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Combined sewer systems were common when urban sewerage systems were first developed, in the late 19th and early 20th centuries. | 1 | Applied and Interdisciplinary Chemistry |
Differences in plant disease resistance are often incremental or quantitative rather than qualitative. The term quantitative resistance (QR) refers to plant disease resistance that is controlled by multiple genes and multiple molecular mechanisms that each have small or minor effects on the overall resistance trait. QR is important in plant breeding because the resulting resistance is often more durable (effective for more years), and more likely to be effective against most or all strains of a particular pathogen. QR is typically effective against one pathogen species or a group of closely related species, rather than being broadly effective against multiple pathogens. QR is often obtained through plant breeding without knowledge of the causal genetic loci or molecular mechanisms. QR is likely to depend on many of the plant immune system components discussed in this article, as well as traits that are unique to certain plant-pathogen pairings (such as sensitivity to certain pathogen effectors), as well as general plant traits such as leaf surface characteristics or root system or plant canopy architecture. The term QR is synonymous with minor gene resistance. | 1 | Applied and Interdisciplinary Chemistry |
Another method of ensuring the ecological health of streams while limiting impacts on human infrastructures is to delineate a corridor within which the stream is expected to migrate over time. This method is based on the concept of minimum intervention within this corridor, whose limits should be determined based on the streams hydrology and geomorphology. Although this concept is often restricted to the lateral mobility of streams (related to bank erosion), some systems also integrate the space necessary for floods of various return periods. This concept has been developed and adapted in various countries around the world, resulting in the notion of "stream corridor" or "river corridor" in the U.S., "room for the river" in the Netherlands, "" ("freedom space") in France (where the concept of "erodible corridor" is also used) and Québec (Canada), "" ("space reserved for water(courses)") in Switzerland, "'" in Italy, "fluvial territory" in Spain and "making space for water" in the United Kingdom. A cost-benefit analysis has shown that this approach could be beneficial in the long term due to lower stream stabilization and maintenance costs, lower damages resulting from erosion and flooding, and ecological services rendered by the restored streams. However, this approach cannot be implemented alone if watershed-scale stressors contribute to stream degradation. | 1 | Applied and Interdisciplinary Chemistry |
When the pipe surface is smooth (the "smooth pipe" curve in Figure 2), the friction factor's variation with Re can be modeled by the Kármán–Prandtl resistance equation for turbulent flow in smooth pipes with the parameters suitably adjusted
The numbers 1.930 and 0.537 are phenomenological; these specific values provide a fairly good fit to the data. The product (called the "friction Reynolds number") can be considered, like the Reynolds number, to be a (dimensionless) parameter of the flow: at fixed values of , the friction factor is also fixed.
In the Kármán–Prandtl resistance equation, can be expressed in closed form as an analytic function of through the use of the Lambert function:
In this flow regime, many small vortices are responsible for the transfer of momentum between the bulk of the fluid to the pipe wall. As the friction Reynolds number increases, the profile of the fluid velocity approaches the wall asymptotically, thereby transferring more momentum to the pipe wall, as modeled in Blasius boundary layer theory. | 1 | Applied and Interdisciplinary Chemistry |
Most floral VOCs belong to three main chemical classes. VOCs in the same chemical class are synthesized from a shared precursor, but the biochemical pathway is specific for each VOC and often varies from one plant species to another.
Terpenoids (or isoprenoids) are derived from isoprene and synthesized via the mevalonate pathway or the erythritol phosphate pathway. They represent the majority of floral VOCs and are often the most abundant compounds in floral scent blends.
The second chemical class is composed of the fatty acid derivatives synthesized from acetyl-CoA, most of which are known as green leaf volatiles, because they are also emitted by vegetative parts (i.e.: leaves and stems) of plants, and sometimes higher in abundance than from floral tissue.
The third chemical class is composed of benzenoids/phenylpropanoids, also known as aromatic compounds; they are synthesized from phenylalanine. | 1 | Applied and Interdisciplinary Chemistry |
Several software graphic tools will let you create 2D patterns using wallpaper symmetry groups. Usually you can edit the original tile and its copies in the entire pattern are updated automatically.
* [http://www.madpattern.com/ MadPattern], a free set of Adobe Illustrator templates that support the 17 wallpaper groups
* [http://www.peda.com/tess/ Tess], a shareware tessellation program for multiple platforms, supports all wallpaper, frieze, and rosette groups, as well as Heesch tilings.
*[http://math.hws.edu/eck/js/symmetry/wallpaper.html Wallpaper Symmetry] is a free online JavaScript drawing tool supporting the 17 groups. The [http://math.hws.edu/eck/js/symmetry/symmetry-info.html main page] has an explanation of the wallpaper groups, as well as drawing tools and explanations for the other planar symmetry groups as well.
* [https://en.oiler.education/tales TALES GAME], a free software designed for educational purposes which includes the tessellation function.
* [http://www.scienceu.com/geometry/handson/kali/ Kali] , online graphical symmetry editor Java applet (not supported by default in browsers).
* [http://www.geometrygames.org/Kali/index.html Kali] , free downloadable Kali for Windows and Mac Classic.
* Inkscape, a free vector graphics editor, supports all 17 groups plus arbitrary scales, shifts, rotates, and color changes per row or per column, optionally randomized to a given degree. (See [http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Tiles-Symmetries.html])
* [http://www.artlandia.com/products/SymmetryWorks/ SymmetryWorks] is a commercial plugin for Adobe Illustrator, supports all 17 groups.
* [https://eschersket.ch/ EscherSketch] is a free online JavaScript drawing tool supporting the 17 groups.
* [https://repper.app/ Repper] is a commercial online drawing tool supporting the 17 groups plus a number of non-periodic tilings | 0 | Theoretical and Fundamental Chemistry |
An unstable atomic nucleus with an excess of neutrons may undergo β decay, where a neutron is converted into a proton, an electron, and an electron antineutrino (the antiparticle of the neutrino):
This process is mediated by the weak interaction. The neutron turns into a proton through the emission of a virtual W boson. At the quark level, W emission turns a down quark into an up quark, turning a neutron (one up quark and two down quarks) into a proton (two up quarks and one down quark).
The virtual W boson then decays into an electron and an antineutrino.
β− decay commonly occurs among the neutron-rich fission byproducts produced in nuclear reactors. Free neutrons also decay via this process. Both of these processes contribute to the copious quantities of beta rays and electron antineutrinos produced by fission-reactor fuel rods. | 0 | Theoretical and Fundamental Chemistry |
The Gastrin family is a group of peptides evolutionarily similar in structure and function. Commonly synthesized in antroduodenal G-cells. Regulate gastric function along with gastric acid secretion and mucosal growth.
#Gastrin
#<nowiki/>Cholecystokinin (CCK) | 1 | Applied and Interdisciplinary Chemistry |
Alchemy in the medieval Islamic world refers to both traditional alchemy and early practical chemistry (the early chemical investigation of nature in general) by Muslim scholars in the medieval Islamic world. The word alchemy was derived from the Arabic word كيمياء or kīmiyāʾ and may ultimately derive from the ancient Egyptian word kemi, meaning black.
After the fall of the Western Roman Empire and the Islamic conquest of Roman Egypt, the focus of alchemical development moved to the Caliphate and the Islamic civilization. Much more is known about Islamic alchemy as it was better documented; most of the earlier writings that have come down through the years were preserved as Arabic translations. | 1 | Applied and Interdisciplinary Chemistry |
Chemical compounds that come as mirror-image pairs are referred to by chemists as chiral or handed molecules. Each twin is called an enantiomer. Drugs that exhibit handedness are referred to as chiral drugs. Chiral drugs that are equimolar (1:1) mixture of enantiomers are called racemic drugs and these are obviously devoid of optical rotation. The most commonly encountered stereogenic unit, that confers chirality to drug molecules are stereogenic center. Stereogenic center can be due to the presence of tetrahedral tetra coordinate atoms (C,N,P) and pyramidal tricoordinate atoms (N,S). The word chiral describes the three-dimensional architecture of the molecule and does not reveal the stereochemical composition. Hence "chiral drug" does not say whether the drug is racemic (racemic drug), single enantiomer (chiral specific drug) or some other combination of stereoisomers. To resolve this issue Joseph Gal introduced a new term called unichiral. Unichiral indicates that the stereochemical composition of a chiral drug is homogenous consisting of a single enantiomer.
Many medicinal agents important to life are combinations of mirror-image twins. Despite the close resemblance of such twins, the differences in their biological properties can be profound. In other words, the component enantiomers of a racemic chiral drug may differ wildly in their pharmacokinetic, pharmacodynamic profile. The tragedy of thalidomide illustrates the potential for extreme consequences resulting from the administration of a racemate drug that exhibits multiple effects attributable to individual enantiomers. With the advancements in chiral technology and the increased awareness about three-dimensional consequences of drug action and disposition emerged specialized field "chiral pharmacology". Simultaneously the chirality nomenclature system also evolved. A brief overview of chirality history and terminology/descriptors is given below. A detailed chirality timeline is not the focus of this article. | 0 | Theoretical and Fundamental Chemistry |
Ninhydrin can be used in Kaiser test to monitor deprotection in solid phase peptide synthesis. The chain is linked via its C-terminus to the solid support, with the N-terminus extending off it. When that nitrogen is deprotected, a ninhydrin test yields blue. Amino-acid residues are attached with their N-terminus protected, so if the next residue has been successfully coupled onto the chain, the test gives a colorless or yellow result.
Ninhydrin is also used in qualitative analysis of proteins. Most of the amino acids, except proline, are hydrolyzed and react with ninhydrin. Also, certain amino acid chains are degraded. Therefore, separate analysis is required for identifying such amino acids that either react differently or do not react with ninhydrin at all. The rest of the amino acids are then quantified colorimetrically after separation by chromatography.
A solution suspected of containing the ammonium ion can be tested by ninhydrin by dotting it onto a solid support (such as silica gel); treatment with ninhydrin should result in a dramatic purple color if the solution contains this species. In the analysis of a chemical reaction by thin layer chromatography (TLC), the reagent can also be used (usually 0.2% solution in either n-butanol or in ethanol). It will detect, on the TLC plate, virtually all amines, carbamates and also, after vigorous heating, amides.
Upon reaction with ninhydrin, amino acids undergo decarboxylation. The released CO originates from the carboxyl carbon of the amino acid. This reaction has been used to release the carboxyl carbons of bone collagen from ancient bones for stable isotope analysis in order to help reconstruct the palaeodiet of cave bears. Release of the carboxyl carbon (via ninhydrin) from amino acids recovered from soil that has been treated with a labeled substrate demonstrates assimilation of that substrate into microbial protein. This approach was successfully used to reveal that some ammonium oxidizing bacteria, also called nitrifying bacteria use urea as a carbon source in soil. | 0 | Theoretical and Fundamental Chemistry |
Alcohol inhibits neuronal excitability through acting on gamma-aminobutyric acid (GABA) receptors. Alcohol is often accessible in a number of social situations across many cultures and is frequently connected with uninhibited social activities. Alcohol has been shown in human research to have surprising effects on the human libido.
While some studies indicates that alcohol improves sexual behavior and desire, other research indicates that alcohol impairs sexual function.
The conditions under which the drinking occurs, laboratory research vs self-report studies from users, as well as the amounts of alcohol consumed, may all contribute to these controversial outcomes.
Laboratory studies have demonstrated that while low blood alcohol levels have no effect on or slightly enhance sexual arousal and responsiveness in men, elevated blood alcohol levels result in decreased erectile responsiveness, decreased arousal, and impaired ability to ejaculate. Other laboratory research, on the other hand, found no significant influence of either low or high blood alcohol levels on measures of arousal.
Even with mild alcohol use, women have decreased vaginal flow responses. In apparent contrast, women self-report heightened sexual desire and pleasure when they consume more alcohol and are more likely to engage in sexual activities with someone when intoxicated.
Heavy alcohol intake impairs sexual and reproductive function, erectile, and ejaculatory dysfunction in males, and sexual arousal, interest, and orgasm in women.
