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Compounds with the formula [PR]X comprise the phosphonium salts. These species are tetrahedral phosphorus(V) compounds. From the commercial perspective, the most important member is tetrakis(hydroxymethyl)phosphonium chloride, [P(CHOH)]Cl, which is used as a fire retardant in textiles. Approximately 2M kg are produced annually of the chloride and the related sulfate. They are generated by the reaction of phosphine with formaldehyde in the presence of the mineral acid:
:PH + HX + 4 CHO → [P(CHOH)]X
A variety of phosphonium salts can be prepared by alkylation and arylation of organophosphines:
:PR + RX → [PRR]X
The methylation of triphenylphosphine is the first step in the preparation of the Wittig reagent.
The parent phosphorane (σλ) is PH, which is unknown. Related compounds containing both halide and organic substituents on phosphorus are fairly common. Those with five organic substituents are rare, although P(CH) is known, being derived from P(CH) by reaction with phenyllithium.
Phosphorus ylides are unsaturated phosphoranes, known as Wittig reagents, e.g. CHP(CH). These compounds feature tetrahedral phosphorus(V) and are considered relatives of phosphine oxides. They also are derived from phosphonium salts, but by deprotonation not alkylation. | 0 | Theoretical and Fundamental Chemistry |
Biological molecular machines have been known and studied for years given their vital role in sustaining life, and have served as inspiration for synthetically designed systems with similar useful functionality. The advent of conformational analysis, or the study of conformers to analyze complex chemical structures, in the 1950s gave rise to the idea of understanding and controlling relative motion within molecular components for further applications. This led to the design of "proto-molecular machines" featuring conformational changes such as cog-wheeling of the aromatic rings in triptycenes. By 1980, scientists could achieve desired conformations using external stimuli and utilize this for different applications. A major example is the design of a photoresponsive crown ether containing an azobenzene unit, which could switch between cis and trans isomers on exposure to light and hence tune the cation-binding properties of the ether. In his seminal 1959 lecture Theres Plenty of Room at the Bottom', Richard Feynman alluded to the idea and applications of molecular devices designed artificially by manipulating matter at the atomic level. This was further substantiated by Eric Drexler during the 1970s, who developed ideas based on molecular nanotechnology such as nanoscale "assemblers", though their feasibility was disputed.
Though these events served as inspiration for the field, the actual breakthrough in practical approaches to synthesize artificial molecular machines (AMMs) took place in 1991 with the invention of a "molecular shuttle" by Sir Fraser Stoddart. Building upon the assembly of mechanically linked molecules such as catenanes and rotaxanes as developed by Jean-Pierre Sauvage in the early 1980s, this shuttle features a rotaxane with a ring that can move across an "axle" between two ends or possible binding sites (hydroquinone units). This design realized the well-defined motion of a molecular unit across the length of the molecule for the first time. In 1994, an improved design allowed control over the motion of the ring by pH variation or electrochemical methods, making it the first example of an AMM. Here the two binding sites are a benzidine and a biphenol unit; the cationic ring typically prefers staying over the benzidine ring, but moves over to the biphenol group when the benzidine gets protonated at low pH or if it gets electrochemically oxidized. In 1998, a study could capture the rotary motion of a decacyclene molecule on a copper-base metallic surface using a scanning tunneling microscope. Over the following decade, a broad variety of AMMs responding to various stimuli were invented for different applications. In 2016, the Nobel Prize in Chemistry was awarded to Sauvage, Stoddart, and Bernard L. Feringa for the design and synthesis of molecular machines. | 0 | Theoretical and Fundamental Chemistry |
Toshiko K. Mayeda (née Kuki) (1923–13 February 2004) was a Japanese American chemist who worked at the Enrico Fermi Institute in the University of Chicago. She worked on climate science and meteorites from 1958 to 2004. | 0 | Theoretical and Fundamental Chemistry |
After his PhD, he joined, in 2001 Prof. Dr. Robert H. Crabtree's research team at Yale, USA, to develop the coordination chemistry of N-Heterocyclic carbene (NHC) ligands with various metals and to study their application as catalysts in C–H activation reactions.
This period was followed by a short stay, 2002–2003, as researcher R&D Coating Effects, in Ciba Specialty Chemicals (Basel, CH). Then, Martin Albrecht accepted a position as Alfred Werner assistant professorship in Fribourg, Switzerland working on NHC coordination chemistry, on the edge with biology. For this research, he was granted a European Research Council starting grant in 2005 for the CARBENZYMES project that aimed to understand the bonding properties of metalloenzymes.
In 2009, he joined the University College Dublin as a full Professor. He developed a productive research program using novel 1,2,3-triazolylidene mesoionic carbene ligands.
At that time, he received a European Research Council Consolidator Grant in 2014 for the synMICs project that aimed at the exploration of sustainable pathways for the efficient production of pharmaceutical drugs and for energy storage with 3d metals.
In 2015, he moved with his research group back to Bern, Switzerland to continue his research on donor flexible ligands as Professor of Inorganic Chemistry. Since 2021, he has been deputy director of the Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern. In 2021, the 1st year Biology Bachelor students recognized his commitment to teach young undergraduate students, to inspire them and to act as a scientific role model by nominating him for the "Teacher of the year 2021" award. | 0 | Theoretical and Fundamental Chemistry |
The concept and use of the power spectrum of a signal is fundamental in electrical engineering, especially in electronic communication systems, including radio communications, radars, and related systems, plus passive remote sensing technology. Electronic instruments called spectrum analyzers are used to observe and measure the power spectra of signals.
The spectrum analyzer measures the magnitude of the short-time Fourier transform (STFT) of an input signal. If the signal being analyzed can be considered a stationary process, the STFT is a good smoothed estimate of its power spectral density. | 0 | Theoretical and Fundamental Chemistry |
Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites. The oldest preserved chitin dates to the Oligocene, about , consisting of a beetle encased in amber. | 1 | Applied and Interdisciplinary Chemistry |
The swelling and bioadhesion of hydrogels can be controlled based on the fluid environment they are introduced to in the body. These properties make them excellent for use as controlled drug delivery devices. Where the hydrogel adheres in the body will be determined by its chemistry and reactions with the surrounding tissues. If introduced by mouth, the hydrogel could adhere to anywhere in the gastrointestinal tract including the mouth, the stomach, the small intestine, or the colon. Adhesion in a specifically targeted region will cause for a localized drug delivery and an increased concentration of the drug taken up by the tissues. | 0 | Theoretical and Fundamental Chemistry |
Cytocidal infections are often associated with changes in cell morphology, physiology and are thus important for the complete viral replication and transformation. Cytopathic Effects, often include a change in cells morphology such as fusion with adjacent cells to form polykaryocytes as well as the synthesis of nuclear and cytoplasmic inclusion bodies. Physiological changes include the insufficient movement of ions, formation of secondary messengers, and activation of cellular cascades to continue cellular activity. Biochemically, many viruses inhibit the synthesis of host DNA, RNA, proteins directly or even interfere with protein-protein, DNA-protein, RNA-protein interactions at the subcellular level. Genotoxicity involves breaking, fragmenting, or rearranging chromosomes of the host. Lastly, biologic effects include the viruses ability to affect the activity of antigens and immunologlobulins in the host cell.
There are two types of cytocidal infections, productive and abortive. In productive infections, additional infectious viruses are produced. Abortive infections do not produce infectious viruses. One example of a productive cytocidal infection is the herpes virus. | 1 | Applied and Interdisciplinary Chemistry |
The height of the jump is derived from the application of the equations of conservation of mass and momentum. There are several methods of predicting the height of a hydraulic jump.
They all reach common conclusions that:
* The ratio of the water depth before and after the jump depend solely on the ratio of velocity of the water entering the jump to the speed of the wave over-running the moving water.
* The height of the jump can be many times the initial depth of the water.
For a known flow rate as shown by the figure below, the approximation that the momentum flux is the same just up- and downstream of the energy principle yields an expression of the energy loss in the hydraulic jump. Hydraulic jumps are commonly used as energy dissipators downstream of dam spillways.
; Applying the continuity principle
In fluid dynamics, the equation of continuity is effectively an equation of conservation of mass. Considering any fixed closed surface within an incompressible moving fluid, the fluid flows into a given volume at some points and flows out at other points along the surface with no net change in mass within the space since the density is constant. In case of a rectangular channel, then the equality of mass flux upstream () and downstream () gives:
: or
with the fluid density, and the depth-averaged flow velocities upstream and downstream, and and the corresponding water depths.
; Conservation of momentum flux
For a straight prismatic rectangular channel, the conservation of momentum flux across the jump, assuming constant density, can be expressed as:
In rectangular channel, such conservation equation can be further simplified to dimensionless M-y equation form, which is widely used in hydraulic jump analysis in open channel flow.
Jump height in terms of flow
Dividing by constant and introducing the result from continuity gives
which, after some algebra, simplifies to:
where Here is the dimensionless Froude number, and relates inertial to gravitational forces in the upstream flow. Solving this quadratic yields:
Negative answers do not yield meaningful physical solutions, so this reduces to:
: so
known as Bélanger equation. The result may be extended to an irregular cross-section.
This produces three solution classes:
* When , then (i.e., there is no jump)
* When , then (i.e., there is a negative jump – this can be shown as not conserving energy and is only physically possible if some force were to accelerate the fluid at that point)
* When , then (i.e., there is a positive jump)
This is equivalent to the condition that . Since the is the speed of a shallow gravity wave, the condition that is equivalent to stating that the initial velocity represents supercritical flow (Froude number > 1) while the final velocity represents subcritical flow (Froude number < 1).
;Undulations downstream of the jump
Practically this means that water accelerated by large drops can create stronger standing waves (undular bores) in the form of hydraulic jumps as it decelerates at the base of the drop. Such standing waves, when found downstream of a weir or natural rock ledge, can form an extremely dangerous "keeper" with a water wall that "keeps" floating objects (e.g., logs, kayaks, or kayakers) recirculating in the standing wave for extended periods. | 1 | Applied and Interdisciplinary Chemistry |
Examples of distillation for zeotropic mixtures can be found in industry. Refining crude oil is an example of multi-component distillation in industry that has been used for more than 75 years. Crude oil is separated into five components with main and side columns in a sharp split configuration. In addition, ethylene is separated from methane and ethane for industrial purposes using multi-component distillation.
Separating aromatic substances requires extractive distillation, for example, distilling a zeotropic mixture of benzene, toluene, and p-xylene. | 1 | Applied and Interdisciplinary Chemistry |
Conservation of substance implies that the volume of wine in the barrel holding mostly water has to be equal to the volume of water in the barrel holding mostly wine.
