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* Interdisciplinary field involving processes that
** make use of microbes, usually bacteria and archaea
** mainly take place in aqueous environment
** deal with metal production and treatment of metal containing materials and solutions
*"Biohydrometallurgy may generally referred to as the branch of biotechnology dealing with the study and application of the economic potential of the interactions between microbes and minerals. It concerns, thus, all those engaged, directly or indirectly, in the exploitation of mineral resources and in environmental protection: geologists, economic geologists, mining engineers, metallurgists, hydrometallurgists, chemists and chemical engineers. In addition to these specialists, there are the microbiologists whose work is indispensable in the design, implementation and running of biohydrometallurgical processes."
*Biohydrometallurgy was first used more than 300 years ago to recover copper. The uses have evolved to extracting gold, uranium, and other metals. | 8 | Metallurgy |
In allometric scaling, maximum potential life span (MPLS) is directly related to metabolic rate (MR), where MR is the recharge rate of a biomass made up of covalent bonds. That biomass (W) is subjected to deterioration over time from thermodynamic, entropic pressure. Metabolism is essentially understood as redox coupling, and has nothing to do with thermogenesis. Metabolic efficiency (ME) is then expressed as the efficiency of this coupling, a ratio of amperes captured and used by biomass, to the amperes available for that purpose. MR is measured in watts, W is measured in grams. These factors are combined in a power law, an elaboration on Kleiber's law relating MR to W and MPLS, that appears as MR = W^ (4ME-1)/4ME. When ME is 100%, MR = W^3/4; this is popularly known as quarter power scaling, a version of allometric scaling that is premised upon unrealistic estimates of biological efficiency.
The equation reveals that as ME drops below 20%, for W < one gram, MR/MPLS increases so dramatically as to endow W with virtual immortality by 16%. The smaller W is to begin with, the more dramatic is the increase in MR as ME diminishes. All of the cells of an organism fit into this range, i.e., less than one gram, and so this MR will be referred to as BMR.
But the equation reveals that as ME increases over 25%, BMR approaches zero. The equation also shows that for all W > one gram, where W is the organization of all of the BMRs of the organism's structure, but also includes the activity of the structure, as ME increases over 25%, MR/MPLS increases rather than decreases, as it does for BMR. An MR made up of an organization of BMRs will be referred to as an FMR. As ME decreases below 25%, FMR diminishes rather than increases as it does for BMR.
The antagonism between FMR and BMR is what marks the process of aging of biomass W in energetic terms. The ME for the organism is the same as that for the cells, such that the success of the organism's ability to find food (and lower its ME), is key to maintaining the BMR of the cells driven, otherwise, by starvation, to approaching zero; while at the same time a lower ME diminishes the FMR/MPLS of the organism. | 1 | Biochemistry |
Ibuprofen, like other 2-arylpropionate derivatives such as ketoprofen, flurbiprofen and naproxen, contains a stereocenter in the α-position of the propionate moiety.
The product sold in pharmacies is a racemic mixture of the S and R-isomers. The S (dextrorotatory) isomer is the more biologically active; this isomer has been isolated and used medically (see dexibuprofen for details).
The isomerase enzyme, alpha-methylacyl-CoA racemase, converts (R)-ibuprofen into the (S)-enantiomer.
(S)-ibuprofen, the eutomer, harbors the desired therapeutic activity. Interestingly, the inactive (R)-enantiomer, the distomer, undergoes a unidirectional chiral inversion to offer the active (S)-enantiomer. That is, when the ibuprofen is administered as a racemate the distomer is converted in vivo into the eutomer while the latter is unaffected. | 4 | Stereochemistry |
In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It is published in the Nomenclature of Organic Chemistry (informally called the [https://iupac.org/what-we-do/books/bluebook/ Blue Book]). Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be created. There is also an IUPAC nomenclature of inorganic chemistry.
To avoid long and tedious names in normal communication, the official IUPAC naming recommendations are not always followed in practice, except when it is necessary to give an unambiguous and absolute definition to a compound. IUPAC names can sometimes be simpler than older names, as with ethanol, instead of ethyl alcohol. For relatively simple molecules they can be more easily understood than non-systematic names, which must be learnt or looked over. However, the common or trivial name is often substantially shorter and clearer, and so preferred. These non-systematic names are often derived from an original source of the compound. Also, very long names may be less clear than structural formulas. | 0 | Organic Chemistry |
In inner-sphere ET, the two redox centers are covalently linked during the ET. This bridge can be permanent, in which case the electron transfer event is termed intramolecular electron transfer. More commonly, however, the covalent linkage is transitory, forming just prior to the ET and then disconnecting following the ET event. In such cases, the electron transfer is termed intermolecular electron transfer. A famous example of an inner sphere ET process that proceeds via a transitory bridged intermediate is the reduction of [CoCl(NH)] by [Cr(HO)]. In this case, the chloride ligand is the bridging ligand that covalently connects the redox partners. | 7 | Physical Chemistry |
Lipotoxicity is a metabolic syndrome that results from the accumulation of lipid intermediates in non-adipose tissue, leading to cellular dysfunction and death. The tissues normally affected include the kidneys, liver, heart and skeletal muscle. Lipotoxicity is believed to have a role in heart failure, obesity, and diabetes, and is estimated to affect approximately 25% of the adult American population. | 1 | Biochemistry |
Shortly after its inauguration the society began publishing the Journal of Exploration Geochemistry in 1972. Today the societys flagship journal is Geochemistry: Exploration, Environment, Analysis, co-published with the Geological Society of London. The journal covers fields relating to the application of geochemistry to the exploration and study of mineral resources. It aims to promote interchange between exploration and environmental geochemistry. The journal is a hybrid open-access journal, publishing both subscription and open access articles. It also publishes Explore, a newsletter, and co-publishes Elements', a membership magazine. | 9 | Geochemistry |
Electrokinetic phenomena are a family of several different effects that occur in heterogeneous fluids or in porous bodies filled with fluid. The sum of these phenomena deals with the effect on a particle from some outside resulting in a net electrokinetic effect.
The common source of all these effects stems from the interfacial double layer of charges. Particles influenced by an external force generate tangential motion of a fluid with respect to an adjacent charged surface. This force may consist of electric, pressure gradient, concentration gradient, gravity. In addition, the moving phase might be either the continuous fluid or dispersed phase.
Sedimentation potential is the field of electrokinetic phenomena dealing with the generation of an electric field by sedimenting colloid particles. | 7 | Physical Chemistry |
In underwater diving, gas is breathed at the ambient pressure which increases with depth due to the hydrostatic pressure. Solubility of gases increases with greater depth (greater pressure) according to Henry's law, so the body tissues take on more gas over time in greater depths of water. When ascending the diver is decompressed and the solubility of the gases dissolved in the tissues decreases accordingly. If the supersaturation is too great, bubbles may form and grow, and the presence of these bubbles can cause blockages in capillaries, or distortion in the more solid tissues which can cause damage known as decompression sickness. To avoid this injury the diver must ascend slowly enough that the excess dissolved gas is carried away by the blood and released into the lung gas. | 7 | Physical Chemistry |
Aryl alkynes are typically made utilizing the Sonogashira reaction which is the palladium catalyzed cross-coupling reaction of terminal alkynes and aryl halides. Instead of the terminal alkynes, alkyne carboxylic acids has advantages, easy handling and storage. The first decarboxylative coupling of alkyne carboxylic acids was reported in 2008 by S. Lee. They employed propiolic acid as an alkyne source. One year later, S. Lee applied the decarboxylative coupling reactions toward 2-octynoic acid and phenylpropiolic acid. In 2010, Xue et al. reported the coupling of an aryl halide and alkynyl carboxylic acid under mild reactions conditions and a copper-only catalyst to obtain aryl alkynes. | 0 | Organic Chemistry |
In this pathway CO is fixed (i.e. incorporated) by the action of two enzymes, acetyl-CoA carboxylase and propionyl-CoA carboxylase. These enzymes generate malonyl-CoA and (S)-methylmalonyl-CoA, respectively. | 1 | Biochemistry |
Experimental archaeometallurgy is a subset of experimental archaeology that specifically involves past metallurgical processes most commonly involving the replication of copper and iron objects as well as testing the methodology behind the production of ancient metals and metal objects. Metals and elements used primarily as alloying materials, such as tin, lead, and arsenic, are also a part of experimental research. | 8 | Metallurgy |
* Arthur C. Cope Scholar Awards (2020)
* Chemical Research Society of India Medal (2013)
* Fellow of the American Association for the Advancement of Science (2012)
* Distinguished Alumnus, Indian Institute of Technology, Madras (2008) | 0 | Organic Chemistry |
The two particular features of PTMS that have determined its applications so far are 1) spectroscopic mapping may be performed at a spatial resolution well below the diffraction limit of IR radiation, ultimately at a scale of 20-30 nm. In principle, this opens the way to sub-wavelength IR microscopy (see scanning probe microscopy) where the image contrast is to be determined by the thermal response of individual sample regions to particular spectral wavelengths and 2) in general, no special preparation technique is required when solid samples are to be studied. For most standard FTIR methods, this is not the case. | 7 | Physical Chemistry |
Rational thermodynamics is a school of thought in statistical thermodynamics developed in the 1960s.
Its introduction is attributed to Clifford Truesdell (1919–2000), Bernard Coleman (b. 1929) and Walter Noll (1925–2017).
The aim was to develop a mathematical model of thermodynamics that would go beyond the traditional "thermodynamics of irreversible processes" or TIP developed in the late 19th to early 20th centuries.
Truesdell's "flamboyant style" and "satirical verve" caused controversy between "rational thermodynamics" and proponents of traditional thermodynamics. | 7 | Physical Chemistry |
Compounds with allylic and benzylic C−H bonds are especially susceptible to oxygenation. Such reactivity is exploited industrially on a large scale for the production of phenol by the Cumene process or Hock process for its cumene and cumene hydroperoxide intermediates. Such reactions rely on radical initiators that reacts with oxygen to form an intermediate that abstracts a hydrogen atom from a weak C-H bond. The resulting radical binds , to give hydroperoxyl (ROO•), which then continues the cycle of H-atom abstraction. | 0 | Organic Chemistry |
The nitrogen compounds through which excess nitrogen is eliminated from organisms are called nitrogenous wastes () or nitrogen wastes. They are ammonia, urea, uric acid, and creatinine. All of these substances are produced from protein metabolism. In many animals, the urine is the main route of excretion for such wastes; in some, it is the feces. | 1 | Biochemistry |
He helped start MITs chemical engineering curriculum in the late 1880s. In 1887, he was appointed by the newly formed Massachusetts Board of Health to a landmark study of sanitary quality of the states inland waters. As consulting chemist to the Massachusetts State Board of Health, he was in charge of the famous Lawrence Experiment Station laboratory conducting the water sampling, testing, and analysis. There he put to work the environmental chemist and first female graduate of MIT, Ellen Swallow Richards. This research created the famous "normal chlorine" map of Massachusetts that was the first of its kind and was the template for others. As a result, Massachusetts established the first water-quality standards in America, and the first modern sewage treatment plant was created.
