous fluids are recommended. People with moderate or severe hypothermia should be moved gently. In severe hypothermia, extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass may be useful. In those without a pulse, cardiopulmonary resuscitation (CPR) is indicated along with the above measures. Rewarming is typically continued until a person's temperature is greater than . If there is no improvement at this point or the blood potassium level is greater than 12 millimoles per litre at any time, resuscitation may be discontinued.
Hypothermia is the cause of at least 1,500 deaths a year in the United States. It is more common in older people and males. One of the lowest documented body temperatures from which someone with accidental hypothermia has survived is in a 2-year-old boy from Poland named Adam. Survival after more than six hours of CPR has been described. In individuals for whom ECMO or bypass is used, survival is around 50%. Deaths due to hypothermia have played an important role in many wars.
The term is from Greek ῠ̔πο (ypo), meaning "under", and θέρμη (thérmē), meaning "heat". The opposite of hypothermia is hyperthermia, an increased body temperature due to failed thermoregulation. | 1 | Biochemistry |
Hierlemann's research initially was mostly in the area of chemical sensors and microsensors. In particular, he worked on the detection of organic volatiles and the discrimination of enantiomers in the gas phase. He then adopted microtechnology and, specifically, CMOS-based microelectronics to devise complex microsensor systems. The current interdisciplinary research is rooted in engineering and physics and targeted at questions in biology and medicine. It includes the development of CMOS-based integrated chemical and biomicrosystems, as well as bioelectronics and high-density microelectrode arrays. The high-density microelectrode arrays are used for fundamental research in information processing and signaling characteristics of neurons or brain cells. Moreover, the research group is engaged in the development of microfluidics for investigating the characteristics of single cells and microtissues.
Applications of Hierlemanns and his groups technologies are in the fields of systems biology, drug testing, personalized medicine, and neuroscience. | 7 | Physical Chemistry |
Ballentine earned his Ph.D. at the University of Cambridge in 1992. He went on to hold research positions at the Paul Scherrer Institut, Switzerland, the University of Michigan, and ETH Zurich, Switzerland. From 2001 to 2013, he held positions at the University of Manchester before joining the faculty at the University of Oxford.
Ballentine has held the vice president, president, and past president positions with the European Association of Geochemistry. He is a member of the Board of Governors of the Oxford Museum of Natural History and the American Geophysical Union, as well as a former scientific steering committee member for the Deep Carbon Observatory. In 2008, he won the Geological Society of London Bigsby medal for significant contributions to geology. The AGU chose Ballentine as a Fellow in 2013, and in 2016, he won the Eni Award, given to researchers who make advanced scientific breakthroughs in the field of energy, for "New Frontiers of Hydrocarbons". | 9 | Geochemistry |
A separation process is a method that converts a mixture or a solution of chemical substances into two or more distinct product mixtures, a scientific process of separating two or more substances in order to obtain purity. At least one product mixture from the separation is enriched in one or more of the source mixture's constituents. In some cases, a separation may fully divide the mixture into pure constituents. Separations exploit differences in chemical properties or physical properties (such as size, shape, mass, density, or chemical affinity) between the constituents of a mixture.
Processes are often classified according to the particular properties they exploit to achieve separation. If no single difference can be used to accomplish the desired separation, multiple operations can often be combined to achieve the desired end.
With a few exceptions, elements or compounds exist in nature in an impure state. Often these raw materials must go through a separation before they can be put to productive use, making separation techniques essential for the modern industrial economy.
The purpose of separation may be:
* analytical: to identify the size of each fraction of a mixture is attributable to each component without attempting to harvest the fractions.
* preparative: to "prepare" fractions for input into processes that benefit when components are separated.
