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Copper technology may date back to the 4th millennium BCE in the Himalaya region.
It is the first element to be discovered in metallurgy,
Copper and its alloys were also used to create copper-bronze images such as Buddhas or Hindu/Mahayana Buddhist deities. Xuanzang also noted that there were copper-bronze Buddha images in Magadha. In Varanasi, each stage of the image manufacturing process is handled by a specialist.
Other metal objects made by Indian artisans include lamps. Copper was also a component in the razors for the tonsure ceremony.
One of the most important sources of history in the Indian subcontinent are the royal records of grants engraved on copper-plate grants (tamra-shasan or tamra-patra). Because copper does not rust or decay, they can survive indefinitely. Collections of archaeological texts from the copper-plates and rock-inscriptions have been compiled and published by the Archaeological Survey of India during the past century. The earliest known copper-plate known as the Sohgaura copper-plate is a Maurya record that mentions famine relief efforts. It is one of the very few pre-Ashoka Brahmi inscriptions in India. | 8 | Metallurgy |
Molecular geometry is the three-dimensional arrangement of the atoms that constitute a molecule. It includes the general shape of the molecule as well as bond lengths, bond angles, torsional angles and any other geometrical parameters that determine the position of each atom.
Molecular geometry influences several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism and biological activity. The angles between bonds that an atom forms depend only weakly on the rest of molecule, i.e. they can be understood as approximately local and hence transferable properties. | 4 | Stereochemistry |
Quinone methides are cross-conjugated rather than aromatic. Nucleophilic addition at the exo-cyclic double bond will result in rearomatisation, making such reactions highly favourable. As a result, quinone methides are excellent, electrophilic Michael acceptors, react quickly with nucleophiles and can be easily reduced. They are able to act as radical scavengers via a similar process, a behaviour exploited by certain polymerisation inhibitors. Quinone methides are more polar than quinones, and therefore more chemically reactive. Simple unhindered quinone methides are short lived reactive intermediates that are not stable enough to be isolated under normal circumstances, they will trimerise in the absence of nucleophiles. Sterically hindered quinone methides can be sufficiently stable to be isolated, with some examples being commercially available. | 0 | Organic Chemistry |
Ideally, the reference set in CAI is composed of highly expressed genes, so that CAI provides an indication of gene expression level under the assumption that there is translational selection to optimize gene sequences according to their expression levels. The rationale for this is dual: highly expressed genes need to compete for resources (i.e. ribosomes) in fast-growing organisms and it makes sense for them to be also more accurately translated. Both hypotheses lead to highly expressed genes using mostly codons for tRNA species that are abundant in the cell. | 1 | Biochemistry |
Generally speaking, there are two distinct mechanistic pathways that lead to C-C bond activation: (a) the β-carbon elimination of metal complexes. In this mechanism, a M–C intermediate and a double bond are formed at the same time; and (b) the direct oxidative addition of C–C bonds into low-valent metal adducts to form a bis(organyl)metal complex. | 0 | Organic Chemistry |
High intensity ultrashort pulse lasers can create ATI features with 20 or more peaks. The photoelectron spectrum of electron energies is continuous since actual light sources contain a spread of energies. | 7 | Physical Chemistry |
In chemistry, metal-catalysed hydroboration is a reaction used in organic synthesis. It is one of several examples of homogeneous catalysis. | 0 | Organic Chemistry |
Some metabolic myopathies involve the under- or over-utilization of the purine nucleotide cycle. Metabolic myopathies cause a low ATP reservoir in muscle cells (ADP > ATP), resulting in exercise-induced excessive AMP buildup in muscle, and subsequent exercise-induced hyperuricemia (myogenic hyperuricemia) through conversion of excessive AMP into uric acid by way of either AMP → adenosine or AMP → IMP.
During strenuous exercise, AMP is created through the use of the adenylate kinase (myokinase) reaction after the phosphagen system has been depleted of creatine phosphate and not enough ATP is being produced yet by other pathways (see above reaction in Occurrence section). In those affected by metabolic myopathies, exercise that normally wouldn't be considered strenuous for healthy people, is however strenuous for them due to their low ATP reservoir in muscle cells. This results in regular use of the myokinase reaction for normal, everyday activities.
Besides the myokinase reaction, a high ATP consumption and low ATP reservoir also increases protein catabolism and salvage of IMP, which results in increased AMP and IMP. These two nucleotides can then enter the purine nucleotide cycle to produce fumarate which will then produce ATP by oxidative phosphorylation. If the purine nucleotide cycle is blocked (such as AMP deaminase deficiency) or if exercise is stopped and increased fumarate production is no longer needed, then the excess nucleotides will be converted into uric acid. | 1 | Biochemistry |
Single-cell transcriptomics uses sequencing techniques similar to single cell genomics or direct detection using fluorescence in situ hybridization. The first step in quantifying the transcriptome is to convert RNA to cDNA using reverse transcriptase so that the contents of the cell can be sequenced using NGS methods as was done in genomics. Once converted, there is not enough cDNA to be sequenced so the same DNA amplification techniques discussed in single cell genomics are applied to the cDNA to make sequencing possible. Alternately, fluorescent compounds attached to RNA hybridization probes are used to identify specific sequences and sequential application of different RNA probes will build up a comprehensive transcriptome. | 1 | Biochemistry |
Propanephosphonic acid anhydride (PPAA, T3P) is an anhydride of propanephosphonic acid. Its structure is a cyclic trimer, with a phosphorus–oxygen core and propyl groups and additional oxygens attached. The chemical is a useful reagent for peptide synthesis reactions, where it activates the carboxylic acid partner for subsequent reaction with amines. It is commercially available as 50 % solution in DMF or ethyl acetate as a slightly yellow mixture. | 0 | Organic Chemistry |
Froth flotation is a process for separating minerals from gangue by exploiting differences in their hydrophobicity. Hydrophobicity differences between valuable minerals and waste gangue are increased through the use of surfactants and wetting agents. The flotation process is used for the separation of a large range of sulfides, carbonates and oxides prior to further refinement. Phosphates and coal are also upgraded (purified) by flotation technology. "Grade-recovery curves" are tools for weighing the trade-off of producing a high grade of concentrate vs cost. These curves only compare the grade-recovery relations of a specific feed grade and feed rate. | 8 | Metallurgy |
More useful generally than the Gilman reagents are the so-called mixed cuprates with the formula [RCuX] and [RCuX]. Such compounds are often prepared by the addition of the organolithium reagent to copper(I) halides and cyanide. These mixed cuprates are more stable and more readily purified. One problem addressed by mixed cuprates is the economical use of the alkyl group. Thus, in some applications, the mixed cuprate has the formula is prepared by combining thienyllithium and cuprous cyanide followed by the organic group to be transferred. In this higher order mixed cuprate, both the cyanide and thienyl groups do not transfer, only the R group does. | 0 | Organic Chemistry |
A non-combustible material is a substance that does not ignite, burn, support combustion, or release flammable vapors when subject to fire or heat, in the form in which it is used and under conditions anticipated. Any solid substance complying with either of two sets of passing criteria listed in Section 8 of ASTM E 136 when the substance is tested in accordance with the procedure specified in ASTM E 136 is considered to be non-combustible. | 7 | Physical Chemistry |
Perovskite solar cells are solar cells that include a perovskite-structured material as the active layer. Most commonly, this is a solution-processed hybrid organic-inorganic tin or lead halide based material. Efficiencies have increased from below 5% at their first usage in 2009 to 25.5% in 2020, making them a very rapidly advancing technology and a hot topic in the solar cell field. Researchers at University of Rochester reported in 2023 that significant further improvements in cell efficiency can be achieved by utilizing Purcell effect.
Perovskite solar cells are also forecast to be extremely cheap to scale up, making them a very attractive option for commercialisation. So far most types of perovskite solar cells have not reached sufficient operational stability to be commercialised, although many research groups are investigating ways to solve this. Energy and environmental sustainability of perovskite solar cells and tandem perovskite are shown to be dependent on the structures. Photonic front contacts for light management can improve the perovskite cells' performance, via enhanced broadband absorption, while allowing better operational stability due to protection against the harmful high-energy (above Visible) radiation. The inclusion of the toxic element lead in the most efficient perovskite solar cells is a potential problem for commercialisation. | 7 | Physical Chemistry |
Ancyronyx, commonly known as spider water beetles or spider riffle beetles, is a genus of aquatic riffle beetles from North America, South Asia, China, and Southeast Asia. They are small beetles with extremely long legs ending in strong claws. Both the adults and the larvae are found underwater in the shallow riffles of streams and rivers, clinging to rocks or submerged wood. They feed on algae and decaying wood tissue. The genus contains twenty-one species, eleven of which are endemic to the Philippines. | 2 | Environmental Chemistry |
Black shales are organic rich, microlaminated sedimentary rocks often associated with bottom water anoxia. This is because anoxia slows the degradation of organic matter, allowing for greater burial in the sediments. Other evidence for anoxic burial of black shale includes the lack of bioturbation, meaning that there were no organisms burrowing into the sediment because there was no oxygen for respiration. There must also be a source of organic matter for burial, generally from production near the oxic surface. Many papers discussing ancient euxinic events use the presence of black shale as a preliminary proxy for anoxic bottom waters, but their presence does not in and of itself indicate euxinia or even strong anoxia. Generally geochemical testing is needed to provide better evidence for conditions. | 9 | Geochemistry |
The model represents individuals as networks of interacting transcriptional regulators. Each individual expresses genes encoding transcription factors. The product of each gene can regulate the expression level of itself and/or the other genes through cis-regulatory elements. The interactions among genes constitute a gene network that is represented by a × regulatory matrix in the model. The elements in matrix R represent the interaction strength. Positive values within the matrix represent the activation of the target gene, while negative ones represent repression. Matrix elements with value 0 indicate the absence of interactions between two genes. | 1 | Biochemistry |
There is an overall 2–3 kcal/mol error using the Benson group-increment theory to calculate the ΔH. The value of each group is estimated on the base of the average ΔΔH° shown above and there will be a dispersion around the average ΔΔH°. Also, it can only be as accurate as the experimental accuracy. That's the derivation of the error, and there is nearly no way to make it more accurate. | 7 | Physical Chemistry |
Heme A differs from heme B in that a methyl side chain at ring position 8 is oxidized to a formyl group and a hydroxyethylfarnesyl group, an isoprenoid chain, has been attached to the vinyl side chain at ring position 2 of the iron tetrapyrrole heme. Heme A is similar to heme o, in that both have this farnesyl addition at position 2 but heme O does not have the formyl group at position 8, still containing the methyl group. The correct structure of heme A, based upon NMR and IR experiments of the reduced, Fe(II) form of the heme, was published in 1975. The structure was confirmed by synthesis of the dimethyl ester of the iron-free form. | 1 | Biochemistry |
* Phase Change Material (PCM) Based Energy Storage Materials and Global Application Examples, Zafer URE M.Sc., C.Eng. MASHRAE [https://www.pcmproducts.net/Building_Temperature_Control.htm HVAC Applications]
* Phase Change Material Based Passive Cooling Systems Design Principal and Global Application Examples, Zafer URE M.Sc., C.Eng. MASHRAE [https://www.pcmproducts.net/Passive_Enclosure_Cooling.htm Passive Cooling Application] | 7 | Physical Chemistry |
Beyond the most common perovskite symmetries (cubic, tetragonal, orthorhombic), a more precise determination leads to a total of 23 different structure types that can be found. These 23 structure can be categorized into 4 different so-called tilt systems that are denoted by their respective Glazer notation.
