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To curate and maintain SBO, a dedicated resource has been developed and the public interface of the SBO browser can be accessed at [http://www.ebi.ac.uk/sbo http://www.ebi.ac.uk/sbo].
A relational database management system (MySQL) at the back-end is
accessed through a web interface based on Java Server Pages (JSP) and JavaBeans. Its
content is encoded in UTF-8, therefore supporting a large set of
characters in the definitions of terms. Distributed curation is made possible
by using a custom-tailored locking system allowing concurrent access.
This system allows a continuous update of the ontology with immediate
availability and suppress merging problems.
Several exports formats ([http://www.godatabase.org/dev/doc/obo_format_spec.html OBO] flat file, [http://www.ebi.ac.uk/sbo/docs/sboxml_schema.xsd SBO-XML] and [http://www.w3.org/TR/owl-features/ OWL]) are generated daily or on request and can be downloaded from the web interface.
To allow programmatic access to the resource, Web Services have been implemented based on [http://ws.apache.org/axis/ Apache Axis] for the communication layer and [http://www.castor.org/ Castor] for the validation. The libraries, full documentation, samples and tutorial are available [http://www.ebi.ac.uk/sbo/SBOWSLib/ws.html online].
The SourceForge project can be accessed at [http://sourceforge.net/projects/sbo/ http://sourceforge.net/projects/sbo/]. | 1 | Biochemistry |
The calculation of the structure factor for cases differing from ideal polymer chains can be quite cumbersome, and sometimes impossible to complete analytically. However, when the small-angle scattering condition is met, , the sinc term can be expanded so one gets:
and by utilising the definition of the radius of gyration:
where the final transition utilises once again the small-angle approximation.
We can thus approximate the scattering intensity in the small-angle regime as:
and by plotting vs. , a so-called "Guinier plot", we may determine the radius of gyration from the slope of this linear curve. This measure is one of many examples of how scattering experiments of polymers can reveal basic properties of those polymer chains. | 7 | Physical Chemistry |
* In patients with hyperthyroidism, there will be fewer available binding sites on TBG (due to the increased circulating T3 / T4). This will lead to an increased thyroid hormone binding ratio.
* In patients with hypothyroidism, there will be more free binding sites on TBG (due to the decreased amount of circulating T3 / T4) and as such the THBR will be decreased.
* In general, High with High thyroid activity and Low with Low thyroid activity. | 1 | Biochemistry |
A quaternary carbon is a carbon atom bound to four other carbon atoms. For this reason, quaternary carbon atoms are found only in hydrocarbons having at least five carbon atoms. Quaternary carbon atoms can occur in branched alkanes, but not in linear alkanes. | 0 | Organic Chemistry |
Silver nanoparticles are used for catalyzing chemical reactions, Raman imaging, and antimicrobial sterilization. Along with its antimicrobial properties, its low mammalian cell toxicity makes these particles a common addition to consumer products. Washing textiles embedded with silver nanoparticles results in the oxidation and transformation of metallic Ag into AgCl.
Silver nanoparticles have different physicochemical characteristics from the free silver ion, Ag and possess increased optical, electromagnetic, and catalytic properties. Particles with one dimension of 100 nm or less can generate reactive oxygen species. Smaller particles less than 10 nm may pass through cellular membranes and accumulate within the cell. Silver nanoparticles were also found to attach to cellular membranes, eventually dissipating the proton motive force, leading to cell death.
Silver nanoparticles that are larger than the openings of membrane channel proteins can easily clog channels, leading to the disruption of membrane permeability and transport. However, the antimicrobial effectiveness of silver nanoparticles has been shown to decrease when dissolved in liquid media.
The free silver ion are potentially toxic to bacteria and planktonic species in the water. The positively charged silver ion can also attach to the negatively charged cell walls of bacteria, leading to deactivation of cellular enzymes, disruption of membrane permeability, and eventually, cell lysis and death. However, its toxicity to microorganisms is not overtly observed since the free silver ion is found in low concentrations in wastewater treatment systems and the natural environment due to its complexation with ligands such as chloride, sulfide, and thiosulfate. | 2 | Environmental Chemistry |
The original CAGE method (Shiraki et al., 2003) was using CAP Trapper for capturing the 5′ ends, oligo-dT primers for synthesizing the cDNAs, the type IIs restriction enzyme MmeI for cleaving the tags, and the Sanger method for sequencing them.
Random reverse-transcription primers were introduced in 2006 by Kodzius et al. to better detect the non-polyadenylated RNAs.
In DeepCAGE (Valen et al., 2008), the tag concatemers were sequenced at a higher throughput on the 454 “next-generation” sequencing platform.
In 2008, barcode multiplexing was added to the DeepCAGE protocol (Maeda et al., 2008).
In nanoCAGE (Plessy et al., 2010), the 5′ ends or RNAs were captured with the template-switching method instead of CAP Trapper, in order to analyze smaller starting amounts of total RNA. Longer tags were cleaved with the type III restriction enzyme EcoP15I and directly sequenced on the Solexa (then Illumina) platform without concatenation.
The CAGEscan methodology (Plessy et al., 2010), where the enzymatic tag cleavage is skipped, and the 5′ cDNAs sequenced paired-end, was introduced in the same article to connect novel promoters to known annotations.
With HeliScopeCAGE (Kanamori-Katayama et al., 2011), the CAP-trapped CAGE protocol was changed to skip the enzymatic tag cleavage and sequence directly the capped 5′ ends on the HeliScope platform, without PCR amplification. It was then automated by Itoh et al. in 2012.
In 2012, the standard CAGE protocol was updated by Takahashi et al. to cleave tags with EcoP15I and sequence them on the Illumina-Solexa platform.
In 2013, Batut et al. combined CAP trapper, template switching, and 5′-phosphate-dependent exonuclease digestion in RAMPAGE to maximize promoter specificity.
In 2014, Murata et al. published the nAnTi-CAGE protocol, where capped 5′ ends are sequenced on the Illumina platform with no PCR amplification and no tag cleavage.
In 2017, Poulain et al. updated the nanoCAGE protocol to use the tagmentation method (based on Tn5 transposition) for multiplexing.
In 2018, Cvetesic et al. increased the sensitivity of CAP-trapped CAGE by introducing selectively degradable carrier RNA (SLIC-CAGE, "Super-Low Input Carrier-CAGE").
In 2021, Takahashi et al. simplified the sequencing of CAGE libraries on Illumina sequencers by skipping second-strand synthesis directly loading single-strand cDNAs (Low Quantity Single Strand CAGE, "LQ-ssCAGE"). | 1 | Biochemistry |
The development of the APCI interface for LC–MS started with Horning and collaborators in the early 1973. However, its commercial application was introduced at the beginning of the 1990s after Henion and collaborators improved the LC–APCI–MS interface in 1986. The APCI ion source/ interface can be used to analyze small, neutral, relatively non-polar, and thermally stable molecules (e.g., steroids, lipids, and fat soluble vitamins). These compounds are not well ionized using ESI. In addition, APCI can also handle mobile phase streams containing buffering agents. The liquid from the LC system is pumped through a capillary and there is also nebulization at the tip, where a corona discharge takes place. First, the ionizing gas surrounding the interface and the mobile phase solvent are subject to chemical ionization at the ion source. Later, these ions react with the analyte and transfer their charge. The sample ions then pass through small orifice skimmers by means of or ion-focusing lenses. Once inside the high vacuum region, the ions are subject to mass analysis. This interface can be operated in positive and negative charge modes and singly-charged ions are mainly produced. APCI ion source can also handle flow rates between 500 and 2000 μl/min and it can be directly connected to conventional 4.6 mm ID columns. | 3 | Analytical Chemistry |
Humans and other mammals have chitinase and chitinase-like proteins that can degrade chitin; they also possess several immune receptors that can recognize chitin and its degradation products, initiating an immune response.
Chitin is sensed mostly in the lungs or gastrointestinal tract where it can activate the innate immune system through eosinophils or macrophages, as well as an adaptive immune response through T helper cells. Keratinocytes in skin can also react to chitin or chitin fragments. | 1 | Biochemistry |
In physics, the terms order and disorder designate the presence or absence of some symmetry or correlation in a many-particle system.
In condensed matter physics, systems typically are ordered at low temperatures; upon heating, they undergo one or several phase transitions into less ordered states.
Examples for such an order-disorder transition are:
* the melting of ice: solid–liquid transition, loss of crystalline order;
* the demagnetization of iron by heating above the Curie temperature: ferromagnetic–paramagnetic transition, loss of magnetic order.
The degree of freedom that is ordered or disordered can be translational (crystalline ordering), rotational (ferroelectric ordering), or a spin state (magnetic ordering).
The order can consist either in a full crystalline space group symmetry, or in a correlation. Depending on how the correlations decay with distance, one speaks of long range order or short range order.
If a disordered state is not in thermodynamic equilibrium, one speaks of quenched disorder. For instance, a glass is obtained by quenching (supercooling) a liquid. By extension, other quenched states are called spin glass, orientational glass. In some contexts, the opposite of quenched disorder is annealed disorder. | 3 | Analytical Chemistry |
If the "strange matter hypothesis" is true, then nuclear matter is metastable against decaying into strange matter. The lifetime for spontaneous decay is very long, so we do not see this decay process happening around us. However, under this hypothesis there should be strange matter in the universe:
# Quark stars (often called "strange stars") consist of quark matter from their core to their surface. They would be several kilometers across, and may have a very thin crust of nuclear matter.
# Strangelets are small pieces of strange matter, perhaps as small as nuclei. They would be produced when strange stars are formed or collide, or when a nucleus decays. | 7 | Physical Chemistry |
Karl A. Smith is a metallurgical engineer, academic and author. He is an emeritus Cooperative Learning Professor of Engineering Education at Purdue University's School of Engineering Education, as well as an emeritus Professor of Civil, Environmental, and Geo-Engineering, Morse-Alumni Distinguished University Teaching Professor, and Faculty Member at the Technological Leadership Institute at the University of Minnesota.
Smiths work has focused on developing research and innovation capabilities in engineering education, exploring cooperation in learning and design, and managing projects and knowledge. His publications comprise research articles and eight books including Teamwork and Project Management, How to Model it: Problem Solving for the Computer Age and New Paradigms for College Teaching'. He is the recipient of the University of Minnesota Distinguished Alumni Award (2006), an Honorary Doctorate from the Universiti Teknologi Malaysia (2014) along with the Chester F. Carlson Award (2001), the Distinguished Service Award (2006), and the Lifetime Achievement Award (2015), all from the American Society for Engineering Education.