Alcohol and sex although alcohol may have varying impacts on sexual performance depending on the amount drank, it generally impairs sexual functioning and contributes to increased sexual risk taking. | 1 | Applied and Interdisciplinary Chemistry |
Claus was known for his negligent attitude towards his health. In particular, he often tasted his chemicals and new compounds and tested the strength of the acids by dipping a finger in them and touching his tongue with it. Once he severely burned his mouth while tasting one of the new ruthenium compounds that he had synthesized. When he isolated osmium tetroxide – a rather toxic chemical – he described its taste as astringent and pepper-like. In April 1845, he was poisoned by osmium tetroxide vapors and had to stop working for two weeks. In 1852, Klaus moved from Kazan back to the University of Tartu and assumed position of professor in pharmacy. He died in Tartu in 1864. | 1 | Applied and Interdisciplinary Chemistry |
Liquid molecules can form a layer around the solid particles and there by enhance the local ordering of the atomic structure at the interface region.hence, the atomic structure of such liquid layer is more ordered than that of the bulk liquid. | 0 | Theoretical and Fundamental Chemistry |
Generally speaking for highly expressed genes, translation elongation rates are faster along transcripts with higher codon adaptation to tRNA pools, and slower along transcripts with rare codons. This correlation between codon translation rates and cognate tRNA concentrations provides additional modulation of translation elongation rates, which can provide several advantages to the organism. Specifically, codon usage can allow for global regulation of these rates, and rare codons may contribute to the accuracy of translation at the expense of speed. | 1 | Applied and Interdisciplinary Chemistry |
Photoactivated adenylyl cyclase (PAC) is a protein consisting of an adenylyl cyclase enzyme domain directly linked to a BLUF (blue light receptor using FAD) type light sensor domain. When illuminated with blue light, the enzyme domain becomes active and converts ATP to cAMP, an important second messenger in many cells. In the unicellular flagellate Euglena gracilis, PACα and PACβ (euPACs) serve as a photoreceptor complex that senses light for photophobic responses and phototaxis. Small but potent PACs were identified in the genome of the bacteria Beggiatoa (bPAC) and Oscillatoria acuminata (OaPAC). While natural bPAC has some enzymatic activity in the absence of light, variants with no dark activity have been engineered (PACmn). | 1 | Applied and Interdisciplinary Chemistry |
Metal porphyrin complexes are almost always prepared by direct reaction of a metal halide with the free porphyrin, abbreviated here as HP:
:MCl + HP → M(P)Cl + 2HCl
Two pyrrole protons are lost. The porphyrin dianion is an LX ligand.
These syntheses require somewhat forcing conditions, consistent with the tight fit of the metal in the N "pocket." In nature, the insertion is mediated by chelatase enzymes. The insertion of a metal proceeds by the intermediacy of a "sitting atop complex" (SAC), whereby the entering metal interacts with only one or a few of the nitrogen centers.
In contrast to natural porphyrins, synthetic porphyrin ligands are typically symmetrical (i.e., their dianionic conjugate bases). Two major varieties are well studied, those with substituents at the meso positions, the premier example being tetraphenylporphyrin. These ligands are easy to prepare in one-pot procedures. A large number of aryl groups can be deployed aside from phenyl.
A second class of synthetic porphyrins have hydrogen at the meso positions. Octaethylporphyrin (HOEP) is the subject of many such studies. It is more expensive than tetraphenylporphyrin.
Protoporphyrin IX, which occurs naturally, can be modified by removal of the vinyl groups and esterification of the carboxylic acid groups to gives deuteroporphyin IX dimethyl ester. | 1 | Applied and Interdisciplinary Chemistry |
Achieving Fellow status in the chemical profession denotes to the wider community a high level of accomplishment as a professional chemist. Eligibility for Fellow status applies to applicants who are Members of the Royal Society of Chemistry (MRSC), with a minimum of 5 years professional experience. In addition, they must have made an outstanding contribution to the advancement of the chemical sciences; or to the advancement of the chemical sciences as a profession; or have been distinguished in the management of a chemical sciences organization.
In all cases FRSC sponsor references are required. The award of designatory letters FRSC is subject to the final approval of the RSC Applications Committee. In addition to the above, all RSC membership requires acceptance and adherence to a specific code of conduct and an established set of high standards of ethical and professional behavior.
The RSC continuously establishes, and evaluates professional qualifications and the awarding of its designatory letters and awards. See Category:Fellows of the Royal Society of Chemistry for examples of fellows.
Honorary Fellowship of the Society ("HonFRSC") is awarded for distinguished service in the field of chemistry. | 1 | Applied and Interdisciplinary Chemistry |
An international nonproprietary name (INN) is an official generic and nonproprietary name given to a pharmaceutical drug or an active ingredient. INNs are intended to make communication more precise by providing a unique standard name for each active ingredient, to avoid prescribing errors. The INN system has been coordinated by the World Health Organization (WHO) since 1953.
Having unambiguous standard names for each drug (standardization of drug nomenclature) is important because a drug may be sold by many different brand names, or a branded medication may contain more than one drug. For example, the branded medications Celexa, Celapram and Citrol all contain the same active ingredient: citalopram; and the antibiotic widely known by the brand name Bactrim contains two active ingredients: trimethoprim and sulfamethoxazole. This combination of two antibiotic agents in one tablet has been available as a generic for decades, but the brand names Bactrim and Septra are still in common use.
Each drugs INN is unique but may contain a word stem that is shared with other drugs of the same class; for example, the beta blocker drugs propranolol and atenolol share the -olol suffix, and the benzodiazepine drugs lorazepam and diazepam share the -azepam' suffix.
The WHO issues INNs in English, Latin, French, Russian, Spanish, Arabic, and Chinese, and a drugs INNs are often cognate across most or all of the languages, with minor spelling or pronunciation differences, for example: paracetamol (en) (la), (fr) and (ru). An established INN is known as a recommended INN (rINN), while a name that is still being considered is called a proposed' INN (pINN). | 1 | Applied and Interdisciplinary Chemistry |
The history of spectroscopy began with Isaac Newton's optics experiments (1666–1672). According to Andrew Fraknoi and David Morrison, "In 1672, in the first paper that he submitted to the Royal Society, Isaac Newton described an experiment in which he permitted sunlight to pass through a small hole and then through a prism. Newton found that sunlight, which looks white to us, is actually made up of a mixture of all the colors of the rainbow." Newton applied the word "spectrum" to describe the rainbow of colors that combine to form white light and that are revealed when the white light is passed through a prism.
Fraknoi and Morrison state that "In 1802, William Hyde Wollaston built an improved spectrometer that included a lens to focus the Sun's spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the spectrum." During the early 1800s, Joseph von Fraunhofer made experimental advances with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics, and astronomy. Per Fraknoi and Morrison, "Later, in 1815, German physicist Joseph Fraunhofer also examined the solar spectrum, and found about 600 such dark lines (missing colors), are now known as Fraunhofer lines, or Absorption lines."
In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy of a photon is related to its frequency by where is Planck's constant, and so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can also excite resonant interactions.
Spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first successfully explained by the Rutherford–Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be a single transition if the density of energy states is high enough. Named series of lines include the principal, sharp, diffuse and fundamental series. | 0 | Theoretical and Fundamental Chemistry |
Microwave reactors are frequently used for small-scale batch chemistry. However, due to the extremes of temperature and pressure reached in a microwave it is often difficult to transfer these reactions to conventional non-microwave apparatus for subsequent development, leading to difficulties with scaling studies. A flow reactor with suitable high-temperature ability and pressure control can directly and accurately mimic the conditions created in a microwave reactor. This eases the synthesis of larger quantities by extending reaction time. | 1 | Applied and Interdisciplinary Chemistry |
Protein Arginine Phosphatase (PAPs), also known as Phosphoarginine Phosphatase, is an enzyme that catalyzes the dephosphorylation of phosphoarginine residues in proteins. Protein phosphatases (PPs) are "obligatory heteromers" made up of two maximum catalytic subunits attached to a non-catalytic subunit. Arginine modification is a post-translational protein modification in gram-positive bacteria. McsB and YwIE were recently identified as phosphorylating enzymes in Bacillus Subtilis (B.Subtilis). YwIE was thought to be a protein-tyrosine-phosphatase, and McsB a tyrosine-kinase, however in 2012 Elsholz et al. showed that McsB is a protein-arginine-kinase (PAK) and YwlE is a phosphatase-arginine-phosphatase (PAP).
Many proteins rely on protein phosphatase activity for regulating their stability, localization, and interaction with other proteins. Arginine modification is a post-translational protein modification in gram-positive bacteria, and protein arginine phosphorylation regulates transcription factors, in addition to tagging rogue proteins for degradation in gram-positive bacteria. Like phosphorylation, dephosphorylation is a reversible post-translational event. It is reversible through the action of kinases (enzymes that adds a phosphate group to a protein via phosphorylation), and this antagonist activity of phosphorylation and dephosphorylation of proteins controls all aspect of prokaryotic and eukaryotic life. In general, protein phosphatases play a crucial role in cell signaling regulation in both eukaryotes and prokaryotes. They act by removing a phosphate group from proteins, and their activity counteracts that of protein kinases. | 1 | Applied and Interdisciplinary Chemistry |
Each chemical species (for example, "water molecules", "sodium ions", "electrons", etc.) has an electrochemical potential (a quantity with units of energy) at any given point in space, which represents how easy or difficult it is to add more of that species to that location. If possible, a species will move from areas with higher electrochemical potential to areas with lower electrochemical potential; in equilibrium, the electrochemical potential will be constant everywhere for each species (it may have a different value for different species). For example, if a glass of water has sodium ions (Na) dissolved uniformly in it, and an electric field is applied across the water, then the sodium ions will tend to get pulled by the electric field towards one side. We say the ions have electric potential energy, and are moving to lower their potential energy. Likewise, if a glass of water has a lot of dissolved sugar on one side and none on the other side, each sugar molecule will randomly diffuse around the water, until there is equal concentration of sugar everywhere. We say that the sugar molecules have a "chemical potential", which is higher in the high-concentration areas, and the molecules move to lower their chemical potential. These two examples show that an electrical potential and a chemical potential can both give the same result: A redistribution of the chemical species. Therefore, it makes sense to combine them into a single "potential", the electrochemical potential, which can directly give the net redistribution taking both into account.
It is (in principle) easy to measure whether or not two regions (for example, two glasses of water) have the same electrochemical potential for a certain chemical species (for example, a solute molecule): Allow the species to freely move back and forth between the two regions (for example, connect them with a semi-permeable membrane that lets only that species through). If the chemical potential is the same in the two regions, the species will occasionally move back and forth between the two regions, but on average there is just as much movement in one direction as the other, and there is zero net migration (this is called "diffusive equilibrium"). If the chemical potentials of the two regions are different, more molecules will move to the lower chemical potential than the other direction.
Moreover, when there is not diffusive equilibrium, i.e., when there is a tendency for molecules to diffuse from one region to another, then there is a certain free energy released by each net-diffusing molecule. This energy, which can sometimes be harnessed (a simple example is a concentration cell), and the free-energy per mole is exactly equal to the electrochemical potential difference between the two regions. | 0 | Theoretical and Fundamental Chemistry |
ISTD using TCH was developed by Shell Oil Co. in the late 1980s and grew out of research and development for enhanced oil recovery. During the mid-1990s Shell Oil Company commercialized ISTD with an investment of over $30 million. | 1 | Applied and Interdisciplinary Chemistry |
Aerobic fermentation or aerobic glycolysis is a metabolic process by which cells metabolize sugars via fermentation in the presence of oxygen and occurs through the repression of normal respiratory metabolism. Preference of aerobic fermentation over aerobic respiration is referred to as the Crabtree effect in yeast, and is part of the Warburg effect in tumor cells. While aerobic fermentation does not produce adenosine triphosphate (ATP) in high yield, it allows proliferating cells to convert nutrients such as glucose and glutamine more efficiently into biomass by avoiding unnecessary catabolic oxidation of such nutrients into carbon dioxide, preserving carbon-carbon bonds and promoting anabolism. | 1 | Applied and Interdisciplinary Chemistry |
Durrant was appointed Commander of the Order of the British Empire (CBE) in the 2022 Birthday Honours for services to photochemistry and solar energy research.
*2018: Awarded Hughes Medal by the Royal Society
*2017: Elected a Fellow of the Royal Society (FRS) for his research contributions in photochemistry of new materials for use in solar energy conversion – specifically targeting both solar cells in photovoltaic systems and solar to fuel in artificial photosynthesis.
*2016: Elected a Fellow of the Learned Society of Wales
*2016: Awarded president's award for excellence in research supervision.
*2012: Awarded the Tilden Prize by the Royal Society of Chemistry
*2009: Awarded the Environment Prize by the Royal Society of Chemistry
*1994: Awarded the Meldola Medal and Prize by the Royal Society of Chemistry | 0 | Theoretical and Fundamental Chemistry |
In negative-sense MVM genomes, the left-end hairpin is 121 nucleotides in length and exists in a single flip sequence orientation. This telomere is Y-shaped and contains small internal palindromes that fold into the "ears" of the Y, a duplex stem region 43 nucleotides in length that is interrupted by an asymmetric thymidine residue, and a mismatched "bubble" sequence in which the 5′-GAA-3′ sequence on the inboard arm is opposite of 5′-GA-3′ in the outboard strand. Sequences in this hairpin are involved in both replication and regulation of transcription. The elements involved in these two functions separate the two arms of the hairpin.
