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Lockyer was born in Rugby, Warwickshire. His early introduction to science was through his father, who was a pioneer of the electric telegraph. After a conventional schooling supplemented by travel in Switzerland and France, he worked for some years as a civil servant in the British War Office. He settled in Wimbledon, South London after marrying Winifred James, who helped translate at least four French scientific works into English. He was a keen amateur astronomer with a particular interest in the Sun. In 1885 he became the world's first professor of astronomical physics at the Royal College of Science, South Kensington, now part of Imperial College. At the college, the Solar Physics Observatory was built for him and here he directed research until 1913.
In the 1860s Lockyer became fascinated by electromagnetic spectroscopy as an analytical tool for determining the composition of heavenly bodies. He conducted his research from his new home in West Hampstead, with a -inch telescope which he had already used in Wimbledon.
In 1868 a prominent yellow line was observed in a spectrum taken near the edge of the Sun. Its wavelength was about 588 nm, slightly less than the so-called "D" lines of sodium. The line could not be explained as due to any material known at the time, and so it was suggested by Lockyer, after he had observed it from London, that the yellow line was caused by an unknown solar element. He named this element helium after the Greek word Helios meaning sun. An observation of the new yellow line had been made earlier by Janssen at the 18 August 1868 solar eclipse
, and because their papers reached the French academy on the same day, he and Lockyer usually are awarded joint credit for helium's discovery. Terrestrial helium was found about 27 years later by the Scottish chemist William Ramsay. In his work on the identification of helium, Lockyer collaborated with the noted chemist Edward Frankland.
To facilitate the transmission of ideas between scientific disciplines, Lockyer established the general science journal Nature in 1869. He was elected as a member of the American Philosophical Society in 1874. He remained its editor until shortly before his death.
Lockyer led eight expeditions to observe solar eclipses for example in 1870 to Sicily, 1871 to India and 1898 to India.
Lockyer is among the pioneers of archaeoastronomy. Travelling 1890 in Greece he noticed the east–west orientation of many temples, in Egypt he found an orientation of temples to sunrise at midsummer and towards Sirius. Assuming orientation of the Heel-Stone of Stonehenge to sunrise at midsummer he calculated the construction of the monument to have taken place in 1680 BC. Radiocarbon dating in 1952 gave a date of 1800 BC. He also confirmed the alignment of the Parthenon on the rising point of the Pleiades and did extensive work on the solar and stellar alignments of Egyptian temples and their dating, presented in his book The Dawn Of Astronomy.
Lockyer's first wife Winifred née James died in 1879. They had six sons and two daughters in all. In 1903, Lockyer started a second marriage, to suffragist Thomazine Mary Brodhurst (née Browne). After his retirement in 1913, Lockyer established an observatory near his home in Salcombe Regis near Sidmouth, Devon. Originally known as the Hill Observatory, the site was renamed the Norman Lockyer Observatory after his death and directed by his fifth son William J.S. Lockyer. For a time the observatory was a part of the University of Exeter, but is now owned by the East Devon District Council, and run by the Norman Lockyer Observatory Society. The Norman Lockyer Chair in Astrophysics at the University of Exeter is currently held by Professor Tim Naylor, who is the member of the Astrophysics group there which studies star formation and extrasolar planets. Naylor was the lead scientist for the eSTAR Project.
Lockyer died at his home in Salcombe Regis in 1920, and was buried there in the churchyard of St Peter and St Mary. | 1 | Applied and Interdisciplinary Chemistry |
Maxwell’s thermodynamic surface is an 1874 sculpture made by Scottish physicist James Clerk Maxwell (1831–1879). This model provides a three-dimensional space of the various states of a fictitious substance with water-like properties. This plot has coordinates volume (x), entropy (y), and energy (z). It was based on the American scientist Josiah Willard Gibbs’ graphical thermodynamics papers of 1873. The model, in Maxwell's words, allowed "the principal features of known substances [to] be represented on a convenient scale." | 0 | Theoretical and Fundamental Chemistry |
An important aspect of improving chemical reactions is the understanding of the underlying reaction mechanism. To answer this question for C-H activation, time-resolved spectroscopic techniques can be used to follow the dynamics of the chemical reaction. This technique requires a trigger for initiating the process, which is in most cases illumination of the compound. Photoinitiated reactions of transition metal complexes with alkanes serve as a powerful model systems for understanding the cleavage of the strong C-H bond.
In such systems, the sample is illuminated with UV-light which excites an electron from the metal center to an unoccupied, antibonding ligand orbitals (MLCT), leading to ligand dissociation. This creates a highly reactive, electron deficient 16-electron intermediate, with a vacant coordination site. This species then binds to an alkane molecule, forming a σ-complex coordinating to a C-H bond. In a third step, the metal atom inserts into the C-H bond, cleaving it and yielding the C-H bond activated product.
The intermediates and their kinetics can be observed using different time-resolved spectroscopic techniques (e.g. TR-IR, TR-XAS, TR-RIXS). Time-resolved infrared spectroscopy (TR-IR) is a rather convenient method to observe these intermediates. However, it is only limited to complexes which have IR-active ligands and is prone to correct assignments on the femtosecond timescale due to underlying vibrational cooling. To answer the question of difference in reactivity for distinct complexes, the electronic structure of those needs to be investigated. This can be achieved by X-ray absorption spectroscopy (XAS) or resonant inelastic X-ray scattering (RIXS). These methods have been successfully used to follow the steps of C-H activation with orbital resolution and provide detailed insights into the responsible interactions for the C-H bond breaking.
Full characterization of the structure of methane bound to a metal center was reported by Girolami in 2023: isotopic perturbation of equilibrium (IPE) studies involving deuterated isotopologs showed that methane binds to the metal center through a single M···H-C bridge; changes in the J coupling constants indicate clearly that the structure of the methane ligand is significantly perturbed relative to the free molecule. | 0 | Theoretical and Fundamental Chemistry |
Where the viscosity is naturally high, such as polymer solutions and polymer melts, flow is normally laminar. The Reynolds number is very small and Stokes' law can be used to measure the viscosity of the fluid. Spheres are allowed to fall through the fluid and they reach the terminal velocity quickly, from which the viscosity can be determined.
The laminar flow of polymer solutions is exploited by animals such as fish and dolphins, who exude viscous solutions from their skin to aid flow over their bodies while swimming. It has been used in yacht racing by owners who want to gain a speed advantage by pumping a polymer solution such as low molecular weight polyoxyethylene in water, over the wetted surface of the hull.
It is, however, a problem for mixing polymers, because turbulence is needed to distribute fine filler (for example) through the material. Inventions such as the "cavity transfer mixer" have been developed to produce multiple folds into a moving melt so as to improve mixing efficiency. The device can be fitted onto extruders to aid mixing. | 1 | Applied and Interdisciplinary Chemistry |
In the sixth chapter puṇya (virtue) and pāpa (sin) are examined both as moral precepts and as discussed in the Vedas and Upanishads. | 1 | Applied and Interdisciplinary Chemistry |
For caisson closures, it is crucial to maintain the largest effective flow profile possible during installation. Additionally, the discharge coefficient must be as high as possible, indicating the degree to which flow is obstructed by the caisson's shape. | 1 | Applied and Interdisciplinary Chemistry |
Immunofluorescence (IF) is a light microscopy-based technique that allows detection and localization of a wide variety of target biomolecules within a cell or tissue at a quantitative level. The technique utilizes the binding specificity of antibodies and antigens. The specific region an antibody recognizes on an antigen is called an epitope. Several antibodies can recognize the same epitope but differ in their binding affinity. The antibody with the higher affinity for a specific epitope will surpass antibodies with a lower affinity for the same epitope.
By conjugating the antibody to a fluorophore, the position of the target biomolecule is visualized by exciting the fluorophore and measuring the emission of light in a specific predefined wavelength using a fluorescence microscope. It is imperative that the binding of the fluorophore to the antibody itself, do not interfere with the immunological specificity of the antibody or the binding capacity of its antigen.
Immunofluorescence is a widely used example of immunostaining (using antibodies to stain proteins) and is a specific example of immunohistochemistry (the use of the antibody-antigen relationship in tissues). This technique primarily utilizes fluorophores to visualize the location of the antibodies, while others provoke a color change in the environment containing the antigen of interest or make use of a radioactive label. Immunofluorescent techniques that utilized labelled antibodies was conceptualized in the 1940’s by Albert H. Coons.
Immunofluorescence is employed in foundational scientific investigations and clinical diagnostic endeavors, showcasing its multifaceted utility across diverse substrates, including tissue sections, cultured cell lines, or individual cells. Its usage includes analysis of the distribution of proteins, glycans, small biological and non-biological molecules, and visualization of structures such as intermediate-sized filaments.
If the topology of a cell membrane is undetermined, epitope insertion into proteins can be used in conjunction with immunofluorescence to determine structures within the cell membrane. Immunofluorescence (IF) can also be used as a “semi-quantitative” method to gain insight into the levels and localization patterns of DNA methylation. IF can additionally be used in combination with other, non-antibody methods of fluorescent staining, e.g., the use of DAPI to label DNA.
Examination of immunofluorescence specimens can be conducted utilizing various microscope configurations, including the epifluorescence microscope, confocal microscope, and widefield microscope. | 1 | Applied and Interdisciplinary Chemistry |
Knowing Newton’s Second Law stating force is equivalent to mass times acceleration, or , and that acceleration is the derivative of velocity, or (characteristic speed/time) in the case of fluid mechanics, we see
Since characteristic speed can be represented as length per unit time, , we get
where,
: m = mass,
: U = characteristic speed,
: L = characteristic length.
Dividing both sides by , we get
where,
: m = mass,
: U = characteristic speed,
: F = net external forces,
: L = characteristic length.
This provides a dimensionless basis for a relationship between mass, characteristic speed, net external forces, and length (size) which can be used to analyze the effects of fluid mechanics on a body with mass.
If the net external forces are predominantly elastic, we can use Hooke’s Law to see
where,
: k = spring constant (stiffness of elastic element),
: ΔL = deformation (change in length).
Assuming , then . With the natural resonant frequency of the elastic system, , being equal to , we get
where,
: m = mass,
: U = characteristic speed,
: = natural resonant frequency,
: ΔL = deformation (change in length).
Given that cyclic motion frequency can be represented by we get,
where,
: f = frequency,
: L = characteristic length,
: U = characteristic speed. | 1 | Applied and Interdisciplinary Chemistry |
When radiation enters the body, it will interact with the atoms and molecules of the cells (mainly made of water) to produce free radicals and molecules that are able to diffuse far enough to reach the critical target in the cell, the DNA, and damage it indirectly through some chemical reaction. This is the main damage mechanism for photons as they are used for example in external beam radiation therapy.
Typically, the radiolytic events that lead to the damage of the (tumor)-cell DNA are subdivided into different stages that take place on different time scales:
* The physical stage (), consists in the energy deposition by the ionizing particle and the consequent ionization of water.
* During the physico-chemical stage () numerous processes occur, e.g. the ionized water molecules may split into a hydroxyl radical and a hydrogen molecule or free electrons may undergo solvation.
* During the chemical stage (), the first products of radiolysis react with each other and with their surrounding, thus producing several reactive oxygen species which are able to diffuse.
* During the bio-chemical stage ( to days) these reactive oxygen species might break the chemical bonds of the DNA, thus triggering the response of enzymes, the immune-system, etc.
* Finally, during the biological stage (days up to years) the chemical damage may translate into biological cell death or oncogenesis when the damaged cells attempt to divide. | 0 | Theoretical and Fundamental Chemistry |
In geometric phase analysis, crystallographic quantities are not determined at one particular point of the input image. Instead, they are quantified across the whole image resulting in a two-dimensional map of given quantity. Quantities which can be mapped with geometric phase analysis include interplanar distances (d-spacing), strain tensor and displacement vector.
Since the calculations are performed in frequential domain, the input image of crystal lattice must be transformed into frequential representation using Fourier transform. From mathematical point of view, the frequential image is a complex matrix with the size equal to the original image. From crystallographic point of view, it can be seen as an artificial diffraction pattern or reciprocal image as it depicts reciprocal lattice. In this representation, the intensity peaks (or power peaks) correspond to the crystallographic planes depicted in the original image.
