text stringlengths 105 4.57k | label int64 0 1 | label_text stringclasses 2
values |
|---|---|---|
Stripping is a physical separation process where one or more components are removed from a liquid stream by a vapor stream. In industrial applications the liquid and vapor streams can have co-current or countercurrent flows. Stripping is usually carried out in either a packed or trayed column. | 0 | Theoretical and Fundamental Chemistry |
The water dimer consists of two water molecules loosely bound by a hydrogen bond. It is the smallest water cluster. Because it is the simplest model system for studying hydrogen bonding in water, it has been the target of many theoretical (and later experimental) studies that it has been called a "theoretical Guinea pig". | 0 | Theoretical and Fundamental Chemistry |
Binucleating ligands bind two metal ions. Usually binucleating ligands feature bridging ligands, such as phenoxide, pyrazolate, or pyrazine, as well as other donor groups that bind to only one of the two metal ions. | 0 | Theoretical and Fundamental Chemistry |
Chemoenzymatic glycorandomization was inspired by the early pathway engineering work of Hutchinson and coworkers that suggested natural product glycosyltransferases were capable of utilizing non-native sugar nucleotide donors. The initial platform for chemoenzymatic glycorandomization was based upon a set of two highly permissive sugar activation enzymes (a sugar anomeric kinase and sugar-1-phosphate nucleotidyltransferase) to afford sugar nucleotide libraries as donors for these promiscuous glycosyltransferases where the permissivity of the corresponding sugar kinase and nucleotidyltransferase was expanded by enzyme engineering and directed evolution. The first application of this three enzyme (kinase, nucleotidyltransferase and glycosyltransferase) strategy enabled the product of a set of >30 differentially glycosylated vancomycins, some members of which were further diversified chemoselectively by virtue of the installation of sugars bearing chemoselective handles. This enzymatic platform has been further advanced through glycosyltransferase evolution and capitalizing upon the discovery of the reversibility of glycosyltransferase-catalyzed reactions first discovered in the context of calicheamicin biosynthesis. | 0 | Theoretical and Fundamental Chemistry |
CK2 typically appears as a tetramer of two α subunits; α being 42 kDa and α’ being 38 kDa, and two β subunits, each weighing in at 28 kDa. The β regulatory domain only has one isoform and therefore within the tetramer will have two β subunits. The catalytic α domains appear as an α or α’ variant and can either be formed in a homodimer (α & α, or α’ & α’) formation or heterodimer formation (α & α’). It is worth noting that other β isoforms have been found in other organisms but not in humans.
The α subunits do not require the β regulatory subunits to function, this allows dimers to form of the catalytic domains independent of β subunit transcription. The presence of these α subunits does have an effect on the phosphorylation targets of CK2. A functional difference between α and α’ has been found but the exact nature of differences isn't fully understood yet. An example is that Caspase 3 is preferentially phosphorylated by α’ based tetramers over α based tetramers. | 1 | Applied and Interdisciplinary Chemistry |
Yttrium is used in the production of a large variety of synthetic garnets, and yttria is used to make yttrium iron garnets (, also "YIG"), which are very effective microwave filters which were recently shown to have magnetic interactions more complex and longer-ranged than understood over the previous four decades. Yttrium, iron, aluminium, and gadolinium garnets (e.g. and ) have important magnetic properties. YIG is also very efficient as an acoustic energy transmitter and transducer. Yttrium aluminium garnet ( or YAG) has a hardness of 8.5 and is also used as a gemstone in jewelry (simulated diamond). Cerium-doped yttrium aluminium garnet (YAG:Ce) crystals are used as phosphors to make white LEDs.
YAG, yttria, yttrium lithium fluoride (), and yttrium orthovanadate () are used in combination with dopants such as neodymium, erbium, ytterbium in near-infrared lasers. YAG lasers can operate at high power and are used for drilling and cutting metal. The single crystals of doped YAG are normally produced by the Czochralski process. | 1 | Applied and Interdisciplinary Chemistry |
Like all chemical reactions, the unimolecular decomposition of ions is subject to thermodynamic versus kinetic reaction control: the kinetic product forms faster, whereas the thermodynamic product is more stable. In the decomposition of ABCD, the reaction to form AD is thermodynamically favored and the reaction to form ABis kinetically favored. This is because the AD reaction has favorable enthalpy and the AB has favorable entropy.
In the reaction depicted schematically in the figure, the rearrangement reaction forms a double bond B=C and a new single bond A-D, which offsets the cleavage of the A-B and C-D bonds. The formation of AB requires bond cleavage without the offsetting bond formation. However, the steric effect makes it more difficult for the molecule to achieve the rearrangement transition state and form AD. The activated complex with strict steric requirements is referred to as a "tight complex" whereas the transition state without such requirements is called a "loose complex". | 0 | Theoretical and Fundamental Chemistry |
RNA polymerase 1 (also known as Pol I) is, in higher eukaryotes, the polymerase that only transcribes ribosomal RNA (but not 5S rRNA, which is synthesized by RNA polymerase III), a type of RNA that accounts for over 50% of the total RNA synthesized in a cell. | 1 | Applied and Interdisciplinary Chemistry |
Inorganic nanoparticles, such as gold, silica, iron oxide (ex. magnetofection) and calcium phosphates have been shown to be capable of gene delivery. Some of the benefits of inorganic vectors is in their storage stability, low manufacturing cost and often time, low immunogenicity, and resistance to microbial attack. Nanosized materials less than 100 nm have been shown to efficiently trap the DNA or RNA and allows its escape from the endosome without degradation. Inorganics have also been shown to exhibit improved in vitro transfection for attached cell lines due to their increased density and preferential location on the base of the culture dish. Quantum dots have also been used successfully and permits the coupling of gene therapy with a stable fluorescence marker. Engineered organic nanoparticles are also under development, which could be used for co-delivery of genes and therapeutic agents. | 1 | Applied and Interdisciplinary Chemistry |
The 3 poly(A) tail is a long sequence of adenine nucleotides (often several hundred) added to the 3 end of the pre-mRNA. This tail promotes export from the nucleus and translation, and protects the mRNA from degradation. | 1 | Applied and Interdisciplinary Chemistry |
If the pressure gradient is not measured, it can still be obtained by measuring the velocity at the centre line. The measured velocity has only the real part of the full expression in the form of
Noting that , the full physical expression becomes
at the centre line. The measured velocity is compared with the full expression by applying some properties of complex number. For any product of complex numbers (), the amplitude and phase have the relations and , respectively. Hence,
and
which finally yield | 1 | Applied and Interdisciplinary Chemistry |
Assuming a single, well-mixed, homogeneous fluid and a single acceleration due to gravity (both are good assumptions in natural rivers, and the second is a good assumption for processes on Earth, or any planetary body with a dominant influence on the local gravitational field), the only two variables that determine the boundary shear stress are the depth and the slope. This is the significance of the name of the formula.
For natural streams, in the mks or SI system (units of pascals for shear stress), a typical useful relationship to remember is that:
for water with a density of 1000 kg/m and approximating the acceleration due to gravity as 10 m/s (the error in this assumption is typically much smaller than the error from measurements). | 1 | Applied and Interdisciplinary Chemistry |
Preimplantation genetic screening (PGS) or preimplantation genetic diagnosis (PGD) has been suggested to be able to be used in IVF to select an embryo that appears to have the greatest chances for successful pregnancy. However, a systematic review and meta-analysis of existing randomised controlled trials came to the result that there is no evidence of a beneficial effect of PGS with cleavage-stage biopsy as measured by live birth rate. On the contrary, for those of advanced maternal age, PGS with cleavage-stage biopsy significantly lowers the live birth rate. Technical drawbacks, such as the invasiveness of the biopsy, and non-representative samples because of mosaicism are the major underlying factors for inefficacy of PGS.
Still, as an expansion of IVF, patients who can benefit from PGS/PGD include:
* Those who have a family history of inherited disease
* Those who want prenatal sex discernment. This can be used to diagnose monogenic disorders with sex linkage. It can potentially be used for sex selection, wherein a fetus is aborted if having an undesired sex.
* Those who already have a child with an incurable disease and need compatible cells from a second healthy child to cure the first, resulting in a "saviour sibling" that matches the sick child in HLA type.
PGS screens for numeral chromosomal abnormalities while PGD diagnosis the specific molecular defect of the inherited disease. In both PGS and PGD, individual cells from a pre-embryo, or preferably trophectoderm cells biopsied from a blastocyst, are analysed during the IVF process. Before the transfer of a pre-embryo back to a person's uterus, one or two cells are removed from the pre-embryos (8-cell stage), or preferably from a blastocyst. These cells are then evaluated for normality. Typically within one to two days, following completion of the evaluation, only the normal pre-embryos are transferred back to the uterus. Alternatively, a blastocyst can be cryopreserved via vitrification and transferred at a later date to the uterus. In addition, PGS can significantly reduce the risk of multiple pregnancies because fewer embryos, ideally just one, are needed for implantation. | 1 | Applied and Interdisciplinary Chemistry |
In combustion, a Burke–Schumann flame is a type of diffusion flame, established at the mouth of the two concentric ducts, by issuing fuel and oxidizer from the two region respectively. It is named after S.P. Burke and T.E.W. Schumann, who were able to predict the flame height and flame shape using their simple analysis of infinitely fast chemistry (which is now called as Burke–Schumann limit) in 1928 at the First symposium on combustion. | 1 | Applied and Interdisciplinary Chemistry |
The experiments described in the instruction manual typically require a number of chemicals not shipped with the chemistry set, because they are common household chemicals:
* Acetic acid (in vinegar)
* Ammonium carbonate ("baker's ammonia" or "salts of hartshorn")
* Citric acid (in lemons)
* Ethanol (in denatured alcohol)
* Sodium bicarbonate (baking soda)
* Sodium chloride ("table salt")
Other chemicals, including strong acids, bases and oxidizers cannot be safely shipped with the set and others having a limited shelf life have to be purchased separately from a drug store:
* Hydrochloric acid
* Hydrogen peroxide
* Silver nitrate
* Sodium hydroxide | 1 | Applied and Interdisciplinary Chemistry |
The Wohl degradation in carbohydrate chemistry is a chain contraction method for aldoses. The classic example is the conversion of glucose to arabinose as shown below. The reaction is named after the German chemist Alfred Wohl (1863–1939).
