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Aluminium granules are manufactured by the melting of primary or secondary aluminium and blown in air or vacuum, or are cast in sand and then sieved off. Other methods include casting of molten aluminium in water. | 8 | Metallurgy |
In anaerobic sediments and soils, 5β-coprostanol is stable for many hundreds of years enabling it to be used as an indicator of past faecal discharges. As such, records of 5β-coprostanol from paleo-environmental archives have been used to further constrain the timing of human settlements in a region, as well as reconstruct relative changes in human populations and agricultural activities over several thousand years. | 2 | Environmental Chemistry |
The enzyme responsible for apoptotic DNA fragmentation is the Caspase-Activated DNase (CAD). CAD is normally inhibited by another protein, the Inhibitor of Caspase Activated DNase (ICAD). During apoptosis, the apoptotic effector caspase, caspase-3, cleaves ICAD and thus causes CAD to become activated.
CAD cleaves DNA at internucleosomal linker sites between nucleosomes, protein-containing structures that occur in chromatin at ~180-bp intervals. This is because the DNA is normally tightly wrapped around histones, the core proteins of the nucleosomes. The linker sites are the only parts of the DNA strand that are exposed and thus accessible to CAD.
Degradation of nuclear DNA into nucleosomal units is one of the hallmarks of apoptotic cell death. It occurs in response to various apoptotic stimuli in a wide variety of cell types. Molecular characterization of this process identified a specific DNase (CAD, caspase-activated DNase) that cleaves chromosomal DNA in a caspase-dependent manner. CAD is synthesized with the help of ICAD (inhibitor of CAD), which works as a specific chaperone for CAD and is found complexed with ICAD in proliferating cells. When cells are induced to undergo apoptosis, caspase 3 cleaves ICAD to dissociate the CAD:ICAD complex, allowing CAD to cleave chromosomal DNA. Cells that lack ICAD or that express caspase-resistant mutant ICAD thus do not show DNA fragmentation during apoptosis, although they do exhibit some other features of apoptosis and die.
Even though much work has been performed on the analysis of apoptotic events, little information is available to link the timing of morphological features at the cell surface and in the nucleus to the biochemical degradation of DNA in the same cells. Apoptosis can be initiated by a myriad of different mechanisms in different cell types, and the kinetics of these events vary widely, from only a few minutes to several days depending on the cell system. The presence or absence of particular apoptotic event(s), including DNA fragmentation, depends on the "time window" at which the kinetic process of apoptosis is being investigated. Often this may complicate identification of apoptotic cells if cell populations are analyzed only at a single time point e.g. after induction of apoptosis. | 1 | Biochemistry |
dactinomycin - decarboxylation reaction - delta opioid receptor - denaturation (biochemistry) - dendrite - dendritic cell - dendritic spine - deoxyribonucleoprotein - deoxyribose - desmopressin - deuterium - developmental biology - dialysis (chemical) - diffusion - dimer - dinucleotide repeat - diploid - disaccharide - dissociation constant - disulfide bond - disulfide bridge - DNA - DNA fragmentation - DNA replication - DNA sequence - DNA topology - DNA transposable element - DNA virus - DNA-binding protein - dopamine D1 receptor - dopamine D2 receptor - dopamine receptor - double helix - Drosophila - drugs - dynorphin | 1 | Biochemistry |
Chirality can be traced back to 1812, when physicist Jean-Baptiste Biot found out about a phenomenon called "optical activity." Louis Pasteur, a famous student of Biot's, made a series of observations that led him to suggest that the optical activity of some substances is caused by their molecular asymmetry, which makes nonsuperimposable mirror-images. In 1848, Pasteur grew two different kinds of crystals from the racemic sodium ammonium salt of tartaric acid. He was the first person to separate enantiomeric crystals by hand. In fact Pasteur laid the foundations of stereochemistry and chirality.
In 1874, Jacobus Henricus van t Hoff came up with the idea of an asymmetric carbon atom. He said that all optically active carbon compounds have an asymmetric carbon atom. In the same year, Joseph Achille Le Bel only used asymmetry arguments and talked about the asymmetry of the molecules as a whole instead of the asymmetry of each carbon atom. So, Le Bels idea could be seen as the general theory of stereoisomerism, while van t Hoffs could be seen as a special case (restricted to tetrahedral carbon).
Soon, scientists started to look into what chiral compounds meant for living things. In 1903, Cushny was the first person to show that enantiomers of a chiral molecule have different biological effects. Lord Kelvin used the word "chiral" for the first time in 1904. | 4 | Stereochemistry |
Calcitriol enters the target cell and binds to the vitamin D receptor in the cytoplasm. This activated receptor enters the nucleus and binds to vitamin D response elements (VDRE) which are specific DNA sequences on genes. Transcription of these genes is stimulated and produces greater levels of the proteins which mediate the effects of vitamin D.
Some reactions of the cell to calcitriol appear to be too fast for the classical VDRE transcription pathway, leading to the discovery of various non-genomic actions of vitamin D. The membrane-bound PDIA3 likely serves as an alternate receptor in this pathway. The classical VDR may still play a role. | 1 | Biochemistry |
The synthesis of Malonyl-CoA consists of two half reactions. The first being the carboxylation of biotin with bicarbonate and the second being the transfer of the CO group to acetyl-CoA from carboxybiotin to allow for the formation of malonyl-CoA. Two different protein subassemblies, along with BCCP, are required for this two step reaction to be successful: biotin carboxylase (BC) and carboxyltransferase (CT). BCCP contains the biotin cofactor which is covalently bound to a lysine residue.
In fungi, mammals, and plant cytosols, all three of these components (BCCP, BC, and CT) exist on one polypeptide chain. However, most studies of this protein have been conducted on the E. coli form of the enzyme, where all three components exist as three separate complexes rather than being united on one polypeptide chain. | 1 | Biochemistry |
Robert Bob Ramage FRS (4 October 1935 — 16 October 2019) was an organic chemist, born in Glasgow, who specialised in the synthesis and biosynthesis of natural products, peptides, and proteins.
Following his undergraduate degree in chemistry and the University of Glasgow, he stayed on for a PhD in organic chemistry. After his time at Glasgow, he followed his interest in natural products synthesis to Harvard and then Basel, before taking up a lectureship in organic chemistry at the University of Liverpool where his attention was drawn to peptides.
His peptide synthesis research continued at the University of Manchester Institute of Science and Technology (UMIST), where he also served as head of department. He returned to Scotland in 1984, taking up the Forbes chair of organic chemistry at the University of Edinburgh, where he remained until retirement in 2000.
Outside of academia, in 1994 he founded the company Albachem, which utilised his work with peptides.
He was elected Fellow of the Royal Society of Chemistry (1977), Royal Society of Edinburgh (1986), and the Royal Society (1992). | 0 | Organic Chemistry |
Fast Sulphon Black F is a complexometric indicator used with EDTA, almost exclusively used in copper complexation determination. | 3 | Analytical Chemistry |
An E1 reaction consists of a unimolecular elimination, where the rate determining step of the mechanism depends on the removal of a single molecular species. This is a two-step mechanism. The more stable the carbocation intermediate is, the faster the reaction will proceed, favoring the products. Stabilization of the carbocation intermediate lowers the activation energy. The reactivity order is (CH3)3C- > (CH3)2CH- > CH3CH2- > CH3-.
Furthermore, studies describe a typical kinetic resolution process that starts out with two enantiomers that are energetically equivalent and, in the end, forms two energy-inequivalent intermediates, referred to as diastereomers. According to Hammond's postulate, the more stable diastereomer is formed faster. | 7 | Physical Chemistry |
STAT1 loss of function, therefore STAT1 deficiency can have many variants. There are two main genetic impairments that can cause response to interferons type I and III. First there can be autosomal recessive partial or even complete deficiency of STAT1. That causes intracellular bacterial diseases or viral infections and impaired IFN a, b, g and IL27 responses are diagnosed. In partial form there can also be found high levels of IFNg in blood serum. When tested from whole blood, monocytes do not respond to BCG and IFNg doses with IL-12 production. In complete recessive form there is a very low response to anti-viral and antimycotical medication. Second, partial STAT1 deficiency can also be an autosomal dominant mutation; phenotypically causing impaired IFNg responses and causing patients to suffer with selective intracellular bacterial diseases (MSMD).
In knock-out mice prepared in the 90s, a low amount of CD4 and CD25 regulatory T-cells and almost no IFNa, b and g response was discovered, which lead to parasital, viral and bacterial infections. The very first reported case of STAT1 deficiency in human was an autosomal dominant mutation and patients were showing propensity to mycobacterial infections. Another case reported was about an autosomal recessive form. 2 related patients had a homozygous missense STAT1 mutation which caused impaired splicing, therefore a defect in mature protein. Patients had partially damaged response to both IFNa and IFNg. Scientists now claim that recessive STAT1 deficiency is a new form of primary immunodeficiency and whenever a patient suffers sudden, severe and unexpected bacterial and viral infections, should be considered as potentially STAT1 deficient.
Interferons induce the formation of two transcriptional activators: gamma-activating factor (GAF) and interferon-stimulated gamma factor 3 (ISGF3). A natural heterozygous germline STAT1 mutation associated with susceptibility to mycobacterial but not viral disease was found in two unrelated patients with unexplained mycobacterial disease. This mutation caused a loss of GAF and ISGF3 activation but was dominant for one cellular phenotype and recessive for the other. It impaired the nuclear accumulation of GAF but not of ISGF3 in cells stimulated by interferons, implying that the antimycobacterial but not the antiviral effects of human interferons are mediated by GAF. More recently, two patients have been identified with homozygous STAT-1 mutations who developed both post–BCG vaccination disseminated disease and lethal viral infections. The mutations in these patients caused a complete lack of STAT-1 and resulted in a lack of formation of both GAF and ISGF3. | 1 | Biochemistry |
William C. Brown demonstrated in 1964, during Walter Cronkite's CBS News program, a microwave-powered model helicopter that received all the power it needed for flight from a microwave beam. Between 1969 and 1975, Bill Brown was technical director of a JPL Raytheon program that beamed 30 kW of power over a distance of at 9.6% efficiency.
