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Most multiferroic materials identified to date are transition-metal oxides, which are compounds made of (usually 3d) transition metals with oxygen and often an additional main-group cation. Transition-metal oxides are a favorable class of materials for identifying multiferroics for a few reasons:
* The localised 3d electrons on the transition metal are usually magnetic if they are partially filled with electrons.
* Oxygen is at a "sweet spot" in the periodic table in that the bonds it makes with transition metals are neither too ionic (like its neighbor fluorine, F) or too covalent (like its neighbor nitrogen, N). As a result, its bonds with transition metals are rather polarizable, which is favorable for ferroelectricity.
* Transition metals and oxygen tend to be earth abundant, non-toxic, stable and environmentally benign.
Many multiferroics have the perovskite structure. This is in part historical most of the well-studied ferroelectrics are perovskites and in part because of the high chemical versatility of the structure.
Below is a list of some the most well-studied multiferroics with their ferroelectric and magnetic ordering temperatures. When a material shows more than one ferroelectric or magnetic phase transition, the most relevant for the multiferroic behavior is given. | 7 | Physical Chemistry |
The binding process is reversible, indicating that the associate constant (k) is not far larger than disassociate constant (k). Combing the rate of the reaction, k, k, concentration, and time, the relation of the free guest molecule and time can be calculated. By calculating the integration of UV spectrum or NMR, the concentration as a function of time curve can be obtained. | 6 | Supramolecular Chemistry |
Cavity ring-down spectroscopy is a form of laser absorption spectroscopy. In CRDS, a laser pulse is trapped in a highly reflective (typically R > 99.9%) detection cavity. The intensity of the trapped pulse will decrease by a fixed percentage during each round trip within the cell due to absorption, scattering by the medium within the cell, and reflectivity losses. The intensity of light within the cavity is then determined as an exponential function of time.
The principle of operation is based on the measurement of a decay rate rather than an absolute absorbance. This is one reason for the increased sensitivity over traditional absorption spectroscopy, as the technique is then immune to shot-to-shot laser fluctuations. The decay constant, τ, which is the time taken for the intensity of light to fall to 1/e of the initial intensity, is called the ring-down time and is dependent on the loss mechanism(s) within the cavity. For an empty cavity, the decay constant is dependent on mirror loss and various optical phenomena like scattering and refraction:
where n is the index of refraction within the cavity, c is the speed of light in vacuum, l is the cavity length, R is the mirror reflectivity, and X takes into account other miscellaneous optical losses. This equation uses the approximation that ln(1+x) ≈ x for x close to zero, which is the case under cavity ring-down conditions. Often, the miscellaneous losses are factored into an effective mirror loss for simplicity. An absorbing species in the cavity will increase losses according to the Beer-Lambert law. Assuming the sample fills the entire cavity,
where α is the absorption coefficient for a specific analyte concentration at the cavitys resonance wavelength. The decadic absorbance, A', due to the analyte can be determined from both ring-down times.
Alternatively, the molar absorptivity, ε, and analyte concentration, C, can be determined from the ratio of both ring-down times. If X can be neglected, one obtains
When a ratio of species' concentrations is the analytical objective, as for example in carbon-13 to carbon-12 measurements in carbon dioxide, the ratio of ring-down times measured for the same sample at the relevant absorption frequencies can be used directly with extreme accuracy and precision. | 7 | Physical Chemistry |
In chemistry, a mixture is a material made up of two or more different chemical substances which are physically bonded. A mixture is the physical combination of two or more substances in which the identities are retained and are mixed in the form of solutions, suspensions and colloids.
Mixtures are one product of mechanically blending or mixing chemical substances such as elements and compounds, without chemical bonding or other chemical change, so that each ingredient substance retains its own chemical properties and makeup. Despite the fact that there are no chemical changes to its constituents, the physical properties of a mixture, such as its melting point, may differ from those of the components. Some mixtures can be separated into their components by using physical (mechanical or thermal) means. Azeotropes are one kind of mixture that usually poses considerable difficulties regarding the separation processes required to obtain their constituents (physical or chemical processes or, even a blend of them). | 7 | Physical Chemistry |
This form factor is useful for applications where the spectrum analyzer can be plugged into AC power, which generally means in a lab environment or production/manufacturing area. Bench top spectrum analyzers have historically offered better performance and specifications than the portable or handheld form factor. Bench top spectrum analyzers normally have multiple fans (with associated vents) to dissipate heat produced by the processor. Due to their architecture, bench top spectrum analyzers typically weigh more than . Some bench top spectrum analyzers offer optional battery packs, allowing them to be used away from AC power. This type of analyzer is often referred to as a "portable" spectrum analyzer. | 7 | Physical Chemistry |
Chan is a current member of the Professional Teachers' Union (HK), Hong Kong Marine Biological Association, Society of Toxicology (SOT) in the US, American Fisheries Society, American Physiological Society, etc.
He is now chairman (elected) of the Teachers' Association of Chinese University (2011–12). He also serves as warden of Student Hostel 2 of Shaw College, member of the board of trustees of Shaw College, and member of the Assembly of Fellows, Shaw College, Chinese University. | 1 | Biochemistry |
Brønsted and Lowry characterized an acid–base equilibrium as involving a proton exchange reaction:
:acid + base conjugate base + conjugate acid.
An acid is a proton donor; the proton is transferred to the base, a proton acceptor, creating a conjugate acid. For aqueous solutions of an acid HA, the base is water; the conjugate base is A and the conjugate acid is the solvated hydrogen ion. In solution chemistry, it is usual to use H as an abbreviation for the solvated hydrogen ion, regardless of the solvent. In aqueous solution H denotes a solvated hydronium ion.
The Brønsted–Lowry definition applies to other solvents, such as dimethyl sulfoxide: the solvent S acts as a base, accepting a proton and forming the conjugate acid SH. A broader definition of acid dissociation includes hydrolysis, in which protons are produced by the splitting of water molecules. For example, boric acid, , acts as a weak acid, even though it is not a proton donor, because of the hydrolysis equilibrium
: + + H.
Similarly, metal ion hydrolysis causes ions such as to behave as weak acids:
Acid–base equilibria are important in a very wide range of applications, such as acid–base homeostasis, ocean acidification, pharmacology and analytical chemistry. | 7 | Physical Chemistry |
Borane tert-butylamine is an amine borane complex derived from tert-butylamine and borane. It is a colorless solid.
The compound is prepared by the reaction of tert-butylammonium chloride and sodium borohydride:
:t-BuNHCl + NaBH → t-BuNHBH + H + NaCl
In organic synthesis, borane tert-butylamine can be used for selective reduction of certain functional groups including aldehydes, ketones, oximes, and imines.
In photographic processing, it is used in the E-4 process, as "chemical enlighting" step in the processing of the film. | 0 | Organic Chemistry |
Vectorette PCR can develop a strategy to bring about PCR amplification that is unidirectional. Vectorette PCR comprises three main steps. The first step includes utilizing a restriction enzyme in order to accomplish digestion of the sample DNA. The DNA that is to be utilized for the purpose of investigation has to be capable of being digested by restriction enzymes that are appropriate for that gene otherwise the DNA fragments that form the general population cannot be created. After that is completed, a Vectorette library is brought together by ligating the Vectorette units to the appropriate DNA fragments which were previously digested. Ligation is the act of binding two things together. A Vectorette unit is only partially not completely double stranded with a mismatched section located in the center of the unit. The reason it is mismatched is to help it avoid Vectorette primers’ attempts at causing it to undergo first strand synthesis. By doing this any priming that is nonspecific is also avoided. This ligation brings together the vectorette which is double stranded and the ends of the restriction fragments which were previously made in the first step. By doing this, the known sequence which is used to prime the PCR reaction at one side is introduced while the other is primed on the genomic sequence which is already known to the user. The third and last step has two parts to it. This is due to there being two primers, the initiating primer (IP) and the Vectorette primer (VP), that act in different stages. During the first part, the IP works on amplifying the primer extension while the VP remains hybridized with the product; thus, any background amplification is not carried out at this stage. However, this changes during the last and following part of PCR as the priming that is performed comes from both the IP and the VP. | 1 | Biochemistry |
The field of thermodynamics describes when vapor–liquid equilibrium is possible, and its properties. Much of the analysis depends on whether the vapor and liquid consist of a single component, or if they are mixtures. | 7 | Physical Chemistry |
Herbivores consume ionone-containing carotenoids and convert those to retinal. Some species, including cattle and horses, have measurable amounts of beta-carotene circulating in the blood, and stored in body fat, creating yellow fat cells. Most species have white fat and no beta-carotene in circulation. | 1 | Biochemistry |
* 2014 documentary Whats In My Baggie?' deals with adulterants and additives in recreational drugs.
* Largest public accessible database with reagent test results and their sources | 3 | Analytical Chemistry |
R. R. Schmidt and co-workers have described the selective anomeric activation of O-protected hexopyranoses (glucose, galactose, mannose, glucosamine, galactosamine), hexofuranoses and pentopyranoses with trichloroacetonitrile in the presence of a base, as well as glycosylations under acid catalysis.