In one modification, d-glucose is converted to the glucose oxime by reaction with hydroxylamine and sodium methoxide. In the second step the is formed by reaction with acetic anhydride in acetic acid with sodium acetate. In this reaction step the oxime is converted into the nitrile with simultaneous conversion of all the alcohol groups to acetate groups.
In the final step sodium methoxide in methanol is added, leading to removal of all the acetate groups and ejection of the nitrile group and collapse of the second carbon from a tetrahedral structure to an aldehyde. | 0 | Theoretical and Fundamental Chemistry |
Inclusions are one of the most important factors when it comes to gem valuation. In many gemstones, such as diamonds, inclusions affect the clarity of the gem, diminishing the value. In some gems, however, such as star sapphires, the inclusion actually increases the value of the gem.
Many colored gemstones are expected to have inclusions, and the inclusions do not greatly affect the stone's value. Colored gemstones are categorized into three types as follows:
*Type I colored gems include gems with very little or no inclusions. They include aquamarines, topaz and zircon.
*Type II colored gems include those that often have a few inclusions. They include sapphire, ruby, garnet and spinel.
*Type III colored gems include those that almost always have inclusions. Gems in this category include emerald and tourmaline. | 1 | Applied and Interdisciplinary Chemistry |
The waste discharge can be sent into incineration plant, where the organic solid undergoes combustion process. The combustion process produces heat that can be used to generate electricity. | 0 | Theoretical and Fundamental Chemistry |
(95%W/5%Re–74%W/26%Re, by weight) maximum temperature will be measured by type-c thermocouple is 2329 °C. | 1 | Applied and Interdisciplinary Chemistry |
In a typical non-premixed combustion (fuel and oxidizer are separated initially), mixing of fuel and oxidizer takes place based on the mechanical time scale dictated by the convection/diffusion (the relative importance between convection and diffusion depends on the Reynolds number) terms. Similarly, chemical reaction takes certain amount of time to consume reactants. For one-step irreversible chemistry with Arrhenius rate, this chemical time is given by
where is the pre-exponential factor, is the activation energy, is the universal gas constant and is the temperature. Similarly, one can define appropriate for particular flow configuration. The Damköhler number is then
Due to the large activation energy, the Damköhler number at unburnt gas temperature is , because . On the other hand, the shortest chemical time is found at the flame (with burnt gas temperature ), leading to . Regardless of Reynolds number, the limit guarantees that chemical reaction dominates over the other terms. A typical conservation equation for the scalar (species concentration or energy) takes the following form,
where is the convective-diffusive operator and are the mass fractions of fuel and oxidizer, respectively. Taking the limit in the above equation, we find that
i.e., fuel and oxidizer cannot coexist, since far away from the reaction sheet, only one of the reactant is available (non premixed). On the fuel side of the reaction sheet, and on the oxidizer side, . Fuel and oxygen can coexist (with very small concentrations) only in a thin reaction sheet, where (diffusive transport will be comparable to reaction in this zone). In this thin reaction sheet, both fuel and oxygen are consumed and nothing leaks to the other side of the sheet. Due to the instantaneous consumption of fuel and oxidizer, the normal gradients of scalars exhibit discontinuities at the reaction sheet. | 1 | Applied and Interdisciplinary Chemistry |
Phosphorus occurs naturally in both organic and inorganic forms. The analytical measure of biologically available orthophosphates is referred to as soluble reactive phosphorus (SR-P). Dissolved organic phosphorus and insoluble forms of organic and inorganic phosphorus are generally not biologically available until transformed into soluble inorganic forms.
In freshwater aquatic ecosystems phosphorus is typically the major limiting nutrient. Under undisturbed natural conditions, phosphorus is in short supply. The natural scarcity of phosphorus is demonstrated by the explosive growth of algae in water receiving heavy discharges of phosphorus-rich wastes. Because phosphorus does not have an atmospheric component, unlike nitrogen, the phosphorus cycle can be characterized as closed. The removal and storage of phosphorus from wastewater can only occur within the constructed wetland itself. Phosphorus may be sequestered within a wetland system by:
# The binding of phosphorus in organic matter as a result of incorporation into living biomass,
# Precipitation of insoluble phosphates with ferric iron, calcium, and aluminium found in wetland soils. | 1 | Applied and Interdisciplinary Chemistry |
The third commercial copper ISASMELT plant was installed in MIM's Mount Isa copper smelter at a cost of approximately A$100 million. It was designed to treat 104 t/h of copper concentrate, containing 180,000 t/y of copper, and it began operation in August 1992.
A significant difference between the Mount Isa copper ISASMELT plant and all the others is that it uses an Ahlstrom Fluxflow waste heat boiler to recover heat from the furnace waste gas. This boiler uses a recirculating fluid bed of particles to rapidly quench the gas as it leaves the furnace, and then uses the enhanced heat transfer properties of solid–solid contact to cool the particles as they are carried past boiler tubes that are suspended in a shaft above the bed. The high heat transfer rate means that the Fluxflow boiler is relatively compact compared with conventional waste heat boilers and the rapid cooling of the waste gas limits the formation of sulfur trioxide ("SO"), which in the presence of water forms sulfuric acid that can cause corrosion of cool surfaces.
In its early years, the Fluxflow boiler was the cause of significant down time, because the rate of wear of the boiler tubes was much higher than expected. The problems were solved by understanding the gas flows within the boiler and redesigning the boiler tubes to minimise the effects of erosion.
The life of the refractory bricks in the ISASMELT furnace was initially shorter than expected and a water cooling system was briefly considered to extend them; however, this was not installed and operational improvements resulted in a significant extension of the lining life without this capital and operating expense. Since 1998, the refractory lining lives have exceeded their two-year design, with lives of the 8th and 9th linings nearly reaching three years. The most recent lining lasted for 50 months, with the one before that lasting for 44 months.
In the first years of operation at Mount Isa, the throughput of the ISASMELT furnace was constrained by problems with some of the ancillary equipment in the plant, including the boiler, slag granulation system and concentrate filters. The ultimate constraint was the decision during its construction to keep one of the two reverberatory furnaces on line to increase the copper smelter production to 265,000 t/y of anode copper. The smelter's Peirce-Smith converters became a bottleneck and the feed rate of the ISASMELT furnace had to be restrained to allow sufficient matte to be drawn from the reverberatory furnace to prevent it freezing solid. The ISASMELT 12-month rolling average of the feed rate fell just short of 100 t/h for much of this period, not quite reaching the design annual average of 104 t/h. MIM decided to shut down the reverberatory furnace in 1997, and the ISASMELT plant 12-month rolling mean feed rate quickly exceeded the 104 t/h design when this constraint was lifted.
The performance of the ISASMELT plant was sufficiently encouraging that MIM decided to expand the ISASMELT treatment rate to 166 t/h by adding a second oxygen plant to allow higher enrichment of the lance air. As a result, by late 2001 it had achieved a peak rate of 190 t/h of concentrate, and the smelter produced a peak annual total of 240,000 t of anode copper. At that time, the Mount Isa copper smelter, together with its copper refinery in Townsville, was among the lowest cost copper smelters in the world.
Lance life is typically two weeks, with lance changes taking 30 to 40 minutes, and repairs usually being limited to replacement of the lance tips.
