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Bilirubin is degraded by light. Blood collection tubes containing blood or (especially) serum to be used in bilirubin assays should be protected from illumination. For adults, blood is typically collected by needle from a vein in the arm. In newborns, blood is often collected from a heel stick, a technique that uses a small, sharp blade to cut the skin on the infant's heel and collect a few drops of blood into a small tube. Non-invasive technology is available in some health care facilities that will measure bilirubin by using an bilirubinometer which shines light onto the skin and calculates the amount of bilirubin by analysing how the light is absorbed or reflects. This device is also known as a transcutaneous bilirubin meter.
Bilirubin (in blood) is found in two forms:
Note: Conjugated bilirubin is often incorrectly called "direct bilirubin" and unconjugated bilirubin is incorrectly called "indirect bilirubin". Direct and indirect refer solely to how compounds are measured or detected in solution. Direct bilirubin is any form of bilirubin which is water-soluble and is available in solution to react with assay reagents; direct bilirubin is often made up largely of conjugated bilirubin, but some unconjugated bilirubin (up to 25%) can still be part of the "direct" bilirubin fraction. Likewise, not all conjugated bilirubin is readily available in solution for reaction or detection (for example, if it is hydrogen bonding with itself) and therefore would not be included in the direct bilirubin fraction.
Total bilirubin (TBIL) measures both BU and BC. Total bilirubin assays work by using surfactants and accelerators (like caffeine) to bring all of the different bilirubin forms into solution where they can react with assay reagents. Total and direct bilirubin levels can be measured from the blood, but indirect bilirubin is calculated from the total and direct bilirubin.
Indirect bilirubin is fat-soluble and direct bilirubin is water-soluble. | 1 | Biochemistry |
Crystal structure is described in terms of the geometry of arrangement of particles in the unit cells. The unit cell is defined as the smallest repeating unit having the full symmetry of the crystal structure. The geometry of the unit cell is defined as a parallelepiped, providing six lattice parameters taken as the lengths of the cell edges (a, b, c) and the angles between them (α, β, γ). The positions of particles inside the unit cell are described by the fractional coordinates (x, y, z) along the cell edges, measured from a reference point. It is thus only necessary to report the coordinates of a smallest asymmetric subset of particles, called the crystallographic asymmetric unit. The asymmetric unit may be chosen so that it occupies the smallest physical space, which means that not all particles need to be physically located inside the boundaries given by the lattice parameters. All other particles of the unit cell are generated by the symmetry operations that characterize the symmetry of the unit cell. The collection of symmetry operations of the unit cell is expressed formally as the space group of the crystal structure. | 3 | Analytical Chemistry |
Spinning band distillation may sometimes be used to recycle waste solvents which contain different solvents, and other chemical compounds. | 3 | Analytical Chemistry |
In Canada, modafinil is not specifically included in the lists of controlled drugs and substances specified within the Controlled Drugs and Substances Act. However, it is classified as a Schedule F prescription drug. This means that modafinil can only be obtained legally with a valid prescription from a licensed health care practitioner in Canada, and the import of modafinil to Canada from other countries is subject to restrictions: importing prescription drugs without an import permit may result in the seizure of the drugs at the border, the refusal of entry of the drugs into Canada, or prosecution. | 4 | Stereochemistry |
Chemically pure water has an electrical conductivity of 0.055 μS/cm. According to the theories of Svante Arrhenius, this must be due to the presence of ions. The ions are produced by the water self-ionization reaction, which applies to pure water and any aqueous solution:
: HO + HO HO + OH
Expressed with chemical activities , instead of concentrations, the thermodynamic equilibrium constant for the water ionization reaction is:
which is numerically equal to the more traditional thermodynamic equilibrium constant written as:
under the assumption that the sum of the chemical potentials of H and HO is formally equal to twice the chemical potential of HO at the same temperature and pressure.
Because most acid–base solutions are typically very dilute, the activity of water is generally approximated as being equal to unity, which allows the ionic product of water to be expressed as:
In dilute aqueous solutions, the activities of solutes (dissolved species such as ions) are approximately equal to their concentrations. Thus, the ionization constant, dissociation constant, self-ionization constant, water ion-product constant or ionic product of water, symbolized by K, may be given by:
where [HO] is the molarity (molar concentration) of hydrogen cation or hydronium ion, and [OH] is the concentration of hydroxide ion. When the equilibrium constant is written as a product of concentrations (as opposed to activities) it is necessary to make corrections to the value of depending on ionic strength and other factors (see below).
At 24.87 °C and zero ionic strength, K is equal to . Note that as with all equilibrium constants, the result is dimensionless because the concentration is in fact a concentration relative to the standard state, which for H and OH are both defined to be 1 molal (= 1 mol/kg) when molality is used or 1 molar (= 1 mol/L) when molar concentration is used. For many practical purposes, the molality (mol solute/kg water) and molar (mol solute/L solution) concentrations can be considered as nearly equal at ambient temperature and pressure if the solution density remains close to one (i.e., sufficiently diluted solutions and negligible effect of temperature changes). The main advantage of the molal concentration unit (mol/kg water) is to result in stable and robust concentration values which are independent of the solution density and volume changes (density depending on the water salinity (ionic strength), temperature and pressure); therefore, molality is the preferred unit used in thermodynamic calculations or in precise or less-usual conditions, e.g., for seawater with a density significantly different from that of pure water, or at elevated temperatures, like those prevailing in thermal power plants.
We can also define pK −log K (which is approximately 14 at 25 °C). This is analogous to the notations pH and pK for an acid dissociation constant, where the symbol p denotes a cologarithm. The logarithmic form of the equilibrium constant equation is pK = pH + pOH. | 7 | Physical Chemistry |
The elimination half-life of levomethamphetamine is between 13.3 and 15 hours, whereas dextromethamphetamine has a half-life of about 10.5 hours. | 4 | Stereochemistry |
It was once suggested that CO could be stored in the oceans by direct injection into the deep ocean and storing it there for some centuries. At the time, this proposal was called "ocean storage" but more precisely it was known as "direct deep-sea carbon dioxide injection". However, the interest in this avenue of carbon storage has much reduced since about 2001 because of concerns about the unknown impacts on marine lifeMarine life|, high costs and concerns about its stability or permanence. The "IPCC Special Report on Carbon Dioxide Capture and Storage" in 2005 did include this technology as an option.Marine life| However, the IPCC Fifth Assessment Report in 2014 no longer mentioned the term "ocean storage" in its report on climate change mitigation methods. The most recent IPCC Sixth Assessment Report in 2022 also no longer includes any mention of "ocean storage" in its "Carbon Dioxide Removal taxonomy". | 5 | Photochemistry |
Methemoglobinaemia is a form of abnormal hemoglobin where the iron centre has been oxidised from the ferrous +2 oxidation state (the normal form, which on binding with oxygen changes to the ferric state) to the ferric +3 state. This causes a leftward shift in the oxygen hemoglobin dissociation curve, as any residual heme with oxygenated ferrous iron (+2 state) is unable to unload its bound oxygen into tissues (because 3+ iron impairs hemoglobins cooperativity), thereby increasing its affinity with oxygen. However, methemoglobin has increased affinity for cyanide, and is therefore useful in the treatment of cyanide poisoning. In cases of accidental ingestion, administration of a nitrite (such as amyl nitrite) can be used to deliberately oxidise hemoglobin and raise methemoglobin levels, restoring the functioning of cytochrome oxidase. The nitrite also acts as a vasodilator, promoting the cellular supply of oxygen, and the addition of an iron salt provides for competitive binding of the free cyanide as the biochemically inert hexacyanoferrate(III) ion, [Fe(CN)]. An alternative approach involves administering thiosulfate, thereby converting cyanide to thiocyanate, SCN, which is excreted via' the kidneys. Methemoglobin is also formed in small quantities when the dissociation of oxyhemoglobin results in the formation of methemoglobin and superoxide, O, instead of the usual products. Superoxide is a free radical and causes biochemical damage, but is neutralised by the action of the enzyme superoxide dismutase. | 1 | Biochemistry |
The Ellingham curve for the reaction 2C(s) + (g) → 2CO(g) slopes down and falls below the curves for all the metals. Hence, carbon can normally act as a reducing agent for all metal oxides at very high temperatures. But chromium formed at these temperatures reacts with carbon to form its carbide, which gives undesirable properties to the chromium metal obtained. Hence, for high temperature reduction of chromic oxide, carbon cannot be used. | 8 | Metallurgy |
Sinapaldehyde is an organic compound with the formula HO(CHO)CHCH=CHCHO. It is a derivative of cinnamaldehyde, featuring one hydroxy group and two methoxy groups as substituents. It is an intermediate in the formation of sinapyl alcohol, a lignol that is a major precursor to lignin. | 1 | Biochemistry |
* 1760 Louis Claude Cadet de Gassicourt isolates the organoarenic compound cacodyl
* 1827 William Christopher Zeise produces Zeise's salt; the first platinum / olefin complex
* 1848 Edward Frankland discovers diethylzinc
* 1890 Ludwig Mond discovers nickel carbonyl
* 1899 John Ulric Nef discovers alkynylation using sodium acetylides.
* 1909 Paul Ehrlich introduces Salvarsan for the treatment of syphilis, an early arsenic based organometallic compound
* 1912 Nobel Prize Victor Grignard and Paul Sabatier
* 1930 Henry Gilman invents lithium cuprates, see Gilman reagent
* 1940 Eugene G. Rochow and Richard Müller discover the direct process for preparing organosilicon compounds
* 1930s and 1940s Otto Roelen and Walter Reppe develop metal-catalyzed hydroformylation and acetylene chemistry
* 1951 Walter Hieber was awarded the Alfred Stock prize for his work with metal carbonyl chemistry.
* 1951 Ferrocene is discovered
* 1956 Dorothy Crawfoot Hodgkin determines the structure of vitamin B, the first biomolecule found to contain a metal-carbon bond, see bioorganometallic chemistry
* 1963 Nobel prize for Karl Ziegler and Giulio Natta on Ziegler–Natta catalyst
* 1973 Nobel prize Geoffrey Wilkinson and Ernst Otto Fischer on sandwich compounds
* 1981 Nobel prize Roald Hoffmann and Kenichi Fukui for creation of the Woodward-Hoffman Rules
* 2001 Nobel prize W. S. Knowles, R. Noyori and Karl Barry Sharpless for asymmetric hydrogenation
* 2005 Nobel prize Yves Chauvin, Robert Grubbs, and Richard Schrock on metal-catalyzed alkene metathesis
* 2010 Nobel prize Richard F. Heck, Ei-ichi Negishi, Akira Suzuki for palladium catalyzed cross coupling reactions | 0 | Organic Chemistry |
Isolation of the toxin using cyanobacteria cultured from the original Palm Island strain was achieved by gel filtration of an aqueous extract, followed by reverse-phase HPLC. Structure elucidation was achieved via mass spectrometry (MS) and nuclear magnetic resonance (NMR) experiments, and a structure (later proven slightly incorrect) was proposed (Figure 1).
