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The quality of a given spectroradiometric system is a function of its electronics, optical components, software, power supply, and calibration. Under ideal laboratory conditions and with highly trained experts, it is possible to achieve small (a few tenths to a few percent) errors in measurements. However, in many practical situations, there is the likelihood of errors on the order of 10 percent Several types of error are at play when taking physical measurements. The three basic types of error noted as the limiting factors of accuracy of measurement are random, systematic, and periodic errors
* Random errors are variations about that mean. In the case of spectroradiometric measurements, this could be thought of as noise from the detector, internal electronics, or the light source itself. Errors of this type can be combated by longer integration times or multiple scans.
* Systematic errors are offsets to the predicted "correct" value. Systematic errors generally occur due to the human component of these measurements, the device itself, or the setup of the experiment. Things such as calibration errors, stray light, and incorrect settings, are all potential issues.
* Periodic errors arise from recurrent periodic or pseudo-periodic events. Variations in temperature, humidity, air-motion, or AC interference could all be categorized as periodic error.
In addition to these generic sources of error, a few of the more specific reasons for error in spectroradiometry include:
* The multidimensionality of the measurement. The output signal is dependent on several factors, including magnitude of measured flux, its direction, its polarization, and its wavelength distribution.
* The inaccuracy of measuring instruments, as well as the standards used to calibrate said instruments, cascaded to create a larger error throughout the entire measurement process, and
* The proprietary techniques for reducing multidimensionality and device instability error.
Gamma-scientific, a California-based manufacturer of light measurement devices, lists seven factors affecting the accuracy and performance of their spectroradiometers, due to either the system calibration, the software and power supply, the optics, or the measurement engine itself. | 7 | Physical Chemistry |
Natural phenols can be involved in allelopathic interactions, for example in soil or in water. Juglone is an example of such a molecule inhibiting the growth of other plant species around walnut trees. The aquatic vascular plant Myriophyllum spicatum produces ellagic, gallic and pyrogallic acids and (+)-catechin, allelopathic phenolic compounds inhibiting the growth of blue-green alga Microcystis aeruginosa.
Phenolics, and in particular flavonoids and isoflavonoids, may be involved in endomycorrhizae formation.
Acetosyringone has been best known for its involvement in plant-pathogen recognition, especially its role as a signal attracting and transforming unique, oncogenic bacteria in genus Agrobacterium. The virA gene on the Ti plasmid in the genome of Agrobacterium tumefaciens and Agrobacterium rhizogenes is used by these soil bacteria to infect plants, via its encoding for a receptor for acetosyringone and other phenolic phytochemicals exuded by plant wounds. This compound also allows higher transformation efficiency in plants, in A. tumefaciens mediated transformation procedures, and so is of importance in plant biotechnology. | 0 | Organic Chemistry |
Vitrification in cryopreservation is used to preserve, for example, human egg cells (oocytes) (in oocyte cryopreservation) and embryos (in embryo cryopreservation). It prevents ice crystal formation and is a very fast process: -23,000°C/min.
Currently, vitrification techniques have only been applied to brains (neurovitrification) by Alcor and to the upper body by the Cryonics Institute, but research is in progress by both organizations to apply vitrification to the whole body.
Many woody plants living in polar regions naturally vitrify their cells to survive the cold. Some can survive immersion in liquid nitrogen and liquid helium. Vitrification can also be used to preserve endangered plant species and their seeds. For example, recalcitrant seeds are considered hard to preserve. Plant vitrification solution (PVS), one of application of vitrification, has successfully preserved Nymphaea caerulea seeds.
Additives used in cryobiology or produced naturally by organisms living in polar regions are called cryoprotectants. | 1 | Biochemistry |
MFGM is a structurally complex bioactive milk component, found in human milk as well as the milk of other mammalian species. The MFGM in human milk contains many bioactive components with diverse functions and has been linked to cognitive and health benefits to infants. Some compositional differences are reported to exist between species, but bovine MFGM, the best-studied non-human source, generally contains a lipid and protein composition, which is similar to that of human MFGM.
MFGM makes up an estimated 2-6% of the total fat globules. As raw milk has an average total fat content around 4%, it therefore contains around 0.08-0.24% of MFGM. In other words, 417–1250 kg of raw milk is needed to supply 1 kg of MFGM. The content of MFGM in dairy products varies depending on the processing involved. During dairy processing such as churning or decreaming, the MFGM is disrupted and preferentially distributed into aqueous phases such as buttermilk, butter serum, or certain type of whey. Thus they can be a good source of MFGM for addition into food products.
For example, infant formulas traditionally were lacking the MFGM because this fraction is lost during regular dairy processing. However, more recent advances in technology have facilitated the separation of MFGM from the fat globule, allowing bovine MFGM to be added in concentrated form. The MFGM fraction is now commercially available and can be added to infant formula or other nutritional products. | 1 | Biochemistry |
c-Src is a gene that codes for proto-oncogene tyrosine-protein kinase Src, a protein important for normal mitotic cycling. It is phosphorylated and dephosphorylated to turn signaling on and off. Proto-oncogene tyrosine-protein kinase Src must be localized to the plasma membrane in order to phosphorylate other downstream targets; myristoylation is responsible for this membrane targeting event. Increased myristoylation of c-Src can lead to enhanced cell proliferation and be responsible for transforming normal cells into cancer cells. Activation of c-Src can lead to the so-called "hallmarks of cancer", among them upregulation of angiogenesis, proliferation, and invasion. | 1 | Biochemistry |
Ibuprofen overdose has become common since it was licensed for OTC use. Many overdose experiences are reported in the medical literature, although the frequency of life-threatening complications from ibuprofen overdose is low. Human responses in cases of overdose range from an absence of symptoms to a fatal outcome despite intensive-care treatment. Most symptoms are an excess of the pharmacological action of ibuprofen, and include abdominal pain, nausea, vomiting, drowsiness, dizziness, headache, ear ringing, and nystagmus. Rarely, more severe symptoms, such as gastrointestinal bleeding, seizures, metabolic acidosis, hyperkalemia, low blood pressure, slow heart rate, fast heart rate, atrial fibrillation, coma, liver dysfunction, acute kidney failure, cyanosis, respiratory depression, and cardiac arrest have been reported. The severity of symptoms varies with the ingested dose and the time elapsed; however, individual sensitivity also plays an important role. Generally, the symptoms observed with an overdose of ibuprofen are similar to the symptoms caused by overdoses of other NSAIDs.
Correlation between severity of symptoms and measured ibuprofen plasma levels is weak. Toxic effects are unlikely at doses below 100mg/kg, but can be severe above 400mg/kg (around 150 tablets of 200mg units for an average man); however, large doses do not indicate the clinical course is likely to be lethal. A precise lethal dose is difficult to determine, as it may vary with age, weight, and concomitant conditions of the individual person.
Treatment to address an ibuprofen overdose is based on how the symptoms present. In cases presenting early, decontamination of the stomach is recommended. This is achieved using activated charcoal; charcoal absorbs the drug before it can enter the bloodstream. Gastric lavage is now rarely used, but can be considered if the amount ingested is potentially life-threatening, and it can be performed within 60 minutes of ingestion. Purposeful vomiting is not recommended. Most ibuprofen ingestions produce only mild effects, and the management of overdose is straightforward. Standard measures to maintain normal urine output should be instituted and kidney function monitored. Since ibuprofen has acidic properties and is also excreted in the urine, forced alkaline diuresis is theoretically beneficial. However, because ibuprofen is highly protein-bound in the blood, the kidneys' excretion of unchanged drug is minimal. Forced alkaline diuresis is, therefore, of limited benefit. | 4 | Stereochemistry |
In biochemistry, dephosphorylation is the removal of a phosphate (PO) group from an organic compound by hydrolysis. It is a reversible post-translational modification. Dephosphorylation and its counterpart, phosphorylation, activate and deactivate enzymes by detaching or attaching phosphoric esters and anhydrides. A notable occurrence of dephosphorylation is the conversion of ATP to ADP and inorganic phosphate.
Dephosphorylation employs a type of hydrolytic enzyme, or hydrolase, which cleaves ester bonds. The prominent hydrolase subclass used in dephosphorylation is phosphatase, which removes phosphate groups by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl (-OH) group.
The reversible phosphorylation-dephosphorylation reaction occurs in every physiological process, making proper function of protein phosphatases necessary for organism viability. Because protein dephosphorylation is a key process involved in cell signalling, protein phosphatases are implicated in conditions such as cardiac disease, diabetes, and Alzheimer's disease. | 1 | Biochemistry |
Although the vast majority of seawater has a salinity of between 31 and 38 g/kg, that is 3.1–3.8%, seawater is not uniformly saline throughout the world. Where mixing occurs with freshwater runoff from river mouths, near melting glaciers or vast amounts of precipitation (e.g. monsoon), seawater can be substantially less saline. The most saline open sea is the Red Sea, where high rates of evaporation, low precipitation and low river run-off, and confined circulation result in unusually salty water. The salinity in isolated bodies of water can be considerably greater still about ten times higher in the case of the Dead Sea. Historically, several salinity scales were used to approximate the absolute salinity of seawater. A popular scale was the "Practical Salinity Scale" where salinity was measured in "practical salinity units (PSU)". The current standard for salinity is the "Reference Salinity" scale with the salinity expressed in units of "g/kg". | 9 | Geochemistry |
The term was first coined by Russian chemist V. Pletz in 1935 and originally mistranslated in some articles as plosophore. Also of note is an auxoexplose concept (similar to chromophore and auxochrome concept), which is a group that modifies the explosive capability of the molecule.
The term explosophore has been used more frequently after its use in books such as Organic Chemistry of Explosives by J. Agrawal and R. Hodgson (2007)'. | 0 | Organic Chemistry |
*Hollow tube dispensers are plastic twist-tie type dispensers, plastic hollow fibers or plastic hollow microfibers fibers, filled with synthetic sex pheromone and placed throughout the area to be protected.
*Pheromone Baits and Stations are a stationary, attract and kill type of dispensers. Some are relatively large platform, containing a pheromone lure inside a glue board that ensnares the attracted insect. Other pheromone bait stations contain a pheromone lure in conjunction with a surface containing a dose of insecticide that reduces the attracted insect's fitness, thus reducing its ability to mate and reproduce.
*High-emission dispensers There are several very high dose pheromone dispensers, some do it passively, like pheromone sachets and large dollops of SPLAT pheromone formulations, others do it be actively releasing bursts of sex pheromone at timed intervals. | 1 | Biochemistry |
Another approach of preparing carbenes has relied on the desulfurisation of thioureas with potassium in THF. A contributing factor to the success of this reaction is that the byproduct, potassium sulfide, is insoluble in the solvent. The elevated temperatures suggest that this method is not suitable for the preparation of unstable dimerising carbenes. A single example of the deoxygenation of a urea with a fluorene derived carbene to give the tetramethyldiaminocarbene and fluorenone has also been reported:
The desulfurisation of thioureas with molten potassium to give imidazol-2-ylidenes or diaminocarbenes has not been widely used. The method was used to prepare dihydroimidazole carbenes. | 0 | Organic Chemistry |
The mean free path of a molecule in a gas is the average distance between its collision with other molecules. This is inversely proportional to the pressure of the gas, given constant temperature. In air at STP the mean free path of molecules is about 96 nm. Since electrons are much smaller, their average distance between colliding with molecules is about 5.6 times longer, or about 0.5 μm. This is a substantial fraction of the 7.5 μm spacing between the electrodes for minimal arc voltage. If the electron is in an electric field of 43 MV/m, it will be accelerated and acquire 21.5 eV of energy in 0.5 μm of travel in the direction of the field. The first ionization energy needed to dislodge an electron from nitrogen molecule is about 15.6 eV. The accelerated electron will acquire more than enough energy to ionize a nitrogen molecule. This liberated electron will in turn be accelerated, which will lead to another collision. A chain reaction then leads to avalanche breakdown, and an arc takes place from the cascade of released electrons.