The notation consists of a letter a/b/c, which describes the rotation around a Cartesian axis and a superscript +/—/0 to denote the rotation with respect to the adjacent layer. A “+” denotes that the rotation of two adjacent layers points in the same direction, whereas a “—” denotes that adjacent layers are rotated in opposite directions. Common examples are aaa, aaa and aaa which are visualized here. | 3 | Analytical Chemistry |
After a WGD, one of the duplicated gene pair is often lost through fractionation; less than 10% of WGD gene pairs have remained in S. cerevisiae genome. A little over half of WGD gene pairs in the glycolysis reaction pathway were retained in post-WGD species, significantly higher than the overall retention rate. This has been associated with an increased ability to metabolize glucose into pyruvate, or higher rate of glycolysis. After glycolysis, pyruvate can either be further broken down by pyruvate decarboxylase (Pdc) or pyruvate dehydrogenase (Pdh). The kinetics of the enzymes are such that when pyruvate concentrations are high, due to a high rate of glycolysis, there is increased flux through Pdc and thus the fermentation pathway. The WGD is believed to have played a beneficial role in the evolution of the Crabtree effect in post-WGD species partially due to this increase in copy number of glycolysis genes. | 1 | Biochemistry |
Multiple displacement amplification (MDA) is a DNA amplification technique. This method can rapidly amplify minute amounts of DNA samples to a reasonable quantity for genomic analysis. The reaction starts by annealing random hexamer primers to the template: DNA synthesis is carried out by a high fidelity enzyme, preferentially Φ29 DNA polymerase. Compared with conventional PCR amplification techniques, MDA does not employ sequence-specific primers but amplifies all DNA, generates larger-sized products with a lower error frequency, and works at a constant temperature. MDA has been actively used in whole genome amplification (WGA) and is a promising method for application to single cell genome sequencing and sequencing-based genetic studies. | 1 | Biochemistry |
In analytical chemistry, argentometry is a type of titration involving the silver(I) ion. Typically, it is used to determine the amount of chloride present in a sample. The sample solution is titrated against a solution of silver nitrate of known concentration. Chloride ions react with silver(I) ions to give the insoluble silver chloride:
: Ag (aq) + Cl (aq) → AgCl (s) (K = 5.88 × 10) | 3 | Analytical Chemistry |
In 2017, two research groups from ETH Zurich and from MIT reported on the creation of an ultracold quantum gas with supersolid properties. The Zurich group placed a Bose–Einstein condensate inside two optical resonators, which enhanced the atomic interactions until they started to spontaneously crystallize and form a solid that maintains the inherent superfluidity of Bose–Einstein condensates. This setting realises a special form of a supersolid, the so-called lattice supersolid, where atoms are pinned to the sites of an externally imposed lattice structure. The MIT group exposed a Bose–Einstein condensate in a double-well potential to light beams that created an effective spin–orbit coupling. The interference between the atoms on the two spin–orbit coupled lattice sites gave rise to a characteristic density modulation.
In 2019, three groups from Stuttgart, Florence, and Innsbruck observed supersolid properties in dipolar Bose–Einstein condensates formed from lanthanide atoms. In these systems, supersolidity emerges directly from the atomic interactions, without the need for an external optical lattice. This facilitated also the direct observation of superfluid flow and hence the definitive proof for the existence of the supersolid state of matter.
In 2021, dysprosium was used to create a 2-dimensional supersolid quantum gas. In 2022, the same team created a supersolid disk in a round trap.
In 2021, confocal cavity quantum electrodynamics with a Bose–Einstein condensate was used to create a supersolid that possesses a key property of solids, vibration. That is, a supersolid was created that possesses lattice phonons with a Goldstone mode dispersion exhibiting a 16 cm/s speed of sound. | 7 | Physical Chemistry |
Standard reduction potentials in aqueous solution are also a useful way of predicting the non-aqueous chemistry of the metals involved. Thus, metals with high negative potentials, such as sodium, or potassium, will ignite in air, forming the respective oxides. These fires cannot be extinguished with water, which also react with the metals involved to give hydrogen, which is itself explosive. Noble metals, in contrast, are disinclined to react with oxygen and, for that reason (as well as their scarcity) have been valued for millennia, and used in jewellery and coins.
The adjacent table lists standard reduction potential in volts; electronegativity (revised Pauling); and electron affinity values (kJ/mol), for some metals and metalloids.
The simplified entries in the reaction column can be read in detail from the Pourbaix diagrams of the considered element in water. Noble metals have large positive potentials; elements not in this table have a negative standard potential or are not metals.
Electronegativity is included since it is reckoned to be, "a major driver of metal nobleness and reactivity".
On account of their high electron affinity values, the incorporation of a noble metal in the electrochemical photolysis process, such as platinum and gold, among others, can increase photoactivity.
Arsenic and antimony are usually considered to be metalloids rather than noble metals. However, physically speaking their most stable allotropes are metallic. Semiconductors, such as selenium and tellurium, have been excluded.
The black tarnish commonly seen on silver arises from its sensitivity to hydrogen sulfide:
:2 Ag + HS + O → AgS + HO.
Rayner-Canham contends that, "silver is so much more chemically-reactive and has such a different chemistry, that it should not be considered as a noble metal." In dentistry, silver is not regarded as a noble metal due to its tendency to corrode in the oral environment.
The relevance of the entry for water is addressed by Li et al. in the context of galvanic corrosion. Such a process will only occur when:
:"(1) two metals which have different electrochemical potentials are...connected, (2) an aqueous phase with electrolyte exists, and (3) one of the two metals has...potential lower than the potential of the reaction ( + 4e + = 4 OH</sup>)."
The superheavy elements from hassium (element 108) to livermorium (116) inclusive are expected to be "partially very noble metals"; chemical investigations of hassium has established that it behaves like its lighter congener osmium, and preliminary investigations of nihonium and flerovium have suggested but not definitively established noble behavior. Copernicium's behaviour seems to partly resemble both its lighter congener mercury and the noble gas radon. | 8 | Metallurgy |
Overload, shocks and vibrations (bridges, roads submitted to intense truck traffic...) can induce mechanical stress and deformations in concrete structures and be responsible for the mechanical degradation of concrete. Beside the long-term drying shrinkage of concrete, pre-stressed and post-tensioned civil engineering structures (bridges, primary containment domes of nuclear power plants can also undergo slow concrete creep and deformation. | 8 | Metallurgy |
Hanna Reisler (née Bregman) is an Israeli-American Professor of Chemistry at the University of Southern California. She is interested in the reaction dynamics of molecules and free radicals, as well as the photodissociation in the gas phase. Reisler established the University of Southern California Women In Science and Engineering (WISE) program. | 7 | Physical Chemistry |
In some cases, discordant reads can also indicate a CNV for example in sequences repeats. For larger CNV, the density of the reads will vary accordingly to the copy number. An increase of copy numbers will be reflected by increasing mapping of the same region on the reference genome. | 1 | Biochemistry |
[4+4] reactions are forbidden in the ground state and often entropically disfavored in the excited state. The mechanism of the [4+4] photocycloaddition is proposed to begin with the photoexcitation of a 1,3-diene system into the excited state. Because the orbital symmetry of the highest occupied molecular orbital (HOMO) in the excited diene is the same as that of the lowest unoccupied molecular orbital (LUMO) in another ground state diene, they are able to form an exciplex that decays to form the closed cyclooctane ring structure. Below is a Frontier Molecular Orbital diagram depicting the interaction between the two molecules of dienes. | 5 | Photochemistry |
The aromatic component of the quinine molecule is a quinoline with a methoxy substituent. The amine component has a quinuclidine skeleton and the methylene bridge in between the two components has a hydroxyl group. The substituent at the 3 position is a vinyl group. The molecule is optically active with five stereogenic centers (the N1 and C4 constituting a single asymmetric unit), making synthesis potentially difficult because it is one of 16 stereoisomers. | 0 | Organic Chemistry |
Fluxes are materials added to the ore during smelting to catalyze the desired reactions and to chemically bind to unwanted impurities or reaction products. Calcium carbonate or calcium oxide in the form of lime are often used for this purpose, since they react with sulfur, phosphorus, and silicon impurities to allow them to be readily separated and discarded, in the form of slag. Fluxes may also serve to control the viscosity and neutralize unwanted acids.