This almost-correct molecule possesses a tricyclic guanidine group (rings A, B & C), along with a uracil ring (D). The zwitterionic nature of the molecule makes this highly water-soluble, as the presence of charged areas within the molecule creates a dipole effect, suiting the polar solvent. Sensitivity of key signals in the NMR spectrum to small changes in pH suggested that the uracil ring exists in a keto/enol tautomeric relationship, where a hydrogen transfer results in two distinct structures (Figure 2). It was originally proposed that a hydrogen bond between the uracil and guanidine groups in the enol tautomer would make this the dominant form. | 0 | Organic Chemistry |
Calcium ions (Ca) contribute to the physiology and biochemistry of organisms' cells. They play an important role in signal transduction pathways, where they act as a second messenger, in neurotransmitter release from neurons, in contraction of all muscle cell types, and in fertilization. Many enzymes require calcium ions as a cofactor, including several of the coagulation factors. Extracellular calcium is also important for maintaining the potential difference across excitable cell membranes, as well as proper bone formation.
Plasma calcium levels in mammals are tightly regulated, with bone acting as the major mineral storage site. Calcium ions, Ca, are released from bone into the bloodstream under controlled conditions. Calcium is transported through the bloodstream as dissolved ions or bound to proteins such as serum albumin. Parathyroid hormone secreted by the parathyroid gland regulates the resorption of Ca from bone, reabsorption in the kidney back into circulation, and increases in the activation of vitamin D to calcitriol. Calcitriol, the active form of vitamin D, promotes absorption of calcium from the intestines and bones. Calcitonin secreted from the parafollicular cells of the thyroid gland also affects calcium levels by opposing parathyroid hormone; however, its physiological significance in humans is dubious.
Intracellular calcium is stored in organelles which repetitively release and then reaccumulate Ca ions in response to specific cellular events: storage sites include mitochondria and the endoplasmic reticulum.
Characteristic concentrations of calcium in model organisms are: in E. coli 3mM (bound), 100nM (free), in budding yeast 2mM (bound), in mammalian cell 10-100nM (free) and in blood plasma 2mM. | 1 | Biochemistry |
Uncompetitive antagonists differ from non-competitive antagonists in that they require receptor activation by an agonist before they can bind to a separate allosteric binding site. This type of antagonism produces a kinetic profile in which "the same amount of antagonist blocks higher concentrations of agonist better than lower concentrations of agonist". Memantine, used in the treatment of Alzheimer's disease, is an uncompetitive antagonist of the NMDA receptor. | 1 | Biochemistry |
The [http://hive.biochemistry.gwu.edu/ High-performance Integrated Virtual Environment] (HIVE) is a distributed computing environment used for healthcare-IT and biological research, including analysis of Next Generation Sequencing (NGS) data, preclinical, clinical and post market data, adverse events, metagenomic data, etc. Currently it is supported and continuously developed by US Food and Drug Administration (government domain), George Washington University (academic domain), and by DNA-HIVE, WHISE-Global and Embleema (commercial domain). HIVE currently operates fully functionally within the US FDA supporting wide variety (+60) of regulatory research and regulatory review projects as well as for supporting MDEpiNet medical device postmarket registries. Academic deployments of HIVE are used for research activities and publications in NGS analytics, cancer research, microbiome research and in educational programs for students at GWU. Commercial enterprises use HIVE for oncology, microbiology, vaccine manufacturing, gene editing, healthcare-IT, harmonization of real-world data, in preclinical research and clinical studies. | 1 | Biochemistry |
Throughout his career, Trefonas has focused on materials science and the chemistry of photolithography. By understanding the chemistry of photoresists used in lithography, he has been able to develop anti-reflective coatings and polymer photoresists that support finely-tuned etching used in the production of integrated circuits.
These materials and techniques make it possible to fit more circuits into a given area. Over time, lithographic technologies have developed to allow lithography to use smaller wavelengths of light. Trefonas has helped to overcome a number of apparent limits to the sizes that are achievable, developing photoresists that are responsive to 436-nm and 365-nm ultraviolet light, and as small as 193 nm deep.
In 1989, Trefonas and others at Aspect Systems Inc. reported on extensive studies of polyfunctional photosensitive groups in positive photoresists. They studied diazonaphthoquinone (DNQ), a chemical compound used for dissolution inhibition of novolak resin in photomask creation. They mathematically modeled effects, predicted possible optimizations, and experimentally verified their predictions. They found that chemically bonding together three of the molecules of DNQ to create a new molecule containing three dissolution inhibitors in a single molecule, led to a better feature contrast, with better resolution and miniaturization. These modified DNQs became known as "polyfunctional photoactive components" (PACs). This approach, which they termed polyphotolysis,
has also been referred to as the "Trefonas Effect."
The technology of trifunctional diazonaphthoquinone PACs has become the industry standard in positive photoresists. Their mechanism has been elucidated and relates to a cooperative behavior of each of the three DNQ units in the new trifunctional dissolution inhibitor molecule. Phenolic strings from the acceptor groups of PACs that are severed from their anchors may reconnect to living strings, replacing two shorter polarized strings with one longer polarized string.
Trefonas has also been a leader in the development of fast etch organic Bottom Antireflective Coating (BARC)
BARC technology minimizes the reflection of light from the substrate when imaging the photoresist. Light that is used to form the latent image in the photoresist film can reflect back from the substrate and compromise feature contrast and profile shape. Controlling interference from reflected light results in the formation of a sharper pattern with less variability and a larger process window.
In 2014, Trefonas and others at Dow were named Heroes of Chemistry by the American Chemical Society, for the development of Fast Etch Organic Bottom Antireflective Coatings (BARCs). In 2016, Trefonas was recognized with The SCI Perkin Medal for outstanding contributions to industrial chemistry. In 2018, Trefonas was named as a Fellow of the SPIE for "achievements in design for manufacturing & compact modeling." Peter Trefonas was elected to the National Academy of Engineering in 2018 for the "invention of photoresist materials and microlithography methods underpinning multiple generations of microelectronics". DuPont Company in 2019 recognized Trefonas with its top recognition, the Lavoisier Medal, for "commercialized electronic chemicals which enabled customers to manufacture integrated circuits with higher density and faster speeds". | 5 | Photochemistry |
Dye runs a Youtube channel, personal blog, and has courses on Coursera to teach metallurgy, mathematics and data analysis, continuum mechanics, and engineering Alloys. Dye also is a scientific witness to the Science and Technology Committee of the UK parliament. | 8 | Metallurgy |
There have been a few technical issues that have limited adoption of SFC technology in the past. First of all, is the need to keep a high gas pressure in the operating conditions. High-pressure vessels are expensive and bulky, and special materials are often needed to avoid dissolving gaskets and O-rings in the supercritical fluid. A second drawback is difficulty in maintaining pressure constant (by back-pressure regulation). Whereas liquids are nearly incompressible, so their densities are constant regardless of pressure, supercritical fluids are highly compressible and their physical properties change with pressure – such as the pressure drop across a packed-bed column. Currently, automated backpressure regulators can maintain a constant pressure in the column even if flow rate varies, mitigating this problem. A third drawback is difficulty in gas/liquid separation during collection of product. Upon depressurization, the CO rapidly turns into gas and aerosolizes any dissolved analyte in the process. Cyclone separators have lessened difficulties in gas/liquid separations. | 3 | Analytical Chemistry |
A dendrite in metallurgy is a characteristic tree-like structure of crystals growing as molten metal solidifies, the shape produced by faster growth along energetically favourable crystallographic directions. This dendritic growth has large consequences in regard to material properties. | 8 | Metallurgy |
In chemistry, specific rotation ([α]) is a property of a chiral chemical compound. It is defined as the change in orientation of monochromatic plane-polarized light, per unit distance–concentration product, as the light passes through a sample of a compound in solution. Compounds which rotate the plane of polarization of a beam of plane polarized light clockwise are said to be dextrorotary, and correspond with positive specific rotation values, while compounds which rotate the plane of polarization of plane polarized light counterclockwise are said to be levorotary, and correspond with negative values. If a compound is able to rotate the plane of polarization of plane-polarized light, it is said to be “optically active”.
Specific rotation is an intensive property, distinguishing it from the more general phenomenon of optical rotation. As such, the observed rotation (α) of a sample of a compound can be used to quantify the enantiomeric excess of that compound, provided that the specific rotation ([α]) for the enantiopure compound is known. The variance of specific rotation with wavelength—a phenomenon known as optical rotatory dispersion—can be used to find the absolute configuration of a molecule. The concentration of bulk sugar solutions is sometimes determined by comparison of the observed optical rotation with the known specific rotation. | 4 | Stereochemistry |
In humans, 5ALA is a precursor to heme. Biosynthesized, 5ALA goes through a series of transformations in the cytosol and finally gets converted to Protoporphyrin IX inside the mitochondria. This protoporphyrin molecule chelates with iron in presence of enzyme ferrochelatase to produce Heme.
Heme increases the mitochondrial activity thereby helping in activation of respiratory system Krebs Cycle and Electron Transport Chain leading to formation of adenosine triphosphate (ATP) for adequate supply of energy to the body. | 1 | Biochemistry |
The Pearson symbol does not uniquely identify the space group of a crystal structure. For example, both the NaCl structure (space group Fmm) and diamond (space group Fdm) have the same Pearson symbol cF8.
Confusion also arises in the rhombohedral lattice, which is alternatively described in a centred hexagonal (a = b, c, α = β = 90°, γ = 120°) or primitive rhombohedral (a = b = c, α = β = γ) setting. The more commonly used hexagonal setting has 3 translationally equivalent points per unit cell. The Pearson symbol refers to the hexagonal setting in its letter code (hR), but the following figure gives the number of translationally equivalent points in the primitive rhombohedral setting. Examples: hR1 and hR2 are used to designate the Hg and Bi structures respectively.
Because there are many possible structures that can correspond to one Pearson symbol, a prototypical compound may be useful to specify. Examples of how to write this would be hP12-MgZn or cF8-C. Prototypical compounds for particular structures can be found on the Inorganic Crystal Structure Database (ICSD) or on the AFLOW Library of Crystallographic Prototypes. | 3 | Analytical Chemistry |
The photoacoustic effect or optoacoustic effect is the formation of sound waves following light absorption in a material sample. In order to obtain this effect the light intensity must vary, either periodically (modulated light) or as a single flash (pulsed light). The photoacoustic effect is quantified by measuring the formed sound (pressure changes) with appropriate detectors, such as microphones or piezoelectric sensors. The time variation of the electric output (current or voltage) from these detectors is the photoacoustic signal. These measurements are useful to determine certain properties of the studied sample. For example, in photoacoustic spectroscopy, the photoacoustic signal is used to obtain the actual absorption of light in either opaque or transparent objects. It is useful for substances in extremely low concentrations, because very strong pulses of light from a laser can be used to increase sensitivity and very narrow wavelengths can be used for specificity. Furthermore, photoacoustic measurements serve as a valuable research tool in the study of the heat evolved in photochemical reactions (see: photochemistry), particularly in the study of photosynthesis.
Most generally, electromagnetic radiation of any kind can give rise to a photoacoustic effect. This includes the whole range of electromagnetic frequencies, from gamma radiation and X-rays to microwave and radio. Still, much of the reported research and applications, utilizing the photoacoustic effect, is concerned with the near ultraviolet/visible and infrared spectral regions. | 7 | Physical Chemistry |
Thymidine monophosphate (TMP), also known as thymidylic acid (conjugate base thymidylate), deoxythymidine monophosphate (dTMP), or deoxythymidylic acid (conjugate base deoxythymidylate), is a nucleotide that is used as a monomer in DNA. It is an ester of phosphoric acid with the nucleoside thymidine. dTMP consists of a phosphate group, the pentose sugar deoxyribose, and the nucleobase thymine. Unlike the other deoxyribonucleotides, thymidine monophosphate often does not contain the "deoxy" prefix in its name; nevertheless, its symbol often includes a "d" ("dTMP"). Dorland’s Illustrated Medical Dictionary provides an explanation of the nomenclature variation at its entry for thymidine.
