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Melt spinning is a metal forming technique that is typically used to form thin ribbons of metal or alloys with a particular atomic structure.
Some important commercial applications of melt-spun metals include high-efficiency transformers (Amorphous metal transformer), sensory devices, telecommunications equipment, and power electronics.
A typical melt spinning process involves casting molten metal by jetting it onto a rotating wheel or drum, which is cooled internally, usually by water or liquid nitrogen. The molten material rapidly solidifies upon contact with the large, cold surface area of the drum. The rotation of the drum constantly removes the solidified product while exposing new surface area to the molten metal stream, allowing for continuous production. The resulting ribbon is then directed along the production line to be packaged or machined into further products.
The cooling rates achievable by melt spinning are on the order of 10–10 Kelvins per second (K/s). Consequently, melt spinning is used to develop materials that require extremely high cooling rates in order to form, such as metallic glasses. Due to their rapid cooling, these products have a highly disordered atomic structure which gives them unique magnetic and physical properties (see amorphous metals).
Several variations to the melt spinning process provide specific advantages. These processes include planar flow casting, twin roll melt spinning, and auto ejection melt spinning.
Originating with Robert Pond in a series of related patents from 1958 to 1961 (US Patent Nos. 2825108, 2910744, and 2976590), the current concept of the melt spinner was outlined by Pond and Maddin in 1969. At first, the liquid was quenched on the inner surface of a drum. Liebermann and Graham further developed the process as a continuous casting technique by 1976, this time on the drum's outer surface. The process can continuously produce thin ribbons of material, with sheets several inches in width commercially available. | 8 | Metallurgy |
Electrons form notional shells around the nucleus. These are naturally in a ground state but can be excited by the absorption of energy from light (photons), magnetic fields, or interaction with a colliding particle (typically other electrons).
Electrons that populate a shell are said to be in a bound state. The energy necessary to remove an electron from its shell (taking it to infinity) is called the binding energy. Any quantity of energy absorbed by the electron in excess of this amount is converted to kinetic energy according to the conservation of energy. The atom is said to have undergone the process of ionization.
In the event that the electron absorbs a quantity of energy less than the binding energy, it may transition to an excited state or to a virtual state. After a statistically sufficient quantity of time, an electron in an excited state will undergo a transition to a lower state via spontaneous emission. The change in energy between the two energy levels must be accounted for (conservation of energy). In a neutral atom, the system will emit a photon of the difference in energy. However, if the lower state is in an inner shell, a phenomenon known as the Auger effect may take place where the energy is transferred to another bound electrons causing it to go into the continuum. This allows one to multiply ionize an atom with a single photon.
There are strict selection rules as to the electronic configurations that can be reached by excitation by light—however there are no such rules for excitation by collision processes. | 7 | Physical Chemistry |
In the energy range used in CEMS, the incident radiation can interact with the absorber through two kinds of processes: (a) conventional interactions – photoelectric and Compton effects, and (b) nuclear resonant absorption – Mössbauer effect. Due to conventional interactions the beam is attenuated and electrons are emitted from the sample. The nuclear de-excitation following the resonant absorption takes place by emission of either a gamma ray or an internal conversion (IC) electron. In the latter case, the atom is left in an ‘excited’ state with a hole in an inner shell; the energy excess is given away with emission of Auger electrons and/or X-rays. Thus, the electrons emitted from the sample as a consequence of the Mössbauer absorptions are: (a) primary (IC or Auger) electrons originated in the de-excitations of the nuclei excited by the incident beam, and (b) secondary electrons originated by conventional interactions of photons (or resonant absorption of gamma rays) emitted after resonant absorptions. | 3 | Analytical Chemistry |
DNA replication and RNA transcription both make use of base flipping. DNA polymerase is an enzyme that carries out replication. It can be thought of as a hand that grips the DNA single strand template. As the template passes across the palm region of the polymerase, the template bases are flipped out of the helix and away from the dNTP binding site. During transcription, RNA polymerase catalyzes RNA synthesis. During the initiation phase, two bases in the -10 element flip out from the helix and into two pockets in RNA polymerase. These new interactions stabilize the -10 element and promote the DNA strands to separate or melt.
Base flipping occurs during latter stages of recombination. RecA is a protein that promotes strand invasion during homologous recombination. Base flipping has been proposed as the mechanism by which RecA can enable a single strand to recognize homology in duplex DNA. Other studies indicate that it is also involved in V(D)J Recombination. | 1 | Biochemistry |
A novel application for gel electrophoresis is the separation or characterization of metal or metal oxide nanoparticles (e.g. Au, Ag, ZnO, SiO2) regarding the size, shape, or surface chemistry of the nanoparticles. The scope is to obtain a more homogeneous sample (e.g. narrower particle size distribution), which then can be used in further products/processes (e.g. self-assembly processes). For the separation of nanoparticles within a gel, the key parameter is the ratio of the particle size to the mesh size, whereby two migration mechanisms were identified: the unrestricted mechanism, where the particle size << mesh size, and the restricted mechanism, where particle size is similar to mesh size. | 1 | Biochemistry |
Also located on museum grounds is the Short Track Model Railroad Club, featuring an NTrak model railroad with trains traveling through more than 40 modules, including a drive-in movie theater, a fairgrounds, farms, towns, and a coal mine and other scenes.
The Short Track, N-Scale, Model Railroad club is an educational organization that seeks to further the appreciation of railroad history in the United States. Many members are also National Model Railroad Association (NMRA) members and a few have earned the title of "Master Modeler." Their Donner Pass, N-scale, model railroad exhibit shows the Southern Pacific crossing of the Sierra Mountains between Colfax, CA and West Reno, NV.
There is also a small layout that can be operated by children (The Young & Victorious RR). | 8 | Metallurgy |
Social insects commonly use trail pheromones. For example, ants mark their paths with pheromones consisting of volatile hydrocarbons. Certain ants lay down an initial trail of pheromones as they return to the nest with food. This trail attracts other ants and serves as a guide. As long as the food source remains available, visiting ants will continuously renew the pheromone trail. The pheromone requires continuous renewal because it evaporates quickly. When the food supply begins to dwindle, the trail-making ceases. Pharaoh ants (Monomorium pharaonis) mark trails that no longer lead to food with a repellent pheromone, which causes avoidance behaviour in ants.
Repellent trail markers may help ants to undertake more efficient collective exploration.
The army ant Eciton burchellii provides an example of using pheromones to mark and maintain foraging paths. When species of wasps such as Polybia sericea found new nests, they use pheromones to lead the rest of the colony to the new nesting site.
Gregarious caterpillars, such as the forest tent caterpillar, lay down pheromone trails that are used to achieve group movement. | 1 | Biochemistry |
For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of daily value (%DV). For magnesium labeling purposes 100% of the daily value was 400 mg, but as of May 27, 2016, it was revised to 420 mg to bring it into agreement with the RDA. A table of the old and new adult Daily Values is provided at Reference Daily Intake. | 1 | Biochemistry |
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PICS is a powerful analysis tool that resolves correlations on the nanometer length and millisecond timescale. Adapted from methods of spatio-temporal image correlation spectroscopy, it exploits the high positional accuracy of single-particle tracking. While conventional tracking methods break down if multiple particle trajectories intersect, this method works in principle for arbitrarily large molecule densities and dynamical parameters (e.g. diffusion coefficients, velocities) as long as individual molecules can be identified. It is computationally cheap and robust and allows one to identify and quantify motions (e.g. diffusion, active transport, confined diffusion) within an ensemble of particles, without any a priori knowledge about the dynamics.
A particle image cross-correlation spectroscopy (PICCS) extension is available for biological processes that involve multiple interaction partners, as can observed by two-color microscopy. | 7 | Physical Chemistry |
Structural genomics seeks to describe the 3-dimensional structure of every protein encoded by a given genome. This genome-based approach allows for a high-throughput method of structure determination by a combination of experimental and modeling approaches. The principal difference between structural genomics and traditional structural prediction is that structural genomics attempts to determine the structure of every protein encoded by the genome, rather than focusing on one particular protein. With full-genome sequences available, structure prediction can be done more quickly through a combination of experimental and modeling approaches, especially because the availability of large number of sequenced genomes and previously solved protein structures allows scientists to model protein structure on the structures of previously solved homologs.
Because protein structure is closely linked with protein function, the structural genomics has the potential to inform knowledge of protein function. In addition to elucidating protein functions, structural genomics can be used to identify novel protein folds and potential targets for drug discovery. Structural genomics involves taking a large number of approaches to structure determination, including experimental methods using genomic sequences or modeling-based approaches based on sequence or structural homology to a protein of known structure or based on chemical and physical principles for a protein with no homology to any known structure.
As opposed to traditional structural biology, the determination of a protein structure through a structural genomics effort often (but not always) comes before anything is known regarding the protein function. This raises new challenges in structural bioinformatics, i.e. determining protein function from its 3D structure.
Structural genomics emphasizes high throughput determination of protein structures. This is performed in dedicated centers of structural genomics.
While most structural biologists pursue structures of individual proteins or protein groups, specialists in structural genomics pursue structures of proteins on a genome wide scale. This implies large-scale cloning, expression and purification. One main advantage of this approach is economy of scale. On the other hand, the scientific value of some resultant structures is at times questioned. A Science article from January 2006 analyzes the structural genomics field.
One advantage of structural genomics, such as the Protein Structure Initiative, is that the scientific community gets immediate access to new structures, as well as to reagents such as clones and protein. A disadvantage is that many of these structures are of proteins of unknown function and do not have corresponding publications. This requires new ways of communicating this structural information to the broader research community. The Bioinformatics core of the Joint center for structural genomics (JCSG) has recently developed a wiki-based approach namely Open protein structure annotation network (TOPSAN) for annotating protein structures emerging from high-throughput structural genomics centers. | 1 | Biochemistry |
Plastics are used extensively in the manufacture of electrical items, such as circuit boards and electrical cables. These applications can be harsh, exposing the plastic to a mixture of thermal, chemical and electrochemical attack. Many electric items like transformers, microprocessors or high-voltage cables operate at elevated temperatures for years, or even decades, resulting in low-level but continuous thermal oxidation. This can be exacerbated by direct contact with metals, which can promote the formation of free-radicals, for instance, by the action of Fenton reactions on hydroperoxides. High voltage loads can also damage insulating materials such as dielectrics, which degrade via electrical treeing caused by prolonged electrical field stress. | 7 | Physical Chemistry |
Tear gas generally consists of aerosolized solid or liquid compounds (bromoacetone or xylyl bromide), not gas. Tear gas works by irritating mucous membranes in the eyes, nose, mouth and lungs. It causes crying, sneezing, coughing, difficulty breathing, pain in the eyes, and temporary blindness. With CS gas, symptoms of irritation typically appear after 20 to 60 seconds of exposure and commonly resolve within 30 minutes of leaving (or being removed from) the area. | 1 | Biochemistry |
QR has many uses as a fluorescent probe. The use of QR as a probe is relatively safe, inexpensive, and a sensitive method compared with other fluorescence probes like ethidium bromide or dimeric cyanine dyes. QR is also an ideal fluorescent probe because substrates of interest, such as antibodies, can be detected within a 0.3nM detection limit without the use of radiolabeled or fluorescently labeled oligonucleotides, which are the DNA components. In other words, quinaldine red is preferred tag since its binding increases the fluorescence without extra tags being needed.
