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In fluid dynamics, a stagnation point flow refers to a fluid flow in the neighbourhood of a stagnation point (in three-dimensional flows) or a stagnation line (in two-dimensional flows) with which the stagnation point/line refers to a point/line where the velocity is zero in the inviscid approximation. The flow specifically considers a class of stagnation points known as saddle points wherein incoming streamlines gets deflected and directed outwards in a different direction; the streamline deflections are guided by separatrices. The flow in the neighborhood of the stagnation point or line can generally be described using potential flow theory, although viscous effects cannot be neglected if the stagnation point lies on a solid surface. | 1 | Applied and Interdisciplinary Chemistry |
The untranslated region is seen in prokaryotes and eukaryotes, although the length and composition may vary. In prokaryotes, the 5 UTR is typically between 3 and 10 nucleotides long. In eukaryotes, the 5 UTR can be hundreds to thousands of nucleotides long. This is consistent with the higher complexity of the genomes of eukaryotes compared to prokaryotes. The 3 UTR varies in length as well. The poly-A tail is essential for keeping the mRNA from being degraded. Although there is variation in lengths of both the 5 and 3 UTR, it has been seen that the 5 UTR length is more highly conserved in evolution than the 3' UTR length. | 1 | Applied and Interdisciplinary Chemistry |
Actinic light was first commonly used in early photography to distinguish light that would expose the monochrome films from light that would not. A non-actinic safe-light (e.g., red or amber) could be used in a darkroom without risk of exposing (fogging) light-sensitive films, plates or papers.
Early "non colour-sensitive" (NCS) films, plates and papers were only sensitive to the high-energy end of the visible spectrum from green to UV (shorter-wavelength light). This would render a print of the red areas as a very dark tone because the red light was not actinic. Typically, light from xenon flash lamps is highly actinic, as is daylight as both contain significant green-to-UV light.
In the first half of the 20th century, developments in film technology produced films sensitive to red and yellow light, known as orthochromatic and panchromatic, and extended that through to near infra-red light. These gave a truer reproduction of human perception of lightness across the color spectrum. In photography, therefore, actinic light must now be referenced to the photographic material in question. | 0 | Theoretical and Fundamental Chemistry |
Along with dissolved organic matter, POM drives the lower aquatic food web by providing energy in the form of carbohydrates, sugars, and other polymers that can be degraded. POM in water bodies is derived from terrestrial inputs (e.g. soil organic matter, leaf litterfall), submerged or floating aquatic vegetation, or autochthonous production of algae (living or detrital). Each source of POM has its own chemical composition that affects its lability, or accessibility to the food web. Algal-derived POM is thought to be most labile, but there is growing evidence that terrestrially-derived POM can supplement the diets of micro-organisms such as zooplankton when primary productivity is limited. | 0 | Theoretical and Fundamental Chemistry |
Cleavable detergents, also known as cleavable surfactants, are special surfactants (detergents) that are used in biochemistry and especially in proteomics to enhance protein denaturation and solubility. The detergent is rendered inactive by cleavage, usually under acidic conditions, in order to make the sample compatible with a following procedure or in order to selectively remove the cleavage products.
Applications for cleavable detergents include protease digestion of proteins such as in-gel digestion with trypsin after SDS PAGE and peptide extractions from electrophoresis gels. Cleavable detergents are mainly used in sample preparations for mass spectrometry. | 0 | Theoretical and Fundamental Chemistry |
Between 1998 and 2013, research conducted at BATS has generated over 450 peer-reviewed articles. Among the findings are measurements showing the gradual acidification of the surface ocean, where surface water pH, carbonate ion concentration, and the saturation state for calcium carbonate minerals, such as aragonite, have all decreased since 1998. Additionally, studies at BATS have shown changes in the Revelle factor, suggesting that the capacity of North Atlantic Ocean surface waters to absorb carbon dioxide has diminished, even as seawater pCO has kept pace with increasing atmospheric pCO. | 0 | Theoretical and Fundamental Chemistry |
NanoProfessionals have alternate molecular structures for the top of the head, and possibly include a hat. Most can be synthesized from the NanoKid by an acetal exchange reaction with the desired 1,2- or 1,3- diol, using p-toluenesulfonic acid as catalyst and heated by microwave irradiation for a few minutes. The ultimate set of products was a recognizably diverse population of NanoPutians: NanoAthlete, NanoPilgrim, NanoGreenBeret, NanoJester, NanoMonarch, NanoTexan, NanoScholar, NanoBaker, and NanoChef.
The majority of the figures are easily recognizable in their most stable conformation. A few have as their stable conformation a less recognizable shape, so these are often drawn in the more recognizable but less stable way. Many liberties were taken in the visual depiction of the head dressings of the NanoPutians. Some products are formed as a mixture of diastereomers—the configuration of the "neck" compared to parts of the "hat". | 1 | Applied and Interdisciplinary Chemistry |
The Archiv der Pharmazie (German pronunciation: [ˈ arˈçiːf ˈdeːɐ̯ farmaˈtsiː], English: Archive of Pharmacy) is a monthly peer-reviewed scientific journal covering all aspects of chemistry in the life sciences. The journal was established in 1822 and is published by Wiley-VCH on behalf of the Deutsche Pharmazeutische Gesellschaft. Until 2019, the editor-in-chief was Holger Stark (Heinrich Heine University Düsseldorf). He was succeeded in 2020 by Andreas Link (University of Greifswald). | 1 | Applied and Interdisciplinary Chemistry |
For more than 20 years, microRNAs have been known to act in the cytoplasm to degrade transcriptional expression of specific target gene messenger RNAs (see microRNA history). However, recently, Gagnon et al. showed that as many as 75% of microRNAs may be shuttled back into the nucleus of cells. Some nuclear microRNAs have been shown to mediate transcriptional gene activation or transcriptional gene inhibition. | 1 | Applied and Interdisciplinary Chemistry |
The angular compensation of thermal expansion requires at least two, and for full compensation even three, angular expansion joints. Angular expansion joints offer a wide variety of combination options in so-called two-hinge or three-hinge systems.
Single-plane three-hinged systems make do with one-sided angularly flexible expansion joints, while multi-plane three-hinged systems for absorbing thermal expansion in three axial directions require at least two gimbal expansion joints that are angularly flexible on all sides.
The following basic rules apply to angular compensation:
* Always at least two angular expansion joints are needed.
* Angular expansion joints are always associated with multiple redirections of flow by 90°.
* Because angular expansion joints (as hinged expansion joints) themselves absorb the compressive forces released by the bellows, the fixed points in the pipeline are only loaded by their adjusting forces and torques, by the frictional forces of the pipe guides and by the flow forces.
* Angular compensation is specifically designed for complex multi-plane pipework. | 1 | Applied and Interdisciplinary Chemistry |
Slip bands or stretcher-strain marks are localized bands of plastic deformation in metals experiencing stresses. Formation of slip bands indicates a concentrated unidirectional slip on certain planes causing a stress concentration. Typically, slip bands induce surface steps (e.g., roughness due persistent slip bands during fatigue) and a stress concentration which can be a crack nucleation site. Slip bands extend until impinged by a boundary, and the generated stress from dislocations pile-up against that boundary will either stop or transmit the operating slip depending on its (mis)orientation.
Formation of slip bands under cyclic conditions is addressed as persistent slip bands (PSBs) where formation under monotonic condition is addressed as dislocation planar arrays (or simply slip-bands, see Slip bands in the absence of cyclic loading section). Slip-bands can be simply viewed as boundary sliding due to dislocation glide that lacks (the complexity of ) PSBs high plastic deformation localisation manifested by tongue- and ribbon-like extrusion. And, where PSBs normally studied with (effective) Burgers vector aligned with the extrusion plane because a PSB extends across the grain and exacerbates during fatigue; a monotonic slip-band has a Burger’s vector for propagation and another for plane extrusions both controlled by the conditions at the tip. | 1 | Applied and Interdisciplinary Chemistry |
The compound is highly reactive and pyrophoric, self-igniting in air. The lack of reactivity studies may be in part sourced from its very low solubility in organic solvents. However, it may be able to find use as a specialized source of reactive low-valent iron.
Computational studies have estimated COT dissociation from Fe(COT) to be 57 kcal/mol uphill, which would not be readily accessible at room temperature in solution.
With analogy to Fe(CO), the compound could potentially be susceptible to Fe-Fe bond homolysis via photoexcitation. | 0 | Theoretical and Fundamental Chemistry |
The muscle-type nicotinic receptor is a type of nicotinic acetylcholine receptor consisting of the subunit combination (α1)β1δε (adult receptor) or (α1)β1δγ (fetal receptor). These receptors are found in neuromuscular junctions, where activation leads to an excitatory postsynaptic potential (EPSP), mainly by increased Na and K permeability. | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, the Myers deoxygenation reaction is an organic redox reaction that reduces an alcohol into an alkyl position by way of an arenesulfonylhydrazine as a key intermediate. This name reaction is one of four discovered by Andrew Myers that are named after him; this reaction and the Myers allene synthesis reaction involve the same type of intermediate. The other reactions are Myers' asymmetric alkylation and Myers-Saito Cycloaromatization.
:R–CHOH + HNNHSOAr → R–CHN(SOAr)NH → R–CHN=NH → R–CH + N
The reaction is a three-step one-pot process in which the alcohol first undergoes a Mitsunobu reaction with ortho-nitrobenzenesulfonylhydrazine in the presence of triphenylphosphine and diethyl azodicarboxylate. Unlike hydrazone-synthesis reactions, this reaction occurs on the same nitrogen of the hydrazine that has the arenesulfonyl substituent. Upon warming, this product undergoes an elimination of arylsulfinic acid to give an unstable diazene as a reactive intermediate. A radical process then promptly occurs with loss of dinitrogen to give the final alkyl product.
The alkyl-radical intermediate can instead undergo an intramolecular reaction with various other suitably-positioned functional groups within the molecule, such as alkenes or cyclopropanes, leading to alternate products.
If the diazene intermediate is able to undergo a sigmatropic rearrangement, this process occurs in preference to the simple radical reduction to give a hydrocarbon with a transposed π bond. For example, in the Myers allene synthesis, one of the two π bonds of the alkyne of a propargyl alcohol shifts, forming an allene. Likewise, the benzylic alcohol 1-naphthylmethanol rearranges to give a methylene-cyclohexyl product with loss of aromaticity. | 0 | Theoretical and Fundamental Chemistry |
Recrystallization kinetics are commonly observed to follow the profile shown. There is an initial nucleation period t where the nuclei form, and then begin to grow at a constant rate consuming the deformed matrix. Although the process does not strictly follow classical nucleation theory it is often found that such mathematical descriptions provide at least a close approximation. For an array of spherical grains the mean radius R at a time t is (Humphreys and Hatherly 2004):
where t is the nucleation time and G is the growth rate dR/dt. If N nuclei form in the time increment dt and the grains are assumed to be spherical then the volume fraction will be:
This equation is valid in the early stages of recrystallization when f<<1 and the growing grains are not impinging on each other. Once the grains come into contact the rate of growth slows and is related to the fraction of untransformed material (1-f) by the Johnson-Mehl equation:
While this equation provides a better description of the process it still assumes that the grains are spherical, the nucleation and growth rates are constant, the nuclei are randomly distributed and the nucleation time t is small. In practice few of these are actually valid and alternate models need to be used.