Flux and slag can provide a secondary service after the reduction step is complete; they provide a molten cover on the purified metal, preventing contact with oxygen while still hot enough to readily oxidize. This prevents impurities from forming in the metal. | 8 | Metallurgy |
Some of the most commonly-used biocompatible materials (or biomaterials) are polymers due to their inherent flexibility and tunable mechanical properties. Medical devices made of plastics are often made of a select few including: cyclic olefin copolymer (COC), polycarbonate (PC), polyetherimide (PEI), medical grade polyvinylchloride (PVC), polyethersulfone (PES), polyethylene (PE), polyetheretherketone (PEEK) and even polypropylene (PP). To ensure biocompatibility, there are a series of regulated tests that material must pass to be certified for use. These include the United States Pharmacopoeia IV (USP Class IV) Biological Reactivity Test and the International Standards Organization 10993 (ISO 10993) Biological Evaluation of Medical Devices. The main objective of biocompatibility tests is to quantify the acute and chronic toxicity of material and determine any potential adverse effects during use conditions, thus the tests required for a given material are dependent on its end-use (i.e. blood, central nervous system, etc.). | 1 | Biochemistry |
Ions in their gas-like state are highly reactive and will rapidly interact with ions of opposite charge to give neutral molecules or ionic salts. Ions are also produced in the liquid or solid state when salts interact with solvents (for example, water) to produce solvated ions, which are more stable, for reasons involving a combination of energy and entropy changes as the ions move away from each other to interact with the liquid. These stabilized species are more commonly found in the environment at low temperatures. A common example is the ions present in seawater, which are derived from dissolved salts.
As charged objects, ions are attracted to opposite electric charges (positive to negative, and vice versa) and repelled by like charges. When they move, their trajectories can be deflected by a magnetic field.
Electrons, due to their smaller mass and thus larger space-filling properties as matter waves, determine the size of atoms and molecules that possess any electrons at all. Thus, anions (negatively charged ions) are larger than the parent molecule or atom, as the excess electron(s) repel each other and add to the physical size of the ion, because its size is determined by its electron cloud. Cations are smaller than the corresponding parent atom or molecule due to the smaller size of the electron cloud. One particular cation (that of hydrogen) contains no electrons, and thus consists of a single proton – much smaller than the parent hydrogen atom. | 7 | Physical Chemistry |
Preimplantation genetic screening (PGS) or preimplantation genetic diagnosis (PGD) has been suggested to be able to be used in IVF to select an embryo that appears to have the greatest chances for successful pregnancy. However, a systematic review and meta-analysis of existing randomised controlled trials came to the result that there is no evidence of a beneficial effect of PGS with cleavage-stage biopsy as measured by live birth rate. On the contrary, for those of advanced maternal age, PGS with cleavage-stage biopsy significantly lowers the live birth rate. Technical drawbacks, such as the invasiveness of the biopsy, and non-representative samples because of mosaicism are the major underlying factors for inefficacy of PGS.
Still, as an expansion of IVF, patients who can benefit from PGS/PGD include:
* Those who have a family history of inherited disease
* Those who want prenatal sex discernment. This can be used to diagnose monogenic disorders with sex linkage. It can potentially be used for sex selection, wherein a fetus is aborted if having an undesired sex.
* Those who already have a child with an incurable disease and need compatible cells from a second healthy child to cure the first, resulting in a "saviour sibling" that matches the sick child in HLA type.
PGS screens for numeral chromosomal abnormalities while PGD diagnosis the specific molecular defect of the inherited disease. In both PGS and PGD, individual cells from a pre-embryo, or preferably trophectoderm cells biopsied from a blastocyst, are analysed during the IVF process. Before the transfer of a pre-embryo back to a person's uterus, one or two cells are removed from the pre-embryos (8-cell stage), or preferably from a blastocyst. These cells are then evaluated for normality. Typically within one to two days, following completion of the evaluation, only the normal pre-embryos are transferred back to the uterus. Alternatively, a blastocyst can be cryopreserved via vitrification and transferred at a later date to the uterus. In addition, PGS can significantly reduce the risk of multiple pregnancies because fewer embryos, ideally just one, are needed for implantation. | 1 | Biochemistry |
Chiral recognition implies the ability of chiral stationery phases to interact differently with mirror-image molecules, leading to their separation. The mechanism of enantiomeric resolution using CSPs is generally attributed to the “three-point" interaction model (fig.1.) between the analyte and the chiral selector in the stationary phase. Also known as the Dalgliesh model. Under this model, for chiral recognition, and hence enantiomeric resolution to happen on a CSP one of the enantiomers of the analyte must be involved in three simultaneous interactions. This means to say the one of enantiomers is able to have a good interaction with the complimentary sites on the chiral selector attached to the CSP. While Its mirror-image partner may only interact at two or one such sites. In the figure, enantiomer (a), has the correct configuration of the ligands (X, Y and Z) for three-point interactions with the complimentary sites (X’, Y’ and Z’) on the CSP, while its mirror image (b) can only interact at one site. The dotted lines (-----) indicate interaction with complimentary sites.
The diastereomeric complexes thus formed will have different energies of interaction. The enantiomer forming the more stable complex will have less energy and stay longer in the stationary phase compared to the less stable complex with higher energy. The success of chiral separation basically depends in manipulating the subtle energy differences between the reversibly formed non-covalent transient diastereomeric complexes. The energy difference reflects the magnitude of enantioselectivity. Mobile phase has a major role in stabilizing the diastereomeric complex and thus in chiral separation. This simplified bimolecular interaction model is a treatment suitable for theoretical purposes. Mobile phase plays a key role in chiral recognition mechanism. Components of MP (such as bulk solvents, modifiers, buffer salts, additives) not only influence the conformational flexibility of CS and CA molecules but also their degree of ionization. The types of interaction involved in the analyte-selector interaction vary depending on the nature of the CSP used. These may include hydrogen bonding, dipole-dipole, π-π, electrostatic, hydrophobic or steric interactions, and inclusion complex formation. | 4 | Stereochemistry |
There is considerable interest in applying gene-editing methods to the treatment of diseases with a genetic component. However, there are multiple challenges associated with this approach. An effective treatment would require editing of a large number of target cells, which in turn would require an effective method of delivery and a great level of tissue specificity.
As of 2019, prime editing looks promising for relatively small genetic alterations, but more research needs to be conducted to evaluate whether the technology is efficient in making larger alterations, such as targeted insertions and deletions. Larger genetic alterations would require a longer RT template, which could hinder the efficient delivery of pegRNA to target cells. Furthermore, a pegRNA containing a long RT template could become vulnerable to damage caused by cellular enzymes. Prime editing in plants suffers from low efficiency ranging from zero to a few percent and needs significant improvement.
Some of these limitations have been mitigated by recent improvements to the prime editors, including motifs that protect pegRNAs from degradation. Further research is needed before prime editing could be used to correct pathogenic alleles in humans. Research has also shown that inhibition of certain MMR proteins, including MLH1 can improve prime editing efficiency. | 1 | Biochemistry |
In the 1920s and 30s, Albert H. Taylor, Arthur C. Hardy , and others of the General Electric company developed a series of instruments that were capable of easily recording spectral data "in reflection". Their display preference for the data was "% Reflectance". In 1946, Frank Benford published a series of parametric equations that gave results equivalent to the Stokes formulas. The formulas used fractions to express reflectance and transmittance. | 7 | Physical Chemistry |
Gestonorone caproate is the generic name of the drug and its , , and , while gestronol hexanoate is its . It has also been referred to as norhydroxyprogesterone caproate, and is also known by its former developmental code names SH-582 and SH-80582. | 4 | Stereochemistry |
* EAS Award for Outstanding Achievements in the Fields of Analytical Chemistry (2023)
* Martin Medal (2019)
* Ralph N. Adams Award in Bioanalyical Chemistry (2016)
* ACS Award in Chromatography (2017)
* CASSS Award for Outstanding Achievements in Separation Science (2017)
* Marcel Golay Award for Lifetime Achievement in Capillary Chromatography (2012)
* Eastern Analytical Symposium Award for Separation Science (2012)
* McKnight Award for Technical Innovations in Neuroscience (2010)
* Rackham Distinguished Faculty Achievement Award (2009)
* American Microchemical Society’s Benedetti-Pichler Memorial Award (2001) | 3 | Analytical Chemistry |
In IUPAC nomenclature, 1,1-ethenediyl describes the connectivity >C=CH. The related species ethenylidenes have the connectivity =C=CH. | 0 | Organic Chemistry |
Left-hand traffic (LHT) and right-hand traffic (RHT) are the practices, in bidirectional traffic, of keeping to the left side and to the right side of the road, respectively. They are fundamental to traffic flow, and are sometimes called the rule of the road. The terms right- and left-hand drive refer to the position of the driver and the steering wheel in the vehicle and are, in automobiles, the reverse of the terms right- and left-hand traffic. The rule also includes where on the road a vehicle is to be driven, if there is room for more than one vehicle in the one direction, and the side on which the vehicle in the rear overtakes the one in the front. For example, a driver in an LHT country would typically overtake on the right of the vehicle being overtaken.
RHT is used in 165 countries and territories, mainly in the Americas, Continental Europe, northern Africa and mainland Asia (except South Asia), while 75 countries use LHT, which account for about a sixth of the worlds land area, a quarter of its roads, and about a third of its population. In 1919, 104 of the worlds territories were LHT and an equal number were RHT. Between 1919 and 1986, 34 of the LHT territories switched to RHT.
Many of the countries using LHT were part of the British Empire, while others, including Indonesia, Japan, Nepal, Bhutan, Macao, Thailand, Mozambique, Suriname, United States Virgin Islands, Sweden and Iceland (which use RHT since September 1967 and late May 1968 respectively), were not. Most of the countries that were part of the French colonial empire adopted RHT.
Historical switches of traffic handedness have often been motivated by factors such as changes in political administration, a desire for uniformity within a country or with neighboring states, or availability and affordability of vehicles.
In LHT, traffic keeps left and cars usually have the steering wheel on the right (RHD: right-hand drive) and roundabouts circulate clockwise. RHT is the opposite: traffic keeps right, the driver usually sits on the left side of the car (LHD: left-hand drive), and roundabouts circulate counterclockwise.
In most countries, rail traffic follows the handedness of the roads; but many of the countries that switched road traffic from LHT to RHT did not switch their trains. Boat traffic on rivers is RHT, regardless of location. Boats are traditionally piloted from the starboard side to facilitate priority to the right. | 4 | Stereochemistry |
Low-pressure mercury lamps are very similar to a fluorescent lamp, with a wavelength of 253.7 nm (1182.5 THz).
