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The theory behind experimental archaeology comes from the new archaeology technique of the 1950s to use modern day examples in the form of experiments and ethnologies as analogues to past processes. Experimental archaeometallurgy is considered a part of general experimental archaeology and is rarely separated in the literature and as such, many of the principles stay the same while there is a greater focus on a single subject.
Archaeometallurgy works as a good field for experimental reproduction because of the evidence that is provided from excavation is a good starting point for reconstruction. Metallurgical remains provide a durable product that has relatively durable evidence of production methods such as slag and refractory ceramic remains. Experimentation comes in a varied amount of forms including object replication, system replication, behavioral replication, and process replication. | 8 | Metallurgy |
Yttrium is a soft, silver-metallic, lustrous and highly crystalline transition metal in group 3. As expected by periodic trends, it is less electronegative than its predecessor in the group, scandium, and less electronegative than the next member of period 5, zirconium. However, due to the lanthanide contraction, it is also less electronegative than its successor in the group, lutetium. Yttrium is the first d-block element in the fifth period.
The pure element is relatively stable in air in bulk form, due to passivation of a protective oxide () film that forms on the surface. This film can reach a thickness of 10 µm when yttrium is heated to 750 °C in water vapor. When finely divided, however, yttrium is very unstable in air; shavings or turnings of the metal can ignite in air at temperatures exceeding 400 °C. Yttrium nitride (YN) is formed when the metal is heated to 1000 °C in nitrogen. | 8 | Metallurgy |
Free energies in the presence of small amplitude fluctuations, e.g. in concentration, can be evaluated using an approximation introduced by Ginzburg and Landau to describe magnetic field gradients in superconductors. This approach allows one to approximate the free energy as an expansion in terms of the concentration gradient , a vector. Since free energy is a scalar and we are probing near its minima, the term proportional to is negligible. The lowest order term is the quadratic expression , a scalar. Here is a parameter that controls the free energy cost of variations in concentration .
The Cahn–Hilliard free energy is then
where is the bulk free energy per unit volume of the homogeneous solution, and the integral is over the volume of the system.
We now want to study the stability of the system with respect to small fluctuations in the concentration , for example a sine wave of amplitude and wavevector , for the wavelength of the concentration wave. To be thermodynamically stable, the free energy change due to any small amplitude concentration fluctuation , must be positive.
We may expand about the average composition c as follows:
:and for the perturbation the free energy change is
:when this is integrated over the volume , the gives zero, while . So, then
As , thermodynamic stability requires that the term in brackets be positive. The is always positive but tends to zero at small wavevectors, large wavelengths. Since we are interested in macroscopic fluctuations, , stability requires that the second derivative of the free energy be positive. When it is, there is no spinodal decomposition, but when it is negative, spinodal decomposition will occur. Then fluctuations with wavevectors become spontaneously unstable, where the critical wave number is given by:
:which corresponds to a fluctuations above a critical wavelength | 7 | Physical Chemistry |
Carbohydrate NMR spectroscopy is the application of nuclear magnetic resonance (NMR) spectroscopy to structural and conformational analysis of carbohydrates. This method allows the scientists to elucidate structure of monosaccharides, oligosaccharides, polysaccharides, glycoconjugates and other carbohydrate derivatives from synthetic and natural sources. Among structural properties that could be determined by NMR are primary structure (including stereochemistry), saccharide conformation, stoichiometry of substituents, and ratio of individual saccharides in a mixture. Modern high field NMR instruments used for carbohydrate samples, typically 500 MHz or higher, are able to run a suite of 1D, 2D, and 3D experiments to determine a structure of carbohydrate compounds. | 0 | Organic Chemistry |
Borane–tetrahydrofuran is an adduct derived from borane and tetrahydrofuran (THF). These solutions, which are colorless, are used for reductions and hydroboration, reactions that are useful in synthesis of organic compounds. The use of borane–tetrahydrofuran has been displaced by borane–dimethylsulfide, which has a longer shelf life and effects similar transformations. | 0 | Organic Chemistry |
LFTs derive from paper chromatography, which was developed in 1943 by Martin and Synge, and elaborated in 1944 by Consden, Gordon and Martin. There was an explosion of activity in this field after 1945. The ELISA technology was developed in 1971. A set of LFT patents, including the litigated US 6,485,982 described below, were filed by Armkel LLC starting in 1988. | 1 | Biochemistry |
Bronze Age goldwork is marked by an elegant simplicity of design and fine execution, with decoration usually restricted to relatively simple geometric patterns such as parallel lines, chevron, zig-zag and circular patterns, often extremely small and perfectly executed, especially in Ireland, as can be seen by enlarging the lunula and Irish bracelet illustrated. The objects are nearly all pieces of jewellery, and include clothes-fasteners (somewhat like large one-piece cuff-links), torcs, bracelets, gold lunulae, smaller ornaments that were perhaps worn in the ear, nose or hair, or on clothing as brooches, and a range of thin disc or plaques probably sewn to clothing or worn in the hair. The ends of objects that are essentially bars bent into a round shape often thicken before ending in a flat or concave face, as for example in the Milton Keynes Hoard. The thickening is typically slight in torcs and bracelets, but extreme in clothes fasteners and ear decorations. Tightly wound spirals in pairs are popular, as they were on the continent. | 8 | Metallurgy |
In contrast to the rarity of Möbius aromatic ground state molecular systems, there are many examples of pericyclic transition states that exhibit Möbius aromaticity. The classification of a pericyclic transition state as either Möbius or Hückel topology determines whether 4N or 4N + 2 electrons are required to make the transition state aromatic or antiaromatic, and therefore, allowed or forbidden, respectively. Based on the energy level diagrams derived from Hückel MO theory, (4N + 2)-electron Hückel and (4N)-electron Möbius transition states are aromatic and allowed, while (4N + 2)-electron Möbius and (4N)-electron Hückel transition states are antiaromatic and forbidden. This is the basic premise of the Möbius-Hückel concept. | 7 | Physical Chemistry |
Photocyclization can be used as the final step of a sequence to generate a fused aromatic ring at a benzylic position. After benzylic bromization with N-bromosuccinimide, transformation to the phosphonium salt, and a Wittig reaction with anaromatic aldehyde, photocyclization fuses the aromatic rings. Iteration of this sequence results in helicenes. | 5 | Photochemistry |
Compounds that were historically given the formulae REAlB and REB have the MgAlB structure with an orthorhombic symmetry and space group Imma (No. 74). In this structure, rare-earth atoms enter the Mg site. Aluminium sites are empty for REB. Both metal sites of REAlB structure have partial occupancies of about 60–70%, which shows that the compounds are actually non-stoichiometric. The REB formula merely reflects the average atomic ratio [B]/[RE] = 25. Yttrium borides form both YAlB and YB structures. Experiments have confirmed that the borides based on rare-earth elements from Tb to Lu can have the REAlB structure. A subset of these borides, which contains rare-earth elements from Gd to Er, can also crystallize in the REB structure.
Korsukova et al. analyzed the YAlB crystal structure using a single crystal grown by the high-temperature solution-growth method. The lattice constants were deduced as a = 0.58212(3), b = 1.04130(8) and c = 0.81947(6) nm, and the atomic coordinates and site occupancies are summarized in table I.
Figure 3 shows the crystal structure of YAlB viewed along the x-axis. The large black spheres are Y atoms, the small blue spheres are Al atoms and the small green spheres are the bridging boron sites; B clusters are depicted as the green icosahedra. Boron framework of YAlB is one of the simplest among icosahedron-based borides – it consists of only one kind of icosahedra and one bridging boron site. The bridging boron site is tetrahedrally coordinated by four boron atoms. Those atoms are another boron atom in the counter bridge site and three equatorial boron atoms of one of three B icosahedra. Aluminium atoms are separated by 0.2911 nm and are arranged in lines parallel to the x-axis, whereas yttrium atoms are separated by 0.3405 nm. Both the Y atoms and B icosahedra form zigzags along the x-axis. The bridging boron atoms connect three equatorial boron atoms of three icosahedra and those icosahedra make up a network parallel to the (101) crystal plane (x-z plane in the figure). The bonding distance between the bridging boron and the equatorial boron atoms is 0.1755 nm, which is typical for the strong covalent B-B bond (bond length 0.17–0.18 nm); thus, the bridging boron atoms strengthen the individual network planes. On the other hand, the large distance between the boron atoms within the bridge (0.2041 nm) suggests weaker interaction, and thus the bridging sites contribute little to the bonding between the network planes.
The boron framework of YAlB needs donation of four electrons from metal elements: two electrons for a B icosahedron and one electron for each of the two bridging boron atoms – to support their tetrahedral coordination. The actual chemical composition of YAlB, determined by the structure analysis, is YAlB as described in table I. If both metal elements are trivalent ions then 3.99 electrons can be transferred to the boron framework, which is very close to the required value of 4. However, because the bonding between the bridging boron atoms is weaker than in a typical B-B covalent bond, less than 2 electrons are donated to this bond, and metal atoms need not be trivalent. On the other hand, the electron transfer from metal atoms to the boron framework implies that not only strong covalent B-B bonding within the framework but also ionic interaction between metal atoms and the framework contribute to the YAlB phase stabilization. | 3 | Analytical Chemistry |
The theory of solar cells explains the process by which light energy in photons is converted into electric current when the photons strike a suitable semiconductor device. The theoretical studies are of practical use because they predict the fundamental limits of a solar cell, and give guidance on the phenomena that contribute to losses and solar cell efficiency. | 7 | Physical Chemistry |
Studies have shown that deletion of KAP1 in mice before gastrulation results in death (implicating it as a necessary protein for proliferation) while deletion in adult mice results in increased anxiety and stress-induced alterations in learning and memory. KAP1 has been shown to participate in the maintenance of pluripotency of embryonic stem cells and to promote and inhibit cellular differentiation of adult cell lines. Increased levels of KAP1 have been found in liver, gastric, breast, lung, and prostate cancers as well, indicating that it may play an important role in tumor cell proliferation (possibly by inhibiting apoptosis). | 1 | Biochemistry |
The simplest monoalkene is ethene. Many complexes of ethene are known, including Zeise's salt (see figure), RhCl(CH), Cp*Ti(CH), and the homoleptic Ni(CH). Substituted monoalkene include the cyclic cyclooctene, as found in chlorobis(cyclooctene)rhodium dimer. Alkenes with electron-withdrawing groups commonly bind strongly to low-valent metals. Examples of such ligands are TCNE, tetrafluoroethylene, maleic anhydride, and esters of fumaric acid. These acceptors form adducts with many zero-valent metals. | 0 | Organic Chemistry |
Peptide plane flipping is a type of conformational change that can occur in proteins by which the dihedral angles of adjacent amino acids undergo large-scale rotations with little displacement of the side chains. The plane flip is defined as a rotation of the dihedral angles φ,ψ at amino acids i and i+1 such that the resulting angles remain in structurally stable regions of Ramachandran space. The key requirement is that the sum of the ψ angle of residue i and the φ angle of residue i+1 remain roughly constant; in effect, the flip is a crankshaft move about the axis defined by the C-C¹ and N-C bond vectors of the peptide group, which are roughly parallel. As an example, the type I and type II beta turns differ by a simple flip of the central peptide group of the turn. | 1 | Biochemistry |
A P1-derived artificial chromosome, or PAC, is a DNA construct derived from the DNA of P1 bacteriophages and Bacterial artificial chromosome. It can carry large amounts (about 100–300 kilobases) of other sequences for a variety of bioengineering purposes in bacteria. It is one type of the efficient cloning vector used to clone DNA fragments (100- to 300-kb insert size; average,150 kb) in Escherichia coli cells. | 1 | Biochemistry |
The technique initially incubates a small amount of abnormal prion with an excess of normal protein, so that some conversion takes place. The growing chain of misfolded protein is then blasted with ultrasound, breaking it down into smaller chains and so rapidly increasing the amount of abnormal protein available to cause conversions. By repeating the cycle, the mass of normal protein is rapidly changed into the prion being tested for. | 1 | Biochemistry |
The yeast mediator complex is approximately as massive as a small subunit of a eukaryotic ribosome. The yeast mediator is composed of 25 subunits, while the mammalian mediator complexes are slightly larger. Mediator can be divided into 4 main parts: The head, middle, tail, and the transiently associated CDK8 kinase module.