Under kinetic control with potassium carbonate as the base, β-trichloroacetimidates are formed selectively, whereas with sodium hydride, caesium carbonate or potassium hydroxide and in the presence of phase-transfer catalysts only α-trichloroacetimidates are obtained (thermodynamically controlled).
The trichloroacetimidates are reacted between −40 °C and room temperature with boron trifluoride etherate in dichloromethane with O-protected sugars. This method usually gives better results than the Koenigs–Knorr method using silver salts or the Helferich method which uses problematic mercury salts. Since an inversion occurs at the anomeric center, the reaction leads to β-O-glycosides (when using α-trichloroacetimidates). The trichloroacetimidate method often produces sterically uniform glycosides under mild reaction conditions in very good yields.
Thioacetic acid reacts with acetyl-protected α-galactosyl trichloroacetimidate even without additional acid catalysis to thioglycoside, from which (after cleavage of the protective groups) 1-thio-β--galactose is easily accessible, which is useful for the separation of racemates of amino acids.
Trichloroacetonitrile was an important fumigant in the first half of the 20th century, but today it has become obsolete for this application. | 0 | Organic Chemistry |
The Centers for Disease Control and Prevention has published the following laboratory procedure manuals for measuring thyroid-stimulating hormone:
* [https://www.cdc.gov/NCHS/data/nhanes/nhanes_09_10/THYROD_F_met_TSH.pdf Thyroid Stimulating Hormone (TSH) (University of Washington Medical Center)]. September 2011. Method: Access 2 (Beckman Coulter).
* [https://www.cdc.gov/NCHS/data/nhanes/nhanes_09_10/THYROD_F_met_TSH_CLS.pdf Thyroid Stimulating Hormone (TSH) (Collaborative Laboratory Services)]. September 2011. Method: Access 2 (Beckman Coulter).
* [https://www.cdc.gov/nchs/data/nhanes/nhanes_07_08/THYROD_e_met_Thyroid_Stimulating_Hormone.pdf Thyroid Stimulating Hormone (TSH)]. September 2009. Method: Access 2 (Beckman Coulter).
* [https://www.cdc.gov/nchs/data/nhanes/nhanes_01_02/l18t4_b_met_b_tsh.pdf Lab 18 Thyroid Stimulating Hormone]. 2001-2002. Method: Microparticle Enzyme Immunoassay.
* [https://www.cdc.gov/nchs/data/nhanes/nhanes_99_00/lab18_met_tsh.pdf Lab 18 TSH - Thyroid Stimulating Hormone]. 1999-2000. Method: Microparticle Enzyme Immunoassay. | 1 | Biochemistry |
A DTA curve can be used only as a finger print for identification purposes but usually the applications of this method are the determination of phase diagrams, heat change measurements and decomposition in various atmospheres.
DTA is widely used in the pharmaceutical and food industries.
DTA may be used in cement chemistry, mineralogical research and in environmental studies.
DTA curves may also be used to date bone remains or to study archaeological materials.
Using DTA one can obtain liquidus & solidus lines of phase diagrams. | 3 | Analytical Chemistry |
In presence of molecular orientation anisotropy in the sample, CARS images often display artefacts due to polarization-dependent selection rules that affects the measured intensity with respect of the alignment between the polarization plane of the incident light and the main orientation plane of the molecular bonds.
This is due because the four-wave mixing process is more efficient when the polarization plane of the incident light is aligned with the main orientation plane of the molecular vibrations. | 3 | Analytical Chemistry |
The van Arkel–de Boer process, also known as the iodide process or crystal-bar process, was the first industrial process for the commercial production of pure ductile titanium, zirconium and some other metals. It was developed by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925. Now it is used in the production of small quantities of ultrapure titanium and zirconium. It primarily involves the formation of the metal iodides and their subsequent decomposition to yield pure metal.
This process was superseded commercially by the Kroll process. | 8 | Metallurgy |
Ryōji Noyori and colleagues have developed a methodology for the kinetic resolution of benzylic and allylic secondary alcohols via transfer hydrogenation. The ruthenium complex catalyzes oxidation of the more reactive enantiomer from acetone, yielding an unreacted enantiopure alcohol, an oxidized ketone, and isopropanol. In the example illustrated below, exposure of 1-phenylethanol to the (S,S) enantiomer of the catalyst in the presence of acetone results in a 51% yield of 94% ee (R)-1-phenylethanol, along with 49% acetophenone and isopropanol as a byproduct.
This methodology is essentially the reverse of Noyori's asymmetric transfer hydrogenation of ketones, which yield enantioenriched alcohols via reduction. This limits the attractiveness of the kinetic resolution method, since there is a similar method to achieve the same products without the loss of half the material. Thus, the kinetic resolution would only be carried out in an instance for which the racemic alcohol was at least one half the price of the ketone or significantly easier to access.
In addition, Uemura and Hidai have developed a ruthenium catalyst for the kinetic resolution oxidation of benzylic alcohols, yielding highly enantioenriched alcohols in good yields.
The complex can, like Noyori's catalyst, affect transfer hydrogenation between a ketone and isopropanol to give an enantioenriched alcohol as well as affect kinetic resolution of a racemic alcohol, giving enantiopure alcohol (>99% ee) and oxidized ketone, with acetone as the byproduct. It is highly effective at reducing ketones enantioselectively, giving most benzylic alcohols in >99% ee and can resolve a number of racemic benzylic alcohols to give high yields (up to 49%) of single enantiomers, as shown below. This method has the same disadvantages as the Noyori kinetic resolution, namely that the alcohols can also be accessed via reduction of the ketones enantioselectively. Additionally, only one enantiomer of the catalyst has been reported. | 4 | Stereochemistry |
Chance theories are based on the assumption that "Absolute asymmetric synthesis, i.e., the formation of enantiomerically enriched products from achiral precursors without the intervention of chiral chemical reagents or catalysts, is in practice unavoidable on statistical grounds alone".
Consider the racemic state as a macroscopic property described by a binomial distribution; the experiment of tossing a coin, where the two possible outcomes are the two enantiomers is a good analogy. The discrete probability distribution of obtaining n successes out of Bernoulli trials, where the result of each Bernoulli trial occurs with probability and the opposite occurs with probability is given by:
The discrete probability distribution of having exactly molecules of one chirality and of the other, is given by:
As in the experiment of tossing a coin, in this case, we assume both events ( or ) to be equiprobable, . The probability of having exactly the same amount of both enantiomers is inversely proportional to the square root of the total number of molecules . For one mol of a racemic compound, molecules, this probability becomes . The probability of finding the racemic state is so small that we can consider it negligible.
In this scenario, there is a need to amplify the initial stochastic enantiomeric excess through any efficient mechanism of amplification. The most likely path for this amplification step is by asymmetric autocatalysis. An autocatalytic chemical reaction is that in which the reaction product is itself a reactive, in other words, a chemical reaction is autocatalytic if the reaction product is itself the catalyst of the reaction. In asymmetric autocatalysis, the catalyst is a chiral molecule, which means that a chiral molecule is catalysing its own production. An initial enantiomeric excess, such as can be produced by polarized light, then allows the more abundant enantiomer to outcompete the other. | 4 | Stereochemistry |
Enteric fermentation occurs in the gut of some animals, especially ruminants. In the rumen, anaerobic organisms, including methanogens, digest cellulose into forms nutritious to the animal. Without these microorganisms, animals such as cattle would not be able to consume grasses. The useful products of methanogenesis are absorbed by the gut, but methane is released from the animal mainly by belching (eructation). The average cow emits around 250 liters of methane per day. In this way, ruminants contribute about 25% of anthropogenic methane emissions. One method of methane production control in ruminants is by feeding them 3-nitrooxypropanol. | 1 | Biochemistry |
Archaeologist George Eogan, in his study of Bronze Age gold-working, noted that very few Bronze Age gold artefacts had been discovered through "controlled archaeological investigation", with the majority instead having been unearthed "by chance", as a result of "agricultural activities or peat-cutting". In the 21st century, metal detectorists have become important, for example with the important Shropshire bulla, found in 2018. | 8 | Metallurgy |
Many TRIM proteins are induced by interferons, which are important component of resistance to pathogens and several TRIM proteins are known to be required for the restriction of infection by lentiviruses. TRIM proteins are involved in pathogen-recognition and by regulation of transcriptional pathways in host defence. | 1 | Biochemistry |
Archaeometallurgy is the study of the past use and production of metals by humans. It is a sub-discipline of archaeology and archaeological science. | 8 | Metallurgy |
The mean lifespan of methane in the atmosphere was estimated in a range between 9.6 years and twelve years. These differences are caused by the uncertainties about hydroxyl radical (-OH) concentrations and formation processes. When -OH reacts with methane, it is removed from the atmosphere, so changes in its concentration would also affect the concentration of methane. An increase in methane emissions greater than the regeneration rate of OH radicals would reduce their concentrations and so increase methane's mean atmospheric lifetime.
