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A system's internal state of thermodynamic equilibrium should be distinguished from a "stationary state" in which thermodynamic parameters are unchanging in time but the system is not isolated, so that there are, into and out of the system, non-zero macroscopic fluxes which are constant in time.
Non-equilibrium thermodynamics is a branch of thermodynamics that deals with systems that are not in thermodynamic equilibrium. Most systems found in nature are not in thermodynamic equilibrium because they are changing or can be triggered to change over time, and are continuously and discontinuously subject to flux of matter and energy to and from other systems. The thermodynamic study of non-equilibrium systems requires more general concepts than are dealt with by equilibrium thermodynamics. Many natural systems still today remain beyond the scope of currently known macroscopic thermodynamic methods.
Laws governing systems which are far from equilibrium are also debatable. One of the guiding principles for these systems is the maximum entropy production principle. It states that a non-equilibrium system evolves such as to maximize its entropy production. | 7 | Physical Chemistry |
In chemistry, the dispersity is a measure of the heterogeneity of sizes of molecules or particles in a mixture. A collection of objects is called uniform if the objects have the same size, shape, or mass. A sample of objects that have an inconsistent size, shape and mass distribution is called non-uniform. The objects can be in any form of chemical dispersion, such as particles in a colloid, droplets in a cloud, crystals in a rock,
or polymer macromolecules in a solution or a solid polymer mass. Polymers can be described by molecular mass distribution; a population of particles can be described by size, surface area, and/or mass distribution; and thin films can be described by film thickness distribution.
IUPAC has deprecated the use of the term polydispersity index, having replaced it with the term dispersity, represented by the symbol Đ (pronounced D-stroke) which can refer to either molecular mass or degree of polymerization. It can be calculated using the equation Đ = M/M, where M is the weight-average molar mass and M is the number-average molar mass. It can also be calculated according to degree of polymerization, where Đ = X/X, where X is the weight-average degree of polymerization and X is the number-average degree of polymerization. In certain limiting cases where Đ = Đ, it is simply referred to as Đ. IUPAC has also deprecated the terms monodisperse, which is considered to be self-contradictory, and polydisperse, which is considered redundant, preferring the terms uniform and non-uniform instead. The terms monodisperse and polydisperse are however still preferentially used to describe particles in an aerosol. | 7 | Physical Chemistry |
In molecular biology, an arginine finger is an amino acid residue of some enzymes. Arginine fingers are often found in the protein superfamily of AAA+ ATPases, GTPases, and dUTPases, where they assist in the catalysis of the gamma phosphate or gamma and beta phosphates from ATP or GTP, which creates a release of energy which can be used to perform cellular work. They are also found in GTPase-activating proteins (GAP). Thus, they are essential for many forms of life, and are highly conserved. Arginine fingers function through non-covalent interactions. They may also assist in dimerization, and while they are found in a wide variety of enzymes, they are not ubiquitous. | 1 | Biochemistry |
Usually when describing a space geometrically, a coordinate system is used which consists of a choice of origin and a basis of linearly independent, non-coplanar basis vectors , where is the dimension of the space being described. With reference to this coordinate system, each point in the space can be specified by coordinates (a coordinate -tuple). The origin has coordinates and an arbitrary point has coordinates . The position vector is then,
In -dimensions, the lengths of the basis vectors are denoted and the angles between them . However, most cases in crystallography involve two- or three-dimensional space in which the basis vectors are commonly displayed as with their lengths and angles denoted by and respectively. | 3 | Analytical Chemistry |
The systematic names sulfanediide and sulfide(2−), valid IUPAC names, are determined according to the substitutive and additive nomenclatures, respectively. However, the name sulfide is also used in compositional IUPAC nomenclature which does not take the nature of bonding involved. Examples of such naming include selenium disulfide and titanium sulfide, which contain no sulfide ions. | 0 | Organic Chemistry |
With credit to the previously listed techniques, biomarkers were found in petroleum and source rock extract. These are fossils from organisms, but are closer in size to molecules than to visible hand samples. They display the same structure as their parent biomolecules and are used in the identification of the organic matter from which the petroleum is derived. Biomarkers are also used in correlating oils and source rocks, finding the oil's maturity, regional differences found between multiple samples, and the history of the basin in which the source rock was located. | 9 | Geochemistry |
The flux method is a crystal growth method where starting materials are dissolved in a solvent (flux), and are precipitated out to form crystals of a desired compound. The flux lowers the melting point of the desired compound, analogous to a wet chemistry recrystallization. The flux is molten in a highly stable crucible that does not react with the flux. Metal crucibles, such as platinum, titanium, and niobium are used for the growth of oxide crystals. Ceramic crucibles, such as alumina, zirconia, and boron nitride are used for the growth of metallic crystals. For air-sensitive growths, contents are sealed in ampoules or placed in atmosphere controlled furnaces. | 3 | Analytical Chemistry |
Glycoinformatics is a field of bioinformatics that pertains to the study of carbohydrates involved in protein post-translational modification. It broadly includes (but is not restricted to) database, software, and algorithm development for the study of carbohydrate structures, glycoconjugates, enzymatic carbohydrate synthesis and degradation, as well as carbohydrate interactions. Conventional usage of the term does not currently include the treatment of carbohydrates from the better-known nutritive aspect. | 0 | Organic Chemistry |
The chemical model consists of a set of chemical species present in solution, both the reactants added to the reaction mixture and the complex species formed from them. Denoting the reactants by A, B..., each complex species is specified by the stoichiometric coefficients that relate the particular combination of reactants forming them.
When using general-purpose computer programs, it is usual to use cumulative association constants, as shown above. Electrical charges are not shown in general expressions such as this and are often omitted from specific expressions, for simplicity of notation. In fact, electrical charges have no bearing on the equilibrium processes other that there being a requirement for overall electrical neutrality in all systems.
With aqueous solutions the concentrations of proton (hydronium ion) and hydroxide ion are constrained by the self-dissociation of water.
With dilute solutions the concentration of water is assumed constant, so the equilibrium expression is written in the form of the ionic product of water.
When both H and OH must be considered as reactants, one of them is eliminated from the model by specifying that its concentration be derived from the concentration of the other. Usually the concentration of the hydroxide ion is given by
In this case the equilibrium constant for the formation of hydroxide has the stoichiometric coefficients −1 in regard to the proton and zero for the other reactants. This has important implications for all protonation equilibria in aqueous solution and for hydrolysis constants in particular.
It is quite usual to omit from the model those species whose concentrations are considered negligible. For example, it is usually assumed then there is no interaction between the reactants and/or complexes and the electrolyte used to maintain constant ionic strength or the buffer used to maintain constant pH. These assumptions may or may not be justified. Also, it is implicitly assumed that there are no other complex species present. When complexes are wrongly ignored a systematic error is introduced into the calculations.
Equilibrium constant values are usually estimated initially by reference to data sources. | 7 | Physical Chemistry |
If the thermodynamic operation is entire removal of walls, then extensive state variables of the composed system are the respective sums of those of the component systems. This is called the additivity of extensive variables. | 7 | Physical Chemistry |
NSAIDs such as ibuprofen work by inhibiting the cyclooxygenase (COX) enzymes, which convert arachidonic acid to prostaglandin H (PGH). PGH, in turn, is converted by other enzymes to several other prostaglandins (which are mediators of pain, inflammation, and fever) and to thromboxane A (which stimulates platelet aggregation, leading to the formation of blood clots).
Like aspirin and indomethacin, ibuprofen is a nonselective COX inhibitor, in that it inhibits two isoforms of cyclooxygenase, COX-1 and COX-2. The analgesic, antipyretic, and anti-inflammatory activity of NSAIDs appears to operate mainly through inhibition of COX-2, which decreases the synthesis of prostaglandins involved in mediating inflammation, pain, fever, and swelling. Antipyretic effects may be due to action on the hypothalamus, resulting in an increased peripheral blood flow, vasodilation, and subsequent heat dissipation. Inhibition of COX-1 instead would be responsible for unwanted effects on the gastrointestinal tract. However, the role of the individual COX isoforms in the analgesic, anti-inflammatory, and gastric damage effects of NSAIDs is uncertain, and different compounds cause different degrees of analgesia and gastric damage.
Ibuprofen is administered as a racemic mixture. The R-enantiomer undergoes extensive interconversion to the S-enantiomer in vivo. The S-enantiomer is believed to be the more pharmacologically active enantiomer. The R-enantiomer is converted through a series of three main enzymes. These enzymes include acyl-CoA-synthetase, which converts the R-enantiomer to (−)-R-ibuprofen I-CoA; 2-arylpropionyl-CoA epimerase, which converts (−)-R-ibuprofen I-CoA to (+)-S-ibuprofen I-CoA; and hydrolase, which converts (+)-S-ibuprofen I-CoA to the S-enantiomer. In addition to the conversion of ibuprofen to the S-enantiomer, the body can metabolize ibuprofen to several other compounds, including numerous hydroxyl, carboxyl and glucuronyl metabolites. Virtually all of these have no pharmacological effects.
Unlike most other NSAIDs, ibuprofen also acts as an inhibitor of Rho kinase and may be useful in recovery from spinal-cord injury. Another unusual activity is inhibition of the sweet taste receptor. | 4 | Stereochemistry |
The ECW model created by Russell S. Drago is a quantitative model that describes and predicts the strength of Lewis acid base interactions, . The model assigned and parameters to many Lewis acids and bases. Each acid is characterized by an and a . Each base is likewise characterized by its own and . The and parameters refer, respectively, to the electrostatic and covalent contributions to the strength of the bonds that the acid and base will form. The equation is
The term represents a constant energy contribution for acid–base reaction such as the cleavage of a dimeric acid or base. The equation predicts reversal of acids and base strengths. The graphical presentations of the equation show that there is no single order of Lewis base strengths or Lewis acid strengths. | 7 | Physical Chemistry |
The IX Brigade, led by Okladnikov, worked in the Greater Balkan region of Turkmenistan, and in the plateau of Krasnovodsk. The finds at the Jebel rock shelter site near the Caspian Sea on the southwestern end of the Uly Balkan massif was a stratigraphic sequence of Mesolithic and Neolithic deposits, considered a model for the Turkmenistan Caspian Mesolithic period.
Two other sites, located in the southern escarpments of the Greater Balkan, were examined in great detail by G. E. Markov of Moscow State University; these were the Mesolithic sites of Dam-Dam Cheshme 1 and 2.
