text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Radicals formed on the polymer backbone by either hydrogen abstraction side-group elimination can cause the chain to break by beta scission. As a result the molecular weight decreases rapidly. As new free radicals with high reactivity are formed, monomers cannot be a product of this reaction, also intermolecular chain transfer and disproportion termination reactions can occur.
CH-CH-CH-CH-CH-CH-CH’→
CH-CH-CH=CH + CH-CH-CH’ or
CH’+CH=CH-CH-CH-CH-CH
As polymers approach their ceiling temperature scission starts to take place randomly on the backbone. | 7 | Physical Chemistry |
In 1948, it was discovered that allyltrimethylsilane reacts with hydrobromic acid to give (2-bromopropyl)trimethylsilane. Six years later, the generation of (2-iodoethyl)trimethylsilane from vinylsilane and HI was observed. Since then, a number of studies have firmly established the mechanism of electrophilic attack on vinyl- and allylsilanes The electron-releasing strength of the carbon-silicon bond is large, and as a result, the position of silicon in the unsaturated silane controls the site of reaction and stereoselectivity. Formation of the new carbon-carbon bond is at the γ position of allyl silanes and the β position of vinylsilanes. The robustness of silanes makes them amenable to use in synthesis; however, because silicon is less electropositive than other metals employed in electrophilic additions, stronger electrophiles are required. | 0 | Organic Chemistry |
In ancient alchemy, a protoscience that contributed to the development of modern chemistry and medicine, alchemists developed a structure of basic laboratory techniques, theory, terminology, and experimental methods. Sublimation was used to refer to the process in which a substance is heated to a vapor, then immediately collects as sediment on the upper portion and neck of the heating medium (typically a retort or alembic), but can also be used to describe other similar non-laboratory transitions. It was mentioned by alchemical authors such as Basil Valentine and George Ripley, and in the Rosarium philosophorum, as a process necessary for the completion of the magnum opus. Here, the word sublimation was used to describe an exchange of "bodies" and "spirits" similar to laboratory phase transition between solids and gases. Valentine, in his Le char triomphal de lantimoine' (Triumphal Chariot of Antimony, published 1646) made a comparison to spagyrics in which a vegetable sublimation can be used to separate the spirits in wine and beer. Ripley used language more indicative of the mystical implications of sublimation, indicating that the process has a double aspect in the spiritualization of the body and the corporalizing of the spirit. He writes:
<blockquote><poem>
And Sublimations we make for three causes,
The first cause is to make the body spiritual.
The second is that the spirit may be corporeal,
And become fixed with it and consubstantial.
The third cause is that from its filthy original.
It may be cleansed, and its saltiness sulphurious
May be diminished in it, which is infectious. | 3 | Analytical Chemistry |
The Chesapeake Bay was the site of the Battle of the Chesapeake (also known as the "Battle of the Capes", Cape Charles and Cape Henry) in 1781, during which the French fleet defeated the Royal Navy in the decisive naval battle of the American Revolutionary War. The British defeat enabled General George Washington and his French allied armies under Comte de Rochambeau to march down from New York and bottle up the rampaging southern British Army of Lord Cornwallis from the North and South Carolinas at the siege of Battle of Yorktown in Yorktown, Virginia. Their marching route from Newport, Rhode Island through Connecticut, New York State, Pennsylvania, New Jersey and Delaware to the "Head of Elk" by the Susquehanna River along the shores and also partially sailing down the Bay to Virginia. It is also the subject of a designated National Historic Trail as the Washington–Rochambeau Revolutionary Route.
The Bay would again see conflict during War of 1812. During the year of 1813, from their base on Tangier Island, British naval forces under the command of Admiral George Cockburn raided several towns on the shores of the Chesapeake, treating the Bay as if it were a "British Lake". The Chesapeake Bay Flotilla, a fleet of shallow-draft armed barges under the command of U.S. Navy Commodore Joshua Barney, was assembled to stall British shore raids and attacks. After months of harassment by Barney, the British landed on the west side of the Patuxent at Benedict, Maryland, the Chesapeake Flotilla was scuttled, and the British trekked overland to rout the U.S. Army at Bladensburg and burn the U.S. Capitol in August 1814. A few days later in a "pincer attack", they also sailed up the Potomac River to attack Fort Washington below the National Capital and raided the nearby port town of Alexandria, Virginia.
There were so-called "Oyster Wars" in the late 19th and early 20th centuries. Until the mid-20th century, oyster harvesting rivaled the crab industry among Chesapeake watermen, a dwindling breed whose skipjacks and other workboats were supplanted by recreational craft in the latter part of the century.
In the 1960s, the Calvert Cliffs Nuclear Power Plant on the historic Calvert Cliffs in Calvert County on the Western Shore of Maryland began using water from the Bay to cool its reactor. | 2 | Environmental Chemistry |
Autoinducer-2 (AI-2), a furanosyl borate diester or tetrahydroxy furan (species dependent), is a member of a family of signaling molecules used in quorum sensing. AI-2 is one of only a few known biomolecules incorporating boron. First identified in the marine bacterium Vibrio harveyi, AI-2 is produced and recognized by many Gram-negative and Gram-positive bacteria. AI-2 arises by the reaction of 4,5-dihydroxy-2,3-pentanedione, which is produced enzymatically, with boric acid and is recognized by the two-component sensor kinase LuxPQ in Vibrionaceae.
AI-2 is actively transported by the Lsr ABC-type transporter into the cell in Enterobacteriaceae and few other bacterial taxa such as Pasteurella, Photorhabdus, Haemophilus, and Bacillus, where it is phosphorylated by LsrK. Then, Phospho-AI-2 binds the transcriptional repressor protein, LsrR, which subsequently is released from the promoter/operator region of the lsr operon – and transcription of the lsr genes is initiated. AI-2 signalling is also regulated by glucose and cAMP/CRP via the lsr operon. In the presence of glucose, low levels of cAMP/CRP result in almost no lsr operon (lsrABCDFG) expression. Without glucose, cAMP-CRP is needed to stimulate the lsr expression, while LsrR represses its expression in the absence of the inducer, phospho-AI-2. As AI-2 accumulates, more AI-2 is taken in via LsrABCD, phosphorylated via LsrK, and the lsr transcription is de-repressed, enabling even more AI-2 uptake.
Doubts have been expressed regarding AI-2s status as a universal signal. Although the luxS gene, which encodes the protein responsible for AI-2 production is widespread, the latter has mainly a primary metabolic role in the recycling of S'-adenosyl--methionine, with AI-2 being a by-product of that process. An unequivocally AI-2 related behavior was found to be restricted primarily to organisms bearing known AI-2 receptor genes. Thus, while it is certainly true that some bacteria respond to AI-2, it is doubtful that it is always being produced for purposes of signaling. | 1 | Biochemistry |
In biology, energy homeostasis, or the homeostatic control of energy balance, is a biological process that involves the coordinated homeostatic regulation of food intake (energy inflow) and energy expenditure (energy outflow). The human brain, particularly the hypothalamus, plays a central role in regulating energy homeostasis and generating the sense of hunger by integrating a number of biochemical signals that transmit information about energy balance. Fifty percent of the energy from glucose metabolism is immediately converted to heat.
Energy homeostasis is an important aspect of bioenergetics. | 1 | Biochemistry |
Index inducer or just inducer predictably induce metabolism via a given pathway and are commonly used in prospective clinical drug-drug interaction studies.
Strong, moderate, and weak inducers are drugs that decreases the AUC of sensitive index substrates of a given metabolic pathway by ≥80%, ≥50% to <80%, and ≥20% to <50%, respectively. | 1 | Biochemistry |
However, it is clear that in a general case the behaviour of Bose–Einstein condensate can be described by coupled evolution equations for condensate density, superfluid velocity and distribution function of elementary excitations. This problem was solved in 1977 by Peletminskii et al. in microscopical approach. The Peletminskii equations are valid for any finite temperatures below the critical point. Years after, in 1985, Kirkpatrick and Dorfman obtained similar equations using another microscopical approach. The Peletminskii equations also reproduce Khalatnikov hydrodynamical equations for superfluid as a limiting case. | 7 | Physical Chemistry |
Glycosylamines are a class of biochemical compounds consisting of a glycosyl group attached to an amino group, -NR. They are also known as N-glycosides, as they are a type of glycoside. Glycosyl groups can be derived from carbohydrates. The glycosyl group and amino group are connected with a β-N-glycosidic bond, forming a cyclic hemiaminal ether bond (α-aminoether).