As a professor, Drown published a number of papers on metallurgy, mostly in Transactions of the American Institute of Mining Engineers. He was a founding member of the Institute, and served as its secretary, and editor of its Transactions from 1871 till 1884. He was elected its president in 1897. | 3 | Analytical Chemistry |
Most free-living copepods feed directly on phytoplankton, catching cells individually. A single copepod can consume up to 373,000 phytoplankton per day. They generally have to clear the equivalent to about a million times their own body volume of water every day to cover their nutritional needs. Some of the larger species are predators of their smaller relatives. Many benthic copepods eat organic detritus or the bacteria that grow in it, and their mouth parts are adapted for scraping and biting. Herbivorous copepods, particularly those in rich, cold seas, store up energy from their food as oil droplets while they feed in the spring and summer on plankton blooms. These droplets may take up over half of the volume of their bodies in polar species. Many copepods (e.g., fish lice like the Siphonostomatoida) are parasites, and feed on their host organisms. In fact, three of the 10 known orders of copepods are wholly or largely parasitic, with another three comprising most of the free-living species. | 2 | Environmental Chemistry |
There are several techniques to prove the existence of a liquid layer on a well-ordered surface. Basically it is all about showing that there is a phase on top of the solid which has hardly any order (quasi-liquid, see fig. order parameter). One possibility was done by Frenken and van der Veen using proton scattering on a lead (Pb) single crystal (110) surface. First the surface was atomically cleaned in [UHV], because one obviously has to have a very well ordered surface for such experiments. Then they did proton shadowing and blocking measurements. An ideal shadowing and blocking measurements results in an energy spectrum of the scattered protons that shows only a peak for the first surface layer and nothing else. Due to the non ideality of the experiment the spectrum also shows effects of the underlying layers. That means the spectrum is not one well defined peak but has a tail to lower energies due to protons scattered on deeper layers which results in losing energies because of stopping.
This is different for a liquid film on the surface: This film does hardly (to the meaning of hardly see Landau theory) have any order. So the effects of shadowing and blocking vanish what means all the liquid film contributes the same amount of scattered electrons to the signal. Therefore, the peak does not only have a tail, but also becomes broadened.
During their measurements Frenken and van der Veen raised the temperature to the melting point and hence could show that with increasing temperature a disordered film formed on the surface in equilibrium with a still well ordered Pb crystal. | 7 | Physical Chemistry |
Diffusion-trapping methods utilizes diffusion techniques to get the substrates into the crystal and thereafter different trapping techniques are applied to get the intermediate of interest to accumulate in the crystal prior to collection of the diffraction pattern. These trapping methods could involve changes in pH, use of inhibitor or lowering the temperature in order to slow down the turnover rate or maybe even stop the reaction completely at a specific step. Just starting the reaction and then flash-freeze it, thereby quenching it at a specific time step, is also a possible method. One drawback with diffusion-trapping methods is that they can only be used to study intermediates that can be trapped, thereby limiting the time resolution one can obtain through the methods as compared to the pump-probe method. | 3 | Analytical Chemistry |
Wood flour is commonly used as a filler in thermosetting resins such as bakelite, and in linoleum floor coverings. Wood flour is also the main ingredient in wood/plastic composite building products such as decks and roofs. Prior to 1920, wood flour was used as the filler in ¼-inch thick Edison Diamond Discs.
Wood flour has found a use in plugging small through-wall holes in leaking main condenser (heat exchanger) tubes at electrical power generating stations via injecting small quantities of the wood flour into the cooling water supply lines. Some of the injected wood flour clogs the small holes while the remainder exits the station in a relatively environmentally benign fashion.
Because of its adsorbent properties it has been used as a cleaning agent for removing grease or oil in various occupations. It has also been noted for its ability to remove lead contamination from water.
Wood flour can be used as a binder in grain filler compounds. | 2 | Environmental Chemistry |
Raoults law ( law) is a relation of physical chemistry, with implications in thermodynamics. Proposed by French chemist François-Marie Raoult in 1887, it states that the partial pressure of each component of an ideal mixture of liquids' is equal to the vapor pressure of the pure component (liquid or solid) multiplied by its mole fraction in the mixture. In consequence, the relative lowering of vapor pressure of a dilute solution of nonvolatile solute is equal to the mole fraction of solute in the solution.
Mathematically, Raoult's law for a single component in an ideal solution is stated as
where is the partial pressure of the component in the gaseous mixture above the solution, is the equilibrium vapor pressure of the pure component , and is the mole fraction of the component in the liquid or solid solution.
Where two volatile liquids A and B are mixed with each other to form a solution, the vapor phase consists of both components of the solution. Once the components in the solution have reached equilibrium, the total vapor pressure of the solution can be determined by combining Raoults law with Daltons law of partial pressures to give
In other words, the vapor pressure of the solution is the mole-weighted mean of the individual vapour pressures:
If a non-volatile solute B (it has zero vapor pressure, so does not evaporate) is dissolved into a solvent A to form an ideal solution, the vapor pressure of the solution will be lower than that of the solvent. In an ideal solution of a nonvolatile solute, the decrease in vapor pressure is directly proportional to the mole fraction of solute:
If the solute associates or dissociates in the solution, the expression of the law includes the van 't Hoff factor as a correction factor. | 7 | Physical Chemistry |
Flash vacuum pyrolysis (FVP) is a technique in organic synthesis. It entails heating a precursor molecule intensely and briefly. Two key parameters are the temperature and duration (or residence time), which are adjusted to optimize yield, conversion, and avoidance of intractable products. Often the experiment entails volatilizing a precursor, which is drawn through a "hot zone" followed by rapid condensation. The apparatus typically is conducted under dynamic vacuum. The hot zone must impart heat to the gaseous molecules, so it is generally packed with solids to induce gas-solid collisions. The packing material is generally chemically inert, such as quartz. The precursor (i) volatilizes with gentle heating and under vacuum, (ii) the precursor fragments or rearranges in the hot zone, and finally (iii) the products are collected by rapid cooling. Rapid post-reaction cooling and the dilution inherent in gases both suppress bimolecular degradation pathways. | 0 | Organic Chemistry |
Today, the IIR has 59 member countries representing over two-thirds of the global population.
According to their annual financial contributions to the IIR, these member countries are divided into six category levels and this determines the services they receive and their level of voting power within the IIR. Member Countries take part in IIR activities via their delegates and their nominated commission members. The delegates and commission members determine IIR priorities and take part in the IIR scientific activities and Working Groups, and develop recommendations. Member countries are entitled to host several IIR conferences and meetings per year. | 7 | Physical Chemistry |
Present-day methods of steel and alloy production are unable to attain completely pure metal without any non-metallic inclusions. Inclusions are present in any steel to a greater or lesser extent according to the mixture and conditions of production. Usually the amount of non-metallic inclusions in steel is not higher than 0.1%. However, the number of inclusions in metal is very high because of their extremely small size.
Non-metallic inclusions in steel are foreign substances. They disrupt the homogeneity of structure, so their influence on the mechanical and other properties can be considerable. During deformation, which occurs from flatting, forging, and stamping, non-metallic inclusions can cause cracks and fatigue failure in steel.
When investigating the influence of non-metallic inclusions on the quality of steel, of great importance are the properties of these inclusions: size, shape, chemical and physical characteristics. All these properties depend on the chemical composition of steel, method of smelting and for certain steel grade. These properties can change within wide limits even within the same mode of production.
Different methods for analysis of non-metallic inclusions have been developed and are now in use. These make it possible to determine content, structure and amount of non-metallic inclusions in steel and alloys with high accuracy. | 8 | Metallurgy |
Heart muscle is subject to two kinds of stress: physiologic stress, i.e. exercise; and pathologic stress, i.e. disease related. Likewise, the heart has two potential responses to either stress: cardiac hypertrophy, which is a normal, physiologic, adaptive growth; or cardiac remodeling, which is an abnormal, pathologic, maladaptive growth. Upon being subjected to either stress, the heart "chooses" to turn on one of the responses and turn off the other. If it has chosen the abnormal path, i.e. remodeling, exercise can reverse this choice by turning off remodeling and turning on hypertrophy. The mechanism for reversing this choice is the microRNA miR-222 in cardiac muscle cells, which exercise up-regulates via unknown myokines. miR-222 represses genes involved in fibrosis and cell-cycle control. | 1 | Biochemistry |
Deep sequencing of transcriptomes, also known as RNA-Seq, provides both the sequence and frequency of RNA molecules that are present at any particular time in a specific cell type, tissue or organ. Counting the number of mRNAs that are encoded by individual genes provides an indicator of protein-coding potential, a major contributor to phenotype. Improving methods for RNA sequencing is an active area of research both in terms of experimental and computational methods. | 1 | Biochemistry |
Frzb (pronounced like the toy frisbee) is a Wnt-binding protein especially important in embryonic development. It is a competitor for the cell-surface G-protein receptor Frizzled.
Frizzled is a tissue polarity gene in Drosophila melanogaster and encodes integral proteins that function as cell-surface receptors for Wnts called serpentine receptors. The integral membrane proteins contain a cysteine-rich domain thought to be the Wnt binding domain in extracellular region. The signals are initiated at the 7 transmembrane domain and transmitted through receptor coupling to G-proteins.
This protein is expressed in chondrocytes making it important in skeletal development in the embryo and fetus. Frzb is localized in the extracellular plasma membrane. Unlike frizzled, frzb lacks the 7 transmembrane domains normally found in G-protein-coupled receptors. It is still considered a homolog of frizzled because it contains a Cysteine Rich Domain (CRD), and because of its intracellular C-terminus which is crucial for signaling. The CRD is highly conserved in diverse proteins, such as receptor tyrosine kinases and functions as a ligand binding domain. The C-terminal is a carboxyl terminus located intracellularly and is required for canonical signaling.
The serpentine receptors (frzb) couple binds to ligand (Wnt protein) and activates G-proteins. A signal transduction cascade results in the secretion of first and second group antagonists. First group antagonists are composed of secreted Frizzled Related protein family (Sfrp) and Wnt inhibitory factor (Wif). Both Srfp and Wif bind directly to Wnt proteins blocking activation of the receptor. Second group of antagonists contains a class of Wnt inhibitory proteins known as Frizzled Receptor-like Proteins (FRPs). FRPs bind to the LRP (low-density-lipoprotein-related protein) co-receptors blocking activation of the Wnt signaling pathway.