The XIV Brigade occurred in 1952 and researched primitive settled-agriculturalist settlement attributed to the Copper and Bronze periods. | 8 | Metallurgy |
In general, most hydroamination catalysts require elevated temperatures to function efficiently, and as such, only the thermodynamic product is observed. The isolation and characterization of the rarer and more synthetically valuable kinetic allyl amine product was reported when allenes was used at the unsaturated substrate. One system utilized temperatures of 80 °C with a rhodium catalyst and aniline derivatives as the amine. The other reported system utilized a palladium catalyst at room temperature with a wide range of primary and secondary cyclic and acyclic amines. Both systems produced the desired allyl amines in high yield, which contain an alkene that can be further functionalized through traditional organic reactions. | 0 | Organic Chemistry |
The human hNanog protein coded by the NANOG gene, consists of 305 amino acids and possesses 3 functional domains: the N-terminal domain, the C- terminal domain, and the conserved homeodomain motif. The homeodomain region facilitates DNA binding. The NANOG is located on chromosome 12, and the mRNA contains a 915 bp open reading frame (ORF) with 4 exons and 3 introns.
The N-terminal region of hNanog is rich in serine, threonine and proline residues, and the C-terminus contains a tryptophan-rich domain. The homeodomain in hNANOG ranges from residues 95 to 155. There are also additional NANOG genes (NANOG2, NANOG p8) which potentially affect ESCs differentiation. Scientists have shown that NANOG' is fundamental for self-renewal and pluripotency, and NANOG p8 is highly expressed in cancer cells. | 1 | Biochemistry |
Escape and radiate coevolution is a hypothesis proposing that a coevolutionary arms-race between primary producers and their consumers contributes to the diversification of species by accelerating speciation rates. The hypothesized process involves the evolution of novel defenses in the host, allowing it to "escape" and then "radiate" into differing species. | 1 | Biochemistry |
The TGF-β pathway regulates many cellular processes in developing embryo and adult organisms, including cell growth, differentiation, apoptosis, and homeostasis. There are five kinds of type II receptors and seven types of type I receptors in humans and other mammals. These receptors are known as "dual-specificity kinases" because their cytoplasmic kinase domain has weak tyrosine kinase activity but strong serine/threonine kinase activity. When a TGF-β superfamily ligand binds to the type II receptor, it recruits a type I receptor and activates it by phosphorylating the serine or threonine residues of its "GS" box. This forms an activation complex that can then phosphorylate SMAD proteins. | 1 | Biochemistry |
Chemotronics is an intersection field of chemistry (especially electrochemistry) and electronics dealing with the design of electrochemical and optical chemical sensors. One of pioneers of this field was Alexander Frumkin. | 3 | Analytical Chemistry |
Rust removal from small iron or steel objects by electrolysis can be done in a home workshop using simple materials such as a plastic bucket filled with an electrolyte consisting of washing soda dissolved in tap water, a length of rebar suspended vertically in the solution to act as an anode, another laid across the top of the bucket to act as a support for suspending the object, baling wire to suspend the object in the solution from the horizontal rebar, and a battery charger as a power source in which the positive terminal is clamped to the anode and the negative terminal is clamped to the object to be treated which becomes the cathode. Hydrogen and oxygen gases are produced at the cathode and annode respectively. This mixture is flammable/explosive. Care should also be taken to avoid hydrogen embrittlement. Overvoltage also produces small amounts of ozone, which is highly toxic, so a low voltage phone charger is a far safer source of DC current. Hydrogens effects on global warming have also recently come under scrutiny.
Rust may be treated with commercial products known as rust converter which contain tannic acid or phosphoric acid which combines with rust; removed with organic acids like citric acid and vinegar or the stronger hydrochloric acid; or removed with chelating agents as in some commercial formulations or even a solution of molasses. | 8 | Metallurgy |
The term photoprotein was first used to describe the unusual chemistry of the luminescent system of Chaetopterus (a marine Polychaete worm). This was meant to distinguish them from other light-producing proteins because these do not exhibit the usual luciferin-luciferase reaction. | 1 | Biochemistry |
Tautomers are structural isomers which readily interconvert, so that two or more species co-exist in equilibrium such as
Important examples are keto-enol tautomerism and the equilibrium between neutral and zwitterionic forms of an amino acid. | 4 | Stereochemistry |
STAT3 is a member of the STAT protein family. In response to cytokines and growth factors, STAT3 is phosphorylated by receptor-associated Janus kinases (JAK), forms homo- or heterodimers, and translocates to the cell nucleus where it acts as a transcription activator. Specifically, STAT3 becomes activated after phosphorylation of tyrosine 705 in response to such ligands as interferons, epidermal growth factor (EGF), interleukin (IL-)5 and IL-6. Additionally, activation of STAT3 may occur via phosphorylation of serine 727 by mitogen-activated protein kinases (MAPK) and through c-src non-receptor tyrosine kinase. STAT3 mediates the expression of a variety of genes in response to cell stimuli, and thus plays a key role in many cellular processes such as cell growth and apoptosis.
STAT3-deficient mouse embryos cannot develop beyond embryonic day 7, when gastrulation begins. It appears that at these early stages of development, STAT3 activation is required for self-renewal of embryonic stem cells (ESCs). Indeed, LIF, which is supplied to murine ESC cultures to maintain their undifferentiated state, can be omitted if STAT3 is activated through some other means.
STAT3 is essential for the differentiation of the TH17 helper T cells, which have been implicated in a variety of autoimmune diseases. During viral infection, mice lacking STAT3 in T-cells display impairment in the ability to generate T-follicular helper (Tfh) cells and fail to maintain antibody based immunity.
STAT3 caused upregulation in E-selectin, a factor in metastasis of cancers.
Hyperactivation of STAT3 occurs in COVID-19 infection and other viral infections. | 1 | Biochemistry |
In atomic, molecular, and optical physics, a magneto-optical trap (MOT) is an apparatus which uses laser cooling and a spatially-varying magnetic field to create a trap which can produce samples of cold, neutral atoms. Temperatures achieved in a MOT can be as low as several microkelvin, depending on the atomic species, which is two or three times below the photon recoil limit. However, for atoms with an unresolved hyperfine structure, such as , the temperature achieved in a MOT will be higher than the Doppler cooling limit.
A MOT is formed from the intersection of a weak, quadrupolar, spatially-varying magnetic field and six circularly-polarized, red-detuned, optical molasses beams. As atoms travel away from the field zero at the center of the trap (halfway between the coils), the spatially-varying Zeeman shift brings an atomic transition into resonance which gives rise to a scattering force that pushes the atoms back towards the center of the trap. This is why a MOT traps atoms, and because this force arises from photon scattering in which atoms receive momentum "kicks" in the direction opposite their motion, it also slows the atoms (i.e. cools them), on average, over repeated absorption and spontaneous emission cycles. In this way, a MOT is able to trap and cool atoms with initial velocities of hundreds of meters per second down to tens of centimeters per second (again, depending upon the atomic species).
Although charged particles can be trapped using a Penning trap or a Paul trap using a combination of electric and magnetic fields, those traps are ineffective for neutral atoms. | 7 | Physical Chemistry |
Ketene is produced on a commercial scale by thermal dehydration of acetic acid. Substituted ketenes can be prepared from acyl chlorides by an elimination reaction in which HCl is lost:
In this reaction, a base, usually triethylamine, removes the acidic proton alpha to the carbonyl group, inducing the formation of the carbon-carbon double bond and the loss of a chloride ion:
Ketenes can also be formed from α-diazoketones by the Wolff rearrangement.
Another way to generate ketenes is through flash vacuum thermolysis (FVT) with 2-pyridylamines. Plüg and Wentrup developed a method in 1997 that improved on FVT reactions to produce ketenes with a stable FVT that is moisture insensitive, using mild conditions (480 °C). The N-pyridylamines are prepared via a condensation with R-malonates with N-amino(pyridene) and DCC as the solvent.
A more robust method for preparing ketenes is the carbonylation of metal-carbenes, and in situ reaction of the thus produced highly reactive ketenes with suitable reagents such as imines, amines, or alcohols. This method is an efficient one‐pot tandem protocol of the carbonylation of α‐diazocarbonyl compounds and a variety of N‐tosylhydrazones catalysed by Co(II)–porphyrin metalloradicals leading to the formation of ketenes, which subsequently react with a variety of nucleophiles and imines to form esters, amides and β‐lactams. This system has a broad substrate scope and can be applied to various combinations of carbene precursors, nucleophiles and imines. | 0 | Organic Chemistry |
In 2009 the Chesapeake Bay Foundation (CBF) filed suit against EPA for its failure to finalize a total maximum daily load (TMDL) ruling for the bay, pursuant to the Clean Water Act. The TMDL would restrict water pollution from farms, land development, power plants and sewage treatment plants. EPA, which had been working with the states on various components of the TMDL since the 1980s (e.g. water quality criteria, standards for individual tributaries, improvements in data gathering and modeling techniques), agreed to settle the lawsuit and issued its TMDL for nitrogen, phosphorus and sediment pollution on December 29, 2010. This was the largest, most complex TMDL document that EPA had issued to date. The TMDL was challenged in litigation by the agriculture and construction industries, but EPA's document was upheld by the courts.
In 2020 the CBF filed another lawsuit against EPA for its failure to require the states of New York and Pennsylvania to comply with their TMDL goals and reduce pollution in the bay.
EPAs 2010 TMDL document requires all states in the bay watershed region to develop detailed implementation plans for pollutant reduction. The states have been developing their plans for years, in many cases building upon restoration projects that they had initiated before EPAs TMDL was finalized. These plans are long and complex, involving regular consultation with many stakeholders (i.e. governments, industry, agriculture, citizen groups). The plans include multiple milestone goals for project initiation or continued progress in water quality, through the use of pollution control upgrades (such as at sewage treatment plants) and more widespread utilization of various best management practices (BMPs). The BMPs are designed for specific sites to control pollution from nonpoint sources, principally agriculture, land development and urban runoff. For example, a farmer may install vegetated stream buffers along a stream bank to reduce runoff of sediment, nutrients and other pollutants. A land developer may install stormwater management facilities such as infiltration basins or constructed wetlands during the construction of housing or commercial buildings.
In 2011 both Maryland and Virginia enacted laws to reduce the effects of lawn fertilizer use, by restricting nitrogen and phosphorus content. The Virginia law also banned deicers containing urea, nitrogen or phosphorus.
