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PAVA primarily affects the eyes, causing closure and severe pain. The pain to the eyes is reported to be greater than that caused by CS. The effectiveness rate is very high once PAVA gets into the eyes; however, there have been occasions where PAVA and CS have failed to work—especially when the subject is under the influence of alcohol or other drugs. Exposure to fresh moving air will normally result in a significant recovery from the effects of PAVA, within 15–35 minutes.
Pharmacologically, like other capsaicinoids, PAVA works by direct binding to receptors (TRPV1) that normally produce the pain and sensation of heat, as if exposed to scalding heat. | 1 | Biochemistry |
Type N (Nicrosil–Nisil) thermocouples are suitable for use between −270 °C and +1300 °C, owing to its stability and oxidation resistance. Sensitivity is about 39 μV/°C at 900 °C, slightly lower compared to type K.
Designed at the Defence Science and Technology Organisation (DSTO) of Australia, by Noel A. Burley, type-N thermocouples overcome the three principal characteristic types and causes of thermoelectric instability in the standard base-metal thermoelement materials:
#A gradual and generally cumulative drift in thermal EMF on long exposure at elevated temperatures. This is observed in all base-metal thermoelement materials and is mainly due to compositional changes caused by oxidation, carburization, or neutron irradiation that can produce transmutation in nuclear reactor environments. In the case of type-K thermocouples, manganese and aluminium atoms from the KN (negative) wire migrate to the KP (positive) wire, resulting in a down-scale drift due to chemical contamination. This effect is cumulative and irreversible.
#A short-term cyclic change in thermal EMF on heating in the temperature range about 250–650 °C, which occurs in thermocouples of types K, J, T, and E. This kind of EMF instability is associated with structural changes such as magnetic short-range order in the metallurgical composition.
#A time-independent perturbation in thermal EMF in specific temperature ranges. This is due to composition-dependent magnetic transformations that perturb the thermal EMFs in type-K thermocouples in the range about 25–225 °C, and in type J above 730 °C.
The Nicrosil and Nisil thermocouple alloys show greatly enhanced thermoelectric stability relative to the other standard base-metal thermocouple alloys because their compositions substantially reduce the thermoelectric instabilities described above. This is achieved primarily by increasing component solute concentrations (chromium and silicon) in a base of nickel above those required to cause a transition from internal to external modes of oxidation, and by selecting solutes (silicon and magnesium) that preferentially oxidize to form a diffusion-barrier, and hence oxidation-inhibiting films.
Type N thermocouples are suitable alternative to type K for low-oxygen conditions where type K is prone to green rot. They are suitable for use in vacuum, inert atmospheres, oxidizing atmospheres, or dry reducing atmospheres. They do not tolerate the presence of sulfur. | 8 | Metallurgy |
The initiation factors are divided into three major groups by taxonomic domains. There are some homologies shared (click the domain names to see the domain-specific factors): | 1 | Biochemistry |
Disodium pyrophosphate is prepared by thermal condensation of sodium dihydrogen phosphate or by partial deprotonation of pyrophosphoric acid.
Pyrophosphates are generally white or colorless. The alkali metal salts are water-soluble. They are good complexing agents for metal ions (such as calcium and many transition metals) and have many uses in industrial chemistry. Pyrophosphate is the first member of an entire series of polyphosphates. | 1 | Biochemistry |
Most drugs and drug candidates contain amine functional groups:
* Chlorpheniramine is an antihistamine that helps to relieve allergic disorders due to cold, hay fever, itchy skin, insect bites and stings.
* Chlorpromazine is a tranquilizer that sedates without inducing sleep. It is used to relieve anxiety, excitement, restlessness or even mental disorder.
* Ephedrine and phenylephrine, as amine hydrochlorides, are used as decongestants.
* Amphetamine, methamphetamine, and methcathinone are psychostimulant amines that are listed as controlled substances by the US DEA.
* Thioridazine, an antipsychotic drug, is an amine which is believed to exhibit its antipsychotic effects, in part, due to its effects on other amines.
* Amitriptyline, imipramine, lofepramine and clomipramine are tricyclic antidepressants and tertiary amines.
* Nortriptyline, desipramine, and amoxapine are tricyclic antidepressants and secondary amines. (The tricyclics are grouped by the nature of the final amino group on the side chain.)
* Substituted tryptamines and phenethylamines are key basic structures for a large variety of psychedelic drugs.
* Opiate analgesics such as morphine, codeine, and heroin are tertiary amines. | 0 | Organic Chemistry |
Viruses are so small that they can only be observed under an electron microscope. The structure of a virus is given by its coat of proteins, which surround the viral genome. Assembly of viral particles takes place spontaneously.
Over 50% of known plant viruses are rod-shaped (flexuous or rigid). The length of the particle is normally dependent on the genome but it is usually between 300 and 500 nm with a diameter of 15–20 nm. Protein subunits can be placed around the circumference of a circle to form a disc. In the presence of the viral genome, the discs are stacked, then a tube is created with room for the nucleic acid genome in the middle.
The second most common structure amongst plant viruses are isometric particles. They are 25–50 nm in diameter. In cases when there is only a single coat protein, the basic structure consists of 60 T subunits, where T is an integer. Some viruses may have 2 coat proteins that associate to form an icosahedral shaped particle.
There are three genera of Geminiviridae that consist of particles that are like two isometric particles stuck together.
A few number of plant viruses have, in addition to their coat proteins, a lipid envelope. This is derived from the plant cell membrane as the virus particle buds off from the cell. | 1 | Biochemistry |
In organic chemistry, a tetrose is a monosaccharide with 4 carbon atoms. They have either an aldehyde () functional group in position 1 (aldotetroses) or a ketone () group in position 2 (ketotetroses).
The aldotetroses have two chiral centers (asymmetric carbon atoms) and so 4 different stereoisomers are possible. There are two naturally occurring stereoisomers, the enantiomers of erythrose and threose having the configuration but not the enantiomers. The ketotetroses have one chiral center and, therefore, two possible stereoisomers: erythrulose (- and -form). Again, only the enantiomer is naturally occurring. | 1 | Biochemistry |
Inverse geometry spectrometers at spallation sources include IRIS and OSIRIS at the ISIS neutron source at Rutherford-Appleton, BASIS at the Spallation Neutron Source, and MARS at the Paul Scherrer Institute | 7 | Physical Chemistry |
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI) | 1 | Biochemistry |
Dichlorotris(triphenylphosphine)ruthenium(II) is a coordination complex of ruthenium. It is a chocolate brown solid that is soluble in organic solvents such as benzene. The compound is used as a precursor to other complexes including those used in homogeneous catalysis. | 0 | Organic Chemistry |
A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as a weapon "or its precursor that can cause death, injury, temporary incapacitation or sensory irritation through its chemical action. Munitions or other delivery devices designed to deliver chemical weapons, whether filled or unfilled, are also considered weapons themselves."
Chemical weapons are classified as weapons of mass destruction (WMD), though they are distinct from nuclear weapons, biological weapons, and radiological weapons. All may be used in warfare and are known by the military acronym NBC (for nuclear, biological, and chemical warfare). Weapons of mass destruction are distinct from conventional weapons, which are primarily effective due to their explosive, kinetic, or incendiary potential. Chemical weapons can be widely dispersed in gas, liquid and solid forms, and may easily afflict others than the intended targets. Nerve gas, tear gas, and pepper spray are three modern examples of chemical weapons.
Lethal unitary chemical agents and munitions are extremely volatile and they constitute a class of hazardous chemical weapons that have been stockpiled by many nations. Unitary agents are effective on their own and do not require mixing with other agents. The most dangerous of these are nerve agents (GA, GB, GD, and VX) and vesicant (blister) agents, which include formulations of sulfur mustard such as H, HT, and HD. They all are liquids at normal room temperature, but become gaseous when released. Widely used during the World War I, the effects of so-called mustard gas, phosgene gas, and others caused lung searing, blindness, death and maiming.
During World War II the Nazi regime used a commercial hydrogen cyanide blood agent trade-named Zyklon B to commit industrialised genocide against Jews and other targeted populations in large gas chambers. The Holocaust resulted in the largest death toll to chemical weapons in history.
, CS gas and pepper spray remain in common use for policing and riot control; CS and pepper spray are considered non-lethal weapons. Under the Chemical Weapons Convention (1993), there is a legally binding, worldwide ban on the production, stockpiling, and use of chemical weapons and their precursors. However, large stockpiles of chemical weapons continue to exist, usually justified as a precaution against possible use by an aggressor. Continued storage of these chemical weapons is a hazard, as many of the weapons are now more than 50 years old, raising risks significantly. The United States is now undergoing measures to dispose of their chemical weapons in a safe manner. | 1 | Biochemistry |
The journal began its publication in 1905 as Transactions of the Faraday Society. When the society merged with the other chemistry societies of the United Kingdom to form the Royal Society of Chemistry, the publication of the journal was transferred to the Chemical Society in 1972 as part of the merger negotiations. The journal was renamed Journal of the Chemical Society, Faraday Transactions, and split in two (Faraday Transactions I: Physical Chemistry in Condensed Phases and Faraday Transactions II: Molecular and Chemical Physics). After the merger, the Royal Society carried the publication until its end. In 1990, the two journals merged into a single Journal of the Chemical Society, Faraday Transactions, which continued publication until 1998 when it merged with a number of other physical chemistry journals published by different societies to form Physical Chemistry Chemical Physics. | 7 | Physical Chemistry |
Bioaccumulation is the process by which an organism takes in chemicals through ingestion, exposure, and inhalation. Bioaccumulation is broken down into bioconcentration (uptake of chemicals from the environment) and biomagnification (increasing concentration of chemicals as they move up the food chain). Certain species of aquatic organisms are affected differently from the chemicals released from creosote preservatives. One of the more studied organisms is a mollusk. Mollusks attach to the wooden, marine pilings and are in direct contact with the creosote preservatives. Many studies have been conducted using polycyclic aromatic hydrocarbons (PAH), which are low molecular hydrocarbons found in some creosote-based preservatives. In a study conducted from Pensacola, Florida, a group of native mollusks were kept in a controlled environment, and a different group of native mollusks were kept in an environment contaminated with creosote preservatives. The mollusks in the contaminated environment were shown to have a bioaccumulation of up to ten times the concentration of PAH than the control species. The intake of organisms is dependent on whether the compound is in an ionized or an un-ionized form. To determine whether the compound is ionized or un-ionized, the pH of the surrounding environment must be compared to the pKa or acidity constant of the compound. If the pH of the environment is lower than the pKa, then the compound is un-ionized which means that the compound will behave as if it is non-polar. Bioaccumulation for un-ionized compounds comes from partitioning equilibrium between the aqueous phase and the lipids in the organism. If the pH is higher than the pKa, then the compound is considered to be in the ionized form. The un-ionized form is favored because the bioaccumulation is easier for the organism to intake through partitioning equilibrium. The table below shows a list of pKas from compounds found in creosote preservatives and compares them to the average pH of seawater (reported to be 8.1).