Examples include nucleosides such as adenosine. | 1 | Biochemistry |
In surface science, an instrument called a contact angle goniometer or tensiometer measures the static contact angle, advancing and receding contact angles, and sometimes surface tension. The first contact angle goniometer was designed by William Zisman of the United States Naval Research Laboratory in Washington, D.C. and manufactured by ramé-hart (now ramé-hart instrument company), New Jersey, USA. The original manual contact angle goniometer used an eyepiece with a microscope. Today's contact angle goniometer uses a camera and software to capture and analyze the drop shape, and is better suited for dynamic and advanced studies. | 7 | Physical Chemistry |
Xenin promotes beta-cell survival and xenin has been evaluated in animal models of obesity and diabetes where it has demonstrated an antidiabetic potential. In humans, co-administration of xenin-25 and gastric inhibitory polypeptide (GIP) reduces postprandial glycemia by delaying gastric emptying. | 1 | Biochemistry |
The first scientific publication in which knockout moss was used to identify the function of a hitherto-unknown gene appeared in 1998, and was authored by Ralf Reski and coworkers. They deleted the ftsZ-gene and thus functionally identified the first gene pivotal for the division of an organelle in any eukaryote. | 1 | Biochemistry |
Ceramography is the art and science of preparation, examination and evaluation of ceramic microstructures. Ceramography can be thought of as the metallography of ceramics. The microstructure is the structure level of approximately 0.1 to 100 µm, between the minimum wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, pores, micro-cracks and hardness microindentations. Most bulk mechanical, optical, thermal, electrical and magnetic properties are significantly affected by the microstructure. The fabrication method and process conditions are generally indicated by the microstructure. The root cause of many ceramic failures is evident in the microstructure. Ceramography is part of the broader field of materialography, which includes all the microscopic techniques of material analysis, such as metallography, petrography and plastography. Ceramography is usually reserved for high-performance ceramics for industrial applications, such as 85–99.9% alumina (AlO) in Fig. 1, zirconia (ZrO), silicon carbide (SiC), silicon nitride (SiN), and ceramic-matrix composites. It is seldom used on whiteware ceramics such as sanitaryware, wall tiles and dishware. | 8 | Metallurgy |
The introduction of refrigeration and evolution of additional technologies drastically changed agriculture in the United States. During the beginning of the 20th century, farming was a common occupation and lifestyle for United States citizens, as most farmers actually lived on their farm. In 1935, there were 6.8 million farms in the United States and a population of 127 million. Yet, while the United States population has continued to climb, citizens pursuing agriculture continue to decline. Based on the 2007 US Census, less than one percent of a population of 310 million people claim farming as an occupation today. However, the increasing population has led to an increasing demand for agricultural products, which is met through a greater variety of crops, fertilizers, pesticides, and improved technology. Improved technology has decreased the risk and time involved for agricultural management and allows larger farms to increase their output per person to meet society's demand. | 7 | Physical Chemistry |
Dimetcote is popular in the marine industry. The inorganic zinc coating of Dimetcote can protect metal components from moisture. | 8 | Metallurgy |
In waste water treatment, the most commonly used adsorbent is granular activated carbon (GAC), often used as to treat both liquid and gas phase volatile organic compounds and organic pollutants. Activated carbon beds vary in lifetime depending on the concentration of the pollutant(s) being removed, their associated adsorption isotherms, inlet flow rates and required discharge consents. Life- times of these beds can range between hours and months. Activated carbon is often landfilled at the end of its useful life but sometimes it is possible to regenerate it restoring its adsorptive capacity allowing it to be re-used. Thermal regeneration is the most prolific regeneration technique but has drawbacks in terms of high energy and commercial costs and a significant carbon footprint. These drawbacks have encouraged research into alternative regeneration techniques such as electrochemical regeneration. | 7 | Physical Chemistry |
In many modern studies, the Polanyi theory is widely used in the study of activated carbons, or carbon black. The theory has been successfully used to model a variety of scenarios such as the gas adsorption on activated carbon and the adsorption process of nonionic polycyclic aromatic hydrocarbons. Later on, experiments also showed that it can model ionic polycyclic aromatic hydrocarbons such as phenols and anilines. More recently, the Polyani adsorption isotherm has been used to model to adsorption of carbon nanoparticles. | 7 | Physical Chemistry |
The SQT incorporates three lines of evidence (LOE) to provide direct assessment of sediment quality. The chemistry, toxicity, and benthic components of the triad each provide a LOE, which is then integrated into a Weight of evidence. | 2 | Environmental Chemistry |
Sirpα migratory DCs (mDCs) form second subset of thymic DCs. They rise extrathymically, and were shown to present self antigens, especially blood-borne antigens, in the thymus, which they acquire in the periphery. They were also shown to be more efficient in T regulatory cells selection than clonal deletion. | 1 | Biochemistry |
The process of creating these luxuriously inlaid objects is somewhat complicated and has multiple stages. First, designs are formed on the surface of the metal (usually copper or brass) by relief, piercing, engraving, or chasing. Color is then added to the crevices of the surface by encrustation, overlay or, most commonly, inlay of precious metals. These metal inlays could be sheets or wires hammered into place. The area around the inlaid design was often roughened or covered with some sort of black material. Each craftsman in the industry had their own personal specialization. This specialization could be in a particular metal, technique, object, or step in the process. There are two reasons the casting step of the process usually took place in an urban workshop. The first is simply because most patrons were located in these urban areas. The second is because it would be too difficult to move all of the heavy equipment necessary for casting from one rural location to the next. Inlayers and precious metalworkers were able to travel with ease and were not confined to the workshops as casters were. There were three main inlay innovations that are believed to have originated in Mosul in the thirteenth century- gold inlays, black inlay, and background scrolls inlaid with silver.
The designs themselves are quite varied in subject matter. Some of the popular motifs include: astrology, hunting, enthronements, battles, court life, and genre scenes. Genre scenes, images of everyday life are particularly prominent. Among the original design traditions there is evidence that can trace them to East Asia through the designs within textiles. Mosul was a great textile industry during the same period that they were producing these inlaid objects and they happened to specialize in reproductions of Chinese silks. It is speculated that many of the traditional metalwork designs were heavily influenced or even direct copies of these silk reproductions.
Historically, many scholars have argued that the Mongol sack of Mosul led to the demise of the luxury metalworking industry, however modern scholarship and an abundance of evidence disproves this. For example, it is known that Mosul metalworkers received an imperial commission by Il-Khan Abu Sa'id in the last years of the Ilkanate. Not only did Mosul continue to produce elaborate inlaid objects after the Mongol sack, they also altered their traditional stylistic choices to coalesce with Mongol taste. There was a new emphasis on minuscule style, the figures represented reflect the Ilkanhid fashion of the period, and they started to put more emphasis on pattern over figuration.
One of the finest examples of the Mosul school of metalworking is the Blacas Ewer.
Another item tentatively attributed to Mosul is the Courtauld bag, which is thought to be the world's oldest surviving handbag. | 8 | Metallurgy |
Milk oligosaccharides seem to be more abundant in humans than in other animals and to be more complex and varied. Oligosaccharides in primate milk are generally more complex and diverse than in non-primates.
Human milk oligosaccharides (HMOs) form the third most abundant solid component (dissolved or emulsified or suspended in water) of human milk, after lactose and fat. HMOs are present in a concentration of 11.3 – 17.7 g/L (1.5 oz/gal – 2.36 oz/gal) in human milk, depending on lactation stages. Approximately 200 structurally different human milk oligosaccharides are known, and they can be categorized into fucosylated, sialylated and neutral core HMOs. The composition of human milk oligosaccharides in breast milk is individual to each mother and varies over the period of lactation. The dominant oligosaccharide in 80% of all women is 2′-fucosyllactose, which is present in human breast milk at a concentration of approximately 2.5 g/L; other abundant oligosacchadies include lacto-N-tetraose, lacto-N-neotetraose, and lacto-N-fucopentaose. It has been found by numerous studies that the concentration of each individual human milk oligosaccharide changes throughout the different periods of lactation (colostrum, transitional, mature and late milk) and depend on various factors such as the mother's genetic secretor status and length of gestation. | 0 | Organic Chemistry |
In chemistry and biochemistry, the Henderson–Hasselbalch equation
relates the pH of a chemical solution of a weak acid to the numerical value of the acid dissociation constant, K, of acid and the ratio of the concentrations, of the acid and its conjugate base in an equilibrium.
For example, the acid may be acetic acid
The Henderson–Hasselbalch equation can be used to estimate the pH of a buffer solution by approximating the actual concentration ratio as the ratio of the analytical concentrations of the acid and of a salt, MA.
The equation can also be applied to bases by specifying the protonated form of the base as the acid. For example, with an amine, | 7 | Physical Chemistry |
Producing sponge iron and then working it was the earliest method used to obtain iron in the Middle East, Egypt, and Europe, where it remained in use until at least the 16th century.
The advantage of the bloomery technique is that iron can be obtained at a lower furnace temperature, only about 1,100 °C or so. The disadvantage, relative to a blast furnace, is that only small quantities can be made at a time. | 8 | Metallurgy |
There are two primary mTOR inhibitors used in the treatment of human cancers, temsirolimus and everolimus. mTOR inhibitors have found use in the treatment of a variety of malignancies, including renal cell carcinoma (temsirolimus) and pancreatic cancer, breast cancer, and renal cell carcinoma (everolimus). The complete mechanism of these agents is not clear, but they are thought to function by impairing tumour angiogenesis and causing impairment of the G1/S transition. | 1 | Biochemistry |
There are many ways to help fix cultural eutrophication caused by agriculture. Some recommendations issued by the U.S. Department of Agriculture:
# Nutrient Management Techniques - Anyone using fertilizers should apply fertilizer in the correct amount, at the right time of year, with the right method and placement. Organically fertilized fields can "significantly reduce harmful nitrate leaching" compared to conventionally fertilized fields. Eutrophication impacts are in some cases higher from organic production than they are from conventional production. In Japan the amount of nitrogen produced by livestock is adequate to serve the fertilizer needs for the agriculture industry.
# Year - Round Ground Cover - a cover crop will prevent periods of bare ground thus eliminating erosion and runoff of nutrients even after the growing season has occurred.
# Planting Field Buffers - By planting trees, shrubs and grasses along the edges of fields to help catch the runoff and absorb some nutrients before the water makes it to a nearby water body. Riparian buffer zones are interfaces between a flowing body of water and land, and have been created near waterways in an attempt to filter pollutants; sediment and nutrients are deposited here instead of in water. Creating buffer zones near farms and roads is another possible way to prevent nutrients from traveling too far. Still, studies have shown that the effects of atmospheric nitrogen pollution can reach far past the buffer zone. This suggests that the most effective means of prevention is from the primary source.