As a substituent, it is called by the prefix thymidylyl-. | 0 | Organic Chemistry |
The al-Hijarah missile was an Iraqi liquid propelled inertial Short-range ballistic missile, it was also a Scud missile and considered an upgrade of the al-Hussein missile equipped with chemical warheads. It was developed by 1990 and was first used in the Persian Gulf War where the al-Hijarah missile would release poison gas clouds and kill personnel on the ground, as well as ignite oil wells. One al-Hijarah missile was confirmed to have been fired at Israel during the Gulf War where one landed near Dimona, it was revealed that the missile had a concrete filled warhead. | 1 | Biochemistry |
Humans and chimpanzees share ten NANOG pseudogenes (NanogP2-P11) during evaluation, two of them are located on the X chromosome and they characterized by the 5’ promoter sequences and the absence of introns as a result of mRNA retrotransposition all in the same places: one duplication pseudogene and nine retropseudogenes. Of the nine shared NANOG retropseudogenes, two lack the poly-(A) tails characteristic of most retropseudogenes, indicating that copying errors occurred during their creation. Due to the high improbability that the same pseudogenes (copying errors included) would exist in the same places in two unrelated genomes, evolutionary biologists point to NANOG and its pseudogenes as providing evidence of common descent between humans and chimpanzees. | 1 | Biochemistry |
Effective number of codons (abbreviated as ENC or Nc) is a measure to study the state of codon usage biases in genes and genomes. The way that ENC is computed has obvious similarities to the computation of effective population size in population genetics. Although it is easy to compute ENC values, it has been shown that this measure is one of the best measures to show codon usage bias.
Since the original suggestion of the ENC, several investigators have tried to improve the method, but it seems that there is much room to improve this measure. | 1 | Biochemistry |
The primary application of TPEPICO is the production of internal energy selected ions to study their unimolecular dissociation dynamics as a function of internal energy. The electrons are extracted by a continuous electric field and are velocity map imaged depending on their initial kinetic energy. Ions are accelerated in the opposite direction and their mass is determined by time-of-flight mass spectrometry. The data analysis yields dissociation thresholds, which can be used to derive new thermochemistry for the sample.
The electron imager side can also be used to record photoionization cross sections, photoelectron energy and angular distributions. With the help of circularly polarized light, photoelectron circular dichroism (PECD) can be studied. A thorough understanding of PECD effects could help explain the homochirality of life. Flash pyrolysis can also be used to produce free radicals or intermediates, which are then characterized to complement e.g. combustion studies. In such cases, the photoion mass analysis is used to confirm the identity of the radical produced.
Photoelectron photoion coincidence spectroscopy can be used to shed light on reaction mechanisms, and can also be generalized to study double ionization in (photoelectron) photoion photoion coincidence ((PE)PIPICO), fluorescence using photoelectron photon coincidence (PEFCO), or photoelectron photoelectron coincidence (PEPECO). Times-of-flight of photoelectrons and photoions can be combined in a form of a map, which visualizes the dynamics of the dissociative ionization process. Ion–electron velocity vector correlation functions can be obtained in double imaging setups, in which the ion detector also delivers position information. | 7 | Physical Chemistry |
* Polyethylene
* Polypropylene
* Copolymers of ethylene and 1-alkenes
* Polybutene-1
* Polymethylpentene
* Polycycloolefins
* Polybutadiene
* Polyisoprene
* Amorphous poly-alpha-olefins (APAO)
* Polyacetylene | 7 | Physical Chemistry |
Tests have shown some toxins near blooms can be in the air and thereby be inhaled, which could affect health. | 3 | Analytical Chemistry |
Periana's group was also able to convert methane into acetic acid using similar conditions to the Catalytica system. Palladium(II) salts were used in this process, and the products formed were a mixture of methanol and acetic acid, along with side products of carbon monoxide and possibly carbon dioxide due to over-oxidation. The mechanism of reaction involves another electrophilic activation of methane, and when carbon monoxide is incorporated, the acetic acid derivative is generated through its activation to an acyl intermediate ().
Another example of acetic acid synthesis was demonstrated by Pombeiro et al., which used vanadium-based complexes in trifluoroacetic acid with peroxodisulfate as the oxidant. The proposed mechanism involves a radical mechanism, where methane is the methyl source and trifluoroacetic acid is the carbonyl source. Minor side products were formed, including methyltrifluoroacetate and methylsulfate. | 0 | Organic Chemistry |
Coordination complexes and organometallic compounds are also photoreactive. These reactions can entail cis-trans isomerization. More commonly, photoreactions result in dissociation of ligands, since the photon excites an electron on the metal to an orbital that is antibonding with respect to the ligands. Thus, metal carbonyls that resist thermal substitution undergo decarbonylation upon irradiation with UV light. UV-irradiation of a THF solution of molybdenum hexacarbonyl gives the THF complex, which is synthetically useful:
:Mo(CO) + THF → Mo(CO)(THF) + CO
In a related reaction, photolysis of iron pentacarbonyl affords diiron nonacarbonyl (see figure):
:2 Fe(CO) → Fe(CO) + CO
Select photoreactive coordination complexes can undergo oxidation-reduction processes via single electron transfer. This electron transfer can occur within the inner or outer coordination sphere of the metal. | 5 | Photochemistry |
Studies of retroviruses led to the first demonstrated synthesis of DNA from RNA templates, a fundamental mode for transferring genetic material that occurs in both eukaryotes and prokaryotes. It has been speculated that the RNA to DNA transcription processes used by retroviruses may have first caused DNA to be used as genetic material. In this model, the RNA world hypothesis, cellular organisms adopted the more chemically stable DNA when retroviruses evolved to create DNA from the RNA templates.
An estimate of the date of evolution of the foamy-like endogenous retroviruses placed the time of the most recent common ancestor at > . | 1 | Biochemistry |
The main objective of the AVIRIS project is to identify, measure, and monitor constituents of the Earth's surface/ atmosphere based on molecular absorption and particle scattering signatures. Research with AVIRIS data is predominantly focused on understanding processes related to the global environment and climate change. AVIRIS research areas include ecology, oceanography, geology, snow hydrology, cloud and atmospheric studies. | 7 | Physical Chemistry |
Acylureas (also called N-acylureas or ureides) are a class of chemical compounds formally derived from the acylation of urea. | 0 | Organic Chemistry |
Nucleosomes can be assembled in vitro by either using purified native or recombinant histones. One standard technique of loading the DNA around the histones involves the use of salt dialysis. A reaction consisting of the histone octamers and a naked DNA template can be incubated together at a salt concentration of 2 M. By steadily decreasing the salt concentration, the DNA will equilibrate to a position where it is wrapped around the histone octamers, forming nucleosomes. In appropriate conditions, this reconstitution process allows for the nucleosome positioning affinity of a given sequence to be mapped experimentally. | 1 | Biochemistry |
As MALS can provide molar mass and size of molecules, it permits study into protein-protein binding, oligomerization and the kinetics of self-assembly, association and dissociation. By comparing the molar mass of a sample to its concentration, one can determine the binding affinity and stoichiometry of interacting molecules. | 7 | Physical Chemistry |
The final conversion of the common corrinoid intermediate 2 (fig. 6) from the two approaches into the target cobyric acid required the introduction of the two missing methyl groups at the meso positions of the corrin chromophore between rings A/B and C/D, as well as the conversion of all peripheral carboxyl functions into their amide form, except the critical carboxyl at the ring-D f-side chain (see fig. 6). These steps were collaboratively explored in strictly parallel fashion in both laboratories, the Harvard group using material produced via the A/B approach, the ETH group such prepared by the photochemical A/D approach.
The first decisive identification of a totally synthetic intermediate on the way to cobyric acid was carried out in February 1972 with a crystalline sample of totally synthetic dicyano-cobalt(III)-hexamethyl-cobyrinate-f-amide 3 (fig. 6), found to be identical in all data with a crystalline relay sample made from vitamin B by methanolysis to cobester 4, followed by partial ammonolysis and separation of the resulting mixture. At the time when Woodward announced the "Total Synthesis of Vitamin B" at the IUPAC conference in New Delhi in February 1972, the totally synthetic sample of the f-amide was one that had been made at ETH by the photochemical A/D approach, while the first sample of synthetic cobyric acid, identified with natural cobyric acid, had been obtained at Harvard by partial synthesis from B-derived f-amide relay material. Thus, the Woodward/Eschenmoser achievement around that time had been, strictly speaking, two total syntheses of cobyric acid, as well as two formal total syntheses of the vitamin.
In the later course of 1972, two crystalline epimers of totally synthetic dicyano-cobalt(III)-hexamethyl-cobyrinate-f- 3, as well as two crystalline epimers of the totally synthetic f-nitrile, all prepared via both synthetic approaches, were stringently identified chromatographically and spectroscopically with the corresponding B-derived substances. At Harvard, cobyric acid was then made also from totally synthetic f-amide 3 prepared via the A/B approach. Finally, in 1976 at Harvard, totally synthetic cobyric acid was converted into vitamin B via the pathway pioneered by . | 0 | Organic Chemistry |
Landau–Placzek ratio is a ratio of the integrated intensity of Rayleigh scattering to the combined integrated intensity of Brillouin scattering of a triplet frequency spectrum of light scattered by homogenous liquids or gases. The triplet consists of two frequency shifted Brillouin scattering and a central unshifted Rayleigh scattering line split. The triplet structure was explained by Lev Landau and George Placzek in 1934 in a short publication, summarizing major results of their analysis. Landau and Placzek noted in their short paper that a more detailed discussion will be published later although that paper does not seem to have been published. However, a detailed discussion is provided in Lev Landau and Evgeny Lifshitz's book.
The Landau–Placzek ratio is defined as
where
* is the integral intensity of central Rayleigh peak
* is the integral intensity of Brillouin peak.
The Landau–Placzek formula provides an approximate theoretical prediction for the Landau–Placzek ratio,
where
* is the specific heat at constant pressure
* is the specific heat at constant volume. | 7 | Physical Chemistry |
Autologous mitochondria extracted from healthy tissue and supplied to damaged tissue has been used to treat cardiac-compromised newborns. Alternatives to the approach include use of an extracorporeal membrane oxygenator (ECMO) or tissue or organ transplantation. | 1 | Biochemistry |
The material matrix has a symmetry with respect to a given orthogonal transformation () if it does not change when subjected to that transformation.
For invariance of the material properties under such a transformation we require
Hence the condition for material symmetry is (using the definition of an orthogonal transformation)
Orthogonal transformations can be represented in Cartesian coordinates by a matrix given by
Therefore, the symmetry condition can be written in matrix form as
For a transversely isotropic material, the matrix has the form
where the -axis is the axis of symmetry. The material matrix remains invariant under rotation by any angle about the -axis. | 3 | Analytical Chemistry |
Resorcinarenes can be characterized by a wide upper rim and a narrow lower rim. The upper rim includes eight hydroxyl groups that can participate in hydrogen bonding interactions. Depending on the aldehyde starting material, the lower rim includes four appending groups, usually chosen to give optimal solubility.
The resorcin[n]arene nomenclature is analogous to that of calix[n]arenes, in which n represents the number of repeating units in the ring. Pyrogallolarenes are related macrocycles derived from the condensation of pyrogallol (1,2,3-trihydroxybenzene) with an aldehyde.