Due to the complex nature of the frequential image, it can be used to calculate amplitude and phase. Together with a vector of one crystallographic plane depicted in the image, the amplitude and phase can be used to generate a 2D map of d-spacing. If two vectors of non-parallel planes are known, the method can be used to generate maps of strain and displacement. | 0 | Theoretical and Fundamental Chemistry |
In a solar photoelectrochemical process, hydrogen can be produced by electrolysis. To use sunlight in this process, a photoelectrochemical cell can be used, where one photosensitized electrode converts light into an electric current that is then used for water splitting. One such type of cell is the dye-sensitized solar cell. This is an indirect process, since it produces electricity that then is used to form hydrogen. Another indirect process using sunlight is conversion of biomass to biofuel using photosynthetic organisms; however, most of the energy harvested by photosynthesis is used in life-sustaining processes and therefore lost for energy use.
A semiconductor can also be used as the photosensitizer. When a semiconductor is hit by a photon with an energy higher than the bandgap, an electron is excited to the conduction band and a hole is created in the valence band. Due to band bending, the electrons and holes move to the surface, where these charges are used to split the water molecules. Many different materials have been tested, but none so far have shown the requirements for practical application. | 0 | Theoretical and Fundamental Chemistry |
Maintenance respiration in plants refers to the amount of cellular respiration, measured by the carbon dioxide (CO) released or oxygen (O) consumed, during the generation of usable energy (mainly ATP, NADPH, and NADH) and metabolic intermediates used for (i) resynthesis of compounds that undergo renewal (turnover) in the normal process of metabolism (examples are enzymatic proteins, ribonucleic acids, and membrane lipids); (ii) maintenance of chemical gradients of ions and metabolites across cellular membranes that are necessary for cellular integrity and plant health; and (iii) operation of metabolic processes involved in physiological adjustment (i.e., acclimation) to a change in the plant's environment. The metabolic costs of the repair of injury from biotic or abiotic stress may also be considered a part of maintenance respiration.
Maintenance respiration is essential for biological health and growth of plants. It is estimated that about half of the respiration carried out by terrestrial plants during their lifetime is for the support of maintenance processes. Because typically more than half of global terrestrial plant photosynthesis (or gross primary production) is used for plant respiration, more than one quarter of global terrestrial plant photosynthesis is presumably consumed in maintenance respiration.
Maintenance respiration is a key component of most physiologically based mathematical models of plant growth, including models of crop growth and yield and models of ecosystem primary production and carbon balance. | 1 | Applied and Interdisciplinary Chemistry |
After DNA has been separated and purified by standard biochemical methods, one has a sample in a jar much like in the figure at the top of this article. Below are the main steps involved in generating structural information from X-ray diffraction studies of oriented DNA fibers that are drawn from the hydrated DNA sample with the help of molecular models of DNA that are combined with crystallographic and mathematical analysis of the X-ray patterns. | 0 | Theoretical and Fundamental Chemistry |
Chemistry of inorganic compounds, chemical thermodynamics of inorganic systems, crystal chemistry and electronic structure of inorganic substances etc. | 0 | Theoretical and Fundamental Chemistry |
Radioactivity is generally used in life sciences for highly sensitive and direct measurements of biological phenomena, and for visualizing the location of biomolecules radiolabelled with a radioisotope.
All atoms exist as stable or unstable isotopes and the latter decay at a given half-life ranging from attoseconds to billions of years; radioisotopes useful to biological and experimental systems have half-lives ranging from minutes to months. In the case of the hydrogen isotope tritium (half-life = 12.3 years) and carbon-14 (half-life = 5,730 years), these isotopes derive their importance from all organic life containing hydrogen and carbon and therefore can be used to study countless living processes, reactions, and phenomena. Most short lived isotopes are produced in cyclotrons, linear particle accelerators, or nuclear reactors and their relatively short half-lives give them high maximum theoretical specific activities which is useful for detection in biological systems.
Radiolabeling is a technique used to track the passage of a molecule that incorporates a radioisotope through a reaction, metabolic pathway, cell, tissue, organism, or biological system. The reactant is labeled by replacing specific atoms by their isotope. Replacing an atom with its own radioisotope is an intrinsic label that does not alter the structure of the molecule. Alternatively, molecules can be radiolabeled by chemical reactions that introduce an atom, moiety, or functional group that contains a radionuclide. For example, radio-iodination of peptides and proteins with biologically useful iodine isotopes is easily done by an oxidation reaction that replaces the hydroxyl group with iodine on tyrosine and histadine residues. Another example is to use chelators such DOTA that can be chemically coupled to a protein; the chelator in turn traps radiometals thus radiolabeling the protein. This has been used for introducing Yttrium-90 onto a monoclonal antibody for therapeutic purposes and for introducing Gallium-68 onto the peptide Octreotide for diagnostic imaging by PET imaging. (See DOTA uses.)
Radiolabeling is not necessary for some applications. For some purposes, soluble ionic salts can be used directly without further modification (e.g., gallium-67, gallium-68, and radioiodine isotopes). These uses rely on the chemical and biological properties of the radioisotope itself, to localize it within the organism or biological system.
Molecular imaging is the biomedical field that employs radiotracers to visualize and quantify biological processes using positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. Again, a key feature of using radioactivity in life science applications is that it is a quantitative technique, so PET/SPECT not only reveals where a radiolabelled molecule is but how much is there.
Radiobiology (also known as radiation biology) is a field of clinical and basic medical sciences that involves the study of the action of radioactivity on biological systems. The controlled action of deleterious radioactivity on living systems is the basis of radiation therapy. | 0 | Theoretical and Fundamental Chemistry |
An alternative method of decarburising pig iron was the finery forge, which seems to have been devised in the region around Namur in the 15th century. By the end of that century, this Walloon process spread to the Pay de Bray on the eastern boundary of Normandy, and then to England, where it became the main method of making wrought iron by 1600. It was introduced to Sweden by Louis de Geer in the early 17th century and was used to make the oregrounds iron favoured by English steelmakers.
A variation on this was the German forge. This became the main method of producing bar iron in Sweden. | 1 | Applied and Interdisciplinary Chemistry |
Technetium (Tc) exametazime is a radiopharmaceutical sold under the trade name Ceretec, and is used by nuclear medicine physicians for the detection of altered regional cerebral perfusion in stroke and other cerebrovascular diseases. It can also be used for the labelling of leukocytes to localise intra-abdominal infections and inflammatory bowel disease. Exametazime (the part without technetium) is sometimes referred to as hexamethylpropylene amine oxime or HMPAO, although correct chemical names are:
*(NE)-N-[(3R)-3-[[3-[[(2R,3E)-3-hydroxyiminobutan-2-yl]amino]-2,2-dimethylpropyl]amino]butan-2-ylidene]hydroxylamine
*or 3,3'-((2,2,-dimethyl-1,3-propanediyl)diimino)bis-2-butanone dioxime. | 0 | Theoretical and Fundamental Chemistry |
Metal complexes that have unpaired electrons are magnetic. Considering only monometallic complexes, unpaired electrons arise because the complex has an odd number of electrons or because electron pairing is destabilized. Thus, monomeric Ti(III) species have one "d-electron" and must be (para)magnetic, regardless of the geometry or the nature of the ligands. Ti(II), with two d-electrons, forms some complexes that have two unpaired electrons and others with none. This effect is illustrated by the compounds TiX[(CH)PCHCHP(CH)]: when X = Cl, the complex is paramagnetic (high-spin configuration), whereas when X = CH, it is diamagnetic (low-spin configuration). It is important to realize that ligands provide an important means of adjusting the ground state properties.
In bi- and polymetallic complexes, in which the individual centres have an odd number of electrons or that are high-spin, the situation is more complicated. If there is interaction (either direct or through ligand) between the two (or more) metal centres, the electrons may couple (antiferromagnetic coupling, resulting in a diamagnetic compound), or they may enhance each other (ferromagnetic coupling). When there is no interaction, the two (or more) individual metal centers behave as if in two separate molecules. | 0 | Theoretical and Fundamental Chemistry |
All seven STAT proteins share a common structural motif consisting of an N-terminal domain followed by a coiled-coil, DNA-binding domain, linker, Src homology 2 (SH2), and a C-terminal transactivation domain. Much research has focused on elucidating the roles each of these domains play in regulating different STAT isoforms. Both the N-terminal and SH2 domains mediate homo or heterodimer formation, while the coiled-coil domain functions partially as a nuclear localization signal (NLS). Transcriptional activity and DNA association are determined by the transactivation and DNA-binding domains, respectively. | 1 | Applied and Interdisciplinary Chemistry |
According to labeling experiments carried out in 1997, ammonium is biologically oxidized by hydroxylamine, most likely derived from nitrite, as the probable electron acceptor. The conversion of hydrazine to dinitrogen gas is hypothesized to be the reaction that generates the electron equivalents for the reduction of nitrite to hydroxylamine. In general, two possible reaction mechanisms are addressed:
* One mechanism hypothesizes that a membrane-bound enzyme complex converts ammonium and hydroxylamine to hydrazine first, followed by the oxidation of hydrazine to dinitrogen gas in the periplasm. At the same time, nitrite is reduced to hydroxylamine at the cytoplasmic site of the same enzyme complex responsible for hydrazine oxidation with an internal electron transport (Figure 3a).
* The other mechanism postulates the following: ammonium and hydroxylamine are converted to hydrazine by a membrane-bound enzyme complex, hydrazine is oxidized in the periplasm to dinitrogen gas, and the generated electrons are transferred via an electron transport chain to nitrite reducing enzyme in the cytoplasm where nitrite is reduced to hydroxylamine (Figure 3b).
Whether the reduction of nitrite and the oxidation of hydrazine occur at different sites of the same enzyme or the reactions are catalyzed by different enzyme systems connected via an electron transport chain remains to be investigated. In microbial nitrogen metabolism, the occurrence of hydrazine as an intermediate is rare. Hydrazine has been proposed as an enzyme-bound intermediate in the nitrogenase reaction.
Recently, using detailed molecular analyses and combining complementary methods, Kartal and coworkers published strong evidence supporting the latter mechanism.
Furthermore, the enzyme producing hydrazine, hydrazine synthase was purified and shown to produce hydrazine from NO and ammonium. The production of hydrazine from ammonium and NO was also supported by the resolution of the crystal structure of the enzyme hydrazine sythase.
A possible role of nitric oxide (NO) or nitroxyl (HNO) in anammox was proposed by Hooper et al. by way of condensation of NO or HNO and ammonium on an enzyme related to the ammonium monooxygenase family. The formed hydrazine or imine could subsequently be converted by the enzyme hydroxylamine oxidase to dinitrogen gas, and the reducing equivalents produced in the reaction are required to combine NO or HNO and ammonium or to reduce nitrite to NO. Environmental genomics analysis of the species Candidatus Kuenenia stuttgartiensis, through a slightly different and complementary metabolism mechanism, suggested NO to be the intermediate instead of hydroxylamine (Figure 4). However, this hypothesis also agreed that hydrazine was an important intermediate in the process. In this pathway (Figure 4), there are two enzymes unique to anammox bacteria: hydrazine synthase (hzs) and hydrazine dehydrogenase (hdh). The HZS produces hydrazine from nitric oxide and ammonium, and HDH transfer the electrons from hydrazine to ferredoxin. Few new genes, such as some known fatty acid biosynthesis and S-adenosylmethionine radical enzyme genes, containing domains involved in electron transfer and catalysis have been detected. Anammox microorganisms can also directly couple NO reduction to ammonia oxidation, without the need for nitrite supply.
