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Most drugs and drug candidates contain amine functional groups:
* Chlorpheniramine is an antihistamine that helps to relieve allergic disorders due to cold, hay fever, itchy skin, insect bites and stings.
* Chlorpromazine is a tranquilizer that sedates without inducing sleep. It is used to relieve anxiety, excitement, restlessness or even mental disorder.
* Ephedrine and phenylephrine, as amine hydrochlorides, are used as decongestants.
* Amphetamine, methamphetamine, and methcathinone are psychostimulant amines that are listed as controlled substances by the US DEA.
* Thioridazine, an antipsychotic drug, is an amine which is believed to exhibit its antipsychotic effects, in part, due to its effects on other amines.
* Amitriptyline, imipramine, lofepramine and clomipramine are tricyclic antidepressants and tertiary amines.
* Nortriptyline, desipramine, and amoxapine are tricyclic antidepressants and secondary amines. (The tricyclics are grouped by the nature of the final amino group on the side chain.)
* Substituted tryptamines and phenethylamines are key basic structures for a large variety of psychedelic drugs.
* Opiate analgesics such as morphine, codeine, and heroin are tertiary amines. | 0 | Theoretical and Fundamental Chemistry |
Metal imido complexes are mainly of academic interest. They are however assumed to be intermediates in ammoxidation catalysis, in the Sharpless oxyamination, and in nitrogen fixation. | 0 | Theoretical and Fundamental Chemistry |
Deconvolution can be used to apparently improve spectral resolution. In the case of NMR spectra, the process is relatively straight forward, because the line shapes are Lorentzian, and the convolution of a Lorentzian with another Lorentzian is also Lorentzian. The Fourier transform of a Lorentzian is an exponential. In the co-domain (time) of the spectroscopic domain (frequency) convolution becomes multiplication. Therefore, a convolution of the sum of two Lorentzians becomes a multiplication of two exponentials in the co-domain. Since, in FT-NMR, the measurements are made in the time domain division of the data by an exponential is equivalent to deconvolution in the frequency domain. A suitable choice of exponential results in a reduction of the half-width of a line in the frequency domain. This technique has been rendered all but obsolete by advances in NMR technology. A similar process has been applied for resolution enhancement of other types of spectra, with the disadvantage that the spectrum must be first Fourier transformed and then transformed back after the deconvoluting function has been applied in the spectrum's co-domain. | 0 | Theoretical and Fundamental Chemistry |
Köhler theory describes the process in which water vapor condenses and forms liquid cloud drops, and is based on equilibrium thermodynamics. It combines the Kelvin effect, which describes the change in saturation vapor pressure due to a curved surface, and Raoult's Law, which relates the saturation vapor pressure to the solute. It is an important process in the field of cloud physics. It was initially published in 1936 by Hilding Köhler, Professor of Meteorology in the Uppsala University.
Köhler equation:
where is the droplet water vapor pressure, is the corresponding saturation vapor pressure over a flat surface, is the droplet surface tension, is the density of pure water, is the moles of solute, is the molecular weight of water, and is the cloud drop diameter. | 0 | Theoretical and Fundamental Chemistry |
Given these assumptions, the flux of oxidant through each of the three phases can be expressed in terms of concentrations, material properties, and temperature.
By setting the three fluxes equal to each other the following relations can be derived:
Assuming a diffusion controlled growth i.e. where determines the growth rate, and substituting and in terms of from the above two relations into and equation respectively, one obtains:
If N is the concentration of the oxidant inside a unit volume of the oxide, then the oxide growth rate can be written in the form of a differential equation. The solution to this equation gives the oxide thickness at any time t.
where the constants and encapsulate the properties of the reaction and the oxide layer respectively, and is the initial layer of oxide that was present at the surface. These constants are given as:
where , with being the gas solubility parameter of the Henry's law and is the partial pressure of the diffusing gas.
Solving the quadratic equation for x yields:
Taking the short and long time limits of the above equation reveals two main modes of operation. The first mode, where the growth is linear, occurs initially when is small. The second mode gives a quadratic growth and occurs when the oxide thickens as the oxidation time increases.
The quantities B and B/A are often called the quadratic and linear reaction rate constants. They depend exponentially on temperature, like this:
where is the activation energy and is the Boltzmann constant in eV. differs from one equation to the other. The following table lists the values of the four parameters for single-crystal silicon under conditions typically used in industry (low doping, atmospheric pressure). The linear rate constant depends on the orientation of the crystal (usually indicated by the Miller indices of the crystal plane facing the surface). The table gives values for and silicon. | 1 | Applied and Interdisciplinary Chemistry |
In an ideal plug flow reactor (PFR) the fluid particles leave in the same order they arrived, not mixing with those in front and behind. Therefore, the particles entering at time t will exit at time t + T, all spending a time T inside the reactor. The residence time distribution will be then a Dirac delta function delayed by T:
The mean is T and the variance is zero.
The RTD of a real reactor deviates from that of an ideal reactor, depending on the hydrodynamics within the vessel. A non-zero variance indicates that there is some dispersion along the path of the fluid, which may be attributed to turbulence, a non-uniform velocity profile, or diffusion. If the mean of the distribution is earlier than the expected time T it indicates that there is stagnant fluid within the vessel. If the RTD curve shows more than one main peak it may indicate channeling, parallel paths to the exit, or strong internal circulation.
In PFRs, reactants enter the reactor at one end and react as they move down the reactor. Consequently, the reaction rate is dependent on the concentrations which vary along the reactor requiring the inverse of the reaction rate to be integrated over the fractional conversion. | 0 | Theoretical and Fundamental Chemistry |
Antagonists of the N-terminal domain (NTD) of the AR have been proposed to overcome the limitations of current antiandrogens regarding mutant ARs, by directly blocking AR function from protein surface, outside of the LBP. This direct blockade is thought to provide a more efficient strategy to avoid or overcome abnormal AR action during AWS, as well as allowing for more flexibility in structural modification without the space limitations of the rigid LBP.
Steroid receptors have similarities in gene sequences and protein structures, leading often to functional crosstalk among steroid receptors. One of the criteria for AR NTD antagonists is to achieve high degree of specificity for the AR. It is though important to realize that AR specificity does not necessarily translate in vivo, since NTD antagonists may also interact with protein targets other than AR. | 1 | Applied and Interdisciplinary Chemistry |
Signs and symptoms vary depending on the degree of hypothermia, and may be divided by the three stages of severity. People with hypothermia may appear pale and feel cold to touch.
Infants with hypothermia may feel cold when touched, with bright red skin and an unusual lack of energy.
Behavioural changes such as impaired judgement, impaired sense of time and place, unusual aggression and numbness can be observed in individuals with hypothermia, they can also deny their condition and refuse any help. A hypothermic person can be euphoric and hallucinating.
Cold stress refers to a near-normal body temperature with low skin temperature, signs include shivering. Cold stress is caused by cold exposure and it can lead to hypothermia and frostbite if not treated. | 1 | Applied and Interdisciplinary Chemistry |
Concentrated (50%) aqueous solutions of sodium hydroxide have a characteristic viscosity, 78 mPa·s, that is much greater than that of water (1.0 mPa·s) and near that of olive oil (85 mPa·s) at room temperature. The viscosity of aqueous , as with any liquid chemical, is inversely related to its temperature, i.e., its viscosity decreases as temperature increases, and vice versa. The viscosity of sodium hydroxide solutions plays a direct role in its application as well as its storage. | 0 | Theoretical and Fundamental Chemistry |
In the absence of an effective enantiomeric environment (precursor, chiral catalyst, or kinetic resolution), separation of a racemic mixture into its enantiomeric components is impossible, although certain racemic mixtures spontaneously crystallize in the form of a racemic conglomerate, in which crystals of the enantiomers are physically segregated and may be separated mechanically. However, most racemates form crystals containing both enantiomers in a 1:1 ratio.
In his pioneering work, Louis Pasteur was able to isolate the isomers of sodium ammonium tartrate because the individual enantiomers crystallize separately from solution. To be sure, equal amounts of the enantiomorphic crystals are produced, but the two kinds of crystals can be separated with tweezers. This behavior is unusual. A less common method is by enantiomer self-disproportionation.
The second strategy is asymmetric synthesis: the use of various techniques to prepare the desired compound in high enantiomeric excess. Techniques encompassed include the use of chiral starting materials (chiral pool synthesis), the use of chiral auxiliaries and chiral catalysts, and the application of asymmetric induction. The use of enzymes (biocatalysis) may also produce the desired compound.
A third strategy is Enantioconvergent synthesis, the synthesis of one enantiomer from a racemic precursor, utilizing both enantiomers. By making use of a chiral catalyist, both enantiomers of the reactant result in a single enantiomer of product.
Enantiomers may not be isolable if there is an accessible pathway for racemization (interconversion between enantiomorphs to yield a racemic mixture) at a given temperature and timescale. For example, amines with three distinct substituents are chiral, but with few exceptions (e.g. substituted N-chloroaziridines), they rapidly undergo "umbrella inversion" at room temperature, leading to racemization. If the racemization is fast enough, the molecule can often be treated as an achiral, averaged structure. | 0 | Theoretical and Fundamental Chemistry |
Sealing gaps and cracks around electrical wiring, water pipes and ductwork using acoustical caulk or spray foam will significantly reduce unwanted noise as a preliminary step for ceiling soundproofing. Acoustical caulk should be used along the perimeter of the wall and around all fixtures and duct registers to further seal the treatment. Mineral wool insulation is most commonly used in soundproofing for its density and low cost in comparison to other soundproofing materials. Spray foam insulation should only be used to fill gaps and cracks or as a 1-2 inch layer before installing mineral wool. Cured spray foam and other closed-cell foam can be a sound conductor. Spray foam is not porous enough to absorb sound, it's also not dense enough to stop sound. Avoid recessed lights or any fixtures requiring large holes in the ceiling. One small hole can compromise the efficiency of the entire treatment.
An effective method to reduce impact noise is the resilient isolation channel. The channels decouple the drywall from the joists, reducing the transfer of vibration. | 1 | Applied and Interdisciplinary Chemistry |
The first stage is called roughing, which produces a rougher concentrate. The objective is to remove the maximum amount of the valuable mineral at as coarse a particle size as practical. Grinding costs energy. The goal is to release enough gangue from the valuable mineral to get a high recovery. Some concentrators use a preflotation step to remove low density impurities such as carbonaceous dust. The rougher concentrate is normally subjected to further stages of flotation to reject more of the undesirable minerals that also reported to the froth, in a process known as cleaning. The resulting material is often subject to further grinding (usually called regrinding). Regrinding is often undertaken in specialized regrind mills, such as the IsaMill. The rougher flotation step is often followed by a scavenger flotation step that is applied to the rougher tailings to further recover any of the target minerals. | 1 | Applied and Interdisciplinary Chemistry |
The reaction was initially demonstrated using a ketone as the directing group, but other functional groups have been reported, including esters, imines, nitriles, and imidates. Murai reactions have also been reported with disubstituted alkynes. Bidentate directing groups allow ortho alkylation of aromatic rings with α,β-unsaturated ketones, which typically are unreactive in Murai reactions.
