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Exometabolomics, also known as metabolic footprinting, is the study of extracellular metabolites and is a sub-field of metabolomics.
While the same analytical approaches used for profiling metabolites apply to exometabolomics, including liquid-chromatography mass spectrometry (LC-MS), nuclear magnetic resonance (NMR) and gas chromatography–mass spectrometry (GC–MS), analysis of exometabolites provides specific challenges and is most commonly focused on investigation of the transformations of exogenous metabolite pools by biological systems. Typically, these experiments are performed by comparing metabolites at two or more time points, for example, spent vs. uninoculated/control culture media; this approach can differentiate different physiological states of wild-type yeast and between yeast mutants. Since, in many cases, the exometabolite (extracellular) pool is less dynamic than endometabolite (intracellular) pools (which are often perturbed during sample processing) and chemically defined media can be used, it reduces some of the experimental challenges of metabolomics.
Exometabolomics is also used as a complementary tool with genomic, transcriptomic and proteomic data, to gain insight into the function of genes and pathways. Additionally, exometabolomics can be used to measure polar molecules being consumed or released by an organism, and to measure secondary metabolite production. | 1 | Biochemistry |
In the absence of the original amino acid (-leucine) in an environment, -photo-leucine is used just as its naturally occurring analog in the protein processing mechanisms of the cell. Therefore, it can be used as a substitute for leucine in the primary structure of the protein. This property of photo-leucine is very useful for studying protein-protein interactions (PPIs), due to the fact that the photo-leucine molecule, because of its molecular structure, participates in the covalent cross-linking of proteins in the protein-protein interaction (PPI) domains when it is activated by ultraviolet (UV) light. This fact allows to determine and describe stable and transient protein interactions within cells without using any additional chemical cross-linkers, which could damage the cell structure being studied.
The study of these protein-protein interactions is important because they are crucial in organizing cellular processes in space and time. In fact, interest in protein-protein interactions is not confined only to basic research: many of these interactions involved in viral fusion or in growth-factor signaling are promising targets for antiviral and anticancer drugs. Photo-affinity labeling is a powerful tool to identify protein targets of biologically active small molecules and to probe the structure of ligand binding sites, reason due to which photo amino acids, including photo-leucine, are so useful. | 5 | Photochemistry |
Mechanical work performed on a working fluid causes a change in the mechanical constraints of the system; in other words, for work to occur, the volume must be altered. Hence, volume is an important parameter in characterizing many thermodynamic processes where an exchange of energy in the form of work is involved.
Volume is one of a pair of conjugate variables, the other being pressure. As with all conjugate pairs, the product is a form of energy. The product is the energy lost to a system due to mechanical work. This product is one term which makes up enthalpy :
where is the internal energy of the system.
The second law of thermodynamics describes constraints on the amount of useful work which can be extracted from a thermodynamic system. In thermodynamic systems where the temperature and volume are held constant, the measure of "useful" work attainable is the Helmholtz free energy; and in systems where the volume is not held constant, the measure of useful work attainable is the Gibbs free energy.
Similarly, the appropriate value of heat capacity to use in a given process depends on whether the process produces a change in volume. The heat capacity is a function of the amount of heat added to a system. In the case of a constant-volume process, all the heat affects the internal energy of the system (i.e., there is no pV-work, and all the heat affects the temperature). However, in a process without a constant volume, the heat addition affects both the internal energy and the work (i.e., the enthalpy); thus the temperature changes by a different amount than in the constant-volume case and a different heat capacity value is required. | 7 | Physical Chemistry |
Agnes Luise Wilhelmine Pockels (14 February 1862 – 21 November 1935) was a German chemist whose research was fundamental in establishing the modern discipline known as surface science, which describes the properties of liquid and solid surfaces and interfaces.
Pockels became interested in fundamental research in surface science through observations of soaps and soapy water in her own home while washing dishes. She devised a surface film balance technique to study the behavior of molecules such as soaps and surfactants at air-liquid interfaces. From these studies, Pockels defined the "Pockels Point" which is the minimum area that a single molecule can occupy in monomolecular films.
Pockels was an autodidact. She was not a paid, professional scientist and had no institutional affiliation and so is an example of a citizen scientist.
By contrast, her brother Friedrich Carl Alwin Pockels, for whom the Pockels effect was named, was a professor of theoretical physics at the University of Heidelberg. | 7 | Physical Chemistry |
The kilogram per cubic metre (symbol: kg·m, or kg/m) is the unit of density in the International System of Units (SI). It is defined by dividing the SI unit of mass, the kilogram, by the SI unit of volume, the cubic metre. | 3 | Analytical Chemistry |
Nucleophilic alkylating agents deliver the equivalent of an alkyl anion (carbanion). The formal "alkyl anion" attacks an electrophile, forming a new covalent bond between the alkyl group and the electrophile. The counterion, which is a cation such as lithium, can be removed and washed away in the work-up. Examples include the use of organometallic compounds such as Grignard (organomagnesium), organolithium, organocopper, and organosodium reagents. These compounds typically can add to an electron-deficient carbon atom such as at a carbonyl group. Nucleophilic alkylating agents can displace halide substituents on a carbon atom through the SN2 mechanism. With a catalyst, they also alkylate alkyl and aryl halides, as exemplified by Suzuki couplings.
The SN2 mechanism is not available for aryl substituents, where the trajectory to attack the carbon atom would be inside the ring. Thus, only reactions catalyzed by organometallic catalysts are possible. | 0 | Organic Chemistry |
The reaction mechanism is not clearly understood, but the textbook mechanism revolves around a palladium cycle which is in agreement with the "classical" cross-coupling mechanism, and a copper cycle, which is less well known. | 0 | Organic Chemistry |
This is the point at which the rotating wave approximation is made. The dipole approximation has been assumed, and for this to remain valid the electric field must be near resonance with the atomic transition. This means that and the complex exponentials multiplying and can be considered to be rapidly oscillating. Hence on any appreciable time scale, the oscillations will quickly average to 0. The rotating wave approximation is thus the claim that these terms may be neglected and thus the Hamiltonian can be written in the interaction picture as
Finally, transforming back into the Schrödinger picture, the Hamiltonian is given by
Another criterion for rotating wave approximation is the weak coupling condition, that is, the Rabi frequency should be much less than the transition frequency.
At this point the rotating wave approximation is complete. A common first step beyond this is to remove the remaining time dependence in the Hamiltonian via another unitary transformation. | 7 | Physical Chemistry |
Well characterized modifications to histones include:
*Methylation
Both lysine and arginine residues are known to be methylated. Methylated lysines are the best understood marks of the histone code, as specific methylated lysine match well with gene expression states. Methylation of lysines H3K4 and H3K36 is correlated with transcriptional activation while demethylation of H3K4 is correlated with silencing of the genomic region. Methylation of lysines H3K9 and H3K27 is correlated with transcriptional repression. Particularly, H3K9me3 is highly correlated with constitutive heterochromatin.
*Acetylation - by HAT (histone acetyl transferase); deacetylation - by HDAC (histone deacetylase)
Acetylation tends to define the openness of chromatin as acetylated histones cannot pack as well together as deacetylated histones.
*Phosphorylation
*Ubiquitination
However, there are many more histone modifications, and sensitive mass spectrometry approaches have recently greatly expanded the catalog. | 1 | Biochemistry |
In corrosion, spalling occurs when a substance (metal or concrete) sheds tiny particles of corrosion products as the corrosion reaction progresses. Although they are not soluble or permeable, these corrosion products do not adhere to the parent material's surface to form a barrier to further corrosion, as happens in passivation. Spallation happens as the result of a large volume change during the reaction.
In the case of actinide metals (most notably the depleted uranium used in some types of ammunition), the material expands so strongly upon exposure to air that a fine layer of oxide is forcibly expelled from the surface. A slowly oxidised plug of metallic uranium can sometimes resemble an onion subjected to desquamation. The main hazard however arises from the pyrophoric character of actinide metals which can spontaneously ignite when their specific area is high. This property, along with the inherent toxicity and (for some to a lesser extent) radioactivity of these elements, make them dangerous to handle in metallic form under air. Therefore, they are often handled under an inert atmosphere (nitrogen or argon) inside an anaerobic glovebox. | 8 | Metallurgy |
The adsorption process can be characterized by determining what amount of the ions or molecules are adsorbed to the surface. This amount can be determined experimentally by the construction of an adsorption isotherm. An adsorption isotherm is a graph of Γ(P,T) versus partial pressure of the adsorbate(P/P) for a given constant temperature, where Γ(P,T) is the number of molecules adsorbed per surface area. As the partial pressure of the adsorbate increases, the number of molecules per area also increases. | 7 | Physical Chemistry |
* One application for such a device is measuring the water content of soil, where the volume of water in the total volume of soil most heavily influences the dielectric permittivity of the soil because the dielectric of water (80) is much greater than the other constituents of the soil (mineral soil: 4, organic matter: 4, air: 1). When the amount of water changes in the soil, a probe will measure a change in capacitance due to the change in dielectric permittivity that can be directly correlated with a change in water content. Capacitance sensors are now widely used in irrigation scheduling in agriculture around the world.
* Cure monitoring of Composite materials: Dielectric or capacitance sensors are used to measure the electrical response of thermoset resins and matrices of composite materials at specified depth over the sensor surface. The key model involved in the use of these sensors is the electric field model. The correspondence between electrical properties of the material within the field and the measurement (i.e. capacitance) is fundamental in interpreting the readings from the dielectric sensor.
* Tip clearance measurement in turbomachinery testing.
* The capacitance-sensors also can be used for the measuring of level of some solid materials in structures such as hoppers or silos. | 7 | Physical Chemistry |
Acid flux types (not used in electronics) may contain hydrochloric acid, zinc chloride or ammonium chloride, which are harmful to humans. Therefore, flux should be handled with gloves and goggles, and used with adequate ventilation.