Another, still unexplored, reaction mechanism involves anaerobic ammonium oxidation on anodes of bio-electrical systems. Such systems can be microbial fuel cells or microbial electrolysis cells. In the absence of dissolved oxygen, nitrite, or nitrate, microbes living in the anode compartment are able to oxidize ammonium to dinitrogen gas (N) just as in the classical anammox process. At the same time, they unload the liberated electrons onto the anode, producing electrical current. This electrical current can be used either directly in fuel cell mode or for hydrogen and methane gas production in electrolysis mode. While there is no clarity on the reaction mechanism behind, one hypothesis is that nitrite, nitrate, or dinitrogen oxide play a role as intermediates. However, since the process occurs at very low electrochemical potentials, other, more speculative, reaction mechanisms seem possible as well. | 1 | Applied and Interdisciplinary Chemistry |
Unlike simple dehydration in plants and animals, lichens may experience a complete loss of body water in dry periods. Lichens are capable of surviving extremely low levels of water content (poikilohydric). They quickly absorb water when it becomes available again, becoming soft and fleshy.
In tests, lichen survived and showed remarkable results on the adaptation capacity of photosynthetic activity within the simulation time of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the German Aerospace Center (DLR).
The European Space Agency has discovered that lichens can survive unprotected in space. In an experiment led by Leopoldo Sancho from the Complutense University of Madrid, two species of lichen—Rhizocarpon geographicum and Rusavskia elegans—were sealed in a capsule and launched on a Russian Soyuz rocket 31 May 2005. Once in orbit, the capsules were opened and the lichens were directly exposed to the vacuum of space with its widely fluctuating temperatures and cosmic radiation. After 15 days, the lichens were brought back to earth and were found to be unchanged in their ability to photosynthesize. | 1 | Applied and Interdisciplinary Chemistry |
Due to the initial lack of a formal definition after the initial conception, the term inherent chirality was utilized to describe a variety of chiral molecules that don't fall into other defined chirality types. The first fully formulated definition of inherent chirality was published in 2004 by Mandolini and Schiaffino, (and later modified by Szumna):
Inherent chirality has been known by a variety of names in the literature including bowl chirality (in fullerene fragments), intrinsic chirality, helicity (see section 3a) residual enantiomers (as applied to sterically hindered molecular propellers,) and cyclochirality (though this is often considered to be a more specific example and cannot be applied to all inherently chiral molecules).
A simple example of inherent chirality is that of corannulene commonly referred to as "bowl chirality" in the literature. The chirality of an unsubstituted corranulene (containing no classic stereogenic centers) cannot be seen in a 2D representation, but becomes clear when a 3D representation is evoked, as the C symmetry of corranulenes provides the molecules with a source of chirality (figure 2.) Racemization of these molecules is possible through an inversion of curvature, though some inherently chiral molecules have inversion barriers comparable to a classic chiral center. | 0 | Theoretical and Fundamental Chemistry |
Adult plant resistance (APR) is a specialist term referring to quantitative resistance that is not effective in the seedling stage but is effective throughout many remaining plant growth stages. The difference between adult plant resistance and seedling resistance is especially important in annual crops.
Seedling resistance is resistance which begins in the seedling stage of plant development and continues throughout its lifetime. When used by specialists, the term does not refer to resistance that is only active during the seedling stage. "Seedling resistance" is meant to be synonymous with major gene resistance or all stage resistance (ASR), and is used as a contrast to "adult plant resistance". Seedling resistance is often mediated by single R genes, but not all R genes encode seedling resistance. | 1 | Applied and Interdisciplinary Chemistry |
A proposed alternative source to chemiosmotic energy developing across membranous structures is if an electron acceptor, ferricyanide, is within a vesicle and the electron donor is outside, quinones transported by carbonaceous meteorites pick up electrons and protons from the donor. They would release electrons across the lipid membrane by diffusion to ferricyanide within the vesicles and release protons which produces gradients above pH 2, the process is conducive to the development of proton gradients. | 1 | Applied and Interdisciplinary Chemistry |
Cobalt oleate is an organometallic compound with the formula Co(CHO). When cobalt oleate is added to non-polar solvents, the viscosity rapidly increases, and then continues increasing over time. This unusual viscosity effect is caused by the formation of a weak coordination complex with the solvent molecules. | 0 | Theoretical and Fundamental Chemistry |
Tarenflurbil, Flurizan or R-flurbiprofen, is a single enantiomer of the racemate NSAID flurbiprofen. For several years, research and trials for the drug were conducted by Myriad Genetics, to investigate its potential as a treatment for Alzheimer's disease; that investigation concluded in June 2008 when the company announced it would discontinue development of the compound. | 0 | Theoretical and Fundamental Chemistry |
In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation.
By definition, when a medication is administered intravenously, its bioavailability is 100%. However, when a medication is administered via routes other than intravenous, its bioavailability is lower due to intestinal epithelium absorption and first-pass metabolism. Thereby, mathematically, bioavailability equals the ratio of comparing the area under the plasma drug concentration curve versus time (AUC) for the extravascular formulation to the AUC for the intravascular formulation. AUC is used because AUC is proportional to the dose that has entered the systemic circulation.
Bioavailability of a drug is an average value; to take population variability into account, deviation range is shown as ±. To ensure that the drug taker who has poor absorption is dosed appropriately, the bottom value of the deviation range is employed to represent real bioavailability and to calculate the drug dose needed for the drug taker to achieve systemic concentrations similar to the intravenous formulation. To dose without knowing the drug taker's absorption rate, the bottom value of the deviation range is used in order to ensure the intended efficacy, unless the drug is associated with a narrow therapeutic window.
For dietary supplements, herbs and other nutrients in which the route of administration is nearly always oral, bioavailability generally designates simply the quantity or fraction of the ingested dose that is absorbed. | 1 | Applied and Interdisciplinary Chemistry |
Gustav Robert Kirchhoff (; 12 March 1824 – 17 October 1887) was a German physicist and mathematician who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects.
He coined the term black-body radiation in 1860.
Several different sets of concepts are named "Kirchhoffs laws" after him, which include Kirchhoffs circuit laws, Kirchhoffs law of thermal radiation, and Kirchhoffs law of thermochemistry.
The Bunsen–Kirchhoff Award for spectroscopy is named after Kirchhoff and his colleague, Robert Bunsen. | 1 | Applied and Interdisciplinary Chemistry |
Polymers are susceptible to attack by atmospheric oxygen, especially at elevated temperatures encountered during processing to shape. Many process methods such as extrusion and injection moulding involve pumping molten polymer into tools, and the high temperatures needed for melting may result in oxidation unless precautions are taken. For example, a forearm crutch suddenly snapped and the user was severely injured in the resulting fall. The crutch had fractured across a polypropylene insert within the aluminium tube of the device, and IR spectroscopy of the material showed that it had oxidised, possibly as a result of poor moulding.
Oxidation is usually relatively easy to detect, owing to the strong absorption by the carbonyl group in the spectrum of polyolefins. Polypropylene has a relatively simple spectrum, with few peaks at the carbonyl position (like polyethylene). Oxidation tends to start at tertiary carbon atoms because free radicals here are more stable, so last longer and are attacked by oxygen. The carbonyl group can be further oxidised to break the chain, so weakening the material by lowering the molecular weight, and cracks start to grow in the regions affected. | 0 | Theoretical and Fundamental Chemistry |
Andrée Marquet and her collaborators have been interested in reaction mechanisms in organic chemistry, in particular those involving carbanions (enolates, alpha anions of sulfoxides), and have used the results of these studies in synthesis, for example for total synthesis of biotin.
She then turned to mechanistic enzymology, applying the approach used in organic chemistry to the functioning of enzymes.
The main areas covered are :
* steroid biochemistry: inhibition of the biosynthesis of aldosterone (among the various compounds synthesized and tested, 18-vinyl progesterone proved to be an excellent inhibitor of Cytochrome P450 involved in the last stage of this biosynthesis, making this molecule a potential hypotensor.
* the mechanism of action of vitamin K, an essential cofactor in the cascade of blood coagulation reactions.
* the biotin biosynthesis pathway: the mechanism of several of the enzymes involved has been deciphered and various inhibitors have been designed and synthesized. A particularly difficult problem to which Andrée Marquet and her team have made a decisive contribution is that of the mechanism of biotin synthase, which catalyses the final step.
They have shown that it belongs to the newly discovered family of proteins (Fe-S) dependent on S-Adenosylmethionine, catalysing radical reactions. This is a family that opens a new chapter in enzymology.
Another field of activity of the laboratory, the result of a collaboration with the neurobiology laboratory of the Collège de France (Prof. Jacques Glovinski) concerns the activity of a family of peptide neurotransmitters, the tachykinins. | 0 | Theoretical and Fundamental Chemistry |
Rotating-polarization coherent anti-Stokes Raman spectroscopy, (RP-CARS) is a particular implementation of the coherent anti-Stokes Raman spectroscopy (CARS). RP-CARS takes advantage of polarization-dependent selection rules in order to gain information about molecule orientation anisotropy and direction within the optical point spread function. | 0 | Theoretical and Fundamental Chemistry |
The game of Tetris is a puzzle game in which blocks of 4 are adsorbed onto a surface during game play. Scientists have used Tetris blocks "as a proxy for molecules with a complex shape" and their "adsorption on a flat surface" for studying the thermodynamics of nanoparticles. | 0 | Theoretical and Fundamental Chemistry |
The nomenclature of modified GFPs is often confusing due to overlapping mapping of several GFP versions onto a single name. For example, mGFP often refers to a GFP with an N-terminal palmitoylation that causes the GFP to bind to cell membranes. However, the same term is also used to refer to monomeric GFP, which is often achieved by the dimer interface breaking A206K mutation. Wild-type GFP has a weak dimerization tendency at concentrations above 5 mg/mL. mGFP also stands for "modified GFP," which has been optimized through amino acid exchange for stable expression in plant cells. | 1 | Applied and Interdisciplinary Chemistry |
Cleavage stimulatory factor or cleavage stimulation factor (CstF or CStF) is a heterotrimeric protein, made up of the proteins CSTF1 (55kDa), CSTF2 (64kDa) and CSTF3 (77kDa), totalling about 200 kDa. It is involved in the cleavage of the 3 signaling region from a newly synthesized pre-messenger RNA (mRNA) molecule. CstF is recruited by cleavage and polyadenylation specificity factor (CPSF) and assembles into a protein complex on the 3 end to promote the synthesis of a functional polyadenine tail, which results in a mature mRNA molecule ready to be exported from the cell nucleus to the cytosol for translation.
The amount of CstF in a cell is dependent on the phase of the cell cycle, increasing significantly during the transition from G0 phase to S phase in mouse fibroblast and human splenic B cells. | 1 | Applied and Interdisciplinary Chemistry |
Transcriptomics allows identification of genes and pathways that respond to and counteract biotic and abiotic environmental stresses. The non-targeted nature of transcriptomics allows the identification of novel transcriptional networks in complex systems. For example, comparative analysis of a range of chickpea lines at different developmental stages identified distinct transcriptional profiles associated with drought and salinity stresses, including identifying the role of transcript isoforms of AP2-EREBP. Investigation of gene expression during biofilm formation by the fungal pathogen Candida albicans revealed a co-regulated set of genes critical for biofilm establishment and maintenance.
Transcriptomic profiling also provides crucial information on mechanisms of drug resistance. Analysis of over 1000 isolates of Plasmodium falciparum, a virulent parasite responsible for malaria in humans, identified that upregulation of the unfolded protein response and slower progression through the early stages of the asexual intraerythrocytic developmental cycle were associated with artemisinin resistance in isolates from Southeast Asia.
The use of transcriptomics is also important to investigate responses in the marine environment. In marine ecology, "stress" and "adaptation" have been among the most common research topics, especially related to anthropogenic stress, such as global change and pollution. Most of the studies in this area have been done in animals, although invertebrates have been underrepresented. One issue still is a deficiency in functional genetic studies, which hamper gene annotations, especially for non-model species, and can lead to vague conclusions on the effects of responses studied. | 1 | Applied and Interdisciplinary Chemistry |
The popularity and success of the Joback method mainly originates from the single group list for all properties. This allows one to get all eleven supported properties from a single analysis of the molecular structure.
The Joback method additionally uses a very simple and easy to assign group scheme, which makes the method usable for people with only basic chemical knowledge. | 0 | Theoretical and Fundamental Chemistry |
The solid-gas flow systems are present in many industrial applications, as dry, catalytic reactors, settling tanks, pneumatic conveying of solids, among others. Obviously, in industrial operations the drag rule is not simple as a single sphere settling in a stationary fluid. However, this knowledge indicates how drag behaves in more complex systems, which are designed and studied by engineers applying empirical and more sophisticated tools.