It is generally acknowledged that any useful model must not only account for the initial condition of the material but also the constantly changing relationship between the growing grains, the deformed matrix and any second phases or other microstructural factors. The situation is further complicated in dynamic systems where deformation and recrystallization occur simultaneously. As a result, it has generally proven impossible to produce an accurate predictive model for industrial processes without resorting to extensive empirical testing. Since this may require the use of industrial equipment that has not actually been built there are clear difficulties with this approach. | 1 | Applied and Interdisciplinary Chemistry |
Tephrochronology is a geochronological technique that uses discrete layers of tephra—volcanic ash from a single eruption—to create a chronological framework in which paleoenvironmental or archaeological records can be placed. Such an established event provides a "tephra horizon". The premise of the technique is that each volcanic event produces ash with a unique chemical "fingerprint" that allows the deposit to be identified across the area affected by fallout. Thus, once the volcanic event has been independently dated, the tephra horizon will act as time marker. It is a variant of the basic geological technique of stratigraphy.
The main advantages of the technique are that the volcanic ash layers can be relatively easily identified in many sediments and that the tephra layers are deposited relatively instantaneously over a wide spatial area. This means they provide accurate temporal marker layers which can be used to verify or corroborate other dating techniques, linking sequences widely separated by location into a unified chronology that correlates climatic sequences and events. This results in "age-equivalent dating".
Effective tephrochronology requires accurate geochemical fingerprinting (usually via an electron microprobe). An important recent advance is the use of LA-ICP-MS (i.e. laser ablation ICP-MS) to measure trace-element abundances in individual tephra shards. One problem in tephrochronology is that tephra chemistry can become altered over time, at least for basaltic tephras. Some tephra horizons and the use of zircon directed techniques are more useful than others in linking layers over wide areas and determining eruption details. For example the often very explosive nature of rhyolytic eruptions will cause wider distribution, the higher potassium content of rhyolite allows more accurate time determinations, and the location of a deposit will influence its potential for chemical alteration after being laid down. Zircon techniques applied to tephra and other samples from the same eruption, may allow magma sources, magma residence times and the geochemical conditions of the magma formation to be better understood with dating of more than just the eruption itself, but also when the magma first evolved separately, or incorporated other rocks. | 0 | Theoretical and Fundamental Chemistry |
Signal transducer and activator of transcription 3 (STAT3) is a transcription factor which in humans is encoded by the STAT3 gene. It is a member of the STAT protein family. | 1 | Applied and Interdisciplinary Chemistry |
Tuanku Zara Salim (Jawi: توانكو زارا سليم; born Zara Salim Davidson; 22 March 1973) is the Raja Permaisuri (Queen consort) of Perak as the wife of Sultan Nazrin Muizzuddin Shah, the current Sultan of Perak.
A chemical engineer by training, she was heading an oil and gas consultancy firm based in Kuala Lumpur before her marriage to the Sultan. She and the Sultan, who had been the countrys most eligible royal bachelor for decades, have known each other since the mid-1990s. She was officially installed as the Raja Permaisuri of Perak during Sultan Nazrins enthronement ceremony as the 35th Sultan of Perak on 6 May 2015. | 1 | Applied and Interdisciplinary Chemistry |
The presence of Anti-SSA/Ro in pregnant women with SLE is associated with an increased risk of neonatal lupus erythematosus which can be accompanied by congenital heart block (CHB) in the fetus. SLE-related symptoms in infants that arise from Anti-Ro/SSA resolve in about six months as the mothers antibodies leave the babys system. Mothers of babies with NLE most often do not show signs of autoimmune disease.
The role of Anti-SSA/Ro in NLE is remains under study, as recent studies have suggested that CHB in neonates is more generally linked to instances of autoimmunity in the mother rather than the presence of Anti-Ro/SSA antibody. | 1 | Applied and Interdisciplinary Chemistry |
* Evaporation
* Sublimation
* Cracking of alkanes
* Thermal decomposition
* Hydrolysis
* Nucleosynthesis of elements heavier than nickel in stellar cores
* High-energy neutrons can produce tritium from lithium-7 in an endothermic process, consuming 2.466 MeV. This was discovered when the 1954 Castle Bravo nuclear test produced an unexpectedly high yield.
* Nuclear fusion of elements heavier than iron in supernovae
*Dissolving together barium hydroxide and ammonium chloride
*Dissolving together citric acid and baking soda | 0 | Theoretical and Fundamental Chemistry |
For small-scale hydrogen production, RO is sometimes used to prevent formation of mineral deposits on the surface of electrodes. | 0 | Theoretical and Fundamental Chemistry |
Contamination is the presence of a constituent, impurity, or some other undesirable element that renders something unsuitable, unfit or harmful for both physical body, natural environment, workplace, etc. | 0 | Theoretical and Fundamental Chemistry |
Glycosyltransferases can be segregated into "retaining" or "inverting" enzymes according to whether the stereochemistry of the donor's anomeric bond is retained (α→α) or inverted (α→β) during the transfer. The inverting mechanism is straightforward, requiring a single nucleophilic attack from the accepting atom to invert stereochemistry.
The retaining mechanism has been a matter of debate, but there exists strong evidence against a double displacement mechanism (which would cause two inversions about the anomeric carbon for a net retention of stereochemistry) or a dissociative mechanism (a prevalent variant of which was known as SNi). An "orthogonal associative" mechanism has been proposed which, akin to the inverting enzymes, requires only a single nucleophilic attack from an acceptor from a non-linear angle (as observed in many crystal structures) to achieve anomer retention. | 0 | Theoretical and Fundamental Chemistry |
Receptor theory is the application of receptor models to explain drug behavior. Pharmacological receptor models preceded accurate knowledge of receptors by many years. John Newport Langley and Paul Ehrlich introduced the concept that receptors can mediate drug action at the beginning of the 20th century. Alfred Joseph Clark was the first to quantify drug-induced biological responses (specifically, f-mediated receptor activation). So far, nearly all of the quantitative theoretical modelling of receptor function has centred on ligand-gated ion channels and G protein-coupled receptors. | 1 | Applied and Interdisciplinary Chemistry |
Archaeologist George Eogan, in his study of Bronze Age gold-working, noted that very few Bronze Age gold artefacts had been discovered through "controlled archaeological investigation", with the majority instead having been unearthed "by chance", as a result of "agricultural activities or peat-cutting". In the 21st century, metal detectorists have become important, for example with the important Shropshire bulla, found in 2018. | 1 | Applied and Interdisciplinary Chemistry |
Although usually purchased, BMS can be prepared by absorbing diborane into dimethyl sulfide:
It can be purified by bulb to bulb vacuum transfer. Although a structure of BMS has not been determined crystallographically, (pentafluorophenyl)-borane dimethylsulfide (), has been examined by X-ray crystallography. The boron atom adopts a tetrahedral molecular geometry. | 0 | Theoretical and Fundamental Chemistry |
Intravesical drug administration is the delivery of pharmaceuticals to the urinary bladder through a catheter. This route of administration is used for the therapy of bladder cancer and interstitial cystitis. The retention of dosage forms in the bladder is relatively poor, which is related to the need for a periodical urine voiding. Some mucoadhesive materials are able to stick to mucosal lining in the bladder, resist urine wash out effects and provide a sustained drug delivery. | 1 | Applied and Interdisciplinary Chemistry |
Common to all LOV proteins is the blue-light sensitive flavin chromophore, which in the signaling state is covalently linked to the protein core via an adjacent cysteine residue. LOV domains are e.g. encountered in phototropins, which are blue-light-sensitive protein complexes regulating a great diversity of biological processes in higher plants as well as in micro-algae. Phototropins are composed of two LOV domains, each containing a non-covalently bound flavin mononucleotide (FMN) chromophore in its dark-state form, and a C-terminal Ser-Thr kinase.
Upon blue-light absorption, a covalent bond between the FMN chromophore and an adjacent reactive cysteine residue of the apo-protein is formed in the LOV2 domain. This subsequently mediates the activation of the kinase, which induces a signal in the organism through phototropin autophosphorylation.
While the photochemical reactivity of the LOV2 domain has been found to be essential for the activation of the kinase, the in vivo functionality of the LOV1 domain within the protein complex still remains unclear. | 1 | Applied and Interdisciplinary Chemistry |
Thomas Kurtzman is an American physical chemist most notable for his research into the use of convolutional neural networks (CNNs) to improve pharmaceutical design. According to Bioworld, Kurtzmans research "reached the devastating conclusion that the entirety" of apparent deep learning produced over the course of several years by a CNN dataset highly regarded in academia and industry was illusory. The perceived scientific progress, Kurtzman wrote, was due to CNNs effective learning of the deficiencies in the dataset. "This is alarming," the article continued, "as companies have been built on [https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0220113 this research.]
During the COVID-19 pandemic, a computational tool Kurtzman developed, GIST, was used to research potential new drugs to treat the illness.
Kurtzman is a professor of chemistry at the Lehman College and the Graduate Center of the City University of New York. His research is conducted at the affiliated Kurtzman Lab and funded by the National Institutes of Health.
He is married to Mor Armony, vice dean for faculty and research at New York University's Stern School of Business. | 0 | Theoretical and Fundamental Chemistry |
For flow in a pipe or tube, the Reynolds number is generally defined as
where
* is the hydraulic diameter of the pipe (the inside diameter if the pipe is circular) (m),
* is the volumetric flow rate (m/s),
* is the pipes cross-sectional' area () (m),
* is the mean velocity of the fluid (m/s),
* (mu) is the dynamic viscosity of the fluid (Pa·s = N·s/m = kg/(m·s)),
* (nu) is the kinematic viscosity () (m/s),
* (rho) is the density of the fluid (kg/m),
* is the mass flowrate of the fluid (kg/s).
For shapes such as squares, rectangular or annular ducts where the height and width are comparable, the characteristic dimension for internal-flow situations is taken to be the hydraulic diameter, , defined as
where is the cross-sectional area, and is the wetted perimeter. The wetted perimeter for a channel is the total perimeter of all channel walls that are in contact with the flow. This means that the length of the channel exposed to air is not included in the wetted perimeter.
For a circular pipe, the hydraulic diameter is exactly equal to the inside pipe diameter:
For an annular duct, such as the outer channel in a tube-in-tube heat exchanger, the hydraulic diameter can be shown algebraically to reduce to
where
* is the inside diameter of the outer pipe,
* is the outside diameter of the inner pipe.
