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A colloid has a dispersed phase and a continuous phase, whereas in a solution, the solute and solvent constitute only one phase. A solute in a solution are individual molecules or ions, whereas colloidal particles are bigger. For example, in a solution of salt in water, the sodium chloride (NaCl) crystal dissolves, and the Na and Cl ions are surrounded by water molecules. However, in a colloid such as milk, the colloidal particles are globules of fat, rather than individual fat molecules. Because colloid is multiple phases, it has very different properties compared to fully mixed, continuous solution. | 7 | Physical Chemistry |
Plants have evolved R genes (resistance genes) whose products mediate resistance to specific virus, bacteria, oomycete, fungus, nematode or insect strains. R gene products are proteins that allow recognition of specific pathogen effectors, either through direct binding or by recognition of the effector's alteration of a host protein. Many R genes encode NB-LRR proteins (proteins with nucleotide-binding and leucine-rich repeat domains, also known as NLR proteins or STAND proteins, among other names). Most plant immune systems carry a repertoire of 100–600 different R gene homologs. Individual R genes have been demonstrated to mediate resistance to specific virus, bacteria, oomycete, fungus, nematode or insect strains. R gene products control a broad set of disease resistance responses whose induction is often sufficient to stop further pathogen growth/spread.
Studied R genes usually confer specificity for particular strains of a pathogen species (those that express the recognized effector). As first noted by Harold Flor in his mid-20th century formulation of the gene-for-gene relationship, a plant R gene has specificity for a pathogen avirulence gene (Avr gene). Avirulence genes are now known to encode effectors. The pathogen Avr gene must have matched specificity with the R gene for that R gene to confer resistance, suggesting a receptor/ligand interaction for Avr and R genes. Alternatively, an effector can modify its host cellular target (or a molecular decoy of that target), and the R gene product (NLR protein) activates defenses when it detects the modified form of the host target or decoy. | 1 | Biochemistry |
Marc Julia (23 October 1922 – 29 June 2010) was a French chemist and the winner of the 1990 CNRS Gold Medal in chemistry. He discovered the Julia olefination reaction in 1973. | 0 | Organic Chemistry |
With the spherical-harmonic addition theorem the equation can be rewritten as
where
* are the spherical harmonics and
* the superscript denotes complex conjugation.
Note that the complex conjugation can be interchanged between the two spherical harmonics due to symmetry. | 7 | Physical Chemistry |
Mg(I) dimers have the potential to be reducing agents that can be utilized in organic and organometallic synthesis. The thermal stability, moderate air and water sensitivity, and wide range of solubility in organic solvents may make the dimer attractive to chemists. An example of this can be shown through low oxidation state germanium (Ge) chemistry. Using Mg(I) dimers led to a Ge double bond. It can also be noted that the product had low yield. Additionally, the ligand, Nacnac has poor solubility in the reaction solvent of ether. This allows for easy separation too.
Additionally, hydrogen storage has been gained significant research attention as an alternative to fossil fuels.
Ammonia borane, NHBH, has a high H-content, at 19.6%, concerning hydrogen storage material. However, there are issues regarding the safety, kinetics, and practical characteristics of the compound. Alternatively, more s-block amidoboranes have been researched as an alternative, with some interest lying in magnesium amidoborane. Some studies have shown that using reductive dehydrogenation of ammonia borane can be achieved using Mg(I) dimers. | 7 | Physical Chemistry |
Escitalopram, sold under the brand names Lexapro and Cipralex, among others, is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. Escitalopram is mainly used to treat major depressive disorder and generalized anxiety disorder. It is taken by mouth, available commercially as an oxalate salt exclusively.
Common side effects include trouble sleeping, nausea, sexual problems, and feeling tired. More serious side effects may include suicidal thoughts in people up to the age of 24 years. It is unclear if use during pregnancy or breastfeeding is safe. Escitalopram is the (S)-enantiomer of citalopram (which exists as a racemate), hence the name es-citalopram.
Escitalopram was approved for medical use in the United States in 2002. Escitalopram is rarely replaced by twice the dose of citalopram, though escitalopram is safer and more effective. It is on the World Health Organization's List of Essential Medicines. In 2021, it was the fifteenth most commonly prescribed medication in the United States, with more than 30million prescriptions. | 4 | Stereochemistry |
D-Xylose is a five-carbon aldose (pentose, monosaccharide) that can be catabolized or metabolized into useful products by a variety of organisms.
There are at least four different pathways for the catabolism of D-xylose: An oxido-reductase pathway is present in eukaryotic microorganisms. Prokaryotes typically use an isomerase pathway, and two oxidative pathways, called Weimberg and Dahms pathways respectively, are also present in prokaryotic microorganisms. | 1 | Biochemistry |
A thermosome is a group II chaperonin protein complex that functions in archaea. It is the homolog of eukaryotic CCT. This group II chaperonin is an ATP-dependent chaperonin that is responsible for folding or refolding of incipient or denatured proteins. A thermosome has two rings, each consisting of eight subunits, stacked together to form a cylindrical shape with a large cavity at the center. The thermosome is also defined by its heterooligomeric nature. The complex consists of Protein subunit| that alternate location within its two rings.
Being a Group II chaperonin, the thermosome has a similar structure to group I chaperonins. The main difference, however, lies in the existence of a helical protrusion in the thermosome which composes of a built-in lid of the hydrophilic cavity. Not only is thermosome ATP-dependent, but the mechanism in which thermosome shifts from open to close conformation is also temperature-dependent. The open conformation of the ATP-thermosome exists mainly at low temperatures. Whereas, the closed conformation of the thermosome occurs when heating to physiological temperature.
Similar to the GroEL chaperonins in bacteria, the thermosome shows negative cooperativity since the two rings of the thermosome show different affinities for the binding of ATP. However, unlike the GroEL system, the thermosome is less affected by the concentration of ATP. In the absence of ATP, the thermosome does not have a preference for the T-state over the R-state. There is, however, an inhibition for the loading of the second ring when ADP is bound to the first ring.
The N-terminus and C-terminus of thermosomes are arranged in an anti-parallel fashion and their interactions form part of the intra-ring interactions. Both the N-terminus and C-terminus of the thermosome have charged residues which interact with each other to contribute to the thermal stability of the thermosome. The cpn-α and cpn-β thermosomes specifically show maximum thermal stability in the pH range of 7.0 to 8.0 because this is the range where the charged N- and C-termini residues have net charges close to zero. Under lower or high pH conditions, these residues are charged and repelled each other which negatively affect thermal stability. This shows one possible way in which pH affects the stability of the thermosome. | 1 | Biochemistry |
The sticking probability is the probability that molecules are trapped on surfaces and adsorb chemically. From Langmuir's adsorption isotherm, molecules cannot adsorb on surfaces when the adsorption sites are already occupied by other molecules, so the sticking probability can be expressed as follows:
where is the initial sticking probability and is the surface coverage fraction ranging from 0 to 1.
Similarly, when molecules adsorb on surfaces dissociatively, the sticking probability is
The square is owing to the fact that a disassociation of 1 molecule into 2 parts requires 2 adsorption sites. These equations are simple and can be easily understood but cannot explain experimental results.
In 1958, P. Kisliuk presented an equation for the sticking probability that can explain experimental results. In his theory, molecules are trapped in precursor states of physisorption before chemisorption. Then the molecules meet adsorption sites that molecules can adsorb to chemically, so the molecules behave as follows.
If these sites are not occupied, molecules do the following (with probability in parentheses):
# adsorb on the surface chemically ()
# desorb from the surface ()
# move to the next precursor state ()
and if these sites are occupied, they
# desorb from the surface ()
# move to the next precursor state ()
Note that an occupied site is defined as one where there is a chemically bonded adsorbate so by definition it would be . Then the sticking probability is, according to equation (6) of the reference,
When , this equation is identical in result to Langmuir's adsorption isotherm. | 7 | Physical Chemistry |
Polyurethane dispersion, or PUD, is understood to be a polyurethane polymer resin dispersed in water, rather than a solvent, although some cosolvent maybe used. Its manufacture involves the synthesis of polyurethanes having carboxylic acid functionality or nonionic hydrophiles like PEG (polyethylene glycol) incorporated into, or pendant from, the polymer backbone. Two component polyurethane dispersions are also available. | 7 | Physical Chemistry |
The liberated catalytic subunits can then catalyze the transfer of ATP terminal phosphates to protein substrates at serine, or threonine residues. This phosphorylation usually results in a change in activity of the substrate. Since PKAs are present in a variety of cells and act on different substrates, PKA regulation and cAMP regulation are involved in many different pathways.
The mechanisms of further effects may be divided into direct protein phosphorylation and protein synthesis:
*In direct protein phosphorylation, PKA directly either increases or decreases the activity of a protein.
*In protein synthesis, PKA first directly activates CREB, which binds the cAMP response element (CRE), altering the transcription and therefore the synthesis of the protein. In general, this mechanism takes more time (hours to days). | 1 | Biochemistry |
The p3 protein is anchored to one end of the virion by the C-terminal domain of p3. Infection of host bacteria involves interaction of two different N-terminal regions of p3 with two different sites of the host bacteria. First, the N2 domain of p3 attaches to the outer tip of the F-pilus, and the pilus retracts into the cell. This retraction may involve depolymerization of the pilus subunit assembly into the cell membrane at the base of the pilus by a reversal of the pilus growth and polymerization process. As the tip of the pilus bearing p3 approaches the cell wall, the N1 domain of p3 interacts with the bacterial TolQRA protein to complete infection and release the genome into the cytoplasm of the host. | 1 | Biochemistry |
As awareness about ocean acidification grows, policies geared towards increasing monitoring efforts of ocean acidification have been drafted. Previously in 2015, ocean scientist Jean-Pierre Gattuso had remarked that "The ocean has been minimally considered at previous climate negotiations. Our study provides compelling arguments for a radical change at the UN conference (in Paris) on climate change".
International efforts, such as the UN Cartagena Convention (entered into force in 1986), are critical to enhance the support provided by regional governments to highly vulnerable areas to ocean acidification. Many countries, for example in the Pacific Islands and Territories, have constructed regional policies, or National Ocean Policies, National Action Plans, National Adaptation Plans of Action and Joint National Action Plans on Climate Change and Disaster Risk Reduction, to help work towards SDG 14. Ocean acidification is now starting to be considered within those frameworks. | 9 | Geochemistry |
The SH2 domain of Grb2 binds to phosphorylated tyrosine-containing peptides on receptors or scaffold proteins with a preference for pY-X-N-X, where X is generally a hydrophobic residue such as valine (see [http://sh2domain.org]).
The N-terminal SH3 domain binds to proline-rich peptides and can bind to the Ras-guanine exchange factor SOS.