The mixtures can be visualised as separated into their water and wine components:
To help in grasping this, the wine and water may be represented by, say, 100 red and 100 white marbles, respectively. If 25, say, red marbles are mixed in with the white marbles, and 25 marbles of any color are returned to the red container, then there will again be 100 marbles in each container. If there are now x white marbles in the red container, then there must be x red marbles in the white container. The mixtures will therefore be of equal purity. An example is shown below. | 0 | Theoretical and Fundamental Chemistry |
The Curiosity rover from the Mars Science Laboratory mission, with its Curiosity rover is currently assessing the potential past and present habitability of the Martian environment and is attempting to detect biosignatures on the surface of Mars. Considering the MSL instrument payload package, the following classes of biosignatures are within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. The Curiosity rover targets outcrops to maximize the probability of detecting fossilized organic matter preserved in sedimentary deposits. | 1 | Applied and Interdisciplinary Chemistry |
A simple Taylor–Couette flow is a steady flow created between two rotating infinitely long coaxial cylinders. Since the cylinder lengths are infinitely long, the flow is essentially unidirectional in steady state. If the inner cylinder with radius is rotating at constant angular velocity and the outer cylinder with radius is rotating at constant angular velocity as shown in figure, then the azimuthal velocity component is given by
where | 1 | Applied and Interdisciplinary Chemistry |
In the US, fire protection systems must adhere to the standards set forth in the installation standards of NFPA 13, (NFPA) 13D,(NFPA) 13R, (NFPA 14) and (NFPA) 25which are administered, copyrighted, and published by the National Fire Protection Association. | 1 | Applied and Interdisciplinary Chemistry |
Auger electron spectroscopy (AES; pronounced in French) is a common analytical technique used specifically in the study of surfaces and, more generally, in the area of materials science. It is a form of electron spectroscopy that relies on the Auger effect, based on the analysis of energetic electrons emitted from an excited atom after a series of internal relaxation events. The Auger effect was discovered independently by both Lise Meitner and Pierre Auger in the 1920s. Though the discovery was made by Meitner and initially reported in the journal Zeitschrift für Physik in 1922, Auger is credited with the discovery in most of the scientific community. Until the early 1950s Auger transitions were considered nuisance effects by spectroscopists, not containing much relevant material information, but studied so as to explain anomalies in X-ray spectroscopy data. Since 1953 however, AES has become a practical and straightforward characterization technique for probing chemical and compositional surface environments and has found applications in metallurgy, gas-phase chemistry, and throughout the microelectronics industry. | 0 | Theoretical and Fundamental Chemistry |
Proximity and access to water have been key factors in human settlement through history. Water, along with the spaces around it, create a potential for transport, trade, and power generation. They also provide the human population with resources like recreation and tourism in addition to drinking water and food. Many of the world's largest cities are located near water sources, and networks of urban "blue infrastructure", such as canals, harbors and so forth, have been constructed to capture the benefits and minimize risks. Globally, cities are facing severe water uncertainties such as floods, droughts, and upstream activities on trans-boundary rivers. The increasing pressure, intensity, and speed of urbanization has led to the disappearance of any visible form of water infrastructure in most cities. Urban coastal populations are growing, and many cities have seen an extensive post-industrial transformation of canals, riversides, docks, etc. following changes in global trading patterns. The potential implications of such waterside regeneration in terms of public health have only recently been scientifically investigated. A systematic review conducted in 2017 found consistent evidence of positive associations between exposure of people to blue space and mental health and physical activity.
One-fifth of the world's population, 1.2 billion people, live in areas of water scarcity. Climate change and water-related disasters will place increasing demands on urban systems and will result in increased migration to urban areas. Cities require a very large input of freshwater and in turn have a huge impact on freshwater systems. Urban and industrial water use is projected to double by 2050.
In 2010 the United Nations declared that access to clean water and sanitation is a human right. New solutions for improving the sustainability of cities are being explored. Good urban water management is complex and requires not only water and wastewater infrastructure, but also pollution control and flood prevention. It requires coordination across many sectors, and between different local authorities and changes in governance, that lead to more sustainable and equitable use of urban water resources. | 1 | Applied and Interdisciplinary Chemistry |
In 1960, the biochemist Robert K. Crane revealed his discovery of the sodium-glucose cotransport as the mechanism for intestinal glucose absorption. This was the very first proposal of a coupling between the fluxes of an ion and a substrate that has been seen as sparking a revolution in biology. This discovery, however, would not have been possible if it were not for the discovery of the molecule glucose's structure and chemical makeup. These discoveries are largely attributed to the German chemist Emil Fischer who received the Nobel Prize in chemistry nearly 60 years earlier. | 1 | Applied and Interdisciplinary Chemistry |
French drains can be used in farmers' fields for the tile drainage of waterlogged fields. Such fields are called "tiled". Weeping tiles can be used anywhere that soil needs to be drained.
Weeping tiles are used for the opposite reason in septic drain fields for septic tanks. Clarified sewage from the septic tank is fed into weeping tiles buried shallowly in the drain field. The weeping tile spreads the liquid throughout the drain field. | 1 | Applied and Interdisciplinary Chemistry |
One example of a linear shear rheometer is the Goodyear linear skin rheometer, which is used to test cosmetic cream formulations, and for medical research purposes to quantify the elastic properties of tissue.
The device works by attaching a linear probe to the surface of the tissue under test, a controlled cyclical force is applied, and the resultant shear force measured using a load cell. Displacement is measured using an LVDT. Thus the basic stress–strain parameters are captured and analysed to derive the dynamic spring rate of the tissue under tests. | 1 | Applied and Interdisciplinary Chemistry |
Figure 4 shows an experimental realization of the
Gaspard–Rice system using a laser instead of a point particle.
As anyone who's actually tried this knows, this is not a very effective
method of testing the system—the laser beam gets scattered in every
direction. As shown by Sweet, Ott and Yorke,
a more effective method is to direct coloured light through the gaps
between the discs (or in this case, tape coloured strips of paper across pairs of cylinders)
and view the reflections through an open gap.
The result is a complex pattern of stripes of alternating colour, as
shown below, seen more clearly in the simulated version below that.
Figures 5 and 6 show the basins of attraction for each
impact parameter, b, that is, for a given value of b, through which gap
does the particle exit? The basin boundaries form a Cantor set and
represent members of the stable manifold: trajectories that, once started, never
exit the system. | 0 | Theoretical and Fundamental Chemistry |
In plasma physics and magnetic confinement fusion, neoclassical transport or neoclassical diffusion is a theoretical description of collisional transport in toroidal plasmas, usually found in tokamaks or stellerators. It is a modification of classical diffusion adding in effects of non-uniform magnetic fields due to the toroidal geometry, which give rise to new diffusion effects. | 1 | Applied and Interdisciplinary Chemistry |
Throughout this article, [RL] denotes the concentration of a receptor-ligand complex, [R] the concentration of free receptor, and [L] the concentration of free ligand (so that the total concentration of the receptor and ligand are [R]+[RL] and [L]+[RL], respectively). Let n be the number of binding sites for ligand on each receptor molecule, and let represent the average number of ligands bound to a receptor. Let K denote the dissociation constant between the ligand and receptor. The Scatchard equation is given by
By plotting /[L] versus , the Scatchard plot shows that the slope equals to -1/K while the x-intercept equals the number of ligand binding sites n. | 1 | Applied and Interdisciplinary Chemistry |
Potentiometric solid state gas sensors have been generally classified into three broad groups.
*Type I sensors have an electrolyte containing mobile ions of the chemical species in the gas phase that it is monitoring. The commercial product, YSZ oxygen sensor, is an example of type I.
*Type II sensors do not have mobile ions of the chemical species to be sensed, but an ion related to the target gas can diffuse in the solid electrolyte to allow equilibration with the atmosphere. Therefore, type I and type II sensors have the same design with gas electrodes combined with metal and an electrolyte where oxidized or reduced ions can be electrochemically equilibrated through the electrochemical cell. In the third type of electrochemical sex, auxiliary phases are added to the electrodes to enhance the selectivity and stability.
*Type III sensors make the electrode concept even more confusing. With respect to the design of a solid state sensor, the auxiliary phase looks as part of the electrode. But it cannot be an electrode because auxiliary phase materials are not generally good electrical conductor. In spite of this confusion, type III design offers more feasibility in terms of designing various sensors with different auxiliary materials and electrolytes. | 0 | Theoretical and Fundamental Chemistry |
A negative-calorie food is food that supposedly requires more food energy to be digested than the food provides. Its thermic effect or specific dynamic action—the caloric "cost" of digesting the food—would be greater than its food energy content. Despite its recurring popularity in dieting guides, there is no evidence supporting the idea that any food is calorically negative. While some chilled beverages are calorically negative, the effect is minimal and requires drinking very large amounts of water, which can be dangerous, as it can cause water intoxication. | 1 | Applied and Interdisciplinary Chemistry |
The kiln is a cylindrical vessel, inclined slightly from the horizontal, which is rotated slowly about its longitudinal axis. The process feedstock is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down toward the lower end, and may undergo a certain amount of stirring and mixing. Hot gases pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gases may be generated in an external furnace, or may be generated by a flame inside the kiln. Such a flame is projected from a burner-pipe (or "firing pipe") which acts like a large bunsen burner. The fuel for this may be gas, oil, pulverized petroleum coke or pulverized coal. | 1 | Applied and Interdisciplinary Chemistry |
Balanced chromosomal rearrangements can have a significant contribution to diseases, as demonstrated by the studies of leukemia. However, many of them are undetected by chromosomal microarray. Karyotyping and FISH can identify balanced translocations and inversions but are labor-intensive and provide low resolution (small genomic changes are missed).
A jumping library NGS combined approach can be applied to identify such genomic changes. For example, Slade et al. applied this method to fine map a de novo balanced translocation in a child with Wilms' tumor. For this study, 50 million reads were generated, but only 11.6% of these could be mapped uniquely to the reference genome, which represents approximately a sixfold coverage.
Talkowski et al. compared different approaches to detect balanced chromosome alterations, and showed that modified jumping library in combination with next generation DNA sequencing is an accurate method for mapping chromosomal breakpoints. Two varieties of jumping libraries (short-jump libraries and custom barcoded jumping libraries) were tested and compared to standard sequencing libraries.
For standard NGS, 200-500bp fragments are generated. About 0.03%–0.54% of fragments represent chimeric pairs, which are pairs of end-reads that are mapped to two different chromosomes. Therefore, very few fragments cover the breakpoint area.
When using short-jump libraries with fragments of 3.2–3.8kb, the percentage of chimeric pairs increased to 1.3%. With Custom Barcoded Jumping Libraries, the percentage of chimeric pairs further increased to 1.49%. | 1 | Applied and Interdisciplinary Chemistry |
Bromine is used in flame retardants, pesticides, lighter fuel, antiknocking agents, and for water purification. The organic form of this element is used as flame retardants commercially and in pesticides. These chemicals have led to an increase in the depletion of the stratospheric ozone layer. Some countries use bromine to treat drinking water, similar to chlorination. Bromine is also present as impurities emitted from cooling towers. | 0 | Theoretical and Fundamental Chemistry |
A stink bomb that could be launched with arrows was invented by Leonardo da Vinci.
The 1972 U.S. presidential campaign of Edmund Muskie was disrupted at least four times in Florida in 1972 with the use of stink bombs during the Florida presidential primary. Stink bombs were set off at campaign picnics in Miami and Tampa, at the Muskie campaign headquarters in Tampa and at offices in Tampa where the campaign's telephone bank was located. The stink bomb plantings served to disrupt the picnics and campaign operations, and was deemed by the U.S. Select Committee on Presidential Campaign Activities of the U.S. Senate to have "disrupted, confused, and unnecessarily interfered with a campaign for the office of the Presidency".