Each of the compounds in the table above is found in creosote preservatives; all are in the favored un-ionized form. In another study, various species of small fish were tested to see how the exposure time to PAH chemicals affected the fish. This study showed that an exposure time of 24–96 hours on various shrimp and fish species affected the growth, reproduction, and survival functions of the organisms for most of the compounds tested. | 7 | Physical Chemistry |
In one study the usual regioselectivity of an alkyne hydrozirconation is reversed with the addition of zinc chloride:
One example of a one-pot hydrozirconation - carbonylation - coupling is depicted below:
With certain allyl alcohols, the alcohol group is replaced by nucleophilic carbon forming a cyclopropane ring: The selectivity of the hydrozirconation of alkynes has been studied in detail. Generally, the addition of the Zr–H proceeds via the syn-addition. The rate of addition to unsaturated carbon-carbon bonds is terminal alkyne > terminal alkene ≈ internal alkyne > disubstituted alkene Acyl complexes can be generated by insertion of CO into the C–Zr bond resulting from hydrozirconation. Upon alkene insertion into the zirconium hydride bond, the resulting zirconium alkyl undergoes facile rearrangement to the terminal alkyl and therefore only terminal acyl compounds can be synthesized in this way. The rearrangement most likely proceeds via β-hydride elimination followed by reinsertion. | 0 | Organic Chemistry |
Only a small fraction of the global ridge system (~65000 km) and of the vast continental margin regions have been explored and their communities described. It is the aim of ChEss to improve the knowledge on the diversity, abundance and distribution of species from vents, seeps and other reducing habitats at a global scale, understanding the abiotic and biotic processes that shape and maintain these ecosystems and their biogeography.
Main ChEss Science Questions
* I. What are the species' relationships between different habitats: vents, seeps, whale falls, sunken wood and OMZs?
* II. What is the role of deep-water circulation and geographical barriers in gene flow and biogeography?
* III. What are the factors driving patterns of biodiversity in these habitats?
Objective 1. To create a centralised database
To create a centralised database, [https://web.archive.org/web/20090523105231/http://www.noc.soton.ac.uk/chess/database/db_home.php ChEssBase], of deep-water vent, cold seep, whalefall and OMZ species. ChEssBase is a web-based database that incorporates archived and newly collected biological material. The database is geo- and bio-referenced. ChEssBase is available online and has been integrated with OBIS.
Objective 2. To develop a long-term field programme
To develop a long-term [https://web.archive.org/web/20090523110542/http://www.noc.soton.ac.uk/chess/science/sci_field.php field programme] to locate potential vent and seep sites and continue research on whalefalls and OMZ sites. The field programme aims to explain the main gaps in our knowledge of the diversity, abundance and distribution of chemosynthetic species globally. A limited number of target areas have been selected where specific scientific questions relevant to biogeographical issues will be answered.
The target areas have been grouped into two categories. Category I, combined areas: Area A: Equatorial Atlantic Belt region; Area B: the SE Pacific region; Area C: NZ region; Area D: the Arctic and Antarctic regions, within the International Polar Year. Category II, specific areas: 1 – The ice-covered Gakkel Ridge, 2 – the (ultra)-slow ridges of the Norwegian-Greenland Sea, 3 – the northern MAR between the Iceland and Azores hot-spots; 4 – the Brazilian continental margin, 5 – the East Scotia Ridge and Bransfield Strait, 6 – the SW Indian Ridge, 7 – the Central Indian Ridge.
During the field programme, ChEss will promote the development and refinement of deep-towed, remotely operated (ROV) and autonomous underwater (AUV) vehicle technologies to locate, map and sample new chemosynthetic systems. Using optical, chemical and acoustic techniques, ChEss researchers hope to gain a better understanding of not only biogeographical patterns, but to determine the processes driving these ecosystems.
During the field programme, ChEss will promote the development and refinement of deep-towed, remotely operated (ROV) and autonomous underwater (AUV) vehicle technologies to locate, map and sample new chemosynthetic systems. Using optical, chemical and acoustic techniques, ChEss researchers hope to gain a better understanding of not only biogeographical patterns, but to determine the processes driving these ecosystems.
Objective 3: Outreach and Education
ChEss has multi-lingual [https://web.archive.org/web/20081204112716/http://www.noc.soton.ac.uk/chess/education/edu_home.php education pages] related to vents, seeps and whalefalls. There is a dedicated page for key outreach initiatives such as live cruise diaries, open days, schools activities etc.
ChEss has joined forces with the other deep-sea CoML projects and this has resulted in the creation of the DEep-Sea Education and Outreach group (DESEO) that has produced a book "Deeper than Light" published in 5 languages. | 9 | Geochemistry |
Size exclusion chromatography applications for separating macromolecules based on subtle differences in size typically use resins with large and varied pore sizes in long chromatography columns. However, for buffer exchange and desalting applications, it is mainly the maximum effective pore size (exclusion limit or molecular weight cut off (MWCO) of the resin) that determines the size of molecules that can be separated. Molecules that are significantly smaller than the MWCO penetrate into the pores of the resin, while molecules larger than the MWCO are unable to enter the pores and remain together in the void volume of the column. By passing samples through a column resin bed with sufficient length and volume, macromolecules can be fully separated from small molecules that travel a greater distance though the pores of the resin bed. No significant separation of molecules larger than the exclusion limit occurs.
In order for the desired macromolecules to remain in the void volume, resins with very small pores sizes must be utilized. For typical desalting and buffer exchange applications choosing a resin with a molecular weight cut off between 5 and 10KDa is usually best. For other applications, such as separating peptides from full-sized proteins, resins with larger exclusion limits may be necessary. The macromolecular components are recovered in the buffer used to pre-equilibrate the gel-filtration matrix, while the small molecules can be collected in a later fraction volume or be left trapped in the resin. One important feature to note when choosing a resin is that the small molecules targeted for removal must be several times smaller than the MWCO for proper separation. | 3 | Analytical Chemistry |
BLOSUM80: more related proteins
BLOSUM62: midrange
BLOSUM45: distantly related proteins
An article in Nature Biotechnology revealed that the BLOSUM62 used for so many years as a standard is not exactly accurate according to the algorithm described by Henikoff and Henikoff. Surprisingly, the miscalculated BLOSUM62 improves search performance.
The BLOSUM62 matrix with the amino acids in the table grouped according to the chemistry of the side chain, as in (a). Each value in the matrix is calculated by dividing the frequency of occurrence of the amino acid pair in the BLOCKS database, clustered at the 62% level, divided by the probability that the same two amino acids might align by chance. The ratio is then converted to a logarithm and expressed as a log odds score, as for PAM. BLOSUM matrices are usually scaled in half-bit units. A score of zero indicates that the frequency with which a given two amino acids were found aligned in the database was as expected by chance, while a positive score indicates that the alignment was found more often than by chance, and negative score indicates that the alignment was found less often than by chance. | 1 | Biochemistry |
The Journal of Thermal Analysis and Calorimetry is a bimonthly peer-reviewed scientific journal published by Springer Science+Business Media on behalf of Akadémiai Kiadó. It was established in 1969 as the Journal of Thermal Analysis, obtaining its current title in 1998. The journal covers all aspects of calorimetry, thermal analysis, and experimental thermodynamics. The editor-in-chief is I.M. Szilágyi (Budapest University of Technology and Economics). | 7 | Physical Chemistry |
The movement of grain boundaries (HAGB) has implications for recrystallization and grain growth while subgrain boundary (LAGB) movement strongly influences recovery and the nucleation of recrystallization.
A boundary moves due to a pressure acting on it. It is generally assumed that the velocity is directly proportional to the pressure with the constant of proportionality being the mobility of the boundary. The mobility is strongly temperature dependent and often follows an Arrhenius type relationship:
The apparent activation energy (Q) may be related to the thermally activated atomistic processes that occur during boundary movement. However, there are several proposed mechanisms where the mobility will depend on the driving pressure and the assumed proportionality may break down.
It is generally accepted that the mobility of low-angle boundaries is much lower than that of high-angle boundaries. The following observations appear to hold true over a range of conditions:
* The mobility of low-angle boundaries is proportional to the pressure acting on it.
* The rate controlling process is that of bulk diffusion
* The boundary mobility increases with misorientation.
Since low-angle boundaries are composed of arrays of dislocations and their movement may be related to dislocation theory. The most likely mechanism, given the experimental data, is that of dislocation climb, rate limited by the diffusion of solute in the bulk.
The movement of high-angle boundaries occurs by the transfer of atoms between the neighbouring grains. The ease with which this can occur will depend on the structure of the boundary, itself dependent on the crystallography of the grains involved, impurity atoms and the temperature. It is possible that some form of diffusionless mechanism (akin to diffusionless phase transformations such as martensite) may operate in certain conditions. Some defects in the boundary, such as steps and ledges, may also offer alternative mechanisms for atomic transfer.
Since a high-angle boundary is imperfectly packed compared to the normal lattice it has some amount of free space or free volume where solute atoms may possess a lower energy. As a result, a boundary may be associated with a solute atmosphere that will retard its movement. Only at higher velocities will the boundary be able to break free of its atmosphere and resume normal motion.
Both low- and high-angle boundaries are retarded by the presence of particles via the so-called Zener pinning effect. This effect is often exploited in commercial alloys to minimise or prevent recrystallization or grain growth during heat-treatment. | 8 | Metallurgy |
*Group 3 elements scandium and yttrium form monoanions, [M(CO)] (M = Sc, Y) which are 20-electron carbonyls, as does the lanthanide lanthanum.
*Group 4 elements as dianions resemble neutral group 6 derivatives: [Ti(CO)].
*Group 5 elements as monoanions resemble again neutral group 6 derivatives: [V(CO)].
*Group 7 elements as monoanions resemble neutral group 8 derivatives: [M(CO)] (M = Mn, Tc, Re).
*Group 8 elements as dianaions resemble neutral group 10 derivatives: [[disodium tetracarbonylferrate|[M(CO)] (M = Fe, Ru, Os)]]. Condensed derivatives are also known.
*Group 9 elements as monoanions resemble neutral group 10 metal carbonyl. [Co(CO)] is the best studied member.
Large anionic clusters of nickel, palladium, and platinum are also well known. Many metal carbonyl anions can be protonated to give metal carbonyl hydrides. | 0 | Organic Chemistry |
The human asialoglycoprotein receptors composed of two units, H1 and H2. Each of these units have their N-terminus within the cytoplasm of a liver cell, and a carbohydrate recognition domain (CRD) on the extracellular side. The CRD functions to bind to asialoglycoproteins through a calcium ion-mediated interaction. In particular, the hydroxyl groups of the terminal sugars (usually galactose) of the asialoglycoprotein form hydrogen bonds with the CRD of the asialoglycoprotein receptor; proper positioning and facilitation of these hydrogen bonds is caused by the presence of Ca2+. | 1 | Biochemistry |
Perfluoroalkanes are very stable because of the strength of the carbon–fluorine bond, one of the strongest in organic chemistry.