The most common form of germicidal lamp looks similar to an ordinary fluorescent lamp but the tube contains no fluorescent phosphor. In addition, rather than being made of ordinary borosilicate glass, the tube is made of fused quartz or vycor 7913 glass. These two changes combine to allow the 253.7 nm ultraviolet light produced by the mercury arc to pass out of the lamp unmodified (whereas, in common fluorescent lamps, it causes the phosphor to fluoresce, producing visible light). Germicidal lamps still produce a small amount of visible light due to other mercury radiation bands.
An older design looks like an incandescent lamp but with the envelope containing a few droplets of mercury. In this design, the incandescent filament heats the mercury, producing a vapor which eventually allows an arc to be struck, short circuiting the incandescent filament.
As with all gas-discharge lamps, low- and high-pressure mercury lamps exhibit negative resistance and require the use of an external ballast to regulate the current flow. The older lamps that resembled an incandescent lamp were often operated in series with an ordinary 40 W incandescent "appliance" lamp; the incandescent lamp acted as the ballast for the germicidal lamp. | 5 | Photochemistry |
Ethyl eicosapentaenoic acid (E-EPA) is an ethyl ester of eicosapentaenoic acid, which is an omega-3 fatty acid. | 1 | Biochemistry |
#Microinject the embryo with DNA coding for transposase and a plasmid with the reporter gene and transposase recognition sequences (and often the E. coli reporter gene and origin of replication, etc.).
#Random transposition occurs, inserting the reporter gene randomly. The insertion tends to occur near actively transcribed genes, as this is where the chromatin structure is loosest, so the DNA is most accessible.
#Grow flies and cross to remove genetic variation between the cells of the organism (see above).
#Look for flies expressing the reporter gene. These have experienced a successful transposition, so can be investigated to determine the phenotype due to mutation of existing genes.
Possible mutations:
#Insertion in a translated region => hybrid protein/truncated protein. Usually causes loss of protein function, although more complex effects are seen.
#Insertion in an intron => altered splicing pattern/splicing failure. Usually results in protein truncation or the production of inactive mis-spliced products, although more complex effects are common.
#Insertion in 5 (the sequence that will become the mRNA 5 UTR) untranslated region => truncation of transcript. Usually results in failure of the mRNA to contain a 5' cap, leading to less efficient translation.
#Insertion in promoter => reduction/complete loss of expression. Always results in greatly reduced protein production levels. The most useful type of insertion for analysis due to the simplicity of the situation.
#Insertion between promoter and upstream enhancers => loss of enhancer function/hijack of enhancer function for reporter gene.† Generally reduces the level of protein specificity to cell type, although complex effects are often seen. | 1 | Biochemistry |
Notable members of The Electrochemical Society include numerous Nobel Prize laureates including the three co-winners of the 2019 Nobel Prize for Chemistry.
*Thomas Edison: Edison became a member on April 4, 1903. Early members recall attending a meeting at Edison's home in the Society’s early days. Edison is often credited for inventing the phonograph, the motion picture camera, and the electric light bulb.
*John B. Goodenough, M. Stanley Whittingham, and Akira Yoshino, all long-time ECS members, shared the 2019 Nobel Prize in Chemistry “for the development of lithium-ion batteries”.
*Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura shared the 2014 Nobel Prize in Physics for “the invention of efficient blue light-emitting diodes, which has enabled bright and energy-saving white light sources”.
*Jack Kilby’s invention of the integrated circuit earned him half of the 2000 Nobel Prize in Physics "for basic work on information and communication technology".
*Steven Chu and William D. Phillips were co-recipients of the 1997 Nobel Prize in Physics “for the development of methods to cool and trap atoms with laser light”.
*Richard Smalley shared the 1996 Nobel Prize in Chemistry “for the discovery of fullerenes”.
*Rudolph A. Marcus won the 1992 Nobel Prize in Chemistry “for his contributions to the theory of electron transfer reactions in chemical systems".
*Jean-Marie Lehn, an early innovator in the field of supramolecular chemistry, shared the 1987 Nobel Prize in Chemistry “for the development and use of molecules with structure-specific interactions of high selectivity”.
*Gerd Binnig shared the 1986 Nobel Prize in Physics “for the design of the scanning tunneling microscope”.
*[https://www.electrochem.org/publications/leadership-collections Charles W. Tobias]: A pioneer in the field of electrochemical engineering, Tobias made a long-lasting and far-reaching impact on the field of electrochemical science by forming the Chemical Engineering Department at UC Berkeley in 1947. He served as ECS president from 1970-1971.
*Gordon E. Moore: The co-founder of Intel was known for his 1965 principle which made possible the delivery of more powerful and lower-costing semiconductor chips. This was later known as Moore's law.
*Norman Hackerman: The internationally known expert in metal corrosion served as ECS president from 1957-1958. Hackerman is most recognized for developing the electrochemistry of oxidation.
*Carl Wagner: Often referred to as the father of solid-state chemistry, Wagner's work on oxidation rate theory, counter diffusion of ions, and defect chemistry considerably advanced knowledge of how reactions proceed at the atomic level in the solid state. Wagner was the first recipient of the ECS Palladium Award in 1951.
*Irving Langmuir: received the 1932 Nobel Prize in Chemistry “for his discoveries and investigations in surface chemistry”.
*Edward Goodrich Acheson: The inventor of the Acheson process was a manufacturer of carborundum and graphite. The ECS Acheson Award was named in his honor in 1931.
*Theodore William Richards: Richards, whose research helped confirm the existence of isotopes, received the 1914 Nobel Prize in Chemistry, “in recognition of his accurate determinations of the atomic weight of a large number of chemical elements”.
*Willis R. Whitney: ECS president from 1911-1912, Whitney is most recognized among his many achievements for founding the research laboratory of the General Electric Company.
*Leo Baekeland: Baekland, who served as ECS president in 1909, is most famous for inventing Bakelite in 1907. His entrepreneurial genius and inventive nature made Baekeland one of the most important players in chemical technology.
*Herbert H. Dow: Among his most significant achievements, Dow founded the Dow Chemical Company in 1897. Dow Chemical funded the creation of the ECS Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award in his honor in 1990.
*Edward Weston: Noted for his achievements in electroplating, Weston developed the electrochemical cell – named the Weston cell, for the voltage standard.
*Charles Martin Hall: Hall, is best known for inventing an inexpensive process to produce aluminum, was one of the founders of Alcoa.
*Lawrence Addicks (1878-1964) served as president of The Electrochemical Society from 1915 to 1916. | 7 | Physical Chemistry |
The process typically takes place between 900 and 1100 °C, with an anode (typically carbon) and a cathode (the oxide being reduced) in a solution of molten CaCl. Depending on the nature of the oxide it will exist at a particular potential relative to the anode, which is dependent on the quantity of CaO present in CaCl. | 7 | Physical Chemistry |
* Cost of reactor and replacements (each replacement unit costs ~ $6000)
* Addition of dead volume causes an increase in peak broadening depending on the GC column flow rates and molecule types (5-10% broadening is typical)
** Heteroatoms and oxidation of Polyarc transfer lines increase this broadening
* Susceptible to sulfur, silicon, and halogen poisoning
* Requires constant feed of hydrogen
* Cannot be regenerated in-house; must be shipped back to the manufacturer for a replacement
* Cannot be used with cryogenic oven temperatures, or for GCxGC
* Poor response for species containing C-F bonds
* May contribute to power overload on older GC models, preventing the use of other heated components such as valve boxes or auxiliary detectors | 3 | Analytical Chemistry |
The protein encoded by this gene belongs to the immunoglobulin superfamily. It is a type I membrane protein. The protein may play a role in the adhesive interactions of activated T and NK cells during the late phase of the immune response. It may also function in antigen presentation. Alternative splicing generates multiple transcript variants encoding distinct isoforms. [provided by RefSeq, Jan 2016]. | 1 | Biochemistry |
Bromophenol blue (3′,3″,5′,5″-tetrabromophenolsulfonphthalein, BPB), albutest is used as a pH indicator, an electrophoretic color marker, and a dye. It can be prepared by slowly adding excess bromine to a hot solution of phenolsulfonphthalein in glacial acetic acid. | 3 | Analytical Chemistry |
It has been studied in AIDS-related Kaposis sarcoma, West Nile virus, and to inactivate Staphylococcus aureus', and HIV-1. Phenothiazine dyes and light have been known to have virucidal properties for over 70 years. | 3 | Analytical Chemistry |
As stated above, the STAT3-Ser/Hes3 signaling axis regulates the number of neural stem cells (as well as other cell types) in culture. This prompted experiments to determine if the same pathway can also regulate the number of naturally resident (endogenous) neural stem cells in the adult rodent brain. If so, this would generate a new experimental approach to study the effects of increasing the number of endogenous neural stem cells (eNSCs). For example, would this lead to the replacement of lost cells by newly generated cells from eNSCs? Or, could this lead to the rescue of damaged neurons in models of neurodegenerative disease, since eNSCs are known to produce factors that can protect injured neurons?
Various treatments that input into the STAT3-Ser/Hes3 signaling axis (Delta4, Angiopoietin 2, insulin, or a combined treatment consisting of all three factors and an inhibitor of JAK) induce the increase in numbers of endogenous neural stem cells as well as behavioral recovery in models of neurodegenerative disease. Several pieces of evidence suggest that in the adult brain, pharmacological activation of the STAT3-Ser/Hes3 signaling axis protects compromised neurons through increased neurotrophic support provided by activated neural stem cells / neural precursor cells, which can be identified by their expression of Hes3:
:* These treatments increase the number of Hes3+ cells by several-fold.
:* Hes3+ cells can be isolated and placed in culture where they exhibit stem cell properties.
:* In culture and in vivo, Hes3+ cells express Shh, which supports the survival of certain neurons [Hes3+ cells may also express other pro-survival factors, yet unidentified].
:* The distribution of Hes3+ cells in the adult brain is widespread and can be found in close physical proximity to different types of neurons.
:* Diverse treatments that converge to the STAT3-Ser/Hes3 signaling axis exert similar effects in the normal brain (increase in the number of Hes3+ cells) and in the compromised brain (increase in the number of Hes3+ cells, oppose neuronal death, and improve behavioral state).
:* Macrophage migration inhibitory factor stimulates this signaling pathway and promotes the survival of neural stem cells.