The C-terminal SH3 domain binds to peptides conforming to a P-X-I/L/V/-D/N-R-X-X-K-P motif that allows it to specifically bind to proteins such as Gab-1. | 1 | Biochemistry |
Her publications include;
* Alexander Ryabchun, Federico Lancia, Nathalie Katsonis (2023). "Light‐Responsive Springs from Electropatterned Liquid Crystal Polymer Networks" Advanced Optical Materials. 11: 2300358. | 0 | Organic Chemistry |
Halothane, sold under the brand name Fluothane among others, is a general anaesthetic. It can be used to induce or maintain anaesthesia. One of its benefits is that it does not increase the production of saliva, which can be particularly useful in those who are difficult to intubate. It is given by inhalation.
Side effects include an irregular heartbeat, respiratory depression, and hepatotoxicity. Like all volatile anesthetics, it should not be used in people with a personal or family history of malignant hyperthermia. It appears to be safe in porphyria. It is unclear whether its usage during pregnancy is harmful to the fetus, and its use during a C-section is generally discouraged. Halothane is a chiral molecule that is used as a racemic mixture.
Halothane was discovered in 1951. It was approved for medical use in the United States in 1958. It is on the World Health Organization's List of Essential Medicines. Its use in developed countries has been mostly replaced by newer anesthetic agents such as sevoflurane. It is no longer commercially available in the United States. Halothane also contributes to ozone depletion. | 4 | Stereochemistry |
The average untrained healthy male has a V̇O max of approximately 35–40 mL/(kg·min). The average untrained healthy female has a V̇O max of approximately 27–31 mL/(kg·min). These scores can improve with training and decrease with age, though the degree of trainability also varies widely. | 1 | Biochemistry |
Consider the interface as a curve for where is a free parameter. The free energy to be minimized is
with the constraints which we can write as and fixed volume .
The modified Lagrangian, taking into account the constraints is therefore
where are Lagrange multipliers. By definition, the momentum and the Hamiltonian which is computed to be:
Now, we recall that the boundary is free in the direction and is a free parameter. Therefore, we must have:
At the boundary and , therefore we recover the Young equation. | 7 | Physical Chemistry |
These advancements have produced five main types of Conia-ene reactions characterized by the operative activation mode: namely, enolate, alkyne, or ene-yne activation, and one- or two-metal dual activation. Note that though the mechanisms of Conia-ene variants differ from the initial ene-like cyclization, they are still considered Conia-ene or Conia-ene-type reactions. In addition, due to the complexity of some Conia-ene reaction systems, the true mechanism may lay somewhere between several different activation modes. | 0 | Organic Chemistry |
Escitalopram is among the most effective and well-tolerated antidepressants for the short-term (acute) treatment of major depressive disorder in adults. It is also the safest one to give to children and adolescents.
Controversy existed regarding the effectiveness of escitalopram compared with its predecessor, citalopram. The importance of this issue followed from the greater cost of escitalopram relative to the generic mixture of isomers of citalopram, prior to the expiration of the escitalopram patent in 2012, which led to charges of evergreening. Accordingly, this issue has been examined in at least 10 different systematic reviews and meta analyses. , reviews had concluded (with caveats in some cases) that escitalopram is modestly superior to citalopram in efficacy and tolerability. | 4 | Stereochemistry |
Some spectroscopic curves can be approximated by the sum of a set of component curves. For example, when Beer's law
applies, the measured intensity, I, at wavelength λ, is a linear combination of the intensity due to the individual components, k, at concentration, c. ε is an extinction coefficient. In such cases the curve of experimental data may be decomposed into sum of component curves in a process of curve fitting. This process is also widely called deconvolution. Curve deconvolution and curve fitting are completely different mathematical procedures.
Curve fitting can be used in two distinct ways.
# The line shapes and parameters and of the individual component curves have been obtained experimentally. In this case the curve may be decomposed using a linear least squares process simply to determine the concentrations of the components. This process is used in analytical chemistry to determine the composition of a mixture of the components of known molar absorptivity spectra. For example, if the heights of two lines are found to be h and h, c = h / ε and c = h / ε.
# Parameters of the line shape are unknown. The intensity of each component is a function of at least 3 parameters, position, height and half-width. In addition one or both of the line shape function and baseline function may not be known with certainty. When two or more parameters of a fitting curve are not known the method of non-linear least squares must be used. The reliability of curve fitting in this case is dependent on the separation between the components, their shape functions and relative heights, and the signal-to-noise ratio in the data. When Gaussian-shaped curves are used for the decomposition of set of N spectra into N curves, the and parameters are common to all N spectra. This allows to calculated the heights of each Gaussian curve in each spectrum (N·N parameters) by a (fast) linear least squares fitting procedure, while the and w parameters (2·N parameters) can be obtained with a non-linear least-square fitting on the data from all spectra simultaneously, thus reducing dramatically the correlation between optimized parameters. | 7 | Physical Chemistry |
The Lamberhurst Foundry is believed to have been the maker in 1710–14 of some of the earliest cast-iron railings produced in England, which they made for St Paul's Cathedral, despite the objections of Christopher Wren, who did not want a fence around the Cathedral at all, and said that if there had to be one it should be of wrought rather than cast iron. The railings surrounded the cathedral, including seven gates. It weighed two hundred tons and cost six pence a pound. The total cost was £11,202. No further railings are known to have been cast in the Weald. Other early uses of cast iron railings were at Cambridge Senate House and at St Martin-in-the-Fields, London. | 8 | Metallurgy |
The advantages of the ISASMELT process include:
* High productivity with a small footprint: Glencore's copper smelter in Mount Isa treats over 1 million t/y of copper concentrate through a single furnace 3.75 m in diameter. The small footprint makes the process well suited to retrofitting to existing smelters where there are significant space constraints
* Simple operation: the ISASMELT furnace does not require extensive feed preparation as the feed can be discharged from a belt conveyor directly into the furnace
* high energy efficiency: installing an ISASMELT furnace in the Mount Isa copper smelter reduced energy consumption by over 80% (through better use of the inherent energy contained in the sulfide concentrate) compared with the roaster and reverberatory furnaces previously used there
* Flexibility in feed types: ISASMELT furnaces have been used to smelt copper, lead and nickel concentrates with a wide range of compositions, including high levels of magnetite, and secondary materials, such as copper scrap and lead-acid battery paste
* Flexibility in fuel types: ISASMELT furnaces can operate with a variety of fuels, including lump coal of varying ranks, coke (lump or fine), petroleum coke, oil (including recycled oil), natural gas, and liquid petroleum gas, depending on which is the most economic at the smelter's location
* High turn-down ratio: the feed rate to a single ISASMELT installation can easily be scaled up or down, depending on the availability of concentrate and the needs of the smelter
* Low feed carry over: ISASMELT furnaces typically lose about 1% of the feed as carry-over with the waste gas, meaning that there is less material that needs to be returned to the furnace for retreatment
* Effective containment of fugitive emissions: because the furnace has only two openings at the top, any fugitive emissions can easily be captured
* High elimination of deleterious minor elements: due to the flushing action of the gases injected into the ISASMELT furnace slags, copper ISASMELT furnaces have a high elimination of minor elements, such as bismuth and arsenic, that can have deleterious effects on the properties of the product copper
* High sulfur dioxide concentration in the waste gas: the use of oxygen enrichment gives the ISASMELT plants high sulfur dioxide concentrations in the waste gas stream, making acid plants cheaper to build and operate
* Relatively low operating cost: the energy efficiency of the process, the simple feed preparation, the relative lack of moving parts, low feed carry-over rates, low labour requirements and the ease of replacing lances and refractory linings when they are worn give the ISASMELT process relatively low operating costs
* Relatively low capital cost: the simplicity of the construction of the ISASMELT furnaces and the ability to treat concentrate without drying make it cheaper than other smelting processes. | 8 | Metallurgy |
In acid–base chemistry, homoassociation (an IUPAC term) is an association between a base and its conjugate acid through a hydrogen bond. The alternate term homoconjugation also has wide usage, but is ambiguous because it has another meaning in organic chemistry (see Conjugated system#Mechanism).
Most commonly, homoassociation leads to the enhancement of the acidity of an acid by itself. The effect is accentuated at high concentrations, i.e. the ionization of an acid varies nonlinearly with concentration. This effect arises from the stabilization of the conjugate base by its formation of a hydrogen bond to the parent acid. A well known case is hydrofluoric acid, which is a significantly stronger acid when concentrated than when dilute due to the following equilibria:
:2 HF HF + F (autoionization of HF)
:HF + F HF (homoassociation)
Overall:
:3 HF HF + HF
The bifluoride anion (HF) encourages the ionization of HF by stabilizing the F. Thus, the usual ionization constant for hydrofluoric acid (10) understates the acidity of concentrated solutions of HF.
The effect of homoassociation is often high in nonaqueous solutions, wherein dissociation is often low. Carboxylic acids and phenols exhibit this effect, for example in sodium diacetate. | 7 | Physical Chemistry |
Fermentation begins once the growth medium is inoculated with the organism of interest. Growth of the inoculum does not occur immediately. This is the period of adaptation, called the lag phase. Following the lag phase, the rate of growth of the organism steadily increases, for a certain period—this period is the log or exponential phase.
After a phase of exponential growth, the rate of growth slows down, due to the continuously falling concentrations of nutrients and/or a continuously increasing (accumulating) concentrations of toxic substances. This phase, where the increase of the rate of growth is checked, is the deceleration phase. After the deceleration phase, growth ceases and the culture enters a stationary phase or a steady state. The biomass remains constant, except when certain accumulated chemicals in the culture chemically break down the cells in a process called chemolysis. Unless other microorganisms contaminate the culture, the chemical constitution remains unchanged. If all of the nutrients in the medium are consumed, or if the concentration of toxins is too great, the cells may become senescent and begin to die off. The total amount of biomass may not decrease, but the number of viable organisms will decrease. | 1 | Biochemistry |
The Euglena photoreceptor was identified as a blue-light-activated adenylyl cyclase. Excitation of this receptor protein results in the formation of cyclic adenosine monophosphate (cAMP) as a second messenger. Chemical signal transduction ultimately triggers changes in flagellar beat patterns and cell movement.
The archaeal-type rhodopsins of Chlamydomonas contain an all-trans retinylidene chromatophore which undergoes photoisomerization to a 13-cis isomer. This activates a photoreceptor channel, leading to a change in membrane potential and cellular calcium ion concentration. Photoelectric signal transduction ultimately triggers changes in flagellar strokes and thus cell movement. | 1 | Biochemistry |
Axillary steroids are produced by the testes, ovaries, apocrine glands, and adrenal glands. These chemicals are not biologically active until puberty when sex steroids influence their activity. The change in activity during puberty suggest that humans may communicate through odors. Several axillary steroids have been described as possible human pheromones: androstadienol, androstadienone, androstenol, androstenone, and androsterone.
