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The completed core snRNP-snurportin 1 complex is transported into the nucleus via the protein importin β. Inside the nucleus, the core snRNPs appear in the Cajal bodies, where final assembly of the snRNPs take place. This consists of additional proteins and other modifications specific to the particular snRNP (U1, U2, U4, U5). The biogenesis of the U6 snRNP occurs in the nucleus, although large amounts of free U6 are found in the cytoplasm. The LSm ring may assemble first, and then associate with the U6 snRNA. | 1 | Biochemistry |
The Geochemical Society presents the following annual awards:
*V. M. Goldschmidt Award – the society's highest honor, it is awarded for major achievements in geochemistry or cosmochemistry.
*F.W. Clarke Medal – named after Frank Wigglesworth Clarke (1847–1931), a chemist who determined the composition of the Earth's crust, it goes to an early-career scientist for an outstanding contribution to geochemistry or cosmochemistry.
*C.C. Patterson Medal – named after Clair Cameron Patterson (1922–1995), who developed uranium–lead dating, it recognizes an innovative breakthrough in environmental geochemistry, particularly one of value to society.
*Alfred Treibs Medal – Named after Alfred E. Treibs (1899–1983), whose papers on porphyrins were the beginning of the field of organic chemistry, it is awarded by the Organic Geochemistry Division (OGD) for major achievements in organic geochemistry. The OGD also presents an annual Best Paper Award for a publication in the previous year.
*Geochemical Fellows – Starting in 1996, the Geochemical Society and the European Association of Geochemistry (EAG) bestow this honor on outstanding scientists who have made a major contribution to the field of geochemistry. Holders of the Goldschmidt and Treibs medals, as well as the Urey Medal of the EAG, are automatically inducted.
The Distinguished Service Award, which recognizes outstanding service to the Society or the geochemical community, is not awarded every year.
The Geochemical Society sponsors a special lecture at the annual meeting of the Geological Society of America. Called the F. Earl Ingerson Lecture Series, it honors the first president of the Geochemical Society. At the Goldschmidt Conference, the Paul W. Gast Lecture is awarded to a mid-career scientist (under 45 years old) in honor of the first Goldschmidt medalist. | 9 | Geochemistry |
Quinones methides are commonly invoked in biochemistry, but are rarely observed as long-lived intermediates. | 0 | Organic Chemistry |
Woollins' reagent is commercially available. It can also be conveniently prepared in the laboratory by heating a mixture of dichlorophenylphosphine and sodium selenide (NaSe), (itself prepared from reacting elementary selenium with sodium in liquid ammonia). An alternative synthesis is the reaction of the pentamer (PPh) (pentaphenylcyclopentaphosphine) with elemental selenium. | 0 | Organic Chemistry |
The Bay is well-known for its seafood, especially blue crabs, clams, and oysters. In the middle of the 20th century, the Bay supported 9,000 full-time watermen, according to one account. Today, the body of water is less productive than it used to be because of runoff from urban areas (mostly on the Western Shore) and farms (especially on the Eastern Shore and in the Susquehanna River watershed), over-harvesting, and invasion of foreign species.
The plentiful oyster harvests led to the development of the skipjack, the state boat of Maryland, which is the only remaining working boat type in the United States still under sail power. Other characteristic bay-area workboats include sail-powered boats such as the log canoe, the pungy, the bugeye, and the motorized Chesapeake Bay deadrise, the state boat of Virginia.
In addition to harvesting wild oysters, oyster farming is a growing industry in the Bay. Oyster aquaculture is passive in that the Bay provides all the natural oyster food needed, making it an environmentally friendly practice in contrast to other kinds of fish farming. Oyster farms provide jobs as well as a natural effort for filtering excess nutrients from the water in an effort to reduce the effects of eutrophication pollution (too much algae). The Chesapeake Bay Program promotes oyster restoration projects to reduce the amount of nitrogen compounds entering the bay.
The Bay is famous for its rockfish, a regional name for striped bass. Once on the verge of extinction, rockfish have made a significant comeback because of legislative action that put a moratorium on rockfishing, which allowed the species to re-populate. Rockfish can now be fished in strictly controlled and limited quantities.
Other popular recreational fisheries in the Chesapeake Bay include shad, cobia, croaker, and redfish, winter flounder, and summer flounder. Recently, non-native blue catfish have proliferated in tributaries like the James River and may be moving to other areas of the Bay. A commercial fishery exists for menhaden, too oily for human consumption but instead used for bait, fish oil, and livestock feed. | 2 | Environmental Chemistry |
In the first enantioselective synthesis of (+)-Griseofulvin, a potent antifungal agent, a Curtin–Hammett situation was observed. A key step in the synthesis is the rhodium-catalyzed formation of an oxonium ylide, which then undergoes a [2,3] sigmatropic rearrangement en route to the desired product. However, the substrate contains two ortho-alkoxy groups, either of which could presumably participate in oxonium ylide generation.
Obtaining high selectivity for the desired product was possible, however, due to differences in the activation barriers for the step following ylide formation. If the ortho-methoxy group undergoes oxonium ylide formation, a 1,4-methyl shift can then generate an undesired product. The oxonium ylide formed from the other ortho-alkoxy group is primed to undergo a [2,3] sigmatropic rearrangement to yield the desired compound. Pirrung and coworkers reported complete selectivity for the desired product over the product resulting from a 1,4-methyl shift. This result suggests that oxonium ylide formation is reversible, but that the subsequent step is irreversible. The symmetry-allowed [2,3] sigmatropic rearrangement must follow a pathway that is lower in activation energy than the 1,4-methyl shift, explaining the exclusive formation of the desired product. | 7 | Physical Chemistry |
Compared to normal analyses methods, microanalysis:
* Can resolve fine-scale variations in chemical elements.
* Can be used to identify the presence and distribution of different phases in materials.
* Requires less sample material and therefore can provide information on microscopic objects. | 3 | Analytical Chemistry |
Starch granules are very common in chloroplasts, typically taking up 15% of the organelle's volume, though in some other plastids like amyloplasts, they can be big enough to distort the shape of the organelle. Starch granules are simply accumulations of starch in the stroma, and are not bounded by a membrane.
Starch granules appear and grow throughout the day, as the chloroplast synthesizes sugars, and are consumed at night to fuel respiration and continue sugar export into the phloem, though in mature chloroplasts, it is rare for a starch granule to be completely consumed or for a new granule to accumulate.
Starch granules vary in composition and location across different chloroplast lineages. In red algae, starch granules are found in the cytoplasm rather than in the chloroplast. In plants, mesophyll chloroplasts, which do not synthesize sugars, lack starch granules. | 5 | Photochemistry |
In the mid-20th century, prior to the development of solid state components such as Zener diodes, voltage regulation in circuits was often accomplished with voltage-regulator tubes, which used glow discharge. | 3 | Analytical Chemistry |
Glycerate 3-phosphate (formed from 3-phosphoglycerate) is also a precursor for serine, which, in turn, can create cysteine and glycine through the homocysteine cycle. | 5 | Photochemistry |
* Complexity of library construction - this technology requires high molecular DNA preparation in order to produce long enough DNA molecules for sequencing.
* Limitations in read length may result in limited haplotype resolution, which could reduce the efficacy of this technology in highly complex genomic regions. | 1 | Biochemistry |
Senapathy analyzed the distribution of the ORF lengths in computer-generated random DNA sequences first. Surprisingly, this study revealed that about 200 codons (600 bases) was the upper limit in ORF lengths. The shortest ORF (zero base in length) was the most frequent. At increasing lengths of ORFs, their frequency decreased logarithmically, approaching zero at about 600 bases. When the probability of ORF lengths in a random sequence was plotted, it revealed that the probability of increasing lengths of ORFs decreased exponentially and tailed off at a maximum of about 600 bases. From this “negative exponential” distribution of ORF lengths, it was found that most of ORFs were far shorter than the maximum.This finding was surprising because the coding sequence for the average protein length of 400 AAs (with ~1,200 bases of coding sequence) and longer proteins of thousands of AAs (requiring >10,000 bases of coding sequence) would not occur at a stretch in a random sequence. If this was true, a typical gene with a contiguous coding sequence could not originate in a random sequence. Thus, the only possible way that any gene could originate from a random sequence was to split the coding sequence into shorter segments and select these segments from short ORFs available in the random sequence, rather than to increase the ORF length by eliminating consecutive stop codons. This process of choosing short segments of coding sequences from the available ORFs to make a long ORF would lead to a split structure.
If this hypothesis was true, eukaryotic DNA sequences should reflect it. When Senapathy plotted the distribution of ORF lengths in eukaryotic DNA sequences, the plot was remarkably similar to that from random DNA sequences. This plot was also a negative exponential distribution that tailed off at a maximum of about 600 bases, as with eukaryotic genes, which coincided exactly with the maximum length of ORFs observed in both random DNA and eukaryotic DNA sequences.
The split genes thus originated from random DNA sequences by choosing the best of the short coding segments (exons) and splicing them. The intervening intron sequences were left-over vestiges of the random sequences, and thus were earmarked to be removed by the spliceosome. These findings indicated that split genes could have originated from random DNA sequences with exons and introns as they appear in today's eukaryotic organisms. Nobel Laureate Marshall Nirenberg, who deciphered the codons, stated that these findings strongly showed that the split gene theory for the origin of introns and the split structure of genes must be valid.
Blake proposed the Gilbert-Blake hypothesis in 1979 for the origin of introns and stated that Senapathy's split gene theory comprehensively explained the origin of the split gene structure. In addition, he stated that it explained several key questions including the origin of the splicing mechanism: | 1 | Biochemistry |
Failing home septic systems can allow coliforms in the effluent to flow into the water table, aquifers, drainage ditches and nearby surface waters. Sewage connections that are connected to storm drain pipes can also allow human sewage into surface waters. Some older industrial cities, particularly in the Northeast and Midwest of the United States, use a combined sewer system to handle waste. A combined sewer carries both domestic sewage and stormwater. During high rainfall periods, a combined sewer can become overloaded and overflow to a nearby stream or river, bypassing treatment. | 3 | Analytical Chemistry |
Modafinil, a eugeroic or wakefulness-promoting drug, is primarily used for treating narcolepsy, a sleep disorder characterized by excessive daytime sleepiness and sudden sleep attacks. Being a central nervous system (CNS) stimulant (psychostimulant) itself, modafinil has lower addictive potential than classical psychostimulants, such as amphetamines, cocaine or methylphenidate, but still produces psychoactive, euphoric, and subjective effects typical of classical stimulants.
Narcolepsy causes a strong urge to sleep during the day and can include symptoms like cataplexy (sudden muscle weakness), sleep paralysis (inability to move or speak while falling asleep or waking up), and hallucinations. Narcolepsy is linked to a lack of the brain chemical hypocretin (or orexin), primarily produced in the hypothalamus. Modafinil is not a cure for narcolepsy, but it can help manage the symptoms. While modafinil is primarily used to treat excessive sleepiness, it may also help reduce the frequency and severity of cataplexy attacks in some people. Modafinil is approved for management of narcolepsy with or without cataplexy. However, it is not specifically approved for the treatment of cataplexy.