Installation of stormwater management facilities is already a requirement for most new construction projects in the bay region, under various state and local government requirements. These facilities reduce erosion and keep sediment and other pollutants from entering tributaries and the bay. However retrofitting such facilities into existing developed areas is often expensive due to high land costs, or difficult to install among existing structures. As a result, the extent of such retrofit projects in the bay region has been limited. | 2 | Environmental Chemistry |
Polyurea and polyurethane are copolymers used in the manufacture of spandex, which was invented in 1959.
Polyurea was originally developed in automotive applications in the 1980s but other applications such as protecting tabletop edges followed. Its fast reactivity and relative moisture insensitivity made it useful for coatings on large surface area projects, such as secondary containment, manhole and tunnel coatings, tank liners, and truck bed liners. Excellent adhesion to concrete and steel is obtained with the proper primer and surface treatment. They can also be used for spray molding and armor. Some polyureas reach strengths of 40 MPa (6000 psi) tensile and over 500% elongation making it a tough coating. The quick cure time allows many coats to be built up quickly. The high strength and high impact resistance of polyurea coatings is a key reason for their use.
In 2014, a polyurea elastomer-based material was shown to be self-healing, melding together after being cut in half. The material also includes inexpensive commercially available compounds. The elastomer molecules were tweaked, making the bonds between them longer. The resulting molecules are easier to pull apart from one another and better able to rebond at room temperature with almost the same strength. The rebonding can be repeated. Elastic, self-healing paints and other coatings recently took a step closer to common use, thanks to research being conducted at the University of Illinois. Scientists there have used "off-the-shelf" components to create a polymer that melds back together after being cut in half, without the addition of other chemicals.
Polyurea has become a preferred long term solution for narrowboats. The traditional coating with bitumen, known as "blacking" is being replaced with the practice of polyurea coatings. The clearest advantage is that it is not necessary to reapply a coat every 3–4 years. It is thought that polyurea coatings last 25–30 years.
Commercial trademarks for Polyurea include Line-X, GLS 100R, and Pentens SPU-1000, to name a few. There are multiple possible polyurea formulations. The Polyurea Development Association is a trade association that represents the interests of polyurea coating manufacturers. | 7 | Physical Chemistry |
This form factor is useful for any application where the spectrum analyzer needs to be very light and small. Handheld analyzers usually offer a limited capability relative to larger systems. Attributes that contribute to a useful handheld spectrum analyzer include:
*Very low power consumption.
*Battery-powered operation while in the field to allow the user to move freely outside.
*Very small size
*Light weight (usually less than ). | 7 | Physical Chemistry |
Initial treatment can involve placing the object in a desiccating environment. Deprived of water, the reaction cannot continue. However, re-exposure of the object to even atmospheric water can restart the process. Bronze disease remains an active area of research within object conservation. | 8 | Metallurgy |
*ANXA6
*ANXA7
*ARPC1A Actin-related peptide
*ARPC2
*ARPC5L
*CAPZA2
*CAPZB
*RHOA also implicated in regulation of cell cycle
*RHOB
*RHOT1 mitochondrial trafficking
*RHOT2
*TUBB Tubulin, beta polypeptide
*WDR1 actin disassembly? | 1 | Biochemistry |
The N-Acetylglucosamine (GlcNAc) receptor has been recently found to interact and bind with vimentins at the cell surface. Research indicates that the GlcNAc receptor can therefore be used to target vimentin-expressing cells for gene delivery via receptor-mediated endocytosis. | 1 | Biochemistry |
Viral genes are expressed through the use of the host cells replication machinery; therefore, many viral genes have promoters that support binding of many transcription factors found naturally in the host cells. These transcription factors along with the virus own proteins can repress or activate genes from both the virus and the host cells genome. Many viruses can also increase the production of the cells regulatory proteins. | 1 | Biochemistry |
The most economical source of carbon for recycling into fuel is flue-gas emissions from fossil-fuel combustion where it can be obtained for about US$7.50 per ton. However, this is not carbon-neutral, since the carbon is of fossil origin, therefore moving carbon from the geosphere to the atmosphere. Since carbonic acid in seawater is in chemical equilibrium with atmospheric carbon dioxide, extraction of carbon from seawater has been studied. Researchers have estimated that carbon extraction from seawater would cost about $50 per ton. Carbon capture from ambient air is more costly, at between $94 and $232 per ton and is considered impractical for fuel synthesis or carbon sequestration. Direct air capture is less developed than other methods. Proposals for this method involve using a caustic chemical to react with carbon dioxide in the air to produce carbonates. These can then be broken down and hydrated to release pure CO gas and regenerate the caustic chemical. This process requires more energy than other methods because carbon dioxide is at much lower concentrations in the atmosphere than in other sources.
Researchers have also suggested using biomass as a carbon source for fuel production. Adding hydrogen to the biomass would reduce its carbon to produce fuel. This method has the advantage of using plant matter to cheaply capture carbon dioxide. The plants also add some chemical energy to the fuel from biological molecules. This may be a more efficient use of biomass than conventional biofuel because it uses most of the carbon and chemical energy from the biomass instead of releasing as much energy and carbon. Its main disadvantage is, as with conventional ethanol production, it competes with food production. | 0 | Organic Chemistry |
Zircon (ZrSiO) is commonly found in felsic igneous rock. Because both Ce and Ce can substitute for zirconium, Zircon often has a positive Ce anomaly. Ce substitutes with Zr much more easily than Ce because Ce (ionic radius 0.97Å) has the same charge and a similar ionic radius as Zr (ionic radius 0.84Å). Therefore, the oxidation state of the magma is what determines the Ce anomaly in Zircon. If the oxygen fugacity is high, more Ce will oxidize to Ce and create a larger positive Ce anomaly in the zircon structure. At lower levels of oxygen fugacity, the level of Ce anomaly will also be lower. | 9 | Geochemistry |
Linear PPA is produced by anionic polymerization methods using a strong nucleophile as an initiator. This technique prevents the cyclization of the polymer chain as the propagating species have only one charged terminus that cannot backbite the other terminus which, in turn, is neutral in charge. Although processing linear PPA requires highly sensitive reaction conditions and is more time demanding, this type of polymer has many advantages over its cyclic counterpart. For instance, a control over the polymer's molar mass can easily be achieved by controlling the monomer and alcohol initiator ratios. Furthermore, it has been proven to be more thermally stable than its cyclic counterpart due to the presence of functionalized endcaps that stabilizes the polymer chain from depolymerization. For these reasons, it has been studied to a far greater extent than cyclic PPA. Various linear PPA with distinct end groups have been reported and studied for a variety of applications including sensing, drug delivery, and lithography. For instance, once these end groups are cleaved as a response to the exposure of PPA to a specific stimulus, the polymer will sequentially disassemble from head to tail through an unzipping reaction to form the monomer in short times that can be as low as a few minutes. | 7 | Physical Chemistry |
Base-promoted epoxide isomerization is the conversion of alkyl epoxides to ring-opened products through the action of strong base. Isomerizations of this type are most often used to synthesize allylic alcohols, although other products are possible. | 0 | Organic Chemistry |
Some trace fossils can be used as local index fossils, to date the rocks in which they are found, such as the burrow Arenicolites franconicus which occurs only in a layer of the Triassic Muschelkalk epoch, throughout wide areas in southern Germany.
The base of the Cambrian period is defined by the first appearance of the trace fossil Treptichnus pedum.
Trace fossils have a further utility, as many appear before the organism thought to create them, extending their stratigraphic range. | 2 | Environmental Chemistry |
Accurate determination of core temperature often requires a special low temperature thermometer, as most clinical thermometers do not measure accurately below . A low temperature thermometer can be placed in the rectum, esophagus or bladder. Esophageal measurements are the most accurate and are recommended once a person is intubated. Other methods of measurement such as in the mouth, under the arm, or using an infrared ear thermometer are often not accurate.
As a hypothermic person's heart rate may be very slow, prolonged feeling for a pulse could be required before detecting. In 2005, the American Heart Association recommended at least 30–45 seconds to verify the absence of a pulse before initiating CPR. Others recommend a 60-second check.
The classical ECG finding of hypothermia is the Osborn J wave. Also, ventricular fibrillation frequently occurs below and asystole below . The Osborn J may look very similar to those of an acute ST elevation myocardial infarction. Thrombolysis as a reaction to the presence of Osborn J waves is not indicated, as it would only worsen the underlying coagulopathy caused by hypothermia. | 1 | Biochemistry |
Capnellene derivatives have recently been identified as possible treatments for neuropathic pain. Neuropathic pain is characterized by damage to peripheral or central nerves that results in pathological nociceptive transmission, the neuronal process that responds noxious stimuli. Two capnellene derivatives Δ-capnellene-8β,10α-diol and 8α-acetoxy-Δ-capnellene-10α-ol demonstrate potential as analgesics capable of attenuating neuropathic pain. These compounds have been shown in vivo to reduce two proteins that mediate inflammation, cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). In vivo, Δ-capnellene-8β,10α-diol inhibited hyperalgesia behavior in the mouse model for neuropathic pain in a dose-dependent manner. Additionally, treatment with Δ-capnellene-8β,10α-diol inhibited the up-regulation of immunoreactivity in the mouse model, specifically targeting the production of COX-2. Unlike many non-steroidal anti-inflammatory drugs, Δ-capnellene-8β,10α-diol is advantageous in its selectivity for the COX isoenzyme COX-2, avoiding many of the gastrointestinal side effects associated with the inhibition of COX-1. This fact would allow for the administration of Δ-capnellene-8β,10α-diol in higher doses, potentially offering significant relief from neuropathic pain. | 0 | Organic Chemistry |
Men have a V̇O max that is 26% higher (6.6 mL/(kg·min)) than women for treadmill and 37.9% higher (7.6 mL/(kg·min)) than women for cycle ergometer on average. V̇O max is on average 22% higher (4.5 mL/(kg·min)) when measured using a cycle ergometer compared with a treadmill. | 1 | Biochemistry |
In general, enols are less stable than their keto equivalents because of the favorability of the C=O double bond over C=C double bond. However, enols can be stabilized kinetically or thermodynamically.
Some enols are sufficiently stabilized kinetically so that they can be characterized.