More collisions will take place in the electron path between the electrodes in a higher-pressure gas. When the pressure–gap product is high, an electron will collide with many different gas molecules as it travels from the cathode to the anode. Each of the collisions randomizes the electron direction, so the electron is not always being accelerated by the electric field—sometimes it travels back towards the cathode and is decelerated by the field.
Collisions reduce the electron's energy and make it more difficult for it to ionize a molecule. Energy losses from a greater number of collisions require larger voltages for the electrons to accumulate sufficient energy to ionize many gas molecules, which is required to produce an avalanche breakdown.
On the left side of the Paschen minimum, the product is small. The electron mean free path can become long compared to the gap between the electrodes. In this case, the electrons might gain large amounts of energy, but have fewer ionizing collisions. A greater voltage is therefore required to assure ionization of enough gas molecules to start an avalanche. | 7 | Physical Chemistry |
The process of casting in bronze and brass is known as cire perdue, and is the most primitive and most commonly employed through the centuries, having been described in by the monk Theophilus, and also by Benvenuto Cellini. Briefly, it is as follows: a core, roughly representing the size and form of the object to be produced, is made of pounded brick, plaster or other similar substance and thoroughly dried. Upon this the artist overlays his wax, which he models to the degree required in his finished work. Passing from the core through the wax and projecting beyond are metal rods. The modelling being completed, called lost-wax casting, the outer covering which will form the mould has to be applied; this is a liquid formed of clay and plaster sufficiently thin to find its way into every detail of the wax model. Further coatings of liquid are applied, so that there is, when dry, a solid outer coating and a solid inner core held together by the metal rods, with the work of art modelled in wax between. Heat is applied and the wax melts and runs out, and the molten metal is poured in and occupies every detail which the wax had filled. When cool, the outer casing is carefully broken away, the core raked out as far as possible, the projecting rods are removed and the object modelled in wax appears in bronze. If further finish is required, it is obtained by tooling. | 8 | Metallurgy |
Very low water clarity can be found where high loads of suspended sediments are transported from land. Some examples are estuaries where rivers with high loads of sediments empty into the ocean. One example is the Río de la Plata, an estuary in South America between Uruguay and Argentina where the Uruguay River and the Parana River empty into the Atlantic ocean. The Río de la Plata shows long-term mean TSS concentrations between 20 and 100 grams per cubic meter, higher than most estuaries. Another example is the gulf coast of North America where the Mississippi River meets the Gulf of Mexico. Turbid water from snowmelt and rain washes high loads of sediment downstream each spring, creating a sediment plume and making the water clarity very low. Water bodies can also experience low water clarity after extreme events like volcanic eruptions. After the eruption of Mount St. Helens, the water of Spirit Lake, Washington was darkened by decaying trees in the lake and had a Secchi depth of only 1 to 2 centimeters. | 3 | Analytical Chemistry |
Liquids tend to have better thermal conductivity than gases, and the ability to flow makes a liquid suitable for removing excess heat from mechanical components. The heat can be removed by channeling the liquid through a heat exchanger, such as a radiator, or the heat can be removed with the liquid during evaporation. Water or glycol coolants are used to keep engines from overheating. The coolants used in nuclear reactors include water or liquid metals, such as sodium or bismuth. Liquid propellant films are used to cool the thrust chambers of rockets. In machining, water and oils are used to remove the excess heat generated, which can quickly ruin both the work piece and the tooling. During perspiration, sweat removes heat from the human body by evaporating. In the heating, ventilation, and air-conditioning industry (HVAC), liquids such as water are used to transfer heat from one area to another. | 7 | Physical Chemistry |
Hepatocyte nuclear factors (HNFs) are a group of phylogenetically unrelated transcription factors that regulate the transcription of a diverse group of genes into proteins. These proteins include blood clotting factors and in addition, enzymes and transporters involved with glucose, cholesterol, and fatty acid transport and metabolism. | 1 | Biochemistry |
The Michelson spectrograph is similar to the instrument used in the Michelson–Morley experiment. Light from the source is split into two beams by a half-silvered mirror, one is reflected off a fixed mirror and one off a movable mirror, which introduces a time delay—the Fourier-transform spectrometer is just a Michelson interferometer with a movable mirror. The beams interfere, allowing the temporal coherence of the light to be measured at each different time delay setting, effectively converting the time domain into a spatial coordinate. By making measurements of the signal at many discrete positions of the movable mirror, the spectrum can be reconstructed using a Fourier transform of the temporal coherence of the light. Michelson spectrographs are capable of very high spectral resolution observations of very bright sources.
The Michelson or Fourier-transform spectrograph was popular for infra-red applications at a time when infra-red astronomy only had single-pixel detectors. Imaging Michelson spectrometers are a possibility, but in general have been supplanted by imaging Fabry–Pérot instruments, which are easier to construct. | 7 | Physical Chemistry |
Modern concept of polymers credited to Hermann Staudinger, who substantiated the existence of covalently linked ultralong molecules in 1920, which he called as macromolecules. The preamble of the field of supramolecular polymers can be considered dye-aggregates and host-guest complexes. In early 19th century, scientists working in the field of pigments have noticed certain dye aggregates that may formed via "a special kind of polymerization", however no theory was proposed. After the establishment of the field of supramolecular chemistry and after the award of the Nobel Prize in chemistry in 1987 to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen, chemists started to design and study larger assembled structures from small molecules. In 1988, Takuzo Aida, a Japanese polymer chemist, reported the concept of cofacial assembly wherein the amphiphilic porphyrin monomers are connected via van der Waals interaction forming one-dimensional architectures in solution, which can be considered as a prototype of supramolecular polymers. In the same year 1988, James D. Wuest introduced one-dimensional aggregates based on hydrogen bonding interaction in the crystalline state. With a different strategyusing hydrogen bonds, Jean M. J. Fréchet showed in 1989 that mesogenic molecules with carboxylic acid and pyridyl motifs, upon mixing in bulk, heterotropically dimerize to form a stable liquid crystalline structure. In 1990, Jean-Marie Lehn showed that this strategy can be expanded to form a new category of polymers, which he called "liquid crystalline supramolecular polymer" using complementary triple hydrogen bonding motifs in bulk. In 1993, M. Reza Ghadiri reported a nanotubular supramolecular polymer where a b-sheet-forming macrocyclic peptide monomer assembled together via multiple hydrogen bonding between adjacent macrocycles. In 1994, Anselm. C. Griffin showed an amorphous supramolecular material using a single hydrogen bond between a homotropic molecules having carboxylic acid and pyridine termini. The idea to make mechanically strong polymeric materials by 1D supramolecular association of small molecules requires a high association constant between the repeating building blocks. In 1997, E.W. "Bert" Meijer reported a telechelic monomer with ureidopyrimidinone termini as a "self-complementary" quadruple hydrogen bonding motif and demonstrated that the resulting supramolecular polymer in chloroform shows a temperature-dependent viscoelastic property in solution. This is the first demonstration that supramolecular polymers, when sufficiently mechanically robust, are physically entangled in solution. | 6 | Supramolecular Chemistry |
Biological processes that fractionate Cu isotopes are not well-understood, but play an important role in driving the δCu values of materials observed in the marine and terrestrial environments. The natural Cu/Cu varies according to coppers redox form and the ligand to which copper binds. Oxidized Cu preferentially coordinates with hard donor ligands (e.g., N- or O-containing ligands), while reduced Cu preferentially coordinates with soft donor ligands (e.g., S-containing ligands). As Cu is preferentially oxidized over Cu, these isotopes tend to coordinate with hard and soft donor ligands, respectively. Cu isotopes can fractionate upon Cu-bacteria interactions from processes that include Cu adsorption to cells, intracellular uptake, metabolic regulation and redox speciation. Fractionation of Cu isotopes upon adsorption to cellular walls appears to depend on the surface functional groups that Cu complexes with, and can span positive and negative values. Furthermore, bacteria preferentially incorporate the lighter Cu isotope intracellularly and into proteins. For example, E. coli, B. subtilis and a natural consortia of microbes sequestered Cu with apparent fractionations (εCu) ranging from ~-1.0 to -4.4‰. Additionally, fractionation of Cu upon incorporation into the apoprotein of azurin was ~-1‰ in P. aeruginosa, and -1.5‰ in E. coli', while εCu values of Cu incorporation into Cu-metallothionein and Cu-Zn-SOD in yeast were -1.7 and -1.2‰, respectively. | 9 | Geochemistry |
When foods with a high glycemic index are consumed, the carbohydrates in the food are more easily digested than low glycemic index foods. Hence, more glucose is available for absorption. It should not be misunderstood that glucose is absorbed more rapidly because, once formed, glucose is absorbed at the same rate. It is only available in higher amounts due to the ease of digestion of high glycemic index foods. In individuals with normal carbohydrate metabolism, insulin levels rise concordantly to drive glucose into the body's tissues and maintain blood glucose levels in the normal range. Insulin stimulates the uptake of valine, leucine, and isoleucine into skeletal muscle, but not uptake of tryptophan. This lowers the ratio of these branched-chain amino acids in the bloodstream relative to tryptophan (an aromatic amino acid), making tryptophan preferentially available to the large neutral amino acid transporter at the blood–brain barrier. Uptake of tryptophan by the brain thus increases. In the brain, tryptophan is converted to serotonin, which is then converted to melatonin. Increased brain serotonin and melatonin levels result in sleepiness. | 1 | Biochemistry |
Glucuronoxylans are the primary components of hemicellulose as found in hardwood trees, for example birch.
They are hemicellulosic plant cell wall polysaccharides, containing glucuronic acid and xylose as its main constituents. They are linear polymers of β-D-xylopyranosyl units linked by (1→4) glycosidic bonds, with many of the xylose units substituted with 2, 3 or 2,3-linked glucuronate residue, which are often methylated at position 4. Most of the glucuronoxylans have single 4-O-methyl-α-D-glucopyranosyl uronate residues (MeGlcA) attached at position 2. This structural type is usually named as 4-O-methyl-D-glucurono-D-xylan (MGX).
Angiosperm (hardwood) glucuronoxylans also have a high rate of substitution (70-80%) by acetyl groups, at position 2 and/or 3 of the β-D-xylopyranosyl, conferring on the xylan its partial solubility in water. | 1 | Biochemistry |
Several different morphologies of the block copolymer used to create the polymersome have been used. The most frequently used are the linear diblock or triblock copolymers. In these cases, the block copolymer has one block that is hydrophobic; the other block or blocks are hydrophilic. Other morphologies used include comb copolymers, where the backbone block is hydrophilic and the comb branches are hydrophobic, and dendronized block copolymers, where the dendrimer portion is hydrophilic.