The dye's ability to bind to proteins makes it a great tag. Once bound to a protein, fluorescent signals are emitted which allow the strength of QR binding to the protein to be determined. Using this technique allows for many dynamic interactions to be understood. Another variation to detecting the QR probes is by measuring the fluorescence via a spectrofluorometer. This allows the concentration of the QR-substance (could be a protein or nucleic acids) to be measured. This also indirectly allows the binding ability of QR to the substance to be measured. Using this technique gives an emission wavelength of 520/160 nm.
QR's ability to bind to substrates and fluoresce can be further utilized to determine the location of a substrate with the use of Raman spectroscopy and the electronic absorption spectra. For example, when a cell is not energized, a cell will not take up QR. When a cell is energized, aggregations of red substrate can be found within a cell, and this can be detected with Raman spectroscopy
In addition to being used as a fluorescent probe, QR can also be used as an agent in bleaching. When exposed to intensive rays such as X-rays, gamma rays, and electron beams, the dye is able to photobleach a substance. In the case of dental bleaching, a laser is the source of intensive rays. QR is dissolved in a mixture of water, ethanol, isopropyl alcohol, glycerol, and other solvents and is placed on the teeth. In the presence of oxygen, the QR and carrier particles solution uses its sensitivity to light energy to ultimately bleach teeth, making them whiter.
Quinaldine red is also used as an indicator in experiments. In an assay for inorganic and organic phosphates, QR proved to be a better indicator due to a low blank and its color stability. When being used as an indicator, a color change is involved in order to indicate a change in the pH. For example, in a solution containing inorganic phosphate and ammonium molybdate in sulfuric acid, a reaction could occur where the two substances react forming a phosphomolybdate complex ion, or no reaction could occur. In this case, if pale pink mixture of quinaldine red turns to a colorless solution, this indicates the presence of a free phosphate. If the solution turns a dark red, that indicates the phosphomolybdate complex ion has formed. By using QR as an indicator in this manner, enzymatic activities can be monitored. | 3 | Analytical Chemistry |
Although herbicidal warfare uses chemical substances, its main purpose is to disrupt agricultural food production and/or to destroy plants which provide cover or concealment to the enemy. During the Malayan Emergency (1948–1960), the British military deployed herbicides and defoliants in the Malaysian countryside (including crop fields) in order to deprive Malayan National Liberation Army (MNLA) insurgents of cover, potential sources of food and to flush them out of the jungle. Deployment of herbicides and defoliants served the dual purpose of thinning jungle trails to prevent ambushes and destroying crop fields in regions where the MNLA was active to deprive them of potential sources of food. Herbicides and defoliants were also sprayed from Royal Air Force (RAF) aircraft. The use of herbicides as a chemical weapon by the U.S. military during the Vietnam War has left tangible, long-term impacts upon the Vietnamese people and U.S soldiers that handled the chemicals. More than 20% of South Vietnam's forests and 3.2% of its cultivated land were sprayed at least once between during the war. The government of Vietnam says that up to four million people in Vietnam were exposed to the defoliant, and as many as three million people have suffered illness because of Agent Orange, while the Red Cross of Vietnam estimates that up to one million people were disabled or have health problems as a result of exposure to Agent Orange. The United States government has described these figures as unreliable. | 2 | Environmental Chemistry |
In a 2012 University of Amsterdam study of 120 women, women's luteal phase (higher levels of progesterone, and increasing levels of estrogen) was correlated with lower level of competitive behavior in gambling and math contest scenarios, while their premenstrual phase (sharply-decreasing levels of progesterone, and decreasing levels of estrogen) was correlated with a higher level of competitive behavior. | 0 | Organic Chemistry |
Between 1882 and 1886 Schuyler Wheeler invented a fan powered by electricity. It was commercially marketed by the American firm Crocker & Curtis electric motor company. In 1885 a desktop direct drive electric fan was commercially available by Stout, Meadowcraft & Co. in New York.
In 1882, Philip Diehl developed the world's first electric ceiling mounted fan. During this intense period of innovation, fans powered by alcohol, oil, or kerosene were common around the turn of the 20th century.
In 1909, KDK of Japan pioneered the invention of mass-produced electric fans for home use. In the 1920s, industrial advances allowed steel fans to be mass-produced in different shapes, bringing fan prices down and allowing more homeowners to afford them. In the 1930s, the first art deco fan (the "Silver Swan") was designed by Emerson. By the 1940s, Crompton Greaves of India became the world's largest manufacturer of electric ceiling fans mainly for sale in India, Asia, and the Middle East. By the 1950s, table and stand fans were manufactured in bright colors and eye-catching.
Window and central air conditioning in the 1960s caused many companies to discontinue production of fans, but in the mid-1970s, with an increasing awareness of the cost of electricity and the amount of energy used to heat and cool homes, turn-of-the-century styled ceiling fans became popular again as both decorative and energy-efficient.
In 1998 William Fairbank and Walter K. Boyd invented the high-volume low-speed (HVLS) ceiling fan, designed to reduce energy consumption by using long fan blades rotating at low speed to move a relatively large volume of air. | 7 | Physical Chemistry |
Aside from its environmental impacts, R12, like most chlorofluoroalkanes, forms phosgene gas when exposed to a naked flame. | 2 | Environmental Chemistry |
Rates of reaction can be affected by the size of rings. Essentially each reaction should be studied on a case-by-case basis but some general trends have been seen. Molecular mechanics calculations of strain energy differences SI between a sp2 and sp3 state in cycloalkanes show linear correlations with rates ( as logk ) of many reactions involving the transition between sp2 and sp3 states, such as ketone reduction, alcohol oxidation or nucleophilic substitution, the contribution of transannular strain is below 3 %.
Rings with transannular strain have faster S1, S2, and free radical reactions compared to most smaller and normal sized rings. Five membered rings show an exception to this trend. On the other hand, some nucleophilic addition reactions involving addition to a carbonyl group in general show the opposite trend. Smaller and normal rings, with five membered rings being the anomaly, have faster reaction rates while those with transannular strain are slower.
One specific example of a study of rates of reactions for an S1 reaction is shown on the right. Various sized rings, ranging from four to seventeen members, were used to compare the relative rates and better understand the effect of transannular strain on this reaction. The solvolysis reaction in acetic acid involved the formation of a carbocation as the chloride ion leaves the cyclic molecule. This study fits the general trend seen above that rings with transannular strain show increased reactions rates compared to smaller rings in S1 reactions. | 4 | Stereochemistry |
Dexmedetomidine, sold under the trade name Precedex among others, is a drug used in humans for sedation. Veterinarians use dexmedetomidine for similar purposes in treating cats, dogs, and horses. It is also used in humans to treat acute agitation associated with schizophrenia or bipolar I or II disorder.
Similar to clonidine, it is a sympatholytic drug that acts as an agonist of α-adrenergic receptors in certain parts of the brain. It was developed by Orion Pharma. | 4 | Stereochemistry |
In contrast to receptor uncoupling, endocytosis can occur through multiple pathways. GPCR endocytosis has been shown to be either dependent or independent of arrestin activity, depending on the cell type used in the experiment; however, the former is more common. Furthermore, the same receptor expressed in two distinct cell types can be endocytosed through different mechanisms due to differences in GRK and arrestin expression: either through clathrin-coated vesicles or caveolae. In general, receptor sequestration preferentially affects receptors that are both activated and phosphorylated, but the phosphorylation is not always a necessary component of endocytosis. After being sequestered, the affected receptors can either be degraded by lysosomes or reinserted into the plasma membrane, which is called receptor recycling.
Post-translational modification also affects receptor endocytosis. For example, different glycosylations on the exterior N-terminus of dopamine receptors D and D were associated with specific endocytotic pathways. Additionally, palmitoylation, which primarily mediates receptor localization within the membrane, can also affect endocytosis. It is required for the endocytosis of thyrotropin-releasing hormone and D receptors, and it is inhibitory for leutinizing hormone and vasopressin receptor 1A receptors. It has been shown to have no effect on adrenergic receptors (specifically ß and α). | 1 | Biochemistry |
Endoreversible thermodynamics was discovered multiple times, with Reitlinger (1929), Novikov (1957) and Chambadal (1957), although it is most often attributed to Curzon & Ahlborn (1975).
Reitlinger derived it by considering a heat exchanger receiving heat from a finite hot stream fed by a combustion process.