Prolonged exposure to rosin fumes released during soldering can cause occupational asthma (formerly called colophony disease in this context) in sensitive individuals, although it is not known which component of the fumes causes the problem.
While molten solder has low tendency to adhere to organic materials, molten fluxes, especially of the resin/rosin type, adhere well to fingers. A mass of hot sticky flux can transfer more heat to skin and cause more serious burns than a comparable particle of non-adhering molten metal, which can be quickly shaken off. In this regard, molten flux is similar to molten hot glue. | 8 | Metallurgy |
In the first step the polymers are processed by means of common techniques, such as injection or extrusion, thermoforming, at a temperature (T) at which the polymer melts, obtaining a final shape which is called "permanent" shape.
The next step is called system programming and involves heating the sample to a transition temperature (T). At that temperature the polymer is deformed, reaching a shape called "temporary". Immediately afterwards the temperature of the sample is lowered.
The final step of the effect involves the recovery of the permanent shape. The sample is heated to the transition temperature (T) and within a short time the recovery of the permanent shape is observed.
This effect is not a natural property of the polymer, but results from proper programming of the system with the appropriate chemistry.
For a polymer to exhibit this effect, it must have two components at the molecular level: bonds (chemical or physical) to determine the permanent shape and "trigger" segments with a T to fix the temporary shape. | 7 | Physical Chemistry |
Insulin biosynthesis is regulated by transcriptional and translational levels. The β-cells promote their protein transcription in response to nutrients. The exposure of rat Langerhans islets to glucose for 1 hour is able to remarkably induce the intracellular proinsulin levels. It was noted that the proinsulin mRNA remained stable. This suggests that the acute response to glucose of the insulin synthesis is independent of mRNA synthesis in the first 45 minutes because the blockage of the transcription decelerated the insulin accumulation during that time.
PTBPs, also called Polypyrimidine tract binding proteins, are proteins that regulate the translation of mRNA. They increase the viability of mRNA and provoke the initiation of the translation. PTBP1 enable the insulin gene-specific activation and insulin granule protein mRNA by glucose.
Two aspects of the transduction pathway process are explained below: insulin secretion and insulin action on the cell. | 1 | Biochemistry |
In March, researchers announced the successful use of gene therapy to treat two adult patients for X-linked chronic granulomatous disease, a disease which affects myeloid cells and damages the immune system. The study is the first to show that gene therapy can treat the myeloid system.
In May, a team reported a way to prevent the immune system from rejecting a newly delivered gene. Similar to organ transplantation, gene therapy has been plagued by this problem. The immune system normally recognizes the new gene as foreign and rejects the cells carrying it. The research utilized a newly uncovered network of genes regulated by molecules known as microRNAs. This natural function selectively obscured their therapeutic gene in immune system cells and protected it from discovery. Mice infected with the gene containing an immune-cell microRNA target sequence did not reject the gene.
In August, scientists successfully treated metastatic melanoma in two patients using killer T cells genetically retargeted to attack the cancer cells.
In November, researchers reported on the use of VRX496, a gene-based immunotherapy for the treatment of HIV that uses a lentiviral vector to deliver an antisense gene against the HIV envelope. In a phase I clinical trial, five subjects with chronic HIV infection who had failed to respond to at least two antiretroviral regimens were treated. A single intravenous infusion of autologous CD4 T cells genetically modified with VRX496 was well tolerated. All patients had stable or decreased viral load; four of the five patients had stable or increased CD4 T cell counts. All five patients had stable or increased immune response to HIV antigens and other pathogens. This was the first evaluation of a lentiviral vector administered in a US human clinical trial. | 1 | Biochemistry |
Copper-clad steel wire find applications in grounding, connection of ground rods to metallic structures, ground grid meshes, substations, power installations, and lightning arresters.
This wire is also sometimes used for power transmission.
Copper coated welding wire has become common since wire welding equipment has become popular.
Copper-clad steel is occasionally used for making durable radio antennas, where its HF conductivity is nearly identical to a same-diameter solid copper conductor. It is most often used in antennas with long spans of unsupported wire, which need extra strength to withstand high tension which would cause solid copper or aluminum wire to break or stretch excessively. | 8 | Metallurgy |
Starvation response in animals (including humans) is a set of adaptive biochemical and physiological changes, triggered by lack of food or extreme weight loss, in which the body seeks to conserve energy by reducing metabolic rate and/or non-resting energy expenditure to prolong survival and preserve body fat and lean mass.
Equivalent or closely related terms include famine response, starvation mode, famine mode, starvation resistance, starvation tolerance, adapted starvation, adaptive thermogenesis, fat adaptation, and metabolic adaptation. | 1 | Biochemistry |
Assuming that and Taylor expanding the second exact perturbation theory expression to the second order, one gets the approximation
Note that the first term is the expected value of the energy difference, while the second is essentially its variance. | 7 | Physical Chemistry |
The courses of study are closely related to the research activities to provide interdisciplinary and research-oriented training.
The institute offers a broad bachelor programme with contents of marine, environmental and landscape-ecological sciences as well as four Master Programmes which are: Marine Environmental Sciences, Microbiology (held in English), Environmental Modelling and Marine Sensors. In cooperation with the ICBM, the Jade University of Applied Sciences offers a Bachelor Programme which is fundamental for marine engineering. The ICBM is ERASMUS exchange partner for students. | 9 | Geochemistry |
Meteorites and interplanetary dust shows the composition of solid material at the start of the Solar System, as they have not been modified since its formation. Carbonaceous chondrites are meteorites with around 5% carbon compounds. Their composition resembles the Sun's minus the very volatile elements like hydrogen and noble gases.
The Earth is believed to have formed by the gravitational collapse of material like meteorites.
Important effects on Earth in the first Hadian Era include strong solar winds during the T-Tauri stage of the Sun. The Moon forming impact caused major changes to the surface. Juvenile volatiles outgased from the early molten surface of the Earth. These included carbon dioxide and carbon monoxide. The emissions probably did not include methane, but the Earth was probably free of molecular oxygen. The Late Heavy Bombardment was between 4.0 and 3.8 billion years ago (Ga). To start with, the Earth did not have a crust as it does today. Plate tectonics in its present form commenced about 2.5 Ga.
Early sedimentary rocks formed under water date to 3.8 Ga. Pillow lavas dating from 3.5 Ga prove the existence of oceans. Evidence of early life is given by fossils of stromatolites, and later by chemical tracers.
Organic matter continues to be added to the Earth from space via interplanetary dust, which also includes some interstellar particles. The amounts added to the Earth were around 60,000 tonnes per year about 4 Ga. | 9 | Geochemistry |
This type of carbon-concentrating mechanism (CCM) relies on a contained compartment within the cell into which is shuttled, and where RuBisCO is highly expressed. In many species, biophysical CCMs are only induced under low carbon dioxide concentrations. Biophysical CCMs are more evolutionary ancient than biochemical CCMs. There is some debate as to when biophysical CCMs first evolved, but it is likely to have been during a period of low carbon dioxide, after the Great Oxygenation Event (2.4 billion years ago). Low periods occurred around 750, 650, and 320–270 million years ago. | 5 | Photochemistry |
In 1871, Lord Kelvin (William Thomson) obtained the following relation governing a liquid-vapor interface:
where:
: = vapor pressure at a curved interface of radius
: = vapor pressure at flat interface () =
: = surface tension
: = density of vapor
: = density of liquid
: , = radii of curvature along the principal sections of the curved interface.
In his dissertation of 1885, Robert von Helmholtz (son of the German physicist Hermann von Helmholtz) derived the Ostwald–Freundlich equation and showed that Kelvin's equation could be transformed into the Ostwald–Freundlich equation. The German physical chemist Wilhelm Ostwald derived the equation apparently independently in 1900; however, his derivation contained a minor error which the German chemist Herbert Freundlich corrected in 1909. | 7 | Physical Chemistry |
In analytical chemistry, complexometric indicators are used in complexometric titration to indicate the exact moment when all the metal ions in the solution are sequestered by a chelating agent (most usually EDTA). Such indicators are also called metallochromic indicators.
The indicator may be present in another liquid phase in equilibrium with the titrated phase, the indicator is described as extraction indicator.
Some complexometric indicators are sensitive to air and are destroyed. When such solution loses color during titration, a drop or two of fresh indicator may have to be added. | 3 | Analytical Chemistry |
Spectral signature is the variation of reflectance or emittance of a material with respect to wavelengths (i.e., reflectance/emittance as a function of wavelength). The spectral signature of stars indicates the composition of the stellar atmosphere. The spectral signature of an object is a function of the incidental EM wavelength and material interaction with that section of the electromagnetic spectrum.
The measurements can be made with various instruments, including a task specific spectrometer, although the most common method is separation of the red, green, blue and near infrared portion of the EM spectrum as acquired by digital cameras. Calibrating spectral signatures under specific illumination are collected in order to apply a correction to airborne or satellite imagery digital images.
The user of one kind of spectroscope looks through it at a tube of ionized gas. The user sees specific lines of colour falling on a graduated scale. Each substance will have its own unique pattern of spectral lines.
