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The overlap extension polymerase chain reaction (or OE-PCR) is a variant of PCR. It is also referred to as Splicing by overlap extension / Splicing by overhang extension (SOE) PCR. It is used assemble multiple smaller double stranded DNA fragments into a larger DNA sequence. OE-PCR is widely used to insert mutations at specific points in a sequence or to assemble custom DNA sequence from smaller DNA fragments into a larger polynucleotide. | 1 | Biochemistry |
The explorations in the foothills of the Kopetdag revealed well developed irrigation systems with water control arrangements which resulted in prosperous, well settled large regional centres. The largest of these settlements is Namazga-Tepe with an area of 50 ha. The excavations done at this site lead to the discovery of six distinct periods. Named Namazgadepe I to VI, the periods extended over the late 5th millennium to early 3rd millennium BC. In the process of development over these centuries, the transition observed was from Chalcolithic period to Early Bronze Age with urban characteristics in the settlements. Dwelling houses also emerged from chaotically planned one room houses to larger houses with many rooms with the interiors painted (lac paintings) and with a hearth. Defensive forts were part of the settlements. Chalcolithic stone amulets with geometric shapes, pottery traditions with two-tiered furnaces for firing ceramics, terracotta figurines, stamp seals of clay and stone, and centres of metallurgical production were uncovered. Rosette and zoomorphic patterns were unearthed, representing various periods, both at Namazga-Tepe and also at other settlements in the foothills of the Kopetdag mountains. These are clearly indicative of the village cultures of Central Asia. | 8 | Metallurgy |
Radiative cooling is one of the few ways an object in space can give off energy. In particular, white dwarf stars are no longer generating energy by fusion or gravitational contraction, and have no solar wind. So the only way their temperature changes is by radiative cooling. This makes their temperature as a function of age very predictable, so by observing the temperature, astronomers can deduce the age of the star. | 7 | Physical Chemistry |
SQT measurements are scaled proportionately by relative impact and visually represented on triaxial graphs. Evaluation of sediment integrity and interrelationships between components can be determined by the size and morphology of the triangle. The magnitude of the triangle is indicative of the relative impact of contamination. Equilateral triangles imply agreement among components. (USEPA, 1994) | 2 | Environmental Chemistry |
Substitution reactions involve the replacement of the halogen with another molecule—thus leaving saturated hydrocarbons, as well as the halogenated product. Haloalkanes behave as the R synthon, and readily react with nucleophiles.
Hydrolysis, a reaction in which water breaks a bond, is a good example of the nucleophilic nature of haloalkanes. The polar bond attracts a hydroxide ion, OH (NaOH being a common source of this ion). This OH is a nucleophile with a clearly negative charge, as it has excess electrons it donates them to the carbon, which results in a covalent bond between the two. Thus C–X is broken by heterolytic fission resulting in a halide ion, X. As can be seen, the OH is now attached to the alkyl group, creating an alcohol. (Hydrolysis of bromoethane, for example, yields ethanol). Reactions with ammonia give primary amines.
Chloro- and bromoalkanes are readily substituted by iodide in the Finkelstein reaction. The iodoalkanes produced easily undergo further reaction. Sodium iodide is used as a catalyst.
Haloalkanes react with ionic nucleophiles (e.g. cyanide, thiocyanate, azide); the halogen is replaced by the respective group. This is of great synthetic utility: chloroalkanes are often inexpensively available. For example, after undergoing substitution reactions, cyanoalkanes may be hydrolyzed to carboxylic acids, or reduced to primary amines using lithium aluminium hydride. Azoalkanes may be reduced to primary amines by Staudinger reduction or lithium aluminium hydride. Amines may also be prepared from alkyl halides in amine alkylation, Gabriel synthesis and Delepine reaction, by undergoing nucleophilic substitution with potassium phthalimide or hexamine respectively, followed by hydrolysis.
In the presence of a base, haloalkanes alkylate alcohols, amines, and thiols to obtain ethers, N-substituted amines, and thioethers respectively. They are substituted by Grignard reagent to give magnesium salts and an extended alkyl compound. | 0 | Organic Chemistry |
Bolesatine is a glycoprotein isolated from the Rubroboletus satanas (Boletus satanas Lenz) mushroom which has a lectin function that is specific to the sugar binding site of D-galactose. It is a monomeric protein with a compact globular structure and is thermostable. One tryptophan can be found in its primary sequence along with one disulfide bridge.
Bolesatine causes gastroenteritis in humans and, at high enough concentrations, inhibits protein synthesis. It does not inhibit protein synthesis directly. Instead, it acts as a phosphatase for nucleoside triphosphate, particularly for GTP. At lower concentrations, it is a mitogen to human and rat T lymphocytes. Studies have shown that at low concentrations, protein kinases C (PKC) are activated in vitro and in vero cells, leading to an increase in DNA synthesis activity. | 1 | Biochemistry |
Plithotaxis, from the Greek word "πλήΘος", denotes a crowd, swarm, or throng. In collective cellular migration, plithotaxis is the tendency for each individual cell within a monolayer to migrate along the local orientation of the maximal principal stress, or equivalently, minimal intercellular shear stress. Plithotaxis requires force transmission across many cell-cell junctions and therefore is an emergent property of the cell group.
Plithotaxis is found to hold at the level of both a subcellular grid point and an individual cell of a confluent monolayer, and the stresses must be tensile. | 1 | Biochemistry |
The pyrimidine ring system has wide occurrence in nature
as substituted and ring fused compounds and derivatives, including the nucleotides cytosine, thymine and uracil, thiamine (vitamin B1) and alloxan. It is also found in many synthetic compounds such as barbiturates and the HIV drug zidovudine. Although pyrimidine derivatives such as alloxan were known in the early 19th century, a laboratory synthesis of a pyrimidine was not carried out until 1879, when Grimaux reported the preparation of barbituric acid from urea and malonic acid in the presence of phosphorus oxychloride.
The systematic study of pyrimidines began in 1884 with Pinner,
who synthesized derivatives by condensing ethyl acetoacetate with amidines. Pinner first proposed the name “pyrimidin” in 1885. The parent compound was first prepared by Gabriel and Colman in 1900,
by conversion of barbituric acid to 2,4,6-trichloropyrimidine followed by reduction using zinc dust in hot water. | 1 | Biochemistry |
Ultraviolet helps detect organic material deposits that remain on surfaces where periodic cleaning and sanitizing may have failed. It is used in the hotel industry, manufacturing, and other industries where levels of cleanliness or contamination are inspected.
Perennial news features for many television news organizations involve an investigative reporter using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such. | 5 | Photochemistry |
The catalytic chain transfer process was commercialized very soon after its discovery. The initial commercial outlet was the production of chemically reactive macromonomers to be incorporated into paints for the automotive industry. Federally mandated VOC restrictions are leading to the elimination of solvents from the automotive finishes and the lower molecular weight chain transfer products are often fluids. Incorporation of monomers such as glycidyl methacrylate or hydroxyethylmethacrylate (HEMA) into the macromonomers aid curing processes. Macromonomers incorporating HEMA can be effective in the dispersion of pigments in the paints. The chemistry is very effective under emulsion polymerisation conditions and has been used in the printing industry since 2000. The vinylic end group acts as an addition fragmentation agent and has been utilised to make multi block copolymers and derivatives used as stress relief agents in dental restoration by 3M. | 7 | Physical Chemistry |
Today, optical coatings made from TiO, SiO, TaO etc. (and combinations of these) in most cases consist of amorphous phases of these compounds. Much research is carried out into thin amorphous films as a gas separating membrane layer. The technologically most important thin amorphous film is probably represented by a few nm thin SiO layers serving as isolator above the conducting channel of a metal-oxide semiconductor field-effect transistor (MOSFET). Also, hydrogenated amorphous silicon (Si:H) is of technical significance for thin-film solar cells. | 7 | Physical Chemistry |
The LiMCA method measures the total concentration and size distribution of inclusions present in aluminum alloys. Its measuring principle is based on an objective and user-independent method. The LiMCA CM system can characterize the cleanliness of a melt at time intervals in the order of one minute. It can therefore monitor, in real-time, the evolution of cleanliness along a cast as a function of process parameters and melt-handling practices.
The heart of the LiMCA measuring system consists of a closed glass tube (electrically insulating material) bearing a small orifice at its bottom. The tube is positioned in liquid metal. By creating a vacuum inside the tube, the metal with the suspended inclusions to be detected is forced through the small orifice. Two electrodes are necessary: one inside the tube and the other outside. Both electrodes are immersed in the liquid metal. A constant electric current is applied between the electrodes. The current flows through the
liquid metal by the small orifice in the tube. When an inclusion enters the orifice, it displaces its volume of conducting fluid, temporarily raising the electrical resistance. The increase of resistance generates a voltage pulse. The magnitude of the voltage pulse is a function of the volume of the particle. The duration of the pulse is related to the
transit time of the inclusion. The voltage pulses are amplified and their amplitude measured digitally. The size distribution and total concentration are displayed in real-time on a computer screen. | 8 | Metallurgy |
Liming is the application of calcium- (Ca) and magnesium (Mg)-rich materials in various forms, including marl, chalk, limestone, burnt lime or hydrated lime to soil. In acid soils, these materials react as a base and neutralize soil acidity. This often improves plant growth and increases the activity of soil bacteria, but oversupply may result in harm to plant life. Modern liming was preceded by marling, a process of spreading raw chalk and lime debris across soil, in an attempt to modify pH or aggregate size. Evidence of these practices dates to the 1200's and the earliest examples are taken from the modern British Isles. | 9 | Geochemistry |
Reactions of divinylcyclopropanes containing substituted double bonds are stereospecific with respect to the configurations at the double bonds—cis,cis isomers give cis products, while cis,trans isomers give trans products. Thus, chiral, non-racemic starting materials give rise to chiral products without loss of enantiomeric purity. In the example below, only the isomers depicted were observed in each case. | 0 | Organic Chemistry |
Pre-synthesized LAGP powders can be sprayed on a substrate to form a LAGP film by means of aerosol deposition. The powders are loaded into the aerosol deposition chamber and purified air is used as the carrier gas to drive the particles towards the substrate, where they impinge and coalesce to generate the film. Since the as-produced film is amorphous, an annealing treatment is usually performed to improve the film crystallinity and its conduction properties. | 7 | Physical Chemistry |
Reagents can be pulled through an endergonic reaction, if the reaction products are cleared rapidly by a subsequent exergonic reaction. The concentration of the products of the endergonic reaction thus always remains low, so the reaction can proceed.
A classic example of this might be the first stage of a reaction which proceeds via a transition state. The process of getting to the top of the activation energy barrier to the transition state is endergonic. However, the reaction can proceed because having reached the transition state, it rapidly evolves via an exergonic process to the more stable final products. | 7 | Physical Chemistry |
Methyl red displays pH dependent photochromism, with protonation causing it to adopt a hydrazone/quinone structure.