A brief review of the history of rediscoveries is in. | 7 | Physical Chemistry |
The cytochrome b6f complex is part of the thylakoid electron transport chain and couples electron transfer to the pumping of protons into the thylakoid lumen. Energetically, it is situated between the two photosystems and transfers electrons from photosystem II-plastoquinone to plastocyanin-photosystem I. | 5 | Photochemistry |
In mathematics and physics, surface growth refers to models used in the dynamical study of the growth of a surface, usually by means of a stochastic differential equation of a field. | 7 | Physical Chemistry |
Wire arc spray is a form of thermal spraying where two consumable metal wires are fed independently into the spray gun. These wires are then charged and an arc is generated between them. The heat from this arc melts the incoming wire, which is then entrained in an air jet from the gun. This entrained molten feedstock is then deposited onto a substrate with the help of compressed air. This process is commonly used for metallic, heavy coatings. | 8 | Metallurgy |
For example, consider a receptacle of air at room temperature and pressure with a mean free path of 68nm. If the diameter of the receptacle is less than 68nm, the Knudsen number would greater than 1, and this sample of air would be considered a Knudsen gas. It would not be a Knudsen gas if the diameter of the receptacle is greater than 68nm. | 7 | Physical Chemistry |
Maintaining an electric field in an electrolyte requires Faradaic reactions to occur at the anode and cathode. This is typically electrolysis of water, which generates hydrogen peroxide, hydrogen ions (acid) and hydroxide (base) as well as oxygen and hydrogen gas bubbles. The hydrogen peroxide and/or pH changes generated can adversely affect biological cells and biomolecules such as proteins, while gas bubbles tend to "clog" microfluidic systems. These problems can be alleviated by using alternative electrode materials such as conjugated polymers which can undergo the Faradaic reactions themselves, dramatically reducing electrolysis. | 7 | Physical Chemistry |
* Fred Morrison Scholarship (1994)
* Thieme Journal Award (2012)
* American Chemical Society Young Academic Investigator Award (2013)
* Boston University Ignition Award (2013)
* Boston University Materials Science and Engineering Innovation Award (2013)
* National Science Foundation CAREER Award (2013)
* Alfred P. Sloan Fellowship (2013)
* Boston University Innovation Professorship (2013)
* Camille Dreyfus Teacher-Scholar Award (2014) | 0 | Organic Chemistry |
Microbubble contrast agents are generally used in contrast-enhanced ultrasound applications to enhance the acoustic impact of ultrasound. For sonoporation specifically, microbubbles are used to significantly enhance membrane translocation of molecular therapeutics. | 1 | Biochemistry |
* Berton, Alain Edgard : Montre-bracelet-réveil tactile. 5 décembre 1949 : FR953313-A
* Berton Alain Edgard : Photomètre infrarouge utilisable en analyse physique et chimique. 24 janvier 1955 : FR1084823-A
* Berton Alain: Photomètre simple ultraviolet, avec enregistreur photographique à lecture instantanée, utilisable en analyse physique et chimique. 27 juin 1958 : FR1159401-A
* Berton Alain : Apparatus for detecting and measuring traces of impurities in a gas. 16 juin 1960 : FR1223277-A; idem, 27 juin 1960 : FR1224831-A
* Berton Alain : Dispositif chimique denregistrement sans contact'. 14 octobre 1960 : FR1234235-A
* Berton Alain : Analyseur colorimétrique de vapeurs, portatif. 17 mars 1961 : FR1255988-A
* Berton Alain : Dispositif électrochimique de détection dimpuretés dans les gaz'. 10 août 1962 : FR1300917-A | 3 | Analytical Chemistry |
It is important to note that even while kinetic analysis is a powerful tool for determining the stoichiometry of the turn-over limiting transition state relative to the ground state, it cannot answer all mechanistic questions. It is possible for two mechanisms to be kinetically indistinguishable, especially under catalytic conditions. For any thorough mechanistic evaluation it is necessary to conduct kinetic analysis of both the catalytic process and its individual steps (when possible) in concert with other forms of analysis such as evaluation of linear free energy relationships, isotope effect studies, computational analysis, or any number of alternative approaches. Finally, it is important to note that no mechanistic hypothesis can ever be proven; alternative mechanistic hypothesis can only be disproven. It is, therefore, essential to conduct any investigation in a hypothesis-driven manner. Only by experimentally disproving reasonable alternatives can the support for a given hypothesis be strengthened. | 7 | Physical Chemistry |
Throughout his life, Tom was a committed Christian and contributed to wider society, helping to form over thirty Young Men's Christian Associations across the North of England. He was also Captain of his local Fire Brigade. One of his lasting legacies is the Cleveland Institution of Engineers. The Institution is one of the oldest such engineering bodies in the world. Tom hosted the inaugural meeting at his home on Church Road in Stockton and was the first secretary of the organisation. There were 12 members at that first meeting, but by the time of his death (when he was president) the ranks had grown to over 460. | 8 | Metallurgy |
The first discussion of the RVB state on square lattice using the RVB picture only consider nearest neighbour bonds that connect different sub-lattices. The constructed RVB state is an equal amplitude superposition of all the nearest-neighbour bond configurations. Such a RVB state is believed to contain emergent gapless gauge field which may confine the spinons etc. So the equal-amplitude nearest-neighbour RVB state on square lattice is unstable and does not corresponds to a quantum spin phase. It may describe a critical phase transition point between two stable phases. A version of RVB state which is stable and contains deconfined spinons is the chiral spin state. Later, another version of stable RVB state with deconfined spinons, the Z2 spin liquid, is proposed, which realizes the simplest topological order – Z2 topological order. Both chiral spin state and Z2 spin liquid state have long RVB bonds that connect the same sub-lattice. In chiral spin state, different bond configurations can have complex amplitudes, while in Z2 spin liquid state, different bond configurations only have real amplitudes. The RVB state on triangle lattice also realizes the Z2 spin liquid, where different bond configurations only have real amplitudes. The toric code model is yet another realization of Z2 spin liquid (and Z2 topological order) that explicitly breaks the spin rotation symmetry and is exactly soluble. | 7 | Physical Chemistry |
Levofloxacin is used to treat infections including: respiratory tract infections, cellulitis, urinary tract infections, prostatitis, anthrax, endocarditis, meningitis, pelvic inflammatory disease, traveler's diarrhea, tuberculosis, and plague and is available by mouth, intravenously, and in eye drop form.
As of 2016, the US Food and Drug Administration (FDA) recommended that "serious side effects associated with fluoroquinolone antibacterial drugs generally outweigh the benefits for patients with acute sinusitis, acute bronchitis, and uncomplicated urinary tract infections who have other treatment options. For patients with these conditions, fluoroquinolones should be reserved for those who do not have alternative treatment options."
Levofloxacin is used for the treatment of pneumonia, urinary tract infections, and abdominal infections. As of 2007 the Infectious Disease Society of America (IDSA) and the American Thoracic Society recommended levofloxacin and other respiratory fluoroquinolines as first line treatment for community acquired pneumonia when co-morbidities such as heart, lung, or liver disease are present or when in-patient treatment is required. Levofloxacin also plays an important role in recommended treatment regimens for ventilator-associated and healthcare-associated pneumonia.
As of 2010 it was recommended by the IDSA as a first-line treatment option for catheter-associated urinary tract infections in adults. In combination with metronidazole it is recommended as one of several first-line treatment options for adult patients with community-acquired intra-abdominal infections of mild-to-moderate severity. The IDSA also recommends it in combination with rifampicin as a first-line treatment for prosthetic joint infections. The American Urological Association recommends levofloxacin as a first-line treatment to prevent bacterial prostatitis when the prostate is biopsied. and as of 2004 it was recommended to treat bacterial prostatitis by the NIH research network studying the condition.
Levofloxacin and other fluoroquinolones have also been widely used for the treatment of uncomplicated community-acquired respiratory and urinary tract infections, indications for which major medical societies generally recommend the use of older, narrower spectrum drugs to avoid fluoroquinolone resistance development. Due to its widespread use, common pathogens such as Escherichia coli and Klebsiella pneumoniae have developed resistance. In many countries as of 2013, resistance rates among healthcare-associated infections with these pathogens exceeded 20%.
Levofloxacin is also used as antibiotic eye drops to prevent bacterial infection. Usage of levofloxacin eye drops, along with an antibiotic injection of cefuroxime or penicillin during cataract surgery, has been found to lower the chance of developing endophthalmitis, compared to eye drops or injections alone. | 4 | Stereochemistry |
Pre-mRNA has both introns and exons. As a part of the maturation process, RNA splicing removes the non-coding RNA introns leaving behind the exons, which are then spliced and joined together to form the mature mRNA. Splicing is conducted by the spliceosome. The spliceosome is a large ribonucleoprotein which cleaves the RNA at the splicing site and recombines the exons of the RNA. Similar to polyadenylation, alternative splicing can occur, resulting in several possible proteins being translated from the same portion of DNA. See RNA Splicing for further details. | 1 | Biochemistry |
The product of the blast furnace is pig iron, which contains 4–5% carbon and usually some silicon. To produce a forgeable product a further process was needed, usually described as fining, rather than refining. From the 16th century, this was undertaken in a finery forge. At the end of the 18th century, this began to be replaced by puddling (in a puddling furnace), which was in turn gradually superseded by the production of mild steel by the Bessemer process. | 8 | Metallurgy |
Polyamorphism has been experimentally observed or theoretically suggested in silicon, liquid phosphorus, triphenyl phosphate, mannitol, and in some other molecular network-forming substances. | 7 | Physical Chemistry |
Kiick designs polymer nanostructures for targeted therapies and hydrogel matrices for regenerative medicine. She makes use of biomimetic self-assembly, bioconjugation and biosynthesis. In particular, Kiick has worked on polymer-peptide macromolecular structures that can engage cellular targets. These include the use of polyethylene glycol (PEG) in click chemistry to form hydrogels that degrade selectively in response to molecules present in tissues and extracellular matrix. Kiick has shown it is possible to selectively release small molecule cargo with a tuned release for applications in targeted drug-delivery and vascular grafts. She has developed resilin-like polypeptides (RLP), elastomeric materials that can be cross-linked using small molecules, as well as hydrogels that contain nanoparticles for targeting tumors and inflammatory conditions. Resilin is a primary elastomeric protein that is found in insects, and helps them to jump long distances and produce sound.
She joined the faculty at the University of Delaware in 2001, and earned the rank of associate professor in 2007. In 2011 Kiick was promoted to the rank of professor of materials science and engineering and also named deputy dean of the University of Delaware’s college of engineering. In 2019-2020 she was awarded a Leverhulme Visiting Professorship from the Leverhulme Trust and a Fulbright Scholarship from the Fulbright Program to the University of Nottingham, to develop protocols for fabricating bioelastomeric materials. | 6 | Supramolecular Chemistry |
Electric arc guns operate at low voltages (below 45 V dc), but at relatively high currents. They may be safely hand-held. The power supply units are connected to 440 V AC sources, and must be treated with caution. | 8 | Metallurgy |
Cold-start origin of life theories stem from the idea there may have been cold enough regions on the early Earth that large ice cover could be found. Stellar evolution models predict that the Sun's luminosity was ~25% weaker than it is today. Fuelner states that although this significant decrease in solar energy would have formed an icy planet, there is strong evidence for liquid water to be present, possibly driven by a greenhouse effect. This would create an early Earth with both liquid oceans and icy poles.
Ice melts that form from ice sheets or glaciers melts create freshwater pools, another niche capable of experiencing wet-dry cycles. While these pools that exist on the surface would be exposed to intense UV radiation, bodies of water within and under ice are sufficiently shielded while remaining connected to UV exposed areas through ice cracks. Suggestions of impact melting of ice allow freshwater paired with meteoritic input, a popular vessel for prebiotic components. Near-seawater levels of sodium chloride are found to destabilize fatty acid membrane self-assembly, making freshwater settings appealing for early membranous life.
Icy environments would trade the faster reaction rates that occur in warm environments for increased stability and accumulation of larger polymers. Experiments simulating Europa-like conditions of ~20 °C have synthesised amino acids and adenine, showing that Miller-Urey type syntheses can still occur at cold temperatures. In an RNA world, the ribozyme would have had even more functions than in a later DNA-RNA-protein-world. For RNA to function, it must be able to fold, a process that is hindered by temperatures above 30 °C. While RNA folding in psychrophilic organisms is slower, the process is more successful as hydrolysis is also slower. Shorter nucleotides would not suffer from higher temperatures. | 9 | Geochemistry |
To solve for the concentration of all components appearing in any general biochemical reaction as in (), the Michaelis–Menten kinetics for an enzymatic reaction are coupled with the Monod kinetics for biomass dynamics. The most general case is to assume that the enzyme concentration is proportional to the biomass concentration and that the reaction is not in quasi-steady state. These hypotheses lead to the following system of equations
with , and where is the concentration of the most limiting substrate in each reaction i, z is the enzyme yield coefficient, Y is the yield coefficient expressing the biomass gain per unit of released product and is the biomass mortality rate. | 7 | Physical Chemistry |
3M produces perfluoro(2-methyl-3-pentanone) under different brand names of Novec 1230 and Novec 649. These two products have different purity grades (>99% and >99.9%, respectively) intended for different industrial applications. | 2 | Environmental Chemistry |
Dehydrogenation of amine-boranes is thermodynamically favourable, making the process attractive for hydrogen storage systems. Ammonia borane has attracted particular interest due to its high weight percent of hydrogen (19.6%). Dehydrogenation occurs in three steps, creating polyamino-boranes and borazines as insoluble side products. The dehydrogenation reactions are irreversible, which limits the utility of this process for hydrogen storage. | 0 | Organic Chemistry |
Spectral lines are associated with atomic electronic transitions and polyatomic gases have their own absorption band system. | 7 | Physical Chemistry |
In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The octahedron has eight faces, hence the prefix octa. The octahedron is one of the Platonic solids, although octahedral molecules typically have an atom in their centre and no bonds between the ligand atoms. A perfect octahedron belongs to the point group O. Examples of octahedral compounds are sulfur hexafluoride SF and molybdenum hexacarbonyl Mo(CO). The term "octahedral" is used somewhat loosely by chemists, focusing on the geometry of the bonds to the central atom and not considering differences among the ligands themselves. For example, Cobalt(III) hexammine chloride|, which is not octahedral in the mathematical sense due to the orientation of the bonds, is referred to as octahedral.