# Conservation Tillage - By reducing frequency and intensity of tilling the land will enhance the chance of nutrients absorbing into the ground. | 2 | Environmental Chemistry |
BOND integrates the original Blueprint Initiative databases as well as other databases, such as Genbank, combined with many tools required to analyze these data. Annotation links for sequences, including taxon identifiers, redundant sequences, Gene Ontology descriptions, Online Mendelian Inheritance in Man identifiers, conserved domains, data base cross-references, LocusLink Identifiers and complete genomes are also available. BOND facilitates cross-database queries and is an open access resource which integrates interaction and sequence data. | 1 | Biochemistry |
Often there is more to the analytical method than just performing a reaction or submitting the analyte to direct analysis. Many analytical methods developed in the laboratory, especially these involving the use of a delicate scientific instrument, require a sample preparation, or a pretreatment of the samples prior to being analysed. For example, it might be necessary to heat a sample that is to be analyzed for a particular metal with the addition of acid first (digestion process). The sample may also be diluted or concentrated prior to analysis by means of a given instrument. Additional steps in an analysis method add additional opportunities for errors. Since detection limits are defined in terms of errors, this will naturally increase the measured detection limit. This "global" detection limit (including all the steps of the analysis method) is called the method detection limit (MDL). The practical way for determining the MDL is to analyze seven samples of concentration near the expected limit of detection. The standard deviation is then determined. The one-sided Student's t-distribution is determined and multiplied versus the determined standard deviation. For seven samples (with six degrees of freedom) the t value for a 99% confidence level is 3.14. Rather than performing the complete analysis of seven identical samples, if the Instrument Detection Limit is known, the MDL may be estimated by multiplying the Instrument Detection Limit, or Lower Level of Detection, by the dilution prior to analyzing the sample solution with the instrument. This estimation, however, ignores any uncertainty that arises from performing the sample preparation and will therefore probably underestimate the true MDL. | 3 | Analytical Chemistry |
In a conjugated pi-system, electrons are able to capture certain photons as the electrons resonate along a certain distance of p-orbitals - similar to how a radio antenna detects photons along its length. Typically, the more conjugated (longer) the pi-system is, the longer the wavelength of photon can be captured. Compounds whose molecules contain a sufficient number of conjugated bonds can absorb light in the visible region, and therefore appear colorful to the eye, usually appearing yellow or red.
Many dyes make use of conjugated electron systems to absorb visible light, giving rise to strong colors. For example, the long conjugated hydrocarbon chain in beta-carotene leads to its strong orange color. When an electron in the system absorbs a photon of light of the right wavelength, it can be promoted to a higher energy level. A simple model of the energy levels is provided by the quantum-mechanical problem of a one-dimensional particle in a box of length L, representing the movement of a π electron along a long conjugated chain of carbon atoms. In this model the lowest possible absorption energy corresponds to the energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). For a chain of n C=C bonds or 2n carbon atoms in the molecular ground state, there are 2n π electrons occupying n molecular orbitals, so that the energy gap is
Since the box length L increases approximately linearly with the number of C=C bonds n, this means that the energy ΔE of a photon absorbed in the HOMO–LUMO transition is approximately proportional to 1/n. The photon wavelength λ = hc/ΔE is then approximately proportional to n. Although this model is very approximate, λ does in general increase with n (or L) for similar molecules. For example, the HOMO–LUMO absorption wavelengths for conjugated butadiene, hexatriene and octatetraene are 217 nm, 252 nm and 304 nm respectively. However, for good numerical agreement of the particle in a box model with experiment, the single-bond/double-bond bond length alternations of the polyenes must be taken into account. Alternatively, one can use the Hückel method which is also designed to model the electronic structure of conjugated systems.
Many electronic transitions in conjugated π-systems are from a predominantly bonding molecular orbital (MO) to a predominantly antibonding MO (π to π), but electrons from non-bonding lone pairs can also be promoted to a π-system MO (n to π) as often happens in charge-transfer complexes. A HOMO to LUMO transition is made by an electron if it is allowed by the selection rules for electromagnetic transitions. Conjugated systems of fewer than eight conjugated double bonds absorb only in the ultraviolet region and are colorless to the human eye. With every double bond added, the system absorbs photons of longer wavelength (and lower energy), and the compound ranges from yellow to red in color. Compounds that are blue or green typically do not rely on conjugated double bonds alone.
This absorption of light in the ultraviolet to visible spectrum can be quantified using ultraviolet–visible spectroscopy, and forms the basis for the entire field of photochemistry.
Conjugated systems that are widely used for synthetic pigments and dyes are diazo and azo compounds and phthalocyanine compounds. | 7 | Physical Chemistry |
The nucleophiles used are typically generated from precursors (pronucleophiles) in situ after their deprotonation with base. These nucleophiles are then subdivided into "hard" and "soft" nucleophiles using a paradigm for describing nucleophiles that largely rests on the Acid dissociation constant| of their conjugate acids. "Hard" nucleophiles typically have conjugate acids with greater than 25, while "soft" nucleophiles typically have conjugate acids with less than 25.
This descriptor is important because of the impact these nucleophiles have on the stereoselectivity of the product. Stabilized or "soft" nucleophiles invert the stereochemistry of the -allyl complex. This inversion in conjunction with the inversion in stereochemistry associated with the oxidative addition of palladium yields a net retention of stereochemistry. Unstabilized or "hard" nucleophiles, on the other hand, retain the stereochemistry of the -allyl complex, resulting in a net inversion of stereochemistry.
This trend is explained by examining the mechanisms of nucleophilic attack. "Soft" nucleophiles attack the carbon of the allyl group, while "hard" nucleophiles attack the metal center, followed by reductive elimination. | 0 | Organic Chemistry |
LDH is involved in tumor initiation and metabolism. Cancer cells rely on increased glycolysis resulting in increased lactate production in addition to aerobic respiration in the mitochondria, even under oxygen-sufficient conditions (a process known as the Warburg effect). This state of fermentative glycolysis is catalyzed by the A form of LDH. This mechanism allows tumorous cells to convert the majority of their glucose stores into lactate regardless of oxygen availability, shifting use of glucose metabolites from simple energy production to the promotion of accelerated cell growth and replication.
LDH A and the possibility of inhibiting its activity has been identified as a promising target in cancer treatments focused on preventing carcinogenic cells from proliferating. Chemical inhibition of LDH A has demonstrated marked changes in metabolic processes and overall survival of carcinoma cells. Oxamate is a cytosolic inhibitor of LDH A that significantly decreases ATP production in tumorous cells as well as increasing production of reactive oxygen species (ROS). These ROS drive cancer cell proliferation by activating kinases that drive cell cycle progression growth factors at low concentrations, but can damage DNA through oxidative stress at higher concentrations. Secondary lipid oxidation products can also inactivate LDH and impact its ability to regenerate NADH, directly disrupting the enzymes ability to convert lactate to pyruvate.
While recent studies have shown that LDH activity is not necessarily an indicator of metastatic risk, LDH expression can act as a general marker in the prognosis of cancers. Expression of LDH5 and VEGF in tumors and the stroma has been found to be a strong prognostic factor for diffuse or mixed-type gastric cancers. | 1 | Biochemistry |
Characterization techniques for copolymers are similar to those for other polymeric materials. These techniques can be used to determine the average molecular weight, molecular size, chemical composition, molecular homogeneity, and physiochemical properties of the material. However, given that copolymers are made of base polymer components with heterogeneous properties, this may require multiple characterization techniques to accurately characterize these copolymers.
Spectroscopic techniques, such as nuclear magnetic resonance spectroscopy, infrared spectroscopy, and UV spectroscopy, are often used to identify the molecular structure and chemical composition of copolymers. In particular, NMR can indicate the tacticity and configuration of polymeric chains while IR can identify functional groups attached to the copolymer.
Scattering techniques, such as static light scattering, dynamic light scattering, and small-angle neutron scattering, can determine the molecular size and weight of the synthesized copolymer. Static light scattering and dynamic light scattering use light to determine the average molecular weight and behavior of the copolymer in solution whereas small-angle neutron scattering uses neutrons to determine the molecular weight and chain length. Additionally, x-ray scattering techniques, such as small-angle X-ray scattering (SAXS) can help determine the nanometer morphology and characteristic feature size of a microphase-separated block-copolymer or suspended micelles.
Differential scanning calorimetry is a thermoanalytical technique used to determine the thermal events of the copolymer as a function of temperature. It can indicate when the copolymer is undergoing a phase transition, such as crystallization or melting, by measuring the heat flow required to maintain the material and a reference at a constantly increasing temperature.
Thermogravimetric analysis is another thermoanalytical technique used to access the thermal stability of the copolymer as a function of temperature. This provides information on any changes to the physicochemical properties, such as phase transitions, thermal decompositions, and redox reactions.
Size-exclusion chromatography can separate copolymers with different molecular weights based on their hydrodynamic volume. From there, the molecular weight can be determined by deriving the relationship from its hydrodynamic volume. Larger copolymers tend to elute first as they do not interact with the column as much. The collected material is commonly detected by light scattering methods, a refractometer, or a viscometer to determine the concentration of the eluted copolymer. | 7 | Physical Chemistry |
In molecules whose vibrational mode involves a rotational or pseudorotational mechanism (such as the Berry mechanism or the Bartell mechanism), Van der Waals strain can cause significant differences in potential energy, even between molecules with identical geometry.
PF, for example, has significantly lower potential energy than PCl.
Despite their identical trigonal bipyramidal molecular geometry, the higher electron count of chlorine as compared to fluorine causes a potential energy spike as the molecule enters its intermediate in the mechanism and the substituents draw nearer to each other. | 4 | Stereochemistry |
The bioinformatics core contributes bioinformatic analysis by collecting and curating complete sequence data sets, generating sequence similarity networks, and classification of superfamily members into subgroups and families for subsequent annotation transfer and evaluation as targets for functional characterization.
The protein core develops cloning, expression, and protein purification strategies for the enzymes targeted for study.
The structure core fulfills the structural biology component for EFI by providing high resolution structures of targeted enzymes.
The computation core performs in silico docking to generate rank-ordered lists of predicted substrates for targeted enzymes using both experimentally determined and/or homology modeled protein structures.
The microbiology core examines in vivo functions using genetic techniques and metabolomics to complement in vitro functions determined by the Bridging Projects.
The data and dissemination core maintains a public database for experimental data (EFI-DB). | 1 | Biochemistry |
NMOR is a pale yellow sand-like powder below 84°F.
NMOR is most commonly produced from morpholine, but can also be made by the reaction of dimorpholinomethane in fuming nitric acid. Few reactions using NMOR as a starting material are reported in the organic synthesis literature, but it can be used as a precursor to a nitrogen-centered radical. | 0 | Organic Chemistry |
Encapsulin nanocompartments, or encapsulin protein cages, are spherical bacterial organelle-like compartments roughly 25-30 nm in diameter that are involved in various aspects of metabolism, in particular protecting bacteria from oxidative stress. Encapsulin nanocompartments are structurally similar to the HK97 bacteriophage and their function depends on the proteins loaded into the nanocompartment. The sphere is formed from 60 (for a 25 nm sphere) or 180 (for a 30 nm sphere) copies of a single protomer, termed encapsulin. Their structure has been studied in great detail using X-ray crystallography and cryo-electron microscopy.