Smith is a Fellow of the American Association for the Advancement of Science and the American Society for Engineering Education, where he was inducted into the Hall of Fame in 2023. He served as the Guest Editor of a Special Issue of the Journal of Engineering Education, and as the Editor-in-Chief of Annals of Research on Engineering Education (AREE). | 8 | Metallurgy |
The output beam is collected by a detector and its intensity is calculated using
where is the visible frequency, is the IR frequency and is the SFG frequency. The constant of proportionality varies across literature, many of them including the product of the square of the output frequency, and the squared secant of the reflection angle, . Other factors include index of refractions for the three beams.
The second order susceptibility has two contributions
where is the non-resonating contribution and is the resonating contribution. The non-resonating contribution is assumed to be from electronic responses. Although this contribution has often been considered to be constant over the spectrum, because it is generated simultaneously with the resonant response, the two responses must compete for intensity. This competition shapes the nonresonant contribution in the presence of resonant features by resonant attenuation. Because it is not currently known how to adequately correct for nonresonant interferences, it is very important to experimentally isolate the resonant contributions from any nonresonant interference, often done using the technique of nonresonant suppression.
The resonating contribution is from the vibrational modes and shows changes in resonance. It can be expressed as a sum of a series of Lorentz oscillators
where is the strength or amplitude, is the resonant frequency, is the damping or linewidth coefficient (FWHM), and each indexes the normal (resonant vibrational) mode. The amplitude is a product of , the induced dipole moment, and , the polarizability. Together, this indicates that the transition must be both IR and Raman active.
The above equations can be combined to form
which is used to model the SFG output over a range of wavenumbers. When the SFG system scans over a vibrational mode of the surface molecule, the output intensity is resonantly enhanced. In a graphical analysis of the output intensity versus wavenumber, this is represented by Lorentzian peaks. Depending on the system, inhomogeneous broadening and interference between peaks may occur. The Lorentz profile can be convoluted with a Gaussian intensity distribution to better fit the intensity distribution. | 7 | Physical Chemistry |
He started his research in the chemistry of natural products. At Washington State University he established early steps in metabolism of d-neomethyl-α-D-glucoside in pipermint (Mentha piperita) rhizomes via in vivo studies. Bhushan developed a de novo method for direct resolution of certain racemates by liquid chromatography. Later, the approach was applied for direct enantioseparation of several active pharmaceutical ingredients (APIs). It is now an established approach in literature. 1994 onwards, the method was extended to such resolutions by ligand exchange principle. The method is of significant importance to pharmaceutical industry and analytical laboratories associated with regulatory agencies for determination and control of enantiomeric purity (and isolation of native enantiomers) of a variety of APIs since many of them are marketed and administered as racemic mixture while only one enantiomer is therapeutically useful.
Bhushan supervised the Ph.D. theses of > 30 scholars and has published more than 270 research papers. | 3 | Analytical Chemistry |
Wild-type p53 has been shown to repress survivin expression at the mRNA level. Using an adenovirus vector for wild-type p53, human ovarian cancer cell line 2774qw1 (which expresses mutant p53) was transfected. mRNA levels of survivin were analyzed by real-time quantitative PCR (RT-PCR) and showed time-dependent down regulation of survivin mRNA levels when the cells were infected with wild-type p53. A 3.6 fold decrease of survivin mRNA level was observed 16 hours after infection initiation and decreased 6.7 fold 24 hours after infection. Western blot results do show that there is indeed the p53 from the adenoviral vector was being expressed in the cells using antibody specific for p53. The expression of p53 levels indicative of its role in survivin repression shows that p53 started to be expressed 6 hours into infection and had its highest level at 16–24 hours. To further confirm that endogenous wild-type p53 is really causing the repression of survivin gene expression, the authors induced A549 (human lung cancer cell line with wild-type p53) and T47D (human breast cancer cell line with mutant p53) cells with DNA-damaging agent adriamycin to trigger the physiological p53 apoptotic response in these cancer cells and compare the survivin levels measured to the same cells without DNA damage induction. The A549 line, which intrinsically has functioning wild-type p53, showed significant reduction in survivin levels compared to non-induced cells. This same effect was not seen in T47D cells that carry mutant inactive p53.
P53's normal function is to regulate genes that control apoptosis. As survivin is a known inhibitor of apoptosis, it can be implied that p53 repression of survivin is one mechanism by which cells can undergo apoptosis upon induction by apoptotic stimuli or signals. When survivin is over-expressed in the cell lines mentioned in the previous paragraph, apoptotic response from DNA-damaging agent adriamycin decreased in a dose-dependent manner. This suggests that down-regulation of survivin by p53 is important for p53-mediated apoptotic pathway to successfully result in apoptosis. It is known that a defining characteristic of most tumors is the over-expression of survivin and the complete loss of wild-type p53. The evidence put forth by Mirza et al. shows that there exists a link between survivin and p53 that can possibly explain a critical event that contributes to cancer progression. | 1 | Biochemistry |
In in vivo gene therapy, a vector (typically, a virus) is introduced to the patient, which then achieves the desired biological effect by passing the genetic material (e.g. for a missing protein) into the patients cells. In ex vivo gene therapies, such as CAR-T therapeutics, the patients own cells (autologous) or healthy donor cells (allogeneic) are modified outside the body (hence, ex vivo) using a vector to express a particular protein, such as a chimeric antigen receptor.
In vivo gene therapy is seen as simpler, since it does not require the harvesting of mitotic cells. However, ex vivo gene therapies are better tolerated and less associated with severe immune responses. The death of Jesse Gelsinger in a trial of an adenovirus-vectored treatment for ornithine transcarbamylase deficiency due to a systemic inflammatory reaction led to a temporary halt on gene therapy trials across the United States. , in vivo and ex vivo therapeutics are both seen as safe. | 1 | Biochemistry |
Three key points are taken into consideration regarding MRL values in the EU regulation:
1) the amounts of residues found in food must be safe for consumers and must be as low as possible,
2) the European Commission fixes MRLs for all food and animal feed, and 3) the MRLs for all crops and all pesticides can be found in the MRL database on the Commission website. | 2 | Environmental Chemistry |
Disulfide bonds are usually formed from the oxidation of sulfhydryl () groups, especially in biological contexts. The transformation is depicted as follows:
A variety of oxidants participate in this reaction including oxygen and hydrogen peroxide. Such reactions are thought to proceed via sulfenic acid intermediates. In the laboratory, iodine in the presence of base is commonly employed to oxidize thiols to disulfides. Several metals, such as copper(II) and iron(III) complexes affect this reaction. Alternatively, disulfide bonds in proteins often formed by thiol-disulfide exchange:
Such reactions are mediated by enzymes in some cases and in other cases are under equilibrium control, especially in the presence of a catalytic amount of base.
The alkylation of alkali metal di- and polysulfides gives disulfides. "Thiokol" polymers arise when sodium polysulfide is treated with an alkyl dihalide. In the converse reaction, carbanionic reagents react with elemental sulfur to afford mixtures of the thioether, disulfide, and higher polysulfides. These reactions are often unselective but can be optimized for specific applications. | 0 | Organic Chemistry |
Gaian hypotheses suggest that organisms co-evolve with their environment: that is, they "influence their abiotic environment, and that environment in turn influences the biota by Darwinian process". Lovelock (1995) gave evidence of this in his second book, Ages of Gaia, showing the evolution from the world of the early thermo-acido-philic and methanogenic bacteria towards the oxygen-enriched atmosphere today that supports more complex life.
A reduced version of the hypothesis has been called "influential Gaia" in "Directed Evolution of the Biosphere: Biogeochemical Selection or Gaia?" by Andrei G. Lapenis, which states the biota influence certain aspects of the abiotic world, e.g. temperature and atmosphere. This is not the work of an individual but a collective of Russian scientific research that was combined into this peer-reviewed publication. It states the coevolution of life and the environment through "micro-forces" and biogeochemical processes. An example is how the activity of photosynthetic bacteria during Precambrian times completely modified the Earth atmosphere to turn it aerobic, and thus supports the evolution of life (in particular eukaryotic life).
Since barriers existed throughout the twentieth century between Russia and the rest of the world, it is only relatively recently that the early Russian scientists who introduced concepts overlapping the Gaia paradigm have become better known to the Western scientific community. These scientists include Piotr Alekseevich Kropotkin (1842–1921) (although he spent much of his professional life outside Russia), Rafail Vasil’evich Rizpolozhensky (1862 – c. 1922), Vladimir Ivanovich Vernadsky (1863–1945), and Vladimir Alexandrovich Kostitzin (1886–1963).
Biologists and Earth scientists usually view the factors that stabilize the characteristics of a period as an undirected emergent property or entelechy of the system; as each individual species pursues its own self-interest, for example, their combined actions may have counterbalancing effects on environmental change. Opponents of this view sometimes reference examples of events that resulted in dramatic change rather than stable equilibrium, such as the conversion of the Earth's atmosphere from a reducing environment to an oxygen-rich one at the end of the Archaean and the beginning of the Proterozoic periods.
Less accepted versions of the hypothesis claim that changes in the biosphere are brought about through the coordination of living organisms and maintain those conditions through homeostasis. In some versions of Gaia philosophy, all lifeforms are considered part of one single living planetary being called Gaia. In this view, the atmosphere, the seas and the terrestrial crust would be results of interventions carried out by Gaia through the coevolving diversity of living organisms.
The Gaia paradigm was an influence on the deep ecology movement. | 9 | Geochemistry |
Previtamin D is an intermediate in the production of cholecalciferol (vitamin D).
It is formed by the action of UV light, most specifically UVB light of wavelengths between 295 and 300 nm, acting on 7-dehydrocholesterol in the epidermal layers of the skin.
The B ring of the steroid nucleus structure is broken open, making a secosteroid. This then undergoes spontaneous isomerization into cholecalciferol, the prohormone of the active form of vitamin D, calcitriol.