In 2004, it was reported that the Israeli weapons research and development directorate had created a liquid stink bomb, dubbed the "skunk bomb", with an odor that lingers for five years on clothing. It is a synthetic stink bomb based upon the chemistry of the spray that is emitted from the anal glands of the skunk. It was designed as a crowd control tool to be used as a deterrent that causes people to scatter, such as at a protest. It has been described as a less than lethal weapon. | 1 | Applied and Interdisciplinary Chemistry |
Deformulation refers to a set of analytical procedures used to separate and identify individual components of a formulated chemical substance. Deformulation applies methods of analytical chemistry and is often used to obtain competitive intelligence about chemical products. Deformulation is related to reverse engineering; however, the latter concept is most closely associated with procedures used to discover working principles of a device or a designed system through examination and disassembly of its structure. The term, reverse engineering, has become specifically and almost exclusively linked to the field of software engineering; whereas, deformulation is a term more applicable to the field of chemical manufacturing. Deformulation of a multicomponent chemical mixture may occur in several contexts, including the investigation of causes of chemical product failure, competitive benchmarking, legal inquiry to obtain evidence of patent infringement, or new product research and development. Depending upon this context and upon the level of information sought, the requirements of analyses for deformulation may differ. Deformulation processes typically require the application of several analytical methods, and the selection of methods is dependent upon the degree of confidence required in the results. Methods of deformulation also have similarity to methods of forensic chemistry in which analytical procedures may be applied to discover the causes of material failure or to resolve a legal question. | 0 | Theoretical and Fundamental Chemistry |
A Proton-coupled electron transfer (PCET) is a chemical reaction that involves the transfer of electrons and protons from one atom to another. The term was originally coined for single proton, single electron processes that are concerted, but the definition has relaxed to include many related processes. Reactions that involve the concerted shift of a single electron and a single proton are often called Concerted Proton-Electron Transfer or CPET.
In PCET, the proton and the electron (i) start from different orbitals and (ii) are transferred to different atomic orbitals. They transfer in a concerted elementary step. CPET contrast to step-wise mechanisms in which the electron and proton are transferred sequentially.
:ET
:[HX] + [M] → [HX] + [M]
:PT
:[HX] + [M] → [X] + [HM]
:CPET
:[HX] + [M] → [X] + [HM] | 0 | Theoretical and Fundamental Chemistry |
The partition system of the plasmid R388 has been found within the stb operon. This operon is composed of three genes, stbA, stbB and stbC.
* StbA protein is a DNA-binding protein (identical to [https://www.uniprot.org/uniprot/P11904 ParM]) and is strictly required for the stability and intracellular positioning of plasmid R388 in E. coli. StbA binds a cis-acting sequence, the stbDRs.
The StbA-stbDRs complex may be used to pair plasmid the host chromosome, using indirectly the bacterial partitioning system.
* StbB protein has a Walker-type ATPase motif, it favors for conjugation but is not required for plasmid stability over generations.
* StbC is an orphan protein of unknown function. StbC doesn't seem to be implicated in either partitioning or conjugation.
StbA and StbB have opposite but connected effect related to conjugation.
This system has been proposed to be the type IV partition system. It is thought to be a derivative of the type I partition system, given the similar operon organization.
This system represents the first evidence for a mechanistic interplay between plasmid segregation and conjugation processes. | 1 | Applied and Interdisciplinary Chemistry |
Genome-wide CRISPR screens will ultimately be limited by the properties of the chosen sgRNA library. Each library will contain a different set of sgRNAs, and average coverage per gene may vary. Currently available libraries tend to be biased towards sgRNAs targeting early (5’) protein-coding exons, rather than those targeting the more functional protein domains. This problem was highlighted by Hinze et al. (2019), who noted that genes associated with asparaginase sensitivity failed to score in their genome-wide screen of asparaginase-resistant leukemia cells.
If an appropriate library is not available, creating and amplifying a new sgRNA library is a lengthy process which may take many months. Potential challenges include: (i) effective sgRNA design; (ii) ensuring comprehensive sgRNA coverage throughout the genome; (iii) lentiviral vector backbone design; (iv) producing sufficient amounts of high-quality lentivirus; (v) overcoming low transformation efficiency; (vi) proper scaling of the bacterial culture. | 1 | Applied and Interdisciplinary Chemistry |
Lactams form by copper-catalyzed 1,3-dipolar cycloaddition of alkynes and nitrones in the Kinugasa reaction | 0 | Theoretical and Fundamental Chemistry |
The gun method has also been applied for nuclear artillery shells, since the simpler design can be more easily engineered to withstand the rapid acceleration and g-forces imparted by an artillery gun, and since the smaller diameter of the gun-type design can be relatively easily fitted to projectiles that can be fired from existing artillery.
A US gun-type nuclear artillery weapon, the W9, was tested on May 25, 1953, at the Nevada Test Site. Fired as part of Operation Upshot–Knothole and codenamed Shot GRABLE, a 280 mm shell was fired 10,000 m and detonated 160 m above the ground with an estimated yield of 15 kilotons. This is approximately the same yield as Little Boy, although the W9 had less than 1/10 of Little Boy's weight (365 kg vs. 4,000 kg, or 805 lbs vs. 8,819 lbs). The shell was 1,384 mm long.
This was the only nuclear artillery shell ever actually fired (from an artillery gun) in the US test program. It was fired from a specially built artillery piece, nicknamed Atomic Annie. Eighty shells were produced from 1952 to 1953. It was retired in 1957.
The W19 was also a 280 mm gun-type nuclear shell, a longer version of the W-9. Eighty warheads were produced and the system was retired in 1963.
The W33 was a smaller, 8 inch (203 mm) gun-type nuclear artillery shell, which was produced starting in 1957 and in service until 1992. Two were test fired (detonated, not fired from an artillery gun), one hung under a balloon in the open air, and one in a tunnel.
Later versions were based on the implosion design. | 0 | Theoretical and Fundamental Chemistry |
ATP synthase is an enzyme that catalyzes the formation of the energy storage molecule adenosine triphosphate (ATP) using adenosine diphosphate (ADP) and inorganic phosphate (P). ATP synthase is a molecular machine. The overall reaction catalyzed by ATP synthase is:
* ADP + P + 2H ATP + HO + 2H
ATP synthase lies across a cellular membrane and forms an aperture that protons can cross from areas of high concentration to areas of low concentration, imparting energy for the synthesis of ATP. This electrochemical gradient is generated by the electron transport chain and allows cells to store energy in ATP for later use. In prokaryotic cells ATP synthase lies across the plasma membrane, while in eukaryotic cells it lies across the inner mitochondrial membrane. Organisms capable of photosynthesis also have ATP synthase across the thylakoid membrane, which in plants is located in the chloroplast and in cyanobacteria is located in the cytoplasm.
Eukaryotic ATP synthases are F-ATPases, running "in reverse" for an ATPase. This article deals mainly with this type. An F-ATPase consists of two main subunits, F and F, which has a rotational motor mechanism allowing for ATP production. | 0 | Theoretical and Fundamental Chemistry |
The use of two lasers to heat the sample reduces the axial temperature gradient, this which allows for thicker samples to be heated more evenly. In order for a double-sided heating system to be successful it is essential that the two lasers are aligned so that they are both focused on the sample position. For in situ heating in diffraction experiments, the lasers need to be focused to the same point in space where the X-ray beam is focused. | 0 | Theoretical and Fundamental Chemistry |
The Magnus effect is an observable phenomenon that is commonly associated with a spinning object moving through a fluid. The path of the spinning object is deflected in a manner that is not present when the object is not spinning. The deflection can be explained by the difference in pressure of the fluid on opposite sides of the spinning object. The Magnus effect is dependent on the speed of rotation. | 1 | Applied and Interdisciplinary Chemistry |
The dimensions that can be formed from a given collection of basic physical dimensions, such as T, L, and M, form an abelian group: The identity is written as 1; , and the inverse of L is 1/L or L. L raised to any integer power is a member of the group, having an inverse of L or 1/L. The operation of the group is multiplication, having the usual rules for handling exponents (). Physically, 1/L can be interpreted as reciprocal length, and 1/T as reciprocal time (see reciprocal second).
An abelian group is equivalent to a module over the integers, with the dimensional symbol corresponding to the tuple . When physical measured quantities (be they like-dimensioned or unlike-dimensioned) are multiplied or divided by one other, their dimensional units are likewise multiplied or divided; this corresponds to addition or subtraction in the module. When measurable quantities are raised to an integer power, the same is done to the dimensional symbols attached to those quantities; this corresponds to scalar multiplication in the module.
A basis for such a module of dimensional symbols is called a set of base quantities, and all other vectors are called derived units. As in any module, one may choose different bases, which yields different systems of units (e.g., choosing whether the unit for charge is derived from the unit for current, or vice versa).
The group identity, the dimension of dimensionless quantities, corresponds to the origin in this module, .
In certain cases, one can define fractional dimensions, specifically by formally defining fractional powers of one-dimensional vector spaces, like . However, it is not possible to take arbitrary fractional powers of units, due to representation-theoretic obstructions.
One can work with vector spaces with given dimensions without needing to use units (corresponding to coordinate systems of the vector spaces). For example, given dimensions and , one has the vector spaces and , and can define as the tensor product. Similarly, the dual space can be interpreted as having "negative" dimensions. This corresponds to the fact that under the natural pairing between a vector space and its dual, the dimensions cancel, leaving a dimensionless scalar.
The set of units of the physical quantities involved in a problem correspond to a set of vectors (or a matrix). The nullity describes some number (e.g., ) of ways in which these vectors can be combined to produce a zero vector. These correspond to producing (from the measurements) a number of dimensionless quantities, . (In fact these ways completely span the null subspace of another different space, of powers of the measurements.) Every possible way of multiplying (and exponentiating) together the measured quantities to produce something with the same unit as some derived quantity can be expressed in the general form
Consequently, every possible commensurate equation for the physics of the system can be rewritten in the form
Knowing this restriction can be a powerful tool for obtaining new insight into the system. | 1 | Applied and Interdisciplinary Chemistry |
Chemical reaction engineering (reaction engineering or reactor engineering) is a specialty in chemical engineering or industrial chemistry dealing with chemical reactors. Frequently the term relates specifically to catalytic reaction systems where either a homogeneous or heterogeneous catalyst is present in the reactor. Sometimes a reactor per se is not present by itself, but rather is integrated into a process, for example in reactive separations vessels, retorts, certain fuel cells, and photocatalytic surfaces. The issue of solvent effects on reaction kinetics is also considered as an integral part. | 1 | Applied and Interdisciplinary Chemistry |
Oxidoreductases are classified as EC 1 in the EC number classification of enzymes. Oxidoreductases can be further classified into 21 subclasses:
* EC 1.1 includes oxidoreductases that act on the CH-OH group of donors (alcohol oxidoreductases such as methanol dehydrogenase)
* EC 1.2 includes oxidoreductases that act on the aldehyde or oxo group of donors
* EC 1.3 includes oxidoreductases that act on the CH-CH group of donors (CH-CH oxidoreductases)
* EC 1.4 includes oxidoreductases that act on the CH-NH group of donors (Amino acid oxidoreductases, Monoamine oxidase)
* EC 1.5 includes oxidoreductases that act on CH-NH group of donors
* EC 1.6 includes oxidoreductases that act on NADH or NADPH
* EC 1.7 includes oxidoreductases that act on other nitrogenous compounds as donors
* EC 1.8 includes oxidoreductases that act on a sulfur group of donors
* EC 1.9 includes oxidoreductases that act on a heme group of donors
* EC 1.10 includes oxidoreductases that act on diphenols and related substances as donors
* EC 1.11 includes oxidoreductases that act on peroxide as an acceptor (peroxidases)
* EC 1.12 includes oxidoreductases that act on hydrogen as donors
* EC 1.13 includes oxidoreductases that act on single donors with incorporation of molecular oxygen (oxygenases)
* EC 1.14 includes oxidoreductases that act on paired donors with incorporation of molecular oxygen
* EC 1.15 includes oxidoreductases that act on superoxide radicals as acceptors
* EC 1.16 includes oxidoreductases that oxidize metal ions
* EC 1.17 includes oxidoreductases that act on CH or CH groups
* EC 1.18 includes oxidoreductases that act on iron-sulfur proteins as donors
* EC 1.19 includes oxidoreductases that act on reduced flavodoxin as a donor
* EC 1.20 includes oxidoreductases that act on phosphorus or arsenic in donors
* EC 1.21 includes oxidoreductases that act on X-H and Y-H to form an X-Y bond | 0 | Theoretical and Fundamental Chemistry |
Since ca. 2000 methanesulfonic acid has become a popular replacement for other acids in numerous industrial and laboratory applications, because it:
* is a strong acid,
* has a low vapor pressure (see boiling points in the "Properties" inset),
* is not an oxidant or explosive, like nitric, sulfuric or perchloric acids.
