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After applying a magnetic force, in the unzipped state of the hairpin, a small number of discriminating nucleotides can hybridize to the new individual complementary sequences on the hairpin which can transiently block the refolding of the hairpin. | 1 | Biochemistry |
Anabolism is powered by catabolism, where large molecules are broken down into smaller parts and then used up in cellular respiration. Many anabolic processes are powered by the cleavage of adenosine triphosphate (ATP). Anabolism usually involves reduction and decreases entropy, making it unfavorable without energy input. The starting materials, called the precursor molecules, are joined using the chemical energy made available from hydrolyzing ATP, reducing the cofactors NAD, NADP, and FAD, or performing other favorable side reactions. Occasionally it can also be driven by entropy without energy input, in cases like the formation of the phospholipid bilayer of a cell, where hydrophobic interactions aggregate the molecules. | 1 | Biochemistry |
Multiple chemical approaches exist to encourage selectivity of α- and β-glycosidic bonds. The highly substrate specific nature of the selectivity and the overall activity of the pyranoside can provide major synthetic difficulties. The overall specificity of the glycosylation can be improved by utilizing approaches which take into account the relative transition states that the anomeric carbon can undergo during a typical glycosylation. Most notably, recognition and incorporation of Felkin-Ahn-Eisenstein models into rationale chemical design can generally provide reliable results provided the transformation can undergo this type of conformational control in the transition state.
Fluorine directed glycosylations represent an encouraging handle for both B selectivity and introduction of a non-natural biomimetic C2 functionality on the carbohydrate. One innovative example provided by Bucher et al. provides a way to utilize a fluoro oxonium ion and the trichloroacetimidate to encourage B stereoselectivity through the gauche effect. This reasonable stereoselectivity is clear through visualization of the Felkin-Ahn models of the possible chair forms.
This method represents an encouraging way to selectivity incorporate B-ethyl, isopropyl and other glycosides with typical trichloroacetimidate chemistry. | 0 | Organic Chemistry |
The minerals found in seawater can also play an important role in the ocean and its ecosystems food cycle. For example, the Southern Ocean contributes greatly to the environmental carbon cycle. Given that this body of water does not contain high levels of iron, the deficiency impacts the marine life living in its waters. As a result, this ocean is not able to produce as much phytoplankton which hinders the first source of the marine food chain. One of the main types of phytoplankton are diatoms which is the primary food source of Antarctic krill. As the cycle continues, various larger sea animals feed off of Antarctic krill, but since there is a shortage of iron from the initial phytoplankton/diatoms, then these larger species also lack iron. The larger sea animals include Baleen Whales such as the Blue Whale and Fin Whale. These whales not only rely on iron for a balance of minerals within their diet, but it also impacts the amount of iron that is regenerated back into the ocean. The whales excretions also contain the absorbed iron which would allow iron to be reinserted into the ocean’s ecosystem. Overall, one mineral deficiency such as iron in the Southern Ocean can spark a significant chain of disturbances within the marine ecosystems which demonstrates the important role that seawater plays in the food chain.
Upon further analysis of the dynamic relationship between diatoms, krill, and baleen whales, fecal samples of baleen whales were examined in Antarctic seawater. The findings included that iron concentrations were 10 million times higher than those found in Antarctic seawater, and krill was found consistently throughout their feces which is an indicator that krill is in whale diets. Antarctic krill had an average iron level of 174.3mg/kg dry weight, but the iron in the krill varied from 12 to 174 mg/kg dry weight. The average iron concentration of the muscular tissue of blue whales and fin whales was 173 mg/kg dry weight, which demonstrates that the large marine mammals are important to marine ecosystems such as they are to the Southern Ocean. In fact, to have more whales in the ocean could heighten the amount of iron in seawater through their excretions which would promote a better ecosystem.
Krill and baleen whales act as large iron reservoirs in seawater in the Southern Ocean. Krill can retain up to 24% of iron found on surface waters within its range.The process of krill feeding on diatoms releases iron into seawater, highlighting them as an important part of the ocean's iron cycle. The advantageous relationship between krill and baleen whales increases the amount of iron that can be recycled and stored in seawater. A positive feedback loop is created, increasing the overall productivity of marine life in the Southern Ocean.
Organisms of all sizes play a significant role in the balance of marine ecosystems with both the largest and smallest inhabitants contributing equally to recycling nutrients in seawater. Prioritizing the recovery of whale populations because they boost the overall productivity in marine ecosystems as well as increasing iron levels in seawater would allow for a balanced and productive system for the ocean. However, a more in depth study is required to understand the benefits of whale feces as a fertilizer and to provide further insight in iron recycling in the Southern Ocean. Projects on the management of ecosystems and conservation are vital for advancing knowledge of marine ecology. | 9 | Geochemistry |
Based on the special chemical properties of formed free radicals, ABTS assay has been used to determine the antioxidant capacity of food products. For example, polyphenol compounds, which widely exist in fruit, can quench free radicals inside human body, thus prevent oxidative damage by free radicals. The antioxidant potency of plant extract or food product has been measured by ABTS assay. One example with detailed method is the antioxidant activity analysis of Hibiscus products. | 1 | Biochemistry |
The nomenclature of modified GFPs is often confusing due to overlapping mapping of several GFP versions onto a single name. For example, mGFP often refers to a GFP with an N-terminal palmitoylation that causes the GFP to bind to cell membranes. However, the same term is also used to refer to monomeric GFP, which is often achieved by the dimer interface breaking A206K mutation. Wild-type GFP has a weak dimerization tendency at concentrations above 5 mg/mL. mGFP also stands for "modified GFP," which has been optimized through amino acid exchange for stable expression in plant cells. | 1 | Biochemistry |
Proton gradients in particular are important in many types of cells as a form of energy storage. The gradient is usually used to drive ATP synthase, flagellar rotation, or metabolite transport. This section will focus on three processes that help establish proton gradients in their respective cells: bacteriorhodopsin and noncyclic photophosphorylation and oxidative phosphorylation. | 7 | Physical Chemistry |
Schotten–Baumann reaction between 4-nitro-3-(trifluoromethyl)aniline [393-11-3] (1) with isobutanoyl chloride [79-30-1] (2) in the presence of triethylamine. | 4 | Stereochemistry |
For narrow ridges with large period , the ridges just blocks the part of the wavefront. Then, it can be interpreted in terms of the Fresnel diffraction of the de Broglie wave, or the Zeno effect; such interpretation leads to the estimate the reflectivity
is wavenumber, is period (distance between ridges) and
where the grazing angle is supposed to be small. This estimate predicts enhancement of the reflectivity at the reduction of period . This estimate requires that . | 7 | Physical Chemistry |
The chelation of lithium cation with the methoxy group is one of the most important features of the transition state for Enders hydrazone alkylation reaction. It is necessary to have this chelation effect to achieve high stereoselectivity. The development and modification of Enders hydrazone alkylation reaction mainly focus on the addition of more steric hindrance on the pyrrolidine rings of both SAMP and RAMP, while preserving the methoxy group for lithium chelation.
The most famous four variants of SAMP and RAMP are SADP, SAEP, SAPP and RAMBO, whose structures are shown below.
In 2011, several N-amino cyclic carbamates were synthesized and studied for asymmetric hydrazone alkylation reactions. Both the stereochemistry and regioselectivity of the reactions turned out to be very promising. These new compounds consist of a new class of chiral auxiliary based on the carbamate structure and, therefore, no longer belong to the family of SAMP and RAMP. But they do provide very powerful alternatives to the traditional pyrrolidine systems. | 0 | Organic Chemistry |
Itch has been shown to interact with a number of proteins, including:
* CXCR4,
* c-Jun,
* MAP2K4,
* MAP3K1,
* MAP3K7,
* MAPK8,
* N4BP1,
* NOTCH1,
* TP63, and
* TP73. | 1 | Biochemistry |
Considerable effort and research continues to be made into discovering and refining better methods of tailings disposal. Research at the Porgera Gold Mine is focusing on developing a method of combining tailings products with coarse waste rock and waste muds to create a product that can be stored on the surface in generic-looking waste dumps or stockpiles. This would allow the current use of riverine disposal to cease. Considerable work remains to be done. However, co-disposal has been successfully implemented by several designers including AMEC at, for example, the Elkview Mine in British Columbia. | 8 | Metallurgy |
Progesterone has a number of physiological effects that are amplified in the presence of estrogens. Estrogens through estrogen receptors (ERs) induce or upregulate the expression of the PR. One example of this is in breast tissue, where estrogens allow progesterone to mediate lobuloalveolar development.
Elevated levels of progesterone potently reduce the sodium-retaining activity of aldosterone, resulting in natriuresis and a reduction in extracellular fluid volume. Progesterone withdrawal, on the other hand, is associated with a temporary increase in sodium retention (reduced natriuresis, with an increase in extracellular fluid volume) due to the compensatory increase in aldosterone production, which combats the blockade of the mineralocorticoid receptor by the previously elevated level of progesterone. | 0 | Organic Chemistry |
The derivation starts with Ficks first law using a uniform distance axis y as the coordinate system and having the origin fixed to the location of the markers. It is assumed that the markers move relative to the diffusion of one component and into one of the two initial rods, as was chosen in Kirkendalls experiment. In the following equation, which represents Ficks first law for one of the two components, D is the diffusion coefficient of component one, and C' is the concentration of component one:
This coordinate system only works for short range from the origin because of the assumption that marker movement is indicative of diffusion alone, which is not true for long distances from the origin as stated before. The coordinate system is transformed using a Galilean transformation, y = x − νt, where x is the new coordinate system that is fixed to the ends of the two rods, ν is the marker velocity measured with respect to the x axis. The variable t, time, is assumed to be constant, so that the partial derivative of C with respect to y is equal to the partial of C with respect to x. This transformation then yields
The above equation, in terms of the variable x, only takes into account diffusion, so the term for the motion of the markers must also be included, since the frame of reference is no longer moving with the marker particles. In the equation below, is the velocity of the markers.
Taking the above equation and then equating it to the accumulation rate in a volume results in the following equation. This result is similar to Fick's second law, but with an additional advection term:
The same equation can be written for the other component, designated as component two:
Using the assumption that C, the total concentration, is constant, C and C can be related in the following expression:
The above equation can then be used to combine the expressions for and to yield
Since C is constant, the above equation can be written as
The above equation states that is constant because the derivative of a constant is equal to zero. Therefore, by integrating the above equation it is transforms to , where is an integration constant.
At relative infinite distances from the initial interface, the concentration gradients of each of the components and the marker velocity can be assumed to be equal to zero. Based on this condition and the choice for the coordinate axis, where the x axis fixed at the far ends of the rods, I is equal zero. These conditions then allow the equation to be rearranged to give
Since C is assumed to be constant, . Rewriting this equation in terms of atom fraction and yields | 7 | Physical Chemistry |
Freeze fracture enzyme cytochemistry was initially mentioned in the study of Pinto de silva in 1987. It is a technique that allows the introduction of cytochemistry into a freeze fracture cell membrane. immunocytochemistry is used in this technique to label and visualize the cell membrane's molecules. This technique could be useful in analyzing the ultrastructure of cell membranes. The combination of immunocytochemistry and freeze fracture enzyme technique, research can identify and have a better understanding of the structure and distribution of a cell membrane. | 1 | Biochemistry |
Aryl azides may be prepared by displacement of the appropriate diazonium salt with sodium azide or trimethylsilyl azide. Nucleophilic aromatic substitution is also possible, even with chlorides. Anilines and aromatic hydrazines undergo diazotization, as do alkyl amines and hydrazines. | 0 | Organic Chemistry |
The following table and diagram show experimentally determined surface tensions in the mixture of water and propionic acid.