The reaction of methane and chlorine atoms acts as a primary sink of Cl atoms and is a primary source of hydrochloric acid (HCl) in the stratosphere.
CH + Cl → CH + HCl
The HCl produced in this reaction leads to catalytic ozone destruction in the stratosphere. | 2 | Environmental Chemistry |
The name Golden Gate Assembly comes from a proposal of Yuri Gleba. It shall refer on the one hand to the Gateway Technology, on the other hand picture the higher precision with a bridge connecting the streets of two shores seamlessly. One of the most well known bridges is the Golden Gate Bridge in San Francisco. | 1 | Biochemistry |
The most reliable methods are direct plate count method and membrane filtration method. mEndo Agar is used in the membrane filtration while VRBA Agar is used in the direct plate count method. VRBA stands for violet red bile agar. A media that contains bile salts which promotes the growth of gram negative and has inhibitory characteristic to gram positive although not complete inhibitory.
These media contain lactose which is usually fermented by lactose fermenting bacteria producing colonies that can be identified and characterised. Lactose fermenting produce colored colonies while non lactose fermenting produce colorless ones. Because the analysis is always based on a very small sample taken from a very large volume of water, all methods rely on statistical principles. | 3 | Analytical Chemistry |
The Pearson symbol should only be used to designate simple structures (elements, some binary compound) where the number of atoms per unit cell equals, ideally, the number of translationally equivalent points. | 3 | Analytical Chemistry |
Biomedical spectroscopy is a multidisciplinary research field involving spectroscopic tools for applications in the field of biomedical science. Vibrational spectroscopy such as Raman or infrared spectroscopy is used to determine the chemical composition of a material based on detection of vibrational modes of constituent molecules. Some spectroscopic methods are routinely used in clinical settings for diagnosis of disease; an example is Magnetic resonance imaging (MRI). Fourier transform infrared (FTIR) spectroscopic imaging is a form of chemical imaging for which the contrast is provided by composition of the material. | 7 | Physical Chemistry |
Protein backbones are very stable in water at neutral pH and room temperature, although the rate of hydrolysis of different peptide bonds can vary. The half life of a peptide bond under normal conditions can range from 7 years to 350 years, even higher for peptides protected by modified terminus or within the protein interior. The rate of hydrolysis however can be significantly increased by extremes of pH and heat. Spontaneous cleavage of proteins may also involve catalysis by zinc on serine and threonine.
Strong mineral acids can readily hydrolyse the peptide bonds in a protein (acid hydrolysis). The standard way to hydrolyze a protein or peptide into its constituent amino acids for analysis is to heat it to 105 °C for around 24 hours in 6M hydrochloric acid. However, some proteins are resistant to acid hydrolysis. One well-known example is ribonuclease A, which can be purified by treating crude extracts with hot sulfuric acid so that other proteins become degraded while ribonuclease A is left intact.
Certain chemicals cause proteolysis only after specific residues, and these can be used to selectively break down a protein into smaller polypeptides for laboratory analysis. For example, cyanogen bromide cleaves the peptide bond after a methionine. Similar methods may be used to specifically cleave tryptophanyl, aspartyl, cysteinyl, and asparaginyl peptide bonds. Acids such as trifluoroacetic acid and formic acid may be used for cleavage.
Like other biomolecules, proteins can also be broken down by high heat alone. At 250 °C, the peptide bond may be easily hydrolyzed, with its half-life dropping to about a minute. Protein may also be broken down without hydrolysis through pyrolysis; small heterocyclic compounds may start to form upon degradation. Above 500 °C, polycyclic aromatic hydrocarbons may also form, which is of interest in the study of generation of carcinogens in tobacco smoke and cooking at high heat. | 1 | Biochemistry |
An ultraviolet detector (also known as UV detector or UV-Vis detector) is a type of non-destructive chromatography detector which measures the amount of ultraviolet or visible light absorbed by components of the mixture being eluted off the chromatography column. They are often used as detectors for high-performance liquid chromatography.
The vast majority of Liquid Chromatographic systems are equipped with ultraviolet (UV) absorption detectors, and the vast majority of them are variable wavelength detectors, which are in fact UV spectrophotometers on the flow. In this detector, it is decided in advance at which wavelength is needed for the detection, and its absorbance as function of time is collected in a graphic format called chromatogram.
As can be seen in Figure 1, These detectors have a light source, a dispersion element that is a diffraction grating or prism, a flow cell, to where the sample arrives directly from the chromatographic column, an optical bench of lenses and mirrors, and a diode that receives the light coming from the optical system and translates it into a signal proportional to light intensity. When the user selects a wavelength for the detector, the optical system rotates the grating or prism in the space, so that the desired wavelength passes through optical system, then the flow cell and reaches the diode. The UV/VIS detector then produces a chromatogram as a two-dimensional (2D) output. This output plots time on the x-axis and response in absorbance units (AU) on the y-axis. The chromatogram is then analyzed by integrating the peaks curves to get their area, then getting their retention time (RT) from the peak maximum to identify them, and then perform quantitative analysis, by comparing their area to those of samples whose concentrations are known, i.e, standards. | 3 | Analytical Chemistry |
John William Draper was born May 5, 1811, in St. Helens, Lancashire, England, to John Christopher Draper, a Wesleyan clergyman, and Sarah (Ripley) Draper. He also had three sisters, Dorothy Catherine Draper (August 6, 1807 – December 10, 1901), Elizabeth Johnson, and Sarah Ripley. On June 23, he was baptized by the Wesleyan Methodist minister Jabez Bunting. His father often needed to move the family due to serving various congregations throughout England. John Wm. Draper was home tutored until 1822, when he entered Woodhouse Grove School. He returned to home instruction (1826) prior to entering University College London in 1829. While at University College London, Draper studied chemistry under the direction of Edward Turner (chemist).
On September 13, 1831, John William Draper married Antonia Caetana de Paiva Pereira Gardner (–1870), the daughter of Daniel Gardner, a court physician to John VI of Portugal and Charlotte of Spain. Antonia was born in Brazil after the royal family fled Portugal with Napoleons invasion. There is dispute as to the identity of Antonias mother. Around 1830, Antonia was sent with her brother Daniel to live with their aunt in London.
Following his fathers death in July 1831, John Williams mother was urged to move with her children to the US state of Virginia. John William hoped to acquire a teaching position at a local Methodist college. | 5 | Photochemistry |
For an ideal Bose gas we have the equation of state
where is the per-particle volume, is the thermal wavelength, is the fugacity, and
It is noticeable that is a monotonically growing function of in , which are the only values for which the series converge.
Recognizing that the second term on the right-hand side contains the expression for the average occupation number of the fundamental state , the equation of state can be rewritten as
Because the left term on the second equation must always be positive, , and because , a stronger condition is
which defines a transition between a gas phase and a condensed phase. On the critical region it is possible to define a critical temperature and thermal wavelength:
recovering the value indicated on the previous section. The critical values are such that if or , we are in the presence of a Bose–Einstein condensate.
Understanding what happens with the fraction of particles on the fundamental level is crucial. As so, write the equation of state for , obtaining
: and equivalently
So, if , the fraction , and if , the fraction . At temperatures near to absolute 0, particles tend to condense in the fundamental state, which is the state with momentum . | 7 | Physical Chemistry |
Variable contributions from different lake zones (i.e. littoral, limnetic, benthic) to whole lake metabolism depends mostly on patchiness in algal and bacterial biomass, and light and nutrient availability. In terms of the organisms contributing to metabolism in each of these zones, limnetic metabolism is dominated by phytoplankton, zooplankton, and bacterial metabolism, with low contribution from epiphytes and fish. Benthic metabolism can receive great contributions from macrophytes, macro- and microalgae, invertebrates, and bacteria. Benthic metabolism is usually highest in shallow littoral zones, or in clear-water shallow lakes, in which light reaches the bottom of the lake to stimulate primary production. In dark or turbid deep lakes, primary production may be restricted to shallower waters and aerobic respiration may be reduced or non-existent in deeper waters due to the formation of anoxic deep zones.
The degree of spatial heterogeneity in metabolic rates within a lake depends on lake morphometry, catchment characteristics (e.g. differences in land use throughout the catchment and inputs from streams), and hydrodynamic processes. For example, lakes with more intense hydrodynamic processes, such as strong vertical and lateral mixing, are more laterally and vertically homogeneous in relation to metabolic rates than highly stratified lakes. On the other hand, lakes with more developed littoral areas have greater metabolic heterogeneity laterally than lakes with a more circular shape and low proportions of shallow littoral areas.