Early examples of the reaction suffered from side products of alkylation at both ortho positions. This problem can be partially solved using an ortho methyl blocking group. Unfortunately, with ortho methyl groups both the rate and generality of the reaction are reduced. Substituents at the meta position influence regioselectivity. The reaction preferentially adds at the least sterically hindered ortho position, except when there is a meta group capable of coordinating with the Ru catalyst. Methoxyacetophenones show preferential reaction at the more hindered position. | 0 | Theoretical and Fundamental Chemistry |
The Pulvermacher chain, especially in the form of one being worn on the body, was very familiar in the late 19th and early 20th century and would not have needed to be explained to an audience. For instance, there are references to it in the novel Madame Bovary when the character Homais wearing a number of Pulvermacher chains is described as "more bandaged than a Scythian". | 0 | Theoretical and Fundamental Chemistry |
The higher heating value (HHV; gross energy, upper heating value, gross calorific value GCV, or higher calorific value; HCV) indicates the upper limit of the available thermal energy produced by a complete combustion of fuel. It is measured as a unit of energy per unit mass or volume of substance. The HHV is determined by bringing all the products of combustion back to the original pre-combustion temperature, including condensing any vapor produced. Such measurements often use a standard temperature of . This is the same as the thermodynamic heat of combustion since the enthalpy change for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is condensed to a liquid. The higher heating value takes into account the latent heat of vaporization of water in the combustion products, and is useful in calculating heating values for fuels where condensation of the reaction products is practical (e.g., in a gas-fired boiler used for space heat). In other words, HHV assumes all the water component is in liquid state at the end of combustion (in product of combustion) and that heat delivered at temperatures below can be put to use. | 0 | Theoretical and Fundamental Chemistry |
In 1792, the Real Seminario de Minería (College of Mines) was founded in New Spain by a decree of King Charles III of Spain, with the object of reforming the study of mining and metallurgy in the colony. The institution was initially headed by Fausto Elhúyar (1755–1833), the discoverer of tungsten.
In 1793, Elhúyar offered Del Río a position as chair at the newly organized college. Del Rio refused the chair of chemistry, but accepted that of mineralogy.
Del Río arrived at the port of Veracruz on 20 October 1794, on the ship San Francisco de Alcántara out of Cádiz.
Once in his new position, del Río dedicated himself to teaching and scientific investigation. On 27 April 1795 he opened the first course in mineralogy ever presented in New Spain. He made important studies of minerals and developed innovative methods in mining. He also wrote the first textbook of mineralogy to be published anywhere in America, Elementos de Orictognosía, and the first in Spanish rather than German or English. Volume I appeared in 1795, and volume II in 1805. Santiago Ramírez, his student and later his biographer, described it as "a monumental work, which... will be an object of veneration and consultation".
German naturalist, Alexander von Humboldt, making a survey of resources in Spanish-held colonies for Spain, reported favorably that it was in Mexico where the best work of mineralogy in Spanish had been published, the Elementos de Orictognosia of Señor Del Rio.
Humboldt spent the period from March 1803 to March 1804 in Mexico City, renewing his friendship with del Rio and actively participating in the investigations of the College of Mining. He organized excursions to Chapultepec, to the basaltic zone of Pedregal de San Ángel, the lava fields of the Xitle volcano, and to the hot springs of Peñón de los Baños, a rocky outcrop close to the modern Mexico City International Airport, accumulating data and samples of minerals and rocks that were then submitted to chemical tests for identification.
In 1820 del Río was named a deputy to the Spanish Cortes. He was a liberal who argued for the independence of New Spain. He was in Madrid when Mexico gained its independence. Invited to remain in Spain, he nevertheless returned to Mexico (in 1821), which he considered his homeland.
In 1829, amidst the Spanish attempts to reconquer Mexico, the government of independent Mexico expelled the Spaniards resident in the country, with some notable exceptions. Del Río was one of the exceptions. The expulsion had a major impact on the work of the College of Mining. The director, Fausto Elhúyar, was forced to resign and leave the country.
Indignant over the expulsion of his colleagues, del Río showed solidarity by himself entering voluntary exile in Philadelphia for four years. There he was highly honored. He took part in the scientific activities of the American Philosophical Society (elected 1830) and was elected president of the Geological Society of Philadelphia. John Hurtel of Philadelphia published a new edition of del Rio's book in 1832. Del Rio returned to Mexico in 1834 and again occupied the chair of mineralogy at the college. He was also given the chair of geology. | 1 | Applied and Interdisciplinary Chemistry |
The project began recording on 9 June 2008 and the initial videos were completed on 17 July 2008. The collection includes videos, each just a few minutes long, for all 118 known elements with a video for each element, as well as many additional supplemental chemistry videos. The 118 element videos and introduction videos were all shot unscripted in June and July 2008.
Since the initial videos were completed in 2008 the team has been refining and uploading revised versions of the videos with new video and in higher resolutions. A key example of this revising is with the xenon video that was redone in honour of professor Neil Bartlett who died on 5 August 2008; Bartlett prepared one of the first xenon compounds, xenon hexafluoroplatinate. | 1 | Applied and Interdisciplinary Chemistry |
A bone seeker is an element, often a radioisotope, that tends to accumulate in the bones of humans and other animals when it is introduced into the body.
For example, strontium and radium are chemically similar to calcium and can replace the calcium in bones. Plutonium is also a bone seeker, though the mechanism by which it accumulates in bone tissue is unknown.
Radioactive bone seekers are particular health risks as they irradiate surrounding tissue, though this can be useful for radiotherapyradium-223 is used in this way. Stable bone seekers can also be harmful: excessive strontium absorption has been linked with increased levels of rickets. The salt strontium ranelate, however, is a bone seeker which is sometimes used to strengthen bones as a treatment for osteoporosis. Bone seekers have been proposed as a method of delivering antibiotics to infected bone tissue. | 0 | Theoretical and Fundamental Chemistry |
Functional selectivity (or “agonist trafficking”, “biased agonism”, “biased signaling”, "ligand bias" and “differential engagement”) is the ligand-dependent selectivity for certain signal transduction pathways relative to a reference ligand (often the endogenous hormone or peptide) at the same receptor. Functional selectivity can be present when a receptor has several possible signal transduction pathways. To which degree each pathway is activated thus depends on which ligand binds to the receptor. Functional selectivity, or biased signaling, is most extensively characterized at G protein coupled receptors (GPCRs). A number of biased agonists, such as those at muscarinic M2 receptors tested as analgesics or antiproliferative drugs, or those at opioid receptors that mediate pain, show potential at various receptor families to increase beneficial properties while reducing side effects. For example, pre-clinical studies with G protein biased agonists at the μ-opioid receptor show equivalent efficacy for treating pain with reduced risk for addictive potential and respiratory depression. Studies within the chemokine receptor system also suggest that GPCR biased agonism is physiologically relevant. For example, a beta-arrestin biased agonist of the chemokine receptor CXCR3 induced greater chemotaxis of T cells relative to a G protein biased agonist. | 1 | Applied and Interdisciplinary Chemistry |
In contrast to the Bürgi–Dunitz angle, , and using the case of carbonyl additions as example: the angle adopted during an approach by the nucleophile to a trigonal electrophile depends in complex fashion on:
* the relative steric size of the two substituents attached to (alpha to) the electrophilic carbonyl, which give rise to varying degrees of repulsive van der Waalss interactions (e.g., giving ≈ 7° for hydride attack on pivaldehyde (see image), where R=tertiary-butyl, and R=H),
* the electronic characteristics of substituents alpha to the carbonyl, where heteroatom-containing substituents can, through their stereoelectronic influence, function as overly intrusive steric groups (e.g., giving ≈ 40-50° for esters and amides with small R' groups, since R is an O- and N-substituent, respectively), and
* the nature of the bonds made by more distant atoms to the atoms alpha to the carbonyl, e.g., where the energy of the σ* molecular orbital (MO) between the alpha- and beta-substituents was seen to compete with the foregoing influences,
as well as on the MO shapes and occupancies of the carbonyl and attacking nucleophile. Hence, the observed for nucleophilic attack appears to be influenced primarily by the energetics of the HOMO-LUMO overlap of the nucleophile-electrophile pair in the systems studied—see the Bürgi–Dunitz article, and the related inorganic chemistry concept of the angular overlap model (AOM)—which leads in many cases to a convergence of values (but not all, see below); however, the required to provide optimal overlap between HOMO and LUMO reflect the complex interplay of energetic contributions described with examples above. | 0 | Theoretical and Fundamental Chemistry |
The van der Waals surface of a molecule is an abstract representation or model of that molecule, illustrating where, in very rough terms, a surface might reside for the molecule based on the hard cutoffs of van der Waals radii for individual atoms, and it represents a surface through which the molecule might be conceived as interacting with other molecules.
Also referred to as a van der Waals envelope, the van der Waals surface is named for Johannes Diderik van der Waals, a Dutch theoretical physicist and thermodynamicist who developed theory to provide a liquid-gas equation of state that accounted for the non-zero volume of atoms and molecules, and on their exhibiting an attractive force when they interacted (theoretical constructions that also bear his name).
van der Waals surfaces are therefore a tool used in the abstract representations of molecules, whether accessed, as they were originally, via hand calculation, or via physical wood/plastic models, or now digitally, via computational chemistry software.
Practically speaking, CPK models, developed by and named for Robert Corey, Linus Pauling, and Walter Koltun, were the first widely used physical molecular models based on van der Waals radii, and allowed broad pedagogical and research use of a model showing the van der Waals surfaces of molecules. | 0 | Theoretical and Fundamental Chemistry |
The laser printing of single nanoparticles is a method of applying optical forces that direct single nanoparticles to targeted substrate regions. Van der Waals interactions cause attachment of the single nanoparticles to the substrate areas. This has been accomplished with gold and silicon nanoparticles. | 0 | Theoretical and Fundamental Chemistry |
The reaction of carbon dioxide with epoxides is a general route to the preparation of cyclic 5-membered carbonates. Annual production of cyclic carbonates was estimated at 100,000 tonnes per year in 2010. Industrially, ethylene and propylene oxides readily react with carbon dioxide to give ethylene and propylene carbonates (with an appropriate catalyst). For example:
: CHO + CO → CHOCO | 0 | Theoretical and Fundamental Chemistry |
Subtractive hybridization is a technology that allows for PCR-based amplification of only cDNA fragments that differ between a control (driver) and experimental transcriptome. cDNA is produced from mRNA. Differences in relative abundance of transcripts are highlighted, as are genetic differences between species. The technique relies on the removal of dsDNA formed by hybridization between a control and test sample, thus eliminating cDNAs or gDNAs of similar abundance, and retaining differentially expressed, or variable in sequence, transcripts or genomic sequences.
