text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Pitting resistance equivalent number (PREN) is a predictive measurement of a stainless steel's resistance to localized pitting corrosion based on its chemical composition. In general: the higher PREN-value, the more resistant is the stainless steel to localized pitting corrosion by chloride.
PREN is frequently specified when stainless steels will be exposed to seawater or other high chloride solutions. In some instances stainless steels with PREN-values > 32 may provide useful resistance to pitting corrosion in seawater, but is dependent on optimal conditions. However, crevice corrosion is also a significant possibility and a PREN > 40 is typically specified for seawater service.
These alloys need to be manufactured and heat treated correctly to be seawater corrosion resistant to the expected level. PREN alone is not an indicator of corrosion resistance. The value should be calculated for each heat to ensure compliance with minimum requirements, this is due to chemistry variation within the specified composition limits. | 8 | Metallurgy |
Difluoroethane is an extremely flammable gas, which decomposes rapidly on heating or burning, producing toxic and irritating fumes, including hydrogen fluoride and carbon monoxide.
In a DuPont study, rats were exposed to up to 25,000 ppm (67,485 mg/m) for six hours daily, five days a week for two years. This has become the no-observed-adverse-effect level for this substance. Prolonged exposure to 1,1-difluoroethane has been linked in humans to the development of coronary disease and angina. Repeated or sufficiently high levels of exposure, particularly purposeful inhalation, can precipitate fatal cardiac arrhythmia. | 2 | Environmental Chemistry |
In context of x-rays, opacifiers are additives with high absorption of x-rays; typically these are particles or compounds of lead, barium (often barium sulfate), tungsten, or other high atomic weight elements. Sometimes opacifiers are added to medical implants to make them visible under X-ray imaging. This is especially true in the case of most polymers which are often unrecognizable in the body when viewed using X-rays. | 7 | Physical Chemistry |
Electrons in solids have a chemical potential, defined the same way as the chemical potential of a chemical species: The change in free energy when electrons are added or removed from the system. In the case of electrons, the chemical potential is usually expressed in energy per particle rather than energy per mole, and the energy per particle is conventionally given in units of electronvolt (eV).
Chemical potential plays an especially important role in solid-state physics and is closely related to the concepts of work function, Fermi energy, and Fermi level. For example, n-type silicon has a higher internal chemical potential of electrons than p-type silicon. In a p–n junction diode at equilibrium the chemical potential (internal chemical potential) varies from the p-type to the n-type side, while the total chemical potential (electrochemical potential, or, Fermi level) is constant throughout the diode.
As described above, when describing chemical potential, one has to say "relative to what". In the case of electrons in semiconductors, internal chemical potential is often specified relative to some convenient point in the band structure, e.g., to the bottom of the conduction band. It may also be specified "relative to vacuum", to yield a quantity known as work function, however, work function varies from surface to surface even on a completely homogeneous material. Total chemical potential, on the other hand, is usually specified relative to electrical ground.
In atomic physics, the chemical potential of the electrons in an atom is sometimes said to be the negative of the atom's electronegativity. Likewise, the process of chemical potential equalization is sometimes referred to as the process of electronegativity equalization. This connection comes from the Mulliken electronegativity scale. By inserting the energetic definitions of the ionization potential and electron affinity into the Mulliken electronegativity, it is seen that the Mulliken chemical potential is a finite difference approximation of the electronic energy with respect to the number of electrons, i.e., | 7 | Physical Chemistry |
* The Charlotte, North Carolina Mint – 1835 to 1861. After the Civil War, the plant was reopened in 1868 as an assay office until 1913, when it was ultimately closed.
* The New Orleans, Louisiana Mint – 1835 to 1942. Coinage operations were conducted here from 1838, but were suspended from 1861 until 1879; assay functions were performed from 1876. Coinage resumed in 1879 and continued until 1909. The facility operated as an assay office from 1909 until 1942, when it was closed.
* The U.S. Assay Office, St. Louis, Missouri – 1881 to 1911
* The U.S. Assay Office, Helena, Montana – 1874 to 1933
* The U.S. Assay Office, Salt Lake City, Utah – 1909 to 1933
* The U.S. Assay Office, Deadwood, South Dakota – 1898 to 1927
* The U.S. Assay Office, Boise, Idaho – 1869 to 1933
* The U.S. Assay Office, New York, New York – 1854 to 1982
* The U.S. Assay Office, Seattle, Washington – 1898 to 1955 | 3 | Analytical Chemistry |
Thermophotovoltaic (TPV) energy conversion is a direct conversion process from heat to electricity via photons. A basic thermophotovoltaic system consists of a hot object emitting thermal radiation and a photovoltaic cell similar to a solar cell but tuned to the spectrum being emitted from the hot object.
As TPV systems generally work at lower temperatures than solar cells, their efficiencies tend to be low. Offsetting this through the use of multi-junction cells based on non-silicon materials is common, but generally very expensive. This currently limits TPV to niche roles like spacecraft power and waste heat collection from larger systems like steam turbines. | 7 | Physical Chemistry |
The protein structure of firefly luciferase consists of two compact domains: the N-terminal domain and the C-terminal domain. The N-terminal domain is composed of two β-sheets in an αβαβα structure and a β barrel. The two β-sheets stack on top of each other, with the β-barrel covering the end of the sheets.
The C-terminal domain is connected to the N-terminal domain by a flexible hinge, which can separate the two domains. The amino acid sequences on the surface of the two domains facing each other are conserved in bacterial and firefly luciferase, thereby strongly suggesting that the active site is located in the cleft between the domains.
During a reaction, luciferase has a conformational change and goes into a "closed" form with the two domains coming together to enclose the substrate. This ensures that water is excluded from the reaction and does not hydrolyze ATP or the electronically excited product. | 1 | Biochemistry |
2,6-Di-tert-butylpyridine is prepared by the reaction of tert-butyllithium with pyridine. The synthesis is reminiscent of the Chichibabin reaction.
Some related bulky pyridine compounds have been described, including 2,4,6-tri-t-butylpyridine and 2,6-di-tert-butyl-4-methylpyridine. | 0 | Organic Chemistry |
The chemical structure of DNA is insufficient to understand the complexity of the 3D structures of DNA. In contrast, animated molecular models allow one to visually explore the three-dimensional (3D) structure of DNA. The DNA model shown (far right) is a space-filling, or CPK, model of the DNA double helix. Animated molecular models, such as the wire, or skeletal, type shown at the top of this article, allow one to visually explore the three-dimensional (3D) structure of DNA. Another type of DNA model is the space-filling, or CPK, model.
The hydrogen bonding dynamics and proton exchange is very different by many orders of magnitude between the two systems of fully hydrated DNA and water molecules in ice. Thus, the DNA dynamics is complex, involving nanosecond and several tens of picosecond time scales, whereas that of liquid ice is on the picosecond time scale, and that of proton exchange in ice is on the millisecond time scale. The proton exchange rates in DNA and attached proteins may vary from picosecond to nanosecond, minutes or years, depending on the exact locations of the exchanged protons in the large biopolymers.
A simple harmonic oscillator vibration is only an oversimplified dynamic representation of the longitudinal vibrations of the DNA intertwined helices which were found to be anharmonic rather than harmonic as often assumed in quantum dynamic simulations of DNA. | 4 | Stereochemistry |
In Australia, and the United States, Armodafinil is considered to be a Schedule 4 prescription-only medicine or prescription animal remedy. Schedule 4 is defined as "Substances, the use or supply of which should be by or on the order of persons permitted by State or Territory legislation to prescribe and should be available from a pharmacist on prescription." | 4 | Stereochemistry |
Between May 13–14, 2004 the site was enclosed with temporary mesh fencing and plain-clothed security guards commenced patrols of the public areas. At 02:00 on May 15 bulldozers arrived at the site and tree-felling began at 07:00. The work caused immediate concern to nearby residents who feared the work might unsettle asbestos deposits in the ground. Residents formed the Save Spodden Valley action group the following week. Residents also protested to Rochdale Council, which subsequently issued an emergency tree preservation order on six parts of the site, preventing the removal of trees without permission of planning officers, and carrying a fine of up to £20,000 per tree. The Health and Safety Executive (HSE) also secured a voluntary arrangement to halt any work that could disturb soil on the site pending soil sampling. Former Turner's employees and local residents claimed that, as recently as the 1960s, asbestos dust and fibres were clearly visible hanging from the trees, and that a disused coalmine shaft exposed by the tree felling had been used over a period of decades to dump hundreds of tonnes of asbestos waste. | 2 | Environmental Chemistry |
The cryophorus was first described by William Hyde Wollaston in an 1813 paper titled, "On a method of freezing at a distance." | 7 | Physical Chemistry |
On subcellular distribution, histamine N-methyltransferase protein in humans is mainly localized to the nucleoplasm (which is an organelle, i.e., a subunit of a cell) and cytosol (which is the intracellular fluid, i.e., a fluid inside cells). In addition, it is localized to the centrosome (another organelle).
In humans, the protein is present in many tissues and is most abundantly expressed in the brain, thyroid gland, bronchus, duodenum, liver, gallbladder, kidney, and skin. | 1 | Biochemistry |
:La yielded the highest water splitting rate of photocatalysts without using sacrificial reagents. This ultraviolet-based photocatalyst was reported to show water splitting rates of 9.7 mmol/h and a quantum yield of 56%. The nanostep structure of the material promotes water splitting as edges functioned as production sites and the grooves functioned as production sites. Addition of NiO particles as co-catalysts assisted in production; this step used an impregnation method with an aqueous solution of •6 and evaporated the solution in the presence of the photocatalyst. has a conduction band higher than that of NiO, so photo-generated electrons are more easily transferred to the conduction band of NiO for evolution. | 5 | Photochemistry |
Piperacillin is generally available in their stable form as crystallized potassium or sodium salt, quickly losing bactericidal activity upon dissolution due to their short half-lives. As the gastrointestinal tract does not absorb piperacillin and tazobactam, they are dissolved in a solution before being administered to a patient, through parenteral means. Excreted through renal mechanisms like glomerular or tubular filtration as a component of urine, uncontrolled dosages of the drug can cause renal dysfunction and competitive inhibition of excretion, delaying piperacillin-tazobactam excretion, and endangering patients to drug exposure.
Although the distribution of the drug remained the same, the half-life for elimination increased by three to five folds for patients diagnosed with renal dysfunction. Measured by creatinine clearance (CrCl), patients with less than 30 mL/min of clearance had significantly reduced levels of piperacillin/tazobactam excretion, measuring down to 35% of the initial dosage, while the area under the curve (AUC) for piperacillin increased by about three folds for those with less than 20 mL/min. A reduced dosage or alteration in the interval of administration is recommended for patients lying under 40 mL/min of CrCl, depending on the severity of dysfunction.