Light attenuation occurring throughout the water column, in combination with thermal and chemical stratification and wind- or convective-driven turbulence, contribute to the vertical distribution of nutrients and organisms in the water column. In stratified lakes, organic matter and nutrients tend to be more concentrated at deeper layers, while light is more available at shallower layers. The vertical distribution of primary production responds to a balance between light and nutrient availability, while respiration occurs more independently of light and nutrients and more homogeneously with depth. This often results in strong coupling of gross primary production (GPP) and ecosystem respiration (ER) in lake surface layers but weaker coupling at greater depths. This means that ER rates are strongly dependent on primary production in shallower layers, while in deeper layers it becomes more dependent on a mixture of organic matter from terrestrial sources and sedimentation of algae particles and organic matter produced in shallower layers. In lakes with a low concentration of nutrients in surface waters and with light penetration below the mixed layer, primary production is higher in intermediate depths, where there is sufficient light for photosynthesis and higher nutrient availability. On the other hand, low transparent polymictic lakes have higher primary production on near-surface layers, usually with a net autotrophic balance (GPP > ER) between primary production and respiration.
Laterally, heterogeneity within lakes is driven by differences in metabolic rates in the open water limnetic zones and the more benthic-dominated littoral zones. Littoral areas are usually more complex and heterogeneous, in part because of their proximity with the terrestrial system, but also due to low water volume and high sediment-to-water volume ratio. Thus, littoral zones are more susceptible to changes in temperature, inputs of nutrients and organic matter from the landscape and river inflows, wind shear mixing and wave action, shading from terrestrial vegetation, and resuspension of the sediments (Figure 1). Additionally, littoral zones usually have greater habitat complexity due to the presence of macrophytes, which serve as shelter, nursery, and feeding place for many organisms. Consequently, metabolic rates in the littoral areas usually have high short-term variability and are typically greater than limnetic metabolic rates. | 1 | Biochemistry |
Essential fatty acids (EFAs) are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). | 9 | Geochemistry |
Plastarch Material (PSM) is a biodegradable, thermoplastic resin. It is composed of starch combined with several other biodegradable materials. The starch is modified in order to obtain heat-resistant properties, making PSM one of few bioplastics capable of withstanding high temperatures. PSM began to be commercially available in 2005.
PSM is stable in the atmosphere, but biodegradable in compost, wet soil, fresh water, seawater, and activated sludge where microorganisms exist. It has a softening temperature of 257 °F (125 °C) and a melting temperature of 313 °F (156 °C).
It is also hygroscopic. The material has to be dried in a material dryer at 150 °F (66 °C) for five hours or 180 °F (82 °C) for three hours. For injection molding and extrusion the barrel temperatures should be at 340° +/- 10 °F (171 °C) with the nozzle/die at 360 °F (182 °C).
Due to how similar PSM is to other plastics (such as polypropylene and CPET), PSM can run on many existing thermoforming and injection molding lines. PSM is currently used for a wide variety of applications in the plastic market, such as food packaging and utensils, personal care items, plastic bags, temporary construction tubing, industrial foam packaging, industrial and agricultural film, window insulation, construction stakes, and horticulture planters.
Since PSM is derived from a renewable resource (corn starch), it has become an attractive alternative to petrochemical-derived products. Unlike plastic, PSM can also be disposed of through incineration, resulting in non-toxic smoke and a white residue which can be used as fertilizer. However, concerns have been expressed about the impact of such technologies on food prices. | 7 | Physical Chemistry |
MMC Estates and Rathbone Jersey Limited purchased the site in May 2004, and said: "Any successful regeneration must find alternative uses and following discussions with the council, the site was defined as an area of opportunity for a mixed use urban village type development, comprising primarily employment and residential development supported by an appropriate level of ancillary uses. This will be supported by an environmental impact statement. MMC is a local developer responsible for the sympathetic council-backed regeneration of other sites within the borough, and has commenced some clearance works involving the felling of trees which are not protected by tree preservation orders." A Rochdale Council Draft Unitary Development Plan published earlier in the year had accepted that "the whole site is contaminated as a result of the industrial processes carried out there" and Administrators of Turner's considered the site "an asset of dubious value, (possibly even a liability)." The Administrators also stated that if mesothelioma or asbestos-related cancer deaths arose from any future development on the site, the liability for this would rest with the new owners and developers of the land. | 2 | Environmental Chemistry |
The role of C:N ratio in compost feedstock is similar to that of soil feedstock. The recommendation is around 20-30:1. The microbes prefer a ratio of 30-35:1, but the carbon is usually not completely digested (especially in the case of lignin feedstock), hence the lowered ratio.
An imbalance of C:N ratio causes a slowdown in the composting process and a drop in temperature. When the C:N ratio is less than 15:1, outgassing of ammonium may occur, creating odor and losing nitrogen. A finished compost has a C:N ratio of around 10:1. | 9 | Geochemistry |
Similar to liquid metal embrittlement (LME), solid metal-induced embrittlement results in a decrease in fracture strength of a material. In addition, a decrease in tensile ductility over a temperature range is indicative of metal-induced embrittlement. Although SMIE is greatest just below the embrittler’s melting temperature, the range over which SMIE occurs ranges from to T, where T is the melting temperature of the embrittler. The reduction in ductility is caused by formation and propagation of stable, subcritical intergranular cracks. SMIE produces both intergranular and transgranular fracture surfaces in otherwise ductile materials. | 8 | Metallurgy |
This model for disorder in a crystal starts with the structure factor of a perfect crystal. In one-dimension for simplicity and with N planes, we then start with the expression above for a perfect finite lattice, and then this disorder only changes by a multiplicative factor, to give
where the disorder is measured by the mean-square displacement of the positions from their positions in a perfect one-dimensional lattice: , i.e., , where is a small (much less than ) random displacement. For disorder of the first kind, each random displacement is independent of the others, and with respect to a perfect lattice. Thus the displacements do not destroy the translational order of the crystal. This has the consequence that for infinite crystals () the structure factor still has delta-function Bragg peaks – the peak width still goes to zero as , with this kind of disorder. However, it does reduce the amplitude of the peaks, and due to the factor of in the exponential factor, it reduces peaks at large much more than peaks at small .
The structure is simply reduced by a and disorder dependent term because all disorder of the first-kind does is smear out the scattering planes, effectively reducing the form factor.
In three dimensions the effect is the same, the structure is again reduced by a multiplicative factor, and this factor is often called the Debye–Waller factor. Note that the Debye–Waller factor is often ascribed to thermal motion, i.e., the are due to thermal motion, but any random displacements about a perfect lattice, not just thermal ones, will contribute to the Debye–Waller factor. | 3 | Analytical Chemistry |
* Stalin Prize first degree (1943) - for research in the field of organometallic compounds, the results of which were published in 1941 and 1942 in a series of articles: “On the interaction of diazoacetic ether with tin chloride and ferric chloride”, “From the field of organomercuric compounds ”, “On the reaction of nitroso compounds with nitric oxide” and in the monograph “Synthetic methods in the field of organometallic compounds of mercury” (1942)
* Lenin Prize (1966) - for a cycle of research in the field of organoelement compounds
* Twice Hero of Socialist Labour (1969, 1979)
* Gold medal named after D. I. Mendeleev (1977) - for a series of works in the field of organometallic compounds and obtaining food from non-traditional sources
* V Mendeleev Reader
* Large Gold Medal named after M. V. Lomonosov Academy of Sciences of the Soviet Union (1962)
* Seven Orders of Lenin (11/04/1944; 06/10/1945; 09/19/1953; 09/08/1959; 04/27/1967; 03/13/1969; 09/07/1979)
* Order of the October Revolution (09/13/1974)
* Order of the Red Banner of Labour (09/14/1949)
* Silver medal of the World Peace Council (1959) | 0 | Organic Chemistry |
Volatolomics is a branch of chemistry that studies volatile organic compounds (VOCs) emitted by a biological system, under specific experimental conditions. | 0 | Organic Chemistry |
Nickel allergy is typically diagnosed by patch testing – applying a patch with 2.5% (in North America) or 5% (in Europe) nickel sulfate to the upper back and looking for irritation on the skin. As with other causes of allergic contact dermatitis, patches containing several common allergens are typically applied to the back for 48 hours, removed, then the spots examined for allergic reactions 2 to 5 days later.
SNAS can often mimic IBS and may be more common than is widely appreciated. It therefore should be considered as a differential diagnosis item when a doctor is considering a diagnosis of IBS, and nickel allergy testing is advisable as a means to exclude or confirm SNAS. Even before such testing, some differentiating factors in the medical history are if certain foods prompt the symptoms (for example, peanuts or shellfish), whereas IBS is not specific to those foods. | 1 | Biochemistry |
In certain situations, it is vital for the photosynthetic organism to recycle the electrons being transferred, resulting in the electron from the terminal iron-sulfur cluster F transferring back to the cytochrome b6f complex (adaptor between photosystems II and I). Utilizing the energy of P700, the cyclic pathway creates a proton gradient useful for the production of ATP, while no NADPH is produced, since the protein ferredoxin does not become reduced. | 5 | Photochemistry |
A primary application of defoliants is the selective killing of plants. Two of the oldest chemical herbicides used as defoliants are 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T). 2,4-D and 2,4,5-T are absorbed by broad-leafed plants, killing them by causing excessive hormonal growth. These phenoxy herbicides were designed to selectively kill weeds and unwanted plants in croplands. They were first introduced at the beginning of World War II and became widespread in use in agriculture following the end of the War.