Mediator subunits have many intrinsically disordered regions called "splines", which may be important to allow the structural changes of the mediator that change the function of the complex. The figure shows how the splines of the Med 14 subunit connect a large portion of the complex together while still allowing flexibility.
Mediator complexes that lack a subunit have been found or produced. These smaller mediators can still function normally in some activity, but lack other capabilities. This indicates a somewhat independent function of some of the subunits while being part of the larger complex.
Another example of structural variability is seen in vertebrates, in which 3 paralogues of subunits of the cyclin-dependent kinase module have evolved by 3 independent gene duplication events followed by sequence divergence. There is a report that mediator forms stable associations with a particular type of non-coding RNA, ncRNA-a. These stable associations have also been shown to regulate gene expression in vivo, and are prevented by mutations in MED12 that produce the human disease FG syndrome. Thus, the structure of a mediator complex can be augmented by RNA as well as proteinaceous transcription factors. | 1 | Biochemistry |
Alkylating agents are a type of chemotherapeutic drug which keeps the cell from undergoing mitosis by damaging its DNA. They work in all phases of the cell cycle. The use of alkylating agents may result in leukemia due to them being able to target the cells of the bone marrow. | 1 | Biochemistry |
Isocyanates also can react with themselves. Aliphatic diisocyanates can trimerise to from substituted isocyanuric acid groups. This can be seen in the formation of polyisocyanurate resins (PIR) which are commonly used as rigid thermal insulation. Isocyanates participate in Diels–Alder reactions, functioning as dienophiles. | 0 | Organic Chemistry |
Other lake constituents can influence lake metabolic rates including CO concentration, pH, salinity, and silica, among others. CO can be a limiting (or co-limiting along with other nutrients) resource for primary productivity and can promote more intense phytoplankton blooms. Some algal species, such as chrysophytes, may not have carbon-concentrating mechanisms or the ability to use bicarbonate as a source of inorganic carbon for photosynthesis, thus, elevated levels of CO may increase their rates of photosynthesis. During algal blooms, elevated dissolved CO ensures that CO is not a limiting resource for growth since rapid increases in production deplete CO and raise pH. Changes in pH at short time scales (e.g. sub-daily) from spikes in primary productivity may cause short-term reductions in bacterial growth and respiration, but at longer timescales, bacterial communities can adapt to elevated pH.
Salinity can also cause changes in metabolic rates of lakes through salinity impacts on individual metabolic rates and community composition. Lake metabolic rates can be correlated both positively or negatively with salinity due to interactions of salinity with other drivers of ecosystem metabolism, such as flushing rates or droughts. For example, Moreira-Turcq (2000) found that excess precipitation over evaporation caused reduced salinity in a coastal lagoon, increased nutrient loading, and increased pelagic primary productivity. The positive relationship between primary productivity and salinity might be an indicator of changes in nutrient availability due to increased inflows. However, salinity increases from road salts can cause toxicity in some lake organisms, and extreme cases of salinity increases can restrict lake mixing which could change distribution of metabolism rates throughout the lake water column. | 1 | Biochemistry |
If the enthalpy and entropy are roughly constant as temperature varies over a certain range, then the Van 't Hoff plot is approximately linear when plotted over that range. However, in some cases the enthalpy and entropy do change dramatically with temperature. A first-order approximation is to assume that the two different reaction products have different heat capacities. Incorporating this assumption yields an additional term in the expression for the equilibrium constant as a function of temperature. A polynomial fit can then be used to analyze data that exhibits a non-constant standard enthalpy of reaction:
where
Thus, the enthalpy and entropy of a reaction can still be determined at specific temperatures even when a temperature dependence exists. | 7 | Physical Chemistry |
This complex is used as an indicator in analytical chemistry. The active ingredient is the [Fe(o-phen)] ion, which is a chromophore that can be oxidized to the ferric derivative [Fe(o-phen)]. The potential for this redox change is +1.06 volts in 1 M HSO. It is a popular redox indicator for visualizing oscillatory Belousov–Zhabotinsky reactions.
Ferroin is suitable as a redox indicator, as the color change is reversible, very pronounced and rapid, and the ferroin solution is stable up to 60 °C. It is the main indicator used in cerimetry.
Nitroferroin, the complex of iron(II) with 5-nitro-1,10-phenanthroline, has transition potential of +1.25 volts. It is more stable than ferroin, but in sulfuric acid with Ce ion it requires significant excess of the titrant. It is however useful for titration in perchloric acid or nitric acid solution, where cerium redox potential is higher.
The redox potential of the iron-phenanthroline complex can be varied between +0.84 V and +1.10 V by adjusting the position and number of methyl groups on the phenanthroline core. | 3 | Analytical Chemistry |
Hand boilers date back at least as early as 1767, when the American polymath Benjamin Franklin encountered them in Germany. He developed an improved version in 1768, after which they were called Franklins pulse glass or palm glass or pulse hammer (German: Pulshammer) or water hammer (German: Wasserhammer'). | 7 | Physical Chemistry |
Phosphate affinity electrophoresis utilizes an affinity probe which consists of a molecule that binds specifically to divalent phosphate ions in neutral aqueous solution, known as a "Phos-Tag". This methods also utilizes a separation gel made of an acrylamide-pendent Phos-Tag monomer that is copolymerized. Phosphorylated proteins migrate slowly in the gel compared to non-phosphorylated proteins. This technique gives the researcher the ability to observe the differences in the phosphorylation states of any given protein. This technique allows for the detection of distinct bands even in protein molecules that have the same amount of phosphorylated amino acid residues but are phosphorylated at different amino acid locations. | 1 | Biochemistry |
The enzyme phenylalanine racemase (, phenylalanine racemase, phenylalanine racemase (adenosine triphosphate-hydrolysing), gramicidin S synthetase I) is the enzyme that acts on amino acids and derivatives. It activates both the L & D stereo isomers of phenylalanine to form L-phenylalanyl adenylate and D-phenylalanyl adenylate, which are bound to the enzyme. These bound compounds are then transferred to the thiol group of the enzyme followed by conversion of its configuration, the D-isomer being the more favorable configuration of the two, with a 7 to 3 ratio between the two isomers. The racemisation reaction of phenylalanine is coupled with the highly favorable hydrolysis of adenosine triphosphate (ATP) to adenosine monophosphate (AMP) and pyrophosphate (PP), thermodynamically allowing it to proceed. This reaction is then drawn forward by further hydrolyzing PP to inorganic phosphate (P), via Le Chatelier's principle. | 1 | Biochemistry |
Relativistic heat conduction refers to the modelling of heat conduction (and similar diffusion processes) in a way compatible with special relativity. In special (and general) relativity, the usual heat equation for non-relativistic heat conduction must be modified, as it leads to faster-than-light signal propagation. Relativistic heat conduction, therefore, encompasses a set of models for heat propagation in continuous media (solids, fluids, gases) that are consistent with relativistic causality, namely the principle that an effect must be within the light-cone associated to its cause. Any reasonable relativistic model for heat conduction must also be stable, in the sense that differences in temperature propagate both slower than light and are damped over time (this stability property is intimately intertwined with relativistic causality). | 7 | Physical Chemistry |
X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy for complete structural analysis of complex glycans is a difficult and complex field. However, the structure of the binding site of numerous lectins, enzymes and other carbohydrate-binding proteins have revealed a wide variety of the structural basis for glycome function. The purity of test samples have been obtained through chromatography (affinity chromatography etc.) and analytical electrophoresis (PAGE (polyacrylamide electrophoresis), capillary electrophoresis, affinity electrophoresis, etc.). | 0 | Organic Chemistry |
hnRNPs also play a role in DNA damage response in coordination with p53. hnRNP K is rapidly induced after DNA damage by ionizing radiation. It cooperates with p53 to induce the activation of p53 target genes, thus activating cell-cycle checkpoints. p53 itself is an important tumor-suppressor gene sometimes known by the epithet “the guardian of the genome.” hnRNP K’s close association with p53 demonstrates its importance in DNA damage control.
p53 regulates a large group of RNAs that are not translated into protein, called large intergenic noncoding RNAs (lincRNAs). p53 suppression of genes is often carried out by a number of these lincRNAs, which in turn have been shown to act though hnRNP K. Through physical interactions with these molecules, hnRNP K is targeted to genes and transmits p53 regulation, thus acting as a key repressor within the p53-dependent transcriptional pathway. | 1 | Biochemistry |
Green sulfur bacteria contain a photosystem that is analogous to PSI in chloroplasts:
P840 → P840 → ferredoxin → NADH
cyt c ← bc ← menaquinol
There are two pathways of electron transfer. In cyclic electron transfer, electrons are removed from an excited chlorophyll molecule, passed through an electron transport chain to a proton pump, and then returned to the chlorophyll. The mobile electron carriers are, as usual, a lipid-soluble quinone and a water-soluble cytochrome. The resulting proton gradient is used to make ATP.
In noncyclic electron transfer, electrons are removed from an excited chlorophyll molecule and used to reduce NAD to NADH. The electrons removed from P840 must be replaced. This is accomplished by removing electrons from , which is oxidized to sulfur (hence the name "green sulfur bacteria").
Purple bacteria and green sulfur bacteria occupy relatively minor ecological niches in the present day biosphere. They are of interest because of their importance in precambrian ecologies, and because their methods of photosynthesis were the likely evolutionary precursors of those in modern plants. | 5 | Photochemistry |
Molecular medicine is a new scientific discipline in European universities. Combining contemporary medical studies with the field of biochemistry, it offers a bridge between the two subjects. At present only a handful of universities offer the course to undergraduates. With a degree in this discipline, the graduate is able to pursue a career in medical sciences, scientific research, laboratory work, and postgraduate medical degrees. | 1 | Biochemistry |
Electrophilic fluorinating reagents could in principle operate by electron transfer pathways or an S2 attack at fluorine. This distinction has not been decided. By using a charge-spin separated probe, it was possible to show that the electrophilic fluorination of stilbenes with Selectfluor proceeds through an SET/fluorine atom transfer mechanism.