Renal is the main pathway for drug elimination for both tazobactam and piperacillin in the body. While there are other non-renal means of drug elimination like hepatobiliary excretion, they occur less frequently. A substantial amount (~80%) of piperacillin found in urine when excreted through glomerular and tubular filtration is unmetabolized. Tazobactam renal elimination may be significantly reduced through piperacillin interaction, dropping from 63.7% to 56.8% of the administered dose over a 24-hour period. Piperacillin may be actively diffused through filtration into the biliary tract during renal clearing, indicated by a generally higher concentration of piperacillin than tazobactam in the bile. The metabolites that make up the remaining percentage in the excreted urine are composed of M1 (inactive) and N-desethyl-piperacillin (active), formed from the division of β-lactam rings of both tazobactam and piperacillin respectively.
Due to the hydrophilic nature of piperacillin-tazobactam, a volume distribution of ~15 L amounting to various sites (tissues) is desired, as hydrophilic compounds are not able to pass through plasma membranes as easily as hydrophobic compounds. Concentrations often in the range of 90 MIC or above are located in specific areas including the gallbladder, lung, muscle, and skin, making up 16–85% of the plasma concentrations. The concentration of piperacillin-tazobactam is especially lower in fatty tissue, making up less than 10% of the plasma concentrations. | 4 | Stereochemistry |
Most IPNs do not interpenetrate completely on a molecular scale, but rather form small dispersed or bicontinuous phase morphologies with characteristic length scales on the order of tens of nanometers. However, since these length scales are relatively small, they are often considered homogeneous on a macroscopic scale. The characteristic lengths associated with these domains often scale with the length of chains between crosslinks, and thus the morphology of the phases is often dictated by the crosslinking density of the constituent networks. The kinetics of phase separation in IPNs can arise from both nucleation and growth and spinodal decomposition mechanisms, with the former producing discrete phases akin to dispersed spheres and the latter forming bicontinuous phases akin to interconnected cylinders. Contrary to many typical phase separation processes, coarsening, where the length scale of the phases tends to increase over time, can be impeded by the formation of crosslinks in either network. Furthermore, IPNs are often able to maintain these complex morphologies over long periods of time compared to what could be achieved by simple polymer blends. | 7 | Physical Chemistry |
Despite early successes such as the determination of the positions of hydrogen atoms in NHCl crystals by W. E. Laschkarew and I. D. Usykin in 1933, boric acid by John M. Cowley in 1953 and orthoboric acid by William Houlder Zachariasen in 1954, electron diffraction for many years was a qualitative technique used to check samples within electron microscopes. John M Cowley explains in a 1968 paper: This has changed, in transmission, reflection and for low energies. Some of the key developments (some of which are also described later) from the early days to 2023 have been:
*Fast numerical methods based upon the Cowley-Moodie multislice algorithm, which only became possible once the fast Fourier transform (FFT) method was developed. With these and other numerical methods Fourier transforms are fast, and it became possible to calculate accurate, dynamical diffraction in seconds to minutes with laptops using widely available multislice programs.
*Developments in the convergent-beam electron diffraction approach. Building on the original work of Walther Kossel and Gottfried Möllenstedt in 1939, it was extended by Peter Goodman and Gunter Lehmpfuhl, then mainly by the groups of John Steeds and Michiyoshi Tanaka who showed how to determine point groups and space groups. It can also be used for higher-level refinements of the electron density; for a brief history see CBED history. In many cases this is the best method to determine symmetry.
*The development of new approaches to reduce dynamical effects such as precession electron diffraction and three-dimensional diffraction methods. Averaging over different directions has, empirically, been found to significantly reduce dynamical diffraction effects, e.g., see PED history for further details. Not only is it easier to identify known structures with this approach, it can also be used to solve unknown structures in some cases – see precession electron diffraction for further information.
*The development of experimental methods exploiting ultra-high vacuum technologies (e.g. the approach described by in 1953) to better control surfaces, making LEED and RHEED more reliable and reproducible techniques. In the early days the surfaces were not well controlled; with these technologies they can both be cleaned and remain clean for hours to days, a key component of surface science.
*Fast and accurate methods to calculate intensities for LEED so it could be used to determine atomic positions, for instance references. These have been extensively exploited to determine the structure of many surfaces, and the arrangement of foreign atoms on surfaces.
*Methods to simulate the intensities in RHEED, so it can be used semi-quantitatively to understand surfaces during growth and thereby to control the resulting materials.
*The development of advanced detectors for transmission electron microscopy such as charge-coupled device and direct electron detectors, which improve the accuracy and reliability of intensity measurements. These have efficiencies and accuracies that can be a thousand or more times that of the photographic film used in the earliest experiments, with the information available in real time rather than requiring photographic processing after the experiment. | 7 | Physical Chemistry |
A solute in dilute solution usually follows Henrys law rather than Raoults law, and it is more usual to express the composition of the solution in terms of the molar concentration (in mol/L) or the molality (in mol/kg) of the solute rather than in mole fractions. The standard state of a dilute solution is a hypothetical solution of concentration = 1 mol/L (or molality = 1 mol/kg) which shows ideal behaviour (also referred to as "infinite-dilution" behaviour). The standard state, and hence the activity, depends on which measure of composition is used. Molalities are often preferred as the volumes of non-ideal mixtures are not strictly additive and are also temperature-dependent: molalities do not depend on volume, whereas molar concentrations do.
The activity of the solute is given by: | 7 | Physical Chemistry |
Born on 17 September 1940 in the south Indian state of Tamil Nadu, Paramasivam Natarajan graduated in chemistry from the University of Madras in 1959. He started his career as a lecturer at the Government Arts College of the Madras University in 1959 but later moved to the NGM College, Pollachi in 1963. The next year, he joined the Banaras Hindu University (BHU) as a CSIR Junior Research fellow and during the tenure of the fellowship, obtained his master's degree in 1963. After continuing at BHU for a year more, he became a lecturer at the Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER) where he stayed till 1970. Later he went to the US as a teaching assistant at the University of Southern California, simultaneously pursuing his doctoral studies under the guidance of John F. Endicott. He secured a PhD in 1971 and did his post doctoral studies under his PhD guide, Endicott, at Wayne State University as the latter had moved to the Michigan-based university by that time.
Natarajan returned to India in 1974 and joined his alma mater, Madras University, as a reader of the department of physical chemistry. In 1977, he became a professor in charge of the Post Graduate Centre of the university in Tiruchirappalli. In 1982, he returned to the university headquarters in Chennai as the head of the department of inorganic chemistry. In 1991, he was deputed by the university as the director of Central Salt and Marine Chemicals Research Institute (CSMCRI), a post he held till 1996. After the completion of the assignment at CSMCRI, he resumed his duties at the university and became a senior professor in 1998. At time of his superannuation in 2001, he held the post of an INSA Senior Scientist at the National Centre for Ultrafast Process of the university and served as a member of the university syndicate.
Natarajan was married to Sivabagyam and the couple had two daughters, Shiva Sukanthi and Shakthi. He died on 18 March 2016, at the age of 75, survived by his wife, children and their families. | 5 | Photochemistry |
Sarfati is a chess FIDE Master, and achieved a draw against former world champion Boris Spassky during a tournament in Wellington in 1988, and was New Zealand's national chess champion in 1987–88.
Although tied with Rey Casse for first place in the Australian Junior Championship of 1981, he was not eligible to share the title as he was a resident of New Zealand at the time. He represented New Zealand in three Chess Olympiads: the 27th in Dubai in 1986, the 28th in Thessaloniki in 1988, and the 30th in Manila in 1992. He also represented New Zealand on top board at the 5th Asian Teams in New Delhi.
He has given blindfold chess exhibitions at chess clubs and other events, and has played twelve such games simultaneously. His previous best was winning 11/11 at the Kāpiti Chess Club in New Zealand. | 7 | Physical Chemistry |
Some research has suggested that a deregulation of cAMP pathways and an aberrant activation of cAMP-controlled genes is linked to the growth of some cancers. | 1 | Biochemistry |
Although engineered and modified in a laboratory setting, ELPs share structural characteristics with intrinsically disordered proteins (IDPs) naturally found in the body, such as tropoelastin, from which ELPs were given their name. The repeat sequences found in the biopolymer give each ELP a distinct structure, as well as influence the lower critical solution temperature (LCST), also referred to commonly as the T. It is at this temperature that the ELPs move from a linear, relatively disordered state to a more densely aggregated, partially ordered state Although given as a single temperature, T the ELP phase change process generally begins and ends within a temperature range of approximately 2 °C. Also, T is altered by the addition of unique proteins to the free ELPs. | 7 | Physical Chemistry |
Time crystals do not violate the laws of thermodynamics: energy in the overall system is conserved, such a crystal does not spontaneously convert thermal energy into mechanical work, and it cannot serve as a perpetual store of work. But it may change perpetually in a fixed pattern in time for as long as the system can be maintained. They possess "motion without energy"—their apparent motion does not represent conventional kinetic energy. Recent experimental advances in probing discrete time crystals in their periodically driven nonequilibrium states have led to the beginning exploration of novel phases of nonequilibrium matter.
Time crystals do not evade the Second Law of Thermodynamics, although they spontaneously break "time-translation symmetry", the usual rule that a stable object will remain the same throughout time. In thermodynamics, a time crystal's entropy, understood as a measure of disorder in the system, remains stationary over time, marginally satisfying the second law of thermodynamics by not decreasing. | 3 | Analytical Chemistry |
Fumaric acid has been used as a food acidulant since 1946. It is approved for use as a food additive in the EU, USA and Australia and New Zealand. As a food additive, it is used as an acidity regulator and can be denoted by the E number E297. It is generally used in beverages and baking powders for which requirements are placed on purity. Fumaric acid is used in the making of wheat tortillas as a food preservative and as the acid in leavening. It is generally used as a substitute for tartaric acid and occasionally in place of citric acid, at a rate of 1 g of fumaric acid to every ~1.5 g of citric acid, in order to add sourness, similarly to the way malic acid is used. As well as being a component of some artificial vinegar flavors, such as "Salt and Vinegar" flavored potato chips, it is also used as a coagulant in stove-top pudding mixes.
The European Commission Scientific Committee on Animal Nutrition, part of DG Health, found in 2014 that fumaric acid is "practically non-toxic" but high doses are probably nephrotoxic after long-term use. | 1 | Biochemistry |
In naphtha cracking process, C4R4 refers to C4 residual obtained after separation of 1,3-butadiene, isobutylene, 1-butene, and cis- or trans-2-butene from C4 raffinate stream which mainly consists of n-butane. Normally C4R4 is a side product in tert-butyl alcohol plant if C4R3 is used for feed. | 3 | Analytical Chemistry |
Interactomics is a discipline at the intersection of bioinformatics and biology that deals with studying both the interactions and the consequences of those interactions between and among proteins, and other molecules within a cell. Interactomics thus aims to compare such networks of interactions (i.e., interactomes) between and within species in order to find how the traits of such networks are either preserved or varied.