Modafinil is also prescribed for shift work sleep disorder and excessive daytime sleepiness caused by obstructive sleep apnea, though it is recommended that people with apnea use continuous positive airway pressure (CPAP) therapy before starting modafinil.
Modafinil's use varies by region. In the US, it is approved for adult narcolepsy, shift work sleep disorder, and obstructive sleep apnea, but not for children. In the UK and the EU, since 2014, it is approved solely for narcolepsy, including in children (pediatric narcolepsy), with its use for other conditions restricted by the European Medicines Agency.
both the French and the American Academy of Sleep Medicine strongly recommend modafinil as the first-choice treatment for narcolepsy. In Europe, modafinil is considered one of the primary drugs recommended for treating narcolepsy according to the guidelines. | 4 | Stereochemistry |
Table of the wallpaper groups using the classification of the 2-dimensional space groups:
For each geometric class, the possible arithmetic classes are
* None: no reflection lines
* Along: reflection lines along lattice directions
* Between: reflection lines halfway in between lattice directions
* Both: reflection lines both along and between lattice directions | 4 | Stereochemistry |
Although the passage of food into the gastrointestinal tract results in increased blood flow to the stomach and intestines, this is achieved by diversion of blood primarily from skeletal muscle tissue and by increasing the volume of blood pumped forward by the heart each minute. The flow of oxygen and blood to the brain is extremely tightly regulated by the circulatory system and does not drop after a meal. | 1 | Biochemistry |
UV-A presents a potential hazard when eyes and skin are exposed, especially to high power sources. According to the World Health Organization, UV-A is responsible for the initial tanning of skin and it contributes to skin ageing and wrinkling. UV-A may also contribute to the progression of skin cancers. Additionally, UV-A can have negative effects on eyes in both the short-term and long-term. | 5 | Photochemistry |
A frequency comb or spectral comb is a spectrum made of discrete and regularly spaced spectral lines.
In optics, a frequency comb can be generated by certain laser sources.
A number of mechanisms exist for obtaining an optical frequency comb, including periodic modulation (in amplitude and/or phase) of a continuous-wave laser, four-wave mixing in nonlinear media, or stabilization of the pulse train generated by a mode-locked laser. Much work has been devoted to this last mechanism, which was developed around the turn of the 21st century and ultimately led to one half of the Nobel Prize in Physics being shared by John L. Hall and Theodor W. Hänsch in 2005.
The frequency domain representation of a perfect frequency comb is like a Dirac comb, a series of delta functions spaced according to
where is an integer, is the comb tooth spacing (equal to the mode-locked laser's repetition rate or, alternatively, the modulation frequency), and is the carrier offset frequency, which is less than .
Combs spanning an octave in frequency (i.e., a factor of two) can be used to directly measure (and correct for drifts in) . Thus, octave-spanning combs can be used to steer a piezoelectric mirror within a carrier–envelope phase-correcting feedback loop. Any mechanism by which the combs' two degrees of freedom ( and ) are stabilized generates a comb that is useful for mapping optical frequencies into the radio frequency for the direct measurement of optical frequency. | 7 | Physical Chemistry |
During the early 1800s, consumers preserved their food by storing food and ice purchased from ice harvesters in iceboxes. In 1803, Thomas Moore patented a metal-lined butter-storage tub which became the prototype for most iceboxes. These iceboxes were used until nearly 1910 and the technology did not progress. In fact, consumers that used the icebox in 1910 faced the same challenge of a moldy and stinky icebox that consumers had in the early 1800s.
General Electric (GE) was one of the first companies to overcome these challenges. In 1911, GE released a household refrigeration unit that was powered by gas. The use of gas eliminated the need for an electric compressor motor and decreased the size of the refrigerator. However, electric companies that were customers of GE did not benefit from a gas-powered unit. Thus, GE invested in developing an electric model. In 1927, GE released the Monitor Top, the first refrigerator to run on electricity.
In 1930, Frigidaire, one of GE's main competitors, synthesized Freon. With the invention of synthetic refrigerants based mostly on a chlorofluorocarbon (CFC) chemical, safer refrigerators were possible for home and consumer use. Freon led to the development of smaller, lighter, and cheaper refrigerators. The average price of a refrigerator dropped from $275 to $154 with the synthesis of Freon. This lower price allowed ownership of refrigerators in American households to exceed 50% by 1940. Freon is a trademark of the DuPont Corporation and refers to these CFCs, and later hydro chlorofluorocarbon (HCFC) and hydro fluorocarbon (HFC), refrigerants developed in the late 1920s. These refrigerants were considered — at the time — to be less harmful than the commonly-used refrigerants of the time, including methyl formate, ammonia, methyl chloride, and sulfur dioxide. The intent was to provide refrigeration equipment for home use without danger. These CFC refrigerants answered that need. In the 1970s, though, the compounds were found to be reacting with atmospheric ozone, an important protection against solar ultraviolet radiation, and their use as a refrigerant worldwide was curtailed in the Montreal Protocol of 1987. | 7 | Physical Chemistry |
Molybdenum is an essential element in most organisms. It is most notably present in nitrogenase which is an essential part of nitrogen fixation. | 1 | Biochemistry |
This step is very critical and important for any molecular-based technique since it ensures that the small RNA fragments found in the samples to be analyzed are characterized by a good level of purity and quality. There are different purification methods that can be used, based on the purposes of the experiment:
* acid guanidinium thiocyanate-phenol-chloroform extraction: it is based on the use of a guanidinium-thiocyanate solution combined with acid phenol that disrupts cell membranes bringing in solution the nucleic acids and inactivating cellular ribonucleases (chaotropic agent). After this step an aliquot of chloroform is added in order to separate the aqueous phase (containing the RNA molecules) from the organic phase (cellular debris and other contaminants).
* spin column chromatography: universally used method to purify nucleic acids that exploits a spin column containing a special resin that, after a first step of cell lysis, allows the binding of the RNA molecules, eluting unbound particles (several proteins and rRNA). The protocol includes two separate chromatographic runs: the first one is required to isolate the whole RNA content from the sample, while the second one is specific for the isolation of small RNA by adding a small RNA enriched matrix to the column and by using a specific buffer to finally elute them. This method can separate small RNA molecules without the need of adding phenol.
Once small RNAs have been isolated, it is important to quantify them and to evaluate the quality of the purification. There are two different methods to do this:
* analysis of the absorbances and gel electrophoresis: this practical approach exploits the use of a spectrophotometer to evaluate the absorbance of RNA molecules at 260 nm (1 OD = 40 μg/μL) in order to estimate their concentration and to discover possible contaminations (i.g. proteins or carbohydrates); this can be coupled with an electrophoretic run performed in denaturating conditions (8 M urea) to analyze the quality of the purification extracts (low quality extracts will be degraded and displayed as smears in the gel).
* Agilent bioanalyzer: fully automated technique that is based on the use of a special apparatus composed by a chip that allows to perform capillary electrophoresis (CE) using small aliquots of the starting samples and obtaining an electropherogram that is useful to estimate the quality of the extracts thanks to a score (ranging from 1 to 10) attributed by the system. | 1 | Biochemistry |
These processes consist of an annular furnace in which iron ore mixed with coal is circulated. Hot reducing gases flow over, and sometimes through, the charge. The ore is deposited on a tray, or carts, rotating slowly in the furnace. After one rotation, the ore is reduced; it is then discharged and replaced by oxidized ore.
A number of processes have been developed based on this principle. In the 1970s-1980s, the INMETCO process demonstrated only the validity of the idea, with no industrial application. The MAUMEE (or DryIron) process came to fruition in the US with the construction of two small industrial units in the 1990s. Similarly, in Europe, a consortium of Benelux steelmakers developed the COMET process in the laboratory from 1996 to 1998. Despite the consortium's withdrawal from the research program in 1998, a single industrial demonstrator was extrapolated from it, the SIDCOMET, which was discontinued in 2002. RedIron, whose only operational unit was inaugurated in Italy in 2010, also benefits from this research. Japan has adopted the FASTMET process, with the commissioning of three units dedicated to the recovery of iron-rich powders, and is proposing an improved version, the ITmk3 process, with one unit in operation in the United States.
This non-exhaustive list shows that, despite the keen interest shown by steelmakers in developed countries during the 1990s, none of these processes met with commercial success. | 8 | Metallurgy |
The carboxy-terminal domain is also the binding site for spliceosome factors that are part of RNA splicing. These allow for the splicing and removal of introns (in the form of a lariat structure) during RNA transcription. | 1 | Biochemistry |
Hydrolysis of boronic esters back to the boronic acid and the alcohol can be accomplished in certain systems with thionyl chloride and pyridine.
Aryl boronic acids or esters may be hydrolyzed to the corresponding phenols by reaction with hydroxylamine at room temperature. | 0 | Organic Chemistry |
The column is a glass or plastic cylinder packed with beads of resin and filled with buffer solution. It is normally mounted vertically with the buffer flowing downward from top to bottom. A glass frit at the bottom of the column retains the resin beads in the column while allowing the buffer and dissolved proteins to exit. | 3 | Analytical Chemistry |
Bharat has been awarded many prizes and fellowships. These include a 2018 Vallee Research Scholarship, the 2019 EMBL John Kendrew Award the 2020 Philip Leverhulme Prize for Biological Sciences, the 2021 Eppendorf Award for Young European Investigators, and the 2021 Lister Prize, the 2022 Colworth Medal from the Biochemical Society and the 2023 Fleming Prize from the Microbiology Society. | 1 | Biochemistry |
Mutations are modeled as the changes in gene regulation, i.e., the changes of the elements in the regulatory matrix . | 1 | Biochemistry |
The target of a gene gun is often a callus of undifferentiated plant cells or a group of immature embryos growing on gel medium in a Petri dish. After the DNA-coated gold particles have been delivered to the cells, the DNA is used as a template for transcription (transient expression) and sometimes it integrates into a plant chromosome (stable transformation)
If the delivered DNA construct contains a selectable marker, then stably transformed cells can be selected and cultured using tissue culture methods. For example, if the delivered DNA construct contains a gene that confers resistance to an antibiotic or herbicide, then stably transformed cells may be selected by including that antibiotic or herbicide in the tissue culture media.