Methyl Red has a special use in histopathology for showing acidic nature of tissue and presence of organisms with acidic natured cell walls.
Methyl Red is detectably fluorescent in 1:1 water:methanol (pH 7.0), with an emission maximum at 375 nm (UVA) upon excitation with 310 nm light (UVB). | 3 | Analytical Chemistry |
In the early 2000s, a link between bisphosphonate use and impaired bone physiology was noted. The strong inhibition of osteoclast function precipitated by bisphosphonate therapy can lead to inhibition of normal bone turnover, leading to impaired wound healing following trauma (such as dental surgery) or even spontaneous non-healing bone exposure. Because bisphosphonates are preferentially deposited in bone with high turnover rates, it is possible that the levels of bisphosphonate within the jaw bones are selectively elevated.
With the advent of implant dentistry, more dental patients are undergoing therapies in the oral cavity that involve bone healing, such as surgical implant placement and bone grafting procedures. In order to evaluate the risk of osteonecrosis for a patient taking bisphosphonates, use of the CTX biomarker was introduced in 2000 by Rosen. | 1 | Biochemistry |
Arketamine appears to be more effective as a rapid-acting antidepressant than esketamine in preclinical research.
In rodent studies, esketamine produced hyperlocomotion, prepulse inhibition deficits, and rewarding effects, while arketamine did not, in accordance with its lower potency as an NMDA receptor antagonist and dopamine reuptake inhibitor. As such, arketamine may have a lower propensity for producing psychotomimetic effects and a lower abuse potential in addition to superior antidepressant efficacy.
A study conducted in mice found that ketamine's antidepressant activity is not caused by ketamine inhibiting NMDAR, but rather by sustained activation of a different glutamate receptor, the AMPA receptor, by a metabolite, (2R,6R)-hydroxynorketamine; as of 2017 it was unknown if this was happening in humans. Arketamine is an AMPA receptor agonist.
Paradoxically, arketamine shows greater and longer-lasting rapid antidepressant effects in animal models of depression relative to esketamine. It has been suggested that this may be due to the possibility of different activities of arketamine and esketamine and their respective metabolites at the α-nicotinic receptor, as norketamine and hydroxynorketamine are potent antagonists of this receptor and markers of potential rapid antidepressant effects (specifically, increased mammalian target of rapamycin function) correlate closely with their affinity for it. The picture is unclear however, and other mechanisms have also been implicated. | 4 | Stereochemistry |
UV-Vis absorption SEC is a recent technique that is continuously evolving. However, many advantages have been observed over other techniques. The most outstanding advantages are:
* It generates a large amount of information about the systems.
* Generally, solvents are not a problem when carrying out these kinds of measurements.
* The wavelength selection generates specificity in the measurement of each species.
* Currently, there are commercial devices that allow carrying out a large number of experiments with high reproducibility.
* The kinetics of the reactions can be studied.
* It is used to determine a large number of electrochemical and optical parameters.
* Trilinear signals are obtained.
* Small amounts of sample can be analyzed.
* Faradaic current can be separated from non-faradaic current in an electrode process.
* It is more specific than electrochemistry.
* Quantitative information can be obtained.
UV-Vis absorption SEC has been used mainly in different research fields such as:
* Sensor development.
* Reaction mechanisms.
* Diffusion and adsorption processes.
* Characterization of compounds.
* Study of biological interest substances.
* Study of optical and electrical materials properties.
* Study of liquid/liquid interfaces.
* Study and synthesis of nanomaterials.
* Evaluation of reaction parameters in which electron transfer occurs. | 7 | Physical Chemistry |
Pervaporation is effective for dilute solutions containing trace or minor amounts of the component to be removed. Based on this, hydrophilic membranes are used for dehydration of alcohols containing small amounts of water and hydrophobic membranes are used for removal/recovery of trace amounts of organics from aqueous solutions.
Pervaporation is an efficient energy conserving alternative to processes such as distillation and evaporation. It allows the exchange of two phases without direct contact.
Examples include solvent dehydration: dehydrating the ethanol/water and isopropanol/water azeotropes, continuous ethanol removal from yeast fermentors, continuous water removal from condensation reactions such as esterifications to enhance conversion and rate of the reaction, membrane introduction mass spectrometry, removing organic solvents from industrial waste waters, combination of distillation and pervaporation/vapour permeation, and concentration of hydrophobic flavour compounds in aqueous solutions (using hydrophobic membranes).
Recently, a number of organophilic pervaporation membranes have been introduced to the market. Organophilic pervaporation membranes can be used for the separation of organic-organic mixtures, e.g.: reduction of the aromatics content in refinery streams, breaking of azeotropes, purification of extraction media, purification of product stream after extraction, and purification of organic solvents. | 3 | Analytical Chemistry |
Direct photophoresis is caused by the transfer of photon momentum to a particle by refraction and reflection. Movement of particles in the forward direction occurs when the particle is transparent and has an index of refraction larger compared to its surrounding medium. Indirect photophoresis occurs as a result of an increase in the kinetic energy of molecules when particles absorb incident light only on the irradiated side, thus creating a temperature gradient within the particle. In this situation the surrounding gas layer reaches temperature equilibrium with the surface of the particle. Molecules with higher kinetic energy in the region of higher gas temperature impinge on the particle with greater momenta than molecules in the cold region; this causes a migration of particles in a direction opposite to the surface temperature gradient. The component of the photophoretic force responsible for this phenomenon is called the radiometric force. This comes as a result of uneven distribution of radiant energy (source function within a particle).
Indirect photophoretic force depends on the physical properties of the particle and the surrounding medium.
For pressures , where the free mean path of the gas is much larger than the characteristic size of the suspended particle (direct photophoresis), the longitudinal force is
where the mean temperature of the scattered gas is (thermal accommodation coefficient , momentum accommodation coefficient )
and the black body temperature of the particle (net light flux , Stefan Boltzmann constant , temperature of the radiation field )
is the thermal conductivity of the particle.
The asymmetry factor for spheres is usually (positive longitudinal photophoresis).
For non-spherical particles, the average force exerted on the particle is given by the same equation where the radius is now the radius of the respective volume-equivalent sphere. | 7 | Physical Chemistry |
A wider wire results in smaller current density and, hence, less likelihood of electromigration. Also, the metal grain size has influence; the smaller grains, the more grain boundaries and the higher likelihood of electromigration effects. However, if you reduce wire width to below the average grain size of the wire material, grain boundaries become "crosswise", more or less perpendicular to the length of the wire. The resulting structure resembles the joints in a stalk of bamboo. With such a structure, the resistance to electromigration increases, despite an increase in current density. This apparent contradiction is caused by the perpendicular position of the grain boundaries; the boundary diffusion factor is excluded, and material transport is correspondingly reduced.
However, the maximum wire width possible for a bamboo structure is usually too narrow for signal lines of large-magnitude currents in analog circuits or for power supply lines. In these circumstances, slotted wires are often used, whereby rectangular holes are carved in the wires. Here, the widths of the individual metal structures in between the slots lie within the area of a bamboo structure, while the resulting total width of all the metal structures meets power requirements. | 7 | Physical Chemistry |
Pockels was born in Venice, Austrian Empire, in 1862. At the time, Venice was under Austrian rule, and Pockels' father served in the Austrian Army. When he fell sick, the family moved in 1871 to Brunswick, which was part of the nascent German Empire. There, Pockels attended the Municipal High School for Girls. Agnes was interested in chemistry as a child. However, women were not allowed to enter universities to study. Pockels stated that "I had a passionate interest in natural science, especially physics, and would have liked to study.“ (Agnes Pockels, as translated by Giles from Autobiographical Notes in W. Ostwald, 1932.)
As a child, Pockels was interested in science, especially physics. In those days, women in Germany had no access to universities. Pockels studied science at home while caring for her parents. Pockels' younger brother Friedrich Carl Alwin Pockels studied physics at the University of Göttingen, completing his degree there. Friedrich shared textbooks from the university with Agnes Pockels in order to help her study from home. He later shared academic literature with Agnes Pockels to advance her studies. | 7 | Physical Chemistry |
An electrostatic separator is a device for separating particles by mass in a low energy charged beam.
An example is the electrostatic precipitator used in coal-fired power plants to treat exhaust gas, removing small particles that cause air pollution.
Electrostatic separation is a process that uses electrostatic charges to separate crushed particles of material. An industrial process used to separate large amounts of material particles, electrostatic separating is most often used in the process of sorting mineral ore. This process can help remove valuable material from ore, or it can help remove foreign material to purify a substance. In mining, the process of crushing mining ore into particles for the purpose of separating minerals is called beneficiation.
Generally, electrostatic charges are used to attract or repel differently charged material. When electrostatic separation uses the force of attraction to sort particles, conducting particles stick to an oppositely charged object, such as a metal drum, thereby separating them from the particle mixture. When this type of beneficiation uses repelling force, it is normally employed to change the trajectory of falling objects to sort them into different places. This way, when a mixture of particles falls past a repelling object, the particles with the correct charge fall away from the other particles when they are repelled by the similarly charged object.
An electric charge can be positive or negative — objects with a positive charge repel other positively charged objects, thereby causing them to push away from each other, while a positively charged object would attract to a negatively charged object, thereby causing the two to draw together.
Experiments showing electrostatic sorting in action can help make the process more clear. To exhibit electrostatic separation at home, an experiment can be conducted using peanuts that are still in their shells. When the shells are rubbed off of the peanuts and gently smashed into pieces, an electrostatically charged device, like a comb rubbed quickly against a wool sweater, will pick up the peanut shells with static electricity. The lightweight crushed shells that are oppositely charged from the comb easily move away from the edible peanut parts when the comb is passed nearby.
The electrostatic separation of conductors is one method of beneficiation; another common beneficiation method is magnetic beneficiation. Electrostatic separation is a preferred sorting method when dealing with separating conductors from electrostatic separation non-conductors. In a similar way to that in which electrostatic separation sorts particles with different electrostatic charges magnetic beneficiation sorts particles that respond to a magnetic field. Electrostatic beneficiation is effective for removing particulate matter, such as ash from mined coal, while magnetic separation functions well for removing the magnetic iron ore from deposits of clay in the earth. | 3 | Analytical Chemistry |
The Regional Scale Nodes is connected into the OOI Cyberinfrastructure.
The Cyberinfrastructure component of the OOI links marine infrastructure to scientists and users. The OOI Cyberinfrastructure manages and integrates data from all the different OOI sensors. It will provide a common operating infrastructure, the Integrated Observatory Network (ION), connecting and coordinating the operations of the marine components (global, regional, and coastal scale arrays). It will also provide resource management, observatory mission command and control, product production, data management and distribution (including strong data provenance), and centrally available collaboration tools.