Delocalization can stabilize the enol tautomer. Thus, very stable enols are phenols. Another stabilizing factor in 1,3-dicarbonyls is intramolecular hydrogen bonding. Both of these factors influence the enol-dione equilibrium in acetylacetone. | 0 | Organic Chemistry |
*Acetyl-CoA
*fatty acyl-CoA (activated form of all fatty acids; only the CoA esters are substrates for important reactions such as mono-, di-, and triacylglycerol synthesis, carnitine palmitoyl transferase, and cholesterol esterification)
**Propionyl-CoA
**Butyryl-CoA
**Myristoyl-CoA
**Crotonyl-CoA
*Acetoacetyl-CoA
*Coumaroyl-CoA (used in flavonoid and stilbenoid biosynthesis)
*Benzoyl-CoA
*Phenylacetyl-CoA
* Acyl derived from dicarboxylic acids
**Malonyl-CoA (important in chain elongation in fatty acid biosynthesis and polyketide biosynthesis)
**Succinyl-CoA (used in heme biosynthesis)
**Hydroxymethylglutaryl-CoA (used in isoprenoid biosynthesis)
**Pimelyl-CoA (used in biotin biosynthesis) | 1 | Biochemistry |
Symmetries in nature lead directly to conservation laws, something which is precisely formulated by Noether's theorem.
The basic idea of time-translation symmetry is that a translation in time has no effect on physical laws, i.e. that the laws of nature that apply today were the same in the past and will be the same in the future. This symmetry implies the conservation of energy. | 3 | Analytical Chemistry |
Due to it being a lesser understood post-translational modification, arginylation and its regulation in vivo still remains largely esoteric. The expression of ATE1 can vary significantly within different tissues, but its levels within these tissues peak at mid-development but begin to decline as an organism ages. It has also been observed that a variety of physiological compounds and drugs are able to affect the incorporation of arginine in vivo, but it is hypothesized that this occurs in a non-specific manner. As such, it has been theorized that inhibitors and activators which regulate ATE1 activity, and therefore arginylation, may exist in vivo.
Arginylation's ability to make proteins metabolically unstable, as observed in yeast, makes proteins which have been modified in this way an attractive target for removal. One of the well characterized arginylation regulators is the ubiquitin dependent protein degradation which quickly degrades and removes harmful proteins. This important regulator of arginylation facilitates the specificity of this post-translational modification and efficiently removes proteins which were not meant to be arginylated in vivo.
Lastly, an unproven but highly attractive mechanism of regulating arginylation in vivo suggests the use of de-arginylation enzymes which may be able to remove an arginine that has been added post-translationally to proteins. Enzymes such as Aminopeptidase B and Carboxypeptidase B are able to remove arginine from a proteins N-terminus and from side chain carboxyl groups, respectively, but do not specifically target arginylated sites. The proposed de-arginylation enzymes are theorized to act in the same way as the previously mentioned enzymes Aminopeptidase B and Carboxypeptidase B, but would differ in the fact that they specifically target arginylated protein substrates. Although these enzymes have not been discovered as of yet, the search for and discovery of these enzymes is an exciting path for further studies. | 1 | Biochemistry |
Spegatrine is an α- and α-adrenergic receptor antagonist isolated from Rauvolfia verticillata. Its dimer dispegatrine has greater antagonist affinity for α-adrenergic receptors. | 0 | Organic Chemistry |
Mutations in this gene are associated with glycogen storage disease type IV (also known as Andersen's disease) in newborns and with adult polyglucosan body disease.
Approximately 40 mutations in the GBE1 gene, most resulting in a point mutation in the glycogen branching enzyme, have led to the early childhood disorder, glycogen storage disease type IV (GSD IV). This disease is characterized by a severe depletion or complete absence of GBE, resulting in the accumulation of abnormally structured glycogen, known as polyglucosan bodies. Glycogen buildup leads to increased osmotic pressure resulting in cellular swelling and death. The tissues most affected by this disease are the liver, heart, and neuromuscular system, areas with the greatest levels of glycogen accumulation. Abnormal glycogen buildup in the liver interferes with liver functioning and can result in an enlarged liver and liver disease. In muscles, the inability of cells to efficiently breakdown glycogen due to the severe reduction or absence of branching can lead to muscle weakness and atrophy.
At least three mutations in the GBE1 gene have been found to cause another disease called adult polyglucosan body disease (APBD). While in GSD IV GBE activity is undetectable or minimally detectable, APBD is characterized by reduced or even normal GBE activity. In this disease, abnormal glycogen can build up in neurons leading to a spectrum of problems. Specifically, some disease characteristics are gait difficulties from mixed upper and lower motor neuron involvement sensory loss in lower extremities, and neurogenic bladder, a problem in which a person lacks bladder control due to a brain, spinal cord, or nerve condition. | 1 | Biochemistry |
Tarnish is a product of a chemical reaction between a metal and a nonmetal compound, especially oxygen and sulfur dioxide. It is usually a metal oxide, the product of oxidation; sometimes it is a metal sulfide. The metal oxide sometimes reacts with water to make the hydroxide, or with carbon dioxide to make the carbonate. It is a chemical change. There are various methods to prevent metals from tarnishing. | 8 | Metallurgy |
Mostly, SIRs have been investigated and used for the recovery of heavy metals. Applications include the removal of cadmium, vanadium, copper, chrome, iridium, etc. | 3 | Analytical Chemistry |
In cooperation with the chemical company BASF, Ralf Reski and coworkers established a collection of knockout mosses to use for gene identification. | 1 | Biochemistry |
Keesom forces, also known as dipole–dipole interactions, result from two molecules that have permanent dipoles due to electronegativity differences between atoms in the molecule. This dipole causes a coulombic attraction between the two molecules. | 6 | Supramolecular Chemistry |
In organic chemistry, a lactol is a functional group which is the cyclic equivalent of a hemiacetal () or a hemiketal ().
The compound is formed by the intramolecular, nucleophilic addition of a hydroxyl group () to the carbonyl group () of an aldehyde () or a ketone ().
A lactol is often found as an equilibrium mixture with the corresponding hydroxyaldehyde. The equilibrium can favor either direction depending on ring size and other conformational effects.
The lactol functional group is prevalent in nature as component of aldose sugars. | 0 | Organic Chemistry |
The KRAB domain had initially been identified in 1988 as a periodic array of leucine residues separated by six amino acids 5’ to the zinc finger region of KOX1/ZNF10 coined heptad repeat of leucines (also known as a leucine zipper). Later, this domain was named in association with the C2H2-Zinc finger proteins Krüppel associated box (KRAB). The KRAB domain is confined to genomes from tetrapod organisms. The KRAB containing C2H2-ZNF genes constitute the largest sub-family of zinc finger genes. More than half of the C2H2-ZNF genes are associated with a KRAB domain in the human genome. They are more prone to clustering and are found in large clusters on the human genome.
The KRAB domain presents one of the strongest repressors in the human genome. Once the KRAB domain was fused to the tetracycline repressor (TetR), the TetR-KRAB fusion proteins were the first engineered drug-inducible repressor that worked in mammalian cells. Two distinct types of KRAB A domains can be structurally and functionally distinguished. Ancestral KRAB A domains present in human PDRM9 proteins are even evolutionary conserved in mussel genomes. Modern KRAB A domain sequences are found in coelacanth latimeria chalumnae and in Lungfish genomes. | 1 | Biochemistry |
The electron transport chain of green sulfur bacteria—such as is present in the model organism Chlorobaculum tepidum—uses the reaction center bacteriochlorophyll pair, P840. When light is absorbed by the reaction center, P840 enters an excited state with a large negative reduction potential, and so readily donates the electron to bacteriochlorophyll 663, which passes it on down an electron transport chain. The electron is transferred through a series of electron carriers and complexes until it is used to reduce NAD to NADH. P840 regeneration is accomplished with the oxidation of a sulfide ion from hydrogen sulfide (or of hydrogen or ferrous iron) by cytochrome c. | 5 | Photochemistry |
In terms of molecular structure, one distinguishes first between low-molecular-weight (LMW) and high-molecular-weight (HMW) products. The generally accepted threshold between LMW and HMW is a molecular weight of about 700. LMW fine chemicals, also designated as small molecules, are produced by traditional chemical synthesis, by microorganisms (fermentation or biotransformation), or by extraction from plants and animals. In the production of modern life science products, total synthesis from petrochemicals prevails. The HMW products, respectively large molecules, are obtained mainly through biotechnology processes. Within LMWs, the N-heterocyclic compounds are the most important category; within HMWs they are the peptides and proteins. | 0 | Organic Chemistry |
The SKP technique is based on parallel plate capacitor experiments performed by Lord Kelvin in 1898. In the 1930s William Zisman built upon Lord Kelvin's experiments to develop a technique to measure contact potential differences of dissimilar metals. | 7 | Physical Chemistry |
High concentrations of aldehydes tend to be very pungent and overwhelming, but low concentrations can evoke a wide range of aromas.
* Acetaldehyde (ethereal)
* Hexanal (green, grassy)
* cis-3-Hexenal (green tomatoes)
* Furfural (burnt oats)
* Hexyl cinnamaldehyde
* Isovaleraldehyde – nutty, fruity, cocoa-like
* Anisic aldehyde – floral, sweet, hawthorn. It is a crucial component of chocolate, vanilla, strawberry, raspberry, apricot, and others.
* Cuminaldehyde (4-propan-2-ylbenzaldehyde) – Spicy, cumin-like, green | 0 | Organic Chemistry |
For an infinite two-dimensional lattice, defined by its primitive vectors , its reciprocal lattice can be determined by generating its two reciprocal primitive vectors, through the following formulae,
where is an integer and
Here represents a 90 degree rotation matrix, i.e. a quarter turn. The anti-clockwise rotation and the clockwise rotation can both be used to determine the reciprocal lattice: If is the anti-clockwise rotation and is the clockwise rotation, for all vectors . Thus, using the permutation
we obtain
Notably, in a 3D space this 2D reciprocal lattice is an infinitely extended set of Bragg rods—described by Sung et al. | 3 | Analytical Chemistry |
The IAGC (International Association of GeoChemistry, formerly known as the International Association of Geochemistry and Cosmochemistry) is affiliated with the International Union of Geological Sciences and has been one of the pre-eminent international geochemical organizations for over thirty-five years.
The principal objective of the IAGC is to foster co-operation in, and advancement of, geochemistry in the broadest sense. This is achieved by:
# working with any interested group in planning symposia and other types of meetings related to geochemistry,
# sponsoring publications in geochemistry of a type not normally covered by existing organizations and,
# the activities of working groups which study problems that require, or would benefit from, international co-operation.
The scientific thrust of the IAGC takes place through its Working Groups (many of which organize regular symposia) and the official journal, Applied Geochemistry.