* Androstenol is the putative female pheromone. In a 1978 study by Kirk-Smith, people wearing surgical masks treated with androstenol or untreated were shown pictures of people, animals and buildings and asked to rate the pictures on attractiveness. Individuals with their masks treated with androstenol rated their photographs as being "warmer" and "more friendly". The best-known case study involves the synchronization of menstrual cycles among women based on unconscious odor cues, the McClintock effect, named after the primary investigator, Martha McClintock, of the University of Chicago. A group of women were exposed to a whiff of perspiration from other women. Depending on the time in the month the sweat was collected (before, during, or after ovulation) there was an association with the recipient woman's menstrual cycle to speed up or slow down. The 1971 study proposed two types of pheromone involved: "One, produced prior to ovulation, shortens the ovarian cycle; and the second, produced just at ovulation, lengthens the cycle". However, recent studies and reviews of the methodology have called the validity of her results and existence of menstrual synchronization into question.
* Androstenone is postulated to be secreted only by males as an attractant for women, and thought to be a positive effector for their mood. It seems to have different effects on women, depending on where a female is in her menstrual cycle, with the highest sensitivity to it during ovulation. In 1983, study participants exposed to androstenone were shown to undergo changes in skin conductance. Androstenone has been found to be perceived as more pleasant to women during their time of ovulation.
* Androstadienone seems to affect the limbic system and causes a positive reaction in women, improving mood. Responses to androstadienone depend on the individual and the environment they are in. Androstadienone negatively influences the perception of pain in women. Women tend to react positively after androstadienone presentation, while men react more negatively. In an experiment by Hummer and McClintock, androstadienone or a control odor was put on the upper lips of fifty males and females and they were tested for four effects of the pheromone: 1) automatic attention towards positive and negative facial expressions, 2) the strength of cognitive and emotional information as distractors in a simple reaction time task, 3) relative attention to social and nonsocial stimuli (i.e. neutral faces), and 4) mood and attentiveness in the absence of social interaction. Those treated with androstadienone drew more attention to towards emotional facial expressions and emotional words but no increased attention to neutral faces. These data suggest that androstadienone may increase attention to emotional information causing the individual to feel more focused. It is thought that androstadienone modulates on how the mind attends and processes information.
While it may be expected on evolutionary grounds that humans have pheromones, these three molecules have yet to be rigorously proven to act as such. Research in this field has suffered from small sample sizes, publication bias, false positives, and poor methodology. | 1 | Biochemistry |
There have been two significant periods of study on Frame Lake. One, in the early 1970s, looked at its water. The others, in the mid-2010s, examined the sediments to determine how the lake had reached the point it had by then. | 2 | Environmental Chemistry |
Hydrogen termination removes dangling bonds. All surface Si atoms are tetrahedral. Hydrogen termination confers stability in ambient environments. So again, the surface is both clean (of oxides) and relatively inert. These materials can be handled in air without special care for several minutes.
The Si-H bond in fact is stronger than the Si-Si bonds. Two kinds of Si-H centers are proposed, both featuring terminal Si-H bonds. One kind of site has one Si-H bond. The other kind of site features SiH centers.
Like organic hydrosilanes, the H-Si groups on the surface react with terminal alkenes and diazo groups. The reaction is called hydrosilylation. Many kinds of organic compounds with various functions can be introduced onto the silicon surface by the hydrosilylation of a hydrogen-terminated surface. The infrared spectrum of hydrogen-terminated silicon shows a band near 2090 cm, not very different from νSi-H for organic hydrosilanes. | 6 | Supramolecular Chemistry |
The alloys did not prove to be commercially successful in the long run. However, during World War I and afterwards, uranium-doped steels were used for tools; large amounts of ferrouranium were produced between 1914 and 1916. | 8 | Metallurgy |
Most tests will incorporate a second line which contains a further antibody (one which is not specific to the analyte) that binds some of the remaining colored particles which did not bind to the test line. This confirms that fluid has passed successfully from the sample-application pad, past the test line. By giving confirmation that the sample has had a chance to interact with the test line, this increases confidence that a visibly-unchanged test line can be interpreted as a negative result (or that a changed test line can be interpreted as a negative result in a competitive assay). | 1 | Biochemistry |
A whiting event is a phenomenon that occurs when a suspended cloud of fine-grained calcium carbonate precipitates in water bodies, typically during summer months, as a result of photosynthetic microbiological activity or sediment disturbance. The phenomenon gets its name from the white, chalky color it imbues to the water. These events have been shown to occur in temperate waters as well as tropical ones, and they can span for hundreds of meters. They can also occur in both marine and freshwater environments. The origin of whiting events is debated among the scientific community, and it is unclear if there is a single, specific cause. Generally, they are thought to result from either bottom sediment re-suspension or by increased activity of certain microscopic life such as phytoplankton. Because whiting events affect aquatic chemistry, physical properties, and carbon cycling, studying the mechanisms behind them holds scientific relevance in various ways. | 9 | Geochemistry |
Upon reaction of a CDA with the target analyte, chromatography can be used to separate the resulting products. In general, chromatography can be used to separate chiral compounds to bypass difficult crystallizations and/or to collect all diastereomer pairs in solution. Chromatography also has many variations (e.g. HPLC, Gas Chromatography, flash chromatography) with a wide array of applicability to diverse categories of molecules. The ability for CDAs to separate chiral molecules is dependent on two major mechanisms of chromatography:
#Differential solvation in the mobile phase
#Differential adsorption to the stationary phase | 4 | Stereochemistry |
Coccolithophore biomass is controlled by a combination of bottom-up (physical–biogeochemical environment) and top-down factors (predator–prey interactions), but the relative importance of the two has not yet been assessed for coccolithophores in the Southern Ocean. Bottom-up factors directly impact phytoplankton growth, and diatoms and coccolithophores are traditionally discriminated based on their differing requirements for nutrients, turbulence, and light. Based on this, Margalef's mandala predicts a seasonal succession from diatoms to coccolithophores as light levels increase and nutrient levels decline. In situ studies assessing Southern Ocean coccolithophore biogeography have found coccolithophores under various environmental conditions, thus suggesting a wide ecological niche, but all of the mentioned studies have almost exclusively focused on bottom-up controls.
However, phytoplankton growth rates do not necessarily covary with biomass accumulation rates. Using satellite data from the North Atlantic, Behrenfeld stressed in 2014 the importance of simultaneously considering bottom-up and top-down factors when assessing seasonal phytoplankton biomass dynamics and the succession of different phytoplankton types owing to the spatially and temporally varying relative importance of the physical–biogeochemical and the biological environment.
In the Southern Ocean, previous studies have shown zooplankton grazing to control total phytoplankton biomass, phytoplankton community composition, and ecosystem structure, suggesting that top-down control might also be an important driver for the relative abundance of coccolithophores and diatoms. But the role of zooplankton grazing in current Earth system models is not well considered, and the impact of different grazing formulations on phytoplankton biogeography and diversity is subject to ongoing research.
The diagram on the left shows the spatial distribution of different types of marine sediments in the Southern Ocean. The greenish area south of the Polar Front shows the extension of the subpolar opal belt where sediments have a significant portion of silicous plankton frustules. Sediments near Antarctica mainly consist of glacial debris in any grain size eroded and delivered by the Antarctic Ice. | 9 | Geochemistry |
In crystallography, a Wyckoff position is any point in a set of points whose site symmetry groups (see below) are all conjugate subgroups one of another. Crystallography tables give the Wyckoff positions for different space groups. | 3 | Analytical Chemistry |
Mefloquine may cause abnormalities with heart rhythms that are visible on electrocardiograms. Combining mefloquine with other drugs that cause similar effects, such as quinine or quinidine, can increase these effects. Combining mefloquine with halofantrine can cause significant increases in QTc intervals. | 4 | Stereochemistry |
Dyesol and Tata Steel Europe announced in June the development of the world's largest dye sensitized photovoltaic module, printed onto steel in a continuous line.
Dyesol and CSIRO announced in October a Successful Completion of Second Milestone in Joint Dyesol / CSIRO Project.
Dyesol Director Gordon Thompson said, "The materials developed during this joint collaboration have the potential to significantly advance the commercialisation of DSC in a range of applications where performance and stability are essential requirements.
Dyesol is extremely encouraged by the breakthroughs in the chemistry allowing the production of the target molecules. This creates a path to the immediate commercial utilisation of these new materials."
Dyesol and Tata Steel Europe announced in November the targeted development of Grid Parity Competitive BIPV solar steel that does not require government subsidised feed in tariffs. TATA-Dyesol "Solar Steel" Roofing is currently being installed on the Sustainable Building Envelope Centre (SBEC) in Shotton, Wales. | 5 | Photochemistry |
Winnowing is a process by which chaff is separated from grain. It can also be used to remove pests from stored grain. Winnowing usually follows threshing in grain preparation. In its simplest form, it involves throwing the mixture into the air so that the wind blows away the lighter chaff, while the heavier grains fall back down for recovery. Techniques included using a winnowing fan (a shaped basket shaken to raise the chaff) or using a tool (a winnowing fork or shovel) on a pile of harvested grain. | 3 | Analytical Chemistry |
The cation-exchange capacity of a soil is determined by its constituent materials, which can vary greatly in their individual CEC values. CEC is therefore dependent on parent materials from which the soil developed, and the conditions under which it developed. These factors are also important for determining soil pH, which has a major influence on CEC. | 9 | Geochemistry |
A useful rule in the determination of mechanism is that the concentration factors in the rate law indicate the composition and charge of the activated complex or transition state. For the –CO reaction above, the rate depends on [], so that the activated complex has composition , with 2 entering the reaction before the transition state, and CO reacting after the transition state.
A multistep example is the reaction between oxalic acid and chlorine in aqueous solution: + → 2 + 2 + 2 .
The observed rate law is
which implies an activated complex in which the reactants lose 2 + before the rate-determining step. The formula of the activated complex is + − 2 − +  , or (an unknown number of water molecules are added because the possible dependence of the reaction rate on was not studied, since the data were obtained in water solvent at a large and essentially unvarying concentration).
One possible mechanism in which the preliminary steps are assumed to be rapid pre-equilibria occurring prior to the transition state is
: + HOCl + +
:HOCl + → + + 2 | 7 | Physical Chemistry |
When used for detection of genetic and genomic changes, jumping clones require validation by Sanger sequencing. | 1 | Biochemistry |
Polymers blends, composites, multilayer films and fibers AFM-IR has been used to identify and map polymer components in blends, characterize interfaces in composites, and even reverse engineer multilayer films Additionally AFM-IR has been used to study chemical composition in Poly(3][4-ethylenedioxythiophene) (PEDOT) conducting polymers. and vapor infiltration into polyethylene terephthalate PET fibers. | 3 | Analytical Chemistry |
This reactivity is similar to the tendency of ethers with alpha hydrogen atoms to form peroxides. Reaction with chlorine produces alpha-chloroethers. | 0 | Organic Chemistry |
The plasmid is often transformed into a bacterium like E. coli. Ideally when the bacterium divides the plasmid should also be replicated. In the best case scenario, each bacterial cell should have several copies of the plasmid. After a good number of bacterial colonies have grown, they can be miniprepped to harvest the plasmid DNA. | 1 | Biochemistry |
Depending on the nature of the Detection system assays can be based on:
#Colony forming or virtual colony count: e.g. by multiplying bacteria or proliferating cells.