The Integrated Observatory Network (ION) connects and coordinates the operations of the OOI marine components with the scientific and educational pursuits of oceanographic research communities. The cyberinfrastructure is being designed and constructed by the University of California, San Diego. | 9 | Geochemistry |
Pempidine is an aliphatic, sterically hindered, cyclic, tertiary amine, which is a weak base: in its protonated form it has a pK of 11.25.
Pempidine is a liquid with a boiling point of 187–188 °C and a density of 0.858 g/cm.
Two early syntheses of this compound are those of Leonard and Hauck, and Hall. These are very similar in principle: Leonard and Hauck reacted phorone with ammonia, to produce 2,2,6,6-tetramethyl-4-piperidone, which was then reduced by means of the Wolff–Kishner reduction to 2,2,6,6-tetramethylpiperidine. This secondary amine was then N-methylated using methyl iodide and potassium carbonate.
Halls method involved reacting acetone with ammonia in the presence of calcium chloride to give 2,2,6,6-tetramethyl-4-piperidone, which was then reduced under Wolff–Kishner conditions, followed by N-methylation of the resulting 2,2,6,6-tetramethylpiperidine with methyl p'-toluenesulfonate. | 0 | Organic Chemistry |
Biological hydrogels are derived from preexisting components of body tissues such as collagen, hyaluronic acid (HA), or fibrin. Collagen, HA, and fibrin are components that occur naturally in the extracellular matrix of mammals. Collagen is the main structural component in tissues and it already contains cell-signaling domains that can promote cell growth. In order to mechanically enhance collagen into a hydrogel, it must be chemically crosslinked, crosslinked using UV light or temperature, or mixed with other polymers. Collagen hydrogels would be nontoxic and biocompatible. | 7 | Physical Chemistry |
At low temperatures, some metals can undergo a ductile-brittle transition which makes the material brittle and could lead to catastrophic failure during operation. This temperature is commonly called a ductile-brittle transition temperature or embrittlement temperature. Research has shown that low temperature embrittlement and brittle fracture only occurs under these specific criteria:
# There is enough stress to nucleate a crack.
# The stress at the crack exceeds a critical value that will open up the crack (also known as Griffith's criterion for crack opening).
# High resistance to dislocation movement.
# There should be a small amount of viscous drag of dislocation to ensure opening of crack.
All metals can fulfill criteria 1, 2, 4. However, only BCC and some HCP metals meets the third condition as they have high Peierls barrier and strong energy of elastic interaction of dislocation and defects. All FCC and most HCP metals have low Peierls barrier and weak elastic interaction energy. Plastics and rubbers also exhibit the same transition at low temperatures.
Historically, there are multiple instances where people are operating equipment at cold temperatures that led to unexpected, but also catastrophic, failure. In Cleveland in 1944, a cylindrical steel tank containing liquefied natural gas ruptured because of its low ductility at the operating temperature. Another famous example was the unexpected fracture of 160 World War II liberty ships during winter months. The crack was formed at the middle of the ships and propagated through, breaking the ships in half quite literally. | 8 | Metallurgy |
Cornelis Van Niel made key discoveries explaining the chemistry of photosynthesis. By studying purple sulfur bacteria and green bacteria, he was the first to demonstrate that photosynthesis is a light-dependent redox reaction in which hydrogen reduces (donates its atoms as electrons and protons to) carbon dioxide.
Robert Emerson discovered two light reactions by testing plant productivity using different wavelengths of light. With the red alone, the light reactions were suppressed. When blue and red were combined, the output was much more substantial. Thus, there were two photosystems, one absorbing up to 600 nm wavelengths, the other up to 700 nm. The former is known as PSII, the latter is PSI. PSI contains only chlorophyll "a", PSII contains primarily chlorophyll "a" with most of the available chlorophyll "b", among other pigments. These include phycobilins, which are the red and blue pigments of red and blue algae, respectively, and fucoxanthol for brown algae and diatoms. The process is most productive when the absorption of quanta is equal in both PSII and PSI, assuring that input energy from the antenna complex is divided between the PSI and PSII systems, which in turn powers the photochemistry.
Robert Hill thought that a complex of reactions consisted of an intermediate to cytochrome b (now a plastoquinone), and that another was from cytochrome f to a step in the carbohydrate-generating mechanisms. These are linked by plastoquinone, which does require energy to reduce cytochrome f. Further experiments to prove that the oxygen developed during the photosynthesis of green plants came from water were performed by Hill in 1937 and 1939. He showed that isolated chloroplasts give off oxygen in the presence of unnatural reducing agents like iron oxalate, ferricyanide or benzoquinone after exposure to light. In the Hill reaction:
:2 HO + 2 A + (light, chloroplasts) → 2 AH + O
A is the electron acceptor. Therefore, in light, the electron acceptor is reduced and oxygen is evolved. Samuel Ruben and Martin Kamen used radioactive isotopes to determine that the oxygen liberated in photosynthesis came from the water.
Melvin Calvin and Andrew Benson, along with James Bassham, elucidated the path of carbon assimilation (the photosynthetic carbon reduction cycle) in plants. The carbon reduction cycle is known as the Calvin cycle, but many scientists refer to it as the Calvin-Benson, Benson-Calvin, or even Calvin-Benson-Bassham (or CBB) Cycle.
Nobel Prize–winning scientist Rudolph A. Marcus was later able to discover the function and significance of the electron transport chain.
Otto Heinrich Warburg and Dean Burk discovered the I-quantum photosynthesis reaction that splits CO, activated by the respiration.
In 1950, first experimental evidence for the existence of photophosphorylation in vivo was presented by Otto Kandler using intact Chlorella cells and interpreting his findings as light-dependent ATP formation.
In 1954, Daniel I. Arnon et al. discovered photophosphorylation in vitro in isolated chloroplasts with the help of P.
Louis N. M. Duysens and Jan Amesz discovered that chlorophyll "a" will absorb one light, oxidize cytochrome f, while chlorophyll "a" (and other pigments) will absorb another light but will reduce this same oxidized cytochrome, stating the two light reactions are in series. | 5 | Photochemistry |
Frame Lake is located in Yellowknife, Northwest Territories, Canada. It is an endorheic freshwater body located between the city's downtown section and a larger residential area. The Frame Lake Trail circles it, and city hall and the territorial legislative assembly building are on its shores.
Formed by meltwater after the end of the Wisconsin glaciation 20,000 years ago, Frame has been an important part of Yellowknifes history. The Dene in the area used it as a fishing spot before European settlement. In the early years of the citys growth, gold mines nearby dumped tailings in it and sometimes sewage. Later, when the city's New Town, now its downtown section, was surveyed and developed nearby, Frame offered accessible swimming and boating opportunities.
However, storm sewers diverted much of the runoff that fed it. Later development blocked the lake's only outflow, leaving it endorheic and complicating the problems caused by earlier pollution. By the early 1970s it no longer supported any fish; within two decades residents had stopped swimming or boating it out of fear of leeches. Subsequent studies have shown that the lake completely eutrophied sometime in the mid-1990s. They have not, however, been able to determine whether that was due to climate change, pollution or some combination of both; the possibility exists that the lake has always been at a higher trophic state than others in the area.
Some city residents have agitated for efforts to reclaim the lake so it will once again be a destination for swimmers, anglers and boaters in warm weather. To do so, it will be necessary to reoxygenate the water to the point that fish can again inhabit its waters. This could be accomplished either by aeration or dredging, which would remove the accumulated rotted organic matter on the lake bed that currently renders it anoxic when the lake is frozen over in the winter. | 2 | Environmental Chemistry |
Through photosynthesis, plants use CO from the atmosphere, water from the ground, and energy from the sun to create sugars used for growth and fuel. While using these sugars as fuel releases carbon back into the atmosphere (photorespiration), growth stores carbon in the physical structures of the plant (i.e. leaves, wood, or non-woody stems). With about 19 percent of Earth's carbon stored in plants, plant growth plays an important role in storing carbon on the ground rather than in the atmosphere. In the context of carbon storage, growth of plants is often referred to as biomass productivity. This term is used because researchers compare the growth of different plant communities by their biomass, amount of carbon they contain.
Increased biomass productivity directly increases the amount of carbon stored in plants. And because researchers are interested in carbon storage, they are interested in where most of the biomass is found in individual plants or in an ecosystem. Plants will first use their available resources for survival and support the growth and maintenance of the most important tissues like leaves and fine roots which have short lives. With more resources available plants can grow more permanent, but less necessary tissues like wood.
If the air surrounding plants has a higher concentration of carbon dioxide, they may be able to grow better and store more carbon and also store carbon in more permanent structures like wood. Evidence has shown this occurring for a few different reasons. First, plants that were otherwise limited by carbon or light availability benefit from a higher concentration of carbon. Another reason is that plants are able use water more efficiently because of reduced stomatal conductance. Plants experiencing higher CO concentrations may benefit from a greater ability to gain nutrients from mycorrhizal fungi in the sugar-for-nutrients transaction. The same interaction can may also increase the amount of carbon stored in the soil by mycorrhizal fungi. | 2 | Environmental Chemistry |
Rotavirus mRNAs are capped but not polyadenylated, and viral proteins are translated by the cellular translation machinery. This is accomplished through the action of the viral Nonstructural Protein NSP3 which specifically binds the 3' consensus sequence of viral mRNAs and interacts with the eukaryotic translation initiation factor eIF4G I.
RoXaN (rotavirus X protein associated with NSP3) is 110-kDa cellular protein that contains a minimum of three regions predicted to be involved in protein–protein or nucleic acid–protein interactions. A tetratricopeptide repeat region, a protein–protein interaction domain most often found in multiprotein complexes, is present in the amino-terminal region. In the carboxy terminus, at least five zinc finger motifs are observed, further suggesting the capacity of RoXaN to bind other proteins or nucleic acids. Between these two regions exists a paxillin leucine-aspartate repeat (LD) motif which is involved in protein–protein interactions. | 1 | Biochemistry |
In organic chemistry, enone–alkene cycloadditions are a version of the [[woodward-Hoffman rules|[2+2] cycloaddition]] This reaction involves an enone and alkene as substrates. Although the concerted photochemical [2+2] cycloaddition is allowed, the reaction between enones and alkenes is stepwise and involves discrete diradical intermediates. | 5 | Photochemistry |
The draft (draught in British English) flow rate induced by the stack effect can be calculated with the equation presented below. The equation applies only to buildings where air is both inside and outside the buildings. For buildings with one or two floors, h is the height of the building and A is the flow area of the openings. For multi-floor, high-rise buildings, A is the flow area of the openings and h is the distance from the openings at the neutral pressure level (NPL) of the building to either the topmost openings or the lowest openings. Reference explains how the NPL affects the stack effect in high-rise buildings.
For flue gas stacks or chimneys, where air is on the outside and combustion flue gases are on the inside, the equation will only provide an approximation. Also, A is the cross-sectional flow area and h is the height of the flue gas stack or chimney.