Interactomics is an example of "top-down" systems biology, which takes an overhead view of a biosystem or organism. Large sets of genome-wide and proteomic data are collected, and correlations between different molecules are inferred. From the data new hypotheses are formulated about feedbacks between these molecules. These hypotheses can then be tested by new experiments. | 1 | Biochemistry |
Within a homogeneous medium such as a solution, there is no scattering. For this case, researched extensively by August Beer, the concentration of the absorbing species follows the same linear contribution to absorbance as the path-length. Additionally, the contributions of individual absorbing species are additive. This is a very favorable situation, and made absorbance an absorption metric far preferable to absorption fraction (absorptance). This is the case for which the term "absorbance" was first used.
A common expression of the Beer's law relates the attenuation of light in a material as: where is the absorbance; is the molar attenuation coefficient or absorptivity of the attenuating species; is the optical path length; and is the concentration of the attenuating species. | 7 | Physical Chemistry |
The oxygen-evolving complex is the site of water oxidation. It is a metallo-oxo cluster comprising four manganese ions (in oxidation states ranging from +3 to +4) and one divalent calcium ion. When it oxidizes water, producing oxygen gas and protons, it sequentially delivers the four electrons from water to a tyrosine (D1-Y161) sidechain and then to P680 itself. It is composed of three protein subunits, OEE1 (PsbO), OEE2 (PsbP) and OEE3 (PsbQ); a fourth PsbR peptide is associated nearby.
The first structural model of the oxygen-evolving complex was solved using X-ray crystallography from frozen protein crystals with a resolution of 3.8Å in 2001. Over the next years the resolution of the model was gradually increased to 2.9Å. While obtaining these structures was in itself a great feat, they did not show the oxygen-evolving complex in full detail. In 2011 the OEC of PSII was resolved to a level of 1.9Å revealing five oxygen atoms serving as oxo bridges linking the five metal atoms and four water molecules bound to the cluster; more than 1,300 water molecules were found in each photosystem II monomer, some forming extensive hydrogen-bonding networks that may serve as channels for protons, water or oxygen molecules. At this stage, it is suggested that the structures obtained by X-ray crystallography are biased, since there is evidence that the manganese atoms are reduced by the high-intensity X-rays used, altering the observed OEC structure. This incentivized researchers to take their crystals to a different X-ray facilities, called X-ray Free Electron Lasers, such as SLAC in the USA. In 2014 the structure observed in 2011 was confirmed. Knowing the structure of Photosystem II did not suffice to reveal how it works exactly. So now the race has started to solve the structure of Photosystem II at different stages in the mechanistic cycle (discussed below). Currently structures of the S1 state and the S3 state's have been published almost simultaneously from two different groups, showing the addition of an oxygen molecule designated O6 between Mn1 and Mn4, suggesting that this may be the site on the oxygen evolving complex, where oxygen is produced. | 5 | Photochemistry |
Chloroplast DNA (cpDNA) is the DNA located in chloroplasts, which are photosynthetic organelles located within the cells of some eukaryotic organisms. Chloroplasts, like other types of plastid, contain a genome separate from that in the cell nucleus. The existence of chloroplast DNA was identified biochemically in 1959, and confirmed by electron microscopy in 1962. The discoveries that the chloroplast contains ribosomes and performs protein synthesis revealed that the chloroplast is genetically semi-autonomous. The first complete chloroplast genome sequences were published in 1986, Nicotiana tabacum (tobacco) by Sugiura and colleagues and Marchantia polymorpha (liverwort) by Ozeki et al. Since then, a great number of chloroplast DNAs from various species have been sequenced. | 5 | Photochemistry |
One of the most notable surveillance projects was the Hazardous Substances Emergency Events Surveillance (HSEES) program, which lasted from 1990 to 2009. ATSDR partnered with 15 states to collect information for HSEES in order to track, report, and study chemical spills. The information in the HSEES system was used to plan for emergency events involving hazardous substances (including terrorist attacks). States also used the information to develop policies and programs to strengthen public health and reduce illnesses and deaths that can result from exposure to hazardous substances. For example, states used HSEES data to support legislation addressing the problem of hazardous chemicals at illegal methamphetamine labs. Other states used HSEES data to implement programs designed to minimize exposure to hazardous chemicals and mercury at schools. More than 50 published studies were conducted using HSEES data. | 1 | Biochemistry |
Redox mediators are often added to experimental systems to improve the rate of electron export from the biological material and/or electron transfer to the anode, especially when whole cells are employed as the light harvesting material. Quinones, phenazines, and viologens have all been successfully employed to increase current output from photosynthetic organisms in biological photovoltaic devices. Adding artificial mediators is considered an unsustainable practice in scaled-up applications, so most modern research is on mediator-free systems. | 7 | Physical Chemistry |
A wide range of cellular secretions (say, a specific antibody or cytokine) can be detected using the ELISA technique. The number of cells which secrete those particular substances can be determined using a related technique, the ELISPOT assay. | 1 | Biochemistry |
An amorphous metal (also known as metallic glass, glassy metal, or shiny metal) is a solid metallic material, usually an alloy, with disordered atomic-scale structure. Most metals are crystalline in their solid state, which means they have a highly ordered arrangement of atoms. Amorphous metals are non-crystalline, and have a glass-like structure. But unlike common glasses, such as window glass, which are typically electrical insulators, amorphous metals have good electrical conductivity and can show metallic luster.
There are several ways in which amorphous metals can be produced, including extremely rapid cooling, physical vapor deposition, solid-state reaction, ion irradiation, and mechanical alloying. Previously, small batches of amorphous metals had been produced through a variety of quick-cooling methods, such as amorphous metal ribbons which had been produced by sputtering molten metal onto a spinning metal disk (melt spinning). The rapid cooling (in the order of millions of degrees Celsius a second) is too fast for crystals to form and the material is "locked" in a glassy state. Currently, a number of alloys with critical cooling rates low enough to allow formation of amorphous structure in thick layers (over ) have been produced; these are known as bulk metallic glasses. More recently, batches of amorphous steel with three times the strength of conventional steel alloys have been produced. New techniques as 3D printing, also characterised by their high cooling rates, are an active research topic for manufacturing bulk metallic glasses. | 8 | Metallurgy |
Macronutrients are defined in several ways.
* The chemical elements humans consume in the largest quantities are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur, summarized as CHNOPS.
* The chemical compounds that humans consume in the largest quantities and provide bulk energy are classified as carbohydrates, proteins, and fats. Water must be also consumed in large quantities but does not provide caloric value.
* Calcium, sodium, potassium, magnesium, and chloride ions, along with phosphorus and sulfur, are listed with macronutrients because they are required in large quantities compared to micronutrients, i.e., vitamins and other minerals, the latter often described as trace or ultratrace minerals.
Macronutrients provide energy:
* Carbohydrates are compounds made up of types of sugar. Carbohydrates are classified according to their number of sugar units: monosaccharides (such as glucose and fructose), disaccharides (such as sucrose and lactose), oligosaccharides, and polysaccharides (such as starch, glycogen, and cellulose).
* Proteins are organic compounds that consist of amino acids joined by peptide bonds. Since the body cannot manufacture some of the amino acids (termed essential amino acids), the diet must supply them. Through digestion, proteins are broken down by proteases back into free amino acids.
* Fats consist of a glycerin molecule with three fatty acids attached. Fatty acid molecules contain a -COOH group attached to unbranched hydrocarbon chains connected by single bonds alone (saturated fatty acids) or by both double and single bonds (unsaturated fatty acids). Fats are needed for construction and maintenance of cell membranes, to maintain a stable body temperature, and to sustain the health of skin and hair. Because the body does not manufacture certain fatty acids (termed essential fatty acids), they must be obtained through one's diet.
* Ethanol is not an essential nutrient, but it does provide calories.The United States Department of Agriculture uses a figure of per gram of alcohol ( per ml) for calculating food energy. For distilled spirits, a standard serving in the U.S. is , which at 40% ethanol (80 proof) would be 14 grams and 98 calories. | 9 | Geochemistry |
Tosyl azide is one of the most stable azide compounds but is still regarded as a potential explosive and should be carefully stored, while particular caution is vital for all reactions in which it is heated at or above 100 °C. The initial temperature of the explosive decomposition is about 120 °C. | 0 | Organic Chemistry |
In the history of science, the principle of maximum work was a postulate concerning the relationship between chemical reactions, heat evolution, and the potential work produced there from. The principle was developed in approximate form in 1875 by French chemist Marcellin Berthelot, in the field of thermochemistry, and then in 1876 by American mathematical physicist Willard Gibbs, in the field of thermodynamics, in a more accurate form. Berthelot's version was essentially: "every pure chemical reaction is accompanied by evolution of heat." (and that this yields the maximum amount of work). The effects of irreversibility, however, showed this version to be incorrect. This was rectified, in thermodynamics, by incorporating the concept of entropy. | 7 | Physical Chemistry |
The project was not continued with the change in administrations after the 1980 United States elections. The Office of Technology Assessment concluded that "Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture."
In 1997, NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility. In assessing "What has changed" since the DOE study, NASA asserted that the "US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO [Earth to Orbit] transportation down dramatically. This is, of course, an absolute requirement of space solar power."
Conversely, Pete Worden of NASA claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Worden referred to possible solutions as speculative and not available for decades at the earliest.
On November 2, 2012, China proposed a space collaboration with India that mentioned SBSP, "may be Space-based Solar Power initiative so that both India and China can work for long term association with proper funding along with other willing space faring nations to bring space solar power to earth." | 7 | Physical Chemistry |
Gemperline is author of more than 60 peer-reviewed publications in the field of Chemometrics.