The synthesis of previtamin D is blocked effectively by sunscreens. | 0 | Organic Chemistry |
Two populations of cells are cultivated in cell culture. One of the cell populations is fed with growth medium containing normal amino acids. In contrast, the second population is fed with growth medium containing amino acids labeled with stable (non-radioactive) heavy isotopes. For example, the medium can contain arginine labeled with six carbon-13 atoms (C) instead of the normal carbon-12 (C). When the cells are growing in this medium, they incorporate the heavy arginine into all of their proteins. Thereafter, all peptides containing a single arginine are 6 Da heavier than their normal counterparts. Alternatively, uniform labeling with C or N can be used. Proteins from both cell populations are combined and analyzed together by mass spectrometry as pairs of chemically identical peptides of different stable-isotope composition can be differentiated in a mass spectrometer owing to their mass difference. The ratio of peak intensities in the mass spectrum for such peptide pairs reflects the abundance ratio for the two proteins. | 1 | Biochemistry |
Recent advancements in SPR technology have given rise to novel formats increasing the scope and applicability of SPR sensing. Fiber optic SPR involves the integration of SPR sensors onto the ends of optical fibers, enabling the direct coupling of light with the surface plasmons as the analytes are passed through a hollow SPR core. This format offers enhanced sensitivity and allows for the development of compact sensing devices, making it particularly valuable for applications requiring remote sensing in the field. It also offers an increased surface area for analytes to bind to the inner lining of the fiber optic. | 7 | Physical Chemistry |
After graduating from Ohio University in 1950, Grasselli Brown was offered a job position at Standard Oil (now BP America) in Cleveland as a project leader. From 1950 to 1978, she worked closely with an instrument called an infrared spectrometer. This device is used to measure the absorbance, emission, and reflection of infrared light interacting with a molecule and also measures the vibrations of atoms to identify functional groups.
During her time at Standard Oil, Grasselli Brown used the infrared spectrometer to examine the concentration of materials, and sought to find industrial applications for it.
As a project leader, she analyzed the formulations of World War II German airplane fuels to understand how the German planes were able to extend their flight ranges. She also consulted with the coroner's office in Cleveland to analyze unknown samples at crime scenes.
In 1978, she became the manager of the analytical science laboratory, working there until 1983. In 1983, she became the director of the technological support department, working there until 1985, when she became the first female director of corporate research from 1985 to 1988. Grasselli Brown retired in January 1989 as the company's highest ranking female employee. | 3 | Analytical Chemistry |
The process may be likened to how yeast ferments sugars to produce ethanol for wine, beer, or fuel, but the organisms that carry out the ABE fermentation are strictly anaerobic (obligate anaerobes). The ABE fermentation produces solvents in a ratio of 3 parts acetone, 6 parts butanol to 1 part ethanol. It usually uses a strain of bacteria from the Class Clostridia (Family Clostridiaceae). Clostridium acetobutylicum is the most well-studied and widely used. Although less effective, Clostridium beijerinckii and Clostridium saccharobutylicum bacterial strains have shown good results as well.
The ABE fermentation pathway generally proceeds in two phases. In the initial acidogenesis phase, the cells grow exponentially and accumulate acetate and butyrate. The low pH along with other factors then trigger a metabolic shift to the solventogenesis phase, in which acetate and butyrate are used to produce the solvents.
For gas stripping, the most common gases used are the off-gases from the fermentation itself, a mixture of carbon dioxide and hydrogen gas. | 1 | Biochemistry |
Hydrosilylation of alkenes represents a commercially important method for preparing organosilicon compounds. The process is mechanistically similar to the hydrogenation of alkenes. In fact, similar catalysts are sometimes employed for the two catalytic processes.
The prevalent mechanism, called the Chalk-Harrod mechanism, assumes an intermediate metal complex that contains a hydride, a silyl ligand (RSi), and the alkene substrate. Oxidative addition proceeds by the intermediacy of a sigma-complex, wherein the Si-H bond is not fully broken.
Hydrosilylation of alkenes usually proceeds via anti-Markovnikov addition, i.e., silicon is placed at the terminal carbon when hydrosilylating a terminal alkene Variations of the Chalk-Harrod mechanism exist. Some cases involve insertion of alkene into M-Si bond followed by reductive elimination, the opposite of the sequence in the Chalk-Harrod mechanism. In certain cases, hydrosilylation results in vinyl or allylic silanes resulting from beta-hydride elimination.
Alkynes also undergo hydrosilylation, e.g., the addition of triethylsilane to diphenylacetylene:
:EtSiH + PhC≡CPh → EtSi(Ph)C=CH(Ph) | 7 | Physical Chemistry |
A spectroscopic peak may be fitted to multiples of the above functions or to sums or products of functions with variable parameters. The above functions are all symmetrical about the position of their maximum. Asymmetric functions have also been used. | 7 | Physical Chemistry |
also considered the symmetrized function:
which they referred to as the "divergence", though today the "KL divergence" refers to the asymmetric function (see for the evolution of the term). This function is symmetric and nonnegative, and had already been defined and used by Harold Jeffreys in 1948; it is accordingly called the Jeffreys divergence.
This quantity has sometimes been used for feature selection in classification problems, where and are the conditional pdfs of a feature under two different classes. In the Banking and Finance industries, this quantity is referred to as Population Stability Index (PSI), and is used to assess distributional shifts in model features through time.
An alternative is given via the -divergence,
which can be interpreted as the expected information gain about from discovering which probability distribution is drawn from, or , if they currently have probabilities and respectively.
The value gives the Jensen–Shannon divergence, defined by
where is the average of the two distributions,
We can also interpret as the capacity of a noisy information channel with two inputs giving the output distributions and . The Jensen–Shannon divergence, like all -divergences, is locally proportional to the Fisher information metric. It is similar to the Hellinger metric (in the sense that it induces the same affine connection on a statistical manifold).
Furthermore, the Jensen–Shannon divergence can be generalized using abstract statistical M-mixtures relying on an abstract mean M. | 7 | Physical Chemistry |
A general [p+q]-cycloaddition is a concerted addition reaction between two components, one with p π-electrons, and one with q π-electrons. This reaction is symmetry allowed under the following conditions:
* For a supra/supra or antara/antara cycloaddition, it is thermally allowed if p + q = 4n + 2 and photochemically allowed if p + q = 4n
* For a supra/antara cycloaddition, it is thermally allowed if p + q = 4n and photochemically allowed if p + q = 4n + 2
This is summarized in the following table: | 7 | Physical Chemistry |
PG cooling is typically performed using a 3D optical setup with three pairs of perpendicular laser beams with an atomic ensemble in the center. Each beam is prepared with an orthogonal polarization to its counterpropagating beam. The laser frequency detuned from a selected transition between the ground and excited states of the atom. Since the cooling processes rely on multiple transitions between care must be taken such that the atomic does not fall out of these two states. This is done by using a second, "repumping", laser to pump any atoms that fall out back into the ground state of the transition. For example: in cesium cooling experiments, the cooling laser is typically chosen to be detuned from the to transition and a repumping laser tuned to the to transition is also used to prevent the Cs atoms from being pumped into the state.
The atoms must be cooled before the PG cooling, this can be done using the same setup via Doppler cooling. If the atoms are precooled with Doppler cooling, the laser intensity must be lowered and the detuning increased for PG cooling to be achieved.
The atomic temperature can be measured using the time of flight (ToF) technique. In this technique, the laser beams are suddenly turned off and the atomic ensemble is allowed to expand. After a set time delay t, a probe beam is turned on to image the ensemble and obtain the spatial extent of the ensemble at time t. By imaging the ensemble at several time delays, the rate of expansion is found. By measuring the rate of expansion of the ensemble the velocity distribution is measured and from this, the temperature is inferred.
An important theoretical result is that in the regime where PG cooling functions, the temperature only depends on the ratio of to and that the cooling approaches the recoil limit. These predictions were confirmed experimentally in 1990 when W.D. Phillips et al. observed such scaling in their cesium atoms as well as a temperature of 2.5K, 12 times the recoil temperature of 0.198K for the D2 line of cesium used in the experiment. | 7 | Physical Chemistry |
Fazlul Halim Chowdhury (1 August 19309 April 1996) was a fellow of the Bangladesh Academy of Sciences and one of the longest-serving Vice-Chancellors of the University of Dhaka. He made pioneering contributions to the development of physical chemistry in Bangladesh, publishing more than 20 articles. He focused on cellulose fibers (especially jute), polyelectrolytes, and proteins. | 7 | Physical Chemistry |
The protocol is based on the fact that the formaldehyde cross-linking is more efficient in nucleosome-bound DNA than it is in nucleosome-depleted regions of the genome. This method then segregates the non cross-linked DNA that is usually found in open chromatin, which is then sequenced. The protocol consists of cross linking, phenol extraction and sequencing the DNA in aqueous phase. | 1 | Biochemistry |
An example of a spontaneous (without addition of an external energy source) decomposition is that of hydrogen peroxide which slowly decomposes into water and oxygen ):
: 2 HO → 2 HO + O
This reaction is one of the exceptions to the endothermic nature of decomposition reactions.
Other reactions involving decomposition do require the input of external energy. This energy can be in the form of heat, radiation, electricity, or light. The latter being the reason some chemical compounds, such as many prescription medicines, are kept and stored in dark bottles which reduce or eliminate the possibility of light reaching them and initiating decomposition.
When heated, carbonates will decompose. A notable exception is carbonic acid, (HCO). Commonly seen as the "fizz" in carbonated beverages, carbonic acid will spontaneously decompose over time into carbon dioxide and water. The reaction is written as:
: HCO → HO + CO
Other carbonates will decompose when heated to produce their corresponding metal oxide and carbon dioxide. The following equation is an example, where M represents the given metal:
: MCO → MO + CO
A specific example is that involving calcium carbonate:
: CaCO → CaO + CO
Metal chlorates also decompose when heated. In this type of decomposition reaction, a metal chloride and oxygen gas are the products. Here, again, M represents the metal:
: 2 MClO → 2 MCl+ 3 O
A common decomposition of a chlorate is in the reaction of potassium chlorate where oxygen is the product. This can be written as:
: 2 KClO → 2 KCl + 3 O | 0 | Organic Chemistry |
Many chloroplast DNAs contain two inverted repeats, which separate a long single copy section (LSC) from a short single copy section (SSC).
The inverted repeats vary wildly in length, ranging from 4,000 to 25,000 base pairs long each. Inverted repeats in plants tend to be at the upper end of this range, each being 20,000–25,000 base pairs long.
The inverted repeat regions usually contain three ribosomal RNA and two tRNA genes, but they can be expanded or reduced to contain as few as four or as many as over 150 genes.