The specific objectives of the IAGC are:
# To foster the use of the tools and techniques of chemistry to advance the understanding of the earth and its component systems for the benefit of mankind and modern society;
# To contribute to advancement in geochemical research throughout the world, including both fundamental geochemical research aimed at understanding the global earth system and applied geochemical research that addresses problems of particular relevance to the welfare of mankind and society;
# To promote international and education cooperation in geochemistry through outreach activities that include:
#* establishing internal specialty-area working groups in topic areas that would benefit from international scientific cooperation,
#* sponsoring international scientific meetings related to geochemistry,
#* disseminating new knowledge through publication of the journal “Applied Geochemistry,”
#* fostering communication in geochemistry across the international scientific community,
#* encouraging the early career development of young geochemists,
#* contributing to geochemical education,
#* enhancing the visibility of the science of geochemistry and demonstrating its importance to mankind and society. | 9 | Geochemistry |
Vladimir Vasilyevich Markovnikov, also Markownikoff (; – 11 February 1904) was a Russian chemist, best known for having developed the Markovnikov's rule, that describes addition reactions of hydrogen halides and alkenes. | 0 | Organic Chemistry |
Dye sensitised solar cells operate as a photoanode (n-DSC), where photocurrent result from electron injection by the sensitized dye. Photocathodes (p-DSCs) operate in an inverse mode compared to the conventional n-DSC, where dye-excitation is followed by rapid electron transfer from a p-type semiconductor to the dye (dye-sensitized hole injection, instead of electron injection). Such p-DSCs and n-DSCs can be combined to construct tandem solar cells (pn-DSCs) and the theoretical efficiency of tandem DSCs is well beyond that of single-junction DSCs.
A standard tandem cell consists of one n-DSC and one p-DSC in a simple sandwich configuration with an intermediate electrolyte layer. n-DSC and p-DSC are connected in series, which implies that the resulting photocurrent will be controlled by the weakest photoelectrode, whereas photovoltages are additive. Thus, photocurrent matching is very important for the construction of highly efficient tandem pn-DSCs. However, unlike n-DSCs, fast charge recombination following dye-sensitized hole injection usually resulted in low photocurrents in p-DSC and thus hampered the efficiency of the overall device.
Researchers have found that using dyes comprising a perylenemonoimide (PMI) as the acceptor and an oligothiophene coupled to triphenylamine as the donor greatly improve the performance of p-DSC by reducing charge recombination rate following dye-sensitized hole injection. The researchers constructed a tandem DSC device with NiO on the p-DSC side and TiO on the n-DSC side. Photocurrent matching was achieved through adjustment of NiO and TiO film thicknesses to control the optical absorptions and therefore match the photocurrents of both electrodes. The energy conversion efficiency of the device is 1.91%, which exceeds the efficiency of its individual components, but is still much lower than that of high performance n-DSC devices (6%–11%). The results are still promising since the tandem DSC was in itself rudimentary. The dramatic improvement in performance in p-DSC can eventually lead to tandem devices with much greater efficiency than lone n-DSCs.
As previously mentioned, using a solid-state electrolyte has several advantages over a liquid system (such as no leakage and faster charge transport), which has also been realised for dye-sensitised photocathodes. Using electron transporting materials such as PCBM, TiO and ZnO instead of the conventional liquid redox couple electrolyte, researchers have managed to fabricate solid state p-DSCs (p-ssDSCs), aiming for solid state tandem dye sensitized solar cells, which have the potential to achieve much greater photovoltages than a liquid tandem device. | 5 | Photochemistry |
CDP includes three separate legal entities registered in the United Kingdom, Belgium and the United States of America. In the United Kingdom, CDP Worldwide is a charity registered with the Charity Commission for England and Wales. CDP Europe is a registered charity in Brussels, Belgium and Berlin, Germany. CDP North America, Inc is an independent 501(c)(3) entity based in New York City. The three entities have independent trustee boards. | 2 | Environmental Chemistry |
The ionic mechanism of oxidative addition is similar to the S2 type in that it involves the stepwise addition of two distinct ligand fragments. The key difference being that ionic mechanisms involve substrates which are dissociated in solution prior to any interactions with the metal center. An example of ionic oxidative addition is the addition of hydrogen chloride. | 0 | Organic Chemistry |
The physical properties of solids have been common subjects of scientific inquiry for centuries, but a separate field going by the name of solid-state physics did not emerge until the 1940s, in particular with the establishment of the Division of Solid State Physics (DSSP) within the American Physical Society. The DSSP catered to industrial physicists, and solid-state physics became associated with the technological applications made possible by research on solids. By the early 1960s, the DSSP was the largest division of the American Physical Society.
Large communities of solid state physicists also emerged in Europe after World War II, in particular in England, Germany, and the Soviet Union. In the United States and Europe, solid state became a prominent field through its investigations into semiconductors, superconductivity, nuclear magnetic resonance, and diverse other phenomena. During the early Cold War, research in solid state physics was often not restricted to solids, which led some physicists in the 1970s and 1980s to found the field of condensed matter physics, which organized around common techniques used to investigate solids, liquids, plasmas, and other complex matter. Today, solid-state physics is broadly considered to be the subfield of condensed matter physics, often referred to as hard condensed matter, that focuses on the properties of solids with regular crystal lattices. | 8 | Metallurgy |
GFAJ-1 is a strain of rod-shaped bacteria in the family Halomonadaceae. It is an extremophile that was isolated from the hypersaline and alkaline Mono Lake in eastern California by geobiologist Felisa Wolfe-Simon, a NASA research fellow in residence at the US Geological Survey. In a 2010 Science journal publication, the authors claimed that the microbe, when starved of phosphorus, is capable of substituting arsenic for a small percentage of its phosphorus to sustain its growth. Immediately after publication, other microbiologists and biochemists expressed doubt about this claim, which was robustly criticized in the scientific community. Subsequent independent studies published in 2012 found no detectable arsenate in the DNA of GFAJ-1, refuted the claim, and demonstrated that GFAJ-1 is simply an arsenate-resistant, phosphate-dependent organism. | 1 | Biochemistry |
Craftsmen and designers utilize copper's inherent benefits to build aesthetically pleasing and long-lasting building systems. From cathedrals to castles and from homes to offices, copper is used in many products: low-sloped and pitched roofs, soffits, fascias, flashings, gutters, downspouts, building expansion joints, domes, spires, and vaults. Copper is also used to clad walls and other surfaces in the exterior and interior environment. | 8 | Metallurgy |
The majority of systems utilize two two-cylinder piston pumps, one for each buffer, combining the output of both in a mixing chamber. Some simpler systems use a single peristaltic pump which draws both buffers from separate reservoirs through a proportioning valve and mixing chamber. In either case the system allows the fraction of each buffer entering the column to be continuously varied. The flow rate can go from a few milliliters per minute in bench-top systems to liters per minute for industrial scale purifications. The wide flow range makes it suitable both for analytical and preparative chromatography. | 3 | Analytical Chemistry |
Endothelium is a thin layer of simple squamous epithelial cells that line the interior of both blood and lymph vessels. The endothelium that lines blood vessels is known as vascular endothelium, which is subject to and must withstand the forces of blood flow and blood pressure from the cardiovascular system. To withstand these cardiovascular forces, endothelial cells must simultaneously have a structure capable of withstanding the forces of circulation while also maintaining a certain level of plasticity in the strength of their structure. This plasticity in the structural strength of the vascular endothelium is essential to overall function of the cardiovascular system. Endothelial cells within blood vessels can alter the strength of their structure to maintain the vascular tone of the blood vessel they line, prevent vascular rigidity, and even help to regulate blood pressure within the cardiovascular system. Endothelial cells accomplish these feats by using depolarization to alter their structural strength. When an endothelial cell undergoes depolarization, the result is a marked decrease in the rigidity and structural strength of the cell by altering the network of fibers that provide these cells with their structural support. Depolarization in vascular endothelium is essential not only to the structural integrity of endothelial cells, but also to the ability of the vascular endothelium to aid in the regulation of vascular tone, prevention of vascular rigidity, and the regulation of blood pressure. | 7 | Physical Chemistry |
The protein encoded by this gene contains a RING zinc finger, a motif known to be involved in protein-protein interactions. This protein interacts with androgen receptor (AR) and may function as a coactivator that induces AR target gene expression in prostate. A dominant negative mutant of this gene has been demonstrated to inhibit the AR-mediated growth of prostate cancer. This protein also interacts with class III ubiquitin-conjugating enzymes (E2s) and may act as a ubiquitin-ligase (E3) in the ubiquitination of certain nuclear proteins. Five alternatively spliced transcript variants encoding two distinct isoforms have been reported. Another function of RNF14 protein relates to its regulation of the inter-relationship between bioenergetic status and inflammation. It influences the expression of mitochondrial and immune-related genes in skeletal muscle including cytokines and interferon regulatory factors. | 1 | Biochemistry |
The ability of the immune system to recognize molecules that are broadly shared by pathogens is, in part, due to the presence of immune receptors called toll-like receptors (TLRs) that are expressed on the membranes of leukocytes including dendritic cells, macrophages, natural killer cells, cells of the adaptive immunity T cells, and B cells, and non-immune cells (epithelial and endothelial cells, and fibroblasts).
The binding of ligands - either in the form of adjuvant used in vaccinations or in the form of invasive moieties during times of natural infection - to the TLR marks the key molecular events that ultimately lead to innate immune responses and the development of antigen-specific acquired immunity.
Upon activation, TLRs recruit adaptor proteins (proteins that mediate other protein-protein interactions) within the cytosol of the immune cell to propagate the antigen-induced signal transduction pathway. These recruited proteins are then responsible for the subsequent activation of other downstream proteins, including protein kinases (IKKi, IRAK1, IRAK4, and TBK1) that further amplify the signal and ultimately lead to the upregulation or suppression of genes that orchestrate inflammatory responses and other transcriptional events. Some of these events lead to cytokine production, proliferation, and survival, while others lead to greater adaptive immunity. If the ligand is a bacterial factor, the pathogen might be phagocytosed and digested, and its antigens presented to CD4+ T cells.
In the case of a viral factor, the infected cell may shut off its protein synthesis and may undergo programmed cell death (apoptosis). Immune cells that have detected a virus may also release anti-viral factors such as interferons.