His most-cited publication is his book, Practical Guide to Chemometrics (CRC Press), for which he served as both editor and as a contributor. The chapters he contributed were based on the teaching notes he had developed at East Carolina University for use with undergraduate and master's degree level students. | 3 | Analytical Chemistry |
The coupling of chromatography with MS is a well developed chemical analysis strategy dating back from the 1950s. Gas chromatography (GC)–MS was originally introduced in 1952, when A. T. James and A. J. P. Martin were trying to develop tandem separation – mass analysis techniques. In GC, the analytes are eluted from the separation column as a gas and the connection with electron ionization (EI) or chemical ionization (CI) ion sources in the MS system was a technically simpler challenge. Because of this, the development of GC-MS systems was faster than LC–MS and such systems were first commercialized in the 1970s. The development of LC–MS systems took longer than GC-MS and was directly related to the development of proper interfaces. Victor Talrose and his collaborators in Russia started the development of LC–MS in the late 1960s, when they first used capillaries to connect an LC columns to an EI source. A similar strategy was investigated by McLafferty and collaborators in 1973 who coupled the LC column to a CI source, which allowed a higher liquid flow into the source. This was the first and most obvious way of coupling LC with MS, and was known as the capillary inlet interface. This pioneer interface for LC–MS had the same analysis capabilities of GC-MS and was limited to rather volatile analytes and non-polar compounds with low molecular mass (below 400 Da). In the capillary inlet interface, the evaporation of the mobile phase inside the capillary was one of the main issues. Within the first years of development of LC–MS, on-line and off-line alternatives were proposed as coupling alternatives. In general, off-line coupling involved fraction collection, evaporation of solvent, and transfer of analytes to the MS using probes. Off-line analyte treatment process was time-consuming and there was an inherent risk of sample contamination. Rapidly, it was realized that the analysis of complex mixtures would require the development of a fully automated on-line coupling solution in LC–MS.
The key to the success and widespread adoption of LC–MS as a routine analytical tool lies in the interface and ion source between the liquid-based LC and the vacuum-base MS. The following interfaces were stepping-stones on the way to the modern atmospheric-pressure ionization interfaces, and are described for historical interest. | 3 | Analytical Chemistry |
Imidazolidinones are catalysts for many transformations such as asymmetric Diels-Alder reactions and Michael additions. Chiral catalysts induce asymmetric reactions, often with high enantioselectivities. This catalyst works by forming an iminium ion with carbonyl groups of α,β-unsaturated aldehydes (enals) and enones in a rapid chemical equilibrium. This iminium activation is similar to activation of carbonyl groups by a Lewis acid and both catalysts lower the substrate's LUMO:
The transient iminium intermediate is chiral which is transferred to the reaction product via chiral induction. The catalysts have been used in Diels-Alder reactions, Michael additions, Friedel-Crafts alkylations, transfer hydrogenations and epoxidations.
One example is the asymmetric synthesis of the drug warfarin (in equilibrium with the hemiketal) in a Michael addition of 4-hydroxycoumarin and benzylideneacetone:
A recent exploit is the vinyl alkylation of crotonaldehyde with an organotrifluoroborate salt:
For other examples of its use: see organocatalytic transfer hydrogenation and asymmetric Diels-Alder reactions. | 0 | Organic Chemistry |
Locascio attended James Madison University from 1979 to 1983 where she earned her B.Sc. in chemistry with a minor in biochemistry. In 1982, Locascio was a research assistant in the department of chemistry at West Virginia University. She attended the University of Utah from 1983 to 1986 while working as a research assistant in the department of bioengineering. Locascio completed her M.Sc. in bioengineering in 1986.
From 1986 to 1999, Locascio was a research biomedical engineer in the molecular spectroscopy and microfluidic methods group in the analytical chemistry division of the National Institute of Standards and Technology (NIST). She received a certificate of recognition from the United States Department of Commerce in 1987, 1989, and 1990. Locascio was awarded the Department of Commerce Bronze Medal in 1991. While working at NIST, she was encouraged by her manager Willie E. May and mentor Richard Durst to pursue a doctoral degree. From 1995 to 1999, Locascio completed a Ph.D. in toxicology at the University of Maryland School of Medicine. At the University of Maryland, Katherine S. Squibb and Bruce O. Fowler, the director of the toxicology program, supported Locascios efforts to attend graduate school while also working at NIST. Her dissertation was titled Miniaturization of bioassays for analytical toxicology'. Cheng S. Lee was her doctoral advisor and Mohyee E. Eldefrawi served on her advisory committee. | 3 | Analytical Chemistry |
The breakdown of DNA and RNA is occurring continuously in the cell. Purine and pyrimidine nucleosides can either be degraded to waste products and excreted or can be salvaged as nucleotide components. | 1 | Biochemistry |
Recrystallization kinetics are commonly observed to follow the profile shown. There is an initial nucleation period t where the nuclei form, and then begin to grow at a constant rate consuming the deformed matrix. Although the process does not strictly follow classical nucleation theory it is often found that such mathematical descriptions provide at least a close approximation. For an array of spherical grains the mean radius R at a time t is (Humphreys and Hatherly 2004):
where t is the nucleation time and G is the growth rate dR/dt. If N nuclei form in the time increment dt and the grains are assumed to be spherical then the volume fraction will be:
This equation is valid in the early stages of recrystallization when f<<1 and the growing grains are not impinging on each other. Once the grains come into contact the rate of growth slows and is related to the fraction of untransformed material (1-f) by the Johnson-Mehl equation:
While this equation provides a better description of the process it still assumes that the grains are spherical, the nucleation and growth rates are constant, the nuclei are randomly distributed and the nucleation time t is small. In practice few of these are actually valid and alternate models need to be used.
It is generally acknowledged that any useful model must not only account for the initial condition of the material but also the constantly changing relationship between the growing grains, the deformed matrix and any second phases or other microstructural factors. The situation is further complicated in dynamic systems where deformation and recrystallization occur simultaneously. As a result, it has generally proven impossible to produce an accurate predictive model for industrial processes without resorting to extensive empirical testing. Since this may require the use of industrial equipment that has not actually been built there are clear difficulties with this approach. | 8 | Metallurgy |
Bromatometry is a titration process in which the bromination of a chemical indicator is observed.
Potassium bromate alone can be used for the analysis of organoarsenicals. | 3 | Analytical Chemistry |
Melzer's reagent can be used to test whether spores are amyloid, nonamyloid, or dextrinoid.
* Spores that stain bluish-gray to bluish-black are amyloid
* Spores that stain brown to reddish-brown are dextrinoid
This test is normally performed on white spored mushrooms. If the spores are not light colored, a change will not be readily apparent. It is easiest to see the color change under a microscope, but it is possible to see it with the naked eye with a good spore print. | 3 | Analytical Chemistry |
There has been a severe increase in mass mortality events associated with low oxygen causing mass hypoxia with the majority having been in the last 2 decades. The rise in water temperature leads to an increase in oxygen demand and the increase for ocean deoxygenation which causes these large coral reef dead zones. For many coral reefs, the response to this hypoxia is very dependent on the magnitude and duration of the deoxygenation. The symptoms can be anywhere from reduced photosynthesis and calcification to bleaching. Hypoxia can have indirect effects like the abundance of algae and spread of coral diseases in the ecosystems. While coral is unable to handle such low levels of oxygen, algae is quite tolerant. Because of this, in interaction zones between algae and coral, increased hypoxia will cause more coral death and higher spread of algae. The increase mass coral dead zones is reinforced by the spread of coral diseases. Coral diseases can spread easily when there are high concentrations of sulfide and hypoxic conditions. Due to the loop of hypoxia and coral reef mortality, the fish and other marine life that inhabit the coral reefs have a change in behavioral in response to the hypoxia. Some fish will go upwards to find more oxygenated water, and some enter a phase of metabolic and ventilatory depression. Invertebrates migrate out of their homes to the surface of substratum or move to the tips of arborescent coral colonies.
Around six million people, the majority who live in developing countries, depend on coral reef fisheries. These mass die-offs due to extreme hypoxic events can have severe impacts on reef fish populations. Coral reef ecosystems offer a variety of essential ecosystem services including shoreline protection, nitrogen fixation, and waste assimilation, and tourism opportunities. The continued decline of oxygen in oceans on coral reefs is concerning because it takes many years (decades) to repair and regrow corals. | 9 | Geochemistry |
Because unsaturated alanes are oxygen- and moisture-sensitive, they are most often prepared for immediate use without isolation. However, the method of preparation determines the configuration of the intermediate unsaturated alane, which is directly related to the configuration of the product (transfer of the alkenyl group occurs with retention of configuration). Thus, an understanding of available hydroalumination methods is important for the study of reactions of unsaturated alanes. This second describes the most common methods of hydroalumination, and subsequent chemical reactions that the resulting alkenylalanes may undergo. | 0 | Organic Chemistry |
Vicat softening temperature or Vicat hardness is the determination of the softening point for materials that have no definite melting point, such as plastics. It is taken as the temperature at which the specimen is penetrated to a depth of by a flat-ended needle with a circular or square cross-section. For the Vicat A test, a load of is used. For the Vicat B test, the load is . It is named after the French engineer Louis Vicat.
Standards to determine Vicat softening point include ASTM D 1525 and ISO 306, which are largely equivalent.
The vicat softening temperature can be used to compare the heat-characteristics of different materials.
Four different methods may be used for testing.
ISO 10350 Note
ISO 10350 Vicat values are tested using the B50 method.
Similar Standards: ASTM D1525 | 7 | Physical Chemistry |
Alkyl groups are electron donating groups. The carbon on that is sp hybridized and less electronegative than those that are sp hybridized. They have overlap on the carbon–hydrogen bonds (or carbon–carbon bonds in compounds like tert-butylbenzene) with the ring p orbital. Hence they are more reactive than benzene and are ortho/para directors. | 0 | Organic Chemistry |
Casein kinase activity was found to be present in most cell types and to be associated with multiple enzymes. The type 1 casein kinase family of related gene products are now given designations such as "casein kinase 1 alpha" and "casein kinase 1 epsilon". | 1 | Biochemistry |
The Ryoji Noyori Prize is named in his honour. In 2000 Noyori became Honorary Doctor at the University of Rennes 1, where he taught in 1995, and in 2005, he became Honorary Doctor at Technical University of Munich and RWTH Aachen University, Germany. Noyori was elected a Foreign Member of the Royal Society (ForMemRS) in 2005. and an Honorary Doctorate degree from the Institute of Chemical Technology, Mumbai (formerly known as UDCT) on the 23rd day of February 2018.
He has also been awarded:
*1978 – Matsunaga prize
*1982 – Chu-Nichi Culture Award
*1985 – The Chemical Society of Japan Award
*1991 – John G. Kirkwood Award, American Chemical Society and Yale University
*1992 – Asahi Prize
*1993 – Tetrahedron Prize
*1995 – Japan Academy Prize (academics)
*1997 – Arthur C. Cope Award
*1997 – Chirality Medal
*1999 – King Faisal International Prize
*2001 – Wolf Prize in Chemistry
*2001 – Nobel Prize for Chemistry
*2009 – Lomonosov Gold Medal | 4 | Stereochemistry |
Most living tissues prosper at a near-neutral pH—that is, a pH close to 7. The pH of blood ranges from 7.35 to 7.45, for instance. When cells are grown in tissue culture, the medium in which they grow is held close to this physiological pH. A small amount of phenol red added to this growth medium will have a pink-red color under normal conditions. Typically, 15 mg/L are used for cell culture.