:SI units:
:U.S. customary units:
This equation assumes that the resistance to the draft flow is similar to the resistance of flow through an orifice characterized by a discharge coefficient C. | 7 | Physical Chemistry |
The above uses and effects are consequences of the fact that the solution is a source of effectively free elemental iodine, which is readily generated from the equilibrium between elemental iodine molecules and polyiodide ions in the solution. | 3 | Analytical Chemistry |
* Morawetz, Herbert Polymers: The Origins and Growth of a Science John Wiley and Sons, 1985.
* Utracki, L. A. Commercial Polymer Blends London: Chapman and Hall, 1998.
* https://books.google.com/books?id=aLrrCAAAQBAJ&pg=PA14 | 7 | Physical Chemistry |
Since 2016, Han Seo-jun, then associate professor at the Southern University of Science and Technology (SUSTech) in Shenzhen, with Zhang Renli and Qin Jinzhou, have used human embryo in gene-editing technology for assisted reproductive medicine. On 10 June 2017, a Chinese couple, an HIV-positive father and HIV-negative mother, pseudonymously called Mark and Grace, attended a conference held by He at SUSTech. They were offered in vitro fertilisation (IVF) along with gene-editing of their embryos so as to develop innate resistance to HIV infection in their offspring. They agreed to volunteer through informed consent and the experiment was carried out in secrecy. Six other couples having similar fertility problems were subsequently recruited. The couples were recruited through a Beijing-based AIDS advocacy group called Baihualin China League. When later examined, the consent forms were noted as incomplete and inadequate. The couple were reported to have agreed to this experiment because, by Chinese rules, normally HIV positive fathers were not allowed to have children using IVF.
When the place of the clinical experiment was investigated, SUSTech declared that the university was not involved and that He had been on unpaid leave since February 2018, and his department attested that they were unaware of the research project. | 1 | Biochemistry |
PA is kept low in the bulk of the membrane in order to transiently burst and signal locally in high concentration. For example TREK-1 channels are activated by local association with PLD and production of PA. The dissociation constant of PA for TREK-1 is approximately 10 micromolar. The relatively weak binding combined with a low concentration of PA in the membrane allows the channel to turn off. The local high concentration for activation suggests at least some restrictions in local lipid diffusion. The bulk low concentration of PA combined with high local bursts is the opposite of PIP2 signaling. PIP2 is kept relatively high in the membrane and then transiently hydrolized near a protein in order to transiently reduce PIP2 signaling. PA signaling mirrors PIP2 signaling in that the bulk concentration of signaling lipid need not change to exert a potent local effect on a target protein.
As described above, PLD hydrolyzes PC to form PA and choline. Because choline is very abundant in the cell, PLD activity does not significantly affect choline levels; and choline is unlikely to play any role in signaling.
The role of PLD activation in numerous signaling contexts, combined with the lack of a role for choline, suggests that PA is important in signaling. However, PA is rapidly converted to DAG, and DAG is also known to be a signaling molecule. This raises the question as to whether PA has any direct role in signaling or whether it simply acts as a precursor for DAG production. If it is found that PA acts only as a DAG precursor, then one can raise the question as to why cells should produce DAG using two enzymes when they contain the PLC that could produce DAG in a single step.
PA produced by PLD or by DAGK can be distinguished by the addition of [γ-P]ATP. This will show whether the phosphate group is newly derived from the kinase activity or whether it originates from the PC.
Although PA and DAG are interconvertible, they do not act in the same pathways. Stimuli that activate PLD do not activate enzymes downstream of DAG, and vice versa. For example, it was shown that addition of PLD to membranes results in the production of [P]-labeled PA and [P]-labeled phosphoinositides. The addition of DAGK inhibitors eliminates the production of [P]-labeled PA but not the PLD-stimulated production of phosphoinositides.
It is possible that, though PA and DAG are interconvertible, separate pools of signaling and non-signaling lipids may be maintained. Studies have suggested that DAG signaling is mediated by polyunsaturated DAG, whereas PLD-derived PA is monounsaturated or saturated. Thus functional saturated/monounsaturated PA can be degraded by hydrolysing it to form non-functional saturated/monounsaturated DAG, whereas functional polyunsaturated DAG can be degraded by converting it into non-functional polyunsaturated PA.
This model suggests that PA and DAG effectors should be able to distinguish lipids with the same headgroups but with differing acyl chains. Although some lipid-binding proteins are able to insert themselves into membranes and could hypothetically recognize the type of acyl chain or the resulting properties of the membrane, many lipid-binding proteins are cytosolic and localize to the membrane by binding only the headgroups of lipids. Perhaps the different acyl chains can affect the angle of the head-group in the membrane. If this is the case, it suggests that a PA-binding domain must not only be able to bind PA specifically but must also be able to identify those head-groups that are at the correct angle. Whatever the mechanism is, such specificity is possible. It is seen in the pig testes DAGK that is specific for polyunsaturated DAG and in two rat hepatocyte LPPs that dephosphorylate different PA species with different activities. Moreover, the stimulation of SK1 activity by PS in vitro was shown to vary greatly depending on whether dioleoyl (C18:1), distearoyl (C18:0), or 1-stearoyl, 2-oleoyl species of PS were used.
Thus it seems that, though PA and DAG are interconvertible, the different species of lipids can have different biological activities; and this may enable the two lipids to maintain separate signaling pathways. | 1 | Biochemistry |
A variety of bioaerosols may contribute to cloud condensation nuclei or cloud ice nuclei, possible bioaerosol components are living or dead cells, cell fragments, hyphae, pollen, or spores. Cloud formation and precipitation are key features of many hydrologic cycles to which ecosystems are tied. In addition, global cloud cover is a significant factor in the overall radiation budget and therefore, temperature of the Earth.
Bioaerosols make up a small fraction of the total cloud condensation nuclei in the atmosphere (between 0.001% and 0.01%) so their global impact (i.e. radiation budget) is questionable. However, there are specific cases where bioaerosols may form a significant fraction of the clouds in an area. These include:
* Areas where there is cloud formation at temperatures over -15 °C since some bacteria have developed proteins which allow them to nucleate ice at higher temperatures.
* Areas over vegetated regions or under remote conditions where the air is less impacted by anthropogenic activity.
* Near surface air in remote marine regions like the Southern Ocean where sea spray may be more prevalent than dust transported from continents.
The collection of bioaerosol particles on a surface is called deposition. The removal of these particles from the atmosphere affects human health in regard to air quality and respiratory systems. | 7 | Physical Chemistry |
Primary role of EpoR is to promote proliferation of erythroid progenitor cells and rescue erythroid progenitors from cell death. EpoR induced Jak2-Stat5 signaling, together with transcriptional factor GATA-1, induces the transcription of pro-survival protein Bcl-xL. Additionally, EpoR has been implicated in suppressing expression of death receptors Fas, Trail and TNFa that negatively affect erythropoiesis.
Based on current evidence, it is still unknown whether Epo/EpoR directly cause "proliferation and differentiation" of erythroid progenitors in vivo, although such direct effects have been described based on in vitro work. | 1 | Biochemistry |
Either copper powder or copper salts can be used very generally for intramolecular reactions of diazocarbonyl compounds. This section describes the different types of diazocarbonyl compounds that may undergo intramolecular reactions in the presence of copper. Note that for intermolecular reactions of diazocarbonyl compounds, the use of rhodium catalysts is preferred.
Diazoketones containing pendant double bonds undergo cyclopropanation in the presence of copper. The key step in one synthesis of barbaralone is the selective intramolecular cyclopropanation of a cycloheptatriene.
α,β-Cyclopropyl ketones may act as masked α,β-unsaturated ketones. In one example, intramolecular participation of an aryl group leads to the formation of a polycyclic ring system with complete diastereoselectivity.
α-Diazoesters are not as efficient as diazoketones at intramolecular cyclizations in some cases because of the propensity of esters to exist in the trans conformation about the carbon–oxygen single bond. However, intramolecular reactions of diazoesters do take place—in the example in equation (5), copper(II) sulfate is used to effect the formation of the cyclopropyl ester shown.
In the presence of a catalytic amount of acid, diazomethyl ketone substrates containing a pendant double bond or aryl group undergo cyclization. The mechanism of this process most likely involves protonation of the diazocarbonyl group to form a diazonium salt, followed by displacement of nitrogen by the unsaturated functionality and deprotonation. In the example below, demethylation affords a quinone.
When no unsaturated functionality is present in the substrate, C-H insertion may occur. C-H Insertion is particularly facile in conformationally restricted substrates in which a C-H bond is held in close proximity to the diazo group.
Transannular insertions, which form fused carbocyclic products, have also been observed. Yields are often low for these reactions, however.
Insertion into carbon–carbon bonds has been observed. In the example in equation (9), the methyl group is held in close proximity to the diazo group, facilitating C-C insertion. | 0 | Organic Chemistry |
A systematic review by Schuman 2023 finds that most studies on plant volatiles relate to herbivore interactions. Schuman also finds that laboratory studies are overrepresented despite the wide differences in herbivore behaviour between natural and artificial settings. | 1 | Biochemistry |
No federal legislation lays out protocols or restrictions about human genetic engineering. This subject is governed by overlapping regulations from local and federal agencies, including the Department of Health and Human Services, the FDA and NIH's Recombinant DNA Advisory Committee. Researchers seeking federal funds for an investigational new drug application, (commonly the case for somatic human genetic engineering,) must obey international and federal guidelines for the protection of human subjects.
NIH serves as the main gene therapy regulator for federally funded research. Privately funded research is advised to follow these regulations. NIH provides funding for research that develops or enhances genetic engineering techniques and to evaluate the ethics and quality in current research. The NIH maintains a mandatory registry of human genetic engineering research protocols that includes all federally funded projects.
An NIH advisory committee published a set of guidelines on gene manipulation. The guidelines discuss lab safety as well as human test subjects and various experimental types that involve genetic changes. Several sections specifically pertain to human genetic engineering, including Section III-C-1. This section describes required review processes and other aspects when seeking approval to begin clinical research involving genetic transfer into a human patient. The protocol for a gene therapy clinical trial must be approved by the NIH's Recombinant DNA Advisory Committee prior to any clinical trial beginning; this is different from any other kind of clinical trial.