While a given pair of inverted repeats are rarely completely identical, they are always very similar to each other, apparently resulting from concerted evolution.
The inverted repeat regions are highly conserved among land plants, and accumulate few mutations. Similar inverted repeats exist in the genomes of cyanobacteria and the other two chloroplast lineages (glaucophyta and rhodophyceæ), suggesting that they predate the chloroplast, though some chloroplast DNAs like those of peas and a few red algae have since lost the inverted repeats. Others, like the red alga Porphyra flipped one of its inverted repeats (making them direct repeats). It is possible that the inverted repeats help stabilize the rest of the chloroplast genome, as chloroplast DNAs which have lost some of the inverted repeat segments tend to get rearranged more. | 5 | Photochemistry |
plants often possess a characteristic leaf anatomy called kranz anatomy, from the German word for wreath. Their vascular bundles are surrounded by two rings of cells; the inner ring, called bundle sheath cells, contains starch-rich chloroplasts lacking grana, which differ from those in mesophyll cells present as the outer ring. Hence, the chloroplasts are called dimorphic. The primary function of kranz anatomy is to provide a site in which can be concentrated around RuBisCO, thereby avoiding photorespiration. Mesophyll and bundle sheath cells are connected through numerous cytoplasmic sleeves called plasmodesmata whose permeability at leaf level is called bundle sheath conductance. A layer of suberin is often deposed at the level of the middle lamella (tangential interface between mesophyll and bundle sheath) in order to reduce the apoplastic diffusion of (called leakage). The carbon concentration mechanism in plants distinguishes their isotopic signature from other photosynthetic organisms.
Although most plants exhibit kranz anatomy, there are, however, a few species that operate a limited cycle without any distinct bundle sheath tissue. Suaeda aralocaspica, Bienertia cycloptera, Bienertia sinuspersici and Bienertia kavirense (all chenopods) are terrestrial plants that inhabit dry, salty depressions in the deserts of the Middle East. These plants have been shown to operate single-cell -concentrating mechanisms, which are unique among the known mechanisms. Although the cytology of both genera differs slightly, the basic principle is that fluid-filled vacuoles are employed to divide the cell into two separate areas. Carboxylation enzymes in the cytosol are separated from decarboxylase enzymes and RuBisCO in the chloroplasts. A diffusive barrier is between the chloroplasts (which contain RuBisCO) and the cytosol. This enables a bundle-sheath-type area and a mesophyll-type area to be established within a single cell. Although this does allow a limited cycle to operate, it is relatively inefficient. Much leakage of from around RuBisCO occurs.
There is also evidence of inducible photosynthesis by non-kranz aquatic macrophyte Hydrilla verticillata under warm conditions, although the mechanism by which leakage from around RuBisCO is minimised is currently uncertain. | 5 | Photochemistry |
Over 50 years ago, in a lab in France, Ephrussi, et al. discovered a non-Mendelian inherited factor that is essential to respiration in the yeast, Saccharomyces cerevisiae. S. cerevisiae without this factor, known as the ρ-factor, is described by the development of small colonies when compared to the wild-type yeast. These smaller colonies were dubbed petite colonies. These petite mutants were observed to be spontaneously produced naturally at a rate of 0.1%-1.0% every generation. They also found that treatment of wild-type S. cerevisiae with DNA-intercalating agents would more rapidly produce this mutation.
Schatz identified a region of the yeast's nuclear DNA that was associated with the mitochondria in 1964. Later, it was discovered that mutants without the ρ-factor had no mitochondrial DNA (called ρ isolates), or that they possessed a difference in density or amount of the mitochondrial DNA (called ρ isolates). The use of electron microscopy to view the DNA in the mitochondrial matrix helped to verify the actuality of the mitochondrial genome.
S. cerevisiae has since become a useful model for aging. It has been shown that as yeast ages, it loses functional mitochondrial DNA, which leads to replicative senescence, or the inability to further replicate. It has been suggested that there is a link between mitochondrial DNA loss and replicative life span (RLS), or the number of times a cell can reproduce before it dies, as it has been found that an increase in RLS is established with the same changes in the genome that enhance the propagation of cells that do not contain mitochondrial DNA. Genetic screens for replicative life span associated genes and pathways could be made easier and quicker by selecting genetic suppressors of the petite negative mutants. | 1 | Biochemistry |
Carbenes can be stabilised as organometallic species. These transition metal carbene complexes fall into two categories:
* Fischer carbenes in which carbenes are tethered to a metal and an electron-withdrawing group (usually a carbonyl),
* Schrock carbenes; in which carbenes are tethered to a metal and an electron-donating group. The reactions that such carbenes participate in are very different from those in which organic carbenes participate. | 0 | Organic Chemistry |
The soil vapor extraction remediation technology uses vacuum blowers and extraction wells to induce gas flow through the subsurface, collecting contaminated soil vapor, which is subsequently treated aboveground. SVE systems can rely on gas inflow through natural routes or specific wells may be installed for gas inflow (forced or natural). The vacuum extraction of soil gas induces gas flow across a site, increasing the mass transfer driving force from aqueous (soil moisture), non-aqueous (pure phase), and solid (soil) phase into the gas phase. Air flow across a site is thus a key aspect, but soil moisture and subsurface heterogeneity (i.e., a mixture of low and high permeability materials) can result in less gas flow across some zones. In some situations, such as enhancement of monitored natural attenuation, a passive SVE system that relies on barometric pumping may be employed.
SVE has several advantages as a vadose zone remediation technology. The system can be implemented with standard wells and off-the-shelf equipment (blowers, instrumentation, vapor treatment, etc.). SVE can also be implemented with a minimum of site disturbance, primarily involving well installation and minimal aboveground equipment. Depending on the nature of the contamination and the subsurface geology, SVE has the potential to treat large soil volumes at reasonable costs.
The soil gas (vapor) that is extracted by the SVE system generally requires treatment prior to discharge back into the environment. The aboveground treatment is primarily for a gas stream, although condensation of liquid must be managed (and in some cases may specifically be desired). A variety of treatment techniques are available for aboveground treatment and include thermal destruction (e.g., direct flame thermal oxidation, catalytic oxidizers), adsorption (e.g., granular activated carbon, zeolites, polymers), biofiltration, non-thermal plasma destruction, photolytic/photocatalytic destruction, membrane separation, gas absorption, and vapor condensation. The most commonly applied aboveground treatment technologies are thermal oxidation and granular activated carbon adsorption. The selection of a particular aboveground treatment technology depends on the contaminant, concentrations in the offgas, throughput, and economic considerations. | 2 | Environmental Chemistry |
Pyroelectric charge in minerals develops on the opposite faces of asymmetric crystals. The direction in which the propagation of the charge tends is usually constant throughout a pyroelectric material, but, in some materials, this direction can be changed by a nearby electric field. These materials are said to exhibit ferroelectricity.
All known pyroelectric materials are also piezoelectric. Despite being pyroelectric, novel materials such as boron aluminum nitride (BAlN) and boron gallium nitride (BGaN) have zero piezoelectric response for strain along the c-axis at certain compositions, the two properties being closely related. However, note that some piezoelectric materials have a crystal symmetry that does not allow pyroelectricity.
Pyroelectric materials are mostly hard and crystals; however, soft pyroelectricity can be achieved by using electrets.
Pyroelectricity is measured as the change in net polarization (a vector) proportional to a change in temperature. The total pyroelectric coefficient measured at constant stress is the sum of the pyroelectric coefficients at constant strain (primary pyroelectric effect) and the piezoelectric contribution from thermal expansion (secondary pyroelectric effect). Under normal circumstances, even polar materials do not display a net dipole moment. As a consequence, there are no electric dipole equivalents of bar magnets because the intrinsic dipole moment is neutralized by "free" electric charge that builds up on the surface by internal conduction or from the ambient atmosphere. Polar crystals only reveal their nature when perturbed in some fashion that momentarily upsets the balance with the compensating surface charge.
Spontaneous polarization is temperature dependent, so a good perturbation probe is a change in temperature which induces a flow of charge to and from the surfaces. This is the pyroelectric effect. All polar crystals are pyroelectric, so the 10 polar crystal classes are sometimes referred to as the pyroelectric classes. Pyroelectric materials can be used as infrared and millimeter wavelength radiation detectors.
An electret is the electrical equivalent of a permanent magnet. | 7 | Physical Chemistry |
Over the years, the utility of molecular logic gates has been explored in a wide range of fields such as chemical and biological detection, the pharmaceutical and food industries, and the emerging fields of nanomaterials and chemical computing. | 6 | Supramolecular Chemistry |
In organic chemistry, the principle of least motion is the hypothesis that when multiple species with different nuclear structures could theoretically form as products of a given chemical reaction, the more likely to form tends to be the one requiring the least amount of change in nuclear structure or the smallest change in nuclear positions. | 0 | Organic Chemistry |
One of the most critical steps in the SELEX procedure is obtaining single stranded DNA (ssDNA) after the PCR amplification step. This will serve as input for the next cycle so it is of vital importance that all the DNA is single stranded and as little as possible is lost. Because of the relative simplicity, one of the most used methods is using biotinylated reverse primers in the amplification step, after which the complementary strands can be bound to a resin followed by elution of the other strand with lye. Another method is asymmetric PCR, where the amplification step is performed with an excess of forward primer and very little reverse primer, which leads to the production of more of the desired strand. A drawback of this method is that the product should be purified from double stranded DNA (dsDNA) and other left-over material from the PCR reaction. Enzymatic degradation of the unwanted strand can be performed by tagging this strand using a phosphate-probed primer, as it is recognized by enzymes such as Lambda exonuclease. These enzymes then selectively degrade the phosphate tagged strand leaving the complementary strand intact. All of these methods recover approximately 50 to 70% of the DNA. For a detailed comparison refer to the article by Svobodová et al. where these, and other, methods are experimentally compared. In classical SELEX, the process of randomized single stranded library generation, target incubation, and binding sequence elution and amplification described above are repeated until the vast majority of the retained pool consists of target binding sequences, though there are modifications and additions to the procedure that are often used, which are discussed below. | 1 | Biochemistry |
MER41.AIM2 is an HERV that regulates the transcription of AIM2 (Absent in Melanoma 2) which encodes for a sensor of foreign cytosolic DNA. This acts as a binding site for AIM2, meaning that it is necessary for the transcription of AIM2. Researchers had shown this by deleting MER41.AIM2 in HeLa cells using CRISPR/Cas9, leading to an undetectable transcript level of AIM2 in modified HeLa cells. The control cells, which still contained the MER41.AIM2 ERV, were observed with normal amounts of AIM2 transcript. In terms of immunity, researchers concluded that MER41.AIM2 is necessary for an inflammatory response to infection. | 1 | Biochemistry |
There are several consequences the formation of a transcription factory has on nuclear and genomic structures. It has been proposed that the factories are responsible for nuclear organisation; they have been suggested to promote chromatin loop formation by two potential mechanisms:
The first mechanism suggests that loops form because 2 genes on the same chromosome require the same transcription machinery that would be found in a specific transcription factory. This requirement will attract the gene loci to the factory thus creating a loop.