Resorcinarenes and pyrogallolarenes self-assemble to give supramolecular assemblies. Both in the crystalline state and in solution, they are known to form hexamers that are akin to certain Archimedean solids with an internal volume of around one cubic nanometer (nanocapsules). (Isobutylpyrogallol[4]arene) is held together by 48 intermolecular hydrogen bonds. The remaining 24 hydrogen bonds are intramolecular. The cavity is filled by solvent. | 6 | Supramolecular Chemistry |
Basic oxygen steelmaking (BOS, BOP, BOF, or OSM), also known as Linz-Donawitz steelmaking or the oxygen converter process, is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into low-carbon steel. The process is known as basic because fluxes of burnt lime or dolomite, which are chemical bases, are added to promote the removal of impurities and protect the lining of the converter.
The process was invented in 1948 by Swiss engineer Robert Durrer and commercialized in 1952–1953 by the Austrian steelmaking company VOEST and ÖAMG. The LD converter, named after the Austrian towns Linz and Donawitz (a district of Leoben) is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen. It reduced capital cost of the plants and smelting time, and increased labor productivity. Between 1920 and 2000, labor requirements in the industry decreased by a factor of 1,000, from more than 3 man-hours per metric ton to just 0.003. The majority of steel manufactured in the world is produced using the basic oxygen furnace. In 2000, it accounted for 60% of global steel output.
Modern furnaces will take a charge of iron of up to 400 tons and convert it into steel in less than 40 minutes, compared to 10–12 hours in an open hearth furnace. | 8 | Metallurgy |
The Human Metabolome Database (HMDB) is a freely available, open-access database containing detailed data on more than 40,000 metabolites that have already been identified or are likely to be found in the human body. The HMDB contains three kinds of information:
# Chemical information,
# Clinical information and
# Biochemical information.
The chemical data includes >40,000 metabolite structures with detailed descriptions, extensive chemical classifications, synthesis information and observed/calculated chemical properties. It also contains nearly 10,000 experimentally measured NMR, GC-MS and LC/MS spectra from more than 1,100 different metabolites. The clinical information includes data on >10,000 metabolite-biofluid concentrations, metabolite concentration information on more than 600 different human diseases and pathway data for more than 200 different inborn errors of metabolism. The biochemical information includes nearly 6,000 protein (and DNA) sequences and more than 5,000 biochemical reactions that are linked to these metabolite entries. The HMDB supports a wide variety of online queries including text searches, chemical structure searches, sequence similarity searches and spectral similarity searches. This makes it particularly useful for metabolomic researchers who are attempting to identify or understand metabolites in clinical metabolomic studies. The first version of the HMDB was released in Jan. 1 2007 and was compiled by scientists at the University of Alberta and the University of Calgary. At that time, they reported data on 2,500 metabolites, 1,200 drugs and 3,500 food components. Since then these scientists have greatly expanded the collection. The version 3.5 of the HMDB contains >16,000 endogenous metabolites, >1,500 drugs and >22,000 food constituents or food metabolites. | 1 | Biochemistry |
An opacifier is a substance added to a material in order to make the ensuing system opaque. An example of a chemical opacifier is titanium dioxide (TiO), which is used as an opacifier in paints, in paper, and in plastics. It has very high refraction index (rutile modification 2.7 and anatase modification 2.55) and optimum refraction is obtained with crystals about 225 nanometers. Impurities in the crystal alter the optical properties. It is also used to opacify ceramic glazes and milk glass; bone ash is also used.
Opacifiers must have a refractive index (RI) substantially different from the system. Conversely, clarity may be achieved in a system by choosing components with very similar refractive indices. | 7 | Physical Chemistry |
In the early 1930s, shortly after much of the initial development of quantum mechanics, those theories began to be applied towards molecular structure by Pauling, Slater, Coulson, and others. In particular, Pauling introduced the concept of hybridisation, where atomic s and p orbitals are combined to give hybrid sp, sp, and sp orbitals. Hybrid orbitals proved powerful in explaining the molecular geometries of simple molecules like methane, which is tetrahedral with an sp carbon atom and bond angles of 109.5° between the four equivalent C-H bonds. However, slight deviations from these ideal geometries became apparent in the 1940s. A particularly well known example is water, where the angle between the two O-H bonds is only 104.5°. To explain such discrepancies, it was proposed that hybridisation can result in orbitals with unequal s and p character. A. D. Walsh described in 1947 a relationship between the electronegativity of groups bonded to carbon and the hybridisation of said carbon atom. Finally, in 1961, Bent published a major review of the literature that related molecular structure, central atom hybridisation, and substituent electronegativities and it is for this work that Bent's rule takes its name.
Bent's original paper considers the group electronegativity of the methyl group to be less than that of the hydrogen atom because methyl substitution reduces the acid dissociation constants of formic acid and of acetic acid. | 4 | Stereochemistry |
Levonorgestrel-containing emergency contraception is available over-the-counter in some countries, such as the United States. On some college campuses, Plan B is available from vending machines.
A policy update in 2015, required all pharmacies, clinics, and emergency departments run by Indian Health Services (for Native Americans) to have Plan B One-Step in stock, to distribute it to any woman (or her representative) who asked for it without a prescription, age verification, registration or any other requirement, to provide orientation training to all staff regarding the medication, to provide unbiased and medically accurate information about emergency contraception, and to make someone available at all times to distribute the pill in case the primary staffer objected to providing it on religious or moral grounds. | 4 | Stereochemistry |
Early studies of the phenomenon were conducted with sodium sulfate, also known as Glauber's Salt because, unusually, the solubility of this salt in water may decrease with increasing temperature. Early studies have been summarised by Tomlinson. It was shown that the crystallization of a supersaturated solution does not simply come from its agitation, (the previous belief) but from solid matter entering and acting as a "starting" site for crystals to form, now called "seeds". Expanding upon this, Gay-Lussac brought attention to the kinematics of salt ions and the characteristics of the container having an impact on the supersaturation state. He was also able to expand upon the number of salts with which a supersaturated solution can be obtained. Later Henri Löwel came to the conclusion that both nuclei of the solution and the walls of the container have a catalyzing effect on the solution that cause crystallization. Explaining and providing a model for this phenomenon has been a task taken on by more recent research. Désiré Gernez contributed to this research by discovering that nuclei must be of the same salt that is being crystallized in order to promote crystallization. | 7 | Physical Chemistry |
The resolution of DamID is a function of the availability of GATC sequences in the genome. A protein can only be mapped within two consecutive GATC sites. The median spacing between GATC fragments is 205 bp in Drosophila (FlyBase release 5), 260 in mouse (Mm9), and 460 in human (HG19). A modified protocol (DamIP), which combines immunoprecipitation of m6A with a Dam variant with less specific target site recognition, may be used to obtain higher resolution data. | 1 | Biochemistry |
There are two different droplet collection schemes: the centrifugal approach and the linear collection scheme. The linear collector is considered to be simpler, more reliable and lighter.
Several different LDR configurations have been proposed and evaluated.
*The spiral LDR employs a generator and collector which rotate at the same angular velocity. This concept was considered more complex due to unnecessary rotation of the collector.
*The enclosed disc LDR contains a droplet generator at the center for creating a disc of droplets. Only the collector rotates. The entire radiator is enclosed by a transparent shroud, which minimizes spacecraft contamination resulting from any errant droplets. This concept was considered more complex due to unnecessary rotation of the collector.
*The annular LDR utilizes a rotating collector to capture an annular sheet of droplets from an annular generator. The annular LDR has an inefficient radiative performance – the sheet radiates to itself more than the droplet sheets of alternate configurations.
*Several proposed variations of the LDR utilize electric fields to control droplet trajectories as in the ink jet printer. The Electrostatic THermal (Energy) Radiator (ETHER) is essentially a proposed variation of the LDR. The droplets are charged and in conjunction with a charge on the spacecraft that is opposite the droplet charge, the droplets will execute a slightly elliptical orbit. This closed trajectory would reduce overall system size. This concept calls for concerns about droplet-plasma interactions. Further, in low Earth orbit the spacecraft will acquire its own potential.
Rectangular and triangular versions of the LDR have been investigated the most.
*The rectangular LDR employs a linear collector which is as wide as the droplet generator. The collector can be two sided, where two droplet sheets traveling in opposite directions impact a single collector. An alternate variation would utilize a one sided collector, with only one generator and droplet sheet. In a rectangular LDR, there is no focusing of the droplet sheet, and the droplet number density remains constant along the flight path. It is the simplest LDR design with the largest radiating area.
*The triangular LDR concept employs a droplet generator to form a converging stream array (sheet) of droplets. The collector, located at the convergence point of the droplet sheet, employs a centrifugal force to capture the droplets. The triangular LDR is inherently less massive, because of the smaller collector. System studies have indicated that a triangular LDR can be 40 percent less massive than a rectangular LDR. However, for any comparable size the triangular LDR has half the area of a rectangular sheet and therefore rejects less heat. Currently, the use of pitot tube pickups has replaced the initial complex rotating seals. Collisions in a focused droplet sheet result in coalescence of the impacting droplets. The triangular LDR is now being developed more extensively.
*The magnetically focused LDR employs a magnetic field to focus streams of droplets directed from the generator toward the collector, thereby assuring that essentially all of the droplets captured, even though some of the streams may be misdirected as they leave the generator. The magnetic focusing means is also effective to suppress splashing of liquid when the droplets impinge on the collector. The magnetically focused LDR was investigated and patented by the Brookhaven National Laboratory (BNL) under a grant by the Department of Energy (Contract DE-AC02-76CH00016). The magnetic means can be achieved with a toroidal shaped electro-magnet or permanent magnets. As only one side of the droplet sheet would be focused by a single permanent magnet, an even number has to be placed across each other adjacent to the collector. A permanent dipole magnet has limited field strength, hence limits radiator size. Electromagnets or (cryogenic cooled) superconducting magnets offer higher field strengths, but may have mass tradeoff. A major conclusion drawn from calculations is that a spacecraft can be maneuvered at accelerations less than 10 g. Higher accelerations require numerous smaller LDRs which will be more massive in the sum, but would to be more likely to survive. | 7 | Physical Chemistry |
Steroid sulfates are endogenous sulfate esters of steroids. They are formed by steroid sulfotransferases via sulfation of endogenous steroids like cholesterol and steroid hormones. Although steroid sulfates do not bind to steroid hormone receptors and hence are hormonally inert, they can be desulfated by steroid sulfatase and in this way serve as precursors and circulating reservoirs for their active unsulfated counterparts. In addition, some steroid sulfates have biological activity in their own right, for instance acting as neurosteroids and modulating ligand-gated ion channels such as the GABA and NMDA receptors among other biological targets. | 1 | Biochemistry |
Electrolyte solutions are normally formed when salt is placed into a solvent such as water and the individual components dissociate due to the thermodynamic interactions between solvent and solute molecules, in a process called "solvation". For example, when table salt (sodium chloride), NaCl, is placed in water, the salt (a solid) dissolves into its component ions, according to the dissociation reaction
:NaCl → Na + Cl
It is also possible for substances to react with water, producing ions. For example, carbon dioxide gas dissolves in water to produce a solution that contains hydronium, carbonate, and hydrogen carbonate ions.