A number of different types of proteins have been identified as being loaded into encapsulin nanocompartments. Peroxidases or proteins similar to ferritins are the two most common types of cargo proteins. While most encapsulin nanocompartments contain only one type of cargo protein, in some species two or three types of cargo proteins are loaded.
Encapsulins purified from Rhodococcus jostii can be assembled and disassembled with changes in pH. In the assembled state, the compartment enhances the activity of its cargo, a peroxidase enzyme. | 1 | Biochemistry |
Nitrogen has two stable isotopes, N and N. The ratio between these is measured relative to nitrogen in ambient air. Nitrogen ratios are frequently linked to agricultural activities. Nitrogen isotope data has also been used to measure the amount of exchange of air between the stratosphere and troposphere using data from the greenhouse gas NO. | 9 | Geochemistry |
Paul S. Wesson examined the cosmological implications of assuming that zero-point energy is real. Among numerous difficulties, general relativity requires that such energy not gravitate, so it cannot be similar to electromagnetic radiation. | 7 | Physical Chemistry |
AAV is capable of transducing multiple cell types within the retina. AAV serotype 2, the most well-studied type of AAV, is commonly administered in one of two routes: intravitreal or subretinal. Using the intravitreal route, AAV is injected in the vitreous humor of the eye. Using the subretinal route, AAV is injected underneath the retina, taking advantage of the potential space between the photoreceptors and RPE layer, in a short surgical procedure. Although this is more invasive than the intravitreal route, the fluid is absorbed by the RPE and the retina flattens in less than 14 hours without complications. Intravitreal AAV targets retinal ganglion cells and a few Muller glial cells. Subretinal AAV efficiently targets photoreceptors and RPE cells.
The reason that different routes of administration lead to different cell types being transfected (e.g., different tropism) is that the inner limiting membrane (ILM) and the various retinal layers act as physical barriers for the delivery of drugs and vectors to the deeper retinal layers. Thus overall, subretinal AAV is 5-10 times more efficient than delivery using the intravitreal route. | 1 | Biochemistry |
Levodropropizine is a cough suppressant. It is the levo isomer of dropropizine. It acts as a peripheral antitussive, with no action in the central nervous system. It does not cause side effects such as constipation or respiratory depression which can be produced by opioid antitussives such as codeine and its derivatives. | 4 | Stereochemistry |
A masking agent is a reagent used in chemical analysis which reacts with chemical species that may interfere in the analysis.
In sports a masking agent is used to hide or prevent detection of a banned substance or illegal drug like anabolic steroids or stimulants. Diuretics are the simplest form of masking agent and work by enhancing water loss via urine excretion and thus diluting the urine, which results in lower concentrations of the banned substance as more of it is being excreted from the body making it more difficult for laboratories to detect. | 3 | Analytical Chemistry |
Trans-Spliced Exon Coupled RNA End Determination (TEC-RED) is a transcriptomic technique that, like SAGE, allows for the digital detection of messenger RNA sequences. Unlike SAGE, detection and purification of transcripts from the 5’ end of the messenger RNA require the presence of a trans-spliced leader sequence. | 1 | Biochemistry |
Miray Bekbölet completed a B.S. with high distinction in chemistry and physics at Ege University in 1973. In 1979, she earned a Ph.D. in food sciences at Ege University. | 5 | Photochemistry |
One stable N-heterocyclic carbene has a structure analogous to borazine with one boron atom replaced by a methylene group. This results in a planar six-electron compound. | 0 | Organic Chemistry |
The function of neurons depends upon cell polarity. The distinctive structure of nerve cells allows action potentials to travel directionally (from dendrites to cell body down the axon), and for these signals to then be received and carried on by post-synaptic neurons or received by effector cells. Nerve cells have long been used as models for cellular polarization, and of particular interest are the mechanisms underlying the polarized localization of synaptic molecules. PIP2 signaling regulated by IMPase plays an integral role in synaptic polarity.
Phosphoinositides (PIP, PIP2, and PIP3) are molecules that have been shown to affect neuronal polarity. A gene (ttx-7) was identified in Caenorhabditis elegans that encodes myo-inositol monophosphatase (IMPase), an enzyme that produces inositol by dephosphorylating inositol phosphate. Organisms with mutant ttx-7 genes demonstrated behavioral and localization defects, which were rescued by expression of IMPase. This led to the conclusion that IMPase is required for the correct localization of synaptic protein components. The egl-8 gene encodes a homolog of phospholipase Cβ (PLCβ), an enzyme that cleaves PIP2. When ttx-7 mutants also had a mutant egl-8 gene, the defects caused by the faulty ttx-7 gene were largely reversed. These results suggest that PIP2 signaling establishes polarized localization of synaptic components in living neurons. | 1 | Biochemistry |
The Reichstein process in chemistry is a combined chemical and microbial method for the production of ascorbic acid from D-glucose that takes place in several steps. This process was devised by Nobel Prize winner Tadeusz Reichstein and his colleagues in 1933 while working in the laboratory of the ETH in Zürich. | 0 | Organic Chemistry |
The space groups in three dimensions are made from combinations of the 32 crystallographic point groups with the 14 Bravais lattices, each of the latter belonging to one of 7 lattice systems. What this means is that the action of any element of a given space group can be expressed as the action of an element of the appropriate point group followed optionally by a translation. A space group is thus some combination of the translational symmetry of a unit cell (including lattice centering), the point group symmetry operations of reflection, rotation and improper rotation (also called rotoinversion), and the screw axis and glide plane symmetry operations. The combination of all these symmetry operations results in a total of 230 different space groups describing all possible crystal symmetries.
The number of replicates of the asymmetric unit in a unit cell is thus the number of lattice points in the cell times the order of the point group. This ranges from 1 in the case of space group P1 to 192 for a space group like Fmm, the NaCl structure. | 4 | Stereochemistry |
At least three plausible mechanisms for the Elbs reaction have been suggested. The first mechanism, suggested by Fieser, begins with a heat-induced cyclisation of the benzophenone, followed by a [[Sigmatropic reaction#%5B1,3%5D-shifts|[1,3]-hydride shift]] to give the compound . A dehydration reaction then affords the polyaromatic.
Alternatively, in the second mechanism, due to Cook, the methylated aromatic compound instead first undergoes a tautomerization followed by an electrocyclic reaction to give the same intermediate, which then similarly undergoes a [1,3]-hydride shift and dehydration.
A third mechanism has also been proposed, involving pyrolytic radical generation. | 0 | Organic Chemistry |
A biochemical cascade, also known as a signaling cascade or signaling pathway, is a series of chemical reactions that occur within a biological cell when initiated by a stimulus. This stimulus, known as a first messenger, acts on a receptor that is transduced to the cell interior through second messengers which amplify the signal and transfer it to effector molecules, causing the cell to respond to the initial stimulus. Most biochemical cascades are series of events, in which one event triggers the next, in a linear fashion. At each step of the signaling cascade, various controlling factors are involved to regulate cellular actions, in order to respond effectively to cues about their changing internal and external environments.
An example would be the coagulation cascade of secondary hemostasis which leads to fibrin formation, and thus, the initiation of blood coagulation. Another example, sonic hedgehog signaling pathway, is one of the key regulators of embryonic development and is present in all bilaterians. Signaling proteins give cells information to make the embryo develop properly. When the pathway malfunctions, it can result in diseases like basal cell carcinoma. Recent studies point to the role of hedgehog signaling in regulating adult stem cells involved in maintenance and regeneration of adult tissues. The pathway has also been implicated in the development of some cancers. Drugs that specifically target hedgehog signaling to fight diseases are being actively developed by a number of pharmaceutical companies. | 7 | Physical Chemistry |
Transcription activator-like effector nucleases (TALENs) also contain a DNA binding domain and a nuclease that can cleave DNA. The DNA binding region consists of amino acid repeats that each recognize a single base pair of the desired targeted DNA sequence. If this cleavage is targeted to a gene coding region, and NHEJ-mediated repair introduces insertions and deletions, a frameshift mutation often results, thus disrupting function of the gene. | 1 | Biochemistry |
The field of oxidative phosphorylation began with the report in 1906 by Arthur Harden of a vital role for phosphate in cellular fermentation, but initially only sugar phosphates were known to be involved. However, in the early 1940s, the link between the oxidation of sugars and the generation of ATP was firmly established by Herman Kalckar, confirming the central role of ATP in energy transfer that had been proposed by Fritz Albert Lipmann in 1941. Later, in 1949, Morris Friedkin and Albert L. Lehninger proved that the coenzyme NADH linked metabolic pathways such as the citric acid cycle and the synthesis of ATP. The term oxidative phosphorylation was coined by in 1939.
For another twenty years, the mechanism by which ATP is generated remained mysterious, with scientists searching for an elusive "high-energy intermediate" that would link oxidation and phosphorylation reactions. This puzzle was solved by Peter D. Mitchell with the publication of the chemiosmotic theory in 1961. At first, this proposal was highly controversial, but it was slowly accepted and Mitchell was awarded a Nobel prize in 1978. Subsequent research concentrated on purifying and characterizing the enzymes involved, with major contributions being made by David E. Green on the complexes of the electron-transport chain, as well as Efraim Racker on the ATP synthase. A critical step towards solving the mechanism of the ATP synthase was provided by Paul D. Boyer, by his development in 1973 of the "binding change" mechanism, followed by his radical proposal of rotational catalysis in 1982. More recent work has included structural studies on the enzymes involved in oxidative phosphorylation by John E. Walker, with Walker and Boyer being awarded a Nobel Prize in 1997. | 1 | Biochemistry |
The strictest form of order in a solid is lattice periodicity: a certain pattern (the arrangement of atoms in a unit cell) is repeated again and again to form a translationally invariant tiling of space. This is the defining property of a crystal. Possible symmetries have been classified in 14 Bravais lattices and 230 space groups.