One such pathway that involves Frizzled (Fz) family is the Wnt/β-Catenin (β-Cat) signaling. β-Cat is an intracellular signal that is held in check by axin. In this pathway, the activation of Wnt receptors can be transduced by the canonical pathway via a series of phosphorylation steps leading to stabilization and nuclear import of β-Cat into the nucleus where β-Cat associates with T-cell factor (TCF), a DNA-binding protein family. The β-Cat and TCF complex activates target genes of the Wnt pathway. In the absence of Wnt, β-Catenin is phosphorylated by complex containing GSK3 (glycogen synthase kinase 3) which targets β-Cat for proteosomal degradation. In the nucleus, members of the T-cell factor (TCF) family of DNA-binding proteins repress Wnt targets along with co-repressors such as Groucho (Gro).
If Wnt is present it binds to Fz-LRP receptors causing axin to bind to intracellular domain of LRP and Fz. Dishevelled (Dvl) is a protein required for Wnt-dependent inhibition complex. The combination of LRP-axin induces Dvl phosphorylation (P) which blocks the APC-axin-GSK3 complex from phosphorylating β-Cat. The accumulated β-Cat then enters the nucleus and converts TCF into a transcriptional activator.
Defects in Frzb are associated with female-specific osteoarthritis (OA) susceptibility which is the most prevalent form of arthritis and common cause of disability.
https://web.archive.org/web/20070930043451/http://jcs.biologists.org/content/vol119/issue3/images/large/JCS02826F1.jpeg
Frzb (known as Frzb1 or Sfrp3, Secreted Frizzled Related Protein 3) was initially identified as a chondrogenic factor during bone morphogenesis, and was described as a novel marker of the neural crest-derived mesenchymal cells that contribute to dental follicle formation, the future periodontium. | 1 | Biochemistry |
Dissimilar metals and alloys have different electrode potentials, and when two or more come into contact in an electrolyte, one metal (that is more reactive) acts as anode and the other (that is less reactive) as cathode. The electropotential difference between the reactions at the two electrodes is the driving force for an accelerated attack on the anode metal, which dissolves into the electrolyte. This leads to the metal at the anode corroding more quickly than it otherwise would and corrosion at the cathode being inhibited. The presence of an electrolyte and an electrical conducting path between the metals is essential for galvanic corrosion to occur. The electrolyte provides a means for ion migration whereby ions move to prevent charge build-up that would otherwise stop the reaction. If the electrolyte contains only metal ions that are not easily reduced (such as Na, Ca, K, Mg, or Zn), the cathode reaction is the reduction of dissolved H to H or O to OH.
In some cases, this type of reaction is intentionally encouraged. For example, low-cost household batteries typically contain carbon-zinc cells. As part of a closed circuit (the electron pathway), the zinc within the cell will corrode preferentially (the ion pathway) as an essential part of the battery producing electricity. Another example is the cathodic protection of buried or submerged structures as well as hot water storage tanks. In this case, sacrificial anodes work as part of a galvanic couple, promoting corrosion of the anode, while protecting the cathode metal.
In other cases, such as mixed metals in piping (for example, copper, cast iron and other cast metals), galvanic corrosion will contribute to accelerated corrosion of parts of the system. Corrosion inhibitors such as sodium nitrite or sodium molybdate can be injected into these systems to reduce the galvanic potential. However, the application of these corrosion inhibitors must be monitored closely. If the application of corrosion inhibitors increases the conductivity of the water within the system, the galvanic corrosion potential can be greatly increased.
Acidity or alkalinity (pH) is also a major consideration with regard to closed loop bimetallic circulating systems. Should the pH and corrosion inhibition doses be incorrect, galvanic corrosion will be accelerated. In most HVAC systems, the use of sacrificial anodes and cathodes is not an option, as they would need to be applied within the plumbing of the system and, over time, would corrode and release particles that could cause potential mechanical damage to circulating pumps, heat exchangers, etc. | 8 | Metallurgy |
The transition to the Late Bronze Age brought societal change to the British Isles, and also apparently increased availability of gold, which led to a trend to much larger and more massive pieces. The largest were jewellery worn round the neck in a range of styles, the most ostentatious wide flat collars or gorgets with ribbed decoration following the shape of the piece, and round discs at the side. The Mold Cape is unique among survivals, but fits in with the trend to massive pieces emphasizing the neck and chest. It was clearly not for prolonged wear, as the wearer could not raise their arms. In Ireland, lunulae were probably replaced as neck ornaments firstly by gold torcs, found from the Irish Middle Bronze Age, and then in the Late Bronze Age by the spectacular "gorgets" of thin ribbed gold, some with round discs at the side, of which 9 examples survive, 7 in the National Museum of Ireland.
Designs based on twisted bars or ribbons giving a spiral became popular, probably influenced by the Continent. "Although over 110 identifiable British [includes Ireland] ribbon torcs are known, the dating of these simple, flexible ornaments is elusive", perhaps indicating "a long-lived preference for ribbon torcs, which continued for over 1,000 years", into the Iron Age. | 8 | Metallurgy |
Soil acidification can cause damage to plants and organisms in the soil. In plants, soil acidification results in smaller, less durable roots. Acidic soils sometimes damage the root tips reducing further growth. Plant height is impaired and seed germination also decreases. Soil acidification impacts plant health, resulting in reduced cover and lower plant density. Overall, stunted growth is seen in plants. Soil acidification is directly linked to a decline in endangered species of plants.
In the soil, acidification reduces microbial and macrofaunal diversity. This can reduce soil structure decline which makes it more sensitive to erosion. There are less nutrients available in the soil, larger impact of toxic elements to plants, and consequences to soil biological functions (such as nitrogen fixation). A recent study showed that sugarcane monoculture induces soil acidity, reduces soil fertility, shifts microbial structure, and reduces its activity. Furthermore, most beneficial bacterial genera decreased significantly due to sugarcane monoculture, while beneficial fungal genera showed a reverse trend. Therefore, mitigating soil acidity, improving soil fertility, and soil enzymatic activities, including improved microbial structure with beneficial service to plants and soil, can be an effective measure to develop a sustainable sugarcane cropping system.
At a larger scale, soil acidification is linked to losses in agricultural productivity due to these effects.
Impacts of acidic water and Soil acidification on plants could be minor or in most cases major. In minor cases which do not result in fatality of plant life include; less-sensitive plants to acidic conditions and or less potent acid rain. Also in minor cases the plant will eventually die due to the acidic water lowering the plants natural pH. Acidic water enters the plant and causes important plant minerals to dissolve and get carried away; which ultimately causes the plant to die of lack of minerals for nutrition. In major cases which are more extreme; the same process of damage occurs as in minor cases, which is removal of essential minerals, but at a much quicker rate. Likewise, acid rain that falls on soil and on plant leaves causes drying of the waxy leaf cuticle; which ultimately causes rapid water loss from the plant to the outside atmosphere and results in death of the plant. To see if a plant is being affected by soil acidification, one can closely observe the plant leaves. If the leaves are green and look healthy, the soil pH is normal and acceptable for plant life. But if the plant leaves have yellowing between the veins on their leaves, that means the plant is suffering from acidification and is unhealthy. Moreover, a plant suffering from soil acidification cannot photosynthesize. Drying out of the plant due to acidic water destroy chloroplast organelles. Without being able to photosynthesize a plant cannot create nutrients for its own survival or oxygen for the survival of aerobic organisms; which affects most species of Earth and ultimately end the purpose of the plants existence. | 9 | Geochemistry |
When a transcript attains the threshold length of ten nucleotides, it enters the RNA exit channel. The polymerase breaks its interactions with the promoter elements and any regulatory proteins associated with the initiation complex that it no longer needs. Promoter escape in eukaryotes requires ATP hydrolysis and, in the case of Pol II-phosphorylation of the CTD. Meanwhile, the transcription bubble collapses down to 12-14 nucleotides, providing kinetic energy required for the escape. | 1 | Biochemistry |
The conversion of the amino acid glutamine to α-ketoglutarate takes place in two reaction steps:
1. Hydrolysis of the amino group of glutamine yielding glutamate and ammonium.
Catalyzing enzyme: glutaminase (EC 3.5.1.2)
2. Glutamate can be excreted or can be further metabolized to α-ketoglutarate.
For the conversion of glutamate to α-ketoglutarate three different reactions are possible:
Catalyzing enzymes:
*glutamate dehydrogenase (GlDH), EC 1.4.1.2
*glutamate pyruvate transaminase (GPT), also called alanine transaminase (ALT), EC 2.6.1.2
*glutamate oxaloacetate transaminase (GOT), also called aspartate transaminase (AST), EC 2.6.1.1 (component of the malate aspartate shuttle) | 1 | Biochemistry |
An approach that is amenable to algebraic calculation by computer algebra methods is to differentiate in log space. Since the elasticity can be defined logarithmically, that is:
differentiating in log space is an obvious approach. Logarithmic differentiation is particularly convenient in algebra software such as Mathematica or Maple, where logarithmic differentiation rules can be defined.
A more detailed examination and the rules differentiating in log space can be found at Elasticity of a function. | 7 | Physical Chemistry |
Electrochemical biosensors contain a biorecognition element that selectively reacts with the target analyte and produces an electrical signal that is proportional to the analyte concentration. In general, there are several approaches that can be used to detect electrochemical changes during a biorecognition event and these can be classified as follows: amperometric, potentiometric, impedance, and conductometric. | 1 | Biochemistry |
Several types of atmospheric aerosol have a significant effect on Earth's climate: volcanic, desert dust, sea-salt, that originating from biogenic sources and human-made. Volcanic aerosol forms in the stratosphere after an eruption as droplets of sulfuric acid that can prevail for up to two years, and reflect sunlight, lowering temperature. Desert dust, mineral particles blown to high altitudes, absorb heat and may be responsible for inhibiting storm cloud formation. Human-made sulfate aerosols, primarily from burning oil and coal, affect the behavior of clouds.
Although all hydrometeors, solid and liquid, can be described as aerosols, a distinction is commonly made between such dispersions (i.e. clouds) containing activated drops and crystals, and aerosol particles. The atmosphere of Earth contains aerosols of various types and concentrations, including quantities of:
* natural inorganic materials: fine dust, sea salt, or water droplets
* natural organic materials: smoke, pollen, spores, or bacteria
* anthropogenic products of combustion such as: smoke, ashes or dusts
Aerosols can be found in urban ecosystems in various forms, for example:
* Dust
* Cigarette smoke
* Mist from aerosol spray cans
* Soot or fumes in car exhaust
The presence of aerosols in the Earth's atmosphere can influence its climate, as well as human health. | 7 | Physical Chemistry |
An energy carrier is a substance (fuel) or sometimes a phenomenon (energy system) that contains energy that can be later converted to other forms such as mechanical work or heat or to operate chemical or physical processes.
Such carriers include springs, electrical batteries, capacitors, pressurized air, dammed water, hydrogen, petroleum, coal, wood, and natural gas. An energy carrier does not produce energy; it simply contains energy imbued by another system. | 7 | Physical Chemistry |
In metallurgy, a flux () is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time. They are used in both extractive metallurgy and metal joining.