Molten salts can also be electrolytes as, for example, when sodium chloride is molten, the liquid conducts electricity. In particular, ionic liquids, which are molten salts with melting points below 100 °C, are a type of highly conductive non-aqueous electrolytes and thus have found more and more applications in fuel cells and batteries.
An electrolyte in a solution may be described as "concentrated" if it has a high concentration of ions, or "dilute" if it has a low concentration. If a high proportion of the solute dissociates to form free ions, the electrolyte is strong; if most of the solute does not dissociate, the electrolyte is weak. The properties of electrolytes may be exploited using electrolysis to extract constituent elements and compounds contained within the solution.
Alkaline earth metals form hydroxides that are strong electrolytes with limited solubility in water, due to the strong attraction between their constituent ions. This limits their application to situations where high solubility is required.
In 2021 researchers have found that electrolyte can "substantially facilitate electrochemical corrosion studies in less conductive media". | 7 | Physical Chemistry |
In crystallography, a periodic graph or crystal net is a three-dimensional periodic graph, i.e., a three-dimensional Euclidean graph whose vertices or nodes are points in three-dimensional Euclidean space, and whose edges (or bonds or spacers) are line segments connecting pairs of vertices, periodic in three linearly independent axial directions. There is usually an implicit assumption that the set of vertices are uniformly discrete, i.e., that there is a fixed minimum distance between any two vertices. The vertices may represent positions of atoms or complexes or clusters of atoms such as single-metal ions, molecular building blocks, or secondary building units, while each edge represents a chemical bond or a polymeric ligand.
Although the notion of a periodic graph or crystal net is ultimately mathematical (actually a crystal net is nothing but a periodic realization of an abelian covering graph over a finite graph
), and is closely related to that of a Tessellation of space (or honeycomb) in the theory of polytopes and similar areas, much of the contemporary effort in the area is motivated by crystal engineering and prediction (design), including metal-organic frameworks (MOFs) and zeolites. | 3 | Analytical Chemistry |
Metal carbonyl hydrides are used as catalysts in the hydroformylation of olefins. The catalyst is usually formed in situ in a reaction of a metal salt precursor with the syngas. The hydroformylation starts with the generation of a coordinatively unsaturated 16-electron metal carbonyl hydride complex like HCo(CO) or HRh(CO)(PPh) by dissociation of a ligand. Such complexes bind olefins in a first step via π-complexation, thus beginning the transformation of the alkene to the aldehyde.
Iron carbonyl hydrides occur in nature at the active sites of hydrogenase enzymes. | 0 | Organic Chemistry |
Prerequisite equipments for sand rammer may vary from case to case basis or testing scenario:<br />
Case 1: If the prepared sand is ready
* Tube filler accessory to fill sample tube with sand. Advantage is it lets the sand fill in from fixed distance and riddles it before filling.
<br />
Case 2: Experiment by preparing new sand sample
If sand needs to be prepared before making specimen following equipments may be needed
* Laboratory sand muller or laboratory sand mixer (for core sands)
<br />
Case 3: For low compressive strength sands and mixtures:
* Split specimen tube | 8 | Metallurgy |
The initiation time is related to the rate at which carbonation propagates in the concrete cover thickness. Once that carbonation reaches the steel surface, altering the local pH value of the environment, the protective thin film of oxides on the steel surface becomes instable, and corrosion initiates involving an extended portion of the steel surface. One of the most simplified and accredited models describing the propagation of carbonation in time is to consider penetration depth proportional to the square root of time, following the correlation
where is the carbonation depth, is time, and is the carbonation coefficient. The corrosion onset takes place when the carbonation depth reaches the concrete cover thickness, and therefore can be evaluated as
where is the concrete cover thickness.
is the key design parameter to assess initiation time in the case of carbonation-induced corrosion. It is expressed in mm/year and depends on the characteristics of concrete and the exposure conditions. The penetration of gaseous CO in a porous medium such as concrete occurs via diffusion. The humidity content of concrete is one of the main influencing factors of CO diffusion in concrete. If concrete pores are completely and permanently saturated (for instance in submerged structures) CO diffusion is prevented. On the other hand, for completely dry concrete, the chemical reaction of carbonation cannot occur. Another influencing factor for CO diffusion rate is concrete porosity. Concrete obtained with higher w/c ratio or obtained with an incorrect curing process presents higher porosity at hardened state, and is therefore subjected to a higher carbonation rate. The influencing factors concerning the exposure conditions are the environmental temperature, humidity and concentration of CO. Carbonation rate is higher for environments with higher humidity and temperature, and increases in polluted environments such as urban centres and inside close spaces as tunnels.
To evaluate propagation time in the case of carbonation-induced corrosion, several models have been proposed. In a simplified but commonly accepted method, the propagation time is evaluated as function of the corrosion propagation rate. If the corrosion rate is considered constant, t can be estimated as:
where is the limit corrosion penetration in steel and is the corrosion propagation rate.
must be defined in function of the limit state considered. Generally for carbonation-induced corrosion the concrete cover cracking is considered as limit state, and in this case a equal to 100 μm is considered. depends on the environmental factors in proximity of the corrosion process, such as the availability of oxygen and water at concrete cover depth. Oxygen is generally available at the steel surface, except for submerged structures. If pores are constantly fully saturated, a very low amount of oxygen reaches the steel surface and corrosion rate can be considered negligible. For very dry concretes is negligible due to the absence of water which prevents the chemical reaction of corrosion. For intermediate concrete humidity content, corrosion rate increases with increasing the concrete humidity content. Since the humidity content in a concrete can significantly vary along the year, it is general not possible to define a constant . One possible approach is to consider a mean annual value of . | 8 | Metallurgy |
Metathesis using Grubbs-type alkylidene complexes can be used to synthesize terminal carbido-containing complexes. One example is RuC(PCy)Cl with a Ru-C distance of 163 pm, typical for a triple bond. The complex can be obtained by metathesis of vinyl acetate to give [Ru(CH-p-CHMe)(PCy)Cl] results in a metastable Ru(Cl)(PCy)CHOAc complex, which eliminates acetic acid.
The "naked" carbido ligand is weakly basic, forming complexes with other metal centers. The C-M bond is typically found to be around 1.65 Å. The C NMR resonance values for the carbido carbons vary widely, but range from δ211-406. Another example of a terminal carbido complex is Li[MoC(NR2)3] (Mo-C distance of 172 pm), which forms upon deprotonation of the respective methylidyne precursor. | 0 | Organic Chemistry |
The tetrahedral molecule features C-I distances of 2.12 ± 0.02 Å. The molecule is slightly crowded with short contacts between iodine atoms of 3.459 ± 0.03 Å, and possibly for this reason, it is thermally and photochemically unstable.
Carbon tetraiodide crystallizes in tetragonal crystal structure (a 6.409, c 9.558 (.10 nm)).
It has zero dipole moment due to its symmetrically substituted tetrahedral geometry. | 0 | Organic Chemistry |
Note that the B shot which begins the Schilling test is enough to go a considerable way toward treating B deficiency, so the test is also a partial treatment for B deficiency. Also, the classic Schilling test can be performed at any time, even after full B repletion and correction of the anemia, and it will still show if the cause of the B deficiency was intrinsic-factor related. In fact, some clinicians have suggested that folate and B replacement for several weeks be normally performed before a Schilling test is done, since folate and B deficiencies are both known to interfere with intestinal cell function, and thus cause malabsorption of B on their own, even if intrinsic factor is being made. This state would then tend to cause a false-positive test for both simple B and intrinsic factor-related B malabsorption. Several weeks of vitamin replacement are necessary, before epithelial damage to the G.I. tract from B deficiency is corrected.
Many labs have stopped performing the Schilling test, due to lack of production of the cobalt radioisotopes and labeled-B test substances. Also, injection replacement of B has become relatively inexpensive, and can be self-administered by patients, as well as megadose oral B. Since these are the same treatments which would be administered for most causes of B malabsorption even if the exact cause were identified, the diagnostic test may be omitted without damage to the patient (so long as follow-up treatment and occasional serum B testing is not allowed to lapse).
It is possible for use of other radiopharmaceuticals to interfere with interpretation of the test. | 1 | Biochemistry |
Sintering is an important cause for loss of catalytic activity, especially on supported metal catalysts. It decreases the surface area of the catalyst and changes the surface structure. For a porous catalytic surface, the pores may collapse due to sintering, resulting in loss of surface area. Sintering is in general an irreversible process.
Small catalyst particles have the highest possible relative surface area and high reaction temperature, both factors that generally increase the reactivity of a catalyst. However, these factors are also the circumstances under which sintering occurs. Specific materials may also increase the rate of sintering. On the other hand, by alloying catalysts with other materials, sintering can be reduced. Rare-earth metals in particular have been shown to reduce sintering of metal catalysts when alloyed.
For many supported metal catalysts, sintering starts to become a significant effect at temperatures over . Catalysts that operate at higher temperatures, such as a car catalyst, use structural improvements to reduce or prevent sintering. These improvements are in general in the form of a support made from an inert and thermally stable material such as silica, carbon or alumina. | 8 | Metallurgy |
During a prolonged drought in Australia at the start of this century, scientists there from a number of research institutions, including Pr. David Solomon, inventor of the polymer banknote, set about developing a product that is efficacious, resistant to the deleterious effects of wind, and affordable. In addition to small and large scale field trials, new techniques were utilised including a novel evaporation tank with a controlled climate system to mimic the effects of wind and waves, and computational modelling was for the first time employed to relate dynamic and geometric properties at the atomistic level, with evaporation suppressing performance at the macroscopic level.
The use of ethylene glycol monooctadecyl ether was found to substantially decrease evaporation resistance in the presence of wind, and the addition of a water-soluble polymer further enhanced its effectiveness. | 7 | Physical Chemistry |
Fritz Weigert (18 September 1876 – 13 April 1947) was a German physical chemist. Weigert has made major contributions in the field of photochemistry. He was born in Berlin. He was the nephew of both Karl Weigert and Paul Ehrlich. He was married to Margarete Behmer. Around 1908, he began teaching and conducting research at Berlin University - after studying there. He was a photochemistry professor at Leipzig University from 1914 until being, like other Jewish scientists, forced out by the Nazis in 1934. On January 1, 1935, he immigrated to England and in 1936 was director of the Physiochemical Department of the Cancer Research Institute at Mount Vernon Hospital, Northwood.
He elucidated the metabolism of the carcinogenic hydrocarbon 3,4-benzpyrene by fluorescence spectroscopy. | 5 | Photochemistry |
The details of an agarose gel electrophoresis experiment may vary depending on methods, but most follow a general procedure. | 1 | Biochemistry |
For many systems of physical and chemical kinetics, detailed balance provides sufficient conditions for the strict increase of entropy in isolated systems. For example, the famous Boltzmann H-theorem states that, according to the Boltzmann equation, the principle of detailed balance implies positivity of entropy production. The Boltzmann formula (1872) for entropy production in rarefied gas kinetics with detailed balance served as a prototype of many similar formulas for dissipation in mass action kinetics and generalized mass action kinetics with detailed balance.
Nevertheless, the principle of detailed balance is not necessary for entropy growth. For example, in the linear irreversible cycle , entropy production is positive but the principle of detailed balance does not hold.
Thus, the principle of detailed balance is a sufficient but not necessary condition for entropy increase in Boltzmann kinetics. These relations between the principle of detailed balance and the second law of thermodynamics were clarified in 1887 when Hendrik Lorentz objected to the Boltzmann H-theorem for polyatomic gases. Lorentz stated that the principle of detailed balance is not applicable to collisions of polyatomic molecules.