Transformed cells can be treated with a series of plant hormones, such as auxins and gibberellins, and each may divide and differentiate into the organized, specialized, tissue cells of an entire plant. This capability of total re-generation is called totipotency. The new plant that originated from a successfully transformed cell may have new traits that are heritable. The use of the gene gun may be contrasted with the use of Agrobacterium tumefaciens and its Ti plasmid to insert DNA into plant cells. See transformation for different methods of transformation in different species. | 1 | Biochemistry |
About 8,100 plant species use carbon fixation, which represents about 3% of all terrestrial species of plants. All these 8,100 species are angiosperms. carbon fixation is more common in monocots compared with dicots, with 40% of monocots using the pathway, compared with only 4.5% of dicots. Despite this, only three families of monocots use carbon fixation compared to 15 dicot families. Of the monocot clades containing plants, the grass (Poaceae) species use the photosynthetic pathway most. 46% of grasses are and together account for 61% of species. has arisen independently in the grass family some twenty or more times, in various subfamilies, tribes, and genera, including the Andropogoneae tribe which contains the food crops maize, sugar cane, and sorghum. Various kinds of millet are also . Of the dicot clades containing species, the order Caryophyllales contains the most species. Of the families in the Caryophyllales, the Chenopodiaceae use carbon fixation the most, with 550 out of 1,400 species using it. About 250 of the 1,000 species of the related Amaranthaceae also use .
Members of the sedge family Cyperaceae, and members of numerous families of eudicots – including Asteraceae (the daisy family), Brassicaceae (the cabbage family), and Euphorbiaceae (the spurge family) – also use .
No large trees (above 15 m in height) use , however a number of small trees or shrubs smaller than 10 m exist which do: six species of Euphorbiaceae all native to Hawaii and two species of Amaranthaceae growing in deserts of the Middle-East and Asia. | 5 | Photochemistry |
Assisted reproduction via MRT involves preimplantation genetic screening of the mother, preimplantation genetic diagnosis after the egg is fertilized, and in vitro fertilization. It has all the risks of those procedures.
In addition, both procedures used in MRT entail their own risks. On one level, the procedures physically disrupt two oocytes, removing nuclear genetic material from the recipient egg or fertilized egg and inserting the nuclear genetic material into the donor unfertilized or fertilized egg; the manipulations for both procedures may cause various forms of damage that were not well understood as of 2016.
Maternal mitochondria will be carried over to the donor egg; as of 2016 it was estimated that using techniques current in the UK, maternal mitochondria will comprise only around 2% or less of mitochondria in the resulting egg, a level that was considered safe by the HFEA and within the limits of mitochondrial variation that most people have.
Because MRT procedures involve actions at precise times during egg development and fertilization, and involves manipulating eggs, there is a risk that eggs may mature abnormally or that fertilization may happen abnormally; as of 2016 the HFEA judged that laboratory techniques in the UK had been well enough developed to manage these risks to proceed cautiously with making MRT available.
Because mitochondria in the final egg will come from a third party, different from the two parties whose DNA is in the nucleus, and because nuclear DNA encodes genes that make some of the proteins and mRNA used by mitochondria, there is a theoretical risk of adverse "mito–nuclear" interactions. While this theoretical risk could possibly be managed by attempting to match the haplotype of the donor and the recipient, as of 2016 there was no evidence that this is an actual risk.
Because MRT is a relatively new technology, there are concerns that it is not yet safe for public use as there have been limited studies that used MRT in large animal models.
Finally, there is a risk of epigenetic modification to DNA in the nucleus and mitochondria, caused by the procedure itself or by mito–nuclear interactions. As of 2016 these risks appeared to be minimal but were being monitored by long-term study of children born from the procedure. | 1 | Biochemistry |
DTDP-glucose goes on to form a variety of compounds in nucleotide sugars metabolism. Many bacteria utilize dTDP-glucose to form exotic sugars that are incorporated into their lipopolysaccharides or into secondary metabolites such as antibiotics. During the syntheses of many of these exotic sugars, dTDP-glucose undergoes a combined oxidation/reduction reaction via the enzyme dTDP-glucose 4,6-dehydratase, producing dTDP-4-keto-6-deoxy-glucose. | 1 | Biochemistry |
In 1990, researchers identified the first HIV bNAb, far more powerful than any antibody seen before. They described the exact viral component, or epitope that triggered the antibody. Six amino acids at the tip of HIV's surface protein, gp120, were responsible. The first bNAb turned out to be clinically irrelevant, but in 1994 another team isolated a bNAb that worked on cells taken from patients. This antibody attached to a "conserved" portion of gp120 that outlasts many of its mutations, affecting 17/24 tested strains at low doses. Another bNAb was discovered that acted on protein gp41 across many strains. Antibodies require antigens to trigger them and these were not originally identified.
Over time more bNAbs were isolated, while single cell antibody cloning made it possible to produce large quantities of the antibodies for study. Low levels of bNAbs are now found in up to 25% of HIV patients. bNAbs evolve over years, accumulating some three times as many mutations as other antibodies.
By 2006, researchers had identified a few so-called "broadly neutralizing antibodies" (bNAbs) that worked on multiple HIV strains. They analyzed 1800 blood samples from HIV-infected people from Africa, South Asia and the English-speaking world. They individually probed 30,000 of one woman's antibody-producing B cells and isolated two that were able to stop more than 70% of 162 divergent HIV strains from establishing an infection. Since 2009, researchers have identified more than 50 HIV bNAbs. Integrated web resource BNAber, focused on broadly neutralizing HIV-1 antibodies, has recently been introduced.
In 2006, a Malawian man joined a study within weeks of becoming infected. Over a year, he repeatedly donated blood, which researchers used to create a timeline of changes in his virus' gp120, his antibody response and the ultimate emergence of a bNAb. Researchers want to direct this evolution in other subjects to achieve similar results. A screen of massive gp120 libraries led to one that strongly bound both an original antibody and the mature bNAb that evolved from it. Giving patients a modified gp120 that contains little more than the epitope that both antibodies target could act to "prime" the immune system, followed by a booster that contains trimer spikes in the most natural configuration possible. However, it is still under study whether bNAbs could prevent HIV infection.
In 2009, researchers isolated and characterized the first HIV bNAbs seen in a decade. The two broadest neutralizers were PGT151 and PGT152. They could block about two-thirds of a large panel of HIV strains. Unlike most other bNAbs, these antibodies do not bind to known epitopes, on Env or on Env's subunits (gp120 or gp41). Instead, they attach to parts of both. Gp120 and gp41 assemble as a trimer. The bNAbs binding site occurs only on the trimer structure, the form of Env that invades host cells.
Recent years have seen an increase in HIV-1 bNAb discovery. | 1 | Biochemistry |
If an initially isolated physical system, without internal walls that establish adiabatically isolated subsystems, is left long enough, it will usually reach a state of thermal equilibrium in itself, in which its temperature will be uniform throughout, but not necessarily a state of thermodynamic equilibrium, if there is some structural barrier that can prevent some possible processes in the system from reaching equilibrium; glass is an example. Classical thermodynamics in general considers idealized systems that have reached internal equilibrium, and idealized transfers of matter and energy between them.
An isolated physical system may be inhomogeneous, or may be composed of several subsystems separated from each other by walls. If an initially inhomogeneous physical system, without internal walls, is isolated by a thermodynamic operation, it will in general over time change its internal state. Or if it is composed of several subsystems separated from each other by walls, it may change its state after a thermodynamic operation that changes its walls. Such changes may include change of temperature or spatial distribution of temperature, by changing the state of constituent materials. A rod of iron, initially prepared to be hot at one end and cold at the other, when isolated, will change so that its temperature becomes uniform all along its length; during the process, the rod is not in thermal equilibrium until its temperature is uniform. In a system prepared as a block of ice floating in a bath of hot water, and then isolated, the ice can melt; during the melting, the system is not in thermal equilibrium; but eventually, its temperature will become uniform; the block of ice will not re-form. A system prepared as a mixture of petrol vapour and air can be ignited by a spark and produce carbon dioxide and water; if this happens in an isolated system, it will increase the temperature of the system, and during the increase, the system is not in thermal equilibrium; but eventually, the system will settle to a uniform temperature.
Such changes in isolated systems are irreversible in the sense that while such a change will occur spontaneously whenever the system is prepared in the same way, the reverse change will practically never occur spontaneously within the isolated system; this is a large part of the content of the second law of thermodynamics. Truly perfectly isolated systems do not occur in nature, and always are artificially prepared. | 7 | Physical Chemistry |
Methyl methanesulfonate (MMS), also known as methyl mesylate, is an alkylating agent and a carcinogen. It is also a suspected reproductive toxicant, and may also be a skin/sense organ toxicant. It is used in cancer treatment. | 0 | Organic Chemistry |
The most well-known example of a coarctate transition state is that of the epoxidation of an olefin by dimethyldioxirane. In this transition state, the oxygen atom transferred to the olefin forms a cycle with the acetone leaving group and a cycle with the olefin undergoing epoxidation. Another well-studied reaction is the fragmentation of spirocyclic ozonides into formaldehyde, CO, and an olefin.
Selection rules, resembling the Woodward-Hoffmann rules, have been proposed to explain patterns in reaction activation energy related to transition state topology or orbital symmetry. | 0 | Organic Chemistry |
Excitatory amino acid receptor ligands are ligands of excitatory amino acid receptors (EAARs), also known as glutamate receptors. They include excitatory amino acid receptor agonists and excitatory amino acid receptor antagonists. | 1 | Biochemistry |
In Australia, the average age of women undergoing ART treatment is 35.5 years among those using their own eggs (one in four being 40 or older) and 40.5 years among those using donated eggs. While IVF is available in Australia, Australians using IVF are unable to choose their baby's gender. | 1 | Biochemistry |
Comex provides sorting technologies for mining industries using multi-sensory solution integrated in the same sorting units, like X-ray, hyper-spectral IR and color optical sensors and 3D cameras, which can be very effective in identifying and sorting of various mineral particles. Integration of AI models for sensor data processing is of critical importance to achieve good sorting results. | 3 | Analytical Chemistry |
The Freundlich isotherm is the most important multi-site adsorption isotherm for rough surfaces.
where α and C are fitting parameters. This equation implies that if one makes a log–log plot of adsorption data, the data will fit a straight line. The Freundlich isotherm has two parameters, while Langmuirs equations has only one: as a result, it often fits the data on rough surfaces better than the Langmuirs equations. However, the Freundlich equation is unique; consequently, if the data fit the equation, it is only likely, but not proved, that the surface is heterogeneous. The heterogeneity of the surface can be confirmed with calorimetry. Homogeneous surfaces (or heterogeneous surfaces that exhibit homogeneous adsorption (single-site)) have a constant of adsorption as a function of the occupied-sites fraction. On the other hand, heterogeneous adsorption (multi-site) have a variable of adsorption depending on the sites occupation. When the adsorbate pressure (or concentration) are low, high-energy sites are occupied, and as the pressure (or concentration) increases, the lesser-energy sites become occupied, resulting in a lower of adsorption.
A related equation is the Toth equation. Rearranging the Langmuir equation, one can obtain
Toth modified this equation by adding two parameters α</sub> to formulate the Toth equation: | 7 | Physical Chemistry |
Communist party Chairman Mao Zedong disdained the cities and put his faith in the Chinese peasantry for a Great Leap Forward. Mao saw steel production as the key to overnight economic modernization, promising that within 15 years China's steel production would surpass that of Britain. In 1958 he decided that steel production would double within the year, using backyard steel furnaces run by inexperienced peasants. The plan was a fiasco, as the small amounts of steel produced were of very poor quality, and the diversion of resources out of agriculture produced a massive famine in 1959–61 that killed millions.