* is a liquid at room temperature,
* is soluble in many organic solvents,
* forms water-soluble salts with all inorganic cations and with most organic cations,
* does not form complexes with metal ions in water,
* its anion, mesylate, is non-toxic and suitable for pharmaceutical preparations.
The closely related p-toluenesulfonic acid (PTSA) is solid.
Methanesulfonic acid can be used in the generation of borane (BH) by reacting methanesulfonic acid with NaBH in an aprotic solvent such as THF or DMSO, the complex of BH and the solvent is formed. | 0 | Theoretical and Fundamental Chemistry |
Direct thrombin inhibitors (DTIs) are a class of anticoagulant drugs that can be used to prevent and treat embolisms and blood clots caused by various diseases. They inhibit thrombin, a serine protease which affects the coagulation cascade in many ways. DTIs have undergone rapid development since the 90's. With technological advances in genetic engineering the production of recombinant hirudin was made possible which opened the door to this new group of drugs. Before the use of DTIs the therapy and prophylaxis for anticoagulation had stayed the same for over 50 years with the use of heparin derivatives and warfarin which have some well known disadvantages. DTIs are still under development, but the research focus has shifted towards factor Xa inhibitors, or even dual thrombin and fXa inhibitors that have a broader mechanism of action by both inhibiting factor IIa (thrombin) and Xa. A recent review of patents and literature on thrombin inhibitors has demonstrated that the development of allosteric and multi-mechanism inhibitors might lead the way to a safer anticoagulant. | 1 | Applied and Interdisciplinary Chemistry |
A compound with a desired size of effects in an HTS is called a hit. The process of selecting hits is called hit selection. The analytic methods for hit selection in screens without replicates (usually in primary screens) differ from those with replicates (usually in confirmatory screens). For example, the z-score method is suitable for screens without replicates whereas the t-statistic is suitable for screens with replicates. The calculation of SSMD for screens without replicates also differs from that for screens with replicates
For hit selection in primary screens without replicates, the easily interpretable ones are average fold change, mean difference, percent inhibition, and percent activity. However, they do not capture data variability effectively. The z-score method or SSMD, which can capture data variability based on an assumption that every compound has the same variability as a negative reference in the screens.
However, outliers are common in HTS experiments, and methods such as z-score are sensitive to outliers and can be problematic. As a consequence, robust methods such as the z*-score method, SSMD*, B-score method, and quantile-based method have been proposed and adopted for hit selection.
In a screen with replicates, we can directly estimate variability for each compound; as a consequence, we should use SSMD or t-statistic that does not rely on the strong assumption that the z-score and z*-score rely on. One issue with the use of t-statistic and associated p-values is that they are affected by both sample size and effect size.
They come from testing for no mean difference, and thus are not designed to measure the size of compound effects. For hit selection, the major interest is the size of effect in a tested compound. SSMD directly assesses the size of effects.
SSMD has also been shown to be better than other commonly used effect sizes.
The population value of SSMD is comparable across experiments and, thus, we can use the same cutoff for the population value of SSMD to measure the size of compound effects | 1 | Applied and Interdisciplinary Chemistry |
In an conventional CCC experiment the biphasic solvent system is pre-equilibrated before the instrument is filled with the stationary phase and equilibrated with the mobile phase. An ion-exchange mode has been created by modifying both of the phases after pre-equilibration. Generally, an ionic displacer (or eluter) is added to mobile phase and an ionic retainer is added to the stationary phase. For example, the aqueous mobile phase may contain NaI as a displacer and the organic stationary phase may be modified with the quaternary ammonium salt called Aliquat 336 as a retainer. The mode known a pH-zone-refining is a type of ion-exchange mode that utilizes acids and/or bases as solvent modifiers. Typically, the analytes are eluted in an order determined by their pKa values. For example, 6 oxindole alkaloids were isolated from a 4.5g sample of Gelsemium elegans stem extract with a biphasic solvent system composed of hexane–ethyl acetate–methanol–water (3:7:1:9, v/v) where 10 mM triethylamine (TEA) was added to the upper organic stationary phase as a retainer and 10 mM hydrochloric acid (HCl) to the aqueous mobile phase as an eluter. Ion-exchange modes such as pH-zone-refining have tremendous potential because high sample loads can be achieved without sacrificing separation power. It works best with ionizable compounds such as nitrogen containing alkaloids or carboxylic acid containing fatty acids. | 0 | Theoretical and Fundamental Chemistry |
Phenylboronic acid or benzeneboronic acid, abbreviated as PhB(OH) where Ph is the phenyl group CH-, is a boronic acid containing a phenyl substituent and two hydroxyl groups attached to boron. Phenylboronic acid is a white powder and is commonly used in organic synthesis. Boronic acids are mild Lewis acids which are generally stable and easy to handle, making them important to organic synthesis. | 0 | Theoretical and Fundamental Chemistry |
The frames are split into a large number of interrogation areas, or windows. It is then possible to calculate a displacement vector for each window with help of signal processing and autocorrelation or cross-correlation techniques. This is converted to a velocity using the time between laser shots and the physical size of each pixel on the camera. The size of the interrogation window should be chosen to have at least 6 particles per window on average. A visual example of PIV analysis can be seen [http://demo.interactiveflows.com/analyze/ here.]
The synchronizer controls the timing between image exposures and also permits image pairs to be acquired at various times along the flow. For accurate PIV analysis, it is ideal that the region of the flow that is of interest should display an average particle displacement of about 8 pixels. This is a compromise between a longer time spacing which would allow the particles to travel further between frames, making it harder to identify which interrogation window traveled to which point, and a shorter time spacing, which could make it overly difficult to identify any displacement within the flow.
The scattered light from each particle should be in the region of 2 to 4 pixels across on the image. If too large an area is recorded, particle image size drops and peak locking might occur with loss of sub pixel precision. There are methods to overcome the peak locking effect, but they require some additional work.
If there is in house PIV expertise and time to develop a system, even though it is not trivial, it is possible to build a custom PIV system. Research grade PIV systems do, however, have high power lasers and high end camera specifications for being able to take measurements with the broadest spectrum of experiments required in research.
An example of PIV analysis without installation: [https://mybinder.org/v2/gh/openpiv/openpiv-python-example/master?filepath=index.ipynb]
PIV is closely related to digital image correlation, an optical displacement measurement technique that uses correlation techniques to study the deformation of solid materials. | 1 | Applied and Interdisciplinary Chemistry |
Venton joined the Department of Chemistry at University of Virginia as an assistant professor in 2005, received tenure and was promoted to an associate professor in 2011, and was promoted to full professor in 2016. Venton develops analytical tools such as carbon-fiber microelectrodes for sensing molecules in the brain to achieve real-time monitoring of neurotransmitters to help understand the brain functions both under normal physiological conditions and in neurological disorders. | 0 | Theoretical and Fundamental Chemistry |
Gerhart Jander (26 October 1892 – 8 December 1961) was a German inorganic chemist. His book, now normally only called "Jander-Blasius", on analytical chemistry is still used in German universities. His involvement in the chemical weapon research and close relation to the NSDAP have been uncovered by recent research. | 0 | Theoretical and Fundamental Chemistry |
In 1935, Perey read a paper by American scientists claiming to have discovered a type of radiation called beta particles being emitted by actinium and was skeptical because the reported energy of the beta particles didnt seem to match actinium. She decided to investigate for herself, theorizing that actinium was decaying into another element (a daughter atom) and that the observed beta particles were actually coming from that daughter atom. She confirmed this by isolating extremely pure actinium and studying its radiation very quickly; she detected a small amount of alpha radiation, a type of radiation that involves the loss of protons and therefore changes an atoms identity. Loss of an alpha particle (consisting of 2 protons and 2 neutrons) would turn actinium (element 89, with 89 protons) into the theorized but never-before-seen element 87.
Perey announced the discovery of the never-before-seen element 87 as a note in the Comptes Rendus presented at the Académie des Sciences by Jean Baptiste Perrin on 9 January 1939 with the title "On an element 87, derived from actinium." Pereys discovery was announced by Perrin, not Perey herself, because she was only a laboratory assistant with no university degree. Perey named the element francium, after her home country, and it joined the other alkali metals in Group 1 of the periodic table of elements. Francium is the second rarest element (after astatine) - only about 550g exists in the entire Earths crust - and it was the last element to be discovered in nature. (Five elements that were discovered synthetically were later found to exist in nature: technetium, promethium, astatine, neptunium, and plutonium.) | 1 | Applied and Interdisciplinary Chemistry |
A system in a state Y is said to be adiabatically accessible from a state X if X can be transformed into Y without the system suffering transfer of energy as heat or transfer of matter. X may, however, be transformed to Y by doing work on X. For example, a system consisting of one kilogram of warm water is adiabatically accessible from a system consisting of one kilogram of cool water, since the cool water may be mechanically stirred to warm it. However, the cool water is not adiabatically accessible from the warm water, since no amount or type of work may be done to cool it. | 0 | Theoretical and Fundamental Chemistry |
Orobol can be found in Streptomyces neyagawaensis (an Actinobacterium). Phenolic compounds can be found in the cyanobacterium Arthrospira maxima, used in the dietary supplement, Spirulina. The three cyanobacteria Microcystis aeruginosa, Cylindrospermopsis raciborskii and Oscillatoria sp. are the subject of research into the natural production of butylated hydroxytoluene (BHT), an antioxidant, food additive and industrial chemical.
The proteobacterium Pseudomonas fluorescens produces phloroglucinol, phloroglucinol carboxylic acid and diacetylphloroglucinol. Another example of phenolics produced in proteobacteria is 3,5-dihydroxy-4-isopropyl-trans-stilbene, a bacterial stilbenoid produced in Photorhabdus bacterial symbionts of Heterorhabditis nematodes. | 0 | Theoretical and Fundamental Chemistry |
In 2010, more than 25 years after the initial work of Peregrine, researchers took advantage of the analogy that can be drawn between hydrodynamics and optics in order to generate Peregrine solitons in optical fibers. In fact, the evolution of light in fiber optics and the evolution of surface waves in deep water are both modelled by the nonlinear Schrödinger equation (note however that spatial and temporal variables have to be switched). Such an analogy has been exploited in the past in order to generate optical solitons in optical fibers.
More precisely, the nonlinear Schrödinger equation can be written in the context of optical fibers under the following dimensional form :
with being the second order dispersion (supposed to be anomalous, i.e. ) and being the nonlinear Kerr coefficient. and are the propagation distance and the temporal coordinate respectively.
In this context, the Peregrine soliton has the following dimensional expression:
is a nonlinear length defined as with being the power of the continuous background. is a duration defined as .