Boltzmann immediately invented a new, more general condition sufficient for entropy growth. Boltzmann's condition holds for all Markov processes, irrespective of time-reversibility. Later, entropy increase was proved for all Markov processes by a direct method. These theorems may be considered as simplifications of the Boltzmann result. Later, this condition was referred to as the "cyclic balance" condition (because it holds for irreversible cycles) or the "semi-detailed balance" or the "complex balance". In 1981, Carlo Cercignani and Maria Lampis proved that the Lorentz arguments were wrong and the principle of detailed balance is valid for polyatomic molecules. Nevertheless, the extended semi-detailed balance conditions invented by Boltzmann in this discussion remain the remarkable generalization of the detailed balance. | 7 | Physical Chemistry |
Transmetalation (alt. spelling: transmetallation) is a type of organometallic reaction that involves the transfer of ligands from one metal to another. It has the general form:
:M–R + M–R′ → M–R′ + M–R
where R and R′ can be, but are not limited to, an alkyl, aryl, alkynyl, allyl, halogen, or pseudohalogen group. The reaction is usually an irreversible process due to thermodynamic and kinetic reasons. Thermodynamics will favor the reaction based on the electronegativities of the metals and kinetics will favor the reaction if there are empty orbitals on both metals. There are different types of transmetalation including redox-transmetalation and redox-transmetalation/ligand exchange. During transmetalation the metal-carbon bond is activated, leading to the formation of new metal-carbon bonds. Transmetalation is commonly used in catalysis, synthesis of main group complexes, and synthesis of transition metal complexes. | 0 | Organic Chemistry |
After obtaining his Ph.D., Negishi decided to become an academic researcher. Although he was hoping to work at a Japanese university, he could not find a position. In 1966 he resigned from Teijin, and became a postdoctoral associate at Purdue University, working under future Nobel laureate Herbert C. Brown. From 1968 to 1972 he was an instructor at Purdue.
In 1972, he became an assistant professor at Syracuse University, where began his lifelong study of transition metal–catalyzed reactions, and was promoted to associate professor in 1979. He returned to Purdue University as a full professor in the same year.
He discovered Negishi coupling, a process which condenses organic zinc compounds and organic halides under a palladium or nickel catalyst to obtain a C-C bonded product. For this achievement, he was awarded the Nobel Prize in Chemistry in 2010. Negishi also reported that organoaluminum compounds and organic zirconium compounds can be used for cross-coupling. He did not seek a patent for this coupling technology and explained his reasoning as follows: "If we did not obtain a patent, we thought that everyone could use our results easily."
In addition, Zr(CH) obtained by reducing zirconocene dichloride is also called Negishi reagent, which can be used in oxidative cyclisation reactions. The technique he developed is estimated to be used in a quarter of all reactions in the pharmaceutical industry.
By the time Negishi retired in 2019, he had published more than 400 academic papers. He was committed to instilling rigorous practices in his lab, emphasizing the need of keeping organized and comprehensive records. Before any separations, he asked his student to evaluate crude reaction mixtures in order to minimize loss of any useful scientific information. | 0 | Organic Chemistry |
When one is considering allylic strain, one needs to consider the possible conformers and the possible stereoelectronic demand of the reaction. For example, in the conformation of (Z)-4-methylpent-2-ene, the molecule isn't frozen in the favored conformer but rotates in the dihedral angle around 30° at <1kcal/mol cost. In stereoselective reactions, there are 2 effects of allylic strain on the reaction which is the sterics effect and the electronic effects. The sterics effect is where the largest group prefer to be the farthest from the alkene. The electronic effect is where the orbitals of the substituents prefer to align anti or outside of the orbitals depending on the reaction. | 4 | Stereochemistry |
Other chemicals are being tested for their efficacy for removing cyanobacteria during blooms. Modified clays, such as aluminum chloride modified clay (AC-MC), aluminum sulfide modified clay (AS-MC) and polyaluminum chloride modified clay (PAC-MC) have shown positive results in vitro for the removal of Aureococcus by trapping the microalgae in the sediment of clay, removing it from the top layer of water where harmful blooms can occur.
Many efforts have been made in an attempt to control HABs so that the harm that they cause can be kept at a minimum. Studies into the use of clay to control HABs have proven that this method may be an effective way to reduce the negative effects caused by HABs. The addition of aluminum chloride, aluminum sulfate, or polyaluminum chloride to clay can modify the clay surface and increase its efficiency in the removal of HABs from a body of water. The addition of aluminum-containing compounds causes the clay particles to achieve a positive charge, with these particles then undergoing flocculation with the harmful algae cells. The algae cells then group together: becoming a sediment instead of a suspension. The process of flocculation will limit the bloom growth and reduce the impact in which the bloom can have on an area.
In the Netherlands, successful algae and phosphate removal from surface water has been obtained by pumping affected water through a hydrodynamic separator. The treated water is then free from algae and contains a significant lower amount of phosphate since the removed algae cells contain a lot of phosphate. The treated water also gets a lower turbidity. Future projects will study the positive effects on the ecology and marine life as it is expected plant life will be restored and a reduction in bottom dwelling fish will automatically reduce the turbidity of the cleaned water. The removed algae and phosphate may find its way not as waste but as infeed to bio digesters. | 3 | Analytical Chemistry |
In thermodynamics, the compressibility factor (Z), also known as the compression factor or the gas deviation factor, describes the deviation of a real gas from ideal gas behaviour. It is simply defined as the ratio of the molar volume of a gas to the molar volume of an ideal gas at the same temperature and pressure. It is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behaviour. In general, deviation from ideal behaviour becomes more significant the closer a gas is to a phase change, the lower the temperature or the larger the pressure. Compressibility factor values are usually obtained by calculation from equations of state (EOS), such as the virial equation which take compound-specific empirical constants as input. For a gas that is a mixture of two or more pure gases (air or natural gas, for example), the gas composition must be known before compressibility can be calculated. <br />
Alternatively, the compressibility factor for specific gases can be read from generalized compressibility charts that plot as a function of pressure at constant temperature.
The compressibility factor should not be confused with the compressibility (also known as [http://glossary.ametsoc.org/wiki/Coefficient_of_compressibility coefficient of compressibility] or [http://petrowiki.org/Isothermal_compressibility_of_gases isothermal compressibility]) of a material, which is the measure of the relative volume change of a fluid or solid in response to a pressure change. | 7 | Physical Chemistry |
Asemota conducted PhD research at the University of Benin and Frankfurt University, where she studied the molecular genetics and metabolism of the browning of yam tubers in storage.
Upon moving to Jamaica, prompted by ongoing problems with production and storage in the Jamaican yam industry, Asemota continued researching yams, founding the multidisciplinary UWI Yam Biotechnology Project. Initially, Asemota investigated the biochemical effects of removing yam heads at harvest, a common farming practice in Jamaica. Over the ensuing decades, Asemota's research team has investigated many aspects of yam biochemistry and physiology, from DNA fingerprinting studies of Jamaican yam varieties to the carbohydrate metabolism of yam tubers in storage.
In addition to her work on yam production and storage, Asemota has studied the metabolic effects of yams and yam-derived products on animal models of diseases such as diabetes. More recently, the Yam Biotechnology Project has moved towards a farm to finished products strategy, with the goal of producing yam-based food, medical, and biofuel products to benefit the Jamaican economy. She has also applied similar research techniques to other types of tropical crop.
Asemota has served as Principal Investigator for the National Institute of Health (NIH) and National Science Foundation (NSF) grants. She has lectured undergraduates, postgraduates and postdoctoral levels worldwide, and has supervised or advised at least 30 postgraduate students in Biochemistry or Biotechnology. She has over 250 publications, and owns four patents from her research. | 1 | Biochemistry |
A series of samples are prepared with all the same receptor (R) concentration but in which the ligand (L) concentration is titrated. After equilibrium is reached each sample is measured by flowing it through the column (Figure 2).
For 1:1 reversible binding Equilibrium Kd is defined as
(1) K≡k/k =R*L/RL
the binding is reversible so conservation of mass can be written as
(2) R = R+RL
(3) L = L +RL
Where:
K = equilibrium dissociation constant
k = forward rate constant
k = reverse rate constant
R = free receptor site concentration at equilibrium
L = free ligand site concentration at equilibrium
RL = concentration of complex at equilibrium
R= total concentration of receptors
L = total concentration of ligand
A simple equation relating the free fraction of R (=R/R) to the K and L is then fit to the measured data to find the K of the interaction. | 1 | Biochemistry |
Excitotoxicity can occur from substances produced within the body (endogenous excitotoxins). Glutamate is a prime example of an excitotoxin in the brain, and it is also the major excitatory neurotransmitter in the central nervous system of mammals. During normal conditions, glutamate concentration can be increased up to 1mM in the synaptic cleft, which is rapidly decreased in the lapse of milliseconds. When the glutamate concentration around the synaptic cleft cannot be decreased or reaches higher levels, the neuron kills itself by a process called apoptosis.
This pathologic phenomenon can also occur after brain injury and spinal cord injury. Within minutes after spinal cord injury, damaged neural cells within the lesion site spill glutamate into the extracellular space where glutamate can stimulate presynaptic glutamate receptors to enhance the release of additional glutamate. Brain trauma or stroke can cause ischemia, in which blood flow is reduced to inadequate levels. Ischemia is followed by accumulation of glutamate and aspartate in the extracellular fluid, causing cell death, which is aggravated by lack of oxygen and glucose. The biochemical cascade resulting from ischemia and involving excitotoxicity is called the ischemic cascade. Because of the events resulting from ischemia and glutamate receptor activation, a deep chemical coma may be induced in patients with brain injury to reduce the metabolic rate of the brain (its need for oxygen and glucose) and save energy to be used to remove glutamate actively. (The main aim in induced comas is to reduce the intracranial pressure, not brain metabolism).
Increased extracellular glutamate levels leads to the activation of Ca permeable NMDA receptors on myelin sheaths and oligodendrocytes, leaving oligodendrocytes susceptible to Ca influxes and subsequent excitotoxicity. One of the damaging results of excess calcium in the cytosol is initiating apoptosis through cleaved caspase processing. Another damaging result of excess calcium in the cytosol is the opening of the mitochondrial permeability transition pore, a pore in the membranes of mitochondria that opens when the organelles absorb too much calcium. Opening of the pore may cause mitochondria to swell and release reactive oxygen species and other proteins that can lead to apoptosis. The pore can also cause mitochondria to release more calcium. In addition, production of adenosine triphosphate (ATP) may be stopped, and ATP synthase may in fact begin hydrolysing ATP instead of producing it, which is suggested to be involved in depression.
Inadequate ATP production resulting from brain trauma can eliminate electrochemical gradients of certain ions. Glutamate transporters require the maintenance of these ion gradients to remove glutamate from the extracellular space. The loss of ion gradients results in not only the halting of glutamate uptake, but also in the reversal of the transporters. The Na-glutamate transporters on neurons and astrocytes can reverse their glutamate transport and start secreting glutamate at a concentration capable of inducing excitotoxicity. This results in a buildup of glutamate and further damaging activation of glutamate receptors.