In the case of diblock, comb and dendronized copolymers the polymersome membrane has the same bilayer morphology of a liposome, with the hydrophobic blocks of the two layers facing each other in the interior of the membrane. In the case of triblock copolymers the membrane is a monolayer that mimics a bilayer, the central block filling the role of the two facing hydrophobic blocks of a bilayer.
In general they can be prepared by the methods used in the preparation of liposomes. Film rehydration, direct injection method or dissolution method. | 1 | Biochemistry |
Current flowing in the BPE because it provides less resistive current path than the electrolyte. As illustrated in the Figure; as consequence of the current entering side (D/Blue) from the anode, side D will polarise cathodically (potential will become more negative). At the other hand, side (B/Red) where the current is leaving, it will polarise anodically (potential will become more positive) and will corrode. This is due to polarisation which occurs opposite to the current direction.
This theory is almost accepted in all classic and recent cathodic protection books, and NACE publications and standards, as explanation of corrosion and coating disbondment caused by DC interference between pipelines and different structures (e.g. cathodically protected or unprotected structures, railways and HVDC). This because it is more suitable for large-scale structures in highly resistive, heterogeneous environments where solution potential (V) plays a less pivotal role and the reactions are primarily concentrated only at the poles (where current enters and leaves). | 7 | Physical Chemistry |
Prior to the invention of the theodolite, the goniometer was used in surveying. The application of triangulation to geodesy was described in the second (1533) edition of Cosmograficus liber by Petri Appiani as a 16-page appendix by Frisius entitled Libellus de locorum describendorum ratione. | 7 | Physical Chemistry |
Afterwards, as biofilm becomes established, EPS provides physical stability and resistance to mechanical removal, antimicrobials, and host immunity. Exopolysaccharides and environmental DNA (eDNA) contribute to viscoelasticity of mature biofilms so that detachment of biofilm from the substratum will be challenging even under sustained fluid shear stress or high mechanical pressure. In addition to mechanical resistance, EPS also promotes protection against antimicrobials and enhanced drug tolerance. Antimicrobials cannot diffuse through the EPS barrier, resulting in limited drug access into the deeper layers of the biofilm. Moreover, positively charged agents will bind to negatively charged EPS contributing to the antimicrobial tolerance of biofilms, and enabling inactivation or degradation of antimicrobials by enzymes present in biofilm matrix. EPS also functions as local nutrient reservoir of various biomolecules, such as fermentable polysaccharides. A study on V. cholerae in 2017 suggested that due to osmotic pressure differences in V. cholerae biofilms, the microbial colonies physically swell, therefore maximizing their contact with nutritious surfaces and thus, nutrient uptake. | 1 | Biochemistry |
In addition to the oxidation routes, diaryl sulfoxides can be prepared by two Friedel–Crafts arylations of sulfur dioxide using an acid catalyst:
:2 ArH + SO → ArSO + HO
Both aryl sulfinyl chlorides and diaryl sulfoxides can be also prepared from arenes through reaction with thionyl chloride in the presence of Lewis acid catalysts such as BiCl, Bi(OTf), LiClO, or NaClO. | 0 | Organic Chemistry |
The first record of the pyroelectric effect was made in 1707 by Johann Georg Schmidt, who noted that the "[hot] tourmaline could attract the ashes from the warm or burning coals, as the magnet does iron, but also repelling them again [after the contact]". In 1717 Louis Lemery noticed, as Schmidt had, that small scraps of non-conducting material were first attracted to tourmaline, but then repelled by it once they contacted the stone. In 1747 Linnaeus first related the phenomenon to electricity (he called tourmaline Lapidem Electricum, "the electric stone"), although this was not proven until 1756 by Franz Ulrich Theodor Aepinus.
Research into pyroelectricity became more sophisticated in the 19th century. In 1824 Sir David Brewster gave the effect the name it has today. Both William Thomson in 1878 and Woldemar Voigt in 1897 helped develop a theory for the processes behind pyroelectricity. Pierre Curie and his brother, Jacques Curie, studied pyroelectricity in the 1880s, leading to their discovery of some of the mechanisms behind piezoelectricity.
It is mistakenly attributed to Theophrastus (c. 314 BC) the first record of pyroelectricity. The misconception arose soon after the discovery of the pyroelectric properties of tourmaline, which made mineralogists of the time associate the legendary stone Lyngurium with it. Lyngurium is described in the work of Theophrastus as being similar to amber, without specifying any pyroelectric properties. | 7 | Physical Chemistry |
In the negative feedback loops, CK1ε periodically binds to and phosphorylates the PER proteins (PER1, PER2, and PER3), which form heterodimers with each other and interact with CRY1 and CRY2. The effects of phosphorylation are two-fold. It has been shown in Drosophila that phosphorylation of the PER proteins increase their ubiquitination, which leads to degradation. Phosphorylation of the PER proteins also leaves them unable to enter the nucleus, where they suppress transcription of clock genes. The blocking of nuclear translocation occurs via phosphorylation of PER at the nuclear localization signal, which masks the signal and prevents nuclear entry. However, this CK1ε-mediated constraint to the cytoplasm can be overcome when the PER protein complex is bound to CRY. CK1ε has been shown to phosphorylate CRY when both CK1ε and CRY are complexed with PER in vitro, but the functional significance of this remains undetermined.
CK1ε may also have a role in positive feedback; the transcription factor BMAL1 is a CK1ε substrate in vitro, and increased CK1ε activity has been shown to positively regulate transcription of genes under the influence of BMAL1-dependent circadian gene promoters. This has not yet been studied in vivo. | 1 | Biochemistry |
In the ideal regime, the usual ideal-gas behavior is qualitatively recovered. For an ideal gas, in fact, the value of the fundamental derivative reduces to the constant value , where is the heat capacity ratio. By definition, is the ratio between the constant pressure and the constant volume specific heats, so it is larger than 1, leading to a value of larger than 1 too.
In this regime, only quantitative differences with respect to the ideal model are encountered. The flow evolution in fact depends on total, or stagnation, thermodynamic conditions. For example, the Mach number evolution of an ideal gas in a supersonic nozzle depends only on the heat capacity ratio (namely on the fluid) and on the exhaust-to-stagnation pressure ratio. Considering real-gas effects, instead, even fixing the fluid and the pressure ratio, different total states yield different Mach profiles.
Typically, for single-phase fluids made of simple molecules, only the ideal gasdynamic regime can be reached, even for thermodynamic conditions very close to saturation. It is for example the case of diatomic or triatomic molecules, such as nitrogen or carbon dioxide, which can only experience small departure from the ideal behavior. | 7 | Physical Chemistry |
Anthropogenic sources emit about 142 teragrams (1.42 × 10 kg) of carbon per year in the form of VOCs.
The major source of man-made VOCs are:
* Fossil fuel use and production, e.g. incompletely combusted fossil fuels or unintended evaporation of fuels. The most prevalent VOC is ethane, a relatively inert compound.
* Solvents used in coatings, paints, and inks. Approximately 12 billion litres of paint are produced annually. Typical solvents include aliphatic hydrocarbons, ethyl acetate, glycol ethers, and acetone. Motivated by cost, environmental concerns, and regulation, the paint and coating industries are increasingly shifting toward aqueous solvents.
* Compressed aerosol products, mainly butane and propane, estimated to contribute 1.3 billion tonnes of VOC emissions per year globally.
* Biofuel use, e.g., cooking oils in Asia and bioethanol in Brazil.
* Biomass combustion, especially from rain forests. Although combustion principally releases carbon dioxide and water, incomplete combustion affords a variety of VOCs. | 0 | Organic Chemistry |
PhSnH, as it is more commonly abbreviated, is prepared by treatment of triphenyltin chloride with lithium aluminium hydride. Although PhSnH is treated as a source of "H·", in fact it does not release free hydrogen atoms, which are extremely reactive species. Instead, PhSnH transfers H to substrates usually via a radical chain mechanism. This reactivity exploits the relatively good stability of "PhSn·" | 0 | Organic Chemistry |
Neither Liebig nor Pasteur was completely right. However, each of their arguments led to more discoveries that created a lot of today's fields in science and medicine.
Berzelius had defined the word "ferment" as being an example of catalytic activity. Soon after, Schwann discovered pepsin was the substance responsible for albuminous digestion in the stomach. He believed this was what Berzelius defined as catalysts, or the force for chemical reactions of mineral, organic and living matter. Liebig opposed the idea by saying that the terms catalysts and pepsin are not supposed to be used as they are only representatives of an idea.
Charles Cagniard-Latour, Theodor Schwann and Friedrich Traugott Kützing identified independently yeast as a living organism that nourishes itself by the sugar it ferments, a process which referred to the ethanol fermentation (alcoholic fermentation). Liebig, Berzelius, and Wohler rejected the ideas of Schwann, Latour and Kutzing. In 1839, Liebig and Wohler published a paper on the role of yeast in alcoholic fermentation. In 1858, Liebig's student Moritz Traube enunciated the theorem, which was used for alcoholic fermentation, that all fermentations produced by living organisms are based on chemical reactions rather than a vital force itself.
The dispute between Liebig and Pasteur had, in a way, slowed down the advances of science and medicine in the area of fermentation, alcohol fermentation, and the enzymes. On the other hand, the conflicting ideas sped up the research in the area of fermentation and enzymes through other scientists and chemists. Through Büchner and his experiment in fermentation, the world of science and medicine went further as to pave ways in enzyme and fermentation studies and marked one of the critical points of the history of modern chemistry. | 1 | Biochemistry |
SRAS++ utilises SRAS imaging to provide the raw measurement of single grain velocity surfaces, this is input to a novel inverse solver that mitigates the problem of the inversion being very ill-conditioned, by simultaneously solving for multiple uniquely orientated grains at once in a brute-force approach. This allows simultaneous determination of the elastic constants and crystallographic orientation. Furthermore, this technique has the potential to work on polycrystalline materials with minimal preparation and is capable of high accuracy, with the potential to realise errors in the determination of elastic constants values of less than 1 GPa. | 7 | Physical Chemistry |
An enthalpy–entropy chart, also known as the H–S chart or Mollier diagram, plots the total heat against entropy, describing the enthalpy of a thermodynamic system. A typical chart covers a pressure range of 0.01–1000 bar, and temperatures up to 800 degrees Celsius. It shows enthalpy in terms of internal energy , pressure and volume using the relationship (or, in terms of specific enthalpy, specific entropy and specific volume, ). | 7 | Physical Chemistry |
Pd-mediated Sonogashira, Heck, and Suzuki-Miyaura cross-coupling reactions have been applied widely to modify peptides and proteins, where diverse Pd reagents have been developed for the application in aqueous solutions. Those reactions require the protein or peptide substrate bearing unnatural functional groups such as alkyne, aryl halides, and aryl boronic acids, which can be achieved through genetic code expansion or post-translational modifications. | 1 | Biochemistry |
First results to these problems were obtained by Leonard Adleman.
* In 1994: Solving a Hamiltonian path in a graph with 7 summits.