Transcription factories are also suggested to be responsible for gene clustering, this is because related genes would require the same transcriptional machinery and if a factory satisfies these needs the genes would be attracted to the factory
. While the clustering of genes can be beneficial for transcriptional efficiency, there could be negative consequences to this. Gene translocation events occur when genes are in close proximity to one another; which will occur more often when a transcriptional factory is present. Gene translocation events, like point mutations, generally are detrimental to the organism and so therefore could lead to the possibility of disease. However, on the other hand recent research has suggested that there is no correlation between inter-gene interactions and translocation frequencies. | 1 | Biochemistry |
Choren Industries has built a plant in Germany that converts biomass to syngas and fuels using the Shell FT process structure. The company went bankrupt in 2011 due to impracticalities in the process.
Biomass gasification (BG) and Fischer–Tropsch (FT) synthesis can in principle be combined to produce renewable transportation fuels (biofuels). | 0 | Organic Chemistry |
The speed of sound in a liquid is given by where is the bulk modulus of the liquid and the density. As an example, water has a bulk modulus of about 2.2 GPa and a density of 1000 kg/m, which gives c = 1.5 km/s. | 7 | Physical Chemistry |
The trihexagonal tiling has Schläfli symbol of r{6,3}, or Coxeter diagram, , symbolizing the fact that it is a rectified hexagonal tiling, {6,3}. Its symmetries can be described by the wallpaper group p6mm, (*632), and the tiling can be derived as a Wythoff construction within the reflectional fundamental domains of this group. The trihexagonal tiling is a quasiregular tiling, alternating two types of polygons, with vertex configuration (3.6). It is also a uniform tiling, one of eight derived from the regular hexagonal tiling. | 3 | Analytical Chemistry |
He was born in Bratislava, then Czechoslovakia in a family of Slovak actor Juraj Kukura. In 1984 the family emigrated to Germany. In 2002 he graduated with a Master of Chemistry from the University of Oxford and competed in the 2001 and 2002 Rugby League Varsity matches. In 2006 he completed his PhD in Chemistry from the University of California, Berkeley College of Chemistry. | 7 | Physical Chemistry |
In Fick's original method, the following variables are measured:
* V̇O, oxygen consumption in ml of pure gaseous oxygen per minute. This may be measured using a spirometer within a closed rebreathing circuit incorporating a CO absorber
* C, the oxygen content of blood taken from the pulmonary vein (representing oxygenated blood)
* C, the oxygen content of blood from an intravenous cannula (representing deoxygenated blood) | 1 | Biochemistry |
Group 6 metal carbonyls upon photolytic activation catalyze dehydrogenation of AB. Secondary amine-boranes dehydrogenate to form cyclic dimers, or monomeric aminoboranes in the case of more bulky groups on the amine. Similarly, primary amine-boranes dehydrogenate through a two step intramolecular process to give aminoborane polymers, which further dehydrogenate to form borazines. [[Cyclopentadienyliron dicarbonyl dimer|[CpFe(CO)]]] is also an effective precatalyst, requiring photolytic activation. The two step process is proposed to occur first by dehydrogenation of the amine-borane coordinated to the metal, followed by cyclodimerization in an off-metal step. | 0 | Organic Chemistry |
In thermodynamics, a thermodynamic state of a system is its condition at a specific time; that is, fully identified by values of a suitable set of parameters known as state variables, state parameters or thermodynamic variables. Once such a set of values of thermodynamic variables has been specified for a system, the values of all thermodynamic properties of the system are uniquely determined. Usually, by default, a thermodynamic state is taken to be one of thermodynamic equilibrium. This means that the state is not merely the condition of the system at a specific time, but that the condition is the same, unchanging, over an indefinitely long duration of time. | 7 | Physical Chemistry |
Cancer is a complex, heterogeneous disease that can be hereditary or the result of environmental stimuli. Minigenes are used to help oncologists understand the roles pre-mRNA splicing plays in different cancer types. Of particular interest are cancer specific genetic mutations that disrupt normal splicing events, including those affecting spliceosome components and RNA-binding proteins such as heterogeneous nuclear ribonucleoparticules (hnRNP), serine/arginine-rich (SR) proteins and small ribonucleoproteins (snRNP). Proteins encoded by aberrantly spliced pre-mRNAs are functionally different and contribute to the characteristic anomalies exhibited by cancer cells, including their ability to proliferate, invade and undergo angiogenesis, and metastasis. Minigenes help researchers identify genetic mutations in cancer that result in splicing errors and determine the downstream effects those splicing errors have on gene expression. Using knowledge obtained from studies employing minigenes, oncologists have proposed tests designed to detect products of abnormal gene expression for diagnostic purposes. Additionally, the prospect of using minigenes as a cancer immunotherapy is being explored. | 1 | Biochemistry |
Carbon nanotubes are meant to potentially solve the typical tradeoff between the permeability and the selectivity of RO membranes. CNTs present many ideal characteristics including: mechanical strength, electron affinity, and also exhibiting flexibility during modification. By restructuring carbon nanotubes and coating or impregnating them with other chemical compounds, scientists can manufacture these membranes to have all of the most desirable traits. The hope with CNT membranes is to find a combination of high water permeability while also decreasing the amount of neutral solutes taken out of the water. This would help decrease energy costs and the cost of remineralization after purification through the membrane. | 3 | Analytical Chemistry |
It has been reported that mammalian glycosylation can improve the therapeutic efficacy of biotherapeutics. For example, therapeutic efficacy of recombinant human interferon gamma, expressed in HEK 293 platform, was improved against drug-resistant ovarian cancer cell lines. | 0 | Organic Chemistry |
Calcineurin (CaN) is a calcium and calmodulin dependent serine/threonine protein phosphatase (also known as protein phosphatase 3, and calcium-dependent serine-threonine phosphatase). It activates the T cells of the immune system and can be blocked by drugs. Calcineurin activates nuclear factor of activated T cell cytoplasmic (NFATc), a transcription factor, by dephosphorylating it. The activated NFATc is then translocated into the nucleus, where it upregulates the expression of interleukin 2 (IL-2), which, in turn, stimulates the growth and differentiation of the T cell response. Calcineurin is the target of a class of drugs called calcineurin inhibitors, which include ciclosporin, voclosporin, pimecrolimus and tacrolimus. | 1 | Biochemistry |
The mechanism of phenoxymethylpenicillin is identical to that of all other penicillins. It exerts a bactericidal action against penicillin-sensitive microorganisms during the stage of active multiplication. It acts by inhibiting the biosynthesis of cell-wall peptidoglycan. | 4 | Stereochemistry |
Kevin Cherry and Lulu Qian at Caltech developed a DNA-based artificial neural network that can recognize 100-bit hand-written digits. They achieve this by programming on computer in advance with appropriate set of weights represented by varying concentrations weight molecules which will later be added to the test tube that holds the input DNA strands. | 1 | Biochemistry |
* Stress corrosion cracking (SCC) is the embrittlement caused by exposure to aqueous, corrosive materials. It relies on both a corrosive environment and the presence of tensile (not compressive) stress.
* Sulfide stress cracking is the embrittlement caused by absorption of hydrogen sulfide.
* Adsorption embrittlement is the embrittlement caused by wetting.
* Liquid metal embrittlement (LME) is the embrittlement caused by liquid metals.
* Metal-induced embrittlement (MIE) is the embrittlement caused by diffusion of atoms of metal, either solid or liquid, into the material. For example, cadmium coating on high-strength steel, which was originally done to prevent corrosion.
* Grain boundary segregation can cause brittle intergranular fracture. During solidification the grain boundaries end up as the repository for the impurities in the alloy by segregation. This grain boundary segregation can create a network of low-toughness paths through the material.
* The primary embrittlement mechanism of plastics is gradual loss of plasticizers, usually by overheating or aging.
* The primary embrittlement mechanism of asphalt is by oxidation, which is most severe in warmer climates. Asphalt pavement embrittlement (aka crocodile cracking) can lead to various forms of cracking patterns, including longitudinal, transverse, and block (hexagonal). Asphalt oxidation is related to polymer degradation, as these materials bear similarities in their chemical composition. | 8 | Metallurgy |
In organic synthesis, aminochlorination is a reaction that installs both a chlorine atom and an amino (or amido) group to give an 2-aminoalkyl chloride. The reaction typically is effected by combining alkene substrates with chloramines. An alternative implementation involves Pd(II)-induced nucleophilic attack of the amine on the alkene followed by oxidation by a cupric chloride. | 0 | Organic Chemistry |
Analytical Solutions Forum (ASF) brings global stakeholders together to identify emerging needs and technologies in scientific analysis of food and related products. | 3 | Analytical Chemistry |
Many coal-firing power stations use flue-gas desulfurization (FGD) to remove sulfur-containing gases from their stack gases. For a typical coal-fired power station, FGD will remove 95% or more of the SO in the flue gases. An example of FGD is the wet scrubber which is commonly used. A wet scrubber is basically a reaction tower equipped with a fan that extracts hot smoke stack gases from a power plant into the tower. Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulfur dioxide present. The calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from the scrubber. That is, the scrubber turns sulfur pollution into industrial sulfates.
In some areas the sulfates are sold to chemical companies as gypsum when the purity of calcium sulfate is high. In others, they are placed in landfill. The effects of acid rain can last for generations, as the effects of pH level change can stimulate the continued leaching of undesirable chemicals into otherwise pristine water sources, killing off vulnerable insect and fish species and blocking efforts to restore native life.
Fluidized bed combustion also reduces the amount of sulfur emitted by power production.