Microwave power transmission of tens of kilowatts has been well proven by existing tests at Goldstone in California (1975) and Grand Bassin on Reunion Island (1997).
More recently, microwave power transmission has been demonstrated, in conjunction with solar energy capture, between a mountaintop in Maui and the island of Hawaii (92 miles away), by a team under John C. Mankins.
Technological challenges in terms of array layout, single radiation element design, and overall efficiency, as well as the associated theoretical limits are presently a subject of research, as it was demonstrated by the Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" held during the 2010 IEEE Symposium on Antennas and Propagation. In 2013, a useful overview was published, covering technologies and issues associated with microwave power transmission from space to ground. It includes an introduction to SPS, current research and future prospects.
Moreover, a review of current methodologies and technologies for the design of antenna arrays for microwave power transmission appeared in the Proceedings of the IEEE. | 7 | Physical Chemistry |
Competitive binding experiments aim to determine the binding of a labeled radioligand at one specific concentration while subjected to various concentrations of a competitor, usually an unlabeled ligand. There are many purposes to competitive binding experiments, including being able to validate that the radioligand of interest will bind to the receptor with the expected affinity and potency even in the presence of a competitor. This experiment would also help determine if the radioligand will be able to recognize and bind to the correct receptor. Competitive binding experiments also serve to study the binding ability of a low-affinity drug, as it can be used as an unlabeled competitor. Finally, receptor number and affinity can also be determined through this experiment. | 1 | Biochemistry |
Histamine N-methyltransferase is encoded by a single gene, called HNMT, which has been mapped to chromosome 2 in humans.
Three transcript variants have been identified for this gene in humans, which produce different protein isoforms due to alternative splicing, which allows a single gene to code for multiple proteins by including or excluding particular exons of a gene in the final mRNA produced from that gene. Of those isoforms, only one has histamine-methylating activity.
In the human genome, six exons from the 50-kb HNMT contribute to forming a unique mRNA species, approximately 1.6 kb in size. This mRNA is then translated into the cytosolic enzyme histamine N-methyltransferase, comprising 292 amino acids, of which 130 amino acids are a conserved sequence. HNMT does not have promoter cis-elements, such as TATA and CAAT boxes. | 1 | Biochemistry |
There have been a number of reported procedures which take advantage of a chemical reagent/catalyst to perform racemization of the starting material and an enzyme to selectively react with one enantiomer, called chemoenzymatic dynamic kinetic resolutions. PSL-C was utilized along with a ruthenium catalyst (for racemization) to produce enantiopure (>95% ee) δ-hydroxylactones.
More recently, secondary alcohols have been resolved by Bäckvall with yields up to 99% and ee's up to >99% utilizing CALB and a ruthenium racemization complex.
A second type of chemoenzymatic dynamic kinetic resolution involves a π-allyl complex from an allylic acetate with palladium. Here, racemization occurs with loss of the acetate, forming a cationic complex with the transition metal center, as shown below. Palladium has been shown to facilitate this reaction, while ruthenium has been shown to affect a similar reaction, also shown below. | 4 | Stereochemistry |
The relative entropy was introduced by Solomon Kullback and Richard Leibler in as "the mean information for discrimination between and per observation from ", where one is comparing two probability measures , and are the hypotheses that one is selecting from measure (respectively). They denoted this by , and defined the "divergence between and " as the symmetrized quantity , which had already been defined and used by Harold Jeffreys in 1948. In , the symmetrized form is again referred to as the "divergence", and the relative entropies in each direction are referred to as a "directed divergences" between two distributions; Kullback preferred the term discrimination information. The term "divergence" is in contrast to a distance (metric), since the symmetrized divergence does not satisfy the triangle inequality. Numerous references to earlier uses of the symmetrized divergence and to other statistical distances are given in . The asymmetric "directed divergence" has come to be known as the Kullback–Leibler divergence, while the symmetrized "divergence" is now referred to as the Jeffreys divergence. | 7 | Physical Chemistry |
Because of the small size of the fluidic conduits, nanofluidic structures are naturally applied in situations demanding that samples be handled in exceedingly small quantities, including Coulter counting,
analytical separations and determinations of biomolecules, such as proteins and DNA,
and facile handling of mass-limited samples. One of the more promising areas of nanofluidics is its potential for integration into microfluidic systems, i.e. micrototal analytical systems or lab-on-a-chip structures. For instance, NCAMs, when incorporated into microfluidic devices, can reproducibly perform digital switching, allowing transfer of fluid from one microfluidic channel to another,
selectivity separate and transfer analytes by size and mass,
mix reactants efficiently,
and separate fluids with disparate characteristics.
In addition, there is a natural analogy between the fluid handling capabilities of nanofluidic structures and the ability of electronic components to control the flow of electrons and holes. This analogy has been used to realize active electronic functions such as rectification
and field-effect
and bipolar transistor
action with ionic currents. Application of nanofluidics is also to nano-optics for producing tuneable microlens array
Nanofluidics have had a significant impact in biotechnology, medicine and clinical diagnostics with the development of lab-on-a-chip devices for PCR and related techniques. Attempts have been made to understand the behaviour of flowfields around nanoparticles in terms of fluid forces as a function of Reynolds and Knudsen number using computational fluid dynamics. The relationship between lift, drag and Reynolds number has been shown to differ dramatically at the nanoscale compared with macroscale fluid dynamics. | 7 | Physical Chemistry |
The Sm proteins are synthesized in the cytoplasm by ribosomes translating Sm messenger RNA, just like any other protein. These are stored in the cytoplasm in the form of three partially assembled rings complexes all associated with the pICln protein. They are a 6S pentamer complex of SmD1, SmD2, SmF, SmE and SmG with pICln, a 2-4S complex of SmB, possibly with SmD3 and pICln and the 20S methylosome, which is a large complex of SmD3, SmB, SmD1, pICln and the arginine methyltransferase-5 (PRMT5) protein. SmD3, SmB and SmD1 undergo post-translational modification in the methylosome. These three Sm proteins have repeated arginine-glycine motifs in the C-terminal ends of SmD1, SmD3 and SmB, and the arginine side chains are symmetrically dimethylated to ω-N, N-dimethyl-arginine. It has been suggested that pICln, which occurs in all three precursor complexes but is absent in the mature snRNPs, acts as a specialized chaperone, preventing premature assembly of Sm proteins. | 1 | Biochemistry |
In the silicification of woods, silica dissolves in hydrothermal fluid and seeps into lignin in cell walls. Precipitation of silica out of the fluids produces silica deposition within the voids, especially in the cell walls. Cell materials are broken down by the fluids, yet the structure remains stable due to the development of minerals. Cell structures are slowly replaced by silica. Continuous penetration of siliceous fluids results in different stages of silicification ie. primary and secondary. The loss of fluids over time leads to the cementation of silicified woods through late silica addition.
The rate of silicification depends on a few factors:
1) Rate of breakage of original cells
2) Availability of silica sources and silica content in the fluid
3) Temperature and pH of silicification environment
4) Interference of other diagenetic processes
These factors affect the silicification process in many ways. The rate of breakage of original cells controls the development of the mineral framework, hence the replacement of silica. Availability of silica directly determines the silica content in fluids. The higher the silica content, the faster silicification could take place. The same concept applies to the availability of hydrothermal fluids. The temperature and pH of the environment determine the condition for silicification to occur. This is closely connected to the burial depth or association with volcanic events. Interference of other diagenetic processes could sometimes create disturbance to silicification. The relative time of silicification to other geological processes could serve as a reference for further geological interpretations. | 9 | Geochemistry |
Ultrapotassic igneous rocks are a class of rare, volumetrically minor, generally ultramafic or mafic silica-depleted igneous rocks.
While there are debates on the exact classifications of ultrapotassic rocks, they are defined by using the chemical screens KO/NaO > 3 in much of the scientific literature. However caution is indicated in interpreting the use of the term "ultrapotassic", and the nomenclature of these rocks continues to be debated, with some classifications using KO/NaO > 2 to indicate a rock is ultrapotassic. | 9 | Geochemistry |
Solventogenesis is the biochemical production of solvents (usually acetone and butanol) by Clostridium species. It is the second phase of ABE fermentation. | 1 | Biochemistry |
As Pol I escapes and clears the promoter, UBF and SL1 remain-promoter bound, ready to recruit another Pol I. Indeed, each active rDNA gene can be transcribed multiple times simultaneously, as opposed to Pol II-transcribed genes, which associate with only one complex at a time. While elongation proceeds unimpeded in vitro, it is unclear at this point whether this process happens in a cell, given the presence of nucleosomes. Pol I does seem to transcribe through nucleosomes, either bypassing or disrupting them, perhaps assisted by chromatin-remodeling activities. In addition, UBF might also act as positive feedback, enhancing Pol I elongation through an anti-repressor function. An additional factor, TIF-IC, can also stimulate the overall rate of transcription and suppress pausing of Pol I. As Pol I proceeds along the rDNA, supercoils form both ahead of and behind the complex. These are unwound by topoisomerase I or II at regular intervals, similar to what is seen in Pol II-mediated transcription.
Elongation is likely to be interrupted at sites of DNA damage. Transcription-coupled repair occurs similarly to Pol II-transcribed genes and requires the presence of several DNA repair proteins, such as TFIIH, CSB, and XPG. | 1 | Biochemistry |
Real-time stability studies simply hold a set of RM units at a proposed storage temperature and test a proportion of them at regular intervals. The results are usually assessed by inspection and by linear regression to determine whether there is a significant change in measured value over time. | 3 | Analytical Chemistry |
The instantaneous motion of a rigid body may be the combination of rotation about an axis (the screw axis) and a translation along that axis. This screw move is characterized by the velocity vector for the translation and the angular velocity vector in the same or opposite direction. If these two vectors are constant and along one of the principal axes of the body, no external forces are needed for this motion (moving and spinning]]). As an example, if gravity and drag are ignored, this is the motion of a bullet fired from a rifled gun. | 3 | Analytical Chemistry |
The carbon center of a nitrile is electrophilic, hence it is susceptible to nucleophilic addition reactions:
* with an organozinc compound in the Blaise reaction
* with alcohols in the Pinner reaction.