:* Mice genetically engineered to lack the Hes3 gene exhibit differences in the amount of myelin basic protein (a protein expressed on myelinating oligodendrocytes), relative to normal mice; Hes3-lacking mice also exhibit a different regulation of this protein after oligodendrocyte damage induced by the chemical cuprizone. | 1 | Biochemistry |
While earlier version of fiber-based laser traps exclusively used single mode beams, M. Kreysing and colleagues recently showed that the careful excitation of further optical modes in a short piece of optical fiber allows the realization of non-trivial trapping geometries. By this the researchers were able to orient various human cell types (individual cells and clusters) on a microscope. The main advantage of the so-called "optical cell rotator" technology over standard optical tweezers is the decoupling of trapping from imaging optics. This, its modular design, and the high compatibility of divergent laser traps with biological material indicates the great potential of this new generation of laser traps in medical research and life science. Recently, the optical cell rotator technology was implemented on the basis of adaptive optics, allowing to dynamically reconfigure the optical trap during operation and adapt it to the sample. | 1 | Biochemistry |
Regions of the short arm of chromosome 8 are frequently deleted in a range of solid tumors, indicating that tumor suppressor genes reside at these loci. Caldwell et al. have shown frequent interstitial deletions in a series of prostate cancers, squamous cell head and neck cancers and colorectal carcinomas. There was also an association between 8p11.2 deletion and local invasion.
The first coding exon contains the whole of the frizzled-related cysteine rich domain (CRD), while the third exon (COOH-terminal domain) contains the netrin-related domain. Netrin is a regulator of apoptosis; the SFRP1 netrin-related motif is also found in a range of other proteins that is thought to mediate protein-protein interactions. The middle exon most likely represents a spacer between the first and third exon. There are 2 introns present within the coding sequence of SFRP1. | 1 | Biochemistry |
CDI is mainly employed to convert amines into amides, carbamates, ureas. It can also be used to convert alcohols into esters. | 0 | Organic Chemistry |
Sedimentation equilibrium in a suspension of different particles, such as molecules, exists when the rate of transport of each material in any one direction due to sedimentation equals the rate of transport in the opposite direction due to diffusion. Sedimentation is due to an external force, such as gravity or centrifugal force in a centrifuge.
It was discovered for colloids by Jean Baptiste Perrin for which he received the Nobel Prize in Physics in 1926. | 1 | Biochemistry |
In the early 2020s, molecular biology entered a golden age defined by both vertical and horizontal technical development. Vertically, novel technologies are allowing for real-time monitoring of biological processes at the atomic level. Molecular biologists today have access to increasingly affordable sequencing data at increasingly higher depths, facilitating the development of novel genetic manipulation methods in new non-model organisms. Likewise, synthetic molecular biologists will drive the industrial production of small and macro molecules through the introduction of exogenous metabolic pathways in various prokaryotic and eukaryotic cell lines.
Horizontally, sequencing data is becoming more affordable and used in many different scientific fields. This will drive the development of industries in developing nations and increase accessibility to individual researchers. Likewise, CRISPR-Cas9 gene editing experiments can now be conceived and implemented by individuals for under $10,000 in novel organisms, which will drive the development of industrial and medical applications. | 1 | Biochemistry |
Hemorphin-4 is an endogenous opioid peptide of the hemorphin family which possesses antinociceptive properties and is derived from the β-chain of hemoglobin in the bloodstream. It is a tetrapeptide with the amino acid sequence Tyr-Pro-Trp-Thr. Hemorphin-4 has affinities for the μ-, δ-, and κ-opioid receptors that are in the same range as the structurally related β-casomorphins, although affinity to the κ-opioid receptor is markedly higher in comparison. It acts as an agonist at these sites. Hemorphin-4 also has inhibitory effects on angiotensin-converting enzyme (ACE), and as a result, may play a role in the regulation of blood pressure. Notably, inhibition of ACE also reduces enkephalin catabolism. | 1 | Biochemistry |
The concept of using reinforced lipids to inhibit lipid peroxidation has been tested in numerous cell and animal
models, including:
* Parkinson's disease (MPTP and a-Syn models in mice and rats)
* Huntington's disease (in mice)
* Alzheimer's disease (APP/PS1 and ALDH2 mouse models)
* Diabetic retinopathy (Akita mice)
* Age-related macular degeneration (light irradiation in rats, eye iron overload in mice)
* Atherosclerosis (Leiden mice) | 1 | Biochemistry |
Since cyclic AMP is a second messenger and plays vital role in cell signalling, it has been implicated in various disorders but not restricted to the roles given below: | 1 | Biochemistry |
Microautoradiography FISH is a technique to combine radio-labeled substrates with conventional FISH to detect phylogenetic groups and metabolic activities simultaneously. | 1 | Biochemistry |
The ratio r between the apparent molar volume of a dissolved electrolyte in a concentrated solution and the molar volume of the solvent (water) can be linked to the statistical component of the activity coefficient of the electrolyte and its solvation shell number h:
where ν is the number of ions due to dissociation of the electrolyte, and b is the molality as above. | 7 | Physical Chemistry |
A Brønsted-Lowry acids strength corresponds with its ability to release a hydrogen ion. One common measure of acid strength for concentrated, superacidic liquid media is the Hammett acidity function, H. Based on its ability to quantitatively protonate benzene, the chlorinated carborane acid was conservatively estimated to have an H value at or below −18, leading to the common assertion that carborane acids are at least a million times stronger than 100% sulfuric acid (H = −12). However, since the H value measures the protonating ability of a liquid medium, the crystalline and high-melting nature of these acids precludes direct measurement of this parameter. In terms of pK, a slightly different measure of acidity defined as the ability of a given solute to undergo ionization in a solvent, carborane acids are estimated to have pK values below −20, even without electron-withdrawing substituents on the boron atoms (e.g., is estimated to have a pK of −24), with the (yet unknown) fully fluorinated analog having a calculated pK of −46. The known acid with one fewer fluorine is expected to be only slightly weaker (pK' < −40).
In the gas phase, has a computed acidity of 216 kcal/mol, compared to an experimentally determined acidity of 241 kcal/mol (in reasonable agreement with the computed value of 230 kcal/mol) for . In contrast, HSbF (a simplified model for the proton donating species in fluoroantimonic acid) has a computed gas phase acidity of 255 kcal/mol, while the previous experimentally determined record holder was (CFSO)NH, a congener of bistriflimide, at 291 kcal/mol. Thus, is likely the most acidic substance so far synthesized in bulk, in terms of its gas phase acidity. In view of its unique reactivity, it is also a strong contender for being the most acidic substance in the condensed phase (see above). Some even more strongly acidic derivatives have been predicted, with gas phase acidities < 200 kcal/mol.
Carborane acids differ from classical superacids in being well-defined one component substances. In contrast, classical superacids are often mixtures of a Brønsted acid and Lewis acid (e.g. HF/SbF). Despite being the strongest acid, the boron-based carborane acids are described as being "gentle", cleanly protonating weakly basic substances without further side reactions. Whereas conventional superacids decompose fullerenes due to their strongly oxidizing Lewis acidic component, carborane acid has the ability to protonate fullerenes at room temperature to yield an isolable salt. Furthermore, the anion that forms as a result of proton transfer is nearly completely inert. This property is what makes the carborane acids the only substances that are comparable in acidity to the mixed superacids that can also be stored in a glass bottle, as various fluoride-donating species (which attack glass) are not present or generated. | 7 | Physical Chemistry |
UV disinfection is most effective for treating high-clarity, purified reverse osmosis distilled water. Suspended particles are a problem because microorganisms buried within particles are shielded from the UV light and pass through the unit unaffected. However, UV systems can be coupled with a pre-filter to remove those larger organisms that would otherwise pass through the UV system unaffected. The pre-filter also clarifies the water to improve light transmittance and therefore UV dose throughout the entire water column. Another key factor of UV water treatment is the flow rate—if the flow is too high, water will pass through without sufficient UV exposure. If the flow is too low, heat may build up and damage the UV lamp.
A disadvantage of UVGI is that while water treated by chlorination is resistant to reinfection (until the chlorine off-gasses), UVGI water is not resistant to reinfection. UVGI water must be transported or delivered in such a way as to avoid reinfection. | 5 | Photochemistry |
Brownian motion is the mathematical model used to describe the random movement of particles suspended in a fluid. The gas particle animation, using pink and green particles, illustrates how this behavior results in the spreading out of gases (entropy). These events are also described by particle theory.
Since it is at the limit of (or beyond) current technology to observe individual gas particles (atoms or molecules), only theoretical calculations give suggestions about how they move, but their motion is different from Brownian motion because Brownian motion involves a smooth drag due to the frictional force of many gas molecules, punctuated by violent collisions of an individual (or several) gas molecule(s) with the particle. The particle (generally consisting of millions or billions of atoms) thus moves in a jagged course, yet not so jagged as would be expected if an individual gas molecule were examined. | 7 | Physical Chemistry |
Calcium is stored in geologic reservoirs, most commonly in the form of calcium carbonate or as calcium silicate. Calcium-containing rocks include calcite, dolomite, phosphate, and gypsum. Rocks slowly dissolve by physical and chemical processes, carrying calcium ions into rivers and oceans. Calcium ions (Ca) and magnesium ions (Mg) have the same charge (+2) and similar sizes, so they react similarly and are able to substitute for each other in some minerals, such as carbonates. Ca-containing minerals are often more easily weathered than Mg minerals, so Ca is often more enriched in waterways than Mg. Rivers containing more dissolved Ca are generally considered more alkaline.
Calcium is one of the most common elements found in seawater. Inputs of dissolved calcium (Ca) to the ocean include the weathering of calcium sulfate, calcium silicate, and calcium carbonate, basalt-seawater reaction, and dolomitization. | 1 | Biochemistry |
The original Fischer glycal synthesis was the reductive elimination with zinc of a glycosyl halide. This glycosyl halide was formed from a monosaccharide starting material. Some other synthetic routes include:
*Ring-closing metathesis
*Reaction of thioglycosides with lithium napthalenide.
*Mesylation of the anomeric hydroxyl and formation of the anomeric palladium complex, which undergoes beta-elimination
A general example of each synthetic route is given below (drawn with first discussed synthesis bottom right, moving clockwise): | 0 | Organic Chemistry |
Chromatographic peak resolution is given by
where t is the retention time and w is the peak width at baseline. Here compound 1 elutes before compound 2.