Toll-like receptors have also been shown to be an important link between innate and adaptive immunity through their presence in dendritic cells. Flagellin, a TLR5 ligand, induces cytokine secretion on interacting with TLR5 on human T cells. | 1 | Biochemistry |
Large amounts of macromolecules in a solution will alter the rates and equilibrium constants of enzyme reactions, through an effect called macromolecular crowding. | 1 | Biochemistry |
The sulfate anions reacting with different phases of the hardened cement paste (HCP) to form more voluminous reaction products can cause 3 types of expansive reactions called sulfate attack inside HCP:
# The delayed ettringite formation (DEF) also known as internal sulfate attack (ISA);
# The external sulfate attack (ESA), and;
# The thaumasite form of sulfate attack (TSA).
These three types of sulfate attack reactions are described into more details in specific sections latter in the text. When the hardened cement paste (HCP) is affected, the detrimental consequences for the structural stability of concrete structures are generally more severe than when aggregates are affected: DEF, ESA and TSA are much more damaging for concrete than ASR and ACR reactions.
A common points to all these various chemical expansive reaction is that they all require water as a reactant and as a reaction medium. The presence of water is always an aggravating factor. Concrete structures immersed in water as dams and bridge piles are therefore particularly sensitive. These reactions are also characterized by slow reaction kinetics, depending on environmental conditions such as temperature and relative humidity. They develop at a slow rate and may take several years before damages become apparent. Often a decade is needed to observe their harmful consequences. Protecting concrete structures from water contact may help to slow down the progression of the damages. | 8 | Metallurgy |
Fenfluramine is an indirect agonist of serotonin receptors. Fenfluramine binds to the serotonin transporter, blocking serotonin reuptake. However, fenfluramine also acts to induce non-exocytotic serotonin release; in a mechanism similar to that of methamphetamine in dopamine neurons, fenfluramine binds to VMAT2, disrupting the compartmentalization of serotonin into vesicles and increasing the concentration of cytoplasmic serotonin available for drug-induced release. | 1 | Biochemistry |
Some of the unsolved problems include:
* Off-target effects – The possibility of unwanted, likely harmful, changes to the genome present a large barrier to the widespread implementation of this technology. Improvements to the specificity of gRNAs and Cas enzymes present viable solutions to this issue as well as the refinement of the delivery method of CRISPR. It is likely that different diseases will benefit from different delivery methods.
* Short-lived nature – Before gene therapy can become a permanent cure for a condition, the therapeutic DNA introduced into target cells must remain functional and the cells containing the therapeutic DNA must be stable. Problems with integrating therapeutic DNA into the nuclear genome and the rapidly dividing nature of many cells prevent it from achieving long-term benefits. Patients require multiple treatments.
* Immune response – Any time a foreign object is introduced into human tissues, the immune system is stimulated to attack the invader. Stimulating the immune system in a way that reduces gene therapy effectiveness is possible. The immune system's enhanced response to viruses that it has seen before reduces the effectiveness to repeated treatments.
* Problems with viral vectors – Viral vectors carry the risks of toxicity, inflammatory responses, and gene control and targeting issues.
* Multigene disorders – Some commonly occurring disorders, such as heart disease, high blood pressure, Alzheimer's disease, arthritis, and diabetes, are affected by variations in multiple genes, which complicate gene therapy.
* Some therapies may breach the Weismann barrier (between soma and germ-line) protecting the testes, potentially modifying the germline, falling afoul of regulations in countries that prohibit the latter practice.
* Insertional mutagenesis – If the DNA is integrated in a sensitive spot in the genome, for example in a tumor suppressor gene, the therapy could induce a tumor. This has occurred in clinical trials for X-linked severe combined immunodeficiency (X-SCID) patients, in which hematopoietic stem cells were transduced with a corrective transgene using a retrovirus, and this led to the development of T cell leukemia in 3 of 20 patients. One possible solution is to add a functional tumor suppressor gene to the DNA to be integrated. This may be problematic since the longer the DNA is, the harder it is to integrate into cell genomes. CRISPR technology allows researchers to make much more precise genome changes at exact locations.
* Cost – Alipogene tiparvovec or Glybera, for example, at a cost of $1.6 million per patient, was reported in 2013, to be the world's most expensive drug. | 1 | Biochemistry |
In the Gusev crater of Mars, the Mars Exploration Rover Spirit inadvertently discovered opaline silica. One of its wheels had earlier become immobilized and thus was effectively trenching the Martian regolith as it dragged behind the traversing rover. Later analysis showed that the silica was evidence for hydrothermal conditions. | 1 | Biochemistry |
An intermediate stage in the process of eukaryotic RNA splicing is the formation of a lariat structure. It is anchored at an adenosine residue in intron between 10 and 50 nucleotides upstream of the 3' splice site. A short conserved sequence (the branch point sequence) functions as the recognition signal for the site of lariat formation. During the splicing process, this conserved sequence towards the end of the intron forms a lariat structure with the beginning of the intron. The final step of the splicing process occurs when the two exons are joined and the intron is released as a lariat RNA.
Several investigators found the branch point sequences in different organisms including yeast, human, fruit fly, rat, and plants. Senapathy found that, in all of these sequences, the codon ending at the branch point adenosine is consistently a stop codon. What is interesting is that two of the three stop codons (TAA and TGA) occur almost all of the time at this position.
These findings led Senapathy to propose that the branch point signal originated from stop codons. The finding that two different stop codons (TAA and TGA) occur within the lariat signal with the branching point as the third base of the stop codons corroborates this proposal. As the branching point of the lariat occurs at the last adenine of the stop codon, it is possible that the spliceosome machinery that originated for the elimination of the stop codons from the primary RNA sequence created an auxiliary stop-codon sequence signal as the lariat sequence to aid its splicing function.
The small nuclear U2 RNA found in splicing complexes is thought to aid splicing by interacting with the lariat sequence. Complementary sequences for both the lariat sequence and the acceptor signal are present in a segment of only 15 nucleotides in U2 RNA. Further, the U1 RNA has been proposed to function as a guide in splicing to identify the precise donor splice junction by complementary base-pairing. The conserved regions of the U1 RNA thus include sequences complementary to the stop codons. These observations enabled Senapathy to predict that stop codons had operated in the origin of not only the splice-junction signals and the lariat signal, but also some small nuclear RNAs. | 1 | Biochemistry |
Elongating polymerase is associated with a set of protein factors required for various types of RNA processing. mRNA is capped as soon as it emerges from the RNA-exit channel of the polymerase. After capping, dephosphorylation of Ser-5 within the CTD repeats may be responsible for dissociation of the capping machinery. Further phosphorylation of Ser-2 causes recruitment of the RNA splicing machinery that catalyzes the removal of non-coding introns to generate mature mRNA. Alternative splicing expands the protein complements in eukaryotes. Just as with 5’-capping and splicing, the CTD tail is involved in recruiting enzymes responsible for 3’-polyadenylation, the final RNA processing event that is coupled with the termination of transcription. | 1 | Biochemistry |
This reagent is not commercially available due to its short shelf life, so it must be freshly prepared in the laboratory. One common preparation involves two steps. First a few drops of dilute sodium hydroxide are added to some aqueous 0.1 M silver nitrate. The ions convert the silver aquo complex form into silver(I) oxide, , which precipitates from the solution as a brown solid:
In the next step, sufficient aqueous ammonia is added to dissolve the brown silver(I) oxide. The resulting solution contains the [Ag(NH)] complexes in the mixture, which is the main component of Tollens' reagent. Sodium hydroxide is reformed:
Alternatively, aqueous ammonia can be added directly to silver nitrate solution. At first, ammonia will induce formation of solid silver oxide, but with additional ammonia, this solid precipitate dissolves to give a clear solution of diamminesilver(I) coordination complex, . Filtering the reagent before use helps to prevent false-positive results. | 3 | Analytical Chemistry |
Thermal mass is effective in improving building comfort in any place that experiences these types of daily temperature fluctuations—both in winter as well as in summer.
When used well and combined with passive solar design, thermal mass can play an important role in major reductions to energy use in active heating and cooling systems.
The use of materials with thermal mass is most advantageous where there is a big difference in outdoor temperatures from day to night (or, where nighttime temperatures are at least 10 degrees cooler than the thermostat set point). The terms heavy-weight and light-weight are often used to describe buildings with different thermal mass strategies, and affects the choice of numerical factors used in subsequent calculations to describe their thermal response to heating and cooling.
In building services engineering, the use of dynamic simulation computational modelling software has allowed for the accurate calculation of the environmental performance within buildings with different constructions and for different annual climate data sets. This allows the architect or engineer to explore in detail the relationship between heavy-weight and light-weight constructions, as well as insulation levels, in reducing energy consumption for mechanical heating or cooling systems, or even removing the need for such systems altogether. | 7 | Physical Chemistry |
Effectively, the postulate states that the structure of a transition state resembles that of the species nearest to it in free energy. This can be explained with reference to potential energy diagrams:
In case (a), which is an exothermic reaction, the energy of the transition state is closer in energy to that of the reactant than that of the intermediate or the product. Therefore, from the postulate, the structure of the transition state also more closely resembles that of the reactant. In case (b), the energy of the transition state is close to neither the reactant nor the product, making none of them a good structural model for the transition state. Further information would be needed in order to predict the structure or characteristics of the transition state. Case (c) depicts the potential diagram for an endothermic reaction, in which, according to the postulate, the transition state should more closely resemble that of the intermediate or the product.
Another significance of Hammond’s postulate is that it permits us to discuss the structure of the transition state in terms of the reactants, intermediates, or products. In the case where the transition state closely resembles the reactants, the transition state is called “early” while a “late” transition state is the one that closely resembles the intermediate or the product.
An example of the “early” transition state is chlorination. Chlorination favors the products because it is an exothermic reaction, which means that the products are lower in energy than the reactants. When looking at the adjacent diagram (representation of an "early" transition state), one must focus on the transition state, which is not able to be observed during an experiment. To understand what is meant by an “early” transition state, the Hammond postulate represents a curve that shows the kinetics of this reaction. Since the reactants are higher in energy, the transition state appears to be right after the reaction starts.
An example of the “late” transition state is bromination. Bromination favors the reactants because it is an endothermic reaction, which means that the reactants are lower in energy than the products. Since the transition state is hard to observe, the postulate of bromination helps to picture the “late” transition state (see the representation of the "late" transition state). Since the products are higher in energy, the transition state appears to be right before the reaction is complete.