* In 2002: Solving a NP-complete problem as well as a 3-SAT problem with 20 variables. | 1 | Biochemistry |
In the late 1800s, with the large investments financed by northern bankers and southern investors, as well as the technological expertise provided by northern and mid-western engineers, the iron and steel industry began to flourish in Birmingham, Alabama. In addition, the growth of Alabamas iron and steel industry was further facilitated by the influx of a large labour force at that time. During the last decades of the nineteenth century, Alabamas agricultural sector was mainly dominated by the economic models of sharecropping and tenant farming. This tenancy system encompassed over 60 percent of the farming population in Alabama; however, under its influence, landless farmers had to suffer from a legacy of illiteracy and poverty. Driven by poverty, many labourers, including unemployed and impoverished freedmen and white people, began to search for jobs in the iron-and-steel manufacturing industry, which was considered to be a more attractive alternative to sharecropping and tenant farming. Moreover, the introduction of convict-lease system also provided Alabamas iron and steel manufacturers with abundant cheap labour. The convict-lease system functioned in the state and counties of Alabama between 1875 and 1928, through which iron manufacturers paid to the local governments in exchange for prison labour. As regulated by the system, prisoners had to work for the companies that leased them from the governments. Until its abolition in 1928, the convict-lease system had provided iron manufacturers, owners of coal mines, and other enterprises in Alabama with a substantial number of prisoners as cheap labourers. At the end of the nineteenth century, due to the regions abundant geographical resources coupled with its low raw-material assembly costs, Alabama experienced a period of rocket development. | 8 | Metallurgy |
Scientists use this beam of charged particles to determine the elemental composition of solid materials (minerals, glasses, metals). The chemical composition of the target can be found from the elemental data extracted through emitted X-rays (in the case where the primary beam consists of charged electrons) or measurement of an emitted secondary beam of material sputtered from the target (in the case where the primary beam consists of charged ions).
When the ion energy is in the range of a few tens of keV (kilo-electronvolt) these microprobes are usually called FIB (Focused ion beam). An FIB makes a small portion of the material into a plasma; the analysis is done by the same basic techniques as the ones used in mass spectrometry.
When the ion energy is higher, hundreds of keV to a few MeV (mega-electronvolt) they are called nuclear microprobes. Nuclear microprobes are extremely powerful tools that utilize ion beam analysis techniques as microscopies with spot sizes in the micro-/nanometre range. These instruments are applied to solve scientific problems in a diverse range of fields, from microelectronics to biomedicine. In addition to the development of new ways to exploit these probes as analytical tools (this application area of the nuclear microprobes is called nuclear microscopy), strong progress has been made in the area of materials modification recently (most of which can be described as PBW, proton beam writing).
The nuclear microprobe's beam is usually composed of protons and alpha particles. Some of the most advanced nuclear microprobes have beam energies in excess of 2 MeV. This gives the device very high sensitivity to minute concentrations of elements, around 1 ppm at beam sizes smaller than 1 micrometer. This elemental sensitivity exists because when the beam interacts with the a sample it gives off characteristic X-rays of each element present in the sample. This type of detection of radiation is called PIXE. Other analysis techniques are applied to nuclear microscopy including Rutherford backscattering(RBS), STIM, etc.
Another use for microprobes is the production of micro and nano sized devices, as in microelectromechanical systems and nanoelectromechanical systems. The advantage that microprobes have over other lithography processes is that a microprobe beam can be scanned or directed over any area of the sample. This scanning of the microprobe beam can be imagined to be like using a very fine tipped pencil to draw your design on a paper or in a drawing program. Traditional lithography processes use photons which cannot be scanned and therefore masks are needed to selectively expose your sample to radiation. It is the radiation that causes changes in the sample, which in turn allows scientists and engineers to develop tiny devices such as microprocessors, accelerometers (like in most car safety systems), etc. | 7 | Physical Chemistry |
Ingesting large amounts of arsenic can cause symptoms similar to food poisoning, with abdominal pain, nausea, vomiting, and diarrhea starting within hours. Bloody diarrhea can cause severe fluid loss, resulting in hypovolemic shock. The heart and nervous system can also be affected, causing disruption to heart rhythms (QT interval prolongation or tachycardia), heart failure, confusion, seizures, brain swelling, coma, and death. Inhaling arsine gas – the most toxic form of arsenic – causes a multisystem disease starting 2 to 24 hours after inhalation. Symptoms include gastrointestinal distress, headache, weakness, difficulty breathing, kidney and liver dysfunction, and the destruction of red blood cells.
Chronic ingestion of lower levels of arsenic causes visible changes in the skin, typically hyperpigmentation (dark areas), but sometimes hypopigmentation (light areas) or an alternating areas of each. Some experience general thickening of the skin on the palms and soles of the feet, or small thickened areas. Around 5% of those affected develop light-colored bands across the fingernail, called Mees' lines. Chronic exposure eventually causes disease across multiple body systems, including peripheral neuropathy (numbness and tingling), enlargement of the liver and spleen, diabetes, heart disease, cognitive impairment, and damage to the portal vein (Non-cirrhotic portal fibrosis and portal hypertension).
Repeated arsenic exposure also increases the risk for developing several cancers, particularly of the skin, lung, liver, bladder, prostate, and blood vessels. The most common arsenic-induced skin cancer is squamous cell carcinoma in situ which typically occurs 2 to 20 years after arsenic exposure. | 1 | Biochemistry |
Many alloys of elements that resemble each other chemically will form a structure at higher temperatures where the two elements occupy similar positions in the lattice at random. At lower temperatures ordering may occur where crystallographic positions are no longer equivalent because one element preferentially occupies one site and the other the other. This partial ordering process may lower the translation symmetry and result in a different, larger unit cell. | 3 | Analytical Chemistry |
For any 3-dimensional lattice, the conventional unit cells are parallelepipeds, which in special cases may have orthogonal angles, or equal lengths, or both. Seven of the fourteen three-dimensional Bravais lattices are represented using conventional primitive cells, as shown below.
The other seven Bravais lattices (known as the centered lattices) also have primitive cells in the shape of a parallelepiped, but in order to allow easy discrimination on the basis of symmetry, they are represented by conventional cells which contain more than one lattice point. | 3 | Analytical Chemistry |
As expected from previous information, diverse ions have a screening effect on dissociated ions which leads to extra dissociation. Solubility will show a clear increase in presence of diverse ions as the solubility product will increase. Look at the following example:
Find the solubility of AgCl (K = 1.0 x 10) in 0.1 M NaNO. The activity coefficients for silver and chloride are 0.75 and 0.76, respectively.
:AgCl(s) = Ag + Cl
We can no longer use the thermodynamic equilibrium constant (i.e. in absence of diverse ions) and we have to consider the concentration equilibrium constant or use activities instead of concentration if we use Kth:
:K = aAg aCl
:K = [Ag] fAg [Cl] fCl
:1.0 x 10 = s x 0.75 x s x 0.76
:s = 1.3 x 10 M
We have calculated the solubility of AgCl in pure water to be 1.0 x 10 M, if we compare this value to that obtained in presence of diverse ions we see % increase in solubility = {(1.3 x 10 – 1.0 x 10) / 1.0 x 10} x 100 = 30%
Therefore, once again we have an evidence for an increase in dissociation or a shift of equilibrium to right in presence of diverse ions. | 3 | Analytical Chemistry |
The Mark III design encompassed the greatest improvement in the technology since its commercialisation. The focus was to make the technology more robust and easier to use in operations. The total redesign of the downcomer assembly allowed it to be isolated and unblocked much more easily compared to the Mark II design. The Mark III design also saw slurry flow per downcomer to be increased from 60 m/h to 75–85 m/h using larger orifice sizes in the slurry lenses.
The Mark III Cell was introduced in 2000. It included the following improvements:
* a new slurry lens orifice design (see Figures 7 and 8)
* a new design downcomer and nozzle
* a new design flat plate bubble dispersers
* a stainless steel adjustable above and in-froth wash water system (see Figure 9)
* automated air and wash water flow control
* air-isolating slurry-eliminating valves ("AISE valves")
* a bottom-fed new slurry distributor.
The earlier models of the Jameson Cell used orifice plates to generate the downcomer jet. The new slurry lens design had a smooth, shallow entry angle that created an optimum flow regime over the ceramic, reducing wear and extending its life. The shape resulted in a decrease in power consumption by the feed slurry pump by up to 10% and resulted in better jet formation that improved air entrainment.
For coal applications, the wash water addition system was changed from a tray to stainless-steel circular rings attached to a manual lifting system. This allowed the flexibility of an easy transition from above-froth wash water addition to the in-froth addition that might be necessary for high concentrate-grade operations. For metals applications, new design wash water trays consisting of removable rubber mats for easy maintenance were used.
The AISE valves were developed to prevent solids being sucked back into the air lines when individual downcomers become blocked. Solids depositing in the air lines and their build up in the air distributor decreases flotation performance as it prevents air from being efficiently entrained in the downcomers. | 8 | Metallurgy |
In an electrochemical cell the faradaic impedance of an electrolyte-electrode interface is the joint electrical resistance and capacitance at that interface.
Let us suppose that the Butler-Volmer relationship correctly describes the dynamic behavior of the redox reaction:
Dynamic behavior of the redox reaction is characterized by the so-called charge transfer resistance defined by:
The value of the charge transfer resistance changes with the overpotential. For this simplest example the faradaic impedance is reduced to a resistance. It is worthwhile to notice that:
for . | 7 | Physical Chemistry |
The explanation of the Fano line-shape first appeared in the context of inelastic electron scattering by helium and autoionization. The incident electron doubly excites the atom to the state, a sort of shape resonance. The doubly excited atom spontaneously decays by ejecting one of the excited electrons. Fano showed that interference between the amplitude to simply scatter the incident electron and the amplitude to scatter via autoionization creates an asymmetric scattering line-shape around the autoionization energy with a line-width very close to the inverse of the autoionization lifetime. | 7 | Physical Chemistry |
In organic chemistry, a carbodiimide (systematic IUPAC name: methanediimine) is a functional group with the formula RN=C=NR. On Earth they are exclusively synthetic, but in interstellar space the parent compound HN=C=NH has been detected by its maser emissions.
A well known carbodiimide is dicyclohexylcarbodiimide, which is used in peptide synthesis. Dialkylcarbodiimides are stable. Some diaryl derivatives tend to convert to dimers and polymers upon standing at room temperature, though this mostly occurs with low melting point carbodiimides that are liquids at room temperature. Solid diaryl carbodiimides are more stable, but can slowly undergo hydrolysis in the presence of water over time. | 0 | Organic Chemistry |
* Ashton, T. S. Iron and Steel in the Industrial Revolution (2nd edn., 1951).
* Bernal, John Desmond, Science and Industry in the Nineteenth Century, Indiana University Press, 1970.