In 2006, MIM commissioned a second rotary holding furnace that operates in parallel with the existing holding furnace. | 1 | Applied and Interdisciplinary Chemistry |
In acute toxicity, people have primarily gastrointestinal symptoms such as vomiting and diarrhea, which may result in volume depletion. During acute toxicity, lithium distributes later into the central nervous system causing dizziness and other mild neurological symptoms. | 1 | Applied and Interdisciplinary Chemistry |
Because of the unique shapes, reactivities, properties, and bioactivities that they engender, cyclic compounds are the largest majority of all molecules involved in the biochemistry, structure, and function of living organisms, and in the man-made molecules (e.g., drugs, herbicides, etc.) through which man attempts to exert control over nature and biological systems. | 0 | Theoretical and Fundamental Chemistry |
Larry Robinson is an American professor and academic administrator, who is the current President of Florida A&M University, a historically black university. | 0 | Theoretical and Fundamental Chemistry |
N NMR is the most effective method for investigation of structure of heterocycles with a high content of nitrogen atoms (tetrazoles, triazines and their annelated analogs). N labeling followed by analysis of C–N and H–N couplings may be used for establishing structures and chemical transformations of nitrogen heterocycles. | 0 | Theoretical and Fundamental Chemistry |
The theory of solar cells explains the process by which light energy in photons is converted into electric current when the photons strike a suitable semiconductor device. The theoretical studies are of practical use because they predict the fundamental limits of a solar cell, and give guidance on the phenomena that contribute to losses and solar cell efficiency. | 0 | Theoretical and Fundamental Chemistry |
Partitioning in digital PCR increases sensitivity and allows for detection of rare events, especially single nucleotide variants (SNVs), by isolating or greatly diminishing the target biomarker signal from potentially competing background. These events can be organized into two classes: rare mutation detection and rare sequence detection. | 1 | Applied and Interdisciplinary Chemistry |
The total number of constructed wetlands in Austria is 5,450 (in 2015). Due to legal requirements (nitrification), only vertical flow constructed wetlands are implemented in Austria as they achieve better nitrification performance than horizontal flow constructed wetlands. Only about 100 of these constructed wetlands have a design size of 50 population equivalents or more. The remaining 5,350 treatment plants are smaller than that. | 1 | Applied and Interdisciplinary Chemistry |
One criticism of the concept of the control coefficient as defined above is that it is dependent on being described relative to a change in enzyme activity. Instead, the Berlin school defined control coefficients in terms of changes to local rates brought about by any suitable parameter, which could include changes to enzyme levels or the action of drugs. Hence a more general definition is given by the following expressions:
and concentration control coefficients by
In the above expression, could be any convenient parameter. For example, a drug, changes in enzyme expression etc. The advantage is that the control coefficient becomes independent of the applied perturbation. For control coefficients defined in terms of changes in enzyme expression, it is often assumed that the effect on the local rate by changes to the enzyme activity is proportional so that: | 1 | Applied and Interdisciplinary Chemistry |
Wind waves are waves at the water surface that are generated due to the shear action of wind stress on the water surface and the aim of gravity, that acts as a restoring force, to return the water surface to its equilibrium position. Wind waves in the ocean are also known as ocean surface waves. The wind waves interact with both the air and water flows above and below the waves. Therefore, the characteristics of wind waves are determined by the coupling processes between the boundary layers of both the atmosphere and ocean. Wind waves also play an important role themselves in the interaction processes between the ocean and the atmosphere. Wind waves in the ocean can travel thousands of kilometers. A proper description of the physical mechanisms that cause the growth of wind waves and is in accordance with observations has yet to be completed. A necessary condition for wind waves to grow is a minimum wind speed of 0.05 m/s. | 1 | Applied and Interdisciplinary Chemistry |
Donnan dialysis is a separation process which is used to exchange ions between two aqueous solutions which are separated by a CEM or an AEM membrane. In the case of a cation exchange membrane separating two solutions with different acidity, protons (H) go through the membrane to the less acidic side. This induces an electrical potential that will instigate a flux of the cations present in the less acidic side to the more acidic side. The process will finish when the variation of concentration of H is the same order of magnitude as the difference of concentration of the separated cation. | 1 | Applied and Interdisciplinary Chemistry |
Julia was born in 1922 in Paris as son of the renowned mathematician Gaston Julia. Julia studied physics at the École Normale Supérieure. After receiving his diploma he joined the group of Ian Heilbron and David G. Jones at the Imperial College London where he received his first PhD in 1948. Back to France he changed his subject to chemistry and subsequently received his second PhD for work with . | 0 | Theoretical and Fundamental Chemistry |
When the incident particle, such as an alpha particle or electron, is diffracted in the Coulomb potential of atoms and molecules, the elastic scattering process is called Rutherford scattering. In many electron diffraction techniques like reflection high energy electron diffraction (RHEED), transmission electron diffraction (TED), and gas electron diffraction (GED), where the incident electrons have sufficiently high energy (>10 keV), the elastic electron scattering becomes the main component of the scattering process and the scattering intensity is expressed as a function of the momentum transfer defined as the difference between the momentum vector of the incident electron and that of the scattered electron. | 0 | Theoretical and Fundamental Chemistry |
* Nearly all RAPD markers are dominant, i.e. it is not possible to distinguish whether a DNA segment is amplified from a locus that is heterozygous (1 copy) or homozygous (2 copies). Codominant RAPD markers, observed as different-sized DNA segments amplified from the same locus, are detected only rarely.
* PCR is an enzymatic reaction, therefore, the quality and concentration of template DNA, concentrations of PCR components, and the PCR cycling conditions may greatly influence the outcome. Thus, the RAPD technique is notoriously laboratory dependent and needs carefully developed laboratory protocols to be reproducible.
* Mismatches between the primer and the template may result in the total absence of PCR product as well as in a merely decreased amount of the product. Thus, the RAPD results can be difficult to interpret, unlike traditional PCR analysis. | 1 | Applied and Interdisciplinary Chemistry |
Consider steady flow of blood through a capillary of radius . The capillary cross section can be divided into a core region and cell-free plasma region near the wall. The governing equations for both regions can be given by the following equations:
where:
: is the pressure drop across the capillary
: is the length of capillary
: is velocity in core region
: is velocity of plasma in cell-free region
: is viscosity in core region
: is viscosity of plasma in cell-free region
: is the cell-free plasma layer thickness | 1 | Applied and Interdisciplinary Chemistry |
The basic room purge equation is used in industrial hygiene. It determines the time required to reduce a known vapor concentration existing in a closed space to a lower vapor concentration. The equation can only be applied when the purged volume of vapor or gas is replaced with "clean" air or gas. For example, the equation can be used to calculate the time required at a certain ventilation rate to reduce a high carbon monoxide concentration in a room.
Sometimes the equation is also written as:
where
*D = time required; the unit of time used is the same as is used for Q
*V = air or gas volume of the closed space or room in cubic feet, cubic metres or litres
*Q = ventilation rate into or out of the room in cubic feet per minute, cubic metres per hour or litres per second
*C = initial concentration of a vapor inside the room measured in ppm
*C = final reduced concentration of the vapor inside the room in ppm | 0 | Theoretical and Fundamental Chemistry |
The choice of metallic substrate is determined by the dimensional, mechanical and corrosion resistance properties required of the coated product in use. The most common metallic substrates that are organically coated are:
* Hot dip galvanised steel (HDG) which consists of a cold reduced steel substrate onto which a layer of zinc is coated via a hot dip process to impart enhanced corrosion properties onto the base steel.
* Galvanized mild steel (GMS) can be used as balustrade and handrail of staircase, pipe, etc.
* Other zinc-based alloys are coated onto steel and used as a substrate for coil coating, giving different properties. They give improved corrosion resistance in particular conditions.
* Electro-galvanised (EG) coated steel consists of a cold reduced substrate onto which a layer of zinc is coated by an electrolytic process.
* Cold reduced steel (CR) without any zinc coating
* Wrought aluminium alloys
* Many other substrates are organically coated: zinc/iron, stainless steel, tinplate, brass, zinc and copper. | 1 | Applied and Interdisciplinary Chemistry |
The Born equation can be used for estimating the electrostatic component of Gibbs free energy of solvation of an ion. It is an electrostatic model that treats the solvent as a continuous dielectric medium (it is thus one member of a class of methods known as continuum solvation methods).
It was derived by Max Born.
where:
*N = Avogadro constant
*z = charge of ion
*e = elementary charge, 1.6022 C
*ε = permittivity of free space
*r = effective radius of ion
*ε = dielectric constant of the solvent | 0 | Theoretical and Fundamental Chemistry |
A wide variety of alkyl Nb compounds have been prepared. Low coordination number complexes require the absence of any β-hydrogen to prevent rapid β-hydride elimination. The simplest compounds are salts of , which is prepared by alkylation of using methyl lithium: | 0 | Theoretical and Fundamental Chemistry |
The sum of the atomic mass of the two atoms produced by the fission of one fissile atom is always less than the atomic mass of the original atom. This is because some of the mass is lost as free neutrons, and once kinetic energy of the fission products has been removed (i.e., the products have been cooled to extract the heat provided by the reaction), then the mass associated with this energy is lost to the system also, and thus appears to be "missing" from the cooled fission products.
Since the nuclei that can readily undergo fission are particularly neutron-rich (e.g. 61% of the nucleons in uranium-235 are neutrons), the initial fission products are often more neutron-rich than stable nuclei of the same mass as the fission product (e.g. stable zirconium-90 is 56% neutrons compared to unstable strontium-90 at 58%). The initial fission products therefore may be unstable and typically undergo beta decay to move towards a stable configuration, converting a neutron to a proton with each beta emission. (Fission products do not decay via alpha decay.)
A few neutron-rich and short-lived initial fission products decay by ordinary beta decay (this is the source of perceptible half life, typically a few tenths of a second to a few seconds), followed by immediate emission of a neutron by the excited daughter-product. This process is the source of so-called delayed neutrons, which play an important role in control of a nuclear reactor.
The first beta decays are rapid and may release high energy beta particles or gamma radiation. However, as the fission products approach stable nuclear conditions, the last one or two decays may have a long half-life and release less energy. | 0 | Theoretical and Fundamental Chemistry |
Although the cost of acquiring hyperspectral images is typically high for specific crops and in specific climates, hyperspectral remote sensing use is increasing for monitoring the development and health of crops. In Australia, work is under way to use imaging spectrometers to detect grape variety and develop an early warning system for disease outbreaks. Furthermore, work is under way to use hyperspectral data to detect the chemical composition of plants, which can be used to detect the nutrient and water status of wheat in irrigated systems. On a smaller scale, NIR hyperspectral imaging can be used to rapidly monitor the application of pesticides to individual seeds for quality control of the optimum dose and homogeneous coverage.
Another application in agriculture is the detection of animal proteins in compound feeds to avoid bovine spongiform encephalopathy (BSE), also known as mad-cow disease. Different studies have been done to propose alternative tools to the reference method of detection, (classical microscopy). One of the first alternatives is near infrared microscopy (NIR), which combines the advantages of microscopy and NIR. In 2004, the first study relating this problem with hyperspectral imaging was published. Hyperspectral libraries that are representative of the diversity of ingredients usually present in the preparation of compound feeds were constructed. These libraries can be used together with chemometric tools to investigate the limit of detection, specificity and reproducibility of the NIR hyperspectral imaging method for the detection and quantification of animal ingredients in feed.