In certain cases Selectfluor can transfer fluorine to alkyl radicals. | 0 | Organic Chemistry |
Ethylene – π
In the most simple linear π systems, bonding to metals takes place by two interactions. Electron density is donated directly to the metal like a sigma bond would be formed. Also, the metal can donate electron density back to the linear π system (ethylene) from the metal's d orbital to the empty π* orbital of ethylene.
Allyl–π
Allyl groups can bond to metals as trihapto or monohapto ligands. Monohapto ligands bind mostly sigma orbitals and trihapto ligands bind using delocalized π orbitals. In essence the monohapto ligand binds the metal as an allyl group and the trihapto ligand binds over all three carbons, where the lowest energy π orbital donates electron density and the highest energy π orbital accepts electron density.
The allyl complex is diverse because it can alter the metal's electron count by transferring between a monohapto (1 electron, η) and trihapto ligand (3 electrons, η). This fluctuation allows stability when a two-electron-donating group bonds or breaks from the metal. | 6 | Supramolecular Chemistry |
The chloroplasts of some hornworts and algae contain structures called pyrenoids. They are not found in higher plants. Pyrenoids are roughly spherical and highly refractive bodies which are a site of starch accumulation in plants that contain them. They consist of a matrix opaque to electrons, surrounded by two hemispherical starch plates. The starch is accumulated as the pyrenoids mature. In algae with carbon concentrating mechanisms, the enzyme RuBisCO is found in the pyrenoids. Starch can also accumulate around the pyrenoids when CO is scarce. Pyrenoids can divide to form new pyrenoids, or be produced "de novo". | 5 | Photochemistry |
Heat capacity is a measurable physical quantity equal to the ratio of the heat added to an object to the resulting temperature change. The molar heat capacity is the heat capacity per unit amount (SI unit: mole) of a pure substance, and the specific heat capacity, often called simply specific heat, is the heat capacity per unit mass of a material. Heat capacity is a physical property of a substance, which means that it depends on the state and properties of the substance under consideration.
The specific heats of monatomic gases, such as helium, are nearly constant with temperature. Diatomic gases such as hydrogen display some temperature dependence, and triatomic gases (e.g., carbon dioxide) still more.
Before the development of the laws of thermodynamics, heat was measured by changes in the states of the participating bodies.
Some general rules, with important exceptions, can be stated as follows.
In general, most bodies expand on heating. In this circumstance, heating a body at a constant volume increases the pressure it exerts on its constraining walls, while heating at a constant pressure increases its volume.
Beyond this, most substances have three ordinarily recognized states of matter, solid, liquid, and gas. Some can also exist in a plasma. Many have further, more finely differentiated, states of matter, such as glass and liquid crystal. In many cases, at fixed temperature and pressure, a substance can exist in several distinct states of matter in what might be viewed as the same body. For example, ice may float in a glass of water. Then the ice and the water are said to constitute two phases within the body. Definite rules are known, telling how distinct phases may coexist in a body. Mostly, at a fixed pressure, there is a definite temperature at which heating causes a solid to melt or evaporate, and a definite temperature at which heating causes a liquid to evaporate. In such cases, cooling has the reverse effects.
All of these, the commonest cases, fit with a rule that heating can be measured by changes of state of a body. Such cases supply what are called thermometric bodies, that allow the definition of empirical temperatures. Before 1848, all temperatures were defined in this way. There was thus a tight link, apparently logically determined, between heat and temperature, though they were recognized as conceptually thoroughly distinct, especially by Joseph Black in the later eighteenth century.
There are important exceptions. They break the obviously apparent link between heat and temperature. They make it clear that empirical definitions of temperature are contingent on the peculiar properties of particular thermometric substances, and are thus precluded from the title absolute. For example, water contracts on being heated near 277 K. It cannot be used as a thermometric substance near that temperature. Also, over a certain temperature range, ice contracts on heating. Moreover, many substances can exist in metastable states, such as with negative pressure, that survive only transiently and in very special conditions. Such facts, sometimes called anomalous, are some of the reasons for the thermodynamic definition of absolute temperature.
In the early days of measurement of high temperatures, another factor was important, and used by Josiah Wedgwood in his pyrometer. The temperature reached in a process was estimated by the shrinkage of a sample of clay. The higher the temperature, the more the shrinkage. This was the only available more or less reliable method of measurement of temperatures above 1000 °C (1,832 °F). But such shrinkage is irreversible. The clay does not expand again on cooling. That is why it could be used for the measurement. But only once. It is not a thermometric material in the usual sense of the word.
Nevertheless, the thermodynamic definition of absolute temperature does make essential use of the concept of heat, with proper circumspection. | 7 | Physical Chemistry |
A formerly unknown derivative of palytoxin, ovatoxin-a, produced as a marine aerosol by the tropical dinoflagellate Ostreopsis ovata caused hundreds of people in Genoa, Italy, to fall ill. In 2005 and 2006 blooms of these algae occurred in the Mediterranean sea. All those affected needed hospitalization. Symptoms were high fever, coughs and wheezes. | 0 | Organic Chemistry |
Surface-enhanced laser desorption/ionization (SELDI) is a soft ionization method in mass spectrometry (MS) used for the analysis of protein mixtures. It is a variation of matrix-assisted laser desorption/ionization (MALDI). In MALDI, the sample is mixed with a matrix material and applied to a metal plate before irradiation by a laser, whereas in SELDI, proteins of interest in a sample become bound to a surface before MS analysis. The sample surface is a key component in the purification, desorption, and ionization of the sample. SELDI is typically used with time-of-flight (TOF) mass spectrometers and is used to detect proteins in tissue samples, blood, urine, or other clinical samples, however, SELDI technology can potentially be used in any application by simply modifying the sample surface. | 1 | Biochemistry |
Rosin fluxes are categorized by grades of activity: L for low, M for moderate, and H for high. There are also other abbreviations for different rosin flux grades:
* R (Rosin) – pure rosin, no activators, low activity, mildest
* WW (water-white) – purest rosin grade, no activators, low activity, sometimes synonymous with R
* RMA (rosin mildly activated) - contains mild activators, typically no halides
* RA (rosin activated) – rosin with strong activators, high activity, contains halides
* OA (organic acid) – rosin activated with organic acids, high activity, highly corrosive, aqueous cleaning
* SA (synthetically activated) – rosin with strong synthetic activators, high activity; formulated to be easily soluble in organic solvents (chlorofluorocarbons, alcohols) to facilitate cleaning
* WS (water-soluble) – usually based on inorganic or organic halides; highly corrosive residues
* SRA (superactivated rosin) – rosin with very strong activators, very high activity
* IA (inorganic acid) – rosin activated with inorganic acids (usually hydrochloric acid or phosphoric acid), highest activities, highly corrosive
R, WW, and RMA grades are used for joints that can not be easily cleaned or where there is too high corrosion risk. More active grades require thorough cleaning of the residues. Improper cleaning can actually aggravate the corrosion by releasing trapped activators from the flux residues. | 8 | Metallurgy |
Examples of simple tests are shown below that rely on the production of the molybdenum blue colour either due to reduction:
*tests for Sn(II) and Sb(III)
*tests for organic reducing agents
or by detection of the heteroatom
*silicate
*phosphate
Dittmer's spray reagent for phospholipids is used in thin layer chromatography to detect phospholipids. The spray reagent is prepared as follows:
*Molybdenum(VI) oxide, MoO, is dissolved in sulfuric acid
*A second solution is made up from molybdenum metal dissolved in some of the first solution.
*The spray is made up of a diluted mixture of the first and second solutions.
When applied to the TLC plate, compounds containing phosphate ester show up immediately as blue spots. | 7 | Physical Chemistry |
The Uncompahgre Ute indigenous people from Central Colorado are one of the first documented groups of people in the world credited with the application of mechanoluminescence involving the use of quartz crystals to generate light. The Ute constructed unique ceremonial rattles made from buffalo rawhide which they filled with clear quartz crystals collected from the mountains of Colorado and Utah. When the rattles were shaken at night during ceremonies, the friction and mechanical stress of the quartz crystals impacting together produced flashes of light visible through the translucent buffalo hide. | 5 | Photochemistry |
(AD 900–1500)
Utilitarian and ceremonial objects; objects of personal adornment
#Chiapa de Corzo, Chiapas
#El Paredón, Chiapas
#Polol, Guatemala
#Santa Rita Corozal, Belize
#Nojpetén, Guatemala
#Tikal, Guatemala
#Yaxhá, Guatemala
#Palenque, Chiapas
#Wild Cane Cay, Belize
#Lamanai, Belize | 8 | Metallurgy |
Despite receiving considerable focus, the glycobiological literature do not contain evidence for the presence of paucimannosidic proteins within Fungi. Fungal species within this kingdom are therefore considered devoid of protein paucimannosylation and instead carry high mannosylated N-glycoproteins comprising extended and branched mannose-decorated antennae. | 1 | Biochemistry |
An energy diagram can be created based on the Enthalpy of Reaction of the individual steps. The energy diagram can be used to compare homogeneous and heterogeneous reactions: Due to the high activation energy of the dissociation of nitrogen, the homogeneous gas phase reaction is not realizable. The catalyst avoids this problem as the energy gain resulting from the binding of nitrogen atoms to the catalyst surface overcompensates for the necessary dissociation energy so that the reaction is finally exothermic. Nevertheless, the dissociative adsorption of nitrogen remains the rate-determining step: not because of the activation energy, but mainly because of the unfavorable pre-exponential factor of the rate constant. Although hydrogenation is endothermic, this energy can easily be applied by the reaction temperature (about 700 K). | 7 | Physical Chemistry |
Molecular interactions can occur between molecules belonging to different biochemical families (proteins, nucleic acids, lipids, carbohydrates, etc.) and also within a given family. Whenever such molecules are connected by physical interactions, they form molecular interaction networks that are generally classified by the nature of the compounds involved. Most commonly, interactome refers to protein–protein interaction (PPI) network (PIN) or subsets thereof. For instance, the Sirt-1 protein interactome and Sirt family second order interactome is the network involving Sirt-1 and its directly interacting proteins where as second order interactome illustrates interactions up to second order of neighbors (Neighbors of neighbors). Another extensively studied type of interactome is the protein–DNA interactome, also called a gene-regulatory network, a network formed by transcription factors, chromatin regulatory proteins, and their target genes. Even metabolic networks can be considered as molecular interaction networks: metabolites, i.e. chemical compounds in a cell, are converted into each other by enzymes, which have to bind their substrates physically.