Suppression subtractive hybridization has also been successfully used to identify strain- or species-specific DNA sequences in a variety of bacteria including Vibrio species (Metagenomics). | 1 | Applied and Interdisciplinary Chemistry |
Red plague is an accelerated corrosion of copper when plated with silver. After storage, damage or use in high-humidity environment, cuprous oxide forms on the surface of the parts. The corrosion is identifiable by presence of patches of brown-red powder deposit on the exposed copper.
Red plague is caused by normally occurring electrode potential difference between the copper and silver, leading to galvanic corrosion occurring in pits or breaks in the silver plating. It develops in the presence of moisture and oxygen when the porosity of the silver layer allows them to come in contact with the copper-silver interface. It is an electrochemical corrosion—a copper-silver galvanic cell forms and the copper acts as sacrificial anode. In suitable conditions, the corrosion can proceed rather quickly and lead to total circuit failure.
More details can be seen in ESA document PSS-01-720, with details on determining the susceptibility of silver-plated copper wire to red plague corrosion found in ECSS-Q-ST-70-20C.
It is not to be confused with purple plague, a type of galvanic corrosion that occurs between gold and aluminum. | 1 | Applied and Interdisciplinary Chemistry |
Due to its material properties, Terfenol-D is excellent for use in the manufacturing of low frequency, high powered underwater acoustics. Its initial application was in naval sonar systems. It sees application in magnetomechanical sensors, actuators, and acoustic and ultrasonic transducers due to its high energy density and large bandwidth capabilities, e.g. in the SoundBug device (its first commercial application by FeONIC). Its strain is also larger than that of another normally used material (PZT8), which allows Terfenol-D transducers to reach greater depths for ocean explorations than past transducers. Its low Young's modulus brings some complications due to compression at large depths, which are overcome in transducer designs that may reach 1000 ft in depth and only lose a small amount of accuracy of around 1 dB. Due to its high temperature range, Terfenol-D is also useful in deep hole acoustic transducers where the environment may reach high pressure and temperatures like oil holes. Terfenol-D may also be used for hydraulic valve drivers due to its high strain and high force properties. Similarly, magnetostrictive actuators have also been considered for use in fuel injectors for diesel engines because of the high stresses that can be produced. | 1 | Applied and Interdisciplinary Chemistry |
Magnetometers can give an indication of auroral activity before the light from the aurora becomes visible. A grid of magnetometers around the world constantly measures the effect of the solar wind on the Earth's magnetic field, which is then published on the K-index. | 0 | Theoretical and Fundamental Chemistry |
Schott and many scientists and engineers afterwards applied the additivity principle to experimental data measured in their own laboratory within sufficiently narrow composition ranges (local glass models). This is most convenient because disagreements between laboratories and non-linear glass component interactions do not need to be considered. In the course of several decades of systematic glass research thousands of glass compositions were studied, resulting in millions of published glass properties, collected in glass databases. This huge pool of experimental data was not investigated as a whole, until Bottinga, Kucuk, Priven, Choudhary, Mazurin, and Fluegel published their global glass models, using various approaches. In contrast to the models by Schott the global models consider many independent data sources, making the model estimates more reliable. In addition, global models can reveal and quantify non-additive influences of certain glass component combinations on the properties, such as the mixed-alkali effect as seen in the adjacent diagram, or the boron anomaly. Global models also reflect interesting developments of glass property measurement accuracy, e.g., a decreasing accuracy of experimental data in modern scientific literature for some glass properties, shown in the diagram. They can be used for accreditation of new data, experimental procedures, and measurement institutions (glass laboratories). In the following sections (except melting enthalpy) empirical modeling techniques are presented, which seem to be a successful way for handling huge amounts of experimental data. The resulting models are applied in contemporary engineering and research for the calculation of glass properties.
Non-empirical (deductive) glass models exist. They are often not created to obtain reliable glass property predictions in the first place (except melting enthalpy), but to establish relations among several properties (e.g. atomic radius, atomic mass, chemical bond strength and angles, chemical valency, heat capacity) to gain scientific insight. In future, the investigation of property relations in deductive models may ultimately lead to reliable predictions for all desired properties, provided the property relations are well understood and all required experimental data are available. | 0 | Theoretical and Fundamental Chemistry |
Carbon dioxide has unique long-term effects on climate change that are nearly "irreversible" for a thousand years after emissions stop (zero further emissions). The greenhouse gases methane and nitrous oxide do not persist over time in the same way as carbon dioxide. Even if human carbon dioxide emissions were to completely cease, atmospheric temperatures are not expected to decrease significantly in the short term. This is because the air temperature is determined by a balance between heating, due to greenhouse gases, and cooling due to heat transfer to the ocean. If emissions were to stop, CO levels and the heating effect would slowly decrease, but simultaneously the cooling due to heat transfer would diminish (because sea temperatures would get closer to the air temperature), with the result that the air temperature would decrease only slowly. Sea temperatures would continue to rise, causing thermal expansion and some sea level rise. Lowering global temperatures more rapidly would require carbon sequestration or geoengineering.
Various techniques have been proposed for removing excess carbon dioxide from the atmosphere. | 1 | Applied and Interdisciplinary Chemistry |
Isotopes are distinct nuclear species (or nuclides) of the same chemical element. They have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), but differ in nucleon numbers (mass numbers) due to different numbers of neutrons in their nuclei. While all isotopes of a given element have similar chemical properties, they have different atomic masses and physical properties.
The term isotope is derived from the Greek roots isos (ἴσος "equal") and topos (τόπος "place"), meaning "the same place"; thus, the meaning behind the name is that different isotopes of a single element occupy the same position on the periodic table. It was coined by Scottish doctor and writer Margaret Todd in a 1913 suggestion to the British chemist Frederick Soddy, who popularized the term.
The number of protons within the atoms nucleus is called its atomic number and is equal to the number of electrons in the neutral (non-ionized) atom. Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atoms mass number, and each isotope of a given element has a different mass number.
For example, carbon-12, carbon-13, and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13, and 14, respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons so that the neutron numbers of these isotopes are 6, 7, and 8 respectively. | 0 | Theoretical and Fundamental Chemistry |
Chemical process miniaturization refers to a philosophical concept within the discipline of process design that challenges the notion of "economy of scale" or "bigger is better". In this context, process design refers to the discipline taught primarily to chemical engineers. However, the emerging discipline of process miniaturization will involve integrated knowledge from many areas; as examples, systems engineering and design, remote measurement and control using intelligent sensors, biological process systems engineering, and advanced manufacturing robotics, etc.
One of the challenges of chemical engineering has been to design processes based on chemical laboratory-scale methods, and to scale-up processes so that products can be manufactured that are economically affordable.
As a process becomes larger, more product can be produced per unit time, so when a process technology becomes established or mature, and operates consistently without upsets or “downtime”, more economic efficiency can be gained from scale-up. Given a fixed price for the feedstock (e.g. the price per barrel of crude oil), the product cost can be decreased using a larger scale process because the capital investment and operational costs do not normally increase linearly with scale. For example, the capacity or volume of a cylindrical vessel used to produce a product increases proportional to the square of the radius of the cylinder, so cost of materials per unit volume decreases. But the costs to design and fabricate the vessel have traditionally been less sensitive to scale. In other words, one can design a small vessel and fabricate it for about the same cost as the larger vessel. In addition, the cost to control and operate a process (or a process unit component) does not change substantially with the scale. For example, if it takes one operator to operate a small process, that same operator can probably operate the larger process.
The economy of scale concept, as taught to chemical engineers, has led to the notion that one of the objectives of process development and design is to achieve “economy of scale” by scaling-up to the largest possible size processing plant so that the product cost can be economically affordable. This disciplinary philosophy has been reinforced by example designs in the petroleum refining and petrochemical industries, where feedstocks have been transported as fluids in pipelines, large tanker ships, and railcars.
Fluids, by definition are materials that flow and can be transferred using pumps or gravity. Therefore, large pumps, valves, and pipelines exist to transfer large amounts of fluids in the process industries. Process miniaturization, in contrast, will involve processing of large amounts of solids from renewable biomass resources; therefore, new thinking towards process designs optimized for solids processing will be required.
The concept of a microprocess has been defined by S. S. Sofer while a professor at the New Jersey Institute of Technology. A microprocess has the following characteristics:
:1) Portability
:2) Capable of being mass produced using advanced robotic manufacturing methods
:3) Approaching total automation
:4) A new technology | 1 | Applied and Interdisciplinary Chemistry |
The Meixner test (also known as the Wieland test) uses concentrated hydrochloric acid and newspaper to test for the deadly amatoxins found in some species of Amanita, Lepiota, and Galerina. The test yields false positives for some compounds, such as psilocin. | 0 | Theoretical and Fundamental Chemistry |
Potential root causes of metallurgical failures are vast, spanning the lifecycle of component from design to manufacturing to usage. The most common reasons for failures can be classified into the following categories: | 1 | Applied and Interdisciplinary Chemistry |
The Peregrine soliton can also be seen as the limiting case of the time-periodic Kuznetsov-Ma breather when the period tends to infinity. | 1 | Applied and Interdisciplinary Chemistry |
Six essential amino acids and three nonessential are synthesized from oxaloacetate and pyruvate. Aspartate and alanine are formed from oxaloacetate and pyruvate, respectively, by transamination from glutamate. Asparagine is synthesized by amidation of aspartate, with glutamine donating the NH4.
These are nonessential amino acids, and their simple biosynthetic pathways occur in all organisms. Methionine, threonine, lysine, isoleucine, valine, and leucine are essential amino acids in humans and most vertebrates. Their biosynthetic pathways in bacteria are complex and interconnected. | 1 | Applied and Interdisciplinary Chemistry |
In shallower waters, evidence supports that activity of local fisherman and marine life such as fish and certain shark species can disturb bottom sediments containing calcium carbonate particles and lead to their suspension. In addition, as microorganisms impact water chemistry in observable ways and require certain nutrient levels to thrive, whiting events found occurring in nutrient-poor waters where no significant alkalinity difference exists between whiting and non-whiting waters support the idea of sediment re-suspension as a primary cause. | 0 | Theoretical and Fundamental Chemistry |
The term antiaromaticity was first proposed by Ronald Breslow in 1967 as "a situation in which a cyclic delocalisation of electrons is destabilising". The IUPAC criteria for antiaromaticity are as follows:
#The molecule must be cyclic.
#The molecule must be planar.
#The molecule must have a complete conjugated π-electron system within the ring.
#The molecule must have 4n π-electrons where n is any integer within the conjugated π-system.