For example, settling tanks are used for separating solids and/or oil from another liquid. In food processing, the vegetable is crushed and placed inside of a settling tank with water. The oil floats to the top of the water then is collected. In drinking water and waste water treatment a flocculant or coagulant is often added prior to settling to form larger particles that settle out quickly in a settling tank or (lamella) clarifier, leaving the water with a lower turbidity.
In winemaking, the French term for this process is débourbage. This step usually occurs in white wine production before the start of fermentation. | 0 | Theoretical and Fundamental Chemistry |
Electrochemical reactions in water are better analyzed by using the ion-electron method, where H, OH ion, HO and electrons (to compensate the oxidation changes) are added to the cell's half-reactions for oxidation and reduction. | 0 | Theoretical and Fundamental Chemistry |
Homochirality is a uniformity of chirality, or handedness. Objects are chiral when they cannot be superposed on their mirror images. For example, the left and right hands of a human are approximately mirror images of each other but are not their own mirror images, so they are chiral. In biology, 19 of the 20 natural amino acids are homochiral, being -chiral (left-handed), while sugars are -chiral (right-handed). Homochirality can also refer to enantiopure substances in which all the constituents are the same enantiomer (a right-handed or left-handed version of an atom or molecule), but some sources discourage this use of the term.
It is unclear whether homochirality has a purpose; however, it appears to be a form of information storage. One suggestion is that it reduces entropy barriers in the formation of large organized molecules. It has been experimentally verified that amino acids form large aggregates in larger abundance from an enantiopure samples of the amino acid than from racemic (enantiomerically mixed) ones.
It is not clear whether homochirality emerged before or after life, and many mechanisms for its origin have been proposed. Some of these models propose three distinct steps: mirror-symmetry breaking creates a minute enantiomeric imbalance, chiral amplification builds on this imbalance, and chiral transmission is the transfer of chirality from one set of molecules to another. | 0 | Theoretical and Fundamental Chemistry |
The basis for the COD test is that nearly all organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic conditions. The amount of oxygen required to oxidize an organic compound to carbon dioxide, ammonia, and water is given by:
This expression does not include the oxygen demand caused by nitrification, the oxidation of ammonia into nitrate:
Dichromate, the oxidizing agent for COD determination, does not oxidize ammonia into nitrate, so nitrification is not included in the standard COD test.
The International Organization for Standardization describes a standard method for measuring chemical oxygen demand in ISO 6060 [http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=12260&ICS1=13&ICS2=60&ICS3=50]. | 0 | Theoretical and Fundamental Chemistry |
Unlike ideal gases, the temperature of a real gas will change during a Joule expansion. At temperatures below their inversion temperature gases will cool during Joule expansion, while at higher temperatures they will heat up. The inversion temperature of a gas is typically much higher than room temperature; exceptions are helium, with an inversion temperature of about 40 K, and hydrogen, with an inversion temperature of about 200 K. Since the internal energy of the gas during Joule expansion is constant, cooling must be due to the conversion of internal kinetic energy to internal potential energy, with the opposite being the case for warming.
Intermolecular forces are repulsive at short range and attractive at long range (for example, see the Lennard-Jones potential). Since distances between gas molecules are large compared to molecular diameters, the energy of a gas is usually influenced mainly by the attractive part of the potential. As a result, expanding a gas usually increases the potential energy associated with intermolecular forces. Some textbooks say that for gases this must always be the case and that a Joule expansion must always produce cooling. When molecules are close together, however, repulsive interactions are much more important and it is thus possible to get an increase in temperature during a Joule expansion.
It is theoretically predicted that, at sufficiently high temperature, all gases will warm during a Joule expansion The reason is that at any moment, a very small number of molecules will be undergoing collisions; for those few molecules, repulsive forces will dominate and the potential energy will be positive. As the temperature rises, both the frequency of collisions and the energy involved in the collisions increase, so the positive potential energy associated with collisions increases strongly. If the temperature is high enough, that can make the total potential energy positive, in spite of the much larger number of molecules experiencing weak attractive interactions. When the potential energy is positive, a constant energy expansion reduces potential energy and increases kinetic energy, resulting in an increase in temperature. This behavior has only been observed for hydrogen and helium; which have very weak attractive interactions. For other gases this "Joule inversion temperature" appears to be extremely high. | 0 | Theoretical and Fundamental Chemistry |
Vinylphosphonic acid can be prepared by the reaction of PCl and acetaldehyde:
:PCl + CHCHO → CHCH(O)
This adduct reacts with acetic acid:
: CHCH(O) + 2 CHCOH → CHCH(Cl)PO(OH) + 2 CHCOCl
This chloride undergoes dehydrochlorination to afford the target:
:CHCH(Cl)PO(OH) → CH=CHPO(OH) + HCl
In the Kinnear–Perren reaction alkylphosphonyl dichlorides and esters are generated by alkylation of phosphorus trichloride in the presence of aluminium trichloride. Alkyltrichlorophosphonium salts are intermediates:
:PCl + RCl + AlCl → RPCl + AlCl
The RPCl product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl. | 0 | Theoretical and Fundamental Chemistry |
In electrochemistry, the Butler–Volmer equation (named after John Alfred Valentine Butler and Max Volmer), also known as Erdey-Grúz–Volmer equation, is one of the most fundamental relationships in electrochemical kinetics. It describes how the electrical current through an electrode depends on the voltage difference between the electrode and the bulk electrolyte for a simple, unimolecular redox reaction, considering that both a cathodic and an anodic reaction occur on the same electrode: | 0 | Theoretical and Fundamental Chemistry |
Thalidomide, sold under the brand names Contergan and Thalomid among others, is an oral medication used to treat a number of cancers (e.g., multiple myeloma), graft-versus-host disease, and many skin disorders (e.g., complications of leprosy such as skin lesions). While thalidomide has been used in a number of HIV-associated conditions, such use is associated with increased levels of the virus.
Common side effects include sleepiness, rash, and dizziness. Severe side effects include tumor lysis syndrome, blood clots, and peripheral neuropathy. Thalidomide is a known human teratogen and carries an extremely high risk of severe, life-threatening birth defects if administered during pregnancy. It causes skeletal deformities such as amelia (absence of legs and/or arms), absence of bones, and phocomelia (malformation of the limbs). A single dose of thalidomide, regardless of dosage, is enough to cause teratogenic effects.
Thalidomide was first marketed in 1957 in West Germany, where it was available over the counter. When first released, thalidomide was promoted for anxiety, trouble sleeping, "tension", and morning sickness. While it was initially thought to be safe in pregnancy, concerns regarding birth defects arose, resulting in its removal from the market in Europe in 1961. The total number of infants affected by thalidomide use during pregnancy is estimated at 10,000, of whom about 40% died around the time of birth. Those who survived had limb, eye, urinary tract, and heart problems. Its initial entry into the US market was prevented by Frances Kelsey, a reviewer at the FDA. The birth defects caused by thalidomide led to the development of greater drug regulation and monitoring in many countries.
It was approved in the United States in 1998 for use as a treatment for cancer. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. | 0 | Theoretical and Fundamental Chemistry |
Photofermentation via purple nonsulfur producing bacteria has been explored as a method for the production of biofuel. The natural fermentation product of these bacteria, hydrogen gas, can be harnessed as a natural gas energy source. Photofermentation via algae instead of bacteria is used for bioethanol production, among other liquid fuel alternatives. | 1 | Applied and Interdisciplinary Chemistry |
Triatomic hydrogen or H is an unstable triatomic molecule containing only hydrogen. Since this molecule contains only three atoms of hydrogen it is the simplest triatomic molecule and it is relatively simple to numerically solve the quantum mechanics description of the particles. Being unstable the molecule breaks up in under a millionth of a second. Its fleeting lifetime makes it rare, but it is quite commonly formed and destroyed in the universe thanks to the commonness of the trihydrogen cation. The infrared spectrum of H due to vibration and rotation is very similar to that of the ion, . In the early universe this ability to emit infrared light allowed the primordial hydrogen and helium gas to cool down so as to form stars. | 0 | Theoretical and Fundamental Chemistry |
Taurates (or taurides) are a group of mild anionic surfactants. They are composed of a hydrophilic head group, consisting of N-methyltaurine (2-methylaminoethanesulfonic acid) and a lipophilic residue, consisting of a long-chain carboxylic acid (fatty acid), both linked via an amide bond. The fatty acids used could be lauric (C), myristic (C), palmitic (C) or stearic acid (C), but mainly mixtures of oleic acid (C) and coconut fatty acid (C – C) are used. Besides sodium, no other counterions play a relevant role (these could be e. g. ammonium or other alkali or alkaline earth metals). | 0 | Theoretical and Fundamental Chemistry |
Protein foams contain natural proteins as the foaming agents. Unlike synthetic foams, protein foams are bio-degradable. They flow and spread slower, but provide a foam blanket that is more heat-resistant and more durable.
Protein foams include regular protein foam (P), fluoroprotein foam (FP) (a mixture of protein foam and fluorinated surfactants), film-forming fluoroprotein (FFFP), alcohol-resistant fluoroprotein foam (AR-FP), and alcohol-resistant film-forming fluoroprotein (AR-FFFP). | 0 | Theoretical and Fundamental Chemistry |
Synthetic accessibility is a simple approach to network simulation whose goal is to predict which metabolic gene knockouts are lethal. The synthetic accessibility approach uses the topology of the metabolic network to calculate the sum of the minimum number of steps needed to traverse the metabolic network graph from the inputs, those metabolites available to the organism from the environment, to the outputs, metabolites needed by the organism to survive. To simulate a gene knockout, the reactions enabled by the gene are removed from the network and the synthetic accessibility metric is recalculated. An increase in the total number of steps is predicted to cause lethality. Wunderlich and Mirny showed this simple, parameter-free approach predicted knockout lethality in E. coli and S. cerevisiae as well as elementary mode analysis and flux balance analysis in a variety of media. | 1 | Applied and Interdisciplinary Chemistry |
In biochemistry, the Corey-Pauling rules are a set of three basic statements that govern the secondary nature of proteins, in particular, the CO-NH peptide link. They were originally proposed by Robert Corey and Linus Pauling.
The rules are as follows:
#The atoms in a peptide link all lie on the same plane.
#The nitrogen, hydrogen, and oxygen atoms in a hydrogen bond are approximately in a straight line.
#The carbon-oxygen and nitrogen-hydrogen groups are all involved in bonding. | 0 | Theoretical and Fundamental Chemistry |
Oxygen saturation (symbol S) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can be measured with a dissolved oxygen probe such as an oxygen sensor or an optode in liquid media, usually water. The standard unit of oxygen saturation is percent (%).
Oxygen saturation can be measured regionally and noninvasively. Arterial oxygen saturation (Sa) is commonly measured using pulse oximetry. Tissue saturation at peripheral scale can be measured using NIRS. This technique can be applied on both muscle and brain. | 0 | Theoretical and Fundamental Chemistry |
The crystal field stabilization energy (CFSE) is the stability that results from placing a transition metal ion in the crystal field generated by a set of ligands. It arises due to the fact that when the d-orbitals are split in a ligand field (as described above), some of them become lower in energy than before with respect to a spherical field known as the barycenter in which all five d-orbitals are degenerate. For example, in an octahedral case, the t set becomes lower in energy than the orbitals in the barycenter. As a result of this, if there are any electrons occupying these orbitals, the metal ion is more stable in the ligand field relative to the barycenter by an amount known as the CFSE. Conversely, the e orbitals (in the octahedral case) are higher in energy than in the barycenter, so putting electrons in these reduces the amount of CFSE.