#Photometry / spectrophotometry When the absorbance of a specific wavelength of light while passing through a fixed path-length through a cuvette of liquid test sample is measured and the absorbance is compared with a blank and standards with graded amounts of the target compound. If the emitted light is of a specific visible wavelength it may be called colorimetry, or it may involve specific wavelength of light e.g. by use of laser and emission of fluorescent signals of another specific wavelength which is detected via very specific wavelength optical filters.
#Transmittance of light may be used to measure e.g. clearing of opacity of a liquid created by suspended particles due to decrease in number of clumps during a platelet agglutination reaction.
#Turbidimetry when the opacity of straight-transmitted light passing through a liquid sample is measured by detectors placed straight across the light source.
#Nephelometry where a measurement of the amount of light scattering that occurs when a beam of light is passed through the solution is used to determine size and/or concentration and/or size distribution of particles in the sample.
#Reflectometry When color of light reflected from a (usually dry) sample or reactant is assessed e.g. the automated readings of the strip urine dipstick assays.
#Viscoelastic measurements e.g. viscometry, elastography (e.g. thromboelastography)
#Counting assays: e.g. optic Flow cytometric cell or particle counters, or coulter/impedance principle based cell counters
#Imaging assays, that involve image analysis manually or by software:
##Cytometry: When the size statistics of cells is assessed by an image processor.
#Electric detection e.g. involving amperometry, Voltammetry, coulometry may be used directly or indirectly for many types of quantitative measurements.
#Other physical property based assays may use
##Osmometer
##Viscometer
##Ion Selective electrodes
##Syndromic testing | 1 | Biochemistry |
Gelation is promoted by gelling agents.
Gelation can occur either by physical linking or by chemical crosslinking. While the physical gels involve physical bonds, chemical gelation involves covalent bonds. The first quantitative theories of chemical gelation were formulated in the 1940s by Flory and Stockmayer. Critical percolation theory was successfully applied to gelation in 1970s. A number of growth models (diffusion limited aggregation, cluster-cluster aggregation, kinetic gelation) were developed in the 1980s to describe the kinetic aspects of aggregation and gelation. | 7 | Physical Chemistry |
Maharram Mammadyarov was born in Yayji, Julfa, Nakhichivan ASSR. In 1941, he graduated from Nakhchivan Pedagogical Technical School. He participated in WWII, serving in the Army. Mammadyarov graduated from Azerbaijan State University in 1949, and in 1953 from Leningrad Technical University by obtaining PhD. During 1953–1955, he worked as scientific secretary at Institute of Chemistry of Azerbaijan of National Academy of Sciences of Azerbaijan Soviet Socialist Republic. In 1955–1959 he was Senior Research Fellow at the Institute of Organic Chemistry named after N. Zelinski of the USSR Academy of Sciences. In 1959–1969 Mammadyarov worked at the Institute of Petrochemical Processes named after Y.H. Mammadaliyev. In 1973–1979 he was the head of Nakhchivan regional scientific center of ANAS. For his work on the use of carbon dioxide in the industry, he was awarded the State Prize of the Republic of Azerbaijan. In 1975–1978 Mammadyarov worked as teacher at the Nakhchivan State Pedagogical Institute (present Nakhchivan State University). From 1981 to 1994 he worked as the head of the department, and from 1994 to 2002 he worked as director of the Microbiology Institute of ANAS. Since 1969 he had been working at the Institute of Petrochemical Processes named after Y.H. Mammadaliyev as the Head of Synthesis and Technology of Synthetic Fats laboratory until his death in 2022.
Mammadyarov died on 2 January 2022, at the age of 97. He was the father of Minister of Foreign Affairs of Azerbaijan, Elmar Mammadyarov. | 0 | Organic Chemistry |
The operation of the diamond anvil cell relies on a simple principle:
where is the pressure, the applied force, and the area. Typical culet sizes for diamond anvils are 100–250 micrometres (µm), such that a very high pressure is achieved by applying a moderate force on a sample with a small area, rather than applying a large force on a large area. Diamond is a very hard and virtually incompressible material, thus minimising the deformation and failure of the anvils that apply the force. | 7 | Physical Chemistry |
sAC activation by bicarbonate is necessary for motility and other aspects of capacitation in the spermatozoa of mammals. In human males, mutations in the ADCY10 gene that lead to the inactivation of sAC have been linked to cases of sterility. Due to this essential role in male fertility, sAC has been explored as a potential target for non-hormonal male contraception. | 1 | Biochemistry |
Metabolic network modelling, also known as metabolic network reconstruction or metabolic pathway analysis, allows for an in-depth insight into the molecular mechanisms of a particular organism. In particular, these models correlate the genome with molecular physiology. A reconstruction breaks down metabolic pathways (such as glycolysis and the citric acid cycle) into their respective reactions and enzymes, and analyzes them within the perspective of the entire network. In simplified terms, a reconstruction collects all of the relevant metabolic information of an organism and compiles it in a mathematical model. Validation and analysis of reconstructions can allow identification of key features of metabolism such as growth yield, resource distribution, network robustness, and gene essentiality. This knowledge can then be applied to create novel biotechnology.
In general, the process to build a reconstruction is as follows:
# Draft a reconstruction
# Refine the model
# Convert model into a mathematical/computational representation
# Evaluate and debug model through experimentation
The related method of flux balance analysis seeks to mathematically simulate metabolism in genome-scale reconstructions of metabolic networks. | 1 | Biochemistry |
Adrenodoxin (adrenal ferredoxin; ), putidaredoxin, and terpredoxin make up a family of soluble FeS proteins that act as single electron carriers, mainly found in eukaryotic mitochondria and Pseudomonadota. The human variant of adrenodoxin is referred to as ferredoxin-1 and ferredoxin-2. In mitochondrial monooxygenase systems, adrenodoxin transfers an electron from NADPH:adrenodoxin reductase to membrane-bound cytochrome P450. In bacteria, putidaredoxin and terpredoxin transfer electrons between corresponding NADH-dependent ferredoxin reductases and soluble P450s. The exact functions of other members of this family are not known, although Escherichia coli Fdx is shown to be involved in biogenesis of Fe–S clusters. Despite low sequence similarity between adrenodoxin-type and plant-type ferredoxins, the two classes have a similar folding topology.
Ferredoxin-1 in humans participates in the synthesis of thyroid hormones. It also transfers electrons from adrenodoxin reductase to CYP11A1, a CYP450 enzyme responsible for cholesterol side chain cleavage. FDX-1 has the capability to bind to metals and proteins. Ferredoxin-2 participates in heme A and iron–sulphur protein synthesis. | 5 | Photochemistry |
LAGP is a solid ionic conductor and features the two fundamental properties to be used as a solid-state electrolyte in lithium-ion batteries, namely a sufficiently high ionic conductivity and a negligible electronic conductivity. Indeed, during battery operations, LAGP should guarantee the easy and fast motion of lithium ions between cathode and anode, while preventing the transfer of electrons.
As stated in the description of the crystal structure, three kinds of sites are available for hosting lithium ions in the LAGP NASICON structure, i.e. the Li(1) sites, the Li(2) sites and the Li(3) sites. Ionic conduction occurs because of hopping of lithium ions from Li(1) to Li(2) sites or across two Li(3) sites. The bottleneck to ionic motion is represented by a triangular window delimited by three oxygen atoms between Li(1) and Li(2) sites.
The ionic conductivity in LAGP follows the usual dependency on temperature expressed by an Arrhenius-type equation, which is typical of most of solid-state ionic conductors:
where
: is the pre-exponential factor,
: is the absolute temperature,
: is the activation energy for ionic transport,
: is the Boltzmann constant.
Typical values for the activation energies of bulk LAGP materials are in the range of 0.35 - 0.41 eV. Similarly, the room-temperature ionic conductivity is closely related to the synthesis conditions and to the actual material microstructure, therefore the conductivity values reported in scientific literature span from 10 S/cm up to 10 mS/cm, the highest value close to room temperature reported up to now. Compared to LGP, the room-temperature ionic conductivity of LAGP is increased by 3-4 orders of magnitude upon partial substitution of Ge by Al. Aluminium ions have a lower charge compared to Ge ions and additional lithium is incorporated in the NASICON structure to maintain charge balance, resulting in an enlarged number of charge carriers. The beneficial effect of aluminium is maximized for x around 0.4 - 0.5; for larger Al content, the single-phase NASICON structure is not stable and secondary phases appear, mainly AlPO, , and GeO. Secondary phases are typically nonconductive; however, small and controlled amounts of AlPO exert a densification effect which affects in a positive way the overall ionic conductivity of the material.
The prefactor in the Arrhenius equation can in turn be written as a function of fundamental constants and conduction parameters:
where
: is ion valence,
: is the elementary charge,
: is the absolute temperature,
: is the Boltzmann constant,
: is the concentration of charge carriers,
: is the average velocity of the ions,
: is the mean free path.
The prefactor is directly proportional to the concentration of mobile lithium-ion carriers, which increases with the aluminium content in the material. As a result, since the dependency of the activation energy on aluminium content is negligible, the ionic conductivity is expected to increase with increasing Ge substitution by Al, until secondary phases are formed. The introduction of aluminium also reduces the grain boundary resistivity of the material, positively impacting on the total (bulk crystal + grain boundary) ionic conductivity of the LAGP material.
As expected for solid ionic conductors, the ionic conductivity of LAGP increases with increasing temperature.
Regarding the electronic conductivity of LAGP, it should be as low as possible to prevent electrical short circuit between anode and cathode. As for ionic conductivity, the exact stoichiometry and microstructure, strongly connected to the synthesis method, have an influence on the electronic conductivity, even if the reported values are very low and close to (or lower than) 10 S/cm. | 7 | Physical Chemistry |
Variations in the DNA sequences of humans can affect how humans develop diseases and respond to pathogens, chemicals, drugs, vaccines, and other agents. SNPs are also critical for personalized medicine. Examples include biomedical research, forensics, pharmacogenetics, and disease causation, as outlined below. | 1 | Biochemistry |
There are two common mathematical descriptions of the work hardening phenomenon. Hollomon's equation is a power law relationship between the stress and the amount of plastic strain:
where σ is the stress, K is the strength index or strength coefficient, ε is the plastic strain and n is the strain hardening exponent. Ludwik's equation is similar but includes the yield stress:
If a material has been subjected to prior deformation (at low temperature) then the yield stress will be increased by a factor depending on the amount of prior plastic strain ε:
The constant K is structure dependent and is influenced by processing while n is a material property normally lying in the range 0.2–0.5. The strain hardening index can be described by:
This equation can be evaluated from the slope of a log(σ) – log(ε) plot. Rearranging allows a determination of the rate of strain hardening at a given stress and strain: | 8 | Metallurgy |
James Camerons core idea for the Avatars fictional creatures was for them to be "superslick and aerodynamic, and be like a race car with racing stripes". Neville Page worked on Avatar as the lead creature designer. He, Wayne Barlowe (author, artist, and initial lead creature designer), and Yuri Bartoli (concept designer and supervising virtual art director) adapted Camerons conceptions of the fauna into a design that served three purposes: to appear expressive, to function with animation technology, and to seem realistic. He and creature designer Wayne Barlowe sought to base the design of Pandora's creatures on race cars, but they struggled to adapt the concept. Page drew on his education in automotive design, recognizing the irony that race cars were based on real-life animals in having "bone lines". Existing automotive designs drew from seashells, turtle shells, and insects, so the designers returned the design to the fictional creatures. They found that the prime challenge in designing most creatures was to give them organic appearances, including skin texture. Some creatures were also designed to have special breathing holes located in the trachea, copying how cars have intakes. Challenges that the creatures posed for visual effects technicians were to form "walk and run" cycles for six-legged creatures and to impart credible flying for creatures that had four wings. Many of the animals also have four eyes, with an apparent major and minor eye on either side of their head.