This example shows a good agreement between the published value a=2.6*10 and the calculated value a=2.59*10 at the smallest given mole fraction of 0.00861 but at higher concentrations of propionic acid the value of an increases considerably, showing deviations from the predicted value. | 7 | Physical Chemistry |
Polycyclic aromatic hydrocarbons (PAH) are the most common and abundant polyatomic molecules in the observable universe, and are a major store of carbon. They seem to have formed shortly after the Big Bang, and are associated with new stars and exoplanets. They are a likely constituent of Earth's primordial sea. PAHs have been detected in nebulae, and in the interstellar medium, in comets, and in meteorites.
The PAH world hypothesis posits PAHs as precursors to the RNA world. A star, HH 46-IR, resembling the sun early in its life, is surrounded by a disk of material which contains molecules including cyanide compounds, hydrocarbons, and carbon monoxide. PAHs in the interstellar medium can be transformed through hydrogenation, oxygenation, and hydroxylation to more complex organic compounds used in living cells. | 9 | Geochemistry |
The electrical conduction system of the heart has been robustly established. However, newer research has been challenging some of the previously accepted models. The role of ephaptic coupling in cardiac cells is becoming more apparent. One author even goes so far as to say, “While previously viewed as a possible alternative to electrotonic coupling, ephaptic coupling has since come to be viewed as operating in tandem with gap junctions, helping sustain conduction when gap junctional coupling is compromised.” Ephaptic interactions among cardiac cells help fill in the gaps that electrical synapses alone cannot account for. The proximity of sodium channels to gap junction plaques has been shown to relate to their effectiveness in driving ephaptic coupling action potential transmission. There are also a number of mathematical models that now incorporate ephaptic coupling into predictions about electrical conductance in the heart. Experimental work suggests that sodium channel-rich nanodomains located at sites of close contact between cardiac myocytes may constitute functional units of ephaptic coupling and selective disruption of these nanodomains resulted in arrhythmogenic conduction slowing, suggesting an important role for ephaptic coupling in the heart. Potential ephaptic connections are now being considered in heart therapeutics. | 1 | Biochemistry |
Most monitoring programmes involve the periodic collection of low volume spot samples (bottle or grab) of water, which is challenging, particularly where levels fluctuate over time and when chemicals are only present at trace, yet toxicologically relevant concentrations. Chemcatcher® is used to measure time-weighted average (TWA) or equilibrium concentrations of a wide range of pollutants in water. This allows the end user to obtain a more representative picture of the chemicals that may be present in the aquatic environment. | 3 | Analytical Chemistry |
Mitochondrial abundant heat soluble (MAHS) proteins are localized in mitochondria and are responsible for protecting mitochondria during desiccation. Because of its role in metabolizing reactive oxygen species, the mitochondrion is an important organelle to protect in extreme environments. During dehydration, the mitochondria of tardigrades grow much smaller and lose their cristae. MAHS proteins may act to replace water in the membrane of the mitochondria, preventing uneven rehydration and membrane rupture. | 1 | Biochemistry |
Ethanol is formed in E. coli by the reduction of acetyl coenzyme A using NADH. This two-step reaction requires the enzyme alcohol dehydrogenase (ADHE).
acetyl-CoA + NADH + H → acetaldehyde + NAD + CoA
acetaldehyde + NADH + H → ethanol + NAD | 1 | Biochemistry |
PTWA can be used to apply a coating to wear surfaces of engine or transmission components, serving as a plain bearing. For the cylinder bores of hypoeutectic aluminum-silicon alloy blocks, PTWA's main advantages over cast iron liners are reduced weight and cost. The thinner bore surface also allows for more compact bore spacing, and can potentially provide better heat transfer.
Automotive engines that use PTWA include the BMW B58, Nissan VR38DETT, and Ford Coyote. Caterpillar and Ford also use PTWA to remanufacture engines. | 8 | Metallurgy |
Bacteriological water analysis is a method of analysing water to estimate the numbers of bacteria present and, if needed, to find out what sort of bacteria they are. It represents one aspect of water quality. It is a microbiological analytical procedure which uses samples of water and from these samples determines the concentration of bacteria. It is then possible to draw inferences about the suitability of the water for use from these concentrations. This process is used, for example, to routinely confirm that water is safe for human consumption or that bathing and recreational waters are safe to use.
The interpretation and the action trigger levels for different waters vary depending on the use made of the water. Whilst very stringent levels apply to drinking water, more relaxed levels apply to marine bathing waters, where much lower volumes of water are expected to be ingested by users. | 3 | Analytical Chemistry |
*American Chemical Society PROGRESS/Dreyfus Lectureship Award (Camille and Henry Dreyfus Foundation Special Grant Program in the Chemical Sciences)
*NSF CAREER Award on Mechanistic Studies of Nucleotide Reactivity
*Alfred P. Sloan Fellow
*Faculty of Arts and Sciences Award for Distinguished Contributions to Undergraduate Education
*Sigma Chi Scientific Honor Society | 0 | Organic Chemistry |
N-Methylmorpholine is the organic compound with the formula O(CHCH)NCH. It is a colorless liquid. It is a cyclic tertiary amine. It is used as a base catalyst for generation of polyurethanes and other reactions. It is produced by the reaction of methylamine and diethylene glycol as well as by the hydrogenolysis of N-formylmorpholine. It is the precursor to N-methylmorpholine N-oxide, a commercially important oxidant. | 0 | Organic Chemistry |
The flotation process is also widely used in industrial waste water treatment plants, where it removes fats, oil, grease and suspended solids from waste water. These units are called dissolved air flotation (DAF) units. In particular, dissolved air flotation units are used in removing oil from the wastewater effluents of oil refineries, petrochemical and chemical plants, natural gas processing plants and similar industrial facilities. | 8 | Metallurgy |
K values are used, among others, to assess the environmental fate of persistent organic pollutants. Chemicals with high partition coefficients, for example, tend to accumulate in the fatty tissue of organisms (bioaccumulation). Under the Stockholm Convention, chemicals with a log K greater than 5 are considered to bioaccumulate.
Furthermore, the parameter plays an important role in drug research (Rule of Five) and toxicology. Ernst Overton and Hans Meyer discovered as early as 1900 that the efficacy of an anaesthetic increased with increasing K value (the so-called Meyer-Overton rule).
K values also provide a good estimate of how a substance is distributed within a cell between the lipophilic biomembranes and the aqueous cytosol. | 7 | Physical Chemistry |
Cleveland Potash Limited extracts and refines sylvinite ore from a deposit in North Yorkshire, England. Its processing plant uses froth flotation to produce a product rich in potassium chloride ("KCl"). After a test work campaign in which it compared the performance of the Cell with mechanical flotation cells in various duties in the flotation circuit, Cleveland Potash ordered a Cell with 6 downcomers for recovering potash slimes. The test work had shown a 4.8% increase in the recovery of potash slimes, equivalent at the time to an increase in revenue of approximately £518,000 per year. | 8 | Metallurgy |
Though the KaiABC gene cluster has been found to exist only in cyanobacteria, evolutionarily KaiC contains homologs that occur in Archaea and Pseudomonadota. It is the oldest circadian gene that has been discovered in prokaryotes. KaiC has a double-domain structure and sequence that classifies it as part of the RecA gene family of ATP-dependent recombinases. Based on a number of single-domain homologous genes in other species, KaiC is hypothesized to have horizontally transferred from Bacteria to Archaea, eventually forming the double-domain KaiC through duplication and fusion. KaiC<nowiki/>s key role in circadian control and homology to RecA suggest its individual evolution before its presence in the KaiABC' gene cluster. | 1 | Biochemistry |
Contact angles are extremely sensitive to contamination; values reproducible to better than a few degrees are generally only obtained under laboratory conditions with purified liquids and very clean solid surfaces. If the liquid molecules are strongly attracted to the solid molecules then the liquid drop will completely spread out on the solid surface, corresponding to a contact angle of 0°. This is often the case for water on bare metallic or ceramic surfaces, although the presence of an oxide layer or contaminants on the solid surface can significantly increase the contact angle. Generally, if the water contact angle is smaller than 90°, the solid surface is considered hydrophilic and if the water contact angle is larger than 90°, the solid surface is considered hydrophobic. Many polymers exhibit hydrophobic surfaces. Highly hydrophobic surfaces made of low surface energy (e.g. fluorinated) materials may have water contact angles as high as ≈ 120°. Some materials with highly rough surfaces may have a water contact angle even greater than 150°, due to the presence of air pockets under the liquid drop. These are called superhydrophobic surfaces.
If the contact angle is measured through the gas instead of through the liquid, then it should be replaced by 180° minus their given value. Contact angles are equally applicable to the interface of two liquids, though they are more commonly measured in solid products such as non-stick pans and waterproof fabrics. | 7 | Physical Chemistry |
Soon after it was discovered and recognized as the principle of meat smoking, wood-tar creosote became used as a replacement for the process. Several methods were used to apply the creosote. One was to dip the meat in pyroligneous acid or a water of diluted creosote, as Reichenbach did, or brush it over with them, and within one hour the meat would have the same quality of that of traditionally smoked preparations. Sometimes the creosote was diluted in vinegar rather than water, as vinegar was also used as a preservative. Another was to place the meat in a closed box, and place with it a few drops of creosote in a small bottle. Because of the volatility of the creosote, the atmosphere was filled with a vapour containing it, and it would cover the flesh.
The application of wood tar to seagoing vessels was practiced through the 18th century and early 19th century, before the creosote was isolated as a compound. Wood-tar creosote was found not to be as effective in wood treatments, because it was harder to infuse the creosote into the wood cells, but still experiments were done, including by many governments, because it proved to be less expensive on the market. | 7 | Physical Chemistry |
As more electrons are added to a 5n cluster, the number of electrons per vertex approaches 6. Instead of adopting structures based on 4n or 5n rules, the clusters tend to have structures governed by the 6n rules, which are based on rings. The rules for the 6n structures are as follows.
Example: S
:Electron count = 8 × S = 8 × 6 = 48 electrons.
:Since n = 8, 6n = 48, so the cluster is an 8-membered ring.
Hexane (CH)
:Electron count = 6 × C + 14 × H = 6 × 4 + 14 × 1 = 38
:Since n = 6, 6n = 36 and 6n + 2 = 38, so the cluster is a 6-membered chain. | 7 | Physical Chemistry |
Manganese(III)-mediated radical reactions begin with the single-electron oxidation of a carbonyl compound to an α-oxoalkyl radical. Addition to an olefin then occurs, generating adduct radical 2. The fate of 2 is primarily determined by reaction conditions—in the presence of copper(II) acetate, this intermediate undergoes further oxidation to a carbocation and may eliminate to form β,γ-unsaturated ketone 4. Manganese acetate itself can effect the second oxidation of resonance-stabilized adduct radicals to carbocations 5; unstabilized radicals undergo further transformations before reacting with Mn(OAc). Atom transfer from another molecule of substrate may generate saturated compound 3. Adduct radicals or carbocations may undergo ligand-transfer reactions, yielding γ-functionalized carbonyl compounds. When lithium chloride is used as an additive, chlorination takes place. Alternatively, carbocations may be trapped intramolecularly by the carbonyl oxygen to form dihydrofurans after β-elimination. | 0 | Organic Chemistry |
The original Jameson Cell design had the following features:
* small (200 mm diameter) downcomers
* no wash water
* no tailings recycle
* no bubble dispersers
* low capacity.