The concept of octahedral coordination geometry was developed by Alfred Werner to explain the stoichiometries and isomerism in coordination compounds. His insight allowed chemists to rationalize the number of isomers of coordination compounds. Octahedral transition-metal complexes containing amines and simple anions are often referred to as Werner-type complexes. | 4 | Stereochemistry |
Electrical resistance heating (ERH) is an intensive environmental remediation method that uses the flow of alternating current electricity to heat soil and groundwater and evaporate contaminants. Electric current is passed through a targeted soil volume between subsurface electrode elements. The resistance to electrical flow that exists in the soil causes the formation of heat; resulting in an increase in temperature until the boiling point of water at depth is reached. After reaching this temperature, further energy input causes a phase change, forming steam and removing volatile contaminants. ERH is typically more cost effective when used for treating contaminant source areas. | 2 | Environmental Chemistry |
* Reviews some of the history and the issues of the saprobic system.
* Contains a short introduction to the saprobity index, and compares Pantle & Buck's method to the more complicated Zelinka & Marvan method.
;German | 2 | Environmental Chemistry |
The Qubit assays (formerly known as Quant-iT) were previously developed and manufactured by Molecular Probes (now part of Life Technologies). Each dye is specialized for one type of molecule (DNA, RNA, or protein). These dyes exhibit extremely low fluorescence until bound to their target molecule. Upon binding to DNA, the dye molecules assume a more rigid shape and increase in fluorescence by several orders of magnitude, most likely due to intercalation between the bases.
The Qubit fluorometer, a device designed to measure fluorescence signals from samples, operates by correlating these signals with known concentrations of probes. This process enables it to transform the fluorescence data into a quantified concentration measurement. The device uses this established relationship to accurately determine the concentration of a sample.
A specific instance of this technology is the Qubit 2.0 fluorometer, which is often used in conjunction with the "dsDNA BR Assay Kit." This kit, along with others in the Qubit quantification system, incorporates dyes. These dyes are sensitive to different biomolecules and their concentrations. In this context, "ds" denotes double-stranded and "ss" signifies single-stranded DNA, indicating the specific types of DNA that the dyes can detect. | 7 | Physical Chemistry |
Eichengrün has made his name through numerous inventions, such as processes for synthesizing chemical compounds. Aside from Aspirin, Eichengrün held 47 patents.
Bayer's official story credits Felix Hoffmann, a young Bayer chemist, with the invention of aspirin in 1897. Impure acetylsalicylic acid (ASA, the active compound of aspirin) had been synthesized already in 1853 by French chemist Charles Frédéric Gerhardt; the 1897 process developed at Bayer was the first to produce pure ASA that could be used for medical purposes.
Due to the rise of the Nazis in Germany, Eichengrün was unable to object when Hoffmann first made the claim that he (Hoffman) invented aspirin, in the footnote of a 1934 German Encyclopedia. Hoffmann's claim was once widely accepted, but many historians now consider it to be discredited. Eichengrün first claimed to have invented aspirin in a 1944 letter from Theresienstadt concentration camp, addressed to IG Farben (of which Bayer was a part), where he cited his many contributions to the company (which was highly influential in the concentration camps), including the invention of aspirin, as reasons for why he should be released.
Five years later, Arthur Eichengrün published a paper in Pharmazie in 1949, where he explained that he had instructed Hoffmann to synthesise acetylsalicylic acid and that the latter had done so without knowing the purpose of the work. The paper elucidated how he planned and directed the synthesis of aspirin along with the synthesis of several related compounds, describing these events in detail. He also claimed to be responsible for aspirins initial surreptitious clinical testing. Finally, he explained that Hoffmanns role was restricted to the initial lab synthesis using his (Eichengrün's) process and nothing more.
Eichengrüns account was largely ignored by historians and chemists until 1999, when Walter Sneader of the Department of Pharmaceutical Sciences at the University of Strathclyde in Glasgow re-examined the case and came to the conclusion that indeed Eichengrüns account was convincing and correct and that Eichengrün deserved credit for the invention of aspirin. Bayer denied this in a press release, asserting that the invention of aspirin was due to Hoffmann.
;Evidence supporting Eichengrün's claims to the invention
Walter Sneader based his claims that Eichengrün both invented the process for synthesizing aspirin and oversaw its clinical testing on old and newly released archived materials, including letters, patents, and lab work. He found that Hoffmann was not credited with inventing the process for synthesizing Aspirin in any documents prior to 1934, 37 years after its initial synthesis. Further he found reason to doubt the footnotes credibility, not just for being published during the "Aryanization" period of Nazi Germany, but for its inaccurate claims about the testing of salicylic acid derivates other than acetyl ester. The vague reference did not specify which derivatives were tested, but claimed they had been discovered earlier but had been synthesized for "other purposes". No indication was given of what the others were, but in 1899 Heinrich Dreser, head of the experimental pharmacology laboratory at Elberfeld, named them in a publication as propionyl, butyryl, valeryl, and benzoyl salicylic acids. He further alluded to these derivatives in 1907 and again in 1918. However, the assertion that these salicylic acid derivates had been synthesized for non-therapeutic reasons is demonstrably false. Hoffmanns colleague Otto Bonhoeffer (who also worked under Eichengrün) had been awarded a US and UK patent in 1900 for several of these compounds. The patents indicate that the derivatives were prepared for the exact purpose of finding a salicylic acid derivative with therapeutic value. Sneader concluded that because of this error the 1934 footnote is unreliable. | 5 | Photochemistry |
The conventional understanding of pi stacking involves quadrupole interactions between delocalized electrons in p-orbitals. In other words, aromaticity should be required for this interaction to occur. However, several groups have provided contrary evidence, calling into question whether pi stacking is a unique phenomenon or whether it extends to other neutral, closed-shell molecules.
In an experiment not dissimilar from others mentioned above, Paliwal and coauthors constructed a molecular torsion balance from an aryl ester with two conformational states. The folded state had a well-defined pi stacking interaction with a T-shaped geometry, whereas the unfolded state had no aryl–aryl interactions. The NMR chemical shifts of the two conformations were distinct and could be used to determine the ratio of the two states, which was interpreted as a measure of intramolecular forces. The authors report that a preference for the folded state is not unique to aryl esters. For example, the cyclohexyl ester favored the folded state more so than the phenyl ester, and the tert-butyl ester favored the folded state by a preference greater than that shown by any aryl ester. This suggests that aromaticity is not a strict requirement for favorable interaction with an aromatic ring.
Other evidence for non-aromatic pi stacking interactions results include critical studies in theoretical chemistry, explaining the underlying mechanisms of empirical observations. Grimme reported that the interaction energies of smaller dimers consisting of one or two rings are very similar for both aromatic and saturated compounds. This finding is of particular relevance to biology, and suggests that the contribution of pi systems to phenomena such as stacked nucleobases may be overestimated. However, it was shown that an increased stabilizing interaction is seen for large aromatic dimers. As previously noted, this interaction energy is highly dependent on geometry. Indeed, large aromatic dimers are only stabilized relative to their saturated counterparts in a sandwich geometry, while their energies are similar in a T-shaped interaction.
A more direct approach to modeling the role of aromaticity was taken by Bloom and Wheeler. The authors compared the interactions between benzene and either 2-methylnaphthalene or its non-aromatic isomer, 2-methylene-2,3-dihydronaphthalene. The latter compound provides a means of conserving the number of p-electrons while, however, removing the effects of delocalization. Surprisingly, the interaction energies with benzene are higher for the non-aromatic compound, suggesting that pi-bond localization is favorable in pi stacking interactions. The authors also considered a homodesmotic dissection of benzene into ethylene and 1,3-butadiene and compared these interactions in a sandwich with benzene. Their calculation indicates that the interaction energy between benzene and homodesmotic benzene is higher than that of a benzene dimer in both sandwich and parallel displaced conformations, again highlighting the favorability of localized pi-bond interactions. These results strongly suggest that aromaticity is not required for pi stacking interactions in this model.
Even in light of this evidence, Grimme concludes that pi stacking does indeed exist. However, he cautions that smaller rings, particularly those in T-shaped conformations, do not behave significantly differently from their saturated counterparts, and that the term should be specified for larger rings in stacked conformations which do seem to exhibit a cooperative pi electron effect. | 6 | Supramolecular Chemistry |
Setting the first term in brackets equal to zero yields
A slight rearrangement gives a reciprocity relation,
There are two more permutations of the foregoing derivation that give a total of three reciprocity relations between , and . | 7 | Physical Chemistry |
In thermodynamics, a component is one of a collection of chemically independent constituents of a system. The number of components represents the minimum number of independent chemical species necessary to define the composition of all phases of the system.
Calculating the number of components in a system is necessary when applying Gibbs' phase rule in determination of the number of degrees of freedom of a system.
The number of components is equal to the number of distinct chemical species (constituents), minus the number of chemical reactions between them, minus the number of any constraints (like charge neutrality or balance of molar quantities). | 7 | Physical Chemistry |
The relevance of observations from fission yeast mating-type regions and centromeres to mammals is not clear, as some evidence suggests that heterochromatin maintenance in mammalian cells is independent of the components of the RNAi pathway. It is known, however, that plants and animals have analogous mechanism for small RNA-guided heterochromatin formation, and it is believed that the mechanisms described above for S. pombe are highly conserved and play some role in heterochromatin formation in mammals as well. In higher eukaryotes, RNAi-dependent heterochromatic silencing appears to play a larger role in germline cells than in primary cells or cell lines, and is only one of the many different forms of gene silencing used throughout the genome, making it more difficult to study.
The role of RNAi in transcriptional gene silencing in plants has been characterized fairly well, and functions primarily through DNA methylation via the RdDM pathway. In this process, which is distinct from the process described above, argonaut-bound siRNA recognizes nascent RNA transcripts or the target DNA to guide the methylation and silencing of the target genomic region. | 1 | Biochemistry |
Pollution of the Hudson River is largely due to dumping of PCBs by General Electric from 1947 to 1977. GE dumped an estimated 1.3 million pounds of PCBs into the Hudson River during these years. The PCBs came from the company's two capacitor manufacturing plants at Hudson Falls and Fort Edward, New York. This pollution caused a range of harmful effects to wildlife and people who eat fish from the river or drink the water. In 1984, EPA declared a 200-mile (320 km) stretch of the river, from Hudson Falls to New York City, to be a Superfund site requiring cleanup. Extensive remediation actions on the river began in the 1970s with the implementation of wastewater discharge permits and consequent control or reduction of wastewater discharges, and sediment removal operations, which have continued into the 21st century.