HSI cameras can also be used to detect stress from heavy metals in plants and become an earlier and faster alternative to post-harvest wet chemical methods. | 0 | Theoretical and Fundamental Chemistry |
Jameson's research into flotation began when he was at Imperial College London, in 1969. A colleague, Dr J. A. Kitchener of the Royal School of Mines, pointed out that many of the new mineral deposits being found around the world required fine grinding to separate the valuable particles from the rock in which they were embedded, and the flotation technologies available at the time were relatively inefficient for recovering fine particles. Kitchener felt that improvements could best be achieved by an increased knowledge of the physics of flotation, rather than the chemistry of the reagents. Jameson had gained some expertise in the properties of bubbles and particles in suspensions whilst a PhD student at Cambridge. He began research into the fluid mechanics of the flotation process and set in train a series of experimental projects into the effect of particle diameter and bubble size on the flotation rate constant. Much of the research was conducted by honours students in chemical engineering. Jameson accepted the challenge of coming up with practical solutions to remedy the situation, if these could be identified.
Jameson's research showed that the kinetics of flotation of fine particles was a strong function of the bubble diameter and that the way to improve recoveries was to use small bubbles in the order of 300 microns (μm) in diameter. What was needed was a practical method of making such bubbles in large quantities, of the order of billions per second. The device needed to be simple to construct and operate, capable of running for long periods with minimal maintenance, and should be resistant to blockage by stray large particles in the feed. He began to look at the theory of bubble breakup in sheared flows, that is, in flow fields in which layers of liquid slide over each other. Lewis and Davidson had recently published a theory to predict the maximum size of bubbles in a well-characterised flow environment. By balancing the forces acting on a bubble in a shearing flow, including the disruptive dynamic stresses from the liquid motion and the restoring force of surface tension, it was possible to predict the critical shear rate required to produce a bubble of given size. Jameson then looked for simple and practical ways of generating the required shear rates, and found inspiration in the kitchen sink. If a jet of water from a tap plunges into a basin full of water, a shear layer develops around the jet, that entrains air from the atmosphere into the water, and at the same time, breaks up the entrained air into fine bubbles. The effect is magnified if there is a detergent in the water. Detergents, known as frothers, are used in flotation to prevent bubble coalescence, and to create stable froths. By the correct choice of jet velocity and diameter, it is possible to provide a controlled shear environment that can generate bubbles of a suitable size for flotation, with the added advantage that the air is naturally aspirated by the jet, so there is no need for a compressor or blower. Thus the idea of the Jameson Cell was born.
After a number of failures, the radical new process for flotation emerged in the laboratory at the University of Newcastle. Jameson filed a provisional patent application in 1986. After an initial trial at the Renison Bell tin mine in Tasmania, certain design features were modified. He led a further plant trial with a small cell in the lead-zinc concentrator at Mt Isa Mines Ltd in Queensland, initially working alone. The plant metallurgists took an interest in the technology and helped to refine it, particularly checking the scale-up procedures that Jameson had devised. In 1988 a recent graduate was assigned full-time for a year to verify and validate the performance of the Cell. In 1989 a worldwide exclusive license was negotiated between Tunra Ltd on behalf of the University of Newcastle, Jameson, and MIM Holdings Limited, for the use of the Cell for metallurgical purposes. Summary papers on the theory and practice have been published.
There have been ongoing significant changes to the design of the Cell since it was first developed in the late 1980s. | 1 | Applied and Interdisciplinary Chemistry |
*Chlorofluorocarbons (CFCs): when derived from methane and ethane these compounds have the formulae CClF and CClF, where m is nonzero.
*Hydro-chlorofluorocarbons (HCFCs): when derived from methane and ethane these compounds have the formula CClFH and CClFH, where m, n, x, and y are nonzero.
* and bromofluorocarbons have formulae similar to the CFCs and HCFCs but also include bromine.
*Hydrofluorocarbons (HFCs): when derived from methane, ethane, propane, and butane, these compounds have the respective formulae CFH, CFH, CFH, and CFH, where m is nonzero. | 1 | Applied and Interdisciplinary Chemistry |
Current RO membranes, thin-film composite (TFC) polyamide membranes, are being studied to find ways of improving their permeability. Through new imaging methods, researchers were able to make 3D models of membranes and examine how water flowed through them. They found that TFC membranes with areas of low flow significantly decreased water permeability. By ensuring uniformity of the membranes and allowing water to flow continuously without slowing down, membrane permeability could be improved by 30%-40%. | 0 | Theoretical and Fundamental Chemistry |
High potential iron–sulfur proteins (HiPIPs) form a unique family of FeS ferredoxins that function in anaerobic electron transport chains. Some HiPIPs have a redox potential higher than any other known iron–sulfur protein (e.g., HiPIP from Rhodopila globiformis has a redox potential of ca. -450 mV). Several HiPIPs have so far been characterized structurally, their folds belonging to the α+β class. As in other bacterial ferredoxins, the [FeS] unit forms a cubane-type cluster and is ligated to the protein via four Cys residues. | 0 | Theoretical and Fundamental Chemistry |
One contributing structure may resemble the actual molecule more than another (in the sense of energy and stability). Structures with a low value of potential energy are more stable than those with high values and resemble the actual structure more. The most stable contributing structures are called major contributors. Energetically unfavourable and therefore less favorable structures are minor contributors. With rules listed in rough order of diminishing importance, major contributors are generally structures that
# obey as much as possible the octet rule (8 valence electrons around each atom rather than having deficiencies or surplus, or 2 electrons for Period 1 elements);
# have a maximum number of covalent bonds;
# carry a minimum of formally charged atoms, with the separation for unlike and like charges minimized and maximized, respectively;
# place negative charge, if any, on the most electronegative atoms and positive charge, if any, on the most electropositive;
# do not deviate substantially from idealized bond lengths and angles (e.g., the relative unimportance of Dewar-type resonance contributors for benzene);
# maintain aromatic substructures locally while avoiding anti-aromatic ones (see Clar sextet and biphenylene).
A maximum of eight valence electrons is strict for the Period 2 elements Be, B, C, N, O, and F, as is a maximum of two for H and He and effectively for Li as well. The issue of expansion of the valence shell of third period and heavier main group elements is controversial. A Lewis structure in which a central atom has a valence electron count greater than eight traditionally implies the participation of d orbitals in bonding. However, the consensus opinion is that while they may make a marginal contribution, the participation of d orbitals is unimportant, and the bonding of so-called hypervalent molecules are, for the most part, better explained by charge-separated contributing forms that depict three-center four-electron bonding. Nevertheless, by tradition, expanded octet structures are still commonly drawn for functional groups like sulfoxides, sulfones, and phosphorus ylides, for example. Regarded as a formalism that does not necessarily reflect the true electronic structure, such depictions are preferred by the IUPAC over structures featuring partial bonds, charge separation, or dative bonds.
Equivalent contributors contribute equally to the actual structure, while the importance of nonequivalent contributors is determined by the extent to which they conform to the properties listed above. A larger number of significant contributing structures and a more voluminous space available for delocalized electrons lead to stabilization (lowering of the energy) of the molecule. | 0 | Theoretical and Fundamental Chemistry |
Nanoclusters are agglomerates of nanoparticles with at least one dimension between 1 and 10 nanometers and a narrow size distribution. Nanopowders are agglomerates of ultrafine particles, nanoparticles, or nanoclusters. Nanometer-sized single crystals, or single-domain ultrafine particles, are often referred to as nanocrystals.
The terms colloid and nanoparticle are not interchangeable. A colloid is a mixture which has particles of one phase dispersed or suspended within an other phase. The term applies only if the particles are larger than atomic dimensions but small enough to exhibit Brownian motion, with the critical size range (or particle diameter) typically ranging from nanometers (10 m) to micrometers (10 m). Colloids can contain particles too large to be nanoparticles, and nanoparticles can exist in non-colloidal form, for examples as a powder or in a solid matrix. | 0 | Theoretical and Fundamental Chemistry |
The Cape York meteorite, also known as the Innaanganeq meteorite, is one of the largest known iron meteorites, classified as a medium octahedrite in chemical group IIIAB. In addition to many small fragments, at least eight large fragments with a total mass of 58 tonnes have been recovered, the largest weighing . The meteorite is named after the location where the largest fragment was found: east of Cape York, in Savissivik, Meteorite Island, Greenland.
The date of the meteorite fall is debated, but was likely within the last few thousand years. It was known to the Inughuit (the local Inuit) for centuries, who used it as a source of meteoritic iron for tools. The first foreigner to reach the meteorite was Robert Peary in 1894, with the assistance of Inuit guides. Large pieces are on display at the American Museum of Natural History and the University of Copenhagen Geological Museum. | 1 | Applied and Interdisciplinary Chemistry |
It is usually recommended not to declare a person dead until their body is warmed to a near normal body temperature of greater than , since extreme hypothermia can suppress heart and brain function. This is summarized in the common saying "Youre not dead until youre warm and dead." Exceptions include if there are obvious fatal injuries or the chest is frozen so that it cannot be compressed. If a person was buried in an avalanche for more than 35 minutes and is found with a mouth packed full of snow without a pulse, stopping early may also be reasonable. This is also the case if a person's blood potassium is greater than 12 mmol/L.
Those who are stiff with pupils that do not move may survive if treated aggressively. Survival with good function also occasionally occurs even after the need for hours of CPR. Children who have near-drowning accidents in water near can occasionally be revived, even over an hour after losing consciousness. The cold water lowers the metabolism, allowing the brain to withstand a much longer period of hypoxia. While survival is possible, mortality from severe or profound hypothermia remains high despite optimal treatment. Studies estimate mortality at between 38% and 75%.