On the molecular level, calcium influx is not the only factor responsible for apoptosis induced by excitoxicity. Recently, it has been noted that extrasynaptic NMDA receptor activation, triggered by both glutamate exposure or hypoxic/ischemic conditions, activate a CREB (cAMP response element binding) protein shut-off, which in turn caused loss of mitochondrial membrane potential and apoptosis. On the other hand, activation of synaptic NMDA receptors activated only the CREB pathway, which activates BDNF (brain-derived neurotrophic factor), not activating apoptosis. | 1 | Biochemistry |
Earlier mechanistic proposals for the EPOC phenomenon with solid electrolytes mainly emphasized tuning of the local work function of the surface of conductive catalysts by spilled-over species, which are in-situ generated during electrochemical polarization processes. It has been proposed that the spilled-over species can subsequently modulate the chemisorption strength between surface adsorbates (intermediates) and catalyst binding sites, thereby influencing the rate or selectivity of the target reactions significantly. Particularly in the case of oxygen-ion conducting electrolyte systems, for instance, the migrated anionic O species from the solid electrolyte to the metal-gas interface has been suggested as the origin of the corresponding EPOC effects along with the evidence that the migrated charged species on the surface can be identified via in-situ spectroscopic methods. On the other hand, the hypothesis of modification of the local work function to explain the origin of EPOC was recently criticized with a different view that heterogeneous catalysis needs to be explained by more recent concepts such as d-band center theory, rather than the surface work function, which might play a more trivial role in understanding of surface reactions. | 7 | Physical Chemistry |
In UV-Vis absorption SEC, depending on the configuration of the light beam respect to the electrode/solution interface, two types of optical arrangements can be distinguished: normal and parallel configuration. | 7 | Physical Chemistry |
Typical weatherization procedures include:
*Sealing bypasses (cracks, gaps, holes), especially around doors, windows, pipes and wiring that penetrate the ceiling and floor, and other areas with high potential for heat loss, using caulk, foam sealant, weather-stripping, window film, door sweeps, electrical receptacle gaskets, and so on to reduce infiltration.
*Sealing recessed lighting fixtures (can lights or high-hats), which leak large amounts of air into unconditioned attic space.
*Sealing air ducts, which can account for 20% of heat loss, using fiber-reinforced mastic (not duck/duct tape, which is not suitable for this purpose)
*Installing/replacing dampers in exhaust ducts, to prevent outside air from entering the house when the exhaust fan or clothes dryer is not in use.
*Protecting pipes from corrosion and freezing.
*Installing footing drains, foundation waterproofing membranes, interior perimeter drains, sump pump, gutters, downspout extensions, downward-sloping grading, French drains, swales, and other techniques to protect a building from both surface water and ground water.
*Providing proper ventilation to unconditioned spaces to protect a building from the effects of condensation. See Ventilation issues in houses
*Installing roofing, building wrap, siding, flashing, skylights or solar tubes and making sure they are in good condition on an existing building.
*Installing insulation in walls, floors, and ceilings, around ducts and pipes, around water heaters, and near the foundation and sill.
*Installing storm doors and storm windows.
*Replacing old drafty doors with tightly sealing, foam-core doors.
*Retrofitting older windows with a stop or parting bead across the sill where it meets the sash.
*Replacing older windows with low-energy, double-glazed windows.
The phrase "whole-house weatherization" extends the traditional definition of weatherization to include installation of modern, energy-saving heating and cooling equipment, or repair of old, inefficient equipment (furnaces, boilers, water heaters, programmable thermostats, air conditioners, and so on). The "Whole-House" approach also looks at how the house performs as a system. | 7 | Physical Chemistry |
Consider next the necessary requirements for the appearance of lateral growth. It is evident that the lateral growth mechanism will be found when any area in the surface can reach a metastable equilibrium in the presence of a driving force. It will then tend to remain in such an equilibrium configuration until the passage of a step. Afterward, the configuration will be identical except that each part of the step will have advanced by the step height. If the surface cannot reach equilibrium in the presence of a driving force, then it will continue to advance without waiting for the lateral motion of steps.
Thus, Cahn concluded that the distinguishing feature is the ability of the surface to reach an equilibrium state in the presence of the driving force. He also concluded that for every surface or interface in a crystalline medium, there exists a critical driving force, which, if exceeded, will enable the surface or interface to advance normal to itself, and, if not exceeded, will require the lateral growth mechanism.
Thus, for sufficiently large driving forces, the interface can move uniformly without the benefit of either a heterogeneous nucleation or screw dislocation mechanism. What constitutes a sufficiently large driving force depends upon the diffuseness of the interface, so that for extremely diffuse interfaces, this critical driving force will be so small that any measurable driving force will exceed it. Alternatively, for sharp interfaces, the critical driving force will be very large, and most growth will occur by the lateral step mechanism.
Note that in a typical solidification or crystallization process, the thermodynamic driving force is dictated by the degree of supercooling. | 3 | Analytical Chemistry |
Orphan MTases are common in bacteria and archea CcrM is found in almost every group of Alphaproteobacteria, excepting in Rickettsiales and Magnetococcales, and homologs can be found in Campylobacterota and Gammaproteobacteria. Alphaproteobacteria are organisms with different life stages from free living to substrate associated, some of them are intracellular pathogens of plants, animal and even human, in those groups the CcrMs must have an important role in cell cycle progression.
CcrM miss regulation have shown to produce severe miss control of cell cycle regulation and differentiation in various Alphaproteobacteria; C. crescentus , the plant symbiont Sinorhizobium meliloti and in the human pathogen Brucella abortus. Also CcrM gene has proven to be essential for the viability of various Alphaproteobacteria. | 1 | Biochemistry |
Another area of active research is using TPV as the basis of a thermal storage system. In this concept, electricity being generated in off-peak times is used to heat a large block of material, typically carbon or a phase-change material. The material is surrounded by TPV cells which are in turn backed by a reflector and insulation. During storage, the TPV cells are turned off and the photons pass through them and reflect back into the high-temperature source. When power is needed, the TPV is connected to a load. | 7 | Physical Chemistry |
Vitalism was a widespread conception that substances found in organic nature are formed from the chemical elements by the action of a "vital force" or "life-force" (vis vitalis) that only living organisms possess.
In the 1810s, Jöns Jacob Berzelius argued that a regulative force must exist within living bodies. Berzelius also contended that compounds could be distinguished by whether they required any organisms in their synthesis (organic compounds) or whether they did not (inorganic compounds). Vitalism taught that formation of these "organic" compounds were fundamentally different from the "inorganic" compounds that could be obtained from the elements by chemical manipulations in laboratories.
Vitalism survived for a short period after the formulation of modern ideas about the atomic theory and chemical elements. It first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A further experiment was Wöhlers 1828 synthesis of urea from the inorganic salts potassium cyanate and ammonium sulfate. Urea had long been considered an "organic" compound, as it was known to occur only in the urine of living organisms. Wöhlers experiments were followed by many others, in which increasingly complex "organic" substances were produced from "inorganic" ones without the involvement of any living organism, thus disproving vitalism. | 0 | Organic Chemistry |
The business of automated mineralogy is concerned with the commercialisation of the technology and software in terms of development and marketing of integrated solutions. This includes all aspects of: service; maintenance; customer support; R&D; marketing and sales. Customers of automated mineralogy solutions include: laboratory facilities; mine sites, well sites, and research institutions. | 7 | Physical Chemistry |
Phenotypic threshold effect is when there is a certain amount of wild-type mtDNA present in the mitochondrion which is able to balance out the number of mutated mtDNA. As a result, the phenotype is normal. However, if the number of wild-type mtDNA decreases and the number of mutant mtDNA increases, resulting in an imbalance between the two, the threshold level has been altered which causes complications. This occurs because the wild-type mtDNA present are able to keep the electron transport chain and ATP synthesis functioning despite there being a few number of them present. They are able to counterbalance the mutated mtDNA, however, when the number drops below threshold level the mutant mtDNA take over. | 1 | Biochemistry |
The term "operon" was first proposed in a short paper in the Proceedings of the French Academy of Science in 1960. From this paper, the so-called general theory of the operon was developed. This theory suggested that in all cases, genes within an operon are negatively controlled by a repressor acting at a single operator located before the first gene. Later, it was discovered that genes could be positively regulated and also regulated at steps that follow transcription initiation. Therefore, it is not possible to talk of a general regulatory mechanism, because different operons have different mechanisms. Today, the operon is simply defined as a cluster of genes transcribed into a single mRNA molecule. Nevertheless, the development of the concept is considered a landmark event in the history of molecular biology. The first operon to be described was the lac operon in E. coli. The 1965 Nobel Prize in Physiology and Medicine was awarded to François Jacob, André Michel Lwoff and Jacques Monod for their discoveries concerning the operon and virus synthesis. | 1 | Biochemistry |
Dynamic light scattering provides insight into the dynamic properties of soft materials by measuring single scattering events, meaning that each detected photon has been scattered by the sample exactly once. In principle, the DLS measurements can be performed with the detector positioned at any angle. The choice of the best angle depends on the sample properties, such as turbidity and particle size. Back scattering detection (e.g., 173° or 175°) is particularly interesting for turbid and highly concentrated samples, which contain large particles. Side scattering detection (90°) is recommended for weakly scattering samples, including small particles and transparent samples. Finally, forward scattering detection (e.g., 13° or 15°) is suitable for detection of samples containing small particles with few large particles. Some DLS instruments in the market also allow automatic angle selection based on a continuous transmittance measurement.
At the lower end of the turbidity range, the Cavity Amplified Scattering Spectroscopy method makes use of an integrating cavity to elongate photon paths through quasi non-scattering samples. As opposed to conventional DLS instruments, this method is angle independent as it probes samples isotropically from all directions.
Even though the DLS measurement using a single-angle detection has been the most diffuse technique, the application to many systems of scientific and industrial relevance has been limited due to often-encountered multiple scattering, wherein photons are scattered multiple times by the sample before being detected. Accurate interpretation becomes exceedingly difficult for systems with non-negligible contributions from multiple scattering. Especially for larger particles and those with high refractive index contrast, this limits the technique to very low particle concentrations, and a large variety of systems are, therefore, excluded from investigations with dynamic light scattering. However, as shown by Schaetzel, it is possible to suppress multiple scattering in dynamic light scattering experiments via a cross-correlation approach. The general idea is to isolate singly scattered light and suppress undesired contributions from multiple scattering in a dynamic light scattering experiment. Different implementations of cross-correlation light scattering have been developed and applied. Currently, the most widely used scheme is the so-called 3D-dynamic light scattering method. The same method can also be used to correct static light scattering data for multiple scattering contributions. Alternatively, in the limit of strong multiple scattering, a variant of dynamic light scattering called diffusing-wave spectroscopy can be applied. | 7 | Physical Chemistry |
The Kelvin equation describes the change in vapour pressure due to a curved liquid–vapor interface, such as the surface of a droplet. The vapor pressure at a convex curved surface is higher than that at a flat surface. The Kelvin equation is dependent upon thermodynamic principles and does not allude to special properties of materials. It is also used for determination of pore size distribution of a porous medium using adsorption porosimetry. The equation is named in honor of William Thomson, also known as Lord Kelvin. | 7 | Physical Chemistry |
Sarah Elaine B. Petrie is a Canadian and American physical chemist who worked for the research laboratories of Eastman Kodak and became known for her research on the thermal properties of glasses, polymers, and liquid crystals.