Love Canal is a neighborhood in Niagara Falls, New York, that was heavily contaminated with toxic waste including PCBs. Eighteen Mile Creek in Lockport, New York, is an EPA Superfund site for PCBs contamination.
PCB pollution at the State Office Building in Binghamton was responsible for what is now considered to be the first indoor environmental disaster in the United States. In 1981, a transformer explosion in the basement spewed PCBs throughout the entire 18-story building. The contamination was so severe that cleanup efforts kept the building closed for 13 years. | 2 | Environmental Chemistry |
The sample mass and size distribution requirements are dictated by the kind of mathematical model that will be used to simulate the process plant, and the test work required to provide the appropriate model parameters. Flotation testing usually requires several kg of sample and grinding/hardness testing can required between 2 and 300 kg.
The sample selection procedure is performed to optimize granularity, sample support, and cost. Samples are usually core samples composited over the height of the mining bench. For hardness parameters, the variogram often increases rapidly near the origin and can reach the sill at distances significantly smaller than the typical drill hole collar spacing. For this reason the incremental model precision due to additional test work is often simply a consequence of the central limit theorem, and secondary correlations are sought to increase the precision without incurring additional sampling and testing costs. These secondary correlations can involve multi-variable regression analysis with other, non-metallurgical, ore parameters and/or domaining by rock type, lithology, alteration, mineralogy, or structural domains. | 8 | Metallurgy |
During a hydroelectric plant project, in the southern foothills of the Central Highlands, Samanalawewa, in Sri Lanka, a wind-driven furnace was found in an excavation site. Such furnaces were powered by the monsoon winds and have been dated to 300 BC using radiocarbon-dating techniques. These ancient Lankan furnaces might have produced the best-quality steel for legendary Damascus swords as referred in earlier Syrian records. Field trials using replica furnaces confirmed that this furnace type uses a wind-based air-supply principle that is distinct from either forced or natural draught, and show also that they are capable of producing high-carbon steel.
Wrought iron was used in the construction of monuments such as the iron pillar of Delhi, built in the third century AD during the Gupta Empire. The latter was built using a towering series of disc-shaped iron blooms. Similar to China, high-carbon steel was eventually used in India, although cast iron was not used for architecture until modern times. | 8 | Metallurgy |
The Taft equation is a linear free energy relationship (LFER) used in physical organic chemistry in the study of reaction mechanisms and in the development of quantitative structure–activity relationships for organic compounds. It was developed by Robert W. Taft in 1952 as a modification to the Hammett equation. While the Hammett equation accounts for how field, inductive, and resonance effects influence reaction rates, the Taft equation also describes the steric effects of a substituent. The Taft equation is written as:
where is the ratio of the rate of the substituted reaction compared to the reference reaction, ρ* is the sensitivity factor for the reaction to polar effects, σ* is the polar substituent constant that describes the field and inductive effects of the substituent, δ is the sensitivity factor for the reaction to steric effects, and E is the steric substituent constant. | 7 | Physical Chemistry |
The coupling of a terminal alkyne and an aromatic ring is the pivotal reaction when talking about applications of the copper-promoted or copper-free Sonogashira reaction. The list of cases where the typical Sonogashira reaction using aryl halides has been employed is large, and choosing illustrative examples is difficult. A recent use of this methodology is shown below for the coupling of iodinated phenylalanine with a terminal alkyne derived from d-biotin using an in situ generated Pd species as catalyst, which allowed the preparation of alkyne-linked phenylalanine derivative for bioanalytical applications. There are also examples of the coupling partners both being attached to allyl resins, with the Pd catalyst effecting cleavage of the substrates and subsequent Sonogashira
coupling in solution. | 0 | Organic Chemistry |
Peptidoglycan is immunologically active, which can stimulate immune cells to increase the expression of cytokines and enhance antibody-dependent specific response when combined with vaccine or as adjuvant alone. MDP, which is the basic unit of peptidoglycan, was initially used as the active component of Freunds adjuvant. Peptidoglycan from Staphylococcus aureus was used as a vaccine to protect mice, showing that after vaccine injection for 40 weeks, the mice survived from S. aureus' challenge at an increased lethal dose. | 1 | Biochemistry |
To enhance the performance of surfactant properties of natural sophorolipids, chemical modification methods have been actively pursued. Recently, researchers demonstrated the possibility of applying sophorolipids as building blocks via ring-opening metathesis polymerization for a new type of polymers, known as polysophorolipids which show promising potentials in biomaterials applications. | 0 | Organic Chemistry |
The phenomenon in which organic luminophores show higher photoluminescence efficiency in the aggregated state than in solution is called aggregation-induced emission enhancement (AIEE). Some luminophores, e.g., diketopyrrolopyrrole-based and sulfonamide-based luminophores, only display enhanced emission upon entering the crystalline state. That is, these luminophores are said to exhibit crystallization-induced emission enhancement (CIEE).
Luminophores such as noble metallic nanoclusters show higher
photoluminescence efficiency in the aggregated state than homogenous
dispersion in solution. This phenomenon is known as
Aggregation-Induced Emission (AIE). | 7 | Physical Chemistry |
Group-specific CSIs are commonly shared by different species belonging to a particular taxon (e.g. genus, family, class, order, phylum) but they are not present in other groups. These CSIs were most likely introduced in an ancestor of the group of species before the members of the taxa diverged. They provide molecular means for distinguishing members of a particular taxon from all other organisms.
Figure 1 shows an example of 5aa CSI found in all species belonging to the taxon X. This is a distinctive characteristic of this taxon as it is not found in any other species. This signature was likely introduced in a common ancestor of the species from this taxon. Similarly other group-specific signatures (not shown) could be shared by either A1 and A2 or B1 and B2, etc., or even by X1 and X2 or by X3 and X4, etc. The groups A, B, C, D and X, in this diagram could correspond to various bacterial or Eukaryotic phyla.
Group-specific CSIs have been used in the past to determine the phylogenetic relationship of a number of bacterial phyla and subgroups within it. For example a 3 amino acid insert was uniquely shared by members of the phylum Thermotogota (formerly Thermotogae) in the essential 50S ribosomal protein L7/L12, within a highly conserved region (82-124 amino acid). This is not present in any other bacteria species and could be used to characterize members of Thermotogota from all other bacteria. Group-specific CSIs were also used to characterize subgroups within Thermotogota. | 1 | Biochemistry |
Plants that contribute to nitrogen fixation include those of the legume family—Fabaceae— with taxa such as kudzu, clover, soybean, alfalfa, lupin, peanut and rooibos. They contain symbiotic rhizobia bacteria within nodules in their root systems, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants; this helps to fertilize the soil. The great majority of legumes have this association, but a few genera (e.g., Styphnolobium) do not. In many traditional farming practices, fields are rotated through various types of crops, which usually include one consisting mainly or entirely of clover.
Fixation efficiency in soil is dependent on many factors, including the legume and air and soil conditions. For example, nitrogen fixation by red clover can range from . | 1 | Biochemistry |
Nowadays, synthetic polymers are used in almost all walks of life. Modern society would look very different without them. The spreading of polymer use is connected to their unique properties: low density, low cost, good thermal/electrical insulation properties, high resistance to corrosion, low-energy demanding polymer manufacture and facile processing into final products. For a given application, the properties of a polymer can be tuned or enhanced by combination with other materials, as in composites. Their application allows to save energy (lighter cars and planes, thermally insulated buildings), protect food and drinking water (packaging), save land and lower use of fertilizers (synthetic fibres), preserve other materials (coatings), protect and save lives (hygiene, medical applications). A representative, non-exhaustive list of applications is given below.
* Clothing, sportswear and accessories: polyester and PVC clothing, spandex, sport shoes, wetsuits, footballs and billiard balls, skis and snowboards, rackets, parachutes, sails, tents and shelters.
* Electronic and photonic technologies: organic field effect transistors (OFET), light emitting diodes (OLED) and solar cells, television components, compact discs (CD), photoresists, holography.
* Packaging and containers: films, bottles, food packaging, barrels.
* Insulation: electrical and thermal insulation, spray foams.
* Construction and structural applications: garden furniture, PVC windows, flooring, sealing, pipes.
* Paints, glues and lubricants: varnish, adhesives, dispersants, anti-graffiti coatings, antifouling coatings, non-stick surfaces, lubricants.
* Car parts: tires, bumpers, windshields, windscreen wipers, fuel tanks, car seats.
* Household items: buckets, kitchenware, toys (e.g., construction sets and Rubik's cube).
* Medical applications: blood bag, syringes, rubber gloves, surgical suture, contact lenses, prosthesis, controlled drug delivery and release, matrices for cell growth.
* Personal hygiene and healthcare: diapers using superabsorbent polymers, toothbrushes, cosmetics, shampoo, condoms.
* Security: personal protective equipment, bulletproof vests, space suits, ropes.
* Separation technologies: synthetic membranes, fuel cell membranes, filtration, ion-exchange resins.
* Money: polymer banknotes and payment cards.
* 3D printing. | 7 | Physical Chemistry |
Currently orbiting satellites detect an average of about one gamma-ray burst per day. Because gamma-ray bursts are visible to distances encompassing most of the observable universe, a volume encompassing many billions of galaxies, this suggests that gamma-ray bursts must be exceedingly rare events per galaxy.
Measuring the exact rate of gamma-ray bursts is difficult, but for a galaxy of approximately the same size as the Milky Way, the expected rate (for long GRBs) is about one burst every 100,000 to 1,000,000 years. Only a few percent of these would be beamed toward Earth. Estimates of rates of short GRBs are even more uncertain because of the unknown beaming fraction, but are probably comparable.
A gamma-ray burst in the Milky Way, if close enough to Earth and beamed toward it, could have significant effects on the biosphere. The absorption of radiation in the atmosphere would cause photodissociation of nitrogen, generating nitric oxide that would act as a catalyst to destroy ozone.
The atmospheric photodissociation
would yield
* NO (consumes up to 400 ozone molecules)
* CH (nominal)
* CH (nominal)
* CO
(incomplete)
According to a 2004 study, a GRB at a distance of about a kiloparsec could destroy up to half of Earth's ozone layer; the direct UV irradiation from the burst combined with additional solar UV radiation passing through the diminished ozone layer could then have potentially significant impacts on the food chain and potentially trigger a mass extinction. The authors estimate that one such burst is expected per billion years, and hypothesize that the Ordovician-Silurian extinction event could have been the result of such a burst.