In those who have hypothermia due to another underlying health problem, when death occurs it is frequently from that underlying health problem. | 1 | Applied and Interdisciplinary Chemistry |
Chemogenetics and usage of DREADDs have allowed researchers to advance in biomedical research areas including many neurodegenerative and psychiatric conditions. Chemogenetics have been used in these fields to induce specific and reversible brain lesions and therefore, study specific activities of neuron population. Although chemogenetics offers specificity and high spatial resolution, it still faces some challenges when used in investigating neuropsychiatric disorders. Neuropsychiatric disorders usually have a complex nature where lesions in the brain have not been identified as the main cause. Chemogenetics has been used to reverse some of the deficits revolving such conditions; however, it has not been able to identify the main cause of neuropsychiatric diseases and cure these conditions completely due to complex nature of these conditions. Nevertheless, chemogenetics has been used successfully in a preclinical model of drug-resistant epilepsy, where seizures arise from a discrete part of the brain. | 1 | Applied and Interdisciplinary Chemistry |
Originally used with a different meaning, the term took its current definition after Lwoff and collaborators (1946). | 0 | Theoretical and Fundamental Chemistry |
N decays by positron emission with a half-life of 9.97 min. It is produced by the nuclear reaction
:H + O → N + He
N is used in positron emission tomography (PET scan). | 0 | Theoretical and Fundamental Chemistry |
John William Strutt, 3rd Baron Rayleigh, (; 12 November 1842 – 30 June 1919) was a British mathematician and physicist who made extensive contributions to science. He spent all of his academic career at the University of Cambridge. Among many honours, he received the 1904 Nobel Prize in Physics "for his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies." He served as president of the Royal Society from 1905 to 1908 and as chancellor of the University of Cambridge from 1908 to 1919.
Rayleigh provided the first theoretical treatment of the elastic scattering of light by particles much smaller than the lights wavelength, a phenomenon now known as "Rayleigh scattering", which notably explains why the sky is blue. He studied and described transverse surface waves in solids, now known as "Rayleigh waves". He contributed extensively to fluid dynamics, with concepts such as the Rayleigh number (a dimensionless number associated with natural convection), Rayleigh flow, the Rayleigh–Taylor instability, and Rayleighs criterion for the stability of Taylor–Couette flow. He also formulated the circulation theory of aerodynamic lift. In optics, Rayleigh proposed a well-known criterion for angular resolution. His derivation of the Rayleigh–Jeans law for classical black-body radiation later played an important role in the birth of quantum mechanics (see Ultraviolet catastrophe). Rayleighs textbook The Theory of Sound' (1877) is still used today by acousticians and engineers. He introduced the Rayleigh test for circular non-uniformity, of which the Rayleigh plot visualizes. | 1 | Applied and Interdisciplinary Chemistry |
In elementary applications, Raoults law is generally valid when the liquid phase is either nearly pure or a mixture of similar substances. Raoults law may be adapted to non-ideal solutions by incorporating two factors that account for the interactions between molecules of different substances. The first factor is a correction for gas non-ideality, or deviations from the ideal-gas law. It is called the fugacity coefficient (). The second, the activity coefficient , is a correction for interactions in the liquid phase between the different molecules.
This modified or extended Raoult's law is then written as | 0 | Theoretical and Fundamental Chemistry |
The EPOC effect is greatest soon after the exercise is completed and decays to a lower level over time. One experiment, involving exertion above baseline, found EPOC increasing metabolic rate to an excess level that decays to 13% three hours after exercise, and 4% after 16 hours, for the studied exercise dose. Another study, specifically designed to test whether the effect existed for more than 16 hours, conducted tests for 48 hours after the conclusion of the exercise and found measurable effects existed up to the 38-hour post-exercise measurement, for the studied exercise dose. | 1 | Applied and Interdisciplinary Chemistry |
Lithium is present in biological systems in trace amounts; its functions are uncertain. Lithium salts have proven to be useful as a mood stabilizer and antidepressant in the treatment of mental illness such as bipolar disorder. | 1 | Applied and Interdisciplinary Chemistry |
The leaf surface is also host to a large variety of microorganisms; in this context it is referred to as the phyllosphere.
;Lepidote: Covered with fine scurfy scales. | 0 | Theoretical and Fundamental Chemistry |
In contrast to most organic compounds, many inorganic compounds are magnetic and/or colored. These properties provide information on the bonding and structure. The magnetism of inorganic compounds can be comlex.For example, most copper(II) compounds are paramagnetic but Cu(OAc)(HO) is almost diamagnetic below room temperature. The explanation is due to magnetic coupling between pairs of Cu(II) sites in the acetate. | 0 | Theoretical and Fundamental Chemistry |
4-Nitrophenol can be prepared by nitration of phenol using dilute nitric acid at room temperature. The reaction produces a mixture of 2-nitrophenol and 4-nitrophenol. | 0 | Theoretical and Fundamental Chemistry |
Microbial food cultures preserve food through formation of inhibitory metabolites such as organic acid (lactic acid, acetic acid, formic acid, propionic acid), ethanol, bacteriocins, etc., often in combination with decrease of water activity (by drying or use of salt). Further, microbial food cultures help to improve food safety through inhibition of pathogens or removing of toxic compounds. Microbial food cultures also improve the nutritional value and organoleptic quality of the food.
The microbial food cultures used in food fermentation can be divided into three major groups: bacteria, yeasts and moulds. | 1 | Applied and Interdisciplinary Chemistry |
Akkaya and coworkers demonstrated a molecular NOR gate using a boradiazaindacene system. Fluorescence of the highly-emissive boradiazaindacene (input “1”) was found to be quenched in the presence of either a zinc salt [Zn(II)] or trifluoroacetic acid (TFA). The system, thus, could realize the truth table of a NOR logic gate. | 0 | Theoretical and Fundamental Chemistry |
External spray systems for buildings are well documented for protection from fires in adjacent buildings. However, up there is little published scientific research on scientific information pertaining to the effectiveness of EWSS under varying wildfire conditions. | 1 | Applied and Interdisciplinary Chemistry |
The Gallic acid reagent is used as a simple spot-test to presumptively identify drug precursor chemicals. It is composed of a mixture of gallic acid and concentrated sulfuric acid.
0.05 g of gallic acid is used for every 10 mls of sulfuric acid. The same ratio of gallic acid n-propyl ester in sulfuric acid can also be used.
Because of its short shelf life (changing to pale violet color) it is sometimes prepared by dissolving gallic acid into ethanol and adding the sulfuric acid at the time of testing from a separate bottle. In this case 100 mL ethanol is used and one drop of sulfuric acid is used per drop of gallic acid in ethanol. | 0 | Theoretical and Fundamental Chemistry |
Synthetic chelates such as ethylenediaminetetraacetic acid (EDTA) proved too stable and not nutritionally viable. If the mineral was taken from the EDTA ligand, the ligand could not be used by the body and would be expelled. During the expulsion process the EDTA ligand randomly chelated and stripped other minerals from the body. According to the Association of American Feed Control Officials (AAFCO), a metal–amino acid chelate is defined as the product resulting from the reaction of metal ions from a soluble metal salt with amino acids, with a mole ratio in the range of 1–3 (preferably 2) moles of amino acids for one mole of metal. The average weight of the hydrolyzed amino acids must be approximately 150 and the resulting molecular weight of the chelate must not exceed 800 Da. Since the early development of these compounds, much more research has been conducted, and has been applied to human nutrition products in a similar manner to the animal nutrition experiments that pioneered the technology. Ferrous bis-glycinate is an example of one of these compounds that has been developed for human nutrition. | 0 | Theoretical and Fundamental Chemistry |
Hahn echos have also been observed at optical frequencies. For this, resonant light is applied to a material with an inhomogeneously broadened absorption resonance. Instead of using two spin states in a magnetic field, photon echoes use two energy levels that are present in the material even in zero magnetic field. | 0 | Theoretical and Fundamental Chemistry |
In medical training, thermochromic ink can be used to imitate human blood because it shares its color changing property. It is currently being tested in medical simulations involving extracorporeal membrane oxygenation (ECMO). In these procedures, a change in color of blood between a dark and light red indicates blood oxygenation and blood deoxygenation, which describes the oxygen concentration levels within a persons blood sample. Its important to accurately identify this change in order to safely and correctly operate the ECMO machines. This has led to simulation-based trainings (SBT) which allows medical students to run simulations that mimic real ECMO machines before using them in serious situations. By using thermochromic ink in these simulations, the color changing effect can be realistically copied and observed without using real human blood or other costly methods.
Artificial blood or animal blood is typically used in these simulations; however, there are some advantages in using thermochromic ink as an alternative. It can be reused for multiple simulations with minimal variance in the outcomes and it is more cost effective. There are limitations to using this as the ink does not share any other properties with blood, so its only practical use is to observe the change in color of blood. | 0 | Theoretical and Fundamental Chemistry |
PSII and PSI are connected by a transmembrane proton pump, cytochrome bf complex (plastoquinol—plastocyanin reductase; ). Electrons from PSII are carried by plastoquinol to cyt bf, where they are removed in a stepwise fashion (re-forming plastoquinone) and transferred to a water-soluble electron carrier called plastocyanin. This redox process is coupled to the pumping of four protons across the membrane. The resulting proton gradient (together with the proton gradient produced by the water-splitting complex in PSI) is used to make ATP via ATP synthase.
The structure and function of cytochrome bf (in chloroplasts) is very similar to cytochrome bc (Complex III in mitochondria). Both are transmembrane structures that remove electrons from a mobile, lipid-soluble electron carrier (plastoquinone in chloroplasts; ubiquinone in mitochondria) and transfer them to a mobile, water-soluble electron carrier (plastocyanin in chloroplasts; cytochrome c in mitochondria). Both are proton pumps that produce a transmembrane proton gradient. In fact, cytochrome b and subunit IV are homologous to mitochondrial cytochrome b and the Rieske iron-sulfur proteins of the two complexes are homologous. However, cytochrome f and cytochrome c are not homologous. | 0 | Theoretical and Fundamental Chemistry |
The asymmetric Darzens reaction between aldehydes and (alpha)-haloesters is an effective method for the synthesis of glycidic esters. Chiral auxiliaries, chiral boron enolates, and asymmetric phase transfer catalysis have been used successfully to effect asymmetric induction in the Darzens reaction.