The fictional creatures are not connected telepathically according to Cameron and the designers. However, even though they discussed the idea of the creatures being part of Pandoras "Worldmind", they preferred to interpret the creatures as having heightened instincts. Page explained, "Animals are hooked up to this planet. Were the ones who are detached.... The way I dealt with it was, We have so much rich [material] here to reference, that we don't have to dream up a whole new process of animal awareness."
The fictional moon has less gravity than Earth, so the creatures larger sizes match their environment. Most Pandoran wildlife is hexapodal, or six-legged. Much of the fauna and flora is bioluminescent, which is seen in creatures on Earth such as fireflies, many deep sea animals, and some microscopic algae. The aforementioned breathing holes, located on multiple parts of a creatures body other than the mouth, are similar to spiracles in some of Earths animals. The flying reptile-like creatures in the film can be compared to extinct flying reptiles such as pterosaurs and to the modern gliding lizard Draco sumatranus'. | 1 | Biochemistry |
Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to treat ores or concentrates containing copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.
Bioleaching falls into two broad categories. The first, is the use of microorganisms to oxidize refractory minerals to release valuable metals such and gold and silver. Most commonly the minerals that are the target of oxidization are pyrite and arsenopyrite.
The second category is leaching of sulphide minerals to release the associated metal, for example, leaching of pentlandite to release nickel, or the leaching of chalcocite, covellite or chalcopyrite to release copper. | 8 | Metallurgy |
Ge-V can be created during the diamond growth, or by ion implantation and subsequent annealing at 800 °C. The former way results in lower lattice strain, as revealed by the spread in the position and width of the Ge-V ZPL. | 7 | Physical Chemistry |
The composition of sea foam is generally a mixture of decomposed organic materials, including zooplankton, phytoplankton, algae (including diatoms), bacteria, fungi, protozoans, and vascular plant detritus, though each occurrence of sea foam varies in its specific contents. In some areas, sea foam is found to be made up of primarily protein, dominant in both fresh and old foam, as well as lipids and carbohydrates. The high protein and low carbohydrate concentration suggest that sugars originally present in the surrounding mucilage created by algae or plant matter has been quickly consumed by bacteria. Additional research has shown that a small fraction of the dry weight in sea foam is organic carbon, which contains phenolics, sugars, amino sugars, and amino acids. In the Bay of Fundy, high mortality rates of an abundant tube-dwelling amphipod (Corophium volutator) by natural die-offs as well as predation by migrating seabirds contributed to amino sugars released in the surrounding environment and thus, in sea foam.
The organic matter in sea foam has been found to increase dramatically during phytoplankton blooms in the area. Some research has shown very high concentrations of microplankton in sea foam, with significantly higher numbers of autotrophic phytoplankton than heterotrophs Some foams are particularly rich in their diatom population which can make up the majority of the microalgal biomass in some cases. A diversity of bacteria is also present in sea foam; old foam tends to have a higher density of bacteria. One study found that 95% of sea foam bacteria were rod-shaped, while the surrounding surface water contained mostly coccoid-form bacteria and only 5% - 10% rod-shaped bacteria. There is also seasonal variability of sea foam composition; in some regions there is a seasonal occurrence of pollen in sea foam which can alter its chemistry. Though foam is not inherently toxic, it may contain high concentrations of contaminants. Foam bubbles can be coated with or contain these materials which can include petroleum compounds, pesticides, and herbicides. | 9 | Geochemistry |
The Nevada Test Site (NTS), is a United States Department of Energy reservation located in southeastern Nye County, Nevada, about 65 miles (105 km) northwest of the city of Las Vegas. Formerly known as the Nevada Proving Grounds, the site was established on 11 January 1951 for the testing of nuclear devices, covering approximately of desert and mountainous terrain. Nuclear testing at the Nevada Test Site began with a bomb dropped on Frenchman Flat on 27 January 1951. Many of the iconic images of the nuclear era come from the NTS.
During the 1950s, the mushroom clouds from atmospheric tests could be seen for almost . The city of Las Vegas experienced noticeable seismic effects, and the distant mushroom clouds, which could be seen from the downtown hotels, became tourist attractions. St. George, Utah, received the brunt of the fallout of above-ground nuclear testing in the Yucca Flats/Nevada Test Site. Winds routinely carried the fallout of these tests directly through St. George and southern Utah. Marked increases in cancers, such as leukemia, lymphoma, thyroid cancer, breast cancer, melanoma, bone cancer, brain tumors, and gastrointestinal tract cancers, were reported from the mid-1950s through 1980.
From 1986 through 1994, two years after the United States put a hold on full-scale nuclear weapons testing, 536 anti-nuclear protests were held at the Nevada Test Site involving 37,488 participants and 15,740 arrests, according to government records. Those arrested included the astronomer Carl Sagan and the actors Kris Kristofferson, Martin Sheen, and Robert Blake.
The Nevada Test Site contains 28 areas, 1,100 buildings, 400 miles (640 km) of paved roads, 300 miles of unpaved roads, ten heliports, and two airstrips. The most recent test was a sub-critical test of the properties of plutonium, conducted underground on December 7, 2012. | 2 | Environmental Chemistry |
In general, the analysis of the capacitance transients in the DLTS measurements assumes that the concentration of investigated traps is much smaller than the material doping concentration. In cases when this assumption is not fulfilled then the constant capacitance DLTS (CCDLTS) method is used for more accurate determination of the trap concentration. When the defects recharge and their concentration is high then the width of the device space region varies making the analysis of the capacitance transient inaccurate. The additional electronic circuitry maintaining the total device capacitance constant by varying the device bias voltage helps to keep the depletion region width constant. As a result, the varying device voltage reflects the defect recharge process. An analysis of the CCDLTS system using feedback theory was provided by Lau and Lam in 1982. | 7 | Physical Chemistry |
Proteins are translated by reading tri-nucleotides on the mRNA strand, also known as codons, from one end of the mRNA to the other (from the 5 to the 3 end) starting with the amino acid methionine as the start (initiation) codon AUG. Each codon is translated into a single amino acid. The code itself is considered degenerate, meaning that a particular amino acid can be specified by more than one codon. However, a shift of any number of nucleotides that is not divisible by 3 in the reading frame will cause subsequent codons to be read differently. This effectively changes the ribosomal reading frame. | 1 | Biochemistry |
The third line shape that has a theoretical basis is the Voigt function, a convolution of a Gaussian and a Lorentzian,
where σ and γ are half-widths. The computation of a Voigt function and its derivatives are more complicated than a Gaussian or Lorentzian. | 7 | Physical Chemistry |
Melted micrometeorites (cosmic spherules) were first collected from deep-sea sediments during the 1873 to 1876 expedition of HMS Challenger. In 1891, Murray and Renard found "two groups [of micrometeorites]: first, black magnetic spherules, with or without a metallic nucleus; second, brown-coloured spherules resembling chondr(ul)es, with a crystalline structure". In 1883, they suggested that these spherules were extraterrestrial because they were found far from terrestrial particle sources, they did not resemble magnetic spheres produced in furnaces of the time, and their nickel-iron (Fe-Ni) metal cores did not resemble metallic iron found in volcanic rocks. The spherules were most abundant in slowly accumulating sediments, particularly red clays deposited below the carbonate compensation depth, a finding that supported a meteoritic origin. In addition to those spheres with Fe-Ni metal cores, some spherules larger than 300 µm contain a core of elements from the platinum group.
Since the first collection of HMS Challenger, cosmic spherules have been recovered from ocean sediments using cores, box cores, clamshell grabbers, and magnetic sleds. Among these a magnetic sled, called the "Cosmic Muck Rake", retrieved thousands of cosmic spherules from the top 10 cm of red clays on the Pacific Ocean floor. | 9 | Geochemistry |
Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones commonly have facets cut into them in order to improve their appearance by allowing them to reflect light. | 3 | Analytical Chemistry |
While semiconductors have been studied using microwave radiation since the 1950s, it was not until the late 1970s and early 1980s that John Warman at the Delft University of Technology exploited microwaves for time-resolved measurements of photoconductivity. The first reports used electrons then photons to generate charges in fluids. The technique was later refined to study semiconductors by Kunst and Beck at the Hahn Meitner Institute in Berlin.
Delft remains a significant center for TRMC, however the technique is now used at a number of institutions around the world, notably the National Renewable Energy Laboratory and Kyoto University. | 7 | Physical Chemistry |
Fluid particle is the smallest unit (atoms or molecules) in the fluid phase (gas, liquid or plasma) without breaking any chemical bond. Energy of fluid particle is divided into potential, electronic, translational, vibrational, and rotational energies. The heat (thermal) energy storage in fluid particle is through the temperature-dependent particle motion (translational, vibrational, and rotational energies). The electronic energy is included only if temperature is high enough to ionize or dissociate the fluid particles or to include other electronic transitions. These quantum energy states of the fluid particles are found using their respective quantum Hamiltonian. These are H = −(ħ/2m)∇, H = −(ħ/2m)∇ + Γx/2 and H = −(ħ/2I)∇ for translational, vibrational and rotational modes. (Γ: spring constant, I: the moment of inertia for the molecule). From the Hamiltonian, the quantized fluid particle energy state E and partition functions Z [with the Maxwell–Boltzmann (MB) occupancy distribution] are found as
* translational
* vibrational
* rotational
* total
Here, g is the degeneracy, n, l, and j are the transitional, vibrational and rotational quantum numbers, T is the characteristic temperature for vibration (= ħω/k, : vibration frequency), and T is the rotational temperature [= ħ/(2Ik)]. The average specific internal energy is related to the partition function through Z,
With the energy states and the partition function, the fluid particle specific heat capacity c is the summation of contribution from various kinetic energies (for non-ideal gas the potential energy is also added). Because the total degrees of freedom in molecules is determined by the atomic configuration, c has different formulas depending on the configuration,
* monatomic ideal gas
* diatomic ideal gas
* nonlinear, polyatomic ideal gas
where R is the gas constant (= Nk, N: the Avogadro constant) and M is the molecular mass (kg/kmol). (For the polyatomic ideal gas, N is the number of atoms in a molecule.) In gas, constant-pressure specific heat capacity c has a larger value and the difference depends on the temperature T, volumetric thermal expansion coefficient β and the isothermal compressibility κ [c – c = Tβ/(ρκ), ρ : the fluid density]. For dense fluids that the interactions between the particles (the van der Waals interaction) should be included, and c and c would change accordingly.