Separations may be performed on a small scale, as in a laboratory for analytical purposes, or on a large scale, as in a chemical plant. | 3 | Analytical Chemistry |
Classical variables that time reversal negates include:
:, the time when an event occurs
:, velocity of a particle
:, linear momentum of a particle
:, angular momentum of a particle (both orbital and spin)
:, electromagnetic vector potential
:, magnetic field
:, magnetic auxiliary field
:, density of electric current
:, magnetization
:, Poynting vector
:, power (rate of work done). | 7 | Physical Chemistry |
Traces are better known in their fossilized form than in modern sediments. This makes it difficult to interpret some fossils by comparing them with modern traces, even though they may be extant or even common. The main difficulties in accessing extant burrows stem from finding them in consolidated sediment, and being able to access those formed in deeper water.
Trace fossils are best preserved in sandstones; the grain size and depositional facies both contributing to the better preservation. They may also be found in shales and limestones. | 2 | Environmental Chemistry |
Regular achiral organocatalysts are based on nitrogen such as piperidine used in the Knoevenagel condensation. DMAP used in esterifications and DABCO used in the Baylis-Hillman reaction. Thiazolium salts are employed in the Stetter reaction. These catalysts and reactions have a long history but current interest in organocatalysis is focused on asymmetric catalysis with chiral catalysts, called asymmetric organocatalysis or enantioselective organocatalysis. A pioneering reaction developed in the 1970s is called the Hajos–Parrish–Eder–Sauer–Wiechert reaction. Between 1968 and 1997, there were only a few reports of the use of small organic molecules as catalysts for asymmetric reactions (the Hajos–Parrish reaction probably being the most famous), but these chemical studies were viewed more as unique chemical reactions than as integral parts of a larger, interconnected field.
In this reaction, naturally occurring chiral proline is the chiral catalyst in an Aldol reaction. The starting material is an achiral triketone and it requires just 3% of proline to obtain the reaction product, a ketol in 93% enantiomeric excess. This is the first example of an amino acid-catalyzed asymmetric aldol reaction.
The asymmetric synthesis of the Wieland-Miescher ketone (1985) is also based on proline and another early application was one of the transformations in the total synthesis of Erythromycin by Robert B. Woodward (1981). A mini-review digest article focuses on selected recent examples of total synthesis of natural and pharmaceutical products using organocatalytic reactions.
Many chiral organocatalysts are an adaptation of chiral ligands (which together with a metal center also catalyze asymmetric reactions) and both concepts overlap to some degree.
A breakthrough in the field of organocatalysis came in 1997 when Yian Shi reported the first general, highly enantioselective organocatalytic reaction with the catalytic asymmetric epoxidation of trans- and trisubstituted olefins with chiral dioxiranes. Since that time, several different types of reactions have been developed. | 0 | Organic Chemistry |
It takes a noble gas atom in an excited electronic state to form an excimer molecule such as a noble gas dimer or noble gas halide. Sufficiently high energy (approximately 10 eV) is required to obtain a noble gas atom in the lowest excited electronic state, which provides the formation of an excimer molecule. The most convenient way to excite gases is by an electric discharge. That is why such excimer molecules are generated in a plasma (see excimer molecule formation). | 5 | Photochemistry |
Geometrical constraints in a molecule can cause a severe distortion of idealized tetrahedral geometry. In compounds featuring "inverted" tetrahedral geometry at a carbon atom, all four groups attached to this carbon are on one side of a plane. The carbon atom lies at or near the apex of a square pyramid with the other four groups at the corners.
The simplest examples of organic molecules displaying inverted tetrahedral geometry are the smallest propellanes, such as [[1.1.1-Propellane|[1.1.1]propellane]]; or more generally the paddlanes, and pyramidane ([3.3.3.3]fenestrane). Such molecules are typically strained, resulting in increased reactivity. | 4 | Stereochemistry |
These forces arise due to dipole–dipole interactions (induced/permanent) between molecules of bilayers. As molecules come closer, this attractive force arises due to the ordering of these dipoles; like in the case of magnets that align and attract each other as they approach. This also implies that any surface would experience a van der waals attraction. In bilayers, the form taken by van der Waals interaction potential V is given by
where H is the Hamaker constant and D and z are the bilayers thickness and the distance of separation respectively. | 6 | Supramolecular Chemistry |
The temperature of a muscle has a significant effect on the velocity and power of the muscle contraction, with performance generally declining with decreasing temperatures and increasing with rising temperatures. The Q coefficient represents the degree of temperature dependence a muscle exhibits as measured by contraction rates. A Q of 1.0 indicates thermal independence of a muscle whereas an increasing Q value indicates increasing thermal dependence. Values less than 1.0 indicate a negative or inverse thermal dependence, i.e., a decrease in muscle performance as temperature increases.