As with other kinds of drugs, the FDA regulates the quality and safety of gene therapy products and supervises how these products are used clinically. Therapeutic alteration of the human genome falls under the same regulatory requirements as any other medical treatment. Research involving human subjects, such as clinical trials, must be reviewed and approved by the FDA and an Institutional Review Board. | 1 | Biochemistry |
Zeolitic imidazolate frameworks (ZIFs) are metal-organic frameworks similar to zeolites. Because of their porosity, chemical stability and thermal resistance, ZIFs are being examined for their capacity to capture carbon dioxide. | 5 | Photochemistry |
In Cartesian coordinates the basis vectors are represented by a cell tensor :
The hypervolume of the unit cell, , is given by the determinant of the cell tensor: | 3 | Analytical Chemistry |
The journal is run by an Ownership Board, on which all the member societies have equal representation. The eighteen participating societies are:
* Canadian Society for Chemistry
* Deutsche Bunsen-Gesellschaft für Physikalische Chemie (Germany)
* Institute of Chemistry of Ireland
* Israel Chemical Society
* Kemian Seurat (Finland)
* Kemisk Forening (Denmark)
* Koninklijke Nederlandse Chemische Vereniging (Netherlands)
* Korean Chemical Society
* New Zealand Institute of Chemistry
* Norsk Kjemisk Selskap (Norway)
* Polskie Towarzystwo Chemiczne (Poland)
* Real Sociedad Española de Química (Spain)
* Royal Australian Chemical Institute
* Royal Society of Chemistry (United Kingdom)
* Società Chimica Italiana (Italy)
* Svenska Kemisamfundet (Sweden)
* Swiss Chemical Society
* Türkiye Kimya Dernegi (Turkey) | 7 | Physical Chemistry |
A number of engineered genetic sequences must be incorporated into the host cell to perform two-hybrid analysis or one of its derivative techniques. The considerations and methods used in the construction and delivery of these sequences differ according to the needs of the assay and the organism chosen as the experimental background.
There are two broad categories of hybrid library: random libraries and cDNA-based libraries. A cDNA library is constituted by the cDNA produced through reverse transcription of mRNA collected from specific cells of types of cell. This library can be ligated into a construct so that it is attached to the BD or AD being used in the assay. A random library uses lengths of DNA of random sequence in place of these cDNA sections. A number of methods exist for the production of these random sequences, including cassette mutagenesis. Regardless of the source of the DNA library, it is ligated into the appropriate place in the relevant plasmid/phagemid using the appropriate restriction endonucleases. | 1 | Biochemistry |
Biomaterials are used in:
# Joint replacements
# Bone plates
# Intraocular lenses (IOLs) for eye surgery
# Bone cement
# Artificial ligaments and tendons
# Dental implants for tooth fixation
# Blood vessel prostheses
# Heart valves
# Skin repair devices (artificial tissue)
# Cochlear replacements
# Contact lenses
# Breast implants
# Drug delivery mechanisms
# Sustainable materials
# Vascular grafts
# Stents
# Nerve conduits
# Surgical sutures, clips, and staples for wound closure
# Pins and screws for fracture stabilisation
# Surgical mesh
Biomaterials must be compatible with the body, and there are often issues of biocompatibility, which must be resolved before a product can be placed on the market and used in a clinical setting. Because of this, biomaterials are usually subjected to the same requirements as those undergone by new drug therapies. All manufacturing companies are also required to ensure traceability of all of their products, so that if a defective product is discovered, others in the same batch may be traced. | 1 | Biochemistry |
The pKa of the related acids can be guessed from the number of double bonds to oxygen. Thus perchloric acid is a very strong acid while hypochlorous acid is very weak. A simple rule usually works to within about 1 pH unit. | 7 | Physical Chemistry |
In order for plasmids to replicate independently within a cell, they must possess a stretch of DNA that can act as an origin of replication. The self-replicating unit, in this case, the plasmid, is called a replicon. A typical bacterial replicon may consist of a number of elements, such as the gene for plasmid-specific replication initiation protein (Rep), repeating units called iterons, DnaA boxes, and an adjacent AT-rich region. Smaller plasmids make use of the host replicative enzymes to make copies of themselves, while larger plasmids may carry genes specific for the replication of those plasmids. A few types of plasmids can also insert into the host chromosome, and these integrative plasmids are sometimes referred to as episomes in prokaryotes.
Plasmids almost always carry at least one gene. Many of the genes carried by a plasmid are beneficial for the host cells, for example: enabling the host cell to survive in an environment that would otherwise be lethal or restrictive for growth. Some of these genes encode traits for antibiotic resistance or resistance to heavy metal, while others may produce virulence factors that enable a bacterium to colonize a host and overcome its defences or have specific metabolic functions that allow the bacterium to utilize a particular nutrient, including the ability to degrade recalcitrant or toxic organic compounds. Plasmids can also provide bacteria with the ability to fix nitrogen. Some plasmids, however, have no observable effect on the phenotype of the host cell or its benefit to the host cells cannot be determined, and these plasmids are called cryptic plasmids.
Naturally occurring plasmids vary greatly in their physical properties. Their size can range from very small mini-plasmids of less than 1-kilobase pairs (kbp) to very large megaplasmids of several megabase pairs (Mbp). At the upper end, little differs between a megaplasmid and a minichromosome. Plasmids are generally circular, but examples of linear plasmids are also known. These linear plasmids require specialized mechanisms to replicate their ends.
Plasmids may be present in an individual cell in varying number, ranging from one to several hundreds. The normal number of copies of plasmid that may be found in a single cell is called the plasmid copy number, and is determined by how the replication initiation is regulated and the size of the molecule. Larger plasmids tend to have lower copy numbers. Low-copy-number plasmids that exist only as one or a few copies in each bacterium are, upon cell division, in danger of being lost in one of the segregating bacteria. Such single-copy plasmids have systems that attempt to actively distribute a copy to both daughter cells. These systems, which include the parABS system and parMRC system, are often referred to as the partition system or partition function of a plasmid.
Plasmids of linear form are unknown among phytopathogens with one exception, Rhodococcus fascians. | 1 | Biochemistry |
Considering a plane wave the electron quantum parameter can be rewritten using this relation between electric and magnetic fields:where is the wavevector of the plane wave and the wavevector magnitude. Inserting this expression in the formula of :where the vectorial identity was used. Elaborating the expression:Since for a plane wave and the last two terms under the square root compensate each other, reduces to:
In the simplified configuration of a plane wave impinging on the electron, higher values of the electron quantum parameter are obtained when the plane wave is counter-propagating with respect to the electron velocity. | 7 | Physical Chemistry |
CREB-regulated transcription coactivator 3 is a protein that in humans is encoded by the CRTC3 gene.
This gene has been shown to be linked to weight gain. | 1 | Biochemistry |
Ceronapril (INN, proposed trade names Ceranapril, Novopril) is a phosphonate ACE inhibitor that was never marketed. | 4 | Stereochemistry |
Some plasmids or microbial hosts include an addiction system or postsegregational killing system (PSK), such as the hok/sok (host killing/suppressor of killing) system of plasmid R1 in Escherichia coli. This variant produces both a long-lived poison and a short-lived antidote. Several types of plasmid addiction systems (toxin/ antitoxin, metabolism-based, ORT systems) were described in the literature and used in biotechnical (fermentation) or biomedical (vaccine therapy) applications. Daughter cells that retain a copy of the plasmid survive, while a daughter cell that fails to inherit the plasmid dies or suffers a reduced growth-rate because of the lingering poison from the parent cell. Finally, the overall productivity could be enhanced.
In contrast, plasmids used in biotechnology, such as pUC18, pBR322 and derived vectors, hardly ever contain toxin-antitoxin addiction systems, and therefore need to be kept under antibiotic pressure to avoid plasmid loss. | 1 | Biochemistry |
Diffusion-controlled (or diffusion-limited) reactions are reactions in which the reaction rate is equal to the rate of transport of the reactants through the reaction medium (usually a solution). The process of chemical reaction can be considered as involving the diffusion of reactants until they encounter each other in the right stoichiometry and form an activated complex which can form the product species. The observed rate of chemical reactions is, generally speaking, the rate of the slowest or "rate determining" step. In diffusion controlled reactions the formation of products from the activated complex is much faster than the diffusion of reactants and thus the rate is governed by collision frequency.
Diffusion control is rare in the gas phase, where rates of diffusion of molecules are generally very high. Diffusion control is more likely in solution where diffusion of reactants is slower due to the greater number of collisions with solvent molecules. Reactions where the activated complex forms easily and the products form rapidly are most likely to be limited by diffusion control. Examples are those involving catalysis and enzymatic reactions. Heterogeneous reactions where reactants are in different phases are also candidates for diffusion control.
One classical test for diffusion control of a heterogeneous reaction is to observe whether the rate of reaction is affected by stirring or agitation; if so then the reaction is almost certainly diffusion controlled under those conditions. | 7 | Physical Chemistry |
Mitochondria may have a number of different shapes. A mitochondrion contains outer and inner membranes composed of phospholipid bilayers and proteins. The two membranes have different properties. Because of this double-membraned organization, there are five distinct parts to a mitochondrion:
# The outer mitochondrial membrane,
# The intermembrane space (the space between the outer and inner membranes),
# The inner mitochondrial membrane,
# The cristae space (formed by infoldings of the inner membrane), and
# The matrix (space within the inner membrane), which is a fluid.
Mitochondria have folding to increase surface area, which in turn increases ATP (adenosine triphosphate) production.
Mitochondria stripped of their outer membrane are called mitoplasts. | 1 | Biochemistry |
Surface roughness scattering or interface roughness scattering is the elastic scattering of particles against a rough solid surface or imperfect interface between two different materials. This effect has been observed in classical systems, such as microparticle scattering, as well as quantum systems, where it arises electronic devices, such as field effect transistors and quantum cascade lasers. | 7 | Physical Chemistry |
Stripping is a physical separation process where one or more components are removed from a liquid stream by a vapor stream. In industrial applications the liquid and vapor streams can have co-current or countercurrent flows. Stripping is usually carried out in either a packed or trayed column. | 3 | Analytical Chemistry |
A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Definitions vary, but nanocrystalline material is commonly defined as a crystallite (grain) size below 100 nm. Grain sizes from 100 to 500 nm are typically considered "ultrafine" grains.
The grain size of a NC sample can be estimated using x-ray diffraction. In materials with very small grain sizes, the diffraction peaks will be broadened. This broadening can be related to a crystallite size using the Scherrer equation (applicable up to ~50 nm), a Williamson-Hall plot, or more sophisticated methods such as the Warren-Averbach method or computer modeling of the diffraction pattern. The crystallite size can be measured directly using transmission electron microscopy. | 8 | Metallurgy |
Ash content of coal is the non-combustible residue left after coal is burnt. It represents the bulk mineral matter after carbon, oxygen, sulfur and water (including from clays) has been driven off during combustion. Analysis is fairly straightforward, with the coal thoroughly burnt and the ash material expressed as a percentage of the original weight. It can also give an indication about the quality of coal.
Ash content may be determined as air dried basis and on oven dried basis. The main difference between the two is that the latter is determined after expelling the moisture content in the sample of coal. | 3 | Analytical Chemistry |
Favipiravir, sold under the brand name Avigan among others, is an antiviral medication used to treat influenza in Japan. It is also being studied to treat a number of other viral infections, including SARS-CoV-2. Like the experimental antiviral drugs T-1105 and T-1106, it is a pyrazinecarboxamide derivative.