If the splitting of the d-orbitals in an octahedral field is Δ, the three t orbitals are stabilized relative to the barycenter by / Δ, and the e orbitals are destabilized by / Δ. As examples, consider the two d configurations shown further up the page. The low-spin (top) example has five electrons in the t orbitals, so the total CFSE is 5 x / Δ = 2Δ. In the high-spin (lower) example, the CFSE is (3 x / Δ) - (2 x / Δ) = 0 - in this case, the stabilization generated by the electrons in the lower orbitals is canceled out by the destabilizing effect of the electrons in the upper orbitals. | 0 | Theoretical and Fundamental Chemistry |
Many examples exist that demonstrate the utility of DCvC in macrocycle synthesis. This type of chemistry is effective for large macrocycle synthesis because the thermodynamic template effect is well suited to stabilize ring structures. Furthermore, the error-correcting ability inherent to DCvC allows large structures to be made without flaws. | 0 | Theoretical and Fundamental Chemistry |
NPP3 is probably a major contributor to nucleotide metabolism in the intestine and liver.
Intestinal NPP3 would be involved in hydrolyzing food-derived nucleotides.
The liver releases ATP and ADP into the bile to regulate bile secretion. It subsequently reclaims adenosine via a pathway that probably contains NPP3. | 1 | Applied and Interdisciplinary Chemistry |
The most general form of the equation, suitable for use in thermodynamics in case of (quasi) steady flow, is:
Here is the enthalpy per unit mass (also known as specific enthalpy), which is also often written as (not to be confused with "head" or "height").
Note that
where is the thermodynamic energy per unit mass, also known as the specific internal energy. So, for constant internal energy the equation reduces to the incompressible-flow form.
The constant on the right-hand side is often called the Bernoulli constant and denoted . For steady inviscid adiabatic flow with no additional sources or sinks of energy, is constant along any given streamline. More generally, when may vary along streamlines, it still proves a useful parameter, related to the "head" of the fluid (see below).
When the change in can be ignored, a very useful form of this equation is:
where is total enthalpy. For a calorically perfect gas such as an ideal gas, the enthalpy is directly proportional to the temperature, and this leads to the concept of the total (or stagnation) temperature.
When shock waves are present, in a reference frame in which the shock is stationary and the flow is steady, many of the parameters in the Bernoulli equation suffer abrupt changes in passing through the shock. The Bernoulli parameter remains unaffected. An exception to this rule is radiative shocks, which violate the assumptions leading to the Bernoulli equation, namely the lack of additional sinks or sources of energy. | 1 | Applied and Interdisciplinary Chemistry |
Nicotinamide adenine dinucleotide consists of two nucleosides joined by pyrophosphate. The nucleosides each contain a ribose ring, one with adenine attached to the first carbon atom (the 1' position) (adenosine diphosphate ribose) and the other with nicotinamide at this position.
The compound accepts or donates the equivalent of H. Such reactions (summarized in formula below) involve the removal of two hydrogen atoms from the reactant (R), in the form of a hydride ion (H), and a proton (H). The proton is released into solution, while the reductant RH is oxidized and NAD reduced to NADH by transfer of the hydride to the nicotinamide ring.
:RH + NAD → NADH + H + R;
From the hydride electron pair, one electron is attracted to the slightly more electronegative atom of the nicotinamide ring of NAD, becoming part of the nicotinamide moiety. The second electron and proton atom are transferred to the carbon atom adjacent to the N atom. The midpoint potential of the NAD/NADH redox pair is −0.32 volts, which makes NADH a moderately strong reducing agent. The reaction is easily reversible, when NADH reduces another molecule and is re-oxidized to NAD. This means the coenzyme can continuously cycle between the NAD and NADH forms without being consumed.
In appearance, all forms of this coenzyme are white amorphous powders that are hygroscopic and highly water-soluble. The solids are stable if stored dry and in the dark. Solutions of NAD are colorless and stable for about a week at 4 °C and neutral pH, but decompose rapidly in acidic or alkaline solutions. Upon decomposition, they form products that are enzyme inhibitors.
Both NAD and NADH strongly absorb ultraviolet light because of the adenine. For example, peak absorption of NAD is at a wavelength of 259 nanometers (nm), with an extinction coefficient of 16,900 Mcm. NADH also absorbs at higher wavelengths, with a second peak in UV absorption at 339 nm with an extinction coefficient of 6,220 Mcm. This difference in the ultraviolet absorption spectra between the oxidized and reduced forms of the coenzymes at higher wavelengths makes it simple to measure the conversion of one to another in enzyme assays – by measuring the amount of UV absorption at 340 nm using a spectrophotometer.
NAD and NADH also differ in their fluorescence. Freely diffusing NADH in aqueous solution, when excited at the nicotinamide absorbance of ~335 nm (near-UV), fluoresces at 445–460 nm (violet to blue) with a fluorescence lifetime of 0.4 nanoseconds, while NAD does not fluoresce. The properties of the fluorescence signal changes when NADH binds to proteins, so these changes can be used to measure dissociation constants, which are useful in the study of enzyme kinetics. These changes in fluorescence are also used to measure changes in the redox state of living cells, through fluorescence microscopy.
NADH can be converted to NAD+ in a reaction catalysed by copper, which requires hydrogen peroxide. Thus, the supply of NAD+ in cells requires mitochondrial copper(II). | 0 | Theoretical and Fundamental Chemistry |
Large dams and the production of hydropower are an important part of today's energy supply and cover a broad part of river engineering. The approach of releasing small quantities of water through turbines responds to the growing power demand from rapidly growing cities; however, it also flattens the rivers hydrographs, and is responsible for a decline in seasonal hydraulic variability and for the loss of delta-building dynamics, as the sediments are stored in the reservoir. Small-scale users of the deltas lose the biodiversity and ecosystem productivity on which they depend.
The aquatic ecosystem consists of a chain of organisms which are dependent on each other. When pollution causes harm to one organism only, this process can start a chain reaction and danger the entire aquatic habitat. When the proliferation of newly introduces nutrients evoke plant and algae growth, oxygen levels in the water decrease. This process, known as eutrophication, suffocates plants and animals and leads to dead zones i.e. water habitats without any life. Chemicals and heavy metals from industrial wastewater are also toxic to aquatic life. They can shorten an organism's life span and its ability to reproduce while also endangering humans, since humans may feed on these organisms and any toxic impacts on these organisms may adversely impact humans. | 1 | Applied and Interdisciplinary Chemistry |
In the case of capillary rise between two parallel plates, height of capillary rise can be predicted as Jurin's height if plates are rigid. Longer the plates, more flexible they become, consequently plates coalesce as a result of deformation induced by capillary force. As observed, length of capillary rise L between elastic plates increases linearly with total length of plates L, sets length of dry L=L-L nearly a constant. By balancing gain of surface energy by capillary force and loss of elastic energy by banding a flexible sheet and minimizing with respect to L, dry length was found to be:
Where
is the elastocapillary length of sheets
w is the distance between two parallel sheets
This L sets the minimum length for parallel sheets to collapse, sheets spontaneously coalesce if they are longer than L.
Above result can be generalized to multiple parallel plates when N elastic plates were used. By assuming these N sheets is N times more rigid than single sheet, such system can be treated as two bundles of N/2 sheets with a distance Nw/2. Thus the dry length can be written as: | 1 | Applied and Interdisciplinary Chemistry |
In 2013, Dr. Earle McBride, a researcher studying sandstone diagenesis and the textual and compositional maturation of sand during transportation, mixed samples collected from Omaha Beach in 1988 with a blue epoxy, creating an "artificial sandstone", before slicing it into thin sections. Utilising an optical microscope and an external light source, shiny, opaque grains could be identified. Although wave action had elicited rounding on the edges of some coarser grains, the shard-like angularity and corrosion of both coarse and fine grains suggested these grains were man-made. It is believed that the roughness of said grains was imparted by microporous surfaces produced during production and corrosion products post-explosion.
This inspection, alongside tests revealing that the grains were magnetic, led McBride to conclude these grains were pieces of shrapnel. | 1 | Applied and Interdisciplinary Chemistry |
Evidence showing neurturin’s role in neuron survival and management has made it a popular candidate for the potential treatment or reversal of neurodegeneration. In addition, mice models have shown the dying neurons exposed to trophic factors can be rescued. Neurturin is an example of a trophic factor that is difficult to utilize clinically because of its inability to cross the blood-brain barrier of the CNS (central nervous system). Ceregene sponsored a double-blind phase II clinical trial of CERE-120, a viral vector mediated gene transfer drug that allows for the continuous delivery of neurturin to the nigrostratial system. The hope was to reverse damaged and diseased tissue in Parkinson's patients and overall slow the progression of the disease. However, results were inconclusive and showed that while the drug appears to be relatively safe, there was no statistically significant data supporting the improvement of motor function or neuronal health. Neurturin’s therapeutic potential is unknown and future studies aim to improve delivery of the drug. | 1 | Applied and Interdisciplinary Chemistry |
The Lippmann-Schwinger equation for Green's operator is called the resolvent identity,
Its solution by iteration leads to the Born series for the full Green's operator | 0 | Theoretical and Fundamental Chemistry |
Siderophile (from sideron, "iron", and phileo, "love") elements are the transition metals which tend to sink into the core because they dissolve readily in iron either as solid solutions or in the molten state, although some sources include elements which are not transition metals in their list of siderophiles, such as germanium. Other sources may also differ in their list based on the temperature being discussed – niobium, vanadium, chromium, and manganese may be considered siderophiles or not, depending on the assumed temperature and pressure. Also confusing the issue is that some elements, such as the aforementioned manganese, as well as molybdenum, form strong bonds with oxygen, but in the free state (as they existed on the primitive Earth when free oxygen did not exist) can mix so easily with iron that they do not concentrate in the siliceous crust, as do true lithophile elements. Iron, meanwhile, is simply everywhere.
The siderophile elements include the highly siderophilic ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, and gold, the moderately siderophilic cobalt and nickel, in addition to the "disputed" elements mentioned earlier – some sources even include tungsten and silver.
Most siderophile elements have practically no affinity whatsoever for oxygen: indeed oxides of gold are thermodynamically unstable with respect to the elements. They form stronger bonds with carbon or sulfur, but even these are not strong enough to separate out with the chalcophile elements. Thus, siderophile elements are bound through metallic bonds with iron in the dense layer of the Earths core, where pressures may be high enough to keep the iron solid. Manganese, iron, and molybdenum do form strong bonds with oxygen, but in the free state (as they existed on the primitive Earth when free oxygen did not exist) can mix so easily with iron that they do not concentrate in the siliceous crust, as do true lithophile elements. However, ores of manganese are found in much the same sites as are those of aluminium and titanium, owing to manganeses great reactivity towards oxygen.
Because they are so concentrated in the dense core, siderophile elements are known for their rarity in the Earths crust. Most of them have always been known as precious metals because of this. Iridium is the rarest transition metal occurring within the Earths crust, with an abundance by mass of less than one part per billion. Mineable deposits of precious metals usually form as a result of the erosion of ultramafic rocks, but are not highly concentrated even compared to their crustal abundances, which are typically several orders of magnitude below their solar abundances. However, because they are concentrated in the Earth's mantle and core, siderophile elements are believed to be present in the Earth as a whole (including the core) in something approaching their solar abundances. | 0 | Theoretical and Fundamental Chemistry |
Since DPP-4 is a protease, it is not unexpected that inhibitors would likely have a peptide nature and this theme has carried through to contemporary research. | 1 | Applied and Interdisciplinary Chemistry |
Signatures of mass-anomalous sulfur isotope fractionation preserved in the rock record have been an important piece of evidence for understanding the Great Oxidation Event, the sudden rise of oxygen on the ancient Earth. Nonzero values of ΔS and ΔS are present in the sulfur-bearing minerals of Precambrian rock formed greater than 2.45 billion years ago, but completely absent from rock less than 2.09 billion years old. Multiple mechanisms have been proposed for how oxygen prevents the fingerprints of mass-anomalous fractionation from being created and preserved; nevertheless, all studies of ΔS and ΔS records conclude that oxygen was essentially absent from Earth's atmosphere prior to 2.45 billion years ago. | 0 | Theoretical and Fundamental Chemistry |
Cyanate is an ambidentate ligand which can donate the pair of electrons on the nitrogen atom or the oxygen atom, or both. Structurally the isomers can be distinguished by the geometry of the complex. In N-bonded cyanate complexes the M−NCO unit sometimes has a linear structure, but with O-bonded cyanate the M−O−C unit is bent. Thus, the silver cyanato complex, , has a linear structure as shown by X-ray crystallography. However, the crystal structure of silver cyanate shows zigzag chains of nitrogen atoms and silver atoms. There also exists a structure
NCO
Ni Ni
OCN
in which the Ni-N-C group is bent.