With economic reforms brought in by Deng Xiaoping, who led China from 1978 to 1992, China began to develop a modern steel industry by building new steel plants and recycling scrap metal from the United States and Europe. As of 2013 China produced 779 million metric tons of steel each year, making it by far the largest steel producing country in the world. This is compared to 165 for the European Union, 110 for Japan, 87 for the United States and 81 for India. China's 2013 steel production was equivalent to an average of 3.14 cubic meters of steel per second. | 8 | Metallurgy |
Elementary modes may be considered minimal realizable flow patterns through a biochemical network that can sustain a steady state. This means that elementary modes cannot be decomposed further into simpler pathways. All possible flows through a network can be constructed from linear combinations of the elementary modes.
The set of elementary modes for a given network is unique (up to an arbitrary scaling factor). Given the fundamental nature of elementary modes in relation to uniqueness and non-decomposability, the term `pathway' can be defined as an elementary mode. Note that the set of elementary modes will change as the set of expressed enzymes change during transitions from one cell state to another. Mathematically, the set of elementary modes is defined as the set of flux vectors, , that satisfy the steady state condition,
where is the stoichiometry matrix, is the vector of rates, the vector of steady state floating (or internal) species and , the vector of system parameters.
An important condition is that the rate of each irreversible reaction must be non-negative, .
A more formal definition is given by:
An elementary mode, , is defined as a vector of fluxes, , such that the three conditions listed in the following criteria are satisfied.
# The vector must satisfy: , that is: the steady state condition.
# For all irreversible reactions: . This means that all flow patterns must use reactions that proceed in their most natural direction. This makes the pathway described by the elementary mode a thermodynamically feasible pathway.
# The vector must be elementary. That is, it should not be possible to generate by combining two other vectors that satisfy the first and second requirements using the same set of enzymes that appear as non-zero entries in . In other words, it should not be possible to decompose into two other pathways that can themselves sustain a steady state. This is called elementarity. A more formal test is that the null space of the submatrix of that only involves the reactions of is of dimension one and has no zero entries. | 1 | Biochemistry |
Classical thermodynamics is the description of the states of thermodynamic systems at near-equilibrium, that uses macroscopic, measurable properties. It is used to model exchanges of energy, work and heat based on the laws of thermodynamics. The qualifier classical reflects the fact that it represents the first level of understanding of the subject as it developed in the 19th century and describes the changes of a system in terms of macroscopic empirical (large scale, and measurable) parameters. A microscopic interpretation of these concepts was later provided by the development of statistical mechanics. | 7 | Physical Chemistry |
The application of kinetic theory to ideal gases makes the following assumptions:
* The gas consists of very small particles. This smallness of their size is such that the sum of the volume of the individual gas molecules is negligible compared to the volume of the container of the gas. This is equivalent to stating that the average distance separating the gas particles is large compared to their size, and that the elapsed time during a collision between particles and the container's wall is negligible when compared to the time between successive collisions.
* The number of particles is so large that a statistical treatment of the problem is well justified. This assumption is sometimes referred to as the thermodynamic limit.
* The rapidly moving particles constantly collide among themselves and with the walls of the container, and all these collisions are perfectly elastic.
* Interactions (i.e. collisions) between particles are strictly binary and uncorrelated, meaning that there are no three-body (or higher) interactions, and the particles have no memory.
* Except during collisions, the interactions among molecules are negligible. They exert no other forces on one another.
Thus, the dynamics of particle motion can be treated classically, and the equations of motion are time-reversible.
As a simplifying assumption, the particles are usually assumed to have the same mass as one another; however, the theory can be generalized to a mass distribution, with each mass type contributing to the gas properties independently of one another in agreement with Daltons Law of partial pressures. Many of the models predictions are the same whether or not collisions between particles are included, so they are often neglected as a simplifying assumption in derivations (see below).
More modern developments, such as Revised Enskog Theory and the Extended BGK model, relax one or more of the above assumptions. These can accurately describe the properties of dense gases, and gases with internal degrees of freedom, because they include the volume of the particles as well as contributions from intermolecular and intramolecular forces as well as quantized molecular rotations, quantum rotational-vibrational symmetry effects, and electronic excitation. While theories relaxing the assumptions that the gas particles occupy negligible volume and that collisions are strictly elastic have been successful, it has been shown that relaxing the requirement of interactions being binary and uncorrelated will eventually lead to divergent results. | 7 | Physical Chemistry |
In humans, there are three genes in the Akt family: AKT1, AKT2, and AKT3. These enzymes are members of the serine/threonine-specific protein kinase family ().
Akt1 is involved in cellular survival pathways and inhibition of apoptotic processes. Akt1 is also able to induce protein synthesis pathways, and is therefore a key signaling protein in the cellular pathways that lead to skeletal muscle hypertrophy, and general tissue growth. Since it can block apoptosis, and thereby promote cell survival, Akt1 has been implicated as a major factor in many types of cancer. Akt (now also called Akt1) was originally identified as the oncogene in the transforming retrovirus, AKT8.
Akt2 is important in the insulin signaling pathway. It is required to induce glucose transport.
These separate roles for Akt1 and Akt2 were demonstrated by studying mice in which either the Akt1 or the Akt2 gene was deleted, or "knocked out". In a mouse that is null for Akt1 but normal for Akt2, glucose homeostasis is unperturbed, but the animals are smaller, consistent with a role for Akt1 in growth. In contrast, mice that do not have Akt2 but have normal Akt1 have mild growth deficiency and display a diabetic phenotype (insulin resistance), again consistent with the idea that Akt2 is more specific for the insulin receptor signaling pathway.
The role of Akt3 is less clear, though it appears to be expressed predominantly in brain. It has been reported that mice lacking Akt3 have small brains. | 1 | Biochemistry |
Physically based models (sometimes known as deterministic, comprehensive or process-based models) try to represent the physical processes observed in the real world. Typically, such models contain representations of surface runoff, subsurface flow, evapotranspiration, and channel flow, but they can be far more complicated. "Large scale simulation experiments were begun by the U.S. Army Corps of Engineers in 1953 for reservoir management on the main stem of the Missouri River". This, and other early work that dealt with the River Nile and the Columbia River are discussed, in a wider context, in a book published by the Harvard Water Resources Seminar, that contains the sentence just quoted. Another early model that integrated many submodels for basin chemical hydrology was the Stanford Watershed Model (SWM). The SWMM (Storm Water Management Model), the HSPF (Hydrological Simulation Program – FORTRAN) and other modern American derivatives are successors to this early work.
In Europe a favoured comprehensive model is the Système Hydrologique Européen (SHE), which has been succeeded by MIKE SHE and SHETRAN. MIKE SHE is a watershed-scale physically based, spatially distributed model for water flow and sediment transport. Flow and transport processes are represented by either finite difference representations of partial differential equations or by derived empirical equations. The following principal submodels are involved:
:* Evapotranspiration: Penman-Monteith formalism
:* Erosion: Detachment equations for raindrop and overland flow
:* Overland and Channel Flow: Saint-Venant equations of continuity and momentum
:* Overland Flow Sediment Transport: 2D total sediment load conservation equation
:* Unsaturated Flow: Richards equation
:* Saturated Flow: Darcy's law and the mass conservation of 2D laminar flow
:* Channel Sediment Transport 1D mass conservation equation.
This model can analyze effects of land use and climate changes upon in-stream water quality, with consideration of groundwater interactions.
Worldwide a number of basin models have been developed, among them RORB (Australia), Xinanjiang (China), Tank model (Japan), ARNO (Italy), TOPMODEL (Europe), UBC (Canada) and HBV (Scandinavia), MOHID Land (Portugal). However, not all of these models have a chemistry component. Generally speaking, SWM, SHE and TOPMODEL have the most comprehensive stream chemistry treatment and have evolved to accommodate the latest data sources including remote sensing and geographic information system data.
In the United States, the Corps of Engineers, Engineer Research and Development Center in conjunction with a researchers at a number of universities have developed the Gridded Surface/Subsurface Hydrologic Analysis GSSHA model. GSSHA is widely used in the U.S. for research and analysis by U.S. Army Corps of Engineers districts and larger consulting companies to compute flow, water levels, distributed erosion, and sediment delivery in complex engineering designs. A distributed nutrient and contaminant fate and transport component is undergoing testing. GSSHA input/output processing and interface with GIS is facilitated by the Watershed Modeling System (WMS).
Another model used in the United States and worldwide is Vflo, a physics-based distributed hydrologic model developed by Vieux & Associates, Inc. Vflo employs radar rainfall and GIS data to compute spatially distributed overland flow and channel flow. Evapotranspiration, inundation, infiltration, and snowmelt modeling capabilities are included. Applications include civil infrastructure operations and maintenance, stormwater prediction and emergency management, soil moisture monitoring, land use planning, water quality monitoring, and others. | 2 | Environmental Chemistry |
In the case of step-growth polymerisation of monomers carrying functional groups of the same type (so called polymerisation) the degree distribution is given by: where is bond conversion, is the average functionality, and is the initial fractions of monomers of functionality . In the later expression unit reaction rate is assumed without loss of generality. According to the theory, the system is in the gel state when , where the gelation conversion is . Analytical expression for average molecular weight and molar mass distribution are known too. When more complex reaction kinetics are involved, for example chemical substitution, side reactions or degradation, one may still apply the theory by computing using numerical integration. In which case, signifies that the system is in the gel state at time t (or in the sol state when the inequality sign is flipped). | 7 | Physical Chemistry |
When an antigen-presenting cell interacts with a T cell receptor on T cells, there is an increase in the cytoplasmic level of calcium, which activates calcineurin by binding a regulatory subunit and activating calmodulin binding. Calcineurin induces transcription factors (NFATs) that are important in the transcription of IL-2 genes. IL-2 activates T-helper lymphocytes and induces the production of other cytokines. In this way, it governs the action of cytotoxic lymphocytes. The amount of IL-2 being produced by the T-helper cells is believed to influence the extent of the immune response significantly. | 1 | Biochemistry |
The analytical pipeline for preparation of sample material for Zn isotope measurements is similar to that of Cu, consisting of digestion of host material or concentration from seawater, isolation and purification via anion-exchange chromatography, removal of ions of interfering mass (in particular, Ni) and isotope measurement via MC-ICP-MS (see Copper Isotope Measurement section for more details). | 9 | Geochemistry |
*Chlorofluorocarbons (CFCs): when derived from methane and ethane these compounds have the formulae CClF and CClF, where m is nonzero.
*Hydro-chlorofluorocarbons (HCFCs): when derived from methane and ethane these compounds have the formula CClFH and CClFH, where m, n, x, and y are nonzero.
* and bromofluorocarbons have formulae similar to the CFCs and HCFCs but also include bromine.