The left-end telomere of MVM, and likely of all heterotelomeric parvoviruses, cannot function as a replication origin in its hairpin configuration. Instead, a single origin on the lower strand is created when the hairpin is unfolded, extended, and copied to form a duplex basepaired sequence that spans adjacent genomes in the dimer RF. Within this structure, the sequence from the outboard arm that surrounds a GA/TC dinucleotide serves as an origin, OriL. The equivalent GAA/TTC sequence on the inboard arm that contains the bubble trinucleotide, called OriL, does not serve as an origin. The inboard arm and hairpin configuration of the terminus instead appear to function as upstream control elements for the viral transcriptional promoter P4. Additionally, the ability to segregate one arm from nicking appears essential for replication.
The minimal linear left-end origin is about 50 basepairs long and extends from two 5′-ACGT-3′ motifs, spaced five nucleotides apart at one end, to a position seven basepairs beyond the nick site. The bubble's GA sequence itself is relatively unimportant, but the space that it occupies is necessary for the origin to function. Within the origin, there are three recognition sequences: an NS1-binding site that orients the NS1 complex over the nick site 5′-CTWWTCA-3′, which is located 17 nucleotides downstream (toward the 3′-end), and the two ACGT motifs. These motifs bind a heterodimeric cellular factor called either parvovirus initiation factor (PIF) or glucocorticoid modulating element-binding protein (GMEB).
PIF is a site-specific DNA-binding heterodimeric complex that contains two subunits, p96 and p79, and functions as a transcription modulator in the host cell. It binds DNA via a KDWK fold and recognizes two ACGT half-sites. The spacing between these sites can vary significantly for PIF, from one to nine nucleotides, with an optimal spacing of six. PIF stabilizes the binding of NS1 on the active form of the left-end origin, OriL, but not on the inactive form, OriL, because the two complexes are able to establish contact over the bubble binucleotide. The left-end hairpin of all other species in the Protoparvovirus genus, of which MVM belongs, have bubble asymmetries and PIF-binding sites, though with slight variation in spacing. This suggests that they all share a similar origin segregation mechanism. | 1 | Applied and Interdisciplinary Chemistry |
Cobalt-59 nuclear magnetic resonance is a form of nuclear magnetic resonance spectroscopy that uses cobalt-59, a cobalt isotope. Co is a nucleus of spin 7/2 and 100% abundancy. The nucleus has a magnetic quadrupole moment. Among all NMR active nuclei, Co has the largest chemical shift range and the chemical shift can be correlated with the spectrochemical series. Resonances are observed over a range of 20000 ppm, the width of the signals being up to 20 kHz. A widely used standard is potassium hexacyanocobaltate (0.1M KCo(CN) in DO), which, due to its high symmetry, has a rather small line width. Systems of low symmetry can yield broadened signals to an extent that renders the signals unobservable in fluid phase NMR, in these cases signals can still be observable in solid state NMR. | 0 | Theoretical and Fundamental Chemistry |
Thalidomide is racemic; while S-thalidomide is the bioactive form of the molecule, the individual enantiomers can racemize to each other due to the acidic hydrogen at the chiral centre, which is the carbon of the glutarimide ring bonded to the phthalimide substituent. The racemization process can occur in vivo. The process of conversion of one enantiomer to its mirror-image version with no other change in the molecule is called chiral inversion.
Celgene Corporation originally synthesized thalidomide using a three-step sequence starting with -glutamic acid treatment, but this has since been reformed by the use of -glutamine. As shown in the image below, N-carbethoxyphthalimide (1) can react with -glutamine to yield N-phthaloyl--glutamine (2). Cyclization of N-phthaloyl--glutamine occurs using carbonyldiimidazole, which then yields thalidomide (3). Celgene Corporations original method resulted in a 31% yield of S'-thalidomide, whereas the two-step synthesis yields 85–93% product that is 99% pure. | 0 | Theoretical and Fundamental Chemistry |
Starting from the late 1980s, more modern calculations and the lack of spectroscopic evidence reveal that the P 3d contribution is negligible, invalidating the earlier hypothesis. Instead, a charge separated model is generally accepted.
According to this description, the P–N bond is viewed as a very polarised one (between notional and ), with sufficient ionic character to account for most of the bond strength.
The rest (~15%) of the bond strength may be attributed to a negative hyperconjugation interaction: the N lone pairs can donate some electron density into π-accepting σ* molecular orbitals on the P. | 0 | Theoretical and Fundamental Chemistry |
Mutagens can cause changes to the DNA and are therefore genotoxic. They can affect the transcription and replication of the DNA, which in severe cases can lead to cell death. The mutagen produces mutations in the DNA, and deleterious mutation can result in aberrant, impaired or loss of function for a particular gene, and accumulation of mutations may lead to cancer. Mutagens may therefore be also carcinogens. However, some mutagens exert their mutagenic effect through their metabolites, and therefore whether such mutagens actually become carcinogenic may be dependent on the metabolic processes of an organism, and a compound shown to be mutagenic in one organism may not necessarily be carcinogenic in another.
Different mutagens act on DNA differently. Powerful mutagens may result in chromosomal instability, causing chromosomal breakages and rearrangement of the chromosomes such as translocation, deletion, and inversion. Such mutagens are called clastogens.
Mutagens may also modify the DNA sequence; the changes in nucleic acid sequences by mutations include substitution of nucleotide base-pairs and insertions and deletions of one or more nucleotides in DNA sequences. Although some of these mutations are lethal or cause serious disease, many have minor effects as they do not result in residue changes that have significant effect on the structure and function of the proteins. Many mutations are silent mutations, causing no visible effects at all, either because they occur in non-coding or non-functional sequences, or they do not change the amino-acid sequence due to the redundancy of codons.
Some mutagens can cause aneuploidy and change the number of chromosomes in the cell. They are known as aneuploidogens.
In Ames test, where the varying concentrations of the chemical are used in the test, the dose response curve obtained is nearly always linear, suggesting that there may be no threshold for mutagenesis. Similar results are also obtained in studies with radiations, indicating that there may be no safe threshold for mutagens. However, the no-threshold model is disputed with some arguing for a dose rate dependent threshold for mutagenesis. Some have proposed that low level of some mutagens may stimulate the DNA repair processes and therefore may not necessarily be harmful. More recent approaches with sensitive analytical methods have shown that there may be non-linear or bilinear dose-responses for genotoxic effects, and that the activation of DNA repair pathways can prevent the occurrence of mutation arising from a low dose of mutagen. | 0 | Theoretical and Fundamental Chemistry |
Nanoparticles are created by EWM when the ambient gas of the system cools the recently produced vaporous metal. EWM can be used to cheaply and efficiently produce nanoparticles at a rate of 50 – 300 grams per hour and at a purity of above 99%. The process requires a relatively low energy consumption as little energy is lost in an electric to thermal energy conversion. Environmental effects are minimal due to the process taking place in a closed system. The Particles can be as small as 10 nm but are most commonly below 100 nm in diameter. Physical attributes of the nanopowder can be altered depending on the parameters of the explosion. For example, as the voltage of the capacitor is raised, the particle diameter decreases. Also, the pressure of the gas environment can change the dispersiveness of the nanoparticles. Through such manipulations the functionality of the nanopowder may be altered.
When EWM is performed in a standard atmosphere containing oxygen, metal oxides are formed. Pure metal nanoparticles can also be produced with EWM in an inert environment, usually argon gas or distilled water. Pure metal nanopowders must be kept in their inert environment because they ignite when exposed to oxygen in air. Often, the metal vapor is contained by operating the mechanism within a steel box or similar container.
Nanoparticles are a relatively new material used in medicine, manufacturing, environmental cleanup and circuitry. Metal oxide and pure metal nanoparticles are used in Catalysis, sensors, oxygen antioxident, self repairing metal, ceramics, UV ray protection, odor proofing, improved batteries, printable circuits, optoelectronic materials, and Environmental remediation. The demand for metal nanoparticles, and therefore production methods, has increased as interest in nanotechnology continues to rise. Despite its overwhelming simplicity and efficiency, it is difficult to modify the experimental apparatus to be used on an industrial scale. As such, EWM has not seen widespread utilization in material production industry due to issues in manufacturing quantity. Still, for some time, Argonide offered metal nanopowders made by the exploding wire method that that were manufactured in Russia. | 0 | Theoretical and Fundamental Chemistry |
Stable, isolable, diradicals include singlet oxygen and triplet oxygen. Other important diradicals are certain carbenes, nitrenes, and their main group elemental analogues. Lesser known diradicals are nitrenium ions, carbon chains and organic so-called non-Kekulé molecules in which the electrons reside on different carbon atoms. Main group cyclic structures can also exhibit diradicals, such as disulfur dinitride, or diradical character, such as diphosphadiboretanes. In inorganic chemistry, both homoleptic and heteroleptic 1,2-dithiolene complexes of d transition metal ions show a large degree of diradical character in the ground state. | 0 | Theoretical and Fundamental Chemistry |
Table of the wallpaper groups using the classification of the 2-dimensional space groups:
For each geometric class, the possible arithmetic classes are
* None: no reflection lines
* Along: reflection lines along lattice directions
* Between: reflection lines halfway in between lattice directions
* Both: reflection lines both along and between lattice directions | 0 | Theoretical and Fundamental Chemistry |
Media filters are also used for cleaning the effluent from septic tanks and primary settlement tanks. The materials commonly used are sand, peat and natural stone fibre. | 1 | Applied and Interdisciplinary Chemistry |
The arrangement of the groups in the structure of cubic ZrWO is analogous to the simple NaCl structure, with ZrO octahedra at the Na sites, and WO groups at the Cl sites. The unit cell consists of 44 atoms aligned in a primitive cubic Bravais lattice, with unit cell length 9.15462 Angstroms.
The ZrO octahedra are only slightly distorted from a regular conformation, and all oxygen sites in a given octahedron are related by symmetry. The WO unit is made up of two crystallographically distinct WO tetrahedra, which are not formally bonded to each other. These two types of tetrahedra differ with respect to the W-O bond lengths and angles. The WO tetrahedra are distorted from a regular shape since one oxygen is unconstrained (an atom that is bonded only to the central tungsten (W) atom), and the three other oxygens are each bonded to a zirconium atom (i.e. the corner-sharing of polyhedra).
The structure has P23 space group symmetry at low temperatures. At higher temperatures, a centre of inversion is introduced by the disordering of the orientation of tungstate groups, and the space group above the phase transition temperature (~180C) is Pa.
Octahedra and tetrahedra are linked together by sharing an oxygen atom. In the image, note the corner-touching between octahedra and tetrahedra; these are the location of the shared oxygen. The vertices of the tetrahedra and octahedra represent the oxygen, which are spread about the central zirconium and tungsten. Geometrically, the two shapes can "pivot" around these corner-sharing oxygens, without a distortion of the polyhedra themselves. This pivoting is what is thought to lead to the negative thermal expansion, as in certain low frequency normal modes this leads to the contracting RUMs mentioned above. | 0 | Theoretical and Fundamental Chemistry |
A frequency comb allows a direct link from radio frequency standards to optical frequencies. Current frequency standards such as atomic clocks operate in the microwave region of the spectrum, and the frequency comb brings the accuracy of such clocks into the optical part of the electromagnetic spectrum. A simple electronic feedback loop can lock the repetition rate to a frequency standard.
There are two distinct applications of this technique. One is the optical clock, where an optical frequency is overlapped with a single tooth of the comb on a photodiode, and a radio frequency is compared to the beat signal, the repetition rate, and the CEO-frequency (carrier–envelope offset). Applications for the frequency-comb technique include optical metrology, frequency-chain generation, optical atomic clocks, high-precision spectroscopy, and more precise GPS technology.
The other is doing experiments with few-cycle pulses, like above-threshold ionization, attosecond pulses, highly efficient nonlinear optics or high-harmonics generation. These can be single pulses, so that no comb exists, and therefore it is not possible to define a carrier–envelope offset frequency, rather the carrier–envelope offset phase is important. A second photodiode can be added to the setup to gather phase and amplitude in a single shot, or difference-frequency generation can be used to even lock the offset on a single-shot basis, albeit with low power efficiency.
Without an actual comb one can look at the phase vs frequency. Without a carrier–envelope offset all frequencies are cosines. This means that all frequencies have the phase zero. The time origin is arbitrary. If a pulse comes at later times, the phase increases linearly with frequency, but still the zero-frequency phase is zero. This phase at zero frequency is the carrier–envelope offset. The second harmonic not only has twice the frequency, but also twice the phase. Thus for a pulse with zero offset the second harmonic of the low-frequency tail is in phase with the fundamental of the high-frequency tail, and otherwise it is not. Spectral phase interferometry for direct electric-field reconstruction (SPIDER) measures how the phase increases with frequency, but it cannot determine the offset, so the name “electric field reconstruction” is a bit misleading.