Lattice periodicity implies long-range order: if only one unit cell is known, then by virtue of the translational symmetry it is possible to accurately predict all atomic positions at arbitrary distances. During much of the 20th century, the converse was also taken for granted – until the discovery of quasicrystals in 1982 showed that there are perfectly deterministic tilings that do not possess lattice periodicity.
Besides structural order, one may consider charge ordering, spin ordering, magnetic ordering, and compositional ordering. Magnetic ordering is observable in neutron diffraction.
It is a thermodynamic entropy concept often displayed by a second-order phase transition. Generally speaking, high thermal energy is associated with disorder and low thermal energy with ordering, although there have been violations of this. Ordering peaks become apparent in diffraction experiments at low energy. | 3 | Analytical Chemistry |
Oxyhydrogen will combust when brought to its autoignition temperature. For the stoichiometric mixture in air, at normal atmospheric pressure, autoignition occurs at about 570 °C (1065 °F). The minimum energy required to ignite such a mixture, at lower temperatures, with a spark is about 20 microjoules. At standard temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume.
When ignited, the gas mixture converts to water vapor and releases energy, which sustains the reaction: 241.8 kJ of energy (LHV) for every mole of burned. The amount of heat energy released is independent of the mode of combustion, but the temperature of the flame varies. The maximum temperature of about is achieved with an exact stoichiometric mixture, about hotter than a hydrogen flame in air.
When either of the gases are mixed in excess of this ratio, or when mixed with an inert gas like nitrogen, the heat must spread throughout a greater quantity of matter and the flame temperature will be lower. | 7 | Physical Chemistry |
miRNA-324-5p is a relatively new and understudied microRNA. It is an important regulator in several diseases, and its effects span across the body from neuronal dysregulation in seizure to hepatocellular carcinoma and cardiac disease. Because microRNAs have numerous targets, they are capable of regulating multiple pathways and circuits, an ability that may be useful in the treatment of complex disorders like epilepsy in which many subsystems are dysregulated. However, the wide-ranging functions of miRNAs may be limiting as well. microRNA expression modulation could lead to unanticipated physiological effects and not provide adequate specificity. | 1 | Biochemistry |
The first magnesium transporter isolated in any multicellular organism, AtMHX shows no similarity to any previously isolated Mg transport protein. The gene was initially identified in the A. thaliana genomic DNA sequence database, by its similarity to the SLC8 family of Na+/Ca exchanger genes in humans.
The cDNA sequence of 1990 bp is predicted to produce a 539-amino acid protein. AtMHX is quite closely related to the SLC8 family at the amino acid level and shares a topology with eleven predicted TM domains (Figure A10.5). There is one major difference in the sequence, in that the long non-membranal loop (see Figure A10.5) is 148 amino acids in the AtMHX protein but 500 amino acids in the SLC8 proteins. However, this loop is not well conserved and is not required for transport function in the SLC8 family.
The AtMHX gene is expressed throughout the plant but most strongly in the vascular tissue. The authors suggest that the physiological role of the protein is to store Mg in these tissues for later release when needed. The protein localisation to the vacuolar membrane supports this suggestion (see also Chapter 1.5).
The protein transports Mg into the vacuolar space and H out, as demonstrated by electrophysiological techniques. The transport is driven by the ΔpH maintained between the vacuolar space (pH 4.5 – 5.9) and the cytoplasm (pH 7.3 – 7.6) by an H-ATPase. How the transport of Mg by the protein is regulated was not determined. Currents were observed to pass through the protein in both directions, but the Mg out current required a ‘cytoplasmic’ pH of 5.5, a condition not found in plant cells under normal circumstances. In addition to the transport of Mg, Shaul et al. (1999) also showed that the protein could transport Zn and Fe, but did not report on the capacity of the protein to transport other divalent cations (e.g. Co and Ni) or its susceptibility to inhibition by cobalt (III) hexaammine.
The detailed kinetics of Mg transport have not been determined for AtMHX. However, physiological effects have been demonstrated. When A. thaliana plants were transformed with overexpression constructs of the AtMHX gene driven by the CaMV 35S promoter, the plants over-accumulated the protein and showed a phenotype of necrotic lesions in the leaves, which the authors suggest is caused by a disruption in the normal function of the vacuole, given their observation that the total Mg (or Zn) content of the plants was not altered in the transgenic plants.
The image has been adapted from Shaul et al. (1999) and Quednau et al. (2004), and combined with an analysis using HMMTOP, this figure shows the computer predicted membrane topology of the AtMHX protein in Arabidopsis thaliana. At this time the topology shown should be considered a tentative hypothesis. The TM domains are shown in light blue, the orientation in the membrane and the positions of the N- and C-termini are indicated, and the figure is not drawn to scale. The α1 and α2 domains, shown in green, are both quite hydrophobic and may both be inserted into the membrane. | 1 | Biochemistry |
The basic room purge equation can be used only for purge scenarios. In a scenario where a liquid continuously evaporates from a container in a ventilated room, a differential equation has to be used:
where the ventilation rate has been adjusted by a mixing factor K:
*C = concentration of a gas
*G = generation rate
*V = room volume
*Q′ = adjusted ventilation rate of the volume | 3 | Analytical Chemistry |
Simple alcohols are found widely in nature. Ethanol is the most prominent because it is the product of fermentation, a major energy-producing pathway. Other simple alcohols, chiefly fusel alcohols, are formed in only trace amounts. More complex alcohols, however, are pervasive, as manifested in sugars, some amino acids, and fatty acids. | 0 | Organic Chemistry |
Sociophysics uses tools and concepts from physics and physical chemistry to describe some aspects of social and political behavior. It attempts to explain why and how humans behave much like atoms, at least in some aspects of their collective lives. The law of mass action (generalized if it is necessary) is the main tool to produce the equation of interactions of humans in sociophysics. | 7 | Physical Chemistry |
The calicheamicins are a sub-family of enediynes that were isolated from Micromonospora echinospora calichensis. All calicheamicin family members demonstrate potent antimicrobial activity against Gram-positive and Gram-negative organisms. Calicheamicin γ1 exhibited significant antitumor activity against leukemia and melanoma cells in vivo. The calicheamicins are notably similar in structure to the esperamicins.</p> | 0 | Organic Chemistry |
The existence of a special structure at the ends of chromosomes was independently proposed in 1938 by Hermann Joseph Muller, studying the fruit fly Drosophila melanogaster, and in 1939 by Barbara McClintock, working with maize. Muller observed that the ends of irradiated fruit fly chromosomes did not present alterations such as deletions or inversions. He hypothesized the presence of a protective cap, which he coined "telomeres", from the Greek telos (end) and meros (part).
In the early 1970s, Soviet theorist Alexei Olovnikov first recognized that chromosomes could not completely replicate their ends; this is known as the "end replication problem". Building on this, and accommodating Leonard Hayflick's idea of limited somatic cell division, Olovnikov suggested that DNA sequences are lost every time a cell replicates until the loss reaches a critical level, at which point cell division ends. According to his theory of marginotomy DNA sequences at the ends of telomeres are represented by tandem repeats, which create a buffer that determines the number of divisions that a certain cell clone can undergo. Furthermore, it was predicted that a specialized DNA polymerase (originally called a tandem-DNA-polymerase) could extend telomeres in immortal tissues such as germ line, cancer cells and stem cells. It also followed from this hypothesis that organisms with circular genome, such as bacteria, do not have the end replication problem and therefore do not age.
In 1975–1977, Elizabeth Blackburn, working as a postdoctoral fellow at Yale University with Joseph G. Gall, discovered the unusual nature of telomeres, with their simple repeated DNA sequences composing chromosome ends. Blackburn, Carol Greider, and Jack Szostak were awarded the 2009 Nobel Prize in Physiology or Medicine for the discovery of how chromosomes are protected by telomeres and the enzyme telomerase. | 1 | Biochemistry |
In organic chemistry, the Soai reaction is the alkylation of pyrimidine-5-carbaldehyde with diisopropylzinc. The reaction is autocatalytic and leads to rapidly increasing amounts of the same enantiomer of the product. The product pyrimidyl alcohol is chiral and induces that same chirality in further catalytic cycles. Starting with a low enantiomeric excess ("ee") produces a product with very high enantiomeric excess. The reaction has been studied for clues about the origin of homochirality among certain classes of biomolecules.
The Japanese chemist Kensō Soai (1950–) discovered the reaction in 1995. For his work in "elucidating the origins of chirality and homochirality", Soai received the Chemical Society of Japan award in 2010.
Other chiral additives can be used as the initial source of asymmetric induction, with the major product of that first reaction being rapidly amplified. For example, Soai's group has demonstrated that even chiral quaternary hydrocarbons, which have no clear Lewis basic site for binding the nucleophile, are nonetheless capable of inducing asymmetric catalysis in the reaction.
The chiral induction is believed to occur as a result of interactions between the C–H bonds of the alkane and the pi electrons of the aldehyde.
In another example, Soai and coworkers showed that even [N](2R, 3S)-bis(dimethylamino)butane, whose chirality results solely due to the difference between N and N (7% isotopic mass difference), gave 45% ee when used as a stoichiometric ligand. | 4 | Stereochemistry |
The process of carrying salts by water to the sea or a land-locked lake from a river basin is called salt export. When adequate salt export is not occurring, the river basin area gradually converts into saline soils and/or alkali soils, particularly in lower reaches. | 9 | Geochemistry |
* TUBA Prize of the Turkish Academy of Sciences (2015)
* Wittgenstein-Preis (2012)
* Honorary doctorate awarded by the University of Bucharest in Romania (2012)
* Honorary doctorate awarded by the Åbo Akademi in Finland (2011)
* Kardinal-Innitzer Award (2010)
* Humanity Medal of the City of Linz (2010)
* Austrians of 2008, category Education (ORF and Die Presse)
* Turkish National Science Prize (TUBITAK Bilim Ödülü) 2006
* ENERGY GLOBE Upper Austria 2003, sponsored by the OÖN
* Basic Award 2001 sponsored by the "Open Upper Austria" | 7 | Physical Chemistry |
Depending on the virus, a variety of genetic changes can occur in the host cell. In the case of a lytic cycle virus, the cell will only survive long enough to the replication machinery to be used to create additional viral units. In other cases, the viral DNA will persist within the host cell and replicate as the cell replicates. This viral DNA can either be incorporated into the host cells genetic material or persist as a separate genetic vector. Either case can lead to damage of the host cells chromosomes. It is possible that the damage can be repaired; however, the most common result is an instability in the original genetic material or suppression or alteration of the gene expression. | 1 | Biochemistry |
In proteins and amino acids, the α-carbon is the backbone carbon before the carbonyl carbon atom in the molecule. Therefore, reading along the backbone of a typical protein would give a sequence of –[N—Cα—carbonyl C]– etc. (when reading in the N to C direction). The α-carbon is where the different substituents attach to each different amino acid. That is, the groups hanging off the chain at the α-carbon are what give amino acids their diversity. These groups give the α-carbon its stereogenic properties for every amino acid except for glycine. Therefore, the α-carbon is a stereocenter for every amino acid except glycine. Glycine also does not have a β-carbon, while every other amino acid does.