Some of the earliest known fluxes were sodium carbonate, potash, charcoal, coke, borax, lime, lead sulfide and certain minerals containing phosphorus. Iron ore was also used as a flux in the smelting of copper. These agents served various functions, the simplest being a reducing agent, which prevented oxides from forming on the surface of the molten metal, while others absorbed impurities into slag, which could be scraped off molten metal.
Fluxes are also used in foundries for removing impurities from molten nonferrous metals such as aluminium, or for adding desirable trace elements such as titanium.
As cleaning agents, fluxes facilitate soldering, brazing, and welding by removing oxidation from the metals to be joined. In some applications molten flux also serves as a heat-transfer medium, facilitating heating of the joint by the soldering tool or molten solder. | 8 | Metallurgy |
In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bonds. Imines are common in synthetic and naturally occurring compounds and they participate in many reactions. | 0 | Organic Chemistry |
It is important to note that although some cycles have a typical combustion location (internal or external), they often can be implemented with the other. For example, John Ericsson developed an external heated engine running on a cycle very much like the earlier Diesel cycle. In addition, externally heated engines can often be implemented in open or closed cycles. In a closed cycle the working fluid is retained within the engine at the completion of the cycle whereas is an open cycle the working fluid is either exchanged with the environment together with the products of combustion in the case of the internal combustion engine or simply vented to the environment in the case of external combustion engines like steam engines and turbines. | 7 | Physical Chemistry |
The study of materials at extreme conditions, high pressure and high temperature uses a wide array of techniques to achieve these conditions and probe the behavior of material while in the extreme environment. Percy Williams Bridgman, the great pioneer of high-pressure research during the first half of the 20th century, revolutionized the field of high pressures with his development of an opposed anvil device with small flat areas that were pressed one against the other with a lever-arm. The anvils were made of tungsten carbide (WC). This device could achieve pressure of a few gigapascals, and was used in electrical resistance and compressibility measurements.
The first diamond anvil cell was created in 1957-1958. The principles of the DAC are similar to the Bridgman anvils, but in order to achieve the highest possible pressures without breaking the anvils, they were made of the hardest known material: a single crystal diamond. The first prototypes were limited in their pressure range and there was not a reliable way to calibrate the pressure.
The diamond anvil cell became the most versatile pressure generating device that has a single characteristic that sets it apart from the other pressure devices – its optical transparency. This provided the early high pressure pioneers with the ability to directly observe the properties of a material while under pressure. With just the use of an optical microscope, phase boundaries, color changes and recrystallization could be seen immediately, while x-ray diffraction or spectroscopy required time to expose and develop photographic film. The potential for the diamond anvil cell was realized by Alvin Van Valkenburg while he was preparing a sample for IR spectroscopy and was checking the alignment of the diamond faces.
The diamond cell was created at the National Bureau of Standards (NBS) by Charles E. Weir, Ellis R. Lippincott, and Elmer N. Bunting. Within the group, each member focused on different applications of the diamond cell. Van Valkenburg focused on making visual observations, Weir on XRD, Lippincott on IR Spectroscopy. The group members were well experienced in each of their techniques before they began outside collaboration with university researchers such as William A. Bassett and Taro Takahashi at the University of Rochester.
During the first experiments using diamond anvils, the sample was placed on the flat tip of the diamond (the culet) and pressed between the diamond faces. As the diamond faces were pushed closer together, the sample would be pressed and extrude out from the center. Using a microscope to view the sample, it could be seen that a smooth pressure gradient existed across the sample with the outermost portions of the sample acting as a kind of gasket. The sample was not evenly distributed across the diamond culet but localized in the center due to the "cupping" of the diamond at higher pressures. This cupping phenomenon is the elastic stretching of the edges of the diamond culet, commonly referred to as the "shoulder height". Many diamonds were broken during the first stages of producing a new cell or any time an experiment is pushed to higher pressure. The NBS group was in a unique position where almost endless supplies of diamonds were available to them. Customs officials occasionally confiscated diamonds from people attempting to smuggle them into the country. Disposing of such valuable confiscated materials could be problematic given rules and regulations. One solution was simply to make such materials available to people at other government agencies if they could make a convincing case for their use. This became an unrivaled resource as other teams at the University of Chicago, Harvard University, and General Electric entered the high pressure field.
During the following decades DACs have been successively refined, the most important innovations being the use of gaskets and the ruby pressure calibration. The DAC evolved to be the most powerful lab device for generating static high pressure. The range of static pressure attainable today extends to 640 GPa, much higher than the estimated pressures at the Earth's center (~360 GPa). | 7 | Physical Chemistry |
Protide, deuteride and tritide are used to describe ions or compounds that contain enriched hydrogen-1, deuterium or tritium, respectively.
In the classic meaning, hydride refers to any compound hydrogen forms with other elements, ranging over groups 1–16 (the binary compounds of hydrogen). The following is a list of the nomenclature for the hydride derivatives of main group compounds according to this definition:
*alkali and alkaline earth metals: metal hydride
*boron: borane, BH
*aluminium: alumane, AlH
*gallium: gallane, GaH
*indium: indigane, InH
*thallium: thallane, TlH
*carbon: alkanes, alkenes, alkynes, and all hydrocarbons
*silicon: silane
*germanium: germane
*tin: stannane
*lead: plumbane
*nitrogen: ammonia ("azane" when substituted), hydrazine
*phosphorus: phosphine (note "phosphane" is the IUPAC recommended name)
*arsenic: arsine (note "arsane" is the IUPAC recommended name)
*antimony: stibine (note "stibane" is the IUPAC recommended name)
*bismuth: bismuthine (note "bismuthane" is the IUPAC recommended name)
*helium: helium hydride (only exists as an ion)
According to the convention above, the following are "hydrogen compounds" and not "hydrides":
*oxygen: water ("oxidane" when substituted; synonym: hydrogen oxide), hydrogen peroxide
*sulfur: hydrogen sulfide ("sulfane" when substituted)
*selenium: hydrogen selenide ("selane" when substituted)
*tellurium: hydrogen telluride ("tellane" when substituted)
*polonium: hydrogen polonide ("polane" when substituted)
*halogens: hydrogen halides
Examples:
*nickel hydride: used in NiMH batteries
*palladium hydride: electrodes in cold fusion experiments
*lithium aluminium hydride: a powerful reducing agent used in organic chemistry
*sodium borohydride: selective specialty reducing agent, hydrogen storage in fuel cells
*sodium hydride: a powerful base used in organic chemistry
*diborane: reducing agent, rocket fuel, semiconductor dopant, catalyst, used in organic synthesis; also borane, pentaborane and decaborane
*arsine: used for doping semiconductors
*stibine: used in semiconductor industry
*phosphine: used for fumigation
*silane: many industrial uses, e.g. manufacture of composite materials and water repellents
*ammonia: coolant, fuel, fertilizer, many other industrial uses
*hydrogen sulfide: component of natural gas, important source of sulfur
*Chemically, even water and hydrocarbons could be considered hydrides.
All metalloid hydrides are highly flammable. All solid non-metallic hydrides except ice are highly flammable. But when hydrogen combines with halogens it produces acids rather than hydrides, and they are not flammable. | 0 | Organic Chemistry |
There are currently two accepted models for the creation of human artificial chromosome vectors. The first is to create a small minichromosome by altering a natural human chromosome. This is accomplished by truncating the natural chromosome, followed by the introduction of unique genetic material via the Cre-Lox system of recombination. The second method involves the literal creation of a novel chromosome de novo. Progress regarding de novo HAC formation has been limited, as many large genomic fragments will not successfully integrate into de novo vectors. Another factor limiting de novo vector formation is limited knowledge of what elements are required for construction, specifically centromeric sequences. However, challenges involving centromeric sequences have begun to be overcome. | 1 | Biochemistry |
Chemical oceanographers collect and measure chemicals in seawater, using the standard toolset of analytical chemistry as well as instruments like pH meters, electrical conductivity meters, fluorometers, and dissolved CO₂ meters. Most data are collected through shipboard measurements and from autonomous floats or buoys, but remote sensing is used as well. On an oceanographic research vessel, a CTD is used to measure electrical conductivity, temperature, and pressure, and is often mounted on a rosette of Nansen bottles to collect seawater for analysis. Sediments are commonly studied with a box corer or a sediment trap, and older sediments may be recovered by scientific drilling. | 9 | Geochemistry |
In physics, the Lamb–Mössbauer factor (LMF, after Willis Lamb and Rudolf Mössbauer) or elastic incoherent structure factor (EISF) is the ratio of elastic to total incoherent neutron scattering, or the ratio of recoil-free to total nuclear resonant absorption in Mössbauer spectroscopy. The corresponding factor for coherent neutron or X-ray scattering is the Debye–Waller factor; often, that term is used in a more generic way to include the incoherent case as well.
When first reporting on recoil-free resonance absorption, Mössbauer (1959) cited relevant theoretical work by Lamb (1939). The first use of the term "Mössbauer–Lamb factor" seems to be by Tzara (1961); from 1962 on, the form "Lamb–Mössbauer factor" came into widespread use.
Singwi and Sjölander (1960) pointed out the close relation to incoherent neutron scattering. With the invention of backscattering spectrometers, it became possible to measure the Lamb–Mössbauer factor as a function of the wavenumber (whereas Mössbauer spectroscopy operates at a fixed wavenumber). Subsequently, the term elastic incoherent structure factor became more frequent. | 7 | Physical Chemistry |
The van Deemter equation in chromatography, named for Jan van Deemter, relates the variance per unit length of a separation column to the linear mobile phase velocity by considering physical, kinetic, and thermodynamic properties of a separation. These properties include pathways within the column, diffusion (axial and longitudinal), and mass transfer kinetics between stationary and mobile phases. In liquid chromatography, the mobile phase velocity is taken as the exit velocity, that is, the ratio of the flow rate in ml/second to the cross-sectional area of the ‘column-exit flow path.’ For a packed column, the cross-sectional area of the column exit flow path is usually taken as 0.6 times the cross-sectional area of the column. Alternatively, the linear velocity can be taken as the ratio of the column length to the dead time. If the mobile phase is a gas, then the pressure correction must be applied. The variance per unit length of the column is taken as the ratio of the column length to the column efficiency in theoretical plates. The van Deemter equation is a hyperbolic function that predicts that there is an optimum velocity at which there will be the minimum variance per unit column length and, thence, a maximum efficiency. The van Deemter equation was the result of the first application of rate theory to the chromatography elution process. | 3 | Analytical Chemistry |
Tank leaching is usually differentiated from vat leaching on the following factors:
# In tank leaching the material is ground sufficiently fine to form a slurry or pulp, which can flow under gravity or when pumped. In vat leaching typically a coarser material is placed in the vat for leaching, this reduces the cost of size reduction;
# Tanks are typically equipped with agitators, baffles, gas introduction equipment designed to maintain the solids in suspension in the slurry, and achieve leaching. Vats usually do not contain much internal equipment, except for agitators.