*Hydrofluorocarbons (HFCs): when derived from methane, ethane, propane, and butane, these compounds have the respective formulae CFH, CFH, CFH, and CFH, where m is nonzero. | 2 | Environmental Chemistry |
* adenylosuccinate synthase converts IMP to adenylosuccinate
* adenylosuccinate lyase converts adenylosuccinate into AMP
* AMP deaminase converts AMP back into IMP | 1 | Biochemistry |
Light alone does not rapidly degrade methyl violet, but the process is accelerated upon the addition of large band-gap semiconductors, TiO or ZnO. | 3 | Analytical Chemistry |
In organic chemistry, a methiodide is a chemical derivative produced by the reaction of a compound with methyl iodide. Methiodides are often formed through the methylation of tertiary amines:
: RN + CHI → (CH)RNI
Whereas the parent amines are hydrophobic and often oily, methiodides, being salts, are somewhat hydrophilic and exhibit high melting points. Methiodides exhibit altered pharmacological properties as well.
Examples include:
* Cocaine methiodide, a charged cocaine analog which cannot pass the blood brain barrier and enter the brain
* Bicuculline methiodide, a water-soluble form of bicuculline
Tertiary phosphines and phosphite esters also form methiodides. | 0 | Organic Chemistry |
Biotechnology,
Bioluminescence,
Molecular chemistry,
Enzymatic chemistry,
Genetic engineering,
Pharmaceuticals,
Endocrinology,
Neurochemistry,
Hematology,
Nutrition,
Photosynthesis,
Environmental,
Toxicology | 1 | Biochemistry |
* 2015 (forthcoming) Providence, RI, September 27-October 2, 2015
* 2014 (forthcoming) Reno, NV, September 28-October 3, 2014
* 2013 (forthcoming) Milwaukee, WI, September 29-October 3, 2013, which will be the 40th annual meeting of the FACSS organization
* 2012 - Kansas City, MO
* 2011 - Reno, NV
*2010 - Raleigh, NC
*2009 - Louisville, KY
*2008 - Reno, NV
*2007 - Memphis, TN
*2006 - Lake Buena Vista, FL
*2005 - Quebec City, Canada
*2004 - Portland, OR
*2003 - Ft. Lauderdale, FL
*2002 - Providence, RI
*2001 - Detroit, Michigan
*2000 - Nashville, Tennessee
*1999 - Vancouver, BC
*1998 - Austin, TX
Accompanying each conference, attendees receive a final program book of abstracts which includes the schedule of talks, profiles of award winners, a list of exhibitors, and much more. Copies of these final programs for all forty of the conferences held by FACSS are available for download as .pdf files from the FACSS website, under [https://web.archive.org/web/20130827101831/http://facss.org/facss-presents/past-events Past Events]. | 7 | Physical Chemistry |
Glycoside hydrolases are predicted to gain increasing roles as catalysts in biorefining
applications in the future bioeconomy. These enzymes have a variety of uses including degradation of plant materials (e.g., cellulases for degrading cellulose to glucose, which can be used for ethanol production), in the food industry (invertase for manufacture of invert sugar, amylase for production of maltodextrins), and in the paper and pulp industry (xylanases for removing hemicelluloses from paper pulp). Cellulases are added to detergents for the washing of cotton fabrics and assist in the maintenance of colours through removing microfibres that are raised from the surface of threads during wear.
In organic chemistry, glycoside hydrolases can be used as synthetic catalysts to form glycosidic bonds through either reverse hydrolysis (kinetic approach) where the equilibrium position is reversed; or by transglycosylation (kinetic approach) whereby retaining glycoside hydrolases can catalyze the transfer of a glycosyl moiety from an activated glycoside to an acceptor alcohol to afford a new glycoside.
Mutant glycoside hydrolases termed glycosynthases have been developed that can achieve the synthesis of glycosides in high yield from activated glycosyl donors such as glycosyl fluorides. Glycosynthases are typically formed from retaining glycoside hydrolases by site-directed mutagenesis of the enzymic nucleophile to some other less nucleophilic group, such as alanine or glycine. Another group of mutant glycoside hydrolases termed thioglycoligases can be formed by site-directed mutagenesis of the acid-base residue of a retaining glycoside hydrolase. Thioglycoligases catalyze the condensation of activated glycosides and various thiol-containing acceptors.
Various glycoside hydrolases have shown efficacy in degrading matrix polysaccharides within the extracellular polymeric substance (EPS) of microbial biofilms. Medically, biofilms afford infectious microorganisms a variety of advantages over their planktonic, fre-floating counterparts, including greatly increased tolerances to antimicrobial agents and the host immune system. Thus, degrading the biofilm may increase antibiotic efficacy, and potentiate host immune function and healing ability. For example, a combination of alpha-amylase and cellulase was shown to degrade polymicrobial bacterial biofilms from both in vitro and in vivo sources, and increase antibiotic effectiveness against them. | 0 | Organic Chemistry |
Much research has been conducted on the discovery of catalysts for nitrogen fixation, often with the goal of lowering energy requirements. However, such research has thus far failed to approach the efficiency and ease of the Haber process. Many compounds react with atmospheric nitrogen to give dinitrogen complexes. The first dinitrogen complex to be reported was (). Some soluble complexes do catalyze nitrogen fixation. | 1 | Biochemistry |
Overdose of levonorgestrel as an emergency contraceptive has not been described. Nausea and vomiting might be expected. | 4 | Stereochemistry |
Photosensitizers are dye compounds that absorb the photons from incoming light and eject electrons, producing an electric current that can be used to power a device or a storage unit. According to a new study performed by Michael Grätzel and fellow scientist Anders Hagfeldt, advances in photosensitizers have resulted in a substantial improvement in performance of DSSC’s under solar and ambient light conditions. Another key factor to achieve power-conversion records is cosensitization, due to its ability combine dyes that can absorb light across a wider range of the light spectrum. Cosensitization is a chemical manufacturing method that produces DSSC electrodes containing two or more different dyes with complementary optical absorption capabilities, enabling the use of all available sunlight.
The researchers from Switzerland’s École polytechnique fédérale de Lausanne (EPFL) found that the efficiency to cosensitized solar cells can be raised by the pre-adsorption of a monolayer of hydroxamic acid derivative on a surface of nanocrystalline mesoporous titanium dioxide, which functions as the electron transport mechanism of the electrode. The two photosensitizer molecules used in the study were the organic dye SL9, which served as the primary long wavelength-light harvester, and the dye SL10, which provided an additional absorption peak that compensates the SL9’s inefficient blue light harvesting. It was found that adding this hydroxamic acid layer improved the dye layer’s molecular packing and ordering. This slowed down the adsorption of the sensitizers and augmented their fluorescence quantum yield, improving the power conversion efficiency of the cell.
The DSSC developed by the team showed a record-breaking power conversion efficiency of 15.2% under standard global simulated sunlight and long-term operational stability over 500 hours. In addition, devices with a larger active area exhibited efficiencies of around 30% while maintaining high stability, offering new possibilities for the DSSC field. | 5 | Photochemistry |
As the world attempts to move towards a low-carbon economy, the technique of using carbon capture by using carbon dioxide from the atmosphere is gaining attention and research being done. Using carbon dioxide in PUD production is being researched. High bio-based content is similarly prized. Coating materials that are vegetable based, waterborne and UV curable are considered very green and have been studied. | 7 | Physical Chemistry |
The Henry volatility can also be expressed as the dimensionless ratio between the gas-phase concentration of a species and its aqueous-phase concentration
In chemical engineering and environmental chemistry, this dimensionless constant is often called the air–water partitioning coefficient | 7 | Physical Chemistry |
In statistical mechanics, a semi-classical derivation of entropy that does not take into account the indistinguishability of particles yields an expression for entropy which is not extensive (is not proportional to the amount of substance in question). This leads to a paradox known as the Gibbs paradox, after Josiah Willard Gibbs, who proposed this thought experiment in 1874‒1875. The paradox allows for the entropy of closed systems to decrease, violating the second law of thermodynamics. A related paradox is the "mixing paradox". If one takes the perspective that the definition of entropy must be changed so as to ignore particle permutation, in the thermodynamic limit, the paradox is averted. | 7 | Physical Chemistry |
Thallium(III) nitrate, also known as thallic nitrate, is a thallium compound with chemical formula Tl(NO). It is normally found as the trihydrate. It is a colorless and highly toxic salt. It is a strong oxidizing agent useful in organic synthesis. Among its many transformations, it oxidizes methoxyl phenols to quinone acetals, alkenes to acetals, and cyclic alkenes to ring-contracted aldehydes. | 0 | Organic Chemistry |
Translation in plants is tightly regulated as in animals, however, it is not as well understood as transcriptional regulation. There are several levels of regulation including translation initiation, mRNA turnover and ribosome loading. Recent studies have shown that translation is also under the control of the circadian clock. Like transcription, the translation state of numerous mRNAs changes over the diel cycle (day night period). | 1 | Biochemistry |
Many problems in molecular reaction dynamics demand the simultaneous measurement of a particle's speed and angular direction; the most demanding require the measurement of this velocity in coincidence with internal energy. Studies of molecular reactions, energy transfer processes and photodissociation can only be understood completely if the internal energies and velocities of all products can be specified.
Product imaging approaches this goal by determining the three-dimensional velocity distribution of one state-selected product of the reaction. For a reaction producing two products, because the speed of the unobserved sibling product is related to that of the measured product through conservation of momentum and energy, the internal state of the sibling can often be inferred. | 7 | Physical Chemistry |
*Patricia A. M. Huntington. [http://www.meteorman.org/Cape%20York.pdf Robert E Peary and the Cape York meteorites] | 8 | Metallurgy |
Another theory suggests that alarm signals function to attract further predators, which fight over the prey organism, giving it a better chance of escape. Others still suggest they are a deterrent to predators, communicating the preys alertness to the predator. One such case is the western swamphen (Porphyrio porphyrio'), which gives conspicuous visual tail flicks (see also aposematism, handicap principle and stotting). | 1 | Biochemistry |
Exemestane is indicated for the adjuvant treatment of postmenopausal women with estrogen-receptor positive early breast cancer who have received two to three years of tamoxifen and are switched to it for completion of a total of five consecutive years of adjuvant hormonal therapy.
US FDA approval was in October 1999.
Exemestane is also indicated for the treatment of advanced breast cancer in postmenopausal women whose disease has progressed following tamoxifen therapy.
For premenopausal women with hormone-receptor–positive breast cancer, adjuvant treatment with ovarian suppression plus the aromatase inhibitor exemestane, as compared with ovarian suppression plus tamoxifen, provides a new treatment option that reduces the risk of recurrence. The TEXT and SOFT trials demonstrated improved disease free survival in patients treated with exemestane and ovarian suppression compared to the tamoxifen and ovarian suppression group. Premenopausal women who receive ovarian suppression may now benefit from an aromatase inhibitor, a class of drugs that until now has been recommended only for postmenopausal women. | 4 | Stereochemistry |
Classical thermodynamics deals with states of dynamic equilibrium. The state of a system at thermodynamic equilibrium is the one for which some thermodynamic potential is minimized (in the absence of an applied voltage), or for which the entropy (S) is maximized, for specified conditions. One such potential is the Helmholtz free energy (A), for a closed system at constant volume and temperature (controlled by a heat bath):
Another potential, the Gibbs free energy (G), is minimized at thermodynamic equilibrium in a closed system at constant temperature and pressure, both controlled by the surroundings:
where T denotes the absolute thermodynamic temperature, P the pressure, S the entropy, V the volume, and U the internal energy of the system. In other words, is a necessary condition for chemical equilibrium under these conditions (in the absence of an applied voltage).