By using exclusively standard optical communication components, it has been shown that even with an approximate initial condition (in the case of this work, an initial sinusoidal beating), a profile very close to the ideal Peregrine soliton can be generated. However, the non-ideal input condition lead to substructures that appear after the point of maximum compression. Those substructures have also a profile close to a Peregrine soliton, which can be analytically explained using a Darboux transformation.
The typical triangular spectral shape has also been experimentally confirmed. | 1 | Applied and Interdisciplinary Chemistry |
The water vapor, carbon dioxide and other products can be separated via gas chromatography and analysed via a thermal conductivity detector. | 0 | Theoretical and Fundamental Chemistry |
For gas flow in small characteristic dimensions (e.g., very fine sand, nanoporous structures etc.), the particle-wall interactions become more frequent, giving rise to additional wall friction (Knudsen friction). For a flow in this region, where both viscous and Knudsen friction are present, a new formulation needs to be used. Knudsen presented a semi-empirical model for flow in transition regime based on his experiments on small capillaries. For a porous medium, the Knudsen equation can be given as
where is the molar flux, is the gas constant, is the temperature, is the effective Knudsen diffusivity of the porous media. The model can also be derived from the first-principle-based binary friction model (BFM). The differential equation of transition flow in porous media based on BFM is given as
This equation is valid for capillaries as well as porous media. The terminology of the Knudsen effect and Knudsen diffusivity is more common in mechanical and chemical engineering. In geological and petrochemical engineering, this effect is known as the Klinkenberg effect. Using the definition of molar flux, the above equation can be rewritten as
This equation can be rearranged into the following equation
Comparing this equation with conventional Darcy's law, a new formulation can be given as
where
This is equivalent to the effective permeability formulation proposed by Klinkenberg:
where is known as the Klinkenberg parameter, which depends on the gas and the porous medium structure. This is quite evident if we compare the above formulations. The Klinkenberg parameter is dependent on permeability, Knudsen diffusivity and viscosity (i.e., both gas and porous medium properties). | 1 | Applied and Interdisciplinary Chemistry |
Employment of scavenger resins has become increasingly popular in solution-phase combinatorial chemistry. Used primarily in the synthesis of medicinal drugs, solution-phase combinatorial chemistry allows for the creation of large libraries of structurally related compounds. When purifying a solution, many approaches can be taken. In general chemical synthesis laboratories, a number of traditional techniques for purification are used as opposed to the employment of scavenger resins. Whether or not scavenger resins are used often depends on the quantity of product desired, how much time you have to produce the wanted product, and the use of the product. Some of the advantages and disadvantages to using scavenger resins as a means for purification are described later. Traditional methods of purification of these compounds becomes time consuming and does not always produce entirely pure products. The ability to specialize a scavenger resin allows for significantly reduce purification times and more pure products. Furthermore, the use of scavenger resins creates a situation where the product can remain in solution and the reaction can be monitored. Conversely, many scavenger resins must be used in large amounts to purify a given product, presenting physical purification issues. Furthermore, when discussing the use of scavenger resins it is important to think about the different types of solid support "beads" that will hold the selected functional group. These polymer beads can be describe most often in two ways, lightly crosslinked and highly crosslinked. The different solid supports are chosen at the preference of the chemist. | 0 | Theoretical and Fundamental Chemistry |
Drug use among elderly Americans has been studied; in a group of 2377 people with an average age of 71 surveyed between 2005 and 2006, 84% took at least one prescription drug, 44% took at least one over-the-counter (OTC) drug, and 52% took at least one dietary supplement; in a group of 2245 elderly Americans (average age of 71) surveyed over the period 2010 – 2011, those percentages were 88%, 38%, and 64%. | 1 | Applied and Interdisciplinary Chemistry |
Early studies suggested a minimum of two RNAPs: one which synthesized rRNA in the nucleolus, and one which synthesized other RNA in the nucleoplasm, part of the nucleus but outside the nucleolus. In 1969, biochemists Robert G. Roeder and William Rutter discovered there are total three distinct nuclear RNA polymerases, an additional RNAP that was responsible for transcription of some kind of RNA in the nucleoplasm. The finding was obtained by the use of ion-exchange chromatography via DEAE coated Sephadex beads. The technique separated the enzymes by the order of the corresponding elutions, Ι,ΙΙ,ΙΙΙ, by increasing the concentration of ammonium sulfate. The enzymes were named according to the order of the elutions, RNAP I, RNAP II, RNAP IΙI. This discovery demonstrated that there was an additional enzyme present in the nucleoplasm, which allowed for the differentiation between RNAP II and RNAP III.
RNA polymerase II (RNAP2) undergoes regulated transcriptional pausing during early elongation. Various studies has shown that disruption of transcription elongation is implicated in cancer, neurodegeneration, HIV latency etc. | 1 | Applied and Interdisciplinary Chemistry |
Water gas shift is the most widespread industrial process for the production of dihydrogen, H. It involves the reaction of carbon monoxide and water (syngas) to form hydrogen and carbon dioxide as a byproduct. In many catalytic reaction schemes, one of the elementary reactions is the oxidation of CO with an adsorbed oxygen species. Gold catalysts have been proposed as an alternative for water gas shift at low temperatures, viz. O catalyst has been proven highly active and stable for low-temperature water gas shift. Titania and ceria have also been used as supports for effective catalysts. Unfortunately, Au/CeO is prone to deactivation caused by surface-bound carbonate or formate species.
Although gold catalysts are active at room temperature to CO oxidation, the high amounts of water involved in water gas shift require higher temperatures. At such temperatures, gold is fully reduced to its metallic form. However, the activity of e.g. Au/CeO has been enhanced by CN treatment, whereby metallic gold is leached, leaving behind highly active cations. According to DFT calculations, the presence of such Au cations on the catalyst is allowed by empty, localized nonbonding f states in CeO. On the other hand, STEM studies of Au/CeO have revealed nanoparticles of 3 nm in diameter. Water gas shift has been proposed to occur at the interface of Au nanoparticles and the reduced CeO support. | 0 | Theoretical and Fundamental Chemistry |
In crystallography, the orientations of crystal axes and faces in three-dimensional space are a central geometric concern, for example in the interpretation of X-ray and electron diffraction patterns. These orientations can be visualized as in the section Visualization of lines and planes above. That is, crystal axes and poles to crystal planes are intersected with the northern hemisphere and then plotted using stereographic projection. A plot of poles is called a pole figure.
In electron diffraction, Kikuchi line pairs appear as bands decorating the intersection between lattice plane traces and the Ewald sphere thus providing experimental access to a crystal's stereographic projection. Model Kikuchi maps in reciprocal space, and fringe visibility maps for use with bend contours in direct space, thus act as road maps for exploring orientation space with crystals in the transmission electron microscope. | 0 | Theoretical and Fundamental Chemistry |
Marshes, intertidal ecosystems dominated by herbaceous vegetation, can be found globally on coastlines from the arctic to the subtropics. In the tropics, marshes are replaced by mangroves as the dominant coastal vegetation.
Marshes have high productivity, with a large portion of primary production in belowground biomass. This belowground biomass can form deposits up to 8m deep. Marshes provide valuable habitat for plants, birds, and juvenile fish, protect coastal habitat from storm surge and flooding, and can reduce nutrient loading to coastal waters. Similarly to mangrove and seagrass habitats, marshes also serve as important carbon sinks. Marshes sequester C in underground biomass due to high rates of organic sedimentation and anaerobic-dominated decomposition. Salt marshes cover approximately 22,000 to 400,000 km globally, with an estimated carbon burial rate of 210 g C m yr.
Salt marshes may not be expansive worldwide in relation to forests, but they have a C burial rate that is over 50 times faster than tropical rainforests. Rates of burial have been estimated at up to 87.2 ± 9.6 Tg C yr which is greater than that of tropical rainforests, 53 ± 9.6 Tg C yr. Since the 1800s salt marshes have been disturbed due to development and a lack of understanding of their importance. The 25% decline since that time has led to a decrease in potential C sink area coupled with the release of once buried C. Consequences of increasingly degraded marsh habitat are a decrease in C stock in sediments, a decrease in plant biomass and thus a decrease in photosynthesis reducing the amount of CO taken up by the plants, failure of C in plant blades to be transferred into the sediment, possible acceleration of erosive processes due to the lack of plant biomass, and acceleration of buried C release to the atmosphere.
Tidal marshes have been impacted by humans for centuries, including modification for grazing, haymaking, reclamation for agriculture, development and ports, evaporation ponds for salt production, modification for aquaculture, insect control, tidal power and flood protection. Marshes are also susceptible to pollution from oil, industrial chemicals, and most commonly, eutrophication. Introduced species, sea-level rise, river damming and decreased sedimentation are additional longterm changes that affect marsh habitat, and in turn, may affect carbon sequestration potential. | 0 | Theoretical and Fundamental Chemistry |
At small (but still positive) values of and , the pulsation decays slowly, and this decay can be described analytically. In the first approximation, the parameters and give additive contributions to the decay; the decay rate, as well as the amplitude and phase of the nonlinear oscillation, can be approximated with elementary functions in a manner similar to the period above. In describing the behavior of the idealized Toda oscillator, the error of such approximations is smaller than the differences between the ideal and its experimental realization as a self-pulsing laser at the optical bench. However, a self-pulsing laser shows qualitatively very similar behavior. | 0 | Theoretical and Fundamental Chemistry |
In 1953, Alfred Day Hershey reported that soon after infection with phage, bacteria produced a form of RNA at a high level and this RNA was also broken down rapidly. However, the first clear indication of mRNA was from the work of Elliot Volkin and Lazarus Astrachan in 1956 by infecting E.coli with T2 bacteriophages and putting them into the medium with P. They found out that the protein synthesis of E.coli was stopped and phage proteins were synthesized. Then, in May 1961, their collaborated researchers Sydney Brenner, François Jacob, and Jim Watson announced the isolation of mRNA. For a few decades after mRNA discovery, people focused on understanding the structural, functional, and metabolism pathway aspects of mRNAs. However, in 1990, Jon A. Wolff demonstrated the idea of nucleic acid-encoded drugs by direct injecting in vitro transcribed (IVT) mRNA or plasmid DNA (pDNA) into the skeletal muscle of mice which expressed the encoded protein in the injected muscle.
Once IVT mRNA has reached the cytoplasm, the mRNA is translated instantly. Thus, it does not need to enter the nucleus to be functional. Also, it does not integrate into the genome and therefore does not have the risk of insertional mutagenesis. Moreover, IVT mRNA is only transiently active and is completely degraded via physiological metabolic pathways. Due to these reasons, IVT mRNA has undergone extensive preclinical investigation. | 1 | Applied and Interdisciplinary Chemistry |
Chromosome jumping libraries help address the complication of standard cloning techniques with large molecular distances. This process allowed the possibility to use the chromosome jumping library for other genetic disorders that requires 100 kilobases jumps. Particularly for genetic disorders such as cystic fibrosis, its gene is located in human chromosome 7, was able to utilize the chromosome jumping library to search for a jumping clone, met oncogene. Identification of the cystic fibrosis was complicated due to it existing in eukaryotic genes that is composed with coding (exons) and non-coding (introns) segments, where introns are small in size making them difficult for detection. Another struggle in recognizing cystic fibrosis gene is because mammalian cells contains variety of repetitive DNA that can lead to incorrect cloning and blockage of DNA Replication and can cause instability. Both these complications, traditional cloning techniques are unable to process because large yield of exons would have to be visible to produce a signal for the cystic fibrosis gene to be identified and DNA would have to be free of any repetitive elements. | 1 | Applied and Interdisciplinary Chemistry |
In June 2002, West Australian resident Rob Hall was convicted for using a canister of pepper spray to break up an altercation between two guests at his home in Midland. He was sentenced to a good behavior bond and granted a spent conviction order, which he appealed to the Supreme Court. Justice Christine Wheeler ruled in his favor, thereby legalizing pepper spray in the state on a case-by-case basis for those who are able to show a reasonable excuse.