This differs from aromaticity only in the fourth criterion: aromatic molecules have 4n +2 π-electrons in the conjugated π system and therefore follow Hückel’s rule. Non-aromatic molecules are either noncyclic, nonplanar, or do not have a complete conjugated π system within the ring.
Having a planar ring system is essential for maximizing the overlap between the p orbitals which make up the conjugated π system. This explains why being a planar, cyclic molecule is a key characteristic of both aromatic and antiaromatic molecules. However, in reality, it is difficult to determine whether or not a molecule is completely conjugated simply by looking at its structure: sometimes molecules can distort in order to relieve strain and this distortion has the potential to disrupt the conjugation. Thus, additional efforts must be taken in order to determine whether or not a certain molecule is genuinely antiaromatic.
An antiaromatic compound may demonstrate its antiaromaticity both kinetically and thermodynamically. As will be discussed later, antiaromatic compounds experience exceptionally high chemical reactivity (being highly reactive is not “indicative” of an antiaromatic compound, it merely suggests that the compound could be antiaromatic). An antiaromatic compound may also be recognized thermodynamically by measuring the energy of the cyclic conjugated π electron system. In an antiaromatic compound, the amount of conjugation energy in the molecule will be significantly higher than in an appropriate reference compound.
In reality, it is recommended that one analyze the structure of a potentially antiaromatic compound extensively before declaring that it is indeed antiaromatic. If an experimentally determined structure of the molecule in question does not exist, a computational analysis must be performed. The potential energy of the molecule should be probed for various geometries in order to assess any distortion from a symmetric planar conformation.
This procedure is recommended because there have been multiple instances in the past where molecules which appear to be antiaromatic on paper turn out to be not truly so in actuality. The most famous (and heavily debated) of these molecules is cyclobutadiene, as is discussed later.
Examples of antiaromatic compounds are pentalene (A), biphenylene (B), cyclopentadienyl cation (C). The prototypical example of antiaromaticity, cyclobutadiene, is the subject of debate, with some scientists arguing that antiaromaticity is not a major factor contributing to its destabilization. Cyclooctatetraene appears at first glance to be antiaromatic, but is an excellent example of a molecule adopting a non-planar geometry to avoid the destabilization that results from antiaromaticity. Because antiaromatic compounds are often short-lived and difficult to work with experimentally, antiaromatic destabilization energy is often modeled by simulation rather than by experimentation. | 0 | Theoretical and Fundamental Chemistry |
In boilers, economizers are heat exchange devices that heat fluids, usually water, up to but not normally beyond the boiling point of that fluid. Economizers are so named because they can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boilers efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used to fill it (the feed water').
Steam boilers use large amounts of energy raising feed water to the boiling temperature, converting the water to steam and sometimes superheating that steam above saturation temperature. Heat transfer efficiency is improved when the highest temperatures near the combustion sources are used for boiling and superheating, while using the residual heat of the cooled combustion gases exhausting from the boiler through an economizer to raise the temperature of feed water entering the steam drum.
An indirect contact or direct contact condensing economizer will recover the residual heat from the combustion products. A series of dampers, an efficient control system, as well as a ventilator, allow all or part of the combustion products to pass through the economizer, depending on the demand for make-up water and/or process water. The temperature of the gases can be lowered from the boiling temperature of the fluid to little more than the incoming feed water temperature while preheating that feed water to the boiling temperature. High pressure boilers typically have larger economizer surfaces than low pressure boilers. Economizer tubes often have projections like fins to increase the heat transfer surface on the combustion gas side. On average over the years, boiler combustion efficiency has risen from 80% to more than 95%. The efficiency of heat produced is directly linked to boiler efficiency. The percentage of excess air and the temperature of the combustion products are two key variables in evaluating this efficiency.
The combustion of natural gas needs a certain quantity of air in order to be complete, so the burners need a flow of excess air in order to operate. Combustion produces water steam, and the quantity depends on the amount of natural gas burned. Also, the evaluation of the dew point depends on the excess air. Natural gas has different combustion efficiency curves linked to the temperature of the gases and the excess air. For example, if the gases are chilled to 38 °C and there is 15% excess air, then the efficiency will be 94%. The condensing economizer can thus recover the sensible and latent heat in the steam condensate contained in the flue gases for the process.
The economizer is made of an aluminium and stainless steel alloy. The gases pass through the cylinder, and the water passes through the finned tubes. It condenses about 11% of the water contained in the gases. | 0 | Theoretical and Fundamental Chemistry |
Transition metal hydrides include compounds that can be classified as covalent hydrides. Some are even classified as interstitial hydrides and other bridging hydrides. Classical transition metal hydride feature a single bond between the hydrogen centre and the transition metal. Some transition metal hydrides are acidic, e.g., and . The anions potassium nonahydridorhenate and are examples from the growing collection of known molecular homoleptic metal hydrides. As pseudohalides, hydride ligands are capable of bonding with positively polarized hydrogen centres. This interaction, called dihydrogen bonding, is similar to hydrogen bonding, which exists between positively polarized protons and electronegative atoms with open lone pairs. | 0 | Theoretical and Fundamental Chemistry |
Lithium treatment has been found to inhibit the enzyme inositol monophosphatase, involved in degrading inositol monophosphate to inositol required in PIP synthesis. This leads to lower levels of inositol triphosphate, created by decomposition of PIP. This effect has been suggested to be further enhanced with an inositol triphosphate reuptake inhibitor. Inositol disruptions have been linked to memory impairment and depression. It is known with good certainty that signals from the receptors coupled to the phosphoinositide signal transduction are affected by lithium. myo-inositol is also regulated by the high affinity sodium mI transport system (SMIT). Lithium is hypothesized to inhibit mI entering the cells and mitigating the function of SMIT. Reductions of cellular levels of myo-inositol results in the inhibition of the phosphoinositide cycle. | 1 | Applied and Interdisciplinary Chemistry |
Initial glance, forensic intelligence may appear as a nascent facet of forensic science facilitated by advancements in information technologies such as computers, databases, and data-flow management software. However, a more profound examination reveals that forensic intelligence represents a genuine and emerging inclination among forensic practitioners to actively participate in investigative and policing strategies. In doing so, it elucidates existing practices within scientific literature, advocating for a paradigm shift from the prevailing conception of forensic science as a conglomerate of disciplines merely aiding the criminal justice system. Instead, it urges a perspective that views forensic science as a discipline studying the informative potential of traces—remnants of criminal activity. Embracing this transformative shift poses a significant challenge for education, necessitating a shift in learners' mindset to accept concepts and methodologies in forensic intelligence.
Recent calls advocating for the integration of forensic scientists into the criminal justice system, as well as policing and intelligence missions, underscore the necessity for the establishment of educational and training initiatives in the field of forensic intelligence. This article contends that a discernible gap exists between the perceived and actual comprehension of forensic intelligence among law enforcement and forensic science managers, positing that this asymmetry can be rectified only through educational interventions
The primary challenge in forensic intelligence education and training is identified as the formulation of programs aimed at heightening awareness, particularly among managers, to mitigate the risk of making suboptimal decisions in information processing. The paper highlights two recent European courses as exemplars of educational endeavors, elucidating lessons learned and proposing future directions at an initial glance, forensic intelligence may appear as a nascent facet of forensic science facilitated by advancements in information technologies such as computers, databases, and data-flow management software.
However, a more profound examination reveals that forensic intelligence represents a genuine and emerging inclination among forensic practitioners to actively participate in investigative and policing strategies. In doing so, it elucidates existing practices within scientific literature, advocating for a paradigm shift from the prevailing conception of forensic science as a conglomerate of disciplines merely aiding the criminal justice system. Instead, it urges a perspective that views forensic science as a discipline studying the informative potential of traces—remnants of criminal activity. Embracing this transformative shift poses a significant challenge for education, necessitating a shift in learners' mindset to accept concepts and methodologies in forensic intelligence.
The overarching conclusion is that the heightened focus on forensic intelligence has the potential to rejuvenate a proactive approach to forensic science, enhance quantifiable efficiency, and foster greater involvement in investigative and managerial decision-making. A novel educational challenge is articulated for forensic science university programs worldwide: a shift in emphasis from a fragmented criminal trace analysis to a more comprehensive security problem-solving approach. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, Markovnikovs rule or Markownikoffs rule describes the outcome of some addition reactions. The rule was formulated by Russian chemist Vladimir Markovnikov in 1870. | 0 | Theoretical and Fundamental Chemistry |
Alchemy (from Arabic: al-kīmiyā; from Ancient Greek: χυμεία, khumeía) is an ancient branch of natural philosophy, a philosophical and protoscientific tradition that was historically practised in China, India, the Muslim world, and Europe. In its Western form, alchemy is first attested in a number of pseudepigraphical texts written in Greco-Roman Egypt during the first few centuries AD.
Alchemists attempted to purify, mature, and perfect certain materials. Common aims were chrysopoeia, the transmutation of "base metals" (e.g., lead) into "noble metals" (particularly gold); the creation of an elixir of immortality; and the creation of panaceas able to cure any disease. The perfection of the human body and soul was thought to result from the alchemical magnum opus ("Great Work"). The concept of creating the philosophers' stone was variously connected with all of these projects.
Islamic and European alchemists developed a basic set of laboratory techniques, theories, and terms, some of which are still in use today. They did not abandon the Ancient Greek philosophical idea that everything is composed of four elements, and they tended to guard their work in secrecy, often making use of cyphers and cryptic symbolism. In Europe, the 12th-century translations of medieval Islamic works on science and the rediscovery of Aristotelian philosophy gave birth to a flourishing tradition of Latin alchemy. This late medieval tradition of alchemy would go on to play a significant role in the development of early modern science (particularly chemistry and medicine).
Modern discussions of alchemy are generally split into an examination of its exoteric practical applications and its esoteric spiritual aspects, despite criticisms by scholars such as Eric J. Holmyard and Marie-Louise von Franz that they should be understood as complementary. The former is pursued by historians of the physical sciences, who examine the subject in terms of early chemistry, medicine, and charlatanism, and the philosophical and religious contexts in which these events occurred. The latter interests historians of esotericism, psychologists, and some philosophers and spiritualists. The subject has also made an ongoing impact on literature and the arts. | 1 | Applied and Interdisciplinary Chemistry |
Few transition metals can achieve the +6 oxidation state in an oxide, so oxides with the stoichiometry MO are rare. | 0 | Theoretical and Fundamental Chemistry |
In free-radical chain-growth polymerization, chain termination can occur by a disproportionation step in which a hydrogen atom is transferred from one growing chain molecule to another one, which produces two dead (non-growing) chains.
:: Chain—CH–CHX + Chain—CH–CHX → Chain—CH=CHX + Chain—CH–CHX
in which, Chain— represents the already formed polymer chain, and indicates a reactive free radical. | 0 | Theoretical and Fundamental Chemistry |
Many of the properties of transition metal complexes are dictated by their electronic structures. The electronic structure can be described by a relatively ionic model that ascribes formal charges to the metals and ligands. This approach is the essence of crystal field theory (CFT). Crystal field theory, introduced by Hans Bethe in 1929, gives a quantum mechanically based attempt at understanding complexes. But crystal field theory treats all interactions in a complex as ionic and assumes that the ligands can be approximated by negative point charges.