For calculation involving flow in non-circular ducts, the hydraulic diameter can be substituted for the diameter of a circular duct, with reasonable accuracy, if the aspect ratio AR of the duct cross-section remains in the range < AR < 4. | 1 | Applied and Interdisciplinary Chemistry |
The crossed molecular beam technique was developed by Dudley Herschbach and Yuan T. Lee, for which they were awarded the 1986 Nobel Prize in Chemistry. While the technique was demonstrated in 1953 by Taylor and Datz of Oak Ridge National Laboratory, Herschbach and Lee refined the apparatus and began probing gas-phase reactions in unprecedented detail.
Early crossed beam experiments investigated alkali metals such as potassium, rubidium, and cesium. When the scattered alkali metal atoms collided with a hot metal filament, they ionized, creating a small electric current. Because this detection method is nearly perfectly efficient, the technique was quite sensitive. Unfortunately, this simple detection system only detects alkali metals. New techniques for detection were needed to analyze main group elements.
Detecting scattered particles through a metal filament gave a good indication of angular distribution but has no sensitivity to kinetic energy. In order to gain insight into the kinetic energy distribution, early crossed molecular beam apparatuses used a pair of slotted disks placed between the collision center and the detector. By controlling the rotation speed of the disks, only particles with a certain known velocity could pass through and be detected. With information about the velocity, angular distribution, and identity of the scattered species, useful information about the dynamics of the system can be derived.
Later improvements included the use of quadrupole mass filters to select only the products of interest, as well as time-of-flight mass spectrometers to allow easy measurement of kinetic energy. These improvements also allowed the detection of a vast array of compounds, marking the advent of the "universal" crossed molecular beam apparatus.
The inclusion of supersonic nozzles to collimate the gases expanded the variety and scope of experiments, and the use of lasers to excite the beams (either before impact or at the point of reaction) further broadened the applicability of this technique. | 0 | Theoretical and Fundamental Chemistry |
was a Japanese organic chemist. One of the most prolific chemists of the 20th century in the field of organic synthesis, Mukaiyama helped establish the field of organic chemistry in Japan after World War II. | 0 | Theoretical and Fundamental Chemistry |
Due to the short range of absorption and inability to penetrate the outer layers of skin, alpha particles are not, in general, dangerous to life unless the source is ingested or inhaled. Because of this high mass and strong absorption, if alpha-emitting radionuclides do enter the body (upon being inhaled, ingested, or injected, as with the use of Thorotrast for high-quality X-ray images prior to the 1950s), alpha radiation is the most destructive form of ionizing radiation. It is the most strongly ionizing, and with large enough doses can cause any or all of the symptoms of radiation poisoning. It is estimated that chromosome damage from alpha particles is anywhere from 10 to 1000 times greater than that caused by an equivalent amount of gamma or beta radiation, with the average being set at 20 times. A study of European nuclear workers exposed internally to alpha radiation from plutonium and uranium found that when relative biological effectiveness is considered to be 20, the carcinogenic potential (in terms of lung cancer) of alpha radiation appears to be consistent with that reported for doses of external gamma radiation i.e. a given dose of alpha-particles inhaled presents the same risk as a 20-times higher dose of gamma radiation. The powerful alpha emitter polonium-210 (a milligram of Po emits as many alpha particles per second as 4.215 grams of Ra) is suspected of playing a role in lung cancer and bladder cancer related to tobacco smoking. Po was used to kill Russian dissident and ex-FSB officer Alexander V. Litvinenko in 2006.
When alpha particle emitting isotopes are ingested, they are far more dangerous than their half-life or decay rate would suggest, due to the high relative biological effectiveness of alpha radiation to cause biological damage. Alpha radiation is an average of about 20 times more dangerous, and in experiments with inhaled alpha emitters, up to 1000 times more dangerous than an equivalent activity of beta emitting or gamma emitting radioisotopes. | 0 | Theoretical and Fundamental Chemistry |
:See Immobilized enzyme for more information.
There are several reasons for immobilizing an enzyme. In addition to more convenient handling of the enzyme, it provides for its facile separation from the product, thereby minimizing or eliminating protein contamination of the product. Immobilization also facilitates the efficient recovery and re-use of costly enzymes, in many applications a conditio sine qua non for economic viability, and enables their use in continuous, fixed-bed operation. A further benefit is often enhanced stability, under both storage and operational conditions, e.g. towards denaturation by heat or organic solvents or by autolysis. Enzymes are rather delicate molecules that can easily lose their unique three-dimensional structure, essential for their activity, by denaturation (unfolding). Improved enzyme performance via enhanced stability, over a broad pH and temperature range as well as tolerance towards organic solvents, coupled with repeated re-use is reflected in higher catalyst productivities (kg product/kg enzyme) which, in turn, determine the enzyme costs per kg product.
Basically, three traditional methods of enzyme immobilization can be distinguished: binding to a support(carrier), entrapment (encapsulation) and cross-linking. Support binding can be physical, ionic, or covalent in nature. However, physical bonding is generally too weak to keep the enzyme fixed to the carrier under industrial conditions of high reactant and product concentrations and high ionic strength. The support can be a synthetic resin, a biopolymer or an inorganic polymer such as (mesoporous) silica or a zeolite. Entrapment involves inclusion of an enzyme in a polymer network (gel lattice) such as an organic polymer or a silica sol-gel, or a membrane device such as a hollow fiber or a microcapsule. Entrapment requires the synthesis of the polymeric network in the presence of the enzyme. The third category involves cross-linking of enzyme aggregates or crystals, using a bifunctional reagent, to prepare carrier-free macroparticles.
The use of a carrier inevitably leads to ‘dilution of activity’, owing to the introduction of a large portion of non-catalytic ballast, ranging from 90% to >99%, which results in lower space-time yields and productivities. Moreover, immobilization of an enzyme on a carrier often leads to a substantial loss of activity, especially at high enzyme loadings. Consequently, there is an increasing interest in carrier-free immobilized enzymes, such as cross-linked enzyme crystals (CLECs) and cross-linked enzyme aggregates (CLEAs) that offer the advantages of highly concentrated enzyme activity combined with high stability and low production costs owing to the exclusion of an additional (expensive) carrier. | 0 | Theoretical and Fundamental Chemistry |
Hand boilers date back at least as early as 1767, when the American polymath Benjamin Franklin encountered them in Germany. He developed an improved version in 1768, after which they were called Franklins pulse glass or palm glass or pulse hammer (German: Pulshammer) or water hammer (German: Wasserhammer'). | 0 | Theoretical and Fundamental Chemistry |
There are two simple regular lattices that achieve this highest average density. They are called face-centered cubic (FCC) (also called cubic close packed) and hexagonal close-packed (HCP), based on their symmetry. Both are based upon sheets of spheres arranged at the vertices of a triangular tiling; they differ in how the sheets are stacked upon one another. The FCC lattice is also known to mathematicians as that generated by the A root system. | 0 | Theoretical and Fundamental Chemistry |
Imaging cleared tissues generates massive volumes of complex data, which requires powerful computational hardware and software to store, process, analyze, and visualize. A single mouse brain can generate terabytes of data. Both commercial and open-source software exists to address this need, some of it adapted from solutions for two-dimensional images and some of it designed specifically for the three-dimensional images produced by imaging of cleared tissues. | 1 | Applied and Interdisciplinary Chemistry |
A growing body of research evidence is challenging the perception that sustainable buildings are significantly more costly to design and build than those that simply adhere to regulatory requirements. Research by the Sweett Group into projects using BREEAM, for example, demonstrates that sustainable options often add little or no capital cost to a development project. Where such measures do incur additional costs, these can frequently be paid back through lower running expenses, ultimately leading to saving over the life of the building.
Research studies have also highlighted the enhanced value and quality of sustainable buildings. Achieving the standards required by BREEAM requires careful planning, design, specification and detailing, and a good working relationship between the client and project team—the very qualities that can produce better buildings and better conditions for building users. A survey commissioned by Schneider Electric and undertaken by BSRIA examined the experiences of a wide range of companies that had used BREEAM. The findings included, for example, that 88% think it is a good thing, 96% would use the scheme again and 88% would recommend BREEAM to others.
The greater efficiency and quality associated with sustainability are also helping to make such building more commercially successful. There is growing evidence, for example, that BREEAM-rated buildings provide increased rates of return for investors, and increased rental rates and sales premiums for developers and owners. A Maastricht University document, published by RICS Research, reported on a study of the effect of BREEAM certification on office buildings in London from 2000–2009. It found, for example, that these buildings achieved a 21% premium on transaction prices and an 18% premium on rents. | 1 | Applied and Interdisciplinary Chemistry |
Sulfilimine bonds stabilize collagen IV strands found in the extracellular matrix and arose at least 500 mya. These bonds covalently connect hydroxylysine and methionine residues of adjacent polypeptide strands to form a larger collagen trimer. | 0 | Theoretical and Fundamental Chemistry |
In Complex III (cytochrome bc complex or CoQH-cytochrome c reductase; ), the Q-cycle contributes to the proton gradient by an asymmetric absorption/release of protons. Two electrons are removed from QH at the Q site and sequentially transferred to two molecules of cytochrome c, a water-soluble electron carrier located within the intermembrane space. The two other electrons sequentially pass across the protein to the Q site where the quinone part of ubiquinone is reduced to quinol. A proton gradient is formed by one quinol () oxidations at the Q site to form one quinone () at the Q site. (In total, four protons are translocated: two protons reduce quinone to quinol and two protons are released from two ubiquinol molecules.)
When electron transfer is reduced (by a high membrane potential or respiratory inhibitors such as antimycin A), Complex III may leak electrons to molecular oxygen, resulting in superoxide formation.
This complex is inhibited by dimercaprol (British Antilewisite, BAL), naphthoquinone and antimycin. | 1 | Applied and Interdisciplinary Chemistry |
As typical for the CMGC kinase group, the catalytic site of MAP kinases has a very loose consensus sequence for substrates. Like all their relatives, they only require the target serine / threonine amino acids to be followed by a small amino acid, preferably proline ("proline-directed kinases"). But as SP/TP sites are extremely common in all proteins, additional substrate-recognition mechanisms have evolved to ensure signaling fidelity. Unlike their closest relatives, the cyclin-dependent kinases (CDKs), where substrates are recognized by the cyclin subunit, MAPKs associate with their substrates via auxiliary binding regions on their kinase domains. The most important such region consists of the hydrophobic docking groove and the negatively charged CD-region. Together they recognize the so-called MAPK docking or D-motifs (also called kinase interaction motif / KIM). D-motifs essentially consist of one or two positively charged amino acids, followed by alternating hydrophobic residues (mostly leucines), typically upstream of the phosphorylation site by 10–50 amino acids. Many of the known MAPK substrates contain such D-motifs that can not only bind to, but also provide specific recognition by certain MAPKs. D-motifs are not restricted to substrates: MAP2 kinases also contain such motifs on their N-termini that are absolutely required for MAP2K-MAPK interaction and MAPK activation. Similarly, both dual-specificity MAP kinase phosphatases and MAP-specific tyrosine phosphatases bind to MAP kinases through the same docking site. D-motifs can even be found in certain MAPK pathway regulators and scaffolds (e.g. in the mammalian JIP proteins).