* D’Costa, Anthony P. The Global Restructuring of the Steel Industry: Innovations, Institutions, and Industrial Change London: Routledge, 1999
* Hasegawa, Harukiyu. The Steel Industry in Japan: A Comparison with Britain 1996
* Landes, David S., The Unbound Prometheus: Technical Change and Industrial Development in Western Europe from 1750 to the Present (2nd ed. Cambridge University Press, 2003)
* Pounds, Norman J. G., and William N. Parker; Coal and Steel in Western Europe; the Influence of Resources and Techniques on Production (Indiana University Press, 1957)
* Singer, Charles Joseph, ed. A history of technology: vol 4: The Industrial Revolution c 1750–c 1860 (1960) ch 4, and vol 5: The Late Nineteenth Century, c 1850–c 1900, ch 3; [http://ets.umdl.umich.edu/cgi/t/text/text-idx?c=acls;cc=acls;view=toc;idno=heb02191.0004.001 online at ACLS e-books]
* Stoddard, Brooke C. Steel: From Mine to Mill, the Metal that Made America (2015) short, global popular history [https://www.amazon.com/Steel-Mine-Mill-Metal-America/dp/0760347425/ excerpt]
* Woytinsky, W. S., and E. S. Woytinsky. World Population and Production Trends and Outlooks (1953) pp 1098–1143, with many tables and maps on the worldwide steel industry
* Yonekura, Seiichiro. The Japanese iron and steel industry: Continuity and discontinuity, 1850–1970 (1994) [https://www.amazon.com/Japanese-Iron-Steel-Industry-1850-1990/dp/0312106734/ excerpt and text search] | 8 | Metallurgy |
This pathway has been demonstrated in Chloroflexus, a nonsulfur photosynthetic bacterium; however, other studies suggest that 3-hydroxypropionate bicycle is used by several chemotrophic archaea. T In E. coli 3-hydroxypropionate bicycle has been studied and found to be insensitive to oxygen. This means that within the pathways there is nothing that oxygen can affect because in either part of the pathway or the oxygen is used to drive the reaction forward. | 1 | Biochemistry |
In organic chemistry, the term 2-norbornyl cation (or 2-bicyclo[2.2.1]heptyl cation) describes one of the three carbocations formed from derivatives of norbornane. Though 1-norbornyl and 7-norbornyl cations have been studied, the most extensive studies and vigorous debates have been centered on the exact structure of the 2-norbornyl cation.
The 2-norbornyl cation has been formed from a variety of norbornane derivatives and reagents. First reports of its formation and reactivity published by Saul Winstein sparked controversy over the nature of its bonding, as he invoked a three-center two-electron bond to explain the stereochemical outcome of the reaction. Herbert C. Brown challenged this assertion on the grounds that classical resonance structures could explain these observations without needing to adapt a new perspective of bonding. Both researchers' views had its supporters, and dozens of scientists contributed ingeniously designed experiments to provide evidence for one viewpoint or the other. Over time, the dispute became increasingly bitter and acrimonious, and the debate took on a personal or ad hominem character.
Evidence of the non-classical nature of the 2-norbornyl cation grew over the course of several decades, mainly through spectroscopic data gathered using methods such as nuclear magnetic resonance (NMR). Crystallographic confirmation of its non-classical nature did not come until 2013. Although most chemists now agree that 2-norbornyl cation itself is non-classical, it is also widely recognized that the energetic landscape for carbocations tends to be "flat", with many potential structures differing only minutely in energy. Certainly, not all bicyclic carbocations are non-classical; the energy difference between classical and non-classical structures is often delicately balanced. Thus, certain alkyl-substituted 2-bicyclo[2.2.1]heptyl cations are now known to adopt classical structures.
The nature of bonding in the 2-norbornyl cation incorporated many new ideas into the field’s understanding of chemical bonds. Similarities can be seen between this cation and others, such as boranes. | 7 | Physical Chemistry |
* Orbifold signature:
* Coxeter notation (rectangular): [∞,2,∞] or [∞]×[∞]
* Coxeter notation (square): [4,1,4] or [1,4,4,1]
* Lattice: rectangular
* Point group: D
* The group pmm has reflections in two perpendicular directions, and four rotation centres of order two (180°) located at the intersections of the reflection axes.
;Examples of group pmm | 3 | Analytical Chemistry |
About 1 in 4,000 children in the United States will develop mitochondrial disease by the age of 10 years. Up to 4,000 children per year in the US are born with a type of mitochondrial disease. Because mitochondrial disorders contain many variations and subsets, some particular mitochondrial disorders are very rare.
The average number of births per year among women at risk for transmitting mtDNA disease is estimated to approximately 150 in the United Kingdom and 800 in the United States. | 1 | Biochemistry |
Feedlots play an integral role in the Australian livestock industry and are strongly influenced by the environment they are in. Only 25% of Australia (including its feedlots) have a growing season of more than 5 months. This is due to the Australian climate being incapable of sustaining crops and pastures over a sustained period of time. Characteristically, cattle and grain supplies are located in close proximity to feedlots, and the 2012 Australian Lot feeders Association Industry survey indicated that feedlot capacity is typically divided into particular sectors.
Whilst the southern states account for 51% of total feedlot capacity in Australia, NSW only possesses 45% of total feedlots. The effect of this feedlot distribution is that the southern states produce 1 266 710 heads of cows whilst NSW only owns 788 625 heads of cattle. These figures demonstrate how environmental and infrastructural conditions must be accounted for throughout Australian pastoral systems, thereby indicating how these influences have had an effect on the Southern and Northern rangeland industry. Further, in the Southern rangelands where there is a growing season of less than 5 months, sheep stations have been implemented to complement the farming of cattle. In comparison, the Northern beef zone takes up 116 million hectares of Australia's total land mass, which equates to 24.3% of the total land mass available; this figure is markedly different form the 265 million hectares consumed by the Southern rangelands (sheep and beef) which amounts to 55.3% of total land mass. The Northern rangelands are operated by multiple companies which occupy more than one station. | 2 | Environmental Chemistry |
Anion exchange sorbents are derivatized with positively charged functional groups that interact and retain negatively charged anions, such as acids. Strong anion exchange sorbents contain quaternary ammonium groups that have a permanent positive charge in aqueous solutions, and weak anion exchange sorbents use amine groups which are charged when the pH is below about 9. Strong anion exchange sorbents are useful because any strongly acidic impurities in the sample will bind to the sorbent and usually will not be eluted with the analyte of interest; to recover a strong acid a weak anion exchange cartridge should be used. To elute the analyte from either the strong or weak sorbent, the stationary phase is washed with a solvent that neutralizes the charge of either the analyte, the stationary phase, or both. Once the charge is neutralized, the electrostatic interaction between the analyte and the stationary phase no longer exists and the analyte will elute from the cartridge. | 3 | Analytical Chemistry |
Modafinil, sold under the brand name Provigil among others, is a wakefulness-promoting medication used primarily to treat narcolepsy. Modafinil is also approved for stimulating wakefulness in people with sleep apnea and shift work sleep disorder. It is taken by mouth. Modafinil is not approved by the US Food and Drug Administration (FDA) for use in people under age 17.
Modafinil has potential for causing severe allergic reactions, mental (psychiatric) effects, hypersensitivity, adverse interactions with prescription drugs, and misuse or abuse. Modafinil may harm the fetus if taken during or two months prior to pregnancy.
While modafinil is used as a cognitive enhancer or "smart drug" among healthy individuals seeking improved focus and productivity, its use outside medical supervision raises concerns regarding potential misuse or abuse. Research on the cognitive enhancement effects of modafinil in non-sleep-deprived individuals has yielded mixed results, with some studies suggesting modest improvements in attention and executive functions, while others show no significant benefits or even a decline in cognitive functions. | 4 | Stereochemistry |
Acid orange 5 may be prepared by diazotization of sulfanilic acid, followed by reaction with diphenylamine: | 3 | Analytical Chemistry |
RdRp differs from DNA dependent RNA polymerase as it works to catalyze the synthesis of an RNA strand complementary to a given RNA template, rather than using a DNA template. The RNA replication process is a four-step mechanism, as described.
# Nucleoside triphosphate (NTP) binding – initially, the RdRp presents with a vacant active site in which an NTP binds, complementary to the corresponding nucleotide on the template strand. Correct NTP binding causes the RdRp to undergo a conformational change.
# Active site closure – the conformational change, initiated by the correct NTP binding, results in the restriction of active site access and produces a catalytically competent state.
# Phosphodiester bond formation – two Mg ions are present in the catalytically active state and arrange themselves in such a way around the newly synthesized RNA chain that the substrate NTP is able to undergo a phosphatidyl transfer and form a phosphodiester bond with the newly synthesized chain. Without the use of these Mg ions, the active site is no longer catalytically stable and the RdRp complex changes to an open conformation.
# Translocation – once the active site is open, the RNA template strand is able to move by one position through the RdRp protein complex and continue chain elongation by binding a new NTP, unless otherwise specified by the template.
RNA synthesis can be performed by means of a primer-independent (de novo) or a primer-dependent mechanism that utilizes a viral protein genome-linked (VPg) primer. The de novo initiation consists in the addition of a nucleoside triphosphate (NTP) to the 3'-OH of the first initiating NTP. During the following so-called elongation phase, this nucleotidyl transfer reaction is repeated with subsequent NTPs to generate the complementary RNA product. Termination of the nascent RNA chain produced by RdRp is not completely known, however, it has been shown that RdRp termination is sequence-independent.
One major drawback of RNA-dependent RNA polymerase replication is the immense error rate during transcription. RdRps are known to have a lack of fidelity on the order of 10 nucleotides, which is thought to be a direct result of its insufficient proofreading abilities. This high rate of variation is favored in viral genomes as it allows for the pathogen to overcome defenses developed by hosts trying to avoid infection allowing for evolutionary growth. | 1 | Biochemistry |
Thermal radiation is the emission of electromagnetic waves from all matter that has a temperature greater than absolute zero. Thermal radiation reflects the conversion of thermal energy into electromagnetic energy. Thermal energy is the kinetic energy of random movements of atoms and molecules in matter. It is present in all matter of nonzero temperature. These atoms and molecules are composed of charged particles, i.e., protons and electrons. The kinetic interactions among matter particles result in charge acceleration and dipole oscillation. This results in the electrodynamic generation of coupled electric and magnetic fields, resulting in the emission of photons, radiating energy away from the body. Electromagnetic radiation, including visible light, will propagate indefinitely in vacuum.
The characteristics of thermal radiation depend on various properties of the surface from which it is emanating, including its temperature and its spectral emissivity, as expressed by Kirchhoffs law. The radiation is not monochromatic, i.e., it does not consist of only a single frequency, but comprises a continuous spectrum of photon energies, its characteristic spectrum. If the radiating body and its surface are in thermodynamic equilibrium and the surface has perfect absorptivity at all wavelengths, it is characterized as a black body. A black body is also a perfect emitter. The radiation of such perfect emitters is called black-body radiation. The ratio of any bodys emission relative to that of a black body is the body's emissivity, so a black body has an emissivity of one.
Absorptivity, reflectivity, and emissivity of all bodies are dependent on the wavelength of the radiation. Due to reciprocity, absorptivity and emissivity for any particular wavelength are equal at equilibrium – a good absorber is necessarily a good emitter, and a poor absorber is a poor emitter. The temperature determines the wavelength distribution of the electromagnetic radiation.