More sophisticated models embrace covalency, and this approach is described by ligand field theory (LFT) and Molecular orbital theory (MO). Ligand field theory, introduced in 1935 and built from molecular orbital theory, can handle a broader range of complexes and can explain complexes in which the interactions are covalent. The chemical applications of group theory can aid in the understanding of crystal or ligand field theory, by allowing simple, symmetry based solutions to the formal equations.
Chemists tend to employ the simplest model required to predict the properties of interest; for this reason, CFT has been a favorite for the discussions when possible. MO and LF theories are more complicated, but provide a more realistic perspective.
The electronic configuration of the complexes gives them some important properties: | 0 | Theoretical and Fundamental Chemistry |
In a modern diesel engine, the fuel is part of the engine lubrication process. Diesel fuel naturally contains compounds that provide lubricity, but because of regulations in many countries (such as the US and the EU countries), sulphur must be removed from the fuel before it can be sold. The hydrotreatment of diesel fuel to remove sulphur also removes the compounds that provide lubricity. Reformulated diesel fuel that does not have biodiesel added has a lower lubricity and requires lubricity improving additives to prevent excessive engine wear. | 1 | Applied and Interdisciplinary Chemistry |
Nociception is the form of somatic sensation that detects potentially tissue-damaging noxious stimuli. Peripheral nociceptors uniquely express transient receptor potentials which are sensitive to potentially-damaging mechanical, chemical, or thermal stimuli. Nociceptors also contain receptors for pain and inflammatory-related mediators or cytokines. Peripheral nociceptors transmit noxious stimuli to the dorsal root ganglia, the dorsal horn, and further to the trigeminal ganglia in the brain. Pain has both a localizing somatic sensory component and an aversive emotional and motivational component. Pain travels through a variety of pathways via first pain on Alpha Delta fibers and second pain on slowly conducting C-fibers.
The dorsal horn of the spinal cord serves as a major integration center for both ascending nociceptive information and descending antinociceptive influences from the brain. Plasticity within the dorsal horn is mediated by NMDA glutamate receptors and key in the initiation of chronic pain by decreasing the excitability threshold in nociceptive pathways. Additionally, damage to neurons in nociceptive pathways leads to neuropathic pain. Three families in northern Pakistan were congenitally unable to perceive pain due to their homozygous loss of function mutation in the SCN9A gene which codes for the voltage-gated sodium channel Na1.7 . This key finding allowed pharmacologists to begin researching if the Na1.7 is a substantial molecular target for analgesic (antipain) medications.
Sensitization, in the clinical sense of the word, is a phenomenon in which nociceptors in an area beyond a tissue injury exhibit decreased thresholds for activation. Sensitization can be initiated by inflammatory prostaglandins or leukotrienes and are therefore the targets of nonsteroidal anti-inflammatory (NSAIDs) which block key enzymes in their synthesis. Additionally, opioid drugs suppress nociceptions by binding to endogenous opioid receptors. | 1 | Applied and Interdisciplinary Chemistry |
The sialic acid family includes many derivatives of the nine-carbon sugar neuraminic acid, but these acids rarely appear free in nature. Normally they can be found as components of oligosaccharide chains of mucins, glycoproteins and glycolipids occupying terminal, nonreducing positions of complex carbohydrates on both external and internal membrane areas where they are very exposed and develop important functions.
The numbering of the carbon atoms starts at the carboxylate carbon and continues along the chain. The configuration that places the carboxylate in the axial position is the alpha-anomer.
The alpha-anomer is the form that is found when sialic acid is bound to glycans. However, in solution, it is mainly (over 90%) in the beta-anomeric form. A bacterial enzyme with sialic acid mutarotase activity, NanM, that is able to rapidly equilibrate solutions of sialic acid to the resting equilibrium position of around 90% beta/10% alpha has been discovered.
In contrast to other animals, humans are genetically unable to produce the sialic acid variant N-glycolylneuraminic acid (Neu5Gc). Small amounts of Neu5Gc detected in human tissue however may be incorporated from exogenous (nutrient) sources. | 0 | Theoretical and Fundamental Chemistry |
Researchers have begun to focus on decellularization for organ transplants since it reduces the chance of rejection to almost none. This process was used in the first successful stem-cell based organ transplant by removing the cells and MHC antigens from the donor organ. There are different ways to remove the cells from the organ which can include physical, chemical, and enzymatic treatments. This method is especially useful when trying to create a neo-heart because the heart needs to be created in a way where the structure remains. Since the stem cells used are currently not able to maintain a shape, researchers have started to look more into decellularization of existing organs to be able to perform successful transplant procedures without the problem of rejection. While this method may assist with the problem of rejection, donors are still needed to provide this structure to patients. | 1 | Applied and Interdisciplinary Chemistry |
In a flow distribution network that progresses from a large tube to many small tubes (e.g. a blood vessel network), the frequency, density, and dynamic viscosity are (usually) the same throughout the network, but the tube radii change. Therefore, the Womersley number is large in large vessels and small in small vessels. As the vessel diameter decreases with each division the Womersley number soon becomes quite small. The Womersley numbers tend to 1 at the level of the terminal arteries. In the arterioles, capillaries, and venules the Womersley numbers are less than one. In these regions the inertia force becomes less important and the flow is determined by the balance of viscous stresses and the pressure gradient. This is called microcirculation.
Some typical values for the Womersley number in the cardiovascular system for a canine at a heart rate of 2 Hz are:
*Ascending aorta – 13.2
*Descending aorta – 11.5
*Abdominal aorta – 8
*Femoral artery – 3.5
*Carotid artery – 4.4
*Arterioles – 0.04
*Capillaries – 0.005
*Venules – 0.035
*Inferior vena cava – 8.8
*Main pulmonary artery – 15
It has been argued that universal biological scaling laws (power-law relationships that describe variation of quantities such as metabolic rate, lifespan, length, etc., with body mass) are a consequence of the need for energy minimization, the fractal nature of vascular networks, and the crossover from high to low Womersley number flow as one progresses from large to small vessels. | 1 | Applied and Interdisciplinary Chemistry |
Abiotic factors that can damage plants include heat, freezing, flooding, lightning strikes, ozone gas, and pollutant chemicals.
Heat can kill any plant, given a sufficient temperature. Alpine plants tend to die at around 47 Celsius; temperate plants at around 51 Celsius; and tropical plants at nearly 58 Celsius: but there is some overlap depending on species. Similarly among cereal crops, temperate barley and oat die at around 49 Celsius, but tropical maize at 55 Celsius.
Freezing affects plants variously, according to each species' ability to resist frost damage. Many forbs, including many garden flowers, are tender with little tolerance to frost, and die or are seriously damaged when frozen. Many woody plants are able to supercool, with tough buds and stems containing molecules that lower the freezing point or help to prevent the nucleation of ice crystals, and cell walls that mechanically protect cells against freezing.
Flooding of soil quickly kills or injures many plants. The leaves become yellow (chlorosis) and die, progressively up the stem, within about five days after the roots are flooded. The roots lose the ability to absorb water and nutrients.
Lightning strikes kill or injure plants, from root crops like beet and potato, which are instantly cooked in the ground, to trees such as coconut, through effects such as sudden heat and pressure shock waves created when water inside the plant flashes to steam. This can rupture stems and scorch any plant parts.
Ozone, a gas, causes injury to leaves at concentrations from as little as 0.1 part per million in the atmosphere, such as may be found in or near large cities.
It is one of many pollutant chemicals that can damage plants. | 1 | Applied and Interdisciplinary Chemistry |
Compounds such as 2,2,2-trichloroethanol, which contain multiple geminal halogens adjacent to a hydroxyl group may be considered halohydrins (although, strictly speaking, they fail the IUPAC definition) as they possess similar chemistry. In particular they also undergo intramolecular cyclisation to form dihaloepoxy groups. These species are both highly reactive and synthetically useful, forming the basis of the Jocic–Reeve reaction, Bargellini reaction and Corey–Link reaction. | 0 | Theoretical and Fundamental Chemistry |
After the initial carousel stripping machine development and the later development of the linear stripping machine, Falconbridge personnel developed the Kidd Process High Capacity Linear Machine (“HCLM”). This machine included a loading and unloading system that was based on robotics.
The new design improved, among other things, the discharge area of the stripper. This had been a problem area for the carousel stripping machines, in which copper released from the cathode plate fell into an envelope and was then transferred to a material handling device. Copper that misbehaved and failed to transfer often required manual intervention. The new robot discharge system eliminated the free falling of the copper and physically transferred the released copper to the discharge location. | 1 | Applied and Interdisciplinary Chemistry |
Structurally, sea foam is thermodynamically unstable, though some sea foam can persist in the environment for several days at most. There are two types of sea foam categorized based on their stability: 1) Unstable or transient foams have very short lifetimes of only seconds. The bubbles formed in sea foam may burst releasing aerosols into the air, contributing to sea spray. 2) Metastable foams can have a lifetime of several hours to several days; their duration is sometimes attributed to small particles of silica, calcium, or iron which contribute to foam stability and longevity. Additionally, seawater that contains released dissolved organic material from phytoplankton and macrophytic algae that is then agitated in its environment is most likely to produce stable, longer-lasting foam when compared with seawater lacking one of those components. For example, filtered seawater when added to the fronds of the kelp, Ecklonia maxima, produced foam but it lacked the stability that unfiltered seawater provided. Additionally, kelp fronds that were maintained in flowing water therefore reducing their mucus coating, were unable to help foam form. Different types of salt are also found to have varying effects on bubble proximity within sea foam, therefore contributing to its stability. | 0 | Theoretical and Fundamental Chemistry |
Reductions of carbon-carbon double and triple bonds are most commonly accomplished through catalytic hydrogenation:
However, diimide reduction offers the advantages that the handling of gaseous hydrogen is unnecessary and removal of catalysts and byproducts (one of which is gaseous dinitrogen) is straightforward. Hydrogenolysis side reactions do not occur during diimide reductions, and N–O and O–O bonds are not affected by the reaction conditions. On the other hand, diimide reductions often require long reaction times, and reductions of highly substituted or polarized double bonds are sluggish.