The net motion of particles (under gravity or external pressure) gives rise to the convection heat flux q = ρcuT. Conduction heat flux q for ideal gas is derived with the gas kinetic theory or the Boltzmann transport equations, and the thermal conductivity is
where ⟨u⟩ is the RMS (root mean square) thermal velocity (3kT/m from the MB distribution function, m: atomic mass) and τ is the relaxation time (or intercollision time period) [(2π dn ⟨u⟩) from the gas kinetic theory, ⟨u⟩: average thermal speed (8kT/πm), d: the collision diameter of fluid particle (atom or molecule), n: fluid number density].
k is also calculated using molecular dynamics (MD), which simulates physical movements of the fluid particles with the Newton equations of motion (classical) and force field (from ab initio or empirical properties). For calculation of k, the equilibrium MD with Green–Kubo relations, which express the transport coefficients in terms of integrals of time correlation functions (considering fluctuation), or nonequilibrium MD (prescribing heat flux or temperature difference in simulated system) are generally employed.
Fluid particles can interact with other principal particles. Vibrational or rotational modes, which have relatively high energy, are excited or decay through the interaction with photons. Gas lasers employ the interaction kinetics between fluid particles and photons, and laser cooling has been also considered in CO gas laser. Also, fluid particles can be adsorbed on solid surfaces (physisorption and chemisorption), and the frustrated vibrational modes in adsorbates (fluid particles) is decayed by creating e-h pairs or phonons. These interaction rates are also calculated through ab initio calculation on fluid particle and the Fermi golden rule. | 7 | Physical Chemistry |
Because most HERVs have no function, are selectively neutral, and are very abundant in primate genomes, they easily serve as phylogenetic markers for linkage analysis. They can be exploited by comparing the integration site polymorphisms or the evolving, proviral, nucleotide sequences of orthologs. To estimate when integration occurred, researchers used distances from each phylogenetic tree to find the rate of molecular evolution at each particular locus. It is also useful that ERVs are rich in many species genomes (i.e. plants, insects, mollusks, fish, rodents, domestic pets, and livestock) because its application can be used to answer a variety of phylogenetic questions. | 1 | Biochemistry |
Linear free-energy relationships (LFERs) exist when the relative influence of changing substituents on one reactant is similar to the effect on another reactant, and include linear Hammett plots, Swain–Scott plots, and Brønsted plots. LFERs are not always found to hold, and to see when one can expect them to, we examine the relationship between the free-energy differences for the two reactions under comparison. The extent to which the free energy of the new reaction is changed, via a change in substituent, is proportional to the extent to which the reference reaction was changed by the same substitution. A ratio of the free-energy differences is the reaction quotient or constant .
The above equation may be rewritten as the difference () in free-energy changes ():
Substituting the Gibbs free-energy equation () into the equation above yields a form that makes clear the requirements for LFERs to hold.
One should expect LFERs to hold if one of three conditions are met:
#s are coincidentally the same for both the new reaction under study and the reference reaction, and the s are linearly proportional for the two reactions being compared.
#s are coincidentally the same for both the new reaction under study and the reference reaction, and the s are linearly proportional for the two reactions being compared.
#s and s are linearly related to each other for both the reference reaction and the new reaction.
The third condition describes the enthalpy–entropy effect and is the condition most commonly met. | 7 | Physical Chemistry |
To design a transition state analogue, the pivotal step is the determination of transition state structure of substrate on the specific enzyme of interest with experimental method, for example, kinetic isotope effect. In addition, the transition state structure can also be predicted with computational approaches as a complementary to KIE. We will explain these two methods in brief. | 1 | Biochemistry |
Cucurbiturils have been used by chemists for various applications, including drug delivery, asymmetric synthesis, molecular switching, and dye tuning. | 6 | Supramolecular Chemistry |
Since BioCyc Database family comprises a long list of organism specific databases and also data at different systems level in a living system, the usage in research has been in a wide variety of context. Here, two studies are highlighted which show two different varieties of uses, one on a genome scale and other on identifying specific SNPs (Single Nucleotide Polymorphisms) within a genome.
AlgaGEM
AlgaGEM is a genome scale metabolic network model for a compartmentalized algae cell developed by Gomes de Oliveira Dal’Molin et al. based on the Chlamydomonas reinhardtii genome. It has 866 unique ORFs, 1862 metabolites, 2499 gene-enzyme-reaction-association entries, and 1725 unique reactions. One of the Pathway databases used for reconstruction is MetaCyc.
SNPs
The study by Shimul Chowdhury et al. showed association differed between maternal SNPs and metabolites involved in homocysteine, folate, and transsulfuration pathways in cases with Congenital Heart Defects (CHDs) as opposed to controls. The study used HumanCyc to select candidate genes and SNPs. | 1 | Biochemistry |
The magnetic properties of metal clusters are strongly influenced by their size and surface ligands. In general, the magnetic moments in small metal clusters are larger than in the case of a macroscopic bulk metal structure. For example, the average magnetic moment per atom in Ni clusters was found to be 0.7-0.8 μB, as compared with 0.6 μB for bulk Ni. This is explained by longer metal–metal bonds in cluster structures than in bulk structures, a consequence of a larger s character of metal–metal bonds in clusters. Magnetic moments approach bulk values as cluster size increases, though this is often difficult to predict computationally.
Magnetic quenching is an important phenomenon that is well documented for Ni clusters, and represents a significant effect of ligands on metal cluster magnetism. It has been shown that CO ligands cause the magnetic moments of surface Ni atoms to go to zero and the magnetic moment of inner Ni atoms to decrease to 0.5 μB. In this case, the 4s-derived Ni–Ni bonding molecular orbitals experience repulsion with the Ni-CO σ orbital, which causes its energy level to increase so that 3d-derived molecular orbitals are filled instead. Furthermore, Ni-CO π backbonding leaves Ni slightly positive, causing more transfer of electrons to 3d-derived orbitals, which are less disperse than those of 4s. Together, these effects result in a 3d, diamagnetic character of the ligated Ni atoms, and their magnetic moment decreases to zero.
Density functional theory (DFT) calculations have shown that these ligand-induced electronic effects are limited to only surface Ni atoms, and inner cluster atoms are virtually unperturbed. Experimental findings have described two electronically distinct cluster atoms, inner atoms and surface atoms. These results indicate the significant effect that a cluster's size has on its properties, magnetic and other. | 7 | Physical Chemistry |
Aside from decorative dentistry which they wore in life and carried the grave with them, ranking datus were often buried with items of gold, either in the form of gold burial goods, or as specifically designed funerary art such as death masks.
Burial goods found in graves from early Philippine history includes various beads earrings rings pendants, combs, strips, and other ornaments.
Another gold feature commonly discovered in elite burials from early historic Philippines are death mask artifacts, meant to cover either part or all of the deceased's face in the grave
When this practice was discovered by the Spanish colonizers, they created a rule that a government representative should always be present whenever the Spanish settlers dug up a grave - so that the Spanish government could get its designated 1/5 of the dug up goods.
Burial goods are among the most common surviving gold artifacts in the Philippines because gold which was not buried was typically eventually reforged into other forms as the colonial period proceeded. | 8 | Metallurgy |
Sodium methylsulfinylmethylide is prepared by heating sodium hydride or sodium amide in DMSO
:CHSOCH + NaH → CHSOCHNa + H
:CHSOCH + NaNH → CHSOCHNa + NH | 0 | Organic Chemistry |
Assuming that catalytic activity largely depends on the catalyst's affinity to the transition state, one could synthesize a transition state analog (TSA), a structure that resembles the transition state of the reaction. Then one could link the TSA to a solid-support or identifiable tag and use that TSA to select an optimal catalyst from a mixture of many different potential catalysts generated chemically or biologically by a diversity oriented synthesis. This method allows quick screening of a library of diverse compounds. It does not require as much synthetic effort and it allows a study of various catalytic factors simultaneously. Hence the method could potentially yield an efficient catalyst that we could not have designed with our current knowledge.
Many catalytic antibodies were developed and studied using this approach. | 6 | Supramolecular Chemistry |
In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation. In gemology, an inclusion is a characteristic enclosed within a gemstone, or reaching its surface from the interior.
According to Hutton's law of inclusions, fragments included in a host rock are older than the host rock itself. | 8 | Metallurgy |
It is a potent anesthetic with a minimum alveolar concentration (MAC) of 0.74%. Its blood/gas partition coefficient of 2.4 makes it an agent with moderate induction and recovery time. It is not a good analgesic and its muscle relaxation effect is moderate. | 4 | Stereochemistry |
Heteroepitaxial growth is classified into three primary growth modes-- Volmer–Weber (VW), Frank–van der Merwe (FM) and Stranski–Krastanov (SK).
In the VW growth regime, the epitaxial film grows out of 3D nuclei on the growth surface. In this mode, the adsorbate-adsorbate interactions are stronger than adsorbate-surface interactions, leading to island formation by local nucleation and the epitaxial layer is formed when the islands join.
In the FM growth mode, adsorbate-surface and adsorbate-adsorbate interactions are balanced, which promotes 2D layer-by-layer or step-flow epitaxial growth.
The SK mode is a combination of VW and FM modes. In this mechanism, the growth initiates in the FM mode, forming 2D layers, but after reaching a critical thickness, enters a VW-like 3D island growth regime.
Practical epitaxial growth, however, takes place in a high supersaturation regime, away from thermodynamic equilibrium. In that case, the epitaxial growth is governed by adatom kinetics rather than thermodynamics, and 2D step-flow growth becomes dominant. | 3 | Analytical Chemistry |
In chromatography substances are separated by partition between a stationary phase and a mobile phase. The analyte is dissolved in the mobile phase, and passes over the stationary phase. Separation occurs because of differing affinities of the analytes for the stationary phase. A distribution constant, K can be defined as
where a and a are the equilibrium activities in the stationary and mobile phases respectively. It can be shown that the rate of migration, , is related to the distribution constant by
f is a factor which depends on the volumes of the two phases. Thus, the higher the affinity of the solute for the stationary phase, the slower the migration rate.
There is a wide variety of chromatographic techniques, depending on the nature of the stationary and mobile phases. When the stationary phase is solid, the analyte may form a complex with it. A water softener functions by selective complexation with a sulfonate ion exchange resin. Sodium ions form relatively weak complexes with the resin. When hard water is passed through the resin, the divalent ions of magnesium and calcium displace the sodium ions and are retained on the resin, R.