Other, less well characterised substrate-binding sites also exist. One such site (the DEF site) is formed by the activation loop (when in the active conformation) and the MAP kinase-specific insert below it. This site can accommodate peptides with an FxFP consensus sequence, typically downstream of the phosphorylation site. Note that the latter site can only be found in proteins that need to selectively recognize the active MAP kinases, thus they are almost exclusively found in substrates. Different motifs may cooperate with each other, as in the Elk family of transcription factors, that possess both a D-motif and an FxFP motif. The presence of an FxFP motif in the KSR1 scaffold protein also serves to make it an ERK1/2 substrate, providing a negative feedback mechanism to set the correct strength of ERK1/2 activation. | 1 | Applied and Interdisciplinary Chemistry |
* I.L. Rozowsky (1957) "Flow of Water in bends of open channels", English Translation, Israel Progr. For Scientific Transl., Jerusalem
* R. Galappatti and C.B. Vreugdenhil (1985) "A depth-integrated model for suspended transport", Journal of Hydraulic Research, Vol.23, No.4
* H.G. Enggrob and S. Tjerry (1998) "Simulation of Morphological Characteristics of a Braided River", Proc IAHR-Symp on River, Coastal and Estuarine morphodynamics, University of Genova, Dept Environmental Eng., Genova, 585–594. | 1 | Applied and Interdisciplinary Chemistry |
Self-contained units, typically square in shape, that require only the soil medium and vegetative layer for a functioning green roof. These systems are easy to install and remove. Some modular systems are pre-grown at nurseries to client specifications, forming an instant vegetative layer. | 1 | Applied and Interdisciplinary Chemistry |
A biographical film of Ehrlich Dr. Ehrlichs Magic Bullet was made in 1940 by Warner Bros. It was directed by William Dieterle and starring Edward G. Robinson. The US Public Health Service adopted the abridged film as Magic Bullets' for educational campaigns.
Dr. Lowell Wood famously bought an IBM Stretch computer from Lawrence Livermore Laboratories, with the hope that it would enable him to "design starships and find a magic bullet for cancer".
Critics of the Warren Commission's investigation of the John F. Kennedy assassination refer to the single-bullet theory as the "Magic Bullet Theory" for the counterintuitively complex and precise way a single bullet is proposed to have caused multiple injuries in Kennedy and Texas Governor John Connally. | 1 | Applied and Interdisciplinary Chemistry |
The Arrhenius equation gives the quantitative basis of the relationship between the activation energy and the rate at which a reaction proceeds. From the equation, the activation energy can be found through the relation
where A is the pre-exponential factor for the reaction, R is the universal gas constant, T is the absolute temperature (usually in kelvins), and k is the reaction rate coefficient. Even without knowing A, E can be evaluated from the variation in reaction rate coefficients as a function of temperature (within the validity of the Arrhenius equation).
At a more advanced level, the net Arrhenius activation energy term from the Arrhenius equation is best regarded as an experimentally determined parameter that indicates the sensitivity of the reaction rate to temperature. There are two objections to associating this activation energy with the threshold barrier for an elementary reaction. First, it is often unclear as to whether or not reaction does proceed in one step; threshold barriers that are averaged out over all elementary steps have little theoretical value. Second, even if the reaction being studied is elementary, a spectrum of individual collisions contributes to rate constants obtained from bulk (bulb) experiments involving billions of molecules, with many different reactant collision geometries and angles, different translational and (possibly) vibrational energies—all of which may lead to different microscopic reaction rates. | 0 | Theoretical and Fundamental Chemistry |
* Journal of Sound and Vibration.
* Journal of Ship Research.
* Applied Ocean research.
* Journal of Engineering Mechanics.
* IEEE Journal of Oceanic Engineering.
* Journal of Fluids and Structures | 1 | Applied and Interdisciplinary Chemistry |
It typically has a strong maximum at the minimal number of photons to ionize the system, with successive peaks (known as ATI peaks) separated by the photon energy and thus corresponding to higher numbers of photons being absorbed.
In the non-perturbative regime the bound states are dressed with the electric field, shifting the ionization energy. If the ponderomotive energy of the field is greater than the photon energy , then the first peak disappears. | 0 | Theoretical and Fundamental Chemistry |
Some assumptions of the fluid dynamics involved in the process must be made in order to simplify the process to a point where it is solvable. The assumptions made by Ekman were:
* no boundaries;
* infinitely deep water;
* eddy viscosity, , is constant (this is only true for laminar flow. In the turbulent atmospheric and oceanic boundary layer it is a strong function of depth);
* the wind forcing is steady and has been blowing for a long time;
* barotropic conditions with no geostrophic flow;
* the Coriolis parameter, is kept constant.
The simplified equations for the Coriolis force in the x and y directions follow from these assumptions:
where is the wind stress, is the density, is the east–west velocity, and is the north–south velocity.
Integrating each equation over the entire Ekman layer:
where
Here and represent the zonal and meridional mass transport terms with units of mass per unit time per unit length. Contrarily to common logic, north–south winds cause mass transport in the east–west direction.
In order to understand the vertical velocity structure of the water column, equations and can be rewritten in terms of the vertical eddy viscosity term.
where is the vertical eddy viscosity coefficient.
This gives a set of differential equations of the form
In order to solve this system of two differential equations, two boundary conditions can be applied:
* as
* friction is equal to wind stress at the free surface ().
Things can be further simplified by considering wind blowing in the y-direction only. This means is the results will be relative to a north–south wind (although these solutions could be produced relative to wind in any other direction):
where
* and represent Ekman transport in the u and v direction;
* in equation the plus sign applies to the northern hemisphere and the minus sign to the southern hemisphere;
* is the wind stress on the sea surface;
* is the Ekman depth (depth of Ekman layer).
By solving this at z=0, the surface current is found to be (as expected) 45 degrees to the right (left) of the wind in the Northern (Southern) Hemisphere. This also gives the expected shape of the Ekman spiral, both in magnitude and direction. Integrating these equations over the Ekman layer shows that the net Ekman transport term is 90 degrees to the right (left) of the wind in the Northern (Southern) Hemisphere. | 1 | Applied and Interdisciplinary Chemistry |
In 1810, French physicist André-Marie Ampère suggested that hydrofluoric acid was a compound of hydrogen with an unknown element, analogous to chlorine. Fluorite was then shown to be mostly composed of calcium fluoride.
Sir Humphry Davy originally suggested the name fluorine, taking the root from the name of "fluoric acid" and the -ine suffix, similarly to other halogens. This name, with modifications, came to most European languages. (Greek, Russian, and several other languages use the name ftor or derivatives, which was suggested by Ampère and comes from the Greek φθόριος (phthorios), meaning "destructive".) The New Latin name (fluorum) gave the element its current symbol, F, although the symbol Fl has been used in early papers. The symbol Fl is now used for the super-heavy element flerovium. | 1 | Applied and Interdisciplinary Chemistry |
Through a set of small scale experiments at varying pressures, Birch et al. formulated an equation that allowed the estimation of a virtual surface source, considering the conservation of mass between the exit plane of the orifice and the virtual surface. This approach allows to simulate a compressible, under-expanded jet as an incompressible, fully-expanded jet. As a consequence, a simpler CFD model can be simulated by using the following diameter (named pseudo-diameter) as the new exit plane: | 1 | Applied and Interdisciplinary Chemistry |
The 2001 Heart Outcomes and Prevention Evaluation trial seemed to show ramipril possessed cardioprotective qualities which extended beyond its qualities as an antihypertensive. However, the trial and the interpretation of its results have been criticised.
The Acute Infarction Ramipril Efficacy (AIRE) trial showed a 27% reduction in mortality for patients receiving ramipril for chronic heart failure following a myocardial infarction.
Ramipril was found to have similar results as telmisartan, an angiotensin II receptor blocker. | 0 | Theoretical and Fundamental Chemistry |
In physics, the expression noble metal is sometimes confined to copper, silver, and gold, since their full d-subshells contribute to what noble character they have. In contrast, the other noble metals, especially the platinum group metals, have notable catalytic applications, arising from their partially filled d-subshells. This is the case with palladium which has a full d-subshell in the atomic state but in condensed form has a partially filled sp band at the expense of d-band occupancy.
The difference in reactivity can be seen during the preparation of clean metal surfaces in an ultra-high vacuum: surfaces of "physically defined" noble metals (e.g., gold) are easy to clean and keep clean for a long time, while those of platinum or palladium, for example, are covered by carbon monoxide very quickly. | 1 | Applied and Interdisciplinary Chemistry |
In 1756 Thomas Melvill observed the emission of distinct patterns of colour when salts were added to alcohol flames. By 1785 James Gregory discovered the principles of diffraction grating and American astronomer David Rittenhouse made the first engineered diffraction grating. In 1821 Joseph von Fraunhofer solidified this significant experimental leap of replacing a prism as the source of wavelength dispersion improving the spectral resolution and allowing for the dispersed wavelengths to be quantified.
In 1835, Charles Wheatstone reported that different metals could be distinguished by bright lines in the emission spectra of their sparks, thereby introducing an alternative to flame spectroscopy.
In 1849, J. B. L. Foucault experimentally demonstrated that absorption and emission lines at the same wavelength are both due to the same material, with the difference between the two originating from the temperature of the light source.
In 1853, the Swedish physicist Anders Jonas Ångström presented observations and theories about gas spectra. Ångström postulated that an incandescent gas emits luminous rays of the same wavelength as those it can absorb. At the same time George Stokes and William Thomson (Kelvin) were discussing similar postulates. Ångström also measured the emission spectrum from hydrogen later labeled the Balmer lines.
In 1854 and 1855, David Alter published observations on the spectra of metals and gases, including an independent observation of the Balmer lines of hydrogen.
By 1859, Gustav Kirchhoff and Robert Bunsen noticed that several Fraunhofer lines (lines in the solar spectrum) coincide with characteristic emission lines identified in the spectra of heated elements. It was correctly deduced that dark lines in the solar spectrum are caused by absorption by chemical elements in the solar atmosphere. | 0 | Theoretical and Fundamental Chemistry |
The École Nationale Supérieure de Chimie de Montpellier, or ENSCM, is one of the French Grandes Ecoles, situated in Montpellier. Although it may share academic staff and research activities with the University as well as research bodies such as CNRS, the ENSCM has a particular status as an independent body with its own research laboratories.
Teaching chemistry in Montpellier started in 1676 with the creation of the first chair of chemistry at the University of Medicine. Later on, in 1803 the School of Pharmacy was established with a chair of Chemistry and then the Faculty of Science in 1809. The original Institute of Chemistry was founded in 1889 in order to gather the professors who were teaching the same subjects in different Faculties. In 1934, it left the old historic centre to settle in larger and more functional new buildings.