* with amines, e.g. the reaction of the amine sarcosine with cyanamide yields creatine
* Nitriles react in Friedel–Crafts acylation in the Houben–Hoesch reaction to ketones | 0 | Organic Chemistry |
Jelly-falls are marine carbon cycling events whereby gelatinous zooplankton, primarily cnidarians, sink to the seafloor and enhance carbon and nitrogen fluxes via rapidly sinking particulate organic matter. These events provide nutrition to benthic megafauna and bacteria. Jelly-falls have been implicated as a major “gelatinous pathway” for the sequestration of labile biogenic carbon through the biological pump. These events are common in protected areas with high levels of primary production and water quality suitable to support cnidarian species. These areas include estuaries and several studies have been conducted in fjords of Norway. | 9 | Geochemistry |
Iron was extracted from iron–nickel alloys, which comprise about 6% of all meteorites that fall on the Earth. That source can often be identified with certainty because of the unique crystalline features (Widmanstätten patterns) of that material, which are preserved when the metal is worked cold or at low temperature. Those artifacts include, for example, a bead from the 5th millennium BC found in Iran and spear tips and ornaments from ancient Egypt and Sumer around 4000 BC.
These early uses appear to have been largely ceremonial or decorative. Meteoric iron is very rare, and the metal was probably very expensive, perhaps more expensive than gold. The early Hittites are known to have bartered iron (meteoric or smelted) for silver, at a rate of 40 times the iron's weight, with Assyria in the first centuries of the second millennium BC.
Meteoric iron was also fashioned into tools in the Arctic when the Thule people of Greenland began making harpoons, knives, ulus and other edged tools from pieces of the Cape York meteorite. Typically pea-size bits of metal were cold-hammered into disks and fitted to a bone handle. These artifacts were also used as trade goods with other Arctic peoples: tools made from the Cape York meteorite have been found in archaeological sites more than distant. When the American polar explorer Robert Peary shipped the largest piece of the meteorite to the American Museum of Natural History in New York City in 1897, it still weighed over 33 tons. Another example of a late use of meteoric iron is an adze from around 1000 AD found in Sweden. | 8 | Metallurgy |
Recovery of metals from oxide matrixes is generally carried out using mineral acids. However, electrochemical dissolution of metal oxides in DES can allow to enhance the dissolution up to more than 10 000 times in pH neutral solutions.
Studies have shown that ionic oxides such as ZnO tend to have high solubility in ChCl:malonic acid, ChCl:urea and Ethaline, which can resemble the solubilities in aqueous acidic solutions, e.g., HCl. Covalent oxides such as TiO, however, exhibits almost no solubility. The electrochemical dissolution of metal oxides is strongly dependent on the proton activity from the HBD, i.e. capability of the protons to act as oxygen acceptors, and on the temperature. It has been reported that eutectic ionic fluids of lower pH-values, such as ChCl:oxalic acid and ChCl:lactic acid, allow a better solubility than that of higher pH (e.g., ChCl:acetic acid). Hence, different solubilities can be obtained by using, for instance, different carboxylic acids as HBD. | 8 | Metallurgy |
Gluconeogenesis is a metabolic pathway consisting of a series of eleven enzyme-catalyzed reactions, resulting in the generation of glucose from non-carbohydrates substrates. The beginning of this process takes place in the mitochondrial matrix, where pyruvate molecules are found. A pyruvate molecule is carboxylated by a pyruvate carboxylase enzyme, activated by a molecule each of ATP and water. This reaction results in the formation of oxaloacetate. NADH reduces oxaloacetate to malate. This transformation is needed to transport the molecule out of the mitochondria. Once in the cytosol, malate is oxidized to oxaloacetate again using NAD+. Then oxaloacetate remains in the cytosol, where the rest of reactions will take place. Oxaloacetate is later decarboxylated and phosphorylated by phosphoenolpyruvate carboxykinase and becomes 2-phosphoenolpyruvate using guanosine triphosphate (GTP) as phosphate source. Glucose is obtained after further downstream processing. | 1 | Biochemistry |
The components of bitumen include four main classes of compounds:
* Naphthene aromatics (naphthalene), consisting of partially hydrogenated polycyclic aromatic compounds
* Polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material
* Saturated hydrocarbons; the percentage of saturated compounds in asphalt correlates with its softening point
* Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds
Bitumen typically contains, elementally 80% by weight of carbon; 10% hydrogen; up to 6% sulfur; and molecularly, between 5 and 25% by weight of asphaltenes dispersed in 90% to 65% maltenes. Most natural bitumens also contain organosulfur compounds, Nickel and vanadium are found at <10 parts per million, as is typical of some petroleum. The substance is soluble in carbon disulfide. It is commonly modelled as a colloid, with asphaltenes as the dispersed phase and maltenes as the continuous phase. "It is almost impossible to separate and identify all the different molecules of bitumen, because the number of molecules with different chemical structure is extremely large".
Asphalt may be confused with coal tar, which is a visually similar black, thermoplastic material produced by the destructive distillation of coal. During the early and mid-20th century, when town gas was produced, coal tar was a readily available byproduct and extensively used as the binder for road aggregates. The addition of coal tar to macadam roads led to the word "tarmac", which is now used in common parlance to refer to road-making materials. However, since the 1970s, when natural gas succeeded town gas, bitumen has completely overtaken the use of coal tar in these applications. Other examples of this confusion include La Brea Tar Pits and the Canadian tar sands, both of which actually contain natural bitumen rather than tar. "Pitch" is another term sometimes informally used at times to refer to asphalt, as in Pitch Lake. | 7 | Physical Chemistry |
In chemistry, the Biuret test (IPA: , ), also known as Piotrowskis test, is a chemical test used for detecting the presence of at least two peptide bonds in a molecule. In the presence of peptides, a copper(II) ion forms mauve-colored coordination complexes in an alkaline solution. The reaction was first observed in 1833; In Poland, the biuret test is also known as Piotrowskis test in honor of the Polish physiologist who independently rediscovered it in 1857. Several variants on the test have been developed, such as the BCA test and the Modified Lowry test.
The biuret reaction can be used to assess the concentration of proteins because peptide bonds occur with the same frequency per amino acid in the peptide. The intensity of the color, and hence the absorption at 540 nm, is directly proportional to the protein concentration, according to the Beer–Lambert law.
Despite its name, the reagent does not in fact contain biuret . The test is named so because it also gives a positive reaction to the peptide-like bonds in the biuret molecule.
In this assay, the copper(II) binds with nitrogen atoms present in the peptides of proteins. In a secondary reaction, the copper(II) is reduced to copper(I). Buffers, such as Tris and ammonia interfere with this assay, therefore rendering this assay inappropriate for protein samples purified from ammonium sulfate precipitation. Due to its insensitivity and little interference by free amino acids, this assay is most useful for whole tissue samples and other sources with high protein concentration. | 3 | Analytical Chemistry |
In condensed matter physics, an ultracold atom is an atom with a temperature near absolute zero. At such temperatures, an atom's quantum-mechanical properties become important.
To reach such low temperatures, a combination of several techniques typically has to be used. First, atoms are trapped and pre-cooled via laser cooling in a magneto-optical trap. To reach the lowest possible temperature, further cooling is performed using evaporative cooling in a magnetic or optical trap. Several Nobel prizes in physics are related to the development of the techniques to manipulate quantum properties of individual atoms (e.g. 1989, 1996, 1997, 2001, 2005, 2012, 2018).
Experiments with ultracold atoms study a variety of phenomena, including quantum phase transitions, Bose–Einstein condensation (BEC), bosonic superfluidity, quantum magnetism, many-body spin dynamics, Efimov states, Bardeen–Cooper–Schrieffer (BCS) superfluidity and the BEC–BCS crossover. Some of these research directions utilize ultracold atom systems as quantum simulators to study the physics of other systems, including the unitary Fermi gas and the Ising and Hubbard models. Ultracold atoms could also be used for realization of quantum computers. | 7 | Physical Chemistry |
Electrochemical quartz crystal microbalance (EQCM) is the combination of electrochemistry and quartz crystal microbalance, which was generated in the eighties. Typically, an EQCM device contains an electrochemical cells part and a QCM part. Two electrodes on both sides of the quartz crystal serve two purposes. Firstly, an alternating electric field is generated between the two electrodes for making up the oscillator. Secondly, the electrode contacting electrolyte is used as a working electrode (WE), together with a counter electrode (CE) and a reference electrode (RE), in the potentiostatic circuit constituting the electrochemistry cell. Thus, the working electrode of electrochemistry cell is the sensor of QCM.