If the peaks have the same width | 3 | Analytical Chemistry |
Public Analysts are scientists in the British Isles whose principal task is to ensure the safety and correct description of food by testing for compliance with legislation. Most Public Analysts are also Agricultural Analysts who carry out similar work on animal feedingstuffs and fertilisers. Nowadays this includes checking that the food labelling is accurate. They also test drinking water, and may carry out chemical and biological tests on other consumer products. While much of the work is done by other scientists and technicians in the laboratory, the Public Analyst has legal responsibility for the accuracy of the work and the validity of any opinion expressed on the results reported. The UK-based Association of Public Analysts includes members with similar roles if different titles in other countries. | 2 | Environmental Chemistry |
Minigenes were first described as the somatic assembly of DNA segments and consisted of DNA regions known to encode the protein and the flanking regions required to express the protein. The term was first used in a paper in 1977 to describe the cloning of two minigenes that were designed to express a peptide.
RNA splicing was discovered in the late 1970s through the study of adenoviruses that invade mammals and replicate inside them. Researchers identified RNA molecules that contained sequences from noncontiguous parts of the virus’s genome. This discovery led to the conclusion that regulatory mechanisms existed which affected mature RNA and the genes it expresses. Using minigenes as a splice reporting vector to explore the effects of RNA splicing regulation naturally followed and remains the major use of minigenes to date. | 1 | Biochemistry |
The divinylcyclopropane-cycloheptadiene rearrangement is an organic chemical transformation that involves the isomerization of a 1,2-divinylcyclopropane into a cycloheptadiene or -triene. It is conceptually related to the Cope rearrangement, but has the advantage of a strong thermodynamic driving force due to the release of ring strain. This thermodynamic power is recently being considered as an alternative energy source. | 0 | Organic Chemistry |
Laser-induced breakdown spectroscopy (LIBS) is a type of atomic emission spectroscopy which uses a highly energetic laser pulse as the excitation source. The laser is focused to form a plasma, which atomizes and excites samples. The formation of the plasma only begins when the focused laser achieves a certain threshold for optical breakdown, which generally depends on the environment and the target material. | 7 | Physical Chemistry |
Born in Sydney, Cornforth was the son and the second of four children of English-born, Oxford-educated schoolmaster and teacher John Warcup Cornforth and Hilda Eipper (1887–1969), a granddaughter of pioneering missionary and Presbyterian minister Christopher Eipper. Before her marriage, Eipper had been a maternity nurse.
Cornforth was raised in Sydney as well as Armidale, in the north of New South Wales, where he undertook primary school education.
At about 10 years old, Cornforth had noted signs of deafness, which led to a diagnosis of otosclerosis, a disease of the middle ear which causes progressive hearing loss. This left him completely deaf by the age of 20 but also fatefully influenced his career direction away from law, his original intended field of study, and towards chemistry. In an interview with Sir Harry Kroto for the Vega Science Trust, Cornforth explained: | 0 | Organic Chemistry |
Indirect calorimetry measures O consumption and CO production. On the assumption that all the oxygen is used to oxidize degradable fuels and all the CO thereby evolved is recovered, it is possible to estimate the total amount of energy produced from the chemical energy of nutrients and converted into the chemical energy of ATP, with some loss of energy during the oxidation process.
Respiratory indirect calorimetry (IC) is a noninvasive and highly accurate method of metabolic rate, which has an error of less than 1%. It has high reproducibility and has been considered a gold standard method. This method allows estimating BEE and REE as well as identification of energy substrates that are predominantly metabolized by the body at a specific moment. It is based on the indirect measurement of the heat produced by oxidation of macronutrients, which is estimated by monitoring O consumption and CO production for a certain period of time.
The calorimeter has a gas collector that adapts to the subject and through a unidirectional valve minute by minute collects and quantifies the volume and concentration of O inspired and CO expired by the subject. After a volume is met, Resting Energy Expenditure is calculated by the Weir formula and results are displayed in software attached to the system. Another formula used is:
where RQ is the respiratory quotient (ratio of volume CO produced to volume of O consumed), is , the heat released per litre of oxygen by the oxidation of carbohydrate, and is , the value for fat. This gives the same result as the Weir formula at RQ = 1 (burning only carbohydrates), and almost the same value at RQ = 0.7 (burning only fat). | 1 | Biochemistry |
Similar principles guide the lowest energy conformations of larger ring systems. Along with the acyclic stereocontrol principles outlined below, subtle interactions between remote substituents in large rings, analogous to those observed for 8-10 membered rings, can influence the conformational preferences of a molecule. In conjunction with remote substituent effects, local acyclic interactions can also play an important role in determining the outcome of macrocyclic reactions. The conformational flexibility of larger rings potentially allows for a combination of acyclic and macrocyclic stereocontrol to direct reactions. | 0 | Organic Chemistry |
Grinding is abrasion of the surface of interest by abrasive particles, usually diamond, that are bonded to paper or a metal disc. Grinding erases saw marks, coarsely smooths the surface, and removes stock to a desired depth. A typical grinding sequence for ceramics is one minute on a 240-grit metal-bonded diamond wheel rotating at 240 rpm and lubricated by flowing water, followed by a similar treatment on a 400-grit wheel. The specimen is washed in an ultrasonic bath after each step. | 8 | Metallurgy |
Synapses can be classified by the type of cellular structures serving as the pre- and post-synaptic components. The vast majority of synapses in the mammalian nervous system are classical axo-dendritic synapses (axon synapsing upon a dendrite), however, a variety of other arrangements exist. These include but are not limited to axo-axonic, dendro-dendritic, axo-secretory, axo-ciliary, somato-dendritic, dendro-somatic, and somato-somatic synapses.
In fact, the axon can synapse onto a dendrite, onto a cell body, or onto another axon or axon terminal, as well as into the bloodstream or diffusely into the adjacent nervous tissue. | 1 | Biochemistry |
At a temperature below the boiling point, any matter in liquid form will evaporate until reaching equilibrium with the reverse process of condensation of its vapor. At this point the vapor will condense at the same rate as the liquid evaporates. Thus, a liquid cannot exist permanently if the evaporated liquid is continually removed. A liquid at or above its boiling point will normally boil, though superheating can prevent this in certain circumstances.
At a temperature below the freezing point, a liquid will tend to crystallize, changing to its solid form. Unlike the transition to gas, there is no equilibrium at this transition under constant pressure, so unless supercooling occurs, the liquid will eventually completely crystallize. However, this is only true under constant pressure, so that (for example) water and ice in a closed, strong container might reach an equilibrium where both phases coexist. For the opposite transition from solid to liquid, see melting. | 7 | Physical Chemistry |
Cyclic salt is salt that is carried by the wind when it comes in contact with breaking waves. It is estimated that more than 300 million tons of cyclic salt is deposited on the Earths surface each year, and it is considered to be a significant factor in the chlorine content of the Earths river water. In general, cyclic salt deposits are lower at sites further inland and are most abundant along the shoreline, although this pattern varies depending on the given environmental conditions.
Use of the term "cyclic" refers to the cycle in which the salt moves from sea to land and is then washed by rainwater back to the sea. The salt (and other solid matter) cannot evaporate as water does. Instead it leaves the ocean surface in fine droplets of drop impacts or bubble bursts. Wave-crests and other turbulence form foam. When drops splash or bubbles burst, fine droplets of solute are ejected from the water or bubble surface into the air. Some of the droplets are small enough to allow the water to evaporate before it falls back into the sea, leaving in the air a mote of the light enough to stay suspended by Brownian motion and be carried away on the wind. | 9 | Geochemistry |
5,6-Dichloro-1-β--ribofuranosylbenzimidazole (DRB) is a chemical compound that inhibits transcription elongation by RNA Polymerase II. Sensitivity to DRB is dependent on DRB sensitivity inducing factor (DSIF), negative elongation factor (NELF), and positive transcription elongation factor b (P-TEFb). DRB is a nucleoside analog and also inhibits some protein kinases. | 1 | Biochemistry |
According to Entertainment Weekly, "The Navi can commune with animals on their planet by literally plugging their braid into the creatures nerve systems. To become a warrior, a Navi must tame and ride a flying creature known as Ikran." The Navi also use this neural bonding system, called "tsaheylu", to mate with a "life partner", a bond that, when made, cannot be broken in the Navis lifetime. This is akin to human marriage.
The Navi way of life revolves around their religion, and the Home Tree. The Navi sleep in hammocks in large groups for comfort and as a warning system.
Conceived for the film was the Navi language, a constructed language often spoken by the actors when they played Navi characters. The Navi language was created by communications professor emeritus and linguistics consultant Paul Frommer of the University of Southern California. He designed the language so as to be speakable by human actors, combining syntactic and grammatical rules from other existing languages. Frommer created over a thousand words for the Navi language and coached the actors who narrated Navi characters. When communicating to humans in the film, Navi characters – especially Neytiri – speak in accented and broken English.
Human visitors see the Navi as possessing a religion, whose chief and possibly sole deity is a benevolent goddess known as Eywa. The Navi are able to physically connect to Eywa when they use their braids to connect to the Tree of Souls and other similar flora which function as the global brain's interfaces. Eywa is said to have a connection to all things Pandoran.