In recent years, the frequency comb has been garnering interest for astro-comb applications, extending the use of the technique as a spectrographic observational tool in astronomy.
There are other applications that do not need to lock the carrier–envelope offset frequency to a radio-frequency signal. These include, among others, optical communications, the synthesis of optical arbitrary waveforms, spectroscopy (especially dual-comb spectroscopy) or radio-frequency photonics.
On the other hand, optical frequency combs have found new applications in remote sensing. Ranging lidars based on dual comb spectroscopy have been developed, enabling high-resolution range measurements at fast update rates. Optical frequency combs can also be utilized to measure greenhouse gas emissions with great precision. For instance, in 2019, scientists at NIST employed spectroscopy to quantify methane emissions from oil and gas fields . More recently, a greenhouse gas lidar based on electro-optic combs has been successfully demonstrated. | 0 | Theoretical and Fundamental Chemistry |
The fundamental building block of any industrial control system is the control loop, which controls just one process variable. An example is shown in the accompanying diagram, where the flow rate in a pipe is controlled by a PID controller, assisted by what is effectively a cascaded loop in the form of a valve servo-controller to ensure correct valve positioning.
Some large systems may have several hundreds or thousands of control loops. In complex processes the loops are interactive, so that the operation of one loop may affect the operation of another. The system diagram for representing control loops is a Piping and instrumentation diagram.
Commonly used control systems include programmable logic controller (PLC), Distributed Control System (DCS) or SCADA.
A further example is shown. If a control valve were used to hold level in a tank, the level controller would compare the equivalent reading of a level sensor to the level setpoint and determine whether more or less valve opening was necessary to keep the level constant. A cascaded flow controller could then calculate the change in the valve position. | 1 | Applied and Interdisciplinary Chemistry |
The resistance arises from the prevailing limitations on availability (local concentration) and mobility of the ions whose motion between the electrolyte and the electrode constitutes the faradaic current. The capacitance is that of the capacitor formed by the electrolyte and the electrode, separated by the Debye screening length and giving rise to the double-layer capacitance at the electrolyte-electrode interface. When the supply of ions does not meet the demand created by the potential the resistance increases, the effect being that of a constant current source or sink, and the cell is then said to be polarized at that electrode. The extent of polarization, and hence the faradaic impedance, can be controlled by varying the concentration of electrolyte ions and the temperature, by stirring the electrolyte, etc. The chemistry of the electrolyte-electrode interface is also a crucial factor.
Electrodes constructed as smooth planar sheets of metal have the least surface area. The area can be increased by using a woven mesh or porous or sintered metals. In this case faradaic impedance may be more appropriately modeled as a transmission line consisting of resistors in series coupled by capacitors in parallel. | 0 | Theoretical and Fundamental Chemistry |
Lake metabolism represents a lake's balance between carbon fixation (gross primary production) and biological carbon oxidation (ecosystem respiration). Whole-lake metabolism includes the carbon fixation and oxidation from all organism within the lake, from bacteria to fishes, and is typically estimated by measuring changes in dissolved oxygen or carbon dioxide throughout the day.
Ecosystem respiration in excess of gross primary production indicates the lake receives organic material from the surrounding catchment, such as through stream or groundwater inflows or litterfall. Lake metabolism often controls the carbon dioxide emissions from or influx to lakes, but it does not account for all carbon dioxide dynamics since inputs of inorganic carbon from the surrounding catchment also influence carbon dioxide within lakes. | 1 | Applied and Interdisciplinary Chemistry |
Heterogeneous nuclear ribonucleoproteins (hnRNPs) are complexes of RNA and protein present in the cell nucleus during gene transcription and subsequent post-transcriptional modification of the newly synthesized RNA (pre-mRNA). The presence of the proteins bound to a pre-mRNA molecule serves as a signal that the pre-mRNA is not yet fully processed and therefore not ready for export to the cytoplasm. Since most mature RNA is exported from the nucleus relatively quickly, most RNA-binding protein in the nucleus exist as heterogeneous ribonucleoprotein particles. After splicing has occurred, the proteins remain bound to spliced introns and target them for degradation.
hnRNPs are also integral to the 40S subunit of the ribosome and therefore important for the translation of mRNA in the cytoplasm. However, hnRNPs also have their own nuclear localization sequences (NLS) and are therefore found mainly in the nucleus. Though it is known that a few hnRNPs shuttle between the cytoplasm and nucleus, immunofluorescence microscopy with hnRNP-specific antibodies shows nucleoplasmic localization of these proteins with little staining in the nucleolus or cytoplasm. This is likely because of its major role in binding to newly transcribed RNAs. High-resolution immunoelectron microscopy has shown that hnRNPs localize predominantly to the border regions of chromatin, where it has access to these nascent RNAs.
The proteins involved in the hnRNP complexes are collectively known as heterogeneous ribonucleoproteins. They include protein K and polypyrimidine tract-binding protein (PTB), which is regulated by phosphorylation catalyzed by protein kinase A and is responsible for suppressing RNA splicing at a particular exon by blocking access of the spliceosome to the polypyrimidine tract. hnRNPs are also responsible for strengthening and inhibiting splice sites by making such sites more or less accessible to the spliceosome. Cooperative interactions between attached hnRNPs may encourage certain splicing combinations while inhibiting others. | 1 | Applied and Interdisciplinary Chemistry |
Mutatochrome (5,8-epoxy-β-carotene) is a carotenoid. It is the predominant carotenoid in the cap of the bolete mushroom Boletus luridus. | 1 | Applied and Interdisciplinary Chemistry |
Feringa found that the early introduction of chiroptical molecular switches, based on the design of the first chiral overcrowded alkenes and the demonstration of optically controlled molecular switching and amplification of chirality in mesoscopic systems, lead to molecular rotary motors in which chirality plays a critical role in achieving the same function achieved by nature, for example, the unidirectional rotation of retinal in rhodopsin. This work led to the discovery of the worlds first unidirectional molecular rotary motor and this work has been laying the ground-work for a key component of future molecular nanotechnology i.e. nanomachines and nanorobots powered by molecular motors. Feringas design and synthesis of nanomolecular machines, specifically molecular switches and molecular motors, have initiated major novel approaches towards complex and dynamic chemical systems and the dynamic control of function.
Applications of molecular switches developed in his group include responsive materials and surfaces, liquid crystals, electrochromic devices for optoelectronics, photo-switchable DNA as a molecular memory stick, responsive gels, polymers, and light-switchable protein channels for nanoscale drug delivery systems, anion sensing, responsive catalysts and photopharmacology as well as entirely novel approaches using responsive drugs toward anticancer agents, antibiotic treatment and antibiotic resistance, and biofilm formation. Interfacing molecular motors with the macroscopic world by surface assembly on gold nanoparticles and a macroscopic gold film, has shown that the motor functions while chemically bound to a surface, a key result for future nanomachines such as a molecular conveyor belt. Experiments that involve doping liquid crystals with molecular motors demonstrate that the motion of the motor can be harnessed to make macroscopic objects rotate on a liquid crystal film and drive molecular systems out-of-equilibrium. Several of these discoveries were selected for the list of most important chemical discoveries of the year by Chemical & Engineering News.
In 2011, molecular ‘nanocar’, a molecule that contains molecular motor-based wheels and was shown to move on a solid surface upon subjection to electric current from an STM tip, was highlighted in international daily newspapers & magazines worldwide and selected by the Chinese Academy of Sciences as one of the 10 major discoveries in sciences worldwide. Towards the future discipline of Systems chemistry, the development of a multistage chiral catalysts which comprises an integrated supramolecular system that brings together molecular recognition, chirality transfer, catalysis, stereoelectronic control and enantio-selectivity while all these processes can be enabled or disabled via an internal motor function, moves the design and application of molecular motors to a whole new level of sophistication.
Aside from molecular motors and switches, Feringa's work has crossed many disciplines and includes the use of phosphoramidites as ligands in asymmetric catalysis, an excellent stereocontrol was archived in copper-catalysed C–C bond formation, which led to a breakthrough in catalytic asymmetric conjugate addition. As phosphoramidites found use in industry, recently they utilised them as starting reagents for asymmetric C-P bond formation. Traditionally, an external chiral ligand is used for chiral induction in a C–P coupling reaction, but the competitive coordination of initial and final phosphorus compounds with the metal catalysts, together with an external chiral ligand, reduces the enantioselectivity. As BINOL-containing phosphoramidites have the properties of an intrinsic chiral ligand and simultaneously can serve as a substrate, they hypothesized that they would increase stereoselectivity in C–P coupling processes with aryl compounds, and were delighted when that data confirmed that they did.
Moreover, many other highlighted works are chiral electromagnetic radiation to generate enantioselectivity, low molecular weight gelators, imaging porphyrins with STM, drying induced self-assembly, organic synthesis, CD spectroscopy, asymmetric catalysis, exploring the origins of chirality including the possibility of an extraterrestrial source and various aspects of surface science including surface modification, surface energy control, and porphyrin allayers. | 0 | Theoretical and Fundamental Chemistry |
In 1960 Almin was bought by Imperial Aluminium Company (Impalco), a company formed between the Aluminium Company of America (Alcoa) and Imperial Chemical Industries (ICI) which incorporated the whole of ICIs aluminium facilities. Impalcos primary interest in buying Almin was to acquire the facilities of International Alloys, a member of the Almin group. Thus Fulmer was acquired incidentally and it did not fit easily into the Impalco group. Since Impalco had huge research facilities in-house, it had no need of Fulmers services. Impalcos rival companies were also reluctant to place large contracts with Fulmer under this ownership. | 1 | Applied and Interdisciplinary Chemistry |
Magnetization transfer (MT), in NMR and MRI, refers to the transfer of nuclear spin polarization and/or spin coherence from one population of nuclei to another population of nuclei, and to techniques that make use of these phenomena. There is some ambiguity regarding the precise definition of magnetization transfer, however the general definition given above encompasses all more specific notions. NMR active nuclei, those with non-zero spin, can be energetically coupled to one another under certain conditions. The mechanisms of nuclear-spin energy-coupling have been extensively characterized and are described in the following articles: Angular momentum coupling, Magnetic dipole–dipole interaction, J-coupling, Residual dipolar coupling, Nuclear Overhauser effect, Spin–spin relaxation, and Spin saturation transfer. Alternatively, some nuclei in a chemical system are labile and exchange between non-equivalent environments. A more specific example of this case is presented in the section Chemical Exchange Magnetization transfer.
In either case, magnetization transfer techniques probe the dynamic relationship between two or more distinguishable nuclei populations, in so far as energy exchange between the populations can be induced and measured in an idealized NMR experiment. | 0 | Theoretical and Fundamental Chemistry |
Trans-Spliced Exon Coupled RNA End Determination (TEC-RED) is a transcriptomic technique that, like SAGE, allows for the digital detection of messenger RNA sequences. Unlike SAGE, detection and purification of transcripts from the 5’ end of the messenger RNA require the presence of a trans-spliced leader sequence. | 1 | Applied and Interdisciplinary Chemistry |
Cytochromes are proteins that contain iron. They are found in two very different environments.
Some cytochromes are water-soluble carriers that shuttle electrons to and from large, immobile macromolecular structures imbedded in the membrane. The mobile cytochrome electron carrier in mitochondria is cytochrome c. Bacteria use a number of different mobile cytochrome electron carriers.
Other cytochromes are found within macromolecules such as Complex III and Complex IV. They also function as electron carriers, but in a very different, intramolecular, solid-state environment.
Electrons may enter an electron transport chain at the level of a mobile cytochrome or quinone carrier. For example, electrons from inorganic electron donors (nitrite, ferrous iron, electron transport chain) enter the electron transport chain at the cytochrome level. When electrons enter at a redox level greater than NADH, the electron transport chain must operate in reverse to produce this necessary, higher-energy molecule. | 1 | Applied and Interdisciplinary Chemistry |
cOFM (Figure 5) is used to conduct PK/PD preclinical studies in the animal brain. Access to the brain includes monitoring of the blood-brain barrier function and drug transport across the intact blood-brain barrier. cOFM allows taking a look behind the blood-brain barrier and assesses concentrations and effects of neuroactive substances directly in the targeted brain tissue.