In the event of problems, waste products produced by dying cells or overgrowth of contaminants will cause a change in pH, leading to a change in indicator color. For example, a culture of relatively slowly dividing mammalian cells can be quickly overgrown by bacterial contamination. This usually results in an acidification of the medium, turning it yellow. Many biologists find this a convenient way to rapidly check on the health of tissue cultures. In addition, the waste products produced by the mammalian cells themselves will slowly decrease the pH, gradually turning the solution orange and then yellow. This color change is an indication that even in the absence of contamination, the medium needs to be replaced (generally, this should be done before the medium has turned completely orange).
Since the color of phenol red can interfere with some spectrophotometric and fluorescent assays, many types of tissue culture media are also available without phenol red. | 3 | Analytical Chemistry |
A demonstration-scale Fischer–Tropsch plant was built and operated by Rentech, Inc., in partnership with ClearFuels, a company specializing in biomass gasification. Located in Commerce City, Colorado, the facility produces about of fuels from natural gas. Commercial-scale facilities were planned for Rialto, California; Natchez, Mississippi; Port St. Joe, Florida; and White River, Ontario. Rentech closed down their pilot plant in 2013, and abandoned work on their FT process as well as the proposed commercial facilities. | 0 | Organic Chemistry |
There are a variety of ethical positions regarding the possibilities of cloning, especially human cloning. While many of these views are religious in origin, the questions raised by cloning are faced by secular perspectives as well. Perspectives on human cloning are theoretical, as human therapeutic and reproductive cloning are not commercially used; animals are currently cloned in laboratories and in livestock production.
Advocates support development of therapeutic cloning to generate tissues and whole organs to treat patients who otherwise cannot obtain transplants, to avoid the need for immunosuppressive drugs, and to stave off the effects of aging. Advocates for reproductive cloning believe that parents who cannot otherwise procreate should have access to the technology.
Opponents of cloning have concerns that technology is not yet developed enough to be safe and that it could be prone to abuse (leading to the generation of humans from whom organs and tissues would be harvested), as well as concerns about how cloned individuals could integrate with families and with society at large. Cloning humans could lead to serious violations of human rights.
Religious groups are divided, with some opposing the technology as usurping "Gods place" and, to the extent embryos are used, destroying a human life; others support therapeutic clonings potential life-saving benefits. There is at least one religion, Raëlism, in which cloning plays a major role.
Contemporary work on this topic is concerned with the ethics, adequate regulation and issues of any cloning carried out by humans, not potentially by extraterrestrials (including in the future), and largely also not replication – also described as mind cloning – of potential whole brain emulations.
Cloning of animals is opposed by animal-groups due to the number of cloned animals that suffer from malformations before they die, and while food from cloned animals has been approved as safe by the US FDA, its use is opposed by groups concerned about food safety.
In practical terms, the inclusion of "licensing requirements for embryo research projects and fertility clinics, restrictions on the commodification of eggs and sperm, and measures to prevent proprietary interests from monopolizing access to stem cell lines" in international cloning regulations has been proposed, albeit e.g. effective oversight mechanisms or cloning requirements have not been described. | 1 | Biochemistry |
As miraculin is a readily soluble protein and relatively heat stable, it is a potential sweetener in acidic food, such as soft drinks. While attempts to express it in yeast and tobacco plants have failed, researchers have succeeded in preparing genetically modified E. coli bacteria that express miraculin. Lettuce and tomato have also been used for mass production of miraculin.
The use of miraculin as a food additive was denied in 1974 by the United States Food and Drug Administration. Since 2011, the FDA has imposed a ban on importing Synsepalum dulcificum (specifying miraculin) from its origin in Taiwan, declaring it as an "illegal undeclared sweetener". The ban does not apply to the use of manufactured miraculin in dietary supplements. Miraculin has a novel food status in the European Union. It is approved in Japan as a safe food additive, according to the List of Existing Food Additives published by the Ministry of Health and Welfare (published by the Japan External Trade Organization). | 1 | Biochemistry |
Some ylides are 1,3-dipoles and interact in 1,3-dipolar cycloadditions. For instance an azomethine ylide is a dipole in the Prato reaction with fullerenes. | 0 | Organic Chemistry |
The CHondritic Uniform Reservoir (CHUR) is a scientific model in astrophysics and geochemistry for the mean chemical composition of the part of the Solar Nebula from which, during the formation of the Solar System, chondrites formed. This hypothetical chemical reservoir is thought to have been similar in composition to the current photosphere of the Sun.
When the Sun formed from its protostar, around 4.56 billion years ago, the solar wind blew all gas particles from the central part of the Solar Nebula. In this way most lighter volatiles (e.g. hydrogen, helium, oxygen, carbon dioxide), that had not yet condensed in the inner, warmer regions of the nebula, were lost. This fractionation process is the reason why the terrestrial planets and asteroid belt are relatively enriched in heavy elements in respect to the Sun or the gas planets.
Certain type of meteorites, CI-chondrites, have chemical compositions that are almost identical to the solar photosphere, except for the abundances of volatiles. Because the Sun contains 99.86% of the mass of the Solar System, they are considered to have the same composition as the solar nebula (with the exception of volatile loss) and are therefore representative of the material from which the terrestrial planets, including the Earth, were formed. | 9 | Geochemistry |
FAHFAs (fatty acid esters of hydroxy fatty acids) are formed in adipose tissue, improve glucose tolerance and also reduce adipose tissue inflammation. Palmitic acid esters of hydroxy-stearic acids (PAHSAs) are among the most bioactive members able to activate G-protein coupled receptors 120. Docosahexaenoic acid ester of hydroxy-linoleic acid (DHAHLA) exert anti-inflammatory and pro-resolving properties. | 1 | Biochemistry |
The belt-type machine is generally more applicable to smaller and to adhesive feed. In addition, the feed presentation is more stable which makes it more applicable for more difficult and heterogenous applications. | 3 | Analytical Chemistry |
The malate–aspartate shuttle (sometimes simply the malate shuttle) is a biochemical system for translocating electrons produced during glycolysis across the semipermeable inner membrane of the mitochondrion for oxidative phosphorylation in eukaryotes. These electrons enter the electron transport chain of the mitochondria via reduction equivalents to generate ATP. The shuttle system is required because the mitochondrial inner membrane is impermeable to NADH, the primary reducing equivalent of the electron transport chain. To circumvent this, malate carries the reducing equivalents across the membrane. | 1 | Biochemistry |
Non-thermal microwave effects or specific microwave effects have been posited in order to explain unusual observations in microwave chemistry. The main effect of the absorption of microwaves by dielectric materials is a brief displacement in the permanent dipoles which causes rotational entropy. Since the frequency of the microwave energy is much faster than the electrons can absorb, the resultant energy can cause frictional heating of nearby atoms or molecules. If the material is rigid there will be no release of rotational energy, and therefore no heating. There are no "Non-thermal effects". If the material is not a dielectric material with dipoles or an ionic distribution, there is no interaction with microwaves and no heating. Non-thermal effects in liquids are almost certainly non-existent, as the time for energy redistribution between molecules in a liquid is much less than the period of a microwave oscillation. A 2005 review has illustrated this in application to organic chemistry, though clearly supports the existence of non-thermal effects. It has been shown that such non-thermal effects exist in the reaction of O + HCl(DCl) -> OH(OD) + Cl in the gas phase and the authors suggest that some mechanisms may also be present in the condensed phase. Non-thermal effects in solids are still part of an ongoing debate. It is likely that through focusing of electric fields at particle interfaces, microwaves cause plasma formation and enhance diffusion in solids via second-order effects. As a result, they may enhance solid-state sintering processes. Debates continued in 2006 about non-thermal effects of microwaves that have been reported in solid-state phase transitions. A 2013 essay concluded the effect did not exist in organic synthesis involving liquid phases. A 2015 perspective discusses the non-thermal microwave effect (a resonance process) in relation to selective heating by Debye relaxation processes. | 7 | Physical Chemistry |
They were the first set of nonsense mutations to be discovered, isolated by Richard H. Epstein and Charles Steinberg and named after their friend and graduate Caltech student Harris Bernstein, whose last name means "amber" in German (cf. Bernstein).
Viruses with amber mutations are characterized by their ability to infect only certain strains of bacteria, known as amber suppressors. These bacteria carry their own mutation that allows a recovery of function in the mutant viruses. For example, a mutation in the tRNA that recognizes the amber stop codon allows translation to "read through" the codon and produce a full-length protein, thereby recovering the normal form of the protein and "suppressing" the amber mutation.
Thus, amber mutants are an entire class of virus mutants that can grow in bacteria that contain amber suppressor mutations. Similar suppressors are known for ochre and opal stop codons as well.
tRNA molecules carrying unnatural aminoacids have been designed to recognize the amber stop codon in bacterial RNA. This technology allows for incorporation of orthogonal aminoacids (such as p-azidophenylalanine) at specific locations of the target protein. | 1 | Biochemistry |
Over the years, for example in his 1879 thesis, but particularly in 1926, Planck advocated regarding the generation of heat by rubbing as the most specific way to define heat. Planck criticised Carathéodory for not attending to this. Carathéodory was a mathematician who liked to think in terms of adiabatic processes, and perhaps found friction to tricky to think about, while Planck was a physicist. | 7 | Physical Chemistry |
Proteins are the product of a gene that are formed from translation of a mature mRNA molecule. Proteins contain 4 elements in regards to their structure: primary, secondary, tertiary and quaternary. The linear amino acid sequence is also known as the primary structure. Hydrogen bonding between the amino acids of the primary structure results in the formation of alpha helices or beta sheets. These stable foldings are the secondary structure. The particular combination of the primary and secondary structures form the tertiary structure of a polypeptide. The quaternary structure refers to the way multiple chains of polypeptides fold together. | 1 | Biochemistry |
PyBOP (benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate) is a peptide coupling reagent used in solid phase peptide synthesis. It is used as a substitute for the BOP reagent - avoiding the formation of the carcinogenic waste product HMPA. | 1 | Biochemistry |
GUIDE-Seq (Genome-wide, Unbiased Identification of DSBs Enabled by Sequencing) is a molecular biology technique that allows for the unbiased in vitro detection of off-target genome editing events in DNA caused by CRISPR/Cas9 as well as other RNA-guided nucleases in living cells. Similar to LAM-PCR, it employs multiple PCRs to amplify regions of interest that contain a specific insert that preferentially integrates into double-stranded breaks. As gene therapy is an emerging field, GUIDE-Seq has gained traction as a cheap method to detect the off-target effects of potential therapeutics without needing whole genome sequencing.
__TOC__ | 1 | Biochemistry |
The Carius halogen method in analytical chemistry is a method for the quantitative determination of halogens in chemical substances.