Most remote sensing applications process digital images to extract spectral signatures at each pixel and use them to divide the image in groups of similar pixels (segmentation) using different approaches. As a last step, they assign a class to each group (classification) by comparing with known spectral signatures. Depending on pixel resolution, a pixel can represent many spectral signature "mixed" together - that is why much remote sensing analysis is done to "unmix mixtures". Ultimately correct matching of spectral signature recorded by image pixel with spectral signature of existing elements leads to accurate classification in remote sensing. | 7 | Physical Chemistry |
CARS is used for species selective microscopy and combustion diagnostics. The first exploits the selectivity of vibrational spectroscopy. More recently, CARS microscopy has been utilized as a method for non-invasive imaging of lipids in biological samples, both in vivo and in vitro. Moreover, RP-CARS, a particular implementation of the Coherent anti-Stokes Raman spectroscopy microscopy, is used to study myelin and myelopathies. In 2020, Scully and team used femtosecond adaptive spectroscopic techniques via CARS to identify individual virus particles. | 3 | Analytical Chemistry |
A thermodynamic operation is an externally imposed manipulation that affects a thermodynamic system. The change can be either in the connection or wall between a thermodynamic system and its surroundings, or in the value of some variable in the surroundings that is in contact with a wall of the system that allows transfer of the extensive quantity belonging that variable. It is assumed in thermodynamics that the operation is conducted in ignorance of any pertinent microscopic information.
A thermodynamic operation requires a contribution from an independent external agency, that does not come from the passive properties of the systems. Perhaps the first expression of the distinction between a thermodynamic operation and a thermodynamic process is in Kelvins statement of the second law of thermodynamics: "It is impossible, by means of inanimate material agency, to derive mechanical effect from any portion of matter by cooling it below the temperature of the surrounding objects." A sequence of events that occurred other than "by means of inanimate material agency" would entail an action by an animate agency, or at least an independent external agency. Such an agency could impose some thermodynamic operations. For example, those operations might create a heat pump, which of course would comply with the second law. A Maxwells demon conducts an extremely idealized and naturally unrealizable kind of thermodynamic operation.
Another commonly used term that indicates a thermodynamic operation is change of constraint, for example referring to the removal of a wall between two otherwise isolated compartments.
An ordinary language expression for a thermodynamic operation is used by Edward A. Guggenheim: "tampering" with the bodies. | 7 | Physical Chemistry |
Explosive decomposition of organo nitro compounds are redox reactions, wherein both the oxidant (nitro group) and the fuel (hydrocarbon substituent) are bound within the same molecule. The explosion process generates heat by forming highly stable products including molecular nitrogen (N), carbon dioxide, and water. The explosive power of this redox reaction is enhanced because these stable products are gases at mild temperatures. Many contact explosives contain the nitro group. | 0 | Organic Chemistry |
Mineralogists, in particular, are interested in morphological appearances of individual crystals, as defined by the actually formed crystal faces (tracht) and their relative sizes (habit). More advanced visualization capabilities allow for displaying surface characteristics, imperfections inside the crystal, lighting (reflection, shadow, and translucency), and 3D effects (interactive rotatability, perspective, and stereo viewing).
Crystal physicists, in particular, are interested in anisotropic physical properties of crystals. The directional dependence of a crystal's physical property is described by a 3D tensor and depends on the orientation of the crystal. Tensor shapes are more palpable by adding lighting effects (reflection and shadow). 2D sections of interest are selected for display by rotating the tensor interactively around one or more axes.
Crystal morphology or physical property data can be stored in specialized databases or added to more comprehensive crystal structure databases. [https://web.archive.org/web/20091219215419/http://nanocrystallography.research.pdx.edu/search.py/search?database=cmd The Crystal Morphology Database (CMD)] is an example for a web-based crystal morphology database with integrated visualization capabilities. | 7 | Physical Chemistry |
The docking of IP to its receptor, which is called the inositol trisphosphate receptor (InsP3R), was first studied using deletion mutagenesis in the early 1990s. Studies focused on the N-terminus side of the IP receptor. In 1997 researchers localized the region of the IP receptor involved with binding of IP to between amino acid residues 226 and 578 in 1997. Considering that IP is a negatively charged molecule, positively charged amino acids such as arginine and lysine were believed to be involved. Two arginine residues at position 265 and 511 and one lysine residue at position 508 were found to be key in IP docking. Using a modified form of IP, it was discovered that all three phosphate groups interact with the receptor, but not equally. Phosphates at the 4th and 5th positions interact more extensively than the phosphate at the 1st position and the hydroxyl group at the 6th position of the inositol ring. | 1 | Biochemistry |
A magnesium(I) dimer is a molecular compound containing a magnesium to magnesium bond (Mg-Mg), giving the metal an apparent +1 oxidation state.
Alkaline earth metals are commonly found in the +2-oxidation state, such as magnesium. The M are considered as redox-inert, meaning that the +2 state is significant. However, recent advancements in main group chemistry have yielded low-valent magnesium(I) dimers, also given as Mg(I), with the first compound being reported in 2007. They can be generally represented as LMg-MgL, with L being a monoanionic ligand. For example, β-diketiminate, commonly referred to as Nacnac, is a useful chelate regarding these complexes. By tuning the ligand, the thermodynamics of the complex change. For instance, the ability to add substituents onto Nacnac can contribute to the steric bulk, which can affect reactivity and stability. As their discovery has grown, so has their usefulness. They are employed in organic and inorganic reduction reactions. It is soluble in a hydrocarbon solvent, like toluene, stoichiometric, selective, and safe. | 7 | Physical Chemistry |
CCCTC-Binding factor or CTCF was initially discovered as a negative regulator of the chicken c-myc gene. This protein was found to be binding to three regularly spaced repeats of the core sequence CCCTC and thus was named CCCTC binding factor. | 1 | Biochemistry |
Closantel and triclosan are known inhibitors of quorum sensing enzymes. Closantel induces aggregation of the histidine kinase sensor in two-component signalling. The latter disrupts the synthesis of a class of signalling molecules known as N-acyl homoserine lactones (AHLs) by blocking the enoyl-acyl carrier protein (ACP) reductase. | 1 | Biochemistry |
According to the rule, a casting with a larger surface area and smaller volume will cool more quickly than a casting with a smaller surface area and a larger volume under otherwise comparable conditions. The relationship can be mathematically expressed as:
Where is the solidification time, is the volume of the casting, is the surface area of the casting that contacts the mold, is a constant, and is the mold constant.
This relationship can be expressed more simply as:
Where the modulus is the ratio of the casting's volume to its surface area:
The mold constant depends on the properties of the metal, such as density, heat capacity, heat of fusion and superheat, and the mold, such as initial temperature, density, thermal conductivity, heat capacity and wall thickness. | 8 | Metallurgy |
Saccharides are a food source rich in energy. Large polymers such as starch are partially hydrolyzed in the mouth by the enzyme amylase before being cleaved further into sugars. Many mammals have seen great expansions in the copy number of the amylase gene. These duplications allow for the pancreatic amylase AMY2 to re-target to the salivary glands, allowing animals to detect starch by taste and to digest starch more efficiently and in higher quantities. This has happened independently in mice, rats, dogs, pigs, and most importantly, humans after the agricultural revolution.
Following the agricultural revolution 12,000 years ago, human diet began to shift more to plant and animal domestication in place of hunting and gathering. Starch has become a staple of the human diet.
Despite the obvious benefits, early humans did not possess salivary amylase, a trend that is also seen in evolutionary relatives of the human, such as chimpanzees and bonobos, who possess either one or no copies of the gene responsible for producing salivary amylase.
Like in other mammals, the pancreatic alpha-amylase AMY2 was duplicated multiple times. One event allowed it to evolve salivary specificity, leading to the production of amylase in the saliva (named in humans as AMY1). The 1p21.1 region of human chromosome 1 contains many copies of these genes, variously named AMY1A, AMY1B, AMY1C, AMY2A, AMY2B, and so on.
However, not all humans possess the same number of copies of the AMY1 gene. Populations known to rely more on saccharides have a higher number of AMY1 copies than human populations that, by comparison, consume little starch. The number of AMY1 gene copies in humans can range from six copies in agricultural groups such as European-American and Japanese (two high starch populations) to only two to three copies in hunter-gatherer societies such as the Biaka, Datog, and Yakuts.
The correlation that exists between starch consumption and number of AMY1 copies specific to population suggest that more AMY1 copies in high starch populations has been selected for by natural selection and considered the favorable phenotype for those individuals. Therefore, it is most likely that the benefit of an individual possessing more copies of AMY1 in a high starch population increases fitness and produces healthier, fitter offspring.
This fact is especially apparent when comparing geographically close populations with different eating habits that possess a different number of copies of the AMY1 gene. Such is the case for some Asian populations that have been shown to possess few AMY1 copies relative to some agricultural populations in Asia. This offers strong evidence that natural selection has acted on this gene as opposed to the possibility that the gene has spread through genetic drift.
Variations of amylase copy number in dogs mirrors that of human populations, suggesting they acquired the extra copies as they followed humans around. Unlike humans whose amylase levels depend on starch content in diet, wild animals eating a broad range of foods tend to have more copies of amylase. This may have to do with mainly detection of starch as opposed to digestion. | 1 | Biochemistry |
* Bello, Phillip A., [https://ieeexplore.ieee.org/document/1088793 "Characterization of randomly time-variant linear channels"], IEEE Transactions on Communications Systems, vol. 11, iss. 4, pp. 360-393, December 1963. | 7 | Physical Chemistry |
The first mathematical fit to an isotherm was published by Freundlich and Kuster (1906) and is a purely empirical formula for gaseous adsorbates:
where is the mass of adsorbate adsorbed, is the mass of the adsorbent, is the pressure of adsorbate (this can be changed to concentration if investigating solution rather than gas), and and are empirical constants for each adsorbent–adsorbate pair at a given temperature. The function is not adequate at very high pressure because in reality has an asymptotic maximum as pressure increases without bound. As the temperature increases, the constants and change to reflect the empirical observation that the quantity adsorbed rises more slowly and higher pressures are required to saturate the surface. | 7 | Physical Chemistry |
For solid materials with a significant length, like rods or cables, an estimate of the amount of thermal expansion can be described by the material strain, given by and defined as:
where is the length before the change of temperature and is the length after the change of temperature.