# Tank leaching is typically continuous, while vat leaching is operated in a batch fashion, this is not always the case, and commercial processes using continuous vat leaching have been tested;
# Typically the retention time required for vat leaching is more than that for tank leaching to achieve the same percentage of recovery of the valuable material being leached;
In a tank leach the slurry is moved, while in a vat leach the solids remain in the vat, and solution is moved. | 8 | Metallurgy |
1,3-Propanedithiol is mainly used for the protection of aldehydes and ketones via their reversible formation of dithianes. A prototypical reaction is its formation of 1,3-dithiane from formaldehyde. The reactivity of this dithiane illustrates the concept of umpolung. Alkylation gives thioethers, e.g. 1,5-dithiacyclooctane.
The unpleasant odour of 1,3-propanedithiol has encouraged the development of alternative reagents that generate similar derivatives.
1,3-Propanedithiol is used in the synthesis of tiapamil. | 0 | Organic Chemistry |
Isotropic formulations are thermodynamically stable microemulsions possessing lyotropic liquid crystal properties. They inhabit a state of matter and physical behaviour somewhere between conventional liquids and that of solid crystals. Isotropic formulations are amphiphillic, exhibiting selective synchronicity with both the water and lipid phases of the substrate to which they are applied. Most recently, isotropic formulations have been used extensively in dermatology for drug delivery. | 7 | Physical Chemistry |
Chime was used by a wide range of biochemistry web sites for the visualization of macromolecules, many of which were linked to the World Index of Molecular Visualization Resources MolVisIndex.Org. Chime was also used until 2006 at the Protein Data Bank (PDB) to examine structures stored there.
Although available in 1996 in both Windows 95 and classic Mac OS versions for both Netscape and Internet Explorer browsers, development of Chime did not follow the move to Mac OS X for the Mac and support for Windows-based browsers other than Internet Explorer was limited (although it works well in Mozilla Firefox). One significant feature added in 1997 was the ability to display spectroscopic data in the form of the IUPAC JCAMP-DX protocols. Apart from this, most subsequent updates were for the installation package to follow the development of Windows and Internet Explorer. Accelrys announced in 2012 that Chime was no longer supported and would remain available for download until the end of 2012. Chime was part of the ISIS product line acquired by Symyx Technologies from scientific publisher Elsevier in October 2007. Now Chime is owned by Dassault Systemes BIOVIA (formerly Accelrys), and has been merged into Discovery Studio, but no longer exists as a free browser plugin.
Chime largely has been superseded by Jmol, a non-proprietary open-source Java molecular visualization application and JavaScript applet that has maintained most Chime command compatibility while adding numerous features. | 4 | Stereochemistry |
Each process is one of the following:
*isothermal (at constant temperature, maintained with heat added or removed from a heat source or sink)
*isobaric (at constant pressure)
*isometric/isochoric (at constant volume), also referred to as iso-volumetric
*adiabatic (no heat is added or removed from the system during adiabatic process)
*isentropic (reversible adiabatic process, no heat is added or removed during isentropic process) | 7 | Physical Chemistry |
There are a number of different dielectric mechanisms, connected to the way a studied medium reacts to the applied field (see the figure illustration). Each dielectric mechanism is centered around its characteristic frequency, which is the reciprocal of the characteristic time of the process. In general, dielectric mechanisms can be divided into relaxation and resonance processes. The most common, starting from high frequencies, are: | 7 | Physical Chemistry |
* 1983 - I. I. Rabi
* 1984 - David W. Allan
* 1985 - Norman Ramsey, Nobel Prize in 1989
* 1986 - Jerrold R. Zacharias
* 1987 - Louis Essen
* 1988 - Gernot M. R. Winkler
* 1989 - Leonard S. Cutler
* 1990 - Claude Audoin
* 1991 - Andrea De Marchi
* 1992 - James A. Barnes
* 1993 - Robert F. C. Vessot
* 1994 - Jacques Vanier
* 1995 - Fred L. Walls
* 1996 - Andre Clairon and Robert E. Drullinger
* 1997 - Harry E. Peters and Nikolai A. Demidov
* 1998 - David J. Wineland, Nobel Prize in 2012
* 1999 - Bernard Guinot
* 2000 - William J. Riley Jr.
* 2001 - Lute Maleki
* 2002 - Jon H. Shirley
* 2003 - Andreas Bauch
* 2005 - Theodor W. Hänsch, Nobel Prize in 2005
* 2004 - John L. Hall, Nobel Prize in 2005
* 2006 - James C. Bergquist
* 2007 - Patrick Gill and Leo Hollberg
* 2008 - Hidetoshi Katori
* 2009 - John D. Prestage
* 2010 - Long Sheng Ma
* 2011 - Fritz Riehle
* 2012 - James Camparo
* 2013 - Judah Levine
* 2014 - Harald R. Telle
* 2015 - Ulrich_L._Rohde
* 2016 - John Kitching
* 2017 - Scott Diddams
* 2018 - Jun Ye
* 2019 - Steven Jefferts
* 2020 - Robert Lutwak
* 2021 - Ekkehard Peik | 7 | Physical Chemistry |
Electrophilic aromatic substitution is famously affected by EWGs. The effect is transmitted by inductive and resonance effects. Benzene with an EWG typically undergoes electrophilic substitution at meta positions. Overall the rates are diminished. thus EWGs are called deactivating.
When it comes to nucleophilic substitution reactions, electron-withdrawing groups are more prone to nucleophilic substitution. For example, chlorodinitrobenzene is far more susceptible to reactions displacing chloride compared to chlorobenzene. | 7 | Physical Chemistry |
For translation to occur, eukaryotic mRNAs require a 5' Cap structure. This means that viruses must also have one. This normally consists of 7MeGpppN where N is normally adenine or guanine. The viruses encode a protein, normally a replicase, with a methyltransferase activity to allow this.
Some viruses are cap-snatchers. During this process, a G-capped host mRNA is recruited by the viral transcriptase complex and subsequently cleaved by a virally encoded endonuclease. The resulting capped leader RNA is used to prime transcription on the viral genome.
However some plant viruses do not use cap, yet translate efficiently due to cap-independent translation enhancers present in 5 and 3 untranslated regions of viral mRNA. | 1 | Biochemistry |
Genes are regulated so that they are expressed only when the product is needed, since expression draws on limited resources. A cell regulates its gene expression depending on its external environment (e.g. available nutrients, temperature and other stresses), its internal environment (e.g. cell division cycle, metabolism, infection status), and its specific role if in a multicellular organism. Gene expression can be regulated at any step: from transcriptional initiation, to RNA processing, to post-translational modification of the protein. The regulation of lactose metabolism genes in E. coli (lac operon) was the first such mechanism to be described in 1961. | 1 | Biochemistry |
In contrast to the use of mercury (which relies on amalgamation of the gold to coalesce it and separate it from impurities) this method relies on boraxs ability to lower all the minerals melting points. Since the gold is usually the heaviest of these minerals, it allows for concentrating the gold on the bottom of the crucible. The process requires considerably less heat than conventional refining methods, which can be obtainable even in remote locations (using charcoal).
After the ore is crushed into a fine powder, its lightly panned to leave only the heaviest minerals in the pan. Its then thoroughly mixed by three times (by volume) as much of borax and a few drops of water. This mixture is then heated until the whole mixture is molten, after which molten droplets of gold collect on the bottom of the crucible. | 8 | Metallurgy |
At 62 °C and atmospheric pressure, phosphonium iodide sublimates and dissociates reversibly into phosphine and hydrogen iodide (HI). It oxidizes slowly in air to give iodine and phosphorus oxides; it is hygroscopic and is hydrolyzed into phosphine and HI:
Phosphine gas may be devolved from phosphonium iodide by mixing an aqueous solution with potassium hydroxide:
It reacts with elemental iodine and bromine in a nonpolar solution to give phosphorus halides; for example:
Phosphonium iodide is a powerful substitution reagent in organic chemistry; for example, it can convert a pyrilium into a phosphinine via substitution. In 1951, Glenn Halstead Brown found that PHI reacts with acetyl chloride to produce an unknown phosphine derivative, possibly . | 0 | Organic Chemistry |
Most cancer cells cause mutation in the bodies' metabolic activities to increase glucose metabolism in order to rapidly proliferate. Mutations that increase the cells metabolic activity and turn a normal cell into a tumor cell are called oncogenes. Cancer cells are unlike many other cells. They have very little vulnerabilities, but experiments in which the inhibition of transamination of malate-shuttle slowed proliferation due to the fact metabolism of glucose was being slowed. | 1 | Biochemistry |
* Acetonyl group
* Acyl group (e.g. acetyl group, benzoyl group)
* Alkyl group (e.g., methyl group, ethyl group)
* Alkenyl group (e.g., vinyl group, allyl group)
* Alkynyl group (propargyl group)
* Benzyloxycarbonyl group (Cbz)
* tert-butoxycarbonyl group (Boc)
* Carboxyl group | 0 | Organic Chemistry |
The preinitiation complex (PIC) assembles in a stepwise fashion on the promoter of genes to initiate transcription. The TFIID binds to the TATA box in order to begin the assembly of the TFIIA, recruiting other transcription factors and components needed in the PIC. Data suggests that pRb is able to repress transcription by both pRb being recruited to the promoter as well as having a target present in TFIID.
The presence of pRb may change the conformation of the TFIIA/IID complex into a less active version with a decreased binding affinity. pRb can also directly interfere with their association as proteins, preventing TFIIA/IID from forming an active complex. | 1 | Biochemistry |
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 not in stationary states, 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. | 7 | Physical Chemistry |
The equations and their parameters are calibrated for adult humans with a body mass of 70 kg and a plasma volume of ca. 2.5 L. | 1 | Biochemistry |
In the United States, the ECOTOX, ERED (sediment) and Toxicity Residue Databases are used by many regulatory agencies such as state environmental quality agencies and the EPA to determine regulatory environmental toxicant concentration levels. Under the Clean Water Act the EPA has used the ECOTOX database among other information to set wastewater toxicant concentration standards for industry as well as water quality standards for all contaminants in surface waters. Under the CWA, individual states must regulate water quality criteria at or below the concentrations set forth by the EPA. Sediment toxicant concentrations, however, are generally not regulated in the same way. The determination of sediment quality criteria and sediment toxicity testing is highly complex and is often regulated by states or some state run environmental agency. Sediment toxicity evaluations of contaminated sediments are very site specific and toxicant effect levels are often much more variable than those of surface waters. For this reason it may be nearly impossible to develop feasible acceptable sediment concentration regulations that apply to all aquatic systems or regions.