In fact, all interactome types are interconnected. For instance, protein interactomes contain many enzymes which in turn form biochemical networks. Similarly, gene regulatory networks overlap substantially with protein interaction networks and signaling networks. | 1 | Biochemistry |
On 28 March 2017, Drahoš announced his intention to stand in the 2018 presidential election. On 24 April 2017, he started gathering the signatures required to be registered as a candidate. In July 2017, after meeting with Drahoš, the leaders of Populars and Mayors, Pavel Bělobrádek and Petr Gazdík, announced that they would ask their respective parties members to nominate and endorse Drahošs candidacy. Mayors and Independents endorsed Drahoš on 25 July 2017 while the Christian and Democratic Union – Czechoslovak People's Party (KDU–ČSL) endorsed him on 14 November 2017. Young Social Democrats also endorsed Drahoš on 9 December 2017. Polls in late 2017 showed Drahoš as the second strongest candidate behind Zeman.
Drahoš received campaign donations from several influential businessmen, including Dalibor Dědek, Jiří Grygar and Luděk Sekyra. Drahoš started gathering signatures for his nomination in May 2017. On 19 August 2017, Drahoš announced he had gathered 78,000 signatures. He submitted his nomination on 3 November 2017 with 142,000 signatures.
On 4 November 2017 on Facebook, Drahoš criticized Mirek Topolánek, who had announced his candidacy that day, describing Topolánek as similar to Miloš Zeman and calling his candidacy a bad joke. The two candidates met during a presidential debate at Charles University; Drahoš reflected that the status he posted was "Topolánek-like", to which Topolánek replied that it was written either by "a woman or PR mage".
Drahoš received media attention when he expressed his fear that the election could be influenced by Russia. He met outgoing Prime Minister Bohuslav Sobotka to discuss the matter and stated he would also meet the new Prime Minister Andrej Babiš. The incumbent president Miloš Zeman criticized Drahoš and compared his actions to Hillary Clinton's when she lost to Donald Trump.
Drahoš received criticism when he published a status on social media about Václav Klaus' amnesty, when it was revealed that he had copied a similar status by his fellow presidential candidate Michal Horáček. Drahoš apologised and attributed the mistake to an external member of staff.
The first round was held on 12 and 13 January 2018. Drahoš received 1,369,601 (26.6%) votes, and advanced to the second round against the incumbent president Miloš Zeman. In the second round, held on 26–27 January 2018, Drahoš received 48.63% of the vote and thus lost to Zeman. Drahoš conceded defeat to Zeman, telling a crowd of his supporters that "I would like to congratulate election winner Miloš Zeman". | 7 | Physical Chemistry |
The reactions in this category behave like a clock reaction, however they are irreproducible, unpredictable and hard to control. Examples are chlorite/thiosulfate and iodide/chlorite reactions. | 7 | Physical Chemistry |
The metal-carbon bond in organometallic compounds is generally highly covalent. For highly electropositive elements, such as lithium and sodium, the carbon ligand exhibits carbanionic character, but free carbon-based anions are extremely rare, an example being cyanide.
Most organometallic compounds are solids at room temperature, however some are liquids such as methylcyclopentadienyl manganese tricarbonyl, or even volatile liquids such as nickel tetracarbonyl. Many organometallic compounds are air sensitive (reactive towards oxygen and moisture), and thus they must be handled under an inert atmosphere. Some organometallic compounds such as triethylaluminium are pyrophoric and will ignite on contact with air. | 0 | Organic Chemistry |
The M and H subunits are encoded by two different genes:
* The M subunit is encoded by LDHA, located on chromosome 11p15.4 ().
* The H subunit is encoded by LDHB, located on chromosome 12p12.2-p12.1 ().
* A third isoform, LDHC or LDHX, is expressed only in the testis (); its gene is likely a duplicate of LDHA and is also located on the eleventh chromosome (11p15.5-p15.3).
* The fourth isoform is localized in the peroxisome. It is tetramer containing one LDHBx subunit, which is also encoded by the LDHB gene. The LDHBx protein is seven amino acids longer than the LDHB (LDH-H) protein. This amino acid extension is generated by functional translational readthrough.
Mutations of the M subunit have been linked to the rare disease exertional myoglobinuria (see OMIM article), and mutations of the H subunit have been described but do not appear to lead to disease. | 1 | Biochemistry |
"Acid rain" is a popular term referring to the deposition of a mixture from wet (rain, snow, sleet, fog, cloudwater, and dew) and dry (acidifying particles and gases) acidic components. Distilled water, once carbon dioxide is removed, has a neutral pH of 7. Liquids with a pH less than 7 are acidic, and those with a pH greater than 7 are alkaline. "Clean" or unpolluted rain has an acidic pH, but usually no lower than 5.7, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid according to the following reaction:
Carbonic acid then can ionize in water forming low concentrations of carbonate and hydronium ions:
Unpolluted rain can also contain other chemicals which affect its pH (acidity level). A common example is nitric acid produced by electric discharge in the atmosphere such as lightning. Acid deposition as an environmental issue (discussed later in the article) would include additional acids other than .
Occasional pH readings in rain and fog water of well below 2.4 have been reported in industrialized areas.
The main sources of the SO and NO pollution that causes acid rain are burning fossil fuels to generate electricity and power internal combustion vehicles, to refine oil, and in industrial manufacturing and other processes. | 2 | Environmental Chemistry |
Many problems in the chemical and physical sciences can be related to packing problems where more than one size of sphere is available. Here there is a choice between separating the spheres into regions of close-packed equal spheres, or combining the multiple sizes of spheres into a compound or interstitial packing. When many sizes of spheres (or a distribution) are available, the problem quickly becomes intractable, but some studies of binary hard spheres (two sizes) are available.
When the second sphere is much smaller than the first, it is possible to arrange the large spheres in a close-packed arrangement, and then arrange the small spheres within the octahedral and tetrahedral gaps. The density of this interstitial packing depends sensitively on the radius ratio, but in the limit of extreme size ratios, the smaller spheres can fill the gaps with the same density as the larger spheres filled space. Even if the large spheres are not in a close-packed arrangement, it is always possible to insert some smaller spheres of up to 0.29099 of the radius of the larger sphere.
When the smaller sphere has a radius greater than 0.41421 of the radius of the larger sphere, it is no longer possible to fit into even the octahedral holes of the close-packed structure. Thus, beyond this point, either the host structure must expand to accommodate the interstitials (which compromises the overall density), or rearrange into a more complex crystalline compound structure. Structures are known which exceed the close packing density for radius ratios up to 0.659786.
Upper bounds for the density that can be obtained in such binary packings have also been obtained.
In many chemical situations such as ionic crystals, the stoichiometry is constrained by the charges of the constituent ions. This additional constraint on the packing, together with the need to minimize the Coulomb energy of interacting charges leads to a diversity of optimal packing arrangements. | 3 | Analytical Chemistry |
A proton pump is any process that creates a proton gradient across a membrane. Protons can be physically moved across a membrane, as seen in mitochondrial Complexes I and IV. The same effect can be produced by moving electrons in the opposite direction. The result is the disappearance of a proton from the cytoplasm and the appearance of a proton in the periplasm. Mitochondrial Complex III is this second type of proton pump, which is mediated by a quinone (the Q cycle).
Some dehydrogenases are proton pumps, while others are not. Most oxidases and reductases are proton pumps, but some are not. Cytochrome bc is a proton pump found in many, but not all, bacteria (not in E. coli). As the name implies, bacterial bc is similar to mitochondrial bc (Complex III). | 1 | Biochemistry |
The hydrogen cycle consists of hydrogen exchanges between biotic (living) and abiotic (non-living) sources and sinks of hydrogen-containing compounds.
Hydrogen (H) is the most abundant element in the universe. On Earth, common H-containing inorganic molecules include water (HO), hydrogen gas (H), hydrogen sulfide (HS), and ammonia (NH). Many organic compounds also contain H atoms, such as hydrocarbons and organic matter. Given the ubiquity of hydrogen atoms in inorganic and organic chemical compounds, the hydrogen cycle is focused on molecular hydrogen, H.
As a consequence of microbial metabolisms or naturally occurring rock-water interactions, hydrogen gas can be created. Other bacteria may then consume free H2, which may also be oxidised photochemically in the atmosphere or lost to space. Hydrogen is also thought to be an important reactant in pre-biotic chemistry and the early evolution of life on Earth, and potentially elsewhere in the Solar System. | 1 | Biochemistry |
Exciplexes provide one of the three dynamic mechanisms by which fluorescence is quenched. A regular exciplex has some charge-transfer (CT) character, and in the extreme case there are distinct radical ions with unpaired electrons. If the unpaired electrons can spin-pair to form a covalent bond, then the covalent bonding interaction can lower the energy of the charge transfer state. Strong CT stabilisation has been shown to lead to a conical intersection of this exciplex state with the ground state in a balance of steric effects, electrostatic interactions, stacking interactions, and relative conformations that can determine the formation and accessibility of bonded exciplexes.
As an exception to the conventional radical ion pair model, this mode of covalent bond formation is of interest to photochemistry research, as well as the many biological fields using fluorescence spectroscopy techniques. Evidence for the bonded exciplex intermediate has been given in studies of steric and Coulombic effects on the quenching rate constants and from extensive density functional theory computations that show a curve crossing between the ground state and the low-energy bonded exciplex state. | 5 | Photochemistry |
In cell adhesion laminin-111 and other isoforms are important proteins that anchor cells to the extracellular matrix (ECM). The linkage between cells and the ECM is formed by binding cell surface receptors to one end of the laminin α chain and binding ECM components to another region of the laminin. Globular domains (G-Domain) of the α chain are the regions on laminin-111 that allow the binding of integrins, glycoproteins, sulfated glycolipids and dystroglycan. | 0 | Organic Chemistry |
Trimethylenemethane is a neutral, four-carbon molecule composed of four pi bonds; thus, it must be expressed either as a non-Kekulé molecule or a zwitterion. The orbital energy levels of TMM reveal that it possesses singlet and triplet states; generally, these states exhibit different reactivity and selectivity profiles. A singlet (3+2) cycloaddition, when it is concerted, is believed to proceed under frontier orbital control. When electron-rich TMMs are involved, the A orbital serves as the HOMO (leading to fused products if the TMM is cyclic). When electron-poor (or unsubstituted) TMMs are involved, the S orbital serves as the HOMO (leading to bridged products if the TMM is cyclic). Cycloadditions involving the triplet state are stepwise, and usually result in configurational scrambling in the two-atom component.