For most solids, thermal expansion is proportional to the change in temperature:
Thus, the change in either the strain or temperature can be estimated by:
where
is the difference of the temperature between the two recorded strains, measured in degrees Fahrenheit, degrees Rankine, degrees Celsius, or kelvin, and is the linear coefficient of thermal expansion in "per degree Fahrenheit", "per degree Rankine", "per degree Celsius", or "per kelvin", denoted by , , , or , respectively. In the field of continuum mechanics, thermal expansion and its effects are treated as eigenstrain and eigenstress. | 7 | Physical Chemistry |
Halothane is an ozone depleting substance with an ODP of 1.56 and it is calculated to be responsible for 1% of total stratospheric ozone layer depletion. | 4 | Stereochemistry |
An induction furnace consists of a nonconductive crucible holding the charge of metal to be melted, surrounded by a coil of copper wire. A powerful alternating current flows through the wire. The coil creates a rapidly reversing magnetic field that penetrates the metal. The magnetic field induces eddy currents, circular electric currents, inside the metal, by electromagnetic induction. The eddy currents, flowing through the electrical resistance of the bulk metal, heat it by Joule heating. In ferromagnetic materials like iron, the material may also be heated by magnetic hysteresis, the reversal of the molecular magnetic dipoles in the metal. Once melted, the eddy currents cause vigorous stirring of the melt, assuring good mixing.
An advantage of induction heating is that the heat is generated within the furnace's charge itself rather than applied by a burning fuel or other external heat source, which can be important in applications where contamination is an issue.
Operating frequencies range from utility frequency (50 or 60 Hz) to 400 kHz or higher, usually depending on the material being melted, the capacity (volume) of the furnace and the melting speed required. Generally, the smaller the volume of the melts, the higher the frequency of the furnace used; this is due to the skin depth which is a measure of the distance an alternating current can penetrate beneath the surface of a conductor. For the same conductivity, the higher frequencies have a shallow skin depth—that is less penetration into the melt. Lower frequencies can generate stirring or turbulence in the metal.
A preheated, one-ton furnace melting iron can melt cold charge to tapping readiness within an hour. Power supplies range from 10 kW to 42 MW, with melt sizes of 20 kg to 65 tons of metal respectively.
An operating induction furnace usually emits a hum or whine (due to fluctuating magnetic forces and magnetostriction), the pitch of which can be used by operators to identify whether the furnace is operating correctly or at what power level. | 8 | Metallurgy |
Valerie has two daughters, and her father is the honorary president of the Johannesburg Sephardic Hebrew Congregation. She grew up speaking Judeo-Spanish at home. | 1 | Biochemistry |
Initiation of transcription requires promoter regions, which are specific nucleotide consensus sequences that tell the σ-factor on RNA polymerase where to bind to the DNA. The promoters are usually located 15 to 19 bases apart and are most commonly found upstream of the genes they control. RNA polymerase is made up of 4 subunits, which include two alphas, a beta, and a beta prime (α, α, β, and β). A fifth subunit, sigma (called the σ-factor), is only present during initiation and detaches prior to elongation. Each subunit plays a role in the initiation of transcription, and the σ-factor must' be present for initiation to occur. When all σ-factor is present, RNA polymerase is in its active form and is referred to as the holoenzyme. When the σ-factor detaches, it is in core polymerase form. The σ-factor recognizes promoter sequences at -35 and -10 regions and transcription begins at the start site (+1). The sequence of the -10 region is TATAAT and the sequence of the -35 region is TTGACA.
* The σ-factor binds to the -35 promoter region. At this point, the holoenzyme is referred to as the closed complex because the DNA is still double stranded (connected by hydrogen bonds).
*Once the σ-factor binds, the remaining subunits of the polymerase attach to the site. The high concentration of adenine-thymine bonds at the -10 region facilitates the unwinding of the DNA. At this point, the holoenzyme is called the open complex. This open complex is also called the transcription bubble. Only one strand of DNA, called the template strand (also called the noncoding strand or nonsense/antisense strand), gets transcribed.
*Transcription begins and short "abortive" nucleotide sequences approximately 10 base pairs long are produced. These short sequences are nonfunctional pieces of RNA that are produced and then released. Generally, this nucleotide sequence consists of about twelve base pairs and aids in contributing to the stability of RNA polymerase so it is able to continue along the strand of DNA.
* The σ-factor is needed to initiate transcription but is not needed to continue transcribing the DNA. The σ-factor dissociates from the core enzyme and elongation proceeds. This signals the end of the initiation phase and the holoenzyme is now in core polymerase form.
The promoter region is a prime regulator of transcription. Promoter regions regulate transcription of all genes within bacteria. As a result of their involvement, the sequence of base pairs within the promoter region is significant; the more similar the promoter region is to the consensus sequence, the tighter RNA polymerase will be able to bind. This binding contributes to the stability of elongation stage of transcription and overall results in more efficient functioning. Additionally, RNA polymerase and σ-factors are in limited supply within any given bacterial cell. Consequently, σ-factor binding to the promoter is affected by these limitations. All promoter regions contain sequences that are considered non-consensus and this helps to distribute σ-factors across the entirety of the genome. | 1 | Biochemistry |
As described above, same-excess experiments are conducted with two or more experiments holding the excess, (e) constant while changing the absolute concentrations of the substrates (in this case, the catalyst is also treated as a substrate.) Note that this construction causes the number of equivalents and therefore the mole percentage of each reagent/catalyst to differ between reactions. These experiments enable one to artificially "enter" the reaction at any point, as the initial concentrations of one experiment (the intercepting reaction) are chosen to map directly onto the anticipated concentrations at some intermediate time, t, in another (the parent reaction). One would expect the reaction progress, described by the rate vs. substrate concentration plots detailed above, to map directly onto each other from that interception point onward. This will hold true, however, only if the rate of the reaction is not altered by changes to the active substrate/catalyst concentration (such as by catalyst activation, catalyst deactivation, or product inhibition) before that interception.
A perfect overlay of multiple experiments with the same-excess but different initial substrate loadings suggests that no changes in the active substrate/catalyst concentration occur over the course of the reaction. The failure of the plots to overlay is generally indicative of catalyst activation, deactivation, or product inhibition under the reaction conditions. These cases may be distinguished by the position of the reaction progress curves relative to each other. Intercepting reactions lying below (slower rates at the same substrate concentration) the parent reactions on the rate vs. substrate concentration plot, are indicative of catalyst activation under reaction conditions. Intercepting reactions lying above (faster rates at the same substrate concentration) the parent reactions on the rate vs. substrate concentration plot, are indicative of catalyst deactivation under reaction conditions; further experimentation is necessary to distinguish product inhibition from other forms of catalyst death.
One key difference between the intercepting reaction and the parent reaction described above is the presence of some amount of product in the parent reaction at the interception point. Product inhibition has long been known to influence catalyst efficiency of many systems, and in the case of same-excess experiments, it prevents the intercepting and parent reactions from overlaying. While same-excess experiments as described above cannot attribute catalyst deactivation to any particular cause, product inhibition can be probed by further experiments in which some initial amount of product is added to the intercepting reaction (designed to mimic the amount of product expected to be present in the parent reaction at the same substrate concentration). A perfect overlay of the rate vs. substrate concentration plots under same-excess-same product conditions indicates that product inhibition does occur under the reaction conditions used. While the failure of the rate vs. substrate concentration plots to overlay under same-excess-same product conditions does not preclude product inhibition, it does, at least, indicate that other catalyst deactivation paths must also be active.
Same-excess experiments probing catalyst deactivation and product inhibition are among the most widely used applications of reaction progress kinetic analysis. Among the numerous examples in the literature, some include investigation of the amino alcohol-catalyzed zinc alkylation of aldehydes, the amido-thiourea catalyzed asymmetric Strecker synthesis of unnatural amino acids, and the SOMO-activation of organocatalysts. | 7 | Physical Chemistry |
Dragendorffs reagent is a color reagent to detect alkaloids in a test sample or as a stain for chromatography plates. Alkaloids, if present in the solution of sample, will react with Dragendorffs reagent and produce an orange or orange-red precipitate. This reagent was invented by the German pharmacologist, Johann Georg Dragendorff (1836–1898) at the University of Dorpat. | 3 | Analytical Chemistry |
One of the more complex hydration reactions utilises sulfuric acid as a catalyst. This reaction occurs in a similar way to the addition reaction but has an extra step in which the OSOH group is replaced by an OH group, forming an alcohol:
:CH + HO → CHOH
As can be seen, the HSO does take part in the overall reaction, however it remains unchanged so is classified as a catalyst.
This is the reaction in more detail:
#The H–OSOH molecule has a δ+ charge on the initial H atom. This is attracted to and reacts with the double bond in the same way as before.
#The remaining (negatively charged) OSOH ion then attaches to the carbocation, forming ethyl hydrogensulphate (upper way on the above scheme).
#When water (HO) is added and the mixture heated, ethanol (CHOH) is produced. The "spare" hydrogen atom from the water goes into "replacing" the "lost" hydrogen and, thus, reproduces sulfuric acid. Another pathway in which water molecule combines directly to the intermediate carbocation (lower way) is also possible. This pathway become predominant when aqueous sulfuric acid is used.
Overall, this process adds a molecule of water to a molecule of ethene.