Acceptable concentrations or sediment quality guidelines have been developed and are used in risk assessments and the management of dredged materials. "Sediment quality guidelines" (SQGs), as defined at the 2002 Society of Environmental Toxicology and Chemistry (SETAC) Pellston Workshop, are numerical chemical concentrations intended to be either protective of biological resources, or predictive of adverse effects to those resources, or both. SQGs for assessing sediment quality relative to the potential for adverse effects on sediment-dwelling organisms have been derived using both mechanistic and empirical approaches. | 1 | Biochemistry |
A radical is a molecule with an odd number of electrons, and is induced in a variety of ways, including ultra-violet radiation. A sun burn is largely due to radical formation from this radiation. The radical-pair, however, is not simply two radicals. This is because radical-pairs (specifically singlets) are quantum entangled, even as separate molecules. More fundamental to the radical-pair mechanism, however, is the fact that radical-pair electrons both have spin, short for spin angular momentum, which gives each separate radical a magnetic moment. Therefore, spin states can be altered by magnetic fields. | 7 | Physical Chemistry |
Molecular recognition can be subdivided into static molecular recognition and dynamic molecular recognition. Static molecular recognition is likened to the interaction between a key and a keyhole; it is a 1:1 type complexation reaction between a host molecule and a guest molecule to form a host–guest complex. To achieve advanced static molecular recognition, it is necessary to make recognition sites that are specific for guest molecules.
In the case of dynamic molecular recognition the binding of the first guest to the first binding site of a host affects the association constant of a second guest with a second binding site. leading to cooperativity of binding. In the case of positive allosteric systems the binding of the first guest increases the association constant of the second guest. While for negative allosteric systems the binding of the first guest decreases the association constant with the second. The dynamic nature of this type of molecular recognition is particularly important since it provides a mechanism to regulate binding in biological systems.
Dynamic molecular recognition may enhance the ability to discriminate between several competing targets via the conformational proofreading mechanism. Dynamic molecular recognition is also being studied for application in highly functional chemical sensors and molecular devices | 6 | Supramolecular Chemistry |
Ultraviolet radiation is used for very fine resolution photolithography, a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. The exposure causes chemical reactions to occur in the photoresist. After removal of unwanted photoresist, a pattern determined by the mask remains on the sample. Steps may then be taken to "etch" away, deposit on or otherwise modify areas of the sample where no photoresist remains.
Photolithography is used in the manufacture of semiconductors, integrated circuit components, and printed circuit boards. Photolithography processes used to fabricate electronic integrated circuits presently use 193 nm UV and are experimentally using 13.5 nm UV for extreme ultraviolet lithography. | 5 | Photochemistry |
Insulin can also cause postprandial somnolence via another mechanism. Insulin increases the activity of Na/K ATPase, causing increased movement of potassium into cells from the extracellular fluid. The large movement of potassium from the extracellular fluid can lead to a mild hypokalemic state. The effects of hypokalemia can include fatigue, muscle weakness, or paralysis. The severity of the hypokalemic state can be evaluated using Fuller's Criteria. Stage 1 is characterized by no symptoms but mild hypokalemia. Stage 2 is characterized with symptoms and mild hypokalemia. Stage 3 is characterized by only moderate to severe hypokalemia. | 1 | Biochemistry |
Gene symbols are italicised, with all letters in lowercase (shh). Protein designations are the same as the gene symbol, but are not italicised; the first letter is in uppercase and the remaining letters are in lowercase (Shh). | 1 | Biochemistry |
The natural logarithm of the power-law rate equation is
This can be used to estimate the order of reaction of each reactant. For example, the initial rate can be measured in a series of experiments at different initial concentrations of reactant with all other concentrations kept constant, so that
The slope of a graph of as a function of then corresponds to the order with respect to reactant .
However, this method is not always reliable because
# measurement of the initial rate requires accurate determination of small changes in concentration in short times (compared to the reaction half-life) and is sensitive to errors, and
# the rate equation will not be completely determined if the rate also depends on substances not present at the beginning of the reaction, such as intermediates or products. | 7 | Physical Chemistry |
Sulfide compounds can be prepared in several different ways:
#Direct combination of elements:
#:Example: Fe + S → FeS
#Reduction of a sulfate:
#:Example: MgSO + 4C → MgS + 4CO
#Precipitation of an insoluble sulfide:
#:Example: M + HS → MS + 2H | 0 | Organic Chemistry |
Although there is significant insight as to how OPVs work, it is still difficult to relate the devices functionality to local film structures. This difficulty may be attributed to the minimal current generation at a given point within OPVs. Through pc-AFM, OPV devices can be probed at nano-scale level and can help to increase our fundamental knowledge of mechanisms involved in OPVs at nano-scale level. pc-AFM is capable of gathering information such as the mapping of photocurrents, differences in film morphology, determination of donor-acceptor domains, current density-voltage plots, quantum efficiencies, and approximate charge carrier mobilities. One of the other notable characteristics of pc-AFM is its ability to provide concurrent information regarding the topological and photocurrent properties of the device at nano-scale. Using this concurrent sampling method, the sample handling is minimized and can provide more accurate results. In a study by Pingree et al., pc-AFM was used to measure how spatial deviations in the photocurrent generation developed with different processing techniques. The authors were able to compare these photocurrent variations to the duration of the annealing process. They have concluded that lengthening the annealing time allows for improved nano-scale phase separation as well as created a more ordered device. Actual times for the annealing process vary depending on the properties of the polymers used. The authors have shown that external quantum efficiency (EQE) and power conversion efficiency (PCE) levels reach a maximum at certain annealing times whereas while the electron and hole mobilitys do not show the corresponding trends. Therefore, while lengthening the annealing time can increase the photocurrents within the OPV, there is a practical limit to after which the benefits may not be substantial. Besides functional properties, pc-AFM can also be used to interrogate the composition heterogeneity of OPVs when combined with either Raman or infrared (IR) spectroscopy, and it is especially valuable for studying their degradation.
In more recent studies, pc-AFM has been employed to gather information regarding the photoactive regions from the use of quantum dots. Because if their relative ease of use, along with size-tunable excitation attributes, quantum dots have commonly been applied as sensitizers in optoelectronic devices. The authors have studied the photoresponse of sub-surface foundations such as buried indium arsenide (InAs) quantum dots through the implementation of pc-AFM. Through the use of pc-AFM, information regarding quantum dot size, as well as the dispersion of quantum dots within the device, can be recorded in a non-destructive manner. This information can then be used to display local variances in photoactivity relating to heterogeneities within the film morphology. | 6 | Supramolecular Chemistry |
The level of domestication of cotton plants correlates to indirect defense investment in the form of extrafloral nectaries. Wild varieties produce higher volumes of nectar and attract a wider variety of natural enemies. Thus, the process of breeding new cotton varieties has overlooked natural resistance traits in the pursuit of high-yielding varieties that can be protected by pesticides. Plants bearing extrafloral nectaries have lower pest levels along with greater levels of natural enemies. Feeding by herbivores can directly induce nectar production. These findings illustrate the potential benefits that could be gained through incorporating the desirable genetics of wild varieties into cultivated varieties. | 1 | Biochemistry |
Petroleum oil contains aromatic compounds that are toxic to most life forms. Episodic and chronic pollution of the environment by oil causes major disruption to the local ecological environment. Marine environments in particular are especially vulnerable, as oil spills near coastal regions and in the open sea are difficult to contain and make mitigation efforts more complicated. In addition to pollution through human activities, approximately 250 million litres of petroleum enter the marine environment every year from natural seepages. Despite its toxicity, a considerable fraction of petroleum oil entering marine systems is eliminated by the hydrocarbon-degrading activities of microbial communities, in particular by a recently discovered group of specialists, the hydrocarbonoclastic bacteria (HCB). Alcanivorax borkumensis was the first HCB to have its genome sequenced. In addition to hydrocarbons, crude oil often contains various heterocyclic compounds, such as pyridine, which appear to be degraded by similar mechanisms to hydrocarbons. | 2 | Environmental Chemistry |
Iron can be stored in ferritin as ferric iron due to the ferroxidase activity of the ferritin heavy chain. Dysfunctional ferritin may accumulate as hemosiderin, which can be problematic in cases of iron overload. The ferritin storage iron pool is much larger than the labile iron pool, ranging in concentration from 0.7 mM to 3.6 mM. | 1 | Biochemistry |
p75NTR has been implicated as a marker for cancer stem cells in melanoma and other cancers. Melanoma cells transplanted into an immunodeficient mouse model were shown to require expression of CD271 in order to grow a melanoma. Gene knockdown of CD271 has also been shown to abolish neural crest stem cell properties of melanoma cells and decrease genomic stability leading to a reduced migration, tumorigenicity, proliferation and induction of apoptosis. Furthermore, increased levels of CD271 were observed in brain metastatic melanoma cells whereas resistance to the BRAF inhibitor vemurafenib supposedly selects for highly malignant brain and lung-metastasizing melanoma cells. Recently, expression of p75NTR (NGFR) was associated with progressive intracranial disease in melanoma patients | 1 | Biochemistry |
Since coenzyme A is, in chemical terms, a thiol, it can react with carboxylic acids to form thioesters, thus functioning as an acyl group carrier. It assists in transferring fatty acids from the cytoplasm to mitochondria. A molecule of coenzyme A carrying an acyl group is also referred to as acyl-CoA. When it is not attached to an acyl group, it is usually referred to as CoASH or HSCoA. This process facilitates the production of fatty acids in cells, which are essential in cell membrane structure.
Coenzyme A is also the source of the phosphopantetheine group that is added as a prosthetic group to proteins such as acyl carrier protein and formyltetrahydrofolate dehydrogenase. | 1 | Biochemistry |
Upregulation refers to the increase in the number of receptor sites on the membrane. Estrogen upregulates FSH receptor sites. In turn, FSH stimulates granulosa cells to produce estrogens. This synergistic activity of estrogen and FSH allows for follicle growth and development in the ovary. | 1 | Biochemistry |
A total synthesis of (+)-resiniferatoxin was completed by the Paul Wender group at Stanford University in 1997. The process begins with a starting material of 1,4-pentadien-3-ol and consists of more than 25 significant steps. As of 2007, this represented the only complete total synthesis of any member of the daphnane family of molecules.
One of the main challenges in synthesizing a molecule such as resiniferatoxin is forming the three-ring backbone of the structure. The Wender group was able to form the first ring of the structure by first synthesizing Structure 1 in Figure 1. By reducing the ketone of Structure 1 followed by oxidizing the furan nucleus with m-CPBA and converting the resulting hydroxy group to an oxyacetate, Structure 2 can be obtained. Structure 2 contains the first ring of the three-ring structure of RTX. It reacts through an oxidopyrylium cycloaddition when heated with DBU in acetonitrile to form Structure 4 by way of Intermediate 3. Several steps of synthesis are required to form Structure 5 from Structure 4, with the main goal of positioning the allylic branch of the seven-membered ring in a trans conformation. Once this conformation is achieved, zirconocene-mediated cyclization of Structure 5 can occur, and oxidizing the resulting hydroxy group with TPAP will yield Structure 6. Structure 6 contains all three rings of the RTX backbone and can then be converted to resiniferatoxin through additional synthesis steps attaching the required functional groups.