Thermodynamic equilibrium is the unique stable stationary state that is approached or eventually reached as the system interacts with its surroundings over a long time. The above-mentioned potentials are mathematically constructed to be the thermodynamic quantities that are minimized under the particular conditions in the specified surroundings. | 7 | Physical Chemistry |
This involves sampling first onto a sorbent tube. The most widely used tubes are those following the pattern laid out by WG5 (see above). After sampling (for which a variety of accessories are available), the tube is desorbed to transfer the analytes to the focusing trap before the second desorption stage transfers them to the GC. The greater sensitivity of this method has made it increasingly popular for sampling dilute gas streams, or in exploratory work where the target atmosphere is unknown.
*Diffusive (or passive) sampling – A tube is packed with a single sorbent bed and allowed to adsorb analytes from the air diffusively. It is suitable for sampling known compounds over a period of hours (for analyte concentrations of 2–10 μg/m) to weeks (for analyte concentrations of 0.3–300 μg/m).
*Pumped (or active) sampling – A tube is packed with up to three sorbent beds and a flow of the sample gas passed through it. It is suitable for sampling high and low concentrations of known and unknown compounds over timescales of minutes to hours.
*Direct desorption – This is used for sampling emissions from small pieces of solid or semi-solid materials. The material is placed inside a tube and heated to release the vapours directly into the focusing trap.
*Headspace – The material is placed in a (micro-)chamber or other sampling container, and a flow of gas passed through it to transfer the headspace dynamically onto a sorbent tube. | 3 | Analytical Chemistry |
The advantage of TEC-RED over SAGE is that no restriction endonuclease is needed for the initial linker binding. This prevents bias associated with restriction site sequences that will be missing from some genes, as is seen in SAGE. The ability to have a snapshot of specific RNA isoforms allows the deduction of differential regulation of isoforms through alternative selection of promoters. This may also aid in the discernment of expression patterns unique to the SL1 or SL2 sequence. TEC-RED also allows characterization of the 5’ ends of RNA produced and therefore of isoforms that differ by the amino terminal splicing. The technology permits the determination and verification of all known and unknown genes that may be predicted as well as the 5’ splice isoforms or 5’ RNA ends that may be produced. Using TEC-RED in conjunction with SAGE or a modified protocol will allow discernment of the 5’ and 3’ ends of transcripts, respectively. The identification of alternative splice variants, and possibly the relative quantities, containing a trans-spliced leader sequence is therefore possible. | 1 | Biochemistry |
For polymers and polymer complexes that are monodisperse () as determined by static light scattering, a Zimm plot is a conventional means of deriving the parameters such as R, molecular mass M and the second virial coefficient A.
One must note that if the material constant K is not implemented, a Zimm plot will only yield R. Hence implementing K will yield the following equation:
The analysis performed with the Zimm plot uses a double-extrapolation to zero concentration and zero scattering angle resulting in a characteristic rhomboid plot. As the angular information is available, it is also possible to obtain the radius of gyration (R). Experiments are performed at several angles, which satisfy the condition and at least 4 concentrations. Performing a Zimm analysis on a single concentration is known as a partial Zimm analysis and is only valid for dilute solutions of strong point scatterers. The partial Zimm however, does not yield the second virial coefficient, due to the absence of the variable concentration of the sample. More specifically, the value of the second virial coefficient is either assumed to equal zero or is inputted as a known value in order to perform the partial Zimm analysis. | 7 | Physical Chemistry |
According to labeling experiments carried out in 1997, ammonium is biologically oxidized by hydroxylamine, most likely derived from nitrite, as the probable electron acceptor. The conversion of hydrazine to dinitrogen gas is hypothesized to be the reaction that generates the electron equivalents for the reduction of nitrite to hydroxylamine. In general, two possible reaction mechanisms are addressed:
* One mechanism hypothesizes that a membrane-bound enzyme complex converts ammonium and hydroxylamine to hydrazine first, followed by the oxidation of hydrazine to dinitrogen gas in the periplasm. At the same time, nitrite is reduced to hydroxylamine at the cytoplasmic site of the same enzyme complex responsible for hydrazine oxidation with an internal electron transport (Figure 3a).
* The other mechanism postulates the following: ammonium and hydroxylamine are converted to hydrazine by a membrane-bound enzyme complex, hydrazine is oxidized in the periplasm to dinitrogen gas, and the generated electrons are transferred via an electron transport chain to nitrite reducing enzyme in the cytoplasm where nitrite is reduced to hydroxylamine (Figure 3b).
Whether the reduction of nitrite and the oxidation of hydrazine occur at different sites of the same enzyme or the reactions are catalyzed by different enzyme systems connected via an electron transport chain remains to be investigated. In microbial nitrogen metabolism, the occurrence of hydrazine as an intermediate is rare. Hydrazine has been proposed as an enzyme-bound intermediate in the nitrogenase reaction.
Recently, using detailed molecular analyses and combining complementary methods, Kartal and coworkers published strong evidence supporting the latter mechanism.
Furthermore, the enzyme producing hydrazine, hydrazine synthase was purified and shown to produce hydrazine from NO and ammonium. The production of hydrazine from ammonium and NO was also supported by the resolution of the crystal structure of the enzyme hydrazine sythase.
A possible role of nitric oxide (NO) or nitroxyl (HNO) in anammox was proposed by Hooper et al. by way of condensation of NO or HNO and ammonium on an enzyme related to the ammonium monooxygenase family. The formed hydrazine or imine could subsequently be converted by the enzyme hydroxylamine oxidase to dinitrogen gas, and the reducing equivalents produced in the reaction are required to combine NO or HNO and ammonium or to reduce nitrite to NO. Environmental genomics analysis of the species Candidatus Kuenenia stuttgartiensis, through a slightly different and complementary metabolism mechanism, suggested NO to be the intermediate instead of hydroxylamine (Figure 4). However, this hypothesis also agreed that hydrazine was an important intermediate in the process. In this pathway (Figure 4), there are two enzymes unique to anammox bacteria: hydrazine synthase (hzs) and hydrazine dehydrogenase (hdh). The HZS produces hydrazine from nitric oxide and ammonium, and HDH transfer the electrons from hydrazine to ferredoxin. Few new genes, such as some known fatty acid biosynthesis and S-adenosylmethionine radical enzyme genes, containing domains involved in electron transfer and catalysis have been detected. Anammox microorganisms can also directly couple NO reduction to ammonia oxidation, without the need for nitrite supply.
Another, still unexplored, reaction mechanism involves anaerobic ammonium oxidation on anodes of bio-electrical systems. Such systems can be microbial fuel cells or microbial electrolysis cells. In the absence of dissolved oxygen, nitrite, or nitrate, microbes living in the anode compartment are able to oxidize ammonium to dinitrogen gas (N) just as in the classical anammox process. At the same time, they unload the liberated electrons onto the anode, producing electrical current. This electrical current can be used either directly in fuel cell mode or for hydrogen and methane gas production in electrolysis mode. While there is no clarity on the reaction mechanism behind, one hypothesis is that nitrite, nitrate, or dinitrogen oxide play a role as intermediates. However, since the process occurs at very low electrochemical potentials, other, more speculative, reaction mechanisms seem possible as well. | 1 | Biochemistry |
In a centrosymmetric ligand field, such as in octahedral complexes of transition metals, the arrangement of electrons in the d-orbital is not only limited by electron repulsion energy, but it is also related to the splitting of the orbitals due to the ligand field. This leads to many more electron configuration states than is the case for the free ion. The relative energy of the repulsion energy and splitting energy defines the high-spin and low-spin states.
Considering both weak and strong ligand fields, a Tanabe–Sugano diagram shows the energy splitting of the spectral terms with the increase of the ligand field strength. It is possible for us to understand how the energy of the different configuration states is distributed at certain ligand strengths. The restriction of the spin selection rule makes it even easier to predict the possible transitions and their relative intensity. Although they are qualitative, Tanabe–Sugano diagrams are very useful tools for analyzing UV-vis spectra: they are used to assign bands and calculate Dq values for ligand field splitting. | 7 | Physical Chemistry |
In the process of bluing, an oxidizing chemical reaction on an iron surface selectively forms magnetite (FeO), the black oxide of iron (as opposed to rust, the red oxide of iron (FeO)). Black oxide provides some protection against corrosion if also treated with a water-displacing oil to reduce wetting and galvanic action. Bluing is often used with carbon steel and cast iron pans in conjunction with seasoning. | 7 | Physical Chemistry |
Microscopic simulation methods work directly with the equations of motion (classical or quantum) of the constituent molecules. | 7 | Physical Chemistry |
Hexamethylenetetramine was discovered by Aleksandr Butlerov in 1859.
It is prepared industrially by combining formaldehyde and ammonia:
The reaction can be conducted in gas phase and in solution.
The molecule has a tetrahedral cage-like structure, similar to adamantane. Four vertices are occupied by nitrogen atoms, which are linked by methylene groups. Although the molecular shape defines a cage, no void space is available at the interior for binding other atoms or molecules, unlike crown ethers or larger cryptand structures.
The molecule behaves like an amine base, undergoing protonation and N-alkylation (). | 0 | Organic Chemistry |
The terms nucleophile and electrophile were introduced by Christopher Kelk Ingold in 1933, replacing the terms anionoid and cationoid proposed earlier by A. J. Lapworth in 1925. The word nucleophile is derived from nucleus and the Greek word φιλος, philos, meaning friend. | 7 | Physical Chemistry |
Base excess beyond the reference range indicates
* metabolic alkalosis, or respiratory acidosis with renal compensation if too high (more than +2 mEq/L)
* metabolic acidosis, or respiratory alkalosis with renal compensation if too low (less than −2 mEq/L)
Blood pH is determined by both a metabolic component, measured by base excess, and a respiratory component, measured by PaCO (partial pressure of carbon dioxide). Often a disturbance in one triggers a partial compensation in the other. A secondary (compensatory) process can be readily identified because it opposes the observed deviation in blood pH.
For example, inadequate ventilation, a respiratory problem, causes a buildup of CO, hence respiratory acidosis; the kidneys then attempt to compensate for the low pH by raising blood bicarbonate. The kidneys only partially compensate, so the patient may still have a low blood pH, i.e. acidemia. In summary, the kidneys partially compensate for respiratory acidosis by raising blood bicarbonate.