One other useful interpretation of the postulate often found in textbooks of organic chemistry is the following:
:Assume that the transition states for reactions involving unstable intermediates can be closely approximated by the intermediates themselves.
This interpretation ignores extremely exothermic and endothermic reactions which are relatively unusual and relates the transition state to the intermediates which are usually the most unstable. | 7 | Physical Chemistry |
(Diacetoxyiodo)benzene, also known as phenyliodine(III) diacetate (PIDA) is a hypervalent iodine chemical with the formula . It is used as an oxidizing agent in organic chemistry. | 0 | Organic Chemistry |
Metal alkyl complexes are prepared generally by two pathways, use of alkyl nucleophiles and use of alkyl electrophiles. Nucleophilic sources of alkyl ligands include Grignard reagents and organolithium compounds. Since many strong nucleophiles are also potent reductants, mildly nucleophilic alkylating agents are sometimes employed to avoid redox reactions. Organozinc compounds and organoaluminium compounds are such milder reagents.
Electrophilic alkylation commonly starts with low valence metal complexes. Typical electrophilic reagents are alkyl halides. Illustrative is the preparation of the methyl derivative of cyclopentadienyliron dicarbonyl anion:
:CpFe(CO)Na + CHI → CpFe(CO)CH + NaI
Many metal alkyls are prepared by oxidative addition:
An example is the reaction of a Vaska's complex with methyl iodide. | 0 | Organic Chemistry |
Christopher Alexander Hunter, FRS (born 19 February 1965) is a British chemist and academic. Since 2014, he has been Herchel Smith Professor of Organic Chemistry in the Department of Chemistry at the University of Cambridge. His research is currently focused on molecular recognition. He was previously a lecturer at the University of Otago and a lecturer then professor at the University of Sheffield. | 0 | Organic Chemistry |
Tammann was awarded the following prizes:
* Liebig Medal of the Association of German Chemists () in 1925
* Heyn Medal of the German Society for Materials Science () in 1929
* Eagle Shield of the German Empire in 1936
The Tammann Commemorative Medal of the Deutsche Gesellschaft für Materialkunde is named after him. | 7 | Physical Chemistry |
Hot (> 300 °C) hydrothermal fluids from mid ocean ridges are isotopically light, with δFe between -0.2 and -0.8‰. Particles in hydrothermal plumes are isotopically heavy relative to the hydrothermal fluids, with δFe between 0.1 and 1.1‰. Hydrothermal deposits have average δFe between -1.6 and 0.3‰. The sulfide minerals within these deposits have δFe between -2.0 and 1.1‰. | 9 | Geochemistry |
Despite its beneficial properties, NiAl generally suffers from two factors: very high brittleness at low temperatures (Al-based alloys these issues are generally addressed via the integration of other elements. Attempted elements can be broken into three groups depending on their influence of microstructure:
* Elements that form ternary intermetallic phases such as Ti and Hf
* Pseudobinary eutectic forming elements such as Cr
* Elements with high solubility in NiAl such as Fe, Co and Cu
Some of the more successful elements have been shown to be Fe, Co and Cr which drastically increase room temperature ductility as well as hot workability. This increase is due to the formation of γ phase which modifies the β phase grains. Alloying with Fe, Ga and Mo has also been shown to drastically improve room temperature ductility as well. Most recently, refracturing metals such as Cr, W and Mo have been added and resulted in not only increases in room temperature ductility but also increases in strength and fracture toughness at high temperatures. This is due to the formation of unique microstructures such as the eutectic alloy NiAlMo and α-Cr inclusions that contribute to solid solution hardening. It is even being shown that these complex alloys (NiAlCrMo) have the potential to be fabricated via additive manufacturing processes such as selective laser manufacturing, vastly increasing the potential applications for these alloys. | 8 | Metallurgy |
Many invasive plant species interfere with native plants through allelopathy. A famous case of purported allelopathy is in desert shrubs. One of the most widely known early examples was Salvia leucophylla, because it was on the cover of the journal Science in 1964. Bare zones around the shrubs were hypothesized to be caused by volatile terpenes emitted by the shrubs. However, like many allelopathy studies, it was based on artificial lab experiments and unwarranted extrapolations to natural ecosystems. In 1970, Science published a study where caging the shrubs to exclude rodents and birds allowed grass to grow in the bare zones.
A detailed history of this story can be found in Halsey 2004.
Garlic mustard is another invasive plant species that may owe its success partly to allelopathy. Its success in North American temperate forests may be partly due to its excretion of glucosinolates like sinigrin that can interfere with mutualisms between native tree roots and their mycorrhizal fungi.
Allelopathy has been shown to play a crucial role in forests, influencing the composition of the vegetation growth, and also provides an explanation for the patterns of forest regeneration. The black walnut (Juglans nigra) produces the allelochemical juglone, which affects some species greatly while others not at all. However, most of the evidence for allelopathic effects of juglone come from laboratory assays and it thus remains controversial to what extent juglone affects the growth of competitors under field conditions. The leaf litter and root exudates of some Eucalyptus species are allelopathic for certain soil microbes and plant species. The tree of heaven, Ailanthus altissima, produces allelochemicals in its roots that inhibit the growth of many plants. Spotted knapweed (Centaurea) is considered an invasive plant that also utilizes allelopathy.
Another example of allelopathy is seen in Leucaena leucocephala, known as the miracle tree. This plant contains toxic amino acids that inhibit other plants’ growth but not its own species growth. Different crops react differently to these allelochemicals, so wheat yield decreases, while rice increases in the presence of L. leucocephala.
Capsaicin is an allelochemical found in many peppers that are cultivated by humans as a spice/food source. It is considered an allelochemical because it is not required for plant growth and survival, but instead deters herbivores and prevents other plants from sprouting in its immediate vicinity. Among the plants it has been studied on are grasses, lettuce, and alfalfa, and on average, it will inhibit the growth of these plants by about 50%. Capsaicin has been shown to deter both herbivores and certain parasites’ performance. Herbivores such as caterpillars show decreased development when fed a diet high in capsaicin. | 1 | Biochemistry |
Stearoylethanolamide (SEA) is an endocannabinoid neurotransmitter.
Stearoylethanolamide (CHNO; 18:0), also called N-(octadecanoyl)ethanolamine, is an N-acylethanolamine and the ethanolamide of octadecanoic acid (CHO; 18:0) and ethanolamine (MEA: CHNO), and functionally related to an octadecanoic acid.
Levels of SEA correlate with changes in pain intensity, indicating this SEA change, reflect the pain reduction effects of IPRP. | 1 | Biochemistry |
Another important class of condensation polymers are polyesters. They arise from the reaction of a carboxylic acid and an alcohol. An example is polyethyleneterephthalate, the common plastic PETE (recycling #1 in the USA):
:n HO-X-OH + n HOC-Y-COH → [O-X-OC-Y-C(O)] + (2n-1) HO | 7 | Physical Chemistry |
An example of modest stereoselectivity is the dehydrohalogenation of 2-iodobutane which yields 60% trans-2-butene and 20% cis-2-butene. Since alkene geometric isomers are also classified as diastereomers, this reaction would also be called diastereoselective.
Cram's rule predicts the major diastereomer resulting from the diastereoselective nucleophilic addition to a carbonyl group next to a chiral center. The chiral center need not be optically pure, as the relative stereochemistry will be the same for both enantiomers. In the example below the (S)-aldehyde reacts with a thiazole to form the (S,S) diastereomer but only a small amount of the (S,R) diastereomer:
The Sharpless epoxidation is an example of an enantioselective process, in which an achiral allylic alcohol substrate is transformed into an optically active epoxyalcohol. In the case of chiral allylic alcohols, kinetic resolution results. Another example is Sharpless asymmetric dihydroxylation. In the example below the achiral alkene yields only one of the possible 4 stereoisomers.
With a stereogenic center next to the carbocation the substitution can be stereoselective in inter- and intramolecular reactions. In the reaction depicted below the nucleophile (furan) can approach the carbocation formed from the least shielded side away from the bulky t-butyl group resulting in high facial diastereoselectivity: | 4 | Stereochemistry |
Suppressor of cytokine signaling 1 is a protein that in humans is encoded by the SOCS1 gene. SOCS1 orthologs have been identified in several mammals for which complete genome data are available. | 1 | Biochemistry |
An ISFET electrode sensitive to H concentration can be used as a conventional glass electrode to measure the pH of a solution. However, it also requires a reference electrode to operate. If the reference electrode used in contact with the solution is of the AgCl or HgCl classical type, it will suffer the same limitations as conventional pH electrodes (junction potential, KCl leak, and glycerol leak in case of gel electrode). A conventional reference electrode can also be bulky and fragile. A too large volume constrained by a classical reference electrode also precludes the miniaturization of the ISFET electrode, a mandatory feature for some biological or in vivo clinical analyses (disposable mini-catheter pH probe). The breakdown of a conventional reference electrode could also make problem in on-line measurements in the pharmaceutical or food industry if highly valuable products are contaminated by electrode debris or toxic chemical compounds at a late production stage and must be discarded for the sake of safety.
For this reason, since more than 20 years many research efforts have been dedicated to on-chip embedded tiny reference field effect transistors (REFET). Their functioning principle, or operating mode, can vary, depending on the electrode producers and are often proprietary and protected by patents. Semi-conductor modified surfaces required for REFET are also not always in thermodynamical equilibrium with the test solution and can be sensitive to aggressive or interfering dissolved species or not well characterized aging phenomena. This is not a real problem if the electrode can be frequently re-calibrated at regular time interval and is easily maintained during its service life. However, this may be an issue if the electrode has to remain immersed on-line for prolonged period of time, or is inaccessible for particular constrains related to the nature of the measurements itself (geochemical measurements under elevated water pressure in harsh environments or under anoxic or reducing conditions easily disturbed by atmospheric oxygen ingress or pressure changes).
A crucial factor for ISFET electrodes, as for conventional glass electrodes, remains thus the reference electrode. When troubleshooting electrode malfunctions, often, most of the problems have to be searched for from the side of the reference electrode. | 7 | Physical Chemistry |
Different solvents can affect the equilibrium constant of a reaction by differential stabilization of the reactant or product. The equilibrium is shifted in the direction of the substance that is preferentially stabilized.
Stabilization of the reactant or product can occur through any of the different non-covalent interactions with the solvent such as H-bonding, dipole-dipole interactions, van der Waals interactions etc. | 7 | Physical Chemistry |
Since no natural amino acids are strongly nucleophilic, the base in a catalytic triad polarises and deprotonates the nucleophile to increase its reactivity. Additionally, it protonates the first product to aid leaving group departure.