Infrared spectroscopy has been used extensively to distinguish between isomers. Many complexes of divalent metals are N-bonded. O-Bonding has been suggested for complexes of the type , M = Mo(III), Re(IV), and Re(V). The yellow complex and orange complex are linkage isomers and show differences in their infrared spectra which can be used for diagnosis.
The cyanate ion can bridge between two metal atoms by using both its donor atoms. For example, this structure is found in the compound . In this compound both the Ni−N−C unit and Ni−O−C unit are bent, even though in the first case donation is through the nitrogen atom. | 0 | Theoretical and Fundamental Chemistry |
The structure of active centers in Ziegler–Natta catalysts is well established only for metallocene catalysts. An idealized and simplified metallocene complex CpZrCl represents a typical precatalyst. It is unreactive toward alkenes. The dihalide reacts with MAO and is transformed into a metallocenium ion CpCH, which is ion-paired to some derivative(s) of MAO. A polymer molecule grows by numerous insertion reactions of C=C bonds of 1-alkene molecules into the Zr–C bond in the ion:
Many thousands of alkene insertion reactions occur at each active center resulting in the formation of long polymer chains attached to the center. The Cossee–Arlman mechanism describes the growth of stereospecific polymers. This mechanism states that the polymer grows through alkene coordination at a vacant site at the titanium atom, which is followed by insertion of the C=C bond into the Ti−C bond at the active center. | 0 | Theoretical and Fundamental Chemistry |
AOAC International's technical contributions center on the creation, validation, and global publication of reliable analytical test methods. Their areas of focus include, but are not limited to, safety of foods, beverages, dietary supplements, fertilizers, animal feeds, soil and water, and veterinary drugs. The aim of the test methods is to evaluate the purity of materials used in the production of foodstuffs, and their ingredients. The development of these analytical methods in achieved as part of a range of programs operated by AOAC. | 0 | Theoretical and Fundamental Chemistry |
The name modon was coined by M. E. Stern as a pun on the joint USA-USSR oceanographic research program POLYMODE. The modon is a dipole-vortex solution to the potential-vorticity equation that was theorized in order to explain anomalous atmospheric blocking events and eddy structures in rotating fluids, and the first solution was obtained by Stern in 1975. However, this solution was imperfect because it was not continuous at the modon boundary, so other scientists, such as Larichev and Reznik (1976), proposed other solutions that corrected that problem.
Although modons were predicted theoretically in the 1970s, a pair of modons spinning in opposite directions was first identified traveling in 2017 over the Tasman Sea. The study of satellite images has allowed the identification of other modons, at least dating back to 1993, that hadn't been identified as such until then. The scientists that first discovered modons in the wild think that they can absorb small sea creatures and carry them at high speed over long ocean distances. They are also capable of affecting the transport of heat, carbon and nutrients over that area of the ocean. They move about ten times faster than a typical eddy, and can last for six months before being disengaged. | 1 | Applied and Interdisciplinary Chemistry |
As rivers flow onward towards the sea, they experience a considerable diminution in their fall, and a progressive increase in the basin which they drain, owing to the successive influx of their various tributaries. Thus, their current gradually becomes more gentle and their discharge larger in volume and less subject to abrupt variations; and, consequently, they become more suitable for navigation. Eventually, large rivers, under favorable conditions, often furnish important natural highways for inland navigation in the lower portion of their course, as, for instance, the Rhine, the Danube and the Mississippi. River engineering works are only required to prevent changes in the course of the stream, to regulate its depth, and especially to fix the low-water channel and concentrate the flow in it, so as to increase as far as practicable the navigable depth at the lowest stage of the water level.
Engineering works to increase the navigability of rivers can only be advantageously undertaken in large rivers with a moderate fall and a fair discharge at their lowest stage, for with a large fall the current presents a great impediment to up-stream navigation, and there are generally great variations in water level, and when the discharge becomes very small in the dry season. It is impossible to maintain a sufficient depth of water in the low-water channel.
The possibility to secure uniformity of depth in a river by lowering the shoals obstructing the channel depends on the nature of the shoals. A soft shoal in the bed of a river is due to deposit from a diminution in velocity of flow, produced by a reduction in fall and by a widening of the channel, or to a loss in concentration of the scour of the main current in passing over from one concave bank to the next on the opposite side. The lowering of such a shoal by dredging merely effects a temporary deepening, for it soon forms again from the causes which produced it. The removal, moreover, of the rocky obstructions at rapids, though increasing the depth and equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. Where, however, narrow rocky reefs or other hard shoals stretch across the bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour.
The capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in the channel at the lowest stage. The problem in the dry season is the small discharge and deficiency in scour during this period. A typical solution is to restrict the width of the low-water channel, concentrate all of the flow in it, and also to fix its position so that it is scoured out every year by the floods which follow the deepest part of the bed along the line of the strongest current. This can be effected by closing subsidiary low-water channels with dikes across them, and narrowing the channel at the low stage by low-dipping cross dikes extending from the river banks down the slope and pointing slightly up-stream so as to direct the water flowing over them into a central channel. | 1 | Applied and Interdisciplinary Chemistry |
Improving the resolution and enhancing the instrumentation with user-friendly hardware and software will make AFM/NSOM coupled with IR/Raman a useful characterization tool in many areas including biomedical, materials and life sciences. For example, this technique was used in detecting the spin-cast thin film of poly(dimethylsiloxane) with polystyrene on it by scanning the tip over the sample. The shape and size of polystyrene fragments was detected at a high spatial resolution due to its high absorption at specific resonance frequencies. Other examples include inorganic boron nitride thin films characterization with IR-NSOM. The images of single molecule rhodamine 6G (Rh-6G) was obtained with a spatial resolution of 50 nm. These techniques can be also used in numerous biological related applications including the analysis of plant materials, bone, and single cells. Biological application was demonstrated by detecting details of conformation changes of cholesteryl-oleate caused by FEL irradiation with a spatial resolution below the diffraction limit. Researchers also used Raman/NSOM in tracking the formation of energy-storing polymer polyhydroxybutyrate in bacteria Rhodobacter capsulatus.
This characterization tool may also help in the kinetic studies on physical and chemical processes at a wide variety of surfaces giving chemical specificity via IR spectroscopy as well as high-resolution imaging via AFM. For example, the study of the hydrogen termination of Si (100) surface was performed by studying the absorbance of Si-O bond to characterize the reaction between silicon surface and atmospheric oxygen. Studies were also conducted where the reactivity of a polymer, a 1000-nm-thick poly-(tert-butylmethacrylate) (PTBMA) combined with a photochemically modified 500-nm-thick poly(methacrylic acid) (PMAA), with water vapor depicted the different absorption bands before and after water uptake by the polymer. Not only the increased swell of PMAA (280 nm) was observed but also the different absorption ability of water was shown by the different transmission of IR light at a much smaller dimension (<500 nm). These results are related to polymer, chemical and biological sensors, and tissue engineering and artificial organ studies. Because of their high spatial resolution, NSOM/AFM-Raman/IR techniques can be used for measuring the width of multilayer films, including layers which are too small (in the x and y directions) to be probed with conventional IR or Raman spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
Non-ferrous metals were the first metals used by humans for metallurgy. Gold, silver and copper existed in their native crystalline yet metallic form. These metals, though rare, could be found in quantities sufficient to attract the attention of humans. Less susceptible to oxygen than most other metals, they can be found even in weathered outcroppings. Copper was the first metal to be forged; it was soft enough to be fashioned into various objects by cold forging and could be melted in a crucible. Gold, silver and copper replaced some of the functions of other resources, such as wood and stone, owing to their ability to be shaped into various forms for different uses. Due to their rarity, these gold, silver and copper artifacts were treated as luxury items and handled with great care. The use of copper also heralded the transition from the Stone Age to the Copper Age. The Bronze Age, which succeeded the Copper Age, was again heralded by the invention of bronze, an alloy of copper with the non-ferrous metal tin. | 1 | Applied and Interdisciplinary Chemistry |
The oxygen-evolving complex is the site of water oxidation. It is a metallo-oxo cluster comprising four manganese ions (in oxidation states ranging from +3 to +4) and one divalent calcium ion. When it oxidizes water, producing oxygen gas and protons, it sequentially delivers the four electrons from water to a tyrosine (D1-Y161) sidechain and then to P680 itself. It is composed of three protein subunits, OEE1 (PsbO), OEE2 (PsbP) and OEE3 (PsbQ); a fourth PsbR peptide is associated nearby.
The first structural model of the oxygen-evolving complex was solved using X-ray crystallography from frozen protein crystals with a resolution of 3.8Å in 2001. Over the next years the resolution of the model was gradually increased to 2.9Å. While obtaining these structures was in itself a great feat, they did not show the oxygen-evolving complex in full detail. In 2011 the OEC of PSII was resolved to a level of 1.9Å revealing five oxygen atoms serving as oxo bridges linking the five metal atoms and four water molecules bound to the cluster; more than 1,300 water molecules were found in each photosystem II monomer, some forming extensive hydrogen-bonding networks that may serve as channels for protons, water or oxygen molecules. At this stage, it is suggested that the structures obtained by X-ray crystallography are biased, since there is evidence that the manganese atoms are reduced by the high-intensity X-rays used, altering the observed OEC structure. This incentivized researchers to take their crystals to a different X-ray facilities, called X-ray Free Electron Lasers, such as SLAC in the USA. In 2014 the structure observed in 2011 was confirmed. Knowing the structure of Photosystem II did not suffice to reveal how it works exactly. So now the race has started to solve the structure of Photosystem II at different stages in the mechanistic cycle (discussed below). Currently structures of the S1 state and the S3 state's have been published almost simultaneously from two different groups, showing the addition of an oxygen molecule designated O6 between Mn1 and Mn4, suggesting that this may be the site on the oxygen evolving complex, where oxygen is produced. | 0 | Theoretical and Fundamental Chemistry |
Calx is Latin for chalk or limestone, from the Greek χάλιξ (khaliks, “pebble”). (It is not to be confused with the Latin homonym meaning heelbone (or calcaneus in modern medical Latin), which has an entirely separate derivation.) | 0 | Theoretical and Fundamental Chemistry |
Constructing a THz-TDS experiment using low temperature grown GaAs (LT-GaAs) based antennas requires a laser whose photon energy exceeds the band gap of the material. Ti:sapphire lasers tuned to around 800 nm, matching the energy gap in LT-GaAs, are ideal as they can generate optical pulses as short as 10 fs. These lasers are available as commercial, turnkey systems. | 0 | Theoretical and Fundamental Chemistry |
In order to measure the pore size by capillary flow porometry it is necessary to impregnate the samples with a wetting liquid. An inert gas flow is used to displace the liquid that is in the pores and the pressure required to empty the most constricted part of the pore is measured. The most constricted part of the pore is the most challenging one because it offers the highest resistance to remove the wetting liquid. This parameter is very important in filtration and similar applications since it is essential to know the smallest diameter of the through pores.
This measured pressure permits obtaining the pore diameter, which is calculated by using the Young-Laplace formula P= 4*γ*cos θ*/D in which D is the pore size diameter, P is the pressure measured, γ is the surface tension of the wetting liquid and θ is the contact angle of the wetting liquid with the sample.