As a high mass sensitive in-situ measurement, EQCM is suitable to monitor the dynamic response of reactions at the electrode–solution interface at the applied potential. When the potential of a QCM metal electrode changes, a negative or positive mass change is monitored depending on the ratio of anions adoption on the electrode surface and the dissolution of metal ions into solution. | 7 | Physical Chemistry |
The majority of proteins in a cell are the product of messenger RNA transcribed from nuclear genes, including most of the proteins of the organelles, which are produced in the cytoplasm like all nuclear gene products and then transported to the organelle. Genes in the nucleus are arranged in a linear fashion upon chromosomes, which serve as the scaffold for replication and the regulation of gene expression. As such, they are usually under strict copy-number control, and replicate a single time per cell cycle. Nuclear cells such as platelets do not possess nuclear DNA and therefore must have alternative sources for the RNA that they need to generate proteins. With the nuclear genome's 3.3 billion DNA base pairs in humans, one good example of a nuclear gene is MDH1 or the malate dehydrogenase 1 gene. In various metabolic pathways, including the citric acid cycle, MDH1 is a protein-coding gene that encodes an enzyme that catalyzes the NAD/NADH-dependent, reversible oxidation of malate to oxaloacetate. This gene codes for the cytosolic isozyme, which is involved in the malate-aspartate shuttle, which allows malate to cross past the mitochondrial membrane and be converted to oxaloacetate to perform further cellular functions. This gene among many exhibits its huge purposeful role in the entirety of an organism’s physiologic function. Although non-nuclear genes may exist in its functional nature, the role of nuclear genes in response and in coordination with non-nuclear genes is fundamental. | 1 | Biochemistry |
Autophagy is a self-degradative mechanism that regulates energy sources during growth and reaction to dietary stress. Autophagy also cleans up after itself, clearing aggregated proteins, cleaning damaged structures including mitochondria and endoplasmic reticulum and eradicating intracellular infections. Additionally, autophagy has antiviral and antibacterial roles within the cell, and it is involved at the beginning of distinctive and adaptive immune responses to viral and bacterial contamination. Some viruses include virulence proteins that prevent autophagy, while others utilize autophagy elements for intracellular development or cellular splitting. Macro autophagy, micro autophagy, and chaperon-mediated autophagy are the three basic types of autophagy. When macro autophagy is triggered, an exclusion membrane incorporates a section of the cytoplasm, generating the autophagosome, a distinctive double-membraned organelle. The autophagosome then joins the lysosome to create an autolysosome, with lysosomal enzymes degrading the components. In micro autophagy, the lysosome or vacuole engulfs a piece of the cytoplasm by invaginating or protruding the lysosomal membrane to enclose the cytosol or organelles. The chaperone-mediated autophagy (CMA) protein quality assurance by digesting oxidized and altered proteins under stressful circumstances and supplying amino acids through protein denaturation. Autophagy is the primary intrinsic degradative system for peptides, fats, carbohydrates, and other cellular structures. In both physiologic and stressful situations, this cellular progression is vital for upholding the correct cellular balance. Autophagy instability leads to a variety of illness symptoms, including inflammation, biochemical disturbances, aging, and neurodegenerative, due to its involvement in controlling cell integrity. The modification of the autophagy-lysosomal networks is a typical hallmark of many neurological and muscular illnesses. As a result, autophagy has been identified as a potential strategy for the prevention and treatment of various disorders. Many of these disorders are prevented or improved by consuming polyphenol in the meal. As a result, natural compounds with the ability to modify the autophagy mechanism are seen as a potential therapeutic option. The creation of the double membrane (phagophore), which would be known as nucleation, is the first step in macro-autophagy. The phagophore approach indicates dysregulated polypeptides or defective organelles that come from the cell membrane, Golgi apparatus, endoplasmic reticulum, and mitochondria. With the conclusion of the autophagocyte, the phagophore's enlargement comes to an end. The auto-phagosome combines with the lysosomal vesicles to formulate an auto-lysosome that degrades the encapsulated substances, referred to as phagocytosis. | 1 | Biochemistry |
Within molecular and cell biology, temporal feedback, also referred to as interlinked or interlocked feedback, is a biological regulatory motif in which fast and slow positive feedback loops are interlinked to create "all or none" switches. This interlinking produces separate, adjustable activation and de-activation times. This type of feedback is thought to be important in cellular processes in which an "all or none" decision is a necessary response to a specific input. The mitotic trigger, polarization in budding yeast, mammalian calcium signal transduction, EGF receptor signaling, platelet activation, and Xenopus oocyte maturation are examples for interlinked fast and slow multiple positive feedback systems.
In biological systems, temporal feedback is a ubiquitous signal transduction motif that allows systems to convert graded inputs into decisive, all-or-none digital outputs. A system with interlinked fast and slow feedback loops produces a dual-time switch, which is rapidly inducible and robust to noise during stimulus. In contrast, a single fast or slow loop is separately responsible for the speed of switching and the stability of switches. Computer simulation studies have shown that linking two loops of the same kind brings no overall advantage over having a single loop, however the dual-loop switch performs in a monostable regime. Both single and dual loops can behave as a bistable switch. Several computational models have been produced to demonstrate the responses of single and dual positive feedback loop switches to stimuli. | 1 | Biochemistry |
One of the most anticipated targets for cloning was once the woolly mammoth, but attempts to extract DNA from frozen mammoths have been unsuccessful, though a joint Russo-Japanese team is currently working toward this goal. In January 2011, it was reported by Yomiuri Shimbun that a team of scientists headed by Akira Iritani of Kyoto University had built upon research by Dr. Wakayama, saying that they will extract DNA from a mammoth carcass that had been preserved in a Russian laboratory and insert it into the egg cells of an Asian elephant in hopes of producing a mammoth embryo. The researchers said they hoped to produce a baby mammoth within six years. It was noted, however that the result, if possible, would be an elephant-mammoth hybrid rather than a true mammoth. Another problem is the survival of the reconstructed mammoth: ruminants rely on a symbiosis with specific microbiota in their stomachs for digestion.
In 2022, scientists showed major limitations and the scale of challenge of genetic-editing-based de-extinction, suggesting resources spent on more comprehensive de-extinction projects such as of the woolly mammoth may currently not be well allocated and substantially limited. Their analyses "show that even when the extremely high-quality Norway brown rat (R. norvegicus) is used as a reference, nearly 5% of the genome sequence is unrecoverable, with 1,661 genes recovered at lower than 90% completeness, and 26 completely absent", complicated further by that "distribution of regions affected is not random, but for example, if 90% completeness is used as the cutoff, genes related to immune response and olfaction are excessively affected" due to which "a reconstructed Christmas Island rat would lack attributes likely critical to surviving in its natural or natural-like environment".
In a 2021 online session of the Russian Geographical Society, Russias defense minister Sergei Shoigu mentioned using the DNA of 3,000-year-old Scythian warriors to potentially bring them back to life. The idea was described as absurd at least at this point in news reports and it was noted that Scythians likely werent skilled warriors by default.
The idea of cloning Neanderthals or bringing them back to life in general is controversial but some scientists have stated that it may be possible in the future and have outlined several issues or problems with such as well as broad rationales for doing so. | 1 | Biochemistry |
An alternative preparation of Grignard reagents involves transfer of Mg from a preformed Grignard reagent to an organic halide. Other organomagnesium reagents are used as well. This method offers the advantage that the Mg transfer tolerates many functional groups. An illustrative reaction involves isopropylmagnesium chloride and aryl bromide or iodides: | 0 | Organic Chemistry |
CPA-1 and CPA-2 (and, it is presumed, all other CPAs) employ a zinc ion within the protein for hydrolysis of the peptide bond at the C-terminal end of an amino acid residue. Loss of the zinc leads to loss of activity, which can be replaced easily by zinc, and also by some other divalent metals (cobalt, nickel). Carboxypeptidase A is produced in the pancreas and is crucial to many processes in the human body to include digestion, post-translational modification of proteins, blood clotting, and reproduction. | 1 | Biochemistry |
The concatemerization process generates libraries of concatamers for the ELPs. Concatamers are oligomeric products of ligating a single gene with itself. This will result in repeat segments of a gene, all of which can be transcribed and translated immediately to produce the ELP of interest. A major problem with this synthetic route is that the number of gene repeat segments ligated together to form the concatamer cannot be controlled, leading to ELPs of different sizes, from which the ELP of a desired size must be isolated. | 7 | Physical Chemistry |
In TEM, the electron beam passes through a thin film of the material as illustrated in Figure 10. Before and after the sample the beam is manipulated by the electron optics including magnetic lenses, deflectors and apertures; these act on the electrons similar to how glass lenses focus and control light. Optical elements above the sample are used to control the incident beam which can range from a wide and parallel beam to one which is a converging cone and can be smaller than an atom, 0.1 nm. As it interacts with the sample, part of the beam is diffracted and part is transmitted without changing its direction. This occurs simultaneously as electrons are everywhere until they are detected (wavefunction collapse) according to the Copenhagen interpretation.
Below the sample, the beam is controlled by another set of magnetic lneses and apertures. Each set of initially parallel rays (a plane wave) is focused by the first lens (objective) to a point in the back focal plane of this lens, forming a spot on a detector; a map of these directions, often an array of spots, is the diffraction pattern. Alternatively the lenses can form a magnified image of the sample. Herein the focus is on collecting a diffraction pattern; for other information see the pages on TEM and scanning transmission electron microscopy. | 7 | Physical Chemistry |
Dragomabin is a bio-active isolate of marine cyanobacteria, Lyngbya majuscula, which has been shown to have good antimalarial activity. | 0 | Organic Chemistry |
The gal operon is a prokaryotic operon, which encodes enzymes necessary for galactose metabolism. Repression of gene expression for this operon works via binding of repressor molecules to two operators. These repressors dimerize, creating a loop in the DNA. The loop as well as hindrance from the external operator prevent RNA polymerase from binding to the promoter, and thus prevent transcription. Additionally, since the metabolism of galactose in the cell is involved in both anabolic and catabolic pathways, a novel regulatory system using two promoters for differential repression has been identified and characterized within the context of the gal operon. | 1 | Biochemistry |
Primary sources from the group of Irma Rantanen at University of Turku, Finland claim that SLS-containing pastes cause more dry mouth (xerostomia) than their proposed alternative. However, a 2011 Cochrane review of these studies, and of the more general area, concludes that there "is no strong evidence... that any topical therapy is effective for relieving the symptom of dry mouth." | 1 | Biochemistry |
Some researchers also identify a third class of transposable elements, which has been described as "a grab-bag consisting of transposons that dont clearly fit into the other two categories". Examples of such TEs are the Foldback (FB) elements of Drosophila melanogaster, the TU elements of Strongylocentrotus purpuratus', and Miniature Inverted-repeat Transposable Elements. | 1 | Biochemistry |
Many metabolites found in nature contain alkyne or enyne moieties, and therefore, the Sonogashira reaction has found frequent utility in their syntheses. Several of the most recent and promising applications of this coupling methodology toward the total synthesis of natural products exclusively employed the typical copper-cocatalyzed reaction.