In 1994 MIM launched the Mark II model Cell. It incorporated the following changes:
* the downcomer diameter was increased to 280 mm
* wash-water trays were included for froth washing
* a tailings recycle system was added to maintain constant downcomer flow and higher recoveries
* conical bubble dispersers were added
* increased depth of tank from the bottom of the downcomer
* increased distance between the downcomers.
These changes resulted in a higher capacity design.
One of the problems encountered with the Mark I Cell was that its performance was reduced if the feed rate to the cell varied, which was a common occurrence arising from normal fluctuations in operating concentrators. This problem was resolved by recycling some of the tailings to the cell feed via an external splitter box called an "External Recycle Mechanism" or "ERM" box separate to the flotation cell. Thus, when the production of the feed stream to the Jameson Cell decreased as a result of a fluctuation elsewhere in the concentrator, a higher percentage of the tailings was automatically recycled to the downcomers, producing a constant flow rate, hence feed pressure, to the cell. This had the added benefit of giving a proportion of the tailings (typically 40%) a second pass through the system, which resulted in higher recoveries. In coal fines flotation, this allowed a single Cell to achieve the same recovery of combustibles as had previously been achieved in some two-stage Cell systems.
Subsequently, an internal recycling system, referred to as the "internal recycle control" or "IRC" was developed. This was mainly used in integrated rectangular cells (see Figure 6), where the feed tank and tailings recycling system could easily be built in a single unit with the flotation cell. This system reduced the cell installation costs and made the cell more compact.
During this period, the orifice diameter was increased from the 28 mm design used in 1990 to 34 mm with the Mark II model and 38 mm in 1997. This, together with the larger Mark II downcomer diameter, allowed the slurry flow per downcomer to be doubled from 30 m/h in 1990 to 60 m/h in 1997.
The increased distance between the downcomers reduced the interaction of aerated slurry discharging from adjacent downcomers. This interaction could reduce overall cell recovery by causing particles collected by bubbles in the downcomer to detach in the pulp tank.
There was significant turbulence in the areas beneath the downcomers. that could result in particles detaching from bubbles. These turbulent areas were calmed by the addition of conical diffusers beneath each downcomer. They allowed uniform bubble rise velocities across the surface of the cell by slowing the superficial gas velocity in the high void-fraction area immediately around the downcomer and provided a more even bubble dispersion. It was reported that the diffusers reduced the turbulence by 69% compared with a standard downcomer with no diffuser. | 8 | Metallurgy |
Biogenic calcium carbonate is formed when marine organisms, such as coccolithophores, corals, pteropods, and other mollusks transform calcium ions and bicarbonate into shells and exoskeletons of calcite or aragonite, both forms of calcium carbonate. This is the dominant sink for dissolved calcium in the ocean. Dead organisms sink to the bottom of the ocean, depositing layers of shell which over time cement to form limestone. This is the origin of both marine and terrestrial limestone.
Calcium precipitates into calcium carbonate according to the following equation:
Ca + 2HCO → CO+ HO + CaCO
The relationship between dissolved calcium and calcium carbonate is affected greatly by the levels of carbon dioxide (CO) in the atmosphere.
Increased carbon dioxide leads to more bicarbonate in the ocean according to the following equation:
CO + CO + HO → 2HCO
With ocean acidification, inputs of carbon dioxide promote the dissolution of calcium carbonate and harm marine organisms dependent on their protective calcite or aragonite shells. The solubility of calcium carbonate increases with pressure and carbon dioxide and decreases with temperature. Thus, calcium carbonate is more soluble in deep waters than surface waters due to higher pressure and lower temperature. As a result, precipitation of calcium carbonate is more common in shallower oceans. The depth at which the rate of calcite dissolution equals the rate of calcite precipitation is known as calcite compensation depth. | 1 | Biochemistry |
Rare mutation detection occurs when a biomarker exists within a background of a highly abundant counterpart that differs by only a single nucleotide variant (SNV). Digital PCR has been shown to be capable of detecting mutant DNA in the presence of a 200,000-fold excess of wild type background, which is 2,000 times more sensitive than achievable with conventional qPCR. | 1 | Biochemistry |
The psychrometric constant relates the partial pressure of water in air to the air temperature. This lets one interpolate actual vapor pressure from paired dry and wet thermometer bulb temperature readings.
: psychrometric constant [kPa °C],
: P = atmospheric pressure [kPa],
: latent heat of water vaporization, 2.45 [MJ kg],
: specific heat of air at constant pressure, [MJ kg °C],
: ratio molecular weight of water vapor/dry air = 0.622.
Both and are constants.<br>
Since atmospheric pressure, P, depends upon altitude, so does .<br>
At higher altitude water evaporates and boils at lower temperature.
Although is constant, varied air composition results in varied .
Thus on average, at a given location or altitude, the psychrometric constant is approximately constant. Still, it is worth remembering that weather impacts both atmospheric pressure and composition. | 7 | Physical Chemistry |
In December 2008, a number of Irish news sources reported testing had revealed "extremely high" levels of dioxins, by toxic equivalent, in pork products, ranging from 80 to 200 times the EU's upper safe limit of 1.5 pg WHO-TEQ/μg i.e. 0.12 to 0.3 parts per billion.
Brendan Smith, the Minister for Agriculture, Fisheries and Food, stated the pork contamination was caused by PCB-contaminated feed that was used on 9 of Ireland's 400 pig farms, and only one feed supplier was involved. Smith added that 38 beef farms also used the same contaminated feed, but those farms were quickly isolated and no contaminated beef entered the food chain. While the contamination was limited to just 9 pig farms, the Irish government requested the immediate withdrawal and disposal of all pork-containing products produced in Ireland and purchased since September 1, 2008. This request for withdrawal of pork products was confirmed in a press release by the Food Safety Authority of Ireland on December 6.
It is thought that the incident resulted from the contamination of fuel oil used in a drying burner at a single feed processor, with PCBs. The resulting combustion produced a highly toxic mixture of PCBs, dioxins and furans, which was included in the feed produced and subsequently fed to a large number of pigs. | 2 | Environmental Chemistry |
Lisinopril is an ACE inhibitor, meaning it blocks the actions of angiotensin-converting enzyme (ACE) in the renin–angiotensin–aldosterone system (RAAS), preventing angiotensin I from being converted to angiotensin II. Angiotensin II is a potent direct vasoconstrictor and a stimulator of aldosterone release. Reduction in the amount of angiotensin II results in relaxation of the arterioles. Reduction in the amount of angiotensin II also reduces the release of aldosterone from the adrenal cortex, which allows the kidney to excrete sodium along with water into the urine, and increases retention of potassium ions. Specifically, this process occurs in the peritubular capillaries of the kidneys in response to a change in Starling forces. The inhibition of the RAAS system causes an overall decrease in blood pressure. | 4 | Stereochemistry |
Ore deposits formed by lateral secretion are formed by metamorphic reactions during shearing, which liberate mineral constituents such as quartz, sulfides, gold, carbonates, and oxides from deforming rocks, and focus these constituents into zones of reduced pressure or dilation such as faults. This may occur without much hydrothermal fluid flow, and this is typical of podiform chromite deposits.
Metamorphic processes also control many physical processes which form the source of hydrothermal fluids, outlined above. | 9 | Geochemistry |
To perform CRISPR knockouts on a genome-wide scale, collections of sgRNAs known as sgRNA libraries, or CRISPR knockout libraries, must be generated. The first step in creating a sgRNA library is to identify genomic regions of interest based on known sgRNA targeting rules. For example, sgRNAs are most efficient when targeting the coding regions of genes and not the 5’ and 3’ UTRs. Conserved exons present as attractive targets, and position relative to the transcription start site should be considered. Secondly, all the possible PAM sites are identified and selected for. On- and off-target activity should be analysed, as should GC content, and homopolymer stretches should be avoided. The most commonly used Cas9 endonuclease, derived from Streptococcus pyogenes, recognises a PAM sequence of NGG.
Furthermore, specific nucleotides appear to be favoured at specific locations. Guanine is strongly favoured over cytosine on position 20 right next to the PAM motif, and on position 16 cytosine is preferred over guanine. For the variable nucleotide in the NGG PAM motif, it has been shown that cytosine is preferred and thymine disfavoured. With such criteria taken into account, the sgRNA library is computationally designed around the selected PAM sites.
Multiple sgRNAs (at least 4–6) should be created against every single gene to limit false-positive detection, and negative control sgRNAs with no known targets should be included. The sgRNAs are then created by in situ synthesis, amplified by PCR, and cloned into a vector delivery system. | 1 | Biochemistry |
If required, farmers' responses to water logging and soil salinity can be automatically accounted for. The method can gradually decrease:
# the amount of irrigation water applied when the water table becomes shallower;
# the fraction of irrigated land when the available irrigation water is scarce;
# the fraction of irrigated land when the soil salinity increases; for this purpose, the salinity is given a stochastic interpretation.
Response (1) is different for ponded (submerged) rice (paddy) and "dry foot" crops.
The responses influence the water and salt balances, which, in their turn, slow down the process of water logging and salinization. Ultimately an equilibrium situation will be brought about.
The user can also introduce farmers responses by manually changing the relevant input data. Perhaps it will be useful first to study the automatic farmers responses and their effect and thereafter decide what the farmers' responses will be in the view of the user.
The responses influence the water and salt balances, which, in their turn, slow down the process of water logging and salinization. Ultimately an equilibrium situation will be brought about.
The user can also introduce farmers responses by manually changing the relevant input data. Perhaps it will be useful first to study the automatic farmers responses and their effect and thereafter decide what the farmers' responses will be in the view of the user. | 9 | Geochemistry |
The GAIN domain (G-protein-coupled receptor (GPCR) autoproteolysis-inducing domain) is a protein domain found in a number of cell surface receptors, including adhesion-GPCRs and polycystic kidney disease proteins PKD1 and PKD2. The domain is involved in the self-cleavage of these transmembrane receptors, and has been shown to be crucial for their function . Point mutations within the GAIN domain of PKD1 and GPR56 are known to cause polycystic kidney disease and polymicrogyria, respectively. | 1 | Biochemistry |
LHT was introduced by the U.K. in British India (now India, Pakistan, Myanmar, and Bangladesh), British Malaya and British Borneo (now Malaysia, Brunei and Singapore), and British Hong Kong. All are still LHT, as well as neighbour countries Bhutan and Nepal, except Myanmar, which switched to RHT in 1970, although much of its infrastructure is still geared to LHT and its neighbours India, Bangladesh and Thailand use LHT. Most cars are used RHD vehicles imported from Japan. Afghanistan was LHT until the 1950s, in line with Pakistan (former part of British India).
Although Portuguese Timor (present-day East Timor), which shares the island Timor with Indonesia with LHT, switched to RHT as Portugal in 1928, it switched back to LHT in 1976 during the Indonesian occupation of East Timor.