Its strength is a result of the electronegativity of fluorine imparting partial ionic character through partial charges on the carbon and fluorine atoms, which shorten and strengthen the bond (compared to carbon-hydrogen bonds) through favorable covalent interactions. Additionally, multiple carbon–fluorine bonds increase the strength and stability of other nearby carbon–fluorine bonds on the same geminal carbon, as the carbon has a higher positive partial charge. Furthermore, multiple carbon–fluorine bonds also strengthen the "skeletal" carbon–carbon bonds from the inductive effect. Therefore, saturated fluorocarbons are more chemically and thermally stable than their corresponding hydrocarbon counterparts, and indeed any other organic compound. They are susceptible to attack by very strong reductants, e.g. Birch reduction and very specialized organometallic complexes.
Fluorocarbons are colorless and have high density, up to over twice that of water. They are not miscible with most organic solvents (e.g., ethanol, acetone, ethyl acetate, and chloroform), but are miscible with some hydrocarbons (e.g., hexane in some cases). They have very low solubility in water, and water has a very low solubility in them (on the order of 10 ppm). They have low refractive indices.
As the high electronegativity of fluorine reduces the polarizability of the atom, fluorocarbons are only weakly susceptible to the fleeting dipoles that form the basis of the London dispersion force. As a result, fluorocarbons have low intermolecular attractive forces and are lipophobic in addition to being hydrophobic and non-polar. Reflecting the weak intermolecular forces these compounds exhibit low viscosities when compared to liquids of similar boiling points, low surface tension and low heats of vaporization. The low attractive forces in fluorocarbon liquids make them compressible (low bulk modulus) and able to dissolve gas relatively well. Smaller fluorocarbons are extremely volatile. There are five perfluoroalkane gases: tetrafluoromethane (bp −128 °C), hexafluoroethane (bp −78.2 °C), octafluoropropane (bp −36.5 °C), perfluoro-n-butane (bp −2.2 °C) and perfluoro-iso-butane (bp −1 °C). Nearly all other fluoroalkanes are liquids; the most notable exception is perfluorocyclohexane, which sublimes at 51 °C. Fluorocarbons also have low surface energies and high dielectric strengths. | 2 | Environmental Chemistry |
In some cases proteins are attracted to surfaces by an excessive surface charge. When a surface in a fluid has a net charge, ions in the fluid will adsorb to the surface. Proteins also have charged surfaces due to charge amino acid residues on the surface of the protein. The surface and the protein are then attracted by Coulombic forces.
The attraction a protein feels from a charged surface () depends exponentially on the surface's charge, as described by the following formula:
Where
* is the potential felt by the protein
* is the actual potential of the surface
* is the distance from the protein to the surface, and
* is the Debye length.
A proteins surfaces potential is given by the number of charged amino acids it has and its isoelectric point, pI. | 1 | Biochemistry |
The 2nd group of anions consist of Cl, Br, I, NO and CO. The group reagent for Group 2 anion is concentrated sulfuric acid (HSO).
After addition of the acid, chlorides, bromides and iodides will form precipitates with silver nitrate. The precipitates are white, pale yellow, and yellow, respectively. The silver halides formed are completely soluble, partially soluble, or not soluble at all, respectively, in aqueous ammonia solution.
Chlorides are confirmed by the chromyl chloride test. When the salt is heated with KCrO and concentrated HSO, red vapours of chromyl chloride (CrOCl) are produced. Passing this gas through a solution of NaOH produces a yellow solution of NaCrO. The acidified solution of NaCrO gives a yellow precipitate with the addition of (CHCOO)Pb.
Bromides and iodides are confirmed by the layer test. A sodium carbonate extract is made from the solution containing bromide or iodide, and CHCl or carbon disulfide| is added to the solution, which separates into two layers: an orange colour in the or layer indicates the presence of Br, and a violet colour indicates the presence of I.
Nitrates give brown fumes with concentrated HSO due to formation of NO. This is intensified upon adding copper turnings. Nitrate ion is confirmed by adding an aqueous solution of the salt to FeSO and pouring concentrated HSO slowly along the sides of the test tube, which produces a brown ring around the walls of the tube, at the junction of the two liquids caused by the formation of .
Upon treatment with concentrated sulfuric acid, oxalates yield colourless CO and CO gases. These gases burn with a bluish flame and turn lime water milky. Oxalates also decolourise KMnO and give a white precipitate with CaCl. | 3 | Analytical Chemistry |
Linear dichroism (LD) or diattenuation is the difference between absorption of light polarized parallel and polarized perpendicular to an orientation axis. It is the property of a material whose transmittance depends on the orientation of linearly polarized light incident upon it. As a technique, it is primarily used to study the functionality and structure of molecules. LD measurements are based on the interaction between matter and light and thus are a form of electromagnetic spectroscopy.
This effect has been applied across the EM spectrum, where different wavelengths of light can probe a host of chemical systems. The predominant use of LD currently is in the study of bio-macromolecules (e.g. DNA) as well as synthetic polymers. | 7 | Physical Chemistry |
In the nomenclature of organic chemistry, a locant is a term to indicate the position of a functional group or substituent within a molecule. | 0 | Organic Chemistry |
Plasmid vectors are circular strands of DNA, found in virions, that are used in genetic engineering to integrate new genes into a host cell genome.
The small T intron is an intron, that is used in some plasmid vectors, in order to induce gene expression in mammalian cells. | 1 | Biochemistry |
It is a greenhouse gas with warming properties more than 7,000 times that of carbon dioxide over a 100-year period, and, as such, is one of the most potent greenhouse gasses ever discovered. Its concentration in the atmosphere is approximately 0.18 parts per trillion. The compound can persist in the atmosphere for up to 500 years. Sulfur hexafluoride, however, has a GWP of 23,900, which would make it much more powerful. | 2 | Environmental Chemistry |
Supramolecular chemistry has been used to demonstrate computation functions on a molecular scale. In many cases, photonic or chemical signals have been used in these components, but electrical interfacing of these units has also been shown by supramolecular signal transduction devices. Data storage has been accomplished by the use of molecular switches with photochromic and photoisomerizable units, by electrochromic and redox-switchable units, and even by molecular motion. Synthetic molecular logic gates have been demonstrated on a conceptual level. Even full-scale computations have been achieved by semi-synthetic DNA computers. | 6 | Supramolecular Chemistry |
In some chain-growth polymerizations there is also a chain transfer step, in which the growing polymer chain RM° takes an atom X from an inactive molecule XY, terminating the growth of the polymer chain: RM° + XY → RMX + Y°. The Y fragment ls a new active center which adds more monomer M to form a new growing chain YM°. This can happen in free radical polymerization for chains RM°, in ionic polymerization for chains RM or RM, or in coordination polymerization. In most cases chain transfer will generate a by-product and decrease the molar mass of the final polymer. | 7 | Physical Chemistry |
Ketones and imines are related functional groups, and effective technologies for the asymmetric hydrogenation of each are also closely related. Early examples are Noyori's ruthenium-chiral diphosphine-diamine system.
For carbonyl and imine substrates, end-on, η coordination can compete with η mode. For η-bound substrates, the hydrogen-accepting carbon is removed from the catalyst and resists hydrogenation.
Iridium/P,N ligand-based systems have been effective for some ketones and imines. For example, a consistent system for benzylic aryl imines uses the P,N ligand SIPHOX in conjunction with iridium(I) in a cationic complex to achieve asymmetric hydrogenation with ee >90%. An efficient catalyst for ketones, (turnover number (TON) up to 4,550,000 and ee up to 99.9%) is an iridium(I) system with a closely related tridentate ligand.
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The BINAP/diamine-Ru catalyst is effective for the asymmetric reduction of both functionalized and simple ketones, and BINAP/diamine-Ru catalyst can catalyze aromatic, heteroaromatic, and olefinic ketones enantioselectively. Better stereoselectivity is achieved when one substituent is larger than the other (see Flippin-Lodge angle). | 0 | Organic Chemistry |
In organic chemistry, an imide is a functional group consisting of two acyl groups bound to nitrogen. The compounds are structurally related to acid anhydrides, although imides are more resistant to hydrolysis. In terms of commercial applications, imides are best known as components of high-strength polymers, called polyimides. Inorganic imides are also known as solid state or gaseous compounds, and the imido group (=NH) can also act as a ligand. | 0 | Organic Chemistry |
In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee. This discovery led to the production of Sanka. This process was later discontinued. Benzene was historically used as a significant component in many consumer products such as liquid wrench, several paint strippers, rubber cements, spot removers, and other products. Manufacture of some of these benzene-containing formulations ceased in about 1950, although Liquid Wrench continued to contain significant amounts of benzene until the late 1970s. | 2 | Environmental Chemistry |
Typically, this method is used to determine water content levels, carbon levels, amount of organic matter levels, amount of volatile compounds. LOI is also used in the cement industry which operates the furnace in the 950 °C range (e.g. cement kilns), combustion engineers also use LOI but at temperatures lower than 950 °C range. | 3 | Analytical Chemistry |
Blood lactate levels are also maintained at steady state. At rest or low levels of exercise, the rate of lactate production in muscle cells and consumption in muscle or blood cells allows lactate to remain in the body at a certain steady state concentration. If a higher level of exercise is sustained, however, blood lactose levels will increase before becoming constant, indicating that a new steady state of elevated concentration has been reached. Maximal lactate steady state (MLSS) refers to the maximum constant concentration of lactase reached during sustained high-activity. | 7 | Physical Chemistry |
Bawendi was granted the Sloan Research Fellowship in 1994. He won the 1997 Nobel Signature Award for Graduate Education in Chemistry of American Chemical Society (ACS). In 2001, he received the Sackler Prize in Physical Chemistry of Advanced Materials. In 2006, he was awarded the Ernest Orlando Lawrence Award.
He was elected member of the American Association for the Advancement of Science in 2003, of the American Academy of Arts and Sciences in 2004, and of the National Academy of Sciences in 2007.
In 2010 during the National Meeting on March 23, 2010, Bawendi received the ACS Award in Colloid and Surface Chemistry. He also received the 2011 SEMI Award for North America for quantum dot research.
Bawendi was selected as a Clarivate Citation Laureate in Chemistry in 2020, jointly with Christopher B. Murray and Hyeon Taeghwan, "for synthesis of nanocrystals with precise attributes for a wide range of applications in physical, biological, and medical systems."
In 2023, Bawendi was awarded the Nobel Prize in Chemistry jointly with Louis E. Brus and Alexey Ekimov "for the discovery and synthesis of quantum dots". | 7 | Physical Chemistry |
Consequences of loss of pRb function is dependent on cell type and cell cycle status, as pRb's tumor suppressive role changes depending on the state and current identity of the cell.