Diastereoselective epoxidations of chiral, non-racemic alkenes suffer from the limitation that removal of the auxiliary without disturbing the epoxide is often difficult. Nonetheless, diastereoselectivity is high in some cases.
Oxidation of epoxy alcohols generated via Sharpless epoxidation is a third method for the enantioselective synthesis of chiral α,β-epoxy carbonyl compounds. Swern and Parikh-Doering conditions are most commonly applied to accomplish these oxidations. | 0 | Theoretical and Fundamental Chemistry |
Froth flotation is one of the processes used to recover recycled paper. In the paper industry this step is called deinking or just flotation. The target is to release and remove the hydrophobic contaminants from the recycled paper. The contaminants are mostly printing ink and stickies. Normally the setup is a two-stage system with 3,4 or 5 flotation cells in series.
* pH control: sodium silicate and sodium hydroxide
* Calcium ion source: hard water, lime or calcium chloride
* Collector: fatty acid, fatty acid emulsion, fatty acid soap and/or organo-modified siloxane | 1 | Applied and Interdisciplinary Chemistry |
The Tishchenko reaction involve disproportionation of an aldehyde in the presence of an anhydrous base to give an ester. Catalysts are aluminium alkoxides or sodium alkoxides. Benzaldehyde reacts with sodium benzyloxide (generated from sodium and benzyl alcohol) to generate benzyl benzoate. The method is used in the production of ethyl acetate from acetaldehyde. | 0 | Theoretical and Fundamental Chemistry |
Nickel–metal hydride batteries (Ni-MH) largely replaced Ni-Cd batteries in the early 1990s. They replaced the metallic cadmium electrode with a hydrogen-absorbing alloy, allowing it to have over two times the capacity of Ni-Cd batteries while being easier to recycle. Their heyday in computer equipment was in the early- to mid-1990s. By 1995, most motherboard manufacturers switched to non-rechargeable lithium button cells to keep the BIOS chip powered. Lithium-based battery packs replaced Ni-MH packs in all but the lowest-end laptops by the early 2000s.
The practical shelf life of a Ni-MH is roughly five years. Cylindrical jelly-roll Ni-MH cells, like the ones used in 1990s laptop battery packs, discharge at a rate of up to 2% per day, while button cells like the ones used in motherboard batteries discharge at a rate of less than 20% per month. They are said to leak less frequently than alkaline batteries but have a similar failure mode.
Ni-MH leakage can be effectively neutralized with lemon juice or distilled white vinegar. | 1 | Applied and Interdisciplinary Chemistry |
WECs are sub-surface white cracks networks within local microstructural changes that are characterised by a changed microstructure known as white etching area (WEA). The term "white etching" refers to the white appearance of the altered microstructure of a polished and etched steel sample in the affected areas. The WEA is formed by amorphisation (phase transformation) of the martensitic microstructure due to friction at the crack faces during over-rolling, and these areas appear white under an optical microscope due to their low-etching response to the etchant. The microstructure of WECs consists of ultra-fine, nano-crystalline, carbide-free ferrite, or ferrite with a very fine distribution of carbide particles that exhibits a high degree of crystallographic misorientation.
WEC propagation is mostly transgranular and does not follow a certain cleavage plane.
Researchers observed three distinct types of microstructural alterations near the generated cracks: uniform white etching areas (WEAs), thin elongated regions of dark etching areas (DEA), and mixed regions comprising both light and dark etching areas with some misshaped carbides. During repeated stress cycles, the position of the crack constantly shifts, leaving behind an area of intense plastic deformation composed of ferritic, martensite, austenite (due to austenitization) and carbides. nano-grains, i.e., WEAs. The microscopic displacement of the crack plane in a single stress cycle accumulates to form micron-sized WEAs during repeated stress cycles. After the initial development of a fatigue crack around inclusions, the faces of the crack rub against each other during cycles of compressive stress. This results in the creation of WEAs through localised intense plastic deformation. It also causes partial bonding of the opposing crack faces and material transfer between them. Consequently, the WEC reopens at a slightly different location compared to its previous position during the release of stress.
Furthermore, it has been acknowledged that WEA is one of the phases that arise from different processes and is generally observed as a result of a phase transformation in rolling contact fatigue. WEA is harder than the matrix and . Additionally, WECs are caused by stresses higher than anticipated and occur due to bearing rolling contact fatigue as well as accelerated rolling contact fatigue.
WECs in bearings are accompanied with a white etching matter (WEM). WEM forms asymmetrically along WECs. There is no significant microstructural differences between the untransformed material adjacent to cracking and the parent material although WEM exhibits variable carbon content and increased hardness compared to the parent material. A study in 2019 suggests that WEM may initiate ahead of the crack, challenging the conventional crack-rubbing mechanism. | 1 | Applied and Interdisciplinary Chemistry |
In polymer science, the polymer chain or simply backbone of a polymer is the main chain of a polymer. Polymers are often classified according to the elements in the main chains. The character of the backbone, i.e. its flexibility, determines the properties of the polymer (such as the glass transition temperature). For example, in polysiloxanes (silicone), the backbone chain is very flexible, which results in a very low glass transition temperature of . The polymers with rigid backbones are prone to crystallization (e.g. polythiophenes) in thin films and in solution. Crystallization in its turn affects the optical properties of the polymers, its optical band gap and electronic levels. | 0 | Theoretical and Fundamental Chemistry |
One method for preparing β-phenethylamine, set forth in J. C. Robinson and H. R. Snyders Organic Syntheses' (published 1955), involves the reduction of benzyl cyanide with hydrogen in liquid ammonia, in the presence of a Raney-Nickel catalyst, at a temperature of 130 °C and a pressure of 13.8 MPa. Alternative syntheses are outlined in the footnotes to this preparation.
A much more convenient method for the synthesis of β-phenethylamine is the reduction of ω-nitrostyrene by lithium aluminium hydride in ether, whose successful execution was first reported by R. F. Nystrom and W. G. Brown in 1948.
Phenethylamine can also be produced via the cathodic reduction of benzyl cyanide in a divided cell.
Assembling phenethylamine structures for synthesis of compounds such as epinephrine, amphetamines, tyrosine, and dopamine by adding the beta-aminoethyl side chain to the phenyl ring is possible. This can be done via Friedel-Crafts acylation with N-protected acyl chlorides when the arene is activated, or by Heck reaction of the phenyl with N-vinyloxazolone, followed by hydrogenation, or by cross-coupling with beta-amino organozinc reagents, or reacting a brominated arene with beta-aminoethyl organolithium reagents, or by Suzuki cross-coupling. | 1 | Applied and Interdisciplinary Chemistry |
γ-Melanocyte-stimulating hormone (γ-MSH) is an endogenous peptide hormone and neuropeptide. It is a melanocortin, specifically, one of the three types of melanocyte-stimulating hormone (MSH), and is produced from proopiomelanocortin (POMC). It is an agonist of the MC, MC, MC, and MC receptors. It exists in three forms, γ-MSH, γ-MSH, and γ-MSH.
γ-MSH regulated cardiovascular functions. γ-MSH effects are measured through the effects it has on the central neural pathway dispersed throughout the kidney. It is not moderated based on tubular sodium transport. Gamma-MSH activates MC3R in renal tubular cells by limiting sodium absorption by inhibiting the central neural pathway. This regulates sodium balance and blood pressure. If MC3R is absent then there is resistance in γ-MSH which results in hypertension on HSD. | 1 | Applied and Interdisciplinary Chemistry |
Polymorphic and polyamorphic substances have multiple crystal or amorphous phases, which can be graphed in a similar fashion to solid, liquid, and gas phases. | 0 | Theoretical and Fundamental Chemistry |
Following the 2019 redefinition of the SI base units, the value of the triple point of water is no longer used as a defining point. However, its empirical value remains important: the unique combination of pressure and temperature at which liquid water, solid ice, and water vapor coexist in a stable equilibrium is approximately and a vapor pressure of .
Liquid water can only exist at pressures equal to or greater than the triple point. Below this, in the vacuum of outer space, solid ice sublimates, transitioning directly into water vapor when heated at a constant pressure. Conversely, above the triple point, solid ice first melts into liquid water upon heating at a constant pressure, then evaporates or boils to form vapor at a higher temperature.
For most substances, the gas–liquid–solid triple point is the minimum temperature where the liquid can exist. For water, this is not the case. The melting point of ordinary ice decreases with pressure, as shown by the phase diagram's dashed green line. Just below the triple point, compression at a constant temperature transforms water vapor first to solid and then to liquid.
Historically, during the Mariner 9 mission to Mars, the triple point pressure of water was used to define "sea level." Now, laser altimetry and gravitational measurements are preferred to define Martian elevation. | 0 | Theoretical and Fundamental Chemistry |
Stains-all stains nucleic acids, anionic proteins, anionic polysaccharides such as alginate and pectinate, hyaluronic acid and dermatan sulfate, heparin, heparan sulfate and chondroitin sulfate. It is used in SDS-PAGE, agarose gel electrophoresis and histologic staining, e.g. staining of growth lines in bones. | 1 | Applied and Interdisciplinary Chemistry |
Various CBRNE (Chemical, Biological, Radiological, Nuclear, and Explosive) weapons can be used for area denial, as long as the agent is long-lasting. Fallout from nuclear weapons might be used in such a role. While never actually employed in this form, its use had been suggested by Douglas MacArthur during the Korean War, who proposed spreading radioactive waste across transportation corridors to inhibit the movement of Chinese and North Korean forces.