The rapid closure of TMMs to methylidenecyclopropanes is a general problem that affects the rate and yield of (3+2) cycloaddition reactions involving this class of reaction intermediates. The problem is generally less severe for five-membered, cyclic TMMs due to ring strain in the corresponding MCPs. When ring closure and TMM dimerization can be controlled, (3+2) cycloaddition affords isomeric mixtures of methylenecyclopentanes. Three classes of compounds have been used to generate synthetically useful TMM intermediates: diazenes, silyl-substituted allylic acetates and methylenecyclopropenes. Transition metal catalysis can be used with the latter two classes, although polar MCPs may open under light or heat (see below). | 0 | Organic Chemistry |
Standard CD/DVD readers can be used to read the assays. The CD/DVD readers contain a laser, set of optical elements which shape and focus the laser, a disk driver, and a signal detector that function as follows:
# The laser produces light of a selected wavelength.
# The beam of light hits the analyte in the spots of the microarrays and refracts. The mass of the analyte causes the angle of reflected light to be different from the angle of incident light. The reflective properties of the CD/DVD change based on the quantity of analyte in the sample.
# The attenuated signal reaches the photodiode of the drive's pickup.
# Analog signals are extracted, digitized, and converted to an image.
The signal or optical density of the image is inversely proportional to concentration. The refractive index of light, which is directly proportional to concentration, can also be measured. A readable signal is only generated if the sample is at least 200 nm, otherwise it is too small to significantly disrupt reflection of incident laser light.
DVD diagnostic software programs such as Kprobe, ODC, and PlexUtilities can also be used for testing arrays and assays prepared on DVDs. These programs rely on a basic DVD error correcting algorithm. DVDs are organized by sectors which each consist of 2064 bytes. A logical error correction code (ECC) block consists of 16 data sectors. The ECC block is the basic unit for testing disk quality by counting the number of parity inner errors (PIE) or parity inner failures (PIF). The software programs can analyze PIF density which is proportional to analyte concentration. | 1 | Biochemistry |
Carbon tetrachloride, also known by many other names (such as carbon tet for short and tetrachloromethane, also recognised by the IUPAC) is a chemical compound with the chemical formula CCl. It is a non-flammable, dense, colourless liquid with a "sweet" chloroform-like odour that can be detected at low levels. It was formerly widely used in fire extinguishers, as a precursor to refrigerants and as a cleaning agent, but has since been phased out because of environmental and safety concerns. Exposure to high concentrations of carbon tetrachloride can affect the central nervous system and degenerate the liver and kidneys. Prolonged exposure can be fatal.
Tradenames include: Carbon-Tet, Katharin (Germany, 1890s), Benzinoform, Carbona and Thawpit in the cleaning industry, Halon-104 in firefighting, Refrigerant-10 in HVACR, and Necatorina and Seretin as a medication. | 2 | Environmental Chemistry |
Recombination hotspots are DNA sequences that increase local recombination. The HOT1 sequence in yeast is one of the most well studied mitotic recombination hotspots. The HOT1 sequence includes an RNA polymerase I transcription promoter. In a yeast mutant strain defective in RNA polymerase I the HOT1 activity in promoting recombination is abolished. The level of RNA polymerase I transcription activity that is dependent on the promoter in the HOT1 sequence appears to determine the level of nearby mitotic recombination. | 1 | Biochemistry |
STAT6 has been shown to interact with:
* CREB-binding protein,
* EP300,
* IRF4,
* NFKB1,
* Nuclear receptor coactivator 1, and
* SND1. | 1 | Biochemistry |
* Frederick Gowland Hopkins (1914-1943)
* Albert Chibnall (1943-1949)
* Frank George Young (1949-1975)
* Hans Kornberg (1975-1995)
* Tom Blundell (1995-2009)
* Gerard Evan (2009-2022)
* Laura Machesky (2022- ) | 1 | Biochemistry |
Neutron activation analysis is a sensitive multi-element analytical technique used for both qualitative and quantitative analysis of major, minor, trace and rare elements. NAA was discovered in 1936 by Hevesy and Levi, who found that samples containing certain rare-earth elements became highly radioactive after exposure to a source of neutrons. This observation led to the use of induced radioactivity for the identification of elements. NAA is significantly different from other spectroscopic analytical techniques in that it is based not on electronic transitions but on nuclear transitions. To carry out an NAA analysis, the specimen is placed into a suitable irradiation facility and bombarded with neutrons. This creates artificial radioisotopes of the elements present. Following irradiation, the artificial radioisotopes decay with emission of particles or, more importantly gamma rays, which are characteristic of the element from which they were emitted.
For the NAA procedure to be successful, the specimen or sample must be selected carefully. In many cases small objects can be irradiated and analysed intact without the need of sampling. But, more commonly, a small sample is taken, usually by drilling in an inconspicuous place. About 50 mg (one-twentieth of a gram) is a sufficient sample, so damage to the object is minimised. It is often good practice to remove two samples using two different drill bits made of different materials. This will reveal any contamination of the sample from the drill bit material itself. The sample is then encapsulated in a vial made of either high purity linear polyethylene or quartz. These sample vials come in many shapes and sizes to accommodate many specimen types. The sample and a standard are then packaged and irradiated in a suitable reactor at a constant, known neutron flux. A typical reactor used for activation uses uranium fission, providing a high neutron flux and the highest available sensitivities for most elements. The neutron flux from such a reactor is in the order of 10 neutrons cm s. The type of neutrons generated are of relatively low kinetic energy (KE), typically less than 0.5 eV. These neutrons are termed thermal neutrons. Upon irradiation, a thermal neutron interacts with the target nucleus via a non-elastic collision, causing neutron capture. This collision forms a compound nucleus which is in an excited state. The excitation energy within the compound nucleus is formed from the binding energy of the thermal neutron with the target nucleus. This excited state is unfavourable and the compound nucleus will almost instantaneously de-excite (transmutate) into a more stable configuration through the emission of a prompt particle and one or more characteristic prompt gamma photons. In most cases, this more stable configuration yields a radioactive nucleus. The newly formed radioactive nucleus now decays by the emission of both particles and one or more characteristic delayed gamma photons. This decay process is at a much slower rate than the initial de-excitation and is dependent on the unique half-life of the radioactive nucleus. These unique half-lives are dependent upon the particular radioactive species and can range from fractions of a second to several years. Once irradiated, the sample is left for a specific decay period, then placed into a detector, which will measure the nuclear decay according to either the emitted particles, or more commonly, the emitted gamma rays. | 3 | Analytical Chemistry |
A 2018 Cochrane review found that it produced moderate improvement in sleep onset and maintenance. The authors suggest that where preferred non-pharmacological treatment strategies have been exhausted, eszopiclone provides an efficient treatment for insomnia. In 2014, the US Food and Drug Administration asked that the starting dose be lowered from 2 milligrams to 1 milligram after it was observed in a study that even eight hours after taking the drug at night, some people were not able to cope with their next-day activities like driving and other activities that require full alertness.
Eszopiclone is slightly effective in the treatment of insomnia where difficulty in falling asleep is the primary complaint. The benefit over placebo was found to be of questionable clinical significance. Although the drug effect and the placebo response were rather small and of questionable clinical importance, the two together produce a reasonably large clinical response. | 4 | Stereochemistry |
It was introduced by Lyklema in “Fundamentals of Interface and Colloid Science”. A recent IUPAC Technical Report used this term explicitly and detailed several means of measurement in physical systems.
The Dukhin number is a ratio of the surface conductivity multiplied by particle size a:
There is another expression of this number that is valid when the surface conductivity is associated only with ions motion above the slipping plane in the double layer. In this case, the value of the surface conductivity depends on ζ-potential, which leads to the following expression for the Dukhin number for symmetrical electrolyte with equal ions diffusion coefficient:
where the parameter m characterizes the contribution of electro-osmosis into motion of ions within the double layer
* F is Faraday constant
* T is absolute temperature
* R is gas constant
* C is ions concentration in bulk
* z is ion valency
* ζ is electrokinetic potential
* ε is vacuum dielectric permittivity
* ε is fluid dielectric permittivity
* η is dynamic viscosity
* D is diffusion coefficient | 7 | Physical Chemistry |
Self-assembled vesicles are essential components of primitive cells. The second law of thermodynamics requires that the universe becomes increasingly disordered (entropy), yet life is distinguished by its great degree of organization. Therefore, a boundary is needed to separate life processes from non-living matter. This fundamental necessity is underpinned by the universality of the cell membrane which is the only cellular structure found in all organisms on Earth.
In the aqueous environment in which all known cells function, a non-aqueous barrier is required to surround a cell and separate it from its surroundings. This non-aqueous membrane establishes a barrier to free diffusion, allowing for regulation of the internal environment within the barrier. The necessity of thermodynamically isolating a subsystem is an irreducible condition of life. In modern biology, such isolation is ordinarily accomplished by amphiphilic bilayers of a thickness of around 10 meters.
Researchers including Irene A. Chen and Jack W. Szostak have demonstrated that simple physicochemical properties of elementary protocells can give rise to simpler conceptual analogues of essential cellular behaviors, including primitive forms of Darwinian competition and energy storage. Such cooperative interactions between the membrane and encapsulated contents could greatly simplify the transition from replicating molecules to true cells. Competition for membrane molecules would favor stabilized membranes, suggesting a selective advantage for the evolution of cross-linked fatty acids and even the phospholipids of today. This micro-encapsulation allowed for metabolism within the membrane, exchange of small molecules and prevention of passage of large substances across it. The main advantages of encapsulation include increased solubility of the cargo and creating energy in the form of chemical gradients. Energy is thus often said to be stored by cells in molecular structures such as carbohydrates (including sugars), lipids, and proteins, which release energy when chemically combined with oxygen during cellular respiration. | 9 | Geochemistry |
The pressure transmitting medium is an important component in any high-pressure experiment. The medium fills the space within the sample chamber and applies the pressure being transmitted to the medium onto the sample. In a good high-pressure experiment, the medium should maintain a homogeneous distribution of pressure on the sample. In other words, the medium must stay hydrostatic to ensure uniform compressibility of the sample. Once a pressure transmitting medium has lost its hydrostaticity, a pressure gradient forms in the chamber that increases with increasing pressure. This gradient can greatly affect the sample, compromising results. The medium must also be inert, as to not interact with the sample, and stable under high pressures. For experiments with laser heating, the medium should have low thermal conductivity. If an optical technique is being employed, the medium should be optically transparent and for x-ray diffraction, the medium should be a poor x-ray scatterer – as to not contribute to the signal.
Some of the most commonly used pressure transmitting media have been sodium chloride, silicone oil, and a 4:1 methanol-ethanol mixture. Sodium chloride is easy to load and is used for high-temperature experiments because it acts as a good thermal insulator. The methanol-ethanol mixture displays good hydrostaticity to about 10 GPa and with the addition of a small amount of water can be extended to about 15 GPa.
For pressure experiments that exceed 10 GPa, noble gases are preferred. The extended hydrostaticity greatly reduces the pressure gradient in samples at high pressure. Noble gases, such as helium, neon, and argon are optically transparent, thermally insulating, have small X-ray scattering factors, and have good hydrostaticity at high pressures. Even after solidification, noble gases provide quasihydrostatic environments.