The distribution of power that a black body emits with varying frequency is described by Plancks law. At any given temperature, there is a frequency f at which the power emitted is a maximum. Wiens displacement law, and the fact that the frequency is inversely proportional to the wavelength, indicates that the peak frequency f is proportional to the absolute temperature T of the black body. The photosphere of the sun, at a temperature of approximately 6000 K, emits radiation principally in the (human-)visible portion of the electromagnetic spectrum. Earths atmosphere is partly transparent to visible light, and the light reaching the surface is absorbed or reflected. Earths surface emits the absorbed radiation, approximating the behavior of a black body at 300 K with spectral peak at f. At these lower frequencies, the atmosphere is largely opaque and radiation from Earth's surface is absorbed or scattered by the atmosphere. Though about 10% of this radiation escapes into space, most is absorbed and then re-emitted by atmospheric gases. It is this spectral selectivity of the atmosphere that is responsible for the planetary greenhouse effect, contributing to global warming and climate change in general (but also critically contributing to climate stability when the composition and properties of the atmosphere are not changing). | 7 | Physical Chemistry |
The binding of CTCF has been shown to have many effects, which are enumerated below. In each case, it is unknown if CTCF directly evokes the outcome or if it does so indirectly (in particular through its looping role). | 1 | Biochemistry |
The enamine is generally generated in situ from catalytic amine (such as pyrrolidine) and a ketone. The enamine then reacts as the dienophile with a 1,2,4-triazine. The initial adduct then expels nitrogen, and the pyridine is rearomatized with loss of the amine. | 0 | Organic Chemistry |
One form of Cannabis defense is the up-regulation of cannabinoids and specialized terpenes in response to differing biotic stressors in the environment such as pests and predation. In a study from 2019, tobacco hornworm larvae were fed on an artificial diet of wheat germ containing a cannabis agent. The results showed that on average, significantly high dosages of CBD in the new diet may have decreased survival rates of the larvae. In addition, Maduca sexta larvae avoids eating plants containing high amounts of CBD, allowing for the indication that CBD may be a natural pest deterrent. However, research also has shown when the plant is subjected to mechanical wounds from certain insects, CBD levels were unchanged and even decreased. This observation may be due to difference in the species of insect and chemical secretions, thus providing a new hypothesis that CBD levels vary in response to certain species or even have no effect.
Phytocannabinoid and terpene content in the leaves and flowers of C. sativa rises when under attack by Tetranychus urticae, a common pest for the genus. When compared to a control of Cannabis sativa without any pest damage, research from 2022 demonstrated an overall increase of secondary metabolites in plants exposed to Tetranychus urtivae infestation and measured this metabolite rise using liquid and gas chromatograph mass spectrometers. The increase was found to be significant, and is attributed as a defense mechanism in the plant.
The induction and up-regulation of cannabinoids as defense genes in Cannabis can be induced by elicitors. In a study from 2019, salicylic acid (SA) was used with GABA as an elicitor to determine its effects on the expression of metabolites involved in THC and CBD biosynthesis. SA and GABA were demonstrated to effectively up-regulate the expression of THCAS, a cannabigerolic acid used to form THC, which resulted in higher levels of THC. These results support the mechanism in which cannabis elicitors such as salicylic acid and GABA triggers a signal cascade for increased expression of defense genes in response to stress.
One line of defense is the release of volatile organic compounds (VOCs) into the air to defend against herbivores by warning neighboring plants. The release of VOCs may begin with the jasmonic (JA) pathway pathway which up-regulates defensive genes. Jasmonic acid, also called jasmonate, is a hormone linked to wound signaling in plants. Rapid wound signaling involves an influx of calcium after the arrival of an action potential. The increase of calcium triggers a regulatory protein, calmodulin, to turn on a protein kinase releasing JASMONATE-ASSOCIATED VQ-MOTIF GENE1 (JAV1) by combining it with phosphoric acid. From a study in 2020, in response to the necrotrophic pathogen gray mold, JA mediated markers were up-regulated in the leaves that were infected, from beginning of infection to the end. Through a series of signals, the plant detects the presence of fungal elicitors/pathogens, then through the JA pathway the expression of defense genes are increased. | 1 | Biochemistry |
The TFs binding sites are physical DNA sites recognized by transcription factors within a genome, including enhancer, upstream activator (UAS) and operator sites that may bind repressors or activators. | 1 | Biochemistry |
The Berry mechanism in square pyramidal molecules (such as IF) is somewhat like the inverse of the mechanism in bipyramidal molecules. Starting at the "transition phase" of bipyramidal pseudorotation, one pair of fluorines scissors back and forth with a third fluorine, causing the molecule to vibrate. Unlike with pseudorotation in bipyramidal molecules, the atoms and ligands which are not actively vibrating in the "scissor" motion are still participating in the process of pseudorotation; they make general adjustment based on the movement of the actively vibrating atoms and ligands. However, this geometry requires a significant amount of energy to occur of about 26.7 kcal/mol. | 4 | Stereochemistry |
Other compounds having different elements in the corners, various atoms or groups bonded to the corners are all part of this class of structures.
Inorganic cubane-type clusters include selenium tetrachloride, tellurium tetrachloride, and sodium silox.
Cubane clusters are common throughout bioinorganic chemistry. Ferredoxins containing [FeS] iron–sulfur clusters are pervasive in nature. The four iron atoms and four sulfur atoms form an alternating arrangement at the corners. The whole cluster is typically anchored by coordination of the iron atoms, usually with cysteine residues. In this way, each Fe center achieves tetrahedral coordination geometry. Some [FeS] clusters arise via dimerization of square-shaped [FeS] precursors. Many synthetic analogues are known including heterometallic derivatives.
Several alkyllithium compounds exist as clusters in solution, typically tetramers, with the formula [RLi]. Examples include methyllithium and tert-butyllithium. The individual RLi molecules are not observed. The four lithium atoms and the carbon from each alkyl group bonded to them occupy alternating vertices of the cube, with the additional atoms of the alkyl groups projecting off their respective corners.
Octaazacubane is a hypothetical allotrope of nitrogen with formula N; the nitrogen atoms are the corners of the cube. Like the carbon-based cubane compounds, octaazacubane is predicted to be highly unstable due to angle strain at the corners, and it also does not enjoy the kinetic stability seen for its organic analogues. | 4 | Stereochemistry |
First combine template RNA, primer, dNTP mix, and nuclease-free water in a PCR tube. Then, add an RNase inhibitor and reverse transcriptase to the PCR tube. Next, place the PCR tube into a thermal cycler for one cycle wherein annealing, extending, and inactivating of reverse transcriptase occurs. Finally, proceed directly to step two which is PCR or store product on ice until PCR can be performed. | 1 | Biochemistry |
Soils act as a major sink for atmospheric methane through the methanotrophic bacteria that reside within them. This occurs with two different types of bacteria. "High capacity-low affinity" methanotrophic bacteria grow in areas of high methane concentration, such as waterlogged soils in wetlands and other moist environments. And in areas of low methane concentration, "low capacity-high affinity" methanotrophic bacteria make use of the methane in the atmosphere to grow, rather than relying on methane in their immediate environment. Methane oxidation allows methanotrophic bacteria to use methane as a source of energy, reacting methane with oxygen and as a result producing carbon dioxide and water.
: CH + 2O → CO + 2HO
Forest soils act as good sinks for atmospheric methane because soils are optimally moist for methanotroph activity, and the movement of gases between soil and atmosphere (soil diffusivity) is high. With a lower water table, any methane in the soil has to make it past the methanotrophic bacteria before it can reach the atmosphere. Wetland soils, however, are often sources of atmospheric methane rather than sinks because the water table is much higher, and the methane can be diffused fairly easily into the air without having to compete with the soil's methanotrophs.
Methanotrophic bacteria also occur in the underwater sediments. Their presence can often efficiently limit emissions from sources such as the underwater permafrost in areas like the Laptev Sea. | 2 | Environmental Chemistry |
Tokita was born in Sapporo, Japan in 1923. He met his wife Noriko while on an exchange program at Duke University. They married and decided to stay in the United States. He was a close colleague of 2009 Charles Goodyear Medal winner James White, introducing White to his future wife Yoko Masaki. | 7 | Physical Chemistry |
It can be synthesised in the following ways:
* as an intermetallic compound, by direct fusion of pure components according to stoichiometric calculations:
* by reduction of uranium dioxide with hydrogen in the presence of platinum: | 8 | Metallurgy |
The German physicist Rudolf Clausius, in the 1850s, was the first to mathematically quantify the discovery of irreversibility in nature through his introduction of the concept of entropy. In his 1854 memoir "On a Modified Form of the Second Fundamental Theorem in the Mechanical Theory of Heat," Clausius states:
Simply, Clausius states that it is impossible for a system to transfer heat from a cooler body to a hotter body. For example, a cup of hot coffee placed in an area of room temperature will transfer heat to its surroundings and thereby cool down with the temperature of the room slightly increasing (to ). However, that same initial cup of coffee will never absorb heat from its surroundings, causing it to grow even hotter, with the temperature of the room decreasing (to ). Therefore, the process of the coffee cooling down is irreversible unless extra energy is added to the system.
However, a paradox arose when attempting to reconcile microanalysis of a system with observations of its macrostate. Many processes are mathematically reversible in their microstate when analyzed using classical Newtonian mechanics. This paradox clearly taints microscopic explanations of macroscopic tendency towards equilibrium, such as James Clerk Maxwells 1860 argument that molecular collisions entail an equalization of temperatures of mixed gases. From 1872 to 1875, Ludwig Boltzmann reinforced the statistical explanation of this paradox in the form of Boltzmanns entropy formula, stating that an increase of the number of possible microstates a system might be in, will increase the entropy of the system, making it less likely that the system will return to an earlier state. His formulas quantified the analysis done by William Thomson, 1st Baron Kelvin, who had argued that:
Another explanation of irreversible systems was presented by French mathematician Henri Poincaré. In 1890, he published his first explanation of nonlinear dynamics, also called chaos theory. Applying chaos theory to the second law of thermodynamics, the paradox of irreversibility can be explained in the errors associated with scaling from microstates to macrostates and the degrees of freedom used when making experimental observations. Sensitivity to initial conditions relating to the system and its environment at the microstate compounds into an exhibition of irreversible characteristics within the observable, physical realm. | 7 | Physical Chemistry |
Bumblebees produce a signalling pheromone from tergal glands located on their dorsal abdomen as discovered in experiments performed by A. Dornhaus, A. Brockmann and L. Chittka in 2003. They monitored the activity of bee colonies after exposure to products from several glands located along the bee's body. The only one yielding significant changes in activity level came from the tergites VI and VII. This is similar to a pheromone produced from the Nasanov gland in honeybees, but differs in the active compound. It has been suggested that this pheromone may facilitate learning of floral scents, since its release is coupled with the import of the floral scent from the nectar collected by the successful forager. Experiments by Molet, Chittka and Raine in 2009 showed that bumblebees may be able to learn floral scents associated with rewarding flowers better if the particular scent is found in nectar deposited in the honeypots. | 1 | Biochemistry |
Using the above principles, equations that relate a global protein signal, corresponding to the folding states in equilibrium, and the variable value of a denaturing agent, either temperature or a chemical molecule, have been derived for homomeric and heteromeric proteins, from monomers to trimers and potentially tetramers. These equations provide a robust theoretical basis for measuring the stability of complex proteins, and for comparing the stabilities of wild type and mutant proteins. Such equations cannot be derived for pentamers of higher oligomers because of mathematical limitations (Abel–Ruffini theorem). | 7 | Physical Chemistry |
Five common thermodynamic potentials are:
where = temperature, = entropy, = pressure, = volume. is the number of particles of type in the system and is the chemical potential for an -type particle. The set of all are also included as natural variables but may be ignored when no chemical reactions are occurring which cause them to change. The Helmholtz free energy is in ISO/IEC standard called Helmholtz energy or Helmholtz function. It is often denoted by the symbol , but the use of is preferred by IUPAC, ISO and IEC.