In G0 quiescent stem cells, pRb is proposed to maintain G0 arrest although the mechanism remains largely unknown. Loss of pRb leads to exit from quiescence and an increase in the number of cells without loss of cell renewal capacity. In cycling progenitor cells, pRb plays a role at the G1, S, and G2 checkpoints and promotes differentiation. In differentiated cells, which make up the majority of cells in the body and are assumed to be in irreversible G0, pRb maintains both arrest and differentiation.
Loss of pRb therefore exhibits multiple different responses within different cells that ultimately all could result in cancer phenotypes. For cancer initiation, loss of pRb may induce cell cycle re-entry in both quiescent and post-mitotic differentiated cells through dedifferentiation. In cancer progression, loss of pRb decreases the differentiating potential of cycling cells, increases chromosomal instability, prevents induction of cellular senescence, promotes angiogenesis, and increases metastatic potential.
Although most cancers rely on glycolysis for energy production (Warburg effect), cancers due to pRb loss tend to upregulate oxidative phosphorylation. The increased oxidative phosphorylation can increase stemness, metastasis, and (when enough oxygen is available) cellular energy for anabolism.
In vivo, it is still not entirely clear how and which cell types cancer initiation occurs with solely loss of pRb, but it is clear that the pRb pathway is altered in large number of human cancers.[110] In mice, loss of pRb is sufficient to initiate tumors of the pituitary and thyroid glands, and mechanisms of initiation for these hyperplasia are currently being investigated. | 1 | Biochemistry |
Hattori developed analytical methods that demonstrated the high mobility of palladium as soluble neutral to anionic complexes in surface waters. This behavior allows the metal to disperse widely from its sources, and to become incorporated into plants and organic-rich soil. Her research findings have been presented at various industry-oriented workshops, including short courses associated with the International Platinum Conference in Oulu, Finland, and the Prospectors and Developers Association meeting in Toronto. In addition, her research provided a contrasting perspective to the previously assumed origin of metals in peat from the Hudson Bay Lowland. While it was previously assumed that the metals in peat originated from industrial activity far south of the northern region, she demonstrated that the compositions of ombrotrophic peat are strongly influenced by the underlying rocks, even those located as deep as 20 metres below the surface. This observation further highlighted that the composition of peat may serve as a useful indicator to locate concealed deposits, including kimberlites, which are host to diamonds.
Hattori also examined sturdy minerals that can be dispersed by streams and glaciers to evaluate their usefulness in finding mineral deposits. | 9 | Geochemistry |
Polychlorinated biphenyls have been discovered in organisms living in the Mariana trench in the Pacific Ocean. Levels were as high as 1,900 nanograms per gram of amphipod tissue in the organisms analyzed. | 2 | Environmental Chemistry |
* Computational analysis tools such as t-test, hierarchical clustering, self-organizing maps, regulatory network reconstruction, BLAST searches, pattern-motif discovery, protein structure prediction, structure-based protein annotation, etc.
* Visualization of gene expression (heatmaps, volcano plot), molecular interaction networks (through Cytoscape), protein sequence and protein structure data (e.g., MarkUs).
* Integration of gene and pathway annotation information from curated sources as well as through Gene Ontology enrichment analysis.
* Component integration through platform management of inputs and outputs. Among data that can be shared between components are expression datasets, interaction networks, sample and marker (gene) sets and sequences.
* Dataset history tracking - complete record of data sets used and input settings.
* Integration with 3rd party tools such as Genepattern, Cytoscape, and Genomespace.
Demonstrations of each feature described can be found at[http://wiki.c2b2.columbia.edu/workbench/index.php/Tutorials GeWorkbench-web Tutorials]. | 1 | Biochemistry |
* Phenol-Explorer ([http://www.phenol-explorer.eu phenol-explorer.eu]), a database dedicated to phenolics found in food by Augustin Scalbert, INRA Clermont-Ferrand, Unité de Nutrition Humaine (Human food unit)
* [http://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:33853 Phenols] at ChEBI (Chemical Entities of Biological Interest)
* [https://web.archive.org/web/20181002215232/https://www.ebi.ac.uk/chembldb/index.php ChEMBLdb], a database of bioactive drug-like small molecules by the European Bioinformatics Institute
* Foodb, a database of compounds found in food | 0 | Organic Chemistry |
From about the 14th century, water-power began to be applied to bloomeries, but fewer than ten such sites are suspected. | 8 | Metallurgy |
α,β-Unsaturated carbonyls are electrophilic at both the carbonyl carbon as well as the β-carbon. Depending on conditions, either site is attacked by nucleophiles. Additions to the alkene are called conjugate additions. One type of conjugate addition is the Michael addition, which is used commercially in the conversion of mesityl oxide into isophorone. Owing to their extended conjugation, α,β-unsaturated carbonyls are prone to polymerization. In terms of industrial scale, polymerization dominates the use of α,β-unsaturated carbonyls. Again because of their electrophilic character, the alkene portion of α,β-unsaturated carbonyls is good dienophiles in Diels–Alder reactions. They can be further activated by Lewis acids, which bind to the carbonyl oxygen. α,β-Unsaturated carbonyls are good ligands for low-valent metal complexes, examples being Fe(bda)(CO) and tris(dibenzylideneacetone)dipalladium(0).
α,β-Unsaturated carbonyls are readily hydrogenated. Hydrogenation can target the carbonyl or the alkene (conjugate reduction) selectively, or both functional groups.
Enones undergo the Nazarov cyclization reaction and in the Rauhut–Currier reaction (dimerization). | 0 | Organic Chemistry |
In analytical chemistry, a calibration curve, also known as a standard curve, is a general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration. A calibration curve is one approach to the problem of instrument calibration; other standard approaches may mix the standard into the unknown, giving an internal standard. The calibration curve is a plot of how the instrumental response, the so-called analytical signal, changes with the concentration of the analyte (the substance to be measured). | 1 | Biochemistry |
Triple-point cells are used in the calibration of thermometers. For exacting work, triple-point cells are typically filled with a highly pure chemical substance such as hydrogen, argon, mercury, or water (depending on the desired temperature). The purity of these substances can be such that only one part in a million is a contaminant, called "six nines" because it is 99.9999% pure. A specific isotopic composition (for water, VSMOW) is used because variations in isotopic composition cause small changes in the triple point. Triple-point cells are so effective at achieving highly precise, reproducible temperatures, that an international calibration standard for thermometers called ITS–90 relies upon triple-point cells of hydrogen, neon, oxygen, argon, mercury, and water for delineating six of its defined temperature points. | 7 | Physical Chemistry |
The surge of depolarization traveling from the axon hillock to the axon terminal is known as an action potential. Action potentials reach the axon terminal, where the action potential triggers the release of neurotransmitters from the neuron. The neurotransmitters that are released from the axon continue on to stimulate other cells such as other neurons or muscle cells. After an action potential travels down the axon of a neuron, the resting membrane potential of the axon must be restored before another action potential can travel the axon. This is known as the recovery period of the neuron, during which the neuron cannot transmit another action potential. | 7 | Physical Chemistry |
While the photothermal mechanism is universal, there could exist additional other mechanisms, superimposed on the photothermal mechanism, which may contribute significantly to the photoacoustic signal. These mechanisms are generally related to photophysical processes and photochemical reactions following light absorption: (1) change in the material balance of the sample or the gaseous phase around the sample; (2) change in the molecular organization, which results in molecular volume changes. Most prominent examples for these two kinds of mechanisms are in photosynthesis.
The first mechanism above is mostly conspicuous in a photosynthesizing plant leaf. There, the light induced oxygen evolution causes pressure changes in the air phase, resulting in a photoacoustic signal, which is comparable in magnitude to that caused by the photothermal mechanism. This mechanism was tentatively named "photobaric". The second mechanism shows up in photosynthetically active sub-cell complexes in suspension (e.g. photosynthetic reaction centers). There, the electric field which is formed in the reaction center, following the light induced electron transfer process, causes a micro electrostriction effect with a change in the molecular volume. This, in turn, induces a pressure wave which propagates in the macroscopic medium. Another case for this mechanism is Bacteriorhodopsin proton pump. Here the light induced change in the molecular volume is caused by conformational changes that occur in this protein following light absorption. | 7 | Physical Chemistry |
Although research is currently focusing on the bioengineering aspect of self-healing hydrogels, several non-medical applications do exist, including:
*pH meters
*Sealants for acid leaks | 7 | Physical Chemistry |
Light production in Photurius pennsylvanica (Photuris pennsylvanica) larvae occurs in the roughly 2,000 photocytes located in the heavily innervated light organ of the insect which is much simpler than that of the adult organism. The transparent photocytes of the larvae are clearly distinguishable from the opaque dorsal layer cells that cover them. Nervous and intracellular mechanisms contribute to light production in the photocytes. Nervous and intracellular mechanisms contribute to light production in the photocytes.It has been shown that fireflies can modify the amount of oxygen that travels through their trachea system to the light organ which plays a role in oxygen availability for light production. They do this by modifying the amount of fluid present within the trachea system. Because oxygen diffuses more slowly through water than in a gaseous form, this allows fireflies to effectively change the amount of oxygen reaching the photocytes. Spiracles can be opened and closed to control the amount of air that is able to pass through the tracheal system, but this control mechanism is only used as a response to a stressor. | 1 | Biochemistry |
The experimental archaeometallurgy of iron is more recent then that of copper in that for the most part was not widely studied until the mid-20th century. This can be attributed to the modern smelting of wrought iron still being produced as an industry up until 1900, when the last of the large-scale production shut down, along with the belief among researchers that many of the same techniques had been passed down since the inception of bloomery iron. A static technique simply was not the case as the technology used to make Roman Era iron showed the use of a technology that had long since disappeared. That being said research in iron has progressed beyond that of copper due to the greater amount of historic text and surviving remains of iron production.
Several experiments have taken place to reproduce bloomery iron. Clough presents an average example of experimental ironwork with the reproduction possible Roman bowl furnaces. Clough found the reproduction bowl furnaces to be inefficient by producing small amounts of poor quality iron, which, when compared to excavated findings of much larger better quality blooms of iron led to the conclusion that bowl furnaces were not used by the Romans. | 8 | Metallurgy |
Traces of many aldehydes are found in essential oils and often contribute to their favorable odours, e.g. cinnamaldehyde, cilantro, and vanillin. Possibly because of the high reactivity of the formyl group, aldehydes are not common in several of the natural building blocks: amino acids, nucleic acids, lipids. Most sugars, however, are derivatives of aldehydes. These aldoses exist as hemiacetals, a sort of masked form of the parent aldehyde. For example, in aqueous solution only a tiny fraction of glucose exists as the aldehyde. | 0 | Organic Chemistry |
To select zinc finger proteins (ZFPs) for protein engineering, methods adapted from the two-hybrid screening technique have been used with success. A ZFP is itself a DNA-binding protein used in the construction of custom DNA-binding domains that bind to a desired DNA sequence.