Argon is used for experiments involving laser heating because it is chemically insulating. Since it condenses at a temperature above that of liquid nitrogen, it can be loaded cryogenically. Helium and neon have low X-ray scattering factors and are thus used for collecting X-ray diffraction data. Helium and neon also have low shear moduli; minimizing strain on the sample. These two noble gases do not condense above that of liquid nitrogen and cannot be loaded cryogenically. Instead, a high-pressure gas loading system has been developed that employs a gas compression method. | 7 | Physical Chemistry |
Molecular Biology of the Cell is a cellular and molecular biology textbook published by W.W. Norton & Co and currently authored by Bruce Alberts, Rebecca Heald, David Morgan, Martin Raff, Keith Roberts and Peter Walter. The book was first published in 1983 by Garland Science and is now in its seventh edition. The molecular biologist James Watson contributed to the first three editions.
Molecular Biology of the Cell is widely used in introductory courses at the university level, being considered as a reference in many libraries and laboratories around the world. It describes the current understanding of cell biology and includes basic biochemistry, experimental methods for investigating cells, the properties common to most eukaryotic cells, the expression and transmission of genetic information, the internal organization of cells, and the behaviour of cells in multicellular organisms. Molecular Biology of the Cell has been described as "the most influential cell biology textbook of its time". The sixth edition is dedicated to the memory of co-author Julian Lewis who died in early 2014.
The book was the first to position cell biology as a central discipline for biology and medicine, and immediately became a landmark textbook. It was written in intense collaborative sessions in which the authors lived together over periods of time, organized by editor Miranda Robertson, then Biology Editor of Nature. | 1 | Biochemistry |
Symptoms of lithium toxicity can be mild, moderate, or severe.
Mild symptoms include nausea, feeling tired, and tremor occur at a level of 1.5 to 2.5 mEq/L in blood serum. Moderate symptoms include confusion, an increased heart rate, and low muscle tone occur at a level of 2.5 to 3.5 mEq/L. Severe symptoms include coma, seizures, low blood pressure and increased body temperature which occur at a lithium concentration greater than 3.5 mEq/L. When lithium overdoses produce neurological deficits or cardiac toxicity, the symptoms are considered serious and can be fatal. | 1 | Biochemistry |
Complex metallic alloys is an umbrella term for intermetallic compounds with a relatively large unit cell. There is no precise definition of how large the unit cell of a complex metallic alloy has to be, but the broadest definition includes Zintl phases, skutterudites, and Heusler compounds on the most simple end, and quasicrystals on the more complex end. | 8 | Metallurgy |
The resting potential must be established within a cell before the cell can be depolarized. There are many mechanisms by which a cell can establish a resting potential, however there is a typical pattern of generating this resting potential that many cells follow. The generation of a negative resting potential within the cell involves the utilization of ion channels, ion pumps, and voltage-gated ion channels by the cell. However, the process of generating the resting potential within the cell also creates an environment outside the cell that favors depolarization. The sodium potassium pump is largely responsible for the optimization of conditions on both the interior and the exterior of the cell for depolarization. By pumping three positively charged sodium ions (Na) out of the cell for every two positively charged potassium ions (K) pumped into the cell, not only is the resting potential of the cell established, but an unfavorable concentration gradient is created by increasing the concentration of sodium outside the cell and increasing the concentration of potassium within the cell. While there is an excessive amount of potassium in the cell and sodium outside the cell, the generated resting potential maintains the closure of voltage-gated ion channels in the plasma membrane. This not only prevents the diffusion of ions pumped across the membrane but also involves the activity of potassium leak channels, allowing a controlled passive efflux of potassium ions, which contributes to the establishment of the negative resting potential. Additionally, despite the high concentration of positively-charged potassium ions, most cells contain internal components (of negative charge), which accumulate to establish a negative inner charge. | 7 | Physical Chemistry |
Excited-state absorption (ESA) occurs when the pump beam sends an electron into an excited state, then the probe beam sends the electron into a higher excited state. This differs from TPA primarily in the timescale over which it occurs. Since an electron can remain in an excited state for a period of nanoseconds, thus requiring longer pulse durations than TPA. | 7 | Physical Chemistry |
UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma. In addition, UV light, in particular UV‑B radiation, has been shown to induce cell cycle arrest in keratinocytes, the most common type of skin cell. As such, sunlight therapy can be a candidate for treatment of conditions such as psoriasis and exfoliative cheilitis, conditions in which skin cells divide more rapidly than usual or necessary. | 5 | Photochemistry |
The National Center for Functional Glycomics offers the following services:
* Printing custom microarrays on glass slides
* Analysis of qualitative and quantitative changes in glycans associated with diseases and disorders by Glycan Reductive Isotope Labeling and mass spectrometry. | 0 | Organic Chemistry |
Amalgamated zinc is zinc that has been surface treated with mercury to form a surface amalgam containing little contamination from other elements. It is typically used for reduction, and is written as Zn(Hg) in reactions. | 7 | Physical Chemistry |
In a manual colorimeter the cuvettes are inserted and removed by hand. An automated colorimeter (as used in an AutoAnalyzer) is fitted with a flowcell through which solution flows continuously. | 7 | Physical Chemistry |
Quantitative single-pulse nuclear magnetic resonance spectroscopy (NMR) is a method amenable for measuring kinetic fractionation of isotopes for natural abundance KIE measurements. Pascal et al. were inspired by studies demonstrating dramatic variations of deuterium within identical compounds from different sources and hypothesized that NMR could be used to measure deuterium kinetic isotope effects at natural abundance. Pascal and coworkers tested their hypothesis by studying the insertion reaction of dimethyl diazomalonate into cyclohexane. Pascal et al. measured a KIE of 2.2 using NMR for materials of natural abundance.
Singleton and coworkers demonstrated the capacity of NMR based natural abundance KIE measurements for studying the mechanism of the [4 + 2] cycloaddition of isoprene with maleic anhydride. Previous studies by Gajewski on isotopically enrich materials observed KIE results that suggested an asynchronous transition state, but were always consistent, within error, for a perfectly synchronous reaction mechanism.
This work by Singleton et al. established the measurement of multiple KIE's within the design of a single experiment. These and KIE measurements determined at natural abundance found the "inside" hydrogens of the diene experience a more pronounced KIE than the "outside" hydrogens" and the C1 and C4 experience a significant KIE. These key observations suggest an asynchronous reaction mechanism for the cycloaddition of isoprene with maleic anhydride.
The limitations for determining KIE's at natural abundance using NMR are that the recovered material must have a suitable amount and purity for NMR analysis (the signal of interest should be distinct from other signals), the reaction of interest must be irreversible, and the reaction mechanism must not change for the duration of the chemical reaction.
Experimental details for using quantitative single pulse NMR to measure kinetic isotope effect at natural abundance as follows: the experiment needs to be performed under quantitative conditions including a relaxation time of 5 T measured 90° flip angle, a digital resolution of at least 5 points across a peak, and a signal:noise greater than 250. The raw FID is zero-filled to at least 256K points before the Fourier transform. NMR spectra are phased and then treated with a zeroth order baseline correction without any tilt correction. Signal integrations are determined numerically with a minimal tolerance for each integrated signal. | 7 | Physical Chemistry |
The Schultz theory (after D. L. Schultz) is applicable only for very high energy solids. Again, it is similar to the theories of Owens, Wendt, Fowkes, and Wu, but is designed for a situation where conventional measurement required for those theories is impossible. In the class of solids with sufficiently high surface energy, most liquids wet the surface completely with a contact angle of zero degrees, and thus no useful data can be gathered. The Schultz theory and procedure calls to deposit a sessile drop of probe liquid on the solid surface in question, but this is all done while the system is submerged in yet another liquid, rather than being done in the open air. As a result, the higher “atmospheric” pressure due to the surrounding liquid causes the probe liquid droplet to compress so that there is a measurable contact angle. | 7 | Physical Chemistry |
The enzymes that make and use NAD and NADH are important in both pharmacology and the research into future treatments for disease. Drug design and drug development exploits NAD in three ways: as a direct target of drugs, by designing enzyme inhibitors or activators based on its structure that change the activity of NAD-dependent enzymes, and by trying to inhibit NAD biosynthesis.
Because cancer cells utilize increased glycolysis, and because NAD enhances glycolysis, nicotinamide phosphoribosyltransferase (NAD salvage pathway) is often amplified in cancer cells.
It has been studied for its potential use in the therapy of neurodegenerative diseases such as Alzheimers and Parkinsons disease as well as multiple sclerosis. A placebo-controlled clinical trial of NADH (which excluded NADH precursors) in people with Parkinson's failed to show any effect.
NAD is also a direct target of the drug isoniazid, which is used in the treatment of tuberculosis, an infection caused by Mycobacterium tuberculosis. Isoniazid is a prodrug and once it has entered the bacteria, it is activated by a peroxidase enzyme, which oxidizes the compound into a free radical form. This radical then reacts with NADH, to produce adducts that are very potent inhibitors of the enzymes enoyl-acyl carrier protein reductase, and dihydrofolate reductase.
Since many oxidoreductases use NAD and NADH as substrates, and bind them using a highly conserved structural motif, the idea that inhibitors based on NAD could be specific to one enzyme is surprising. However, this can be possible: for example, inhibitors based on the compounds mycophenolic acid and tiazofurin inhibit IMP dehydrogenase at the NAD binding site. Because of the importance of this enzyme in purine metabolism, these compounds may be useful as anti-cancer, anti-viral, or immunosuppressive drugs. Other drugs are not enzyme inhibitors, but instead activate enzymes involved in NAD metabolism. Sirtuins are a particularly interesting target for such drugs, since activation of these NAD-dependent deacetylases extends lifespan in some animal models. Compounds such as resveratrol increase the activity of these enzymes, which may be important in their ability to delay aging in both vertebrate, and invertebrate model organisms. In one experiment, mice given NAD for one week had improved nuclear-mitochrondrial communication.
Because of the differences in the metabolic pathways of NAD biosynthesis between organisms, such as between bacteria and humans, this area of metabolism is a promising area for the development of new antibiotics. For example, the enzyme nicotinamidase, which converts nicotinamide to nicotinic acid, is a target for drug design, as this enzyme is absent in humans but present in yeast and bacteria.
In bacteriology, NAD, sometimes referred to factor V, is used as a supplement to culture media for some fastidious bacteria. | 5 | Photochemistry |
This section explains how the saprobic index of a water body is computed according to the Zelinka & Marvan method; without adjusting for several confounding factors.
In a first iteration, the abundance A of each indicator species is counted and converted to categories ranging from 1 to 7. An abundance of 1 means that only one or two animals was found, while the class 7 means more than 1000 individuals during a survey. There are different abundance classes — for example, some methods use classes where the next-bigger class contains roughly double the number of individuals. The following table follows the DIN 38410-1 (2008) standard used in Germany, where the next-bigger class is about three times larger than the previous one.
The saprobic value s denotes how much organic matter must be present for an aquatic species to thrive. An animal with a saprobic value 1 can only survive in water with little organic matter present, while one with a value of 4 requires water bodies with a large amount of organic matter. The aforementioned example, the Lymnaea stagnalis snail, has a saprobic value of 2.0. The annelid worm Tubifex tubifex needs a lot of organic matter and has an s value of 3.6.