On 14 March 2012, a person dressed entirely in black entered the public gallery of the New South Wales Legislative Council and launched a paper plane into the air in the form of a petition to Police Minister Mike Gallacher calling on the government to allow civilians to carry capsicum spray. | 1 | Applied and Interdisciplinary Chemistry |
Proponents of this approach argue that it is possible to sequence the whole genome at once using large arrays of sequencers, which makes the whole process much more efficient than more traditional approaches. Detractors argue that although the technique quickly sequences large regions of DNA, its ability to correctly link these regions is suspect, particularly for eukaryotic genomes with repeating regions. As sequence assembly programs become more sophisticated and computing power becomes cheaper, it may be possible to overcome this limitation. | 1 | Applied and Interdisciplinary Chemistry |
An advanced thermal recycling system (or an ATR system) is an advancement of existing energy-from-waste (EfW) technology. An ATR system transforms municipal solid waste (MSW) into electricity or steam for district heating or industrial customers. The combustion bottom ash and the combustion fly ash, along with the air pollution control system fly ash, are treated to produce products that can be beneficially reused. Specifically, ATR systems consist of the following:
* Solid waste combustion, boiler and combustion control system, energy recovery and air pollution control equipment;
* Combustion bottom ash and fly ash treatment systems that produce commercially reusable products; and
* An optional pre-processing system to recover recyclable materials contained in the MSW delivered to the facility before the MSW enters the thermal processing area of the facility. | 1 | Applied and Interdisciplinary Chemistry |
The concept of pharmacodynamics has been expanded to include Multicellular Pharmacodynamics (MCPD). MCPD is the study of the static and dynamic properties and relationships between a set of drugs and a dynamic and diverse multicellular four-dimensional organization. It is the study of the workings of a drug on a minimal multicellular system (mMCS), both in vivo and in silico. Networked Multicellular Pharmacodynamics (Net-MCPD) further extends the concept of MCPD to model regulatory genomic networks together with signal transduction pathways, as part of a complex of interacting components in the cell. | 1 | Applied and Interdisciplinary Chemistry |
Winter sea ice is a significant atmospheric contribution of bromine. Organic bromine gases such as CHBr, CHBr, CHIBr are emitted by microorganisms in sea ice and snow at ten-fold higher rates than from other environments. In polar areas, decreasing sea ice releases bromine and at the Arctic and Antarctic boundary layer, bromine is released in the spring when the ice melts.
Inorganic bromine is found in the atmosphere and is quickly cycled between its gas and its particulate phase. Bromine gas (Br) undergoes an autocatalytic cycle known as the bromine explosion, which occurs in the ocean and salt lakes such as the Dead Sea, where a high quantity of salts are exposed to the atmosphere. Bromine contributes to 5-15% of tropospheric ozone layer losses. | 0 | Theoretical and Fundamental Chemistry |
Some volcanic eruptions are explosive because of the mixing between water and magma reaching the surface, which releases energy suddenly. However, in some cases, the eruption is caused by volatiles dissolved in the magma itself. Approaching the surface, pressure decreases and the volatiles come out of solution, creating bubbles that circulate in the liquid. The bubbles become connected together, forming a network. This promotes the fragmentation into small drops or spray or coagulate clots in gas.
Generally, 95-99% of magma is liquid rock. However, the small percentage of gas present represents a very large volume when it expands on reaching atmospheric pressure. Gas is thus important in a volcano system because it generates explosive eruptions. Magma in the mantle and lower crust has a high volatile content. Water and carbon dioxide are not the only volatiles that volcanoes release; other volatiles include hydrogen sulfide and sulfur dioxide. Sulfur dioxide is common in basaltic and rhyolite rocks. Volcanoes also release a large amount of hydrogen chloride and hydrogen fluoride as volatiles. | 0 | Theoretical and Fundamental Chemistry |
A Globar is used as a thermal light source for infrared spectroscopy. The preferred material for making Globar is silicon carbide that is shaped as rods or arches of various sizes. When inserted into a circuit that provides it with electric current, it emits radiation from ~ 2 to 50 micrometres wavelength via the Joule heating phenomenon. Globars are used as infrared sources for spectroscopy because their spectral behavior corresponds approximately to that of a Planck radiator (i.e. a black body). Alternative infrared sources are Nernst lamps, coils of chrome–nickel alloy or high-pressure mercury lamps.
The technical term Globar is an English portmanteau word consisting of glow and bar. The term glowbar is sometimes used synonymously in English (which is an incorrect spelling in the strict sense).
The American Resistor Company in Milwaukee, Wisconsin, had word and lettering Globar registered as a trademark (in a special decorative script font) with the United States Patent and Trademark Office on June 30, 1925 (registration number 0200201) and on October 18, 1927 (registration number 0234147). This registration had been renewed for the third time in 1987 (by various companies throughout 60 years). | 0 | Theoretical and Fundamental Chemistry |
Perovskite structures are adopted by many oxides that have the chemical formula ABO. The idealized form is a cubic structure (space group Pmm, no. 221) which is rarely encountered. The orthorhombic (e.g. space group Pnma, no. 62, or Amm2, no. 68) and tetragonal (e.g. space group I4/mcm, no. 140, or P4mm, no. 99) phases are the most common non-cubic variants. Although the perovskite structure is named after CaTiO, this mineral forms a non-idealized form. SrTiO and CaRbF are examples of cubic perovskites. Barium titanate is an example of a perovskite which can take on the rhombohedral (space group R3m, no. 160), orthorhombic, tetragonal and cubic forms depending on temperature.
In the idealized cubic unit cell of such a compound, the type A atom sits at cube corner position (0, 0, 0), the type B atom sits at the body-center position (1/2, 1/2, 1/2) and oxygen atoms sit at face centered positions (1/2, 1/2, 0), (1/2, 0, 1/2) and (0, 1/2, 1/2). The diagram to the right shows edges for an equivalent unit cell with A in the cube corner position, B at the body center, and O at face-centered positions.
Four general categories of cation-pairing are possible: ABX, or 1:2 perovskites; ABX, or 2:4 perovskites; ABX, or 3:3 perovskites; and ABX, or 1:5 perovskites.
The relative ion size requirements for stability of the cubic structure are quite stringent, so slight buckling and distortion can produce several lower-symmetry distorted versions, in which the coordination numbers of A cations, B cations or both are reduced. Tilting of the BO octahedra reduces the coordination of an undersized A cation from 12 to as low as 8. Conversely, off-centering of an undersized B cation within its octahedron allows it to attain a stable bonding pattern. The resulting electric dipole is responsible for the property of ferroelectricity and shown by perovskites such as BaTiO that distort in this fashion.
Complex perovskite structures contain two different B-site cations. This results in the possibility of ordered and disordered variants. | 0 | Theoretical and Fundamental Chemistry |
*[http://nptel.ac.in/courses/105104102/solids%202.htm National Programme on Technology Enhanced Learning]
*[http://www.ebsbiowizard.com/2011/01/total-suspended-solids-tss-volatile-suspended-solids-vss-2/ Environmental Business Specialists] | 0 | Theoretical and Fundamental Chemistry |
The microarray—the dense, two-dimensional grid of biosensors—is the critical component of a biochip platform. Typically, the sensors are deposited on a flat substrate, which may either be passive (e.g. silicon or glass) or active, the latter
consisting of integrated electronics or micromechanical devices that perform or assist signal transduction. Surface chemistry is used to covalently bind the sensor molecules to the substrate medium. The fabrication of microarrays is non-trivial and is a major economic and technological hurdle that may ultimately decide the success of future biochip platforms. The primary manufacturing challenge is the process of placing each sensor at a specific position (typically on a Cartesian grid) on the substrate. Various means exist to achieve the placement, but typically robotic micro-pipetting or micro-printing systems are used to place tiny spots of sensor material on the chip surface. Because each sensor is unique, only a few spots can be placed at a time. The low-throughput nature of this
process results in high manufacturing costs.
Fodor and colleagues developed a unique fabrication process (later used by Affymetrix) in which a series of microlithography steps is used to combinatorially synthesize hundreds of thousands of unique, single-stranded DNA sensors on a substrate one nucleotide at a time. One lithography step is needed per base type; thus, a total of four steps is required per nucleotide level. Although this technique is very powerful in that many sensors can be created simultaneously, it is currently only feasible for creating short DNA strands (15–25 nucleotides). Reliability and cost factors limit the number of photolithography steps that can be done. Furthermore, light-directed combinatorial synthesis techniques are not currently possible for proteins or other sensing molecules.
As noted above, most microarrays consist of a Cartesian grid of sensors. This approach is used chiefly to map or "encode" the coordinate of each sensor to its function. Sensors in these arrays typically use a universal signalling technique (e.g. fluorescence), thus making coordinates their only identifying feature. These arrays must be made using a serial process (i.e. requiring multiple, sequential steps) to ensure that each sensor is placed at the correct position.
"Random" fabrication, in which the sensors are placed at arbitrary positions on the chip, is an alternative to the serial method. The tedious and expensive positioning process is
not required, enabling the use of parallelized self-assembly techniques. In this approach, large batches of identical sensors can be produced; sensors from each batch are then combined and assembled into an array. A non-coordinate based encoding scheme must be used to identify each sensor. As the figure shows, such a design was first demonstrated (and later commercialized by Illumina) using functionalized beads placed randomly in the wells of an etched fiber optic cable. Each bead was uniquely encoded with a fluorescent signature. However, this encoding scheme is limited in the number of unique dye combinations that can be used and successfully differentiated. | 1 | Applied and Interdisciplinary Chemistry |
Dibasic ester or DBE is an ester of a dicarboxylic acid. Depending on the application, the alcohol may be methanol or higher molecular weight monoalcohols.
Mixtures of different methyl dibasic esters are commercially produced from short-chain acids such as adipic acid, glutaric acid, and succinic acid. They are non-flammable, readily biodegradable, non-corrosive, and have a mild, fruity odour.
Dibasic esters of phthalates, adipates, and azelates with C8 - C10 alcohols have found commercial use as lubricants, spin finishes, and additives. | 0 | Theoretical and Fundamental Chemistry |
Mukaiyama became an assistant professor at the Tokyo Institute of Technology in 1958 and earned his full professorship in 1963. During this time, his main focus was on organophosphorus chemistry. While examining deoxygenation reactions involving phosphines, Mukaiyama found that the mercury(II) acetate employed as a catalyst would react with phosphorus(III) compounds to produce acetic anhydride. This initial example expanded into the concept of the redox condensation reaction, in which a weak acid and weak base catalyze a condensation by means of a redox reaction – this would become a primary research focus for Mukaiyama for much of his career. In the original reaction, the phosphine served as the reducing agent by accepting oxygen, while the mercury(II) was the oxidation agent that accepted hydrogens, resulting in the condensation of carboxylic acids with the loss of a molecule of water.