It is being developed and manufactured by Toyama Chemical (a subsidiary of Fujifilm) and was approved for medical use in Japan in 2014. In 2016, Fujifilm licensed it to Zhejiang Hisun Pharmaceutical Co. It became a generic drug in 2019. | 4 | Stereochemistry |
The use of Pd-NHC complexes in Heck-Mizoroki cross-coupling permits the use of cheaper, ample supplies of aryl chloride substrates. Additionally, the activity and stability of the catalyst in Heck-Mizoroki coupling can be enhanced by adjusting the 1,3 substituents on the imidazole ring. | 0 | Organic Chemistry |
Anoxic events with euxinic (anoxic, sulfidic) conditions have been linked to extreme episodes of volcanic outgassing. Volcanism contributed to the buildup of CO in the atmosphere and increased global temperatures, causing an accelerated hydrological cycle that introduced nutrients into the oceans (stimulating planktonic productivity). These processes potentially acted as a trigger for euxinia in restricted basins where water-column stratification could develop. Under anoxic to euxinic conditions, oceanic phosphate is not retained in sediment and could hence be released and recycled, aiding perpetual high productivity. | 9 | Geochemistry |
When no electrons are exchanged (z = 0), the equilibrium between , , , and only depends on and is not affected by the electrode potential. In this case, the reaction is a classical acid-base reaction involving only protonation/deprotonation of dissolved species. The boundary line will be a vertical line at a particular value of pH. The reaction equation may be written:
and the energy balance is written as , where is the equilibrium constant:
Thus:
or, in base-10 logarithms,
which may be solved for the particular value of pH.
For example consider the iron and water system, and the equilibrium line between the ferric ion Fe ion and hematite FeO. The reaction equation is:
which has . The pH of the vertical line on the Pourbaix diagram can then be calculated:
Because the activities (or the concentrations) of the solid phases and water are equal to unity:O] = [HO] = 1, the pH only depends on the concentration in dissolved :
At STP, for [Fe] = 10, this yields pH = 1.76. | 7 | Physical Chemistry |
The Gag-v-Onc fusion protein from the Rous sarcoma virus illustrates the dual role that the fusion protein plays in the viral and host cellular life cycle. For example, the viral gene Src (as in "sarcoma") is not necessary for viral reproduction, but does affect virulence. Due to evidence of conserved homology between the v-Src gene and its host (animal) genomes, and its non-essential status for viral reproduction, the v-Src gene is likely to have been acquired from a host genome and altered by subsequent mutations. These subsequent mutations are responsible for the oncogenic capabilities of the virus, as the normal (host) version of the Src gene, c-Src promotes survival, angiogenesis, proliferation and invasion pathways. These native pathways are disrupted in the presence of the mutant Src gene (v-Src) such that oncogenesis becomes more likely for the infected host cells, since the v-Src gene is translated into a functionally distinct version of its host counterpart. | 1 | Biochemistry |
Ocean acidification can also lead to increased sea surface temperature. An increase of about 1 or 2 °C can cause the collapse of the relationship between coral and zooxanthellae, possibly leading to bleaching. The average sea surface temperature in the Great Barrier Reef is predicted to increase between 1 and 3 °C by 2100. Bleaching occurs when the zooxanthellae and coralline algae leave the coral skeleton behind due to stresses in the water. This causes the coral to lose its colour because the previous organisms sustained on the coral skeleton vacate, leaving a white skeleton. The bleached coral can no longer complete photosynthesis, and so it slowly dies. The acidity of the water will slowly dissolve the leftover coral skeletons, essentially damaging the structural integrity of the coral reef. There are many organisms that also rely on the algae and zooxanthellae for their main source of food. Therefore, organisms in the bleached coral reef are forced to leave in search of new food sources. Since zooxanthellae and algae grow very slowly, restoring the coral reef to its original form will take a very long time. This breakdown of the relationship between the coral and the zooxanthellae occurs when Photosystem II is damaged, either due to a reaction with the D1 protein or a lack of carbon dioxide fixation; these result in a lack of photosynthesis and can lead to bleaching. | 9 | Geochemistry |
The Mond gas process was designed to convert cheap coal into flammable gas, which was made up of mainly hydrogen, while recovering ammonium sulfate. The gas produced was rich in hydrogen and poor in carbon monoxide. Although it could be used for some industrial purposes and power generation, the gas was limited for heating or lighting.
In 1897, the first Mond gas plant began at the Brunner Mond & Company in Northwich, Cheshire. Mond plants which recovered ammonia needed to be large in order to be profitable, using at least 182 tons of coal per week. | 7 | Physical Chemistry |
In some spoil tips, the waste resulting from industries such as coal or oil shale production can contain a relatively high proportion of hydrocarbons or coal dust. Spontaneous subterranean combustion may result, which can be followed by surface fires. In some coal mining districts, such fires were considered normal and no attempt was made to extinguish them.
Such fires can follow slow combustion of residual hydrocarbons. Their extinction can require complete encasement, which can prove impossible for technical and financial reasons. Sprinkling is generally ineffective and injecting water under pressure counter-productive, because it carries oxygen, bringing the risk of explosion.
The perceived weak environmental and public health effects of these fires leads generally to waiting for their natural extinction, which can take a number of decades. | 8 | Metallurgy |
The Krupp-Renn process, which specialized in the beneficiation of poor ores, was the logical basis for the development of recycling processes for ferrous by-products. In 1957, Krupp tested a furnace at for the treatment of roasted pyrites to extract iron (in the form of Luppen) and zinc (vaporized in the flue gases). This process is therefore a hybrid of the Waelz and Krupp-Renn processes, which is why it is called the "Krupp-Waelz" (or "Renn-Waelz") process. The trials were limited to a single 2.75 m × 40 m demonstrator capable of processing 70 to 80 t/day and were not followed up.
The technical relationship between Krupp-Renn and Japanese direct reduction production processes is often cited. In the 1960s, Japanese steelmakers, sharing the observation that furnace plugging was difficult to control, developed their own low-temperature variants of the Krupp-Renn process. Kawasaki Steel commissioned a direct-reduction furnace at its (1968) and (1975) plants, the most visible feature of which was a pelletizing unit for the site's steelmaking by-products (sludge and dust from the cleaning of converter and blast furnace gases). The "Kawasaki process" also incorporates other developments, such as the combustion of oil instead of pulverized coal and the use of coke powder instead of coal mixed with ore... Almost identical to the Kawasaki process (with a more elaborate pelletizing unit), the "Koho process" was adopted by Nippon Steel, which commissioned a plant of this type at the in 1971. | 8 | Metallurgy |
Stable isotope ratios can be used to infer the environmental conditions during the formation of sedimentary rock. Using stoichiometry and knowledge of redox pathways, paleogeologists can use isotopes ratios of elements to determine the chemical composition of the water and sediments when burial occurred.
Sulfur isotopes are frequently used to look for evidence of ancient euxinia. Low δS in black shales and sedimentary rocks provides positive evidence for euxinic formation conditions. The pyrite (FeS) in euxinic basins typically has higher concentrations of light sulfur isotopes than pyrite in the modern ocean. The reduction of sulfate to sulfide favors the lighter sulfur isotopes (S) and becomes depleted in the heavier isotopes (S). This lighter sulfide then bonds with Fe to form FeS which is then partially preserved in the sediments. In most modern systems, sulfate eventually becomes limiting, and the isotopic weights of sulfur in both sulfate and sulfide (preserved as FeS) become equal.
Molybdenum (Mo), the most common transition metal ion in modern seawater, is also used to look for evidence for euxinia. Weathering of rocks provides an input of MoO into oceans. Under oxic conditions, MoO is very unreactive, but in modern euxinic environments such as the Black Sea, molybdenum precipitates out as oxythiomolybdate (MoOS ). The isotope ratio for Molybdenum (δ Mo) in euxinic sediments appears to be higher than in oxic conditions. Additionally, the concentration of molybdenum is frequently correlated with the concentration of organic matter in euxinic sediments. The use of Mo to indicate euxinia is still under debate. | 9 | Geochemistry |
In chemistry a phosphine imide (sometimes abbreviated to phosphinimide) also known as a iminophosphorane is a functional group with the formula RP=NR. While structurally related to phosphine oxide its chemistry has more in common with phosphonium ylides.
Anions of this group, with the structure RP=N, are called phosphinoimidates and are used as ligands to form phosphinimide complexes which are highly active catalysts in some olefin polymerization reactions. | 0 | Organic Chemistry |
The 2001 Heart Outcomes and Prevention Evaluation trial seemed to show ramipril possessed cardioprotective qualities which extended beyond its qualities as an antihypertensive. However, the trial and the interpretation of its results have been criticised.
The Acute Infarction Ramipril Efficacy (AIRE) trial showed a 27% reduction in mortality for patients receiving ramipril for chronic heart failure following a myocardial infarction.
Ramipril was found to have similar results as telmisartan, an angiotensin II receptor blocker. | 4 | Stereochemistry |
Christoph Weder was born on July 30, 1966. He began elementary school in Mülheim a. Main, Germany, in 1972 before moving to Thalwil, Switzerland, in 1974, where he completed elementary and secondary school. He then attended the high school Kantonsschule Enge in Zurich, from which he graduated in 1985. Following in the footsteps of his father, who was also a polymer chemist, Weder studied chemistry at the Swiss Federal Institute of Technology (ETH Zurich) in Zurich, where he received his diploma in chemistry in 1990. He then joined the research group of Professor Ulrich W. Suter as a doctoral student and in 1994 was awarded the degree of Doctor of Natural Sciences for his dissertation “New Polyamides with Stable Nonlinear Optical Properties.” While at ETH, Weder was also trained as a chemistry teacher and received his teaching certification in 1992. With a fellowship from the Swiss National Science Foundation, Weder then spent one year as a postdoctoral research fellow in the Department of Chemistry at the Massachusetts Institute of Technology, where he worked under the guidance of then-provost Mark S. Wrighton.
Weder returned to the Department of Materials of ETH Zurich in 1995, where he joined the group of Professor Paul Smith and continued to work on photofunctional polymers. Based on his habilitation thesis entitled “Polarizing Light with Polymers,” Weder received his habilitation and, bestowed with the venia legendi, became an independent lecturer in 1999. In 2001, Weder left ETH and joined Case Western Reserve University in Cleveland, Ohio, as an associate professor in the Department of Macromolecular Science and Engineering. He was promoted to professor in 2007, and in 2008 was named the F. Alex Nason Professor.
In 2009, Weder returned to Switzerland and joined the Adolphe Merkle Institute (AMI) as Professor of Polymer Chemistry and Materials. AMI, which was founded in 2008 thanks to a gift from Adolphe Merkle, is an interdisciplinary research center that focuses on fundamental and application-oriented research in soft nano- and materials sciences. In January 2010, Weder was appointed as the institute’s director, serving until April 2022.
Weder led a team that was awarded a grant from the Swiss National Science Foundation (SNSF) to establish the National Competence Center in Research (NCCR) Bio-Inspired Materials. He served as the center’s director from its launch in 2014 until 2020. The NCCRs are a research instrument of the Swiss National Science Foundation (SNSF) that aim to strengthen research in areas of strategic importance for the future of Swiss science, business and society.