Q values for biological processes vary with temperature. Decreasing muscle temperature results in a substantial decline of muscle performance such that a 10 degree Celsius temperature decrease results in at least a 50% decline in muscle performance. Persons who have fallen into icy water may gradually lose the ability to swim or grasp safety lines due to this effect, although other effects such as atrial fibrillation are a more immediate cause of drowning deaths. At some minimum temperature biological systems do not function at all, but performance increases with rising temperature (Q of 2-4) to a maximum performance level and thermal independence (Q of 1.0-1.5). With continued increase in temperature, performance decreases rapidly (Q of 0.2-0.8) up to a maximum temperature at which all biological function again ceases.
Within vertebrates, different skeletal muscle activity has correspondingly different thermal dependencies. The rate of muscle twitch contractions and relaxations are thermally dependent (Q of 2.0-2.5), whereas maximum contraction, e.g., tetanic contraction, is thermally independent.
Muscles of some ectothermic species. e.g., sharks, show less thermal dependence at lower temperatures than endothermic species | 7 | Physical Chemistry |
The fugacity capacity constant (Z) is used to help describe the concentration of a chemical in a system (usually in mol/mPa). Hemond and Hechner-Levy (2000) describe how to utilize the fugacity capacity to calculate the concentration of a chemical in a system. Depending on the chemical, fugacity capacity varies. The concentration in media m equals the fugacity capacity in media m multiplied by the fugacity of the chemical.
For a chemical system at equilibrium, the fugacity of the chemical will be the same in each media/phase/compartment. Therefore equilibrium is sometimes called "equifugacity" in the context of these calculations.
where Z is a proportional constant, termed fugacity capacity. This equation does not necessarily imply that C and f are always linearly related. Non-linearity can be accommodated by allowing Z to vary as a function of C or f.
For a better understanding of the fugacity capacity concept, heat capacity may provide a precedent for introducing Z as a capacity of a phase to absorb particular quantity of chemical. However, phases with high fugacity capacity do not necessarily retain high fugacity.
In calculations of fugacity capacity key factors would be (a) the nature of the solute (chemical), (b) the nature of the medium or compartment, (c) temperature. | 7 | Physical Chemistry |
As of 2006, the most precise measurement of R had been obtained by measuring the speed of sound c(P, T) in argon at the temperature T of the triple point of water at different pressures P, and extrapolating to the zero-pressure limit c(0, T). The value of R is then obtained from the relation:
where:
*γ is the heat capacity ratio ( for monatomic gases such as argon);
*T is the temperature, T = 273.16 K by the definition of the kelvin at that time;
*A(Ar) is the relative atomic mass of argon and M = as defined at the time.
However, following the 2019 redefinition of the SI base units, R now has an exact value defined in terms of other exactly defined physical constants. | 7 | Physical Chemistry |
1954 marks the birth of Markovitsi, daughter of Tryfon and Eleftheria, in Athens. From 1958 to 1969, she resided at Krya Vrysi, Pella. Then she returned to Athens, where she finished with a degree in chemical engineering from the National Technical University (1978). Thanks to a scholarship from the French government, she relocated to France, where she earned a "Diplôme dEtudes Approfondies" (equivalent to a Masters degree) in 1979 on "Energy and Pollution" from the Université Paris VII and, later, a Ph.D. in Chemistry from the Louis Pasteur University at Strasbourg (1983). | 5 | Photochemistry |
To minimize degradation by solvents, reactions involving tert-butyllithium are often conducted at very low temperatures in special solvents, such as the Trapp solvent mixture.