In the 1930s, parts of China like the Shanghai International Settlement, Canton and Japanese-occupied northeast China used LHT. However, in 1946 the Republic of China made RHT mandatory in China (including Taiwan, which used LHT under Japanese colonization 1895–1945), although Portuguese Macau (present-day Macau) remained LHT, as well as British Hong Kong, despite becoming transferred to China in 1999 and 1997 respectively.
Both North Korea and South Korea use RHT since 1946, after liberation from Japanese colonial power.
The Philippines was mostly LHT during its Spanish and American colonial periods, as well as during the Commonwealth era. During the Japanese occupation, the Philippines remained LHT, also because LHT had been required by the Japanese; but during the Battle of Manila, the liberating American forces drove their tanks to the right for easier facilitation of movement. RHT was formalized in 1945 through a decree by then-president Sergio Osmeña. Even though RHT was formalized, RHD vehicles such as public buses were still imported in the Philippines until a law was passed that banned the importation of RHD vehicles except for special cases. These RHD vehicles are required to be converted to LHD
Japan was never part of the British Empire, but its traffic also drives on the left. Although the origin of this habit goes back to the Edo period (1603–1868), it was not until 1872 – the year Japans first railway was introduced, built with technical aid from the British – that this unwritten rule received official acknowledgment. Gradually, a massive network of railways and tram tracks was built, with all railway vehicles driven on the left-hand side. However, it took another half-century, until 1924, until left-hand traffic was legally mandated. Post-World War II Okinawa was ruled by the United States Civil Administration of the Ryukyu Islands until 1972, and was RHT until 6 a.m. the morning of 30 July 1978, when it switched back to LHT. The conversion operation was known as 730 (Nana-San-Maru', which refers to the date of the changeover). Okinawa is one of few places to have changed from RHT to LHT in the late 20th century. While Japan drives on the left and most Japanese vehicles are RHD, imported vehicles (e.g. BMW, Mercedes-Benz, Porsche) are generally bought as LHD as LHD cars are considered to be status symbols.
Vietnam became RHT as part of French Indochina, as did Laos and Cambodia. In Cambodia, RHD cars, many of which were smuggled from Thailand, were banned in 2001, even though they accounted for 80% of vehicles in the country. | 4 | Stereochemistry |
Armstrong introduced macrocyclic glycopeptides (also known as glycopeptide antibiotics) as a new class of chiral selector for liquid chromatography in 1994. At present, vancomycin, teicoplanin and ristocetin are available under the brand names Chirobiotic V, Chirobiotic T and Chirobiotic R respectively. These cyclic glycopeptides have multiple chiral centers and a cup-like inclusion area to which a floating sugar lid is attached. Similar to protein chiral selectors, the amphoteric cyclic glycopeptides consist of peptide and carbohydrate binding sites leading to possibilities for different modes of interaction beside the formation of inclusion complexation. In this chiral selector the cavities are shallower than that of CDs and hence the interactions are weaker, allows more rapid solute exchange between phases, higher column efficiency. operates in normal phase, reversed-phase and polar organic phase.
The complex structural nature of glycopeptide antibiotic class of CSP has made the understanding of the mechanism of chiral recognition at molecular level tricky. For instance, vancomycin molecule has 18 stereogenic centers in the molecule and offers a complex cyclodextrin-like chiral environment. In comparison to a single basket of cyclodextrins, vancomycin consists of three baskets, resulting in a more complex inclusion of appropriate guest molecules. The attractive forces include π-π interactions, hydrogen bonding, ionic interactions, and dipole stacking. A carboxylic acid and a secondary amine group located on the rim of the cup and can participate in ionic interactions. Vancomycin stationary phases operate in reversed, normal and polar organic phase modes.
Wide range of chiral analysis has been done using chirobiotic CSPs. The antihypertensive drugs viz. oxprenolol, pindolol, propranolol have been separated using vancomycin and teicoplanin chirobiotic CSPS. The NSAID drugs ketoprofen and ibuprofen has been separated using ristocetin CSP. | 4 | Stereochemistry |
Prior to 1940, pesticides consisted of inorganic compounds (copper, arsenic, mercury, and lead) and plant derived products. Most of these were abandoned because they were highly toxic and ineffective. Since World War II pesticides composed of synthetic organic compounds were the most important form of pest control. The growth in these pesticides accelerated in late 1940s after Paul Müller discovered DDT in 1939. The effects of pesticides such as aldrin, dieldrin, endrin, chlordane, parathion, captan and 2,4-D were also found at this time. Those pesticides were widely used due to their effective pest control. Problems with environmental issues of DDT became increasingly apparent, since it is persistent and bioaccumulates in the body and the food chain. In the 1960s, Rachel Carson wrote Silent Spring to illustrate a risk of DDT and how it threatened biodiversity. DDT was banned for agricultural use in 1972 and the others in 2001. Persistent pesticides are no longer used for agriculture, and will not be approved by the authorities. Because the half life in soil is long (for DDT 2–15 years) residues can still be detected in humans at levels 5 to 10 times lower than found in the 1970s. | 2 | Environmental Chemistry |
Shadowing and blocking are important concepts in almost all types of ion-surface interactions and result from the repulsive nature of the ion-nucleus interaction. As shown at right, when a flux of ions flows in parallel towards a scattering center (nucleus), they are each scattered according to the force of the Coulomb repulsion. This effect is known as shadowing. In a simple Coulomb repulsion model, the resulting region of “forbidden” space behind the scattering center takes the form of a paraboloid with radius at a distance L from the scattering center. The flux density is increased near the edge of the paraboloid.
Blocking is closely related to shadowing, and involves the interaction between scattered ions and a neighboring scattering center (as such it inherently requires the presence of at least two scattering centers). As shown, ions scattered from the first nucleus are now on diverging paths as they undergo interaction with the second nucleus. This interaction results in another “shadowing cone” now called a blocking cone where ions scattered from the first nucleus are blocked from exiting at angles below . Focusing effects again result in an increased flux density near .
In both shadowing and blocking, the "forbidden" regions are actually accessible to trajectories when the mass of incoming ions is greater than that of the surface atoms (e.g. Ar impacting Si or Al). In this case the region will have a finite but depleted flux density.
For higher energy ions such as those used in MEIS and RBS the concepts of shadowing and blocking are relatively straightforward since ion-nucleus interactions dominate and electron screening effects are insignificant. However, in the case of LEIS these screening effects do interfere with ion-nucleus interactions and the repulsive potential becomes more complicated. Also, multiple scattering events are very likely which complicates analysis. Importantly, due to the lower energy ions used LEIS is typically characterized by large interaction cross-sections and shadow cone radii. For this reason penetration depth is low and the method has much higher first-layer sensitivity than MEIS or RBS. Overall, these concepts are essential for data analysis in impact collision LEIS experiments (see below). | 7 | Physical Chemistry |
China has long been considered the exception to the general use of bloomeries. The Chinese are thought to have skipped the bloomery process completely, starting with the blast furnace and the finery forge to produce wrought iron; by the fifth century BC, metalworkers in the southern state of Wu had invented the blast furnace and the means to both cast iron and to decarburize the carbon-rich pig iron produced in a blast furnace to a low-carbon, wrought iron-like material. Recent evidence, however, shows that bloomeries were used earlier in ancient China, migrating in from the west as early as 800 BC, before being supplanted by the locally developed blast furnace. Supporting this theory was the discovery of "more than ten" iron-digging implements found in the tomb of Duke Jing of Qin (d. 537 BCE), whose tomb is located in Fengxiang County, Shaanxi (a museum exists on the site today). | 8 | Metallurgy |
MTBE removal from groundwater and soil contamination in the U.S. was estimated to cost from $1 billion to US$30 billion, including removing the compound from aquifers and municipal water supplies and replacing leaky underground oil tanks. In one case, the cost to oil companies to clean up the MTBE in wells belonging to the city of Santa Monica, California was estimated to exceed $200 million. In another case, New York City estimated a $250 million cost for cleanup of a single wellfield in the borough of Queens in 2009. In 2013 a jury awarded the State of New Hampshire $236 million in damages in order to treat groundwater contaminated by MTBE.
Many lawsuits are still pending regarding MTBE contamination of public and private drinking water supplies. | 2 | Environmental Chemistry |
The most common powder X-ray diffraction (XRD) refinement technique used today is based on the method proposed in the 1960s by Hugo Rietveld. The Rietveld method fits a calculated profile (including all structural and instrumental parameters) to experimental data. It employs the non-linear least squares method, and requires the reasonable initial approximation of many free parameters, including peak shape, unit cell dimensions and coordinates of all atoms in the crystal structure. Other parameters can be guessed while still being reasonably refined. In this way one can refine the crystal structure of a powder material from PXRD data. The successful outcome of the refinement is directly related to the quality of the data, the quality of the model (including initial approximations), and the experience of the user.
The Rietveld method is an incredibly powerful technique which began a remarkable era for powder XRD and materials science in general. Powder XRD is at heart a very basic experimental technique with diverse applications and experimental options. Despite being slightly limited by the one-dimensionality of PXRD data and limited resolution, powder XRD's power is astonishing. It is possible to determine the accuracy of a crystal structure model by fitting a profile to a 1D plot of observed intensity vs angle. It is important to remember that Rietveld refinement requires a crystal structure model and offers no way to come up with such a model on its own. However, it can be used to find structural details missing from a partial or complete ab initio structure solution, such as unit cell dimensions, phase quantities, crystallite sizes/shapes, atomic coordinates/bond lengths, micro strain in crystal lattice, texture, and vacancies. | 3 | Analytical Chemistry |
Gastrointestinal symptoms are the most common side effects of potassium supplements, including nausea, vomiting, abdominal discomfort, and diarrhea. Taking potassium with meals or taking a microencapsulated form of potassium may reduce gastrointestinal side effects.
Hyperkalemia is the most serious adverse reaction to potassium. Hyperkalemia occurs when potassium builds up faster than the kidneys can remove it. It is most common in individuals with renal failure. Symptoms of hyperkalemia may include tingling of the hands and feet, muscular weakness, and temporary paralysis. The most serious complication of hyperkalemia is the development of an abnormal heart rhythm (arrhythmia), which can lead to cardiac arrest.
Although hyperkalemia is rare in healthy individuals, oral doses greater than 18 grams taken at one time in individuals not accustomed to high intakes can lead to hyperkalemia. | 1 | Biochemistry |
High-light grown plants generally have somewhat larger seeds, but produce many more flowers, and therefore there is a large increase in seed production per plant. Sturdy plants with short internodes and many flowers are important for horticulture, and hence a minimum amount of DLI is required for marketable horticultural plants. Measuring DLI over a growing season and comparing it to results can help determine which varieties of plants will thrive in a specific location. | 5 | Photochemistry |
There exists no theory elucidating correlations among -amino acids. If one takes, for example, alanine, which has a small methyl group, and phenylalanine, which has a larger benzyl group, a simple question is in what aspect, -alanine resembles -phenylalanine more than -phenylalanine, and what kind of mechanism causes the selection of all -amino acids, because it might be possible that alanine was and phenylalanine was .