Weder remains an adjunct professor at CWRU and has served as a visiting professor at Chulalongkorn University in Bangkok, Thailand since 2003. He serves as an Associate Editor of ACS Macro Letters and was a co-editor of the RSC Book Series Polymer Chemistry from 202-2021.
Weder has co-authored more than 300 peer-reviewed articles in scientific journals and over twenty book chapters. He also edited two books. As of March 2022, Weder has an h-index of 87 and his works have been cited more than 27,000 times.
Weder is a co-inventor of more than twenty patent families that protect technologies such as light-polarizing security features, mechanochromic materials, sea-cucumber inspired dynamic mechanical polymer nanocomposites, stimuli-responsive supramolecular polymers, materials for optical upconversion, shape memory polymers, and optical data storage systems. He was a co-founding board member of the ETH-spinoff company Omlidon Technologies, LLC (1999–2002), and served on the board of directors of Gel Instrumente AG (1994–2006).
Weder is the recipient of a 3M Non-Tenured Faculty Award, a DuPont Young Professor Award, an NSF Special Creativity Award, and the Case School of Engineering Award. He was awarded a prestigious European Research Council (ERC) Advanced Grant, and is a Fellow of the American Chemical Society’s Division of Polymer Chemistry. In 2017, he was nominated as a member of the Swiss Academy of Technical Sciences "in recognition of his pioneering work in the development of nanomaterials through combination of fundamental research and practical applications as well as his contribution to the successful establishment of the Adolphe Merkle Institute".
Weder is married and has three children. | 7 | Physical Chemistry |
Inhibitors disrupt the interaction between enzyme and substrate, slowing down the rate of a reaction. There are different types of inhibitor, including both reversible and irreversible forms.
Competitive inhibitors are inhibitors that only target free enzyme molecules. They compete with substrates for free enzyme acceptor and can be overcome by increasing the substrate concentration. They have two mechanisms. Competitive inhibitors usually have structural similarities to the substrates and or ES complex. As a result, they can fit into the active site and trigger favourable interactions to fill in the space and block substrates from entry. They can also induce transient conformational changes in the active site so substrates cannot fit perfectly with it. After a short period of time, competitive inhibitors will drop off and leave the enzyme intact.
Inhibitors are classified as non-competitive inhibitors when they bind both free enzyme and ES complex. Since they do not compete with substrates for the active site, they cannot be overcome by simply increasing the substrate concentration. They usually bind to a different site on the enzyme and alter the 3-dimensional structure of the active site to block substrates from entry or leaving the enzyme.
Irreversible inhibitors are similar to competitive inhibitors as they both bind to the active site. However, irreversible inhibitors form irreversible covalent bonds with the amino acid residues in the active site and never leave. Therefore, the active site is occupied and the substrate cannot enter. Occasionally the inhibitor will leave but the catalytic site is permanently altered in shape. These inhibitors usually contain electrophilic groups like halogen substitutes and epoxides. As time goes by more and more enzymes are bound by irreversible inhibitors and cannot function anymore. | 1 | Biochemistry |
Cytochrome C1 (also known as Complex III subunit 4) is a protein encoded by the CYC1 gene. Cytochrome is a heme-containing subunit of the cytochrome b-c1 complex, which accepts electrons from Rieske protein and transfers electrons to cytochrome c in the mitochondrial respiratory chain. It is formed in the cytosol and targeted to the mitochondrial intermembrane space. Cytochrome c1 belongs to the cytochrome c family of proteins. | 1 | Biochemistry |
There is currently no evidence supporting targeted temperature management use in humans and clinical trials have not been completed. Most of the data concerning hypothermia's effectiveness in treating stroke is limited to animal studies. These studies have focused primarily on ischemic stroke as opposed to hemorrhagic stroke, as hypothermia is associated with a lower clotting threshold. In these animal studies, hypothermia was represented an effective neuroprotectant. The use of hypothermia to control intracranial pressure (ICP) after an ischemic stroke was found to be both safe and practical. | 1 | Biochemistry |
vaccine - vacuole - valence - valine - van der Waals force - van der Waals radius - vapor pressure - vapour pressure - vasoactive intestinal peptide - vasoactive intestinal peptide receptor - vasopressin - vasopressin receptor - venom - vertebrate photoreceptor - vesicle - vestibular system - vimentin - viral envelope protein - viral oncogene protein - viral protein - virology - virus (biology) - vitamin - vitamin D-dependent calcium-binding protein - vitellogenin - vitronectin - von Willebrand factor | 1 | Biochemistry |
In biochemistry and molecular biology, a binding site is a region on a macromolecule such as a protein that binds to another molecule with specificity. The binding partner of the macromolecule is often referred to as a ligand. Ligands may include other proteins (resulting in a protein–protein interaction), enzyme substrates, second messengers, hormones, or allosteric modulators. The binding event is often, but not always, accompanied by a conformational change that alters the protein's function. Binding to protein binding sites is most often reversible (transient and non-covalent), but can also be covalent reversible or irreversible. | 1 | Biochemistry |
The PI (or photosynthesis-irradiance) curve is a graphical representation of the empirical relationship between solar irradiance and photosynthesis. A derivation of the Michaelis–Menten curve, it shows the generally positive correlation between light intensity and photosynthetic rate. It is a plot of photosynthetic rate as a function of light intensity (irradiance). | 5 | Photochemistry |
Companion planting approaches in use or being trialled include:
* Square foot gardening attempts to protect plants from issues such as weed infestation by packing them as closely together as possible. This is facilitated by using companion plants, which can be closer together than normal.
* Forest gardening, where companion plants are intermingled to simulate an ecosystem, emulates the interaction of plants of up to seven different heights in a woodland. | 1 | Biochemistry |
While photosystem II photolyzes water to obtain and energize new electrons, photosystem I simply reenergizes depleted electrons at the end of an electron transport chain. Normally, the reenergized electrons are taken by NADP, though sometimes they can flow back down more H-pumping electron transport chains to transport more hydrogen ions into the thylakoid space to generate more ATP. This is termed cyclic photophosphorylation because the electrons are recycled. Cyclic photophosphorylation is common in plants, which need more ATP than NADPH. | 5 | Photochemistry |
Generally speaking, carbohydrates can be classified into two groups, simple sugars, and complex carbohydrates. Simple sugars, also called monosaccharides, are carbohydrates that cannot be further broke down by hydrolysis. When glycosidic linkages connect two or more monosaccharide units, complex carbohydrates are formed. Complex carbohydrates, according to the different number of monosaccharide units, can be classed into three groups, disaccharides, oligosaccharides, and polysaccharides. A disaccharide is formed from two monosaccharides. When a carbohydrate contains 3-10 monosaccharides, it is called a oligosaccharide. Higher oligosaccharides with more than 10 monosaccharides are polysaccharides.
So far, there has not been a unified synthetic strategy of consistent oligosaccharide production because of the nuances in the anomeric effects of monomers and the complexity in the carbohydrate structures. The facile procedures such as the one-pot and solid phase synthesis which ensures atom economy are used. However, further developments in those synthetic approaches are needed since still not fully controlled and automated. | 0 | Organic Chemistry |
Freshly prepared sodium nitroprusside solution is added to the sodium fusion extract, turning the solution deep violet due to formation of sodium thionitroprusside. </blockquote>
In case, both nitrogen and sulfur are present in an organic compound, sodium thiocyanate is formed which gives blood red color since there are no free cyanide ions.
</blockquote> | 3 | Analytical Chemistry |
An assay is a type of biological titration used to determine the concentration of a virus or bacterium. Serial dilutions are performed on a sample in a fixed ratio (such as 1:1, 1:2, 1:4, 1:8, etc.) until the last dilution does not give a positive test for the presence of the virus. The positive or negative value may be determined by inspecting the infected cells visually under a microscope or by an immunoenzymetric method such as enzyme-linked immunosorbent assay (ELISA). This value is known as the titer. | 3 | Analytical Chemistry |
Vincent Marks (10 June 1930 – 6 November 2023) was an English pathologist and clinical biochemist known for his works on studying insulin and hypoglycemia. His contributions to medical science include simplifying low blood glucose testing, introducing insulin radioimmunoassay, and advancing diabetes research. Marks played an important role in high-profile medico-legal cases, notably providing expert testimony that helped acquit Danish-born British socialite Claus von Bülow in 1985, a case that was the basis of the Oscar-winning movie Reversal of Fortune (1990).
Marks was also a nutritionist who studied intestinal hormones and coined the term muesli belt malnutrition, referring to parents feeding their children what is considered extremely healthy foods, but, in the process depriving them of essential fats. | 1 | Biochemistry |
Hydroxybenzotriazole (abbreviated HOBt) is an organic compound that is a derivative of benzotriazole. It is a white crystalline powder, which as a commercial product contains some water (~11.7% wt as the HOBt monohydrate crystal). Anhydrous HOBt is explosive.
It is mainly used to suppress the racemization of single-enantiomer chiral molecules and to improve the efficiency of peptide synthesis. | 1 | Biochemistry |
* [http://bascoe.oma.be/index.php/bascoe BASCOE] - A data assimilation system based on a chemical transport model and created by the Belgian Institute for Space Aeronomy (BIRA-IASB)
* [https://tropo.aeronomie.be/index.php/12-boream Boream] - Model for the degradation of alpha-pinene
* [https://www2.acom.ucar.edu/modeling/boxmox-box-model-extensions-kpp BOXMOX] - Box model extensions to KPP
* [https://doi.org/10.5194/gmd-14-2867-2021 CMAQ] - Community Multiscale Air Quality model
* [http://wiki.seas.harvard.edu/geos-chem/index.php/DSMACC_chemical_box_model DSMACC] - Dynamically Simple Model of Atmospheric Chemical Complexity
* [http://wiki.seas.harvard.edu/geos-chem/index.php/KPP_solvers_FAQ GEOS–Chem] - Global 3-D chemical transport model for atmospheric composition
* [https://www2.helsinki.fi/en/researchgroups/multi-scale-modelling/malte-box MALTE] - Model to predict new aerosol formation in the lower troposphere
* [http://mcm.york.ac.uk MCM] - Master Chemical Mechanism
* [http://www.mecca.messy-interface.org/ MECCA] - Module Efficiently Calculating the Chemistry of the Atmosphere
* [https://github.com/Mistra-UEA/Mistra Mistra] - Microphysical Stratus model
* [https://doi.org/10.1029/2021JD036140 PACT-1D] - Platform for Atmospheric Chemistry and vertical Transport in 1-dimension
* [https://palm.muk.uni-hannover.de/trac/wiki/doc/app/chemdesc PALM] - Meteorological modeling system for atmospheric and oceanic boundary layer flows
* [https://doi.org/10.1029/97JD00849 RACM] - Regional Atmospheric Chemistry Mechanism gas-phase chemistry mechanism
* [https://www2.acom.ucar.edu/wrf-chem WRF-Chem] - Weather Research & Forecasting Model with Chemistry | 7 | Physical Chemistry |
(Also see: Eyespot apparatus)
*Channelrhodopsin: in unicellular algae, mediates phototaxis
*Chlamyopsin and volvoxopsin
*Flavoproteins | 1 | Biochemistry |
In n dimensions, an affine space group, or Bieberbach group, is a discrete subgroup of isometries of n-dimensional Euclidean space with a compact fundamental domain. proved that the subgroup of translations of any such group contains n linearly independent translations, and is a free abelian subgroup of finite index, and is also the unique maximal normal abelian subgroup. He also showed that in any dimension n there are only a finite number of possibilities for the isomorphism class of the underlying group of a space group, and moreover the action of the group on Euclidean space is unique up to conjugation by affine transformations. This answers part of Hilberts eighteenth problem. showed that conversely any group that is the extension of Z by a finite group acting faithfully is an affine space group. Combining these results shows that classifying space groups in n dimensions up to conjugation by affine transformations is essentially the same as classifying isomorphism classes for groups that are extensions of Z by a finite group acting faithfully.