The blood-brain barrier is a natural shield that protects the brain and limits the exchange of nutrients, metabolites and chemical messengers between blood and brain. The blood-brain barrier also prevents potential harmful substances from entering and damaging the brain. However, this highly effective barrier also prevents neuroactive substances from reaching appropriate targets. For researchers that develop neuroactive drugs, it is therefore of major interest to know whether and to what extent an active pharmaceutical component can pass the blood-brain barrier. Experiments have shown that the blood-brain barrier has fully reestablished 15 days after implantation of the cOFM probe in the brain of rats. The cOFM probe has been specially designed to avoid a reopening of the blood-brain barrier or causing additional trauma to the brain after implantation. cOFM enables continuous sampling of cerebral ISF with intact blood-brain barrier cOFM and thus allows continuous PK monitoring in brain tissue. | 1 | Applied and Interdisciplinary Chemistry |
In heterotrimeric G proteins, catalysis of GTP can be assisted by aluminum tetrafluoride () and RGS4. Heterotrimeric G proteins are larger three-part proteins serve in signal transduction of many pathways. The catalytic mechanism for GTP hydrolysis in heterotrimeric G proteins consists of an active state where catalysis is likely to occur and an inactive state where catalysis is unlikely. In the active state, stabilizes the transition state and points the arginine finger residue towards GTP. This causes increased charge density on the beta phosphate of GTP and planarization of the gamma phosphate, which creates an opening and reduces steric hindrance for water to hydrolyze the phosphoanhydride beta-gamma bond. This is because the gamma phosphate's bond to the beta phosphate bends, exposing its connection and allowing the subsequent nucleophilic substitution reaction initiated by water. The complex formed with RGS4 assists in this process by creating strain on the bond between the gamma and beta phosphates and assisting in distributing more charge onto the beta phosphate. | 1 | Applied and Interdisciplinary Chemistry |
Photocatalysts must conform to several key principles in order to be considered effective at water splitting. A key principle is that and evolution should occur in a stoichiometric 2:1 ratio; significant deviation could be due to a flaw in the experimental setup and/or a side reaction, neither of which indicate a reliable photocatalyst for water splitting. The prime measure of photocatalyst effectiveness is quantum yield (QY), which is:
: QY (%) = (Photochemical reaction rate) / (Photon absorption rate) × 100%
To assist in comparison, the rate of gas evolution can also be used. A photocatalyst that has a high quantum yield and gives a high rate of gas evolution is a better catalyst.
The other important factor for a photocatalyst is the range of light that is effective for operation. For example, a photocatalyst is more desirable to use visible photons than UV photons. | 0 | Theoretical and Fundamental Chemistry |
For globular proteins, interior atomic packing (arising from short-range, local interactions) of side-chains has been shown to be pivotal in the structural stabilization of the protein-fold. On the other hand, the electrostatic harmony (non-local, long-range) of the overall fold has also been shown to be essential for its stabilization. Packing anomalies include steric clashes, short contacts, holes and cavities while electrostatic disharmony refer to unbalanced partial charges in the protein core (particularly relevant for designed protein interiors). While the clash-score of [http://molprobity.biochem.duke.edu/ Molprobity] identifies steric clashes at a very high resolution, the Complementarity Plot combines packing anomalies with electrostatic imbalance of side-chains and signals for either or both. | 1 | Applied and Interdisciplinary Chemistry |
Non-stop decay (NSD) is a cellular mechanism of mRNA surveillance to detect mRNA molecules lacking a stop codon and prevent these mRNAs from translation. The non-stop decay pathway releases ribosomes that have reached the far 3' end of an mRNA and guides the mRNA to the exosome complex, or to RNase R in bacteria for selective degradation. In contrast to nonsense-mediated decay (NMD), polypeptides do not release from the ribosome, and thus, NSD seems to involve mRNA decay factors distinct from NMD. | 1 | Applied and Interdisciplinary Chemistry |
Hofmann was born in Munich in 1903 and the son of the German chemist Karl Andreas Hofmann. He studied chemistry at the Technical University of Berlin and obtained a diploma in 1925. He went on to receive his doctorate in 1926 from his father with the work Glanzkohlenstoff und die Reihe des schwarzen kristallinen Kohlenstoffs (Lustrous carbon and the series of black crystalline carbon). In 1931 he received habilitation on graphite oxide and then worked as a lecturer at the Technical University of Berlin.
In 1937, Hofmann became a member of the NSDAP. In the same year, he also became a professor of chemistry and the head of the Institute of Chemistry at the University of Rostock. He did only a short military service in World War II, since he was released for war-related work. In 1942 he became head of the Institute for Inorganic and Analytical Chemistry at the Technical University of Vienna, where he also installed an electron microscope by Manfred von Ardenne. In 1945, Hofmann left Vienna and from 1948 taught chemistry and set up his laboratory at the Philosophical-Theological University of Regensburg (now University of Regensburg), where no chemistry had previously been taught. In 1951, he became professor of inorganic and physical chemistry at Technical University of Darmstadt. In 1960, Hofmann became head of the Institute for Inorganic Chemistry at the University of Heidelberg, where he later retired in 1971. | 0 | Theoretical and Fundamental Chemistry |
Many reactions in organometallic chemistry involve insertion of one ligand (L) into a metal-hydride or metal-alkyl/aryl bond. Generally it is the hydride, alkyl, or aryl group that migrates onto L, which is often CO, an alkene, or alkyne. | 0 | Theoretical and Fundamental Chemistry |
Campbells mona monkeys also generate alarm calls, but in a different way than vervet monkeys. Instead of having discrete calls for each predator, Campbell monkeys have two distinct types of calls which contain different calls which consist in an acoustic continuum of affixes which change meaning. It has been suggested that this is a homology to human morphology. Similarly, the cotton-top tamarin is able to use a limited vocal range of alarm calls to distinguish between aerial and land predators. Both the Campbell monkey and the cotton-top tamarin have demonstrated abilities similar to vervet monkeys ability to distinguish likely direction of predation and appropriate responses.
That these three species use vocalizations to warn others of danger has been called by some proof of proto-language in primates. However, there is some evidence that this behavior does not refer to the predators themselves but to threat, distinguishing calls from words. | 1 | Applied and Interdisciplinary Chemistry |
In the case of Cs the precursor to this isotope is stable Cs which is formed by the decay of much longer lived xenon and iodine isotopes. No Cs is formed without neutron activation as Xe is a stable isotope. As a result of this different mode of formation the physical location of Cs can differ from that of Cs.
These fission yields were calculated for U assuming thermal neutrons (0.0253 eV) using data from the chart of the nuclides. | 0 | Theoretical and Fundamental Chemistry |
Microscope-based diagnostics are widely performed and served as a gold standard in histological analysis. However this procedure generally requires a series time-consuming lab-based procedures including fixation, paraffin embedment, sectioning, and staining to produce microscope slides with optically thin tissue slides (4–6 µm). While in developed regions histology is commonly used, people who live in areas with limited resources can hardly access it and consequently are in need for a low-cost, more efficient way to access pathological diagnosis. The main significance of MUSE system comes from its capacity to produce high-resolution microscopic image with subcellular features in a time-efficient manner with less costs and less lab-expertises requirements.
With 280 nm deep UV excitation and simple but robust hardware design, MUSE system can collect fluorescence signals without the need for fluorescence filtering techniques or complex mathematical image reconstruction. It has potential for generate high quality images containing more information than microscope slides in terms of its 2.5 dimensional features. MUSE images have been validated with diagnostic values. The system is capable to produce images from various tissue type in different sizes, either fresh or fixed. | 0 | Theoretical and Fundamental Chemistry |
Halo ketones and halo carbonyl compounds in general are synthesized by reaction of carbonyl compounds with sources of X (X = halogen), which is provided using halogens:
:RC(O)CH + X → RC(O)CHX + HX
Specialized sources of electrophilic halogenating agents include N-Bromosuccinimide and 1,3-dibromo-5,5-dimethylhydantoin (DBDMH). In the Nierenstein reaction an acyl chloride reacts with diazomethane | 0 | Theoretical and Fundamental Chemistry |
* Member of the American Philosophical Society (1902)
*Lowell Lectures (1908)
* Davy Medal (1910)
* Faraday Lectureship (1911)
* Willard Gibbs Medal (1912)
* President of the American Chemical Society (1914)
* Nobel Prize in Chemistry (1914)
* Franklin Medal (1916)
* President of the American Association for the Advancement of Science (1917)
* Honorary Member of the Royal Irish Academy (1918)
* Foreign Member of the Royal Society of London (1919)
* President of the American Academy of Arts and Sciences President (1919 – 1921)
* Lavoisier Medal (1922)
* Le Blanc Medal (1922)
* Honorary Fellow of the Royal Society of Edinburgh (1923)
* Member of the International Atomic Weights Committee
* Theodore Richards Medal (1932, awarded posthumously) | 1 | Applied and Interdisciplinary Chemistry |
Patients usually start progesterone medication after egg (also called oocyte) retrieval. While daily intramuscular injections of progesterone-in-oil (PIO) have been the standard route of administration, PIO injections are not FDA-approved for use in pregnancy. A recent meta-analysis showed that the intravaginal route with an appropriate dose and dosing frequency is equivalent to daily intramuscular injections. In addition, a recent case-matched study comparing vaginal progesterone with PIO injections showed that live birth rates were nearly identical with both methods. A duration of progesterone administration of 11 days results in almost the same birth rates as longer durations.
Patients are also given estrogen medication in some cases after the embryo transfer. Pregnancy testing is done typically two weeks after egg retrieval. | 1 | Applied and Interdisciplinary Chemistry |
In the 5th century BC, Leucippus and his pupil Democritus proposed that all matter was composed of small indivisible particles which they called "atoms". Nothing whatsoever is known about Leucippus except that he was the teacher of Democritus. Democritus, by contrast, wrote prolifically, producing over eighty known treatises, none of which have survived to the present day complete. However, a massive number of fragments and quotations of his writings have survived. These are the main source of information on his teachings about atoms. Democritus's argument for the existence of atoms hinged on the idea that it is impossible to keep dividing matter infinitely - and that matter must therefore be made up of extremely tiny particles. The atomistic theory aimed to remove the "distinction which the Eleatic school drew between the Absolute, or the only real existence, and the world of change around us."
Democritus believed that atoms are too small for human senses to detect, that they are infinitely many, that they come in infinitely many varieties, and that they have always existed. They float in a vacuum, which Democritus called the "void", and they vary in form, order, and posture. Some atoms, he maintained, are convex, others concave, some shaped like hooks, and others like eyes. They are constantly moving and colliding into each other. Democritus wrote that atoms and void are the only things that exist and that all other things are merely said to exist by social convention. The objects humans see in everyday life are composed of many atoms united by random collisions and their forms and materials are determined by what kinds of atom make them up. Likewise, human perceptions are caused by atoms as well. Bitterness is caused by small, angular, jagged atoms passing across the tongue; whereas sweetness is caused by larger, smoother, more rounded atoms passing across the tongue.
Previously, Parmenides had denied the existence of motion, change and void. He believed all existence to be a single, all-encompassing and unchanging mass (a concept known as monism), and that change and motion were mere illusions. He explicitly rejected sensory experience as the path to an understanding of the universe and instead used purely abstract reasoning. He believed there is no such thing as void, equating it with non-being. This in turn meant that motion is impossible, because there is no void to move into. Parmenides doesn't mention or explicitly deny the existence of the void, stating instead that what is not does not exist. He also wrote all that must be an indivisible unity, for if it were manifold, then there would have to be a void that could divide it. Finally, he stated that the all encompassing Unity is unchanging, for the Unity already encompasses all that is and can be.
Democritus accepted most of Parmenides' arguments, except for the idea that change is an illusion. He believed change was real, and if it was not then at least the illusion had to be explained. He thus supported the concept of void, and stated that the universe is made up of many Parmenidean entities that move around in the void. The void is infinite and provides the space in which the atoms can pack or scatter differently. The different possible packings and scatterings within the void make up the shifting outlines and bulk of the objects that organisms feel, see, eat, hear, smell, and taste. While organisms may feel hot or cold, hot and cold actually have no real existence. They are simply sensations produced in organisms by the different packings and scatterings of the atoms in the void that compose the object that organisms sense as being "hot" or "cold".
The work of Democritus survives only in secondhand reports, some of which are unreliable or conflicting. Much of the best evidence of Democritus theory of atomism is reported by Aristotle (384–322 BCE) in his discussions of Democritus and Plato's contrasting views on the types of indivisibles composing the natural world. | 1 | Applied and Interdisciplinary Chemistry |
Methylcyclopentadiene is any of three isomeric cyclic dialkenes with the formula CMeH (Me = CH). These isomers are the organic precursor to the methylcyclopentadienyl ligand (CHMe, often denoted as Cp′), commonly found in organometallic chemistry.