More so than other alkyllithium compounds, tert-butyllithium reacts with ethers. In diethyl ether, the half-life of tert-butyllithium is about 60 minutes at 0 °C. It is even more reactive toward tetrahydrofuran (THF); the half-life in THF solutions is about 40 minutes at −20 °C. In dimethoxyethane, the half-life is about 11 minutes at −70 °C
In this example, the reaction of tert-butyllithium with (THF) is shown: | 0 | Organic Chemistry |
Most of the characterized thiopeptides have been isolated from Actinobacteria. General structural features of thiopeptide macrocycles, are dehydrated amino acids and thiazole rings formed from dehydrated serine/threonine and cyclized cysteine residues, respectively
The thiopeptide macrocycle is closed with a six-membered nitrogen-bearing ring. Oxidation state and substitution pattern of the nitrogenous ring determines the series of the thiopeptide natural product. While the mechanism of macrocyclization is not known, the nitrogenous ring can exist in thiopeptides as a piperidine, dehydropiperidine, or a fully oxidized pyridine. Additionally, some thiopeptides bear a second macrocycle, which bears a quinaldic acid or indolic acid residue derived from tryptophan. Perhaps the most well-characterized thiopeptide, thiostrepton A, contains a dehydropiperidine ring and a second, quinaldic acid-containing macrocycle. Four residues are dehydrated during posttranslational modification, and the final natural product also bears four thiazoles and one azoline. | 1 | Biochemistry |
An example of the operations of the nucleic acid extraction apparatus which incorporates
Tajima pipette are typically as shown in Fig. 1. | 1 | Biochemistry |
The European Food Safety Authority (EFSA) in 2016 reviewed the current evidence, finding the relationship between serum 25(OH)D concentration and musculoskeletal health outcomes is widely variable. They considered that average requirements and population reference intakes values for vitamin D cannot be derived, and that a serum 25(OH)D concentration of 50nmol/L was a suitable target value. For all people over the age of 1, including women who are pregnant or lactating, they set an adequate intake of 15μg/day (600IU).
The EFSA reviewed safe levels of intake in 2012, setting the tolerable upper limit for adults at 100μg/day (4000IU), a similar conclusion as the IOM.
The Swedish National Food Agency recommends a daily intake of 10μg (400IU) of vitamin D for children and adults up to 75 years, and 20μg (800IU) for adults 75 and older.
Non-government organisations in Europe have made their own recommendations. The German Society for Nutrition recommends 20μg. The European Menopause and Andropause Society recommends postmenopausal women consume 15μg (600IU) until age 70, and 20μg (800IU) from age 71. This dose should be increased to 100μg (4,000IU) in some patients with very low vitamin D status or in case of co-morbid conditions. | 1 | Biochemistry |
As a hybrid technique, GISAS combines concepts from transmission small-angle scattering (SAS), from grazing-incidence diffraction (GID), and from diffuse reflectometry. From SAS it uses the form factors and structure factors. From GID it uses the scattering geometry close to the critical angles of substrate and film, and the two-dimensional character of the scattering, giving rise to diffuse rods of scattering intensity perpendicular to the surface. With diffuse (off-specular) reflectometry it shares phenomena like the Yoneda/Vinyard peak at the critical angle of the sample, and the scattering theory, the distorted wave Born approximation (DWBA). However, while diffuse reflectivity remains confined to the incident plane (the plane given by the incident beam and the surface normal), GISAS explores the whole scattering from the surface in all directions, typically utilizing an area detector. Thus GISAS gains access to a wider range of lateral and vertical structures and, in particular, is sensitive to the morphology and preferential alignment of nanoscale objects at the surface or inside the thin film.
As a particular consequence of the DWBA, the refraction of x-rays or neutrons has to be always taken into account in the case of thin film studies, due to the fact that scattering angles are small, often less than 1 deg. The refraction correction applies to the perpendicular component of the scattering vector with respect to the substrate while the parallel component is unaffected. Thus parallel scattering can often be interpreted within the kinematic theory of SAS, while refractive corrections apply to the scattering along perpendicular cuts of the scattering image, for instance along a scattering rod.