A high base excess, thus metabolic alkalosis, usually involves an excess of bicarbonate. It can be caused by
* Compensation for primary respiratory acidosis
* Excessive loss of HCl in gastric acid by vomiting
* Renal overproduction of bicarbonate, in either contraction alkalosis or Cushing's disease
A base deficit (a below-normal base excess), thus metabolic acidosis, usually involves either excretion of bicarbonate or neutralization of bicarbonate by excess organic acids. Common causes include
* Compensation for primary respiratory alkalosis
* Diabetic ketoacidosis, in which high levels of acidic ketone bodies are produced
* Lactic acidosis, due to anaerobic metabolism during heavy exercise or hypoxia
* Chronic kidney failure, preventing excretion of acid and resorption and production of bicarbonate
* Diarrhea, in which large amounts of bicarbonate are excreted
* Ingestion of poisons such as methanol, ethylene glycol, or excessive aspirin
The serum anion gap is useful for determining whether a base deficit is caused by addition of acid or loss of bicarbonate.
* Base deficit with elevated anion gap indicates addition of acid (e.g., ketoacidosis).
* Base deficit with normal anion gap indicates loss of bicarbonate (e.g., diarrhea). The anion gap is maintained because bicarbonate is exchanged for chloride during excretion. | 1 | Biochemistry |
There are multiple approaches to measuring a persons exposure to pesticides, each of which provides an estimate of an individuals internal dose. Two broad approaches include measuring biomarkers and markers of biological effect. The former involves taking direct measurement of the parent compound or its metabolites in various types of media: urine, blood, serum. Biomarkers may include a direct measurement of the compound in the body before its been biotransformed during metabolism. Other suitable biomarkers may include the metabolites of the parent compound after theyve been biotransformed during metabolism. Toxicokinetic data can provide more detailed information on how quickly the compound is metabolized and eliminated from the body, and provide insights into the timing of exposure.
Markers of biological effect provide an estimation of exposure based on cellular activities related to the mechanism of action. For example, many studies investigating exposure to pesticides often involve the quantification of the acetylcholinesterase enzyme at the neural synapse to determine the magnitude of the inhibitory effect of organophosphate and carbamate pesticides.
Another method of quantifying exposure involves measuring, at the molecular level, the amount of pesticide interacting with the site of action. These methods are more commonly used for occupational exposures where the mechanism of action is better understood, as described by WHO guidelines published in "Biological Monitoring of Chemical Exposure in the Workplace". Better understanding of how pesticides elicit their toxic effects is needed before this method of exposure assessment can be applied to occupational exposure of agricultural workers.
Alternative methods to assess exposure include questionnaires to discern from participants whether they are experiencing symptoms associated with pesticide poisoning. Self-reported symptoms may include headaches, dizziness, nausea, joint pain, or respiratory symptoms. | 2 | Environmental Chemistry |
In the two examples (on the right) the isoelectric point is shown by the green vertical line. In glycine the pK values are separated by nearly 7 units. Thus in the gas phase, the concentration of the neutral species, glycine (GlyH), is effectively 100% of the analytical glycine concentration. Glycine may exist as a zwitterion at the isoelectric point, but the equilibrium constant for the isomerization reaction in solution
is not known.
The other example, adenosine monophosphate is shown to illustrate the fact that a third species may, in principle, be involved. In fact the concentration of is negligible at the isoelectric point in this case.
If the pI is greater than the pH, the molecule will have a positive charge. | 7 | Physical Chemistry |
The quenching process produces a high strength bar from inexpensive low carbon steel. The process quenches the surface layer of the bar, which pressurizes and deforms the crystal structure of intermediate layers, and simultaneously begins to temper the quenched layers using the heat from the bar's core.
Steel billets 130mm² ("pencil ingots") are heated to approximately 1200°C to 1250°C in a reheat furnace. Then, they are progressively rolled to reduce the billets to the final size and shape of reinforcing bar. After the last rolling stand, the billet moves through a quench box. The quenching converts the billet's surface layer to martensite, and causes it to shrink. The shrinkage pressurizes the core, helping to form the correct crystal structures. The core remains hot, and austenitic. A microprocessor controls the water flow to the quench box, to manage the temperature difference through the cross-section of the bars. The correct temperature difference assures that all processes occur, and bars have the necessary mechanical properties.
The bar leaves the quench box with a temperature gradient through its cross section. As the bar cools, heat flows from the bars centre to its surface so that the bars heat and pressure correctly tempers an intermediate ring of martensite and bainite.
Finally, the slow cooling after quenching automatically tempers the austenitic core to ferrite and pearlite on the cooling bed.
These bars therefore exhibit a variation in microstructure in their cross section, having strong, tough, tempered martensite in the surface layer of the bar, an intermediate layer of martensite and bainite, and a refined, tough and ductile ferrite and pearlite core.
When the cut ends of TMT bars are etched in Nital (a mixture of nitric acid and methanol), three distinct rings appear: 1. A tempered outer ring of martensite, 2. A semi-tempered middle ring of martensite and bainite, and 3. a mild circular core of bainite, ferrite and pearlite. This is the desired micro structure for quality construction rebar.
In contrast, lower grades of rebar are twisted when cold, work hardening them to increase their strength. However, after thermo mechanical treatment (TMT), bars do not need more work hardening. As there is no twisting during TMT, no torsional stress occurs, and so torsional stress cannot form surface defects in TMT bars. Therefore TMT bars resist corrosion better than cold, twisted and deformed (CTD) bars.
After thermomechanical processing, some grades in which TMT Bars can be covered includes Fe: 415 /500 /550/ 600. These are much stronger compared with conventional CTD Bars and give up to 20% more strength to concrete structure with same quantity of steel. | 8 | Metallurgy |
Alkylation with geminal dihalides gives 1,3-dithiepanes. Oxidation gives the cyclic disulfide 1,2-dithiane:
It forms self-assembled monolayers on gold.
It is also used in polyadditions along with 1,4-butanediol to form sulfur-containing polyester and polyurethanes containing diisocyanate. Several of these polymers are considered biodegradable and many of their components are sourced from non-petroleum oils. | 0 | Organic Chemistry |
Using the dielectric formalism, the IMFP can be calculated by solving the following integral:
with the minimum (maximum) energy loss (), the dielectric function , the energy loss function (ELF) and the smallest and largest momentum transfer . In general, solving this integral is quite challenging and only applies for energies above 100 eV. Thus, (semi)empirical formulas were introduced to determine the IMFP.
A first approach is to calculate the IMFP by an approximate form of the relativistic Bethe equation for inelastic scattering of electrons in matter. Equation holds for energies between 50 eV and 200 keV:
with
and
and the electron energy in eV above the Fermi level (conductors) or above the bottom of the conduction band (non-conductors). is the electron mass, the vacuum velocity of light, is the number of valence electrons per atom or molecule, describes the density (in ), is the atomic or molecular weight and , , and are parameters determined in the following. Equation calculates the IMFP and its dependence on the electron energy in condensed matter.
Equation was further developed to find the relations for the parameters , , and for energies between 50 eV and 2 keV:
Here, the bandgap energy is given in eV. Equation an are also known as the TTP-2M equations and are in general applicable for energies between 50 eV and 200 keV. Neglecting a few materials (diamond, graphite, Cs, cubic-BN and hexagonal BN) that are not following these equations (due to deviations in ), the TTP-2M equations show precise agreement with the measurements.
Another approach based on Equation to determine the IMFP is the S1 formula. This formula can be applied for energies between 100 eV and 10 keV:
with the atomic number (average atomic number for a compound), or ( is the heat of formation of a compound in eV per atom) and the average atomic spacing :
with the Avogadro constant and the stoichiometric coefficients and describing binary compounds . In this case, the atomic number becomes
with the atomic numbers and of the two constituents. This S1 formula shows higher agreement with measurements compared to Equation .
Calculating the IMFP with either the TTP-2M formula or the S1 formula requires different knowledge of some parameters. Applying the TTP-2M formula one needs to know , and for conducting materials (and also for non-conductors). Employing S1 formula, knowledge of the atomic number (average atomic number for compounds), and is required for conductors. If non-conducting materials are considered, one also needs to know either or .
An analytical formula for calculating the IMFP down to 50 eV was proposed in 2021. Therefore, an exponential term was added to an analytical formula already derived from that was applicible for energies down to 500 eV:
For relativistic electrons it holds:
with the electron velocity , and . denotes the velocity of light. and are given in nanometers. The constants in and are defined as following: | 7 | Physical Chemistry |
At GABAergic synapses, the cycle is called the GABA-glutamine cycle. Here the glutamine taken up by neurons is converted to glutamate, which is then metabolized into GABA by glutamate decarboxylase (GAD). Upon release, GABA is taken up into astrocytes via GABA transporters and then catabolized into succinate by the joint actions of GABA transaminase and succinate-semialdehyde dehydrogenase. Glutamine is synthesized from succinate via the TCA cycle, which includes a condensation reaction of oxaloacetate and acetyl-CoA-forming citrate. Then the synthesis of α-ketoglutarate and glutamate occurs, after which glutamate is again metabolized into GABA by GAD. The supply of glutamine to GABAergic neurons is less significant, because these neurons exhibit a larger proportion of reuptake of the released neurotransmitter compared to their glutamatergic counterparts | 1 | Biochemistry |
Electroporation, or electropermeabilization, is a technique in which an electrical field is applied to cells in order to increase the permeability of the cell membrane. This may allow chemicals, drugs, electrode arrays or DNA to be introduced into the cell (also called electrotransfer).
In microbiology, the process of electroporation is often used to transform bacteria, yeast, or plant protoplasts by introducing new coding DNA. If bacteria and plasmids are mixed together, the plasmids can be transferred into the bacteria after electroporation, though depending on what is being transferred, cell-penetrating peptides or cell squeeze could also be used. Electroporation works by passing thousands of volts (~8 kV/cm) across suspended cells in an electroporation cuvette. Afterwards, the cells have to be handled carefully until they have had a chance to divide, producing new cells that contain reproduced plasmids. This process is approximately ten times more effective in increasing cell membrane's permeability than chemical transformation, although many laboratories lack the specialized equipment needed for electroporation.
Electroporation is also highly efficient for the introduction of foreign genes into tissue culture cells, especially mammalian cells. For example, it is used in the process of producing knockout mice, as well as in tumor treatment, gene therapy, and cell-based therapy. The process of introducing foreign DNA into eukaryotic cells is known as transfection. Electroporation is highly effective for transfecting cells in suspension using electroporation cuvettes. Electroporation has proven efficient for use on tissues in vivo, for in utero applications as well as in ovo transfection. Adherent cells can also be transfected using electroporation, providing researchers with an alternative to trypsinizing their cells prior to transfection. One downside to electroporation, however, is that after the process the gene expression of over 7,000 genes can be affected. This can cause problems in studies where gene expression has to be controlled to ensure accurate and precise results.
Although bulk electroporation has many benefits over physical delivery methods such as microinjections and gene guns, it still has limitations, including low cell viability. Miniaturization of electroporation has been studied, leading to microelectroporation and nanotransfection of tissue utilizing electroporation-based techniques via nanochannels to minimally invasively deliver cargo to the cells.