Anthrax spores can contaminate the ground for long periods of time, thus providing a form of area denial. However, the short-term (tactical) effects are likely to be low - the psychological effects on an opponent would likely be more significant.
The massive use of defoliants such as Agent Orange can be used as an interdiction measure because they leave areas empty of any form of vegetation cover. In the desert-like terrain that ensues, it is impossible for the enemy to travel without being seen, and there is little cover in case of an attack, especially from the air.
Many chemical weapons also produce toxic effects on any personnel in an affected area. However, this usually has no tactical value, as the effects of indirect exposure do not develop fast or substantially enough - though again, the psychological effect upon an enemy aware of the chemical usage may be considerable. There are however some chemical agents that are by design non-degrading, such as the nerve agent VX. Sulfur mustard (mustard gas) was extensively used by both German and allied forces on the west front in World War I as an effective area-denial weapon, usually through contaminating large land stripes by extensive shelling with HD/Gelbkreuz ordnance. Since sulfur mustard is very persistent, involatile, hard-to-decontaminate and highly effective in inflicting debilitating casualties at even low doses, this tactic proved to be very effective. | 1 | Applied and Interdisciplinary Chemistry |
The flaw in Clark's receptor-occupancy model was that it was insufficient to explain the concept of a partial agonist. This led to the development of agonist models of drug action by Ariens in 1954 and by Stephenson in 1956 to account for the intrinsic activity (efficacy) of a drug (that is, its ability to induce an effect after binding). | 1 | Applied and Interdisciplinary Chemistry |
The principle of minimum energy can be generalized to apply to constraints other than fixed entropy. For other constraints, other state functions with dimensions of energy will be minimized. These state functions are known as thermodynamic potentials. Thermodynamic potentials are at first glance just simple algebraic combinations of the energy terms in the expression for the internal energy. For a simple, multicomponent system, the internal energy may be written:
where the intensive parameters (T, P, μ) are functions of the internal energy's natural variables via the equations of state. As an example of another thermodynamic potential, the Helmholtz free energy is written:
where temperature has replaced entropy as a natural variable. In order to understand the value of the thermodynamic potentials, it is necessary to view them in a different light. They may in fact be seen as (negative) Legendre transforms of the internal energy, in which certain of the extensive parameters are replaced by the derivative of internal energy with respect to that variable (i.e. the conjugate to that variable). For example, the Helmholtz free energy may be written:
and the minimum will occur when the variable T becomes equal to the temperature since
The Helmholtz free energy is a useful quantity when studying thermodynamic transformations in which the temperature is held constant. Although the reduction in the number of variables is a useful simplification, the main advantage comes from the fact that the Helmholtz free energy is minimized at equilibrium with respect to any unconstrained internal variables for a closed system at constant temperature and volume. This follows directly from the principle of minimum energy which states that at constant entropy, the internal energy is minimized. This can be stated as:
where and are the value of the internal energy and the (fixed) entropy at equilibrium. The volume and particle number variables have been replaced by x which stands for any internal unconstrained variables.
The minimization is with respect to the unconstrained variables. In the case of chemical reactions this is usually the number of particles or mole fractions, subject to the conservation of elements. At equilibrium, these will take on their equilibrium values, and the internal energy will be a function only of the chosen value of entropy . By the definition of the Legendre transform, the Helmholtz free energy will be:
The Helmholtz free energy at equilibrium will be:
where is the (unknown) temperature at equilibrium. Substituting the expression for :
By exchanging the order of the extrema:
showing that the Helmholtz free energy is minimized at equilibrium.
The Enthalpy and Gibbs free energy, are similarly derived. | 0 | Theoretical and Fundamental Chemistry |
In 1811, Amedeo Avogadro verified that equal volumes of pure gases contain the same number of particles. His theory was not generally accepted until 1858 when another Italian chemist Stanislao Cannizzaro was able to explain non-ideal exceptions. For his work with gases a century prior, the physical constant that bears his name (the Avogadro constant) is the number of atoms per mole of elemental carbon-12 (). This specific number of gas particles, at standard temperature and pressure (ideal gas law) occupies 22.40 liters, which is referred to as the molar volume.
Avogadro's law states that the volume occupied by an ideal gas is proportional to the amount of substance in the volume. This gives rise to the molar volume of a gas, which at STP is 22.4 dm/mol (liters per mole). The relation is given by
where n is the amount of substance of gas (the number of molecules divided by the Avogadro constant). | 0 | Theoretical and Fundamental Chemistry |
Except for tritium, which was determined by the helium gas emitted by radioactive decay, these measurements were taken using mass spectroscopy.
* Deuterium (H / H) – , about 1 in 6420 hydrogen atoms
* Tritium (H / H) – = , measured on 16 September 1976, about 1 in 5.4010 hydrogen atoms
* Oxygen-18 (O / O) – , about 1 in 499 oxygen atoms
* Oxygen-17 (O / O) – , about 1 in 2640 oxygen atoms | 0 | Theoretical and Fundamental Chemistry |
Germicidal UV for disinfection is most typically generated by a mercury-vapor lamp. Low-pressure mercury vapor has a strong emission line at 254 nm, which is within the range of wavelengths that demonstrate strong disinfection effect. The optimal wavelengths for disinfection are close to 260 nm.
Mercury vapor lamps may be categorized as either low-pressure (including amalgam) or medium-pressure lamps. Low-pressure UV lamps offer high efficiencies (approx. 35% UV-C) but lower power, typically 1 W/cm power density (power per unit of arc length). Amalgam UV lamps utilize an amalgam to control mercury pressure to allow operation at a somewhat higher temperature and power density. They operate at higher temperatures and have a lifetime of up to 16,000 hours. Their efficiency is slightly lower than that of traditional low-pressure lamps (approx. 33% UV-C output), and power density is approximately 2–3 W/cm. Medium-pressure UV lamps operate at much higher temperatures, up to about 800 degrees Celsius, and have a polychromatic output spectrum and a high radiation output but lower UV-C efficiency of 10% or less. Typical power density is 30 W/cm or greater.
Depending on the quartz glass used for the lamp body, low-pressure and amalgam UV emit radiation at 254 nm and also at 185 nm, which has chemical effects. UV radiation at 185 nm is used to generate ozone.
The UV lamps for water treatment consist of specialized low-pressure mercury-vapor lamps that produce ultraviolet radiation at 254 nm, or medium-pressure UV lamps that produce a polychromatic output from 200 nm to visible and infrared energy. The UV lamp never contacts the water; it is either housed in a quartz glass sleeve inside the water chamber or mounted externally to the water, which flows through the transparent UV tube. Water passing through the flow chamber is exposed to UV rays, which are absorbed by suspended solids, such as microorganisms and dirt, in the stream. | 0 | Theoretical and Fundamental Chemistry |
There are many applications in which viral transformation can be artificially induced in a cell culture in order to treat an illness or other condition. A cell culture is infected with a virus causing the transformation; transformed cells can then be used to either produce treatments or be directly introduced into the body. | 1 | Applied and Interdisciplinary Chemistry |
The EWOC Conference structure consists of a combination of scientific presentations, workshops, topical networking sessions, career panel and also includes a poster session. Examples of Workshops have included Cultivate Belonging in the Workplace for Yourself and Others; How to Create, Build and Leverage Networks for Sustained Leadership and Career Success and Cultural Change to Enable Diversity & Inclusion, the Psychology of Selves: Beyond Imposter Syndrome, Leading through Influence, Allies Help Turn the Tide, Take Control of Your Time: Say No, Negotiate, Delegate, Beyond Pajamas: Coming out of COVID Isolation Mindfully, Beyond Pajamas: Coming out of COVID Isolation Mindfully, and a Discussion Toward Diversity, Equity and Inclusion in Organic Chemistry. Examples of topical networking sessions have focused on Work/Life Balance Discussion, How to start an EWOC Chapter, Publishing like a Boss, Creating a Culture of Safety, Interviewing and choosing a company, and various peer networking discussions for graduate students, postdocs, early career faculty, LGBTQ+, Black, Indigenous, & People of Color (BIPOC), and Allies and Advocates, among others. The virtual format of EWOC has been cited as an example of the benefits of virtual conferences because they are "more accessible to people who couldn’t otherwise attend because of travel costs or restrictions or because they have family obligations that make travel onerous." | 0 | Theoretical and Fundamental Chemistry |
In 1848, Louis Pasteur became the first scientist to discover chirality and enantiomers while he was working with tartaric acid. During the experiments, he noticed that there were two crystal structures produced but these structures looked to be non-superimposable mirror images of each other; this observation of isomers that were non-superimposable mirror images became known as enantiomers. A couple years later, in 1857, Pasteur then discovered enantioselectivity when he noticed that the two enantiomer structures he had previously discovered metabolized at much different speeds. This suggested that one configuration was preferred over the other in vivo. As organic chemistry knowledge became more advanced, the discovery of enantioselectivity was used in the creation of enantiopure drugs. | 0 | Theoretical and Fundamental Chemistry |
Naturally occurring minerals that are sometimes given the chemical name, sodium aluminosilicate include albite (NaAlSiO, an end-member of the plagioclase series) and jadeite (NaAlSiO). | 0 | Theoretical and Fundamental Chemistry |
The Berry mechanism, or Berry pseudorotation mechanism, is a type of vibration causing molecules of certain geometries to isomerize by exchanging the two axial ligands (see Figure at right) for two of the equatorial ones. It is the most widely accepted mechanism for pseudorotation and most commonly occurs in trigonal bipyramidal molecules such as PF, though it can also occur in molecules with a square pyramidal geometry. The Berry mechanism is named after R. Stephen Berry, who first described this mechanism in 1960. | 0 | Theoretical and Fundamental Chemistry |
Based on her extraction, Wright thinks the "glomalin molecule is a clump of small glycoproteins with iron and other ions attached... glomalin contains from 1 to 9% tightly bound iron.... We've seen glomalin on the outside of hyphae, and we believe this is how the hyphae seal themselves so they can carry water and nutrients. It may also be what gives them the rigidity they need to span the air spaces between soil particles."