The α-carbon of an amino acid is significant in protein folding. When describing a protein, which is a chain of amino acids, one often approximates the location of each amino acid as the location of its α-carbon. In general, α-carbons of adjacent amino acids in a protein are about 3.8 ångströms (380 picometers) apart. | 0 | Organic Chemistry |
To insert a mutation into a DNA sequence, a specific primer is designed. The primer may contain a single substitution or contain a new sequence at its 5 end. If a deletion is required, a sequence that is 5 of the deletion is added, because the 3' end of the primer must have complementarity to the template strand so that the primer can sufficiently anneal to the template DNA.
Following annealing of the primer to the template, DNA replication proceeds to the end of the template. The duplex is denatured and the second primer anneals to the newly formed DNA strand, containing sequence from the first primer. Replication proceeds to produce a strand of the required sequence, containing the mutation.
The duplex is denatured again and the first primer can now bind to the latest DNA strand. The replication reaction continues to produce a fully dimerised DNA fragment. After further PCR cycles, to amplify the DNA, the sample can be separated by agarose gel electrophoresis, followed by electroelution for collection.
Efficiently generating oligonucleotides beyond ~110 nucleotides in length is very difficult, so to insert a mutation further into a sequence than a 110 nt primer will allow, it is necessary to employ overlap extension PCR. In OE-PCR the sequence being modified is used to make two modified strands with the mutation at opposite ends, using the technique described above. After mixing and denaturation, the strands are allowed to anneal to produce three different combinations as detailed in the diagram. Only the duplex without overlap at the 5 end will allow extension by DNA polymerase in 3 to 5' direction.
Following the extension of the OE-PCR reaction, the PCR mix or the eluted fragments of appropriate size are subject to normal PCR, using the outermost primers used in the initial, mutagenic PCR reactions.
In addition, the combination of OE-PCR and asymmetric PCR could be used to improved the efficiency of site-directed mutagenesis. | 1 | Biochemistry |
Nanog is a transcription factor that controls both self-renewal and pluripotency of embryonic stem cells. Similarly, the expression of Nanog family proteins is increased in many types of cancer and correlates with a worse prognosis. | 1 | Biochemistry |
Dexlansoprazole ((R)-(+)-lansoprazole) has the same binding affinity to the proton pump as the (S)-enantiomer, but is associated with a three- to five-fold greater area under the plasma drug concentration time curve (AUC) compared with (S)-lansoprazole. With its dual release pharmaceutical formulation, the first quick release produces a plasma peak concentration about one hour after application, with a second delayed release producing another peak about four hours later. | 4 | Stereochemistry |
A transmetallation involves a ligand transfer to one another such as this:
M is not limited to any main group and/or transition metal. R can be limited to almost any phosphine, aryl, alkyl, halogen, hydrogen and/or carbene.
In this case organoberyllium can form reactions such as: | 0 | Organic Chemistry |
The arginine catabolic mobile element (ACME) is a mobile genetic element of Staphylococcus bacterial species. This genetic element provides for several immune modulating functions, including resistance to polyamines which serve as a non-specific immune response both on intact skin and following the inflammatory response in wound healing. Diverse ACME are present in several species of Staphylococcus, including Staphylococcus epidermidis. | 1 | Biochemistry |
New chloroplasts may contain up to 100 copies of their DNA, though the number of chloroplast DNA copies decreases to about 15–20 as the chloroplasts age. They are usually packed into nucleoids, which can contain several identical chloroplast DNA rings. Many nucleoids can be found in each chloroplast.
In primitive red algae, the chloroplast DNA nucleoids are clustered in the center of the chloroplast, while in green plants and green algae, the nucleoids are dispersed throughout the stroma.
Though chloroplast DNA is not associated with true histones, in red algae, similar proteins that tightly pack each chloroplast DNA ring into a nucleoid have been found. | 5 | Photochemistry |
Embalming is the process of preserving human remains by delaying decomposition. This is acquired through the use of embalming fluid, which is a mixture of formaldehyde, methanol, and various other solvents. The most common reasons to preserve the body are for viewing purposes at a funeral, for above-ground interment or distant transportation of the deceased, and for medical or religious practices. | 1 | Biochemistry |
The solid medium is used to grow lactose-fermenting coliforms and utilizes a neutral red pH indicator. Pink colonies appear when lactose is fermented and are surrounded by bile that has precipitated out. To confirm if these colonies are coliforms, they are transferred to brilliant green lactose bile (BGLB) and incubated. If gas is visible after incubation, it can be confirmed that the sample had coliforms present. | 3 | Analytical Chemistry |
Local exhaust ventilation (LEV) systems rely on air pulled with a suction force through piping systems from the point of dust formation to a waste disposal unit. They consist of four elements: dust hoods at the point of dust formation, ventilation ducts, an air cleaning device (waste separator or dust collector) and an air moving device (a fan, otherwise known as an impeller). The air, containing dust and chips from the woodworking operation, is sucked by an impeller. The impeller is usually built into, or placed close to, the waste disposal unit, or dust collector.
Guidelines of performance for woodworking LEV systems exist, and these tie into occupational air quality regulations that exist in many countries. The LEV guidelines often referred to are those set by the ACIAH. | 2 | Environmental Chemistry |
The Shell process uses cobalt complexes modified with phosphine ligands for the hydroformylation of C7–C14 olefins. The resulting aldehydes are directly hydrogenated to the fatty alcohols, which are separated by distillation, which allows the catalyst to be recycled. The process has good selectivity to linear products, which find use as feedstock for detergents. The process is carried out at a pressure of about 4 to 8 MPa and at a temperature range of about 150–190 °C. | 0 | Organic Chemistry |
Apamin is an 18 amino acid globular peptide neurotoxin found in apitoxin (bee venom). Dry bee venom consists of 2–3% of apamin. Apamin selectively blocks SK channels, a type of Ca-activated K channel expressed in the central nervous system. Toxicity is caused by only a few amino acids, in particular cysteine, lysine, arginine, arginine and histidine. These amino acids are involved in the binding of apamin to the Ca-activated K channel. Due to its specificity for SK channels, apamin is used as a drug in biomedical research to study the electrical properties of SK channels and their role in the afterhyperpolarizations occurring immediately following an action potential. | 1 | Biochemistry |
When fasting, the activation of lipolysis provides fatty acids as the preferred fuel source for respiration. In the liver β-oxidation of fatty acids fulfills the local energy needs and may lead to ketogenesis (creating ketone bodies out of fatty acids.) The ketone bodies are then used to meet the demands of tissues other than the liver. This inhibition of glucose oxidation at the level of pyruvate dehydrogenase preserves pyruvate and lactate, both of which are gluconeogenic precursors. | 1 | Biochemistry |
RMR measurements are recommended when estimating total daily energy expenditure (TEE). Since BMR measures are restricted to the narrow time frame (and strict conditions) upon waking, the looser-conditions RMR measure is more typically conducted. In the review organized by the USDA, most publications documented specific conditions of resting measurements, including time from latest food intake or physical activities; this comprehensive review estimated RMR is 10 – 20% higher than BMR due to thermic effect of feeding and residual burn from activities that occur throughout the day. | 1 | Biochemistry |
For a general unimolecular reaction involving interconversion of different species, whose concentrations at time are denoted by through , an analytic form for the time-evolution of the species can be found. Let the rate constant of conversion from species to species be denoted as , and construct a rate-constant matrix whose entries are the .
Also, let be the vector of concentrations as a function of time.
Let be the vector of ones.
Let be the identity matrix.
Let be the function that takes a vector and constructs a diagonal matrix whose on-diagonal entries are those of the vector.
Let be the inverse Laplace transform from to .
Then the time-evolved state is given by
thus providing the relation between the initial conditions of the system and its state at time . | 7 | Physical Chemistry |
In chemistry, chemical purity is the measurement of the amount of impurities found in a sample. Several grades of purity are used by the scientific, pharmaceutical, and industrial communities. Some of the commonly used grades of purity include:
* ACS grade is the highest level of purity, and meets the standards set by the American Chemical Society (ACS). The official descriptions of the ACS levels of purity is documented in the Reagent Chemicals publication, issued by the ACS. It is suitable for food and laboratory uses.
* Reagent grade is almost as stringent as the ACS grade.
* USP grade meets the purity levels set by the United States Pharmacopeia (USP). USP grade is equivalent to the ACS grade for many drugs.
* NF grade is a purity grade set by the National Formulary (NF). NF grade is equivalent to the ACS grade for many drugs.
* British Pharmacopoeia: Meets or exceeds requirements set by the British Pharmacopoeia (BP). Can be used for food, drug, and medical purposes, and also for most laboratory purposes.
*Japanese Pharmacopeia: Meets or exceeds requirements set by the Japanese Pharmacopoeia (JP). Can be used for food, drug, and medical purposes, and also for most laboratory purposes.
* Laboratory grade is suitable for use in educational settings, but is not acceptable for food or drug use.
* Purified grade is not precisely defined, and it is not suitable for drug or food usage.