The base is most commonly histidine since its pK allows for effective base catalysis, hydrogen bonding to the acid residue, and deprotonation of the nucleophile residue. β-lactamases such as TEM-1 use a lysine residue as the base. Because lysines pK is so high (pK=11), a glutamate and several other residues act as the acid to stabilise its deprotonated state during the catalytic cycle. Threonine proteases use their N-terminal amide as the base, since steric crowding by the catalytic threonines methyl prevents other residues from being close enough. | 1 | Biochemistry |
The use of antioxidants to prevent some diseases is controversial. In a high-risk group like smokers, high doses of beta carotene increased the rate of lung cancer since high doses of beta-carotene in conjunction of high oxygen tension due to smoking results in a pro-oxidant effect and an antioxidant effect when oxygen tension is not high. In less high-risk groups, the use of vitamin E appears to reduce the risk of heart disease. However, while consumption of food rich in vitamin E may reduce the risk of coronary heart disease in middle-aged to older men and women, using vitamin E supplements also appear to result in an increase in total mortality, heart failure, and hemorrhagic stroke. The American Heart Association therefore recommends the consumption of food rich in antioxidant vitamins and other nutrients, but does not recommend the use of vitamin E supplements to prevent cardiovascular disease. In other diseases, such as Alzheimers, the evidence on vitamin E supplementation is also mixed. Since dietary sources contain a wider range of carotenoids and vitamin E tocopherols and tocotrienols from whole foods, ex post facto epidemiological studies can have differing conclusions than artificial experiments using isolated compounds. AstraZenecas radical scavenging nitrone drug NXY-059 shows some efficacy in the treatment of stroke.
Oxidative stress (as formulated in Denham Harmans free-radical theory of aging) is also thought to contribute to the aging process. While there is good evidence to support this idea in model organisms such as Drosophila melanogaster and Caenorhabditis elegans, recent evidence from Michael Ristows laboratory suggests that oxidative stress may also promote life expectancy of Caenorhabditis elegans by inducing a secondary response to initially increased levels of reactive oxygen species. The situation in mammals is even less clear. Recent epidemiological findings support the process of mitohormesis, but a 2007 meta-analysis finds that in studies with a low risk of bias (randomization, blinding, follow-up), some popular antioxidant supplements (vitamin A, beta carotene, and vitamin E) may increase mortality risk (although studies more prone to bias reported the reverse).
The USDA removed the table showing the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods Release 2 (2010) table due to the lack of evidence that the antioxidant level present in a food translated into a related antioxidant effect in the body. | 1 | Biochemistry |
When a microscopic machine (e.g. a MEM) performs useful work it generates heat and entropy as a byproduct of the process, however it is also predicted that this machine will operate in "reverse" or "backwards" over appreciable short periods. That is, heat energy from the surroundings will be converted into useful work. For larger engines, this would be described as a violation of the second law of thermodynamics, as entropy is consumed rather than generated. Loschmidt's paradox states that in a time reversible system, for every trajectory there exists a time-reversed anti-trajectory. As the entropy production of a trajectory and its equal anti-trajectory are of identical magnitude but opposite sign, then, so the argument goes, one cannot prove that entropy production is positive.
For a long time, exact results in thermodynamics were only possible in linear systems capable of reaching equilibrium, leaving other questions like the Loschmidt paradox unsolved. During the last few decades fresh approaches have revealed general laws applicable to non-equilibrium system which are described by nonlinear equations, pushing the range of exact thermodynamic statements beyond the realm of traditional linear solutions. These exact results are particularly relevant for small systems where appreciable (typically non-Gaussian) fluctuations occur. Thanks to stochastic thermodynamics it is now possible to accurately predict distribution functions of thermodynamic quantities relating to exchanged heat, applied work or entropy production for these systems. | 7 | Physical Chemistry |
Plasma spraying systems can be categorized by several criteria.
Plasma jet generation:
*direct current (DC plasma), where the energy is transferred to the plasma jet by a direct current, high-power electric arc
*induction plasma or RF plasma, where the energy is transferred by induction from a coil around the plasma jet, through which a radio-frequency current passes. This electrode-free technology allows to produce coatings with high purity and high density.
Plasma-forming medium:
*gas-stabilized plasma (GSP), where the plasma forms from a gas; typically argon, hydrogen, helium or their mixtures
*water-stabilized plasma (WSP), where plasma forms from water (through evaporation, dissociation and ionization) or other suitable liquid
*hybrid plasma – with combined gas and liquid stabilization, typically argon and water
Spraying environment:
*atmospheric plasma spraying (APS), performed in ambient air
*controlled atmosphere plasma spraying (CAPS), usually performed in a closed chamber, either filled with inert gas or evacuated
*variations of CAPS: high-pressure plasma spraying (HPPS), low-pressure plasma spraying (LPPS), the extreme case of which is vacuum plasma spraying (VPS, see below)
*underwater plasma spraying
Another variation consists of having a liquid feedstock instead of a solid powder for melting, this technique is known as Solution precursor plasma spray | 8 | Metallurgy |
LH is released from the pituitary gland along with FSH in response to GnRH release into the hypophyseal portal system. Pulsatile GnRH release causes pulsatile LH and FSH release to occur, which modulates and maintains appropriate levels of bioavailable gonadal hormone: testosterone in males and estradiol in females subject to the requirements of a superior feedback loop. In females the levels of LH is typically 1–20 IU/L during the reproductive period and is estimated to be 1.8–8.6 IU/L in males over 18 years of age. | 1 | Biochemistry |
One of the earliest smelted iron artifacts, a dagger with an iron blade found in a Hattic tomb in Anatolia, dated from 2500 BC. About 1500 BC, increasing numbers of non-meteoritic, smelted iron objects appeared in Mesopotamia, Anatolia and Egypt. Nineteen meteoric iron objects were found in the tomb of Egyptian ruler Tutankhamun, who died in 1323 BC, including an iron dagger with a golden hilt, an Eye of Horus, the mummys head-stand and sixteen models of an artisans tools. An Ancient Egyptian sword bearing the name of pharaoh Merneptah as well as a battle axe with an iron blade and gold-decorated bronze shaft were both found in the excavation of Ugarit.
Although iron objects dating from the Bronze Age have been found across the Eastern Mediterranean, bronzework appears to have greatly predominated during this period. As the technology spread, iron came to replace bronze as the dominant metal used for tools and weapons across the Eastern Mediterranean (the Levant, Cyprus, Greece, Crete, Anatolia and Egypt).
Iron was originally smelted in bloomeries, furnaces where bellows were used to force air through a pile of iron ore and burning charcoal. The carbon monoxide produced by the charcoal reduced the iron oxide from the ore to metallic iron. The bloomery, however, was not hot enough to melt the iron, so the metal collected in the bottom of the furnace as a spongy mass, or bloom. Workers then repeatedly beat and folded it to force out the molten slag. This laborious, time-consuming process produced wrought iron, a malleable but fairly soft alloy.
Concurrent with the transition from bronze to iron was the discovery of carburization, the process of adding carbon to wrought iron. While the iron bloom contained some carbon, the subsequent hot-working oxidized most of it. Smiths in the Middle East discovered that wrought iron could be turned into a much harder product by heating the finished piece in a bed of charcoal, and then quenching it in water or oil. This procedure turned the outer layers of the piece into steel, an alloy of iron and iron carbides, with an inner core of less brittle iron. | 8 | Metallurgy |
* Carnot, Sadi (1824). Réflexions sur la puissance motrice du feu et sur les machines propres à développer cette puissance (in French). Paris: Bachelier.
* Dobroborsky B.S. Machine safety and the human factor / Edited by Doctor of Technical Sciences, prof. S.A. Volkov. — St. Petersburg: SPbGASU, 2011. — pp. 33-35. — 114 p. — . (Ru) | 7 | Physical Chemistry |
Proteins are essential macromolecules of living organisms. They are continuously being degraded into their constituent amino acids which can be reused in the synthesis of new proteins. Every cellular protein has its own half-life time. In humans, for instance, 50% of the liver and plasma proteins are replaced in 10 days, whereas in muscles it takes 180 days. In average, every 80 days about 50% of our proteins are totally replaced. Although the regulation of protein degradation is as important as their synthesis to keep each cell protein concentration at the optimum level, research in this area remained until the end of the 1970s. Up to this time, lysosomes, discovered in the 1950s by the Belgian cytologist Christian de Duve, were thought responsible for the complete digestion of intra- and extracellular proteins by the lysosomal hydrolytic enzymes.
Between the 1970s and 1980s, this view drastically changed. New experimental evidences showed that, under physiological conditions, non-lysosomal proteases were responsible for limited proteolysis of intra- and/or extracellular proteins, a concept originally conceived by Linderstᴓm-Lang in 1950. Endogenous or exogenous proteins are processed by non-lysosomal proteases into intermediate-sized polypeptides, which display gene and metabolic regulation, neurologic, endocrine, and immunological roles, whose dysfunction might explain a number of pathologies. Consequently, protein degradation did not represent anymore the end of the biological function of proteins, but rather the beginning of a yet unexplored side of the biology of the cells. A number of intra- or extracellular proteases release protein fragments endowed with essential biological activities. These hydrolytic processes could be carried out by proteases such as Proteasomes, Proprotein Convertases, Caspases, Rennin and Kallikreins. Among the products released by the non-lysosomal proteases are the bioactive oligopeptides such as hormones, neuropeptides and epitopes that, once released, could be modulated in their biological activities by specific peptidases, which promote the trimming, conversion and/or inactivation of the bioactive oligopeptides. | 1 | Biochemistry |
According to Sazonov and Shaw, the dimensionless Bunsen coefficient is defined as "the volume of saturating gas, V1, reduced to T° = 273.15 K, p° = 1 bar, which is absorbed by unit volume V* of pure solvent at the temperature of measurement and partial pressure of 1 bar." If the gas is ideal, the pressure cancels out, and the conversion to is simply
with = 273.15K. Note, that according to this definition, the conversion factor is not temperature-dependent. Independent of the temperature that the Bunsen coefficient refers to, 273.15K is always used for the conversion. The Bunsen coefficient, which is named after Robert Bunsen, has been used mainly in the older literature, and IUPAC considers it to be obsolete. | 7 | Physical Chemistry |
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