Electroporation has also been used as a mechanism to trigger cell fusion. Artificially induced cell fusion can be used to investigate and treat different diseases, like diabetes, regenerate axons of the central nerve system, and produce cells with desired properties, such as in cell vaccines for cancer immunotherapy. However, the first and most known application of cell fusion is production of monoclonal antibodies in hybridoma technology, where hybrid cell lines (hybridomas) are formed by fusing specific antibody-producing B lymphocytes with a myeloma (B lymphocyte cancer) cell line. | 1 | Biochemistry |
A galvanic cell or voltaic cell, named after the scientists Luigi Galvani and Alessandro Volta, respectively, is an electrochemical cell in which an electric current is generated from spontaneous oxidation–reduction reactions. A common apparatus generally consists of two different metals, each immersed in separate beakers containing their respective metal ions in solution that are connected by a salt bridge or separated by a porous membrane.
Volta was the inventor of the voltaic pile, the first electrical battery. Common usage of the word battery has evolved to include a single Galvanic cell, but the first batteries had many Galvanic cells. | 8 | Metallurgy |
There are many types of titrations with different procedures and goals. The most common types of qualitative titration are acid–base titrations and redox titrations. | 3 | Analytical Chemistry |
For the past years, researchers have been trying to reduce the price of solar cells while maximizing efficiency. Thin-film solar cell is a cost-effective second generation solar cell with much reduced thickness at the expense of light absorption efficiency. Efforts to maximize light absorption efficiency with reduced thickness have been made. Surface texturing is one of techniques used to reduce optical losses to maximize light absorbed. Currently, surface texturing techniques on silicon photovoltaics are drawing much attention. Surface texturing could be done in multiple ways. Etching single crystalline silicon substrate can produce randomly distributed square based pyramids on the surface using anisotropic etchants. Recent studies show that c-Si wafers could be etched down to form nano-scale inverted pyramids. Multicrystalline silicon solar cells, due to poorer crystallographic quality, are less effective than single crystal solar cells, but mc-Si solar cells are still being used widely due to less manufacturing difficulties. It is reported that multicrystalline solar cells can be surface-textured to yield solar energy conversion efficiency comparable to that of monocrystalline silicon cells, through isotropic etching or photolithography techniques. Incident light rays onto a textured surface do not reflect back out to the air as opposed to rays onto a flat surface. Rather some light rays are bounced back onto the other surface again due to the geometry of the surface. This process significantly improves light to electricity conversion efficiency, due to increased light absorption. This texture effect as well as the interaction with other interfaces in the PV module is a challenging optical simulation task. A particularly efficient method for modeling and optimization is the OPTOS formalism. In 2012, researchers at MIT reported that c-Si films textured with nanoscale inverted pyramids could achieve light absorption comparable to 30 times thicker planar c-Si. In combination with anti-reflective coating, surface texturing technique can effectively trap light rays within a thin film silicon solar cell. Consequently, required thickness for solar cells decreases with the increased absorption of light rays. | 7 | Physical Chemistry |
Biomolecular Adsorption Database (BAD) is a freely available online database with experimental protein adsorption data collected from the literature.
The database can be used for the selection of materials for microfluidic device fabrication and for the selection of optimum operating conditions of lab-on-a-chip devices. The amount of protein adsorbed to the surface can be predicted using neural networks-based prediction available at BAD. This prediction has been validated to be below 5% error for the overall data available in the BAD. Other parameters, such as the thickness of protein layers and the surface tension of protein-covered surfaces, can also be estimated. | 1 | Biochemistry |
A magneto-optical trap (MOT) is commonly used for cooling and trapping a substance by Doppler cooling. In the process of Doppler cooling, the red detuned light would be absorbed by atoms from one certain direction and re-emitted in a random direction. The electrons of the atoms would decay to an alternative ground states if the atoms have more than one hyperfine ground level. There is the case of all the atoms in the other ground states rather than the ground states of Doppler cooling, then system cannot cool the atoms further.
In order to solve this problem, the other re-pumping light would be incident on the system to repopulate the atoms to restart the Doppler cooling process. This would induce higher amounts of fluorescence being emitted from the atoms which can be absorbed by other atoms, acting as a repulsive force. Due to this problem, the Doppler limit would increase and is easy to meet. When there is a dark spot or lines on the shape of the re-pumping light, the atoms in the middle of the atomic gas would not be excited by the re-pumping light which can decrease the repulsion force from the previous cases.
This can help to cool the atoms to a lower temperature than the typical Doppler cooling limit. This is called a dark magneto-optical trap (DMOT). | 7 | Physical Chemistry |
Typically, the rearrangement is carried out just after the formation of the divinylcyclopropane, in the same pot. Heating is sometimes necessary, particularly for trans substrates, which must undergo epimerization prior to rearrangement. With enough energy to surmount activation barriers, however, the isomerization is usually very efficient. | 0 | Organic Chemistry |
In materials science, environmental stress fracture or environment assisted fracture is the generic name given to premature failure under the influence of tensile stresses and harmful environments of materials such as metals and alloys, composites, plastics and ceramics.
Metals and alloys exhibit phenomena such as stress corrosion cracking, hydrogen embrittlement, liquid metal embrittlement and corrosion fatigue all coming under this category. Environments such as moist air, sea water and corrosive liquids and gases cause environmental stress fracture. Metal matrix composites are also susceptible to many of these processes.
Plastics and plastic-based composites may suffer swelling, debonding and loss of strength when exposed to organic fluids and other corrosive environments, such as acids and alkalies. Under the influence of stress and environment, many structural materials, particularly the high-specific strength ones become brittle and lose their resistance to fracture. While their fracture toughness remains unaltered, their threshold stress intensity factor for crack propagation may be considerably lowered. Consequently, they become prone to premature fracture because of sub-critical crack growth. This article aims to give a brief overview of the various degradation processes mentioned above. | 8 | Metallurgy |
In genetics, a super-enhancer is a region of the mammalian genome comprising multiple enhancers that is collectively bound by an array of transcription factor proteins to drive transcription of genes involved in cell identity. Because super-enhancers are frequently identified near genes important for controlling and defining cell identity, they may thus be used to quickly identify key nodes regulating cell identity.
Enhancers have several quantifiable traits that have a range of values, and these traits are generally elevated at super-enhancers. Super-enhancers are bound by higher levels of transcription-regulating proteins and are associated with genes that are more highly expressed. Expression of genes associated with super-enhancers is particularly sensitive to perturbations, which may facilitate cell state transitions or explain sensitivity of super-enhancer—associated genes to small molecules that target transcription. | 1 | Biochemistry |
The human interactome is the set of protein–protein interactions (the interactome) that occur in human cells. The sequencing of reference genomes, in particular the Human Genome Project, has revolutionized human genetics, molecular biology, and clinical medicine. Genome-wide association study results have led to the association of genes with most Mendelian disorders, and over 140 000 germline mutations have been associated with at least one genetic disease. However, it became apparent that inherent to these studies is an emphasis on clinical outcome rather than a comprehensive understanding of human disease; indeed to date the most significant contributions of GWAS have been restricted to the “low-hanging fruit” of direct single mutation disorders, prompting a systems biology approach to genomic analysis. The connection between genotype and phenotype (how variation in genotype affects the disease or normal functioning of the cell and the human body) remain elusive, especially in the context of multigenic complex traits and cancer. To assign functional context to genotypic changes, much of recent research efforts have been devoted to the mapping of the networks formed by interactions of cellular and genetic components in humans, as well as how these networks are altered by genetic and somatic disease. | 1 | Biochemistry |
β-Melanocyte-stimulating hormone (β-MSH) is an endogenous peptide hormone and neuropeptide. It is a melanocortin, specifically, one of the three types of melanocyte-stimulating hormone (MSH), and is produced from proopiomelanocortin (POMC). It is an agonist of the MC, MC, MC, and MC receptors.
β-MSH is artificially generated because it does not exist in humans naturally.
β-MSH is also known to decrease food intake in animals such as rats, chicken due to the effect of proopiomelanocortin (POMC). Research was performed to see the effect β-MSH has on chicks, and it has been found that chicks responded with a decrease in food and water intake when treated with β-MSH. The experiment showed that β-MSH causes anorexigenic effects in chicks. | 1 | Biochemistry |
Serine/arginine-rich splicing factor 1 (SRSF1) also known as alternative splicing factor 1 (ASF1), pre-mRNA-splicing factor SF2 (SF2) or ASF1/SF2 is a protein that in humans is encoded by the SRSF1 gene. ASF/SF2 is an essential sequence specific splicing factor involved in pre-mRNA splicing. SRSF1 is the gene that codes for ASF/SF2 and is found on chromosome 17. The resulting splicing factor is a protein of approximately 33 kDa. ASF/SF2 is necessary for all splicing reactions to occur, and influences splice site selection in a concentration-dependent manner, resulting in alternative splicing. In addition to being involved in the splicing process, ASF/SF2 also mediates post-splicing activities, such as mRNA nuclear export and translation. | 1 | Biochemistry |
A bloomery is a type of metallurgical furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called a bloom. The mix of slag and iron in the bloom, termed sponge iron, is usually consolidated and further forged into wrought iron. Blast furnaces, which produce pig iron, have largely superseded bloomeries. | 8 | Metallurgy |
BioModels is composed of several branches. The curated branch hosts models that are well curated and annotated. The non-curated-branch provides models that are still not curated, are non-curatable (spatial models, steady-state models etc.), or too huge to be curated. Non-curated models can be later moved into the curated branch. The repository also hosts models which were automatically generated from pathways databases.
All the models are freely available under the Creative Commons CC0 Public Domain Dedication, and can be easily accessed via the website or [http://www.ebi.ac.uk/biomodels-main/webservices Web Services]. One can also download archives of all the models from the [http://ftp.ebi.ac.uk/pub/databases/biomodels/releases/latest/ EBI FTP server].
BioModels announced its 31st release on June 26, 2017. It now publicly provides 144,710 models. This corresponds to 1,640 models published in the literature and 143,070 models automatically generated from pathway resources.
Deposition of models in BioModels is advocated by many scientific journals, included Molecular Systems Biology, all the journals of the Public Library of Science, all the journals of BioMed Central and all the journals published by the Royal Society of Chemistry. | 1 | Biochemistry |
Sortilin is required for many apoptosis-promoting p75NTR reactions, functioning as a co-receptor for the binding of neurotrophins such as BDNF. pro-neurotrophins (such as proBDNF) bind especially well to p75NTR when sortilin is present. | 1 | Biochemistry |
VIM is used in particular for producing alloys with melting points beyond those practical for other kinds of melting. Nickel, nickel-iron, and superalloys are frequently produced using this process. The VIM process is often used for small batch sizes and allows for a high level of control over the composition of the alloy. There is low environmental contamination (dust etc) and oxidation, while elements that are often undesired such as hydrogen or nitrogen can be removed from the process. | 8 | Metallurgy |
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