It also acquired new facilities on a second site, 3 kilometers away from the main one, called "La Galéra", which is equipped with a kilo-lab and on a third site, close to Montpellier 2 University : the "Institut Européen des Membranes".
Since 2017, the ENSCM has moved into its new premises within the Pole Balard Formation located on Avenue du Professeur Emile Jeanbrau, just beside the "Institut Européen des Membranes".
The ENSCM provides high level training for engineers and researchers in Chemistry and is renowned for its research activities in the following fields:
* Macromolecular Chemistry (particularly Heterochemistry)
* Soft Chemistry
* Design and development of solids (macromolecules, hybrid materials, catalytic materials and membranes), study of the properties and uses of these materials.
Research is carried out in “Unités Mixtes de Recherche”
* UMR 5076 : Molecular and Macromolecular Heterochemistry
* UMR 5618 : Catalytic Materials and Catalysis in Organic Chemistry
* UMR 5635 : Institut Européen des Membranes.
Some ENSCM Professors and researchers are members of a team carrying out research in the field of Biology and Health : Health Pharmacology and Biotechnologies Centre, CNRS, Montpellier 2 University, University of Montpellier.
The ENSCM is also a member of the “Fédération Gay Lussac” – network of “Grandes Ecoles” gathering 17 Schools of Chemistry and Chemical Engineering. Within this network, the ENSCM ranks very high both by the level of the student it recruits and the importance of the research activities carried out in its internationally renowned laboratories. | 1 | Applied and Interdisciplinary Chemistry |
Organic Preparations and Procedures International is a bimonthly scientific journal focusing on organic chemists engaged in synthesis. Topics include original preparative chemistry in association with the synthesis of organic and organometallic compounds. | 0 | Theoretical and Fundamental Chemistry |
The McCumber relation (or McCumber theory) is a relationship between the effective cross-sections of absorption and emission of light in the physics of solid-state lasers. It is named after Dean McCumber, who proposed the relationship in 1964. | 0 | Theoretical and Fundamental Chemistry |
As of December 20, 2006, ORegAnno contained 4220 regulatory sequences (excluding deprecated records) for 2190 transcription factor binding sites, 1853 regulatory regions (enhancers, promoters, etc.), 170 regulatory polymorphisms, and 7 regulatory haplotypes for 17 different organisms (predominantly Drosophila melanogaster, Homo sapiens, Mus musculus, Caenorhabditis elegans, and Rattus norvegicus in that order). These records were obtained by manual curation of 828 publications by 45 ORegAnno users from the gene regulation community. The ORegAnno publication queue contained 4215 publications of which 858 were closed, 34 were in progress (open status), and 3321 were awaiting annotation (pending status). ORegAnno is continually updated and therefore current database contents should be obtained from [http://www.oreganno.org www.oreganno.org]. | 1 | Applied and Interdisciplinary Chemistry |
Inclusion compounds are often molecules, whereas . Intercalation compounds are not 3-dimensional, unlike clathrate compounds. Photolytically-sensitive caged compounds have been examined as containers for releasing a drug or reagent.
Zeolites are another type of crystalline structures that form a framework with cavities in which guest species can reside. Unlike clathrates, zeolites are defined by the tetrahedra linking of four oxygen atoms surrounding a cation. The guests are also not required to fill the open cavities. Zeolite structures are defined by the diverse building units of the framework, as opposed to cavity structures in clathrates. Similar applications have been explored.
Silica clathrasil are compounds structurally similar to clathrate hydrates with a SiO framework and can be found in a range of marine sediment. | 0 | Theoretical and Fundamental Chemistry |
The minor spliceosome is a ribonucleoprotein complex that catalyses the removal (splicing) of an atypical class of spliceosomal introns (U12-type) from messenger RNAs in some clades of eukaryotes. This process is called noncanonical splicing, as opposed to U2-dependent canonical splicing. U12-type introns represent less than 1% of all introns in human cells. However they are found in genes performing essential cellular functions. | 1 | Applied and Interdisciplinary Chemistry |
However, if the detector is shot noise dominated (which is typically the case for a photomultiplier tube), noise will be proportional to the square root of the power, so that for a broad flat spectrum the noise will be proportional to the square root of m, where m is the number of sample points comprising the spectrum, thus this disadvantage precisely offsets the Fellgett advantage. Shot noise is the main reason Fourier transform spectroscopy has never been popular for UV and visible light spectrometry. | 0 | Theoretical and Fundamental Chemistry |
Its production was first described by Basil Valentine in Currus Triumphalis Antimonii. In 1659, Johann Rudolf Glauber gave a relatively exact chemical interpretation of the reaction.
Vittorio Algarotti introduced the substance into medicine, and derivatives of his name (algarot, algoroth) were associated with this compound for many years.
The exact composition was unknown for a very long time. The suggestion of SbOCl being a mixture of antimony trichloride and antimony oxide or pure SbOCl were raised. Today the hydrolysis of antimony trichloride is understood; first the SbOCl oxychloride is formed which later forms SbOCl. | 1 | Applied and Interdisciplinary Chemistry |
Many pesticides achieve their intended use of killing pests by disrupting the nervous system. Due to similarities in brain biochemistry among many different organisms, there is much speculation that these chemicals can have a negative impact on humans as well. Children are especially vulnerable to exposure to pesticides, especially at critical windows of development. Infants and children consume higher amounts of food relative to their body-weight, and have a more permeable blood–brain barrier, all of which can contribute to increased risks from exposure to pesticide residues. However in 2008 the OECD report that the existing guideline represents the best available science for assessing the potential for developmental neurotoxicity in human health risk assessment. | 1 | Applied and Interdisciplinary Chemistry |
DNA methylation, referring to the reversible methylation of the 5 position of cytosine by methyltransferases, is a major epigenetic modification in multicellular organisms. In mammals, this modification primarily occurs at CpG sites, which in turn tend to cluster in regions called CpG islands. There is a small fraction of CpG islands that can overlap or be in close proximity to promoter regions of transcription start sites. The modification may also occur at other sites, but methylation at either of these sites can repress gene expression by either interfering with the binding of transcription factors or modifying chromatin structure to a repressive state.
Disease condition studies have largely fueled the effort in understanding the role of DNA methylation. Currently, the major research interest lies in investigating disease conditions such as cancer to identify regions of the DNA that has undergone extensive methylation changes. The genes contained in these regions are of functional interest as they may offer a mechanistic explanation to the underlying genetic causes of a disease. For instance, the abnormal methylation pattern of cancer cells was initially shown to be a mechanism through which tumor suppressor-like genes are silenced, although it was later observed that a much broader range of gene types are affected. | 1 | Applied and Interdisciplinary Chemistry |
Carbonate is a pseudohalide ligand. With a saturated pi-system, it has no pi-acceptor properties. With multiple electronegative elements, it is not strongly basic. The latter is consistent with the pK’s of carbonic acid: pK = 6.77 and pK = 9.93.
To a single metal ion, carbonate is observed to bind in both unidentate (κ-) and bidentate (κ-) fashions. In the covalent bond classification method, κ-carbonate is anX ligand and κ-carbonate is an X ligand. With two metals, the number of bonding modes increases because carbonate often serves as a bridging ligand. It can span metal-metal bonds as in [Ru(CO)Cl], where again it functions as an (X) ligand. More commonly all three oxygen centers bind, as illustrated by . In such cases, carbonate is an LX ligand, providing 3e to each metal. More complicated motifs have been characterized by X-ray crystallography including {(VO)(μ-OH)(CO)}. | 0 | Theoretical and Fundamental Chemistry |
Considering a two dimensional flow in the plane, the flow velocity at a point at a time can be expressed as – | 1 | Applied and Interdisciplinary Chemistry |
RNA silencing or RNA interference refers to a family of gene silencing effects by which gene expression is negatively regulated by non-coding RNAs such as microRNAs. RNA silencing may also be defined as sequence-specific regulation of gene expression triggered by double-stranded RNA (dsRNA). RNA silencing mechanisms are conserved among most eukaryotes. The most common and well-studied example is RNA interference (RNAi), in which endogenously expressed microRNA (miRNA) or exogenously derived small interfering RNA (siRNA) induces the degradation of complementary messenger RNA. Other classes of small RNA have been identified, including piwi-interacting RNA (piRNA) and its subspecies repeat associated small interfering RNA (rasiRNA). | 1 | Applied and Interdisciplinary Chemistry |
The three-dimensional isotropic and non-relativistic uniform Fermi gas case is known as the Fermi sphere.
A three-dimensional infinite square well, (i.e. a cubical box that has a side length L) has the potential energy
The states are now labelled by three quantum numbers n, n, and n. The single particle energies are
where n, n, n are positive integers. In this case, multiple states have the same energy (known as degenerate energy levels), for example . | 0 | Theoretical and Fundamental Chemistry |
Metal-organic frameworks are crystalline porous polymers assembled from organic monomers connected by coordination to metal atom centers. | 0 | Theoretical and Fundamental Chemistry |
Due to the growing need to find a more efficient and environmentally friendly alternative to conventional waste removal methods, industries are paying more attention to the function of bacteria and their EPS sugars in bioremediation.
Researchers found that adding EPS sugars from cyanobacteria to wastewaters removes heavy metals such as copper, cadmium and lead. EPS sugars alone can physically interact with these heavy metals and take them in through biosorption. The efficiency of removal can be optimized by treating the EPS sugars with different acids or bases before adding them to wastewater. Some contaminated soils contain high levels of polycyclic aromatic hydrocarbons (PAHs); EPSs from the bacterium Zoogloea sp. and the fungus Aspergillus niger, are efficient at removing these toxic compounds. EPSs contain enzymes such as oxidoreductase and hydrolase, which are capable of degrading PAHs. The amount of PAH degradation depends on the concentration of EPSs added to the soil. This method proves to be low cost and highly efficient.
In recent years, EPS sugars from marine bacteria have been found to speed up the cleanup of oil spills. During the Deepwater Horizon oil spill in 2010, these EPS-producing bacteria were able to grow and multiply rapidly. It was later found that their EPS sugars dissolved the oil and formed oil aggregates on the ocean surface, which sped up the cleaning process. These oil aggregates also provided a valuable source of nutrients for other marine microbial communities. This let scientists modify and optimize the use of EPS sugars to clean up oil spills. | 1 | Applied and Interdisciplinary Chemistry |
Globally, mangroves stored 4.19 ± 0.62 Pg (CI 95%) of carbon in 2012, with Indonesia, Brazil, Malaysia and Papua New Guinea accounting for more than 50% of the global stock. 2.96 ± 0.53 Pg of the global carbon stock is contained within the soil and 1.23 ± 0.06 Pg in the living biomass. Of this 1.23 Pg, approximately 0.41 ± 0.02 Pg is in the belowground biomass in the root system and approximately 0.82 ± 0.04 Pg is in the aboveground living biomass.