An example of the coupling of an aryl iodide to an aryl acetylene can be seen in the reaction of an iodinated alcohol and tris(isopropyl)silylacetylene, which gave an alkyne, an intermediate in the total synthesis of the benzindenoazepine alkaloid bulgaramine.
There are other recent examples of the use of aryl iodides for the preparation of intermediates under typical Sonogashira conditions, which, after cyclization, yield natural products such as benzylisoquinoline or indole alkaloids An example is the synthesis of the benzylisoquinoline alkaloids (+)-(S)-laudanosine and (–)-(S)-xylopinine. The synthesis of these natural products involved the use of Sonogashira cross-coupling to build the carbon backbone of each molecule. | 0 | Organic Chemistry |
Some hydrogen sulfide gas diffuses into the headspace environment above the wastewater. Moisture evaporated from warm sewage may condense on unsubmerged walls of sewers, and is likely to hang in partially formed droplets from the horizontal crown of the sewer. As a portion of the hydrogen sulfide gas and oxygen gas from the air above the sewage dissolves into these stationary droplets, they become a habitat for sulfur oxidizing bacteria (SOB), of the genus Acidithiobacillus. Colonies of these aerobic bacteria metabolize the hydrogen sulfide gas to sulfuric acid. | 8 | Metallurgy |
Brian Halton (9 March 1941 – 23 February 2019) was a New Zealand organic chemist. He is noted for his investigation of highly strained and fused aromatic compounds, and was also active as an historian of chemistry. | 0 | Organic Chemistry |
CMTM7 protein levels are low in the malignant tissues of various cancers such as those of esophagus, stomach, pancreas, liver, lung, cervix, and breast. as compared with its expression in the normal tissues of these organs. Furthermore, the forced overexpression of CMTM7 protein in various cancer immortalized cell lines inhibit their proliferation and motility in culture as well as their ability to form tumors in a nude mouse experimental model of cancer. These findings suggest that the CMTM7 protein acts to inhibit the development and/or progression of these cancers and therefore that the CMTM7 gene acts as tumor suppressor in these cancers. However, further studies are needed to support these suggestion and determine if expression of the CMTM7 can be used as a clinical marker of these cancers severity/prognosis and/or as therapeutic targets for treating them. | 1 | Biochemistry |
VMA synthesis is the first step of a two-step process practiced by Rhodia since the 1970s to synthesize artificial vanilla. Specifically the reaction entails the condensation of guaiacol and glyoxylic acid in an ice cold, aqueous solution with sodium hydroxide. | 1 | Biochemistry |
If creating an mRNA library (i.e. with cDNA clones), there are several possible protocols for isolating full length mRNA. To extract DNA for genomic DNA (also known as gDNA) libraries, a DNA mini-prep may be useful. | 1 | Biochemistry |
Recently, various carbonyls have been turned into organometallic reagent surrogates via hydrazone umpolung by C.-J. Li et al. In the presence of a catalyst, similar to organometallic reagents, hydrazones can undergo nucleophilic additions, conjugate additions, and transition-metal catalyzed cross-couplings with various electrophiles to form new C-C bonds. | 0 | Organic Chemistry |
*http://www.informatics.jax.org/searches/accession_report.cgi?id=MGI:71287
*[https://web.archive.org/web/20070927190226/http://www.roswellpark.org/files/1_2_1/photos/smiragliaweb2.jpg a picture of an auto-rad from Roswell Park Comprehensive Cancer Center] | 1 | Biochemistry |
Recent research has implicated the UPR in the transformation of cells in to cancer cells. Researchers have identified the SIRT3 axis of UPR as a marker to differentiate between metastatic and non-metastatic breast cancer. As many cancers exhibit a metabolic shift from oxidative phosporylation-depentent energy production to aerobic glycolysis dependent energy production, also known as the Warburg effect, researchers suggest that cancer cells rely on the UPR to maintain the mitochondrial integrity. Furthermore, multiple studies have shown that inhibition of UPR, specifically ATF5, selectively kills human and rat cancer cells rather than non-cancer cells. | 1 | Biochemistry |
This gene encodes a retina-specific guanylate cyclase, which is a member of the membrane guanylyl cyclase family. Like other membrane guanylyl cyclases, this enzyme has a hydrophobic amino-terminal signal sequence followed by a large extracellular domain, a single membrane spanning domain, a kinase homology domain, and a guanylyl cyclase catalytic domain. In contrast to other membrane guanylyl cyclases, this enzyme is not activated by natriuretic peptides.
The nomenclature for members of the Gucy2 gene family is not consistent across species. In many mammals, including mice and rats, the Gucy2d gene encodes a related protein – GC-D – that is specifically expressed in a subpopulation of olfactory sensory neurons. This gene is a pseudogene in humans and most other primates. In rodents, the corresponding (orthologous) gene to human GUCY2D is Gucy2e. | 1 | Biochemistry |
The genomic basis of the Crabtree effect is still being investigated, and its evolution likely involved multiple successive molecular steps that increased the efficiency of the lifestyle. | 1 | Biochemistry |
The MRL is usually determined by repeated (on the order of 10) field trials, where the crop has been treated according to good agricultural practice (GAP) and an appropriate pre harvest interval or withholding period has elapsed. For many pesticides this is set at the limit of determination (LOD) – since only major pesticides have been evaluated and understanding of acceptable daily intake (ADI) is incomplete (i.e. producers or public bodies have not submitted MRL data – often because these were not required in the past). LOD can be considered a measure of presence/absence, but certain residues may not be quantifiable at very low levels. For this reason the limit of quantification (LOQ) is often used instead of the LOD. As a rule of thumb the LOQ is approximately two times the LOD. For substances that are not included in any of the annexes in EU regulations, a default MRL of 0.01 mg/kg normally applies.
It follows that adoption of GAP at the farm level must be a priority, and includes the withdrawal of obsolete pesticides. With increasingly sensitive detection equipment, a certain amount of pesticide residue will often be measured following field use. In the current regulatory environment, it would be wise for cocoa producers to focus only on pest control agents that are permitted for use in the EU and US. It should be stressed that MRLs are set on the basis of observations and not on ADIs. | 2 | Environmental Chemistry |
The amyloid-β precursor protein (AβPP), and all associated secretases, are expressed early in development and play a key role in the endocrinology of reproduction – with the differential processing of AβPP by secretases regulating human embryonic stem cell (hESC) proliferation as well as their differentiation into neural precursor cells (NPC). The pregnancy hormone human chorionic gonadotropin (hCG) increases AβPP expression and hESC proliferation while progesterone directs AβPP processing towards the non-amyloidogenic pathway, which promotes hESC differentiation into NPC.
AβPP and its cleavage products do not promote the proliferation and differentiation of post-mitotic neurons; rather, the overexpression of either wild-type or mutant AβPP in post-mitotic neurons induces apoptotic death following their re-entry into the cell cycle. It is postulated that the loss of sex steroids (including progesterone) but the elevation in luteinizing hormone, the adult equivalent of hCG, post-menopause and during andropause drives amyloid-β production and re-entry of post-mitotic neurons into the cell cycle. | 1 | Biochemistry |
The parameter most commonly used to characterize exposures to wood dust in air is total wood dust concentration, in mass per unit volume. In countries that use the metric system, this is usually measured in mg/m (milligram per cubic metre)
A study to estimate occupational exposure to inhalable wood dust by country, industry, the level of exposure and type of wood dust in 25 member states of the European Union (EU-25) found that in 2000–2003, about 3.6 million workers (2.0% of the employed EU-25 population) were occupationally exposed to inhalable wood dust. The highest exposure levels were estimated to occur in the construction sector and furniture industry. | 2 | Environmental Chemistry |
Two general types of instruments exist: filter fluorometers that use filters to isolate the incident light and fluorescent light and spectrofluorometers that use diffraction grating monochromators to isolate the incident light and fluorescent light.
Both types use the following scheme: the light from an excitation source passes through a filter or monochromator, and strikes the sample. A proportion of the incident light is absorbed by the sample, and some of the molecules in the sample fluoresce. The fluorescent light is emitted in all directions. Some of this fluorescent light passes through a second filter or monochromator and reaches a detector, which is usually placed at 90° to the incident light beam to minimize the risk of transmitted or reflected incident light reaching the detector.
Various light sources may be used as excitation sources, including lasers, LED, and lamps; xenon arcs and mercury-vapor lamps in particular. A laser only emits light of high irradiance at a very narrow wavelength interval, typically under 0.01 nm, which makes an excitation monochromator or filter unnecessary. The disadvantage of this method is that the wavelength of a laser cannot be changed by much. A mercury vapor lamp is a line lamp, meaning it emits light near peak wavelengths. By contrast, a xenon arc has a continuous emission spectrum with nearly constant intensity in the range from 300-800 nm and a sufficient irradiance for measurements down to just above 200 nm.
Filters and/or monochromators may be used in fluorimeters. A monochromator transmits light of an adjustable wavelength with an adjustable tolerance. The most common type of monochromator utilizes a diffraction grating, that is, collimated light illuminates a grating and exits with a different angle depending on the wavelength. The monochromator can then be adjusted to select which wavelengths to transmit. For allowing anisotropy measurements, the addition of two polarization filters is necessary: One after the excitation monochromator or filter, and one before the emission monochromator or filter.