These five common potentials are all potential energies, but there are also entropy potentials. The thermodynamic square can be used as a tool to recall and derive some of the potentials.
Just as in mechanics, where potential energy is defined as capacity to do work, similarly different potentials have different meanings like the below:
* Internal energy () is the capacity to do work plus the capacity to release heat.
* Gibbs energy () is the capacity to do non-mechanical work.
* Enthalpy () is the capacity to do non-mechanical work plus the capacity to release heat.
* Helmholtz energy () is the capacity to do mechanical work plus non-mechanical work.
From these meanings (which actually apply in specific conditions, e.g. constant pressure, temperature, etc.), for positive changes (e.g., ), we can say that is the energy added to the system, is the total work done on it, is the non-mechanical work done on it, and is the sum of non-mechanical work done on the system and the heat given to it.
Note that the sum of internal energy is conserved, but the sum of Gibbs energy, or Helmholtz energy, are not conserved, despite being named "energy". They can be better interpreted as the potential to perform "useful work", and the potential can be wasted.
Thermodynamic potentials are very useful when calculating the equilibrium results of a chemical reaction, or when measuring the properties of materials in a chemical reaction. The chemical reactions usually take place under some constraints such as constant pressure and temperature, or constant entropy and volume, and when this is true, there is a corresponding thermodynamic potential that comes into play. Just as in mechanics, the system will tend towards a lower value of a potential and at equilibrium, under these constraints, the potential will take the unchanging minimum value. The thermodynamic potentials can also be used to estimate the total amount of energy available from a thermodynamic system under the appropriate constraint.
In particular: (see principle of minimum energy for a derivation)
* When the entropy and "external parameters" (e.g. volume) of a closed system are held constant, the internal energy decreases and reaches a minimum value at equilibrium. This follows from the first and second laws of thermodynamics and is called the principle of minimum energy. The following three statements are directly derivable from this principle.
* When the temperature and external parameters of a closed system are held constant, the Helmholtz free energy decreases and reaches a minimum value at equilibrium.
* When the pressure and external parameters of a closed system are held constant, the enthalpy decreases and reaches a minimum value at equilibrium.
* When the temperature , pressure and external parameters of a closed system are held constant, the Gibbs free energy decreases and reaches a minimum value at equilibrium. | 7 | Physical Chemistry |
Adsorption of an indicator molecule was first proposed by Hammett for ordering the strength of solid acids and bases. This technique is only applicable to surface Brønsted sites on metal oxides. According to Hammett, the strength of a Brønsted surface site can be determined by the Hammett acidity function,
where B is the basic indicator molecule. The concentration of Brønsted acid sites can be determined by titrating a suspension of the oxide with an acid/base indicator present. However, this method is subject to many problems. For instance only Bronsted acid sites can be quantified with this method. Metal oxide surfaces can have both Brønsted and Lewis acid sites present at the same time which leads to a nonspecific interaction between the oxide and the indicator. Also, as outlined in the theory section, the perturbation of neighboring sites upon adsorption of indicator molecules compromises the integrity of this model. | 7 | Physical Chemistry |
Grignard was drafted into the French military as part of obligatory military service in 1892. Within the two years of his first session of service he rose to the rank of corporal. He was demobilized in 1894 and returned to Lyon to pursue his education. He was awarded a medal of the Legion of Honour and made a Chevalier in 1912 after winning the Nobel Prize. When World War I broke out, Grignard was drafted back into the military, keeping his rank of corporal. He was placed on sentry duty, and served there for several months until he was brought to the attention of the General Staff. Grignard had been wearing his Medal of the Legion of Honour, despite being ordered to take it off by a superior. After looking more into Grignard, the General Staff decided that he would be better suited for research than sentry duty, so they assigned him to the explosives division. Grignard's research shifted to antidotes to chemical weapons when production of TNT was no longer sustainable, and eventually Grignard was assigned to research new chemical weapons for the French army. | 0 | Organic Chemistry |
The use of ionic liquids in carbon capture is a potential application of ionic liquids as absorbents for use in carbon capture and sequestration. Ionic liquids, which are salts that exist as liquids near room temperature, are polar, nonvolatile materials that have been considered for many applications. The urgency of climate change has spurred research into their use in energy-related applications such as carbon capture and storage. | 7 | Physical Chemistry |
The most widely described RNA modification in mammalian viruses is mA, which was first identified in Influenza virus mRNAs, in 1976. The epitranscriptomic analysis of viral transcripts has revealed that mA levels in viral and cellular transcripts are similar. Nevertheless, in some viruses such as adenovirus-2, mA levels are higher in viral mRNAs. As with cellular RNAs, mA is predominantly added in the nucleus by METTL3, with the assistance of several cofactors such as METTL14, WTAP, KIAA1429 and RBM15/RMB15B. A recent study demonstrates the presence of mA in the small T antigen of Merkel cell polyomavirus (MCPyV) in Merkel cell carcinoma, a fatal skin cancer.
Studies of the viral mA mark have mostly been conducted with HIV. Despite the high mutagenic rate of this virus, mA sites have been evolutionarily conserved. This is due to the fact that mA is involved in regulating multiple stages in the HIV life-cycle. In addition to the normal functions mA has in pre-mRNA splicing, nuclear export, mRNA stability and translation; this mark also inhibits the recognition of viral transcripts by Toll-like receptors and RIG-1 receptors. As a result, mA positively influences viral replication. On the other hand, HIV also regulates the addition of the mA mark in a number of cellular mRNAs. For instance, 56 cellular transcripts that only contain mA during HIV infection have been identified. The effect this mark has on cellular transcripts during the course of the viral infection remains unknown.
Even if mA-marked viral transcripts are involved in regulating gene expression of a number of different viruses, the mechanisms by which this happens have not been identified. To date, three possible models have been proposed.
Although METTL3 and METTL14 are mostly localized in the nucleus, they can also be found in the cytoplasm, where they methylate the genomes and transcripts of cytoplasmic RNA viruses. As opposed to nuclear viruses, loss of mA on hepatitis C virus (HCV, a cytoplasmic RNA virus) increases the production of infectious HCV virions, which indicates that in this particular virus the mA mark has a negative effect on virus production. Nevertheless, in other cytoplasmic RNA viruses such as dengue virus and yellow fever virus, mA sites have been selected for during evolution, suggesting that the mA mark is beneficial for these viruses.
Since mA enhances viral replication, mA can be used as a target for antiviral therapy. The major challenge is to target this mark in viral transcripts without causing major effects to the host cells, as normally occurring cellular mA marks will also be depleted. The S-adenosylhomocysteine (SAC) hydrolase inhibitor 3-dezaadenosine (DAA) can be used as an antiviral drug, because it inhibits the addition of mA. However, it is yet to be determined whether this drug has any off-target effects. | 1 | Biochemistry |
The Ames process is a process by which pure uranium metal is obtained. It can be achieved by mixing any of the uranium halides (commonly uranium tetrafluoride) with magnesium metal powder or aluminium metal powder. | 8 | Metallurgy |
Viral transformation disrupts the normal expression of the host cell's genes in favor of expressing a limited number of viral genes. The virus also can disrupt communication between cells and cause cells to divide at an increased rate. | 1 | Biochemistry |
* Мир-Бабаев М.Ф. Научный подвиг гения (к 100-летию со дня рождения Ю.Г. Мамедалиева) – «Consulting & Business», 2005, No.8, с.8–12.
* Mir-Babayev M.F. The role of Azerbaijan in the World's oil industry – “Oil-Industry History” (USA), 2011, v. 12, no. 1, p. 109–123.
* Mir-Babayev M.F. Formula of Victory (Yusif Mamedaliyev) - "SOCAR plus", 2012, Autumn, p. 100–111. | 0 | Organic Chemistry |
Several species of fungi can be used for bioleaching. Fungi can be grown on many different substrates, such as electronic scrap, catalytic converters, and fly ash from municipal waste incineration. Experiments have shown that two fungal strains (Aspergillus niger, Penicillium simplicissimum) were able to mobilize Cu and Sn by 65%, and Al, Ni, Pb, and Zn by more than 95%. Aspergillus niger can produce some organic acids such as citric acid. This form of leaching does not rely on microbial oxidation of metal but rather uses microbial metabolism as source of acids that directly dissolve the metal. | 8 | Metallurgy |
Laid down in the environment, territorial pheromones mark the boundaries and identity of an organisms territory. In cats and dogs, these hormones are present in the urine, which they deposit on landmarks serving to mark the perimeter of the claimed territory. In social seabirds, the preen gland is used to mark nests, nuptial gifts, and territory boundaries with behavior formerly described as displacement activity'. | 1 | Biochemistry |
Organoberyllium phosphines are another class of compounds that is used in synthesis. Phosphine donates two electrons into the beryllium center. Phosphines are L-type ligands. Unlike most metal ammine complexes, metal phosphine complexes tend to be lipophilic, displaying good solubility in organic solvents. Phosphine ligands are also π-acceptors. Their π-acidity arises from overlap of P-C σ* anti-bonding orbitals with filled metal orbitals. Beryllium can coordinate with a phosphine due to its good π-acceptor ability, which is used extensively in beryllium chemistry literature. An organoberyllium phosphine can be prepared through coordination with a beryllium halide to form a four-coordinate tetrahedral compound. | 0 | Organic Chemistry |
Fixed aRME are established either by silencing of one allele that previously has been biallelically expressed, or by activation of a single allele from previously silent gene. Expression activation of the silent allele is coupled with a feedback mechanism that prevents expression of the second allele. Another scenario is also possible due to limited time-window of low-probability initiation, that could lead to high frequencies of cells with single-allele expression. It is estimated that 2-10% of all genes are fixed aRME. Studies
of fixed aRME require either expansion of monoclonal cultures or lineage-traced in vivo or in vitro cells that are mitotically.