By using a selection gene with the desired target sequence included in the UAS, and randomising the relevant amino acid sequences to produce a ZFP library, cells that host a DNA-ZFP interaction with the required characteristics can be selected. Each ZFP typically recognises only 3–4 base pairs, so to prevent recognition of sites outside the UAS, the randomised ZFP is engineered into a scaffold consisting of another two ZFPs of constant sequence. The UAS is thus designed to include the target sequence of the constant scaffold in addition to the sequence for which a ZFP is selected.
A number of other DNA-binding domains may also be investigated using this system. | 1 | Biochemistry |
When white light passes through a polarizer, the extent of rotation of light depends on its wavelength. Short wavelengths are rotated more than longer wavelengths, per unit of distance. Because the wavelength of light determines its color, the variation of color with distance through the tube is observed. This dependence of specific rotation on wavelength is called optical rotatory dispersion.
In all materials the rotation varies with wavelength. The variation is caused by two quite different phenomena. The first accounts in most cases for the majority of the variation in rotation and should not strictly be termed rotatory dispersion. It depends on the fact that optical activity is actually circular birefringence. In other words, a substance which is optically active transmits right circularly polarized light with a different velocity from left circularly polarized light.
In addition to this pseudodispersion which depends on the material thickness, there is a true rotatory dispersion which depends on the variation with wavelength of the indices of refraction for right and left circularly polarized light.
For wavelengths that are absorbed by the optically active sample, the two circularly polarized components will be absorbed to differing extents. This unequal absorption is known as circular dichroism. Circular dichroism causes incident linearly polarized light to become elliptically polarized. The two phenomena are closely related, just as are ordinary absorption and dispersion. If the entire optical rotatory dispersion spectrum is known, the circular dichroism spectrum can be calculated, and vice versa. | 4 | Stereochemistry |
Tetraethylammonium (TEA) is a molecule found to be a weak agonist of the muscle‐type nicotinic receptor. Since receptor activation occurs as isolated bursts, it has been proposed that the receptors have a very low channel‐opening rate constant when bound to TEA. | 1 | Biochemistry |
Particle physicists have only observed or inferred left-chiral fermions and right-chiral antifermions engaging in the charged weak interaction. In the case of the weak interaction, which can in principle engage with both left- and right-chiral fermions, only two left-handed fermions interact. Interactions involving right-handed or opposite-handed fermions have not been shown to occur, implying that the universe has a preference for left-handed chirality. This preferential treatment of one chiral realization over another violates parity, as first noted by Chien Shiung Wu in her famous experiment known as the Wu experiment. This is a striking observation, since parity is a symmetry that holds for all other fundamental interactions.
Chirality for a Dirac fermion is defined through the operator , which has eigenvalues ±1; the eigenvalues sign is equal to the particles chirality: +1 for right-handed, −1 for left-handed. Any Dirac field can thus be projected into its left- or right-handed component by acting with the projection operators or on .
The coupling of the charged weak interaction to fermions is proportional to the first projection operator, which is responsible for this interaction's parity symmetry violation.
A common source of confusion is due to conflating the , chirality operator with the helicity operator. Since the helicity of massive particles is frame-dependent, it might seem that the same particle would interact with the weak force according to one frame of reference, but not another. The resolution to this paradox is that , for which helicity is not frame-dependent. By contrast, for massive particles, chirality is not the same as helicity, or, alternatively, helicity is not Lorentz invariant, so there is no frame dependence of the weak interaction: a particle that couples to the weak force in one frame does so in every frame.
A theory that is asymmetric with respect to chiralities is called a chiral theory, while a non-chiral (i.e., parity-symmetric) theory is sometimes called a vector theory. Many pieces of the Standard Model of physics are non-chiral, which is traceable to anomaly cancellation in chiral theories. Quantum chromodynamics is an example of a vector theory, since both chiralities of all quarks appear in the theory, and couple to gluons in the same way.
The electroweak theory, developed in the mid 20th century, is an example of a chiral theory. Originally, it assumed that neutrinos were massless, and assumed the existence of only left-handed neutrinos and right-handed antineutrinos. After the observation of neutrino oscillations, which imply that neutrinos are massive (like all other fermions) the revised theories of the electroweak interaction now include both right- and left-handed neutrinos. However, it is still a chiral theory, as it does not respect parity symmetry.
The exact nature of the neutrino is still unsettled and so the electroweak theories that have been proposed are somewhat different, but most accommodate the chirality of neutrinos in the same way as was already done for all other fermions. | 4 | Stereochemistry |
As the smelting stage is necessary to obtain alloys and shape the product, direct reduction processes are frequently combined with downstream smelting facilities.
Most pre-reduced iron ore is smelted in electric furnaces: in 2003, 49 of the 50 Mt produced went into electric furnaces. Process integration is generally highly advanced, to take advantage of the high temperature (over 600 °C) of the prereduct from the direct reduction reactor.
One idea is to carry out the entire reduction-melting process in the arc furnace installed downstream of the reduction plant. Several plasma processes operating above 1530 °C have been devised and sometimes tested. Furnaces can be either non-transferred arc (Plasmasmelt, Plasmared) or transferred arc (ELRED, EPP, SSP, The Toronto System, falling plasma film reactor). All these processes share the electric furnace's advantage of low investment cost, and its disadvantage of using an expensive energy source. In the case of direct reduction, this disadvantage is outweighed by the fact that a great deal of heat is required, both for the reduction process and because of the gangue to be melted.
An alternative to the electric furnace is to melt the pre-reduction with a fuel. The cupola furnace is ideally suited to this task, but since one reason for the existence of direct reduction processes is the non-use of coke, other melting furnaces have emerged. The COREX process, in operation since 1987, consists of a direct-reduction shaft reactor feeding a blast furnace crucible, in which the pre-reduced ore is brought to a liquid smelting state, consuming only coal. This process also produces a hot reducing gas, which can be valorized in a Midrex-type unit. An equivalent to COREX, based on the FINMET fluidized bed instead of the Midrex vessel, is the Korean FINEX process (a contraction of FINMET and COREX). Both processes are in industrial operation at several plants around the world.
Last but not least, a number of reduction-melting furnaces in the same reactor have been studied, but have not yet led to industrial development. For example, the ISARNA process and its derivative HISARNA (a combination of the ISARNA and HISMELT processes), is a cyclonic reactor that performs melting before reduction. These processes have culminated in an industrial demonstrator tested in the Netherlands since 2011. Similarly, Japanese steelmakers joined forces in the 1990s to develop the DIOS process which, like many reduction-fusion processes, is similar to oxygen converters. The TECNORED process, studied in Brazil, also performs reduction-melting in the same vessel, but is more akin to a blast furnace modified to adapt to any type of solid fuel. Of all the processes of this type that have been developed, a single ISASMELT-type industrial unit built in Australia, with a capacity of 0.8 Mt/year, operated from 2005 to 2008 before being dismantled and shipped to China, where it was restarted in 2016. | 8 | Metallurgy |
In organic chemistry, acetophenide is a functional group which is composed of the cyclic ketal of a diol with acetophenone. In pharmaceutical chemistry, it is present in algestone acetophenide (dihydroxyprogesterone acetophenide) and amcinafide (triamcinolone acetophenide). | 0 | Organic Chemistry |
Paiis can be used as quality control and marketing tools in commerce and as a quick and easy way to assess and/or map the activities of new photocatalytic materials in research. In addition, it has also been demonstrated that such inks can be used on highly coloured and black surfaces, provided the oxidised and/or reduced form of the redox dye is luminescent, and that they can be effectively used to demonstrate the activity of visible light photocatalysts. In light of the need for in situ testing of commercial photocatalyst materials, paii labels have been developed that can be applied simply in the field on any surface to be tested, in both a non-reusable and reusable form. One noteworthy application of paiis is where a uniform film has been applied to a photocatalytic surface, and the variation in the rate of colour change across the surface has been monitored and used to generate a surface map of the photoactivity. By this method the uniformity of the surface activity may be investigated, and any "hotspots" of photoactivity identified. By varying the composition of a semiconductor photocatalyst surface across the surface itself, a paii photoactivity surface map may be used to determine the optimal composition which yields the greatest photocatalytic response.
The rapid colour change of paiis makes them suitable for such applications as:
* Quality control (in laboratory, factory and on site);
* Marketing;
* Counterfeit identification;
* Research material assessment. | 5 | Photochemistry |
In chemistry, isomorphism has meanings both at the level of crystallography and at a molecular level. In crystallography, crystals are isomorphous if they have identical symmetry and if the atomic positions can be described with a set of parameters (unit cell dimensions and fractional coordinates) whose numerical values differ only slightly.
Molecules are isomorphous if they have similar shapes. The coordination complexes tris(acetylacetonato)iron (Fe(acac)) and tris(acetylacetonato)aluminium (Al(acac)) are isomorphous. These compounds, both of D symmetry have very similar shapes, as determined by bond lengths and bond angles. Isomorphous compounds give rise to isomorphous crystals and form solid solutions. Historically, crystal shape was defined by measuring the angles between crystal faces with a goniometer. Whereas crystals of Fe(acac) are deep red and crystals of Al(acac) are colorless, a solid solution of the two, i.e. FeAl(acac) will be deep or pale pink depending on the Fe/Al ratio, x.
Double sulfates, such as Tutton's salt, with the generic formula MM(SO).6HO, where M is an alkali metal and M is a divalent ion of Mg, Mn, Fe, Co, Ni, Cu or Zn, form a series of isomorphous compounds which were important in the nineteenth century in establishing the correct atomic weights of the transition elements. Alums, such as KAl(SO).12HO, are another series of isomorphous compounds, though there are three series of alums with similar external structures, but slightly different internal structures. Many spinels are also isomorphous.
In order to form isomorphous crystals two substances must have the same chemical formulation (i.e., atoms in the same ratio), they must contain atoms which have corresponding chemical properties and the sizes of corresponding atoms should be similar. These requirements ensure that the forces within and between molecules and ions are approximately similar and result in crystals that have the same internal structure. Even though the space group is the same, the unit cell dimensions will be slightly different because of the different sizes of the atoms involved. | 3 | Analytical Chemistry |
Air is liquefied by the Linde process, in which air is alternately compressed, cooled, and expanded, each expansion results in a considerable reduction in temperature. With the lower temperature the molecules move more slowly and occupy less space, so the air changes phase to become liquid. | 7 | Physical Chemistry |
Through negative feedback inhibition, the end-products UTP and UDP prevent the enzyme CAD from catalyzing the reaction in animals. Conversely, PRPP and ATP act as positive effectors that enhance the enzyme's activity. | 1 | Biochemistry |
The TIC translocon, or translocon on the inner chloroplast membrane translocon is another protein complex that imports proteins across the inner chloroplast envelope. Chloroplast polypeptide chains probably often travel through the two complexes at the same time, but the TIC complex can also retrieve preproteins lost in the intermembrane space.