Global mangrove canopy cover is estimated as between 83,495 km and 167,387 km in 2012 with Indonesia containing approximately 30% of the entire global mangrove forest area. Mangrove forests are responsible for approximately 10% of global carbon burial, with an estimated carbon burial rate of 174 g C m yr.
Mangroves, like seagrasses, have potential for high levels of carbon sequestration. They account for 3% of the global carbon sequestration by tropical forests and 14% of the global coastal ocean's carbon burial.
Mangroves are naturally disturbed by floods, tsunamis, coastal storms like cyclones and hurricanes, lightning, disease and pests, and changes in water quality or temperature. Although they are resilient to many of these natural disturbances, they are highly susceptible to human impacts including urban development, aquaculture, mining, and overexploitation of shellfish, crustaceans, fish and timber. Mangroves provide globally important ecosystem services and carbon sequestration and are thus an important habitat to conserve and repair when possible.
Dams threaten habitats by slowing the amount of freshwater reaching mangroves. Coral reef destruction also plays a role in mangrove habitat health as reefs slow wave energy to a level that mangroves are more tolerant of. | 0 | Theoretical and Fundamental Chemistry |
The glycosylation of proteins has an array of different applications from influencing cell to cell communication to changing the thermal stability and the folding of proteins. Due to the unique abilities of glycoproteins, they can be used in many therapies. By understanding glycoproteins and their synthesis, they can be made to treat cancer, Crohn's Disease, high cholesterol, and more.
The process of glycosylation (binding a carbohydrate to a protein) is a post-translational modification, meaning it happens after the production of the protein. Glycosylation is a process that roughly half of all human proteins undergo and heavily influences the properties and functions of the protein. Within the cell, glycosylation occurs in the endoplasmic reticulum. | 0 | Theoretical and Fundamental Chemistry |
Methods for the stereoselective synthesis of cyclopropanes from diazocarbonyl compounds and olefins have relied on either the use of pre-formed chiral rhodium catalysts or chiral auxiliaries on the diazocarbonyl compound. For example, Rh[S-DOSP] is a highly effective catalyst for the enantioselective cyclopropanation of alkenes.
Chiral auxiliaries derived from readily available chiral alcohols (such as pantolactone) may be used for diastereoselective cyclopropanations with diazo esters. | 0 | Theoretical and Fundamental Chemistry |
According to empirical calibrations, the difference in δSi (denoted as ΔSi) between sponges and their hosting water is correlated with the Si concentration of the hosting solution. Therefore, it has been suggested that the Si concentrations in bottom waters of ancient oceans can be interpreted from the δSi of coexisting sponge spicules, which are preserved in the rock record. It has been proposed that this relation is determined by the growth rate and the Si uptake kinetics of sponges, but the current understanding of sponge biomineralization pathways is limited. Although the mechanism behind this relation is yet to be clear, it appears consistent among various laboratory experiments, modern environments, and core top sediments. However, there is also evidence that the δSi of carnivorous sponges may differ significantly from the expected correlation. | 0 | Theoretical and Fundamental Chemistry |
Class I TEs are copied in two stages: first, they are transcribed from DNA to RNA, and the RNA produced is then reverse transcribed to DNA. This copied DNA is then inserted back into the genome at a new position. The reverse transcription step is catalyzed by a reverse transcriptase, which is often encoded by the TE itself. The characteristics of retrotransposons are similar to retroviruses, such as HIV.
Retrotransposons are commonly grouped into three main orders:
* Retrotransposons, with long terminal repeats (LTRs), which encode reverse transcriptase, similar to retroviruses
* Retroposons, long interspersed nuclear elements (LINEs, LINE-1s, or L1s), which encode reverse transcriptase but lack LTRs, and are transcribed by RNA polymerase II
* Short interspersed nuclear elements (SINEs) do not encode reverse transcriptase and are transcribed by RNA polymerase III
Retroviruses can also be considered TEs. For example, after the conversion of retroviral RNA into DNA inside a host cell, the newly produced retroviral DNA is integrated into the genome of the host cell. These integrated DNAs are termed proviruses. The provirus is a specialized form of eukaryotic retrotransposon, which can produce RNA intermediates that may leave the host cell and infect other cells. The transposition cycle of retroviruses has similarities to that of prokaryotic TEs, suggesting a distant relationship between the two. | 1 | Applied and Interdisciplinary Chemistry |
Siderophores become important in the ecological niche defined by low iron availability, iron being one of the critical growth limiting factors for virtually all aerobic microorganisms. There are four major ecological habitats: soil and surface water, marine water, plant tissue (pathogens) and animal tissue (pathogens). | 1 | Applied and Interdisciplinary Chemistry |
Neuromelanin gives specific brain sections, such as the substantia nigra or the locus coeruleus, distinct color. It is a type of melanin and similar to other forms of peripheral melanin. It is insoluble in organic compounds, and can be labeled by silver staining. It is called neuromelanin because of its function and the color change that appears in tissues containing it. It contains black/brown pigmented granules. Neuromelanin is found to accumulate during aging, noticeably after the first 2–3 years of life. It is believed to protect neurons in the substantia nigra from iron-induced oxidative stress. It is considered a true melanin due to its stable free radical structure and it avidly chelates metals. | 1 | Applied and Interdisciplinary Chemistry |
Any periodic tiling can be seen as a wallpaper. More particularly, we can consider as a wallpaper a tiling by identical tiles edge‑to‑edge, necessarily periodic, and conceive from it a wallpaper by decorating in the same manner every tiling element, and eventually erase partly or entirely the boundaries between these tiles. Conversely, from every wallpaper we can construct such a tiling by identical tiles edge‑to‑edge, which bear each identical ornaments, the identical outlines of these tiles being not necessarily visible on the original wallpaper. Such repeated boundaries delineate a repetitive surface added here in dashed lines.
Such pseudo‑tilings connected to a given wallpaper are in infinite number. For example image 1 shows two models of repetitive squares in two different positions, which have Another repetitive square has an We could indefinitely conceive such repetitive squares larger and larger. An infinity of shapes of repetitive zones are possible for this Pythagorean tiling, in an infinity of positions on this wallpaper. For example in red on the bottom right‑hand corner of image 1, we could glide its repetitive parallelogram in one or another position. In common on the first two images: a repetitive square concentric with each small square tile, their common center being a point symmetry of the wallpaper.
Between identical tiles edge‑to‑edge, an edge is not necessarily a segment of a straight line. On the top left‑hand corner of image 3, point C is a vertex of a repetitive pseudo‑rhombus with thick stripes on its whole surface, called pseudo‑rhombus because of a concentric repetitive rhombus constructed from it by taking out a bit of surface somewhere to append it elsewhere, and keep the area unchanged. By the same process on image 4, a repetitive regular hexagon filled with vertical stripes is constructed from a rhombic repetitive zone Conversely, from elementary geometric tiles edge‑to‑edge, an artist like M. C. Escher created attractive surfaces many times repeated. On image 2, the minimum area of a repetitive surface by disregarding colors, each repetitive zone in dashed lines consisting of five pieces in a certain arrangement, to be either a square or a hexagon, like in a proof of the Pythagorean theorem.
In the present article, a pattern is a repetitive parallelogram of minimal area in a determined position on the wallpaper. Image 1 shows two parallelogram‑shaped patterns — a square is a particular parallelogram —. Image 3 shows rhombic patterns — a rhombus is a particular parallelogram —.
On this page, all repetitive patterns (of minimal area) are constructed from two translations that generate the group of all translations under which the wallpaper is invariant. With the circle shaped symbol ⵔ of function composition, a pair like or generates the group of all translations that transform the Pythagorean tiling into itself. | 0 | Theoretical and Fundamental Chemistry |
This technology allows a (very) large number of experiments to be performed, allowing explorative screening. Cell-based systems are mainly used in chemical genetics where large, diverse small molecule collections are systematically tested for their effect on cellular model systems. Novel drugs can be found using screens of tens of thousands of molecules, and these have promise for the future of drug development.
Beyond drug discovery, chemical genetics is aimed at functionalizing the genome by identifying small molecules that acts on most of the 21,000 gene products in a cell. High-content technology will be part of this effort which could provide useful tools for learning where and when proteins act by knocking them out chemically. This would be most useful for gene where knock out mice (missing one or several genes) can not be made because the protein is required for development, growth or otherwise lethal when it is not there. Chemical knock out could address how and where these genes work.
Further the technology is used in combination with RNAi to identify sets of genes involved in specific mechanisms, for example cell division. Here, libraries of RNAis, covering a whole set of predicted genes inside the target organism's genome can be used to identify relevant subsets, facilitating the annotation of genes for which no clear role has been established beforehand.
The large datasets produced by automated cell biology contain spatially resolved, quantitative data which can be used for building for systems level models and simulations of how cells and organisms function. Systems biology models of cell function would permit prediction of why, where and how the cell responds to external changes, growth and disease. | 1 | Applied and Interdisciplinary Chemistry |
The isoelectric point (pI, pH(I), IEP), is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. The standard nomenclature to represent the isoelectric point is pH(I). However, pI is also used. For brevity, this article uses pI. The net charge on the molecule is affected by pH of its surrounding environment and can become more positively or negatively charged due to the gain or loss, respectively, of protons (H).
Surfaces naturally charge to form a double layer. In the common case when the surface charge-determining ions are H/HO, the net surface charge is affected by the pH of the liquid in which the solid is submerged.
The pI value can affect the solubility of a molecule at a given pH. Such molecules have minimum solubility in water or salt solutions at the pH that corresponds to their pI and often precipitate out of solution. Biological amphoteric molecules such as proteins contain both acidic and basic functional groups. Amino acids that make up proteins may be positive, negative, neutral, or polar in nature, and together give a protein its overall charge. At a pH below their pI, proteins carry a net positive charge; above their pI they carry a net negative charge. Proteins can, thus, be separated by net charge in a polyacrylamide gel using either preparative native PAGE, which uses a constant pH to separate proteins, or isoelectric focusing, which uses a pH gradient to separate proteins. Isoelectric focusing is also the first step in 2-D gel polyacrylamide gel electrophoresis.
In biomolecules, proteins can be separated by ion exchange chromatography. Biological proteins are made up of zwitterionic amino acid compounds; the net charge of these proteins can be positive or negative depending on the pH of the environment. The specific pI of the target protein can be used to model the process around and the compound can then be purified from the rest of the mixture. Buffers of various pH can be used for this purification process to change the pH of the environment. When a mixture containing a target protein is loaded into an ion exchanger, the stationary matrix can be either positively-charged (for mobile anions) or negatively-charged (for mobile cations). At low pH values, the net charge of most proteins in the mixture is positive – in cation exchangers, these positively-charged proteins bind to the negatively-charged matrix. At high pH values, the net charge of most proteins is negative, where they bind to the positively-charged matrix in anion exchangers. When the environment is at a pH value equal to the protein's pI, the net charge is zero, and the protein is not bound to any exchanger, and therefore, can be eluted out. | 0 | Theoretical and Fundamental Chemistry |
Certain diagnostic tests are available for the quantification of the end-products of lipid peroxidation, to be specific, malondialdehyde (MDA). The most commonly used test is called a TBARS Assay (thiobarbituric acid reactive substances assay). Thiobarbituric acid reacts with malondialdehyde to yield a fluorescent product. However, there are other sources of malondialdehyde, so this test is not completely specific for lipid peroxidation. | 1 | Applied and Interdisciplinary Chemistry |
* As a mordant when performing a Gram stain. It is applied for 1 minute after staining with crystal violet, but before ethanol to ensure that gram positive organisms' peptidoglycan remains stained, easily identifying it as a gram positive in microscopy.