In addition, an excess of the reagent used to generate diimide (e.g. dipotassium azodicarboxylate) is required for hydrogenation because of the two competing processes of disproportionation (to and ) and decomposition (to and ) that the liberated diimide can also undergo. Unfortunately, this means that in the case of alkyne reduction, over-reduction to the alkane can occur resulting in diminished yields where the cis alkene is the desired product. | 0 | Theoretical and Fundamental Chemistry |
Several properties make NiSi an important local contact material in the area of microelectronics, among them a reduced thermal budget, low resistivity of 13–14 μΩ·cm and a reduced Si consumption when compared to alternative compounds. | 1 | Applied and Interdisciplinary Chemistry |
The light and dark bottle method uses the same concept as the free-water method to estimate rates of metabolism - GPP only occurs during the day with solar energy while ER occurs in both the presence and absence of light. This method incubates lake water in two separate bottles, one that is clear and exposed to natural or artificial light regime and another that is sealed off from the light by wrapping the bottle in foil, paint, or another method. Changes in carbon fixation or dissolved gases are then measured over a certain time period (e.g. several hours to a day) to estimate the rate of metabolism for specific lake depths or an integrated lake water column. Carbon fixation is measured by injecting radioactive carbon isotope C into light and dark bottles and sampling the bottles over the time - the samples are filtered onto filter paper and the amount of C incorporated into algal (and bacterial) cells is estimated by measuring samples on a scintillation counter. The difference between the light and dark bottle C can be considered the rate of primary productivity; however, due to non-photosynthetic uptake of CO there is debate as to whether dark bottles should be used with the C method or if only a light bottle and a bottle treated with the algicide DCMU should be used. Rates of change in dissolved gases, either carbon dioxide or oxygen, need both the light and dark bottles to estimate rates of productivity and respiration. | 1 | Applied and Interdisciplinary 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 | Applied and Interdisciplinary Chemistry |
In fluid mechanics, dimensional analysis is performed to obtain dimensionless pi terms or groups. According to the principles of dimensional analysis, any prototype can be described by a series of these terms or groups that describe the behaviour of the system. Using suitable pi terms or groups, it is possible to develop a similar set of pi terms for a model that has the same dimensional relationships. In other words, pi terms provide a shortcut to developing a model representing a certain prototype. Common dimensionless groups in fluid mechanics include:
* Reynolds number (), generally important in all types of fluid problems:
* Froude number (), modeling flow with a free surface:
* Euler number (), used in problems in which pressure is of interest:
* Mach number (), important in high speed flows where the velocity approaches or exceeds the local speed of sound: where is the local speed of sound. | 1 | Applied and Interdisciplinary Chemistry |
pHT01 is a plasmid used as a cloning vector for expressing proteins in Bacillus subtilis. It is 7,956 base pairs in length. pHT01 carries Pgrac, an artificial, strong, IPTG-inducible promoter consisting of the Bacillus subtilis groE promoter, a lac operator, and the gsiB ribosome binding site. It was first found on plasmid pNDH33. The plasmid also carries replication regions from the pMTLBs72. The plasmid also carries genes to confer resistance to ampicillin and chloramphenicol.
Plasmid pHT01 is generally stable in both B. subtilis and Escherichia coli, and can be used for protein expression in these host strains. pNDH33/pHT01 have been used to produce up to 16% of total protein output in B. subtilis. Pgrac100 is an improved version of Pgrac, which can produce up to 30% of total cellular proteins in B. subtilis. | 1 | Applied and Interdisciplinary Chemistry |
Heme A was first isolated by the German biochemist Otto Warburg in 1951 and shown by him to be the active component of the integral membrane metalloprotein cytochrome c oxidase. | 1 | Applied and Interdisciplinary Chemistry |
Generally mineral names should not be used to specify chemical composition. However a mineral name can be used to specify the structure type in a formula e.g.
* (perovskite type) | 0 | Theoretical and Fundamental Chemistry |
Mycosubtilin is a natural lipopeptide. It is produced by the strains of Bacillus spp mainly by Bacillus subtilis. It was discovered due to its antifungal activities. It belongs to the family of iturin lipopeptides | 0 | Theoretical and Fundamental Chemistry |
The ICRP definition of the sievert is:
: "The sievert is the special name for the SI unit of equivalent dose, effective dose, and operational dose quantities. The unit is joule per kilogram."
The sievert is used for a number of dose quantities which are described in this article and are part of the international radiological protection system devised and defined by the ICRP and ICRU. | 0 | Theoretical and Fundamental Chemistry |
Self-assembly can also be observed in the presence of organic ligands and various metals centers through coordinative bonds or supramolecular interactions. Molecular self- assembly involves the association by many weak, reversible interactions to obtain a final structure that represents a thermodynamic minimum. A class of coordination polymers, known also as metal-organic frameworks (MOFs), are metal-ligand compounds that extend "infinitely" into one, two or three dimensions. | 0 | Theoretical and Fundamental Chemistry |
* The Rhine carries much river traffic, and major inland ports are found at its confluence with the Ruhr at Duisburg, and with the Neckar at Mannheim; see Mannheim Harbour.
* The Main flows into the Rhine just south of Mainz.
* The Mosel flows into the Rhine further north at Koblenz. The name "Koblenz" itself has its origin in the Latin name "Confluentes". In German, this confluence is known as the "Deutsches Eck" ("German corner") and is the site of an imposing monument to German unification featuring an equestrian statue of Kaiser Wilhelm I.
* Upstream in Switzerland, a small town also named Koblenz (for the same reason) is where the Aare joins the Rhine. | 1 | Applied and Interdisciplinary Chemistry |
A single conductive wire is used as feedstock for the system. A supersonic plasma jet—formed by a transferred arc between a non-consumable cathode and the wire—melts and atomizes the wire. A stream of air transports the atomized metal onto the substrate. The particles flatten upon striking the surface of the substrate due to their high kinetic energy. The particles rapidly solidify upon contact and can assume both crystalline and amorphous phases. There is also the possibility of producing multi-layer coatings via stacked layers of particles, increasing wear resistance. All conductive wires up to and including can be used as feedstock material, including "cored" wires. Refractory metals, as well as low melt materials, are easily deposited. | 1 | Applied and Interdisciplinary Chemistry |
It is considered to be the most difficult Chemistry exam throughout the world, the difficulty of Final round is much harder than IChO. The difficulty of the preliminary round is often enough to surpass IChO, also. Its problems are often beyond the abilities of an overwhelming majority of undergraduates. (As a consequence, IChO problems are regarded as "beginners' exercises" among those Chinese students.) | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, an ionophore () is a chemical species that reversibly binds ions. Many ionophores are lipid-soluble entities that transport ions across the cell membrane. Ionophores catalyze ion transport across hydrophobic membranes, such as liquid polymeric membranes (carrier-based ion selective electrodes) or lipid bilayers found in the living cells or synthetic vesicles (liposomes). Structurally, an ionophore contains a hydrophilic center and a hydrophobic portion that interacts with the membrane.
Some ionophores are synthesized by microorganisms to import ions into their cells. Synthetic ion carriers have also been prepared. Ionophores selective for cations and anions have found many applications in analysis. These compounds have also shown to have various biological effects and a synergistic effect when combined with the ion they bind. | 0 | Theoretical and Fundamental Chemistry |
Because the compounds that exhibit bioluminescence are typically fluorescent, fluorescence can be used to identify photocytes in organisms. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, π-effects or π-interactions are a type of non-covalent interaction that involves π systems. Just like in an electrostatic interaction where a region of negative charge interacts with a positive charge, the electron-rich π system can interact with a metal (cationic or neutral), an anion, another molecule and even another π system. Non-covalent interactions involving π systems are pivotal to biological events such as protein-ligand recognition. | 0 | Theoretical and Fundamental Chemistry |
Processes can be characterized as batch, continuous, or hybrid. Batch applications require that specific quantities of raw materials be combined in specific ways for particular duration to produce an intermediate or end result. One example is the production of adhesives and glues, which normally require the mixing of raw materials in a heated vessel for a period of time to form a quantity of end product. Other important examples are the production of food, beverages and medicine. Batch processes are generally used to produce a relatively low to intermediate quantity of product per year (a few pounds to millions of pounds).
A continuous physical system is represented through variables that are smooth and uninterrupted in time. The control of the water temperature in a heating jacket, for example, is an example of continuous process control. Some important continuous processes are the production of fuels, chemicals and plastics. Continuous processes in manufacturing are used to produce very large quantities of product per year (millions to billions of pounds). Such controls use feedback such as in the PID controller A PID Controller includes proportional, integrating, and derivative controller functions.
Applications having elements of batch and continuous process control are often called hybrid applications. | 1 | Applied and Interdisciplinary Chemistry |
The COCO Simulator is a free-of-charge, non-commercial, graphical, modular and CAPE-OPEN compliant, steady-state, sequential simulation process modeling environment. It was originally intended as a test environment for CAPE-OPEN modeling tools but now provides free chemical process simulation for students. It is an open flowsheet modeling environment allowing anyone to add new unit operations or thermodynamics packages.
The COCO Simulator uses a graphical representation, the Process Flow Diagram (PFD), for defining the process to be simulated. Clicking on a unit operation with the mouse allows the user to edit the unit operation parameters it defines via the CAPE-OPEN standard or to open the unit operations own user interface, when available. This interoperability of process modeling software was enabled by the advent of the CAPE-OPEN standard. COCO thermodynamic library "TEA" and its chemical compound data bank are based on ChemSep LITE, a free equilibrium column simulator for distillation columns and liquid-liquid extractors. COCOs thermodynamic library exports more than 100 property calculation methods with their analytical or numerical derivatives. COCO includes a LITE version of COSMOtherm, an activity coefficient model based on Ab initio quantum chemistry methods. The simulator entails a set of unit-operations such as stream splitters/mixers, heat-exchangers, compressors, pumps and reactors. COCO features a reaction numerics package to power its simple conversion, equilibrium, CSTR, Gibbs minimization and plug flow reactor models. | 1 | Applied and Interdisciplinary Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V). | 1 | Applied and Interdisciplinary Chemistry |
Septic drain fields, also called leach fields or leach drains, are subsurface wastewater disposal facilities used to remove contaminants and impurities from the liquid that emerges after anaerobic digestion in a septic tank. Organic materials in the liquid are catabolized by a microbial ecosystem.
A septic drain field, a septic tank, and associated piping compose a septic system.
The drain field typically consists of an arrangement of trenches containing perforated pipes and porous material (often gravel) covered by a layer of soil to prevent animals (and surface runoff) from reaching the wastewater distributed within those trenches. Primary design considerations are both hydraulic for the volume of wastewater requiring disposal and catabolic for the long-term biochemical oxygen demand of that wastewater. The land area that is set aside for the septic drain field may be called a septic reserve area (SRA).