Like the TOC translocon, the TIC translocon has a large core complex surrounded by some loosely associated peripheral proteins like Tic110, Tic40, and Tic21.
The core complex weighs about one million daltons and contains Tic214, Tic100, Tic56, and Tic20 I, possibly three of each. | 5 | Photochemistry |
Born on 13 June 1923, Corbett was the son of Walter Corbett and Margaret Whitehead Corbett (née Robertson). He studied at the University of Otago, graduating Master of Science with first-class honours in chemistry in 1945. Corbett later undertook doctoral studies at the University of Cambridge under Alexander Todd on the structures of some of the metabolites—puberulic acid, puberulonic acid, and stipitatic acid—of Penicillium species. He showed that they contain the tropolone skeleton, and his PhD thesis, titled The structure of certain antibiotics was completed in 1950.
In 1949, Corbett married Enid Mary Carter in Cambridge, England, and they went on to have two children. | 0 | Organic Chemistry |
Rydberg series describe the energy levels associated with partially removing an electron from the ionic core. Each Rydberg series converges on an ionization energy threshold associated with a particular ionic core configuration. These quantized Rydberg energy levels can be associated with the quasiclassical Bohr atomic picture. The closer you get to the ionization threshold energy, the higher the principal quantum number, and the smaller the energy difference between "near threshold Rydberg states." As the electron is promoted to higher energy levels, the spatial excursion of the electron from the ionic core increases and the system is more like the Bohr quasiclassical picture. | 7 | Physical Chemistry |
Under Japanese law, levetiracetam and other racetams cannot be brought into the country except for personal use by a traveler for whom it has been prescribed. Travelers who plan to bring more than a month's worth must apply for an import certificate, known as a . | 4 | Stereochemistry |
Two mechanisms of fractionation occur that alter sulfur stable isotope ratios: kinetic effects, especially due to the metabolism of sulfate-reducing bacteria, and isotope exchange reactions that occur between sulfide phases based on temperature. With VCDT as the reference standard, natural δS value variations have been recorded between -72‰ and +147‰.
The presence of sulfate-reducing bacteria, which reduce sulfate () to hydrogen sulfide (HS), has played a significant role in the oceanic δS value throughout the earth's history. Sulfate-reducing bacteria metabolize S more readily than S, resulting in an increase in the value of the δS in the remaining sulfate in the seawater. Archean pyrite found in barite in the Warrawoona Group, Western Australia, with sulfur fractionations as great as 21.1‰ hint at the presence of sulfate-reducers as early as .
It is now better known that the degree of isotope fractionation during microbial sulfate reduction depends on the cell-specific sulfate reduction rate of the sulfate-reducing microorganism. The relative extent of sulfur isotope fractionating activities, including sulfate reduction, sulfide reoxidation and disproportionation, determines the isotopic compositions of the minerals or fluid measured. Other than microbial activities and environmental conditions, isotopic compositions also change due to diffusion, accumulation and mixing after burial.
The δS value, recorded by sulfate in marine evaporites, can be used to chart the sulfur cycle throughout earths history. The Great Oxygenation Event around altered the sulfur cycle radically, as increased atmospheric oxygen permitted an increase in the mechanisms that could fractionate sulfur isotopes, leading to an increase in the δS value from ~0‰ pre-oxygenation. Approximately , the δS values in seawater sulfates began to vary more and those in sedimentary sulfates grew more negative. Researchers have interpreted this excursion as indicative of an increase in water column oxygenation with continued periods of anoxia in the deepest waters. Modern seawater sulfate δS values are consistently 21.0 ± 0.2‰ across the worlds oceans, while sedimentary sulfides vary widely. Seawater sulfate δS and δO values exhibit similar trends not seen in sedimentary sulfide minerals. | 9 | Geochemistry |
Coupling of RNA polymerase II (pol II) transcription can influence processing reactions in three ways.
# localization
#* positions mRNA processing factors at the elongation complex, which raises their local concentration in the vicinity of the nascent transcript
# kinetic coupling
#* the rate of transcript can have profound effects on RNA folding and the assembly of RNA-protein complexes
# allosteric
#* contact between the pol II elongation complex and mRNA processing factors can allosterically inhibit or activate mRNA processing factors | 1 | Biochemistry |
By 1964, the ETH group had accomplished the first corrin model synthesis, and also the preparation of a ring-B precursor as part of a construction of the B molecule itself. Since independent progress of the two groups towards their long-term objective was so clearly complementary, Woodward and Eschenmoser decided in 1965 to join forces and to pursue from then on the project of a B synthesis collaboratively, planning to utilize the ligand construction (ring coupling of components) strategy of the ETH model system.
By 1966, the ETH group had succeeded in synthesizing the B-C-component ("eastern half") by coupling their ring-B precursor to the ring-C precursor. The latter had also been prepared at Harvard from (−)-camphor by a strategy conceived and used earlier by A. Pelter and J. W. Cornforth in 1961. At ETH, the synthesis of the B-C-component involved the implementation of the C,C-condensation reaction via sulfide contraction. This newly developed method turned out to provide a general solution to the problem of constructing the characteristic structural elements of the corrin chromophore, the vinylogous amidine systems bridging the four peripheral rings.
Early in 1967, the Harvard group accomplished the synthesis of the model A-D-component, with the f-side chain undifferentiated, bearing a methyl ester function like all other side chains. From then on, the two groups systematically exchanged samples of their respective halves of the corrinoid target structure. By 1970, they had collaboratively connected Harvards undifferentiated A-D-component with ETHs B-C-component, producing dicyano-cobalt(III)-5,15-bisnor-heptamethyl-cobyrinate 1 (fig. 4). The ETH group identified this totally synthetic corrinoid intermediate by direct comparison with a sample produced from natural vitamin B.
In this advanced model study, reaction conditions for the demanding processes of the C/D-coupling and the A/B-cyclization via sulfide contraction method were established. Those for the C/D-coupling were successfully explored in both laboratories, the superior conditions were those found at Harvard, while the method for the A/B-ring closure via an intramolecular version of the sulfide contraction was developed at ETH. Later it was shown at Harvard that the A/B-ring closure could also be achieved by -iminoester/enamine condensation.
By early 1971, the Harvard group had accomplished the synthesis of the final A-D-component, containing the f-side chain carboxyl function at ring D differentiated from all the carboxyl functions as a nitrile group (as shown in 2 in fig. 4; see also fig. 3). The A/D-part of the B structure incorporates the constitutionally and configurationally most intricate part of the vitamin molecule; its synthesis is regarded as the apotheosis of the Woodwardian art in natural product total synthesis. | 0 | Organic Chemistry |
Regioselective and stereoselective formation of carbon-carbon bonds adjacent to carbonyl group is an important procedure in organic chemistry. Alkylation reaction of enolates has been the main focus of the field. Both A. G. Myers and D. A. Evans developed asymmetric alkylation reactions for enolates.
The apparent shortcoming for enolate alkylation reactions is over-alkylation, even if the amount of base added for enolization as well as the reaction temperature are carefully controlled. The ketene formation during the deprotonation process for substrates possessing Evans' oxazolidinone is also a main side reaction for the related alkylation reactions. Development in the field of enamine chemistry and the utilization of imine derivatives of enolates managed to provide an alternative for enolate alkylation reactions.
In 1963, G. Stork reported the first enamine alkylation reaction for ketones - Stork enamine alkylation reaction.
In 1976, Meyers reported the first alkylation reaction of metallated azaenolates of hydrazones with an acyclic amino acid-based auxiliary. Compared with the free carbonyl compounds and the chiral enamine species reported previously, the hydrazones exhibit higher reactivity, regioselectivity and stereoselectivity.
The combination of cyclic amino acid derivatives (SAMP and RAMP) and the powerful hydrazone techniques were pioneered by E. J. Corey and D. Enders in 1976, and were independently developed by D. Enders later. Both SAMP and RAMP are synthesized from amino acids. The detailed synthesis of these two auxiliaries are shown below. | 0 | Organic Chemistry |
Petroleum, or evidence of its immediate occurrence, can be found on the surface of the Earth. Oil seeps can be found near a fault zone, where the movement of Earth's crust can expose petroleum source rock, and thus the crude oil itself. They can also be found on the ocean floor, and can be found using satellite imaging. | 9 | Geochemistry |
Phosphatidylethanols (PEth) are a group of phospholipids formed only in the presence of ethanol via the action of phospholipase D (PLD). It accumulates in blood and is removed slowly, making it a useful biomarker for alcohol consumption. PEth is also thought to contribute to the symptoms of alcohol intoxication. | 1 | Biochemistry |
*Uranium
*Enriched uranium
*Nuclear weapon design
*The technology of mining and metallurgy [http://www.unu.edu/unupress/unupbooks/uu29me/uu29me08.htm], retrieved 7 October 2005. | 8 | Metallurgy |
In a chain termination step, the active center disappears, resulting in the termination of chain propagation. This is different from chain transfer in which the active center only shifts to another molecule but does not disappear.
For radical polymerization, termination involves a reaction of two growing polymer chains to eliminate the unpaired electrons of both chains. There are two possibilities.