There is other circumstantial evidence to show that glomalin is of AM fungal origin. When AM fungi are eliminated from soil through incubation of soil without host plants, the concentration of GRSP declines. A similar decline in GRSP has also been observed in incubated soils from forested, afforested, and agricultural land and grasslands treated with fungicide.
It is important to emphasize that glomalin is not synonym of GRSP. Glomalin is the protein that binds to the Mab32B11 antibody, while GRSP is a crude extract containing many substances, including humic acids.
The chemistry of GRSP is not yet fully understood, and the link between glomalin, GRSP, and AM fungi is not yet clear. The physiological function of glomalin in fungi is also a topic of current research. | 0 | Theoretical and Fundamental Chemistry |
Eating fish or shellfish from lakes with a bloom nearby is not recommended. Potent toxins are accumulated in shellfish that feed on the algae. If the shellfish are consumed, various types of poisoning may result. These include amnesic shellfish poisoning (ASP), diarrhetic shellfish poisoning, neurotoxic shellfish poisoning, and paralytic shellfish poisoning. A 2002 study has shown that algal toxins may be the cause for as many as 60,000 intoxication cases in the world each year.
In 1987 a new illness emerged: amnesic shellfish poisoning (ASP). People who had eaten mussels from Prince Edward Island were found to have ASP. The illness was caused by domoic acid, produced by a diatom found in the area where the mussels were cultivated. A 2013 study found that toxic paralytic shellfish poisoning in the Philippines during HABs has caused at least 120 deaths over a few decades. After a 2014 HAB incident in Monterey Bay, California, health officials warned people not to eat certain parts of anchovy, sardines, or crab caught in the bay. In 2015 most shellfish fisheries in Washington, Oregon and California were shut down because of high concentrations of toxic domoic acid in shellfish. People have been warned that inhaling vapors from waves or wind during a HAB event may cause asthma attacks or lead to other respiratory ailments.
In 2018 agricultural officials in Utah worried that even crops could become contaminated if irrigated with toxic water, although they admit that they can't measure contamination accurately because of so many variables in farming. They issued warnings to residents, however, out of caution. | 0 | Theoretical and Fundamental Chemistry |
Mikhail Semyonovich Tsvet, also spelt Tsvett, Tswett, Tswet, Zwet, and Cvet (Russian: Михаил Семёнович Цвет; 14 May 1872 – 26 June 1919) was a Russian-Italian botanist who invented chromatography. His last name is Russian for "colour" and is also the root word of "flower." | 0 | Theoretical and Fundamental Chemistry |
UVC radiation is able to break chemical bonds. This leads to rapid aging of plastics and other material, and insulation and gaskets. Plastics sold as "UV-resistant" are tested only for the lower-energy UVB since UVC does not normally reach the surface of the Earth. When UV is used near plastic, rubber, or insulation, these materials may be protected by metal tape or aluminum foil. | 0 | Theoretical and Fundamental Chemistry |
Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from thermo- referring to temperature and referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of about 1000 years) upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. The water in these circuits transport both energy (in the form of heat) and mass (dissolved solids and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth.
The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt, coined by climate scientist Wallace Smith Broecker. It is also referred to as the meridional overturning circulation, or MOC. This name is used because not every circulation pattern caused by temperature and salinity gradients is necessarily part of a single global circulation. Further, it is difficult to separate the parts of the circulation driven by temperature and salinity alone from those driven by other factors, such as the wind and tidal forces.
This global circulation has two major limbs - Atlantic Meridional Overturning circulation (AMOC), centered in the north Atlantic Ocean, and Southern Ocean overturning circulation or Southern Ocean meridional circulation (SMOC), around Antarctica. Because 90% of the human population lives in the Northern Hemisphere, the AMOC has been far better studied, but both are very important for the global climate. Both of them also appear to be slowing down due to climate change, as the melting of the ice sheets dilutes salty flows such as the Antarctic bottom water. Either one could outright collapse to a much weaker state, which would be an example of tipping points in the climate system. The hemisphere which experiences the collapse of its circulation would experience less precipitation and become drier, while the other hemisphere would become wetter. Marine ecosystems are also likely to receive fewer nutrients and experience greater ocean deoxygenation. In the Northern Hemisphere, AMOC's collapse would also substantially lower the temperatures in many European countries, while the east coast of North America would experience accelerated sea level rise. The collapse of either circulation is generally believed to be more than a century away and may only occur under high warming, but there is a lot of uncertainty about these projections. | 0 | Theoretical and Fundamental Chemistry |
Joseph Priestley, in Observations on different kinds of air, was one of the first people to describe air as being composed of different states of matter, and not as one element. Priestley elaborated on the notions of fixed air (CO), mephitic air and inflammable air to include "inflammable nitrous air," "vitriolic acid air," "alkaline air" and "dephlogisticated air". Priestley also described the process of respiration in terms of phlogiston theory. Priestley also established a process for treating scurvy and other ailments using fixed air in his Directions for impregnating water with fixed air. Priestley's work on pneumatic chemistry had an influence on his natural world views. His belief in an "aerial economy" stemmed from his belief in "dephlogisticated air" being the purest type of air and that phlogiston and combustion were at the heart of nature.
Joseph Priestley chiefly researched with the pneumatic trough, but he was responsible for collecting several new water-soluble airs. This was achieved primarily by his substitution of mercury for water, and implementing a shelf under the head for increased stability, capitalizing on the idea Cavendish proposed and popularizing the mercury pneumatic trough. | 1 | Applied and Interdisciplinary Chemistry |
Low-energy electrons are produced from a tungsten filament, a lanthanum hexaboride crystal cathode or a field emission electron source and accelerated by a positively biased anode plate to 3 to 30 thousand electron volts (keV). The anode plate has central aperture and electrons that pass through it are collimated and focused by a series of magnetic lenses and apertures. The resulting electron beam (approximately 5 nm to 10 μm diameter) may be rastered across the sample or used in spot mode to produce excitation of various effects in the sample. Among these effects are: phonon excitation (heat), cathodoluminescence (visible light fluorescence), continuum X-ray radiation (bremsstrahlung), characteristic X-ray radiation, secondary electrons (plasmon production), backscattered electron production, and Auger electron production.
When the beam electrons (and scattered electrons from the sample) interact with bound electrons in the innermost electron shells of the atoms of the various elements in the sample, they can scatter the bound electrons from the electron shell producing a vacancy in that shell (ionization of the atom). This vacancy is unstable and must be filled by an electron from either a higher energy bound shell in the atom (producing another vacancy which is in turn filled by electrons from yet higher energy bound shells) or by unbound electrons of low energy. The difference in binding energy between the electron shell in which the vacancy was produced and the shell from which the electron comes to fill the vacancy is emitted as a photon. The energy of the photon is in the X-ray region of the electromagnetic spectrum. As the electron structure of each element is unique, the series X-ray line energies produced by vacancies in the innermost shells is characteristic of that element, although lines from different elements may overlap. As the innermost shells are involved, the X-ray line energies are generally not affected by chemical effects produced by bonding between elements in compounds except in low atomic number (Z) elements ( B, C, N, O and F for K and Al to Cl for K) where line energies may be shifted as a result of the involvement of the electron shell from which vacancies are filled in chemical bonding.
The characteristic X-rays are used for chemical analysis. Specific X-ray wavelengths or energies are selected and counted, either by wavelength dispersive X-ray spectroscopy (WDS) or energy dispersive X-ray spectroscopy (EDS). WDS utilizes Bragg diffraction from crystals to select X-ray wavelengths of interest and direct them to gas-flow or sealed proportional detectors. In contrast, EDS uses a solid state semiconductor detector to accumulate X-rays of all wavelengths produced from the sample. While EDS yields more information and typically requires a much shorter counting time, WDS is generally more precise with lower limits of detection due to its superior X-ray peak resolution and greater peak to background ratio.
Chemical composition is determined by comparing the intensities of characteristic X-rays from the sample with intensities from standards of known composition. Counts from the sample must be corrected for matrix effects (depth of production of the X-rays, absorption and secondary fluorescence) to yield quantitative chemical compositions. The resulting chemical data is gathered in textural context. Variations in chemical composition within a material (zoning), such as a mineral grain or metal, can be readily determined.
Volume from which chemical information is gathered (volume of X-rays generated) is 0.3 – 3 cubic micrometers. | 0 | Theoretical and Fundamental Chemistry |
Observed atmospheric Xe is depleted relative to Chondritic meteorites by a factor of 4 to 20 when compared to Kr. In contrast, the stable isotopes of Kr are barely fractionated. This mechanism is unique to Xe since Kr ions are quickly neutralized via
Therefore, Kr can be rapidly returned to neutral and wouldn't be dragged away by the charged ion wind in the polar region. Hence Kr is retained in the atmosphere. | 0 | Theoretical and Fundamental Chemistry |
Within EPANET, pumps are modeled using a head-flow curve, which defines the relationship between hydraulic head imparted to the system by the pump and flow conveyed by the pump. The model calculates the flow conveyed by the pump element for a given system head condition based on this curve. EPANET can also model a pump as a constant power input, effectively adding a given amount of energy to the system downstream of the pump element. | 1 | Applied and Interdisciplinary Chemistry |
Hydrocyanation was first reported by Arthur and Pratt in 1954, when they homogeneously catalyzed the hydrocyanation of linear alkenes.
The industrial process for catalytic hydrocyanation of butadiene to adiponitrile was invented by William C. Drinkard. | 0 | Theoretical and Fundamental Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.