The weighting factor g has a value of either 1, 2, 4, 8 or 16, and denotes a tolerance range. If a species can survive in both unpolluted and heavily polluted water, g is very small because finding the species in a survey has little predictive value. In practice, only indicator species with a weighting factor g ≥ 4 are used. For example, a caddisfly, Agapetus fuscipes, has a g value of 16, while the zebra mussel's value is g = 4.
The saprobic index of a water body - the water quality - is finally computed with the following formula:
</div>
The water body's quality, in Roman numerals, is the rounded value of S. | 2 | Environmental Chemistry |
Yonekura shows the steel industry was central to the economic development of Japan. The nation's sudden transformation from feudal to modern society in the late nineteenth century, its heavy industrialization and imperialist war ventures in 1900–1945, and the post-World War II high-economic growth, all depended on iron and steel. The other great Japanese industries, such as shipbuilding, automobiles, and industrial machinery are closely linked to steel. From 1850 to 1970, the industry increased its crude steel production from virtually nothing to 93.3 million tons (the third largest in the world).
The government's activist Ministry of International Trade and Industry (MITI) played a major role in coordination. The transfer of technology from the West and the establishment of competitive firms involved far more than buying foreign hardware. MITI located steel mills and organized a domestic market; it sponsored Yawata Steel Company. Japanese engineers and entrepreneurs internally developed the necessary technological and organizational capabilities, planned the transfer and adoption of technology, and gauged demand and sources of raw materials and finances. | 8 | Metallurgy |
The 17-bp transcriptional complex has an 8-bp DNA-RNA hybrid, that is, 8 base-pairs involve the RNA transcript bound to the DNA template strand. As transcription progresses, ribonucleotides are added to the 3′ end of the RNA transcript and the RNAP complex moves along the DNA. The characteristic elongation rates in prokaryotes and eukaryotes are about 10–100 nts/sec.
Aspartyl (asp) residues in the RNAP will hold on to Mg ions, which will, in turn, coordinate the phosphates of the ribonucleotides. The first Mg will hold on to the α-phosphate of the NTP to be added. This allows the nucleophilic attack of the 3′-OH from the RNA transcript, adding another NTP to the chain. The second Mg will hold on to the pyrophosphate of the NTP. The overall reaction equation is:
:(NMP) + NTP → (NMP) + PP | 1 | Biochemistry |
This phenomenon was first discovered by Dorn in 1879. He observed that a vertical electric field had developed in a suspension of glass beads in water, as the beads were settling. This was the origin of sedimentation potential, which is often referred to as the Dorn effect.
Smoluchowski built the first models to calculate the potential in the early 1900s. Booth created a general theory on sedimentation potential in 1954 based on Overbeeks 1943 theory on electrophoresis. In 1980, Stigter extended Booths model to allow for higher surface potentials. Ohshima created a model based on OBrien and White s 1978 model used to analyze the sedimentation velocity of a single charged sphere and the sedimentation potential of a dilute suspension. | 7 | Physical Chemistry |
The above standard treatment of a macroscopic Bose gas is straightforward, but the inclusion of the ground state is somewhat inelegant. Another approach is to include the ground state explicitly (contributing a term in the grand potential, as in the section below), this gives rise to an unrealistic fluctuation catastrophe: the number of particles in any given state follow a geometric distribution, meaning that when condensation happens at T and most particles are in one state, there is a huge uncertainty in the total number of particles. This is related to the fact that the compressibility becomes unbounded for T . Calculations can instead be performed in the canonical ensemble, which fixes the total particle number, however the calculations are not as easy.
Practically however, the aforementioned theoretical flaw is a minor issue, as the most unrealistic assumption is that of non-interaction between bosons. Experimental realizations of boson gases always have significant interactions, i.e., they are non-ideal gases. The interactions significantly change the physics of how a condensate of bosons behaves: the ground state spreads out, the chemical potential saturates to a positive value even at zero temperature, and the fluctuation problem disappears (the compressibility becomes finite). See the article Bose–Einstein condensate. | 7 | Physical Chemistry |
Researchers have been using carbon nanotubes (CNTs) to mimic the papillae of lotus leaves. CNT nanoforests can be made using chemical vapor deposition techniques. CNT’s can be applied on a surface to modify its water contact angle. Lau et al. created vertical CNT forests with a polytetrafluroethylene (PTFE) coating that was both stable and superhydrophobic with an advancing and receding contact angle of 170° and 160°. Jung and Bhushan have created a superhydrophobic surface by spray coating CNTs with an epoxy resin. The spacing and alignment of the CNTs have been shown to impact the degree of hydrophobicity a surface has. Sun et al., have found that CNTs aligned vertically with a medium spacing display the best hydrophobic properties. Small and large spacing shows increased drop spreading, while horizontal orientation may even display hydrophilic properties.
Glass silica beads in an epoxy resin, and the electrochemical deposition of gold into dendritic structures has also created synthetic biomimetic surfaces similar to lotus leaves. | 7 | Physical Chemistry |
In 1934 he was appointed as professor at the University of Oslo. He is well known in the Nordic countries for his textbook Lærebok i organisk kjemi. The first modern Norwegian textbook in organic chemistry, it was first released in 1942 and then re-released several times, the last in 1964. The 1958 edition became known for introducing new Norwegian-language names of several chemical elements: hydrogen, nitrogen, karbon (carbon) og oksygen (oxygen).
During the occupation of Norway by Nazi Germany, his academic career was interrupted. When the Nazi authorities were about to change the rules for admission to the university in autumn 1943, a protest ensued. In retaliation, the authorities arrested 11 staff, 60 male students and 10 female students. The staff Johannes Andenæs, Eiliv Skard, Johan Christian Schreiner, Harald Krabbe Schjelderup, Anatol Heintz, Odd Hassel, Ragnar Frisch, Carl Jacob Arnholm, Bjørn Føyn and Endre Berner were sent to Grini concentration camp. Berner was first incarcerated at Berg concentration camp from 22 November 1943, then at Grini until 24 December 1944.
After the war Berner continued as professor at the University of Oslo until 1962, except for a stay at the Imperial College London from 1954 to 1955. He was also active as a professor emeritus until his death. He was elected as a member of the Royal Norwegian Society of Sciences and Letters in 1927, of the Norwegian Academy of Science and Letters in 1933 and of the Society of Chemical Industry in 1951. In 1959, he earned the Nansen medal for Outstanding Research and in 1969 he was decorated with the Order of St. Olav. He was the president of the Norwegian Chemical Society from 1946 to 1950, having co-founded the Trondheim branch of the society, and ultimately received honorary membership. | 0 | Organic Chemistry |
In lipidomics, the process of shotgun lipidomics (named by analogy with shotgun sequencing) uses analytical chemistry to investigate the biological function, significance, and sequelae of alterations in lipids and protein constituents mediating lipid metabolism, trafficking, or biological function in cells.
Lipidomics has been greatly facilitated by recent advances in, and novel applications of, electrospray ionization mass spectrometry (ESI/MS).
Lipidomics is a research field that studies the pathways and networks of cellular lipids in biological systems (i.e., lipidomes) on a large scale. It involves the identification and quantification of the thousands of cellular lipid molecular species and their interactions with other lipids, proteins, and other moieties in vivo. Investigators in lipidomics examine the structures, functions, interactions, and dynamics of cellular lipids and the dynamic changes that occur during pathophysiologic perturbations. Lipidomic studies play an essential role in defining the biochemical mechanisms of lipid-related disease processes through identifying alterations in cellular lipid metabolism, trafficking and homeostasis. The two major platforms currently used for lipidomic analyses are HPLC-MS and shotgun lipidomics. | 1 | Biochemistry |
GIS in environmental contamination is the use of GIS software in mapping out the contaminants in soil and water using the spatial interpolation tools from GIS. Spatial interpolation allows for more efficient approach to remediation and monitoring of soil and water contaminants. Soil and water contamination by metals and other contaminants have become a major environmental problem after the industrialization across many parts of the world. As a result, environmental agencies are placed in charge in remediating, monitoring, and mitigating the soil contamination sites. GIS is used to monitor the sites for metal contaminants in the soil, and based on the GIS analysis, highest risk sites are identified in which majority of the remediation and monitoring takes place. | 2 | Environmental Chemistry |
The formation of a disaccharide molecule from two monosaccharide molecules proceeds by displacing a hydroxy group from one molecule and a hydrogen nucleus (a proton) from the other, so that the new vacant bonds on the monosaccharides join the two monomers together. Because of the removal of the water molecule from the product, the term of convenience for such a process is "dehydration reaction" (also "condensation reaction" or "dehydration synthesis"). For example, milk sugar (lactose) is a disaccharide made by condensation of one molecule of each of the monosaccharides glucose and galactose, whereas the disaccharide sucrose in sugar cane and sugar beet, is a condensation product of glucose and fructose. Maltose, another common disaccharide, is condensed from two glucose molecules.
The dehydration reaction that bonds monosaccharides into disaccharides (and also bonds monosaccharides into more complex polysaccharides) forms what are called glycosidic bonds. | 0 | Organic Chemistry |
By integrating the above four data sets, CTD automatically constructs putative chemical-gene-phenotype-disease networks to illuminate molecular mechanisms underlying environmentally-influenced diseases.
These inferred relationships are statistically scored and ranked and can be used by scientists and computational biologists to generate and verify testable hypotheses about toxicogenomic mechanisms and how they relate to human health.
Users can search CTD to explore scientific data for chemicals, genes, diseases, or interactions between any of these three concepts. Currently, CTD integrates toxicogenomic data for vertebrates and invertebrates.
CTD integrates data from or hyperlinks to these databases:
*ChemIDplus, a dictionary of more than 400,000 chemicals housed in the US National Library of Medicine
*DrugBank
*Data Infrastructure for Chemical Safety project (diXa) Data Warehouse by the European Bioinformatics Institute which as of November 2015 contained 469 compounds, 188 disease datasets in three sub-categories liver, kidney and cardiovascular disease.
*Gene Ontology Consortium
*KEGG
*NCBI Entrez-Gene
*NCBI PubMed
*NCBI Taxonomy
*NLM Medical Subject Headings
*OMIM
*Reactome | 1 | Biochemistry |
The nucleus of deuterium is called a deuteron. It has a mass of (just over ).
The charge radius of the deuteron is .
Like the proton radius, measurements using muonic deuterium produce a smaller result: . | 9 | Geochemistry |
Lead has four stable isotopes: Pb, Pb, Pb, and Pb.
Lead is created in the Earth via decay of actinide elements, primarily uranium and thorium.
Lead isotope geochemistry is useful for providing isotopic dates on a variety of materials. Because the lead isotopes are created by decay of different transuranic elements, the ratios of the four lead isotopes to one another can be very useful in tracking the source of melts in igneous rocks, the source of sediments and even the origin of people via isotopic fingerprinting of their teeth, skin and bones.