* Technical grade is suitable for industrial applications, but is not acceptable for food or drug use. | 2 | Environmental Chemistry |
Such equilibrium inhomogeneity, induced by external forces, does not occur for the intensive variable temperature. According to E.A. Guggenheim, "The most important conception of thermodynamics is temperature." Planck introduces his treatise with a brief account of heat and temperature and thermal equilibrium, and then announces: "In the following we shall deal chiefly with homogeneous, isotropic bodies of any form, possessing throughout their substance the same temperature and density, and subject to a uniform pressure acting everywhere perpendicular to the surface." As did Carathéodory, Planck was setting aside surface effects and external fields and anisotropic crystals. Though referring to temperature, Planck did not there explicitly refer to the concept of thermodynamic equilibrium. In contrast, Carathéodorys scheme of presentation of classical thermodynamics for closed systems postulates the concept of an "equilibrium state" following Gibbs (Gibbs speaks routinely of a "thermodynamic state"), though not explicitly using the phrase thermodynamic equilibrium', nor explicitly postulating the existence of a temperature to define it.
The temperature within a system in thermodynamic equilibrium is uniform in space as well as in time. In a system in its own state of internal thermodynamic equilibrium, there are no net internal macroscopic flows. In particular, this means that all local parts of the system are in mutual radiative exchange equilibrium. This means that the temperature of the system is spatially uniform. This is so in all cases, including those of non-uniform external force fields. For an externally imposed gravitational field, this may be proved in macroscopic thermodynamic terms, by the calculus of variations, using the method of Langrangian multipliers. Considerations of kinetic theory or statistical mechanics also support this statement.
In order that a system may be in its own internal state of thermodynamic equilibrium, it is of course necessary, but not sufficient, that it be in its own internal state of thermal equilibrium; it is possible for a system to reach internal mechanical equilibrium before it reaches internal thermal equilibrium. | 7 | Physical Chemistry |
An ideal polarizable electrode (also ideally polarizable electrode or ideally polarized electrode or IPE) is a hypothetical electrode characterized by an absence of net DC current between the two sides of the electrical double layer, i.e., no faradic current exists between the electrode surface and the electrolyte. Any transient current that may be flowing is considered non-faradaic. The reason for this behavior is that the electrode reaction is infinitely slow, with zero exchange current density, and behaves electrically as a capacitor.
The concept of the ideal polarizability has been first introduced by F.O. Koenig in 1934. | 7 | Physical Chemistry |
A riffle box is a box containing a number (between 3 and 12) of "chutes" - slotted paths through which particles of the sample may slide. The sample is dropped into the top, and the box produces two equally divided subsamples. Riffle boxes are commonly used in mining to reduce the size of crushed rock samples prior to assaying. | 3 | Analytical Chemistry |
Naturally occurring methane is not utilized as a chemical feedstock, despite its abundance and low cost. Current technology makes prodigious use of methane by steam reforming to produce syngas, a mixture of carbon monoxide and hydrogen. This syngas is then used in Fischer-Tropsch reactions to make longer carbon chain products or methanol, one of the most important industrial chemical feedstocks. An intriguing method to convert these hydrocarbons involves C-H activation. Roy A. Periana, for example, reported that complexes containing late transition metals, such as Pt, Pd, Au, and Hg, react with methane (CH) in HSO to yield methyl bisulfate. The process has not however been implemented commercially. | 0 | Organic Chemistry |
Dynamic recrystallization (DRX) is a type of recrystallization process, found within the fields of metallurgy and geology. In dynamic recrystallization, as opposed to static recrystallization, the nucleation and growth of new grains occurs during deformation rather than afterwards as part of a separate heat treatment. The reduction of grain size increases the risk of grain boundary sliding at elevated temperatures, while also decreasing dislocation mobility within the material. The new grains are less strained, causing a decrease in the hardening of a material. Dynamic recrystallization allows for new grain sizes and orientation, which can prevent crack propagation. Rather than strain causing the material to fracture, strain can initiate the growth of a new grain, consuming atoms from neighboring pre-existing grains. After dynamic recrystallization, the ductility of the material increases.
In a stress–strain curve, the onset of dynamic recrystallization can be recognized by a distinct peak in the flow stress in hot working data, due to the softening effect of recrystallization. However, not all materials display well-defined peaks when tested under hot working conditions. The onset of DRX can also be detected from inflection point in plots of the strain hardening rate against stress. It has been shown that this technique can be used to establish the occurrence of DRX when this cannot be determined unambiguously from the shape of the flow curve.
If stress oscillations appear before reaching the steady state, then several recrystallization and grain growth cycles occur and the stress behavior is said to be of the cyclic or multiple peak type. The particular stress behavior before reaching the steady state depends on the initial grain size, temperature, and strain rate.
DRX can occur in various forms, including:
* Geometric dynamic recrystallization
* Discontinuous dynamic recrystallization
* Continuous dynamic recrystallization
Dynamic recrystallization is dependent on the rate of dislocation creation and movement. It is also dependent on the recovery rate (the rate at which dislocations annihilate). The interplay between work hardening and dynamic recovery determines grain structure. It also determines the susceptibility of grains to various types of dynamic recrystallization. Regardless of the mechanism, for dynamic crystallization to occur, the material must have experienced a critical deformation. The final grain size increases with increased stress. To achieve very fine-grained structures the stresses have to be high.
Some authors have used the term postdynamic or metadynamic to describe recrystallization that occurs during the cooling phase of a hot-working process or between successive passes. This emphasises the fact that the recrystallization is directly linked to the process in question, while acknowledging that there is no concurrent deformation. | 8 | Metallurgy |
Axe-monies (Spanish: Tajaderos) refer to bronze artifacts found in both western Mesoamerica and the northern Andes. Based on ethnohistorical, archaeological, chemical, and metallurgical analyses, the scholars Hosler, Lechtman and Holm have argued for their use in both regions (which are separated by thousands of miles) through trade. In contrast to naipes, bow-tie- or card-shaped metal objects which appear in the archaeological record only in the northern Andean coastal region, axe-monies are found in both Mesoamerican and Andean cultural zones. More specifically, it is argued that the system of money first arose on the north coast of Peru and Ecuador in the early second millennium CE. In both regions, bronze was smelted, likely by family units, and hammered into thin, axe-shaped forms and bundled in multiples of five, usually twenty. As they are often found in burials, it is likely that in addition to their presumed economic use, they also had ceremonial value. | 8 | Metallurgy |
In the expansion step of the working fluid in transcritical cycles, as in subcritical ones, the working fluid can be discharged either in wet or dry conditions.
Typical dry expansions are those involving organic or other unconventional working fluids, which are characterized by non-negligible molecular complexities and high molecular weights.
The expansion step occurs in turbines: depending on the application and on the nameplate power produced by the power plant, both axial turbines and radial turbines can be exploited during fluid expansion. Axial turbines favour lower rotational speed and higher power production, while radial turbines are suitable for limited powers produced and high rotational speed.
Organic cycles are appropriate choices for low enthalpy applications and are characterized by higher average densities across the expanders than those occurring in transcritical steam cycles: for this reason a low blade height is normally designed and the volumetric flow rate is kept limited to relatively small values. On the other hand in large scale application scenarios the expander blades typically show heights that exceed one meter and that are exploited in the steam cycles. Here, in fact, the fluid density at the outlet of the last expansion stage is significantly low.
In general, the specific work of the cycle is expressed as:
Even though the specific work of any cycle is strongly dependent on the actual working fluid considered in the cycle, transcritical cycles are expected to exhibit higher specific works than the corresponding subcritical and supercritical counterparts (i.e., that exploit the same working fluid). For this reason, at fixed boundary conditions, power produced and working fluid, a lower mass flow rate is expected in transcritical cycles than in other configurations. | 7 | Physical Chemistry |
An aldehyde differs from a ketone in that it has a hydrogen atom attached to its carbonyl group, making aldehydes easier to oxidize. Ketones do not have a hydrogen atom bonded to the carbonyl group, and are therefore more resistant to oxidation. They are oxidized only by powerful oxidizing agents which have the ability to cleave carbon–carbon bonds. | 0 | Organic Chemistry |
The journal is abstracted and indexed in:
According to the Journal Citation Reports, the journal has a 2012 impact factor of 2.125. | 1 | Biochemistry |
The protein encoded by this gene is a member of the tumor necrosis factor receptor superfamily, which also contains TNFRSF1A. This protein and TNF-receptor 1 form a heterocomplex that mediates the recruitment of two anti-apoptotic proteins, c-IAP1 and c-IAP2, which possess E3 ubiquitin ligase activity. The function of IAPs in TNF-receptor signalling is unknown, however, c-IAP1 is thought to potentiate TNF-induced apoptosis by the ubiquitination and degradation of TNF-receptor-associated factor 2 (TRAF2), which mediates anti-apoptotic signals. Knockout studies in mice also suggest a role of this protein in protecting neurons from apoptosis by stimulating antioxidative pathways. | 1 | Biochemistry |
Grain strength generally follows the Hall–Petch relation, which states that material strength decreases with the square root of the grain size. A higher number of smaller subgrains leads to a higher yield stress, and so some materials may be purposefully manufactured to have many subgrains, and in this case subgrain rotation recrystallization should be avoided.
Precipitates may also form in grain boundaries. It has been observed that precipitates in subgrain boundaries grow in a more elongated shape parallel to the adjacent grains, whereas precipitates in HAGB are blockier. This difference in aspect ratio may provide different strengthening effects to the material; long plate-like precipitates in the LAGB may delaminate and cause brittle failure under stress. Subgrain rotation recrystallization reduces the number of LAGB, thus reducing the number of flat, long precipitates, and also reducing the number of available pathways for this brittle failure. | 8 | Metallurgy |
The idea of relative entropy as discrimination information led Kullback to propose the Principle of (MDI): given new facts, a new distribution should be chosen which is as hard to discriminate from the original distribution as possible; so that the new data produces as small an information gain as possible.