1. Recombination is the reaction of the unpaired electrons of two chains to form a covalent bond between them. The product is a single polymer molecule with the combined length of the two reactant chains:
* RM° + RM° → P
2. Disproportionation is the transfer of a hydrogen atom from one chain to the other, so that the two product chain molecules are unchanged in length but are no longer free radicals:
* RM° + RM° → P + P
Initiation, propagation and termination steps also occur in chain reactions of smaller molecules. This is not true of the chain transfer and branching steps considered next. | 7 | Physical Chemistry |
Zeaxanthin 7,8-dioxygenase - Zfp14 zinc finger protein - Zfp28 zinc finger protein - zinc finger - Zinc finger and scan domain containing 30 - Zinc finger containing ubiquitin peptidase 1 - Zinc finger nfx1-type containing 1 - Zinc finger protein 93 - Zinc finger protein 101 - Zinc finger protein 175 - Zinc finger protein 222 - Zinc finger protein 230 - Zinc finger protein 280b - Zinc finger protein 296 - Zinc finger protein 414 - Zinc finger protein 433 - Zinc finger protein 490 - Zinc finger protein 530 - Zinc finger protein 556 - Zinc finger protein 562 - Zinc finger protein 574 - Zinc finger protein 577 - Zinc finger protein 585b - Zinc finger protein 586 - Zinc finger protein 730 - Zinc finger protein 770 - Zinc finger protein 773 - Zinc finger protein 780a - Zinc finger protein 780b - Zinc finger protein 791 - Zinc finger protein 836 - Zinc finger protein 846 | 1 | Biochemistry |
As stated above, BGIT can be used to calculate heats of formation, which are important in understanding the strengths of bonds and entire molecules. Furthermore, the method can be used to quickly estimate whether a reaction is endothermic or exothermic. These values are for gas-phase thermodynamics and typically at 298 K. Benson and coworkers have continued collecting data since their 1958 publication and have since published even more group increments, including strained rings, radicals, halogens, and more. Even though BGIT was introduced in 1958 and would seem to be antiquated in the modern age of advanced computing, the theory still finds practical applications. In a 2006 article, Gronert states: "Aside from molecular mechanics computer packages, the best known additivity scheme is Benson's." Fishtik and Datta also give credit to BGIT: "Despite their empirical character, GA methods continue to remain a powerful and relatively accurate technique for the estimation of thermodynamic properties of the chemical species, even in the era of supercomputers"
When calculating the heat of formation, all the atoms in the molecule must be accounted for (hydrogen atoms are not included as specific groups). The figure above displays a simple application for predicting the standard enthalpy of isobutylbenzene. First, it is usually very helpful to start by numbering the atoms. It is much easier then to list the specific groups along with the corresponding number from the table. Each individual atom is accounted for, where C−(H) accounts for one benzene carbon bound to a hydrogen atom. This would be multiplied by five, since there are five C−(H) atoms. The C−(C) molecule further accounts for the other benzene carbon attached to the butyl group. The C−(C)(C)(H)2 accounts for the carbon linked to the benzene group on the butyl moiety. The 2 carbon of the butyl group would be C−(C)(H) because it is a tertiary carbon (connecting to three other carbon atoms). The final calculation comes from the CH groups connected to the 2 carbon; C−(C)(H). The total calculations add to −5.15 kcal/mol (−21.6 kJ/mol), which is identical to the experimental value, which can be found in the National Institute of Standards and Technology Chemistry WebBook
Another example from the literature is when the BGIT was used to corroborate experimental evidence of the enthalpy of formation of benzo[k]fluoranthene. The experimental value was determined to be 296.6 kJ/mol with a standard deviation of 6.4 kJ/mol. This is within the error of the BGIT and is in good agreement with the calculated value. Notice that the carbons at the fused rings are treated differently than regular benzene carbons. Not only can the BGIT be used to confirm experimental values, but can also to confirm theoretical values.
BGIT also can be used for comparing the thermodynamics of simplified hydrogenation reactions for alkene (2-methyl-1-butene) and ketone(2-butanone). This is a thermodynamic argument, and kinetics are ignored. As determined by the enthalpies below the corresponding molecules, the enthalpy of reaction for 2-methyl-1-butene going to 2-methyl-butane is −29.07 kcal/mol, which is in great agreement with the value calculated from NIST, −28.31 kcal/mol. For 2-butanone going to 2-butanol, enthalpy of reaction is −13.75 kcal/mol, which again is in excellent agreement with −14.02 kcal/mol. While both reactions are thermodynamically favored, the alkene will be far more exothermic than the corresponding ketone. | 7 | Physical Chemistry |
Hyrax middens contain well-preserved micro plant material including pollen, which is sealed in middens by hyraceum, protecting it from microbial activity and decay. The earliest study of fossil pollen from a hyrax midden was undertaken in the late 1950s by Pons and Quézel. in the Hoggar Massif of Algeria, whereas the first palynological analyses of southern African middens were undertaken during the late 1980s and early 1990s, and demonstrated that hyrax middens are very useful as pollen and microfossil traps. Subsequently, hyrax middens have been become an important archive for fossil pollen analysis in South Africa and Namibia. Studies of fossil pollen in hyrax middens have also been undertaken in Jordan Ethiopia, Yemen and Oman | 9 | Geochemistry |
A common route to primary amidines is the Pinner reaction. Reaction of the nitrile with alcohol in the presence of acid gives an iminoether. Treatment of the resulting compound with ammonia then completes the conversion to the amidine. Instead of using a Bronsted acid, Lewis acids such as aluminium trichloride promote the direct amination of nitriles. They are also generated by amination of an imidoyl chloride.
They are also prepared by the addition of organolithium reagents to diimines, followed by protonation or alkylation.
Dimethylformamide acetal reacts with primary amines to give amidines:
:MeNC(H)(OMe) + RNH → MeNC=NHR + 2 MeOH | 0 | Organic Chemistry |
Two formulations of different dispersing agents for oil spills, Dispersit and Omni-Clean, are shown below. A key difference between the two is that Omni-Clean uses ionic surfactants and Dispersit uses entirely non-ionic surfactants. Omni-Clean was formulated for little or no toxicity toward the environment. Dispersit, however, was designed as a competitor with Corexit. Dispersit contains non-ionic surfactants, which permit both primarily oil-soluble and primarily water-soluble surfactants. The partitioning of surfactants between the phases allows for effective dispersion. | 2 | Environmental Chemistry |
Crystallography is used by materials scientists to characterize different materials. In single crystals, the effects of the crystalline arrangement of atoms is often easy to see macroscopically because the natural shapes of crystals reflect the atomic structure. In addition, physical properties are often controlled by crystalline defects. The understanding of crystal structures is an important prerequisite for understanding crystallographic defects. Most materials do not occur as a single crystal, but are poly-crystalline in nature (they exist as an aggregate of small crystals with different orientations). As such, powder diffraction techniques, which take diffraction patterns of samples with a large number of crystals, play an important role in structural determination.
Other physical properties are also linked to crystallography. For example, the minerals in clay form small, flat, platelike structures. Clay can be easily deformed because the platelike particles can slip along each other in the plane of the plates, yet remain strongly connected in the direction perpendicular to the plates. Such mechanisms can be studied by crystallographic texture measurements.
In another example, iron transforms from a body-centered cubic (bcc) structure called ferrite to a face-centered cubic (fcc) structure called austenite when it is heated. The fcc structure is a close-packed structure unlike the bcc structure; thus the volume of the iron decreases when this transformation occurs.
Crystallography is useful in phase identification. When manufacturing or using a material, it is generally desirable to know what compounds and what phases are present in the material, as their composition, structure and proportions will influence the material's properties. Each phase has a characteristic arrangement of atoms. X-ray or neutron diffraction can be used to identify which structures are present in the material, and thus which compounds are present. Crystallography covers the enumeration of the symmetry patterns which can be formed by atoms in a crystal and for this reason is related to group theory. | 3 | Analytical Chemistry |
The contact angle is defined as the angle made by the intersection of the liquid/solid interface and the liquid/air interface. It can be alternately described as the angle between solid samples surface and the tangent of the droplets ovate shape at the edge of the droplet. A high contact angle indicates a low solid surface energy or chemical affinity. This is also referred to as a low degree of wetting. A low contact angle indicates a high solid surface energy or chemical affinity, and a high or sometimes complete degree of wetting. For example, a contact angle of zero degrees will occur when the droplet has turned into a flat puddle; this is called complete wetting. | 7 | Physical Chemistry |
Taking results gathered largely from ‘real world’ exposure sites, automotive companies, led originally by the Japanese automobile industry, developed their own Cyclic Corrosion Tests. These have evolved in different ways for different vehicle manufacturers, and such tests still remain largely industry specific, with no truly international CCT standard. However, they all generally require most of the following conditions to be created, in a repeating sequence or ‘cycle’, though not necessarily in the following order:
• A salt spray ‘pollution’ phase. This may be similar to the traditional salt spray test although in some cases direct impingement by the salt solution on the test specimens, or even complete immersion in salt water, is required. However, this ‘pollution’ phase is generally shorter in duration than a traditional salt spray test.
• An air drying phase. Depending on the test, this may be conducted at ambient temperature, or at an elevated temperature, with or without control over the relative humidity and usually by introducing a continuous supply of relatively fresh air around the test samples at the same time. It is generally required that the samples under test should be visibly ‘dry’ at the end of this test phase.
• A condensation humidity ‘wetting’ phase. This is usually conducted at an elevated temperature and generally a high humidity of 95-100%RH. The purpose of this phase is to promote the formation of condensation on the surfaces of the samples under test.
• A controlled humidity/humidity cycling phase. This requires the tests samples to be exposed to a controlled temperature and controlled humidity climate, which can either be constant or cycling between different levels. When cycling between different levels, the rate of change may also be specified.
The above list is not exhaustive, since some automotive companies may also require other climates to be created in sequence as well, for example; sub-zero refrigeration, but it does list the most common requirements. | 8 | Metallurgy |
A classic example of vinylogy is the relatively high acidity of the γ-hydrogen in . The acidity of the terminal methyl group is similar to that for the methyl ketone .
Vinylogous reactions also include conjugate additions, where a nucleophile reacts at the vinyl terminus, akin to the addition of the nucleophile to the carbonyl of the methyl ketone. In a vinylogous variation of the aldol reaction, an electrophile is attacked by a nucleophilic vinylogous enolate (see first and following image). The vinylogous enolate reacts at the terminal position of the double bond system (the γ-carbon), rather than the α-carbon immediately adjacent to the carbonyl, as would a simple enolate. Allylic electrophiles often react by vinylogous attack of a nucleophile rather than direct addition.
A further example of vinylogous reactivity: ascorbic acid (Vitamin C) behaves as a vinylogous carboxylic acid by involvement of its carbonyl moiety, a vinyl group within the ring, and the lone pair on the hydroxyl group acting as the conjugated system. Acidity of the hydroxyl proton at the terminus of the vinyl group in ascorbic acid is more comparable to a typical carboxylic acid than an alcohol because two major resonance structures stabilize the negative charge on the conjugate base of ascorbic acid (center and right structures in last image), analogous to the two resonance structures that stabilize the negative charge on the anion that results from removal of a proton from a simple carboxylic acid (cf. first image). Analogously, sorbic acid derivatives, extended by another "vinyl" moiety show vinylogous behaviour as well.
<br> | 7 | Physical Chemistry |
NaK has been used as the coolant in experimental fast neutron nuclear reactors. Unlike commercial plants, these are frequently shut down and defuelled. Use of lead or pure sodium, the other materials used in practical reactors, would require continual heating to maintain the coolant as a liquid. Use of NaK overcomes this. The Dounreay Fast Reactor is an example.
The Soviet RORSAT radar satellites were powered by a BES-5 reactor, which was cooled with NaK. In addition to the wide liquid temperature range, NaK has a very low vapor pressure, which is important in the vacuum of space.
An unintended consequence of the usage as a coolant on orbiting satellites has been the creation of additional space debris. NaK coolant has leaked from a number of satellites, including Kosmos 1818 and Kosmos 1867. The coolant self-forms into droplets of sodium–potassium of up to several centimeters in size. These objects are space debris.
The Danamics LMX Superleggera CPU cooler uses NaK to transport heat from the CPU to its cooling fins. | 8 | Metallurgy |
Like mitochondria, chloroplasts are usually inherited from a single parent. Biparental chloroplast inheritance—where plastid genes are inherited from both parent plants—occurs in very low levels in some flowering plants.