In the interpretation of GISAS images some complication arises in the scattering from low-Z films e.g. organic materials on silicon wafers, when the incident angle is in between the critical angles of the film and the substrate. In this case, the reflected beam from the substrate has a similar strength as the incident beam and thus the scattering from the reflected beam from the film structure can give rise to a doubling of scattering features in the perpendicular direction. This as well as interference between the scattering from the direct and the reflected beam can be fully accounted for by the DWBA scattering theory.
These complications are often more than offset by the fact that the dynamic enhancement of the scattering intensity is significant. In combination with the straightforward scattering geometry, where all relevant information is contained in a single scattering image, in-situ and real-time experiments are facilitated. Specifically self-organization during MBE growth and re-organization processes in block copolymer films under the influence of solvent vapor have been characterized on the relevant timescales ranging from seconds to minutes. Ultimately the time resolution is limited by the x-ray flux on the samples necessary to collect an image and the read-out time of the area detector. | 7 | Physical Chemistry |
The previously described work of Martin and Synge impacted the development of the previously known column chromatography and inspired new forms of chromatography such as countercurrent distribution, paper chromatography, and gas-liquid chromatography which is more commonly known as gas chromatography. The modification of silica gel stationary phase led to many creative ways of modifying stationary phases in order to influence the separation characteristics. The most notable modification was the chemical bonding of alkane functional groups to silica gel to produce reversed-phase media. The original problem that Martin and Synge encountered with devising an instrument that would employ two free-flowing liquid phases was solved by Lyman C. Craig in 1944, and commercial counter-current distribution instruments were used for many important discoveries. The introduction of paper chromatography was an important analytical technique which gave rise to thin-layer chromatography. Finally, gas-liquid chromatography, a fundamental technique in modern analytical chemistry, was described by Martin with coauthors A. T. James and G. Howard Smith in 1952. | 3 | Analytical Chemistry |
When any group is present at ortho position to an amide group (NH) in aniline then the basic character of that compound becomes weaker. For example, see the order of basicity of following substituted aniline:-
* p-Toluidine > m-Toluidine > Aniline > o-Toluidine
* Aniline > m-Nitroaniline > p-Nitroaniline > o-Nitroaniline
* Aniline > p-Haloaniline > m-Haloaniline > o-Haloaniline
* p-Aminophenol pKb=8.50 > o-Aminophenol pKb=9.28 > Aniline pKb=9.38 > m-Aminophenol pKb=9.80
The protonation of substituted aniline is inhibited by steric hindrance. When protonated, the nitrogen in the amino group changes its orbital hybridization from sp to sp, becoming non-planar. This leads to steric hindrance between the ortho-substituted group and the hydrogen atom of the amino group, reducing the stability of the conjugate acid and consequently decreasing the pH of substituted aniline. | 4 | Stereochemistry |
Recent excavations in Middle Ganga Valley done by archaeologist Rakesh Tewari show iron working in India may have begun as early as 1800 BCE. Archaeological sites in India, such as Malhar, Dadupur, Raja Nala Ka Tila and Lahuradewa in the state of Uttar Pradesh show iron implements in the period between 1800 BCE – 1200 BCE. Sahi (1979: 366) concluded that by the early 13th century BCE, iron smelting was definitely practiced on a bigger scale in India, suggesting that the date the technology's inception may well be placed as early as the 16th century BCE.
The Black and Red Ware culture was another early Iron Age archaeological culture of the northern Indian subcontinent. It is dated to roughly the 12th – 9th centuries BCE, and associated with the post-Rigvedic Vedic civilization. It extended from the upper Gangetic plain in Uttar Pradesh to the eastern Vindhya range and West Bengal.
Perhaps as early as 500 BCE, although certainly by 200 CE, high quality steel was being produced in southern India by what Europeans would later call the crucible technique. In this system, high-purity wrought iron, charcoal, and glass were mixed in crucibles and heated until the iron melted and absorbed the carbon. The resulting high-carbon steel, called fūlāḏ by the Arabs () and wootz by later Europeans, was exported throughout much of Asia and Europe.
Will Durant wrote in The Story of Civilization I: Our Oriental Heritage: | 8 | Metallurgy |
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