An alternative approach to synthesizing the three-ring backbone makes use of radical reactions to create the first and third rings in a single step, followed by the creation of the remaining ring. It has been proposed by the Masayuki Inoue group of the University of Tokyo. | 0 | Organic Chemistry |
Penetration depth is a measure of how deep light or any electromagnetic radiation can penetrate into a material. It is defined as the depth at which the intensity of the radiation inside the material falls to 1/e (about 37%) of its original value at (or more properly, just beneath) the surface.
When electromagnetic radiation is incident on the surface of a material, it may be (partly) reflected from that surface and there will be a field containing energy transmitted into the material. This electromagnetic field interacts with the atoms and electrons inside the material. Depending on the nature of the material, the electromagnetic field might travel very far into the material, or may die out very quickly. For a given material, penetration depth will generally be a function of wavelength. | 7 | Physical Chemistry |
Rather than requiring endogenous or external mitogens to continue the cell cycle, cancer cells are able to grow, survive, and replicate without mitogens. Cancer cells may lose their dependence on external mitogens by a variety of pathways.
First, cancer cells can produce their own mitogens, a term called autocrine stimulation. This can result in a deadly positive feedback loop - tumor cells produce their own mitogens, which stimulate more tumor cells to replicate, which can then produce even more mitogens. For example, consider one of the earliest oncogenes to be identified, p28sis from the simian sarcoma virus, which causes tumorigenesis in the host animal. Scientists found that p28sis has a nearly identical amino acid sequence as human platelet-derived growth factor (PDGF). Thus, tumors formed by the simian sarcoma virus are no longer dependent on the fluctuations of PDGF that control cell growth; instead, they can produce their own mitogens in the form of p28sis. With enough p28sis activity, the cells can proliferate without restriction, resulting in cancer.
Second, cancer cells can have mutated cell-surface receptors for mitogens. The protein kinase domain found on mitogenic receptors is often hyperactivated in cancer cells, remaining turned on even in the absence of external mitogens. Additionally, some cancers are associated with an overproduction of mitogenic receptors on the cell surface. With this mutation, cells are stimulated to divide by abnormally low levels of mitogens. One such example is HER2, a receptor tyrosine kinase that responds to the mitogen EGF. Overexpression of HER2 is common in 15-30% of breast cancers, allowing the cell cycle to progress even with extremely low concentrations of EGF. The overexpression of kinase activity in these cells aids in their proliferation. These are known as hormone-dependent breast cancers, as the kinase activation in these cancers is connected to exposure to both growth factors and estradiol.
Third, downstream effectors of mitogenic signaling are often mutated in cancer cells. An important mitogenic signaling pathway in humans is the Ras-Raf-MAPK pathway. Mitogenic signaling normally activates Ras, a GTPase, that then activates the rest of the MAPK pathway, ultimately expressing proteins that stimulate cell cycle progression. It is likely that most, if not all, cancers have some mutation in the Ras-Raf-MAPK pathway, most commonly in Ras. These mutations allow the pathway to be constitutively activated, regardless of the presence of mitogens. | 1 | Biochemistry |
Before the discovery of ribozymes, enzymes—which are defined as catalytic proteins—were the only known biological catalysts. In 1967, Carl Woese, Francis Crick, and Leslie Orgel were the first to suggest that RNA could act as a catalyst. This idea was based upon the discovery that RNA can form complex secondary structures. These ribozymes were found in the intron of an RNA transcript, which removed itself from the transcript, as well as in the RNA component of the RNase P complex, which is involved in the maturation of pre-tRNAs. In 1989, Thomas R. Cech and Sidney Altman shared the Nobel Prize in chemistry for their "discovery of catalytic properties of RNA". The term ribozyme was first introduced by Kelly Kruger et al. in a paper published in Cell in 1982.
It had been a firmly established belief in biology that catalysis was reserved for proteins. However, the idea of RNA catalysis is motivated in part by the old question regarding the origin of life: Which comes first, enzymes that do the work of the cell or nucleic acids that carry the information required to produce the enzymes? The concept of "ribonucleic acids as catalysts" circumvents this problem. RNA, in essence, can be both the chicken and the egg.
In the 1980s, Thomas Cech, at the University of Colorado Boulder, was studying the excision of introns in a ribosomal RNA gene in Tetrahymena thermophila. While trying to purify the enzyme responsible for the splicing reaction, he found that the intron could be spliced out in the absence of any added cell extract. As much as they tried, Cech and his colleagues could not identify any protein associated with the splicing reaction. After much work, Cech proposed that the intron sequence portion of the RNA could break and reform phosphodiester bonds. At about the same time, Sidney Altman, a professor at Yale University, was studying the way tRNA molecules are processed in the cell when he and his colleagues isolated an enzyme called RNase-P, which is responsible for conversion of a precursor tRNA into the active tRNA. Much to their surprise, they found that RNase-P contained RNA in addition to protein and that RNA was an essential component of the active enzyme. This was such a foreign idea that they had difficulty publishing their findings. The following year, Altman demonstrated that RNA can act as a catalyst by showing that the RNase-P RNA subunit could catalyze the cleavage of precursor tRNA into active tRNA in the absence of any protein component.
Since Cechs and Altmans discovery, other investigators have discovered other examples of self-cleaving RNA or catalytic RNA molecules. Many ribozymes have either a hairpin – or hammerhead – shaped active center and a unique secondary structure that allows them to cleave other RNA molecules at specific sequences. It is now possible to make ribozymes that will specifically cleave any RNA molecule. These RNA catalysts may have pharmaceutical applications. For example, a ribozyme has been designed to cleave the RNA of HIV. If such a ribozyme were made by a cell, all incoming virus particles would have their RNA genome cleaved by the ribozyme, which would prevent infection. | 7 | Physical Chemistry |
For U.S. food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For iodine specifically, 100% of the Daily Value is considered 150 μg, and this figure remained at 150 μg in the May 27, 2016 revision.
A table of the old and new adult daily values is provided at Reference Daily Intake. | 1 | Biochemistry |
Members of Ancyronyx superficially resemble spiders and are aquatic, hence their common name, "spider water beetles". They are typically very small, with an average body length (without legs) of . They are characterized by extremely long legs (longer than the body length). The legs have widely separated coxae, with the procoxae (coxae attached to the prothorax) usually visible dorsally. The legs are tipped with large claws, each with two or three basal teeth. The distal teeth are the largest. The pair of antennae are typically 11-segmented. Most of the species possess brightly colored patterns on their elytra, but not all. The elytra also possess eight to eleven grooves (elytral striae), as well as small depressions (elytral punctures) of varying depth and number. The pronotum possesses a transverse groove and a more or less straight front margin, with pronotal carinae absent or weakly present.
Spider water beetles can be divided into two species groups, based on morphological and ecological adaptation patterns.
*The Ancyronyx variegatus species group are larger in size (usually larger than ), with very long legs, stout coxites on the ovipositor, and a transverse prosternal process. Their larvae are also larger, depressed in cross-section, and possess large side-pointing projections on the sides of the abdomen.
*The Ancyronyx patrolus species group have small and slender bodies, with comparatively shorter legs, long and slender coxites on the ovipositor, and a squarish prosternal process. Their larvae are smaller, with a more vaulted cross-section, and backwards pointing projections from the sides of the abdomen.
Ancyronyx is closely related to the genus Podelmis, but can be distinguished from the latter by the more or less straight and slender last segment of the ovipositor (versus the conical sideways-bent terminal segment of the ovipositor of Podelmis), and the absence of an anterior process on the prosternum. | 2 | Environmental Chemistry |
One proprietary material for ISCR is the EHC technology created by Adventus. This particular product is actually a mixture of carbon, nutrients, and zero-valent iron. The theory behind this product is that the carbon in the mixture will promote bacterial growth in the subsurface. The growing bacteria consume oxygen, which easily accepts electrons, present in the subsurface which increases reducing potential. The growing bacteria also ferment and produce fatty acids that act as electron donors to other bacteria and substances. Adventus uses this combination of biotic and abiotic processes to implement ISCR. EHC is injected as a "slurry" (a mixture that is 15 to 40% solids and weight with the rest being liquid) into the substratum.
Another material worth mentioning is EZVI (emulsified ZVI) which is a NASA technology. EZVI is used mainly to treat halogenated hydrocarbons and DNAPLs. EZVI is nanoscale iron that is placed into a biodegradable oil emulsion. The emulsion is then injected into the substratum. | 2 | Environmental Chemistry |
Auger electron spectroscopy (AES; pronounced in French) is a common analytical technique used specifically in the study of surfaces and, more generally, in the area of materials science. It is a form of electron spectroscopy that relies on the Auger effect, based on the analysis of energetic electrons emitted from an excited atom after a series of internal relaxation events. The Auger effect was discovered independently by both Lise Meitner and Pierre Auger in the 1920s. Though the discovery was made by Meitner and initially reported in the journal Zeitschrift für Physik in 1922, Auger is credited with the discovery in most of the scientific community. Until the early 1950s Auger transitions were considered nuisance effects by spectroscopists, not containing much relevant material information, but studied so as to explain anomalies in X-ray spectroscopy data. Since 1953 however, AES has become a practical and straightforward characterization technique for probing chemical and compositional surface environments and has found applications in metallurgy, gas-phase chemistry, and throughout the microelectronics industry. | 7 | Physical Chemistry |
Halohydrins react with base to give epoxides. The reaction is spontaneous because the energetic cost of introducing the ring strain (13 kcal/mol) is offset by the larger bond enthalpy of the newly introduced C-O bond (when compared to that of the cleaved C-halogen bond).
Formation of epoxides from secondary halohydrins is predicted to occur faster than from primary halohydrins due to increased entropic effects in the secondary halohydrin, and tertiary halohydrins react (if at all) extremely slowly due to steric crowding.
Starting with propylene chlorohydrin, most of the world's supply of propylene oxide arises via this route.
An intramolecular epoxide formation reaction is one of the key steps in the Darzens reaction.