This framework was expanded to include the formation of a variety of other functional groups, including esters and amides, but the most significant was the synthesis of phosphoric esters using DEAD and an alcohol in 1967. The same year that paper was published, Mukaiyama's co-author and former student Oyo Mitsunobu attacked the products of the reaction with a carboxylic acid in the presence of triphenylphosphine to yield an ester, creating what is now known as the Mitsunobu reaction. | 0 | Theoretical and Fundamental Chemistry |
In addition to anchoring artificial metal center on a protein, researchers like Frances Arnold also focused on changing the native environment of natural metal cofactor. Due to the protein context in which the metal catalytic center located, ArMs have a large sequence space to evolve to meet different demands on substance specificity and regio- and enantioselectivity. Directed evolution was used to tailor the catalytic capacity and repurpose the enzyme function. Mostly based on native porphyrin-metal cofactor, Arnold's lab has developed many ArMs has unique ArMs to catalyze regioselective and/or enantioselective Carbon-Boron bond formation, carbene insertion, and aminohydroxylation by evolving the sequence context of the corresponding ArMs. | 0 | Theoretical and Fundamental Chemistry |
The South Turkmenistan Complex Archaeological Expedition (STACE), also called the South Turkmenistan Archaeological Inter-disciplinary Expedition of the Academy of Sciences of the Turkmen Soviet Socialist Republic (YuTAKE) was endorsed by the Turkmenistan Academy of Sciences. It was initially organized by the orientalist Mikhail Evgenievich Masson in 1946. The expedition had several excavations or "Brigades", based on sites and periods, and were spread over many years.
The Chalcolithic settlements of southern Turkmenistan, according to Masson, date to the late 5th millennium – early 3rd millennium BC, as assessed by carbon dating and paleomagnetic studies of the findings from the excavations carried out by STACE in the Altyndepe and Tekkendepe. The foothills of the Kopetdag mountains have revealed the earliest village cultures of Central Asia in the areas of Namazga-Tepe (more than 50 ha) and Altyndepe (26 ha), Ulug Depe (20 ha), Kara Depe (15 ha), and Geok-Syur (12 ha). In 1952, Boris Kuftin, established the basic Chalcolithics to Late Bronze Age sequence based on the excavations carried out at Namazga-Tepe (termed Namazga (NMG) I-VI).
However, the Chalcolithic period ended about 2700 BC due to natural factors of ecology, with the Geok-Syur oasis becoming desertified. This resulted in the migration of people to the ancient delta of the Tedzhen River. This also led to the Early Bronze Age Settlements at Khapuz-depe. | 1 | Applied and Interdisciplinary Chemistry |
Is the classical geometry to create a magnetic field with an electric current. Even for a limited number of windings this geometry provides a reasonable homogeneous B field and a good filling factor is possible by winding the coil directly onto a holder containing the sample. Miniaturization to a scale of several hundred micrometers (µm) is not very difficult although the wire diameter (typically 20 to 50 µm) becomes very small and a freestanding coil is a very delicate object.
A reduction to below 100 µm diameter is possible but the machining and handling of such coils will be rather tedious. For this reason other microsystem fabrication technology such as bulk micromachining, LIGA and micro-injection molding should be applied.
For solenoid coils adding more turns to the coil will enhance the B/i ratio and thus both the inductance and the signal response. At the same time the coil resistance will increase linearly, so the improvement in sensitivity will be proportional to the square root of the number of turns (n). At the same time we will have a larger ohmic heating at the center of
the coil and an enhanced danger for arcing, so the optimum is generally found for only a limited number of turns. Besides RF performance, static field distortions due to susceptibility effects are an important factor in the design of microcoil probeheads. | 0 | Theoretical and Fundamental Chemistry |
Diimide is most effective at reducing unpolarized carbon-carbon double or triple bonds. In reactions with other unsaturated systems, disproportionation of diimide to nitrogen gas and hydrazine is a competing process that significantly degrades the reducing agent. Many groups that are ordinarily sensitive to reductive conditions, including peroxides, are not affected by the conditions of diimide reductions.
Diimide will selectively reduce less substituted double bonds under some conditions. Discrimination between terminal and disubstituted double bonds is often low, however.
Allenes are reduced to the more highly substituted alkene in the presence of diimide, although yields are low.
Iodoalkynes represent an exception to the rule that alkenes cannot be obtained from alkynes. After diimide reduction of iodoalkynes, cis-iodoalkenes may be isolated in good yield.
Recently, diimide has been generated catalytically through the oxidation of hydrazine by a flavin-based organocatalyst. This system selectively reduces terminal double bonds.
In general, diimide does not efficiently reduce polarized double bonds; however, a limited number of examples do exist in the literature. Aromatic aldehydes are reduced by diimide generated through the decarboxylation of potassium azodicarboxylate. | 0 | Theoretical and Fundamental Chemistry |
Centromeres are the sites where spindle fibers attach to newly replicated chromosomes in order to segregate them into daughter cells when the cell divides. Each eukaryotic chromosome has a single functional centromere that is seen as a constricted region in a condensed metaphase chromosome. Centromeric DNA consists of a number of repetitive DNA sequences that often take up a significant fraction of the genome because each centromere can be millions of base pairs in length. In humans, for example, the sequences of all 24 centromeres have been determined and they account for about 6% of the genome. However, it is unlikely that all of this noncoding DNA is essential since there is considerable variation in the total amount of centromeric DNA in different individuals. Centromeres are another example of functional noncoding DNA sequences that have been known for almost half a century and it is likely that they are more abundant than coding DNA. | 1 | Applied and Interdisciplinary Chemistry |
There are two basic types of magnetometer measurement. Vector magnetometers measure the vector components of a magnetic field. Total field magnetometers or scalar magnetometers measure the magnitude of the vector magnetic field. Magnetometers used to study the Earths magnetic field may express the vector components of the field in terms of declination (the angle between the horizontal component of the field vector and true, or geographic, north) and the inclination' (the angle between the field vector and the horizontal surface).
Absolute magnetometers measure the absolute magnitude or vector magnetic field, using an internal calibration or known physical constants of the magnetic sensor. Relative magnetometers measure magnitude or vector magnetic field relative to a fixed but uncalibrated baseline. Also called variometers, relative magnetometers are used to measure variations in magnetic field.
Magnetometers may also be classified by their situation or intended use. Stationary magnetometers are installed to a fixed position and measurements are taken while the magnetometer is stationary. Portable or mobile magnetometers are meant to be used while in motion and may be manually carried or transported in a moving vehicle. Laboratory magnetometers are used to measure the magnetic field of materials placed within them and are typically stationary. Survey magnetometers are used to measure magnetic fields in geomagnetic surveys; they may be fixed base stations, as in the INTERMAGNET network, or mobile magnetometers used to scan a geographic region. | 0 | Theoretical and Fundamental Chemistry |
P-NMR spectroscopy is widely used for studies of phospholipid bilayers and biological membranes in native conditions. The analysis of P-NMR spectra of lipids could provide a wide range of information about lipid bilayer packing, phase transitions (gel phase, physiological liquid crystal phase, ripple phases, non bilayer phases), lipid head group orientation/dynamics, and elastic properties of pure lipid bilayer and as a result of binding of proteins and other biomolecules.
In addition, a specific N-H...(O)-P experiment (INEPT transfer using three-bond scalar coupling J~5 Hz) could provide a direct information about formation of hydrogen bonds between amine protons of protein to phosphate of lipid headgroups, which is useful in studies of protein/membrane interactions. | 0 | Theoretical and Fundamental Chemistry |
Eoxin C4, also known as 14,15-leukotriene C4, is an eoxin. Cells make eoxins by metabolizing arachidonic acid with a 15-lipoxygenase enzyme to form 15(S)-hydroperoxyeicosapentaenoic acid (i.e. 15(S)-HpETE). This product is then converted serially to eoxin A4 (i.e. EXA4), EXC4, EXD4, and EXE4 by LTC4 synthase, an unidentified gamma-glutamyltransferase, and an unidentified dipeptidase, respectively, in a pathway which appears similar if not identical to the pathway which forms leukotreines, i.e. LTA4, LTC4, LTD4, and LTE4. This pathway is schematically shown as follows:
EXA is viewed as an intracellular-bound, short-lived intermediate which is rapidly metabolized to the down-stream eoxins. The eoxins down stream of EXA4 are secreted from their parent cells and, it is proposed but not yet proven, serve to regulate allergic responses and the development of certain cancers (see Eoxins). | 1 | Applied and Interdisciplinary Chemistry |
Alkyl groups are electron donating groups. The carbon on that is sp hybridized and less electronegative than those that are sp hybridized. They have overlap on the carbon–hydrogen bonds (or carbon–carbon bonds in compounds like tert-butylbenzene) with the ring p orbital. Hence they are more reactive than benzene and are ortho/para directors. | 0 | Theoretical and Fundamental Chemistry |
In astronomy, the photosphere of a star is defined as the surface where its optical depth is 2/3. This means that each photon emitted at the photosphere suffers an average of less than one scattering before it reaches the observer. At the temperature at optical depth 2/3, the energy emitted by the star (the original derivation is for the Sun) matches the observed total energy emitted.
Note that the optical depth of a given medium will be different for different colors (wavelengths) of light.
For planetary rings, the optical depth is the (negative logarithm of the) proportion of light blocked by the ring when it lies between the source and the observer. This is usually obtained by observation of stellar occultations. | 0 | Theoretical and Fundamental Chemistry |
The overwhelming majority of rare-earth elements, tantalum, and lithium are found within pegmatite. Ore genesis theories for these ores are wide and varied, but most involve metamorphism and igneous activity. Lithium is present as spodumene or lepidolite within pegmatite.
Carbonatite intrusions are an important source of these elements. Ore minerals are essentially part of the unusual mineralogy of carbonatite. | 0 | Theoretical and Fundamental Chemistry |
Suppose that we are studying an isolated, quantum mechanical many-body system. In this context, "isolated" refers to the fact that the system has no (or at least negligible) interactions with the environment external to it. If the Hamiltonian of the system is denoted , then a complete set of basis states for the system is given in terms of the eigenstates of the Hamiltonian,
where is the eigenstate of the Hamiltonian with eigenvalue . We will refer to these states simply as "energy eigenstates." For simplicity, we will assume that the system has no degeneracy in its energy eigenvalues, and that it is finite in extent, so that the energy eigenvalues form a discrete, non-degenerate spectrum (this is not an unreasonable assumption, since any "real" laboratory system will tend to have sufficient disorder and strong enough interactions as to eliminate almost all degeneracy from the system, and of course will be finite in size). This allows us to label the energy eigenstates in order of increasing energy eigenvalue. Additionally, consider some other quantum-mechanical observable , which we wish to make thermal predictions about. The matrix elements of this operator, as expressed in a basis of energy eigenstates, will be denoted by
We now imagine that we prepare our system in an initial state for which the expectation value of is far from its value predicted in a microcanonical ensemble appropriate to the energy scale in question (we assume that our initial state is some superposition of energy eigenstates which are all sufficiently "close" in energy). The eigenstate thermalization hypothesis says that for an arbitrary initial state, the expectation value of will ultimately evolve in time to its value predicted by a microcanonical ensemble, and thereafter will exhibit only small fluctuations around that value, provided that the following two conditions are met:
# The diagonal matrix elements vary smoothly as a function of energy, with the difference between neighboring values, , becoming exponentially small in the system size.
# The off-diagonal matrix elements , with , are much smaller than the diagonal matrix elements, and in particular are themselves exponentially small in the system size.