: RNa + M RM + Na
The water coming out of the column is relatively rich in sodium ions and poor in calcium and magnesium which are retained on the column. The column is regenerated by passing a strong solution of sodium chloride through it, so that the resin–sodium complex is again formed on the column. Ion-exchange chromatography utilizes a resin such as chelex 100 in which iminodiacetate residues, attached to a polymer backbone, form chelate complexes of differing strengths with different metal ions, allowing the ions such as Cu and Ni to be separated chromatographically.
Another example of complex formation is in chiral chromatography in which is used to separate enantiomers from each other. The stationary phase is itself chiral and forms complexes selectively with the enantiomers. In other types of chromatography with a solid stationary phase, such as thin-layer chromatography the analyte is selectively adsorbed onto the solid.
In gas–liquid chromatography (GLC) the stationary phase is a liquid such as polydimethylsiloxane, coated on a glass tube. Separation is achieved because the various components in the gas have different solubility in the stationary phase. GLC can be used to separate literally hundreds of components in a gas mixture such as cigarette smoke or essential oils, such as lavender oil. | 7 | Physical Chemistry |
The etymology of the words "urethane" and "carbamate" are highly similar but not the same. The word "urethane" was first coined in 1833 by French chemist Jean-Baptiste Dumas. Dumas states "Urethane. The new ether, brought into contact with liquid and concentrated ammonia, exerts on this substance a reaction so strong that the mixture boils, and sometimes even produces a sort of explosion. If the ammonia is in excess, all the ether disappears. It forms ammonium hydrochlorate and a new substance endowed with interesting properties." Dumas appears to be naming this compound urethane. However, later Dumas states "While waiting for opinion to settle on the nature of this body, I propose to designate by the names of urethane and oxamethane the two materials which I have just studied, and . These names which, in my eyes, do not prejudge anything in the question of alcohol and ethers, will at least have the advantage of satisfying chemists who still refuse to accept our theory." The word urethane is derived from the words "urea" and "ether" with the suffix "-ane" as a generic chemical suffix, making it specific for the R2NC(=O)OR (R not = H) bonding structure.
The use of the word "carbamate" appears to come later only being traced back to at least 1849, in a description of Dumas's work by Henry Medlock. Medlock states "It is well known that the action of ammonia on chloro-carbonate (phosgene) of ethyl gives rise to the formation of the substance which Dumas, the discoverer, called urethane, and which we are now in the habit of considering as the ether of carbamic acid." This suggests that instead of continuing with the urethane family naming convention Dumas coined, they altered the naming convention to ethyl ether of carbamic acid. Carbamate is derived from the words "carbamide", otherwise known as urea, and "-ate" a suffix which indicates the salt or ester of an acid.
Both words have roots deriving from urea. Carbamate is less-specific because the -ate suffix is ambiguous for either the salt or ester of a carbamic acid. However, the -ate suffix is also more specific because it suggests carbamates must be derived from the acid of carbamate, or carbamic acids. Although, a urethane has the same chemical structure as a carbamate ester moiety, a urethane not derived from a carbamic acid is not a carbamate ester. In other words, any synthesis of the R2NC(=O)OR (R not = H) moiety that does not derive from carbamic acids is not a carbamate ester but instead a urethane. Furthermore, carbamate esters are urethanes but not all urethanes are carbamate esters. This further suggests that polyurethanes are not simply polycarbamate-esters because polyurethanes are not typically synthesized using carbamic acids.
IUPAC states "The esters are often called urethanes or urethans, a usage that is strictly correct only for the ethyl esters." But also states, "An alternative term for the compounds R2NC(=O)OR (R not = H), esters of carbamic acids, R,NC(=O)OH, in strict use limited to the ethyl esters, but widely used in the general sense". IUPAC provides these statements without citation. | 0 | Organic Chemistry |
Fluorapatite (Ca(PO)F) is mined along with other apatites for its phosphate content and is used mostly for production of fertilizers. Most of the Earth's fluorine is bound in this mineral, but because the percentage within the mineral is low (3.5%), the fluorine is discarded as waste. Only in the United States is there significant recovery. There, the hexafluorosilicates produced as byproducts are used to supply water fluoridation. | 9 | Geochemistry |
British physiologist Archibald Hill introduced the concepts of maximal oxygen uptake and oxygen debt in 1922. Hill and German physician Otto Meyerhof shared the 1922 Nobel Prize in Physiology or Medicine for their independent work related to muscle energy metabolism. Building on this work, scientists began measuring oxygen consumption during exercise. Key contributions were made by Henry Taylor at the University of Minnesota, Scandinavian scientists Per-Olof Åstrand and Bengt Saltin in the 1950s and 60s, the Harvard Fatigue Laboratory, German universities, and the Copenhagen Muscle Research Centre. | 1 | Biochemistry |
One standard increasingly used (e.g. in the United States) is J-STD-004. It is very similar to DIN EN 61190-1-1.
Four characters (two letters, then one letter, and last a number) represent flux composition, flux activity, and whether activators include halides:
* First two letters: Base
** RO: rosin
** RE: resin
** OR: organic
** IN: inorganic
* Third letter: Activity
** L: low
** M: moderate
** H: high
* Number: Halide content
** 0: less than 0.05% in weight (“halide-free”)
** 1: halide content depends on activity:
*** less than 0.5% for low activity
*** 0.5% to 2.0% for moderate activity
*** greater than 2.0% for high activity
Any combination is possible, e.g. ROL0, REM1 or ORH0.
J-STD-004 characterizes the flux by reliability of residue from a surface insulation resistance (SIR) and electromigration standpoint. It includes tests for electromigration and surface insulation resistance (which must be greater than 100 MΩ after 168 hours at elevated temperature and humidity with a DC bias applied). | 8 | Metallurgy |
GLD-2 primarily stabilizes mRNAs that are translationally repressed as well as it strongly promotes bulk polyadenylation. Surprisingly, those functions seem to have little impact on dynamizing efficient target mRNA translation, as it is an efficient Poly(A) Polymerase which helps developing polyadenylation activity. This activity is stimulated by its interaction with a putative RNA-binding protein: GLD-3. It is proposed by some studies that GLD-3 stimulates GLD-2 by recruiting it to the RNA. If so, then bringing GLD-2 to the RNA by other means also should stimulate its activity. | 1 | Biochemistry |
DNA replication is for the most part extremely accurate, however errors (mutations) do occur. The error rate in eukaryotic cells can be as low as 10 per nucleotide per replication, whereas for some RNA viruses it can be as high as 10. This means that each generation, each human genome accumulates around 30 new mutations. Small mutations can be caused by DNA replication and the aftermath of DNA damage and include point mutations in which a single base is altered and frameshift mutations in which a single base is inserted or deleted. Either of these mutations can change the gene by missense (change a codon to encode a different amino acid) or nonsense (a premature stop codon). Larger mutations can be caused by errors in recombination to cause chromosomal abnormalities including the duplication, deletion, rearrangement or inversion of large sections of a chromosome. Additionally, DNA repair mechanisms can introduce mutational errors when repairing physical damage to the molecule. The repair, even with mutation, is more important to survival than restoring an exact copy, for example when repairing double-strand breaks.
When multiple different alleles for a gene are present in a speciess population it is called polymorphic. Most different alleles are functionally equivalent, however some alleles can give rise to different phenotypic traits. A genes most common allele is called the wild type, and rare alleles are called mutants. The genetic variation in relative frequencies of different alleles in a population is due to both natural selection and genetic drift. The wild-type allele is not necessarily the ancestor of less common alleles, nor is it necessarily fitter.
Most mutations within genes are neutral, having no effect on the organisms phenotype (silent mutations). Some mutations do not change the amino acid sequence because multiple codons encode the same amino acid (synonymous mutations). Other mutations can be neutral if they lead to amino acid sequence changes, but the protein still functions similarly with the new amino acid (e.g. conservative mutations). Many mutations, however, are deleterious or even lethal, and are removed from populations by natural selection. Genetic disorders are the result of deleterious mutations and can be due to spontaneous mutation in the affected individual, or can be inherited. Finally, a small fraction of mutations are beneficial, improving the organisms fitness and are extremely important for evolution, since their directional selection leads to adaptive evolution. | 1 | Biochemistry |
The main impregnation techniques are wet impregnation and dry impregnation. During wet impregnation, the porous particles are dissolved in the extractant and allowed to soak with the respective fluid. In this approach, the particles are either contacted with a precalculated amount of extractant, which completely soaks into the porous matrix, or the particles are contacted with an excess of extractant. After soaking, the remaining extractant, which is not inside the pores, is evaporated.
If the wet method is used, the extractant is dissolved in an additional solvent prior to impregnation. The porous particles are then dispersed in the extractant-solvent solution. After soaking the particles, the excess solvent can either be filtered off or evaporated. In the first case, an extractant-solvent mixture would be retained within the pores. This would be of interest for extractants which would be solid at design conditions when pure. In the second case, only the extractant would remain inside the pores. Figure 3 shows porous particles dispersed in an aqueous solution after wet impregnation. The cut-out in Figure 3 shows an enlarge segment of the surface of such an impregnated particle.
An additional, albeit not so frequently used technique is the modifier addition method. This technique relies on the use of an extractant/solvent/modifier system. The additional modifier is supposed to enhance the penetration of the extractant into the particle pores. The solvent is subsequently evaporated, leaving extractant and modifier in the particle pores.
Furthermore, the dynamic column method can be used. The particles are contacted with a solvent until they are completely soaked. This can be done prior or after packing into the column. The packed bed is then rinsed with the liquid extractant until inlet and outlet concentrations are the same. This approach is particularly interesting when particles are already packed in a column and shall be reused for a SIR application. | 3 | Analytical Chemistry |
In Arabidopsis thaliana, there are three main families of transcription factors that contain B3 domain:
* ARF (Auxin Response Factors)
* ABI3 (ABscisic acid Insensitive3)
* RAV (Related to ABI3/VP1)
and are only known NMR solution phase structures of the B3 DNA Binding Domain. | 1 | Biochemistry |
Below are band gap values for some selected materials. For a comprehensive list of band gaps in semiconductors, see List of semiconductor materials. | 7 | Physical Chemistry |
Different material coatings for neural electrode surfaces are being researched to improve the long-term integration of electrodes in the neural tissue by improving biocompatibility, mechanical properties, and the charge transport between the electrode and the living tissue. The electrode functionality can be increased by adding a surface modification on the electrode of a conducting porous polymer with the incorporation of cell adhesion peptides, proteins, and anti-inflammatory drugs. | 7 | Physical Chemistry |
Due to the essential role of NADPH in lipid and DNA biosynthesis and the hyperproliferative nature of most cancers, NADK is an attractive target for cancer therapy. Furthermore, NADPH is required for the antioxidant activities of thioredoxin reductase and glutaredoxin. Thionicotinamide and other nicotinamide analogs are potential inhibitors of NADK, and studies show that treatment of colon cancer cells with thionicotinamide suppresses the cytosolic NADPH pool to increase oxidative stress and synergizes with chemotherapy.