Vehicle emissions control reduces emissions of nitrogen oxides from motor vehicles. | 2 | Environmental Chemistry |
The most common bases used in plastic scintillators are the aromatic plastics, polymers with aromatic rings as pendant groups along the polymer backbone, amongst which polyvinyltoluene (PVT) and polystyrene (PS) are the most prominent. While the base does fluoresce in the presence of ionizing radiation, its low yield and negligible transparency to its own emission make the use of fluors necessary in the construction of a practical scintillator. Aside from the aromatic plastics, the most common base is polymethylmethacrylate (PMMA), which carries two advantages over many other bases: high ultraviolet and visible light transparency and mechanical properties and higher durability with respect to brittleness. The lack of fluorescence associated with PMMA is often compensated through the addition of an aromatic co-solvent, usually naphthalene. A plastic scintillator based on PMMA in this way boasts transparency to its own radiation, helping to ensure uniform collection of light.
Other common bases include polyvinyl xylene (PVX) polymethyl, 2,4-dimethyl, 2,4,5-trimethyl styrenes, polyvinyl diphenyl, polyvinyl naphthalene, polyvinyl tetrahydronaphthalene, and copolymers of these and other bases. | 5 | Photochemistry |
During the synthesis of proteins, polypeptide chains, which are created by ribosomes translating mRNA, must be processed before assuming a mature conformation. The dephosphorylation of proteins is a mechanism for modifying behavior of a protein, often by activating or inactivating an enzyme. Components of the protein synthesis apparatus also undergo phosphorylation and dephosphorylation and thus regulate the rates of protein synthesis.
As part of posttranslational modifications, phosphate groups may be removed from serine, threonine, or tyrosine. As such, pathways of intracellular signal transduction depend on sequential phosphorylation and dephosphorylation of a wide variety of proteins. | 1 | Biochemistry |
A 1971 study published by the Harvard Medical School identified methylglyoxal, a form of glycerol, as a product of lethal synthesis in a specific E.coli mutant. In E.coli, the synthesis of triose phosphate from glycerol is a reaction regulated by the synthesis rate of glycerol kinase and by feedback inhibition by fructose-1,6-bisphosphate. The study demonstrated that, in E.coli mutants that had lost both control mechanisms, glycerol kinase no longer reacted to feedback regulation and instead produced the cytotoxic methylglyoxal. A more recent review of research done on methylglyoxal metabolism concluded that the compound's cytotoxic nature is dependent on its ability to form advanced glycation end products (AGEs). These compounds, which are thought to be factors in ageing and in the progression of degenerative diseases, have been shown to hinder the functions of the proteins they target. | 1 | Biochemistry |
When arachidonic acid is a substrate, isomers of hydroperoxyeicosatetraenoic acid (HPETEs) and hydroxyeicosatetraenoic acids (HETEs) are formed. | 1 | Biochemistry |
Isozymes were first described by R. L. Hunter and Clement Markert (1957) who defined them as different variants of the same enzyme having identical functions and present in the same individual. This definition encompasses (1) enzyme variants that are the product of different genes and thus represent different loci (described as isozymes) and (2) enzymes that are the product of different alleles of the same gene (described as allozymes).
Isozymes are usually the result of gene duplication, but can also arise from polyploidisation or nucleic acid hybridization. Over evolutionary time, if the function of the new variant remains identical to the original, then it is likely that one or the other will be lost as mutations accumulate, resulting in a pseudogene. However, if the mutations do not immediately prevent the enzyme from functioning, but instead modify either its function, or its pattern of expression, then the two variants may both be favoured by natural selection and become specialised to different functions. For example, they may be expressed at different stages of development or in different tissues.
Allozymes may result from point mutations or from insertion-deletion (indel) events that affect the coding sequence of the gene. As with any other new mutations, there are three things that may happen to a new allozyme:
* It is most likely that the new allele will be non-functional—in which case it will probably result in low fitness and be removed from the population by natural selection.
* Alternatively, if the amino acid residue that is changed is in a relatively unimportant part of the enzyme (e.g., a long way from the active site), then the mutation may be selectively neutral and subject to genetic drift.
* In rare cases, the mutation may result in an enzyme that is more efficient, or one that can catalyse a slightly different chemical reaction, in which case the mutation may cause an increase in fitness, and be favoured by natural selection. | 1 | Biochemistry |
Torquoselectivity is a special kind of stereoselectivity observed in electrocyclic reactions in organic chemistry, defined as "the preference for inward or outward rotation of substituents in conrotatory
or disrotatory electrocyclic reactions." Torquoselectivity is not to be confused with the normal diastereoselectivity seen in pericyclic reactions, as it represents a further level of selectivity beyond the Woodward-Hoffman rules. The name derives from the idea that the substituents in an electrocyclization appear to rotate over the course of the reaction, and thus selection of a single product is equivalent to selection of one direction of rotation (i.e. the direction of torque on the substituents). The concept was originally developed by Kendall N. Houk.
For ring closing reactions, it is an example of enantioselectivity, wherein a single enantiomer of a cyclization product is formed from the selective ring closure of the starting material. In a typical electrocyclic ring closing, selection for either conrotatory or disrotatory reactions modes still produces two enantiomers. Torquoselectivity is a discrimination between these possible enantiomers that requires asymmetric induction.
Torquoselectivity is also used to describe selective electrocyclic ring openings, in which different directions of rotation produce distinct structural isomers. In these cases, steric strain is often the driving force for the selectivity. Studies have shown that the selectivity can also be changed by the presence of electron donating and electron withdrawing groups.
Other mechanisms by which torquoselectivity can operate include chiral Lewis acid catalysts, induction via neighboring stereocenters (in which case the torquoselectivity is a case of diastereoselectivity), and axial-to-tetrahedral chirality transfer. An example of the latter case is shown below for the torquoselective Nazarov cyclization reaction of a chiral allenyl vinyl ketone. | 4 | Stereochemistry |
The last process in aerobic respiration is oxidative phosphorylation, also known as the electron transport chain. Here NADH and FADH deliver their electrons to oxygen and protons at the inner membranes of the mitochondrion, facilitating the production of ATP. Oxidative phosphorylation contributes the majority of the ATP produced, compared to glycolysis and the Krebs cycle. While the ATP count is glycolysis and the Krebs cycle is two ATP molecules, the electron transport chain contributes, at most, twenty-eight ATP molecules. A contributing factor is due to the energy potentials of NADH and FADH. A second contributing factor is that cristae, the inner membranes of mitochondria, increase the surface area and therefore the amount of proteins in the membrane that assist in the synthesis of ATP. Along the electron transport chain, there are separate compartments, each with their own concentration gradient of H + ions, which are the power source of ATP synthesis. To convert ADP to ATP, energy must be provided. That energy is provided by the H+ gradient. On one side of the membrane compartment, there is a high concentration of H+ ions compared to the other. The shuttling of H+ to one side of the membrane is driven by the exergonic flow of electrons throughout the membrane. These electrons are supplied by NADH and FADH as they transfer their potential energy. Once the H+ concentration gradient is established, a proton-motive force is established, which provides the energy to convert ADP to ATP. The H+ ions that were initially forced to one side of the mitochondrion membrane now naturally flow through a membrane protein called ATP synthase, a protein that converts ADP to ATP with the help of H+ ions. | 1 | Biochemistry |
Examples of oxygen nucleophiles are water (HO), hydroxide anion, alcohols, alkoxide anions, hydrogen peroxide, and carboxylate anions.
Nucleophilic attack does not take place during intermolecular hydrogen bonding. | 7 | Physical Chemistry |
In the first step, sulfur is burned to produce sulfur dioxide.
The sulfur dioxide is oxidized to sulfur trioxide by oxygen in the presence of a vanadium(V) oxide catalyst. This reaction is reversible and the formation of the sulfur trioxide is exothermic.
The sulfur trioxide is absorbed into 97–98% to form oleum (), also known as fuming sulfuric acid or pyrosulphuric acid. The oleum is then diluted with water to form concentrated sulfuric acid.
Directly dissolving in water, called the "wet sulfuric acid process", is rarely practiced because the reaction is extremely exothermic, resulting in a hot aerosol of sulfuric acid that requires condensation and separation. | 7 | Physical Chemistry |
The Ellis R. Lippincott Award is awarded annually to recognize "an individual who has made significant contributions to vibrational spectroscopy as judged by his or her influence on other scientists."
It was jointly established in 1975 by The Optical Society, The Coblentz Society, and The Society for Applied Spectroscopy. The award honors Ellis R. Lippincott, a vibrational spectroscopist who worked at the University of Maryland. Lippincott was one of the developers of the Diamond anvil cell, which is used in high pressure research. | 7 | Physical Chemistry |
In a method termed magnetofection, DNA is complexed to magnetic particles, and a magnet is placed underneath the tissue culture dish to bring DNA complexes into contact with a cell monolayer. | 1 | Biochemistry |
The oxaloacetate/aspartate family of amino acids is composed of lysine, asparagine, methionine, threonine, and isoleucine. Aspartate can be converted into lysine, asparagine, methionine and threonine. Threonine also gives rise to isoleucine.
The associated enzymes are subject to regulation via feedback inhibition and/or repression at the genetic level. As is typical in highly branched metabolic pathways, additional regulation at each branch point of the pathway. This type of regulatory scheme allows control over the total flux of the aspartate pathway in addition to the total flux of individual amino acids. The aspartate pathway uses L-aspartic acid as the precursor for the biosynthesis of one-fourth of the building block amino acids. | 1 | Biochemistry |
Polysaccharides are considered to be polymers of monosaccharides containing ten or more monosaccharide residues. Polysaccharides have been given trivial names that reflect their origin. Two common examples are cellulose, a main component of the cell wall in plants, and starch, a name derived from the Anglo-Saxon stercan, meaning to stiffen.