Political power is exceedingly diffused, with each clan being a sovereign entity under either the diarchical rule of both a temporal chieftain (known as an Oloeyktan) and a spiritual chieftain (known as a Tsahik), or the monarchical rule of a single individual who holds the two separate offices simultaneously. The numerous clans are seemingly only ever brought together as a tribe by Toruk Makto, a messianic war chief whose office is both non-permanent and apparently the only one with an authority that covers the entire race of Navi. By the time of the film, there had only been five Toruk Maktos in the history of the tribe, and the last one had ruled no fewer than four generations before the present day. This may be due to the fact that the Toruk Maktos seem to draw their power from a situation of explicitly external danger, and therefore are not really necessary for the day to day internal running of the tribal clans. Succession to the various offices is smooth, however, based more on popular recognition and customary worthiness than on anything else, and respect for hierarchical superiors appears to be high. | 1 | Biochemistry |
* Reduced cellular defense mechanisms
** Children younger than 4 months exposed to various environmental agents
** Pregnant women are considered vulnerable to exposure of high levels of nitrates in drinking water
** Cytochrome b5 reductase deficiency
** G6PD deficiency
** Hemoglobin M disease
** Pyruvate kinase deficiency
* Various pharmaceutical compounds
** Local anesthetic agents, especially prilocaine and benzocaine.
** Amyl nitrite, chloroquine, dapsone, nitrates, nitrites, nitroglycerin, nitroprusside, phenacetin, phenazopyridine, primaquine, quinones and sulfonamides
* Environmental agents
** Aromatic amines (e.g. p-nitroaniline, [http://www.gtfch.org/cms/images/stories/media/tk/tk73_2/Bakdash.pdf patient case])
** Arsine
** Chlorobenzene
** Chromates
** Nitrates/nitrites
** Umbellulone
* Inherited disorders
** Some family members of the Fugate family in Kentucky, due to a recessive gene, had blue skin from an excess of methemoglobin.
* In cats
**Ingestion of paracetamol (i.e. acetaminophen, tylenol) | 1 | Biochemistry |
The high intensity of the Jameson Cell means that it is much shorter than conventional column flotation cells (see Figure 1), and it does not require air compressors to aerate the suspension of ground ore particles and water (known as a slurry or pulp) in the flotation cell. The lack of a requirement for compressed air and the lack of moving parts means that power consumption is less than for the equivalent mechanical or conventional column flotation cell.
In contrast to most types of flotation cell, the Cell introduces the feed and the air to the Cell in a combined stream via one or more cylindrical columns referred to as "downcomers". Other types of flotation cell typically introduce the feed and the air separately to the cell.
The Cell produces fast mineral flotation rates, especially for very fine mineral particles. It produces high concentrate grades from fast floating liberated particles and is able to do this from a single stage of flotation. The high carrying capacity of the Jameson Cell is particularly beneficial when high yields (mass pulls) are required, such as in recleaning in metals flotation and in the flotation of metallurgical coal, where yields can exceed 80%.
The Cell was initially developed as a lower-cost alternative to conventional column flotation cells for recovering fine particles, and was first used in the Mount Isa lead–zinc concentrator in 1988. Since then, use of the technology has spread to include coal flotation, base and precious metal flotation, potash flotation, oil sands flotation, molybdenum flotation, graphite flotation and cleaning solvent extraction liquors. Xstrata Technology, Glencore Xstratas technology marketing arm, listed 328 Jameson Cell installations in May 2013. Cells have been installed by 94 companies in 27 countries. Today, the technology is the standard in the Australian Coal Industry where well over one hundred Cells have been installed to recover coal fines. It is mainly used in metals applications to solve final grade and capacity issues from conventional cell cleaner circuits. It has found a niche in transforming traditional circuit designs where its inclusion allows cleaner circuits to be designed with fewer cells in a smaller footprint, while achieving cleaner and/or higher grade concentrates. It has also made possible the recovery of previously discarded fine materials, such as coal and phosphate fines, thereby increasing the efficiency and extending the life of the worlds non-renewable natural resources. | 8 | Metallurgy |
Despite the highly attractive nature of 3D optical data storage, the development of commercial products has taken a significant length of time. This results from limited financial backing in the field, as well as technical issues, including:
Destructive reading. Since both the reading and the writing of data are carried out with laser beams, there is a potential for the reading process to cause a small amount of writing. In this case, the repeated reading of data may eventually serve to erase it (this also happens in phase change materials used in some DVDs). This issue has been addressed by many approaches, such as the use of different absorption bands for each process (reading and writing), or the use of a reading method that does not involve the absorption of energy.
Thermodynamic stability. Many chemical reactions that appear not to take place in fact happen very slowly. In addition, many reactions that appear to have happened can slowly reverse themselves. Since most 3D media are based on chemical reactions, there is therefore a risk that either the unwritten points will slowly become written or that the written points will slowly revert to being unwritten. This issue is particularly serious for the spiropyrans, but extensive research was conducted to find more stable chromophores for 3D memories.
Media sensitivity. two-photon absorption is a weak phenomenon, and therefore high power lasers are usually required to produce it. Researchers typically use Ti-sapphire lasers or Nd:YAG lasers to achieve excitation, but these instruments are not suitable for use in consumer products. | 5 | Photochemistry |
A characteristic reaction of is its easy hydrolysis, signaled by the release of HCl vapors and titanium oxides and oxychlorides. Titanium tetrachloride has been used to create naval smokescreens, as the hydrochloric acid aerosol and titanium dioxide that is formed scatter light very efficiently. This smoke is corrosive, however.
Alcohols react with to give alkoxides with the formula (R = alkyl, n = 1, 2, 4). As indicated by their formula, these alkoxides can adopt complex structures ranging from monomers to tetramers. Such compounds are useful in materials science as well as organic synthesis. A well known derivative is titanium isopropoxide, which is a monomer. Titanium bis(acetylacetonate)dichloride results from treatment of titanium tetrachloride with excess acetylacetone:
Organic amines react with to give complexes containing amido (-containing) and imido (-containing) complexes. With ammonia, titanium nitride is formed. An illustrative reaction is the synthesis of tetrakis(dimethylamido)titanium , a yellow, benzene-soluble liquid: This molecule is tetrahedral, with planar nitrogen centers. | 0 | Organic Chemistry |
To determine five-day biochemical oxygen demand (BOD), several dilutions of a sample are analyzed for dissolved oxygen before and after a five-day incubation period at 20 °C in the dark. In some cases, bacteria are used to provide a standardized community to uptake oxygen while consuming the organic matter in the sample; these bacteria are known as "seed". The difference in DO and the dilution factor are used to calculated BOD. The resulting number (usually reported in parts per million or milligrams per liter) is useful in determining the relative organic strength of sewage or other polluted waters.
The BOD test is an example of analysis that determines classes of materials in a sample. | 3 | Analytical Chemistry |
The injection loop is a segment of tubing of known volume which is filled with the sample solution before it is injected into the column. Loop volume can range from a few microliters to 50 ml or more. | 3 | Analytical Chemistry |
For a circular bleach spot of radius and diffusion-dominated recovery, the fluorescence is described by an equation derived by Soumpasis (which involves modified Bessel functions and )
with the characteristic timescale for diffusion, and is the time. is the normalized fluorescence (goes to 1 as goes to infinity). The diffusion timescale for a bleached spot of radius is , with D the diffusion coefficient.
Note that this is for an instantaneous bleach with a step function profile, i.e., the fraction of protein assumed to be bleached instantaneously at time is , and , for is the distance from the centre of the bleached area. It is also assumed that the recovery can be modelled by diffusion in two dimensions, that is also both uniform and isotropic. In other words, that diffusion is occurring in a uniform medium so the effective diffusion constant D is the same everywhere, and that the diffusion is isotropic, i.e., occurs at the same rate along all axes in the plane.
In practice, in a cell none of these assumptions will be strictly true.
#Bleaching will not be instantaneous. Particularly if strong bleaching of a large area is required, bleaching may take a significant fraction of the diffusion timescale . Then a significant fraction of the bleached protein will diffuse out of the bleached region actually during bleaching. Failing to take account of this will introduce a significant error into D.
#The bleached profile will not be a radial step function. If the bleached spot is effectively a single pixel then the bleaching as a function of position will typically be diffraction limited and determined by the optics of the confocal laser scanning microscope used. This is not a radial step function and also varies along the axis perpendicular to the plane.
#Cells are of course three-dimensional not two-dimensional, as is the bleached volume. Neglecting diffusion out of the plane (we take this to be the xy plane) will be a reasonable approximation only if the fluorescence recovers predominantly via diffusion in this plane. This will be true, for example, if a cylindrical volume is bleached with the axis of the cylinder along the z axis and with this cylindrical volume going through the entire height of the cell. Then diffusion along the z axis does not cause fluorescence recovery as all protein is bleached uniformly along the z axis, and so neglecting it, as Soumpasis equation does, is harmless. However, if diffusion along the z' axis does contribute to fluorescence recovery then it must be accounted for.
#There is no reason to expect the cell cytoplasm or nucleoplasm to be completely spatially uniform or isotropic.
Thus, the equation of Soumpasis is just a useful approximation, that can be used when the assumptions listed above are good approximations to the true situation, and when the recovery of fluorescence is indeed limited by the timescale of diffusion . Note that just because the Soumpasis can be fitted adequately to data does not necessarily imply that the assumptions are true and that diffusion dominates recovery. | 1 | Biochemistry |
Engine manufacturers typically rate their engines fuel consumption by the lower heating values since the exhaust is never condensed in the engine, and doing this allows them to publish more attractive numbers than are used in conventional power plant terms. The conventional power industry had used HHV (high heat value) exclusively for decades, even though virtually all of these plants did not condense exhaust either. American consumers should be aware that the corresponding fuel-consumption figure based on the higher heating value will be somewhat higher.
The difference between HHV and LHV definitions causes endless confusion when quoters do not bother to state the convention being used. since there is typically a 10% difference between the two methods for a power plant burning natural gas. For simply benchmarking part of a reaction the LHV may be appropriate, but HHV should be used for overall energy efficiency calculations if only to avoid confusion, and in any case, the value or convention should be clearly stated. | 7 | Physical Chemistry |
The G-less assay can be performed on a circular plasmid to measure levels of transcription. A circular plasmid provides a more efficient template in many systems when compared to other assays such as runoff transcription, in which a cleaved end is required. This method generates radiolabeled transcripts very efficiently because it bypasses the unnecessary process of performing other indirect mRNA product measurements. The promoter is inserted into a circular plasmid containing the G-less cassette, which will generate a transcript of a certain length that omits random and nonspecific transcription throughout the plasmid. Most crude systems, such as HeLa nuclear extracts, are used because they contain low amounts of contaminating GTP that lead to background transcription and may occasionally cause random transcription to read through the G-less cassette. | 1 | Biochemistry |
Naturally occurring siRNAs have a well-defined structure that is a short (usually 20 to 24-bp) double-stranded RNA (dsRNA) with phosphorylated 5 ends and hydroxylated 3 ends with two overhanging nucleotides.