While the role of NADK in increasing the NADPH pool appears to offer protection against apoptosis, there are also cases where NADK activity appears to potentiate cell death. Genetic studies done in human haploid cell lines indicate that knocking out NADK may protect from certain non-apoptotic stimuli. | 1 | Biochemistry |
A proton conductor is an electrolyte, typically a solid electrolyte, in which H are the primary charge carriers. | 7 | Physical Chemistry |
Carbon dioxide, like other gases, is soluble in water. However, unlike many other gases (oxygen for instance), it reacts with water and forms a balance of several ionic and non-ionic species (collectively known as dissolved inorganic carbon, or DIC). These are dissolved free carbon dioxide (CO ), carbonic acid (HCO), bicarbonate (HCO) and carbonate (CO), and they interact with water as follows :
The balance of these carbonate species (which ultimately affects the solubility of carbon dioxide), is dependent on factors such as pH, as shown in a Bjerrum plot. In seawater this is regulated by the charge balance of a number of positive (e.g. Na, K, Mg, Ca) and negative (e.g. CO itself, Cl, SO, Br) ions. Normally, the balance of these species leaves a net positive charge. With respect to the carbonate system, this excess positive charge shifts the balance of carbonate species towards negative ions to compensate. The result of which is a reduced concentration of the free carbon dioxide and carbonic acid species, which in turn leads to an oceanic uptake of carbon dioxide from the atmosphere to restore balance. Thus, the greater the positive charge imbalance, the greater the solubility of carbon dioxide. In carbonate chemistry terms, this imbalance is referred to as alkalinity.
In terms of measurement, four basic parameters are of key importance: Total inorganic carbon (TIC, T or C), Total alkalinity (T or A), pH, and pCO. Measuring any two of these parameters allows for the determination of a wide range of pH-dependent species (including the above-mentioned species). This balance can be changed by a number of processes. For example, the air-sea flux of CO, the dissolution/precipitation of CaCO, or biological activity such as photosynthesis/respiration. Each of these has different effects on each of the four basic parameters, and together they exert strong influences on global cycles. The net and local charge of the oceans remains neutral during any chemical process. | 9 | Geochemistry |
Litmus can be found in different species of lichens. The dyes are extracted from such species as Roccella tinctoria (South American), Roccella fuciformis (Angola and Madagascar), Roccella pygmaea (Algeria), Roccella phycopsis, Lecanora tartarea (Norway, Sweden), Variolaria dealbata, Ochrolechia parella, Parmotrema tinctorum, and Parmelia. Currently, the main sources are Roccella montagnei (Mozambique) and Dendrographa leucophoea (California). | 3 | Analytical Chemistry |
The strength of the electronic coupling of the donor and acceptor decides whether the electron transfer reaction is adiabatic or non-adiabatic. In the non-adiabatic case the coupling is weak, i.e. H in Fig. 3 is small compared to the reorganization energy and donor and acceptor retain their identity. The system has a certain probability to jump from the initial to the final potential energy curves. In the adiabatic case the coupling is considerable, the gap of 2 H is larger and the system stays on the lower potential energy curve.
Marcus theory as laid out above, represents the non-adiabatic case. Consequently, the semi-classical Landau-Zener theory can be applied, which gives the probability of interconversion of donor and acceptor for a single passage of the system through the region of the intersection of the potential energy curves
where H is the interaction energy at the intersection, v the velocity of the system through the intersection region, s and s the slopes there.
Fig. 3 Energy diagram for Electron Transfer including inner and outer sphere reorganization and electronic coupling: The vertical axis is the free energy, and the horizontal axis is the "reaction coordinate" – a simplified axis representing the motion of all the atomic nuclei (inclusive solvent reorganization)
Working this out, one arrives at the basic equation of Marcus theory
where is the rate constant for electron transfer, is the electronic coupling between the initial and final states, is the reorganization energy (both inner and outer-sphere), and is the total Gibbs free energy change for the electron transfer reaction ( is the Boltzmann constant and is the absolute temperature).
Thus Marcus's theory builds on the traditional Arrhenius equation for the rates of chemical reactions in two ways:
1. It provides a formula for the activation energy, based on a parameter called the reorganization energy, as well as the Gibbs free energy. The reorganization energy is defined as the energy required to "reorganize" the system structure from initial to final coordinates, without making the charge transfer.
2. It provides a formula for the pre-exponential factor in the Arrhenius equation, based on the electronic coupling between the initial and final state of the electron transfer reaction (i.e., the overlap of the electronic wave functions of the two states). | 7 | Physical Chemistry |
Dragendorff's reagent is prepared by mixing a concentrated solution of potassium iodide with a solution of bismuth subnitrate in a diluted acid (acetic acid or tartaric acid, hydrochloric acid or sulfuric acid is rarely being used) as a low pH is mandatory for this reagent.
The formation is as follows:
The black precipitate of bismuth iodide is formed from the reaction of bismuth ion and potassium iodide.
Then, the reaction between bismuth ion and excess potassium iodide will produce a soluble complex of potassium tetraiodobismuthate which has an orange color.
Many compositions degrade over time and are sensitive to light, so for long-term storage it is often prepared as two separate solutions to be mixed before use, one containing bismuth subnitrate and acid with the other containing potassium iodide.
The most common composition is as follows:
Part A: 0.85g bismuth subnitrate, 40mL water, and 10mL glacial acetic acid.
Part B: 8g potassium iodide and 20mL water.
There are many different compositions in literature for the combined reagent. Some combine the entire volume of both solutions without dilution, but most involve diluting equal parts of these solutions with acid and water. One common composition is 5mL each of part A & B with 20mL of glacial acetic acid and 70-100mL of water. | 3 | Analytical Chemistry |
The respiratory quotient (RQ or respiratory coefficient) is a dimensionless number used in calculations of basal metabolic rate (BMR) when estimated from carbon dioxide production. It is calculated from the ratio of carbon dioxide produced by the body to oxygen consumed by the body. Such measurements, like measurements of oxygen uptake, are forms of indirect calorimetry. It is measured using a respirometer. The respiratory quotient value indicates which macronutrients are being metabolized, as different energy pathways are used for fats, carbohydrates, and proteins. If metabolism consists solely of lipids, the respiratory quotient is approximately 0.7, for proteins it is approximately 0.8, and for carbohydrates it is 1.0. Most of the time, however, energy consumption is composed of both fats and carbohydrates. The approximate respiratory quotient of a mixed diet is 0.8. Some of the other factors that may affect the respiratory quotient are energy balance, circulating insulin, and insulin sensitivity.
It can be used in the alveolar gas equation. | 1 | Biochemistry |
Photo-reflectance is a particularly convenient type of modulation spectroscopy, as it may be performed at room temperature and only requires the sample have a reflecting surface. It is an established tool for non-contact determination of material and electronic properties of semiconductor films. In photo-reflectance, a pump laser beam is used to modulate the free charge density in a semiconductor sample (via photo-injection), thereby modulating one or more physical quantities (e.g. the internal electric field). The measured signal ΔR is the change in amplitude of the reflected probe light as the intensity modulated pump radiation interacts with the sample. The normalized signal is ΔR/R, i.e. the pump-induced change in reflectance (AC) divided by the baseline reflectance (DC). The conventional photo-reflectance apparatus uses a spectroscopic source for the probe beam, such that the signal may be recorded as a function of the probe light's wavelength. Generally, the signal may be written:
where ΔR/R is the normalized change in reflectance, α (≡1/R×∂R/∂ε) and β (≡1/R×∂R/∂ε) are the "Seraphin coefficients" which contain filmstack information, and Δε and Δε are the pump induced changes in the complex dielectric function. However, in conventional photo-reflectance analysis, it is not necessary to independently determine the refractive and absorptive components (the first and second terms in ΔR/R, respectively) of the signal. Rather, a fit to the overall signal is performed using the third derivative functional form given by Aspnes. This fit procedure yields the interband transition energies, amplitudes, and widths. However, because the signal depends on the uniformity of the perturbation, the extraction of such parameters must be treated with care. | 7 | Physical Chemistry |
Confusion between inversion domains and antiphase domains is common, even in the published literature, and particularly in the case of GaAs grown on silicon. (Similar defects form in GaN on silicon, where they are correctly identified as inversion domains). An example is illustrated in the diagram below.
Figure 4. Highlighted area showing an inversion domain, incorrectly called an antiphase domain, in GaAs on Si.
The shaded region, B, is an example of an APD. In the figure, GaAs is grown on a misoriented surface of Si (details are not discussed here). The misorientation causes the Ga and As atoms in region B to be on opposite sites compared to the crystal matrix. The presence of the APD results in Ga sites 1, 1’, 2, 2’, 3, 3’ being bonded to Ga atoms in the APD to form an APB.
In mixed oxidation state materials like magnetite, antiphase domains and antiphase domain boundaries can occur as a result of charge-ordering even though there are no changes in atom locations. For example, the reconstructed magnetite (100) surface contains alternating Fe pairs and Fe pairs in the first subsurface layer. An antiphase domain boundary can form if two subsurface Fe pairs meet when two terraces grow together. | 3 | Analytical Chemistry |
* The compressive residual stresses imparted by laser peening are precisely controlled both in location and intensity and can be applied to mitigate sharp transitions into tensile regions. Laser peening imparts deep compressive residual stresses on the order of 10 to 20 times deeper than conventional shot peening, making them significantly more beneficial at preventing SCC. Laser peening is widely used in the aerospace and power generation industries in gas fired turbine engines.
* Material Selection: Choosing the right material for a specific environment can help prevent SCC. Materials with higher resistance to corrosion and stress corrosion cracking should be used in corrosive environments. For example, using stainless steel instead of carbon steel in a marine environment can reduce the likelihood of SCC.
* Protective Coatings: Applying a protective coating or barrier can help prevent corrosive substances from coming into contact with the metal surface, thus reducing the likelihood of SCC. For example, using an epoxy coating on the interior surface of a pipeline can reduce the likelihood of SCC.
* Cathodic Protection: Cathodic protection is a technique used to protect metals from corrosion by applying a small electrical current to the metal surface. This technique can also help prevent SCC by reducing the corrosion potential of the metal.
* Environmental Controls: Controlling the environment around the metal can help prevent SCC. For example, reducing the temperature or acidity of the environment can help prevent SCC.
* Inspection and Maintenance: Regular inspections and maintenance can help detect SCC before it causes a failure. This includes visual inspections, non-destructive testing, and monitoring of environmental factors. | 8 | Metallurgy |
Colloids can be classified as follows:
Homogeneous mixtures with a dispersed phase in this size range may be called colloidal aerosols, colloidal emulsions, colloidal suspensions, colloidal foams, colloidal dispersions, or hydrosols. | 7 | Physical Chemistry |
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