Sewage farms similarly dispose of wastewater through a series of ditches and lagoons (often with little or no pre-treatment). These are more often found in arid countries as the waterflow on the surface allows for irrigation (and fertilization) of agricultural land. | 1 | Applied and Interdisciplinary Chemistry |
Some PSM products - such as cutlery - contain a mix of PSM and plastics. These plastics prevent the PSM from degrading, making the entire product non-biodegradable. | 0 | Theoretical and Fundamental Chemistry |
Due to the crucial role of base, specific amines must be added in excess or as solvent for the reaction to proceed. It has been discovered that secondary amines such as piperidine, morpholine, or diisopropylamine in particular can react efficiently and reversibly with trans– complexes by substituting one ligand. The equilibrium constant of this reaction is dependent on R, X, a factor for basicity, and the amine's steric hindrance. The result is competition between the amine and the alkyne group for this ligand exchange, which is why the amine is generally added in excess to promote preferential substitution. | 0 | Theoretical and Fundamental Chemistry |
As with many signal transduction pathways, plant gene expression during immune responses can be regulated by degradation. This often occurs when hormone binding to hormone receptors stimulates ubiquitin-associated degradation of repressor proteins that block expression of certain genes. The net result is hormone-activated gene expression. Examples:
* Auxin: binds to receptors that then recruit and degrade repressors of transcriptional activators that stimulate auxin-specific gene expression.
* Jasmonic acid: similar to auxin, except with jasmonate receptors impacting jasmonate-response signaling mediators such as JAZ proteins.
* Gibberellic acid: Gibberellin causes receptor conformational changes and binding and degradation of Della proteins.
* Ethylene: Inhibitory phosphorylation of the EIN2 ethylene response activator is blocked by ethylene binding. When this phosphorylation is reduced, EIN2 protein is cleaved and a portion of the protein moves to the nucleus to activate ethylene-response gene expression. | 1 | Applied and Interdisciplinary Chemistry |
The Heck–Matsuda (HM) reaction is an organic reaction and a type of palladium catalysed arylation of olefins that uses arenediazonium salts as an alternative to aryl halides and triflates.
The use of arenediazonium salts presents some advantages over traditional aryl halide electrophiles, for example, the use of phosphines as ligand are not required and thus negating the requirement for anaerobic conditions, which makes the reaction more practical and easier to handle. Additionally, the reaction can be performed with or without a base and is often faster than traditional Heck protocols.
Allylic alcohols, conjugated alkenes, unsaturated heterocycles and unactivated alkenes are capable of being arylated with arenediazonium salts using simple catalysts such as palladium acetate (Pd(OAc)) or tris(dibenzylideneacetone)dipalladium(0) (Pddba) at room temperature in air, and in benign and conventional solvents.
In addition to the intermolecular variant of the HM reaction, intramolecular cyclization processes have also been developed for the construction of a range of oxygen and nitrogen heterocycles.
The catalytic cycle for the Heck-Matsuda arylation reaction has four main steps: oxidative addition, migratory insertion or carbopalladation, syn β-elimination and reductive elimination. The proposed Heck catalytic cycle involving cationic palladium with diazonium salts was reinforced by studies with mass spectrometry (ESI) by Correia and co-workers. These results also show the complex interactions that occur in the coordination sphere of palladium during the Heck reaction with arenediazonium salt.
A related reaction is the Meerwein arylation that precedes the Heck reaction. Meerwein arylation often use copper salts, but may in some cases be done without a transition metal. | 0 | Theoretical and Fundamental Chemistry |
Glypiation is a special form of glycosylation that features the formation of a GPI anchor. In this kind of glycosylation a protein is attached to a lipid anchor, via a glycan chain. (See also prenylation.) | 0 | Theoretical and Fundamental Chemistry |
# Extract from carbonates by reaction with anhydrous phosphoric acid. (there is no direct way to measure the abundance of COs in with high enough precision). The phosphoric acid temperature is often held between 25° and 90 °C and can be as high as 110 °C.
# Purify the that has been extracted. This step removes contaminant gases like hydrocarbons and halocarbons which can be removed by gas chromatography.
# Mass spectrometric analyses of purified , to obtain δC, δO, and Δ47 (abundance of mass-47 ) values. (Precision needs to be as high as ≈10, for the isotope signals of interest are often less than ≈10) | 0 | Theoretical and Fundamental Chemistry |
Relaxometry refers to the study and/or measurement of relaxation variables in Nuclear Magnetic Resonance and Magnetic Resonance Imaging. Often referred to as Time-Domain NMR. In NMR, nuclear magnetic moments are used to measure specific physical and chemical properties of materials.
Relaxation of the nuclear spin system is crucial for all NMR applications. The relaxation rate depends strongly on the mobility (fluctuations, diffusion) of the microscopic environment and the strength of the applied magnetic field. As a rule of thumb, strong magnetic fields lead to increased sensitivity on fast dynamics while low fields lead to increased sensitivity on slow dynamics. Thus, the relaxation rate as a function of the magnetic field strength is a fingerprint of the microscopic dynamics.
Key Materials science properties are often described in different fields using the terms mobility / dynamics / stiffness / viscosity / rigidity of the sample. These properties are usually dependent on atomic and molecular motion in the sample, which may be measured using time-domain NMR and fast field cycling relaxometry. | 0 | Theoretical and Fundamental Chemistry |
LB buffer, also known as lithium borate buffer, is a buffer solution used in agarose electrophoresis, typically for the separation of nucleic acids such as DNA and RNA. It is made up of Lithium borate (lithium hydroxide monohydrate and boric acid).
LB(R) is a registered (USPTO) trademark of Faster Better Media LLC, which owns US patent 7,163,610 covering low-conductance lithium borate polynucleotide electrophoresis.
Lithium Borate buffer has a lower conductivity, produces crisper resolution, and can be run at higher speeds than can gels made from TBE or TAE (5-50 V/cm as compared to 5-10 V/cm). At a given voltage, the heat generation and thus the gel temperature is much lower than with TBE/TAE buffers, therefore the voltage can be increased to speed up electrophoresis so that a gel run takes only a fraction of the usual time. Downstream applications, such as isolation of DNA from a gel slice or Southern blot analysis, work as expected with lithium boric acid gels.
SB buffer containing sodium borate is similar to lithium borate and has nearly all of its advantages at a somewhat lower cost, but the lithium buffer permits use of even higher voltages due to the lower conductivity of lithium ions as compared to sodium ions and has a better resolution for fragments above 4kb. | 1 | Applied and Interdisciplinary Chemistry |
Solitons can occur in materials, such as ferroelectrics, in the form of domain walls. Ferroelectric materials exhibit spontaneous polarization, or electric dipoles, which are coupled to configurations of the material structure. Domains of oppositely poled polarizations can be present within a single material as the structural configurations corresponding to opposing polarizations are equally favorable with no presence of external forces. The domain boundaries, or “walls”, that separate these local structural configurations are regions of lattice dislocations. The domain walls can propagate as the polarizations, and thus, the local structural configurations can switch within a domain with applied forces such as electric bias or mechanical stress. Consequently, the domain walls can be described as solitons, discrete regions of dislocations that are able to slip or propagate and maintain their shape in width and length.
In recent literature, ferroelectricity has been observed in twisted bilayers of van der Waal materials such as molybdenum disulfide and graphene. The moiré superlattice that arises from the relative twist angle between the van der Waal monolayers generates regions of different stacking orders of the atoms within the layers. These regions exhibit inversion symmetry breaking structural configurations that enable ferroelectricity at the interface of these monolayers. The domain walls that separate these regions are composed of partial dislocations where different types of stresses, and thus, strains are experienced by the lattice. It has been observed that soliton or domain wall propagation across a moderate length of the sample (order of nanometers to micrometers) can be initiated with applied stress from an AFM tip on a fixed region. The soliton propagation carries the mechanical perturbation with little loss in energy across the material, which enables domain switching in a domino-like fashion.
It has also been observed that the type of dislocations found at the walls can affect propagation parameters such as direction. For instance, STM measurements showed four types of strains of varying degrees of shear, compression, and tension at domain walls depending on the type of localized stacking order in twisted bilayer graphene. Different slip directions of the walls are achieved with different types of strains found at the domains, influencing the direction of the soliton network propagation.
Nonidealities such as disruptions to the soliton network and surface impurities can influence soliton propagation as well. Domain walls can meet at nodes and get effectively pinned, forming triangular domains, which have been readily observed in various ferroelectric twisted bilayer systems. In addition, closed loops of domain walls enclosing multiple polarization domains can inhibit soliton propagation and thus, switching of polarizations across it. Also, domain walls can propagate and meet at wrinkles and surface inhomogeneities within the van der Waal layers, which can act as obstacles obstructing the propagation. | 1 | Applied and Interdisciplinary Chemistry |
Radon concentrations found in natural environments are much too low to be detected by chemical means: for example, a 1000 Bq/m (relatively high) concentration corresponds to 0.17 picogram per cubic meter. The average concentration of radon in the atmosphere is about 6 atoms of radon for each molecule in the air, or about 150 atoms in each mL of air. The entire radon activity of the Earth's atmosphere at any one time is due to some tens of grams of radon, constantly being replaced by decay of larger amounts of radium and uranium. Its concentration can vary greatly from place to place. In the open air, it ranges from 1 to 100 Bq/m, even less (0.1 Bq/m) above the ocean. In caves, aerated mines, or poorly ventilated dwellings, its concentration can climb to 20–2,000 Bq/m.
In mining contexts, radon concentrations can be much higher. Ventilation regulations try to maintain concentrations in uranium mines under the "working level", and under 3 WL (546 pCi per liter of air; 20.2 kBq/m measured from 1976 to 1985) 95 percent of the time.
The concentration in the air at the (unventilated) Gastein Healing Gallery averages 43 kBq/m (about 1.2 nCi/L) with maximal value of 160 kBq/m (about 4.3 nCi/L).
Radon emanates naturally from the ground and from some building materials all over the world, wherever there are traces of uranium or thorium, and particularly in regions with soils containing granite or shale, which have a higher concentration of uranium. In every 1 square mile of surface soil, the first (of depth) contains about 0.035 oz of radium (0.4 g per km) which releases radon in small amounts to the atmosphere. Sand used in making concrete is the major source of radon in buildings.
On a global scale, it is estimated that 2,400 million curies (91 TBq) of radon are released from soil annually. Not all granitic regions are prone to high emissions of radon. Being an unreactive noble gas, it usually migrates freely through faults and fragmented soils, and may accumulate in caves or water. Due to its very small half-life (four days for ), its concentration decreases very quickly when the distance from the production area increases.
Its atmospheric concentration varies greatly depending on the season and conditions. For instance, it has been shown to accumulate in the air if there is a meteorological inversion and little wind.
Because atmospheric radon concentrations are very low, radon-rich water exposed to air continually loses radon by volatilization. Hence, ground water generally has higher concentrations of than surface water, because the radon is continuously replenished by radioactive decay of present in rocks. Likewise, the saturated zone of a soil frequently has a higher radon content than the unsaturated zone because of diffusional losses to the atmosphere. As a below-ground source of water, some springs—including hot springs—contain significant amounts of radon. The towns of Boulder, Montana; Misasa; Bad Kreuznach, and the country of Japan have radium-rich springs which emit radon. To be classified as a radon mineral water, radon concentration must be above a minimum of 2 nCi/L (7 Bq/L). The activity of radon mineral water reaches 2,000 Bq/L in Merano and 4,000 Bq/L in the village of Lurisia (Ligurian Alps, Italy).