It was reported in 2004 that excess racemic ,-asparagine (Asn), which spontaneously forms crystals of either isomer during recrystallization, induces asymmetric resolution of a co-existing racemic amino acid such as arginine (Arg), aspartic acid (Asp), glutamine (Gln), histidine (His), leucine (Leu), methionine (Met), phenylalanine (Phe), serine (Ser), valine (Val), tyrosine (Tyr), and tryptophan (Trp). The enantiomeric excess of these amino acids was correlated almost linearly with that of the inducer, i.e., Asn. When recrystallizations from a mixture of 12 ,-amino acids (Ala, Asp, Arg, Glu, Gln, His, Leu, Met, Ser, Val, Phe, and Tyr) and excess ,-Asn were made, all amino acids with the same configuration with Asn were preferentially co-crystallized. It was incidental whether the enrichment took place in - or -Asn, however, once the selection was made, the co-existing amino acid with the same configuration at the α-carbon was preferentially involved because of thermodynamic stability in the crystal formation. The maximal ee was reported to be 100%. Based on these results, it is proposed that a mixture of racemic amino acids causes spontaneous and effective optical resolution, even if asymmetric synthesis of a single amino acid does not occur without an aid of an optically active molecule.
This is the first study elucidating reasonably the formation of chirality from racemic amino acids with experimental evidences. | 4 | Stereochemistry |
In the finery, a workman known as the "finer" remelted pig iron so as to oxidise the carbon (and silicon). This produced a lump of iron (with some slag) known as a bloom. This was consolidated using a water-powered hammer (see trip hammer) and returned to the finery.
The next stages were undertaken by the "hammerman", who in some iron-making areas such as South Yorkshire was also known as the "stringsmith", who heated his iron in a string-furnace. Because the bloom is highly porous, and its open spaces are full of slag, the hammermans or stringsmiths tasks were to beat (work) the heated bloom with a hammer to drive the molten slag out of it, and then to draw the product out into a bar to produce what was known as anconies or bar iron. In order to do this, he had to reheat the iron, for which he used the chafery. The fuel used in the finery had to be charcoal (later coke), as impurities in any mineral fuel would affect the quality of the iron. | 8 | Metallurgy |
The mechanism of fluorination by SF is assumed to resemble chlorination by phosphorus pentachloride. Hydrogen fluoride, a useful solvent for these reactions, activates SF:
Species of the type ROSF are often invoked as intermediates. In the case of aldehydes and ketones, SF4 is thought to initially add across the double bond to give R2CFOSF. | 0 | Organic Chemistry |
Apoptosis triggered by FasR-Fas ligand binding plays a fundamental role in the regulation of the immune system. Its functions include:
*T-cell homeostasis: the activation of T-cells leads to their expression of the Fas ligand. T cells are initially resistant to Fas-mediated apoptosis during clonal expansion, but become progressively more sensitive the longer they are activated, ultimately resulting in activation-induced cell death (AICD). This process is needed to prevent an excessive immune response and eliminate autoreactive T-cells. Humans and mice with deleterious mutations of Fas or Fas ligand develop an accumulation of aberrant T-cells, leading to lymphadenopathy, splenomegaly, and lupus erythematosus.
*Cytotoxic T-cell activity: Fas-induced apoptosis and the perforin pathway are the two main mechanisms by which cytotoxic T lymphocytes induce cell death in cells expressing foreign antigens.
*Immune privilege: Cells in immune privileged areas such as the cornea or testes express Fas ligand and induce the apoptosis of infiltrating lymphocytes. It is one of many mechanisms the body employs in the establishment and maintenance of immune privilege.
*Maternal tolerance: Fas ligand may be instrumental in the prevention of leukocyte trafficking between the mother and the fetus, although no pregnancy defects have yet been attributed to a faulty Fas-Fas ligand system.
*Tumor counterattack: Tumors may over-express Fas ligand and induce the apoptosis of infiltrating lymphocytes, allowing the tumor to escape the effects of an immune response. The up-regulation of Fas ligand often occurs following chemotherapy, from which the tumor cells have attained apoptosis resistance. | 1 | Biochemistry |
Micro RNAs (miRNAs) are short, ~19-23 base pair long RNA oligonucleotides that are involved in the microRNA-induced silencing complex. Specifically, once loaded onto the ARGONAUTE enzyme, miRNAs work with mRNAs to repress translation and post-translationally destabilize mRNA. While they are functionally similar to siRNAs, miRNAs do not require extensive base-pairing for mRNA silencing (can require as few as seven base-pairs with target), thus allowing them to broadly affect a wider range of mRNA targets. In the cell, miRNA uses switch, tuning, and neutral interactions to finely regulate gene repression. As a therapeutic, miRNA has the potential to affect biochemical pathways throughout the organism.
With more than 400 miRNA identified in humans, discerning their target gene for repression is the first challenge. Multiple databases have been built, for example TargetScan, using miRNA seed matching. In vitro assays assist in determining the phenotypic effects of miRNAs, but due to the complex nature of gene regulation not all identified miRNAs have the expected effect. Additionally, several miRNAs have been found to act as either tumor suppressors or oncogenes in vivo, such as the oncogenic miR-155 and miR-17-92.
In clinical trials, miRNA are commonly used as biomarkers for a variety of diseases, potentially providing earlier diagnosis as well as disease progression, stage, and genetic links. Phase 1 and 2 trials currently test miRNA mimics (to express genes) and miRNA (to repress genes) in patients with cancers and other diseases. In particular, mimic miRNAs are used to introduce miRNAs that act as tumor suppressors into cancerous tissues, while miRNA antagonists are used to target oncogenic miRNAs to prevent their cancer-promoting activity. Therapeutic miRNA is also used in addition to common therapies (such as cancer therapies) that are known to overexpress or destabilize the patient miRNA levels. An example of one mimic miRNA therapy that demonstrated efficacy in impeding lung cancer tumor growth in mouse studies is miR-34a.
One concerning aspect of miRNA-based therapies is the potential for the exogeneous miRNA to affect miRNA silencing mechanisms within normal body cells, thereby affecting normal cellular biochemical pathways. However, in vivo studies have indicated that miRNAs display little to no effect in non-target tissues/organs. | 1 | Biochemistry |
Stereoisomers are compounds that are identical in composition and connectivity but have a different spatial arrangement of atoms around the central atom. A molecule having multiple stereocenters will produce many possible stereoisomers. In compounds whose stereoisomerism is due to tetrahedral (sp) stereogenic centers, the total number of hypothetically possible stereoisomers will not exceed 2, where n is the number of tetrahedral stereocenters. However, this is an upper bound because molecules with symmetry frequently have fewer stereoisomers.
The stereoisomers produced by the presence of multiple stereocenters can be defined as enantiomers (non-superposable mirror images) and diastereomers (non-superposable, non-identical, non-mirror image molecules). Enantiomers and diastereomers are produced due to differing stereochemical configurations of molecules containing the same composition and connectivity (bonding); the molecules must have multiple (two or more) stereocenters to be classified as enantiomers or diastereomers. Enantiomers and diastereomers will produce individual stereoisomers that contribute to the total number of possible stereoisomers.
However, the stereoisomers produced may also give a meso compound, which is an achiral compound that is superposable on its mirror image; the presence of a meso compound will reduce the number of possible stereoisomers. Since a meso compound is superposable on its mirror image, the two "stereoisomers" are actually identical. Resultantly, a meso compound will reduce the number of stereoisomers to below the hypothetical 2 amount due to symmetry.
Additionally, certain configurations may not exist due to steric reasons. Cyclic compounds with chiral centers may not exhibit chirality due to the presence of a two-fold rotation axis. Planar chirality may also provide for chirality without having an actual chiral center present. | 4 | Stereochemistry |
The standard state for a gas is the hypothetical state it would have as a pure substance obeying the ideal gas equation at standard pressure. IUPAC recommends using a standard pressure p or P° equal to , or 1 bar. No real gas has perfectly ideal behavior, but this definition of the standard state allows corrections for non-ideality to be made consistently for all the different gases. | 7 | Physical Chemistry |
The phosphate ion has a molar mass of 94.97 g/mol, and consists of a central phosphorus atom surrounded by four oxygen atoms in a tetrahedral arrangement. It is the conjugate base of the hydrogen phosphate ion , which in turn is the conjugate base of the dihydrogen phosphate ion , which in turn is the conjugate base of orthophosphoric acid, .
Many phosphates are soluble in water at standard temperature and pressure. The sodium, potassium, rubidium, caesium, and ammonium phosphates are all water-soluble. Most other phosphates are only slightly soluble or are insoluble in water. As a rule, the hydrogen and dihydrogen phosphates are slightly more soluble than the corresponding phosphates. | 0 | Organic Chemistry |
Q-cytochrome c oxidoreductase is also known as cytochrome c reductase, cytochrome bc complex, or simply complex III. In mammals, this enzyme is a dimer, with each subunit complex containing 11 protein subunits, an [2Fe-2S] iron–sulfur cluster and three cytochromes: one cytochrome c and two b cytochromes. A cytochrome is a kind of electron-transferring protein that contains at least one heme group. The iron atoms inside complex III's heme groups alternate between a reduced ferrous (+2) and oxidized ferric (+3) state as the electrons are transferred through the protein.
The reaction catalyzed by complex III is the oxidation of one molecule of ubiquinol and the reduction of two molecules of cytochrome c, a heme protein loosely associated with the mitochondrion. Unlike coenzyme Q, which carries two electrons, cytochrome c carries only one electron.
As only one of the electrons can be transferred from the QH donor to a cytochrome c acceptor at a time, the reaction mechanism of complex III is more elaborate than those of the other respiratory complexes, and occurs in two steps called the Q cycle. In the first step, the enzyme binds three substrates, first, QH, which is then oxidized, with one electron being passed to the second substrate, cytochrome c. The two protons released from QH pass into the intermembrane space. The third substrate is Q, which accepts the second electron from the QH and is reduced to Q, which is the ubisemiquinone free radical. The first two substrates are released, but this ubisemiquinone intermediate remains bound. In the second step, a second molecule of QH is bound and again passes its first electron to a cytochrome c acceptor. The second electron is passed to the bound ubisemiquinone, reducing it to QH as it gains two protons from the mitochondrial matrix. This QH is then released from the enzyme.
As coenzyme Q is reduced to ubiquinol on the inner side of the membrane and oxidized to ubiquinone on the other, a net transfer of protons across the membrane occurs, adding to the proton gradient. The rather complex two-step mechanism by which this occurs is important, as it increases the efficiency of proton transfer. If, instead of the Q cycle, one molecule of QH were used to directly reduce two molecules of cytochrome c, the efficiency would be halved, with only one proton transferred per cytochrome c reduced. | 1 | Biochemistry |
Loam molding has been used to produce large symmetrical objects such as cannon and church bells. Loam is a mixture of clay and sand with straw or dung. A model of the produced is formed in a friable material (the chemise). The mold is formed around this chemise by covering it with loam. This is then baked (fired) and the chemise removed. The mold is then stood upright in a pit in front of the furnace for the molten metal to be poured. Afterwards the mold is broken off. Molds can thus only be used once, so that other methods are preferred for most purposes. | 8 | Metallurgy |
Phosphonamidates are related to phosphonates by substitution of an oxygen atom for a nitrogen. They are a rarely encountered functional group. The nerve agent Tabun is an example. | 0 | Organic Chemistry |
EPIC-seq may be more effective in cancers with prominent genes or well-defined molecular subtypes. Consequently, its utility may be limited in cancers with less distinct genetic profiles or those characterized by significant interpatient variability. This restricts its generalizability across different cancer types and necessitates cautious interpretation of results in diverse oncological contexts. | 1 | Biochemistry |
Enzymes, which are composed of chiral amino acids, catalyze chemical reactions with high stereoselectivity. Specifically, esterase enzymes catalyze the hydrolysis of esters to carboxylic acids. This transformation may be rendered asymmetric if two enantiotopic ester groups exist in the substrate or if a racemic mixture of chiral esters is used. In the former case (desymmetrization), the chiral environment of the enzyme active site leads to selective hydrolysis of the ester that is closer to the catalytically active serine residue when the substrate is bound to the enzyme. In the latter case (kinetic resolution), one of the enantiomers is hydrolyzed faster than the other, leading to an excess of hydrolyzed product from one enantiomer. Both strategies rely on the fact that the transition states for hydrolysis of enantiotopic or enantiomorphic ester groups by the chiral enzyme are diastereomeric.