For example, if one had a prior distribution over and , and subsequently learnt the true distribution of was , then the relative entropy between the new joint distribution for and , , and the earlier prior distribution would be:
i.e. the sum of the relative entropy of the prior distribution for from the updated distribution , plus the expected value (using the probability distribution ) of the relative entropy of the prior conditional distribution from the new conditional distribution . (Note that often the later expected value is called the conditional relative entropy (or conditional Kullback–Leibler divergence) and denoted by ) This is minimized if over the whole support of ; and we note that this result incorporates Bayes' theorem, if the new distribution is in fact a δ function representing certainty that has one particular value.
MDI can be seen as an extension of Laplaces Principle of Insufficient Reason, and the Principle of Maximum Entropy of E.T. Jaynes. In particular, it is the natural extension of the principle of maximum entropy from discrete to continuous distributions, for which Shannon entropy ceases to be so useful (see differential entropy'), but the relative entropy continues to be just as relevant.
In the engineering literature, MDI is sometimes called the Principle of Minimum Cross-Entropy (MCE) or Minxent for short. Minimising relative entropy from to with respect to is equivalent to minimizing the cross-entropy of and , since
which is appropriate if one is trying to choose an adequate approximation to . However, this is just as often not the task one is trying to achieve. Instead, just as often it is that is some fixed prior reference measure, and that one is attempting to optimise by minimising subject to some constraint. This has led to some ambiguity in the literature, with some authors attempting to resolve the inconsistency by redefining cross-entropy to be , rather than . | 7 | Physical Chemistry |
The first observations of intracellular structures that probably represented mitochondria were published in 1857, by the physiologist Albert von Kolliker. Richard Altmann, in 1890, established them as cell organelles and called them "bioblasts." In 1898, Carl Benda coined the term "mitochondria" from the Greek , , "thread", and , , "granule." Leonor Michaelis discovered that Janus green can be used as a supravital stain for mitochondria in 1900. In 1904, Friedrich Meves made the first recorded observation of mitochondria in plants in cells of the white waterlily, Nymphaea alba, and in 1908, along with Claudius Regaud, suggested that they contain proteins and lipids. Benjamin F. Kingsbury, in 1912, first related them with cell respiration, but almost exclusively based on morphological observations. In 1913, Otto Heinrich Warburg linked respiration to particles which he had obtained from extracts of guinea-pig liver and which he called "grana". Warburg and Heinrich Otto Wieland, who had also postulated a similar particle mechanism, disagreed on the chemical nature of the respiration. It was not until 1925, when David Keilin discovered cytochromes, that the respiratory chain was described.
In 1939, experiments using minced muscle cells demonstrated that cellular respiration using one oxygen molecule can form four adenosine triphosphate (ATP) molecules, and in 1941, the concept of the phosphate bonds of ATP being a form of energy in cellular metabolism was developed by Fritz Albert Lipmann. In the following years, the mechanism behind cellular respiration was further elaborated, although its link to the mitochondria was not known. The introduction of tissue fractionation by Albert Claude allowed mitochondria to be isolated from other cell fractions and biochemical analysis to be conducted on them alone. In 1946, he concluded that cytochrome oxidase and other enzymes responsible for the respiratory chain were isolated to the mitochondria. Eugene Kennedy and Albert Lehninger discovered in 1948 that mitochondria are the site of oxidative phosphorylation in eukaryotes. Over time, the fractionation method was further developed, improving the quality of the mitochondria isolated, and other elements of cell respiration were determined to occur in the mitochondria.
The first high-resolution electron micrographs appeared in 1952, replacing the Janus Green stains as the preferred way to visualize mitochondria. This led to a more detailed analysis of the structure of the mitochondria, including confirmation that they were surrounded by a membrane. It also showed a second membrane inside the mitochondria that folded up in ridges dividing up the inner chamber and that the size and shape of the mitochondria varied from cell to cell.
The popular term "powerhouse of the cell" was coined by Philip Siekevitz in 1957.
In 1967, it was discovered that mitochondria contained ribosomes. In 1968, methods were developed for mapping the mitochondrial genes, with the genetic and physical map of yeast mitochondrial DNA completed in 1976. | 1 | Biochemistry |
Growth factor and clotting factors are paracrine signaling agents. The local action of growth factor signaling plays an especially important role in the development of tissues. Also, retinoic acid, the active form of vitamin A, functions in a paracrine fashion to regulate gene expression during embryonic development in higher animals.
In insects, Allatostatin controls growth through paracrine action on the corpora allata.
In mature organisms, paracrine signaling is involved in responses to allergens, tissue repair, the formation of scar tissue, and blood clotting. Histamine is a paracrine that is released by immune cells in the bronchial tree. Histamine causes the smooth muscle cells of the bronchi to constrict, narrowing the airways. | 1 | Biochemistry |
Pressure (along with temperature) determines the super- or subcritical state of solvents as well as overall reaction kinetics and the energy inputs required to yield the desirable HTL products (oil, gas, chemicals, char etc.). | 0 | Organic Chemistry |
Some hydrogels are able to respond to stimuli and their surrounding environments. Examples of these stimuli include light, temperature, pH, and electrical fields. Hydrogels that are temperature sensitive are known as thermogels. Thermo-responsive hydrogels undergo reversible, thermally induced phase transition upon reaching either the upper or lower critical solution temperature. By definition, a crosslinked polymer gel is a macromolecule that cannot dissolve. Due to the polymeric domains created by crosslinking, in the gel microstructure, hydrogels are not homogenous within the solvent system in which they are placed into. Swelling of the network, however, does occur in the presence of a proper solvent. Voids in the microstructure of the gel where crosslinking agent or monomer has aggregated during polymerization can cause solvent to diffuse into or out of the hydrogel. The microstructure of hydrogel therefore are not constant, and imperfections occur where water from outside of the gel can accumulate these voids. This process is temperature dependent, and solvent behavior depends on whether the solvent-gel system has reached, or surpassed, the critical solution temperature (LCST). The LCST defines a boundary between which a gel or polymer chain will separate solvent into one or two phases. The spinodial and binodial regions of a polymer-solvent phase diagram represent the energetic favorability of the hydrogel becoming miscible in solution or separating into two phases. | 7 | Physical Chemistry |
An orbifold can be viewed as a polygon with face, edges, and vertices which can be unfolded to form a possibly infinite set of polygons which tile either the sphere, the plane or the hyperbolic plane. When it tiles the plane it will give a wallpaper group and when it tiles the sphere or hyperbolic plane it gives either a spherical symmetry group or Hyperbolic symmetry group. The type of space the polygons tile can be found by calculating the Euler characteristic, χ = V − E + F, where V is the number of corners (vertices), E is the number of edges and F is the number of faces. If the Euler characteristic is positive then the orbifold has an elliptic (spherical) structure; if it is zero then it has a parabolic structure, i.e. a wallpaper group; and if it is negative it will have a hyperbolic structure. When the full set of possible orbifolds is enumerated it is found that only 17 have Euler characteristic 0.
When an orbifold replicates by symmetry to fill the plane, its features create a structure of vertices, edges, and polygon faces, which must be consistent with the Euler characteristic. Reversing the process, one can assign numbers to the features of the orbifold, but fractions, rather than whole numbers. Because the orbifold itself is a quotient of the full surface by the symmetry group, the orbifold Euler characteristic is a quotient of the surface Euler characteristic by the order of the symmetry group.
The orbifold Euler characteristic is 2 minus the sum of the feature values, assigned as follows:
*A digit n without or before a * counts as .
*A digit n after a * counts as .
*Both * and × count as 1.
*The "no symmetry" o counts as 2.
For a wallpaper group, the sum for the characteristic must be zero; thus the feature sum must be 2.
;Examples
Now enumeration of all wallpaper groups becomes a matter of arithmetic, of listing all feature strings with values summing to 2.
Feature strings with other sums are not nonsense; they imply non-planar tilings, not discussed here. (When the orbifold Euler characteristic is negative, the tiling is hyperbolic; when positive, spherical or bad). | 3 | Analytical Chemistry |
The MACS method allows cells to be separated by using magnetic nanoparticles coated with antibodies against a particular surface antigen. This causes the cells expressing this antigen to attach to the magnetic nanoparticles. After incubating the beads and cells, the solution is transferred to a column in a strong magnetic field. In this step, the cells attached to the nanoparticles (expressing the antigen) stay on the column, while other cells (not expressing the antigen) flow through. With this method, the cells can be separated positively or negatively with respect to the particular antigen(s). | 1 | Biochemistry |
: To identify genes associated with traits, it is important to measure the trait value - known as phenotype. The "omics" for measurement of phenotypes is called phenomics. The phenotype can be indicative of the measurement of the trait itself or an indirectly related or correlated trait. | 1 | Biochemistry |
para-Dimethylaminobenzaldehyde is an organic compound containing amine and aldehyde moieties which is used in Ehrlichs reagent and Kovacs reagent to test for indoles. The carbonyl group typically reacts with the electron rich 2-position of the indole but may also react at the C-3 or N-1 positions. It may also be used for determination of hydrazine. | 3 | Analytical Chemistry |
Quantum photoelectrochemistry is the investigation of the quantum mechanical nature of photoelectrochemistry, the subfield of study within physical chemistry concerned with the interaction of light with electrochemical systems, typically through the application of quantum chemical calculations. Quantum photoelectrochemistry provides an expansion of quantum electrochemistry to processes involving also the interaction with light (photons). It therefore also includes essential elements of photochemistry. Key aspects of quantum photoelectrochemistry are calculations of optical excitations, photoinduced electron and energy transfer processes, excited state evolution, as well as interfacial charge separation and charge transport in nanoscale energy conversion systems.
Quantum photoelectrochemistry in particular provides fundamental insight into basic light-harvesting and photoinduced electro-optical processes in several emerging solar energy conversion technologies for generation of both electricity (photovoltaics) and solar fuels. Examples of such applications where quantum photoelectrochemistry provides insight into fundamental processes include photoelectrochemical cells, semiconductor photochemistry, as well as light-driven electrocatalysis in general, and artificial photosynthesis in particular.
Quantum photoelectrochemistry constitutes an active line of current research, with several publications appearing in recent years that relate to several different types of materials and processes, including light-harvesting complexes, light-harvesting polymers, as well as nanocrystalline semiconductor materials. | 7 | Physical Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.