This is an important reaction in industry, as it produces ethanol, whose purposes include fuels and starting material for other chemicals. | 7 | Physical Chemistry |
Despite most other life forms being killed by the lack of oxygen, jellyfish can thrive and are sometimes present in dead zones in vast numbers. Jellyfish blooms produce large quantities of mucus, leading to major changes in food webs in the ocean since few organisms feed on them. The organic carbon in mucus is metabolized by bacteria which return it to the atmosphere in the form of carbon dioxide in what has been termed a "jelly carbon shunt". The potential worsening of jellyfish blooms as a result of human activities has driven new research into the influence of dead zones on jelly populations. The primary concern is the potential for dead zones to serve as breeding grounds for jelly populations as a result of the hypoxic conditions driving away competition for resources and common predators of jellyfish. The increased population of jellyfish could have high commercial costs with loss of fisheries, destruction and contamination of trawling nets and fishing vessels, and lowered tourism revenue in coastal systems. | 9 | Geochemistry |
The technique was developed in 1983 by Kary Mullis, PCR is now a common and important technique used in medical and biological research labs for a variety of applications.
PCR, or Polymerase Chain Reaction, is a widely used molecular biology technique to amplify a specific DNA sequence.
Amplification is achieved by a series of three steps:
1- Denaturation : In this step, the DNA is heated to 95 °C to dissociate the hydrogen bonds between the complementary base pairs of the double-stranded DNA.
2-Annealing : During this stage the reaction is cooled to 50-65 °C . This enables the primers to attach to a specific location on the single -stranded template DNA by way of hydrogen bonding.
3-Extension : A thermostable DNA polymerase which is Taq polymerase is commonly used at this step. This is done at a temperature of 72 °C . DNA polymerase adds nucleotides in the 5-6 direction and synthesizes the complementary strand of the DNA template . | 1 | Biochemistry |
In addition to various primary data formats (e.g. GPML, BioPAX, Reactome, KEGG, and RDF), WikiPathways supports a variety of ways to integrate and interact with pathway content. These include directed link-outs, image maps, RSS feeds and deep web services. This enables reuse in projects like COVID19 Disease Map.
WikiPathways content is used to annotate and cross-link Wikipedia articles covering various genes, proteins, metabolites and pathways. Here are a few examples:
* Citric acid cycle § Interactive pathway map
* Articles that link to Citric acid cycle template
* :Category:WikiPathways templates | 1 | Biochemistry |
Oxidoreductases are enzymes that catalyze the transfer of a hydride ion between a substrate and a cofactor, in many cases, particularly those in metabolic reactions, that cofator is a form of nicotinamide adenine dinucleotide. Nicotinamide adenine dinucleotide phosphate (NADPH) is used in anabolic reactions while nicotinamide adenine dinucleotide (NAD+) is used in catabolic reactions. | 1 | Biochemistry |
The basic principle of the phenol-chloroform extraction is that DNA and RNA are relatively insoluble in phenol and chloroform, while other cellular components are relatively soluble in these solvents. The addition of a phenol/chloroform mixture will dissolve protein and lipid contaminants, leaving the nucleic acids in the aqueous phase. It also denatures proteins, like DNase, which is especially important if the plasmids are to be used for enzyme digestion. Otherwise, smearing may occur in enzyme restricted form of plasmid DNA. | 1 | Biochemistry |
An advanced or future space mission must have a power source or propulsion that will require the rejection of waste heat.
Disposing large quantities of waste heat must be considered in order to realize a large-space structure (LSS) that handle high power such as a nuclear reactor or a space solar power satellite (SPS).
Such space systems require advanced high-temperature thermal control systems.
Liquid metal heat pipes with conventional radiators are considered ideally suited for such applications.
However, the required radiator surface area is huge, hence, the system mass is very large. The liquid droplet radiator (LDR) has an advantage in terms of the rejected heat power-weight ratio. The results of the studies indicate that for rejection temperatures below approximately 700 K, the LDR system is significantly lighter in weight than the other advanced radiator concepts. A LDR can be seven times lighter than conventional heat pipe radiators of similar size.
The LDR is more resistant to meteorite impacts due to less critical surface or windage, and requires less storage volume.
Therefore, the LDR has attracted attention as an advanced radiator for high-power space systems.
In 1978, John M. Hedgepeth proposed, in "Ultralightweight Structures for Space Power," in Radiation Energy Conversion in Space, Vol. 61 of Progress in Astronautics and Aeronautics, K. W. Billman, ed. (AIAA, New York, 1978), p. 126,
the use of a dust radiator to reduce the radiator weight of solar power satellites. Practical problems of this dust system led to the LDR concept in 1979.
Numerous studies have been made by companies, organizations and universities around the world.
Practical experiments were carried out for example with STS-77 and at drop shafts in Japan: Japan Microgravity Center (JAMIC) and Microgravity Laboratory of Japan. | 7 | Physical Chemistry |
Supramolecular systems are rarely designed from first principles. Rather, chemists have a range of well-studied structural and functional building blocks that they are able to use to build up larger functional architectures. Many of these exist as whole families of similar units, from which the analog with the exact desired properties can be chosen. | 6 | Supramolecular Chemistry |
Langmuir is indexed in Chemical Abstracts Service, Scopus, EBSCOhost, British Library, PubMed, Web of Science, and SwetsWise. | 7 | Physical Chemistry |
The several RNA polymerases in eukaryotes each have their own means of termination. Pol I is stopped by TTF1 (yeast Nsi1), which recognizes a downstream DNA sequence; the endonuclease is XRN2 (yeast Rat1). Pol III is able to terminate on its on on a stretch of As on the template strand.
Finally, Pol II also have poly(A)-independent modes of termination, which is required when it transcribes snRNA and snoRNA genes in yeast. The yeast protein Nrd1 is responsible. Some human mechanism, possibly PCF11, seems to cause premature termination when pol II transcribes HIV genes. | 1 | Biochemistry |
Young-Tae Chang is a South Korean chemist. He is a professor of chemistry at Pohang University of Science and Technology (POSTECH) and Associate Director under Kim Kimoon at the Center for Self-assembly and Complexity at the Institute for Basic Science located on the POSTECH campus.
Young-Tae Chang was born in Pusan, South Korea in 1968. He obtained a Bachelor of Science degree in chemistry from POSTECH, working on the divergent synthesis of all regioisomers of myo-inositol phosphates, under guide of Prof. Sung-Kee Chung. Doctoral requirements at POSTECH require a student study at least three years, but Young-Tae finished in two, requiring his advisor to appeal for a revision of the rules which allowed him to receive his doctorate in February 1997. He then engaged in postdoctoral research in the laboratory of Prof. Peter G. Schultz at University of California, Berkeley and Scripps Research in 2000.
He was appointed assistant professor at New York University (NYU) and promoted to associated professor in 2005. In September 2007, he moved to the National University of
Singapore and the [http://www.sbic.a-star.edu.sg/index.php Singapore Bioimaging Consortium] at Biopolis. From 2017, he is a Full Professor in the [http://chem.postech.ac.kr/eng/ Department of Chemistry, POSTECH] and head of the [http://www.sbic.a-star.edu.sg/research/lbpd/index.php Laboratory of Bioimaging Probe Development] at [http://www.sbic.a-star.edu.sg/index.php SBIC]. He pioneered diversity-oriented fluorescence library approach (DOFLA), and developed embryonic stem cell probe CDy1, neuronal stem cell probe CDr3, and neron specific probe, NeuO. He also developed a method for background-free live cell imaging with tamed fluorescent probe.
He is an editorial board member of MedChemComm and RSC Advances, Royal Society of Chemistry, and [http://ajnmmi.us/ American Journal of Nuclear Medicine and Molecular Imaging]. He has published more than 300 scientific papers and 3 books resulting in more than 22,000 citations. Additionally, he has filed more than 50 patents. | 0 | Organic Chemistry |
There are no expected pharmacokinetic interactions between thalidomide and other medicines due to its neutral effects on P-glycoprotein and the cytochrome P450 family. It may interact with sedatives due to its sedative action and bradycardic agents, like beta-blockers, due to its bradycardia-inducing effects. Risk of peripheral neuropathy may be increased by concomitant treatment of thalidomide with other agents known to cause peripheral neuropathy. The risk of venous thromboembolisms with thalidomide seems to be increased when patients are treated with oral contraceptives or other cytotoxic agents (including doxorubicin and melphalan) concurrently. Thalidomide may interfere with various contraceptives, and hence it is advised that women of reproductive age use at least two different means of contraception to ensure that no child will be conceived while they are taking thalidomide. | 4 | Stereochemistry |
Diphenylamine is considered practically insoluble according to the 2014 MSDS. It exhibits very low persistence in direct water photolysis experiments in the laboratory and is moderately volatile. Indirect photooxidation in the atmosphere through reaction with hydroxyl radicals was estimated. Despite limited data, the information was sufficient for the EC to characterize the environmental risk as negligible, because the intended use of diphenylamine was indoors. | 3 | Analytical Chemistry |
α-Naphtholphthalein (CHO) is a phthalein dye used as a pH indicator with a visual transition from colorless/reddish to greenish blue at pH 7.3–8.7. | 3 | Analytical Chemistry |
The above systems produce an economizer effect by using compressors, meters, valves and heat exchangers within the refrigeration cycle. In some refrigeration systems the economizer can be an independent refrigeration mechanism. Such is the case of subcooling the liquid line by any other means that draws the heat out of the main system. For example, a heat exchanger that preheats cold water needed for another process or human use, may take heat from the liquid line, effectively subcooling it and increasing the system's capacity.
Recently, machines exclusively designed for this purpose have been developed. In Chile, the manufacturer EcoPac Systems developed a cycle optimizer able to stabilize the temperature of the liquid line and allow either an increase in the refrigeration capacity of the system, or a reduction of the power consumption. Such systems have the advantage of not interfering with the original design of the refrigeration system and are a way to expand a single staged system that does not possess an economizer compressor. | 7 | Physical Chemistry |
One advantage of spectrograph mode is the ability to acquire IPES spectra over a wide range of photon energies simultaneously. Additionally, the incident electron energy remains fixed which allows better focusing of the electron beam on the sample. Furthermore, by changing the incident electron energy the electronic structure can be studied in great detail. Although the grating spectrometer is very stable over time, the set-up can be very complex and its maintenance can be very expensive. The advantages of isochromat mode are its low cost, simple design and higher count rates. | 7 | Physical Chemistry |
Although any stereographic projection misses one point on the sphere (the projection point), the entire sphere can be mapped using two projections from distinct projection points. In other words, the sphere can be covered by two stereographic parametrizations (the inverses of the projections) from the plane. The parametrizations can be chosen to induce the same orientation on the sphere. Together, they describe the sphere as an oriented surface (or two-dimensional manifold).