A known mass of an organic compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass tube known as carius tube, in a furnace. Carbon and hydrogen present in the compound are oxidised to carbon dioxide and water. The halogen present forms the corresponding silver halide (AgX). It is filtered, washed, dried and weighed.
This chemical test works equally well for the determination of sulfur but without addition of silver nitrate. The sulfuric acid intermediate formed after reaction of sulfur with fuming nitric acid forms insoluble barium sulfate on addition of barium chloride. The purpose of adding the nitric acid is to oxidise the carbon and hydrogen. Concentrated nitric acid only oxidises iodine to iodic acid and doesn't affect any other halogens. Even the oxidation of iodine by concentrated nitric acid happens only at high temperatures.
This test was invented by the German Chemist, Georg Ludwig Carius (1829–1875). | 3 | Analytical Chemistry |
In humans, consumption of cobalt-containing vitamin B meets all needs for cobalt. For cattle and sheep, which meet vitamin B needs via synthesis by resident bacteria in the rumen, there is a function for inorganic cobalt. In the early 20th century, during the development of farming on the North Island Volcanic Plateau of New Zealand, cattle suffered from what was termed "bush sickness". It was discovered that the volcanic soils lacked the cobalt salts essential for the cattle food chain. The "coast disease" of sheep in the Ninety Mile Desert of the Southeast of South Australia in the 1930s was found to originate in nutritional deficiencies of trace elements cobalt and copper. The cobalt deficiency was overcome by the development of "cobalt bullets", dense pellets of cobalt oxide mixed with clay given orally for lodging in the animal's rumen. | 1 | Biochemistry |
Endergonic reactions can be achieved if they are either pulled or pushed by an exergonic (stability increasing, negative change in free energy) process. Of course, in all cases the net reaction of the total system (the reaction under study plus the puller or pusher reaction) is exergonic. | 7 | Physical Chemistry |
Generally, the main process in a rotary vacuum drum filter is continuous filtration whereby solids are separated from liquids through a filter medium by a vacuum. The filter cloth is one of the most important components on a filter and is typically made of weaving polymer yarns. The best selection of cloth can increase the performance of filtration. Initially, slurry is pumped into the trough and as the drum rotates, it is partially submerged in the slurry. The vacuum draws liquid and air through the filter media and out the shaft hence forming a layer of cake. An agitator is used to regulate the slurry if the texture is coarse and it is settling rapidly. Solids that are trapped on the surface of the drum are washed and dried after 2/3 of revolution, removing all the free moisture.
During the washing stage, the wash liquid can either be poured onto the drum or sprayed on the cake. Cake pressing is optional but its advantages are preventing cake cracking and removing more moisture. Cake discharge is when all the solids are removed from the surface of the cake by a scraper blade, leaving a clean surface as drum re-enters the slurry. There are a few types of discharge which are scraper, roller, string, endless belt and pre coat. The filtrate and air flow through internal pipes, valve and into the vacuum receiver where the separation of liquid and gas occurs producing a clear filtrate. Pre coat filtration is an ideal method to produce a high clarity of filtrate. Basically, the drum surface is pre coated with a filter aid such as diatomaceous earth (DE) or perlite to improve filtration and increase cake permeability. It then undergoes the same process cycle as the conventional rotary vacuum drum filter however, pre coat filtration uses a higher precision blade to scrape off the cake.
The filter is assessed by the size of the drum or filter area and its possible output. Typically, the output is in the units of pounds per hour of dry solids per square foot of filter area. The size of the auxiliary parts depends on the area of the filter and the type of usage. Rotary vacuum filters are flexible in handling variety of materials therefore the estimated solids yield from 5 to 200 pounds per hour per square foot. For pre coat discharge, the solid output is approximately 2 to 40 gallons per hour per square foot. Filtration efficiencies can also be improved in terms dryness of filter cake by significantly preventing filtrate liquid from getting stuck in the filter drum during filtration phase. Usage of multiple filters for example, running 3 filter units instead of 2 units yields a thicker cake hence, producing a clearer filtrate. This becomes beneficial in terms of production cost and also quality. | 3 | Analytical Chemistry |
The conventional food contaminant test methods may be limited by complicated/tedious sample preparing procedure, long testing time, sumptuous instrument, and professional operator. However, some rapid, novel, sensitive, and easy to use and affordable methods were developed including:
* Cyanidin quantification by naphthalimide-based azo dye colorimetric probe.
* Lead quantification by modified immunoassay test strip based on a heterogeneously sized gold amplified probe.
* Microbial toxin by HPLC with UV-Vis or fluorescence detection and competitive immunoassays with ELISA configuration.
* Bacterial virulence genes detection reverse-transcription polymerase chain reaction (RT-PCR) and DNA colony hybridization.
* Pesticide detection and quantification by strip-based immunoassay, a test strip based on functionalized AuNPs, and test strip, surface-enhanced raman spectroscopy (SERS).
* Enrofloxacin (chickens antibiotic) quantification by a Ru(phen)3 2+- doped silica fluorescent nanoparticle (NP) based immunochromatographic test strip and a portable fluorescent strip reader.
* Nitrite quantification by The PRhB-based electrochemical sensors and Ion selective electrodes (ISEs). | 9 | Geochemistry |
Samples spotted on a SELDI surface are typically analyzed using time-of-flight mass spectrometry. An irradiating laser ionizes peptides from crystals of the sample/matrix mixture. The matrix absorbs the energy of the laser pulse, preventing destruction of the molecule, and transfers charge to the sample molecules, forming ions. The ions are then briefly accelerated through an electric potential and travel down a field-free flight tube where they are separated by their velocity differences. The mass-to-charge ratio of each ion can be determined from the length of the tube, the kinetic energy given to ions by the electric field, and the velocity of the ions in the tube. The velocity of the ions is inversely proportional to the square root of the mass-to-charge ratio of the ion; ions with low mass-to-charge ratios are detected earlier than ions with high mass-to-charge ratios. | 1 | Biochemistry |
In general terms, different plant species are adapted to soils of different pH ranges. For many species, the suitable soil pH range is fairly well known. Online databases of plant characteristics, such as USDA PLANTS and Plants for a Future can be used to look up the suitable soil pH range of a wide range of plants. Documents like Ellenbergs indicator values for British plants' can also be consulted.
However, a plant may be intolerant of a particular pH in some soils as a result of a particular mechanism, and that mechanism may not apply in other soils. For example, a soil low in molybdenum may not be suitable for soybean plants at pH 5.5, but soils with sufficient molybdenum allow optimal growth at that pH. Similarly, some calcifuges (plants intolerant of high-pH soils) can tolerate calcareous soils if sufficient phosphorus is supplied. Another confounding factor is that different varieties of the same species often have different suitable soil pH ranges. Plant breeders can use this to breed varieties that can tolerate conditions that are otherwise considered unsuitable for that species – examples are projects to breed aluminium-tolerant and manganese-tolerant varieties of cereal crops for food production in strongly acidic soils.
The table below gives suitable soil pH ranges for some widely cultivated plants as found in the USDA PLANTS Database. Some species (like Pinus radiata and Opuntia ficus-indica) tolerate only a narrow range in soil pH, whereas others (such as Vetiveria zizanioides) tolerate a very wide pH range.
In natural or near-natural plant communities, the various pH preferences of plant species (or ecotypes) at least partly determine the composition and biodiversity of vegetation. While both very low and very high pH values are detrimental to plant growth, there is an increasing trend of plant biodiversity along the range from extremely acidic (pH 3.5) to strongly alkaline (pH 9) soils, i.e. there are more calcicole than calcifuge species, at least in terrestrial environments. Although widely reported and supported by experimental results, the observed increase of plant species richness with pH is still in need of a clearcut explanation. Competitive exclusion between plant species with overlapping pH ranges most probably contributes to the observed shifts of vegetation composition along pH gradients. | 9 | Geochemistry |
In the low- limit, as the system is probed over large length scales, the structure factor contains thermodynamic information, being related to the isothermal compressibility of the liquid by the compressibility equation: | 3 | Analytical Chemistry |
By the time of the 2nd Chapman Conference on the Gaia Hypothesis, held at Valencia, Spain, on 23 June 2000, the situation had changed significantly. Rather than a discussion of the Gaian teleological views, or "types" of Gaia hypotheses, the focus was upon the specific mechanisms by which basic short term homeostasis was maintained within a framework of significant evolutionary long term structural change.
The major questions were:
# "How has the global biogeochemical/climate system called Gaia changed in time? What is its history? Can Gaia maintain stability of the system at one time scale but still undergo vectorial change at longer time scales? How can the geologic record be used to examine these questions?"
# "What is the structure of Gaia? Are the feedbacks sufficiently strong to influence the evolution of climate? Are there parts of the system determined pragmatically by whatever disciplinary study is being undertaken at any given time or are there a set of parts that should be taken as most true for understanding Gaia as containing evolving organisms over time? What are the feedbacks among these different parts of the Gaian system, and what does the near closure of matter mean for the structure of Gaia as a global ecosystem and for the productivity of life?"
# "How do models of Gaian processes and phenomena relate to reality and how do they help address and understand Gaia? How do results from Daisyworld transfer to the real world? What are the main candidates for "daisies"? Does it matter for Gaia theory whether we find daisies or not? How should we be searching for daisies, and should we intensify the search? How can Gaian mechanisms be collaborated with using process models or global models of the climate system that include the biota and allow for chemical cycling?"