The surface tension γ is a measurable physical property and depends on the wetting liquid used. The contact angle θ depends on the interaction between the material and the wetting liquid. In capillary flow porometry, in opposition to mercury intrusion porosimetry, the wetting liquid enters spontaneously the pores of the sample ensuring a total wetting of the material, and therefore the contact angle of the wetting liquid with the sample is 0 and the previous formula can be simplified as: P= 4*γ/D. | 1 | Applied and Interdisciplinary Chemistry |
Each one of the assumptions listed below adds to the complexity of the problems solution. As the density of a gas increases with rising pressure, the intermolecular forces play a more substantial role in gas behavior which results in the ideal gas law no longer providing "reasonable" results. At the upper end of the engine temperature ranges (e.g. combustor sections – 1300 K), the complex fuel particles absorb internal energy by means of rotations and vibrations that cause their specific heats to vary from those of diatomic molecules and noble gases. At more than double that temperature, electronic excitation and dissociation of the gas particles begins to occur causing the pressure to adjust to a greater number of particles (transition from gas to plasma). Finally, all of the thermodynamic processes were presumed to describe uniform gases whose velocities varied according to a fixed distribution. Using a non-equilibrium situation implies the flow field must be characterized in some manner to enable a solution. One of the first attempts to expand the boundaries of the ideal gas law was to include coverage for different thermodynamic processes by adjusting the equation to read pV = constant and then varying the n through different values such as the specific heat ratio, γ'.
Real gas effects include those adjustments made to account for a greater range of gas behavior:
*Compressibility effects (Z allowed to vary from 1.0)
*Variable heat capacity (specific heats vary with temperature)
*Van der Waals forces (related to compressibility, can substitute other equations of state)
*Non-equilibrium thermodynamic effects
*Issues with molecular dissociation and elementary reactions with variable composition.
For most applications, such a detailed analysis is excessive. Examples where real gas effects would have a significant impact would be on the Space Shuttle re-entry where extremely high temperatures and pressures were present or the gases produced during geological events as in the image of the 1990 eruption of Mount Redoubt. | 0 | Theoretical and Fundamental Chemistry |
Triphenylphosphine dichloride is usually prepared fresh by the addition of chlorine to triphenylphosphine.
:PhP + Cl → PhPCl
Both reagents are typically used in solution to ensure the correct stoichiometry.
PhPCl can also be obtained by the reaction of iodobenzene dichloride (PhICl) and triphenylphosphine.
Alternatively, PhPCl can be obtained by chlorination of triphenylphosphine oxide with, for example, phosphorus trichloride, as in Grignard's original 1931 synthesis. | 0 | Theoretical and Fundamental Chemistry |
In microholography, focused beams of light are used to record submicrometre-sized holograms in a photorefractive material, usually by the use of collinear beams. The writing process may use the same kinds of media that are used in other types of holographic data storage, and may use two–photon processes to form the holograms. | 0 | Theoretical and Fundamental Chemistry |
Carbon dioxide is also available as a spray and is used to treat a variety of benign spots. Less frequently, doctors use carbon dioxide "snow" formed into a cylinder or mixed with acetone to form a slush that is applied directly to the treated tissue. | 1 | Applied and Interdisciplinary Chemistry |
Another part of Crabtrees research centers on a novel form of hydrogen bonding that involves metal hydrides, resulting in unconventional bonding interactions. Traditional hydrogen bonds feature a protic hydrogen donor and an electronegative acceptor, while Crabtrees discoveries include aromatic ring π electrons as weaker acceptors in X–H···π hydrogen bonds (X = N, O). Surprisingly, Crabtree also observed Y–H σ bonds (Y= B or metal) acting as acceptors, leading to X–H···H–Y structures with significantly shorter H···H distances compared to typical contacts. Known as "dihydrogen bonds," these interactions exhibit bond lengths of approximately 1.8 Å, in contrast to the regular H···H length of 2.4 Å. Crabtree's findings shed light on the diverse nature of hydrogen bonding, with implications for understanding molecular structures and designing catalysts with tailored properties. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, an ynone is an organic compound containing a ketone () functional group and a triple bond. Many ynones are α,β-ynones, where the carbonyl and alkyne groups are conjugated. Capillin is a naturally occurring example. Some ynones are not conjugated. | 0 | Theoretical and Fundamental Chemistry |
Camille Alphonse Faure (21 May 1840, Vizille – 14 September 1898) was a French chemical engineer who in 1881 significantly improved the design of the lead-acid battery, which had been invented by Gaston Planté in 1859. Faure's improvements greatly increased the capacity of such batteries and led directly to their manufacture on an industrial scale. The patents were assigned to the Société La Force et la Lumière. The right to use these patents in the British Isles were sold to the Faure Electric Accumulator Company on 29 March 1881. Faure was a consultant engineer with William Edward Ayrton for this company. | 0 | Theoretical and Fundamental Chemistry |
An external voltage divider is used to apply 100 volts to the acceleration optics (for electron detection), each MCP, the gap between the MCPs, the backside of the last MCP, and the collector (anode). The last voltage dictates the time of flight of the electrons and in this way, the pulse-width.
The anode is a 0.4 mm thick plate with an edge of 0.2 mm radius to avoid high field strengths. It is just large enough to cover the active area of the MCP, because the backside of the last MCP, and the anode, together act as a capacitor with 2 mm separation - and large capacitance slows down the signal. The positive charge in the MCP influences positive charge in the backside metalization. A hollow torus conducts this around the edge of the anode plate. A torus is the optimum compromise between low capacitance and short path and for similar reasons, usually no dielectric (Markor) is placed into this region. After a 90° turn of the torus it is possible to attach a large coaxial waveguide. A taper permits minimizing the radius so that an SMA connector can be used. To save space and make the impedance match less critical, the taper is often reduced to a small 45° cone on the backside of the anode plate.
The typical 500 volts between the backside of the last MCP and the anode cannot be fed directly into the preamplifier; the inner or the outer conductor needs a DC block, that is, a capacitor. Often it is chosen to only have 10-fold capacitance compared to the MCP-anode capacitance and is implemented as a plate capacitor. Rounded, electro-polished metal plates and the ultra high vacuum allow very high field strengths and high capacitance without a dielectric. The bias for the center conductor is applied via resistors hanging through the waveguide (see bias tee). If the DC block is used in the outer conductor, it is aligned in parallel with the larger capacitor in the power supply. Assuming good screening, the only noise is due to current noise from the linear power regulator. Because the current is low in this application and space for large capacitors is available, and because the DC-block capacitor is fast, it is possible to have very low voltage noise, so that even weak MCP signals can be detected. Sometimes the preamplifier is on a potential (off ground) and gets its power through a low-power isolation transformer and outputs its signal optically.
The gain of an MCP is very noisy, especially for single particles. With two thick MCPs (>1 mm) and small channels (< 10 µm), saturation occurs, especially at the ends of the channels after many electron multiplications have taken place. The last stages of the following semiconductor amplifier chain also go into saturation. A pulse of varying length, but stable height and a low jitter leading edge is sent to the time to digital converter. The jitter can be further reduced by means of a constant fraction discriminator. That means that the MCP and the preamplifier are used in the linear region (space charge negligible) and the pulse shape is assumed to be due to an impulse response, with variable height but fixed shape, from a single particle.
Because MCPs have a fixed charge that they can amplify in their life, the second MCP especially, has a lifetime problem. It is important to use thin MCPs, low voltage and instead of greater voltage, more sensitive and fast semiconductor amplifiers after the anode. (see: Secondary emission#Special amplifying tubes,).
With high count rates or slow detectors (MCPs with phosphor screen or discrete photomultipliers), pulses overlap. In this case, a high impedance (slow, but less noisy) amplifier and an ADC are used. Since the output signal from the MCP is generally small, the presence of the thermal noise limits the measurement of the time structure of the MCP signal. With fast amplification schemes, however, it is possible to have valuable information on the signal amplitude even at very low signal levels, yet not on the time structure information of the wideband signals. | 0 | Theoretical and Fundamental Chemistry |
The equation also explains the energy required to create an emulsion. To form the small, highly curved droplets of an emulsion, extra energy is required to overcome the large pressure that results from their small radius.
The Laplace pressure, which is greater for smaller droplets, causes the diffusion of molecules out of the smallest droplets in an emulsion and drives emulsion coarsening via Ostwald ripening. | 1 | Applied and Interdisciplinary Chemistry |
Iron-sulfur proteins are involved in various biological electron transport processes, such as photosynthesis and cellular respiration, which require rapid electron transfer to sustain the energy or biochemical needs of the organism. To serve their various biological roles, iron-sulfur proteins effect rapid electron transfers and span the whole range of physiological redox potentials from -600 mV to +460 mV.
Fe-SR bonds have unusually high covalency which is expected. When comparing the covalency of Fe with the covalency of Fe, Fe has almost double the covalency of Fe (20% to 38.4%). Fe is also much more stabilized than Fe. Hard ions like Fe normally have low covalency because of the energy mismatch of the metal lowest unoccupied molecular orbital with the ligand highest occupied molecular orbital.
External water molecules positioned close to the iron-sulfur active site reduces covalency; this can be shown by lyophilization experiments where water is removed from the protein. This reduction is because external water hydrogen bonds with cysteine S, decreasing the latter's lone pair electron donation to the Fe by pulling away S electrons. Since covalency stabilizes Fe more than Fe, Fe is more destabilized by the HOH-S hydrogen-bonding.
The Fe 3d orbital energies follow the "inverted" bonding scheme which fortuitously has the Fe d-orbitals closely matched in energy with the sulfur 3p orbitals, giving high covalency in the resulting bonding molecular orbital. This high covalency lowers the inner sphere reorganization energy and ultimately contributes to a rapid electron transfer. | 0 | Theoretical and Fundamental Chemistry |
Advance earthquake warning is possible by detecting the nondestructive primary waves that travel more quickly through the Earth's crust than do the destructive secondary and Rayleigh waves.
The amount of warning depends on the delay between the arrival of the P wave and other destructive waves, generally on the order of seconds up to about 60 to 90 seconds for deep, distant, large quakes such as the 2011 Tohoku earthquake. The effectiveness of a warning depends on accurate detection of the P waves and rejection of ground vibrations caused by local activity (such as trucks or construction). Earthquake early warning systems can be automated to allow for immediate safety actions, such as issuing alerts, stopping elevators at the nearest floors, and switching off utilities. | 1 | Applied and Interdisciplinary Chemistry |
Chemical WorkBench has an extensive library of physicochemical models:
*Thermodynamic Models
*Gas-Phase Kinetic Models
*Flame model
*Heterogeneous Kinetic Models
*Non-Equilibrium Plasma Models
*Detonation and Aerodynamic Models
*Membrane Separation Models
*Mechanism Analysis and Reduction | 0 | Theoretical and Fundamental Chemistry |
Simple modelling will enable many properties of fully developed, turbulent plumes to be investigated. Many of the classic scaling arguments were developed in a combined analytic and laboratory study described in an influential paper by Bruce Morton, G.I. Taylor and Stewart Turner and this and subsequent work is described in the popular monograph of Stewart Turner.
# It is usually sufficient to assume that the pressure gradient is set by the gradient far from the plume (this approximation is similar to the usual Boussinesq approximation).
# The distribution of density and velocity across the plume are modelled either with simple Gaussian distributions or else are taken as uniform across the plume (the so-called top hat model).
# The rate of entrainment into the plume is proportional to the local velocity. Though initially thought to be a constant, recent work has shown that the entrainment coefficient varies with the local Richardson number. Typical values for the entrainment coefficient are of about 0.08 for vertical jets and 0.12 for vertical, buoyant plumes whilst for bent-over plumes, the entrainment coefficient is about 0.6.
# Conservation equations for mass (including entrainment), and momentum and buoyancy fluxes are sufficient for a complete description of the flow in many cases. For a simple rising plume these equations predict that the plume will widen at a constant half-angle of about 6 to 15 degrees.
The value of the entrainment coefficient is the key parameter in simple plume models. Research continues into assessing how the entrainment coefficient is affected by, for example, the geometry of a plume, suspended particles within a plume, and background rotation. | 1 | Applied and Interdisciplinary Chemistry |
Redox buffers were developed in part to control oxygen fugacities in laboratory experiments to investigate mineral stabilities and rock histories. Each of the curves plotted in the fugacity-temperature diagram is for an oxidation reaction occurring in a buffer. These redox buffers are listed here in order of decreasing oxygen fugacity at a given temperature—in other words, from more oxidizing to more reducing conditions in the plotted temperature range. As long as all the pure minerals (or compounds) are present in a buffer assemblage, the oxidizing conditions are fixed on the curve for that buffer. Pressure has only a minor influence on these buffer curves for conditions in the Earth's crust.