Defoliants have a practical use in the harvesting of certain crops, particularly cotton, in the United States as well as a number of other cotton-producing countries. The use of defoliants aids in the effective harvesting of cotton and finer lint quality. The effectiveness of defoliant use in cotton harvesting depends on the type of defoliant(s) used, the number of applications, the amount applied, and environmental variables. Common harvest-aiding chemical defoliants include tribufos, dimethipin, and thidiazuron. According to a 1998 report by the U.S. Department of Agriculture National Agricultural Statistics Service (NASS), tribufos and thidiazuron accounted for 60% of crop area that was treated by defoliants during that crop year. | 2 | Environmental Chemistry |
The permanent Venusian clouds produce a concentrated acid rain, as the clouds in the atmosphere of Earth produce water rain. Jupiter's moon Europa is also thought to have an atmosphere containing sulfuric acid hydrates. | 7 | Physical Chemistry |
A fiber (or other hydrophilic material) that has been exposed to the atmosphere will usually contain some water even if it feels dry. The water can be driven off by heating in an oven, leading to a measurable decrease in weight, which will gradually be regained if the fiber is returned to a normal atmosphere. This effect is crucial in the textile industry – where the proportion of a materials weight made up by water is called the moisture regain'. | 7 | Physical Chemistry |
Fluorescence-detected linear dichroism (FDLD) is a very useful technique to the experimentalist as it combines the advantages of UV LD whilst also offering the confocal detection of the fluorescence emission. FDLD has applications in microscopy, where can be used as a means of two-dimensional surface mapping through differential polarisation spectroscopy (DPS) where the anisotropy of the scanned object allows an image to be recorded. FDLD can also be used in conjunction with intercalating fluorescent dyes (which can also be monitored using UV LD). The intensity difference recorded between the two types of polarised light for the fluorescence reading is proportional to the UV LD signal, allowing the use of DPS to image surfaces | 7 | Physical Chemistry |
All ETS (Erythroblast Transformation Specific) family members are identified through a highly conserved DNA binding domain, the ETS domain, which is a winged helix-turn-helix structure that binds to DNA sites with a central GGA(A/T) DNA sequence. As well as DNA-binding functions, evidence suggests that the ETS domain is also involved in protein-protein interactions.
There is limited similarity outside the ETS DNA binding domain.
Other domains are also present and vary from ETS member to ETS member, including the Pointed domain, a subclass of the SAM domain family. | 1 | Biochemistry |
Mitsubishi Chemical Holdings was reported to be developing its own artificial photosynthesis research by using sunlight, water and carbon dioxide to "create the carbon building blocks from which resins, plastics and fibers can be synthesized." This was confirmed with the establishment of the KAITEKI Institute later that year, with carbon dioxide reduction through artificial photosynthesis as one of the main goals. | 5 | Photochemistry |
Oxidation originally implied a reaction with oxygen to form an oxide. Later, the term was expanded to encompass substances that accomplished chemical reactions similar to those of oxygen. Ultimately, the meaning was generalized to include all processes involving the loss of electrons or the increase in the oxidation state of a chemical species. Substances that have the ability to oxidize other substances (cause them to lose electrons) are said to be oxidative or oxidizing, and are known as oxidizing agents, oxidants, or oxidizers. The oxidant removes electrons from another substance, and is thus itself reduced. Because it "accepts" electrons, the oxidizing agent is also called an electron acceptor. Oxidants are usually chemical substances with elements in high oxidation states (e.g., , , , , ), or else highly electronegative elements (e.g. O, F, Cl, Br, I) that can gain extra electrons by oxidizing another substance.
Oxidizers are oxidants, but the term is mainly reserved for sources of oxygen, particularly in the context of explosions. Nitric acid is a strong oxidizer. | 9 | Geochemistry |
β-elimination or elimination reactions occur through the loss of a substituent leaving group and loss of a proton to form a pi bond. E1 and E2 are two different mechanisms for elimination reactions, and E1 involves a carbocation intermediate. In E1, a leaving group detaches from a carbon to form a carbocation reaction intermediate. Then, a solvent removes a proton, but the electrons used to form the proton bond form a pi bond, as shown in the pictured reaction on the right. | 7 | Physical Chemistry |
When replicating its (+)ssRNA genome, the poliovirus RdRp is able to carry out recombination. Recombination appears to occur by a copy choice mechanism in which the RdRp switches (+)ssRNA templates during negative strand synthesis. Recombination frequency is determined in part by the fidelity of RdRp replication. RdRp variants with high replication fidelity show reduced recombination, and low fidelity RdRps exhibit increased recombination. Recombination by RdRp strand switching also occurs frequently during replication in the (+)ssRNA plant carmoviruses and tombusviruses. | 1 | Biochemistry |
Forskolin is commonly used as a tool in biochemistry to raise levels of cAMP in the study and research of cell physiology. | 1 | Biochemistry |
A number bioplastic classes have been synthesized from plant and animal derived fats and oils. Polyurethanes, polyesters, epoxy resins and a number of other types of polymers have been developed with comparable properties to crude oil based materials. The recent development of olefin metathesis has opened a wide variety of feedstocks to economical conversion into biomonomers and polymers. With the growing production of traditional vegetable oils as well as low cost microalgae derived oils, there is huge potential for growth in this area. | 7 | Physical Chemistry |
Liquid–liquid transitions were originally considered by Rapoport in 1967 in order to explain high pressure melting curve maxima of some liquid metals. Rapoport's theory requires the existence of a melting curve maximum in polyamorphic systems. | 7 | Physical Chemistry |
The first example of cyclopropane being activated by a metal complex was reported in 1955, involving the reaction of cyclopropane and hexachloroplatinic acid. This reaction produces the polymeric platinacyclobutane complex Pt(CH)Cl. The bis(pyridine) adduct of this complex was characterized by X-ray crystallography.
The electrophile Cp*Ir(PMe)(Me)OTf reacts with cyclopropane to give the allyl complex:
:Cp*Ir(PMe)(Me)OTf + CH → [Cp*Ir(PMe)(η-CH)]OTf + CH | 0 | Organic Chemistry |
Roberts was made a fellow of the American Association for the Advancement of Science, and a chemistry professorship at Wellesley now bears her name. | 4 | Stereochemistry |
Dilution is the process of decreasing the concentration of a solute in a solution, usually simply by mixing with more solvent like adding more water to the solution. To dilute a solution means to add more solvent without the addition of more solute. The resulting solution is thoroughly mixed so as to ensure that all parts of the solution are identical.
The same direct relationship applies to gases and vapors diluted in air for example. Although, thorough mixing of gases and vapors may not be as easily accomplished.
For example, if there are 10 grams of salt (the solute) dissolved in 1 litre of water (the solvent), this solution has a certain salt concentration (molarity). If one adds 1 litre of water to this solution, the salt concentration is reduced. The diluted solution still contains 10 grams of salt (0.171 moles of NaCl).
Mathematically this relationship can be shown by equation:
where
*c = initial concentration or molarity
*V = initial volume
*c = final concentration or molarity
*V = final volume | 3 | Analytical Chemistry |
Dissociative pathways are characterized by a rate determining step that involves release of a ligand from the coordination sphere of the metal undergoing substitution. The concentration of the substituting nucleophile has no influence on this rate, and an intermediate of reduced coordination number can be detected. The reaction can be described with k, k and k, which are the rate constants of their corresponding intermediate reaction steps:
Normally the rate determining step is the dissociation of L from the complex, and [L'] does not affect the rate of reaction, leading to the simple rate equation:
However, in some cases, the back reaction (k) becomes important, and [L] can exert an effect on the overall rate of reaction. The backward reaction k therefore competes with the second forward reaction (k), thus the fraction of intermediate (denoted as "Int") that can react with L to form the product is given by the expression , which leads us to the overall rate equation:
When [L] is small and negligible, the above complex equation reduces to the simple rate equation that depends on k and [LM-L] only. | 0 | Organic Chemistry |
Recent developments in LED technology have led to commercially available UV-C LEDs. UV-C LEDs use semiconductors to emit light between 255 nm and 280 nm. The wavelength emission is tuneable by adjusting the material of the semiconductor. , the electrical-to-UV-C conversion efficiency of LEDs was lower than that of mercury lamps. The reduced size of LEDs opens up options for small reactor systems allowing for point-of-use applications and integration into medical devices. Low power consumption of semiconductors introduce UV disinfection systems that utilized small solar cells in remote or Third World applications.