Pig liver esterase (PLE) is a widely used enzyme for asymmetric ester hydrolysis. Although it was originally used for the desymmetrizing hydrolysis of glutarate esters, PLE also hydrolyzes malonates, cyclic diesters, monoesters, and other substrates. Active site models have been advanced to explain the selectivity of PLE. | 0 | Organic Chemistry |
There are two types of conductivity detectors, direct and membrane.
Direct conductivity provides an all-encompassing approach of measuring CO. This detection method uses no carrier gas, is good at the parts per billion (ppb) ranges, but has a very limited analytical range.
Membrane conductivity relies upon the filtering of the CO prior to measuring it with a conductivity cell. Both methods analyze sample conductivity before and after oxidization, attributing this differential measurement to the TOC of the sample. During the sample oxidization phase, CO (directly related to the TOC in the sample) and other gases are formed. The dissolved CO forms a weak acid, thereby changing the conductivity of the original sample proportionately to the TOC in the sample. Conductivity analyses assume that only CO is present within the solution. As long as this holds true, then the TOC calculation by this differential measurement is valid. However, depending on the chemical species present in the sample and their individual products of oxidation, they may present either a positive or a negative interference to the actual TOC value, resulting in analytical error. Some of the interfering chemical species include Cl, HCO, SO, SO, ClO, and H. Small changes in pH and temperature fluctuations also contribute to inaccuracy.
Membrane conductivity analyzers have improved upon the direct conductivity approach by incorporating the use of hydrophobic gas permeation membranes to allow a more “selective” passage of the dissolved CO gas and nothing else. This provides a more precise and accurate measurement of the organics that were converted to CO. | 3 | Analytical Chemistry |
For a Morpholino to be effective, it must be delivered past the cell membrane into the cytosol of a cell. Once in the cytosol, Morpholinos freely diffuse between the cytosol and nucleus, as demonstrated by the nuclear splice-modifying activity of Morpholinos observed after microinjection into the cytosol of cells. Different methods are used for delivery into embryos, into cultured cells or into adult animals. A microinjection apparatus is usually used for delivery into an embryo, with injections most commonly performed at the single-cell or few-cell stage; an alternative method for embryonic delivery is electroporation, which can deliver oligos into tissues of later embryonic stages. Common techniques for delivery into cultured cells include the Endo-Porter peptide (which causes the Morpholino to be released from endosomes), the Special Delivery system (no longer commercially available, used a Morpholino-DNA heteroduplex and an ethoxylated polyethylenimine delivery reagent), electroporation, or scrape loading.
Delivery into adult tissues is usually difficult, though there are a few systems allowing useful uptake of unmodified Morpholino oligos (including uptake into muscle cells with Duchenne muscular dystrophy or the vascular endothelial cells stressed during balloon angioplasty). Though they permeate through intercellular spaces in tissues effectively, unconjugated PMOs have limited distribution into the cytosol and nuclear spaces within healthy tissues following IV administration. Systemic delivery into many cells in adult organisms can be accomplished by using covalent conjugates of Morpholino oligos with cell-penetrating peptides, and, while toxicity has been associated with moderate doses of the peptide conjugates, they have been used in vivo for effective oligo delivery at doses below those causing observed toxicity. An octa-guanidinium dendrimer attached to the end of a Morpholino can deliver the modified oligo (called a Vivo-Morpholino) from the blood to the cytosol. Delivery-enabled Morpholinos, such as peptide conjugates and Vivo-Morpholinos, show promise as therapeutics for viral and genetic diseases. | 1 | Biochemistry |
This effect is significantly less common in ceramics which are typically more resilient to chemical attack. Although phase changes are common in ceramics under stress these usually result in toughening rather than failure (see Zirconium dioxide). Recent studies have shown that the same driving force for this toughening mechanism can also enhance oxidation of reduced cerium oxide, resulting in slow crack growth and spontaneous failure of dense ceramic bodies. | 8 | Metallurgy |
Cieplak's proposal is supported by investigating the effects of various electronic substituents on product distribution. By installing an electron-withdrawing substituent such as a methoxy group at the C2 position, the reduction of substituted cyclohexanones begins to favor equatorial attack. This is because the axial C-O bond is a worse electron donor than a C–C bond, so axial attack is less favored.
Cieplak also demonstrated this effect by introducing electron withdrawing substituents on C3, which decrease the electron-donating capability of the ring C–C bond and therefore disfavor equatorial attack, which is antiperiplanar to this bond. Electron-donating substituents at C3 subsequently favor equatorial approach, since increasing C–C electron density favors σ donation into σ* and thereby encourages equatorial approach.
This effect can also be investigated by changing the electronic nature of the nucleophile. In the case of an electron-deficient nucleophile, the σ* of the forming C-Nuc bond is lower in energy and better stabilized by attack antiperiplanar to electron-rich axial C-H bonds. Attack therefore occurs axially. If the nucleophile is electron-rich, however, the donation of more electron density is less favored and equatorial attack may prevail. These trends have been observed even when normalizing for steric bulk of the nucleophile.
In substituted norbornones, nucleophilic attack will come antiperiplanar to the bonds which can best donate into σ*. The bonds positioned for this interaction are the bridgehead C–C bonds on the six-membered ring. Substituents which donate electron density to these bonds, such as ethyl groups, increase the rate of addition anti to the alkyl groups, which is the antiperiplanar trajectory. If electron-withdrawing substituents such as esters are appended to the C–C bonds, however, the selectivity favors syn addition, so that the bonds donating into σ* are the more electron-rich C–C bonds which are hydrogen-substituted.
A similar example is seen in substituted 2-adamantones, where varying the electronic properties at the remote 5 position has profound effects on product distribution. A hydroxyl group is able to donate electron density inductively to the forming σ* bond antiperiplanar, so attack from that side is favored. The electron-withdrawing ester substituent, however, lacks this stabilization ability. Instead, the C–H bonds are better electron donors than the C–COMe bonds, so attack comes anti to the hydrogen substituents and subsequently syn to the ester group. This explains the effect of remote electron-donor groups on stereochemical outcomes, which has been difficult to explain with other stereochemical models. The rigidity of the adamantone skeleton allows for tight control of conformation and minimization of competing effects. | 0 | Organic Chemistry |
The Schiff base rotates away from the extracellular side of the protein towards the cytoplasmic side, in preparation to accept a new proton. | 5 | Photochemistry |
* A birth–death process is a linear one-dimensional Markovian kinetic scheme.
* Michaelis–Menten kinetics are a type of a Markovian kinetic scheme when solved with the steady state assumption for the creation of intermediates in the reaction pathway. | 7 | Physical Chemistry |
Solubility is sensitive to changes in temperature. For example, sugar is more soluble in hot water than cool water. It occurs because solubility products, like other types of equilibrium constants, are functions of temperature. In accordance with Le Chatelier's Principle, when the dissolution process is endothermic (heat is absorbed), solubility increases with rising temperature. This effect is the basis for the process of recrystallization, which can be used to purify a chemical compound. When dissolution is exothermic (heat is released) solubility decreases with rising temperature.
Sodium sulfate shows increasing solubility with temperature below about 32.4 °C, but a decreasing solubility at higher temperature. This is because the solid phase is the decahydrate () below the transition temperature, but a different hydrate above that temperature.
The dependence on temperature of solubility for an ideal solution (achieved for low solubility substances) is given by the following expression containing the enthalpy of melting, ΔH, and the mole fraction of the solute at saturation:
where is the partial molar enthalpy of the solute at infinite dilution and the enthalpy per mole of the pure crystal.
This differential expression for a non-electrolyte can be integrated on a temperature interval to give:
For nonideal solutions activity of the solute at saturation appears instead of mole fraction solubility in the derivative with respect to temperature: | 7 | Physical Chemistry |
Leng has several roles, her most current is Chief Scientist for Environmental Change Adaptation and Resilience at the British Geological Survey. She is also Director of the Centre for Environmental Geochemistry, a collaboration between the British Geological Survey and the University of Nottingham, Leng leads research around environmental change, human impact, food security, and resource management. Leng has been involved in deep drilling as part of the International Continental Scientific Drilling Program, and worked in Lake Ohrid in Macedonia and Lake Chala in East Africa. She also heads the Stable Isotope Facility at the British Geological Survey, which is part of the National Environmental Isotope Facility. Stable isotopes can be used to better understand climate change and human-landscape interactions, with increasing importance on the Anthropocene and the modern calibration period; tracers of modern pollution; and understanding the hydrological cycle especially in areas suffering human impact. Leng takes part in expeditions, most recently the Natural Environment Research Council (NERC) mission called Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA). She actively blogs about her research.
Leng serves on the editorial board of the journals Quaternary Research, Quaternary Science Reviews, Scientific Reports and the Journal of Paleolimnology.
She has written several articles about successfully undertaking a PhD. | 9 | Geochemistry |
The first type of molecular marker developed and run on gel electrophoresis were allozymes. These markers are used for the detection of protein variation. The word "allozyme" (also known as "alloenzyme") comes from "allelic variants of enzymes." When run on a gel, proteins are separated by size and charge. Although allozymes may seem dated when compared to the other markers available, they are still used today, mainly due to their low cost. One major downside is that since there is only a limited amount available, specificity an issue. | 1 | Biochemistry |
Products containing dexmethylphenidate have a side effect profile comparable to those containing methylphenidate. | 4 | Stereochemistry |
Enolisation of RuBP is the conversion of the keto tautomer of RuBP to an enediol(ate). Enolisation is initiated by deprotonation at C3. The enzyme base in this step has been debated, but the steric constraints observed in crystal structures have made Lys210 the most likely candidate. Specifically, the carbamate oxygen on Lys210 that is not coordinated with the Mg ion deprotonates the C3 carbon of RuBP to form a 2,3-enediolate. | 5 | Photochemistry |
Patrick Forterre has been working on a novel hypothesis, called "three viruses, three domains": that viruses were instrumental in the transition from RNA to DNA and the evolution of Bacteria, Archaea, and Eukaryota. He believes the last universal common ancestor was RNA-based and evolved RNA viruses. Some of the viruses evolved into DNA viruses to protect their genes from attack. Through the process of viral infection into hosts the three domains of life evolved.
Another interesting proposal is the idea that RNA synthesis might have been driven by temperature gradients, in the process of thermosynthesis.
Single nucleotides have been shown to catalyze organic reactions.