It is essential in Bieberbach's theorems to assume that the group acts as isometries; the theorems do not generalize to discrete cocompact groups of affine transformations of Euclidean space. A counter-example is given by the 3-dimensional Heisenberg group of the integers acting by translations on the Heisenberg group of the reals, identified with 3-dimensional Euclidean space. This is a discrete cocompact group of affine transformations of space, but does not contain a subgroup Z. | 4 | Stereochemistry |
Interface and colloid science is an interdisciplinary intersection of branches of chemistry, physics, nanoscience and other fields dealing with colloids, heterogeneous systems consisting of a mechanical mixture of particles between 1 nm and 1000 nm dispersed in a continuous medium. A colloidal solution is a heterogeneous mixture in which the particle size of the substance is intermediate between a true solution and a suspension, i.e. between 1–1000 nm. Smoke from a fire is an example of a colloidal system in which tiny particles of solid float in air. Just like true solutions, colloidal particles are small and cannot be seen by the naked eye. They easily pass through filter paper. But colloidal particles are big enough to be blocked by parchment paper or animal membrane.
Interface and colloid science has applications and ramifications in the chemical industry, pharmaceuticals, biotechnology, ceramics, minerals, nanotechnology, and microfluidics, among others.
There are many books dedicated to this scientific discipline, and there is a glossary of terms, Nomenclature in Dispersion Science and Technology, published by the US National Institute of Standards and Technology. | 7 | Physical Chemistry |
Actinism () is the property of solar radiation that leads to the production of photochemical and photobiological effects. Actinism is derived from the Ancient Greek ἀκτίς, ἀκτῖνος ("ray, beam"). The word actinism is found, for example, in the terminology of imaging technology (esp. photography), medicine (concerning sunburn), and chemistry (concerning containers that protect from photo-degradation), and the concept of actinism is applied, for example, in chemical photography and X-ray imaging.
Actinic () chemicals include silver salts used in photography and other light sensitive chemicals. | 7 | Physical Chemistry |
The Elizabeth River estuary is used for commercial and military use and is one of the most commonly used ports on the East Coast of the USA. From 2015-2019, 11 different conditions were measured in various areas of the Elizabeth River. Throughout the river, there were consistently high levels of nitrogen and phosphorus, along with high levels of other contaminants contributing to the poor quality of life for bottom feeders along the river. The main cause of the pollution to the Elizabeth river has been the military and industrial activities through the 1990s. In 1993, the Elizabeth River Project was started in attempt to do a restoration project on the river. Adopting one of the fish whose species had been largely impacted by the pollution, the Fundulus heteroclitus (Mummichog), the group was able to gain traction and carry out multiple projects and has removed thousands of tons of contaminated sediment. In 2006, Maersk-APM, a major shipping company, wanted to build a new port on the Elizabeth River. As part of the environmental mitigation they worked with the Elizabeth River Project to create the Money Point Project, which was an effort to restore Money Point, which had been deemed biologically depleted due to a black tar like substance called creosote laying at the bottom. Maersk-APM gave $5 million to help get the project up and running. By 2012, they were able to restore over 7 acres of tidal marsh, 3 acres of oyster reef and created a new shoreline. In 2019, the Money Point Project received the "Best Restored Shore" award from the American Shore and Beach Preservation Association. | 9 | Geochemistry |
Among mutations in esterases, carbamate resistance most commonly involves acetylcholinesterase (AChE) desensitization, while organophosphate resistance most commonly is carboxylesterase metabolization. | 0 | Organic Chemistry |
The unexpected fall in 2011 of a heavy light fixture from the ceiling of the Big Dig vehicular tunnel in Boston revealed that corrosion had weakened its support. Improper use of aluminium in contact with stainless steel had caused rapid corrosion in the presence of salt water. The electrochemical potential difference between stainless steel and aluminium is in the range of 0.5 to 1.0V, depending on the exact alloys involved, and can cause considerable corrosion within months under unfavorable conditions. Thousands of failing lights would have to be replaced, at an estimated cost of $54 million. | 8 | Metallurgy |
Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by a nitrogenase enzyme. The overall reaction for BNF is:
The process is coupled to the hydrolysis of 16 equivalents of ATP and is accompanied by the co-formation of one equivalent of . The conversion of into ammonia occurs at a metal cluster called FeMoco, an abbreviation for the iron-molybdenum cofactor. The mechanism proceeds via a series of protonation and reduction steps wherein the FeMoco active site hydrogenates the substrate. In free-living diazotrophs, nitrogenase-generated ammonia is assimilated into glutamate through the glutamine synthetase/glutamate synthase pathway. The microbial nif genes required for nitrogen fixation are widely distributed in diverse environments.
For example, decomposing wood, which generally has a low nitrogen content, has been shown to host a diazotrophic community. The bacteria enrich the wood substrate with nitrogen through fixation, thus enabling deadwood decomposition by fungi.
Nitrogenases are rapidly degraded by oxygen. For this reason, many bacteria cease production of the enzyme in the presence of oxygen. Many nitrogen-fixing organisms exist only in anaerobic conditions, respiring to draw down oxygen levels, or binding the oxygen with a protein such as leghemoglobin. | 1 | Biochemistry |
Ependymin is a glycoprotein found in the cerebrospinal fluid of many teleost fish. The humans homolog is called ependymin related 1 that is encoded by the EPDR1 gene.
Ependymin is associated with the consolidation of long-term memory, possibly providing protection from strokes, and contributing to neuronal regeneration. This encoded protein was originally detected in elevated amounts of fluid within the central nervous system of teleost fishes. Along with long-term memory and neuronal regeneration, ependymin has been connected to specific aspects of changes in signaling within nerve cells leading to brain plasticity, as well as behavioral performance in response to environment stress in fishes. For example, this glycoprotein interaction in the extracellular matrix influences cell adhesion and migration processes in the central nervous system of teleost fishes. The presence of ependymin-related proteins can be found in both vertebrates and invertebrates. They have variety of functional roles in non-neural sites of organisms. For example, an ependymin-related gene that is upregulated in colon cancer known as UCC1 was found in human colorectal tumor cells. | 1 | Biochemistry |
Many LGBT communities centre their support around cisgender gay, lesbian and bisexual people and neglect to include proper support for transgender people. The same 2020 literature review analyses the social, emotional and physical experiences of pregnant transgender men. A common obstacle faced by pregnant transgender men is the possibility of gender dysphoria. Literature shows that transgender men report uncomfortable procedures and interactions during their pregnancies as well as feeling misgendered due to gendered terminology used by healthcare providers. Outside of the healthcare system, pregnant transgender men may experience gender dysphoria due to cultural assumptions that all pregnant people are cisgender women. These people use three common approaches to navigating their pregnancy: passing as a cisgender woman, hiding their pregnancy, or being out and visibly pregnant as a transgender man. Some transgender and gender diverse patients describe their experience in seeking gynaecological and reproductive health care as isolating and discriminatory, as the strictly binary healthcare system often leads to denial of healthcare coverage or unnecessary revelation of their transgender status to their employer.
Many transgender people retain their original sex organs and choose to have children through biological reproduction. Advances in assisted reproductive technology and fertility preservation have broadened the options transgender people have to conceive a child using their own gametes or a donor's. Transgender men and women may opt for fertility preservation before any gender affirming surgery, but it is not required for future biological reproduction. It is also recommended that fertility preservation is conducted before any hormone therapy. Additionally, while fertility specialists often suggest that transgender men discontinue their testosterone hormones prior to pregnancy, research on this topic is still inconclusive. However, a 2019 study found that transgender male patients seeking oocyte retrieval via assisted reproductive technology (including IVF) were able to undergo treatment four months after stopping testosterone treatment, on average. All patients experienced menses and normal AMH, FSH and E levels and antral follicle counts after coming off testosterone, which allowed for successful oocyte retrieval. Despite assumptions that the long-term androgen treatment negatively impacts fertility, oocyte retrieval, an integral part of the IVF process, does not appear to be affected.
Biological reproductive options available to transgender women include, but are not limited to, IVF and IUI with the trans womans sperm and a donor or a partners eggs and uterus. Fertility treatment options for transgender men include, but are not limited to, IUI or IVF using his own eggs with a donors sperm and/or donors eggs, his uterus, or a different uterus, whether that is a partners or a surrogates. | 1 | Biochemistry |
Apparent quantities can underline interactions in electrolyte – non-electrolyte systems which show interactions like salting in and salting out, but also give insights in ion-ion interactions, especially by their dependence on temperature. | 7 | Physical Chemistry |
In fact, however, the observed reaction rate is second-order in and zero-order in CO, with rate equation r = k[]. This suggests that the rate is determined by a step in which two molecules react, with the CO molecule entering at another, faster, step. A possible mechanism in two elementary steps that explains the rate equation is:
# + → NO + (slow step, rate-determining)
# + CO → + (fast step)
In this mechanism the reactive intermediate species is formed in the first step with rate r and reacts with CO in the second step with rate r. However, can also react with NO if the first step occurs in the reverse direction (NO + → 2 ) with rate r, where the minus sign indicates the rate of a reverse reaction.
The concentration of a reactive intermediate such as [] remains low and almost constant. It may therefore be estimated by the steady-state approximation, which specifies that the rate at which it is formed equals the (total) rate at which it is consumed. In this example is formed in one step and reacts in two, so that
The statement that the first step is the slow step actually means that the first step in the reverse direction is slower than the second step in the forward direction, so that almost all is consumed by reaction with CO and not with NO. That is, r ≪ r, so that r − r ≈ 0. But the overall rate of reaction is the rate of formation of final product (here ), so that r = r ≈ r. That is, the overall rate is determined by the rate of the first step, and (almost) all molecules that react at the first step continue to the fast second step. | 7 | Physical Chemistry |
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