This construction has special significance in complex analysis. The point in the real plane can be identified with the complex number . The stereographic projection from the north pole onto the equatorial plane is then
Similarly, letting be another complex coordinate, the functions
define a stereographic projection from the south pole onto the equatorial plane. The transition maps between the - and -coordinates are then and , with approaching 0 as goes to infinity, and vice versa. This facilitates an elegant and useful notion of infinity for the complex numbers and indeed an entire theory of meromorphic functions mapping to the Riemann sphere. The standard metric on the unit sphere agrees with the Fubini–Study metric on the Riemann sphere. | 3 | Analytical Chemistry |
Not just one but multiple mitogenic mutations are required for cancer to proliferate. Generally, multiple mutations in different subsystems (an oncogene and a tumor suppressor gene) are the most effective at causing cancer. For example, a mutation that hyperactivates the oncogene Ras and another that inactivates the tumor suppressor pRb is far more tumorigenic than either protein alone.
Tumor cells are also resistant to the hyperproliferation stress response. Normal cells have apoptotic proteins that will respond to an overstimulation of mitogenic signaling pathways by triggering cell death or senescence. This generally prevents the onset of cancer from a single oncogenic mutation. In tumor cells, there is generally another mutation that inhibits apoptotic proteins as well, suppressing the hyperproliferation stress response. | 1 | Biochemistry |
Molecular self-assembly is a key concept in supramolecular chemistry. This is because assembly of molecules in such systems is directed through non-covalent interactions (e.g., hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi-stacking interactions, and/or electrostatic) as well as electromagnetic interactions. Common examples include the formation of colloids, biomolecular condensates, micelles, vesicles, liquid crystal phases, and Langmuir monolayers by surfactant molecules. Further examples of supramolecular assemblies demonstrate that a variety of different shapes and sizes can be obtained using molecular self-assembly.
Molecular self-assembly allows the construction of challenging molecular topologies. One example is Borromean rings, interlocking rings wherein removal of one ring unlocks each of the other rings. DNA has been used to prepare a molecular analog of Borromean rings. More recently, a similar structure has been prepared using non-biological building blocks. | 6 | Supramolecular Chemistry |
Key thermophysical properties of phase-change materials include: Melting point (T), Heat of fusion (ΔH), Specific heat (c) (of solid and liquid phase), Density (ρ) (of solid and liquid phase) and thermal conductivity. Values such as volume change and volumetric heat capacity can be calculated there from. | 7 | Physical Chemistry |
Principal component analysis (PCA) was one of the earliest methods used for pump–probe data analysis, as it is commonly used for hyperspectral data analysis. PCA decomposes the data into orthogonal components. In melanoma studies, the principal components have shown good agreement with the signals obtained from the different forms of melanin. An advantage of PCA is that noise can be reduced by keeping only the principal components that account for majority of the variance in the data. However, the principal components do not necessarily reflect actual properties of the underlying chemical species, which are typically non-orthogonal. Therefore, a limitation is that the number of unique chemical species cannot be inferred using PCA. | 7 | Physical Chemistry |
NCAs are prone to hydrolysis to the parent amino acid:
:RCHNHC(O)OC(O) + HO → HNCH(R)COH + CO
Some derivatives however tolerate water briefly.
NCAs convert to homopolypeptides ( [N(H)CH(R)CO)]) through ring-opening polymerization:
:nRCHNHC(O)OC(O) → [N(H)CH(R)CO)] + nCO
Poly--lysine has been prepared from N-carbobenzyloxy-α-N-carboxy--lysine anhydride, followed by deprotection with phosphonium iodide. Peptide synthesis from NCAs does not require protection of the amino acid functional groups. N-Substituted NCAs, such as sulfenamide derivatives have also been examined. The ring-opening polymerization of NCAs is catalyzed by metal catalysts.
The polymerization of NCA’s have been considered as a prebiotic route to polypeptides. | 0 | Organic Chemistry |
In organic and organometallic chemistry, an organyl group is an organic substituent with one (sometimes more) free valence(-s) at a carbon atom. The term is often used in chemical patent literature to protect claims over a broad scope. | 0 | Organic Chemistry |
The process of translation is highly regulated in both eukaryotic and prokaryotic organisms. Regulation of translation can impact the global rate of protein synthesis which is closely coupled to the metabolic and proliferative state of a cell.
To delve deeper into this intricate process, scientists typically use a technique known as ribosome profiling. This method enables researchers to take a snapshot of the translatome, showing which parts of the mRNA are being translated into proteins by ribosomes at a given time. Ribosome profiling provides valuable insights into translation dynamics, revealing the complex interplay between gene sequence, mRNA structure, and translation regulation. For example, research utilizing this method has revealed that genetic differences and their subsequent expression as mRNAs can also impact translation rate in an RNA-specific manner.
Expanding on this concept, a more recent development is single-cell ribosome profiling, a technique that allows us to study the translation process at the resolution of individual cells. This is particularly significant as cells, even those of the same type, can exhibit considerable variability in their protein synthesis. Single-cell ribosome profiling has the potential to shed light on the heterogeneous nature of cells, leading to a more nuanced understanding of how translation regulation can impact cell behavior, metabolic state, and responsiveness to various stimuli or conditions. | 1 | Biochemistry |
DNA is extracted from cells used to create test fragments. These test fragments are added to a solution containing a variety of microsphere beads. Each type of microsphere bead contains a known DNA probe with a unique fluorescent identity. Test fragments and probes on the microsphere beads are allowed to hybridize to each other. Once hybridized, the microsphere beads are sorted, usually using flow cytometry. This allows for the detection of each of the gene variants from the original sample. The resulting data collected will indicate the relative abundance of each hybridized sample to the microsphere. | 1 | Biochemistry |
EWGs enhance the Lewis acidity, making compounds more reactive as Lewis acids. For example, fluorine is a stronger electron-withdrawing substituent than methyl, resulting in an increased Lewis acidity of boron trifluoride relative to trimethylborane. Electron-withdrawing groups also tend to reduce Lewis basicity. | 7 | Physical Chemistry |
In 2017, the FDA granted deulinoleate ethyl orphan drug designation in the treatment of phospholipase 2G6-associated neurodegeneration (PLAN). | 1 | Biochemistry |
The Macfarlane Burnet Medal and Lecture is a biennial award given by the Australian Academy of Science to recognise outstanding scientific research in the biological sciences.
It was established in 1971 and honours the memory of the Nobel laureate Sir Frank Macfarlane Burnet, OM KBE MD FAA FRS, the Australian virologist best known for his contributions to immunology and is the academy's highest award for biological sciences. | 1 | Biochemistry |
The Blepharisma nuclear code (translation table 15) is a genetic code found in the nuclei of Blepharisma. | 1 | Biochemistry |
For solution of substances which ionize in solution the activity coefficients of the cation and anion cannot be experimentally determined independently of each other because solution properties depend on both ions. Single ion activity coefficients must be linked to the activity coefficient of the dissolved electrolyte as if undissociated. In this case a mean stoichiometric activity coefficient of the dissolved electrolyte, γ, is used. It is called stoichiometric because it expresses both the deviation from the ideality of the solution and the incomplete ionic dissociation of the ionic compound which occurs especially with the increase of its concentration.
For a 1:1 electrolyte, such as NaCl it is given by the following:
where and are the activity coefficients of the cation and anion respectively.
More generally, the mean activity coefficient of a compound of formula is given by
Single-ion activity coefficients can be calculated theoretically, for example by using the Debye–Hückel equation. The theoretical equation can be tested by combining the calculated single-ion activity coefficients to give mean values which can be compared to experimental values.