As with cyclopentadiene, methylcyclopentadiene is prepared by thermal cracking of its Diels–Alder dimer, followed by distillation for removal of cyclopentadiene, a common impurity. | 0 | Theoretical and Fundamental Chemistry |
Ribulose 1,5-bisphosphate (RuBP) is an organic substance that is involved in photosynthesis, notably as the principal acceptor in plants. It is a colourless anion, a double phosphate ester of the ketopentose (ketone-containing sugar with five carbon atoms) called ribulose. Salts of RuBP can be isolated, but its crucial biological function happens in solution. RuBP occurs not only in plants but in all domains of life, including Archaea, Bacteria, and Eukarya. | 0 | Theoretical and Fundamental Chemistry |
Robert Bunsen invented the now-famous Bunsen burner in 1855, which was useful in flame tests due to its non-luminous flame that did not disrupt the colors emitted by the test materials. The Bunsen burner, combined with a prism (filtering the color interference of contaminants), led to the creation of the spectroscope, capable of emitting the spectral emission of various elements. In 1860, the unexpected appearance of sky-blue and dark red was observed in spectral emissions by Robert Bunsen and Gustav Kirchhoff, leading to the discovery of two alkali metals, caesium (sky-blue) and rubidium (dark red). Today, this low-cost method is used in secondary education to teach students to detect metals in samples qualitatively. | 1 | Applied and Interdisciplinary Chemistry |
Recently, preliminary results reported SNPs as important components of the epigenetic program in organisms. Moreover, cosmopolitan studies in European and South Asiatic populations have revealed the influence of SNPs in the methylation of specific CpG sites. In addition, meQTL enrichment analysis using GWAS database, demonstrated that those associations are important toward the prediction of biological traits. | 1 | Applied and Interdisciplinary Chemistry |
The pneumatic barrier consists of a perforated pipe and a compressed air source. Air escaping from the pipe provides a "hump" of rising water and air which contains the oil spill. Anchors to keep the pipe in a particular spot are helpful. In case of a density current due to salinity differences the barrier mixes the salt water, but also slows down the speed of the density current. | 1 | Applied and Interdisciplinary Chemistry |
For a long time, cyanobacteria were considered incapable of performing non-photochemical quenching (NPQ) as a photoprotective mechanism, relying instead on a mechanism of energy redistribution between the two photosynthetic reaction centers, PSII and PSI, known as "state transitions".
OCP is found in a majority of cyanobacterial genomes, with remarkable conservation of its amino acid sequence, implying evolutionary constraints to preserve an important function. Mutant cells engineered to lack OCP photobleach under high light and become photoinhibited more rapidly under fluctuating light. Under nutrient stress conditions, which are expected to be norm in marine environments, photoprotective mechanisms such as OCP become important even at lower irradiances.
This protein is not found in chloroplasts, and appears to be specific to cyanobacteria. | 0 | Theoretical and Fundamental Chemistry |
RACE can provide the sequence of an RNA transcript from a small known sequence within the transcript to the 5 end (5 RACE-PCR) or 3 end (3 RACE-PCR) of the RNA. This technique is sometimes called one-sided PCR or anchored PCR.
The first step in RACE is to use reverse transcription to produce a cDNA copy of a region of the RNA transcript. In this process, an unknown end portion of a transcript is copied using a known sequence from the center of the transcript. The copied region is bounded by the known sequence, at either the 5 or 3 end.
The protocols for 5 or 3 RACES differ slightly. 5 RACE-PCR begins using mRNA as a template for a first round of cDNA synthesis (or reverse transcription) reaction using an anti-sense (reverse) oligonucleotide primer that recognizes a known sequence in the middle of the gene of interest; the primer is called a gene specific primer (GSP). The primer binds to the mRNA, and the enzyme reverse transcriptase adds base pairs to the 3 end of the primer to generate a specific single-stranded cDNA product; this is the reverse complement of the mRNA. Following cDNA synthesis, the enzyme terminal deoxynucleotidyl transferase (TdT) is used to add a string of identical nucleotides, known as a homopolymeric tail, to the 3 end of the cDNA. (There are some other ways to add the 3-terminal sequence for the first strand of the de novo cDNA synthesis which are much more efficient than homopolymeric tailing, but the sense of the method remains the same).
PCR is then carried out, which uses a second anti-sense gene specific primer (GSP2) that binds to the known sequence, and a sense (forward) universal primer (UP) that binds the homopolymeric tail added to the 3 ends of the cDNAs to amplify a cDNA product from the 5 end.
3 RACE-PCR uses the natural polyA tail that exists at the 3 end of all eukaryotic mRNAs for priming during reverse transcription, so this method does not require the addition of nucleotides by TdT. cDNAs are generated using an Oligo-dT-adaptor primer (a primer with a short sequence of deoxy-thymine nucleotides) that complements the polyA stretch and adds a special adaptor sequence to the 5 end of each cDNA. PCR is then used to amplify 3 cDNA from a known region using a sense GSP, and an anti-sense primer complementary to the adaptor sequence. | 1 | Applied and Interdisciplinary Chemistry |
Bracken is known to have various biological effects, such as carcinogenicity and its well-defined syndromes in livestock and laboratory animals. Ptaquiloside is proved to be responsible for several of these biological effects, some of which are species specific. | 0 | Theoretical and Fundamental Chemistry |
Adverse effects of drospirenone alone occurring in more than 1% of women may include unscheduled menstrual bleeding (breakthrough or intracyclic) (40.3–64.4%), acne (3.8%), metrorrhagia (2.8%), headache (2.7%), breast pain (2.2%), weight gain (1.9%), dysmenorrhea (1.9%), nausea (1.8%), vaginal hemorrhage (1.7%), decreased libido (1.3%), breast tenderness (1.2%), and irregular menstruation (1.2%). | 0 | Theoretical and Fundamental Chemistry |
Surprisal analysis is an information-theoretical analysis technique that integrates and applies principles of thermodynamics and maximal entropy. Surprisal analysis is capable of relating the underlying microscopic properties to the macroscopic bulk properties of a system. It has already been applied to a spectrum of disciplines including engineering, physics, chemistry and biomedical engineering. Recently, it has been extended to characterize the state of living cells, specifically monitoring and characterizing biological processes in real time using transcriptional data. | 0 | Theoretical and Fundamental Chemistry |
Typically ranging 1–20 minutes for a broad survey scan that measures the amount of all detectable elements, typically 1–15 minutes for high resolution scan that reveal chemical state differences (for a high signal/noise ratio for count area result often requires multiple sweeps of the region of interest), 1–4 hours for a depth profile that measures 4–5 elements as a function of etched depth (this process time can vary the most as many factors will play a role). The time to complete a measurement is generally dependent on the brilliance of the X-ray source. | 0 | Theoretical and Fundamental Chemistry |
In stereochemistry, macrocyclic stereocontrol refers to the directed outcome of a given intermolecular or intramolecular chemical reaction that is governed by the conformational preference of a macrocycle (a molecule containing a ring of 8 or more atoms). | 0 | Theoretical and Fundamental Chemistry |
The Krische allylation involves “transfer hydrogenative” carbon-carbon bond formations. In a series of papers published in the early 2000s, Krische and coworkers demonstrated that allenes, dienes, and allyl acetates could be converted to transient allylmetal nucleophiles via hydrogenation, transfer hydrogenation or hydrogen auto-transfer. This strategy for enantioselective carbonyl allylation avoids preformed organometallic reagents or metallic reductants. A remarkable feature of these reactions is the ability to conduct carbonyl allylation from the alcohol oxidation state. Due to a kinetic preference for primary alcohol dehydrogenation, diols containing both primary and secondary alcohols undergo site-selective carbonyl allylation at the primary alcohol without the need for protecting groups. Additionally, by using alcohol reactants, the use of chiral α-stereogenic aldehydes, which are prone to racemization, can be avoided.
The excellent functional group compatibility of the Krische allylation combined with the tractability of the allyl acetate pronucleophiles enables the use of allyl donors bearing highly complex nitrogen-rich substituents.
The figure below shows some of the different allyl donors that have been used in the Krische allylation. These methods are summarized in the review literature. | 0 | Theoretical and Fundamental Chemistry |
According to the description of an atom interacting with the electromagnetic field, the absorption of light by the atom depends on the frequency of the incident photons. More precisely, the absorption is characterized by a Lorentzian of width Γ/2 (for reference, for common rubidium D-line transitions). If we have a cell of atomic vapour at room temperature, then the distribution of velocity will follow a Maxwell–Boltzmann distribution
where is the number of atoms, is the Boltzmann constant, and is the mass of the atom. According to the Doppler effect formula in the case of non-relativistic speeds,
where is the frequency of the atomic transition when the atom is at rest (the one which is being probed). The value of as a function of and can be inserted in the distribution of velocities. The distribution of absorption as a function of the pulsation will therefore be proportional to a Gaussian with full width at half maximum
For a rubidium atom at room temperature,
Therefore, without any special trick in the experimental setup probing the maximum of absorption of an atomic vapour, the uncertainty of the measurement will be limited by the Doppler broadening and not by the fundamental width of the resonance. | 0 | Theoretical and Fundamental Chemistry |
The cross-flow or tangential fan, sometimes known as a tubular fan, was patented in 1893 by Paul Mortier, and is used extensively in heating, ventilation, and air conditioning (HVAC), especially in ductless split air conditioners. The fan is usually long relative to its diameter, so the flow remains approximately two-dimensional away from the ends. The cross-flow fan uses an impeller with forward-curved blades, placed in a housing consisting of a rear wall and a vortex wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice.
The flow within a cross-flow fan may be broken up into three distinct regions: a vortex region near the fan discharge, called an eccentric vortex, the through-flow region, and a paddling region directly opposite. Both the vortex and paddling regions are dissipative, and as a result, only a portion of the impeller imparts usable work on the flow. The cross-flow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the crossflow fan in HVAC comes from its compactness, shape, quiet operation, and ability to provide a high pressure coefficient. Effectively a rectangular fan in terms of inlet and outlet geometry, the diameter readily scales to fit the available space, and the length is adjustable to meet flow rate requirements for the particular application.
Common household tower fans are also cross-flow fans. Much of the early work focused on developing the cross-flow fan for both high- and low-flow-rate conditions and resulted in numerous patents. Key contributions were made by Coester, Ilberg and Sadeh, Porter and Markland, and Eck. One interesting phenomenon particular to the cross-flow fan is that, as the blades rotate, the local air incidence angle changes. The result is that in certain positions the blades act as compressors (pressure increase), while at other azimuthal locations the blades act as turbines (pressure decrease).
Since the flow both enters and exits the impeller radially, the crossflow fan has been studied and prototyped for potential aircraft applications. Due to the two-dimensional nature of the flow, the fan can be integrated into a wing for use in both thrust production and boundary-layer control. A configuration that utilizes a crossflow fan is located at the wing leading edge is the FanWing design concept initially developed around 1997 and under development by a company of the same name. This design creates lift by deflecting the wake downward due to the rotational direction of the fan, causing a large Magnus force, similar to a spinning leading-edge cylinder. Another configuration utilizing a crossflow fan for thrust and flow control is the propulsive wing, another experimental concept prototype initially developed in the 1990s and 2000s. In this design, the crossflow fan is placed near the trailing edge of a thick wing and draws the air of the wing's suction (top) surface. By doing this, the propulsive wing is nearly stall-free, even at extremely high angles of attack, producing very high lift. However, the fanwing and propulsive wing concepts remain experimental and have only been used for unmanned prototypes.
A cross-flow fan is a centrifugal fan in which the air flows straight through the fan instead of at a right angle. The rotor of a cross-flow fan is covered to create a pressure differential. Cross-flow fans are made to have a double circular arc rear wall with a thick vortex wall that decreases in radial gap. The gap decreases in the direction of the fans impeller rotation. The rear wall has a log-spiral profile while the vortex stabilizer is a horizontal thin wall with rounded edge. The resultant pressure difference allows air to flow straight through the fan, even though the fan blades counter the flow of air on one side of the rotation. Cross-flow fans give airflow along the entire width of the fan; however, they are noisier than ordinary centrifugal fans. Cross-flow fans are often used in ductless air conditioners, air doors, in some types of laptop coolers, in automobile ventilation systems, and for cooling in medium-sized equipment such as photocopiers. | 0 | Theoretical and Fundamental Chemistry |
The speed of sound in a plasma for the common case that the electrons are hotter than the ions (but not too much hotter) is given by the formula (see here)
where
* m is the ion mass;
* μ is the ratio of ion mass to proton mass ;
* T is the electron temperature;
* Z is the charge state;
* k is Boltzmann constant;
* γ is the adiabatic index.