These conditions can be written as
where and are smooth functions of energy, is the many-body Hilbert space dimension, and is a random variable with zero mean and unit variance. Conversely if a quantum many-body system satisfies the ETH, the matrix representation of any local operator in the energy eigen basis is expected to follow the above ansatz. | 0 | Theoretical and Fundamental Chemistry |
Pesticides may affect health negatively. mimicking hormones causing reproductive problems, and also causing cancer. A 2007 systematic review found that "most studies on non-Hodgkin lymphoma and leukemia showed positive associations with pesticide exposure" and thus concluded that cosmetic use of pesticides should be decreased. There is substantial evidence of associations between organophosphate insecticide exposures and neurobehavioral alterations. Limited evidence also exists for other negative outcomes from pesticide exposure including neurological, birth defects, and fetal death.
The American Academy of Pediatrics recommends limiting exposure of children to pesticides and using safer alternatives:
Pesticides are also found in majority of U.S. households with 88 million out of the 121.1 million households indicating that they use some form of pesticide in 2012. As of 2007, there were more than 1,055 active ingredients registered as pesticides, which yield over 20,000 pesticide products that are marketed in the United States.
Owing to inadequate regulation and safety precautions, 99% of pesticide-related deaths occur in developing countries that account for only 25% of pesticide usage.
One study found pesticide self-poisoning the method of choice in one third of suicides worldwide, and recommended, among other things, more restrictions on the types of pesticides that are most harmful to humans.
A 2014 epidemiological review found associations between autism and exposure to certain pesticides, but noted that the available evidence was insufficient to conclude that the relationship was causal. | 1 | Applied and Interdisciplinary Chemistry |
Nesfatin-1 can cross the blood–brain barrier without saturation.
The receptors within the brain are in the hypothalamus and the solitary nucleus, where nesfatin-1 is believed to be produced via peroxisome proliferator-activated receptors (PPARs). It appears there is a relationship between nesfatin-1 and cannabinoid receptors. Nesfatin-1-induced inhibition of feeding may be mediated through the inhibition of orexigenic NPY neurons.
Nesfatin/NUCB2 expression has been reported to be modulated by starvation and re-feeding in the Paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the brain. Nesfatin-1 influences the excitability of a large proportion of different subpopulations of neurons located in the PVN. It is also reported that magnocellular oxytocin neurons are activated during feeding, and ICV infusion of oxytocin antagonist increases food intake, indicating a possible role of oxytocin in the regulation of feeding behavior. In addition, it is proposed that feeding-activated nesfatin-1 neurons in the PVN and SON could play an important role in the postprandial regulation of feeding behavior and energy homeostasis.
Nesfatin-1 immunopositive neurons are also located in the arcuate nucleus (ARC). Nesfatin-1 immunoreactive neurons in the ARC are activated by simultaneous injection of ghrelin and desacyl ghrelin, nesfatin-1 may be involved in the desacyl ghrelin-induced inhibition of the orexigenic effect of peripherally administered ghrelin in freely fed rat.
Nesfatin-1 was co-expressed with melanin concentrating hormone (MCH) in tuberal hypothalamic neurons. Nesfatin-1 co-expressed in MCH neurons may play a complex role not only in the regulation of food intake, but also in other essential integrative brain functions involving MCH signaling, ranging from autonomic regulation, stress, mood, cognition to sleep. | 1 | Applied and Interdisciplinary Chemistry |
From a 2010 study by the University of Maryland, photosynthesizing cyanobacteria have been shown to be a significant species in the global carbon cycle, accounting for 20–30% of Earth's photosynthetic productivity and convert solar energy into biomass-stored chemical energy at the rate of ~450 TW.
Some pigments such as B-phycoerythrin that are mostly found in red algae and cyanobacteria has much higher light-harvesting efficiency compared to that of other plants. Such organisms are potentially candidates for biomimicry technology to improve solar panels design. | 0 | Theoretical and Fundamental Chemistry |
A droplet with a diameter of 3 mm has a terminal velocity of approximately 8 m/s.
Drops smaller than in diameter will attain 95% of their terminal velocity within . But above this size the distance to get to terminal velocity increases sharply. An example is a drop with a diameter of that may achieve this at . | 1 | Applied and Interdisciplinary Chemistry |
This technique complements X-ray crystallography in that it is frequently applicable to molecules in an amorphous or liquid-crystalline state, whereas crystallography, as the name implies, is performed on molecules in a crystalline phase. In electronically conductive materials, the Knight shift of the resonance frequency can provide information on the mobile charge carriers. Though nuclear magnetic resonance is used to study the structure of solids, extensive atomic-level structural detail is more challenging to obtain in the solid state. Due to broadening by chemical shift anisotropy (CSA) and dipolar couplings to other nuclear spins, without special techniques such as MAS or dipolar decoupling by RF pulses, the observed spectrum is often only a broad Gaussian band for non-quadrupolar spins in a solid.
Professor Raymond Andrew at the University of Nottingham in the UK pioneered the development of high-resolution solid-state nuclear magnetic resonance. He was the first to report the introduction of the MAS (magic angle sample spinning; MASS) technique that allowed him to achieve spectral resolution in solids sufficient to distinguish between chemical groups with either different chemical shifts or distinct Knight shifts. In MASS, the sample is spun at several kilohertz around an axis that makes the so-called magic angle θ (which is ~54.74°, where 3cosθ-1 = 0) with respect to the direction of the static magnetic field B; as a result of such magic angle sample spinning, the broad chemical shift anisotropy bands are averaged to their corresponding average (isotropic) chemical shift values. Correct alignment of the sample rotation axis as close as possible to θ is essential for cancelling out the chemical-shift anisotropy broadening. There are different angles for the sample spinning relative to the applied field for the averaging of electric quadrupole interactions and paramagnetic interactions, correspondingly ~30.6° and ~70.1°. In amorphous materials, residual line broadening remains since each segment is in a slightly different environment, therefore exhibiting a slightly different NMR frequency.
Dipolar and J-couplings to nearby H nuclei are usually removed by radio-frequency pulses applied at the H frequency during signal detection. The concept of cross polarization developed by Sven Hartmann and Erwin Hahn was utilized in transferring magnetization from protons to less sensitive nuclei by M.G. Gibby, Alex Pines and John S. Waugh. Then, Jake Schaefer and Ed Stejskal demonstrated the powerful use of cross polarization under MAS conditions (CP-MAS) and proton decoupling, which is now routinely employed to measure high resolution spectra of low-abundance and low-sensitivity nuclei, such as carbon-13, silicon-29, or nitrogen-15, in solids. Significant further signal enhancement can be achieved by dynamic nuclear polarization from unpaired electrons to the nuclei, usually at temperatures near 110 K. | 0 | Theoretical and Fundamental Chemistry |
Some patients with ovarian hyperstimulation syndrome may have mutations in the gene for FSHR, making them more sensitive to gonadotropin stimulation.
Women with 46 XX gonadal dysgenesis experience primary amenorrhea with hypergonadotropic hypogonadism. There are forms of 46 xx gonadal dysgenesis wherein abnormalities in the FSH-receptor have been reported and are thought to be the cause of the hypogonadism.
Polymorphism may affect FSH receptor populations and lead to poorer responses in infertile women receiving FSH medication for IVF.
Alternative splicing of the FSHR gene may be implicated in subfertility in males | 1 | Applied and Interdisciplinary Chemistry |
It has been uncertain for a long time whether metal carbonyl hydrides contain a direct metal-hydrogen bond, although this has been suspected by Hieber for HFe(CO). The precise structure cannot be identified by X-ray diffraction, particularly the length of a possible metal-hydrogen bond remained uncertain. The exact structure of the metal carbonyl hydrides has been determined by using neutron diffraction and nuclear magnetic resonance spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
Bromochlorofluoromethane or fluorochlorobromomethane, is a chemical compound and trihalomethane derivative with the chemical formula CHBrClF. As one of the simplest possible stable chiral compounds, it is useful for fundamental research into this area of chemistry. However, its relative instability to hydrolysis, and lack of suitable functional groups, made separation of the enantiomers of bromochlorofluoromethane especially challenging, and this was not accomplished until almost a century after it was first synthesised, in March 2005, though it has now been done by a variety of methods. More recent research using bromochlorofluoromethane has focused on its potential use for experimental measurement of parity violation, a major unsolved problem in quantum physics. | 0 | Theoretical and Fundamental Chemistry |
Chimeric small molecule therapeutics are a class of drugs designed with multiple active domains to operate outside of the typical protein inhibition model. While most small molecule drugs inhibit target proteins by binding their active site, chimerics form protein-protein ternary structures to induce degradation or, less frequently, other protein modifications. | 1 | Applied and Interdisciplinary Chemistry |
In electrochemistry, faradaic impedance is the resistance and capacitance acting jointly at the surface of an electrode of an electrochemical cell. The cell may be operating as either a galvanic cell generating an electric current or inversely as an electrolytic cell using an electric current to drive a chemical reaction. In the simplest nontrivial case faradaic impedance is modeled as a single resistor and single capacitor connected in parallel, as opposed say to in series or as a transmission line with multiple resistors and capacitors. | 0 | Theoretical and Fundamental Chemistry |
In the ovary, the LHCG receptor is necessary for follicular maturation and ovulation, as well as luteal function. Its expression requires appropriate hormonal stimulation by FSH and estradiol. The LHCGR is present on granulosa cells, theca cells, luteal cells, and interstitial cells The LCGR is restimulated by increasing levels of chorionic gonadotropins in case a pregnancy is developing. In turn, luteal function is prolonged and the endocrine milieu is supportive of the nascent pregnancy. | 1 | Applied and Interdisciplinary Chemistry |
The fluorescent-dye DNA sequencing is a molecular biology technique that involves labeling single-strand DNA sequences of varied length with 4 fluorescent dyes (corresponding to 4 different bases used in DNA) and subsequently separating the DNA sequences by "slab gel"- or capillary-electrophoresis method (see DNA Sequencing). The electrophoresis run is monitored by a CCD on the DNA sequencer and this produces a time "trace" data (or "chromatogram") of the fluorescent "peaks" that passed the CCD point. Examining the fluorescence peaks in the trace data, we can determine the order of individual bases (nucleobase) in the DNA. Since the intensity, shape and the location of a fluorescence peak are not always consistent or unambiguous, however, sometimes it is difficult or time-consuming to determine (or "call") the correct bases for the peaks accurately if it is done manually.
Automated DNA sequencing techniques have revolutionized the field of molecular biology – generating vast amounts of DNA sequence data. However, the sequence data is produced at a significantly higher rate than can be manually processed (i.e. interpreting the trace data to produce the sequence data), thereby creating a bottleneck. To remove the bottleneck, both automated software that can speed up the processing with improved accuracy and a reliable measure of the accuracy are needed. To meet this need, many software programs have been developed. One such program is Phred. | 1 | Applied and Interdisciplinary Chemistry |
Junk DNA is DNA that has no biologically relevant function such as pseudogenes and fragments of once active transposons. Bacteria and viral genomes have very little junk DNA but some eukaryotic genomes may have a substantial amount of junk DNA. The exact amount of nonfunctional DNA in humans and other species with large genomes has not been determined and there is considerable controversy in the scientific literature.
The nonfunctional DNA in bacterial genomes is mostly located in the intergenic fraction of non-coding DNA but in eukaryotic genomes it may also be found within introns. It is important to note that there are many examples of functional DNA elements in non-coding DNA and that it is erroneous to equate non-coding DNA with junk DNA. | 1 | Applied and Interdisciplinary Chemistry |
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