The Dicer enzyme catalyzes production of siRNAs from long dsRNAs and small hairpin RNAs. siRNAs can also be introduced into cells by transfection. Since in principle any gene can be knocked down by a synthetic siRNA with a complementary sequence, siRNAs are an important tool for validating gene function and drug targeting in the post-genomic era. | 1 | Biochemistry |
The interpretation of scattering measurements made at the multiangular locations relies upon some knowledge of the a priori properties of the particles or molecules measured. The scattering characteristics of different classes of such scatterers may be interpreted best by application of an appropriate theory. For example, the following theories are most often applied.
Rayleigh scattering is the simplest and describes elastic scattering of light or other electromagnetic radiation by objects much smaller than the incident wavelength. This type of scattering is responsible for the blue color of the sky during the day and is inversely proportional to the fourth power of wavelength.
The Rayleigh–Gans approximation is a means of interpreting MALS measurements with the assumption that the scattering particles have a refractive index, n, very close to the refractive index of the surrounding medium, n. If we set m = n/n and assume that , then such particles may be considered as composed of very small elements, each of which may be represented as a Rayleigh-scattering particle. Thus each small element of the larger particle is assumed to scatter independently of any other.
Lorenz–Mie theory is used to interpret the scattering of light by homogeneous spherical particles. The Rayleigh–Gans approximation and the Lorenz–Mie theory produce identical results for homogeneous spheres in the limit as .
Lorenz–Mie theory may be generalized to spherically symmetric particles per reference.
More general shapes and structures have been treated by Erma.
Scattering data is usually represented in terms of the so-called excess Rayleigh ratio defined as the Rayleigh ratio of the solution or single particle event from which is subtracted the Rayleigh ratio of the carrier fluid itself and other background contributions, if any. The Rayleigh Ratio measured at a detector lying at an angle θ and subtending a solid angle ΔΩ is defined as the intensity of light per unit solid angle per unit incident intensity, I, per unit illuminated scattering volume ΔV. The scattering volume ΔV from which scattered light reaches the detector is determined by the detectors field of view generally restricted by apertures, lenses and stops. Consider now a MALS measurement made in a plane from a suspension of N identical particles/molecules per ml illuminated by a fine beam of light produced by a laser. Assuming that the light is polarized perpendicular to the plane of the detectors. The scattered light intensity measured by the detector at angle θ' in excess of that scattered by the suspending fluid would be
where i(θ) is the scattering function of a single particle, k = 2πn/λ, n is the refractive index of the suspending fluid, and λ is the vacuum wavelength of the incident light. The excess Rayleigh ratio, R(θ), is then given by
Even for a simple homogeneous sphere of radius a whose refractive index, n, is very nearly the same as the refractive index "n" of the suspending fluid, i.e. Rayleigh–Gans approximation, the scattering function in the scattering plane is the relatively complex quantity
:, where
and λ is the wavelength of the incident light in vacuum. | 7 | Physical Chemistry |
Cell engineering is the purposeful process of adding, deleting, or modifying genetic sequences in living cells to achieve biological engineering goals such as altering cell production, changing cell growth and proliferation requirements, adding or removing cell functions, and many more. Cell engineering often makes use of DNA technology to achieve these modifications as well as closely related tissue engineering methods. Cell engineering can be characterized as an intermediary level in the increasingly specific disciplines of biological engineering which includes organ engineering, tissue engineering, protein engineering, and genetic engineering.
The field of cellular engineering is gaining more traction as biomedical research advances in tissue engineering and becomes more specific. Publications in the field have gone from several thousand in the early 2000s to nearly 40,000 in 2020. | 1 | Biochemistry |
Because the net variation in state properties during a thermodynamic cycle is zero, it forms a closed loop on a PV diagram. A PV diagrams Y axis shows pressure (P) and X axis shows volume (V). The area enclosed by the loop is the work (W') done by the process:
This work is equal to the balance of heat (Q) transferred into the system:
Equation (2) is consistent with the First Law; even though the internal energy changes during the course of the cyclic process, when the cyclic process finishes the system's internal energy is the same as the energy it had when the process began.
If the cyclic process moves clockwise around the loop, then W will be positive, and it represents a heat engine. If it moves counterclockwise, then W will be negative, and it represents a heat pump. | 7 | Physical Chemistry |
A buffer solution contains an acid and its conjugate base or a base and its conjugate acid. Addition of the conjugate ion will result in a change of pH of the buffer solution. For example, if both sodium acetate and acetic acid are dissolved in the same solution they both dissociate and ionize to produce acetate ions. Sodium acetate is a strong electrolyte, so it dissociates completely in solution. Acetic acid is a weak acid, so it only ionizes slightly. According to Le Chatelier's principle, the addition of acetate ions from sodium acetate will suppress the ionization of acetic acid and shift its equilibrium to the left. Thus the percent dissociation of the acetic acid will decrease, and the pH of the solution will increase. The ionization of an acid or a base is limited by the presence of its conjugate base or acid.
: NaCHCO(s) → Na(aq) + CHCO(aq)
: CHCOH(aq) H(aq) + CHCO(aq)
This will decrease the hydronium concentration, and thus the common-ion solution will be less acidic than a solution containing only acetic acid. | 7 | Physical Chemistry |
In this technique siRNA first must be designed against the target gene. Once the siRNA is configured against the gene it has to be effectively delivered through a transfection protocol. Delivery is usually done by cationic liposomes, polymer nanoparticles, and lipid conjugation. This method is advantageous because it can deliver siRNA to most types of cells, has high efficiency and reproducibility, and is offered commercially. The most common commercial reagents for transfection of siRNA are Lipofectamine and Neon Transfection. However, it is not compatible with all cell types and has low in vivo efficiency. | 1 | Biochemistry |
Self-interstitial defects are interstitial defects which contain only atoms which are the same as those already present in the lattice.
The structure of interstitial defects has been experimentally determined in some metals and semiconductors.
Contrary to what one might intuitively expect, most self-interstitials in metals with a known structure have a split structure, in which two atoms share the same lattice site. Typically the center of mass of the two atoms is at the lattice site, and they are displaced symmetrically from it along one of the principal lattice directions. For instance, in several common face-centered cubic (fcc) metals such as copper, nickel and platinum, the ground state structure of the self-interstitial is the split [100] interstitial structure, where two atoms are displaced in a positive and negative [100] direction from the lattice site. In body-centered cubic (bcc) iron the ground state interstitial structure is similarly a [110] split interstitial.
These split interstitials are often called dumbbell interstitials, because plotting the two atoms forming the interstitial with two large spheres and a thick line joining them makes the structure resemble a dumbbell weight-lifting device.
In other bcc metals than iron, the ground state structure is believed based on recent density-functional theory calculations to be the [111] crowdion interstitial, which can be understood as a long chain (typically some 10–20) of atoms along the [111] lattice direction, compressed compared to the perfect lattice such that the chain contains one extra atom.
In semiconductors the situation is more complex, since defects may be charged and different charge states may have different structures. For instance, in silicon, the interstitial may either have a split [110] structure or a tetrahedral truly interstitial one.
Carbon, notably in graphite and diamond, has a number of interesting self-interstitials - recently discovered using Local-density approximation-calculations is the "spiro-interestitial" in graphite, named after spiropentane, as the interstitial carbon atom is situated between two basal planes and bonded in a geometry similar to spiropentane. | 8 | Metallurgy |
The Derjaguin approximation (or sometimes also referred to as the proximity approximation), named after the Russian scientist Boris Derjaguin, expresses the force profile acting between finite size bodies in terms of the force profile between two planar semi-infinite walls. This approximation is widely used to estimate forces between colloidal particles, as forces between two planar bodies are often much easier to calculate. The Derjaguin approximation expresses the force F(h) between two bodies as a function of the surface separation as
where W(h) is the interaction energy per unit area between the two planar walls and R the effective radius. When the two bodies are two spheres of radii R and R, respectively, the effective radius is given by
Experimental force profiles between macroscopic bodies as measured with the surface forces apparatus (SFA) or colloidal probe technique are often reported as the ratio F(h)/R. | 7 | Physical Chemistry |
This technique is most commonly used by mineralogists and petrologists. Most rocks are aggregates of small mineral grains. These grains may preserve chemical information acquired during their formation and subsequent alteration. This information may illuminate geologic processes such as crystallization, lithification, volcanism, metamorphism, orogenic events (mountain building), and plate tectonics. This technique is also used for the study of extraterrestrial rocks (meteorites), and provides chemical data which is vital to understanding the evolution of the planets, asteroids, and comets.
The change in elemental composition from the center (also known as core) to the edge (or rim) of a mineral can yield information about the history of the crystal's formation, including the temperature, pressure, and chemistry of the surrounding medium. Quartz crystals, for example, incorporate a small, but measurable amount of titanium into their structure as a function of temperature, pressure, and the amount of titanium available in their environment. Changes in these parameters are recorded by titanium as the crystal grows. | 3 | Analytical Chemistry |
This reagent was originally prepared by Conrad Willgerodt by reacting iodobenzene with a mixture of acetic acid and peracetic acid:
PIDA can also be prepared from iodosobenzene and glacial acetic acid:
More recent preparations direct from iodine, acetic acid, and benzene have been reported, using either sodium perborate or potassium peroxydisulfate as the oxidizing agent:
The PIDA molecule is termed hypervalent as its iodine atom (technically a hypervalent iodine) is in its +III oxidation state and has more than typical number of covalent bonds. It adopts a T-shaped molecular geometry, with the phenyl group occupying one of the three equatorial positions of a trigonal bipyramid (lone pairs occupy the other two) and the axial positions occupied by oxygen atoms from the acetate groups. The "T" is distorted in that the phenyl-C to I to acetate-O bond angles are less than 90°. A separate investigation of the crystal structure confirmed that it has orthorhombic crystals in space group Pnn2 and reported unit-cell dimensions in good agreement with the original paper. The bond lengths around the iodine atom were 2.08 Å to the phenyl carbon atom and equal 2.156 Å bonds to the acetate oxygen atoms. This second crystal structure determination explained the distortion in the geometry by noting the presence of two weaker intramolecular iodine–oxygen interactions, resulting in an "overall geometry of each iodine [that] can be described as a pentagonal-planar arrangement of three strong and two weak secondary bonds." | 0 | Organic Chemistry |
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