UV-C LEDs don't necessarily last longer than traditional germicidal lamps in terms of hours used, instead having more-variable engineering characteristics and better tolerance for short-term operation. A UV-C LED can achieve a longer installed time than a traditional germicidal lamp in intermittent use. Likewise, LED degradation increases with heat, while filament and HID lamp output wavelength is dependent on temperature, so engineers can design LEDs of a particular size and cost to have a higher output and faster degradation or a lower output and slower decline over time. | 5 | Photochemistry |
Common thermodynamic equations and quantities in thermodynamics, using mathematical notation, are as follows: | 7 | Physical Chemistry |
In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, although specular backscattering can occur at normal incidence with a surface. Backscattering has important applications in astronomy, photography, and medical ultrasonography. The opposite effect is forward scatter, e.g. when a translucent material like a cloud diffuses sunlight, giving soft light. | 7 | Physical Chemistry |
Ethyl eicosapentaenoic acid (E-EPA, icosapent ethyl), sold under the brand name Vascepa among others, is a medication used to treat dyslipidemia and hypertriglyceridemia. It is used in combination with changes in diet in adults with hypertriglyceridemia ≥ 150 mg/dL. Further, it is often required to be used with a statin (maximally-tolerated dose).
The most common side effects are musculoskeletal pain, peripheral edema (swelling of legs and hands), atrial fibrillation, and arthralgia (joint pain). Other common side effects include bleeding, constipation, gout, and rash.
It is made from the omega-3 fatty acid eicosapentaenoic acid (EPA). The US Food and Drug Administration (FDA) granted the approval of icosapent ethyl in 2012 to Amarin Corporation, and it became the second fish oil-based medication after omega-3-acid ethyl esters (brand named Lovaza, itself approved in 2004). On 13 December 2019, the FDA also approved Vascepa as the first drug specifically "to reduce cardiovascular risk among people with elevated triglyceride levels". It is available as a generic medication. In 2020, it was the 285th most commonly prescribed medication in the United States, with more than 1million prescriptions. | 1 | Biochemistry |
Among the array of substrates that can be altered by CK2 many of them have been found in increased prevalence in cancers of the breast, lung, colon, and prostate. An increased concentration of substrates in cancerous cells infers a likely survival benefit to the cell, and activation of many of these substrates requires CK2. As well the anti-apoptotic function of CK2 allows the cancerous cell to escapes cell death and continue proliferating. Having roles in cell cycle regulation may also indicate CK2's role in allowing cell cycle progression when normally it should have been ceased. This also promotes CK2 as a possible therapeutic target for cancer drugs. When added with other potent anti-cancer therapies, a CK2 inhibitor may increase the effectiveness of the other therapy by allowing drug-induced apoptosis to occur at a normal rate. | 1 | Biochemistry |
During quiescence, the DREAM complex represses G1/S and G2/M gene expression. In mammalian systems, chromatin-immunoprecipitation (ChIP) studies have revealed that DREAM components are found together at promoters of genes that peak in G1/S or G2/M phase. Abrogation of the DREAM complex on the other hand, led to increased expression of E2F regulated genes normally repressed in the G0 phase. Contrary to mammalian cells, the fly dREAM complex was found at almost one-third of all promoters, which may reflect a broader role for dREAM in gene regulation, such as programmed cell death of neural precursor cells.
Docking of the DREAM complex to promoters is achieved by binding of LIN-54 to regions known as cell cycle genes homology region (CHR). These are specific sequence of nucleotides that are commonly found in the promoters of genes expressed during late S phase or G2/M phase. Docking can also be achieved via E2F proteins binding to sequences known as cell cycle-dependent element sites (CDEs). Some cell cycle dependent genes have been found where both CHRs and CDEs are in proximity to one another. Because p130-E2F4 can form stable associations with the MuvB complex, the proximity of CHRs to CDEs suggests that affinity of binding of the DREAM complex to target genes is cooperatively improved by association with both the binding sites.
When DREAM is docked onto the promoter, p130 is bound to LIN52, and this association inhibits LIN52 binding to chromatin modifier proteins. Therefore, unlike RB-E2F, the DREAM complex is unlikely to directly recruit chromatin modifiers to repress gene expression, although some associations have been suggested. DREAM complex may instead down-regulate gene expression by affecting nucleosome positioning. Compacted DNA at transcription start sites inhibit gene expression by blocking the docking of RNA polymerase. In worms for example, loss of a MuvB complex protein, LIN35, leads to loss of repressive histone associations and high expression of cell cycle dependent genes. However, direct evidence for the link between repressive histones and the DREAM complex remains to be elucidated. | 1 | Biochemistry |
Diphosphines are also available in primary, secondary, and tertiary phosphorus substituents. Triphosphines etc. are similar. | 0 | Organic Chemistry |
The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for minerals in 2001. For manganese there was not sufficient information to set EARs and RDAs, so needs are described as estimates for Adequate Intakes (AIs). As for safety, the IOM sets Tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of manganese the adult UL is set at 11 mg/day. Collectively the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes (DRIs). Manganese deficiency is rare.
The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For people ages 15 and older the AI is set at 3.0 mg/day. AIs for pregnancy and lactation is 3.0 mg/day. For children ages 1–14 years the AIs increase with age from 0.5 to 2.0 mg/day. The adult AIs are higher than the U.S. RDAs. The EFSA reviewed the same safety question and decided that there was insufficient information to set a UL.
For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For manganese labeling purposes 100% of the Daily Value was 2.0 mg, but as of 27 May 2016 it was revised to 2.3 mg to bring it into agreement with the RDA. A table of the old and new adult daily values is provided at Reference Daily Intake. | 1 | Biochemistry |
A 2014 paper described how Mapp and its collaborators, including investigators at Public Health Agency of Canada, Kentucky BioProcessing, and the National Institute of Allergy and Infectious Diseases, first chimerized the three antibodies comprising ZMAb, then tested combinations of MB-003 and the chimeric ZMAb antibodies in guinea pigs and then primates to determine the best combination, which turned out to be c13C6 from MB-003 and two chimeric mAbs from ZMAb, c2G4 and c4G7. This is ZMapp.
In an experiment also published in the 2014 paper, 21 rhesus macaque primates were infected with the Kikwit Congolese variant of EBOV. Three primates in the control arm were given a non-functional antibody, and the 18 in the treatment arm were divided into three groups of six. All primates in the treatment arm received three doses of ZMapp, spaced 3 days apart. The first treatment group received its first dose on 3rd day after being infected; the second group on the 4th day after being infected, and the third group, on the 5th day after being infected. All three primates in the control group died; all 18 primates in the treatment arm survived. Mapp then went on to show that ZMapp inhibits replication of a Guinean strain of EBOV in cell cultures.
Mapp remains involved in the production of the drug through its contracts with Kentucky BioProcessing, a subsidiary of Reynolds American. To produce the drug, genes coding for the chimeric mAbs were inserted into viral vectors, and tobacco plants are infected with the viral vector encoding for the antibodies, using Agrobacterium cultures. Subsequently, antibodies are extracted and purified from the plants. Once the genes encoding the chimeric mAbs are in hand, the entire tobacco production cycle is believed to take a few months. The development of these production methods was funded by the U.S. Defense Advanced Research Projects Agency as part of its bio-defense efforts following the 9/11 terrorist attacks. | 1 | Biochemistry |
The CCT evolved from the archaeal thermosome ~2Gya, with the two subunits diversifying into multiple units. The CCT changed from having one type of subunit, to having two, three, five, and finally eight types. | 1 | Biochemistry |
The core of amides is called the amide group (specifically, carboxamide group).
In the usual nomenclature, one adds the term "amide" to the stem of the parent acids name. For instance, the amide derived from acetic acid is named acetamide (CHCONH). IUPAC recommends ethanamide, but this and related formal names are rarely encountered. When the amide is derived from a primary or secondary amine, the substituents on nitrogen are indicated first in the name. Thus, the amide formed from dimethylamine and acetic acid is N,N'-dimethylacetamide (CHCONMe, where Me = CH). Usually even this name is simplified to dimethylacetamide. Cyclic amides are called lactams; they are necessarily secondary or tertiary amides. | 0 | Organic Chemistry |
The Mouse Genome Database collects and curates comprehensive phenotype and functional annotations for mouse genes and alleles. This is an NHGRI-funded project which contributes to the Mouse Genome Informatics database. | 1 | Biochemistry |
The basic building block (monomer) of polyethylene is ethylene. Ethylene is chemically similar to, and can be derived from ethanol, which can be produced by fermentation of agricultural feedstocks such as sugar cane or corn. Bio-derived polyethylene is chemically and physically identical to traditional polyethylene – it does not biodegrade but can be recycled. The Brazilian chemicals group Braskem claims that using its method of producing polyethylene from sugar cane ethanol captures (removes from the environment) 2.15 tonnes of per tonne of Green Polyethylene produced. | 7 | Physical Chemistry |
Some chain-growth polymerizations include chain transfer steps, in which another atom (often hydrogen) is transferred from a molecule in the system to the polymer radical. The original polymer chain is terminated and a new one is initiated. The kinetic chain is not terminated if the new radical can add monomer. However the degree of polymerization is reduced without affecting the rate of polymerization (which depends on kinetic chain length), since two (or more) macromolecules are formed instead of one. For the case of termination by disproportionation, the degree of polymerization becomes:
where R is the rate of transfer. The greater R is, the shorter the final macromolecule. | 7 | Physical Chemistry |
There is a need for a computer program that is easier to operate and that requires a simpler data structure then most currently available models. Therefore, the SahysMod program was designed keeping in mind a relative simplicity of operation to facilitate the use by field technicians, engineers and project planners instead of specialized geo-hydrologists.<br>
It aims at using input data that are generally available, or that can be estimated with reasonable accuracy, or that can be measured with relative ease. Although the calculations are done numerically and have to be repeated many times, the final results can be checked by hand using the formulas in this manual.