There are strong indications that long gamma-ray bursts preferentially or exclusively occur in regions of low metallicity. Because the Milky Way has been metal-rich since before the Earth formed, this effect may diminish or even eliminate the possibility that a long gamma-ray burst has occurred within the Milky Way within the past billion years. No such metallicity biases are known for short gamma-ray bursts. Thus, depending on their local rate and beaming properties, the possibility for a nearby event to have had a large impact on Earth at some point in geological time may still be significant. | 5 | Photochemistry |
Polymers have been essential components of commodities since the early days of humankind. The use of wool (keratin), cotton and linen fibres (cellulose) for garments, paper reed (cellulose) for paper are just a few examples of how ancient societies exploited polymer-containing raw materials to obtain artefacts. The latex sap of "caoutchouc" trees (natural rubber) reached Europe in the 16th century from South America long after the Olmec, Maya and Aztec had started using it as a material to make balls, waterproof textiles and containers.
The chemical manipulation of polymers dates back to the 19th century, although at the time the nature of these species was not understood. The behaviour of polymers was initially rationalised according to the theory proposed by Thomas Graham which considered them as colloidal aggregates of small molecules held together by unknown forces.
Notwithstanding the lack of theoretical knowledge, the potential of polymers to provide innovative, accessible and cheap materials was immediately grasped. The work carried out by Braconnot, Parkes, Ludersdorf, Hayward and many others on the modification of natural polymers determined many significant advances in the field. Their contributions led to the discovery of materials such as celluloid, galalith, parkesine, rayon, vulcanised rubber and, later, Bakelite: all materials that quickly entered industrial manufacturing processes and reached households as garments components (e.g., fabrics, buttons), crockery and decorative items.
In 1920, Hermann Staudinger published his seminal work "Über Polymerisation", in which he proposed that polymers were in fact long chains of atoms linked by covalent bonds. His work was debated at length, but eventually it was accepted by the scientific community. Because of this work, Staudinger was awarded the Nobel Prize in 1953.
After the 1930s polymers entered a golden age during which new types were discovered and quickly given commercial applications, replacing naturally-sourced materials. This development was fuelled by an industrial sector with a strong economic drive and it was supported by a broad academic community that contributed innovative syntheses of monomers from cheaper raw material, more efficient polymerisation processes, improved techniques for polymer characterisation and advanced, theoretical understanding of polymers.
Since 1953, six Nobel prizes have been awarded in the area of polymer science, excluding those for research on biological macromolecules. This further testifies to its impact on modern science and technology. As Lord Todd summarised in 1980, "I am inclined to think that the development of polymerization is perhaps the biggest thing that chemistry has done, where it has had the biggest effect on everyday life". | 7 | Physical Chemistry |
The term "quantitative analysis" is often used in comparison (or contrast) with "qualitative analysis", which seeks information about the identity or form of substance present. For instance, a chemist might be given an unknown solid sample. They will use "qualitative" techniques (perhaps NMR or IR spectroscopy) to identify the compounds present, and then quantitative techniques to determine the amount of each compound in the sample. Careful procedures for recognizing the presence of different metal ions have been developed, although they have largely been replaced by modern instruments; these are collectively known as qualitative inorganic analysis. Similar tests for identifying organic compounds (by testing for different functional groups) are also known.
Many techniques can be used for either qualitative or quantitative measurements. For instance, suppose an indicator solution changes color in the presence of a metal ion. It could be used as a qualitative test: does the indicator solution change color when a drop of sample is added? It could also be used as a quantitative test, by studying the color of the indicator solution with different concentrations of the metal ion. (This would probably be done using ultraviolet-visible spectroscopy.) | 3 | Analytical Chemistry |
Thionyl chloride is a component of lithium–thionyl chloride batteries, where it acts as the positive electrode (in batteries: cathode) with lithium forming the negative electrode (anode); the electrolyte is typically lithium tetrachloroaluminate. The overall discharge reaction is as follows:
These non-rechargeable batteries had many advantages over other forms of lithium batteries such as a high energy density, a wide operational temperature range, and long storage and operational lifespans. However, their high cost, non-rechargeability, and safety concerns have limited their use. The contents of the batteries are highly toxic and require special disposal procedures; additionally, they may explode if shorted. The technology was used on the Sojourner Mars rover. | 0 | Organic Chemistry |
An innovative use of the diamond anvil cell is testing the sustainability and durability of life under high pressures, including the search for life on extrasolar planets. Testing portions of the theory of panspermia (a form of interstellar travel) is one application of DAC. When interstellar objects containing life-forms impact a planetary body, there is high pressure upon impact and the DAC can replicate this pressure to determine if the organisms could survive. Another reason the DAC is applicable for testing life on extrasolar planets is that planetary bodies that hold the potential for life may have incredibly high pressure on their surface.
In 2002, scientists at the Carnegie Institution of Washington examined the pressure limits of life processes. Suspensions of bacteria, specifically Escherichia coli and Shewanella oneidensis, were placed in the DAC, and the pressure was raised to 1.6 GPa, which is more than 16,000 times Earth's surface pressure (985 hPa). After 30 hours, only about 1% of the bacteria survived. The experimenters then added a dye to the solution. If the cells survived the squeezing and were capable of carrying out life processes, specifically breaking down formate, the dye would turn clear. 1.6 GPa is such great pressure that during the experiment the DAC turned the solution into ice-IV, a room-temperature ice. When the bacteria broke down the formate in the ice, liquid pockets would form because of the chemical reaction. The bacteria were also able to cling to the surface of the DAC with their tails.
Skeptics debated whether breaking down formate is enough to consider the bacteria living. Art Yayanos, an oceanographer at the Scripps Institute of Oceanography in La Jolla, California, believes an organism should only be considered living if it can reproduce. Subsequent results from independent research groups have shown the validity of the 2002 work. This is a significant step that reiterates the need for a new approach to the old problem of studying environmental extremes through experiments. There is practically no debate whether microbial life can survive pressures up to 600 MPa, which has been shown over the last decade or so to be valid through a number of scattered publications.
Similar tests were performed with a low-pressure (0.1–600 MPa) diamond anvil cell, which has better imaging quality and signal collection. The studied microbes, Saccharomyces cerevisiae (baker's yeast), continued to grow at pressures of 15–50 MPa, and died at 200 MPa. | 7 | Physical Chemistry |
Fluorescence is used in the life sciences generally as a non-destructive way of tracking or analysing biological molecules.
Some proteins or small molecules in cells are naturally fluorescent, which is called intrinsic fluorescence or autofluorescence (such as NADH, tryptophan or endogenous chlorophyll, phycoerythrin or green fluorescent protein). Alternatively, specific or general proteins, nucleic acids, lipids or small molecules can be "labelled" with an extrinsic fluorophore, a fluorescent dye which can be a small molecule, protein or quantum dot. Several techniques exist to exploit additional properties of fluorophores, such as fluorescence resonance energy transfer, where the energy is passed non-radiatively to a particular neighbouring dye, allowing proximity or protein activation to be detected; another is the change in properties, such as intensity, of certain dyes depending on their environment allowing their use in structural studies. | 1 | Biochemistry |
The core was probably originally compiled around AD 600, perhaps in Alexandria in Egypt, in Greek. The core contains items traceable to earlier Alexandrian Greek texts, particularly the Stockholm papyrus and Leiden Papyrus X, which are Greek texts dated to the 2nd or 3rd century AD that contain some of the same and similar recipes. The first few recipes in the Phillipps-Corning manuscript of the Mappae clavicula were long considered integral, but they form a distinct separate entity, the De coloribus et mixtionibus, which survives (in whole or in part) in at least 62 manuscripts. The core of the Latin Mappae clavicula is very likely a translation of a Greek text, although the original Greek text (if it existed) does not exist today.
The best manuscripts of the Mappae clavicula date from the eighth to the twelfth century.
One of the fullest collections of recipes is in a certain manuscript dated late 12th century in which about 300 recipes are presented. In this manuscript, called the Phillipps-Corning manuscript, some of the names for some materials are Arabic names (e.g. alquibriz from the Arabic for sulphur, atincar from the Arabic for borax, alcazir from the Arabic for tin). The recipes containing the Arabic names are historically later, and are in all likelihood no earlier than the 12th century. Certain earlier manuscripts have about 200 recipes. | 8 | Metallurgy |
SPR can be used to study the real-time kinetics of molecular interactions. Determining the affinity between two ligands involves establishing the equilibrium dissociation constant, representing the equilibrium value for the product quotient. This constant can be determined using dynamic SPR parameters, calculated as the dissociation rate divided by the association rate.
In this process, a ligand is immobilized on the dextran surface of the SPR crystal. Through a microflow system, a solution with the analyte is injected over the ligand-covered surface. The binding of the analyte to the ligand causes an increase in the SPR signal (expressed in response units, RU). Following the association time, a solution without the analyte (typically a buffer) is introduced into the microfluidics to initiate the dissociation of the bound complex between the ligand and analyte. As the analyte dissociates from the ligand, the SPR signal decreases. From these association (on rate, ) and dissociation rates (off rate, ), the equilibrium dissociation constant (binding constant, ) can be calculated.
The detected SPR signal is a consequence of the electromagnetic coupling of the incident light with the surface plasmon of the gold layer. This interaction is particularly sensitive to the characteristics of the layer at the gold–solution interface, which is usually just a few nanometers thick. When substances bind to the surface, it alters the way light is reflected, causing a change in the reflection angle, which can be measured as a signal in SPR experiments. One common application is measuring the kinetics of antibody-antigen interactions. | 7 | Physical Chemistry |
The Shilov system was discovered by Alexander E. Shilov in 1969-1972 while investigating H/D exchange between isotopologues of CH and HO catalyzed simple transition metal
coordination complexes. The Shilov cycle is the partial oxidation of a hydrocarbon to an alcohol or alcohol precursor (RCl) catalyzed by PtCl in an aqueous solution with [[Platinum(IV) chloride|[PtCl]]] acting as the ultimate oxidant. The cycle consists of three major steps, the electrophilic activation of the C-H bond, oxidation of the complex, and the nucleophilic oxidation of the alkane substrate. An equivalent transformation is performed industrially by steam reforming methane to syngas then reducing the carbon monoxide to methanol. The transformation can also performed biologically by methane monooxygenase.
Overall Transformation
RH + HO + [PtCl] → ROH + 2H + PtCl + 4Cl | 0 | Organic Chemistry |
The synthesized laminin–111 formed in an embryo contributes to the formation of Reichert’s membrane, a thick extra-embryonic basement membrane. When the laminin α1 chain is deficient in an organism, an embryo dies, likely as a result of a defective Reichert’s membrane due to a lack of laminin–111 being produced. Laminin-111 has been identified as a crucial molecule for development of the embryo as shown by the consequences that occur when laminin-111 is lacking.
Laminin-111 is expressed very early on in development and is present in the blastocyst. When various parts of the trimer chains are knocked out by mutations, devastating consequences occur in the embryo. If the β1 or γ1 chains of laminin-111 are absent the basement membrane fails to form. Without a basement membrane cells have nowhere to attach and all dependent activities such as cell migration and epithelial formation can no longer occur. The self-assembly and tight network formation by laminin-111 are essential for holding the basement membrane together.