In 1997, Tyler Volk argued that a Gaian system is almost inevitably produced as a result of an evolution towards far-from-equilibrium homeostatic states that maximise entropy production, and Axel Kleidon (2004) agreed stating: "...homeostatic behavior can emerge from a state of MEP associated with the planetary albedo"; "...the resulting behavior of a symbiotic Earth at a state of MEP may well lead to near-homeostatic behavior of the Earth system on long time scales, as stated by the Gaia hypothesis". M. Staley (2002) has similarly proposed "...an alternative form of Gaia theory based on more traditional Darwinian principles... In [this] new approach, environmental regulation is a consequence of population dynamics. The role of selection is to favor organisms that are best adapted to prevailing environmental conditions. However, the environment is not a static backdrop for evolution, but is heavily influenced by the presence of living organisms. The resulting co-evolving dynamical process eventually leads to the convergence of equilibrium and optimal conditions". | 9 | Geochemistry |
A range of different sources can be used:
* A nuclear reactor
* An actinoid such as californium which emits neutrons through spontaneous fission
* An alpha source such as radium or americium, mixed with beryllium; this generates neutrons by a (α,C+n) reaction
* A D-T fusion reaction in a gas discharge tube | 3 | Analytical Chemistry |
As an acid–base indicator, its useful range lies between pH 3.0 and 4.6. It changes from yellow at pH 3.0 to blue at pH 4.6; this reaction is reversible. Bromophenol blue is structurally related to phenolphthalein (a popular indicator). | 3 | Analytical Chemistry |
Transferrin is also associated with the innate immune system. It is found in the mucosa and binds iron, thus creating an environment low in free iron that impedes bacterial survival in a process called iron withholding. The level of transferrin decreases in inflammation. | 1 | Biochemistry |
The 4-1BB/4-1BBL complex consists of three monomeric 4-1BBs bound to a trimeric 4-1BBL. Each 4-1BB monomer binds to two 4-1BBLs via cysteine-rich domains (CRDs). The interaction between 4-1BB and the second 4-1BBL is required to stabilize their interactions. The link with 4-1BBL is largely made up of amino acids from the dynamic loops of the CRD2 and the β sheet of CRD3 of 4-1BB, according to a detailed study of the binding between the 4-1BB and 4-1BBL interface. CRD2 amino acids (T61, Q67, and K69) interact with the AA′ loop (Y110 and G114) and the intra-H-strand loop (Q227 and Q230) of 4-1BBL to form various hydrogen bond interactions. | 1 | Biochemistry |
Animal and human data have revealed evidence of harm to the embryo and teratogenicity associated with ACE inhibitors. | 4 | Stereochemistry |
While several experiments yielded negative results, in the 1980s, John Goodkind discovered the first anomaly in a solid by using ultrasound. Inspired by his observation, in 2004 Eun-Seong Kim and Moses Chan at Pennsylvania State University saw phenomena which were interpreted as supersolid behavior. Specifically, they observed a non-classical rotational moment of inertia of a torsional oscillator. This observation could not be explained by classical models but was consistent with superfluid-like behavior of a small percentage of the helium atoms contained within the oscillator.
This observation triggered a large number of follow-up studies to reveal the role played by crystal defects or helium-3 impurities. Further experimentation has cast some doubt on the existence of a true supersolid in helium. Most importantly, it was shown that the observed phenomena could be largely explained due to changes in the elastic properties of the helium. In 2012, Chan repeated his original experiments with a new apparatus that was designed to eliminate any such contributions. In this experiment, Chan and his coauthors found no evidence of supersolidity. | 7 | Physical Chemistry |
Ethylenediamine pyrocatechol (EDP), also known as ethylenediamine-pyrocatechol-water (EPW), is an anisotropic etchant solution for silicon. A typical formulation consists of ethylenediamine, pyrocatechol, pyrazine and water. It is carcinogenic and very corrosive. It is mainly used in research labs, and is not used in mainstream semiconductor fabrication processes. | 0 | Organic Chemistry |
Ecologically, V. fischeri is known to have symbiotic associations with a number of eukaryotic hosts, including the Hawaiian Bobtail Squid (Euprymna scolopes). In this relationship, the squid host maintains the bacteria in specialized light organs. The host provides a safe, nutrient rich environment for the bacteria and in turn, the bacteria provide light. Although bioluminescence can be used for mating and other purposes, in E. scolopes it is used for counter illumination to avoid predation.
The autoinducer molecule used by V. fischeri is N-(3-oxohexanoyl)-homoserine lactone. This molecule is produced in the cytoplasm by the LuxI synthase enzyme and is secreted through the cell membrane into the extracellular environment. As is true of most autoinducers, the environmental concentration of N-(3-oxohexanoyl)-homoserine lactone is the same as the intracellular concentration within each cell. N-(3-oxohexanoyl)-homoserine lactone eventually diffuses back into cells where it is recognized by LuxR once a threshold concentration (~10 μg/ml) has been reached. LuxR binds the autoinducer and directly activates transcription of the luxICDABE operon. This results in an exponential increase in both the production of autoinducer and in bioluminescence. LuxR bound by autoinducer also inhibits the expression of luxR, which is thought to provide a negative feedback compensatory mechanism to tightly control levels of the bioluminescence genes. | 1 | Biochemistry |
Research has indicated that MFGM, or components thereof, may potentially play roles in brain development and cognitive function, immunity and gut health, and cardiovascular health.
MFGM has a set of proteins and lipids unique to breast milk: lactoferrin, Immunoglobulin G, sialic acid, cholesterol, phospholipids, sphingolipids, gangliosides and choline. All components of the MFGM are important for child development. Phospholipids and gangliosides influence the formation and folding of the cerebral cortex. These structures translate directly into neuronal development and cognitive abilities. The use of MFGM in Geo-Poland [https://laktowit.pl/mfgm/ infant formula] is essential to mimic breast milk. A not insignificant proportion of studies investigating the health effects of formula supplementation with MFGM on infant health were (co-)funded by the cow's milk and formula industry. | 1 | Biochemistry |
Several photons of energy below the ionization threshold may actually combine their energies to ionize an atom. This probability decreases rapidly with the number of photons required, but the development of very intense, pulsed lasers still makes it possible. In the perturbative regime (below about 10 W/cm at optical frequencies), the probability of absorbing N photons depends on the laser-light intensity I as I. For higher intensities, this dependence becomes invalid due to the then occurring AC Stark effect.
Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms and small molecules in which a tunable laser can be used to access an excited intermediate state.
Above-threshold ionization (ATI) is an extension of multi-photon ionization where even more photons are absorbed than actually would be necessary to ionize the atom. The excess energy gives the released electron higher kinetic energy than the usual case of just-above threshold ionization. More precisely, the system will have multiple peaks in its photoelectron spectrum which are separated by the photon energies, indicating that the emitted electron has more kinetic energy than in the normal (lowest possible number of photons) ionization case. The electrons released from the target will have approximately an integer number of photon-energies more kinetic energy. | 7 | Physical Chemistry |
Lipid:In marine sediments, a stable lipid called IP25 (Ice Proxy with 25 carbon atoms), which is biosynthesized by sea-ice dwelling diatom, has been found to be generally related to spring sea-ice cover in the Arctic region, Thus this proxy could be used to reconstruct sea-ice coverage. A different biomarker, IPSO25 (Ice Proxy Southern Ocean with 25 carbon atoms) has been documented as a useful proxy for the sea-ice cover in the Antarctic region. | 9 | Geochemistry |
Heat transfer physics describes the kinetics of energy storage, transport, and energy transformation by principal energy carriers: phonons (lattice vibration waves), electrons, fluid particles, and photons. Heat is thermal energy stored in temperature-dependent motion of particles including electrons, atomic nuclei, individual atoms, and molecules. Heat is transferred to and from matter by the principal energy carriers. The state of energy stored within matter, or transported by the carriers, is described by a combination of classical and quantum statistical mechanics. The energy is different made (converted) among various carriers.
The heat transfer processes (or kinetics) are governed by the rates at which various related physical phenomena occur, such as (for example) the rate of particle collisions in classical mechanics. These various states and kinetics determine the heat transfer, i.e., the net rate of energy storage or transport. Governing these process from the atomic level (atom or molecule length scale) to macroscale are the laws of thermodynamics, including conservation of energy. | 7 | Physical Chemistry |
Heart muscle primarily metabolizes fat for energy and Acyl-CoA metabolism has been identified as a critical molecule in early stage heart muscle pump failure.
Cellular acyl-CoA content correlates with insulin resistance, suggesting that it can mediate lipotoxicity in non-adipose tissues. Acyl-CoA: diacylglycerol acyltransferase (DGAT) plays an important role in energy metabolism on account of key enzyme in triglyceride biosynthesis. The synthetic role of DGAT in adipose tissue such as the liver and the intestine, sites where endogenous levels of its activity and triglyceride synthesis are high and comparatively clear. Also, any changes in the activity levels might cause changes in systemic insulin sensitivity and energy homeostasis.
A rare disease called multiple acyl-CoA dehydrogenase deficiency (MADD) is a fatty acid metabolism disorder. Acyl-CoA is important because this enzyme helps make Acyl-CoA from free fatty acids, and this activates the fatty acid to be metabolized. This compromised fatty acid oxidation leads to many different symptoms, including severe symptoms such as cardiomyopathy and liver disease and mild symptoms such as episodic metabolic decomposition, muscle weakness and respiratory failure. MADD is a genetic disorder, caused by a mutation in the ETFA, ETFB, and ETFDH genes. MADD is known as an "autosomal recessive disorder" because for one to get this disorder, one must receive this recessive gene from both parents. | 1 | Biochemistry |
Roderick MacKinnon commissioned Birth of an Idea, a tall sculpture based on the KcsA potassium channel. The artwork contains a wire object representing the channel's interior with a blown glass object representing the main cavity of the channel structure. | 1 | Biochemistry |
Chemical measures of water quality include dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total dissolved solids (TDS), pH, nutrients (nitrates and phosphorus), heavy metals, soil chemicals (including copper, zinc, cadmium, lead and mercury), and pesticides. | 2 | Environmental Chemistry |
From 1875 to 1920 American steel production grew from 380,000 tons to 60 million tons annually, making the U.S. the world leader. The annual growth rates in steel 1870–1913 were 7.0% for the US; 1.0% for Britain; 6.0% for Germany; and 4.3% for France, Belgium, and Russia, the other major producers. This explosive American growth rested on solid technological foundations and the continuous rapid expansion of urban infrastructures, office buildings, factories, railroads, bridges and other sectors that increasingly demanded steel. The use of steel in automobiles and household appliances came in the 20th century.
Some key elements in the growth of steel production included the easy availability of iron ore, and coal. Iron ore of fair quality was abundant in the eastern states, but the Lake Superior region contained huge deposits of exceedingly rich ore; the Marquette Iron Range was discovered in 1844; operations began in 1846. Other ranges were opened by 1910, including the Menominee, Gogebic, Vermilion, Cuyuna, and, greatest of all, (in 1892) the Mesabi range in Minnesota. This iron ore was shipped through the Great Lakes to ports such as Chicago, Detroit, Cleveland, Erie and Buffalo for shipment by rail to the steel mills. Abundant coal was available in Pennsylvania, West Virginia, and Ohio. Manpower was short. Few Native Americans wanted to work in the mills, but immigrants from Britain and Germany (and later from Eastern Europe) arrived in great numbers.
In 1869 iron was already a major industry, accounting for 6.6% of manufacturing employment and 7.8% of manufacturing output. By then the central figure was Andrew Carnegie, who made Pittsburgh the center of the industry. He sold his operations to US Steel in 1901, which became the world's largest steel corporation for decades.