In contrast to a gas, the pressure and the density are provided by separate species: the pressure by the electrons and the density by the ions. The two are coupled through a fluctuating electric field. | 1 | Applied and Interdisciplinary Chemistry |
The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes. Thus, for example, fumaroles from the Laguna Caliente crater of Poás Volcano create extremely high amounts of acid rain and fog, with acidity as high as a pH of 2, clearing an area of any vegetation and frequently causing irritation to the eyes and lungs of inhabitants in nearby settlements. Acid-producing gasses are also created by biological processes that occur on the land, in wetlands, and in the oceans. The major biological source of sulfur compounds is dimethyl sulfide.
Nitric acid in rainwater is an important source of fixed nitrogen for plant life, and is also produced by electrical activity in the atmosphere such as lightning.
Acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe. | 1 | Applied and Interdisciplinary Chemistry |
Flotation processes are described in ancient Greek and Persian literature. During the late 19th century, the process basics were discovered through a slow evolutionary phase. During the first decade of the 20th century, a more rapid investigation of oils, froths, and agitation led to proven workplace applications, especially in Broken Hill, Australia, that brought the technological innovation known as “froth flotation.” During the early 20th century, froth flotation revolutionized mineral processing.
Initially, naturally occurring chemicals such as fatty acids and oils were used as flotation reagents in large quantities to increase the hydrophobicity of the valuable minerals. Since then, the process has been adapted and applied to a wide variety of materials to be separated, and additional collector agents, including surfactants and synthetic compounds have been adopted for various applications. | 1 | Applied and Interdisciplinary Chemistry |
Life That Glows (also known as David Attenborough’s Light on Earth) is a 2016 British nature documentary programme made for BBC Television, first shown in the UK on BBC Two on 9 May 2016. The programme is presented and narrated by Sir David Attenborough.
Life That Glows depicts the biology and ecology of bioluminescent organisms, that is, organisms capable of creating light. The programme features fireflies, who use light as a means of sexual attraction, luminous fungi, luminous marine bacteria responsible for the Milky seas effect, the flashlight fish, the aposematism of the Sierra luminous millipede, earthworms, and the bioluminescent tides created by blooms of dinoflagellates in Tasmania, as well as dolphins swimming in the bloom in the Sea of Cortez, the defensive flashes of brittle stars and ostracods, sexual attraction in ostracods, prey attraction by luminous click beetles in Cerrado, Brazil and Arachnocampa gnats in New Zealand.
The programme then introduces many luminous deep sea animals, including the vampire squid, the polychaete worm Tomopteris that generates yellow light, the jellyfish Atolla, the comb jelly Beroe, the viper fish, pyrosomes, a dragonfish, and the polychaete worm Flota. Next, the programme discusses specialised adaptations in the eyes of particular animals to see bioluminescence, such as the barreleye fish and the cock-eyed squid. Lastly, the programme features the mass spawning event of the firefly squid in Japan. | 1 | Applied and Interdisciplinary Chemistry |
NMR spectroscopy is often the method of choice for monitoring reaction progress, where substrate consumption and/or product formation may be observed over time from the change of peak integration relative to a non-reactive standard. From the concentration data, the rate of reaction over time may be obtained by taking the derivative of a polynomial fit to the experimental curve. Reaction progress NMR may be classified as an integral technique as the primary data collected are proportional to concentration vs. time. While this technique is extremely convenient for clearly defined systems with distinctive, isolated product and/or reactant peaks, it has the drawback of requiring a homogeneous system amenable to reaction in an NMR tube. While NMR observation may allow for the identification of a reaction intermediates, the presence of any given species over the course of the reaction does not necessarily implicate it in a productive process. Reaction progress NMR may, however, often be run at variable temperature, allowing the rate of reaction to be adjusted to a level convenient for observation. Examples of utilization of reaction progress NMR abound, with notable examples including investigation of Buchwald–Hartwig amination (One might note that considerable debate surrounded the best approach to mechanistic development of the Buchwald-Hartwig amination as indicated by a number of contradictory and competing reports published over a short period of time. See the designated article and references therein.) | 0 | Theoretical and Fundamental Chemistry |
The length of the multiple conjugated double bonds determines their color and photophysics. After absorbing a photon, the carotenoid transfers its excited electron to chlorophyll for use in photosynthesis. Upon absorption of light, carotenoids transfer excitation energy to and from chlorophyll. The singlet-singlet energy transfer is a lower energy state transfer and is used during photosynthesis. The triplet-triplet transfer is a higher energy state and is essential in photoprotection. Light produces damaging species during photosynthesis, with the most damaging being reactive oxygen species (ROS). As these high energy ROS are produced in the chlorophyll the energy is transferred to the carotenoid’s polyene tail and undergoes a series of reactions in which electrons are moved between the carotenoid bonds in order to find the most balanced (lowest energy) state for the carotenoid.
Carotenoids defend plants against singlet oxygen, by both energy transfer and by chemical reactions. They also protect plants by quenching triplet chlorophyll. By protecting lipids from free-radical damage, which generate charged lipid peroxides and other oxidised derivatives, carotenoids support crystalline architecture and hydrophobicity of lipoproteins and cellular lipid structures, hence oxygen solubility and its diffusion therein. | 0 | Theoretical and Fundamental Chemistry |
After Chadwick discovered the neutron in 1932, Irène Curie and Frédéric Joliot irradiated aluminium foil with alpha particles, and found that this results in a short-lived radioactive isotope of phosphorus. They noted that positron emission continued after the neutron emissions ceased. Not only had they discovered a new form of radioactive decay, they had transmuted an element into a hitherto unknown radioactive isotope of another, thereby inducing radioactivity where there had been none before. Radiochemistry was now no longer confined to certain heavy elements, but extended to the entire periodic table. Chadwick noted that being electrically neutral, neutrons could penetrate the atomic nucleus more easily than protons or alpha particles. Enrico Fermi and his colleagues in Rome picked up on this idea, and began irradiating elements with neutrons.
The radioactive displacement law of Fajans and Soddy said that beta decay causes isotopes to move one element up on the periodic table, and alpha decay causes them to move two down. When Fermis group bombarded uranium atoms with neutrons, they found a complex mix of half lives. Fermi therefore concluded that the new elements with atomic numbers greater than 92 (known as transuranium elements) had been created. Meitner and Hahn had not collaborated for many years, but Meitner was eager to investigate Fermis results. Hahn, initially, was not, but he changed his mind when Aristid von Grosse suggested that what Fermi had found was an isotope of protactinium. "The only question", Hahn later wrote, "seemed to be whether Fermi had found isotopes of transuranium elements, or isotopes of the next-lower element, protactinium. At that time Lise Meitner and I decided to repeat Fermi's experiments in order to find out whether the 13-minute isotope was a protactinium isotope or not. It was a logical decision, having been the discoverers of protactinium."
Between 1934 and 1938, Hahn, Meitner, and Strassmann found a great number of radioactive transmutation products, all of which they regarded as transuranic. At that time, the existence of actinides was not yet established, and uranium was wrongly believed to be a group 6 element similar to tungsten. It followed that the first transuranic elements would be similar to group 7 to 10 elements, i.e. rhenium and platinoids. They established the presence of multiple isotopes of at least four such elements, and (mistakenly) identified them as elements with atomic numbers 93 through 96. They were the first scientists to measure the 23-minute half life of the synthetic radioisotope uranium-239 and to establish chemically that it was an isotope of uranium, but with their weak neutron sources they were unable to continue this work to its logical conclusion and identify the real element 93. They identified ten different half lives, with varying degrees of certainty. To account for them, Meitner had to hypothesise a new class of reaction and the alpha decay of uranium, neither of which had ever been reported before, and for which physical evidence was lacking. Hahn and Strassmann refined their chemical procedures, while Meitner devised new experiments to shine more light on the reaction processes.
In May 1937, Hahn and Meitner issued parallel reports, one in Zeitschrift für Physik with Meitner as the first author, and one in Chemische Berichte with Hahn as the first author. Hahn concluded his by stating emphatically: Vor allem steht ihre chemische Verschiedenheit von allen bisher bekannten Elementen außerhalb jeder Diskussion ("Above all, their chemical distinction from all previously known elements needs no further discussion"); Meitner was increasingly uncertain. She considered the possibility that the reactions were from different isotopes of uranium; three were known: uranium-238, uranium-235 and uranium-234. However, when she calculated the neutron cross section, it was too large to be anything other than the most abundant isotope, uranium-238, and concluded that it must be another case of the nuclear isomerism that Hahn had discovered in protactinium years before. She therefore ended her report on a very different note to Hahn, reporting that: "The process must be neutron capture by uranium-238, which leads to three isomeric nuclei of uranium-239. This result is very difficult to reconcile with current concepts of the nucleus." | 1 | Applied and Interdisciplinary Chemistry |
An elementary reaction is a chemical reaction in which one or more chemical species react directly to form products in a single reaction step and with a single transition state. In practice, a reaction is assumed to be elementary if no reaction intermediates have been detected or need to be postulated to describe the reaction on a molecular scale. An apparently elementary reaction may be in fact a stepwise reaction, i.e. a complicated sequence of chemical reactions, with reaction intermediates of variable lifetimes.
In a unimolecular elementary reaction, a molecule dissociates or isomerises to form the products(s)
At constant temperature, the rate of such a reaction is proportional to the concentration of the species
In a bimolecular elementary reaction, two atoms, molecules, ions or radicals, and , react together to form the product(s)
The rate of such a reaction, at constant temperature, is proportional to the product of the concentrations of the species and
The rate expression for an elementary bimolecular reaction is sometimes referred to as the law of mass action as it was first proposed by Guldberg and Waage in 1864. An example of this type of reaction is a cycloaddition reaction.
This rate expression can be derived from first principles by using collision theory for ideal gases. For the case of dilute fluids equivalent results have been obtained from simple probabilistic arguments.
According to collision theory the probability of three chemical species reacting simultaneously with each other in a termolecular elementary reaction is negligible. Hence such termolecular reactions are commonly referred as non-elementary reactions and can be broken down into a more fundamental set of bimolecular reactions, in agreement with the law of mass action. It is not always possible to derive overall reaction schemes, but solutions based on rate equations are often possible in terms of steady-state or Michaelis-Menten approximations. | 0 | Theoretical and Fundamental Chemistry |
Eriochrome Black T is a complexometric indicator that is used in complexometric titrations, e.g. in the water hardness determination process. It is an azo dye. Eriochrome is a trademark of Huntsman Petrochemical, LLC.
In its deprotonated form, Eriochrome Black T is blue. It turns red when it forms a complex with calcium, magnesium, or other metal ions. | 0 | Theoretical and Fundamental Chemistry |
Replication-defective vectors always contain a "transfer construct". The transfer construct carries the gene to be transduced or "transgene". The transfer construct also carries the sequences which are necessary for the general functioning of the viral genome: packaging sequence, repeats for replication and, when needed, priming of reverse transcription. These are denominated cis-acting elements, because they need to be on the same piece of DNA as the viral genome and the gene of interest. Trans-acting elements are viral elements, which can be encoded on a different DNA molecule. For example, the viral structural proteins can be expressed from a different genetic element than the viral genome. | 1 | Applied and Interdisciplinary Chemistry |
The curie (symbol Ci) is a non-SI unit of radioactivity originally defined in 1910. According to a notice in Nature at the time, it was to be named in honour of Pierre Curie, but was considered at least by some to be in honour of Marie Curie as well, and is in later literature considered to be named for both.
It was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium (element)", but is currently defined as 1 Ci = decays per second after more accurate measurements of the activity of Ra (which has a specific activity of ).
In 1975 the General Conference on Weights and Measures gave the becquerel (Bq), defined as one nuclear decay per second, official status as the SI unit of activity.
Therefore:
: 1 Ci = = 37 GBq
and
: 1 Bq ≅ ≅ 27 pCi
While its continued use is discouraged by the National Institute of Standards and Technology (NIST) and other bodies, the curie is still widely used throughout government, industry and medicine in the United States and in other countries.
At the 1910 meeting, which originally defined the curie, it was proposed to make it equivalent to 10 nanograms of radium (a practical amount). But Marie Curie, after initially accepting this, changed her mind and insisted on one gram of radium. According to Bertram Boltwood, Marie Curie thought that "the use of the name curie for so infinitesimally small [a] quantity of anything was altogether inappropriate".
The power emitted in radioactive decay corresponding to one curie can be calculated by multiplying the decay energy by approximately 5.93 mW / MeV.
A radiotherapy machine may have roughly 1000 Ci of a radioisotope such as caesium-137 or cobalt-60. This quantity of radioactivity can produce serious health effects with only a few minutes of close-range, unshielded exposure.
Radioactive decay can lead to the emission of particulate radiation or electromagnetic radiation. Ingesting even small quantities of some particulate emitting radionuclides may be fatal. For example, the median lethal dose (LD-50) for ingested polonium-210 is 240 μCi; about 53.5 nanograms. However, millicurie quantities of electromagnetic emitting radionuclides are routinely used in nuclear medicine.