Although it is expressed abundantly during the early embryonic stage, laminin-111 is mostly absent in adults. The injection of laminin-111, however, helps with Duchenne muscular dystrophy, a neuromuscular disease in which the connection between the extracellular matrix and cell cytoskeleton is lost. Increased levels of laminin-111 triggered an increase in the expression of α7-integrin receptor and this prevented onset of the disease. Additionally, the presence of laminin-111 increased muscle strength and protected it from injury. When injected with myoblast transplants, laminin–111 decreased degeneration and inflammatory reactions and increased the success of the transplantation. The experiments utilizing laminin–111 as a source of therapy for Duchenne muscular dystrophy suggest that it has protective qualities in addition to its association with muscle tissue. | 0 | Organic Chemistry |
The spiciness can be calculated in several programming languages with the Gibbs SeaWater (GSW) toolbox. It is used to derive thermodynamic seawater properties and is adopted by the Intergovernmental Oceanographic Commission (IOC), International Association for the Physical Sciences of the Oceans (IAPSO) and the Scientific Committee on Oceanic Research (SCOR). They use the definition of spiciness (gsw_spiciness0(), gsw_spiciness1(), gsw_spiciness2() at respectively 0, 1000 and 2000 dbar) provided by. These isobars are chosen because they correspond to commonly used potential density surfaces. Areas with constant density but different spiciness have a net water flow of heat and salinity due to diffusion. | 7 | Physical Chemistry |
The conventional photo-reflectance experimental setup uses a xenon or tungsten based lamp source passed through a monochromator to form the incident probe beam. The pump beam may be formed by the output of a continuous wave (CW) laser (e.g. a He-Ne or He-Cd laser) passed through a chopper wheel, or may be formed by the output of a directly modulated semiconductor diode laser. The pump beam is focused to a spot on the sample where it interacts with the sample. The probe beam is co-focused onto the sample where it is reflected. The reflected probe beam is collected and passed through an optical filter to eliminate any unwanted pump light and/or photoluminescence signal. Thereafter the probe beam is directed onto a photodetector (e.g. a Si or InGaAs photodiode), which converts the probe intensity to an electrical signal. The electrical signal is processed to eliminate unwanted noise, typically using a lock-in circuit referenced to the modulation frequency. The photo-reflectance signal is then recorded as a function of probe beam wavelength using a computer or the like. | 7 | Physical Chemistry |
Holmes is a keen hillwalker and an enthusiastic aficionado of classical music, from baroque to romantic opera. During his time in Cambridge he was a member and regular volunteer at St Columba's United Reformed Church. He lives in Melbourne and Lorne, Victoria with his wife Jennifer. | 0 | Organic Chemistry |
Native gels are run in non-denaturing conditions so that the analytes natural or bioactive structure is maintained. This allows the physical size of the folded or assembled complex to affect the mobility, allowing for analysis of all four levels of the biomolecular structure. For biological samples, detergents are used only to the extent that they are necessary to lyse lipid membranes in the cell. Complexes normally remain associated and folded as they would be in the cell. One downside, however, is that complexes may not separate cleanly or predictably, as it is difficult to predict how the molecules shape and size will affect its mobility. Addressing and solving this problem is a major aim of preparative native PAGE.
Unlike denaturing methods, native gel electrophoresis does not use a charged denaturing agent. The molecules being separated (usually proteins or nucleic acids), therefore, differ not only in molecular mass and intrinsic charge, but also the cross-sectional area, and thus experience different electrophoretic forces dependent on the shape of the overall structure. For proteins, since they remain in the native state they may be visualized not only by general protein staining reagents but also by specific enzyme-linked staining.
A specific experiment example of an application of native gel electrophoresis is to check for enzymatic activity to verify the presence of the enzyme in the sample during protein purification. For example, for the protein alkaline phosphatase, the staining solution is a mixture of 4-chloro-2-2-methylbenzenediazonium salt with 3-phospho-2-naphthoic acid-2-4-dimethyl aniline in Tris buffer. This stain is commercially sold as a kit for staining gels. If the protein is present, the mechanism of the reaction takes place in the following order: it starts with the de-phosphorylation of 3-phospho-2-naphthoic acid-2-4-dimethyl aniline by alkaline phosphatase (water is needed for the reaction). The phosphate group is released and replaced by an alcohol group from water. The electrophile 4-chloro-2-2-methylbenzenediazonium (Fast Red TR Diazonium salt) displaces the alcohol group forming the final product Red Azo dye. As its name implies, this is the final visible-red product of the reaction. In undergraduate academic experimentation of protein purification, the gel is usually run next to commercial purified samples to visualize the results and conclude whether or not purification was successful.
Native gel electrophoresis is typically used in proteomics and metallomics. However, native PAGE is also used to scan genes (DNA) for unknown mutations as in single-strand conformation polymorphism. | 1 | Biochemistry |
Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two types of material. This effect is commonly used in camping and portable coolers and for cooling electronic components and small instruments. Peltier coolers are often used where a traditional vapor-compression cycle refrigerator would be impractical or take up too much space, and in cooled image sensors as an easy, compact and lightweight, if inefficient, way to achieve very low temperatures, using two or more stage peltier coolers arranged in a cascade refrigeration configuration, meaning that two or more Peltier elements are stacked on top of each other, with each stage being larger than the one before it, in order to extract more heat and waste heat generated by the previous stages. Peltier cooling has a low COP (efficiency) when compared with that of the vapor-compression cycle, so it emits more waste heat (heat generated by the Peltier element or cooling mechanism) and consumes more power for a given cooling capacity. | 7 | Physical Chemistry |
Pervaporation (or pervaporative separation) is a processing method for the separation of mixtures of liquids by partial vaporization through a non-porous or porous membrane. | 3 | Analytical Chemistry |
Peptide signals play a role in information processing that is different from that of conventional neurotransmitters, and many appear to be particularly associated with specific behaviours. For example, oxytocin and vasopressin have striking and specific effects on social behaviours, including maternal behaviour and pair bonding. CCAP has several functions including regulating heart rate, allatostatin and proctolin regulate food intake and growth, bursicon controls tanning of the cuticle and corazonin has a role in cuticle pigmentation and moulting. | 1 | Biochemistry |
Some harmful algal blooms resulting from eutrophication, are toxic to plants and animals. Freshwater algal blooms can pose a threat to livestock. When the algae die or are eaten, neuro- and hepatotoxins are released which can kill animals and may pose a threat to humans. An example of algal toxins working their way into humans is the case of shellfish poisoning. Biotoxins created during algal blooms are taken up by shellfish (mussels, oysters), leading to these human foods acquiring the toxicity and poisoning humans. Examples include paralytic, neurotoxic, and diarrhoetic shellfish poisoning. Other marine animals can be vectors for such toxins, as in the case of ciguatera, where it is typically a predator fish that accumulates the toxin and then poisons humans. | 2 | Environmental Chemistry |
A crystal can be described as a lattice of atoms, which in turn this leads to the reciprocal lattice. With electrons, neutrons or x-rays there is diffraction by the atoms, and if there is an incident plane wave with a wavevector , there will be outgoing wavevectors and as shown in the diagram after the wave has been diffracted by the atoms.
The energy of the waves (electron, neutron or x-ray) depends upon the magnitude of the wavevector, so if there is no change in energy (elastic scattering) these have the same magnitude, that is they must all lie on the Ewald sphere. In the Figure the red dot is the origin for the wavevectors, the black spots are reciprocal lattice points (vectors) and shown in blue are three wavevectors. For the wavevector the corresponding reciprocal lattice point lies on the Ewald sphere, which is the condition for Bragg diffraction. For the corresponding reciprocal lattice point is off the Ewald sphere, so where is called the excitation error. The amplitude and also intensity of diffraction into the wavevector depends upon the Fourier transform of the shape of the sample, the excitation error , the structure factor for the relevant reciprocal lattice vector, and also whether the scattering is weak or strong. For neutrons and x-rays the scattering is generally weak so there is mainly Bragg diffraction, but it is much stronger for electron diffraction. | 3 | Analytical Chemistry |
In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space. This contrasts with structural isomers, which share the same molecular formula, but the bond connections or their order differs. By definition, molecules that are stereoisomers of each other represent the same structural isomer. | 4 | Stereochemistry |
Some forms of ribosomal pause are reversible without needing to discard the translated peptide and mRNA. This sort, usually described as a slowdown, is usually caused by polyproline stretches (resolved by EFP or eIF5A) and uncharged tRNA. Slowdowns are important for the cell to control how much protein is produced; it also aids co-translational folding of the nascent polypeptide on the ribosome, and delays protein translation while its encoding mRNA; this can trigger ribosomal frameshifting.
More severe "stalls" can be caused an actual lack of tRNA or by the mRNA terminating without a stop codon. In this case, ribosomal quality control (RQC) performs crisis rescue by translational abandonment. This releases the ribosome from the mRNA. The incomplete polypeptide is targeted for destruction; in eukaryotes, mRNA no-go decay is also triggered.
It is difficult for RQC machinery to differentiate between a slowdown and a stall. It is possible for a mRNA sequence that normally produces a protein slowly to produce nothing instead due to intervention by RQC under different conditions. | 1 | Biochemistry |
DNA array to protein array (DAPA) is a method developed in 2007 to repeatedly produce protein arrays by ‘printing’ them from a single DNA template array, on demand (Figure 5). It starts with the spotting and immobilization of an array of DNA templates onto a glass slide. The slide is then assembled face-to-face with a second slide pre-coated with a protein-capturing reagent, and a membrane soaked with cell extract is placed between the two slides for transcription and translation to take place. The newly synthesized his-tagged proteins are then immobilized onto the slide to form the array. In the publication in 18 of 20 replications a protein microarray copy could be generated. Potentially the process can be repeated as often as needed, as long as the DNA is unharmed by DNAses, degradation or mechanical abrasion. | 1 | Biochemistry |
Aerobic metabolism occurs in Bacteria, Archaea and Eucarya. Although most bacterial species are anaerobic, many are facultative or obligate aerobes. The majority of archaeal species live in extreme environments that are often highly anaerobic. There are, however, several cases of aerobic archaea such as Haiobacterium, Thermoplasma, Sulfolobus and Yymbaculum. Most of the known eukaryotes carry out aerobic metabolism within their mitochondria which is an organelle that had a symbiogenesis origin from prokarya . All aerobic organisms contain oxidases of the cytochrome oxidase super family, but some members of the Pseudomonadota (E. coli and Acetobacter) can also use an unrelated cytochrome bd complex as a respiratory terminal oxidase. | 1 | Biochemistry |
RNA may be too complex to be the first nucleic acid, so before the RNA world several simpler nucleic acids that differ in the backbone, such as GNA, PNA, and TNA have been offered as candidates for the first nucleic acids. | 1 | Biochemistry |
The gonadotropin receptors are a group of receptors that bind a group of pituitary hormones called gonadotropins. They include the:
* Follicle-stimulating hormone receptor (FSHR) - binds follicle-stimulating hormone (FSH)
* Luteinizing hormone receptor (LHR) - binds luteinizing hormone (LH) and human chorionic gonadotropin (hCG) | 1 | Biochemistry |
The shape of a powder diffraction reflection is influenced by the characteristics of the beam, the experimental
arrangement, and the sample size and shape. In the case of monochromatic neutron sources the convolution
of the various effects has been found to result in a reflex almost exactly Gaussian in shape. If this
distribution is assumed then the contribution of a given reflection to the profile at position
is:
where is the full width at half peak height (full-width half-maximum), is the center of the reflex, and is the calculated intensity of the reflex (determined from the structure factor,
the Lorentz factor, and multiplicity of the reflection).