Dynamic aRME occurs as a consequence of stochastic allelic expression. Transcription happens in bursts, which results in RNA molecules being synthesized from each allele separately. So over time, both alleles have a probability to initiate transcription. Transcriptional bursts are allelically stochastic, and lead to either maternal or paternal allele being accumulated in the cell. The gene transcription burst frequency and intensity combined with RNA-degradation rate form the shape of RNA distribution at the moment of observation and thus whether the gene is bi- or monoallelic. Studies that distinguish fixed and dynamic aRME require single-cell analyses of clonally related cells. | 1 | Biochemistry |
Metabolic rates in lakes and reservoirs are controlled by many environmental factors, such as light and nutrient availability, temperature, and water column mixing regimes. Thus, spatial and temporal changes in those factors cause spatial and temporal variability in metabolic rates, and each of those factors affect metabolism at different spatial and temporal scales. | 1 | Biochemistry |
Burks-Houck began her education in Anniston, Alabama, having attended both elementary and high school in the city. Burks-Houck continued her education and earned a Bachelor of Arts degree in chemistry from Dillard University followed by a Master of Science Degree in Organic Chemistry from Atlanta University. | 0 | Organic Chemistry |
Electrophilic additions of allylsilanes generally occur via an anti S2 process. Allylsilanes react through a conformation in which the smallest substituent on the carbon attached to silicon is essentially eclipsing the double bond. The silyl moiety forces electrophilic attack on the face opposite the silyl group for steric and electronic reasons, although the effects are not large. This model predicts that when the double bond is 1,2-disubstituted, the Z isomer should exhibit greater selectivity than the E' isomer, and this has been observed
Vinylsilane additions proceed with retention of double bond configuration, and follow a similar principle. After addition of the electrophile to the top or bottom face of the double bond, the silyl moiety rotates to become parallel to the adjacent empty 2p orbital. The principle of least motion provides that the electrophile moves into a position close to that formerly occupied by the silyl group. Thus, the configuration of the double bond is retained after loss of the silyl group. | 0 | Organic Chemistry |
Point defects (as well as stationary dislocations, jogs, and kinks) present in a material create stress fields within a material that disallow traveling dislocations to come into direct contact. Much like two particles of the same electric charge feel a repulsion to one another when brought together, the dislocation is pushed away from the already present stress field. | 8 | Metallurgy |
Protein separate techniques, such as 2D PAGE, are limited in that they cannot handle very high or low molecular weight protein species. Alternative methods have been developed to deal with such cases. These include liquid chromatography mass spectrometry along with sodium dodecyl sulfate polyacrylamide gel electrophoresis, or liquid chromatography mass spectrometry run in multiple dimensions. Compared to simple 2D page, liquid chromatography mass spectrometry can handle a larger range of protein species size, but it is limited in the amount of protein sample it handle at once. Liquid chromatography mass spectrometry is also limited in its lack of a reference map from which to work with. Complex algorithms are usually used to analyze the fringe results that occur after a procedure is run. The unknown portions of the protein species are usually not analyzed in favor of familiar proteomes, however. This fact reveals a fault with current technology; new techniques are needed to increase both the specificity and scope of proteome mapping. | 1 | Biochemistry |
A Rho factor acts on an RNA substrate. Rho's key function is its helicase activity, for which energy is provided by an RNA-dependent ATP hydrolysis. The initial binding site for Rho is an extended (~70 nucleotides, sometimes 80–100 nucleotides) single-stranded region, rich in cytosine and poor in guanine, called the rho utilisation site (rut), in the RNA being synthesised, upstream of the actual terminator sequence. Several rho binding sequences have been discovered. No consensus is found among these, but the different sequences each seem specific, as small mutations in the sequence disrupts its function. Rho binds to RNA and then uses its ATPase activity to provide the energy to translocate along the RNA until it reaches the RNA–DNA helical region, where it unwinds the hybrid duplex structure. RNA polymerase pauses at the termination sequence, which is because there is a specific site around 100 nt away from the Rho binding site called the Rho-sensitive pause site. So, even though the RNA polymerase is about 40 nt per second faster than Rho, it does not pose a problem for the Rho termination mechanism as the RNA polymerase allows Rho factor to catch up.
In short, Rho factor acts as an ATP-dependent unwinding enzyme, moving along the newly forming RNA molecule towards its 3′ end and unwinding it from the DNA template as it proceeds. | 1 | Biochemistry |
The Sørensen formol titration(SFT) invented by S. P. L. Sørensen in 1907 is a titration of an amino acid with potassium hydroxide in the presence of formaldehyde. It is used in the determination of protein content in samples.
If instead of an amino acid an ammonium salt is used the reaction product with formaldehyde is hexamethylenetetramine:
The liberated hydrochloric acid is then titrated with the base and the amount of ammonium salt used can be determined.
With an amino acid the formaldehyde reacts with the amino group to form a methylene amino (R-N=CH) group. The remaining acidic carboxylic acid group can then again be titrated with base. | 1 | Biochemistry |
;From PCl
Phosphite esters are typically prepared by treating phosphorus trichloride with an alcohol. For alkyl alcohols the displaced chloride ion can attack the phosphite, causing dealkylation to give a dialkylphosphite and an organochlorine compound. The overall reaction is as follows:
:PCl + 3 CHOH → (CHO)P(O)H + 2 HCl + CHCl
Alternatively, when the alcoholysis is conducted in the presence of proton acceptors (typically an amine base), one obtains the C-symmetric trialkyl derivatives:
:PCl + 3 CHOH + 3 RN → (CHO)P + 3 RNHCl
A base is not essential when using aromatic alcohols such as phenols, as they are not susceptible to attack by chloride, however it does catalyse the esterification reaction and is therefore often included.
;By transesterification
Phosphite esters can also be prepared by transesterification, as they undergo alcohol exchange upon heating with other alcohols. This process is reversible and can be used to produce mixed alkyl phosphites. Alternatively, if the phosphite of a volatile alcohol is used, such as trimethyl phosphite, then the by product (methanol) can be removed by distillation, allowing the reaction to be driven to completion. | 0 | Organic Chemistry |
Metal carbonyl hydrides are complexes of transition metals with carbon monoxide and hydride as ligands. These complexes are useful in organic synthesis as catalysts in homogeneous catalysis, such as hydroformylation. | 0 | Organic Chemistry |
SDS is used in cleaning procedures, and is commonly used as a component for lysing cells during RNA extraction or DNA extraction, inhibiting the activity of nucleases, enzymes that can degrade DNA, protecting the integrity of the isolated genetic material, and for denaturing proteins in preparation for electrophoresis in the SDS-PAGE technique.
In the case of SDS-PAGE, the compound works by disrupting non-covalent bonds in the proteins, and so denaturing them, i.e. causing the protein molecules to lose their native conformations and shapes. By binding to proteins at a ratio of one SDS molecule per 2 amino acid residues, the negatively charged detergent provides all proteins with a similar net negative charge and therefore a similar charge-to-mass ratio. In this way, the difference in mobility of the polypeptide chains in the gel can be attributed solely to their length as opposed to both their native charge and shape. This separation based on the size of the polypeptide chain simplifies the analysis of protein molecules. | 1 | Biochemistry |
writing the potential energy as depending on a continuous parameter,
one has the exact result
This can either be directly verified from definitions or seen from the limit of the above Gibbs-Bogoliubov inequalities when
we can therefore write
which is the thermodynamic integration (or TI) result. It can be approximated by dividing the range between states A and B into many values of λ at which the expectation value is estimated, and performing numerical integration. | 7 | Physical Chemistry |
# Yang, Dong, Xijun Chang, Yongwen Liu, and Sui Wang. "Synthesis and Efficiency of a Spherical Macroporous Epoxy-Polyamide Chelating Resin for Preconcentrating and Separating Trace Noble Metal Ions." Annali di Chimica 95.1-2 (2005): 111-14.
# Zougagh, Mohammed, J. M. Cano Pav N, and A. Garcia De Torres. "Chelating Sorbents Based on Silica Gel and Their Application in Atomic Spectrometry." Anal Bioanal Chem Analytical and Bioanalytical Chemistry 381.6 (2005): 1103-113.
# R. R. Greenberg" and H. M. Kingston. “Trace Element Analysis of Natural Water Samples by Neutron Activation Analysis with Chelating Resin.” Center for Analytical Chemistry, National Bureau of Standards, Washington, D.C. 20234. | 3 | Analytical Chemistry |
The methylation of certain CpG clusters (i.e. DNA areas high in cytosine and guanine) regulate the transcriptional activity of nearby genes. That is, the methylation of a cluster(s) regulates its nearby gene by blocking it from making mRNAs and thereby the proteins encoded by these mRNAs. Studies find that the CMTM5 gene in the DNA isolated from the blood of individuals with the autoimmune diseases of systemic lupus erythematosus and primary Sjögrens syndrome (i.e. Sjorgens syndrome not associated with other health problems or connective tissue diseases) is hyper-methylated at its CpG cluster(s) and thereby less active or inactive. On the other hand, the CpG cluster(s) controlling the CMTM5 gene in the blood of individuals with the autoimmune disease of rheumatoid arthritis are hypo-methylated and therefore highly active. These methylation changes, the studies suggest, regulate the function of immunologically active blood cells (and, perhaps, blood platelets) and thereby the development, maintenance, and/or worsening of the cited autoimmune diseases. Further studies are required to prove that these methylations contribute to the immunologic dysregulations occurring in these (and perhaps other) autoimmune diseases and can serve as clinical markers of disease severity and/or as therapeutic targets for controlling the diseases. | 1 | Biochemistry |
Variant annotation tools use machine learning algorithms to predict variant annotations. Different annotation tools use different algorithms. Common algorithms include:
* Interval/Random forest-eg.MutPred, SNPeff
* Neural networks-eg.SNAP
* Support Vector Machines-e.g. PhD-SNP, SNPs&GO
* Bayesian classification-eg.PolyPhen-2 | 1 | Biochemistry |
Like most fruit, grapes vary in the number of phenolic compounds they have. This characteristic is used as a parameter in judging the quality of the wine. The general process of winemaking is initiated by the enzymatic oxidation of phenolic compounds by polyphenol oxidases. Contact between the phenolic compounds in the vacuole of the grape cell and the polyphenol oxidase enzyme (located in the cytoplasm) triggers the oxidation of the grape. Thus, the initial browning of grapes occurs as a result of "compartmentalization modification" in the cells of the grape. | 1 | Biochemistry |
Ultraviolet germicidal irradiation (UVGI) is a disinfection technique employing ultraviolet (UV) light, particularly UV-C (180-280 nm), to kill or inactivate microorganisms. UVGI primarily inactivates microbes by damaging their genetic material, thereby inhibiting their capacity to carry out vital functions.
The use of UVGI extends to an array of applications, encompassing food, surface, air, and water disinfection. UVGI devices can inactivate microorganisms including bacteria, viruses, fungi, molds, and other pathogens. Recent studies have substantiated the ability of UV-C light to inactivate SARS-CoV-2, the strain of coronavirus that causes COVID-19.
UV-C wavelengths demonstrate varied germicidal efficacy and effects on biological tissue. Many germicidal lamps like low-pressure mercury (LP-Hg) lamps, with peak emissions around 254 nm, contain UV wavelengths that can be hazardous to humans. As a result, UVGI systems have been primarily limited to applications where people are not directly exposed, including hospital surface disinfection, [https://www.cdc.gov/coronavirus/2019-ncov/community/ventilation/uvgi.html upper-room UVGI], and water treatment. More recently, the application of wavelengths between 200-235 nm, often referred to as far-UVC, has gained traction for surface and air disinfection. These wavelengths are regarded as much safer due to their significantly reduced penetration into human tissue.
Notably, UV-C light is virtually absent in sunlight reaching the Earth's surface due to the absorptive properties of the ozone layer within the atmosphere. | 5 | Photochemistry |
DMAP can be prepared in a two-step procedure from pyridine, which is first oxidized to 4-pyridylpyridinium cation. This cation then reacts with dimethylamine: | 0 | Organic Chemistry |
Pioneered by Stanley Fields and Ok-Kyu Song in 1989, the technique was originally designed to detect protein–protein interactions using the Gal4 transcriptional activator of the yeast Saccharomyces cerevisiae. The Gal4 protein activated transcription of a gene involved in galactose utilization, which formed the basis of selection. Since then, the same principle has been adapted to describe many alternative methods, including some that detect protein–DNA interactions or DNA-DNA interactions, as well as methods that use different host organisms such as Escherichia coli or mammalian cells instead of yeast. | 1 | Biochemistry |
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