To name a polysaccharide composed of a single type of monosaccharide, that is a homopolysaccharide, the ending “-ose” of the monosaccharide is replaced with “-an”. For example, a glucose polymer is named glucan, a mannose polymer is named mannan, and a galactose polymer is named galactan. When the glycosidic linkages and configurations of the monosaccharides are known, they may be included as a prefix to the name, with the notation for glycosidic linkages preceding the symbols designating the configuration. The following example will help illustrate this concept:
-Glucan</div>
A heteropolysaccharide is a polymer containing more than one kind of monosaccharide residue. The parent chain contains only one type of monosaccharide and should be listed last with the ending “-an”, and the other types of monosaccharides listed in alphabetical order as “glyco-” prefixes. When there is no parent chain, all different monosaccharide residues are to be listed alphabetically as “glyco-” prefixes and the name should end with “-glycan”. The following example will help illustrate this concept:
-galacto)-(1→4)-β--Glucan</div> | 0 | Organic Chemistry |
One challenge when synthesising a metallic glass is that the techniques often only produce very small samples, due to the need for high cooling rates. 3D-printing methods have been suggested as a method to create larger bulk samples. Selective laser melting (SLM) is one example of an additive manufacturing method that has been used to make iron based metallic glasses. Laser foil printing (LFP) is another method where foils of the amorphous metals are stacked and welded together, layer by layer. | 8 | Metallurgy |
*Winkler test for dissolved oxygen: Used to determine oxygen concentration in water. Oxygen in water samples is reduced using manganese(II) sulfate, which reacts with potassium iodide to produce iodine. The iodine is released in proportion to the oxygen in the sample, thus the oxygen concentration is determined with a redox titration of iodine with thiosulfate using a starch indicator.
*Vitamin C: Also known as ascorbic acid, vitamin C is a powerful reducing agent. Its concentration can easily be identified when titrated with the blue dye Dichlorophenolindophenol (DCPIP) which becomes colorless when reduced by the vitamin.
*Benedicts reagent: Excess glucose in urine may indicate diabetes in a patient. Benedicts method is the conventional method to quantify glucose in urine using a prepared reagent. During this type of titration, glucose reduces cupric ions to cuprous ions which react with potassium thiocyanate to produce a white precipitate, indicating the endpoint.
*Bromine number: A measure of unsaturation in an analyte, expressed in milligrams of bromine absorbed by 100 grams of sample.
*Iodine number: A measure of unsaturation in an analyte, expressed in grams of iodine absorbed by 100 grams of sample. | 3 | Analytical Chemistry |
A Kingdon trap consists of a thin central wire, an outer cylindrical electrode and isolated end cap electrodes at both ends. A static applied voltage results in a radial logarithmic potential between the electrodes. In a Kingdon trap there is no potential minimum to store the ions; however, they are stored with a finite angular momentum about the central wire and the applied electric field in the device allows for the stability of the ion trajectories. In 1981, Knight introduced a modified outer electrode that included an axial quadrupole term that confines the ions on the trap axis. The dynamic Kingdon trap has an additional AC voltage that uses strong defocusing to permanently store charged particles. The dynamic Kingdon trap does not require the trapped ions to have angular momentum with respect to the filament. An Orbitrap is a modified Kingdon trap that is used for mass spectrometry. Though the idea has been suggested and computer simulations performed neither the Kingdon nor the Knight configurations were reported to produce mass spectra, as the simulations indicated mass resolving power would be problematic. | 7 | Physical Chemistry |
Electroanalytical methods utilize the potential or current of a electrochemical cell. The three main sections of this type of analysis are potentiometry, coulometry and voltammetry. Potentiometry measures the cells potential, coulometry measures the cells current, and voltammetry measures the change in current when cell potential changes. | 3 | Analytical Chemistry |
A myokine is one of several hundred cytokines or other small proteins (~5–20 kDa) and proteoglycan peptides that are produced and released by skeletal muscle cells (muscle fibers) in response to muscular contractions. They have autocrine, paracrine and/or endocrine effects; their systemic effects occur at picomolar concentrations.
Receptors for myokines are found on muscle, fat, liver, pancreas, bone, heart, immune, and brain cells. The location of these receptors reflects the fact that myokines have multiple functions. Foremost, they are involved in exercise-associated metabolic changes, as well as in the metabolic changes following training adaptation. They also participate in tissue regeneration and repair, maintenance of healthy bodily functioning, immunomodulation; and cell signaling, expression and differentiation. | 1 | Biochemistry |
Arthur Derek Campbell (27 May 1925 – 20 December 2020) was a New Zealand analytical chemist. He was a faculty member in the Department of Chemistry at the University of Otago from 1948 to 1988, becoming a professor emeritus on his retirement. | 3 | Analytical Chemistry |
The specific activity of an enzyme is another common unit. This is the activity of an enzyme per milligram of total protein (expressed in μmol min mg). Specific activity gives a measurement of enzyme purity in the mixture. It is the micro moles of product formed by an enzyme in a given amount of time (minutes) under given conditions per milligram of total proteins. Specific activity is equal to the rate of reaction multiplied by the volume of reaction divided by the mass of total protein. The SI unit is katal/kg, but a more practical unit is μmol/mgmin.
Specific activity is a measure of enzyme processivity (the capability of enzyme to be processed), at a specific (usually saturating) substrate concentration, and is usually constant for a pure enzyme.
An active site titration process can be done for the elimination of errors arising from differences in cultivation batches and/or misfolded enzyme and similar issues. This is a measure of the amount of active enzyme, calculated by e.g. titrating the amount of active sites present by employing an irreversible inhibitor. The specific activity should then be expressed as μmol min mg active enzyme. If the molecular weight of the enzyme is known, the turnover number, or μmol product per second per μmol of active enzyme, can be calculated from the specific activity. The turnover number can be visualized as the number of times each enzyme molecule carries out its catalytic cycle per second. | 1 | Biochemistry |
Faraday discovered that when the same amount of electric current is passed through different electrolytes connected in series, the masses of the substances deposited or liberated at the electrodes are directly proportional to their respective chemical equivalent/equivalent weight (). This turns out to be the molar mass () divided by the valence () | 7 | Physical Chemistry |
In organic chemistry, a guaianolide is a type of sesquiterpene lactone consisting of a gamma-lactone and either a cyclopentane or cyclopentene, both fused to a central cycloheptane or cycloheptene structure. There are two subclasses, structural isomers differing in the location that part of the lactone is bonded to the central ring, known as 6,12-guaianolides and 8,12-guaianolides.
Because some of the natural products in this class of tricyclic phytochemical have been found to be potentially biologically active, there has been interest in their chemical syntheses. The full biosynthetic origin of most of the known guaianolides has not been established, but the pathway is generally presumed to begin with the formation of a germacrene lactone derived from farnesyl pyrophosphate. | 0 | Organic Chemistry |
The membrane assembly consists of a pressure vessel with a membrane that allows feedwater to be pushed against it. The membrane must be strong enough to withstand the pressure. RO membranes are made in a variety of configurations. The two most common are spiral-wound and hollow-fiber.
Only part of the water pumped onto the membrane passes through. The left-behind "concentrate" passes along the saline side of the membrane and flushes away the salt and other remnants. The percentage of desalinated water is the "recovery ratio". This varies with salinity and system design parameters: typically 20% for small seawater systems, 40% – 50% for larger seawater systems, and 80% – 85% for brackish water. The concentrate flow is typically 3 bar/50 psi less than the feed pressure, and thus retains much of the input energy.
The desalinated water purity is a function of the feed water salinity, membrane selection and recovery ratio. To achieve higher purity a second pass can be added which generally requires another pumping cycle. Purity expressed as total dissolved solids typically varies from 100 to 400 parts per million (ppm or mg/litre) on a seawater feed. A level of 500 ppm is generally the upper limit for drinking water, while the US Food and Drug Administration classifies mineral water as water containing at least 250 ppm. | 3 | Analytical Chemistry |
The silicic acid leakage hypothesis (SALH) is a suggested mechanism that aims to explain the atmospheric CO variations between glacial and interglacial periods. This hypothesis proposes that during glacial periods, as a result of enhanced dust deposition in the southern ocean, diatoms consume less Si relative to nitrogen. The decrease in the Si:N uptake ratios leads to Si excess in the southern ocean, which leaks to lower latitudes of the ocean that are dominated by coccolithophores. As the Si concentrations rise, the diatom population may outcompete the coccolithophores, reducing the CaCO precipitation and altering ocean alkalinity and the carbonate pump. These changes would induce a new ocean-atmosphere steady state with lower atmospheric CO concentrations, consistent with the draw down of CO observed in the last glacial period. The δSi and δN isotopic values archived in the southern ocean diatom sediments has been used to examine this hypothesis, as the dynamics of Si and N supply and utilization during the last deglaciation could be interpreted from this record. In alignment with the silicic acid leakage hypothesis, these isotopic archives suggest that Si utilization in the southern ocean increased during the deglaciation. | 9 | Geochemistry |
Some patients with ovarian hyperstimulation syndrome may have mutations in the gene for FSHR, making them more sensitive to gonadotropin stimulation.
Women with 46 XX gonadal dysgenesis experience primary amenorrhea with hypergonadotropic hypogonadism. There are forms of 46 xx gonadal dysgenesis wherein abnormalities in the FSH-receptor have been reported and are thought to be the cause of the hypogonadism.
Polymorphism may affect FSH receptor populations and lead to poorer responses in infertile women receiving FSH medication for IVF.
Alternative splicing of the FSHR gene may be implicated in subfertility in males | 1 | Biochemistry |
Artificial chromosomes are manufactured chromosomes in the context of yeast artificial chromosomes (YACs), bacterial artificial chromosomes (BACs), or human artificial chromosomes (HACs). An artificial chromosome can carry a much larger DNA fragment than other vectors. YACs and BACs can carry a DNA fragment up to 300,000 nucleotides long. Three structural necessities of an artificial chromosome include an origin of replication, a centromere, and telomeric end sequences. | 1 | Biochemistry |
The alternative yeast nuclear code (translation table 12) is a genetic code found in certain yeasts. However, other yeast, including Saccharomyces cerevisiae, Candida azyma, Candida diversa, Candida magnoliae, Candida rugopelliculosa, Yarrowia lipolytica, and Zygoascus hellenicus, definitely use the standard (nuclear) code. | 1 | Biochemistry |
A hydrogen analyzer can be used for direct measurement of hydrogen in liquid aluminium. Direct monitoring of hydrogen is possible using an on-line quantitative measurement technology based on a closed-loop gas recirculation method though a porous ceramic probe.
Since its introduction in 1989, this gas recirculation method has been increasingly used by major aluminum producers.