SahysMod's objective is to predict the long-term hydro-salinity in terms of general trends, not to arrive at exact predictions of how, for example, the situation would be on the first of April in ten years from now.<br>
Further, SahysMod gives the option of the re-use of drainage and well water (e.g. for irrigation) and it can account for farmers' responses to waterlogging, soil salinity, water scarcity and over-pumping from the aquifer. Also it offers the possibility to introduce subsurface drainage systems at varying depths and with varying capacities so that they can be optimized.
Other features of SahysMod are found in the next section. | 9 | Geochemistry |
Finding a suitable nanoscale motor capable of autonomous, unidirectional, linear motion is considered important to the development of DNA nanotechnology. The walkers have been shown to be capable of autonomous motion over linear, 2-dimensional and 3-dimensional DNA tracks through a large number of schemes. In July 2005, Bath et al. showed that another way to control DNA walker motion is to use restriction enzymes to strategically cleave the track, causing the forward motion of the walkers. In 2010, two different sets of researchers exhibited the walkers more complex abilities to selectively pick up and drop off molecular cargo and to perform DNA-templated synthesis as the walker moves along the track. In late 2015, Yehl et al. showed that three orders of magnitude higher than the speeds of motion seen previously were possible when using DNA-coated spherical particles that would "roll" on a surface modified with RNA complementary to the nanoparticles DNA. RNase H was used to hydrolyse the RNA, releasing the bound DNA and allowing the DNA to hybridize to RNA further downstream. In 2018, Valero et al. described a DNA walker based on two interlocked, catenated circular double-stranded DNAs (dsDNAs) and an engineered T7 RNA polymerase (T7RNAP) firmly attached to one of the DNA circles. This stator-ring unidirectionally rotated the interlocked rotor-ring by rolling circle transcription (RCT), driven by nucleotide triphosphate (NTP) hydrolysis, thereby constituting a catenated DNA wheel motor. The wheel motor produces long, repetitive RNA transcripts that remain attached to the DNA-catenane and are used to guide its directional walking along predefined ssDNA tracks arranged on a DNA nanotube. | 6 | Supramolecular Chemistry |
Fitness in this model is the probability that an individual survives to reproduce. In the simplest implementation of the model, developmentally stable genotypes survive (i.e. their fitness is ) and developmentally unstable ones do not (i.e. their fitness is ). | 1 | Biochemistry |
Modern puddling was one of several processes developed in the second half of the 18th century in Great Britain for producing bar iron from pig iron without the use of charcoal. It gradually replaced the earlier charcoal-fueled process, conducted in a finery forge. | 8 | Metallurgy |
Microbial metabolism is the means by which a microbe obtains the energy and nutrients (e.g. carbon) it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles. | 1 | Biochemistry |
Potassium ion channels play a key role in maintaining the membrane's electric potential. These ion channels are present in many various biological systems. They frequently play a role in regulation of cellular level processes, many of these processes including muscle relaxation, hypertension, insulin secretion etc. Some examples of potassium ion channels within biological systems include K channels, BK channels, and ether-a-go-go potassium channels | 7 | Physical Chemistry |
The modern perspective is that rate-limitingness should be quantitative and that it is distributed through a pathway to varying degrees. This idea was first considered by Higgins in the late 1950s as part of his PhD thesis where he introduced the quantitative measure he called the ‘reflection coefficient.’ This described the relative change of one variable to another for small perturbations. In his Ph.D. thesis, Higgins describes many properties of the reflection coefficients, and in later work, three groups, Savageau, Heinrich and Rapoport and Jim Burns in his thesis (1971) and subsequent publications independently and simultaneously developed this work into what is now called metabolic control analysis or, in the specific form developed by Savageau, biochemical systems theory. These developments extended Higgins’ original ideas significantly, and the formalism is now the primary theoretical approach to describing deterministic, continuous models of biochemical networks.
The variations in terminology between the different papers on metabolic control analysis were later harmonized by general agreement. | 1 | Biochemistry |
Since the U.S. Food and Drug Administration issued a rule in 2001 requiring that virtually all fruit and vegetable juice producers follow HACCP controls, and mandating a 5-log reduction in pathogens, UVGI has seen some use in sterilization of juices such as fresh-pressed. | 5 | Photochemistry |
Ancient milk glasses used crystals of calcium antimonate, formed in the melt from calcium present in the glass and an antimony additive. Opaque yellow glasses contained crystals of lead antimonate; bindheimite mineral may have been used as the additive. Under oxidizing condition, lead also forms incompletely dissolved lead pyroantimonate (PbSbO). From 2nd century BC tin oxide appears in use as opacifier, likely in the form of cassiterite mineral. Opaque yellow can be produced as lead stannate; the color is paler than the lead antimonate one. Later calcium and sodium phosphates became used; bone ash contains calcium phosphate in a high proportion. Calcium fluoride was also used, especially in China.
For dental ceramics, several approaches are in use. Spodumene or mica crystals can be precipitated. Fluorides of aluminium, calcium, barium, and magnesium can be used with suitable heat treatment. Tin oxide can be used, but zirconia and titania give better results; for titania, the appropriate resulting particle size is between submicron to 20 μm. Another desirable opacifier is zinc oxide.
Opacifiers must also form small particles in the system. Opacifiers are generally inert. | 7 | Physical Chemistry |
Analyte-specific reagents (ASRs) are a class of biological molecules which can be used to identify and measure the amount of an individual chemical substance in biological specimens. | 1 | Biochemistry |
In certain cases, the plane stress model can be used in the analysis of gently curved surfaces. For example,
consider a thin-walled cylinder subjected to an axial compressive load uniformly distributed along its rim, and filled with a pressurized fluid. The internal pressure will generate a reactive hoop stress on the wall, a normal tensile stress directed perpendicular to the cylinder axis and tangential to its surface. The cylinder can be conceptually unrolled and analyzed as a flat thin rectangular plate subjected to tensile load in one direction and compressive load in another other direction, both parallel to the plate. | 8 | Metallurgy |
Metal carbonyls react with reducing agents such as metallic sodium or sodium amalgam to give carbonylmetalate (or carbonylate) anions:
:Mn(CO) + 2 Na → 2 Na[Mn(CO)]
For iron pentacarbonyl, one obtains the tetracarbonylferrate with loss of CO:
:Fe(CO) + 2 Na → Na[Fe(CO)] + CO
Mercury can insert into the metal–metal bonds of some polynuclear metal carbonyls:
:Co(CO) + Hg → (CO)Co−Hg−Co(CO) | 0 | Organic Chemistry |
As cyclamin is not yet used as pharmaceutical drug such as for chemotherapy, no side effects were yet determined. | 0 | Organic Chemistry |
The Faraday Medal is awarded by the Electrochemistry Group of the Royal Society of Chemistry. Since 1977, it honours distinguished mid-career electrochemists working outside of the United Kingdom and the Republic of Ireland for their research advancements. | 7 | Physical Chemistry |
Anhydrous is a very polar liquid, having a dielectric constant of around 100. It has a high electrical conductivity, a consequence of autoprotolysis, i.e. self-protonation :
The equilibrium constant for autoprotolysis (25 °C) is:
The corresponding equilibrium constant for water, K is 10, a factor of 10 (10 billion) smaller.
In spite of the viscosity of the acid, the effective conductivities of the and ions are high due to an intramolecular proton-switch mechanism (analogous to the Grotthuss mechanism in water), making sulfuric acid a good conductor of electricity. It is also an excellent solvent for many reactions. | 7 | Physical Chemistry |
A vibration spectrum analyzer allows to analyze vibration amplitudes at various component frequencies, In this way, vibration occurring at specific frequencies can be identified and tracked. Since particular machinery problems generate vibration at specific frequencies, machinery faults can be detected or diagnosed. Vibration Spectrum Analyzers use the signal from different types of sensor, such as: accelerometers, velocity transducers and proximity sensors. The uses of a vibration spectrum analyzer in machine condition monitoring allows to detect and identify machine faults such as: rotor imbalance, shaft misalignment, mechanical looseness, bearing defects, among others. Vibration analysis can also be used in structures to identify structural resonances or to perform modal analysis. | 7 | Physical Chemistry |
Modified zeolite on which the external surface was partly covered with alkylsilane, called phase-boundary catalyst was prepared in two steps. First, titanium dioxide made from titanium isopropoxide was impregnated into NaY zeolite powder to give sample W-Ti-NaY. In the second step, alkysilane from n-octadecyltrichlorosilane (OTS) was impregnated into the W-Ti-NaY powder containing water. Due to the hydrophilicity of the w-Ti-NaY surface, addition of a small amount of water led to aggregation owing to the capillary force of water between particles. Under these conditions, it is expected that only the outer surface of aggregates, in contact with the organic phase can be modified with OTS, and indeed almost all of the particles were located at the phase boundary when added to an immiscible water–organic solvent (W/O) mixture. The partly modified sample is denoted w/o-Ti-NaY. Fully modified Ti-NaY (o-Ti-NaY), prepared without the addition of water in the above second step, is readily suspended in an organic solvent as expected. | 7 | Physical Chemistry |
Quantitatively, the smooth endoplasmic reticulum of the liver cell is the principal organ of drug metabolism, although every biological tissue has some ability to metabolize drugs.