As mentioned before, the fluorescence is most often measured at a 90° angle relative to the excitation light. This geometry is used instead of placing the sensor at the line of the excitation light at a 180° angle in order to avoid interference of the transmitted excitation light. No monochromator is perfect and it will transmit some stray light, that is, light with other wavelengths than the targeted. An ideal monochromator would only transmit light in the specified range and have a high wavelength-independent transmission. When measuring at a 90° angle, only the light scattered by the sample causes stray light. This results in a better signal-to-noise ratio, and lowers the detection limit by approximately a factor 10000, when compared to the 180° geometry. Furthermore, the fluorescence can also be measured from the front, which is often done for turbid or opaque samples
The detector can either be single-channeled or multichanneled. The single-channeled detector can only detect the intensity of one wavelength at a time, while the multichanneled one detects the intensity of all wavelengths simultaneously, making the emission monochromator or filter unnecessary.
The most versatile fluorimeters with dual monochromators and a continuous excitation light source can record both an excitation spectrum and a fluorescence spectrum. When measuring fluorescence spectra, the wavelength of the excitation light is kept constant, preferably at a wavelength of high absorption, and the emission monochromator scans the spectrum. For measuring excitation spectra, the wavelength passing through the emission filter or monochromator is kept constant and the excitation monochromator is scanning. The excitation spectrum generally is identical to the absorption spectrum as the fluorescence intensity is proportional to the absorption. | 7 | Physical Chemistry |
The lipid world theory postulates that the first self-replicating object was lipid-like. Phospholipids form lipid bilayers in water while under agitation—the same structure as in cell membranes. These molecules were not present on early Earth, but other amphiphilic long-chain molecules also form membranes. These bodies may expand by insertion of additional lipids, and may spontaneously split into two offspring of similar size and composition. The main idea is that the molecular composition of the lipid bodies is a preliminary to information storage, and that evolution led to the appearance of polymers like RNA that store information. Studies on vesicles from amphiphiles that might have existed in the prebiotic world have so far been limited to systems of one or two types of amphiphiles.
A lipid bilayer membrane could be composed of a huge number of combinations of arrangements of amphiphiles. The best of these would have favored the constitution of a hypercycle, actually a positive feedback composed of two mutual catalysts represented by a membrane site and a specific compound trapped in the vesicle. Such site/compound pairs are transmissible to the daughter vesicles leading to the emergence of distinct lineages of vesicles, which would have allowed natural selection.
A protocell is a self-organized, self-ordered, spherical collection of lipids proposed as a stepping-stone to the origin of life. The theory of classical irreversible thermodynamics treats self-assembly under a generalized chemical potential within the framework of dissipative systems.
A central question in evolution is how simple protocells first arose and differed in reproductive contribution to the following generation, thus driving the evolution of life. A functional protocell has (as of 2014) not yet been achieved in a laboratory setting. Self-assembled vesicles are essential components of primitive cells. The second law of thermodynamics requires that the universe move in a direction in which entropy increases, yet life is distinguished by its great degree of organization. Therefore, a boundary is needed to separate life processes from non-living matter. Irene Chen and Jack W. Szostak suggest that elementary protocells can give rise to cellular behaviors including primitive forms of differential reproduction, competition, and energy storage. Competition for membrane molecules would favor stabilized membranes, suggesting a selective advantage for the evolution of cross-linked fatty acids and even the phospholipids of today. Such micro-encapsulation would allow for metabolism within the membrane and the exchange of small molecules, while retaining large biomolecules inside. Such a membrane is needed for a cell to create its own electrochemical gradient to store energy by pumping ions across the membrane. Fatty acid vesicles in conditions relevant to alkaline hydrothermal vents can be stabilized by isoprenoids which are synthesized by the formose reaction, the advantages and disadvantages of isoprenoids incorporated within the lipid bilayer in different microenvironments might have led to the divergence of the membranes of archaea and bacteria. | 9 | Geochemistry |
Eukaryote expression vectors require sequences that encode for:
*Polyadenylation tail: Creates a polyadenylation tail at the end of the transcribed pre-mRNA that protects the mRNA from exonucleases and ensures transcriptional and translational termination: stabilizes mRNA production.
*Minimal UTR length: UTRs contain specific characteristics that may impede transcription or translation, and thus the shortest UTRs or none at all are encoded for in optimal expression vectors.
*Kozak sequence: Vectors should encode for a Kozak sequence in the mRNA, which assembles the ribosome for translation of the mRNA. | 1 | Biochemistry |
The CYP11B1 gene encodes 11β-hydroxylase, a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases that catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. The product of this CYP11B1 gene is the 11β-hydroxylase protein. This protein localizes to the mitochondrial inner membrane and is involved in the conversion of various steroids in the adrenal cortex. Transcript variants encoding different isoforms have been noted for this gene.
The CYP11B1 gene is reversibly inhibited by etomidate and metyrapone. | 1 | Biochemistry |
Atomic, molecular, and optical physics (AMO) is the study of matter–matter and light–matter interactions, at the scale of one or a few atoms and energy scales around several electron volts. The three areas are closely interrelated. AMO theory includes classical, semi-classical and quantum treatments. Typically, the theory and applications of emission, absorption, scattering of electromagnetic radiation (light) from excited atoms and molecules, analysis of spectroscopy, generation of lasers and masers, and the optical properties of matter in general, fall into these categories. | 7 | Physical Chemistry |
Synovial Sarcoma X chromosome breakpoint-2 (SSX2) proteins are known to localize in nucleus and work as a transcriptional repressor. In addition, expression of SSX2 is frequently observed in melanoma, but the role of the gene has not been evaluated. Thus, researchers have used the principle of ectopic expression to express SSX2 to different cell lines including cancer model cells. They found important phenotypes of ectopic SSX2 expression that is involved in tumorigenesis: 1) immediate induction of genomic instability, 2) long-term support of tumor cell growth. | 1 | Biochemistry |
Transcription can also be studied at the level of individual cells by single-cell transcriptomics. Single-cell RNA sequencing (scRNA-seq) is a recently developed technique that allows the analysis of the transcriptome of single cells, including bacteria. With single-cell transcriptomics, subpopulations of cell types that constitute the tissue of interest are also taken into consideration. This approach allows to identify whether changes in experimental samples are due to phenotypic cellular changes as opposed to proliferation, with which a specific cell type might be overexpressed in the sample. Additionally, when assessing cellular progression through differentiation, average expression profiles are only able to order cells by time rather than their stage of development and are consequently unable to show trends in gene expression levels specific to certain stages. Single-cell trarnscriptomic techniques have been used to characterize rare cell populations such as circulating tumor cells, cancer stem cells in solid tumors, and embryonic stem cells (ESCs) in mammalian blastocysts.
Although there are no standardized techniques for single-cell transcriptomics, several steps need to be undertaken. The first step includes cell isolation, which can be performed using low- and high-throughput techniques. This is followed by a qPCR step and then single-cell RNAseq where the RNA of interest is converted into cDNA. Newer developments in single-cell transcriptomics allow for tissue and sub-cellular localization preservation through cryo-sectioning thin slices of tissues and sequencing the transcriptome in each slice. Another technique allows the visualization of single transcripts under a microscope while preserving the spatial information of each individual cell where they are expressed. | 1 | Biochemistry |
Charge modulation microscopy is a new technology which combines the confocal microscopy with charge modulation spectroscopy. Unlike the charge modulation spectroscopy which is focused on the whole transistor, the charge modulation microscopy give us the local spectra and map. Thanks for this technology, the channel spectra and electrode spectra can be obtained individually. A more local dimension of charge modulation spectra (around submicrometer) can be observed without a significant Electro-absorption feature. Of course, this depends on the resolution of the optical microscopy.
The high resolution of charge modulation microscopy allows mapping of the charge carrier distribution at the active channel of the organic field-effect transistor. In other words, a functional carrier morphology can be observed. It is well known that the local carrier density can be related to the polymer microstructure. Based on Density functional theory calculations, a polarized charge modulation microscopy can selectively map the charge transport associated with a relative direction of the transition dipole moment. The local direction can be correlated to the orientational order of polymer domains. More ordered domains show a high carrier mobility of the organic field-effect transistor device. | 7 | Physical Chemistry |
The perilipins are considered to have their origins in a common ancestral gene which, during the first and second vertebrate genome duplication, gave rise to six types of PLIN genes. | 1 | Biochemistry |
Response factor, usually in chromatography and spectroscopy, is the ratio between a signal produced by an analyte, and the quantity of analyte which produces the signal. Ideally, and for easy computation, this ratio is unity (one). In real-world scenarios, this is often not the case. | 7 | Physical Chemistry |
Consider two equal bodies (not affected by gravity), each of mass m, attached to three springs, each with spring constant k. They are attached in the following manner, forming a system that is physically symmetric:
where the edge points are fixed and cannot move. Well use x(t) to denote the horizontal displacement of the left mass, and x(t') to denote the displacement of the right mass.
If one denotes acceleration (the second derivative of x(t) with respect to time) as , the equations of motion are:
Since we expect oscillatory motion of a normal mode (where ω is the same for both masses), we try:
Substituting these into the equations of motion gives us:
Since the exponential factor is common to all terms, we omit it and simplify:
And in matrix representation:
If the matrix on the left is invertible, the unique solution is the trivial solution (A, A) = (x, x) = (0,0). The non trivial solutions are to be found for those values of ω whereby the matrix on the left is singular i.e. is not invertible. It follows that the determinant of the matrix must be equal to 0, so:
Solving for , we have two positive solutions:
If we substitute ω into the matrix and solve for (A, A), we get (1, 1). If we substitute ω, we get (1, −1). (These vectors are eigenvectors, and the frequencies are eigenvalues.)
The first normal mode is:
Which corresponds to both masses moving in the same direction at the same time. This mode is called antisymmetric.
The second normal mode is:
This corresponds to the masses moving in the opposite directions, while the center of mass remains stationary. This mode is called symmetric.
The general solution is a superposition of the normal modes where c, c, φ, and φ, are determined by the initial conditions of the problem.