In the Johnson–Corey–Chaykovsky reaction epoxides are generated from carbonyl groups and sulfonium ylides. In this reaction, a sulfonium is the leaving group instead of chloride. | 0 | Organic Chemistry |
Certain types of broadening are the result of conditions over a large region of space rather than simply upon conditions that are local to the emitting particle. | 7 | Physical Chemistry |
Piping corrosion circuit or Corrosion loop
/ Piping Circuitization and Corrosion Modelling, is carried out as part of either a Risk Based Inspection analysis (RBI) or Materials Operating Envelope analysis (MOE). It is the systematization of the piping components versus failure modes analysis into materials operating envelope. It groups piping materials / chemical make-up into systems / sub systems and assigns corrosion mechanisms. These are then monitored over the operating lifetime of the facility. This analysis is performed on circuit inspection results to determine and optimize circuit corrosion rates and measured thickness/dates for circuit components. Corrosion Circuits are utilized in the Integrity Management Plan (IMP) which forms a part of the overall Asset integrity management system and is an integral part of any RBI analysis. Many times a "system" will be a broad overview of the facilities process flow, broken by stream constituents, while a circuit level analysis breaks systems into smaller "circuits" that group common metallurgies, equal (or roughly equal) temperatures and pressures, and expected damage mechanisms. | 8 | Metallurgy |
Finally since
we find that
Since the Gibbs free energy per mole of the mixture is
then
At last we can calculate the molar entropy of mixing since
and | 7 | Physical Chemistry |
In neuroscience, Dales principle (or Dales law) is a rule attributed to the English neuroscientist Henry Hallett Dale. The principle basically states that a neuron performs the same chemical action at all of its synaptic connections to other cells, regardless of the identity of the target cell. However, there has been disagreement about the precise wording.
Because of an ambiguity in the original statement, there are actually two versions of the principle, one that has been shown definitively to be false, and another that remains a valuable rule of thumb. The term "Dales principle" was first used by Sir John Eccles in 1954, in a passage reading, "In conformity with Dales principle (1934, 1952) that the same chemical transmitter is released from all the synaptic terminals of a neurone…" Some modern writers have understood the principle to state that neurons release one and only one transmitter at all of their synapses, which is false. Others, including Eccles himself in later publications, have taken it to mean that neurons release the same set of transmitters at all of their synapses.
Dale himself never stated his "principle" in an explicit form. The source that Eccles referred to was a lecture published by Dale in 1934, called Pharmacology and nerve endings, describing some of the early research into the physiology of neurotransmission. At that time, only two chemical transmitters were known, acetylcholine and noradrenaline (then thought to be adrenaline). In the peripheral nervous system, cholinergic and adrenergic transmission were known to arise from different groups of nerve fibers. Dale was interested in the possibility that a neuron releasing one of these chemicals in the periphery might also release the same chemical at central synapses. He wrote:
And near the end of the paper:
With only two transmitter chemicals known to exist at the time, the possibility of a neuron releasing more than one transmitter at a single synapse did not enter anybody's mind, and so no care was taken to frame hypotheses in a way that took this possibility into account. The resulting ambiguity in the initial statements led to some confusion in the literature about the precise meaning of the principle. Nicoll and Malenka, for example, understood it to state that a neuron always releases one and only one neurotransmitter at all of its synapses. In this form it is certainly false. Many neurons release more than one neurotransmitter, in what is called "cotransmission". Although there were earlier hints, the first formal proposal of this discovery did not come until 1976. Most neurons release several different chemical messengers. In modern neuroscience, neurons are often classified by their neurotransmitter and most important cotransmitter, for example striatal GABA neurons utilize either opioid peptides or substance P as the primary cotransmitter.
In a 1976 publication, however, Eccles interpreted the principle in a subtly different way:
The addition of "or substances" is critical. With this change, the principle allows for the possibility of neurons releasing more than one transmitter, and only asserts that the same set are released at all synapses. In this form, it continues to be an important rule of thumb, with only a few known exceptions, including David Sulzer and Stephen Rayport's finding that dopamine neurons also release glutamate as a neurotransmitter, but at separate release sites. | 1 | Biochemistry |
Metabolic labeling of glycans can be used as a way to detect glycan structures. A well known strategy involves the use of azide-labeled sugars which can be reacted using the Staudinger ligation. This method has been used for in vitro and in vivo imaging of glycans. | 0 | Organic Chemistry |
The relationship between gene targeting, gene editing and genetic modification is outlined in the Venn diagram below. It displays how Genetic engineering encompasses all 3 of these techniques. Genome editing is characterised by making small edits to the genome at a specific location, often following cutting of the target DNA region by a site-specific-nuclease such as CRISPR. Genetic modification usually describes the insertion of a transgene (foreign DNA, i.e. a gene from another species) into a random location within the genome. Gene-targeting is a specific biotechnological tool that can lead to small changes to the genome at a specific site - in which case the edits caused by gene-targeting would count as genome editing. However gene targeting is also capable of inserting entire genes (such as transgenes) at the target site if the transgene is incorporated into the homology repair template that is used during gene-targeting. In such cases the edits caused by gene-targeting would, in some jurisdictions, be considered as equivalent to Genetic Modification as insertion of foreign DNA has occurred.
Gene targeting is one specific form of genome editing tool. Other genome editing tools include targeted mutagenesis, base editing and prime editing, all of which create edits to the endogenous DNA (DNA already present in the organism) at a specific genomic location. This site-specific or ‘targeted’ nature of genome editing is typically what makes genome-editing different to traditional ‘genetic modification’ which inserts a transgene at a non-specific location in the organisms genome, as well as gene-editing making small edits to the DNA already present in the organisms, verses genetic modification insertion foreign' DNA from another species.
Because gene editing makes smaller changes to endogenous DNA, many mutations created through genome-editing could in theory occur through natural mutagenesis or, in the context of plants, through mutation breeding which is part of conventional breeding (in contrast the insertion of a transgene to create a Genetically Modified Organism (GMO) could not occur naturally). However, there are exceptions to this general rule; as explained in the introduction, GT can introduce a range of possible size of edits to DNA; from very small edits such as changing, inserting or deleting 1 base-pair, through to inserting much longer DNA sequences, which could in theory include insertion of an entire transgene. However, in practice GT is more commonly used to insert smaller sequences. The range of edits possible through GT can make it challenging to regulate (see Regulation).
The two most established forms of gene editing are gene-targeting and targeted-mutagenesis. While gene targeting relies on the Homology Directed Repair (HDR) (also called Homologous Recombination, HR) DNA repair pathway, targeted-mutagenesis uses Non-Homologous-End-Joining (NHEJ) of broken DNA. NHEJ is an error-prone DNA repair pathway, meaning that when it repairs the broken DNA it can insert or delete DNA bases, creating insertions or deletions (indels). The user cannot specify what these random indels will be, hence they cannot control exactly what edits are made at the target site. However they can control where these edits will occur (i.e. dictate the target site) through using a site-specific nuclease (previously Zinc Finger Nucleases & TALENs, now commonly CRISPR) to break the DNA at the target site. A summary of gene-targeting through HDR (also called Homologous Recombination) and targeted mutagenesis through NHEJ is shown in the figure below.
The more newly developed gene-editing techniques of prime editing and base editing, based on CRISPR-Cas methods, are alternatives to gene targeting, which can also create user-defined edits at targeted genomic locations. However each is limited in the length of DNA sequence insertion possible; base editing is limited to single base pair conversions while prime editing can only insert sequences of up to ~44bp. Hence GT remains the primary method of targeted (location-specific) insertion of long DNA sequences for genome engineering. | 1 | Biochemistry |
Dynabeads were developed after John Ugelstad managed to create uniform polystyrene spherical beads (defined as microbeads) of exactly the same size, at the University of Trondheim, Norway in 1976, something otherwise only achieved by NASA in the weightless conditions of SkyLab. Dynabeads are typically 1 to 5 micrometers in diameter. This is in contrast to the Magnetic-activated cell sorting beads, which are approximately 50 nm.
This discovery revolutionised the liquid-phase kinetic separation of many biological materials. The technology behind the beads, called Dynabeads, was licensed to Dynal in 1980 and this magnetic separation technology has been since used for the isolation and manipulation of biological material, including cells, nucleic acids, proteins and pathogenic microorganisms. The uniformity in size, shape, and surface area allow for reproducibility and help to minimize chemical agglutination.
Dynabeads are frequently used for cell isolation. Cell-types often of interest to purify may be specific leukocytes, such as CD4+ T cells, stem cells, or circulating tumor cells (CTCs). Dynabeads may be covalently linked to an antibody that recognizes a specific protein on the surface of the target cell-type. Alternatively, Dynabeads may attach to the cell indirectly, either via streptavidin on the Dynabead linking to a biotinylated primary antibody, or a secondary antibody on the Dynabead linking to the primary antibody. Streptavidin linkage to the primary antibody allows Dynabeads to capture cells with lower expression of the surface protein.
Following a series of mergers and acquisitions, Dynal and Dynabeads are currently owned and produced by Invitrogen, part of Thermo Fisher Scientific. | 7 | Physical Chemistry |
As it is only effective for primary amines, the carbylamine reaction can be used as a chemical test for their presence. In this context, the reaction is also known as Saytzeff's isocyanide test. In this reaction, the analyte is heated with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide (carbylamine) is formed, as indicated by a foul odour. The carbylamine test does not give a positive reaction with secondary and tertiary amines. | 0 | Organic Chemistry |
Kallidin is a bioactive kinin formed in response to injury from kininogen precursors through the action of kallikreins.
Kallidin is a decapeptide whose sequence is H-Lys-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg-OH. It can be converted to bradykinin by the aminopeptidase enzyme.
It can be a substrate for carboxypeptidase M and N.
Kallidin is identical to bradykinin with an additional lysine residue added at the N-terminal end and signals through the bradykinin receptor. | 1 | Biochemistry |
A method employing very gentle cell lysis in yeast followed by co-immunoprecipitation with an antibody to a mediator subunit (Med 17) has confirmed almost all previously reported or predicted interactions and revealed many previously unsuspected specific interactions of various proteins with mediator. | 1 | Biochemistry |
In statistical mechanics, the thermodynamic limit or macroscopic limit, of a system is the limit for a large number of particles (e.g., atoms or molecules) where the volume is taken to grow in proportion with the number of particles.
The thermodynamic limit is defined as the limit of a system with a large volume, with the particle density held fixed.
In this limit, macroscopic thermodynamics is valid. There, thermal fluctuations in global quantities are negligible, and all thermodynamic quantities, such as pressure and energy, are simply functions of the thermodynamic variables, such as temperature and density. For example, for a large volume of gas, the fluctuations of the total internal energy are negligible and can be ignored, and the average internal energy can be predicted from knowledge of the pressure and temperature of the gas.
Note that not all types of thermal fluctuations disappear in the thermodynamic limit—only the fluctuations in system variables cease to be important.
There will still be detectable fluctuations (typically at microscopic scales) in some physically observable quantities, such as
* microscopic spatial density fluctuations in a gas scatter light (Rayleigh scattering)
* motion of visible particles (Brownian motion)
* electromagnetic field fluctuations, (blackbody radiation in free space, Johnson–Nyquist noise in wires)
Mathematically an asymptotic analysis is performed when considering the thermodynamic limit. | 7 | Physical Chemistry |
The idea that superfluidity exists inside neutron stars was first proposed by Arkady Migdal. By analogy with electrons inside superconductors forming Cooper pairs because of electron-lattice interaction, it is expected that nucleons in a neutron star at sufficiently high density and low temperature can also form Cooper pairs because of the long-range attractive nuclear force and lead to superfluidity and superconductivity. | 7 | Physical Chemistry |
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