It has been used to date ice cores from the Arctic shelf, and provides information on the source of atmospheric lead pollution.
Lead–lead isotopes has been successfully used in forensic science to fingerprint bullets, because each batch of ammunition has its own peculiar Pb/Pb vs Pb/Pb ratio. | 9 | Geochemistry |
The zone plate microscope uses a zone plate (that acts roughly like as a classical lens) instead of a pinhole to focus the atom beam into a small focal spot. This means that the beam width equation changes significantly (see below).
Here, is the zone plate magnification and is the width of the smallest zone. Note the presence of chromatic aberrations (). The approximation sign indicates the regime in which the distance between the zone plate and the skimmer is much bigger than its focal length.
The first term in this equation is similar to the geometric contribution in the pinhole case: a bigger zone plate (taken all parameters constant) corresponds to a bigger focal spot size. The third term differs from the pinhole configuration optics as it includes a quadratic relation with the skimmer size (which is imaged through the zone plate) and a linear relation with the zone plate magnification, which will at the same time depend on its radius.
The equation to maximise, the intensity, is the same as the pinhole case with the substitution . By substitution of the magnification equation:
where is the average de-Broglie wavelength of the beam. Taking a constant , which should be made equal to the smallest achievable value, the maxima of the intensity equation with respect to the zone plate radius and the skimmer-zone plate distance can be obtained analytically. The derivative of the intensity with respect to the zone plate radius can be reduced the following cubic equation (once it has been set equal to zero):
Here some groupings are used: is a constant that gives the relative size of the smallest aperture of the zone plate compared with the average wavelength of the beam and is the modified beam width, which is used through the derivation to avoid explicitly operating with the constant airy term: .
This cubic equation is obtained under a series of geometrical assumptions and has a closed-form analytical solution that can be consulted in the original paper or obtained through any modern-day algebra software. The practical consequence of this equation is that zone plate microscopes are optimally designed when the distances between the components are small, and the radius of the zone plate is also small. This goes in line with the results obtained for the pinhole configuration, and has as its practical consequence the design of smaller scanning helium microscopes. | 7 | Physical Chemistry |
AMPP administers accreditation programs for contractors working in the protective coatings and linings industries. "QP" stands for "Qualification Procedure", a reference to the technical standard that underlies each program.
*QP 1, Field Application to Complex Industrial and Marine Structures
*QP 2, Field Removal of Hazardous Coatings
*QP 3, Shop Painting (QP 3 is a joint standard also used by AISC for their sophisticated paint endorsement.)
*QP 5, Coating and Lining Inspection Companies
*QP 6, Metallizing
*QP 7, Painting Contractor Introductory Program
*QP 8, Installation of Polymer Coatings and Surfacings on Concrete and Other Cementitious Surfaces
*QP 9, Commercial Painting and Coating Contractors
*QN 1, Nuclear Coating Supplement
*QS 1, Advanced Quality Management System (ISO 9001-compliant) | 8 | Metallurgy |
Optical sensors are growing in popularity due to the low-cost, low power requirements and long term stability. They provide viable alternatives to electrode-based sensors or more complicated analytical instrumentation, especially in the field of environmental monitoring although in the case of oxygen optrodes, they do not have the resolution as the most recent cathodic microsensors. | 7 | Physical Chemistry |
Though the majority of information on transposons is in relation to their parasitic effect, it is sometimes unclear as to how exactly they hurt the host organism. To clarify, there are several ways in which a negative effect can be produced by transposable elements.
* Production of siRNA or miRNA that target specific cellular mRNAs, resulting in their destruction or inhibiting their translation through an RNAi-related mechanism
* Production of siRNA or miRNA that stimulates in RNA-Directed DNA Methylation (Rdrm) silencing of a similarly coded gene
* Insertion into a specific gene, interrupting its normal function
Any one of these can have an extreme or minimal effect, depending on what systems the mutation affects. For example, if a transposon were to interrupt the coding for the enzyme which allows for seeds to digest the nourishing endosperm, then the seed would fail to propagate at all, meaning that the mutation was, in essence, fatal. As a counter example, a transposon could be inserted into a non-coding region (which is likely the remnant of a now inactive transposon) and have no effect at all. | 1 | Biochemistry |
Ribosomal RNA (rRNA) includes non-coding RNAs that play essential roles in rRNA regulation. Ribosomal RNA (rRNA) takes part in protein synthesis. Occasional RNA molecules act catalytically, as RNA enzymes (ribozymes) or take part in protein export. The most important ribozyme is the major rRNA of the large subunit of the ribosome (28s rRNA in eukaryotes). It is now accepted that 28S rRNA catalyzes the critical step in polypeptide synthesis in addition to playing a major structural role. | 1 | Biochemistry |
The Molecular Kink Paradigm proceeds from the intuitive notion that molecular chains that make up a natural rubber (polyisoprene) network are constrained by surrounding chains to remain within a ‘tube’. Elastic forces produced in a chain, as a result of some applied strain, are propagated along the chain contour within this tube. Fig. 2 shows a representation of a four-carbon isoprene backbone unit with an extra carbon atom at each end to indicate its connections to adjacent units on a chain. It has three single C-C bonds and one double bond. It is principally by rotating about the C-C single bonds that a polyisoprene chain randomly explores its possible conformations. Sections of chain containing between two and three isoprene units have sufficient flexibility that they may be considered statistically de-correlated from one another. That is, there is no directional correlation along the chain for distances greater than this distance, referred to as a Kuhn length. These non-straight regions evoke the concept of ‘kinks’ and are in fact a manifestation of the random-walk nature of the chain. Since a kink is composed of several isoprene units, each having three carbon-carbon single bonds, there are many possible conformations available to a kink, each with a distinct energy and end-to-end distance. Over time scales of seconds to minutes, only these relatively short sections of the chain, i.e. kinks, have sufficient volume to move freely amongst their possible rotational conformations. The thermal interactions tend to keep the kinks in a state of constant flux, as they make transitions between all of their possible rotational conformations. Because the kinks are in thermal equilibrium, the probability that a kink resides in any rotational conformation is given by a Boltzmann distribution and we may associate an entropy with its end-to-end distance. The probability distribution for the end-to-end distance of a Kuhn length is approximately Gaussian and is determined by the Boltzmann probability factors for each state (rotational conformation). As a rubber network is stretched, some kinks are forced into a restricted number of more extended conformations having a greater end-to-end distance and it is the resulting decrease in entropy that produces an elastic force along the chain.
There are three distinct molecular mechanisms that produce these forces, two of which arise from changes in entropy that we shall refer to as low chain extension regime, Ia and moderate chain extension regime, Ib. The third mechanism occurs at high chain extension, as it is extended beyond its initial equilibrium contour length by the distortion of the chemical bonds along its backbone. In this case, the restoring force is spring-like and we shall refer to it as regime II. The three force mechanisms are found to roughly correspond to the three regions observed in tensile stress vs. strain experiments, shown in Fig. 1.
The initial morphology of the network, immediately after chemical cross-linking, is governed by two random processes: (1) The probability for a cross-link to occur at any isoprene unit and, (2) the random walk nature of the chain conformation. The end-to-end distance probability distribution for a fixed chain length, i.e. fixed number of isoprene units, is described by a random walk. It is the joint probability distribution of the network chain lengths and the end-to-end distances between their cross-link nodes that characterizes the network morphology. Because both the molecular physics mechanisms that produce the elastic forces and the complex morphology of the network must be treated simultaneously, simple analytic elasticity models are not possible; an explicit 3-dimensional numerical model is required to simulate the effects of strain on a representative volume element of a network. | 7 | Physical Chemistry |
Dimethyl methylphosphonate can be prepared from trimethyl phosphite and a halomethane (e.g. iodomethane) via the Michaelis–Arbuzov reaction.
Dimethyl methylphosphonate is a schedule 2 chemical as it may be used in the production of chemical weapons. It will react with thionyl chloride to produce methylphosphonic acid dichloride, which is used in the production of sarin and soman nerve agents. Various amines can be used to catalyse this process. It can be used as a sarin-simulant for the calibration of organophosphorus detectors. | 1 | Biochemistry |
A formyl group, –CHO, can be introduced by treating the aryl diazonium salt with formaldoxime (), followed by hydrolysis of the aryl aldoxime to give the aryl aldehyde. This reaction is known as the Beech reaction. | 0 | Organic Chemistry |
*Ensembl: [http://www.ensembl.org/biomart/martview/4e6c01c28faed033db52d0d30e4c21ab]
*OmicTools: [https://omictools.com/mtd-3-tool]
*Transcriptome Browser: [http://tagc.univ-mrs.fr/tbrowser/]
*ArrayExpress: [http://www.ebi.ac.uk/arrayexpress/] | 1 | Biochemistry |
The first such attempt is found in the Swain–Scott equation derived in 1953:
This free-energy relationship relates the pseudo first order reaction rate constant (in water at 25 °C), k, of a reaction, normalized to the reaction rate, k, of a standard reaction with water as the nucleophile, to a nucleophilic constant n for a given nucleophile and a substrate constant s that depends on the sensitivity of a substrate to nucleophilic attack (defined as 1 for methyl bromide).
This treatment results in the following values for typical nucleophilic anions: acetate 2.7, chloride 3.0, azide 4.0, hydroxide 4.2, aniline 4.5, iodide 5.0, and thiosulfate 6.4. Typical substrate constants are 0.66 for ethyl tosylate, 0.77 for β-propiolactone, 1.00 for 2,3-epoxypropanol, 0.87 for benzyl chloride, and 1.43 for benzoyl chloride.
The equation predicts that, in a nucleophilic displacement on benzyl chloride, the azide anion reacts 3000 times faster than water. | 7 | Physical Chemistry |
In 2008, Alpert coined the term, ERLIC (electrostatic repulsion hydrophilic interaction chromatography), for HILIC separations where an ionic column surface chemistry is used to repel a common ionic polar group on an analyte or within a set of analytes, to facilitate separation by the remaining polar groups. Electrostatic effects have an order of magnitude stronger chemical potential than neutral polar effects. This allows one to minimize the influence of a common, ionic group within a set of analyte molecules; or to reduce the degree of retention from these more polar functional groups, even enabling isocratic separations in lieu of a gradient in some situations. His subsequent publication further described orientation effects which others have also called ion-pair normal phase or e-HILIC, reflecting retention mechanisms sensitive to a particular ionic portion of the analyte, either attractive or repulsive. ERLIC (eHILIC) separations need not be isocratic, but the net effect is the reduction of the attraction of a particularly strong polar group, which then requires less strong elution conditions, and the enhanced interaction of the remaining polar (opposite charged ionic, or non-ionic) functional groups of the analyte(s).Based on the ERLIC column invented by Andrew Alpert, a new peptide mapping methodology was developed with unique properties of separation of asparagine deamidation and isomerization. This unique properties would be very beneficial for future mass spectrometry based multi-attributes monitoring in biologics quality control. | 1 | Biochemistry |
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