Factors responsible for the liver's contribution to drug metabolism include that it is a large organ, that it is the first organ perfused by chemicals absorbed in the gut, and that there are very high concentrations of most drug-metabolizing enzyme systems relative to other organs.
If a drug is taken into the GI tract, where it enters hepatic circulation through the portal vein, it becomes well-metabolized and is said to show the first pass effect.
Other sites of drug metabolism include epithelial cells of the gastrointestinal tract, lungs, kidneys, and the skin.
These sites are usually responsible for localized toxicity reactions. | 1 | Biochemistry |
The waste stream is irradiated with Ultraviolet radiation. The UV radiation disinfect by disrupting the pathogen cell to be mutated and prevent the cell from replicating. Eventually the mutated cell becomes extinct and this process eliminates odour. | 3 | Analytical Chemistry |
Trimethyl orthoformate is prepared on an industrial scale by the methanolysis of hydrogen cyanide:
:HCN + 3 HOCH → HC(OCH) + NH
Trimethyl orthoformate can also be prepared from the reaction between chloroform and sodium methoxide, an example of the Williamson ether synthesis. | 0 | Organic Chemistry |
This form was developed in the 2000s and introduced commercially around 2009. Also called cast-mono, this design uses polycrystalline casting chambers with small "seeds" of mono material. The result is a bulk mono-like material that is polycrystalline around the outsides. When sliced for processing, the inner sections are high-efficiency mono-like cells (but square instead of "clipped"), while the outer edges are sold as conventional poly. This production method results in mono-like cells at poly-like prices. | 7 | Physical Chemistry |
The decrease in the Racah parameter B indicates that in a complex there is less repulsion between the two electrons in a given doubly occupied metal d-orbital than there is in the respective M gaseous metal ion, which in turn implies that the size of the orbital is larger in the complex. This electron cloud expansion effect may occur for one (or both) of two reasons. One is that the effective positive charge on the metal has decreased. Because the positive charge of the metal is reduced by any negative charge on the ligands, the d-orbitals can expand slightly. The second is the act of overlapping with ligand orbitals and forming covalent bonds increases orbital size, because the resulting molecular orbital is formed from two atomic orbitals.
The reduction of B from its free ion value is normally reported in terms of the nephelauxetic parameter β:
Experimentally, it is observed that size of the nephelauxetic parameter always follows a certain trend with respect to the nature of the ligands present. | 7 | Physical Chemistry |
An exergonic process is one which there is a positive flow of energy from the system to the surroundings. This is in contrast with an endergonic process. Constant pressure, constant temperature reactions are exergonic if and only if the Gibbs free energy change is negative (∆G < 0). "Exergonic" (from the prefix exo-, derived for the Greek word ἔξω exō, "outside" and the suffix -ergonic, derived from the Greek word ἔργον ergon, "work") means "releasing energy in the form of work". In thermodynamics, work is defined as the energy moving from the system (the internal region) to the surroundings (the external region) during a given process.
All physical and chemical systems in the universe follow the second law of thermodynamics and proceed in a downhill, i.e., exergonic, direction. Thus, left to itself, any physical or chemical system will proceed, according to the second law of thermodynamics, in a direction that tends to lower the free energy of the system, and thus to expend energy in the form of work. These reactions occur spontaneously.
A chemical reaction is also exergonic when spontaneous. Thus in this type of reactions the Gibbs free energy decreases. The entropy is included in any change of the Gibbs free energy. This differs from an exothermic reaction or an endothermic reaction where the entropy is not included. The Gibbs free energy is calculated with the Gibbs–Helmholtz equation:
where:
: T = temperature in kelvins (K)
: ΔG = change in the Gibbs free energy
: ΔS = change in entropy (at 298 K) as ΔS = ΣS(Product) − ΣS(Reagent)
: ΔH = change in enthalpy (at 298 K) as ΔH = ΣH(Product) − ΣH(Reagent)
A chemical reaction progresses spontaneously only when the Gibbs free energy decreases, in that case the ΔG is negative. In exergonic reactions the ΔG is negative and in endergonic reactions the ΔG is positive:
: exergon
: endergon
where:
: equals the change in the Gibbs free energy after completion of a chemical reaction. | 7 | Physical Chemistry |
Certain nonlinear optical phenomena such as the electro-optic effect cause a variation of a medium's permittivity tensor when an external electric field is applied, proportional (to lowest order) to the strength of the field. This causes a rotation of the principal axes of the medium and alters the behaviour of light travelling through it; the effect can be used to produce light modulators.
In response to a magnetic field, some materials can have a dielectric tensor that is complex-Hermitian; this is called a gyro-magnetic or magneto-optic effect. In this case, the principal axes are complex-valued vectors, corresponding to elliptically polarized light, and time-reversal symmetry can be broken. This can be used to design optical isolators, for example.
A dielectric tensor that is not Hermitian gives rise to complex eigenvalues, which corresponds to a material with gain or absorption at a particular frequency. | 3 | Analytical Chemistry |
Thiolate-protected gold clusters are a type of ligand-protected metal cluster, synthesized from gold ions and thin layer compounds that play a special role in cluster physics because of their unique stability and electronic properties. They are considered to be stable compounds.
These clusters can range in size up to hundreds of gold atoms, above which they are classified as passivated gold nanoparticles. | 7 | Physical Chemistry |
Lithium dimethylcuprate exists as a dimer in diethyl ether forming an 8-membered ring. Similarly, lithium diphenylcuprate crystallizes as a dimeric etherate, .
If the Li ions is complexed with the crown ether 12-crown-4, the resulting diorganylcuprate anions adopt a linear coordination geometry at copper.
For the higher order cyanocuprate LiCuCN(CH), the cyanide ligand is coordinated to Li and π-bound to Cu. | 0 | Organic Chemistry |
The two major types of austenitic stainless steels are characterized by the oxide layer that forms on the steel surface: either chromia-forming or alumina-forming. Cr-forming stainless steel is the most common type. However, Cr-forming steels do not exhibit high creep resistance at high temperatures, especially in environments with water vapor. Exposure to water vapor at high temperatures can increase internal oxidation in Cr-forming alloys and rapid formation of volatile Cr (oxy)hydroxides, both of which can reduce durability and lifetime.
Al-forming austenitic stainless steels feature a single-phase matrix of austenite iron (FCC) with an Al-oxide at the surface of the steel. Al is more thermodynamically stable in oxygen than Cr. More commonly, however, precipitate phases are introduced to increase strength and creep resistance. In Al-forming steels, NiAl precipitates are introduced to act as Al reservoirs to maintain the protective alumina layer. In addition, Nb and Cr additions help form and stabilize Al by increasing precipitate volume fractions of NiAl.
At least 5 grades of alumina-forming austenitic (AFA) alloys, with different operating temperatures at oxidation in air + 10% water vapor have been realized:
* AFA Grade: (50-60)Fe-(20-25)Ni-(14-15)Cr-(2.5-3.5)Al-(1-3)Nb wt.% base
** 750-800 °C operating temperatures at oxidation in air + 10% water vapor
* Low Nickel AFA Grade: 63Fe-12Ni-14Cr-2.5Al-0.6Nb-5Mn3Cu wt.% base
** 650 °C operating temperatures at oxidation in air + 10% water vapor
* High Performance AFA Grade: (45-55)Fe-(25-30)Ni-(14-15)Cr(3.5-4.5)Al-(1-3)Nb-(0.02-0.1)Hf/Y wt.% base
** 850-900 °C operating temperatures at oxidation in air + 10% water vapor
* Cast AFA Grade: (35-50)Fe-(25-35)Ni-14Cr-(3.5-4)Al-1Nb wt.% base
** 750-1100 °C operating temperatures at oxidation in air + 10% water vapor, depending upon Ni wt.%
* AFA superalloy (40-50)Fe-(30-35)Ni-(14-19)Cr-(2.5-3.5)Al-3Nb
** 750-850 °C operating temperatures at oxidation in air + 10% water vapor
Operating temperatures with oxidation in air and no water vapor are expected to be higher. In addition, an AFA superalloy grade exhibits creep strength approaching that of nickel alloy UNS N06617. | 8 | Metallurgy |
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