* This solution is used as an indicator test for the presence of starches in organic compounds, with which it reacts by turning a dark-blue/black. Elemental iodine solutions like Lugols will stain starches due to iodines interaction with the coil structure of the polysaccharide. Starches include the plant starches amylose and amylopectin and glycogen in animal cells. Lugol's solution will not detect simple sugars such as glucose or fructose. In the pathologic condition amyloidosis, amyloid deposits (i.e., deposits that stain like starch, but are not) can be so abundant that affected organs will also stain grossly positive for the Lugol reaction for starch.
* It can be used as a cell stain, making the cell nuclei more visible and for preserving phytoplankton samples.
* Lugol's solution can also be used in various experiments to observe how a cell membrane uses osmosis and diffusion.
* Lugols solution is also used in the marine aquarium industry. Lugols solution provides a strong source of free iodine and iodide to reef inhabitants and macroalgae. Although the solution is thought to be effective when used with stony corals, systems containing xenia and soft corals are assumed to be particularly benefited by the use of Lugols solution. Used as a dip for stony and soft or leather corals, Lugols may help rid the animals of unwanted parasites and harmful bacteria. The solution is thought to foster improved coloration and possibly prevent bleaching of corals due to changes in light intensity, and to enhance coral polyp expansion. The blue colors of Acropora spp. are thought to be intensified by the use of potassium iodide. Specially packaged supplements of the product intended for aquarium use can be purchased at specialty stores and online. | 0 | Theoretical and Fundamental Chemistry |
By modern definition, dynamic combinatorial chemistry is generally considered to be a method of facilitating the generation of new chemical species by the reversible linkage of simple building blocks, under thermodynamic control. This principle is known to select the most thermodynamically stable product from an equilibrating mixture of a number of components, a concept commonly utilised in synthetic chemistry to direct the control of reaction selectivity. Although this approach was arguably utilised in the work of Fischer and Werner as early as the 19th century, their respective studies of carbohydrate and coordination chemistry were restricted to rudimentary speculation, requiring the rationale of modern thermodynamics. It was not until supramolecular chemistry revealed early concepts of molecular recognition, complementarity and self-organisation that chemists could begin to employ strategies for the rational design and synthesis of macromolecular targets. The concept of template synthesis was further developed and rationalised through the pioneering work of Busch in the 1960s, which clearly defined the role of a metal ion template in stabilising the desired ‘thermodynamic’ product, allowing for its isolation from the complex equilibrating mixture. Although the work of Busch helped to establish the template method as a powerful synthetic route to stable macrocyclic structures, this approach remained exclusively within the domain of inorganic chemistry until the early 1990s, when Sanders et al. first proposed the concept of dynamic combinatorial chemistry. Their work combined thermodynamic templation in tandem with combinatorial chemistry, to generate an ensemble complex porphyrin and imine macrocycles using a modest selection of simple building blocks.
Sanders then developed this early manifestation of dynamic combinatorial chemistry as a strategy for organic synthesis; the first example being the thermodynamically-controlled macrolactonisation of oligocholates to assemble cyclic steroid-derived macrocycles capable of interconversion via component exchange. Early work by Sanders et al. employed transesterification to generate dynamic combinatorial libraries. In retrospect, it was unfortunate that esters were selected for mediating component exchange, as transesterification processes are inherently slow and require vigorous anhydrous conditions. However, their subsequent investigations identified that both the disulfide and hydrazone covalent bonds exhibit effective component exchange processes and so present a reliable means of generating dynamic combinatorial libraries capable of thermodynamic templation. This chemistry now forms the basis of much research in the developing field of dynamic covalent chemistry, and has in recent years emerged as a powerful tool for the discovery of molecular receptors. | 1 | Applied and Interdisciplinary Chemistry |
A somewhat similar concept is that of a clonal colony (also called a genet), wherein the cells (usually unicellular) also share a common ancestry, but which also requires the products of clonal expansion to reside at "one place", or in close proximity. A clonal colony would be well exemplified by a bacterial culture colony, or the bacterial films that are more likely to be found in vivo (e.g., in infected multicellular hosts). Whereas, the cells of clones dealt with here are specialized cells of a multicellular organism (usually vertebrates), and reside at quite distant places. For instance, two plasma cells belonging to the same clone could be derived from different memory cells (in turn with shared clonality) and could be residing in quite distant locations, such as the cervical (in the neck) and inguinal (in the groin) lymph nodes. | 1 | Applied and Interdisciplinary Chemistry |
The Choi research group studies electrodes and catalysts for use in photoelectrochemical and electrochemical applications. Earlier work in the group has included the crystallization of cuprous oxide in various morphologies, in which the authors utilized electrochemistry to control the crystallization process and resultant crystal morphologies.
The Choi group has extensively studied bismuth vanadate, a photoanode for light-driven water splitting. This material suffers from facile bulk electron-hole recombination, but by combining the bismuth vanadate catalyst with oxygen-evolution catalysts such as FeOOH and NiOOH, Choi and coworkers were able to minimize this deleterious process and achieve higher catalytic efficiencies. The Choi group has also studied the stability of the bismuth vanadate catalyst, as well as the effects of surface composition on the interfacial energetics of photoelectrochemical catalysis.
In one report, Choi and coworkers developed a photoelectrochemical cell (PEC), a device that can split water into hydrogen and oxygen given inputs of light and electricity. PECs are promising devices for hydrogen production, for use in a hydrogen economy. However, the anodic reaction, the oxygen evolution reaction (OER), is slow and limits the overall process. To sidestep this problem, Choi and coworkers paired the hydrogen evolution reaction (HER) with oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). This allows them to generate FDCA, a valuable commodity chemical used in plastic production, from HMF, which can be derived from cellulose. | 0 | Theoretical and Fundamental Chemistry |
When pans are overheated beyond approximately 260°C (500°F) the PTFE coating begins to dissociate, releasing hydrofluoric acid and a variety of organofluorine compounds which can cause polymer fume fever in humans and can be lethal to birds. Concerns have been raised over the possible negative effects of using PTFE-coated cooking pans.
Processing of PTFE in the past used to include PFOA as an emulsifier; however, PFOA is a persistent organic pollutant and poses both environmental and health concerns, and is now being phased out of use in PTFE processing.
PFOA is now replaced by the GenX product manufactured by the DuPont spin-off Chemours, which seems to pose similar health issues as the now banned PFOA. | 0 | Theoretical and Fundamental Chemistry |
IgE antibodies against plant/insect CCD determinants were shown to have both strict specificity and high affinity, so in principle they might be expected to lead to clinical symptoms just as habitual for anti-peptide IgE. In vitro experiments (histamine-release tests) with polyvalent glyco-allergens corroborated this view. Provocation tests with patients as well as empirical evidence however, indicate that CCDs never cause any ponderable allergic symptoms. It is assumed that the frequent contact with CCD containing foods induces tolerance akin a specific immune therapy. | 0 | Theoretical and Fundamental Chemistry |
A 1990 Michael Winner film Bullseye!, starring Michael Caine and Roger Moore, referenced the Fleischmann and Pons experiment. The film – a comedy – concerned conmen trying to steal scientists' purported findings. However, the film had a poor reception, described as "appallingly unfunny".
In Undead Science, sociologist Bart Simon gives some examples of cold fusion in popular culture, saying that some scientists use cold fusion as a synonym for outrageous claims made with no supporting proof, and courses of ethics in science give it as an example of pathological science. It has appeared as a joke in Murphy Brown and The Simpsons. It was adopted as a software product name Adobe ColdFusion and a brand of protein bars (Cold Fusion Foods). It has also appeared in advertising as a synonym for impossible science, for example a 1995 advertisement for Pepsi Max.
The plot of The Saint, a 1997 action-adventure film, parallels the story of Fleischmann and Pons, although with a different ending. In Undead Science, Simon posits that film might have affected the public perception of cold fusion, pushing it further into the science fiction realm.
Similarly, the tenth episode of 2000 science fiction TV drama Life Force ("Paradise Island") is also based around cold fusion, specifically the efforts of eccentric scientist Hepzibah McKinley (Amanda Walker), who is convinced she has perfected it based on her father's incomplete research into the subject. The episode explores its potential benefits and viability within the ongoing post-apocalyptic global warming scenario of the series.
In the 2023 video game Atomic Heart, cold fusion is responsible for nearly all of the technological advances. | 0 | Theoretical and Fundamental Chemistry |
* ρ = sea level air density (kg/m)
* v = 44.7 (100 mph = 44.7 m/s)
* P = 0.5 × ρ × v
* P = 1224 (pressure in Pa = N/m) | 1 | Applied and Interdisciplinary Chemistry |
Wu et al. reported a C–X cross coupling using CuX (X= Br, Cl) and a silver catalyst to obtain aryl halides. | 0 | Theoretical and Fundamental Chemistry |
One ancient view of the origin of life, from Aristotle until the 19th century, is of spontaneous generation. This theory held that "lower" animals were generated by decaying organic substances, and that life arose by chance. This was questioned from the 17th century, in works like Thomas Brownes Pseudodoxia Epidemica'. In 1665, Robert Hooke published the first drawings of a microorganism. In 1676, Antonie van Leeuwenhoek drew and described microorganisms, probably protozoa and bacteria. Van Leeuwenhoek disagreed with spontaneous generation, and by the 1680s convinced himself, using experiments ranging from sealed and open meat incubation and the close study of insect reproduction, that the theory was incorrect. In 1668 Francesco Redi showed that no maggots appeared in meat when flies were prevented from laying eggs. By the middle of the 19th century, spontaneous generation was considered disproven. | 0 | Theoretical and Fundamental Chemistry |
There are also current approaches that are manufacturing scaffolds and coupling them with biological cues. Fabricated scaffolds can also be manufactured using either biological, synthetic, or a combination of both materials from scratch to mimic the native heart valve observed using imaging techniques. Since the scaffold is created from raw materials, there is much more flexibility in controlling the scaffold's properties and can be more tailored. Some types of fabricated scaffolds include solid 3-D porous scaffolds that have a large pore network that permits the flow through of cellular debris, allowing further tissue and vascular growth. 3-D porous scaffolds can be manufactured through 3-D printing or various polymers, ranging from polyglycolic acid (PGA) and polylactic acid (PLA) to more natural polymers such as collagen.