An example of analyzer for direct hydrogen measurement in liquid aluminium is the Accurity. It works with a probe immersed in liquid aluminium and it uses the closed-loop recirculation method. | 8 | Metallurgy |
The majority of bitumen used commercially is obtained from petroleum. Nonetheless, large amounts of bitumen occur in concentrated form in nature. Naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic algae (diatoms) and other once-living things. These natural deposits of bitumen have been formed during the Carboniferous period, when giant swamp forests dominated many parts of the Earth. They were deposited in the mud on the bottom of the ocean or lake where the organisms lived. Under the heat (above 50 °C) and pressure of burial deep in the earth, the remains were transformed into materials such as bitumen, kerogen, or petroleum.
Natural deposits of bitumen include lakes such as the Pitch Lake in Trinidad and Tobago and Lake Bermudez in Venezuela. Natural seeps occur in the La Brea Tar Pits and the McKittrick Tar Pits in California, as well as in the Dead Sea.
Bitumen also occurs in unconsolidated sandstones known as "oil sands" in Alberta, Canada, and the similar "tar sands" in Utah, US.
The Canadian province of Alberta has most of the world's reserves, in three huge deposits covering , an area larger than England or New York state. These bituminous sands contain of commercially established oil reserves, giving Canada the third largest oil reserves in the world. Although historically it was used without refining to pave roads, nearly all of the output is now used as raw material for oil refineries in Canada and the United States.
The world's largest deposit of natural bitumen, known as the Athabasca oil sands, is located in the McMurray Formation of Northern Alberta. This formation is from the early Cretaceous, and is composed of numerous lenses of oil-bearing sand with up to 20% oil. Isotopic studies show the oil deposits to be about 110 million years old. Two smaller but still very large formations occur in the Peace River oil sands and the Cold Lake oil sands, to the west and southeast of the Athabasca oil sands, respectively. Of the Alberta deposits, only parts of the Athabasca oil sands are shallow enough to be suitable for surface mining. The other 80% has to be produced by oil wells using enhanced oil recovery techniques like steam-assisted gravity drainage.
Much smaller heavy oil or bitumen deposits also occur in the Uinta Basin in Utah, US. The Tar Sand Triangle deposit, for example, is roughly 6% bitumen.
Bitumen may occur in hydrothermal veins. An example of this is within the Uinta Basin of Utah, in the US, where there is a swarm of laterally and vertically extensive veins composed of a solid hydrocarbon termed Gilsonite. These veins formed by the polymerization and solidification of hydrocarbons that were mobilized from the deeper oil shales of the Green River Formation during burial and diagenesis.
Bitumen is similar to the organic matter in carbonaceous meteorites. However, detailed studies have shown these materials to be distinct. The vast Alberta bitumen resources are considered to have started out as living material from marine plants and animals, mainly algae, that died millions of years ago when an ancient ocean covered Alberta. They were covered by mud, buried deeply over time, and gently cooked into oil by geothermal heat at a temperature of . Due to pressure from the rising of the Rocky Mountains in southwestern Alberta, 80 to 55 million years ago, the oil was driven northeast hundreds of kilometres and trapped into underground sand deposits left behind by ancient river beds and ocean beaches, thus forming the oil sands. | 7 | Physical Chemistry |
A small fraction of electrons leave the electron transport chain before reaching complex IV. Premature electron leakage to oxygen results in the formation of superoxide. The relevance of this otherwise minor side reaction is that superoxide and other reactive oxygen species are highly toxic and are thought to play a role in several pathologies, as well as aging (the free radical theory of aging). Electron leakage occurs mainly at the Q site and is stimulated by antimycin A. Antimycin A locks the b hemes in the reduced state by preventing their re-oxidation at the Q site, which, in turn, causes the steady-state concentrations of the Q semiquinone to rise, the latter species reacting with oxygen to form superoxide. The effect of high membrane potential is thought to have a similar effect. Superoxide produced at the Qo site can be released both into the mitochondrial matrix and into the intermembrane space, where it can then reach the cytosol. This could be explained by the fact that Complex III might produce superoxide as membrane permeable HOO rather than as membrane impermeable O. | 1 | Biochemistry |
T. H. Henry analyzed and recorded the composition of wootz steel samples provided by the Royal School of Mines. Recording:
*Carbon (Combined) 1.34%
* Carbon (Uncombined) 0.31%
* Sulfur 0.17%
* Silicon 0.04%
* Arsenic 0.03%
Wootz steel was analyzed by Michael Faraday and recorded to contain 0.01-0.07% aluminium. Faraday, Messrs (et al.), and Stodart hypothesized that aluminium was needed in the steel and was important in forming the excellent properties of wootz steel. However T. H. Henry deduced that presence of aluminium in the Wootz used by these studies was due to slag, forming as silicates. Percy later reiterated that the quality of wootz steel does not depend on the presence of aluminium. | 8 | Metallurgy |
Some research has aimed to understand how OMZs have changed over geological time scales. Throughout the history of Earth's oceans, OMZs have fluctuated on long time scales, becoming larger or smaller depending on multiple variables. The factors that change OMZs are the amount of oceanic primary production resulting in increased respiration at greater depths, changes in the oxygen supply due to poor ventilation, and amount of oxygen supplied through thermohaline circulation. | 9 | Geochemistry |
Limit values for VOC emissions into indoor air are published by AgBB, AFSSET, California Department of Public Health, and others. These regulations have prompted several companies in the paint and adhesive industries to adapt with VOC level reductions their products. VOC labels and certification programs may not properly assess all of the VOCs emitted from the product, including some chemical compounds that may be relevant for indoor air quality. Each ounce of colorant added to tint paint may contain between 5 and 20 grams of VOCs. A dark color, however, could require 5–15 ounces of colorant, adding up to 300 or more grams of VOCs per gallon of paint. | 0 | Organic Chemistry |
Moungi Bawendi was born in Paris, France, the son of Tunisian mathematician Mohammed Salah Baouendi. After periods living in France and Tunisia, Bawendi and his family migrated to the United States when he was a child. They lived in West Lafayette, Indiana, as Salah worked in the math department at Purdue University. Bawendi graduated from West Lafayette Junior-Senior High School in 1978. | 7 | Physical Chemistry |
A miscibility gap is a region in a phase diagram for a mixture of components where the mixture exists as two or more phases – any region of composition of mixtures where the constituents are not completely miscible.
The IUPAC Gold Book defines miscibility gap as "Area within the coexistence curve of an isobaric phase diagram (temperature vs composition) or an isothermal phase diagram (pressure vs composition)."
A miscibility gap between isostructural phases may be described as the solvus, a term also used to describe the boundary on a phase diagram between a miscibility gap and other phases.
Thermodynamically, miscibility gaps indicate a maximum (e.g. of Gibbs energy) in the composition range. | 9 | Geochemistry |
Copper-catalyzed allylic substitutions are chemical reactions with unique regioselectivity compared to other transition-metal-catalyzed allylic substitutions such as the Tsuji-Trost reaction. They involve copper catalysts and "hard" carbon nucleophiles. The mechanism of copper-catalyzed allylic substitutions involves the coordination of copper to the olefin, oxidative addition and reductive elimination. Enantioselective versions of these reactions have been used in the synthesis of complex molecules, such as (R)-(-)-sporochnol and (S)-(-)-zearalenone. | 0 | Organic Chemistry |
Although most consider the French physicist Nicolas Sadi Carnot to be the first true thermodynamicist, the term thermodynamics itself wasnt coined until 1849 by Lord Kelvin in his publication An Account of Carnots Theory of the Motive Power of Heat.
The first thermodynamic textbook was written in 1859 by William Rankine, a civil and mechanical engineering professor at the University of Glasgow. | 7 | Physical Chemistry |
Colonies of the ant Temnothorax albipennis nest in small crevices between rocks. When the rocks shift and the nest is broken up, these ants must quickly choose a new nest to move into. During the first phase of the decision-making process, a small portion of the workers leave the destroyed nest and search for new crevices. When one of these scout ants finds a potential nest, she assesses the quality of the crevice based on a variety of factors including the size of the interior, the number of openings (based on light level), and the presence or absence of dead ants. The worker then returns to the destroyed nest, where she waits for a short period before recruiting other workers to follow her to the nest that she has found, using a process called tandem running. The waiting period is inversely related to the quality of the site; for instance, a worker that has found a poor site will wait longer than a worker that encountered a good site. As the new recruits visit the potential nest site and make their own assessment of its quality, the number of ants visiting the crevice increases. During this stage, ants may be visiting many different potential nests. However, because of the differences in the waiting period, the number of ants in the best nest will tend to increase at the greatest rate. Eventually, the ants in this nest will sense that the rate at which they encounter other ants has exceeded a particular threshold, indicating that the quorum number has been reached. Once the ants sense a quorum, they return to the destroyed nest and begin rapidly carrying the brood, queen, and fellow workers to the new nest. Scouts that are still tandem-running to other potential sites are also recruited to the new nest, and the entire colony moves. Thus, although no single worker may have visited and compared all of the available options, quorum sensing enables the colony as a whole to quickly make good decisions about where to move. | 1 | Biochemistry |
Khimera is a software product from Kintech Lab intended for calculation of the kinetic parameters of microscopic processes, thermodynamic and transport properties of substances and their mixtures in gases, plasmas and also of heterogeneous processes.
The development of a kinetic mechanism is a key stage of present-day technologies for the creation of hi-tech devices and processes in a wide range of fields, such as microelectronics, chemical industry, and the design and optimization of combustion engines and power stations.
Khimera with Chemical WorkBench, another software product from Kintech Lab, allows both the development of complex physical and chemical mechanisms and their validation. Essential feature of Khimera is its user-friendly interface for importing and utilizing the results of quantum-chemical calculations for estimating rate constants of elementary processes and thermodynamic and transport properties. | 7 | Physical Chemistry |
The Haber–Bosch process relies on catalysts to accelerate N hydrogenation. The catalysts are heterogeneous, solids that interact with gaseous reagents.
The catalyst typically consists of finely divided iron bound to an iron oxide carrier containing promoters possibly including aluminium oxide, potassium oxide, calcium oxide, potassium hydroxide, molybdenum, and magnesium oxide. | 7 | Physical Chemistry |
The plasticity region is at the top of deformation map (at the highest normalized stresses), and is below the boundary set by the ideal strength. In this region the strain rate involves an exponential term. This equation is shown below, where is the applied shear stress, is the shear modulus, is the energy barrier to dislocation glide, k is the Boltzmann constant, and is the "athermal flow strength" which is a function of the obstacles to dislocation glide. | 8 | Metallurgy |
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