Many mechanisms prevent biparental chloroplast DNA inheritance, including selective destruction of chloroplasts or their genes within the gamete or zygote, and chloroplasts from one parent being excluded from the embryo. Parental chloroplasts can be sorted so that only one type is present in each offspring.
Gymnosperms, such as pine trees, mostly pass on chloroplasts paternally, while flowering plants often inherit chloroplasts maternally. Flowering plants were once thought to only inherit chloroplasts maternally. However, there are now many documented cases of angiosperms inheriting chloroplasts paternally.
Angiosperms, which pass on chloroplasts maternally, have many ways to prevent paternal inheritance. Most of them produce sperm cells that do not contain any plastids. There are many other documented mechanisms that prevent paternal inheritance in these flowering plants, such as different rates of chloroplast replication within the embryo.
Among angiosperms, paternal chloroplast inheritance is observed more often in hybrids than in offspring from parents of the same species. This suggests that incompatible hybrid genes might interfere with the mechanisms that prevent paternal inheritance. | 5 | Photochemistry |
In addition to monitoring oil contamination and wear metals, modern usage of OA includes the analysis of the additives in oils to determine if an extended drain interval may be used. Maintenance costs can be reduced using OA to determine the remaining useful life of additives in the oil. By comparing the OA results of new and used oil, a tribologist can determine when an oil must be replaced. Careful analysis might even allow the oil to be "sweetened" to its original additive levels by either adding fresh oil or replenishing additives that were depleted.
Oil analysis professionals and analysts can get certified in compliance with ISO standards by passing exams administered by the International Council for Machinery Lubrication (ICML).
For purposes of Oil Analysis Program (OAP) trend analysis, replacement, replenishment or drain and flush of lubricating fluids in excess of half an engine’s oil capacity (2.5 gallons or more) will be considered an Oil Change and the engine will be placed in code Charlie (C) for three flights to establish a new working trend. Oil-Wetted Maintenance (OWM) is any replacement of engine components within an oil-lubricated system (bearings, gearbox, pumps, etc.). OWM actions shall be documented on DD Form 2026 and submitted to OAP lab for update of Oil Analysis database.
(a) Special Samples can be requested by the laboratory whenever they feel its necessary.
(b) Whenever directed by the unit maintenance activity to investigate suspected deficiencies.
The NDI/JOAP laboratory will set the standards and intervals of oil analysis.
A typical predictive maintenance technique is ferrography, which analyses iron in oil. | 3 | Analytical Chemistry |
One main function of plasma and cell membranes is to maintain asymmetric concentrations of inorganic ions in order to maintain an ionic steady state different from electrochemical equilibrium. In other words, there is a differential distribution of ions on either side of the cell membrane - that is, the amount of ions on either side is not equal and therefore a charge separation exists. However, ions move across the cell membrane such that a constant resting membrane potential is achieved; this is ionic steady state. In the pump-leak model of cellular ion homeostasis, energy is utilized to actively transport ions against their electrochemical gradient. The maintenance of this steady state gradient, in turn, is used to do electrical and chemical work, when it is dissipated though the passive movement of ions across the membrane.
In cardiac muscle, ATP is used to actively transport sodium ions out of the cell through a membrane ATPase. Electrical excitation of the cell results in an influx of sodium ions into the cell, temporarily depolarizing the cell. To restore the steady state electrochemical gradient, ATPase removes sodium ions and restores potassium ions in the cell. When an elevated heart rate is sustained, causing more depolarizations, sodium levels in the cell increase until becoming constant, indicating that a new steady state has been reached. | 7 | Physical Chemistry |
Recent advances in ultraviolet nanophotonics has led to development of single molecule study on label-free protein by exciting them with deep ultraviolet light and studying the dynamic processes. | 7 | Physical Chemistry |
CLIPZ is a database of post-transcriptional regulatory elements (RNA-binding proteins) built from cross-linking and immunoprecipitation data. | 1 | Biochemistry |
* An exergonic reaction is a spontaneous chemical reaction that releases energy. It is thermodynamically favored, indexed by a negative value of ΔG (Gibbs free energy). Over the course of a reaction, energy needs to be put in, and this activation energy drives the reactants from a stable state to a highly energetically unstable transition state to a more stable state that is lower in energy (see: reaction coordinate). The reactants are usually complex molecules that are broken into simpler products. The entire reaction is usually catabolic. The release of energy (called Gibbs free energy) is negative (i.e. −ΔG) because energy is released from the reactants to the products.
* An endergonic reaction is an anabolic chemical reaction that consumes energy. It is the opposite of an exergonic reaction. It has a positive ΔG because it takes more energy to break the bonds of the reactant than the energy of the products offer, i.e. the products have weaker bonds than the reactants. Thus, endergonic reactions are thermodynamically unfavorable. Additionally, endergonic reactions are usually anabolic.
The free energy (ΔG) gained or lost in a reaction can be calculated as follows: ΔG = ΔH − TΔS
where ∆G = Gibbs free energy, ∆H = enthalpy, T = temperature (in kelvins), and ∆S = entropy. | 1 | Biochemistry |
Nested polymerase chain reaction involves two sets of primers, used in two successive runs of polymerase chain reaction, the second set intended to amplify a secondary target within the first run product. This allows amplification for a low number of runs in the first round, limiting non-specific products. The second nested primer set should only amplify the intended product from the first round of amplification and not non-specific product. This allows running more total cycles while minimizing non-specific products. This is useful for rare templates or PCR with high background. | 1 | Biochemistry |
Sewage treatment plants, such as Blue Plains in Washington, D.C., USA, have adopted thermal hydrolysis of sewage sludge in order to produce commercially valuable products (such as electricity and high quality biosolid fertilizers) out of the wastewater. The full-scale commercial application of thermal hydrolysis enables the plant to utilize the solids portion of the wastewater to make power and fine fertilizer directly from sewage waste. | 7 | Physical Chemistry |
If the incoming photon is polarized, the scattered photon is no longer isotropic with respect to the azimuthal angle. For a linearly polarized photon scattered with a free electron at rest, the differential cross section is instead given by:
where is the azimuthal scattering angle. Note that the unpolarized differential cross section can be obtained by averaging over . | 7 | Physical Chemistry |
Full spectral imaging (FSI) is a form of imaging spectroscopy and is the successor to hyperspectral imaging. Full spectral imaging was developed to improve the capabilities of remote sensing including Earth remote sensing. | 7 | Physical Chemistry |
Ultrasonic cure monitoring methods are based on the relationships between changes in the characteristics of propagating ultrasound and the real-time mechanical properties of a component, by measuring:
*ultrasonic time of flight, both in through-transmission and pulse-echo modes;
*natural frequency using impact excitation and laser-induced surface acoustic wave velocity measurement. | 7 | Physical Chemistry |
Buoyant density centrifugation (also isopycnic centrifugation or equilibrium density-gradient centrifugation) uses the concept of buoyancy to separate molecules in solution by their differences in density. | 3 | Analytical Chemistry |
The human body needs iron for oxygen transport. Oxygen (O) is required for the functioning and survival of nearly all cell types. Oxygen is transported from the lungs to the rest of the body bound to the heme group of hemoglobin in red blood cells. In muscles cells, iron binds oxygen to myoglobin, which regulates its release. | 1 | Biochemistry |
Methenamine silver stains are used for staining in histology, including the following types:
*Grocott's methenamine silver stain, used widely as a screen for fungal organisms.
*Jones' stain, a methenamine silver-Periodic acid-Schiff that stains for basement membrane, availing to view the "spiked" Glomerular basement membrane associated with membranous glomerulonephritis. | 0 | Organic Chemistry |
The total number of particles is found from the grand potential by
This increases monotonically with z (up to the maximum z = +1). The behaviour when approaching z = 1 is however crucially dependent on the value of α (i.e., dependent on whether the gas is 1D, 2D, 3D, whether it is in a flat or harmonic potential well).
For α > 1, the number of particles only increases up to a finite maximum value, i.e., is finite at z = 1:
where ζ(α) is the Riemann zeta function (using Li(1) = ζ(α)). Thus, for a fixed number of particles , the largest possible value that β can have is a critical value β. This corresponds to a critical temperature T=1/kβ, below which the Thomas–Fermi approximation breaks down (the continuum of states simply can no longer support this many particles, at lower temperatures). The above equation can be solved for the critical temperature:
For example, for the three-dimensional Bose gas in a box ( and using the above noted value of ) we get:
For α ≤ 1, there is no upper limit on the number of particles ( diverges as z approaches 1), and thus for example for a gas in a one- or two-dimensional box ( and respectively) there is no critical temperature. | 7 | Physical Chemistry |
An electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinized electrode. Homogeneous electrocatalysts, which are soluble, assist in transferring electrons between the electrode and reactants, and/or facilitate an intermediate chemical transformation described by an overall half reaction. Major challenges in electrocatalysts focus on fuel cells. | 7 | Physical Chemistry |
The action potential generated at the axon hillock propagates as a wave along the axon. The currents flowing inwards at a point on the axon during an action potential spread out along the axon, and depolarize the adjacent sections of its membrane. If sufficiently strong, this depolarization provokes a similar action potential at the neighboring membrane patches. This basic mechanism was demonstrated by Alan Lloyd Hodgkin in 1937. After crushing or cooling nerve segments and thus blocking the action potentials, he showed that an action potential arriving on one side of the block could provoke another action potential on the other, provided that the blocked segment was sufficiently short.
Once an action potential has occurred at a patch of membrane, the membrane patch needs time to recover before it can fire again. At the molecular level, this absolute refractory period corresponds to the time required for the voltage-activated sodium channels to recover from inactivation, i.e., to return to their closed state. There are many types of voltage-activated potassium channels in neurons. Some of them inactivate fast (A-type currents) and some of them inactivate slowly or not inactivate at all; this variability guarantees that there will be always an available source of current for repolarization, even if some of the potassium channels are inactivated because of preceding depolarization. On the other hand, all neuronal voltage-activated sodium channels inactivate within several milliseconds during strong depolarization, thus making following depolarization impossible until a substantial fraction of sodium channels have returned to their closed state. Although it limits the frequency of firing, the absolute refractory period ensures that the action potential moves in only one direction along an axon. The currents flowing in due to an action potential spread out in both directions along the axon. However, only the unfired part of the axon can respond with an action potential; the part that has just fired is unresponsive until the action potential is safely out of range and cannot restimulate that part. In the usual orthodromic conduction, the action potential propagates from the axon hillock towards the synaptic knobs (the axonal termini); propagation in the opposite direction—known as antidromic conduction—is very rare. However, if a laboratory axon is stimulated in its middle, both halves of the axon are "fresh", i.e., unfired; then two action potentials will be generated, one traveling towards the axon hillock and the other traveling towards the synaptic knobs. | 7 | Physical Chemistry |
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