Steven Benner has argued that chemical conditions on the planet Mars, such as the presence of boron, molybdenum, and oxygen, may have been better for initially producing RNA molecules than those on Earth. If so, life-suitable molecules, originating on Mars, may have later migrated to Earth via mechanisms of panspermia or similar process. | 9 | Geochemistry |
Heterologous gene expression is used in many biotechnological applications, including protein production and metabolic engineering. Because tRNA pools vary between different organisms, the rate of transcription and translation of a particular coding sequence can be less efficient when placed in a non-native context. For an overexpressed transgene, the corresponding mRNA makes a large percent of total cellular RNA, and the presence of rare codons along the transcript can lead to inefficient use and depletion of ribosomes and ultimately reduce levels of heterologous protein production. In addition, the composition of the gene (e.g. the total number of rare codons and the presence of consecutive rare codons) may also affect translation accuracy. However, using codons that are optimized for tRNA pools in a particular host to overexpress a heterologous gene may also cause amino acid starvation and alter the equilibrium of tRNA pools. This method of adjusting codons to match host tRNA abundances, called codon optimization, has traditionally been used for expression of a heterologous gene. However, new strategies for optimization of heterologous expression consider global nucleotide content such as local mRNA folding, codon pair bias, a codon ramp, codon harmonization or codon correlations. With the number of nucleotide changes introduced, artificial gene synthesis is often necessary for the creation of such an optimized gene.
Specialized codon bias is further seen in some endogenous genes such as those involved in amino acid starvation. For example, amino acid biosynthetic enzymes preferentially use codons that are poorly adapted to normal tRNA abundances, but have codons that are adapted to tRNA pools under starvation conditions. Thus, codon usage can introduce an additional level of transcriptional regulation for appropriate gene expression under specific cellular conditions. | 1 | Biochemistry |
A CHN analyzer (also known as a carbon hydrogen and nitrogen analyzer) is a scientific instrument which is used to measure carbon, hydrogen and nitrogen elemental concentrations in a given sample with accuracy and precision. Sample sizes are most often just a few milligrams, but may differ depending on system. For some sample matrices larger mass is preferred due to sample heterogeneity. These analysers are capable of handling a wide variety of sample types, including solids, liquids, volatile and viscous samples, in the fields of pharmaceuticals, polymers, chemicals, environment, food and energy.
This instrument calculates the percentages of elemental concentrations based on the Dumas method, using flash combustion of the sample to cause an instantaneous oxidization into simple compounds which are then detected with thermal conductivity detection or infrared spectroscopy. Separation of interference is done by chemical reagents. | 0 | Organic Chemistry |
The expression of the enzyme in adrenocortical cells is regulated by the trophic hormone corticotropin (ACTH). | 1 | Biochemistry |
The melting point of iron is experimentally well defined for pressures less than 50 GPa.
For greater pressures, published data (as of 2007) put the γ-ε-liquid triple point at pressures that differ by tens of gigapascals and 1000 K in the melting point. Generally speaking, molecular dynamics computer simulations of iron melting and shock wave experiments suggest higher melting points and a much steeper slope of the melting curve than static experiments carried out in diamond anvil cells.
The melting and boiling points of iron, along with its enthalpy of atomization, are lower than those of the earlier group 3d elements from scandium to chromium, showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and more into the inert core by the nucleus; however, they are higher than the values for the previous element manganese because that element has a half-filled 3d subshell and consequently its d-electrons are not easily delocalized. This same trend appears for ruthenium but not osmium. | 8 | Metallurgy |
A Kaminsky catalyst is a catalytic system for alkene polymerization. Kaminsky catalysts are based on metallocenes of group 4 transition metals (Ti, Zr, Hf) activated with methylaluminoxane (MAO). These and other innovations have inspired development of new classes of catalysts that in turn led to commercialization of novel engineering polyolefins.
__TOC__ | 7 | Physical Chemistry |
Section 3.8 introduces atomic units and gives a table of atomic units of various physical quantities and the conversion factor to the SI units. Section 7.3(v) gives a concise but clear tutorial on practical use of atomic units, in particular how to understand equations "written in atomic units". | 3 | Analytical Chemistry |
Numerous sAC splice variants are present in osteoclast and osteoblasts, and mutation in the human sAC gene is associated with low spinal density. Calcification by osteoblasts is intrinsically related with bicarbonate and calcium. Bone density experiments in mouse calvaria cultured indicates that HCO-sensing sAC is a physiological appropriate regulator of bone formation and/or reabsorption. | 1 | Biochemistry |
Silver standards refer to the standards of millesimal fineness for the silver alloy used in the manufacture or crafting of silver objects. This list is organized from highest to lowest millesimal fineness, or purity of the silver.
* Fine silver has a millesimal fineness of 999. Also called pure silver, or three nines fine, fine silver contains 99.9% silver, with the balance being some trace amounts of impurities. This grade of silver is used to make bullion bars for international commodities trading and investment in silver. In the modern world, fine silver is understood to be too soft for general use.
* Britannia silver has a millesimal fineness of at least 958. The alloy is 95.84% pure silver and 4.16% copper or other metals. The Britannia standard was developed in Britain in 1697 to help prevent British sterling silver coins from being melted to make silver plate. It was obligatory in Britain between 1697 and 1720, when the sterling silver standard was restored. It became an optional standard thereafter.
* The French 1st standard has a milessimal fineness of 950. The French 1st alloy is 95% silver and 5% copper or other metals.
* 91 zolotnik Russian silver has a millesimal fineness of 947. The zolotnik (Russian золотник, from the Russian zoloto, or золото, meaning gold) was used in Russia as early as the 11th century to denote the weight of gold coins. In its earliest usage, the zolotnik was 1/96 of a pound, but it later was changed to represent 1/72 of a pound. Ninety-one (91) zolotniks have the equivalent millesimal fineness of 947[9]. Thus, the alloy contains 94.79% pure silver and 5.21% copper or other metals.
* Sterling silver has a millesimal fineness of 925. The sterling silver alloy is 92.5% pure silver and 7.5% copper or other metals. This alloy was used by the United Kingdom from the early 12th century, and Canada, Australia and other countries associated with the British Empire (and later Commonwealth) from the 19th century up to the mid-20th century when debasement took place; Sterling silver’s copper content means that it has a stronger tendency to tarnish than other alloys used in coins.
*Following a program of debasements in the early-to-mid 20th century, circulating Canadian coinage (with the exception of the nickel) had a millesimal fineness of 800 until 1968. The alloy used contained 80% silver and 20% copper.
* 88 zolotnik Russian silver has the equivalent millesimal fineness of 916[6]. The alloy contains 91.66% pure silver and 8.34% copper or other metals. (The description of the zolotnik is above.)
* Coin silver has a millesimal fineness of 900. The term "coin silver" was derived from the fact that much of it was made from melting down silver coins. It is important here to note that there are differences between the coin silver standard and the coin silver alloy, as actually used in making silver objects. The coin silver standard in the United States was 90% silver and 10% copper, as dictated by US FTC guidelines. However, in silversmithing, coins could come from other nations besides the United States, and thus coin silver objects could vary from 750 millesimal fineness (75% silver) to 900 (90% silver). Coins were used as a source of silver in the US until 1868, shortly after the discovery of the Comstock silver lodes in Nevada, which provided a significant source of silver. Around this time the sterling standard was adopted by the American silver industry.
* 84 zolotnik Russian silver has the equivalent millesimal fineness of 875. The alloy contains 87.5% pure silver and 12.5% copper or other metals. (See above for description of the zolotnik.)
* has a millesimal fineness of 830. The Scandinavian silver alloy contains 83% pure silver and 17% copper or other metals.
* German silver will be marked with a millesimal fineness of 800 or 835 (80% or 83.5% pure silver). Any items simply marked "German silver", "nickel silver" or "Alpaca" have no silver content at all, but are mere alloys of other base metals.
* Decoplata has the equivalent millesimal fineness of 720. The alloy contains 72% pure silver and 28% copper. It was used by a number of countries between the 19th century and the present, but it is most associated with coins made in Mexico and the Netherlands in the mid-20th Century. | 8 | Metallurgy |
In chemistry and physics, the dimensionless mixing ratio is the abundance of one component of a mixture relative to that of all other components. The term can refer either to mole ratio (see concentration) or mass ratio (see stoichiometry). | 3 | Analytical Chemistry |
Adsorbents are used usually in the form of spherical pellets, rods, moldings, or monoliths with a hydrodynamic radius between 0.25 and 5 mm. They must have high abrasion resistance, high thermal stability and small pore diameters, which results in higher exposed surface area and hence high capacity for adsorption. The adsorbents must also have a distinct pore structure that enables fast transport of the gaseous vapors.
Most industrial adsorbents fall into one of three classes:
* Oxygen-containing compounds – Are typically hydrophilic and polar, including materials such as silica gel, limestone (calcium carbonate) and zeolites.
* Carbon-based compounds – Are typically hydrophobic and non-polar, including materials such as activated carbon and graphite.
* Polymer-based compounds – Are polar or non-polar, depending on the functional groups in the polymer matrix. | 7 | Physical Chemistry |
Quantum theory states that orbiting electrons of an atom must occupy discrete energy levels in order to be stable. Bombardment with ions of sufficient energy (usually MeV protons) produced by an ion accelerator, will cause inner shell ionization of atoms in a specimen. Outer shell electrons drop down to replace inner shell vacancies, however only certain transitions are allowed. X-rays of a characteristic energy of the element are emitted. An energy dispersive detector is used to record and measure these X-rays.
Only elements heavier than fluorine can be detected. The lower detection limit for a PIXE beam is given by the ability of the X-rays to pass through the window between the chamber and the X-ray detector. The upper limit is given by the ionisation cross section, the probability of the K electron shell ionisation, this is maximal when the velocity of the proton matches the velocity of the electron (10% of the speed of light), therefore 3 MeV proton beams are optimal. | 7 | Physical Chemistry |
In plants, animals and bacteria the glycine cleavage system catalyzes the following reversible reaction:
: Glycine + Hfolate + NAD ↔ 5,10-methylene-Hfolate + CO + NH + NADH + H
In the enzymatic reaction, H-protein activates the P-protein, which catalyzes the decarboxylation of glycine and attaches the intermediate molecule to the H-protein to be shuttled to the T-protein. The H-protein forms a complex with the T-protein that uses tetrahydrofolate and yields ammonia and 5,10-methylenetetrahydrofolate. After interaction with the T-protein, the H-protein is left with two fully reduced thiol groups in the lipoate group. The glycine protein system is regenerated when the H-protein is oxidized to regenerate the disulfide bond in the active site by interaction with the L-protein, which reduces NAD to NADH and H.
When coupled to serine hydroxymethyltransferase, the glycine cleavage system overall reaction becomes:
: 2 glycine + NAD + HO → serine + CO + NH + NADH + H
In humans and most vertebrates, the glycine cleavage system is part of the most prominent glycine and serine catabolism pathway. This is due in large part to the formation 5,10-methylenetetrahydrofolate, which is one of the few C donors in biosynthesis. In this case the methyl group derived from the catabolism of glycine can be transferred to other key molecules such as purines and methionine.
This reaction, and by extension the glycine cleavage system, is required for photorespiration in C plants. The glycine cleavage system takes glycine, which is created from an unwanted byproduct of the Calvin cycle, and converts it to serine which can reenter the cycle. The ammonia generated by the glycine cleavage system, is assimilated by the Glutamine synthetase-Glutamine oxoglutarate aminotransferase cycle but costs the cell one ATP and one NADPH. The upside is that one CO is produced for every two O that are mistakenly taken up by the cell, generating some value in an otherwise energy depleting cycle. Together the proteins involved in these reactions comprise about half the proteins in mitochondria from spinach and pea leaves. The glycine cleavage system is constantly present in the leaves of plants, but in small amounts until they are exposed to light. During peak photosynthesis, the concentration of the glycine cleavage system increases ten-fold.