Petrie earned a Ph.D. in chemistry in 1957 from the University of Toronto, with the dissertation Dielectric behaviour of vapours adsorbed on porous and non-porous adsorbents, supervised by Robert L. McIntosh. By the same year she was working for the Kodak Research Laboratories. In 1977 she was appointed to a panel on polymers in the National Bureau of Standards and as an advisor to the office of chemistry and chemical technology of the National Research Council. She also served as a councilor to the American Chemical Society Division of Polymer Chemistry from 1979 to 1981. By 1994, when she served on the Committee on Polymer Science and Engineering of the National Research Council, she was listed as retired from Kodak.
In 1976, Petrie was named a Fellow of the American Physical Society (APS), after a nomination from the APS Division of Polymer Physics. | 7 | Physical Chemistry |
In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups (). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nitro group is also strongly electron-withdrawing. Because of this property, bonds alpha (adjacent) to the nitro group can be acidic. For similar reasons, the presence of nitro groups in aromatic compounds retards electrophilic aromatic substitution but facilitates nucleophilic aromatic substitution. Nitro groups are rarely found in nature. They are almost invariably produced by nitration reactions starting with nitric acid. | 0 | Organic Chemistry |
In 1941, science fiction writer Isaac Asimov published the science fiction short story "Reason", in which a space station transmits energy collected from the Sun to various planets using microwave beams. The SBSP concept, originally known as satellite solar-power system (SSPS), was first described in November 1968. In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g. from an SPS to Earth's surface) using microwaves from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a rectenna, on the ground.
Glaser then was a vice president at Arthur D. Little, Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems – chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space – it showed enough promise to merit further investigation and research. | 7 | Physical Chemistry |
If the catalyst is a moderate base such as hydroxide ion or an alkoxide, the aldol reaction occurs via nucleophilic attack by the resonance-stabilized enolate on the carbonyl group of another molecule. The product is the alkoxide salt of the aldol product. Then aldol, the aldol addition product itself is then formed.
After which it may undergo dehydration to give a unsaturated carbonyl compound, the aldol condensation product. The scheme shows a simple mechanism for the base-catalyzed aldol reaction of an aldehyde with itself.
Base-catalyzed aldol reaction
Base-catalyzed dehydration
Although only a catalytic amount of base is required in some cases, the more usual procedure is to use a stoichiometric amount of a strong base such as LDA or NaHMDS. In this case, enolate formation is irreversible, and the aldol product is not formed until the metal alkoxide of the aldol product is protonated in a separate workup step. | 0 | Organic Chemistry |
Hydroxyl groups (-OH), found in alcohols, are polar and therefore hydrophilic (water liking) but their carbon chain portion is non-polar which make them hydrophobic. The molecule increasingly becomes overall more nonpolar and therefore less soluble in the polar water as the carbon chain becomes longer. Methanol has the shortest carbon chain of all alcohols (one carbon atom) followed by ethanol (two carbon atoms), and 1-propanol along with its isomer 2-propanol, all being miscible with water. Tert-Butyl alcohol, with four carbon atoms, is the only one among its isomers to be miscible with water. | 6 | Supramolecular Chemistry |
In 1931, Paul Kubelka (with Franz Munk) published "An article on the optics of paint", the contents of which has come to be known as the Kubelka-Munk theory. They used absorption and remission (or back-scatter) constants, noting (as translated by Stephen H. Westin) that "an infinitesimal layer of the coating absorbs and scatters a certain constant portion of all the light passing through it". While symbols and terminology are changed here, it seems clear from their language that the terms in their differential equations stand for absorption and backscatter (remission) fractions. They also noted that the reflectance from an infinite number of these infinitesimal layers is "solely a function of the ratio of the absorption and back-scatter (remission) constants , but not in any way on the absolute numerical values of these constants". This turns out to be incorrect for layers of finite thickness, and the equation was modified for spectroscopic purposes (below), but Kubelka-Munk theory has found extensive use in coatings.
However, in revised presentations of their mathematical treatment, including that of Kubelka, Kortüm and Hecht (below), the following symbolism became popular, using coefficients rather than fractions:
* is the Absorption Coefficient ≡ the limiting fraction of absorption of light energy per unit thickness, as thickness becomes very small.
* is the Back-Scattering Coefficient ≡ the limiting fraction of light energy scattered backwards per unit thickness as thickness tends to zero. | 7 | Physical Chemistry |
The CCR family of receptors are a group of g-protein coupled receptors (GPCRs) that normally operate as chemokine receptors. They are primarily found on immunological cells, especially T-cells. CCR receptors are also expressed on neuronal cells, such as dendrites and microglia. Perhaps the most famous and well-studied of the CCR family is CCR5 (and its near-homologue CXCR4) which acts as the primary co-receptor for HIV viral infection. The HIV envelope glycoprotein GP120 binds to CD4 as its primary receptor, CCR5 then forms a complex with CD4 and HIV, allowing viral entry into the cell. CCR5 is not the only member of the CCR family that allows for HIV infection. Due to the commonality of structures found throughout the family, CCR2b, CCR3, and CCR8 can be utilized by some HIV strains as co-receptors to facilitate infection. CXCR4 is very similar to CCR5 in structure. While only some HIV strains can utilize CCR2b, CCR3 and CCR8, all HIV strains can infect through CCR5 and CXCR4.
CCR5 is known to have an affinity for macrophage inflammatory protein (MIP) and is thought to play a role in inflammatory immunological responses. The primary role of this receptor is less understood than its role in HIV infection, as inflammation responses remain a poorly understood facet of the immune system. CCR5's affinity for MIP makes it of great interest for practical applications such as tissue engineering, where attempts are being made to control host inflammatory and immunological responses at a cellular signalling level. The affinity for MIP has been utilized in-vitro to prevent HIV infection through ligand competition; however, these entry-inhibitors have failed in-vivo due to the highly adaptive nature of HIV and toxicity concerns. | 1 | Biochemistry |
Mixtures of cryoprotectants have less toxicity and are more effective than single-agent cryoprotectants. A mixture of formamide with DMSO (dimethyl sulfoxide), propylene glycol, and a colloid was for many years the most effective of all artificially created cryoprotectants. Cryoprotectant mixtures have been used for vitrification (i.e. solidification without crystal ice formation). Vitrification has important applications in preserving embryos, biological tissues and organs for transplant. Vitrification is also used in cryonics, in an effort to eliminate freezing damage. | 1 | Biochemistry |
According to Sazonov and Shaw, the Kuenen coefficient is defined as "the volume of saturating gas V(g), reduced to T° = 273.15 K, p° = bar, which is dissolved by unit mass of pure solvent at the temperature of measurement and partial pressure 1 bar." If the gas is ideal, the relation to is
where is the density of the solvent, and = 273.15 K. The SI unit for is m/kg. The Kuenen coefficient, which is named after Johannes Kuenen, has been used mainly in the older literature, and IUPAC considers it to be obsolete. | 7 | Physical Chemistry |
According to an ancient Hawaiian legend, on the island of Maui near the harbor of Hana there was a village of fishermen haunted by a curse. Upon their return from the sea, one of the fishermen would go missing. One day, enraged by another loss, the fishermen assaulted a hunchbacked hermit deemed to be the culprit of the town's misery. While ripping the cloak off the hermit the villagers were shocked because they uncovered rows of sharp and triangular teeth within huge jaws. A shark god had been caught. It was clear that the missing villagers had been eaten by the god on their journeys to the sea. The men mercilessly tore the shark god into pieces, burned him and threw the ashes into a tide pool near the harbor of Hana. Shortly after, a thick brown "moss" started to grow on the walls of the tide pool causing instant death to victims hit by spears smeared with the moss. Thus was the evil of the demon. The moss growing in the cursed tide pool became known as "limu-make-o-Hana" which literally means "seaweed of death from Hana." The Hawaiians believed that an ill curse came over them if they tried to collect the deadly "seaweed". | 0 | Organic Chemistry |
The red component of color television cathode ray tubes is typically emitted from an yttria () or yttrium oxide sulfide () host lattice doped with europium (III) cation (Eu) phosphors. The red color itself is emitted from the europium while the yttrium collects energy from the electron gun and passes it to the phosphor. Yttrium compounds can serve as host lattices for doping with different lanthanide cations. Tb can be used as a doping agent to produce green luminescence. As such yttrium compounds such as yttrium aluminium garnet (YAG) are useful for phosphors and are an important component of white LEDs.
Yttria is used as a sintering additive in the production of porous silicon nitride.
Yttrium compounds are used as a catalyst for ethylene polymerization. As a metal, yttrium is used on the electrodes of some high-performance spark plugs. Yttrium is used in gas mantles for propane lanterns as a replacement for thorium, which is radioactive. | 8 | Metallurgy |
Despite being one of the most abundant elements in the Earth's crust, iron is not readily bioavailable. In most aerobic environments, such as the soil or sea, iron exists in the ferric (Fe) state, which tends to form insoluble rust-like solids. To be effective, nutrients must not only be available, they must be soluble. Microbes release siderophores to scavenge iron from these mineral phases by formation of soluble Fe complexes that can be taken up by active transport mechanisms. Many siderophores are nonribosomal peptides, although several are biosynthesised independently.
Siderophores are also important for some pathogenic bacteria for their acquisition of iron. In mammalian hosts, iron is tightly bound to proteins such as hemoglobin, transferrin, lactoferrin and ferritin. The strict homeostasis of iron leads to a free concentration of about 10 mol L, hence there are great evolutionary pressures put on pathogenic bacteria to obtain this metal. For example, the anthrax pathogen Bacillus anthracis releases two siderophores, bacillibactin and petrobactin, to scavenge ferric ion from iron containing proteins. While bacillibactin has been shown to bind to the immune system protein siderocalin, petrobactin is assumed to evade the immune system and has been shown to be important for virulence in mice.
Siderophores are amongst the strongest binders to Fe known, with enterobactin being one of the strongest of these. Because of this property, they have attracted interest from medical science in metal chelation therapy, with the siderophore desferrioxamine B gaining widespread use in treatments for iron poisoning and thalassemia.
Besides siderophores, some pathogenic bacteria produce hemophores (heme binding scavenging proteins) or have receptors that bind directly to iron/heme proteins. In eukaryotes, other strategies to enhance iron solubility and uptake are the acidification of the surroundings (e.g. used by plant roots) or the extracellular reduction of Fe into the more soluble Fe ions. | 1 | Biochemistry |
Control of petroleum production has been a significant driver of international relations during much of the 20th and 21st centuries. Organizations like OPEC have played an outsized role in international politics. Some historians and commentators have called this the "Age of Oil" With the rise of renewable energy and addressing climate change some commentators expect a realignment of international power away from petrostates. | 7 | Physical Chemistry |
In 2014, a 72-year-old man from Falmouth died at the site after what was initially thought to be a cycling accident. It was later found that the man had been murdered. A 34-year-old was found guilty and sentenced to life and to serve at least 28 years. | 2 | Environmental Chemistry |
Substituting for f the Metropolis function defined above (which satisfies the detailed balance condition), and setting C to zero, gives
The advantage of this formulation (apart from its simplicity) is that it can be computed without performing two simulations, one in each specific ensemble. Indeed, it is possible to define an extra kind of "potential switching" Metropolis trial move (taken every fixed number of steps), such that the single sampling from the "mixed" ensemble suffices for the computation. | 7 | Physical Chemistry |
An agrochemical or agrichemical, a contraction of agricultural chemical, is a chemical product used in industrial agriculture. Agrichemical refers to biocides (pesticides including insecticides, herbicides, fungicides and nematicides) and synthetic fertilizers. It may also include hormones and other chemical growth agents.
Agrochemicals are counted among speciality chemicals. | 2 | Environmental Chemistry |
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