In the 1880s, the transition from wrought iron puddling to mass-produced Bessemer steel greatly increased worker productivity. Highly skilled workers remained essential, but the average level of skill declined. Nevertheless, steelworkers earned much more than ironworkers despite their fewer skills. Workers in an integrated, synchronized mass production environment wielded greater strategic power, for the greater cost of mistakes bolstered workers' status. The experience demonstrated that the new technology did not decrease worker bargaining leverage by creating an interchangeable, unskilled workforce. | 8 | Metallurgy |
Due to the potential for widespread usage and the evolving needs of researchers, many different mutants of GFP have been engineered. The first major improvement was a single point mutation (S65T) reported in 1995 in Nature by Roger Tsien. This mutation dramatically improved the spectral characteristics of GFP, resulting in increased fluorescence, photostability, and a shift of the major excitation peak to 488 nm, with the peak emission kept at 509 nm. This matched the spectral characteristics of commonly available FITC filter sets, increasing the practicality of use by the general researcher. A 37 °C folding efficiency (F64L) point mutant to this scaffold, yielding enhanced GFP (EGFP), was discovered in 1995 by the laboratories of Thastrup and Falkow. EGFP allowed the practical use of GFPs in mammalian cells. EGFP has an extinction coefficient (denoted ε) of 55,000 Mcm. The fluorescence quantum yield (QY) of EGFP is 0.60. The relative brightness, expressed as ε•QY, is 33,000 Mcm.
Superfolder GFP (sfGFP), a series of mutations that allow GFP to rapidly fold and mature even when fused to poorly folding peptides, was reported in 2006.
Many other mutations have been made, including color mutants; in particular, blue fluorescent protein (EBFP, EBFP2, Azurite, mKalama1), cyan fluorescent protein (ECFP, Cerulean, CyPet, mTurquoise2), and yellow fluorescent protein derivatives (YFP, Citrine, Venus, YPet). BFP derivatives (except mKalama1) contain the Y66H substitution.They exhibit a broad absorption band in the ultraviolet centered close to 380 nanometers and an emission maximum at 448 nanometers. A green fluorescent protein mutant (BFPms1) that preferentially binds Zn(II) and Cu(II) has been developed. BFPms1 have several important mutations including and the BFP chromophore (Y66H),Y145F for higher quantum yield, H148G for creating a hole into the beta-barrel and several other mutations that increase solubility. Zn(II) binding increases fluorescence intensity, while Cu(II) binding quenches fluorescence and shifts the absorbance maximum from 379 to 444 nm. Therefore, they can be used as Zn biosensor.
Chromophore binding. The critical mutation in cyan derivatives is the Y66W substitution, which causes the chromophore to form with an indole rather than phenol component. Several additional compensatory mutations in the surrounding barrel are required to restore brightness to this modified chromophore due to the increased bulk of the indole group. In ECFP and Cerulean, the N-terminal half of the seventh strand exhibits two conformations. These conformations both have a complex set of van der Waals interactions with the chromophore. The Y145A and H148D mutations in Cerulean stabilize these interactions and allow the chromophore to be more planar, better packed, and less prone to collisional quenching.
Additional site-directed random mutagenesis in combination with fluorescence lifetime based screening has further stabilized the seventh β-strand resulting in a bright variant, mTurquoise2, with a quantum yield (QY) of 0.93. The red-shifted wavelength of the YFP derivatives is accomplished by the T203Y mutation and is due to π-electron stacking interactions between the substituted tyrosine residue and the chromophore. These two classes of spectral variants are often employed for Förster resonance energy transfer (FRET) experiments. Genetically encoded FRET reporters sensitive to cell signaling molecules, such as calcium or glutamate, protein phosphorylation state, protein complementation, receptor dimerization, and other processes provide highly specific optical readouts of cell activity in real time.
Semirational mutagenesis of a number of residues led to pH-sensitive mutants known as pHluorins, and later super-ecliptic pHluorins. By exploiting the rapid change in pH upon synaptic vesicle fusion, pHluorins tagged to synaptobrevin have been used to visualize synaptic activity in neurons.
Redox sensitive GFP (roGFP) was engineered by introduction of cysteines into the beta barrel structure. The redox state of the cysteines determines the fluorescent properties of roGFP. | 1 | Biochemistry |
For heterogeneous surfaces (consisting of two or more different types of material), the contact angle of a drop of liquid at each point along the three phase contact line with a solid surface is a result of the surface tension of the surface at that point. For example, if the heterogeneous regions of the surface form very large domains, and the drop exists entirely within a homogeneous domain, then it will have a contact angle corresponding to the surface tension of that homogeneous region. Likewise, a drop that straddles two domains of differing surface tensions will have different contact angles along the three phase contact line corresponding to the different surface tensions at each point. However, with sufficiently small domains (such as in those of a block copolymer), the observed surface energy of the surface approaches the weighted average of the surface energies of each of the constituents of the surface:
where:
: is the overall surface energy of the polymer
: is the fraction of the component of the polymer's surface
: is the surface energy of the component
This occurs because as the size of the homogeneous domains become very small compared to the size of the drop, the differences in contact angles along different homogeneous regions becomes indistinguishable from the average of the contact angles.
The observed contact angle is given by the following formula:
where:
:is the fraction of component
: is the contact angle component
If the polymer is made out of only two different monomers, it is possible use the above equation to determine the composition of the polymer simply by measuring the contact angle of a drop of liquid placed on it:
where:
: is the observed contact angle
: is the area fraction of one component, and the area fraction of the other.
: and are the contact angles of the first and second components of the polymer. | 7 | Physical Chemistry |
Ozone depletion
A team of researchers at the University of East Anglia analysed unpolluted air samples from Tasmania dating from the period 1978 to 2012. They concluded that the CFC's they studied had started entering the atmosphere from anthropogenic sources in the 1960s and that while the abundance of certain CFCs had decreased, owing to the Montreal Protocol, the abundance of CFC-113a in the atmosphere was still growing. Its source remained uncertain, but production of hydrofluorocarbons in East Asia was suspected by some. Between 2012 and 2017, concentrations of the gas jumped by 40 percent. In 2020, the global mean concentration of CFC-113a was 1.02 ppt with global emissions of 2.5 ± 0.4 ODP-Gg yr. | 2 | Environmental Chemistry |
RANKL is a member of the TNF superfamily of ligands. Through binding to the RANK receptor it activates various molecules, like NF-kappa B, MAPK, NFAT and PI3K52. The RANKL/RANK signaling pathway regulates osteoclastogenesis, as well as, the survival and activation of osteoclasts. | 7 | Physical Chemistry |
Dissolved inorganic carbon is a key component of the biological pump, which is defined as the amount of biologically produced organic carbon flux from the upper ocean to the deep ocean. Dissolved inorganic carbon in the form of carbon dioxide is fixed into organic carbon is produced through photosynthesis. Respiration is the reverse process and consumes organic carbon to produce inorganic carbon. Photosynthesis, and the biological pump, is dependent on the availability of inorganic nutrients and carbon dioxide.
:Photosynthesis: 6 CO + 6 HO + light → CHO + 6 O
:Respiration: CHO + 6 O → 6 CO + 6 HO + energy
Oceanographers seek to understand the metabolic state of the ocean, or the efficiency of the biological pump, by estimating the net community production (NCP) which is the gross primary productivity (GPP) minus the community respiration (sum of the respiration of the local autotrophs and heterotrophs). An efficient biological pump increases biological export to the deeper ocean which has been hypothesized to suppress CO outgassing in the upper ocean. | 9 | Geochemistry |
In the Old World, the first metals smelted were tin and lead. The earliest known cast lead beads were found in the Çatalhöyük site in Anatolia (Turkey), and dated from about 6500 BC, but the metal may have been known earlier.
Since the discovery happened several millennia before the invention of writing, there is no written record of how it was made. However, tin and lead can be smelted by placing the ores in a wood fire, leaving the possibility that the discovery may have occurred by accident. Recent scholarship however has called this find into question.
Lead is a common metal, but its discovery had relatively little impact in the ancient world. It is too soft to use for structural elements or weapons, though its high density relative to other metals makes it ideal for sling projectiles. However, since it was easy to cast and shape, workers in the classical world of Ancient Greece and Ancient Rome used it extensively to pipe and store water. They also used it as a mortar in stone buildings.
Tin was much less common than lead, is only marginally harder, and had even less impact by itself. | 8 | Metallurgy |
A detailed and comprehensive literature review on the various aspects of sophorolipids production (e.g. producing micro-organisms, bio-synthetic pathway, effect of medium components and other fermentation conditions and downstream process of sophorolipids is available in the published work of Van Bogaert et al. This work also discusses potential application of sophorolipids (and their derivatives) as well as the potential for genetic engineering strains to enhance sophorolipid yields. Researchers have focused on optimization of sophorolipid production in submerged fermentation, but some efforts have also investigated the possibility of sophorololipid production using solid state fermentation (SSF). The production process can be significantly impacted by the specific properties of the carbon and oil substrates used; and several inexpensive alternatives to more traditional substrates have been investigated. These potential substrates include: biodiesel by-product streams, waste frying oil, restaurant waste oil, industrial fatty acid residues, mango seed fat, and soybean dark oil. The use of most of these substrates have resulted in lower yields compared to traditional fermentation substrates. | 0 | Organic Chemistry |
In the nervous system there are primarily two ways of propagating signals. By far the most common method of intracellular signal propagation is the action potential. The dendrites of neurons contain ionotropic (aka ligand-gated ion channel) and metabotropic neurotransmitter receptors that bind chemical neurotransmitters. At ionotropic receptors, these chemical neurotransmitters cause quick changes in ion flux into or out of the cell. The resulting internal voltage change in the dendrites is propagated towards the cell body and axon hillock, where a large concentration of voltage-gated ion channels typically exists. If some voltage threshold is met, voltage gated sodium channels open up, letting in a critical charge of sodium, and the positive current propagates down the axon towards the presynaptic axon terminal. This action potential leads to neurotransmitter vesicular release at in this terminal.
While action potentials are the typical means of signal propagation in the nervous system, some sensory neurons use graded potentials to trigger vesicular release. These cells are typically short enough that regenerative action potentials aren't needed to cause a large enough voltage change at the presynaptic terminal. For example, photoreceptor cells in the eye produce graded potentials in response to light, and these graded potentials can directly lead to neurotransmitter release. | 1 | Biochemistry |
In coordination chemistry, Tanabe–Sugano diagrams are used to predict absorptions in the ultraviolet (UV), visible and infrared (IR) electromagnetic spectrum of coordination compounds. The results from a Tanabe–Sugano diagram analysis of a metal complex can also be compared to experimental spectroscopic data. They are qualitatively useful and can be used to approximate the value of 10Dq, the ligand field splitting energy. Tanabe–Sugano diagrams can be used for both high spin and low spin complexes, unlike Orgel diagrams, which apply only to high spin complexes. Tanabe–Sugano diagrams can also be used to predict the size of the ligand field necessary to cause high-spin to low-spin transitions.
In a Tanabe–Sugano diagram, the ground state is used as a constant reference, in contrast to Orgel diagrams. The energy of the ground state is taken to be zero for all field strengths, and the energies of all other terms and their components are plotted with respect to the ground term. | 7 | Physical Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.