In the anaerobic bacteria, Clostridium acidiurici, the glycine cleavage system runs mostly in the direction of glycine synthesis. While glycine synthesis through the cleavage system is possible due to the reversibility of the overall reaction, it is not readily seen in animals. | 1 | Biochemistry |
In June 2018 Australian Senates Senate Community Affairs References Committee recommended a move towards legalising MRT, and in July 2018 the Australian senate endorsed it. Research and clinical applications of MRT were overseen by laws made by federal and state governments. State laws were, for the most part, consistent with federal law. In all states, legislation prohibited the use of MRT techniques in the clinic, and except for Western Australia, research on a limited range of MRT was permissible up to day 14 of embryo development, subject to a license being granted. In 2010, the Hon. Mark Butler MP, then Federal Minister for Mental Health and Ageing, had appointed an independent committee to review the two relevant acts: the Prohibition of Human Cloning for Reproduction Act 2002 and the Research Involving Human Embryos Act 2002. The committees report, released in July 2011, recommended the existing legislation remain unchanged. The Australian National Health and Medical Research Council issued two reports on legalising MRT in June 2020. In 2022, Maeve's Law was passed by the Australian Parliament, legalising MRT under a specified mitochondrial donation licence for research and training, and in clinical settings.
Singapore was also considering whether to permit the MRT in 2018.
In 2018, researchers announced the use of MRT to restore function to heart tissue in cardiac-compromised newborns. The damaged heart cells absorbed mitochondria extracted from healthy tissue and returned to useful activity. | 1 | Biochemistry |
* No external power sources required.
* Relatively easy to install.
* Lower voltages and current mean that risk of causing stray current interference on other structures is low.
* Require less frequent monitoring than impressed current CP systems.
* Relatively low risk of overprotection.
* Once installed, testing the system components is relatively simple for trained personnel. | 7 | Physical Chemistry |
WeNMR is a worldwide e-Infrastructure for NMR spectroscopy and structural biology. It is the largest virtual Organization in the life sciences and is supported by EGI. | 1 | Biochemistry |
In 1891, approximately ten years after Pockels first surface tension measurements, through her brother Friedrich Pockels, she became aware that John William Strutt, 3rd Baron Rayleigh [Lord Rayleigh] was publishing studies of the effect of small amounts of oils on the surface of water. It was clear to her that Lord Rayleighs research was closely related to her own. At the encouragement of her brother, Agnes Pockels wrote to Lord Rayleigh to describe her apparatus, her findings, and the fact that she was unable to publish her findings in the scientific journals of the time. Pockels original correspondence with Rayleigh was in the German language and was translated for Rayleigh by his wife. In an act of generosity and unthreatened by correspondence from an unknown amateur, Rayleigh forwarded Pockels findings to the journal Nature with a suitable cover letter to enable Pockels' findings to be published. Her first paper was "Surface Tension," describing her measurements and findings with her sliding trough.
The letter to Lord Rayleigh was described in a 1971 journal article on the origin of the surface film balance as being "a landmark in the history of surface chemistry." Lord Rayleigh retained his correspondence, and Pockels’s letter to him dated 10 January 1891 began:
The body of Pockels's letter to Rayleigh then described her sliding trough method, her initial findings, and her assessment of the limitations of her experimental methods. The closing of her letter stated:
Lord Rayleigh forwarded Pockelss correspondence to the editor of the journal Nature', with a covering letter dated 2 March 1891. The editor at the time was Sir Joseph Norman Lockyer who chose to publish the correspondence from Rayleigh and Pockels. The covering letter stated:
Ostwald's biography of Pockels reports that Pockels had initially approached physicists at the University of Göttingen about her findings and received no expression of interest. | 7 | Physical Chemistry |
Japan has one assay office, situated at the Saitama branch of Japan Mint in Saitama Prefecture. Japan Mint has assayed and hallmarked from 1929, and the Saitama branch moved from Tokyo in 2016. Japanese hallmarking is optional. Gold, silver and platinum are subject to assay. The articles combined with the golden parts and the platinum parts are hallmarked with special marks. | 3 | Analytical Chemistry |
The first reported method of methylation analysis using bisulfite-treated DNA utilized PCR and standard dideoxynucleotide DNA sequencing to directly determine the nucleotides resistant to bisulfite conversion. Primers are designed to be strand-specific as well as bisulfite-specific (i.e., primers containing non-CpG cytosines such that they are not complementary to non-bisulfite-treated DNA), flanking (but not involving) the methylation site of interest. Therefore, it will amplify both methylated and unmethylated sequences, in contrast to methylation-specific PCR. All sites of unmethylated cytosines are displayed as thymines in the resulting amplified sequence of the sense strand, and as adenines in the amplified antisense strand. By incorporating high throughput sequencing adaptors into the PCR primers, PCR products can be sequenced with massively parallel sequencing. Alternatively, and labour-intensively, PCR product can be cloned and sequenced. Nested PCR methods can be used to enhance the product for sequencing.
All subsequent DNA methylation analysis techniques using bisulfite-treated DNA is based on this report by Frommer et al. (Figure 2). Although most other modalities are not true sequencing-based techniques, the term "bisulfite sequencing" is often used to describe bisulfite-conversion DNA methylation analysis techniques in general. | 1 | Biochemistry |
The Mehler reaction is named after Alan H. Mehler, who, in 1951, presented data to the effect that isolated chloroplasts reduce oxygen to form hydrogen peroxide (). Mehler observed that the formed in this way does not present an active intermediate in photosynthesis; rather, as a reactive oxygen species, it can be toxic to surrounding biological processes as an oxidizing agent. In scientific literature, the Mehler reaction often is used interchangeably with the Water-Water Cycle to refer to the formation of by photosynthesis. Sensu stricto, the Water Water Cycle encompasses the Hill reaction, in which water is split to form oxygen, as well as the Mehler Reaction, in which oxygen is reduced to form and, finally, the scavenging of this by antioxidants to form water.
Beginning in the 1970s, Professor Kozi Asada elucidated that oxygen can be reduced by electrons emerging from ferredoxin of photosystem I, to form superoxide, which is then reduced by superoxide dismutase to form . This photochemical is then reduced by the action of ascorbate peroxidase to form water and oxidized ascorbate. Asada argued that oxygen presents an important sink for excess excitation energy acquired during plant exposure to bright light. He would often begin seminars by asking: Why arent plants sunburnt despite being exposed to light?'.
How much of a photoprotective role the Water Water Cycle plays has been occasion for some debate. In terrestrial plants, transfer of electrons to oxygen from ferredoxin at PSI accounts for easily less than 10% of total photosynthetic electron transport. In algae and other uni-cellular photosynthetic organisms, however, this amount can account for 20 to 30% of total electron transport. It is possible that the reduction of oxygen by free electrons emerging from PSI prevents components of the electron transport chain from becoming over-reduced.
The Water Water Cycle is not related to photorespiration, as it comprises different reactions and results in no net oxygen consumption. | 5 | Photochemistry |
FISH is a very general technique. The differences between the various FISH techniques are usually due to variations in the sequence and labeling of the probes; and how they are used in combination. Probes are divided into two generic categories: cellular and acellular. In fluorescent "in situ" hybridization refers to the cellular placement of the probe
Probe size is important because shorter probes hybridize less specifically than longer probes, so that long enough strands of DNA or RNA (often 10–25 nucleotides) which are complementary to a given target sequence are often used to locate a target. The overlap defines the resolution of detectable features. For example, if the goal of an experiment is to detect the breakpoint of a translocation, then the overlap of the probes — the degree to which one DNA sequence is contained in the adjacent probes — defines the minimum window in which the breakpoint may be detected.
The mixture of probe sequences determines the type of feature the probe can detect. Probes that hybridize along an entire chromosome are used to count the number of a certain chromosome, show translocations, or identify extra-chromosomal fragments of chromatin. This is often called "whole-chromosome painting." If every possible probe is used, every chromosome, (the whole genome) would be marked fluorescently, which would not be particularly useful for determining features of individual sequences. However, it is possible to create a mixture of smaller probes that are specific to a particular region (locus) of DNA; these mixtures are used to detect deletion mutations. When combined with a specific color, a locus-specific probe mixture is used to detect very specific translocations. Special locus-specific probe mixtures are often used to count chromosomes, by binding to the centromeric regions of chromosomes, which are distinctive enough to identify each chromosome (with the exception of Chromosome 13, 14, 21, 22.)
A variety of other techniques uses mixtures of differently colored probes. A range of colors in mixtures of fluorescent dyes can be detected, so each human chromosome can be identified by a characteristic color using whole-chromosome probe mixtures and a variety of ratios of colors. Although there are more chromosomes than easily distinguishable fluorescent dye colors, ratios of probe mixtures can be used to create secondary colors. Similar to comparative genomic hybridization, the probe mixture for the secondary colors is created by mixing the correct ratio of two sets of differently colored probes for the same chromosome. This technique is sometimes called M-FISH.
The same physics that make a variety of colors possible for M-FISH can be used for the detection of translocations. That is, colors that are adjacent appear to overlap; a secondary color is observed. Some assays are designed so that the secondary color will be present or absent in cases of interest. An example is the detection of BCR/ABL translocations, where the secondary color indicates disease. This variation is often called double-fusion FISH or D-FISH. In the opposite situation—where the absence of the secondary color is pathological—is illustrated by an assay used to investigate translocations where only one of the breakpoints is known or constant. Locus-specific probes are made for one side of the breakpoint and the other intact chromosome. In normal cells, the secondary color is observed, but only the primary colors are observed when the translocation occurs. This technique is sometimes called "break-apart FISH". | 1 | Biochemistry |
The term zero-point energy (ZPE) is a translation from the German .
Sometimes used interchangeably with it are the terms zero-point radiation and ground state energy. The term zero-point field (ZPF) can be used when referring to a specific vacuum field, for instance the QED vacuum which specifically deals with quantum electrodynamics (e.g., electromagnetic interactions between photons, electrons and the vacuum) or the QCD vacuum which deals with quantum chromodynamics (e.g., color charge interactions between quarks, gluons and the vacuum). A vacuum can be viewed not as empty space but as the combination of all zero-point fields. In quantum field theory this combination of fields is called the vacuum state, its associated zero-point energy is called the vacuum energy and the average energy value is called the vacuum expectation value (VEV) also called its condensate. | 7 | Physical Chemistry |
Typically, ellipsometry is done only in the reflection setup. The exact nature of the polarization change is determined by the sample's properties (thickness, complex refractive index or dielectric function tensor). Although optical techniques are inherently diffraction-limited, ellipsometry exploits phase information (polarization state), and can achieve sub-nanometer resolution. In its simplest form, the technique is applicable to thin films with thickness of less than a nanometer to several micrometers. Most models assume the sample is composed of a small number of discrete, well-defined layers that are optically homogeneous and isotropic. Violation of these assumptions requires more advanced variants of the technique (see below).
Methods of immersion or multiangular ellipsometry are applied to find the optical constants of the material with rough sample surface or presence of inhomogeneous media. New methodological approaches allow the use of reflection ellipsometry to measure physical and technical characteristics of gradient elements in case the surface layer of the optical detail is inhomogeneous. | 7 | Physical Chemistry |
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