The prevailing view that single ion activity coefficients are unmeasurable independently, or perhaps even physically meaningless, has its roots in the work of Guggenheim in the late 1920s. However, chemists have never been able to give up the idea of single ion activities, and by implication single ion activity coefficients. For example, pH is defined as the negative logarithm of the hydrogen ion activity. If the prevailing view on the physical meaning and measurability of single ion activities is correct then defining pH as the negative logarithm of the hydrogen ion activity places the quantity squarely in the unmeasurable category. Recognizing this logical difficulty, International Union of Pure and Applied Chemistry (IUPAC) states that the activity-based definition of pH is a notional definition only. Despite the prevailing negative view on the measurability of single ion coefficients, the concept of single ion activities continues to be discussed in the literature, and at least one author presents a definition of single ion activity in terms of purely thermodynamic quantities and proposes a method of measuring single ion activity coefficients based on purely thermodynamic processes. | 7 | Physical Chemistry |
Ceramography evolved along with other branches of materialography and ceramic engineering. Alois de Widmanstätten of Austria etched a meteorite in 1808 to reveal proeutectoid ferrite bands that grew on prior austenite grain boundaries. Geologist Henry Clifton Sorby, the "father of metallography," applied petrographic techniques to the steel industry in the 1860s in Sheffield, England. French geologist Auguste Michel-Lévy devised a chart that correlated the optical properties of minerals to their transmitted color and thickness in the 1880s. Swedish metallurgist J.A. Brinell invented the first quantitative hardness scale in 1900. Smith and Sandland developed the first microindentation hardness test at Vickers Ltd. in London in 1922. Swiss-born microscopist A.I. Buehler started the first metallographic equipment manufacturer near Chicago in 1936. Frederick Knoop and colleagues at the National Bureau of Standards developed a less-penetrating (than Vickers) microindentation test in 1939. Struers A/S of Copenhagen introduced the electrolytic polisher to metallography in 1943. George Kehl of Columbia University wrote a book that was considered the bible of materialography until the 1980s. Kehl co-founded a group within the Atomic Energy Commission that became the International Metallographic Society in 1967. | 8 | Metallurgy |
R-22 was mostly phased out in new equipment in the United States by regulatory action by the EPA under the Significant New Alternatives Program (SNAP) by rules 20 and 21 of the program, due to its high global warming potential. The EPA program was consistent with the Montreal Accords, but international agreements must be ratified by the US Senate to have legal effect. A 2017 decision of the US Court of Appeals for the District of Columbia Circuit held that the US EPA lacked authority to regulate the use of R-22 under SNAP. In essence the court ruled the EPA's statutory authority was for ozone reduction, not global warming. The EPA subsequently issued guidance to the effect that the EPA would no longer regulate R-22. A 2018 ruling by the same court held that the EPA failed to conform with required procedure when it issued its guidance pursuant to the 2017 ruling, voiding the guidance, but not the prior ruling that required it. The refrigeration and air conditioning industry had already discontinued production of new R-22 equipment. The practical effect of these rulings is to reduce the cost of imported R-22 to maintain aging equipment, extending its service life, while preventing the use of R-22 in new equipment. | 2 | Environmental Chemistry |
A half-life often describes the decay of discrete entities, such as radioactive atoms. In that case, it does not work to use the definition that states "half-life is the time required for exactly half of the entities to decay". For example, if there is just one radioactive atom, and its half-life is one second, there will not be "half of an atom" left after one second.
Instead, the half-life is defined in terms of probability: "Half-life is the time required for exactly half of the entities to decay on average". In other words, the probability of a radioactive atom decaying within its half-life is 50%.
For example, the accompanying image is a simulation of many identical atoms undergoing radioactive decay. Note that after one half-life there are not exactly one-half of the atoms remaining, only approximately, because of the random variation in the process. Nevertheless, when there are many identical atoms decaying (right boxes), the law of large numbers suggests that it is a very good approximation to say that half of the atoms remain after one half-life.
Various simple exercises can demonstrate probabilistic decay, for example involving flipping coins or running a statistical computer program. | 7 | Physical Chemistry |
LEDs and laser diodes usually emit photons with energy close to and slightly larger than the band gap of the semiconductor material from which they are made. Therefore, as the band gap energy increases, the LED or laser color changes from infrared to red, through the rainbow to violet, then to UV. | 7 | Physical Chemistry |
Delapril is a prodrug; it is converted into two active metabolites, 5-hydroxy delapril diacid and delapril diacid. These metabolites bind completely to and inhibit angiotensin-converting enzyme (ACE), hence blocking angiotensin I to angiotensin II conversion. The resulting vasodilation prevents the vasoconstrictive effects of angiotensin II. Angiotensin II-induced aldosterone secretion by the adrenal cortex is also decreased by Delapril, leading to increases in excretion of sodium and therefore increases water outflow. | 4 | Stereochemistry |
Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymers, ceramics or composites) can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behaviour or wear resistance. These properties in turn govern the application of these materials in industrial practice.
Microstructure at scales smaller than can be viewed with optical microscopes is often called nanostructure, while the structure in which individual atoms are arranged is known as crystal structure. The nanostructure of biological specimens is referred to as ultrastructure. A microstructure’s influence on the mechanical and physical properties of a material is primarily governed by the different defects present or absent of the structure. These defects can take many forms but the primary ones are the pores. Even if those pores play a very important role in the definition of the characteristics of a material, so does its composition. In fact, for many materials, different phases can exist at the same time. These phases have different properties and if managed correctly, can prevent the fracture of the material. | 8 | Metallurgy |
Hydrogen gas porosity is an aluminium casting defect in the form of a porosity or void in an aluminium casting caused by a high level of hydrogen gas (H) dissolved in the aluminium at liquid phase. The solubility of hydrogen in solid aluminium is much smaller than in liquid aluminium. As the aluminium freezes, some of the hydrogen comes out of solution and forms bubbles, creating porosity in the solid aluminium.
Aluminium foundries want to produce high-quality aluminum castings with minimum porosity. Hydrogen porosity can be reduced by reducing the amount of hydrogen in the liquid aluminium alloy, by degassing or sparging. (Sometimes a small hydrogen concentration is intentionally maintained; some very fine hydrogen porosity can be preferable to internal voids caused by shrinkage.) Directional solidification can drive impurities to one end of the casting. | 8 | Metallurgy |
Sensor-based sorting is a coarse particle separation technology applied in mining for the dry separation of bulk materials. The functional principle does not limit the technology to any kind of segment or mineral application but makes the technical viability mainly depend on the liberation characteristics at the size range , which is usually sorted. If physical liberation is present there is a good potential that one of the sensors available on industrial scale sorting machines can differentiate between valuable and non-valuable particles.
The separation is based on features measured with a detection technology that are used to derive a yes/no decision for actuation of usually pneumatic impulses. Sensor-based sorting is a disruptive technology in the mining industry which is universally applicable for all commodities. A comprehensive study examines both the technologys potential and its limitations, whilst providing a framework for application development and evaluation. All relevant aspects, from sampling to plant design and integration into mining and mineral processing systems, are covered. Other terminologies used in the industry include ore sorting, automated sorting, electronic sorting, and optical sorting'. | 3 | Analytical Chemistry |
Casein kinase 2 ()(CK2/CSNK2) is a serine/threonine-selective protein kinase that has been implicated in cell cycle control, DNA repair, regulation of the circadian rhythm, and other cellular processes. De-regulation of CK2 has been linked to tumorigenesis as a potential protection mechanism for mutated cells. Proper CK2 function is necessary for survival of cells as no knockout models have been successfully generated. | 1 | Biochemistry |
Normality can be used for acid-base titrations. For example, sulfuric acid (HSO) is a diprotic acid. Since only 0.5 mol of HSO are needed to neutralize 1 mol of OH, the equivalence factor is:
:f(HSO) = 0.5
If the concentration of a sulfuric acid solution is c(HSO) = 1 mol/L, then its normality is 2 N. It can also be called a "2 normal" solution.
Similarly, for a solution with c(HPO) = 1 mol/L, the normality is 3 N because phosphoric acid contains 3 acidic H atoms. | 3 | Analytical Chemistry |
Sneaths index takes into account 134 categories of activity and structure. Dissimilarity index D is a percentage value of the sum of all properties not shared between two replaced amino acids. It is percentage value expressed by , where S' is Similarity. | 1 | Biochemistry |
Chlorination is one of the oldest known substitution reactions in chemistry. The French chemist Jean-Baptiste Dumas investigated the substitution of hydrogen for chlorine by acetic acid in candle wax as early as 1830. He showed that for each mole of chlorine introduced into a hydrocarbon, one mole of hydrogen chloride is also formed and noted the light-sensitivity of this reaction.
The idea that these reactions might be chain reactions is attributed to Max Bodenstein (1913). He assumed that in the reaction of two molecules not only the end product of the reaction can be formed, but also unstable, reactive intermediates which can continue the chain reaction.
Photochlorination garnered commercial attention with the availability of cheap chlorine from chloralkali electrolysis.
Chlorinated alkanes found an initial application in pharyngeal sprays. These contained chlorinated alkanes in relatively large quantities as solvents for chloramine T from 1914 to 1918. The Sharpless Solvents Corporation commissioned the first industrial photochloration plant for the chlorination of pentane in 1929. The commercial production of chlorinated paraffins for use as high-pressure additives in lubricants began around 1930. Around 1935 the process was technically stable and commercially successful. However, it was only in the years after World War II that a greater build-up of photochloration capacity began. In 1950, the United States produced more than 800,000 tons of chlorinated paraffin hydrocarbons. The major products were ethyl chloride, tetrachlorocarbon and dichloromethane. Because of concerns about health and environmentally relevant problems such as the ozone depletion behavior of light volatile chlorine compounds, the chemical industry developed alternative procedures that did not require chlorinated compounds. As a result of the following replacement of chlorinated by non-chlorinated products, worldwide production volumes have declined considerably over the years. | 5 | Photochemistry |
In chemistry, a molecule or ion is called chiral () if it cannot be superposed on its mirror image by any combination of rotations, translations, and some conformational changes. This geometric property is called chirality (). The terms are derived from Ancient Greek (cheir) hand; which is the canonical example of an object with this property.
A chiral molecule or ion exists in two stereoisomers that are mirror images of each other, called enantiomers; they are often distinguished as either "right-handed" or "left-handed" by their absolute configuration or some other criterion. The two enantiomers have the same chemical properties, except when reacting with other chiral compounds. They also have the same physical properties, except that they often have opposite optical activities. A homogeneous mixture of the two enantiomers in equal parts is said to be racemic, and it usually differs chemically and physically from the pure enantiomers.
Chiral molecules will usually have a stereogenic element from which chirality arises. The most common type of stereogenic element is a stereogenic center, or stereocenter. In the case of organic compounds, stereocenters most frequently take the form of a carbon atom with four distinct (different) groups attached to it in a tetrahedral geometry. A given stereocenter has two possible configurations (R and S), which give rise to stereoisomers (diastereomers and enantiomers) in molecules with one or more stereocenter. For a chiral molecule with one or more stereocenter, the enantiomer corresponds to the stereoisomer in which every stereocenter has the opposite configuration. An organic compound with only one stereogenic carbon is always chiral. On the other hand, an organic compound with multiple stereogenic carbons is typically, but not always, chiral. In particular, if the stereocenters are configured in such a way that the molecule can take a conformation having a plane of symmetry or an inversion point, then the molecule is achiral and is known as a meso compound. Less commonly, other atoms like N, P, S, and Si can also serve as stereocenters, provided they have four distinct substituents (including lone pair electrons) attached to them.