The typical human body contains roughly 0.1 μCi (14 mg) of naturally occurring potassium-40. A human body containing of carbon (see Composition of the human body) would also have about 24 nanograms or 0.1 μCi of carbon-14. Together, these would result in a total of approximately 0.2 μCi or 7400 decays per second inside the person's body (mostly from beta decay but some from gamma decay). | 0 | Theoretical and Fundamental Chemistry |
Often in informal, non-technical language, concentration is described in a qualitative way, through the use of adjectives such as "dilute" for solutions of relatively low concentration and "concentrated" for solutions of relatively high concentration. To concentrate a solution, one must add more solute (for example, alcohol), or reduce the amount of solvent (for example, water). By contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute. Unless two substances are miscible, there exists a concentration at which no further solute will dissolve in a solution. At this point, the solution is said to be saturated. If additional solute is added to a saturated solution, it will not dissolve, except in certain circumstances, when supersaturation may occur. Instead, phase separation will occur, leading to coexisting phases, either completely separated or mixed as a suspension. The point of saturation depends on many variables, such as ambient temperature and the precise chemical nature of the solvent and solute.
Concentrations are often called levels, reflecting the mental schema of levels on the vertical axis of a graph, which can be high or low (for example, "high serum levels of bilirubin" are concentrations of bilirubin in the blood serum that are greater than normal). | 0 | Theoretical and Fundamental Chemistry |
Although the development of transparent wood composites is still at a lab-scale and prototype level, their potential for energy efficiency and operational savings in the building industry are very promising. An essential advantage with transparent wood is its combination of structural and functional performance for load-bearing structures that combine optical, heat-shielding, or magnetic functionalities. Transparent wood is also researched for potential use for touch-sensitive surfaces. | 0 | Theoretical and Fundamental Chemistry |
Arterial spin labeling utilizes the water molecules circulating with the brain, and using a radiofrequency pulse, tracks the blood water as it circulates throughout the brain. After a period of time in microseconds (enough to allow the blood to circulate through the brain), a label image is captured. A control image is also acquired before the labeling of the blood water. A subtraction technique gives a measurement of perfusion. In order to increase SNR, collections of control and label images can be averaged. There are also other specifications in the MRI that can increase SNR, like the amount of head coils of the MRI, or a stronger field strength (3 T is standard, but 1.5 T is satisfactory). In order to properly scale the perfusion values into cerebral blood flow units (CBF, ml/100g/1 min), a separate proton density map with the same parameters (but longer TR to fully relax the blood spins) is recommended to be acquired as well. Alternatively, the average control image can be used to generate CBF, which is the case for Phillips pCASL readouts. Usually background suppression is also applied to increase the SNR. Due to the different variations of each implementations, it is recommended that a large multi-scanner study should design a protocol minimizing the variety of readout methods used by each scanner.
One study has shown that although there are voxel differences when different readout methods are used, average gray matter CBF are still comparable. Differences in SNR are apparent when each voxel compared, but collectively are negligible. | 0 | Theoretical and Fundamental Chemistry |
Foams are commonly made by injecting a gas or mixing a foaming agent into molten metal. Molten metal can be foamed by creating gas bubbles in the material. Normally, bubbles in molten metal are highly buoyant in the high-density liquid and rise quickly to the surface. This rise can be slowed by increasing the viscosity of the molten metal by adding ceramic powders or alloying elements to form stabilizing particles in the molten metal, or by other means. Molten metal can be foamed in one of three ways:
* by injecting gas into the liquid metal from an external source;
* by causing gas formation in the liquid by admixing gas-releasing blowing agents with the molten metal;
* by causing the precipitation of gas that was previously dissolved in the molten metal.
To stabilize the molten metal bubbles, high temperature foaming agents (nano- or micrometer- sized solid particles) are required. The size of the pores, or cells, is usually 1 to 8 mm. When foaming or blowing agents are used, they are mixed with the powdered metal before it is melted. This is the so-called "powder route" of foaming, and it is probably the most established (from an industrial standpoint). After metal (e.g. aluminium) powders and foaming agent (e.g. TiH) have been mixed, they are compressed into a compact, solid precursor, which can be available in the form of a billet, a sheet, or a wire. Production of precursors can be done by a combination of materials forming processes, such as powder pressing, extrusion (direct or conform) and flat rolling. | 0 | Theoretical and Fundamental Chemistry |
When a solution of a substance in one solvent is brought into equilibrium with a second solvent that is immiscible with the first solvent, the dissolved substance may be partitioned between the two solvents. The ratio of concentrations in the two solvents is known as a partition coefficient or distribution coefficient. The partition coefficient is defined as the ratio of the analytical concentrations of the solute in the two phases. By convention the value is reported in logarithmic form.
The partition coefficient is defined at a specified temperature and, if applicable, pH of the aqueous phase. Partition coefficients are very important in pharmacology because they determine the extent to which a substance can pass from the blood (an aqueous solution) through a cell wall which is like an organic solvent. They are usually measured using water and octanol as the two solvents, yielding the so-called octanol-water partition coefficient. Many pharmaceutical compounds are weak acids or weak bases. Such a compound may exist with a different extent of protonation depending on pH and the acid dissociation constant. Because the organic phase has a low dielectric constant the species with no electrical charge will be the most likely one to pass from the aqueous phase to the organic phase. Even at pH 7–7.2, the range of biological pH values, the aqueous phase may support an equilibrium between more than one protonated form. log p is determined from the analytical concentration of the substance in the aqueous phase, that is, the sum of the concentration of the different species in equilibrium.
Solvent extraction is used extensively in separation and purification processes. In its simplest form a reaction is performed in an organic solvent and unwanted by-products are removed by extraction into water at a particular pH.
A metal ion may be extracted from an aqueous phase into an organic phase in which the salt is not soluble, by adding a ligand. The ligand, L, forms a complex with the metal ion, M, [ML] which has a strongly hydrophobic outer surface. If the complex has no electrical charge it will be extracted relatively easily into the organic phase. If the complex is charged, it is extracted as an ion pair. The additional ligand is not always required. For example, uranyl nitrate, UO(NO), is soluble in diethyl ether because the solvent itself acts as a ligand. This property was used in the past for separating uranium from other metals whose salts are not soluble in ether. Currently extraction into kerosene is preferred, using a ligand such as tri-n-butyl phosphate, TBP. In the PUREX process, which is commonly used in nuclear reprocessing, uranium(VI) is extracted from strong nitric acid as the electrically neutral complex [UO(TBP)(NO)]. The strong nitric acid provides a high concentration of nitrate ions which pushes the equilibrium in favour of the weak nitrato complex. Uranium is recovered by back-extraction (stripping) into weak nitric acid. Plutonium(IV) forms a similar complex, [PuO(TBP)(NO)] and the plutonium in this complex can be reduced to separate it from uranium.
Another important application of solvent extraction is in the separation of the lanthanoids. This process also uses TBP and the complexes are extracted into kerosene. Separation is achieved because the stability constant for the formation of the TBP complex increases as the size of the lanthanoid ion decreases.
An instance of ion-pair extraction is in the use of a ligand to enable oxidation by potassium permanganate, KMnO, in an organic solvent. KMnO is not soluble in organic solvents. When a ligand, such as a crown ether is added to an aqueous solution of KMnO, it forms a hydrophobic complex with the potassium cation which allows the uncharged ion pair [KL][MnO] to be extracted into the organic solvent. See also: phase-transfer catalysis.
More complex partitioning problems (i.e. 3 or more phases present) can sometimes be handled with a fugacity capacity approach. | 0 | Theoretical and Fundamental Chemistry |
Examples of Living Machines are mechanical composters for industrial kitchens, effective microorganisms as fertilizer for agricultural purposes, and Integrated Biotectural systems in landscaping and architecture like Earthships or the IBTS Greenhouse.
Components like tomato plants (for more water purification) and fish (for food) have been part of the living, ecosystem-like designs. The theory does not limit the size of the system, or the amount of species. One design optimum is a natural ecosystem which is designed for a special purpose like a sewage treating wetland in a suitable ecosystem for the locality. Another optimum is an economically viable system returning profit for the investor. The practice of permaculture is one example for a compromise between the two optimum design points.
The scale of Living Machine systems ranges from the individual building to community-scale public works. Some of the earliest Living Machines were used to treat domestic wastewater in small, ecologically-conscious villages, such as Findhorn Community in Scotland,. The latest-generation Tidal Flow Wetland Living Machines are being used in major urban office buildings, military bases, housing developments, resorts and institutional campuses. | 1 | Applied and Interdisciplinary Chemistry |
The term backscatter in photography refers to light from a flash or strobe reflecting back from particles in the lenss field of view causing specks of light to appear in the photo. This gives rise to what are sometimes referred to as orb artifacts'. Photographic backscatter can result from snowflakes, rain or mist, or airborne dust. Due to the size limitations of the modern compact and ultra-compact cameras, especially digital cameras, the distance between the lens and the built-in flash has decreased, thereby decreasing the angle of light reflection to the lens and increasing the likelihood of light reflection off normally sub-visible particles. Hence, the orb artifact is commonplace with small digital or film camera photographs. | 0 | Theoretical and Fundamental Chemistry |
The body of a ChemFET is generally found to be robust. However, the unavoidable requirement for a separate reference electrode makes the system more bulky overall and potentially more fragile. | 0 | Theoretical and Fundamental Chemistry |
The journal is abstracted and indexed in:
According to the Journal Citation Reports, the journal has a 2021 impact factor of 4.290. | 0 | Theoretical and Fundamental Chemistry |
Many UVGI systems use UV wavelengths that can be harmful to humans, resulting in both immediate and long-term effects. Acute impacts on the eyes and skin can include conditions such as photokeratitis (often termed "snow blindness") and erythema (reddening of the skin), while chronic exposure may heighten the risk of skin cancer.
However, the safety and effects of UV vary extensively by wavelength, implying that not all UVGI systems pose the same level of hazards. Humans typically encounter UV light in the form of solar UV, which comprises significant portions of UV-A and UV-B, but excludes UV-C. The UV-B band, able to penetrate deep into living, replicating tissue, is recognized as the most damaging and carcinogenic.
Many standard UVGI systems, such as low-pressure mercury (LP-Hg) lamps, produce broad-band emissions in the UV-C range and also peaks in the UV-B band. This often makes it challenging to attribute damaging effects to a specific wavelength. Nevertheless, longer wavelengths in the UV-C band can cause conditions like photokeratitis and erythema. Hence, many UVGI systems are used in settings where direct human exposure is limited, such as with upper-room UVGI air cleaners and water disinfection systems.
Precautions are commonly implemented to protect users of these UVGI systems, including:
* Warning labels: Labels alert users to the dangers of UV light.
* Interlocking systems: Shielded systems, such as closed water tanks or air circulation units, often have interlocks that automatically shut off the UV lamps if the system is opened for human access. Clear viewports that block UV-C are also available.
* Personal protective equipment: Most protective eyewear, particularly those compliant with ANSI Z87.1, block UV-C. Similarly, clothing, plastics, and most types of glass (excluding fused silica) effectively impede UV-C.
Since the early 2010s there has been growing interest in the far-UVC wavelengths of 200-235 nm for whole-room exposure. These wavelengths are generally considered safer due to their limited penetration depth caused by increased protein absorption. This feature confines far-UVC exposure to the superficial layers of tissue, such as the outer layer of dead skin (the stratum corneum) and the tear film and surface cells of the cornea. As these tissues do not contain replicating cells, damage to them poses less carcinogenic risk. It has also been demonstrated that far-UVC does not cause erythema or damage to the cornea at levels many times that of solar UV or conventional 254 nm UVGI systems. | 0 | Theoretical and Fundamental Chemistry |
Mongo foot refers to the use of the rider's front foot for pushing. Normally, a skateboarder will feel more comfortable using their back foot to push, while their front foot remains on the board. In the minority case of mongo-footed skateboarders, the opposite is true. Some skateboarders who do not push mongo in their regular stance may still push mongo when riding in switch stance, rather than push with their weaker back foot. Some well-known skaters who change between mongo and normal when pushing switch include Jacob Vance, Stevie Williams, and Eric Koston.
Although its origins remain uncertain, it is widely believed that the term derives from the pejorative use of "mongoloid". | 0 | Theoretical and Fundamental Chemistry |
Animal testing in the research-based pharmaceutical industry has been reduced in recent years both for ethical and cost reasons. However, most research will still involve animal based testing for the need of similarity in anatomy and physiology that is required for diverse product development. | 1 | Applied and Interdisciplinary Chemistry |
With Tamás Turányi, Tomlin is coauthor of the book Analysis of Kinetic Reaction Mechanisms (Springer, 2014). | 0 | Theoretical and Fundamental Chemistry |
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