Radon is also found in some petroleum. Because radon has a similar pressure and temperature curve to propane, and oil refineries separate petrochemicals based on their boiling points, the piping carrying freshly separated propane in oil refineries can become partially radioactive due to radon decay particles. Residues from the oil and gas industry often contain radium and its daughters. The sulfate scale from an oil well can be radium rich, while the water, oil, and gas from a well often contains radon. The radon decays to form solid radioisotopes which form coatings on the inside of pipework. In an oil processing plant, the area of the plant where propane is processed is often one of the more contaminated areas, because radon has a similar boiling point to propane. | 1 | Applied and Interdisciplinary Chemistry |
Liming can also improve aggregate stability on clay soils. For this purpose structure lime, products containing calcium oxide (CaO) or hydroxide (Ca(OH)) in mixes with calcium carbonate (CaCO), are often used. Structure liming can reduce losses of clay and nutrients from soil aggregates. The degree to which a given amount of lime per unit of soil volume will increase soil pH depends on the buffer capacity of the soil (this is generally related to soil cation exchange capacity or CEC).
Most acid soils are saturated with aluminum rather than hydrogen ions. The acidity of the soil is therefore a result of hydrolysis of aluminum. This concept of "corrected lime potential" to define the degree of base saturation in soils became the basis for procedures now used in soil testing laboratories to determine the "lime requirement" of soils.
Soils with low CEC will usually show a more marked pH increase than soils with high CEC. But the low-CEC soils will witness more rapid leaching of the added bases, and so will see a quicker return to original acidity unless additional liming is done. Over-liming is most likely to occur on soil that has low CEC, such as sand which is deficient in buffering agents such as organic matter and clay. | 0 | Theoretical and Fundamental Chemistry |
The oxyallyl diradical (OXA) is a trimethylenemethane molecule with one methylene group replaced by oxygen. This reactive intermediate is postulated to occur in ring opening of cyclopropanones, allene oxides and in the Favorskii rearrangement. The intermediate has been produced by reaction of oxygen radical anions with acetone and studied by photoelectron spectroscopy. The experimental electron affinity of OXA is 1.94 eV. | 0 | Theoretical and Fundamental Chemistry |
The goniometric SPR method was researched alongside focused beam SPR and Otto configurations at VTT Technical Research Centre of Finland since 1980s by Dr. Janusz Sadowski. The goniometric SPR optics was commercialized by Biofons Oy for use in point-of-care applications. Introduction of additional measurement laser wavelengths and first thin film analyses were performed in 2011 giving way to MP-SPR method. | 0 | Theoretical and Fundamental Chemistry |
An experimental iodine clock sequence has also been established for a system consisting of iodine potassium-iodide, sodium chlorate and perchloric acid that takes place through the following reactions.
Triiodide is present in equilibrium with iodide anion and molecular iodine:
Chlorate ion oxidizes iodide ion to hypoiodous acid and chlorous acid in the slow and rate-determining step:
Chlorate consumption is accelerated by reaction of hypoiodous acid to iodous acid and more chlorous acid:
More autocatalysis when newly generated iodous acid also converts chlorate in the fastest reaction step:
In this clock the induction period is the time it takes for the autocatalytic process to start after which the concentration of free iodine falls rapidly as observed by UV–visible spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
* Adrien Albert
* Albert Ernest Alexander
* Jane Foss Barff
* Henry H. Bauer
* James K. Beattie
* Arthur Birch
* Alexander Boden
* Brice Bosnich
* Mary Elizabeth Brown
* A. David Buckingham
* Samuel Warren Carey
* Warwick Cathro
* John Cornforth
* James Charles Cox
* David P. Craig
* Liz Dennis
* Francis Patrick Dwyer
* Jane Dyson
* Michelle Engelsman
* David Foster
* Hans Freeman
* Joan Maie Freeman
* Philip A. Gale
* Ruth Gall
* Robert Gilbert
* Frederick Bickell Guthrie
* Margaret Harding
* George Harker
* Rita Harradence
* Noel Hush
* Joseph Jacobs
* T. H. Laby
* Raymond Le Fèvre
* Don Levy
* Leonard Francis Lindoy
* Archibald Liversidge
* Lew Mander
* Thomas Maschmeyer
* Betty R. Moore
* P. A. P. Moran
* Alice Motion
* Lionel Murphy
* Elizabeth New
* Ronald Sydney Nyholm
* Ruby Payne-Scott
* Leo Radom
* John Read
* Edward Rennie
* Ezio Rizzardo
* Robert Robinson
* Alison Rodger
* Peter Rutledge
* Henry Chamberlain Russell
* Alan Sargeson
* Roberta Shepherd
* Charles Shoppee
* Henry George Smith
* John Smith
* John McGarvie Smith
* Sever Sternhell
* Matthew H. Todd
* Jill Trewhella
* Ian Wark
* David Warren
* David Weatherburn
* Jenny Zhang | 1 | Applied and Interdisciplinary Chemistry |
Spectral absorbance in frequency and spectral absorbance in wavelength of a material, denoted and respectively, are given by
where
* is the spectral radiant flux in frequency by that material;
* is the spectral radiant flux in frequency by that material;
* is the spectral transmittance in frequency of that material;
* is the spectral radiant flux in wavelength by that material;
* is the spectral radiant flux in wavelength by that material; and
* is the spectral transmittance in wavelength of that material.
Spectral absorbance is related to spectral optical depth by
where
* is the spectral optical depth in frequency, and
* is the spectral optical depth in wavelength.
Although absorbance is properly unitless, it is sometimes reported in "absorbance units", or AU. Many people, including scientific researchers, wrongly state the results from absorbance measurement experiments in terms of these made-up units. | 0 | Theoretical and Fundamental Chemistry |
Magnesium oxalate is a skin and eye irritant. If inhaled, it will irritate the lungs and mucous membranes. Magnesium oxalate has no known chronic effects nor any carcinogenic effects. Magnesium oxalate is non-flammable and stable, but in fire conditions it will give off toxic fumes. According to OSHA, magnesium oxalate is considered to be hazardous. | 0 | Theoretical and Fundamental Chemistry |
Carl Gustaf Mosander (10 September 1797 – 15 October 1858) was a Swedish chemist. He discovered the rare earth elements lanthanum, erbium and terbium. | 1 | Applied and Interdisciplinary Chemistry |
Schneider flow describes the axisymmetric outer flow induced by a laminar or turbulent jet having a large jet Reynolds number or by a laminar plume with a large Grashof number, in the case where the fluid domain is bounded by a wall. When the jet Reynolds number or the plume Grashof number is large, the full flow field constitutes two regions of different extent: a thin boundary-layer flow that may identified as the jet or as the plume and a slowly moving fluid in the large outer region encompassing the jet or the plume. The Schneider flow describing the latter motion is an exact solution of the Navier-Stokes equations, discovered by Wilhelm Schneider in 1981. The solution was discovered also by A. A. Golubinskii and V. V. Sychev in 1979, however, was never applied to flows entrained by jets. The solution is an extension of Taylor's potential flow solution to arbitrary Reynolds number. | 1 | Applied and Interdisciplinary Chemistry |
In the 1980s, most of the dioxane produced was used as a stabilizer for 1,1,1-trichloroethane for storage and transport in aluminium containers. Normally aluminium is protected by a passivating oxide layer, but when these layers are disturbed, the metallic aluminium reacts with trichloroethane to give aluminium trichloride, which in turn catalyses the dehydrohalogenation of the remaining trichloroethane to vinylidene chloride and hydrogen chloride. Dioxane "poisons" this catalysis reaction by forming an adduct with aluminium trichloride. | 0 | Theoretical and Fundamental Chemistry |
* Reduction of an epoxide with lithium aluminium hydride or aluminium hydride produces the corresponding alcohol. This reduction process results from the nucleophilic addition of hydride (H).
* Reductive cleavage of epoxides gives β-lithioalkoxides.
* Epoxides undergo ring expansion reactions, illustrated by the insertion of carbon dioxide to give cyclic carbonates.
* When treated with thiourea, epoxides convert to the episulfide, which are called thiiranes.
* An epoxide adjacent to an alcohol can undergo the Payne rearrangement in base. | 0 | Theoretical and Fundamental Chemistry |
Ferritin is used in materials science as a precursor in making iron nanoparticles for carbon nanotube growth by chemical vapor deposition.
Cavities formed by ferritin and mini-ferritins (Dps) proteins have been successfully used as the reaction chamber for the fabrication of metal nanoparticles (NPs). Protein shells served as a template to restrain particle growth and as a coating to prevent coagulation/aggregation between NPs. Using various sizes of protein shells, various sizes of NPs can be easily synthesized for chemical, physical and bio-medical applications.
Experimental COVID-19 vaccines have been produced that display the spike protein's receptor binding domain on the surface of ferritin nanoparticles. | 1 | Applied and Interdisciplinary Chemistry |
According to the IUPAC definition, flocculation is "a process of contact and adhesion whereby the particles of a dispersion form larger-size clusters". Flocculation
is synonymous with agglomeration and coagulation/coalescence.
Basically, coagulation is a process of addition of coagulant to destabilize a stabilized charged particle. Meanwhile, flocculation is a mixing technique that promotes agglomeration and assists in the settling of particles. The most common used coagulant is alum, Al(SO)·14HO.
The chemical reaction involved:
:Al(SO) · 14 HO → 2 Al(OH) + 6 H + 3 + 8 HO
During flocculation, gentle mixing accelerates the rate of particle collision, and the destabilized particles are further aggregated and enmeshed into larger precipitates. Flocculation is affected by several parameters, including mixing speeds, mixing intensity, mixing time and pH. The product of the mixing intensity and mixing time is used to describe flocculation processes. | 1 | Applied and Interdisciplinary Chemistry |
The carbon cycle was first described by Antoine Lavoisier and Joseph Priestley, and popularised by Humphry Davy. The global carbon cycle is now usually divided into the following major reservoirs of carbon (also called carbon pools) interconnected by pathways of exchange:
* Atmosphere
* Terrestrial biosphere
* Ocean, including dissolved inorganic carbon and living and non-living marine biota
* Sediments, including fossil fuels, freshwater systems, and non-living organic material.
* Earth's interior (mantle and crust). These carbon stores interact with the other components through geological processes.
The carbon exchanges between reservoirs occur as the result of various chemical, physical, geological, and biological processes. The ocean contains the largest active pool of carbon near the surface of the Earth.
The natural flows of carbon between the atmosphere, ocean, terrestrial ecosystems, and sediments are fairly balanced; so carbon levels would be roughly stable without human influence. | 0 | Theoretical and Fundamental Chemistry |
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