Molecules with chirality arising from one or more stereocenters are classified as possessing central chirality. There are two other types of stereogenic elements that can give rise to chirality, a stereogenic axis (axial chirality) and a stereogenic plane (planar chirality). Finally, the inherent curvature of a molecule can also give rise to chirality (inherent chirality). These types of chirality are far less common than central chirality. BINOL is a typical example of an axially chiral molecule, while trans-cyclooctene is a commonly cited example of a planar chiral molecule. Finally, helicene possesses helical chirality, which is one type of inherent chirality.
Chirality is an important concept for stereochemistry and biochemistry. Most substances relevant to biology are chiral, such as carbohydrates (sugars, starch, and cellulose), all but one of the amino acids that are the building blocks of proteins, and the nucleic acids. Naturally occurring triglycerides are often chiral, but not always. In living organisms, one typically finds only one of the two enantiomers of a chiral compound. For that reason, organisms that consume a chiral compound usually can metabolize only one of its enantiomers. For the same reason, the two enantiomers of a chiral pharmaceutical usually have vastly different potencies or effects. | 4 | Stereochemistry |
Determining the parameters of the Michaelis–Menten equation typically involves running a series of enzyme assays at varying substrate concentrations , and measuring the initial reaction rates , i.e. the reaction rates are measured after a time period short enough for it to be assumed that the enzyme-substrate complex has formed, but that the substrate concentration remains almost constant, and so the equilibrium or quasi-steady-state approximation remain valid. By plotting reaction rate against concentration, and using nonlinear regression of the Michaelis–Menten equation with correct weighting based on known error distribution properties of the rates, the parameters may be obtained.
Before computing facilities to perform nonlinear regression became available, graphical methods involving linearisation of the equation were used. A number of these were proposed, including the Eadie–Hofstee plot of against , the Hanes plot of against , and the Lineweaver–Burk plot (also known as the double-reciprocal plot) of against . Of these, the Hanes plot is the most accurate when is subject to errors with uniform standard deviation. From the point of view of visualizaing the data the Eadie–Hofstee plot has an important property: the entire possible range of values from to occupies a finite range of ordinate scale, making it impossible to choose axes that conceal a poor experimental design.
However, while useful for visualization, all three linear plots distort the error structure of the data and provide less precise estimates of and than correctly weighted non-linear regression. Assuming an error on , an inverse representation leads to an error of on (Propagation of uncertainty), implying that linear regression of the double-reciprocal plot should include weights of . This was well understood by Lineweaver and Burk, who had consulted the eminent statistician W. Edwards Deming before analysing their data. Unlike nearly all workers since, Burk made an experimental study of the error distribution, finding it consistent with a uniform standard error in , before deciding on the appropriate weights. This aspect of the work of Lineweaver and Burk received virtually no attention at the time, and was subsequently forgotten.
The direct linear plot is a graphical method in which the observations are represented by straight lines in parameter space, with axes and : each line is drawn with an intercept of on the axis and on the axis. The point of intersection of the lines for different observations yields the values of and . | 7 | Physical Chemistry |
The N−C−C geometry is linear in nitriles, reflecting the sp hybridization of the triply bonded carbon. The C−N distance is short at 1.16 Å, consistent with a triple bond. Nitriles are polar, as indicated by high dipole moments. As liquids, they have high relative permittivities, often in the 30s. | 0 | Organic Chemistry |
Crystallization requires an initiation step. This can be spontaneous or can be done by adding a small amount of the pure compound (a seed crystal) to the saturated solution, or can be done by simply scratching the glass surface to create a seeding surface for crystal growth. It is thought that even dust particles can act as simple seeds. | 3 | Analytical Chemistry |
It is also possible to switch the charge state of the NV center (i.e. between NV, NV and NV) by applying a gate voltage. | 7 | Physical Chemistry |
This pathway does not produce any ATP, this pathway does not replace glycolysis, it runs simultaneously to glycolysis and is only initiated with an increased concentration of sugar phosphates. One believed purpose of the methylglyoxal pathway is to help release the stress of elevated sugar phosphate concentration. Also when methylglyoxal is formed from DHAP, an inorganic phosphate is given off which can be used to replenish a low concentration of needed inorganic phosphate. The methylglyoxal pathway is a rather dangerous tactic, both because less energy is produced and a toxic compound, methylglyoxal is formed. ([http://mic.sgmjournals.org/cgi/reprint/151/3/707 Weber] 715). | 1 | Biochemistry |
In 2021, the first brain metabolome atlas of the mouse brain – and of an animal (a mammal) across different life stages – was released online. The data differentiates by brain regions and the metabolic changes could be "mapped to existing gene and protein brain atlases". | 1 | Biochemistry |
The PKM1 isozyme is expressed in organs that are strongly dependent upon a high rate of energy regeneration, such as muscle and brain. | 1 | Biochemistry |
CDs and DVDs have a protective film which must be stripped to reveal the gold reflective film or polycarbonate (PC) base. The surface of the disk can be activated to reveal the metal layer which allows compounds to bind to it. Compounds such as UV/ozone or an oxygen plasma treatment can be used to activate the disk to produce a hydrophilic surface with densely packed carboxylic acid groups.
As one-off microassay can be printed onto the activated disks using a noncontact printer to dispel nanoliter quantities of coating conjugates onto the disk. Proteins or antibodies acting as probe molecules can then covalently bind to the disk surface and can be incubated. A polydimethylsiloxane (PDMS) channel plate can also be used to immobilize the probes in a line array. The plate is removed, and the process is repeated with another plate to deliver analyte samples in a line array perpendicular to the probe array. The probe and analyte samples can bind or hybridize at the intersections of the arrays to create rectangular hybridization sites. The disk is washed, rinsed, and dried prior to reading. This process can be done manually or automated; in theory discs with pre-made assays could be manufactured and sold en masse. | 1 | Biochemistry |
Sand casting has many defects that can occur due to the mould failing. The mould usually fails because of one of two reasons: the wrong material is used or it is improperly rammed.
The first type is mould erosion, which is the wearing away of the mould as the liquid metal fills the mould. This type of defect usually only occurs in sand castings because most other casting processes have more robust moulds. The castings produced have rough spots and excess material. The moulding sand becomes incorporated into the casting metal and decreases the ductility, fatigue strength, and fracture toughness of the casting. This can be caused by a sand with too little strength or a pouring velocity that is too fast. The pouring velocity can be reduced by redesigning the gating system to use larger runners or multiple gates. A related source of defects are drops, in which part of the moulding sand from the cope drops into the casting while it is still a liquid. This also occurs when the mould is not properly rammed.
The second type of defect is metal penetration, which occurs when the liquid metal penetrates into the moulding sand. This causes a rough surface finish. This is caused by sand particles which are too coarse, lack of mould wash, or pouring temperatures that are too high. An alternative form of metal penetration into the mould known as veining is caused by cracking of the sand.
If the pouring temperature is too high or a sand of low melting point is used then the sand can fuse to the casting. When this happens the surface of the casting produced has a brittle, glassy appearance.
A run out occurs when the liquid metal leaks out of the mould because of a faulty mould or flask.
s are a thin layer of metal that sits proud of the casting. They are easy to remove and always reveal a underneath, which is an indentation in the casting surface. s are similar to buckles, except they are thin line indentations and not associated with scabs. Another similar defect is s, which are buckles that occur in the cope of sand castings. All of these defects are visual in nature and are no reason to scrap the workpiece. These defects are caused by overly high pouring temperatures or deficiencies of carbonaceous material.
A swell occurs when the mould wall gives way across a whole face, and is caused by an improperly rammed mould.
occurs when metallic oxides interact with impurities in silica sands. The result is sand particles embedded in the surface of the finished casting. This defect can be avoided by reducing the temperature of the liquid metal, by using a mould wash, and by using various additives in the sand mixture. | 8 | Metallurgy |
The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases steel and brass. The strips are joined together throughout their length by riveting, brazing or welding. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its initial temperature. The metal with the higher coefficient of thermal expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled. The sideways displacement of the strip is much larger than the small lengthways expansion in either of the two metals.
In some applications, the bimetal strip is used in the flat form. In others, it is wrapped into a coil for compactness. The greater length of the coiled version gives improved sensitivity.
The radius of curvature of a bimetallic strip depends on temperature according the formula derived by French physicist Yvon Villarceau in 1863 in his research for improving the precision of clocks:
where is the total thickness of the bimetal and is the coefficient of thermal expansion and is the thickness. The formula can also be rewritten as a function of the thermal misfit strain . And if the modulus and height are similar, we simply have .
An equivalent formula can be derived from the beam theory. | 8 | Metallurgy |
Solutions of urea and ammonium nitrate in water (UAN) are commonly used as a liquid fertilizer. In admixture, the combined solubility of ammonium nitrate and urea is so much higher than that of either component alone that it gives a stable solution with a total nitrogen content (32%) approaching that of solid ammonium nitrate (33.5%), though not, of course, that of urea itself (46%). UAN allows use of ammonium nitrate without the explosion hazard. In UAN accounts for 80% of the liquid fertilizers in the US. | 0 | Organic Chemistry |
Ostrowska-Czubenko attended the Nicolaus Copernicus University in Toruń, majoring in chemistry. She graduated in 1972, defended her doctoral thesis eight years later, and completed her habilitation in 2002. She is associate professor in the Department of Chemistry at the Nicolaus Copernicus University, where she specializes in physical Chemistry and physicochemistry of polymers. | 7 | Physical Chemistry |
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