The process demonstrated here can be generalized and formulated using the formalism of Lagrangian mechanics or Hamiltonian mechanics. | 7 | Physical Chemistry |
The geometry of TAP like all known geometries of tetraarylporphyrins is distorted to take a very characteristic “saddle” shape. | 1 | Biochemistry |
If the Gaussian profile is centered at and the Lorentzian profile is centered at , the convolution is centered at and the characteristic function is:
The probability density function is simply offset from the centered profile by :
where:
The mode and median are both located at . | 7 | Physical Chemistry |
Iron is important for the growth of phytoplankton. In phytoplankton, iron is used for electron transfer reactions in photosynthesis in both photosystem I and photosystem II. Additionally, iron is an important component of the enzyme nitrogenase, which is used to fix nitrogen. In measurements at open ocean stations, phytoplankton are isotopically light, with the fractionation as a result of biological uptake measured between -0.25‰ and -0.13‰. Improvement in the understanding of this fractionation will enable the more precise understanding of phytoplankton photosynthetic processes. | 9 | Geochemistry |
The following tables offer estimates of oxygen cycle reservoir capacities and fluxes.
These numbers are based primarily on estimates from (Walker, J. C. G.): More recent research indicates that ocean life (marine primary production) is actually responsible for more than half the total oxygen production on Earth.
<br>
Table 2: Annual gain and loss of atmospheric oxygen (Units of 10 kg O per year) | 5 | Photochemistry |
Archaeometallurgical slag is slag discovered and studied in the context of archaeology. Slag, the byproduct of iron-working processes such as smelting or smithing, is left at the iron-working site rather than being moved away with the product. As it weathers well, it is readily available for study. The size, shape, chemical composition and microstructure of slag are determined by features of the iron-working processes used at the time of its formation. | 8 | Metallurgy |
Chemical cycling describes systems of repeated circulation of chemicals between other compounds, states and materials, and back to their original state, that occurs in space, and on many objects in space including the Earth. Active chemical cycling is known to occur in stars, many planets and natural satellites.
Chemical cycling plays a large role in sustaining planetary atmospheres, liquids and biological processes and can greatly influence weather and climate. Some chemical cycles release renewable energy, others may give rise to complex chemical reactions, organic compounds and prebiotic chemistry. On terrestrial bodies such as the Earth, chemical cycles involving the lithosphere are known as geochemical cycles. Ongoing geochemical cycles are one of the main attributes of geologically active worlds. A chemical cycle involving a biosphere is known as a biogeochemical cycle. | 9 | Geochemistry |
The primary structure of the SUI1 protein is made up of 108 amino acids. The protein domain has a structure made of a seven-bladed beta-propeller and it also contains a C-terminal alpha helix. Homologues of SUI1 have been found in mammals, insects and plants. SUI1 is also evolutionary related to proteins from Escherichia coli (yciH), Haemophilus influenzae (HI1225) and Methanococcus vannielii. | 1 | Biochemistry |
A second class of Ziegler–Natta catalysts are soluble in the reaction medium. Traditionally such homogeneous catalysts were derived from metallocenes, but the structures of active catalysts have been significantly broadened to include nitrogen-based ligands. | 7 | Physical Chemistry |
Free gases exhibit very sharp spectral features, and different gas species have their own unique spectral fingerprints. At atmospheric pressure, absorption linewidths are typically on the order of 0.1 cm (i.e. ~3 GHz in optical frequency or 0.006 nm in wavelength), while solid media have dull spectral behavior with absorption features thousand times wider. By looking for the sharp absorption imprints in light emerging from porous samples, it is thus possible to detect gases confined in solids – even though the solid often attenuates light much stronger than the gas itself.
The basic principle of GASMAS is shown in figure 1. Laser light is sent into a sample with gas cavities, which could either be small pores (left) or larger gas-filled chambers. The heterogeneous nature of the porous material often give rise to strong light scattering, and pathlengths are often surprisingly long (10 or 100 times the sample dimension are not uncommon). In addition, light will experience absorption related to the solid material. When travelling through the material, light will travel partly through the pores, and will thus experience the spectrally sharp gas absorption. Light leaving the material will carry this information, and can be collected by a detector either in a transmission mode (left) or in a reflection mode (right).
In order to detect the spectrally sharp fingerprints related to the gas, GASMAS has so far relied on high-resolution tunable diode laser absorption spectroscopy (TDLAS). In principle, this means that a nearly monochromatic (narrow-bandwidth) laser is scanned across an absorption line of the gas, and a detector records the transmission profile. In order to increase sensitivity, modulation techniques are often employed.
The strength of the gas absorption will depend, as given by the Beer-Lambert law, both on the gas concentration and the path-length that the light has travelled through the gas. In conventional TDLAS, the path-length is known and the concentration is readily calculated from the transmittance. In GASMAS, extensive scattering renders the pathlength unknown and the determination of gas concentration is aggravated. In many applications, however, the gas concentration is known and other parameters are in focus. Furthermore, as discussed in 2.2, there are complementing techniques that can provide information on the optical pathlength, thus allowing evaluation also of gas concentrations. | 7 | Physical Chemistry |
Studies on the poorly immunogenic Ag104A sarcoma and the extremely tumorigenic P815 mastocytoma provided the first systematic proof that anti-4-1BB antibodies have potent anti-tumor effects. Anti-4-1BB administration to mice with the aforementioned tumors was shown to substantially inhibit tumor growth by increasing CTL activity. In the years to come, more studies verified and legitimized the effect of 4-1BB signaling to inhibit tumor growth.
The interaction between 4-1BB and 4-1BBL provide costimulatory signals to a variety of T cells, which can be used to discover cancer immunotherapy. The 4-1BB/4-1BBL complex together with a signal provided by a T-cell receptor can provide costimulatory signals to CD4 and CD8 T cells in mice, leading to the activation of CD4 and CD8 T cells. The activation of CD8 T cells is essential in antitumor immunity. The 4-1BB/4-1BBL complex with the help of T-cell receptor signals can co-stimulate human CD28 T cells and trigger the increase in CD28 T cells. Unlike the activation of CD8 T cells, the proliferation of CD28 T cells can negatively affect cancer state and other diseases. Therefore, this pathway can be targeted for immunotherapy. | 1 | Biochemistry |
The replacement of silica involves two processes:
1) Dissolution of rock minerals
2) Precipitation of silica
It could be explained through the carbonate-silica replacement. Hydrothermal fluids are undersaturated with carbonates and supersaturated with silica. When carbonate rocks get in contact with hydrothermal fluids, due to the difference in gradient, carbonates from the original rock dissolve into the fluid whereas silica precipitate out of it. The carbonate that dissolved is therefore pulled out from the system while the silica precipitated recrystallizes into various silicate minerals, depending on the silica phase. The solubility of silica strongly depends on the temperature and pH value of the environment where pH9 is the controlling value. Under a condition of pH lower than 9, silica precipitates out of the fluid; when the pH value is above 9, silica becomes highly soluble. | 9 | Geochemistry |
Standard approaches of this type, using atomic contributions, have been named by those formulating them with a prefix letter: AlogP, XlogP, MlogP, etc. A conventional method for predicting log P through this type of method is to parameterize the distribution coefficient contributions of various atoms to the overall molecular partition coefficient, which produces a parametric model. This parametric model can be estimated using constrained least-squares estimation, using a training set of compounds with experimentally measured partition coefficients. In order to get reasonable correlations, the most common elements contained in drugs (hydrogen, carbon, oxygen, sulfur, nitrogen, and halogens) are divided into several different atom types depending on the environment of the atom within the molecule. While this method is generally the least accurate, the advantage is that it is the most general, being able to provide at least a rough estimate for a wide variety of molecules. | 7 | Physical Chemistry |
The applications of chemotactic drug delivery systems include but are not limited to cancer therapy, wound healing, and inflammation. The ability to target specific cells and locations within the body through chemical cues has opened up new avenues for the field of drug delivery, allowing for increased drug efficacy and reducing harmful side effects. | 1 | Biochemistry |
Minerals are the exogenous chemical elements indispensable for life. Although the four elements: carbon, hydrogen, oxygen, and nitrogen (CHON) are essential for life, they are so plentiful in food and drink that these are not considered nutrients and there are no recommended intakes for these as minerals. The need for nitrogen is addressed by requirements set for protein, which is composed of nitrogen-containing amino acids. Sulfur is essential, but again does not have a recommended intake. Instead, recommended intakes are identified for the sulfur-containing amino acids methionine and cysteine.
The essential nutrient trace elements for humans, listed in order of Recommended Dietary Allowance (expressed as a mass), are potassium, chloride, sodium, calcium, phosphorus, magnesium, iron, zinc, manganese, copper, iodine, chromium, molybdenum, selenium. Additionally, cobalt is a component of Vitamin B which is essential. There are other minerals which are essential for some plants and animals, but may or may not be essential for humans, such as boron and silicon. | 9 | Geochemistry |
In the 1950s, transport due to collisions in non-magnetized plasmas was simultaneously studied by two groups at University of California, Berkeley's Radiation Laboratory. They quoted each other’s results in their respective papers. The first reference deals with the mean-field part of the interaction by using perturbation theory in electric field amplitude. Within the same approximations, a more elegant derivation of the collisional transport coefficients was provided, by using the Balescu–Lenard equation (see Sec. 8.4 of and Secs. 7.3 and 7.4 of ). The second reference uses the Rutherford picture of two-body collisions. The calculation of the first reference is correct for impact parameters much larger than the interparticle distance, while those of the second one work in the opposite case. Both calculations are extended to the full range of impact parameters by introducing each a single ad hoc cutoff, and not two as in the above simplified mathematical treatment, but the transport coefficients depend only logarithmically thereon; both results agree and yield the above expression for the diffusion constant. | 7 | Physical Chemistry |
Methylene blue is used in aquaculture and by tropical fish hobbyists as a treatment for fungal infections. It can also be effective in treating fish infected with ich although a combination of malachite green and formaldehyde is far more effective against the parasitic protozoa Ichthyophthirius multifiliis. It is usually used to protect newly laid fish eggs from being infected by fungus or bacteria. This is useful when the hobbyist wants to artificially hatch the fish eggs.