At very low diffraction angles the reflections may acquire an asymmetry due to the vertical divergence of the beam.
Rietveld used a semi-empirical correction factor, to account for this asymmetry:
where is the asymmetry factor and is , , or depending on the difference being positive, zero, or negative respectively.
At a given position more than one diffraction peak may contribute to the profile. The intensity is simply the sum of all reflections contributing at the point . | 3 | Analytical Chemistry |
High emissivity coatings that facilitate radiative cooling may be used in reusable thermal protection systems (RTPS) in spacecraft and hypersonic aircraft. In such heat shields a high emissivity material, such as molybdenum disilicide (MoSi) is applied on a thermally insulating ceramic substrate. In such heat shields high levels of total emissivity, typically in the range 0.8 - 0.9, need to be maintained across a range of high temperatures. Planck's law dictates that at higher temperatures the radiative emission peak shifts to lower wavelengths (higher frequencies), influencing material selection as a function of operating temperature. In addition to effective radiative cooling, radiative thermal protection systems should provide damage tolerance and may incorporate self-healing functions through the formation of a viscous glass at high temperatures. | 7 | Physical Chemistry |
Progesterone enhances the function of serotonin receptors in the brain, so an excess or deficit of progesterone has the potential to result in significant neurochemical issues. This provides an explanation for why some people resort to substances that enhance serotonin activity such as nicotine, alcohol, and cannabis when their progesterone levels fall below optimal levels.
* Sex differences in hormone levels may induce women to respond differently than men to nicotine. When women undergo cyclic changes or different hormonal transition phases (menopause, pregnancy, adolescence), there are changes in their progesterone levels. Therefore, females have an increased biological vulnerability to nicotine's reinforcing effects compared to males and progesterone may be used to counter this enhanced vulnerability. This information supports the idea that progesterone can affect behavior.
* Similar to nicotine, cocaine also increases the release of dopamine in the brain. The neurotransmitter is involved in the reward center and is one of the main neurotransmitters involved with substance abuse and reliance. In a study of cocaine users, it was reported that progesterone reduced craving and the feeling of being stimulated by cocaine. Thus, progesterone was suggested as an agent that decreases cocaine craving by reducing the dopaminergic properties of the drug. | 0 | Organic Chemistry |
Atalla was awarded the Stuart Ballantine Medal (now the Benjamin Franklin Medal in physics) at the 1975 Franklin Institute Awards, for his important contributions to silicon semiconductor technology and his invention of the MOSFET. In 2003, Atalla received a Distinguished Alumnus doctorate from Purdue University.
In 2009, he was inducted into the National Inventors Hall of Fame for his important contributions to semiconductor technology as well as data security. He was referred to as one of the "Sultans of Silicon" along with several other semiconductor pioneers.
In 2014, the 1959 invention of the MOSFET was included on the list of IEEE milestones in electronics. In 2015, Atalla was inducted into the IT History Society's IT Honor Roll for his important contributions to information technology. | 7 | Physical Chemistry |
Ligands can be decomplexed by displacement with another ligand, e.g., a highly basic ligand or the use of high pressures of carbon monoxide. Arenes are liberated from (arene)Cr(CO) with pyridine:
:(arene)Cr(CO) + 3 CHN → Cr(CO)(NCH) + arene
In this case Cr(CO)(pyridine) can be recycled. Illustrative of this approach is the synthesis of (–)-steganone via a chromium haloarene complex. The synthesis is completed by decomplexation, liberating the natural product.
1,4,7-Trithiacyclononane can be prepared within the coordination sphere of a metal, and then isolated by decomplexation. | 0 | Organic Chemistry |
Transfer RNA introns that depend upon proteins for removal occur at a specific location within the anticodon loop of unspliced tRNA precursors, and are removed by a tRNA splicing endonuclease. The exons are then linked together by a second protein, the tRNA splicing ligase. Note that self-splicing introns are also sometimes found within tRNA genes. | 1 | Biochemistry |
Amphibians, particularly anurans (frogs and toads), are increasingly used as bioindicators of contaminant accumulation in pollution studies. Anurans absorb toxic chemicals through their skin and their larval gill membranes and are sensitive to alterations in their environment. They have a poor ability to detoxify pesticides that are absorbed, inhaled, or ingested by eating contaminated food. This allows residues, especially of organochlorine pesticides, to accumulate in their systems. They also have permeable skin that can easily absorb toxic chemicals, making them a model organism for assessing the effects of environmental factors that may cause the declines of the amphibian population. These factors allow them to be used as bioindicator organisms to follow changes in their habitats and in ecotoxicological studies due to humans increasing demands on the environment.
Knowledge and control of environmental agents is essential for sustaining the health of ecosystems. Anurans are increasingly utilized as bioindicator organisms in pollution studies, such as studying the effects of agricultural pesticides on the environment. Environmental assessment to study the environment in which they live is performed by analyzing their abundance in the area as well as assessing their locomotive ability and any abnormal morphological changes, which are deformities and abnormalities in development. Decline of anurans and malformations could also suggest increased exposure to ultra-violet light and parasites. Expansive application of agrochemicals such as glyphosate have been shown to have harmful effects on frog populations throughout their lifecycle due to run off of these agrochemicals into the water systems these species live and their proximity to human development.
Pond-breeding anurans are especially sensitive to pollution because of their complex life cycles, which could consist of terrestrial and aquatic living. During their embryonic development, morphological and behavioral alterations are the effects most frequently cited in connection with chemical exposures. Effects of exposure may result in shorter body length, lower body mass and malformations of limbs or other organs. The slow development, late morphological change, and small metamorph size result in increased risk of mortality and exposure to predation. | 2 | Environmental Chemistry |
The investigation of Mg in animals, including humans, has lagged behind that in bacteria and yeast. This is largely because of the complexity of the systems involved, but also because of the impression within the field that Mg was maintained at high levels in all cells and was unchanged by external influences. Only in the last 25 years has a series of reports begun to challenge this view, with new methodologies finding that free Mg content is maintained at levels where changes might influence cellular metabolism. | 1 | Biochemistry |
A general sigmatropic rearrangement can be classified as order [i,j], meaning that a σ bond originally between atoms denoted 1 and 1, adjacent to one or more π systems, is shifted to between atoms i and j. Thus it migrates (i − 1), (j' − 1) atoms away from its original position.
A formal symmetry analysis via correlation diagrams is of no use in the study of sigmatropic rearrangements as there are, in general, only symmetry elements present in the transition state. Except in special cases (e.g. [3,3]-rearrangements), there are no symmetry elements that are conserved as the reaction coordinate is traversed. Nevertheless, orbital correlations between starting materials and products can still be analyzed, and correlations of starting material orbitals with high energy product orbitals will, as usual, result in "symmetry-forbidden" processes. However, an FMO based approach (or the Dewar-Zimmerman analysis) is more straightforward to apply.
One of the most prevalent classes of sigmatropic shifts is classified as [1,j], where j is odd. That means one terminus of the σ-bond migrates (j − 1) bonds away across a π-system while the other terminus does not migrate. It is a reaction involving j + 1 electrons: j − 1 from the π-system and 2 from σ-bond. Using FMO analysis, [1,j]-sigmatropic rearrangements are allowed if the transition state has constructive overlap between the migrating group and the accepting p orbital of the HOMO. In [1,j]-sigmatropic rearrangements if j + 1 = 4n, then supra/antara is thermally allowed, and if j + 1 = 4n + 2, then supra/supra or antara/antara is thermally allowed.
The other prevalent class of sigmatropic rearrangements are [3,3], notably the Cope and Claisen rearrangements. Here, the constructive interactions must be between the HOMOs of the two allyl radical fragments in the transition state. The ground state HOMO Ψ of the allyl fragment is shown below. As the terminal p-orbitals are of opposite sign, this reaction can either take place in a supra/supra topology, or an antara/antara topology.
The selection rules for an [i,j]-sigmatropic rearrangement are as follows:
* For supra/supra or antara/antara [i,j]-sigmatropic shifts, if i + j = 4n + 2 they are thermally allowed and if i + j = 4n they are photochemically allowed
* For supra/antara [i,j]-sigmatropic shifts, if i + j = 4n they are thermally allowed, and if i + j = 4n + 2 they are photochemically allowed
This is summarized in the following table: | 7 | Physical Chemistry |
The classic Monod–Wyman–Changeux model (MWC) for cooperativity is generally published in an irreversible form. That is, there are no product terms in the rate equation which can be problematic for those wishing to build metabolic models since there are no product inhibition terms. However, a series of publications by Popova and Sel'kov derived the MWC rate equation for the reversible, multi-substrate, multi-product reaction.
The same problem applies to the classic Hill equation which is almost always shown in an irreversible form. Hofmeyr and Cornish-Bowden first published the reversible form of the Hill equation. The equation has since been discussed elsewhere and the model has also been used in a number of kinetic models such as a model of Phosphofructokinase and Glycolytic Oscillations in the Pancreatic β-cells or a model of a glucose-xylose co-utilizing S. cerevisiae strain. The model has also been discussed in modern enzyme kinetics textbooks. | 7 | Physical Chemistry |
In 1999, Smith and his co-workers reported the first gram-scale synthesis of (+)-discodermolide, which make the development of (+)-discodermolide as a potential chemotherapeutic agent possible. This synthetic route was licensed to Novartis Pharmaceuticals. One of the major improvements was that no purification was required in the first four steps of the five-step sequence towards the common precursor as the intermediate, aldol adduct, is a crystalline solid. A chelation-controlled Mukaiyama-aldol reaction was used to set the stereogenicity at C(5) of the lactone fragment.
Two years later, Smith and his co-workers publish a third-generation synthesis in which the bulky TBS ether protecting group at C(11) of the precursor iodide was replaced by a less sterically encumbering group, MOM. This modification favors the formation of the desired phosphonium salt. The Smith third-generation synthesis of (+)-discodermolide has an overall yield of 6.0% with a longest linear sequence of 21 steps and 35 total steps. | 0 | Organic Chemistry |
The S.I. unit for the mold constant is seconds per metre squared (). According to Askeland, the constant is usually 2, however Degarmo claims it is between 1.5 and 2. The mold constant can be calculated using the following formula:
Where
: = melting or freezing temperature of the liquid (in kelvins),
: = initial temperature of the mold (in kelvins),
: = superheat (in kelvins),
: = latent heat of fusion (in ),
: = thermal conductivity of the mold (in ),
: = density of the mold (in ),
: = specific heat of the mold (in ),
: = density of the metal (in ),
: = specific heat of the metal (in ).
It is most useful in determining if a riser will solidify before the casting, because if the riser solidifies first then defects like shrinkage or porosity can form. | 8 | Metallurgy |
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