MH: magnetite-hematite:
: 4 FeO + O ⇌ 6 FeO
NiNiO: nickel-nickel oxide:
: 2 Ni + O ⇌ 2 NiO
FMQ: fayalite-magnetite-quartz:
: 3 FeSiO + O ⇌ 2 FeO + 3 SiO
WM: wustite-magnetite:
: 3 FeO + O ~ FeO
IW: iron-wustite:
: 2 (1-x) Fe + O ⇌ 2 FeO
QIF: quartz-iron-fayalite:
: 2 Fe + SiO + O ⇌ FeSiO | 0 | Theoretical and Fundamental Chemistry |
The adapters that annealed successfully are extended and synthesized by a DNA polymerase to complete a double-stranded adapter containing complementary tags (Figure 1). | 1 | Applied and Interdisciplinary Chemistry |
In the flow of compressible fluids such as air, and particularly the high-speed flow of compressible fluids, (the dynamic pressure) is no longer an accurate measure of the difference between stagnation pressure and static pressure. Also, the familiar relationship that stagnation pressure is equal to total pressure does not always hold true. (It is always true in isentropic flow, but the presence of shock waves can cause the flow to depart from isentropic.) As a result, pressure coefficients can be greater than one in compressible flow. | 1 | Applied and Interdisciplinary Chemistry |
In 1855 he was a lecturer on chemistry and natural science at Scotch College, having been engaged for the position before leaving Scotland.
In 1857 he was awarded an MD ad eundem from the University of Melbourne in acknowledgment of his MD from the University of Glasgow.
In 1857-1858 he also taught at Geelong Church of England Grammar School (now Geelong Grammar School). In 1858, he was appointed the Victorian government analytical chemist. In 1860 he became health officer to the City of Melbourne. He wrote several reports on public health.
On 3 March 1862 he was appointed as the first lecturer in medicine (chemistry and practical chemistry) at the University of Melbourne School of Medicine. For the next few years he held classes for a small number of medical students in the Analytical Laboratory behind the Public Library. He was also a member of the Board of Agriculture. | 0 | Theoretical and Fundamental Chemistry |
*ARPES, Angle-resolved photoemission spectroscopy
*UPS, Ultraviolet photoelectron spectroscopy
*PES, Photoemission spectroscopy
*ZEKE, Zero electron kinetic energy spectroscopy
*AES, Auger electron spectroscopy
*EDS, Energy-dispersive X-ray spectroscopy, (EDX or EDXRF)
*PEEM, Photoelectron emission microscopy | 0 | Theoretical and Fundamental Chemistry |
The dead time is the time for the solutions to go from the mixing point to the observation point, it is the part of the kinetics which cannot be observed. So the lower the dead time, the more information the user can get. In older instruments this could be of the order of 1 ms, but improvements now allow a dead time of about 0.3 ms. | 0 | Theoretical and Fundamental Chemistry |
Specific protein complexes, known as histone-modifying complexes catalyze addition or removal of various chemical elements on histones. These enzymatic modifications include acetylation, methylation, phosphorylation, and ubiquitination and primarily occur at N-terminal histone tails. Such modifications affect the binding affinity between histones and DNA, and thus loosening or tightening the condensed DNA wrapped around histones, e.g., Methylation of specific lysine residues in H3 and H4 causes further condensation of DNA around histones, and thereby prevents binding of transcription factors to the DNA that lead to gene repression. On the contrary, histone acetylation relaxes chromatin condensation and exposes DNA for TF binding, leading to increased gene expression. | 1 | Applied and Interdisciplinary Chemistry |
Iron export occurs in a variety of cell types, including neurons, red blood cells, macrophages and enterocytes. The latter two are especially important since systemic iron levels depend upon them. There is only one known iron exporter, ferroportin. It transports ferrous iron out of the cell, generally aided by ceruloplasmin and/or hephaestin (mostly in enterocytes), which oxidize iron to its ferric state so it can bind ferritin in the extracellular medium. Hepcidin causes the internalization of ferroportin, decreasing iron export. Besides, hepcidin seems to downregulate both TFR1 and DMT1 through an unknown mechanism. Another player assisting ferroportin in effecting cellular iron export is GAPDH. A specific post translationally modified isoform of GAPDH is recruited to the surface of iron loaded cells where it recruits apo-transferrin in close proximity to ferroportin so as to rapidly chelate the iron extruded.
The expression of hepcidin, which only occurs in certain cell types such as hepatocytes, is tightly controlled at the transcriptional level and it represents the link between cellular and systemic iron homeostasis due to hepcidin's role as "gatekeeper" of iron release from enterocytes into the rest of the body. Erythroblasts produce erythroferrone, a hormone which inhibits hepcidin and so increases the availability of iron needed for hemoglobin synthesis. | 1 | Applied and Interdisciplinary Chemistry |
After starting her career in pharmacy, she went on to study radioactivity at the Sorbonne and work in Marie Curies laboratory from 1907 to 1912. At the Curie Institute, Gleditsch performed a technique called fractional crystallisations', which purified radium. The work, which was highly specialized and few could complete, allowed her laboratory fees to be waived. She spent five years of analysis with Curie and returned even after leaving the lab to supervise experiments. In 1911, she received a "Licenciée en sciences degree" from the Sorbonne and was awarded a teaching post at University of Oslo where she worked with Margot Dorenfeldt. After working one year, Gleditsch won the first scholarship ever given to a woman from the American-Scandinavian Association to study in the United States, but was turned down by both of the schools at which she applied.
She went anyway and despite having been rejected was able to work at the laboratory of Bertram Boltwood at Yale University, where she measured the half-life of radium, creating a standard measurement that was used for many years. One of the scientists who had originally turned her away from Yale, co-authored two articles with her and in June 1914, Smith College awarded her an honorary doctorate for her work. In 1913–14, she returned to the University of Oslo and became the second woman to be elected to Oslo's Academy of Science in 1917. During the 1920s, Gleditsch made several trips to France to assist Curie, as well as a trip to Cornwall to investigate a mine located there.
In 1919, Gleditsch co-founded the Norwegian Women Academics' Association, to focus on development of science and the conditions under which women scientists worked. She also believed that cooperation of scientists would foster peace. She served as president of the organization from 1924 to 1928. Joining the International Federation of University Women in 1920, she served as its President from 1926 to 1929, working to provide scholarships to enable women to study abroad. In 1929, she made a trip to the United States traveling from New York to California with the intention of promoting scholarships for women.
Though her appointment as professor at Oslo in 1929 caused controversy, she successfully started a radioactivity research group there. Throughout the 1930s, she continued to produce articles in English, French, German and Norwegian. She also hosted a series of radio shows to promote and popularize scientific study. In the 1930s she directed, a laboratory doing radiochemistry in Norway, which was used as an underground laboratory by scientists fleeing from the Nazi regime. In 1939, she was appointed to the International committee on intellectual cooperation, where Marie Curie had also been sitting a few years earlier. When Norway was occupied during the war, she hid scientists and continued using her home for experiments. During a raid on her laboratory in 1943, the women scientists were able to rescue the radioactive minerals, but all of the men were arrested.
She retired from the university in 1946 and began working with UNESCO in their efforts to end illiteracy. In 1949, she was actively involved on the working committee and in 1952 was named to the Norwegian commission working to control use of the atomic bomb. That same year she resigned from UNESCO in protest over the admittance of Spain under Franco's fascist regime as a member. In 1962 at the age of 83, she received an honorary doctorate from the Sorbonne, the first woman to receive such an honor. | 0 | Theoretical and Fundamental Chemistry |
The main fuel stored in the bodies of animals is fat. A young adult human's fat stores average between about , but varies greatly depending on age, sex, and individual disposition. In contrast, the human body stores only about of glycogen, of which is locked inside the skeletal muscles and is unavailable to the body as a whole. The or so of glycogen stored in the liver is depleted within one day of starvation. Thereafter the glucose that is released into the blood by the liver for general use by the body tissues, has to be synthesized from the glucogenic amino acids and a few other gluconeogenic substrates, which do not include fatty acids.
Fatty acids are broken down to acetyl-CoA by means of beta oxidation inside the mitochondria, whereas fatty acids are synthesized from acetyl-CoA outside the mitochondrion, in the cytosol. The two pathways are distinct, not only in where they occur, but also in the reactions that occur, and the substrates that are used. The two pathways are mutually inhibitory, preventing the acetyl-CoA produced by beta-oxidation from entering the synthetic pathway via the acetyl-CoA carboxylase reaction. It can also not be converted to pyruvate as the pyruvate decarboxylation reaction is irreversible. Instead it condenses with oxaloacetate, to enter the citric acid cycle. During each turn of the cycle, two carbon atoms leave the cycle as in the decarboxylation reactions catalyzed by isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. Thus each turn of the citric acid cycle oxidizes an acetyl-CoA unit while regenerating the oxaloacetate molecule with which the acetyl-CoA had originally combined to form citric acid. The decarboxylation reactions occur before malate is formed in the cycle. Malate is the only substance that can be removed from the mitochondrion to enter the gluconeogenic pathway to form glucose or glycogen in the liver or any other tissue. There can therefore be no net conversion of fatty acids into glucose.
Only plants possess the enzymes to convert acetyl-CoA into oxaloacetate from which malate can be formed to ultimately be converted to glucose.
;Regulation
Acetyl-CoA is formed into malonyl-CoA by acetyl-CoA carboxylase, at which point malonyl-CoA is destined to feed into the fatty acid synthesis pathway. Acetyl-CoA carboxylase is the point of regulation in saturated straight-chain fatty acid synthesis, and is subject to both phosphorylation and allosteric regulation. Regulation by phosphorylation occurs mostly in mammals, while allosteric regulation occurs in most organisms. Allosteric control occurs as feedback inhibition by palmitoyl-CoA and activation by citrate. When there are high levels of palmitoyl-CoA, the final product of saturated fatty acid synthesis, it allosterically inactivates acetyl-CoA carboxylase to prevent a build-up of fatty acids in cells. Citrate acts to activate acetyl-CoA carboxylase under high levels, because high levels indicate that there is enough acetyl-CoA to feed into the Krebs cycle and conserve energy.
High plasma levels of insulin in the blood plasma (e.g. after meals) cause the dephosphorylation of acetyl-CoA carboxylase, thus promoting the formation of malonyl-CoA from acetyl-CoA, and consequently the conversion of carbohydrates into fatty acids, while epinephrine and glucagon (released into the blood during starvation and exercise) cause the phosphorylation of this enzyme, inhibiting lipogenesis in favor of fatty acid oxidation via beta-oxidation. | 1 | Applied and Interdisciplinary Chemistry |
Ammonia exhibits a quantum tunnelling due to a narrow tunneling barrier, and not due to thermal excitation. Superposition of two states leads to energy level splitting, which is used in ammonia masers. | 0 | Theoretical and Fundamental Chemistry |
Most pharmaceutical drugs are small molecules which elicit a physiological response by "binding" to enzymes or receptors, causing an increase or decrease in the enzymes ability to function. The binding of a small molecule to a protein is governed by a combination of steric, or spatial considerations, in addition to various non-covalent interactions, although some drugs do covalently modify an active site (see irreversible inhibitors). Using the "lock and key model" of enzyme binding, a drug (key) must be of roughly the proper dimensions to fit the enzymes binding site (lock). Using the appropriately sized molecular scaffold, drugs must also interact with the enzyme non-covalently in order to maximize binding affinity binding constant and reduce the ability of the drug to dissociate from the binding site. This is achieved by forming various non-covalent interactions between the small molecule and amino acids in the binding site, including: hydrogen bonding, electrostatic interactions, pi stacking, van der Waals interactions, and dipole–dipole interactions.
Non-covalent metallo drugs have been developed. For example, dinuclear triple-helical compounds in which three ligand strands wrap around two metals, resulting in a roughly cylindrical tetracation have been prepared. These compounds bind to the less-common nucleic acid structures, such as duplex DNA, Y-shaped fork structures and 4-way junctions. | 0 | Theoretical and Fundamental Chemistry |
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