Methylene blue is also very effective when used as part of a "medicated fish bath" for treatment of ammonia, nitrite, and cyanide poisoning as well as for topical and internal treatment of injured or sick fish as a "first response". | 3 | Analytical Chemistry |
In 1987 the private New York laboratory, Lifecodes, began assisting Dr. Ferrara in his efforts to establish a DNA laboratory for the state of Virginia.
In 1988 Timothy Spencer, the "Southside Strangler", became first serial killer in the United States to be convicted on the basis of DNA evidence. Spencer committed three rapes and murders in Richmond Virginia, and one in Arlington, Virginia in the fall of 1987.
Ferrara recognized the potential utility of the precedent that had been set in Spencer case, and immediately focused his political savvy on convincing the Virginia General Assembly to fund the creation of the first State DNA Database in the country.
In 1989 under his leadership, Virginia became the first state laboratory capable of performing DNA fingerprinting. The FBI had started its limited DNA laboratory operations just four months earlier.
In addition to his directorship of the Virginia Department of Forensic Science (VA-DFS), Dr. Ferrara was an honorary professor at Virginia Commonwealth University. Through his passion for teaching and research, as well as his commitment to developing a nationally recognized Forensic Science educational program at VCU, the program officially became a department in 2005. | 0 | Organic Chemistry |
Henrys law is a limiting law that only applies for "sufficiently dilute" solutions, while Raoults law is generally valid when the liquid phase is almost pure or for mixtures of similar substances. The range of concentrations in which Henry's law applies becomes narrower the more the system diverges from ideal behavior. Roughly speaking, that is the more chemically "different" the solute is from the solvent.
For a dilute solution, the concentration of the solute is approximately proportional to its mole fraction x, and Henry's law can be written as
This can be compared with Raoult's law:
where p* is the vapor pressure of the pure component.
At first sight, Raoults law appears to be a special case of Henrys law, where H = p*. This is true for pairs of closely related substances, such as benzene and toluene, which obey Raoult's law over the entire composition range: such mixtures are called ideal mixtures.
The general case is that both laws are limit laws, and they apply at opposite ends of the composition range. The vapor pressure of the component in large excess, such as the solvent for a dilute solution, is proportional to its mole fraction, and the constant of proportionality is the vapor pressure of the pure substance (Raoults law). The vapor pressure of the solute is also proportional to the solutes mole fraction, but the constant of proportionality is different and must be determined experimentally (Henry's law). In mathematical terms:
:Raoult's law:
:Henry's law:
Raoult's law can also be related to non-gas solutes. | 7 | Physical Chemistry |
In enzymatic labeling, a DNA construct is first formed, using a gene and the DNA of a fluorescent protein. After transcription, a hybrid RNA + fluorescent is formed. The object of interest is attached to an enzyme that can recognize this hybrid DNA. Usually fluorescein is used as the fluorophore. | 1 | Biochemistry |
Cerrosafe is a fusible alloy with a low melting point. It is a non-eutectic mixture consisting of 42.5% bismuth, 37.7% lead, 11.3% tin, and 8.5% cadmium that melts between and . It is useful for making reference castings whose dimensions can be correlated to those of the mold or other template due to its well-known thermal expansion properties during cooling. The alloy contracts during the first 30 minutes, allowing easy removal from a mold, then expands during the next 30 minutes to return to the exact original size. It then continues expanding at a known rate for 200 hours, allowing conversion of measurements of the casting back to those of the mold. | 8 | Metallurgy |
In 1938, Pyotr Kapitsa, John Allen and Don Misener discovered that helium-4 became a new kind of fluid, now known as a superfluid, at temperatures less than 2.17 K (the lambda point). Superfluid helium has many unusual properties, including zero viscosity (the ability to flow without dissipating energy) and the existence of quantized vortices. It was quickly believed that the superfluidity was due to partial Bose–Einstein condensation of the liquid. In fact, many properties of superfluid helium also appear in gaseous condensates created by Cornell, Wieman and Ketterle (see below). Superfluid helium-4 is a liquid rather than a gas, which means that the interactions between the atoms are relatively strong; the original theory of Bose–Einstein condensation must be heavily modified in order to describe it. Bose–Einstein condensation remains, however, fundamental to the superfluid properties of helium-4. Note that helium-3, a fermion, also enters a superfluid phase (at a much lower temperature) which can be explained by the formation of bosonic Cooper pairs of two atoms (see also fermionic condensate). | 7 | Physical Chemistry |
The three-year WeNMR project started in November 2010 as the natural successor of the eNMR project. Financial support was provided by the European Community grants 213010 (eNMR) and 261572 (WeNMR) in the 7th Framework Programme (e-Infrastructure RI-261571). | 1 | Biochemistry |
If the polymers of interest are ideal gaussian chains (or freely-jointed chains), in the limit of very long chains (allows performing a sort of "continuum transition"), the calculation of the structure can be carried out explicitly and result in a sort of Debye function:
With being the polymer's radius of gyration.
in many practical scenarios, the above formula is approximated by the (much more convenient) Lorentzian:
which has a relative error of no more than 15% compared to the exact expression. | 7 | Physical Chemistry |
The symbol used to represent density in equations is ρ (rho) with SI units of kilograms per cubic meter. This term is the reciprocal of specific volume.
Since gas molecules can move freely within a container, their mass is normally characterized by density. Density is the amount of mass per unit volume of a substance, or the inverse of specific volume. For gases, the density can vary over a wide range because the particles are free to move closer together when constrained by pressure or volume. This variation of density is referred to as compressibility. Like pressure and temperature, density is a state variable of a gas and the change in density during any process is governed by the laws of thermodynamics. For a static gas, the density is the same throughout the entire container. Density is therefore a scalar quantity. It can be shown by kinetic theory that the density is inversely proportional to the size of the container in which a fixed mass of gas is confined. In this case of a fixed mass, the density decreases as the volume increases. | 7 | Physical Chemistry |
pCO, pCO, or is the partial pressure of carbon dioxide (CO), often used in reference to blood but also used in meteorology, climate science, oceanography, and limnology to describe the fractional pressure of CO as a function of its concentration in gas or dissolved phases. The units of pCO are mmHg, atm, torr, Pa, or any other standard unit of atmospheric pressure. The pCO of Earth's atmosphere has risen from approximately 280 ppm (parts-per-million) to a mean 2019 value of 409.8 ppm as a result of anthropogenic release of carbon dioxide from fossil fuel burning. This is the highest atmospheric concentration to have existed on Earth for at least the last 800,000 years. | 7 | Physical Chemistry |
Spin column-based nucleic acid purification is a method of purifying DNA, RNA or plasmid from a sample using a spin column filter. The method is based on the principle of selectively binding nucleic acids to a solid matrix in the spin column, while other contaminants, such as proteins and salts, are washed away. The conditions are then changed to elute the purified nucleic acid off the column using a suitable elution buffer. | 1 | Biochemistry |
A consumption map or efficiency map shows the brake-specific fuel consumption in g per kWh over mean effective pressure per rotational speed of an internal combustion engine.
The x-axis shows the rotational speed range. The y-axis represents the load on the engine. The contour lines show the specific fuel consumption, indicating the areas of the speed/load regime where the engine is more or less efficient.
The map contains each possible condition, combining rotational speed and mean effective pressure. It shows the result of specific fuel consumption. A typical rotation power output P (linear to ) is reached on several locations on the map but differing in the amount of fuel consumption. Automatic transmissions, are designed to keep the engine at the speed with the lowest possible fuel consumption, given the power demand.
The map also shows the efficiency of the engine. Depending on the fuel type, diesel and gasoline engines reach up to 210 g/kWh and about 40% efficiency. Using natural gas this efficiency is reached at 200 g/kWh.
Average values are 160–180 g/kWh for slow moving two stroke diesel cargoship engines using fuel oil, reaching up to 55% efficiency at 300 rpm. 195–210 g/kWh at cooled and pre-charged diesel engines for passenger cars, trucks 195–225 g/kWh. Non-charged Otto cycle gasoline engines for passenger cars 250–350 g/kWh. | 7 | Physical Chemistry |
Calcium deficiency can sometimes be rectified by adding agricultural lime to acid soils, aiming at a pH of 6.5, unless the subject plants specifically prefer acidic soil. Organic matter should be added to the soil to improve its moisture-retaining capacity. However, because of the nature of the disorder (i.e. poor transport of calcium to low transpiring tissues), the problem cannot generally be cured by the addition of calcium to the roots. In some species, the problem can be reduced by prophylactic spraying with calcium chloride of tissues at risk.
Plant damage is difficult to reverse, so corrective action should be taken immediately, supplemental applications of calcium nitrate at 200 ppm nitrogen, for example. Soil pH should be tested, and corrected if needed, because calcium deficiency is often associated with low pH.
Early fruit will generally have the worst symptoms, with them typically lessening as the season progresses. Preventative measures, such as irrigating prior to especially high temperatures and stable irrigation will minimize the occurrence. | 1 | Biochemistry |
An allosteric site is a site on an enzyme, unrelated to its active site, which can bind an effector molecule. This interaction is another mechanism of enzyme regulation. Allosteric modification usually happens in proteins with more than one subunit. Allosteric interactions are often present in metabolic pathways and are beneficial in that they allow one step of a reaction to regulate another step. They allow an enzyme to have a range of molecular interactions, other than the highly specific active site. | 1 | Biochemistry |
Thermal irradiation is the rate at which radiation is incident upon a surface per unit area. It is measured in watts per square meter. Irradiation can either be reflected, absorbed, or transmitted. The components of irradiation can then be characterized by the equation
where, represents the absorptivity, reflectivity and transmissivity. These components are a function of the wavelength of the electromagnetic wave as well as the material properties of the medium. | 7 | Physical Chemistry |
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