Fibrous scaffolds have the potential to closely match the structure of ECM through its use of fibers, which have a high growth factor. Techniques to produce fibrous scaffolds include electrospinning, in which a liquid solution of polymers is stretched from an applied high electric voltage to produce thin fibers. Conversely to the 3-D porous scaffolds, fibrous scaffolds have a very small pore size that prevents the pervasion of cells within the scaffold.
Hydrogel scaffolds are created by cross-linking hydrophilic polymers through various reaction such as free radical polymerization or conjugate addition reaction. Hydrogels are beneficial because they have a high water content, which allows the ease of nutrients and small materials to pass through. | 1 | Applied and Interdisciplinary Chemistry |
The protein encoded by this gene is a member of the tumor necrosis factor receptor superfamily, which also contains TNFRSF1A. This protein and TNF-receptor 1 form a heterocomplex that mediates the recruitment of two anti-apoptotic proteins, c-IAP1 and c-IAP2, which possess E3 ubiquitin ligase activity. The function of IAPs in TNF-receptor signalling is unknown, however, c-IAP1 is thought to potentiate TNF-induced apoptosis by the ubiquitination and degradation of TNF-receptor-associated factor 2 (TRAF2), which mediates anti-apoptotic signals. Knockout studies in mice also suggest a role of this protein in protecting neurons from apoptosis by stimulating antioxidative pathways. | 1 | Applied and Interdisciplinary Chemistry |
Although there are 25 known isotopes of sulfur, only four are stable and of geochemical importance. Of those four, two (S, light and S, heavy) comprise (99.22%) of sulfur on Earth. The vast majority (95.02%) of sulfur occurs as S with only 4.21% in S. The ratio of these two isotopes is fixed in the Solar System and has been since its formation. The bulk Earth sulfur isotopic ratio is thought to be the same as the ratio of 22.22 measured from the Canyon Diablo troilite (CDT), a meteorite. That ratio is accepted as the international standard and is therefore set at δ = 0.00. Deviation from 0.00 is expressed as the δS which is a ratio in per mill (‰). Positive values correlate to increased levels of S, whereas negative values correlate with greater S in a sample.
Formation of sulfur minerals through non-biogenic processes does not substantially differentiate between the light and heavy isotopes, therefore sulfur isotope ratios in gypsum or barite should be the same as the overall isotope ratio in the water column at their time of precipitation. Sulfate reduction through biologic activity strongly differentiates between the two isotopes because of the more rapid enzymic reaction with S. Average present day seawater values of δS are on the order of +21‰.
Prior to 2010s, it was thought that sulfate reduction could fractionate sulfur isotopes up to 46 permil and fractionation larger than 46 permil recorded in sediments must be due to disproportionation of sulfur intermediates in the sediment. This view has changed since the 2010s that sulfate reduction can fractionate to 66 permil. As substrates for disproportionation are limited by the product of sulfate reduction, the isotopic effect of disproportionation should be less than 16 permil in most sedimentary settings.
Throughout geologic history the sulfur cycle and the isotopic ratios have coevolved with the biosphere becoming overall more negative with the increases in biologically driven sulfate reduction, but also show substantial positive excursion. In general positive excursions in the sulfur isotopes mean that there is an excess of pyrite deposition rather than oxidation of sulfide minerals exposed on land. | 0 | Theoretical and Fundamental Chemistry |
This property is used to measure atoms and molecules in the gaseous state only, since in a solid or liquid state their energy levels would be changed by contact with other atoms or molecules.
A list of the electron affinities was used by Robert S. Mulliken to develop an electronegativity scale for atoms, equal to the average of the electrons
affinity and ionization potential. Other theoretical concepts that use electron affinity include electronic chemical potential and chemical hardness. Another example, a molecule or atom that has a more positive value of electron affinity than another is often called an electron acceptor and the less positive an electron donor. Together they may undergo charge-transfer reactions. | 0 | Theoretical and Fundamental Chemistry |
The specific conductance of a solution containing one electrolyte depends on the concentration of the electrolyte. Therefore, it is convenient to divide the specific conductance by concentration. This quotient, termed molar conductivity, is denoted by | 0 | Theoretical and Fundamental Chemistry |
Water vapor is a by-product of respiration in plants and animals. Its contribution to the pressure, increases as its concentration increases. Its partial pressure contribution to air pressure increases, lowering the partial pressure contribution of the other atmospheric gases (Dalton's Law). The total air pressure must remain constant. The presence of water vapor in the air naturally dilutes or displaces the other air components as its concentration increases.
This can have an effect on respiration. In very warm air (35 °C) the proportion of water vapor is large enough to give rise to the stuffiness that can be experienced in humid jungle conditions or in poorly ventilated buildings. | 1 | Applied and Interdisciplinary Chemistry |
The definition of a genetically modified organism (GMO) is not clear and varies widely between countries, international bodies, and other communities. At its broadest, the definition of a GMO can include anything that has had its genes altered, including by nature. Taking a less broad view, it can encompass every organism that has had its genes altered by humans, which would include all crops and livestock. In 1993, the Encyclopedia Britannica defined genetic engineering as "any of a wide range of techniques ... among them artificial insemination, in vitro fertilization (e.g., test-tube babies), sperm banks, cloning, and gene manipulation." The European Union (EU) included a similarly broad definition in early reviews, specifically mentioning GMOs being produced by "selective breeding and other means of artificial selection" These definitions were promptly adjusted with a number of exceptions added as the result of pressure from scientific and farming communities, as well as developments in science. The EU definition later excluded traditional breeding, in vitro fertilization, induction of polyploidy, mutation breeding, and cell fusion techniques that do not use recombinant nucleic acids or a genetically modified organism in the process.
Another approach was the definition provided by the Food and Agriculture Organization, the World Health Organization, and the European Commission, stating that the organisms must be altered in a way that does "not occur naturally by mating and/or natural recombination". Progress in science, such as the discovery of horizontal gene transfer being a relatively common natural phenomenon, further added to the confusion on what "occurs naturally", which led to further adjustments and exceptions. There are examples of crops that fit this definition, but are not normally considered GMOs. For example, the grain crop triticale was fully developed in a laboratory in 1930 using various techniques to alter its genome.
Genetically engineered organism (GEO) can be considered a more precise term compared to GMO when describing organisms genomes that have been directly manipulated with biotechnology. The Cartagena Protocol on Biosafety used the synonym living modified organism (LMO') in 2000 and defined it as "any living organism that possesses a novel combination of genetic material obtained through the use of modern biotechnology." Modern biotechnology is further defined as "In vitro nucleic acid techniques, including recombinant deoxyribonucleic acid (DNA) and direct injection of nucleic acid into cells or organelles, or fusion of cells beyond the taxonomic family."
Originally, the term GMO was not commonly used by scientists to describe genetically engineered organisms until after usage of GMO became common in popular media. The United States Department of Agriculture (USDA) considers GMOs to be plants or animals with heritable changes introduced by genetic engineering or traditional methods, while GEO specifically refers to organisms with genes introduced, eliminated, or rearranged using molecular biology, particularly recombinant DNA techniques, such as transgenesis.
The definitions focus on the process more than the product, which means there could be GMOS and non-GMOs with very similar genotypes and phenotypes. This has led scientists to label it as a scientifically meaningless category, saying that it is impossible to group all the different types of GMOs under one common definition. It has also caused issues for organic institutions and groups looking to ban GMOs. It also poses problems as new processes are developed. The current definitions came in before genome editing became popular and there is some confusion as to whether they are GMOs. The EU has adjudged that they are changing their GMO definition to include "organisms obtained by mutagenesis", but has excluded them from regulation based on their "long safety record" and that they have been "conventionally been used in a number of applications". In contrast the USDA has ruled that gene edited organisms are not considered GMOs.
Even greater inconsistency and confusion is associated with various "Non-GMO" or "GMO-free" labeling schemes in food marketing, where even products such as water or salt, which do not contain any organic substances and genetic material (and thus cannot be genetically modified by definition), are being labeled to create an impression of being "more healthy". | 1 | Applied and Interdisciplinary Chemistry |
In the case of ions it is common to speak about delocalized charge (charge delocalization). An example of delocalized charge in ions can be found in the carboxylate group, wherein the negative charge is centered equally on the two oxygen atoms. Charge delocalization in anions is an important factor determining their reactivity (generally: the higher the extent of delocalization the lower the reactivity) and, specifically, the acid strength of their conjugate acids. As a general rule, the better delocalized is the charge in an anion the stronger is its conjugate acid. For example, the negative charge in perchlorate anion () is evenly distributed among the symmetrically oriented oxygen atoms (and a part of it is also kept by the central chlorine atom). This excellent charge delocalization combined with the high number of oxygen atoms (four) and high electronegativity of the central chlorine atom leads to perchloric acid being one of the strongest known acids with a pK value of −10.
The extent of charge delocalization in an anion can be quantitatively expressed via the WAPS (weighted average positive sigma) parameter parameter and an analogous WANS (weighted average negative sigma) parameter is used for cations.
WAPS and WANS values are given in e/Å. Larger values indicate more localized charge in the corresponding ion. | 0 | Theoretical and Fundamental Chemistry |
In 1963, a group of researchers observed that specific radioactive amino acids were being incorporated into proteins obtained from ribosome-free cell and tissue extracts. This incorporation of amino acids into ribosome-lacking cells was first observed in prokaryotes using leucine (Leu) and phenylalanine (Phe), and was further discovered in mammalian liver extracts using arginine. The incorporation of other amino acids into ribosome-lacking cells failed to yield similar results, suggesting that the mechanism was specific to leucine and phenylalanine in bacteria and arginine in mammals. One of the most interesting aspects of arginylation is that the amino acids used for arginylation are transferred from aminoacyl tRNAs onto the target protein, without the use of any other translational components. This way of modifying proteins post-translationally does not occur in any other amino acid addition to proteins, such as in glycylation, glutamylation, and tyrosination making arginylation truly unique.
Upon discovery of this modification and its mechanism, further research was performed to identify an enzyme or enzymes which promote this modification. After identifying the enzyme responsible for this modification in both plants and guinea-pig hair follicles, it was cloned and characterized in yeast and given the name ATE1 due to its ability. Later studies have also identified various genes which code for ATE1 enzymes in multiple species, leading to the conclusion that ATE1 is present in all eukaryotes. | 1 | Applied and Interdisciplinary Chemistry |
Common water masses in the world ocean are:
* Antarctic Bottom Water (AABW): Antarctic Bottom Water is a very important water mass. Antarctic Bottom Water is the left over part when sea ice is being made. It is very cold but, not quite freezing so the water moves down and along the ocean floor.
* North Atlantic Deep Water (NADW)
* Circumpolar Deep Water (CDW)
* Antarctic Intermediate Water (AAIW)
* Subantarctic Mode Water (SAMW)
* Arctic Intermediate Water (AIW)
* North Pacific Intermediate Water (NPIW)
* The central waters of various oceanic basins
* Various ocean surface waters. | 0 | Theoretical and Fundamental Chemistry |
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